PHOTORESIST-FREE METAL DEPOSITION
Selectively accelerated or selectively inhibited metal deposition is performed to form metal structures of an electronic device. A desired pattern of an accelerator or of an inhibitor is applied to the substrate; for example, by stamping the substrate with a patterned stamp or spraying a solution using an inkjet printer. In other embodiments, a global layer of accelerator or inhibitor is applied to a substrate and selectively modified in a desired pattern. Thereafter, selective metal deposition is performed.
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This application is a divisional of U.S. patent application Ser. No. 11/827,800, filed Jul. 13, 2007, the contents of which are hereby incorporated by reference in its entirety, and which claims the benefit of U.S. Provisional Patent App. No. 60/832,534, filed Jul. 21, 2006, and U.S. Provisional Patent App. No. 60/836,711, filed Aug. 9, 2006.
FIELD OF THE INVENTIONThe invention relates in general to methods and systems for depositing material in patterns to form structures in electronic equipment, particularly for forming metal features in electronic equipment, and more particularly to the plating of metal wiring in integrated circuits, printed wiring boards and semiconductor packaging as well as to creating relevant structures for micro- and nano-electro-mechanical systems (MEMS and NEMS).
BACKGROUND OF THE INVENTIONIntegrated circuits are formed on wafers by well-known processes and materials. These processes typically include the deposition of thin film layers by sputtering, organo-metallic decomposition, chemical vapor deposition, plasma vapor deposition, electrodeposition (electroplating) and other techniques. These layers are further processed by a variety of well-known etching technologies and subsequent deposition and polishing steps to provide a completed integrated circuit.
A crucial component of integrated circuits is the various wiring or metallization layers that interconnect the individual circuits. Conventional metal deposition techniques include physical vapor deposition, sputtering and evaporation, and chemical vapor deposition techniques. Also, integrated circuit and equipment manufacturers have developed electrochemical deposition techniques, (including electroless and electrolytic plating) to deposit primary conductor films on various semiconductors (e.g., Si, GaAs), ceramics, printed circuit boards and a variety of other suitable substrates.
Integrated circuit wiring layers traditionally contained aluminum and a plurality of other metal layers that are compatible with the aluminum. In 1997, IBM was the first to introduce copper damascene and dual damascene technology that facilitated a transition from aluminum to copper wiring layers. This technology demanded corresponding changes in process architecture, as well as new process technologies. Today, damascene processing is commonly used not only in the manufacture of integrated circuits, but also in memory fabrication; it is even displacing a variety of other back-end packaging applications, such as in printed circuit board manufacture.
For damascene integrated circuit and memory applications (where wiring is relatively close to the copper-sensitive silicon substrate), the conductive layers are typically deposited on a dielectric layer and typically comprise metals such as tantalum (Ta), tungsten (W), titanium (Ti), aluminum (AI), copper (Cu), and alloys thereof, and semiconductors, such as doped silicon (Si), doped polysilicon, and refractory metal silicides. The three dimensional structure consist of multiple dielectric layers with openings, or feature cavities, (vias and trenches) that are filled with conductive material that provide circuit paths through dielectric material within and between the various layers and eventually to transistor circuit devices. After the deposition of metal at each level, the conductive layer is typically polished, and only the conductive material filling the feature cavities remains in the dielectric layer.
A typical damascene or dual damascene process flow scheme for fabricating copper interconnects, such as copper lines and vias, typically includes: forming a trench pattern on a layer dielectric layer using an etch-resistant photoresist; etching a trench pattern; removing the photoresist; forming a via pattern on a dielectric material using etch resistant photoresist; etching vias; removing resist; depositing a barrier (e.g., tantalum, tantalum nitride, combinations of these) and a copper seed layer (e.g., using plasma vapor deposition, PVD); electroplating copper to fill the etched feature cavities; and polishing copper and barrier off the wafer face leaving copper-filled electrically isolated interconnect circuitry.
As the number of levels in an interconnect technology increases, the stacking of additional layers produces more rugged and complex topography. Compounding this problem, electroplating bath additives are now commonly utilized to promote rapid “bottomup” filling of high aspect-ratio features in damascene copper electroplating processes to ensure complete void-free metal fill of high aspect ratio features (features deeper than they are wide). Baths with good “bottom-up” filling characteristics fill high aspect ratio features more rapidly and without creating voids or seams when compared to baths with less effective combinations of such additives. While the action of plating bath additives is still a subject of active investigation, it is now generally accepted that bottom-up filling of high aspect ratio features is controlled by the geometrical concentration of a strongly adsorbed plating bath “accelerator” bound within and on the walls of the feature. As a metal film within the feature grows, the surface area decreases within the feature and concentrates the adsorbate, lowering the resistance to charge transfer in the feature compared to the flatter exposed regions of the surface, thereby creating an “acceleration” of the plating rate within the recessed feature region. (See, for example, J. Osterwald and J. Schulz-Harder, Galvanotechnik, 66, 360 (1975), J. Osterwald, Oberflache-Surface, 17, 89 (1976), J. Reid and S. Mayer, in Advanced Metallization Conference, 1999, M. E. Gross, T. Gessner, N. Kobayashi, and Y. Yauda, Editors, pg 53, MRS, Warrendale, Pa. (2000), A. C. West, S. Mayer, and J. Reid, Electrochem. Solid-State Letters, 4, C50 (2001), T. P. Moffat, D. Wheeler, and D. Josell, “Superfilling and the Curvature Enhanced Accelerator Coverage Mechanism, The Electrochemical Society Interface, Winter, 2004). Therefore, baths with good “bottom-up” filling characteristics typically fill smaller (higher aspect ratio) features more rapidly than larger (lower aspect ratio) features because their surface to volume ratio is larger. In some cases (e.g., plating baths with superior bottom-up filling characteristics and little or no leveling additives), plating continues at an accelerated rate after completing the small-feature filling stage. When many high-aspect ratio features are located in close proximity, the amount of adsorbed accelerator originally associated with the high surface area of that region remains after the features have filled. Hence, growth continues at an accelerated rate beyond the point of features-fill and into a period in which metal between the features has merged. When this happens, a macroscopic raised area forms over the entire region of underlying high aspect ratio features, initially as a series of thicker metallized bumps, and after they merge, as a raised plateau. This formation of raised topography is also termed “feature overplating” or “momentum plating”.
The use of advanced “bottom-up” electrofilling techniques with wafers having low and high aspect-ratio features has created a problem of deposited metal surfaces with a wide range of topography, that is, topography containing a large range or aspect ratios of both recessed and raised areas. Commonly, features vary in width by two to three orders of magnitude on a single layer. As a specific example, a 0.5 μm-deep (thick dielectric) level can have feature widths of from 0.1 μm to 100 μm. Therefore, while electroplating is the preferred method of metallization, various aspects of improved plating regimens create challenging topography for subsequent planarization.
A principal objective of damascene circuit interconnect fabrication is to create metal isolated by and embedded in a dielectric medium. The preferential filling of recessed features in modern bottom-up electroplating techniques requires careful control of process conditions. U.S. Pat. No. 6,946,065, titled “Process for Electroplating Metal into Microscopic Recessed Features”, issued Sep. 20, 2005 to Mayer et. al., which is hereby incorporated by reference for all purposes, teaches techniques for reducing or mitigating the formation of seams and/or voids in electroplating the interior regions of microscopic recessed features. For the most part, prior processes are largely isotropic and do not preferentially fill and planarize low-aspect-ratio features and therefore they require significant excess metal deposition (“overburden”). Overburden is the additional copper deposited on the substrate to ensure that all low-aspect-ratio features are completely filled (essentially in an isotropic fashion) to the plane of a base layer, that is, to the plane of the isolating dielectric surface (the “field”). Since the preferential “bottom-up” filling generally does not occur in low-aspect-ratio features, the surface of the overburden above low-aspect-ratio features typically follows the contours within the dielectric and of the underlying low-aspect-ratio features. In most cases, the overburden on field regions is slightly thicker than the thickness of the damascene dielectric layer, typically on the order of 1.2 times the depth of the deepest feature. So, for example, a damascene structure that has 0.5 micrometers (μm) deep features typically requires an overburden of at least approximately 0.7 to 0.8 micrometers.
Overburden is undesirable for a number of reasons. It requires deposition of considerable amounts of excess copper over the field that is essentially wasted and it requires extra effort associated with removing the overburden material. Thus, overburden represents additional materials costs (excess copper deposited and removed), as well as decreased throughput and productivity. In current processes, overburden is removed by a planarization technique such as chemical mechanical polishing (CMP), electrochemical chemical polishing (eCMP), or electropolishing. CMP and eCMP are particularly expensive processes that generally use corrosive chemical and slurry formulations on large (wafer scale or larger) pads to polish the surface of the integrated circuit substrate. Such pad-rubbing processes are often difficult to control and the polishing end-point can be difficult to detect. The high equipment cost, waste handling cost, and low throughput contribute to the overall expense of CMP and eCMP. Also, with the introduction of porous low-k dielectrics in semiconductor devices, modification of traditional CMP and even eCMP processes is required, as current methods can crack and/or delaminate low-k materials, which typically have a very low compression strength and extreme fragility. Furthermore, none of these techniques achieve perfect planarization at all length scales.
Relatively large copper lines in electronic equipment, for example, in a printed wiring board (“PWB”), are typically formed by a process including lamination, photolithography, screen-printing, and wet etching.
Another method of patterning copper lines, which was also commonly used for making small lines until the invention of the damascene process, is through-resist plating. In this technique, a metal seed layer is first deposited to cover completely a base plane substrate, resist is applied over the seed layer, and areas to be plated-up are optically exposed and developed (wherein the resist is removed to expose copper seed at the base). Thereafter, during electroplating, metal is deposited only in the exposed and developed areas. In such a technique, copper can be plated controllably only to the thickness of the resist. If additional copper is plated, it is no longer confined by the walls of the lines defined by the resist, and will tend to grow laterally and encroach into other lines due to the loss of confinement and due to plating both upwards and sideways. Also, in such techniques, the plating solution contacts the resist. As a result of leaching of organic electroactive contamination from the resist, the lifetime of the plating solution is often reduced, adding cost to the overall process. A damascene process is well suited for producing lines of small depth (or height or thickness) in features having high aspect ratio, but is prohibitively expensive for thick copper layers due to the high cost of removing copper from the insulating dielectric surface (“field”). In a damascene process, copper plates onto the field area to a thickness corresponding to the desired height (or thickness) of the wiring line, and all of this excess copper must be removed by chemical mechanical planarization in order to form the copper line.
None of the techniques described is ideally suited to the production of small or large metal features, such as copper lines, interlevel connections, metal pads, and device connectors, and each technique incurs considerable costs associated with consumed material and waste disposal. Therefore, it would be desirable to have a technique for depositing copper or other metal wiring that would create the desired wiring without the need to add, pattern and remove dielectric or photoresist layers, and without the need to remove a large amount of copper (or other metal), and that would avoid electrolyte contamination associated with through-resist plating, allowing for longer plating bath lifetimes. Preferably, a technique for forming large copper lines would not have to be defined through etching of vias and trenches in a dielectric.
Osterwald et aI., in “Wirkung von Badzusatzen bei der kathodischen Metallabscheidung”, Galvanotechnik, 66, Nr. 5, pp. 360-365 (1975), Leuze Verlag, Saulgau, Germany, and “Leveling and Roughening by Inhibitors and Catalysts” Oberfläche-Surface, 17, 89 (1976), teach an additive in solution that absorbs onto a cathode surface. The absorbed additive acts as a catalyst of metal deposition thereby increasing a metal deposition rate. The relative catalytic effect is related to the surface concentration of the adsorbate. Due to geometrical considerations, when the catalyzing additive is absorbed onto a surface having a recess, the surface concentration of catalyzing additive in the recess increases compared to its concentration in non-recessed areas as metal deposition proceeds. As a result, the rate of metal deposition in the recess becomes greater than the metal deposition rate at non-recessed areas. This leads to relative planarization of the deposited metal compared to topography resulting from metal plating on a substrate without adsorbed catalyzing additive. Later, others confirmed that specific chemical additives exhibit this behavior, and this behavior is conceptually useful in interpreting, modeling and controlling preferential filling of small damascene features. (See, for example, J. Reid and S. Mayer, in Advance Metallization Conference Proceedings, 1999, p. 53; A. C. West, S. Mayer, and J. Reid, Electrochem Solid State Lett., 4, CSO [2001]; T. P. Moffat, D. Wheeler, W. H. Huber, and D. Josell, Electrochem Solid State Lett, 4, C26 [2001]; and T. P. Moffat, D. Wheeler, and D. Josell, Electrochemical Society Interface, p. 46, Winter 2004). U.S. patent application Ser. No. 10/739,822, filed Dec. 17, 2003, by Mayer et al., having the title “Method for Planar. Electroplating”, teaches a method of selectively attaching a plating accelerator to recessed regions of the dielectric layer before electroplating to achieve selectively accelerated plating (SAP) of metal in the recessed regions.
There exists a need for improved technology for depositing conductive wiring embedded in dielectric substrates having varying feature sizes, particularly having both very narrow (submicron) and very wide (on the order of 100 μm) feature widths.
SUMMARY OF THE INVENTIONThe invention helps to solve some of the problems mentioned above by providing systems, apparatuses and methods for depositing metal during fabrication of electronic devices; for example, integrated circuit wiring and back-end metallization. Embodiments in accordance with the invention utilize one or more techniques, such as selective application of a deposition accelerator or deposition inhibitor, selective accelerator removal (SAR) or selective inhibitor removal, selectively inhibited plating, selectively accelerated plating (SAP), and selective anodic dissolution of a substrate surface to produce an intermediate structure characterized by a metal layer having an “embossed” structure; that is, a metal layer with metal protrusions. The metal protrusions in some embodiments preferably have substantially the same height. Thereafter, the metal is partially removed (preferably isotropically) to isolate metal features and form a desired metal pattern on a dielectric base layer.
Embodiments in accordance with the invention reduce or eliminate standard repetitive surface patterning processing, such as photoresist processing, thereby reducing or eliminating the associated material and equipment expenses, processing time, and environmental costs.
Some embodiments in accordance with the invention utilize membrane-mediated elements to achieve electrochemical oxidization and planarization. Membrane-mediated elements also help to avoid well-known terminal effect phenomena (ohmic-resistance current distribution problems in thin metal layers).
Methods in accordance with the invention allow use of relatively simple, low-cost wet-etching techniques after metal plating that selectively remove remains of metal (e.g., copper) and typically stop at a dielectric or a barrier/etch-stop layer. One basic embodiment of a method in accordance with the invention of forming a metal structure on a substrate comprises applying selectively a pre-deposition agent to the substrate to form a pattern of the pre-deposition agent, while simultaneously attaching substantially none of the pre-deposition agent to the substrate outside of the pattern. This forms a treated pattern region containing the pre-deposition agent and a non-treated region outside of the pattern. Thereafter, metal is deposited on the substrate. The pre-deposition agent in the treated pattern region causes a treated metal-deposition rate in the treated pattern region to be different from a non-treated metal-deposition rate in the non-treated region.
In some embodiments, the substrate is initially substantially smooth during the step of selectively applying pre-deposition agent to form the pattern. In some embodiments, applying selectively the pre-deposition agent includes physically contacting the substrate with a stamp. The stamp has a contact surface of the pattern and contains the pre-deposition agent at its stamping surface. In some embodiments, selectively applying pre-deposition agent to form the pattern includes applying the pre-deposition agent to the substrate using inkjet printing. In some embodiments, the substrate comprises a metal layer above a dielectric base layer, and pre-deposition agent is selectively applied to the metal layer.
In some embodiments, the pre-deposition agent is selected from a group including a deposition accelerator and a deposition accelerator precursor, and the treated pattern region comprises an accelerated pattern region. Some embodiments utilizing a deposition accelerator precursor further include activating the deposition accelerator precursor in the treated pattern region before depositing metal. Typically, embodiments having an accelerated pattern region further comprise steps of continuing depositing metal until a thickness of deposited metal in the accelerated pattern region is thicker than a thickness of metal in the non-treated region. Thereafter, removing metal from the non-treated region forms a desired metal pattern. In some embodiments, removing metal from the non-treated region results in isolating raised metal portions in the accelerated pattern region to form a desired metal structure. In some embodiments, removing metal from the non-treated region comprises isotropically removing metal from the substrate. In some embodiments, isotropically removing metal from the substrate comprises wet etching.
In some embodiments, the pre-deposition agent comprises a pre-deposition agent selected from the group consisting of a deposition inhibitor and a deposition inhibitor precursor, and the treated pattern region comprises an inhibited pattern region. Some embodiments utilizing a deposition inhibitor precursor further include activating the deposition inhibitor precursor in the treated pattern region before depositing metal. Typically, embodiments having an inhibited pattern region further comprise continuing depositing metal until a thickness of deposited metal in the non-treated region is thicker than a thickness of metal in the inhibited pattern region. Thereafter, removing metal from the inhibited pattern region forms a desired metal pattern. In some embodiments, removing metal from the inhibited pattern region results in isolating raised metal portions in the non-treated region to form a desired metal pattern. In some embodiments, removing metal from the inhibited pattern region comprises isotropically removing metal from the substrate. In some embodiments, isotropically removing metal from the substrate comprises wet etching.
Another basic embodiment of a method in accordance with the invention is useful to form a metal structure on an initially smooth substrate includes steps of: applying globally a pre-deposition agent to an initially smooth substrate to form a global layer of pre-deposition agent; modifying a portion of the global layer of pre-deposition agent in a modifying pattern to form a treated pattern region and a non-treated region outside of the pattern; and thereafter depositing metal on the substrate. A treated metal-deposition rate in the treated pattern region is different from a non-treated metal-deposition rate in the non-treated region.
In some embodiments, the initially smooth substrate comprises a metal layer above a dielectric base layer, and the pre-deposition agent is globally applied to the metal layer. Some embodiments further comprise activating the pre-deposition agent before depositing metal.
In some embodiments, the steps of applying globally a pre-deposition agent and modifying a portion of the global layer of pre-deposition agent include a combination of steps selected from a group including: applying a global accelerator precursor layer and thereafter activating a portion of the global accelerator precursor layer to form an accelerated pattern region; applying a global accelerator layer and thereafter deactivating a portion of the global accelerator layer to form an accelerated pattern region; applying a global inhibitor precursor layer and thereafter activating a portion of the global inhibitor precursor layer to form an inhibited pattern region; and applying a global inhibitor layer and thereafter deactivating a portion of the global inhibitor layer to form an inhibited pattern region. In some embodiments, activating or deactivating or other modifying species are applied to a substrate before (rather than after) applying a global layer of pre-deposition agent.
It is understood that various embodiments in accordance with the invention include intervening steps and processes between the process steps described and claimed herein. For example, in some embodiments, after applying a global accelerator precursor layer, a substrate is annealed and rinsed, and thereafter, a portion of the global accelerator layer is deactivated.
In some embodiments, modifying a portion of the global layer of pre-deposition agent in a pattern to form a treated pattern region comprises applying selectively a pre-deposition modifier to the global layer to form a modification pattern, while attaching relatively little or none of the pre-deposition modifier to the global layer outside of the modification pattern. In some embodiments, a modification pattern is a positive pattern of a desired metal pattern of a device or structure. In some embodiments, a modification pattern is a negative pattern of a desired metal pattern of a device or structure. In some embodiments, a pre-deposition modifier is applied to the substrate before applying a global layer of pre-deposition agent to the substrate.
In some embodiments, applying selectively a pre-deposition modifier to the global layer includes physically contacting the global layer with a stamp. The stamp comprises a contact surface of the modification pattern, and the stamp contains pre-deposition modifier at its stamping surface. In some embodiments, applying selectively a pre-deposition modifier to the global layer includes using inkjet printing. Some embodiments further comprise activating a pre-deposition modifier before depositing metal.
In some embodiments, applying a pre-deposition modifier to the global layer comprises applying a pre-deposition modifier selected from the group including an accelerator precursor activator, an accelerator deactivator, an inhibitor precursor activator, and an inhibitor deactivator.
In some embodiments, modifying a portion of the global layer of pre-deposition agent in a pattern to form a treated pattern region comprises applying radiation to the global layer of pre-deposition agent. Examples include applying radiation through a patterned mask, applying radiation using a focused light source, and applying radiation using computer-controlled scanning.
In some embodiments, modifying a portion of the global layer of pre-deposition agent in a pattern to form a treated pattern region comprises selectively removing portions of the global layer, thereby forming a treated pattern region containing the pre-deposition agent and a non-treated region outside of the pattern. An example of a technique for selectively removing portions of a global layer includes laser ablation.
In some embodiments in accordance with the invention, the initially smooth substrate comprises a metal layer above a dielectric base layer. A pre-deposition agent is applied globally above the metal layer. Selectively removing portions of the global layer comprises removing portions of the global layer and portions of the metal layer to form the treated pattern region. In some embodiments, selectively removing portions of the global layer includes performing selective anodic dissolution. In some embodiments, selectively removing portions of the global layer comprises performing selective non-electrolytic chemical oxidation.
In some embodiments, the treated pattern region comprises a region selected from the group including an accelerated pattern region and a non-inhibited region. Depositing metal is continued until a thickness of deposited metal in the treated pattern region is thicker than a thickness of metal in the non-treated region. Then, metal is removed from the non-treated region to form a desired metal pattern. In some embodiments, removing metal from the non-treated region comprises isolating raised metal portions in the treated pattern region to form a desired metal pattern. In some embodiments, removing metal from the non-treated region comprises isotropically removing metal from the substrate. In some embodiments, isotropically removing metal from the substrate comprises wet etching.
In some embodiments, the treated pattern region comprises a region selected from the group including an inhibited region and a non-accelerated region. Metal deposition is continued until a thickness of deposited metal in the non-treated region is thicker than a thickness of metal in the treated pattern region. Then, metal is removed from the treated pattern region after the processes of depositing metal to form a desired metal pattern. In some embodiments, removing metal from the treated pattern region comprises isolating raised metal portions in the non-treated region to form a desired metal pattern. In some embodiments, removing metal from the treated pattern region comprises isotropically removing metal from the substrate.
Methods in accordance with the invention are generally useful to deposit a material on a substrate during fabrication of electronic equipment. Exemplary embodiments include electroplating metal on a substrate. Methods in accordance with the invention are also useful with other metal deposition techniques, including electroless metal plating, physical vapor deposition, and chemical vapor deposition. A feature of embodiments in accordance with the invention is the ability to form metal structures on a substrate without photoresist processing, patterning an etch resist layer, or etching a resist layer.
Other features, characteristics and advantages of embodiments in accordance with the invention will become apparent in the detailed description below.
A more complete understanding of the invention may be obtained by reference to the drawings, in which:
The invention is described herein with reference to
The word “substrate” herein can mean an entire workpiece, an underlying material on which another material is deposited or from which material is removed, and generally any object on which some treatment is performed. In this disclosure, the terms “substrate”, “substrate surface” and related terms generally mean the surface of the workpiece as it exists at a particular phase of fabrication and on which a particular fabrication process is being conducted. The terms “substrate”, “workpiece” and related terms are often used interchangably. The terms “substrate”, “workpiece” and related terms generally refer to a whole substrate and its surface area or to a substantial (macroscopic) portion of the substrate.
In this specification, terms of orientation, such as “face-up”, “above”, “below”, “up”, “down”, “top”, “bottom”, and “vertical” used to describe embodiments relate to the relative directions in
The terms “accelerator”, “accelerant”, “accelerated”, “accelerator species” and related terms are used interchangeably in this specification to designate a chemical condition of a workpiece, as well as associated chemical species that interact with the surface of a workpiece and enable a greater rate of metal deposition than in areas with less or no accelerator. Often the acceleration occurs in association with the simultaneous use of other chemicals, for example, a plating bath “suppressor”, and acceleration is relative to the behavior prevalent in the absence of the accelerant compared to behavior in the presence of the other chemical of chemicals. The terms “accelerator precursor”, “accelerator precursor species” and related terms designate a chemical species that transforms during a method in accordance with the invention into another species that produces a greater rate of metal deposition at the surface of a workpiece. The terms “accelerator”, “accelerator precursor”, “accelerating species” and related terms are often used in this specification interchangeably. Their meanings are clear from the context in which they are used. The term “species” is used broadly to include an atom, a molecule, a molecular fragment or group, and their combinations and complexes. The terms “accelerator”, “accelerator film” and related terms are also used broadly to designate both accelerator species and also a formulation that includes accelerator species, but which can also include other materials, such as liquid or dried solvent, precursor compounds of accelerator species, and formulation materials. While the term “accelerator solution” is used broadly here to mean any material suitable for use as an accelerator (without restriction to its physical state or to its being a dissolved compound in another material), it is perhaps easier to understand the concepts presented by considering an accelerator solution in accordance with the invention as typically comprising a known amount of accelerator molecules dissolved in a liquid solvent. It is understood, however, that an accelerator can be attached to the workpiece via a vapor or solid phase interaction, negating the need for forming a liquid accelerator solution. In such embodiments, accelerator is applied to the surface from an accelerator gas or gas mixture, or by physical contact with a transferring material, from which accelerator is transferred directly to the substrate surface and/or by diffusion of accelrator from within the solid transferring material. Furthermore, pure chemicals or a solution of accelerator in a supercritical state (fluids at pressures and temperatures about the critical point) are also useful. The meaning of the various terms as used is clearfrom their context. While not being bound to a particular theory or mechanism, it is believed that accelerators referred to in the specification provide accelerator species that are strongly adsorbed (typically chemisorbed) on a workpiece surface, which accelerator species activate the surface. Generally, when the accelerator is a molecule, a portion of the molecule is functional in binding the molecule strongly to the surface, while one or more other portions of the molecule are effective in catalyzing (or mitigrating suppression of) the deposition process. Exemplary accelerators in accordance with the invention are described in co-owned and co-pending U.S. patent application Ser. Nos. 10/739,822, filed Dec. 17, 2003, by Mayer et al., and 10/824,069, filed Apr. 13, 2004, by Drewery et al., which are incorporated by reference. Exemplary embodiments of accelerator molecules suitable for making an electroplating accelerator solution in accordance with the invention include, among others: 2-mercaptoethane sulfonic acid (MESA), 3-mercapto-1-propane sulfonic acid (MPSA), mercaptopyruvate, 3-mercapto-2-butanol, 1-thioglycerol, dimercaptopropane sulfonic acid (DMPSA), dimercaptoethane sulfonic acid (DMESA), and salts thereof. Derivatives of these compounds having the same functional groups are also suitable accelerators (e.g., 5-mercapto-1-pentane-sulphonic acid). These are typically used in aqueous solutions having a concentration in a range of about 1 ppm to 1000 ppm. With the exception of the dimercaptides listed above (that are believed to be converted to the monomer under electrochemical reduction), these and similar accelerators have been found to adsorb strongly to a workpiece surface (e.g., to copper metal seed layer) upon simple contact by spraying or immersion. In some cases, the accelerators acting alone show slight inhibitory (polarizing) influence when compared to plating from a simple bath (e.g., metal ions; pH and conductivity adjusting acids: bases or salts in the absence of other, typically organic, surface-kinetics-influencing chemicals), and do not interfere substantially with the kinetics of an overall electrochemical charge transfer process. In some embodiments, accelerators are used in plating baths containing strongly specifically adsorbing species, such as halides (commonly either chloride or bromide anions in a 20 ppm to 100 ppm concentration range) and organic suppressors (e.g., polyethylene oxide, polyproplene oxide, and their copolymers). In such embodiments, the addition of the halide/suppressor components to a plating bath substantially increases plating resistance compared to baths without these components, and the accelerator substantially removes the combined polarizing effect of the halide/suppressor combination. Various accelerator and inhibitor molecules are suitable for use in accordance with the invention. Preferred accelerators in accordance with the invention have some of the following attributes: They can be adsorbed (or otherwise attached) onto a workpiece surface or region; are able to be removed selectively from. exposed regions (e.g., using a technique such as: non-electrochemical reaction and dissolution, anodic electrochemical dissolution of underlying metal, laser ablation); are able to increase substantially the metal deposition rate in a plating bath over a rate observed without the accelerator; and have long sustained influence (e.g., as a result of not being significantly incorporated into the deposited metal during the deposition process) and hence remain accelerating throughout a metal deposition process. Preferred solvents for dissolving accelerators include deionized water, alcohols and ketones. Accelerators with more organic/hydrophobic character (e.g., long chain organic mercaptosulphonates) may be more suitably dissolved in non-polar/organic solvents. Although the presence of accelerator on a substrate is depicted for clarity in the drawings in this specification as having relatively substantial thickness, it is believed that only a very thin film, often as thin as a monolayer or submonolayer of accelerator species, is actually required to achieve an accelerating effect.
The accelerating effect of certain accelerator species in accordance with the invention is long lived. The accelerating effect persists even when surfaces (and associated metal atoms) on which the accelerator was initially deposited/attached have been embedded deep inside a growing plated film. The accelerator appears to “float” on the metal surface and avoids being buried in the deposited metal. Because the accelerator avoids substantial incorporation into a deposited metal film, the accelerating effect on film growth does not significantly diminish during subsequent deposition of metal atoms. Without being bound to a particular theory, it is assumed for purposes of explanation that an accelerator remains on the surface throughout the deposition process unless removed (e.g., removed by laser ablation).
On the one hand, the terms “accelerated region”, “activated accelerator” and related terms and, on the other hand, the terms “non-accelerated region”, “inhibited area”, “inhibited region” and similar terms are relative terms. The terms accelerated region and related terms (non-inhibited region) refer to a region or area comprising a higher concentration of attached accelerator species (or a lower concentration of inhibitor species) relative to a non-accelerated (or inhibited region), and the higher concentration of accelerator species in an accelerated region (or lower concentration of inhibitor species in a non-inhibited region) is able to cause a faster rate of metal deposition than in a non-accelerated (or inhibited) region.
The terms “inhibitor”, “inhibitor species” and related terms are used interchangeably in this specification to designate chemical species that diminish, resist, impede, obstruct or suppress the deposition (e.g., by electroplating) of metal onto the surface of a workpiece and cause (often in association with the simultaneous use of other chemicals, e.g., in a plating bath) a slower rate of metal deposition than in areas with less or no inhibitor. The terms “inhibitor precursor” and “inhibitor precursor species” and related terms designate a chemical species that transforms during a method in accordance with the invention into another species that inhibits, diminishes, impedes, obstructs, resists, or slows metal plating at the surface of a workpiece. The terms “inhibitor”, “inhibitor precursor”, “inhibitor species” and related terms are often used in this specification interchangeably. Their meanings are clear from the context in which they are used. The term “species” is used broadly to include an atom, a molecule, a molecular fragment or group, and their combinations and complexes. The terms “inhibitor”, “inhibitor film” and related terms are also used broadly to designate both inhibitor species and also a formulation that includes inhibitor species, but which can' also include other materials, such as liquid or dried solvent, precursor compounds of inhibitor species, and formulation materials. While the term “inhibitor solution” is used broadly here to mean any material suitable for use as an inhibitor, (without restriction to its physical state or being a dissolved compound in another material), it is perhaps easier to understand the concepts presented by considering an inhibitor solution in accordance with the invention typically comprising a known amount of inhibitor molecules dissolved in a liquid solvent. It is understood that, alternatively, the inhibitor can be attached to the workpiece via a vapor phase or solid interaction, negating the need for forming a liquid inhibitor solution. In such a case, the inhibitor is applied to the surface from an inhibitor gas or gas mixture or by physical contact and transfer and/or diffusion from the surface of the solid or from within the solid. Furthermore, pure inhibitor species or a solution of inhibitors in a supercritical state (fluid at pressures and temperatures about the critical point) are also useful in accordance with the invention.
The word “inhibitor” and related terms used herein should not be confused with the word “suppressor” (sometimes called “carrier”) and related terms as often used in the art of electroplating. Suppressor molecules differ from inhibitors fundamentally by (1) their relative strength of adsorption to the metal surface and (2) their method of utilization in a metal plating process. While both inhibitors and suppressors inhibit metal deposition and add kinetic resistance (surface overpotential or overvoltage) to the plating process, not all suppressors are useful as inhibitors in accordance with the invention. The meaning of the various terms will also be clear from their context. While not being bound to a particular theory or mechanism, suppressors mentioned in the specification provide suppressor species that can be considered weakly bound and weakly physically adsorbed to a workpiece surface. In contrast, inhibitor species in accordance with the invention are strongly bound or strongly chemisorbed. When a suppressor is in a plating bath, it tends to suppress plating and increase polarization by mechanisms such as blocking molecular transport to the interface and interfering with the charge transfer of depositing species, or otherwise retarding plating at the surface. Suppressors are generally easily removed from the surface and, therefore, able to move over the surface and disconnect from the surface in a dynamic fashion under normal operating conditions (temperature, pressures, pH). As a result, they are able to maintain the suppressing effect, typically a required component of a plating baths. Also, suppressors are typically not substantially incorporated into the electrodeposit.
Although an inhibitor on a substrate is depicted for clarity in the drawings in this specification having relatively substantial thickness, it is believed that only a fractional monoloayer to a few monolayers of inhibitor species is actually adsorbed to a workpiece surface (e.g., to a seed layer).
Similar to accelerators in their affinity for a substrate surface, inhibitors are generally not free to move across the surface or re-dissolve into a plating bath. Also, the inhibiting effect of certain inhibitor species in accordance with the invention is long lived. The inhibition persists even when surfaces on which the inhibitor was initially deposited have not received additional inhibitor and the metal atoms onto which the inhibitor was originally attached have been embedded inside a growing plated film. The inhibitor can be viewed as strongly attached to the surface, unable to move laterally substantially, but able to “float” on the metal surface as the metal film is deposited, and not be substantially incorporated into the film during the film growth process (at least not to an extent of significantly diminishing the inhibiting effect). Without being bound to a particular theory, it is assumed for purposes of explanation that the inhibitor remains on the surface throughout the deposition process unless removed (e.g., removed by laser ablation). In embodiments in which the inhibitor is a large molecule, it may have two different functional and spatially separated elements, one that reacts with the surface and attaches the molecule to the surface, and another portion that inhibits the deposition process. Although not being bound to a particular theory, one or more possible inhibition mechanisms include: interacting with another species in the electrolyte; blocking the transport of certain species necessary for the deposition process from reaching the surface; and interfering with an intermediate deposition atom or complex.
Some chemicals useful as inhibitors have been utilized in the past as “levelers” in electroplating baths. Like “suppressor”, the term “leveler” is also quite colloquial and requires some explanation. In generally, levelers are plating bath additives used to diminish plating and polarize the surface at targeted surface regions; primarily raised regions and corners that would otherwise see amplified growth due to their exposure to the supply of chemicals and to an electric field. Not all conventional levelers are effective as inhibitors. For example, some levelers' primary mode of action is by diffusion-limited transport in combination with direct incorporation (consumption) into the electrodeposit. On the other hand, other levelers, useful as inhibitors, are strongly attached to the surface, are strongly polarizing, but are not significantly incorporated into the deposit during electrodeposition. Some inhibitors act in tandum with accelerators and/or suppressors to achieve their useful effect. For example, in some embodiments, an inhibitor acts as a deactivator of an accelerator by being more strongly reacting and attached to the surface than the accelerator molecule, effectively displacing the chemisorbed accelerator. Therefore, a combination of various types of species, such accelerators, inhibitors, and suppressors, is utilized in some embodiments and is within the scope of this invention.
The terms “accelerator”, “suppressor”, “leveler”, “inhibitor” and related terms are also used in this specification to designate certain additives used in plating solutions, such as additives in electroplating solutions used in the art for bottom-up filling of high-aspect ratio features. Co-owned U.S. Pat. No. 7,232,513, issued Jun. 19, 2007, to Webb et al., entitled “Electroplating Bath Containing Wetting Agent For Defect Reduction”, which is hereby incorporated by reference, further describes additives used to control plating characteristics of electroplating solutions. In summary, often, species useful as additives in electroplating solutions are also useful as accelerator or inhibitors in accordance with the present invention. When used in accordance with the invention, however, an accelerator and an inhibitor are directly applied globally or selectively to specific regions of a substrate surface, in contrast to being merely dissolved in a plating bath.
The terms “deactivator”, “deactivating species”, “pre-deposition agent poison” and related terms in this specification refer to a species suitable for deactivating a pre-deposition agent or removing it from the surface. An exemplary deactivator of an accelerator functions by reacting with an accelerator to convert the accelerator to a species that is non-accelerating or less accelerating than the accelerator species, or by weakening the accelerator-to-surface bond to facilitate its release from the surface. Typically, an accelerator-deactivator is applied in a modifying pattern that is a negative of a desired metal pattern to a substrate that has been previously globally treated with an accelerator. In some embodiments, a deactivating species adheres to a substrate surface to mask or to smother an accelerator, rather than to react chemically with the accelerator. In still other embodiments, a deactivating species adsorbed to an accelerated surface interferes with metal deposition directly, virtually preventing deposition of metal onto the negative pattern of deactivating species. In still other embodiments, a deactivating species is applied to a substrate before the accelerator. The deactivator adsorbed to a substrate surface interferes selectively with subsequent global application of an accelerator species to the substrate, ultimately preventing deposition of metal onto the negative pattern of deactivating species. In summary, a deactivating species in accordance with the invention results in less deposition of metal on deactivated surfaces compared to deposition of metal on accelerated surfaces. An exemplary accelerator solution for globally accelerating a substrate surface is a solution of 100 ppm MPSA in ethanol. An exemplary deactivating material suitable for deactivating MPSA is any reactant that converts the acid to an alcohol.
A deactivator of an inhibitor selectively applied in a modifying pattern to a substrate modifies a global layer of inhibitor or inhibitor precursor. In some embodiments, inhibitor-deactivator is applied onto a previously applied global layer of inhibitor species. In some embodiments, a modifying pattern of inhibitor-deactivator is applied to the substrate first, and then a global layer of inhibitor species is applied above the deactivator. A deactivator of an inhibitor is applied in a modifying pattern that is a positive of a desired metal pattern. The deactivation of the inhibitor causes the rate of metal deposition to be faster than in inhibited regions.
Some essentially organic compounds that are used as suppressor additives in conventional bottom-up filling plating solutions actually act as plating accelerators in accordance with the invention when present on a substrate that is being plated using an inorganic plating solution without organic additives (such as levelers, suppressors, accelerators).
When a mercapto-alcohol is used an accelerator in accordance with the invention, it can be deactivated by reacting the molecule with sulfuric acid to turn the alcohol into its acid form.
The term “liquid” is used broadly herein to include not only liquids, but also combinations of liquids and solids, such as slurries and suspensions.
The term “substrate-treating species” and similar terms are used in this specification to refer broadly to species that effect, directly or indirectly, a rate of deposition of a material onto a substrate. The term “pre-deposition agent” refers to a type of substrate-treating species that is applied to a substrate and that, either in its applied form or in a modified form, directly affects a rate of material deposition onto a substrate. Examples of a pre-deposition agent in accordance with the invention include an accelerator species, an accelerator precursor, an inhibitor, and an inhibitor precursor. The term “pre-deposition modifier” is another type of substrate-treating species that is applied to a substrate and that modifies in some way the behavior of a pre-deposition agent. Typically, a pre-deposition modifier is applied selectively to a substrate above a previously applied global layer of pre-deposition agent. In some embodiments, a pre-deposition modifier is applied selectively to a substrate before application of a global layer of pre-deposition agent. Examples of a pre-deposition modifier in accordance with the example include an activator of an accelerator precursor, a deactivator of an accelerator, and activator of an inhibitor, and a deactivator of an inhibitor. Implicitly included among deactivators are a deactivator of an accelerator precursor and a deactivator of an inhibitor precursor. Relative terms such as “substantially none”, “relatively little” and similar terms are sometimes used in the specification to denote the relative absence of a substrate-treating species within or outside a pattern region of a substrate compared to the presence of a substrate treating species in a different region of the substrate. The difference in the amount of a substrate-treating species between a treated region and a non-treated region is sufficient to cause a substantial difference in metal deposition rates between the regions in accordance with the invention.
Some embodiments in accordance with the invention involve imprinting (or stamping) a substrate to apply selectively a substrate-treating species in a pattern corresponding to a positive or a negative image of a desired metal pattern. Selection criteria of stamp materials of composition include, among others: stamp material hardness, compliance and flexibility; substrate flexibility; stamp material absorption properties for a particular substrate-treating species (e.g., accelerator species and solvent; deactivating species and solvent); relative adsorption affinities of selected substrate-treating species to the stamping material and to substrate material; size of pattern lines; applied pressure between the imprinting element and the substrate; desired throughput (stamping rate); stamp life (total number of useful imprints without loss of line-defining desired resolution) and other characteristics. In some embodiments, a stamp 104 (
The term “anodizing” herein means establishing on a conductive material an electrical bias that is positive relative to some reference material, such as electroplating liquid or a negatively-biased cathode. Similarly, the term “cathodizing” means establishing on a conductive material an electrical bias that is negative relative to some reference material, such as electroplating liquid or a positively-biased conductive material (e.g., an anode). The terms “cathodic plating”, “electrochemical deposition” and related terms are used synonymously in this specification. The terms “anodic dissolution”, “electrochemical dissolution” and related terms are used synonymously in this specification. The terms “unbiased”, “electrically unbiased” and related terms imply that there is substantially no electrical or ionic current. The term “nonconductive” means electronically nonconductive or ionically nonconductive or both.
The word “area” is used in this specification generally to refer to an area on a substrate surface. The term “nominal area” refers to the area of surface that would be measured if the surface were smooth, without embedded features, raised areas, and other area-increasing topography. The word “region” used in this specification refers generally to a three-dimensional region of a substrate.
Etching is used to describe a process in which metal is removed without an imposed external power supply and is generally facilitated by the presence of an oxidizer (a chemical that is reduced to oxidize the metal). Examples of oxidizers for the etching of copper include oxygen, chlorine, bromine, various peroxides (e.g., hydrogen peroxide), permanganate, and persulfate. The term “isotropic etching”, “isotropic removal” and related terms are used in this specification in their usual sense to designate an etching process or other type of material removal operation in which the rate of the etching reaction or other material removal technique is the same in any direction. The term “kinetically-controlled isotropic removal”, “surface-kinetics-controlled isotropic etching” and related terms relate to metal removal techniques in which the material removal rate from a substrate surface is apparently controlled by the reaction kinetics of etching reactions rather than by diffusion processes to or from the surface. Kinetics-controlled etching is characteristically different from diffusion-controlled etching in that kinetics-controlled etching is generally independent of transport phenomena (fluid agitation), and results in an etching rate that is largely independent of feature size, feature separation, feature density, position within a feature and other geometric factors. In some embodiments, kinetics-controlled isotropic etching is more desirable than diffusion-controlled isotropic etching.
The term “topography” and related terms used in the specification refer principally to the topographic relief of a substrate, that is, to characteristics of surface relief such as surface contours, protrusions, planar field areas, feature cavities and recesses. This is in contrast to other uses of the word “topography” in the semiconductor arts that are related to the circuit patterns and their material compositions in integrated circuits.
The terms “smooth surface”, “initially smooth” and related terms are used in the specification to refer to a substrate surface that is substantially free of recesses and raised features on at least a portion of the surface on which a metal structure is to be formed in accordance with the invention. A characteristic feature of some embodiments in accordance with the invention is that metal is plated or otherwise deposited onto an initially substantially smooth surface. This is in contrast with the prior art in which metal is commonly plated into a recessed cavity (e.g., a gap or trench) or between raised features of a substrate. The term “global treatment”, “global etching”, “global removal” and related terms are used in this specification to refer to a substrate treatment process conducted over the whole or a substantial portion of a substrate surface at a given time. The term “localized treating”, “localized etching”, “local removal” and related terms refer to a treatment or process that is conducted in a relatively small portion of a substrate surface at any given time. It is understood that a series of sequential operations involving localized treatment typically result in treatment of a substantial portion or of the whole of a substrate surface.
Methods in accordance with the invention for forming metal features in electronic devices through selective substrate treatment and selective acceleration or inhibition of metal deposition are described herein with reference to
As described herein with reference to
As depicted in
In contrast to conventional techniques known in the art, metal wirings 162 shown in
A variation of an embodiment described with reference to
As described herein with reference to
In another embodiment (not depicted in the drawings), a global layer of accelerator precursor is applied to a substrate, and precursor activator is selectively applied in a modification pattern that is a positive pattern of a desired metal pattern.
As described herein with reference to
A variation of an embodiment described with reference to
It is understood that embodiments in accordance with the invention may include other intervening or follow-up steps, such as heating, irradiation, annealing, chemical activation using vapor and liquid phase, rinsing and drying.
Other embodiments (not depicted in the drawings) involve global application of an inhibitor precursor (a pre-deposition agent) on a substrate, followed by selective application of an inhibitor-precursor-activator (a pre-deposition modifier) in a modification pattern that is a negative of the desired metal pattern. Other embodiments (not depicted in the drawings) involve global application of an inhibitor (a pre-deposition agent) on a substrate, followed by selective application of an inhibitor-deactivator (inhibitor poison) (a pre-deposition modifier) in a modification pattern that is a positive of the desired metal pattern. In some embodiments, a pre-deposition modifier is applied to the substrate before application of a pre-deposition agent.
In another embodiment in accordance with the invention, a stamp die (e.g., stamped die 330) is used as a positive to impress a stamp blank and thereby fabricate a stamp for selectively applying a substrate-treating species to a substrate surface.
Some embodiments in accordance with the invention utilize an inkjet-type device to apply selectively a substrate-treating species to a substrate surface, particularly to apply a species that regulates metal deposition on a substrate surface in a positive or negative of a desired metal pattern.
Substrate 436 includes base dielectric layer 438 and metal seed layer 440, which is located on dielectric layer 438. As depicted in
Some embodiments in accordance with the invention apply a pattern of a selected form of electromagnetic radiation to a global layer of a substrate-treating species (including a precursor of a substrate-treating species) to create a pattern of corresponding substrate-treating species on the substrate. In some embodiments, energy applied to the substrate activates or alternatively deactivates a patterned portion of the global layer. In some embodiments, the energy removes, or ablates, substrate-treating species or precursor from the substrate. Generally, radiation is directed through a patterned mask towards the substrate. Techniques for making patterned masks operable to selectively irradiate and to shield a substrate are known in the field of photolithography. Alternatively, in some embodiments, radiation is applied to various portions of the surface by scanning a focused beam of energy along and across the surface to activate, deactivate, or remove/ablate substrate-treating species, such as by a focused laser.
Techniques in accordance with the invention for global application of substrate-treating species, such as an accelerator or an inhibitor (or precursor species), to a substrate surface include one or more of a variety of means including, but not limited to: dipping the surface in a solution containing substrate-treating species; spraying the surface with a solution containing dissolved substrate-treating species; drying a surface of a liquid containing dissolved substrate-treating species or precursors of substrate-treating species; depositing a film from a vapor containing the substrate-treating species; electrochemically transforming precursors of substrate-treating species to form a chemically active substrate-treating species, and electrolessly forming a substrate-treating species.
In some embodiments, energy applied to the substrate in additional steps activates the patterned portion of substrate-treating precursor species.
A lamp 164, 502, 522, 542, 562, 592 that is operable to a irradiate a substrate in accordance with the invention typically supplies radiation selected from a group including, among others: UV radiation, microwave, X-ray, excimer laser light, and infrared. It is understood that various other techniques in addition to irradiation are suitable to convert a precursor species to an active species, and to deactivate an active species, such as particle and ion bombardment. Still other techniques include, among others: oven heating; and addition of chemical reactants to cause chemical reaction.
Laser ablation is similar to conventional photolithography in that light is projected through a patterned mask onto a substrate or focuses and scans over the surface. Techniques for making dielectric masks suitable for use with constant-source, pulsed, and excimer laser ablation are known in the art. Exemplary mask materials include chrome coated glass. Exemplary specification and operating ranges are: laser wavelength, 200 to 800 nanometer (nm); pulse width, 1 ps to continuous (1% to 100% duty cycle); pulse frequency, 1 to 100000 per second; intensity, 10 mW to 100 W; 0.3 to 1000 μm spot size).
Some embodiments in accordance with the invention combine some of the techniques of classical damascence feature filling and a global inhibition of the raised (field) surface with inhibitor or inhibitor precursor species to achieve improved damascene feature filling. Such techniques are able to enhance the relative rates of plating within and outside the features, allowing filling of features that could not be accomplished by more classical means. Generally, a structure similar to that shown in
Because in some embodiments the recessed region may be quite wide and narrow (i.e., it can have a very low aspect ratio), it is important that the stamp used be of considerable stiffness to avoid bending it into the wider features, thereby avoiding contacting the stamp with the bottom of the features and imparting inhibitor into a region where it is not desired. In some cases, the damascene surface is not perfectly flat (due to mechanical construction tolerances or underlying topography of a multilayered device), so some degree of compliance is required on a longer length scale. Therefore, a balancing between having the stamp not penetrate certain features, but not having it be too rigid to make good contact, is often required. In some embodiments, this balancing is done by, among other techniques: choosing a stamp material that does not touch the bottom of the widest features with the target applied pressure; by dividing the stamp into sub-sections connected by very thin regions, allowing a group of relatively stiff blocks to comply to the surface independently.
Once the inhibitor has been applied to the surface (or inhibitor precursor has been applied and converted by appropriated means to an inhibitive species), metal deposition on the substrate surface is performed. Due to the relative polarization of the recess accelerated regions and the inhibited raised regions, extremely large relative rates of electroplating can be achieved. In other embodiments, accelerator is not applied to the recessed areas. Inhibitor or inhibitor precursor is applied by stamping or other technique to the field areas or other exposed raised areas of the substrate as explained above. Thereafter, metal deposition in the untreated (recessed) regions is faster than in the inhibited (treated) regions of the exposed field and raised areas.
Some embodiments in accordance with the invention include systems and methods for selective anodic dissolution of metal corresponding to a desired metal pattern of an electronic device. Generally, in preferred embodiments, a cationic membrane having an embossed pattern is pressed against the top surface of a substrate which is subsequently anodized. The raised surfaces of the patterned membrane displace, or make less accessible, electrolyte liquid from portions of the substrate surface in physical contact with the membrane. Because there is little or no fluid/electrolyte between the membrane and portions of the substrate surface in contact with the membrane, this substantially prevents anodic dissolution. Electrolyte liquid is present, however, in the hollows, or pockets, of the membrane between raised membrane surfaces. This electrolyte liquid is in contact with the anodized substrate surface. While not wanting to be limited by any particular theory or mechanism, it is suggested that in at least some cases, the electrolyte is a necessary component for the complexing of the anodically formed metal ions, for the formation of protons to enable the dissolution of metal ions, and for other mechanisms. Osmotic drag of the solvent bound to the metal and to protons created during the anodic processes often accompanies the transport of cations through a cationic membrane to maintain its transport properties. Therefore, in some cases, the lack of solvent/electrolyte in between the embossed sections of the membrane and the surface directly or indirectly hinders the anodic dissolution process. In some embodiments, the solvent is a highly resistive electrolyte, or simply pure solvent (e.g., water). In some embodiments, the anodic reaction that removes metal is accompanied by electrolysis of the solvent (e.g., water), which forms protons.
2H2O→4H++O2+4e−
In such embodiments, the formation of protons decreases the pH (Le., makes the electrolyte more acidic), which facilitates dissolution of a soluble form of metal ion (rather than formation or precipitation of an oxide).
Cationic membranes, also known as proton exchange membranes, are known in the fields of fuel cell technology, medical dialysis and the chloro-alkali industry. A characteristic of the cationic membrane in accordance with the invention is the ability to transport protons and smaller cations (A+) particularly small metal cations (M+) away from the anodized substrate surface towards the counterelectrode, while substantially preventing the migration and diffusion of electrolyte anions from electrolyte solution 612 towards anodic substrate 606. The action of the electric field in combination with the properties of the membrane enable positive charge species to carry nearly all their current and enable substantially one-way transport of positive ions from anode to cathode, while simultaneously substantially preventing the migration of cations towards the anode due to migration (which would occur in the absence of the membrane). Hence, these membranes allow a cationic transference number approaching unity. The combination of the membrane properties and a large electric field generated from a highly resistive electrolyte allow maintains a substantial difference in ionic strength between the electrolyte side of the membrane and the anode side. See
As a result of anodic dissolution of metal as described with reference to
Selective, patterned anodic dissolution and selective, patterned plating were discussed with reference to
In some embodiments, selective, patterned anodic dissolution of a global metal layer on a substrate is conducted to form a desired pattern of metal features directly.
In system 650, global metal layer 652 located on base dielectric layer 654 of substrate 656 functions as an anode. Power supply 608 generates a positive bias on metal layer 652 relative to counterelectrode 610. Conductive electrolyte liquid 612 is located between counterelectrode 610 and cationic membrane 614. Cationic membrane 614 having contact surface 620 is pressed against top surface 666 of substrate 656. Highly-resistive electrolyte liquid (e.g., deionized water) 622 is present in pockets 624 located between adjacent raised surfaces 626 of membrane 614. Raised surfaces 626 of membrane 614, however, dispel highly-resistive electrolyte liquid 622 away from top surface 666 of substrate 656. As a result, anodic dissolution of metal in metal layer 652 occurs under membrane pockets 624, but anodic dissolution is suppressed or does not occur at all under raised surfaces 626 of membrane 614 that are in contact with top surface 666 of substrate 656. As a result of anodic dissolution of metal as described with reference to
As depicted in
During anodic dissolution processes, preferably a layer of highly-resistive electrolyte 706 (e.g., deionized water) is located on at least a portion of top surface 708 of substrate 704 that is undergoing anodic dissolution. System 700 further includes mounting plate 710 located above substrate holder 702. System 700 includes counterelectrode 712 mounted on mounting plate 710 and located substantially opposite a substrate 704 on substrate holder 702. During anodic dissolution processes, a power supply 714 generates a positive bias in anode substrate 704. System 700 further includes cationic (proton exchange) membrane 716 located between counterelectrode 712 and anode substrate 704. Membrane 716 has a pattern-embossed contact surface 717, which contains a pattern (typically a positive) corresponding to a desired metal pattern of an electronic device. System 700 further includes conductive electrolyte 718 located between counterelectrode 712 and contact surface 717 of membrane 716. System 700 further includes clamp 720 located at the periphery of mounting plate 710 and which serves to clamp peripheral edges of membrane 716 to the bottom surface 722 of mounting plate 710. System 700 typically includes peripheral seal 724, which forms a liquid-tight seal of the inside space 726 between mounting plate 710 and membrane 716. As depicted in
During anodic dissolution processes, contact surface 717 is in contact with top surface 708 of anode substrate 704. As explained above with reference to
In some alternative embodiments, chemical oxidation (etching) is utilized in place of electrochemical oxidation, that is, in place of anodic dissolution. This approach offers certain advantages over electrochemical techniques because of the even further simplified apparatus required. On the other hand, a chemical oxidation technique typically requires more careful control. In an exemplary method that utilizes chemical oxidation, a microporous or nanoporous material, suitably processed to create a patterned stamp, or membrane, as described above, is impregnated with an etching solution. In some embodiments, this is accomplished by taking a dry piece of porous material and immersing it in an etching solution. In some embodiments, the porous material is exposed to the etching solution and allowed to exchange with the active chemical composition of the solution over an appropriate time period. Thereafter, the patterned stamp, or membrane, is placed onto the surface of the substrate and metal is preferentially oxidized at the locations where the stamp makes direct contact with the substrate surface. Due to the microporous nature of the stamp and associated surface tension effects, etching fluid does not appreciably flow outside of the stamp pattern itself, but rather is retained within the stamp and its patterned surfaces. Hence, only in the areas where actual physical contact is made is the etching agent delivered to the surface, where it reacts with metal to remove the metal.
In some embodiments, the functional part of the chemical oxidation stamp consists essentially of a cationic membrane material, such as NAFION®. Typically, one of the last steps in manufacturing a cationic membrane is to make the membrane acidic by treating it with a strong acid solution. Protons are thereby complexed to the polymer-bound tethered negative ions located within the membranes pores. In the case of NAFION®, sulphonic acid groups are tethered to a fluorinated polymeric backbone. Water used in the acidification step is removable by evaporation/drying, leaving the protons behind. This is the state in which most commercial cationic membranes are manufactured and supplied to customers. In some embodiments in accordance with the invention, the membrane is hydrated with solution containing an oxidizer and the membrane soaks up the solvent and oxidizer. Preferably, the oxidizer molecule is non-ionic and has a relatively small molecular size. An exemplary solution suitable for this step is a water/hydrogen peroxide solution. Hydrogen peroxide, neutral, very small and similar in size to water, enters into the pores of the membrane, hydrating the ions. When a patterned stamp containing the oxidizer is thereafter placed in contact with a substrate, oxidizer and protons are supplied to the surface from the membrane pores. While not bound by any theory, it is believed that the process progresses more or less by the following sequence of events. The oxidizer (e.g., hydrogen peroxide) oxides the surface to a surface oxide (e.g., copper forms cuprous and/or cupric oxide), preferentially, but not necessarily exclusively specific to the areas under the location of the “lands” (actual areas of contact by membrane to substrate); that is, some oxidizer may creep away from a land-contact area. Next, protons from the membrane react with the oxide, to form water and metal ion. As the metal reacts (i.e., etches), water and metal cations are produced. The protons for driving this reaction are spatially confined and limited because, being positively charged, they cannot easily diffuse very far from the membrane without leaving a large net negative charge behind in the membrane. Hence, they are substantially “bound” to the general vicinity of the membrane stamp, and more specifically to the vicinity of the stamp surface area that makes direct contact with the substrate surface. After protons have reacted with the oxide, the metal cations produced tend to diffuse into the membrane. The cations, being positively charged, are tethered to the general vicinity of the membrane and generally enter the membrane pores to maintain charge neutrality.
Typically, the techniques utilized to make a membrane ready for continuous use or for reuse include ion-exchange. The membrane is replenished with oxidizer and protons by exposure to one or more refreshing solutions; for example, one or more fresh solutions containing hydrogen peroxide and acid. Alternatively, the back of the membrane is exposed to a refreshing solution continuously, and a replenishment process occurs substantially in parallel with the etching process, only the replenishment is occurring through the backside of the membrane. The rate of replenishment and the amount of replenishment required depends on the membrane's capacity, thickness, temperature, and amount of metal being etched, along with other process-dependent parameters, as understood by one skilled in the field of chemical engineering.
Similar to electrochemical oxidation (anodic dissolution) approaches described above, several groups of approaches are suitable for using an etching membrane stamp to create isolated metal features, such as interconnect lines. In some embodiments, a membrane is used to remove substantially all metal of a metal layer, down to an underlying dielectric material, from areas in actual contact with the membrane. In such embodiments, metal remains in areas in which no actual contact is made; that is, metal remains between the areas where the patterned stamp-membrane features make contact with the surface. This technique has the advantage of not requiring a subsequent isotropic etching procedure. Nevertheless, due to the finite capacity of a membrane to supply etching reactants and to remove products (e.g., in the case of cation membranes, a finite capacity to supply oxidizer and protons and a finite capacity to hold metal-ion product), the reaction rate slows continuously as the membrane becomes depleted of reactants and full of reaction products. For similar reasons, some time is required to replenish a membrane after its use to make it ready for reuse.
Some embodiments include initially applying a global layer of substrate-treating species, particularly a pre-deposition agent, such as a deposition accelerator or deposition inhibitor, to a substrate surface. Thereafter, the substrate-treating species is removed selectively by placing an oxidizer-containing cationic patterned membrane in contact with the substrate surface. The substrate-treating species is dislodged selectively from the substrate surface where the oxidative etching occurs. Typically, only about 10 Å to 100 Å of metal need be removed to remove most or all of a surface-active pre-deposition agent in accordance with the invention. In embodiments involving a pre-electroplating agent, metal is thereafter selectively deposited on the workpiece substrate using an electroplating bath containing metal ions and other appropriate components as needed, such as suppressors, accelerators, and/or levelers, halagon ions, and acid or metal complexing agents. In other embodiments, selective metal deposition is performed using a suitable electroless plating process. An example of a suitable inhibitor of electroless copper-plating is benzotriazol.
After selective metal deposition results in formation of a metal deposit having topography, metal is removed (e.g., using an isotropic etch) completely from regions having less thickness to isolate metal structures in a desired pattern.
As described with reference to
An exemplary embodiment of a method of forming a stamp in accordance with the invention suitable for selectively applying a substrate-treating species to a substrate surface is described herein with reference to
A circular piece of blank (unpatterned) nanoporous material having a diameter of about 400 mm is fastened to a flat, circular polymeric support having a diameter of about 330 mm. The nanoporous membrane material is attached to the support by a circular ring that slides down around the outside edge of the circular support. One example of a suitable nanoporous membrane material is NAFION®, commercially available from Dupont. Another is resorcinol formaldehyde aerogel, as described in U.S. Pat. No. 4,873,218, issued Oct. 10, 1989, to Pekala, and in U.S. Pat. No. 4,997,804, issued Mar. 5, 1991, to Pekala, which are hereby incorporated by reference as if fully contained herein. NAFION® is prepared by the free radical copolymerization of tetrafluoroethylene and sulfonated comonomer. About 13 mole percent vinyl ether containing a pendant sulfonyl fluoride is utilized. The sulfonyl fluoride is hydrolyzed to the sulfonic acid once the polymer has been converted to membrane form. NAFION® has a wide range of pore sizes, with an average value on the order of 2 nm. A layer of RISTON® (DuPont) photoresist is applied to the blank surface of the membrane (
Alternatively, an oxidative plasma etch as known in the art is used to pattern the blank stamp membrane.
Example 2A 300 mm semiconductor wafer is located face-up on a substrate holder. The wafer comprises a flat base dielectric SiO2 layer covered by a smooth 40 nm copper seed layer. A patterned membrane stamp as described in Example 1 is attached by a circular clamp to a face-down stamping head having a diameter of 330 mm. The material composition of the stamping head is essentially porous polyvinylidene difluoride (PVDF). The stamping head contains an integral liquid reservoir having a total volume of about 200 ml containing 1 g/L MPSA in water accelerator solution. The stamping head is lowered so that the membrane make physical contact with the substrate with a pressure of approximately 1 psi for approximately 2 minutes to form an accelerated pattern region containing accelerator on the substrate (e.g.,
Thereafter, the substrate surface is electrochemically plated in a copper plating apparatus for 60 seconds at 15 mA/cm2 in a bath containing 50 ppm dimercaptopropane sulphonic acid, 50 g/L copper sulfate, 100 g/L sulfuric acid and 500 ppm L-92 polyetheylene oxide suppressor. The resulting plated substrate has an embossed metal layer containing protrusions in the accelerated pattern region and thinly-plated non-treated regions (e.g.,
A 300 mm semiconductor wafer is located face-up on a substrate holder. The wafer comprises a base dielectric SiO2 layer covered by a 20 mm copper seed layer. A patterned membrane stamp as described in Example 1 is attached by a circular clamp to a face-down stamping head having a diameter of 330 mm, as described in Example 2. The stamping head contains an integral liquid reservoir having a total volume of about 600 ml containing 1 g/L 3-mercapto-1-butanol in water accelerator precursor solution. The stamping head is lowered so that the membrane make physical contact with the substrate with a pressure of approximately 1 psi for approximately 2 minutes to form a treated pattern region containing accelerator precursor on the substrate (e.g.,
The accelerator precursor is converted to an active accelerator by converting the alcohol group to a sulfonic acid. This acidification is effected by exposing the substrate surface to 10% sulfuric acid at room temperature for about 1 minute.
Thereafter, the substrate surface is electrochemically plated in a copper plating apparatus for 60 seconds at 15 mA/cm2 in a bath containing 50 ppm dimercaptopropane sulphonic acid, 50 g/L copper sulfate, 100 g/L sulfuric acid and 500 ppm L-92 polyetheylene oxide suppressor. The resulting plated substrate has an embossed metal layer containing protrusions in the accelerated pattern regions and thinly-plated non-accelerated regions (e.g.,
A 300 mm semiconductor wafer is located face-up on a substrate holder. The wafer comprises a base dielectric SiO2 layer covered by a 20 mm copper seed layer. A patterned membrane stamp as described in Example 1 is attached by a circular clamp to a face-down stamping head having a diameter of 330 mm, as described in Example 2. The stamping head contains an integral liquid reservoir having a total volume of about 200 ml containing 1 g/L 6-mercapto-1-hexanol inhibitor in water solution. The stamping head is lowered so that the membrane make physical contact with the substrate with a pressure of approximately 1 psi for approximately 2 minutes to form an inhibited pattern regions containing inhibitor on the substrate (e.g.,
Thereafter, the substrate surface is electrochemically plated in a copper plating apparatus for 60 seconds at 15 mA/cm2 in a bath containing 50 ppm dimercaptopropane sulphonic acid, 50 g/L copper sulfate, 100 g/L sulfuric acid and 500 ppm L-92 polyetheylene oxide suppressor. The resulting plated substrate has an embossed metal layer containing protrusions in the non-inhibited regions and thinly-plated regions in the inhibited pattern regions (e.g.,
To form a global layer of accelerator pre-deposition agent, a 300 mm wafer as described in Example 2 is sprayed with an accelerator solution containing 1 g/L MPSA in water for 1 minute. Then, the substrate is rinsed with deionized water.
Anodic dissolution is then utilized to modify the global layer of accelerator. The substrate is placed on the substrate holder of an anodic dissolution system as depicted in
Approximately 2 volts bias current is applied to the substrate for approximately 2 to 3 seconds, sufficiently to remove about 25 Å to 100 Å of metal seed layer. As described with reference to
Then, the substrate surface is electrochemically plated in a copper plating apparatus for 60 seconds at 15 mA/cm2 in a bath containing 50 ppm dimercaptopropane sulphonic acid, 50 g/L copper sulfate, 100 g/L sulfuric acid and 500 ppm L-92 polyetheylene oxide suppressor. The resulting plated substrate has an embossed metal layer containing protrusions in the accelerated pattern regions and thinly-plated non-accelerated regions (e.g.,
To form a global layer of accelerator, a 300 mm wafer as described in Example 2 is sprayed with an accelerator solution containing 1 g/L MPSA in water for 1 minute. Then, the substrate is rinsed with deionized water. The resulting substrate wafer with globally applied accelerator is placed on a substrate holder 1.0 cm beneath a patterned mask, as described with reference to
Parameters of a Xe—F excimer gas laser having a laser wavelength of 351 nm are selected to heat the substrate surface sufficiently to cause desorption of the accelerator from the substrate surface or to cause deactivation (destruction) of the accelerator present on the surface. The laser has a pulse width of 20 nanosecond (nsec) and a duty cycle of 90 percent. The laser beam has a 10 μm spot size and is applied at a power density of about 3×1018 W/m3. The laser beam is scanned across the substrate surface to create a desired positive pattern of accelerator by selective laser ablation of the adsorbed accelerator. The relative movement of the laser beam relative to the substrate is controlled by a computer program. The laser pulses are overlapped to avoid undesired isolated missed spots.
Then, the substrate surface is electrochemically plated in a copper plating apparatus for 60 seconds at 15 mA/cm2 in a bath containing 50 ppm dimercaptopropane sulphonic acid, 50 g/L copper sulfate, 100 g/L sulfuric acid and 500 ppm L-92 polyetheylene oxide suppressor. The resulting plated substrate has an embossed metal layer containing protrusions in the accelerated pattern regions and thinly-plated regions in the nonaccelerated regions from which accelerator was removed (e.g.,
The particular systems, designs, methods and compositions described herein are intended to illustrate the functionality and versatility of the invention, but they should not be construed to limit the invention to those particular embodiments. Systems and methods in accordance with the invention are useful in a wide variety of circumstances and applications to fabricate metal features embedded in a base layer of an electronic device. It is evident that those skilled in the art may now make numerous uses and modifications of the specific embodiments described, without departing from the inventive concepts. It is also evident that the steps recited may, in some instances, be performed in a different order; or equivalent structures and processes may be substituted for the structures and processes described. For example, a method involving global application of an accelerator precursor, selective application of a deactivator of an accelerator precursor to form a treated pattern region containing accelerator precursor, and subsequent activation of the accelerator precursor has not been explicitly described in this specification. Nevertheless, it is clear that such a method is within the scope of the invention as described above and defined in the claims below. Since certain changes may be made in the above systems and methods without departing from the scope of the invention, it is intended that all subject matter contained in the above description or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features present in or inherently possessed by the systems, methods and compositions described in the claims below and by their equivalents.
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52. A method comprising:
- selectively adsorbing in a pattern a pre-deposition agent to a substrate to form a treated region comprising the pre-deposition agent and a non-treated region not comprising the pre-deposition agent, wherein the pre-deposition agent is selected from the group consisting of deposition inhibitor and deposition inhibitor precursor; and
- after selectively adsorbing in the pattern the pre-deposition agent to the substrate, plating copper on the substrate, wherein a deposition rate of the copper in the non-treated region is higher than a deposition rate of the copper in the treated region.
53. The method of claim 52, wherein the pre-deposition agent is deposition inhibitor.
54. The method of claim 52, wherein the pre-deposition agent is deposition inhibitor precursor and further comprising, before depositing the copper on the substrate, activating the deposition inhibitor precursor.
55. The method of claim 54, wherein activating the deposition inhibitor precursor comprises providing radiant energy from a lamp.
56. The method of claim 52, wherein selectively adsorbing in the pattern the pre-deposition agent to the substrate comprises physically contacting the substrate with a stamp, wherein the stamp comprises a contact surface comprising the pattern and wherein the stamp comprises the pre-deposition agent at the contact surface.
57. The method of claim 56, wherein the stamp comprises a material selected from the group consisting of carbon and silicon based polymer/plastics, plastics with incorporated plasticizers, elastic material, micro and nanoporous materials, and hydrogel polymers and ionomers, polyethylene, polyproprylene, polyvylidene difluoride, polytetrafluoroethylene, polyvinyl alcohol, and PFA-f, polyvinylchloride, ethylene-propylene-diene monomer, natural rubber, polybutadiene, silicon rubber, silicon aerogel, and organic aerogels.
58. The method of claim 52, wherein, before selectively adsorbing in the pattern the pre-deposition agent to the substrate, the substrate is substantially smooth.
59. The method of claim 52, wherein selectively adsorbing in the pattern the pre-deposition agent to the substrate does not include photolithography of the substrate.
60. The method of claim 52, wherein the substrate comprises a seed layer above a dielectric base layer, and wherein selectively adsorbing in the pattern the pre-deposition agent to the substrate comprises selectively adsorbing in the pattern the pre-deposition agent to the seed layer.
61. The method of claim 52, wherein plating the copper on the substrate continues at least until a thickness of the plated copper in the non-treated region is thicker than a thickness of the plated copper in the treated region.
62. The method of claim 61, further comprising, after plating the copper on the substrate, removing copper from the treated region to form a desired copper pattern.
63. The method of claim 62, wherein removing the copper from the treated region comprises isolating raised copper portions in the non-treated region.
64. The method of claim 62, wherein removing the copper from the treated region comprises isotropically removing the copper from the treated region and the non-treated region.
65. The method of claim 64, wherein isotropically removing the copper from the treated region and the non-treated region comprises wet etching.
66. A method comprising:
- adsorbing a pre-deposition agent to a substrate, wherein the pre-deposition agent is selected from the group consisting of deposition inhibitor and deposition inhibitor precursor;
- selectively patterning the pre-deposition agent to form a first region comprising the pre-deposition agent and a second region not comprising the pre-deposition agent; and
- after selectively patterning, plating copper on the substrate, wherein a deposition rate of the copper in the second region is higher than a deposition rate of the copper in the first region.
67. The method of claim 66, wherein selectively patterning the pre-deposition agent comprises anodically dissolving the pre-deposition agent in the second region.
68. The method of claim 66, wherein plating the copper on the substrate continues at least until a thickness of the plated copper in the second region is thicker than a thickness of the plated copper in the first region.
69. A method comprising:
- adsorbing a deposition inhibitor precursor to a substrate;
- selectively activating in a pattern the deposition inhibitor precursor to form a first region comprising the activated inhibitor and a second region not comprising the activated inhibitor; and
- after selectively activating in the pattern, plating copper on the substrate, wherein a deposition rate of the copper in the second region is higher than a deposition rate of the copper in the first region.
70. The method of claim 69, wherein selectively activating the deposition inhibitor precursor comprises providing radiant energy from a lamp.
71. The method of claim 69, wherein plating the copper on the substrate continues at least until a thickness of the plated copper in the second region is thicker than a thickness of the plated copper in the first region.
Type: Application
Filed: Jul 23, 2013
Publication Date: Jan 16, 2014
Applicant: Novellus Systems, Inc. (Fremont, CA)
Inventors: Steven T. Mayer (Lake Oswego, OR), John Stephen Drewery (Santa Clara, CA), Eric G. Webb (Tigard, OR)
Application Number: 13/948,551
International Classification: C25D 5/02 (20060101);
