CMP SYSTEM HAVING AN EDDY CURRENT SENSOR OF REDUCED HEIGHT
By providing an eddy current sensor element in a polishing tool at a reduced height level in combination with a corresponding optical endpoint detection system, standard polishing pads may be used, thereby enhancing the lifetime of the polishing pad and increasing tool utilization.
1. Field of the Invention
Generally, the subject matter disclosed herein relates to the field of manufacturing integrated circuits, and, more particularly, to chemical mechanical polishing (CMP) process tools used for the formation of advanced metallization structures, such as so-called damascene structures, in which metal trenches and vias are formed in an insulating layer, while subsequently filling the vias and trenches with a metal and planarizing the structure by removing the excess metal using a polishing process.
2. Description of the Related Art
Typically, the fabrication of modern integrated circuits requires a large number of individual process steps, wherein a typical process sequence involves the deposition of conductive, semiconductive or insulating layers on an appropriate substrate. After deposition of the corresponding layer, device features are produced by patterning the corresponding layer with well-known means, such as photolithography and etching. As a consequence, by patterning a deposited layer, a certain topography will be created that also affects deposition and patterning of subsequent layers. Since sophisticated integrated circuits require the formation of a plurality of subsequent layers, it has become standard practice to periodically planarize the surface of the substrate to provide well-defined conditions for deposition and patterning of subsequent material layers. This especially holds true for so-called metallization layers in which metal interconnects are formed to electrically connect the individual device features, such as transistors, capacitors, resistors and the like, to establish the functionality required by the circuit design.
In this respect, CMP has become a widely used process technique for reducing “imperfections” in the substrate topography caused by preceding processes in order to establish enhanced conditions for a subsequent process, such as photolithography and the like. The polishing process itself causes mechanical damage to the polished surface, however, in an extremely low range, i.e., at an atomic level, depending on the process conditions. CMP processes also have a plurality of side effects that have to be addressed so as to be applicable to processes required for forming sophisticated semiconductor devices.
For example, recently, the so-called damascene or inlaid technique has become a preferred method in forming metallization layers wherein a dielectric layer is deposited and patterned to receive trenches and vias that are subsequently filled with an appropriate metal, such as aluminum, copper, copper alloys, silver, tungsten and the like. Since the process of providing the metal may be performed as a “blanket” deposition process based on, for instance, electrochemical deposition techniques, the respective pattern of the dielectric material may require a significant over-deposition in order to reliably fill narrow openings and wide regions or trenches in a common process. The excess metal is then removed and the resulting surface is planarized by performing a process sequence comprising one or more mechanical polishing processes, which also include a chemical component. Chemical mechanical polishing (CMP) has proven to be a reliable technique to remove the excess metal and planarize the resulting surface so as to leave behind metal trenches and vias that are electrically insulated from each other as required by the corresponding circuit layout. Chemical mechanical polishing typically requires the substrate to be attached to a carrier, a so-called polishing head, such that the substrate surface to be planarized is exposed and may be placed against a polishing pad. The polishing head and polishing pad are usually moved relative to each other by individually moving the polishing head and the polishing pad. Typically, the head and pad are rotated against each other while the relative motion is controlled to locally achieve a target material removal. During the polishing operation, typically a slurry, that may include a chemically reactive agent and possibly abrasive particles, is supplied to the surface of the polishing pad.
One problem involved in the chemical mechanical polishing of substrates is the very different removal rates of differing materials, such as of a metal and a dielectric material from which the excess metal has to be removed. For instance, at a polishing state where the dielectric material and the metal are simultaneously treated, i.e., after the major portion of the metal has already been removed, the removal rate for the metal exceeds the removal rate for the dielectric material. This may be desirable because all metal is reliably ablated from all insulating surfaces, thereby insuring the required electrical insulation. On the other hand, significant metal removal from trenches and vias may result in a trench or via that exhibits an increased electrical resistance due to the reduced cross-sectional area. Moreover, the local removal rate may significantly depend on the local structure, i.e., on the local pattern density, which may result in a locally varying degree of erosion of the dielectric material in a final state of the polishing process. In order to more clearly demonstrate a typical damascene process, reference is made to
In
Subsequently, the semiconductor structure 100 will be subjected to the chemical mechanical polishing in which, as previously mentioned, the slurry and polishing pad are selected to optimally remove the excess metal in the metal layer 105. During the chemical mechanical polishing, the excess metal is removed and finally surface portions 120 of the dielectric material 102 will be exposed, wherein it is necessary to continue the polishing operation for a certain overpolish time to ensure clearance of the metal from all insulating surfaces in order to avoid any electrical short between adjacent metal lines. As previously mentioned, the removal rate of the dielectric material and the metal may differ significantly from each other so that, upon overpolishing the semiconductor structure 100, the copper in the trenches 103, 109 and 104 will be recessed.
Therefore, complex control strategies are typically used in advanced CMP tools in order to generate in situ measurement data for estimating an appropriate end point of the polishing process and/or control the uniformity of the polishing process. For example, the layer thickness may be monitored at various sites on the substrate in order to determine the local removal rate during the process and/or to identify an appropriate point in time for terminating the process. To this end, optical measurement techniques, such as spectroscopic ellipsometry or other reflectivity measurement techniques, may be used. Since the optical probing of the substrate surface is difficult due to the nature of the polishing process, significant efforts have been made to provide appropriate CMP tools comprising optical measurement capabilities. For this purpose, appropriately configured polishing pads and platens have been developed that allow optical access to the substrate surface during polish. This may be accomplished by providing respective transparent windows in the pad. Respective optical measurement data may therefore be obtained for a plurality of dielectric materials and very thin metal layers during polishing, thereby enabling efficient control and endpoint detection strategies. For moderately thick initial metal layers as are typically encountered in forming metallization layers, as described above, enhanced process control may also be important during any stage of the polishing process of initially thick metal layers, which may not be efficiently addressed by presently available optical systems.
For this reason, other in situ measurement strategies have been proposed, such as sensors operating on the basis of inductive coupling. In this case, eddy currents may be induced in the metal layer, which may depend on the layer thickness. The response of a sensing coil to the eddy currents may then be used to evaluate the local thickness of the layer. Respective sensor systems may be very efficient for situations as described above with reference to
In advanced CMP techniques, an important factor is the cost of ownership for respective tools, since in the last years CMP costs have increased significantly. The delivery and management of slurries, pads, conditioners, cleansers and the like is very cost intensive. Thus, respective process and control strategies requiring special and thus expensive consumables, such as polishing pads, as described above, may have to be enhanced with respect to consumable consumption and the like, since these factors may significantly contribute to increased production costs due to frequent change of consumables, less tool utilization and availability and the like. In the case described above, the specifically designed pad may be very expensive and may suffer from a reduced life time due to window delamination and/or degradation of the thin material portion in the pad window.
The present disclosure is directed to various devices that may avoid, or at least reduce, the effects of one or more of the problems identified above.
SUMMARY OF THE INVENTIONThe following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an exhaustive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.
Generally, the subject matter disclosed herein is directed to CMP tools and related components, such as polishing pads, sensor components and the like, which enable an in situ monitoring of the polishing process, wherein at least an inductive sensor may be provided that generates a signal related to the amount of conductive material formed on a surface to be treated. As previously explained, in highly advanced CMP tools, typically optical process control and process control based on inductive sensor concepts, for instance using the eddy current principle, may be provided concurrently in order to enhance controllability and flexibility of the respective CMP tools. In these conventional CMP tools, sophisticated polishing pads may have to be used including extra thin pad windows for enabling both efficient optical coupling and efficient inductive coupling. Due to the sophisticated design of the respective polishing pad, significantly increased cost of ownership may be encountered, in particular as reduced lifetime of the corresponding window portions may require more frequent replacement of a polishing pad. In illustrative embodiments disclosed herein, a respective inductive sensor is provided that is appropriately designed to enable the usage of pad windows of increased thickness and/or standard polishing pads as are typically used in optical endpoint detection systems of CMP tools without additional eddy current sensor elements, thereby increasing the overall lifetime of the polishing pad.
In one illustrative embodiment disclosed herein, a polishing tool comprises a polishing platen having a surface configured to receive a sub pad and a top pad that comprises a polishing surface and a lower surface in contact with the sub pad, wherein the sub pad has a first opening covered by a portion of the top pad. Furthermore, the polishing tool comprises an inductive sensor comprising a sensing surface positioned to extend from the surface of the platen into the first opening, wherein the sensing surface is positioned at a height level that is less than a height level of the lower surface of the top pad.
An illustrative polishing tool disclosed herein comprises a polishing platen having a surface configured to receive a polishing pad having a substantially uniform thickness. Furthermore, the polishing tool comprises an inductive sensor comprising a sensing surface positioned to extend from the surface of the platen and to support the polishing pad.
In a further illustrative embodiment, a polishing pad for a CMP tool comprises a base material configured to be mounted on a polishing platen, wherein the base material comprises laterally restricted areas having included therein a magnetic material. The polishing pad further comprises a surface for polishing a substrate.
The disclosure may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:
While the subject matter disclosed herein is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTIONVarious illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
The present subject matter will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present disclosure with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present disclosure. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase.
The subject matter disclosed herein addresses the issue of increased production costs and reduced tool availability of sophisticated CMP tools or any other type of polishing tools in which advanced in situ process monitoring may be required on the basis of inductive sensor concepts. As previously explained, complex polishing processes for removing excess material and planarizing the surface topography may require precise control of the removal rate, even prior to a final polishing phase, in order to reliably control the respective polishing process. For example, during the removal of excess copper, reliable monitoring of the remaining amount of copper material may be important, even at an initial or intermediate process stage, so as to enable high removal rates without introducing undue process non-uniformities. During a corresponding polishing process, an optical detection system may be less efficient, since the corresponding reflectivity may not efficiently provide information on the remaining material amount, since the initially present surface topography may increasingly be planarized, thereby providing a highly uniform scattering behavior of the respective surface, while the remaining thickness of the metal may not allow the extraction of information with respect to the remaining layer thickness. In this case, efficient non-contact measurement techniques, for instance based on inductive principles by generating eddy currents in the metal surface to be treated, may be used for estimating the remaining material thickness, wherein the respective measurement information may also be used for determining an appropriate endpoint of, for instance, a polishing phase with high removal rate and entering a subsequent phase of reduced removal rate so as to substantially completely clear the respective dielectric surface and electrically isolating the respective metal regions contained therein. During this polishing phase, optical endpoint detection or process monitoring techniques may be efficiently used, possibly in combination with the inductive sensor components, so as to obtain a substantially uniform material removal with an efficient clearance of the respective dielectric surface portions substantially without significantly contributing to erosion of the dielectric material and dishing of exposed metal regions. Thus, in particular, the combination of optical measurement strategies and inductive sensor concepts may be highly advantageous in respective manufacturing sequences, in which highly conductive metals, such as copper, copper alloys, silver, tungsten and the like, may be formed over a patterned dielectric material, the surface topography of which has to be planarized in a subsequent step based on a polishing process. However, in addition to high process quality of respective process steps, other factors during the complex manufacturing process for forming microstructure devices are of comparable importance, such as tool utilization, tool availability, cost of ownership of respective process tools and the like, since in addition to a high production yield, the overall throughput for a given equipment may also determine the profitability of the entire manufacturing sequence. Since, in particular, polishing processes in the form of chemical mechanical polishing or electrochemical mechanical polishing and the like have significantly gained in importance during the fabrication of complex semiconductor devices, a significant reduction of cost of ownership of polishing processes in combination with an increase of tool availability may contribute to reduced overall production costs.
In illustrative embodiments disclosed herein, respective inductive sensor systems may be provided in sophisticated polishing tools without requiring extremely sophisticated and thus expensive and sensitive polishing pads, as is the case in a plurality of advanced conventional CMP tools, such as the polishing tool “Reflexion LK,” available from Applied Materials Inc. In some illustrative embodiments, a standard polishing pad including a standard pad window used for optical process control may be used wherein the corresponding sensor assembly may be appropriately adapted to the respective thickness of the standard polishing pad. In other illustrative embodiments, the corresponding height level of a respective sensing surface of an inductive sensor may be appropriately positioned in an adjustable manner so as to provide enhanced flexibility in selecting an appropriate pad configuration in sophisticated polishing tools. As a consequence, in advanced polishing tools, respective optical measurement systems and inductive sensor systems may be combined without requiring specifically designed polishing pads.
It should be appreciated that the subject matter disclosed herein may be applied to polishing tools, such as electrochemical mechanical polishing tools and the like, used for the fabrication of highly complex semiconductor devices, such as CPUs, memory chips and the like, in which advanced metallization structures have to be formed for electrically connecting circuit elements, such as transistors and the like, having critical dimensions of approximately 50 nm and significantly less. However, the principles of the subject matter disclosed herein may also be applied to any situation in which polishing tools may be used, at least temporarily, for the removal of conductive materials from respective substrate surfaces, wherein the provision of an inductive sensor system in combination with a less critical polishing pad may provide enhanced tool flexibility, in particular when the corresponding inductive sensor system may be combined with a respective optical detection system. Thus, unless specifically pointed out in the specification or the appended claims, the subject matter disclosed herein should not be considered as being restricted to polishing processes for forming copper-based metallization layers.
The polishing tool 200 may further comprise a respective sensor portion 221 formed in the polishing platen 220, in which may be provided at least an inductive sensor 240 having a respective sensing surface 241 that may be positioned close to a corresponding surface of a substrate to be treated during the operation of the polishing tool 200. In some illustrative embodiments, the sensor portion 221 may further be configured to allow optical access of a corresponding substrate surface during the operation of the tool 200 wherein the sensor portion 221 may have an appropriately designed surface portion in the respective polishing pad that is substantially transparent for a respective wavelength range, as will be described later on in more detail.
During operation of the polishing tool 200, a substrate may be loaded onto the polishing head 230 on the basis of well-known components, such as robot handlers and the like, wherein the polishing head 230 may itself be configured to provide the respective substrate handling and transport activities within the polishing tool 200. Furthermore, the substrate loaded onto the polishing head 230 may be brought into a respective operating position and the corresponding relative motion between the polishing platen 220 and the polishing head 230 may be established on the basis of respective rotational motions of these components, wherein prior to and/or during the relative motion, an appropriate slurry substance may be supplied, which may include a chemical agent or any other component for enhancing the overall removal rate, or providing enhanced surface conditions during the corresponding polishing process. The pad conditioner 260 may be continuously or temporarily in contact with the corresponding polishing surface so as to “rework” the respective surface structure. During operation of the polishing tool 200, the sensor portion 221 may pass the substrate surface, wherein the sensing surface 241 may generate eddy currents in the substrate to be treated when a sufficiently conductive material or a magnetic material may be provided thereon. For example, the inductive sensor 240 may comprise an exciting coil and a sense coil (not shown), both of which may be coupled to the sensing surface 241, wherein the exciting coil may generate a respective varying magnetic field, which may thus cause respective eddy currents in a conductive material provided in the vicinity of the sensing surface 241 and in particular at a surface of the substrate to be treated. Thus, the electrical response of the respective sense coil may indicate the amount of conductive material located in the vicinity of the sensing surface 241, thereby providing an efficient means for estimating the corresponding polishing process in a highly dynamic manner. In other cases, the sensor 240 may comprise a single coil or a system of coils coupled to the sensing surface 241, wherein the overall inductance of the respective system may be influenced by the amount of conductive material and thus eddy currents induced therein. Consequently, upon driving the respective coil with an appropriate AC signal, the responsiveness of the coil may also be indicative of the amount of conductive material and thus of the present state of the polishing process.
As is evident, during the operation of the polishing tool 200, the respective surface of a polishing pad may interact with the substrate to be treated and the pad conditioner 260, thereby restricting the overall lifetime of the respective polishing pad. Similarly, the surface of the sensor portion 221 may come into contact with the substrate surface and the pad conditioner 260, which may significantly influence the status of the respective material covering the sensor portion 221, which may also be referred to as a window, as will be described later on in more detail. In sophisticated applications, the respective window may be comprised of a substantially transparent material having a different configuration compared to the remaining polishing surface, which may therefore be less durable compared to the remaining surface portion of the polishing pad.
In conventional devices, a respective pad window may be provided with an even reduced material thickness in order to reduce the corresponding gap between a respective sensing surface and the substrate to be treated. In this case, an even more accelerated wear of the respective window portion may be observed, thereby also reducing the overall lifetime of the respective polishing pad, even though the remaining polishing surface is still in an operable state. For this reason, the sensing surface 241 as described herein may be appropriately positioned such that an increased material thickness may be provided between the surface 241 and the corresponding substrate, thereby reducing the risk for material delamination or premature wear of the corresponding window material.
During operation of the polishing tool 200 comprising the configuration of the inductive sensor 240, as for instance shown in
Furthermore, in the embodiment described with reference to
Consequently, upon operation of the tool 200 as shown in
As a result, the subject matter disclosed herein provides an enhanced sensor configuration for sensor systems in polishing tools based on inductive coupling, such as eddy currents, in order to avoid or reduce the necessity for applying highly sophisticated and thus expensive polishing pads with a reduced material thickness at respective pad windows. For this purpose, the height level of a corresponding inductive sensing surface may be reduced compared to conventional designs or may at least be provided in an adjustable manner, thereby providing the potential for using standard polishing pads, which may have a significantly increased lifetime compared to sophisticated polishing pads including windows of reduced material thickness. Consequently, the overall cost of ownership may be reduced and tool availability may be increased thereby contributing to an enhanced overall throughput.
The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. For example, the process steps set forth above may be performed in a different order. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.
Claims
1. A polishing tool, comprising:
- a polishing platen having a surface configured to receive a sub pad and a top pad, said top pad having a polishing surface and a lower surface in contact with said sub pad, said sub pad having a first opening covered by a portion of said top pad; and
- an inductive sensor positioned in said first opening, said inductive sensor having a sensing surface that is positioned at a height level that is less than a height level of said lower surface of said top pad.
2. The polishing tool of claim 1, wherein said top pad comprises a substantially transparent window.
3. The polishing tool of claim 2, wherein said window is positioned above said first opening in said sub pad.
4. The polishing tool of claim 2, wherein said window is positioned above a second opening formed in said sub pad.
5. The polishing tool of claim 1, wherein said sensing surface is substantially flush with a surface of said sub pad that is in contact with said top pad.
6. The polishing tool of claim 1, further comprising a control unit coupled to said inductive sensor to obtain a signal responsive to the presence of a conductive material above said top pad.
7. The polishing tool of claim 2, further comprising an optical measurement system optically coupled to said window for optically probing a surface portion of a substrate placed on said top pad.
8. The polishing tool of claim 1, wherein said top pad comprises a magnetic material at a portion located above said sensing surface.
9. The polishing tool of claim 1, further comprising a height adjustment unit coupled to said sensing surface and configured to vary a height of said sensing surface.
10. The polishing tool of claim 1, wherein a thickness of said top pad is substantially uniform across said polishing platen.
11. A polishing tool, comprising:
- a polishing platen having a surface configured to receive a polishing pad having a substantially uniform thickness; and
- an inductive sensor comprising a sensing surface positioned to extend from said surface of said platen and to support said polishing pad.
12. The polishing tool of claim 11, further comprising a sub pad provided below said polishing pad, said sub pad having at least one opening for receiving said sensing surface.
13. The polishing tool of claim 11, wherein said sensing surface is covered by a window portion of said polishing pad.
14. The polishing tool of claim 11, further comprising a control unit coupled to said inductive sensor to obtain a signal responsive to the presence of a conductive material provided above said polishing pad.
15. The polishing tool of claim 13, further comprising an optical measurement system optically coupled to said window for optically probing a surface portion of a substrate placed on said polishing pad.
16. The polishing tool of claim 11, wherein said polishing pad comprises a magnetic material at a portion supported by said sensing surface.
17. The polishing tool of claim 11, further comprising a height adjustment unit coupled to said sensing surface and configured to vary a height of said sensing surface.
18. A polishing pad for a polishing tool, comprising:
- a base material configured to be mounted on a polishing platen, said base material comprising laterally restricted areas having included therein a magnetic material; and
- a surface for polishing a substrate.
19. The polishing pad of claim 18, wherein said magnetic material is comprised of ferrite particles.
Type: Application
Filed: Nov 15, 2007
Publication Date: Oct 2, 2008
Inventors: Jens Heinrich (Wachau), Axel Kiesel (Chemnitz), Uwe Stoeckgen (Dresden), Mike Schlicker (Hirschfeld)
Application Number: 11/940,361
International Classification: B24B 13/00 (20060101);