Apparatus and method for electrochemically processing a microelectronic workpiece
A reactor for use in electrochemical processing of a microelectronic workpiece is set forth and described herein. The apparatus comprises one or more walls defining a processing space therebetween for containing a processing fluid. The processing space includes at least a first fluid flow region and a second fluid flow region. A first electrode is disposed in the processing fluid of the first fluid flow region while a second electrode, comprising at least a portion of the microelectronic workpiece, is disposed in the processing fluid of the second fluid flow region. Fluid flow within the first fluid flow region is generally directed toward the first electrode and away from the second electrode while fluid flow within the second fluid flow region is generally directed toward the second electrode and away from the first electrode. Depending on the particular electrochemical process that is to be executed, the first e electrode may constitute either an anode or a cathode in the electrochemical processing of the microelectronic workpiece. The foregoing reactor architecture is particularly useful in connection with electroplating of the microelectronic workpiece and, more particularly, in electroplating operations that employ a consumable anode, such as a phosphorized copper anode.
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STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTNot Applicable
BACKGROUND OF THE INVENTIONThe present invention is directed to an apparatus for electrochemically processing a microelectronic workpiece. More particularly, the present invention is directed to a reactor assembly for electrochemically depositing, electrochemically removing and/or electrochemically altering the characteristics of a thin film material, such as a metal or dielectric, at the surface of a microelectronic workpiece, such as a semiconductor wafer. For purposes of the present application, a microelectronic workpiece is defined to include a workpiece formed from a substrate upon which microelectronic circuits or components, data storage elements or layers, and/or micro-mechanical elements are formed.
Production of semiconductor integrated circuits and other microelectronic devices from workpieces, such as semiconductor waters, typically requires formation and/or electrochemical processing of one or more thin film layers on the wafer. These thin film layers are often in the form of a deposited metal that is used, for example, to electrically interconnect the various devices of the integrated circuit. Further, the structures formed from the metal layers may constitute microelectronic devices such as read/write heads, etc.
The microelectronic manufacturing industry has applied a wide range of thin film layer materials to form such microelectronic structures. These thin film materials include metals and metal alloys such as, for example, nickel, tungsten, tantalum, solder, platinum, copper, copper-zinc, etc., as well as dielectric materials, such as metal oxides, semiconductor oxides, and perovskite materials.
A wide range of processing techniques have been used to deposit and/or alter the characteristics of such thin film layers. These techniques include, for example, chemical vapor deposition (CVD), physical vapor deposition (PVD), anodizing, electroplating, and electroless plating. Of these techniques, electrochemical processing techniques (i.e., electroplating, anodizing, and electroless plating) tend to be the most economical and, as such, the most desirable. Such electrochemical processing techniques can be used in the deposition and/or alteration of blanket metal layers, blanket dielectric layers, patterned metal layers, and patterned dielectric layers.
One of the process sequences used in the microelectronic manufacturing industry to deposit a metal onto semiconductor wafers is referred to as “damascene” processing. In such processing, holes, commonly called “vias”, trenches and/or other micro-recesses are formed onto a workpiece and filled with a metal, such as copper and/or a copper alloy. In the damascene process, the wafer is first provided with a metallic seed layer which is used to conduct electrical current during a subsequent metal electroplating step. If a metal such as copper is used, the seed layer is disposed over a barrier layer material, such as Ti, TiN, etc. The seed layer is a very thin layer of metal, such as copper, gold, nickel, palladium, etc., which can be applied using one or more of several processes. The seed layer is formed over the surface of the semiconductor wafer, which is convoluted by the presence of the vias, trenches, or other recessed device features.
A metal layer is then electroplated onto the seed layer in the form of a blanket layer. The blanket layer is plated to form an overlying layer, with the goal of providing a metal layer that fills the trenches and vias and extends a certain amount above these features. Such a blanket layer will typically have a thickness on the order of 10,000 to 15,000 angstroms (1-1.5 microns).
After the blanket layer has been electroplated onto the semiconductor wafer, excess metal material present outside of the vias, trenches, or other recesses is removed. The metal is removed to provide a resulting pattern of metal layer in the semiconductor integrated circuit being formed. The excess plated material can be removed, for example, using chemical mechanical planarization. Chemical mechanical planarization is a processing step which uses the combined action of a chemical removal agent and an abrasive which grinds and polishes the exposed metal surface to remove undesired parts of the metal layer applied in the electroplating step.
The electroplating of the semiconductor wafers takes place in a reactor assembly. In such an assembly, an anode electrode is disposed in a plating bath, and the wafer with the seed layer thereon is used as a cathode. Only a lower face of the wafer contacts the surface of the plating bath. The wafer is held by a support system that also conducts the requisite electroplating power (e.g., cathode current) to the wafer.
Several technical problems must be overcome in designing reactors used in the electrochemical processing of microelectronic workpieces, such as semiconductor wafers. One such problem relates to the formation of particulates contamination, gas bubbles, etc., that form at the surface of the anode (or, in the case of anodization, both the cathode and anode) during the electrochemical process. Although such problems exist in connection with the wide range of electrochemical processes, the discussion below focuses on those problems associated with electroplating a metal onto the surface of the microelectronic workpiece.
Generally stated, electroplating occurs as a result of an electrochemical reduction reaction that takes place at the cathode, where atoms of the material to be plated are deposited onto the cathode by supplying electrons to attract positively charged ions. The atoms are formed from ions present in the plating bath. In order to sustain the reaction, the ions in the plating bath must be replenished. Replenishment is generally accomplished through the use of a consumable anode or through the use of an external chemical source, such as a bath additive, containing the ions or an ion-forming compound.
As the thin film layer is deposited onto the cathode, a corresponding electrochemical oxidation reaction takes place at the anode. During this corresponding electrochemical reaction, byproducts from the electrochemical reaction, such as particulates, precipitates, gas bubbles, etc. may be formed at the surface of the anode. Such byproducts may then be released into the processing bath and interfere with the proper formation of the thin-film layer at the surface of the microelectronic workpiece. Furthermore if these byproducts are allowed to remain present in the processing fluid at elevated levels near the anode, they can affect current flow during the plating process and/or affect further reactions that must take place at the anode if the electroplating is to continue. For example, if copper concentrations are allowed to increase excessively, copper sulfate will precipitate due to the common ion effect. In order to reduce and or eliminate this problem, electrolyte flow near the anode is maintained at a sufficient level to allow mixing of the dissolved species in the electrolyte.
Such byproducts can be particularly problematic in those instances in which the anode is consumable. For example, when copper is electroplated onto a workpiece using a consumable phosphorized copper anode, a black anode film is produced. The presence and consistency of the black film is important to ensure uniform anode erosion. This oxide/salt film is fragile, however. As such, it is possible to dislodge particulates from this black film into the electroplating solution. These particulates can then potentially be incorporated into the deposited film with the undesired consequences.
One technique for limiting the introduction of particulates and/or precipitates produced at the anode into the plating bath, has been to enclose the anode in an anode bag. The anode bag is typically made of a porous material, which generally traps larger size particulates within the anode bag, while allowing smaller size particulates to be released external to the bag and into the plating bath. As the features of the structures and devices formed on the microelectronic workpiece decrease in size, however, the performance of the structures and devices may be degraded by even the smaller size particulates. Furthermore, while the use of an anode bag will restrict the larger particulates from traveling toward the cathode and contaminating the plating surface or affecting the plating process taking place at the cathode, the anode bag will also trap the larger particulates within the proximity of the anode creating elevated levels of these byproducts, which may limit the forward electrochemical reaction taking place at the anode. Still further, the larger particulates can eventually block the porous nature of the anode bag and ultimately restrict even the regular fluid flow.
The present inventors have recognized the foregoing problems and have developed a method and apparatus that assists in isolating byproducts that form at an electrode of an electrochemical processing apparatus to prevent them from interfering with the uniform electrochemical processing of the workpiece.
BRIEF SUMMARY OF THE INVENTIONA reactor for use in electrochemical processing of a microelectronic workpiece is set forth and described herein. The apparatus comprises one or more walls defining a processing space therebetween for containing a processing fluid. The processing space includes at least a first fluid flow region and a second fluid flow region. A first electrode is disposed in the processing fluid of the first fluid flow region while a second electrode, comprising at least a portion of the microelectronic workpiece, is disposed in the processing fluid of the second fluid flow region. Fluid flow within the first fluid flow region is generally directed toward the first electrode and away from the second electrode while fluid flow within the second fluid flow region is generally directed toward the second electrode and away from the first electrode. Depending on the particular electrochemical process that is to be executed, the first electrode may constitute either an anode or a cathode in the electrochemical processing of the microelectronic workpiece. The foregoing reactor architecture is particularly useful in connection with electroplating of the microelectronic workpiece and, more particularly, in electroplating operations that employ a consumable anode, such as a phosphorized copper anode.
In accordance with one embodiment of the invention, the reactor comprises at least one pressure drop member disposed in the processing fluid of the processing space in an intermediate position between the first and second fluid flow regions and the first and second fluid flow regions are adjacent one another.
The pressure drop member may comprise a permeable membrane that is disposed over an open end of a cup assembly wherein the membrane is permeable to at least one of the ionic species in the processing fluid. The cup assembly may comprise an electrode housing assembly having an inverted lip, and an outer cup assembly. In accordance with a further enhancement of this embodiment, the cup assembly further includes at least one outlet tube having an opening, which extends into the space within the inverted unshaped lip of the electrode housing assembly. The outlet tube provides a path for processing fluid, gas bubbles, and particulates to exit the cup assembly, while the pressure drop member restricts movement of the same into the second fluid flow region of the cup assembly.
A method for processing a microelectronic workpiece is also set forth. In accordance with one embodiment of the method, a processing space containing processing fluid is divided into at least a first fluid flow region and a second fluid flow region. A first electrode is located within the processing fluid of the first fluid flow region and a second electrode comprising at least a portion of the microelectronic workpiece is located within the processing fluid of the second fluid flow region. A fluid flow of the processing fluid is generated within the first fluid flow region that is generally directed toward the first electrode and generally away from the second electrode while a fluid flow of the processing fluid within the second fluid flow region is generated that is generally directed toward the second electrode and generally away from the first electrode.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
The reactor 10 has a reactor head assembly 20 that assists in supporting the workpiece during processing, and a corresponding processing space in the form of a reactor bowl assembly 30. Reactor bowl assembly 30 includes one or more walls that define a processing space that contains a processing fluid, as will be set forth in further detail below. This type of reactor assembly is particularly suited for effecting electroplating of semiconductor waters or like workpieces, in which the wafer is electroplated with a blanket or patterned metallic layer.
The reactor head assembly 20 and the reactor bowl assembly 30 of the illustrated embodiment may be moved relative to one another. For example, a lift and rotate mechanism, not shown, may be used in conjunction with the head and bowl assemblies 20, 30 to drive the reactor head 20 in a vertical direction with respect to the reactor bowl assembly 30 and to rotate the reactor head assembly 20 about a horizontally disposed axis. By lifting and rotating the reactor head assembly 20, a workpiece 45, such as a semiconductor wafer, may be moved between a load position that allows the workpiece 45 to be placed upon the head assembly 20, and a processing position in which at least a portion of the workpiece 45 is brought into contact with processing fluid in the processing space of the reactor bowl assembly 30. When the workpiece is in the processing position, it is generally oriented with the process side down within the processing space. When the workpiece 45 is in the load position, the workpiece 45 is generally exposed outside of the reactor bowl assembly 30 with the process side directed upward, for loading and unloading by, for example, a robotic wafer transfer mechanism. One example of a suitable lift and rotate mechanism is described in connection with U.S. patent application Ser. No. 09/351,980, filed Jul. 12, 1999, entitled “Lift and Rotate Mechanism for Use in a Workpiece Processing Apparatus”, the disclosure of which is incorporated herein by reference.
Preferably, the reactor head assembly 20 includes a stationary assembly 50 and a rotor assembly 55. The rotor assembly 55 is configured with one or more structures that serve to support the workpiece and to rotate the workpiece 45 about a generally vertical axis during, for example, workpiece processing.
In the reactor embodiment of
During processing, the workpiece 45 is brought into contact with processing fluid located within, the reactor bowl assembly 30. In the illustrated embodiment, reactor bowl assembly 30 comprises a reactor base assembly 65 that, in turn, includes process cup assembly 75 and an electrode housing assembly 70. The process cup assembly 75 includes a plurality of wall structures that define a processing space therebetween. The electrode housing assembly 70 is located within the process cup assembly 75 and includes therein an electrode 105 used in electrochemical processing of a workpiece 45.
Generally stated, the processing space within the process cup assembly 75 includes at least two process fluid flow regions. The first fluid flow region is proximate the upper end and interior to the electrode housing assembly 70 while the second flow region includes the region at the upper end of processing cup 75 proximate workpiece 45. As will be explained in further detail below, processing fluid flow in the first fluid flow region is generally directed toward the interior of the electrode housing assembly 70 and, more particularly, toward a surface of the electrode 105, and generally away from the workpiece 45. In contrast, the flow of processing fluid in the second fluid flow region is generally directed toward the workpiece 45 and generally away from electrode 105. One arrangement of structures that can be used to accomplish this fluid flow pattern is described in detail below.
The electrode housing assembly 70 of the illustrated embodiment includes a housing member 72, which is generally bowl shaped and includes an end that is open toward the workpiece 45. A pressure drop member 90 is disposed over the open end of the housing member 72. The pressure drop member 90 assists in dividing the processing space into the aforementioned first fluid flow region 95 and second fluid flow region 100.
The housing member 72 may have a lip 80 located at the opening or the rim thereof that extends radially inwards and then downward toward the base of the assembly. The lip 80 may have a cross section in the shape of an inverted “u” that defines a space 85 located therein, which extends around the circumference of the electrode housing assembly 70. The lip 80 may serve as the locus of the engagement between the housing member 72 and the pressure drop member 90. Together, the housing member 72 and pressure drop member 90 define an interior electrode chamber in which electrode 105 is disposed.
The pressure drop member 90 may be conically shaped, and have an apex oriented so as to extend downward into the interior electrode chamber. To this end, the pressure drop member 90 may comprise a conically shaped frame 110, and a permeable membrane 115 that is fixed with the surface of the conically shaped frame 110. The conically shaped frame 110 is particularly illustrated in
The circular base member 120, ribs 125 and membrane 115 are preferably formed from polypropylene, polyethylene, polyvinylidene fluoride, or other fluorocarbon type plastic. Such plastics are generally chemically inert with respect to the processing which is likely to take place in the plating reactor 10.
In an alternative embodiment, the pressure drop membrane is formed from a sufficiently resilient membrane which does not require an underlying frame structure.
Further alternative embodiments include the pressure drop member being formed from a pressed disk of porous ceramic or porous glass.
Referring back to
The processing fluid received via the fluid inlet 155 initially enters the second fluid flow region 100 of the cup assembly 65 via the space 165 formed between the electrode housing assembly 70 and the process cup assembly 75. The processing fluid generally follows a flow corresponding to the direction of arrows illustrated in
By placing the anode 105 in the first fluid flow region 95 within the electrode housing assembly 70 and having the processing fluid enter the cup assembly 65 via the second fluid flow region 100, the anode 105 is isolated from the fluid flow when the processing fluid initially enters the cup assembly 65. Correspondingly, the processing fluid does not directly impinge upon the anode 105, which may be a consumable anode. As a result the useful life of the anode 105 is prolonged.
In connection with the electrode housing assembly 70, the plating reactor includes a fluid outlet tube 165. The fluid outlet tube 165 has an opening 170, which extends into the space 85 formed within the inverted unshaped lip 80 of the electrode housing assembly 70. The addition of processing fluid into second fluid flow region 100 via the fluid inlet 155 and the exit of fluid from the first fluid flow region 95 via the opening 170 in the fluid outlet tube 165, creates a pressure differential between the first fluid flow region 95 and the second fluid flow region 100 in which the pressure in the first fluid flow region 95 is lower than the pressure in the second fluid flow region 100. In the upper region of the reactor, fluid will flow from the second fluid flow region 100 into the first fluid flow region 95 through the pressure drop member 90 in an attempt to equalize pressure between the regions.
The pressure drop member 90 provides some resistance to the flow of fluid across the semi-porous membrane 115. As such, the pressure equalizing flow of processing fluid is somewhat restricted. Restricting the flow of fluid across the pressure drop member 90 has several effects. For example, the flow of process fluid across the pressure drop member 90 is distributed more evenly along the surface of the pressure drop member 90. Further, the restricted flow facilitates generation of a pressure differential between the first fluid flow region 95 and the second fluid flow region 100. Because the pressure in the second fluid flow region 100 is maintained at a level that is slightly higher than the pressure in the first region, fluid flow from the first fluid flow region 95 into the second fluid flow region 100 across the pressure drop member 90 is unlikely. This pressure differential, in turn, effectively restricts passage of any byproducts formed at electrode 105 during the electrochemical reaction to an area within the first fluid flow region 95 and assists in preventing such byproducts from reaching the surface of the workpiece 45. Rather, the byproducts generated within fluid flow region 95 can be directed from the processing space through the fluid outlet tube 165. Such an arrangement allows for separate processing of the processing fluid overflowing weir 180 and fluid exiting fluid outlet 165. Special filtering or processing of the processing fluid exiting the first fluid flow may be employed to particularly remove any of the unwanted byproducts before the processing fluid is mixed and/or processed with the processing fluid overflowing weir 180 for recirculation to the plating reactor 10 via the fluid inlet 155. As a result, exposure of the workpiece 45 to potentially harmful byproducts produced at the electrode 105 is substantially limited and/or can more easily be controlled using the illustrated reactor architecture.
Since the pressure drop member 90 is conically shaped and extends downward into the electrode housing assembly 70, it has a surface at the interior electrode chamber that is oriented at an angle. The angle at which the surface of the pressure drop member is defined so that the highest point of the pressure drop member 90 is proximate to the u-shaped lip 80 of the electrode housing assembly 70. The angled surface of the pressure drop member directs any particulates, precipitates or gas bubbles formed at the electrode 105 away from the center of the electrode housing assembly toward the periphery and into the space 85 within the u-shaped lip 80 of the electrode housing assembly 70. Not only does the angled surface of the pressure drop member move the byproducts away from the center of the processing area where they can otherwise adversely affect uniform current flow, the pressure drop member also assists in driving the byproducts toward the opening 170 of the fluid outlet tube 165. Eventually the particulates, precipitates and/or gas bubbles exit the cup assembly 65 along with the processing fluid via fluid outlet tube 165. This is more clearly shown in connection with
Specifically, the fluid pressure at the opening 170 and inside the fluid outlet tube 165 is lower than the fluid pressure located elsewhere in the cup assembly 65. This is due in part to the opening 170 of the fluid outlet tube 165 being below the overall level of the processing fluid. As a result of the lower pressure proximate the opening 170 of the fluid outlet tube 165, fluid will migrate towards the opening 165 from elsewhere in the cup assembly. More specifically, the fluid from the first region will generally migrate towards the space 85 within the U-shaped lip 80, which extends circumferentially around the outer perimeter of the cup assembly 65, proximate the opening 170. The fluid then enters the tube 165 via the opening 170 and exits the reactor bowl assembly 30.
Although the fluid flow from the first fluid flow region 95 to the second fluid flow region 100 is restricted, charged particles required for electrochemical processing of the workpiece 45 can still flow from the first fluid flow region 95 to the second fluid flow region 100 across the pressure drop member 90, as charged particles will flow independent of the fluid flow. This is possible if the particles are suitably charged and are sized appropriately to make it through the pressure drop barrier.
In addition to fluid outlet tube 165, the processing fluid can further exit the cup assembly 65 via an overflow weir 180 located at the lip of the wall of the process cup assembly 75. The processing fluid, which has overflowed the overflow weir 180, can then be drained via a cup drain valve 185 located near the bottom of the reactor bowl assembly 30.
In the embodiment illustrated in
Field shaping elements provide for fluid and/or current shaping or tailoring. The field shaping elements mounted in one of the lower generally horizontal grooves 190 further from the workpiece 45 provides for more global shaping or tailoring of the flow of processing fluid and current, while field shaping elements mounted in one of the higher horizontal grooves 190 closer to the workpiece 45 provide for fluid and current shaping in connection with a more specific point on the workpiece 45.
In accordance with one embodiment used in the electroplating of copper onto the surface of the workpiece, a consumable phosphorized copper anode and two field shaping elements are used. The field shaping elements include a lower field shaping element 195 or diffuser plate (illustrated in
Examples of field shaping elements or diffuser plates, including diffuser plates having alternative opening patterns, are further described in connection with U.S. patent application Ser. No. 09/351,864, filed Jul. 12, 1999, entitled “Diffuser with Spiral Opening Pattern for Electroplating Reactor Vessel”, the disclosure of which is incorporated herein by reference.
Use of the present invention in an electroplating process is not only envisioned with respect the plating of copper onto a workpiece using a consumable phosphorized anode, but is further envisioned as having utility in any electroplating process where there is a desire to limit exposure of the cathode/workpiece to the products produced at the anode. For example, the above noted electroplating process is further envisioned as having utility in connection with a process for plating nickel onto a workpiece using a consumable nickel sulfur anode, and a process for plating solder onto a workpiece using a consumable tin lead anode, or for anodic processing of a workpiece, in which gas is produced at the cathode.
Numerous modifications may be made to the foregoing system without departing from the basic teachings thereof. Although the present invention has been described in substantial detail with reference to one or more specific embodiments, those of skill in the art will recognize that changes may be made thereto without departing from the scope and spirit of the invention as set forth in the appended claims.
Claims
1-52. (canceled)
53. A reactor for electrochemically processing a microelectronic workpiece comprising:
- a fluid vessel;
- an ion selective membrane positioned in the vessel between a first fluid flow region and a second fluid flow region;
- a first fluid flow entry positioned to provide a first processing fluid to the first fluid flow region;
- a first fluid flow exit positioned to remove the first processing fluid from the first fluid flow region;
- a first electrode in fluid communication with the first fluid flow region;
- a second fluid flow entry positioned to provide a second processing fluid different than the first processing fluid to the second fluid flow region;
- a second fluid flow exit positioned to remove the second processing fluid from the second fluid flow region; and
- a second electrode positioned to contact the microelectronic workpiece while the second electrode and the microelectronic workpiece are in fluid communication with the second fluid flow region.
54. The reactor of claim 53 wherein the membrane is selectively permeable to an ionic species in at least one of the first and second processing fluids.
55. The reactor of claim 53 wherein the first electrode is an anodic electrode and wherein the second electrode is a cathodic electrode.
56. The reactor of claim 53, further comprising the first and second processing fluids.
57. The reactor of claim 56 wherein the first and second processing fluids provide chemical species for applying a metallic material to the microelectronic workpiece.
58. The reactor of claim 56 wherein the membrane is selectively permeable to an ionic species in at least one of the first and second processing fluids.
59. The reactor of claim 53, further comprising a fluid reservoir coupled to the second fluid entry.
60. The reactor of claim 53 wherein the membrane has an at least partially conical shape.
61. The reactor of claim 53 wherein the membrane inclines upwardly in a radially outward direction.
62. The reactor of claim 53, further comprising a perforated element positioned between the second electrode and the membrane.
63. The reactor of claim 53 wherein the first electrode includes an anode positioned in the vessel.
Type: Application
Filed: Apr 27, 2006
Publication Date: Aug 31, 2006
Inventors: Kyle Hanson (Kalispell, MT), Scott Grace (Kalispell, MT), Matt Johnson (Kalispell, MT), Ken Gibbons (Kalispell, MT)
Application Number: 11/413,666
International Classification: G01N 27/26 (20060101);