US20050077188A1

US20050077188A1 - Endpoint for electrochemical processing

Info

Publication number: US20050077188A1
Application number: US10/940,603
Authority: US
Inventors: Daxin Mao; Renhe Jia; Zhihong Wang; Yuan Tian; Feng Liu; Vladimir Galburt; Sen Ko; Stan Tsai; Liang-Yuh Chen
Original assignee: Applied Materials Inc
Current assignee: Applied Materials Inc
Priority date: 2002-01-22
Filing date: 2004-09-14
Publication date: 2005-04-14
Also published as: US6837983B2; TWI278378B; CN100425404C; JP2005516383A; DE60314841D1; JP2010147489A; EP1467840B1; ATE366641T1; KR101011095B1; DE60314841T2; TW200302150A; US20030136684A1; WO2003061905A1; CN1652898A; EP1467840A1; KR20040078131A; CN101176988A

Abstract

A method and apparatus for electrochemically processing a substrate is provided. In one embodiment, a method for electrochemically processing a substrate includes the steps of establishing an electrically-conductive path through an electrolyte between an exposed layer of barrier material on the substrate and an electrode, electrochemically removing a portion of the exposed layer during a first electrochemical processing step in a barrier processing station, detecting an endpoint of the first electrochemical processing step at or just prior to breakthrough of the exposed layer of barrier material, electrochemically processing the exposed layer of barrier material in a second electrochemical processing step in the barrier processing station, and detecting an endpoint of the second electrochemical processing step.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 10/056,316 (Attorney Docket No. 6339), filed Jan. 22, 2002, entitled ENDPOINT DETECTION FOR ELECTRO CHEMICAL MECHANICAL POLISHING AND ELECTROPOLISHING PROCESSES, which is herein incorporated by reference in its entirety.
This application is related to U.S. patent application Ser. No. ______ (Attorney Docket No. 7187P2), filed ______, by Antoine Manens, entitled END POINT COMPENSATION IN ELECTROPROCESSING, which is herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention
Embodiments of the present invention generally relate to a method for endpoint detection for electrochemical processing.
2. Description of the Related Art
Electrochemical mechanical planarizing (ECMP) is a technique used to remove conductive materials from a substrate surface by electrochemical dissolution while concurrently polishing the substrate with reduced mechanical abrasion compared to conventional planarization processes. ECMP systems may generally be adapted for deposition of conductive material on the substrate by reversing the polarity of the bias. Electrochemical dissolution is performed by applying a bias between a cathode and a substrate surface to remove conductive materials from the substrate surface into a surrounding electrolyte. Typically, the bias is applied to the substrate surface by a conductive polishing pad on which the substrate is processed. A mechanical component of the polishing process is performed by providing relative motion between the substrate and the conductive polishing pad that enhances the removal of the conductive material from the substrate.
Since the removal rate of the conductive film being processed may not be uniform across the diameter of the substrate, another film underlying this conductive can be exposed through the polished film. For example, during processing of a copper layer, the underlying barrier layer may be exposed when the remaining copper layer is about 2000-1000 Å thick. As the copper layer (or other conductive film being processed) no longer completely covers the original deposited area, remaining copper is removed rapidly as more and more of the underlying barrier layer is exposed. With further processing to remove residual copper from the substrate, the copper lines in the trenches in the exposed area tend to dish, and the exposed barrier layer maybe polished together with the oxide underneath, leading to erosion. The same holds true for ECMP of tungsten and other metals.
Moreover, as systems for electroprocessing copper generally rely on conventional chemical mechanical processing for barrier removal, such systems are complex, and require disparate utilities and share few common components between electroprocessing and conventional processing stations. Thus, it would be advantageous to have a system capable of removing barrier materials, such as tantalum, tantalum nitride, titanium and the like, through an electrochemical process.
Thus, there is a need for an improved method and apparatus for electrochemical processing of copper, tungsten and other conductive materials.

SUMMARY OF THE INVENTION

Embodiments of the invention generally provide a method for processing a substrate in an electrochemical mechanical planarizing system. In one embodiment, the method includes the steps of establishing an electrically-conductive path through an electrolyte between an exposed layer of barrier material on the substrate and an electrode, electrochemically removing a portion of the exposed layer during a first electrochemical processing step in a barrier processing station, detecting an endpoint of the first electrochemical processing step at or just prior to breakthrough of the exposed layer of barrier material, electrochemically processing the exposed layer of barrier material in a second electrochemical processing step in the barrier processing station, and detecting an endpoint of the second electrochemical processing step.
In another embodiment, a method for electrochemically processing a substrate includes removing a conductive layer having a barrier layer disposed thereunder at a first processing station of a system and electrochemically removing the barrier layer at a second processing station of the system. The system may include a processing station disposed between the first and second processing stations for residual removal of the conductive layer using a multi-step removal process.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited embodiments of the invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
FIG. 1 is a plan view of an electrochemical mechanical planarizing system;
FIG. 2 is a sectional view of one embodiment of a first electrochemical mechanical planarizing (ECMP) station of the system of FIG. 1;
FIG. 3A is a partial sectional view of the first ECMP station through two contact assemblies;
FIGS. 3B-C are sectional views of alternative embodiments of contact assemblies;
FIG. 3D-E are sectional views of plugs;
FIGS. 4A and 4B are side, exploded and sectional views of one embodiment of a contact assembly;
FIG. 5 is one embodiment of a contact element;
FIG. 6 is a vertical sectional view of another embodiment of an ECMP;
FIG. 7 is a flow diagram of one embodiment of a method for electroprocessing conductive material;
FIG. 8 is a graph of voltage and current plots for an exemplary electroprocess;
FIG. 9 is a flow diagram of another embodiment of a method for electroprocessing conductive material; and
FIG. 10 is a graph of current and voltage plots for an exemplary electroprocess.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.

DETAILED DESCRIPTION

Embodiments for a system and method for removal of conductive and barrier materials from a substrate are provided. Although the embodiments disclosed below focus primarily on removing material from, e.g., planarizing, a substrate, it is contemplated that the teachings disclosed herein may be used to electroplate a substrate by reversing the polarity of an electrical bias applied between the substrate and an electrode of the system.
Apparatus
FIG. 1 is a plan view of one embodiment of a planarization system 100 having an apparatus for electrochemically processing a substrate. The exemplary system 100 generally comprises a factory interface 102, a loading robot 104, and a planarizing module 106. The loading robot 104 is disposed proximate the factory interface 102 and the planarizing module 106 to facilitate the transfer of substrates 122 therebetween.
A controller 108 is provided to facilitate control and integration of the modules of the system 100. The controller 108 comprises a central processing unit (CPU) 110, a memory 112, and support circuits 114. The controller 108 is coupled to the various components of the system 100 to facilitate control of, for example, the planarizing, cleaning, and transfer processes.
The factory interface 102 generally includes a cleaning module 116 and one or more wafer cassettes 118. An interface robot 120 is employed to transfer substrates 122 between the wafer cassettes 118, the cleaning module 116 and an input module 124. The input module 124 is positioned to facilitate transfer of substrates 122 between the planarizing module 106 and the factory interface 102 by grippers, for example vacuum grippers or mechanical clamps.
The planarizing module 106 includes at least a first electrochemical mechanical planarizing (ECMP) station 128, disposed in an environmentally controlled enclosure 188. Examples of planarizing modules 106 that can be adapted to benefit from the invention include MIRRA®, MIRRA MESA™, REFLEXION®, REFLEXION® LK, and REFLEXION LK Ecmp™ Chemical Mechanical Planarizing Systems, all available from Applied Materials, Inc. of Santa Clara, Calif. Other planarizing modules, including those that use processing pads, planarizing webs, or a combination thereof, and those that move a substrate relative to a planarizing surface in a rotational, linear or other planar motion may also be adapted to benefit from the invention.
In the embodiment depicted in FIG. 1, the planarizing module 106 includes the first ECMP station 128, a second ECMP station 130 and a third ECMP station 132. Bulk removal of conductive material disposed on the substrate 122 may be performed through an electrochemical dissolution process at the first ECMP station 128. After the bulk material removal at the first ECMP station 128, the remaining conductive material is removed from the substrate at the second ECMP station 130 through a multi-step electrochemical mechanical process, wherein part of the multi-step process is configured to remove residual conductive material. It is contemplated that more than one ECMP station may be utilized to perform the multi-step removal process after the bulk removal process performed at a different station. Alternatively, each of the first and second ECMP stations 128, 130 may be utilized to perform both the bulk and multi-step conductive material removal on a single station. It is also contemplated that all ECMP stations (for example 3 stations of the module 106 depicted in FIG. 1) may be configured to process the conductive layer with a two step removal process.
The exemplary planarizing module 106 also includes a transfer station 136 and a carousel 134 that are disposed on an upper or first side 138 of a machine base 140. In one embodiment, the transfer station 136 includes an input buffer station 142, an output buffer station 144, a transfer robot 146, and a load cup assembly 148. The input buffer station 142 receives substrates from the factory interface 102 by means of the loading robot 104. The loading robot 104 is also utilized to return polished substrates from the output buffer station 144 to the factory interface 102. The transfer robot 146 is utilized to move substrates between the buffer stations 142, 144 and the load cup assembly 148.
In one embodiment, the transfer robot 146 includes two gripper assemblies, each having pneumatic gripper fingers that hold the substrate by the substrate's edge. The transfer robot 146 may simultaneously transfer a substrate to be processed from the input buffer station 142 to the load cup assembly 148 while transferring a processed substrate from the load cup assembly 148 to the output buffer station 144. An example of a transfer station that may be used to advantage is described in U.S. Pat. No. 6,156,124, issued Dec. 5, 2000 to Tobin, which is herein incorporated by reference in its entirety.
The carousel 134 is centrally disposed on the base 140. The carousel 134 typically includes a plurality of arms 150, each supporting a planarizing head assembly 152. Two of the arms 150 depicted in FIG. 1 are shown in phantom such that the transfer station 136 and a planarizing surface 126 of the first ECMP station 128 may be seen. The carousel 134 is indexable such that the planarizing head assemblies 152 may be moved between the planarizing stations 128, 130, 132 and the transfer station 136. One carousel that may be utilized to advantage is described in U.S. Pat. No. 5,804,507, issued Sep. 8, 1998 to Perlov, et al., which is hereby incorporated by reference in its entirety.
A conditioning device 182 is disposed on the base 140 adjacent each of the planarizing stations 128, 130, 132. The conditioning device 182 periodically conditions the planarizing material disposed in the stations 128, 130,132 to maintain uniform planarizing results.
FIG. 2 depicts a sectional view of one of the planarizing head assemblies 152 positioned over one embodiment of the first ECMP station 128. The second and third ECMP stations 130, 132 may be similarly configured. The planarizing head assembly 152 generally comprises a drive system 202 coupled to a planarizing head 204. The drive system 202 generally provides at least rotational motion to the planarizing head 204. The planarizing head 204 additionally may be actuated toward the first ECMP station 128 such that the substrate 122 retained in the planarizing head 204 may be disposed against the planarizing surface 126 of the first ECMP station 128 during processing. The drive system 202 is coupled to the controller 108 that provides a signal to the drive system 202 for controlling the rotational speed and direction of the planarizing head 204.
In one embodiment, the planarizing head may be a TITAN HEAD™ or TITAN PROFILER™ wafer carrier manufactured by Applied Materials, Inc. Generally, the planarizing head 204 comprises a housing 214 and retaining ring 224 that defines a center recess in which the substrate 122 is retained. The retaining ring 224 circumscribes the substrate 122 disposed within the planarizing head 204 to prevent the substrate from slipping out from under the planarizing head 204 while processing. The retaining ring 224 can be made of plastic materials such as PPS, PEEK, and the like, or conductive materials such as stainless steel, Cu, Au, Pd, and the like, or some combination thereof. It is further contemplated that a conductive retaining ring 224 may be electrically biased to control the electric field during ECMP. Conductive or biased retaining rings tend to slow the polishing rate proximate the edge of the substrate. It is contemplated that other planarizing heads may be utilized.
The first ECMP station 128 generally includes a platen assembly 230 that is rotationally disposed on the base 140. The platen assembly 230 is supported above the base 140 by a bearing 238 so that the platen assembly 230 may be rotated relative to the base 140. An area of the base 140 circumscribed by the bearing 238 is open and provides a conduit for the electrical, mechanical, pneumatic, control signals and connections communicating with the platen assembly 230.
Conventional bearings, rotary unions and slip rings, collectively referred to as rotary coupler 276, are provided such that electrical, mechanical, fluid, pneumatic, control signals and connections may be coupled between the base 140 and the rotating platen assembly 230. The platen assembly 230 is typically coupled to a motor 232 that provides the rotational motion to the platen assembly 230. The motor 232 is coupled to the controller 108 that provides a signal for controlling for the rotational speed and direction of the platen assembly 230.
A top surface 260 of the platen assembly 230 supports a processing pad assembly 222 thereon. The processing pad assembly may be retained to the platen assembly 230 by magnetic attraction, vacuum, clamps, adhesives and the like.
A plenum 206 is defined in the platen assembly 230 to facilitate uniform distribution of electrolyte to the planarizing surface 126. A plurality of passages, described in greater detail below, are formed in the platen assembly 230 to allow electrolyte, provided to the plenum 206 from an electrolyte source 248, to flow uniformly though the platen assembly 230 and into contact with the substrate 122 during processing. It is contemplated that different electrolyte compositions may be provided during different stages of processing.
The processing pad assembly 222 includes an electrode 292 and at least a planarizing portion 290. The electrode 292 is typically comprised of a conductive material, such as stainless steel, copper, aluminum, gold, silver and tungsten, among others. The electrode 292 may be solid, impermeable to electrolyte, permeable to electrolyte or perforated. At least one contact assembly 250 extends above the processing pad assembly 222 and is adapted to electrically couple the substrate being processing on the processing pad assembly 222 to the power source 242. The electrode 292 is also coupled to the power source 242 so that an electrical potential may be established between the substrate and electrode 292.
A meter 244 is provided to detect a metric indicative of the electrochemical process. The meter 244 may be coupled or positioned between the power source 242 and at least one of the electrode 292 or contact assembly 250. The meter 244 may also be integral to the power source 242. In one embodiment, the meter 244 is configured to provide the controller 108 with a metric indicative of processing, such a charge, current and/or voltage. This metric may be utilized by the controller 108 to adjust the processing parameters in-situ or to facilitate endpoint or other process stage detection.
A window 246 is provided through the pad assembly 222 and/or platen assembly 230, and is configured to allow a sensor 254, positioned below the pad assembly 222, to sense a metric indicative of polishing performance. For example, the sensor 704 may be an eddy current sensor or an interferometer, among other sensors. The metric, provided by the sensor 254 to the controller 108, provides information that may be utilized for processing profile adjustment in-situ, endpoint detection or detection of another point in the electrochemical process. In one embodiment, the sensor 254 an interferometer capable of generating a collimated light beam, which during processing, is directed at and impinges on a side of the substrate 122 that is being polished. The interference between reflected signals is indicative of the thickness of the conductive layer of material being processed. One sensor that may be utilized to advantage is described in U.S. Pat. No. 5,893,796, issued Apr. 13, 1999, to Birang, et al., which is hereby incorporated by reference in its entirety.
Embodiments of the processing pad assembly 222 suitable for removal of conductive material from the substrate 122 may generally include a planarizing surface 126 that is substantially dielectric. Other embodiments of the processing pad assembly 222 suitable for removal of conductive material from the substrate 122 may generally include a planarizing surface 126 that is substantially conductive. At least one contact assembly 250 is provided to couple the substrate to the power source 242 so that the substrate may be biased relative to the electrode 292 during processing. Apertures 210, formed through the planarizing layer 290, allow the electrolyte to establish a conductive path between the substrate 112 and electrode 292.
In one embodiment, the planarizing portion 290 of the processing pad assembly 222 is a dielectric, such as polyurethane. Examples of processing pad assemblies that may be adapted to benefit from the invention are described in U.S. patent application Ser. No. 10/455,941, filed Jun. 6, 2003 by Y. Hu et al. (entitled “CONDUCTIVE PLANARIZING ARTICLE FOR ELECTROCHEMICAL MECHANICAL PLANARIZING”) and U.S. patent application Ser. No. 10/455,895, filed Jun. 6, 2003 by Y. Hu et al. (entitled “CONDUCTIVE PLANARIZING ARTICLE FOR ELECTROCHEMICAL MECHANICAL PLANARIZING”), both of which are hereby incorporated by reference in their entireties.
FIG. 3A is a partial sectional view of the first ECMP station 128 through two contact assemblies 250, and FIGS. 4A-C are side, exploded and sectional views of one of the contact assemblies 250 shown in FIGS. 3A. The platen assembly 230 includes at least one contact assembly 250 projecting therefrom and coupled to the power source 242 that is adapted to bias a surface of the substrate 122 during processing. The contact assemblies 250 may be coupled to the platen assembly 230, part of the processing pad assembly 222, or a separate element. Although two contact assemblies 250 are shown in FIG. 3A, any number of contact assemblies may be utilized and may be distributed in any number of configurations relative to the centerline of the platen assembly 230.
The contact assemblies 250 are generally electrically coupled to the power source 242 through the platen assembly 230 and are movable to extend at least partially through respective apertures 368 formed in the processing pad assembly 222. The positions of the contact assemblies 250 may be chosen to have a predetermined configuration across the platen assembly 230. For predefined processes, individual contact assemblies 250 may be repositioned in different apertures 368, while apertures not containing contact assemblies may be plugged with a stopper 392 or filled with a nozzle 394 (as shown in FIGS. 3D-E) that allows flow of electrolyte from the plenum 206 to the substrate. One contact assembly that may be adapted to benefit from the invention is described in U.S. patent application Ser. No. 10/445,239, filed May 23, 2003, by Butterfield, et a., and is hereby incorporated by reference in its entirety.
Although the embodiments of the contact assembly 250 described below with respect to FIG. 3A depicts a rolling ball contact, the contact assembly 250 may alternatively comprise a structure or assembly having a conductive upper layer or surface suitable for electrically biasing the substrate 122 during processing. For example, as depicted in FIG. 3B, the contact assembly 250 may include a pad structure 350 having an upper layer 352 made from a conductive material or a conductive composite (i.e., the conductive elements are dispersed integrally with or comprise the material comprising the upper surface), such as a polymer matrix 354 having conductive particles 356 dispersed therein or a conductive coated fabric, among others. The pad structure 350 may include one or more of the apertures 210 formed therethrough for electrolyte delivery to the upper surface of the pad assembly. Other examples of suitable contact assemblies are described in U.S. Provisional Patent Application Ser. No. 60/516,680, filed Nov. 3, 2003, by Hu, et al., which is hereby incorporated by reference in its entirety.
In one embodiment, each of the contact assemblies 250 includes a hollow housing 302, an adapter 304, a ball 306, a contact element 314 and a clamp bushing 316. The ball 306 has a conductive outer surface and is movably disposed in the housing 302. The ball 306 may be disposed in a first position having at least a portion of the ball 306 extending above the planarizing surface 126 and at least a second position where the ball 306 is substantially flush with the planarizing surface 126. It is also contemplated that the ball 306 may move completely below the planarizing surface 126. The ball 306 is generally suitable for electrically coupling the substrate 122 to the power source 242. It is contemplated that a plurality of balls 306 for biasing the substrate may be disposed in a single housing 358 as depicted in FIG. 3C.
The power source 242 generally provides a positive electrical bias to the ball 306 during processing. Between planarizing substrates, the power source 242 may optionally apply a negative bias to the ball 306 to minimize attack on the ball 306 by process chemistries.
The housing 302 is configured to provide a conduit for the flow of electrolyte from the source 248 to the substrate 122 during processing. The housing 302 is fabricated from a dielectric material compatible with process chemistries. A seat 326 formed in the housing 302 prevents the ball 306 from passing out of the first end 308 of the housing 302. The seat 326 optionally may include one or more grooves 348 formed therein that allow fluid flow to exit the housing 302 between the ball 306 and seat 326. Maintaining fluid flow past the ball 306 may minimize the propensity of process chemistries to attack the ball 306.
The contact element 314 is coupled between the clamp bushing 316 and the adapter 304. The contact element 314 is generally configured to electrically connect the adapter 304 and ball 306 substantially or completely through the range of ball positions within the housing 302. In one embodiment, the contact element 314 may be configured as a spring form.
In the embodiment depicted in FIGS. 3 and 4A-C and detailed in FIG. 5, the contact element 314 includes an annular base 342 having a plurality of flexures 344 extending therefrom in a polar array. The flexure 344 is generally fabricated from a resilient and conductive material suitable for use with process chemistries. In one embodiment, the flexure 344 is fabricated from gold plated beryllium copper.
Returning to FIGS. 3A and 4A-B, the clamp bushing 316 includes a flared head 424 having a threaded post 422 extending therefrom. The clamp bushing 316 may be fabricated from either a dielectric or conductive material, or a combination thereof, and in one embodiment, is fabricated from the same material as the housing 302. The flared head 424 maintains the flexures 344 at an acute angle relative to the centerline of the contact assembly 250 so that the flexures 344 of the contact elements 314 are positioned to spread around the surface of the ball 306 to prevent bending, binding and/or damage to the flexures 344 during assembly of the contact assembly 250 and through the range of motion of the ball 306.
The ball 306 may be solid or hollow and is typically fabricated from a conductive material. For example, the ball 306 may be fabricated from a metal, conductive polymer or a polymeric material filled with conductive material, such as metals, conductive carbon or graphite, among other conductive materials. Alternatively, the ball 306 may be formed from a solid or hollow core that is coated with a conductive material. The core may be non-conductive and at least partially coated with a conductive covering.
The ball 306 is generally actuated toward the planarizing surface 126 by at least one of spring, buoyant or flow forces. In the embodiment depicted in FIG. 3, flow through the passages formed through the adapter 304 and clamp bushing 316 and the platen assembly 230 from the electrolyte source 248 urge the ball 306 into contact with the substrate during processing.
FIG. 6 is a sectional view of one embodiment of the second ECMP station 130. The first and third ECMP stations 128, 132 may be configured similarly. The second ECMP station 130 generally includes a platen 602 that supports a fully conductive processing pad assembly 604. The platen 602 may be configured similar to the platen assembly 230 described above to deliver electrolyte through the processing pad assembly 604, or the platen 602 may have a fluid delivery arm 606 disposed adjacent thereto configured to supply electrolyte to a planarizing surface of the processing pad assembly 604. The platen assembly 602 includes at least one of a meter 244 or sensor 254 (shown in FIG. 2) to facilitate endpoint detection.
In one embodiment, the processing pad assembly 604 includes interposed pad 612 sandwiched between a conductive pad 610 and an electrode 614. The conductive pad 610 is substantially conductive across its top processing surface and is generally made from a conductive material or a conductive composite (i.e., the conductive elements are dispersed integrally with or comprise the material comprising the planarizing surface), such as a polymer matrix having conductive particles dispersed therein or a conductive coated fabric, among others. The conductive pad 610, the interposed pad 612, and the electrode 614 may be fabricated into a single, replaceable assembly. The processing pad assembly 604 is generally permeable or perforated to allow electrolyte to pass between the electrode 614 and top surface 620 of the conductive pad 610. In the embodiment depicted in FIG. 6, the processing pad assembly 604 is perforated by apertures 622 to allow electrolyte to flow therethrough. In one embodiment, the conductive pad 610 is comprised of a conductive material disposed on a polymer matrix disposed on a conductive fiber, for example, tin particles in a polymer matrix disposed on a woven copper coated polymer. The conductive pad 610 may also be utilized for the contact assembly 250 in the embodiment of FIG. 3C.
A conductive foil 616 may additionally be disposed between the conductive pad 610 and the subpad 612. The foil 616 is coupled to a power source 242 and provides uniform distribution of voltage applied by the source 242 across the conductive pad 610. In embodiments not including the conductive foil 616, the conductive pad 610 may be coupled directly, for example, via a terminal integral to the pad 610, to the power source 242. Additionally, the pad assembly 604 may include an interposed pad 618, which, along with the foil 616, provides mechanical strength to the overlying conductive pad 610. Examples of suitable pad assemblies are described in the previously incorporated U.S. patent application Ser. Nos. 10/455,941 and 10/455,895.
Multi-Step Polishing Method
FIG. 7 depicts one embodiment of a method 700 for electroprocessing conductive material, such as copper, tungsten, tantalum, tantalum nitride, titanium, titanium nitride, and the like, that may be practice on the system 100 described above. The method 700 may also be practiced on other electroprocessing systems. The method 700 is generally stored in the memory 112 of the controller 108, typically as a software routine. The software routine may also be stored and/or executed by a second CPU (not shown) that is remotely located from the hardware being controlled by the CPU 110.
Although the process of the present invention is discussed as being implemented as a software routine, some of the method steps that are disclosed therein may be performed in hardware as well as by the software controller. As such, the invention may be implemented in software as executed upon a computer system, in hardware as an application specific integrated circuit or other type of hardware implementation, or a combination of software and hardware.
The method 700 begins at step 702 by performing a bulk electrochemical process on the conductive layer, for example, copper, formed on the substrate 122. In one embodiment, the bulk process step 702 is at the first ECMP station 128. The bulk process step 702 generally is terminated when the conductive layer is about 2000 to about 1000 Å thick.
Next, a multi-step electrochemical clearance step 704 is performed to remove the remaining copper material to expose an underlying barrier layer, typically tantalum, tantalum nitride, titanium, titanium nitride and the like. The clearance step 704 may be performed on the first ECMP station 128, or one of the other ECMP stations 130, 132.
Following the clearance step 704, an electrochemical barrier removal step 706 is performed. Typically, the electrochemical barrier removal step 706 is performed on the third ECMP station 132, but may alternatively be performed one of the other ECMP stations 128, 130.
In one embodiment, the bulk processing step 702 begins at step 712 by moving the substrate 122 retained in the planarizing head 204 over the processing pad assembly 222 disposed in the first ECMP station 128. Although the pad assembly of FIGS. 2, 3A, 4A-C and 5, are utilized in one embodiment it is contemplated that pad and contact assemblies as described in FIGS. 3B-C and 6 may alternatively be utilized. At step 714, the planarizing head 204 is lowered toward the platen assembly 230 to place the substrate 122 in contact with the top surface of the pad assembly 222. In one embodiment, the substrate 122 is urged against the pad assembly 222 with a force less than about 2 pounds per square inch (psi).
At step 716, relative motion is provided between the substrate 122 and processing pad assembly 222. In one embodiment, the planarizing head 204 is rotated at less than about 50 revolutions per minute, while the pad assembly 222 is rotated at least about 50 revolutions per minute.
At step 718, electrolyte is supplied to the processing pad assembly 222 to establish a conductive path therethrough between the substrate 122 and the electrode 222. At step 719, current is provided from the power source 242 and runs between the top surface of the pad assembly 222 and the electrode 294. In one embodiment, the current is held at a constant magnitude in the range of about 4 to about 5 amperes. Steps 716, 718 and 719 are performed at substantially the same time.
In embodiments where tungsten is being processed, the current is about three times that utilized in copper processing to obtain the same removal rates. For example, step 719 may provide about 12 to about 15 amperes to remove a tungsten conductive layer.
The top surface of the pad assembly 222 is in contact with the substrate 122 and allows the current to be coupled thereto. The electrolyte filling the apertures 210 between the electrode 292 and the substrate 122 provides a conductive path between the power source 242 and substrate 122 to drive an electrochemical mechanical planarizing process that results in the removal of conductive material, such as copper, disposed on the surface of the substrate 122, by an anodic dissolution method at step 720. The process of step 720 generally has a removal rate of about 6000 Å/min.
At step 722, an endpoint of the bulk electroprocess is determined. The endpoint may be determined using a first metric of processing provided by the meter 244. The meter 244 may provide charge, voltage or current information utilized to determine the remaining thickness of the conductive material (e.g., the copper layer) on the substrate. In another embodiment, interferometer techniques, utilizing the sensor 254 may be utilized. The remaining thickness may be directly measured or calculated by subtracting the amount of material removed from a predetermined starting film thickness. In one embodiment, the endpoint is determined by comparing the charge removed from the substrate to a target charge amount for a predetermined area of the substrate. Examples of endpoint techniques that may be utilized are described in U.S. patent application Ser. No. 10/056,316, filed Jan. 22, 2002, and U.S. patent application Ser. No. 10/456,851, filed Jun. 6, 2002, both of which are hereby incorporated by reference in their entireties.
The step 722 is configured to detect the endpoint of the process prior to the breakthrough of the copper layer. In one embodiment, the remaining copper layer at step 722 has a thickness between about 1000 to about 2000 Å.
One embodiment of the clearance processing step 704 is now discussed with additional reference to a graph 800 of current and voltage traces 802, 804 depicted in FIG. 8. Amplitude is plotted on the y-axis 806 and time is plotted on the x-axis 808.
The clearance processing step 704 begins at step 724 by moving the substrate 122 retained in the planarizing head 204 over the processing pad assembly 604 disposed in the second ECMP station 130. At step 726, the planarizing head 204 is lowered toward the platen assembly 602 to place the substrate 122 in contact with the top surface of the pad assembly 604. Although the pad assembly of FIG. 6 is utilized in one embodiment it is contemplated that pad and contact assemblies as described in FIGS. 2, 3A-C, 4A-C and 5 may alternatively be utilized. In one embodiment, the substrate 122 is urged against the pad assembly 604 with a force less than about 2 pounds per square inch (psi). At step 728, electrolyte is supplied to the processing pad assembly 604 to establish a conductive path therethrough between the substrate 122 and the electrode 614.
At a first clearance process step 730, a first current is provided from the power source 242 and runs between the top surface of the pad assembly 604 and the electrode 614. In one embodiment, the current (as illustrated by the current trace 802) is held at a constant magnitude in the range of about 5 to about 4 amperes and passes through the electrolyte filling the apertures 622 between the electrode 614 and the substrate 122 to drive an electrochemical mechanical planarizing process. The process of step 730 generally has a removal rate of about similar to step 722.
At step 732, an endpoint of the electroprocess step 730 is determined. The endpoint may be determined using a first metric of processing provided by the meter 244 or by the sensor 254. In one embodiment, the endpoint is determined by detecting a first discontinuity 810 in voltage sensed by the meter 244. The first discontinuity 810 appears when the underlying layer begins to break through the conductive layer (e.g., copper layer). As the underlying layer has a different resistivity than the copper layer, the resistance across the processing cell (i.e., from the conductive portion of the substrate to the electrode 292) changes as the area of copper layer relative to the exposed area of the underlying layer changes.
Utilizing current (or voltage) for endpoint detection is particularly useful in tungsten removal processes as the close reflexivity between tungsten and underlying titanium nitride materials makes convention optical detection difficult.
In response to the endpoint detection at step 732, a second clearance process step 734 is performed to remove the residual copper layer. At step 734, a second current is provided from the power source 242. The current is held at a constant magnitude less than the current of step 730 and passes through the electrolyte filling the apertures 620 between the electrode 614 and the substrate 122 to drive an electrochemical mechanical planarizing process. For example, current may be provided in the range of about 1.5 to about 4.5 amperes. The process of step 734 generally has a removal rate of about 500 to about 1500 Å/min. In tungsten processes, the current may be in the range of about 4.5 to about 13.5 amperes to obtain removal rates of 500-2000 Å/min.
At step 736, an endpoint of the electroprocess step 734 is determined. The endpoint may be determined using a second metric of processing provided by the meter 244 or by the sensor 254. In one embodiment, the endpoint is determined by detecting a second discontinuity 812 in voltage sensed by the meter 244. The discontinuity 812 appears when the underlying barrier layer is fully exposed and copper layer that remains substantially in the features formed in the substrate 122 (e.g., copper lines and vias).
Optionally, a third clearance process step 738 may be performed to remove any remaining debris from the conductive layer. The third clearance process step 738 is typically a timed process, and is performed at the same or reduced current levels relative to the second clearance process step 732. In one embodiment, the third clearance process step 738 (also referred to as an overpolish step) has a duration of about 15 to about 30 seconds. During the step 738, the current may be lowered to less than the current level for the previous processing step, for example, to about 0.5-3 amperes.
The electrochemical barrier removal step 706 begins at step 740 by moving the substrate 122 retained in the planarizing head 204 over the processing pad assembly 604 disposed in the third ECMP station 132. At step 742, the planarizing head 204 is lowered toward the platen assembly 602 to place the substrate 122 in contact with the top surface of the pad assembly 604. Although the pad assembly of FIG. 6 is utilized in one embodiment it is contemplated that pad and contact assemblies as described in FIGS. 2, 3A-C, 4A-C and 5 may alternatively be utilized. In one embodiment, the substrate 122 is urged against the pad assembly 604 with a force less than about 2 pounds per square inch (psi). At step 744, electrolyte is supplied to the processing pad assembly 604 to establish a conductive path therethrough between the substrate 122 and the electrode 614. The electrolyte utilized for barrier removal may be different than the electrolyte utilized for copper removal.
In one embodiment, electrolyte composition provided at the third ECMP station 132 includes phosphoric or sulfuric acid and a catalyst. The electrolyte may be adapted to prevent or inhibit oxide formation on the barrier layer. The catalyst is selected to activate the Ti or other barrier layer to react selectively with a complexing agent so that the barrier layer may be removed and/or dissolved easily with minimal or no removal of copper or tungsten. The electrolyte composition may additionally include pH adjusters and clelating agents, such as amino acids, organic amines and phthalic acid or other organic carbolic acids, picolinic acid or its derivatives. The electrolyte may optionally contain abrasives. Abrasives may be desirable to remove a portion of the underlying oxide layer.
At a first barrier process step 746, a first current is provided from the power source 242 and runs between the top surface of the pad assembly 604 and the electrode 614. In one embodiment, the current is held at a constant magnitude in the range of about 1.5 to about 6 amperes and passes through the electrolyte filling the apertures 620 between the electrode 614 and the substrate 122 to drive an electrochemical mechanical planarizing process. The process of step 746 generally has a removal rate of about 500-2000 Å/min.
At step 748, an endpoint of the electroprocess step 746 is determined. The endpoint may be determined using a first metric of processing provided by the meter 244 or by the sensor 254. The current and voltage traces of the electrochemical barrier removal step 706 are similar is form to the traces depicted in FIG. 8, and as such, have been omitted for brevity. In one embodiment, the endpoint of step 748 is determined by detecting a first discontinuity in voltage sensed by the meter 244. The first discontinuity appears when the underlying layer (typically an oxide) begins to breakthrough the barrier layer. As the underlying oxide layer has a different resistivity than the barrier layer, the change in resistance across the processing cell is indicative of the breakthrough of the barrier layer.
In response to the endpoint detection at step 748, a second clearance process step 750 is performed to remove the residual copper layer. At step 748, a second current is provided from the power source 242. The current is held at a constant magnitude less than the current of step 746 and passes through the electrolyte filling the apertures 620 between the electrode 614 and the substrate 122 to drive an electrochemical mechanical planarizing process. For example, in one embodiment, current may be provided in the range of about 3.5 to about 2.5 amperes The process of step 748 generally has a removal rate of about 1000 Å/min.
At step 752, an endpoint of the electroprocess step 750 is determined. The endpoint may be determined using a second metric of processing provided by the meter 244 or by the sensor 254. In one embodiment, the endpoint is determined by detecting a second discontinuity in voltage sensed by the meter 244. The second discontinuity appears when the oxide layer is fully exposed.
Optionally, a third clearance process step 754 may be performed to remove any remaining debris from the barrier layer. The third clearance process step 754 is typically a timed process, and is performed at the same or reduced current levels relative to the second clearance process step 746. In one embodiment, the third clearance process step 754 (also referred to as an overpolish step) has a duration of about 15 to about 30 seconds.
FIG. 9 is a flow diagram of another embodiment of a method 900 for electrochemical processing. The method 900 is substantially similar to the method 800 described above, except wherein the electrochemical process is driven by a constant voltage provided by the power source 242 as depicted in a graph 1000 of current and voltage traces 1002, 1004 shown in FIG. 10. Amplitude is plotted on the y-axis 1006 and time is plotted on the x-axis 1008
In one embodiment, the method 900 begins at step 902 by performing a bulk electrochemical process on the conductive layer, for example, a copper layer, formed on the substrate 112. The bulk process step 902 generally is terminated when the conductively layer is about 2000 to about 1000 Å thick.
Next, a multi-step electrochemical clearance step 904 is performed to remove the remaining copper material to expose an underlying barrier layer. The clearance step 904 may be performed on the first ECMP station 128, or one of the other ECMP stations 130, 132. Following the clearance step 904, an electrochemical barrier removal step 906 is performed. Typically, the electrochemical barrier removal step 906 is performed on the third ECMP station 132, but may alternatively be performed one of the other ECMP stations 128, 130.
In one embodiment, the bulk processing step 902 is substantially similar to the bulk processing step 702 described above. The bulk processing step 702 utilizes substantially constant voltage provided from the power source 242 to drive the electrochemical process. In one embodiment, the voltage is held at a substantially constant magnitude in the range of about 1 to about 4 volts. The endpoint of the bulk electroprocess is determined as discussed above, for example, by summation of charge removed from the conductive layer, among other methods for endpoint detection. It should be noted that during the first processing step illustrated on the left portion of trace 1002, the current decreases as the conductive layer thins. This is particularly measurable when removing tungsten, and thus, the slope of the trace may be utilized to determine removal rates or the remaining thickness of the conductive layer. Thickness versus current change information may be empirically found or calculated and stored in a database accessible to the controller 108 of use in endpoint detection, removal profile control or other process control.
The clearance processing step 904 is now performed. The clearance processing step 904 is similar to the step 904 described above, except that the electrochemical process is driven at a constant voltage. In one embodiment, the voltage is constant over both the bulk and clearance processing steps 902, 904. In another embodiment, the voltage driving the clearance processing step 904 may be less than the preceding processing step.
A first endpoint of the processing step 904 is identified by detecting a first discontinuity 1010 in the current trace 1002 as monitored by the meter 244. The first endpoint may alternatively be determined by other methods. The detection of the first discontinuity 1010 signifies the breakthrough of the copper layer.
A second endpoint of the processing step 904 is identified by detecting a second discontinuity 1012 in the current trace 1002. The second endpoint may be identified by alternative methods. The second discontinuity identifies clearance of the copper layer. Optionally, a timed overpolish step may be performed during the clearance processing step 904 after detection of the second endpoint as identified by the second discontinuity 1012.
The electrochemical barrier removal step 906 is substantially similar to the barrier removal step 706 described above, except that the electrochemical process is driven at a substantially constant voltage. The voltage is generally held at a substantially constant magnitude equal to or less than the voltage utilized for the steps 902, 904. In one embodiment, the voltage is held at a substantially constant magnitude less than about 3 volts for at least the bulk portion of barrier removal. The voltage may optionally be reduced for the residual removal portion of the barrier removal process.
Thus, the present invention provides an improved apparatus and method for electrochemically planarizing a substrate. The apparatus advantageously facilitates efficient bulk and residual copper and barrier materials removal from a substrate. It is contemplated that a method and apparatus as described by the teachings herein, may be utilized to deposit materials onto a substrate by reversing the polarity of the bias applied to the electrode and the substrate.
While the foregoing is directed to embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. A method for electroprocessing a substrate, comprising:

establishing an electrically-conductive path through an electrolyte between an exposed layer of barrier material on the substrate and an electrode;

electrochemically removing a portion of the exposed layer during a first electrochemical processing step in a barrier processing station;

detecting an endpoint of the first electrochemical processing step at or just prior to breakthrough of the exposed layer of barrier material;

electrochemically processing the exposed layer of barrier material in a second electrochemical processing step in the barrier processing station; and

detecting an endpoint of the second electrochemical processing step.

2. The method of claim 1, wherein the step of establishing a conductive path further comprises:

flowing electrolyte from below the electrode and through a processing pad assembly into contact with the substrate.

3. The method of claim 1 comprising:

contacting the barrier material on the substrate with a processing pad assembly; and

moving the substrate relative to the pad assembly in a polishing motion;

4. The method of claim 1, wherein the second electrochemical processing step further comprises:

detecting a first endpoint;

processing the substrate at a slower rate; and

detecting a second endpoint indicative of residual barrier material being cleared from the substrate.

5. The method of claim 4, wherein the second electrochemical processing step further comprises:

overpolishing the substrate after detection of the second endpoint.

6. The method of claim 4, wherein the step of detecting the first endpoint further comprises:

detecting a first discontinuity in a potential difference between the substrate and the electrode.

7. The method of claim 6, wherein the step of detecting the second endpoint further comprises:

detecting a second discontinuity in a potential difference between the substrate and the electrode.

8. The method of claim 4, wherein the step of detecting the first endpoint further comprises:

detecting a first discontinuity in a current passing between the substrate and the electrode.

9. The method of claim 8, wherein the step of detecting the second endpoint further comprises:

detecting a second discontinuity in the current passing between the substrate and the electrode.

10. The method of claim 5, wherein the over polish step has a duration of 15 to 35 seconds.

11. The method of claim 1, wherein the barrier processing station is disposed within an enclosure of a processing system.

12. The method of claim 11 further comprising:

removing, within the processing system, a conductive layer disposed over the barrier layer.

13. The method of claim 12 further comprising:

electrochemically processing the conductive layer.

14. The method of claim 13 further comprising:

transferring the substrate between a first electrochemical processing station to the barrier processing station.

15. The method of claim 1 further comprising:

determining a remaining thickness of the barrier layer from a change in current between the substrate and the electrode.

16. A method of electrochemically processing a substrate having an exposed conductive layer and an underlying barrier layer, comprising:

establishing an electrically-conductive path through an electrolyte between the exposed layer of conductive material on the substrate and an electrode;

electrochemically removing a portion of the exposed layer during a first electrochemical processing step in a first processing station;

detecting an endpoint of the first electrochemical processing step at or just prior to breakthrough of the exposed layer of conductive material;

electrochemically processing the exposed layer of conductive material in a second electrochemical processing step;

detecting an endpoint of the second electrochemical processing step;

transferring the substrate to a barrier removal station; and

electrochemically processing the barrier layer.

17. The method of claim 16, wherein the second electrochemical processing step is performed in the first processing station.

18. The method of claim 16 further comprising:

transferring the substrate to a second processing station where the second electrochemical processing step is performed.

19. The method of claim 16, wherein the step of establishing a conductive path further comprises:

20. The method of claim 17, wherein the second electrochemical processing step further comprises:

detecting a first endpoint;

processing the substrate at a slower rate; and

detecting a second endpoint indicative of residual conductive material being cleared from the substrate.

21. The method of claim 20, wherein the second electrochemical processing step further comprises:

overpolishing the substrate after detection of the second endpoint.

22. The method of claim 20, wherein the step of detecting the first endpoint further comprises:

23. The method of claim 22, wherein the step of detecting the second endpoint further comprises:

24. The method of claim 20, wherein the step of detecting the first endpoint further comprises:

25. The method of claim 24, wherein the step of detecting the second endpoint further comprises:

26. The method of claim 21, wherein the over polish step has a duration of 15 to 35 seconds.

27. The method of claim 16, wherein the barrier electrochemical processing step further comprises:

detecting a first endpoint;

processing the substrate at a slower rate; and

detecting a second endpoint indicative of barrier material being cleared from the substrate.

28. The method of claim 27, wherein the barrier electrochemical processing step further comprises:

overpolishing the substrate after detection of the second endpoint.

29. The method of claim 28, wherein the step of detecting the first endpoint further comprises:

30. The method of claim 27, wherein the step of detecting the second endpoint further comprises:

31. The method of claim 27, wherein the step of detecting the first endpoint further comprises:

32. The method of claim 27, wherein the step of detecting the second endpoint further comprises:

33. The method of claim 28, wherein the over polish step has a duration of 15 to 35 seconds.

34. The method of claim 16 comprising:

contacting an exposed layer of conductive material on the substrate with a polishing pad; and

moving the substrate relative to the pad in a polishing motion.

35. The method of claim 15 further comprising:

determining a thickness remaining of the conductive material from a change in current.

36. A method of electrochemically processing a substrate having an exposed conductive layer and an underlying barrier layer, comprising:

disposing the substrate on a processing pad assembly in a first processing station of a processing system;

providing a polishing motion between the processing pad assembly and the substrate in contact therewith;

electrochemically removing a portion of the exposed layer during a first electrochemical processing step in the first processing station;

detecting an endpoint of the second electrochemical processing step;

transferring the substrate to a barrier removal station;

establishing an electrically-conductive path through an electrolyte between the barrier layer and an electrode disposed in the barrier removal station;

electrochemically removing a portion of the barrier layer during a first electrochemical barrier processing step in a barrier processing station;

detecting an endpoint of the first electrochemical barrier processing step at or just prior to breakthrough of barrier material;

electrochemically processing the barrier material in a second electrochemical barrier processing step in the barrier processing station; and

detecting an endpoint of the second electrochemical processing step.

37. The method of claim 36, wherein the step of detecting at least two of endpoints of the barrier and conductive material processing steps further comprises:

detecting discontinuities in a potential difference between the substrate and the electrode.

38. The method of claim 36, wherein the step of detecting at least two of endpoints of the barrier and copper processing steps further comprises:

detecting discontinuities in current measured between the substrate and the electrode.

39. The method of claim 36 further comprising: