US20070062815A1

US20070062815A1 - Method for stabilized polishing process

Info

Publication number: US20070062815A1
Application number: US11/532,258
Authority: US
Inventors: Renhe Jia; Jie Diao; Stan Tsai; You Wang; Laksh Karuppiah
Original assignee: Applied Materials Inc
Current assignee: Applied Materials Inc
Priority date: 2005-09-19
Filing date: 2006-09-15
Publication date: 2007-03-22
Also published as: WO2007035408A1; TW200721296A

Abstract

A method for electrochemically processing a substrate is provided. In one embodiment, a method for electrochemically processing a substrate includes processing a substrate using a multi-step routine that includes a first processing period performed using a varying voltage to achieve a target removal current followed by a second processing period performed using a constant voltage.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional patent application Ser. No. 60/718,851 (Attorney Docket No 010581 L), filed Sep. 19, 2005, which application is 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 electrochemical processing.
2. Description of the Related Art
Electrochemical mechanical planarizing (ECMP) is a technique used to remove conductive materials, such as copper and tungsten, from a substrate surface by electrochemical dissolution while concurrently polishing the substrate with reduced mechanical abrasion compared to conventional planarization processes. 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. ECMP systems may generally be adapted for deposition of conductive material on the substrate by reversing the polarity of the bias.
Stability is a very important factor in determining a successful ECMP process. For many ECMP processes, a fixed voltage is applied to a substrate through a conductive pad surface as a means to drive metal removal from the substrate. In this process, any variation in electrical resistance or the mechanical properties, either with time or with different process previously done on the conductive surface, will lead to varied polishing rate (as may be detected by monitoring current) with a certain applied voltage. This variation, in turn, may lead to varied process time for a certain amount of material removal, and thus process instability.
Therefore, there is a need for an improved method and apparatus for electrochemical processing of 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 processing a substrate using a routine that includes a first processing period performed to achieve a target removal current followed by a second processing period performed using a constant voltage based on the target removal current.
In one embodiment, the first processing period includes setting a specific current value (that may indicate a specific removal rate) as the targeted removal current for the process, and adjusting the voltage based on the measured current to achieve the targeted removal current. If the measured current is lower than the targeted removal current, the voltage is increased to get the current closer to the target. Similarly, if the measured current is higher than the target removal current, the voltage is decreased to lower the current. This can be done through a closed loop feedback system, so that the polishing tool can automatically adjust the voltage, leading to the targeted removal rate. When the targeted removal current is reached (stabilized), the voltage is measured and set at the target voltage. So from this point forward in the polishing routine, the polishing will be done with this constant voltage.
This method is especially useful when removing residual metal from the substrate. The first step (determining a voltage for the target removal current) will determine a suitable voltage for subsequent polishing. The second step includes fixing the voltage once the target removal current is reached. Once voltage is fixed, an endpoint may be determined by monitoring the current.
In another embodiment, a method for electroprocessing a substrate is described. The method includes establishing an electrically-conductive path through an electrolyte between an exposed layer of material on the substrate and an electrode, electrochemically removing a first portion of the exposed layer while adjusting voltage to achieve a target removal current, and electrochemically removing a second portion of the exposed layer with a constant voltage corresponding to the target removal current.
In another embodiment, a method for processing a substrate in an electrochemical mechanical planarizing system is described. The method includes processing a first substrate on a polishing pad for a first processing period performed to achieve a target removal current, and processing the first substrate on the polishing pad for a second processing period performed using a constant voltage based on the target removal current.
As a result, this process, with determining a voltage for a target removal current and then fixing the voltage for that specific removal current for the remaining metal residue polishing, may minimize process variations due to changes in a full conductive pad over time. Additionally, the method may minimize the variation among different pads, meaning the rate of a certain full conductive pad under a certain applied voltage might be different from that of another pad, however this variation will be compensated with the constant current plus the fixed voltage polishing.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of 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 processing 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. 3 is a sectional view of another embodiment of an ECMP station;
FIG. 4 is a flow diagram of one embodiment of a method for electroprocessing conductive material;
FIG. 5 is a graph of process results for a conventional electroprocess; and
FIG. 6 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. It is also contemplated that elements and features of one embodiment may be beneficially incorporated on other embodiments without further recitation.

DETAILED DESCRIPTION

Embodiments for a method for electroprocessing of conductive materials and other 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, or transfer processes of embodiments of the present invention.
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 stations 128, 130, 132 may be configured to process the conductive layer with a removal process having at least two steps.
The exemplary planarizing module 106 also includes a transfer station 136 and a carousel 134 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, filed Oct. 6, 1999 and issued Dec. 5, 2000, 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. On carousel that may be utilized to advantage is described in U.S. Pat. No. 5,804,507, filed Oct. 27, 2005 and issued Sep. 8, 1998, 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, copper, gold, palladium, 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 240 is provided to detect a metric indicative of the electrochemical process. The meter 240 may be coupled or positioned between the power source 242 and at least one of the electrode 292 or contact assembly 250. The meter 240 may also be integral to the power source 242. In one embodiment, the meter 240 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 in a closed loop feedback system 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 254 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, filed Aug. 16, 1996 and issued Apr. 13, 1999, 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 portion 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. Pat. No. 6,991,528, filed Jun. 6, 2003 and issued Jan. 31, 2006, and United States Patent Publication No. 2004/0020789, filed Jun. 6, 2003 and published on Feb. 5, 2004, both of which are hereby incorporated by reference in their entireties.
The at least one contact assembly 250 disposed in the processing pad assembly of FIG. 2 may be coupled to the platen assembly 230 and is adapted to bias a surface of the substrate 122. The at least one contact assembly 250 is generally electrically coupled to the power source 242 through the platen assembly 230 and is movable to extend at least partially through a respective aperture (not shown) formed in the processing pad assembly 222. One contact assembly that may be adapted to benefit from the invention is described in U.S. Pat. No. 6,884,153, filed May 23, 2003 and issued Apr. 26, 2005, and is hereby incorporated by reference in its entirety. 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.
The at least one contact assembly 250 may comprise a rolling ball contact although 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, the contact assembly 250 may include a pad structure (not shown) having an upper layer 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 having conductive particles dispersed therein, or a conductive coated fabric, among others.
FIG. 3 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 302 that supports a fully conductive processing pad assembly 304. The platen 302 may be configured similar to the platen assembly 230 described above to deliver electrolyte through the processing pad assembly 304, or the platen 302 may have a fluid delivery arm 306 disposed adjacent thereto configured to supply electrolyte to a planarizing surface of the processing pad assembly 304. The platen assembly 302 may include at least one of a meter 240 or sensor 254 (shown in FIG. 2) to facilitate endpoint detection.
In one embodiment, the processing pad assembly 304 includes interposed pad 312 sandwiched between a conductive pad 310 and an electrode 314. The conductive pad 310 is substantially conductive across its top processing surface 320 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 elements or particles may be conductive metals, such as copper, tin, gold, silver, or combinations thereof.
The conductive pad 310, the interposed pad 312, and the electrode 314 may be fabricated into a single, replaceable assembly. The processing pad assembly 304 is generally permeable or perforated to allow electrolyte to pass between the electrode 314 and top surface 320 of the conductive pad 310. In the embodiment depicted in FIG. 3, the processing pad assembly 304 is perforated by apertures 322 to allow electrolyte to flow therethrough. In one embodiment, the conductive pad 310 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 310 may also be utilized for the contact assembly 250 in the embodiment of FIG. 2.
A conductive foil 316 may additionally be disposed between the conductive pad 310 and the interposed pad 312. The foil 316 is coupled to a power source 242 and provides uniform distribution of voltage applied by the source 242 across the conductive pad 310. In embodiments not including the conductive foil 316, the conductive pad 310 may be coupled directly, for example, via a terminal integral to the pad 310, to the power source 242. Additionally, the pad assembly 304 may include an interposed pad 318, which, along with the foil 316, provides mechanical strength to the overlying conductive pad 310. Examples of suitable pad assemblies are described in U.S. Pat. No. 6,991,528, and United States Patent Publication No. 2004/0020789, both of which have been previously incorporated by reference. Another suitable pad assembly is described in U.S. patent application Ser. No. 11/327,527, filed Jan. 5, 2006, entitled “Fully Conductive Pad for Electrochemical Mechanical Processing,” which is incorporated in reference in its entirety.
In one embodiment, the pad assembly 304 depicted in FIG. 3 may include an electrode 314 that comprises a plurality of zones, such as outer zone 315A, and inner zone 315B. The zones 315A, 315B may be any shape or configuration, such as annular or concentric circles as shown, or any other geometric shape. The zones 315A, 315B are insulated from each other in order to facilitate independent voltage application to each zone. The independent voltage application may facilitate enhanced removal of materials from the substrate 122 by applying different voltages or biases to the independent zones based on an incoming thickness profile of the substrate and/or the amount of polishing time the substrate 122 spends over each zone. In this manner, the potential difference between the substrate 122 and each zone 315A, 315B may be different, for example between the center of the substrate relative to the perimeter of the substrate, thus providing enhanced control of removal of material from different regions of the substrate.
For example, the incoming thickness profile of the substrate 122 may include a greater thickness of conductive material on the periphery of the substrate as compared to the center region of the substrate. Due to the positioning and rotation of the head assembly 152 and/or the pad assembly 304, the periphery of the substrate 122 may spend more time over the outer zone 315A relative to the inner zone 315B. In this example, the voltage or bias applied to the outer zone 315A may be different than the voltage or bias applied to the inner zone 315B in order to compensate for the difference in material thicknesses in different regions of the substrate 122. Although two zones 315A, 315B are shown, any number of independently biasable zones may be used.
Multi-Step Polishing Method
FIG. 4 shows one embodiment of a method 400 for electroprocessing conductive material, such as copper, tungsten, tantalum, tantalum nitride, titanium, titanium nitride, and the like, that may be practiced on the system 100 described above, although the method 400 may also be practiced on other electroprocessing systems. The method 400 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 is discussed as being implemented as a software routine, some of the method steps that are disclosed herein 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 400 begins at step 402 by electroprocessing the substrate for a first processing period to achieve a target removal current by measuring the current and adjusting the voltage. The first processing step 402 is followed at step 404 by electroprocessing the substrate (on the same pad) for a second processing period using a constant voltage measured for the target removal current.
In one embodiment, the first processing step 402 includes setting a specific current value as the targeted removal current for the process. The specific current value may indicate a specific average removal rate that is determined, for example, by historical data, and/or an algorithm. The specific current value may also be determined by an algorithm based on an incoming thickness profile of the substrate 122. Voltage is then increased or decreased based on feed back from measurement of the current and/or the initial voltage, which may be a closed-loop system. If the measured current is lower than the targeted removal current, the voltage is increased to get the current closer to the target. Similarly, if the measured current is higher than the targeted removal current, the voltage will be decreased to lower the current. This can be done through the closed loop feedback system, so that the polishing tool can automatically adjust the voltage, leading to the targeted removal rate.
In one embodiment, the second processing step 404 includes fixing an instantaneous voltage as soon as the targeted current is reached. For example, when the target current has reached a stabilized state, the voltage at the targeted current is locked in. After the voltage is fixed in the polishing routine, the remainder of polishing will be done with the fixed, constant voltage. The method 400 may be repeated for each incoming wafer and eliminates or minimizes pad variations over time. Additionally, the method 400 will substantially eliminate the variation among new, unused, different pads, and/or variations between the same pad relative to multiple substrates. For example, the average removal rate of a certain full conductive pad under a certain applied voltage might differ from that of another pad, and/or the same pad after a number of substrates have been processed, however this pad variation will be minimized or compensated by the method 400.
As an example, a new pad may include a surface to provide a first removal rate of material from the substrate, either as-is, or with a conditioning process to prepare the pad for polishing. The pad may be pre-conditioned before a polishing process, conditioned in-situ while polishing, or a combination of both. In any case, the new pad may include a surface with a first removal rate. However, after polishing multiple substrates, the pad surface may become less efficient. Subsequent or concurrent conditioning processes may enhance the pad surface, but the removal rate of the pad surface may decrease. For example, the pad surface may exhibit a lower removal rate due to accumulation of polishing by-products and/or wear of the polishing surface. Pad properties, such as resistivity may increase after a number of substrates have been processed due to deterioration or other changes in the pad surface. This deterioration may result in higher voltages to achieve the desired current for subsequent polishing processes on subsequent substrates. However, in some cases, an in-situ conditioning process may enhance to surface of the pad resulting in lower polishing voltages required to drive the same polishing current. In other cases, the pad surface may not be changed significantly and the higher voltage, relative to the voltage used for previous polishing processes, may be needed to drive the desired current. In any case, the method 400 may be configured to compensate for these variations and enhance the polishing process for multiple substrates on the same or different pads.
The method 400 may be used during polishing on the planarizing module 106 of FIG. 1 with the polishing pads disposed on the ECMP stations 128, 130, and 132. For example, the method 400 may be used to determine and set a constant voltage on the first ECMP station 128, to perform bulk removal of conductive material, and the method 400 may be repeated to determine and set a constant voltage for residual material removal on the second ECMP station 130. Alternatively, the bulk and residual polishing processes may be performed on a single station. Optionally, the bulk and residual polishing process may be performed in a single application of the method 400.
In one exemplary embodiment, the first step 402 includes determining a corresponding voltage for obtaining a target removal current under actual processing conditions. The second step 404 includes polishing with the determined voltage a certain amount of time to reach an endpoint. In another example, the incoming thickness profile of the substrate 122 may be determined prior to polishing, and a specific current may be determined based on an algorithm and/or data acquired from substrates having a similar incoming thickness. For example, the substrate 122 may include an incoming thickness of conductive material in a range between about 7000 Angstroms (Å) to about 9000 Å, such as about 8000 Å. The polishing process may commence with the historically and/or algorithmically determined current for a first processing period as the voltage is monitored. After the current has stabilized, the voltage driving the stabilized current will be fixed, and the voltage will remain constant throughout a second processing period. The first and second processing periods of the bulk removal process performed on the first ECMP station 128 may include leaving about 1000 Å to about 2000 Å of conductive material on the substrate 122 for subsequent removal on the second ECMP station 130 in a residual removal process.
During the first processing period, the voltage is adjusted to drive the targeted current and the rate of change of voltage (ΔV) or adjustment during this period may be very rapid. However, as the polishing process continues, ΔV may decrease and reach a stabilized or near-stabilized state. A voltage fixing point may be determined when ΔV has reached a stabilized or near stabilized state. At this fixing point, the voltage may be stablized and the second processing period may continue until an endpoint in the polishing process is determined.
The first and second processing periods, relative to time, may be substantially the same amount of time, or have different times. However, experiments have shown that the first processing period to reach a fixed voltage is less than half of the time needed for both the first and second processing periods. In one embodiment, the second processing period may be typically much greater than the first processing period.
The method 400 is especially useful when removing residual material from the substrate, which may include residual conductive material and barrier material. The first step 402, which includes determining a corresponding voltage for the target removal current, at the beginning of the method 400 will determine a suitable voltage for subsequent polishing, and then the determined voltage at step 404 will substantially provide this removal rate for a certain amount of time. Step 404 is terminated at an endpoint, such as an endpoint determined by current. The endpoint may also be determined when the metal film breaks through or when residual metal film has been cleared. The endpoint may be determined by monitoring current passing between the substrate and counter electrode, monitoring the potential difference between the substrate and counter electrode, and monitoring charge removed from the substrate, optical devices, among others. Examples of suitable endpoint routines are described in United States Patent Publication No. 2004/0182721, filed Mar. 18, 2003 and published on Sep. 23, 2004; U.S. Pat. No. 6,837,983, filed Jan. 22, 2002 and issued on Jan. 1, 2003; United States Publication No. 2005/0061674, filed Sep. 24, 2004 and published on Mar. 24, 2005; and United States Publication No. 2006/0166500, filed Jan. 26, 2005 and published on Jul. 27, 2006; all of which are incorporated by reference in their entireties.
In another example, the method 400 may include moving the substrate 122 retained in the planarizing head 204 over the processing pad assembly 304 disposed in the second ECMP station 130. The planarizing head 204 is lowered toward the platen assembly 302 to place the substrate 122 in contact with the top surface of the pad assembly 304. Although the pad assembly of FIG. 3 is utilized in one embodiment, it is contemplated that other pad and contact assemblies as described in FIG. 2 may alternatively be utilized. In one embodiment, the substrate 122 is urged against the pad assembly 304 with a force less than about 2 pounds per square inch (psi). Electrolyte is supplied to the processing pad assembly 304 to establish a conductive path therethrough between the substrate 122 and the electrode 314.
At a first clearance process step 402, a variable voltage is provided from the power source 242 and runs between the top surface of the pad assembly 304 and the electrode 314 until a target removal current is achieved. In one embodiment, the voltage is adjusted until the current achieves a target removal current in the range of about 5 to about 4 amperes and passes through the electrolyte filling the apertures 322 between the electrode 314 and the substrate 122 to drive an electrochemical mechanical planarizing process.
Once the voltage is stabilized at the target removal current, a constant voltage is utilized at step 404 to conduct the remainder of the electroprocess. An endpoint of the second step 404 is determined by detecting a metric indicative of endpoint, such as current, voltage, charge, interferometry or other suitable endpoint detection technique.
The method 400 may be used in the embodiment shown in FIG. 3 when the pad assembly includes an electrode with independently biasable zones, such as outer zone 315A and inner zone 315B. For example, the processing steps 402, 404 may be applied to the outer zone 315A independent of the processing steps 402, 404 applied to the inner zone 315B. In this example, the targeted removal current for the outer zone 315A may be determined and the voltage may be locked when the targeted current has reached a stabilized state for the outer zone 315A, while a different targeted current for zone 315B results in the voltage driving and locked for the inner zone 315B being different. Moreover, the sequence in which the voltage in each zone 315A, 315B is locked first, may vary.
FIG. 5 is a graph 500 of a conventional electroprocess that utilizes constant voltage to drive electroprocessing of the substrate. For comparison, FIG. 6 is a graph 600 of an exemplary electroprocess that utilized the method of the present invention to drive electroprocessing of the substrate with a first constant current step followed by a constant voltage step. The results illustrated in FIG. 5 show current (representative of the polishing rate) dropping gradually over time, which is evidence of process instability. The results illustrated FIG. 6 show a very stable removal rate over time, which is evidence of the stability of the process of the present invention.
Thus, the present invention provides an improved method for electrochemically planarizing a substrate. The method advantageously provides process repeatability and minimizes or eliminates process variations due to changes in the electrical characteristics of a conductive pad over time. Furthermore, the method will substantially eliminate variation among different pads, meaning that the rate of a certain full conductive pad under a certain applied voltage might be different from that of another pad, however this variation will be compensated with the constant current plus the fixed voltage polishing.
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 present 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 material on the substrate and an electrode;

electrochemically removing a first portion of the exposed layer while adjusting voltage to achieve a target removal current; and

electrochemically removing a second portion of the exposed layer with a constant voltage corresponding to the target removal current.

2. The method of claim 1, further comprising:

pressing the exposed layer of material against a partially conductive surface of a polishing pad.

3. The method of claim 2, wherein the pressing further comprises:

pressing the substrate against the polishing pad with a pressure of less than 2 pounds per square inch.

4. The method of claim 1, wherein the target removal current is determined before removing the first portion of the exposed layer.

5. The method of claim 1, wherein the target removal current is determined by an incoming thickness profile of the substrate using historical data and/or an algorithm based on the incoming thickness profile.

6. The method of claim 1, further comprising:

adjusting a first processing voltage across a first processing zone of the electrode while removing the first portion; and

adjusting a second processing voltage across a second processing zone of the electrode while removing the second portion.

7. The method of claim 1, further comprising:

fixing the voltage to provide the constant voltage corresponding to the target removal current after the adjusted voltage has reached a near stabilized state.

8. A method for processing a substrate in an electrochemical mechanical planarizing system, comprising:

processing a first substrate on a polishing pad for a first processing period performed to achieve a target removal current; and

processing the first substrate on the polishing pad for a second processing period performed using a constant voltage based on the target removal current.

9. The method of claim 8, wherein processing the first substrate for the first processing period further comprises:

adjusting a processing voltage during the first processing period.

10. The method of claim 8, wherein processing the first substrate for the first processing period further comprises:

adjusting a first processing voltage across a first processing zone during the first processing period; and

adjusting a second processing voltage across a second processing zone during the first processing period.

11. The method of claim 10, wherein adjusting the first and second processing voltages further comprises:

applying different voltages to an outer portion of the first substrate relative to an inner portion of the first substrate.

12. The method of claim 8, wherein processing the first substrate for the first and second period includes establishing an electrochemical circuit between an exposed layer of conductive material on the first substrate in contact with the polishing pad, and an electrode disposed in the polishing pad through an electrolyte.

13. The method of claim 8, wherein processing the first substrate for the first and second period includes establishing an electrochemical circuit between an exposed layer of conductive material on the first substrate and an electrode disposed in the polishing pad in the presence of an electrolyte, wherein an upper surface of the pad includes a partially conductive surface to bias the exposed layer of conductive material.

14. The method of claim 8 further comprising:

processing a second substrate for a first processing period performed to achieve a second target removal current; and

processing the second substrate for a second processing period performed using a second constant voltage based on the second target removal current.

15. The method of claim 14, wherein the processing the second substrate for the second processing period further comprises:

applying the second constant voltage greater than the first constant voltage.

16. The method of claim 14 further comprising:

conditioning a processing surface of the polishing pad; and

applying the second constant voltage less than the first constant voltage.

17. The method of claim 8 further comprising:

removing a conductive material from the first substrate in a bulk processing step on a processing tool; and

processing the conductive material on the first substrate for the first and second period on the processing tool in-situ in a residual processing step.

18. The method of claim 17, wherein processing the conductive material for the first and second periods further comprises:

processing the first substrate on a single polishing pad disposed on the polishing tool.

19. The method of claim 17, wherein processing the conductive material for the first and second periods further comprises:

processing the first substrate on two polishing pads disposed on the polishing tool.

20. The method of claim 17, wherein processing the conductive material for the first and second periods further comprises:

processing the first substrate on a fully conductive processing pad.

21. The method of claim 20, wherein processing the first substrate for the first and second period includes establishing an electrochemical circuit between an exposed layer of conductive material on the first substrate in contact with the polishing pad, and an electrode disposed in the polishing pad through an electrolyte.

22. The method of claim 8, wherein the second processing period is much greater than the first processing period.

23. The method of claim 8, further comprising:

fixing the voltage to provide the constant voltage based on the target removal current after the adjusted voltage has reached a near stabilized state.

24. The method of claim 8, further comprising:

adjusting a first processing voltage across a first processing zone of an electrode disposed in the polishing pad while removing the first portion; and