US20090163114A1

US20090163114A1 - Systems and Methods for Dynamic Slurry Blending and Control

Info

Publication number: US20090163114A1
Application number: US11/960,175
Authority: US
Inventors: Ronald Carpio
Original assignee: Advanced Technology Development Facility Inc
Current assignee: Advanced Technology Development Facility Inc
Priority date: 2007-12-19
Filing date: 2007-12-19
Publication date: 2009-06-25

Abstract

Systems and methods for dynamic slurry blending and control are described. A method comprises applying a slurry to a wafer during a polishing process, detecting a wafer property during the polishing process, and changing a slurry property during the polishing process based, at least in part, upon the detected wafer property. In another embodiment, a system comprises a slurry mixer, a polisher coupled to the slurry mixer via a slurry feeder, the polisher being configured to receive a slurry from the slurry mixer via the slurry feeder and to apply the slurry to a wafer during a polishing process, and a computer coupled to the slurry mixer and to the polisher, the computer being configured to receive a signal indicative of a detected wafer property and to control the slurry mixer to change a slurry property during the polishing process based, at least in part, upon the detected wafer property.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates generally to semiconductor fabrication and, more particularly, to systems and methods for dynamic slurry blending and control.
2. Description of Related Art
Chemical mechanical polishing (CMP) is a process for planarizing wafer surfaces and removing films during semiconductor fabrication. In a typical CMP process, a chemical slurry is applied to a wafer and moved under controlled conditions (e.g., pressure) about its surface using a polishing pad. The abrasive action of solid particles present in the slurry planarize the wafer and/or remove a desired amount of film.
As described in U.S. Pat. No. 6,796,703 to Lemke, a few different methods have been proposed for monitoring slurry quality in CMP processes. These methods involve making either “off-line” or “on-line” measurements of the slurry itself. Examples of off-line measurements—i.e., those performed before or after the CMP process—include density or specific gravity measurements, measurement of the relative amount of nonvolatile solids, etc. On-line measurements-i.e., those performed during the CMP process-include pH measurements, density measurements, and the like. Lemke also proposes a system that utilizes conductivity measurements of the slurry during the mixing of its components to monitor slurry quality.

BRIEF SUMMARY OF THE INVENTION

The present invention provides systems and methods for dynamic slurry blending and control. The present invention also provides systems and methods for making dynamic changes to a CMP process such as, for example, the composition, injection point(s), and/or temperature of a slurry, as well as other control variables. In one embodiment, a method comprises applying a slurry to a semiconductor wafer during a polishing process, detecting a semiconductor wafer property during the polishing process, and changing a slurry property during the polishing process based, at least in part, upon the detected semiconductor wafer property. In another embodiment, a system comprises a slurry mixer, a polisher coupled to the slurry mixer via a slurry feeder, the polisher being configured to receive a slurry from the slurry mixer via the slurry feeder and to apply the slurry to a semiconductor wafer during a polishing process, and a computer coupled to the slurry mixer and to the polisher, the computer being configured to receive a signal indicative of a detected semiconductor wafer property and to control the slurry mixer to change a slurry property during the polishing process based, at least in part, upon the detected semiconductor wafer property. In yet another embodiment, a computer readable medium comprises computer-readable instructions that, when executed, cause a computer to perform steps including detecting a property of a semiconductor wafer undergoing a polishing process, and changing a slurry property during the polishing process based, at least in part, upon the detected semiconductor wafer property.
The term “coupled” is defined as connected, although not necessarily directly, and not necessarily mechanically. The terms “a” and “an” are defined as one or more unless this disclosure explicitly requires otherwise. The terms “substantially,” “approximately,” “about,” and variations thereof are defined as being largely but not necessarily wholly what is specified, as understood by a person of ordinary skill in the art. In one non-limiting embodiment, the term substantially refers to ranges within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5% of what is specified.
The terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”) and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises,” “has,” “includes” or “contains” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more elements. Likewise, a step of a method or an element of a device that “comprises,” “has,” “includes” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but it may also be configured in ways other than those specifically described herein.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a more complete understanding of the present invention, reference is now made to the following drawings, in which:

FIG. 1 is a block diagram of a CMP system according to an illustrative embodiment of the present invention;

FIG. 2 is a diagram of a slurry mixing system according to an illustrative embodiment of the present invention;

FIG. 3 is a cross-section view of a wafer sensor system according to an illustrative embodiment of the present invention;

FIG. 4 is a top view of a slurry injection system according to an illustrative embodiment of the present invention; and

FIG. 5 is a block diagram of a computer system adapted to implement certain embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, reference is made to the accompanying drawings that illustrate embodiments of the present invention. These embodiments are described in sufficient detail to enable a person of ordinary skill in the art to practice the invention without undue experimentation. It should be understood, however, that the embodiments and examples described herein are given by way of illustration only, and not by way of limitation. Various substitutions, modifications, additions, and rearrangements may be made without departing from the spirit of the present invention. Therefore, the description that follows is not to be taken in a limited sense, and the scope of the present invention is defined only by the appended claims.
A method according to certain embodiments of the present invention comprises applying a slurry to a semiconductor wafer during a CMP process, measuring a property of the semiconductor wafer during the CMP process, and changing the composition of the applied slurry during the CMP process based, at least in part, upon the measured wafer property. Additionally or alternatively, the method may comprise applying the slurry to the semiconductor wafer during the CMP process, measuring a property of the waste—i.e., a portion of the slurry leaving the CMP process after it has interacted with the wafer—and changing the composition of the applied slurry based, at least in part, upon the measured waste properties. A feedback-based system may be provided for dynamically altering the composition of the slurry as one or more wafer and/or waste properties change over time.
FIG. 1 is a block diagram of CMP system 100 according to one embodiment of the present invention. Dynamic slurry mixer 101 is coupled to polishing tool 103. Both mixer 101 and polishing tool 103 are coupled to computer 107. In operation, mixer 101 provides slurry 102 to polishing tool 103 during a semiconductor wafer polishing process. A portion of slurry 102 is disposed of as waste 104. Computer 107 receives signal 105 indicative of a semiconductor wafer property (e.g., reflectivity, resistance, temperature, friction, etc.). In response to signal 105, computer 107 may control parameters of polishing tool 103 (e.g., rotational speed, etc.) via control signal 106. Computer 107 may also change the composition of slurry 102 by controlling valves within mixer 101 via control signal 108. Additionally, sensors within mixer 101 may provide information about slurry components to computer 107 via signal 109.
FIG. 2 is a diagram of slurry mixing system 200 according to one embodiment of the present invention. Slurry mixing system 200 may be used, for example, as slurry mixer 101 depicted in FIG. 1. Containers 201-203 comprise a slurry component or substance. Each of containers 201-203 is coupled to mixing reservoir 207 via computer-controllable valves 204-206, respectively, and each of its components may be mixed using impellor stirrer 208. In some embodiments, stirrer 208 may be replaced by a coil or the like. Solution 209 is mixed with an ammonium persulfate (APS) solution or the like within container 201 via mixer 212 and under control of computer-controllable valve 211. Slurry 213 is coupled to feeding mechanism 218, which may comprise one or more feeding paths leading to a different site of the pad of a polishing tool (such as, for example, polishing tool 103 of FIG. 1) under control of computer-controllable valves 214-217.
With respect to slurry removal rate control, oxidant concentration (e.g., hydrogen peroxide or APS ) and/or abrasive component concentration (e.g., alumina, ceria, and/or silica) may be modified. Corrosion inhibitors such as benzotriazole (BTA), complexing agents such as citric or oxalic acid, and pH adjusting buffers may modify the removal rate for some types of slurries. Blending may be achieved by mixing controlled flows from the individual components or substances. The dead volume between the mixing point and the delivery point on the polishing pad may be minimized to insure a rapid response to changing wafer conditions. In some embodiments, slurry components may be mixed directly on the polishing pad using multiple feed lines which terminate at the pad surface near the same point. More often, however the components of the slurry prior are mixed prior to dispensing the slurry on the polishing pad.
In some cases, it may be beneficial to have multiple pre-blended slurries of different composition dispensed at different locations on the polishing pad surface, especially if the pre-blended slurries have a long pot life. In one embodiment, the position of the slurry dispensing/injecting point or points may be changed (as discussed in more detail below) to effect changes in the removal rate and uniformity of the CMP process. The slurry flow rates may also be altered. In another embodiment, multiple slurries of different compositions may be injected onto the pad at different sites, or various combinations of slurries and chemicals such as pH buffers or solutions of complexing agents may be dispensed during the process. In addition to slurry composition, the slurry temperature may be varied in certain processes. Moreover, these changes may be made under computer control based upon feedback obtained on the state of the film being polished and/or the state of the slurry on the pad which is being used for feedback purposes.
Slurry mixing system 200 allows the slurry composition to be altered during the polishing process to effect changes in removal rate and selectivity to underlying films. Provisions may be made for rapid changes to the slurry composition, which in most slurries includes the abrasive component and in the case of metal slurries it includes oxidizing agents such as hydrogen peroxide. Provisions may also be made for changing the slurry temperature and/or the slurry flow rate. For example, heating elements (not shown) within the slurry mixing and delivery system may be under computer control. For slurries that are used for polishing dielectric films such as oxides and nitrides, the properties of the slurry may be altered by pH changes. Furthermore, concentration sensors may be used to ensure that the desired changes are achieved. For example, an amperometry sensor may used for oxidizer concentration measurements. Additionally or alternatively, Raman spectroscopy may also be used to perform concentration monitoring. In one embodiment, concentration sensors may operate on slurry 213 and/or waste slurry 104 to provide concentration information to computer 107 of FIG. 1 via signal 109. For example, computer 107 may perform differential measurements for use in controlling the polishing process and/or slurry blending. In other embodiments, thermal analytical methods may be used to monitor and control the composition of the slurry. For instance, the heat produced when a metal probe is inserted in the slurry stream to catalyze the decomposition of hydrogen peroxide is proportional to the concentration of the hydrogen peroxide. In other embodiments, a slip stream may be used for flow injection analysis of certain oxidizing agents such as ammonium persulfate and the like.
FIG. 3 is a cross-section view of wafer sensor system 300 according to one embodiment of the present invention. Wafer sensor system 300 may be implemented, for example, within polishing tool 103 shown in FIG. 1. Semiconductor wafer 301 may be placed upon polishing pad 303 with a thin layer of slurry 302 formed therebetween. Slurry 302 may be, for example, slurry 213 of FIG. 2 and/or slurry 102 of FIG. 1. Polishing 303 comprises optical window 307. Laser source 304 emits electromagnetic radiation reflected by mirror 305 and directed to the surface of wafer 301, a reflection of which reaches optical detector 306. The output of optical detector 306 is transmitted to a computer such as computer 107 shown in FIG. 1.
Wafer sensor system 300 may be, for example, a reflectivity or optical endpoint trace sensor system that allows the change in reflectivity the across the wafer to be used a guide to control the slurry blending. At the initial stages of copper polishing, for example, the reflectivity is due to the copper metal exclusively. Thereafter, the reflectivity changes as the metal is removed from portions of the wafer and the underlying barrier layer is exposed. As such, the sensor provides information on the change in the thickness of films such as dielectric films which are transmissive to the radiation used by the sensor. Changes in the interference pattern may be monitored and correlated to changes in the film parameters for use in an intelligent feedback system. In the case of reflective metal films, there is usually a reduction in reflectance as the metal film is polished but the resolution of the non-uniformity of the process is not great; however, this type of sensor is particularly sensitive to non-uniformity of the process when the metal has been removed in certain areas (“breakthrough”) and the nonuniformity of the process is more clearly shown. Accordingly, by changing the slurry composition as a function of wafer reflectivity, temperature, and/or slurry placement on the pad, the removal rate and the uniformity of the polishing process may be varied in a desired manner.
Wafer sensor system 300 may comprise additional or alternative sensors. For example, other types of endpoint sensors include eddy current sensors for measurement of metal thickness, thermal sensors for measuring heat changes associated with the polish process, and current measurement systems and/or other friction measurement systems which provide information on the changes in the friction associated with changes in film composition. The information provided by these sensors may be used to make adjustments to the CMP process as it occurs.
In one embodiment an eddy current detector is used in conjunction with a reflectance sensor, particularly early in the process, to monitor the removal rate of the metal film, to acquire data during the course of process which is to be well characterized for the purpose of training a feedback algorithm (e.g., using chemometric techniques or the like), and/or to employ multiple reflectance sensors positioned on different parts of the pad, rather than just one site. Thermal, friction, chemical, and/or electrochemical sensors positioned on multiple locations across the radius of the polishing pad may also be used. These sensors may provide further feedback on the rate and uniformity of the polishing process. The nature of the sensor response may be related to the film and wafer properties at given stages of the polishing process. This may enable reference or training data to be stored in the computer being used for feedback control.
FIG. 4 is a top view of slurry injection system 400 according to one embodiment of the present invention. Wafer 406 is located immediately above polishing pad 407, which may be wafer 301 and pad 303 of FIG. 3, respectively. A plurality of slurry injection points 401-405 are provided in different areas of the pad. In the embodiment shown, slurry injection points 401-405 are distributed over pad 407 to allow a non-uniform slurry delivery with respect to wafer 406—i.e., at different radial distances from the center of wafer 406. Although five (5) injections points are shown, more or less points may be used in alternative embodiments. Moreover, different locations on the pad (e.g., directly under or above wafer 405 may also be used. At least some of injection points 401-405 may be controlled by valves such as, for example, valves 214-217 of FIG. 2.
In operation, the embodiment shown in FIG. 4 allows for spatial variations in the removal rate and other polishing properties of the slurry. The spatial variation may be achieved by having separate mixing and/or feeding systems injecting slurry at different sites on the wafer polishing pad. This is in contrast with conventional CMP tools, which comprise a single slurry arm with a line which usually injects only one slurry. Certain embodiments of the present invention comprise a combination of dynamic slurry blending along with the feeding of differently blended slurries to different sites on the polishing pad. For example, at the outset of a copper polish process, it may be desirable to have an edge fast process because the plated copper is usually thicker at the edge of the wafer. Accordingly, the composition and/or flow rate of slurry being applied to the edge of the wafer may differ from the composition and/or flow rate of slurry being applied to the center of the wafer.
In alternative embodiments of the present invention, other adjustments to the CMP process may be dynamically made based on one or more feedback signals driven by changes in one or more wafer properties during the CMP process. These changes may be programmed, for instance, as ramps or discrete changes. For example, adjustments may be made to the pressures applied to the membrane, retaining ring, and/or inner tube, and/or the rotational rates of the head and/or platen. Moreover, it may also be desirable to employ high removal rates during the outset and to slow the polish process near the breakthrough stage.
As previously noted, computer 107 of FIG. 1 may implement a feedback control system by receiving signals from polishing tool 103 and/or slurry mixer 101, interpreting those signals, and then controlling elements of slurry mixer 101 (e.g., valves) and/or polishing tool 103 (e.g., slurry injection points or rotational speed). In some embodiments, a certain program sequence can be derived for a particular metal polishing process and adopted with little change for the remainder of wafers within the same lot and/or wafers of the same product type on a continuing basis. Thus, once a slurry control algorithm has been determined for a certain batch of wafers, it may no longer be necessary to operate the system in feedback mode.
The functions and algorithms described above may be implemented, for example, as software or as a combination of software and human implemented procedures. The software may comprise instructions executable on a digital signal processor (DSP), application-specific integrated circuit (ASIC), microprocessor, or any other type of processor. The software implementing various embodiments of the present invention may be stored in a computer readable medium of a computer program product. The term “computer readable medium” includes any medium operable to store or transfer information. Examples of the computer program products include an electronic circuit, semiconductor memory device, random access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), read only memory (ROM), erasable ROM (EROM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), flash memory, floppy diskette, compact disk (CD), optical disk, hard disk, or the like. The software may be downloaded via computer networks such as the Internet or the like.
FIG. 5 illustrates computer system 500 adapted to use embodiments of the present invention (e.g., storing and/or executing software associated with these embodiments). For example, computer system 500 may serve as computer 107 shown in FIG. 1. Central processing unit (CPU) 501 is coupled to system bus 502. CPU 501 may be any general purpose CPU. However, embodiments of the present invention are not restricted by the architecture of CPU 501 as long as CPU 501 supports the inventive operations as described herein. Bus 502 is coupled to RAM 503, which may be SRAM, DRAM, or SDRAM. ROM 504 is also coupled to bus 502, which may be PROM, EPROM, or EEPROM.
Bus 502 is also coupled to input/output (“I/O”) controller card 505, communications adapter card 511, user interface card 508, and display card 509. I/O adapter card 505 connects storage devices 506, such as one or more of a hard drive, a CD drive, a floppy disk drive, a tape drive, to computer system 500. I/O adapter 505 is also connected to a printer (not shown), which would allow computer system 500 to print paper copies of information such as documents, photographs, articles, and the like. The printer may be a printer (e.g., dot matrix, laser, and the like), a fax machine, scanner, or a copier machine. (not shown), which may be one or more of a telephone network, a local (“LAN”) and/or a wide-area (“WAN”) network, an Ethernet network, and/or the Internet. In certain embodiments, communications card 511 may also be adapted to send and/or receive signals to and from dynamic slurry mixer 101 and polisher 103, respectively, as shown in FIG. 1. User interface card 508 couples user input devices, such as keyboard 512, pointing device 507, and the like, to computer system 500. Display card 509 is driven by CPU 501 to control the display on display device 510.
The systems and methods described herein may be applied, for example, to copper polishing steps (e.g., damascene processing), barrier polishing steps, other metal polishing processes such as tungsten polishing and the like. Furthermore, the systems and methods described herein may also be used for oxide and STI polishing. Furthermore, dynamic slurry blending under feedback control can be applied to electropolishing, and electromechanical deposition, and even to spin-etch planarization processes which may not require an abrasive component. Dynamic blending makes possible more widespread use of normal CMP processes which do not need an abrasive component.
As a person of ordinary skill in the art will recognize in light of this disclosure, the present invention provides numerous advantages. These advantages include example, removal rate modulations, across wafer uniformity improvements, reductions in dishing and erosion, better stress control, reduction in cost, higher throughput, and greater tool capability and versatility.
Although certain embodiments of the present invention and their advantages have been described herein in detail, it should be understood that various changes, substitutions and alterations can be made without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present invention is not intended to be limited to the particular embodiments of the processes, machines, manufactures, means, methods, and steps described herein. As a person of ordinary skill in the art will readily appreciate from this disclosure, other processes, machines, manufactures, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufactures, means, methods, or steps.

Claims

1. A method comprising:

applying a slurry to a semiconductor wafer during a polishing process;

detecting a semiconductor wafer property during the polishing process; and

changing a slurry property during the polishing process based, at least in part, upon the detected semiconductor wafer property.

2. The method of claim 1, the slurry property comprising at least one of: a slurry composition, a slurry injection point, and a slurry temperature.

3. The method of claim 1, the polishing process comprising copper removal.

4. The method of claim 1, the polishing process comprising barrier removal.

5. The method of claim 1, the detected semiconductor wafer property comprising at least one of an optical reflectivity, an eddy current, a temperature, and a friction coefficient.

6. A method comprising:

applying a slurry to a semiconductor wafer during a polishing process;

detecting a waste property during the polishing process; and

changing a slurry property during the polishing process based, at least in part, upon the detected waste property.

7. The method of claim 6, where detecting the waste property further comprises performing a Raman spectroscopy measurement.

8. The method of claim 6, where detecting the waste property further comprises performing a differential Raman spectroscopy measurement.

9. The method of claim 6, the slurry property comprising at least one of: a slurry composition, a slurry injection point, and a slurry temperature.

10. A system comprising:

a slurry mixer;

a polisher coupled to the slurry mixer via a slurry feeder, the polisher being configured to receive a slurry from the slurry mixer via the slurry feeder and to apply the slurry to a semiconductor wafer during a polishing process; and

a computer coupled to the slurry mixer and to the polisher, the computer being configured to receive a signal indicative of a detected semiconductor wafer property and to control the slurry mixer to change a slurry property during the polishing process based, at least in part, upon the detected semiconductor wafer property.

11. The method of claim 10, the slurry property comprising at least one of: a slurry composition, a slurry injection point, and a slurry temperature.

12. The system of claim 10, the slurry feeder comprising a plurality of feeding outlets, each of the plurality of feeding outlets being directed to a different area of the semiconductor wafer in a non-uniform arrangement.

13. The system of claim 12, the computer being further configured to control usage of one or more of the plurality of feeding outlets based, at least in part, upon the detected semiconductor wafer property.

14. The system of claim 10, further comprising a wafer measurement device coupled to the polisher and configured to measure the detected semiconductor wafer property.

15. The system of claim 14, the wafer measurement device comprising an optical sensor.

16. A computer readable medium comprising computer-readable instructions that, when executed, cause a computer to perform steps comprising:

detecting a property of a semiconductor wafer undergoing a polishing process; and

17. The computer readable medium of claim 16, the slurry property comprising at least one of: a slurry composition, a slurry injection point, and a slurry temperature.

18. The computer readable medium of claim 17, where changing the slurry property comprises at least one of:

controlling a plurality of valves of a slurry mixer;

controlling a plurality of slurry injection points; and

controlling a slurry temperature.

19. The computer readable medium of claim 18, where detecting the semiconductor wafer property comprises controlling an optical sensor.

20. The computer readable medium of claim 19, the semiconductor wafer property comprising an optical reflectivity.