METHODS AND APPARATUS FOR CHEMICAL-MECHANICAL POLISHING UTILIZING LOW SUSPENDED SOLIDS POLISHING COMPOSITIONS
The present invention provides chemical-mechanical polishing (CMP) methods and apparatus suitable for polishing a substrate utilizing a low suspended solids slurry composition. The CMP methods of the invention comprise polishing a substrate with CMP slurry containing a low suspended solids level (e.g., about 0.01 percent by weight to about 1.0 percent by weight) of a particulate abrasive material in a CMP apparatus, while continuously monitoring and accurately maintaining a predetermined total suspended solids (TSS) level in the slurry. Preferably, maximum TSS variability of the slurry is less than about 20 percent (i.e., ±20% of the target TSS level), more preferably less than about 10 percent TSS variability (i.e., ±10% of the target TSS level) during the course of the polishing process.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/201,001, filed on Dec. 5, 2008, which is incorporated herein by reference.
FIELD OF THE INVENTIONThis invention relates to polishing methods and apparatus for polishing a substrate. More particularly, this invention relates to chemical-mechanical polishing methods and apparatus utilizing low suspended solids abrasive polishing compositions.
BACKGROUND OF THE INVENTIONCompositions and methods for chemical-mechanical polishing (CMP) the surface of a substrate are well known in the art. Polishing compositions (also known as polishing slurries, CMP slurries, and CMP compositions) for polishing metal-containing surfaces of semiconductor substrates (e.g., integrated circuits) typically contain abrasives, various additive compounds, and the like, and frequently are used in combination with an oxidizing agent. Such CMP compositions are often designed for removal of specific substrate materials such as metals (e.g., tungsten or copper), insulators (e.g., silicon dioxide, such as plasma-enhanced tertraethylorthosilicate (PETEOS)-derived silica), and semiconductive materials (e.g., silicon or gallium arsenide).
In conventional CMP techniques, a substrate carrier (polishing head) is mounted on a carrier assembly and positioned in contact with a polishing pad in a CMP apparatus. The carrier assembly provides a controllable pressure (down force) to urge the substrate against the polishing pad. The pad and carrier, with its attached substrate, are moved relative to one another. The relative movement of the pad and substrate serves to abrade the surface of the substrate to remove a portion of the material from the substrate surface, thereby polishing the substrate. The polishing of the substrate surface typically is further aided by the chemical activity of the polishing composition (e.g., by oxidizing agents present in the CMP composition) and/or the mechanical activity of an abrasive suspended in the polishing composition. Typical abrasive materials include, for example, silicon dioxide (silica), cerium oxide (ceria), aluminum oxide (alumina), zirconium oxide (zirconia), titanium dioxide (titania), and tin oxide.
The abrasive desirably is suspended in the CMP composition as a colloidal dispersion, which preferably is colloidally stable. The term “colloid” refers to the suspension of abrasive particles in the liquid carrier. “Colloidal stability” refers to the maintenance of that suspension during a selected period of time with minimal settling. In the context of this invention, an abrasive is considered colloidally stable if, when the abrasive is placed into a 100 mL graduated cylinder and allowed to stand without agitation for a period of time of about 2 hours, the difference between the concentration of particles in the bottom 50 mL of the graduated cylinder ([B] in terms of g/mL) and the concentration of particles in the top 50 mL of the graduated cylinder ([T] in terms of g/mL) divided by the initial concentration of particles in the abrasive composition ([C] in terms of g/mL) is less than or equal to about 0.5 (i.e., ([B]−[T])/[C]≦0.5). The value of ([B]−[T])/[C] desirably is less than or equal to about 0.3, and preferably is less than or equal to about 0.1.
U.S. Pat. No. 5,527,423 to Neville, et al., for example, describes a method for chemically-mechanically polishing a metal layer by contacting the surface of the metal layer with a polishing slurry comprising high purity fine metal oxide particles suspended in an aqueous medium. Alternatively, the abrasive material may be incorporated into the polishing pad. U.S. Pat. No. 5,489,233 to Cook et al. discloses the use of polishing pads having a surface texture or pattern, and U.S. Pat. No. 5,958,794 to Bruxvoort et al. discloses a fixed abrasive polishing pad.
For some CMP compositions (e.g., ceria-based slurries) it often is desirable to use a relatively low-solids dispersion (i.e., having an abrasive concentration at a total suspended solids (TSS) level of about 1 percent by weight or less). For example, low-solids cerium oxide compositions such as iDiel™ 6600 (Cabot Microelectronics Corp., Aurora, Ill.), which contains about 0.6 percent by weight cerium oxide, provides for highly effective silicon dioxide (PETEOS) removal rates comparable to or exceeding silica-based slurries containing over 12 percent by weight of suspended abrasive, while simultaneously providing lower polishing defectivity than the silica slurries. We have recently recognized that when such low-TSS slurries are utilized in a CMP process, slight absolute variations (e.g., 0.05 to 0.1 percent by weight variability) in the TSS level of the slurry being delivered to the substrate can occur during polishing, which can have a dramatic and undesirable negative effect on the reproducibility of the polishing process. The colloidal stability of low-solids abrasive dispersions can be negatively impacted by a variety of process parameters and physico-chemical characteristics of the polishing composition, such as pH, contamination with CMP by-products (e.g., in recycled polishing compositions), the configuration of the slurry delivery system, the slurry delivery flow rate, the residence time of the slurry in un-agitated portions of the delivery system, and the like.
There is an ongoing need to develop new CMP methods and apparatus for utilizing relatively low-solids CMP slurries with a reduced level of TSS variability and reduced polishing variability. The present invention provides such improved CMP methods and apparatus. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.
SUMMARY OF THE INVENTIONThe present invention provides a chemical-mechanical polishing (CMP) method for polishing a substrate comprising, contacting a surface of the substrate with an aqueous slurry comprising a low level of a suspended particulate abrasive material, monitoring the TSS level in the slurry at one or more points in a CMP process using a suspended solids sensor, and maintaining a predetermined TSS level in the slurry by adjusting the level of the suspended particulate abrasive material in the slurry based upon the monitoring by the suspended solids sensor. The CMP methods of the invention comprise polishing a substrate with a CMP slurry containing a low level of a suspended particulate abrasive material (e.g., about 0.01 percent by weight to about 1.0 percent by weight) in a CMP apparatus, while continuously maintaining a predetermined TSS level in the CMP slurry by monitoring the TSS level at one or more points in the CMP process using a suspended solids sensor. Preferably the slurry has a maximum TSS variability of less than about 20 percent (i.e., ±20% of the target TSS level), preferably less than about 10 percent TSS variability (i.e., ±10% of the target TSS level) during the course of the polishing process.
When the TSS level of the low level abrasive slurry is maintained within a tight variance, the performance characteristics of the substrate polishing process are desirably enhanced. For example, the variability in substrate removal rate and/or defectivity desirably can be reduced due to the reduced variability in TSS level. This is particularly pronounced in slurries containing low levels of suspended particulate abrasive material. The tight process control provided by the methods and apparatus of the present invention can lead, for example, to improved polishing productivity, reduced levels of reworking, more predictable substrate throughput, and reduced production costs relative to conventional polishing methods without tight TSS control.
The tight control over the TSS level of the slurry used in the polishing methods of the invention can be achieved by monitoring the TSS level of the slurry during the polishing process and adjusting the slurry TSS level when it deviates beyond a predetermined amount from the predetermined target TSS value. The slurry TSS level can be adjusted by changing the ratio of slurry concentrate and diluent used to make up the slurry. In some cases the slurry TSS level may be adversely affected by insufficient mixing or agitation in the slurry delivery system, in which case the TSS level may be adjusted by changing the mixing parameters or configuration of the slurry delivery system.
The present invention also provides a CMP apparatus comprising a movable platen adapted to hold a polishing pad on the platen, and a movable carrier assembly adapted to hold a substrate and to urge a surface of the substrate against the polishing pad; the apparatus also including a slurry delivery system adapted to contact an aqueous slurry comprising a low level of a suspended particulate abrasive material with the surface of the substrate; wherein during use the platen and carrier assembly are disposed in an opposed, parallel relation to one another with the pad and substrate therebetween; the delivery system being adapted to deposit at least a portion of the slurry between the pad and the surface of the substrate; the CMP slurry delivery system including at least one suspended solids sensor for measuring the TSS of the slurry. In some preferred embodiments, CMP apparatus of the invention includes a plurality of TSS sensors within the slurry delivery system, to monitor the TSS level of the slurry at multiple places within the slurry delivery system.
The present invention also provides a method of diluting a CMP slurry concentrate to a target TSS concentration comprising, monitoring the TSS of the slurry in real time using a suspended solids sensor and adding a diluent until the target TSS concentration is achieved.
Particulate abrasives useful in the CMP methods of the invention include any abrasive material suitable for use in CMP of semiconductor materials. Non-limiting examples of suitable abrasive materials include metal oxides such as silica (e.g., fumed silica and/or colloidal silica), alumina, titania, ceria, zirconia, or a combination of two or more of the foregoing abrasives, which are well known in the CMP art. A preferred abrasive comprises ceria (cerium oxide). The abrasive material preferably is present in the CMP slurry in an amount of not more than about 1 percent by weight (10,000 ppm). Preferably, the abrasive material is present in the CMP composition in an amount in the range of about 0.01 to about 1 percent by weight, more preferably in the range of about 0.05 to about 0.6 percent by weight.
The CMP methods of the present invention can be used to polish any suitable substrate, and are especially useful for polishing substrates comprising silicon dioxide (e.g., PETEOS).
The CMP methods of the present invention are particularly suited for use in conjunction with a chemical-mechanical polishing apparatus. Typically, the CMP apparatus comprises a platen, which, when in use, is in motion and has a velocity that results from orbital, linear, and/or circular motion. A polishing pad is mounted on the platen and moves with the platen. A carrier assembly holds a substrate to be polished in contact with the pad and moves relative to the surface of the polishing pad, while urging the substrate against the pad at a selected pressure (down force) to aid in abrading the surface of the substrate. A CMP slurry is pumped onto the polishing pad to aid in the polishing process. The polishing of the substrate is accomplished by the combined abrasive action of the moving polishing pad and the CMP composition of the invention present on the polishing pad, which abrades at least a portion of the surface of the substrate, and thereby polishes the surface.
The methods and apparatus of the present invention can utilize any suitable polishing pad (e.g., polishing surface). Non-limiting examples of suitable polishing pads include woven and non-woven polishing pads, which can include fixed abrasives, if desired. Moreover, suitable polishing pads can comprise any suitable polymer of varying density, hardness, thickness, compressibility, ability to rebound upon compression, and compression modulus. Suitable polymers include, for example, polyvinylchloride, polyvinylfluoride, nylon, fluorocarbon, polycarbonate, polyester, polyacrylate, polyether, polyethylene, polyamide, polyurethane, polystyrene, polypropylene, coformed products thereof, and mixtures thereof.
Desirably, the CMP apparatus further comprises an in situ polishing endpoint detection system, many of which are known in the art. Techniques for inspecting and monitoring the polishing process by analyzing light or other radiation reflected from a surface of the workpiece are known in the art. Such methods are described, for example, in U.S. Pat. No. 5,196,353 to Sandhu et al., U.S. Pat. No. 5,433,651 to Lustig et al., U.S. Pat. No. 5,949,927 to Tang, and U.S. Pat. No. 5,964,643 to Birang et al. Desirably, the inspection or monitoring of the progress of the polishing process with respect to a workpiece being polished enables the determination of the polishing end-point, i.e., the determination of when to terminate the polishing process with respect to a particular workpiece.
A key component of a CMP apparatus of the invention is a TSS monitoring device, which comprises at least one suspended solids sensor capable of providing an output signal to a recording and/or display device. The output signal is proportional to the TSS of the abrasive slurry. The sensor can be permanently mounted in the slurry delivery system for continuous, periodic, or intermittent monitoring or can be a “hand-held” meter which is intermittently placed into the slurry stream, and which may also be used to measure the TSS of samples withdrawn from the slurry delivery system.
Suitable recording and display devices for receiving and displaying the output signal of the TSS sensor include analog and digital devices. Non-limiting examples of analog devices include plotters, strip charts, cathode ray tubes, and the like. Digital recording devices typically include a microprocessor for receiving the output signal and for converting the signal into a human or machine readable format, and preferably include a display device and/or a data storage device.
Adjustment of the TSS level can be performed automatically, in direct response to the output signal of the sensor or in response to a feedback signal from the recording device. Alternatively, the TSS level of the slurry can be adjusted manually based on the output signal or suitable output from the recording device.
The following example further illustrates a non-limiting example of a TSS sensor suitable for use in the methods and apparatus of the present invention.
Example 1 Evaluation of Total Suspended Solids (TSS) Sensor with iDiel™ 6600 DilutionThis example illustrates a commercial TSS meter sold under the trade name COSMOS-25 XL, available from Rosemont Analytical Inc. (LaHabra, Calif.).
The purpose of this test was to evaluate the feasibility of monitoring the dilution of a commercial slurry concentrate, iDiel™ 6600 and detecting the suspended solids concentration using an in-line total suspended solids (TSS) meter.
A dilution evaluation was performed to verify the responses of in-line TSS readings as parts-per-million (ppm) with step-down addition of various volumes of a DI water diluent. The TSS data was collected during 14 different dilution stages. Significant observations made during this evaluation include the observation that the tested TSS sensor had an accuracy range for TSS in the range of about 0.1% to about 6.1% over the TSS range of 0.1 percent by weight to about 0.6 5 percent by weight solids. The variability in repeated tests was less than about 1%. By contrast, the standard muffle furnace method for measuring weight percent solids has a repeatability variation of about 36% for low suspended solids slurry measurements.
The slurry distribution loop set-up used in these tests is shown in
TSS sensor calibration was performed using the calibration procedure from the manufacturer's operations manual. Calibration of the TSS sensor for this application used two (2) standard dispersions of iDiel™ 6600 at 6,000 ppm (0.6% solids) and at 1,500 ppm (0.15% solids; made by diluting 2,500 g iDiel™ 6600 with 7,500 g DI water (1:3). The TSS readings for the 1st and 2nd calibration dispersion can be seen in
A drum of iDiel™ 6600 was mixed with an A310 impeller mixer for about an hour at about 1,725 rpm and about 18,000 g of iDiel™ 6600 was transferred into the 30-gallon container.
The bellows pump was started and was run continuously for about 3 hours at about 5 gallons-per-minute (gpm). DI water was added to the slurry in the 30 gallon container at various stages. Details of the amounts of DI water added are provided in Table 1.
Data acquisition was performed throughout the testing period to record TSS as ppm. After Stage 14, the final DI water dilution was equivalent to 5 parts of DI water to 1 part of slurry, and the original 0.6 percent by weight solids of the concentrated slurry was diluted to about 0.1 percent by weight. The final total weight of diluted slurry was 108,000 g (90,000 g of DI water and 18,000 g of iDiel™ 6600).
A first repeatability test was then performed. After completing the Dilution Test (described above), the slurry from Stage 14 was continuously recirculated in the loop for about 115 hours (about 4.8 days) to test the repeatability of the TSS sensor. After completing this first repeatability test, all slurry was drained from the loop/pump system. The system was then flushed with DI water and drained. A second repeatability test was then performed. A new diluted (1:5) batch of iDiel™ 6600 (2,900 g dispersion and 14,500 g DI water) was made for this second test. All the setup and process parameters were the same as for the first repeatability test, except that a 5 hour run time was used. The results of the tests are shown in
From the TSS repeatability test, the mean solids concentration for the 115 hour first repeatability test (see
According to the data collected during each dilution stage, the variability in repeated TSS measurements was less than about 1% during short term (less than 5 minutes in
The accuracy of the TSS sensor ranges from about 0.1% to about 6.1% error during the various dilution stages (see Table 2). The actual TSS vs. projected TSS had a good fit on linearity and accuracy (R2=0.9986,
From the data shown in
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
Claims
1. A chemical-mechanical polishing (CMP) method for polishing a substrate comprising: (a) contacting a surface of the substrate with an aqueous slurry comprising a low level of a suspended particulate abrasive material; (b) monitoring the TSS level in the slurry at one or more points in a CMP process using a suspended solids sensor; (c) maintaining a predetermined TSS level in the slurry by adjusting the level of the suspended particulate abrasive material in the slurry based upon the monitoring by the suspended solids sensor.
2. The method of claim 1 wherein the TSS level of the slurry is in the range of about 0.01 percent by weight to about 1.0 percent by weight.
3. The method of claim 1 wherein the TSS level of the slurry is in the range of about 0.05 percent by weight to about 0.6 percent by weight.
4. The method of claim 1 wherein the particulate abrasive material comprises a metal oxide.
5. The method of claim 4 wherein the metal oxide is cerium oxide.
6. The method of claim 1 wherein the TSS of the CMP slurry has a maximum TSS variability during the CMP process of less than about 20%.
7. The method of claim 1 wherein the TSS of the CMP slurry has a maximum TSS variability during the CMP process of less than about 10%.
8. A CMP apparatus comprising a movable platen adapted to hold a polishing pad on the platen, and a movable carrier assembly adapted to hold a substrate and to urge a surface of the substrate against the polishing pad; the apparatus also including a slurry delivery system adapted to contact an aqueous slurry comprising a low level of a suspended particulate abrasive material with the surface of the substrate; wherein during use the platen and carrier assembly are disposed in an opposed, parallel relation to one another with the pad and substrate therebetween; the delivery system being adapted to deposit at least a portion of the slurry between the pad and the surface of the substrate; the CMP slurry delivery system including at least one suspended solids sensor for measuring the TSS of the slurry.
9. The apparatus of claim 8 wherein the at least one suspended solids sensor comprises an in-line TSS monitoring device disposed within the slurry delivery system near an outlet for depositing the slurry onto the polishing pad.
10. A method of diluting a CMP slurry concentrate to a target TSS concentration comprising, monitoring the TSS of the slurry in real time using a suspended solids sensor and adding a diluents until the target TSS concentration is achieved.
11. The method of claim 10 wherein the target TSS concentration of the CMP slurry is in the range of about 0.01 percent by weight to about 1.0 percent by weight.
12. The method of claim 10 wherein the target TSS concentration of the CMP slurry is in the range of about 0.05 percent by weight to about 0.6 percent by weight.
13. The method of claim 10 wherein the particulate abrasive material comprises a metal oxide.
14. The method of claim 13 wherein the metal oxide is cerium oxide.
Type: Application
Filed: Dec 7, 2009
Publication Date: Jun 10, 2010
Inventors: Shei-Kai CHANG (Darien, IL), Theodore Myers (Oswego, IL)
Application Number: 12/631,977
International Classification: B24B 1/00 (20060101); B24B 37/04 (20060101); B24B 57/02 (20060101);
