JP2013529560A - Closed loop control of CMP slurry flow - Google Patents

Abstract

  Embodiments of the present invention generally relate to a method for chemical mechanical polishing a substrate. The method generally includes measuring the thickness of a polishing pad having a groove or other slurry transport mechanism on the polishing surface. Once the groove depth on the polishing surface is determined, the flow rate of the polishing slurry is adjusted according to the determined groove depth. A predetermined number of substrates are polished on the polishing surface. The method can then optionally be repeated.

Description

  Embodiments of the present invention generally relate to a method of chemical mechanical polishing a substrate.

  Chemical mechanical polishing (CMP) is a common technique used to planarize a substrate. CMP utilizes two modes to planarize the substrate. One mode is a chemical reaction that uses a chemical composition, typically a slurry or other fluid medium, to remove material from the substrate, and the other mode is a mechanical force. In conventional CMP techniques, a substrate carrier or 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 on the substrate and presses the substrate against the polishing pad. The pad moves with respect to the substrate by an external driving force. Therefore, the CMP apparatus performs a polishing movement or a friction movement between the substrate surface and the polishing pad while dispensing the polishing composition to achieve both chemical and mechanical functions. However, as the number of substrates to be polished in the CMP apparatus increases, the efficiency of the polishing pad changes, and eventually the polishing pad needs to be replaced. The polishing pad and polishing slurry are expensive components and preferably reduce the downtime required to replace the polishing pad. Therefore, it is preferable to reduce the frequency of replacing the pad and use the polishing slurry more efficiently.

  Accordingly, there is a need for a method of polishing a substrate using a polishing pad having a longer useful life and efficiently utilizing a polishing slurry delivered to the substrate.

  Embodiments of the present invention generally relate to a method for chemical mechanical polishing a substrate. The method generally includes measuring the thickness of a polishing pad having grooves or other slurry transport mechanisms on the polishing surface. When the depth of the groove on the polishing substrate is determined, the flow rate of the polishing slurry is adjusted according to the determined groove depth. A predetermined number of substrates are polished on the polishing surface. The method can then optionally be repeated.

  In one embodiment, the method includes measuring a thickness of the polishing pad having grooves disposed in the polishing surface on the polishing pad. The depth of the grooves disposed in the polishing surface is determined, and the flow rate of the polishing slurry introduced into the polishing surface is adjusted according to the determined depth of the grooves disposed in the polishing surface. A predetermined number of substrates are polished and the method is repeated.

  In another embodiment, the method includes measuring a thickness of the polishing pad having grooves disposed in the polishing surface of the polishing pad. The measured polishing pad thickness is compared with the initial pre-polishing thickness of the polishing pad to determine the reduction in polishing pad thickness. Next, the depth of the groove disposed in the polishing surface is calculated. The flow rate of the polishing slurry introduced to the polishing surface is adjusted according to the calculated depth of the grooves disposed in the polishing surface. A predetermined number of substrates are then polished. Polishing includes contacting each of a predetermined number of substrates with the polishing pad and introducing a polishing slurry into the polishing pad at a regulated flow rate for each of the predetermined number of substrates. The method is then repeated.

  In another embodiment, the method includes measuring the thickness of a polishing pad having grooves disposed in the polishing surface. The measured polishing pad thickness is compared to the initial pre-polishing thickness of the polishing pad to determine the amount of reduction in polishing pad thickness and to calculate the depth of the grooves disposed in the polishing surface. The calculated groove depth is compared with the value stored in the lookup table. Slurry is introduced into the polishing pad at a predetermined flow rate, which depends on the calculated groove depth. A predetermined number of substrates are polished and then the method is repeated.

  In order that the features of the present invention described above may be understood in more detail, a more specific description of the invention briefly summarized above is made with reference to the embodiments, some of which are illustrated in the accompanying drawings. However, the attached drawings merely illustrate exemplary embodiments of the present invention and therefore should not be considered as limiting the scope of the present invention as the invention may allow other equally effective embodiments. Please note that.

1 is a top schematic view illustrating one embodiment of a chemical mechanical polishing system. 2 is a partial perspective view of a polishing station having a pad conditioning assembly. FIG. 2 is a flow diagram illustrating one embodiment of chemical mechanical polishing. It is a cross-sectional schematic diagram which shows the depth of the groove | channel of a polishing pad. It is a cross-sectional schematic diagram which shows the depth of the groove | channel of a polishing pad. It is a cross-sectional schematic diagram which shows the depth of the groove | channel of a polishing pad. It is a cross-sectional schematic diagram which shows the depth of the groove | channel of a polishing pad. 5 is a graph showing the flow rate of slurry versus the amount of oxide film removed for polishing pads having various groove depths.

  To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized with respect to other embodiments without special description.

  Embodiments of the present invention generally relate to a method for chemical mechanical polishing a substrate. The method generally includes measuring the thickness of a polishing pad having grooves or other slurry transport mechanisms on the polishing surface. Once the groove depth on the polishing surface is determined, the flow rate of the polishing slurry is adjusted according to the determined groove depth. A predetermined number of substrates are polished on the polishing surface. The method is then optionally repeated.

  Specific devices on which the embodiments described herein can be implemented include, but are not limited to, Applied Materials, Inc. It is particularly beneficial to perform this embodiment on the REFLEXION GT ™ system, the REFLEXION ™ LK CMP system, and the MIRRA MESA ™ system sold by of Santa Clara, California. In addition, CMP systems available from other manufacturers can also benefit from the embodiments described herein.

  FIG. 1 is a top schematic view illustrating one embodiment of a chemical mechanical polishing system 100. The CMP system 100 includes a factory interface 102, a cleaning machine 104, and a polishing module 106. The wet robot 108 is provided to transfer the substrate 170 between the factory interface 102 and the polishing module 106. The wet robot 108 is configured to transfer a substrate between the polishing module 106 and the cleaning machine 104. The factory interface 102 includes a drying robot 110 configured to transfer a substrate 170 between one or more cassettes 114 and one or more transfer platforms 116. The drying robot 110 has a sufficient range of motion to facilitate transfer between the four cassettes 114 and one or more transfer platforms 116. Optionally, the drying robot 110 is mounted on rails or tracks 112 to position the robot 110 longitudinally within the factory interface 102, thereby requiring large or complex robotic connections. Without this, the range of motion of the drying robot 110 can be increased. Further, the drying robot 110 is configured to receive a substrate from the cleaning machine 104 and return this clean polished substrate to the substrate storage cassette 114. In the embodiment shown in FIG. 1, one substrate transfer platform 116 is shown, but more than one substrate transfer platform may be provided, so that at least two substrates can be simultaneously transferred to the wet robot 108. Can be lined up for transfer to the polishing module 106.

  The polishing module 106 includes a plurality of polishing stations 124 where the substrate is polished while held in one or more carrier heads 126a, 126b. The polishing station 124 is sized to interface simultaneously with two or more carrier heads 126a, 126b so that two or more substrates can be polished simultaneously using a single polishing station 124. it can. The carrier heads 126a and 126b are coupled to a carriage (not shown) that is attached to an overhead track 128 shown in broken lines in FIG. Overhead track 128 allows the carriage to be selectively positioned about polishing module 106, thereby facilitating selective positioning of carrier heads 126 a, 126 b over polishing station 124 and stacking cup 122. . The overhead track 128 has a circular configuration so that the carriage holding the carrier heads 126a, 126b can be over the loading cup 122 and the polishing station 124 and / or away from the loading cup 122 and the polishing station 124. It becomes possible to rotate selectively and independently. The overhead track 128 may have an oval, oval, straight line or other configuration including other suitable orientations, and the carrier heads 126a, 126b can be easily moved using other suitable devices. .

  Two polishing stations 124 are shown located at opposite corners of the polishing module 106. At least one loading cup 122 is in the corner of the polishing module 106 between the polishing stations 124, closest to the wet robot 108. The loading cup 122 facilitates transfer between the wet robot 108 and the carrier heads 126a and 126b. Optionally, a third polishing station 124 (shown in dashed lines) can be positioned at the corner of the polishing station 124 opposite the stacking cup 122. Alternatively, a second pair of stacking cups 122 (also indicated by dashed lines) can be located at the corner of the polishing module 106 opposite the stacking cups 122 positioned near the wet robot. The additional polishing station 124 may be integrated into the polishing module 106 in a system with a larger ground area.

  Each polishing station 124 includes a polishing pad having a polishing surface 130 that can simultaneously polish at least two substrates. The polishing pad can be formed from polyurethane. Each polishing station 124 also includes a pad conditioning assembly 140. In one embodiment, the pad conditioning assembly 140 can include a conditioning head 132 and a polishing fluid delivery arm 134 that condition the polishing surface 130 of the polishing pad by removing polishing debris and perforating the pad. In one embodiment, each polishing station 124 includes multiple pad conditioning assemblies 140. The polishing pad is supported on a platen assembly that rotates the polishing surface 130 during processing. The polishing surface 130 is suitable for at least one of a chemical mechanical polishing and / or an electrochemical mechanical polishing process. System 100 is coupled to a power source 180.

  A controller 190 comprising a central processing unit (CPU) 192, a memory 194, and support circuitry 196 is connected to the polishing system 100 to facilitate control of the polishing system 100 and processing performed on the polishing system. . The CPU 192 may be one of any form of computer processor that can be used in industrial equipment to control various drives and pressures. The memory 194 is connected to the CPU 192. The memory 194, or computer readable medium, is one or more readily available memories, such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or any other form of digital storage. It can be local or remote. Support circuit 196 is connected to CPU 192 to support the processor in a conventional manner. These circuits include a cache, a power supply, a clock circuit, an input / output circuit, a subsystem, and the like.

  A CMP polishing system, such as the polishing system 100 shown in FIG. 1, typically uses a polishing pad having one or more grooves (not shown) on the polishing surface 130 to help remove material from the substrate. To do. A typical groove depth is about 15 mils or about 30 mils, and the pad may have a thickness of about 80 mils. When a polishing pad is used to polish, the polishing surface wears and the groove depth is reduced. In order to increase the useful life of the polishing pad, the thickness of the polishing pad can be increased to, for example, 120 mils. Correspondingly, the depth of the groove is also increased, for example to about 40 mil, 50 mil, or 60 mil. However, if the groove depth of the polishing pad is increased and all other processing parameters are kept constant, a pad having a 40 mil groove depth will be more than a pad having a 30 mil groove depth. It has a low polishing rate. Thus, the amount of polishing slurry applied to a polishing pad having a 40 mil groove depth is greater than the amount of polishing slurry applied to a polishing pad having a 30 mil groove depth to produce an equal polishing rate. Should be more. Conversely, as the depth of the groove on the polishing pad decreases, the polishing removal rate increases if all other processing parameters are kept constant. In addition to or as an alternative to the groove, the polishing pad may utilize other slurry transport mechanisms such as perforations. Although the embodiments herein refer to grooves as a whole, it is understood that the use of pads having other slurry transport mechanisms such as perforations can also be utilized and benefited by the embodiments herein. I want.

  When a polishing pad having a groove depth of 40 mils polishes the substrate, the groove depth decreases and the polishing rate increases. Since the polishing rate has already increased due to pad wear, it would be useless to continue to supply a certain amount of polishing slurry. Accordingly, embodiments of the present invention provide a method for closed-loop control of the polishing slurry flow rate as a function of the measured groove depth of the polishing pad.

  FIG. 2 is a partial perspective view of a polishing station 224 having a pad conditioning assembly 240 according to embodiments described herein. In one embodiment, the pad adjustment assembly 240 includes an adjustment head 232 supported by a support assembly 246 having a support arm 244 between the support assembly 246 and the adjustment head 232. The pad adjustment assembly 240 further includes a displacement sensor 260 coupled to the support arm 244. In another embodiment, the displacement sensor 260 can be coupled to the adjustment head 232. Carrier heads 226 a and 226 b are disposed above polishing surface 230. A polishing fluid delivery arm 234 is positioned above the polishing surface 230 and is adapted to supply polishing fluid or slurry to the polishing pad 236 during processing. The flow rate of the polishing slurry supplied via the polishing fluid delivery arm 234 is controlled by a controller (not shown). Further, the adjustment disk 248 is positioned adjacent to the polishing pad surface 230 and is adapted to adjust the polishing pad 236.

  The support assembly 246 is adapted to position the adjustment head 232 in contact with the polishing surface 230 and is further adapted to provide relative movement between the adjustment head 232 and the polishing surface 230. Support arm 244 has a distal end that couples to adjustment head 232 and a proximal end that couples to base 247. The base 247 rotates to sweep the conditioning head 232 across the polishing surface 230 to condition the polishing surface 230. The polishing surface 230 of the polishing pad 236 has a groove 201 disposed within the polishing surface 230. As a result of the relative movement of the conditioning head 232 relative to the polishing surface 230 of the polishing pad 236, the displacement sensor 260 can make a thickness measurement of the polishing surface 230 and the polishing pad 236.

  A sensor coupled to the adjustment arm allows the thickness of the polishing pad 236 to be measured at various points during part of the normal operating cycle, and the measurement data is captured and displayed by the associated logic circuitry. it can. In some embodiments, the displacement sensor 260 may utilize an inductive sensor.

  In embodiments where the displacement sensor 260 is a laser based sensor, the thickness of the polishing pad 236 is measured directly. The support arm 244 is in a fixed position with respect to the platen assembly 241 and the laser is in a fixed position with respect to this arm. Thus, the laser is in a fixed position relative to the platen assembly 241. By measuring the distance to the processing pad and calculating the difference between the distance to the polishing pad 236 and the distance to the platen assembly 241, the remaining thickness of the polishing pad 236 can be determined. In some embodiments, the resolution of thickness measurement using a laser-based displacement sensor 260 can be within 25 μm.

  In embodiments where the displacement sensor 260 is an inductive sensor, the thickness of the polishing pad 236 is measured indirectly. The support arm 244 operates around the pivot point until the adjustment head 232 contacts the processing pad 236. An inductive sensor that emits an electromagnetic field is attached to the end of the pivot-based adjustment support arm 244. According to Faraday's law for induction, the voltage in the closed loop is directly proportional to the change in the magnetic field with time. The stronger the applied magnetic field, the greater the eddy current created and the greater the opposite magnetic field. The signal from the sensor is directly related to the distance from the sensor tip to the metal platen assembly 241. As the platen assembly 241 rotates, the adjustment head 232 rides on the surface of the pad and the inductive sensor moves up and down with the adjustment support arm 244 according to the shape of the polishing pad 236. As the inductive sensor gets closer to the metal platen assembly 241, the signal voltage indicating the wear of the processing pad increases. The signal from the sensor is processed to capture changes in the thickness of the processing pad 236. In some embodiments, the resolution of thickness measurement using the inductive sensor 260 can be within 1 μm.

  FIG. 3 is a flow diagram illustrating one embodiment of chemical mechanical polishing. In step 380, the thickness of the polishing pad is measured using at least one of the sensors described above. This measurement value is taken over by the controller. In step 382, the measured polishing pad thickness is compared to the initial pre-polishing polishing pad thickness, eg, the pad thickness at the start of processing. Usually, the initial pre-polishing thickness is also stored in the controller. For example, if the polishing pad is a new pad and the initial thickness is known, this value can be input to the controller. Alternatively, if the thickness of the processing pad is not known, the thickness of the polishing pad prior to the initial polishing can be measured by the sensor and taken over to the controller for storage.

  By comparing the measured polishing pad thickness with the initial pre-polishing pad thickness, changes in the pad thickness can be determined by the controller. Because the polishing pad wears at the polishing surface, the difference in pad thickness is also directly related to the difference in the depth of the grooves disposed in the polishing surface. For example, the thickness of the polishing pad and the depth of the groove decrease at the same rate. Thus, by measuring the change in polishing pad thickness, the change in groove depth can also be determined. In addition, since the number and position (or pitch) of the grooves are determined during pad fabrication, and a typical polishing pad comprises grooves with substantially vertical sidewalls, the determined groove depth is the groove volume. Can also be used to calculate

  In step 384, the closed loop controller adjusts the flow rate of the polishing slurry supplied to the polishing pad in accordance with the polishing pad groove depth determined in step 382. Usually, before starting the polishing process, a look-up table input by the user is stored in the controller. The look-up table correlates a predetermined flow rate of the polishing slurry with the determined or measured groove depth. The flow rate may vary from process to process and may depend on the pad composition, slurry composition, or substrate material. Usually, the flow rate is determined experimentally.

  In step 386, the polishing slurry is supplied to the polishing pad at a flow rate corresponding to each subsequent substrate to be processed, and a predetermined number of substrates are subsequently processed. For example, 200, 300, 500, or 1000 wafers may be continuously polished using a polishing slurry flow rate that corresponds to the last determined polishing pad groove depth. In optional step 388, steps 380, 382, 384, and 386 are repeated. Steps 380, 382, 384, and 386 may be repeated more often than every few hundred substrates, for example after all substrates have been polished, but doing so is generally not advantageous. Typically, after polishing only a single substrate, there is not enough change in groove depth to cause a significant change in the polishing slurry flow rate. Therefore, it is sufficient to determine the depth of the polishing pad groove and adjust the polishing slurry flow rate after at least about 500 substrates have been polished. However, as the polishing pad thickness decreases and the polishing pad approaches the end of its processing life, it may be desirable to more frequently measure the polishing pad thickness and determine the groove depth. This is due to the fact that the polishing pad encounters a “spike” in the polishing removal rate near the end of the useful life of the pad. By measuring the pad thickness more often, it is easier to identify when the pad needs to be replaced. In addition, measuring the pad more often helps avoid substrate damage caused by overpolishing during "spikes" and helps avoid excessive waste of consumables such as polishing slurries. It can be.

  FIG. 4 is a schematic cross-sectional view showing the depth of the groove of the polishing pad. In the embodiment shown in FIG. 4, the polishing pad 436 can have grooves 401 of various depths. The grooves initially have a pre-polishing depth of about 40 mils. However, after polishing, the groove 401 may have a reduced depth, such as about 30 mils, 15 mils. Additionally or alternatively, the pad can be provided with multiple grooves having various depths prior to polishing. When the groove 401 approaches or exceeds the depth of about 5 mil, the pad should generally be replaced.

  5A to 5C are schematic cross-sectional views showing the depth of the groove of the polishing pad. In FIG. 5A, the polishing pad 536a includes a groove 501a having a depth of 40 mil. The thickness of the polishing pad 536a can be between about 80 mils and 120 mils. FIG. 5B shows a polishing pad 536b with grooves 501b. The groove 501b has a depth of about 30 mil. The polishing pad 536b can have a thickness of about 100 mils. When the groove depth reaches about 5 mils, the pad is considered worn out and usually needs to be replaced soon after. FIG. 5C shows a polishing pad 536c with a groove 501c having a depth of about 15 mils. In order to increase the usable lifetime of the polishing pad, the thickness of the polishing pad and the depth of the groove of the polishing pad can be increased. For example, the groove depth can be increased from about 30 mils for a conventional pad to about 40 mils as shown in FIG. 5A. In other embodiments, the groove depth can be increased to about 50 mils or about 60 mils. As noted above, a polishing pad having a groove depth of about 40 mils generally has a higher polishing slurry flow rate to produce a similar polishing rate than a polishing pad having a groove depth of 30 mils. I need. Thus, as the groove depth decreases, the polishing slurry flow rate also decreases, but the polishing rate can be maintained substantially constant.

  FIG. 6 is a graph showing slurry flow rate versus silicon oxide film removal for polishing pads having various groove depths. As can be seen from FIG. 6, a polishing pad having a 40 mil groove depth requires a higher polishing slurry flow rate to obtain the same polishing removal rate as a polishing pad having a 30 mil groove depth (eg, Slurry flow shifts to the right). For a polishing pad with a 30 mil groove depth, it is possible to remove about 1200 angstroms per minute at a slurry flow rate of 100 milliliters per minute. If the slurry flow rate is increased to 200 milliliters per minute, a polishing pad with a 30 mil groove depth can remove about 1750 angstroms per minute. If the slurry flow rate is increased to 300 milliliters per minute, a polishing pad with a 30 mil groove depth can remove about 1800 angstroms per minute.

  In comparison, a polishing pad having a groove depth of 40 mils can only remove about 1400 angstroms of material per minute when the polishing slurry flow rate is 200 milliliters per minute. If the slurry flow rate is increased to 300 milliliters per minute, a polishing pad having a 40 mil groove depth can remove about 1600 angstroms per minute. A polishing pad with a 40 mil groove depth requires a slurry flow rate of 400 milliliters per minute to produce a removal rate of about 1750 angstroms per minute, which is approximately 30 mils. The rate at which the pad having the groove depth is removed at a flow rate of 200 milliliters of slurry per minute.

  Further, the methods herein can be used for pads having grooves with an initial depth of less than 40 mils, for example about 30 mils. However, if the groove depth is less than 30 mils, the groove depth is only a secondary factor that affects the polishing rate. It can be seen that when the groove depth exceeds 30 mils, there is a stronger relationship between the groove depth and removal rate, and therefore when using pads with groove depths exceeding 30 mils, closed-loop control of the slurry flow. Using is a greater concern.

  A closed loop control system can maintain a constant polishing rate while reducing the amount of slurry delivered to the polishing pad as the pad wears. Closed loop control of the slurry flow allows the use of pads with a longer useful life, thereby reducing the frequency with which pad replacement is required. In addition, by controlling the slurry flow in a closed loop depending on the pad thickness, the slurry flow rate can be adjusted to the pad thickness and groove depth, which ensures that excess slurry is removed. It helps to prevent the pad from being wasted. Closed loop control of the polishing slurry should lead to significant cost savings over the life of the polishing pad by not wasting consumable material. The embodiments disclosed herein allow for the efficient use of a relatively thick polishing pad with a longer useful life and further maintain the high throughput of 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 of the invention is In accordance with the following claims.

100 Chemical Mechanical Polishing System, CMP System, System, Polishing System 102 Factory Interface 104 Cleaning Machine 106 Polishing Module 108 Wet Robot 110 Drying Robot 112 Rail or Track 114 Cassette, Substrate Storage Cassette 116 Transfer Platform 122 Loading Cup 124 Polishing Station 126a Carrier Head 126b Carrier Head 128 Overhead Track 130 Polishing Surface 132 Conditioning Head 134 Polishing Fluid Delivery Arm 140 Pad Conditioning Assembly 170 Substrate 180 Power Supply 190 Controller 192 Central Processing Unit, CPU
194 Memory 196 Support circuit 201 Groove 224 Polishing station 226A Carrier head 226B Carrier head 230 Polishing surface 232 Adjustment head 234 Delivery arm 236 Polishing pad 240 Pad adjustment assembly 241 Platen assembly 244 Support arm 246 Support assembly 247 Base 248 Adjustment disk 260 Displacement sensor Inductive sensor 380 Step 382 Step 384 Step 386 Step 388 Step 401 Groove 436 Polishing pad 501a Groove 501b Groove 501c Groove 536a Polishing pad 536b Polishing pad 536c Polishing pad

Claims (15)

(A) measuring the thickness of the polishing pad having grooves disposed in the polishing surface of the polishing pad;
(B) determining a depth of the groove disposed in the polishing surface;
(C) adjusting the flow rate of the polishing slurry introduced into the polishing surface according to the determined depth of the groove disposed in the polishing surface;
(D) polishing a predetermined number of substrates;
(E) repeating (a) to (d).   The method of claim 1, wherein the predetermined number of substrates is about 500 substrates.   The method of claim 1, wherein the predetermined number of substrates is about 1000 substrates.   The method of claim 1, wherein the groove disposed in the polishing pad surface has an initial depth of about 40 mils.   The method of claim 1, wherein the adjusting the flow rate comprises reducing the flow rate of the polishing slurry as the depth of the groove is reduced.   The method of claim 5, wherein the step of measuring the thickness of the polishing pad includes measuring the thickness using an inductive sensor.   The step of adjusting the flow rate comprises associating the determined depth of the groove with a predetermined slurry flow rate located in a look-up table stored on a computer readable medium. The method described. (A) measuring the thickness of the polishing pad having grooves disposed in the polishing surface of the polishing pad;
(B) comparing the measured thickness of the polishing pad with an initial pre-polishing thickness of the polishing pad to calculate a reduction in polishing pad thickness;
(C) calculating a depth of the groove disposed in the polishing surface;
(D) adjusting the flow rate of the polishing slurry introduced into the polishing surface according to the determined depth of the groove disposed in the polishing surface;
(E) contacting each of a predetermined number of substrates with the polishing pad; and introducing the polishing slurry into the polishing pad at the adjusted flow rate for each of the predetermined number of substrates. Polishing the predetermined number of substrates;
(F) repeating (a) to (e).   The step of adjusting the flow rate of the polishing slurry reduces the depth of the grooves disposed in the polishing surface and maintains the flow rate of the polishing slurry so that a substantially constant polishing removal rate is maintained. 9. A method according to claim 8, comprising the step of reducing.   The method of claim 9, wherein the step of adjusting a flow rate comprises associating the determined depth of the groove with a slurry flow rate located in a look-up table stored in a computer readable medium. .   The method of claim 10, wherein measuring the thickness of the polishing pad comprises measuring the thickness using an inductive sensor. (A) measuring the thickness of the polishing pad having grooves disposed in the polishing surface of the polishing pad;
(B) comparing the measured thickness of the polishing pad with an initial pre-polishing thickness of the polishing pad to determine a reduction in polishing pad thickness;
(C) calculating a depth of the groove disposed in the polishing surface;
(D) comparing the calculated depth of the groove with a value stored in a lookup table;
(E) introducing slurry into the polishing pad at a predetermined flow rate depending on the calculated depth of the groove;
(F) polishing a predetermined number of substrates;
(G) repeating (a) to (f).   The method of claim 12, further comprising replacing the polishing pad if the groove has a depth of about 5 mils or less.   The step of introducing slurry into the polishing pad reduces the depth of the grooves disposed in the polishing surface so that a substantially constant polishing removal rate is maintained, and The method of claim 13, comprising reducing the flow rate.   Measuring the thickness of the polishing pad comprises measuring the thickness using an inductive sensor, and calculating the depth of the groove disposed in the polishing surface; The method of claim 14, further comprising determining a volume of the groove disposed within the polishing surface.

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