Asymmetry correction via oriented wafer loading

Abstract

A chemical mechanical polishing system includes a metering station having a sensor configured to measure a thickness profile of a substrate; a robot arm configured to transfer the substrate from the metering station to a polishing station, the polishing station having: a platform for supporting a polishing pad having a polishing surface; a carrier head on the abrasive surface, the carrier head having a film configured to apply pressure to the substrate in the carrier head; and a controller configured to receive a measurement value from the sensor and configured to control the robotic arm to orient the substrate in the carrier head according to the substrate profile and the removal profile of the carrier head.

Description

[0001] This application is a divisional application filed on August 25, 2020, with application number 202080058447.8, entitled "Asymmetry Correction via Oriented Wafer Loading". Technical Field

[0002] This disclosure relates to chemical mechanical grinding (CMP). Background Technology

[0003] Integrated circuits are typically formed on a substrate by sequentially depositing conductive, semiconductor, or insulating layers onto a semiconductor wafer. Various manufacturing processes require planarizing layers on the substrate. For example, one manufacturing step involves depositing a filler layer onto a non-planar surface and then planarizing the filler layer. For some applications, the filler layer is planarized until the top surface of the patterned layer is exposed. For example, a metal layer may be deposited on a patterned insulating layer to fill trenches or holes in the insulating layer. After planarization, vias, inserts, and lines are formed in the remaining metal portions of the trenches and holes in the patterned layer to provide conductive paths between thin-film circuits on the substrate. As another example, a dielectric layer may be deposited on a patterned conductive layer and then planarized for subsequent photolithography steps.

[0004] Chemical mechanical polishing (CMP) is an accepted planarization method. This planarization method typically requires mounting a substrate on a carrier head. The exposed surface of the substrate is usually placed against a rotating polishing pad. The carrier head provides a controlled load on the substrate to push the substrate toward the polishing pad. An abrasive slurry containing abrasive particles is typically supplied to the surface of the polishing pad. Summary of the Invention

[0005] In one aspect, a chemical mechanical polishing system includes: a metering station having a sensor configured to measure the thickness profile of a substrate; a robotic arm configured to transfer a substrate from the metering station to a polishing station, the polishing station having: a platform for supporting a polishing pad having a polishing surface; a bearing head on the polishing surface, the bearing head having a membrane configured to apply pressure to the substrate in the bearing head; and a controller configured to receive measurements from the sensor and to control the robotic arm to orient the substrate in the bearing head according to the substrate profile and the removal profile of the bearing head.

[0006] Specific embodiments of any of the foregoing aspects may include one or more of the following features.

[0007] The retaining ring can enclose the substrate within the carrier head. The diameter of the substrate can be 1-3 mm smaller than the inner surface diameter of the retaining ring.

[0008] The sensor can be a camera.

[0009] The sensor can be configured to perform line scanning.

[0010] The carrier head may have one or more markings indicating the orientation of the carrier head.

[0011] The substrate may have one or more markings indicating the orientation of the substrate. The markings may be notches or planes on the substrate.

[0012] The controller can assign markers to indicate the orientation of the substrate.

[0013] The base of the metering station can support the base plate.

[0014] In another aspect, a method for chemical mechanical polishing includes: measuring the thickness of a first substrate; determining a first substrate thickness profile based on the measured thickness; conveying the first substrate to a carrier head and loading the first substrate into the carrier head, wherein the first substrate and the carrier head are at a zero position; polishing the first substrate; measuring the polishing thickness of the first substrate; determining a first substrate polishing thickness profile based on the measured polishing thickness; calculating a removal profile caused by the carrier head by comparing the first substrate thickness profile and the first substrate polishing thickness profile; measuring a second substrate thickness profile; rotating the carrier head to a desired angle relative to the second substrate, wherein the orientation of the carrier head at the desired angle relative to the second substrate is configured such that the removal profile reduces the second substrate thickness profile; conveying the second substrate to the carrier head and loading the second substrate into the carrier head; and polishing the second substrate.

[0015] Specific embodiments of any of the foregoing aspects may include one or more of the following features.

[0016] The first and second substrates are held in the carrier head using retaining rings.

[0017] The sensor can be used to measure the thickness of a first substrate, the thickness of the first substrate grinding process, and the thickness of a second substrate. The sensor can be a camera. The sensor can be used to perform line scanning.

[0018] The markings on the bearing head can be aligned with the markings on the first substrate. The markings on the first substrate can be a notch or a flat surface on the first substrate.

[0019] The markings on the bearing head can be aligned at a certain angle with the markings on the second substrate. The markings on the second substrate can be a notch or a flat surface of the second substrate.

[0020] The advantages described above may include (but are not limited to) the following: Substrate asymmetry can be reduced by orienting the substrate in the carrier head so that the removal profile of the carrier head at least partially offsets the asymmetric thickness profile of the substrate. This improves intra-wafer uniformity and inter-wafer uniformity.

[0021] Details of one or more specific embodiments are set forth in the accompanying drawings and the description below. Other aspects, features, and advantages will become apparent from the description, the drawings, and the claims. Attached Figure Description

[0022] Figure 1 This is a schematic cross-sectional view of the grinding system.

[0023] Figure 2 This is a schematic diagram of the substrate loading station, metering station, and polishing system.

[0024] Figure 3 This is a schematic top view of a substrate oriented in the bearing head of a grinding system. Detailed Implementation

[0025] In some polishing systems, pressure is applied to the substrate using a membrane within a carrier head during polishing. However, even when the carrier head is operated in a manner intended to apply uniform pressure to the substrate, the substrate may still experience an asymmetric removal profile; that is, the amount of removal varies with angular position around the center of the substrate (rather than simply with radial distance from the center). This asymmetry can be caused by processing variations across the entire substrate or by pressure differentials from the carrier head, which can occur even when the chambers within the carrier head are pressurized uniformly. Furthermore, the substrate may have an initial asymmetric, non-uniform thickness profile before polishing. The combination of an asymmetric removal profile and the substrate's initial asymmetric thickness profile can result in a polished substrate with a highly asymmetric final thickness profile.

[0026] One solution to this problem is to determine a specific removal profile for the carrier head and orient the substrate within the carrier head such that the removal profile and the thickness profile of the substrate at least partially cancel each other out, thereby reducing the asymmetry of the final thickness profile.

[0027] Figure 1 An example of a polishing system 100 including polishing apparatus 104 is shown. Polishing apparatus 104 includes one or more carrier heads 140 (only one is shown). Each carrier head 140 is operable to hold a substrate 10, such as a wafer, against a polishing pad 110. Each carrier head 140 may have independent control over polishing parameters (e.g., pressure) associated with each individual substrate. Each carrier head 140 includes a retaining ring 142 to hold the substrate 10 on the polishing pad 110 and in a suitable position below a flexible film 144.

[0028] Each carrier head 140 may optionally include a plurality of independently controllable pressurizable chambers defined by a membrane, such as three chambers 146a-146c, which can apply independently controllable pressurization to associated areas on the flexible membrane 144 (and therefore on the substrate 10).

[0029] Each support head 140 is suspended from a support structure 150 (e.g., a turntable or track) and connected to a support head rotation motor 154 by a drive shaft 152, allowing the support head to rotate about an axis 155. Alternatively, each support head 140 may oscillate laterally, for example, on a slider on the support structure 150; by rotational oscillation of the turntable itself; or by movement of the support brackets supporting the support head 140 along the track.

[0030] The grinding apparatus 104 includes a platform 120, which is a rotatable disc platform, on which a grinding pad 110 is located. The platform is operable to rotate about an axis 125. For example, a motor 121 can rotate a drive shaft 124 to rotate the platform 120. The grinding pad 110 may be a double-layered grinding pad having an outer grinding layer 112 and a softer backing layer 114.

[0031] The grinding apparatus 104 may include a port 130 for dispensing a grinding liquid 132 (such as a slurry) onto the grinding pad 110. The grinding apparatus may also include a grinding pad conditioner for grinding the grinding pad 110 to maintain the grinding pad 110 in a consistent abrasive state.

[0032] During operation, platform 120 rotates about platform central axis 125, and each bearing head 140 rotates about bearing head central axis 155 and translates laterally across the top surface of the polishing pad. Typically, the rotation of bearing heads 140 causes substrate 10 to rotate at the same rotational rate. Without being limited by any particular theory, although the substrate is not “glued” to the film 144 in the bearing head 140, the friction of the inner surface of the rotating retaining ring 142 relative to the edge of substrate 10 results in equal rotational rates of substrate 10.

[0033] Although only one carrier head 140 is illustrated, more carrier heads can be provided to hold additional substrates, allowing the surface area of ​​the polishing pad 110 to be used efficiently. Therefore, the number of carrier head assemblies suitable for holding substrates for simultaneous polishing can be at least partially based on the surface area of ​​the polishing pad 110.

[0034] In some embodiments, the polishing apparatus includes an in-situ monitoring system 160. The in-situ monitoring system may be an optical monitoring system, such as a spectral monitoring system, which can be used to measure the spectrum of reflected light from the substrate being polished. Optical access through the polishing pad is provided by including a hole (i.e., a hole through the polishing pad) or a solid window 118. The in-situ monitoring system may alternatively or additionally include an eddy current monitoring system.

[0035] In some embodiments, the optical monitoring system 160 is a sequential optical monitoring system having probes (not shown) positioned between two polishing devices or between a polishing device and a transfer station. The monitoring system 160 can continuously or periodically monitor one or more features of a region of the substrate during polishing. For example, one feature is the thickness of each region of the substrate.

[0036] In in-situ or sequential embodiments, the optical monitoring system 160 may include a light source 162, a photodetector 164, and a circuit system 166 for transmitting and receiving signals between a remote controller 190, such as a computer, and the light source 162 and the photodetector 164. One or more optical fibers 170 may be used to transmit light from the light source 162 to an optical access point in the polishing pad and to transmit light reflected from the substrate 10 to the detector 164.

[0037] Reference Figure 1-3 The bearing head 140 is configured to tightly enclose the substrate 10 at its edges, for example, the diameter of the substrate 10 is 1-3 mm smaller than the diameter of the inner surface of the retaining ring 142 of the bearing head 140. When the substrate 10 is ground in the bearing head 140, the edge of the substrate 10 (e.g., the leading edge of the substrate 10) rolls against the inner surface of the bearing head 140, for example, against the inner surface of the retaining ring 142. Due to friction between the leading edge of the substrate 10 and the inner surface of the bearing head 140, the substrate 10 can roll against the inner surface of the bearing head 140 (e.g., against the inner surface of the retaining ring 142) so that the substrate 10 rotates as the bearing head 140 rotates. Hypothetically, for example, due to the difference in relative speed between areas closer to or farther from the axis of rotation of the platform, the rotation of the substrate 10 may uniformly reduce the asymmetric grinding effect. However, in practice, since the substrate is held in a roughly fixed angular position relative to the bearing head, the substrate 10 may be affected by the unique removal profile of the bearing head 140. The removal profile of the carrier head can be determined, for example, empirically as discussed below, and then stored for use in selecting the orientation of the substrate during loading.

[0038] Reference Figure 2 and Figure 3Before being loaded into the bearing head 140 and ground by the grinding apparatus 104, the pre-grinding thickness profile of the substrate 10 is determined. To determine this pre-grinding thickness profile, the substrate 10 can be loaded onto the base 182 of the metrology station 180. A sensor 186 is configured to measure the thickness of the substrate 10, for example, the thickness of the outermost layer deposited on the substrate (including thickness differences). The thickness of the substrate 10 can be measured at multiple locations arranged in a two-dimensional array across the substrate 10. The sensor 186 can be, for example, a camera or other similar metrology device configured to scan the substrate 10. For example, the sensor 186 can perform a line scan of the substrate 10 to generate a two-dimensional color image of the substrate. The sensor 186 can produce a thickness measurement or a measurement that scales linearly with the thickness.

[0039] To measure the thickness of substrate 10, sensor 186 can measure selected points within a circle surrounding the center of substrate 10 (e.g., at the same radial distance from the center of substrate 10). For example, base 182 can be rotated such that sensor 186 scans a circular path on substrate 10. In some embodiments, sensor 186 can make measurements at multiple angular locations around the center of substrate 10 and at multiple radial distances from the center of substrate 10; these can provide angular profiles within multiple circles of different radii on substrate 10. Alternatively, sensor 186 can make measurements across the entire substrate 10 in a regular array (e.g., a rectangular array) to form a two-dimensional array of the thickness of substrate 10.

[0040] The measurements taken by sensor 186 can be sent to controller 190, which can then process the measurements to generate a thickness profile of substrate 10. For example, the measurements can be combined to generate a thickness profile of substrate 10, such as an angular thickness profile. An angular thickness profile can indicate the thickness of substrate 10 at different angular locations around the center of substrate 10. For example, for each of a plurality of angles around the center of substrate 10, the angular thickness profile can indicate the average thickness value at a radial distance from the center of substrate 10. An angular thickness profile can also indicate the substrate thickness at different angular locations at a plurality of different radial distances from the center of substrate 10. Alternatively, the thickness profile can be a two-dimensional array of the thicknesses of substrate 10 measured by sensor 186 and generated by controller 190.

[0041] After determining the thickness profile of substrate 10, the desired orientation of substrate 10 in carrier head 140 is calculated. As described above, controller 190 can store the removal profile of carrier head 140. For example, controller 190 can store multiple thickness removal values ​​that vary with the angle around the center of substrate.

[0042] The substrate 10 can be positioned within the carrier head 140 such that asymmetry in the final thickness profile is at least partially offset by asymmetry in the removal profile of the carrier head. The controller can be configured to base its position on a known removal profile R of the carrier head 140. H (θ) and the thickness profile R of substrate 10 before polishing S (θ) is used to determine the desired relative orientation θ of the substrate 10 relative to the carrier head 140. D For example, the angle difference Δθ can increase in increments of 1 degree or 5 degrees between, for example, 0 degrees and 360 degrees. At each value of Δθ, the known removed profile R is calculated. H (θ) and thickness profile R before grinding S The total difference between (θ) can be calculated as the sum of squared differences, for example,

[0043] Although other difference measures can be used, such as the sum of the absolute values ​​of the differences.

[0044] Desired angle θ D It should be equal to the Δθ value that provides the minimum value for the total difference.

[0045] The carrier head can rotate relative to the substrate at a desired angle θ. D In other words, the carrier head 140 can be rotated to a certain angle so that the removal profile of the carrier head 140 is complementary to the pre-grinding thickness profile of the substrate 10. For example, the carrier head 140 can be rotated relative to the substrate 10 so that during grinding, the maximum removal portion of the removal profile can correspond to the thickest portion of the pre-grinding thickness profile.

[0046] In order to place the substrate 10 in the carrier head 140 with the desired orientation, as described above, the desired relative angle θ between the carrier head 140 and the substrate 10 was calculated. D .

[0047] The absolute angular position θ of the measuring substrate 10 P (For example, a fixed frame relative to the grinding equipment). When the substrate 10 is on the base 182, it can be measured by the sensor 186. For example, an optical sensor can be used to perform the measurement, which can detect markings on the substrate 10, such as notches or planes (e.g., Figure 3 (B) Based on the absolute angular position of the substrate on the base, the controller can calculate the absolute angular position θ of the substrate when it is loaded into the carrier head 140. S θ can be determined based on the predetermined motion of the robot 184 as it moves the substrate from the base 182 to the support head 140. P and θ SThe difference between them, for example, imagine robot 184 rotating substrate 10 by 90° or 180° when moving the substrate.

[0048] The absolute angular orientation θ of the bearing head can be measured, for example, by optically detecting a mark (e.g., position A or C) on the bearing head 140 or by using a motor encoder 188 that measures the rotation of the bearing head 140. H .

[0049] Once the absolute angular position θ of substrate 10 is determined S and the required relative angle θ between the substrate 10 and the carrier head 140 D The carrier head 140 is then rotated to an absolute angular orientation, which provides the required angle θ relative to the substrate 10. D For example, θ H =θ S +θ D The controller 190 can be used to rotate the carrier head 140 to the appropriate angular orientation using feedback from the encoder or optical monitor.

[0050] Then, the controller 190 can cause the robotic arm 184 to transfer the substrate 10 from the metering station 180 (e.g., from the base 182) to the carrier head 140.

[0051] When the substrate 10 is loaded into the carrier head 140, the grinding of the substrate 10 in the carrier head 140 results in a grinding profile with lower asymmetry because the removal profile of the carrier head reduces the asymmetry of the thickness profile of the substrate 10.

[0052] The test substrate 10 can be used to determine the removal profile of the carrier head 140. First, before loading the substrate 10 into the carrier head 140, the sensor 186 can measure the pre-grinding thickness profile of the substrate 10. For example, the pre-grinding thickness profile of the substrate 10 can be measured at the metering station 180. Then, using a robotic arm 184, the substrate 10 can be transferred from the metering station 180 and loaded into the carrier head 140, where both are at a “zero position” (or other known position and orientation) relative to each other. For example, the position mark B of the substrate 10 and the position mark A of the carrier head 140 can be aligned. The substrate 10 can then be ground in the carrier head 140. After grinding, the robotic arm 184 can be used to transfer the substrate 10 from the carrier head 140 to the metering station 180, where the post-grinding thickness profile of the substrate 10 can be measured. The removal profile of the carrier head 140 can then be calculated by comparing the thickness profiles of the substrate 10 before and after grinding, for example, by subtracting the pre-grinding thickness profile from the post-grinding thickness profile.

[0053] When the bearing head 140 wears out, it can be replaced. Each replacement bearing head 140 will also have a unique removal profile. To measure and calibrate the removal profile of each bearing head 140, a substrate (e.g., a test substrate for each replacement bearing head 140) can be ground to determine the removal profile of the bearing head 140. A comparison of the thickness profile and the ground profile can determine the removal profile of the bearing head 140. For example, the controller 190 will compare a measurement of the thickness profile of the substrate 10 before grinding in the bearing head 140 with the ground thickness profile of the substrate 10 after grinding in the bearing head 140. Comparing the thickness profile and the ground profile of the substrate 10 reveals the removal profile resulting from the bearing head 140 (e.g., due to the radial distribution of pressure within the bearing head 140).

[0054] The controller and other computing device components of the system described herein may be implemented by a digital electronic circuit system, or by computer software, solid-state or hardware. For example, the controller may include a processor to execute a computer program, such as one stored in a computer program product (e.g., on a non-transitory machine-readable storage medium). Such a computer program (also referred to as a program, software, software application, or code) may be written in any form of programming language, including compiled or interpreted languages, and may be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment.

[0055] Although this document contains numerous specific implementation details, these details should not be construed as limiting the scope of any invention or the scope of what may be claimed, but rather as descriptions of features specific to particular embodiments of a particular invention. Certain features described in the context of individual embodiments may also be implemented in combination within a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented individually in multiple embodiments or in any suitable sub-combination. Furthermore, although features may be described above as functioning in certain combinations, and even initially claimed to be so, one or more features from a claimed combination may be removed from the combination in some cases, and the claimed combination may be for sub-combinations or variations thereof.

[0056] Several embodiments of the present invention have been described. However, it should be understood that various modifications can be made without departing from the spirit and scope of the invention. Therefore, other embodiments exist within the scope of the following claims.

Claims

1. A chemical mechanical grinding system, comprising: A grinding station having a platform for supporting a grinding pad, a support head for holding a substrate, and a motor for rotating the support head; A robotic arm configured to transfer the substrate to the polishing station; and Controller, the controller is configured to The angle removal profile of the carrier head is stored, and the angle thickness profile of the substrate is received. The loading orientation of the carrier head relative to the substrate is selected based on the angular removal profile and the angular thickness profile, wherein the loading orientation is selected such that the removal profile and the thickness profile at least partially cancel each other out and thus reduce asymmetry in the final thickness profile. To cause the motor to rotate the bearing head so that the bearing head is in the loading orientation, and The substrate is loaded into the carrier head when the carrier head is in the loading orientation.

2. The system of claim 1, wherein the controller is configured to calculate, for each of a plurality of angle differences, a total thickness difference between the final thickness profiles of the angle removal profile and the angle thickness profile, using the angle difference as an angle offset between the angle removal profile and the angle thickness profile.

3. The system of claim 2, wherein the controller is configured to select from the plurality of angle differences an angle difference having the minimum total thickness difference.

4. The system of claim 2, wherein the controller is configured to determine the angular orientation based on the angle difference.

5. The system of claim 2, wherein the controller is configured to calculate the final thickness profile as the sum of the least squared differences between the angle removal profile and the angle thickness profile.

6. The system of claim 1, further comprising a metering station having a sensor configured to measure the angular thickness profile of the substrate.

7. The system of claim 6, wherein the sensor comprises a line scan camera.

8. The system of claim 1, further comprising a sensor that determines the angular orientation of the substrate before loading the substrate into the carrier head.

9. The system of claim 8, wherein the sensor is configured to detect a mark on the substrate.

10. The system of claim 8, comprising a metrology station for measuring the angular thickness profile of the substrate, wherein the sensor is located in the metrology station to determine the angular orientation of the substrate in the metrology station.

11. A method for chemical mechanical grinding, the method comprising the following steps: Store the angle of the bearing head to remove the contour; Receives measurements of the angular thickness profile of the substrate; The loading orientation of the carrier head relative to the substrate is selected based on the angle removal profile and the angle thickness profile, wherein the loading orientation is selected such that the removal profile and the thickness profile at least partially cancel each other out and thus reduce the asymmetry in the final thickness profile. Rotate the bearing head to the loading orientation; The substrate is conveyed to the carrier head and the substrate is loaded into the carrier head, wherein the carrier head is in the loading orientation; and The substrate is ground.

12. The method of claim 11, wherein, Selecting the loading orientation includes, for each of a plurality of angle differences, using the angle difference as an angle offset between the angle removal profile and the angle thickness profile to calculate the total thickness difference of the final thickness profile between the angle removal profile and the angle thickness profile.

13. The method of claim 12, wherein, Selecting the loading orientation includes choosing the angle difference with the smallest total thickness difference from the plurality of angle differences.

14. The method of claim 11, wherein the method comprises the following steps: Measure the angle thickness profile of the test substrate before polishing; The test substrate is loaded into the carrier head, wherein the carrier head is at zero position relative to the substrate; Grind the test substrate; Measure the angular thickness profile of the test substrate after grinding; The angle removal profile caused by the bearing head is calculated by comparing the angle thickness profile before grinding and the angle thickness profile after grinding.

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