Asymmetry correction via oriented wafer loading

Abstract

To provide a method of loading substrates, the method reducing the asymmetry of a final thickness profile.SOLUTION: A chemical mechanical polishing system includes a metrology station having a sensor 186 configured to measure a thickness profile of a substrate, a robotic arm 184 configured to transfer the substrate 10 from the metrology station 180 to a polishing station 180 having a platen to support a polishing pad 110 having a polishing surface, a carrier head 140 on the polishing surface, the carrier head 140 having a membrane configured to apply pressure to the substrate 10 in the carrier head 140, and a controller 190 configured to receive measurements from the sensor 186 and configured to control the robotic arm 184 to orient the substrate 10 in the carrier head 140 according to substrate profile and a removal profile for the carrier head 140.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] This disclosure relates to chemical mechanical polishing (CMP). [Background technology]

[0002] Integrated circuits are typically formed on a substrate by successively depositing conductive, semiconducting, or insulating layers on a semiconductor wafer. Various manufacturing processes require planarization of layers on the substrate. For example, one manufacturing step involves depositing a filler layer on a non-planar surface and planarizing the filler layer. For certain 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, filling the trenches and holes of the insulating layer. After planarization, the remaining portions of the metal in the trenches and holes of the patterned layer form vias, plugs, and lines 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 to allow for subsequent photolithography steps.

[0003] Chemical mechanical polishing (CMP) is one accepted method of planarization. Planarization methods typically require that a substrate be mounted on a carrier head. The exposed surface of the substrate is typically positioned against a rotating polishing pad. The carrier head provides a controllable load on the substrate, pressing the load against the polishing pad. An abrasive slurry containing abrasive particles is typically supplied to the surface of the polishing pad. Summary of the Invention

[0004] In one aspect, a chemical mechanical polishing system includes a metrology station having a sensor configured to measure a thickness profile of a substrate; a robot arm configured to transfer a substrate from the metrology station to a polishing station having a platen supporting a polishing pad having a polishing surface; a carrier head over the polishing surface, the carrier head having a membrane configured to apply pressure to the substrate in the carrier head; and a controller configured to receive measurements from the sensor and configured to control the robot arm to orient the substrate in the carrier head in response to the substrate profile and a removal profile of the carrier head.

[0005] Implementations of any of the above aspects can include any one or more of the following features.

[0006] A retaining ring may surround the substrate within the carrier head, the diameter of the substrate may be 1-3 mm smaller than the diameter of the inner surface of the retaining ring.

[0007] The sensor may be a camera.

[0008] The sensor may be configured to perform a scan of a line.

[0009] The carrier head may have one or more indicia that indicate the orientation of the carrier head.

[0010] The substrate may have one or more indicia that indicate the orientation of the substrate. The indicia may be a notch or a flat on the substrate.

[0011] The controller may assign a visual indicator to the substrate.

[0012] A pedestal of the metrology station may support a substrate.

[0013] In another aspect, a method of chemical mechanical polishing includes measuring a first substrate thickness, determining a first substrate thickness profile from the measured thickness, transferring the first substrate to a carrier head and loading the first substrate into the carrier head, where the first substrate and the carrier head are in a zero position, polishing the first substrate, measuring a polished thickness of the first substrate, determining a polished thickness profile of the first substrate from the measured polished thickness, calculating a removal profile by the carrier head by comparing the thickness profile of the first substrate to the polished thickness profile of the first substrate, measuring a thickness profile of a second substrate, rotating the carrier head to a desired angle relative to the second substrate, where an orientation of the carrier head at the desired angle relative to the second substrate is configured to reduce the second substrate thickness profile to a removal profile, transferring the second substrate to the carrier head and loading the second substrate into the carrier head, and polishing the second substrate.

[0014] Implementations of any of the above aspects can include any one or more of the following features.

[0015] Retaining the first substrate and the second substrate in the carrier head using a retaining ring.

[0016] The sensor may be used to measure the thickness of the first substrate, the polished thickness of the first substrate, and the thickness of the second substrate. The sensor may be a camera. The sensor may be used to perform a scan of the line.

[0017] The indicia on the carrier head may be aligned with the indicia on the first substrate, which may be a notch or a flat in the first substrate.

[0018] The indicia on the carrier head may be aligned at an angle to the indicia on the second substrate, which may be a notch or a flat in the second substrate.

[0019] The aforementioned advantages may include, but are not limited to, the following: Substrate asymmetry may be reduced by orienting the substrate within the carrier head to at least partially offset the asymmetric thickness profile of the substrate using the carrier head removal profile, which may improve within-wafer and between-wafer uniformity.

[0020] The details of one or more embodiments are set forth in the accompanying drawings and the description which follows. Other aspects, features, and advantages will become apparent from the description and drawings, and from the claims. [Brief description of the drawings]

[0021] [Figure 1] 1 is a schematic cross-sectional view of a polishing system. [Diagram 2] 1 is a schematic diagram of a substrate loading station and a metrology station and a polishing system. [Diagram 3] 2 is a schematic top view of a substrate oriented in a carrier head of a polishing system; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] In some polishing systems, a membrane in a carrier head is used to apply pressure to the substrate during polishing. However, even if the carrier head is operated in a manner that is intended to apply uniform pressure on the substrate, the substrate may be subject to an asymmetric removal profile, i.e., the amount removed varies with angular position around the center of the substrate (rather than only with radial distance from the center). This asymmetry may occur due to process variations across the substrate, or pressure differences from the carrier head that occur even if the chamber in the carrier head is uniformly pressurized. Furthermore, before being polished, the substrate may have an initial asymmetric non-uniform thickness profile. The asymmetric removal profile combined with the initial asymmetric thickness profile of the substrate may result in a polished substrate having a highly asymmetric final thickness profile.

[0023] One solution to address this is to determine an individual 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, thereby reducing the asymmetry in the final thickness profile.

[0024] 1 illustrates an example of a polishing system 100 that includes a polishing apparatus 104. The 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 of a polishing parameter, such as, for example, pressure, associated with each corresponding substrate. Each carrier head 140 includes a retaining ring 142 to hold the substrate 10 in place above the polishing pad 110 and beneath a flexible membrane 144.

[0025] Each carrier head 140 may optionally include multiple independently controllable pressurizable chambers defined by a membrane, such as, for example, three chambers 146a-146c, that can apply independently controllable pressure to associated zones on the flexible membrane 144 and thus on the substrate 10.

[0026] Each carrier head 140 is suspended from a support structure 150, such as a carousel or track, and is connected by a drive shaft 152 to a carrier head rotation motor 154 such that the carrier head may rotate about an axis 155. Optionally, each carrier head 140 may be oscillated laterally, for example on a slider on support structure 150, by rotational oscillation of the carousel itself, or by movement of a carriage supporting carrier head 140 along the track.

[0027] The platen 120 contained within the polishing apparatus 104 is a rotatable, disk-shaped platen on which the polishing pad 110 is disposed. The platen is rotatable about an axis 125. For example, a motor 121 may rotate the platen 120, which rotates a drive shaft 124. The polishing pad 110 may be a two-layer polishing pad comprising an outer polishing layer 112 and a softer support layer 114.

[0028] The polishing apparatus 104 may include a port 130 to the pad for supplying a polishing fluid 132, such as a slurry, onto the polishing pad 110. The polishing apparatus may also include a polishing pad conditioner to polish the polishing pad 110 to maintain a consistent polished condition.

[0029] During operation, the platen 120 rotates about its central axis 125 and each carrier head 140 rotates about its central axis 155 and is translated laterally across the upper surface of the polishing pad. Generally, rotation of the carrier heads 140 results in rotation of the substrate 10 at the same rotational speed. Without being limited to any particular theory, the substrate is not "fixed" to the membrane 144 in the carrier heads 140, but friction of the inner surface of the rotating retaining ring 142 against the edge of the substrate 10 may result in an even rotational speed of the substrate 10.

[0030] Although only one carrier head 140 is shown, more carrier heads may be provided to hold additional substrates such that the surface area of ​​the polishing pad 110 may be effectively utilized. Thus, the number of carrier head assemblies adapted to hold substrates for simultaneous polishing processes may be based, at least in part, on the surface area of ​​the polishing pad 110.

[0031] 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 spectroscopic monitoring system, that may be used to measure the spectrum of reflected light from the substrate being polished. Optical access through the optical polishing pad may be provided by including an aperture (i.e., a hole through the pad) or a solid window 118. The in-situ monitoring system may alternatively or additionally include an eddy current monitoring system.

[0032] In some embodiments, optical monitoring system 160 is a sequential optical monitoring system having a probe (not shown) positioned between two polishing apparatuses or between a polishing apparatus and a transfer station. Monitoring system 160 may continuously or periodically monitor one or more characteristics of a zone of the substrate during polishing. For example, one characteristic is the thickness of each zone of the substrate.

[0033] In either the in situ or sequential embodiments, the optical monitoring system 160 may include a light source 162, a light detector 164, and circuitry 166 for sending and receiving signals between a remote control device 190, such as a computer, and the light source 162 and the light detector 164. One or more optical fibers 170 may be used to transmit light from the light source 162 to an optical access in the polishing pad and to transmit light reflected from the substrate 10 to the detector 164.

[0034] 1-3, the carrier head 140 is configured to closely surround the substrate 10 at its edge, e.g., 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 carrier head 140. When the substrate 10 is polished in the carrier head 140, the edge of the substrate 10 (e.g., the leading edge of the substrate 10) rolls against the inner surface of the carrier head 140, e.g., against the inner surface of the retaining ring 142. The substrate 10 may roll against the inner surface of the carrier head 140 (e.g., against the inner surface of the retaining ring 142) due to friction between the leading edge of the substrate 10 and friction of the inner surface of the carrier head 140 such that the substrate 10 rotates when the carrier head 140 rotates. Hypothetically, the rotation of the substrate 10 may equalize asymmetric polishing effects due to, e.g., relative speed differences between regions closer or farther from the platen's axis of rotation. In practice, however, because the substrate remains in a generally constant angular position relative to the carrier head, the substrate 10 may be subjected to a removal profile that is specific to the carrier head 140. The removal profile of the carrier head may be determined, e.g., empirically measured as described below, and stored for use in loading and selecting a substrate orientation.

[0035] 2 and 3, a pre-polishing thickness profile of the substrate 10 is determined before it is loaded into the carrier head 140 and polished by the polishing apparatus 104. To determine the pre-polishing thickness profile, the substrate 10 may be loaded onto the pedestal 182 of the metrology station 180. The sensor 186 is configured to measure the thickness of the substrate 10, such as the outermost thickness (including thickness differential) of the layers deposited on the substrate. The thickness of the substrate 10 may be measured at multiple locations in a two-dimensional array across the substrate 10. The sensor 186 may be, for example, a camera or other similar metrology device configured to scan the substrate 10. For example, the sensor 186 may perform a line scan of the substrate 10 and generate a two-dimensional color image of the substrate. The sensor 186 may generate thickness measurements or measurements that are proportional to the thickness.

[0036] To measure the thickness of the substrate 10, the sensor 186 may measure selected locations in a circle around the center of the substrate 10, for example at the same radial distance from the center of the substrate 10. For example, the pedestal 182 may rotate such that the sensor 186 scans a circular path over the substrate 10. In some implementations, the sensor 186 may take measurements at multiple angular positions around the center of the substrate and multiple radial distances from the center of the substrate 10, which may provide an angular profile in circles of different radii on the substrate 10. Alternatively, the sensor 186 may take measurements in a regular array, such as a rectangular array across the substrate 10, to form a two-dimensional array of thicknesses of the substrate 10.

[0037] The measurements of the sensor 186 may be transmitted to a controller 190, which may then process the measurements to generate a thickness profile of the substrate 10. For example, the measurements may be integrated to generate a thickness profile, such as an angular thickness profile of the substrate 10. The angular thickness profile may indicate the thickness of the substrate 10 at different angular positions around the center of the substrate 10. For example, for multiple angles around the center of the substrate 10, the angular thickness profile may indicate an average thickness value at a radial distance from the center of the substrate 10. The angular thickness profile may also indicate the thickness of the substrate at different angular positions at multiple different radial distances from the center of the substrate 10. Alternatively, the thickness profile may be a two-dimensional array of thicknesses of the substrate 10, as measured by the sensor 186 and generated by the controller 190.

[0038] After the thickness profile of the substrate 10 is determined, the desired orientation of the substrate 10 within the carrier head 140 is calculated. As described above, the controller 190 may store the removal profile of the carrier head 140. For example, the controller 190 may store a number of thickness removal values ​​as a function of angle about the center of the substrate.

[0039] The substrate 10 can be positioned within the carrier head 140 such that the asymmetry of the final thickness profile is at least partially offset by the asymmetry of the removal profile of the carrier head. H (θ), and the pre-polishing thickness profile R of the substrate 10. S Based on (θ), the desired relative orientation θ of the substrate 10 with respect to the carrier head 140 D For example, the angular difference ΔΘ may be incremented across a range, e.g., between 0 and 360 degrees in 1 degree increments or 5 degree increments. At each value of ΔΘ, a known removal profile R H (θ) and the thickness profile before polishing R S (θ) is calculated, although other measures of difference, such as the sum of the absolute values ​​of the differences, may be used. It can be calculated as the sum of squared differences such as TIFF2025069147000002.tif25170.

[0040] Desired angle θ D will be equal to the value of ΔΘ that provides the minimum overall difference.

[0041] The carrier head is aligned at a desired angle θ with respect to the substrate. D In other words, carrier head 140 can be rotated at an angle such that the removal profile of carrier head 140 and the pre-polishing thickness profile of substrate 10 are complementary. For example, carrier head 140 can be rotated relative to substrate 10 during polishing such that the maximum removal portion of the removal profile can correspond to the thickest portion of the pre-polishing thickness profile.

[0042] To position the substrate 10 in the carrier head 140 at a desired orientation, a desired relative angle θ between the carrier head 140 and the substrate 10 is determined. D may be calculated as described above.

[0043] Absolute angular position θ of the substrate 10 P The absolute angular position of the substrate 10 (e.g., relative to a fixed frame of the polishing apparatus) is measured. The measurement may be taken by the sensor 186 when the substrate 10 is on the pedestal 182. For example, the measurement may be taken using an optical sensor that may detect a marker on the substrate 10, such as a notch or flat (e.g., B in FIG. 3). Based on the absolute angular position of the substrate on the pedestal, the controller determines the absolute angular position θ of the substrate. S However, we can calculate what happens when it is loaded onto the carrier head 140. P and θ S The difference between may be determined based on a predetermined movement of the robot 184 when the robot 184 moves the substrate 10 from the pedestal 182 to the carrier head 140, for example, if the robot 184 rotates the substrate 10 through an angle of 90° or 180° when moving the substrate.

[0044] Absolute angle orientation of the carrier head θ H may be measured, for example, by optically detecting a landmark on the carrier head 140 (eg, position A or C), or using the motor encoder 188 to measure the rotation of the carrier head 140.

[0045] Absolute angular position θ of the substrate 10 S and the desired relative angle θ between the substrate 10 and the carrier head 140 D Once determined, carrier head 140 is aligned at a desired angle θ relative to substrate 10. D Provides an absolute angular orientation, e.g., θ H =θ S +θ D The controller 190 may be used to rotate the carrier head 140 to the appropriate angular orientation using feedback from encoders or optical monitoring.

[0046] The controller 190 may then cause the robot arm 184 to transfer the substrate 10 from the metrology station 180 (eg, from the pedestal 182 ) to the carrier head 140 .

[0047] When the substrate 10 is loaded into the carrier head 140, polishing of the substrate 10 in the carrier head 140 results in a polished profile with less asymmetry because the removal profile of the carrier head reduces the asymmetry in the thickness profile of the substrate 10.

[0048] A test substrate 10 may be used to determine the removal profile of the carrier head 140. First, the sensor 186 may measure the pre-polishing thickness profile of the substrate 10 before loading the substrate 10 into the carrier head 140. For example, the pre-polishing thickness profile of the substrate 10 may be measured at the metrology station 180. Then, using the robot arm 184, the substrate 10 may be transferred from the metrology station 180 and loaded into the carrier head 140, both in the "zero position" (or other known position and orientation) relative to each other. For example, the positional marker B of the substrate 10 and the positional marker A of the carrier head 140 may be aligned. The substrate 10 may then be polished in the carrier head 140. Following polishing, the substrate 10 may be transferred from the carrier head 140 to the metrology station 180 using the robot arm 184, where the post-polishing thickness profile of the substrate 10 may be measured. The removal profile of carrier head 140 can then be calculated by comparing the thickness profiles before and after polishing of substrate 10, eg, by subtracting the pre-polish thickness profile from the post-polish thickness profile.

[0049] When the carrier head 140 wears out, it can be replaced. The replacement carrier head 140 will also have a unique removal profile. To measure and calibrate the removal profile of each carrier head 140, a substrate (e.g., a test substrate for each replacement carrier head 140) can be polished to determine the removal profile of the carrier head 140. A comparison of the thickness profile and the polished profile can determine the removal profile of the carrier head 140. For example, the controller 190 compares measurements of the thickness profile of the substrate 10 before polishing in the carrier head 140 and the polished thickness profile of the substrate 10 after polishing in the carrier head 140. Comparing the thickness profile of the substrate 10 to the polished profile clarifies the removal profile due to the carrier head 140 (e.g., due to the radial pressure distribution in the carrier head 140).

[0050] The controllers and other computing devices that are part of the systems illustrated herein may be implemented in digital electronic circuitry, or in computer software, firmware, or hardware. For example, a controller may include a processor to execute a computer program, such as stored in a computer program product, e.g., in a non-transitory machine-readable storage medium. Such computer programs (also known as programs, software, software applications, 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 an independent program or as a module, component, subroutine, or other unit suitable for use in a computing environment.

[0051] While this document contains many specific implementation details, these should not be construed as limitations on the scope of any invention, or for which rights may be claimed, but rather as descriptions of features specific to individual embodiments of individual inventions. Certain features described in this document in the context of individual embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination. Also, although features may be described above as functioning in a certain combination and initially claimed as such, one or more features from the claimed combination may in some cases be cut out of the combination, and the claimed combination may be directed to a subcombination or a variation of the subcombination.

[0052] Although several embodiments of the present invention have been described, it will be understood that various modifications may be made without departing from the spirit and scope of the present invention. Accordingly, other embodiments are within the scope of the following claims.

Claims

1. a polishing station having a platen for supporting a polishing pad, a carrier head for holding a substrate, and a motor for rotating the carrier head; a robotic arm configured to transfer the substrate to the polishing station; 11. A chemical mechanical polishing system comprising: a controller configured to: store an angular removal profile of the carrier head and receive an angular thickness profile of the substrate; determine a loading orientation of the carrier head relative to the substrate based on the angular removal profile and the angular thickness profile; cause the motor to rotate the carrier head so that the carrier head is in the loading orientation; and load the substrate into the carrier head with the carrier head in the loading orientation.

2. 2. The system of claim 1, wherein the controller is configured to determine a loading orientation to reduce angular asymmetry of a final thickness profile determined based on the angular removal profile and the angular thickness profile.

3. 2. The system of claim 1, wherein the controller is configured to calculate, for each angle difference among a plurality of angle differences, an overall thickness difference between the angular removal profile and the angular thickness profile, and a final thickness profile uses the angular difference as an angular offset between the angular removal profile and the angular thickness profile.

4. The system of claim 3 , wherein the controller is configured to select an angle difference from the plurality of angle differences that has a minimum overall thickness difference.

5. The system of claim 3 , wherein the controller is configured to determine an orientation of the angle based on the angle difference.

6. 4. The system of claim 3, wherein the controller is configured to calculate the final thickness profile as a sum of minimum squared differences between the angular removal profile and the angular thickness profile.

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

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

9. The system of claim 1 , comprising a sensor for determining an angular orientation of the substrate prior to loading the substrate into the carrier head.

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

11. The system of claim 10 , wherein the sensor is configured to detect a flat or a notch on the substrate.

12. The system of claim 10 , wherein the controller is configured to assign indicia indicative of an orientation of the substrate.

13. 10. The system of claim 9, comprising a metrology station for measuring the angular thickness profile of the substrate, the sensor being disposed within the metrology station to determine an angular orientation of the substrate within the metrology station.

14. 1. A method for chemical mechanical polishing, comprising: receiving an angular thickness profile measurement of the substrate; selecting a desired angle of a carrier head relative to the substrate to reduce angular non-uniformity in polishing; rotating the carrier head to the desired angle; transferring the substrate to the carrier head and loading the substrate into the carrier head with the carrier head at the desired angle; and polishing the substrate.

15. Measuring a pre-polished angular thickness profile of the test substrate; loading the test substrate into the carrier head with the carrier head in a null position relative to the substrate; polishing the test substrate; measuring a polished angular thickness profile of the test substrate; and calculating an angular removal profile by the carrier head by comparing the pre-polishing angular thickness profile and the post-polishing angular thickness profile.

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