Underlayer topography metal residue detection and over-polishing strategy

Abstract

An apparatus for processing a substrate includes a polishing assembly and a controller. The polishing assembly is configured to (a) polish a substrate surface. The controller is configured to (b) detect a first substrate measurement corresponding to a first region of the substrate, (c) detect a second substrate measurement corresponding to a second region of the substrate; (d) determining a difference between the first substrate measurement at the first region and the second substrate measurement at the second region; in response to determining that the difference between the first substrate measurement and the second substrate measurement is within a tolerance threshold, stopping polishing of the substrate surface; and repeating (a) to (d) in response to determining that the difference between the first substrate measurement and the second substrate measurement is outside the tolerance threshold.

Description

Technical Field

[0001] Examples of the present disclosure generally relate to methods, systems, and apparatuses for processing substrates such as semiconductor substrates. More specifically, inspection systems and methods of using the same are disclosed. Background Art

[0002] Integrated circuits are typically formed on a substrate by sequentially depositing conductive, semiconductive, or insulating layers on a silicon wafer. One manufacturing step involves depositing a filler layer over a non-flat surface and 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 conductive filler layer can be deposited over a patterned insulating layer to fill trenches or vias in the insulating layer. After planarization, portions of the conductive layer remaining between the raised patterns of the insulating layer form vias, plugs, and lines that provide conductive paths between thin film circuits on the substrate. For other applications, such as oxide polishing, the filler layer is planarized until a predetermined thickness remains over the non-flat surface. Additionally, planarization of the substrate surface is generally required for lithography.

[0003] Chemical mechanical polishing (CMP) is a well-known planarization method. This planarization method generally requires mounting the substrate on a carrier or polishing head. The exposed surface of the substrate is typically placed against a rotating polishing pad or belt pad. The polishing pad can be a standard pad or a fixed abrasive pad. The standard pad has a durable rough surface, while the fixed abrasive pad has abrasive particles retained in a holding medium. The carrier head provides a controllable, typically supplied to the surface of the polishing pad. The polishing slurry includes at least one chemically reactive reagent and, if used with a standard polishing pad, includes abrasive particles.

[0004] One problem in CMP is determining whether the polishing process is complete. In other words, whether the substrate layer has been planarized to a desired flatness or thickness, or when a desired amount of material has been completely removed from the substrate surface. Over-polishing of the conductive layer or film (removing too much material) results in an increase in circuit resistance. However, over-polishing is often necessary to ensure that all covered portions of the conductive layer (e.g., portions above the field regions of the substrate) have been removed and only the remaining portions of the conductive layer disposed within the features formed in the substrate surface remain. On the other hand, under-polishing of the conductive layer (removing too little material) results in an electrical short circuit between the circuits formed on the substrate surface due to the presence of the remaining portions of the covered portions of the conductive layer. Conventionally, it has been difficult to detect the end point of the polishing process when the conductive layer becomes discontinuous on the substrate surface, such as at points near the end of the polishing process. Determining the end point of the polishing process becomes particularly difficult where, due to the underlying surface topography formed previously, a portion of the overlying film layer is disposed within a groove formed in the substrate surface and thus the remaining portions of the conductive layer form electrical short circuits in various regions of the substrate surface. Additionally, variations in the initial thickness of the layer to be polished, the slurry composition, the condition of the polishing pad, the relative speed between the polishing pad and the substrate, and the load on the substrate can result in variations in the material removal rate.

[0005] Accordingly, there is a need in the art for improved methods, systems, and apparatuses for detecting the end point of a polishing process that address the problems described above and, more particularly, that can reduce the likelihood of unwanted discontinuous portions of the polished film layer remaining on the substrate surface after polishing. Summary of the Invention

[0006] Embodiments of the present disclosure may provide a method for detecting residues at a substrate, where detecting residues at the substrate includes: receiving a substrate for chemical mechanical polishing; applying a first test signal to the substrate; in response to the first test signal, detecting a first response corresponding to a first region of the substrate; in response to the first test signal, detecting a second response corresponding to a second region of the substrate; determining a first test signal metric indicative of a difference between the first response and the second response; and in response to the first test signal metric being outside a tolerance threshold, providing an indication of the presence of residues at the substrate.

[0007] Embodiments of the present disclosure may provide a polishing apparatus for processing a substrate, comprising: a polishing pad support; a carrier head configured to hold the substrate and apply one or more independently controllable pressures to multiple regions of the substrate; an in-situ monitoring system for monitoring characteristics of the substrate within the multiple regions during polishing; and a controller. The controller includes computer program instructions stored in a memory, which when executed by a processor of the controller cause: (a) the carrier head to push the substrate against the surface of a polishing pad positioned on the polishing pad support, wherein pushing the substrate against the surface of the polishing pad includes applying one or more independently controllable pressures to the surface of the substrate; (b) the in-situ monitoring system to detect a first substrate measurement corresponding to a first region among the multiple regions of the substrate; (c) the in-situ monitoring system to detect a second substrate measurement corresponding to a second region among the multiple regions of the substrate; (d) the controller to determine a difference between the first substrate measurement at the first region and the second substrate measurement at the second region; and (e) the controller, in response to determining that the difference between the first substrate measurement and the second substrate measurement is within a tolerance threshold, to stop pushing the substrate against the surface of the polishing pad by the carrier head; or in response to determining that the difference between the first substrate measurement and the second substrate measurement is outside the tolerance threshold, to repeat (a) to (d).

[0008] Embodiments of the present disclosure may also provide a polishing system, comprising: a polishing assembly configured to polish a substrate surface; a controller configured to generate a first series of substrate measurements corresponding to a first region of the substrate; generate a second series of substrate measurements corresponding to a second region of the substrate; determine a slope of the first series of substrate measurements over time; determine a slope of the second series of substrate measurements over time; determine that the slope of the first series of substrate measurements or the slope of the second series of substrate measurements is within a threshold range; and determine a difference between the first series of substrate measurements and the second series of substrate measurements; and in response to determining that the difference between the first series of substrate measurements and the second series of substrate measurements is within a tolerance threshold, stop polishing the substrate surface; in response to determining that the first series of substrate measurements and the second series of substrate measurements are outside the tolerance threshold, indicate the presence of residues at the substrate and update aspects of the polishing operation, and repeat (a) to (c) and (f); and in response to determining that the first series of substrate measurements and the second series of substrate measurements cross into the tolerance threshold, indicate the removal of residues from the substrate.

[0009] Embodiments of the present disclosure may also provide a method for processing a substrate, the method comprising: polishing a substrate surface; detecting a first substrate measurement corresponding to a first region of the substrate; detecting a second substrate measurement corresponding to a second region of the substrate; determining a difference between the first substrate measurement and the second substrate measurement; and in response to the determined difference being outside a tolerance threshold, providing an indication of the presence of residues at the first region or the second region of the substrate.

[0010] Embodiments of the present disclosure may also provide a method that includes pushing a substrate against a surface of a polishing pad positioned on a polishing pad support, wherein pushing the substrate against the surface of the polishing pad includes applying one or more independently controllable pressures to the surface of the substrate. Subsequently, a first substrate measurement corresponding to a first region among a plurality of regions of the substrate is detected, and a second substrate measurement corresponding to a second region among the plurality of regions of the substrate is detected. Subsequently, a difference between the first substrate measurement at the first region and the second substrate measurement at the second region is determined, and then: in response to determining that the difference between the first substrate measurement and the second substrate measurement is within a tolerance threshold, stop the carrier head from pushing the substrate against the surface of the polishing pad; or in response to determining that the difference between the first substrate measurement and the second substrate measurement is outside the tolerance threshold, repeat (a) to (d). Brief Description of the Drawings

[0012] To enable a detailed understanding of the manner in which the above-described features of the present disclosure are utilized, a more specific description of the present disclosure briefly summarized above may be made with reference to aspects of the present disclosure, some of which are illustrated in the drawings. It should be noted, however, that the drawings only illustrate common aspects of the present disclosure and are thus not considered to limit its scope, as the present disclosure may admit other equally effective aspects.

[0013] Figure 1 is a partially exploded view of a polishing apparatus according to an example of the present disclosure.

[0014] Figure 2 is according to another example of the present disclosure Figure 1 cross-sectional view of a polishing apparatus.

[0015] Figure 3 is a top view of a polishing apparatus according to another example of the present disclosure.

[0016] Figure 4 is a cross-sectional view of a detection element according to another example of the present disclosure.

[0017] Figures 5A to 5D is a cross-sectional view of a detection element during a polishing operation according to an example of the present disclosure.

[0018] Figures 6A to 6C illustrates a response to a test signal from a corresponding region of a substrate according to an example of the present disclosure.

[0019] Figure 7 is a method for detecting residues at a substrate according to another example of the present disclosure.

[0020] For purposes of promoting understanding, like reference numerals have been used, where possible, to designate like elements common to the figures. Additionally, elements of one example may be advantageously adapted for use in other examples described herein. Detailed Description

[0021] A method for detecting residues at a substrate, and a system and apparatus for performing the method, includes receiving a substrate for chemical mechanical polishing. The method also includes applying a first test signal to the substrate. The method also includes detecting a first response corresponding to a first region of the substrate in response to the first test signal. The method also includes detecting a second response corresponding to a second region of the substrate in response to the first test signal. The method also includes determining a first test signal metric indicative of a difference between the first response and the second response. The method also includes providing an indication of the presence of residues at the substrate in response to the first test signal metric being outside a tolerance threshold.

[0022] Figure 1 is a partial exploded view of a polishing apparatus according to an example of the present disclosure. In some embodiments, one or more substrates 10 may be polished by a chemical mechanical (CMP) apparatus 20. The polishing apparatus 20 may include a series of polishing stations 22a, 22b, and 22c, and a transfer station 23. The transfer station 23 may be configured to transfer the substrate 10 between a carrier head and a loading apparatus.

[0023] Each polishing station includes a rotatable platen 24 on which a polishing pad 30 is positioned. The first polishing station 22a and the second polishing station 22b may include a dual-layer polishing pad having a hard durable outer surface, or a fixed abrasive pad having embedded abrasive particles. The final polishing station 22c may include a relatively soft pad or a dual-layer pad. Each polishing station may also include a pad conditioner device 28 to maintain the condition of the polishing pad such that the polishing pad will effectively polish the substrate.

[0024] Figure 2 is a cross-sectional view of a polishing apparatus according to another example of the present disclosure Figure 1 In some embodiments, the dual-layer polishing pad 30 may include a backing layer 32 that abuts the surface of the platen 24 and a cover layer 34 for polishing the substrate 10.

[0025] During a polishing operation, a polishing liquid 38, such as an abrasive slurry or a non-abrasive solution, may be supplied to the surface of the polishing pad 30 by a slurry supply port or a combined slurry / rinse arm 39. The same slurry solution may be used at the first and second polishing stations, while another slurry solution may be used at the third polishing station.

[0026] Returning to Figure 1, the rotatable multi - head turntable 60 supports four carrier heads 70. The turntable rotates about a turntable axis 64 by a central column 62 to perform orbital motion around the carrier head system and the substrate attached thereto between the polishing stations 22a to 22c and the transfer station 23. Three carrier head systems can receive and hold substrates and polish the substrates by pressing them against a polishing pad. In some embodiments, one carrier head system delivers the polished substrate to the transfer station 23 and receives the unpolished substrate from the transfer station 23.

[0027] Each carrier head 70 is connected to a carrier head rotation motor 76 by a carrier drive shaft 74 (illustrated by removing a part of the cover 68), so that each carrier head can rotate independently about its axis. Each carrier head 70 can independently swing laterally in a radial slot 72 formed in the turntable support plate 66. In operation, the platen rotates about its central axis, and the carrier head rotates about its central axis and translates laterally across the surface of the polishing pad.

[0028] In some embodiments, uniform pressure can be applied to the substrate. In other embodiments, variable pressure can be applied to different parts or regions of the substrate. As can be seen in Figure 2 and Figure 3 , the carrier head 70 can independently apply different pressures to different radial regions of the substrate. For example, the carrier head can include mechanical or electromechanical elements, such as a flexible membrane having a substrate receiving surface, and three independently pressurizable concentric chambers 50, 52, and 54 behind the membrane. Thus, the inner circular chamber 50 can apply pressure to the inner circular region 50a of the substrate, the middle annular chamber 52 can apply pressure to the middle annular region 52a of the substrate, and the outer annular chamber 54 can apply pressure to the outer annular region 54a of the substrate, and the regions or areas can be seen in Figure 3 .

[0029] In some embodiments, a recess 26 is formed in the platen 24 and a transparent section 36 is formed in the polishing pad 30 covering the recess 26. The transparent section 36 can be electromagnetically transparent, optically transparent, etc. This section 36 can be positioned such that the section passes under the substrate 10 during a portion of the platen rotation, independent of the translational position of the carrier head. Assuming the polishing pad 30 is a dual-layer pad, the transparent section 36 can be constructed by cutting a hole in the backing layer 32 and replacing a section of the overlay 34 with a transparent plug. The plug can be a relatively pure polymer or polyurethane, for example, formed without fillers. Generally, the material of the transparent section 36 should be non-magnetic and non-conductive. Additionally, the system can include a transparent cover, such as glass or hard plastic, placed over the recess 26 but beneath the polishing pad (the top surface of the cover can be coplanar with the top of the platen 24). In this case, the core of the eddy current sensor can extend through the cover and project partially into the polishing pad, or be located entirely beneath the cover (see Figure 4 ).

[0030] At least one of the polishing stations (e.g., the first polishing station 22a or the second polishing station 22b) includes an in-situ detection element 40, such as an eddy current monitoring system. The detection element can be used as a polishing process control and endpoint detection system. The first polishing station 22a can include a single detection element and the final polishing station 22c can include another detection element and / or an optical or other detection element.

[0031] The CMP apparatus 20 also includes a controller 90 that includes a programmable central processing unit (CPU) operable with a memory (e.g., non-volatile memory) and support circuitry. Support circuitry is conventionally coupled to the CPU and includes a cache, clock circuits, input / output subsystems, power supplies, etc., and combinations thereof, coupled to respective components of the CMP apparatus 20 to facilitate control thereof. The CPU is one of any form of general computer processor used in an industrial setting, such as a programmable logic controller (PLC), for controlling the respective components and sub-processors of the processing system. The memory coupled to the CPU is non-transitory and is typically one or more of readily available memories, such as random access memory (RAM), read only memory (ROM), floppy disk drives, hard disks, or any other form of digital memory (local or remote). Generally, the memory includes computer program instructions that, when executed by the CPU, facilitate the operation of the CMP apparatus 20. The program instructions in the memory are in the form of a program product, such as a software algorithm implementing the methods of the present disclosure. The program instructions may conform to any of several different programming languages. In one example, the present disclosure may be implemented as a program product stored on a computer-readable storage medium for use with a computer system. The program instructions of the program product define the functionality of the embodiments (including the methods described herein). The program instructions and data may be encoded and stored in the memory for instructing the CPU. The program instructions readable by a processing unit within the system controller determine which tasks may be executed in the processing system. For example, the non-transitory computer-readable medium includes a program product that, when executed by the processing unit, is configured to execute one or more of the methods described herein. Preferably, the program instructions include code for performing tasks related to monitoring, performing, and controlling measurements, fluid delivery, polishing hardware, and substrate movement, along with various process recipe tasks.

[0032] Figure 3 is a top view of a polishing apparatus according to another example of the present disclosure. In some embodiments, the sensor assembly of the monitoring system is embedded in the platen and sweeps under the substrate 10 with each rotation of the platen. Each time the sensor assembly sweeps under the substrate, data may be collected from the sensing elements 40. Specifically, as the sensor assembly sweeps across the substrate in path 96, the monitoring system will make a series of measurements 98 (e.g., illustrated as ~15). Each measurement 98 may be associated with a radial position or radial region on the surface of the substrate that is generated and defined by using endpoint detection software running on the controller 90.

[0033] The sensing element 40 senses and detects eddy currents in a conductive (e.g., metal) layer on the substrate and provides a signal indicative of the measurement to the controller 90. The sensor assembly for the sensing element 40 includes a core 42 positioned in the recess 26 to rotate with the platen, and a coil 44 wound around the core 42. The coil 44 is connected to the control system. The control system can be located entirely or partially locally or remotely to the recess 26. For example, the control system can include a printed circuit board 58 inside the recess 26. The controller 90 (such as a computer) can be coupled to components in the platen through a rotary electrical joint 92, including the printed circuit board 58.

[0034] Figure 4 is a cross-sectional view of a sensing element according to another example of the present disclosure. In some embodiments, the core 42 can be a U-shaped or E-shaped body formed of a non-conductive material having a relatively high magnetic permeability. The exact winding configuration, core composition and shape, and capacitor size can be determined experimentally. As shown, the lower surface of the transparent section 36 can include two rectangular indentations 29, and two tips 42a and 42b of the core 42 can extend into the indentations to be positioned closer to the substrate.

[0035] In some embodiments, an oscillator in the controller drives the coil 44 to generate an oscillating magnetic field 48 that extends through the body of the core 42 and into the gap 46 between the two tips 42a and 42b of the core. At least a portion of the magnetic field 48 extends through the polishing pad 30 and into the substrate 10. If there is a metal layer 16 on the substrate 10, the oscillating magnetic field 48 generates eddy currents in the metal layer 16. The eddy currents cause the metal layer 16 to act as an impedance source for a sensing circuit coupled to or communicating with the controller 90. As the thickness of the metal layer changes, the impedance changes. By detecting this change, the eddy current sensor can sense a change in the eddy current intensity and thus sense a change in the thickness of the metal layer 16.

[0036] As Figure 5A and Figure 5BAs shown, for the polishing operation, the substrate 10 is placed in contact with the polishing pad 30. The substrate 10 may include a silicon wafer 12 and a conductive layer 16 (e.g., a metal such as copper, titanium, etc.) disposed over one or more patterned underlying layers 14, which may be semiconductor, conductor, or insulator layers. A barrier layer 18 (such as tantalum, tantalum nitride, etc.) may separate the metal layer from the underlying patterned layer. In some cases, defects may be included in the conductive layer in the form of residues or residue 502 structures. The residues may be underlying defects caused by integration due to inconsistent or defective underlying topography. In the illustrated embodiment, due to underlying topography problems in the surface of the substrate on which the barrier layer 18 is disposed, the residue 502 is formed from conductive material from the conductive layer 16. In some embodiments, the residue 502 may extend into the underlying layer 14, thereby causing the formation of an undesired conductive region in the underlying layer 14.

[0037] After polishing, the portions of the metal layer remaining between the patterns of the underlying layer formed on the substrate will provide metal features, e.g., vias, pads, and interconnects. However, as Figure 5A shown, prior to polishing, the bulk of the conductive layer 16 is initially relatively thick and continuous over the field region of the substrate and has a low resistivity, and relatively strong eddy currents can be generated in the conductive layer 16. As previously mentioned, the eddy currents cause the metal layer to act as an impedance source parallel to the coil 44 for detecting the presence of the conductive layer 16.

[0038] As Figure 5B shown, as the substrate 10 is polished, the bulk portion of the conductive layer 16 is thinned. As the conductive layer 16 is thinned, its sheet resistivity increases and the eddy currents in the metal layer are attenuated. Thereafter, the coupling between the metal layer 16 and the sensor is reduced (i.e., the resistivity of the virtual impedance source is increased) and the detected impedance increases.

[0039] As Figure 5C shown, the bulk portion of the conductive layer 16 is finally removed, thereby exposing the barrier layer 18 and leaving the conductive interconnect 16' in the trenches between the residue 502 of the conductive layer between the patterned insulating layer 14 and the conductive interconnect. At this time, the coupling between the conductive portions in the substrate, which are typically small and usually discontinuous, and the sensor reaches a minimum, except for the residue 502, which may result in a stronger eddy current signal and reading.

[0040] Returning to Figure 2 , the sensing element 40 may be positioned within the recess 26 of the platen 24. As the platen 24 rotates and the substrate 10 translates across the surface of the rotating platen 24, the sensing element 40 may measure the eddy currents across a portion of the substrate. Specifically, the sensing element 40 is configured to measure a portion of the substrate at a radial distance from the axis of rotation of the platen 24, and the measurement is associated with a corresponding portion of the substrate 10.

[0041] See Figure 2 and Figure 3 ,the CMP device 20 may also include a position sensor 80, such as an optical interrupter, for sensing when the core 42 is beneath the substrate 10. For example, the optical interrupter may be mounted at a fixed point opposite the carrier head 70. A marker 82 may be attached to the perimeter of the platen. The attachment point and length of the marker 82 are selected such that the marker interrupts the optical signal of the sensor 80 as the transparent section 36 sweeps beneath the substrate 10. Alternatively, the CMP device may include an encoder to determine the angular position of the platen. Data corresponding to the relative position of the sensing element 40 with respect to the substrate 10 may be used to determine which portion (e.g., radial region) of the substrate 10 is associated with the measurement generated by the sensing element 40 relative to the substrate 10 during each pass.

[0042] The controller 90 receives signals from the sensing element. Since the sensor assembly sweeps beneath the substrate with each rotation of the platen, information about the underlying metal layer thickness and exposure accumulates in-situ and on a continuous real-time basis (once per platen rotation). The controller 90 is programmed to sample the measurements from the monitoring system when the substrate passes the sensor 80. As polishing proceeds, the endpoint detection metric of the metal layer changes, and the sampled signal varies over time. The time-varying sampled signal may be referred to as a trace, such as Figures 6A to 6C shown. The measurements from the monitoring system may be displayed on an output device 94 during polishing to allow an operator of the device to visually monitor the progress of the polishing operation. Additionally, as discussed below, the trace may be used to control the polishing process and determine the endpoint of the metal layer polishing operation.

[0043] In operation, the CMP device 20 uses the sensing element 40 to determine when the bulk of the conductive and barrier layers have been removed and when the underlying patterned insulating layer has been substantially exposed with no significant residue. The controller 90 applies process control and endpoint detection logic to the sampled signal to determine when to change process parameters and detect the polishing endpoint.

[0044] Figure 6A Shows the response to a test signal from a corresponding region of the substrate according to an example of the present disclosure. Figure 6A Includes traces 602a, 602b, and 602c corresponding to the response to test signals at different regions of the substrate. For example, trace 602a may correspond to the inner circular region 50a of the substrate ( Figure 3 shown), while trace 602b may correspond to the intermediate annular region 52a, and trace 602c may correspond to the outer annular region 54a.

[0045] In some embodiments, the controller applies box logic for identifying trends in the traces by using isolation boxes 604a to 604c generated in real time for each trace to determine the convergence of the traces. For example, the box logic can be an algorithm running on the controller 90 that is applied to determine the slope trends in the traces 602a to 602c for identifying a steady state condition indicating a weakening of the polishing effect. The algorithm can be applied over a certain time period or, as shown, can be shown after a target threshold (such as a slope value or trend, relative change in slope, etc.) is met. After the target threshold is reached, the algorithm can trigger a convergence analysis of the traces. In some embodiments, one or more traces can reach the target threshold indicating a relatively steady state condition while another trace has not reached the target threshold. Polishing can continue until the other traces have reached the target threshold, which is related to the nature of the traces determined by the box logic. In one example, the target threshold is related to the desired slope of the trace at a certain moment. In one example, the slope of the trace at the moment it reaches the threshold causes it to leave a horizontally oriented box by crossing the vertical edge of the box rather than crossing the bottom edge of the box, as Figures 6A to 6C shown. Once two or more traces meet the box logic for reaching the target threshold, the convergence of two or more or all of the traces can be measured. The convergence of the traces can be measured by determining the range of the differences 606 between the traces at any given time point 608 after it is determined that the box logic threshold has been met. Convergence can be measured by the maximum difference of the traces, the minimum difference of the traces, the standard deviation of the traces, and the average deviation of the traces, or other comparative analyses can be applied. In Figure 6A the illustrated embodiment shown, the difference 606 can be within a tolerance threshold that indicates sufficient removal of residues from the substrate. In some embodiments, convergence measurements are continuously made during over-polishing or other operations until the traces 602a to 602c reach the target convergence. In other embodiments, after it is determined that the box logic threshold has been met, over-polishing or other operations can be performed for a dynamic amount of time calculated based on the differences required to reach convergence, or for a fixed amount of time stored in the memory of the controller 90.

[0046] In some embodiments, the tolerance threshold is a value below which the differences in the traces are sufficient to indicate a lack of residues at the substrate and above which the differences indicate the presence of residues at the substrate. For example, the differences can be visually equivalent to a certain gap between one or more of the traces 602a to 602c and another trace. As can be in Figure 6AAs can be seen, the traces do not overlap, but the difference 606 may be small enough such that the difference is within the tolerance threshold. Convergence indicates that measurements from eddy current measurements or other inspection techniques have reached the level of the art, and at least two or more regions of the substrate 10 have a similar amount of conductive features on the substrate surface. Thus, convergence can be used to indicate that neither region includes anomalies, such as subsurface residues, etc. The tolerance threshold stored in memory can be provided manually or can be determined through machine learning, big data analysis, or other automated means. The tolerance threshold can be fixed or can be adjusted by lot, build, and / or other parameters.

[0047] Figure 6B shows an embodiment where, since the difference 606a is greater than the threshold stored in memory, at the first time 608a, the traces 602a to 602c are not within the tolerance threshold. Thus, the polishing operation can be updated to indicate additional polishing time, a change in the slurry application rate, material, etc., polishing pressure, or other aspects of the polishing operation. At the second time 608b, convergence of the traces can be determined to indicate successful removal of residual material and no residue at the substrate surface where the polishing operation needs to be updated to remove any underlying residue.

[0048] Figure 6C An embodiment is shown where the traces indicate a first difference 606a that is not within the tolerance threshold at the first time 608a. At the second time 608b, a second difference 606b remains outside the tolerance threshold. This relative behavior in the trend indicates the presence of residue at the substrate region corresponding to the first trace 602a. Although three separate traces are illustrated, two or more traces can be used to perform the analysis. In the illustrated embodiment, an over-polishing operation can be performed to reduce the residue on the substrate. In some embodiments, a notification indicating the detection of residue on the substrate can be sent to an operator or other parts of the system. Further analysis can be performed at a subsequent time to determine the slope, convergence, range, or other absolute or relative characteristics of the traces. The polishing operation can be updated to reduce the residue, thereby reducing overall yield loss and improving efficiency.

[0049] Return Figure 2 , in response to detecting that the difference is outside the tolerance threshold, as Figure 6C shown, the controller 90 can be programmed to divide the measurements from each sweep under the substrate from the detection element 40 into a plurality of measurement regions 98 for calculating the radial position of each region on the substrate, classify the measurements into radial regions, determine the minimum, maximum, and average measurements for each region, and use the plurality of radial regions to determine the polishing endpoint.

[0050] The controller 90 may also be coupled to a pressure generating mechanism (e.g., a gas supplier), which controls the pressure applied by the flexible membrane of the carrier head 70 to the substrate, the pressure applied to the carrier head rotation motor 76 to control the carrier head rotation rate, the pressure applied to a platen rotation motor (not shown) to control the platen rotation rate, or the pressure applied to the slurry dispensing system 39 to control the slurry composition supplied to the polishing pad. For example, the controller may determine that the outer radial region has met the endpoint criteria, but the inner radial region does not meet the endpoint criteria. This would indicate that the residues in the underlying annular outer region have been removed, but the residues in the inner region of the substrate have not been removed. In this case, the controller is configured to update the polishing operation.

[0051] Return to Figure 5D , the continued polishing and / or updated polishing operation reduces the residues 502 and sufficiently exposes the underlying insulating layer 14, leaving the conductive interconnects 16' and the buried barrier layer film 18' in the trenches between the patterned insulating layers 14.

[0052] Figure 7 is a flowchart of a method 700 according to an example method described herein. Method 700 begins at operation 702. In operation 702, the surface of the substrate 10 is engaged for chemical mechanical polishing, as Figure 2 shown. The process of engaging the surface of the substrate 10 for chemical mechanical polishing includes: causing the carrier head 70 to hold the substrate 10 by using the carrier head 70 and applying one or more independently controllable pressures to multiple regions of the substrate 10 through the independently pressurizable chambers 50, 52, and 54 behind the membrane, for pushing the surface of the substrate 10 onto the surface of the polishing pad 30, and thus performing a polishing process on the surface of the substrate 10. Operation 702 also includes the rotation of the polishing pad 30, the rotation of the carrier head 70, the translational relative movement between the carrier head 70 and the polishing pad 30, and the delivery of the slurry composition to the polishing pad surface during the chemical mechanical polishing process.

[0053] In operation 704 of method 700, a first substrate measurement corresponding to a first region of the substrate is detected. The first substrate measurement may be a response from the middle, inner, or outer region of the substrate. The first substrate measurement may be a response to the eddy current sensor or other detection element 40 as the eddy current sensor or other detection element 40 passes near the substrate, as Figure 3As shown. The first substrate measurement corresponds to a first region of the substrate. In one example, the first substrate measurement can be a response to an eddy current sensor signal detected in response to delivering a first test signal provided within a first region on the surface of the substrate, such as a measurement within an outer radial region of the substrate. The outer radial region can extend between a first radius R1 of the substrate and the outer edge of the circular substrate. The first substrate measurement can be recorded as part of a trace that includes a series of detected measurements at different times for a first defined region (i.e., the outer region) of the substrate, such as trace 602a, as Figures 6A to 6C shown.

[0054] In operation 706, a second substrate measurement corresponding to a second region of the substrate is detected. For example, the second substrate measurement can be a response to an eddy current sensor signal detected in response to delivering a second test signal. The second substrate measurement corresponds to a second region on the surface of the substrate, such as a measurement within a middle radial region of the substrate. In one example, the middle radial region can extend between a first radius R1 of the substrate and a second radius R2, where the second radius R2 is less than the first radius R1. For example, the second response can be a response from the middle of the substrate, as detected by the detection element 40 as it passes near the middle region of the substrate, as Figure 3 shown. The second response can be recorded as part of a trace that includes a series of detected signals measured at different times for a second defined region (e.g., the middle region) of the substrate, such as trace 602b, as Figures 6A to 6C shown.

[0055] Optionally, although not further discussed below for reasons of simplicity of discussion, additional measurement operations can be performed between operation 706 and operation 708. For example, a third substrate measurement can be a response to an eddy current sensor signal detected in response to delivering a third test signal. The third substrate measurement corresponds to a third region on the surface of the substrate, such as a measurement within an inner radial region of the substrate. In one example, the inner radial region can extend between the center of the substrate and the second radius R2 of the substrate. For example, the third response can be a response from the inner region of the substrate, as detected by the detection element 40 as it passes near the inner region of the substrate, as Figure 3 shown. The third response can be recorded as part of a trace that includes a series of detected signals measured at different times for a third defined region (e.g., the inner region) of the substrate, such as trace 602c, as Figures 6A to 6C shown.

[0056] In operation 708, the difference between the first substrate measurement and the second substrate measurement is determined. In some embodiments, the difference between the first substrate measurement and the second substrate measurement is performed after it has been determined that the characteristics of one or more traces have reached a threshold. AsFigure 7 As shown in Figure 7 , during operation 707, an operation is performed to determine that the characteristics of one or more traces have reached a threshold. For example, changes in the characteristics of each trace such as traces 602a and 602b can be analyzed to determine whether the characteristics of the trace meet a certain threshold. In some embodiments, the characteristics (i.e., a series of measurement values) of each trace being evaluated are slope values or trends, changes in slope, or other characteristics of the trace. In some embodiments, block logic can be applied to identify slopes or changes in slope that meet the threshold range or target value or behavior in the slope. In some examples, the slope can be evaluated to determine stability or trend in the slope towards a steady state or other behavior, such as the slope of the trace being close to or approaching zero, such as Figure 6A shown by the rightmost trace 602a in Figure 6A .

[0057] In one example, during operation 708, an algorithm executed by a processor within controller 90 is used to compare first trace 602a with second trace 602b at time point 608 to determine the relative difference 606 between the first trace and the second trace after the characteristics of at least one of traces 602a, 602b have met a certain threshold, as Figures 6A to 6C shown. The algorithm for determining the difference between the first substrate measurement and the second substrate measurement can be automatically triggered by the analysis of the characteristics of at least one trace performed in operation 707. In one example, once the first trace and the second trace meet the block logic for reaching the target threshold, the difference (e.g., convergence) between the first substrate measurement and the second substrate measurement is performed. Determining difference 606 at time 608 can be based on signal values provided by sensors in different regions of the trace formed on the substrate, as Figures 6A to 6C shown.

[0058] In operation 710, in response to the difference 606 determined in operation 708 being outside the tolerance threshold stored in the memory of controller 90, controller 90 then uses the determined difference as an indication of the presence of residue at the first region of the substrate or the second region of the substrate. For example, residue 502 can be an integrated inclusion caused by underlying topographical anomalies, as Figures 5A to 5CAs shown. The resulting residue may increase the eddy current response (i.e., the detected eddy current signal), thus causing a difference in the signal level in the corresponding trace. Determining the difference between the traces allows identification of the corresponding area where the residue is located. For example, the measurement from the third area can be compared with the measurements corresponding to the first area and the second area to determine which of the first area, the second area, or the third area may be affected by the residue. In one example, trace 602a has an eddy current signal significantly higher than that of traces 602b and 602c on the right side of the figure. This difference can lead the controller 90 to conclude that the area where trace 602a is formed includes some residue, or at least a certain amount of residue, which is more than the other areas 602b and 602c on the substrate.

[0059] Operation 710 may include repeating operations 702 to 708 by updating the chemical mechanical polishing process based on the difference relative to the tolerance threshold determined during operation 708. For example, since the difference is outside the tolerance threshold, additional polishing may help to better align the traces. The update may include increasing at least one of the polishing time, the pressure applied to one or more areas of the flexible film of the polishing head, changing the polishing slurry composition, the slurry feed rate, the polishing head rotation speed, the platen rotation speed, etc. In some embodiments, the update of the polishing operation may constitute over-polishing based on the difference from the tolerance threshold. For example, if the difference is far beyond the tolerance threshold, the controller 90 may call for a more aggressive (e.g., higher flexible film pressure, carrier head rotation speed, etc.) or longer over-polishing. If the difference is close to the tolerance threshold, a milder over-polishing may be called for. Over-polishing can be used to remove excess material and residue at the substrate, as Figures 5A to 5D shown.

[0060] If the difference determined in operation 708 is outside the desired threshold, operations 702 to 708 of method 700 may be performed one or more times. Operations 702 to 708 of method 700 may be performed until the detected residue is sufficiently reduced in the corresponding area of the substrate.

[0061] Operations 702 to 708 of method 700 may also be performed an additional one or more times, even if the difference determined in operation 708 is within the desired threshold, to verify that the previously generated results remain within the desired threshold at a subsequent time.

[0062] In operation 712, in response to the difference determined during operation 708 being within the tolerance threshold, an indication of the lack of residue at the substrate is provided. For example, if it is determined that the traces have a low enough difference or a trend towards a low difference over time (see Figure 6B) If so, the controller may indicate a lack of residue and stop or complete the polishing operation, or alternatively, perform a corresponding update to thereby reduce or otherwise adjust the polishing operation accordingly. When the difference is within the tolerance threshold, as part of operation 712, method 700 may call the endpoint of the polishing process.

[0063] Examples of the present disclosure result in increased process yield by identifying and reducing residue during a polishing operation. Due to the direct correlation between residue detection and reduction and process yield, an increase in residue reduction results in an increase in process yield.

[0064] Although the foregoing is directed to examples of the present disclosure, other and further examples of the present disclosure may be devised without departing from its basic scope, which is determined by the appended claims.

Claims

1. A polishing apparatus for processing a substrate, the polishing apparatus comprising: A polishing pad support; A carrier head configured to hold the substrate and apply one or more independently controllable pressures to multiple regions of the substrate; An in-situ monitoring system for monitoring characteristics of the substrate in the multiple regions during polishing; A controller including computer program instructions stored in a memory that, when executed by a processor of the controller, cause: (a) The carrier head to push the substrate against a surface of a polishing pad positioned on the polishing pad support, wherein pushing the substrate against the surface of the polishing pad includes applying the one or more independently controllable pressures to the surface of the substrate; (b) The in-situ monitoring system to detect a first substrate measurement corresponding to a first region among the multiple regions of the substrate; (c) The in-situ monitoring system to detect a second substrate measurement corresponding to a second region among the multiple regions of the substrate; (d) The controller to determine a difference between the first substrate measurement at the first region and the second substrate measurement at the second region; and (e) The controller: In response to determining that the difference between the first substrate measurement and the second substrate measurement is within a tolerance threshold, stop the carrier head from pushing the substrate against the surface of the polishing pad; Or In response to determining that the difference between the first substrate measurement and the second substrate measurement is outside the tolerance threshold, repeat (a) to (d).

2. The apparatus according to claim 1, wherein the controller is configured to detect at least one of the first substrate measurement or the second substrate measurement during the polishing.

3. The apparatus according to claim 1, wherein the first substrate measurement forms part of a first series of measurement values, and the second substrate measurement forms part of a second series of measurement values.

4. The apparatus according to claim 3, wherein the controller is configured to determine a slope of the first or the second series of measurement values.

5. The apparatus according to claim 3, wherein the program instructions executed by the processor are further configured to cause the controller to: Determine that a slope of the first or the second series of measurement values is within a threshold; and Subsequently, determine the difference between the first substrate measurement at the first region and the second substrate measurement by determining a maximum difference between the first substrate measurement and the second substrate measurement.

6. The apparatus according to claim 3, wherein the program instructions executed by the processor are further configured to cause the controller to: Determine that a slope of the first or the second series of measurement values is within a threshold; and Subsequently, determine the difference between the first substrate measurement at the first region and the second substrate measurement by determining a minimum difference between the first substrate measurement and the second substrate measurement.

7. The apparatus according to claim 3, wherein the program instructions executed by the processor are further configured to cause the controller to: Determine that the slope of the first or the second series of measurement values is within a threshold; and Subsequently, determine the difference between the first substrate measurement and the second substrate measurement at the first region by determining the average difference between the first substrate measurement and the second substrate measurement.

8. A method for processing a substrate, the method comprising: Polish the surface of the substrate; Detect a first substrate measurement corresponding to a first region of the substrate; Detect a second substrate measurement corresponding to a second region of the substrate; Determine the difference between the first substrate measurement and the second substrate measurement; And In response to the determined difference being outside a tolerance threshold, provide an indication of the presence of residue at the first region or the second region of the substrate.

9. The method of claim 8, the method further comprising updating a chemical mechanical polishing operation based on the determined difference relative to the tolerance threshold.

10. The method of claim 8, the method further comprising: Detect a third substrate measurement corresponding to the first region of the substrate; Detect a fourth substrate measurement corresponding to the second region; And Based on a comparison of the third substrate measurement and the fourth substrate measurement, provide an indication of the status of the residue at the substrate.

11. The method of claim 10, wherein the third substrate measurement and the fourth substrate measurement are completed after the first substrate measurement and the second substrate measurement, and the time difference between the first and third measurements and the second and fourth measurements corresponds to at least a portion of the time for performing the polishing of the surface of the substrate.

12. The method of claim 10, the method further comprising: Detect a change in the difference with respect to the tolerance threshold; And Based on determining that the difference is within or near the tolerance threshold, reduce the polishing of the surface of the substrate.

13. The method of claim 8, the method further comprising providing an indication of the absence of residue at the substrate in response to the difference being within the tolerance threshold.

14. The method of claim 8, wherein the tolerance threshold is a user input value.

15. The method of claim 8, wherein the tolerance threshold is determined based on a machine learning model.

16. A polishing system, the polishing system comprising: A polishing assembly configured to: (a) Polish the surface of the substrate; A controller configured to: (b) Generate a first series of substrate measurements corresponding to a first region of the substrate; (c) Generate a second series of substrate measurements corresponding to a second region of the substrate; (c) Determine the slope of the first series of substrate measurements over time; (d) Determine the slope of the second series of substrate measurements over time; (e) Determine that the slope of the first series of substrate measurements or the slope of the second series of substrate measurements is within a threshold range; And (f) Determine the difference between the first series of substrate measurements and the second series of substrate measurements; (g) In response to determining that the difference between the first series of substrate measurements and the second series of substrate measurements is within a tolerance threshold, stop the polishing of the surface of the substrate; (h) In response to determining that the first series of substrate measurements and the second series of substrate measurements are outside the tolerance threshold, indicate the presence of residues at the substrate, and update aspects of the polishing operation and repeat (a) to (c) and (f); and (i) In response to determining that the first series of substrate measurements and the second series of substrate measurements cross into the tolerance threshold, indicate the removal of residues from the substrate.

17. The polishing system according to claim 16, wherein the controller is configured to apply an inspection signal while the polishing assembly is polishing the surface of the substrate.

18. The polishing system according to claim 16, wherein the controller is further configured to adjust the polishing time.

19. The polishing system according to claim 16, wherein the controller is further configured to adjust the polishing pressure.

20. The polishing system according to claim 16, wherein the controller is further configured to adjust at least one of the polishing speed, the slurry composition, or the slurry application rate.

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