Subsurface topography metal residue detection and overpolishing strategies

Abstract

An apparatus for processing a substrate, the apparatus comprising: a polishing assembly configured to (a) polish a surface of the substrate; and a controller 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, and (d) determine a difference between the first substrate measurement at the first region and the second substrate measurement at the second region, and to stop polishing the surface of the substrate in response to determining that the difference between the first substrate measurement and the second substrate measurement is within an acceptable threshold, and to repeat steps (a) through (d) in response to determining that the difference between the first substrate measurement and the second substrate measurement is outside the acceptable threshold.

Description

[Technical Field]

[0001]

[0001] Embodiments of the present disclosure generally relate to methods, systems, and apparatus for processing substrates, such as semiconductor substrates. More specifically, an inspection system and method for using the same are disclosed. [Background technology]

[0002]

[0002] Integrated circuits are typically formed on substrates by sequentially depositing conductive, semiconductive, or insulating layers on silicon wafers. One manufacturing step involves depositing a filler layer over a non-planar surface and planarizing the filler layer. In certain applications, the filler layer is planarized until the top surface of a patterned layer is exposed. For example, a conductive filler layer can be deposited over a patterned insulating layer to fill trenches or holes in the insulating layer. After planarization, portions of the conductive layer remaining between the raised pattern of the insulating layer form vias, plugs, and lines, which provide conductive paths between thin-film circuits on the substrate. In other applications, such as oxide polishing, the filler layer is planarized until a predetermined thickness remains on the non-planar surface. Furthermore, planarization of the substrate surface is typically required for photolithography.

[0003] Chemical mechanical polishing (CMP) is a recognized method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is typically placed against a rotating abrasive disk pad or belt pad. The polishing pad can be either a standard pad or a fixed-abrasive pad. Standard pads have a durable rough surface, while fixed-abrasive pads have abrasive particles held in a containment media. The carrier head applies a controllable load to the substrate, pressing it against the polishing pad. Typically, an abrasive slurry is supplied to the surface of the polishing pad. The abrasive slurry contains at least one chemically reactive agent and, when used with standard polishing pads, abrasive particles.

[0004] One of the challenges in CMP is determining whether the polishing process is complete. In other words, determining whether a substrate layer has been planarized to a desired flatness or thickness, or when a desired amount of material has been completely removed from the surface of the substrate. Overpolishing a conductive layer or film (removing too much material) can lead to increased circuit resistance. However, overpolishing is often necessary to remove all of the blanket portions of the conductive layer (e.g., those portions over the field regions of the substrate) and leave only the remaining portions of the conductive layer located within features formed on the surface of the substrate. On the other hand, underpolishing a conductive layer (removing too little material) can lead to electrical shorts between circuits formed on the surface of the substrate due to the remaining blanket portions of the conductive layer. Conventionally, it has been difficult to detect the endpoint of a polishing process (e.g., a point near the end of the polishing process) when the conductive layer becomes discontinuous across the substrate surface. Determining the endpoint of a polishing process is particularly difficult when portions of the blanket film layer are located within recesses formed on the surface of the substrate due to the surface topology of a previously formed underlying layer, resulting in electrical shorts in various regions of the substrate surface. Additionally, variations in the initial thickness of the layer being polished, the composition of the slurry, the condition of the polishing pad, the relative velocity between the polishing pad and the substrate, and the load on the substrate can cause variations in the material removal rate.

[0005]

[0005] Therefore, there is a need in the art for methods, systems, and apparatus that can improve endpoint detection of polishing processes that address the above-mentioned problems and, more specifically, reduce the likelihood of undesirable discontinuities in the polishing film layer remaining on the surface of the substrate after polishing. Summary of the Invention

[0006]

[0006] Embodiments of the present disclosure may provide a method for detecting residue in a substrate, including accepting the substrate for a chemical-mechanical polishing operation, applying a first test signal to the substrate, detecting a first response in response to the first test signal corresponding to a first region of the substrate, detecting a second response in response to the first test signal corresponding to a second region of the substrate, determining a first test signal measurement indicative of a difference between the first response and the second response, and providing an indication of the presence of residue in the substrate in response to the first test signal measurement being outside an acceptable threshold.

[0007]

[0007] Embodiments of the present disclosure may provide a polishing apparatus for processing a substrate. The polishing apparatus includes a polishing pad support, a carrier head configured to hold a substrate and apply one or more independently controllable pressures to multiple regions of the substrate, an in-situ monitoring system that monitors properties of the substrate in the multiple regions during polishing, and a controller. The controller includes computer program instructions stored in a memory. When executed by a processor of the controller, the computer program instructions (a) cause the carrier head to urge the substrate against a surface of a polishing pad positioned on the polishing pad support, where urging the substrate against the surface of the polishing pad includes applying one or more independently controllable pressures to the surface of the substrate; (b) cause the in-situ monitoring system to detect a first substrate measurement corresponding to a first region of the multiple regions of the substrate; and (c) cause the in-situ monitoring system to monitor the properties of the substrate in the multiple regions. (d) detecting a second substrate measurement corresponding to a second region of the regions; (d) causing the controller to determine a difference between the first substrate measurement in the first region and the second substrate measurement in the second region; and (e) causing the controller to either stop the carrier head from urging the substrate against the surface of the polishing pad in response to determining that the difference between the first substrate measurement and the second substrate measurement is within an acceptable threshold, or repeat (a) through (d) in response to determining that the difference between the first substrate measurement and the second substrate measurement is outside the acceptable threshold.

[0008]

[0008] Embodiments of the present disclosure may further provide a polishing system. The polishing system includes a polishing assembly configured to polish a surface of a substrate, and 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 a slope of the first series of substrate measurements or a slope of the second series of substrate measurements within a threshold range; determine a difference between the first series of substrate measurements and the second series of substrate measurements; stop polishing of the surface of the substrate in response to determining that the difference between the first series of substrate measurements and the second series of substrate measurements is within an acceptance threshold; indicate the presence of residue in the substrate and update an aspect of the polishing operation in response to determining that the first series of substrate measurements and the second series of substrate measurements are outside the acceptance threshold;

[0009] Embodiments of the present disclosure may provide a method of processing a substrate, the method including polishing a surface of the substrate, 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 an acceptance threshold, providing an indication of the presence of residue in the first region of the substrate or the second region of the substrate.

[0010]

[0010] Embodiments of the present disclosure may further provide a method that includes urging a substrate against a surface of a polishing pad positioned on a polishing pad support. Forcing the substrate against the surface of the polishing pad includes applying one or more independently controllable pressures to the surface of the substrate. The method may then include detecting a first substrate measurement corresponding to a first region of the plurality of regions of the substrate and detecting a second substrate measurement corresponding to a second region of the plurality of regions of the substrate. The method may then include determining a difference between the first substrate measurement in the first region and the second substrate measurement in the second region, and either causing the carrier head to stop urging the substrate against the surface of the polishing pad in response to determining that the difference between the first substrate measurement and the second substrate measurement is within an acceptable threshold, or repeating steps (a) through (d) in response to determining that the difference between the first substrate measurement and the second substrate measurement is outside the acceptable threshold.

[0011]

[0011] So that the features of the present disclosure as described above may be fully understood, a more particular description of the present disclosure, briefly summarized above, will be had by reference to embodiments of the present disclosure, some of which are illustrated in the accompanying drawings. However, since the present disclosure may admit of other equally effective embodiments, it should be noted that the accompanying drawings illustrate only typical embodiments of the present disclosure and therefore should not be considered as limiting the scope of the present disclosure. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a partially exploded view of a polishing apparatus according to an embodiment of the present disclosure. [Figure 2] 2 is a cross-sectional view of the polishing apparatus of FIG. 1 according to another embodiment of the present disclosure. [Figure 3] FIG. 10 is a top view of a polishing apparatus according to another embodiment of the present disclosure. [Figure 4] FIG. 10 is a cross-sectional view of a detection element according to another embodiment of the present disclosure. [Figure 5A-D] 1 is a cross-sectional view of a sensing element during a polishing operation according to an embodiment of the present disclosure. [Figure 6A-C]4 shows responses to test signals from corresponding areas of a substrate according to an embodiment of the present disclosure. [Figure 7] 10 is a method for detecting residue on a substrate according to another embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013]

[0019] For ease of understanding, wherever possible, the same reference numerals have been used to designate identical elements common to the figures. Furthermore, elements of one embodiment may be advantageously adapted for use in other embodiments described herein.

[0014]

[0020] A method for detecting residues on a substrate, as well as systems and apparatus for performing the method, is provided. The method includes accepting a substrate for a chemical mechanical polishing operation. The method further includes applying a first test signal to the substrate. The method further includes detecting a first response corresponding to a first region of the substrate in response to the first test signal. The method further includes detecting a second response corresponding to a second region of the substrate in response to the first test signal. The method further includes determining a first test signal measurement indicative of a difference between the first response and the second response. The method further includes providing an indication of the presence of residues on the substrate in response to the first test signal measurement being outside an acceptable threshold.

[0015]

[0021] 1 is a partially exploded view of a polishing apparatus according to one embodiment of the present disclosure. In some embodiments, one or more substrates 10 may be polished by a chemical mechanical polishing (CMP) apparatus 20. The polishing apparatus 20 may include a series of polishing stations 22 a, 22 b, and 22 c, and a transfer station 23. The transfer station 23 may be configured to transfer the substrates 10 between a carrier head and a loading apparatus.

[0016]

[0022] Each polishing station includes a rotatable platen 24 on which a polishing pad 30 is positioned. The first and second polishing stations 22a and 22b may include a two-layer polishing pad with a hard, durable outer surface or a fixed-type polishing pad with embedded abrasive particles. The final polishing station 22c may include a relatively soft pad or a two-layer pad. Each polishing station may further include a pad conditioner device 28 to maintain the condition of the polishing pad so that it can effectively polish substrates.

[0017]

[0023] 2 is a cross-sectional view of the polishing apparatus of FIG. 1 according to another embodiment of the present disclosure. In some embodiments, a two-layer polishing pad 30 can include a backing layer 32 that can abut the surface of the platen 24 and a cover layer 34 that is used to polish the substrate 10.

[0018]

[0024] During the polishing operation, a polishing liquid 38 (e.g., a polishing slurry or an abrasive-free solution) can 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 can be used at the first and second polishing stations, while a different slurry solution can be used at the third polishing station.

[0019]

[0025] Returning to FIG. 1 , a rotatable multi-head carousel 60 supports four carrier heads 70. The carousel is rotated about a carousel axis 64 by a central post 62 to orbit carrier head systems and substrates mounted thereon between polishing stations 22 a-22 c and transfer station 23. Three of the carrier head systems can receive and hold substrates and polish them by pressing them against a polishing pad. In some embodiments, one of the carrier head systems delivers polished substrates to transfer station 23 and receives unpolished substrates from transfer station 23.

[0020]

[0026] Each carrier head 70 is connected to a carrier head rotation motor 76 (shown with cover 68 partially removed) by a carrier drive shaft 74, allowing each carrier head to rotate independently about its own axis. Each carrier head 70 can swing independently laterally within a radial slot 72 formed in carousel 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.

[0021]

[0027] In some embodiments, uniform pressure can be applied to the substrate. In other embodiments, variable pressure can be applied to different portions or regions of the substrate. As seen in FIGS. 2 and 3, the carrier head 70 can independently apply different pressures to different radial regions of the substrate. For example, the carrier head can include a mechanical or electromechanical element (e.g., a flexible membrane having a substrate receiving surface) and three independently pressurizable concentric chambers 50, 52, 54 behind the membrane. Thus, the inner annular chamber 50 can apply pressure to the inner annular 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. One or more of these regions can be seen in FIG. 3.

[0022]

[0028] In some embodiments, a recess 26 is formed in the platen 24, and a transparent portion 36 is formed in the polishing pad 30 covering the recess 26. The transparent portion 36 may be electromagnetically transparent, optically transparent, or the like. This portion 36 can be positioned to pass under the substrate 10 during a portion of the platen's rotation, regardless of the translational position of the carrier head. Assuming the polishing pad 30 is a two-layer pad, the transparent portion 36 can be constructed by cutting an opening in the backing layer 32 and replacing a portion of the cover layer 34 with a transparent plug. The plug may be a relatively pure polymer or polyurethane (e.g., formed without a filler). Generally, it is desirable that the material of the transparent portion 36 be nonmagnetic and nonconductive. Additionally, the system may include a transparent cover, e.g., made of glass or hard plastic, positioned over the recess 26 but below the polishing pad (the top surface of the cover may be flush with the top surface of the platen 24). In this case, the core of the eddy current sensor may extend through the cover and protrude partially into the polishing pad, or may be located completely below the cover (see FIG. 4).

[0023]

[0029] 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 (e.g., an eddy current monitoring system). The detection element can function as a polishing process control and endpoint detection system. The first polishing station 22a may include a single detection element, and the final polishing station 22c may include another detection element and / or optical or other detection element.

[0024]

[0030] The CMP apparatus 20 further includes a controller 90 having a programmable central processing unit (CPU) operable with memory (e.g., non-volatile memory) and support circuits. The support circuits traditionally include cache, clock circuits, input / output subsystems, power supplies, etc. (and combinations thereof) coupled to the CPU and to its various components to facilitate control of the CMP apparatus 20. The CPU is any form of general-purpose computer processor used in industrial settings to control the various components and sub-processors of a processing system, such as a programmable logic controller (PLC). The memory coupled to the CPU is non-transitory and typically is one or more readily available memories, such as random access memory (RAM), read-only memory (ROM), a floppy disk drive, a hard disk, or any other form of local or remote digital storage. Typically, the memory contains computer program instructions that, when executed by the CPU, facilitate 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, that implements the methods of the present disclosure. The program instructions may conform to any one 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 functions of embodiments (including the methods described herein). Software instructions and data for instructing a CPU may be coded and stored in memory. The program instructions, readable by a processing unit in a system controller, determine which tasks are executable within the processing system. For example, a non-transitory computer-readable medium may include a program product that, when executed by a processing unit, is configured to perform one or more of the methods described herein. Preferably, the program instructions include code for performing tasks related to monitoring, executing, and controlling measurement, fluid delivery, polishing hardware, and substrate movement, along with various process recipe tasks.

[0025]

[0031] 3 is a top view of a polishing apparatus according to another embodiment of the present disclosure. In some embodiments, the sensor assembly of the monitoring system is embedded within the platen and sweeps under the substrate 10 with each rotation of the platen. Data can be collected from the sensing elements 40 as the sensor assembly sweeps under the substrate. In particular, as the sensor assembly sweeps a path 96 across the substrate, the monitoring system takes a series of measurements 98 (e.g., 15 shown). Each measurement 98 can be associated with a radial position or radial region on the substrate surface, which is generated and defined using endpoint detection software running on the controller 90.

[0026]

[0032] The sensing element 40 induces and senses eddy currents in a conductive (e.g., metal) layer on the substrate and provides a signal indicative of the measurement to a controller 90. The sensor assembly for the sensing element 40 includes a core 42 positioned within the recess 26 to rotate with the platen, and a coil 44 wound around the core 42. The coil 44 is connected to a control system. The control system may be local or remote, in whole or in part, to the recess 26. For example, the control system may include a printed circuit board 58 inside the recess 26. A controller 90, such as a computer, may be coupled to components within the platen, including the printed circuit board 58, via a rotary electrical coupling 92.

[0027]

[0033] FIG. 4 is a cross-sectional view of a sensing element according to another embodiment of the present disclosure. In some embodiments, the core 42 can be a U- or E-shaped body formed of a non-conductive material with a relatively high magnetic permeability. The exact winding configuration, core configuration and shape, and capacitor size can be determined experimentally. As shown, the bottom surface of the transparent portion 36 can include two rectangular recesses 29. Two protrusions 42a and 42b of the core 42 can extend into the recesses to be positioned closer to the substrate.

[0028]

[0034] In some embodiments, an oscillator within the controller 90 oscillates the coil 44, generating an oscillating magnetic field 48 that extends through the body of the core 42 into the gap 46 between the core's two protrusions 42a and 42b. At least a portion of the magnetic field 48 extends through the polishing pad 30 and into the substrate 10. If a metal layer 16 is present 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 coupled to a sensing circuit within or in communication with the controller 90. A change in the thickness of the metal layer results in a change in impedance. By detecting this change, the eddy current sensor can sense changes in the strength of the eddy currents, and therefore, the thickness of the metal layer 16.

[0029]

[0035] As shown in FIGS. 5A and 5B, for a polishing operation, a substrate 10 is placed in contact with a polishing pad 30. The substrate 10 may include a silicon wafer 12 and a conductive layer 16 (e.g., a metal such as copper or titanium) disposed on one or more patterned underlayers 14, which may be semiconductor, conductive, or insulator layers. A barrier layer 18, such as tantalum or tantalum nitride, may separate the metal layer from the underlying patterned layer. In some cases, the conductive layer may contain defects in the form of residue or residue 502 structures. The residue may be a collection of defects in the underlying layer due to inconsistent or defective topography of the underlying layer. In the illustrated embodiment, the residue 502 is formed of conductive material from the conductive layer 16 due to underlying topographical challenges at the surface of the substrate where the barrier layer 18 is disposed. In some embodiments, the residue 502 may extend into the underlying layer 14, resulting in the formation of undesirable conductive regions in the underlying layer 14.

[0030]

[0036] After polishing, the portions of the metal layer remaining between the underlying patterns formed on the substrate result in metal features (e.g., vias, pads, and interconnects). However, as shown in FIG. 5A, the bulk of the conductive layer 16 before polishing is initially relatively thick and continuous across the field region of the substrate, with low resistivity, which can generate relatively strong eddy currents within the conductive layer 16. As previously mentioned, the eddy currents cause the metal layer to act as an impedance source in parallel with the coil 44. The coil 44 is used to detect the presence of the conductive layer 16.

[0031]

[0037] As shown in Figure 5B, when substrate 10 is polished, the bulk of conductive layer 16 becomes thinner. As conductive layer 16 becomes thinner, its sheet resistance increases, and eddy currents within the metal layer decay. As a result, the coupling between metal layer 16 and the sensor becomes weaker (i.e., the resistivity of the virtual impedance source increases), and the detected impedance increases.

[0032]

[0038] 5C, the bulk portion of conductive layer 16 is eventually removed, exposing barrier layer 18, leaving conductive interconnects 16' in the trenches between patterned insulating layer 14, and conductive layer remnants 502 remaining between the conductive interconnects. At this point, the coupling between the conductive portion of the substrate and the sensor, which is generally small and generally discontinuous, is reached to a minimum, except for remnants 502, which may result in stronger eddy current signals and measurements.

[0033]

[0039] 2, sensing element 40 may be positioned within recess 26 of platen 24. Sensing element 40 may measure eddy currents across a portion of the substrate as platen 24 rotates and substrate 10 moves across the surface of rotatable platen 24. In particular, sensing element 40 is configured to measure a portion of the substrate that is a radial distance from the axis of rotation of platen 24. The measurements are then related to the corresponding portion of substrate 10.

[0034]

[0040] 2 and 3, the CMP apparatus 20 may further include a position sensor 80 (e.g., an opto-isolator) for sensing when the core 42 is below the substrate 10. For example, the opto-isolator may be mounted at a fixed point opposite the carrier head 70. A flag 82 may be attached to the periphery of the platen. The attachment position and length of the flag 82 are selected so that the flag 82 blocks the optical signal from the sensor 80 while the transparent portion 36 sweeps below the substrate 10. Alternatively, the CMP apparatus may include an encoder that determines the angular position of the platen. Data corresponding to the relative positions of the sensing element 40 and the substrate 10 can be used to determine which portion of the substrate 10 (e.g., radial area) is associated with the measurement generated by the sensing element 40 for each pass relative to the substrate.

[0035]

[0041] A controller 90 receives signals from the sensing elements. Because the sensor assembly can sweep under the substrate with each platen rotation, information regarding the thickness of the metal layer and the exposure of the underlying layer is accumulated in situ (once per platen rotation) on a continuous, real-time basis. As the substrate passes over the sensor 80, the controller 90 is programmed to take sample measurements from the monitoring system. As polishing progresses, the endpoint detection indicators for the metal layer change, and the sampled signal varies over time. The sampled signal that varies over time can be referred to as a trace, as shown in Figures 6A-6C. During polishing, measurements from the monitoring system can be displayed on an output device 94, allowing an operator of the device to visually monitor the progress of the polishing operation. Furthermore, as described below, the trace can be used to control the polishing process and determine the endpoint of the metal layer polishing operation.

[0036]

[0042] In operation, CMP apparatus 20 uses sensing element 40 to determine when the bulk of the conductive and barrier layers have been removed and when the underlying patterned insulating layer is substantially exposed without significant residue. Controller 90 applies process control and endpoint detection logic to the sampled signals to determine when to change process parameters and to detect the polishing endpoint.

[0037]

[0043] 6A illustrates responses to test signals from corresponding regions of a substrate according to an embodiment of the present disclosure. Figure 6A includes traces 602a, 602b, and 602c corresponding to the responses to the test signals at various regions of the substrate. For example, trace 602a may correspond to inner annular region 50a of the substrate (shown in FIG. 3), trace 602b may correspond to middle annular region 52a, and trace 602c may correspond to outer annular region 54a.

[0038]

[0044] In some embodiments, the controller applies box logic to identify trends in the traces using separation boxes 604a-c. Separation boxes 604a-c are generated in real time for each of the traces to determine the convergence of the traces. For example, the box logic may be an algorithm running on the controller 90 and applied to determine the slope trends of the traces 602a-c and identify a steady state indicative of reduced polishing effectiveness. The algorithm may be applied over a specific period of time, or, as shown, may be indicated when a target threshold (e.g., slope value or trend, relative change in slope, etc.) is met. When the target threshold is reached, the algorithm may trigger an analysis of the traces for convergence. In some embodiments, one or more of the traces may reach a target threshold indicative of a relatively steady state, while another of the traces does not. Polishing may continue until the other trace reaches the target threshold. This target threshold is related to the characteristics 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 given moment. In one example, the slope of a trace at the moment it reaches the threshold may exit a horizontally oriented box through a vertical edge or through the bottom edge of the box, as shown in FIGS. 6A-6C. When two or more of the traces satisfy the box logic for reaching the target threshold, 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 difference 606 between the traces at any point 608 after the box logic threshold is determined to be 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 mean deviation of the traces, or other comparative analysis can be applied. In the illustrated embodiment shown in FIG. 6A, the difference 606 can be within an acceptable threshold indicating the substrate is sufficiently clear of residue. In some embodiments, convergence measurements are performed continuously during overpolishing or other operations until traces 602a-c reach target convergence.In other embodiments, the overpolishing or other operation may be performed for a dynamic amount of time calculated based on the difference required to reach convergence, or for a fixed amount of time stored in the memory of the controller 90 after a box logic threshold is deemed met.

[0039]

[0045] In some embodiments, the tolerance threshold is a value below which the difference between the traces is sufficient to indicate the absence of residue on the substrate, and above which the difference is sufficient to indicate the presence of residue on the substrate. For example, the difference may be visually equivalent to a particular gap between one or more of traces 602a-c and another trace. As seen in FIG. 6A , the traces do not overlap, but the difference 606 may be small enough to fall within the tolerance threshold. Convergence indicates that measurements from eddy current measurements or other inspection techniques have reached a level where at least two or more regions of the substrate 10 have similar amounts of conductive features on the substrate's surface. Thus, convergence can be used to indicate that neither region contains anomalies such as subsurface residue. The tolerance threshold, stored in memory, may be provided manually or determined by machine learning, big data analysis, or other automated approaches. The tolerance threshold may be fixed or adjustable by batch, build, and / or other parameters.

[0040]

[0046] 6B illustrates an embodiment in which traces 602a-c are not within the tolerance threshold at a first time 608a because difference 606a is greater than a threshold stored in memory. Therefore, updating the polishing operation may indicate additional polishing time, a change in slurry application rate, material, polishing pressure, or other aspects of the polishing operation. At a second time 608b, it may be determined that convergence of the traces indicates successful removal of residual material and that no residue is present on the surface of the substrate that would require updating the polishing operation to remove any underlying residue.

[0041]

[0047] FIG. 6C illustrates an embodiment in which the traces show a first difference 606a that is not within the tolerance threshold at a first time 608a. At a second time 608b, a second difference 606b is outside the tolerance threshold. The relative behavior of this trend indicates the presence of residue in the region of the substrate corresponding to the first trace 602a. Although three distinct traces are shown, two or more traces may be used to perform the analysis. In the illustrated embodiment, an over-polishing operation may be performed to reduce residue on the substrate. In some embodiments, a notification indicating the detection of residue on the substrate may be sent to an operator or other part of the system. Further analysis may be performed at a subsequent time to determine the slope, convergence, range, or other absolute or relative characteristics of the traces. Polishing operation updates may be performed to reduce residue, reduce overall yield loss, and improve efficiency.

[0042]

[0048] Returning to FIG. 2, in response to detecting a difference outside an acceptable threshold as shown in FIG. 6C, the controller 90 can be programmed to divide the measurements from the sensing element 40 from each sweep below the substrate into multiple measurement regions 98, calculate a radial position on the substrate for each region, sort the measurements into multiple radial regions, determine minimum, maximum, and average measurement values ​​for each region, and use the multiple radial regions to determine the polishing endpoint.

[0043]

[0049] The controller 90 may further be coupled to a pressure generating mechanism (e.g., a gas supply) that controls the pressure applied to the substrate by the flexible membrane of the carrier head 70, a carrier head rotation motor 76 that controls the carrier head rotation speed, a platen rotation motor (not shown) that controls the platen rotation speed, or a slurry distribution system 39 for controlling the slurry composition supplied to the polishing pad. For example, the controller may determine that the endpoint criterion is met for the outer radial region but not for the inner radial region. This indicates that the underlayer has been removed of residue in the annular outer region of the substrate but not in the inner region. In this case, the controller is configured to update the polishing operation.

[0044]

[0050] Returning to FIG. 5D, continued polishing and / or renewed polishing operations reduce the residue 502, sufficiently exposing the underlying insulating layer 14 and leaving conductive interconnects 16′ and buried barrier layer film 18′ in the trenches between the patterned insulating layer 14.

[0045]

[0051] 7 is a flowchart of a method 700 according to an embodiment of the method described herein. The method 700 begins with operation 702, in which a surface of a substrate 10 is subjected to chemical mechanical polishing, as shown in FIG. 2 . The process of chemical mechanical polishing the surface of the substrate 10 includes using a carrier head 70 to hold the substrate 10 thereon, and using the independently pressurizable chambers 50, 52, and 54 behind the membrane to apply one or more independently controllable pressures to multiple regions of the substrate 10 to urge the surface of the substrate 10 against the surface of the polishing pad 30, thereby performing a polishing process on the surface of the substrate 10. Operation 702 further includes rotating the polishing pad 30, rotating the carrier head 70, providing translational relative motion between the carrier head 70 and the polishing pad 30, and providing a slurry composition to the polishing pad surface during the chemical mechanical polishing process.

[0046]

[0052] 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 a central, inner, or outer region of the substrate. The first substrate measurement may be a response to an eddy current sensor or other sensing element 40 as the eddy current sensor or other sensing element 40 passes near the substrate, as shown in FIG. 3 . The first substrate measurement corresponds to the first region of the substrate. In one example, the first substrate measurement may be a response to an eddy current sensor signal detected in response to application of a first test signal applied within a first region on the surface of the substrate (e.g., a measurement within an outer radial region of the substrate). The outer radial region may extend between a first radius R1 of the substrate and an outer edge of a circular substrate. The first substrate measurement may be recorded as part of a trace including a series of detected measurements at various times for a first defined region of the substrate (i.e., the outer region), such as trace 602a, as shown in FIGS. 6A-C .

[0047]

[0053] 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 applying a second test signal. The second substrate measurement corresponds to a second region of the surface of the substrate, such as a measurement within a mid-radius region of the substrate. In one example, the mid-radius region can extend between a first radius R1 and a second radius R2 of the substrate, where the second radius R2 is smaller than the first radius R1. For example, the second response can be a response from a central portion of the substrate detected by the sensing element 40 as the sensing element 40 passes near the central region of the substrate, as shown in FIG. 3. The second response can be recorded as part of a trace including a series of detected signals measured at various times for a second defined region of the substrate (e.g., the mid-region), such as trace 602b, as shown in FIGS. 6A-C.

[0048]

[0054] Optionally, additional measurement operations may be performed between operations 706 and 708, although these will not be described further below for ease of explanation. For example, the third substrate measurement may be a response to an eddy current sensor signal detected in response to applying a third test signal. The third substrate measurement may correspond to a third region of the surface of the substrate, such as a measurement within an inner radial region of the substrate. In one example, the inner radial region may extend between the center of the substrate and the second radius R2 of the substrate. For example, the third response may be a response from the inner region of the substrate detected by the sensing element 40 as the sensing element 40 passes near the inner region of the substrate, as shown in FIG. 3 . The third response may be recorded as part of a trace including a series of detected signals measured at various times for a third defined region (e.g., the inner region) of the substrate, such as trace 602c, as shown in FIGS. 6A-C .

[0049]

[0055] In operation 708, a difference of the first substrate measurement relative to the second substrate measurement is determined. In some embodiments, the difference of the first substrate measurement relative to the second substrate measurement is performed after it is determined that a characteristic of one or more traces has reached a threshold. As shown in FIG. 7, the operation of determining that a characteristic of one or more traces has reached a threshold is performed during operation 707. For example, a change in the characteristic of each trace, such as traces 602a and 602b, may be analyzed to determine whether the characteristic of the trace has met a threshold. In some embodiments, the characteristic of each trace (i.e., a series of measurements) that is evaluated is a value or trend of slope, a change in slope, or other characteristic of the trace. In some embodiments, box logic may be applied to identify slopes or changes in slope that meet a threshold range or target value or slope behavior. In some examples, as illustrated for the right-most trace 602a in FIG. 6A, the slope may be evaluated to determine a dip or trend toward steady state or other behavior (e.g., the slope of the trace is near or approaching zero).

[0050]

[0056] In one embodiment, during operation 708, an algorithm executed by the processor in the controller 90 is used to compare the first trace 602a and the second trace 602b at time 608 to determine a relative difference 606 between the first and second traces after a characteristic of at least one of the traces 602a, 602b meets some threshold, as shown in FIGS. 6A-C. The algorithm used to determine the difference of the first substrate measurement relative to the second substrate measurement may be automatically triggered by the analysis of at least one characteristic of the traces performed in operation 707. In one embodiment, once the first and second traces meet the box logic for reaching a target threshold, a difference (e.g., convergence) of the first substrate measurement relative to the second substrate measurement is performed. The determination of the difference 606 at time 608 may be based on values ​​of signals provided by sensors in various regions on the substrate forming the traces, as shown in FIGS. 6A-C.

[0051]

[0057] In operation 710, the controller 90 then, in response to the difference 606 determined in operation 708 being outside a tolerance threshold stored in the memory of the controller 90, uses the determined difference as an indication of the presence of residue in the first region of the substrate or the second region of the substrate. For example, residue 502 may be accumulated inclusions resulting from anomalies in the underlying topography, as shown in FIGS. 5A-C. The resulting residue may increase the eddy current response (i.e., the detected eddy current signal), resulting in a difference in signal level between corresponding traces. Determining the difference between the traces may enable identification of corresponding regions where residue is located. For example, measurements from a third region may be compared with measurements corresponding to the first and second regions to determine which of the first, second, or third regions may be affected by residue. In one example, trace 602a has a much higher eddy current signal than traces 602b and 602c on the right side of the graph. This difference may lead the controller 90 to conclude that the area forming the trace 602a contains some residue, or at least a certain amount of residue, that exceeds other areas 602b and 602c on the substrate.

[0052]

[0058] Operation 710 may include repeating operations 702-708 by updating the chemical-mechanical polishing process based on the difference from the tolerance threshold determined during operation 708. For example, because the difference is outside the tolerance threshold, additional polishing may be helpful to make the traces more consistent. The update may include at least one of increasing the polishing time, the pressure applied to one or more regions of the flexible membrane of the polishing head, changing the polishing slurry composition, the slurry supply rate, the polishing head rotation speed, the platen rotation speed, etc. In some embodiments, the update to the polishing operation may constitute overpolishing based on the difference from the tolerance threshold. For example, if the difference is significantly outside the tolerance threshold, the controller 90 may call for more aggressive overpolishing (e.g., higher flexible membrane pressure, carrier head rotation speed, etc.) or a longer overpolishing time. If the difference is closer to the tolerance threshold, a gentler overpolishing may be required. Overpolishing may be used to remove excess material and residue on the substrate, as shown in FIGS. 5A-D.

[0053]

[0059] If the determined difference performed in operation 708 is outside a desired threshold, operations 702-708 of method 700 may be performed one or more times. Operations 702-708 of method 700 may be performed until the detected residue is sufficiently reduced in the corresponding region of the substrate.

[0054]

[0060] Operations 702-708 of method 700 may be performed one or more additional times to verify that the previously generated results remain within the desired threshold at subsequent times, even if the determined difference performed in operation 708 is within the desired threshold.

[0055]

[0061] In operation 712, in response to the difference determined during operation 708 being within an acceptable threshold, an indication of the absence of residue on the substrate is provided. For example, if the difference in the traces is determined to be sufficiently low or the traces have a trend toward lower difference over time (see FIG. 6B ), the controller may indicate the absence of residue and make a corresponding update that stops or completes the polishing operation, or alternatively, reduces or otherwise adjusts the polishing operation accordingly. If the difference is within an acceptable threshold, method 700 may require an endpoint of the polishing process as part of operation 712.

[0056]

[0062] Embodiments of the present disclosure provide process yield improvement through residue identification and reduction during polishing operations. Since there is a direct correlation between residue detection and process yield reduction, increased residue reduction translates into process yield improvement.

[0057]

[0063] While the above description is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, the scope of which is determined by the claims that follow.

Claims

1. 1. A polishing apparatus for processing a substrate, comprising: a polishing pad support; a carrier head configured to hold a substrate and apply one or more independently controllable pressures to multiple regions of the substrate; an in-situ monitoring system that monitors properties of the substrate in the plurality of regions during polishing; and a controller including computer program instructions stored in memory; wherein the computer program instructions, when executed by a processor of the controller, (a) causing the carrier head to urge the substrate against a surface of a polishing pad positioned on the polishing pad support, wherein urging the substrate against the surface of the polishing pad comprises applying the one or more independently controllable pressures to the surface of the substrate; (b) causing the in-situ monitoring system to detect a first substrate measurement corresponding to a first region of the plurality of regions of the substrate; (c) causing the in-situ monitoring system to detect a second substrate measurement corresponding to a second region of the plurality of regions of the substrate; (d) causing the controller to determine a difference between the first substrate measurement in the first region and the second substrate measurement in the second region; (e) the controller: in response to determining that a difference between the first substrate measurement and the second substrate measurement is within an acceptable threshold, ceasing the carrier head from biasing the substrate against the surface of the polishing pad; or and (d) repeating (a) through (d) in response to determining that a difference between the first substrate measurement and the second substrate measurement is outside an acceptable threshold. A polishing apparatus for processing a substrate.

2. The apparatus of 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 of claim 1 , wherein the first substrate measurement forms part of a first series of measurements and the second substrate measurement forms part of a second series of measurements.

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

5. The program instructions executed by the processor may cause the controller to: determining that a slope of the first series of measurements or the second series of measurements is within a threshold; then determining a difference between the first substrate measurement and the second substrate measurement in the first region by determining a maximum difference between the first substrate measurement and the second substrate measurement; The apparatus of claim 3 , further configured to cause the execution of:

6. The program instructions executed by the processor may cause the controller to: determining that a slope of the first series of measurements or the second series of measurements is within a threshold; then determining a difference between the first substrate measurement and the second substrate measurement in the first region by determining a minimum difference between the first substrate measurement and the second substrate measurement; The apparatus of claim 3 , further configured to cause the execution of:

7. The program instructions executed by the processor may cause the controller to: determining that a slope of the first series of measurements or the second series of measurements is within a threshold; then determining a difference between the first substrate measurement and the second substrate measurement in the first region by determining an average difference between the first substrate measurement and the second substrate measurement; The apparatus of claim 3 , further configured to cause the execution of:

8. 1. A method of processing a substrate, comprising: Polishing the surface of the substrate; 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 an acceptable threshold, providing an indication of the presence of residue in the first region of the substrate or the second region of the substrate. A method comprising:

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

10. Detecting a third substrate measurement corresponding to the first region of the substrate; and Detecting a fourth substrate measurement corresponding to the second region; and providing an indication of the residue condition on the substrate based on a comparison of the third substrate measurement and the fourth substrate measurement; and The method of claim 8 further comprising:

11. 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 a time difference between the first and third measurements and the second and fourth measurements corresponds to at least a portion of a time during which polishing of the surface of the substrate is performed.

12. detecting a change in the difference relative to the tolerance threshold; reducing polishing of the surface of the substrate based on a determination that the difference is within or approaching the tolerance threshold. The method of claim 10 further comprising:

13. The method of claim 8 , comprising providing an indication of an absence of the residue on 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-entered value.

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

16. 1. A polishing system comprising: (a) configured to polish a surface of a substrate; a polishing assembly; (b) generating a first series of substrate measurements corresponding to a first region of the substrate; (c) generating a second series of substrate measurements corresponding to a second region of the substrate; (c) determining a slope of the first series of substrate measurements over time; (d) determining a slope of the second series of substrate measurements over time; (e) determining 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; (f) determining a difference between the first series of substrate measurements and the second series of substrate measurements; (g) stopping polishing of the surface of the substrate in response to determining that the difference between the first series of substrate measurements and the second series of substrate measurements is within an acceptable threshold; (h) in response to determining that the first series of substrate measurements and the second series of substrate measurements are outside of an acceptable threshold, indicating the presence of residue on the substrate, updating aspects of the polishing operation, and repeating (a)-(c) and (f); (i) configured to indicate removal of the residue from the substrate in response to determining that the first series of substrate measurements and the second series of substrate measurements fall within the tolerance threshold. controller A polishing system comprising:

17. 17. The polishing system of 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 of claim 16 , wherein the controller is further configured to adjust a polishing time.

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

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

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