Patent Application
20240165768
Examples of the present disclosure generally relate to methods, systems, and apparatuses for processing substrates, such as semiconductor substrates. More particularly, an inspection system and methods for use thereof, are disclosed.
An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive, or insulative layers on a silicon wafer. One fabrication step involves depositing a filler layer over a non-planar surface and planarizing the filler layer. For certain applications, the filler layer is planarized until the top surface of a patterned layer is exposed. A conductive filler layer, for example, can be deposited on a patterned insulative layer to fill the trenches or holes in the insulative layer. After planarization, the portions of the conductive layer remaining between the raised pattern of the insulative 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 is left over the non-planar surface. In addition, planarization of the substrate surface is usually required for photolithography.
Chemical mechanical polishing (CMP) is one accepted 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 polishing disk pad or belt pad. The polishing pad can be either a standard pad or a fixed abrasive pad. A standard pad has a durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. The carrier head provides a controllable load on the substrate to push it against the polishing pad. A polishing slurry is typically supplied to the surface of the polishing pad. The polishing slurry includes at least one chemically reactive agent and, if used with a standard polishing pad, abrasive particles.
One problem in CMP is determining whether the polishing process is complete. In other words, 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 (removing too much material) of a conductive layer or film leads to increased circuit resistance. However, overpolishing is often necessary to assure that all of a blanket portion of a conductive layer (e.g., portion over the field region of the substrate) has been removed and only the remaining portions of the conductive layer disposed within the features formed in the surface of the substrate remain. On the other hand, underpolishing (removing too little material) of a conductive layer leads to electrical shorts between the circuits formed on the surface of the substrate due to the presence of the remaining portion of the blanket portion of the conductive layer. Traditionally, it is hard to detect an endpoint of a polishing process when the conductive layer becomes discontinuous across the surface of the substrate, such as a point in the polishing process near the end of the process. Determining an endpoint of a polishing process becomes especially hard where a portion of the blanket film layer is disposed within recesses formed in the surface of the substrate due to prior formed underlying layer surface topology, and thus the remaining portions of a conductive layer form electrical shorts in various regions of the substrate surface. Moreover, variations in the initial thickness of the layer that is to be polished, the slurry composition, the polishing pad condition, the relative speed between the polishing pad and the substrate, and the load on the substrate can cause variations in the material removal rate.
Therefore, there is a need in the art for methods, systems, and apparatuses that improve detection of an endpoint of a polishing process that solves the problems described above, and, more specifically, is able to reduce the likelihood that undesirable discontinuous portions of a polished film layer remain on the surface of the substrate after polishing.
Embodiments of the disclosure may provide a method for detecting a residue at a substrate, wherein detecting a residue at the substrate comprises receiving a substrate for chemical mechanical polishing; applying a first test signal to the substrate; detecting, in response to the first test signal, a first response corresponding to a first region of the substrate; detecting, in response to the first test signal, a second response corresponding to a second region of the substrate; determining a first test signal measure indicative of a difference in the first response relative to the second response; and providing an indication of a presence of the residue at the substrate in response to the first test signal measure being outside of a tolerance threshold.
Embodiments of the disclosure may provide 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 a plurality of regions of the substrate, an in-situ monitoring system to monitor a characteristic of substrate within the plurality of regions during polishing, and a controller. The controller includes computer program instructions that are stored in memory, which when executed by a processor of the controller cause: (a) 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 a polishing pad includes applying the one or more independently controllable pressures to a surface of the substrate; (b) 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) 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) 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 to either: stop the carrier head from urging the substrate against a surface of a polishing pad in response to a determination that the difference between the first substrate measurement and the second substrate measurement is within a tolerance threshold; or repeat (a)-(d) in response to a determination that the difference between the first substrate measurement and the second substrate measurement is outside of the tolerance threshold.
Embodiments of the disclosure may also provide a polishing system, comprising a polishing assembly configured to polish a surface of a substrate; a controller configured to generate a first series of substrate measurements corresponding with a first region of the substrate, generate a second series of substrate measurements corresponding with 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 stop the polishing of the surface of the substrate in response to a determination that the difference between the first series of substrate measurements and the second series of substrate measurements is within a tolerance threshold; indicate a presence of a residue at the substrate in response to a determination that the first series of substrate measurements and the second series of substrate measurements is outside the tolerance threshold and update an aspect of the polishing operation and repeating (a)-(c) and (f); and indicate a removal of the residue from the substrate in response to a determination that the first series of substrate measurements and the second series of substrate measurements cross into the tolerance threshold.
Embodiments of the disclosure may also provide a method for processing a substrate, the method comprising: polishing a surface of a 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 in the first substrate measurement relative to the second substrate measurement; and providing an indication of a presence of a residue at the first region of the substrate or the second region of the substrate in response to the determined difference being outside of a tolerance threshold.
Embodiments of the disclosure may also provide a method that includes urging a substrate against a surface of a polishing pad positioned on a polishing pad support, wherein urging the substrate against the surface of a polishing pad includes applying the one or more independently controllable pressures to a surface of the substrate. Then 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. Then determining a difference between the first substrate measurement at the first region and the second substrate measurement at the second region, and then either: stoping the carrier head from urging the substrate against a surface of a polishing pad in response to a determination that the difference between the first substrate measurement and the second substrate measurement is within a tolerance threshold; or repeat (a)-(d) in response to a determination that the difference between the first substrate measurement and the second substrate measurement is outside of the tolerance threshold.
So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to aspects of the disclosure, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical aspects of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective aspects.
To facilitate understanding, identical reference numerals have been used, wherever possible, to designate identical elements that are common to the Figures. Additionally, elements of one example may be advantageously adapted for utilization in other examples described herein.
A method for detecting a residue at a substrate and systems and apparatuses for performing the method, which 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, in response to the first test signal, a first response corresponding to a first region of the substrate. The method also includes detecting, in response to the first test signal, a second response corresponding to a second region of the substrate. The method also includes determining a first test signal measure indicative of a difference in the first response relative to the second response. The method also includes providing an indication of a presence of the residue at the substrate in response to the first test signal measure being outside of a tolerance threshold.
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 can include a two-layer polishing pad with a hard durable outer surface or a fixed-abrasive pad with embedded abrasive particles. The final polishing station 22c can include a relatively soft pad or a two-layer pad. Each polishing station can also include a pad conditioner apparatus 28 to maintain the condition of the polishing pad so that it will effectively polish substrates.
During a polishing operation, a polishing liquid 38, such as an abrasive slurry or abrasive-free solution can be supplied to the surface of the polishing pad 30 by a slurry supply port or combined slurry/rinse arm 39. The same slurry solution may be used at the first and second polishing stations, whereas another slurry solution may be used at the third polishing station.
Returning to
Each carrier head 70 is connected by a carrier drive shaft 74 to a carrier head rotation motor 76 (shown by the removal of a portion of cover 68) so that each carrier head can independently rotate about its own axis. Each carrier head 70 may independently laterally oscillate in a radial slot 72 formed in carousel support plate 66. In operation, the platen is rotated about its central axis, and the carrier head is rotated about its central axis and translated laterally across the surface of the polishing pad.
In some embodiments, a uniform pressure may be applied to the substrate. In other embodiments, a variable pressure may be applied to different portions or regions of the substrate. As can be seen in
In some embodiments, a recess 26 is formed in the platen 24, and a transparent section 36 is formed in the polishing pad 30 overlying the recess 26. The transparent section 36 may be electromagnetically transparent, optically transparent, or the like. This section 36 may be positioned such that it passes beneath the substrate 10 during a portion of the platen's rotation, regardless of the translational position of the carrier head. Assuming that the polishing pad 30 is a two-layer pad, the transparent section 36 can be constructed by cutting an aperture in the backing layer 32, and by replacing a section of the cover layer 34 with a transparent plug. The plug can be a relatively pure polymer or polyurethane, e.g., formed without fillers. In general, the material of the transparent section 36 should be non-magnetic and non-conductive. In addition, the system can include a transparent cover, e.g., of glass or a hard plastic, that is placed over the recess 26 but is located below 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 below the cover (see
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 may function 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 may include another detection element and/or an optical or other detection element.
The CMP apparatus 20 also includes a controller 90 that comprises a programmable central processing unit (CPU) which is operable with a memory (e.g., non-volatile memory) and support circuits. The support circuits are conventionally coupled to the CPU and comprise cache, clock circuits, input/output subsystems, power supplies, and the like, and combinations thereof coupled to the various components of the CMP apparatus 20, to facilitate control thereof. The CPU is one of any form of general purpose computer processor used in an industrial setting, such as a programmable logic controller (PLC), for controlling various 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 drive, hard disk, or any other form of digital storage, local or remote. Typically, the memory includes computer program instructions, which when executed by the CPU, facilitates 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 that implements the methods of the present disclosure. The program instructions may conform to any one of a number of different programming languages. In one example, the disclosure may be implemented as a program product stored on computer-readable storage media for use with a computer system. The program instructions of the program product define functions of the embodiments (including the methods described herein). Program instructions and data can be coded and stored within the memory for instructing the CPU. Program instructions readable by the processing unit within the system controller determines which tasks are performable in the processing system. For example, the non-transitory computer readable medium includes a program product which when executed by the processing unit are configured to perform one or more of the methods described herein. Preferably, the program instructions includes code to perform tasks relating to monitoring, execution and control of the measurements, fluid delivery, polishing hardware and movement of a substrate along with the various process recipe tasks.
The detection 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 the controller 90. The sensor assembly for the detection 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 a control system. The control system may be wholly or partially local or remote 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 can be coupled to the components in the platen, including the printed circuit board 58, through a rotary electrical union 92.
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 prongs 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 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 that is coupled to the sense circuitry within or in communication 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 the change in the strength of the eddy currents, and thus the change in thickness of the metal layer 16.
As shown in
After polishing, the portion of the metal layer remaining between the pattern of the underlying layer formed on the substrate will provide metal features, e.g., vias, pads and interconnects. However, as illustrated in
As illustrated in
As illustrated in
Returning to
Referring to
A controller 90, receives signals from the detection element. Since the sensor assembly may sweep beneath the substrate with each rotation of the platen, information on the metal layer thickness and exposure of the underlying layer is accumulated in-situ and on a continuous real-time basis (once per platen rotation). The controller 90 is programmed to take sample measurements from the monitoring system when the substrate passes over the sensor 80. As polishing progresses, the endpoint detection metrics of the metal layer changes, and the sampled signals vary with time. The time varying sampled signals may be referred to as traces, such as shown in
In operation, the CMP apparatus 20 uses the detection element 40 to determine when the bulk of the conductive and barrier layer has been removed and to determine when the underlying patterned insulative layer has been substantially exposed without significant residue. The controller 90 applies process control and endpoint detection logic to the sampled signals to determine when to change process parameter and to detect the polishing endpoint.
In some embodiments, the controller applies a box logic identifying trends in the traces by use of isolating boxes 604a-c that are generated for each of the traces in real-time to determine a convergence of the traces. For example, the box logic may be an algorithm running on the controller 90 that is applied to determine a slope trend in the traces 602a-c to identify a steady-state condition indicating a diminishing effect of polishing. The algorithm may be applied over a certain time period or, as shown, may be illustrated upon satisfaction of a target threshold, such as a slope value or trend, a relative change in slope, or the like. Upon, reaching the target threshold, the algorithm may trigger analysis of the convergence of the traces. In some embodiment, one or more of the traces may reach the target threshold indicating the relatively steady-state condition while another of the traces has not reached the target threshold. Polishing may continue until the other of the traces have reached the target threshold, which relates to a property of a trace determined by the box logic. In one example, the target threshold relates to a desired slope of the trace at an instant in time. In one example, the slope of the trace at an instant in time when it reaches a threshold is such that it exits a horizontally oriented box, as shown in
In some embodiments, the tolerance threshold is a value under which the difference in the traces is sufficient to indicate a lack of residue at the substrate and above which the difference is indicative of a presence of the residue at the substrate. For example, the difference may visually equate to a certain gap between one or more of the traces 602a-c and another of the traces. As can be seen in
Returning to
The controller 90 may also be coupled to a pressure generating mechanisms (e.g., gas supply) that control the pressure applied by the flexible membrane of the carrier head 70 to a substrate, to the carrier head rotation motor 76 to control the carrier head rotation rate, to the platen rotation motor (not shown) to control the platen rotation rate, or to the slurry distribution system 39 to control the slurry composition supplied to the polishing pad. For example, the controller may determine that the endpoint criteria have been satisfied for the outer radial regions but not for the inner radial regions. This would indicate that the underlying layer has been cleared of residue in an annular outer region but not in an inner region of the substrate. In this case, the controller is configured to update the polishing operation.
Returning to
In operation 704 of the 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 middle, inner, or outer region of the substrate. The first substrate measurement may be a response to an eddy current sensor or other detection element 40 as it passes near the substrate, as shown in
In operation 706, a second substrate measurement corresponding to a second region of the substrate is detected. For example, the second substrate measurement may be a response to an eddy current sensor signal that is detected in response to the delivery of 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 may extend between the 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 may be a response from a middle of the substrate, as detected by the detection element 40 as it passes near the middle region of the substrate, as shown in
Optionally, while not discussed further below for simplicity of discussion reasons, additional measurement operations between operation 706 and operation 708 may be performed. For example, the third substrate measurement may be a response to an eddy current sensor signal that is detected in response to the delivery of 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 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, as detected by the detection element 40 as it passes near the inner region of the substrate, as shown in
In operation 708, a difference in the first substrate measurement relative to the second substrate measurement is determined. In some embodiments, the difference between the first substrate measurement relative to the second substrate measurement is performed after it has been determined that the characteristic of one or more of traces has reached a threshold value. As illustrated in
In one example, during operation 708 an algorithm executed by a processor within the controller 90 is used to compare the first trace 602a to the second trace 602b at a point in time 608 to determine a relative difference 606 between the first trace and the second trace after a characteristic of at least one of the traces 602a, 602b has met some threshold value, as shown in
In operation 710, the controller 90 then uses the determined difference as an indication of a presence of a residue at the first region of the substrate or the second region of the substrate in response to the difference 606 determined in operation 708 being outside of a tolerance threshold stored in memory of the controller 90. For example, the residue 502 may be an integrated inclusion resulting from an underlayer topographical anomaly, as shown in
The operation 710 may include repeating operations 702-708 by updating a chemical mechanical polishing process based on the difference relative to the tolerance threshold determined during operation 708. For example, because the difference is outside the tolerance threshold, additional polishing may be helpful to bring the traces into greater alignment. An update may include increasing at least one of a polishing time, a pressure applied to one or more regions of the flexible membrane of the polishing head, changing a polishing slurry composition, slurry feed rate, polishing head rotation speed, platen rotation speed or the like. In some embodiments, the update to the polishing operation may constitute an overpolish based on the difference from the tolerance threshold. For example, if the difference is well outside the tolerance threshold a more aggressive (e.g., higher flexible membrane pressure, carrier head rotation speed, etc.) or lengthy overpolish may be called by the controller 90. If the difference is near the tolerance threshold, a more mild overpolish may be called. The overpolish may be used to remove excess material and the residue at the substrate, as shown in
The operations 702-708 of the method 700 may be performed one or more times if the determined difference performed in operation 708 is outside of a desired threshold. The operations 702-708 of the method 700 may be performed until the detected residue is sufficiently reduced in the corresponding regions of the substrate.
Operations 702-708 of the method 700 may also be performed one or more additional times even if the determined difference performed in operation 708 is inside of a desired threshold to verify that the prior generated results remain within the desired threshold value at a subsequent time.
In operation 712, an indication of a lack of the residue at the substrate is provided in response to the difference determined during operation 708 being within the tolerance threshold. For example, if the traces are determined to have a sufficiently low difference or a trend toward a low difference over time (see
Examples of the present disclosure result in increased process yield through the identification and reduction of residue during the polishing operation. Since there is a direct correlation between residue detection and reduction and process yield, the increased residue reduction leads to an increase in process yield.
While the foregoing is directed to examples of the present disclosure, other and further examples of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
