US20230009048A1 - Coupling of acoustic sensor for chemical mechanical polishing - Google Patents
Coupling of acoustic sensor for chemical mechanical polishing Download PDFInfo
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- US20230009048A1 US20230009048A1 US17/855,520 US202217855520A US2023009048A1 US 20230009048 A1 US20230009048 A1 US 20230009048A1 US 202217855520 A US202217855520 A US 202217855520A US 2023009048 A1 US2023009048 A1 US 2023009048A1
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Images
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B37/00—Lapping machines or devices; Accessories
- B24B37/005—Control means for lapping machines or devices
- B24B37/013—Devices or means for detecting lapping completion
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B37/00—Lapping machines or devices; Accessories
- B24B37/11—Lapping tools
- B24B37/20—Lapping pads for working plane surfaces
- B24B37/205—Lapping pads for working plane surfaces provided with a window for inspecting the surface of the work being lapped
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B49/00—Measuring or gauging equipment for controlling the feed movement of the grinding tool or work; Arrangements of indicating or measuring equipment, e.g. for indicating the start of the grinding operation
- B24B49/10—Measuring or gauging equipment for controlling the feed movement of the grinding tool or work; Arrangements of indicating or measuring equipment, e.g. for indicating the start of the grinding operation involving electrical means
Definitions
- This disclosure relates to in-situ monitoring of chemical mechanical polishing, and in particular to acoustic monitoring.
- 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 metallic 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.
- CMP CMP determining whether the polishing process is complete, i.e., whether a substrate layer has been planarized to a desired flatness or thickness, or when a desired amount of material has been removed. Variations in the slurry distribution, 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. These variations, as well as variations in the initial thickness of the substrate layer, cause variations in the time needed to reach the polishing endpoint. Therefore, the polishing endpoint usually cannot be determined merely as a function of polishing time.
- Signal strength of an acoustic sensor can be increased. Acoustic coupling between the polishing layer and the sensor can be established more reliably. Exposure of an underlying layer can be detected more reliably. Polishing can be halted more reliably, and wafer-to-wafer uniformity can be improved. Polishing parameters can be varied upon detection of planarization, i.e., smoothing of the substrate surface, which can improve uniformity or increase the polishing rate. Polishing can be halted upon detection of planarization or after expiration of a preset time following detection of planarization. This can provide an alternative endpoint technique.
- FIG. 2 A illustrates a schematic cross-sectional view of an acoustic monitoring sensor that engages a portion of a polishing pad.
- the acoustic emissions to be monitored can be caused by energy released when the substrate material undergoes deformation, and the resulting acoustic spectrum is related to the material properties of the substrate.
- possible sources of this energy also termed “stress energy”, and its characteristic frequencies include breakage of chemical bonds, characteristic phonon frequencies, slip-stick mechanisms, etc. It may be noted that this stress energy acoustic effect is not the same as noise generated by vibrations induced by friction of the substrate against the polishing pad (which is also sometimes referred to as an acoustic signal), or of noise generated by cracking, chipping, breakage or similar generation of defects on the substrate.
- Adhering the acoustic sensor to the coupling window can reduce noise in the acoustic signal associated with movement of the acoustic sensor within the housing.
- the adhesive can provide superior coupling of the sensor to the polishing pad and provide more reliable acoustic attenuation on a sensor-to-sensor basis.
- the polishing apparatus 100 can include a port 130 to dispense polishing liquid 132 , such as abrasive slurry, onto the polishing pad 110 to the pad.
- the polishing apparatus can also include a polishing pad conditioner to abrade the polishing pad 110 to maintain the polishing pad 110 in a consistent abrasive state.
- the carrier head 140 can include a retaining ring 142 to retain the substrate 10 below a flexible membrane 144 .
- the carrier head 140 also includes one or more independently controllable pressurizable chambers defined by the membrane, e.g., three chambers 146 a - 146 c , which can apply independently controllable pressurizes to associated zones on the flexible membrane 144 and thus on the substrate 10 (see FIG. 1 ). Although only three chambers are illustrated in FIG. 1 for ease of illustration, there could be one or two chambers, or four or more chambers, e.g., five chambers.
- the carrier head 140 is suspended from a support structure 150 , e.g., a carousel or track, and is connected by a drive shaft 152 to a carrier head rotation motor 154 , e.g., a DC induction motor, so that the carrier head can rotate about an axis 155 .
- a carrier head rotation motor 154 e.g., a DC induction motor
- each carrier head 140 can oscillate laterally, e.g., on sliders on the carousel 150 , or by rotational oscillation of the carousel itself, or by sliding along the track.
- the platen is rotated about its central axis 125
- each carrier head is rotated about its central axis 155 and translated laterally across the top surface of the polishing pad.
- a controller 190 such as a programmable computer, is connected to the motors 121 , 154 to control the rotation rate of the platen 120 and carrier head 140 .
- each motor can include an encoder that measures the rotation rate of the associated drive shaft.
- a feedback control circuit which could be in the motor itself, part of the controller, or a separate circuit, receives the measured rotation rate from the encoder and adjusts the current supplied to the motor to ensure that the rotation rate of the drive shaft matches at a rotation rate received from the controller.
- the polishing apparatus 100 includes at least one in-situ acoustic monitoring system 160 .
- the in-situ acoustic monitoring system 160 includes one or more acoustic signal sensors 162 . Each acoustic signal sensor can be installed at one or more locations on the upper platen 120 .
- the in-situ acoustic monitoring system can be configured to detect acoustic emissions caused by stress energy when the material of the substrate 10 undergoes deformation.
- the acoustic sensor 162 can be connected by circuitry 168 to a power supply and/or other signal processing electronics 166 through a rotary coupling, e.g., a mercury slip ring.
- a rotary coupling e.g., a mercury slip ring.
- the in-situ acoustic monitoring system 160 is a passive acoustic monitoring system.
- signals are monitored by the acoustic sensor 162 without generating signals from an acoustic signal generator (or the acoustic signal generator can be omitted entirely from the system).
- the passive acoustic signals monitored by the acoustic sensor 162 can be in 50 kHz to 1 MHz range, e.g., 200 to 400 kHz, or 200 Khz to 1 MHz.
- a frequency range of 225 kHz to 350 kHz can be monitored.
- the housing 163 material is acoustically dampening to reduce noise received by the acoustic sensor 162 from surfaces in contact with the housing 163 , such as the backing layer 114 or polishing layer 112 through which the housing 163 extends.
- the housing 163 can be composed of a metal, e.g., aluminum or stainless steel, or a polymer material, e.g., polycarbonate, polyvinyl chloride (PVC), or polymethyl-methacrylate (PMMA).
- a support 167 is arranged beneath the spring 165 which provides a stationary block which the spring 165 can push against opposite the housing 163 .
- the support 167 can be any material sufficient to rigidly support the spring 165 and housing 163 without movement or compressive buckling.
- the acoustic window 119 is formed of a different material than the polishing layer 112 .
- the material of the acoustic window has sufficient acoustic transmission characteristics, e.g., an acoustic impedance of between 1 and 4 MRayl and an acoustic attenuation coefficient lower than 2 (e.g., lower than 1, lower than 0.5). to provide a signal satisfactory for acoustic monitoring.
- the acoustically transmissive layer 172 can be selected to have a compressibility similar to the compressibility of the backing layer 114 , e.g., within 20%, e.g., within 10%, of the compressibility of the surrounding backing layer 114 .
- a substrate 10 is formed by the sequential deposition of conductive, semiconductive, or insulative layers on a silicon wafer.
- a filler layer is deposited over a non-planar surface and planarized such that the filler and non-planar surface, such as a patterned layer, have a common coplanar surface and/or the non-planar surface is exposed.
- the in-situ acoustic monitoring system 160 detects transitions between layers, or topography information related to one or more layers of the substrate 10 . This provides information to be used between process steps.
- a substrate 10 including a filler layer can have non-uniform surface roughness, e.g., topography, from the deposition process. Detecting when the topography has been planarized allows the system to modify one or more process conditions based on the transition.
- the apparatus 100 can stop a high carrier head 140 pressure step once the filler layer surface has been planarized.
- a layer transition occurs when the topography 509 has been removed by the apparatus 100 .
- the surface of the remaining filler layer 508 is substantially planar.
- the polishing of the planar surface may correspond to a second region 604 of the acoustic signal 600 .
- the acoustic signal 600 is substantially constant (albeit subject to noise).
- the second region 604 continues in time until the filler layer 508 extending above the patterned layer 504 has been removed.
- the patterned layer 504 is composed of a different material than the filler layer 508 and interacts with the polishing layer 112 surface and materials differently, thereby creating a third region 606 of the acoustic signal 600 .
- continued polishing can create dishing, and this topology may again increase the acoustic signal.
- the third region 606 is not constant, e.g., can be increasing or decreasing.
- the acoustic signal 600 can be processed using additional steps prior to application of a slope-change detection algorithm.
- the acoustic signal 600 can be subjected to one or more filters, e.g., a bandpass filter, and/or one or more transformations, e.g., a fast Fourier transformation.
- the bandpass filter can be used to isolate preferred frequencies of the acoustic signal 600 before processing, such as frequencies in a range from 50 to 500 kHz, or in a range from 200 to 700 kHz.
- the apparatus 100 modifies one or more polishing parameter responsive to differentiating the regions 602 , 604 , and 606 .
- the apparatus 100 can dispense first abrasive polishing liquid 132 for rapid removal of the topography 509 .
- a different polishing liquid 132 having a lower polishing rate or a lower selectivity can be dispensed to the pad 110 .
- a location e.g., wavelength
- bandwidth of a local maxima or minima in a selected frequency range crosses a threshold value
- this can indicate exposure of an underlying layer, which can be used to trigger endpoint.
- a frequency range of 225 kHz to 350 kHz can be monitored.
- the positions of the sensors 162 relative to the substrate 10 are known, e.g., using a motor encoder signal or an optical interrupter attached to the platen 120 , the positions of the acoustic events on the substrate can be calculated, e.g., the radial distance of the event from the center of the substrate can be calculated. Determination of the position of a sensor relative to the substrate is discussed in U.S. Pat. Nos. 6,159,073 and in 6,296,548, incorporated by reference.
- Various process-meaningful acoustic events include micro-scratches, film transition break through, and film clearing.
- Various methods can be used to analyze the acoustic emission signal from the waveguide. Fourier transformation and other frequency analysis methods can be used to determine the peak frequencies occurring during polishing. Experimentally determined thresholds and monitoring within defined frequency ranges are used to identify expected and unexpected changes during polishing. Examples of expected changes include the sudden appearance of a peak frequency during transitions in film hardness. Examples of unexpected changes include problems with the consumable set (such as pad glazing or other process-drift-inducing machine health problems).
- an acoustic signal is collected from the in-situ acoustic monitoring system 160 .
- the signal is monitored to detect exposure of the underlying layer of the substrate 10 .
- a specific frequency range can be monitored, and the intensity can be monitored and compared to an experimentally determined threshold value.
- a computer program (also known as a program, software, software application, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment.
- a computer program does not necessarily correspond to a file.
- a program can be stored in a portion of a file that holds other programs or data, in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code).
- a computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.
- the processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output.
- the processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).
- the above described polishing apparatus and methods can be applied in a variety of polishing systems.
- Either the polishing pad, or the carrier head, or both can move to provide relative motion between the polishing surface and the wafer.
- the platen may orbit rather than rotate.
- the polishing pad can be a circular (or some other shape) pad secured to the platen.
- Some aspects of the endpoint detection system may be applicable to linear polishing systems (e.g., where the polishing pad is a continuous or a reel-to-reel belt that moves linearly).
- the polishing layer can be a standard (for example, polyurethane with or without fillers) polishing material, a soft material, or a fixed-abrasive material. Terms of relative positioning are used; it should be understood that the polishing surface and wafer can be held in a vertical orientation or some other orientations.
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Mechanical Treatment Of Semiconductor (AREA)
- Finish Polishing, Edge Sharpening, And Grinding By Specific Grinding Devices (AREA)
Abstract
A chemical mechanical polishing apparatus includes a platen to support a polishing pad, a carrier head to hold a surface of a substrate against the polishing pad, a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate, an in-situ acoustic monitoring system comprising an acoustic window having a top surface to contact the substrate, and a controller configured to detect a polishing endpoint based on received acoustic signals from the in-situ acoustic monitoring system.
Description
- This application claims the benefit of priority to U.S. Application No. 63/218,893, filed on Jul. 6, 2021, the contents of which are hereby incorporated by reference.
- This disclosure relates to in-situ monitoring of chemical mechanical polishing, and in particular to acoustic monitoring.
- 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 metallic 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, e.g., by polishing for a predetermined time period, to leave a portion of the filler layer over the nonplanar 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 pad. The carrier head provides a controllable load on the substrate to push it against the polishing pad. An abrasive polishing slurry is typically supplied to the surface of the polishing pad.
- One problem in CMP is determining whether the polishing process is complete, i.e., whether a substrate layer has been planarized to a desired flatness or thickness, or when a desired amount of material has been removed. Variations in the slurry distribution, 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. These variations, as well as variations in the initial thickness of the substrate layer, cause variations in the time needed to reach the polishing endpoint. Therefore, the polishing endpoint usually cannot be determined merely as a function of polishing time.
- In some systems, the substrate is monitored in-situ during polishing, e.g., by monitoring the torque required by a motor to rotate the platen or carrier head. Acoustic monitoring of polishing has also been proposed.
- In one aspect, a chemical mechanical polishing apparatus includes a platen to support a polishing pad, a carrier head to hold a surface of a substrate against the polishing pad, a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate, an in-situ acoustic monitoring system comprising an acoustic window having a top surface to contact the substrate, and a controller configured to detect a polishing endpoint based on received acoustic signals from the in-situ acoustic monitoring system.
- In another aspect, a chemical mechanical polishing apparatus includes a platen, a polishing pad supported on the platen, a carrier head to hold a surface of a substrate against the polishing pad, a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate, an in-situ acoustic monitoring system comprising an acoustic sensor that receives acoustic signals from the surface of the substrate, and a controller configured to detect a polishing endpoint based on received acoustic signals from the in-situ acoustic monitoring system. The acoustic sensor is adhesively attached to a bottom surface of the polishing pad.
- Implementations may include one or more of the following features. The sensor may be secured to the polishing pad, e.g., by an adhesive. The acoustic window may have a diameter smaller than the acoustic sensor. The acoustic sensor may be a piezoelectric acoustic sensor. The polishing endpoint may be an exposure of an underlying layer due to the polishing of the substrate. The controller may be configured to, in response to the detection, adjust a pressure of the carrier head or adjust a baseline pressure of a subsequent polishing of a new substrate.
- One or more of the following possible advantages may be realized. Signal strength of an acoustic sensor can be increased. Acoustic coupling between the polishing layer and the sensor can be established more reliably. Exposure of an underlying layer can be detected more reliably. Polishing can be halted more reliably, and wafer-to-wafer uniformity can be improved. Polishing parameters can be varied upon detection of planarization, i.e., smoothing of the substrate surface, which can improve uniformity or increase the polishing rate. Polishing can be halted upon detection of planarization or after expiration of a preset time following detection of planarization. This can provide an alternative endpoint technique.
- The details of one or more implementations are set forth in the accompanying drawings and the description below. Other aspects, features, and advantages will be apparent from the description and drawings, and from the claims.
-
FIG. 1 illustrates a schematic cross-sectional view of an example of a polishing apparatus. -
FIG. 2A illustrates a schematic cross-sectional view of an acoustic monitoring sensor that engages a portion of a polishing pad. -
FIG. 2B illustrates a schematic cross-sectional view of another implementation of an acoustic monitoring sensor that acoustically transmissive layer. -
FIG. 2C illustrates a schematic cross-sectional view of another implementation of an acoustic monitoring sensor. -
FIG. 2D illustrates a schematic cross-sectional view of another implementation of an acoustic monitoring sensor in which an acoustic window is formed in the polishing layer and an acoustically transmissive layer is formed in the backing layer of the polishing pad. -
FIG. 3 illustrates a schematic top view of a platen having multiple acoustic monitoring sensor windows. -
FIG. 4 illustrates a schematic top view of a platen having a planar portion surrounding the acoustic monitoring sensor window. -
FIGS. 5A-5C illustrate planarization of a surface of a substrate. -
FIG. 6 illustrates a graph of a sum of spectral power density over a frequency range as a function of time. - Like reference symbols in the various drawings indicate like elements.
- In some semiconductor chip fabrication processes an overlying layer, e.g., metal, silicon oxide or polysilicon, is polished until an underlying layer, e.g., a dielectric, such as silicon oxide, silicon nitride or a high-K dielectric, is exposed. For some applications, when the underlying layer is exposed, the acoustic emissions from the substrate will change. The polishing endpoint can be determined by detecting this change in acoustic signal. However, existing monitoring techniques may not satisfy increasing demands of semiconductor device manufacturers.
- The acoustic emissions to be monitored can be caused by energy released when the substrate material undergoes deformation, and the resulting acoustic spectrum is related to the material properties of the substrate. Without being limited to any particular theory, possible sources of this energy, also termed “stress energy”, and its characteristic frequencies include breakage of chemical bonds, characteristic phonon frequencies, slip-stick mechanisms, etc. It may be noted that this stress energy acoustic effect is not the same as noise generated by vibrations induced by friction of the substrate against the polishing pad (which is also sometimes referred to as an acoustic signal), or of noise generated by cracking, chipping, breakage or similar generation of defects on the substrate. The stress energy can be distinguished from other acoustic signals, e.g., from friction of the substrate against the polishing pad or of noise generated by generation of defects on the substrate, through appropriate filtering. For example, the signal from the acoustic sensor can be compared to a signal measured from a test substrate that is known to represent stress energy.
- However, a potential problem with acoustic monitoring is transmission of the acoustic signal to the sensor. Some polishing pads have poor transmission of acoustic energy. In addition, poor coupling between the polishing pad and the sensor tends to dampen the acoustic signal. Moreover, establishing a consistent coupling from sensor-to-sensor can be difficult.
- Thus, it would be advantageous to have the acoustic sensor in contact with an acoustic “window” with low attenuation of the acoustic signal. In some implementations, a second layer of transmissive material is added to the in-situ acoustic monitoring system to further increase the acoustic signal coupling to the acoustic sensor.
- Adhering the acoustic sensor to the coupling window, e.g., with an adhesive, can reduce noise in the acoustic signal associated with movement of the acoustic sensor within the housing. The adhesive can provide superior coupling of the sensor to the polishing pad and provide more reliable acoustic attenuation on a sensor-to-sensor basis.
- Any of these features could be used independent of the other features.
-
FIG. 1 illustrates an example of apolishing apparatus 100. The polishingapparatus 100 includes a rotatable disk-shapedplaten 120 on which apolishing pad 110 is situated. Thepolishing pad 110 can be a two-layer polishing pad with anouter polishing layer 112 and asofter backing layer 114. The platen is operable to rotate about anaxis 125. For example, amotor 121, e.g., a DC induction motor, can turn adrive shaft 124 to rotate theplaten 120. - The polishing
apparatus 100 can include aport 130 to dispense polishingliquid 132, such as abrasive slurry, onto thepolishing pad 110 to the pad. The polishing apparatus can also include a polishing pad conditioner to abrade thepolishing pad 110 to maintain thepolishing pad 110 in a consistent abrasive state. - The polishing
apparatus 100 includes at least onecarrier head 140. Thecarrier head 140 is operable to hold asubstrate 10 against thepolishing pad 110. Eachcarrier head 140 can have independent control of the polishing parameters, for example pressure, associated with each respective substrate. - The
carrier head 140 can include a retainingring 142 to retain thesubstrate 10 below aflexible membrane 144. Thecarrier head 140 also includes one or more independently controllable pressurizable chambers defined by the membrane, e.g., three chambers 146 a-146 c, which can apply independently controllable pressurizes to associated zones on theflexible membrane 144 and thus on the substrate 10 (seeFIG. 1 ). Although only three chambers are illustrated inFIG. 1 for ease of illustration, there could be one or two chambers, or four or more chambers, e.g., five chambers. - The
carrier head 140 is suspended from asupport structure 150, e.g., a carousel or track, and is connected by adrive shaft 152 to a carrierhead rotation motor 154, e.g., a DC induction motor, so that the carrier head can rotate about anaxis 155. Optionally eachcarrier head 140 can oscillate laterally, e.g., on sliders on thecarousel 150, or by rotational oscillation of the carousel itself, or by sliding along the track. In typical operation, the platen is rotated about itscentral axis 125, and each carrier head is rotated about itscentral axis 155 and translated laterally across the top surface of the polishing pad. - A
controller 190, such as a programmable computer, is connected to themotors platen 120 andcarrier head 140. For example, each motor can include an encoder that measures the rotation rate of the associated drive shaft. A feedback control circuit, which could be in the motor itself, part of the controller, or a separate circuit, receives the measured rotation rate from the encoder and adjusts the current supplied to the motor to ensure that the rotation rate of the drive shaft matches at a rotation rate received from the controller. - The polishing
apparatus 100 includes at least one in-situacoustic monitoring system 160. The in-situacoustic monitoring system 160 includes one or moreacoustic signal sensors 162. Each acoustic signal sensor can be installed at one or more locations on theupper platen 120. In particular, the in-situ acoustic monitoring system can be configured to detect acoustic emissions caused by stress energy when the material of thesubstrate 10 undergoes deformation. - A position sensor, e.g., an optical interrupter connected to the rim of the platen or a rotary encoder, can be used to sense the angular position of the
platen 120. This permits only portions of the signal measured when thesensor 162 is in proximity to the substrate, e.g., when thesensor 162 is below the carrier head or substrate, to be used in endpoint detection. - In the implementation shown in
FIG. 1 , theacoustic monitoring system 160 includes anacoustic sensor 162 positioned supported by theplaten 120 to receive acoustic signals through thepolishing pad 110 from thesubstrate 10. Theacoustic sensor 162 can be partially or entirely in arecess 164 in the top surface of theplaten 120. In some implementations, a top surface of theacoustic sensor 162 is coplanar with the top surface of theplaten 120. - The portion of the polishing pad directly above the
acoustic sensor 162 can include anacoustic window 119. Theacoustic window 119 can be narrower than theacoustic sensor 162, e.g., as shown inFIG. 2A , or the two can be of substantially equal width (e.g., within 10%), e.g., as shown inFIG. 2C . Where theacoustic window 119 is narrower than theacoustic sensor 119, the sensor can also abut the bottom of thepolishing layer 112. - The
acoustic sensor 162 is a contact acoustic sensor having a surface connected to (e.g., in direct contact with or having just an adhesive layer) a portion of thepolishing layer 112 and/or theacoustic window 119. For example, theacoustic sensor 162 can be an electromagnetic acoustic transducer or piezoelectric acoustic transducer. A piezoelectric sensor can include a rigid contact plate, e.g., of stainless steel or the like, which is placed into contact with the body to be monitored, and a piezoelectric assembly, e.g., a piezoelectric layer sandwiched between two electrodes, on the backside of the contact plate. - In some implementations, the
acoustic sensor 162 is positioned within arecess 169 in ahousing 163. Anoptional spring 165 can be arranged between thehousing 163 and asupport 167 provides pressure against thehousing 163. The pressure on thehousing 163 presses theacoustic sensor 162 into contact with a portion of thepolishing pad 110. Alternatively, thespring 165 can press directly against theacoustic sensor 162, e.g., if a housing is not used. In some implementations, thespring 165 is along travel spring 165 supplying similar pressure as thestrong spring 165 over larger compression ranges. - The
acoustic sensor 162 can be connected bycircuitry 168 to a power supply and/or othersignal processing electronics 166 through a rotary coupling, e.g., a mercury slip ring. - In some implementations, the in-situ
acoustic monitoring system 160 is a passive acoustic monitoring system. In this case, signals are monitored by theacoustic sensor 162 without generating signals from an acoustic signal generator (or the acoustic signal generator can be omitted entirely from the system). The passive acoustic signals monitored by theacoustic sensor 162 can be in 50 kHz to 1 MHz range, e.g., 200 to 400 kHz, or 200 Khz to 1 MHz. For example, for monitoring of polishing of inter-layer dielectric (ILD) in a shallow trench isolation (STI), a frequency range of 225 kHz to 350 kHz can be monitored. - The signal from the
sensor 162 can be amplified by a built-in internal amplifier. In some implementations, the amplification gain is between 40 and 60 dB (e.g., 50 dB). The signal from theacoustic sensor 162 can then be further amplified and filtered if necessary, and digitized through an A/D port to a high speed data acquisition board, e.g., in theelectronics 166. Data from theacoustic sensor 162 can be recorded at a similar range as that of thegenerator 163 or at a different, e.g., higher, range, e.g., from 1 to 10 Mhz, e.g., 1-3 MHz or 6-8 Mz. In implementations in which theacoustic sensor 162 is a passive acoustic sensor, a frequency range from 100 kHz to 2 MHz can be monitored, such as 500 kHz to 1 MHz (e.g., 750 kHz). - If positioned in the
platen 120, theacoustic sensor 162, can be located at the center of theplaten 120, e.g., at the axis ofrotation 125, at the edge of theplaten 120, or at a midpoint (e.g., 5 inches from the axis of rotation for a 20 inch diameter platen). - Referring now to
FIG. 2A , further details of theacoustic monitoring system 160 are shown. Theacoustic sensor 162 can be held within arecess 169 in a top surface of thehousing 163. Thehousing 163 can assist in proper positioning of thesensor 162. Thehousing 163 is composed of a rigid, durable material sufficient to protect theacoustic sensor 162 from damage. However, in some implementations, e.g., as shownFIGS. 2C and 2D , a housing is not necessary, e.g., thesensor 162 can simply fit between and secured to by the side walls of therecess 169. The various implementations described as using a housing can omit the housing. - In some implementations, e.g., as shown in
FIG. 2B , thehousing 163 extends through thebacking layer 114, and in some implementations, e.g., as shown inFIG. 2A , thehousing 163 extends through a portion of thepolishing layer 112. However, in some implementations thehousing 163 fits entirely within therecess 164 in theplaten 120, e.g., if the top surface of thesensor 163 is coplanar with the top surface of theplaten 120 and contact the bottom surface of thepolishing pad 110. - In some implementations, the
housing 163 material is acoustically dampening to reduce noise received by theacoustic sensor 162 from surfaces in contact with thehousing 163, such as thebacking layer 114 or polishinglayer 112 through which thehousing 163 extends. Thehousing 163 can be composed of a metal, e.g., aluminum or stainless steel, or a polymer material, e.g., polycarbonate, polyvinyl chloride (PVC), or polymethyl-methacrylate (PMMA). - Assuming a spring is used, one end of the
spring 165 contacts thehousing 163 on a surface opposing theacoustic sensor 162. In some implementations, the other end of thespring 165 is in contact with asupport 167 that rests on theplaten 120. Such a support can provide a stable base for the forces generated by compression of thespring 165. In some implementations, the other end of thespring 165 is in contact with the bottom surface of therecess 164, i.e., in direct contact with the platen. Thespring 165 presses thehousing 163 toward a polishingsurface 112 a of thepolishing layer 112, which urges theacoustic sensor 162 into contact with the bottom surface of thepolishing layer 112. This can improve the acoustic coupling between the polishing layer and the sensor. However, the various implementations described as using a spring can omit the spring, e.g., assuming the sensor is adhesively attached to the bottom of theacoustic window 119 and/or polishingpad 110. - In some implementations, a
support 167 is arranged beneath thespring 165 which provides a stationary block which thespring 165 can push against opposite thehousing 163. Thesupport 167 can be any material sufficient to rigidly support thespring 165 andhousing 163 without movement or compressive buckling. - In addition to or instead of the spring, the
acoustic sensor 162 can be secured to a portion of the polishing layer 112 (and/or to anacoustic window 119 described below) by anadhesive layer 170. Theadhesive layer 170 increases the contact area between theacoustic sensor 162 and thepolishing layer 112 and/oracoustic window 119, reduces undesirable motion in theacoustic sensor 162 during polishing operations, and can reduce the presence of gas pockets between theacoustic sensor 162 and thepolishing layer 112 and/oracoustic window 119 thereby improving the coupling to the sensor, thus reducing noise in the acoustic signal received by theacoustic sensor 162. Theadhesive layer 170 can be a glue applied between theacoustic sensor 162 and thepolishing layer 112 and/oracoustic window 119, or an adhesive strip (e.g., tape). For example, theadhesive layer 170 can be a cyanocrylate, a pressure sensitive adhesive, a hot melt adhesive, etc. - Returning to
FIG. 2A , thepolishing layer 112 includes anacoustic window 119 arranged above theadhesive layer 170 and theacoustic sensor 162. However, in some implementations, theacoustic sensor 162 contacts theacoustic window 119 directly. - In implementations with an acoustic window, the
acoustic window 119 is formed of a different material than thepolishing layer 112. The material of the acoustic window has sufficient acoustic transmission characteristics, e.g., an acoustic impedance of between 1 and 4 MRayl and an acoustic attenuation coefficient lower than 2 (e.g., lower than 1, lower than 0.5). to provide a signal satisfactory for acoustic monitoring. - The acoustic impedance of a material is a measure of the opposition that a material presents to the acoustic flow resulting from an acoustic pressure applied to the material. The acoustic attenuation coefficient quantifies how transmitted acoustic amplitude decreases as a function of frequency for a specific material. Without wishing to be bound by theory, the specific acoustic impedance of the acoustic window 119 (AIwindow) coupling the liquid 132 and polishing
surface 112 a to theacoustic signal sensor 162, theacoustic window 119 specific acoustic impedance can be beneficially within the range -
- In particular, the
window 119 can have lower acoustic attenuation than thesurrounding polishing layer 112. This permits thepolishing layer 112 to be composed of a wider range of materials to meet the needs of the CMP operation. The window can be composed of a non-porous material, e.g., a solid body. In contrast, thepolishing layer 112 can be porous, e.g., be microporous, such as a polymer matrix in which hollow plastic microspheres are embedded. - The
acoustic window 119 extends through thepolishing layer 112 such that one surface, e.g., an upper surface, is coplanar with the polishingsurface 112 a of thepolishing layer 112. The opposing surface, e.g., a bottom surface, can be coplanar with alower surface 112 b of thepolishing layer 112. In some implementations, anindentation 118 is formed in thelower surface 112 b opposing the polishingsurface 112 a. The portion of thepolishing layer 112 that includes theindentation 118 forms a thin portion of thepolishing layer 112 having a thickness that is less than the remainingpolishing layer 112, and theacoustic window 119 is located in the thin portion. - The
acoustic window 119 can be composed of a non-porous material. In general, non-porous materials transmit acoustic signals with reduced noise and dispersion compared to porous materials. Theacoustic window 119 material can have a compressibility within a range of the compressibility of thesurrounding polishing layer 112 material that reduces the effect of theacoustic window 119 on the polishing characteristics of the polishing surface on the substrate. In some implementations, theacoustic window 119 compressibility is within 10% of thepolishing layer 112 compressibility (e.g., within 8%, within 5%, within 3%). In some implementations, theacoustic window 119 is opaque to light, e.g., visible light. Theacoustic window 119 can be composed of one or more of polyurethane, polyacrylate, polyethylene, or other polymers with low acoustic impedance and low acoustic attenuation. - Referring to
FIG. 2C , theacoustic window 119 is shown extending through the total thickness of thepolishing layer 112 such that thelower surface 112 b is planar. Thesensor 162 extends through anaperture 114 a in thebacking layer 114 to contact the underside of thewindow 119. - In some implementations, the
acoustic monitoring system 160 includes an acousticallytransmissive layer 172 in contact with theadhesive layer 170. Thetransmissive layer 172 is an index-matching material which provides increased acoustic signal coupling between the elements in contact with thetransmissive layer 172. Thetransmissive layer 172 can be arranged between theacoustic window 119 and theadhesive layer 170, or between theadhesive layer 170 and theacoustic sensor 162, as shown inFIG. 2B . In some implementations, theacoustic monitoring system 160 includes theadhesive layer 170, thetransmissive layer 172, or both. For example, thetransmissive layer 172 can be a layer of Aqualink™, Rexolite, or Aqualene™. In some implementations, thetransmissive layer 172 has an acoustic attenuation that is within 20%, e.g., 10%, of the acoustic attenuation of theacoustic window 119. The acousticallytransmissive layer 172 can have an acoustic attenuation less than the acoustic attenuation of thesurrounding backing layer 114. - The acoustically
transmissive layer 172 can be selected to have a compressibility similar to the compressibility of thebacking layer 114, e.g., within 20%, e.g., within 10%, of the compressibility of thesurrounding backing layer 114. -
FIG. 2D is an implementation in which theacoustic window 119 extends through the thickness of thepolishing layer 112 and thetransmissive layer 172 extends through the thickness of thebacking layer 114. However, thetransmissive layer 172 could be thinner than thebacking layer 114. In this case, thesensor 162 could project above the top surface of theplaten 120 to engage thetransmissive layer 172. - Additionally, the
acoustic signal sensor 162 is shown having dimensions sufficient to contact both thetransmissive layer 172 and the opposing surface of therecess 164. In such implementations, therecess 164 provides the support for theacoustic signal sensor 162 while the pressure of the polishing operation brings theacoustic signal sensor 162 into contact with thetransmissive layer 172. Arranged between thetransmissive layer 172 and theacoustic window 119 is anadhesive layer 170, as those described herein. In some implementations, additional adhesive affixes the contact surface between theacoustic signal sensor 162 and thetransmissive layer 172. - In some implementations, the
acoustic monitoring system 160 includes an active acoustic monitoring system. Such implementations include an acoustic signal generator and an acoustic sensor, such asacoustic sensor 162. - The acoustic signal generator generates (i.e., emits) acoustic signals from a side of the substrate closer to the
polishing pad 110. The acoustic signal generator can be connected bycircuitry 168 to a power supply and/or othersignal processing electronics 166 through a rotary coupling, e.g., a mercury slip ring. Thesignal processing electronics 166 can be connected in turn to thecontroller 190, which can be additionally configured to control the magnitude or frequency of the acoustic energy transmitted by the generator, e.g., by variably increasing or decreasing the current supply to the generator. Theacoustic signal generator 163 andacoustic sensor 162 can be coupled to one another, though this is not required. Thesensor 162 and the generator can be decoupled and physically separated from one another. For the generator, commercially available acoustic signal generators can be used. The generator can be attached toplaten 120 and held in place, e.g., with a clamp or by threaded connection to theplaten 120. - As depicted in
FIG. 3 , in some implementations a plurality ofacoustic signal sensors 162 3 can be installed in theplaten 120, eachacoustic sensor 162 being associated with anacoustic window 119. Eachsensor 162 can be configured in the manner described for any ofFIGS. 1 and 2A-2B . The signals from thesensors 162 can be used by thecontroller 190 to compute the positional distribution of acoustic emission events occurring on thesubstrate 10 during polishing. In some implementations, the plurality ofsensors 162 can be positioned at different angular positions around the axis of rotation of theplaten 120, but at the same radial distance from the axis of rotation. In some implementations, such as the implementation ofFIG. 3 , the plurality ofsensors 162 are positioned at different radial distances from the axis of rotation of theplaten 120, but at the same angular position. In some implementations, the plurality ofsensors 162 are be positioned at different angular positions around and different radial distances from the axis of rotation of theplaten 120. - In some implementations, the
acoustic window 119 is surrounded by asmooth portion 174 of thepolishing layer 112. Thesmooth portion 174 lacksgrooves 116 and is coplanar with the upper surface of theacoustic window 119. Implementations including asmooth portion 174 surrounding theacoustic window 119 can reduce noise associated with thesubstrate 10 interacting with thegrooves 116 of apolishing layer 112 during a polishing operation. - A
substrate 10 is formed by the sequential deposition of conductive, semiconductive, or insulative layers on a silicon wafer. A filler layer is deposited over a non-planar surface and planarized such that the filler and non-planar surface, such as a patterned layer, have a common coplanar surface and/or the non-planar surface is exposed. In some implementations, the in-situacoustic monitoring system 160 detects transitions between layers, or topography information related to one or more layers of thesubstrate 10. This provides information to be used between process steps. For example, asubstrate 10 including a filler layer can have non-uniform surface roughness, e.g., topography, from the deposition process. Detecting when the topography has been planarized allows the system to modify one or more process conditions based on the transition. For example, theapparatus 100 can stop ahigh carrier head 140 pressure step once the filler layer surface has been planarized. -
FIGS. 5A-5C depict intermediary layer transitions present in a planarization process for a substrate 500.FIG. 6 depicts an exemplaryacoustic signal 600 comparing the summed power spectral density (PSD) across a frequency range on the y-axis against time, in seconds (s). Theacoustic signal 600 has distinct regions, such asfirst region 602,second region 604, andthird region 606. In some implementations, theregions FIGS. 5A-5C . -
FIG. 5A shows anexemplary substrate 10 prior to polishing. Thesubstrate 10 include awafer 502, e.g., a silicon wafer, apatterned layer 504, and afiller layer 508. Prior to a planarization step, thefiller layer 508 is non-planar and includestopography 509. Thetopography 509 can result from deposition of thefiller layer 508 over the patternedlayer 504, and has dimensions on order of the feature size, e.g., the metal line width. - During operation the carrier head holds the
substrate 10 and relative motion is generated between thepolishing layer 112 and thesubstrate 10. The acoustic signal sensor receives an acoustic signal, such asacoustic signal 600, based upon the contact of the polishingsurface 112 a and the outer-most layer of thesubstrate 10. InFIG. 5A , at the initiation of polishing, thetopography 509 and thepolishing layer 112 are in contact. - Without wishing to be bound by theory, the
acoustic signal 600 changes based upon the changing contact surface of thefiller layer 508 material and thepolishing layer 112 material. In particular, initially the uneven topography may create a significant acoustic signal. However, as polishing progresses and thetopography 509 of thefiller layer 508 is planarized, the interface between the polishingsurface 110 and thesubstrate 10 become smoother, and the acoustic signal may decrease. The polishing of thetopography 509 may corresponds to afirst region 602 of thesignal 600 inFIG. 6 . - Again without wishing to be bound by theory, a layer transition occurs when the
topography 509 has been removed by theapparatus 100. As shown inFIG. 5B , the surface of the remainingfiller layer 508 is substantially planar. The polishing of the planar surface may correspond to asecond region 604 of theacoustic signal 600. In thesecond region 604 of thesignal 600 theacoustic signal 600 is substantially constant (albeit subject to noise). - Still without wishing to be bound by theory, the
second region 604 continues in time until thefiller layer 508 extending above the patternedlayer 504 has been removed. As shown inFIG. 5C , the patternedlayer 504 is composed of a different material than thefiller layer 508 and interacts with thepolishing layer 112 surface and materials differently, thereby creating athird region 606 of theacoustic signal 600. In addition, continued polishing can create dishing, and this topology may again increase the acoustic signal. Thethird region 606 is not constant, e.g., can be increasing or decreasing. - In some implementations, the differentiation, e.g., detection of the layer transitions, between the
regions acoustic monitoring system 160 and/or thecontroller 190 of theapparatus 100. The detection can be accomplished through various calculations known to the field for detection of slope change, but can include calculation of one or more differential, rolling average, windowing, or box logic algorithms. - In additional implementations, the
acoustic signal 600 can be processed using additional steps prior to application of a slope-change detection algorithm. For example, theacoustic signal 600 can be subjected to one or more filters, e.g., a bandpass filter, and/or one or more transformations, e.g., a fast Fourier transformation. For example, the bandpass filter can be used to isolate preferred frequencies of theacoustic signal 600 before processing, such as frequencies in a range from 50 to 500 kHz, or in a range from 200 to 700 kHz. - In some implementations, the
apparatus 100 modifies one or more polishing parameter responsive to differentiating theregions first region 602 in which thetopography 509 is being removed, theapparatus 100 can dispense first abrasive polishing liquid 132 for rapid removal of thetopography 509. Once the transition from thefirst region 602 to thesecond region 604 is detected, a different polishing liquid 132 having a lower polishing rate or a lower selectivity can be dispensed to thepad 110. - Alternatively or in addition, once the transition from the
second region 604 to thethird region 606 is detected, the pressure applied by thecarrier head 140 can be reduced. This can reduce the danger of dishing or erosion of thefiller layer 508. - Turning now to the signal from the
sensor 162 of any of the prior implementations, the signal, e.g., after amplification, preliminary filtering and digitization, can be subject to data processing, e.g., in thecontroller 190, for either endpoint detection or feedback or feedforward control. - In some implementations, the
controller 190 is configured to monitor acoustic loss. For example, the received signal strength is compared to the emitted signal strength to generate a normalized signal, and the normalized can be monitored over time to detect changes. Such changes can indicate a polishing endpoint, e.g., if the signal crosses a threshold value. - In some implementations, a frequency analysis of the signal is performed. For example, frequency domain analysis can be used to determine changes in the relative power of spectral frequencies, and to determine when a film transition has occurred at a particular radius. Information about time of transition by radius can be used to trigger endpoint. As another example, a Fast Fourier Transform (FFT) can be performed on the signal to generate a frequency spectrum. A particular frequency band can be monitored, and if the intensity in the frequency band crosses a threshold value, this can indicate exposure of an underlying layer, which can be used to trigger endpoint. Alternatively, if a location (e.g., wavelength) or bandwidth of a local maxima or minima in a selected frequency range crosses a threshold value, this can indicate exposure of an underlying layer, which can be used to trigger endpoint. For example, for monitoring of polishing of inter-layer dielectric (ILD) in a shallow trench isolation (STI), a frequency range of 225 kHz to 350 kHz can be monitored.
- As another example, a wavelet packet transform (WPT) can be performed on the signal to decompose the signal into a low-frequency component and a high frequency component. The decomposition can be iterated if necessary to break the signal into smaller components. The intensity of one of the frequency components can be monitored, and if the intensity in the component crosses a threshold value, this can indicate exposure of an underlying layer, which can be used to trigger endpoint.
- Assuming the positions of the
sensors 162 relative to thesubstrate 10 are known, e.g., using a motor encoder signal or an optical interrupter attached to theplaten 120, the positions of the acoustic events on the substrate can be calculated, e.g., the radial distance of the event from the center of the substrate can be calculated. Determination of the position of a sensor relative to the substrate is discussed in U.S. Pat. Nos. 6,159,073 and in 6,296,548, incorporated by reference. - Various process-meaningful acoustic events include micro-scratches, film transition break through, and film clearing. Various methods can be used to analyze the acoustic emission signal from the waveguide. Fourier transformation and other frequency analysis methods can be used to determine the peak frequencies occurring during polishing. Experimentally determined thresholds and monitoring within defined frequency ranges are used to identify expected and unexpected changes during polishing. Examples of expected changes include the sudden appearance of a peak frequency during transitions in film hardness. Examples of unexpected changes include problems with the consumable set (such as pad glazing or other process-drift-inducing machine health problems).
- In operation, as a
device substrate 10 is being polished at the polishingstation 100, an acoustic signal is collected from the in-situacoustic monitoring system 160. The signal is monitored to detect exposure of the underlying layer of thesubstrate 10. For example, a specific frequency range can be monitored, and the intensity can be monitored and compared to an experimentally determined threshold value. - Detection of the polishing endpoint triggers halting of the polishing, although polishing can continue for a predetermined amount of time after endpoint trigger. Alternatively or in addition, the data collected and/or the endpoint detection time can be fed forward to control processing of the substrate in a subsequent processing operation, e.g., polishing at a subsequent station, or can be fed back to control processing of a subsequent substrate at the same polishing station. For example, detection of the polishing endpoint can trigger modification to the current pressures of the polishing head. As another example, detection of the polishing endpoint can trigger modification to the baseline pressures of the subsequent polishing of a new substrate.
- Implementations and all of the functional operations described in this specification can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structural means disclosed in this specification and structural equivalents thereof, or in combinations of them. Implementations described herein can be implemented as one or more non-transitory computer program products, i.e., one or more computer programs tangibly embodied in a machine readable storage device, for execution by, or to control the operation of, data processing apparatus, e.g., a programmable processor, a computer, or multiple processors or computers.
- A computer program (also known as a program, software, software application, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file. A program can be stored in a portion of a file that holds other programs or data, in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.
- The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).
- The term “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer.
- Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.
- The above described polishing apparatus and methods can be applied in a variety of polishing systems. Either the polishing pad, or the carrier head, or both can move to provide relative motion between the polishing surface and the wafer. For example, the platen may orbit rather than rotate. The polishing pad can be a circular (or some other shape) pad secured to the platen. Some aspects of the endpoint detection system may be applicable to linear polishing systems (e.g., where the polishing pad is a continuous or a reel-to-reel belt that moves linearly). The polishing layer can be a standard (for example, polyurethane with or without fillers) polishing material, a soft material, or a fixed-abrasive material. Terms of relative positioning are used; it should be understood that the polishing surface and wafer can be held in a vertical orientation or some other orientations.
- While this specification contains many specifics, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. In some implementations, the method could be applied to other combinations of overlying and underlying materials, and to signals from other sorts of in-situ monitoring systems, e.g., optical monitoring or eddy current monitoring systems.
Claims (20)
1. A chemical mechanical polishing apparatus, comprising:
a platen;
a polishing pad supported on the platen, the polishing pad having a polishing layer;
a carrier head to hold a surface of a substrate against the polishing pad;
a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate;
an in-situ acoustic monitoring system comprising an acoustic window in the polishing pad and an acoustic sensor acoustically coupled to the acoustic window, wherein the acoustic window has a lower acoustic attenuation than the polishing layer, and wherein the acoustic window has a top surface that is coplanar with the polishing surface to contact the substrate; and
a controller configured to detect a polishing endpoint based on received acoustic signals from the in-situ acoustic monitoring system.
2. The apparatus of claim 1 , wherein a bottom surface of the acoustic window is coplanar with a lower surface of the polishing layer.
3. The apparatus of claim 1 , wherein the polishing pad has a backing layer below the polishing pad.
4. The apparatus of claim 3 , wherein the bottom surface of the acoustic window is coplanar with a top surface of the backing layer.
5. The apparatus of claim 4 , wherein an aperture is formed through the backing layer.
6. The apparatus of claim 5 , wherein the sensor is at least partially positioned in the aperture to contact the bottom surface of the acoustic window.
7. The apparatus of claim 5 , further including an acoustically transmissive layer positioned in an aperture through the backing layer between the acoustic sensor and the acoustic window, wherein the acoustically transmissive layer has a lower acoustic attenuation than the backing layer.
8. The apparatus of claim 7 , wherein a bottom surface of the acoustically transmissive layer is coplanar with a bottom surface of the polishing pad.
9. The apparatus of claim 1 , wherein an indentation is formed in an underside of the polishing layer to form a thin portion of the polishing layer, the acoustic window is positioned in the thin portion of the polishing layer, and the sensor is at least partially positioned in the indentation.
10. The apparatus of claim 1 , wherein the acoustic window is a non-porous material.
11. The apparatus of claim 10 , wherein the polishing layer is porous and the acoustic window is solid.
12. The apparatus of claim 1 , wherein a compressibility of the acoustic window is within 20% of a compressibility of the polishing layer.
13. The apparatus of claim 1 , wherein the acoustic sensor is adhesively attached to the acoustic window to receive acoustic signals from the substrate.
14. The apparatus of claim 1 , further including an acoustically transmissive layer arranged between the acoustic sensor and the acoustic window.
15. The apparatus of claim 14 , wherein the acoustically transmissive layer is adhesively attached to the acoustic window.
16. The apparatus of claim 15 , wherein the acoustic sensor is adhesively attached to the acoustically transmissive layer.
17. The apparatus of claim 1 , wherein the in-situ acoustic monitoring system comprises a housing to support the acoustic sensor, and a spring arranged to press the housing and the acoustic sensor against a portion of the polishing layer.
18. The apparatus of claim 17 , wherein the spring comprises a strong spring or a long-travel spring.
19. The apparatus of claim 1 , wherein the controller is configured to perform frequency domain analysis to determine changes in relative power of spectral frequencies.
20. A chemical mechanical polishing apparatus, comprising:
a platen;
a polishing pad supported on the platen;
a carrier head to hold a surface of a substrate against the polishing pad;
a motor to generate relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate;
an in-situ acoustic monitoring system comprising an acoustic sensor that receives acoustic signals from the surface of the substrate, the acoustic sensor adhesively attached to a bottom surface of the polishing pad; and
a controller configured to detect a polishing endpoint based on received acoustic signals from the in-situ acoustic monitoring system.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US17/855,520 US20230009048A1 (en) | 2021-07-06 | 2022-06-30 | Coupling of acoustic sensor for chemical mechanical polishing |
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DE69635816T2 (en) * | 1995-03-28 | 2006-10-12 | Applied Materials, Inc., Santa Clara | Method for producing an apparatus for in situ control and determination of the end of chemical mechanical grading operations |
US8485862B2 (en) * | 2000-05-19 | 2013-07-16 | Applied Materials, Inc. | Polishing pad for endpoint detection and related methods |
US6884146B2 (en) * | 2002-02-04 | 2005-04-26 | Kla-Tencor Technologies Corp. | Systems and methods for characterizing a polishing process |
JP5142866B2 (en) * | 2008-07-16 | 2013-02-13 | 富士紡ホールディングス株式会社 | Polishing pad |
KR101601346B1 (en) * | 2008-12-12 | 2016-03-08 | 아사히 가라스 가부시키가이샤 | Grinding device, grinding method, and method of manufacturing glass sheet |
US10478937B2 (en) * | 2015-03-05 | 2019-11-19 | Applied Materials, Inc. | Acoustic emission monitoring and endpoint for chemical mechanical polishing |
US9446498B1 (en) * | 2015-03-13 | 2016-09-20 | rohm and Hass Electronic Materials CMP Holdings, Inc. | Chemical mechanical polishing pad with window |
US10593574B2 (en) * | 2015-11-06 | 2020-03-17 | Applied Materials, Inc. | Techniques for combining CMP process tracking data with 3D printed CMP consumables |
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