Acoustic monitoring and sensors for chemical mechanical polishing.

Abstract

The chemical mechanical polishing apparatus includes a platen supporting a polishing pad, a carrier head in contact with the polishing pad and relative to a surface of the substrate, a motor generating relative motion between the platen and the carrier head to polish an upper layer on the substrate, an in-situ acoustic monitoring system, and a controller. In some implementations, the in-situ acoustic monitoring system includes an acoustic signal generator that emits an acoustic signal and an acoustic signal sensor that receives an acoustic signal reflected from the surface of the substrate. The controller is configured to detect exposure of an underlying layer due to polishing of the substrate based on measurements from the in-situ acoustic monitoring system.

Description

[Technical Field]

[0001] The present disclosure relates to in-situ monitoring of chemical mechanical polishing. [Background technology]

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

[0003] Chemical mechanical polishing (CMP) is one accepted planarization method. This planarization method typically requires the substrate to 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, pressing it against the polishing pad. Typically, an abrasive polishing slurry is supplied to the surface of the polishing pad.

[0004] One problem in CMP is determining whether the polishing process is complete, i.e., whether the substrate layer has been planarized to the desired flatness or thickness, or whether the desired amount of material has been removed. Variations in slurry distribution, polishing pad condition, relative speed between the polishing pad and the substrate, and load on the substrate can cause variations in material removal rate. These variations, as well as variations in the initial thickness of the substrate layer, can result in variations in the time required to reach the polishing endpoint. Therefore, the polishing endpoint cannot usually be determined simply as a function of polishing time.

[0005] In some systems, the substrate is monitored in situ during polishing, for example, by monitoring the torque required by a motor to rotate the platen or carrier head. Acoustic monitoring of polishing has also been proposed. Summary of the Invention

[0006] In one aspect, a chemical mechanical polishing apparatus includes a platen that supports a polishing pad, a carrier head that holds a surface of a substrate in contact with the polishing pad, a motor that generates relative motion between the platen and the carrier head to polish an upper layer on the substrate, an in-situ acoustic monitoring system that includes an acoustic signal generator that emits an acoustic signal and an acoustic signal sensor that receives an acoustic signal reflected from the surface of the substrate, and a controller configured to detect exposure of an underlying layer due to polishing of the substrate based on measurements from the in-situ acoustic monitoring system.

[0007] In another aspect, a chemical mechanical polishing apparatus includes a platen supporting a polishing pad, a carrier head that holds a surface of a substrate in contact with the polishing pad, a motor that generates relative motion between the platen and the carrier head to polish an upper layer on the substrate, an in-situ acoustic monitoring system including an acoustic signal sensor that receives an acoustic signal generated by stress energy of the substrate, and a controller configured to detect exposure of an underlying layer due to polishing of the substrate based on measurements from the in-situ acoustic monitoring system that are based on comparing the signal with previous measurements of acoustic signals generated by stress energy of test substrates.

[0008] In another aspect, a chemical mechanical polishing apparatus includes a platen, a polishing pad supported on the platen and having an aperture therethrough, a liquid source that delivers liquid into the aperture, a carrier head that holds a surface of the substrate in contact with the polishing pad, a motor that generates relative motion between the platen and the carrier head to polish an upper layer on the substrate, and an in-situ acoustic monitoring system that includes an acoustic signal sensor supported on the platen and positioned below the aperture that receives an acoustic signal from the substrate that propagates through the liquid in the aperture.

[0009] In another aspect, a chemical mechanical polishing apparatus includes a platen, a polishing pad supported on the platen, a carrier head that holds a surface of a substrate in contact with the polishing pad, a motor that generates relative motion between the platen and the carrier head to polish an upper layer on the substrate, and an in-situ acoustic monitoring system including an acoustic signal sensor. The polishing pad includes a polishing layer having a polishing surface and an insert having a lower porosity than the remainder of the polishing layer. The acoustic signal sensor includes a waveguide that incorporates the insert within the polishing layer.

[0010] Embodiments may include one or more of the following features. The controller may be configured to determine the polishing endpoint and adjust the current pressure of the carrier head or adjust the baseline pressure for polishing a subsequent new substrate in response to the determination. The fluid may include water. The acoustic signal sensor may interface with the liquid in the aperture directly without a waveguide. The acoustic signal sensor may be a piezoelectric acoustic sensor. The controller may be configured to receive a signal from the acoustic signal sensor and detect the polishing endpoint. The controller may be configured to normalize the signal received from the sensor by comparison with the generator output power. The controller may be configured to detect the endpoint by comparing the normalized signal to a threshold. The insert and the remainder of the polishing pad may be polyurethane.

[0011] One or more of the following possible advantages may be realized: The signal strength of the acoustic sensor can be increased; Exposure of the underlying layer can be detected more reliably; Polishing can be stopped more reliably, improving wafer-to-wafer uniformity.

[0012] 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. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a polishing apparatus. [Figure 2A] 1 is a schematic cross-sectional view showing an acoustic monitoring sensor engaging a portion of a polishing pad. [Figure 2B] 10 is a schematic cross-sectional view illustrating another implementation of an acoustic monitoring sensor having an aperture through a polishing pad. [Figure 2C] 10 is a schematic cross-sectional view illustrating another implementation of an acoustic monitoring sensor engaging an insert in a polishing pad. [Figure 3]FIG. 1 is a schematic top view showing a platen with an acoustic monitoring sensor. DETAILED DESCRIPTION OF THE INVENTION

[0014] Like reference symbols in the various drawings indicate like elements.

[0015] In some semiconductor chip manufacturing processes, an upper layer, such as a metal, silicon oxide, or polysilicon, is polished until an underlying layer, such as a silicon oxide, silicon nitride, or high-k dielectric, is exposed. In some configurations, the exposure of the underlying layer changes acoustic emissions from the substrate. By detecting this change in acoustic signal, the polishing endpoint can be determined. However, existing monitoring techniques may not meet the increasing demands of semiconductor device manufacturers.

[0016] The monitored acoustic emissions may be caused by the energy released by deformation of the substrate material, and the resulting acoustic spectrum is related to the material properties of the substrate. Without being limited by any particular theory, possible sources of this energy, also referred to as "stress energy," and its characteristic frequencies include chemical bond breaking, specific phonon frequencies, and slip-stick mechanisms. The acoustic effects of this stress energy are not the same as the noise (sometimes referred to as an acoustic signal) caused by vibrations induced by friction of the substrate against the polishing pad, or the noise caused by cracking, chipping, breakage, or similar defects in the substrate. Possible frequency ranges for this energy are 50 kHz to 10 MHz, e.g., 100 kHz to 700 kHz, e.g., 400 kHz to 700 kHz. With appropriate filtering, stress energy can be distinguished from other acoustic signals, such as noise caused by friction of the substrate against the polishing pad or the occurrence of defects in the substrate. For example, the signal from the acoustic sensor can be compared to a signal measured from a test substrate known to represent stress energy.

[0017] However, a potential problem with acoustic monitoring is the transmission of the acoustic signal to the sensor. Even when using a waveguide, the polishing pad tends to attenuate the acoustic signal. Therefore, it would be advantageous to have the sensor in a location where the acoustic signal is less attenuated.

[0018] Another challenge is that acoustic emissions caused by stress energy can contain significant noise. Lower layers tend to have different acoustic properties, such as reflection and attenuation, than upper layers. It may be possible to reduce the noise by actively generating an acoustic signal and measuring the reflection of the acoustic signal from the substrate.

[0019] 1 shows an example of a polishing apparatus 100. The polishing apparatus 100 includes a rotatable, disk-shaped platen 120 on which a polishing pad 110 rests. The polishing pad 110 can be a dual-layer polishing pad having an outer polishing layer 112 and a softer backing layer 114. The platen is operable to rotate about an axis 125. For example, a motor 121, e.g., a DC / induction motor, can orbit a drive shaft 124 to rotate the platen 120.

[0020] The polishing apparatus 100 can include a port 130 that dispenses a polishing fluid 132, such as an abrasive slurry, onto the polishing pad 110. The polishing apparatus can also include a polishing pad conditioner that abrades the polishing pad 110 to maintain the polishing pad 110 in a consistent abrasive state.

[0021] The polishing apparatus 100 includes at least one carrier head 140. The carrier head 140 is operable to hold the substrate 10 against the polishing pad 110. Each carrier head 140 can have independent control of the polishing parameters, such as pressure, associated with the respective substrate.

[0022] Carrier head 140 may include a retaining ring 142 that retains substrate 10 beneath flexible membrane 144. Carrier head 140 also includes one or more independently controllable pressurizable chambers defined by the membrane, e.g., three chambers 146a-146c (see FIG. 1), that can apply independently controllable pressures to associated zones on flexible membrane 144 and, therefore, on substrate 10. For ease of illustration, only three chambers are shown in FIG. 1, but there may be one or two chambers, or four or more chambers, e.g., five chambers.

[0023] Carrier heads 140 are suspended from a support structure 150, e.g., a carousel or track, and are connected by drive shafts 152 to carrier head rotation motors 154, e.g., DC / induction motors, so that the carrier heads can rotate about axes 155. Optionally, each carrier head 140 can oscillate laterally, e.g., on a slider on carousel 150, or by rotational oscillation of the carousel itself, or by sliding along a track. During typical operation, the platen is rotated about its central axis 125, and each carrier head is rotated about its central axis 155 and translated laterally across the top surface of the polishing pad.

[0024] A controller 190, such as a programmable computer, is connected to the motors 121, 154 to control the rotational speed of the platen 120 and carrier head 140. For example, each motor may include an encoder that measures the rotational speed of its associated drive shaft. A feedback control circuit, which may be within the motor itself, part of the controller, or a separate circuit, receives the measured rotational speed from the encoder and adjusts the current supplied to the motor so that the rotational speed of the drive shaft matches the rotational speed received from the controller.

[0025] 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 and, in some embodiments, one or more acoustic signal generators 163, each configured to dynamically transmit acoustic energy toward the side of the substrate 10 proximal to the polishing pad 110. Each acoustic signal sensor or generator may be located at one or more locations on the upper platen 120. In particular, the in-situ acoustic monitoring system may be configured to detect acoustic emissions caused by stress energy when the material of the substrate 10 deforms, and, in embodiments including an acoustic signal generator 163, may be configured to detect reflections of the dynamically generated acoustic signals from the surface of the substrate 10.

[0026] A position sensor, for example, an opto-isolator or rotary encoder connected to the rim of the platen, can be used to sense the angular position of the platen 120. This allows only the portion of the signal measured when the sensor 162 is in the vicinity of the substrate, for example, when the sensor 162 is below the carrier head or substrate, to be used for endpoint detection.

[0027] 1 , the acoustic signal sensor 162 is positioned within a recess 164 in the platen 120 and is positioned to receive an acoustic signal from the side of the substrate closest to the polishing pad 110. Similarly, the acoustic signal generator 163 is positioned within the recess 164 in the platen 120 and is positioned to generate (i.e., emit) an acoustic signal from the side of the substrate closest to the polishing pad 110. The acoustic signal sensor 162 and the acoustic signal generator 163 can be connected by circuitry 168 through a rotary coupling, e.g., a mercury slip ring, to a power supply and / or other signal processing electronics 166. The signal processing electronics 166 can then be connected to a controller 190, which can be configured to control the magnitude or frequency of the acoustic energy transmitted by the generator 163, for example, by variably increasing or decreasing the current supply to the generator 163.

[0028] In some embodiments, in-situ acoustic monitoring system 160 is a passive acoustic monitoring system. In this case, signals are monitored by acoustic signal sensor 162 without generating a signal from acoustic signal generator 163 (or acoustic signal generator 163 can be omitted from the system entirely). The passive acoustic signal monitored by acoustic signal sensor 162 can be in the range of 50 kHz to 1 MHz, e.g., 200 to 400 kHz, or 200 kHz to 1 MHz. For example, when monitoring the polishing of an inter-layer dielectric (ILD) in shallow trench isolation (STI), a frequency range of 225 kHz to 350 kHz can be monitored.

[0029] In some embodiments, in-situ acoustic monitoring system 160 is an active acoustic monitoring system. The active acoustic signal generated by acoustic signal generator 163 can have a frequency range of 5 MHz to 50 MHz.

[0030] In either case, the signal from sensor 162 may be amplified by a built-in internal amplifier with a gain of 40-60 dB. The signal from sensor 162 may then be further amplified and filtered as needed and digitized through an A / D port to a high speed data acquisition board, for example, in electronics 166. Data from sensor 162 may be recorded in a similar frequency range as generator 163 or in a different, e.g., higher frequency range, e.g., 1-10 MHz, e.g., 1-3 MHz or 6-8 MHz.

[0031] If located within the platen 120, the acoustic signal sensor 162, the acoustic signal generator 163, or both, can be located in the center of the platen 120, for example, at the axis of rotation 125, at the edge of the platen 120, or at the midpoint (e.g., 5 inches (12.7 cm) from the axis of rotation for a 20 inch (50.8 cm) diameter platen). While FIG. 1 shows the acoustic signal sensor 162 and the acoustic signal generator 163 as being coupled together, this is not required. The sensor 162 and the generator 163 can be separate and physically separated from one another.

[0032] In some examples, a gas can be directed into recess 164. For example, a gas, such as air or nitrogen, can be directed into recess 164 from a pressure source 180, such as a pump or gas supply line, through a conduit 182 provided by piping and / or a passage in platen 120. An outlet port 184 can connect recess 164 to the external environment and allow the gas to escape from recess 164. The gas flow can pressurize recess 164 to reduce leakage of slurry into recess 164 and / or remove any slurry that leaks into recess 164 through outlet port 184 to reduce potential contamination of sensor 162 and generator 163 or potential damage to electronics or other components.

[0033] In some embodiments, the acoustic signal sensor 162, the acoustic signal generator 163, or both can be coupled to a respective probe 170, which provides a waveguide for transmitting acoustic energy. The probe 170 can protrude above the upper surface 128 of the platen 120 that supports the polishing pad 110. The probe 170 can be, for example, a needle-like body with a sharp tip that extends from the main body of the sensor 162 into the polishing pad 110 (see, for example, FIG. 2A). The probe can be fabricated from any dense material, ideally made from corrosion-resistant stainless steel.

[0034] For the sensor 162 to which the waveguide is coupled, a commercially available acoustic emission sensor (such as a Physical Acoustics Nano 30) having an operating frequency between 50 kHz and 1 MHz, e.g., 125 kHz and 1 MHz, e.g., 125 kHz and 550 kHz, can be used. Advantageously, a piezoelectric acoustic sensor capable of efficient high frequency acoustic energy detection can be used. The sensor can be attached to the distal end of the waveguide and held in place, e.g., with a clamp or by a threaded connection to the platen 120.

[0035] A commercially available acoustic signal generator can be used for the generator 163 to which the waveguide is coupled. The generator can be attached to the distal end of the waveguide and held in place, for example, with a clamp or by a threaded connection to the platen 120.

[0036] Alternatively, in some other embodiments, aperture 138 can be formed in polishing pad 110, and aperture 138 can extend through the entire thickness of polishing layer 112 and backing layer 114. In embodiments in which multiple slurry-transport grooves 116 are formed in the upper surface of polishing layer 112 of polishing pad 110, aperture 138 can be aligned with one of grooves 116, i.e., aperture 138 can be formed in polishing pad 110 directly below the groove, through the thin portion of polishing layer 112 remaining below groove 116, and through the backing layer 114 of polishing pad 110 (see, e.g., FIG. 2B ).

[0037] A liquid, e.g., water, can be directed into the aperture 138. For example, the liquid can be directed into the aperture 138 from a liquid source 139, e.g., a liquid supply line, through piping and / or passages in the platen 120. As another example, the acoustic signal sensor 162 itself can include a fluid purge port, e.g., one or more passages through the body of the sensor 162, through which liquid can be directed into the aperture 138. In either example, the aperture 138 extending through the thickness of the polishing pad 110 allows the liquid to directly contact the slurry, i.e., slurry present on the top surface, in the grooves 116 of the polishing pad 110, or both.

[0038] In such an embodiment, acoustic signal sensor 162 is positioned in platen 120 below aperture 138 to receive reflected acoustic signals from substrate 10 that propagate through the liquid in aperture 138. The horizontal cross-sectional size of aperture 138 may depend on (e.g., be equal to or smaller than) the exact size of the body of acoustic signal sensor 162 so that sensor 162 extends across the lower opening of aperture 138 and effectively keeps aperture 138 sealed while sealing the upper volume to reduce leakage of liquid or slurry through aperture 138.

[0039] 2A , in some embodiments, a plurality of slurry-transport grooves 116 are formed in the upper surface of the polishing layer 112 of the polishing pad 110. The grooves 116 extend partially, but not entirely, through the thickness of the polishing layer 112. In the embodiment shown in FIG. 2A , a probe 170 extends through the polishing layer 172, for example, through the thin portion of the polishing layer remaining below the groove 116, so that a tip 172 is positioned in one of the grooves 116. This allows the probe 170 to directly sense the acoustic signal propagating through the slurry present in the groove 116. Compared to a probe that extends simply into the polishing layer, this can improve the coupling of the acoustic emission sensor to the acoustic emissions from the substrate 10.

[0040] The tip 172 of the probe 170 is positioned low enough within the groove 116 so that the tip does not contact the substrate 10 when the polishing pad 110 is compressed by the substrate 10 .

[0041] Although not shown in FIG. 2A, the acoustic signal generator 163 may similarly be coupled to a probe of the same or a different type such that the dynamic acoustic signal generated by the generator 163 can be propagated directly to the slurry present in the groove 116.

[0042] For example, instead of passively monitoring acoustic emissions caused by stress energy as the substrate material deforms, actively emitting an acoustic signal toward the substrate 10 and monitoring the reflected acoustic signal can reduce unwanted noise and increase signal strength, thereby allowing for more accurate monitoring of endpoint detection.

[0043] In some embodiments, the vertical position of the probe tip 172 is adjustable. This allows the vertical position of the sensing tip 172 to be precisely positioned relative to the bottom of the groove in the polishing pad 110. For example, the acoustic signal sensor 162 can include a cylinder that fits into an aperture through a portion of the platen 120. Threads on the outer surface of the cylinder can engage threads on the inner surface of the aperture in the platen 120, so that adjustment of the vertical position of the tip 172 can be accomplished by rotating the cylinder. However, other mechanisms for vertical adjustment, such as a piezoelectric actuator, can be used. Vertical positioning of the probe tip 172 can be combined with the embodiments shown in FIGS. 1 and 2A.

[0044] Probe 170 can extend through and contact backing layer 114. Alternatively, aperture 118 can be formed in backing layer 114, whereby probe 170 extends through aperture 118 and does not directly contact backing layer 114. Using a thin, needle-like probe 170 that pierces polishing layer 112 can effectively keep polishing layer 112 sealed while reducing leakage of slurry through the aperture created by probe 170. Additionally, the waveguide can penetrate backing layer 114 without mechanically compromising the physical properties of backing layer 114.

[0045] Because it can be difficult to align the probes 170 with respect to the grooves 116, the acoustic signal sensor 162, the acoustic signal generator 163, or both may be coupled with multiple probes 170. For example, the probes may be multiple parallel needles. Assuming the probes 170 extend over an area at least equal to the spacing between the grooves 116, at least one of the tips 172 of the probes 170 should be positioned within the grooves 116 when the polishing pad is placed on the platen 120.

[0046] 2B , in some embodiments, polishing pad 110 has apertures 138 therethrough that can be substantially filled with liquid delivered through liquid source 139. Here, acoustic signals can propagate through the liquid in apertures 138 instead of or in addition to propagating through material in polishing pad 110, which, for example, would result in significant noise, eliminating the need for a waveguide, which would otherwise be necessary to reduce noise due to coupling sensor 162 to a slurry in the grooves of polishing pad 110. Notably, the size of the contact surface between sensor 162 and the liquid in apertures 138 is substantially equivalent to the size of the sensor 162 (measurement head). For example, if sensor 162 has a cylindrical body with a blunt (e.g., flat) upper end, the contact surface size may be equal to the entire horizontal cross-sectional area of ​​the cylindrical sensor body, unlike embodiments including a waveguide, where the size of the contact surface, e.g., the tip of the probe, is much smaller.

[0047] During operation, liquid such as water directed into the aperture 138 can improve acoustic coupling of the sensor 162 to the substrate 10. Additionally, this can prevent slurry from accumulating in the aperture 138. This configuration allows the sensor 162 to receive acoustic signals through the liquid and slurry that is in direct contact with the substrate, thereby improving transmission of the acoustic signal to the sensor 162.

[0048] 2C, in some implementations, the probe 170 has an aperture 138 that can pass through a portion of the polishing pad 110 and can be substantially filled with liquid delivered through a liquid source 139. The probe 170 need not extend into a groove in the polishing pad.

[0049] To improve acoustic coupling, portion 119 of polishing layer 112 can be replaced with an insert made of a material with a higher acoustic transmissivity than the rest of the polishing pad. The insert 119 remains compatible with the polishing process, e.g., inert to the polishing process. In particular, polishing layer 112 can be a microporous polymer layer, while insert 119 can be a non-porous polymer material. Where insert 119 is of the same base polymer as the rest of polishing layer 112, for example, both can be polyurethane. Insert 119 can have the same grooves as the rest of polishing layer 112. The grooves can help prevent hydroplaning above insert 119.

[0050] In some embodiments, it is useful for insert 119 to have the same compressibility as the rest of polishing layer 112. In this case, compressibility can be adjusted by the degree of polymerization or by the specific ratio of components in the polymer. In some embodiments, the insert is formed to have the same acoustic impedance as the polishing fluid. Insert 119 does not necessarily have to be optically transparent.

[0051] As shown in FIG. 3 , in some embodiments, multiple acoustic signal sensors 162, and optionally multiple acoustic signal generators 163, can be installed on the platen 120. Each sensor 162 or generator 163 can be configured as described with respect to any of FIGS. 1 and 2A-2B . Signals from the sensors 162 can be used by the controller 190 to calculate the positional distribution of acoustic emission events occurring on the substrate 10 during polishing. In some embodiments, the multiple sensors 162 can be positioned at different angular positions around the axis of rotation of the platen 120, but at the same radial distance from the axis of rotation. In some embodiments, the multiple sensors 162 are positioned at different radial distances from the axis of rotation of the platen 120, but at the same angular position. In some embodiments, the multiple sensors 162 are positioned at different angular positions around the axis of rotation of the platen 120, but at different radial distances from the axis of rotation.

[0052] Turning now to the signal from the sensor 162 in any of the above-described embodiments, for example, after amplification, pre-filtering, and digitization, the signal can be data processed, for example, by the controller 190, for either endpoint detection or feedback or feedforward control.

[0053] In some embodiments, 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, which can be monitored over time to detect changes. Such changes can indicate a polishing endpoint, for example, when the signal crosses a threshold value.

[0054] In some embodiments, 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 to determine when a film transition occurs at a particular radius. Information about the transition time per radius can be used to trigger an endpoint. As another example, a fast Fourier transform (FFT) can be performed on the signal to generate a frequency spectrum. Specific frequency bands can be monitored, and if the intensity of the frequency band crosses a threshold, this can indicate exposure of the underlying layer and can be used to trigger an endpoint. Alternatively, if the location (e.g., wavelength) or bandwidth of a local maximum or minimum at a selected frequency crosses a threshold, this can indicate exposure of the underlying layer and can trigger an endpoint. For example, when monitoring the polishing of an interlayer dielectric (ILD) in shallow trench isolation (STI), a frequency range of 225 kHz to 350 kHz can be monitored.

[0055] As another example, a wavelet packet transform (WPT) can be performed on a signal to decompose it into low- and high-frequency components. The decomposition can be repeated as necessary to divide the signal into smaller components. The intensity of one of the frequency components can be monitored; if the component's intensity crosses a threshold, this can indicate exposure of the underlying layer and can be used to trigger an endpoint.

[0056] Assuming the position of the sensor 162 relative to the substrate 10 is known, the position of the acoustic event on the substrate can be calculated, for example, using motor encoder signals or an opto-isolator attached to the platen 120, e.g., the radial distance of the event from the center of the substrate. Determining the position of the sensor relative to the substrate is discussed in U.S. Patent No. 6,159,073 and U.S. Patent No. 6,296,548, which are incorporated by reference.

[0057] Acoustic events of various process significance include microscratches, film transition breakthrough, and film clearing. Various methods can be used to analyze the acoustic emission signal from the waveguide. Fourier transform and other frequency analysis methods can be used to determine peak frequencies that occur during polishing. Experimentally determined thresholds and monitoring within defined frequency ranges can be used to identify expected and unexpected changes during polishing. An example of an expected change is the sudden appearance of a peak frequency during a transition in film hardness. An example of an unexpected change is a problem with the consumable set (pad glazing or machine health issues due to other process drift).

[0058] In operation, acoustic signals are collected from the in-situ acoustic monitoring system 160 while the device substrate 10 is being polished at the polishing station 100. The signals are monitored to detect exposure of underlying layers of the substrate 10. For example, a particular frequency range can be monitored, and the intensity can be monitored and compared to an experimentally determined threshold.

[0059] Detection of the polishing endpoint triggers the cessation of polishing, but polishing can continue for a predetermined time after the endpoint trigger. Alternatively or additionally, the collected data and / or the endpoint detection time can be used as a feedforward control to control the processing of substrates in subsequent processing operations, such as polishing at a subsequent station, or as a feedback control to control the processing of subsequent substrates at the same polishing station. For example, detection of the polishing endpoint can trigger a modification of the current pressure of the polishing head. As another example, detection of the polishing endpoint can trigger a modification of the baseline pressure in subsequent polishing of a new substrate.

[0060] All of the embodiments and functional operations described herein can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structural means disclosed herein and their structural equivalents, or in combinations of the above. The embodiments 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 medium for execution by or controlling the operation of a data processing apparatus, e.g., a programmable processor, a computer, or multiple processors or computers.

[0061] 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 can be deployed in any form, including as a stand-alone program or as modules, components, subroutines, or other units 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 compound files (e.g., a file storing one or more modules, subprograms, 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 communications network.

[0062] The processes and logic flows described herein may be implemented by one or more programmable processors that execute one or more computer programs to perform functions by manipulating input data and generating output. The processes and logic flows may also be implemented by, and apparatus may be implemented as, special purpose logic circuitry, such as an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

[0063] The term "data processing apparatus" encompasses all apparatus, devices, and machines that process data, including, by way of example, a programmable processor, a computer, or multiple processors or computers. In addition to hardware, an apparatus may include code that creates the 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 one or more combinations thereof. Processors suitable for the execution of computer programs include, by way of example, both general-purpose and special-purpose microprocessors, and any one or more processors of any kind of digital computer.

[0064] Suitable computer-readable media for storing computer program instructions and data include, by way of example, all forms of non-volatile memory, media, and memory devices, including semiconductor memory elements, such as EPROM, EEPROM, and flash memory devices, magnetic disks, such as 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.

[0065] The above-described polishing apparatus and method can be applied in various 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 fixed to the platen. Some embodiments of the endpoint detection system may be applicable to linear polishing systems (e.g., where the polishing pad is a linearly moving continuous belt or reel-to-reel belt). The polishing layer can be a standard abrasive material (e.g., polyurethane with or without fillers), a soft material, or a fixed-abrasive material. Although the term relative positioning is used, it should be understood that the polishing surface and wafer can be held in a vertical orientation or some other orientation.

[0066] While this specification contains many specific details, these should not be construed as limitations on the scope of the claims, but rather as descriptions of features that may be specific to particular embodiments of a particular invention. In some examples, the methods may be applied to other combinations of upper and lower layer materials, as well as to signals from other types of in-situ monitoring systems, such as optical or eddy current monitoring systems.

Claims

1. A platen supporting a polishing pad having an aperture therethrough; a carrier head that holds the surface of the substrate in contact with the polishing pad; a motor that generates relative motion between the platen and the carrier head to polish an upper layer on the substrate; an in-situ acoustic monitoring system including an acoustic signal sensor that receives an acoustic signal generated by stress energy in the substrate, the acoustic signal sensor being in direct contact with the liquid in the aperture without an intervening waveguide; a controller configured to detect exposure of an underlying layer of the substrate due to the polishing based on measurements from the in-situ acoustic monitoring system based on a comparison of the signal with past measurements of acoustic signals generated by stress energy of a test substrate; and A chemical mechanical polishing apparatus comprising:

2. The device of claim 1 , wherein the acoustic signal sensor is configured to monitor acoustic energy at frequencies between 200 kHz and 1 MHz.

3. The apparatus of claim 2 , wherein the acoustic signal sensor is configured to monitor acoustic energy at frequencies between 200 kHz and 400 kHz.

4. The apparatus of claim 1 , wherein the controller is configured to perform a frequency domain analysis to determine changes in relative power of spectral frequencies.

5. 5. The apparatus of claim 4, wherein the controller is configured to determine a radial position of an acoustic signal sensor relative to a center of a carrier head and determine when a film transition occurs at a particular radius based on a change in the detected relative output.

6. 10. The apparatus of claim 1, wherein the in-situ acoustic monitoring system includes a waveguide positioned to couple the acoustic signal sensor to slurry within the grooves of the polishing pad.

7. 7. The apparatus of claim 6, comprising the polishing pad, the polishing pad having a polishing layer and a plurality of slurry-transporting grooves in a polishing surface of the polishing layer, the waveguide extending through the polishing pad and into the grooves.

8. A platen and a polishing pad supported on the platen and having an aperture therethrough; a liquid source that delivers liquid into the aperture; a carrier head that holds the surface of the substrate in contact with the polishing pad; a motor that generates relative motion between the platen and the carrier head to polish an upper layer on the substrate; an in-situ acoustic monitoring system supported on the platen and positioned below the aperture to receive an acoustic signal from the substrate that propagates through the liquid in the aperture, the acoustic signal sensor being in direct contact with the liquid in the aperture without a waveguide; and A chemical mechanical polishing apparatus comprising:

9. The apparatus of claim 8 , wherein the acoustic signal sensor extends across the aperture to seal the aperture.

10. 9. The apparatus of claim 8, wherein the polishing pad comprises a polishing layer and a plurality of slurry-transporting grooves in the polishing surface of the polishing layer, the apertures extending through the polishing pad and into the grooves.

11. A platen and a polishing pad supported on the platen and including a polishing layer having a polishing surface, the polishing layer including an insert having a lower porosity than a remainder of the polishing layer, the insert having a sidewall that contacts a sidewall of the remainder of the polishing layer; a carrier head that holds the surface of the substrate in contact with the polishing pad; a motor that generates relative motion between the platen and the carrier head to polish an upper layer on the substrate; an in-situ acoustic monitoring system including an acoustic signal sensor including a waveguide that engages the insert with the abrasive layer; A chemical mechanical polishing apparatus comprising:

12. The apparatus of claim 11 , wherein the insert has the same compressibility as the remainder of the polishing pad.

13. The apparatus of claim 11 , wherein the insert has the same composition as the remainder of the polishing pad.

14. The apparatus of claim 11 , wherein the insert is the same material as the remainder of the polishing pad but with a lower degree of polymerization.

15. The device of claim 11 , wherein the insert is pore-free.

16. The apparatus of claim 11 , wherein a groove pattern extends across both the insert and the remaining portion of the polishing pad.

17. The apparatus of claim 16 , wherein the grooving pattern comprises concentric circular grooves.

18. 17. The device of claim 16, wherein the waveguide engages a plateau of the insert between grooves in the insert.

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