KR20240023190A - Combination of acoustic sensors for chemical mechanical polishing - Google Patents

Abstract

A chemical mechanical polishing device includes a platen to support a polishing pad, a carrier head to hold the surface of the substrate relative to the polishing pad, and a platen to create relative motion between the platen and the carrier head to polish the top layer on the substrate. An in-situ acoustic monitoring system including a motor, an acoustic window having a top surface for contacting the substrate, and a controller configured to detect a polishing endpoint based on received acoustic signals from the in-situ acoustic monitoring system. .

Description

Combination of acoustic sensors for chemical mechanical polishing

The present disclosure relates to in-situ monitoring of chemical mechanical polishing, and in particular to acoustic monitoring.

Integrated circuits are typically formed on a substrate by sequential deposition of conductive, semiconducting, 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 the patterned layer is exposed. A conductive filler layer, for example, can be deposited on the patterned insulating layer to fill the trenches or holes in the insulating layer. After planarization, the portions of the metallic layer that remain between the raised patterns of the insulating layer form vias, plugs and lines that provide conductive paths between the thin film circuits on the substrate. For other applications, such as oxide polishing, the filler layer is planarized, for example by polishing for a predetermined period of time, to leave a portion of the filler layer above the non-planar surface. Additionally, planarization of the substrate surface is generally essential for photolithography.

Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires the substrate to be mounted on a carrier or polishing head. The exposed surface of the substrate is typically positioned against a rotating polishing pad. The carrier head provides a controllable force on the substrate to press the substrate against the polishing pad. Abrasive polishing slurry is typically supplied to the surface of a polishing pad.

One challenge in CMP is determining whether the polishing process has been completed, i.e., whether the substrate layer has been planarized to the desired flatness or thickness, or when the desired amount of material has been removed. Variations in slurry distribution, polishing pad conditions, relative speed between the polishing pad and the substrate, and load on the substrate can cause variations in material removal rates. These variations, as well as variations in the initial thickness of the substrate layer, cause variations in the time required to reach the polishing endpoint. Therefore, the polishing endpoint generally cannot be determined solely as a function of polishing time.

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

In one aspect, a chemical mechanical polishing device includes a platen to support a polishing pad, a carrier head to maintain the surface of the substrate relative to the polishing pad, and a relative motion between the platen and the carrier head to polish an upper layer on the substrate. an in-situ acoustic monitoring system comprising a motor for generating an acoustic window having a top surface for contacting the substrate, and configured to detect a polishing endpoint based on received acoustic signals from the in-situ acoustic monitoring system. Includes a controller.

In another aspect, a chemical mechanical polishing device includes a platen, a polishing pad supported on the platen, a carrier head for holding the surface of the substrate relative to the polishing pad, and between the platen and the carrier head for polishing an upper layer on the substrate. an in-situ acoustic monitoring system including a motor for generating relative motion, an acoustic sensor for receiving acoustic signals from the surface of the substrate, and determining a polishing endpoint based on the received acoustic signals from the in-situ acoustic monitoring system. and a controller configured to detect. The acoustic sensor is adhesively attached to the 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, for example, by adhesive. The acoustic window may have a smaller diameter than the acoustic sensor. The acoustic sensor may be a piezoelectric acoustic sensor. The polishing endpoint may be exposure of the underlying layer due to polishing of the substrate. The controller may be configured, in response to the detection, to adjust the pressure of the carrier head or the baseline pressure of subsequent polishing of the new substrate.

One or more of the following possible advantages may be realized. The signal strength of the acoustic sensor can be increased. The acoustic coupling between the polishing layer and the sensor can be established more reliably. Exposure of lower layers can be detected more reliably. Polishing can be stopped more reliably and wafer-to-wafer uniformity can be improved. Polishing parameters can be changed upon detection of planarization, i.e., upon smoothing of the substrate surface, which can improve uniformity or increase polishing speed. Polishing may be stopped upon detection of flattening or after expiration of a preset time following detection of flattening. This may provide an alternative endpoint technique.

Details of one or more implementations are set forth in the description below and the accompanying drawings. Other aspects, features and advantages will be apparent from the description and drawings and from the claims.

1 illustrates a schematic cross-sectional view of an example of a polishing device.
2A illustrates a schematic cross-sectional view of an acoustic monitoring sensor engaged with a portion of a polishing pad.
Figure 2b illustrates a schematic cross-sectional view of another implementation of an acoustic monitoring sensor that is an acoustically transparent layer.
Figure 2C illustrates a schematic cross-sectional view of another implementation of an acoustic monitoring sensor.
2D illustrates a schematic cross-sectional view of another implementation of an acoustic monitoring sensor, where an acoustic window is formed in the polishing layer and an acoustically transparent layer is formed in the backside layer of the polishing pad.
Figure 3 illustrates a schematic plan view of a platen with multiple acoustic monitoring sensor windows.
Figure 4 illustrates a schematic top view of a platen with a planar portion surrounding an acoustic monitoring sensor window.
Figures 5A-5C illustrate planarization of the surface of a substrate.
Figure 6 illustrates a graph of the sum of spectral power density over a range of frequencies as a function of time.
Like reference numbers in the various drawings represent similar elements.

In some semiconductor chip manufacturing processes, the top layer, e.g., metal, silicon oxide, or polysilicon, is polished until the lower layer, e.g., dielectric, e.g., silicon oxide, silicon nitride, or high-K dielectric is exposed. do. For some applications, the acoustic emissions from the substrate will change as the underlying layer is exposed. The polishing endpoint can be determined by detecting this change in the acoustic signal. However, existing monitoring techniques may not meet the increasing needs of semiconductor device manufacturers.

The acoustic emissions to be monitored may be caused by the 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 referred to as “stress energy”, and its characteristic frequencies include the breaking of chemical bonds, characteristic phonon frequencies, slip-stick mechanisms, etc. Includes. This stress energy acoustic effect is generated by noise (sometimes also referred to as an acoustic signal) produced by vibrations induced by friction of the substrate against the polishing pad, or by cracking, chipping, breakage or similar occurrence of defects on the substrate. It can be noted that this is not the same as the noise. Stress energy can, through appropriate filtering, be distinguished from other acoustic signals, for example from friction of the substrate against a polishing pad, or from noise generated by the occurrence of defects on the substrate. For example, a signal from an acoustic sensor can be compared to a signal measured from a test board, which is known to represent stress energy.

However, a potential problem in acoustic monitoring is the transmission of acoustic signals to the sensor. Some polishing pads have poor transmission of acoustic energy. Additionally, poor coupling between the polishing pad and the sensor tends to attenuate the acoustic signal. Moreover, it can be difficult to establish consistent binding from sensor to sensor.

Therefore, it would be advantageous to have an acoustic sensor in contact with an acoustic "window" where the attenuation of the acoustic signal is low. In some implementations, a second layer of transmissive material is added to the in-situ acoustic monitoring system to further increase acoustic signal coupling to the acoustic sensor.

For example, bonding an acoustic sensor to a bonding window using an adhesive can reduce noise in the acoustic signal associated with movement of the acoustic sensor within the housing. The adhesive can provide superior bonding of the sensor to the polishing pad and can provide more reliable acoustic attenuation on a sensor-specific basis.

Any of these features may be used independently of the other features.

1 illustrates an example of a polishing device 100. The polishing device 100 includes a rotatable disk-shaped platen 120 on which a polishing pad 110 is positioned. Polishing pad 110 may be a two-layer polishing pad having an outer polishing layer 112 and a softer back layer 114. The platen is operable to rotate about axis 125. For example, motor 121, such as a DC induction motor, can rotate drive shaft 124 to rotate platen 120.

The polishing device 100 may include a port 130 facing the pad 130 for dispensing a polishing liquid 132, such as a polishing slurry, onto the polishing pad 110 . The polishing device may also include a polishing pad conditioner for polishing the polishing pad 110 to maintain the polishing pad 110 in a consistent polishing condition.

The polishing device 100 includes at least one carrier head 140. Carrier head 140 is operable to hold substrate 10 relative to polishing pad 110 . Each carrier head 140 may have independent control of polishing parameters associated with each substrate, such as pressure.

Carrier head 140 may include a retaining ring 142 to retain 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, which can be configured to flexibly adjust independently controllable pressures. It may be applied to associated regions on membrane 144 and therefore on substrate 10 (see Figure 1). For ease of illustration, only three chambers are illustrated in Figure 1, but there could be one or two chambers, or four or more chambers, for example five chambers.

The carrier head 140 is suspended from a support structure 150, for example a carousel or track, and is driven by a drive shaft 152 to rotate the carrier head by a motor (152) so that the carrier head rotates about an axis 155. 154), for example, connected to a DC induction motor. Optionally, each carrier head 140 may oscillate laterally, for example on sliders on the carousel 150, or by rotational vibration of the carousel itself, or by sliding along a track. . In a typical operation, the platen is rotated about the central axis 125 of the platen and each carrier head is rotated about the central axis 155 of the carrier head and laterally across the top surface of the polishing pad. It is translated.

A controller 190, such as a programmable computer, is coupled to the motors 121 and 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 on the motor itself, part of the controller, or a separate circuit, receives the measured rotational speed from the encoder and is configured to ensure that the rotational speed of the drive shaft matches the rotational speed received from the controller. , adjusts the current supplied to the motor.

Polishing device 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 may be installed 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 as the material of substrate 10 undergoes deformation.

A position sensor, for example, an optical interrupter or a rotary encoder connected to the rim of the platen, may be used to sense the angular position of the platen 120. This allows only those portions of the signal that are measured when sensor 162 is in close proximity to the substrate, for example, when sensor 162 is below the carrier head or substrate, to be used for endpoint detection.

In the implementation shown in FIG. 1 , the acoustic monitoring system 160 includes an acoustic sensor 162 positioned and supported by the platen 120 to receive acoustic signals from the substrate 10 through the polishing pad 110. do. The acoustic sensor 162 may be partially or entirely in a recess 164 of the top surface of the platen 120. In some implementations, the top surface of acoustic sensor 162 is coplanar with the top surface of platen 120.

The portion of the polishing pad immediately above the acoustic sensor 162 may include an acoustic window 119 . The acoustic window 119 may be narrower than the acoustic sensor 162, for example as shown in Figure 2A, or the two may have substantially the same width (for example, as shown in Figure 2C). For example, within 10%). If the acoustic window 119 is narrower than the acoustic sensor 119, the sensor may also contact the bottom of the abrasive layer 112.

Acoustic sensor 162 is a contact acoustic sensor having a surface connected (eg, in direct contact or with only an adhesive layer) to a portion of acoustic window 119 and/or abrasive layer 112 . For example, acoustic sensor 162 may be an electromagnetic acoustic transducer or a piezoelectric acoustic transducer. A piezoelectric sensor may include a rigid contact plate, e.g., stainless steel, etc., placed in contact with the body to be monitored, and a piezoelectric assembly on the back side of the contact plate, e.g., a piezoelectric layer sandwiched between two electrodes. You can.

In some implementations, acoustic sensor 162 is located within recess 169 of housing 163. An optional spring 165 may be arranged between the housing 163 and the support 167 and provides pressure against the housing 163. Pressure against the housing 163 presses the acoustic sensor 162 into contact with a portion of the polishing pad 110. Alternatively, for example, if the housing is not used, the spring 165 may press directly against the acoustic sensor 162. In some implementations, spring 165 is a long stroke spring 165 that supplies pressure similar to rigid spring 165 over larger compression ranges.

The acoustic sensor 162 may be connected by circuitry 168 to a power supply and/or other signal processing electronics 166 via a rotary coupling, for example a mercury slip ring.

In some implementations, in-situ acoustic monitoring system 160 is a passive acoustic monitoring system. In this case, the signals are monitored by the acoustic sensor 162 without generating signals from the acoustic signal generator (or the acoustic signal generator can be omitted from the system altogether). The passive acoustic signals monitored by acoustic sensor 162 may be in the range of 50 kHz to 1 MHz, for example, 200 to 400 kHz, or 200 kHz to 1 MHz. For example, to monitor polishing of interlayer dielectric (ILD) in shallow trench isolation (STI), a frequency range of 225 kHz to 350 kHz can be monitored.

The signal from sensor 162 can be amplified by a built-in internal amplifier. In some implementations, the amplification gain is 40 to 60 dB (eg, 50 dB). The signal from acoustic sensor 162 may then be further amplified and filtered as needed and digitized, for example, via an A/D port to a high-speed data acquisition board of electronics 166. Data from acoustic sensor 162 may be in a range similar to that of generator 163, or in a different, e.g., higher range, e.g., 1 to 10 MHz, e.g., 1-3 MHz or 6-MHz. Can record at 8 MHz. In implementations where acoustic sensor 162 is a passive acoustic sensor, a frequency range of 100 kHz to 2 MHz may be monitored, such as 500 kHz to 1 MHz (e.g., 750 kHz).

When positioned on the platen 120, the acoustic sensor 162 is at the center of the platen 120, for example, at the axis of rotation 125, at an edge of the platen 120, or at the midpoint ( For example, a 20 inch diameter platen may be positioned 5 inches from the axis of rotation.

Referring now to Figure 2A, additional details of acoustic monitoring system 160 are shown. Acoustic sensor 162 may be retained within a recess 169 in the top surface of housing 163. Housing 163 may assist in proper positioning of sensor 162. Housing 163 is comprised of a durable material that is sufficiently rigid to protect acoustic sensor 162 from damage. However, in some implementations, for example as shown in Figures 2C and 2D, the housing is not necessary, for example sensor 162 simply fits between the sidewalls of recess 169 and It can be secured by its side walls. Various implementations described as using housing may omit the housing.

In some implementations, e.g., as shown in FIG. 2B, housing 163 extends through back layer 114, and in some implementations, e.g., as shown in FIG. 2A, housing 163 extends through back layer 114. 163 extends through a portion of the polishing layer 112. However, in some implementations, housing 163 is configured such that, for example, the top surface of sensor 163 is coplanar with the top surface of platen 120 and contacts the bottom surface of polishing pad 110. In this case, it fits completely within the recess 164 of the platen 120.

In some implementations, the housing 163 material can be applied to acoustic sensor 162 from surfaces in contact with housing 163, such as backside layer 114 or abrasive layer 112 through which housing 163 extends. It is acoustically attenuated to reduce noise received. Housing 163 may be constructed of metal, such as aluminum or stainless steel, or polymeric material, such as polycarbonate, polyvinyl chloride (PVC), or polymethyl-methacrylate (PMMA).

Assuming a spring is used, one end of spring 165 contacts housing 163 on the surface opposite acoustic sensor 162. In some implementations, the other end of spring 165 contacts support 167 resting on platen 120. Such supports can provide a stable base for the forces generated by compression of spring 165. In some implementations, the other end of spring 165 contacts the bottom surface of recess 164, that is, directly contacts the platen. The spring 165 presses the housing 163 toward the polishing surface 112a of the polishing layer 112, which forces the acoustic sensor 162 into contact with the bottom surface of the polishing layer 112. This can improve the acoustic coupling between the polishing layer and the sensor. However, various implementations described as using a spring may omit the spring, for example, assuming that the sensor is adhesively attached to the polishing pad 110 and/or the bottom of the acoustic window 119.

In some implementations, a support 167 is arranged beneath the spring 165 that provides a stationary block against which the spring 165 can be pushed against the housing 163. Support 167 may be any material sufficient to rigidly support spring 165 and housing 163 without movement or compression buckling.

In addition to or instead of a spring, the acoustic sensor 162 may be secured to a portion of the abrasive layer 112 (and/or to the acoustic window 119 described below) by an adhesive layer 170. . Adhesive layer 170 increases the contact area between acoustic sensor 162 and polishing layer 112 and/or acoustic window 119, reduces undesirable movement of acoustic sensor 162 during polishing operations, and , may reduce the presence of gas pockets between the acoustic sensor 162 and the abrasive layer 112 and/or the acoustic window 119, thereby improving the coupling to the sensor and, thus, the acoustic sensor 162 Reduces the noise of the acoustic signal received by. Adhesive layer 170 may be an adhesive, or an adhesive strip (e.g., tape) applied between acoustic sensor 162 and abrasive layer 112 and/or acoustic window 119. For example, adhesive layer 170 may be cyanoacrylate, pressure sensitive adhesive, hot melt adhesive, etc.

Returning to FIG. 2A , the polishing layer 112 includes an adhesive layer 170 and an acoustic window 119 arranged over the acoustic sensor 162 . However, in some implementations, acoustic sensor 162 contacts acoustic window 119 directly.

In implementations with an acoustic window, the acoustic window 119 is formed of a different material than the abrasive layer 112. The material of the acoustic window has sufficient acoustic transmission characteristics, e.g. an acoustic impedance of 1 to 4 MRayl, and an acoustic impedance of less than 2 (e.g. less than 1, less than 0.5) to provide a satisfactory signal for acoustic monitoring. It has an acoustic attenuation coefficient.

The acoustic impedance of a material is a measure of the repulsion that the material exhibits against the acoustic flow resulting from the acoustic pressure applied to the material. The acoustic attenuation coefficient quantifies how the transmitted sound amplitude decreases as a function of frequency for a particular material. Without wishing to be bound by theory, the specific acoustic impedance of the acoustic window 119 (AI _window ) coupling the liquid 132 and the polishing surface 112a to the acoustic signal sensor 162, the specific acoustic impedance of the acoustic window 119 is advantageous, It may be within the range of .

In particular, window 119 may have lower acoustic attenuation than surrounding abrasive layer 112. This allows the polishing layer 112 to be comprised of a wider range of materials to meet the needs of CMP operations. The window may be constructed of a non-porous material, for example a solid body. In contrast, the polishing layer 112 may be a porous, eg, microporous, eg, polymer matrix in which hollow plastic microspheres are embedded.

The acoustic window 119 extends through the polishing layer 112 such that one surface, eg, the top surface, is coplanar with the polishing surface 112a of the polishing layer 112. The opposing surface, for example the bottom surface, may be coplanar with the lower surface 112b of the polishing layer 112. In some implementations, an indentation 118 is formed in the lower surface 112b opposite the polishing surface 112a. The portion of the polishing layer 112 containing the indentations 118 forms a thin portion of the polishing layer 112 having a smaller thickness than the remainder of the polishing layer 112, and the acoustic window 119 is located in the thin portion. .

Acoustic window 119 may be comprised of a non-porous material. In general, non-porous materials transmit acoustic signals with reduced noise and dispersion compared to porous materials. The acoustic window 119 material may have a compressibility within the range of the compressibility of the surrounding polishing layer 112 material, which reduces the effect of the acoustic window 119 on the polishing characteristics of the polishing surface on the substrate. In some implementations, the acoustic window 119 compressibility is within 10% (e.g., within 8%, within 5%, within 3%) of the abrasive layer 112 compressibility. In some implementations, acoustic window 119 is opaque to light, for example, visible light. Acoustic window 119 may be composed of one or more of polyurethane, polyacrylate, polyethylene, or other polymers with low acoustic impedance and low acoustic attenuation.

2C, an acoustic window 119 is shown extending through the total thickness of the abrasive layer 112 such that the bottom surface 112b is flat. Sensor 162 extends through aperture 114a of back layer 114 to contact the underside of window 119.

In some implementations, acoustic monitoring system 160 includes an acoustically transparent layer 172 in contact with adhesive layer 170. Transmissive layer 172 is an index matching material that provides increased acoustic signal coupling between elements in contact with transmissive layer 172. Transmissive layer 172 may be arranged between adhesive layer 170 and acoustic sensor 162, or between acoustic window 119 and adhesive layer 170, as shown in FIG. 2B. In some implementations, acoustic monitoring system 160 includes an adhesive layer 170, a transmissive layer 172, or both. For example, the transmission layer 172 may be a layer of Aqualink™, Rexolite, or Aqualene™. In some implementations, the transmissive layer 172 has an acoustic attenuation that is within 20% of the acoustic attenuation of the acoustic window 119, for example, within 10%. The acoustically transparent layer 172 may have an acoustic attenuation that is less than that of the surrounding back layer 114 .

The acoustically transparent layer 172 may be selected to have a compressibility similar to that of the backside layer 114, e.g., within 20%, e.g., within 10% of the compressibility of the peripheral backside layer 114. .

Figure 2D is an implementation where the acoustic window 119 extends through the thickness of the abrasive layer 112 and the transmissive layer 172 extends through the thickness of the backside layer 114. However, transmission layer 172 may be thinner than back layer 114. In this case, sensor 162 may protrude above the top surface of platen 120 to engage transmissive layer 172 .

Additionally, the acoustic signal sensor 162 is shown as having sufficient dimensions to contact both the transparent layer 172 and the opposing surfaces of the recess 164. In such implementations, the pressure of the polishing operation brings the acoustic signal sensor 162 into contact with the transmissive layer 172 while the recess 164 provides support for the acoustic signal sensor 162 . An adhesive layer 170 is arranged between the transmissive layer 172 and the acoustic window 119, such as those described herein. In some implementations, an additional adhesive attaches the contact surface between acoustic signal sensor 162 and transmission layer 172.

In some implementations, acoustic monitoring system 160 includes an active acoustic monitoring system. Such implementations include an acoustic signal generator and an acoustic sensor, such as acoustic sensor 162.

The acoustic signal generator generates (i.e., emits) acoustic signals from the side of the substrate closer to the polishing pad 110. The acoustic signal generator may be connected by circuit 168 to a power supply and/or other signal processing electronics 166 via a rotary coupling, for example a mercury slip ring. Signal processing electronics 166 may, in turn, be coupled to a controller 190 that may, for example, variably increase or decrease the current supply to the generator to increase or decrease the amount of acoustic energy transmitted by the generator. It can be additionally configured to control frequency. The acoustic signal generator 163 and the acoustic sensor 162 may be coupled to each other, but this is not required. Sensor 162 and generator may be separate and physically separate from each other. For the generator, commercially available acoustic signal generators can be used. The generator may be attached to the platen 120 and held in place, for example, using clamps or by a threaded connection to the platen 120.

3 , in some implementations, a plurality of acoustic signal sensors 1623 may be installed on the platen 120, with each acoustic sensor 162 associated with an acoustic window 119. . Each sensor 162 may be configured in the manner described for any of FIGS. 1 and 2A-2B. Signals from sensors 162 may be used by controller 190 to calculate the location distribution of acoustic emission events that occur on substrate 10 during polishing. In some implementations, the plurality of sensors 162 may be located at different angular positions about the axis of rotation of platen 120, but at the same radial distance from the axis of rotation. In some implementations, such as the implementation of Figure 3, the plurality of sensors 162 are located at different radial distances from the axis of rotation of platen 120, but at the same angular position. In some implementations, the plurality of sensors 162 are located at different radial distances from the axis of rotation of platen 120 and at different angular positions about the axis of rotation.

In some implementations, acoustic window 119 is surrounded by a smooth portion 174 of abrasive layer 112. The smooth portion 174 is free of grooves 116 and is flush with the upper surface of the acoustic window 119 . Implementations that include a smooth portion 174 surrounding the acoustic window 119 can reduce noise associated with the substrate 10 interacting with the grooves 116 of the polishing layer 112 during a polishing operation.

Substrate 10 is formed by sequential deposition of conductive, semiconductive, or insulating layers on a silicon wafer. A filler layer is deposited over the non-planar surface and planarized such that the filler and the non-planar surface, such as the patterned layer, have a common coplanar surface and/or the non-planar surface is exposed. In some implementations, in-situ acoustic monitoring system 160 detects transitions between layers, or topographic information related to one or more layers of substrate 10. It provides information to be used between process steps. For example, the substrate 10 including the filler layer may have non-uniform surface roughness, such as topography, from the deposition process. Detecting when the topography has flattened allows the system to modify one or more process conditions based on the transition. For example, once the filler layer surface is planarized, the apparatus 100 may stop the high carrier head 140 pressure stage.

Figures 5A-5C illustrate intermediate layer transitions present in the planarization process for substrate 500. 6 shows an example acoustic signal 600 comparing the summed power spectral density (PSD) over a range of frequencies on the y-axis versus time in seconds (s). The acoustic signal 600 has distinct regions, such as a first region 602, a second region 604, and a third region 606. In some implementations, regions 602, 604, and 606 correspond to layer transitions in substrate 500, such as those shown in FIGS. 5A-5C.

Figure 5A shows an example substrate 10 before polishing. Substrate 10 includes a wafer 502, for example a silicon wafer, a patterned layer 504, and a filler layer 508. Prior to the planarization step, the filler layer 508 is non-planar and includes a topography 509. The topography 509 may result from the deposition of a filler layer 508 over the patterned layer 504 and has dimensions on the order of the feature size, eg, a metal line width.

During operation, the carrier head holds the substrate 10 and relative motion is created between the polishing layer 112 and the substrate 10. The acoustic signal sensor receives an acoustic signal, e.g., acoustic signal 600, based on contact of the polishing surface 112a with the outermost layer of the substrate 10. 5A, at the start of polishing, topography 509 and polishing layer 112 come into contact.

Without wishing to be bound by theory, the acoustic signal 600 changes based on the changing contact surfaces of the filler layer 508 material and the polishing layer 112 material. In particular, initially non-uniform topography can produce significant acoustic signals. However, as polishing progresses and the topography 509 of the filler layer 508 becomes planar, the interface between the polishing surface 110 and the substrate 10 becomes smoother, and the acoustic signal may decrease. Polishing of topography 509 may correspond to first region 602 of signal 600 in FIG. 6 .

Again, without wishing to be bound by theory, a layer transition occurs when topography 509 is removed by device 100. As shown in Figure 5B, the surface of the remaining filler layer 508 is substantially planar. Polishing the planar surface may correspond to the second region 604 of the acoustic signal 600. In the second region 604 of signal 600, acoustic signal 600 is substantially constant (although subject to noise).

Still, without wishing to be bound by theory, the second region 604 continues in time until the filler layer 508 extending over the patterned layer 504 is removed. As shown in Figure 5C, the patterned layer 504 is composed of a different material than the filler layer 508 and interacts differently with the polishing layer 112 surface and materials, thereby producing an acoustic signal ( The third area 606 of 600 is created. Additionally, continued polishing can produce dishing, and this topology can again increase the acoustic signal. The third area 606 is not constant, for example, may increase or decrease.

In some implementations, differentiation between regions 602, 604, and 606, e.g., detection of layer transitions, may be accomplished by the controller 190 and/or acoustic monitoring system 160 of device 100. there is. Detection may be accomplished through a variety of calculations known in the art for detection of slope changes, but may include the calculation of one or more differentiation, rolling average, windowing, or box logic algorithms.

In additional implementations, acoustic signal 600 may be processed using additional steps prior to application of a tilt change detection algorithm. For example, the acoustic signal 600 may undergo one or more filters, such as a band-pass filter, and/or one or more transforms, such as a fast Fourier transform. For example, a band-pass filter can be used to isolate desirable frequencies of the acoustic signal 600 prior to processing, such as frequencies in the 50 to 500 kHz range, or 200 to 700 kHz range.

In some implementations, device 100 modifies one or more polishing parameters in response to distinguishing regions 602, 604, and 606. For example, during the first region 602 where the topography 509 is being removed, the device 100 may dispense a first abrasive polishing liquid 132 for rapid removal of the topography 509 . Once the transition from first region 602 to second region 604 is detected, a different polishing liquid 132 with a lower polishing rate or lower selectivity may be dispensed to pad 110.

Alternatively or additionally, once a transition from second region 604 to third region 606 is detected, the pressure applied by carrier head 140 may be reduced. This may reduce the risk of dishing or erosion of the filler layer 508.

Now, referring to the signal from the sensor 162 of any of the previous implementations, for example, the signal after amplification, pre-filtering and digitization may be used for endpoint detection or feedback or feedforward control, e.g. , data can be processed by the controller 190.

In some implementations, controller 190 is configured to monitor acoustic loss. For example, the received signal intensity is compared to the emitted signal intensity to generate a normalized signal, and the normalized signal can be monitored over time to detect changes. Such changes may indicate a polishing endpoint, for example when the signal crosses a threshold.

In some implementations, 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 membrane transition occurs at a particular radius. Information about the time of transition by radius can be used to trigger the endpoint. As another example, a fast Fourier transform (FFT) may be performed on the signal to generate a frequency spectrum. A specific frequency band can be monitored, and if the intensity of the frequency band exceeds a threshold, this may indicate exposure of the underlying layer, which can be used to trigger an endpoint. Alternatively, if the location (e.g. wavelength) or bandwidth of a local maximum or minimum in a selected frequency range exceeds a threshold, this may indicate exposure of the underlying layer, which can be used to trigger an endpoint. . For example, to monitor polishing of interlayer dielectric (ILD) in shallow trench isolation (STI), a frequency range of 225 kHz to 350 kHz can be monitored.

As another example, wavelet packet transform (WPT) may be performed on the signal to decompose the signal into low-frequency and high-frequency components. The decomposition can be repeated as needed to divide the signal into smaller components. The intensity of one of the frequency components can be monitored, and if the intensity of the component exceeds a threshold, this may indicate exposure of the underlying layer, which can be used to trigger an endpoint.

Assuming that the positions of the sensors 162 relative to the substrate 10 are known, the positions of acoustic events on the substrate can be calculated, for example, using a motor encoder signal or an optical interrupt attached to the platen 120. For example, the radial distance of the event from the center of the substrate can be calculated. Determination of the position of the sensor relative to the substrate is discussed in US Patent No. 6,159,073 and US Patent No. 6,296,548, which are incorporated by reference.

Various process significant acoustic events include microscratches, membrane transition break-through, and membrane 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 the peak frequencies that occur during polishing. Monitoring within defined frequency ranges and experimentally determined thresholds are used to identify expected and unexpected changes during polishing. Examples of expected changes include the sudden appearance of peak frequencies during transitions in membrane stiffness. Examples of unexpected changes include problems in the consumable set (eg, pad glazing or other process drift-inducing machine health issues).

In operation, when the device substrate 10 is being polished at the polishing station 100, acoustic signals are collected from the in-situ acoustic monitoring system 160. The signal is monitored to detect exposure of the lower layer of substrate 10. For example, a specific frequency range can be monitored, and the intensity can be monitored and compared to an experimentally determined threshold.

Detection of a polishing endpoint triggers a stop to polishing, but polishing may continue for a predetermined amount of time after triggering the endpoint. Alternatively or additionally, the collected data and/or endpoint detection time may be fed forward to control processing of a substrate in a subsequent processing operation, e.g., polishing at a subsequent station, or a subsequent substrate at the same polishing station. Can be fed back to control processing. For example, detection of a polishing endpoint can trigger modifications to the current pressures of the polishing head. As another example, detection of a polishing endpoint may trigger modifications to baseline pressures for subsequent polishing of a new substrate.

All of the implementations and functional operations described herein may be implemented in digital electronic circuitry, including the structural means disclosed herein and structural equivalents thereof, or in computer software, firmware or hardware, or combinations thereof. You can. Implementations described herein may be implemented as one or more non-transitory computer program products, i.e., for execution by one or more computer programs (data processing devices, e.g., programmable processors, computers, or multiple processors or computers). , or tangibly embodied in a machine-readable storage device, to control its operation.

A computer program (also known as a program, software, software application, or code) may be written in any form of programming language, including compiled or interpreted languages, as a stand-alone program, or as a module, component, subroutine, or module. It may be distributed in any form, including as another unit suitable for use in a computing environment. Computer programs do not necessarily correspond to files. A program can be stored in other programs or as part of a file that holds data, in a single file dedicated to that program, or in a number of cooperating files (e.g., files that store one or more modules, subprograms, or portions of code). ) can be stored in . A computer program may be distributed to run on a single computer or on multiple computers located in one location or distributed across multiple locations and interconnected by a communications network.

The processes and logic flows described herein may be performed by one or more programmable processors executing one or more computer programs to perform functions by manipulating input data and generating output. Processes and logic flows may also be performed by special purpose logic circuitry, such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC), and the device may also be implemented as such special purpose logic circuitry. It can be.

The term “data processing apparatus” includes all apparatus, devices and machines for processing data, including, for example, a programmable processor, a computer, or multiple processors or computers. In addition to the hardware, the device may include code that creates an execution environment for the computer program in question, such as code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of these. . Processors suitable for executing computer programs include, by way of example, both general-purpose and special-purpose microprocessors, and any one or more processors of any type of digital computer.

Computer-readable media suitable for storing computer program instructions and data include, for example, semiconductor memory devices such as EPROM, EEPROM, and flash memory devices; magnetic disks, such as internal hard disks or removable disks; magneto-optical disks; and all forms of non-volatile memory, media and memory devices, including CD ROM and DVD-ROM disks. The processor and memory may be supplemented by or included in special purpose logic circuitry.

The polishing apparatus and methods described above can be applied to various polishing systems. The polishing pad, the carrier head, or both can be moved to provide relative motion between the polishing surface and the wafer. For example, the platen can orbit instead of rotating. The polishing pad may be a circular (or any other shaped) pad fixed to the platen. Some aspects of the endpoint detection system may be applicable to linear polishing systems (eg, where the polishing pad is a continuous or reel-to-reel belt that moves linearly). The abrasive layer can be a standard (eg, polyurethane with or without fillers) abrasive 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 may be maintained in a homeotropic orientation or in some other orientations.

Although this specification contains many specific details, these should not be construed as limitations on the scope of the subject matter that may be claimed, but rather as descriptions of features that may be specific to specific embodiments of specific inventions. In some implementations, the method can be applied to other combinations of overlying and underlying materials, and to signals from other types of in-situ monitoring systems, such as optical monitoring or eddy current monitoring systems.

Claims (20)

A chemical mechanical polishing device, comprising:
platen;
a polishing pad supported on the platen, the polishing pad having a polishing layer;
a carrier head for holding the surface of the substrate against the polishing pad;
a motor for generating relative motion between the platen and the carrier head to polish an upper layer on the substrate;
An in-situ acoustic monitoring system comprising an acoustic window of the polishing pad and an acoustic sensor acoustically coupled to the acoustic window, the acoustic window having a lower acoustic attenuation than the polishing layer, the acoustic window contacting the substrate. having an uppermost surface on the same plane as the polishing surface; and
A controller configured to detect a polishing endpoint based on received acoustic signals from the in-situ acoustic monitoring system.
Device, including. According to paragraph 1,
The apparatus of claim 1, wherein the bottom surface of the acoustic window is coplanar with the bottom surface of the polishing layer. According to paragraph 1,
The device of claim 1, wherein the polishing pad has a backing layer beneath the polishing pad. According to paragraph 3,
The apparatus of claim 1, wherein the bottom surface of the acoustic window is coplanar with the top surface of the back layer. According to paragraph 4,
wherein an aperture is formed through the backside layer. According to clause 5,
wherein the sensor is positioned at least partially in the aperture to contact the bottom surface of the acoustic window. According to clause 5,
The device further comprising an acoustically transmissive layer positioned in an aperture through the back layer between the acoustic sensor and the acoustic window, wherein the acoustically transmissive layer has a lower acoustic attenuation than the back layer. In clause 7,
The apparatus of claim 1, wherein the bottom surface of the acoustically transmissive layer is coplanar with the bottom surface of the polishing pad. According to paragraph 1,
an indentation is formed on the lower side of the polishing layer to form a thin portion of the polishing layer, the acoustic window is located in the thin portion of the polishing layer, and the sensor is at least partially located in the indentation portion. Device. According to paragraph 1,
The device of claim 1, wherein the acoustic window is a non-porous material. According to clause 10,
The device of claim 1, wherein the polishing layer is porous and the acoustic window is solid. According to paragraph 1,
wherein the compressibility of the acoustic window is within 20% of the compressibility of the polishing layer. According to paragraph 1,
wherein the acoustic sensor is adhesively attached to the acoustic window to receive acoustic signals from the substrate. According to paragraph 1,
The device further comprising an acoustically transparent layer arranged between the acoustic sensor and the acoustic window. According to clause 14,
The device of claim 1, wherein the acoustically transparent layer is adhesively attached to the acoustic window. According to clause 15,
The device of claim 1, wherein the acoustic sensor is adhesively attached to the acoustically transmissive layer. According to paragraph 1,
The in-situ acoustic monitoring system includes a housing for supporting the acoustic sensor, and a spring arranged to press the housing and the acoustic sensor against a portion of the polishing layer. According to clause 17,
The device of claim 1, wherein the spring comprises a rigid spring or a long-travel spring. According to paragraph 1,
wherein the controller is configured to perform frequency domain analysis to determine changes in relative power of spectral frequencies. A chemical mechanical polishing device, comprising:
platen;
a polishing pad supported on the platen;
a carrier head for holding the surface of the substrate against the polishing pad;
a motor for generating relative motion between the platen and the carrier head to polish an upper 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 being adhesively attached to the 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.
Device, including.

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