CN117715729A - Detecting planarization from acoustic signals during chemical mechanical polishing - Google Patents

Abstract

A chemical mechanical polishing apparatus comprising: a platform; a polishing pad supported on the platen; a carrier head for holding a substrate surface against a polishing pad; a motor for producing relative motion between the platen and the carrier head for polishing an upper cladding on the substrate; an in situ acoustic monitoring system comprising an acoustic sensor that receives an acoustic signal from a substrate surface; and a controller configured to detect planarization of topography on the substrate based on signals from the in situ acoustic monitoring system.

Description

Detecting planarization from acoustic signals during chemical mechanical polishing

Technical Field

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

Background

Integrated circuits are typically formed on a substrate by sequentially depositing conductive, semiconductive, or insulative layers on a silicon wafer. One fabrication step involves depositing a filler layer over a non-planar surface and planarizing the filler layer. For some applications, the filler layer is planarized until the top surface of the patterned layer is exposed. For example, a conductive filler layer may be deposited on the patterned insulating layer to fill the trenches or holes in the insulating layer. After planarization, the portions of the metal layer remaining 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, for example by polishing for a predetermined period of time, to leave a portion of the filler layer over the non-planar surface. Furthermore, photolithography typically requires planarization of the substrate surface.

Chemical Mechanical Polishing (CMP) is a well-known planarization method. Such planarization methods typically require the substrate to be mounted on a carrier head or polishing head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to urge the substrate against the polishing pad. An abrasive polishing slurry is typically supplied to the surface of the polishing pad.

One problem with CMP is determining whether the polishing process is complete, i.e., whether the substrate layer has been planarized to a desired level or thickness, or when a desired amount of material has been removed. Variations in slurry distribution, polishing pad condition, relative velocity between the polishing pad and the substrate, and loading on the substrate can result in variations in the material removal rate. These variations, as well as variations in the initial thickness of the substrate layer, result in variations in the time required to reach the polishing endpoint. Thus, it is generally not possible to determine the polishing endpoint as a function of polishing time alone.

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.

Disclosure of Invention

In one aspect, a chemical mechanical polishing apparatus includes: a platform; a polishing pad supported on the platen; a carrier head for holding a surface of a substrate against a polishing pad; a motor for producing relative motion between the platen and the carrier head for polishing an upper cladding on the substrate; an in situ acoustic monitoring system comprising an acoustic sensor that receives an acoustic signal from a substrate surface; and a controller configured to detect planarization of the topography on the substrate based on signals from the in situ acoustic monitoring system.

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. The exposure of the lower cladding layer can be detected more reliably. Polishing can be stopped more reliably, and wafer-to-wafer uniformity can be improved. The polishing parameters may be varied after planarization (i.e., smoothing the substrate surface) is detected, which may improve uniformity or increase polishing rate. Polishing may be stopped after planarization is detected or after expiration of a preset time after planarization is detected. This may provide an alternative endpoint technique.

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

Drawings

Fig. 1 shows a schematic cross-sectional view of an example of a polishing apparatus.

Fig. 2A shows a schematic cross-sectional view of an acoustic monitoring sensor engaging a portion of a polishing pad.

Fig. 2B shows a schematic cross-sectional view of another embodiment of an acoustic monitoring sensor having an acoustically transmissive layer.

Fig. 2C shows a schematic cross-sectional view of another embodiment of an acoustic monitoring sensor.

Fig. 2D shows a schematic cross-sectional view of another embodiment of an acoustic monitoring sensor in which an acoustic window is formed in a polishing layer and an acoustically transmissive layer is formed in a backing layer of a polishing pad.

Fig. 3 shows a schematic top view of a platform with a plurality of acoustic monitoring sensor windows.

Fig. 4 shows a schematic top view of a platform with a flat portion surrounding an acoustic monitoring sensor window.

Fig. 5A to 5C illustrate planarization of a substrate surface.

Fig. 6 shows a graph of the sum of the spectral power densities over a frequency range as a function of time.

Like reference symbols in the various drawings indicate like elements.

Detailed Description

In some semiconductor chip manufacturing processes, an upper cladding layer (e.g., metal, silicon oxide, or polysilicon) is polished until a lower cladding layer, e.g., a dielectric such as silicon oxide, silicon nitride, or a high-K dielectric, is exposed. For some applications, the acoustic emission from the substrate will change when the lower cladding is exposed. The polishing endpoint may be determined by detecting such a change in the acoustic signal. However, existing monitoring techniques may not meet the increasing demands 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 spectrum is related to the material properties of the substrate. Without being limited to any particular theory, possible sources of such energy (also referred to as "stress energy") and its characteristic frequency include breaking of chemical bonds, characteristic phonon frequencies, slip adhesion mechanisms, and the like. It may be noted that such stress energy acoustic effects are different from noise generated by vibrations caused by friction of the substrate against the polishing pad (which is sometimes also referred to as acoustic signals), or from noise generated by cracking, chipping, breaking, or the like of defects on the substrate. Via suitable filtering, the stress energy can be distinguished from other acoustic signals, for example, from friction of the substrate against the polishing pad or noise generated by defects on the substrate. For example, the signal from the acoustic sensor may be compared to a signal measured from the test substrate that is known to represent stress energy.

However, a potential problem with acoustic monitoring is the transmission of acoustic signals to the sensor. Some polishing pads have poor acoustic energy transmission. Furthermore, poor coupling between the polishing pad and the sensor tends to attenuate the acoustic signal. Furthermore, establishing a consistent coupling from sensor to sensor can be difficult.

It is therefore advantageous to bring the acoustic sensor into contact with an acoustic "window" having low acoustic signal attenuation. In some embodiments, a second layer of transmissive material is added to the in situ acoustic monitoring system to further increase the acoustic signal coupled to the acoustic sensor.

For example, adhering the acoustic sensor to the coupling window with an adhesive may reduce noise in the acoustic signal associated with movement of the acoustic sensor within the enclosure. The adhesive can provide excellent coupling of the sensor to the polishing pad and more reliable acoustic attenuation from sensor to sensor.

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

Fig. 1 shows an example of a polishing apparatus 100. The polishing apparatus 100 includes a rotatable dished platen 120, and the polishing pad 110 is disposed on the rotatable dished platen 120. The polishing pad 110 may be a dual layer polishing pad having an outer polishing layer 112 and a softer backing layer 114. The platform is operable to rotate about an axis 125. For example, a motor 121 (e.g., a DC induction motor) may rotate the drive shaft member 124 to rotate the platform 120.

The polishing apparatus 100 can include a port 130 for dispensing a polishing liquid 132, such as an abrasive slurry, onto the polishing pad 110 and, in turn, onto the pad. The polishing apparatus may further include a polishing pad conditioner for abrading the polishing pad 110 to maintain the polishing pad 110 in a consistent abraded state.

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 may have independent control of polishing parameters (e.g., pressure) associated with each respective substrate.

Carrier head 140 may include a retaining ring 142 to secure substrate 10 under flexible membrane 144. The carrier head 140 also includes one or more independently controllable pressurizable chambers (e.g., three chambers 146a-146 c) defined by the membrane that can apply independently controllable pressures to associated areas on the flexible membrane 144 and, thus, on the substrate 10 (see fig. 1). Although only three chambers are shown in fig. 1 for ease of illustration, there may be one or two chambers, or four or more chambers, e.g., five chambers.

The carrier head 140 is suspended from a support structure 150 (e.g., a turntable or track) and is connected by a drive shaft member 152 to a carrier head rotating motor 154 (e.g., a DC induction motor) so that the carrier head can rotate about an axis 155. Alternatively, each carrier head 140 may oscillate laterally (e.g., on a slider on the turntable 150), or by rotational oscillation of the turntable itself, or by sliding along a track. In common operation, the platen rotates about its central axis 125 and each carrier head rotates about its central axis 155 and translates laterally across the top surface of the polishing pad.

A controller 190 (such as a programmable computer) is connected to the motors 121, 154 to control the rotational rate of the platform 120 and carrier head 140. For example, each motor may include an encoder that measures the rotational rate of the associated drive shaft member. The feedback control circuit, which may be in the motor itself, as part of the controller, or as a separate circuit, receives the measured rotation rate from the encoder and adjusts the current supplied to the motor to ensure that the rotation rate of the drive shaft member matches the rotation rate received from the controller.

Polishing apparatus 100 includes at least one in situ acoustic monitoring system 160. The in situ acoustic monitoring system 160 includes one or more acoustic signal sensors 162. Each acoustic signal sensor may be mounted at one or more locations on the upper platform 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 undergoes deformation.

A position sensor (e.g., an optical interrupter connected to an edge of the platform, or a rotary encoder) may be used to sense the angular position of the platform 120. This allows only the portion of the signal measured when the sensor 162 is near the substrate (e.g., when the sensor 162 is below the carrier head or substrate) to be used in endpoint detection.

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

The portion of the polishing pad directly above the acoustic sensor 162 may include an acoustic window 119. The acoustic window 119 may be narrower than the acoustic sensor 162 (e.g., as shown in fig. 2A), or both may have substantially equal widths (e.g., within 10%), e.g., as shown in fig. 2C. Where the acoustic window 119 is narrower than the acoustic sensor 119, the sensor may also be adjacent the bottom of the polishing layer 112.

The acoustic sensor 162 is a contact acoustic sensor having a surface that is coupled to (e.g., in direct contact with) or has only an adhesive layer with a portion of the polishing layer 112 and/or the acoustic window 119. For example, the acoustic sensor 162 may be an electromagnetic acoustic transducer or a piezoelectric acoustic transducer. The piezoelectric sensor may comprise a rigid contact plate, e.g. stainless steel or similar, placed in contact with the body to be monitored, and a piezoelectric component on the back side of the contact plate, e.g. a piezoelectric layer sandwiched between two electrodes.

In some embodiments, the acoustic sensor 162 is positioned within a recess 169 in the housing 163. An optional spring 165 may be disposed between the housing 163 and the support 167 to provide pressure to the housing 163. Pressure on the housing 163 presses the acoustic sensor 162 into contact with a portion of the polishing pad 110. Alternatively, for example, if a housing is not used, the spring 165 may press directly against the acoustic sensor 162. In some embodiments, the spring 165 is a long Cheng Danhuang, 165, the long Cheng Danhuang providing a similar pressure to the strong spring 165 over a larger compression range.

The acoustic sensor 162 may be connected to a power source and/or other signal processing electronics 166 via a rotational coupling (e.g., mercury slip ring) through circuitry 168.

In some embodiments, in situ acoustic monitoring system 160 is a passive acoustic monitoring system. In this case, the signal is monitored by the acoustic sensor 162 without generating a signal from the acoustic signal generator (or the acoustic signal generator may be omitted from the system entirely). The passive acoustic signal monitored by the acoustic sensor 162 may be in the range of 50kHz to 1MHz, such as 200kHz to 400kHz, or 200kHz to 1 MHz. For example, to monitor the polishing of an interlayer dielectric (ILD) in Shallow Trench Isolation (STI), a frequency range of 225kHz to 350kHz may be monitored.

The signal from sensor 162 may be amplified by a built-in internal amplifier. In some implementations, the amplification gain is between 40dB and 60dB (e.g., 50 dB). The signal from the acoustic sensor 162 may then be further amplified and filtered (if desired) and digitized via an a/D port to a high-speed data collection pad, for example in electronics 166. The data from the acoustic sensor 162 may be recorded in a similar range as the generator 163 or in a different (e.g., higher) range (e.g., from 1Mhz to 10Mhz, such as 1-3MHz or 6-8 Mz). In embodiments in which acoustic sensor 162 is a passive acoustic sensor, a frequency range from 100kHz to 2MHz, such as 500kHz to 1MHz (e.g., 750 kHz), may be monitored.

If the acoustic sensor 162 is positioned in the platform 120, the acoustic sensor 162 may be located at the center of the platform 120, for example, at the axis of rotation 125, at the edge of the platform 120, or at the midpoint (e.g., 5 inches from the axis of rotation for a 20 inch diameter platform).

Referring now to FIG. 2A, further details of the acoustic monitoring system 160 are shown. The acoustic sensor 162 may be retained within a recess 169 in the top surface of the housing 163. The housing 163 may facilitate proper positioning of the sensor 162. The housing 163 is composed of a rigid, durable material sufficient to protect the acoustic sensor 162 from damage. However, in some embodiments, for example, as shown in fig. 2C and 2D, a housing is not necessary, for example, the sensor 162 may simply fit between and be secured by the sidewalls of the recess 169. Various embodiments described as using a housing may omit the housing.

In some embodiments, for example, as shown in fig. 2B, the housing 163 extends through the backing layer 114, and in some embodiments, for example, as shown in fig. 2A, the housing 163 extends through a portion of the polishing layer 112. However, in some embodiments, for example, if the top surface of the sensor 163 is coplanar with the top surface of the platen 120 and contacts the bottom surface of the polishing pad 110, the housing 163 fits completely within the recess 164 in the platen 120.

In some embodiments, the housing 163 material is acoustically attenuated to reduce noise received by the acoustic sensor 162 from surfaces in contact with the housing 163, such as the backing layer 114 or the polishing layer 112 through which the housing 163 extends. The housing 163 may be composed of a metal (e.g., aluminum or stainless steel), or a polymeric material (e.g., polycarbonate, polyvinyl chloride (PVC), or polymethyl methacrylate (PMMA)).

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

In some embodiments, the support 167 is disposed below the spring 165, which provides a fixed mass against which the spring 165 can urge with respect to the housing 163. The support 167 may be any material that is sufficiently rigid to support the spring 165 and the housing 163 without moving or compressing buckling.

In addition to or in lieu of springs, the acoustic sensor 162 may be secured to a portion of the polishing layer 112 (and/or acoustic window 119 described below) by an adhesive layer 170. The adhesion layer 170 increases the contact area between the acoustic sensor 162 and the polishing layer 112 and/or the acoustic window 119, reduces unwanted movement in the acoustic sensor 162 during the polishing operation, and may reduce the presence of air pockets between the acoustic sensor 162 and the polishing layer 112 and/or the acoustic window 119, thereby improving coupling to the sensor, thereby reducing noise in acoustic signals received by the acoustic sensor 162. The adhesive layer 170 may be glue or an adhesive tape (e.g., adhesive tape) applied between the acoustic sensor 162 and the polishing layer 112 and/or acoustic window 119. For example, the adhesive layer 170 may be cyanoacrylate, pressure sensitive adhesive, hot melt adhesive, or the like.

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

In embodiments having an acoustic window, the acoustic window 119 is formed of a different material than the polishing layer 112. The material of the acoustic window has sufficient acoustic transmission characteristics, e.g., acoustic impedance between 1 megarayl (MRayl) and 4 megarayl and acoustic attenuation coefficient below 2 (e.g., below 1, below 0.5), to provide signal satisfaction for acoustic monitoring.

MaterialIs a measure of the reaction of a material to the acoustic flow generated by the acoustic pressure applied to the material. The acoustic attenuation coefficient quantifies how the transmitted acoustic amplitude decreases with changes in the frequency of a particular material. Without wishing to be bound by theory, the acoustic window 119 has an acoustic impedance (Al _Window ) Coupling the liquid 132 and polished surface 112a to the acoustic signal sensor 162, the acoustic window 119 may advantageously have an acoustic impedance that is in the range

In particular, the window 119 may have a lower acoustic attenuation than the surrounding polishing layer 112. This allows the polishing layer 112 to be composed of a wide range of materials to meet the needs of the CMP operation. The window may be composed of a non-porous material (e.g., a solid body). In contrast, the polishing layer 112 can be porous, e.g., microporous, such as a polymer matrix in which hollow plastic microspheres are embedded.

The acoustic window 119 extends through the polishing layer 112 such that one surface (e.g., the upper surface) is coplanar with the polishing surface 112a of the polishing layer 112. The opposing surface (e.g., bottom surface) can be coplanar with the lower surface 112b of the polishing layer 112. In some embodiments, indentations 118 are formed in lower surface 112b opposite polishing surface 112 a. The portion of polishing layer 112 that includes indentations 118 forms a thin portion of polishing layer 112 that is less thick than the remaining polishing layer 112, and acoustic window 119 is located in the thin portion.

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

Referring to fig. 2C, acoustic window 119 is illustrated as extending through the total thickness of polishing layer 112 such that lower surface 112b is planar. The sensor 162 extends through the aperture 114a in the backing layer 114 to contact the underside of the window 119.

In some embodiments, the acoustic monitoring system 160 includes an acoustically transmissive layer 172 in contact with the adhesive layer 170. The transmissive layer 172 is an index matching material that provides increased acoustic signal coupling between elements in contact with the transmissive layer 172. The transmissive layer 172 may be disposed between the acoustic window 119 and the adhesive layer 170 or between the adhesive layer 170 and the acoustic sensor 162, as shown in fig. 2B. In some implementations, the acoustic monitoring system 160 includes an adhesive layer 170, a transmissive layer 172, or both. For example, the transmissive layer 172 may be Aqualink ^TM Rexolite, or Aqualene ^TM Is a layer of (c). In some embodiments, the transmissive layer 172 has an acoustic attenuation within 20% (e.g., 10%) of the acoustic attenuation of the acoustic window 119. The acoustically transmissive layer 172 may have an acoustic attenuation that is less than the acoustic attenuation of the surrounding backing layer 114.

The acoustically transmissive layer 172 can be selected to have a compressibility similar to that of the backing layer 114, for example, within 20% (e.g., within 10%) of the compressibility of the surrounding backing layer 114.

Fig. 2D is an embodiment in which acoustic window 119 extends through the thickness of polishing layer 112 and transmissive layer 172 extends through the thickness of backing layer 114. However, the transmissive layer 172 may be thinner than the backing layer 114. In this case, the sensor 162 may protrude above the top surface of the platform 120 to engage the transmissive layer 172.

Further, the acoustic signal sensor 162 is shown as having dimensions sufficient to contact both the transmissive layer 172 and the opposing surface of the recess 164. In such embodiments, the recess 164 provides support for the acoustic signal sensor 162 while the pressure of the polishing operation brings the acoustic signal sensor 162 into contact with the transmissive layer 172. An adhesive layer 170 is disposed between the transmissive layer 172 and the acoustic window 119, such as those adhesive layers 170 described herein. In some embodiments, additional adhesive secures the contact surface between the acoustic signal sensor 162 and the transmissive layer 172.

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

The acoustic signal generator generates (i.e., emits) an acoustic signal from the side of the substrate that is closer to the polishing pad 110. The acoustic signal generator may be connected to a power source and/or other signal processing electronics 166 via a rotational coupling (e.g., mercury slip ring) by circuitry 168. The signal processing electronics 166 may in turn be connected to a controller 190, and the controller 190 may additionally be configured to control the magnitude or frequency of the acoustic energy transmitted through the generator, for example, by variably increasing or decreasing the current supplied to the generator. The acoustic signal generator 163 and the acoustic sensor 162 may be coupled to each other, although this is not required. The sensor 162 and the generator may be decoupled and physically separated from each other. For the generator, a commercially available acoustic signal generator may be used. The generator may be attached to the platform 120 and held in place on the platform 120, for example, with clamps or by a threaded connection.

As depicted in fig. 3, in some embodiments, a plurality of acoustic signal sensors 162 may be mounted in the platform 120, each acoustic sensor 162 being associated with an acoustic window 119. Each sensor 162 may be configured in the manner described in any of fig. 1 and 2A-2B. The signals from the sensors 162 may be used by the controller 190 to calculate the location distribution of acoustic emission events occurring on the substrate 10 during polishing. In some embodiments, the plurality of sensors 162 may be positioned at different angular positions around the axis of rotation of the platform 120, but at the same radial distance from the axis of rotation. In some embodiments, such as the embodiment of fig. 3, the plurality of sensors 162 are positioned at different radial distances from the axis of rotation of the platform 120, but at the same angular position. In some embodiments, the plurality of sensors 162 are positioned at different angular positions about the axis of rotation of the platform 120 and at different radial distances from the axis of rotation of the platform 120.

In some embodiments, the acoustic window 119 is surrounded by a smooth portion 174 of the polishing layer 112. The smooth portion 174 lacks the groove 116 and is coplanar with the upper surface of the acoustic window 119. Embodiments including a smooth portion 174 surrounding the acoustic window 119 may reduce noise associated with the substrate 10, the substrate 10 interacting with the grooves 116 of the polishing layer 112 during a polishing operation.

The substrate 10 is formed by sequentially depositing a conductive layer, a semiconductive layer, or an insulating layer on a silicon wafer. A filler layer is deposited over the non-planar surface and planarized such that the filler and non-planar surface (such as a patterned layer) have a shared coplanar surface and/or expose the non-planar surface. In some embodiments, the in-situ acoustic monitoring system 160 detects transitions between layers, or topographical information about one or more layers of the substrate 10. This provides information to be used between processing steps. For example, the substrate 10 including the filler layer may have a non-uniform surface roughness, e.g., topography, from the deposition process. Detecting when the topography has been planarized allows the system to modify one or more process conditions based on the transition. For example, once the filler layer surface has been planarized, the apparatus 100 may stop the high carrier head 140 pressure step.

Fig. 5A-5C depict intermediate layer transitions present in a planarization process for a substrate 500. Fig. 6 depicts an exemplary acoustic signal 600 comparing the summed Power Spectral Density (PSD) over a frequency range on the y-axis to time in seconds(s). The acoustic signal 600 has different regions, such as a first region 602, a second region 604, and a third region 606. In some implementations, the regions 602, 604, and 606 correspond to layer transitions in the substrate 500, such as those depicted in fig. 5A-5C.

Fig. 5A illustrates an exemplary substrate 10 prior to polishing. The substrate 10 includes a wafer 502 (e.g., 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 be caused by depositing a filler layer 508 over the patterned layer 504 and have dimensions on the order of feature sizes (e.g., metal linewidths).

During operation, the carrier head holds the substrate 10 and produces relative motion between the polishing layer 112 and the substrate 10. The acoustic signal sensor receives an acoustic signal, such as acoustic signal 600, based on contact of the polishing surface 112a with the outermost layer of the substrate 10. In fig. 5A, the topography 509 is in contact with the polishing layer 112 when polishing is initiated.

Without wishing to be bound by theory, the acoustic signal 600 varies based on the varying contact surface of the material of the filler layer 508 and the material of the polishing layer 112. In particular, initially, non-uniform topography may produce significant acoustic signals. However, as polishing progresses and the topography 509 of the filler layer 508 is planarized, the interface between the polished surface 110 and the substrate 10 becomes smoother and the acoustic signal may decrease. The polishing of the topography 509 may correspond to the first region 602 of the signal 600 in fig. 6.

Again, without wishing to be bound by theory, layer transitions occur when the topography 509 has been removed by the apparatus 100. As shown in fig. 5B, the surface of the remaining filler layer 508 is substantially planar. The polishing of the planar surface may correspond to the second region 604 of the acoustic signal 600. In a second region 604 of the signal 600, the acoustic signal 600 is substantially constant (although affected by noise).

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 has been removed. As shown in fig. 5C, patterned layer 504 is composed of a different material than filler layer 508 and interacts with the surface and material of polishing layer 112 in a different manner, thereby creating a third region 606 of acoustic signal 600. Further, continuing polishing may create dishing (dishing), and this topography may again increase the acoustic signal. The third region 606 is not constant, e.g., may increase or decrease.

In some implementations, the distinction between regions 602, 604, and 606 (e.g., detecting layer transitions) may be achieved by acoustic monitoring system 160 and/or controller 190 of device 100. Detection may be accomplished via various calculations known in the art for detecting slope changes, but may include calculating one or more differential, rolling averages, windowing, or box algorithms.

In additional embodiments, the acoustic signal 600 may be processed using additional steps prior to applying the slope change detection algorithm. For example, the acoustic signal 600 may undergo one or more filters (e.g., bandpass filters), and/or one or more transformations (e.g., fast fourier transforms). For example, a band pass filter may be used to isolate preferred frequencies of the acoustic signal 600 prior to processing, such as frequencies in the range from 50kHz to 500kHz, or in the range from 200kHz to 700 kHz.

In some embodiments, the apparatus 100 modifies one or more polishing parameters in response to distinguishing the regions 602, 604, and 606. For example, during a first region 602 in which the topography 509 is removed, the apparatus 100 may dispense a first abrasive polishing liquid 132 for rapid removal of the topography 509. Upon detecting a transition from the first region 602 to the second region 604, a different polishing liquid 132 having a lower polishing rate or lower selectivity may be dispensed onto the pad 110.

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

Turning now to the signals from the sensors 162 of any of the previous embodiments, for example, after amplification, preliminary filtering, and digitizing, the signals may undergo data processing, for example, in the controller 190 for endpoint detection or feedback or feed forward control.

In some implementations, the controller 190 is configured to monitor acoustic losses. For example, the received signal strength is compared to the transmitted signal strength to produce a normalized signal, and the normalized signal may be monitored over time to detect changes. Such a change may indicate a polishing endpoint, for example, if the signal crosses a threshold.

In some embodiments, frequency analysis of the signal is performed. For example, frequency domain analysis may be used to determine changes in the relative power of the spectral frequencies and to determine when a film transition occurs at a particular radius. Information about the transition time through the radius may be used to trigger the endpoint. As another example, a Fast Fourier Transform (FFT) may be performed on the signal to produce a spectrum. A particular frequency band may be monitored and if the intensity in the frequency band crosses a threshold, this may indicate exposure of the underlying layer, which may be used to trigger an endpoint. Alternatively, if the location (e.g., wavelength) or bandwidth of a local maximum or minimum in the selected frequency range crosses a threshold, this may indicate exposure of the underlying layer, which may be used to trigger an endpoint. For example, to monitor the polishing of an interlayer dielectric (ILD) in Shallow Trench Isolation (STI), a frequency range of 225kHz to 350kHz may be monitored.

As another example, wavelet Packet Transform (WPT) may be performed on a signal to decompose the signal into a low frequency component and a high frequency component. If the signal needs to be decomposed into smaller components, the decomposition may be iterated. The intensity of one of the frequency components may be monitored and if the intensity of the component crosses a threshold, this may indicate exposure of the underlying layer, which may be used to trigger an endpoint.

Assuming that the position of the sensor 162 relative to the substrate 10 is known, for example, using motor encoder signals or an optical interrupter attached to the platform 120, the position of the acoustic event on the substrate may be calculated, for example, the radial distance of the event from the center of the substrate may be calculated. Determination of 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.

Various technologically significant acoustic events include micro-scratches, membrane transition breakthroughs, and membrane cleaning. Various methods may be used to analyze the acoustic emission signal from the waveguide. Fourier transforms and other frequency analysis methods can be used to determine the peak frequencies that occur during polishing. The experimentally determined threshold and monitoring over the defined frequency range is used to identify desired and undesired changes during polishing. Examples of desired changes include sudden occurrences of peak frequencies during transitions in film hardness. Examples of undesirable changes include problems associated with the consumable set (such as pad glazing or other process drift induced machine health problems).

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 110. The signal is monitored to detect exposure of the underlying layer of the substrate 10. For example, a specific frequency range may be monitored and the intensity may be monitored and compared to an experimentally determined threshold.

Detecting the polishing endpoint triggers stops polishing, although polishing may continue for a predetermined amount of time after the endpoint triggers. Alternatively or additionally, the collected data and/or endpoint detection time may be fed forward to control processing of the substrate in a subsequent processing operation, e.g., polishing at a subsequent station, or may be fed back to control processing of a subsequent substrate at the same polishing station. For example, detecting the polishing endpoint may trigger a modification to the current pressure of the polishing head. As another example, detecting the polishing endpoint may trigger a modification of the baseline pressure for subsequent polishing of the new substrate.

The embodiments and all of the functional operations described in this specification may be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structural components disclosed in this specification and structural equivalents thereof, or in combinations of the above. Embodiments described herein may be implemented as one or more non-transitory computer program products, i.e., one or more computer programs tangibly embodied in a machine-readable storage device for execution by, or to control the operation of, data processing apparatus, e.g., a programmable processor, a computer, or multiple processors or computers.

Computer programs (also known as programs, software applications, or code) may be written in any form of programming language, including compiled or interpreted languages; and a computer program may be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. The computer program does not necessarily correspond to a file. A program can be stored in a portion of a file that holds other programs or data, in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub-programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.

The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit).

The term "data processing apparatus" encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. In addition to hardware, the device may also include code that establishes an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of the foregoing. Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer.

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

The polishing apparatus and method described above can be applied to various polishing systems. Either or both of the polishing pad or carrier head can be moved to provide relative motion between the polishing surface and the wafer. For example, the platform may rotate about an orbit rather than spin. The polishing pad can be a circular (or some other shape) pad secured to the platen. Some aspects of the endpoint detection system may be applicable to linear polishing systems (e.g., where the polishing pad is a linearly moving continuous belt or a roll-to-roll belt). The polishing layer can be a standard (e.g., polyurethane with or without filler) polishing material, a soft material, or a fixed abrasive material. Relative positioning terminology is used; it should be appreciated that the polishing surface and wafer may be held in a vertical orientation or some other orientation.

Although this description contains many specifics, these should not be construed as limiting the scope of what may be claimed, but rather as describing features of particular embodiments that may be specific to particular inventions. In some embodiments, the method may be applied to other combinations of overlying and underlying materials, as well as signals from other types of in situ monitoring systems (e.g., optical monitoring or eddy current monitoring systems).

Claims (18)

1. A chemical mechanical polishing apparatus comprising:

a platform;

a polishing pad supported on the platen;

a carrier head for holding a surface of a substrate against the polishing pad;

a motor for producing relative motion between the platen and the carrier head for polishing an upper cladding on the substrate;

an in situ acoustic monitoring system comprising an acoustic sensor that receives an acoustic signal from the surface of the substrate; and

a controller configured to detect planarization of topography on the substrate based on signals from the in situ acoustic monitoring system.

2. The apparatus of claim 1, wherein the controller is configured to switch the dispenser from dispensing the first polishing liquid to dispensing the second polishing liquid after the planarization is detected.

3. The apparatus of claim 1, wherein the controller is configured to switch the carrier head from applying a first pressure to the substrate to applying a second pressure after the planarization is detected.

4. The apparatus of claim 1, wherein the controller is configured to perform a fourier transform on the signal and sum spectral power densities over a frequency range to produce a power signal.

5. The apparatus of claim 4, wherein the controller is configured to detect a change in a slope of the power signal to detect the flattening of topography.

6. The apparatus of claim 4, wherein the controller is configured to detect a decrease in the magnitude of the slope of the power signal to detect the flattening of topography.

7. A method of chemical mechanical polishing apparatus, comprising:

contacting a substrate with a polishing pad and producing relative motion between the substrate and the polishing pad to polish an overlying layer on the substrate;

acoustically monitoring the substrate during polishing with a sensor of an in situ acoustic monitoring system; and

planarization of topography on the substrate is detected based on signals from the sensors.

8. The method of claim 7, comprising: switching from dispensing the first polishing liquid to dispensing the second polishing liquid after the planarization is detected.

9. The method of claim 7, comprising: switching from applying a first pressure to the substrate to applying a second pressure after the planarization is detected.

10. The method of claim 7, comprising: a fourier transform is performed on the signal and the spectral power densities are summed over a frequency range to produce a power signal.

11. The method of claim 10, comprising: a change in the slope of the power signal is detected to detect the flattening of the topography.

12. The method of claim 10, comprising: a decrease in the magnitude of the slope of the power signal is detected to detect the flattening of a topography.

13. A non-transitory computer-readable medium encoded with a computer program comprising instructions for causing one or more computers to:

receiving signals of a sensor of an in-situ acoustic monitoring system during polishing of a substrate; and

planarization of topography on the substrate is detected based on the signals from the sensors.

14. The computer readable medium of claim 13, comprising instructions for switching from dispensing a first polishing liquid to dispensing a second polishing liquid after the planarization is detected.

15. The computer readable medium of claim 13, comprising instructions for switching from applying a first pressure to applying a second pressure to the substrate after the planarization is detected.

16. The computer readable medium of claim 13, comprising instructions for performing a fourier transform on the signal and summing spectral power densities over a frequency range to produce a power signal.

17. The computer readable medium of claim 16, comprising instructions for detecting a change in a slope of the power signal to detect the flattening of topography.

18. The computer readable medium of claim 16, comprising instructions for detecting a decrease in the magnitude of the slope of the power signal to detect the flattening of topography.