Incorporation of acoustic sensors for chemical mechanical polishing.

Abstract

A chemical mechanical polishing apparatus includes a platen supporting a polishing pad, a carrier head holding a surface of a substrate against the polishing pad, a motor generating relative motion between the platen and the carrier head to polish a layer overlying the substrate, an in-situ acoustic monitoring system including an acoustic window having a top surface in contact with the substrate, and a controller configured to detect a polishing endpoint based on acoustic signals received from the in-situ acoustic monitoring system.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to in-situ monitoring of chemical mechanical polishing, and in particular to acoustic monitoring. [Background technology]

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

[0003] 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 placed against a rotating polishing pad. The carrier head applies a controllable load to the substrate, pressing it against the polishing pad. An abrasive polishing slurry is typically supplied to the surface of the polishing pad.

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

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

[0006] In one aspect, a chemical mechanical polishing apparatus includes a platen that supports a polishing pad, a carrier head that holds a surface of a substrate against the polishing pad, a motor that generates relative motion between the platen and the carrier head to polish an overlying layer of the substrate, an in-situ acoustic monitoring system that includes an acoustic window having a top surface that contacts the substrate, and a controller configured to detect a polishing endpoint based on acoustic signals received from the in-situ acoustic monitoring system.

[0007] In another aspect, a chemical mechanical polishing apparatus includes a platen, a polishing pad supported on the platen, a carrier head that holds a surface of a substrate against the polishing pad, a motor that generates relative motion between the platen and the carrier head to polish an overlying layer of the substrate, an in-situ acoustic monitoring system including an acoustic sensor that receives acoustic signals from the surface of the substrate, and a controller configured to detect a polishing endpoint based on the acoustic signals received from the in-situ acoustic monitoring system. The acoustic sensor is adhesively attached to a bottom surface of the polishing pad.

[0008] Embodiments may include one or more of the following features: The sensor may be secured to the polishing pad, for example, by an 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 polishing of the substrate to expose an underlying layer; The controller may be configured to adjust the carrier head pressure or adjust the base pressure for subsequent polishing of a new substrate in response to the detection.

[0009] One or more of the following possible advantages may be realized: The signal strength of the acoustic sensor may be increased; Acoustic coupling between the polishing layer and the sensor may be more reliably established; Exposure of the underlying layer may be more reliably detected; Polishing may be stopped more reliably, improving wafer-to-wafer uniformity; When planarization, i.e., smoothing of the substrate surface, is detected, polishing parameters may be changed to improve uniformity or increase the polishing rate; Polishing may be stopped upon detection of planarization or after a preset time following detection of planarization, which may provide an alternative endpoint technique.

[0010] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other aspects, features, and advantages will become apparent from the description, drawings, and claims. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic cross-sectional view of an example of a polishing apparatus. [Figure 2A] 1 is a schematic cross-sectional view of an acoustic monitoring sensor engaging a portion of a polishing pad. [Figure 2B] 1 is a schematic cross-sectional view of another embodiment of an acoustic monitoring sensor including an acoustically transmissive layer. [Figure 2C] 1 is a schematic cross-sectional view of another embodiment of an acoustic monitoring sensor. [Figure 2D]FIG. 10 is a schematic cross-sectional view of another embodiment of an acoustic monitoring sensor in which an acoustic window is formed in the polishing layer and an acoustically transmissive layer is formed in the backing layer of the polishing pad. [Figure 3] FIG. 1 is a schematic top view of a platen having multiple acoustic monitoring sensor windows. [Figure 4] FIG. 1 is a schematic top view of a platen having a planar portion surrounding an acoustic monitoring sensor window. [Figures 5A-5C] The surface of the substrate is flattened. [Figure 6] 1 is a graph of the sum of spectral power density over a frequency range as a function of time. DETAILED DESCRIPTION OF THE INVENTION

[0012] Like reference symbols in the various drawings indicate like elements.

[0013] In some semiconductor chip manufacturing processes, an overlying layer (e.g., metal, silicon oxide, or polysilicon) is polished until an underlying layer (e.g., silicon oxide, silicon nitride, or a dielectric such as a high-k dielectric) is exposed. In some applications, when the underlying layer is exposed, the acoustic emission from the substrate changes. The polishing endpoint can be determined by detecting this change in the acoustic signal. However, existing monitoring techniques may not meet the growing demands of semiconductor device manufacturers.

[0014] The acoustic emissions to be monitored may be caused by energy released when the substrate material deforms, and the resulting acoustic spectrum is related to the material properties of the substrate. Without being limited to a particular theory, possible sources of this energy, also referred to as "stress energy," and its characteristic frequencies include chemical bond scission, characteristic phonon frequencies, and slip-stick mechanisms. It should be noted that this stress energy acoustic effect is not the same as noise generated by vibrations induced by friction of the substrate against the polishing pad (also sometimes referred to as an acoustic signal) or noise generated by the occurrence of cracks, chips, cuts, or similar defects on the substrate. With appropriate filtering, stress energy can be distinguished from other acoustic signals, such as noise caused by friction of the substrate against the polishing pad or the occurrence of defects on the substrate. For example, the signal from the acoustic sensor can be compared to a signal measured from a test substrate known to represent stress energy.

[0015] However, a potential problem with acoustic monitoring is the transmission of the acoustic signal to the sensor. Some polishing pads transmit acoustic energy poorly. In addition, poor coupling between the polishing pad and the sensor tends to attenuate the acoustic signal. Furthermore, establishing a consistent coupling between the sensors can be difficult.

[0016] Therefore, it would be advantageous to have an acoustic sensor in contact with an acoustic "window" that provides less attenuation of the acoustic signal. In some embodiments, 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.

[0017] The acoustic sensor can be bonded to the coupling window, for example with an adhesive, to reduce noise in the acoustic signal associated with movement of the acoustic sensor within the housing. The adhesive can provide a better bond between the sensor and the polishing pad, providing more reliable acoustic attenuation between the sensors.

[0018] Any of these features can be used independently of the others.

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

[0020] The polishing apparatus 100 may include a port 130 for dispensing a polishing fluid 132 (e.g., a polishing slurry) onto the polishing pad 110. The polishing apparatus may also include a polishing pad conditioner that scrubs the polishing pad 110 to maintain the polishing pad 110 in a consistent polishing condition.

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

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

[0023] Carrier heads 140 are suspended from support structure 150 (e.g., a carousel or track) and connected by drive shaft 152 to carrier head rotation motors 154 (e.g., DC induction motors), which may rotate the carrier heads about axis 155. Optionally, each carrier head 140 may reciprocate laterally, for example, on a slider in carousel 150, either by rotational oscillation of the carousel itself, or by sliding along a track. In a typical process, 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.

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

[0025] The polishing apparatus 100 includes at least one in-situ acoustic monitoring system 160. The in-situ acoustic monitoring system 160 includes one or more acoustic signal sensors 162. Each acoustic signal sensor may be located at one or more locations on the upper platen 120. Specifically, the in-situ acoustic monitoring system may be configured to detect acoustic emissions caused by stress energy as the material of the substrate 10 deforms.

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

[0027] 1, the acoustic monitoring system 160 includes an acoustic sensor 162 supported by and positioned on the platen 120 to receive acoustic signals from the substrate 10 through the polishing pad 110. The acoustic sensor 162 can be partially or entirely mounted within a recess 164 in the top surface of the platen 120. In some embodiments, the top surface of the acoustic sensor 162 is flush with the top surface of the platen 120.

[0028] 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, as shown in FIG. 2A, for example, or the two may be of substantially equal width (e.g., within 10%), as shown in FIG. 2C, for example. If the acoustic window 119 is narrower than the acoustic sensor 162, the sensor may also abut the bottom of the polishing layer 112.

[0029] The acoustic sensor 162 is a contact-type acoustic sensor having a surface connected (e.g., in direct contact or with only an adhesive layer) to a portion of the polishing layer 112 and / or the acoustic window 119. For example, the acoustic sensor 162 can be an electromagnetic acoustic transducer or a piezoelectric acoustic transducer. A piezoelectric sensor can include a hard contact plate, such as stainless steel, that is placed in contact with the body to be monitored, with a piezoelectric assembly (e.g., a piezoelectric layer sandwiched between two electrodes) behind the contact plate.

[0030] In some embodiments, the acoustic sensor 162 is disposed within a recess 169 in the housing 163. An optional spring 165 can be disposed between the housing 163 and the support 167 to provide pressure against the housing 163. The pressure on the housing 163 urges the acoustic sensor 162 into contact with a portion of the polishing pad 110. Alternatively, the spring 165 can press directly against the acoustic sensor 162, for example, if no housing is used. In some embodiments, the spring 165 is a long-travel spring 165 that provides a pressure similar to that of a strong spring 165 over a larger compression range.

[0031] The acoustic sensor 162 may be connected by circuitry 168 through a rotary coupling (eg, mercury slip ring) to a power supply and / or other signal processing electronics 166 .

[0032] In some embodiments, in-situ acoustic monitoring system 160 is a passive acoustic monitoring system. In this case, signals are monitored by acoustic sensor 162 without generating a signal from an acoustic signal generator (or the acoustic signal generator can be omitted from the system entirely). The passive acoustic signal monitored by acoustic sensor 162 can be in the range of 50 kHz to 1 MHz, e.g., 200 to 400 kHz, or 200 kHz to 1 MHz. For example, for monitoring interlayer dielectric (ILD) polishing in shallow trench isolation (STI), a frequency range of 225 kHz to 350 kHz can be monitored.

[0033] The signal from the sensor 162 may be amplified by a built-in internal amplifier. In some embodiments, the amplification gain is 40-60 dB (e.g., 50 dB). The signal from the acoustic sensor 162 may then be further amplified, filtered, and digitized through an A / D port, if necessary, before reaching a high-speed data acquisition board (e.g., within the electronics 166). Data from the acoustic sensor 162 may be recorded in a range similar to that of the generator 163, or may be recorded in a different, e.g., higher, range (e.g., 1-10 MHz (e.g., 1-3 MHz or 6-8 MHz)). In embodiments where the acoustic sensor 162 is a passive acoustic sensor, it may monitor a frequency range of 100 kHz to 2 MHz (e.g., 500 kHz to 1 MHz (e.g., 750 kHz)).

[0034] When placed on the platen 120, the acoustic sensor 162 can be placed at the center of the platen 120 (e.g., at the axis of rotation 125), at the edge of the platen 120, or at a midpoint (e.g., 5 inches from the axis of rotation for a 20-inch diameter platen).

[0035] 2A, further details of acoustic monitoring system 160 are shown. Acoustic sensor 162 may be held within a recess 169 in the top surface of housing 163. Housing 163 may aid in proper placement of sensor 162. Housing 163 is constructed of a material that is rigid and durable enough to protect acoustic sensor 162 from damage. However, in some embodiments, such as those shown in FIGS. 2C and 2D, a housing is not necessary; for example, sensor 162 may simply fit between and be secured by the sidewalls of recess 169. Various embodiments described as using a housing may omit the housing.

[0036] In some embodiments, such as shown in Figure 2B, the housing 163 penetrates the backing layer 114, and in some embodiments, such as shown in Figure 2A, the housing 163 penetrates a portion of the polishing layer 112. However, in some embodiments, the housing 163 fits completely within the recess 164 in the platen 120, e.g., when the top surface of the sensor 163 is flush with the top surface of the platen 120 and contacts the bottom surface of the polishing pad 110.

[0037] In some embodiments, the material of housing 163 is acoustically attenuating to reduce noise received by acoustic sensor 162 from surfaces in contact with housing 163, such as backing layer 114 or polishing layer 112 through which housing 163 passes. Housing 163 may be constructed of a metal (e.g., aluminum or stainless steel), or a polymeric material (e.g., polycarbonate, polyvinyl chloride (PVC), or polymethyl methacrylate (PMMA)).

[0038] Assuming a spring is used, one end of the spring 165 contacts the housing 163 on the surface facing the acoustic sensor 162. In some embodiments, the other end of the spring 165 contacts a support 167 on the platen 120. Such a support may provide a stable base for the force generated by the compression of the spring 165. In some embodiments, the other end of the spring 165 contacts the bottom surface of the recess 164, i.e., directly with the platen. The spring 165 presses the housing 163 toward the polishing surface 112a of the polishing layer 112, thereby urging the acoustic sensor 162 to contact the bottom surface of the polishing layer 112. This may improve acoustic coupling between the polishing layer and the sensor. However, various embodiments described as using a spring may omit the spring, for example, assuming the sensor is adhesively attached to the acoustic window 119 and / or the bottom of the polishing pad 110.

[0039] In some embodiments, a support 167 is placed below the spring 165 to provide a stationary block against which the spring 165 can be pressed against the housing 163. The support 167 can be any material sufficient to rigidly support the spring 165 and housing 163 without movement or compressive buckling.

[0040] In addition to or instead of a spring, acoustic sensor 162 may be secured to a portion of polishing layer 112 (and / or acoustic window 119, described below) by adhesive layer 170. Adhesive layer 170 may increase the contact area between acoustic sensor 162 and polishing layer 112 and / or acoustic window 119, reducing unwanted movement of acoustic sensor 162 during the polishing process and reducing the presence of gas pockets between acoustic sensor 162 and polishing layer 112 and / or acoustic window 119, thereby improving coupling to the sensor and thus reducing noise in the acoustic signal received by acoustic sensor 162. Adhesive layer 170 may be an adhesive or adhesive strip (e.g., tape) applied between acoustic sensor 162 and polishing layer 112 and / or acoustic window 119. For example, adhesive layer 170 may be a cyanoacrylate, a pressure-sensitive adhesive, a hot-melt adhesive, etc.

[0041] 2A, polishing layer 112 includes an acoustic window 119 disposed above adhesive layer 170 and acoustic sensor 162. However, in some embodiments, acoustic sensor 162 directly contacts acoustic window 119.

[0042] In embodiments having an acoustic window, the acoustic window 119 is formed of a different material than the polishing layer 112. The acoustic window material has sufficient acoustic transmission properties, e.g., an acoustic impedance of 1-4 MRayl and an acoustic attenuation coefficient of less than 2 (e.g., less than 1, less than 0.5), to provide a sufficient signal for acoustic monitoring.

[0043] The acoustic impedance of a material is the measure of resistance the material offers to the flow of sound resulting from an 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 acoustic window 119 (AI) that couples the liquid 132 and polished surface 112a to the acoustic signal sensor 162 may be configured to have a constant amplitude. window ) specific acoustic impedance is usefully in the range It could be in TIFF0007815413000001.tif15170.

[0044] In particular, the window 119 may have lower acoustic attenuation than the surrounding polishing layer 112. This allows the polishing layer 112 to be constructed from a wider range of materials to meet the needs of the CMP process. The window may be constructed from a non-porous material, e.g., a solid. In contrast, the polishing layer 112 may be porous, e.g., microporous, such as a polymer matrix with hollow plastic microparticles embedded therein.

[0045] The acoustic window 119 penetrates the polishing layer 112 such that one surface (e.g., the top surface) is flush with the polishing surface 112a of the polishing layer 112. The opposite surface (e.g., the bottom surface) can be flush with the lower surface 112b of the polishing layer 112. In some embodiments, a recess 118 is formed in the lower surface 112b opposite the polishing surface 112a. The portion of the polishing layer 112 that includes the recess 118 forms a thin portion of the polishing layer 112 that has a thickness less than the remainder of the polishing layer 112, and the acoustic window 119 is located in the thin portion.

[0046] The acoustic window 119 may be composed of a non-porous material. Generally, 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 to reduce the effect of the acoustic window 119 on the polishing characteristics of the polishing surface on the substrate. In some embodiments, the compressibility of the acoustic window 119 is within 10% (e.g., within 8%, within 5%, within 3%) of the compressibility of the polishing layer 112. In some embodiments, the acoustic window 119 is opaque to light (e.g., visible light). The 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.

[0047] 2C, an acoustic window 119 is shown extending through the full thickness of the polishing layer 112 so that the lower surface 112b is planar. A sensor 162 extends through an aperture 114a in the backing layer 114 to contact the underside of the window 119.

[0048] In some embodiments, acoustic monitoring system 160 includes an acoustically transmissive layer 172 in contact with adhesive layer 170. The transmissive layer 172 is an index-matching material that increases 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 adhesive layer 170, or between the adhesive layer 170 and the acoustic sensor 162, as shown in FIG. 2B. In some embodiments, acoustic monitoring system 160 includes adhesive layer 170, transmissive layer 172, or both. For example, the transmissive layer 172 may be a layer of Aqualink™, Rexolite™, or Aqualene™. In some embodiments, the transmissive layer 172 has an acoustic attenuation within 20% (e.g., within 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.

[0049] Acoustically transmissive layer 172 may be selected to have a compressibility similar to that of backing layer 114 (e.g., within 20% (e.g., within 10%) of the compressibility of the surrounding backing layer 114).

[0050] 2D is an embodiment in which the acoustic window 119 penetrates the thickness of the polishing layer 112 and the transmissive layer 172 penetrates the thickness of the backing layer 114. However, the transmissive layer 172 can be thinner than the backing layer 114. In this case, the sensor 162 can protrude above the top surface of the platen 120 and engage the transmissive layer 172.

[0051] Additionally, acoustic signal sensor 162 is shown with dimensions sufficient to contact both transmissive layer 172 and the surface opposite recess 164. In such embodiments, recess 164 supports acoustic signal sensor 162, while the pressure of the polishing process causes acoustic signal sensor 162 to contact transmissive layer 172. Disposed between transmissive layer 172 and acoustic window 119 is adhesive layer 170, as described herein. In some embodiments, an additional adhesive bonds the contact surfaces between acoustic signal sensor 162 and transmissive layer 172.

[0052] In some embodiments, acoustic monitoring system 160 includes an active acoustic monitoring system, which includes an acoustic signal generator and an acoustic sensor, such as acoustic sensor 162.

[0053] The acoustic signal generator generates (i.e., emits) an acoustic signal from the side of the substrate near the polishing pad 110. The acoustic signal generator may be connected by circuitry 168 through a rotary coupling (e.g., a mercury slip ring) to a power supply and / or other signal processing electronics 166. The signal processing electronics 166 may be connected to a controller 190, which may additionally be configured to control the magnitude or frequency of the acoustic energy transmitted by the generator, for example, by variably increasing or decreasing the current supply to the generator. The acoustic signal generator 163 and the acoustic sensor 162 may be coupled to each other, but this is not required. The sensor 162 and the generator may be decoupled and physically separated from each other. Commercially available acoustic signal generators may be used for the generator. The generator may be attached to the platen 120 and held in place, for example, by a clamp or a threaded connection to the platen 120.

[0054] As shown in FIG. 3 , in some embodiments, multiple acoustic signal sensors 162 can be installed on the platen 120, with each acoustic sensor 162 associated with an acoustic window 119. Each sensor 162 can be configured in a manner described in any of FIGS. 1 and 2A-2B. Signals from the sensors 162 can be used by the controller 190 to calculate the positional distribution of acoustic emission events occurring on the substrate 10 during polishing. In some embodiments, the multiple sensors 162 can be positioned around the axis of rotation of the platen 120 at different angular positions but at the same radial distance from the axis of rotation. In some embodiments, such as the embodiment of FIG. 3 , the multiple sensors 162 are positioned at different radial distances from the axis of rotation of the platen 120 but at the same angular position. In some embodiments, the multiple sensors 162 are positioned around the axis of rotation of the platen 120 at different angular positions and at different radial distances from the axis of rotation of the platen 120.

[0055] In some embodiments, the acoustic window 119 is surrounded by a smooth portion 174 of the polishing layer 112. The smooth portion 174 is free of the grooves 116 and is flush with the top surface of the acoustic window 119. Embodiments that include a smooth portion 174 surrounding the acoustic window 119 may reduce noise associated with the substrate 10 interacting with the grooves 116 of the polishing layer 112 during the polishing process.

[0056] Substrate 10 is formed by sequentially depositing conductive, semiconductive, or insulating layers on a silicon wafer. A filler layer is deposited over a non-planar surface and planarized so that the filler and the non-planar surface (e.g., a patterned layer) have a common coplanar surface, and / or the non-planar surface is exposed. In some embodiments, in-situ acoustic monitoring system 160 detects transitions between layers or topographic information associated with one or more layers of substrate 10, providing information used between process steps. For example, substrate 10 including a filler layer may have a non-uniform surface roughness (e.g., topography) from a deposition process. By detecting when the topography has been planarized, the system can modify one or more process conditions based on the transition. For example, apparatus 100 can stop a high carrier head 140 pressure step once the filler layer surface is planarized.

[0057] 5A-5C illustrate interlayer transitions present in the planarization process of a substrate 500. FIG. 6 illustrates an example acoustic signal 600 comparing the sum of the power spectral density (PSD) over a frequency range 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 embodiments, regions 602, 604, and 606 correspond to layer transitions in the substrate 500 as illustrated in FIGS. 5A-5C.

[0058] 5A shows an exemplary substrate 10 before polishing. The substrate 10 includes a wafer 502 (e.g., a silicon wafer), a patterned layer 504, and a fill layer 508. Prior to the planarization step, the fill layer 508 is non-planar and includes a topography 509. The topography 509 may result from depositing the fill layer 508 over the patterned layer 504 and has dimensions on the order of the feature size (e.g., metal line width).

[0059] During processing, the carrier head holds the substrate 10, and relative motion occurs 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 between the polishing surface 112a and the outermost layer of the substrate 10. In Figure 5A, at the start of polishing, the topography 509 and the polishing layer 112 are in contact.

[0060] Without wishing to be bound by theory, the acoustic signal 600 changes based on changes in the interface between the fill layer 508 material and the polishing layer 112 material. In particular, an initially uneven topography may produce a large acoustic signal. However, as polishing progresses and the topography 509 of the fill layer 508 is planarized, the interface between the polishing surface 110 and the substrate 10 is smoothed, 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 .

[0061] Again, without wishing to be bound by theory, the layer transition occurs when the topography 509 is removed by the apparatus 100. As shown in FIG. 5B, the surface of the remaining fill layer 508 is substantially planar. The polishing of the planar surface may correspond to a second region 604 of the acoustic signal 600. In the second region 604 of the signal 600, the acoustic signal 600 is substantially constant (even if affected by noise).

[0062] Without wishing to be bound by theory, it is believed that second region 604 continues in time until fill layer 508 extending above patterned layer 504 is removed. As shown in FIG. 5C , patterned layer 504 is composed of a different material than fill layer 508 and interacts differently with the polishing layer 112 surface and material, thereby producing third region 606 of acoustic signal 600. Additionally, continued polishing can produce dishing, and this topography can again increase the acoustic signal. Third region 606 is not constant and may, for example, increase or decrease.

[0063] In some embodiments, differentiation 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. This detection may be achieved by various calculations known in the art for detecting gradient changes, but may include one or more of differentiation, rolling average, window, or box logic algorithm calculations.

[0064] In further embodiments, further steps can be used to process the acoustic signal 600 before applying the gradient change detection algorithm. For example, the acoustic signal 600 can be subjected to one or more filters (e.g., bandpass filters) and / or one or more transforms (e.g., fast Fourier transforms). For example, a bandpass filter can be used to isolate preferred frequencies (e.g., frequencies in the range of 50-500 kHz) or frequencies in the range of 200-700 kHz of the acoustic signal 600 before processing.

[0065] In some embodiments, apparatus 100 modifies one or more polishing parameters in response to distinguishing between regions 602, 604, and 606. For example, during first region 602, when topography 509 is being removed, apparatus 100 may dispense a first polishing polishing fluid 132 to quickly remove topography 509. When a transition from first region 602 to second region 604 is detected, a different polishing fluid 132 having a lower polishing rate or lower selectivity may be dispensed onto pad 110.

[0066] Alternatively or additionally, when a transition from second region 604 to third region 606 is detected, the pressure applied by carrier head 140 may be reduced, thereby reducing the risk of dishing or erosion of fill layer 508.

[0067] Now, looking at the signal from the sensor 162 in any of the preceding embodiments, the signal, after amplification, pre-filtering, and digitization, for example, in the controller 190, may undergo data processing, either for endpoint detection or feedback or feedforward control.

[0068] In some embodiments, the controller 190 is configured to monitor acoustic loss. For example, the received signal strength can be compared to the emitted signal strength to generate a normalized signal, and the normalized signal can be monitored over time to detect changes. Such changes can indicate a polishing endpoint, such as when the signal exceeds a threshold value.

[0069] In some embodiments, a frequency analysis of the signal is performed. For example, frequency domain analysis can be used to determine the change in relative power of spectral frequencies to determine when a film transition occurs at a particular radius. Information about the time of the transition with radius can be used to trigger an endpoint. As another example, a fast Fourier transform (FFT) can be performed on the signal to generate a frequency spectrum. A specific frequency band can be monitored, and if the intensity of this frequency band exceeds a threshold, it can indicate that an underlying layer has been exposed, 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, it can also indicate that an underlying layer has been exposed, which can be used to trigger an endpoint. For example, for monitoring the polishing of an interlayer dielectric (ILD) in shallow trench isolation (STI), a frequency range of 225 kHz to 350 kHz can be monitored.

[0070] As another example, a wavelet packet transform (WPT) may be performed on the signal to decompose it into low- and high-frequency components. This decomposition can be repeated as necessary to decompose the signal into smaller components. The intensity of one of the frequency components may be monitored; if the intensity of this component exceeds a threshold, this may indicate exposure of the underlying layer and can be used to trigger an endpoint.

[0071] Given that the position of the sensor 162 relative to the substrate 10 is known, for example using a motor encoder signal or an optical isolator attached to the platen 120, the position of an acoustic event on the substrate can be calculated, for example, the radial distance of the event from the center of the substrate. Determining the position of a sensor relative to a substrate is discussed in U.S. Patent No. 6,159,073 and U.S. Patent No. 6,296,548, which are incorporated by reference.

[0072] Various acoustic events of process significance include micro-scratches, film transition breakthrough, and film clearing. Various methods can be used to analyze the acoustic emission signal from the waveguide. Fourier transform and other frequency analysis methods can be used to determine peak frequencies that occur during polishing. Using experimentally determined thresholds and monitoring within predetermined frequency ranges, expected and unexpected changes during polishing are identified. An example of an expected change includes the sudden appearance of a peak frequency during a film hardness transition. An example of an unexpected change includes a problem with the consumable set (such as pad glazing or other machine health issues that induce process changes).

[0073] During processing, the device substrate 10 is polished in the polishing station 100 and acoustic signals are collected from the in-situ acoustic monitoring system 160. The signals are monitored to detect exposure of underlying layers of the substrate 10. For example, a particular frequency range may be monitored, and its intensity may be monitored and compared to an experimentally determined threshold.

[0074] Although detecting a polishing endpoint triggers a stop of polishing, polishing may continue for a predetermined amount of time after the endpoint is triggered. Alternatively or additionally, the collected data and / or the endpoint detection time may be fed forward to control the processing of the substrate in a subsequent process (e.g., polishing at a subsequent station) or fed back to control the processing of a subsequent substrate at the same polishing station. For example, detecting a polishing endpoint may trigger a modification to the current pressure of the polishing head. As another example, detecting a polishing endpoint may trigger a modification to the baseline pressure for polishing a subsequent new substrate.

[0075] All of the embodiments and functional processes described herein may be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structural means disclosed herein and their structural equivalents, or in combinations of these. The embodiments described herein may also 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 a data processing apparatus (e.g., a programmable processor, a computer, or multiple processors or computers).

[0076] A computer program (also known as a program, software, software application, or code) can be written in any programming language, including compiled or translated languages, and can 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. A computer program does not necessarily correspond to a file. A program can be stored as part of a file that holds other programs or data, in a single file dedicated to the program in question, or in multiple cooperative files (e.g., files that store one or more modules, subprograms, or portions of code). A computer program can be deployed to be executed on one or more computers, or on multiple computers at one site or distributed across multiple sites and interconnected by a communications network.

[0077] The processes and logic flows described herein may be performed by one or more programmable processors executing one or more computer programs that perform functions by operating on input data and generating output. The processes and logic flows may also be performed by, and apparatus may be implemented as, special purpose logic circuitry (e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit)).

[0078] The term "data processing apparatus" encompasses all apparatus, devices, and machines for processing data, including, by way of example, a programmable processor, computer, or multiple processors or computers. In addition to hardware, an apparatus may include code that creates the execution environment for the computer program in question (e.g., code comprising processor firmware, a protocol stack, a database management system, an operating system, or any 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 kind of digital computer.

[0079] 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 or removable disks), magneto-optical disks, and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

[0080] The polishing apparatus and method described above can be applied to a wide variety of polishing systems. The polishing pad, the carrier head, or both can move to provide relative motion between the polishing surface and the wafer. For example, the platen can orbit rather than rotate. The polishing pad can be a circular (or some other shape) pad fixed to the platen. Some aspects of the endpoint detection system may be applicable to linear polishing systems, for example, when the polishing pad is a linearly moving continuous belt or a reel-to-reel belt. The polishing layer can be a standard abrasive material (e.g., polyurethane with or without fillers), a soft material, or a fixed abrasive material. It should be understood that the term relative orientation is used, and the polishing surface and wafer can be held in a vertical orientation or in several other orientations.

[0081] Although this specification is replete with specifics, they should not be construed as limitations on the scope of the claims, but rather as descriptions of features that may be unique to particular embodiments of a particular invention. In some embodiments, the method may be applied to other combinations of overlying and underlying materials, and to signals from other types of in-situ monitoring systems (e.g., optical or eddy current monitoring systems).

Claims

1. 1. A chemical mechanical polishing apparatus, comprising: A platen and a polishing pad supported on the platen, the polishing pad having a polishing layer; a carrier head for holding a surface of the substrate against the polishing pad; a motor that generates relative motion between the platen and the carrier head to polish a layer overlying the substrate; an in-situ acoustic monitoring system including an acoustic window extending through the polishing pad and an acoustic sensor acoustically coupled to the acoustic window, the acoustic window having an acoustic attenuation coefficient less than that of the polishing layer, the acoustic window having an upper surface coplanar with the polishing surface that contacts the substrate; a controller configured to detect a polishing endpoint based on a change in an acoustic signal received from the in-situ acoustic monitoring system; A chemical mechanical polishing apparatus comprising:

2. The apparatus of claim 1 , wherein a bottom surface of the acoustic window is flush with a lower surface of the polishing layer.

3. The apparatus of claim 1 , wherein the polishing pad has a backing layer beneath the polishing pad.

4. The device of claim 3 , wherein a bottom surface of the acoustic window is flush with a top surface of the backing layer.

5. The device of claim 4 , wherein apertures are formed through the backing layer.

6. The apparatus of claim 5 , wherein the sensor is positioned at least partially within the aperture so as to directly contact the bottom surface of the acoustic window.

7. 6. The apparatus of claim 5, further comprising an acoustically transmissive layer disposed in an aperture through the backing layer between the acoustic sensor and the acoustic window, the acoustically transmissive layer having a lower acoustic attenuation coefficient than the backing layer.

8. 8. The apparatus of claim 7, wherein a bottom surface of the acoustically transmissive layer is coplanar with a bottom surface of the polishing pad.

9. 2. The device of claim 1, wherein a recess is formed under the polishing layer to form a thinned portion of the polishing layer, the acoustic window is disposed within the thinned portion of the polishing layer, and the sensor is at least partially disposed in the recess.

10. The device of claim 1 , wherein the acoustic window is a non-porous material.

11. The device of claim 10 , wherein the polishing layer is porous and the acoustic window is solid.

12. The device of claim 1 , wherein the compressibility of the acoustic window is within 20% of the compressibility of the polishing layer.

13. The apparatus of claim 1 , wherein the acoustic sensor is adhesively attached to the acoustic window to receive acoustic signals from the substrate.

14. The apparatus of claim 1 , further comprising an acoustically transmissive layer disposed between the acoustic sensor and the acoustic window.

15. The device of claim 14 , wherein the acoustically transmissive layer is adhesively attached to the acoustic window.

16. The apparatus of claim 15 , wherein the acoustic sensor is adhesively attached to the acoustically transmissive layer.

17. The apparatus of claim 1 , wherein the in-situ acoustic monitoring system comprises a housing that supports the acoustic sensor and a spring configured to urge the housing and the acoustic sensor against a portion of the polishing layer.

18. The apparatus of claim 1 , wherein the controller is configured to obtain a frequency spectrum of the acoustic signal from the acoustic signal and detect a polishing endpoint based on a change in intensity of a specific frequency range within the frequency spectrum.

19. 1. A chemical mechanical polishing apparatus, comprising: A platen and a polishing pad supported on the platen; a carrier head for holding a surface of the substrate against the polishing pad; a motor that generates relative motion between the platen and the carrier head to polish a layer overlying the substrate; an in-situ acoustic monitoring system including an acoustic window extending through the polishing pad and an acoustic sensor receiving acoustic signals from the surface of the substrate, the acoustic window having an acoustic attenuation coefficient less than that of the polishing pad and having a top surface coplanar with a polishing surface contacting the substrate, the acoustic sensor being attached to a bottom surface of the acoustic window with an acoustically transmissive adhesive; a controller configured to detect a polishing endpoint based on a change in an acoustic signal received from the in-situ acoustic monitoring system; A chemical mechanical polishing apparatus comprising:

20. The device of claim 1 , wherein the acoustic window comprises a non-porous polymeric material.

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