Acoustic signal planarization detection during chemical mechanical polishing

Abstract

To provide in-situ monitoring of chemical mechanical polishing, in particular, acoustic monitoring.SOLUTION: A chemical mechanical polishing apparatus includes a platen, a polishing pad 110 supported on the platen, a carrier head to hold a surface of a substrate 10 against the polishing pad 110, a motor to generate relative motion between the platen and the carrier head to polish a top layer on the substrate 10, an in-situ acoustic monitoring system comprising an acoustic signal sensor to receive an acoustic signal from the surface of the substrate, and a controller configured to detect planarization of topology on the substrate based on the signal from the in-situ acoustic monitoring system.SELECTED DRAWING: Figure 5A-C

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to in-situ monitoring, particularly acoustic monitoring, of chemical mechanical polishing. [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 a 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 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, leaving portions of the filler layer 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 planarization method. This planarization method typically requires the substrate to be mounted on a carrier or polishing head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate, pressing it against the polishing pad. Typically, an abrasive polishing slurry is supplied to the surface of the polishing pad.

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

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

[0006] In one aspect, a chemical mechanical polishing apparatus includes a platen, a polishing pad supported on the platen, a carrier head that holds a surface of a substrate in contact with the polishing pad, a motor that generates relative motion between the platen and the carrier head to polish an upper layer on the substrate, 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 planarization of a topology on the substrate based on signals from the in-situ acoustic monitoring system.

[0007] 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 more reliably stopped, improving wafer-to-wafer uniformity; Polishing parameters may be changed in response to detection of planarization, i.e., smoothing of the substrate surface, thereby improving uniformity or increasing the polishing rate; Polishing may be stopped upon detection of planarization or after a preset time has elapsed after detection of planarization. This may provide an alternative endpoint technique.

[0008] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other aspects, features, and advantages will be apparent from the description and drawings, and from the claims. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a polishing apparatus. [Figure 2A] 1 is a schematic cross-sectional view showing an acoustic monitoring sensor engaging a portion of a polishing pad. [Figure 2B] 1 is a schematic cross-sectional view illustrating another embodiment of an acoustic monitoring sensor including an acoustically transparent layer. [Figure 2C] 10 is a schematic cross-sectional view illustrating another embodiment of an acoustic monitoring sensor. [Figure 2D] FIG. 10 is a schematic cross-sectional view illustrating another embodiment of an acoustic monitoring sensor in which an acoustic window is formed in the polishing layer and an acoustically transparent layer is formed in the backing layer of the polishing pad. [Figure 3] FIG. 1 is a schematic top view showing a platen having multiple acoustic monitoring sensor windows. [Figure 4] FIG. 1 is a schematic top view showing a platen with a platen portion surrounding an acoustic monitoring sensor window. [Figure 5A-C] 1A and 1B are diagrams illustrating planarization of the surface of a substrate. [Figure 6] 1 is a graph showing the sum of spectral power density over a frequency range as a function of time. DETAILED DESCRIPTION OF THE INVENTION

[0010] Like reference symbols in the various drawings indicate like elements.

[0011] In some semiconductor chip manufacturing processes, an upper layer, e.g., metal, silicon oxide, or polysilicon, is polished until an underlying layer, e.g., a dielectric such as silicon oxide, silicon nitride, or a high-k gate dielectric, is exposed. For some applications, the exposure of the underlying layer changes the acoustic emissions from the substrate. By detecting this change in acoustic signal, the polishing endpoint can be determined. However, existing monitoring techniques may not meet the increasing demands of semiconductor device manufacturers.

[0012] The monitored acoustic emissions may be caused by energy released as the substrate material deforms, and the resulting acoustic spectrum is related to the material properties of the substrate. Without being bound by any particular theory, possible sources of this energy, also referred to as "stress energy," and its characteristic frequencies include chemical bond scission, specific phonon frequencies, and slip-stick mechanisms. The acoustic effects of this stress energy are not the same as noise (sometimes referred to as an acoustic signal) caused by vibrations induced by friction of the substrate against the polishing pad, or noise caused by cracking, chipping, breakage, or similar defects in 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 in the substrate. For example, the signal from the acoustic sensor can be compared to a signal measured from a test substrate known to represent stress energy.

[0013] 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, the weak coupling between the polishing pad and the sensor tends to attenuate the acoustic signal. Furthermore, it can be difficult to establish a consistent coupling between the sensors.

[0014] Therefore, it may be advantageous to have the acoustic sensor in contact with an acoustic "window" that provides low acoustic signal attenuation. In some embodiments, a second layer of transparent material is added to the in-situ acoustic monitoring system to further increase acoustic signal coupling to the acoustic sensor.

[0015] Adhering the acoustic sensor to the coupling window, for example with an adhesive, can reduce noise in the acoustic signal associated with movement of the acoustic sensor within the housing. The adhesive can provide superior coupling of the sensor to the polishing pad and more reliable acoustic attenuation on a sensor-to-sensor basis.

[0016] Any of these features can be used independently of the others.

[0017] 1 shows an example of a polishing apparatus 100. The polishing apparatus 100 includes a rotatable, disk-shaped platen 120 on which a polishing pad 110 rests. The polishing pad 110 can be a dual-layer polishing pad having an outer polishing layer 112 and a softer backing layer 114. The platen is operable to rotate about an axis 125. For example, a motor 121, e.g., a DC induction motor, can orbit a drive shaft 124 to rotate the platen 120.

[0018] The polishing apparatus 100 can include a port 130 that dispenses a polishing fluid 132, such as an abrasive slurry, onto the polishing pad 110. The polishing apparatus can also include a polishing pad conditioner that abrades the polishing pad 110 to maintain the polishing pad 110 in a consistent abrasive state.

[0019] The polishing apparatus 100 includes at least one carrier head 140. The carrier head 140 is operable to hold the substrate 10 against the polishing pad 110. Each carrier head 140 can have independent control of the polishing parameters, such as pressure, associated with the respective substrate.

[0020] Carrier head 140 may include a retaining ring 142 that retains substrate 10 beneath flexible membrane 144. Carrier head 140 also includes one or more independently controllable pressurizable chambers defined by the membrane, e.g., three chambers 146a-146c (see FIG. 1), that can apply independently controllable pressures to associated zones on flexible membrane 144 and, therefore, on substrate 10. For ease of illustration, only three chambers are shown in FIG. 1, but there may be one or two chambers, or four or more chambers, e.g., five chambers.

[0021] Carrier heads 140 are suspended from a support structure 150, e.g., a carousel or track, and are connected by drive shafts 152 to carrier head rotation motors 154, e.g., DC induction motors, so that the carrier heads can rotate about axes 155. Optionally, each carrier head 140 can be oscillated laterally, e.g., on a slider on carousel 150, or by rotational oscillation of the carousel itself, or by sliding along a track. During typical operation, the platen is rotated about its central axis 125, and each carrier head is rotated about its central axis 155 and translated laterally across the upper surface of the polishing pad.

[0022] A controller 190, such as a programmable computer, is connected to the motors 121, 154 to control the rotational speed of the platen 120 and carrier head 140. For example, each motor may include an encoder that measures the rotational speed of its associated drive shaft. A feedback control circuit, which may be within the motor itself, part of the controller, or a separate circuit, receives the measured rotational speed from the encoder and adjusts the current supplied to the motor so that the rotational speed of the drive shaft matches the rotational speed received from the controller.

[0023] 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. 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 is deformed.

[0024] A position sensor, for example, an opto-isolator connected to the rim of the platen or a rotary encoder, can be used to sense the angular position of the platen 120. This allows only the portion of the signal measured when the sensor 162 is in the vicinity of the substrate, for example, when the sensor 162 is below the carrier head or substrate, to be used for endpoint detection.

[0025] 1 , the acoustic monitoring system 160 includes an acoustic sensor 162 supported and positioned by the platen 120 that receives acoustic signals from the substrate 10 through the polishing pad 110. The acoustic sensor 162 can be partially or entirely within a recess 164 in the top surface of the platen 120. In some embodiments, the top surface of the acoustic sensor 162 is coplanar with the top surface of the platen 120.

[0026] The portion of the polishing pad directly above the acoustic sensor 162 can include an acoustic window 119. For example, as shown in Figure 2A, the acoustic window 119 can be narrower than the acoustic sensor 162, or the two can be substantially equal in width (e.g., within 10%), as shown in Figure 2C. If the acoustic window 119 is narrower than the acoustic sensor 162, the sensor can also abut the bottom of the polishing layer 112.

[0027] Acoustic sensor 162 is a contact acoustic sensor that has a surface that is connected (e.g., in direct contact or simply with an adhesive layer) to a portion of polishing layer 112 and / or acoustic window 119. For example, acoustic sensor 162 can be an electromagnetic acoustic transducer or a piezoelectric acoustic transducer. A piezoelectric sensor can include a rigid contact plate, e.g., stainless steel, that is positioned in contact with the body to be monitored, and a piezoelectric assembly, e.g., a piezoelectric layer sandwiched between two electrodes on the back side of the contact plate.

[0028] In some embodiments, the acoustic sensor 162 is positioned 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 against the housing 163 urges the acoustic sensor 162 into contact with a portion of the polishing pad 110. Alternatively, for example, if no housing is used, the spring 165 can urge directly against the acoustic sensor 162. In some embodiments, the spring 165 is a long travel spring 165 that provides a pressure similar to that of the heavy duty spring 165 over a wider compression range.

[0029] The acoustic signal sensor 162 may be connected by circuitry 168 to a power supply and / or other signal processing electronics 166 through a rotary coupling, such as a mercury slip ring.

[0030] In some embodiments, the in-situ acoustic monitoring system 160 is a passive acoustic monitoring system. In this case, signals are monitored by the 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 the 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, when monitoring the polishing of an inter-layer dielectric (ILD) in shallow trench isolation (STI), a frequency range of 225 kHz to 350 kHz can be monitored.

[0031] The signal from the sensor 162 can be amplified by a built-in internal amplifier with a gain of 40-60 dB. In some embodiments, the amplification gain is 40-60 dB (e.g., 50 dB). The signal from the acoustic sensor 162 can then be further amplified and filtered as needed and digitized through an A / D port to a high-speed data acquisition board, for example, in the electronics 166. Data from the acoustic sensor 162 can be recorded in a similar frequency range as the generator 163 or in a different, e.g., higher, frequency range, e.g., 1-10 MHz, e.g., 1-3 MHz, or 6-8 MHz. In embodiments where the acoustic sensor 162 is a passive acoustic sensor, it can monitor a frequency range of 100 kHz to 2 MHz, such as 500 kHz to 1 MHz (e.g., 750 kHz).

[0032] When positioned within the platen 120, the acoustic sensor 162 can be located in the center of the platen 120, for example at the axis of rotation 125, at the edge of the platen 120, or at the midpoint (e.g., 5 inches (12.7 cm) from the axis of rotation for a 20 inch (50.8 cm) diameter platen).

[0033] 2A , further details of acoustic monitoring system 160 are shown. Acoustic sensor 162 can be held within a recess 169 in the top surface of housing 163. Housing 163 can assist in proper positioning of sensor 162. Housing 163 is constructed of a rigid and durable material sufficient to protect acoustic sensor 162 from damage. However, in some embodiments, such as those shown in FIGS. 2C and 2D , a housing is not required; for example, sensor 162 can simply fit between and be secured by the side walls of recess 169. Various embodiments described as using a housing can omit the housing.

[0034] In some embodiments, the housing 163 extends through the backing layer 114, as shown, for example, in Figure 2B, and in some embodiments, the housing 163 extends through a portion of the polishing layer 112, as shown, for example, in Figure 2A. However, in some embodiments, the housing 163 fits perfectly within the recess 164 in the platen 120, for example, when the top surface of the sensor 162 is coplanar with the top surface of the platen 120 and contacts the bottom surface of the polishing pad 110.

[0035] 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 extends. Housing 163 can be constructed of a metal, such as aluminum or stainless steel, or a polymeric material, such as polycarbonate, polyvinyl chloride (PVC), or polymethyl methacrylate (PMMA).

[0036] Assuming 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 contacts a support 167 located on the platen 120. Such a support can 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 biasing the acoustic sensor 162 into contact with the bottom surface of the polishing layer 112. This can improve acoustic coupling between the polishing layer and the sensor. However, various embodiments described as using a spring can 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.

[0037] In some embodiments, support 167 is placed below spring 165 and provides a fixed block against which spring 165 can press housing 163. Support 167 can be any material sufficient to firmly support spring 165 and housing 163 without movement or compressive buckling.

[0038] In addition to, or instead of, a spring, the acoustic sensor 162 can be secured to a portion of the polishing layer 112 (and / or to the acoustic window 119, described below) by an adhesive layer 170. The adhesive layer 170 can improve coupling to the sensor and reduce noise in the acoustic signal received by the acoustic sensor 162 by increasing the contact area between the acoustic sensor 162 and the polishing layer 112 and / or acoustic window 119, reducing unwanted movement within the acoustic sensor 162 during the polishing operation, and reducing the presence of gas pockets between the acoustic sensor 162 and the polishing layer 112 and / or acoustic window 119. The adhesive layer 170 can be an adhesive or adhesive strip (e.g., tape) applied between the acoustic sensor 162 and the polishing layer 112 and / or acoustic window 119. For example, the adhesive layer 170 can be a cyanoacrylate, a pressure-sensitive adhesive, a hot-melt adhesive, or the like.

[0039] 2A, the polishing layer 112 includes an acoustic window 119 disposed above the adhesive layer 170 and the acoustic sensor 162. However, in some embodiments, the acoustic sensor 162 directly contacts the acoustic window 119.

[0040] 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 to provide a sufficient signal for acoustic monitoring, 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).

[0041] The acoustic impedance of a material is a measure of the repulsion that the material presents to acoustic streaming caused by acoustic pressure applied to the material. The acoustic attenuation coefficient quantifies how the transmitted acoustic amplification decreases as a function of frequency for a particular material. While not wishing to be bound by theory, the specific acoustic impedance (AI) of the acoustic window 119 is window ) couples the liquid 132 and polished surface 112a to the acoustic signal sensor 162, and the acoustic impedance characteristic of the acoustic window 119 is beneficially: TIFF2026000990000002.tif14170 The range can be:

[0042] In particular, the window 119 can 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 operation. The window can be constructed from a non-porous material, e.g., a solid. In contrast, the polishing layer 112 can be porous, e.g., microporous, such as a polymer matrix with hollow plastic microspheres embedded in it.

[0043] Acoustic window 119 extends through polishing layer 112 such that one surface, e.g., the top surface, is coplanar with polishing surface 112a of polishing layer 112. The opposite surface, e.g., the bottom surface, can be coplanar with lower surface 112b of polishing layer 112. In some embodiments, a recess 118 is formed in lower surface 112b opposite polishing surface 112a. The portion of polishing layer 112 that includes recess 118 forms a thin portion of polishing layer 112 that has a thickness less than the remainder of polishing layer 112, and acoustic window 119 is located in the thin portion.

[0044] The acoustic window 119 can be made of a non-porous material. Generally, non-porous materials transmit acoustic signals with reduced noise and dispersion compared to porous materials. The material of the acoustic window 119 can have a compressibility within the compressibility range of the surrounding material of the polishing layer 112, thereby reducing 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 can be made of one or more of polyurethane, polyacrylate, polyethylene, or other polymers with low acoustic impedance and low acoustic attenuation.

[0045] 2C, an acoustic window 119 is shown extending through the entire 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.

[0046] In some embodiments, acoustic monitoring system 160 includes an acoustically transparent layer 172 in contact with adhesive layer 170. The transparent layer 172 is an index-matching material that increases acoustic signal coupling between elements in contact with the transparent layer 172. The transparent layer 172 can 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, transparent layer 172, or both. For example, the transparent layer 172 can be a layer of Aqualink™, Rexolite™, or Aqualene™. In some embodiments, the transparent layer 172 has an acoustic attenuation within 20% of the acoustic attenuation of the acoustic window 119, e.g., 10%. The acoustically transparent layer 172 can have an acoustic attenuation lower than that of the surrounding backing layer 114.

[0047] The acoustically transparent layer 172 may be selected to have a compressibility similar to that of the backing layer 114, for example, within 20%, such as within 10%, of the compressibility of the surrounding backing layer 114.

[0048] 2D is an embodiment in which the acoustic window 119 extends through the thickness of the polishing layer 112 and the transmissive layer 172 extends through the thickness of the 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 platen 120 and engage the transmissive layer 172.

[0049] Additionally, acoustic signal sensor 162 is shown having dimensions sufficient to contact both transmission layer 172 and the opposite side of recess 164. In such embodiments, recess 164 provides support for acoustic signal sensor 162, and the pressure of the polishing operation causes acoustic signal sensor 162 to contact transmission layer 172. An adhesive layer 170, as described herein, is disposed between transmission layer 172 and acoustic window 119. In some embodiments, an additional adhesive secures the contact surface between acoustic signal sensor 162 and transmission layer 172.

[0050] In some embodiments, 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.

[0051] The acoustic signal generator generates (i.e., emits) an acoustic signal from the side of the substrate closer to the polishing pad 110. The acoustic signal generator can be connected to a power supply and / or other signal processing electronics 166 by a circuit 168 through a rotary coupling, e.g., a mercury slip ring. The signal processing electronics 166 can then be connected to a controller 190, which can be configured to control the magnitude or frequency of the acoustic energy transmitted by the generator, for example, by variably increasing or decreasing the current supply to the generator. The acoustic signal generator and acoustic sensor 162 can be coupled to each other, but this is not required. The sensor 162 and the generator can be separate and physically separated from each other. Commercially available acoustic signal generators can be used for the generator. The generator can be attached to the platen 120 and held in place, for example, using a clamp or by a threaded connection to the platen 120.

[0052] As shown in FIG. 3 , in some embodiments, multiple acoustic signal sensors 162 can be grounded to the platen 120, with each acoustic sensor 162 associated with an acoustic window 119. Each sensor 162 can be configured as described with respect to any of FIGS. 1 and 2A-2B . Signals from the sensors 162 can be used by a controller 190 to calculate a positional distribution of acoustic emission events occurring on the substrate 10 during polishing. In some embodiments, the multiple sensors 162 can be positioned at different angular positions around the axis of rotation of the platen 120, but at the same radial distance from the axis of rotation. In some embodiments, 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 at different angular positions around the axis of rotation of the platen 120, but at different radial distances from the axis of rotation.

[0053] In some embodiments, the acoustic window 119 is surrounded by a smooth portion 174 of the polishing layer 112. The smooth portion 174 does not have grooves 116 and is coplanar with the top surface of the acoustic window 119. Embodiments that include a smooth portion 174 surrounding the acoustic window 119 can reduce noise associated with the substrate 10 interacting with the grooves 116 of the polishing layer 112 during the polishing operation.

[0054] Substrate 10 is formed by sequentially depositing conductive, semiconductive, or insulating layers on a silicon wafer. A fill layer is deposited over a non-planar surface, and the non-planar surfaces, such as fill and patterned layers, are planarized to have a common coplanar surface and / or to expose the non-planar surface. In some embodiments, the 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 during process steps. For example, a substrate 10 including a fill layer may have a non-uniform surface roughness, e.g., topography, due to the deposition process. Detecting that the topography has been planarized allows the system to modify one or more processes based on the transition. For example, the apparatus 100 can stop a high carrier head 140 pressure step once the fill layer surface is planarized.

[0055] 5A-5C illustrate interlayer transitions present in the planarization process of a substrate 500. FIG. 6 illustrates an example acoustic signal 600 comparing the total power spectral density (PSD) across a range of frequencies on the y-axis versus time in seconds (s). The acoustic signal 600 has distinct regions, such as a first region 602, a second region 604, and a third region 606. In some embodiments, the regions 602, 604, and 606 correspond to layer transitions in the substrate 500, such as those illustrated in FIGS. 5A-5C.

[0056] 5A shows an exemplary substrate 10 before polishing. Substrate 10 includes a wafer 502, e.g., a silicon wafer, a patterned layer 504, and a fill layer 508. Before the planarization step, fill layer 508 is non-planar and includes a topography 509. Topography 509 is obtained by depositing fill layer 508 over patterned layer 504 and has dimensions on the order of the feature size, e.g., the width of a metal line.

[0057] 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 acoustic signals, such as 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.

[0058] Without wishing to be bound by theory, the acoustic signal 600 varies based on the varying interface between the fill layer 508 material and the polishing layer 112 material. In particular, an initially uneven topography can create a significant acoustic signal. However, as polishing progresses and the topography 509 of the fill layer 508 is planarized, the interface between the polishing surface 112a and the substrate 10 becomes smoother, and the acoustic signal can decrease. The polishing of the topography 509 may correspond to the first region 602 of the signal 600 in FIG. 6 .

[0059] Again, without wishing to be bound by theory, a layer transition occurs when topography 509 is removed by apparatus 100. As shown in FIG. 5B, the surface of remaining fill layer 508 is substantially flat. Polishing of the flat surface may correspond to second region 604 of acoustic signal 600. In second region 604 of signal 600, acoustic signal 600 is substantially constant (albeit affected by noise).

[0060] Again, without wishing to be bound by theory, the second region 604 continues in time until the fill layer 508 extending over the patterned layer 504 is removed. As shown in FIG. 5C , the patterned layer 504 is composed of a different material than the fill layer 508 and interacts differently with the surface and material of the polishing layer 112, thereby creating a third region 606 of the acoustic signal 600. Additionally, continued polishing may create dishing, a topology that may also increase the acoustic signal. The third region 606 may be inconsistent, e.g., increasing or decreasing.

[0061] In some embodiments, differentiation between regions 602, 604, and 606, e.g., detection of layer transitions, may be performed by acoustic monitoring system 160 and / or controller 190 of apparatus 100. Detection may be performed through various calculations known in the art of slope change detection, but may include one or more difference, moving average, windowing, or box logic algorithm calculations.

[0062] In additional embodiments, acoustic signal 600 can be processed using additional steps before applying the slope change detection algorithm. For example, one or more filters, such as bandpass filters, and / or one or more transforms, such as fast Fourier transforms, can be applied to acoustic signal 600. For example, a bandpass filter can be used to isolate preferred frequencies of acoustic signal 600 before processing, such as frequencies in the range of 50-500 kHz, or in the range of 200-700 kHz.

[0063] In some embodiments, the apparatus 100 modifies one or more polishing parameters in response to the differentiation of the regions 602, 604, and 606. For example, during the first region 602 where the topography 509 is being removed, the apparatus 100 can dispense a first abrasive polishing liquid 132 for rapid removal of the topography 509. When a transition from the first region 602 to the second region 604 is detected, a different polishing liquid 132 having a lower polishing rate or lower selectivity can be dispensed onto the pad 110.

[0064] Alternatively or additionally, once the transition from second region 604 to third region 606 is detected, the pressure applied by carrier head 140 can be reduced, which can reduce the risk of dishing or erosion of fill layer 508.

[0065] Turning now to the signal from the sensor 162 in any of the above-described embodiments, for example, after amplification, pre-filtering, and digitization, the signal can be data processed, for example, by the controller 190, for either endpoint detection or feedback or feedforward control.

[0066] In some embodiments, the controller 190 is configured to monitor acoustic loss. For example, the received signal strength is compared to the emitted signal strength to generate a normalized signal, which can be monitored over time to detect changes. Such changes can indicate a polishing endpoint, for example, when the signal crosses a threshold value.

[0067] In some embodiments, a frequency analysis of the signal is performed. For example, frequency domain analysis can be used to determine the relative power of spectral frequencies and determine when film transitions occur at specific radii. Information about transitions with radius can be used to trigger endpoints. As another example, a fast Fourier transform (FFT) can be performed on the signal to generate a frequency spectrum. Specific frequency bands can be monitored, and if the intensity of the frequency band crosses a threshold, this can indicate exposure of the underlying layer and can be used to trigger an endpoint. Alternatively, if the location (e.g., wavelength) or bandwidth of a local maximum or minimum at a selected frequency crosses a threshold, this can indicate exposure of the underlying layer and can trigger an endpoint. For example, when monitoring the polishing of an interlayer dielectric (ILD) in shallow trench isolation (STI), a frequency range of 225 kHz to 350 kHz can be monitored.

[0068] As another example, a wavelet packet transform (WPT) can be performed on a signal to decompose it into low- and high-frequency components. The decomposition can be repeated as necessary to divide the signal into smaller components. The intensity of one of the frequency components can be monitored; if the component's intensity crosses a threshold, this can indicate exposure of the underlying layer and can be used to trigger an endpoint.

[0069] Assuming the position of the sensor 162 relative to the substrate 10 is known, the position of the acoustic event on the substrate can be calculated, for example, using motor encoder signals or an opto-isolator attached to the platen 120, e.g., the radial distance of the event from the center of the substrate. Determining the position of the sensor relative to the substrate is discussed in U.S. Patent No. 6,159,073 and U.S. Patent No. 6,296,548, which are incorporated by reference.

[0070] Acoustic events of various process significance include micro-scratches, film transition ruptures, and film cleaning. Various methods can be used to analyze the acoustic emission signal from the waveguide. Fourier transform and other frequency analysis methods can be used to determine peak frequencies that occur during polishing. Experimentally determined thresholds and monitoring within defined frequency ranges can be used to identify expected and unexpected changes during polishing. An example of an expected change is the sudden appearance of a peak frequency during a film hardness transition. An example of an unexpected change is a problem with the consumable set (pad glazing or machine health issues due to other process drift).

[0071] In operation, acoustic signals are collected from the in-situ acoustic monitoring system 160 while the device substrate 10 is being polished at the polishing station 100. The signals are monitored to detect exposure of underlying layers of the substrate 10. For example, a particular frequency range can be monitored and the intensity can be monitored and compared to an empirically determined threshold value.

[0072] Detection of the polishing endpoint triggers an interruption of polishing, but polishing can continue for a predetermined amount of time after the endpoint trigger. Alternatively or additionally, the collected data and / or the endpoint detection time can be fed forward to control the processing of substrates in subsequent processing operations, such as polishing at a subsequent station, or fed back to control the processing of subsequent substrates at the same polishing station. For example, detection of the polishing endpoint can trigger a modification of the current pressure of the polishing head. As another example, detection of the polishing endpoint can trigger a modification of the baseline pressure in subsequent polishing of a new substrate.

[0073] The embodiments and all of the functional operations described herein can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structural means disclosed herein and their structural equivalents, or in combinations of the above. The embodiments described herein can be implemented as one or more non-transitory computer program products, i.e., one or more computer programs tangibly embodied in a machine-readable storage medium for execution by or controlling the operation of a data processing apparatus, e.g., a programmable processor, a computer, or multiple processors or computers.

[0074] A computer program (also known as a program, software, software application, or code) can be written in any form of programming language, including compiled or interpreted languages, and can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file. A program can be stored in a portion of a file that holds other programs or data, in a single file dedicated to the program in question, or in multiple compound files (e.g., a file storing one or more modules, subprograms, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communications network.

[0075] The processes and logic flows described herein may be implemented by one or more programmable processors that execute one or more computer programs to perform functions by manipulating input data and generating output. The processes and logic flows may also be implemented by, and apparatus may be implemented as, special purpose logic circuitry, such as an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

[0076] The term "data processing apparatus" encompasses all apparatus, devices, and machines that process data, including, by way of example, a programmable processor, a computer, or multiple processors or computers. In addition to hardware, an apparatus may include code that creates the execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or one or more combinations thereof. Processors suitable for the execution of computer programs include, by way of example, both general-purpose and special-purpose microprocessors, and any one or more processors of any kind of digital computer.

[0077] Suitable computer-readable media for storing computer program instructions and data include, by way of example, all forms of non-volatile memory, media, and memory devices, including semiconductor memory elements, such as EPROM, EEPROM, and flash memory devices, magnetic disks, such as internal hard disks or removable disks, magneto-optical disks, and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

[0078] The above-described polishing apparatus and method can be applied in various polishing systems. Either the polishing pad or the carrier head, or both, can move to provide relative motion between the polishing surface and the wafer. For example, the platen may orbit rather than rotate. The polishing pad can be a circular (or some other shape) pad fixed to the platen. Some 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 reel-to-reel belt). The polishing layer can be a standard abrasive material (e.g., polyurethane with or without filling), a soft material, or a fixed-abrasive material. Although the term relative position is used, it should be understood that the polishing surface and wafer can be held in a vertical orientation or some other orientation.

[0079] While this specification contains many specific details, these should not be construed as limitations on the scope that may be claimed, but rather as descriptions of features that may be specific to particular embodiments of a particular invention. In some embodiments, the methods may be applied to other combinations of upper and lower layer materials, as well as to signals from other types of in-situ monitoring systems, for example, optical or eddy current monitoring systems.

Claims

1. A platen and a polishing pad supported on the platen; a carrier head that holds the surface of the substrate in contact with the polishing pad; a motor for generating relative motion between the platen and the carrier head to polish an upper layer on the substrate; an in-situ acoustic monitoring system comprising an acoustic sensor that receives an acoustic signal from the surface of the substrate; a controller configured to detect planarization of a topology on the substrate based on signals from the in-situ acoustic monitoring system; and A chemical mechanical polishing apparatus comprising:

2. The apparatus of claim 1 , wherein the controller is configured to cause a dispenser to switch from dispensing a first polishing liquid to dispensing a second polishing liquid upon detecting the planarization.

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

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 range of frequencies to generate a power signal.

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

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 flattening of the topology.

7. contacting a substrate with a polishing pad and generating relative motion between the substrate and the polishing pad to polish an upper layer on the substrate; acoustically monitoring the substrate during polishing using a sensor of an in-situ acoustic monitoring system; detecting planarization of a topology on the substrate based on signals from the sensor; and A method of a chemical mechanical polishing system comprising:

8. The method of claim 7 , comprising switching from dispensing a first polishing fluid to dispensing a second polishing fluid upon detecting said planarization.

9. The method of claim 7 , comprising switching from applying a first pressure to applying a second pressure to the substrate upon detecting the planarization.

10. The method of claim 7 , comprising performing a Fourier transform on the signal and summing the spectral power densities over a range of frequencies to generate a power signal.

11. 11. The method of claim 10, comprising detecting a change in the slope of the power signal to detect flattening of the topology.

12. 11. The method of claim 10, comprising detecting a decrease in the magnitude of the slope of the power signal to detect flattening of the topology.

13. On one or more computers, receiving a signal from a sensor of an in-situ acoustic monitoring system while polishing the substrate; detecting planarization of a topology on the substrate based on the signal from the sensor; A non-transitory computer-readable medium having a computer program including instructions recorded thereon.

14. The computer-readable medium of claim 13 , comprising instructions for switching from dispensing a first polishing liquid to dispensing a second polishing liquid upon detecting said planarization.

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 upon detecting the planarization.

16. 14. The computer-readable medium of claim 13, comprising instructions for performing a Fourier transform on the signal and summing spectral power densities over a range of frequencies to generate a power signal.

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

18. 17. 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 flattening of the topology.

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