Method and apparatus for in situ adjustment of wafer slip detection during workpiece polishing

Abstract

To provide a method and apparatus for in situ adjustment of wafer slip detection during workpiece polishing.SOLUTION: In one aspect, a chemical mechanical planarization (CMP) system includes: a carrier configured to retain a substrate; a platen supporting a polishing pad; and a slip sensor configured to generate a signal indicative of a characteristic of a surface of the polishing pad. The system further includes a processor configured to: receive the signal from the slip sensor; calibrate a steady-state value of the signal when the CMP system is in a steady-state condition; compare the signal received from the slip sensor to the calibrated steady-state value during CMP polishing; and detect, in response to the signal received from the slip sensor during the CMP polishing, a wafer slip differing from the calibrated steady-state value by more than a threshold value.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The disclosed technology relates to methods and apparatus for improving chemical mechanical planarization (CMP) performance for the planarization of thin films.

[0002] During chemical mechanical planarization (CMP) or polishing, an abrasive slurry, either acidic or alkaline, is applied to a rotating polishing pad / platen via a metering pump or mass flow control regulator system. The substrate or wafer is held by a wafer carrier that is rotated and pressed against the polishing pad on the polishing platen for a specific period of time. The slurry is typically delivered to the polishing platen with a single pass distribution system. The wafer is polished (i.e., planarized) by both mechanical (e.g., abrasion) and chemical (e.g., corrosion) means during the CMP process.

[0003] During the CMP process, the interactions between the substrate, wafer carrier, polishing pad, and polishing platen generate significant forces. A substrate that is not held securely during this contact can slip from its position and adversely affect the process. Thus, there is a need to improve the ability to detect such slippage of a substrate during processing to improve CMP efficiency and reduce manufacturing costs. Summary of the Invention

[0004] One aspect of the disclosed technology is a method for insitu adjustment of wafer slip detection during polishing of a wafer. In one aspect, a chemical mechanical planarization (CMP) system includes a carrier configured to hold a substrate, a platen supporting a polishing pad, a slip sensor configured to generate a signal indicative of a characteristic of a surface of the polishing pad, and a processor configured to receive a signal from the slip sensor, calibrate a steady-state value of the signal when the CMP system is in a steady state, compare the signal received from the slip sensor during CMP polishing to the calibrated steady-state value, and detect wafer slip that differs from the calibrated steady-state value by more than a threshold value in response to the signal received from the slip sensor during CMP polishing.

[0005] In certain embodiments, the slip sensor includes an optical sensor configured to measure the reflectivity of a surface of the polishing pad.

[0006] In a particular embodiment, the processor is further configured to recalibrate the steady-state value in real-time based on a signal received from the slip sensor during CMP polishing.

[0007] In certain embodiments, the processor is further configured to determine that the CMP system is in a steady state based on at least one of a rotation of the platen, a rotation of the carrier, a pressure applied to the substrate, a pressure applied to a retaining ring configured to hold the substrate in the carrier, and / or a flow rate of a fluid supplied to the polishing pad.

[0008] In a particular embodiment, the processor is further configured to stop all movement of components of the CMP system in response to detecting the wafer slip.

[0009] In certain embodiments, calibrating the steady-state value includes reading a signal from the slip sensor for a set length of time to obtain a series of expected slip sensor values.

[0010] In certain embodiments, the set length of time allows the slip sensor to measure each portion of the polishing pad measured by the slip sensor during CMP polishing.

[0011] In another aspect, a method for detecting wafer slip during chemical mechanical planarization (CMP) polishing includes receiving a signal from a slip sensor of a CMP system including a polishing pad, the slip sensor configured to generate a signal indicative of a characteristic of a surface of the polishing pad, calibrating a steady-state value of the signal when the CMP system is in a steady state, comparing the signal received from the slip sensor during CMP polishing to the calibrated steady-state value, and detecting wafer slip that differs from the calibrated steady-state value by more than a threshold value in response to the signal received from the slip sensor during CMP polishing.

[0012] In certain embodiments, the slip sensor includes an optical sensor configured to measure the reflectivity of a surface of the polishing pad.

[0013] In a particular embodiment, the method further includes recalibrating the steady-state value in real-time based on a signal received from the slip sensor during CMP polishing.

[0014] In certain embodiments, the method further includes determining that the CMP system is in a steady state based on at least one of a rotation of the platen, a rotation of the carrier, a pressure applied to the substrate, a pressure applied to a retaining ring configured to hold the substrate in the carrier, and / or a flow rate of a fluid supplied to the polishing pad.

[0015] In a particular embodiment, the method further includes stopping all movement of components of the CMP system in response to detecting the wafer slip.

[0016] In certain embodiments, calibrating the steady-state value includes reading a signal from the slip sensor for a set length of time to obtain a series of expected slip sensor values.

[0017] In certain embodiments, the set length of time allows the slip sensor to measure each portion of the polishing pad measured by the slip sensor during CMP polishing.

[0018] In accordance with yet another aspect, a chemical mechanical planarization (CMP) system includes a carrier configured to hold a substrate, a platen supporting a polishing pad, a slip sensor configured to generate a signal indicative of a characteristic of a surface of the polishing pad, and a processor configured to receive a signal from the slip sensor, obtain a set of expected sensor values ​​over a set length of time, compare the signal received from the slip sensor during CMP polishing to the set of expected sensor values, and detect wafer slip that differs from the set of expected sensor values ​​by more than a threshold value in response to the signal received from the slip sensor during CMP polishing.

[0019] In certain embodiments, the slip sensor includes an optical sensor configured to measure the reflectivity of a surface of the polishing pad.

[0020] In a particular embodiment, the processor is further configured to recalibrate the steady-state value in real-time based on a signal received from the slip sensor during CMP polishing.

[0021] In a particular embodiment, the processor is further configured to stop all movement of components of the CMP system in response to detecting the wafer slip.

[0022] In certain embodiments, the set length of time allows the slip sensor to measure each portion of the polishing pad that is measured by the slip sensor during CMP polishing. [Brief description of the drawings]

[0023] The above, as well as additional objects, features and advantages of the disclosed technology will be better understood through the following illustrative and non-limiting detailed description of specific embodiments of the disclosed technology, with reference to the accompanying drawings, in which like reference numerals are used for like elements unless otherwise noted.

[0024] [Figure 1] FIG. 1 is a schematic diagram of a chemical mechanical planarization system with a process improvement system, showing a wafer carrier holding a wafer in a processing position. [Diagram 2] 2 is a diagram of the chemical mechanical planarization system of FIG. 1 showing a wafer carrier holding a wafer in a loading position. [Diagram 3] FIG. 1 is a schematic diagram of a chemical mechanical planarization system with a process improvement system mounted on a moveable support structure. [Figure 4] FIG. 1 is a schematic diagram of a chemical mechanical planarization system with a process improvement system embedded in the polishing pad to enable in-situ application of the improvement system process to or on the surface of the wafer. [Diagram 5] FIG. 1 illustrates an exemplary CMP system including a slip sensor according to an embodiment of the present disclosure. [Figure 6] FIG. 1 is a schematic diagram of a slip sensor according to an aspect of the present disclosure. [Figure 7] FIG. 7 is an exploded view of the slip sensor shown in FIG. [Figure 8] 4 is a flow chart illustrating an exemplary method for detecting a lost or slipped wafer. [Figure 9] 5 is a flow chart illustrating another exemplary method for detecting a lost or slipped wafer. [Figure 10] 5 is a flow chart illustrating yet another exemplary method for detecting a lost or slipped wafer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Detailed embodiments of the disclosed technology will be described below with reference to the drawings.

[0026] Introduction to Chemical Mechanical Polishing (CMP) Systems The adoption and use of chemical mechanical polishing (CMP) for thin film planarization in the manufacturing of semiconductor ICs, MEMS devices, and LEDs is common among companies that manufacture the "chips" for these types of devices, among many other similar applications. This adoption includes manufacturing chips for cell phones, tablets, and other portable devices, as well as desktop and laptop computers. The growth of nanotechnology and micromachining continues to hold great promise as it is widely used and adapted in digital devices in the medical field, automotive field, and the Internet of Things ("IoT"). Chemical mechanical polishing for thin film planarization was invented and developed in the early 1980s by IBM scientists and engineers. Today, the process is widespread worldwide and is one of the truly enabling technologies in the manufacturing of almost all digital devices.

[0027] Integrated circuits are fabricated with multiple and alternating layers of conductive materials (copper, tungsten, aluminum, etc.), insulating layers (silicon dioxide, silicon nitride, etc.) and semiconductive materials (polysilicon). Successive combinations of these layers are applied sequentially to the surface of the wafer in which the devices are embedded, building up topographical undulations on the device structures, as in the case of silicon dioxide insulator layers. These undesirable topographical undulations must be flattened or "planarized" before the next layer is deposited. In the case of copper layers, copper is deposited on the surface to fill the contact vias and to create effective vertical paths for electron movement from device to device and from layer to layer. This procedure continues with each layer that is applied (usually applied by a deposition process). In the case of multiple layers of conductive materials (multiple layers of metals), this can result in multiple polishing procedures (one for each layer of conductor, insulator and semiconducting material) to make the circuit successful.

[0028] The CMP process is the enabling technology in the manufacture of multi-layer circuits that makes all of this possible.

[0029] The major cost driver in the CMP process consists of the overall cost associated with the set of consumables, such as polishing slurries and polishing pads. Typical polishing slurries used in CMP processing include, for example, colloidal suspensions of abrasive particles (e.g., colloidal silica, colloidal alumina, colloidal ceria, etc.) suspended or contained in an aqueous medium.

[0030] Polishing pads are typically polyurethane-based. Moreover, typical CMP polishing pads are usually 18" to 24" in diameter, a dimension determined by the size of the polishing platen (i.e., table) on typical polishing machines used around the world. However, in some applications (e.g., precision optics applications), the diameter can be much larger (e.g., up to 48" or more). These polishing pads are attached to a very flat polishing platen (i.e., polishing table) by a pressure sensitive adhesive.

[0031] During the CMP process, the slurry is applied to the rotating polishing pad via a metering pump or a mass-flow-control regulator system. The substrate or wafer is also held by a wafer carrier that is rotated and pressed against the polishing platen for a certain period of time. The terms "substrate" and "wafer" are used interchangeably herein and include, for example, semiconductor or silicon wafers, flat panel displays, glass plates or disks, plastic workpieces, and other substantially rigid, flat, thin workpieces having various shapes (e.g., circular, square, rectangular, etc.) and sizes that enable the implementation of one or more embodiments of the apparatus and processes disclosed herein. Moreover, the slurry may be delivered to the polishing platen, for example, in a single pass distribution system. Typically, the expectation is that the slurry particles in their media are evenly distributed between the rotating wafer and the rotating platen and / or polishing pad. However, it is quite typical that this is ineffective and unproductive because much of the polishing slurry is swept to the edge of the polishing pad / platen by centrifugal force and / or by the "squeegee" action of the wafer against the polishing pad / platen. As such, this portion of the polishing slurry may never reach the surface of the wafer, making that portion of the slurry an inactive participant in the polishing operation. In some cases, the hydrophobic nature of the surface of the polishing pad contributes to the polishing slurry being easily swept away and ultimately swept into a waste drain.

[0032] A force is applied to the wafer (e.g., by the substrate carrier head, e.g., via pressure applied to a membrane in the carrier head) to provide pressure between the wafer and the polishing pad, forcing the wafer into the pad for processing. Also, both the wafer and the pad have motion to create a relative velocity. The motion and force causes abrasive particles or other abrasives to be pressed against the wafer (i.e., substrate) while moving across the surface of the wafer, causing wear on parts of the pad. The corrosive chemicals in the slurry change the material being polished on the surface of the wafer. This mechanical effect of wear combined with chemical change is called chemical mechanical planarization or polishing (CMP). Thus, the rate of material removal from the substrate can be orders of magnitude higher by using both chemical and mechanical effects simultaneously, compared to using either the chemical or mechanical effects alone. Similarly, the smoothness of the polished surface may also be optimized by using both chemical and mechanical effects in combination.

[0033] Yield is the driving force that determines the manufacturing level success of many products (e.g., integrated circuits, MEMS, LEDs, etc.). Thus, the cumulative cost for manufacturing a solid-state device is called the “Cost-of-Ownership” (CoO), a term that is also applied to each of the required manufacturing steps. Ultimately, the CoO of the CMP process has one of the highest CoO figures of the 500-800 manufacturing steps required to produce a semiconductor “chip” and its associated digital devices.

[0034] Two challenges in the CMP process are to reduce the optimum amount of polishing slurry required per layer being polished and to extend the life of the polishing pad and polishing slurry. Another challenge is to prevent the substrate from slipping or being lost from the carrier during polishing, which can damage the substrate and / or the equipment, thereby reducing yield and increasing CoO.

[0035] For several years, various individuals and innovative companies have attempted to produce polishing slurry reclamation systems. Most of these systems are either offline in nature (i.e., separate from the polishing room) or in-line in nature (i.e., in a point-of-use (POU) slurry distribution system located near each polisher). Four important factors for monitoring and controlling an effective CMP polishing slurry are the pH of the slurry, the particle size of the abrasive components, the specific gravity of the slurry, and the cleanliness of the slurry.

[0036] When the slurry is distributed on the polishing pad, environmental factors such as evaporation tend to change the content of the fluid medium in the slurry. This change in content tends to affect the pH of the slurry, which in turn tends to adversely affect the specific gravity of the slurry. During the polishing process, material (e.g., copper, polysilicon, etc.) is removed from the surface of the wafer, generating fine particles. These fine particles either remain suspended in the slurry or become embedded in the polishing pad, or both. These fine particles cause scratches on the surface of the film being polished, causing catastrophic failure of the circuit.

[0037] These physical changes in the composition of the polishing slurry, while not catastrophic for certain lapping or milling slurries in machine shop and precision optical manufacturing applications, can tragically, catastrophically, and / or permanently damage the surface of semiconductor silicon wafers. These scratches and failures can negatively impact yields by rendering the damaged chips useless. For these and other reasons, slurry reclamation / recirculation systems, while common in metal lapping applications and some precision optical applications where surface quality tolerances are measured in microns, have not been particularly successful in the CMP process industry (e.g., semiconductor manufacturing plants) or, for example, in foundries, where surface quality tolerances are measured in nanometers and even angstroms.

[0038] The disclosed technology aims to address many of the above issues by improving CMP yields and improving the CMP process overall in terms of substrate waste, yield and CoO, for example, through the use of an in-situ wafer slip detection system in the CMP process.

[0039] FIG. 1 is a schematic diagram of a chemical mechanical planarization (CMP) system 100 that includes a process improvement system 130 to improve the CMP process. The system 100 can include a wafer carrier 150 configured to hold and process a wafer. In the illustrated embodiment, the wafer carrier 150 is in a processing (i.e., lower) position and holds a wafer or substrate 155 (not shown in FIG. 1 ) against a polishing pad 110. The polishing pad 110 can be positioned on a support surface, such as a surface of a platen 120. In some embodiments, the platen 120 can be configured to rise upwardly to contact components of the system 100, such as the wafer carrier, the pad conditioning arm, the process improvement system, and the slurry delivery system.

[0040] FIG. 2 is a diagram of the chemical mechanical planarization system of FIG. 1, showing a wafer 155 held in a loading (e.g., upper or top) position by a wafer carrier 150. In some embodiments, the wafer 155 can be held by, for example, vacuum force. For example, the wafer carrier 150 can hold or mount the wafer 155 with a vacuum system such that the surface of the wafer 155 to be polished faces the polishing pad 110 when the wafer 155 is mounted on the wafer carrier 150. With reference to both FIG. 1 and FIG. 2, the system 100 can include a slurry delivery system 140 configured to deliver a process slurry to the wafer 155 and enable the process slurry to be chemically / mechanically planarized against the polishing pad 110. The system 100 can include a pad conditioning arm 160 that includes a pad conditioner at one end and can be configured to treat or "refresh" the surface roughness of the pad (as well as other process characteristics of the pad) during or between process cycles. System 100 may further include a controller 165 that may be configured to provide the functionality of the methods described herein as well as additional functionality. In some implementations, controller 165 may be configured to detect the occurrence of a wafer loss or slip in situ, as described in the "Systems and Methods for Insitu Wafer Slip Detection" section below. Depending on the embodiment, controller 165 may include a processor and a memory that stores instructions configured to cause the processor to perform the methods described herein. For example, controller 165 may be configured to communicate (e.g., electronically) with and provide functionality to process improvement systems (e.g., slip detection systems) and / or mechanical or electromechanical devices and / or other CMP equipment components described herein, or other systems or components.

[0041] 1 and 2, the polishing pad 110 rests on top of a platen 120 that rotates about an axis. As one of ordinary skill in the art would readily appreciate, other orientations and directions of movement can be implemented (e.g., counterclockwise, clockwise about a vertical axis, etc.). The platen 120 may be configured to rotate back and forth clockwise, counterclockwise, with a ratcheting motion, etc.

[0042] The process improvement system 130 may be mounted stationary relative to or on the surface of the polishing pad 110, as shown in Figures 1 and 2, or may be mounted to a movable support structure, as described further herein. In some embodiments, the process improvement system 130 may be configured to lower the process improvement system 130 so that it is in close proximity to the polishing pad 110. In some embodiments, the process improvement system 130 may be configured (e.g., moving or stationary) so that the process improvement system 130 is in close proximity to the carrier 150. The process improvement system 130 may be oriented or configured in any manner suitable for improving the CMP process described elsewhere herein (e.g., by measuring the reflectivity of the polishing pad during polishing and avoiding substrate slippage). The process improvement system may provide process improvements during the wafer polishing process.

[0043] In one embodiment, the slurry delivery system 140 can deliver a slurry (e.g., an abrasive slurry) to the surface of the treated polishing pad 110. The abrasive slurry includes or contains sub-micron abrasive and corrosive particles. In a non-limiting example, the abrasive slurry typically includes a colloidal suspension of abrasive particles (e.g., colloidal silica, colloidal alumina, colloidal ceria, etc.). In some embodiments, the abrasive particles are suspended in an aqueous medium or any other suitable medium. In various embodiments, the slurry delivery system 140 includes a metering pump, a mass flow control regulator system, or any other suitable fluid delivery component, as will be appreciated by those skilled in the art.

[0044] Thus, the abrasive particles and corrosive chemicals in the slurry deposited by the slurry delivery system 140 on the polishing pad 110 mechanically and chemically polish the wafer by abrasion and erosion, respectively. As shown, the slurry delivery system 140 delivers a slurry that flows downward through the system and ultimately onto the polishing pad 110. In some embodiments, the wafer carrier 150 and polishing pad 110 can move relative to one another in any of a number of different ways to provide polishing. For example, the wafer carrier 150 can apply a downward force against the platen 120 such that the wafer 155 is pressed against the polishing pad 110, and the abrasive particles and corrosive chemicals of the slurry between the wafer 155 and polishing pad 110 can provide chemical and mechanical polishing as the polishing pad 110 and the wafer carrier 150 move relative to one another. As will be appreciated by those skilled in the art, the relative motion between the polishing pad and the wafer carrier can be configured in a variety of ways, with one or both configured to oscillate, move linearly, and / or rotate counterclockwise and / or clockwise relative to one another. This motion can be provided via a variety of mechanical or electromechanical devices, such as motors, linear actuators, robots, encoders, gearboxes, transmissions, and combinations thereof.

[0045] The pad conditioning arm 160 conditions the surface of the polishing pad 110 by applying a force against the polishing pad 110 through relative movement therebetween, such as the relative movement described above with respect to the polishing pad and wafer carrier 155. The pad conditioning arm 160 in the illustrated embodiment can oscillate with a pad conditioner at one end. In some embodiments, the pad conditioner is configured to rotate, for example, clockwise or counterclockwise. In some embodiments, the pad conditioner may contact the polishing pad 110 as it rotates.

[0046] FIG. 3 is a schematic diagram of a chemical mechanical planarization system with a process improvement system 133 mounted on a support structure. For example, the support structure may be movable to provide variable positioning before, after, and / or during polishing. The process improvement system 133 can be mounted either to an existing conditioning arm or to a separate arm dedicated to positioning independent of the pad conditioner and pad conditioner sweep control mechanism. For example, the process improvement system 133 can be mounted to an arm or other support structure, such as a moving or vibrating pad conditioning arm 160, to provide such movement functionality. The system 300 of FIG. 3 includes the polishing pad 110, platen 120, slurry delivery system 140, wafer carrier 150, wafer 155, and pad conditioning arm 160, as described above with respect to FIGS. 1 and 2. However, the system of FIG. 3 differs from the systems of FIGS. 1 and 2 in that the process improvement system 133 is mounted on the pad conditioning arm 160 to allow variable positioning of the process improvement system and contact with the polishing pad 110, for example, before and / or during polishing. In various embodiments, the process improvement system 133 can be mounted to a different support structure, such as a separate arm (not shown), to allow for independent positioning of the process improvement system 133 relative to the movement provided by the pad conditioning arm 160. For example, the process improvement system can be positioned and configured to allow for contact with one or more locations and / or components of the CMP system. For example, the process improvement system can be configured to contact the surface of the wafer. The process improvement system can be configured to contact two or more components of the CMP system, such as the surface of the wafer and / or the surface of the polishing pad. In another example, two or more process improvement systems can be implemented within the CMP systems described herein. For example, a system with multiple platens for CMP processing may include two process improvement systems per platen.

[0047] FIG. 4 is a schematic diagram of a chemical mechanical planarization system 400 with one or more process improvement systems 136 embedded in another component of the system 400. For example, the one or more process improvement systems 136 can be embedded in a platen, a wafer carrier, or a polishing pad. In a non-limiting example, the process improvement system 136 may be positioned and assembled with respect to the polishing pad to allow the process improvement system to contact the polishing pad from within the polishing pad. Such an embodiment can allow for in-situ interaction between the process improvement system and, for example, the surface of a wafer. The system of FIG. 4 includes a polishing pad 110, a platen 120, a slurry delivery system 140, a wafer carrier 150, a wafer 155, and a pad conditioning arm 160, as described above with respect to FIGS. 1-3. However, the system of FIG. 4 differs from the systems of FIGS. 1-3 in that the process improvement system 136 is embedded in the polishing pad 110.

[0048] Although FIGS. 1-4 show aspects of a CMP apparatus (e.g., wafer carrier 150, wafer 155), as one of ordinary skill in the art will appreciate, a CMP machine can be assembled in a number of different ways. Also, FIGS. 1-4 do not necessarily illustrate a complete CMP apparatus (which may otherwise include references to a wafer carrier head membrane with a retaining ring therearound for holding a substrate under pressure, the body of the CMP apparatus, a system for delivering a wafer substrate to a particular CMP apparatus, etc.), but are merely intended to be illustrative examples to highlight the disclosed techniques that are the subject of this disclosure. As one of ordinary skill in the art will appreciate, additional components of a CMP system (e.g., membrane, etc.) may be incorporated into the systems described herein. For example, the wafer carrier head 150 may further include a vacuum system configured to secure the wafer against the membrane using vacuum pressure or suction. The resilient membrane may include one or more distinct zones, where compressed gas is applied to the top or backside of the membrane. The pressure may be transferred through the membrane to the top or backside of the wafer to affect material removal during CMP. The wafer carrier head may include one or more rigid support components that provide a means for securing the membrane to its mating components, holding the membrane in its desired shape and dimensions, and / or clamping and sealing the membrane to provide an enclosed volume for containing a controlled gas pressure. Additionally, any of the apparatus and systems described herein may include a controller (e.g., controller 165 in FIG. 2) that may be configured to provide the functionality of the methods described herein and additional functionality. Additionally, reference numeral 170 indicates the relative position of a complete CMP apparatus (not shown) that applies a downward force to a wafer 150 attached to the wafer carrier head 150 as the wafer is polished against a polishing pad fixed to a rotating platen. For example, the CMP apparatus applies a downward force to the wafer carrier against the polishing pad 110 to polish the wafer 155 when the wafer carrier is configured in the lower position as shown in FIG. 1. Additionally, the wafer carrier head 150 may include a membrane attached to the remaining body of the wafer carrier head 150.A membrane (not shown) can be configured to provide pressure between the wafer 155 and the polishing pad 110 .

[0049] Additionally, the CMP system, including the wafer carrier, polishing platen, and / or slurry distribution system, may be configured to be controlled by a control system 165 (FIG. 2). The control system may be configured to receive feedback from the CMP system and provide control signals to the CMP system. For example, the control system may be configured to provide variable distribution or variable speed functionality to various components based on feedback signals received from the system. Thus, the system may adjust the rotational speed of the wafer and polishing platen during the CMP process in response to detecting the occurrence of wafer loss or slip.

[0050] As will be appreciated, the process improvement systems, methods, and apparatus described herein can be implemented without the complete CMP system shown in Figures 1-4. Moreover, other CMP equipment can perform the process improvement system functions described herein, including multi-head CMP systems, orbital CMP systems, or other CMP systems. For example, the process improvement systems, methods, and apparatus described herein can be implemented in a sub-aperture CMP system. A sub-aperture CMP system can include a polishing pad that is smaller in diameter than the wafer. Typically, the wafer is oriented face-up with a slurry applied to its surface, and the wafer and polishing pad rotate as the pad sweeps across the wafer.

[0051] For CMP processes, in-line adoption of the process improvement system is appropriate both as a steady-state POU change to existing legacy CMP planarization tools (polisher) and as a feature of new CMP planarization tools.

[0052] SYSTEM AND METHOD FOR IN SITU WAFER SLIP DETECTION - Patent application The equipment described herein, such as the equipment shown in Figures 1-4 or generally described elsewhere herein, can be adapted in the context of a process improvement system to provide improved methods and apparatus for detecting the occurrence of wafer loss or slip during a workpiece polishing process, such as CMP polishing. For example, an optical reflectance sensor or another type of optical sensor can be positioned to measure the reflectance of a wafer and / or a portion of the wafer carrier 150. For example, one or more sensors can be positioned on or within a portion of the carrier 150 to measure the reflectance or other parameter of a backside of a wafer 155 positioned within the carrier 150. One or more sensors can be positioned on or within a portion of the polishing pad 110 or platen 120 to measure the reflectance or other parameter of a frontside of a wafer 155 positioned within the carrier 150. As described below, the reflectance values ​​or other parameters received from the sensors can be used to detect the occurrence of wafer loss or slip during CMP.

[0053] FIG. 5 is a diagram of an exemplary CMP system 200 including a slip sensor according to an embodiment of the present disclosure. The CMP system 200 can be similar to the system 100 of FIGS. 1-4. For example, in a particular implementation, the CMP system 200 includes a polishing pad 210 positioned on a platen 220, a wafer carrier 250 configured to hold a wafer or substrate (e.g., wafer 155 shown in FIG. 2) against the polishing pad 210 in a processing (e.g., lower) position, and a slip sensor 300. The slip sensor 300 can be connected to a system control unit (e.g., controller 165 shown in FIG. 2). In some implementations, the slip sensor 300 is connected via an intermediate device such as an IO-Link Master Omron PLC card, a Beckhoff Auto IO-Link Master Hub, or the like. The slip sensor 300 can be mounted to a support structure or otherwise implemented within the system 200, as generally described with respect to the process improvement systems 130, 133, and 136 with respect to the CMP systems of FIGS. 1-4.

[0054] Figure 6 is a schematic diagram of a slip sensor 300 according to an embodiment of the present disclosure, and Figure 7 is an exploded view of the slip sensor 300 shown in Figure 6. With reference to Figures 6 and 7, the slip sensor can include an optical sensor 310 configured to measure reflectance within a field of view, connection hardware 320, and a switch 330. The connection hardware can be used to connect the slip sensor 300 to a wafer carrier 250, as shown in Figure 5.

[0055] The optical sensor 310 can be configured to detect wafer loss or slip by measuring the reflectivity of the polishing pad 210 during polishing. The optical sensor 310 can be in communication with a controller (e.g., controller 165 of FIG. 2) and / or other firmware and software to provide the functionality herein.

[0056] A method for detecting wafer loss or slip may rely on positioning an optical reflectance sensor positioned "downstream" of a wafer carrier that holds the wafer during polishing. Detection of a wafer that has slipped from the carrier may be performed as outlined below and shown in Figure 8. In particular, Figure 8 is a flow chart illustrating an exemplary method 1100 for detecting wafer loss or slip.

[0057] The method 1100 begins at block 1101. At block 1102, the method 1100 includes measuring the reflectance of a surface of a polishing pad without a wafer. At block 1104, the method 1100 includes measuring the reflectance of an upward facing surface of a wafer. At block 1106, the method 1100 includes setting a threshold for the sensor 300 between the two reflectance values ​​measured at blocks 1102 and 1104. In some implementations, the threshold may be the midpoint between the two measured reflectance values. At block 1108, the method 1100 includes starting the wafer polishing process.

[0058] At block 1110, the method 1100 includes detecting whether the wafer has slipped from the carrier during polishing based on the reflectance measured by the sensor 300. For example, the sensor 300 detects a change in reflectance within its field of view and provides a signal to the polisher control system regarding whether the wafer has slipped from the wafer carrier. In response to the reflectance exceeding the threshold set at block 1106, a signal generated by the sensor 300 indicates that the wafer has slipped from the wafer carrier. At block 1112, in response to the signal received from the sensor 300 exceeding the threshold, the polisher control system immediately stops all movement of the relevant components of the CMP system (e.g., movement of the polishing pad, platen, and wafer carrier) to prevent or minimize damage thereto and / or to the wafer. If the reflectance measured by the sensor 300 does not exceed the threshold, the sensor continues to measure the reflectance at block 1110 until the CMP process is complete. The method 1100 ends at block 1114.

[0059] One possible drawback of the method of FIG. 8 is that the reflectivity of the polishing pad can change over time due to several variables, including the type of pad (e.g., color, material, etc.), the accumulation of effluent on the surface of the polishing pad due to the polishing process, the presence or absence of fluids on the surface of the pad, such as water, chemicals and / or slurries, and / or changes in the surface texture of the pad.

[0060] The reflectivity of a wafer can change over time due to other variables including different wafer materials, different films deposited on the wafer, different "upstream" processes applied to the surface of the wafer such as oxidation, polishing, grinding and etching, and / or the presence or absence of fluids remaining on the surface of the wafer. Such upstream processes and variables can affect sensor reflectivity and downstream slip detection accuracy.

[0061] Due to these shortcomings, there is a need to provide a more reliable method for detecting slipped wafers during polishing. In some embodiments, a more reliable method and apparatus for detecting wafer slip may be performed as follows and as shown in Figure 9. In particular, Figure 9 is a flow chart illustrating another exemplary method 1200 for detecting wafer loss or slip.

[0062] Method 1200 begins at block 1201. At block 1202, method 1200 includes initiating a polishing process such that the field of view of sensor 300 includes a state substantially representative of a steady state achieved during polishing. Such steady states may include the actual color of pad 210, the presence or absence of any fluids on the surface of the pad, such as slurry, water and / or chemicals, and / or the texture of the pad surface, which may or may not change over the life of the pad and from one pad to another.

[0063] At block 1204, the method 1200 includes waiting for a steady state based on one or more of pad / platen rotation, wafer / carrier rotation, wafer and retaining ring pressure, and / or fluid flow, or any combination thereof. Once a steady state is established, the method 1200 may continue at block 1206 where the sensor 300 may be programmed or calibrated for a set of steady states. This operation may be performed, for example, via a technology commercially referred to as "IO Link," which allows the background reference to be reprogrammed or recalibrated in real time.

[0064] In block 1208, the method 1200 includes the sensor 300 continuously measuring the conditions in the field of view of the sensor 300 during the remaining polishing process and comparing the output from the sensor 300 to the programmed or calibrated steady state determined in block 1206. If the wafer slips from the carrier during polishing, the conditions in the field of view of the sensor will generally differ significantly from the programmed / calibrated conditions, thereby reliably detecting such a condition under various conditions and variables. Therefore, in response to a reading from the sensor 300 that deviates from the steady state (e.g., exceeds a threshold), the method 1200 proceeds to block 1210, where all motion of the CMP system is stopped to avoid damage to the substrate and / or equipment. If no deviation from the steady state is detected, the method 1200 can remain in block 1208 until the CMP process is completed.

[0065] By performing method 1200, sensor 300 provides a more reliable signal to the polisher control system, which can then immediately stop all motion in block 1210 based on the signal received from the sensor to prevent or minimize damage to the wafer, polishing pad, carrier, etc. By providing a more reliable signal, the methods and systems described herein can prevent false detection of slip due to changes in polishing conditions that may occur before a steady state is achieved, which can be a limitation to other conventional techniques.

[0066] FIG. 10 is a flow chart illustrating yet another exemplary method 1300 for detecting a lost or slipped wafer.

[0067] Method 1300 begins at block 1301. In block 1302, method 1300 includes lowering carrier 250 onto platen 220 and setting polishing parameters to be used during the CMP polishing process. In block 1304, method 1300 includes reading sensor values ​​over a set length of time to obtain a series of expected sensor values. In some implementations, the set length of time may be about 5 seconds, while in other embodiments, the set length of time may be longer or shorter. The set length of time allows the sensor to see each portion of the polishing pad that is measured by the sensor during polishing. The expected sensor values ​​may correspond to a range of color changes that the sensor can be expected to read over the course of the CMP process. Thus, the system can "learn" expected sensor values ​​that can be used to detect wafer slip.

[0068] In block 1306, the method 1300 includes starting monitoring the sensor output. In some implementations, the sensor monitoring may begin in response to the start of a polishing recipe. For example, the system may set a flag in software to start continuous monitoring of the sensor for wafer slip detection. The sensor value output from the sensor may be monitored to determine whether the wafer has slipped. In block 1308, the method 1300 includes determining whether the slip sensor has been triggered, for example, the system may compare the current sensor output to the expected sensor value obtained in block 1304. If the current sensor output does not differ from the expected sensor value by more than a threshold, the system may determine that a wafer slip has not occurred and the method 1300 may remain at block 1308. If the current sensor output differs from the expected sensor value by more than a threshold, the system may determine that the wafer has slipped and the method 1300 may continue to block 1310. At block 1310, the method 1300 includes stopping all movement to prevent damage to the CMP system and / or to avoid breaking the wafer. The method 1300 ends at block 1312.

[0069] Additionally, other CMP equipment may perform the wafer slip detection functions described herein, including multi-head CMP systems, orbital CMP systems, or other CMP systems.

[0070] It should be understood that many variations and modifications can be made to the above-described embodiments, and that the elements are among the other acceptable examples. All such modifications and variations are intended to be included herein within the scope of the present disclosure. The foregoing description details certain embodiments. However, it should be understood that no matter how detailed the above appears in the text, the systems and methods can be implemented in many ways. As mentioned above, it should be noted that the use of a particular term in describing a particular feature or aspect of the systems and methods should not be interpreted as meaning that the term is redefined herein to be limited to include any particular characteristic of the feature or aspect of the systems and methods to which the term is related.

[0071] In particular, conditional language such as "can," "could," "might," or "may," unless otherwise specified or understood within the context in which it is used, is intended to generally convey that certain embodiments include certain features, elements, and / or steps, while other embodiments do not. Thus, such conditional language is not generally intended to imply that the features, elements, and / or steps are somehow required in one or more embodiments, or that one or more embodiments necessarily include logic for determining whether or not those features, elements, and / or steps are included or performed in any particular embodiment, with or without user input or prompting.

[0072] Conjunction language such as the phrases "at least one of X, Y, and Z" or "at least one of X, Y, or Z" is understood within the context in which it is commonly used to convey that an item, term, etc. may be either X, Y, or Z, or any combination thereof, unless otherwise noted. For example, the term "or" is used in an inclusive (rather than exclusive) sense, such that, for example, when used to connect a list of elements, the term "or" may mean one, some, or all of the elements in the list. As such, such conjunctive language is not generally intended to imply that a particular embodiment requires at least one of X, at least one of Y, and at least one of Z, respectively, to be present.

[0073] The term "a" as used herein is to be given an inclusive rather than an exclusive interpretation. For example, unless otherwise specified, the term "a" is not to be understood to mean "exactly one" or "only one", but instead, the term "a" means "one or more" or "at least one", regardless of the use of quantifiers such as "at least one", "one or more", or "plurality" in the claims or specification, whether used in the claims or elsewhere in the specification.

[0074] The term "comprising" as used herein should be given an inclusive rather than an exclusive interpretation. For example, a general purpose computer including one or more processors should not be interpreted as excluding other computer components, and may include components such as memory, input / output devices, and / or network interfaces, among others.

[0075] Although the above detailed description illustrates, describes, and points out novel features as applied to various embodiments, it is understood that various omissions, substitutions, and changes in the form and details of the illustrated devices or processes may be made without departing from the spirit of the present disclosure. As will be recognized, certain embodiments of the disclosed technology described herein may be embodied in forms that do not provide all of the features and advantages described herein, since some features may be used or practiced separately from others. The scope of certain aspects of the technology disclosed herein is indicated by the appended claims, rather than the foregoing description. All changes that come within the meaning and range of equivalency of the claims are intended to be embraced within their scope.

Claims

1. 1. A chemical mechanical planarization (CMP) system comprising: a carrier configured to hold a substrate; a platen supporting the polishing pad; a slip sensor configured to generate a signal indicative of a characteristic of a surface of the polishing pad; receiving the signal from the slip sensor; calibrating a steady-state value of the signal when the CMP system is in a steady state; comparing the signal received from the slip sensor during CMP polishing with the calibrated steady-state value; and a processor configured to detect wafer slip that differs from the calibrated steady-state value by more than a threshold in response to the signal received from the slip sensor during the CMP polishing.

2. The system of claim 1 , wherein the slip sensor comprises an optical sensor configured to measure a reflectivity of the surface of the polishing pad.

3. The processor further comprises: The system of claim 1 , configured to recalibrate the steady-state value in real-time based on the signal received from the slip sensor during CMP polishing.

4. The processor further comprises:

2. The system of claim 1, configured to determine that the CMP system is in the steady state based on at least one of a rotation of the platen, a rotation of the carrier, a pressure applied to the substrate, a pressure applied to a retaining ring configured to hold the substrate in the carrier, and / or a flow rate of a fluid supplied to the polishing pad.

5. 10. The system of claim 1, wherein the processor is further configured to stop all movement of the CMP system components in response to detecting the wafer slip.

6. Calibrating the steady-state value includes: The system of claim 1 including reading the signal from the slip sensor for a set length of time to obtain a series of expected slip sensor values.

7. 7. The system of claim 6, wherein the set length of time allows the slip sensor to measure each portion of the polishing pad measured by the slip sensor during the CMP polishing.

8. 1. A method for detecting wafer slip during chemical mechanical planarization (CMP) polishing, comprising: receiving a signal from a slip sensor of a CMP system including a polishing pad, the slip sensor configured to generate a signal indicative of a characteristic of a surface of the polishing pad; calibrating a steady-state value of the signal when the CMP system is in a steady state; comparing the signal received from the slip sensor during CMP polishing with the calibrated steady-state value; and detecting a wafer slip that differs from the calibrated steady-state value by more than a threshold value in response to the signal received from the slip sensor during the CMP polishing.

9. The method of claim 8 , wherein the slip sensor comprises an optical sensor configured to measure the reflectivity of the surface of the polishing pad.

10. The method of claim 8 , further comprising recalibrating the steady-state value in real-time based on the signal received from the slip sensor during CMP polishing.

11. 10. The method of claim 8, further comprising determining that the CMP system is in the steady state based on at least one of a rotation of a platen, a rotation of a carrier, a pressure applied to a substrate, a pressure applied to a retaining ring configured to hold the substrate in the carrier, and / or a flow rate of a fluid supplied to the polishing pad.

12. 10. The method of claim 8, further comprising: in response to detecting the wafer slip, ceasing all movement of components of the CMP system.

13. Calibrating the steady-state value includes:

9. The method of claim 8, including reading the signal from the slip sensor for a set length of time to obtain a series of expected slip sensor values.

14. 14. The method of claim 13, wherein the set length of time allows the slip sensor to measure each portion of the polishing pad measured by the slip sensor during the CMP polishing.

15. 1. A chemical mechanical planarization (CMP) system comprising: a carrier configured to hold a substrate; a platen supporting the polishing pad; a slip sensor configured to generate a signal indicative of a characteristic of a surface of the polishing pad; receiving the signal from the slip sensor; obtaining a series of expected sensor values ​​over a set length of time and comparing the signal received from the slip sensor during CMP polishing to the series of expected sensor values; and a processor configured to detect a wafer slip that differs from the set of expected sensor values ​​by more than a threshold in response to the signal received from the slip sensor during the CMP polishing.

16. The system of claim 15 , wherein the slip sensor comprises an optical sensor configured to measure a reflectivity of the surface of the polishing pad.

17. The processor further comprises: The system of claim 15 , configured to recalibrate a steady-state value in real-time based on the signal received from the slip sensor during CMP polishing.

18. The processor further comprises:

16. The system of claim 15, configured to stop all movement of the CMP system components in response to detecting the wafer slip.

19. 16. The system of claim 15, wherein the set length of time allows the slip sensor to measure each portion of the polishing pad measured by the slip sensor during CMP polishing.

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