Method for processing semiconductor wafers using a double-sided grinding operation - Patent Application 20070122997

Abstract

A method for processing a semiconductor wafer includes placing the wafer on a carrier so that a first grinding wheel engages the front side of the wafer and a second grinding wheel engages the back side of the wafer. The method also includes performing a first grinding operation, where the first and second grinding wheels are rotated in opposite directions and the wafer is rotated in a first direction corresponding to the direction of rotation of the first grinding wheel, thereby removing a portion of the front and / or back side of the wafer. The method also includes performing a second grinding operation, where the first and second grinding wheels are rotated in opposite directions and the wafer is rotated in a second direction corresponding to the direction of rotation of the second grinding wheel, thereby removing another portion of the front and / or back side of the wafer.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims priority to U.S. Patent Application No. 18 / 160,071, filed January 26, 2023, the disclosure of which is incorporated by reference in its entirety.

[0002] The field relates generally to simultaneous double-sided grinding of semiconductor wafers, and more particularly to methods of processing semiconductor wafers using multiple double-sided grinding operations. [Background technology]

[0003] Semiconductor wafers (e.g., single crystal silicon wafers) are commonly used in the manufacture of integrated circuit chips with printed circuits. Precision circuitry requires that both sides of the wafer be extremely flat and parallel to each other so that the circuitry can be properly printed across the entire surface of the wafer. To achieve this, wafer treatment processes can be used to improve certain characteristics of the wafer (e.g., flatness and parallelism) after it is cut from an ingot (e.g., a single crystal silicon ingot grown using a Czochralski growth process or a float zone growth process).

[0004] Double-sided simultaneous grinding operates on both sides of a semiconductor wafer simultaneously. To perform the grinding operation on both sides of the wafer, a double-sided grinding apparatus generally includes a pair of hydrostatic pads and a pair of grinding wheels. The pads and wheels are oriented oppositely and are vertically mirror images of one or more wafers supported therebetween. The hydrostatic pads can create a fluid barrier by introducing a grinding fluid (e.g., water) between each pad and the wafer surface, thereby limiting or preventing the rigid pad from physically contacting the wafer during grinding. This barrier reduces damage to the wafer that can occur due to physical clamping and allows the wafer to move (rotate) tangentially relative to the pad surface with less friction. The grinding wheels rotate and engage the respective wafer surfaces, removing a portion of each wafer surface. The wafer also rotates between the grinding wheels and the hydrostatic pad. Wafer rotation can be enabled by a drive ring that engages a notch formed in the wafer's periphery.

[0005] This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and / or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. As such, it should be understood that these statements are to be read in this light, and not as admissions of prior art. Summary of the Invention

[0006] One aspect is a method for processing semiconductor wafers using a double-sided grinding apparatus including a first grinding wheel, a second grinding wheel, and a carrier for supporting the wafer between the first and second grinding wheels. The wafer has a front side and a back side. The method includes placing the wafer in the carrier so that the first grinding wheel engages the front side of the wafer and the second grinding wheel engages the back side of the wafer. The method also includes performing a first grinding operation with the double-sided grinding apparatus, where the first and second grinding wheels rotate in opposite directions and the wafer rotates in a first direction corresponding to the direction of rotation of the first grinding wheel, thereby removing a first portion of at least one of the front side and the back side of the wafer. The method also includes performing a second grinding operation with the double-sided grinding apparatus, where the first and second grinding wheels rotate in opposite directions and the wafer rotates in a second direction corresponding to the direction of rotation of the second grinding wheel, thereby removing a second portion of at least one of the front side and the back side of the wafer.

[0007] Another aspect is a method for processing semiconductor wafers using a double-sided grinding apparatus including a first grinding wheel, a second grinding wheel, and a carrier for supporting the wafer between the first and second grinding wheels. The wafer has a front side and a back side. The method includes placing the wafer in the carrier so that the first grinding wheel engages the front side of the wafer and the second grinding wheel engages the back side of the wafer. The method also includes performing a first grinding operation on the double-sided grinding apparatus, wherein the first and second grinding wheels rotate counter-rotatingly and the wafer is rotated in a wafer rotation direction that coincides with the rotation direction of one of the first and second grinding wheels, thereby removing a first portion of at least one of the front side and the back side of the wafer. The method also includes performing a second grinding operation on the double-sided grinding apparatus, wherein at least one processing parameter is adjusted relative to the first grinding operation, thereby removing a second portion of at least one of the front side and the back side of the wafer and improving at least one of in-plane displacement, bow, and nanotopology of the wafer.

[0008] Another aspect is a method for processing a plurality of semiconductor wafers using a double-sided grinding apparatus including a plurality of first grinding wheels, a plurality of second grinding wheels, each corresponding to one of the plurality of first grinding wheels, and a plurality of carriers for supporting each of the plurality of wafers between one of the plurality of first grinding wheels and the corresponding second grinding wheel during a grinding operation. Each wafer has a front side and a back side. The method includes, for each wafer, placing the wafer in a respective carrier such that the first grinding wheel engages the front side of the respective wafer and the corresponding second grinding wheel engages the back side of the respective wafer. The method also includes performing a first grinding operation on the double-sided grinding apparatus, wherein the first and corresponding second grinding wheels counter-rotate with respect to each other and each wafer rotates in a first direction corresponding to the direction of rotation of the first grinding wheel, thereby removing a first portion of at least one of the front side and back side of each wafer. The method also includes performing a second grinding operation on the double-sided grinding machine, wherein the first and corresponding second grinding wheels are rotated in counter-rotational directions relative to each other and each wafer is rotated in a second direction corresponding to the rotational direction of the second grinding wheel, thereby removing a second portion of at least one of the front and back sides of each wafer.

[0009] Various refinements of the above features exist in connection with various aspects of the disclosure. Additionally, additional features may be incorporated into these various aspects. These refinements and additional features may exist individually or in any combination. For example, various features described below in connection with one or more of the illustrated embodiments may be incorporated alone or in any combination into any of the above-described aspects of the disclosure. Again, the brief summary provided above is not intended to limit the claimed subject matter, but merely to familiarize the reader with certain aspects and contexts of the disclosure. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view of a pair of grinding wheels and a corresponding pair of hydrostatic pads of a double-sided grinding machine. FIG.

[0011] [Figure 2] 2 is a schematic front view of a grinding wheel and a corresponding hydrostatic pad of the double-sided grinding machine of FIG. 1.

[0012] [Figure 3] 2 is a schematic perspective view of a semiconductor wafer positioned between the grinding wheels shown in FIG. 1, with the hydrostatic pads omitted.

[0013] [Figure 4A] 1 is a schematic diagram of an example process flow for multiple double-sided grinding operations performed on a semiconductor wafer. [Figure 4B] 1 is a schematic diagram of an example process flow for multiple double-sided grinding operations performed on a semiconductor wafer.

[0014] [Figure 5] 4C is a plot comparing the in-plane displacement of a wafer resulting from a conventional double-sided grinding operation with the in-plane displacement of a wafer resulting from the exemplary process shown in FIGS. 4A and 4B.

[0015] [Figure 6] 4C is a plot comparing wafer bow resulting from a conventional double sided grinding operation with the process example shown in FIGS. 4A and 4B.

[0016] [Figure 7] 4C is a plot comparing the nanotopology of a wafer surface resulting from a conventional double-sided grinding operation with the nanotopology of a wafer surface resulting from the exemplary process shown in FIGS. 4A and 4B.

[0017] [Figure 8A] FIG. 10 is a schematic diagram of another example process flow for multiple double-sided grinding operations performed on a semiconductor wafer. [Figure 8B] FIG. 10 is a schematic diagram of another example process flow for multiple double-sided grinding operations performed on a semiconductor wafer. [Figure 8C]FIG. 10 is a schematic diagram of another example process flow for multiple double-sided grinding operations performed on a semiconductor wafer.

[0018] [Figure 9] 8A-8C are plots comparing the in-plane displacement of a wafer resulting from a conventional double-sided grinding operation with the process example shown in FIGS. 8A-8C.

[0019] [Figure 10] 8A-8C are plots comparing wafer warpage resulting from a conventional double-sided grinding operation with wafer warpage resulting from the exemplary process shown in FIGS. 8A-8C.

[0020] [Figure 11] 8A-8C are plots comparing the nanotopology of a wafer surface resulting from a conventional double-sided grinding operation with the nanotopology of a wafer surface resulting from the exemplary process illustrated in FIGS. 8A-8C.

[0021] Like reference numerals refer to like elements throughout the several views of the drawings. DETAILED DESCRIPTION OF THE INVENTION

[0022] Suitable "semiconductor wafers" (which may also be referred to as "silicon wafers" or "wafers") include monocrystalline silicon wafers, such as silicon wafers obtained from wafers sliced ​​from monocrystalline silicon ingots formed by the Czochralski or float-zone processes. Each semiconductor wafer includes a central axis, a front surface, and a back surface generally parallel to the front surface. The front and back surfaces are generally perpendicular to the central axis. A peripheral edge extends between the front and back surfaces. Wafers may be of any suitable diameter, including, for example, 200 millimeters (mm), 300 mm, 450 mm, or greater in diameter.

[0023] 1-3, a portion of a double-sided grinding apparatus is shown schematically and generally designated 100. Non-limiting examples of double-sided grinders suitable for use as double-sided grinding apparatus 100 include the Model DXSG320 and Model DXSG300A manufactured by Koyo Machine Industry Co., Ltd. The grinding apparatus 100 includes a pair of grinding wheels 102, 104 and a pair of hydrostatic pads 106, 108. During a grinding operation, a semiconductor wafer W is positioned between the grinding wheels 102, 104 and between the hydrostatic pads 106, 108. The grinding wheel 102 and the hydrostatic pad 106 are positioned on one side of the wafer W, and the grinding wheel 104 and the hydrostatic pad 108 are positioned on the opposite side of the wafer W. The semiconductor wafer W has two opposing, generally parallel surfaces 130, 132; one surface may be referred to as the front surface 130 of the wafer W and the other surface may be referred to as the back surface 132 of the wafer W. When the wafer W is placed therebetween, the front surface 130 faces the grinding wheel 102 and hydrostatic pad 106, and the back surface 132 faces the grinding wheel 104 and hydrostatic pad 108. In this manner, both surfaces 130, 132 of the wafer W are ground simultaneously during the grinding operation, thereby improving the flatness and parallelism of the surfaces 130, 132 of the wafer W prior to subsequent wafer processing steps (e.g., polishing and circuit printing).

[0024] As shown in FIG. 1 , the wafer W is preferably supported in a substantially vertical position within the grinding apparatus 100, such that the central axis 134 of the wafer W is substantially perpendicular to the vertical axis V. Alternatively, the wafer W may be supported in other positions within the grinding apparatus 100, such as a substantially horizontal position. In the example grinding apparatus 100, a single wafer W is positioned for grinding between the grinding wheels 102, 104 and the hydrostatic pads 106, 108. A single wafer W or multiple wafers W (i.e., two or more wafers W) may be positioned in the grinding apparatus 100 for grinding operations to be performed on each wafer. The grinding apparatus 100 may include multiple pairs of grinding wheels 102, 104 and multiple pairs of hydrostatic pads 106, 108, with each pair of grinding wheels 102, 104 and each pair of hydrostatic pads 106, 108 working on one of the multiple wafers W for a grinding operation.

[0025] Each of the grinding wheels 102, 104 includes a grinding surface 110, 112, respectively. Each of the grinding wheels 102, 104 is attached to the grinding apparatus 100 via a shaft 114, 116, respectively. The grinding wheels 102, 104 are substantially identical. The grinding wheels 102, 104 are oriented on the shafts 114, 116 so that the grinding surfaces 110, 112 face each other. Additionally, when a wafer is placed between the grinding wheels 102, 104, the grinding surface 110 faces the front surface 130 of the wafer W, and the grinding surface 112 faces the back surface 132 of the wafer W.

[0026] The grinding surfaces 110, 112 of the respective grinding wheels 102, 104 may include outwardly extending annular grinding rings 111, 113. Each grinding ring 111, 113 may be defined by an annular array of grinding teeth. As shown in FIGS. 1 and 2, the annular grinding rings 111, 113 extend circumferentially at or near the outer periphery of the respective grinding surfaces 110, 112. The grinding wheels 102, 104 may be cup-shaped such that the annular grinding rings 111, 113 define the peripheries of the grinding surfaces 110, 112, with the remainder of the respective grinding surfaces 110, 112 depending inwardly from the grinding rings 111, 113. The grinding rings 111, 113 may define portions of their respective grinding surfaces 110, 112 that engage the front and back surfaces 130, 132, respectively, of the wafer W to facilitate the grinding operation, with the remainder of the grinding surfaces 110, 112 not engaging the wafer W during the grinding operation. Alternatively, the grinding wheels 102, 104 may have any configuration that enables the grinding surfaces 110, 112, or portions thereof, to suitably engage the wafer W to facilitate the grinding operation. References to the grinding surfaces 110, 112 engaging the wafer W include examples in which at least a portion of the grinding surfaces 110, 112 (e.g., the grinding rings 111, 113) engage the wafer W.

[0027] The grinding wheels 102, 104 may be mounted or connected to a motor or actuator (not shown) via shafts 114, 116. The motor or actuator enables rotational and translational movement of the grinding wheels 102, 104 relative to a rotation axis 118. The translational movement of the grinding wheels 102, 104 enables the grinding surfaces 110, 112 to engage the front and back surfaces 130, 132, respectively, of the wafer W for the grinding operation. The rotational movement of the grinding wheels 102, 104 during the grinding operation removes portions of the front and back surfaces 130, 132 of the wafer W, thereby improving the flatness and parallelism of the surfaces 130, 132 of the wafer W.

[0028] As shown in Figures 2 and 3, the grinding wheels 102, 104 each include openings 115, 117 extending therethrough. The openings 115, 117 allow a grinding fluid (e.g., water) to be supplied between the grinding surfaces 110, 112 and the wafer W during the grinding operation. The grinding fluid (e.g., water) is supplied to the openings 115, 117 via a grinding fluid source 152 (shown in Figure 1) that is in fluid communication with the grinding wheels 102, 104. The grinding fluid flows through the openings 115, 117 and is sprayed onto the front and back surfaces 130, 132 of the wafer W. The grinding surfaces 110, 112 apply the grinding fluid against the front and back surfaces 130, 132 of the wafer W, removing material from the surfaces of the wafer W and resulting in flatter surfaces 130, 132. The flow rate of the grinding fluid supplied to the openings 115, 117 via the source 152 may be adjusted during the grinding operation to adjust the removal profile at the front surface 130 and back surface 132 of the wafer W. For example, the source 152 may include a pump that is selectively controlled to adjust the flow rate of the grinding fluid supplied to the grinding wheels 102, 104. The grinding fluid may be supplied to each of the openings 115, 117 independently, and the flow rate of the grinding fluid supplied to each of the openings 115, 117 may be independently controlled. Multiple grinding fluid sources 152 may be included in the apparatus 100 to independently supply the grinding fluid to the grinding wheels 102, 104. Alternatively, the grinding fluid may be supplied to the grinding wheels 102, 104 via the same source 152, with the same flow rate supplied to each grinding wheel 102, 104.

[0029] The hydrostatic pads 106, 108 are mounted to a hydrostatic support base (not shown) of the grinding apparatus 100. One or both of the hydrostatic pads 106, 108 may be attached to or connected to a respective hydrostatic support base and a motor or actuator (not shown) that enables translational movement of one or both of the hydrostatic pads 106 relative to the rotation axis 118. The hydrostatic pads 106, 108 are not configured to rotate, as the pads remain substantially stationary during the grinding operation. Each of the hydrostatic pads 106, 108 has a pad surface 120, 122, respectively. The hydrostatic pads 106 and 108 are substantially identical to one another, and the pad surfaces 120, 122 are substantially flat. The hydrostatic pads 106, 108 are oriented so that the pad surfaces 120, 122 face each other. Additionally, when the wafer is placed between the hydrostatic pressure pads 106, 108, the pad surface 120 faces the front surface 130 of the wafer W, and the pad surface 122 faces the back surface 132 of the wafer W.

[0030] As shown in FIG. 2, each hydrostatic pad 106, 108 is generally disk-shaped. Preferably, each hydrostatic pad has a diameter larger than the diameter of the semiconductor wafer W being ground. The hydrostatic pads 106, 108 each have a circular opening 124, 126 formed therein. The openings 124, 126 are formed near the outer periphery of each hydrostatic pad 106, 108, so that the hydrostatic pads 106, 108 have a crescent shape as shown in FIG. 2. The openings 124, 126 are sized and shaped to receive one of the grinding wheels 102, 104 therein. The grinding wheels 102, 104 are positioned within the respective openings 124, 126 and preferably extend beyond the periphery 140 of the wafer W. The grinding wheels 102, 104 are also rotatable relative to the hydrostatic pads 106, 108 during the grinding operation.

[0031] Still referring to FIG. 2 , each hydrostatic pad 106, 108 includes a pocket 128 formed in its respective pad surface 120, 122. Grinding fluid (e.g., water) is supplied to the pocket 128 from a grinding fluid source 152 in fluid communication with the pocket 128. The grinding fluid source 152 may be the same source 152 in fluid communication with the grinding wheels 102, 104, or a different grinding fluid source 152 may be included in the apparatus 100 for supplying grinding fluid to the hydrostatic pads 106, 108. The apparatus 100 may also include separate grinding fluid sources 152 for independently supplying grinding fluid to the grinding wheels 102, 104 and the hydrostatic pads 106, 108, respectively. The grinding fluid supplied to the pocket 128 may be the same grinding fluid as the grinding fluid supplied to the grinding wheels 102, 104, or it may be a different grinding fluid. The grinding fluid supplied to the hydrostatic pads 106, 108 is sprayed onto the front surface 130 and back surface 132 of the wafer W through the pockets 128. The grinding fluid supplied through the pockets 128 forms a fluid layer between the hydrostatic pads 106, 108 and the wafer W, and the wafer W is hydrostatically supported therebetween during the grinding operation in which the grinding surfaces 110, 112 act on the surfaces 130, 132 of the wafer W. The support state of the wafer W between the hydrostatic pads 106, 108 can be adjusted by controlling the flow rate of the grinding fluid supplied to the pockets 128.

[0032] Returning to FIG. 1 , a wafer W is positioned within the grinding apparatus 100 and supported by a wafer carrier (not shown) disposed between the grinding wheels 102, 104 and the hydrostatic pads 106, 108. The wafer W is rotated by a suitable mechanism during the grinding operation. For example, the wafer W is rotated by a drive ring 136. The drive ring 136 imparts rotational movement to the wafer W relative to the grinding wheels 102, 104 and the hydrostatic pads 106, 108. Detents or nibs 138 of the drive ring 136 generally engage the wafer W at notches N formed in the periphery 140 of the wafer W, imparting rotational movement to the wafer about a central axis 134. Simultaneously, the grinding wheels 102, 104 engage the front and back surfaces 130, 132, respectively, of the wafer W and rotate in counter-rotational directions (i.e., in opposite directions). One of the wheels 102, 104 rotates in the same direction as the wafer W, and the other wheel 102, 104 rotates in the opposite direction to the wafer W.

[0033] The grinding wheels 102, 104 are oriented such that the diametric axes 119a, 119b (shown in FIG. 3) of the grinding wheels 102, 104 extend substantially parallel to the respective front and back surfaces 130, 132 of the wafer W, and thus extend substantially parallel to the vertical axis V. In some grinding operations, one or both of the grinding wheels 102, 104 may be oriented or tilted at an oblique angle relative to the front and back surfaces 130, 132 of the wafer W, such that the diametric axes 119a and / or 119b extend at an oblique angle relative to the vertical axis V, as described below with reference to FIG. 8A. The orientation or "tilt" of the grinding wheels 102, 104 may be selected to control the removal profile of the respective surfaces 130, 132 of the wafer W during the grinding operation.

[0034] 1 , grinding apparatus 100 also includes a controller 142 that allows an operator to select and control processing parameters of grinding apparatus 100 during a grinding operation. For example, the operator may select the direction of rotation of wafer W, the rotational speed of wafer W, the rotational speed of one or both of grinding wheels 102, 104, the orientation or "tilt" of one or both of grinding wheels 102, 104, and / or the flow rate of grinding fluid supplied to grinding wheels 102, 104. Controller 142 is connected to and communicates with grinding wheels 102, 104 (e.g., via motors or actuators operably connected thereto), hydrostatic pads 106, 108 (e.g., via motors or actuators operably connected thereto), grinding fluid source 152 (e.g., via a grinding fluid pump of grinding fluid source 152), and drive ring 136.

[0035] Controller 142 may be any known computing device or computer system and includes one or more processors 144 and memory area 146. Processor 144 executes instructions stored in memory area 146. As used herein, the term "processor" refers to a central processing unit, microprocessor, microcontroller, reduced instruction set circuit (RISC), application specific integrated circuit (ASIC), logic circuit, and other circuit or processor capable of performing the functions described herein. The above is exemplary and is not intended to limit the definition and / or meaning of the term "processor." Additionally, one or more processors 144 may be present within a single computing device or within multiple computing devices operating in parallel.

[0036] Stored in memory area 146 are processor-executable instructions for, for example, receiving and processing input received from an operator (e.g., via user interface 148) and controlling processing parameters of grinding apparatus 100 based on the input received and processed from the operator. Memory area 146 may include, but is not limited to, any computer-operated hardware suitable for storing and / or retrieving processor-executable instructions and / or data. Memory area 146 may include random access memory (RAM), such as dynamic RAM (DRAM) or static RAM (SRAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), and nonvolatile RAM (NVRAM). Additionally, memory area 146 may include multiple storage units, such as hard disks or solid-state disks in a redundant array of inexpensive disks (RAID) configuration. Memory area 146 may also include a storage area network (SAN) and / or a network-attached storage (NAS) system. In some embodiments, memory area 146 may include memory integral with controller 142. For example, controller 142 may include one or more hard disk drives as memory area 146. Memory area 146 may also include memory that is external to controller 142 and that may be accessed by multiple computing devices. The above memory types are exemplary and thus do not limit the types of memory that may be used to store processor-executable instructions and / or data.

[0037] The controller 142 also includes a user input device 148, or user interface 148, for receiving input from an operator. The information may be one or more selected process parameters for the grinding operation. The input device 148 may include, for example, a keyboard, a pointing device, a mouse, a stylus, a touch-sensitive panel (e.g., a touchpad or touchscreen), a gyroscope, an accelerometer, a position detector, or an audio input device. A single component, such as a touchscreen, may function as both an output device (e.g., a media output component) for the controller 142 and the input device 148.

[0038] Controller 142 may also include a communication interface 150 that may be communicatively coupled to one or more remote devices. Communication interface 150 may include, for example, a wired or wireless network adapter or a wireless data transceiver for use with a cellular network (e.g., Global System for Mobile communications (GSM), 3G, 4G, or Bluetooth®) or other mobile data network (e.g., Worldwide Interoperability for Microwave Access (WIMAX)).

[0039] 1-3, during operation, a wafer W is placed in a wafer carrier between the grinding wheels 102, 104 and the hydrostatic pads 106, 108. The grinding apparatus 100 may be configured to grind multiple wafers W simultaneously and may include multiple pairs (e.g., two or more) of grinding wheels 102 and 104 and multiple pairs (e.g., two or more) of hydrostatic pads 106 and 108 corresponding to the pairs of grinding wheels 102, 104. Multiple wafers W may be placed in the grinding apparatus 100 for a grinding operation. Each wafer W is placed between a respective pair of grinding wheels 102, 104 and a corresponding pair of hydrostatic pads 106, 108.

[0040] The grinding wheels 102, 104 and / or hydrostatic pads 106, 108 may be in an initial or "idle" position when the wafer W is placed therebetween. In the idle position, the grinding wheels 102, 104 and / or hydrostatic pads 106, 108 may be positioned away from the wafer W. The grinding wheels 102, 104 and / or hydrostatic pads 106, 108 are then brought into grinding engagement with the wafer W by translational movement of the grinding wheels 102, 104 and / or hydrostatic pads 106, 108 toward the respective surfaces 130, 132 of the wafer W.

[0041] When the grinding wheels 102, 104 and hydrostatic pads 106, 108 engage the respective surfaces 130, 132 of the wafer W, the grinding wheels 102, 104 and hydrostatic pads 106, 108 suitably apply a clamping force to the wafer W. The clamping force applied by the grinding wheels 102, 104 may be independent of the clamping force applied by the hydrostatic pads 106, 108. In this manner, the grinding wheels 102, 104 and the hydrostatic pads 106, 108 may support the wafer W independently of one another. The center of clamping pressure of the grinding wheels 102, 104 against the wafer W is at the wheel axis of rotation 118, and the center of clamping pressure of the hydrostatic pads 106, 108 against the wafer W is near the central axis 134 of the wafer W. Preferably, the clamping pressure applied by the grinding wheels 102, 104 is maintained consistent with the clamping pressure applied by the hydrostatic pads 106, 108 during grinding so that the wafer W remains flat (i.e., not bent) and is ground uniformly by the grinding wheels 102, 104.

[0042] To perform the grinding operation, the grinding wheels 102, 104 engaging the front and back surfaces 130, 132 of the wafer W are rotated at a suitable rotational speed. The grinding wheels 102, 104 counter-rotate (i.e., rotate in opposite directions). Suitable rotational speeds for the grinding wheels 102, 104 include, for example, speeds between 3000 and 5400 rpm. The wafer W also rotates at a suitable wafer rotational speed during grinding. The wafer W rotates in the same direction as one of the grinding wheels 102, 104 and therefore in the opposite direction to the other of the grinding wheels 102, 104. Suitable wafer rotational speeds include, for example, speeds between 12 and 48 rpm. The front and back surfaces 130, 132 of the wafer W are covered by the grinding surfaces 110, 112 and pad surfaces 120, 122 so that the grinding operation occurs completely across the surfaces 130, 132. During grinding, a grinding fluid (e.g., water) is sprayed onto the front and back surfaces 130 and 132 of the wafer W through openings 115 and 117 in the grinding wheels 102 and 104. The grinding surfaces 110 and 112 apply the grinding fluid against the front and back surfaces 130 and 132 of the wafer W, removing material from the surfaces of the wafer W and resulting in flatter surfaces 130 and 132. The grinding fluid (e.g., water) is also supplied through pockets 128 in the hydrostatic pads 106 and 108. The grinding fluid supplied through the pockets 128 forms a fluid layer between the hydrostatic pads 106 and 108 and the wafer W, and the wafer W is hydrostatically supported therebetween during the grinding operation as the grinding surfaces 110 and 112 move against the surfaces 130 and 132 of the wafer W.

[0043] A grinding "recipe" design is established with the goal of generating a target removal profile for the sides 130, 132 of the wafer W and achieving desired wafer flatness characteristics (e.g., wafer shape, bow, and / or nanotopology) through the grinding operation. The grinding recipe determines various process parameters that are controlled during the double-side grinding operation. An operator may select the process parameters via the controller 142. For example, the operator may select grinding process parameters via the controller 142, such as the rotation direction of the wafer W, the rotation speed of the wafer W, the rotation speed of one or both of the grinding wheels 102, 104, the orientation or "tilt" of one or both of the grinding wheels 102, 104, and / or the flow rate of grinding fluid supplied to the grinding wheels 102 and / or 104.

[0044] In recent years, the rapid miniaturization of integrated circuit chips has led to increasingly stringent flatness characteristics for semiconductor wafers used in the manufacture of integrated circuit chips. This trend continues to impose stringent requirements related to acceptable wafer flatness parameters, such as backside ideal flatness / area (SBIR), global backside ideal flatness / area (GBIR), frontside least squares focal plane coverage (SFQR), and edge frontside least squares focal plane coverage (ESFQR). Typically, these wafer flatness parameters are determined after additional processing (e.g., polishing) is performed on the wafer surface. However, meeting these wafer flatness parameters requires meeting certain flatness characteristics (e.g., shape, warpage, and / or nanotopology) of double-sided ground wafers.

[0045] It has been found that conventional double-sided grinding operations involving only one grinding operation do not consistently achieve the required wafer characteristics. Large quantities of double-sided ground wafers may not have the wafer flatness characteristics necessary to meet current demands, resulting in significant yield loss. This yield loss can be exacerbated by the delay between the time a double-sided ground wafer with undesirable flatness characteristics (e.g., nanotopology features) is produced and the time the wafer's unsuitability for further processing is discovered. This is because wafer flatness metrics (e.g., nanotopology, bow, and / or shape) cannot be measured until the double-sided ground wafer is polished. At this stage, a significant amount of time may have passed since the wafer was double-sided processed, and before the problem is recognized and corrected, many more wafers may be double-sided ground, each with undesirable flatness characteristics, further increasing yield loss. Furthermore, substandard wafers may not be salvageable after the wafer is polished. As a result, double-sided ground wafers that are unsuitable for further processing to produce wafer substrates for device manufacturing (e.g., integrated circuit chip manufacturing) may need to be discarded if defects are discovered during subsequent processing (e.g., after polishing processes).

[0046] In an illustrative method, multiple (i.e., two or more) grinding operations are performed on a single wafer W (or multiple wafers W simultaneously) to achieve desired wafer flatness characteristics (e.g., wafer shape, bow, nanotopology). In a first grinding operation, first and second grinding wheels 102, 104 counter-rotate relative to each other, and the wafer W (or multiple wafers W) is rotated in a wafer rotation direction that matches the rotation direction of one of the grinding wheels 102, 104, to remove a first portion of at least one of the front surface 130 and back surface 132 of the wafer. In a second grinding operation, at least one process parameter is adjusted relative to the first grinding operation to remove a second portion of at least one of the front surface 130 and back surface 132 of the wafer W (or multiple wafers W) to improve wafer flatness characteristics of the wafer W (or multiple wafers W), such as in-plane displacement, bow, and / or nanotopology of the wafer W. For example, the direction of rotation of the wafer W, the rotational speed of the wafer W, the rotational speed of one or both of the grinding wheels 102, 104, the orientation or "tilt" of one or both of the grinding wheels 102, 104, and / or the flow rate of grinding fluid supplied to the grinding wheels 102 and / or 104 may be adjusted for the second grinding operation. Additional grinding operations (e.g., a third grinding operation, a fourth grinding operation, a fifth grinding operation, a sixth grinding operation) may be performed, and process parameters may be adjusted for each grinding operation. Any number of grinding operations may be performed, such as between 2 and 10, and at least one process parameter may be adjusted for each grinding operation.

[0047] 4A and 4B, an example process flow includes a first grinding operation, generally designated 200a in FIG. 4A, and a second grinding operation, generally designated 200b in FIG. 4B, performed on a wafer W using grinding apparatus 100. The process flow illustrated in FIG. 4A and 4B may be performed on multiple wafers W simultaneously, or on a single wafer W.

[0048] As shown in FIG. 4A, in the first grinding operation 200a, the wafer W rotates in a first direction that coincides with the rotational direction of the grinding wheel 104. In the second grinding operation 200b, shown in FIG. 4B, the wafer W rotates in a second direction that coincides with the rotational direction of the second grinding wheel 102. Although the wafer W rotates in a direction that coincides with one of the grinding wheels 102, 104 in each operation 200a, 200b, the rotational speed of the wafer W and the rotational speed of each of the grinding wheels 102, 104 may be different. For example, the wafer W may preferably rotate at a rotational speed between 12 and 48 rpm in both the first and second wafer directions. The grinding wheels 102, 104 may preferably rotate at a rotational speed between 3000 and 5400 rpm in each of the first and second grinding operations 200a, 200b. The process flow illustrated in FIGS. 4A and 4B is not limited to the specific order shown. For example, the second grinding operation 200b may be performed before the first grinding operation 200a. Additional grinding operations may be performed before, after, or as intermediate grinding operations between the first grinding operation 200a and the second grinding operation 200b.

[0049] In addition to changing the rotational direction of the wafer W, one or more other process parameters may be adjusted between the first grinding operation 200a and the second grinding operation 200b. For example, the rotational speed of the wafer W, the rotational speed of one or both of the grinding wheels 102, 104, the orientation or "tilt" of one or both of the grinding wheels 102, 104, and / or the flow rate of grinding fluid supplied to the grinding wheels 102 and / or 104 may be adjusted between the first grinding operation 200a and the second grinding operation 200b. In one example, the wafer W rotates at different speeds between the first grinding operation 200a and the second grinding operation 200b. For example, in the first grinding operation 200a, the wafer W rotates in a first direction at a first rotational speed between 12 and 24 rpm, and in the second grinding operation 200b, the wafer W rotates in a second direction at a second rotational speed between 24 and 36 rpm. In another example, at least one of the grinding wheels 102, 104 has a different orientation or "tilt" with respect to the wafer W between the first and second grinding operations 200a, 200b. For example, in the first grinding operation 200a, at least one of the grinding wheels 102, 104 may be positioned in a first orientation in which the diametric axis 119a and / or the diametric axis 119b are substantially parallel to the front and back surfaces 130, 132 of the wafer W and the vertical axis V, and in the second grinding operation 200b, at least one of the grinding wheels 102, 104 may be positioned in a second orientation in which the diametric axis 119a and / or the diametric axis 119b are at an oblique angle with respect to the front and back surfaces 130, 132 of the wafer W and the vertical axis V. In another example, grinding fluid may be supplied to the grinding wheels 102 and / or the grinding wheels 104 at different flow rates between the first and second grinding operations 200a, 200b. Any combination of the adjusted process parameters described above may be applied between the first and second grinding operations 200a, 200b.

[0050] Referring to FIGS. 5-7, the process flow shown in FIGS. 4A and 4B results in improved wafer flatness characteristics for double-sided ground wafers compared to double-sided grinding operations that include only one grinding operation. In particular, performing the first and second grinding operations shown in FIGS. 4A and 4B improves the in-plane displacement, bow, and nanotopology of the wafer W compared to performing only one grinding operation. Wafer flatness characteristics can be determined using, for example, a KLA-Tencor wafer inspection system using WaferSight2 or WaferSight2+ analysis hardware (Milpitas, CA). FIG. 5 shows that the in-plane displacement of the wafer is reduced when the first and second grinding operations 200a, 200b are performed. FIG. 6 shows that the bow of the wafer is reduced when the first and second grinding operations 200a, 200b are performed. FIG. 7 shows that the nanotopology of the wafer is improved when the first and second grinding operations 200a, 200b are performed.

[0051] 8A-8C, another exemplary process flow is shown in which a first grinding operation, generally designated 300a in FIG. 8A, a second grinding operation, generally designated 300b in FIG. 8B, and a third grinding operation, generally designated 300c in FIG. 8C, are performed on a wafer W using the grinding apparatus 100. The process flow shown in FIGS. 8A-8C may be performed on multiple wafers W simultaneously, or on a single wafer W. As shown in FIG. 8A, in the first grinding operation 300a, the wafer W rotates in a first direction that coincides with the rotational direction of the grinding wheel 104. Additionally, each of the grinding wheels 102, 104 is oriented such that its diameter axes 119a, 119b extend at an oblique angle relative to the front and back surfaces 130, 132 of the wafer W and to the vertical axis V. Thus, the grinding wheels 102, 104 rotate about respective rotation axes 118a, 118b that are offset from the central axis 134 of the wafer W. The grinding wheels 102, 104 may be oriented at the same angle or at different angles. In some examples, only one of the grinding wheels 102, 104 is oriented at an angle relative to the surfaces 130, 132 and the vertical axis V, while the other grinding wheel 102, 104 is oriented such that its respective diametric axis 119a or diametric axis 119b extends substantially parallel to the surfaces 130, 132 and the vertical axis V. The tilt angle of the grinding wheels 102, 104, measured as the angle between their respective diametric axes 119a, 119b and the vertical axis V, may be from about 0.000001° to about 0.0001°, or from about 0.00005° to about 0.0001°, such as from about 0.00001° to about 0.0001°. The tilt of the grinding wheels 102, 104 shown in FIG. 8A has been exaggerated for ease of illustration and description.

[0052] In the second grinding operation 300b shown in FIG. 8B , the wafer rotates in a second direction that coincides with the rotational direction of the second grinding wheel 102. Additionally, the grinding wheels 102, 104 are oriented substantially parallel to the front and back surfaces 130, 132 of the wafer W and the vertical axis V during the second grinding operation 300b. The rotational speed of the wafer W and / or the rotational speed of one or both of the grinding wheels 102, 104 may be adjusted between the first and second grinding operations 300a, 300b. For example, in the first grinding operation 300a, the wafer W may rotate at a speed between 12 and 24 rpm, and in the second grinding operation, the wafer W may rotate at a speed between 24 and 36 rpm. The grinding fluid may be supplied to the grinding wheel 102 and / or the grinding wheel 104 at different flow rates during the first and second grinding operations 300a, 300b. The grinding wheels 102, 104 may also rotate at a different speed during the second grinding operation 300b than during the first grinding operation 300a. Suitable rotational speeds of the grinding wheels 102, 104 for each of the first and second grinding operations 300a, 300b may be selected from speeds between 3000 and 5400 rpm.

[0053] In the third grinding operation 300c shown in FIG. 8C, the wafer rotates in a first direction, similar to the first grinding operation 300a (FIG. 8A). Additionally, the grinding wheels 102, 104 are oriented substantially parallel to the front and back surfaces 130, 132 of the wafer W and the vertical axis V, similar to the second grinding operation 300b (FIG. 8B). The rotational speed of the wafer W and / or the rotational speed of one or both of the grinding wheels 102, 104 may be adjusted for the third grinding operation 300c. For example, the wafer W may rotate at a speed between 12 and 24 rpm, similar to the first grinding operation 300a, or at a speed between 24 and 36 rpm, similar to the second grinding operation 300b. Grinding fluid may be supplied to grinding wheel 102 and / or grinding wheel 104 at a different flow rate during third grinding operation 300c than during first grinding operation 300a and / or second grinding operation 300b. Grinding wheels 102, 104 may also rotate at a different speed during third grinding operation 300c than during first grinding operation 300a and / or second grinding operation 300b. Suitable rotational speeds for each of grinding wheels 102, 104 for third grinding operation 300c may be selected from speeds between 3000 and 5400 rpm.

[0054] The above adjustment parameters for grinding operations 300a-300c are exemplary, and grinding process parameters may be adjusted in any alternative manner between grinding operations 300a-300c to achieve wafer flatness characteristics. The process flow illustrated in FIGS. 8A-8C is not limited to the specific order shown. For example, the third grinding operation 300c may be performed before the first grinding operation 300a and / or the second grinding operation 300b. The second grinding operation 300b may be performed before the first grinding operation 300a. The first grinding operation 300a may be performed after the second grinding operation 300b and / or the third grinding operation 300c. Additional grinding operations may be performed before, after, or as intermediate grinding operations between the first grinding operation 300a, the second grinding operation 300b, and the third grinding operation 300c.

[0055] Referring to FIGS. 9-11, the process flow shown in FIGS. 8A-8C results in improved wafer flatness characteristics for double-sided ground wafers compared to double-sided grinding operations that include only one grinding operation. In particular, performing the first, second, and third grinding operations shown in FIGS. 8A-8C improves the in-plane displacement, bow, and nanotopology of the wafer W compared to performing only one grinding operation. Wafer flatness characteristics can be determined using, for example, a KLA-Tencor wafer inspection system using WaferSight2 or WaferSight2+ analysis hardware (Milpitas, CA). FIG. 9 shows that performing grinding operations 300a-300c reduces the in-plane displacement of the wafer. FIG. 10 shows that performing grinding operations 300a-300c reduces wafer bow. FIG. 11 shows that performing grinding operations 300a-300c improves the nanotopology of the wafer. 9-11 further illustrate that wafer flatness characteristics can be improved between the second grinding operation 300b and the third grinding operation 300c. Thus, providing additional grinding operations facilitates optimizing the flatness characteristics of the wafer resulting from the double-sided grinding process.

[0056] Compared to conventional semiconductor wafer processing methods using double-sided grinding, the disclosed method has several advantages. By performing multiple (i.e., two or more) grinding operations on a semiconductor wafer, wafer flatness characteristics can be significantly improved. In particular, grinding process parameters can be adjusted and optimized between multiple grinding operations to achieve desired wafer flatness characteristics. This produces semiconductor wafers that can meet the stringent flatness requirements necessary for device manufacturing (e.g., integrated circuit chip manufacturing). As a result, production costs and yield losses associated with low-quality semiconductor wafers can be substantially reduced. Grinding process parameters can be adjusted to consistently produce semiconductor wafers with desired wafer flatness characteristics, further improving yield and reducing production costs associated with low-quality wafers.

[0057] As used herein, when used in conjunction with a range of dimensions, concentrations, temperatures, or other physical or chemical properties or characteristics, the terms "about," "substantially," "essentially," and "about" are meant to cover variations that may exist at the upper and / or lower limits of the property or range of properties, including, for example, variations due to rounding, measurement method, or other statistical variations.

[0058] When introducing elements of the disclosure or embodiments thereof, the articles "a," "an," "the," and "said" are intended to mean that there are one or more elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. The use of specific directional terms (e.g., "top," "bottom," "side," "below," "above," etc.) is for convenience of description and does not require a particular orientation of the items described.

[0059] Since various changes may be made in the above structures and methods without departing from the scope of the present disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.

[0060] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems, and performing any methods incorporated therein. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements that do not differ substantially from the literal language of the claims.

Claims

1. 1. A method for processing a semiconductor wafer using a double side grinding apparatus including a first grinding wheel, a second grinding wheel, and a carrier for supporting the wafer between the first grinding wheel and the second grinding wheel, the wafer having a front side and a back side, the method comprising: placing the wafer in the carrier such that the first grinding wheel engages the front side of the wafer and the second grinding wheel engages the back side of the wafer; performing a first grinding operation of the double side grinding machine, wherein the first grinding wheel and the second grinding wheel rotate in opposite directions and the wafer rotates in a first direction that coincides with the rotation direction of the first grinding wheel, thereby removing a first portion of at least one of the front side and the back side of the wafer; performing a second grinding operation of the double-side grinding machine, wherein the first grinding wheel and the second grinding wheel rotate in opposite directions and the wafer rotates in a second direction that coincides with the rotation direction of the second grinding wheel, thereby removing a second portion of at least one of the front and back surfaces of the wafer; A method comprising:

2. performing the second grinding operation includes rotating at least one of the first grinding wheel, the second grinding wheel, and the wafer at a second rotational speed that is different from a first rotational speed of at least one of the first grinding wheel, the second grinding wheel, and the wafer during the first grinding operation. The method of claim 1.

3. performing the second grinding operation includes rotating the wafer at a second rotational speed that is different from the first rotational speed of the wafer during the first grinding operation. The method of claim 2.

4. the second rotation speed of the wafer is greater than the first rotation speed of the wafer; The method of claim 3.

5. performing the second grinding operation includes positioning at least one of the first grinding wheel and the second grinding wheel at a second orientation relative to the wafer that is different from a first orientation of at least one of the first grinding wheel and the second grinding wheel during the first grinding operation. The method of claim 1.

6. In one of the first orientation and the second orientation, the at least one of the first grinding wheel and the second grinding wheel is oriented at an oblique angle to the wafer, and in the other of the first orientation and the second orientation, the at least one of the first grinding wheel and the second grinding wheel is oriented substantially parallel to the wafer. The method of claim 5.

7. performing the second grinding operation includes supplying grinding fluid to the double-side grinding machine at a second flow rate different from a first flow rate at which the grinding fluid is supplied during the first grinding operation; The method of claim 1.

8. performing a third grinding operation, wherein the first grinding wheel and the second grinding wheel rotate in counter-rotations and the wafer rotates in the first direction, thereby removing a third portion of at least one of the front and back surfaces of the wafer. The method of claim 1.

9. performing the second grinding operation further includes adjusting at least one process parameter for the first grinding operation selected from the group consisting of a rotational speed of the wafer, a rotational speed of the first grinding wheel, a rotational speed of the second grinding wheel, an orientation of the first grinding wheel relative to the wafer, an orientation of the second grinding wheel relative to the wafer, and a flow rate of a grinding fluid supplied to the double-sided grinding apparatus; The method of claim 1.

10. performing the second grinding operation to remove the second portion of at least one of the front and back surfaces of the wafer improves at least one of in-plane displacement, bow, and nanotopology of the wafer; The method of claim 1.

11. 1. A method for processing a semiconductor wafer using a double side grinding apparatus including a first grinding wheel, a second grinding wheel, and a carrier for supporting the wafer between the first grinding wheel and the second grinding wheel, the wafer having a front side and a back side, the method comprising: placing the wafer in the carrier such that the first grinding wheel engages the front side of the wafer and the second grinding wheel engages the back side of the wafer; performing a first grinding operation of the double side grinding machine, wherein the first grinding wheel and the second grinding wheel rotate in opposite directions and the wafer rotates in a wafer rotation direction that coincides with the rotation direction of one of the first grinding wheel and the second grinding wheel, thereby removing a first portion of at least one of the front side and the back side of the wafer; performing a second grinding operation of the double side grinding machine, adjusting at least one process parameter with respect to the first grinding operation, thereby removing a second portion of at least one of the front side and the back side of the wafer to improve at least one of in-plane displacement, bow, and nanotopology of the wafer. A method comprising:

12. the at least one processing parameter is selected from the group consisting of: a wafer rotation direction, a wafer rotation speed, a first grinding wheel rotation speed, a second grinding wheel rotation speed, an orientation of the first grinding wheel relative to the wafer, an orientation of the second grinding wheel relative to the wafer, and a flow rate of grinding fluid supplied to the double side grinding apparatus. The method of claim 11.

13. performing a third grinding operation of the double side grinding machine, wherein at least one processing parameter is adjusted for the first grinding operation or the second grinding operation, thereby removing a third portion of at least one of the front side and the back side of the wafer and improving at least one of in-plane displacement, bow, and nanotopology of the wafer. The method of claim 11.

14. performing the second grinding operation includes rotating the wafer in a reverse wafer direction that corresponds to a rotational direction of the other of the first grinding wheel and the second grinding wheel. The method of claim 11.

15. the at least one processing parameter is a rotational speed of the wafer, and performing the second grinding operation includes rotating the wafer at a second rotational speed greater than the first rotational speed of the wafer during the first grinding operation. The method of claim 11.

16. the at least one processing parameter includes at least one of an orientation of the first grinding wheel relative to the wafer and an orientation of the second grinding wheel relative to the wafer, and performing the second grinding operation includes positioning at least one of the first grinding wheel and the second grinding wheel in a second orientation relative to the wafer that is different from a first orientation of at least one of the first grinding wheel and the second grinding wheel during the first grinding operation. The method of claim 11.

17. the at least one processing parameter includes a flow rate of a grinding fluid supplied to the double-sided grinding machine, and performing the second grinding operation includes supplying the grinding fluid to the double-sided grinding machine at a second flow rate that is different from a first flow rate at which the grinding fluid is supplied during the first grinding operation. The method of claim 11.

18. 1. A method for processing a plurality of semiconductor wafers using a double side grinding apparatus including a plurality of first grinding wheels, a plurality of second grinding wheels each corresponding to one of the plurality of first grinding wheels, and a plurality of carriers for respectively supporting each of a plurality of wafers between one of the plurality of first grinding wheels and the corresponding second grinding wheel during a grinding operation, each wafer having a front side and a back side, the method for each wafer comprising: placing the wafers on the respective carriers such that the first grinding wheel engages the front side of the respective wafer and a corresponding second grinding wheel engages the back side of the respective wafer; performing a first grinding operation of the double side grinding machine, wherein the first grinding wheel and the corresponding second grinding wheel rotate in counter-rotations with respect to each other and the respective wafers rotate in a wafer rotation direction that coincides with the rotation direction of the first grinding wheel, thereby removing a first portion of at least one of the front side and the back side of each of the wafers; performing a second grinding operation of the front double-sided grinding machine, wherein the first grinding wheel and the corresponding second grinding wheel rotate in opposite directions and the respective wafers rotate in a second direction that coincides with the rotation direction of the second grinding wheel, thereby removing a second portion of at least one of the front and back surfaces of the respective wafers; A method comprising:

19. performing a third grinding operation for each wafer, wherein at least one processing parameter selected from the group consisting of a rotational speed of the respective wafer, a rotational speed of the first grinding wheel, a rotational speed of the second grinding wheel, an orientation of the first grinding wheel relative to the respective wafer, an orientation of the second grinding wheel relative to the respective wafer, and a flow rate of grinding fluid supplied to the double sided grinding apparatus is adjusted for at least one of the first grinding operation and the second grinding operation.

20. The method of claim 18.

20. performing the second grinding operation to remove the second portion of at least one of the front surface and the back surface of the respective wafer improves at least one of in-plane displacement, bow, and nanotopology of the respective wafer; 20. The method of claim 18.

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