WORKPIECE EDGE GRINDING MACHINE AND METHOD

Abstract

A grinding machine for edge grinding the peripheral wafer edge of a semiconductor wafer is configured for conducting an in situ dressing operation to refurbish or dress the peripheral grinding rim surface of a grinding wheel. The grinding machine includes at least one wafer-holding chuck, a grinding wheel, and a dressing tool that are linearly spaced apart and can be respectively moved relative to each other to selectively conduct the grinding and dressing operations. In one form plural grinding stations are disclosed.

Description

BACKGROUND

Work pieces such as semiconductor wafers are thin slices of semiconductor material from a single crystal of silicon carbide (SiC) and are used for the fabrication of microelectronic devices through a series of deposition and etch steps that form the desired circuitry and components. From a processing perspective, SiC has a hardness value second only to diamond among naturally occurring materials. One of the processes that must be performed on as-cut wafers after they are sliced from a SiC ingot or boule is edge grinding or beveling. The thin, flat wafers may have an outer peripheral wafer edge that corresponds to the wafer thickness and typically has a circular or partially circular outline. Two primary purposes for edge grinding are: 1) reduce the wafer diameter to the target specified diameter within a tight tolerance (typically within +/−0.25 mm) and 2) contour the edge to a smoother profile to reduce the risk of chipping during subsequent process operations (both wafer and device fabrication).

Edge grinding may be accomplished at a grinding station on an edge grinding machine where the thin, flat wafer is supported on a rotatable wafer-holding plate or chuck. A rotational grinding wheel disposed in an essentially co-planar relation with the wafer is engaged into contact with the wafer's peripheral edge. The grinding wheel may have a peripheral grinding rim surface that is contoured to produce the desired shape and finish on the peripheral wafer edge during an abrasive grinding operation. The grinding wheel may contain abrasives that are made of a material that is physically harder than the silicon carbide of the wafer, such as small diamonds or particles that may be bonded in a ceramic or polymer matrix. The peripheral grinding rim surface may need to be periodically re-machined, or dressed, to expose fresh abrasives or refurbish the desired working surface which may become dulled during the grinding operation on a number of wafers.

SUMMARY OF THE DISCLOSURE

The arrangement of the present disclosure enables the edge grinding wheel to be dressed or machined in situ without removing it from the edge grinding machine. This keeps the rim surface profile of the grinding wheel in a more optimal state and extends the number of wafers that can be ground between more involved maintenance interruptions. When implemented, this on-board dressing station reduces average downtime and potentially improves average performance over the life of each grinding wheel.

Typically during operation of a wafer edge grinder, the abrasive elements (generally small diamonds in a bond matrix) that comprise a rotating grinding wheel rim surface are brought into contact with the outer perimeter or edge of a wafer rotating upon the wafer-carrying chuck. This contact grinds material off of the wafer edge but also causes wear of the grinding wheel rim surface that gradually becomes dull over time.

In an aspect of the disclosure, the grinding machine can incorporate an integral dressing tool having a dressing face with a complementary forming shape to the grinding wheel peripheral rim surface revitalize the dulled grinding rim surface and expose fresh abrasive.

The dressing tool is mounted on a motor-driven spindle on a linear translation path which allows the dressing tool dressing face to be moved into contact with the grinding wheel working rim surface or retracted back out of the way. The dressing tool can be used periodically after a programmable number of wafer grinds.

The in-situ dressing tool can be connected to a rotating dressing spindle assembly that can be driven by a variable speed servo motor with controlled speeds from a few revolutions per minute (“rpm”) to about 100 rpm. The dressing tool or wheel is mounted to be essentially co-planar with the rotational plane of the outer peripheral grinding rim surface of the grinding wheel. The dressing tool and the grinding wheel can be rotated relative to one another and moved relative to one another to make controlled contact at the peripheral grinding rim surface during a dressing operation or to be retracted a distance from the grinding wheel during a grinding operation conducted on a wafer edge.

An advantage of the arrangement of the disclosure is the inclusion of an in-situ dressing station for dressing the peripheral grinding rim surface of a grinding wheel in a wafer edge grinding machine. This enables periodic in-situ dressing of the grinding wheel grinding rim surface without requiring maintenance downtime to remove the grinding wheel from the system for dressing elsewhere. It also eliminates time to set up and calibrate a replacement grinding wheel which is a recognized difficult and time consuming task. This reduces downtime and increases the average productivity while also improving consistency of the wafer edge beveling performance over the life of the grinding wheel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the exterior enclosure of an edge grinding or beveling machine for grinding the peripheral edges of thin, flat semiconductor wafers configured with an automated computer numeric control system.

FIG. 2 is a perspective view of the edge grinding or beveling machine of FIG. 1 without the exterior housing panels and illustrating a multi-axis Cartesian robot within an articulating arm for transporting wafers with respect to a plurality of edge grinding modules.

FIG. 3 is a top view of the machine of FIG. 2 showing the plurality of edge grinding modules each with a wafer-holding plate or chuck and a grinding wheel in essentially co-planar relation.

FIG. 4 is a top view of the machine of FIGS. 1 and 2 showing a grinding wheel dressing station or module with the dressing tool in a co-planar relation to the wafer-holding chuck and the grinding wheel of a grinding station module.

FIG. 5 is a cut-away view of the grinding module showing the wafer-holding chuck spindle assembly, the grinding wheel spindle assembly, and the dressing tool spindle assembly disposed in spaced relation along a common vertical plane.

FIG. 6 is a rear perspective view of the dressing module with the dressing tool that is configured for linear movement.

FIG. 7 is a front perspective view of the dressing station of FIG. 6.

FIG. 8 is a perspective view of a grinding wheel having a plurality of annular grooves or tracks disposed in the peripheral grinding rim surface.

FIG. 9 is perspective view of a dressing tool having a peripheral dressing face configured for simultaneously dressing the plurality of annular grooves or tracks on the grinding wheel of FIG. 8.

FIG. 10 is a detailed sectional view of the annular shaping rings radial protruding from the peripheral dressing face of the dressing tool.

FIG. 11 is a perspective view of another embodiment of a dressing tool for individually dressing the plurality of annular grooves or tracks on the peripheral grinding rim surface of the grinding wheel of FIG. 8.

FIG. 12 is a fragmentary sectional view of the dressing tool of FIG. 11.

FIG. 13 is a flow diagram representing an automated method for conducting an edge grinding process and a dressing process within the edge grinding or beveling machine of FIG. 1.

DETAILED DESCRIPTION

Now referring to the drawings, where whenever possible like reference numbers will refer to like elements, there is illustrated in FIG. 1 an edge grinding or beveling machine 100 for the automated grinding of a work piece such as a semiconductor wafer 102 used to fabricate microelectronic parts. The thin, flat semiconductor wafers 102 are macroscopically planar and may be sliced from a larger cylindrical boule or ingot of a crystalline semiconductor material such as silicon carbide (SiC). The wafer 102 can be generally circular in shape with opposing first and second planar wafer surfaces 104, 106 and a peripheral wafer edge 108 that outlines the work piece. To facilitate locating and orientation of the wafer 102 during processing and fabrication, a flat 109 or segment may be cut into the otherwise circular peripheral wafer edge 108.

To prepare a sliced wafer 102 for processing in the grinding machine 100, the wafer 102 may be subjected to initial grinding and/or polishing operations elsewhere that machines the planar wafer surfaces 104, 106. Machine 100 focuses on the wafer peripheral edge 108 to have a desired surface finish or profile with tightly controlled dimensional variations. The grinding machine 100 can have an exterior housing 110 including a plurality of removable housing panels and/or doors that cover the internal operations of the grinding machine 100. The grinding machine 100 can receive a plurality of wafers 102, which may be accommodated in a wafer cassette 112, at a wafer loading station 114. The wafers 102 are transported and operatively processed through the grinding machine 100 and the ground wafers 102 can be removed at a wafer unloading station 116. The machining operations of the grinding machine 100 can be numerically controlled by a programmable logic controller (PLC). The grinding machine 100 can include a human-machine interface (HMI) 118 to interact with a human operator. To interface with and receive electrical power lines, data communication cables conducing digital electronic signals, and processing fluid conduits for coolants, pressurized air and pneumatic vacuum, etc., the grinding machine 100 can have a control cabinet 119.

Referring to FIG. 2, the grinding machine 100 can be configured for modular operation and can include a plurality of edge grinding modules 120 or stations that are adjacently aligned between the wafer loading station 114 and the wafer unloading station 116.

The edge grinding modules 120 can be of an identical design and can be configured to conduct a profile or edge grinding operation on the peripheral wafer edge 108 of the wafer 102. Profile or edge grinding produces wafers 102 having a desired diameter and contoured profile of the peripheral wafer edge 108 to facilitate subsequent handling and to avoid chipping of the wafer 102. In the illustrated embodiment, three edge grinding modules 120 are included in the grinding machine 100, but in other embodiments, a fewer or greater number of modules 120 may be included. The exemplary machine 100 illustrated here, with three modules or stations 120, provides a fifty percent (50%) increase in production capacity over other commercially known edge grinding equipment.

To transport the wafer 102 between the wafer loading and unloading stations 114, 116 and the edge grinding modules 120, the grinding machine 100 of the illustrated embodiment can include a Cartesian robot 122 that includes an articulated positioning arm 134 spatially movable with respect to the edge grinding modules 120. For referential purposes, the positioning arm of the Cartesian robot 122 is movable with respect to the grinding machine 100 in multiple Cartesian axes that include a horizontal linear (X) axis 124, a horizontal lateral (Y) axis 126, and a vertical (Z) axis 128. The Cartesian robot 122 can be driven laterally above the modules 120 by a suitably arranged electric motor 130 and associated linear actuator such as geared track 132 that allow for tight tolerance control and high precision positioning.

To move a wafer 102 with respect to the grinding machine 100, the positioning arm of the Cartesian robot 122 can have an end effector with vacuum securement capability. The arm 134 is moveable in the multiple axes between the wafer loading and unloading stations 114, 116 and the edge grinding modules 120. The end effector of arm 134 can secure to, or release from, an individual wafer 102 using negative vacuum and/or pressurized air.

Other internal components of the grinding machine 100 can include an alignment station 136 (seen in FIG. 2) that can utilize the flat 109 on the peripheral wafer edge 108 to orientate and align the wafer 102 for handling and processing through the machine and a cleaning station 138 (see FIG. 2) where the ground wafer 102 can be cleaned and blow dried after the grinding operation.

Referring to FIGS. 3 and 4, the edge grinding modules 120 can each include a housing or a module enclosure 140 that may be a hollow, rectangular box-like structure inside of which the edge grinding operation occurs. The module enclosure 140 can be formed in any suitable shape to define an internal modular chamber 142 within which can occur the edge grinding operation conducted on the wafer 102. To access the internal modular chamber 142 and allow for the introduction and removal of wafers 102, a retractable door 144 can be constructed into an upper panel of each module enclosure 140.

To perform the edge grinding operation, the edge grinding module 120 can include a wafer-holding chuck 146 disposed inside and rotatable within the module enclosure 140. That wafer-holding chuck 146 can be a flat, planar structure of, for example, porous ceramic and can have a circular shape and diameter that may be correspondingly smaller than the diameter of the wafer 102. The flat wafer-holding chuck 146 has a vacuum securement capability to maintain a wafer 150 in place for edge processing. The flat wafer-holding chuck 146 can be situated in a plane defined by the linear axis 124 and the lateral axis 126. The circular shape of the wafer-holding chuck 146 can delineate a circular peripheral chuck edge 148 that establishes the circular outline of the chuck. During the edge grinding operation, the wafer 102 can be placed on the planer upper surface of the wafer-holding chuck 146 and securely held thereto by a vacuum or suction force.

To contact and grind the peripheral wafer edge 108 of a wafer 102 supported on the wafer-holding chuck 146, a grinding wheel 150 can be located inside the module enclosure 140 adjacent to and generally co-planar with the wafer-holding chuck 146. The grinding wheel 150 can be spatially located adjacent to and aligned with the wafer-holding chuck 146 with respect to the linear axis 124 of the grinding machine 100. The grinding wheel 150 may have a flat, circular shape similar to the wafer-holding chuck 146 and can be configured to rotate with respect to the rotatable wafer-holding chuck 146 in a plane defined by the linear axis 124 and the lateral axis 126. The imaginary horizontal plane 164 within which the grinding and dressing operations of the machine 100 occur is illustrated in FIG. 5. The wafer-holding chuck 146 and the grinding wheel 150 may rotate in complementary or opposing directions and at varying speeds.

Best seen in FIG. 8, the grinding wheel 150 can have a peripheral grinding rim surface 152 that defines a grinding rim profile to provide a desired wafer edge contour. During the edge grinding operation, the wafer holding chuck 146 is linearly moved with respect to the linear axis 124 toward the wafer-holding chuck 146 so the peripheral grinding rim surface 152 tangentially contacts the peripheral wafer edge 108 of the wafer 102.

The relative rotation of the wafer-holding chuck 146 and the grinding wheel 150 causes the abrasive peripheral grinding rim surface 152 to frictionally grind and remove the semiconductor material of the wafer 102 and form the desired shape of the peripheral wafer edge 108. To operatively grind the flat 109 of the peripheral wafer edge 108, in the illustrated embodiment, the wafer-holding chuck 146 can be moved in the lateral axis 126 in a lateral or side-to-side motion with the rotation of the wafer-holding chuck stopped at a defined position. To control temperature of the edge grinding process and flush away the semiconductor material removed from the wafer 102, the edge grinding modules 120 can include one or more fluid nozzles attached to adjustable hoses that can deliver cleaning and/or coolant fluid into the internal modular chamber 142.

The peripheral grinding rim surface 152 of grinding wheel 150 can be made of a material that may be physically characterized as relatively harder and more abrasive than the semiconductor material of the wafer 102. For example, the grinding wheel 150 can be constructed to include at its rim surface a plurality of synthetic diamond bits that are bonded together in a bond matrix such as a ceramic that is cast or molded to the desired shape and dimension. However, over the course of several grinding operations on a corresponding number of wafers 102, the profile defined on the peripheral grinding rim surface 152 may be become dulled or worn.

Therefore, to periodically refurbish the peripheral grinding rim surface 152, each edge grinding module 120 can be configured with an integral dressing station 154 that, as shown in FIGS. 3 and 4, and can include a dressing tool 156. As best seen in FIG. 5, the dressing tool 156 can be located inside a dressing station enclosure 158 that defines a dressing station chamber 160. The dressing station enclosure 158 can be constructed similarly to the module enclosure 140 but can be comparatively smaller in shape and dimension. The dressing station enclosure 158 can be attached to the module enclosure 140 in alignment with the linear axis 124 such that the dressing tool 156 is located adjacent to grinding wheel 150 linearly opposite of the wafer-holding chuck 146.

The dressing tool 156 can be situated essentially co-planar with the grinding wheel 150 and the wafer-holding chuck 146 in the imaginary horizontal plane 164 defined by the linear and lateral axes 124, 126 and can be rotatable within that plane. In the illustrated embodiment, the dressing tool 156 is aligned in a common imaginary vertical plane along the linear axis 124 with respect to the wafer-holding chuck 146 and the grinding wheel 150, however, in other embodiments, the dressing tool 156 may be located laterally to the side of the grinding wheel 150 with respect to the lateral axis 126, or may be located at another orientation with respect to the wafer-holding chuck 146 and the grinding wheel 150.

During a dressing operation, conducted when edge grinding within a module 120) is paused, the dressing tool 156 can be linearly moved along the linear axis 124 into tangential contact with the peripheral grinding rim surface 152 of the grinding wheel 150. In an embodiment, the dressing tool 156 can be circular in shape and can have dressing face with a diameter dimensionally smaller than the peripheral grinding rim surface 152 of the grinding wheel 150. As seen in FIG. 9, the dressing tool 156 can define a peripheral dressing face 162 that may have a profile or contour that is complementary to the desired profile of the peripheral grinding rim surface 152. The peripheral dressing face 162 of dressing tool 156 can be a material that is relatively harder and more abrasive than the material of the grinding wheel 150 such that relative rotation of the grinding wheel and the dressing tool will grind and remove material at the peripheral grinding rim surface 152. By way of example, the material of the peripheral dressing face 162 of dressing tool 156 can compromise solid synthetic diamonds or sharp diamond bits bonded together in a bonding matrix.

In another possible embodiment, the dressing tool 156 can compromise a polyhedron block with the peripheral dressing face 162 formed on one of the planar faces of the block. The peripheral dressing face 162 can present a profile or contour that is complementary to the desired profile of the peripheral grinding rim surface 152. The dressing tool 156 in the embodiment of a polyhedron block can be fixed in relation to the rotatable grinding wheel 150 which, when rotated, results in grinding and removal of the semiconductor material at the peripheral grinding rim surface 152.

In yet another possible embodiment, in addition to a dressing tool 156, the dressing station 154 can be configured to also incorporate a profiling tool designed to physically change the shape of the grinding wheel 150 by removing a relatively greater amount of material from the peripheral grinding rim surface 152. The profiling tool can be made of a significantly harder material than the grinding wheel 150 or the dressing tool 156 to reshape the peripheral grinding rim surface 152. In operation, the profiling tool can be physically configured and operate similar to the dressing tool 156.

In the embodiment illustrated in FIGS. 1 to 4, to enable relative rotational, vertical and linear movement of the wafer-holding chuck 146, the grinding wheel 150, and the dressing tool 156, of each edge grinding station 120 can include an arrangement of drive spindles and electrically powered motors. For example, referring to FIG. 5, each of the wafer-holding chuck 146, and the dressing tool 156 are mounted essentially coplanar with the horizontal rotational plane of grinding wheel 150. They additionally can translate within the common rotational plane referred to herein as the operational plane 164 and in the illustrated embodiment, the wafer holding chuck 146 of each module 120 be made to move vertically with respect to the operational plane. The operational plane 164 is oriented parallel with respect to the linear and lateral axes 124, 126 and is perpendicular to the vertical axis 128 and may spatially define the location of the grinding and dressing operations of the edge grinding module 120.

The wafer-holding chuck 146 may be attached within a wafer-holding chuck spindle assembly 170 that is aligned in the vertical axis 128 and configured to enable the wafer-holding chuck to rotate within the operational plane 164 defined by the linear and lateral axes 124, 126. The wafer-holding chuck spindle assembly 170 can define a first rotational axis 172 that is aligned with the vertical axis 128. The wafer-holding chuck spindle assembly 170 can include an elongated spindle shaft 174 that may be cylindrical in shape and is rotationally supported in a spindle housing 176. To enable the spindle shaft 174 to rotate with respect to the spindle housing 176, the structures may be operatively supported upon one or more ball bearing assemblies. To cause rotation of the spindle shaft 174 and the wafer-holding chuck 146 connected thereto, the wafer-holding chuck spindle assembly 170 is operatively associated with an electric variable speed wafer motor 178.

To selectively adjust and change the position of the wafer-holding chuck 146 with respect to the grinding wheel 150, a plurality of servo motors are operatively associated with the wafer-holding chuck spindle assembly 170 via ball screws or roller screws (linear actuators). For example, in an embodiment, to move the coplanar wafer-holding chuck 146 and the grinding wheel 150 linearly together or apart within the operational plane 164, a linear wafer motor 180 can be arranged within the edge grinding module 120 to translate the wafer-holding chuck spindle assembly 170 along the linear axis 124. The linear wafer motor 180 may be embodied as a servo motor that can be selectively rotated in a series of discrete angular steps enabling precise linear positioning of the wafer-holding chuck 146 with respect to the grinding wheel 150. In another embodiment, the linear motor 180 may move the grinding wheel 150 with respect to the wafer-holding chuck 146. Similarly, to vertically position the wafer-holding chuck 146 with respect to the grinding wheel 150 along the vertical axis 128, the edge grinding module 120 can include a vertical wafer motor 182, which may also be a servo motor, operatively connected with and enabling vertical motion of the wafer-holding chuck spindle assembly 170. In an embodiment, the edge grinding module 120 may additionally include a lateral wafer motor 184 arranged to laterally move the wafer-holding chuck spindle assembly 170 in the lateral axis 126 to, for example, grind the flat 109 on the peripheral wafer edge 108 of the wafers 102.

In the illustrated embodiment, the grinding wheel 150 may be fixed in location with respect to the linear, lateral, and vertical axes 124, 126, 128; however, in other contemplated embodiments, the grinding wheel may also be configured for movable translation and the wafer-holding chuck spindle assembly 170 may be stationary.

To enable rotational motion of the grinding wheel 150 within the operational plane 164 defined by the linear and lateral axes 124, 126, the grinding wheel 150 may be operatively coupled within a grinding wheel spindle assembly 190 located in the edge grinding module 120. The grinding wheel spindle assembly 190 defines a second rotational axis 192 that can be vertically positioned and co-axially arranged with respect to the vertical axis 128. The grinding wheel spindle assembly 190 can include a spindle shaft 194 that is rotatably supported in a spindle housing 196 by one or more ball bearing assemblies. To cause rotation of the grinding wheel 150, the grinding wheel spindle assembly 190 can be operatively associated with an electric variable speed grinding motor 198 through pulleys 197 and drive belt 199. In the disclosed embodiment, the grinding wheel spindle assembly 190 may be fixed and stationary within the edge grinding module 120. This embodiment is exemplary and not limiting: an embodiment with vertical movement of the grinding wheel spindle assembly 190 is also contemplated.

In the illustrated embodiment, the grinding wheel 150 can be releasably connected to the grinding wheel spindle assembly 190 for periodic removal and refurbishing. For example, as seen in FIG. 8, the grinding wheel 150 can be annular in shape and can include a central wheel hub 200 that is concentrically positioned with respect to the peripheral grinding rim surface 152. To connect and disconnect with the grinding wheel spindle assembly 190, the distal end of the spindle shaft 194 can include a grinding wheel coupling chuck 202. (Seen in FIG. 5) The grinding wheel coupling chuck 202 can be mechanically configured to extend into and clamp with the radially symmetrical central wheel hub 200.

As indicated above, to reduce periodic replacement of the grinding wheel 150, the present embodiment of the edge grinding module 120 includes the dressing station 154 with the dressing tool 156 accommodated therein. In an embodiment, the dressing tool 156 may be circular and rotatable with respect to the grinding wheel 150, although in other embodiments, a dressing tool fixed against rotation with respect to the grinding wheel 150 may be used.

In the illustrated embodiment, to rotate the dressing tool 156, the dressing tool can be releasably coupled to a dressing tool spindle assembly 210 that is vertically arranged in the edge grinding module 120. The dressing tool spindle assembly 210 thus defines a third rotational axis 212 aligned with the vertical axis 128 and aligned in the same imaginary vertical plane with the first and second rotational axes 172, 192. The dressing tool spindle assembly 210 can also include a cylindrical spindle shaft 214 that is rotationally supported within a spindle housing 216 by one or more ball bearing assemblies and can be operatively caused to rotate by an electric variable speed motor 218 operatively connected to spindle shaft 214 by belt 219 and pulleys 221. (See FIG. 7)

In an embodiment and as illustrated in FIG. 9, the dressing tool 156 can also be cylindrically annular in shape and can include a central tool hub 220 concentrically disposed with respect to the circumferential peripheral dressing face 162. To releasably connect with a dressing tool 156, the distal end of the spindle shaft 214 of the dressing tool spindle assembly 210 can include a tool coupling chuck 222 that radially clamps to the central tool hub 220 such that the dressing tool 156 and spindle shaft 214 of the dressing tool drive spindle assembly 210 correspondingly rotate together. In some embodiments, the tool coupling chuck 222 can facilitate changing between dressing tools 156 of different shapes or abrasiveness, or utilizing the dressing station 154 with different types of tools for conducting different operations on the grinding wheel 150, including profiling.

Normally during the grinding operation of the wafer 102, the dressing tool 156 may be retracted within the dressing station chamber 160 of the dressing station enclosure 158 and thus removed from the internal modular chamber 142 defined by module enclosure 140. To periodically conduct the dressing operation and refurbish the grinding wheel 150, the dressing tool 156 can be extended from the dressing station enclosure 158 and linearly moved into the internal modular chamber 142 along the linear axis 124 so the peripheral dressing face 162 contacts the peripheral grinding rim surface 152. To allow for the linear motion of the dressing tool 156 into the internal modular chamber 142, the dressing tool 156 can translate laterally through an opening or window 224 in module enclosure 140 disposed between and interconnecting the internal modular chamber 142 and the adjacent dressing station chamber 160 where the module enclosure 140 and the dressing station enclosure 158 are separated by a common wall. (See FIG. 5). Again, this arrangement is exemplary, not limiting. For example, it is contemplated that grinding wheel spindle assembly 190 could be linearly moveable for engagement with a linearly stationary wafer holding chuck spindle assembly 170 and/or a linearly stationary dressing tool drive assembly 210.

Referring to FIGS. 6 and 7, to drive movement of the dressing tool 156, the dressing tool spindle assembly 210 can be operatively associated with an electrically powered servo motor. For example, the dressing station 154 can include a linear dressing motor 226 that is operatively connected with the dressing tool spindle assembly 210 via a ball screw to move the dressing tool 156 along the linear axis 124. The dressing tool 156 can be vertically fixed in location to rotate in the operational plane 164. To rigidly brace the dressing tool 156 during the dressing operation, the dressing tool spindle assembly 210 and the associated linear motor 226 can be structurally interconnected by a frame truss 230 on a base 231 and made of structural steel or other suitable material. The base 231 and truss 230 can be designed to accommodate the significant counter forces that may be produced during the dressing operation and can facilitate precise alignment and positioning of the dressing tool 156. In the illustrated embodiment, the spindle shafts 174, 194 and 214 of the spindle assemblies 170, 190 and 210 rotate respectively about vertical axes 172, 192 and 212 that reside in a common vertical plane as illustrated in FIG. 5.

Referring to FIG. 8, there is illustrated an embodiment of the grinding wheel 150 for use with the disclosed modular grinding station 120. The circular grinding wheel 150 can have a generally planar cylindrical shape with the peripheral grinding rim surface 152 defining the outer circumference concentric to the central wheel hub 200 and co-axially aligned to the second rotational axis 192. In an embodiment, the grinding wheel 150 can have an axial wheel thickness 240 defined between an upper planar wheel face 242 and a lower planar wheel face 244 that are axially spaced apart and concentric with respect to the second rotational axis 192. The peripheral grinding rim surface 152 extends between the upper and lower planar wheel faces 242, 244 at the circumference of the grinding wheel 150 and defines the wheel axial thickness 240.

A plurality of annular grooves or tracks 246 extend into the peripheral grinding rim surface 152 and are axially spaced from each other with respect to the second rotational axis 192. The cross-sectional shape of the plurality of annular grooves or tracks 246 can define a grinding rim profile 248. The annular grooves or tracks 246 are each the inverse of the desired wafer edge profile to be formed on the peripheral wafer edge 108 of a wafer 102. During the edge grinding operation, the outer peripheral edge 108 of a wafer 102 supported on the wafer-holding chuck 146 is received into one of the plurality of annular grooves or tracks 246 and the wafer 102 and the grinding wheel 150 are respectively rotated, thus machining upon the wafer, the wafer edge profile as the inverse of the engaged annular groove or track 146 of the peripheral grinding rim surface 152. The vertical adjustment capability of wafer holding chuck 146 and the inclusion of a plurality of axially spaced annular grooves or tracks 246 in the peripheral grinding rim surface 152 allows for grinding the wafer edge profile of numerous wafers 102 sequentially placed into and ground by fresh annular grooves or tracks 246 as the grooves initially used become worn. This enables the grinding process to be conducted on a larger number of wafers 102 before refurbishing, i.e., dressing, of the grinding wheel 150 is required. The number of axially spaced annular grooves or tracks 146 on grinding rim surface 152 is optional.

Accordingly, in an embodiment, to simultaneously dress the plurality of annular grooves or tracks 246 of a grinding wheel 150 during the dressing operation, the dressing tool 156 may have an inverse configuration to the peripheral grinding rim surface 152. Referring to FIGS. 9 and 10, the illustrated dressing tool 156 has an annular shape with the peripheral dressing face 162 and central tool hub 220 for concentric alignment with the third rotational axis 212. The dressing tool 156 can also have an axial tool thickness 250 defined between an upper planar tool surface 252 and a lower planar tool surface 254. To simultaneously dress the plurality of annular grooves or tracks 246 of the grinding wheel 150 of FIG. 8, the dressing tool 156 has a corresponding number of annular shaping rings 256 radially protruding from the peripheral dressing face 162 (see FIG. 10). The plurality of annular shaping rings 256 can be axially spaced apart with respect to the vertical axis 128 (that is aligned with the third rotational axis 212) with the same axial spacing as the plurality of annular grooves or tracks 246 of the grinding wheel 150. Seen in FIG. 9, the cross-sectional shape of the radially protruding annular shaping rings 256 defines a dressing face profile 258 that can be the inverse of the desired shape of the annular grooves or tracks 246 and thus directly analogue to the desired contour of the peripheral wafer edge 108.

Referring to FIG. 5 with continued reference to FIGS. 8 and 9, during a dressing operation, conducted when wafer edge grinding is paused, the dressing tool 156 can be linearly translated from the dressing station enclosure 158 through the opening or window 224 toward the grinding wheel 150 by actuation of the linear dressing motor 226. The dressing tool 156 can also be rotated about the third rotational axis 212 by the dressing motor 218 operatively associated with the dressing tool spindle assembly 210 by belt 219 on pulleys 221. The peripheral dressing face 162 is engaged with the peripheral grinding rim surface 152 by the linear tool motor 226 and the plurality of annular shaping rings 256 mesh with the complementarily, axially spaced plurality of annular grooves or tracks 246. The lateral force engaging the dressing face 162 against the grinding rim surface 152 is controlled by the linear dressing motor 226.

During the dressing operation, rotation of the wafer-holding chuck 146 may be stopped and the wafer-holding chuck spindle assembly 170 can be linearly retracted along the linear axis 124 with respect to the grinding wheel 150. After the dressing operation is complete, the dressing tool spindle assembly 210 can be linearly retracted with respect to the linear axis 124 to move the dressing tool 156 into the dressing station enclosure 158.

Referring to FIGS. 11 and 12, there is illustrated another embodiment of a dressing tool designated 260 in the drawings for dressing the grinding wheel 150 shown in FIG. 8. The dressing tool 260, seen in FIG. 11, can be a flat, planar structure having a circular shape outlined by a peripheral dressing face 262 that circumscribes the third rotational axis 212. The dressing tool 260 may be axially thin and have a tool thickness 264 that is defined between an upper planar tool surface 266 and an axially opposing lower planar tool surface 268. In contrast to the embodiment of FIGS. 9 and 10, the dressing face 262 of dressing tool 260 includes a single annular shaping ring 270 that radially protrudes from the peripheral dressing face 262. The single annular shaping ring 270 defines a dressing face profile 272 that corresponds with a single annular groove or track 246 on the grinding wheel rim surface 152. As used herein, the term “dressing” specifically refers to the refurbishing of the abrasive material of the grinding wheel rim surface to expose fresh abrasive, but is also intended to embrace other operations such as profiling in which the physical shape of the grinding wheel rim surface is changed. Dressing tools referred to herein are envisioned to conduct these and similar operations on the grinding wheel rim surface.

Referring to FIG. 5 with continued reference to FIGS. 8 and 11, during the dressing operation, the dressing tool 260 of this embodiment can be linearly translated with respect to the linear axis 124 into the grinding module enclosure 140 through the window or opening 224 to contact the peripheral grinding rim surface 152 of the grinding wheel 150 by operation of the linear dressing motor 226. The annular shaping ring 270 can be received in a single one of the plurality of annular grooves or tracks 246 disposed on peripheral grinding rim surface 152. To dress the plurality of axially spaced annular grooves or tracks 246, the dressing tool 260 must be vertically moved along the third rotational axis 212. The dressing station 154 would, in this embodiment, include a motor and linear actuator to vertically position dressing tool 260 sequentially to dress each groove or track 246 of peripheral grinding rim surface 152. Simultaneously, the dressing tool 260 can be sequentially adjusted with respect to the linear axis 124 to move the peripheral dressing edge 262 into and out of operative contact with each one of the annular grooves or tracks 246 of the peripheral grinding rim surface 152 of the grinding wheel 150. The single annular shaping ring 270) can therefore be sequentially moved into and out of contact with each of the axially spaced annular grooves or tracks 246 on the peripheral grinding rim surface 152 to dress the desired shape of each groove or track 246. The lateral force engaging annular shaping ring 270) within each single annular groove or track 246 is controlled by linear dressing motor 226. Notably the dressing tool 260 illustrated in FIG. 11 is particularly suitable for profiling of grinding wheel rim 152 as earlier described.

Referring to FIG. 13, with continued reference to the preceding figures, there is illustrated a flow diagram for edge grinding semiconductor wafers and implementation of a possible method or process for the periodic in-situ refurbishing or dressing of a grinding wheel 150 in a grinding module 120 of a grinding machine 100.

In the illustrated embodiments, the grinding machine 100 is configured for computer numerical control or similar operation. The process may employ a programmable logic controller and be conducted automatically in accordance with programming software embodied as a computer-executable program application written in a suitable programming code. In an initial wafer placement step 300, an unprocessed flat wafer 102 may be transported from the wafer loading station 114 to one of a plurality of edge grinding modules 120 of the grinding machine 100 by the Cartesian robot 122. More particularly, the wafer 102 can be secured to a wafer-holding chuck 146 located in the edge grinding module 120 by a vacuum or suction force.

In a wheel rotation step 302, the grinding wheel 150 situated linearly adjacent to the wafer-holding chuck 146 can be rotated relative to the wafer-holding chuck essentially within the common operational plane 164. The wafer-holding chuck 146 and the grinding wheel 150 can be rotated in equal or differential angular speeds and in common or opposing angular directions. To grind the desired profile on the peripheral wafer edge 108 of the wafer 102, as part of a grinding operation 304, the wafer-holding chuck 146 and the grinding wheel 150 can be linearly moved together with respect to the linear axis 124 to make contact between the peripheral wafer edge 108 and a track or groove 246 in the peripheral grinding rim surface 152, to thereby grind away and remove material from the wafer edge 108. This process is sometimes referred to as chamfering.

In an embodiment, after completion of the beveling or grinding operation, the process may include a grinding pause step 306 in which rotation of the wafer-holding chuck 146 is stopped and the wafer-holding chuck is linearly retracted out of contact with the grinding wheel 150 along the linear axis 124.

In a condition determination step 308, the process may determine the condition of peripheral grinding rim surface 152 of the grinding wheel 150 as a result of successive number of wafer edge grinding operations. The condition determination step 308 may involve monitoring and measuring the relative torque or rotational force between the rotating wafer-holding chuck 146 and the grinding wheel 150 to assess when the peripheral grinding rim surface 152 has become dulled or otherwise ineffective. The torque may be measured or estimated by the electrical load on the wafer motor 178 and/or the grinding motor 198, quantified for example by the electric current. The condition determination step 308 may alternatively estimate the wear of peripheral grinding rim surface 152 based on a predetermined number of wafer grinds.

If the condition determination step 308 determines the peripheral grinding rim surface 152 is sufficiently in need, the process may conduct an in situ dressing operation 312 to dress and refurbish the grinding wheel 150. Notably, grinding wheel dressing takes place periodically when indicated and wafer edge grinding paused. The wafer-holding chuck 146 and grinding wheel 150 are spaced laterally. Preferably no wafer is present on wafer-holding chuck 146.

In conjunction with the dressing operation 312, the process may include a dressing tool rotation step 310 wherein the dressing tool 156 is rotated about the third rotational axis 212. However, in embodiments wherein the dressing tool 156 is a polyhedron block, the dressing tool may be held stationary with respect to the grinding wheel 150.

As part of the dressing operation 312, the dressing tool 156 is linearly moved along the linear axis 124 so that the peripheral grinding rim surface 152 and the peripheral dressing face 162 come into contact. Relative rotation of the grinding wheel 150 and the dressing tool 156 refurbishes the peripheral grinding rim surface 152 such that the grinding rim profile 248 is revitalized and/or assumes the desired contour or shape of the dressing face profile 258.

In an embodiment wherein the dressing tool 156 includes a single annular shaping ring 270 radially protruding from the peripheral dressing face 162, the process may include a vertical alignment step that is conducted in conjunction with the dressing step 312. In the vertical alignment step, the dressing tool 156 is sequentially and repeatedly moved along the linear axis 124 into and retracted from tangential contact with the grooves or tracks 246 of grinding wheel 150. Also, the dressing tool 158 is sequentially moved along the vertical axis 128, for example, by axial motion along the third rotational axis 212, in incremental steps. The single annular shaping ring 270) can therefore be alternatively inserted into each of the plurality of annular grooves or tracks 246 that are axially spaced along the peripheral grinding rim surface 152.

The machines disclosed herein and the processes carried out thereon include various well known components, features and operating parameters commonly associated with wafer grinding and dressing of the wafer grinding tools. Though not specifically discussed, or shown in the accompanying drawings, these elements are considered inherent to the disclosure and fully understood by persons of ordinary skill in the art.

The use of the terms “a” and “an” and “the” and “at least one” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. The terms “comprising.” “having.” “including.” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

1. An edge grinding module for grinding a peripheral edge of a flat semiconductor wafer comprising: a wafer-holding chuck rotatable about a rotational axis for rotatably supporting a semiconductor wafer having a peripheral wafer edge;a grinding wheel rotatable about a rotational axis having a peripheral grinding rim surface spaced from the wafer-holding chuck; anda dressing tool having a peripheral dressing face spaced from the peripheral grinding rim surface of the grinding wheel;wherein one of the wafer-holding chuck and the grinding wheel is movable to contact the peripheral wafer edge of the semiconductor wafer supported on the wafer-holding chuck and the peripheral grinding rim surface in a grinding operation, and one of the grinding wheel and the dressing tool are movable to contact the peripheral grinding rim surface of the grinding wheel and the peripheral dressing face of the dressing tool during a dressing operation.

2. The edge grinding module of claim 1, wherein the dressing tool comprises a dressing wheel having a dressing face profile and is connectable to a rotatable shaft of a dressing tool spindle assembly rotatable about a rotational axis that is parallel to and spaced from the rotational axis of the grinding wheel.

3. The edge grinding module of claim 2, wherein the grinding wheel is connected to a rotatable shaft of a grinding wheel spindle assembly and the wafer-holding chuck is connected to a rotatable shaft of a wafer-holding chuck spindle assembly having a rotational axis, and the rotational axes of the dressing tool spindle assembly and the grinding wheel spindle assembly are aligned along and linearly movable with respect to a linear axis of the edge grinding module.

4. The edge grinding module of claim 3, wherein the wafer-holding chuck spindle assembly and the grinding wheel spindle assembly are respectively and linearly movable to periodically contact the peripheral grinding rim surface and the peripheral edge of a semiconductor wafer supported on the wafer-holding chuck during a grinding operation.

5. The edge grinding module of claim 4, wherein the rotational axis of the wafer-holding chuck spindle assembly, the rotational axis of the grinding wheel spindle assembly, and the rotational axis of the dressing tool spindle assembly are parallel and aligned in a common vertical plane.

6. The edge grinding module of claim 5, wherein the grinding wheel spindle assembly is located linearly between the wafer-holding chuck spindle assembly and the dressing tool spindle assembly.

7. The edge grinding module of claim 6, wherein the wafer-holding chuck, the grinding wheel, and the dressing tool are rotatable in and co-planar with an operational plane of the grinding module.

8. The edge grinding module of claim 3, wherein the peripheral grinding rim surface of the grinding wheel and the peripheral dressing face of the dressing tool are circular and concentric about the respective second rotational axis and the third rotational axis.

9. The edge grinding module of claim 8, wherein the peripheral grinding rim surface includes a plurality of annular grooves or tracks radially disposed therein that are axially spaced with respect to the second rotational axis.

10. The edge grinding module of claim 9, wherein the peripheral dressing face includes a plurality of annular shaping rings radially protruding therefrom that are axially spaced with respect to the rotational axis of the dressing tool spindle assembly and that inversely correspond to the plurality of annular grooves or tracks.

11. The edge grinding module of claim 10, wherein the peripheral dressing face includes a single annular shaping ring radially protruding therefrom.

12. The edge grinding module of claim 10, wherein the dressing tool spindle assembly is vertically movable along the rotational axis to alternatively align the single annular shaping ring with the plurality of annular grooves or tracks of the grinding wheel.

13. The edge grinding module of claim 3, further comprising a module enclosure that accommodates the wafer-holding chuck spindle assembly and the grinding wheel spindle assembly and a dressing station enclosure that accommodates the dressing tool spindle assembly.

14. The edge grinding module of claim 13, wherein the dressing tool spindle assembly is linearly extendable and retractable with respect to the module enclosure.

15. The edge grinding module of claim 14, wherein the module enclosure and the dressing station enclosure are linearly attached and are interconnected by an opening in a common wall through which the dressing tool spindle assembly can traverse.

16. A method of operation of an edge grinding module for grinding a peripheral edge of a flat semiconductor wafer comprising: securing a wafer to a wafer-holding chuck rotationally disposed along a first rotational axis;rotating a grinding wheel rotationally disposed along a second rotational axis spaced with respect to the wafer-holding chuck;conducting a grinding operation by moving the wafer-holding chuck or the grinding wheel to contact the peripheral edge of the flat semiconductor wafer and a peripheral grinding rim surface of the grinding wheel; and separately conducting a grinding wheel dressing operation compromising,locating a dressing tool having a peripheral dressing face adjacent to the grinding wheel; andconducting the dressing operation by moving the dressing tool or the grinding wheel to contact a peripheral dressing face and the peripheral grinding rim surface.

17. The method of claim 16, wherein the dressing tool is rotationally disposed along a third rotational axis and further comprising the step of rotating the peripheral dressing face in contact with the peripheral grinding rim surface of the grinding wheel.

18. The method of claim 17, wherein the wafer-holding chuck, the peripheral grinding rim surface of the grinding wheel, and the dressing tool are essentially co-planar with an operational plane.

19. The method of claim 18, wherein the grinding wheel includes a plurality of annular grooves or tracks radially disposed in the peripheral grinding rim surface and axially spaced with respect to the second rotational axis.

20. The method of claim 19, wherein the dressing tool include a plurality of annular shaping rings radially disposed on the peripheral dressing face that are axially spaced with respect to the third rotational axis and that inversely correspond to the plurality of annular grooves or tracks.

21. The method of claim 20, further comprising moving the dressing tool with respect to the third rotational axis to vertically align an annular shaping ring radially protruding from the peripheral dressing face to sequentially dress the plurality of annular grooves or tracks.

22. A grinding machine for automated edge grinding of flat semiconductor wafers comprising: a wafer loading station for receiving one or more wafers;a wafer unloading station for removal of the one or more wafers;a plurality of edge grinding modules aligned between the wafer loading station and the wafer unloading station, each edge grinding module including a wafer-holding chuck rotationally aligned on a first rotational axis, a grinding wheel rotationally aligned on a second rotational axis, and a dressing tool rotationally aligned a third rotational axis, wherein the wafer-holding chuck, the grinding wheel, and the dressing tool are relatively movable to periodically conduct a grinding operation on the one or more wafers and to separately conduct a dressing operation on the grinding wheel to dress the grinding wheel with the dressing tool; anda Cartesian robot to transport the one or more wafer between the wafer loading station, the wafer unloading station, and the plurality of edge grinding modules.