Method and apparatus for cleaning grinding work chuck using a scraper
A scraper assembly for removing debris deposited on the surface of a porous work chuck during a wafer grinding process.
This Application is based on Provisional Application No. 61/632,262 filed on Jan. 23, 2012.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to a method and apparatus for cleaning the porous ceramic grind work chuck used in semiconductor wafer grinding machines.
2. Background of the Invention
U.S. Pat. No. 7,118,446, issued to Thomas A. Walsh and Salman Kassir and assigned to the assignee of the present invention exemplifies the status of prior art grinder apparatus technology. A chuck is provided in the apparatus to hold the work piece in place so that the work piece does not slip or otherwise move while being shaped by a grind wheel.
The chuck is porous i.e. holes are drilled therethrough it or otherwise comprises a porous material; a partial vacuum being provided below the chuck to hold the work piece in place. Coolant is pumped directly onto an area of contact between a grind wheel and the workpiece surface, providing cooling and cleaning of grind debris (swarf) from the surface of the workpiece.
During the grinding process, vacuum is applied through the porous portion of the work chuck to hold the wafer. If there is a particle (from the work chuck or from the incoming wafer) between the bottom of the wafer and the top of the work chuck, a crack in the wafer will be produced. This type of crack is called a “star crack” and propagating cracks originate at the particle.
Additionally, the wafers themselves may introduce particles onto the work chuck. The particles can lead to star cracks and/or non-uniformities in the grind.
What is thus desired is to provide a work chuck cleaning particle removal procedure wherein the cleaning can be done either automatically or manually.
SUMMARY OF THE INVENTIONThe present invention provides method and apparatus for removing particles from the surface of a chuck used to hold a workpiece, such as a wafer, in position during grinding, the process being accomplished manually or automatically. In particular, a scraper assembly is positioned within a wafer grinder apparatus adjacent the edge of the work chuck. The assembly comprises a razor mechanism positioned on the face surface of a gimbal block, a plurality of brush members being positioned adjacent to the razor. The assembly further comprises a fluid source which, when activated, directs fluid to the chuck surface which in turn causes debris to be removed from work chuck surface. The razor mechanism is then moved from the center of the work chuck to the edge to remove any particles from the chuck surface. A source of sonic energy may be positioned on the assembly, or in the fluid path, the sonic energy loosening particles that may be tightly adhering to the chuck surface.
For a better understanding of the present invention as well as other objects and further features thereof, reference is made to the following description which is to be read in conjunction with the accompanying drawing therein:
In order to put the present invention in proper perspective,
Referring to
The grind spindle 102 is coupled with the spindle support column 104, and the spindle support column 104 is engaged with the rails 120 and the ball screw 122. The cabinet 108 supports the rails 120, balls screw 122, the work spindle 106 and the splash pan 110. The thickness probe 111 is coupled with the work spindle 106 and is shown positioned above the work chuck 112.
The grind spindle 102 is moved along a vertical axis by the ball screw assembly 114 and includes at least one grinding wheel (not shown) in order to shape a work piece, for example, semiconductor wafers.
The work chuck 112 holds the work piece in place so that the work piece does not slip while rotating and being shaped by a grinding wheel of the grind spindle 102. For example, the work chuck 112 is porous, e.g. it has holes drilled through it or otherwise comprises a porous material, and a partial vacuum is provided by a device (not shown) positioned below the work chuck 112 to hold the work piece in place.
The spindle support column 104, supports the grind spindle 102, and is moveably engaged with the rails 120, bed 118 and ball screw 122, to translate back and forth in a horizontal direction. Specifically, the spindle support column 104, and the grind spindle 102 move with respect to the cabinet 108, the work spindle 106, and thus a surface of a stationary work piece attached on the work chuck 112.
The ability to translate the grind spindle assembly 102 allows shaping of a work piece to be achieved on both a face and an edge of the work piece with a single machine. Specifically, a grinding wheel of the grind spindle 102 is first positioned over an edge of the work piece and then moved into contact with the edge of the work piece until the edge is shaped as desired. The grind spindle 102 is then raised vertically above the work piece, translated horizontally over a face of the work piece so the grinding wheel is positioned over the face of the work piece, and then the grinding wheel is then placed in contact with the face of the work piece by lowering the grind spindle 102 until the grinding wheel is in contact with a portion of the face of the work piece, typically contact with the center of the wafer mounted on work chuck.
Referring to
Referring to
The operation of the assembly 200 is shown in more detail in
Work chuck 112 then is then rotated and the tip of the razor 210 (adjusted so that the tip engages its surface) causing the projecting debris particles to be removed.
Assembly 200 may be activated manually for most applications. However, if cleaning is required for every work piece, a control signal can be provided from the system control software to actuate the scraper assembly 200 before grinding each wafer (or every Nth wafer).
The operative cycle of assembly 200 is as follows:
After the wafer is removed from the top surface of work chuck 202, the work chuck blow-off (air) and back flush fluid, such as distilled water is turned on to purge the majority of the particulates that were sucked into the porous work chuck material during the grinding cycle. During this process, the work chuck is spinned causing the particles to be removed from its edge. After the majority of particulates now have been removed, scraper assembly 200 is then actuated and placed on the work chuck. Most of the remaining particulates will be trapped where the perimeter of the wafer made contact with the porous section of work chuck 202. Scraper assembly 200 typically starts in the center of the work chuck 202 and moves radially outward until it reaches the location where the most of the particulates are trapped. The scraper assembly 200 stays in this position as work chuck 202 slowly rotates. After the user defined scraper time has been reached, the scraper assembly will lift and rotate back to the center home position or away from the work chuck. Note that assembly 200 never (other than the tip of razor 210 touches the surface of the work chuck because of brushes 214, and/or if required, a layer of water. Note that the scraper device itself may also be rotated although this is not the preferred technique.
While the invention has been described with reference to its preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its essential teachings.
Claims
1. A method for cleaning particles from the surface of a circular cylinder shaped and rotatable work chuck used in a grind apparatus comprising the steps of:
- providing a work chuck having first and second surfaces, said work chuck being operable in conjunction with said grind apparatus;
- positioning a scraper device adjacent said first surface of said work chuck; and
- activating said scraper device whereby said particles are substantially removed from the first surface of said work chuck.
2. The method of claim 1 wherein said work chuck has an edge portion along its perimeter.
3. The method of claim 2 wherein said scraper device is positioned above said edge portion of said work chuck.
4. A grind apparatus for grinding a surface of a workpiece comprising:
- a grind wheel;
- a porous work chuck having top and bottom surfaces;
- means for rotating said work chuck and said grind wheel;
- a scraper device positioned adjacent to said top surface of said work chuck;
- means for moving said scraper device across the top surface of said work chuck; and
- means for energizing said scraper device whereby particles on the top surface of said work chuck remaining after grinding of said workpiece are substantially removed.
Type: Application
Filed: Jan 23, 2013
Publication Date: Jul 24, 2014
Inventors: Michael Vogtmann (Paso Robles, CA), Larry A. Spiegel (Atascadero, CA), Malcolm K. Roe (Creston, CA)
Application Number: 13/694,998
International Classification: B24B 55/00 (20060101);