Abrading – Work feeder – Ejector or unloader
Reexamination Certificate
2001-02-02
2002-06-04
Hail, III, Joseph J. (Department: 3723)
Abrading
Work feeder
Ejector or unloader
C451S388000, C451S398000, C438S692000
Reexamination Certificate
active
06398631
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to semiconductor wafer processing, and in particular to a method and apparatus for inserting or extracting a wafer from a machine while avoiding contact damage on the wafer.
Semiconductor wafers are generally prepared from a single crystal ingot, such as a silicon ingot, which is sliced into individual wafers. Each wafer is subjected to a number of processing operations to facilitate the installation of integrated circuit devices and to improve their yield, performance, and reliability. Typically, these operations reduce the thickness of the wafer, remove damage caused by the slicing operation, and create a flat and highly reflective facial surface. Lapping and chemical-mechanical polishing are two of these operations. Lapping involves rubbing a face of the wafer relative to a lapping plate while dispensing an abrasive slurry to remove material and embedded damage by mechanical abrasion. Chemical-mechanical polishing involves rubbing the face relative to a polishing pad, such as a polyurethane impregnated polyester felt, while dispensing a slurry containing both an abrasive and chemicals so that both mechanical action and chemical reaction contribute to the removal of material.
To maximize throughput, a lapping or polishing operation is typically accomplished using a machine that simultaneously holds between 15 and 30 wafers. Each machine has several wafer carriers which move relative to a rotating, abrasive surface of a lapping plate or polishing pad to effect a relative rubbing motion. Each carrier typically includes three or more openings for receiving wafers and guiding motion of the wafers relative to the surface. Some machines have two abrasive surfaces for simultaneous processing of top and bottom faces. To begin a lapping or polishing operation, unpolished wafers are initially transferred from a container such as a cassette and inserted into the openings of the carrier. Afterwards, each wafer is removed from its corresponding opening in the carrier and transferred to a second cassette for transport or delivery.
Unfortunately, the wafer handling steps associated with lapping and polishing operations can degrade wafer quality and yield. Each wafer is easily damaged by contact during transfer, especially after polishing when the wafer surfaces are especially reactive and vulnerable to contamination. Any contact carries the risk of smudges, scratches, or contamination damage. Accordingly, devices for handling the wafer, such as manual gripping tools, preferably contact edges only and avoid contact with faces. Removal of the wafer from a polishing pad without damage is especially difficult because a film of slurry underneath the wafer creates a strong adhering, capillary force which holds the wafer to the polishing pad. Also, the edge of the wafer is not easily accessible for engagement by an edge handling tool. Accordingly, the wafer is removed by contacting the face of the wafer with a vacuum-type gripping tool, such as a vacuum pencil, which has a tube through which suction is applied and a rubber tip that engages the face. Contact of the tip against the face degrades wafer quality, leaving a residual impression that is frequently noticeable on finished wafers. Placing a new wafer on to the polishing pad also may damage the wafer. The entire lower face of the wafer should seal against the pad, which requires some downward force on the wafer. Often, operators use a gloved finger or thumb to press down on the wafer so that it seals. That can break the wafer or cause contamination. Additionally, the steps of placing and removing wafers are time-consuming and expensive.
BRIEF SUMMARY OF THE INVENTION
Among the several objects and features of the present invention may be noted the provision of an apparatus and method for inserting and removing a semiconductor wafer from a machine while avoiding contact with a face of the wafer; the provision of such an apparatus and method that minimize damage and contamination; the provision of such an apparatus and method that are either manual or automated; the provision of such an apparatus and method which do not require substantial modification of the lapping or polishing machines; and the provision of such an apparatus and method that are rapid and economical in operation.
Briefly, a system according to the present invention facilitates transfer of a semiconductor wafer into or out of a machine for removing material from the wafer. The machine has a wafer carrier for holding the wafer and for guiding motion of the wafer relative to an underlying abrading member while a face of the wafer engages the abrading member. The wafer carrier includes at least one opening for receiving the wafer, the opening having an outer rim that generally circumscribes a peripheral edge margin of the wafer. The system comprises a wafer transport suitable for placement above the wafer carrier of the machine. The transport has a top surface, a bottom surface, and at least one open cavity therethrough with an internal edge wall. The cavity has a size and shape suitable for registering alignment with at least one opening of the wafer carrier when the edge wall of the cavity is positioned above the outer rim of the opening and the bottom surface rests on the wafer carrier. The cavity and opening together form a compartment having an open top wherein the edge wall and outer rim define a bounded perimeter. The compartment is adapted to receive and hold the wafer. A liquid delivery conduit is associated with the wafer transport to deliver liquid to a position generally beneath the transport for moving the wafer between a first position resting on the abrading member and a second position in the cavity. The liquid delivery conduit has an outlet located above the abrading member.
In another aspect, a method of the present invention transfers a semiconductor wafer to or from a machine used to remove material from the wafer. The machine has a wafer carrier for holding the wafer and for guiding motion of the wafer relative to an underlying abrading member while a face of the wafer engages the abrading member. The wafer carrier includes at least one opening receiving the wafer, the opening having an outer rim that generally circumscribes a peripheral edge margin of the wafer. The method comprises the steps of placing a wafer transport over the wafer carrier in aligned registration wherein an open cavity of the wafer transport is positioned above the opening and an edge wall of the cavity is above the outer rim of the opening. The wafer transport and wafer carrier together form a compartment for containing the wafer. A liquid is delivered through a passage having an outlet located above the abrading member to a position beneath the wafer thereby moving the wafer in the compartment between a first position resting on the abrading member and a second position spaced above the abrading member.
Other objects and features of the present invention will be in part apparent and in part pointed out hereinafter.
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Anderson Gary L.
Buese Dennis
Callahan James
Loeschen Randy Gene
Schmidt Judy
Hail III Joseph J.
MEMC Electronic Materials , Inc.
Senniger Powers Leavitt & Roedel
Shakeri Hadi
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