Abrading – Precision device or process - or with condition responsive... – Controlling temperature
Reexamination Certificate
2000-02-23
2001-07-10
Banks, Derris H. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
Controlling temperature
C451S043000, C451S044000
Reexamination Certificate
active
06257954
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to semiconductor wafer polishing, and in particular to an apparatus and process for polishing peripheral edges of wafers at elevated temperature for improved throughput.
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 and remove damage caused by the slicing operation. Chemical-mechanical polishing of semiconductor wafers is one of these operations. It generally involves rubbing a wafer with a polishing pad, such as a polyurethane impregnated polyester felt, while dispensing a polishing solution, or slurry. The slurry contains an abrasive and chemicals, such as a colloidal silica and an alkaline etchant, so that both mechanical action and chemical reaction contribute to the removal of material. The polishing process produces surfaces that are flat, highly reflective, and damage-free.
It is crucial that each wafer undergo polishing not only on at least one of its flat, facial surfaces but also along its peripheral edge. Wafer edges frequently contain micro-cracks and chip damage from the slicing operation and from a grinding operation, or profiling, along the edges that forms a selected edge profile shape. During handling and processing, edges often receive impact forces or high local stresses that cause additional fractures, chips, or roughness. If left in place, these imperfections become local stress points for the nucleation of damage to the lattice of the crystal structure. They significantly increase the likelihood of subsequent growth of slips and dislocations that can ruin the wafer. Further, edge roughness tends to facilitate adherence of impurities, such as dust particles and inorganic anions. These impurities can diffuse from wafer edges to facial surfaces and detrimentally contaminate wafers. Accordingly, edges are polished to remove imperfections or reduce their size.
One type of machine that is used for polishing semiconductor wafer edges is shown in U.S. Pat. No. 5,094,037, which is hereby incorporated by reference. The machine includes at least one rotatable wafer holder that presses the edge of the wafer against a rotating cylindric drum. The drum is covered with a polishing pad so that as the drum rotates, the polishing pad rubs against the edge of the wafer. The drum oscillates vertically as it rotates, evenly exposing all portions of the polishing pad against the wafer edge. Simultaneously, the wafer holder rotates the wafer in a direction opposite to that of the drum, thereby increasing the relative speed between the wafer edge and the polishing pad. Slurry may be prepared in a container having an agitator for mixing the slurry and maintaining a preselected pH level. The slurry is dispensed at a controllable flowrate onto the polishing pad at a location where the wafer engages the pad.
A limitation to the chemical mechanical polishing process, including machines of this type, is that polishing requires a substantial amount of time. A typical duration for the chemical reaction and mechanical action to effect an acceptable level of smoothness along a first side or bevel of an edge is 85 seconds. That time duration must then be repeated to polish a second, opposite side of the edge. To shorten the time, polishing has been conducted at elevated temperatures which accelerates the chemical reaction between the slurry and the wafer. However, there have been difficulties implementing high temperature edge polishing and there are no machines of the type described above that permit it. Throughput with edge polishing machines is typically limited to between 32 and 42 wafers per hour, and the edge polishing process is a hindrance to efficient processing of wafers.
SUMMARY OF THE INVENTION
Among the several objects and features of the present invention may be noted the provision of an apparatus and process for polishing edges of semiconductor wafers that shorten the time needed to conduct edge polishing; the provision of such an apparatus and process which increase manufacturing throughput of semiconductor wafers; the provision of such an apparatus and process for polishing at a precisely controlled elevated temperature; the provision of such an apparatus and process which efficiently and thoroughly remove microcracks in the edges of the wafers; and the provision of an apparatus and process that are efficient and economical.
In general, an apparatus of the present invention for polishing edges of silicon wafers at elevated temperature for high throughput comprises a rotatable drum having a cylindric outer surface, a heatable mat positioned around the outer surface of the drum, and a polishing pad in generally parallel arrangement with the mat on the drum. The pad has an outwardly facing polishing surface around the drum. A wafer holder is disposed relative to the polishing pad and adapted to hold a wafer so that a peripheral edge of the wafer is held in pressed engagement against the polishing pad. The apparatus includes a container of liquid slurry and a slurry delivery system for delivering slurry from the container to a location generally where the wafer is held against the pad.
In another aspect, an improvement of the present invention is for a wafer edge polishing apparatus of a type having a drum that is generally cylindric and rotatable with a polishing pad mounted thereon and forming an outermost surface around a circumference of the drum. A wafer holder positions a peripheral edge of a wafer in engagement against the polishing pad. The improvement of the present invention comprises a heatable mat positioned around the circumference of the drum between the drum and the polishing pad for applying heat to the polishing pad.
A process according to the present invention for chemical-mechanical polishing an edge of a semiconductor wafer using a liquid chemical slurry and a polishing pad, the pad having a polishing side and an underside, comprises the steps of heating the liquid slurry to an elevated temperature and applying heat to the polishing pad from the underside of the polishing pad to elevate the temperature of the polishing pad. A peripheral edge of a semiconductor wafer is engaged against the polishing side of the polishing pad. A relative motion is effected between the wafer and the pad while simultaneously dispensing the heated slurry generally onto a region where the edge of the wafer engages the pad, thereby polishing the edge while both the pad and the slurry are at elevated temperatures.
Other objects and features of the present invention will be in part apparent and in part pointed out hereinafter.
REFERENCES:
patent: 4276114 (1981-06-01), Takano et al.
patent: 5094037 (1992-03-01), Hakomori et al.
patent: 5097630 (1992-03-01), Maeda et al.
patent: 5117590 (1992-06-01), Kudo et al.
patent: 5274959 (1994-01-01), Dyer et al.
patent: 5547415 (1996-08-01), Hasegawa et al.
patent: 5595522 (1997-01-01), Simpson et al.
patent: 5643056 (1997-07-01), Hirose et al.
patent: 5643060 (1997-07-01), Sandhu et al.
patent: 5658189 (1997-08-01), Kagamida
patent: 5842909 (1998-12-01), Sandhu et al.
Buese Dennis
Erk Henry
Ng Kan-Yin
Walsh Robert J.
Banks Derris H.
MEMC Electronic Materials , Inc.
Senniger Powers Leavitt & Roedel
LandOfFree
Apparatus and process for high temperature wafer edge polishing does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and process for high temperature wafer edge polishing, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and process for high temperature wafer edge polishing will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2493694