Most processes for fabricating semiconductor electronic components start with monocrystalline, or single crystal, silicon in the form of wafers. In general, semiconductor wafers are produced by thinly slicing or cutting a generally cylindrical single crystal silicon ingot. After slicing, each wafer undergoes a number of processing operations to shape the wafer, reduce its thickness, remove damage caused by the slicing operation, and to create a highly reflective surface.

Known wafering processes include chamfering, or beveling, a peripheral portion of an as-cut wafer to remove its straight edge (see FIG. 5). Since the wafer is relatively hard and brittle and is prone to break along a plane of cleavage, the edge of the wafer is particularly susceptible to chipping or breaking if it has a right angle as it was cut. By subjecting the peripheral portion of the wafer to a chamfering process, the impact strength of the wafer edge may be improved. In chamfering the wafer, for example, the wafer's edge is pressed against a predetermined groove in a grinding wheel, or grindstone, and subjected to grinding with dashing water.

Due in part to the larger diameters of modern wafers, chamfering typically occurs in two stages: rough grinding and precision grinding. FIGS. 3 and 4 schematically illustrate the shape of a groove 12 for rough grinding and the shape of a groove 14 for precision grinding according to conventional chamfering processes. Conventional chamfering processes, however, use grinding wheels that have the same shape groove for both rough grinding and precision grinding. Use of the rough grinding groove 12 in a conventional grinding wheel results in a machining allowance X2 at an outer edge surface of the wafer and a machining allowance X, at a tapered portion of the chamfered edge

when subjecting the wafer to precision grinding in the groove 14. The machining allowance X2, however, does not coincide with a machining allowance X,. In this instance, X2 > X,. As a result, sufficient work precision in the wafer's peripheral edge portion cannot be obtained upon precision grinding.

For these reasons, a method and apparatus are desired for providing multiple chamfering of wafer in which differences in machining allowances of the wafer are reduced with dimensional precision in a peripheral portion of the wafer.

SUMMARY OF THE INVENTION The invention meets the above needs and overcomes the deficiencies of the prior art by providing an improved method and apparatus for multiple chamfering of a wafer.

Among the several objects and features of the present invention may be noted the provision of a method and apparatus that permits two stage grinding; the provision of such method and apparatus that reduces machining allowance differences; the provision of such method and apparatus that optimizes the shape of the groove in a grinding wheel for rough grinding the wafer; the provision of such method and apparatus that permits the peripheral portion of the wafer to uniformly contact the groove in a grinding wheel during precision grinding; and the provision of such method and apparatus that are economically feasible and commercially practical.

Briefly described, an embodiment of the present invention is directed a method of multiple chamfering of a wafer. The method uses a rotating grinding wheel having a first groove therein for rough grinding a peripheral edge margin of the wafer and a rotating grinding wheel having a second groove therein for precision grinding the peripheral edge margin. The peripheral edge margin of the wafer includes a radially outwardly facing edge surface and edge portions adjacent to the edge surface generally on front and back surfaces of the wafer. The method includes the step of defining a profile of each of the first and second grooves so that a first machining allowance corresponding to the edge surface of

the peripheral edge margin is substantially equal to a second machining allowance corresponding to at least one of the edge portions of the peripheral edge margin. The profiles of the first and second grooves differ from each other. The method also includes the steps of grinding the peripheral edge margin in the first groove for rough grinding and further grinding the peripheral edge margin in the second groove for precision grinding.

An apparatus embodying aspects of the invention includes a rotating grinding wheel having a first groove therein for rough grinding a peripheral edge margin of the wafer and a rotating grinding wheel having a second groove therein for precision grinding the peripheral edge margin after rough grinding. The peripheral edge margin of the wafer includes a radially outwardly facing edge surface and edge portions adjacent to the edge surface generally on front and back surfaces of the wafer. The first and second grooves have profiles such that a first machining allowance corresponding to the edge surface of the peripheral edge margin is substantially equal to a second machining allowance corresponding to at least one of the edge portions of the peripheral edge margin. The profiles of the first and second grooves differ from each other.

Alternatively, the invention may comprise various other methods and apparatuses.

Other objects and features will be in part apparent and in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a groove in a grinding wheel for rough grinding and a groove in a grinding wheel for precision grinding according to a preferred embodiment of the present invention.

FIG. 2 is a schematic view of a groove in a grinding wheel for rough grinding and a groove in a grinding wheel for precision grinding according to another preferred embodiment of the present invention.

FIG. 3 is a schematic view of a groove in a conventional grinding wheel for rough grinding and a groove in a conventional grinding wheel for precision grinding.

FIG. 4 is a schematic view of a groove in another conventional grinding wheel for rough grinding and a groove in a conventional grinding wheel for precision grinding.

FIG. 5 is a fragmentary, cross-sectional view of a wafer having a chamfered edge.

FIG. 6 is a schematic view of an apparatus for multiple chamfering of a wafer.

Corresponding reference characters indicate corresponding parts throughout the drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, FIG. 6 schematically illustrates a grinding apparatus for chamfering, or beveling, a wafer 30. The grinding apparatus includes a rotating grinding wheel, or grindstone, 10 having a groove into which a peripheral edge margin 32 of the wafer 30 is pressed for grinding. The shape of the groove in grinding wheel 10 determines the shape of the peripheral edge margin 32 after grinding. Those skilled in the art are familiar with the practice of introducing dashing water or slurry to the grinding surface during chamfering.

Due in part to the larger diameters of modern wafers, chamfering typically occurs in two stages: rough grinding and precision grinding. As described above, conventional chamfering processes use grinding wheels that have the same shape groove for both rough grinding and precision grinding. FIG. 3 and FIG. 4 each illustrate a groove 12 of a conventional grinding wheel for rough grinding and a corresponding groove 14 of a conventional grinding wheel for precision grinding. As shown in FIGS. 3 and 4, conventional grinding results in a machining allowance X2 associated with a radially outwardly facing edge surface of the wafer's peripheral edge margin 32 and a machining allowance X, associated with an adjacent edge portion of the chamfered edge. The machining allowance X2, however, does not coincide with the machining allowance XI. In

this instance, X2> X,. As a result, sufficient work precision in the wafer's chamfered edge margin 32 cannot be obtained upon precision grinding.

Referring now to FIGS. 1 and 2, the present invention is described in connection with schematic views of the groove 12 in grinding wheel 10 for rough grinding and the corresponding groove 14 in grinding wheel 10 for precision grinding. In a preferred embodiment of the invention, machining allowances are made substantially equal by optimizing the shape of groove 12 in grinding wheel 10 for rough grinding in consideration of machining allowances in peripheral edge margin 32 set at the time of precision grinding. Specifically, a machining allowance associated with the radially outwardly facing edge surface of edge margin 32 and a machining allowance associated with the adjacent edge portions of edge margin 32, generally on the front and back surfaces of wafer 30, are made substantially equal. Advantageously, multiple chamfering according. to the invention enables machining allowance differences to be reduced with dimensional precision at peripheral edge margin 32 of wafer 30.

In a preferred embodiment of the invention shown in FIG. 1, the shape, or profile, of groove 12 in grinding wheel 10 for rough grinding is optimized according to a formula: Ra=Rb+X where Ra is a radius of curvature of groove 12 for rough grinding, Rb is a radius of curvature of groove 14 for precision grinding, and X is a machining allowance of wafer 30 upon precision grinding. As shown in FIG. 1, the radiuses of curvature Ra and Rb are preferably measured at a position in grooves 12,14 corresponding to the intersection of the edge surface and one adjacent edge portion of peripheral edge margin 32.

In an alternative embodiment of the invention shown in FIG. 2, the shape of groove 12 in grinding wheel 10 for rough grinding is optimized according to a formula: Ta = Tb + 2X (l-sinO)/cosE where Ta is a relatively flat length at the base of groove 12 for rough grinding, Tb is a relatively flat length at the base of groove 14 for precision grinding, X is a machining allowance of wafer 30 upon precision grinding, and 0 is a tapered angle of groove 14. As

shown in FIG. 2, the base lengths Ta and Tb are preferably measured in grooves 12,14 along a length corresponding to the edge surface of peripheral edge margin 32.

By optimizing the shape of groove 12 in accordance with the foregoing, it is possible to make the peripheral edge margin 32 of wafer 30 uniformly contact precision grinding groove 14 in grinding wheel 10 at the time of the precision grinding. In other words, the present invention sets the machining allowance X of wafer 30 upon rough grinding and, thus, permits the machining allowance X2 for the edge surface of peripheral edge margin 32 and the machining allowance X, for the tapered adjacent edge portion of peripheral edge margin 32 to be made substantially equal (i. e., X2 = XI).

In a method of chamfering according to the present invention, machining allowance of wafer 30 can be reduced upon chamfering with dimensional precision in the peripheral edge margin 32 of wafer 30 being maintained.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.