An apparatus 22 for double-side polishing semiconductor wafers as shown in FIGS. 4 to 7, wherein only the main functional members are shown in FIG. 4, is well known as an apparatus for polishing the two sides of each of semiconductor wafers W at the same time.
The apparatus 22 shown in FIG. 4 comprises a lower polishing turn table 24 and upper polishing turn table 26 both of which are arranged in a face to face relation with each other. Lower and upper polishing pads 24a, 26a are fixedly applied on the upper face of the lower polishing turn table 24 and the lower face of the upper polishing turn table 26 respectively. The lower and upper polishing turn tables 24, 26 are respectively rotated in opposed directions by a driving means which is not shown for clarity.
A sun gear 28 is at the center of the lower polishing turn table 24 and held on the surface thereof and an internal gear 30 in an annular shape is located near the outside of the periphery thereof. Each of wafer carriers 32 has the shape of a disc and lies between the upper surface of the lower polishing pad 24a and the lower surface of the upper polishing pad 26a. The wafer carriers 32 are moved around in a space between the lower and upper polishing pads 24a, 26a, while each of the wafer carriers 32 turns not only about its own center but revolves around the centers of the polishing pads 24a, 26a by the actions of the sun gear 28 and internal gear 30. Each of the carriers 32 has a plurality of carrier holes 34 and semiconductor wafers W to be polished are placed in the respective carrier holes 34. In polishing the wafers W, polishing slurry is supplied between a wafer W and each of the polishing pads 24a, 26a through a hole 38 communicating between the upper and lower surfaces of the upper polishing turn table 26 from a nozzle 36. As a wafer carrier 32 turns about its center and at the same time revolves around the centers of the lower and upper polishing turn tables 24, 26, the wafers W placed in the carrier holes 34 turn about the respective centers of their own and at the same time revolve around not only the centers of the polishing turn tables 24, 26 but also the center of the carrier 32, so that the wafers W are moved around between the lower and upper polishing pads 24a, 26a and the two sides of each wafer W are polished at the same time.
The inner peripheral edge of a carrier hole 34 has an annular member A secured along the same edge for the purpose of preventing cracking or chipping of the edge of a semiconductor wafer W. The annular member A is produced by injection molding of plastics or it may be produced from glass fiber reinforced epoxy resin composite. Structures similar to or same as the wafer carrier 32 including the annular member A are respectively disclosed in laid open publications of Japanese Utility Model Application No. 57-177641, 58-4349 and 58-59559, and laid open publication of Japanese Patent Application No. 6-226618.
When double-side polishing of a semiconductor wafer W is conducted by the use of the conventional apparatus 22 for double-side polishing semiconductor wafers above mentioned, a surface of a peripheral portion of an edge of the wafer W can be polished by the function of an annular member A as a polishing buff because of a relative rotational speed of the wafer W to the carrier hole 34 due to the rotation of the wafer W within the carrier hole 34, but the upper and lower chamfered portion of the edge of the wafer W remain unpolished. Therefore, generation of particles from such portion of the edge of the wafer W cannot be prevented in the conventional double-side polishing operation. In light of the problem, it is required that the whole edge portions are polished in double-side polishing. There are additional other problems in realizing the perfect polishing of the whole edge portions in double-side polishing that the perfect edge polishing as an additional process step is a costly operation because of its technical difficulty and moreover, the main surfaces of the wafer W are contaminated during edge polishing process.