Method and apparatus for mirror-polishing a wafer portion

Abstract: A method and an apparatus for mirror-polishing a peripheral chamfered portion (1) of a semiconductor wafer (W) polishes a peripheral side surface (1a) of the chamfered portion (1), the bevelled surfaces (1b, 1c), and the rounded edges (1d, 1e) formed between the peripheral side surface (1a) and each of the bevelled surfaces (1b, 1c) separately.

Description: The present invention relates to a method for mirror-polishing a peripheral chamfered portion of a semiconductor wafer and to an apparatus for mirror-polishing useful for carrying out the method. The semiconductor wafer to which the present invention may be applied, as shown in FIG. 1, comprises a peripheral chamfered portion 1 comprising a peripheral side surface 1a, front and back beveled surfaces 1b and 1c formed on front and back surfaces, respectively, along the periphery of the wafer W, and rounded edges 1d and 1e formed between the peripheral side surface 1a and each of the front and back beveled surfaces 1b and 1c. Conventionally, as shown in FIG. 5 and as disclosed in EP-A-0 393 951, in order to mirror-polish such a peripheral chamfered portion 1 of a semiconductor wafer W, a mirror-polishing device 31 having a polishing portion 31a with the so-called a form chamfering buff which has a circumferential buff groove on a peripheral surface thereof, with a section corresponding to that of the chamfered portion 1 of the wafer W, has been used. If there were no variation in shape of the chamfered portion, and the section of the chamfered portion completely corresponded to the section of the buff groove, such a mirror-polishing apparatus 31 with a form chamfering buff has an advantage of mirror-polishing the chamfered portion 1 of the wafer W effectively because the entirety of the chamfered portion 1 is in contact with the inner surface including the bottom surface of the groove of the buff member 31a simultaneously, so that mirror-polishing for the entirety of the chamfered portion 1 is performed at a time. However, in practice, there are variations not only in thickness of wafer W but in shape of the peripheral chamfered portion 1 which are created in a wafer chamfering step, a lapping step, an etching step or the like. Therefore, during mirror-polishing step of the chamfered portion 1, it often happens that all of a peripheral side surface 1a, beveled surfaces 1b and 1c and rounded edges 1d and 1e are not in contact with the inner surface of the polishing portion 31a in the groove at a time. When the thickness of a wafer W is larger than a desired one, at first mirror-polishing about the beveled surfaces 1b and 1c of the chamfered portion 1 of the wafer W is carried out by the inner surface of the buff groove. After the portion of the beveled surfaces 1b and 1c have been worn out to a certain extent by the mirror-polishing, the rounded edges 1d and 1e of the chamfered portion 1 of the wafer W come into contact with the inner surface of the buff groove. Then, after the portions of the bevelled surface 1b and 1c have been worn out to a further extent by the mirror-polishing, the peripheral side surface la comes into contact with the bottom surface of the buff groove. On the contrary, when the thickness of a wafer W is smaller than a desired one, at first mirror-polishing about the peripheral side surface 1a is carried out by the bottom surface of the buff groove, however, the bevelled surfaces 1b and 1c and the rounded edges 1d and 1e of the chamfered portion are scarcely mirror-polished by the inner surface of the buff groove, until the portion of the peripheral side surface 1a is worn to a certain extent. Therefore, there is a problem that when there is variations in thickness of the wafer W or in shape of the peripheral chamfered portion 1 thereof, mirror-polishing for the peripheral chamfered portion of the wafer W requires considerable time. According to a first aspect of this invention a method of mirror-polishing a peripheral chamfered portion of a semiconductor wafer which comprises a peripheral side surface, bevelled surfaces formed on front and back surfaces around the periphery of the wafer, and rounded edges formed between the peripheral side surface and each of the bevelled surfaces, comprising: a step of rotating the wafer around its centre, and the steps of mirror-polishing the peripheral side surface, the bevelled surfaces, and the rounded edges by a polishing device, is characterised in that the mirror-polishing of both the bevelled surfaces (1b,1c) is carried out simultaneously, in one step, and the mirror-polishing of both the rounded edges (1d,1e) is carried out simultaneously, in another step and in that at least one of the mirror-polishing steps is performed independently of another. Preferably, each mirror-polishing of the peripheral side surface, the bevelled surfaces, and the rounded edges, is individually performed. According to the above described means, because the peripheral side surface, the bevelled surfaces and the rounded edges, of the peripheral chamfered portion of the wafer, are individually mirror-polished, each of the peripheral side surface, the bevelled surfaces and the rounded edges can be securely pressed against respective polishing portions as soon as the respective polishing step begins. Consequently, the peripheral side surface, the bevelled surfaces and the rounded edges, of the peripheral chamfered portion of the wafer, can be securely and effectively polished even if there are variations in thickness of wafer, or in shape of the peripheral chamfered portion which were created in a wafer chamfering step, a lapping step, an etching step or the like. The mirror-polishing of the peripheral side surface, the bevelled surfaces, and the rounded edges of the peripheral chamfered portion, may be performed by bringing the peripheral side surface, the bevelled surfaces, and the rounded edges into contact with first, second, and third polishing portions, which are provided on the polishing device independent of one another, respectively, in an appropriate order. The first polishing portion may comprise a first buff which can be in contact with the peripheral side surface of the peripheral chamfered portion, the second polishing portion may comprise a second buff which can be in contact with the bevelled surfaces, and the third polishing portion may comprise a third buff which can be in contact with the rounded edges. According to a second aspect of this invention, an apparatus for mirror-polishing a peripheral chamfered portion of a semiconductor wafer which comprises a peripheral side surface, bevelled surfaces formed on front and back surfaces around the periphery of the wafer, and rounded edges formed between the peripheral side surface and each of the bevelled surfaces, comprising a cylindrical rotary polishing device which comprises: a first polishing portion having a first buff to contact the peripheral side surface, a second polishing portion having a second buff to contact the bevelled surfaces, and a third polishing portion having a third buff to contact the rounded edges formed between the peripheral side surface and each of the bevelled surfaces, is characterised in that the first, second, and third polishing portions are provided on the peripheral surface of the apparatus independently of one another, in that the second buff contacts both the bevelled surfaces (1b,1c) simultaneously, and in that the third buff contacts both the rounded edges (1d,1e) simultaneously. The apparatus may further comprise a wafer holding device for holding the wafer, which can rotate around the centre thereof and can horizontally and vertically move relatively to the polishing device. According to the apparatus, it is possible to securely and effectively polish the peripheral side surface, the bevelled surfaces and the rounded edges even if there were variations in thickness of wafer, or in shape of the peripheral chamfered portion which were created in a wafer chamfering step, a lapping step, an etching step or the like. Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, in which:- FIG. 1 is a view showing a shape of the peripheral chamfered portion of a wafer; FIG. 2 is a view of the apparatus for mirror-polishing according to an embodiment of the present invention; FIG. 3 is a view for explaining the method according to an embodiment of the present invention; FIG. 4 is a view for explaining the method according to another embodiment of the present invention; and FIG. 5 is a view for explaining a conventional method. In the semiconductor wafer W which is the object to be mirror-polished by applying the present invention, as shown in FIG. 1, the beveled angle of each of the front and back beveled surfaces 1b and 1c, i.e., the angle between each plane of the beveled surfaces 1b and 1c and the plane of the front or back surface, is determined to a value which can prevent the periphery of the wafer W from being chipped off when the wafer is housed in a cassette in a handling step or when the periphery of the wafer hits to a positioning member in a wafer-positioning step. Further, a wafer W for fabricating semiconductor integrated circuits requires values of the beveled angles for the beveled surface 1b and 1c which can suppress occurrence of crown in the vicinity of the boundary between the main surface of the wafer W and the beveled surfaces 1b and 1c when a semiconductor single crystal layer is deposited thereon by a chemical vapor deposition method. The rounded edges 1d and 1e can prevent the boundary between the peripheral side surface 1a and the beveled surfaces 1b and 1c of the wafer W from being chipped-off or cracked. Next, an embodiment of an apparatus for mirror-polishing the peripheral chamfered portion of a semiconductor wafer according to the present invention will be explained. FIG. 2 shows the apparatus 10 for mirror-polishing. The apparatus 10 comprises a cylindrical rotary polishing device 11 for mirror-polishing the peripheral chamfered portion 1 of the wafer W, and a wafer holding device 12 for holding to carry the wafer W to desired positions. The polishing device 11 comprises a cylindrical polishing member 13 and a motor M for rotating the polishing member 13 through a rotary shaft 14. The polishing member 13 comprises a first polishing portion 11a, a second polishing portion 11b, and a third polishing portion 11c, which are provided independent of one another, on the peripheral surfaces of which a first buff, a second buff, and a third buff are respectively adhered, as shown in FIGS. 2 and 3. The first polishing portion 11a is for polishing the peripheral side surface 1a of the chamfered portion 1 of the wafer W, and therefore, it has no grooves on the surface. The first polishing portion 11a polishes the peripheral side surface 1a of the wafer W by the flexibility of the first buff. On the periphery of the second polishing portion 11b, a peripheral groove is formed and the second buff is adhered on the inner surface in the groove, for polishing the beveled surfaces 1b and 1c of the chamfered portion 1 of the wafer W. The second buff in the groove has a depth larger than the ideal length of the chamfered portion 1 in a radial direction, in due consideration of variations of the radial length of the chamfered portion 1. The depth and the shape of the groove of the second buff are determined so that the second buff in the groove can mirror-polish about the beveled surfaces 1b and 1c, that is, so that the peak of contact pressure distribution between the second buff of the second polishing portion 11b and the chamfered portion 1 is on each of the beveled surface 1b and 1c. On the periphery of the third polishing portion 11c, a peripheral groove is formed and the third buff is adhered on the inner surface in the groove, for polishing the rounded edges 1d and 1e of the chamfered portion 1 of the wafer W. The depth and the shape of the groove of the third buff are determined so that the third buff in the groove can mirror-polish about the rounded edges 1d and 1e formed between the peripheral side surface 1a and each of the beveled surfaces 1b and 1c, that is, so that the peak of contact pressure distribution between the third buff of the third polishing portion 11c and the chamfered portion 1 is on each of the rounded edges 1d and 1e. The wafer holding device 12 comprises a suction disc 15 for holding the wafer W, which is communicated with a vacuum system (not shown), so that the wafer W can be held on the lower surface of the suction disc 15 by vacuum suction, a motor which is not shown, for rotating the suction disc 15 together with the wafer W through a shaft 16, a lifting device for lifting up and down the suction disc 15 with the wafer W to desired positions, and a pushing device which is not shown, for carrying the wafer W held on the suction disc 12 horizontally and pushing the wafer W against the polishing member 13. The main surface of the wafer W is approximately perpendicular to the rotation axis of the polishing device 11. Therefore, the suction disc 15 can rotate around the central axis thereof and can horizontally and vertically move relatively to the polishing device 11. Next, an embodiment of the method for mirror-polishing using the above described apparatus for mirror-polishing will be explained. As shown in FIG. 2, a wafer W is adhered to the lower surface of the suction disc 15 by vacuum suction and is rotated by the motor for the disc. The polishing member 13 is rotated on the rotary shaft 14 by the motor M. The height of the held wafer W is adjusted to correspond with that of the first polishing portion 11a of the polishing device 11 by the lifting device. The chamfered portion 1 of the wafer W is transferred to the first polishing portion 11a of the polishing device 11, as shown in FIG. 3, by using the pushing device. Then, the peripheral side surface 1a of the chamfered portion 1 of the wafer W comes into contact with and pushes against the first buff on the first polishing portion 11a, and mirror-polishing about the peripheral side surface 1a is carried out. Next, the wafer W is separated from the first polishing portion 11a by the pushing means and the height of the wafer W is adjusted to correspond with that of the second polishing portion 11b by the lifting device. The chamfered portion 1 of the wafer W is transferred to the second polishing portion by using the pushing device. The beveled surfaces 1b and 1c of the chamfered portion 1 of the wafer W come into contact with and push against the second buff on the inner surface of the second polishing portion 11b in the groove, and mirror-polishing about the beveled surfaces 1b and 1c is carried out. Then, the wafer W is separated from the second polishing portion by the pushing device and the height of the wafer W is adjusted to correspond with that of the third polishing portion 11c. The chamfered portion 1 of the wafer W is transferred to the third polishing portion 11c of the buff 11 by using the pushing device. The rounded edges 1d and 1e of the wafer W come into contact with and push against the third buff of the inner surface of the third polishing portion 11c in the groove, and mirror-polishing about the rounded edges 1d and 1e is carried out. In the method and the apparatus 10 for mirror-polishing having such a construction, mirror-polishing of the peripheral side surface 1a, the beveled surfaces 1b and 1c, and the rounded edges 1d and 1e, of the peripheral chamfered portion 1 of the wafer W, are carried out by using individual polishing portions 11a, 11b, and 11c which are separated to one another. The first, second, and third polishing portions 11a, 11b, and 11c are concentrated in mirror-polishing of the peripheral side surface 1a, the beveled surfaces 1b and 1c, and the rounded edges 1d and 1e, of the peripheral chamfered portion 1, respectively. Accordingly, mirror-polishing for the every portions of the peripheral chamfered portion 1 of the wafer W can be performed securely and quickly with a small variations of the required processing time for polishing. Although the present invention has been described in its preferred form with a certain degree of particularity, it should also be understood that the present invention is not limited to the preferred embodiment and that various changes and modifications may be made to the invention without departing from the spirit and scope thereof. In the above-described embodiment, mirror-polishing of the peripheral chamfered portion 1 of the wafer W was carried out for the peripheral side surface 1a, the beveled surfaces 1b and 1c, and the rounded edges 1d and 1e, in that order. Although the present invention requires to individually carry out at least a part of mirror-polishings of the peripheral side surface 1a, the beveled surfaces 1b and 1c, and the rounded edges 1d and 1e, the order is not limited. The change of order also enables a secure and quick mirror-polishing of the peripheral chamfered portion with a small variations of the required processing time for polishing, similar to the above-described embodiment. FIG. 4 shows another embodiment of the method for mirror-polishing of the present invention. In this embodiment, the polishing device 21 comprises a first polishing portion 21a and a second polishing portion 21b, which are provided independent of the other. On the peripheral surfaces of the first and second polishing portions 21a and 21b, a first buff and a second buff are respectively adhered. The first polishing portion 21a is for mirror-polishing the peripheral side surface 1a of the chamfered portion 1 of the wafer W, and therefore, it has no grooves on the surface, similar to the first polishing portion 11a in the first embodiment. On the periphery of the second polishing portion 21b, a peripheral groove is formed and the second buff is adhered on the inner surface in the groove, for mirror-polishing the beveled surfaces 1b and 1c and the rounded edges 1d and 1e of the chamfered portion 1 of the wafer W. The depth and the shape of the groove of the second buff are determined so that the second buff in the groove can mirror-polish about each of the beveled surface 1b and 1c and the rounded edges 1d and 1e, that is, so that the peak of contact pressure distribution between the second buff of the second polishing portion 21b and the chamfered portion 1 is on each of the beveled surface 1b and 1c and the rounded edges 1d and 1e. In the embodiment, first, mirror-polishing about the peripheral side surface 1a of the wafer W is carried out by using the first polishing portion 21a. Thereafter, mirror-polishing of the beveled surfaces 1b and 1c and the rounded edges 1d and 1e is carried out by using the second polishing portion 21b, in a manner similar to the first embodiment. According to the embodiment, it is possible to securely and quickly mirror-polish the every portion of the peripheral chamfered portion 1 of the wafer W with a small variations of the required processing time for polishing, in comparison with the conventional method. In order to see the effects, the following experiment was carried out. In the experiment, similar comparisons were made between the required time for obtaining a predetermined mirror-finished surface of the peripheral chamfered portion 1 of a wafer W by using the conventional polishing device 31 having only one polishing portion 31a, i.e., the so-called a form chamfering buff, as shown in FIG. 5, that of using the polishing device 21 having two polishing portions 21a and 21b according to the second embodiment of the present invention, as shown in FIG. 4, and that of use of the polishing device 11 according to the first embodiment, as shown in FIG. 3. As a result, the mirror-polishing by using the conventional polishing device 31 shown in FIG. 5 required about 12±9 min., and that of using the polishing device 21 of the second embodiment required about 5±2 min. On the other hand, according to use of the polishing device 11 of the first embodiment, in spite of having three steps, the entire surfaces of the peripheral chamfered portion 1 were mirror-polished for the total time of about 4±1 min.

Claims: A method of mirror-polishing a peripheral chamfered portion (1) of a semiconductor wafer (W) which comprises a peripheral side surface (1a), bevelled surfaces (1b, 1c) formed on front and back surfaces around the periphery of the wafer (W), and rounded edges (1d, 1e) formed between the peripheral side surface and each of the bevelled surfaces, comprising: a step of rotating the wafer (W) around its centre, and the steps of mirror-polishing the peripheral side surface (1a), the bevelled surfaces (1b, 1c), and the rounded edges (1d, 1e) by a polishing device, characterised in that the mirror-polishing of both the bevelled surfaces (1b,1c) is carried out simultaneously in one step, and the mirror-polishing of both the rounded edges (1d,1e) is carried out simultaneously, in another step and in that at least one of the mirror-polishing steps is performed independently of another. A method according to claim 1, wherein the steps of mirror-polishing the peripheral side surface (1a), the bevelled surfaces (1b, 1c) and the rounded edges (1d, 1e) are carried out individually by a polishing device. A method according to claim 2, wherein the steps of mirror-polishing of the peripheral side surface (1a), the bevelled surfaces (1b, 1c) and the rounded edges (1d, 1e) of the peripheral chamfered portion (1) are performed by bringing the peripheral side surface (1a), the bevelled surfaces (1b, 1c) and the rounded edges (1d, 1e) into contact with the first (11a), second (11b) and third (11c) polishing portions, which are provided on the polishing device (11) independent of one another. A method according to claim 3, wherein the first polishing portion comprises a first buff (11a) which contacts the peripheral side surface (1a) of the peripheral chamfered portion (1), the second polishing portion comprises a second buff (11b) which contacts the bevelled surfaces (1b, 1c), and the third polishing portion comprises a third buff (11c) which contacts the rounded edges (1d, 1e). An apparatus for mirror-polishing a peripheral chamfered portion (1) of a semiconductor wafer (W) which comprises a peripheral side surface (1a), bevelled surfaces (1b, 1c) formed on front and back surfaces around the periphery of the wafer (W), and rounded edges (1d, 1e) formed between the peripheral side surface and each of the bevelled surfaces, comprising a cylindrical rotary polishing device (11) which comprises: a first polishing portion (11a) having a first buff to contact the peripheral side surface (1a), a second polishing portion (11b) having a second buff to contact the bevelled surfaces (1b, 1c), and a third polishing portion (11c) having a third buff to contact the rounded edges (1d, 1e) formed between the peripheral side surface and each of the bevelled surfaces, characterised in that the first, second, and third polishing portions (11a, 11b, 11c) are provided on the peripheral surface of the apparatus independently of one another, in that the second buff contacts both the bevelled surfaces (1b,1c) simultaneously, and in that the third buff contacts both the rounded edges (1d,1e) simultaneously. An apparatus according to claim 5 or 6, further comprising a wafer holding device (12) for holding the wafer (W) and which can rotate around its central axis and can move horizontally and vertically relative to the polishing device (11). An apparatus according to claim 7, wherein the wafer holding device includes a suction disc (15) for holding the wafer (W) by vacuum suction.

Inventors: HASEGAWA FUMIHIKO, ICHIKAWA KOICHIRO, INADA YASUO, KURODA YASUYOSHI, OHTANI TATSUO, HASEGAWA, FUMIHIKO, ICHIKAWA, KOICHIRO, INADA, YASUO, KURODA, YASUYOSHI, OHTANI, TATSUO, HASEGAWA, FUMIHIKO, SHIN-ETSU HANDOTAI CO., LTD., ICHIKAWA, KOICHIRO, C/O FUJIKOSHI MACHINERY CORP., INADA, YASUO, C/O FUJIKOSHI MACHINERY CORP., KURODA, YASUYOSHI, SHIN-ETSU HANDOTAI CO., LTD., OHTANI, TATSUO, SHIN-ETSU HANDOTAI CO., LTD.
Applicants: FUJIKOSHI MACHINERY CORP, SHINETSU HANDOTAI KK, FUJIKOSHI MACHINERY CORPORATION, SHIN-ETSU HANDOTAI COMPANY LIMITED
Application year: 1995
Main classification: B24B9
IPC codes: H01L21, B24B9