Apparatus for chamfering notch of wafer

Abstract: A notch of a semiconductor wafer is chamfered very accurately and efficiently by the use of an apparatus which is provided with a rotary disklike grindstone, a wafer retaining mechanism for retaining the wafer, and a drive mechanism for relatively moving the grindstone and wafer, and characterized by the fact that the grindstone comprises an elastic matrix material and a particulate abrasive buried or dispersed fast in the matric material. The drive mechanism comprises a first drive mechanism capable of rotating the wafer within a predetermined range of angle around the central axis thereof thereby enabling the surface of the notch of the wafer subjected to grinding to be continuously positioned relative to the grinding surface of the grindstone, a second drive mechanism capable of relatively moving the grindstone and wafer toward or away from each other, and a third drive mechanism capable of relatively moving the grindstone and wafer forward and backward in the direction of thickness of the wafer.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION: This invention relates to an apparatus for chamfering a semiconductor wafer and more particularly to an apparatus for chamfering a notch of the wafer by the use of an elastic grindstone. DESCRIPTION OF THE PRIOR ART: On account of effective application of photolithography, it has been customary for wafers such as semiconductor wafers to have an orientation flat (hereinafter referred to as "OF") formed thereon by grinding off to leave a short linear cut in part of the periphery of a wafer thereby facilitating correct positioning of the wafer on an exposure device. The formation of the OF, however, inevitably results in removal of a large portion of the wafer. Particularly in the production of wafers of a large diameter, the cumulative amount of portions wasted by this removal is so large as to impair the yield of products conspicuously. The fact that this impaired yield prevents expensive semiconductor wafers from being efficiently utilized has posed a problem. In the circumstances, the practice of forming a notch substantially in the shape of the letter V or substantially in the shape of an arc to the periphery of a given wafer has come to prevail for the purpose of efficiently utilizing produced wafers. Particularly the V-shaped notches have been finding extensive utility by reason of their outstanding accuracy of positioning. Since the wafers are destined to be conveyed a number of times on production lines as in the process for manufacture of devices, their peripheries are possibly subject to chippings on colliding with parts of devices used in the manufacturing process and the produced devices consequently suffer from degradation of characteristic properties. It has been customary, therefore, for the wafers to have their peripheral parts chamfered. SUMMARY OF THE INVENTION The wafers furnished with a notch as described above, however, have come to entail the drawback that the notch thereof is subject to chippings when the wafers are positioned in the process of device production by aligning the notch to a pin of rigid material. Since sharp edges of the wafers are not easily removed by machining, the sharp edges conspicuously increase occurrence of dust and the effort to preclude infliction of chippings fails. This fact has posed a problem too serious to be ignored. One solution using an abrasive wheel having an edge which is shaped like a notch is described in EP-A- 0 360 939. This invention, initiated in the light of this problem, has as an object the provision of an apparatus for chamfering a notch of a wafer, which apparatus is capable of easily and accurately chamfering even edges such as of the notch and enabling the work of chamfering the notch to be carried out in high efficiency. Moreover, this apparatus enjoys simplicity of construction. To accomplish the object described above, this invention contemplates an apparatus which is provided with a rotary disklike grindstone, a wafer retaining mechanism for retaining a wafer, and a drive mechanism for relatively moving the grindstone and wafer, and characterized by the fact that the grindstone comprises an elastic matrix material and a particulate abrasive buried or dispersed fast in the matrix material. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective explanatory diagram of an apparatus for chamfering a notch of a wafer as an embodiment of this invention. Fig. 2 is an explanatory diagram of the work of chamfering performed on the notch in the direction of thickness of the wafer. Fig. 3 is an explanatory diagram illustrating the elastic matrix part of a grindstone in a state deformed under the pressure of the wafer. Fig. 4 is an explanatory diagram of a wafer which has undergone the work of chamfering. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the apparatus of this invention for chamfering the notch of a wafer, the work of chamfering the notch of the wafer is accomplished by relatively moving the grindstone and wafer by dint of the operation of the drive mechanism. In this case, the grindstone has the matrix thereof formed of an elastic material. Since the elasticity of the matrix is utilized in causing the particulate abrasive to be pressed against the site of chamfering, the survival of any sharpness on the chamfered part can be easily precluded. Since the grindstone has the matrix thereof formed of an elastic material, the cross section of the circumferential edge of the grindstone has a shape roughly resembling the letter V having a radius in the bottom part thereof. When the angle formed between the oblique lines of the letter V is slightly larger than the corresponding angle of the plan figure of the notch and the radius at the leading terminal of the notch in the direction of center of the wafer and the grindstone, during the grinding operation, is kept applied to the notch subjected to the grinding with the center of rotation of the grindstone set at a position higher than the position of the wafer surface, the chamfering of the notch can be completed by simply moving the grindstone only slightly in the vertical direction. By suitably adjusting the softness of the matrix of the grindstone, the formation of a concave surface in the chamfered part due to the contour of the grindstone is precluded and the chamfering of-the notch is ideally effected to give rise to a smoothly curved rather outwardly protruding surface. In this case, in the first, second, and third drive mechanism recited in claim 3, particularly the first and second drive mechanism are used for accurately controlling and adjusting the position of the grindstone prior to the chamfering work. The apparatus for chamfering the notch of a wafer according to this invention will be described below with reference to the accompanying drawings which illustrate one embodiment of this invention. In Fig. 1, the reference numeral 10 stands for an apparatus for chamfering the notch as one embodiment of this invention. This notch chamfering apparatus 10 comprises a wafer retaining mechanism 14 capable of retaining a wafer 12 in a prescribed posture, a first drive mechanism 15 capable of rotating the wafer 12 within a prescribed range of angle around (in the direction of the arrow ϑ ) an axis perpendicular to the main surface of the wafer 12, a rotary drive mechanism 18 capable of setting a disklike grindstone 16 in such a manner that the surface of the grindstone 16 intersects (perpendicularly in this embodiment) the surface of the wafer 12, a second drive mechanism 20 provided in the wafer retaining mechanism 14 for producing a relative motion of the grindstone 16 and wafer 12 toward or away from each other in the direction of radius of the grindstone 16 (in the direction of arrow X), and a third drive mechanism 22 provided in the rotary drive mechanism 18 for producing a relative motion of the grindstone 16 and wafer 12 toward or away from each other in the direction of wall thickness of the wafer 12 (in the direction of the arrow Z). The wafer retaining mechanism 14 is provided with a base stand 28 and the base stand 28 is provided with a cylindrical part 30. A rotary stand 32 is disposed on the cylindrical part 30. In the upper end surface of this rotary stand 32, a plurality of suction holes 34 communicating with a vacuum pump not shown in the diagram and serving to attract the wafer 12 by suction are formed. The first drive mechanism 15 is provided with a pulse motor 36 which is a servomotor in type. A feed screw 38 is connected to the pulse motor 36 and the feed screw 38 is coaxially interlocked with the rotary stand 32. The second drive mechanism 20 is provided with a pulse motor 40. A feed screw 42 which is connected to the rotary shaft of the pulse motor 40 is interlocked with the wafer retaining mechanism 14. The rotary drive mechanism 18 is provided with an electric motor 44 and the grindstone 16 is rotatably fixed to a rotary shaft 46 of the electric motor 44. With this rotary drive mechanism 18 is interlocked a feed screw 50 which is connected to a pulse motor 48 forming a component of the third drive mechanism 22. The grindstone 16 comprises a matrix part 52 formed of an elastic material such as, for example, a synthetic resin type material like urethane rubber and a particulate abrasive 54 buried in a comparatively soft peripheral surface portion of the matrix part 52 destined to serve as a grinding surface. The grindstone 16 may be otherwise formed by dispersing the particulate abrasive in the synthetic resin material and shaping the resultant dispersion and the peripheral part of this grindstone may be used for the grinding aimed at by this invention. Now, the operation of the notch chamfering apparatus 10 constructed as set forth above will be described below. First, the disklike wafer 12 is set in place on the rotary stand 32 which is one of the components of the wafer retaining mechanism 14. By the action of the vacuum pump not shown in the diagram, the wafer 12 is attracted through the suction holes 34 to the rotary stand 32 by suction. After a notch 24 of the wafer 12 and the grindstone 16 have been disposed at prescribed positions necessary for perpendicular intersection of their respective surfaces, the first drive mechanism 15 to third drive mechanism 22 are selectively or synchronously driven and controlled. As a result, by the action of the pulse motor 36 and through the medium of the feed screw 38, the rotary stand 32 is rotated at a prescribed speed in the direction of the arrow ϑ . At the same time, the feed screw 42 is rotated by the pulse motor 40 to move the wafer retaining mechanism 14 forward and backward in the direction of the arrow X. In the meanwhile, the grindstone 16 is rotated through the medium of the rotary shaft 46 by the driving action of the electric motor 44. Consequently, the wafer 12 is rotated in the direction of the arrow ϑ and the chamfering work is performed within a relatively small width on the notch 24 of the wafer 12 in the direction of circumference of the notch 24 to form the innermost of the angular part 24a while the wafer 12 and the grindstone 16 in rotation are moved toward or away from each other (Fig. 2). While the chamfering work performed on the angular part 24a in the direction of circumference of the notch 24 is continued, the grindstone 16 is moved along the angular part 24a at a comparatively low speed in the direction of the arrow as illustrated in Fig. 2. To be specific, when a signal to drive is input into the pulse motor 48 which is one of the components of the third drive mechanism 22, the feed screw 50 is rotated through the medium of this pulse motor 48 in the given direction and the rotary drive mechanism 18 interlocked with this feed drive 50 is slowly moved in the direction of the arrow Z₁. Synchronously with this motion, the pulse motor 40 is set into motion to move the grindstone 16 and the wafer 12 relatively in the direction of the arrow X₁ and position the grindstone 16 relative to the angular part 24a. After the chamfering work to be performed, within the first width as described above, in the direction of circumference of the notch 24 has been completed, the chamfering work is repeated on a neighboring width of the angular part 24a in the same direction as the first try to cover the full thickness of the angular part 24a. Then, a circumferential surface part 24b and an angular part 24c in reverse to the angular part 24a of the wafer 12 are similarly subjected to a continuous shaping work on a plurality of working rounds as spaced by predetermined widths of interval. Here, the grindstone 16 is moved in the direction of the arrow Z₂ while the outer circumferential surface part 24b perpendicular to the main surface of the wafer 12 is undergoing the chamfering work, whereas the grindstone 16 and the wafer 12 are relatively moved respectively in the direction of the arrows X₂ and Z₃ while the angular part 24c is undergoing the chamfering work. This procedure brings about the effect of enabling the chamfering work of the wafer 12 in the circumferential direction and in the direction of the wafer thickness to be continuously and efficiently carried out. In this case, since the grindstone 16 of this embodiment has the matrix part 52 thereof formed of an elastic material, the chamfering work of the wafer 12 can be carried out with this grindstone 16 kept pressed against the wafer 12 with predetermined pressure. Specifically, when the grindstone 16 is pressed against the wafer 12 as illustrated in Fig. 3, the comparatively soft circumferential surface part of the matrix part 52 which is one of the component of this grindstone 16 is deformed to be pressed against the wafer 12. Consequently, the abrasive particles 54 buried in the circumferential surface part come into generous contact with the wafer 12 and grind the wafer 12, particularly the corner parts A to D of the surface of the wafer 12 subjected to grinding (as indicated by a broken line in Fig. 4), and give rise to radiuses, one in each of the corner parts A to D (as indicated by a solid line in Fig. 4). This fact gives rise to the effect of obviating the necessity for complicate control and allowing easy formation of radiuses with a simple construction without inducing infliction of cracks and chippings on the corner parts A to D. Particularly, the fact that the wafer 12 and the grindstone 16 are so disposed that the respective surfaces thereof intersect perpendicularly gives birth to the advantage of enabling the chamfering work of high accuracy to be performed, by dint of the grinding surface of the grindstone 16, on the surface of the notch 24 which is appreciably small as compared with the size of the wafer 12. This embodiment has been described as representing a case in which the chamfering work of the whole of the notch 24 is effected by moving the grindstone 16 in the direction of thickness of the wafer 12 (in the direction of the arrow Z) while continuing the chamfering work in the circumferential direction of the notch 24. Optionally, this procedure may be reversed by moving the grindstone 16 and the wafer 12 in the circumferential direction of the wafer 12 while continuing the chamfering work on the notch 24 in the direction of thickness thereof. To be specific, the chamfering work is performed on the notch 24 in part of the direction of thickness by synchronously driving and controlling the second drive mechanism 20 and the third drive mechanism 22 thereby moving the wafer 12 in the direction of the arrow X and moving the grindstone 16 in the direction of the arrow Z and, at the same time, the wafer 12 is slowly rotated around the central axis thereof (in the direction of the arrow ϑ ) by rotating the pulse motor 36 at a comparatively low speed. As a result, the grindstone 16 is enabled to perform the chamfering work continuously on the notch 24 in the circumferential direction while chamfering the notch 24 in the direction of the wafer thickness. The apparatus of this invention for chamfering the notch of the wafer produces the following effects. During the chamfering work performed on the notch of the wafer through relative motion of the grindstone and wafer by the operation of the driving mechanisms, the survival of any sharpness on the chamfered part is easily precluded because the matrix part forming one component of the grindstone is formed of an elastic material and the particulate abrasive is pressed against the site of chamfering by dint of the elasticity of this elastic material. By the simple construction resorting to the use of this elastic grindstone, the chamfering work of the notch of a small size in the circumferential direction and/or in the direction of the wafer thickness can be carried out very accurately and efficiently.

Claims: An apparatus (10) for chamfering a notch (24) of a wafer (12), provided with a rotary disklike grindstone (16), a wafer retaining mechanism (14) for retaining the wafer (12), and a drive mechanism (15, 20, 22) for relatively moving said grindstone (16) and wafer (12), and characterized by the fact that said grindstone (16) comprises an elastic matrix material (52) and a particulate abrasive (54) buried or dispersed fast in said matrix material (52). An apparatus according to claim 1, wherein said wafer retaining mechanism (14) is capable of disposing said wafer (12) in such a manner that the surface of said wafer (12) intersects the surface of said grindstone (16). An apparatus according to claim 1, wherein said drive mechanism comprises a first drive mechanism (15) capable of rotating said wafer (12) within a predetermined range of angle (ϑ) around the central axis thereof thereby enabling the surface of the notch (24) of said wafer (12) subjected to grinding to be continuously positioned relative to the grinding surface of said grindstone (16), a second drive mechanism (20) capable of relatively moving said grindstone (16) and wafer (12) toward or away from each other, and a third drive mechanism (22) capable of relatively moving said grindstone (16) and wafer (12) forward and backward in the direction of thickness of said wafer (12). An apparatus acccording to claim 1, wherein said matrix material (52) is a synthetic resin type material.

Inventors: HOSOKAWA KAORU, HOSOKAWA, KAORU
Applicants: SHINETSU HANDOTAI KK, SHIN-ETSU HANDOTAI COMPANY LIMITED
Application year: 1992
Main classification: H01L21
IPC codes: H01L21, B24B9