A method of slicing a semiconductor wafer and an apparatus therefor

Abstract: The present invention aims at proposing a method of slicing a semiconductor wafer and an apparatus therefor which can manufacture a bowl-shaped wafer. When the blade displacement is detected with the sensor (32), the displacement value of the blade (14) to the outer peripheral edge of the ingot (18) is obtained by the control unit (26). The air pad (30) is moved under controlling the air pressure control device (36) by the control unit (26) to make the blade displacement at the outer peripheral edge zero. As a result of this, the displacement of the wafer at the outer peripheral edge becomes zero, so that a bowl-shaped wafer can be manufactured.

Description: The present invention relates to a method of slicing a semiconductor wafer and an apparatus therefor. From EP-A-0 456 223 there are known a method of slicing a semiconductor wafer and an apparatus therefor as set out in the respective preambles of independent claims 1 and 4. A blade tip portion of an inner peripheral cutting edge or an outer peripheral cutting edge is composed of fine diamond grains. The blade tip is abraded partially by use. A cutting curve in either direction is drawn according to this partial abrasion. For instance, when a cutting blade is curved upward by the abrasion, a shape of a wafer is curved more upwardly according to an increase in a cutting resistance as cutting progresses, so that the curving displacement of the upper side becomes the maximum because the cutting resistance is made maximum at the maximum cutting length. When the cutting is further progressed, the cutting resistance becomes small accordingly as a cutting length gradually becomes small, so that the curving displacement becomes also small gradually. The method of slicing referred to above has a problem in that a wafer is produced in a shape curved upwardly or downwardly. Conventionally, a curving control of the wafer is executed to eliminate the problem. That is, the blade displacement is detected with a sensor, and the curving control is performed in such a manner that the blade displacement at the position of this sensor becomes zero by moving the air pad. In another conventional curving control, an air pad is moved in a manner that the displacement of the center part at the cutting position of a semiconductor material becomes zero, and the semiconductor material is cut. However, the conventional method of slicing has a disadvantage in that a wafer is formed like a part of cylinder or a saddle as shown in Figs. 4 (A) and (B) because the air pad is controlled in such a manner that the blade displacement of a sensor position or a center position becomes zero. The wafer forming a part of cylinder and the saddle-shaped wafer are disadvantageous for the postprocessing of the wafer. A main object of the present invention is to provide a method of slicing a bowl-shaped semiconductor wafer and an apparatus therefor. According to the present invention there are provided a method of slicing a bowl-shaped semiconductor wafer and an apparatus therefor, as set out in the independent claims 1 and 4. According to this invention, the movement value of the air pad is determined in such a manner that the blade displacement at the circumferential edge of the wafer to be cut which edge is changeable during cutting becomes zero from the positional relationship between said sensor and said air pad, so that the displacement of the wafer to be cut at each cutting position of the semiconductor material can be adjusted to zero. Therefore, a bowl-shaped wafer can be manufactured. Preferred embodiments of the method are subjects of the subclaims. BRIEF DESCRIPTION OF THE DRAWING The exact nature of this invention, as well as other objects and advantages thereof, will be readily apparent from consideration of the following specification relating to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof and wherein: Fig. 1 is a schematic front view of a slicing machine according to the invention; Fig. 2 is a schematic plane view of a slicing machine according to the invention; Fig. 3 is an explanatory view of showing a partial displacement of an inner peripheral cutting edge; Figs. 4 (A) and (B) are explanatory views of a wafer manufactured by the conventional method of slicing; Fig. 5 is an explanatory view of a wafer manufactured by the method of slicing according to the invention; Fig. 6 is a contour-lined shape view of a wafer manufactured by the conventional method of slicing; Fig. 7 is a contour-lined shape view of a wafer manufactured by the method of slicing according to the invention; Fig. 8 is a control curve of rotational speed of a blade according to the invention; Fig. 9 is a control curve of a relationship between work delivery speed and cut-in value according to the invention; and, Fig. 10 is a control curve of a relationship between blade displacement at a position of a blade sensor and cut-in value according to the invention. DESCRIPTION OF THE PREFERRED EMBODIMENT Detailed description will hereunder be given of the preferred embodiment of a method of slicing a semiconductor wafer and an apparatus therefor according to the present invention with reference to the accompanying drawings. Referring to Fig. 1, a chuck body 12 is firmly secured to the upper end portion of a spindle 10, while the lower end portion of a spindle 10 is connected to a motor (which is not shown). The spindle 10 and the chuck body 12 can be rotated by means of the motor. The outer peripheral edge of a doughnut-shaped blade 14 is stretched up onto the chuck body 12. The blade 14 includes an inner peripheral cutting edge 16 along the inner peripheral cutting edge portion thereof. The inner peripheral cutting edge 16 is made up fine diamond grains and the like. The blade 14 is also arranged such that the tension of the outer peripheral edge thereof can be adjusted by a well known stretching mechanism (not shown) provided in the chuck body 12. The upper end portion of a semiconductor ingot 18 is secured fixedly to a work support base 21. The ingot 18 can be moved in a cutting/feeding direction (that is, a direction of X-X) with a cutting/feeding mechanism 22 and the work support base 21 can be moved in the work indexing direction (that is, a direction of Z-Z) with a work indexing mechanism 24. The cutting/feeding mechanism 22 and the work dividing mechanism 24 are driven by instruction signals from a control unit 26. Further, as shown in Figs. 1 and 2, a pair of air pads 30, 30 of a non-contact type and a pair of blade sensors 32, 32 are arranged on the upper surface of the blade 14. The displacement of the blade 14 is detected with the blade sensors 32, 32 and can be corrected with the air pads 30, 30. Further, the blade sensor 32, 32 are connected with the control unit 26. The control unit 26 controls a air pressure control device 36 to move the air pads 30, 30. By use of the slicing machined constructed in the above mentioned manner, a slicing method according to the present invention can be effected in the following manner. At first, the ingot 18 is moved in the direction of X aiming at the inner peripheral cutting edge 16, and then cutting is started. Generally, the relationship between the cutting resistance, the cutting length and the ingot delivery speed are that the cutting resistance increases in proportion as the cutting length becomes longer and as the ingot delivery speed becomes higher. Moreover, when the cutting resistance increases, it is in the nature that the displacement of the blade 14 becomes larger and the blade 14 becomes to curve easily. When the sensor 32 detects the displacement of the blade 14 as shown in Fig. 3, the air pad 30 is controlled in curve according to the curve (c) shown in Fig. 10, which indicates the control relationship between the displacement value and the cut-in value of the blade 14 at the position of the sensor 32 in such a manner that the displacement of the circumferential edge of the semiconductor material to be cut becomes zero from the relationship of the cutting position, the position of the sensor 32, the position of the air pad 30 and the blade displacement value which the sensor 32 detects. Incidentally, the curve (c) in Fig. 10 is described later. Here are the following three examples to control more accurately. Figs. 8-10 are described to explain these examples. First, a curve in Fig. 8 indicates the relationship between the blade rotation speed R and the cut-in value e, the maximum value of the cut-in value is 200mm. Here, the blade rotation speed R is expressed by the following formulas; R = B + (A - B) 100 2 (e - 100) 2 ( e ≦ 100) R = B + (C - B) 100 2 (e - 100) 2 (100< e ≦ 200) when e = cut-in value of workpiece (mm) e min = 0mm e max = 200mm A = blade rotation speed (rpm) (e = 0mm) B = blade rotation speed (rpm) (e = 100mm) C = blade rotation speed (rpm) (e = 100mm). Curves in Fig. 9 indicate the relationship between the work delivery speed and the cut-in value to make the displacement on the center line of the wafer an oval when the outer peripheral displacement of the wafer is controlled to be zero. A curve (a) indicates a case that the blade rotation speed is not controlled. A curve (b) indicates a case that the blade rotation speed is controlled. Moreover, curves Fig. 10 indicate the relationship between the blade displacement and the cut-in value at the position of the sensor when the outer peripheral displacement of the wafer is controlled to be zero. A curve (c) indicates a case that both the blade rotation speed and the work delivery speed are not controlled. A curve (d) indicates a case that the blade rotation speed is controlled but the work delivery speed is not controlled. A curve (e) indicates a case that the work delivery speed is controlled regardless whether the blade rotation speed is controlled or not. In the first example, the curving control is performed by the blade rotation speed control shown in Fig. 8, the work delivery speed control indicated by the curve (b) in Fig. 9 and the blade displacement control indicated by the curve (e) in Fig. 10. Next, in the second example, the curving control is performed by the work delivery speed control indicated by the curve (a) in Fig. 9 and the blade displacement control indicated by the curve (e) in Fig. 10. Further, in the third example, the curving control is performed by the blade rotation speed control shown in Fig. 8 and the blade displacement control indicated by the curve (d) in Fig.10. As a result of this, when the ingot 18 is cut at each cutting position under the curving control, the displacement of the circumferential edge of the inner peripheral cutting edge 16 to the ingot 18 becomes zero, so that a bowl-shaped wafer can be manufactured. In the above-mentioned embodiment, the displacement of the blade 14 is detected with a pair of sensors 32, 32 to perform the curving control. However, it is not limited to this. That is, the blade displacement of the center of the cutting position is detected with a eddy-current sensor provided at the center of the cutting position. Then, the displacement of the wafer circumferential edge may be found by the blade displacement. As has been described heretofore, in a method of slicing a semiconductor wafer and an apparatus therefor according to the invention, the cutting blade displacement value at the circumferential edge of the semiconductor material to be cut is obtained by the cutting blade displacement value detected with the sensor and the air pads control the displacement at the circumferential edge of the semiconductor wafer, so that a bowl-shaped wafer can be manufactured. It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the invention is to cover all modifications, alternate constructions and equivalents falling within the scope of the invention as expressed in the appended claims.

Claims: A method of slicing a semiconductor wafer, wherein a cutting edge (14) is mounted on a rotatable spindle (10), a semiconductor material (18) is pressed on the cutting edge (14), the cutting edge (14) and the semiconductor material (18) are moved one relative to the other in a manner causing them to come closer together, and the semiconductor material (18) is cut into thin pieces, said method comprising the steps of sensing an axial displacement of the cutting edge (14) by a sensor (32) and cutting the wafer while correcting the displacement by an air pad (30), charaterized in that for producing a bowl-shaped wafer said air pad (30) is controlled in such a manner that the displacement value of the cutting edge (14) at the circumferential edge of the wafer to be cut becomes zero from the positional relationship between said sensor (32) and said air pad (30) relative to the circumferential edge of the semiconductor material (18) to be cut, which edge is changeable during the cutting. The method of slicing a semiconductor wafer as set forth in claim 1, wherein said air pad (30) is controlled in such a manner that the displacement value of the cutting edge (14) at the circumferential edge of the wafer to be cut becomes zero by the rotational speed control of said cutting edge (14), the delivery speed control of said semiconductor material (18) and the displacement value control of said cutting edge (14) at the position of said sensor (32). The method of slicing a semiconductor wafer as set forth in claim 1, wherein said air pad (30) is controlled in such a manner that the displacement value of the cutting edge (14) at the circumferential edge of the wafer to be cut becomes zero by the rotational speed control of said cutting edge (14) and the displacement value control of said cutting edge (14) at the position of said sensor (32). An apparatus for slicing a semiconductor wafer, wherein a cutting edge (14) is mounted on a rotatable spindle (10), a semiconductor material (18) is pressed on the cutting edge (14), the cutting edge (14) and the semiconductor material (18) are moved to relatively one relative to the other in a manner causing them to come closer together and the semiconductor material (18) is cut into thin pieces, said apparatus comprising a sensor (32) for sensing an axial displacement of the cutting edge (14) and an air pad (30) for correcting the displacement, and means for establishing a control relationship between the axial displacement of the blade and a cut-in distance value of the blade relative to the semiconductor material (18), characterized in that said apparatus further comprises a control system for controlling said air pad (30) in such a manner that the displacement value of the cutting edge (14) at the circumferential edge of the wafer to be cut becomes zero from the positional relationship between said sensor (32) and said air pad (30) relative to the circumferential edge of the semiconductor material (18) to be cut, which edge is changeable during the cutting, based upon the control relationship established by said means for establishing, as a means for providing a bowl-shaped wafer.

Inventors: DOI TAKESHI, TSUKADA SHUICHI, DOI, TAKESHI, TSUKADA, SHUICHI
Applicants: TOKYO SEIMITSU CO LTD, TOKYO SEIMITSU CO.,LTD.
Application year: 1993
Main classification: B23D59
IPC codes: H01L21, B23D59, B28D5, B24B27