Semiconductor silicon wafer and manufacturing method thereof

Abstract: A semiconductor silicon wafer (1) having bevelled circumferential edges (1a, 1b) in which the angles of bevelling (ϑ₃, ϑ₄) are different. The edges are thus less likely to be chipped.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a semiconductor silicon wafer used to manufacture a semiconductor integrated circuit (IC) (i.e.semiconductor silicon wafer for IC). Description of the Related Art Figure 3 shows a semiconductor silicon wafer for IC having symmetrical beveled portions 21a and 21b formed on the front and back surfaces thereof. The beveled portions 21a and 21b of the semiconductor silicon wafer 21 are arranged as follows. Assuming that the beveled portion 21a on the front surface has a beveled width w 1 and a beveled depth d 1 , and the beveled portion 21b on the back surface thereof has a beveled width w 2 and a beveled depth d 2 , w 1 = w 2 , and d 1 = d 2 , and the angle  1 between the inclining surface of the beveled portion 21a and the main surface on the front surface side [ 1 = arc tan(d 1 /w 1 )] is equal to the angle  2 between the inclining surface of the beveled ported 21b and the main surface on the back surface side [ 2 - arc tan(d 2 /w 2 )]. Note that, in this case, the beveled width w 1 of the beveled portion 21a of the front surface and the beveled angle  1 of the front surface are set to such values that do not cause crown along the wafer edge when photoresist is applied or an epitaxial layer is formed later on the front surface. Nevertheless, the following problems arise in the above technology. As described above, according to the above semiconductor silicon wafer 21, the beveled width w 1 of the front beveled portion 21a is set to a width equal to or larger than a prescribed value and the front beveled angle 1 is set to so that crown is not formed in the application of photoresist or the subsequent formation of an epitaxial layer later. Along with the above consideration, the equations w 1 = w 2 and d 1 = d 2 are observed and the beveling therefore is symmetrically effected on the front and back surfaces, and thus the beveling of the back surface gives an adverse effect to chipping free due to too much beveling applied, aside from the above-mentioned effect of the beveling of the front surface. More specifically, when  1 has a small value, e.g., 20 o or less, the width of the remained outer circumference of the wafer is narrowed, in other words, the outer circumferential edge of the wafer has a sharp wedge-shaped cross section. As a result, a problem arises in that the semiconductor silicon wafer is liable to be chipped off in the following processes. Reference is made to Brieger et al , IEEE Transactions on Electron Devices, vol. ED-31, no. 6, June 1984, p.733-738, US-A-4 630 093 and JP-A-5 424 571 as disclosures of wafers having asymmetric bevelled edges, and to FR-A-2 531 108 as a disclosure of symmetric Chamfering of the periphery of a semiconductor wafer. SUMMARY OF THE INVENTION Taking the above into consideration, it is an object of the present invention to provide a semiconductor silicon wafer and manufacturing method thereof capable of effectively preventing the silicon wafer from being chipped off and to avoid crown formation at the front surface of the wafer. This object is met by the wafer defined in claim which can be made by a process as defined in claim 4. Other objects and novel advantages of the present invention will be apparent from the following description and accompanying drawings. Since the angle between the inclining surface of the beveled portion and the main surface on the back surface side is selected larger than that of the beveled portion on the front surface side to make the front and back beveled portions unsymmetrical, the front beveled portion and the back beveled portion are independently arranged so that the former can sufficiently prevent the occurrence of crown and the latter can prevent the semiconductor silicon wafer from being chipped off. The beveled portions formed on the front and back surface sides have the same beveled width, and thus when the front and back beveled portions are simultaneously ground by the grindstone having the grinding surface which will conform with the circumferential edges of the semiconductor silicon wafer after it is finished, the peripheral corners of the front and back surfaces are simultaneously applied against the grinding surface of the grindstone, and the semiconductor silicon wafer is ground and finished at both the peripheral edges. As a result, applied force on one of the surfaces being ground is always supported by that on the other surface being ground, whereby the occurrence of undesirable strain due to grinding and the chip-off of the semiconductor silicon wafer can be prevented. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram showing the circumferential edges and the vicinity thereof of an embodiment of a semiconductor silicon wafer according to the present invention; Figure 2 is a diagram showing a semiconductor silicon wafer and the vicinity of the grinding surface of a grindstone used to grind the semconiductor silicon wafer; and Figure 3 is a diagram showing the circumferential portion and the vicinity thereof of an embodiment of a conventional semiconductor silicon wafer. DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a semiconductor silicon wafer according to the present invention will be described below with reference to drawings. Figure 1 shows the semiconductor silicon wafer of the embodiment. In the figure, numeral 1 designates the semiconductor silicon wafer, and beveled portions 1a and 1b are formed around the circumferential edges of the silicon wafer 1. The semiconductor silicon wafer 1 can be, for example, a semiconductor silicon wafer for IC having the beveled portions 1a and 1b formed unsymmetrically and used for forming a semiconductor integrated circuit. More specifically, the semiconductor silicon wafer 1 of the embodiment is such that the beveled width w 3 of the beveled portion 1a on the front surface side is selected equal to the beveled width w 4 of the beveled portion 1b on the back surface side, and the beveled angle  4 of the back surface [ 4 = arc tan(d 4 /w 4 )] is larger than the beveled angle  3 of the front surface [ 3 = arc tan(d 3 /w 3 )]. That is, the beveled depth d 4 of the back surface is larger than the beveled depth d 3 of the front surface. Further, the outermost circumferential edges of the wafer at the beveled portions 1a and 1b are rounded the radius of which curvature are shown R 1 and R 2 , respectively. These R 1 and R 2 may be shaped simultaneously when the beveled portions are machined, or may be formed by etching after the beveled portions have been machined. The front beveled width w 3 and the beveled angle  3 [ = arc tan(d 3 /w 3 )] are set to such values that do not cause crown in the application of photoresist and the following formation of an epitaxial layer. In addition, the back beveled depth d 4 is set to the value which can prevent the semiconductor silicon wafer from being chipped off or to a value larger than that of the front one. The values of w 3 , d 3 , w 4 and d 4 are, for example, set such that when the thickness T of the semiconductor silicon wafer 1 is ⊘.6 mm, w 3 3⊘⊘ µm, d 3 is 6⊘ µm, w 4 is 3⊘⊘ µm, d 4 is 31⊘ µm, R 1 is 2⊘⊘ µm, and R 2 is 4⊘⊘ µm. Next, a method of manufacturing the above semiconductor silicon wafer 1 will be described. First, an ingot of a silicon monocrystal is cut into round slices to provide a semiconductor silicon wafer 11 having a prescribed depth (numeral 11 is used to discriminate this wafer before the beveling from the semiconductor silicon wafer 1 to which the beveled portions 1a and 1b have already been formed). Next, the beveled portions 1a and 1b are formed using a grindstone 2 shown in Figure 2. To describe here the grinding surfaces 2a, 2b and 2c of the rotary grindstone 2 about an axis parallel with the perpendicular on the main surface of a wafer to be beveled shown in Figure 2, the configuration of the grinding surfaces 2a, 2b, and 2c of the grindstone 2 is in conformity with the predetermined configuration of the circumferential edges of the semiconductor silicon wafer 1 according to the invention. More specifically, the configuration of the grinding surface 2a, 2b and 2c of the grindstone 2 is such that the circumferential edges of the semiconductor silicon wafer 1 according to the invention conforms therewith. When the above semiconductor silicon wafer 11 is ground using this grindstone 2, the wafer 11 is gradually moved in the direction approaching the rotation axis the grindstone 2, while it is rotated in the direction opposite to that of the grindstone 2, whereby the beveled portions 1a and 1b are formed along the circumferential edges of the semiconductor silicon wafer 11. The following effects can be obtained by the semiconductor silicon wafer 1 of the above embodiment and the manufacturing method thereof. For the above semiconductor silicon wafer 1, since the angle  4 between inclining surface of the back beveled portion 1b and the main surface on the back surface side (the beveling angle of the back surface) is larger than the angle  3 between the inclining surface of the beveled portion 1a and the main surface on the front surface side (the angle of the front surface), and the beveled portions 1a and 1b of the front and back surfaces are made unsymmetrical, the front beveled portion 1a and the back beveled portion 1b can be differently shaped so that the former can sufficiently prevent the occurrence of crown and the latter can prevent the semiconductor silicon wafer 1 from being chipped off. More specifically, with respect to the above semiconductor silicon wafer 1, the effect of the back beveled portion thereof is more increased than that of a conventional wafer in preventing from being chipped off in the following process. Further, the beveled portions 1a and 1b formed on the front and back surface sides have the same widths w 3 and w 4 , and thus when the beveled portions 1a and 1b of the front and back surface sides are simultaneously formed using the grindstone having the grinding surfaces 2a, 2b, and 2c which will conform with the desired circumferential edges of the semiconductor silicon wafer 1 after it is finished, the corners of the front and back surfaces are simultaneously applied against the grinding surfaces 2a, and 2c, whereby the grinding operation thereof is simultaneously started to finish. As a result, while the beveled portions 1a and 1b are ground, pressure on one of the surfaces being ground is always supported by that on the other surface being ground, whereby the occurrence of undesirable strain due to grinding and thus the chip-off of the semiconductor silicon wafer can be prevented. Further, according to the above manufacturing method, since the beveled portions 1a and 1b of the front and back surfaces are simultaneously formed by the grinder 2 having the grinding surfaces 2a, 2b, and 2c which will conform with the circumferential edges of the semiconductor silicon wafer 1 after it is finished, the peripheral corners of the front and back surfaces can be simultaneously applied against the grinding surfaces 2a and 2c of the grindstone 2, and further the grinding operation of the semiconductor silicon wafer 1 is simultaneously started and finished. As a result, the occurrence of undesirable strain due to grinding and thus the chip-off of the semiconductor silicon wafer can be prevented.

Claims: A semiconductor silicon wafer (1) having a front surface and a back surface, the circumferential edge of each surface having been bevelled to form a bevelled portion (1a,1b) inclined at an acute angle ( 3 , 4 ) below its respective surface, wherein the widths (W 3 ,W 4 ) of the bevelled portions in a direction parallel to the front and back surfaces are equal, the angle ( 3 ) of bevelling at the front surface is less than 20° and the angle ( 4 ) at the back surface is substantially larger than the angle at the front surface, the widths and angles being selected to prevent crown formation at the front surface and chipping at the back surface, and wherein at the outer periphery of the wafer the ends of the bevelled portions are separated by a thickness of at least one-third of the thickness (T) of the wafer. A wafer according to claim 1, wherein the angle ( 4 ) of bevelling at the back surface is more than 30°. A wafer according to claim 2, wherein at the outer periphery of the wafer the ends of the bevelled portions are separated by a thickness of one-half of the thickness of the wafer. A method of manufacturing a bevelled wafer (1) according to any preceding claim, comprising simultaneously forming a bevelled portion on both the front and the back surface of a corresponding unbevelled wafer (11), by using a grindstone (2) whose grinding surface (2a,2b and 2c) has a configuration complementary to that of the bevelled wafer.

Inventors: OGINO NOBUYOSHI, OGINO, NOBUYOSHI, OGINO, NOBUYOSHI, C/O SHIN-ETSU HANDOTAI CO., LTD.
Applicants: SHINETSU HANDOTAI KK, SHIN-ETSU HANDOTAI COMPANY LIMITED
Application year: 1990
Main classification: H01L21
IPC codes: H01L29, H01L21