JPH06114745A - Grinding wheel for grinding semiconductor wafer - Google Patents

Abstract

PURPOSE:To prevent geometric distortion of chamfering shape of a wafer by forming a grinding surface into a shape of previously adding the amount locally worn by grinding the semiconductor wafer. CONSTITUTION:A wafer chamfering shape of tapered parts 2b, 2c of a grinding wheel 2 is set first to initial shapes 3 such as coming into contact with one value, that is, small side value of permissible tolerance. The shape is set so as to obtain the final grinding wheel shape 5 such as coming into contact with the other value, that is, large side value of the permissible tolerance via an objective shape 4 according to increasing a number of times of polishing a wafer. That is, the initial shape 3 of the grinding wheel 2 is formed into a shape of previously adding a grinding wheel wearing amount different in each position. When polished by this grinding wheel 2, a grinding amount is increased in accordance with approaching an end part of the wafer, accordingly to increase also a grinding wheel wearing amount. The shape arrives at the final shape 5 of permissible limit via the target shape 4 with a number of times of grinding. This condition is a limit of use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grindstone for grinding a semiconductor wafer.

[0002]

2. Description of the Related Art In the process of grinding a semiconductor wafer (hereinafter, simply referred to as a wafer), the chamfered shape of the wafer has a round shape and a tapered shape, and a copying method is generally used as a grinding method. When the tapered shape is ground by the copying method, as shown in FIG. 6, when the side end 1a of the wafer 1 is ground, the cylindrical portion 2 of the grindstone 2 is used.
In the case of grinding the taper parts 1a and 1c with a, and the taper parts 2b and 2c of the grindstone 2, a method of grinding is known (for example, Japanese Patent Publication No. 57-10568).
Precision processing technology for crystal materials for electronics (Science Forum, published in January 1985, P.228, P.231-23
See 2) etc.). At this time, the tapered portions 2b, 2c of the grindstone 2
Is generally given the same angle as the taper angle of the finished shape of the wafer 1.

[0003]

However, as described above, when the taper portions 2b and 2c of the grindstone 2 are at the same angle as the taper angle of the finished shape of the wafer 1, the grinding becomes closer to the bottom of the grindstone 2. As a result, the grinding wheel itself wears as it gets closer to the bottom, and as a result, the tapered portions 2b and 2c are deformed as the number of grindings increases, and the chamfered shape of the wafer 1 greatly differs from the target. was there.

An object of the present invention is to provide a grindstone for grinding a semiconductor wafer, which solves the above problems of the prior art.

[0005]

DISCLOSURE OF THE INVENTION The present invention is a grinding wheel used for grinding a semiconductor wafer, and the grinding surface of the grinding wheel has a shape in which an amount of local wear due to grinding of the semiconductor wafer is added in advance. A grinding stone for grinding a semiconductor wafer.

[0006]

[Operation] The present invention has been made by focusing on the tolerance of the chamfered shape of the wafer in order to solve the above problems, and it is said that the wear amount of each grinding surface of the grindstone is proportional to the grinding amount of the wafer. Based on the premise, the wafer surface shape that copied the shape of the grindstone before and after the wafer surface grinding was investigated and examined, and this was confirmed.

That is, as shown in FIG. 1, the chamfered shape of the wafer in the taper portions 2b and 2c of the grindstone 2 is initially set to an initial shape 3 so as to come into contact with one of the tolerances.
After that, the target shape 4 is formed in the process of increasing the number of times of grinding the wafer, and the final grinding wheel shape 5 is formed so that the number of times of grinding is further increased and the wafer is in contact with the other value of the tolerance. .

More specifically, as for the initial shape 3 of the grindstone 2, a normal grindstone shape is manufactured so as to match the target shape of the wafer 1, whereas a different grindstone wear amount is added in advance for each position. It is to have a shape. When the wafer 1 is ground by using the grindstone 2 having this shape, the grinding amount is larger as the end portion of the wafer 1 is closer, and thus the grindstone wear amount is also larger. As a result, the grinding wheel shape approaches the target shape 4 as the number of grinding times increases. In subsequent use, it will wear out like a normal whetstone,
The final shape 5 is full of the allowable limit, and its life is exhausted. Therefore, when the grindstone having the shape according to the present invention is used, the life of the grindstone becomes longer than that of the normal shape.

Here, the reason why the portion to which the grindstone wear amount is added is limited to the tapered portions 2b and 2c will be described. First,
Consider the shape of the cylindrical part of the grindstone. Now, as shown in FIG. 2, the radius is L (the distance from the center to the cylindrical portion 2a).
When the side end surface of the wafer 1 having the radius R and the thickness D is grinded by d using the grindstone 2 in which the width of the cylindrical portion 2a is d _n , the grinding amount S per unit area by the cylindrical portion 2a is S.
₁ can be expressed as _{S 1 = 2π · R · d} · D / (2π · L · d n) ──── (1).

Therefore, in the grindstone 2, R; 75 mm, d;
0.5 mm, D; 0.7 mm, L; 100 mm, d n; When 5 mm, grinding amount S ₁ obtained in the above (1) becomes 0.05 mm. That is, the side end surface of the wafer 1 is evenly ground by the cylindrical portion 2a of the grindstone 2 having the width d _n , but the grinding amount S ₁ per unit area is very small at 0.05 mm,
Therefore, the wear of the cylindrical portion 2a is negligible.

Next, the shape of the tapered portion of the grindstone will be examined. As shown in FIG. 3, the wafer 1 has its side edge 1
When the taper is ground from a to the position of x _{1 in} the width direction to y ₁ in the thickness direction to form the taper parts 1b and 1c, the unit of the taper parts 2b and 2c of the grindstone 2 is The grinding amount S ₂ of S is expressed as S ₂ = 2π · R · y ₁ / (2π · L) ───── (2), and assuming that the maximum value of y ₁ is 0.25 mm, S
₂ = 0.19 mm, which is about four times the grinding amount S ₁ per unit area of the cylindrical portion 2a. Therefore, it suffices to pay attention to the grinding at the tapered portions 2b and 2c.

The method of calculating the amount of wear of the grindstone will be specifically described below. The target shape at the tapered portions 2b and 2c of the grindstone 2 is set as an initial shape, for example, x and y coordinates are taken as shown in FIG. 4, and the grindstone shape after grinding n times is y = f _n ( When x) ──── (3), 1 batch of the grinding wheel wear amount after n times F _{n is, F n = k {f n} (x 1) -f n (x)} ──── (4 ). Here, k is a grindstone wear amount per unit area per unit grinding amount, and is an empirical numerical value obtained from past grinding results.

Therefore, the whetstone shape f _N (x) after N times of grinding
Is given by equation (5) below.

[0014]

[Equation 1]

Here, k varies depending on the specifications of the grindstone, the object to be ground, the grinding conditions, etc., but from past experience, k = 8.5 ×
If 10 ⁻⁶ (mm ⁻² ) is adopted, f ₀ (x) can be approximated as follows. f ₀ (x) = tan 11 ° x + 8.5 × 10 ^-6 × 10000 × tan 11 ° x +0.3 × 8.5 × 10 ^-6 × 10000 × tan 11 ° = 1.085 tan 11 ° x + 0.005 ≈ tan 11.9 ° x + 0.005 ≈ tan 12 ° x Therefore, it can be seen that a chamfering angle of about 12 ° is appropriate.

[0016]

[Example] A grinding wheel having a taper angle of 12 ° was manufactured by trial with a chamfering angle of 11 ° as a target shape. FIG. 5 shows the results of examining the change in the wafer finishing angle with the increase in the number of grindings using this grindstone. Here, when the allowable range of the shape was set to be 10 ° to 12 ° (11 ° ± 1 °) in chamfering angle, it could be used up to 27,000 times. In addition,
Since the life of the conventional example is usually 15000 times, the example of the present invention
The life can be extended by 80%.

[0017]

As described above, according to the present invention,
Since the initial shape is created by locally adding an amount equivalent to grinding wear locally to the part of the wheel where wear is large, the target shape is achieved when the number of grinding operations is increased, and further grinding progresses to an allowable limit shape. It is possible to use up to and to extend the life of the grindstone. Since the amount of wear of the grindstone is calculated mathematically, it can be applied not only to the tapered shape but also to any target shape.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a configuration of a grindstone of the present invention.

FIG. 2 is a diagram showing a state in which a wafer is ground by the grindstone of the present invention.

FIG. 3 is an end view of a wafer.

FIG. 4 is a diagram showing coordinates that mathematically represent a grindstone shape.

FIG. 5 is a characteristic diagram showing an embodiment of a grindstone of the present invention.

FIG. 6 is a diagram illustrating a configuration of a conventional grindstone.

[Explanation of symbols]

 1 Wafer 1b, 1c Tapered part 2 Whetstone 2b, 2c Tapered part 3 Initial shape 4 Target shape 5 Final whetstone shape

Claims (1)

[Claims] 1. A grinding grindstone used for grinding a semiconductor wafer, wherein a grinding surface of the grindstone has a shape in which an amount of local wear due to grinding of the semiconductor wafer is added in advance. Grindstone.