JP2821408B2 - Semiconductor wafer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor wafer, and more particularly, to a large-diameter semiconductor wafer having device elements formed and a back surface ground.

[0002]

2. Description of the Related Art In the process of manufacturing a semiconductor device, device elements are formed on a flat surface of a semiconductor wafer (hereinafter simply referred to as a wafer), but the end face of the wafer limits the thickness of a resist film in a photolithography process. It has a rounded shape to reduce chipping and chipping of the end face.

In recent years, the diameter of wafers has been increased, and accordingly, the thickness of wafers has been increased to 725 μm for 8-inch wafers and 775 μm for 12-inch wafers. Since the increase in the diameter of the wafer inevitably increases the volume of the semiconductor chip, as shown in FIG. 2, the back surface 1B of the wafer 1 having a thickness T in which device elements are formed on the front surface 1A is ground. It has a thickness t of 250 to 300 μm and is sent to the next step.

[0004] However, the horizontal distance l of the edge portion 4 of the wafer 2 thus ground is equal to the wafer 2 after the grinding.
Is longer than the thickness t of the semiconductor device, and its tip 5 is thin and sharp, so that it comes into mechanical contact with the manufacturing equipment in the subsequent manufacturing process of the semiconductor device, and the edge portion 4 is chipped and adheres to the semiconductor chip. There is a drawback that the semiconductor device manufacturing yield is reduced by short-circuiting the wafer or causing cracks in the wafer 2 after grinding.

As a countermeasure for this, as shown in FIG. 3, a method of setting a round edge at a position where a roundness and a tapered shape remain on the outermost end surface 3A of the wafer 2 even after grinding the back surface is disclosed in, for example, JP-A-4-34931. Has been proposed. In FIG. 3, t is the thickness of the wafer 2 after grinding, and t ₁ is the thickness of the edge end surface.

[0006]

However, in the conventional semiconductor wafer described with reference to FIG. 3, since the outermost end face is made thin and sharp before grinding, the edge of the wafer is formed in a semiconductor element forming step before grinding. Part is missing,
It has been found that there is a new problem that the wafer itself is cracked.

An object of the present invention is to solve the above problems and to provide a semiconductor wafer capable of suppressing occurrence of chipping of a wafer edge portion and cracking of a wafer in processes before and after grinding.

[0008]

In the semiconductor wafer of the present invention, device elements are formed on a flat surface of a wafer having a rounded end surface, and the back surface of the wafer is ground to a specified thickness. In a semiconductor wafer, a horizontal distance from an edge of a flat surface of the wafer to a tip of an edge portion of the wafer after grinding is smaller than the specified thickness.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a wafer for explaining an embodiment of the present invention.

In FIG. 1, a wafer 1 having a thickness T has a rounded end face 3, and after a device element is formed on a flat surface 1A, the flat back surface 1B is ground to form a specified thickness. t, the flat wafer surfaces 1A, 1
The horizontal distance L from the end of B (points P and Q) to the tip 5 of the edge of the wafer 2 after grinding is set smaller than t. Hereinafter, a case where the arc of the end face 3 is an ellipse will be specifically described.

The thickness T of the wafer 1 is 775 μm, the thickness t of the wafer 2 after grinding is 250 μm, the u-axis connecting the ends P and Q of the flat wafer surface and the v-axis passing through the center of the thickness of the wafer 1. Is 0, and the intersection of the v-axis and the arc of the end face 3 is A. The ellipse including the arc of the end face 3 is expressed by the following equation (1).

U ² / (T / 2) ² + v ² / A ² = 1 (1) Next, the coordinates (v, u) of the edge tip 5 at this time are obtained. In equation (1), T = 775 μm and u = 387.5 μm−
Substituting 250 μm = 137.5 μm, v = 0.9
35A.

0.935A = 25 when the horizontal distance L to the edge tip 5 is equal to the thickness t of the wafer 2 after grinding.
A becomes 267 μm from 0 μm. In the present invention, from t, L
Smaller. For example, if L = 0.9t, A = 2
It becomes 41 μm. That is, the formula of the ellipse including the arc of the end face 3 is u ² /(387.5) ² + v ² / (241) ² =
Expressed as 1.

In order to form the wafer 1 having an end surface having an arc formed by such an elliptical trajectory, a blade for processing the wafer is formed with the profile of the end surface of the wafer, and the end surface of the wafer is processed while rotating the wafer. I just need.
When the wafer 1 is ground by this processing, a wafer having a horizontal distance L to the tip of the edge portion smaller than the thickness t of the ground wafer is obtained.

According to the wafer 1 configured as described above, the horizontal distance L from the edge of the flat wafer surface to the edge of the edge of the ground wafer can be made smaller than the thickness t of the ground wafer 2. However, unlike the conventional wafer, the edge portion is not thin and long, and the angle of the tip of the edge portion becomes close to a right angle and the sharpness disappears. For this reason, in all the manufacturing steps of the semiconductor device, chipping of the tip of the edge portion of the wafer and generation of cracks in the wafer itself were suppressed. Some small chipping that occurred before the end of the wafer grinding process occurred in about 30% of wafers in the past, but according to the present embodiment, it could be reduced to 10% or less.

In the above embodiment, the wafer 1
Is 775 μm, and the thickness t of the wafer after grinding is 2
Although the case where the thickness is set to 50 μm has been described, it is needless to say that these thicknesses can be appropriately changed.

[0017]

As described above, according to the present invention, the horizontal distance from the edge of the flat wafer surface to the tip of the edge of the wafer after grinding is made smaller than the thickness of the wafer after grinding. In the manufacturing process, there is an effect that occurrence of chipping of the wafer edge portion and cracking of the wafer can be suppressed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a wafer for describing an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a conventional wafer.

FIG. 3 is a cross-sectional view of another conventional wafer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wafer 1A Front surface 1B Back surface 2 Wafer after grinding 3 End face 3A Top end face 4 Edge part 5 Edge part tip

Claims (1)

(57) [Claims] 1. A semiconductor wafer in which device elements are formed on a flat surface of a wafer having a rounded end surface, and the back surface of the wafer is ground to a specified thickness. A semiconductor wafer wherein a horizontal distance from an edge to a tip of an edge portion of the wafer after grinding is smaller than the specified thickness.