METHOD OF MAKING A WAFER HAVING AN ASYMMETRIC EDGE PROFILE
A wafer having an asymmetric edge profile is provided. The wafer has a disk-like body. The disc-like body has a first main surface, a second main surface parallel to the first main surface, and an edge region. The disk-like body has a central line defined between the first main surface and the second main surface, the edge region has an edge profile, and the edge profile is asymmetric with respect to the central line of the first main surface and the second main surface.
This divisional application claims the benefit of co-pending U.S. application Ser. No. 11/456,090, filed on Jul. 7, 2006 and included herein by reference.
BACKGROUND OF THE INVENTION1. Field of the Invention
The invention relates to a wafer having an asymmetric edge profile and a method of making the same, and more particularly, to a low stress wafer and a method of making the same.
2. Description of the Prior Art
Wafers are important bases of fabricating ultra-large scale integrated (ULSI) circuit components. With the development of crystal growth technologies, the diameters of wafers have increased from 25 millimeters in the early days of the technology to 300 millimeters (12 inches) at present. The fabricating process of the wafers includes the following main steps. First, a semiconductor liquid raw material, such as silicon, is prepared. Subsequently, a crystal pulling process is performed utilizing a seed to form a columnar ingot. Next, the ingot is cut into a plurality of disk-like wafers by slicing.
The wafers are stored in cassettes, and clipped by robots so as to transfer the wafers to each process unit. As a result, if the edge region of a wafer is perpendicular to the first main surface (front side) and the second surface (back side) of the wafer, the wafer may easily stick in the cassettes or be damaged by the robots' clipping. Furthermore, the perpendicular edge region of the wafer may easily crack due to the stress generated by temperature change in the following processes. Thus, the edge region of a wafer should be polished after the wafer is formed, so that the wafer includes an arc-shaped edge profile.
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Generally speaking, the thickness of the standard wafer 10 is changed according to the size of its diameter. For example, the thickness of the standard wafer 10 having a diameter of 8 inches is usually about 725 micrometers. With regard to the general semiconductor processes, the standard wafer 10 can prevent the aforementioned problems of cracking and damage. However, some processes, such as the micro-electromechanical system (MEMS) processes, use thinned wafers and the thicknesses of said wafers must be in the range of 50 to 250 micrometers. In consideration of these processes, the probability of damaging and cracking occurring to the standard wafer 10 is greatly increased. Please refer to
It is therefore an objective of the present invention to provide a wafer having an asymmetric edge profile, and a method of making the same, to reduce the probability of cracking to the wafer, and to increase the yield.
According to the present invention, a wafer having an asymmetric edge profile is provided. The above-mentioned wafer includes a disk-like body, and the disk-like body includes a first main surface, a second main surface parallel to the first main surface, and an edge region. The first main surface and the second main surface define a central line between them, and the edge region has an edge profile, the edge profile being asymmetric with respect to the central line of the first main surface and the second main surface.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
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Hence, the wafer 30 of the present invention has an asymmetric edge profile that consists of the first inclined surface S1, the arc-shaped surface S2, and the second inclined surface S3. As a result, an included angle between a tangential line to any point on the edge profile and the first main surface 34 or the second main surface 36 is always an obtuse angle, whether the wafer 30 is at its initial thickness or the wafer 30 is thinned for the following processes. This effectively decreases the stress, and the probability of cracking to the wafer 30 occurring. It should be noted that the asymmetric edge profile consisting of the first inclined surface S1 and the arc-shaped surface S2 is merely a preferred embodiment of the present invention, and the edge profile of the wafer 30 is not limited to this embodiment. For instance, the specification of the inclined surface or of the arc-shaped surface can be adjusted by an appropriate degree, the edge profile may merely consist of a single arc-shaped surface, or the edge profile can consist of a plurality of arc-shaped surfaces. Therefore, no matter what thickness the wafer 30 is during the processes, the wafer 30 has a comparatively low stress.
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In sum, because the wafer of the present invention has an asymmetric edge profile, the included angle between a tangential line to any point on the edge profile and the first main surface or the second main surface is always an obtuse angle, whether the wafer is at its initial thickness before any processes have been performed, or the wafer is thinned to another thickness during the processes. Thus, the present invention can effectively reduce the stress, reduce the probability of cracking, and prevent the wafer from sticking in the cassettes.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
Claims
1. A method of fabricating a wafer having an asymmetric edge profile comprising:
- providing a wafer, the wafer comprising a first main surface, a second main surface parallel to the first main surface, and an edge region perpendicular to the first main surface and the second main surface, wherein the first main surface and the second main surface define a central line between them;
- polishing the edge region of the wafer, so that the edge region has an edge profile asymmetric with respect to the central line of the first main surface and the second main surface;
- thinning the wafer from the second main surface until the wafer reaches a predetermined thickness, an included angle between a tangential line to any point on the edge profile and the first main surface or the second main surface being an obtuse angle according to the predetermined thickness.
2. The method of claim 1, wherein the predetermined thickness is in a range of 50 to 250 micrometers.
3. The method of claim 1, wherein the step of polishing the edge region of the wafer comprises:
- polishing the edge region by utilizing a predetermined radius of curvature; and
- utilizing a point which does not lie in the central line to be a center of curvature, so as to form the edge profile.
4. The method of claim 3 further comprising:
- polishing the edge region to make the edge profile comprise at least an inclined surface.
Type: Application
Filed: Sep 18, 2008
Publication Date: Jan 22, 2009
Inventor: Chih-Ping Kuo (Kao-Hsiung City)
Application Number: 12/212,653
International Classification: B24B 1/00 (20060101); B24B 9/00 (20060101);