Wafer Grinding Method for Crystal Orientation Control
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Solution Overview
Problem
Existing wafer grinding methods often result in chips with low die strength due to saw marks extending in easily breakable directions, related to crystal orientation, and can cause wafer chipping during grinding.
Innovation Solution
A two-step grinding method where the first step reduces wafer thickness by rotating a chuck table and grinding ring through the center, followed by a second step that positions the wafer to avoid saw marks in weak die strength directions, ensuring continuous contact and smooth grinding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the wafer is ground by rotating the chuck table and feeding the grinding wheel through the center, then the wafer can be efficiently ground to obtain predetermined thickness, but saw marks are formed extending radially from center to outer circumference, causing some chips to have remarkably low die strength
Solution Approach 1:
The grinding process is divided into two distinct steps: a first grinding step that removes the majority of material efficiently, and a second grinding step that performs precise finishing to eliminate saw marks. This segmentation allows each step to be optimized for its specific function, resolving the contradiction between productivity and reliability.
Solution Approach 2:
The first grinding step performs preliminary material removal to achieve near-final thickness, preparing the wafer for the second grinding step. This preliminary action enables the second step to focus solely on eliminating saw marks and achieving the final precise thickness, thereby ensuring high die strength without sacrificing overall efficiency.
2Ease of manufacture
If the outer circumferential surface of the wafer comes into impactive contact with the grinding wheel, then grinding can be performed, but chipping of the wafer may occur
Solution Approach 1:
The first grinding step performs preliminary material removal, reducing the wafer thickness to near-final dimensions. This preliminary action allows the second grinding step to use lighter, more controlled feeding that prevents impactive contact and chipping at the outer circumference.
Solution Approach 2:
The grinding parameters are changed between the two steps: the first step uses higher feeding rates for efficient material removal, while the second step uses lower feeding rates and precise control to eliminate saw marks without causing chipping. This parameter change resolves the contradiction between ease of manufacture and manufacturing precision.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Prevents the generation of low die strength chips and reduces the risk of wafer chipping while maintaining grinding efficiency by controlling saw mark direction and ensuring consistent grinding contact.
Implementation Method 1
grinding means having an annular grinding wheel for grinding the upper surface (back side) of the wafer held on the chuck table
Data Source
AI summary
A grinding method for a wafer having a mark indicating the crystal orientation. The grinding method includes a first grinding step for grinding the upper surface of the wafer by rotating a chuck table holding the wafer thereon, rotating a grinding ring, positioning the grinding ring so that the grinding ring is passed through the center of the wafer, and feeding the grinding ring in a direction perpendicular to the chuck table; a wafer positioning step for positioning the upper surface of an outer circumferential portion of the wafer directly below the locus of rotation of the grinding ring; and a second grinding step for grinding the upper surface of the wafer by first stopping the rotation of the chuck table so that the mark indicating the crystal orientation of the wafer held on the chuck table is pointed in a predetermined direction, next feeding the grinding ring in the direction perpendicular to the chuck table, and next relatively moving the chuck table and the grinding ring in parallel.