Semiconductor Wafer Grinding with Variable Abrasive Pellet Sizes
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Solution Overview
Problem
The challenge in grinding large silicon wafers of 450 mm diameter is achieving the same level of flatness as smaller wafers while maintaining production efficiency, as conventional methods result in peripheral sagging and uneven grinding due to differences in peripheral speed and abrasive grain distribution.
Innovation Solution
A semiconductor wafer grinding method and device that positions the wafers on a carrier with a circle radius ratio of 1.33 to 2.0, using rotating surface plates with fixed abrasive grains where pellets in the center and peripheral portions are larger than those in the intermediate portion, arranged in a grid-like fashion to evenly distribute pressure and compensate for speed differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional planetary gear-type grinding devices are used for large silicon wafers, then productivity is improved by simultaneous grinding of multiple wafers, but outer circumference sagging occurs resulting in poor flatness
Solution Approach 1:
The invention applies different pellet sizes in different regions of the surface plate. Larger pellets are used in the outer circumference region where sagging occurs, while smaller pellets are used in the center region. This local differentiation of grinding characteristics compensates for the speed difference between center and periphery, preventing peripheral sagging while maintaining overall flatness during simultaneous multi-wafer grinding.
2Ease of manufacture
If uniform abrasive grains are used across the surface plate, then manufacturing simplicity is maintained, but uneven grinding occurs due to differences in peripheral speed between center and outer circumference
Solution Approach 1:
The surface plate is divided into multiple regions (center, intermediate, outer circumference) with each region having different pellet sizes. This creates locally optimized grinding conditions that match the varying peripheral speeds at different radii, ensuring uniform material removal across the entire wafer surface despite the speed gradient.
Solution Approach 2:
The invention changes the physical parameter of abrasive grain size as a function of radial position on the surface plate. By systematically varying pellet size from center to periphery, the grinding pressure and material removal rate are adjusted to compensate for the increasing peripheral speed, achieving uniform flatness across the wafer.
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
This approach allows for high-flatness grinding of large silicon wafers by ensuring uniform grinding across the wafer surface, preventing protrusion at the center and maintaining production efficiency by adjusting pellet sizes and arrangements to match varying circumferential speeds.
Implementation Method 1
simultaneously grinding both surfaces of multiple semiconductor wafers being ground by rotating the multiple semiconductor wafers between a pair of upper and lower rotating surface plates
Data Source
AI summary
A method of grinding semiconductor wafers including simultaneously grinding both surfaces of multiple semiconductor wafers by rotating the wafers between a pair of upper and lower rotating surface plates in a state where the wafers are held on a carrier so that centers of the wafers are positioned on a circumference of a single circle, wherein a ratio of an area of a circle passing through the centers of the wafers to an area of one of the wafers is greater than or equal to 1.33 but less than 2.0; surfaces of the fixed abrasive grains comprised in the surface plates are comprised of pellets disposed in a grid-like fashion, with the pellets provided in a center portion and pellets provided in a peripheral portion being larger in size than the pellets provided in an intermediate portion.