Wafer Holder Pre-Biasing for Flat Coating of Thin Wafers
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Solution Overview
Problem
Thin wafers undergoing coating processes experience deformation (sagging) due to compressive stress, leading to varying coating thickness and performance inconsistencies across the wafer, resulting in reduced yield and increased rejection rates.
Innovation Solution
A wafer holder apparatus with a jig structure and spring structure that includes angled surfaces and a widened compression surface to minimize deformation by pre-biasing the wafer against the coating-induced deformation, maintaining flatness and optimizing the coating process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a wafer is held during coating process, then the wafer can be coated with material layers, but the wafer experiences deformation (sagging) due to compressive stress from the holder
Solution Approach 1:
The holder applies a preliminary counter-bending force to the wafer before coating, creating an initial deformation that opposes the expected sagging. This pre-applied force counteracts the compressive stress that will occur during coating, preventing net deformation and maintaining wafer flatness throughout the process.
Solution Approach 2:
The wafer is pre-positioned and pre-loaded onto the holder with specific positioning features (angled surfaces, positioning pins) that establish the correct initial geometry and stress state before the coating process begins, ensuring the wafer starts in an optimized configuration.
2Manufacturing precision
If the wafer is clamped with a wide press ring to prevent deformation, then wafer flatness is maintained, but the contact area increases causing more deformation
Solution Approach 1:
The holder applies clamping force locally at specific regions of the wafer rather than uniformly across the entire edge. The press ring contacts the wafer at discrete locations with positioning pins and angled surfaces, concentrating the holding function at critical points while minimizing overall contact area and associated compressive stress.
Solution Approach 2:
The continuous press ring is effectively segmented into multiple discrete contact points through the use of positioning pins and angled surfaces that engage with specific features on the wafer. This segmentation allows the holder to secure the wafer firmly at key locations while maintaining large gaps between contact points, reducing total compressed area.
3Manufacturing precision
If the wafer is held firmly to prevent movement during coating, then coating uniformity is achieved, but yield is reduced due to deformation-related failures
Solution Approach 1:
The holder pre-applies a counter-bending moment to the wafer that opposes the coating-induced sagging. This preliminary anti-action ensures that as material is deposited and compressive stress develops, the wafer remains substantially flat throughout the coating process, preventing deformation-related defects that would otherwise reduce yield.
Solution Approach 2:
The holder design incorporates adjustable parameters including the magnitude of pre-applied force, the angle of contact surfaces, and the position of clamping points. These parameters can be optimized for different wafer sizes, materials, and coating processes to achieve the best balance between holding firmness and minimizing deformation, thereby maximizing yield.
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
The solution increases yield by reducing deformation-related failures and improves the uniformity of coating thickness, enhancing the performance of components formed from the wafer.
Implementation Method 1
a spring structure to compress an end of the wafer against the first angled surface
Implementation Method 2
compress an end of the wafer against the press ring such that at least 3 mm of width of the wafer is in contact with the press ring
Data Source
AI summary
In some implementations, a wafer holder apparatus includes a jig structure to receive a wafer, wherein the jig structure includes a first angled surface with respect to a nominal coating plane; and a spring structure to compress an end of the wafer against the first angled surface, wherein the spring structure includes: a spring; and a compression surface attached to the spring, wherein the compression surface includes a second angled surface matched to the first angled surface.