Susceptor Ring Projections for Epitaxial Wafer Edge Uniformity
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Solution Overview
Problem
Existing methods for depositing epitaxial layers on wafers with orientation notches result in periodic variations in thickness and reduced flatness in the edge region, as the growth rates vary with crystal orientation, and previous solutions either require changing the susceptor or wafer shape.
Innovation Solution
A device with a rotatable susceptor support shaft and susceptor support arms holds a susceptor ring with azimuthal projections that reduce deposition along high growth rate crystal orientations, ensuring improved thickness uniformity by positioning the orientation notch aligning with these projections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If thermal radiation is used to heat the wafer to deposition temperature, then the deposition process can be carried out, but periodic variations in thickness occur in the edge region due to different growth rates linked to crystal orientation
Solution Approach 1:
The patent applies local quality by introducing azimuthal projections at specific locations on the susceptor ring to selectively influence deposition in high-growth-rate regions. These projections are positioned to correspond with crystal orientations that exhibit increased deposition rates, creating localized modifications that counteract the periodic thickness variations without altering the entire susceptor or wafer structure.
Solution Approach 2:
The azimuthal projections act as an intermediary element between the thermal radiation source and the wafer surface. By positioning these projections between the radiation and the high-growth-rate regions, they modify the local deposition conditions and reduce the harmful effects of orientation-dependent growth rate variations.
2Manufacturing precision
If the susceptor structure is changed to homogenize thickness in the edge region, then thickness uniformity improves, but device complexity increases
Solution Approach 1:
Rather than redesigning the entire susceptor structure, the patent segments the solution by adding only the necessary azimuthal projections to the susceptor ring. This segmentation approach maintains the existing susceptor design while introducing minimal, targeted modifications only where needed to address the thickness uniformity issue.
3Manufacturing precision
If the wafer shape is changed to reduce periodic variations, then thickness uniformity improves, but manufacturing complexity and cost increase
Solution Approach 1:
The patent extracts the problem-solving function from the wafer itself and transfers it to the susceptor. Instead of modifying the wafer shape, the solution is taken out and implemented as azimuthal projections on the susceptor ring, thereby maintaining standard wafer geometry while still achieving thickness uniformity improvement.
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 enhances the uniformity of epitaxial layer thickness and flatness in the edge region without altering the susceptor or wafer shape, effectively mitigating periodic variations in thickness.
Implementation Method 1
The susceptor and a wafer rested on top is heated by means of thermal radiation by lamp arrays arranged above and below the domes
Implementation Method 2
the deposition of an epitaxial layer on the front side of a wafer is usually done by means of CVD (chemical vapour deposition) in a CVD reactor
Data Source
AI summary
Variations in wafer thickness due to non-uniform CVD depositions at angular positions corresponding to crystallographic orientation of the wafer are reduced by providing a ring below the susceptor having inward projections at azimuthal positions which reduce radiant heat impinging upon the wafer at positions of increased deposition.