Wafer Boat Contact Geometry for Low-Stress Furnace Annealing
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Solution Overview
Problem
Conventional semiconductor wafer boats fail to adequately reduce local gravitational and thermal stresses on larger diameter wafers during high-temperature annealing, leading to slip and plastic deformation, which can result in production issues such as photolithography overlay failures and yield losses.
Innovation Solution
The wafer boat design features a vertical rod with radially extending fingers, each with an angled contact protuberance that is raised and arranged in a rotationally symmetric pattern to distribute the weight of the wafer evenly, reducing stress and slip, and optionally includes a pin and gimbal to adjust for uneven loading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional wafer boats with three or more rods and laterally extending fingers are used, then the structure is simple and easy to manufacture, but larger diameter wafers experience excessive local gravitational and thermal stress leading to slip and plastic deformation
Solution Approach 1:
The patent applies local quality by creating a contact protuberance with a specific geometric configuration (angled at approximately 45 degrees relative to the finger axis) at the precise location where wafer contact occurs. This localized geometric modification concentrates support forces optimally to reduce stress on larger diameter wafers without requiring complex changes to the entire wafer boat structure.
Solution Approach 2:
The invention introduces a new dimensional aspect by angling the contact protuberance relative to the finger axis, creating a three-dimensional contact geometry rather than a simple planar finger-wafer interface. This angular configuration in the third dimension optimizes force distribution to prevent slip while maintaining structural simplicity.
2Reliability
If support rings are used to provide greater surface area for supporting larger diameter wafers, then wafer stability improves, but the time for loading and unloading of semiconductor wafers increases
Solution Approach 1:
The patent applies segmentation by dividing the support function into discrete contact protuberances positioned at specific locations on the fingers, rather than using a continuous support ring. This segmented approach provides adequate support stability while allowing faster wafer placement and removal compared to the constraint of a full support ring structure.
3Reliability
If the contact protuberance is angled relative to the finger axis in a rotationally symmetric pattern, then stress distribution improves and slip is reduced, but the manufacturing precision requirements increase
Solution Approach 1:
The patent employs asymmetry by angling the contact protuberance at approximately 45 degrees relative to the finger axis, creating an asymmetric contact geometry that optimizes stress distribution. The rotationally symmetric arrangement of multiple such asymmetric protuberances around the wafer provides uniform overall support while each individual protuberance benefits from the asymmetric angular configuration.
Data Source
AI summary
A wafer boat for supporting a plurality of semiconductor wafers in a furnace is disclosed. The wafer boat includes a set of fingers each having a contact protuberance which contacts and supports a semiconducting wafer. The contact protuberances may be arranged in a rotationally symmetric pattern about the wafer boat.