Lift Pin Surface Roughness for Epitaxial Wafer Scratch Prevention
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Solution Overview
Problem
The existing epitaxial growth devices using SiC lift pins cause scratches on the back surface of silicon wafers due to the high hardness of the material, and also generate particles during the epitaxial growth process, leading to increased defects and contamination.
Innovation Solution
The use of lift pins made from materials with lower hardness than SiC, specifically glassy carbon, with varying surface roughness to prevent scratches and particle attachment, where the surface roughness of the lift pin's upper region is between 0.1 μm to 0.3 μm and the lower region is between 1 μm to 10 μm, to enhance slidability and reduce contact issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If SiC lift pins are used, then the lift pins have high hardness and wear resistance, but they cause scratches on the back surface of silicon wafers and generate particles during epitaxial growth
Solution Approach 1:
The patent changes the material parameter of the lift pin from high-hardness SiC to lower-hardness glassy carbon, which fundamentally alters the interaction between the lift pin and wafer surface. This parameter change reduces the hardness from approximately 25-30 GPa (SiC) to about 2-3 GPa (glassy carbon), eliminating the scratch-inducing effect while maintaining sufficient mechanical strength for wafer handling.
Solution Approach 2:
The patent employs glassy carbon, which is a composite material with unique properties combining the benefits of carbon-based materials (low hardness, chemical inertness) with amorphous structure characteristics. This composite material approach allows the lift pin to have both low hardness (reducing scratches) and adequate mechanical properties (maintaining structural integrity during operation).
2Stability of the object's composition
If SiC lift pins are used, then the lift pins maintain structural integrity, but they generate particles during the epitaxial growth process
Solution Approach 1:
The patent changes the material composition parameter from SiC to glassy carbon, which has different tribological and thermal properties. Glassy carbon exhibits lower particle generation during high-temperature epitaxial growth processes while maintaining sufficient structural stability through its amorphous carbon network structure and cross-linked bonding.
Solution Approach 2:
Glassy carbon inherently provides a chemically inert environment during epitaxial growth, reducing chemical reactions that could generate particles. The material's resistance to oxidation and chemical attack at high temperatures creates a cleaner process environment, minimizing particle contamination on the wafer surface.
3Object-affected harmful factors
If the lift pin surface is made smooth, then particle attachment is reduced, but slidability within the through-hole deteriorates
Solution Approach 1:
The patent applies different surface quality characteristics to different regions of the lift pin structure. The portion contacting the wafer is maintained with low roughness (Ra ≤ 0.03 μm) to minimize particle attachment, while the portion passing through the supporting arm through-hole has higher roughness to ensure adequate slidability and prevent sticking. This local differentiation of surface properties resolves the contradiction between smoothness and slidability.
Data Source
AI summary
An epitaxial growth device includes; a chamber; a susceptor; a supporting shaft, having a main column located coaxially with the center of the susceptor and supporting arms; and a lift pin, at least the surface layer region of the lift pin is made of a material having a hardness lower than the susceptor, the lift pin has a straight trunk part upper region configured to pass through the through-hole of the susceptor and having a surface roughness of from not less than 0.1 μm to not more than 0.3 μm, and the lift pin has a straight trunk part lower region configured to pass through the through-hole of the supporting arm and having a surface roughness of from not less than 1 μm to not more than 10 μm.