Free-Standing Ceramic Interposer Sheet for Semiconductor Grain Control
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Solution Overview
Problem
Existing methods for producing semiconductor bodies, such as solar cell wafers, face challenges in achieving large grain sizes and clean separation from the forming surface due to rapid nucleation and adhesion issues during the solidification process from molten semiconductor materials.
Innovation Solution
The use of a free-standing, thin, flexible, and porous ceramic interposer sheet is introduced between the forming surface and the molten semiconductor material to suppress grain nucleation, control heat flow, and facilitate clean separation by providing a controlled interface that allows for larger grain growth and independent thermal expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If direct contact between mold sheet and molten semiconductor material is used, then heat transfer efficiency is improved, but grain nucleation increases and grain size decreases
Solution Approach 1:
A free-standing interposer sheet made of ceramic material (such as alumina, silica, or silicon carbide) is introduced between the mold sheet and the molten semiconductor material. This interposer sheet acts as a mediator that reduces excessive grain nucleation while allowing controlled heat transfer. The interposer sheet has specific properties including thickness of 1-50 micrometers, porosity of 10-50%, and thermal conductivity that can be adjusted to optimize both heat transfer and grain growth control.
2Ease of operation
If mold sheet is used for forming semiconductor body, then semiconductor body can be released from melt, but adhesion between solidified body and forming surface occurs
Solution Approach 1:
The interposer sheet serves as an intermediary layer between the mold sheet and the solidifying semiconductor material. This intermediate ceramic layer prevents direct adhesion between the solidified semiconductor body and the forming surface of the mold sheet, enabling clean release. The interposer sheet maintains sufficient thermal contact for heat extraction while providing a non-stick interface due to its ceramic material properties.
Solution Approach 2:
The interposer sheet is designed with controlled porosity (10-50%) which allows for gas permeability and reduces density. This porous structure prevents strong adhesion between the solidified semiconductor and the forming surface while maintaining adequate thermal contact for solidification. The porous ceramic structure creates a physical barrier that reduces contact area and adhesion forces.
3Use of energy by moving object
If thin interposer sheet is used, then heat flow control is improved, but sheet stability decreases
Solution Approach 1:
The interposer sheet is designed as a thin (1-50 micrometers), flexible ceramic film that can conform to the mold sheet surface while maintaining structural integrity. The flexibility allows the thin sheet to maintain stable contact with the molten semiconductor material during the forming process, ensuring consistent heat flow control. The thin film structure provides sufficient thermal resistance for heat flow control while the flexibility compensates for potential deformation.
Solution Approach 2:
The interposer sheet is made of ceramic materials (alumina, silica, silicon carbide) that combine multiple desirable properties: thermal resistance for heat flow control, mechanical strength for stability, and chemical inertness for compatibility with semiconductor materials. The composite nature of these ceramics provides both the thin-film flexibility needed for heat control and the structural stability required for reliable operation.
4Productivity
If rapid solidification is used, then productivity is improved, but grain size decreases and dislocations increase
Solution Approach 1:
The interposer sheet mediates the solidification process by providing controlled heat extraction. It allows rapid solidification for productivity while simultaneously controlling grain nucleation to maintain large grain sizes. The ceramic material's thermal properties enable faster heat removal than direct mold contact, achieving rapid solidification without excessive nucleation that would occur with direct mold sheet contact.
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 results in semiconductor bodies with significantly increased grain sizes and clean release from the forming surface, minimizing dislocations and stress, while ensuring reproducibility and reliability across multiple formations.
Implementation Method 1
control heat flow from the melt, which controls the timing of solidification of the semiconductor body
Implementation Method 2
The composition of the interposer sheet helps to suppress grain nucleation, leading to relatively large grain sizes
Implementation Method 3
providing a controlled interface that allows for larger grain growth and independent thermal expansion
Implementation Method 4
Vacuum suction is applied at port 7
Implementation Method 5
The interposer sheet is free-standing, very thin, flexible, porous and able to withstand the chemical and thermal environment
Data Source
AI summary
An interposer sheet can be used for making semiconductor bodies, such as of silicon, such as for solar cell use. It is free-standing, very thin, flexible, porous and able to withstand the chemical and thermal environment of molten semiconductor without degradation. It is typically of a ceramic material, such as silica, silicon nitride, silicon oxynitride, silicon oxycarbide, silicon carbide, silicon carbonitride, silicon oxycarbonitride and others. It is provided between a forming surface of a mold sheet, and the molten material from which a semiconductor body will be formed. It may be secured to the forming surface or deposited upon the melt. The interposer sheet suppresses grain nucleation, and limits heat flow from the melt. It promotes separation of the semiconductor body from the forming surface. It can be fabricated before its use. Because free-standing and not adhered to the forming surface, problems of mismatch of CTE are minimized. The interposer sheet and semiconductor body are free to expand and contract relatively independently of the forming surface.