SiC Free-Standing Substrate Warpage Reduction via Recessed Etching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge is to manufacture SiC free-standing substrates with minimal warpage, as thick SiC films on Si substrates experience warpage due to differences in physical properties like lattice constants and thermal expansion coefficients between Si and SiC, making it difficult to produce large-area substrates with reduced warpage.
Innovation Solution
A method involving forming a SiC film on a Si substrate, creating a recessed part, and then removing part of the Si substrate using wet etching with a mask layer, while moving the Si substrate and SiC film relative to the etching liquid to minimize warpage and mechanical stress on the SiC film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a thick SiC film is formed on a Si substrate to ensure mechanical strength, then the mechanical strength of the substrate is improved, but warpage is generated in the SiC film due to the difference between physical properties (lattice constant and thermal expansion coefficient) between Si and SiC
Solution Approach 1:
The Si substrate is divided into a remaining peripheral portion and a removed central portion. By selectively removing only the central part of the Si substrate while leaving the peripheral portion intact, the SiC film is supported at the edges which prevents warpage while maintaining mechanical strength. This segmentation approach allows the thick SiC film to be supported where needed without the warpage-inducing constraints elsewhere.
2Strength
If a thick SiC film is formed on a Si substrate, then the mechanical strength is improved, but it becomes difficult to produce large-area substrates with reduced warpage
Solution Approach 1:
Different regions of the substrate are given different properties: the peripheral region retains Si substrate support for structural integrity, while the central region is freed from the Si substrate to eliminate warpage. This local differentiation allows large-area substrates to be produced with uniform quality, as each region is optimized for its specific function.
3Ease of manufacture
If the Si substrate is removed by wet etching, then the SiC free-standing substrate is obtained, but mechanical stress is applied to the SiC film during etching which may cause damage
Solution Approach 1:
A recessed part is formed in the Si substrate before the wet etching process. This preliminary action creates a cavity that will accommodate the SiC film during etching, preventing mechanical stress and damage. The recessed part is prepared in advance so that when the Si substrate is removed, the SiC film already has space to move freely without experiencing damaging stresses.
Solution Approach 2:
The recessed part formed in the Si substrate serves as a cushioning space before the actual substrate removal. This pre-prepared cavity protects the SiC film from mechanical stress during the wet etching process by providing room for the film to expand and move without constraint, thereby preventing damage before it can occur.
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 effectively reduces warpage in SiC free-standing substrates by managing mechanical stress and preventing damage during etching, allowing for the production of substrates with improved mechanical strength and reduced defects.
Implementation Method 1
at least a part of another of the principal surfaces of the Si substrate is removed by wet etching, in the step of removing a part of the Si substrate, and the Si substrate and the SiC film are relatively moved with respect to liquid chemical used for the wet etching
Data Source
Figure 1
Figure 2(a)~2(c)
Figure 3
AI summary
A method for manufacturing a substrate with less warpage includes a step of forming SiC film 121 on a surface of Si substrate 11, a step of removing bottom surface RG2 which is at least a part of the Si substrate 11 contacting with the SiC film 121, and a step of forming another SiC film on a surface of SiC film 121 after the step of removing the bottom surface RG2.