SOI Undercut Cavity Etching for Faster 300 mm Fabrication
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Solution Overview
Problem
The existing method for creating undercuts in Silicon on Insulator (SOI) structures is time-consuming and requires specialized equipment, making it inefficient and costly to scale up to a 300mm platform.
Innovation Solution
A method combining bulk silicon dry etches and short wet etches, with alternating cycles to break and expand cavities, allowing for efficient creation of undercut cavities underneath the insulator layer without the need for additional processing equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a selective isotropic bulk silicon etch followed by a long wet etch is used to create UCUT, then the desired cavity dimensions are achieved, but the total process time increases to about 3 hours or more
Solution Approach 1:
The patent segments the UCUT formation process into multiple alternating dry etch and wet etch cycles. Each cycle consists of a dry etch step followed by a wet etch step, allowing the process to achieve the desired cavity dimensions through incremental progression rather than requiring a single long wet etch step.
Solution Approach 2:
The patent employs periodic alternating action between dry etching and wet etching. The dry etch steps create initial cavities and define geometry, while the wet etch steps expand the cavities isotropically. This periodic alternation continues for multiple cycles to achieve the target UCUT dimensions, significantly reducing total process time compared to a single prolonged wet etch.
2Manufacturing precision
If a dedicated wet etching bench is required for the wet etch process, then the UCUT can be created with desired dimensions, but specific processing equipment must be invested in
Solution Approach 1:
The patent makes the processing equipment universal by enabling both dry etching and wet etching to be performed in the same tool. The etching tool is configured with a reaction chamber that can accommodate wet etch chemistry, allowing a single piece of equipment to perform multiple functions (dry etching and wet etching) rather than requiring separate dedicated wet etching and dry etching benches.
Solution Approach 2:
The patent merges the wet etching and dry etching processes into a single integrated tool. The etching tool combines the capabilities of both wet and dry etching systems, allowing the UCUT formation process to be completed in one piece of equipment through alternating cycles of dry and wet etching, thereby eliminating the need for separate dedicated wet etching equipment.
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 significantly reduces process time and allows for scalable production of undercut cavities in the 300mm platform using existing tools, achieving desired dimensions efficiently.
Implementation Method 1
performing a first dry etch of the silicon substrate to create the one or more cavities underneath the insulator layer
Implementation Method 2
performing a first wet etch of the silicon substrate to expand the one or more cavities
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3(a)~3(b)
AI summary
The present disclosure relates to a process for creating an undercut (UCUT) in a Silicon on Insulator (SOI) structure, in particular, a process for a 300mm SOI platform. To this end, the disclosure provides a method for fabricating one or more cavities in a silicon substrate underneath an insulator layer of the SOI structure. The method comprises performing a first dry etch of the silicon substrate to create the one or more cavities, performing a first wet etch of the silicon substrate to expand the one or more cavities, performing a second dry etch of the silicon substrate to further expand the one or more cavities and to break silicon facets created by the first wet etch, and performing a second wet etch to further expand the one or more cavities.