MEMS Fabrication Using Handle Substrate Support
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Solution Overview
Problem
Micromachined structures formed from thin processing wafers or layers are fragile and prone to cracking during grinding or polishing, leading to yield loss due to external mechanical forces.
Innovation Solution
A method involving the use of intermediate and handle substrates with adhesive layers to protect and support the thin silicon layers during thinning and bonding processes, preventing cracking by inverting the order of bonding and grinding/polishing steps and employing protective layers to mitigate mechanical stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If thin processing wafers or layers are used to enable quick response of micromachined structures, then response speed is improved, but the structures become floppy and fragile, leading to cracking during grinding or polishing
Solution Approach 1:
A thick first handle substrate is introduced as an intermediary support during the fabrication process. This handle substrate provides mechanical strength and stability to the thin second layer during grinding and polishing operations, preventing cracking while allowing the final micromachined structure to maintain its thin profile for quick response
Solution Approach 2:
The thinning of the processing wafer to create the thin second layer is performed before bonding to the final substrate. This preliminary action allows the thin structure to be formed while still supported by the handle substrate, avoiding the need to handle and process the thin structure independently when it would be most vulnerable
2Speed
If thin processing wafers or layers are used to enable quick response of micromachined structures, then response speed is improved, but manufacturing complexity increases due to additional handling precautions
Solution Approach 1:
The first handle substrate serves as a temporary intermediary that simplifies handling of the thin second layer. By providing a rigid support during fabrication, it eliminates the need for complex specialized handling procedures, making the process as straightforward as handling standard thick wafers
Solution Approach 2:
The fabrication process is segmented into distinct stages: forming the thin second layer on the handle substrate, performing all necessary processing while supported, bonding to the final substrate, and then releasing the handle substrate. This segmentation allows each stage to be optimized independently
3Speed
If thin processing wafers or layers are used to enable quick response of micromachined structures, then response speed is improved, but yield loss increases due to cracking from external mechanical forces
Solution Approach 1:
The thick first handle substrate provides beforehand cushioning and protection during grinding and polishing operations. This protective support prevents mechanical forces from directly affecting the thin second layer, eliminating cracking and ensuring high yield rates
Solution Approach 2:
The handle substrate acts as a mediator that absorbs and distributes mechanical stresses during fabrication. By intervening between the processing equipment and the thin structure, it prevents harmful forces from reaching the vulnerable thin layer
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
The method effectively prevents cracking of thin silicon cantilevered or suspended structures, reducing yield loss and enabling the formation of robust micromachined structures for MEMS applications.
Implementation Method 1
adhering the patterned free surface of the second layer to a first handle substrate, such as a first handle wafer, via a first adhesive layer
Implementation Method 2
bonding the patterned free surface of the second layer to a substrate, such as a wafer or a glass substrate, with integrate circuit devices
Data Source
AI summary
The invention provides a method of fabricating a micromachined structure, and in particular to a method of forming a micro-electro-mechanical system (MEMS) structure. A thin silicon cantilevered or suspended structure used to make micromachined structures is first formed from a SOI wafer or a bulk silicon wafer, followed by formation of the micromachined structures by semiconductor manufacturing techniques.