Silicon Wafer Thinning for MEMS Sensors Using Two-Phase Etching
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Solution Overview
Problem
Existing methods for manufacturing thin silicon structures, such as those used in sensors and mechanical devices, are costly and prone to yield losses due to the need for expensive EPI and SOI wafers, surface defects, and non-uniform membrane thickness, which complicates mass production and increases costs.
Innovation Solution
A two-phase thinning method using grinding, polishing, and etching with alkaline solutions, such as sodium hydroxide or potassium hydroxide, to achieve a uniform final thickness for silicon structures, eliminating the need for expensive EPI and SOI wafers and reducing defects and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If expensive EPI and SOI wafers are used for manufacturing thin silicon structures, then manufacturing precision and reliability are improved, but production costs increase and yield losses occur due to surface defects
Solution Approach 1:
The patent replaces expensive EPI and SOI wafers with standard silicon wafers that can be discarded after a single use. The wafer is bonded to a carrier substrate, processed to create the thin membrane structure, and then the carrier substrate with the finished product is separated. This disposable approach eliminates the need for costly reusable wafers while maintaining high manufacturing precision through controlled bonding and processing procedures.
Solution Approach 2:
The patent introduces a carrier substrate as an intermediary element that temporarily holds the standard silicon wafer during processing. The carrier substrate enables precise thickness control and membrane formation without requiring the wafer itself to be expensive or specially prepared. After processing, the carrier substrate serves as the final support structure, eliminating the need for costly EPI/SOI wafers.
2Ease of manufacture
If standard silicon wafers are used instead of expensive EPI and SOI wafers, then production costs decrease, but manufacturing precision and membrane thickness uniformity worsen
Solution Approach 1:
The patent performs preliminary bonding of the standard silicon wafer to the carrier substrate before any thinning or processing operations. This preliminary action establishes a stable foundation that enables subsequent precise thickness control through controlled etching or mechanical removal. The carrier substrate provides mechanical support that maintains wafer flatness and uniformity throughout the thinning process, achieving precision that would be difficult to obtain with standard wafers alone.
Solution Approach 2:
The patent changes the processing parameters and sequence to accommodate standard wafers. Instead of relying on pre-prepared EPI/SOI wafers with controlled doping and structure, the method uses parameter-controlled bonding temperatures, pressures, and subsequent etching rates to achieve the desired membrane thickness uniformity. The carrier substrate parameters (material, thickness, surface properties) are optimized to maintain wafer flatness during processing.
3Length of moving object
If membrane thickness is reduced to achieve thinner silicon structures, then device performance is improved, but yield losses increase due to membrane breakage and non-uniform thickness
Solution Approach 1:
The patent provides beforehand cushioning by bonding the silicon wafer to a mechanically robust carrier substrate before the thinning process. The carrier substrate acts as a cushion that prevents membrane breakage during handling and processing. Even when the membrane becomes very thin, the carrier substrate provides mechanical support that maintains reliability and prevents catastrophic failures, thereby preserving process yield.
Solution Approach 2:
The carrier substrate serves as an intermediary that protects the thin membrane during processing. It absorbs mechanical stresses and prevents direct handling of the fragile thin structure. The intermediary carrier enables the production of ultra-thin membranes with high yield by providing mechanical protection throughout the manufacturing process.
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 method allows for higher yield and more uniform thinning of silicon structures, reducing production costs and improving the reliability of membrane thickness, enabling more economical and efficient mass production of silicon-based sensors and devices.
Implementation Method 1
a second thinning phase for thinning said surface finally to a second thickness
Implementation Method 2
said first thinning phase may comprise a phase of grinding
Implementation Method 3
said first thinning phase may comprise a phase of grinding, polishing and/or etching
Data Source
AI summary
A method for thinning a wafer layer to a predetermined thickness comprises two phases of thinning. A first thinning phase and a second thinning phase, wherein the first thinning phase is a preparatory thinning phase and the second thinning phase is a final thinning phase, so performed that the structure comprising silicon meets as thinned the final thickness as predetermined. Such thinned layer in a wafer for instance, can be used in a sensor to be used in normal sized, micromechanical or even nano-sized devices for the device specific sensing applications in electro-mechanical devices.