MEMS Microphone Recess Etching Precision vs Speed
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Solution Overview
Problem
Conventional deep reactive ion etching (DRIE) techniques for forming recesses in MEMS microphones often result in non-well-defined walls near the membrane, leading to deviations in membrane shape and performance, which are costly and time-consuming to correct.
Innovation Solution
A method involving a substrate with a trench formed on the upper surface, filled with a material of lower etching rate, and then etched from the backside to create a recess with defined regions, allowing for precise definition of the upper recess region with high accuracy and tolerance, while allowing faster and less precise etching techniques for the intermediate and lower regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fast backside DRIE etching is used to achieve high etching rates of at least 20 µm/min into silicon substrate, then productivity is improved, but manufacturing precision deteriorates due to non-well-defined walls of the recess in vicinity of the membrane
Solution Approach 1:
The recess is divided into three distinct regions (upper, intermediate, lower) with different etching requirements. The upper recess region near the membrane is etched with high precision using slow DRIE, while the intermediate and lower regions are etched faster using optimized DRIE parameters, thereby resolving the contradiction between speed and precision in different spatial zones.
Solution Approach 2:
Different etching qualities are applied to different parts of the recess. The upper region adjacent to the membrane receives high-precision etching to ensure well-defined walls, while the lower regions accept faster etching with relaxed precision requirements, optimizing the overall process by matching etching quality to local functional needs.
2Manufacturing precision
If etching rate is reduced and elaborate bias voltage application to masks is used to improve precision of recess wall, then manufacturing precision is improved, but productivity deteriorates due to slow and expensive modification of the process
Solution Approach 1:
The etching process is segmented into multiple steps with different parameters. The first step uses slow DRIE for the upper region to achieve precision, while subsequent steps use faster etching for the remaining regions, avoiding the need to slow down the entire process and maintaining overall productivity.
Solution Approach 2:
Etching parameters (such as bias voltage, gas flow rates, and power) are changed between different etching steps and regions. The process transitions from high-precision parameters for the upper recess to faster etching parameters for lower regions, optimizing both precision and speed through dynamic parameter adjustment.
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 enables the creation of a well-defined recess near the membrane with reduced deviations, enhancing the membrane's sensitivity and robustness while maintaining fast and cost-efficient fabrication processes.
Implementation Method 1
a preliminary recess is formed in the substrate by a second etching technique applied from the side of the lower substrate surface
Data Source
AI summary
In an embodiment a device includes a substrate including an upper substrate surface and a lower substrate surface and a membrane-layer suspended above the upper substrate surface, wherein the substrate includes a recess penetrating the substrate between the lower substrate surface and the upper substrate surface, wherein the membrane-layer spans the recess, wherein the recess includes an upper recess region, an intermediate recess region, and a lower recess region, wherein the upper recess region is a part of the recess in direct vicinity to the upper substrate surface, the intermediate recess region is a part of the recess directly below the upper recess region, and the lower recess region is a part of the recess other than the upper recess region and the intermediate recess region, and wherein a cross-sectional area of the upper recess region determined parallel to the upper substrate surface is larger than a respective cross-sectional area of the intermediate recess region.