MEMS Cavity Capillary Slots for Etching Bubble Removal
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Solution Overview
Problem
During the manufacturing of MEMS devices, such as microphones and loudspeakers, deep cavities with high aspect ratios can trap bubbles, preventing etching agents from reaching the sacrificial layer, leading to incomplete etching and residual material.
Innovation Solution
Incorporating capillary slots into the sidewalls of cavities to enhance wetting by creating a capillary force that pulls the etching agent into the cavity, reducing bubble formation and ensuring complete etching of the sacrificial layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If deep cavities with high aspect ratio are formed in MEMS manufacturing, then the cavity depth is increased, but bubble formation occurs that prevents etching agent from reaching the sacrificial layer
Solution Approach 1:
The cavity opening is segmented into multiple capillary slots distributed around the perimeter, which divide the single large opening into several smaller channels. This segmentation allows etching agent to enter through multiple paths simultaneously, preventing bubble entrapment and ensuring complete wetting of the sacrificial layer at the cavity bottom.
Solution Approach 2:
The cavity sidewall is structured with capillary slots that create a porous-like structure. This porous structure enables capillary action to draw the etching agent into the deep cavity, ensuring thorough penetration and complete removal of the sacrificial layer without bubble formation.
2Shape
If the cavity opening is made small relative to depth (high aspect ratio), then the device dimensions are optimized, but wetting of the sacrificial layer becomes incomplete
Solution Approach 1:
Capillary slots are introduced into the cavity sidewall, creating a porous structure that leverages capillary action. This allows the etching agent to be drawn into the deep, narrow cavity effectively, ensuring complete wetting and removal of the sacrificial layer despite the high aspect ratio geometry.
Solution Approach 2:
The patent utilizes capillary pressure (a hydraulic principle) to drive the etching agent into the cavity. The capillary slots create negative pressure that draws the liquid etching agent into the deep cavity, ensuring complete penetration and sacrificial layer removal without requiring large opening dimensions.
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 capillary slots effectively prevent bubble formation, ensuring thorough wetting and complete removal of the sacrificial layer, even in deep cavities with small diameters, thereby improving the manufacturing process and reducing residual material.
Implementation Method 1
Incorporating capillary slots into the sidewalls of cavities to enhance wetting by creating a capillary force that pulls the etching agent into the cavity
Data Source
AI summary
A method for manufacturing a MEMS device includes providing a cavity within a layer adjacent to a sacrificial layer. The cavity extends to the sacrificial layer and includes a capillary slot protruding into the layer. The sacrificial layer is removed by exposing the sacrificial layer to an etching agent that is introduced through the cavity.