MEMS Cap Via Structure for Higher Gap Height
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Solution Overview
Problem
Conventional MEMS fabrication processes face challenges in optimizing the height of the gap and through via structure due to conflicting requirements and inefficiencies in etching processes, leading to suboptimal use of wafer thickness and increased manufacturing costs.
Innovation Solution
A MEMS structure is designed with a through via separated by an isolation structure that includes a hollow section and a via fill section of solid electrically insulating material, allowing for a streamlined manufacturing process that maximizes gap height and reduces etching steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If separate etch steps are used to create through via structure and high gap, then manufacturing precision can be maintained, but device complexity and manufacturing time increase
Solution Approach 1:
The patent combines the formation of through vias and gap structures into a single etch step by using a unified etch mask pattern that defines both features simultaneously. This merging of operations reduces the number of separate etch steps while maintaining the precision required for both the through via dimensions and the gap height, thereby reducing device complexity without sacrificing manufacturing precision.
Solution Approach 2:
The etch mask is segmented into different regions with distinct pattern densities - higher pattern density in via regions and lower pattern density in gap regions. This segmentation allows the single etch process to selectively form through vias and gaps with appropriate dimensions by controlling etch rate variations across different mask regions, achieving precise dimensional control without multiple etch steps.
2Reliability
If large safety margins are used in manufacturing processes, then manufacturing reliability improves, but gap height optimization is prevented
Solution Approach 1:
The patent changes the pattern density parameter of the etch mask to control etch rate variations. By adjusting pattern density from high (in via regions) to low (in gap regions), the etch process achieves different etch rates that compensate for conventional safety margins, allowing optimal gap height to be achieved while maintaining bonding reliability through precise dimensional control.
3Productivity
If through via and gap are formed in the same wafer structure, then manufacturing efficiency increases, but manufacturing precision becomes more difficult to maintain
Solution Approach 1:
The etch mask is designed with locally varying pattern densities - high pattern density in via regions to control via dimensions and low pattern density in gap regions to achieve optimal gap height. This local quality variation allows the single etch process to maintain appropriate dimensional tolerances for both through vias and gaps simultaneously, preserving manufacturing precision while improving efficiency.
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A microelectromechanical structure including a first wafer structure attached by bonding to a second wafer structure. The first wafer structure includes a build part of silicon wafer material, a through via, and an isolation structure separating the through via from the build part. The through via extends between a first electrical contact and a second electrical contact through the first wafer structure in a first direction. The first electrical contact of the first wafer structure is accessible externally and the second electrical contact of the first wafer structure connects to an internal electrical contact on the second wafer structure. In the first direction, the extent of the isolation structure includes a hollow section and a via fill section where the isolation structure is filled with solid electrically insulating material. Enables considerable increase of gap height in MEMS structures