Self-Aligned Vertical Comb Drive Fabrication via Etch Stop Mask
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Solution Overview
Problem
Conventional methods for fabricating self-aligned vertical comb drive structures face challenges such as misalignment and lateral etching, leading to reduced performance and difficulty in removing etch stop layers, especially with increased aspect ratios.
Innovation Solution
A method involving a multi-layer structure with a self-aligned pattern on a stop layer, allowing for inter-digitated comb structures to be formed with precise alignment and etching, using the self-aligned pattern as a mask to limit etch depth and prevent misalignment, and tapering comb fingers towards a gap to reduce lateral etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If two comb structures are formed from one side of the wafer using conventional photolithography, then the fabrication process is simpler, but misalignment between comb structures occurs leading to reduced performance
Solution Approach 1:
The patent transitions from forming both comb structures from a single wafer side to forming them from opposite sides of the wafer. This dimensional change allows each comb structure to be independently patterned and etched, achieving precise alignment while maintaining fabrication simplicity through the self-aligned nature of the process.
Solution Approach 2:
The patent applies preliminary actions by first forming the stop layer with self-aligned patterns before etching the comb structures. The stop layer patterns are created in advance to guide the subsequent etching process, ensuring that the comb structures are formed with precise alignment from the beginning of the fabrication sequence.
2Manufacturing precision
If etch depth is increased to form deep trenches between adjacent fingers, then the aspect ratio increases improving performance, but lateral etching occurs distorting the inner comb structure shape
Solution Approach 1:
The patent introduces a stop layer as an intermediary between the comb structure and the trench. This stop layer with self-aligned patterns acts as a mediator that limits the etch depth and prevents lateral etching from distorting the inner comb structure, while still allowing sufficient trench depth to achieve the required aspect ratio for performance.
Solution Approach 2:
The patent applies preliminary anti-action by forming the stop layer pattern before etching the trenches. This pre-formed pattern creates a barrier that prevents the harmful lateral etching effect from occurring, counteracting the distortion that would otherwise result from deep trench etching.
3Manufacturing precision
If etch stop layer is disposed between two device layers, then alignment is improved, but removal of the etch stop layer becomes difficult due to increased aspect ratio preventing etching agent access
Solution Approach 1:
The patent extracts the stop layer from the conventional position between device layers and places it on the opposite side of the wafer. This extraction allows the stop layer to be removed more easily through the self-aligned patterns without requiring deep etching through high aspect ratio trenches, while still maintaining its function in preventing lateral etching and ensuring alignment.
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 ensures accurate alignment and formation of comb structures with expected shapes, reduces the potential difference required for operation, and enhances sensitivity when used as a sensor, while allowing for easier removal of insulating layers.
Implementation Method 1
the first comb structure and the second comb structure that are inter-digitated and that are formed via etching using the self-aligned pattern as a mask
Implementation Method 2
using the self-aligned pattern as a mask to limit etch depth and prevent misalignment
Implementation Method 3
when a potential difference is applied to the comb structures, one of the comb finger portions (e.g., a movable comb finger portion) moves with respect to the other one of the comb finger portions (e.g., a fixed comb finger portion)
Data Source
AI summary
In a method for fabricating a self-aligned vertical comb drive structure, a multi-layer structure is first formed. The multi-layer structure includes inter-digitated first and second comb structures formed via etching using a first mask layer as a mask. The first comb structure includes a plurality of first comb fingers, each having a first finger portion formed in a first device layer and a second finger portion formed in a second device layer and separated from the first finger portion by a self-aligned pattern on a stop layer. The second comb structure includes a plurality of second comb fingers formed solely in the second device layer. The second finger portions of the first comb fingers are subsequently removed.