MEMS Actuator Hard Mask Patterning for Standoff Lithography
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existence of standoffs in MEMS sensors causes non-uniform thicknesses of photoresist, leading to lithography variations, and previous solutions either increase die size or complicate processing by altering standoff heights or sizes, failing to reduce size effectively while maintaining performance.
Innovation Solution
The use of a hard mask coated on the MEMS surface during fabrication to create a planar topography, reducing the distance between standoffs and key MEMS features, thereby preventing photoresist buildup and allowing etch processes to form features closer to standoffs, achieving size reductions without compromising performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standoffs are used in MEMS sensors, then structural support and alignment are provided, but non-uniform photoresist thickness occurs leading to lithography variations
Solution Approach 1:
A hard mask layer is introduced as an intermediary between the non-uniform photoresist and the substrate. This hard mask is deposited over the standoffs and patterned to define the final MEMS structure. The hard mask serves as a mediator that decouples the lithography process from the underlying topography, allowing precise patterning despite the non-uniform photoresist thickness caused by standoffs.
Solution Approach 2:
The patterning process is segmented into multiple stages: first, a hard mask is deposited and patterned to define the MEMS structure; second, anisotropic etching is used to remove material selectively; third, isotropic etching completes the removal. This segmentation allows each step to be optimized independently, with the hard mask providing a stable reference for precise patterning while the etching steps handle the complex topography.
2Area of stationary object
If standoff height is reduced to minimize photoresist buildup, then die size is reduced, but processing complexity increases
Solution Approach 1:
The hard mask acts as a mediator that simplifies the processing by providing a planar reference surface. Instead of requiring the standoffs to be perfectly flat or requiring complex compensation techniques, the hard mask is deposited over the standoffs and planarized, creating a uniform surface for photoresist deposition and patterning. This intermediary layer absorbs the complexity of the underlying topography.
Solution Approach 2:
The hard mask is deposited and patterned before the final MEMS structure is formed. This preliminary action establishes the precise pattern definition early in the process, allowing subsequent etching steps to proceed with simpler, more controlled processes. The hard mask pattern is transferred to the MEMS structure through anisotropic etching, eliminating the need for complex in-situ patterning.
3Ease of manufacture
If conventional etching is used without hard mask, then process steps are simplified, but precise feature formation near standoffs is difficult
Solution Approach 1:
The hard mask serves as a mediator between the simple etching process and the precise feature formation requirement. It provides a stable, precisely patterned reference surface that guides the anisotropic etching process. Without the hard mask, the etching would lack a precise reference, making it difficult to form features accurately near the standoffs. The hard mask enables precise feature formation while keeping the etching process itself relatively simple.
Solution Approach 2:
The etching process is segmented into anisotropic etching (for precise vertical sidewalls and feature definition) followed by isotropic etching (for complete material removal). This segmentation allows the first step to focus on precise feature formation guided by the hard mask pattern, while the second step completes the removal without requiring additional precision control. The hard mask enables this segmentation to work effectively.
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 reduces die size while maintaining performance by preventing photoresist buildup and allowing precise etching near standoffs, simplifying the processing complexity of corresponding CMOS wafers.
Implementation Method 1
fusion bonding a handle wafer to a first side of a device wafer
Data Source
AI summary
Provided herein is a method including fusion bonding a handle wafer to a first side of a device wafer. Standoffs are formed on a second side of the device wafer. A first hardmask is deposited on the second side. A second hardmask is deposited on the first hardmask. A surface of the second hardmask is planarized. A photoresist is deposited on the second hardmask, wherein the photoresist includes a MEMS device pattern. The MEMS device pattern is etched into the second hardmask. The MEMS device pattern is etched into the first hardmask, wherein the etching stops before reaching the device wafer. The photoresist and the second hardmask are removed. The MEMS device pattern is further etched into the first hardmask, wherein the further etching reaches the device wafer. The MEMS device pattern is etched into the device wafer. The first hardmask is removed.