Dual Sacrificial Layer MEMS Fabrication Sidewall Stress
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Solution Overview
Problem
Conventional methods for fabricating microelectromechanical structures (MEMS) often result in peeling or cracking between sacrificial layers due to stress induced during photolithography and development, leading to deformation of the microstructure mold and subsequent microelectromechanical elements.
Innovation Solution
A method involving the formation of a first patterned sacrificial layer with a bulk and protrusion portion on a substrate, followed by a second patterned sacrificial layer that covers only the protrusion and bulk portions of the first layer, but not its sidewalls, to prevent stress-induced cracking and peeling, thereby ensuring the integrity of the microstructure mold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the second sacrificial layer covers the sidewalls of the first sacrificial layer, then complete coverage and mold integrity are improved, but stress-induced cracking and peeling occur due to photolithography and development stress
Solution Approach 1:
The patent extracts the harmful sidewall coverage of the second sacrificial layer, deliberately leaving the sidewalls of the first sacrificial layer uncovered. This removes the source of stress-induced cracking and peeling while maintaining adequate coverage of the protrusion portion through the top surface coverage approach
Solution Approach 2:
The patent applies different coverage characteristics to different regions: the second sacrificial layer fully covers the top surface of the protrusion portion while deliberately excluding the sidewalls. This local differentiation allows stress relief at critical sidewall interfaces while maintaining mold definition through top surface coverage
2Manufacturing precision
If the second sacrificial layer is formed to cover the protrusion portion completely, then accurate mold formation is improved, but stress concentration at sidewalls causes deformation
Solution Approach 1:
The patent removes the second sacrificial layer material from the sidewall regions, preventing stress concentration that would deform the protrusion portion shape while maintaining accurate mold formation through proper top surface coverage
Solution Approach 2:
The patent creates a localized coverage pattern where the second sacrificial layer is present on the top surface for accurate molding but absent from the sidewalls to prevent stress-induced deformation, achieving both mold accuracy and shape integrity
3Manufacturing precision
If photolithography and development are performed on the second layer to form patterns, then microstructure patterning is achieved, but stress induces cracking where layers meet
Solution Approach 1:
The patent extracts the second sacrificial layer from the sidewall regions before photolithography and development, eliminating the interface where stress-induced cracking occurs during these processes while preserving pattern accuracy through top surface patterning
Solution Approach 2:
The patent preemptively removes the second sacrificial layer from sidewalls before the photolithography and development process, preventing the stress-induced cracking that would otherwise occur during these steps by eliminating the vulnerable interface in advance
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 effectively prevents deformation and damage to the microelectromechanical structure by avoiding stress-induced cracking and peeling, ensuring the accurate formation and functionality of the microstructure.
Implementation Method 1
the patterned sacrificial layers 104 and 106 comprise photosensitive materials such as photoresists, photosensitive polymers or other materials and can be therefore patterned by a method such as photolithography
Data Source
AI summary
Methods of fabricating a microelectromechanical structure are provided. An exemplary embodiment of a method of fabricating a microelectromechanical structure comprises providing a substrate. A first patterned sacrificial layer is formed on portions of the substrate, the first patterned sacrificial layer comprises a bulk portion and a protrusion portion. A second patterned sacrificial layer is formed over the first sacrificial layer, covering the protrusion portion and portions of the bulk portion of the first patterned sacrificial layer, wherein the second patterned sacrificial layer does not cover sidewalls of the first patterned sacrificial layer. An element layer is formed over the substrate, covering portions of the substrate, the first patterned sacrificial layer and second patterned sacrificial layer. The first and second patterned sacrificial layers are removed, leaving a microstructure on the substrate.