MEMS Epi-Poly Cap Layer Surface Smoothing via ALD Barrier
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Solution Overview
Problem
Microelectromechanical systems (MEMS) devices face challenges in maintaining a smooth and anti-stiction surface on their cap layers, leading to surface roughness and polysilicon migration issues during the etching process.
Innovation Solution
The implementation of a barrier layer made from Aluminum Oxide (Al2O3) using the atomic layer deposition (ALD) process over the epi-poly cap layer and access openings, combined with epitaxial growth of a refill material to seal cavities and prevent polysilicon migration, results in a smoothed and anti-stiction surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an etching process is performed on the sacrificial layer to form an etched structure, then access openings and cavities can be formed, but polysilicon migration occurs causing surface roughness
Solution Approach 1:
A barrier layer made of aluminum oxide (Al2O3) is deposited using atomic layer deposition (ALD) as an intermediary between the polysilicon cap layer and the etched structure. This barrier layer prevents polysilicon migration during the etching process while allowing the formation of access openings and cavities, thereby resolving the contradiction between ease of manufacture and manufacturing precision
Solution Approach 2:
The barrier layer is applied in advance before the etching process to prevent polysilicon migration. By establishing this protective layer beforehand, the harmful effect of polysilicon migration is counteracted before it can occur during the etching process, maintaining surface smoothness while enabling the etching operations
2Reliability
If the cap layer surface is maintained smooth, then stiction is reduced, but polysilicon migration during etching creates surface roughness
Solution Approach 1:
The aluminum oxide barrier layer serves as a mediator that prevents polysilicon from migrating to the cap layer surface during etching. This maintains the smooth surface required for anti-stiction properties while allowing the etching process to proceed, thus preserving reliability without sacrificing surface smoothness
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 reduces surface roughness and prevents polysilicon migration, maintaining a smooth and functional MEMS device surface by sealing access openings and preserving scallops, enhancing the device's performance and reliability.
Implementation Method 1
A barrier layer formed from Aluminum Oxide (Al2O3) with a thickness is formed over the epi-poly cap layer, the access openings, and the cavity using ALD process
Implementation Method 2
A material such as a polysilicon layer is epitaxially grown in the etched structure and over the sacrificial layer, defines a cap layer
Implementation Method 3
The refill material layer is epitaxially grown in the access openings until the access openings are sealed with the refill material
Data Source
AI summary
A method of fabricating a MEMS device includes an epi-polysilicon cap layer epitaxially growth on one of a substrate or a sacrificial layer deposited on the substrate. A portion of the epi-polysilicon cap layer has been removed to form a plurality of access openings. The sacrificial layer is etched away to form a cavity below the access openings. A barrier layer is deposited over the epi-polysilicon cap layer, inner walls of the cavity, and inner walls of the access openings using an atomic layer deposition (ALD) process. A refill epi-polysilicon layer is epitaxially grown in the access openings and seals the openings after the cavity is formed.