MEMS Cavity Etch Sublayer Protection via Protective Masking
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Solution Overview
Problem
During the cavity etch process in MEMS devices, the exposed sublayer of the overlying dielectric layer stack is susceptible to damage due to its high etch rate, leading to undesired etching and potential contamination.
Innovation Solution
The exposed surfaces of the etchable sublayer are covered with protective material, such as a cavity etch mask or formed protective sidewalls through an etchback process, to isolate the sublayer during the cavity etch, and an isotropic etch is used in conjunction with a reflow operation to recess and protect the etchable sublayer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the cavity etch process is performed through the access hole to form the MEMS device cavity, then the cavity is successfully formed underlapping the overlying dielectric layer stack, but the etchable sublayer is undesirably etched and damaged due to its high etch rate
Solution Approach 1:
A protective material is introduced as an intermediary between the etchable sublayer and the cavity etch process. This protective material selectively covers the exposed surfaces of the etchable sublayer, allowing the cavity etch to proceed while preventing etchant contact with the sublayer, thus eliminating the harmful etching effect while maintaining cavity formation precision
Solution Approach 2:
The protective material is applied in advance before the cavity etch process begins. By pre-coating the exposed sublayer surfaces with the protective material, the sublayer is prepared and protected before exposure to the harmful etchant, preventing damage while enabling precise cavity formation
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 material loss from the etchable sublayer and minimizes damage during the cavity etch process, ensuring precise formation of the MEMS device cavity while maintaining the integrity of the etch-resistant lower portion.
Implementation Method 1
Exposed surfaces of the etchable sublayer are subsequently covered by protective material to isolate the sublayer during a subsequent cavity etch
Implementation Method 2
The exposed lateral face of the etchable sublayer may be recessed by an isotropic etch
Implementation Method 3
an isolated by a reflow operation which causes edges of an access hole etch mask to drop and cover the exposed lateral face of the etchable sublayer
Data Source
AI summary
A process of forming a MEMS device with a device cavity underlapping an overlying dielectric layer stack having an etchable sublayer over an etch-resistant lower portion, including: etching through at least the etchable sublayer of the overlying dielectric layer stack in an access hole to expose a lateral face of the etchable sublayer, covering exposed surfaces of the etchable sublayer by protective material, and subsequently performing a cavity etch. A cavity etch mask may cover the exposed surfaces of the etchable sublayer. Alternatively, protective sidewalls may be formed by an etchback process to cover the exposed surfaces of the etchable sublayer. Alternatively, the exposed lateral face of the etchable sublayer may be recessed by an isotropic etch, than isolated by a reflow operation which causes edges of an access hole etch mask to drop and cover the exposed lateral face of the etchable sublayer.