MEMS Fabrication Using Passivation Layer Etch Masks
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Solution Overview
Problem
Conventional microelectromechanical systems (MEMS) devices face issues with incomplete formation of micromachined structures due to limited etch resistance of patterned metal layers during fabrication, leading to partial or complete removal of film layers and compromised device functionality.
Innovation Solution
A method involving sequential etching processes using a passivation layer and photoresist layer as masks to form trenches in a semiconductor substrate, ensuring the formation of suspended micromachined structures with complete film layers, including the use of an upper capping substrate to create a sealed chamber for enhanced functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an uppermost patterned metal layer is used as an etching mask during fabrication, then the micromachined structure can be formed, but the metal layer shows limited etch resistance causing partial or entire removal of film layers
Solution Approach 1:
A passivation layer is formed over the interconnect structure before the etching process to protect the metal layers from being removed. This preliminary protective action ensures that the metal interconnect structure remains intact during subsequent etching operations while still allowing the etching mask to function properly.
Solution Approach 2:
The passivation layer acts as an intermediary between the etching process and the metal interconnect structure. It provides the necessary etch resistance to protect the metal layers while allowing the etching mask to define the micromachined structure profile accurately.
2Manufacturing precision
If multiple etching processes are performed to form trenches and suspended structures, then complete micromachined structures with sealed chambers can be formed, but the fabrication process complexity increases
Solution Approach 1:
The fabrication process is divided into multiple sequential etching steps, each forming specific features (first trenches, second trenches, third trenches). This segmentation allows each etching process to be optimized for its specific purpose while maintaining overall control of the complex structure formation.
Solution Approach 2:
The passivation layer is formed preliminarily to enable subsequent etching steps that would otherwise damage the metal interconnect structure. This preliminary protective measure makes the complex multi-step process feasible by ensuring metal layer preservation throughout all fabrication stages.
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 the completeness of film layers in MEMS devices, improving their functionality and reliability by maintaining the desired profile of micromachined structures and reducing fabrication costs through wafer-level processes.
Implementation Method 1
A first etching process is performed using the photoresist layer as an etching mask to remove the passivation layer exposed by the openings and the interconnect structure thereunder
Implementation Method 2
An upper capping substrate is attached to the passivation layer to form a first composite substrate
Data Source
AI summary
A method of fabricating a microelectromechanical system (MEMS) device includes providing a semiconductor substrate having a semiconductor layer and an interconnect structure. A passivation layer and a photoresist layer are formed over the interconnect structure and a plurality of openings are formed in the photoresist layer to expose portions of the passivation layer. The passivation layer exposed by the openings and the interconnect structure thereunder are removed, forming a plurality of first trenches. The semiconductor layer exposed by the first trenches is removed, forming a plurality of second trenches in the semiconductor layer. An upper capping substrate is provided over the passivation layer, forming a first composite substrate. The semiconductor layer in the first composite substrate is thinned and portions of the thinned semiconductor layer are etched to form a third trench, wherein a suspended micromachined structure is formed in a region between the first, second and third trenches.