MEMS Hermetic Seal Using Mask Layer for Profile Control
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Solution Overview
Problem
The manufacturing of microelectromechanical systems (MEMS) devices faces challenges in sealing cavities due to high aspect ratio etches, which result in reduced yields and difficulties in controlling the seal opening profile and applying a sufficient etchant, leading to challenges in forming a seal layer within the seal opening.
Innovation Solution
The method involves leaving the mask layer intact after the first etch to reseal the cavity, using a mask layer to form a seal opening with a smaller top width, allowing for easier formation of a seal layer over the mask opening without the need to fill the high aspect ratio seal opening, thereby simplifying the sealing process and improving yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a high aspect ratio etch is performed to form a seal opening in communication with the cavity, then the cavity can be sealed, but the seal opening profile becomes difficult to control and lateral etching effects increase
Solution Approach 1:
A mask layer is introduced as an intermediary element between the etch tool and the cavity structure. This mask layer defines a mask opening that is smaller than the desired seal opening, allowing the etch to create a tapered seal opening while the mask layer prevents lateral etching from compromising the cavity seal. The mask layer acts as a mediator that enables precise profile control during the etching process.
Solution Approach 2:
The mask layer is formed and patterned before the etching process begins. This preliminary action establishes the boundaries for the seal opening formation, allowing subsequent etching to proceed with controlled lateral expansion. By preparing the mask structure in advance, the process ensures that the seal opening achieves the desired profile without excessive lateral etching that would compromise manufacturing precision.
2Productivity
If the mask layer is removed after the first etch, then the seal opening can be accessed, but the sealing process becomes more difficult and yield decreases
Solution Approach 1:
The mask layer serves as a temporary intermediary structure that remains in place during the sealing process. Rather than removing the mask layer, the process forms a seal layer that works in conjunction with the mask layer to achieve hermetic sealing. This intermediary approach simplifies the manufacturing process by eliminating the need to remove the mask layer while still achieving the desired seal.
Solution Approach 2:
The seal layer is formed to overhang the mask opening, creating a nested structure where the seal layer encapsulates the mask layer and the mask opening. This nesting arrangement allows the seal to be formed without removing the mask layer, as the seal layer itself provides the hermetic barrier while the mask layer continues to define the structural boundaries.
3Reliability
If a seal layer is formed to fill the high aspect ratio seal opening, then the cavity can be hermetically sealed, but the process becomes complex and time-consuming
Solution Approach 1:
Instead of requiring the seal layer to completely fill the high aspect ratio seal opening, the process uses partial action where the seal layer is deposited to a thickness that provides hermetic sealing while overhanging the mask opening. This excessive deposition ensures complete coverage and hermetic seal without requiring precise control to fill the entire depth of the high aspect ratio opening, thereby reducing process time and complexity.
Solution Approach 2:
The process changes the deposition parameters to form a seal layer with sufficient thickness to overhang the mask opening. By adjusting the deposit ion thickness parameter, the seal layer achieves hermetic sealing functionality without needing to precisely fill the high aspect ratio seal opening, significantly reducing the time and complexity of the sealing process while maintaining reliable hermetic seals.
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 improves the yield of MEMS devices by allowing for more precise control over the seal opening size and simplifies the resealing process, enabling the formation of MEMS devices with different target pressures from the same wafers without significant lateral etching effects.
Implementation Method 1
The capping device is fusion bonded to a first side of a MEMS substrate through the capping dielectric layer
Implementation Method 2
A second etch is performed into the capping substrate, through the mask opening, to form a seal opening
Data Source
AI summary
A microelectromechanical systems (MEMS) structure with a cavity hermetically sealed using a mask layer is provided. A capping substrate is arranged over a MEMS substrate, which includes a movable element. The capping substrate includes the cavity arranged over and opening to the movable element, and includes a seal opening in fluid communication with the cavity. The mask layer is arranged over the capping substrate. The mask layer overhangs the seal opening and laterally surrounds a mask opening arranged over the seal opening. A seal layer is arranged over the mask layer and the mask opening. The seal layer is configured to hermetically seal the cavity. A method for manufacturing the MEMS structure is also provided.