MEMS Wafer Cavity Etching for Bond Area Preservation
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Solution Overview
Problem
The challenge in Micro-Electro-Mechanical System (MEMS) devices is to reduce air pressure in cavities while maintaining a sufficient bonding area for reliable wafer bonding, as enlarging cavities reduces the bonding area and increases manufacturing costs due to the need for separate lithography masks for cap wafer modifications.
Innovation Solution
The solution involves using anisotropic etching followed by isotropic etching to form openings in MEMS or cap wafers, which increases the volume of cavities without reducing the bonding area, allowing for reduced air pressure and improved device performance by maintaining mechanical strength and reliability of bonds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If the volume of air cavities is increased to reduce air pressure and resistance, then the movement of movable elements is improved, but the bonding area is reduced which compromises bond reliability
Solution Approach 1:
The patent transitions from planar cavity formation to three-dimensional cavity structures by forming cavities that extend through the thickness of the wafer. This dimensional change allows the cavity volume to be maximized while the bonding surfaces remain intact on the wafer faces, resolving the contradiction between cavity volume and bonding area.
Solution Approach 2:
The wafer is segmented into multiple functional regions: cavity regions where material is removed to form air cavities, and bonding regions where material is preserved for wafer bonding. This segmentation allows simultaneous optimization of cavity volume for reduced air resistance and bonding area for reliable connections.
2Manufacturing precision
If separate lithography masks are used for cap wafer modifications to form cavities and expose bond pads, then the manufacturing precision is improved, but the manufacturing cost increases
Solution Approach 1:
Multiple lithography masks that were previously used separately for different functions (cavity formation, bond pad exposure) are merged into a single integrated mask design. This consolidation maintains the precision needed for cavity formation while reducing manufacturing complexity and cost by eliminating separate masking steps.
Solution Approach 2:
The lithography mask is designed to serve multiple functions simultaneously: defining cavity boundaries, exposing bond pads, and guiding subsequent processing steps. This multi-functional mask reduces the total number of masks needed while maintaining manufacturing precision through careful design.
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 method effectively reduces air pressure in MEMS device cavities, enhancing the movement of movable elements while ensuring reliable bonding and reducing manufacturing costs by preserving the bonding area and mechanical integrity.
Implementation Method 1
performing an anisotropic etching on a carrier wafer to form a first plurality of openings
Implementation Method 2
performing an isotropic etching to enlarge the openings
Data Source
AI summary
A device includes a Micro-Electro-Mechanical System (MEMS) wafer having a MEMS device therein. The MEMS device includes a movable element, and first openings in the MEMS wafer. The movable element is disposed in the first openings. A carrier wafer is bonded to the MEMS wafer. The carrier wafer includes a second opening connected to the first openings, wherein the second opening includes an entry portion extending from a surface of the carrier wafer into the carrier wafer, and an inner portion wider than the entry portion, wherein the inner portion is deeper in the carrier wafer than the entry portion.