Bonding Mesa Structure for CMOS-MEMS Wafer Encapsulation
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Solution Overview
Problem
MEMS devices face challenges with bonding wafer encapsulation that requires long-term reliability, including sealing issues and stiction problems due to surface tension and Van der Waals forces, which affect the durability and functionality of these devices.
Innovation Solution
The solution involves fusion bonding of silicon wafers with a thin dielectric film and the use of two-step bonding mesas and anti-stiction bumps to achieve uniform bonding gaps and prevent eutectic overflow, while also using eutectic bonding for electrical connections, thereby enhancing the mechanical strength and reducing stiction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If eutectic bonding is used to bond wafers together, then electrical connection between wafers is achieved, but large deviations and eutectic overflow occur
Solution Approach 1:
The patent applies preliminary action by forming anti-stiction bumps and defining bonding gaps before the eutectic bonding process. The bonding gap, defined by the height difference between first and second bonding mesas, is established in advance to control eutectic flow and prevent overflow. The anti-stiction bumps are formed beforehand to mitigate stiction issues that would otherwise affect bonding reliability.
Solution Approach 2:
The patent implements local quality by creating different structural features at different locations: bonding mesas with specific height differences at bonding regions to control gap uniformity, and anti-stiction bumps at specific locations to prevent stiction. This localized structural differentiation allows precise control over eutectic bonding behavior and prevents both overflow and stiction problems.
2Reliability
If wafer bonding is performed to encapsulate structures in vacuum cavities, then hermetic sealing is achieved, but stiction occurs due to surface tension and Van der Waals forces
Solution Approach 1:
The patent applies preliminary anti-action by forming anti-stiction bumps before the bonding process to counteract the harmful stiction forces. These bumps create a mechanical structure that prevents direct surface-to-surface contact between the movable MEMS element and the substrate, thereby preemptively eliminating the conditions that would lead to stiction from surface tension and Van der Waals forces.
Solution Approach 2:
The anti-stiction bumps act as an intermediary mechanical structure between the bonding surfaces. Instead of allowing direct contact between the MEMS movable element and the substrate that would cause stiction, the bumps provide a mediated contact that maintains the hermetic seal while preventing the harmful adhesive forces from taking effect.
3Manufacturing precision
If bonding gap uniformity is improved using bonding mesas, then eutectic overflow is prevented, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the bonding structure into distinct hierarchical levels: first bonding mesas with a first height, second bonding mesas with a second height, and anti-stiction bumps. This segmented approach allows precise control of the bonding gap through the height difference between mesa levels while organizing the complexity into manageable, functionally distinct segments that can be fabricated using standard semiconductor processes.
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 results in improved bonding uniformity, reduced stiction, and effective prevention of eutectic overflow, leading to increased reliability and performance of MEMS devices by ensuring hermetic sealing and minimizing electrical shorts.
Implementation Method 1
the sensing substrate and the CMOS substrate are bonded through the bonding mesa structure
Implementation Method 2
the sensing substrate and the CMOS substrate are bonded through eutectic metal
Implementation Method 3
stiction, or the surface tension between approximate surfaces under miniature scale
Implementation Method 4
prevent eutectic overflow
Data Source
AI summary
The present disclosure provides a CMOS-MEMS device structure. The CMOS-MEMS device structure includes a sensing substrate and a CMOS substrate. The sensing substrate includes a bonding mesa structure. The CMOS substrate includes a top dielectric layer. The sensing substrate and the CMOS substrate are bonded through the bonding mesa structure, and the bonding mesa structure defines a bonding gap between the CMOS substrate and the sensing substrate.