Wafer-Level Hermetic Packaging with Vertical Feedthroughs
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Solution Overview
Problem
Current wafer-level packaging methods for MEMS components face challenges in achieving hermetic sealing and lead transfer without degrading the encapsulation, particularly due to high-temperature processes, mechanical stress, and complexity in using glass-frit or metal-based alloys, which affect yield, reliability, and compatibility.
Innovation Solution
A method utilizing vertical feedthroughs for lead transfer, compatible with low-temperature bonding processes, that eliminates the need for sealing materials and complex via-fill techniques, allowing simultaneous patterning of encapsulating cavities and feedthroughs, and uses CMOS or MEMS processes to fabricate substrates with integrated circuits, reducing process steps and mechanical stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If glass-frit is used as sealing material for wafer-level encapsulation, then hermetic sealing is achieved, but high bonding temperature (>430°C) limits material compatibility and creates high packaging stress
Solution Approach 1:
The patent changes the bonding temperature parameter from high (>430°C for glass-frit) to low (<200°C for anodic bonding), fundamentally altering the process conditions to enable material compatibility and reduce thermal stress while maintaining hermetic sealing effectiveness
Solution Approach 2:
The patent replaces the thermal bonding mechanism (glass-frit sintering) with an electrochemical bonding mechanism (anodic bonding), substituting a mechanical/thermal system with an electrical field-based system that operates at lower temperatures and provides better stress control
2Reliability
If glass-frit material is used for sealing, then hermetic sealing is achieved, but thick-film paste creates free-to-move frit particles that contaminate MEMS components and reduce reliability
Solution Approach 1:
The patent extracts and eliminates the glass-frit sealing material entirely, replacing it with a bonding process that creates a solid-state hermetic seal without generating contaminating particles, thus removing the source of frit particle contamination
Solution Approach 2:
The patent replaces the thick-film glass-frit paste with a thin-film oxide layer that is deposited and then consumed during the anodic bonding process, creating a clean interface without residual particulate contamination
3Reliability
If metal-based alloys are used as sealing material, then better hermeticity is achieved, but electrically conductive material prevents lead transfer through sealing region
Solution Approach 1:
The patent segments the sealing function and lead transfer function into separate regions: the sealing region uses oxide-based anodic bonding for hermeticity, while the lead transfer region uses through-wafer vias with conductive fill, allowing each function to be optimized independently without interference
Solution Approach 2:
The patent applies different material properties to different locations: the sealing region uses insulating oxide materials for hermetic bonding, while the via regions use conductive materials for lead transfer, creating local quality variations that satisfy both hermeticity and electrical connectivity requirements
4Ease of operation
If vertical feedthroughs are implemented for lead transfer, then lead transfer is achieved without crossing sealing region, but process complexity and number of fabrication steps increase
Solution Approach 1:
The patent merges the via formation and sealing wall formation into a single etching step, and combines the oxide deposition for via insulation with the overall device fabrication process, reducing the number of discrete process steps while maintaining vertical feedthrough functionality
Solution Approach 2:
The patent performs preliminary actions by forming the oxide layer in via regions before the final bonding step, and by creating the vertical via structures early in the fabrication process, so that subsequent bonding and lead transfer operations can proceed without additional complex steps
Data Source
Figure 1A~1D
Figure 2A~2C
Figure 2D~3B
AI summary
A wafer-level packaging method for MEMS structures that are desired to be encapsulated in a hermetic cavity and that need the transfer of at least a single or multiple electrical leads to the outside of the cavity without destroying the hermeticity of the cavity. Lead transfer is achieved using vertical feedthroughs that are patterned on the capping substrate within the same fabrication step to produce the encapsulating cavity. Furthermore, the structure of the vertical feedthroughs and via openings to reach these feedthroughs are arranged in such a way that conventional wirebonding would be sufficient to connect the vertical feedthroughs to the outer world, without a need for conductor-refill inside the via openings. The method is compatible with low-temperature thermocompression-based bonding/sealing processes using various sealing materials such as thin- film metals and alloys, and also with the silicon-glass anodic or silicon-silicon fusion bonding processes.