MEMS Wafer Hermetic Sealing via Indium Depression Bonding
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Solution Overview
Problem
Conventional wafer construction processes for MEMS image intensifiers often damage adhesion metals, preventing the formation of a proper hermetic seal due to scratches and oxidation of indium, which requires handling and exposure of fresh indium for bonding.
Innovation Solution
A method involving spinning resist onto a wafer, forming pathways and depressions, depositing adhesion metals within these depressions, and then applying indium to create a low temperature bond between wafers, ensuring the adhesion metals are protected and allowing continuous patterns of indium to form a hermetic seal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adhesion metals are placed on a planar surface for low temperature hermetic sealing, then the hermetic seal can be formed, but the adhesion metals become scratched or damaged during repeated wafer handling
Solution Approach 1:
The patent applies local quality by creating a non-planar surface structure with raised features and valleys on the wafer surface. The adhesion metal is selectively deposited only in the valley regions, creating localized bonding zones. This localized deposition protects the adhesion metal from damage during handling while maintaining hermetic seal capability at these critical locations.
Solution Approach 2:
The patent employs preliminary action by pre-forming the non-planar surface structure and depositing adhesion metal before the actual hermetic bonding process. This preliminary preparation creates a robust structure that can withstand subsequent handling and processing steps, with the adhesion metal already in position to form seals when needed.
2Reliability
If protrusions are added to the bonding surface to penetrate oxidized indium, then fresh indium can be exposed for bonding, but the seal area increases
Solution Approach 1:
Instead of adding protrusions to penetrate through indium, the patent inverts the approach by creating valleys or recesses where indium is deposited. This inverted geometry allows the indium to be contained in protected regions, and the bonding process occurs at these localized valley sites rather than requiring large-area protrusions, thereby reducing the overall seal area while maintaining bonding capability.
Solution Approach 2:
The patent segments the bonding interface into discrete localized regions (valleys or recesses) rather than requiring a continuous large-area seal. By concentrating the bonding function in these segmented regions, the patent achieves reliable bonding through oxidized indium while minimizing the total seal area required.
3Reliability
If indium is deposited late in the process onto adhesion metals, then handling damage can be avoided, but the adhesion metals are still damaged during repeated wafer handling
Solution Approach 1:
The patent applies local quality by creating a non-planar surface structure with raised features and valleys on the wafer surface. The adhesion metal is selectively deposited only in the valley regions, creating localized bonding zones. This localized deposition protects the adhesion metal from damage during handling while maintaining hermetic seal capability at these critical locations.
Solution Approach 2:
The patent employs preliminary action by pre-forming the non-planar surface structure and depositing adhesion metal before the actual hermetic bonding process. This preliminary preparation creates a robust structure that can withstand subsequent handling and processing steps, with the adhesion metal already in position to form seals when needed.
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 enables double-sided processing of wafers without damaging adhesion metals, forming a reliable low-temperature hermetic seal with reduced seal area and multiple shear points for enhanced bonding, preventing oxidation and ensuring a strong bond between wafers.
Implementation Method 1
spinning a resist onto a first side of a first wafer
Implementation Method 2
bonding a second wafer to the first wafer by compressing the indium between the second wafer and the first wafer
Data Source
AI summary
A method of processing a double sided wafer of a microelectromechanical device includes spinning a resist onto a first side of a first wafer. The method further includes forming pathways within the resist to expose portions of the first side of the first wafer. The method also includes etching one or more depressions in the first side of the first wafer through the pathways, where each of the depressions have a planar surface and edges. Furthermore, the method includes depositing one or more adhesion metals over the resist such that the one or more adhesion metals are deposited within the depressions, and then removing the resist from the first wafer. The method finally includes depositing indium onto the adhesion metals deposited within the depressions and bonding a second wafer to the first wafer by compressing the indium between the second wafer and the first wafer.