Wafer Stacking Bonding with Center-Out Air-Free Interface Control
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Solution Overview
Problem
Existing wafer bonding techniques face challenges in achieving reliable bonds due to air entrapment and misalignment of wafers, which can result in mechanical stress and weakened bonds.
Innovation Solution
A method and apparatus for bonding wafers that involves aligning the wafers vertically and maintaining their parallelism, using flags to separate the wafers initially, and then deforming the top wafer to create a curved profile, allowing the bond to initiate at the center and expand to the edges within a vacuum chamber to prevent air entrapment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wafers are bonded directly without deformation, then bonding speed is fast, but air entrapment occurs and bond quality deteriorates
Solution Approach 1:
The patent applies dynamic deformation to the top wafer during the bonding process. The wafer is deformed from a planar state to a curved state and then back to planar, creating dynamic motion that facilitates air evacuation while maintaining bond quality. This dynamic approach resolves the contradiction between fast bonding and air entrapment prevention.
Solution Approach 2:
The patent intentionally induces curvature in the top wafer during bonding. By deforming the wafer into a curved profile and then returning it to planar, the process creates controlled curvature that helps air escape from the bonding interface, preventing entrapment while maintaining reliable bonds.
2Manufacturing precision
If wafers are aligned precisely, then misalignment is minimized, but alignment time increases
Solution Approach 1:
The patent performs preliminary alignment of wafers before the bonding process begins. Alignment marks are established and wafers are positioned in advance, allowing precise alignment to be achieved before bonding commences. This preliminary action ensures high precision without adding time during the critical bonding phase.
3Reliability
If deformation is applied to initiate bonding at center, then air entrapment is reduced, but wafer stress increases
Solution Approach 1:
The patent employs periodic deformation cycles on the top wafer. The wafer is deformed to initiate bonding at the center, then returned to planar, and this cycle is repeated. This periodic action allows air to be progressively evacuated while distributing stress over time, preventing excessive stress accumulation that would occur with continuous deformation.
Solution Approach 2:
The dynamic nature of the deformation process allows controlled stress application. By deforming and returning the wafer repeatedly, the stress is applied in controlled increments rather than continuously, allowing the wafer to adapt and reducing overall stress accumulation while still preventing air entrapment.
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 effectively mitigates air entrapment and ensures strong, reliable bonds between wafers by maintaining alignment and gradually expanding the bond interface, resulting in improved wafer acceptance test performance.
Implementation Method 1
bonding the first wafer to the second wafer in a vacuum chamber
Data Source
AI summary
In some embodiments, the present disclosure relates to a method that includes aligned a first wafer with a second wafer. The second wafer is spaced apart from the first wafer. The first wafer is arranged on a first electrostatic chuck (ESC). The first ESC has electrostatic contacts that are configured to attract the first wafer to the first ESC. Further, the second wafer is brought toward the first wafer to directly contact the first wafer at an inter-wafer interface. The inter-wafer interface is localized to a center of the first wafer. The second wafer is deformed to gradually expand the inter-wafer interface from the center of the first wafer toward an edge of the first wafer. The electrostatic contacts of the first ESC are turned OFF such that the first and second wafers are bonded to one another by the inter-wafer interface.