Compliant Layer for Wafer Bonding Stress Relaxation
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Solution Overview
Problem
Current wafer-to-wafer bonding techniques often result in undesirable distortions and stress between wafers due to the bonding process, leading to registration issues during post-bonding patterning.
Innovation Solution
The implementation of a compliant layer between the wafers that exhibits visco-elastic behavior, allowing for stress relaxation through heating or prolonged exposure at room temperature, enabling the wafers to accommodate and mitigate distortions and stress caused by the bonding process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If local deformation is applied to initiate wafer bonding, then bonding contact is achieved, but wafer distortion and stress increase
Solution Approach 1:
A compliant layer is introduced as an intermediary between the two wafers during bonding. This layer deforms under compression to accommodate wafer thickness variations and enable reliable bonding contact, while its compliance prevents the transmission of deformation-induced stress to the wafers themselves, thereby avoiding wafer distortion
Solution Approach 2:
The compliant layer's mechanical properties are specifically designed to change under bonding conditions - it compresses and deforms to accommodate wafer variations, then maintains a stable bonded state. The layer's compliance parameter allows it to absorb dimensional mismatches without transferring stress to the rigid wafer structures
2Reliability
If local deformation is used to make wafer contact, then bonding is initiated, but stress between wafers increases
Solution Approach 1:
The compliant layer serves as a stress-absorbing intermediary that undergoes deformation during bonding initiation. It absorbs the mechanical stress generated by local deformation techniques, preventing this stress from being transmitted to the wafer structures, thereby enabling reliable bonding without increasing wafer stress
Solution Approach 2:
The compliant layer is positioned beforehand between the wafers to provide cushioning during the bonding process. It anticipates and absorbs the stress that would otherwise be transmitted to the wafers during local deformation and bonding initiation, protecting the wafer structures from stress damage
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
Significantly reduces or eliminates distortions and stress between wafers, ensuring minimal in-plane distortion and improved registration accuracy during subsequent patterning processes.
Implementation Method 1
the compliant layer exhibits visco-elastic behavior, allowing for stress relaxation through heating or prolonged exposure at room temperature
Implementation Method 2
heating the bonded wafers to an elevated temperature, such that at the elevated temperature, the compliant layer exhibits non-elastic deformations (e.g., visco-elastic or creep) that relaxes stress
Implementation Method 3
the compliant layer exhibits non-elastic deformations (e.g., visco-elastic or creep) that relaxes stress and accommodates the distortions caused by the bonding process
Data Source
AI summary
Techniques and mechanisms for forming a bond between wafers using a compliant layer. In an embodiment, a layer or layers of one or more compliant materials is provided on a first surface of a first wafer, and the one or more compliant layers are subsequently bonded to a second surface of a second wafer. The bonded wafers are heated to an elevated temperature at which a compliant layer exhibits non-elastic deformations to facilitate relaxation of stresses caused by wafer distortions. In another embodiment, a material of the compliant layer exhibits viscoelastic behavior at room temperature, wherein stress is mitigated by allowing wafer distortion to relax at room temperature.