Slotted Submount Wafer Bonding for Warpage Reduction
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Solution Overview
Problem
Wafer bonding of different materials in semiconductor fabrication often results in warpage due to differences in thermal expansion coefficients, which complicates subsequent manufacturing processes and affects the reliability of packaged devices.
Innovation Solution
Scoring the submount wafer with slots before bonding, aligning them with the dicing pattern, to reduce the effective thickness and rigidity, thereby mitigating warpage while maintaining structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If wafers of different materials are bonded together, then wafer bonding enables efficient coupling of elements on different wafers, but warpage occurs due to differences in thermal expansion coefficients
Solution Approach 1:
The submount wafer is segmented by forming an array of slots through its thickness, dividing the continuous substrate into separated regions. This segmentation reduces the effective bonding area and allows differential thermal expansion without causing overall wafer warpage, while still providing structural support at the slot boundaries.
Solution Approach 2:
The slots are strategically positioned and dimensioned to create local variations in the wafer structure. The regions between slots maintain full thickness for structural integrity, while the slot regions provide compliance for thermal expansion, creating different mechanical properties in different locations of the same wafer.
2Shape
If the submount wafer is made thinner to reduce warpage, then thermal expansion issues are mitigated, but structural support and reliability are compromised
Solution Approach 1:
Instead of uniformly thinning the entire wafer, the invention segments the wafer by creating slots that effectively reduce the bonding area thickness locally, while maintaining full thickness in the regions between slots. This provides both warpage reduction and structural integrity.
Solution Approach 2:
The slotted wafer structure creates a composite-like configuration where the remaining material between slots acts as reinforcing elements, similar to I-beams in structural engineering. This allows the wafer to have reduced effective thickness for bonding purposes while maintaining overall structural strength through the distributed support of the slot boundaries.
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
The scoring process reduces warpage and enhances the structural support of the packaged devices, allowing for more efficient manufacturing and improved reliability by matching the wafer characteristics to those of a thinner wafer, thus minimizing thermal expansion-related issues.
Implementation Method 1
Differences in the coefficient of thermal expansion (CTE) between the two wafers, or other layers of the combination, may lead to warpage after assembly, particularly when relatively high temperatures are used to effect the bonding.
Data Source
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AI summary
In a wafer bonding process, one or both of two wafer substrates are scored prior to bonding. By creating slots in the substrate, the wafer's characteristics during bonding are similar to that of a thinner wafer, thereby reducing potential warpage due to differences in CTE characteristics associated with each of the wafers. Preferably, the slots are created consistent with the singulation/dicing pattern, so that the slots will not be present in the singulated packages, thereby retaining the structural characteristics of the full-thickness substrates.