Wafer Stacking with Vacuum Bonding for Void-Free IC Stability
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Solution Overview
Problem
Traditional flip chip fabrication methods face challenges in reducing flexing of integrated circuits (ICs) during heating and cooling, and mechanical stresses, as additional materials are typically added at the IC level rather than the wafer level, which can limit handling efficiency and introduce voids in bonding.
Innovation Solution
A method involving the deposition of epoxy on heated wafers, spinning to spread it evenly, and bonding multiple wafers under vacuum to form a multi-wafer-bonded structure, which is thermally matched and void-free, allowing for improved handling and thermal stability of ICs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If additional materials are added at the IC level to reduce flexing, then mechanical stability is improved, but handling efficiency deteriorates and voids are introduced in bonding
Solution Approach 1:
The solution segments the support function from the IC level to the wafer level by introducing a dedicated support wafer structure. This separates the mechanical support function (performed by the support wafer) from the IC device function, allowing efficient wafer-level handling while providing distributed mechanical support across multiple ICs simultaneously.
Solution Approach 2:
The support wafer acts as an intermediary element between the ICs and the bonding process. It provides a stable base that prevents IC flexing during handling and bonding, while its flat surface enables efficient wafer-level processing. The intermediary support wafer eliminates the need for individual IC-level support structures.
2Manufacturing precision
If epoxy is deposited and spread across the wafer surface, then uniform bond layers are achieved, but processing complexity increases
Solution Approach 1:
The solution replaces manual or complex mechanical deposition methods with spin coating technology. The spin coater uses rotational centrifugal force to automatically spread epoxy uniformly across the wafer surface, achieving precise bond layer uniformity through a standardized, automated process rather than complex manual application.
Solution Approach 2:
The spin coating process controls bond layer uniformity by adjusting rotational speed parameters. By varying the spin speed during different phases of the process, the epoxy is first deposited, then spread uniformly, and finally leveled to create a consistent bond layer thickness across the entire wafer surface.
3Manufacturing precision
If multiple wafers are bonded under vacuum, then void-free structures are achieved, but energy consumption increases
Solution Approach 1:
The solution merges multiple wafer bonding operations into a single vacuum bonding step. By stacking multiple wafers with epoxy layers and bonding them simultaneously under vacuum, the process achieves void-free interfaces across all wafer pairs in one operation, rather than requiring separate bonding steps for each wafer pair.
Solution Approach 2:
The vacuum bonding chamber serves multiple functions: it removes air pockets and voids from all epoxy interfaces simultaneously, cures the epoxy through controlled heating, and maintains precise alignment of stacked wafers. This multi-functional approach achieves superior bonding quality without proportionally increasing energy consumption.
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
Enables efficient handling of a large number of ICs with reduced flexing and mechanical stress, achieving uniform and void-free bond layers that are thermally matched, enhancing the thermal stability and reliability of the multi-wafer-bonded structures.
Implementation Method 1
heating a wafer chuck, heating a first wafer
Implementation Method 2
spinning the wafer chuck to spread the first epoxy at least partially across the first wafer
Implementation Method 3
bonding the second wafer to the first epoxy under vacuum to form a two-wafer-bonded structure
Data Source
Figure 1~2
Figure 3A~3B
Figure 4A~4B
AI summary
In one aspect, a method includes heating a wafer chuck, heating a first wafer, depositing a first epoxy along at least a portion of a surface of the first wafer disposed on the wafer chuck, spinning the wafer chuck to spread the first epoxy at least partially across the first wafer, placing a second wafer on the first epoxy disposed on the first wafer and bonding the second wafer to the first epoxy under vacuum to form a two-wafer-bonded structure.