Liquid-Filled Wafer Bonding Support for Run-Out Reduction
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Solution Overview
Problem
The existing wafer bonding techniques using airbags are susceptible to temperature changes, leading to misalignment and overlay inaccuracies, resulting in a significant number of non-functioning devices due to run-out variations, especially in CMOS image sensors and other electronic devices with small critical dimensions.
Innovation Solution
A liquid-filled bag is used instead of an airbag to deform and support the bottom wafer during the bonding process, which is less susceptible to temperature changes, reducing run-out variations by using a bag filled with a liquid of appropriate compressibility and specific heat capacity, and pre-heating the liquid to minimize mechanical deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an airbag is used to deform and support the wafer during bonding, then the wafer can be supported and deformed, but the system becomes susceptible to temperature changes causing run-out variations and misalignment
Solution Approach 1:
The patent replaces the airbag (gas-based) with a liquid-filled bag. The liquid medium provides hydraulic support to deform and hold the wafer, offering greater stability against temperature changes compared to gas, thereby reducing run-out variations while maintaining support functionality
Solution Approach 2:
The patent changes the physical parameter of the filling medium from gas to liquid. This parameter change exploits the liquid's lower compressibility and different thermal properties to reduce susceptibility to temperature changes, thereby improving alignment accuracy during the bonding process
2Manufacturing precision
If a liquid-filled bag is used instead of an airbag, then temperature susceptibility is reduced and run-out variations decrease, but the device complexity increases
Solution Approach 1:
The patent implements a hydraulic system by filling the bag with liquid, which provides more stable pressure transmission and temperature resistance compared to pneumatic systems. This hydraulic approach improves run-out control despite adding some complexity to the fluid management system
Solution Approach 2:
By changing the medium parameter from gas to liquid, the system gains better thermal stability and reduced compressibility effects. The liquid's physical properties naturally compensate for temperature variations, improving precision without requiring complex active control mechanisms
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 reduces run-out variations, increases the yield of functional devices, and decreases the number of non-functioning devices by stabilizing the bonding process and minimizing mechanical deformation, thereby conserving resources and reducing waste.
Implementation Method 1
A liquid-filled bag is used instead of an airbag to deform and support the bottom wafer during the bonding process
Implementation Method 2
a liquid of appropriate compressibility and specific heat capacity, and pre-heating the liquid to minimize mechanical deformation
Implementation Method 3
The device includes a pipe configured to generate a vacuum between the bag and a first wafer to adhere the first wafer to the bag
Data Source
AI summary
A bag is filled with liquid, instead of an airbag filled with gas, to deform a bottom wafer toward a top wafer during a wafer bonding process. As a result, the liquid is less susceptible to temperature changes, which reduces run-out variation across wafer bonding processes. Reducing run-out variation conserves wasted wafers by increasing yield and reducing a quantity of non-functioning devices that are produced. Additionally, in some implementations, the liquid may be pre-heated before the bag is filled with the liquid. As a result, the bottom wafer (and, to some extent, the top wafer) experiences some thermal deformation and less mechanical deformation, which further increases yield and reduces a quantity of non-functioning devices that are produced.