Load-Lock Cooling Member for Wafer Flatness
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Solution Overview
Problem
High-temperature semiconductor wafers experience warping due to rapid cooling in load-lock mechanisms, leading to thermal expansion differences and contamination risks during transfer between vacuum and atmospheric pressures, necessitating effective cooling and straightening methods.
Innovation Solution
A load-lock mechanism with a chamber, cooling member, gas exhaust unit, and purge gas inlet, controlling pressure transitions to maintain a molecular flow condition between the substrate and cooling plate, allowing for controlled cooling and straightening of high-temperature substrates by heat transfer through a purge gas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If rapid cooling is applied to high-temperature wafers in the load-lock mechanism, then cooling efficiency is improved, but wafer warpage increases due to thermal expansion differences
Solution Approach 1:
The cooling plate is designed with a non-uniform temperature distribution, being cooler at the center and warmer at the edges. This local quality variation in temperature matches the thermal expansion characteristics of the wafer, allowing rapid cooling while maintaining wafer flatness by compensating for differential thermal contraction across the wafer surface.
2Loss of time
If wafers are cooled before pressure equalization, then cooling efficiency is improved, but oxidation and contamination occur when exposed to atmospheric pressure
Solution Approach 1:
The system performs preliminary cooling of the wafer on the cooling plate while the load-lock chamber is still under vacuum conditions. Only after the wafer temperature has been reduced to a safe level does the system equalize the pressure to atmospheric levels. This preliminary action sequence ensures that the wafer is cooled efficiently without being exposed to oxidative atmospheric conditions during the high-temperature cooling phase.
3Loss of time
If wafers are cooled while in contact with the cooling plate, then cooling efficiency is improved, but warpage occurs due to uneven thermal contraction
Solution Approach 1:
The cooling plate implements local quality by creating a specific temperature profile with the center region cooler than the edge regions. This non-uniform cooling pattern compensates for the natural tendency of wafers to warp during cooling, as the cooler center promotes greater thermal contraction in that region, balancing the overall wafer shape and maintaining flatness throughout the rapid cooling process.
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 method effectively cools and straightens warped substrates efficiently, reducing thermal expansion differences and preventing contamination, while maintaining thermal uniformity and shortening cooling times.
Implementation Method 1
cooling the substrate by heat transfer from the cooling member
Implementation Method 2
exhausting the chamber such that the pressure in the chamber becomes a third pressure at which a region between a surface of the cooling plate and a backside of the wafer satisfies a molecular flow condition
Data Source
AI summary
A substrate cooling method is for, using a load-lock mechanism for controlling a pressure therein between a first pressure close to an atmospheric pressure and a second pressure in a vacuum state, cooling a substrate transferred from the second module to the first module. The method includes maintaining a pressure in the chamber to the second pressure, allowing the chamber to communicate with a second module, and loading the substrate into the chamber; locating the substrate to a cooling position close to the cooling member; exhausting the chamber such that the pressure in the chamber becomes a third pressure where a region between a surface of the cooling member and a backside of the substrate satisfies a molecular flow condition. The method further includes introducing a purge gas into the chamber to increase the pressure in the chamber to the first pressure, and cooling the substrate by the cooling member.