Semiconductor Wafer Bonding Thermal Stress Reduction
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Solution Overview
Problem
Current methods for bonding semiconductor wafers to achieve strong vacuum levels are inefficient, leading to increased baking time, thermal mismatch, and mechanical stress, which affect wafer quality and throughput.
Innovation Solution
Pressurizing the bond chamber with an inert gas to enhance heat transfer and temperature uniformity during the baking process, allowing for faster out-gassing of residual gases and reducing thermal stress between wafers before vacuum sealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wafers are baked to remove residual absorbed gases before vacuum sealing, then vacuum level is improved, but baking time increases costs and decreases wafer throughput
Solution Approach 1:
The patent applies preliminary action by performing the baking process under atmospheric pressure before vacuum sealing, rather than attempting to remove gases during or after vacuum sealing. This preliminary outgassing step at atmospheric pressure allows residual absorbed gases to be removed more efficiently, enabling shorter baking times while achieving the required vacuum level, thus improving throughput without sacrificing vacuum quality
Solution Approach 2:
The patent changes the pressure parameter during the baking process by conducting it under atmospheric pressure rather than vacuum. This parameter change enables more effective heat transfer to the wafer, accelerating the outgassing process and reducing the time required to achieve the desired vacuum level, thereby resolving the contradiction between vacuum quality and production efficiency
2Reliability
If a getter material is used to absorb residual gases after vacuum sealing, then vacuum level is improved, but cost and complexity of wafer processing increase
Solution Approach 1:
The patent extracts the gas removal function from the vacuum sealing process itself by performing preliminary outgassing under atmospheric pressure. This separates the outgassing function from the vacuum sealing operation, eliminating the need for additional getter materials or complex post-sealing gas absorption mechanisms, thereby reducing processing complexity while maintaining vacuum quality
Solution Approach 2:
By performing the gas removal action before vacuum sealing rather than relying on getter materials after sealing, the patent eliminates the need for additional components and processing steps. The preliminary outgassing at atmospheric pressure prepares the wafer in advance, making subsequent vacuum sealing simpler and more direct
3Temperature
If bottom wafer experiences poor thermal contact with lower heater while top wafer receives radiant heating, then heating is achieved, but temperature difference forms mechanical stress on bonded wafers
Solution Approach 1:
The patent changes the pressure parameter to atmospheric pressure during heating, which fundamentally alters the heat transfer mechanism. At atmospheric pressure, convection and conduction become more effective, allowing the bottom wafer to receive adequate thermal energy through the heater contact. This parameter change equalizes temperature distribution across both wafers, preventing thermal stress while maintaining effective heating
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 significantly reduces baking time, improves vacuum strength, and minimizes mechanical stress between wafers, enhancing the efficiency and yield of the bonding process.
Implementation Method 1
pressurizing the bond chamber with an inert gas to enhance heat transfer
Implementation Method 2
pressurizing the bond chamber with an inert gas to enhance heat transfer and temperature uniformity during the baking process
Implementation Method 3
allowing for faster out-gassing of residual gases
Implementation Method 4
pressurizing the bond chamber with an inert gas to enhance heat transfer and temperature uniformity during the baking process, allowing for faster out-gassing of residual gases
Implementation Method 5
Pressurizing the bond chamber with an inert gas to enhance heat transfer and temperature uniformity during the baking process
Data Source
AI summary
A method of bonding a cap wafer to a device wafer includes heating the device wafer and the cap wafer in the chamber, cooling the device wafer and the cap wafer in the chamber, pressurizing the chamber, introducing gas into the chamber while the chamber is pressurized to accelerate a rate of one of a group consisting of the heating and the cooling, and applying pressure to the device wafer and the cap wafer while a bond is formed between the device wafer and the cap wafer.