Plasma-Activated Laminated Wafer Bonding
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Solution Overview
Problem
Conventional methods for manufacturing laminated wafers, such as SOI wafers, face issues with cracking and untransferred portions due to differences in thermal expansion coefficients between silicon and handle wafers like quartz and sapphire, leading to insufficient bonding strength and potential wafer breakage during high-temperature heat treatments.
Innovation Solution
A high-temperature laminating method involving plasma surface activation treatment of silicon and insulating substrates, bonding at temperatures between 50°C and 300°C, followed by a heat treatment between 200°C and 350°C, and subsequent thinning of the silicon wafer using grinding, etching, and polishing to achieve strong bonding without cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high temperature heat treatment is applied to bond silicon wafer to handle wafer, then bonding strength is improved, but wafer cracking occurs due to thermal expansion coefficient difference
Solution Approach 1:
The patent applies preliminary plasma treatment to the surfaces of both silicon wafer and handle wafer before bonding. This activation treatment creates hydroxyl groups on the surfaces that form strong hydrogen bonds during subsequent low-temperature bonding, eliminating the need for high-temperature heat treatment that would cause cracking from thermal expansion differences.
Solution Approach 2:
The patent changes the bonding temperature parameter from conventional high temperature (500°C or higher) to low temperature (room temperature or slightly elevated). This parameter change, combined with plasma surface activation, achieves strong bonding without the thermal stress that causes wafer cracking, thus resolving the contradiction between bonding strength and wafer integrity.
2Reliability
If room temperature bonding is used to avoid thermal expansion issues, then wafer cracking is prevented, but bonding strength is insufficient
Solution Approach 1:
The patent applies preliminary plasma treatment to activate the wafer surfaces before bonding. This treatment introduces reactive hydroxyl groups that create strong chemical bonds at low temperatures, achieving both strong bonding strength and prevention of thermal expansion-related cracking.
Solution Approach 2:
The patent replaces the conventional thermal-mechanical bonding mechanism (relying on heat and pressure) with a chemical bonding mechanism based on plasma-activated surface reactions. This substitution allows bonding to occur at low temperatures while maintaining or enhancing bond strength through chemical affinity rather than mechanical compression.
3Strength
If plasma surface activation treatment is applied, then bonding strength at low temperature is improved, but process complexity increases
Solution Approach 1:
The patent replaces complex high-temperature thermal processing equipment and procedures with a plasma treatment system followed by low-temperature bonding. While plasma equipment is specialized, the overall process eliminates the need for high-temperature furnaces and complex thermal management, simplifying the manufacturing workflow and reducing 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
This method ensures strong coupling between wafers with different thermal expansion coefficients without lowering the maximum heat treatment temperature, preventing wafer cracking and achieving robust bonding.
Implementation Method 1
applying a plasma surface activation treatment to a surface of a silicon wafer or a silicon wafer covered with an oxide film and/or to the surface of the insulating substrate
Implementation Method 2
applying a heat treatment of 200°C to 350°C to the laminated wafer
Data Source
Figure 1
Figure 2~3
AI summary
To provide a method of manufacturing a laminated wafer by which a strong coupling is achieved between wafers made of different materials having a large difference in thermal expansion coefficient without lowering a maximum heat treatment temperature as well as in which cracks or chips of the wafer does not occur. A method of manufacturing a laminated wafer 7 by forming a silicon film layer on a surface 4 of an insulating substrate 3 comprising the steps in the following order of: applying a surface activation treatment to both a surface 2 of a silicon wafer 1 or a silicon wafer 1 to which an oxide film is layered and a surface 4 of the insulating substrate 3 followed by laminating in an atmosphere of temperature exceeding 50°C and lower than 300°C, applying a heat treatment to a laminated wafer 5 at a temperature of 200°C to 350°C, and thinning the silicon wafer 1 by a combination of grinding, etching and polishing to form a silicon film layer.