SiC Wafer Reuse With Laser Lift-Off and Thickness Restoration
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Solution Overview
Problem
Current methods for manufacturing SiC device wafers face challenges such as high wafering loss, instability in high temperature processes, warp, bow, and risk of breakage, especially for large diameter substrates, due to varying substrate thicknesses and stress from doping differences.
Innovation Solution
A method involving slicing and polishing of SiC boule crystals to create thick substrates, which are then processed to create device wafers using laser lift-off, with the remaining substrate refurbished by adding SiC to maintain original thickness, allowing for repeated use and reducing material waste.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If conventional laser slicing is used to manufacture SiC device wafers, then device wafers can be produced, but wafering loss is high and substrate thickness varies
Solution Approach 1:
The method performs preliminary action by growing a uniform thick substrate layer to a predetermined thickness before device fabrication. This pre-established uniform thickness foundation enables subsequent device processing without varying substrate thickness, thereby reducing wafering loss while maintaining manufacturing precision.
Solution Approach 2:
The invention changes the substrate thickness parameter by growing substantially the entire thickness of the substrate in a single epitaxial process rather than slicing from a boule. This parameter change from sliced varying thickness to grown uniform thickness directly addresses both the wafering loss and thickness uniformity issues.
2Quantity of substance
If thin substrates are used for device fabrication, then material usage is efficient, but substrate stability in high temperature processes deteriorates
Solution Approach 1:
The invention optimizes the substrate thickness parameter by growing it to a specific uniform thickness that balances material efficiency with mechanical stability. The substantially uniform thickness throughout the substrate ensures adequate strength for high temperature processing while minimizing excess material usage.
Solution Approach 2:
The method creates a new uniform substrate layer through epitaxial growth that copies and replaces the original sliced substrate. This grown substrate layer has superior uniformity and stability characteristics compared to conventionally sliced substrates, enabling reliable high temperature processing with efficient material usage.
3Ease of manufacture
If substrates with varying thicknesses are used, then device fabrication is possible, but warp and bow increase
Solution Approach 1:
The invention fundamentally changes the thickness parameter from varying to substantially uniform throughout the substrate. This uniform thickness parameter is maintained throughout the entire substrate, eliminating the warp and bow that result from thickness variations, while still enabling complete device fabrication processes.
4Strength
If thick substrates are used to improve stability, then substrate strength increases, but material waste increases
Solution Approach 1:
The invention optimizes the thickness parameter by growing substrates to a predetermined uniform thickness that is sufficient for strength requirements but not excessive. This precise parameter control through epitaxial growth ensures adequate substrate strength for handling and processing while minimizing material waste compared to using uniformly thick substrates grown or sliced to maximum thickness.
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 wafering loss, increases substrate stability, minimizes warp and bow, and reduces the risk of breakage, while enabling more efficient handling and processing, particularly for substrates above 150 mm in diameter, and allows for higher geometrical quality and increased yield of device wafers per boule crystal.
Implementation Method 1
subjecting the solid to LASER radiation from the LASER light source so that the laser beams penetrate into the solid via a surface of the solid portion that is to be cut off
Implementation Method 2
a number of modifications is successively created in the crystal lattice by the applied laser radiation, and the crystal lattice fissures at least partially in the regions surrounding the modifications
Data Source
AI summary
There is provided a method for manufacturing a SiC device wafer comprising the steps: a) slicing and polishing a SiC boule to thicker substrates compared to the usual thickness in the prior art, b) creating a device wafer on the substrate, c) removing the device wafer from the remaining substrate, d) adding SiC to the remaining substrate so that the original thickness of the substrate is essentially restored, and repeating steps b)-d). The removal of the device wafer can be made for instance by laser slicing. Advantages include that the SiC material loss is significantly decreased and the boule material used for device wafers is considerably increased, the substrates become more stable especially during high temperature processes, the warp and bow is reduced, the risk of breakage is decreased.