Single Crystal SiC Substrate Fabrication via Glass Interlayer
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Solution Overview
Problem
Current methods for producing single crystal SiC substrates result in expensive, small-sized substrates due to high temperature processing limitations and thermal expansion differences between Si and SiC, leading to substrate warping and size constraints.
Innovation Solution
A method involving phosphorous ion introduction to convert embedded oxide layers into glass layers with lower softening points, allowing for hydrocarbon-based gas processing and cooling to form single crystal SiC substrates with reduced warping and increased size, using a polycrystalline SiC substrate as a base material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SiO2 embedded layer is used in SOI substrate, then substrate structure is formed, but substrate warping occurs due to thermal expansion difference between Si and SiC during cooling after carbonization
Solution Approach 1:
The patent changes the material parameter of the embedded layer from SiO2 (softening point ~1200°C) to a low softening point glass layer (softening point 700-900°C). This parameter change allows the embedded layer to remain flexible during carbonization at 1400-1600°C, accommodating thermal expansion differences between Si and SiC, and preventing substrate warping during cooling.
Solution Approach 2:
The low softening point glass layer acts as an intermediary between the Si base material layer and the SiC layer. It absorbs and compensates for the differential thermal shrinkage during cooling, serving as a buffer that prevents direct stress transmission that would cause warping, while maintaining the structural integrity of the substrate.
2Manufacturing precision
If high temperature carbonization process (1400°C or more) is used to form single crystal SiC, then single crystal SiC layer is formed, but Si base material cannot be subjected to such high temperature
Solution Approach 1:
The patent segments the substrate into three distinct layers: Si base material layer, low softening point glass embedded layer, and surface Si layer. This segmentation allows each layer to experience different thermal conditions during processing - the Si base material remains below its melting point while the surface Si layer undergoes carbonization at 1400-1600°C to form single crystal SiC.
Solution Approach 2:
The low softening point glass layer serves as a thermal intermediary that protects the Si base material from direct exposure to the full thermal stress of carbonization. It absorbs excess thermal energy and prevents heat from reaching the Si base material at temperatures that would cause melting, while still allowing the surface Si layer to achieve the necessary temperature for single crystal SiC formation.
3Reliability
If insulation layer (SiO2) is used in SOI substrate, then electrical insulation is provided, but softening point is too high causing substrate warping during cooling
Solution Approach 1:
The patent changes the softening point parameter of the embedded insulation layer from high (~1200°C for SiO2) to low (700-900°C for low softening point glass). This parameter change enables the layer to provide electrical insulation while remaining flexible during thermal processing, accommodating thermal expansion differences and preventing substrate warping during cooling after carbonization.
Solution Approach 2:
The patent uses a composite material approach by replacing pure SiO2 with a low softening point glass composition that combines insulation properties with thermal flexibility. This composite material provides both electrical insulation functionality and mechanical compliance during thermal processing, resolving the contradiction between insulation performance and warping prevention.
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
The method effectively suppresses substrate warping and maintains high crystallinity, enabling the production of large-sized single crystal SiC substrates with reduced costs by using a polycrystalline SiC substrate and embedded glass layers to manage thermal expansion differences.
Implementation Method 1
a phosphorous ion introduction step for introducing phosphorous ions from a side of a surface Si layer into an SOI substrate
Implementation Method 2
to convert the embedded oxide layer into an embedded glass layer
Implementation Method 3
an SiC forming step for heating the SOI substrate having the embedded glass layer formed therein in an atmosphere of hydrocarbon-based gas to convert the surface Si layer into SiC
Implementation Method 4
cooling the resulting substrate to form a single crystal SiC layer on a surface
Data Source
AI summary
A single crystal SiC substrate is produced with low cost in which a polycrystalline SiC substrate with relatively low cost is used as a base material substrate where the single crystal SiC substrate has less strain, good crystallinity and large size. The method including a P-type ion introduction step for implanting P-type ions from a side of a surface Si layer 3 into an SOI substrate 1 in which the surface Si layer 3 and an embedded oxide layer 4 having a predetermined thickness are formed on an Si base material layer 2 to convert the embedded oxide layer 4 into a PSG layer 6 to lower a softening point, and an SiC forming step for heating the SOI substrate 1 having the PSG layer 6 formed therein in an atmosphere hydrocarbon-based gas to convert the surface Si layer 3 into SiC, and thereafter, cooling the resulting substrate to form a single crystal SiC layer 5 on a surface thereof.