Silicon Carbide Substrate Dopant Distribution for Crack Reduction
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Solution Overview
Problem
Conventional silicon carbide single crystals exhibit uneven dopant incorporation leading to thermal stress, cracking, and increased likelihood of stacking faults due to temperature gradients during growth, resulting in substrates with residual tensile stress and heterogeneous crystal formation.
Innovation Solution
A silicon carbide substrate with a dopant distribution where the resistivity decreases radially outward from the center, maintaining a resistivity difference of 0.015 or less, reducing thermal expansion coefficient disparities and inclination angles, thereby minimizing crack and stacking fault occurrences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional sublimation recrystallization method is used with temperature gradient (lower at center, higher at periphery), then crystal growth can proceed, but crystal growth rate becomes uneven (faster at center, slower at periphery) causing convex curved surface and uneven dopant incorporation
Solution Approach 1:
The patent inverts the temperature distribution pattern during crystal growth, making the center portion hotter and peripheral portion cooler. This parameter change reverses the dopant incorporation pattern, creating a compensating gradient that offsets the convex curvature effect, thereby achieving uniform average dopant concentration across the substrate.
Solution Approach 2:
The patent applies different temperature conditions to different regions of the crystal growth surface. The center region receives higher temperature while peripheral regions receive lower temperature, creating localized quality differences that compensate for the inherent convex curvature and achieve uniform dopant distribution.
2Stability of the object's composition
If temperature gradient during growth causes faster growth at center and slower at periphery, then crystal formation proceeds, but residual tensile stress and cracking occur
Solution Approach 1:
By inverting the temperature distribution (center hotter, periphery cooler), the patent changes the thermal stress pattern during growth. This creates compressive stress at the center that compensates for the tensile stress that would otherwise develop, preventing cracking while maintaining crystal structure formation.
Solution Approach 2:
The patent applies preliminary counter-action by creating opposite thermal gradients during growth that pre-compensate for the stress patterns that would normally develop. The inverted temperature distribution creates preliminary compressive stress that counteracts the eventual tensile stress, preventing crack formation.
3Productivity
If peripheral portion has higher temperature and slower growth rate, then crystal growth occurs, but inclination angle increases and stacking faults occur
Solution Approach 1:
The patent inverts the temperature distribution pattern, making the center hotter and periphery cooler. This parameter change reduces the inclination angle at peripheral regions by slowing growth less dramatically, thereby reducing stacking faults while maintaining overall crystal growth.
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 substrate design effectively reduces the occurrence of cracks, stacking faults, and heterogeneous crystals, even in larger diameters, by controlling dopant distribution and temperature gradients during growth, ensuring improved structural integrity and crystal quality.
Implementation Method 1
A value obtained by dividing a difference between a resistivity of the silicon carbide substrate at the center and a minimum resistivity of the silicon carbide substrate on the off-downstream side with respect to the center by the resistivity of the silicon carbide substrate at the center is 0.015 or less
Data Source
AI summary
A silicon carbide substrate includes a dopant. The silicon carbide substrate has, on an off-downstream side with respect to a center of the silicon carbide substrate in plan view, a portion having a resistivity lower than a resistivity at the center of the silicon carbide substrate in plan view. A value obtained by dividing a difference between the resistivity of the silicon carbide substrate at the center of the silicon carbide substrate in plan view and a minimum resistivity of the silicon carbide substrate on the off-downstream side with respect to the center of the silicon carbide substrate in plan view by the resistivity of the silicon carbide substrate at the center of the silicon carbide substrate in plan view is 0.015 or less. The resistivity of the silicon carbide substrate increases from a position at which the silicon carbide substrate has the minimum resistivity toward the off-downstream side.