Silicon Carbide Crystal Boule Geometry for Reduced Wafer Warping
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Solution Overview
Problem
Silicon carbide crystal boules often have protruding or depressed surfaces, leading to material loss and residual stress during wafer production, which can result in warped wafers.
Innovation Solution
A manufacturing method that controls the axial and radial temperature gradients during crystal growth to form a silicon carbide crystal boule with a specific ratio (ΔTz/ΔTx) of 0.3 to 0.8, resulting in a boule with a flat surface, truncated cone, and annular curved surface, minimizing surface irregularities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the PVT method is used to grow silicon carbide crystal boules, then large single-crystal silicon carbide crystals can be formed, but the resulting crystal boules contain protruding or depressed surfaces that cause material loss and residual stress
Solution Approach 1:
The patent applies parameter changes by precisely controlling the temperature gradient ratio (axial to radial) within the range of 0.3 to 0.8 during the PVT growth process. This parameter optimization enables the formation of crystal boules with flat surfaces and appropriate curvature, eliminating protrusions and depressions while maintaining large crystal size. The controlled temperature distribution ensures uniform material deposition and reduces residual stress.
2Productivity
If the temperature gradient is increased to improve crystal growth rate, then productivity increases, but surface irregularities and residual stress worsen
Solution Approach 1:
The patent resolves this contradiction by optimizing the temperature gradient ratio parameter to a specific range (0.3 to 0.8). This controlled parameter setting enables rapid crystal growth while simultaneously maintaining surface uniformity and preventing protrusions. The balanced temperature distribution achieves both high productivity and high manufacturing precision.
3Manufacturing precision
If material is removed to smooth the surface, then surface quality improves, but material loss increases
Solution Approach 1:
The patent applies preliminary action by controlling the temperature gradient during the crystal growth process itself to prevent surface irregularities from forming in the first place. By maintaining the axial to radial temperature gradient ratio between 0.3 and 0.8, the crystal boule develops a flat surface with appropriate curvature during growth, eliminating the need for subsequent material removal and thereby preventing material loss.
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 produces high-quality silicon carbide boules with reduced surface protrusions, minimizing material loss and residual stress, thereby improving wafer quality and efficiency.
Implementation Method 1
the raw materials are heated in a high temperature furnace to sublime into a gas phase
Implementation Method 2
silicon carbide in the gas phase gradually deposits on the seed crystal to form large single-crystal silicon carbide crystals
Implementation Method 3
the growth body has an axial temperature gradient in the axial direction, and the growth body has a radial temperature gradient in the radial direction
Data Source
AI summary
A silicon carbide crystal boule includes a flat surface, a truncated cone surface, and an annular curved surface. The annular curved surface connects the flat surface and the truncated cone surface. A width of the silicon carbide crystal boule gradually decreases from a first end of the truncated cone surface connecting the annular curved surface to a second end opposite to the first end.