SiC Crystal Ingot Warpage Reduction via Metal Atom Gradient Control
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Solution Overview
Problem
Large-diameter silicon carbide (SiC) single crystal wafers experience warpage due to concentration differences of heavy metal atoms, which are not evenly distributed during the sublimation growth process, leading to strain and quality issues in semiconductor devices.
Innovation Solution
A method involving acid-cleaning of raw material powder to remove heavy metal atoms like titanium, vanadium, or tantalum, followed by vapor-phase growth of SiC crystal ingots with controlled n-type dopant and metal atom concentrations, ensuring a uniform concentration gradient and reduced strain, thereby minimizing warpage in large-diameter wafers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heavy metal atoms are introduced into SiC single crystal ingot during sublimation growth, then strain in the SiC single crystal ingot is alleviated, but concentration difference of heavy metal atoms occurs between top face and bottom face, causing warpage in large-diameter wafers
Solution Approach 1:
The patent optimizes the concentration parameters of heavy metal atoms and n-type dopant atoms within specific ranges (heavy metal: 1×10^14 to 1×10^18 atoms/cm³, n-type dopant: 1×10^15 to 1×10^20 atoms/cm³) and controls the concentration gradient to ≤1×10^17 atoms/(cm³·mm). By adjusting these parameters, the patent achieves strain alleviation while maintaining uniform distribution to prevent warpage in large-diameter wafers.
Solution Approach 2:
The patent introduces both heavy metal atoms and n-type dopant atoms simultaneously during sublimation growth, creating localized compositional control. The heavy metal atoms (with atomic radius larger than silicon) compensate for compression strain caused by n-type dopant atoms (with atomic radius smaller than silicon), achieving balanced strain distribution throughout the crystal ingot.
2Productivity
If large-diameter SiC single crystal wafers are produced to meet market demand, then productivity is improved, but warpage occurs due to concentration difference of heavy metal atoms
Solution Approach 1:
The patent establishes specific concentration ranges and gradient limits for heavy metal atoms that enable production of large-diameter wafers (4 inches or more) while maintaining uniform distribution. The controlled concentration gradient ensures that even in large-diameter wafers, the heavy metal atom distribution remains uniform enough to prevent warpage, thus enabling high-productivity production of large wafers without sacrificing flatness.
3Reliability
If n-type dopant atoms with atomic radius smaller than silicon are introduced, then electrical properties are improved, but compression strain is generated in the SiC single crystal ingot
Solution Approach 1:
The patent introduces heavy metal atoms (with atomic radius larger than silicon) to compensate for the compression strain generated by n-type dopant atoms (with atomic radius smaller than silicon). This dual-introduction strategy creates a balanced local composition where the strain effects of the two types of atoms offset each other, maintaining both electrical properties and mechanical stability.
Solution Approach 2:
The heavy metal atoms act as a counterweight to the compression strain caused by n-type dopant atoms. Since heavy metal atoms have larger atomic radius than silicon, they generate expansion strain that counterbalances the compression strain from the smaller n-type dopant atoms, achieving net strain alleviation while preserving electrical functionality.
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 alleviates strain in SiC crystal ingots and reduces warpage in large-diameter wafers, maintaining favorable electrical resistance and crystallinity, while allowing for the production of high-quality SiC wafers with reduced thickness variations and improved off-angle orientations.
Implementation Method 1
metal single substance of heavy metal atoms such as titanium, vanadium, or tantalum, or a compound thereof (metal compound such as oxide or sulfide with heavy metal as the main component) is added to the SiC raw material powder to grow a SiC single crystal ingot on the seed crystal by sublimation
Implementation Method 2
vapor-phase growing a silicon carbide crystal ingot using the raw material powder
Data Source
AI summary
A silicon carbide crystal ingot having a surface greater than or equal to 4 inches, having an n-type dopant concentration greater than or equal to 1×1015 atoms/cm3 and less than or equal to 1×1020 atoms/cm3, a metal atom concentration greater than or equal to 1×1014 atoms/cm3 and less than or equal to 1×1018 atoms/cm3, and not exceeding the n-type dopant concentration, and a metal atom concentration gradient less than or equal to 1×1017 atoms/(cm3·mm), a silicon carbide single crystal wafer produced using the ingot, and a method for fabricating the silicon carbide crystal ingot.