SiC Epitaxial Growth Nitrogen Reduction via Vanadium Trapping
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Solution Overview
Problem
Conventional methods for forming silicon carbide semiconductor devices with low n-type impurity concentrations face challenges in reducing nitrogen concentration, leading to increased costs and decreased throughput due to prolonged vacuuming and the use of ultrapure gases, especially when growing epitaxial layers on the C-face of silicon carbide substrates.
Innovation Solution
The method involves growing an n-type epitaxial layer in a mixed gas atmosphere containing silicon, carbon, nitrogen, and vanadium, where vanadium tetrachloride is used as a dopant gas, allowing vanadium and nitrogen to bond and form vanadium nitride, reducing the nitrogen concentration in the gas phase and subsequently in the epitaxial layer, with a vanadium concentration lower than nitrogen and a ratio of vanadium to nitrogen flow rates between 1% to 10%.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional methods are used to reduce nitrogen concentration in the epitaxial layer, then nitrogen concentration is reduced, but production cost increases and throughput decreases due to prolonged vacuuming and use of ultrapure gases
Solution Approach 1:
Vanadium is introduced as an intermediary substance that acts as a nitrogen trap during epitaxial growth. The vanadium reacts with nitrogen to form vanadium nitride, effectively removing nitrogen from the gas phase and preventing its incorporation into the epitaxial layer. This mediator approach allows nitrogen reduction without requiring prolonged vacuuming or ultrapure gases, thus maintaining high productivity while achieving low nitrogen concentration.
Solution Approach 2:
The method changes the chemical composition parameters of the growth atmosphere by introducing vanadium tetrachloride gas. By controlling the vanadium to nitrogen flow rate ratio (1% to 10%), the system achieves optimal nitrogen removal efficiency. This parameter change enables the formation of low-nitrogen epitaxial layers under standard vacuum conditions with conventional gases, avoiding the need for extended vacuuming periods and ultrapure gas supplies.
2Manufacturing precision
If conventional methods are used to reduce nitrogen concentration in the epitaxial layer, then nitrogen concentration is reduced, but production cost increases due to prolonged vacuuming and use of ultrapure gases
Solution Approach 1:
Vanadium serves as a cost-effective intermediary that chemically traps nitrogen during the epitaxial growth process. By forming vanadium nitride in the gas phase, it prevents nitrogen incorporation into the crystal structure without requiring expensive ultrapure gas supplies or energy-intensive prolonged vacuuming, thereby significantly reducing production costs while achieving the desired low nitrogen concentration.
Solution Approach 2:
The method employs vanadium tetrachloride as a consumable additive gas that is introduced in controlled amounts (1% to 10% of nitrogen flow rate). This relatively inexpensive substance performs the nitrogen removal function temporarily during growth, after which its role is complete. This approach is more economical than continuously maintaining ultra-high vacuum conditions or using expensive ultrapure gas supplies throughout the process.
3Manufacturing precision
If vanadium is introduced to reduce nitrogen concentration, then nitrogen concentration is reduced, but vanadium concentration increases in the epitaxial layer
Solution Approach 1:
The method precisely controls the vanadium to nitrogen flow rate ratio within 1% to 10%, ensuring that vanadium is introduced at a controlled rate that allows sufficient time for nitrogen removal while preventing excessive vanadium incorporation. This parameter optimization balances nitrogen reduction efficiency with vanadium concentration control, achieving low nitrogen levels while keeping vanadium impurities minimal.
Solution Approach 2:
The potential harm of vanadium contamination is converted into a benefit by carefully controlling the vanadium introduction rate. The controlled vanadium presence serves as an effective nitrogen trap, and by maintaining the vanadium flow at 1% to 10% of nitrogen flow, the system ensures that vanadium is consumed primarily for nitrogen removal rather than accumulating as impurity, thus transforming a potential contaminant into a useful reaction partner.
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 effectively reduces the nitrogen concentration in the n-type epitaxial layer without the need for extended vacuuming or ultrapure gases, thereby lowering production costs and enabling the formation of low-impurity silicon carbide semiconductor devices with high breakdown voltages.
Implementation Method 1
allowing vanadium and nitrogen to bond and form vanadium nitride
Implementation Method 2
thermally decomposing in a carrier gas, a source gas introduced into an epitaxial growth furnace and continuously depositing silicon (Si) atoms
Implementation Method 3
an n−-type epitaxial layer into which nitrogen (N) is introduced (doped) as a dopant is grown
Data Source
AI summary
An n−-type epitaxial layer is grown on a front surface of the silicon carbide substrate by a CVD method in a mixed gas atmosphere containing a source gas, a carrier gas, a doping gas, an additive gas, and a gas containing vanadium. The doping gas is nitrogen gas; and the gas containing vanadium is vanadium tetrachloride gas. In the mixed gas atmosphere, the vanadium bonds with the nitrogen, producing vanadium nitride, whereby the nitrogen concentration in the mixed gas atmosphere substantially decreases. As a result, the nitrogen taken in by the n−-type epitaxial layer decreases and the n−-type epitaxial layer including nitrogen and vanadium as dopants is grown having a low impurity concentration.