PVT method: the "high-temperature dilemma" behind mature processes

Process principles and core processes

PVT method is currently the mainstream technology for commercial silicon carbide single crystals. Its principle is to sublime silicon carbide powder into gas phase at high temperature (>2000 ℃), and then condense and crystallize on the surface of the seed crystal. The key steps include:

Raw material synthesis: High purity silicon powder reacts with carbon powder at temperatures above 2000 ℃ to produce polycrystalline silicon carbide particles;

Crystal growth: In a closed graphite furnace, gas phase transport and crystal diameter expansion are achieved by precise control of temperature gradient (axial temperature difference of about 50 ℃/cm) and pressure (0.2-80kPa);

Cooling processing: After the growth is completed, it is necessary to cool down at a very slow rate (about 1 ℃/minute) to avoid crystal cracking caused by thermal stress.

2. Technical difficulties and industrial bottlenecks

Although PVT method has been developed for more than 40 years, low yield (about 30% -50%) and high cost are still the core pain points:

Black box growth environment: High temperatures above 2000 ℃ limit temperature measurement accuracy, and process parameters rely on accumulated experience, making it difficult to monitor in real time;

Crystal type control challenge: There are over 200 crystal types of silicon carbide, and commercial demand is concentrated on 4H SiC. Small temperature fluctuations during the growth process can trigger phase transitions, leading to various types of inclusions and defects;

High density of crystal defects: defects such as microtubes and dislocations have a density of 102-103/cm ², directly affecting device reliability;

Slow expansion speed: The growth rate is only 0.3-0.5mm/h, and 6-inch ingots need to be continuously grown for 7-10 days, with energy consumption accounting for more than 40% of the total cost.

Liquid phase method: the rise of low-cost disruptors

Technological innovation and breakthrough advantages

The liquid-phase method reduces the melting point of silicon carbide (about 1500 ℃) by using solvents such as silicon-based alloys, and achieves crystal growth in a near equilibrium state. Its core advantages include:

Significant temperature reduction: The growth temperature is reduced by about 500 ℃ compared to PVT method, and equipment loss is reduced by 30%;

Crystal quality leap: defect density can be reduced to 1/10 of PVT method, there is no giant step coalescence phenomenon, and the resistivity is as low as 0.1 Ω· cm;

P-type crystal breakthrough: capable of stable preparation of 4H SiC P-type crystals, providing material basis for high-voltage devices such as IGBT;

High expansion efficiency: The Chinese Academy of Sciences team used liquid-phase method to grow 6-inch and 8-inch P-4H-SiC single crystals. Among them, 8-inch P-type 4H SiC single crystal growth with a thickness of 8mm.

2. Industrialization obstacles and research directions

Despite its broad prospects, liquid-phase methods still face three major challenges:

Solvent impurity control: Residual metal impurities (such as Fe, Al) need to be reduced to below 0.5ppm, otherwise they will affect electrical performance;

Balance of growth rate: Excessive growth can introduce defects, while low growth rate (such as conventional LPE method only 0.01mm/h) is difficult to meet mass production requirements;

Equipment adaptation challenge: It is necessary to develop corrosion-resistant reaction chambers. Although the MPZ technology of a Japanese company has increased the speed by 200 times, the equipment cost is still high.

PVT vs Liquid Phase Method: Technical Roadmap Showdown

Comparison Dimension PVT Method Liquid Phase Method

Maturity level

Commercial mainstream (90% global production capacity)

Transition stage from laboratory to small-scale production

growth temperature 

2000-2500℃

1500-1800℃

Crystal quality

High defect density (10 ² -10 ³/cm ²)

Low defect density (<10 ²/cm ²)

Crystal control

Low yield of 4H SiC (about 50%)

Stable preparation of P-type 4H and 3C SiC

cost structure 

Equipment depreciation and energy consumption account for 70%

Assisting in solvent recovery can reduce costs by 30%

Application scenarios

Mature devices such as MOSFET and SBD

Emerging fields such as high-voltage IGBT and RF devices

Future Trends: Technology Fusion and Size Upgrade

1. 8-inch wafer race acceleration

PVT method: Wolfspeed has already mass-produced 8-inch substrates, and domestic companies such as Tianyue Advanced and Tianke Heda are also rapidly expanding their production capacity;

Liquid phase method: A joint venture of the Chinese Academy of Sciences has broken through the 8-inch P-type crystal, but the yield still needs to be improved.

Conclusion: "Dual track Parallel" in the Silicon Carbide Era

PVT method will still dominate the market in the next 5 years with mature technology, but the potential of liquid-phase method in terms of cost and performance cannot be underestimated. With the explosive demand for 800V high-voltage platforms in new energy vehicles and the thirst for high-temperature resistant devices in photovoltaic inverters, the two technologies may complement each other. The ultimate outcome of this technological game may be determined by who can break through the "defect control" and "cost threshold" first.