Abstract

Silicon carbide (SiC), as a third-generation semiconductor material, exhibits excellent physical and chemical properties, making it highly promising for applications in power electronics, RF devices, and high-temperature, high-frequency fields. Currently, the industrial preparation of SiC single crystals primarily relies on the Physical Vapor Transport (PVT) method, which utilizes high-temperature sublimation, vapor transport, and crystal growth to produce high-quality SiC boules. This paper provides a detailed explanation of the fundamental principles, process flow, key technical parameters, and challenges associated with the PVT method, along with possible improvements for future advancements.

1. Introduction

Silicon carbide (SiC) is a wide-bandgap semiconductor material with high breakdown field strength, excellent electron mobility, superior thermal conductivity, and outstanding high-temperature stability. It has been widely adopted in electric vehicles, photovoltaic inverters, 5G RF communications, and aerospace applications. Compared to traditional silicon (Si), SiC demonstrates superior performance in high-voltage, high-current, and high-temperature environments.

The primary methods for SiC single crystal growth include Physical Vapor Transport (PVT), High-Temperature Chemical Vapor Deposition (HT-CVD), and Solution Growth Method. Among these, the PVT method has become the mainstream technology due to its mature process and ability to produce high-quality single crystals.

2. Fundamental Principles of the PVT Method

The PVT method is based on the process of high-temperature sublimation - vapor transport - deposition crystallization. The core principle is leveraging SiC's sublimation characteristics at high temperatures, where it decomposes into gaseous silicon (Si) and carbon (C). These vapors then migrate under a temperature gradient and recondense on the seed crystal to form high-quality SiC single crystals. The primary chemical reactions involved are:

In this process, parameters such as growth temperature, temperature gradient, growth pressure, and seed crystal quality significantly influence the crystal's quality, defect density, and growth rate.

3. PVT Growth Process

The PVT method for SiC crystal growth typically involves the following key steps:

3.1 Equipment and Raw Material Preparation

SiC Powder Source: High-purity (>99.999%) SiC powder is used to ensure minimal impurities in the growth environment.

SiC Seed Crystal: A 4H-SiC or 6H-SiC seed is selected to determine the polytype and orientation of the grown crystal.

Graphite Crucible: Serves as a high-temperature container for the SiC powder and seed crystal, requiring high thermal stability and excellent thermal conductivity.

High-Temperature Furnace: Provides an ultra-high-temperature environment (2300–2500°C) with a stable temperature gradient.

Gas Atmosphere Control: High-purity argon (Ar) is typically used as a protective gas to prevent oxidation and unwanted chemical reactions.

3.2 Temperature Gradient Control

The temperature gradient in the PVT process is crucial for vapor transport and deposition. Typically:

High-Temperature Zone (Powder Source Area): 2300–2500°C to sublimate SiC powder.

Low-Temperature Zone (Seed Crystal Area): 2100–2300°C to facilitate vapor condensation and single crystal growth.

Temperature Difference: 50–200°C, optimized to control the growth rate and crystal quality.

3.3 Crystal Growth Process

SiC powder sublimates at high temperatures, generating Si and C vapors.

Vapor transport occurs under the influence of the temperature gradient, reaching the seed crystal.

Si and C recondense and crystallize, gradually forming large SiC single crystals.

Precise control of sublimation and vapor transport rates ensures uniform single-crystal growth.

3.4 Cooling and Extraction

After the SiC boule has grown, it undergoes slow cooling to prevent thermal stress-induced cracking. Finally, the boule is extracted from the graphite crucible and processed into wafers for subsequent applications.

4. Key Process Parameters

The PVT method's process parameters play a decisive role in determining SiC crystal quality and production efficiency. The key parameters include:

5. Major Technical Challenges

Despite being the mainstream method for SiC single crystal growth, the PVT process still faces several technical challenges:

Crystal Defects: Common defects such as screw dislocations (SD), micropipes (MP), and stacking faults (SF) affect device performance.

Limited Crystal Size: Current industrial production is mainly focused on 4-inch (100 mm) and 6-inch (150 mm) wafers, while 8-inch (200 mm) technology is still under development.

High-Temperature Equipment Constraints: PVT requires extreme temperatures, posing challenges for graphite crucibles and furnace durability.

Growth Rate and Cost Issues: PVT has a relatively low growth rate, long production cycles, and high costs, making SiC wafers significantly more expensive than Si wafers.

6. Future Development and Improvements

To enhance the efficiency and quality of the PVT method, current research focuses on:

Reducing Defect Density: Utilizing optimized thermal field control, low-defect seed crystals, and epitaxial repair techniques.

Increasing Crystal Size: Developing Isothermal PVT (I-PVT) to improve thermal stress distribution and facilitate 8-inch SiC commercialization.

Exploring Alternative Growth Methods: Investigating High-Temperature Chemical Vapor Deposition (HT-CVD) to enhance growth rates and reduce costs.

7. Conclusion

The PVT method remains the primary technology for industrial SiC single crystal growth, offering a well-established process and scalable production capabilities. However, challenges related to defect control, crystal size, and growth rates must be addressed through continuous process optimization. Future advancements in PVT and alternative growth methods will further drive down manufacturing costs and expand SiC adoption in high-end semiconductor applications.