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The new star of semiconductor materials: CVD diamond
Diamond, also known as diamond, can be divided into single crystals, conjoined crystals and polycrystals according to the crystal shape. Among them, diamond single crystal has an irreplaceable role in certain application fields due to its few defects and high quality. However, natural diamond single crystals are very expensive in nature due to their long formation process and relative scarcity.
However, as artificial synthesis methods become more and more mature, artificial diamonds gradually come to the fore. With their high strength, high hardness, small thermal expansion coefficient, high thermal conductivity, chemical stability, superior light transmittance and electrical properties, they are becoming more and more popular in the world. has attracted widespread research interest. Especially in the field of semiconductors, it is considered to have great potential.
1.Preparation of CVD diamond
At present, the methods for artificially synthesizing diamond single crystals can be mainly divided into two categories: high temperature and high pressure method (HTHP) and chemical vapor deposition (CVD). Among them, the single particle size that can be obtained by the HTHP method is relatively small, and the single crystal synthesized by the high temperature and high pressure method may contain impurities such as catalysts, and cannot effectively do semiconductor doping.
Chemical vapor deposition (CVD) is a common method for preparing thin film materials. It uses gas phase precursors to undergo chemical reactions under specific conditions to deposit the required thin film materials on a specific substrate. In the preparation of single crystal diamond materials, methane and hydrogen are usually used as precursors. Under high temperature (about 1000°C), normal pressure (1 atmosphere) or low pressure conditions, a single crystal diamond substrate is used as the substrate, and vapor phase epitaxy is performed. To grow single crystal diamond, the single crystal diamond substrate used can be natural diamond, HPHT diamond or CVD diamond.
According to scientists from the Key Laboratory of Marine New Materials and Applied Technology of the Chinese Academy of Sciences, the process of cultivating diamonds is like growing food. “First you need a seed wafer, and you also need to use methane gas. Under the action of energy, methane forms a carbon Plasma, this plasma is like dust, slowly depositing on the diamond seed wafer in the air, depositing bit by bit.”
2.Advantages of CVD diamond in the semiconductor field
The appearance and composition of CVD diamond are almost the same as those of natural diamond, and their physical and chemical properties are not much different. To the naked eye, no difference can be seen between the two. However, the main reason why CVD diamond is valued is that it is "pure". Compared with natural diamond, it is cleaner and has almost no impurities.
The extremely high purity allows CVD diamond to have more application possibilities than natural diamond - for example, with its excellent electrical properties, diamond materials currently dominate the semiconductor field. Diamond, C-BN (6.4eV), Ga2O3 (4.8eV), AIN (4.eV) and other materials have a bandgap width of around 5eV, and they are both currently popular ultra-wide bandgap semiconductor materials. Among them, diamond has a bandgap of 5.47eV, which is the material with the widest bandgap among current single-element semiconductor materials. Its electrical properties are extremely excellent:
① Extremely high breakdown electric field: up to 109Vem-1, which is 17 times that of basic gallium material, 2 times that of gallium nitride material, and 2.5 times that of silicon carbide material.
② Saturation carrier speed: In terms of saturation carrier speed, diamond is 2.7 times that of silicon and gallium arsenide, and the carrier speed is greater than the peak value of gallium arsenide, which can be maintained even when the application field intensity increases. its high rate.
③Carrier mobility: The electron mobility and hole mobility of diamond are superior to other semiconductor materials. The electron mobility at room temperature is 4500cm²/V·S, while that of silicon is only 1500cm²/V·S. Gallium arsenide is 8500cm²/V-S, gallium nitride is lower than 1000cm²/V·S; diamond hole mobility is 3800cm²/V·S, while silicon is only 600cm²/VS, gallium arsenide is 400cm²/V·S, and gallium nitride is <50cm²/V·S, therefore, diamond can be used to make high-frequency electronic devices.
④ Low dielectric constant: The dielectric constant of diamond is 5.7, which is about one-half that of gallium arsenide and less than half that of InP. That is, at a given frequency, the diamond semiconductor has superior capacitive load, which is The design of millimeter wave devices provides great convenience.
In the field of semiconductors, the potential of silicon, the most mainstream material at present, has been basically exploited to its extreme, and better materials are needed to continue. With the various advantages mentioned above, CVD diamond does have the opportunity to become an excellent material for the next generation of semiconductors, allowing electronic products to run faster, be more heat-resistant, and not easily damaged. Scientists believe that future quantum computers may be able to rely on chips made of diamond to significantly increase the computer's thermal conductivity, allowing the computer to maintain smooth operation at temperatures close to absolute zero.
3.Development goals of CVD diamond
However, no matter what industry it is, it is not easy to replace the original production model with new raw materials, and it will take time to research and develop.
For diamond to be used in the semiconductor industry, the premise is to produce larger-sized single crystal materials. Therefore, producing larger-sized CVD diamond by improving the preparation process is the current main development goal of this industry. With the advancement of manufacturing technology and the reduction of costs, synthetic diamond is expected to trigger a revolution in next-generation semiconductor technology.
