Gas feedstock
- Purity: The purity of reaction gases such as methane and hydrogen is critical. Impurity gases may introduce defects in the deposition process and reduce the purity and quality of the diamond, e.g. oxygen impurities may cause oxidation of the diamond surface and affect its optical and electrical properties.
- Ratio: The ratio of different gases affects the concentration and activity of carbon atoms in the plasma, which in turn affects the growth rate and quality of diamond. Too high a concentration of methane may lead to the deposition of non-diamond carbon, while too high a concentration of hydrogen may etch away already deposited carbon atoms, slowing the growth rate.
Substrate Material
- Lattice match: The higher the lattice match between the substrate and diamond, the more favorable the epitaxial growth of diamond, which can reduce lattice defects and stress. For example, the use of silicon carbide, which has a similar lattice structure to that of diamond, as the substrate can achieve better growth results.
- Surface quality: The flatness, roughness and cleanliness of the substrate surface have an important influence on the nucleation and growth of diamond. Excessive surface roughness will lead to uneven growth of diamond grains, while contaminants on the surface will hinder the adsorption and deposition of carbon atoms, affecting the nucleation density and quality of diamond.
Deposition process parameters
- Temperature: The deposition temperature affects the decomposition rate of the reaction gas and the diffusion speed of carbon atoms. If the temperature is too low, the decomposition of reaction gas is not sufficient, the growth rate of diamond is slow, and amorphous carbon deposition may occur; if the temperature is too high, it will make the diamond grains grow excessively, leading to the decrease of crystal quality, generally the deposition temperature is between 800 - 1200℃.
- Pressure: The system pressure affects the state of the plasma and the concentration of the reaction gas. Too high pressure will make the reaction gas molecules collide frequently, which is not conducive to the adsorption and deposition of carbon atoms on the substrate surface; too low pressure, the plasma density is reduced, which will also affect the growth rate and quality of diamond.
- Deposition time: the deposition time determines the thickness of the diamond film and the integrity of the crystal growth. If the time is too short, the diamond film is too thin to meet the application requirements and the crystal structure may not be perfect; if the time is too long, more impurities and defects may be introduced, and the production cost will also be increased.
Equipment Performance
- Plasma Source: The stability and uniformity of the plasma source has a significant impact on the quality of diamond growth. Stable and uniform plasma can provide stable energy and active particles for the reaction, so that diamond grows uniformly on the substrate. For example, microwave plasma sources perform better than DC plasma sources in terms of plasma uniformity, which is more conducive to the growth of high-quality single crystal diamond.
- Gas Delivery System: The precision and stability of the gas delivery system affects the supply and mixing ratio of the reaction gas. Precise control of the flow rate and mixing ratio of the gas can ensure the stability of the reaction environment, thus improving the quality of diamond growth.
Environmental Factors
- Vacuum: The deposition process needs to be carried out in a high vacuum environment to minimize the influence of impurity gases. Insufficient vacuum will cause impurity gases to mix into the reaction system and compete with the reaction gases, introducing impurities and defects in the diamond and reducing its quality.
- External vibrations: External vibrations may interfere with the plasma stability and atomic adsorption processes on the substrate surface, resulting in uneven diamond growth or defects. Therefore, CVD equipment usually needs to be mounted on a vibration-damped platform to minimize the effects of external vibrations
