Synthesis of diamond in high power-density microwave methane/hydrogen/oxygen plasmas at elevated substrate temperatures

Effects of elevated substrate temperatures and oxygen additive on the chemical vapor deposition of diamond are presented. High power-density microwave plasmas in a high concentration of methane diluted by hydrogen led to high diamond growth rates at elevated substrate temperatures up to around 1450°C. When methane and hydrogen were the only reactant gases and the substrate temperature was higher than 1450°C, graphitic deposits started to show up. With the addition of a small amount of oxygen (less than 2%), diamond films deposited at substrate temperatures higher than 1450°C at 30 μm h^-1 were achieved. Diamond deposition at substrate temperatures exceeding 1600°C was achieved on molybdenum substrates. At such high temperatures, diamond grows well but the nucleation density was low. Raman spectra and surface morphologies of diamond films are correlated with the growth conditions.