Effect of the Gas Chemistry, Total Pressure, and Microwave Power on the Grain Size and Growth Rate of Polycrystalline Diamond Films Grown by Microwave Plasma Chemical Vapor Deposition Technique

The combined effect of total gas pressure (20-80 mbar), precursor gas chemistry (Ar/CH
₄
/H
₂
) and microwave power on the grain size and growth rate of polycrystalline diamond films, grown by MPCVD, was investigated. The key findings are: 1) Grain size of polycrystalline diamond films depends critically on the total gas pressure such that a minimum pressure of 60 mbar is needed to grow nanocrystalline diamond films (grain size of 100s of nanometers) even when using a hydrogen rich gas chemistry (98% H
₂
, 2% CH
₄
); 2) For a fixed gas pressure, the grain size of polycrystalline diamond films increases as the H
₂
concentration increases, and decreases as the Ar concentration decreases, resulting in a maximum grain size for Ar 0%/CH
₄
2%, H
₂
98% gas mixture and a minimum grain size for Ar 98%/CH
₄
2%, H
₂
0% gas mixture; 3) The microwave power (1900-2500 W) effect on grain size and growth rate.