Low Temperature Synthesis of Polycrystalline Diamond by Microwave Plasma-Enhanced Chemical Vapor Deposition

Abstract

Polycrystalline diamond thin films have been deposited on single crystal silicon substrates at low temperatures (<950°C) using a mixture of methane and hydrogen gases by high pressure microwave plasma assisted chemical vapor deposition. Low temperature deposition has been achieved by cooling the substrate holder with nitrogen gas. For deposition at reduced substrate temperature, it has been found that nucleation of diamond will not occur unless methane/hydrogen ratio is increased significantly from its value at higher substrate temperature. Selective deposition of polycrystalline diamond thin films has been achieved at 600°C using our technique previously used at 930°C. Decrease in the diamond particle size and growth rate, and an increase in surface smoothness have been observed with decreasing substrate temperature during the growth of thin films. The morphology is analyzed by scanning electron microscopy and the as-deposited films are identified by Raman spectroscopy.