Synthesis of Diamond by Plasma-Enhanced Chemical Vapor Deposition.

Diamond possesses many desirable properties, e.g. high thermal conductivity, high electrical resistivity, high breakdown voltage, high resistance to chemical and radiation damage, high transparency over a wide range of optical spectrum, and extreme hardness. Thus diamond have high potential applicability in the fields of semiconductors, optical emitting materials, optical coating materials, abrasion, and high power and high frequency devices. To extend the range of applications, large-area uniformity and low temperature growth of diamond thin films has to be achieved. Low pressure deposition is one solution to the small area and nonuniformity problems of current diamond deposition methods. By decreasing the pressure, the mean free path of electrons becomes larger and the plasma covers a larger area. Low temperature deposition gives a smaller crystalline size of diamond, and hence improves the surface morphology of deposited films. To satisfy the supersaturation condition of diamond crystallization, low temperature growth should be performed at low pressure. This study experimentally investigates optimization of diamond growth at low pressure and low temperature by comparing three deposition systems (i.e. hot filament assisted, microwave induced plasma, and electron cyclotron resonance plasma chemical vapor deposition). The deposition system is designed to clearly show the effects of each experimental parameter on grown films. Thin diamond films were deposited on silicon substrates over a wide range of deposition parameters (e.g. CH _4 concentration 0-10%, substrate temperature 490-850^circC, total pressure 2-50 Torr, microwave power 0-1200 W). In addition, the effects of oxygen addition and substrate bias were studied. The diamond films were characterized by Raman spectroscopy and scanning electron microscopy, and the plasma was characterized by optical emission spectroscopy. Crystalline diamond was successfully deposited on silicon wafers at pressures as low as 2 Torr at substrate temperature of 490 ^circC.