Pulsed plasma processing of CVD diamond

Summary form only given. The efficiency and cost effectiveness of plasma enhanced diamond CVD has been observed experimentally to scale with microwave power. The energy deposited by microwaves in a reactor couples directly to the electron plasma and then from the electrons to the background gas. The channels include: momentum transfer, rotational excitation, vibrational excitation, dissociation, dissociative attachment, electronic excitation, and ionization. With hydrogen as the background gas the dominant processes at typical operating parameters are vibrational excitation, which heats the gas, and electron impact dissociation, which is key to efficient diamond deposition. On the basis of numerical results from a first principles Boltzmann solver for the electron energy distribution, we have observed that the primary parameter that determines which channel dominates is /spl epsi/-E//spl omega/, where E is the electric field strength and /spl omega/ is the microwave frequency. By adjusting the electric field appropriately it is possible to enhance hydrogen dissociation and optimize the diamond deposition efficiency. In general, the choice of E can be used to select among the alternative processes for electron energy transfer to the gas. Our simulations show that by pulsing the microwave field with an appropriate duty factor hydrogen production can be enhanced by an order of magnitude compared to a cw source with the same average power output. In a typical cw process most of the energy goes to heat the gas to a steady state in which dissociation becomes predominately thermal. In a pulsed process it is possible to take advantage of the highly non-thermal character of the electron distribution.