We have investi ated the effects of reactant residence time on the properties of microwav+a88isted
CV % diamond films. Using a constant process pressure of 40 Torr and gas composition of 1% CHb in Hr? the total gas flow rate was adjusted from 25 to 800 seem. For OUT reactor, this correspond8 to resrdence times of 180 to 5 sec., calculated using the plug flow velocities of 3 to 80 cm/min. The flow rate is one of the few parameter8 in the microwave plasma deposition trystem ~~~a~llecoupled from all others, making this a relatively clean study on the effect8 of a single proce88 Two types of samples were repared in this study. One set was prepared by depositing an initial DLC-type layer (60 minutes at 4 & TV CHd/Hr, then 30 minutes in pure Ha, with total gas flow rate of 200 seem) on diamond abraded silicon wafers, followed by a 5 hour diamond film growth. A second set, prepared separately but under otherwise identical growth conditions, was deposited directly on the diamond-eeeded silicon wafers.
The deposited film8 were analyzed using 8cannin electron microscopy (SEM), Raman scattering RS) and photoluminescence (PL) spectroacopies, transmission and x-ray diffraction XRD). The average growth rate was determined from the nal deposition weight, atr well 88 a thicknes8 measurement from IR transmission fringes. Diamond films deposited over the various gas flow rates exhibited a surprising range of material variance.
exhibited a maximum at moderate flow rate, but at different values for the two sample sets. The GRl band in the PL spectrum showed similar behavior with flow rate variation. The IR spectra displayed thin-film interference fringes and a high average transmittance.
The deposition rate showed little variation with flow rate.