MODIFICATION OF DIAMOND FILM GROWTH BY A NEGATIVE BIAS VOLTAGE IN MICROWAVE PLASMA CHEMICAL-VAPOR-DEPOSITION

Diamond growth by microwave plasma chemical vapor deposition (MPCVD) u nder the influence of an additional negative bias voltage has been stu died. From the in-situ measurement of the growth rate and the curvatur e of the silicon substrate, the intrinsic film stress was monitored du ring the deposition for bias voltages ranging from 0 to -200 V and for different process pressures. The mass density of the films, their str uctural properties and the incorporation of hydrogen and nitrogen impu rities from the gas phase were determined ex-situ by Rutherford backsc attering, Raman spectroscopy and elastic recoil detection, respectivel y. For the growth under bias, two regimes have been distinguished. At 50 mbar, the intrinsic stress is tensile between U-bias=0V and -100 V, and the growth is only weakly disturbed by the biasing conditions. At -100 V the macroscopic intrinsic stress vanishes. In the second regim e, compressive stress rises rapidly and saturates at -3 GPa. Furthermo re, the carbon deposition rate increases by a factor of four, accompan ied by an increased incorporation of hydrogen and nitrogen and a deter ioration of the crystalline quality of the films. The results are disc ussed in terms of a modification of the film growth by the additional flux of hyperthermal gas species. (C) 1998 Elsevier Science S.A.