Modification of diamond film growth by a negative bias voltage in microwave plasma chemical vapor deposition

Abstract

Diamond growth by microwave plasma chemical vapor deposition (MPCVD) under the influence of an additional negative bias voltage has been studied. From the in-situ measurement of the growth rate and the curvature of the silicon substrate, the intrinsic film stress was monitored during the deposition for bias voltages ranging from 0 to −200 V and for different process pressures. The mass density of the films, their structural properties and the incorporation of hydrogen and nitrogen impurities from the gas phase were determined ex-situ by Rutherford backscattering, Raman spectroscopy and elastic recoil detection, respectively. For the growth under bias, two regimes have been distinguished. At 50 mbar, the intrinsic stress is tensile between Ubias = 0 V 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 regime, compressive stress rises rapidly and saturates at −3 GPa. Furthermore, the carbon deposition rate increases by a factor of four, accompanied by an increased incorporation of hydrogen and nitrogen and a deterioration of the crystalline quality of the films. The results are discussed in terms of a modification of the film growth by the additional flux of hyperthermal gas species.