Lower pressure limit of diamond growth in inductively coupled plasma

A study of diamond growth at pressures below 20 mTorr by using an inductively coupled radio frequency plasma is presented. Emissive and Langmuir probes, and optical emission spectroscopy were used to examine the plasma, and deposits were obtained on single crystalline silicon and diamond substrates with controlling the bombarding ion energy by the sheath potential (V_sheath). A higher threshold of V_sheath that allowed diamond growth was found in the range of 11-19 V above 20 mTorr, while a shift down of the V_sheath threshold was observed below 10 mTorr, as confirmed by Raman spectroscopy and electron diffraction. The growth at 10 mTorr was successful only when Vsheath was reduced to 2 V, however, the growth at 5 mTorr was no longer possible even when V _sheath was reduced to 2 V. Effects of the pressure decrease on the suppression of diamond growth below 10 mTorr were interpreted in terms of an increase in ion flux relative to radical flux as well as low radical density corresponding to the plasma density of approximately 2×10¹⁰cm^-3.