An attempt was made to deposit diamond at pressures below 100 mTorr using an inductively coupled plasma. In particular, ion bombardment effects in deposition were investigated by applying positive de bias to the substrate. The average ion energy impinging onto the substrate was quantified using the sheath potential (V-sheath), i.e. the potential difference between the plasma and the substrate. The low-pressure limit of the growth of diamond with well-defined facet features was depressed to 20 mTorr with a V-sheath value of 2 V, minimizing ion bombardment energy. A V-sheath value of around 11 V still allowed the growth of diamond, however, the amount of deposit decreased and the deposit was composed of smaller crystallites. The results indicate that the growth of diamond at greatly reduced pressures is possible by regulating ion energy and flux, in addition to increasing the radical flux by using high-density plasmas.