Soft ion impact for surface activation during diamond chemical-vapor deposition on diamond and silicon

Abstract

Extremely low-energy ions with a mean kinetic energy of around 2 eV have been used for surface activation during diamond chemical-vapor deposition at a pressure of 20 mTorr in an inductively coupled plasma. A qualitative model based on a current balance between a positively biased substrate and a surrounding wall was given to describe the variation of ion energy and flux onto the substrate. The deposits with polycrystalline morphologies were obtained on the biased diamond͑100͒ and Si͑100͒ substrates by varying the ion flux. The ion-enhanced surface migration of hydrocarbon adatoms was demonstrated by the ion flux dependent morphologies of diamond films grown on diamond. A high ion flux resulted in large interisland distance and island size, a low island density, and a low fraction of grain boundary. In contrast, the concurrently induced disadvantage like surface defects and etch pits was shown by the ion flux dependent morphologies of nanocrystalline diamonds grown on Si. A high ion flux resulted in nonfacetted crystallites and a high frequency of secondary nucleation. Comprehensive discussion on the role of low-energy ions in the growth kinetics suggests that soft ion impact is promising for modifying thermally dominated behaviors of adsorbed radicals and exploring simple processes.

Plasma Deposition of Diamond at Low Pressures: A Review

“…Moderate ion bombardment is detrimental to diamond growth as it causes the loss of crystal facets typically for E i above 10 eV and no growth (or amorphitization) typically for E i above 20 eV [37], [38]. In contrast, low-energy, soft ion bombardment for E i as low as several eV allows the presence of crystal facets and is useful to assist radical reactions on the growing surface [62]. In fact, little or no deposition of diamond occurs outside an emissive plasma bulk even when the ion energy is reduced adequately.…”

Diagnostic and analytical study on a low-pressure limit of diamond chemical vapor deposition in inductively coupled CO–CH4–H2 plasmas

“…The fact that each crystallite size was as small as 20 nm, almost independent of duration, suggests preference of renucleation over growth. 16 The island density is thus considered to represent the actual nucleation density. The deposits at 20 mTorr were not continuous and composed of spherical islands even after a duration of 9 h due to a low nucleation density.…”

“…Second, the physical removal of surface H is likely caused by bombardment of lowenergy ions. 16 A mean ion energy was as low as a few eV, however, a high-energy component in an IED up to several eV is high enough to break C-H bonds with a typical bond energy of about 4 eV, without bulk damage. The ion-induced removal becomes of importance with decreasing T s and hence pressure since such a physical process can occur independent of T s .…”