Temperature dependence of the chemical sputtering of amorphous hydrogenated carbon films by hydrogen

Abstract

The temperature dependence of chemical erosion and chemical sputtering of amorphous hydrogenated carbon films due to exposure to hydrogen atoms (H 0 ) alone and combined exposure to argon ions and H 0 was measured in the temperature range from 110 to 950 K. The chemical erosion yield for H 0 alone is below the detection limit for temperatures below about 340 K. It increases strongly with increasing temperature, goes through a maximum around 650 to 700 K and decreases again for higher temperatures. Combined exposure to Ar + and H 0 results in substantial chemical sputtering yields in the temperature range below 340 K. In this range the yield does not depend on temperature, but it increases with energy from about 1 (eroded carbon atoms per impinging Ar + ion) to about 4 if the ion energy is increased from 50 to 800 eV. For temperatures above 340 K the measured erosion rates show the same temperature dependence as for the H 0 -only case, but they are higher than for H 0 -only. The difference between the Ar + and H 0 and the H 0 -only cases increases monotonically with increasing ion energy.

Synergistic etch rates during low-energetic plasma etching of hydrogenated amorphous carbon

“…36,38,39 The erosion yield for chemical erosion with H -which is thermally activated -is negligible below 34 meV (400 K) and varies from 0.001 to 0.1 above 34 meV, with a maximum at 52 meV (600 K). 16,18,35,36,40 These yields were reported for an atomic H flux of 10 15 -10 20 m À2 s À1 . H 2 recombination above 600 K causes the reduction in the yield.…”

“…51 The erosion yield (10 À3 -10 1 ) depends furthermore on the ion energy and incident ion flux and, all else being equal, is higher for a-C:H than for graphite. 1,10,14,16,18,40,45,47,48 The fourth and last mechanism explained here is swift chemical sputtering, which first came to light via numerical modelling of very high hydrogen fluxes (up to 10 29 m À2 s À1 ) incident on an a-C:H surface. [52][53][54][55] An incident hydrogen radical enters the space occupied by a carbon-carbon bond.…”

“…13 Chemical sputtering is a similar process, in which the incident ions do break carbon bonds within their surface penetration depth. [17][18][19]49,50 The incident hydrogen radicals immediately passivate the newly formed DBs, thereby creating hydrocarbon groups that will eventually desorb. The energy required to break C-C and C-H bonds is about 3 À 5 eV, with the energy of the incident ion at least a few eV's above that.…”

“…10 Previous studies of carbon etching -with ion energies between 10 eV and 5 keV -have established several etch mechanisms in literature. [11][12][13][14][15][16][17][18] Two of those mechanisms, i.e. chemical sputtering and ion-assisted chemical erosion, describe a synergistic effect in the etch rate when simultaneously exposing a-C:H to both radicals and ions (see also Sec.…”

Raman micro-spectroscopy as a tool to measure the absorption coefficient and the erosion rate of hydrogenated amorphous carbon films heat-treated under hydrogen bombardment

“…For these films the thickness and the imaginary part of the refractive index of the as-deposited sample is known. Erosion rates obtained using Raman micro-spectroscopy are compared to those obtained using ellipsometry, the erosion rate of heattreated a-C:H films varying by more than one order of magnitude between 100 and 450 • C [5]. The imaginary part of the refractive index obtained by the two methods can also be compared, the absorption of visible photons significantly increasing with heat-treatments [6].…”