Wide band-gap silicon-carbon alloys deposited by very high frequency plasma enhanced chemical vapor deposition

Abstract

High rate deposition of diamond like carbon films by very high frequency plasma enhanced chemical vapor deposition at 100 MHz Wide band gap amorphous hydrogenated carbon films grown by plasma enhanced chemical vapor depositionThe use of very high frequency (VHF) plasma enhanced chemical vapor deposition in a capacitive discharge is investigated to fabricate hydrogenated amorphous silicon carbon alloys, using silane and methane as silicon and carbon precursors, respectively, and hydrogen dilution of the gas mixture. The properties of samples differ significantly from that is normally observed for rf deposition. A wide band-gap material is obtained, with a carbon ratio ranging from 0.2 to 0.63. An energy gap up to 3.4 eV is measured, indicating a large sp 3 content. The most interesting properties are observed using 90% hydrogen dilution and 350°C as substrate temperature. In this case, a Siu C bond concentration up to 6 ϫ 10 22 cm −3 was measured for stoichiometric samples, associated to a highly crosslinked structure and no detectable Siu CH 3 bending signal. The role of hydrogen in determining the optical properties of the film is established and is shown to affect mainly the valence electron concentration. Based on the free energy model, hydrogen bonding is observed to lie in between a random and chemically ordered configuration. The results are obtained at a deposition rate much larger than both rf and electron cyclotron resonance deposition, and are associated to a limited gas consumption, both aspects being advantageous for practical applications. The large Siu C bond concentration, associated to a limited silicon and carbon hydrogenation, makes the VHF deposited a-SiC : H a good starting material for subsequent crystallization.

Microstructure analysis of a-SiC:H thin films grown by high-growth-rate PECVD

“…Fig. 1 evidences that, as already observed by Ambrosone et al [4], the deposition rate in a high power regime can be dependent on the silane flux, as found for 'low power regime' [2,6]. In the present work, the analysis of the dependence of the deposition rate on Rc (given by the slope of the fitting curve) shows that growth rate tends to a non-zero value, even with no silane in the chamber.…”

“…1 also shows the marked refractive index decreasing as the methane fraction R c increases due to the C incorporation enhancing. It is worth to underline that also for samples approaching the stoichiometry (i.e., obtained with the higher R c values), the refractive index is quite high if compared with other literature data dealing with high quality a-SiC:H [6]. This behavior could be ascribed to a microscopical chemical heterogeneity yielding the presence of Si-Si clusters even for samples approaching the stoichiometry ([C]/([C] + [Si]) $ 0.5); moreover, also the low hydrogen content in the analyzed films, due to the high power and temperature involved, could contribute in the same way.…”

“…Hence, there is a growing interest for the regime in which high RF-power (power density higher than 0.3 W cm À2 ) and/or high pressure (deposition pressure higher than 1 Torr) are involved [3,4]. Besides standard RF bias, the use of frequencies higher than 13.56 MHz (from 27.12 to 100 MHz) has been recently proposed [5,6]. Actually, very high frequency (VHF) can reduce the ion bombardment and increase the electron density, allowing the growth of low defect films with carbon ratio up to 0.63; however, the deposition rate is still low (few Å /s).…”

Characterization of a-SiCx:H thin films as an encapsulation material for integrated silicon based neural interface devices

“…a-SiC x :H has low dielectric constant (4.4-4.9) and low moisture intake [12,13], thereby satisfies two conditions needed for a device encapsulation layer. Due to the controllable electrical and optical properties, a-SiC x :H has been investigated intensely in the fields of optoelectronics [14,15], solar cell technology [16], and surface passivation [17,18]. However, the use of a-SiC x :H as the biomedical device coating has gained attention only recently.…”

Hydrogenated amorphous silicon–carbon alloys obtained from Ar–SiH4–CH4 gas mixtures: Structural and transport properties

“…1 shows that E g continuously increases with P rf , a behavior that can be attributed to the carbon content ([C]) increase. Though, we have not precisely determined [C] in our films, this quantity was evaluated with the help of previous works [6,7] in which a linear relation was found between [C] and the energy E 04 at which a = 10 4 cm À1 . We found carbon contents in the range of 24-34% evaluated from the E 04 values listed in Table 1.…”