Electrical Measurements and Optical Emission Spectroscopy of Silicon–Carbon Alloys Grown by PACVD: Correlation with Film Microstructure

Abstract

Hard hydrogen-containing silicon±carbon-based films were grown at medium temperatures in the range 453±853 K in a plasma-assisted (PA) CVD device using tetramethylsilane (TMS) as the precursor. TMS plasma chemistry is not clearly understood so, in order to gain a better understanding of this process, both electrical measurements, to estimate ion energy and flux, and optical emission spectroscopy (OES), to identify chemical species occurring in the gas near the film surface, have been used to establish correlations between characteristics of the discharge and the films. In this process, an increase in the energy of the ions tends to lower the silicon to carbon atomic ratio (Si/C) whatever the temperature. Since this is the opposite to what might be expected, it follows that the ion bombardment is a key factor. The Si/C variations are related to the behavior of gaseous emitting species near the plasma sheath close to an a-SiC/H biased surface set in non-reactive (pure argon, argon/H 2 ), then reactive (argon/TMS) plasmas. OES reveals that only a few species (Ar, Ar + , H, and Si + ) are emitting. Their corresponding lines are strongly broadened by the Doppler effect function of the applied bias voltage and plasma nature. The Si + line exhibits two energy populations, fast and slow. The fast one is related to electron dissociative excitation processes involving ions, whereas the slow Si + population seems to originate from neutral groups extracted from the surface or coming from complex species in the plasma gas. Up to three energy components were identified in the H a line profile. One is typical of both the TMS dissociation and the emission of hydrogen-containing species coming from the bombarded deposit. A comparison between the variations of relative densities of Si + and H, and material data, indicates that the deposit can be etched or sputtered (either congruently or non-congruently) leading, in the maximum ion energy range (120±180 eV), to a drastic modification of the film microstructure. This latter point is analyzed in connection with the coating surface hardness (17 GPa < H < 30 GPa).

Plasma Characterization of Oxygen‐Tetramethylsilane Mixtures for the Plasma‐Enhanced CVD of SiOxCyHz Thin Films

“…[29,30] In the case of the plasma of pure TMS, the spectrum was characterized by a continuous profile from 250 to 500 nm associated with the H 2 molecule. [29] In addition, the lines of the Balmer series of H, and the CH bands located at 314 and 390 nm, [14] were also detected. Meanwhile, in the presence of oxygen the OH emission band located at 306 nm was the main feature of the OES images and the atomic oxygen emission lines were hardly distinguished from the background noise, even in the absence of TMS.…”

Argon/tetramethysilane PECVD: From process diagnostic and modeling to a-Si:C:H hard coating composition

“…The H α line profile can be decomposed in three Gaussian components corresponding to three energetic H populations [11]. Two components, NC (narrow) and BC (broad), are attributed to molecular hydrogen dissociation through direct electron collision and ro-vibrational pumping by multiple electron collisions.…”

Crystallisation of magnetron sputtered amorphous Si1−xCxfilms (x= 1/3) studied by grazing incidence X-ray diffractometry

“…For an understanding of crystallisation of silicon carbide it is important to know the chemical order of the amorphous system, which depends on the composition and on the production method [17]. According to the tetrahedron model for amorphous silicon-carbon alloys given in [18], three types of chemical order can be considered: (a) complete random order where no preferential chemical bonding between Si and C atoms exists; (b) complete chemical order with homogenous dispersion, which means that in Si-rich alloys a C atom in the centre of a tetrahedron is surrounded by four Si atoms and a maximum of possible Si-C bonds is realised; and (c) complete chemical order with phase separation, which means that the Si-C bonds are clustered [18].…”