Melting Evaporation and Recrystallization of A-Sic:H Films by Excimer Laser
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substrate temperatures in a remote plasma CVD reactor. The experimental procedure and properties of the films before and after the annealing are reported in this paper. EXPERIMENTAL Films of a-SiC:H were deposited using hexamethyldisilane as the source monomer in a remote hydrogen plasma. The deposition procedure has been explained in details elsewhere.11 Films were deposited at different substrate temperatures ranging from 30- 400 'C. Si (100) and quartz glass were used as the substrates. The thickness of the films deposited varied from 100 800 nm. The nature of chemical bonding in the films was studied by infrared spectroscopy. Auger spectroscopic measurements were performed in estimating the elemental composition of the film. The optical absorption measurements were carried out for the films deposited at different temperatures to determine the absorption coefficient at different wavelengths and the optical bandgap (Eop,) of the films. In estimating Eop,, the plot of (cxhv)" 3 against hv, which is usually referred to as a Tauc plot, was used. Film thickness before and after the annealing was measured by both Dektak and ellipsometer measurements. The dynamic hardness (DH) of the films were monitored by a Shimadzu DUH-50. Laser annealing was carried using a Lumonics excimer laser operating with KrF gas which emits laser pulses of 20 ns. The laser emission wave length is 248 nm. The dimensions of the laser pulse emitted from the laser generator is 30x10 mm. This pulse is focused on to the substrate surface as a lxl0 mm thin line for the annealing process. The sample was placed in a small stainless steel chamber equipped with a quartz window to pass the laser light. First, the sample holding chamber was evacuated to a base pressure of 10-' Torr and flushed several times with Ar (99.99%). Annealing was performed in vacuum (10-4 Torr). The sample chamber was then mounted on a motor controlled stage and moved a pre-set distance after each laser pulse. The pulse energies were varied from 50 - 550 mJ/pulse. In order to measure the electrical properties of a-SiC:H films, depositions were carried out on glass substrates where 2 mm Au strip had been deposited. After the a-SiC:H film deposition, an Al stripe of 2mm width was deposited on the film surface perpendicular to the Au stripe which lies under the film. Therefore, a-SiC:H film is sandwiched between Au and Al stripes. By making electrical contacts with Au and Al stripes, electrical measurements were performed and the resistivity of the film was estimated. In deducing the surface resistivity, two Au electrodes 4.5 cm long and 0.015 cm apart were deposited on the top of the film. RESULTS AND DISCUSSION
SThe elemental composition of the a-SiC:H films is shown in Fig. 1 as a function of substrate temperature. FTIR spectra obtained for the films deposited at different temperatures are shown in Fig. 2. The major peaks shown in these spectra are stretching mode vibration of Si-C at 830 cm-', SiCH2 at 1010 cm-' and Si-H, (n=1,2,3) at 2160 cm-'. The spectra indicate that the
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