Amorphous Diamond-Like Carbon Film Growth by KrF-and ArF-Excimer Laser PLD: Correlation with Plume Properties
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(Model 2960) excimer laser operating on ArF (22 ns FWHM, 600 mJ) or KrF (28 ns FWHM, 900 mJ) was used. The beam was apertured and focused into the chamber with a spherical lens (500 mm f.l. at 248 nm, 445 mm f.l. at 193nm) to a rectangular beam spot (0.18 cm x 0.11 cm) at an incidence angle of 30' onto l"-diameter pyrolytic graphite pellets (Specialty Minerals Inc., less than 10 ppm total impurities). The pellets were rotated during the film deposition and plasma2 plume diagnostics experiments. The maximum laser fluences at the pellet surface were 7 J/cm (ArF) and 20 J/cm 2 (KrF). N-type Si (100) wafers (resistivity 0.2-0.4 ohm-cm) were used as substrates for PLD. The substrates were kept at room temperature and placed at variable distances from the target (d = 4-15 cm). NaC1 crystals were also used as substrates for films deposited especially for EELS analysis. Films were characterized by transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS) and spectroscopic ellipsometry. Gated imaging was done with an intensified charge-coupled device (ICCD), lens-coupled camera system (Princeton Instruments) with variable gain and gate width (5-ns minimum) and a spectral range from 200-820 nm. Spectroscopic measurement of the plume luminescence was performed with a 1.33-meter spectrometer (McPherson 209) equipped with an 1800 g/mm holographic grating, an intensified, gated diode array (Princeton Instruments IRY-700RB) and a photomultiplier tube (Hamamatsu R955). FILMS CHARACTERIZATION The fraction of sp 3-bonded carbon in the films was estimated using the EELS spectra. The spectra were obtained with a VG HB501 UX dedicated scanning transmission electron microscope (STEM) operated at an accelerating voltage of 100 KeV. 5 The 30 nm-thick DLC films for EELS analysis were deposited on NaCl-substrates using ArF-laser irradiation (11.1 Hz repetition rate, 4660 pulses, 5.6 cm substrate-target distance). The substrate was then dissolved in deionized water and the DLC-film was put on the STEM specimen copper grid. In order to estimate the fraction of sp 3 bonded carbon, the EELS spectrum of crystalline carbon was measured as well. Figure 1(a) and 1(b) shows carbon K-edge spectra of an amorphous diamond-like carbon film (a) and a crystalline graphite film (b) after subtraction of background.
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Fig. 1 (a) EELS spectrum of ArF-laser deposited DLC film (NaCI substrate dissolved) in the carbon K-edge core-loss region. (b) EELS spectrum of graphitized carbon, for comparison. The peak at 285.5 eV [Fig. l(b)] corresponds to transitions from Is to 7t*. The Is-Y* transition is responsible for the higher energy peaks. In the amorphous DLC film the Is-ir* peak (286.6 eV) is much smaller than that for the graphitized carbon sample due to the small amount of sp 2 -bonded carbon in the DLC film. The I s-c* peaks (>290 eV) in DLC films are broader 146
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