Properties of Ion Beam Deposited Tetrahedral Fluorinated Amorphous Carbon Films (ta-C:F)
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cal resistance butta-C alsofilms a high stressthe[9-11]. The fraction, effect ofthe incorporation variable amounts of F in on compressive the film density, sp3 bond evolution ofofcompressive stress and the thermal stability is investigated• EXPERIMENTAL Fluorinated carbon thin films were grown on single crystalline silicon cantilever substrates by direct deposition of low energy lZc+ and 19F+ ions at room temperature. We have used 30 keV mass separated ions electrostatically decelerated down to 100 eV before deposition• The deceleration lens system and the substrate holder was mounted in a differentially pumped deposition chamber allowing a pressure below 210.8 mbar during deposition. The films are therefore free of contaminants like oxygen or hydrogen• The details of the UHV-deposition system are described elsewhere [12]. Typical ion current densities are about 10-30 !aA/cm2 on the substrate. A uniform deposition over an area of about 2 cm2 was achieved using a beam sweep in front of the deceleration stage. The film composition was controlled by measuring the ion charge deposited onto the substrate. The charge measurement was used to alternatingly switch the separation magnet between masses 12C and 19F, so that a constant C+:F+ charge ratio was obtained• During each switching cycle, typically 11015 ions/cm2 were deposited ensuring a homogenous film composition. The substrates were cleaned in-situ immediately before deposition by sputtering with 1 keV 4°Ar+ ions. The C+:F+ charge ratio was varied from 1:0, i.e. pure carbon, up to 3:7 for the different samples. Films were characterized in-situ by Auger electron spectroscopy (AES) and electron energy loss spectroscopy (EELS) before they were taken out of the deposition system• Rutherford backscattering spectroscopy (RBS) was conducted using a 900 keV 4He2* ion beam supplied by the G6ttinger heavy ion implanter IONAS [13]. The detector was mounted at an angle of 165° with respect to the beam• For each spectrum a total ion charge of 6 pC was necessary. The spectra were analyzed by means of the computer code NDF [14], which takes for the calculation of the area density and composition of the films not only the shift of the Si-edge into account but also the C and F signals. The substrates were masked with a thin wire during deposition. This allowed us to measure the film thickness after deposition and after each annealing step by means of mechanical surface profiling (Dektak 3sT surface profiler)• The compressive stress of the films was determined by the bending of small cantilevers, which were also coated during growth• The bending radius was optically measured and the stress calculated using the Stoney equation [15] (Esi = 169 GPa, Vsi = 0.064)• The subsequent annealing of the samples was done under vacuum (< 210.5 mbar) at •, 40 ' , , , , , ,/1 , • ' • ' t '• temperatures up to 600 °C in steps of • " / 150 °C for 10 minutes/step.
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Figure 1" Measured F concentration of ta-C:F films deposited onto Si a
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