COMPARISON OF DIAMOND-LIKE CARBON-FILMS DEPOSITED FROM 40 KHZ AND 13.56 MHZ RF PLASMAS

R.f. plasma discharges are a standard method for depositing diamond-li ke carbon (DLC) films. This work looks at the effect of the r.f. drivi ng frequency by studying films deposited at both 40 kHz and 13.56 MHz. Films were grown on a 10 cm diameter driven electrode from CH4-H-2 an d C2H2-H-2 gas mixtures onto 75 x 25 mm(2) soda glass substrates at pr ocess pressures in the range 6-80 Pa (0.05-0.6 Torr). Film growth was monitored by in situ ellipsometry (at 675 mm) which allows measurement of the refractive index, extinction coefficient and thickness. The re fractive index has been shown previously to be a reliable measure of f ilm quality as determined by the hardness, scratch resistance and wear resistance. Films are assessed as a function of deposition pressure a nd r.f frequency. The him quality is seen to improve as the pressure d ecreases and as the r.f. power increases for both driving frequencies. It is necessary to deposit 13.56 MHz films at low pressure, typically less than 12 Pa (0.1 Ton). Similar quality films may be deposited at 40 kHz at pressures up to 80 Pa (0.6 Torr).