Study On The Properties Of Si/Ge Doped Diamond-like Carbon Films

Diamond-like carbon(DLC) film is a metastable amorphous carbon film, which has many excellent properties of diamond film. In optics fields, the DLC film is often used as antireflective and protective film of infrared windows, clue to its excellent transparency in the infrared range, high hardness and good wear-resisting property etc. The DLC film usually has very strong internal stress and low film-substrate adhesion, which greatly limits its application range. To overcome the obstacles, the element doping method is used to improve the comprehensive properties of the DLC film.In this paper, the Si-doped diamond-like carbon(Si-DLC) film and Ge-doped diamond-like carbon(Ge-DLC) film with different atom percent(at.%) of Si or Ge content are deposited on silicon substrates, using a composition pulsed vacuum arc deposition(PVAD) and electron beam evaporation deposition technique. The influences of Si or Ge content on the film optical and mechanical properties are systemically researched. The investigations show that:1) Small amounts of Si or Ge (less than 25%) doping has little effect to the DLC films optical constants at the wavelength of 1-5μm; the film refractive index and extinction coefficient increased with the Si or Ge content increase.2) With the Si or Ge content increasing, the DLC film internal stress and hardness decrease. The DLC film internal stress decreases quickly than that of hardnenss when the Si or Ge content is less than 8%, but the result is just the oppposite while the content is more than 8%.3) With the best atom percent of 8at.%, the DLC films'internal stress reduces substantially and still keeps a high hardness simultaneously. The Si-DLC film internal stress decreases from 6.3GPa to 3.4GPa and hardness reduces only from 3875kgf/mm2 to 3652kgf/mm2, the Ge-DLC film internal stress decreases from 6.3GPa to 3.0GPa and hardness reduces only from 3875kgf/mm2 to 3640kgf/mm2.4) When the Si or Ge content is 8at.%, the peak transmittance of Si-DLC film(63.71%) is slightly higher than that of Ge-DLC film(63.15%) in the infrared band of 3-5μm. 5) The Ge-DLC films internal stress and hardness are smaller compared with Si-DLC film at the same Si(Ge) content. When the Si or Ge content is 8at.%, the Si-DLC films'internal stress and hardness are difference very small with the Ge-DLC film.