Fundamentals towards large area synthesis of multifunctional Ultrananocrystalline diamond films via large area hot filament chemical vapor deposition bias enhanced nucleation/bias enhanced growth for fabrication of broad range of multifunctional devices

This paper describes studies to develop hot filament chemical vapor deposition (HFCVD)/Bias Enhance Nucleation-Bias Enhance Growth (BEN-BEG) process for nucleation/grow of relatively large area uniform multifunctional ultrananocrystalline diamond (UNCD) films on tungsten (W)-coated 100 mm diameter silicon substrates, eliminating conventional wet diamond particles “seeding” of substrate surfaces. The HFCVD/BEN-BEG process generates a plasma, via electric field between positively bias filaments against negative substrates, producing positively charged and neutral Ar, CHx (x = 1 2 3), C and H species and electrons in an Ar-rich/CH₄/H₂ gas mixture. The C⁺-based ions impacting the substrate surface nucleate a W-carbide layer, resulting in nucleation/growth of uniform UNCD films. The studies focused on understanding the HFCVD BEN-BEG mechanism for 0.5–2.5 hrs. BEN, followed by no-bias 2.0 hrs. growth of uniform UNCD films on 100 mm diameter substrates. This approach eliminates the etching of UNCD films observed when doing BEG beyond 2.5 hrs. of BEN, due to ion bombardment-induced sputtering and/or combined atomic hydrogen-induced chemical etching of the films. High Resolution Transmission Electron Microscopy showed formation of (001) and (101) oriented WC grains, inducing (111) diamond grains formations, turning into (220) and (311) orientation upon further growth. Large area HFCVD BEN-BEG process to grow multifunctional UNCD films may enable new generations of UNCD-based multifunctional devices.