Residual stress and hardness behaviors of the two-layer C/Si films

Effect of an amorphous Si (a-Si) underlayer on the residual stress and hardness of the two-layer C/Si films has been investigated. Amorphous carbon films either with or without amorphous Si underlayer were deposited on Si (100) substrates by means of ultra-high-vacuum ion beam sputtering at room temperature (RT). Both kinds of films have amorphous microstructure and smooth morphology. The as-deposited C films were tetrahedral amorphous carbon (ta-C) with primary sp3 bonding and different G-peak shift via Raman spectra. The residual stress of single 100 nm a-C film was about 11.98 GPa in compression and its hardness was 18.35 GPa at RT. The compressive residual stress of the C/Si film was decreased to 5.76 GPa with the addition of 50 nm a-Si underlayer and its hardness retained at about 17.69 GPa at RT. Effect of C thickness on C/a-Si residual stress and hardness were also discussed. The addition of a-Si layer has a great contribution to decrease the compressive residual stress and retains hardness, which is good for the suppression of the buckling or wrinkling in the C film.