Effects on the deposition and mechanical properties of diamond-like carbon film using different inert gases in methane plasma

Diamond-like carbon (DLC) films using various inert gases, He, Ne, Ar-methane mixture were deposited by a magnetically enhanced plasma chemical vapor deposition (CVD). The deposition rates and mechanical properties in terms of stress, hardness and Young's modulus of the DLC films under various substrate bias voltage and inert-gas/methane ratios were studied. At a fixed inert-gas/methane ratio (10%), the deposition rates and mechanical properties of the DLC film were enhanced by adding the inert gases in methane plasma, compared with that of the DLC film deposited using only methane plasma. With increasing the bias voltage, the deposition rate increased, while the stress, hardness and Young's modulus increased and reached to a maximum at a certain bias voltage (250 V), then decreased. At a fixed substrate bias voltage (250 V), with increasing the inert-gas/methane ratio, the deposition rate, stress, hardness and Young's modulus increased, and reached a maximum at a certain inert-gas/methane ratio (30% for deposition rate, 20% for mechanical properties), then decreased. The magnitude of the effect was found to decrease, going from Ne to Ar to He, and is found to depend on the optimum balance between the ionization potential and the atomic mass of the inert-gas.