Control of stress and microstructure in cathodic arc deposited films

The almost fully ionized cathodic arc plasma is a versatile source for the deposition of thin films. Ion energies impinging on the growth surface can easily be controlled by applying substrate bias. The natural energy of the depositing ions is moderate (tens of electron volts) and generates substantial compressive stress in most materials. In hard materials (such as tetrahedral-carbon and titanium nitride), the high-yield stress makes the problem particularly severe. Recent work has shown that stress relaxation can be achieved by pulses of high ion-energy bombardment (~10 keV) applied to the substrate during growth. In this paper, we describe the variation of intrinsic stress as a function of applied pulsed bias voltage (V) and pulse frequency (f) for deposition of carbon and titanium nitride films. We found that stress relaxation depends on the parameter Vf, so it is possible to achieve the same level of stress relief for a range of voltages by selecting appropriate pulsing frequencies. With the right choice of parameters, it is possible to almost completely eliminate the intrinsic stress and deposit very thick coatings. Our experimental results showed correlations between intrinsic stress and film microstructures, such as the preferred orientation. This leads to the possibility of controlling microstructure with high energy ion pulsing during growth. Molecular dynamics computer simulations of isolated impacts provide insight into the atomic-scale processes at work. Using the results of such simulations, we describe a model for how stress relief might take place, based on relaxation in thermal spikes occurring around impact sites of the high-energy ions.