The behavior of neutral component of the plasma during high power impulse magnetron sputtering was studied. Movement of the neutral particles including sputtered metal (Ti) and Ar gas during an impulse (200 µs, 1 kA, 1 kV) has been simulated using direct simulation Monte Carlo method. When the discharge current reaches kA range, very strong gas rarefaction in the main plasma region occurs and the volume density of sputtered metal exceeds the gas density several times. This may contribute to the high ratio of metal ions to Ar ions observed in experiments. Rapid gas movement in the form of a shock wave toward the substrate results in a temporary increase in density and pressure of the substrate. This again influences both the deposition flux and the discharge behavior.
Cross-sectional transmission electron microscopy (XTEM) has been used to investigate the effects of variations in the low-energy ion irradiation flux during the growth of reactively sputter-deposited TiN. The films were deposited on steel substrates with a negative bias of 100 V at 350 °C in mixed Ar–N2 discharges at a pressure of 5 Pa (37 mTorr). The ion-to-Ti arrival rate ratio Jion /JTi at the substrate was varied between 0.3 and 7.1 through the use of a variable external magnetic field. Films grown with Jion /JTi ≲2 had a columnar morphology with a highly underdense microstructure. Increasing Jion /JTi ≳4 was sufficient to cause the growth of dense films with a more equiaxed grain structure due to renucleation. Further increases in Jion /JTi ≳7 resulted in increased TiN grain size and local heteroepitaxy between TiN and the martensitic phase of the substrate.
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