$\hbox{CrN}_{\rm x}$ Films Prepared by DC Magnetron Sputtering and High-Power Pulsed Magnetron Sputtering: A Comparative Study

Abstract

Abstract-CrN x (0 ≤ x ≤ 0.91) films synthesized using highpower pulsed magnetron sputtering, also known as high-power impulse magnetron sputtering (HiPIMS), have been compared with those made by conventional direct-current (dc) magnetron sputtering (DCMS) operated at the same average power. The HiPIMS deposition rate relative to the DCMS rate was found to decrease linearly with increasing emission strength from the Cr ions relative to Cr neutrals, in agreement with the predictions of the target-pathway model. The low deposition rate in HiPIMS is thus a direct consequence of the high ionization level (∼56%) of the target material and effective capturing of Cr ions by the cathode potential. Although the HiPIMS deposition rate did not exceed 40% of the DCMS rate, the drop in the relative deposition rate upon increasing the N 2 -to-Ar flow ratio, f N 2 /Ar , was found to be similar for both sputtering techniques. Films prepared by HiPIMS contained similar amounts of atomic nitrogen as the dc-sputtered samples grown at the same f N 2 /Ar , indicating that the nitride formation at the substrate takes place mostly during the time period of the high-power pulses, and the N 2 uptake between the pulses is negligible. The microstructure evolution in the two types of CrN x films, however, differed clearly from each other. A combination of a high substrate bias and a high flux of doubly charged Cr ions present during the HiPIMS discharge led to a disruption of the grain growth and renucleation, which resulted in column-free films with nanosized grains not observed in the conventional DCMS-based process. The comparison of nanoindentation hardness as a function of f N 2 /Ar revealed superior properties of HiPIMS-sputtered films in the entire range of gas compositions.Index Terms-CrN, high-power impulse magnetron sputtering (HiPIMS), high-power pulsed magnetron sputtering, magnetron sputtering.

High power impulse magnetron sputtering discharge

“…III C is of particular concern for reactive magnetron deposition of oxides due to the low sputter yield of most oxides. This concern has been confirmed by several reports on reactive sputtering with HiPIMS, a factor of 4-7 lower deposition rate for reactive sputtering of TiO 2 from a Ti target, 221 a factor of 3-4 lower for reactive sputtering of AlO x from an Al target 222 and up to a factor of 3 lower for reactive sputter deposition of CrN x from a Cr target, 223 compared to pulsed dcMS at the same average power.…”

“…The current rises sharply as the pulse repetition frequency is lowered as a result of increased target nitridation. However, Greczynski et al 223 report on a decrease in deposition rate with increasing n N 2 /n Ar ratio. They relate this decrease to nitride formation on the surface of the sputtering target (poisoning effect) and lower sputtering efficiency of the N 2 gas compared to argon gas.…”

A review of metal-ion-flux-controlled growth of metastable TiAlN by HIPIMS/DCMS co-sputtering

“…17,25,27,28,29,30,31 The dominant ion species incident at the growth surface during DCMS with N2/Ar gas mixtures optimized to obtain stoichiometric films is typically Ar + , with N2 + and N + both contributing a few percent. 32, 33 The N2 + /N + ratio increases with increasing N2/Ar fraction, while in pure N2 discharges the dominant ion species is N2 + . 32 For magnetron sputtering, in which anode sheaths are typically ≤ 1 mm (that is, essentially collisionless), the average energy Ei of ions incident at the growing film is Ei = o i E + ne(Vs -Vpl), 25,27 in which o i E denotes the average energy of ions entering the anode sheath, n accounts for the charge state of the ion, and Vpl is the plasma potential (typically 3-10 V).…”

Role of N defects in paramagnetic CrN at finite temperatures from first principles

“…In particular, N vacancies (V N ) and also N interstitials (I N ) are believed to be important point defects existing in TMN films grown by physical vapor deposition techniques [26,27]. Several groups have experimentally studied how the electronic and mechanical properties of CrN change due to nitrogen stoichiometry [28][29][30][31].…”