Hysteresis and process stability in reactive high power impulse magnetron sputtering of metal oxides

Abstract

In the further development of reactive sputter deposition, strategies which allow for stabilization of the transition zone between the metallic and compound modes, elimination of the process hysteresis, and increase of the deposition rate, are of particular interest. In this study, the hysteresis behavior and the characteristics of the transition zone during reactive high power impulse magnetron sputtering (HiPIMS) of Al and Ce targets in an Ar-O 2 atmosphere as a function of the pulsing frequency and the pumping speed are investigated.Comparison with reactive direct current magnetron sputtering (DCMS) reveals that HiPIMS allows for suppression/elimination of the hysteresis and a smoother transition from the metallic to the compound sputtering mode. For the experimental conditions employed in the present study, optimum behavior with respect to the hysteresis width is obtained at frequency values between 2 and 4 kHz, while HiPIMS processes with values below or above this range resemble the DCMS behavior. Al-O films are deposited using both HiPIMS and DCMS.Analysis of the film properties shows that elimination/suppression of the hysteresis in HiPIMS facilitates the growth of stoichiometric and transparent Al 2 O 3 at relatively high deposition rates over a wider range of experimental conditions as compared to DCMS.

An introduction to thin film processing using high-power impulse magnetron sputtering

“…The stabilization of the transition zone allows for deposition of stoichiometric films at a lower target coverage when compared to the compound mode in DCMS. 30,73,84 This has been shown to result in deposition rates similar 30 or up to two times higher 84 than those obtained by DCMS. It is worth mentioning that all the studies on reactive HiPIMS have been performed in small-size laboratorial scale deposition systems.…”

“…At the same time there is a tradeoff with the degree of ionization, where the highest reported values are found for the 20 ls pulses. 28 It is also reported that shorter pulses have beneficial consequences for reactive HiPIMS processes, 73 which are discussed in more detail in Section II F.…”

Effect of peak power in reactive high power impulse magnetron sputtering of titanium dioxide

“…At this frequency, the duty cycle was 35% which is substantially higher than that of the typical values used in HiPIMS. Furthermore, the power density within the pulse was low and the condition corresponded to mid-frequency reactive magnetron sputtering [9]. These examples from literature show that with reactive HiPIMS process, under optimized experimental conditions, hysteresis can be suppressed/eliminated.…”

“…We have previously found that there is a range of pulse repetition frequencies at which a HiPIMS process can reduce or completely remove the hysteresis [9]. The range of frequency used was from 1 kHz to 10 kHz where the optimum frequencies were found to be between 2 and 4 kHz for the Al-O system, but are likely to vary depending on various process conditions.…”

“…The most important experimental parameter is the target size along with some other deposition parameters such as pumping speed, sputtering gas pressure, pulsing frequency, and duty cycle for the case of HiPIMS. [9,11].…”