High Power Impulse/Pulsed Magnetron Sputtering (HiPIMS/HPPMS) process has several interesting aspects and is vigorously studied in recent years. In this preface, some trends in HiPIMS research are briefly reviewed: 1) the applicability of HiPIMS to practical deposition processes, 2) the behavior of the transient and high density plasma, and 3) the application of HiPIMS to the reactive sputtering. By this, the author tried to help the readers to overview this field, and to locate the importance of the contributions to this special issue.

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　The characteristics of diamond-like carbon (DLC) films deposited by high power impulse magnetron sputtering (HiPIMS) with multipolar magnetic plasma confinement (MMPC) were investigated. DLC films were prepared on silicon (Si) by HiPIMS and HiPIMS-MMPC over varying substrate bias voltage. Depositions were performed from a graphite target (210 mm in diameter) under argon (Ar) gas atmosphere at chamber pressure of 0.5 Pa. The DLC films were analyzed by several methods. In HiPIMS-MMPC, the peak power density was approximately 690 W/cm² at a duty cycle of 1% (frequency: 200 Hz). According to Raman spectroscopy, the structure of DLC film deposited by HiPIMS-MMPC could be changed from amorphous carbon (a-C) to tetrahedral amorphous carbon (ta-C). The deposition rate in HiPIMS-MMPC was approximately 50% (10 nm/min) lower than that in HiPIMS. However, HiPIMS-MMPC is considered as one of the effective methods to prepare hard and dense DLC films (20 GPa and 2.00 g/cm³ at the maximum).

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　This is to review a novel approach stabilizing reactive mode at transition regime in reactive high-power impulse magnetron sputtering (R-HiPIMS). The proposed method is based on a real-time monitoring of peak discharge current. To stabilize the process conditions at a given set point, a feedback control system, which automatically regulates the pulse frequency, and thereby the average sputtering power, was implemented to maintain a constant maximum discharge current. As a representative result, the variation of the pulse current waveforms over a wide range of reactive gas flows and pulse frequencies during a R-HiPIMS of Hf in an Ar-N₂ atmosphere illustrates that the discharge current waveform is an excellent indicator of the process conditions. Applicability of the proposed method was successfully demonstrated.

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　Intensive ion source for single-size nanoclusters was developed on the basis of high-power impulse magnetron sputtering (HiPIMS) technique combined with a low-pressure, low-temperature gas flow reactor. The nanocluster source exhibits superior characteristics originating from pulsed, high-power sputtering compared to conventional direct-current sputtering; (1) enhanced ion intensities, (2) fascicle tuning of nanocluster sizes, and (3) enhanced selectivity of stable, magic nanoclusters. The metallic (silver, platinum, and palladium) and binary (transition-metal and silicon) nanocluster ions in the size range of several to one hundred atoms can be generated with ion current of 100 pA to 10 nA (10⁸ to 10¹¹ nanoclusters/sec). The growth mechanism of nanoclusters in the source was also explained by the nucleation theory.

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　A relatively new industrial sputtering technology based on High Power Impulse Magnetron Sputtering (HiPIMS) is demonstrated. HiPIMS is a magnetron discharge process like conventional dc magnetron sputtering (DCMS). However, momentarily input power is approximately ten times higher in magnitude. In this study HiPIMS discharge is characterized by Optical Emission Spectroscopy (OES), and compared with DCMS and cathodic arc (CA). The result shows that the HiPIMS provides the high ionization degree of the sputtered metal species. The degree of Ti ionization is found to be increased as the pulse frequency of HiPIMS is decreased, which enables to adjust the sputter plasma properties ranging from low-metal ionization to high-metal ionization by controlling the pulse frequency. This expands an opportunity to tailor the properties of sputtered thin films.

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　Minimal fab is a new manufacturing system to suitably fabricate small numbers of semiconductor devices with very low investment. Minimal fab handles a half-inch wafer, and requires that the process equipment is installed in a small regulated chassis. For the minimal fab, sputter deposition equipment was developed. High power impulse magnetron sputtering (HiPIMS) technology was used for the deposition. The HiPIMS equipment for minimal fab successfully deposit conductive Al films for MOSFET devices. The equipment hardly generated particles that contaminated the fabricated devices. The electrical resistivity of deposited film was 45 nΩm. This resistivity was small enough to work the devices.

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