Muhammad Yasira, Zhenghua Tana, Seyed Ali Rezvanib,Xuebing Yuanb
a School of Materials Science and Engineering, Huazhong University of Science and Engineering, Wuhan, Hubei, 430074, P.R. China b School of Mechanical Science and Engineering, Huazhong University of Science and Engineering, Wuhan, Hubei, 430074, P.R. China
High power pulsed magnetron sputtering ,namely HPPMS for short, is an emerging technology that is gaining substantial and increasing interest not only in academics but also in industrial processes. HPPMS, also known as HIPIMS (high power impulse magnetron sputtering),？ combining the classical, scalable sputtering technology with pulsed power, is an elegant way of ionizing the sputtered atoms. HIPIMS is a physical vapour vapor deposition technique . The power is applied to the target in pulses of low duty cycle (below 10%) and frequency (below 10 kHz) ,which leads to pulse target power densities of several kW cm-2. Ultra-dense plasmas are obtained, which has unique properties ,such as a high degree of ionization of the sputtered atoms and an off-normal transport of ionized species, with respect to the target. These features lead to the deposition of dense and smooth coatings on complex-shaped substrates ,providing new and added parameters to control the deposition process, tailoring the properties and optimizing the performance of elemental and compound films.
Magnetron sputtering has become the process of choice for the deposition of a wide range of industrially important coatings. Compared to other magnetron sputtering , HIPIMS is an exceptionally versatile technique for the deposition of high-quality, well-adhered films,especially when preparing for adhesion enhancing pretreatment of the substrate prior to coating deposition (substrate etching) and deposition of thin films with high microstructure density. Many good-quality coatings have(can) been fabricated with HIPIM ,such as hard, wear-resistant coatings, low friction coatings, corrosion resistant coatings, decorative coatings and coatings with specific optical or electrical properties. As a matter of fact,thin films are widely and increasingly used in diverse technological applications, such as surface protection and decoration, data storage, optical and microelectronic devices , resulting in a strong incentive for research towards not only understanding the fundamentals and technical aspects of thin film growth, but also developing new deposition techniques which allow for a better control of the deposition process. Direct current magnetron sputtering (dcDCMS) is another widely used technique for deposition of a large number of compound and metallic coatings with specified mechanical, electrical and optical properties. Although dcMS is a successful coating technique, it suffers from fundamental problems, such as low target utilization and target poisoning during reactive sputtering, which results in process instabilities and poor deposition rates. In order to alleviate some of these problems, alternative techniques, such as radio frequency magnetron sputtering, additional ionization by rf coils or microwaves, or increased magnetic confinement by a multipolar magnetic setup are exploited.
Fig 1. Schematic representation of the plasma confinement observed in conventional and unbalanced magnetrons. As used to increase the ionization fraction in the discharge,high power unipolar pulsing of the target voltage is operated at low (or zero) power level and pulses to a high voltage for a short time each cycle ,resulting in high electron densities which leads to increased ionization of the sputtered material. With peak power densities typically of several kWcm-2, ionization fractions of the sputtered material ranging from 4.5% for C to 70% for Cu are achieved. HPPMS has been used to grow metallic and compound coatings....