Control of reactive high power impulse magnetron sputtering processes

High power impulse magnetron sputtering (HIPIMS) is a technologically important physical vapour deposition (PVD) process that is able to provide a highly ionised flux of sputtered species. It is thought to be particularly important for applications where there is a need to coat 3D features (e.g. vias and trenches in semiconductor applications). HIPIMS may have other added benefits, as compared to DC or medium frequency AC/pulse-DC magnetron sputtering, related to better coating structure–property relationship control through self-species (sputtered metal) plasma/ion assistance.Many of the technologically important thin films (e.g. transparent conductive oxides, permeation barrier coatings, etc.) are sputtered from metal targets in a reactive gas atmosphere, usually Ar + O2 or N2, to ensure industrially relevant coating deposition rates. Enhanced structure–property relationship control of these thin film materials is highly desirable; hence, it also is desirable to use HIPIMS in a reactive deposition mode. Preliminary trials of reactive HIPIMS however have indicated that the control of this process using conventional means, such as conventional plasma emission monitoring (PEM) is difficult. Thus, the application of reactive HIPIMS is rather limited and the potential benefits are not realised, especially in the areas where precise process control and long term stability in a reactive environment are required.In this paper reactive HIPIMS process (Ti in Ar/O2 atmosphere) is investigated and various control options are evaluated. The application of a recently developed PEM based reactive HIPIMS control method is reported. Performance of the developed technique is compared to that of the conventional PEM, Penning-PEM and λ-sensor based methods. It is shown that conventional PEM is impractical to control reactive HIPIMS, while the constant reactive gas flow method does not lead to a stable deposition process. The new PEM based process control technology was shown to provide precise control and stable operation of reactive HIPIMS discharges anywhere within the hysteresis loop. It was also found to be superior when compared to oxygen partial pressure control based techniques.