Analysis of ion energy distribution at the substrate during a HPPMS (Cr,Al)N process using retarding field energy analyzer and energy resolved mass spectrometer

Abstract

The ion energy is known to have a strong influence on the properties of coatings deposited by physical vapor deposition (PVD). Therefore, the ion energy distribution (IEDF) especially measured at the substrate side is of great interest for understanding the coating growth. In PVD coating processes the ion energy at the substrate can be adjusted by applying a negative voltage (bias) to the substrate table. In the present work, mass integrated measurements of the IEDF were carried out during a high power pulsed magnetron sputtering (HPPMS) (Cr,Al)N process using a Cr target with 20 plugs of Al within an industrial scale PVD coating unit. The HPPMS cathode was operated with different average powers (1kW, 3kW and 5kW) and pulse lengths (ton) of 40μs, 80μs and 200μs at constant frequency of 500Hz. In a first step, measurements of the IEDF using retarding field energy analyzer (RFEA) were carried out on grounded substrate table and later on using −100V substrate bias. Additionally, measurements of the IEDF were carried out using mass spectrometer (MS) exemplary to compare with the results from RFEA. By comparing the measured IEDFs some limitations of these two different measurement methods were found. The MS underestimates that the amount of high energetic ions and the RFEA measurement are influenced by the incidence angle of the ions. Besides those limitations the influence of cathode power and HPPMS pulse length on the IEDF was studied. At high peak power density, i. e. short pulse length and high average cathode power, a much greater high energetic fraction in the IEDF between 10 and 50eV was found in the results of the RFEA compared to MS results presented here. Also the effective mean ion temperature in the high energetic region of the IEDF was found to increase with increasing peak power density. Furthermore, the effective mean ion temperature was not strongly influenced using substrate bias.