Plasma influence in tantalum sputtering

Publisher Website
Google Scholar
Abstract
The angular distribution function (ADF) and the sputtering yield have been measured in a triode sputtering system where a dense ionic current (35 mA/cm2) drawn from an argon plasma confined by a magnetic field impinges upon a tantalum target biased at 1.8 keV. The system was placed in a vacuum chamber at a pressure on the order of 10−4 Torr. The results are the following for the two phases of Ta deposited. For α‐Ta the ADF is Lambertian but the associated yield is lower than the theoretical one; for β‐Ta the ADF curve lies below the Lambertian cosine curve. We suggest the following interpretation based on the influence of impurities. For α‐Ta there are many impurities which can be ionized and contribute to the current. Also, these ions destroy the Ar* metastables and, therefore, lower the Ta‐Ar* collision probability. For β‐Ta there are no impurities. The current is due only to ionized argon and Ar* metastables are not destroyed (i.e., the collision probability is much higher). In such a way, we are able to explain the discrepancies observed in these two cases in terms of both the sputtering yield and the ADF.