Plasma processes for thin film surface treatment

Oxygen plasma treatment of polyimide and metal interfaces is used to remove undesirable organic contamination and improve adhesion of thin films. The authors present the results of some of the experimental and modeling efforts directed toward understanding the basic physics and chemistry of the plasma systems used in thin-film processing. Measured ion densities are correlated with the observed effects on polyimide etch rates as well as with debris removal and polyimide cracking upon exposure to various plasma systems. Comparisons of predicted oxygen atom flux with the measured carbon atom turn-over number indicated that the main etching species are the O³P atoms. However, activation of the polyimide surface by ion bombardment is an essential first step and is the rate-determining process. The polyimide crack threshold is observed to decrease with increasing ion density (decreasing pressure). Plasma-treatment-induced changes of polyimide and metal surfaces have been delineated by XPS (X-ray photoelectron spectroscopy) and Auger spectroscopy and by water contact angle measurements. Surface modification of the polyimide to increase oxygen content resulted in improved wetting and adhesion. The oxidation state of chrome is a strong function of pressure. Plasma processes at 100 mtorr resulted in the formation of a stable Cr₂O₃ oxide layer, while a mixture of Cr₂O₃ and CrO₃ is formed at higher pressures