A Correlation Study of Aluminum Film Wet Etch Uniformity with the Sputter Etch of Oxide Films

Abstract

Recent research in the fabrication process of sputtered aluminum (30 ppm silicon) films for device interconnection shows a correlation between the ability to wet metal etch the film in a uniform manner, and the surface reflectance of the film. Aluminum grain notching of patterned metal lines causing subsequent open device circuits is shown to be related to the amount of residual gas incorporated into the metal film. Reflectance measurements of the deposited aluminum films exhibit lower values of reflectance for films that incorporate residual gases. Low reflectance films show a greater degree of metal grain notching than those of higher surface reflectance when wet metal etched. Removal of the sputter etched by-products from the aluminum deposition is necessary to avoid residual gas incorporation. Two methods are successful in increasing the aluminum reflectance as well as minimizing metal line width grain notching. These two methods are described and compared in their ability to optimize the uniformity of metal wet etching.