MICROSTRUCTURAL CHARACTERIZATION OF SIOX SURFACE CONTAMINANTS ON ASHED ALUMINUM THIN-FILMS

Thin films of aluminum were exposed in short increments to a plasma en vironment using a semiconductor plasma asher. The process gas was a mi xture of air and oxygen. The total exposed oxygen fluence was 1.2 x 10 (21) oxygen atoms cm(-2) accumulated over 34 h. Heavy contamination of film surfaces resulted from plasma etching of the chamber seals. The surface microstructure of this deposited contaminant was studied with atomic force microscopy (AFM). The contaminants appear to nucleate and grow at protruding surface features. These features appear in the AFM data as dome-shaped growths rising rapidly from the surface. The dens ity of these observed growths is much higher on sputtered films than o n electron-beam evaporated films. These differences are most likely du e to the microstructure of the as-deposited films. The as-deposited sp uttered films are rougher than their evaporated counterparts and provi de more sites for nucleation of the observed contaminant growths. The surface roughness of the contaminated films increases quickly by a fac tor of 3-6 within 300 min of exposure and saturates thereafter. It is postulated that the surface roughness increases until a continuous, bu t rough, contaminant layer is formed. After the formation of a continu ous layer, additional material deposits while maintaining the existing surface microstructure. The growth of rough contaminant features has a significant effect on the specular reflectance of the films. Sputter ed films show larger losses in specular reflectance than evaporated fi lms after asher exposure.