SOME EFFECTS OF TEMPERATURE RAMPING ON METAL-ORGANIC CHEMICAL-VAPOR-DEPOSITED AL FILM NUCLEATION

We discuss observations of nucleation density and evolving film textur e as a function of varying substrate temperature during the initial st ages of tri-isobutyl aluminum (TIBA) sourced chemical vapor deposition of aluminum. Films were deposited onto TiNX coated silicon wafers. Nu cleation density, as determined by field emission scanning electron mi croscopy (FESEM), and film orientation, determined by Xray diffraction , are presented for deposition at a constant temperature of 300 degree s C and depositions in which the substrate temperature was ramped up f rom 250 degrees C, down from 400 degrees C, or down from 350 degrees C . Temperature ramp rates were -200 degrees C/min for cooling and 100 d egrees C/min for heating. Depositions were stopped after 5, 15 and 30 s of TIBA exposure for each deposition condition, allowing ex situ ana lysis of films in various stages of formation. Nuclei size distributio ns were determined by image analysis of the FESEM micrographs. The var ious deposition conditions resulted in significantly different nuclei size distributions and coverages. The ratio of aluminum (111) to (200) orientation also depends on deposition conditions. A 30 s deposition with a temperature ramp from 400 to 300 degrees C resulted in a (111) to (200) ratio of 3.0 while a 30 s deposition at 300 degrees C resulte d in an aluminum (111) to (200) ratio of 1.0. A 5 s pulse while rampin g down from 400 degrees C followed by a 25 s deposition at 300 degrees C resulted in an aluminum (111) to (200) ratio of 2.0. However, the r oot mean square (rms) surface roughness, as determined by atomic force microscopy, was approximately half of the rms roughness of the film d eposited while ramping from 400 to 300 degrees C for 30 s. We conclude with a discussion of our efforts to elucidate the role of temperature ramping in the nucleation process and its possible extension in 'micr ostructure engineering' of the fully formed film. (C) 1997 Elsevier Sc ience S.A.