Some effects of temperature ramping on metal organic chemical vapor deposited Al film nucleation

Abstract

We discuss observations of nucleation density and evolving film texture as a function of varying substrate temperature during the initial stages of tri-isobutyl aluminum (TIBA) sourced chemical vapor deposition of aluminum. Films were deposited onto TiN X coated silicon wafers. Nucleation density, as determined by field emission scanning electron microscopy (FESEM), and film orientation, determined by X-ray diffraction, are presented for deposition at a constant temperature of 300°C and depositions in which the substrate temperature was ramped up from 250°C, down from 400°C, or down from 350°C. Temperature ramp rates were −200°C/min for cooling and 100°C/min for heating. Depositions were stopped after 5, 15 and 30 s of TIBA exposure for each deposition condition, allowing ex situ analysis of films in various stages of formation. Nuclei size distributions were determined by image analysis of the FESEM micrographs. The various 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°C resulted in a (111) to (200) ratio of 3.0 while a 30 s deposition at 300°C resulted in an aluminum (111) to (200) ratio of 1.0. A 5 s pulse while ramping down from 400°C followed by a 25 s deposition at 300°C resulted in an aluminum (111) to (200) ratio of 2.0. However, the root mean square (rms) surface roughness, as determined by atomic force microscopy, was approximately half of the rms roughness of the film deposited while ramping from 400 to 300°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 `microstructure engineering' of the fully formed film.