Molecularly engineered low temperature atomic layer growth of aluminum nitride on Si(100)

Abstract

Trimethylamine alane (TMAA) and deuterated ammonia (ND3) were used to grow aluminum nitride (AlN) thin films on Si(100) based upon a molecularly engineered atomic layer growth process. Atomic layer growth requires, in part, self-limiting adsorption of both precursors. Self-limiting behavior of TMAA only occurred at temperatures below 400 K as confirmed by x-ray photoelectron spectroscopy (XPS). Although the adsorption of ND3 on the surface is self-limiting between 300 and 675 K, alternating exposures of TMAA and ND3 at 380 K did not fully dehydrogenate ND3 into nitride. However, by sequentially exposing the substrate to ND3 at 675 K and TMAA at 380 K, we achieved atomic layer growth of AlN. The growth scheme consists of the adsorption of ND3 on Si(100) at 675 K which generates ND2 species on the surface. Then TMAA is exposed to the ND3-derivatized surface at 380 K. As the surface temperature is raised back to 675 K for the next ND3 exposure, AlN was formed by the bridge bonding of Al between two nitrogen centers and desorption of HD. Minor surface species include AlHxNDy (x=1–2, y=1–2). Further adsorption of ND3 at 675 K resulted in (i) direct nitride formation by decomposition of AlHxNDy to AlN and (ii) the formation of ND2 species bonded to surface Al. Similar to the first TMAA dose, the second exposure produced AlN and AlHxNDy. The mechanisms are consistent with the expected D2 and HD desorption during temperature programmed desorption after each exposure cycle. The carbon contamination after each ND3 exposure is below the detection limit of XPS. The layer-by-layer growth mode is confirmed by the close match between predicted and measured attenuation of XPS substrate features and Al/N atomic ratios.