UC San Diego

As the scale of transistors in integrated circuits decreases and the density of transistors increases, the precision with which all processes must be carried out scales in all dimensions. This trend has led to the development of atomic layer deposition, a technique that utilizes complementary precursors to perform successive self-limiting surface reactions to deposit materials on a monolayer-by-monolayer basis. In this work, variations of atomic layer deposition and a complementary physical vapor deposition technique are used to deposit aluminum nitride and gallium nitride films at temperatures compatible with industry limitations.

In chapter two, a technique performed in a similar fashion as atomic layer deposition is described using a novel precursor combination to deposit aluminum nitride at 400 ˚C and 580 ˚C. This technique. pulsed chemical vapor deposition, varies from atomic layer deposition in that the surface reactions are not self-limiting; however, precisely controlling precursor dosing and purging results in process control with equivalent atomic-level precision. This technique is demonstrated to deposit polycrystalline and epitaxial films with near bulk density on silicon and silicon carbide substrates, respectively, at temperatures below reported methods in the literature.

Chapter three describes atomic layer annealing for the deposition of polycrystalline gallium nitride films at 275 ˚C. In this method a brief inert ion bombardment is performed following each precursor dosing cycle to crystallize deposited material. Radio-frequency bias applied to the substrate during deposition is shown to modulate the kinetic energy of bombarding ions. This allows the intensity of the resulting collision cascades to be controlled such that the crystallinity of the deposited film can be maximized. Atomic layer deposition is performed at the same temperature as a control, but results in deposition of only amorphous films.

The final chapter describes DC reactive magnetron sputtering of aluminum nitride. The crystal structure of deposited films as a function of varied process parameters is investigated; improvements in crystal structure correlate to improved thermal conductivity in sub-micron thick films. These studies demonstrate the potential of aluminum nitride as a heat spreading material as three-dimensional integration becomes a means by which to further increase transistor density in integrated circuits.