Diamond seeding process for the heterogenous integration of high quality diamond on semiconductors
MetadataShow full metadata
Diamond thin films grown by chemical vapor deposition (CVD) have a wide band gap, high hardness, chemical inertness, and high thermal conductivity, making them an attractive material for a wide range of applications. Due to high surface energy and low sticking probability of diamond, it is difficult to grow thick coalesced diamond films on non-diamond substrates. To deposit diamond film with acceptable surface roughness, desired grain size, and other properties, nucleation enhancement steps through the diamond seeding process are generally required. In this work, an effort is made to improve seeding density, nucleation process, growth kinetics, film morphology, quality as well as material thermal properties of diamond film on different semiconductors. The growth of high-quality diamond on silicon as well as III-Nitrides were achieved through a series of experiments and characterization in various steps of the process.
The first and foremost experiments were conducted to improve the diamond seeding density on silicon and III-Nitride semiconductors. An innovative approach is developed to disperse dense nano-diamond particles by electrostatic van der Waals bonding between the oxygen terminated diamond nanoparticles and a cationic polymer. Then, a systematic study is reported of the effects of nano-diamond seeding densities 4×108, 8×1010 and 2×1012 cm-2 on silicon wafers on the growth, quality, and morphology of diamond films from sparse to dense range. The growth dynamics, morphology and quality of diamond were found to depend upon the change in seeding density. Diamond crystals were found to develop three dimensionally via Volmer-Weber (VW) growth into large grains with low seeding density. The transition from VW conditions to van der Drift mode (mostly one dimensional) were found with increasing seeding density on the sample. Diamond crystal quality is found to improve both in the near interface region as well as the growth surface with thickness, at a given seed density, and as density increases. The interface thermal property is improved with increasing seed density on the sample with thermal boundary conductance (TBC) between diamond and Si of 256±32.3 MW/m2K, 292±19.7 MW/m2K, and 318±21.8 MW/m2K, for seed densities 4×108, 8×1010 and 2×1012 cm-2, respectively.This work also investigates the effect of diamond seeding density to achieve direct growth of diamond on epitaxial gallium nitride on silicon substrate. A comparative study is performed for the diamond growth on gallium nitride with low 2.3×109 cm-2 and dense 3.1×1012 cm-2 seed density. It is found that the gallium nitride decomposed and creates pinholes in the growing diamond layer or caused it to delaminate at sparse seed density. The quick diamond lateral coverage during early growth stage help to protect the gallium nitride film from etching at high seeding density. Finally, a comparative study is performed on nucleation, growth, and quality of diamond film on ultra-wide bandgap aluminum nitride at 1×108 and 2×1012 cm-2 seed densities. High quality diamond of ~ 10μm thickness is deposited without delamination of the underlying nitride layer. The crystalline quality and diamond phase is found to improve for the diamond film with increasing seed density. The diamond/aluminum nitride interface is seen to be porous when isolated diamond grains coalesce for diamond growth with lower seeding density. The relative absence of pores or voids is found with high seed density.
At its core, this dissertation develops a fundamental way to deposit high quality diamond on semiconductors with improved nucleation using dense nano-diamond seeding density. Such diamond coating on GaN based high electron mobility transistors (HEMTs) is applicable to solve the self-heating issue on the device.