Interfacial integrity enhancement of atomic layer deposited alumina on boron doped diamond by surface plasma functionalization

High dielectric constant (high-κ) thin films are ubiquitous in research as they impart enhanced properties to microelectronic applications. Novel combinations for coupling high-κ and ultra-wide band gap semiconductors are being investigated for niche applications, dependent on the environmental conditions for device operation. Typically, high-κ films such as alumina are deposited by atomic layer deposition (ALD), a technique heavily dependent on surface chemistry. This work investigates the effect of plasma surface functionalization of boron doped diamond (BDD) semiconducting films on interface quality with top-layers of ALD alumina (AlO) films, by analyzing its susceptibility to deformation; being particularly vital for electronics subjected to physically demanding environments. Alumina thin films were deposited unto as-grown (AlO-H-BDD) and O2 plasma treated (AlO-O-BDD) polycrystalline BDD. XPS analysis performed on plasma exposed BDD films, prior to AlO deposition, demonstrated a 3% increase in O surface ligands compared to the as-grown surface. Nanoindentation analysis demonstrated plastic deformation within the alumina layer for AlO-O-BDD, for the tested loads, whereas AlO-H-BDD experienced film delamination and deformation beyond the alumina-BDD interface. TEM analysis revealed that delamination was most likely due to low cohesive strength of alumina near the interface, explained by fewer –OH and –CO (ether) BDD surface ligands on H-BDD.