Structural and chemical transitions in diamond/dielectric/Si heterostructures

Abstract

Interfaces between polycrystalline (PC) diamond and Si substrates with thin dielectric interlayers of SiO₂ or SiC were studied at the atomic scale to understand the impact of the interlayer on phonon transitions from one material to the other. Our previous thermal characterization study had revealed that the dielectric interlayer led to significant reductions in the thermal boundary resistance (TBR) between diamond and Si for both interlayer types. However, the structural and chemical data needed to fully understand the underlying reason(s) for these reductions were unavailable. High-resolution scanning transmission electron microscopy and electron-energy-loss spectroscopy were used here to analyze the structural and chemical transitions within the PC-diamond/interlayer/Si heterostructures, and to correlate these observations with the trends in measured TBR values. The non-abrupt interface observed between PC-diamond and SiO₂ interlayers caused by intermixing of Si, C, and O during growth of the diamond layer, and the gradual changes in the Si:C ratio in SiC interlayers, appear to facilitate smooth phonon mode transitions in both cases. The SiO₂ interlayers exhibited the anticipated trend in TBR as a function of interlayer thickness, whereas the SiC interlayers deviated substantially from expectations, most likely due to gradual variations in the Si:C ratio and the unexpected presence of SiC nanocrystallites within the interlayer. Despite the presence of these nanocrystallites, the substantial reduction of 70 % in TBR value compared to an abrupt interface, is still significant. Overall, these results confirm that interface engineering offers a viable route towards thermal management in compact high-power electronic devices.