Influence of Bias-enhanced nucleation on thermal conductance through plasma-enchanced chemical vapor deposited diamond films

Abstract

This work describes an experimental study of the cross-plane thermal conductance of plasma-enhanced chemical vapor deposited (PECVD) diamond films grown as a result of bias-enhanced nucleation (BEN). The diamond films are grown on silicon wafers using a two-step process in which a nucleation layer of amorphous or diamond like (DLC) carbon is first deposited on the silicon under the influence of a voltage bias. Then, conditions are adjusted to allow for polycrystalline diamond (PD) growth. The nucleation layer is essential for seeding diamond growth with minimal substrate destruction and for optimizing PD properties such as grain size, orientation, transparency, adhesion, and roughness. The effective thermal conductivity of the nucleation layer and the total film are separately measured using a photoacoustic technique. The effective thermal conductivity of the nucleation layer exhibits a thickness dependence for relatively thin layers. A resistive network for the total film is developed. The influence of nucleation layers that are 65, 240, 400, and 650 nm thick on the thermal conductance of the total film is characterized. The minimum total film resistance occurs when the nucleation layer is thinnest. When the nucleation layer is sufficiently thick, it begins to exhibit bulk behavior, and the boundary resistance at the nucleation/PD boundary dominates the total film resistive network