Influence of Bias-Enhanced Nucleation on Thermal Conductance Through Chemical Vapor Deposited Diamond Films

Baratunde A. Cola, Birck Nanotechnology Center, School of Mechanical Engineering, Purdue University
Ratnakar Karru, Purdue University
Changrui Cheng, Butler International, Inc.
Xianfan Xu, Birck Nanotechnology Center, School of Materials Engineering, Purdue University
Timothy Fisher, Birck Nanotechnology Center, Purdue University

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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 on smooth substrates and for optimizing PD properties such as grain size, orientation, transparency, adhesion, and roughness. A photoacoustic (PA) technique is employed to measure the thermal conductivities of and the thermal interface resistances between the layers in the diamond film structure. The influence of nucleation layers that are 70, 240, 400, and 650 nm thick on the thermal conductance of the diamond film structure is characterized. The thermal conductivity of the nucleation layer exhibits a thickness dependence for relatively thin layers. For each sample, the thermal conductivity of the PD is higher than 500 W m 1K 1 (measurement sensitivity limit). A resistive network for the diamond film structure is developed. The resistance at the silicon/nucleation interface is less than 10 9m2 K W 1 (measurement sensitivity limit), which is of the order of theoretical predictions. The minimum diamond film structure resistance occurs when the nucleation layer is thinnest. When the nucleation layer is sufficiently thick, it begins to exhibit bulk behavior, and the resistance at the nucleation/PD interface dominates the thermal resistance of the diamond film structure.