Understanding Field-Dependent Leakage Current Mechanisms in Amorphous Hydrogenated Boron Carbide As a Function of Electronic, Dielectric, and Disorder Parameters

Thin-film carborane-based amorphous hydrogenated boron carbide (a-B_xC:H_y), grown by plasma-enhanced chemical vapor deposition (PECVD), has emerged as a promising semi-insulating, low-dielectric-constant (low-κ) (κ < 3.5) material for intra/interlayer dielectric (ILD) and/or copper diffusion barrier/etch stop applications. Of the many integration challenges faced by candidate materials for low-κ ILDs or more specialized layers, one of the most important is the need for extremely low leakage currents up to high electric fields. In the case of a-B_xC:H_y, the leakage current at a given field can span nearly ten orders of magnitude, depending on the fabrication conditions and resulting physical properties of a given film. In order to go beyond a brute force process–property approach toward optimizing the electrical properties in thin-film a-B_xC:H_y, we explore their origin and relationship to electronic, dielectric, and disorder properties.

This contribution will describe the charge transport mechanisms in a-B_xC:H_y films in different electric field regimes, which include Ohmic, space-charge-limited-current, and Poole–Frenkel behavior. These mechanisms, and the underlying electrical properties that define these mechanisms (e.g., resistivity, mobility, trapping), are related to individual and combined electronic (band gap), dielectric (electronic and atomic/distortion polarization), and disorder (Urbach energy, Tauc parameter, dispersion energy) parameters. We further discuss how balancing the contributions of these different parameters via hydrogen and carbon content, through varying growth parameters, allows us to control the underlying charge transport mechanisms at both low and high fields, to ultimately obtain leakage currents on the order of 10^–8 A/cm²or lower at 2 MV/cm.

Figure 1. (a) Leakage current density (J) as a function of electric field (E) for a selection of a-B_xC:H_y films. (b) and (c) Correlations between charge transport and disorder parameters: zero-field mobility extracted from steady-state space-charge-limited current measurements (μ_0(SS-SCLC)) as a function of E_gE_uB^–1/2 disorder parameter, and resistivity (ρ) extracted in Ohmic regime as a function of dispersion energy (E_d).