Nitrogen doping of polycrystalline, LPCVD 3C-SiC thin films using alternating supply deposition

Abstract

In this paper, we demonstrate the implementation of a doping scheme for 3C-SiC thin films using the alternating supply deposition (ASD) technique in a low-pressure chemical vapor deposition (LPCVD) system. The moment of introduction of the dopant is critical and resulted in different thin film resistivities. By synthesizing 3C-SiC thin films with the most promising dopant scheme and increasing ammonia (NH₃) flow rates we provide insight of the capabilities of ASD doping. The electrical properties were characterized using the circular transfer length method (CTLM). Promising values for the specific contact resistance around 3·10⁻⁶ Ω cm² were measured and resistivities of ρ = 0.02 Ω cm, which is comparable to state-of-the-art thin film resistivities for polycrystalline 3C-SiC. The temperature dependence of undoped and highly doped thin films are compared from room temperature to 300 °C. For both cases a negative temperature coefficient was determined, which is explained by the effect of incomplete ionization of the dopant. Lowest resistivities of 0.014 Ω cm were measured at 300 °C. Chemical analysis demonstrates for elevated NH₃ flow rates a change from highly <111> oriented poly 3C-SiC thin films to amorphous and highly insulating SiCN thin films of only 25 % of the maximum measured thickness. This can be explained by the competition of C and N atoms for Si bonds, which is dominated by nitrogen atoms at higher NH₃ flow rates.