Dry-etching properties of TiN for metal/high-k gate stack using BCl3-based inductively coupled plasma

Abstract

The etch rate of TiN film and the selectivities of TiN∕SiO2 and TiN∕HfO2 were systematically investigated in Cl2∕BCl3∕Ar plasmas as functions of Cl2 flow rate, radio-frequency (rf) power, and direct-current (dc) bias voltage under different substrate temperatures of 10 and 80°C. The etch rate of TiN films increased with increasing Cl2 flow rate, rf power, and dc-bias voltage at a fixed substrate temperature. In addition, the etch rate of TiN films at 80°C were higher than that at 10°C when other plasma parameters were fixed. However, the selectivities of TiN∕SiO2 and TiN∕HfO2 showed different tendencies compared with etch-rate behavior as a function of rf power and dc bias voltage. The relative-volume densities of Ar (750.0nm), Cl (725.2nm), and Cl+ (386.6nm) were monitored with an optical-emission spectroscopy. When rf power increased, the relative-volume densities of all studied particles were increased. X-ray photoelectron spectroscopy was carried out to detect nonvolatile etch by-products from the surface, and nonvolatile peaks (TiClx bonds) in Ti 2p and Cl 2p were observed due to their high melting points. Based on the experimental results, we can conclude that the TiN etch is dependent on the substrate temperature when other plasma parameters are fixed. This can be explained by the enhanced chemical pathway with the assistance of ion bombardment.