Atomic layer deposition of silicon nitride from Bis(tert-butylamino)silane and N2 plasma

Atomic layer deposition (ALD) of silicon nitride (SiNx) is deemed essential for a variety of applications in nanoelectronics, such as gate spacer layers in transistors. In this work an ALD process using bis(tert-butylamino)silane (BTBAS) and N2 plasma was developed and studied. The process exhibited a wide temperature window starting from room temperature up to 500 °C. The material properties and wet-etch rates were investigated as a function of plasma exposure time, plasma pressure, and substrate table temperature. Table temperatures of 300–500 °C yielded a high material quality and a composition close to Si3N4 was obtained at 500 °C (N/Si = 1.4 ± 0.1, mass density = 2.9 ± 0.1 g/cm3, refractive index = 1.96 ± 0.03). Low wet-etch rates of ~1 nm/min were obtained for films deposited at table temperatures of 400 °C and higher, similar to that achieved in the literature using low-pressure chemical vapor deposition of SiNx at >700 °C. For novel applications requiring significantly lower temperatures, the temperature window from room temperature to 200 °C can be a solution, where relatively high material quality was obtained when operating at low plasma pressures or long plasma exposure times