Atomic Layer Deposition of Silicon Nitride from Bis(tertiary-butyl-amino)silane and N₂ Plasma Studied by in Situ Gas Phase and Surface Infrared Spectroscopy

The atomic layer deposition process (ALD) of silicon nitride (SiN x ), employing bis(tertiary-butyl-amino)silane (SiH 2 (NH t Bu) 2, BTBAS) and N 2 plasma, was investigated by means of Fourier transform infrared (FT-IR) spectroscopy. In situ gas phase, film, and surface infrared measurements have been performed during different stages of the ALD process. From gas phase IR measurements it can be concluded that tert -butylamine is the main reaction product released during precursor exposure. Infrared measurements performed on the deposited SiN x films revealed the incorporation of C in the form of CN and SiC, where more C is incorporated at a deposition temperature of 85 °C compared to 155 or 275 °C. Surface IR measurements, employing a four-axes sample manipulator, showed the formation of SiH- and NH-groups on the surface and revealed that most of the H is incorporated during the precursor exposure step. Furthermore, after the N 2 plasma step a vibrational mode around 2090 cm –1 was observed. This mode could be attributed to the formation of Si-NCH complexes and are likely to be formed by the so-called redeposition effect. For higher deposition temperatures, these Si-NCH complexes are removed again during the following precursor exposure step. At 85 °C, some of the complexes remain at the surface. Overall, from the gained knowledge about the surface chemistry, a reaction mechanism of the SiN x ALD process has been proposed.