Effect of NH₃ flow rate to titanium nitride as etch hard mask in thermal atomic layer deposition

Managing the hardness, density, and residual stress of the titanium nitride (TiN) hard mask has become increasingly significant for achieving excellent selectivity in the high aspect ratio etching process. This research investigates the enhancement of hardness, density, residual stress, and etch selectivity of a TiN film during the atomic layer deposition process using varying NH₃ flow rates. Additionally, the study establishes a correlation between the improvement of hard mask properties and NH₃ flow rates, taking into account the film composition, crystallinity, surface roughness, interface layers, and film thickness. The effects of NH₃ could be summarized into three types. High N–N and Ti–N bonds, along with increased film hardness, are achieved by elevating the NH₃ flow rate. Furthermore, this adjustment promotes the growth of crystal planes with higher lattice constants and modifies the interface layer thickness between Si and TiN, directly impacting residual stress. The TiN film exhibits increased roughness and decreased uniformity. In addition, at NH₃ 50 SCCM, hardness, density, and residual stress improved by 81.8%, 110%, and 87.5%, respectively. The selectivity saw a significant increase of 77.7%. This study provides an analysis of the relationship between the NH₃ flow rate and TiN thin film properties, which is essential for improving TiN hard mask properties in flow type reactors.