Synthesis of highly conformal titanium nitride films via tert-butyl chloride-assisted atomic layer deposition

Integrating the desired properties of dynamic random-access memory (DRAM) capacitors is challenging owing to the continuous downscaling of semiconductor devices. In this paper, we propose inhibitor (tert-butyl chloride, t-BCl)-assisted atomic layer deposition (IA ALD) as a technique for obtaining a highly conformal titanium nitride (TiN) film for DRAM capacitor electrodes. IA ALD relies on an ABC-type ALD cycle, where a t-BCl precursor and reactants are sequentially applied in numerous cycles during the film growth process. The t-BCl molecules function as a medium to prevent excess TiN film deposition at the capacitor hole entrance by controlling the surface reactivity of the precursors and the modulation of the growth per cycle (GPC). The results indicated that the step coverage (>99%) of the TiN film deposited on a substrate with an aspect ratio (ratio of height to width) of 20:1 was significantly increased, while the electrical and intrinsic properties of the TiN film remained unaffected. As the t-BCl feeding rate increased from 25 to 100 sccm, the GPC decreased from 0.352 to 0.146 Å, while the film resistivity remained unaffected. X-ray photoelectron spectroscopy confirmed that there was no change in the composition of the TiN film. In addition, secondary ion mass spectroscopy analysis confirmed that t-BCl did not contain C components and that the amount of Cl impurities decreased. Furthermore, density functional theory simulations, which were performed to study the IA ALD process mechanism, suggested that the film growth rate was reduced because the physisorption of t-BCl molecules partially blocked the reactive adsorption sites for the TiCl₄ precursor.