Measurements and modeling of the impact of radical recombination on silicon nitride growth in microwave plasma assisted atomic layer deposition

High material quality silicon nitride thin film deposition by plasma enhanced atomic layer deposition (PEALD) is necessary for many advanced semiconductor device and memory fabrication applications. Understanding film growth mechanism is quite important not only for the device production control but also device performance due to the strong correlation of film growth speed and film chemical property. Nevertheless, predicting film deposition rates, let alone film quality, is difficult as quantitative surface reaction mechanisms are still not well known and the species fluxes that play the central role in film growth are not easy to measure. In this paper, the authors describe how a plasma reactor model for the nitridation step required in PEALD of silicon nitride can be combined with a phenomenological site balance model to predict film growth rate variation with some key process parameters. The relative insensitivity of growth rates to plasma power are explained by competing destruction and regeneration mechanisms for NH₃, an important nitrogen source in Si₃N₄ growth. The model also helps to reveal why H₂ can be important.