AVS 47th International Symposium
    Semiconductors Monday Sessions
       Session SC1+EL+SS-MoM

Paper SC1+EL+SS-MoM3
Quantum Chemical Study of Silicon Nitride Deposition Using Ammonia

Monday, October 2, 2000, 9:00 am, Room 306

Session: Chemistry of Silicon Oxides and Nitrides
Presenter: Y. Widjaja, Stanford University
Authors: Y. Widjaja, Stanford University
C.B. Musgrave, Stanford University
Correspondent: Click to Email
Density functional theory is used to examine the reaction mechanisms of nitridation of the Si(100)-2x1 surface by NH@sub 3@. The surface is modeled using the cluster approximation. A detailed reaction mechanism is investigated including ammonia adsorption and decomposition, insertion of N into Si-Si bonds, and H@sub 2@ desorption. We find that nitrogen prefers to be in the subsurface layer, bonded to three Si atoms. The energy barriers leading to the nitridation of the Si(100) surface are also calculated. The activation barrier of the rate limiting step is found to be higher than the activation barrier for NH@sub 3@ desorption. This confirms the experimental observation that a large fraction of the NH@sub 3@ that dissociates on adsorption will recombine and desorb. Furthermore, we have also calculated the vibrational frequencies of various surface nitride structures. The computed frequencies are then compared with the experimental HREELS spectra. The comparison further allows the unambiguous characterization of the surface species. Using the calculated barriers and frequencies we use transition state theory to estimate a rate for nitridation of the (100) silicon surface. We investigate the validity of the cluster approximation and find that bigger cluster models are necessary to describe the nonlocal electronic effects.