AVS 45th International Symposium
    Plasma Science and Technology Division Tuesday Sessions
       Session PS2-TuM

Paper PS2-TuM10
The Challenge of Predictive Profile Simulators for Dielectric Etch

Tuesday, November 3, 1998, 11:20 am, Room 318/319/320

Session: Oxide Etching
Presenter: J. Kenney, California Institute of Technology
Authors: G.S. Hwang, California Institute of Technology
J. Kenney, California Institute of Technology
K.P. Giapis, California Institute of Technology
Correspondent: Click to Email
Current ULSI technology requires extensive plasma etching of dielectric materials, a need that will further increase with the anticipated move to copper interconnects and low-k dielectrics. The increased importance of dielectric etch, when combined with tighter tolerances for profile control at larger aspect ratios, presents a unique opportunity for fundamental research to assist in the development of etch processes in a timely and cost-effective manner. To be sure, understanding plasma etching of dielectric materials poses a challenge, considerably taller than that of metal or polysilicon etch for two reasons: a) Etching of dielectrics proceeds by more complex surface chemistry, involving simultaneous deposition and etch processes, and b) Differential surface charging is significant. These differences can lead to etch rate dependencies and profile irregularities that are unique to dielectric etching. Direct Simulation Monte Carlo techniques are used to study dielectric etch in high density plasmas. The simulations include sheath theory, microstructure charging, surface currents, and etching by a simple sputtering model. We explicitly investigate the etch rate dependence as a function of etch depth on plasma parameters and dielectric quality (as judged by a surface discharge threshold). The results suggest that ion shadowing (aspect ratio dependent) and surface currents (absolute depth dependent) play a crucial role in dielectric etch. Based on the simulations, we develop an empirical relationship to capture the etch rate dependencies on etch time, ion temperature, ion energy, surface discharge threshold, aspect ratio, and etch depth. The relationship describes well published etch rate data and reported parameter dependencies for various oxide etch chemistries and can be used to predict the etch stop occurrence. Furthermore, profile evolution simulations are performed to investigate the rigin of two profile peculiarities in oxide etch: microtrenching and sidewall bowing. The results indicate that ion scattering is not the dominant mechanism by which these irregularities form. Rather, charging effects at the trench bottom and mask sidewalls appear to be mainly responsible as asserted by a comparison of predicted with experimental profiles.