AVS 50th International Symposium
    Plasma Science and Technology Monday Sessions
       Session PS+MM-MoA

Paper PS+MM-MoA5
Feature Scale Model of Etching High Aspect Ratio Structures in Silicon using SF@sub 6@/O@sub 2@ Plasma

Monday, November 3, 2003, 3:20 pm, Room 315

Session: MEMS Etching
Presenter: J. Belen, University of California, Santa Barbara
Authors: J. Belen, University of California, Santa Barbara
S. Gomez, University of California, Santa Barbara
M.W. Kiehlbauch, Lam Research Corporation
D.J. Cooperberg, Lam Research Corporation
E.S. Aydil, University of California, Santa Barbara
Correspondent: Click to Email
The need to etch high aspect ratio features (depth-to-width) such as deep holes and trenches in Si arises in manufacturing of microelectromechanical systems and capacitors in memory devices. Anisotropic plasma etching of such features is achieved by taking advantage of energetic ion bombardment of the surface in the normal direction in conjunction with sidewall passivation with a film that is resistant to etching. Feature profile evolves as a result of various ion-assisted etching, passivation and deposition processes that occur on the feature surfaces. A fundamental and quantitative understanding of the balance between these processes is necessary for achieving control over the feature profile shape. We have developed a semi-empirical feature scale model of Si etching in an SF@sub 6@/O@sub 2@ plasma. This model is used to quantify etching kinetics and to identify the important parameters that affect profile evolution. Information from plasma diagnostics and previously published data are used to estimate F, O, and ion fluxes as well as ion energy and angular distributions. These estimates are used as input to the profile simulations in order to reduce the degrees of freedom in the model. Experimentally inaccessible parameters such as the spontaneous chemical etch rate constant, F and O sticking coefficients, ion-enhanced etch yield and ion scattering parameters are determined by matching the experimentally observed and simulated feature profiles under different plasma etching conditions. The mask undercut and the slope of the feature sidewalls are controlled by the F-to-O flux ratio. Two distinct mechanisms for sidewall passivation are identified: (a) surface oxidation, which is thought to be prevalent at high and intermediate F-to-O ratios where the sidewalls are either negatively tapered (bowed out) or vertical, and (b) redeposition of reaction products, which results in positively tapered sidewalls at low F-to-O ratios.