AVS 47th International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS2-WeA

Paper PS2-WeA4
Feature Profile Evolution during Pulsed Plasma Etching: Effects of Redeposition of Time-Dependent Etch Products

Wednesday, October 4, 2000, 3:00 pm, Room 311

Session: Feature Evolution
Presenter: K. Ono, Kyoto University, Japan
Authors: K. Ono, Kyoto University, Japan
H. Kousaka, Kyoto University, Japan
Correspondent: Click to Email
Pulsed plasma etching has recently been attracting much attention as an advanced processing technique in the fabrication of microelectronic devi ces. The inclusion of pulse repetition frequency and duty cycle provides us with additional control variables to optimize the plasma process. In contr ast to a relatively deep understanding of gas-phase chemical aspects of puls ed discharges and their effects on the processing, little work has been conc erned with time-varying surface chemistry therein. This paper is concerned with the surface chemistry and the resulting profile evolution during pulsed plasma etching of Si in Cl@sub 2@. The time-dependent behavior of surface chlorination and ion-enhanced desorption of neutral Cl atoms adsorbed as wel l as reaction products SiCl@sub x@ from the surface is calculated in pulsed operation, using a simple model based on Langmuir adsorption kinetics. The etched profile evolution is then simulated for infinitely long trenches with different widths, taking into account the transport of ions and neutrals in microstructural features: geometrical shadowing of the structure, reemissio n of neutrals at the surface on incidence, and also redeposition of etch pro ducts from the surface being etched. The product species desorbed is assume d to be time-dependent, owing to reaction layer dynamics of the ion-assisted processes on a time-scale of micro to milliseconds: on a 1 ms time scale or shorter, tightly bound intermediates such as SiCl and SiCl@sub 2@ are relea sed by momentum of the impinging ions, having large sticking probabilities o n surfaces; on a time scale of tens of milliseconds and longer, the ion-enha nced formation of SiCl@sub 3@ and SiCl@sub 4@ is expected, having smaller st icking probabilities. The numerical results indicate that the effect of red eposition of etch products is more significant for pulsed discharges with sh orter periods and smaller duty ratios, giving outwardly tapered profiles whi ch are more pronounced on narrower pattern-width or higher aspect-ratio feat ures. These results will also be compared with experiments.