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

Paper PS2-WeA2
Origin of Sidewall Deposition during Cl@sub 2@/O@sub 2@ Etching of Sub Micron Features in Inductively Coupled Plasma Reactors

Wednesday, October 4, 2000, 2:20 pm, Room 311

Session: Feature Evolution
Presenter: S.J. Ullal, University of California, Santa Barbara
Authors: S.J. Ullal, University of California, Santa Barbara
A.R. Godfrey, University of California, Santa Barbara
E.S. Aydil, University of California, Santa Barbara
E.A. Edelberg, Lam Research Corporation
L.B. Braly, Lam Research Corporation
V. Vahedi, Lam Research Corporation
J. Daugherty, Lam Research Corporation
Correspondent: Click to Email
Shallow trench isolation (STI), a manufacturing technique used to isolate transistors in integrated circuits (IC), involves etching a trench of specific dimensions and shape into a silicon substrate in a high density inductively coupled plasma reactor. The trench is later filled with a dielectric and polished, resulting in a filled isolated shallow trench. To attain the best device characteristics, the filled trench must not contain any voids, which could be formed during filling, and avoided by engineering tapered sidewalls. These profiles are formed by redeposition of etch products on the sidewalls of the trench. The taper angle depends on a delicate balance between etching and redeposition on the sidewalls. In order to meet the stringent requirements of the IC fabrication industry, the taper angle on the sidewalls must be invariant to the position of the trench on the wafer and also be reproducible from wafer-to-wafer. To achieve these goals, a fundamental understanding of the nature and the origin of sidewall deposition is required. A typical STI etching process using Cl@sub 2@/O@sub 2@ gases was used to illustrate the dependence of sidewall deposition on chamber wall condition. A novel diagnostic method based on in situ multiple total internal reflection Fourier transform infrared spectroscopy was used to study the nature of the species deposited on the walls of the chamber. Etch products such as SiCl@sub x@ were detected by optical emission spectroscopy and Fourier transform infrared spectroscopy within, and downstream of the chamber respectively. Scanning electron micrographs of sub 0.25 µm features were examined to determine the profiles after etching. Simultaneous monitoring of the etch products in the gas phase, on the reactor walls, and in the reactor exhaust provides evidence which suggests that the deposition on the sidewall occurs due to a direct flux of etch products leaving the trench, rather than redeposition from the gas phase.