Kunihide Tachibana

Department of Electronic Science and Engineering, Kyoto University
Yoshida-Honmachi, Sakyo, Kyoto 606-8501, Japan
tatibana@kuee.kyoto-u.ac.jp

Etching selectivity and its reproducibility are key issues in the etching of SiO2 over Si in ULSI processing. In various plasma sources, especially in high density sources such as ICP, ECR, etc., the controlling method of F atom density relative to CFx radical density has become an essential problem. Surface conditions of the substrate and chamber walls, however, are reflected in the gas phase reactions ineviably, so that in situ diagnostics of both gas phase species and surface bonding states are required for understanding the overall chemistry in SiO2 etching.

For the gas phase diagnostics we have developed two new techniques, i.e., VUV laser absorption spectroscopy (VUV-LAS) [1] using a tunable laser around 95.5nm region for the detection of F atoms and electron attachment mass spectrometry (EAMS) [2] for the detection of polymerized species. VUV-LAS has an advantage over previously developed methods in the determination of absolute density with higher accuracy, and EAMS is suited for detecting big clusterized molecules or radicals with less fragmentation. For the in situ surface diagnostics Fourier-transform infrared phase-modulated spectroscopic ellipsometry (FT-IR PMSE) [3] has been developed to diagnose surface bonds on Si and SiO2 substrates formed by exposing to plasmas. Chemical bonds such as -CFx, -CHxFy, -SiFx as well as Si-C and C-C have been detected successfuly by this method.

Systematic measurements of radical densities have been carried out in various source gases such as CF4, CHF3, C2F6 and C4F8, and the effects of dilution gases such as H2 and O2 have also been investigated. For understanding the production and loss processes of those radicals, the rise and fall characteristics of the densities have been measured by pulsing the discharge. At the same time the changes in the surface chemical bonds have been monitored by FT-IR PMSE and their dependence on the discharge conditions and substrate bias conditions have been investigated.

Those data are combined together with other data obtained by laser induced fluorescence measurements of CF and CF2 radicals in the gas phase and XPS analyses of substrates, and the reaction chemistry in the etching of SiO2 will be argued for realizing better selectivity and reproducibility.

1) K. Tachibana and H. Kamisugi: to be submitted.
2) W.W. Stoffels, E. Stoffels and K. Tachibana: J. Vac. Sci. Technol. A, 16, 87 (1998).
3) G.M.W. Kroesen, H-J. Lee, H. Moriguchi, H. Motomura, T. Shirafuji and K. Tachibana: J. Vac. Sci. Technol. A, 16, 225 (1998).