AVS 47th International Symposium
    Plasma Science and Technology Monday Sessions
       Session PS2-MoA

Paper PS2-MoA4
A Drift of Selectivity Depending on Chamber Seasonings in a Poly-Si/Oxide Etching Process using Inductively Coupled Plasma

Monday, October 2, 2000, 3:00 pm, Room 311

Session: Plasma Etching of Conductors
Presenter: K. Miwa, Fujitsu VLSI Ltd., Japan
Authors: K. Miwa, Fujitsu VLSI Ltd., Japan
T. Mukai, Fujitsu Ltd., Japan
M. Nakaishi, Fujitsu Ltd., Japan
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Chamber seasonings after plasma cleanings are useful to stabilize reactor conditions. However, etch-selectivities of poly-Si to oxide with the same recipe were found to drift depending on seasoning methods. After bare-Si wafers were etched with an ICP of HBr/O2 as Si-seasoning, over-etch rates of oxides with the ICP slightly raised and decreased to stop as Si-seasoning time was longer. In cases of blanket-oxide wafers were etched as Oxide-seasoning, over-etch rates of oxides hardly drifted. Over-etch rates of poly-Si were nearly constant after the Si-seasoning or the Oxide-seasoning. Consequently, the etch-selectivity of poly-Si to oxide drifted after the Si-seasoning. Optical emission intensity of SiBr/He in the over-etch plasma increased with increase of Si-seasoning time. Over-etch rates of oxides also drifted as functions of O2 flow rate and Bias Power to the bottom electrode of the ICP-Etcher. The Deposition formed on the oxides during over-etchings after the Si-seasoning were identified as sub-oxides of Si using X-ray Photoelectron Spectroscopy (XPS). These results suggest that etch-rates of oxides are enhanced and decreased by etch-products such as SiBrx (x=1, 2, 3) in the over-etching plasma derived from the deposition on the reactor wall. The deposition would be formed during the Si-seasoning. When SiBrx coverages of the oxide surface are smaller than saturated coverage, the over-etch rates of oxides would be enhanced due to formation of silicon-oxybromide assisted with incident ions toward the surface. In cases of SiBrx coverages are larger than saturated coverage, excess SiBrx react with Oxygen atoms in the plasma to deposit sub-oxides of Si on the oxide surface. The sub-oxides would inhibit or stop the over-etching of oxides.