AVS 47th International Symposium
    Plasma Science and Technology Monday Sessions
       Session PS-MoM

Paper PS-MoM3
Observation of Surface Reaction Layers formed in Highly Selective SiO@sub 2@ Etch Process

Monday, October 2, 2000, 9:00 am, Room 311

Session: Plasma-Surface Interactions I
Presenter: M. Matsui, Association of Super-Advanced Electronics Technologies (ASET), Japan
Authors: M. Matsui, Association of Super-Advanced Electronics Technologies (ASET), Japan
T. Tatsumi, Association of Super-Advanced Electronics Technologies (ASET), Japan
M. Sekine, Association of Super-Advanced Electronics Technologies (ASET), Japan
Correspondent: Click to Email
We characterized the surface reaction layers formed by a fluorocarbon plasma for SiO@sub 2@ selective etching over Si and Si@sub 3@N@sub 4@, in order to understand the etch mechanism and to develop a process and tool for future ULSI processing. Specimens were etched using C@sub 4@F@sub 8@/Ar/O@sub 2@ plasma in a dual-frequency (27/0.8MHz) parallel-plate RIE system. The relationship between ion energy (assumed to be equal to peak to peak voltage (V@sub pp@) of rf bais) and the thickness and composition of the surface reaction layers were quantitatively analyzed using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The CF polymer layer and the SiF@sub x@O@sub y@ layer on the substrates were observed. We found that the etch rate is strongly affected by the ion energy and the thickness of the CF film on etched materials. In a highly selective etch process, the thickness of the CF layer on the SiO@sub 2@ surface is below 1 nm, while those on the Si@sub 3@N@sub 4@ and Si substrates are about 5-6 nm. The difference in the CF layer thickness on each material should be an origin of the selectivity. Both TEM and XPS observations revealed that reaction layers (2-4 nm) were formed at the interface between the CF layer and Si, Si@sub 3@N@sub 4@. The XPS analysis showed the composition of the reaction layer was SiF@sub x@O@sub y@. This SiF@sub x@O@sub y@ layers were thicker when the ion energy was high and the CF film was thin, i.e. a high etch rate condition for Si and Si@sub 3@N@sub 4@. SiF@sub x@O@sub y@ is thought to be an intermediary product of the Si@sub 3@N@sub 4@ and Si etching. In a highly selective etch process, CF film are so thin that ion energy is not reduced when ions pass through the film on SiO@sub 2@. On the other hand, at the surface of Si@sub 3@N@sub 4@ and Si, thicker CF film were formed and reduced the etch rate, resulted in thin SiF@sub x@O@sub y@ layer formation. @FootnoteText@ This work was supported by NEDO.