FIELD ION MICROSCOPIC OBSERVATION OF Si-SiO₂ INTERFACE. M. Umeno, M.Tagawa, N.Ohmae and M.Miyanaga, Department of Material & Life Science, Osaka University, Yamada-oka, Suita, 565 JAPAN.

The atomic arrangement of interfacial layer of Si-SiO₂ system was directly observed with a field ion microscope (FIM). The existence of some structural and/or compositional transition layer at the interface of a-SiO₂ and Si substrate has been pointed out by many reports, yet the direct observation of its structure has been of great concern. Si tips with [001], [011] and [111] axes were prepared with chemical or electrolytic etching from CZ-Si wafers. After some successive treatments for obtaining atomic FIM images, tips were thermally oxidized with 300L of dry oxygen at 1000K in the FIM chamber. The image of an interfacial transition layer was easily recognized, as the oxide image which was composed of diffusely at random distributed bright spots change into the image of dense rather small spots when field evaporation was conducted, and the image of Si substrate partly appeared. The present FIM observation revealed followings:

1. The thickness of the transition layer is so thin as 2 to 3 atomic layers.

2. The transition layer has a crystalline nature.

3. The evaporation field strength has an orientation order, that is (001) < (011) < (111), and this order does not correspond to either of the orientation order for oxidation velocity or of the field strength on the tip.

4. The evaporation field strength of SiO₂ was estimated to be 34V/nm which is somewhat lower than 40V/nm of Si.

A fairly perfect image of substrate Si could be obtained when all oxide layer was removed by the field evapaoration.