FIM Observation of Dynamic Processes of Thin Film Growth by Vapor deposition.

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Thin film growth has been studied by observing fine structures of vapor-deposited metal thin films with a field ion microscope (FIM) well-known with its atmic resolution. In addition to the traditional method (Method 1) to observe the inside structure using field evaporation, we have attempted to directly observe the growing surface by a new method (Method 2) in which the FIM observation is performed during vapor-depositing a metal onto a tip with alternating the imaging voltage on and off. The study with Method 1 on copper deposition on tungsten, contrary to common sense, showed that copper atoms were able to move approximately 7-9nm on the substrate surface from the first hit point even though the tip temperature was very low at 55K.In addition, in the case of deposition of copper onto a high temperature tip (200-400K), the impinged atoms are found to move on the substrate surface in the direction of the momentum of the impinging atoms. The nucleation for the recrystallization under the heat treatment of a copper-covered tip was also revealed to take place at the interface of the copper deposit and the tungsten substrate. Some differences were found between the result with copper and those with iron and chromium. In the case of copper, a single crystal image was not obtained but several concentric step rings were observed on the low index planes of tungsten. On the contrarya single crystal image was observed in the case of iron and chromium. The spreading of the deposited thin film area was also slightly different to each other. With new Method 2, several fundamental problems have come to loght, most important one being the influence of the imaging voltage on the growth itself. Despite of these troubles, some interesting results have begun to come out, e.g., it is slightly hard for atoms to fix on the low index planes but easy to fix at the step rings of tungsten, and so on. More detailed results are being expected now.