Film formation technique by ionized-cluster beam

Abstract

The ionized-cluster beam (ICB) technique (deposition and epitaxial growth) does not use ionized atoms or molecules as in the conventional ion plating method. The cluster is formed from a loosely coupled aggregate of about 10 3 atoms by an adiabatic expansion of pure evaporant material without any inert gas mixing, through a nozzle into high vacuum (10 −7−10 −5 Torr). We have previously shown that the crystal structure could be changed from an amorphous state to a single crystal by changing the acceleration voltage for the deposition at a particular substrate temperature. These experimental data suggested to us the possibility of forming a hydrogenated amorphous Si film useful for electron devices. By using the ICB technique, hydrogenated amorphous Si can be prepared at hydrogen pressure lower than 10 −4 Torr, whereas in the conventional fabrication methods such as glow discharge and reactive sputtering, hydrogenated amorphous Si film is deposited from reactive gas plasma at the pressure higher than 10 −2 Torr. The operation condition requiring high gas pressure may cause serious contamination by gases, and complicates the diagnosing of the deposition conditions. On the other hand, the ICB technique is preferable to overcome these difficulties. In this paper, the required deposition conditions of amorphous Si films are described from a standpoint of the behaviour of incident clusters onto a substrate. The thermally stable amorphous Si film properties are also shown.