A study of nucleation in chemically grown epitaxial silicon films using molecular beam techniques I.—experimental methods

Abstract

The application of molecular beam techniques to the study of the epitaxial growth of silicon by chemical vapour deposition is discussed. The limitations of conventional flow systems in nucleation studies are described, particularly with respect to gas phase diffusion constraints and the length of time required to reach steady state. By use of a molecular beam, in this case of silane, which is decomposed at a heated silicon substrate, these limitations have been overcome. Because the beam is collision-free, there can be no homogeneous component of the decomposition reaction, and neither can gas phase diffusion processes occur. Steady state is obtained almost instantaneously by means of a beam flag. This paper describes the apparatus design, principles of operation and calibration. In order that clean silicon surfaces can be studied the work has been carried out under ultra-high vacuum conditions, and methods of preparation and assessment of the surfaces are also described. In the following paper some preliminary results on nucleation behaviour on clean and carbon contaminated silicon surfaces are reported in which electron microscopy was used to investigate early growth stages.