Molecular Beam Epitaxy For Multilayer Fabrication

Abstract

Molecular Beam Epitaxy (MBE) is a very powerful deposition technique, capable of growing multilayer materials with atomically sharp interfaces.1 However, to date MBE techniques have not been applied to the deposition of multilayer coatings for soft x-ray applications. One reason is that almost all MBE systems in present use are designed with thermal evaporation sources and 800 °C substrate heaters for the growth of GaAs-based semiconductors. However, many of the materials needed for the fabrication of x-ray optical elements require the ability to evaporate high melting point materials such as silicon, molybdenum, tungsten, etc., as well the capability to reach substrate temperatures -1000°C during growth to obtain epitaxy. We describe here the design of a new MBE system in our laboratory, which includes a 1000 0C substrate heater and two electron beam evaporators, as well as the usual evaporation (Knudsen) cells. While conventional UHV electron beam evaporation techniques can deposit refractory materials, MBE also has the advantage of in situ monitoring during growth, using Reflected High and Low Energy Electron Diffraction (RHEED and LEED), for layer thickness control at the atomic level. Initial results on XUV optical coatings using this MBE system are presented.