FORMATION OF 3-DIMENSIONAL MICROELECTRONIC STRUCTURES BY MOLECULAR-BEAM EPITAXY COMBINED WITH ION-BEAM PROCEDURES

The progress in microelectronics is characterized by an increasing density of functional elements on the wafer. This is first of all a result of a reduction of lateral dimensions in patterned geometries. Nevertheless, further progress on this way is limited by a number of reasons, e.g. residual impurities in the ingot materials, physical phenomena, as diffusion processes between adjacent layers as well as electron migration inside electronical structures. Finally, the lithographic means of structuring implies disadvantages which limit the minimization progress. One way to overcome these problems consists in three dimensional structuring of microelectronical objects. Thereby, the third dimension is introduced by growing of thin layers which are again structured in their lateral dimension. This can be done by molecular beam epitaxy (MBE) in combination with Ion Beam (IB) procedures. The present paper gives an overview on materials which exhibit epitaxial growth on Si. The utility of CaF2 for three dimensional structuring by use of ion bombardment will be described. As another example, the conversion of materials will be discussed. For instance, insulating CaF2 can be converted into conductive CaSi2 by help of Si+-ion implantation.