Strain Measurements in Si/Si0.5Ge0.5 and W/Mo Superlattices by He Ion Channeling
He ion channeling experiments have been performed on molecular beam grown Si/Si0.5Ge0.5 superlattices and n-channel Si/Si0.5Ge0.5 MODFET structures. Angular yield scans provide directly the tetragonal strains in the layers. The strain fields in Si/Si0.5Ge0.5 superlattices grown directly on (100) Si and on Si1-yGey buffer layers were compared experimentally. In the first case only the Si0.5Ge0.5 layers are tensilly strained whereas on a Si0.71Ge0.29 buffer layer with a thickness of 230 230 nm almost equal but opposite strains have been found. Strain sym-metrization yields the minimum elastic energy and thus to the most stable structure. An example of strain measurements on an n-channel MODFET structure will be shown. Ion channeling is probably the only technique which allows strain measurements in structures, like the MODFET structure investigated, where the thicknesses vary from layer to layer.