TABLE OF CONTENTS Intercalated structures consist of thin alternating layers grown by vacuum deposition such as the MBE process,[291] chemical vapor deposition including the ARE process,[292] sputtering deposition,[293] and chemical solution deposition.[294] Among these processes, the sputtering process allows the preparation of thin alternating layers of refractory metals and compounds such as oxides, nitrides, and III-V alloys. As described in Secs. 5.1.3.2 and 5.1.4.11, alternating layers of compound oxides, including perovskite dielectrics and superconductors, are made by sputtering from multitargets. Greene, et al., deposited the III-V compound alternating layers of InSb and GaSb (InSb/GaSb/InSb/ ).[295] In multitarget sputtering, the substrate is continuously rotated through two or more electrically and physically isolated sputtering discharges. The structural properties depend on the layer thickness deposited per target pass and the rate of interlayer diffusion. Eltoukhy, et al., have deposited the InSb/GaSb superlattice structures with layer thicknesses ranging from 12.5 to 50 at substrate temperatures of 200 to 250 C.[296] They have suggested that the superlattice structures only a few monolayers thick may easily be grown by sputtering from the multitarget even at relatively high substrate temperatures.
Superlattice structures are also deposited by reactive sputtering. Figure 5.151 shows the construction of the sputtering system for making thin alternating layers of Nb/NbN. For the first layer, the Nb target is sputtered in Ar; later, in a mixed gas of Ar/N 2. Periodic change of the sputtering gas composition results in the formation of the superlattice Nb/NbN. Typical sputtering conditions are shown in...
