Surface And Interface Strains Revealed By X-Ray Diffraction

We measured strain fields near semiconductor surface by X-ray diffraction. The diffraction geometry was using the extremely asymmetric Bragg-case bulk reflection of a small incident angle to the surface and a large angle exiting from the surface. The incident angle of the X-rays was set near critical angle of total reflection by tuning X-ray energy of synchrotron radiation.The X-ray intensity of the silicon substrate 311 reflection was measured to study a Si(111) surface in the ultrahigh vacuum chamber. A cleanSi(111)-(7 × 7)surface was found to give a sharper X-ray diffraction peak than that of the native oxide/Si(111) system. By comparison of experimental results and theoretical calculations, it was concluded that the thin silicon oxide film itself gives strong strain fields to the silicon substrates of lattice expansion toward the [311] direction.The strain fields at the Al- and Ag- induced$(\sqrt{3}\times \sqrt{3}) {\rm R}30^\circ$surface reconstruction on the Si(111) substrate were also measured. By comparison of experimental results and theoretical calculations, Al-induced reconstruction was suggested to give a strain field to the silicon substrate of lattice expansion toward the [311] direction, whereas Ag-induced reconstruction was suggested to give a strain field to the silicon substrate of lattice compression toward the [311] direction.