Mapping of two-dimensional lattice distortions in silicon crystals at submicrometer resolution from X-ray rocking-curve data

Abstract

Lattice distortions perpendicular to the surface in thin surface layers of ion-implanted (111) silicon crystals have been mapped as a function of depth and lateral position with resolutions of 0.05 and 0.65gm, respectively. X-ray triple-crystal diffractometry data were collected near the fundamental 111 and satellite reflections from samples with periodic superstructure modulations in the lateral direction. 300 keV B + ions implanted through surface mask windows are found to produce lattice distortions in a very thin layer of 0.15 gm thickness at 1.05 gm depth below the surface, with interplanar lattice spacings normal to the surface increased by several parts in 104 . The distortions are appreciably extended in the lateral direction, suggesting diffusion of the ions. A 0.5 gm-thick thermaloxide strip is found to contract the interplanar spacing of substrate silicon crystal under the strip region by a few parts in 104, while the strain field created by the parallel oxide edges extends beyond a depth of 3 Bm. A practical procedure is also described for arriving at a solution of the phase problem in the case of a strain field involving heavily distorted layers.

High-Resolution Mapping of Two-Dimensional Lattice Distortions in Ion-Implanted Crystals from X-ray Diffractometry Data

“…In the case where the surface layer is nonuniformly strained in depth, the rocking-curve profile tends to be asymmetric. A comparison with the previous CTR profiles (Nikulin et al, 1994) indicates that subpeaks are much better resolved in the present samples. The calculated penetration of 100 keV B + ions channeling along the silicon [111] axis is 0.5 lam (Hobler, 1995), as compared to 1.1 btm for 300 keV B + ions.…”

“…The spatial resolution achieved by Nikulin, Sakata, Hashizume & Petrashen (1994) was 0.05 and 0.32 ~tm in the depth and lateral directions, respectively. These were defined by the momentum transfer range of qx = -1.4--+ 1.4 x 10 -3 nm-l (in-plane direction) and qz = -2-+ 2 x 10 -3 nm -l (surface normal direction) around the Si 111 Bragg point, measured with the triple-crystal diffractometer on beamline 14B at the Photon Factory synchrotron source.…”

“…The method of ab initio strain-map reconstruction was described in previous publications (Goureev, Nikulin & Petrashen, 1992;Nikulin et al, 1994). Here we outline it and make some new comments.…”

“…Previously, we used a model function for an x section of the displacement profile uh(x, z) at some fixed depth Z=Z0, fmodel(X)=Uh(X, Zo), to determine the signs an (Goureev, Nikulin & Petmshen, 1992;Nikulin et al, 1994). This method works for simple profiles with an easily predictable shape of such an x section.…”

“…In a recent paper, we have demonstrated that lattice distortions in surface layers of ion-implanted silicon crystals can be mapped out with submicrometer spatial resolution using high-resolution X-ray diffractometry data collected at a synchrotron source (Nikulin, Sakata, Hashizume & Petrashen, 1994). The maps show the twodimensional profile of the lattice distortion perpendicular to the surface as a function of lateral position and depth in crystals implanted with 300 keV B ÷ ions through a periodic surface oxide strip pattem.…”