W. Graeff

X-Ray Diffraction Patterns in High-Energy Proton Implanted Silicon

Silicon crystals implanted with 1 and 1.6 MeV protons were studied by means of conventional source double-crystal and synchrotron multi-crystal arrangements. Both the rocking curves and series of topographs were recorded in different parallel settings employing different reflections and wavelengths of radiation. A comparison of rocking curves in different regions of implanted areas was performed in synchrotron multi-crystal arrangement with a beam of a very small diameter. The rocking curves exhibited subsidiary interference maxima with increasing periodicity on the low angle side. The plane wave topographs taken at different angular setting revealed characteristic fringes whose number decreased with increasing distance from the main maximum. The fringe pattern did not depend on the direction of the diffraction vector. The number of fringes for equivalent angular distance from the maximum was larger for higher order of reflection. The shape of the rocking curve and other diffraction patterns were reasonably explained assuming the lattice parameter change depth distribution proportional to the profile obtained from the Biersack-Ziegler theory and lateral non-uniformity of ion dose. A good approximation of the experimental results was obtained using numerical integration of the Takagi-Taupin equations.

Bragg-case section topography of growth defects in Si : Ge crystals

The samples cut out from Si : Ge crystals with 3% and 1.2% of germanium were studied by means of synchrotron white beam Bragg-case section and projection topography as well as conventional transmission Lang topography. The obtained topographs revealed dominant contrast coming from the segregation of germanium. The use of Bragg-case section topography made possible to follow the shape of growth surfaces inside the crystal. The formation of contrast in Bragg-case section topographs for different orientation of growth surfaces with respect to the incident beam is discussed. The applied methods enabled also revealing growth surface instabilities occurring in some regions of Si : Ge crystals.

Numerical simulation of Bragg-case section topographic images of dislocations in silicon

Synchrotron white beam with a wavefront limited by a 5 µm slit was used for obtaining the Bragg-case section patterns in silicon substrates and epitaxial layers. The section images contained various interference fringes, such as the Uragami fringes and fringes caused by crystal curvature. The system of fringes connected with individual defects was also observed. The experimental images were compared with simulated theoretical images obtained by numerical integration of the Takagi-Taupin equations. A reasonably good correspondence was obtained for dislocations inclined to the surface and misfit dislocations. The elements of the image were analysed using the visualization of |Dh|2 and |Do|2 intensities in the plane of diffraction, where an additional amount of transmitted wave intensity indicated the decomposition of wavefields or the reflection of the redirected waves from the surfaces. Comparative studies of simulated precipitation images and modification of dislocation images caused by curvature and by the diffusion of an epitaxial junction were also performed.

Application of Bragg-case section topography for strain profile determination in AIIIBV implanted semiconductors

Simultaneous analysis of strain modulation fringes in synchrotron Bragg-case section patterns and rocking curves recorded with a very narrow probe beam was used for the determination of strain profiles in GaAs implanted with high doses of 1.5 MeV Se ions. The existence of two components of the strain was revealed: the first is due to the introduced interstitial defects of the matrix crystal and the second is directly connected with introduced Se ions. These two components significantly differed in their depth profiles and their behaviour upon thermal annealing.

Interference fringes in plane-wave topography of AlxGa1−xAs epitaxial layers implanted with Se ions

The MOCVD grown Al 0.45 Ga 0.55 As epitaxial layers with low dislocation density, implanted with 1.5 MeV Se + ions to the doses 6×10 13 -4×10 14 ions/cm 2 , were studied using a multicrystal arrangement and applying synchrotron X-ray radiation. A very small size of the probe beam close to 30 μm was used to obtain a good resolution of interference maxima and to study the changes of the rocking curves in different regions of the sample. Due to the curvature of the samples, the interference maxima were revealed in plane wave topographs as interference fringes and the high intensity of the source enabled studying of the fringes also in these regions of the curve where the reflected intensity is very low. The continuity of the fringes across the boundary of implanted region was observed for the high angle side of the maximum due to epitaxial layer. A good approximation of experimental rocking curves and fringe pattern in the plane-wave topographs was obtained by numerical integration of the Takagi-Taupin equations assuming a strain profile with almost constant lattice parameter in a relatively thick layer close to the surface.

White beam pin-hole patterns of implanted layers

Abstract The synchrotron Laue method with a beam limited by a pin hole was applied for studying the implanted layers in silicon and in A III B V multicompound epitaxial layers. A significant difference between the micro-Laue patterns in case of heavy and light ion implantation was observed. In the first case the pin-hole pattern contained spots coming from different layers mutually displaced due to lattice deformation. In the case of light ion implantation into silicon the lattice deformation effects were revealed in strongly overexposed patterns by activation of forbidden reflections due to lattice tetragonalization. It was found that all interference fringes connected with the spherical wave diffraction contributed to a long tail corresponding to the plane of diffraction. The possibility of observation of asymptotic distortion scattering due to dislocation was also proved.

Studies of growth bands in Si:Ge crystals

Si:Ge crystals with approximately 3% of germanium were studied with various topographic methods using both conventional and synchrotron sources of X-rays. The present investigation included various types of white beam synchrotron topography and conventional Lang topographic methods. The topographic results obtained with various methods were dominated by strong contrast coming from growth bands. The Bragg-case section topographs with the beam front limited to 5 μm revealed the distribution of growth bands inside the crystals. Thanks to the low glancing angle the section topographs provided many information about the shape of growth surface despite small thickness of investigated wafers. Additionally taking the topographs at very large film-to-crystal distances it was possible to reveal the character of lattice deformation across the striations and to draw information about germanium distribution.

Synchrotron studies of implanted InxGa1−xAs

Abstract MOCVD grown epitaxial layers of In 0.53 Ga 0.47 As/InP were implanted with 1.5 MeV Se ions or 1.0 MeV Si ions at room temperature and at liquid nitrogen temperature. A wide range of ion doses exceeding 10 15 ions/cm 2 was applied. White beam synchrotron section and projection topography as well as rocking curve measurements were used for the characterisation of samples. The aim of the experiment was the evaluation of the dose dependence of ion implantation induced strain and the determination of amorphisation threshold. It was found that the implantation performed at room temperature did not cause lattice amorphisation even for highest applied doses, i.e. 2×10 15 Se/cm 2 . The strain induced by 1.5 MeV Se ions implantation at room temperature increases with the ion dose and reaches its maximum for 3×10 14 ions/cm 2 . Further increase of the dose resulted in the decrease of the strain. Ion implantation performed at liquid nitrogen temperature led to amorphisation of the sample at doses of the order of 10 13 ions/cm 2 . The amorphisation manifested itself in the significant decrease of the implanted layer maximum in the rocking curve. A strain modulation fringes characteristic for non-monotonic strain profiles were observed in some Bragg-case section topographs.

Lattice Deformation in AlxGa1-xAs Epitaxial Layers Caused by Implantation with High Doses of 1 Mev Si Ions

A series of highly perfect Al0.45 Ga0.55 As epitaxial layers implanted with 1 MeV Si ions to the doses in a range 7 x 10 13 -2 x 10 15 ions/cm 2 were studied with various conventional and synchrotron X-ray diffraction methods. The presently used methods allowed both the measurement of lattice parameter changes and strain induced deformation. The evaluation of complete strain profiles was also performed by numerical simulation of diffraction curves. It was found that the implantation induced considerable change of lattice parameter reached the maximum at the dose 3 x 10 14 ions/cm2 . The recorded curves proved also that the lattice parameter is almost constant in the near surface region of the implanted layers. The applied doses did not cause lattice amorphisation at room temperature. PACS numbers: 61.10.—i, 61.80.—x

Synchrotron White Beam Topographic Studies of Gallium Arsenide Crystals

A series of samples cut out from different types of gallium arsenide crystals with low dislocation density were studied by means of white beam synchrotron topography. The investigation was performed with transmission and back-reflection projection methods and transmission section method. Some of the topography in transmission geometry provided a very high sensitivity suitable for revealing small precipitates. The transmission section images significantly differed depending on the wavelength and absorption. In some cases a distinct Pendellosung fringes and fine details of dislocation and precipitates images were observed. It was possible to reproduce the character of these images by means of numerical simulation based on integration of Takagi-Taupin equations. Due to more convenient choice of radiation, synchrotron back-reflection projection topography provided much better visibility of dislocations than analogous methods realized with conventional X-ray sources.