W. Wierzchowski

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.

Bragg-case synchrotron section topography of silicon implanted with high-energy protons and α particles

Back-reflection section topography using white-beam synchrotron radiation has been applied for the investigation of silicon implanted with 1 and 1.6 MeV protons and 4.8 MeV α particles. The beam width was limited to 5 μm, and a series of spots in the vicinity of a centrally adjusted reflection were indexed and analysed. The back-reflection section pattern of implanted crystals usually exhibits fringes corresponding to the reflection from the surface and a series of fringes corresponding to the rear region of the shot-through layer, the destroyed layer and the bulk. The patterns were used for direct evaluation of ion ranges and thicknesses of the shot-through layer. The overall characteristics of the obtained patterns were successfully reproduced in simulations based on numerical integration of the Takagi-Taupin equations. The agreement between the simulation and experiment proves that the lattice-parameter depth-distribution profiles can be assumed to be proportional to interstitial-vacancy distributions obtained using the Monte Carlo method from the Biersack-Ziegler theory. The simulation also reproduced interference tails observed in some section patterns. It was found that these tails are caused by the ion-dose change along the beam and they were probably formed due to the interference between the radiation reflected from the bulk and those rays reflected by the rear region of the shot-through layer.

Influence of high pressure and temperature on defect structure of silicon crystals implanted with N or Si ions

Abstract (111) oriented Fz-Si crystals were implanted with N + or Si + at 150 keV energy to a dose of 2×10 16 cm −2 . After implantation the samples were treated at a high temperature (up to 1400 K) under hydrostatic argon pressure (up to 1.1 GPa) for 1–5 h. Structural properties of Si:N and Si:Si before and after the treatment were investigated by high-resolution X-ray diffraction, synchrotron topography, transmission electron microscopy and photoluminescence methods. The structural properties of Si:N and Si:Si treated under hydrostatic pressure at 1270 K are different. A buried layer of uniform thickness with smooth interface was formed in Si:N under HP=1.1 GPa; the buried layer/Si interface becomes less smooth with rising treatment time. The shape of interference fringes and their changing distance at rocking curves are explained as an effect of nitrogen diffusion to the buried layer during the treatment. For the treated Si:Si samples, the observed strain changes are related to the out-diffusion of interstitial silicon atoms from the implanted layer to the sample surface and to creation of numerous extended defects near the implanted atoms range. Prolonged treatment (for 5 h) at 1.1 GPa and 1400 K results in creation of dislocations for Si:N while for Si:Si samples the structure of treated samples is more complex, involving also creation of amorphous-like surface film.

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.

Polytypism Study in SiC Epilayers Using Electron Backscatter Diffraction

The electron backscatter diffraction (EBSD) detector placed inside a commercial scanning electron microscope (SEM) has been used to study of different SiC polytypes. Different growth conditions in chemical vapor deposition (CVD) method were applied to obtain the 3C- and 4H-SiC polytypes epitaxial layers. Growth processes were conducted on the Si-face on-axis 4H-SiC substrates. The growth temperature was in the range of 1300-1620°C and the reactor pressure was 75mbar. The initial C/Si ratio was varied from 0.075 reaching final value of 1.8. It was observed that intentional ramping of the C/Si ratio at the first stage of the growth clearly influences the 4H/3C factor. The growth temperature and ramping of the C/Si ratio were the main parameters to achieve a homogeneous 3C and 4H-SiC epitaxial layers.

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.