ISSRNS 2012: Abstracts / Synchrotron Radiation in Natural Science Vol. 11, No 1 – 2 (2012) P 71
THE INVESTIGATIONS OF THE DAMAGES INDUCED BY FLASH PULSES IN SILICON CRYSTALS BY MEANS OF WHITE BEAM
SYNCHROTRON SECTION TOPOGRAPHY
W. Wierzchowski1∗, K. Wieteska2, D. Klinger3, R. Sobierajski3, J. Pelka3, D. Zymierska3, T. Balcer1, and C. Paulmann4
1Institute of Electronic Materials Technology, W´olczy´nska 133, Warszawa 01–919, Poland
2Institute of Atomic Energy POLATOM, Otwock- ´Swierk 05–400, Poland
3Polish Academy of Sciences, Institute of Physics, al. Lotnik´ow 32/46, Warszawa 02–668, Poland
4Institute of Mineralogy and Petrography, University of Hamburg, Notkestr. 85, 22603 Hamburg, Germany Keywords: silicon, FLASH irradiation, X-ray topography, deformation fields
∗e-mail : Wojciech.Wierzchowski@itme.edu.pl
The development of new generation of short ra- diation sources exploring free electron lasers focused the interest in the problem of the interaction of the beam generated by these devices with solid matter.
The strong excitation of electronic state induced by the beam can here reveal a number of new phenom- ena, which are important for practical development of optical elements and design of experiments, but also seems to be very interesting in cognitive as- pects. The information about the phenomena re- quires a very careful structural characterization of the craters especially their geometrical features and the lattice deformation.
It is expected, that the irradiation with very in- tense femtosecond pulses can create states of very strong electronic excitation with a highly reduced influence of optical nonlinearities at the frequencies in the range between the plasma frequencies and the frequency in the inner shall absorption edge [1, 2].
The experiment included generation of the damages by the beam coming from the Free-electron Laser in Hamburg (FLASH) operating in the range 6 – 100 nm and focussed by an ellipsoidal mirror onto the surface of crystalline silicon. The analogous damages were previously studied with the micro- beam diffraction method together with AFM and Nomarski contrast microscopy [3, 4].
In our previous experiment the use of back re- flection section and projection topography enabled us to reveal many important features of the strain fields connected with the craters [5]. It was in par- ticular possible to demonstrate a significant similar- ity of the observed strain field to that of rod-like in- clusion. The last results suggest unexpectedly large depth extension of the strain field connected with the craters.
In the present experiment we performed a suc- cessful attempt to confirm this observation by taking the synchrotron transmission section white beam topographs. Also a successful simulation of contrast in transmission section images were ob- tained using more adequate approximation of crater by droplet-like inclusion.
The observation of the deformation field of craters generated by FLASH pulses along the whole thickness of silicon wafers was performed by taking the synchrotron transmission section topographs us- ing the beam perpendicular to the surface of the sample. Numerous relatively dense series of section topographs spaced by 10 µm provided a precise scan allowing the evaluation of geometrical shape and depth extension some various craters. In the ob- tained topographic images we observed the direct image connected with the boundary of the crater
Figure 1 : Three representative white beam transmission section topographs exposed using 5 µm beam
perpendicular to the crystal surface corresponding to the sweeping of the row of craters with the maximal extension of the dark image from the lower edge of the section image corresponds to its depth extension.
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P 71 ISSRNS 2012: Abstracts / Synchrotron Radiation in Natural Science Vol. 11, No 1 – 2 (2012)
accompanied by the some deformation of the Kato fringes.
The evaluated depth extension was different for individual craters and was in the range 30 – 100 µm and it may be expected that some of the craters were formed including the melting and recrystallization of the material. The evaluated depth values were confirmed also by evaluations basing on the vanish- ing the images of the series of spots in the Bragg case section topographs obtained when the beam entered the crystal at low 4◦ angle.
It was possible to reproduce the topographic contrast of the craters in transmission section to- pographs by numerical simulation based on inte- gration of the Takagi-Taupin equations. The de- fects connected with craters were approximated as droplet-like inclusion.
Figure 2 : The series of three numerical simulations of transmission section images for the beam located at the position differing by 40 µm using the approximation of the craters by droplet-like inclusion — i.e. as the vol- ume in the form of droplet uniformly filled with equally spaced point-like inclusion.
Acknowledgments: The synchrotron investigations were supported by the HASYLAB project I-20110423 EC.
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