TEM measurement of hydrogen pressure within a platelet
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TEM measurement of hydrogen pressure within a platelet
J. Grisolia, G. Ben Assayag, B. de Mauduit, A. Claverie CEMES/CNRS, BP 4347, F-31055 Toulouse R.E. Kroon, J.H. Neethling, Physics Department, PO Box 1600, University of Port Elizabeth, South Africa
ABSTRACT Proton implantation and thermal annealing of silicon result in the formation of a specific type of extended defect involving hydrogen, named “platelets”. These defects have been related to the exfoliation mechanism on which a newly developed process to transfer thin films of silicon onto various substrates is based. In a previous paper, we have shown that these platelets undergo a quasi-conservative Ostwald ripening upon annealing. The measurement of the pressure within such pressurised gas-filled cavities is important to understand and simulate both the growth of these defects and the exfoliation mechanism. To extract this pressure from TEM studies, we have developed and tested an analogy between the platelets and a well-known 2D defect: a dislocation loop. The comparison between simulations of the image of the strain field surrounding a fictitious dislocation loop and experimental TEM images of the platelets shows that the platelets can be described by a Burgers vector of about 0.6nm. Moreover, this vector can be used to deduce the pressure of the molecular hydrogen within a platelet. A typical value of 10 GPa is found for a platelet of 20 nm in diameter at room temperature. Consequently, the atomic density of hydrogen within a platelet and the total number of hydrogen trapped by a population of platelet can be calculated and give reasonable values when compared to the implanted dose.
INTRODUCTION Extended defects formed after high dose hydrogen implantation have been intensively studied during the last years due to their potential technological applications in advanced silicon processing. More specifically, H-rich two dimensional (2D) cavities, the so-called platelets, have recently received considerable attention because they are used in the microelectronic industry to obtain the delamination of a thin film from a thick substrate [1,2]. In a previous paper, we have shown that, after a sufficiently high dose H implantation and low temperature annealing, nucleation and growth of 2D platelets occurs [3]. These platelets are thought to be 2D precipitates of hydrogen atoms bounded either to Si atoms, to vacancies or to other H atoms. During annealing, these defects grow in size and reduce their density with kinetics that has allowed us to identify a conservative Ostwald ripening mechanism. Thus, during annealing these defects exchange H atoms. The driving force for this mechanism is the reduction of the formation energy (the energy cost to add one extra atom to the defect) consecutive to the size increase of the platelets [4]. In the meantime, while the overall elastic energy decreases in the implanted layer, the strain locally increases around the projected range of the protons i.e., where the platelets tend to concentrate and where splitting will ultimate
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