Investigation on C54 nucleation and growth by micro-Raman imaging
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Investigation on C54 nucleation and growth by micro-Raman imaging Stefania Privitera1, Francesco Meinardi2, Simona Quilici2, Francesco La Via3, Corrado Spinella3, Maria Grazia Grimaldi and Emanuele Rimini1 1) INFM and Physics Department, Catania University, Corso Italia 57, 95129 Catania, Italy 2) INFM and Materials Science Department, Milano-Bicocca University, Via Cozzi 53, 20125 Milano, Italy 3) CNR-IMETEM, Stradale Primosole 50, 95121Catania, Italy ABSTRACT The processes of nucleation and growth of the C54 TiSi2 phase into the C49 phase in thin films have been studied by electrical measurements and micro-Raman spectroscopy. The Raman spectra have been acquired scanning large silicide areas (100x50 µm2) in step of 0.5 µm. Images showing the evolution of the C54 grains during the transition have been obtained for temperatures between 680 and 720 °C and the transformed fraction, the density and the size distribution of the C54 grains have been measured as a function of the temperature and the annealing time. The activation energies for the nucleation rate and the growth velocity have been determined obtaining values of 4.9 ± 0.7 eV and 4.5 ± 0.9 eV, respectively. INTRODUCTION The formation of the low resistivity C54 phase of TiSi2 is of great importance for the implementation of Ti salicide process into deep submicron devices[1]. In thin film reactions, however, the C54 phase is always preceded by the metastable high resistivity C49 phase and a high temperature anneal (> 700 °C) is required to transform the silicide into the technologically required phase. The C49-C54 allotropic phase transition has been largely investigated by several techniques but the processes of nucleation and growth of the C54 are still not clear. To understand and control these processes a detailed description of the driving force for the transformation and the nucleation barrier energy is required. The link between the kinetics of the transition and the driving force is the dynamical evolution of the population of C54 grains during the transformation. However, this information is not accessible by the most commonly used techniques, such as electrical measurements and X-ray diffraction, which are only sensitive to the transformed volume fraction. In this work micro-Raman spectroscopy, which allows the silicide phase to be locally identified [2-4], has been used to obtain images showing the morphological evolution of C54 grains into the C49 phase. The transformed fraction, the density of grains and the size distribution have been determined for various temperatures and times and have been interpreted in terms of the classical nucleation and growth theory. EXPERIMENTAL PROCEDURES A 300 nm undoped amorphous silicon layer was grown by low-pressure chemical vapour deposition (LPCDV) on thermally oxidised Si (100) wafers. Immediately before the deposition
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the substrate was cleaned in HF to remove the native oxide and a 15 nm Ti layer has been deposited in a e-gun evaporator at a pressure of 10-9 Torr. The C49 silicide phase was formed in
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