Laser and Thermal Annealing of Co-Implanted Si Studied by Mossbauer Spectroscopy
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LASER AND THERMAL ANNEALING OF Co-IMPLANTED Si STUDIED BY MOSSBAUER SPECTROSCOPY +
G. LANGOUCHE, M. de POTTER, M. VAN ROSSUM, J. DE BRUYN, I. DEZSI , R. COUSSEMENT Instituut voor Kern- en Stralingsfysika, Leuven University, Belgium + on leave from Central Research Institute for Physics, Budapest, Hungary
ABSTRACT Mdssbauer spectroscopy was used to study the lattice location of Fe in Si. Strikingly different spectra were recorded depending on the implantation dose and implantation temperature. Drastic changes were also observed in the spectra upon thermal treatment or laser irradiation of the samples. Implantation profiles of several of these sources were also measured. Laser irradiation and thermal annealing above 4000 C results 57 in surface segregation of the implanted Co activity.
Ever since the first days of the M6ssbauer effect, it was believed that M~ssbauer spectroscopy would yield interesting information on the microscopic lattice surrounding of impurity atoms introduced in semiconductors. One of the 57 most likely impurity atoms for such a study was Fe, the best studied M~ssbauer isotope. A series of electrical, optical and diffusion experiments f i] on irondoped silicon had already suggested that two species of iron might be present in these samples, one of which was interstitially located. Already in 1961 a M6ssbauer experiment was reported [ 21 in which 5 7 Fe was 57 introduced into Si and Ge by diffusion of the Co parent isotope. The large variations in the M6ssbauer spectra [3] immediatly revealed that the surrounding of the Fe atom in Si depends very much on the diffusion temperature and the quenching speeds used in the preparation of the samples. It was soon realized 3 that the extremely low solubility of Co and Fe in Si, S = 2 x 1016 atoms/cm at 1300 OC, and their very high diffusion coefficient, D = 10-5 cm2 /s at 1300 'C [41],make the formation of precipitates in this system extremely likely [5]. In more recent years implantation techniques were used [6-91 to introduce 57 Fe in various semiconductors. With this technique, precipitates are not readily expected, but the damage introduced during the implantation process can easily affect the final lattice site. The first implantation experiment 161, which made use of 5 7 Fe recoil implanted into Si, could not easily be interpreted. It was not clear whether the two resonances observed in the M6ssbauer spectra were due to the presence of two lattice sites, or due to a quadrupole interaction at a single non-symmetric lattice site. Very recently new M6ssbauer studies were undertaken to solve the puzzle of Fe impurities in Si and Ge. It was observed 1101 that strikingly different M6ssbauer spectra were recorded depending on the implantation dose. Above 14 2 an implantation dose of 10 atoms/cm , where the sample is known to be amorphized, it was demonstrated 111-12] that the symmetric doublet in the M6ssbauer spectrum is due to a quadrupole interaction. Below this implantation dose, an additional single line fraction is present in the M6ssbauer sp
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