Generation and Dissociation of Iron-Boron Pairs in Silicon
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GENERATION AND DISSOCIATION OF IRON-BORON PAIRS IN SILICON MASASHI SUEZAWA AND KOJI SUMINO Institute for Materials Research, Tohoku University. Sendai 980, Japan ABSTRACT The generation and dissociation processes of Fe-B pairs in Si crystal are investigated by means of the measurements of electron paramagnetic resonance of Si crystals of various B concentrations doped with Fe. Fe-B pairs are generated due to annealing of the crystals at temperatures around 300 K obeying to the first order reaction kinetics. The activation energy for pair generation is determined to be about 0.65 eV which is almost equal to the migration energy of Fe impurity in a Si crystal. Fe-B pairs are found to be dissociated at tempeatures higher than 150"C leading to the precipitation of Fe. 1. INTRODUCTION Studies of impurity Fe in Si crystals may to be divided into two categories. Those belonging to the first category, which probably started in 1956 [1], have been undertaken as a part of the work to clarify the properties inherent to a variety of impurities in silicon crystals such as the energy level, solubility and diffusivity. Studies belonging to the second category deal with reactions of Fe impurity with other kinds of impurities or defects. One of the most interesting facts in conjunction with the latter is that an Fe atom forms a pair with an acceptor impurity atom at relatively low temperatures [2]. This type of studies was renewed whenever new experimental methods were invented or experimental techniques were improved. On the other hand, in the course of quenching expeiments of Si crystals from high temperatures with the aim to clarify the properties of intrinsic point defects in Si. the most common quenched-in "defect" was identified to be Fe impurity with the use of electron paramagnetic resonance method (EPR) [3]. in spite of that Fe was not intentionally doped into Si. This result tells us how important to clean the environment of a Si crystal is when it is treated especially at an elevated temperature since Fe impurity often degrades the performance of electronic devices. Thus, the behavior of such unintentionally doped Fe impurity in Si crystals is attracting a great deal of attention in conjunction with the development of VLSI technology. The harmful action of Fe impurity in Si may disappear when it reacts with some other appropriate impurity such as a chemical acceptor. Complexes including Fe atoms may have electrical or optical properties which may be positively utilized in device engineering. So, understanding the detailed process of the reaction between Fe impurity and other impurities is important from both fundamental and practical viewpoints. As our first study based on such an idea, we investigate here the generation and dissociation processes of Fe-B pairs in Si and clarify the temperature ranges for the pairing and depairing as well as the kinetics of pairing process in order to establish the fundamental knowledge for control of material property of Si. 2. EXPERIMENT Table 1 gives the characteristics of Si crystals
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