Thermal Stability of SiH n Configurations in FZ Silicon Single Crystals

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MASAMI KOUKETSU AND SEIICHI ISOMAE Central Research Laboratory, Hitachi Ltd., Japan


Tokyo 185,

ABSTRACT Thermal stability of SiHn (n=1-4) configurations in FZ silicon crystals grown in Ar/H 2 has been investigated by means of infrared absorption spectroscopy. Infrared absorption peaks at 2210, 2192, 2123 and 1946 cm-', which are due to SiH4, SiH3, SiH2 and SiH units in silicon lattice, has been observed. It is found that the concentration of SiH4 and SiH increase with the decrease in SiH2 and SiH3 concentration at 500'C, and vice versa at 600 0 C. Annealing results suggest thermally induced structural transformations of SiH configurations. We propose a model of the transformations through the cleavage of adjacent Si-H bonds to form a Si-Si bond and a H2 molecule, as well as the reaction of a H2 molecule with a Si-Si bond.

INTRODUCTION The incorporation of hydrogen into silicon materials improved their electrical and optical properties[l]. In crystalline silicon, hydrogen can passivate the electrical activity of dangling bonds[2], both acceptor and donor impurities[3-61, many deep defects and impurity states[7,8]. It is necessary to investigate the states and motions of hydrogen atoms for a better understanding of the passivation phenomena. Hydrogen atoms are known to be on the bond-centered site [9]. If point defects such as vacancy or self-interstitial exist near hydrogen atoms, the formation of SiHn is expected because of strong interaction between the H atoms and the point defects. E.Tarnow et al. [10] investigated theoretically the interaction of the H atoms, leading to molecule formation, as well as the cooperative reactions of several H atoms with the silicon lattice. Measurements of the infrared absorption have provided the evidence of several SiHn configurations, such as a silane molecule (SiH4) in the tetrahedral site and a hydrogenated (100) split interstitial, in silicon crystals[ll-13]. In the present work, we investigated the thermal stability and annealing behavior of SiHn configurations in silicon crystals. Annealing results suggest that the thermally induced structural transformations of SiHn configurations occur through the cleavage of adjacent Si-H bonds to form a Si-Si bond and a H2 molecule, as well as the reaction of a H2 molecule with a Si-Si bond. Mat. Res. Soc. Symp. Proc. Vol. 262. @1992 Materials Research Society


EXPERIMENTAL Floating zone melted in a Ar/H 2 atmosphere, (100) oriented and n-type silicon single crystals (c-Si:H) of 10mm thickness were used in this experiment. Their resistivities were 4X10 3 fTm, and they contained boron and phosphorous with 1.4XI012 atom/cm3 and 2.4X1012 3 atom/cm , respectively. The oxygen and carbon were not detected and the hydrogen concentration was estimated to be -1016 atom/cm3 (using the calibration of C.J.Fang et al. [14]) from the infrared measurements at 4.2K In order to investigate SiHn configurations in the crystals the infrared spectra were measured us