FZ Si Research Articles

The isotope study of the SiH absorption peaks in the FZSi grown in hydrogen atmosphere

The isotope effects of hydrogen and silicon prove that all the four intense i.r. absorption peaks 2210, 1946, 812 and 791 cm −1 in the floating zone melted silicon crystal grown in hydrogen atmosphere (FZSi:H) are the vibration peaks of SiH bonds. The experiment of the partial substitution of deuterium for hydrogen demonstrates that the hydrogen-defect complex corresponding to 2210 cm −1 peak possesses Td symmetry, while that corresponding to 1946 cm −1 peak is of SiH 1 structure. The fine structure of 2210 cm −1 peak found in the FZSi:H samples at low temperature is shown to be caused by the natural isotopes of silicon.

Effects of Back‐Side Oxidation of Si Substrates on Sb Diffusion at Front Side

The effect of back‐side oxidation of Si wafers on the diffusion of Sb in the front of wafers is investigated with back‐side selective oxidation (BSO) at 1100°C in dry ambients. It is found that the diffusion of Sb in the front of the wafers is retarded by BSO only for FZ Si substrates under directly formed films, and that Sb diffusion in CZ Si substrates and under double‐layered films in both FZ and CZ substrates is not affected by BSO. The effective range over which BSO affects Sb diffusion is found to increase with oxidation time. The range and extent of oxidation retarded diffusion (ORD) for Sb are shown to agree with those of oxidation enhanced diffusion (OED) for B and P. These results are explained with a proposed model: (i) there is a thermal equilibrium between vacancies and interstitials, and (ii) the interface provides sinks and generation centers for point defects in Si, though the interface does not react with point defects.

Preservation of Point Defect Distribution in FZ Silicon

Evidences for the preservation of point defect distribution in FZ Si crystals have been observed by two experimental methods. One is divided selective oxidation and the other is divided backside selective oxidation with Si3N4 as the oxidation resistant films. In both experiments, the selective oxidation is divided into several oxidation steps, and the effects of oxidation division on the range of oxidation effects on impurity diffusion is investigated. The results show that, both laterally and vertically from the oxidizing Si–SiO2 interface, the effect of oxidation on impurity diffusion is determined only by total oxidation time. This suggests that point defect distribution is preserved after heat treatment.

Effects of Backside Oxidation on the Size of Oxidation Induced Stacking Faults at the Front Surface of FZ Si Wafers

The effect of backside oxidation on the size of Oxidation induced Stacking Faults (OSF) at the front side of FZ Si wafers has been investigated by Backside Selective Oxidation (BSO). The results show that shrinkage of OSF under directly formed Si3N4 film is interrupted by BSO. However, shrinkage under double-layered SiO2–Si3N4 film is not affected. These results are consistent with the effects of BSO on diffusion of B, P and Sb. The behavior of the OSF's can be explained by the supposition that the Si–SiO2 interface has the effect of preserving the point defect concentration constant and the Si–Si3N4 interface has no such effect.

The Range of Diffusion Enhancement of B and P in Si during Thermal Oxidation

The lateral range of oxidation enhanced diffusion (OED) of B and P in Si is investigated using selective oxidation at 1100°C with directly formed Si3N4 films as oxidation resistant masks and FZ Si crystals as substrates. It is found that this OED range of B agrees well with that of P and that the range increases with oxidation time. The value of the range is found to be much larger than previously. The results can be explained using a model in which the range is determined by interstitial diffusion.

High Efficiency Silicon Solar Cells Using Minority Carrier MIS Structures

Minority carrier Metal-Insulator-Semiconductor (minMIS) devices are electronically equivalent to ideal p-n junction diodes. Solar cells fabricated using minMIS structures have advantages over actual p-n junction cells. Grating minMIS cells with the semiconductor surface between the grating lines inverted produce the most efficient devices. Record Voc's for Si cells of 655 mV have been obtained on FZ Si substrates, with efficiencies over 17.5% being achieved for both polished and textured surface cells. Using large grain polycrystalline Si substrates, efficiencies of 13.3% have been obtained which are the best for this material.