Hajime Kitagawa

Diffusion Mechanism of Nickel and Point Defects in Silicon

The in-diffusion of nickel into silicon and the annealing of nickel in silicon have been studied experimentally at 900°C. The variations in concentration of substitutional nickel with time are described well by an exponential function predicted from a dissociative mechanism, in both the in-diffusion and annealing processes. The time constant in the annealing process is substantially independent of the initial concentration of substitutional nickel. These results support the theory that nickel in silicon diffuses by a dissociative mechanism and that the dominant point defects in silicon are vacancies.

Amphoteric Property of Electrically Active Nickel in Silicon

Deep levels in nickel-doped n- and p-type silicon have been studied by the Hall effect and deep level transient spectroscopy (DLTS) under various diffusion and isothermal annealing conditions. It was found that nickel introduces an acceptor level of 0.47±0.04 eV from the conduction band and a donor level of 0.18±0.02 eV from the valence band, and that the concentrations of the two levels are practically identical. Isothermal annealing experiments have revealed stable behaviors of the two levels. The results suggest that the two levels are different charge states of the same substitutional nickel atoms in silicon.

Electrical properties of nickel in silicon

Electrical activity and energy levels as well as diffusion properties of nickel in silicon have not yet been reliably established. In this paper, we investigated the diffusion and the electrical properties of nickel in silicon to confirm that nickel is electrically active and introduces one acceptor and one donor level by combined measurements of Hall coefficient and DLTS, and measurements of the distribution of electrically active nickel in various silicon diodes by DLTS. The former experiments show that bothn- andp- type silicon are compensated by nickel and that nickel introduces an acceptor level ofEc-0.47 ± 0.04 eV and a donor level ofEv +0.18 ± 0.02 eV. The concentrations of these two levels are almost identical over the diffusion temperatures from about 800 to 1100° C, indicating that these donor and acceptor levels are due to different charge states of the same nickel center. In the distribution measurements of electrically active nickel in silicon diodes, we inspected how nickel can be observed by DLTS. It was found that the nickel diffusion intop- n junction is rather complicated, the distribution profiles of nickel in the vicinity of thep- n junction being markedly influenced by an additional heating at elevated temperatures after the nickel diffusion. This gives evidence that the difference in silicon devices used in various studies could give rise to different results.

Majority-Carrier Capture Cross Section of Amphoteric Nickel Center in Silicon Studied by Isothermal Capacitance Transient Spectroscopy

Isothermal capacitance transient spectroscopy (ICTS) has been used to measure majority-carrier capture cross section of nickel centers in silicon. Capture cross sections obtained are temperature-independent with values of 3.2×10-17 cm2 for electron capture at the nickel acceptor center in n-type silicon and 1.8×10-16 cm2 for hole capture at the nickel donor center in p-type silicon. These capture cross sections are associated with the neutral capture of the majority carriers at the amphoteric nickel centers.

In-Diffusion and Annealing of Copper in Germanium

The in-diffusion and anealing of copper in germanium are examined experimentally over the temperature range 600 to 805°C, and using the experimental results, discussions are made as to whether the dissociative mechanism or the kick-out mechanism is at work in these processes. The experimental results support the theory that copper in germanium diffuses by the dissociative mechanism and the dominant point defects in germanium are vacancies.

In-Diffusion and Annealing Processes of Substitutional Nickel Atoms in Dislocation-Free Silicon

In-diffusion and annealing processes of substitutional nickel atoms in dislocation-free silicon are studied in the temperature range from 940 to 1020°C to distinguish between the site exchange mechanisms of nickel atoms. The concentration of substitutional nickel atoms varies with time according to the theoretical prediction of the dissociative mechanism. It is found that the in-diffusion and annealing rates are accelerated by nickel precipitation in the bulk. The relationship between the time constant of the two processes and the volume density of the precipitates is discussed.

DIFFUSION AND ELECTRICAL PROPERTIES OF IRON-RELATED DEFECTS IN N-TYPE SILICON GROWN BY CZOCHRALSKI- AND FLOATING ZONE METHOD

Diffusion and electrical properties of iron-related defects in n-type silicon are studied in Czochralski (CZ) and floating zone (FZ) silicon by means of deep level transient spectroscopy and the Hall effect. Introduction and annealing behaviors of electrically active iron-related defects reveal that these defects can be related to complexes containing interstitial iron atoms. The formation of iron-related defects at high temperatures includes defect reaction processes such that the observed complexes could be due to the intermediate states in consecutive reactions of iron-related complex formation. The electrically active complexes are independent of phosphorus or oxygen atoms. The iron-related defects observed in CZ silicon are identical to those observed in FZ silicon.

Point defects in silicon studied by nickel diffusion

Abstract The in-diffusion and the annealing processes of nickel in silicon are studied experimentally at 900°C to distinguish between vacancies and self-interstitials as the dominant point defects in silicon. The experimental results show that, in both the in-diffusion and the annealing processes, the concentration of substitutional nickel atoms varies with time t, following the linear dependence on t during a short time after the onset of both processes, and that the time constant of the annealing process is indpendent of the initial concentration of nickel. These results support the theory that nickel in silicon diffuses by the dissociative mechanism and the dominant point defects in silicon are vacancies.

Distribution of Substitutional Nickel Atoms in Dislocation-Free Silicon Studied by Deep Level Transient Spectroscopy and Theoretical Analyses Based on the Dissociative Mechanism of Diffusion

By means of deep level transient spectroscopy (DLTS), the diffusion profiles of substitutional nickel atoms in silicon are investigated in dislocation-free silicon at 980°C for the in-diffusion process and at 950°C for the annealing process. The results are analyzed on the basis of the dissociative mechanisms of diffusion. It is shown that nickel distribution in dislocation-free silicon can be explained by the dissociative mechanism with the model that sinks and sources of vacancies are present in the bulk in addition to the surfaces.

In-Diffusion and Isothermal Annealing of Iron-Related Defects in n-Type Silicon

In iron-related deep levels in n-type silicon, the introduced concentration of Ec-0.21 eV(B) and Ec-0.41 eV(C) levels decrease with increasing the diffusion time at 1160°C, indicating that the formation process includes the conversion process into other types of complexes. The concentration of the C level decays exponentially with the duration of isothermal annealing up to 200°C, the time constant activation energy being 0.65 eV. The results indicate that the observed defects are due to the intermediate states in consecutive reactions of iron-related complex formation.