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The influence of boron (B), arsenic (As), and antimony (Sb) on oxygen diffusivity at 500–800 °C was investigated in heavily doped Czochralski silicon wafers with resistivities below 0.02 Ω cm. The oxygen diffusivity was determined from the outdiffusion profile measured by secondary ion mass spectrometry after prolonged heat treatments. It was found that the heavily doped As and Sb reduce the oxygen diffusivity more at lower temperature. The increases in the activation energy for diffusion were found to be about 0.64–0.68 and 1.40 eV for As and Sb doping, respectively. Heavy B doping, however, exhibited anomalous temperature dependence showing a reduction rate peak around 600–700 °C, supposedly due to enhanced formation of immobile oxygen aggregates.

A practical computer simulation technique has been developed to predict oxygen precipitation behavior in Czochralski silicon wafers during various thermal processes. In this simulation, an empirical factor is introduced in the initial and boundary conditions of the Fokker-Planck equation of the oxygen precipitation in order to make up an incomplete assumption of a homogeneous nucleation process proposed by Schrems et al. ' The empirical factor is constructed as a function of heat-treatment temperature and interstitial oxygen concentration so as to describe characteristic phenomena of the precipitation nucleation processes in the 450 to 800°C range. Futhermore, an experimentally measured thermal history during a crystal growth process, which strongly influence the oxygen precipitation behavior in the subsequent thermal process, has been taken into consideration. The calculated results agree fairly well with the experimental results for a variety of thermal processes. This semi-empirical simulation technique thus provides an advantageous tool for industrial optimization of the oxygen precipitation characteristics.ABSTRACT A solid-state electrochemical cell of the type Pt/LiCoO 2 -5 mole percent (m/o) Co,,0 4 /LiCO 3 (+5 m/o LiaPO 4 + 6 m/o LiA10 2 )/Au, CO,, 0,, was composed for determining CO 2 concentration, where LiCO,, a lithium ion conductor, is an electrolyte, and LiCoO,-CoO, is used as the solid reference electrode. Electromotive force (EMF) of the cell depended logarithmically on the CO 2 partial pressure in CO,/O, gas mixtures at temperatures between 350 and 400'C. EMF reached a constant value within 1 min after the change of CO 2 partial pressure at 400°C. The sensitivity to CO 2 of this cell was not affected by coexistence of water vapor. The sensor worked stably during a test period of 30 days. The sensing mechanism of CO 2 was discussed together with an explanation to the stability of this sensor.

Diffusivity of oxygen in Czochralski silicon crystal in the temperature range of 400-750°C has been determined from macroscopic oxygen precipitation behavior. The oxygen diffusivities at several nucleation temperatures from 400 to 750°C were deduced from precipitated oxygen concentrations after a series of precipitate growth heat treatments, 800°C/4 h and 1000°C/16 h, using an extended nucleation theory. The measured oxygen diffusivity at 450-650°C is 2 -4 ϫ10 Ϫ14 cm 2 /s, independent of the temperature, and considerably larger than the generally accepted normal diffusivity of D i ϭ0.13 exp(Ϫ2.53 eV/kT). Moreover, the diffusivity at 450°C is found to be roughly proportional to the interstitial oxygen concentration. It is suggested that this dependence of oxygen diffusivity on interstitial oxygen concentration can be explained by a model involving fast diffusing oxygen molecules.

Oxygen precipitation in nitrogen doped Czochralski silicon wafers. I. Formation mechanisms of near-surface and bulk defects

Detaching the crystals from the melt revealed the real state and dynamic change of intrinsic point defects. From this observation it is confirmed that the predominant point defects near the melting point are vacancies. Clusters of interstitial-type dislocation loops (CDL) are eliminated by taking an extremely low growth rate under 0.2 mm/min and nitrogen doping. The anomalous oxygen precipitate (AOP) of the crystals grown in a nitrogen ambient is enhanced. AOP and ring-oxidation induced stacking fault (R-OSF) coexist at the periphery in nitrogen doped crystals. Almost all crystals have defect boundaries between periphery and center region which may be attributed to a stress field in the crystals during growth.

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Microdefects, revealed as ‘flow patterns’ by preferential etching using Secco's etchant, in as-grown silicon crystals have been investigated by means of a transmission electron microscopy and a preferential etching. In as-grown CZ crystals, grown at the pulling speeds of 0.4 or 1.4 mm/min, dislocation loops and clusters were observed with TEM. The dislocation loops in both crystals are interstitial type. From a thermal behavior of flow patterns by heat treatments, we confirmed that the defects revealed as flow patterns in CZ crystals do not have a similar nature of that in D-defect region of FZ crystals.