Magnetic Czochralski Silicon Research Articles

Study of thermal behaviour of oxygen in silicon crystals by analysis of X-rayPendellösungfringes

The thermal behaviour of oxygen in Czochralski (CZ) silicon and magnetic Czochralski (MCZ) silicon crystals was investigated by analysis of Pendellösung sung fringes based on the statistical theory of X-ray dynamical diffraction. The size and the density of oxygen precipitates were determined for different annealing temperatures and/or different times. It was observed that oxide precipitates in the samples increase in size and decrease in density with time during isothermal annealing at 1023 K. The precipitation in MCZ silicon approaches saturation level after annealing for 250 h. It was found that the size of precipitates increases rapidly with annealing temperature in isochronal annealing for 18 h. Comparison of the results of MCZ silicons with those of CZ silicons shows that MCZ crystals are thermally more stable. This suggests that magnetic fields can control the oxygen concentration effectively and that the MCZ and CZ silicon have different thermal behaviours. A powerful technique for detecting microdefects of nanometre size and random distribution is described.

Systematic study of neutron irradiation effects on the performance of FZ and MCZ silicon detectors

Charge collection efficiency dependence on reverse bias voltage ( V B) and on a neutron fluence (φ) was studied for both Float-Zone (FZ) and Magnetic-Czochralski (MCZ) silicon detectors, irradiated with fast neutron fluences, larger than 10 13 n/cm 2. For both types of irradiated detectors, the charge collection efficiency was found to have a logarithime dependence on φ and its dependence on V B indicated that the relation between charge-carrier concentration and full depletion voltage is not according to the standard equation of a p + n n + device.

Record high recombination lifetime in oxidized magnetic Czochralski silicon

This letter demonstrates that recombination lifetimes in excess of 5 ms can be achieved in the oxidized magnetic Czochralski (MCZ) silicon by a combination of high-purity crystal growth, proper cleaning and oxidation conditions. Lifetime studies were conducted at room temperature on as-grown as well as oxidized 2000 Ω cm low oxygen (∼5 ppm) MCZ silicon by an injection sensitive, contactless photoconductive decay technique with controlled injected carrier densities up to 1017 cm−3. Record Shockley–Read–Hall lifetimes of 8.5 and 6.6 ms were achieved in the as-grown and oxidized MCZ wafers, respectively. However, oxidized Czochralski (CZ) silicon with 14.2 ppm oxygen gave lifetime of only 200 μs due to much higher concentrations of as-grown and process-induced defects. Lifetime versus injection level analysis gave ambipolar Auger recombination C coefficient of 1.1×10−30 (±9%) cm6 s−1 before and after the oxidation in both MCZ and CZ silicon. Unlike the C coefficient, the B coefficient (radiative band-to-band + trap-assisted Auger) in low-oxygen MCZ silicon was found to be four times smaller than the value in high oxygen CZ silicon.

Effect of Oxygen Concentration on Lifetime in Magnetic Czochralski Silicon

The effect of oxygen concentration on recombination lifetimes in as‐grown as well as oxidized magnetic Czochralski (MCZ) silicon was investigated. Oxygen concentration was varied in the range of 5–10 ppm within the same ingot by changing the crucible rotational speed. Injection‐sensitive photoconductive decay (PCD) technique was used to measure lifetime and to quantify Shockley‐Read‐Hall recombination, trap‐assisted Auger recombination coefficient , and band‐to‐band Auger recombination coefficient . Recombination lifetime at an injection level of in as‐grown MCZ wafers was as high as 2.1 ms and was found to be independent of interstitial oxygen concentration up to 10 ppm. Contrary to the at relatively lower injection level, the lifetime at moderate injection level of was found to decrease with increasing oxygen concentration due to the increase in trap‐assisted Auger recombination coefficient . It is also shown for the first time that the trap‐assisted Auger coefficient increases monotonically with the oxygen concentration in MCZ silicon. The lifetimes in the oxidized wafers, measured at lower as well as moderate injection levels, showed a decrease with increasing oxygen concentration. The degradation in lifetime at lower injection level was attributed to the interaction between oxygen and diffused‐in impurities during high‐temperature processing. After oxidation, a substantial increase in the coefficient was observed at all oxygen levels. However, band‐to‐band Auger recombination coefficient was found to be independent of oxygen concentration, both before and after oxidation.

Impurities in commercial-scale magnetic czochralski silicon: Axial versus transverse magnetic fields

Magnetic Czochralski (MCZ) silicon crystals, 4 inch diameter, were grown in a HAMCO CG-2000 puller, modified to accommodate either a 5000 G superconducting axial field magnet or a 1500 G transverse field electromagnet. The effect of field strength, crystal and crucible rotation rates on the oxygen concentration and distribution are reported for both field configurations. Results for the axial case demonstrate that the oxygen concentration increases in field strength and crystal rotation rate, while crucible rotation rate has only a small effect. In the case of transverse field, it is shown that the oxygen concentration decreases with increase in field strength and decrease in crucible rotation rate. Crystal rotation rate has negligible effect. The macroscopic radial distribution of oxygen using the transverse field is very uniform under most conditions, compared to the axial field and is comparable to the zero field case. While the application of axial field causes a dramatic increase in the effective segregation coefficient of gallium, no such effects were observed (at least for the low fields used) in the segregation behavior of phosphorous in the transverse field. Probable causes for the various observed differences between the two field configurations are discussed.

Effect of magnetic field on the characteristic of silicon single crystal

The growth striation, the resistant homogeneity, and the oxygen concentration of silicon single crystal grown by both Transverse Magnetic Czochralski (MCZ) and Czochralski growth methods (CZ) were investigated. The oxygen concentration in MCZ silicon is more uniform and controllable. It is concluded that the Magnetic Czochralski method is an effective method to improve the quality of silicon single crystal.

Dopant Segregation in CZ and MCZ Silicon Crystal Growth: A Comparison Between Experiment and Numerical Simulation

Solute transport in Czochralski (CZ) crystal growth and in magnetic Czochralski (MCZ) with a vertical applied field are simulated numerically, and compared with published experimental data on gallium segregation in silicon growth. In the MCZ cases, the low segregation coefficient of 0.008 leads to a steep concentration gradient under the s/l interface due to a boundary layer buildup of rejected gallium. This required a high resolution computation and a segregation model accounting for the melt drift toward the interface. Also, the relatively high density of gallium compared with silicon melt made it necessary to include solutal convection. With these improvements to the simulation code, good agreement with the data was achieved in the CZ growth and in the MCZ growth at 0.1 and 0.3 tesla.