Precipitation Of Iron In Silicon Research Articles

Experimental and theoretical study of heterogeneous iron precipitation in silicon

Heterogeneous iron precipitation in silicon was studied experimentally by measuring the gettering efficiency of oxide precipitate density of 1×1010cm−3. The wafers were contaminated with varying iron concentrations, and the gettering efficiency was studied using isothermal annealing in the temperature range from 300to780°C. It was found that iron precipitation obeys the so-called s-curve behavior: if iron precipitation occurs, nearly all iron is gettered. For example, after 30min annealing at 700°C, the highest initial iron concentration of 8×1013cm−3 drops to 3×1012cm−3, where as two lower initial iron concentrations of 5×1012 and 2×1013cm−3 remain nearly constant. This means that the level of supersaturation plays a significant role in the final gettering efficiency, and a rather high level of supersaturation is required before iron precipitation occurs at all. In addition, a model is presented for the growth and dissolution of iron precipitates at oxygen-related defects in silicon during thermal processing. The heterogeneous nucleation of iron is taken into account by special growth and dissolution rates, which are inserted into the Fokker-Planck equation. Comparison of simulated results to experimental ones proves that this model can be used to estimate internal gettering efficiency of iron under a variety of processing conditions.

Modeling and Optimization of Internal Gettering of Iron in Silicon

We present a model for heterogeneous precipitation of iron in silicon. In the model Fokker-Planck Equation is used to simulate the evolution of size distribution of iron precipitates. From the simulation results we may conclude, that in case of low levels of initial iron concentration (<1×1012 cm-3), internal gettering is difficult to achieve just by cooling. The low level of initial iron concentration can be gettered by using an additional nucleation step, which can be just a fast ramp to room temperature, before isothermal gettering anneal. We also analyze the effect of competitive gettering on the final iron concentration and the iron precipitate density profile. We found that internal gettering can reduce iron concentration and the particular advantage is the reduction of the iron precipitate density in the device layer. The iron precipitation in the device layer can also be reduced by increasing the doping concentration as the segregation increases.

Modeling of heterogeneous precipitation of iron in silicon

A model is presented for the growth and dissolution of iron precipitates at oxygen-related defects in silicon during thermal processing. The heterogeneous nucleation of iron is taken into account by special growth and dissolution rates, which are inserted into a set of modified chemical rate equations. This approach allows us to calculate the size distribution of iron precipitates and the residual iron concentration. By comparing the simulated results with experimental ones, it is proven that this model can be used to estimate the internal gettering efficiency of iron under a variety of processing conditions.

Early stages of iron precipitation in silicon

The early stages of iron precipitation in p-type float-zone silicon have been studied by means of Deep Level Transient Spectroscopy, DLTS, for iron concentrations in the range of 1014 – 3 × 1015 cm3. A DLTS line showing the signatures of extended localized states is observed. The emission characteristics of the associated defect is very similar to that of the interstitial iron donor. It is concluded that large clusters consisting of interstitial iron atoms give rise to the observed DLTS line. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Analysis of Iron Precipitation in Silicon as a Basis for Gettering Simulations

In order to better understand and model internal gettering of iron in silicon, a quantitative investigation of iron precipitation in silicon containing different oxygen precipitate densities was performed. The number of iron precipitation sites was obtained from the iron precipitation kinetics using Ham's law. At low temperatures, the iron precipitation site density corresponded to the oxygen precipitate density. A strong annealing temperature dependence of the iron precipitate density was observed for the samples with larger oxygen precipitate densities. These data were used to simulate iron precipitation during a slow cool. From those simulations, optimal cooling rates were obtained for different silicon materials assuming various iron precipitation site densities in the denuded zone.

Gettering of iron by oxygen precipitates

In order to better understand and model internal gettering of iron in silicon, a quantitative investigation of iron precipitation in silicon containing different oxygen precipitate densities was performed. The number of iron precipitation sites was obtained from the iron precipitation kinetics using Ham’s Law. At low temperatures, the iron precipitate density corresponded to the oxygen precipitate density. A strong temperature dependence of the iron precipitate density was observed for the samples with larger oxygen precipitate densities. These data were used to simulate iron precipitation during a slow cool. From those simulations, optimal cooling rates were obtained for different silicon materials assuming various iron precipitation site densities in the epitaxial layer.

Iron precipitation in float zone grown silicon

Temperature dependent iron precipitation in float zone grown silicon wafers has been experimentally investigated. Results of iron precipitation experiments over a wide thermal process temperature range and time are presented. Precipitation of iron in silicon was analyzed by a quantitative assessment of change in interstitial iron using a surface photovoltage minority carrier lifetime analysis technique. Contamination levels of iron in the range 1011–1013 atoms/cm3 are investigated. It is concluded that maximum iron precipitation occurs in the temperature range of 500–600 °C. Iron precipitation is rapid in this region where more than 90% of the interstitial iron precipitates in a period of 30 min.

Iron Precipitation and Dissolution in Float-Zone Silicon

ABSTRACTA quantitative analysis of the phase changes of iron in silicon from interstitial to precipitate phase and vice-versa is presented. Temperature dependent iron precipitation and dissolution in float-zone grown silicon wafers is experimentally investigated. A quantitative analysis of iron silicide precipitate stability and dissolution with respect to time and temperature is also presented. Precipitation of iron in silicon was analyzed by a quantitative assessment of change in interstitial iron using a surface photo voltage minority carrier lifetime analysis technique. Contamination levels of iron in the range 1011 to 1013 atoms/cm3 are investigated. It is concluded that maximum iron precipitation occurs in the temperature range of 500°C to 600°C. Iron precipitation is rapid in this region where more than 90% of the interstitial iron precipitates in a period of 30 minutes. Iron silicide precipitates were found to dissolve above a temperature of 760°C restoring iron back to an interstitial phase in the silicon matrix.

Precipitation of Iron in Silicon: Gettering to Extended Surface Defects Sites

Precipitation of Iron in Silicon: Gettering to Extended Surface Defects Sites

Charge-state-dependent iron precipitation in silicon

The kinetics of interstitial iron precipitation in p-type silicon are investigated. During annealing, the iron charge state is controlled by the applied reverse voltage and its effect on the precipitation is studied. We observe that iron in the neutral charge state (Fe0i) precipitates preferentially in three-dimensional nucleation centers while Fe+ivanishes in the dislocation lines (rod-like nucleation centers). These centers are created during the fast cooling procedure necessary to dissolve iron in the silicon matrix.