Solid State Phenomena Vols. 156-158

Abstract: We present infrared (IR) spectroscopy measurements on carbon-rich, germanium-doped Czochralski-grown (Cz-Si) subjected to irradiation with 2 MeV electrons. The study is focused on the effect of germanium doping on the production of carbon-related defects CiCs, CiOi and CiOi(SiI). For carbon concentrations [Cs] up to 11017 cm-3 the production of the defects increases with the increase of Ge content, for [Ge] up to 11020 cm-3. However, for carbon concentrations around 21017 cm-3 the production of these defects shows a decrease for samples with [Ge]=21020 cm-3 in comparison with those of [Ge]=21019 cm-3. The results are discussed taking into account the effect of germanium on the annihilation of vacancies and self-interstitials in the course of irradiations. In the first case, due to the temporary trapping of vacancies by Ge atoms in the course of irradiation, more self-interstitials are available for the production of carbon interstitials (Cs+ SiI Ci), leading finally to an increase of the carbon-related defects. In the second case, and for [Ge] of the order of ~1020 cm-3 or higher, Ge atoms tend to form large clusters. These clusters attract primary defects facilitating their annihilation on them. As a result, the availability of self-interstitials decreases, which finally leads to a decrease of the carbon-related defects.

Abstract: The content and uniformity of impurities and precipitates have an important role in the efficiency of solar cells made of multicrystalline silicon. We developed a transient global model of heat and mass transfer for directional solidification for multicrystalline silicon and a dynamic model of SiC particles and silicon nitride precipitation in molten silicon based phase diagrams. Computations were carried out to clarify the distributions of carbon, nitrogen and oxygen based on segregation and the particle formation in molten silicon during a directional solidification process. It was shown that the content of SiC precipitated in solidified ingots increases as a function of the fraction solidified. It was also clarified from the results that Si2N2O was first formed near the melt-crystal interface, since oxygen concentration in the melt decreases and nitrogen concentration in the melt increases with solidification of the molten silicon. Si3N4 was formed after Si2N2O had been formed.

Abstract: Hybrid crystal orientation technology (HOT) substrates comprised of Si (100) and (110) surface orientation paralleling each <110> direction attract considerable attentions as one of the promising technology for high performance bulk CMOS technology. Although HOT substrates are fabricated by wafer bonding of Si (110) and Si (100) surfaces, it is not clear the atomic configuration of interfacial structure. Furthermore, the possibility for the interface to be an effective gettering source of impurity metals was not well studied. In this paper, we studied the interfacial structure and gettering efficiency of the atomic bonded interface by molecular simulations. The results indicate that the simulated atomic configuration and gettering efficiency of the bonded interface agreed well with the experimental results.

Abstract: In this paper a numerical model is investigated to predict and optimize the quality of Czochralski-grown silicon single crystals. The different mechanisms governing the formation, transport, recombination, nucleation and growth of point- and micro-defects in the crystal are put together with a view to getting a reliable picture of the entire set of physical effects governing the crystal quality. Numerical experiments are conducted to illustrate the model predictions.

Abstract: The results of highly sensitive FTIR investigation, ab initio calculations and rate equation modeling of the early stages of oxide precipitation are compared. The attachment of interstitial oxygen to VOn is energetically more favorable than the attachment to On for n  6. For higher n the energy gain is comparable. The point defect species which were detected by highly sensitive FTIR in high oxygen Czochralski silicon wafers are O1, O2, O3, and VO4. Rate equation modeling for I, V, On and VOn with n = (1..4) also yields O1, O2, O3 to appear with decreasing concentration and VO4 as that one of the VOn species which would appear in the highest concentration after RTA.

Abstract: In an application to large diameter Czochralski (CZ) silicon (Si) single crystal growing the influence on crystal temperature field of various thermal shield assemblies located near to its surface is discussed. By means of mathematical modeling the computer model of thermal processes in an application to a hot zone of "Redmet-90" puller [1], intended for 200 and 300 mm diameter Si single crystal growth is developed. The role of the ring shield and the shield assembly, consisting of two shields (an internal cone and an external one is repeating the crucible shape) and being as a basis of some patents, is investigated. On the basis of the carried out calculations the new thermal shield assembly for "Redmet-90" puller was offered. Its influence on formation of the characteristic thermal zones in growing single crystal, corresponding to defect formation processes in dislocation-free Si crystals (the recombination of intrinsic point defect – IPD, and the formation of their agglomerates) is discussed. The influence of a melt flow on the liquid/solid interface (LSI) shape and thermal stability of crystal growing process is analyzed.

Abstract: Interstitial iron (Fei) and iron-boron pairs influence or even limit the recombination lifetime in industrial block cast multicrystalline (mc) silicon, though the proportions in the total iron concentration are generally small. Most of the iron in mc silicon is precipitated and less recombination active. This work aims for a better understanding of the distribution of iron in its different states (precipitated or dissolved) over the block height, as well as in regions of different crystal quality. In experimental studies several features of iron in mc silicon were observed, which occur due to the high extended defect density. In our 2-dimensional model for mc silicon, trapping of interstitial Fe at extended defects and precipitation at the extended defects are taken into account. The results are compared with NAA-data and spatial resolved measurements of the Fei concentration.

Abstract: The efficiency of solar cells produced from crystalline silicon materials is considerably affected by the presence of metal impurities. In order to reduce the concentration of metal impurities, gettering processes as phosphorus diffusion gettering (PDG) and aluminum gettering (AlG) are routinely included in solar cell processing. Further development and optimization of gettering schemes has to ground on physics-based simulations of gettering processes. In this contribution we use quantitative simulations to compare the efficiency and kinetics of PDG and AlG in the presence of precipitates for interstitially dissolved metals, like iron, at different gettering conditions. Recently measured segregation coefficients of iron in liquid AlSi with respect to crystalline silicon are used in order to compare with PDG under typical conditions. It is shown that kinetics of both, PDG and AlG, can be separated into two regimes: (i) at low temperatures kinetics are limited by precipitate dissolution, and (ii) at high temperatures kinetics of AlG is mainly limited by metal impurity diffusion while phosphorus in-diffusion is the limiting factor of PDG.

Abstract: The process of nanowhisker formation on the substrates activated by catalyst drops was investigated by Monte Carlo simulation. Influence of deposition conditions on whisker morphology was considered. Straight whiskers with uniform diameter could be grown using catalyst possessing large contact angle with whisker material. It was demonstrated that variation of growth conditions in such physicochemical system may result in nanotube formation. Atomic mechanism of hollow whisker formation was suggested. The range of model growth conditions for nanowhisker and nanotube formation were identified.

Abstract: A versatile numerical tool for the simulation of electrical properties of a semiconductor such as minority carrier lifetimes and photoconductivity as a function of defect parameters was developed. Unlike the SRH-model this tool enables to simulate e.g. different measurement conditions and even trapping effects. Contrary to the widely used simulation tool PC1D also non-steady state solutions can be obtained. Furthermore the novel contact less method MDP is presented. Using the example of iron determination the new possibilities arising from combining the novel simulation tool and the method MDP are shown. Simulations for different trapping densities and measurement conditions were executed and exemplary measurements of the trap density and the cross-over point of mc-Si wafers were performed. It was found, that the cross-over point and the sensitivity of iron determination at low level injections is effected by trapping and the chosen non- or steady state measurement conditions.