Defects In Czochralski Silicon Research Articles

Electrical properties of oxygen precipitate-related defects in Czochralski silicon

Oxygen precipitate-related defects in Czochralski (Cz) silicon have been studied by electron-beam-induced current (EBIC) and deep-level transient spectroscopy (DLTS). The EBIC results present that oxygen precipitates combined with dislocations can strengthen carrier recombination. The DLTS data reveals two levels of T 1 (E v + 0.43 eV) and T 2 (E v + 0.26 eV), which are related to the oxygen precipitates and dislocations, respectively. Hydrogen can partly passivate the recombination activity of oxygen precipitates and dislocations, as well as their induced electronic states. The results are of interest for deeply understanding the electronic properties of oxygen precipitates and their induced dislocations in Cz silicon used in the semiconductor industry.

Impact of Carbon Codoping on Generation and Dissociation of Boron–Oxygen Defects in Czochralski Silicon

It has been previously reported that boron–oxygen (B–O) defects in Czochralski (CZ) silicon can be effectively suppressed by carbon codoping. In this work, the kinetics of B–O defect generation and dissociation in carbon-codoped CZ (CCZ) silicon has been investigated. It was found that the activation energy for B–O defect generation in CCZ silicon is 0.56 eV, much larger than that in conventional CZ silicon. However, the activation energy for B–O defect dissociation in CCZ silicon is almost the same as that in conventional CZ silicon, viz. ∼ 1.37 eV. Moreover, the binding energy of B–O defects in both CZ and CCZ silicon is determined to be 0.93 eV. Based on these results, it is believed that carbon atoms in CCZ silicon participate in formation of B–O latent centers before transforming into recombination-active centers under illumination.

Impact of interstitial iron on the study of meta-stable B-O defects in Czochralski silicon: Further evidence of a single defect

We explore the influence of interstitial iron (Fei) on lifetime spectroscopy of boron-oxygen (B-O) related degradation in p-type Czochralski silicon. Theoretical and experimental evidence presented in this study indicate that iron-boron pair (Fe-B) related reactions could have influenced several key experimental results used to derive theories on the fundamental properties of the B-O defect. Firstly, the presence of Fei can account for higher apparent capture cross-section ratios (k) of approximately 100 observed in previous studies during early stages of B-O related degradation. Secondly, the association of Fe-B pairs can explain the initial stage of a two-stage recovery of carrier lifetime with dark annealing after partial degradation. Thirdly, Fei can result in high apparent k values after the permanent deactivation of B-O defects. Subsequently, we show that a single k value can describe the recombination properties associated with B-O defects throughout degradation, that the recovery during dark annealing occurs with a single-stage, and both the fast- and slow-stage B-O related degradation can be permanently deactivated during illuminated annealing. Accounting for the recombination activity of Fei provides further evidence that the B-O defect is a single defect, rather than two separate defects normally attributed to fast-forming recombination centers and slow-forming recombination centers. Implications of this finding for the nature of the B-O defect are also discussed.

Identification of Lifetime-limiting Defects in As-received and Heat Treated Seed-end Czochralski Wafers

Major impurity-induced defects in Czochralski silicon are known to be related to oxygen and metallic elements. In this study we focus on seed-end wafers, and submit them to different solar cell process-related annealings. We find that in the as-received state, these seed-end wafers contain a central low carrier lifetime core. We demonstrate that the effective carrier lifetime in the as-received state is simultaneously governed by several defects including oxygen-related thermal donors and a defect deactivated at low temperature. After high temperature steps, a strong recombination center is formed in the central core. Preliminary results of effective carrier lifetime versus temperature measurements directly support oxygen precipitates to be limiting the carrier lifetime. In the light of all results, we propose a qualitative model for the high temperature behavior of these seed-end wafers.

Advanced Hydrogenation of Dislocation Clusters and Boron-oxygen Defects in Silicon Solar Cells

Advanced hydrogenation processes targeting the generation of neutrally charged hydrogen (H°) are applied to passivate structural defects in seeded-cast quasi mono-crystalline silicon wafers and boron-oxygen defects in Czochralski silicon. The application of a one minute laser hydrogenation process onto a finished screen printed solar cell fabricated on the dislocation-rich seeded-cast material resulted in efficiency enhancements of 0.6% absolute through improvements in the implied open circuit voltage and internal quantum efficiency in the vicinity of the dislocated regions. A new insight is presented on the formation of boron-oxygen defects with a strong dependence on illumination intensity. An advanced laser hydrogenation process is presented to rapidly form and hydrogenate boron-oxygen defects simultaneously, in an 8 s process applied directly after belt furnace firing, with the hydrogenation of more than 95% of boron-oxygen defects at a peak temperature of approximately 360°C on lifetime test structures. The same 8 s process is also demonstrated on standard screen-printed solar cells applied directly after belt furnace firing to simultaneously form- and hydrogenate the boron-oxygen defects, with no subsequent loss in electrical performance, hence avoiding a 0.7% absolute loss in efficiency due to light-induced degradation.

Suppression of boron-oxygen defects in Czochralski silicon by carbon co-doping

We have investigated the influence of carbon co-doping on the formation of boron-oxygen defects in Czochralski silicon. It is found that carbon can effectively suppress the formation of boron-oxygen defects. Based on our experiments and first-principle theoretical calculations, it is believed that this effect is attributed to the formation of more energetically favorable carbon-oxygen complexes. Moreover, the diffusion of oxygen dimers in carbon co-doped silicon also becomes more difficult. All these phenomena should be associated with the tensile stress field induced by carbon doping in silicon.

Impurity engineering of Czochralski silicon

Microelectronic devices with high integration level and functional complexity are always requiring larger diameter and more perfect Czochralski (CZ) silicon wafers. Therefore, the defects, playing the key role in the quality control of silicon materials, have to be well controlled during crystal growth and device fabrication. Co-doping nitrogen (N), germanium (Ge) or carbon (C) into CZ silicon to control defect dynamics and to change defect evolution, so-called “impurity engineering”, has been developed in recent years, and has been widely applied in the fabrication of higher quality CZ silicon used for microelectronics nowadays. This article is to present an overview of the current status of impurity engineering in CZ silicon, based on the co-doping technologies of N, Ge and C. The fundamental properties of these three co-dopants and their interaction with point defects in CZ silicon are firstly introduced. The bulk of the article is focused on the effects of co-dopants on the formation of oxygen precipitates related to internal gettering (IG) of devices for metal contaminants, and voids associated with the gate oxide integrity (GOI) of devices in CZ silicon. Finally, the improvement of CZ silicon mechanical strength by co-doping technology is described.

Hydrogen Passivation of B-O Defects in Czochralski Silicon

We report on hydrogen passivation of boron-oxygen defects through manipulation of the hydrogen charge states within the silicon. Standard hydrogenation processes which do not control hydrogen charge states do not appear to passivate a significant quantity of boron-oxygen defects and may result in a reduction in lifetime for wafers with high boron doping concentrations. An improved hydrogenation process through charge state manipulation is observed to lead to substantial improvements in the lifetimes of standard 2Ωcm commercial grade boron-doped Czochralski wafers and experimental compensated 2Ωm Czochralski grown wafers. The passivation of boron-oxygen defects using hydrogen is a fully reversible process, and hence subsequent processes can lead to a net reactivation of boron- oxygen defects if there are insufficient quantities of atomic hydrogen in the correct charge state. Through improved hydrogenation, independently confirmed open circuit voltages in excess of 680mV are demonstrated on solar cells fabricated using standard commercial grade boron-doped Czochralski grown wafers on an industrial production line.

Effect of tin doping on oxygen- and carbon-related defects in Czochralski silicon

Experimental and theoretical techniques are used to investigate the impact of tin doping on the formation and the thermal stability of oxygen- and carbon-related defects in electron-irradiated Czochralski silicon. The results verify previous reports that Sn doping reduces the formation of the VO defect and suppresses its conversion to the VO2 defect. Within experimental accuracy, a small delay in the growth of the VO2 defect is observed. Regarding carbon-related defects, it is determined that Sn doping leads to a reduction in the formation of the CiOi, CiCs, and CiOi(SiI) defects although an increase in their thermal stability is observed. The impact of strain induced in the lattice by the larger tin substitutional atoms, as well as their association with intrinsic defects and carbon impurities, can be considered as an explanation to account for the above observations. The density functional theory calculations are used to study the interaction of tin with lattice vacancies and oxygen- and carbon-related clusters. Both experimental and theoretical results demonstrate that tin co-doping is an efficient defect engineering strategy to suppress detrimental effects because of the presence of oxygen- and carbon-related defect clusters in devices.

Effect of germanium doping on the annealing characteristics of oxygen and carbon-related defects in Czochralski silicon

This paper is devoted to the annealing studies of defects produced in carbon-rich Ge-doped Czochralski-grown Si (Cz-Si) by 2 MeV electron irradiation. The annealing temperature of vacancy-oxygen (VO) complexes, carbon interstitial-oxygen interstitial (CiOi), and carbon interstitial-carbon substitutional (CiCs) pairs as well as the formation temperature of vacancy-two oxygen (VO2) complexes are monitored as a function of Ge concentration. It has been established that the annealing of CiOi and CiCs defects remains practically unaffected by the Ge presence, whereas the annealing temperature of VO defects and the formation temperature of VO2 complexes are substantially lowered at Ge concentrations larger than 1×1019 cm−3. The hydrostatic component of elastic strains introduced by Ge atoms in the Si crystal lattice was calculated. It appears to be very small, at least insufficient to exert a pronounced effect upon the annealing behavior of radiation-produced defects. This conclusion is in line with what is observed for the CiOi and CiCs species. In the case of VO, whose annealing process in Cz-Si is concurrently conducted by two reaction paths VO+Oi→VO2 and VO+SiI→Oi, we suggest that the latter reaction in Ge-doped Cz-Si is enhanced by emitting self-interstitials (SiI) from loosely bound self-interstitial clusters predominantly formed around Ge impurity atoms. As a result, the liberation of self-interstitials at lower annealing temperatures leads to an enhanced annealing of VO defects. An enhanced formation of VO2 complexes at lower temperatures is also discussed in terms of other reactions running in parallel with the reaction VO+SiI→Oi.

Correlation Between Oxygen Precipitation and Extended Defects in Czochralski Silicon: Investigation by Means of Scanning Infrared Microscopy

Through an investigation of oxygen precipitation and extended defects in Czochralski silicon (CZ-Si) specimens subjected to different isothermal anneals, by scanning infrared microscopy and preferential etching combined with optical microscopy, the correlation between the sizes of oxygen precipitates and the generation of extended defects is revealed. It is found that extended defects are generated when oxygen precipitates grow. Afterward, the sizes of extended defects increase, while those of oxygen precipitates do not change significantly. For the onset of the generation of extended defects, we define the maximum size of oxygen precipitates as a critical size for the generation of extended defects. Moreover, it is revealed that this critical size decreases for higher annealing temperatures or more oxidizing ambients.

Neutron irradiation defects in Czochralski silicon

AbstractIn this paper the influence of neutron irradiated on the defects and oxygen precipitation in Czochralski silicon were investigated. The vacancy‐oxygen complex (VO, A‐center) is one of the main defects formed in neutron‐irradiated Czochralski silicon (CZ‐Si). In this defect, the oxygen atom shares a vacancy, it is bonded to two silicon neighbours. Annealing of the A‐center in varied neutron‐irradiated CZ‐Si consists of two processes. The first is trapping of VO by interstitial oxygen (Oi) in low‐dose neutron‐irradiated CZ‐Si and the second is capturing of the wandering vacancy by VO, etc, in high‐dose neutron‐irradiated CZ‐Si. With the increase of the irradiation dose, the annealing behavior of the A‐center is changed and the formation of the VO2 is depressed. It is found that V2 and V4 abound in high‐dose irradiated CZ‐Si. With the increase of the annealing temperature the monovacancy type defect is annihilated. The results show that the formation of V4 is enhanced when the annealing temperature ran up to 400‐600 °C and with the FTIR absorption peak at the wave number of 829 cm–1 (VO) disappearing, five absorption peaks appear. It can be concluded that these defect‐impurity complexes prolong the lifetime of positrons. It is found that the high‐dose irradiated greatly accelerates the oxygen precipitation which leads to a sharp decrease of the interstitial oxygen with the increase of the annealing time. At room temperature, the 1107 cm–1 infrared absorption band of interstitial oxygen becomes weak and broadens to low energy side. The bulk micro‐defects, including stacking faults, dislocations and dislocation loops, were observed by the optical microscopy. New or large stacking faults grow up when the silicon self‐interstitial atoms are created and aggregate with oxygen precipitation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Quench-induced defects in silicon doped with group III acceptor impurities: Generation and annealing

The formation and annealing of quench-induced defects in Czochralski silicon have been studied using IR spectroscopy and Hall effect measurements. The results demonstrate that the behavior of quench-induced defects in Si〈Al〉 differs markedly from that in silicon doped with other Group III acceptor impurities: B, Ga, and In. The elastic fields created in Si by the Ga and In dopants, as well as by the isovalent impurity Sn, increase the density and annealing temperature of quench-induced defects. The highest density of quench-induced defects in Si〈Al〉 was observed at 1100°C.

Germanium effect on oxygen‐related defects in Czochralski silicon

AbstractThe behaviours of germanium doped in Czochralski (CZ) silicon have attracted considerable attention in recent years. In this article, a review concerning recent processes in the study about oxygen related defects in germanium‐doped CZ (GCZ) silicon is presented. The formation of oxygen precipitates during CZ silicon growth can be improved by germanium, and the oxygen precipitation during thermal cycles can be enhanced, so that the internal gettering (IG) ability of GCZ silicon wafers for metallic impurities is improved. Meanwhile, the morphology of oxygen precipitates can be changed in GCZ silicon. Thermal donors (TDs) can be suppressed by germanium doping as the result of the reaction between germanium and point defects, while new donors (NDs) can be strongly enhanced in GCZ silicon because of a process associated with the nucleation enhancement of oxygen precipitates with germanium doping. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of germanium doping on oxygen donors in Czochralski-grown silicon

In this paper the effect of germanium doping on oxygen donors in Czochralski (CZ) silicon has beeninvestigated. It is found that germanium suppresses the formation of thermal donors during annealingat 450 °C, as a result of the reaction of Ge with point defects in CZ silicon. Meanwhile, it is clarifiedthat germanium enhances the formation of new donors in CZ silicon, which is proposed tobe a process associated with the nucleation enhancement of oxygen precipitation bygermanium doping.

Germanium effect on void defects in Czochralski silicon

The effect of germanium (Ge) on void defects in lightly Ge-doped Czochralski (GCZ) silicon (Si) crystals has been investigated. Three GCZ Si crystals with different Ge concentrations (10 15–10 18 cm −3) and one conventional Czochralski (CZ) Si crystal were grown under almost the same growth conditions. It is found that the density of flow pattern defects (FPDs) related to void defects in the as-grown GCZ Si decreases with the increase of Ge concentration. The voids in the GCZ Si could be eliminated more easily during annealing at the high temperatures of 1050–1200°C. It is concluded that Ge can suppress the formation of voids during Si crystal growth. Thus, GCZ Si can be expected to use widely in modern microelectronic industry.

Octahedral void defects in Czochralski silicon

Dual-type octahedral void defects were found in Czochralski silicon in 1995. This was a trigger for a “renaissance” in the field of Si crystal investigation as well as a breakthrough toward the new stage of the next-generation Si-microelectronics development. Crystallographically each void is basically composed of eight sub-planes of (1 1 1), but it is often truncated by a (0 0 1) sub-plane in the crystal-growth direction. This is a clear characterization of void defects and is closely related to some physical phenomenon in Si melt growth. This paper characterizes the occurrence of (0 0 1) sub-planes in void defects.

窒素ドープＣｚｏｃｈｒａｌｓｋｉシリコン結晶の赤外吸収測定

Nitrogen doping is promising to reduce grown-in defects in Czochralski silicon (CZ-Si) crystal. It is necessary to measure the nitrogen concentration accurately. As the nitrogen concentration is very low, nitrogen absorption is affected by various absorptions such as those by lattice vibration and oxygen. Procedures to cancel them were developed. As the result, the detection of weak nitrogen-related peaks became possible. As nitrogen in CZ-Si crystal forms complexes with oxygen, we assigned the peaks and proposed to measure the N-N related peak at 963 cm-1 as well as those at 996 and 1018 cm-1 caused by N-O complexes. Conversion coefficient from the sum of absorption coefficients of these peaks to the nitrogen concentration estimated by segregation coefficient was confirmed to be nearly equal to the value reported for floating zone silicon (FZ-Si) crystal.

Dopant boron concentration dependence on electron irradiation enhanced defects in Czochralski silicon

Positron annihilation lifetime experiments have been performed for CZ-Si with B concentration ranging over 8.3×10 17–2.5×10 20/cm 3 irradiated with 6 MeV electrons at room temperature. The mean lifetimes were hardly changed in the specimens with B below 8.0×10 18/cm 3, and increased in the specimen above 8.6×10 19/cm 3 by irradiation. No remarkable lifetime change with B concentration was obtained with the increase of electron fluence up to 5×10 15 e/cm 2, and the mean lifetimes of the specimens with B more than 8.6×10 19/cm 3 increased with electron fluences higher than 1×10 16 e/cm 2. It is concluded that complex defect clusters of B x O y V z are formed by electron irradiation, which have shorter positron lifetimes than the bulk.

Electron Beam Induced Current Contrast of Oxygen Precipitation Related Defects in Czochralski Silicon

Electron Beam Induced Current Contrast of Oxygen Precipitation Related Defects in Czochralski Silicon