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Lifetime degradation caused by oxygen precipitates combined with metal contamination in Cz-Si for solar cells was evaluated for the samples with different interstitial oxygen concentrations using PL imaging and IR–LST. It was confirmed that phosphorus diffusion gettering is effective for the samples with low oxygen concentration, however the lifetime never recovered for the samples with high oxygen concentration. The enhanced oxygen precipitation process made it more difficult to recover from the metallic contamination. We believe the high density and large size oxygen precipitates are harmful for the lifetime in combination with metal impurities.

We report on the bulk lifetime improvement in Czochralski (CZ) silicon wafers of solar cells by pre-rapid thermal processing (RTP). The commercially available n-type CZ silicon wafers with the thickness of 180 µm were used. Silicon wafers were subjected to pre-RTP followed by the three-step thermal annealing: the first was oxidation at 900 °C for 60 min, the second was isothermal annealing at 1050 °C for 30 min in a nitrogen atmosphere, and the third was oxidation at 900 °C for 10 min, which corresponded to the typical processes of a fully ion-implanted passivated emitters, rear totally diffused silicon solar cell. We investigated the impact of pre-RTP condition on the oxygen precipitation in CZ silicon wafer. A pre-rapid thermal oxidation (RTO) at 1050 °C for 30 sec suppressed the oxygen precipitation during the above three-step annealing, resulting in the lifetime improvement.We report on the bulk lifetime improvement in Czochralski (CZ) silicon wafers of solar cells by pre-rapid thermal processing (RTP). The commercially available n-type CZ silicon wafers with the thickness of 180 µm were used. Silicon wafers were subjected to pre-RTP followed by the three-step thermal annealing: the first was oxidation at 900 °C for 60 min, the second was isothermal annealing at 1050 °C for 30 min in a nitrogen atmosphere, and the third was oxidation at 900 °C for 10 min, which corresponded to the typical processes of a fully ion-implanted passivated emitters, rear totally diffused silicon solar cell. We investigated the impact of pre-RTP condition on the oxygen precipitation in CZ silicon wafer. A pre-rapid thermal oxidation (RTO) at 1050 °C for 30 sec suppressed the oxygen precipitation during the above three-step annealing, resulting in the lifetime improvement.

The behavior of oxygen precipitates under solar cell fabrication processes and the effect on device performance were investigated using TEM observation. Samples were prepared with different carbon concentration and with two sets of growth conditions. The number of precipitates correlates monotonically with the carbon concentration. When the initial carbon concentration is high, the cell efficiency is improved by decreasing the carbon concentration. When the initial carbon concentration is reduced to smaller than 1016 cm−3, the oxygen precipitate grows largely and introduces dislocation. Precipitates grown in a plate form introduce dislocations to the surroundings at a high density, while dislocation density is relatively small around the precipitates polyhedral-grown on the basis of an octahedron. Under the growth conditions for introducing a plate-like precipitate, the cell efficiency was not improved even if the carbon concentration was reduced.

Woongjin Energy Co., Ltd., Daejeon 305-509, Korea(Received November 13, 2014)(Revised November 27, 2014)(Accepted December 5, 2014)Abstract Recent studies have shown methods of improving solar cell efficiency. Especially on single crystalline siliconwafer which is high-efficiency solar cell material that has been widely studied. Interstitial oxygen (Oi) is the main impurityin the Czochralski (Cz) growing method, and excess of this can form precipitates during cell fabrication. We havedemonstrated the effect of Oi impurity and oxygen precipitation concentration of the wafer on Cz-silicon solar cell efficiency.The result showed a decrease in cell efficiency as Oi and oxygen precipitation increase. Moreover, we have found that thecritical point of [Oi] to bring higher cell efficiency is at 14.5 ppma in non-existent Bulk Micro Defect (BMD).Key wordsSolar cells, Efficiency, Czochralski silicon, Oxygen precipitation, BMD

Vacancy depth profiles installed by rapid thermal annealing can be monitored either by Pt diffusion or through vacancy-assisted oxygen precipitation. The features of these profiles clearly show that the vacancy species manifested in these experiments is a “slow vacancy”, Vs. The evolution of Vs depth profiles is controlled by an exchange with another (mobile) kind of vacancy that is likely to be a “Watkins vacancy”, Vw, first observed at cryogenic temperatures. At low T the conversion of Vs into Vw is slow and practically irreversible. At higher T the two species coexist in an equilibrium ratio and diffuse as one entity with an averaged diffusivity. This model provides a good fit to the RTA-installed depth profiles of Vs. The total vacancy community includes, beside Vs and Vw, also a fast vacancy Vf that is responsible for the vacancy contribution into self-diffusion at high T. In RTA experiments, the Vf species seems to be completely annihilated by self-interstitials which leaves only two other vacancy species, Vs and Vw.

A model for the precipitation of oxygen and associated dislocation loops in Czochralski-grown silicon will be presented. Beginning with kinetic rate equations describing the growth and dissolution of oxide precipitates, a reduced model based on the moments of the precipitate size distribution is developed and validated against experimental data. Comparisons with the full, rate equation-based model show that the reduced version is comparably accurate while requiring significantly less computational power. The formation of dislocation loops due to silicon interstitial ejection during precipitate growth is modeled using a simple, moment-based approach.

As of today highly germanium doped Czochralski silicon crystals are used in applications. However it is not clear how a germanium content in the range of 〖10〗^18 atoms/cm³influences the oxygen precipitation behavior, which is highly relevant for the gettering potential of the wafer. In this context high energy X-ray diffraction is a promising tool to monitor real-time the strain introduced by the oxygen agglomeration and growth. Nevertheless in particular in the dynamical limit of X-ray diffraction and at elevated temperatures the strain originating from the precipitation process has to be clearly distinguished from the intensity contribution of thermal vibrations. In Laue geometry dynamical effects can even lead to an increment of the integrated intensity with temperature completely unexpected in the kinematical limit, where temperature is tackled solely by a Debye-Waller factor. Within this work an approach is presented allowing to completely correct the influence of thermal vibrations in the dynamical limit. This approach is applied to undoped and highly germanium doped silicon crystals, clearly revealing an enhanced inventory of grown-in precipitates with germanium doping and suggesting a morphological transformation towards a phase of higher strain of the grown-in precipitates in the range between room temperature and 800 °C. Based on this work, a means of monitoring the growth dynamics at different temperatures and in different precipitation regimes has become available. Moreover, the influence of Ge on O precipitation has been explored via an analysis of the precipitate density.

The swirl defect is observed in both n-type Czochralski (Cz) and non-contact crucible (NOC) Si wafers. It is postulated to be the outcome of oxygen precipitation during crystal growth and/or post-growth high temperature processes, specifically processes involving temperatures in the range of 800°C–1000°C. This defect is characterized by low lifetime ring-like regions that decrease the device performance. We employ a technique based on temperature- and injection-dependent photoluminescence imaging (TIDPLI) to characterize the swirl defect. We compare the calculated fingerprints of the defects responsible for the swirl pattern observed in both Cz and NOC-Si wafers to determine whether the swirls are caused by the same defect. We find significantly different defect fingerprints for the swirl defects in n-type Cz and NOC-Si. The Shockley-Read-Hall (SRH) description of the Cz-Si defects differ not much from the SRH description of intentionally grown oxygen precipitates, whereas the SRH parameters for the NOC-Si defects differ significantly. Identifying the limiting defect, allows us to suggest methods for its annihilation. We then successfully apply a rapid thermal annealing treatment to dissolve swirl defects in Cz-Si samples and homogenize the lifetime.

В роботі вивчено еволюцію рекомбінаційно-чутливих параметрів: часу життя та довжини дифузії нерівноважних носіїв струму у кремнієвих зразках, які піддавались термічним та гетеруючим обробкам. Запропоновано ефективну технологію гетерування рекомбінаційно-активних домішок в кремнії, що полягає в нанесенні плівки Ge на тиловий бік пластини, іонному перемішуванні і постімплантаційному відпалі. Розроблено конструкцію і технологічний маршрут виготовлення конкуренто- спроможних фотовольтаїчних перетворювачів сонячної енергії з використанням відносно низькоякісного дешевого кремнію., Изучено эволюцию рекомбинационно-чувствительных параметров: времени жизни и длины диффузии неравновесных носителей тока в кремниевых образцах, которые подвергались термическим и геттерирующим обработкам. Предложена эффективная технология геттерирования рекомбинационно-активных примесей в кремнии, которая включает нанесение пленки германия на тыльную сторону пластины, ионное переме- шивание и постимплантационный отжиг. Разработано конструкцию и техноло- гический маршрут изготовления конкурентноспособных фотовольтаических преобра- зователей солнечной энергии с использованием относительно низкокачественного недорогого кремния., Evolution of recombination-sensitive parameters such as lifetime and diffusion length of nonequilibrium carriers in silicon wafers subjected to thermal and gettering treatments have been studied. For the first time, it was proposed new technology for gettering of recombination active impurities in silicon. The technology includes deposition of Ge film onto Si wafer back side, ionbeam mixing folowed by post-implantation annealing. Construction and technological route for competitive solar energy converters production have been developed

Oxygen precipitation (OP) and annihilation of voids in heavily phosphorus (P)-doped Czochralski (Cz) silicon have been investigated. It was found that the nucleation anneal at 650°C resulted in much more pronounced OP in the subsequent high temperature anneal than that at 800 or 900 °C. This was due to that SiP precipitates could be formed in heavily P-doped Cz silicon by the 650oC anneal and they acted as the heterogeneous nuclei for OP in the following anneal at high temperatures. The rapid thermal anneal (RTA) at 1200°C was proved to be an effective means to annihilate voids. Moreover, it was found that the significant OP resulting from the two-step anneal of 650°C/8 h + 1000°C/16 h could also cause the substantial annihilation of voids in heavily P-doped Cz silicon. The mechanisms for the annihilation of voids have been tentatively discussed.

Oxygen precipitation (OP) behaviors were investigated for Czochralski (Cz) silicon wafers, which were coated with silicon nitride (SiNx) films or not, subjected to two-step anneal of 800C/4 h+1000°C/16 h following rapid thermal processing (RTP) at different temperatures ranging from 1150 to 1250C for 50 s. It was found that OP in the Cz silicon wafers coated with SiNx films was stronger in each case. This was because that nitrogen atoms diffused into bulk of Cz silicon wafer from the surface coated SiNx film during the high temperature RTP. Furthermore, it was proved that the RTP lamp irradiation facilitated the in-diffusion of nitrogen atoms, which was most likely due to that the ultraviolet light enhanced the breakage of silicon-nitrogen bonds.

National Natural Science Foundation of China [50902116, 50832006]; Fujian Province University; State Key Laboratory of Silicon Materials, China [SKL2009-11]; Scientific and Technological Innovation Platform of Fujian Province, China [2009J1009]

Defect structure of Czochralski grown (1 1 1) oriented silicon single crystals (Cz-Si), irradiated with fast neutrons (energy 5 MeV, dose 5×10 16 cm −2 ) and annealed at up to 1400 K, also under hydrostatic Ar pressure equal to 1.1 GPa, has been investigated by high-resolution X-ray diffraction and synchrotron topography at HASY Laboratory. The annealing, especially at 1270 and 1400 K, results in precipitation of interstitial oxygen and creation of extended defects. A thermally induced oxygen precipitation at high temperatures–pressures in neutron-irradiated Cz-Si reveals the irradiation-related history of investigated samples.

In this paper, the influence of the rapid thermal annealing of single crystalline Cz-Si wafers on the evolution of the concentration of interstitial oxygen as well as oxygen in precipitated oxide phase was investigated by infrared spectroscopy. The wafers were preliminary furnace annealed to create the precipitate seeds. The concentration of interstitial oxygen was shows to decrease considerably as a result of annealing during up to 40 min together with the growth of the concentration of precipitated oxygen. This effect depended on the purity and defect structure of initial wafers. The kinetic model was developed to account for the observed effects based on the modification of the solubility level for interstitial oxygen induced by defects as well as its diffusivity. Obtained results of simulation agree well with the experimental data.

Oxygen precipitation (OP) behaviors in conventional and nitrogen co-doped heavily arsenic-doped Czocharalski silicon crystals subjected to low-high two-step anneals of 650 oC/8 h + 1000 oC/4-256 h have been comparatively investigated. Due to the nitrogen enhanced nucleation of OP during the low temperature anneal, much higher density of oxygen precipitates generated in the nitrogen co-doped specimens. With the extension of high temperature anneal, Oswald ripening of OP in the nitrogen co-doped specimens preceded that in the conventional ones. Moreover, due to the Oswald ripening effect, the oxygen precipitates in the conventional specimens became larger with a wider range of sizes. While, the sizes of oxygen precipitates in the nitrogen co-doped specimens distributed in a much narrower range with respect to the conventional ones.

Low temperature boron and phosphorous diffusion gettering (BDG and PDG) of iron in Czochralski-grown silicon were experimentally studied. Differences and similarities between the gettering techniques were clarified by using intentionally iron contaminated wafers emphasizing especially the effect of oxygen. Experiments showed that the surprisingly high gettering effects of BDG could be explained by B-Si precipitates. Oxygen precipitation was seen to decrease minority carrier diffusion length after long gettering at low temperatures in both BDG and PDG. In the case of BDG oxygen precipitation affected more as a higher thermal budget was needed to obtain similar sheet resistance to that of PDG. According to experiments the efficiency of BDG can not be concluded from the sheet resistance, whereas the efficiency of PDG can. This has practical influences in a process control environment.

Oxygen precipitation in conventional and nitrogen co-doped heavily phosphorus (P)-doped Czochralski silicon (CZ-Si) crystal subjected to various high-temperature annealing in the range of 1000–1150 °C was comparatively investigated. It was revealed that oxygen precipitates hardly generated in conventional heavily P-doped CZ-Si; while they remarkably generated in the nitrogen co-doped one. Moreover, nitrogen doping could enhance oxygen precipitation during the prolonged annealing with a rapid thermal process (RTP) pre-treatment, but it has neglectable influence on oxygen precipitation for short-time annealing. It was believed that nitrogen co-doped heavily P-doped CZ-Si possesses nitrogen-related complexes that act as heterogeneous nuclei for super-saturated interstitial oxygen and then enhanced oxygen precipitation. Finally, it was found that nitrogen doping could hardly enhance oxygen precipitation in heavily P-doped CZ-Si at 1200 °C.

Diffusion doping with gold is shown to reduce the microhardness of silicon single crystals. Oxygen precipitation suppresses this process because diffusing interstitial gold atoms, Aui, interact with oxygen and become captured by growing precipitates.

Oxygen precipitation in heavily phosphorous (P)-doped Czochralski silicon (CZ-Si) subjected to the ramping or two-step anneals was investigated. It was revealed that the grown-in oxygen precipitates exerted significant effect on oxygen precipitation behaviors and then resulted in distinctive oxygen precipitation for the wafers form various positions of the ingot. Moreover, it was found that both the seed and tang-end wafers processed significantly intense nucleation at 650 oC without the influence of grown-in oxygen precipitates. It was considered that the heavily P-doping introduced phosphorus related precipitation at 650 oC. When the annealing temperature increased, the capability for nucleation of oxygen precipitation by heavily P-doping would be gradually weakened but the one by oxygen clustering became pronounced. In this case, it was understandable that the tang-end wafer processed higher density of oxygen precipitates than the seed-end wafer at around 750 oC, while a lower one at 1000 oC.

New evidence for the enhanced oxygen diffusion in Czochralski silicon at temperatures ranging from 450 °C to 650 °C has been obtained from oxygen precipitation in prolonged annealing of 750 °C following a variety of pre-treatments involving slow ramping anneal or single-step anneal. The two previously proposed fast-diffusing species of oxygen–vacancy and oxygen–silicon-interstitial to understand the enhanced oxygen diffusion at low temperatures are questioned. Moreover, the reason as why significant oxygen precipitation can occur at such a low temperature of 750 °C has been elucidated based on the enhanced oxygen diffusion at low temperatures. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Oxygen precipitation in Si is a complex set of processes which has been studied over many years. Here we review theoretical work relating to the precipitation process. At temperatures around 450°C oxygen atoms become mobile and form a family of thermal double donors. The structure of these defects and the origin of their electrical activity is discussed. At temperature around 650°C these donors disappear and there is a growth of SiO2 precipitates along with rod like defects which are extended defects involving Si interstitials. At higher temperatures these collapse into dislocation loops. The structure and electrical properties of the rod like defect are described and compared with those of dislocations.

The properties of n-type silicon with oxygen precipitates introduced by three-stage annealing were studied by the electron beam induced current (EBIC) method, deep-level transient spectroscopy (DLTS), and photoluminescence (PL). The presence of extended defects with concentration of ≤109 cm−3 is revealed by the EBIC method. The concentration of electrically active defects formed in silicon due to oxygen precipitation is estimated from the EBIC contrast and is compared to that obtained from the DLTS data. Comparing the spectra of samples with oxygen precipitates with those of plastically deformed crystals, we can assume that the DLTS and PL spectra of silicon with oxygen precipitates are mainly determined by dislocations.

The effects of two-step rapid thermal processing (RTP) sequentially in different ambients on the formation of denuded zone (DZ) and oxygen precipitation in the Czochralski (CZ) silicon wafers have been investigated. With the first-step RTP in Ar ambient, no obvious DZ but a high density of bulk micro-defects (BMDs) were formed in the sample with the second-step RTP in N2 ambient, while the BMD density in the sample with the second-step RTP in O2 ambient was remarkably low. With the first-step RTP in N2 ambient, a high density of BMDs and a width of DZ could be formed in either of the samples with the second-step RTP in Ar or O2 ambient, but the DZ width in the two samples differed to a certain extent. With the first-step RTP in O2 ambient, the two samples with the second-step RTP in Ar and N2 ambients respectively possessed reasonably comparable DZ width and BMD density. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dislocations and impurities in silicon, even though studied since many years, are now subject of a renewed interest. Moreover, many question related to dislocation- related electronic states remain still unsolved. The present contribution reviews several results, obtained by the authors, on dislocation impurity interactions and their effects on the electronic properties of defect states in silicon. Dislocations introduced by plastic deformation and oxygen precipitation in p-type Czochralski (Cz) silicon have been investigated by junction spectroscopy methods. A deep hole trap, named T1, has been associated to dislocation-related impurity centers, while additional deep traps have been related to contamination by grown-in transition metals and to clusters involving oxygen atoms. Moreover, experimental results obtained by junction spectroscopy assessed the existence of dislocation related shallow states. These were found to be located at 70 and 60 meV from the valence and conduction band edge, respectively. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The influence of enhanced hydrostatic pressure on evolution of dislocations in self-implanted silicon during annealing at different temperatures was investigated by means of electron microscopy methods. It is found that the main cause of the pressure impact differs for various annealing temperatures. The annealing under enhanced pressure at lower temperature (1070 K) has a negligible effect on structure of dislocations located in a thin layer (end-of-range (EOR) defects). At this temperature, enhanced pressure mainly increases the density of microdefects with oxygen precipitation. It is found that after high-temperature annealing (1400 K), enhanced hydrostatic pressure (HP) reduces dislocation density near the surface; however, dislocations extend deeper into the substrate as compared to the samples annealed under atmospheric pressure. The effect is attributed mainly to the reduction of silicon interstitial-atoms migration towards the surface due to increase in energy necessary to make silicon interstitial atom occupy a lattice site at the surface.

The effect of nitrogen on oxygen precipitation in nitrogen- doped Czochralski (NCZ) silicon subjected to the simulated CMOS process was investigated. It was found that nitrogen could enhance oxygen precipitation in silicon during the multi- step thermal process. And the denuded zone in NCZ silicon was formed near the surface, through it was not as wide as that in conventional Czochralski (CZ) silicon. It was also found that the loss rates of oxygen concentration in the NCZ silicon pre- annealed by rapid thermal process (RTP) were higher than those in the CZ silicon. In addition, during the multi-step process the oxygen concentrations in the CZ silicon and NCZ silicon after the multi-step pre-annealing, which could create denuded zone, changed slightly.

Oxygen precipitation in Czochralski (CZ) silicon has been studied for nearly half a century due to its important impact on material and device properties. This paper summarizes the recent understandings of oxygen precipitation in lightly and heavily doped CZ-Si mainly reported by the research groups including the present author. Systematic experiments of annealing condition and dopant effect, and detail analyses of TEM observations and other methods contributed to understand the precipitation mechanism. Further, the theoretical analyses were carried out to explain some experimental results.

The behavior of as-grown oxygen precipitation in Czochralski (Cz) silicon (Si) with the germanium (Ge)-doping has been investigated. It is found that the as-grown oxygen precipitation in Ge-doped Cz (GCz) Si can be enhanced in comparison with the conventional Cz Si at high temperatures, even above the formation temperature of void. It has been ascribed to the effect of heterogeneous nucleus sites supplied by the Ge-related complexes generated in GCz Si. Meanwhile, more large-sized as-grown oxygen precipitates can be formed in GCz Si is revealed through both a controlled ramping annealing and an isothermal annealing performed at high temperatures. This phenomenon is considered to be associated with the reduction in the critical radius of oxygen precipitates for the elevated temperatures.

The effects of vacancies introduced by neutron-irradiation on oxygen precipitation at elevated temperatures in Czochralski (CZ) silicon have been investigated. In comparison with noirradiated CZ silicon, the neutron-irradiated CZ silicon exhibits stronger oxygen precipitation at 1050 °C or 1150 °C due to the existence of supersaturated vacancies in the bulk. Moreover, it is proved that the oxygen out-diffusion at high temperature is not enhanced by the supersaturated vacancies induced by neutron-irradiation. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Oxygen precipitation within the magic denuded zone (MDZ) founded by rapid thermal processing in Czochralski silicon (CZ-Si) wafers is investigated. After the standard MDZ process, the CZ-Si wafers are further subjected to two specific oxygen precipitation annealing, respectively. It is found that the MDZs in CZ-Si wafers shrunk notably because oxygen precipitation occurs within the MDZs. However, a width of substantial DZ still remains within the wafer. Therefore, it is believed that the outer region of the MDZs, which corresponds to the oxygen denuded zone formed in the course of rapid thermal process and high temperature annealing, is a substantial defect-free zone which acts as the active area for semiconductor devices.

This contribution reports the study, by junction spectroscopies, of electronic states induced by thermal and deformation treatments in p-type Si. In order to understand the role that oxygen precipitation, metallic contamination and plastic deformation play on the defect states, several sets of Cz (Czochalski) and Fz (Float-zone) Si samples and different material treatments were investigated. The electronic states were also compared with optical transitions obtained by photoluminescence analyses carried out on the same sample sets. These defect states could thus be microscopically identified with specific defect types.

Neutron-irradiated Czochralski grown silicon subjected to heat treatment (HT) at 350°C and 1000°C under enhanced hydrostatic pressure (HP) was studied in this work. It has been shown that external hydrostatic pressure enhances the creation of VO 2 defects in neutron irradiated silicon subjected to the HP - HT treatment at 350°C. Enhanced formation of platelet-like oxygen precipitates was found in the samples treated at 1000°C under 1.1GPa. This effect was more pronounced in the samples with VO 2 defects. Presented results seem to suggest that probably HP helps to transform VO 2 to some kind of defects or change alone VO 2 defects in the form that can act as an additional nucleus for an additional oxygen precipitation at 1000°C. No correlation between the plate-like oxygen precipitates related absorption at 1225 cm - 1 and dislocation-related emission has been confirmed.

Oxygen precipitation and creation of defects in Czochralski grown silicon (Cz-Si, with interstitial oxygen concentration 1.1 × 1018 cm–3) subjected to irradiation with neutrons (5 MeV, dose 1 × 1017 cm–2) and treated under atmospheric and high hydrostatic pressures (HP, up to 1.1 GPa) at 1270/1400 K are investigated by spectroscopic and X-Ray (synchrotron) methods. The presence of point defects created by neutron irradiation stimulates oxygen precipitation and creation of dislocations under HP, especially at 1270 K. The effect of pressure treatment is related to changes of concentration and mobility of silicon interstitials and vacancies as well as of the VO – type defects. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The formation of a denuded zone (DZ) and the bulk-microdefects (BMDs) region within conventional and nitrogen-doped Czochralski (NCZ) silicon subjected to ramping anneals has been investigated. It was found that the terminal temperature of the ramping anneal should be high enough to create a DZ while the starting temperature should be low enough to generate desirable high density of BMDs. Comparatively speaking, with the same heat treatment, the NCZ silicon possesses higher density of BMDs and a narrower DZ than CZ silicon. Moreover, for NCZ silicon, the ramping anneal can initiate at relatively higher temperature to generate an appropriately high density of BMDs. Of importance is that the ramping anneal with a final isothermal anneal at an elevated temperature such as 1150 °C can effectively create a substantial DZ, where there were no defects generated in the subsequent heat treatment significantly enabling oxygen precipitation.

The effect of rapid thermal processing (RTP) on the oxygen precipitation occurring at 1050 °C in a Czochralski (CZ) silicon wafer has been investigated. It has been proved that the RTP-induced vacancies only enhance the early stage oxygen precipitation at 1050 °C in terms of the precipitation rate. Furthermore, it is somewhat unexpected that after a lengthy 1050 °C anneal the oxygen precipitates generated in the CZ silicon wafer with prior RTP treatment had considerably lower density and larger sizes in comparison with those generated in the CZ silicon wafer without prior RTP treatment. The reason for this is that the prior RTP treatment will dissolve some of the grown-in oxygen precipitates, thus making the RTP-treated wafer possess fewer nuclei contributing to oxygen precipitation in the subsequent 1050 °C anneal. Moreover, the numbers of resulting precipitated oxygen atoms due to a lengthy 1050 °C anneal were nearly the same in the CZ silicon wafers with and without prior RTP treatment. Additionally, it has been illustrated that the high temperature RTP has superior capability to dissolve the existing oxygen precipitates. It is worthwhile to point out that, when addressing the effect of RTP on the oxygen precipitation behaviour during the subsequent anneal, two functions arising from the RTP treatment, that is, the injection of vacancies into the silicon wafer and the dissolution of grown-in oxygen precipitates existing in the silicon wafer, should be taken into account.

In this paper, through the investigation of the effect of rapid thermal processing (RTP) at different temperatures on oxygen precipitation in Czochralski (CZ) silicon wafers subjected to two-step (low?high) anneal and one-step high-temperature anneal, the enhancement role played by vacancies in oxygen precipitation occurring at low temperature and high temperature have been revealed. For the two-step anneal, the RTP-introduced vacancies significantly facilitate the formation of oxygen precipitate nuclei during the low-temperature anneal and, therefore, enhance oxygen precipitation during the subsequent high-temperature anneal. Regarding the one-step high-temperature anneal, the RTP-induced vacancies that later combine with oxygen atoms to become the O2V species significantly enhance the early stage oxygen precipitation in terms of the precipitation rate, however, the RTP-induced vacancies do not increase the amount of precipitated oxygen atoms in the CZ silicon wafer subjected to a prolonged high-temperature anneal. Due to the fact that for the CZ wafer with prior RTP the one-step high-temperature anneal produces much lower density bulk microdefects than the two-step (low?high) anneal, it is believed that the low-temperature anneal is a must for the 'magic denuded zone' process.

The effects of enhanced hydrostatic pressure (HP, up to 1.2 GPa) on the properties of nitrogen-containing Cz-Si:N (N content , interstitial oxygen concentration 9 × 1017 cm−3) and of Czochralski-grown silicon (Cz-Si, reference samples) treated for 5 h at 1070–1570 K–HP have been investigated by photoluminescence, x-ray and infrared absorption methods. HP acts on Cz-Si:N and on Cz-Si in a similar way: oxygen precipitation and creation of numerous cluster-like and extended defects are stimulated, especially at 1230–1400 K. The small cluster-like oxygen-related defects are, however, more numerous in HP treated Cz-Si:N while the extended ones (dislocations) are created at 1230 K in a lowered concentration. A qualitative explanation of the observed effects has been proposed.

The formation of the denuded zone (DZ) in Czochralski silicon preannealed under high pressure was systematically investigated. It was found that the DZ could not form in those specimens. It is considered that the oxygen precipitates generated during preannealing under high pressure are more stable than those grown under atmosphere, so that the oxygen precipitates in the region close to the surface area could not dissociate at the first high-temperature annealing of intrinsic gettering (IG), but grew during the subsequent IG process. The results were also confirmed by the experiments of transmission electron microscopy.