Defects in Fast-Neutron Irradiated Nitrogen-Doped Czochralski Silicon after Annealing at High Temperature

Fast-neutron irradiated nitrogen-doped Czochralski silicon(NCZ-Si)was annealed at 1100℃for different time,then FTIR and optical microscope were used to study the behavior of oxygen.It is found that[Oi]increase at the early stage then decrease along with the increasing of anneal time.High density induced-defects can be found in the cleavage plane.By comparing NCZ-Si with Czochralski silicon(CZ-Si),[Oi]in NCZ-Si decrease more after anneal 24 h.

Impact of Heat Shield Structure in the Growth Process of Czochralski Silicon Derived from Numerical Simulation

Further development of the photovoltaic industry is restricted by the productivity of mono-crystalline silicon technology due to its requirements of low cost and high efficient photocells. The heat shield is not only the important part of the thermal field in Czochralski（Cz） mono-crystalline silicon furnace, but also one of the most important factors influencing the silicon crystal growth. Large-diameter Cz-Si crystal growth process is taken as the study object, Based on FEM numerical simulation, different heat shield structures are analyzed to investigate the heater power, the melt-crystal interface shape, the argon flow field, and the oxygen concentration at the melt-crystal interface in the process of large Cz-Si crystal growth. The impact of these factors on the growth efficiency and crystal quality are analyzed. The results show that the oxygen concentration on the melt-crystal interface and the power consumption of the heater stay high due to the lack of a heat shield in the crystal growth system. Argon circumfluence is generated on the external side of the right angle heat shield. By the right-angle heat shield, the speed of gas flow is lowered on the melt free surface, and the temperature gradient of the free surface is increased around the melt-crystal interface. It is not conducive for the stable growth of crystal. The shape of the melt-crystal interface and the argon circulation above the melt free surface are improved by the inclined heat shield. Compared with the others, the system pulling rate is increased and the lowest oxygen concentration is achieved at the melt-crystal interface with the composite heat shield. By the adoption of the optimized composite heat shield in experiment, the real melt-crystal interface shapes and its deformation laws obtained by Quick Pull Separation Method at different pulling rates agree with the simulation results. The results show that the method of simulation is feasible. The proposed research provides the theoretical foundation for the thermal field design of the large diameter Cz-Si monocrystalline growth.

Annealing behaviors of vacancy in varied neutron irradiated Czochralski silicon

The difference of annealing behaviors of vacancy-oxygen complex (VO) in varied dose neutron irradiated Czochralski silicon: (S1 5×1017 n/cm3 and S2 1.07×1019 n/cm3) were studied. The results show that the VO is one of the main defects formed in neutron irradiated Czochralski silicon (CZ-Si). In this defect, oxygen atom shares a vacancy, it is bonded to two silicon neighbors. Annealed at 200 ℃, divacancies are trapped by interstitial oxygen(Oi) to form V2O (840 cm-1). With the decrease of the 829 cm-1 (VO) three infrared absorption bands at 825 cm-1 (V2O2), 834 cm-1 (V2O3) and 840 cm-1 (V2O) will rise after annealed at temperature range of 200-500 ℃. After annealed at 450-500 ℃ the main absorption bands in S1 sample are 834 cm-1, 825 cm-1 and 889 cm-1 (VO2), in S2 is 825 cm-1. Annealing of A-center in varied neutron irradiated CZ-Si is suggested to consist of two processes. The first is due to trapping of VO by Oi in low dose neutron irradiated CZ-Si (S1) and the second is due to capture the wandering vacancy by VO, etc, in high dose neutron irradiated CZ-Si (S2), the VO2 plays an important role in the annealing of A-center. With the increase of the irradiation dose, the annealing behavior of A-center is changed.

Influence of rapid thermal process on intrinsic gettering in fast neutron irradiated Czochralski silicon

A rapid thermal process (RTP) was first introduced into the intrinsic gettering (IG) processes of fast neutron irradiated Czochralski (CZ) silicon. The effect of RTP conditions on bulk microdefects (BMDs) and denuded zone (DZ) was investigated. Fourier transform infrared absorption spectrometer (FTIR) was used to measure the concentration of interstitial oxygen ([Oi]). Bulk microdefects were observed by optical microscope. The results show that, according to the variation of [Oi], it is found that RTP doesn’t change the processes of oxygen precipitation in fast neutron irradiated Czochralski silicon. Perfect denuded zone, dense oxygen precipitates and defects form in the bulk of irradiated samples. With increasing temperature of RTP, the width of denuded zone decreases. Increasing RTP cooling rate, the density of Bulk microdefects increases. DZ forms in the sample that annealed in nitrogen atmosphere.

Influence of co-precipitation of copper and nickel on the formation of a denuded zone in Czochralski silicon

The influence of co-precipitation of copper and nickel on the formation of a denuded zone （DZ） in Czochralski silicon （Cz Si） was systematically investigated by means of etching and optical microscopy （OM）. It was found that, for conventional high-low-high annealing （CFA）, the DZ could be obtained in all specimens contaminated by copper and nickel co-impurity at different steps of the heat treatment, indicating that no copper precipitates or nickel precipitates were generated in the region just below the surface. However, for rapid thermal annealing （RTA）-low-high annealing, the tendency is not the same; the DZ could not be found in the specimen which was contaminated by copper and nickel contamination before the first RTA annealing. On the basis of the experimental results, it was supposed that the concentration and distribution of the vacancies generating during the RTA can influence the distribution of copper precipitation and nickel precipitation along the cross-section of Cz Si significantly, and thus influence the formation of the DZ to a great extent.

Statistical analysis of recombination properties of the boronoxygen defect in p-type Czochralski silicon

This paper presents the application of lifetime spectroscopy to the study of carrier-induced degradation ascribed to the boron-oxygen （BO） defect. Specifically, a large data set of p-type silicon samples is used to investigate two important aspects of carrier lifetime analysis： ① the methods used to extract the recombination lifetime associated with the defect and ② the underlying assumption that cartier injection does not affect lifetime components unrelated to the defect. The results demonstrate that the capture cross section ratio associated with the donor level of the BO defect （kl） vary widely depending on the specific method used to extract the defect-specific recombination lifetime. For the data set studied here, it was also found that illumination used to form the defect caused minor, but statistically significant changes in the surface passivation used. This violation of the fundamental assumption could be accounted for by applying appropriate curve fitting methods, resulting in an improved estimate of k1 （11.90±0.45） for the fully formed BO defect when modeled using the donor level alone. Illumination also appeared to cause a minor, apparently injectionindependent change in lifetime that could not be attributed to the donor level of the BO defect alone and is likely related to the acceptor level of the BO defect. While specific to the BO defect, this study has implications for the use of lifetime spectroscopy to study other carrier induced defects. Finally, we demonstrate the use of a unit-less regression goodness-of-fit metric for lifetime data that is easy to interpret and accounts for repeatability error.

Microstructure of flow pattern defects in boron-doped Czochralski-grown silicon

The morphology and microstructure of flow pattern defects （FPDs） in lightly boron-doped Czochralski-grown silicon （Cz-Si） crystals were investigated using optical microscopy and atomic force microscopy. The experimental results showed that the morphology of FPDs was parabola-like with several steps. Single-type and dual-type voids were found on the tip of FPDs and two heaves exist on the left and right sides of the void. All the results have proved that FPDs were void-type defects. These results are very useful to investigate FPDs in Cz-Si wafers further and explain the annihilation of FPDs during high-temperature annealing.

Experiment and numerical simulation of melt convection and oxygen distribution in 400-mm Czochralski silicon crystal growth

Single-crystalline silicon materials with large dimensions have been widely used as assemblies in plasma silicon etching machines.However,information about large-diameter low-cost preparation technology has not been sufficiently reported.In this paper,it was focused on the preparation of 400-mm silicon（100） crystal lightly doped with boron from 28-in.hot zones.Resistivity uniformity and oxygen concentration of the silicon crystal were investigated by direct-current（DC） four-point probes method and Fourier transform infrared spectroscopy（FTIR）,respectively.The global heat transfer,melt flow and oxygen distribution were calculated by finite element method（FEM）.The results show that 28-in.hot zones can replace conventional 32 in.ones to grow 400-mm-diameter silicon single crystals.The change in crucible diameter can save energy,reduce cost and improve efficiency.The trend of oxygen distribution obtained in calculations is in good agreement with experimental values.The present model can well predict the 400-mm-diameter silicon crystal growth and is essential for the optimization of furnace design and process condition.

Microstructure of flow pattern defects in boron-doped Czochralski-grown silicon

The morphology and microstructure of flow pattern defects (FPDs) in lightly boron-doped Czochralski-grown silicon (Cz-Si) crystals were investigated using optical microscopy and atomic force microscopy. The experimental results showed that the morphology of FPDs was parabola-like with several steps. Single-type and dual-type voids were found on the tip of FPDs and two heaves exist on the left and right sides of the void. All the results have proved that FPDs were void-type defects. These results are very useful to investigate FPDs in Cz-Si wafers further and explain the annihilation of FPDs during high-temperature annealing.

The Splittings of p_± States in Infrared Spectra of Thermal Donors in Silicon

p -type CZ silicon crystals annealed at 450℃ have been investigated by low temperature infrared spectroscopy with high resolusion. It has been shown that the 2p± and 3p± bands of neutral thermal donors TD~° are all split into two bands, which have not been reported before. In addition, the concentrations ofindi- vidual TD_i and total TD have been derived from the heights of 2po bands, and the boron concentrations de- rived from that of 320 cm^(-1) band. The room temperature resistivities of samples have been evaluated and the comparison with practically measured resistivities have been made.

Influence of Ring Oxidation-Induced Stack Faults on Efficiency in Silicon Solar Cells

We observe a strong correlation between the ring oxidation-induced stack faults （OISF） formed in the course of phosphor diffusion and the efficiency of Czochralski-grown silicon solar cells. The main reason for ring-OISF formation and growth in substrate is the silicon oxidation and phosphorus diffusion process induced silicon selfinterstitial point defect during POCI3 diffusion. The decreasing of minority carrier diffusion length in crystal silicon solar cell induced by ring-OISF defects is identified to be one of the major causes of efficiency loss.

直拉法单晶硅生长原理、工艺及展望

碳达峰、碳中和理念提出后,太阳能作为一种可再生绿色能源备受关注。单晶硅作为主要的光伏材料,其质量决定着太阳能电池效率的高低,为了降低成本和提高产能,人们对单晶硅提出越来越高的要求。直拉法(CZ法)是单晶硅的主要制备方法,其生产效率高,可实现自动化,直拉单晶硅市场占比超过90%,目前正朝着大尺寸、N型、薄片化、低氧低碳的方向发展。然而随着晶棒尺寸增大,热场变化更加复杂,现有CZ工艺难以满足市场需求。未来降低度电成本仍是晶硅光伏发展的驱动力,应通过技术革新、产业标准化、成本控制等手段推动光伏产业发展。本文介绍了CZ法生长单晶硅的基本原理和生长工艺,分别对缺陷控制、热场优化、氧含量控制等进行了分析,在总结工艺现状和单晶生长特点的基础上对直拉法生长单晶硅的发展方向进行了展望。

热氧化法钝化硅片的少数载流子寿命

用高频光电导衰减法 (PCD)研究了热氧化钝化对直拉硅少子寿命的影响 .在 70 0～ 110 0℃范围热氧化不同时间 (0 .5～ 4 h)对直拉硅片表面进行钝化 ,实验结果表明 ,在 10 0 0℃下热氧化对硅片表面钝化的效果最好 ;而且发现热氧化 1.5 h后硅片的少子寿命值达到最大值 ,接近于其真实值 ,而随着热氧化时间的延长 (>1.5 h)少子寿命将会降低 ,这是由于直拉硅中过饱和的氧会沉淀下来形成氧沉淀 ,成为新的少子复合中心 .

微氮硅单晶中的空洞型原生缺陷

研究了掺氮和不掺氮直拉硅单晶中 ,空洞型原生缺陷 (voids)的分布行为和其退火性质 .从两种晶体不同位置取样 ,观察与大尺寸 voids相关的流水花样缺陷 (FPD)沿晶体轴向的分布 ,然后在 10 5 0～ 12 5 0℃下 Ar气中退火不同时间 .实验结果表明在掺氮直拉硅中与较大尺寸 voids相关的 FPD缺陷的密度大量减少 ,其体内这种 FPD缺陷的退火行为与不掺氮直拉硅一样 ,在高温下才能被有效的消除 .这表明在直拉硅中掺氮可以抑制大尺寸的 voids的产生 ,而且掺氮硅中

大直径直拉硅中氮对原生氧沉淀的影响

研究了在大直径直拉硅单晶中掺氮 (N )对原生氧沉淀的影响 .通过高温一步退火 (10 5 0℃ )和低 -高温两步退火 (80 0℃ +10 5 0℃ )发现在掺 N直拉 (NCZ)硅中氧沉淀的行为与一般直拉 (CZ)硅是大不相同的 ,经过高温一步退火后 ,在氧化诱生层错环 (OSF- ring)区氧沉淀的量要小于空洞型缺陷 (voids)区 ,而经过低 -高温两步退火后 ,OSF-ring区的氧沉淀量要远远大于 voids区 .由此可得 ,在晶体生长过程中 ,N通过改变硅晶体中空位的浓度及其分布从而改变原生氧沉淀的尺寸和分布 .并在此基础上讨论了在大直径 NCZ硅中掺 N影响原生氧沉淀的机理 .

直拉硅单晶生长过程建模与控制研究综述

硅单晶是最重要的半导体材料,90%的半导体器件和集成电路芯片都制作在硅单晶上.随着集成电路技术的快速发展,对硅单晶的品质要求也不断提高.直拉法是生产硅单晶的主要方法,其科学原理与方法、生长技术与工艺、控制策略与手段一直是理论界和产业界高度关注和不断研究的热点.本文针对直拉法电子级硅单晶生长过程,以晶体生长基本原理为基础,从生长建模、变量检测、控制方法等方面进行了全面的阐述,特别针对当今大尺寸、高品质硅单晶生长的要求,总结了目前所取得的主要研究成果与面临的问题,并提出了相应的研究思路和方法.

氮对直拉硅片中氧沉淀分布的影响

研究了氮在退火过程中对直拉硅片中的氧沉淀分布的影响 .实验结果表明 ,三步退火后在掺氮硅片截面形成特殊的 M形的氧沉淀密度分布 ,即表面形成没有氧沉淀的洁净区 (DZ) ,体内靠近 DZ区域形成高密度、小尺寸的氧沉淀 ,而在硅片的中心处形成低密度、大尺寸的氧沉淀 .分析认为 ,由于在第一步高温退火过程中氮在硅片表面外扩散 ,同时在硅片体内促进氧沉淀 ,改变了间隙氧的分布 。

紊流模型模拟分析旋转对提拉大直径单晶硅的影响

本文采用紊流模型对提拉大直径单晶硅时,对晶体旋转、坩埚旋转及二者共同作用三种情况下,熔体内的流线、等温线、氧的浓度分布、紊流粘性系数、紊动能等作了数值模拟,发现晶体的旋转能提高氧的径向均匀性,紊流粘性系数和紊动能随着坩埚转速的提高先增加后下降。晶体坩埚同时旋转时并不能有效降低紊流粘性系数,但能使子午面上的流动受到抑制,等温线更为平坦,有利于晶体生长。

重掺杂直拉硅单晶氧沉淀及其诱生二次缺陷

研究了重掺杂直拉硅单晶中掺杂元素硼、磷、砷、锑对氧沉淀及其诱生二次缺陷行为的影响 .实验结果表明 :重掺p型 (硼 )硅片氧沉淀被促进 ,氧沉淀密度高但无诱生二次缺陷 ;重掺n型 (磷、砷、锑 )硅片氧沉淀受抑制 ,氧沉淀密度低却诱生出层错 ;不同掺杂元素及浓度对重掺n型硅片氧沉淀抑制程度不同 ,并对氧沉淀诱生层错的形态产生影响 .讨论了重掺硅单晶中掺杂元素影响氧沉淀及其诱生二次缺陷的机理 ,并利用掺杂元素 本征点缺陷作用模型和原子半径效应模型对实验结果进行了解释 .

水平磁场作用下Φ300mm直拉单晶硅生长三维数值模拟

设计一种二维轴对称和三维混合的数值计算模型,对水平磁场作用下的直拉硅单晶生长进行了研究。结果表明,由于水平磁场的非轴对称性,只有在三维模型中才能获得确切的温度、速度分布。温度场、熔体中的流函数和固液界面形状在水平磁场的作用下也具有非轴对称性,这种非轴对称性随磁场强度的变化而改变。提高晶体旋转速度有利于减小固液界面形状的非轴对称性,并会改变界面形状的凹凸程度;提高坩埚旋转速度则有利于提高熔体中温度分布的均匀性,但会扩大熔体中的径向温度梯度。