【作者】 席珍强；

【导师】 杨德仁； 阙端麟；

【作者基本信息】 浙江大学 ， 材料物理与化学， 2003， 博士

【摘要】 晶体硅不仅是微电子工业的基础材料，也是光伏工业的基础材料，其体内的杂质或缺陷会显著地影响各种硅基器件的性能。其中，过渡族金属就是晶体硅中非常重要的杂质元素。在硅基器件的制备过程中，过渡族金属会不可避免地沾污硅片，并在硅中以单质，复合体或沉淀的形式存在。一般来说，以各种形成存在的过渡族金属都会损害硅基微电子器件或晶体硅太阳能电池的性能，特别是金属沉淀。因此，研究晶体硅中过渡族金属的沉淀规律对于制备高质量的各种硅基器件有着相当重要的现实意义。另外一方面，在理论上研究本征点缺陷，位错以及晶界等缺陷对晶体硅中金属沉淀规律的影响对于丰富和完整“缺陷工程”也是十分必要。其中，铜，镍和铁是硅基器件工艺中最常见也是最重要的三种过渡族金属。在过去的几十年中，虽然对小直径单晶硅中过渡族金属沉淀规律及其对材料的电学性质做了大量的研究，但是很少人研究大直径单晶硅以及铸造多晶硅中这些过渡族金属的沉淀规律。 本文在综述前人工作的基础上，用红外扫描电镜(SIRM)，电子扫描电镜(SEM)结合电子束诱生电流仪(EBIC)，光学显微镜(optical microscopy)结合缺陷腐蚀法(Defect etching)，和透射电镜(TEM)结合X射线能谱(EDX)以及表面光电压仪(SPV)等系统地研究了不同热处理温度和冷却速度下大、小直径直拉单晶硅和铸造多晶硅中铜，镍和铁的沉淀规律及其对材料电学性能和其后氧沉淀形成规律的影响。 研究指出，在晶体硅中，无论是原生点缺陷，还是位错或晶界都会显著影响铜的沉淀规律。当1100℃快冷条件下，在大直径单晶硅中不同的本征点缺陷区域会出现不同的铜沉淀形貌，即在D缺陷区域出现高密度的，细小的铜沉淀团而在A缺陷区域其形貌刚好相反。而在1100℃慢冷条件下，无论A缺陷还是在D缺陷都会出现非常巨大的“星形”铜沉淀团，这种铜沉淀团对硅基体产生很大的压应力。然而无论是快冷还是慢冷，经铜沉淀处理过的大直径单晶硅样品中D缺陷区域的少子扩散长度都是远小于经过相同处理后A缺陷区域的少子扩散长度。这些结果表明，空位促进了铜沉淀的形核，抑制了铜沉淀团的长大。在原生的直拉单晶硅中，铜沉淀的温度为800℃，这与由前人的理论所推导出的结果一致。但是，在铸造多晶硅中，铜沉淀温度大约为700℃，明显低于直拉单晶硅中的沉淀温度。 虽然都是快扩散的过渡族金属元素，镍在单晶硅中的沉淀性质在很多方面与铜不同。在1 100oC快冷条件下，镍会在小直径单晶硅体内沉淀的同时衬在近表面形成无镍沉淀存在的洁净区，而在慢冷条件下镍很难在硅片申形成撰编。然而对于大直径单晶硅，无论是快冷还是慢冷条件下镍都会在硅片的铁内形成沉淀，这与硅片中本征缺陷(空位团)直接相关。在直拉单晶硅中，镊沉淀锡度高于800℃，而且显著依赖于材料种类和冷却速度。在铸造多晶硅中衬锌娜雄的缘度大约为700oc。 然而，用红外扫描电镜等很难观察到热处理温度低于11砂C处率谁的样品中是否存在铁沉淀，所以无论是对于直拉单晶硅还是对于铸造多晶硅)羹象难确雇铁的沉淀温度。在1100oc快冷条件下，在大小直径单晶硅中铁沉烤蒸摩相似)但是在慢冷条件下在大直径单晶硅中形成密度较低的铁沉淀，这也与硅蜘辱生的缺陷直接相关。一 另外，铜，镍和铁都易在晶界或位错上偏聚沉淀，而且不伺的晶鬓毅它们的沉淀规律都有显著的影响。但是无论在哪种晶体硅中，在沉淀温度笋幸热处理硅片，快速冷却都会在晶体硅中形成高密度的金属沉淀，一认而导致辑羹赓都少子扩散长度，而慢冷条件下这些过渡族金属更加容易在缺路处沉淀‘这些实襄结果表明:快冷条件金属沉淀以均匀形核为主，而慢冷条件下以异质形核为主‘在鬓温下，铜沉淀团，镍沉淀和铁沉淀对少数载流子都有很强的复合特性，一龙某彝锋冷条件下所形成的金属沉淀，但是少子的扩散长度主要取决于材料中沉绽的寒度， 无论在普通直拉单晶硅还是在掺氮直拉单晶硅中，80匀弋以上的螂沉淀预处理都会显著促进其随后的氧沉淀形成，特别是快冷条件下的铜娜键预处理。实验还发现，在经过800℃以上的铜沉淀预处理的硅片中形磷了高密库碑舞韧小的氧沉淀，而且氧沉淀一般以异质形核为主。这表明，铜沉淀诱生缺陷作黝舞沉淀异质形核的中心，从而促进了氧沉淀的一形核，而自间隙铜或其复合体雄巍后豹氧沉淀没有明显的影响。然而，无论在普通直拉单晶硅还是在掺氮直拉单晶硅中，镍沉淀预处理都对其随后的氧沉淀形成都没有明显的影响。更多还原

【Abstract】 In microelectronic or photovoltaic industry, crystalline silicon is the main material in which impurities or defects can remarkably influence on the properties of silicon-based devices. Transitional metals are some of important impurities in silicon. During wafer preparation or device processes, they can easily contaminate crystalline silicon and exist in silicon as the form of elements, complexes or silicide precipitates. Generally speaking, each form of transitional metals is detrimental to silicon-based devices, especially silicide precipitate. Therefore, it is very important to investigate the precipitation behavior of transitional metals in crystalline silicon from the view of engineering. Furthermore, it is also necessary to research the influence of intrinsic point defects, dislocations or grain boundaries on the transitional-metal precipitation in crystalline silicon for enriching the defect engineering from the scientific point. Copper, nickel and iron are the most common and important transitional metals in silicon-based device fabrication. In the past decades, the precipitation behavior of transitional metals or their effects on electrical properties in monocrystalline silicon with small diameter have been exhaustively investigated, while the precipitation behavior of transitional metals in large-diameter Cz silicon or cast multicrystalline silicon are still poorly understood.Thereby, on the basis of reviewing previous work, precipitation behaviors of copper, nickel or iron in Cz silicon with deferent diameters and in cast mulitcrystalline silicon treated at different temperatures under air-cooling or slowly cooling were systemically studied by Scanning Infrared Microscopy (SIRM), Scanning Electron Microscopy (SEM) combined with Electron Beam Induced Current (EBIC), Optical Microscopy following Defect Etching, Surface Photo Voltage (SPY) and Transmission Electron Microscopy (TEM). Additional, the influence of transitional-metal precipitation on electrical properties and oxygen precipitation subsequently was also researched in this dissertation.In crystalline silicon, not only intrinsic point defects but also dislocations orgrain boundaries can remarkably influence on the precipitation behavior of copper. High density of tiny copper-precipitate colony occurred in the D-defect zone of the specimen annealed at 1100℃ under air-cooling, while in the A-defect zone the result was inverse. For the specimen annealed at the same temperature under slowly cooling, large star-like copper-precipitate colonies formed both in the D-defect zone and A-defect zone generated great stress on the silicon matrix. However, in spite of different kind of cooling way, the diffusion length of minority carrier in the D-defect zone was always lower than that in the A-defect zone. These results indicated that vacancies in the D-defect zone enhanced the nucleation of copper-precipitates colony but hindered their growth. The copper-precipitation temperature in as-pown Cz silicon was about 800℃, agreeing well with the deduced results from the givenby previous researchers. But in cast multicrystalline silicon, the copper-precipitationtemperature was about 700℃, much lower than that in as-grown Cz silicon.Although both nickel and copper have the highest diffusivity in silicon, theprecipitation behavior of nickel is largely different form that of coppr. Nickel precipitation took place only in the bulk and nickel-precipitate-free formei near thesurface for small-diameter Cz silicon annealed at 1100℃ under air-cooling, And for the specimen annealed at the same temperature but under slowly cooling, it was so difficult to precipitate in the whole specimen for nickel. However, in the large-diameter Cz silicon, nickel precipitation could happen in the bulk notwithstanding different cooling rate, which should be correlated with void in as-grown materials. Nickel-precipitation temperature in Cz silicon was above 800℃ and also did depend on materials quality and cooling rate. In cast multicrystalline silicon更多还原