多晶硅制绒工艺研究

本文讨论了多晶硅制绒工艺技术,对比多晶硅在碱混合液和酸混合液中制绒,酸溶液制绒能更好的改善多晶硅表面减反射作用。采用显微镜及模拟日光器对电池性能检测分析,结果表明,不同绒面的多晶硅电池电学性能参数存在差异,并对多晶硅的最佳刻蚀深度进行了总结。     

快速制备单晶Si片绒面的研究

太阳电池单晶Si片表面制绒已是一项成熟的工艺,但普遍制绒时间较长.为提高制绒效率,本课题研究了较短时间内NaOH/ 异丙醇(IPA)体系制绒时的温度、时间、溶液组分对绒面的影响,以及制绒前去损伤的优劣.最终实现了,在含2.5;NaOH(质量百分比,下同)和10;IPA的溶液中,80℃恒温处理15 min即可制备出比较均匀的绒面.溶液中加入3;Na2SiO3,效果更佳,反射率最低可达9.5;.并发现去损伤后制绒效果并不理想,同时还研究了表面活性剂1,4-环己二醇(CHX)和十二烷基苯磺酸钠(SDBS)代替异丙醇制绒.研究发现,异内醇仍然是性价比较好的添加剂.     

LPCVD法在制绒单晶硅片衬底上制备ZnO∶B透明导电薄膜及其性能的研究

采用低压化学气相沉积法(LPCVD)在制绒的单晶硅片衬底上制备了B掺杂ZnO(BZO)的透明导电薄膜,研究了B2H6掺杂量、沉积时间对BZO薄膜的微观形貌、导电性能及光学减反性能的影响.结果表明,在制绒单晶硅片衬底上制备的BZO薄膜均呈现“类金字塔”的绒面结构,其平均晶粒尺寸在200 ～ 500 nm之间,并随B2H6掺杂量增加而减小;BZO薄膜的方阻随沉积时间的增加而呈线性迅速减小的趋势,当沉积时间为420 s时,BZO薄膜的方块电阻低至28 Ω/□;在制绒单晶硅片上制备BZO薄膜后,表面平均反射率由15;明显降低至5;左右,表现出优异的光学减反性能.     

基于负性光刻胶掩膜的湿法多晶硅制绒

提出了一种用于大规模多晶硅太阳能电池生产的制绒工艺,采用负性光刻胶作为湿法刻蚀的掩膜,制备蜂巢状低反射率绒面.通过研究氢氟酸/硝酸溶液中各向同性刻蚀时腐蚀坑的形成过程,发现随着刻蚀时间的增加,在掩膜图形的开孔下逐渐形成六方分布的球面形状的腐蚀坑,腐蚀坑的深径比(深度/开孔直径)出现先上升然后下降的趋势.同理论计算值对比发现,随着刻蚀时间增加,掩膜和硅片的附着紧密性及掩膜的阻挡效应降低,酸液可能渗入了掩膜和硅片的界面,横向刻蚀速度快速上升,降低了深径比,导致实际的反射率高于理论计算值.尽管如此,本文还是成功制备了孔径15微米的蜂巢状绒面,反射率达到了22.9;.     

晶体硅太阳能电池绒面的反应离子刻蚀制备研究

以SF6和O2为反应气体,采用反应离子刻蚀(RIE)技术,在单晶硅衬底表面制备了锥型绒面结构,系统地研究了关键刻蚀条件对RIE晶硅表面制绒的影响.结果表明,随着反应气压增大,晶体硅表面锥型结构呈现分布均匀和高度增加的趋势,但过高气压下锥型微结构向脊型转变直至消失.在反应气体中掺入CH4,晶体硅表面锥型结构高度增加,表面平均反射率下降到5.63;.该结果可解释为:气压增大导致的F原子刻蚀的增强有利于锥体结构高度增加,小尺寸的SiOyFx聚合物掩模的完全刻蚀使锥型结构的尺寸逐渐均匀,而过高的气压下,掩模及晶体硅的过量刻蚀导致微结构只剩锥体底部的脊型凸起.CH4掺入导致CHx聚合物的掩模和粒子轰击效应均有增强,更有利于高纵横比锥型微结构的形成.     

多晶硅绕镀层的去除工艺研究

本文旨在针对TOPCon(Tunnel Oxide Passivated Contact背面隧穿氧化钝化接触)晶硅电池制备过程中,背面钝化多晶硅层沉积引起的硅片正面边缘沉积多晶硅绕镀层的去除进行工艺研究,进一步解决了电池外观不良和该多晶硅层对电池正面光的吸收影响.文中分别尝试采用HF-HNO3混酸溶液和KOH碱溶液两种方式进行腐蚀处理,然后通过对处理后硅片正面的工艺控制点监控和电池EL检测等手段评估去除效果.其中HF 1wt;、HNO350wt;混合溶液时腐蚀4 min以上可去除该绕镀层,但是大于6 min后硅片正面的方块电阻提升、硼掺杂浓度等变化幅度很大.KOH质量分数0.1wt;、添加剂体积分数5vol;混合溶液60℃时,腐蚀2.5 min以上可去除该绕镀层且方块电阻等测试相对变化幅度较小.故前者对电池后期电极的制备工艺要求更高否则容易引起欧姆接触不良,后者则对电池电极的制备工艺控制窗口更大.所以认为在多晶硅绕镀层的去除方面KOH腐蚀更适合工业批量化生产工艺选择.     

“类金字塔”状ZnO改善硅异质结电池近红外波段外量子效率

因晶体硅是间接带隙半导体材料,其较低的吸收系数限制了对近红外波段入射光的吸收.为此,引入金属有机化学气相沉积(MOCVD)技术制备的ZnO薄膜,并通过改变掺杂流量和沉积时间调节ZnO∶ B(BZO)薄膜的光学和电学性能.将BZO薄膜用于硅异质结(SHJ)太阳电池的背反射电极,相比于传统结构,电池的反射率和外部量子效率在近红外波段得到显著改善.为进一步解释外量子效率增加的原因,在四甲基氢氧化铵(TMAH)湿法制绒的硅衬底上沉积BZO薄膜,得到了新型微纳米嵌套结构,并对其光吸收进行了测试分析.     

ZnO纳米结构减反射层特性优化及对太阳能电池性能的影响

利用电化学沉积法在铜铟镓硒薄膜太阳能电池表面沉积一层ZnO纳米结构阵列减反射层.通过对沉积电位的操控,实现了对该纳米结构减反射层形貌、光学质量、反射率等特性的优化.在电池表面蒸镀电极后测试电池的电流电压曲线可知,相比于没有减反层的电池,沉积了纳米结构减反射层的电池利用氧化锌纳米结构的亚波长尺寸形成的蛾眼效应有效降低了表面光反射,增加光吸收,从而实现短路电流增加6.2;,电池效率提高了9.9;.     

氧化性在硅太阳电池织构中的作用

在单晶硅太阳电池的制备中,碱性腐蚀常被用于在晶体硅上形成金字塔结构,减小光的反射,提高太阳电池的效率.获得小而分布均匀的金字塔绒面结构有利于提高太阳电池的转化效率.本文通过优化NaClO织构工艺,获得了金字塔平均尺寸为1.4 μm,平均表面反射率为11.5;的织构绒面,并探索了形成小金字塔的机理.认为NaClO具有一定的氧化性是其形成小金字塔的可能原因.为了研究氧化性在织构中的作用,采用在无氧化性的NaOH溶液中分别通入了氧气和氩气.实验结果表明,在常规的NaOH织构过程中加入氧化剂有助于减小金字塔的尺寸.由于NaClO溶液自身既具有碱性,又具有氧化性,织构时不需要额外地加入氧化剂.与常规织构所用的NaOH溶液相比,NaClO溶液更易得到小而分布均匀的金字塔绒面,更适用于太阳电池的制备.     

石英衬底上大晶粒多晶Si薄膜的制备与结构表征

利用高频感应加热化学气相沉积工艺,以H2稀释的SiH4作为反应气体源,在未抛光的粗糙石英衬底上直接沉积制备了具有均匀分布的大晶粒多晶Si膜.采用扫描电子显微镜、X射线衍射和可见-紫外分光光度计等检测手段,测量和分析了沉积膜层的表面形貌、晶粒尺寸、择优取向与光反射等特性.结果表明,多晶Si膜中Si晶粒的尺寸大小和密度分布不仅与工艺参数有关,而且强烈依赖于衬底的表面状况.1000℃下沉积薄膜的平均晶粒尺寸为～3μm,择优取向为<111>晶向.反射谱测量表明,920℃下制备薄膜的反射率比1000℃下制备的更低,最低值达18.4;,这应归功于前者具有更大的表面粗糙度.     

单晶硅低裂纹损伤切片加工技术研究进展

单晶硅晶圆衬底的直径增大、厚度减薄和集成电路(IC)制程减小是集成电路领域主流发展趋势。随着集成电路制程减小至5 nm,对单晶硅晶圆衬底质量的要求越来越高。切片加工是晶圆衬底制造的第一道机械加工工序,金刚石线锯切片是大尺寸单晶硅切片加工的主要技术手段。本文介绍了金刚石线锯切片加工的发展趋势和面临的挑战,阐述了以单晶硅刻划加工研究为基础的金刚石线锯切片加工材料去除机制和电镀金刚石线锯三维形貌建模技术,总结了单晶硅切片加工的晶片表面创成机制和裂纹损伤产生机制,展望了单晶硅低裂纹损伤切片加工的工艺措施,指出了单晶硅切片加工技术的发展趋势,对集成电路制造技术的发展具有一定的指导意义。     

十二烷基苯磺酸钠与聚乙烯吡咯烷酮复配表面活性剂对单晶硅制绒的影响

本文采用十二烷基苯磺酸钠(SDBS)与聚乙烯吡咯烷酮(PVP)的复配溶液作为单晶硅制绒添加剂,取代目前常用碱醇制绒液中的异丙醇,不仅降低了绒面的反射率、缩短了制绒时间,而且具有成本低、制绒过程中不需要定时补充等特点。本文研究了SDBS与PVP复配添加剂的比例、浓度、反应时间、反应温度等对单晶硅制绒效果的影响,实验发现当SDBS与PVP的混合体积比为1∶4、复配添加剂的浓度为0.26%(质量分数)、制绒温度为80 ℃、制绒时间为15 min时,在400~1 000 nm波长范围内的平均反射率为9.8%。与传统的碱醇制绒液相比,SDBS与PVP复配添加剂的制绒时间缩短了25 min,反射率降低约2%,是一种非常有发展潜力的产业化单晶硅制绒添加剂。     

Future directions for higher-efficiency HIT solar cells using a Thin Silicon Wafer

To reduce the power generation cost of heterojunction with intrinsic thin layer (HIT) solar cells, it is necessary to use a thinner crystalline silicon wafer, as well as to improve the conversion efficiency. We have experimentally confirmed that V_OC of the HIT solar cell increases with decreasing the wafer thickness, and can reach a very high V_OC of 747 mV with a 58-μm-thick wafer owing to a sufficiently low surface recombination velocity. We also indicate the future directions for improving the efficiency. The uniformization of the texture size of the silicon surface and reduction of the carrier density in TCO film while maintaining an equal or lower conductivity are effective for improving the optical confinement.     

X-ray reflectivity studies of very thin films of silicon oxide and silicon oxide–silicon nitride stacked structures

Oxide/nitride/oxide films were deposited onto bare silicon substrates by low-pressure chemical vapor deposition (LPCVD) of silicon nitride and thermal oxidation. The X-ray reflectivity technique has been used to study the influence of the growth conditions and of different cleaning procedures of the silicon substrate on the structure and morphology of the deposited multilayers. The results revealed how, from an analysis of the X-ray reflectivity data performed by using Fresnel equations for multilayers modified to account for the interface imperfections, we determine, in a non-destructive manner, structural parameters such as density, thickness, roughness, and interface structure of the whole dielectric layers, giving us more information and greater sensitivity respect to cross-section transmission electron microscopy (TEM) and ellipsometric measurements.     

磁控溅射ZrN薄膜的生长机理及光学性能

利用直流反应磁控溅射法在Si衬底上沉积了高结晶质量的氮化锆(ZrN)薄膜。采用X射线衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)、原子力显微镜(AFM)和光谱椭偏仪(SE)研究了沉积时间对ZrN薄膜结构、表面形貌和光学性能的影响。结果表明:所沉积薄膜均为NaCl结构的立方相ZrN,具有(111)面单一取向;沉积时间的增加提高了薄膜的结晶质量;ZrN薄膜的表面形貌、晶粒尺寸以及表面粗糙度随沉积时间发生变化,沉积45 min的薄膜表面出现致密的三角锥晶粒,且表面粗糙度最大,薄膜呈柱状生长。随后利用Extend Structure Zone Model解释了ZrN薄膜的生长机制,最后研究了ZrN薄膜的光反射特性,发现反射光谱与晶粒形状和表面粗糙度密切相关,表面具有三角锥状晶粒的薄膜,其反射谱在300~800 nm波长范围内存在振荡现象,相比于具有不规则晶粒形貌的薄膜其反射率明显下降。本文中研究的生长条件与晶体结构、微观形貌和光学性能之间的关系,可为器件中应用的ZrN薄膜最佳制备条件的优化提供重要的参考价值。     

Optimisation of low-temperature silicon epitaxy on seeded glass substrates by ion-assisted deposition

Using single crystalline Si wafer substrates, ion-assisted deposition (IAD) has recently been shown [J. Crystal Growth 268 (2004) 41] to be capable of high-quality high-rate epitaxial Si growth in a non-ultra-high vacuum (non-UHV) environment at low temperatures of about 600 °C. In the present work the non-UHV IAD method is applied to planar borosilicate glass substrates featuring a polycrystalline silicon seed layer and carefully optimised. Using thin-film solar cells as test vehicle, the best trade-off between various contamination-related processes (seed layer surface as well as bulk contamination) is determined. In the optimised IAD process, the temperature of the glass substrate remains below 600 °C. The as-grown Si material is found to respond well to post-growth treatments (rapid thermal annealing, hydrogenation), enabling respectable open-circuit voltages of up to 420 mV under 1-Sun illumination. This proves that the non-UHV IAD method is capable of achieving device-grade polycrystalline silicon material on seeded borosilicate glass substrates.     

High performance deep red AlAs/AlGaAs top-emitting VCSELs grown by MOVPE at high growth rates

Top-emitting Alas/AlGaAs vertical cavity surface emitting lasers emitting at 765 nm with minimum threshold currents of 0.6 mA and threshold voltages of 1.9 V have been grown by MOVPE. In order to keep the growth time low, we investigated the possibility to grow these structures at growth rates of 5 μm/h. Special attention was paid to the homogeneity that can be achieved over a 2″ wafer under these growth conditions. Spatially resolved reflectivity measurements on GaAs/AlAs distributed Bragg reflectors showed, that the growth rate varies less than 0.3% in the center of the wafer and decreases by 1% at the wafer edge.     

Structure of Polycrystalline Cu Films as Solar Selective Coatings

Copper thin films (5–150 nm) were prepared by vacuum deposition with different rates (0.7, 1.5 and 3 nm/s). The position, intensity and profile of X-ray diffraction lines were analysed to study the phases, the crystallographic preferred orientation as well as the residual strain and crystallite size. The fcc polycrystalline Cu phase was revealed and no oxide phases were identified. The films were highly oriented with 〈111〉 fiber texture. The ratio of P₁₁₁/P₂₀₀ increased with the film thickness. Thus, in case of amorphous substrate, the type of the crystallographic texture of a film depends mainly on the structure of the deposited material. The crystallite size increases while the residual strain decreases, as the film thickness or the deposition rate is increased. The crystallite size was very small compared with the film thickness. The effect of deposition rate was pronounced specially from 0.7 to 1.5 nm/s.     

Epitaxial films of metals from the platinum group (Ir,Rh, Pt and Ru) on YSZ-buffered Si(1 1 1)

In the present work we have grown twin-free single crystal metal films of iridium (Ir), rhodium (Rh), platinum (Pt) and ruthenium (Ru) on silicon (1 1 1) substrates via an yttria-stabilized zirconia (YSZ) buffer layer. A prerequisite for the realisation of heteroepitaxial metal films without additional texture components was the twin-free deposition of the YSZ films by pulsed laser deposition (PLD). For the metal films on top, a novel two-step growth process was applied with an extremely low deposition rate for the first 20 nm. For all metals, a drastic texture improvement by up to a factor of 9 could be observed compared to the oxide buffer layer. Minimum values were 0.18° (Ir) and 0.12° (Rh) for tilt and twist, respectively. For all four metals investigated, twin-free epitaxial films could be grown on YSZ/Si(1 1 1) whereas the twinning problem for platinum films was solved by decoupling the Pt-YSZ interface via an additional iridium interlayer. The grown metal/YSZ/Si(1 1 1) multilayer samples offer the possibility to integrate a variety of interesting nanostructures and functional materials on silicon. They are now available in 4 in wafer size.     

Polycrystalline silicon carbide film deposition using monomethylsilane and hydrogen chloride gases

A polycrystalline silicon carbide film is formed on a silicon surface by chemical vapor deposition using monomethylsilane gas along with hydrogen chloride gas in ambient hydrogen at atmospheric pressure. The film deposition is performed near 1000 K, at which temperature the monomethylsilane maintains a chemical bond between the silicon and carbon present in the molecular structure. The excess amount of silicon on the film surface is reduced using the hydrogen chloride gas. Although the film deposition stops within 1 min after beginning the supply of the monomethylsilane gas and hydrogen chloride gas, annealing at 1273 K in ambient hydrogen after the film deposition allows further deposition so that a thick silicon carbide film can be obtained.