光伏法研究硅单晶表面态真空敏感机理

根据光伏方法研究的半导体表面气体分子吸附机理,提出了硅单晶表面态真空敏感效应的机理模型,解释了表面态敏感型的真空传感器的各有关观测结果.因此可以确认,硅单晶表面态对真空敏感的实质原因就是由于构成大气主要成份的氮气和氧气两种元素的电子亲和势相对于硅元素,具有明显不同的且符号相反的差值,导致吸附于硅表面的N2、O2分子与硅表面态之间不同转移方向的电荷转移差值可以随真空度变化所引起的.     

TMAH+Triton中Si湿法腐蚀机理研究现状

在微机电系统(MEMS)领域硅各向异性湿法腐蚀是制作许多元器件的一项重要技术,加入非离子型表面活性剂的腐蚀液可以在硅基片上制作出各种形状,但是对于真正的腐蚀机理还有待进一步研究。介绍了硅湿法腐蚀机理的研究现状,通过不同腐蚀条件下得出的不同腐蚀结果分析其腐蚀机理。介绍了当非离子型表面活性剂加入碱性溶液时固体表面的活性剂吸附层结构,重点介绍了表面活性剂Triton X-100加入各向异性碱性腐蚀剂四甲基氢氧化铵(TMAH)后对活性剂吸附状态和硅腐蚀速率产生影响的根本原因。不同晶向硅表面的H基和OH基数量会影响其表面活性剂的吸附能力,硅在纯TMAH腐蚀液和加入活性剂Triton后的TMAH腐蚀液中的腐蚀速率存在一定差异,高质量分数的TMAH下加入不同体积分数的Triton时,不同晶面在活性剂吸附和腐蚀速率上也存在不同,给出了出现这些现象的机理分析。研究硅腐蚀机理可以为器件设计提供有效的理论支持,有助于制作更多新的MEMS结构。     

氢吸附开口碳纳米管场发射密度泛函研究(英文)

利用第一性原理密度泛函的方法对氢分子吸附开口碳纳米管的场发射性质进行了综合研究,建立了(5,5)开口碳纳米管吸附不同氢分子数量的吸附模型,并对加电场和未加电场下的模型进行了吸附能、最高占有分子轨道-最低未占分子轨道(HOMO-LUMO)帯隙及诱导偶极矩的计算和分析。计算结果表明吸附能随着电场的增加而变大,吸附稳定性增强。吸附氢分子的碳纳米管在施加外电场后,HOMO-LUMO帯隙明显减小,费米能级附近的局域态密度随着氢分子的吸附而增加。氢分子对碳纳米管的吸附可以在其尖端表面产生诱导偶极矩,导致电荷由碳纳米管向氢分子大量转移,从而驱使电子由碳纳米管尖端发射到真空中,提高了碳纳米管的场发射性能。     

Al掺杂硅烯材料吸附气体分子的第一性原理研究

通过Al原子吸附和取代的方法对硅烯材料进行掺杂,基于第一性原理计算方法研究了Al掺杂硅烯材料的吸附特性,分析H₂、SO₂和NH₃气体分子在其表面的吸附过程。研究发现,Al吸附硅烯体系由于强的物理吸附对H₂敏感,吸附能为-0.51 eV;SO₂和NH₃以成键的方式吸附在两种掺杂材料上,其中Al取代硅烯体系吸附SO₂后打开了0.3 eV的带隙,吸附能为-1.19 eV;Al吸附硅烯体系吸附SO₂后带隙缩小,吸附NH₃后带隙增大,吸附能分别为-1.01和-0.96 eV。结果表明,Al原子的吸附和取代提高了硅烯材料的吸附性能,为研究Al掺杂硅烯材料的储氢和气敏性能提供理论参考。     

硅中注入高剂量氮离子的研究

研究了高剂量氮离子注入硅所形成的高阻层.对该层的研究将有助于使离子注入技术应用于半导体集成电路的隔离工艺. 选用电阻率为0.5Ω-cm,<111>取向的N型硅单晶片作衬底.氮离子注入能量为80keV,注入剂量用1～2×10~(17)cm~(-2),注入后表面可以形成高阻层.这一层的物理、化学、电学性能均较稳定. 用俄歇电子谱仪、背散射沟道技术、红外光谱仪、光电子谱仪等手段对该层的晶体结构及化学键合机理进行了分析.所得结果证明,注入的氮呈高斯分布,该注入层是无序的氮化硅与硅的混合结构. 用8～10Ω-cm的P型硅单晶也可以得到同样的结果.     

激光光声振动谱研究表面吸附

报道在超真空系统中利用激光光声振动谱研究表面吸附的实验结果。通过振动谱在高背景气压下的可逆物理吸附及位相甄别法研究NH_3分子双层吸附生长机理等实例,展示出激光光声谱是一种较理想的表面吸附研究手段。     

Si(100)和Si(111)衬底上的同质分子束外延

用超高真空电子束蒸发系统进行了硅的同质分子束外延.发现采用适当的表面化学处理方法,然后在超高真空中加热,可以在较低温度下(800—814℃)获得清洁和平整的有序表面.Si(100)和Si(111)的外延分别在520℃和714℃进行,外延膜的结构和电学特性良好.     

硅片化学清洗中染色现象的成因

引言 在以硅单晶为基础材料的半导体器件制造过程中,每当用HF去除硅表面SiO_2。层或用HF-HNO_3溶液对硅片进行化学清洗时,硅表面往往会发生染色的异常现象(有人称它为腐蚀花班、着色膜或掩膜)。尽管染色硅膜是在许多不同的偶然机遇中生成的,但多数都表现出不易受HF腐蚀的特点。因此,染色硅膜一旦在硅表面形成,就很难去除。它的存在不仅可以起到掩蔽扩散的作用,还可以造成电极接触不良,严重的可以导致整批硅片报废,直接影响产品合格率和工艺参数的控制,对器件生产危害很大。     

Si(111)面氟吸附的研究

本文先用集团模型和电荷自治的EHT方法研究了Ⅶ族元素F在 Si(111)面的化学吸附,利用能量极小原理确定了化学吸附位置;在此基础上,采用薄片(SLAB)模型和EHT经验紧束缚方法对吸附体系的电子结构作了计算.计算结果表明,F可以吸附在Si(111)面的顶位和三度空位上,但以顶位为更稳状态.顶位吸附时,F与表面的距离为1.53A,吸附能为4.7eV;三度位吸附时,F与表面的距离为-2.2A,吸附能为3.1eV.吸附后,F对总态密度和能带的贡献主要局域在真空能级下-17eV～-19eV之间.此外,顶位吸附使原清洁表面悬键引起的表面态消失.     

真空科学中表面吸附的位势理论的研究

从分子之间的作用力和分子之间相互作用的能量的角度对真空科学中表面吸附的位势理论进行了理论研究，并深入地探讨了固体表面吸附的气体分子层对气体的吸附与脱附的影响。     

Application of liquid phase deposited silicon dioxide tometal-oxide-semiconductor capacitor and amorphous silicon thin-filmtransistor

Liquid phase deposited silicon dioxide (LPD-SiO₂) is applied to crystalline Si metal-oxide-semiconductor (MOS) capacitor as the gate insulator. It is demonstrated that slow states exist at the Si/SiO₂ interface which cause hysteresis in the capacitance-voltage (C-V) characteristics. These slow states can be removed effectively by post-metallization-anneal. By means of C-V measurement and infrared absorption spectroscopy, it is concluded that the slow states are originated from the residual water or hydroxyl molecules in LPD-SiO₂. The LPD-SiO₂ is also applied to fabricate amorphous silicon (a-Si:H) thin film transistor (TFT) based on a new self-aligned process. The performance of this device is comparable to those of thin film transistors employed other kinds of SiO₂, i.e., thermal, plasma, vacuum evaporation, etc., as the gate insulator. The bias-stress measurement shows that the threshold voltage shift is dominated by charge trapping in the gate insulator     

锐钛矿型TiO2(101)面吸附CO2分子的光学气敏传感机理

对金属氧化物光学气敏传感材料TiO2的探索与应用是当前研究的热点问题。采用基于密度泛函理论(DFT)中的平面波超软赝势方法, 模拟计算CO2分子在锐钛矿型TiO2(101)表面的吸附行为, 对吸附能, 吸附距离, 电子态密度以及光学性质进行分析。结果表明: CO2分子在含O空位表面的吸附效果优于无氧空位表面, 且表面O空位的浓度越高, 吸附效果越明显;分子平行于表面放置模型的吸附能为正值, 吸附后的结构稳定, 且以O端吸附为主, 为此, 分子平行于表面放置O端吸附于含两个O空位表面为最可能吸附模型;对电子态密度分析发现, 当最佳模型吸附稳定后, 含O空位表面为P型杂质, 又有CO2分子中的2p电子掺入, 在费米能级附近出现新峰值, 改善了TiO2材料的光学性质, 体现出较好的光学气敏传感特性。     

Enhanced diffusion and improved device performance using dual spectral source rapid thermal processing

In this study, we used a vacuum ultraviolet (VUV) radiation source in conjunction with tungsten halogen lamps based rapid thermal processing (RTP) system. The two light sources were arranged in different configurations to study the phosphorus diffusion in silicon. The high energy VUV photons in conjunction with infrared and visible photons resulted in enhanced diffusion and improved the bulk properties of silicon substrate. An improvement in the leakage currents of the diodes made from VUV irradiated wafers is observed. A qualitative explanation of the results based on the role of high energy photons in RTP is presented. High energy photons from VUV region to about 800 nm results in a decrease in the bond dissociation energies of the molecules, since they are in electronic excited states. Higher activation of dopants and reduction in activation energies is observed. The minority carrier lifetime measurements show that there is an enhanced phosphorus gettering and overall reduction of the recombination-generation centers in silicon.     

Aluminium Schottky barriers on sputter-etched silicon

Schottky barriers have been prepared by sputter-etching a silicon surface immediately prior to the deposition, by sputtering, of an aluminium electrode. The barrier height measured on these diodes is nearly identical to the height found previously for barriers made by cleaving silicon in a vacuum in a stream of evaporating aluminium species. This suggests that the barrier height is controlled by surface states.     

Theory of emission noise from silicon field emitters

A calculation is made of the spectral density of emission fluctuations for silicon emitter tips for two emission mechanisms: emission mainly from surface states, and emission mainly from the conduction band edge. In both cases surface-state occupancy fluctuations, calculated from the generalized Nyquist formula, modulate the field emission current. The basic idea is that emission is likely to come from either surface states or from carriers in the conduction band, or both. If there are generation-recombination (G-R) fluctuations in the surface states at the emission surface, then there will be corresponding fluctuations from surface states. This G-R noise will also cause fluctuation in carrier concentrations in the emission area, and hence noise in emission from the conduction band. A discussion is given of whether the differing spectral densities for these two mechanisms may be compared with measurements to clarify which mechanism is dominant     

真空高温脱O引起Si图形衬底形态变化的研究

利用超高真空化学气相淀积(UHV/CVD)系统,在不同的温度、环境氛围及脱O过程参与等条件下对全息法制备的二维周期图形Si衬底进行退火,通过原子力显微镜(AFM)进行表征与分析,研究真空高温脱O过程对图形衬底表面形态变化的影响。结果表明,真空环境使衬底表面的Si原子可以自由运动,脱O过程增强了Si原子在表面的迁移,温度会影响Si原子的扩散速率,3个因素的共同作用导致图形深度变浅,侧壁坡度变缓。此外,在周期图形台面的边缘,观察到环形有序分布的纳米Si岛。     

热丝法制备硅纳晶颗粒及其发光性质

利用热丝化学气相沉积法,在真空腔中通过选择设定不同加热功率的热丝热解硅烷制备出一系列不同颗粒尺寸的硅纳米颗粒样品。透射电镜分析表明硅纳米颗粒具有结晶良好的纳晶结构。通过自然氧化钝化硅纳米颗粒表面,消除表面悬键的影响,使得硅颗粒具有高效的光致发光特性,发光范围在红光到近红外区,发光特性与量子限域效应相吻合。发光寿命测量表明所制备的硅颗粒的发光寿命在微秒量级,并且通过比较不同硅颗粒分布样品中相同发光波长衰减寿命的差异,揭示了所制备样品中硅纳米颗粒之间存在耦合作用。     

Influence of heat treatments and ionizing irradiations on the charge distribution and the number of surface states in the Si-SiO2system

The number of surface states present at an oxidized silicon surface is generally much larger when oxidation or further heat treatment has been carried out in a dry than in a wet environment. Especially at low temperatures (400-600°C) water very much tends to cause their disappearance. As hydrogen acts in a similar way, the effect seems to be due to a reaction of centers (probably unsaturated silicon bonds) with hydrogen, so that they are no longer able to capture holes or electrons. The hydrogen may also be evolved during the reaction of an Al-electrode on top of the oxide with hydroxyl or water. Irradiation of oxidized silicon by X-rays or ultraviolet light can cause charge redistributions, which may be accompanied by the formation of new centers. The latter effect is most pronounced when hydroxyl groups can be supposed to occur in the oxide. In these cases the irradiation may cause a disappearance of n-type inversion on p-type silicon, especially when X-ray irradiation is followed by ultraviolet (u. v.) illumination. Irradiation experiments have been used to detect differences in Si-SiO2systems in cases where direct electrical measurements failed.     

PECVD制备纳米晶多晶硅薄膜

以Si(100)为衬底,采用磁控溅射和射频等离子体增强化学气相沉积系统制备了Si(100)/Al膜/非晶Si膜结构的样品。对该样品进行Al诱导真空退火以制备多晶硅薄膜,采用X射线衍射仪(XRD)和AFM分析薄膜微结构及表面形貌。实验结果表明,在经过500℃、550℃Al诱导退火后,形成了择优取向为〈111〉晶向的多晶硅薄膜。AFM给出了550℃退火后薄膜表面形貌,为100～200nm大小的圆丘状硅晶粒,密集排列在薄膜表面;并对Al诱导真空退火晶化的机理进行了分析。     

真空环境下飞秒激光制备的微构造硅的吸收和退火特性

在真空环境下利用飞秒激光制备的黑硅材料,其形貌与SF6气氛中制备的黑硅材料有着很大的区别。为了研究这种真空环境下制备的微构造硅的相关光学特性,通过改变入射脉冲能量研究其峰值变化以及吸收特性,发现当峰值达到一定高度时其对200~2 500 nm波段的光波有95%左右的吸收效率,这与SF6气氛中制备的微构造硅的吸收效率不相上下。最后对两种环境下制备的黑硅样品进行退火处理,发现真空环境下制备的黑硅材料比SF6气氛中制备的黑硅样品具有更好的耐退火性。这些结果对于利用真空环境下制备的微构造硅制作红外传感器具有重要意义。