n型SiC的Ni基欧姆接触中C空位作用的实验证明

通过在Si面p型4H-SiC外延层上使用P 离子注入来形成n阱.Ti和Ni依次淀积在有源区的表面,金属化退火后的XRD分析结果表明Ni2Si是主要的合金相.XEDS的结果表明在Ni2Si/SiC界面处存在一层无定型C.去除Ni2Si合金相与无定型C之后重新淀积金属,不经退火即可形成欧姆接触.同时,注入层的方块电阻Rsh从975下降到438Ω/□.结果表明,合金化退火过程中形成了起施主作用的C空位(VC).C空位提高了有效载流子浓度并对最终形成欧姆接触起到了重要作用.     

N型SiC的Ni基欧姆接触研究

对n型SiC的Ni基欧姆接触的机理进行了研究.通过在P型4H-SiC外延层上使用N离子注入来形成N阱,并在此基础上制作Ni/n型SiC欧姆接触的TLM结构,得到的比接触电阻约为1.7X10-4Ω·cm2.合金化的高温退火过程导致了C空位(Vc)的出现,起到了施主的作用,降低了有效肖特基势垒高度,从而形成欧姆接触.通过模拟估计了有效载流子密度的增加,结果表明,高温退火中形成的C空位对于最终欧姆接触的形成起到了重要作用,甚至超过了掺杂水平的影响.     

Ni基n型SiC材料的欧姆接触机理及模型研究

研究了Ni基n型SiC材料的欧姆接触的形成机理,认为合金化退火过程中形成的C空位(Vc)而导致的高载流子浓度层对欧姆接触的形成起了关键作用。给出了欧姆接触的能带结构图,提出比接触电阻ρC由ρC1和ρC2两部分构成。ρC1是Ni硅化物与其下在合金化退火过程中形成的高载流子浓度层间的比接触电阻,ρC2则由高载流子浓度层与原来SiC有源层之间载流子浓度差形成的势垒引入。该模型较好地解释了n型SiC欧姆接触的实验结果,并从衬底的掺杂水平、接触金属的选择、合金化退火的温度、时间、氛围等方面给出了工艺条件的改进建议。     

Co/C/4H-SiC欧姆接触特性的研究

研究了Co/4H-SiC结构的电学特性。通过直流溅射的方式在金属Co 薄膜 与SiC之间淀积了一层碳薄膜,极大地改善了欧姆特性。采用两步快速退火工艺,即500 °C 退火 10 分钟 再 1050 °C 退火 3 分钟,形成了良好的欧姆接触,接触电阻率为2.30×10-6 Ω.cm2。X射线衍射（XRD）分析表明高温退火后Co基金属接触层中的硅化物更加稳定,接触层下形成的富碳层有效地降低了电子输运的势垒高度,对欧姆接触的形成起了关键作用。通过对Au/Co/C/SiC 欧姆接触的热稳定性测试,结果表明经过500oC下20小时的热测试,掺杂浓度为2.8×1018 cm-3的 n型4H-SiC保持了良好的欧姆特性。     

高能量钒注入n型4H-SiC的欧姆接触形成

借助二次离子质谱法分析了注入的钒离子在碳化硅中的分布.即使经过1650℃的高温退火,钒在碳化硅中的再扩散也不显著.退火并没有导致明显的钒向碳化硅表面扩散形成堆积的现象,由于缺少钒的补偿作用,表面薄层的自由载流子浓度保持不变.采用线性传输线模型测量了钒注入n型4H-SiC上的Ni基接触电阻,在1050℃下,在氮、氢混合气体中退火10min,形成的最低比接触电阻为4.4×10-3Ω·cm2.金属化退火后的XRD分析结果表明,镍、碳化硅界面处形成了Ni2Si和石墨相.观测到的石墨相是由于退火导致C原子外扩散并堆积形成,同时在碳化硅表面形成C空位.C空位可以提高有效载流子浓度,降低势垒高度并减小耗尽层宽度,对最终形成欧姆接触起到了关键作用.     

高能量钒注入n型4H-SiC的欧姆接触形成

借助二次离子质谱法分析了注入的钒离子在碳化硅中的分布.即使经过1650℃的高温退火,钒在碳化硅中的再扩散也不显著.退火并没有导致明显的钒向碳化硅表面扩散形成堆积的现象,由于缺少钒的补偿作用,表面薄层的自由载流子浓度保持不变.采用线性传输线模型测量了钒注入n型4H-SiC上的Ni基接触电阻,在1050℃下,在氮、氢混合气体中退火10min,形成的最低比接触电阻为4.4×10-3Ω·cm2.金属化退火后的XRD分析结果表明,镍、碳化硅界面处形成了Ni2Si和石墨相.观测到的石墨相是由于退火导致C原子外扩散并堆积形成,同时在碳化硅表面形成C空位.C空位可以提高有效载流子浓度,降低势垒高度并减小耗尽层宽度,对最终形成欧姆接触起到了关键作用.     

Ti/Al/Ni/Au金属体系在N-polar GaN上的欧姆接触特性

利用金属有机化合物化学气相淀积(MOCVD)在SiC衬底上外延生长了N-polar GaN材料,采用传输线模型(TLM)分析了Ti/Al/Ni/Au金属体系在N-polar GaN上的欧姆接触特性.结果表明,Ti/Al/Ni/Au (20/60/10/50 nm)在N-polar GaN上可形成比接触电阻率为2.2×10-3Ω·cm2的非合金欧姆接触,当退火温度升至200℃,比接触电阻率降为1.44×10-3 Ω·cm2,随着退火温度的进一步上升,Ga原子外逸导致欧姆接触退化为肖特基接触.     

n型4H-SiC上Ni/Pt和Ti/Pt欧姆接触(英文)

研究了Ni/Pt和Ti/Pt金属在n型4H-SiC上的欧姆接触。在1 020℃退火后,Ni/Pt与n型4H-SiC欧姆接触的比接触电阻为2.2×10-6Ω·cm2。Ti/Pt与n型4H-SiC欧姆接触的比接触电阻为5.4×10-6Ω·cm2,退火温度为1 050℃。虽然Ni的功函数比Ti的功函数高,但是Ni比Ti更容易与n型4H-SiC形成欧姆接触。使用能谱分析仪(EDX)分析了Ni/Pt和Ti/Pt金属与4HSiC接触面的元素,观察到C原子相对于Pt原子的原子数分数随退火温度的变化而不同。实验验证了在n型4H-SiC中退火导致的碳空位起施主作用是有利于欧姆接触形成的主要原因。     

Ni/Au与p-GaN的比接触电阻率测量

通过采用环形传输线方法(CILM),电流-电压(I-V)曲线、表面形貌等方法,研究不同的Ni/Au厚度比和空气气氛下合金退火温度对p型氮化镓欧姆接触特性造成的影响。根据Ni/Au与p型氮化镓欧姆接触的形成机制,采用合适的Ni/Au厚度比及退火温度,得到比接触电阻率(ρc)为1.09×10-5Ω.cm2的Ni/Au-p-GaN电极,并分析了Ni在退火过程中对形成良好的欧姆接触中所起到的作用。     

台面型InP/InGaAs PIN光伏探测器的p-InP低阻欧姆接触

研究了电子束蒸发淀积的非合金膜系Au/Pt/Ti/p-InP(2×1018cm-3)接触的物理特性,通过450℃、4 min的快速退火,获得了欧姆接触,其比接触电阻为7.3×10-5 Wcm2.接触电极退火后,采用离子溅射法淀积加厚电极Cr/Au.利用俄歇电子能谱(AES)进行深度剖面分析,表明Pt层能够相对有效地阻挡...     

nc-SiC/SiO_2镶嵌薄膜材料的制备、结构和发光特性

采用二氧化硅/碳化硅复合靶,用射频磁控共溅射技术和后高温退火的方法在Si(111)衬底上制备了碳化硅纳米颗粒/二氧化硅基质(nc-SiC/SiO2)镶嵌结构薄膜材料。用X射线衍射(XRD),傅里叶红外吸收(FTIR),扫描电子显微镜(SEM)和光致发光(PL)实验分析了薄膜的微结构以及光致发光特性。实验结果表明,样品薄膜经高温退火后,部分无定形SiC发生晶化,形成β-SiC纳米颗粒而较均匀地镶嵌在SiO2基质中。以280nm波长光激发薄膜表面,有较强的365nm的紫外光发射以及458nm和490nm处的蓝光发射,其发光强度随退火温度的升高显著增强,发光归结为薄膜中与Si—O相关的缺陷形成的发光中心。     

Investigation of Co/SiC interface reaction

Interface reaction, phase transition, and composition were investigated for Co thin films on amorphous SiC films as a function of heat treatment (600～1000°C). Amorphous SiC layers were grown on (001) Si substrate by magnetron sputter deposition. The SiC layers had a 1:1 stoichiometric ratio of Si to C and an amorphous structure containing microcrystals. The interface reaction between a sputter-deposited Co (250Å thick) and amorphous SiC (2000Å thick) layer on a (001) Si substrate induced by vacuum annealing at temperatures of 600–1000°C was examined. Co₂Si was formed at 700°C as the first crystalline phase and CoSi at 800°C as the final stable phase of the Co/SiC interface reaction. This phase sequence of Co₂Si→CoSi was interpreted in terms of the effective heat of formation and the calculated ternary Co-Si-C phase diagram, and it was consistent with the experimental results. The high formation temperature of the first crystalline Co₂Si phase and no formation of a final stable CoSi₂ phase are discussed in comparison with Co/Si interface reaction and related to the binding energy of the reacting materials. In addition, the behavior of free carbon remaining after the Co/SiC reaction was investigated. This free carbon moved to the top of the reacted cobalt silicide/SiC layer.     

Characteristics of Ni/SiC Schottky diodes grown by ICP-CVD

A Ni/SiC Schottky diode was fabricated with an α-SiC thin film grown by the inductively coupled plasma chemical vapor deposition, ICP-CVD method on a (1 1 1) Si wafer. The α-SiC film was grown on a carbonized Si layer that the Si surface had been chemically converted to a very thin SiC layer by the ICP-CVD method at 700 °C. To reduce defects between the Si and α-SiC, the surface of the Si wafer is slightly carbonized. The film characteristics of α-SiC were investigated by employing TEM and FT-IR. A sputtered Ni thin film was used for the anode metal. The boundary status of the Ni/SiC contact was investigated by AES as a function of annealing temperature. It is shown that the ohmic contact could be acquired below 1000 °C annealing temperature. The forward voltage drop of the Ni/α-SiC Schottky diode is 1.0 V at 100 A/cm². The breakdown voltage is 545 V which is five times larger than the ideal breakdown voltage of a silicon device. Also, the dependence of barrier height on temperature was observed.     

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。     

Granular Films for Use as Thin-Film Resistors

Abstact  In this paper we discuss thin-film electrical resistors utilizing granular films of the type (Co,Ni)-(Al,Si)-O and their electrical resistive properties. Resistive properties of the granular film resistors drastically change with metal content and after annealing at 450°C. The values of temperature coefficient of resistance (TCR) in the optimum metal content of the granular films were as low as those of conventional metallic alloy film resistors. The values of sheet resistance were much higher than those of conventional metallic alloy resistors. Therefore, granular films are useful for application to thin-film resistors with the goal of miniaturizing them.     

Interface reaction between Ni and amorphous SiC

A Ni/amorphous SiC (a-SiC) multilayered sample was prepared by ion-beam sputtering and was used as a model system to study the stability of metal contacts with a-SiC against interface reactions. The diffusion of Ni into the a-SiC layer as well as Si and C into the Ni layer takes place concurrently during the annealing process. An intermediate NiSi phase was identified in the Ni solution layer because of diffusion of Si and C resulting from the decomposition of a-SiC. A phase selection diagram has been developed that accounts for nucleation of the NiSi phase from the Ni solution layer.     

Carbon structural transitions and ohmic contacts on 4H-SiC

The structural properties of sputtered carbon films on SiC are investigated using X-ray photoelectron spectroscopy (XPS) and Raman scattering. The as-deposited films are amorphous with an sp²/sp³ ratio of 1. The sp² carbon structures gradually increase with increasing temperatures and consist of amorphous aromatic-like carbon, polyene-like carbon, and nano-size graphite flakes. Schottky contacts on carbon/SiC are converted to ohmic contacts after annealing. The concentration of nano-graphitic flakes relative to the aromatic-like and polyene-like carbon increases nearly linearly with annealing temperature. Stacked graphitic structures are not observed. The specific contact resistivities are at 10⁻³–10⁻⁴Ωcm² on the carbon/SiC after annealing from 1050°C to 1350°C.     

工作压强和退火温度对SiC薄膜结构的影响

用双射频共溅射和溅射后退火的方法在单晶Si(111)衬底上制备了SiC薄膜。利用X射线衍射仪(XRD)、扫描电镜(SEM)及原子力显微镜(AFM)分析了样品的物相组成、形貌和结构。研究发现,此种方法制备得到8H-SiC薄膜,在1.5～3Pa时增大工作压强有利于SiC薄膜退火之后结晶,同时薄膜沉积速率降低,使生长变致密,粗糙度减小,薄膜表面趋于平滑。对SiC薄膜进行850、1000、1150℃退火,结果表明,适当升高退火温度有利于提高薄膜的结晶质量和晶化程度,提高薄膜的致密度,降低薄膜中的缺陷密度。     

Infrared spectroscopy and transmission electron microscopy of polycrystalline silicon carbide

The polycrystalline structure of silicon carbide was investigated by infrared spectroscopy and transmission electron microscopy (TEM). The films were obtained by annealing in the temperature range 950–1250°C of amorphous silicon carbide films deposited on a silicon substrate by PECVD. The broad absorption band at around 750 cm⁻¹ in the infrared spectrum of amorphous material after annealing at high temperature changes from a Gaussian to a Lorentzian shape, corresponding to the transition from an amorphous to a polycrystalline phase. The SiC peak becomes sharper with increasing the annealing temperature, this effect being related to the growth of crystalline grains. TEM microscopy indicates that the crystallisation occurs homogeneously in the films and the diffraction pattern shows that the film crystallises into cubic 3C–SiC. The distribution of polycrystalline grains as determined by TEM evidences an increase of the grain size with increasing the annealing temperature. A correlation between infrared peak width and mean grain radius has been found.     

金属诱导非晶硅薄膜低温晶化

介绍了一种非晶硅 (a- Si)薄膜低温晶化的新工艺 :金属诱导非晶硅薄膜低温晶化。研究了各种 a- Si/金属双层膜退火后的晶化情况。利用 X射线衍射分析了结晶硅膜的结构 ,通过光学显微镜观察了 Al诱导 a- Si薄膜晶化后的表面形貌 ,并初步探讨了金属诱导非晶硅薄膜低温晶化的机理