硅器件工艺过程中晶体滑移位错的引入和演变

半导体材料硅中存在的原生晶体缺陷(如位错、层错、旋涡缺陷)及半导体硅器件加工工艺过程中的诱生晶体缺陷(如外延层错、热氧化杆状缺陷、扩散导致的缺陷)都会给器件带来有害的影响.为了揭示缺陷是如何影响材料的结构和器件的性能,人们必须设法观察缺陷的位错、形貌,并研究它们是如何引入和演变的. 我们在60kw旋转阳极X光机上,用X射线形貌技术[1]跟踪双极集成电路基本工艺──外延、氧化、扩散过程,观察晶体滑移位错的引入和演变,并研究了滑移位错与器件成品率之间的相关性.在这方面,国内外都有过很好的工作[2,4],现将我们的实验结果报告如…     

热应力作用降低LPE层中的位错

提出由温差造成热剪切应力,引起衬底穿线位错滑移,形成<110>界面位错,从而降低LPE层中位错的模型。稳定自然对流下的温度梯度液相外延,存在衬底厚度方向的温差,能在边缘固定的衬底中造成热剪切应力。生长了厚GaAs和Ga_1-xAl_xAs层(x<0.3),估算的热剪切应力大于产生<110>暗线缺陷的临界剪切应力。表面腐蚀坑观察表明,外延层位错密度下降,或无位错。界面蚀槽和阴极荧光观察表明,衬底穿线位错在界面弯曲成<110>界面位错。透射电子显微镜观察表明,界面位错多 关键词：     

硅基GaN微腔制作及其激射特性(特邀)

提出了一种新的Si衬底上GaN微盘谐振腔的制备方式,避免了传统Si基GaN器件中晶体质量较差以及外延层较厚对器件性能的影响.本工作中GaN的外延生长使用蓝宝石衬底,随后将外延层转移至硅衬底上进行微盘谐振腔的制备.外延生长时靠近衬底侧的GaN富缺陷层可使用减薄抛光的方式去除,并且通过简单湿法刻蚀二氧化硅牺牲层即可实现Ga...     

GaN薄膜拉曼散射光谱的研究

利用拉曼散射光谱对在SiC衬底上采用MOCVD异质外延的未故意掺杂GaN薄膜特性进行研究发现E2模式向频率低的方向漂移表明在GaN薄膜中存在张力,由于SiC衬底不平整度增加引起更多位错的出现,从而引起拉曼谱中E2模式的加宽,因此通过选择平整度较好的衬底可以减小缺陷密度,提高薄膜的质量,此外A1(LO)模式的出现与强度可以用来表征未掺杂GaN的薄膜质量。     

在6H-SiC衬底上用低压MOVPE法生长AlN和GaN的过程中用(AlN/GaN)多层缓冲层来控制残余应力

人们已提出用BAlGaN四元系材料制备紫外光谱区的光发射器件.GaN和AlN二元系是这种四元材料在器件应用中的基础材料.6H-SiC衬底在氮化物生长中因其晶格失配小是一大优势,而且SiC衬底的热膨胀系数也和AlN的很接近.然而,对于AlN外延层来说,需要控制其中的残余应力,因为在SiC衬底上直接生长的AlN外延层中存在着因晶格失配所产生的压缩应力.另一方面,在SiC衬底上直接生长的GaN外延层中存在着拉伸应力.这种拉伸应力起源于GaN比衬底有着更大的热膨胀系数.本文讨论了在6H-SiC衬底上生长的氮化物外延层中残余应力的类型、数量及控制.为此目的,提出了在6H-SiC衬底上,无论是生长AlN,还是生长GaN,都可以采用(GaN/AlN)多层缓冲层的办法,作为控制残余应力的有效方法.我们还讨论了AlN和GaN外延层的结晶质量和残余应力间的关系.     

晶体相场法模拟异质外延过程中界面形态演化与晶向倾侧

采用晶体相场模型研究了异质外延过程中失配应变与应力弛豫对外延层界面形态演化的影响, 并对由衬底倾角引起的外延层晶向倾侧进行了分析.研究结果表明: 在有一定倾角的衬底晶体上进行外延生长时,若衬底和外延层之间失配度较大 (ε>0.08),外延层中弹性畸变能会以失配位错的形式释放, 最终薄膜以稳定的流动台阶形式生长且外延层的晶向倾角与衬底倾角呈近似线性关系. 而当衬底和外延层之间失配度较小(ε<0.04)不足以形成失配位错时, 外延层中弹性畸变能会以表面能的形式释放,最终使薄膜以岛状形态生长. 在高过冷度条件下,衬底倾角和失配度较大时,衬底和外延层之间会形成由大量位错规则排列而成的小角度晶界从而显著改变外延层的生长位向.     

分子束外延生长GaN薄膜中的一种早期位错结构

利用高分辨电子显微术，对在GaP基体上由分子束外延生长六角GaN晶体薄膜中的晶体缺陷结构进行了研究．实验中发现了GaN薄膜外延生长过程中产生的一种典型早期刃型位错结构．此晶体缺陷位于一大块GaN晶粒内部，其外观类似于一段（1120）晶界．它由一条（1120）高能孤立晶界段及其两端的两个1/6［1120］不完全刃型位错组成．从大晶格失配材料之间分子束外延生长的机理上对这种缺陷结构的形成进行了解释． 关键词：     

斜切蓝宝石衬底MOCVD生长GaN薄膜的透射电镜研究

利用MOCVD技术在斜切角度为0.3°的c面蓝宝石衬底上生长了非故意掺杂 GaN 薄膜, 并采用透射电子显微镜对材料的质量和材料内部缺陷进行了分析. 研究发现斜切蓝宝石衬底上外延的GaN材料中,位错在距离衬底0.8 μm附近大量湮灭, 同时位错扎堆出现.基于上述现象, 提出了斜切衬底上GaN材料中位错的湮灭机制, 解释了斜切衬底能够提高GaN晶体质量的原因.     

硅片制备中的损伤问题

单晶硅是目前制造半导体器件、集成电路的最重要的基本材料.但是,利用硅单晶来制造器件,必须经过切片、磨片、抛光等多道工艺,把它加工成符合要求的单晶硅片.这些要求包括:表面高度平整光洁,几何尺寸均匀,有精确的晶向,表面无任何的微小损伤. 七十年代,硅材料方面的大量工作在于从科学上弄清材料的性能.对于材料缺陷的研究,也主要在于研究晶体生长时存在于晶体内的缺陷,即原生缺陷.随着对材料性能和器件工艺问题的深入研究,人们发现,在器件工艺过程中还会诱生大量的缺陷,即所谓二次缺陷如氧化层错、外延层错、位错等.这些缺陷的出现,一方面…     

金属有机物化学气相沉积同质外延GaN薄膜表面形貌的改善

为了获得高质量的GaN薄膜材料,研究了金属有机物气相沉积系统中GaN插入层对GaN衬底同质外延层表面宏观缺陷和晶体质量的影响.研究发现,插入层生长温度是影响GaN同质外延膜表面形貌和晶体质量的关键因素.由于生长模式与插入层生长温度相关,随着插入层生长温度的降低,外延膜生长模式由准台阶流模式转变为层状模式,GaN同质外延膜表面丘壑状宏观缺陷逐渐减少,但微观位错密度逐渐增大.通过对插入层温度和厚度的优化,进一步调控外延层的生长模式,最终有效降低了外延层表面的宏观缺陷,获得了表面原子级光滑平整、位错密度极低的GaN同质外延膜,其X射线衍射摇摆曲线(002),(102)晶面半峰宽分别为125arcsec和85arcsec,表面粗糙度均方根大小为0.23nm.     

4H-SiC中基面位错发光特性研究

本文利用阴极荧光(CL)和选择性刻蚀的方法对4H-SiC同质外延材料中基面位错的发光特性进行了研究. 结果表明螺型基面位错(B_TSD)和混合型基面位错(B_MD)分别具有绿光和蓝绿光特性,其发光峰分别在530 nm附近和480 nm附近. 从测试结果中还发现B_MD 的发光位较B_TSD有所蓝移,分析认为B_TSD位错芯附近原子沿伯格斯 关键词： 4H-SiC 基面位错 发光特性 禁带宽度     

4H-SiC同质外延的绿带发光与缺陷的关系

利用室温光致发光谱(PL)对CVD法生长的4H-SiC同质外延特性进行研究,发现有绿带发光(GL)特性.用扫描电子显微镜(SEM) 、二次离子质谱(SIMS)和X射线光电子谱(XPS)技术获得了4H-SiC样品纵截面形貌和元素相对含量分布.结果表明,GL与4H-SiC晶体中碳空位(V_C)及络合体缺陷相关,V_C和缓冲层的扩展缺陷(点缺陷和刃位错等)是GL微观来源.GL的半峰宽(FWHM) 反映了参与复合发光的V_C及其络合缺陷能级分散的程度.室温下获得的样品GL强度和光谱波长度可用于分析4H-SiC外延中缺陷分布和晶体质量. 关键词： 绿带发光 4H-SiC同质外延 晶体缺陷     

利用金属有机物化学气相沉积技术生长的a面GaN表面形貌和位错的研究

采用金属有机物化学气相淀积技术在r面蓝宝石衬底上制备了a面GaN薄膜,用熔融的KOH在400 ℃对样品分别腐蚀1.0,1.5和2.0 min.用扫描电镜、原子力显微镜、X射线衍射谱和阴极射线荧光对腐蚀前后的表面形貌进行分析.研究表明,400 ℃下腐蚀1.5 min后出现了长平行四边形的条纹状,这是由于无极化的a面GaN表面极性各向异性,c向与m向上N原子悬挂键密度不同,同时稳定性不同,对OH^-离子的吸附能力不同造成的,其中沿c方向易于腐蚀.同时,a面GaN腐蚀后出现了六角突起.我们认为这与穿透位错有关,而其形貌则与GaN薄膜的位错局部极性有关. 关键词： a面GaN')" href="#">a面GaN 堆垛层错 极性     

Intensity variations in the near-band-edge recombination of GaP epitaxial layers, grown on (111) and (001) oriented substrates, as observed by cathodoluminescence imaging

In this study a comparison between GaP layers, grown by metalorganic vapour phase epitaxy on either (111) oriented GaP substrates or (001) oriented GaP substrates, is made with respect to the near-band-edge luminescence. Spectrally resolved cathodoluminescence, CL, images were recorded at ˜ 25 K with detection on either the bound exciton emission or the donor-to-acceptor pair emission. The intensity variations observed in the CL images are interpreted in terms of aggregation of impurities around threading dislocations. Contrary to the layers grown on (001) oriented substrates, the layers grown on (111) oriented substrates show a segregation effect of the acceptor constituent involved in the donor-to-acceptor pair emission.     

Carrier diffusion processes near threading dislocations in GaN and GaN:Si characterized by low voltage cathodoluminescence

We present a low temperature study of GaN epilayers by means of low voltage cathodoluminescence (CL). We show that lowering the primary electrons accelerating voltage down to 1 kV allows imaging of single threading dislocations. By using monochromatic or panchromatic low voltage CL microscopy, it is possible to extract different diffusion lengths related to free excitons, bound excitons or donor-to-acceptor pair transitions.     

Threading dislocations in epitaxial ferroelectric PbZr0.2Ti0.8O3 films and their effect on polarization backswitching

The existence of threading dislocations in ferroelectric heterostructures has been frequently reported. However, their origin and impact on the ferroelectric properties are not sufficiently understood. PbZr_0.2Ti_0.8O₃/SrRuO₃ heterostructures were epitaxially grown by pulsed-laser deposition (PLD) onto vicinal SrTiO₃(001) substrates. The threading dislocations exhibited by the PbZr_0.2Ti_0.8O₃ films were investigated by cross-sectional and plan-view (high-resolution) transmission electron microscopy. Many threading dislocations were dissociated into dipoles spanning a, most probably lead-rich, stacking fault. It is likely that these dislocations are able to pin 180° ferroelectric domains, as suggested by a comparison between piezo-force microscope and transmission electron micrographs obtained on identical samples. Local backswitching of the polarization was observed in the vicinity of such threading dislocations.     

Direct observation of misfit dislocation glide on surfaces

Using scanning tunneling microscopy we have observed thermally induced dislocation glide in monolayer Cu films on Ru(0001) at room temperature. The motion is governed by a Peierls barrier that depends on the detailed structure of the dislocations, in particular upon whether the threading dislocations that terminate them are dissociated or not. Calculations based on the Frenkel-Kontorova model reproduce the threading dislocation structure and provide estimates of the Peierls barrier and dislocation stiffness which are consistent with experiment.     

Investigation of dislocations in 8circ off-axis 4H-SiC epilayer

This paper reports that the etching morphology of dislocations in 8^circ off-axis 4H-SiC epilayer is observed by using a scanning electronic microscope. It is found that different types of dislocations correspond with different densities and basal plane dislcation (BPD) array and threading edge dislocation (TED) pileup group lie along some certain crystal directions in the epilayer. It is concluded that the elastic energy of threading screw dislocations (TSDs) is highest and TEDs is lowest among these dislocations, so the density of TSDs is lower than TEDs. The BPDs can convert to TEDs but TSDs can only propagate into the epilyer in spite of the higher elastic energy than TEDs. The reason of the form of BPDs array in epilayer is that the big step along the basal plane caused by face defects blocked the upstream atoms, and TEDs pileup group is that the dislocations slide is blocked by dislocation groups in epilayer.     

Characterisation of defects in p-GaN by admittance spectroscopy

Mg-doped GaN films have been grown on (0 0 0 1) sapphire using metal organic vapour phase epitaxy. Use of different buffer layer strategies caused the threading dislocation density (TDD) in the GaN to be either approximately 2×10⁹ cm⁻² or 1×10¹⁰ cm⁻². Frequency-dependent capacitance and conductance measurements at temperatures up to 450 K have been used to study the electronic states associated with the Mg doping, and to determine how these are affected by the TDD. Admittance spectroscopy of the films finds a single impurity-related acceptor level with an activation energy of 160±10 meV for [Mg] of about 1×10¹⁹ cm⁻³, and 120±10 eV as the Mg precursor flux decreased. This level is thought to be associated with the Mg acceptor state. The TDD has no discernible effect on the trap detected by admittance spectroscopy. We compare these results with cathodoluminescence measurements reported in the literature, which reveal that most threading dislocations are non-radiative recombination centres, and discuss possible reasons why our admittance spectroscopy have not detected electrically active defects associated with threading dislocations.