Chemical polishing of CdZnTe substrates fabricated from crystals grown by the vertical-gradient freezing method

Chemical polishing is a process of crucial importance in the manufacture of epiready substrates for molecular beam epitaxy (MBE) of high-quality HgCdTe layers. With the aim of fabrication of (211) CdZnTe substrates, we focused on the fundamental research of polishing processes with respect to reducing subsurface damage. Wafers of the orientation (211) were prepared from the as-grown crystals by a process flow including oriented slicing, several steps of mechanical polishing, and finally chemical polishing. In the prechemical polishing process, several free and bound abrasives were applied to reach the surface roughness close to 1 nm. The surface polishing treatment included testing of the surface quality after each polishing step. We used an interferometer profiler, which yields detailed surface maps. Within chemical polishing processing, we have looked for an optimum composition of etchant based on the bromine-methanol/ethylene glycol solution and adequate polishing pad. We studied the substrate surface quality dependence on the rotation speed of the plate, sample loading weights, and duration of polishing. Correlation between the final surface roughness and layer thickness removed was established. The chemical polishing with a very low concentration of Br-methanol/ethylene glycol solution was found to yield very good CdZnTe surfaces with a perfect flatness.     

基底亚表面裂纹对减反射膜激光损伤阈值的影响

利用化学沥滤技术,分析了亚表面裂纹对基底表面和减反射膜激光损伤阈值(LIDT)的影响。通过去除或保留研磨裂纹,获得了亚表面裂纹数密度有明显区别的两类基底。为了凸出亚表面裂纹层的作用,基底采用化学沥滤去除另外一种可能的影响因素,即再沉积层中的抛光杂质。然后采用电子束蒸发镀制HfO2/SiO2减反射膜。355nm激光损伤阈值测试结果和损伤形貌分析证实了基底亚表面裂纹对减反射膜抗激光损伤能力的负面影响。根据熔石英基底抛光表面的烘烤现象,提出了亚表面缺陷影响膜层激光损伤的耦合模型。     

磷化铟的化学机械抛光技术研究进展

磷化铟单晶作为一种重要的外延层衬底材料被广泛应用于光电器件.衬底外延生长和电子器件制备要求磷化铟晶片表面具有极低的表面粗糙度、无表面/亚表面损伤和残余应力等,需对磷化铟晶片表面进行抛光加工,其表面质量决定了后续的外延层质量并最终影响磷化铟基器件的性能.综述了磷化铟晶体化学机械抛光(CMP)技术进展;介绍了磷化铟表面的化学反应原理、CMP去除机理;详细分析了磷化铟抛光液组分及pH值、抛光工艺参数(抛光压力、抛光盘转速、抛光垫特性、磨料种类、粒径及浓度)等对磷化铟抛光质量的影响;介绍了磷化铟抛光片的清洗工艺,并对磷化铟CMP的后续研究方向提出一些建议.     

Effect of surface preparation on Ni Ohmic contact to 3C-SiC

The effect of roughness and chemical treatment of 3C-SiC film surface on Ni ohmic contact was studied in this work. 3C-SiC(1 1 1) film was grown on Si(1 1 1) in a chemical vapor deposition reactor. The 3C-SiC surface was polished using a chemical mechanical polishing (CMP) technique to get a smooth and flat surface. The polished surface was oxidized and then was etched in BHF solution to remove subsurface damages formed during the CMP process. The morphology of thus prepared silicon carbide (SiC) surfaces was investigated using SEM and AFM. Ni contact resistance to the 3C-SiC films was evaluated using linear transmission line method pattern. The formation of good ohmic contact characteristics was observed from Ni contact to all the tested SiC samples. After the CMP process, it was found that the RMS roughness of 3C-SiC surface apparently reduces and the specific contact resistance to 3C-SiC decreases as well, in proportion to the SiC surface roughness. The sacrificial oxidation and etching of the polished SiC surface abruptly decrease the contact resistance to be 3.7×10⁻⁴ Ω cm². It was shown that the surface morphology and subsurface damage concentration of 3C-SiC films are important factors to give a great effect on the contact characteristic of the 3C-SiC films. However, it was considered that the reduction of subsurface damage concentration is essential to get better contact resistance to 3C-SiC surface.     

X-Ray diffraction observation of surface damage in chemical-mechanical polished gallium arsenide

Two novel x-ray diffraction techniques with enhanced surface sensitivity, grazing incidence x-ray diffraction (GIXD) and inclined Bragg plane x-ray diffraction (IBXD), have been used to study surface damage in gallium arsenide (GaAs) due to bromine/methanol (Br₂/MeOH) chemical mechanical (CM) polishing. A factorial design was implemented to determine the effects of four polishing variables on the surface structure of GaAs. Precise lattice parameter measurements were made in both the surface regions using GIXD and deeper into subsurface regions using IBXD after the various CM polishing treatments. Bromine concentration was found to primarily affect the surface lattice parameter, while the total polish time influenced both the surface and subsurface lattice parameters in GaAs samples that were heavily damaged prior to CM polishing. The combined effect of polishing pad rotation speed and the force exerted on the sample was found to have a much greater effect on the surface lattice parameter than either variable had alone.     

固结磨料研磨硫化锌的亚表面损伤预测分析

研磨抛光后产生的工件亚表面损伤是评价工艺优劣及确定加工余量的主要参考,因此对亚表面损伤准确的预测有助于提高加工效率。采用离散元法对典型的软脆材料硫化锌固结磨料研磨过程中产生的亚表面损伤进行模拟,预测不同粒径金刚石加工工件后的亚表面微裂纹层深度。利用角度抛光法将工件抛光出一个斜面,作为亚表面损伤观测平面,通过盐酸的腐蚀使亚表面微裂纹显现,在金相显微镜下寻找微裂纹消失的终点位置并转换成亚表面微裂纹层深度,对仿真结果进行实验验证。结果表明:粒径为5、15、25、30 μm的磨粒造成的亚表面微裂纹层深度预测值分别为2.28、3.62、5.93、7.82 μm,角度抛光法实测值分别为2.02、3.98、6.27、8.27 μm。以上结果表明磨粒粒径对硫化锌亚表面损伤情况有很大的影响,随着磨粒粒径的增大,亚表面微裂纹深度增加,微裂纹数量增多。离散元法预测值与实测值偏差范围处在5%~15%之间,利用离散元法能有较为准确的预测软脆材料硫化锌加工后的亚表面损伤情况,为其研抛工艺的制定提供参考。     

熔石英抛光表面结构的蚀刻和热处理表征

利用HF蚀刻和热处理,结合原子力显微(AFM)分析,对传统抛光和磁流变抛光的表面结构进行了表征。为了分析热处理凸起的形成源,抛光表面在热处理前分别采用超声清洗、化学沥滤和HF蚀刻三种不同的表面处理技术进行处理,去除了不同表面材料。蚀刻形貌和热处理形貌及其关联性表明,传统抛光表面存在着大量纳米级缺陷,这些缺陷由易于诱导激光损伤的纳米级微裂纹和颗粒状分布的抛光杂质组成。结合抛光机制的分析,建立了传统抛光表面的微裂纹-颗粒杂质结构模型。     

化学机械抛光的钛宝石晶体低损伤加工

针对钛宝石晶体表面低损伤加工进行了系统研究,在CCOS数控小磨头抛光机上进行了正交实验,选用不同的抛光液对钛宝石进行化学机械抛光,有效去除精磨阶段的亚表面损伤,实验证明SiO2硅溶液作为磨料的抛光效果好,适合作为钛宝石加工的抛光液。研究了抛光盘种类、抛光盘压力、抛光盘速度、硅溶胶稀释浓度这四个因素和钛宝石晶体表面粗糙度和表面疵病的关系,并获得钛宝石低缺陷加工过程中工艺参数的影响规律。按照优化后的工艺参数进行实验,获得了低缺陷、高精度的钛宝石表面。运用灰色关联分析法对抛光参数进行优化,在最佳加工工艺组合条件下,得到钛宝石表面粗糙度为0.262 nm,表面疵病率为1.410-3 mm-1。     

Surface integrity and removal mechanism of silicon wafers in chemo-mechanical grinding using a newly developed soft abrasive grinding wheel

A new soft abrasive grinding wheel (SAGW) used in chemo-mechanical grinding (CMG) was developed for machining silicon wafers. The wheel consisted of magnesia (MgO) soft abrasives, calcium carbonate (CaCO₃) additives and magnesium oxychloride bond. Surface topography, roughness and subsurface damage of the silicon wafers ground using the new SAGW were comprehensively investigated. The results showed that the grinding with the new SAGW produced a surface roughness of about 0.5 nm in R_a and a subsurface damage layer of about 10 nm in thickness, which is comparable to that produced by chemo-mechanical polishing. This study also revealed that the chemical reactions between MgO abrasive, CaCO₃ additives and silicon material did occur during grinding, thereby generating a soft reactant layer on the ground surface. The reactant layer was easily removed during the grinding process.     

915 nm半导体激光器新型腔面钝化工艺

针对半导体激光器腔面光学灾变损伤的发生机制,设计了一种单管芯半导体激光器腔面真空解理钝化工艺方法。在真空中解理并且直接对半导体激光器腔面蒸镀钝化膜,提出用ZnSe材料作为单管芯半导体激光器真空解理工艺的钝化膜材料,发现利用真空解理钝化工艺方法和ZnSe材料作为钝化膜可以使器件输出功率提高23%。通过电致发光（EL）对半导体激光器腔面损伤机理进行分析。进一步说明对915 nm半导体激光器制备工艺中引入真空解理钝化工艺技术并且选择ZnSe作为钝化膜可以有效保护半导体激光器腔面,提高器件可靠性。     

激光抛光技术在红外探测器组件封装中的应用探索

提出将激光抛光技术应用于杜瓦部件激光焊焊缝的抛光处理中,以解决目前红外探测器杜瓦封装激光焊焊缝粗糙度大、探测器组件长时间使用过程中杜瓦焊缝强度和内部真空度欠佳、影响探测器寿命和使用性能的问题。通过实验研究了主要参数对抛光质量的影响规律,并利用激光共聚焦显微镜等设备测试了激光抛光结果。激光抛光技术可使激光焊焊缝的表面粗糙度Ra从0.25mm降低到0.03mm。研究结果充分表明,绿色高效非接触的激光抛光可以实现红外探测器杜瓦组件外表面激光焊焊缝的高质量抛光,在红外探测器制造领域有重大的潜在应用价值。     

Numerical simulation and experimental investigation of Ti-6Al-4V melted by CW fiber laser at different pressures

The interaction of continuous wave (CW) fiber laser with Ti-6Al-4V alloy is investigated numerically and experimentally at different laser fluence values and ambient pressures of N2 atmosphere to determine the melting time threshold of Ti-6Al-4V alloy. A 2D-axisymmetric numerical model considering heat transfer and laminar flow is established to describe the melting process. The simulation results indicate that material melts earlier at lower pressure (8.0 Pa) than at higher pressure (8.8×104 Pa) in several milliseconds with the same laser fluence. The experimental results demonstrate that the melting time threshold at high laser fluence (above 1.89×108 W/m2) is shorter for lower pressure (vacuum), which is consistent with the simulation. While the melting time threshold at low laser fluence (below 1.89×108 W/m2) is shorter for higher pressure. The possible aspects which can affect the melting process include the increased heat loss induced by the heat conduction between the metal surface and the ambient gas with the increased pressure, and the absorption variation of the coarse surface resulted from the chemical reaction. This work has been supported by the National Natural Science Foundation of China for Young Scholars (No.11402120), the Jiangsu Provincial Natural Science Foundation for Young Scholars (No.BK20140796), and the Fundamental Research Funds for the Central Universities (No.30915015104). E-mail:hanbing@njust.edu.cn      

蓝宝石衬底片的抛光研究

本研究对SiO2磨料抛光蓝宝石衬底片进行了研究,结果表明,采用大粒径、高浓度的SiO2磨料抛光可以获得良好的表面状态和较高的去除速率。抛光的适宜的温度及pH值条件为:T=30℃;13.0>pH≥9.0。并且在抛光时应加入适量添加剂,方可获得较为理想的表面状态和较高的去除速率。实验同样证明,这种低成本、高质量的抛光除可以应用在蓝宝石的抛光以外,还可以应用在其它一些硬质材料的抛光工艺中。     

飞秒激光与硅的相互作用过程理论研究

理解超短激光与材料的相互作用过程与机理是开展超短激光加工等工程应用的基础。首先引入电子激发项、双光子吸收、俄歇复合项等改进双温,使其较准确地适应于飞秒激光与半导体硅材料的相互作用过程。然后,分析了热损伤效应和非热损伤效应的影响。最后,开展了双脉冲飞秒激光与硅的相互过程研究,并分析了电子密度、晶格温度对于损伤积累效应的影响。理论模型得到单脉冲激光损伤阈值为0.25 J/cm2,此时主要表现为热损伤;当入射能量密度大于0.53 J/cm2 时,主要表现为非热损伤。双脉冲激光作用表明,脉冲间隔不大于100 ns（激光重频10 MHz）表现出明显的热积累效应,并显著降低损伤阈值。此时,第一个脉冲造成的电子密度升高（1026/m3）对损伤的贡献较小;而第一个脉冲引起的晶格温升将导致极高的电子激发以及晶格温升（800 K）,对损伤起主要贡献作用。该研究对于激光微加工、激光防护等领域具有参考意义。     

激光清洗应用于清除城市涂鸦

探索了激光清洗去除涂鸦这一新型应用,并且针对清洗技术中的关键问题——激光能量密度对清洗效率的影响,进行研究.给出TEA CO2激光在不同情况下的清除涂鸦的实验数据.验证了TEA CO2激光适用于激光清除涂鸦,效果显著.实验发现,当激光能量密度为4～6 J/cm2时,去除效率最高,实验中单位能量去除的涂鸦面积超过2.5 ...     

HF蚀刻+逐层抛光法表征熔石英亚表面损伤层深度

脆性材料的研磨过程会不可避免地产生亚表面损伤层,对亚表面损伤层的表征和抑制一直是获得高激光损伤阈值熔石英光学元件的关注热点。回顾了几种亚表面有损表征技术,通过实验重新评价了蚀刻表面峰谷(PV)粗糙度法的可行性,分析了其误差较大的原因。在此基础上,提出了一种新的亚表面损伤层深度检测方法——HF蚀刻+逐层抛光法。分别采用这两种表征技术以及粗糙度估计法、磁流变斜面抛光法对不同工艺研磨的熔石英亚表面裂纹深度进行了对比检测,结果表明这几种表征方法相互符合很好。     

熔石英亚表面杂质对激光损伤概率的影响

基于Mie理论和热传导方程,结合ICP-OES对熔石英亚表面杂质粒子的主要成分测量,建立了计算吸收性杂质粒子诱导熔石英光学元件表面损伤概率的模型。通过该模型理论研究了不同种类的杂质粒子诱导损伤所需的临界能量密度随粒子尺寸的变化,以及不同尺寸分布的杂质粒子诱导熔石英表面的损伤概率。通过损伤实验测试获得了不同光斑尺寸的355 nm激光辐照作用下熔石英表面的损伤概率,与理论计算结果进行对比,在相同粒子分布参数下,分析了三种杂质粒子对损伤概率的贡献（Cu Al CeO2）。通过该模型能够分析光学基底或薄膜亚表面中不同潜在的杂质吸收性粒子对光学元件损伤概率的影响。     

激光化学复合抛光工艺参量对304不锈钢性能的影响

为了提高304不锈钢表面抛光质量，采用激光化学复合抛光的方法分别在纯净水和抛光液中对304不锈钢进行抛光实验研究，并对1064nm激光的加工功率和扫描次数对加工区域表面形貌和表面质量的影响进行了分析。气泡对抛光液在不锈钢表面形成的钝化膜产生破坏作用，造成抛光效果不均匀，表面粗糙度增大。结果表明，在抛光液中的激光抛光在抑制表面氧化发黑的同时，能够显著改善表面形貌，表面粗糙度由0.845μm下降到0.181μm；激光化学复合抛光304不锈钢表面质量与抛光功率和扫描次数有密切关系；当抛光功率过高或者扫描次数过大时，304不锈钢表面会产生大量气泡。采用激光化学复合抛光，可以提高不锈钢抛光质量、减少环境污染，该方法具有极大的应用前景。     

In-situ process for AlGaAs compound semiconductor: Materials science and device fabrication

Processing of III-V compound semiconductor devices in an ultra-high vacuum or a controlled environment has received much attention during the past few years. Major advantages ofn- situ processing include the preservation of pristine material surface, improved device performance, and fabrication of novel devices. This paper reviews anin- situ process compatible with molecular beam epitaxy (MBE) with emphasis on the removal of oxides and surface contaminants from air-exposed GaAs and AIGaAs. We have characterized deep-etched and MBE regrown AIGaAs with the etching achieved using electron cyclotron resonance plasma treatment. A buried heterostructure vertical-cavity surface emitting laser diode fabricated using thisin- situ process is presented.     

The influence of nitrogen ion energy on the quality of GaN films grown with molecular beam epitaxy

Since the growth of GaN using molecular beam epitaxy (MBE) occurs under metastable growth conditions, activated nitrogen is required to drive the forward synthesis reaction. In the process of exciting the nitrogen using a plasma or ion-beam source, species with large kinetic energies are generated. Impingement on the growth surface by these species can result in subsurface damage to the growing film, as well as an enhancement of the reverse decomposition reaction rate. In this study, we investigate the effect of the kinetic energy of the impinging nitrogen ions during growth on the resulting optical and structural properties of GaN films. Strong band-edge photoluminescence and cathodoluminescence are found when a kinetic energy of ∼10 eV are used, while luminescence is not detectable when the kinetic energies exceeds 18 eV. Also, we find that the use of conductive SiC substrates results in more homogeneous luminescence than the use of insulating sapphire substrates. This is attributed to sample surface charging in the case of sapphire substrates and subsequent variation in the incident ion flux and kinetic energy across the growth surface. This study clearly shows that the quality of GaN films grown by MBE are presently limited by damage from the impingement of high energy species on the growth surface.