Fabrication of Nanoscale Step Height Structure Using Atomic Layer Deposition Combined with Wet Etching

The current techniques used for the fabrication of nanosteps are normally done by layer growth and then ion beam thinning. There are also extra films grown on the step surfaces in order to reduce the roughness. So the whole process is time consuming. In this paper, a nanoscale step height structure is fabricated by atomic layer deposition （ALD） and wet etching techniques. According to the traceable of the step height value, the fabrication process is controllable. Because ALD technology can grow a variety of materials, aluminum oxide （Al2O3） is used to fabricate the nanostep. There are three steps of Al2O3 in this structure including 8 nm, 18 nm and 44 inn. The thickness of Al2O3 film and the height of the step are measured by anellipsometer. The experimental results show that the thickness of Al2O3 film is consistent with the height of the step. The height of the step is measured by AFM. The measurement results show that the height is related to the number of cycles of ALD and the wet etching time. The bottom and the sidewall surface roughness are related to the wet etching time. The step height is calibrated by Physikaliseh-Technische Bundesanstalt （PTB） and the results were 7.5±1.5 nm, 15.5±2.0 nm and 41.8±2.1 nm, respectively. This research provides a method for the fabrication of step height at nanoscale and the nanostep fabricated is potential used for standard references.

Improvement in a-plane GaN crystalline quality using wet etching method

Nonpolar （1120） GaN films are grown on the etched a-plane GaN substrates via metalorganic vapor phase epitaxy. High-resolution X-ray diffraction analysis shows great decreases in the full width at half maximum of the samples grown on etched substrates compared with those of the sample without etching, both on-axis and off-axis, indicating the reduced dislocation densities and improved crystalline quality of these samples. The spatial mapping of the E2 （high） phonon mode demonstrates the smaller line width with a black background in the wing region, which testifies the reduced dislocation densities and enhanced crystalline quality of the epitaxial lateral overgrowth areas. Raman scattering spectra of the E2 （high） peaks exhibit in-plane compressive stress for all the overgrowth samples, and the E2 （high） peaks of samples grown on etched substrates shift toward the lower frequency range, indicating the relaxations of in-plane stress in these GaN films. Furthermore, room temperature photoluminescence measurement demonstrates a significant decrease in the yellow-band emission intensity of a-plane GaN grown on etched templates, which also illustrates the better optical properties of these samples.

Wet etching and passivation of GaSb-based very long wavelength infrared detectors

The etching and passivation processes of very long wavelength infrared(VLWIR)detector based on the InAs/GaSb/AlSb type-II superlattice have been studied.By studying the effect of each component in the citric acid solution(citric acid,phosphoric acid,hydrogen peroxide,deionized water),the best solution ratio is obtained.After comparing different passivation materials such as sulfide+SiO_(2),Al_(2)O_(3),Si_(3)N_(4) and SU8,it is found that SU8 passivation can reduce the dark current of the device to a greater degree.Combining this wet etching and SU8 passivation,the of VLWIR detector with a mesa diameter of 500μm is about 3.6Ω·cm^(2) at 77 K.

Fabrication of Diamond Microstructures by Using Dry and Wet Etching Methods

Diamond films have great potential for micro-electro-mechanical system（MEMS） application.For device realization,precise patterning of diamond films at micrometer scale is indispensable.In this paper,simple and facile methods will be demonstrated for smart patterning of diamond films,in which two etching techniques,i.e.,plasma dry etching and chemical wet etching（including isotropic-etching and anisotropic-etching） have been developed for obtaining diamond microstructures with different morphology demands.Free-standing diamond micro-gears and micro-combs were achieved as examples by using the experimental procedures.It is confirmed that as-designed diamond structures with a straight side wall and a distinct boundary can be fabricated effectively and efficiently by using such methods.

Physical analysis of normally-off ALD Al_(2)O_(3)/GaN MOSFET with different substrates using self-terminating thermal oxidation-assisted wet etching technique

Based on the self-terminating thermal oxidation-assisted wet etching technique,two kinds of enhancement mode Al_(2)O_(3)/GaN MOSFETs(metal-oxide-semiconductor field-effect transistors)separately with sapphire substrate and Si sub-strate are prepared.It is found that the performance of sapphire substrate device is better than that of silicon substrate.Comparing these two devices,the maximum drain current of sapphire substrate device(401 mA/mm)is 1.76 times that of silicon substrate device(228 mA/mm),and the field-effect mobility(μ_(FEmax))of sapphire substrate device(176 cm^(2)/V·s)is 1.83 times that of silicon substrate device(96 cm^(2)/V·s).The conductive resistance of silicon substrate device is 21.2Ω-mm,while that of sapphire substrate device is only 15.2Ω·mm,which is 61%that of silicon substrate device.The significant difference in performance between sapphire substrate and Si substrate is related to the differences in interface and border trap near Al_(2)O_(3)/GaN interface.Experimental studies show that(i)interface/border trap density in the sapphire substrate device is one order of magnitude lower than in the Si substrate device,(ii)Both the border traps in Al_(2)O_(3) dielectric near Al_(2)O_(3)/GaN and the interface traps in Al_(2)O_(3)/GaN interface have a significantly effect on device channel mobility,and(iii)the properties of gallium nitride materials on different substrates are different due to wet etching.The research results in this work provide a reference for further optimizing the performances of silicon substrate devices.

Paired interference 3-dB coupler based on SOI rib waveguides with anisotropic chemical wet etching

A 3-dB paired interference （PI） optical coupler in silicon-on-insulator （SOI） based on rib waveguides with trapezoidal cross section was designed with simulation by a modified finite-difference beam propagation method （FD-BPM） and fabricated by potassium hydroxide （KOH） anisotropic chemical wet etching. Theoretically, tolerances of width, length, and port distance are more than 1, 100, and 1 μm, respectively. Smooth interface was obtained with the propagation loss of 1.1 dB/cm at the wavelength of 1.55 μm. The coupler has a good uniformity of 0.2 dB and low excess loss of less than 2 dB.

Wet etching characteristics of a HfSiON high-k dielectric in HF-based solutions

The wet etching properties ofa HfSiON high-k dielectric in HF-based solutions are investigated. HF-based solutions are the most promising wet chemistries for the removal of HfSiON, and etch selectivity of HF-based solutions can be improved by the addition of an acid and/or an alcohol to the HF solution. Due to densification during annealing, the etch rate of HfSiON annealed at 900℃ for 30 s is significantly reduced compared with as-deposited HfSiON in HF-based solutions. After the HfSiON film has been completely removed by HF-based solutions, it is not possible to etch the interfacial layer and the etched surface does not have a hydrophobic nature, since N diffuses to the interface layer or Si substrate formation of SiN bonds that dissolves very slowly in HF-based solutions. Existing Si-N bonds at the interface between the new high-k dielectric deposit and the Si substrate may degrade the carrier mobility due to Coulomb scattering. In addition, we show that N2 plasma treatment before wet etching is not very effective in increasing the wet etch rate for a thin HfSiON film in our case.

Selective wet etch of a TaN metal gate with an amorphous-silicon hard mask

The appropriate wet etch process for the selective removal of TaN on the HfSiON dielectric with an amorphous-silicon（a-Si） hardmask is presented.SCI（NH4OH：H2O2：H2O）,which can achieve reasonable etch rates for metal gates and very high selectivity to high-k dielectrics and hardmask materials,is chosen as the TaN etchant. Compared with the photoresist mask and the tetraethyl orthosilicate（TEOS） hardmask,the a-Si hardmask is a better choice to achieve selective removal of TaN on the HfSiON dielectric because it is impervious to the SC1 etchant and can be readily etched with NH4OH solution without attacking the TaN and the HfSiON film.In addition,the surface of the HfSiON dielectric is smooth after the wet etching of the TaN metal gate and a-Si hardmask removal,which could prevent device performance degradation.Therefore,the wet etching of TaN with the a-Si hardmask can be applied to dual metal gate integration for the selective removal of the first TaN metal gate deposition.

TaN wet etch for application in dual-metal-gate integration technology

Wet-etch etchants and the TaN film method for dual-metal-gate integration are investigated. Both HF/HN O3/H2O and NH4OH/H2O2 solutions can etch TaN effectively, but poor selectivity to the gate dielectric for the HF/HNO3/H2O solution due to HF being included in HF/HNO3/H2O, and the fact that TaN is difficult to etch in the NH4OH/H2O2 solution at the first stage due to the thin TaOxNy layer on the TaN surface, mean that they are difficult to individually apply to dual-metal-gate integration. A two-step wet etching strategy using the HF/HNO3/H2O solution first and the NH4OH/H2O2 solution later can fully remove thin TaN film with a photo-resist mask and has high selectivity to the HfSiON dielectric film underneath. High-k dielectric film surfaces are smooth after wet etching of the TaN metal gate and MOSCAPs show well-behaved C-V and Jg-Vg characteristics, which all prove that the wet etching of TaN has little impact on electrical performance and can be applied to dual-metal-gate integration technology for removing the first TaN metal gate in the PMOS region.

A novel oxidation-based wet etching method for AlGaN/GaN heterostructures

A novel wet etching method for AlGaN/GaN heterojunction structures is proposed using thermal oxidation f ollowed by wet etching in KOH solution.It is found that an AlGaN/GaN heterostructure after high temperature oxidation above 700℃could be etched off in a homothermal（70℃） KOH solution while the KOH solution had no etching effects on the region of the AlGaN/GaN heterostructure protected by a SiO_2 layer during the oxidation process.A groove structure with 150 nm step depth on an AlGaN/GaN heterostructure was formed after 8 h thermal oxidation at 900℃followed by 30 min treatment in 70℃KOH solution.As the oxidation time increases,the etching depth approaches saturation and the roughness of the etched surface becomes much better.The physical mechanism of this phenomenon is also discussed.

Etching of quartz crystals in liquid phase environment:A review

Quartz crystals are the most widely used material in resonant sensors,owing to their excellent piezoelectric and mechanical properties.With the development of portable and wearable devices,higher processing efficiency and geometrical precision are required.Wet etching has been proven to be the most efficient etching method for large-scale production of quartz devices,and many wet etching approaches have been developed over the years.However,until now,there has been no systematic review of quartz crystal etching in liquid phase environments.Therefore,this article provides a comprehensive review of the development of wet etching processes and the achievements of the latest research in thisfield,covering conventional wet etching,additive etching,laser-induced backside wet etching,electrochemical etching,and electrochemical discharge machining.For each technique,a brief overview of its characteristics is provided,associated problems are described,and possible solutions are discussed.This review should provide an essential reference and guidance for the future development of processing strategies for the manufacture of quartz crystal devices.

Investigation of chlorine-based etchants in wet and dry etching technology for an InP planar Gunn diode

Mesa etching technology is considerably important in the Gunn diode fabrication process. In this paper we fabricate InP Gunn diodes with two different kinds of chlorine-based etchants for the mesa etching for comparative study. We use two chlorine-based etchants, one is HCl-based solution （HC1/H3PO4）, and the other is Cl2-based gas mixture by utilizing inductively coupled plasma system （ICP）. The results show that the wet etching （HCl-based） offers low cost and approximately vertical sidewall, whilst ICP system （C12-based） offers an excellent and uniform vertical sidewall, and the over-etching is tiny on the top and the bottom of mesa. And the fabricated mesas of Gunn diodes have average etching rates of 0.6 p.m/min and 1.2 pm/min, respectively. The measured data show that the current of Gunn diode by wet etching is lower than that by ICP, and the former has a higher threshold voltage. It provides a low-cost and reliable method which is potentially applied to the fabrication of chip terahertz sources.

Etching Behavior of GaN/GaAs(001) Epilayers Grown by MOVPE

Wet etching characteristics of cubic GaN (c GaN) thin films grown on GaAs(001) by metalorganic vapor phase epitaxy (MOVPE) are investigated.The samples are etched in HCl,H 3PO 4,KOH aqueous solutions,and molten KOH at temperatures in the range of 90～300℃.It is found that different solution produces different etch figure on the surfaces of a sample.KOH based solutions produce rectangular pits rather than square pits.The etch pits elongate in 1 0] direction,indicating asymmetric etching behavior in the two orthogonal <110> directions.An explanation based on relative reactivity of the various crystallographic planes is employed to interpret qualitatively the asymmetric etching behavior.In addition,it is found that KOH aqueous solution would be more suitable than molten KOH and the two acids for the evaluation of stacking faults in c GaN epilayers. direction,indicating asymmetric etching behavior in the two orthogonal <110> directions.An explanation based on relative reactivity of the various crystallographic planes is employed to interpret qualitatively the asymmetric etching behavior.In addition,it is found that KOH aqueous solution would be more suitable than molten KOH and the two acids for the evaluation of stacking faults in c GaN epilayers.

Enhanced etching of silicon didioxide guided by carbon nanotubes in HF solution

This paper describes a new method to create nanoscale SiO2 pits or channels using single-walled carbon nanotubes （SWNTs） in an HF solution at room temperature within a few seconds. Using aligned SWNT arrays, a pattern of nanoscale SiO2 channels can be prepared. The nanoscale SiO2 patterns can also be created on the surface of three- dimensional （3D） SiO2 substrate and even the nanoscale trenches can be constructed with arbitrary shapes. A possible mechanism for this enhanced etching of SiO2 has been qualitatively analysed using defects in SWNTs, combined with H3O＋ electric double layers around SWNTs in an HF solution.

MEMS矢量水听器敏感结构的后CMOS释放工艺研究

纤毛式微机电系统(MEMS)矢量水听器可探测水下质点振速等矢量信息,与互补金属氧化物半导体(CMOS)集成能够很大程度地提升其性能。针对纤毛式MEMS矢量水听器的CMOS集成提出了一种方案,该方案在MEMS后处理工艺中,利用侧墙保护和各向异性湿法腐蚀从正面释放水听器的十字梁敏感结构。整个后处理过程不需要光刻,降低加工难度的同时,保证了加工结构的精确性。设计出了一种验证性的工艺流程,具体分析了4种不同结构的湿法腐蚀过程。最终完成了这4种结构的工艺流片,对实验结果进行了分析。实验验证了该方案的可行性,为纤毛式MEMS矢量水听器的CMOS集成奠定了基础。

湿法刻蚀条件对TFT中Cu电极坡度角和均一性的影响及工艺参数优化

目的 在高世代薄膜晶体管(Thin Film Transistor,TFT)产线的栅极刻蚀制程,明确大气压等离子体(Atmosphere Pressure Plasma,APP)清洗功率、清洗时间及刻蚀时间对刻蚀性能(关键尺寸偏差、均一性、坡度角)的影响规律,并获得最佳工艺条件,进而提升良率。方法 以APP清洗功率、清洗时间和刻蚀时间为影响因素,以关键尺寸偏差(CD Bias)、均一性、坡度角作为因变量,开展正交试验,明确因素影响重要性顺序;然后,对Cu电极坡度角的形成和刻蚀均一性变化进行分析;最后,采用回归分析获得刻蚀性能与刻蚀时间的函数关系式。结果 结果表明:刻蚀时间对刻蚀性能的影响最大,对APP清洁时间和功率的影响较小。刻蚀时间延长,关键尺寸偏差(CD Bias)增加、均一性变差、坡度角变大。为改善均一性和平缓坡度角,应缩短刻蚀时间。最佳工艺组合为:刻蚀时间85 s,APP电压9 kV,APP传输速度5 400 r/min。结论 刻蚀时间延长,未被光刻胶覆盖的Cu膜层被完全刻蚀,形成台阶,该台阶使刻蚀液形成回流路径。沿着回流路径,刻蚀液浓度、温度逐渐下降,刻蚀均一性由此恶化,坡度角因此增加。采用回归分析得到的刻蚀性能与刻蚀时间的函数关系式,为预测刻蚀效果和优选刻蚀时间提供了依据。

界面钻蚀主导的准各向异性湿法刻蚀法制备玻璃微棱镜阵列

玻璃微棱镜具有耐腐蚀、耐高温、寿命长等优点,但在玻璃上加工微棱镜阵列目前仍是一个难题。因此,提出了界面钻蚀主导的玻璃准各向异性湿法刻蚀方法,制备了高质量的微棱镜阵列器件。在元胞自动机中引入界面性质调控,模拟了界面钻蚀与各向同性侧蚀的竞争行为,探究了刻蚀横截面形貌的变化规律,构建了准各向异性湿法刻蚀模型。在此指导下,加工了横截面为梯形的微结构,设计并制备了间距、形状、尺寸均可调控的微棱镜阵列,重复性达到98%。验证了微棱镜阵列对LED灯扩散效果,光亮度提升了4.6倍。本文改变了传统玻璃湿法刻蚀各向同性的固有认识,创新性地开发了准各向异性刻蚀工艺,为玻璃微棱镜阵列等相关器件提供了高效低成本的制备方法。

小闪耀角单晶硅光栅结构参数优化及制备工艺

本文开展了对单晶硅小闪耀角光栅的各向异性湿法刻蚀制备工艺研究,制备了适用于软X射线中波波段的闪耀光栅,以满足国家同步辐射光源的需要。首先,基于严格耦合波法对小闪耀角光栅进行了结构参数优化及工艺容差分析。在晶向对准过程中,先通过环形预刻蚀确定硅片晶向,再基于倍频调整法实现光栅掩模与单晶硅<111>晶向的对准。研究了光刻胶灰化技术及活性剂对光栅槽形质量的影响,并通过单晶硅各向异性湿法刻蚀工艺成功制备了接近于理想锯齿槽形的闪耀光栅。实验结果证明:所制备光栅闪耀角为1°,刻线密度为1200 gr/mm,闪耀面均方根粗糙度在0.5 nm以内。此方法可以应用于软X射线中波波段闪耀光栅的制作,在获得较高衍射效率的同时可以大大减少制作难度及成本。

InAs/GaSb超晶格台面刻蚀工艺研究综述

本文综述了InAs/GaSb超晶格台面刻蚀工艺研究。从湿法和干法刻蚀的物理化学机理以及参数调控等方面进行分析,旨在阐明工艺条件对台面形貌的影响,以抑制带隙较窄的长波和甚长波超晶格表面漏电流。结果表明,湿法刻蚀中恰当的腐蚀液配比可以实现两种组分的均匀性刻蚀,而不会导致粗糙的表面和严重的下切;干法刻蚀中,采用Cl_(2)基和CH 4基混合气体,通过调整刻蚀气体类型及比例可实现物理和化学刻蚀两个过程的平衡,保证台面侧壁平滑性和倾角的垂直度。另外,对于不同组分的超晶格,需要选择不同的工艺参数才能满足InAs和GaSb的协同性刻蚀。最后对InAs/GaSb超晶格台面刻蚀工艺作出了展望。

基于仿生蛾眼结构制备减反射微晶玻璃

目的采用湿法刻蚀制备减反射微晶玻璃,分析晶化时间对透过率、反射率和形貌的影响。方法通过熔融法制备得到基础玻璃,调整晶化时间制备得到一系列不同晶粒尺寸(12.2~27.4nm)的微晶玻璃,将制备得到的基础玻璃及不同晶粒尺寸的微晶玻璃放置在配制好的5%(质量分数)HF、2%(质量分数)SiO_(2)、1.5%(质量分数)BaSO_(4)、2%(质量分数)羧甲基纤维素钠、89.5%(质量分数)H_(2)O的刻蚀液中,在25℃条件下,以40 kHz的超声频率双面蚀刻60 min,通过分光光度计测试刻蚀前后样品的透过率和反射率,利用扫描电子显微镜对刻蚀前后样品的表面和断面形貌进行表征。结果基础玻璃在500℃核化230 min,665℃晶化135 min后,制备得到微晶玻璃的晶粒尺寸约为25.1 nm,进一步经过湿法刻蚀后,刻蚀深度约为150 nm,蛾眼玻璃透过率最高为98.02%。结论微晶玻璃经过湿法刻蚀后增透效果明显,对X射线衍射(XRD)、掠入射X射线衍射(GIXRD)、扫描电子显微镜(SEM)的测试结果进行分析可知,微晶玻璃中存在晶体相和残余玻璃相,经过酸蚀处理后,表面能形成以透锂长石晶体和二硅酸锂晶体均匀分布的蛾眼结构,晶体尺寸为12.2~27.4 nm的微晶玻璃进行湿法刻蚀后透过率分布在95.99%~98.02%。