Tera Tool [terahertz time-domain spectroscopy]

The terahertz differential time-domain spectroscopic method is applied to characterize the dielectric and optical properties of a variety of thin films at terahertz frequency. The results of several samples including silicon dioxide, parylene-n polymer film, tantalum oxide film, and protein thin layer samples were presented. The dielectric property of silicon dioxide thin film is well fitted to that of a bulk. The dielectric properties of parylene-n thin films show good agreement with the result measured by the goniometric terahertz time-domain spectroscopy. The dielectric and optical properties of the tantalum oxide show reasonable data with previously available data. Some properties in thin films are slightly different from the bulk materials. The origin of this discrepancy is considered due to fine grain formation, mechanical stresses, formation of interfacial layers, or rough interfaces during thin-film deposition process. The terahertz differential time-domain spectroscopy may be applied to the measurement of the dielectric and optical properties of thin films (nanometer to micrometer) of several materials, which cannot be done by any other method.     

Effect of deposition methods on dielectric breakdown strength of PECVD low-k carbon doped silicon dioxide dielectric thin films

The effect of deposition methods on dielectric breakdown strength of PECVD low-k dielectric carbon doped silicon dioxide films is investigated. I-V measurements were performed using metal-insulator semiconductor structures for carbon doped silicon dioxide thin films with various thicknesses by single deposition station and six sequential deposition systems. I-t measurements are also performed for films with the thickness of 32 nm prepared using both deposition methods. Comparison studies have been carried out for the thickness dependence, temperature dependence, conduction mechanism and time dependence of dielectric breakdown for carbon doped silicon dioxide with single layer and six sub-layers. Results demonstrated that both films follow the newly obtained relationship between dielectric strength E_B and thickness d, i.e. E_B∝(d−d_c)⁻ⁿ, but with a lower exponential factor n and a larger thickness limit d_c for films with six sub-layers. It is also demonstrated that films with six sub-layers have a higher dielectric strength in all the thickness and temperature ranges, a thickness independent thermal behavior and a longer lifetime under constant voltage stressing. This indicates that by tuning the deposition methods smaller thickness with desired dielectric properties can be achieved.     

Formation mechanism of concave by dielectric breakdown on silicon carbide metal-oxide-semiconductor capacitor

Adjacent concaves are formed commonly on silicon carbide (SiC) MOS capacitor after time-dependent dielectric breakdown (TDDB). This paper describes the formation mechanism of the concave on the SiC MOS capacitor with aluminum gate electrode on thermally grown silicon dioxide gate dielectric by the dielectric breakdown. At the bottom of an approximately 450 nm-deep concave, a stack structure of the concave surface was found to be surface oxide/C-rich layer/Si-rich layer/SiC substrate. Some C-rich debris adhered on the surface of the concave. The concave surface was speculated to be formed by a sequence of the C-rich surface on the Si-rich surface, the debris adhered on the surface, and the oxide layer containing nitrogen and aluminum. Formation of the concave and its surface is explained based on the physical properties of SiC; (i) a peritectic decomposition of SiC to the solid phase carbon and the liquid phase solution containing silicon and carbon, (ii) a normal freezing process of the liquid phase solution, and (iii) a thermal decomposition on the concave surface to form a graphite layer.     

PET复合衬底上梯度介质薄膜厚度的椭偏表征

为了监控3维玻璃上聚对苯二甲酸乙二醇酯(PET)复合衬底介质膜膜厚, 采用将PET复合衬底等效为单层基底材料的建模分析方法, 通过椭偏测量技术实现了复杂衬底上TiO₂梯度折射率材料薄膜厚度的检测。结果表明, 采用该方法测量的PET复合衬底上TiO₂梯度折射率薄膜厚度为212.48nm, 扫描电子显微镜的测量结果为211nm, 结果非常准确。以TiO₂为例验证了等效衬底方法, 该方法也同样适用于其它介质膜。等效衬底法可实现PET复合衬底上的TiO₂薄膜厚度的高精度测量表征, 对镀膜工艺过程监控具有重要意义。     

Terahertz characterisation of UV offset lithographically printed electronic-ink

Inkjet-printed electronics are showing promising potential in practical applications, but methods for real-time, non-contact monitoring of printing quality are lacking. This work explores Terahertz (THz) sensing as an approach for such monitoring. It is demonstrated that alterations in the localised dielectric characteristics of inkjet-printed electronics can be qualitatively distinguished using quasi-optically-based, sub-THz reflection spectroscopy. Decreased reflection coefficients caused by the sintering process are observed and quantified. Using THz near-field scanning imaging, it is shown that sintering produces a more uniform spatial distribution of permittivity in the printed carbon patterns. Images generated using THz-TDS based imaging are presented, demonstrating the combination of high resolution imaging with quantification of complex permittivities. This work, for the first time, demonstrates the feasibility of quality control in printed electronic-ink with THz sensing, and is of practical significance to the development of in-situ and non-contact commercial-quality characterisation methods for inkjet-printed electronics.     

干冰微粒喷射清洗技术

简要介绍了随着工艺节点的缩小,传统RCA清洗方法在硅片清洗工艺中的局限性和弊端,进而提出了以CO2为介质的新型干冰微粒喷射清洗方法。从CO2的物理特性出发,论述了CO2流经喷枪后形成干冰微粒的机理,并简要分析了干冰微粒喷射技术对颗粒污染物和有机污染物的清洗机理。在此基础上,介绍了自主研发的一台基于干冰微粒喷射技术的半导体清洗设备,对该设备的结构和各部分的作用作了简要介绍,论述了使用该设备对硅片进行清洗的工艺流程。通过对比实验发现,采用压强为8 MPa、纯度为5N的CO2作为气源,喷嘴前压强设置为11 MPa,使用该设备可以达到很好的清洗效果。     

Intermetal dielectric deposition by electron cyclotron resonance chemical vapor deposition (ECR CVD)

Advanced microprocessor and logic devices require multiple levels of metal to interconnect the many transistors that form them. Three-, four-, and five level metallization schemes are in production. The insulating material between these layers must fill very narrow gaps, without voids or seams, with a high quality dielectric, and must allow for subsequent global planarization such as chemical mechanical polishing (CMP). These requirements can be met with ECR CVD of silicon dioxide. ECR deposits high quality SiO₂ dielectric in a single wafer process that fills gaps 0.3 μm and smaller at aspect ratios 3:1 and greater on 200 mm wafers. Its electrical, optical, and chemical properties approach those of thermal oxide.     

Double modulated differential THz-TDS for thin film dielectric characterization

Terahertz differential time-domain spectroscopy (DTDS) is a new technique that uses pulsed terahertz radiation to characterize the optical properties of thin dielectric films. Characterizing thin films in the GHz to THz range is critical for the development of new technologies in integrated circuitry, photonic systems and micro-electro-mechanical systems. There are potential applications for gene and protein chips. This paper shows how DTDS can be combined with double modulation in the pump-probe system to improve sensitivity by an order of magnitude. An iterative algorithm is presented to estimate the optical properties of a given thin film. The technique is experimentally verified using 1-μm-thick samples of silicon dioxide on silicon.     

碳纳米管微电极的直流介质阻挡放电特性

研究了一种基于碳纳米管尖端的直流介质阻挡放电(DBD)微结构,使用MEMS加工工艺制作出深宽比0.5的侧壁相对的叉指状金属电极,在电极上电泳多壁碳纳米管,采用真空磁控溅射沉积二氧化硅介质层。在大气压下测试了所制备的DBD微结构样品的直流放电基本特性。实验结果表明,在几伏特的直流加载电压下即可检测到纳安量级的放电电流,并且放电电流对人体呼吸和环境气体变化有明显响应。放电起始电压小于10V并显现出明显的抑制电流自由增长的DBD放电特征,但电流下降持续时间达102～103s量级,大于常规常压DBD时间,显示出碳纳米管尖端的特异效应。     

Reliability challenges for copper low-k dielectrics and copper diffusion barriers

The performance of interconnects containing micro- (pore size smaller than 2 nm) and meso-porous (pore size larger than 2 nm) interlevel dielectrics is influenced by material selection, integration scheme and virtually all fabrication steps. It is generally reported that the reliability margin of the dielectric/barrier/copper system is shrinking. Barrier and dielectric integrity play a most important role in line-to-line leakage and Time Dependent Dielectric Breakdown (TDDB) reliability. TDDB has never been an issue for Cu-SiO₂ interconnects, but for sub-100 nm copper/barrier/low-k systems it becomes challenging. When monitoring the integrated dielectric properties early failures can be caused by weak integration interfaces, dielectric damage during the integration, defective diffusion barrier or other non-uniformities related to the damascene process. Recent advances are reviewed along with examples and reference to state of the art.     

In-situ measurement of dielectric thickness during etching or developing processes

A system has been developed which permits the measurement of dielectric film thicknesses in-situ during development or etching processes. This can be extended to growth or deposition processes. Two examples of its uses are presented: the determination of the thickness of phosphosilicate glass layers on silicon dioxide coated silicon wafers by making use of the etch rate differences, and the monitoring of photoresist thickness during development to characterize the photoresist development process.     

基于Web的温室大棚远程监测系统

温湿度、光照强度和二氧化碳浓度是影响温室大棚作物生长的三大要素,为实时监控这三种关键要素以及大棚作物现场状况,提高大棚作物产量,提出一种基于web的温室大棚远程监测系统设计方案。介绍了系统总体设计方案及主要硬件,在基于ARM的嵌入式linux系统上移植开源软件BOA和Mjpg-streamer搭建web服务器和视频服务器、移植SQLite构建数据库并详细阐述了它们的移植过程。在此基础上设计CGI网关程序,通过接入Internet的任意一台远程PC机或智能手机的浏览器可实时监控棚内环境状况并发送控制命令,真正实现温室作物种植网络化管理。     

Photoreduction of carbon dioxide by graphene–titania and zeolite–titania composites under low-intensity irradiation

As it is the most important of the greenhouse gases, the utilization and reduction of carbon dioxide have attracted a great attention. As compared to the technological demands for carbon capture and storage (CCS), carbon dioxide reduction is a safe and effective way to convert carbon dioxide to fuel. In this research, two different catalysts, graphene–titania and zeolite–titania, are used to achieve the carbon dioxide reduction. The characteristics of these materials are analyzed by Brunnauer–Emmett–Teller, X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet–visible, scanning electron microscope and transmission electron microscopy. Because of the different features of the catalysts, various products can be generated through different pathways. Formic acid and methanol are the final products when graphene is used as the catalyst, but only methanol can be generated when zeolite–titania is used as the catalyst. The reaction mechanisms and pathways are discussed.     

Pulsed DC magnetron sputtering deposition of crystalline photocatalytic titania coatings at elevated process pressures

The use of elevated process pressures is described in the magnetron sputter deposition of titanium dioxide photocatalytic coatings to enable the direct low-temperature formation of the most photoactive titania crystal phase; anatase. Most other works on this subject deal with relatively low ‘conventional’ pressures (0.1–0.5 Pa). However, the present work describes pulsed DC reactive magnetron sputtering deposition of titanium dioxide thin films at process pressures in the range 2–5 Pa in a purpose-built sputtering rig. The influence of the other deposition conditions, such as pulse frequency and duty cycle, is also discussed. Additionally, a series of N-doped titania coatings was produced by using air as the reactive gas. The morphological and compositional properties of the coatings were studied using energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Wettability of the films was studied through measurement of water contact angles under UV light irradiation. Photocatalytic properties of the samples were assessed through the degradation of two model pollutants, methylene blue and stearic acid, under UV light irradiation. The results showed that elevated process pressures (4 Pa and above) allow the direct deposition of anatase titania films, without additional heat treatment, while amorphous titania tends to form at lower process pressures.     

Preparation and properties of thin parylene layers as the gate dielectrics for organic field effect transistors

We report on the fabrication and characterization of parylene C thin layers for organic electronic devices passivation and gate dielectric of organic field effect transistors (OFETs) development. The investigated thin parylene layers were deposited from the vapour phase in thickness ranging from 3 to 800 nm at room temperature. The thickness and surface morphology of parylene layers were characterized by ellipsometry and AFM technique. The quality of parylene structures were analysed by X-ray reflectivity and diffraction as well as micro-Raman spectroscopy. The measurements confirmed perfect homogeneity and structural properties of parylene layers. Two types of pentacene OFETs were prepared on the silicone dioxide and parylene surface with bottom contact structures. The results demonstrated that using parylene, as the gate dielectric layer is an effective method to fabricate OFETs with improved electric characteristics.     

Optical properties of PECVD dielectric thin films: thickness and deposition method dependence

Low-k dielectric carbon doped silicon dioxide films 105-1255 nm in thickness, prepared by plasma-enhanced chemical vapor deposition (PECVD) in a six-station sequential deposition system and in a single deposition station, have been investigated for their optical properties using an optical spectrometer coupled with a hot stage. A decrease in refractive index, n, for films with six sub-layers compared with films with a single layer of similar thickness has been observed. This decreased refractive index is thought to be caused by the different effect of crystallinity of the substrate, as a film interface effect is introduced due to the different deposition methods. Both types of PECVD thin films show an increasing refractive index with increasing thickness, which could be attributed to the increased effective density with the increased thickness indicated from Fourier transform infrared spectroscopy microstructure analysis. Cauchy dispersion function is found to be valid for films within all the thickness range and with different deposition methods from visible spectrum to IR spectrum. The refractive index is found to decrease as the temperature increases from 25 to 450 °C at a fixed wavelength for all the films.     

Study of optical and dielectric properties of annealed ZnO nanoparticles in the terahertz regime

The frequency-dependent optical and dielectric properties of annealed ZnO nanoparticles in the range of 0.1 to 0.9 THz are studied by using terahertz time-domain spectroscopy（THz-TDS）.The refractive index,power absorption and complex dielectric constants are obtained and the experimental results are well fit with a simple effective medium theory in conjunction with a pseudo-harmonic model.This study reveals that annealed ZnO nanoparticles exhibit the similar phonon response characteristics to the single ZnO crystal and other ZnO nanostructures,such as tetrapods and nanowires.     

双层反射膜空芯传能光纤

利用化学气相沉积法 ,在毛细石英管内沉积GeO2 Al双层反射膜结构 ,增加内表面膜的反射率 ,降低传输损耗 ,该光纤可传输功率大于 80W的连续CO2 激光     

低介电常数多孔二氧化硅薄膜的制备与性能研究

利用Sol-Gel的方法制备了多孔二氧化硅薄膜。通过优化薄膜制备工艺,实现了多孔二氧化硅薄膜厚度在450nm～3000nm范围内可控,薄膜孔率为59%。用FTIR光谱分析了不同热处理温度下多孔二氧化硅薄膜的化学结构。研究了多孔二氧化硅薄膜的介电常数、介电损耗、漏电流等电学性能,结果表明多孔二氧化硅薄膜本征的介电常数为1.8左右,是典型的低介电常数材料。并通过原子力显微镜对薄膜的表面形貌进行了表征。     

Cathodoluminescence characterization of β-SiC nanowires and surface-related silicon dioxide

The main goal of our study is to prepare and to understand the properties of cubic SiC nanowires (NWs) and to characterize its native silicon dioxide. The wires, with diameters ranging from 10 nm to 2 μm, have been prepared by a CVD process on Si (0 0 1) substrates, using CO as the carbon source and Ni as the catalyst. A structural and optical analysis, by means of TEM, micro-Raman and cathodoluminescence (CL) spectroscopy, has been performed. Two sets of samples have been studied, labelled A and B, which differ for growth process conditions. Set A showed two broad CL peaks. Set B showed a much weaker CL emission. This difference has been explained by means of TEM investigation and micro-Raman spectra: set A shows a thick amorphous silicon dioxide layer on the wire surface, whereas set B shows a thin or absent oxide layer. Consequently, the nature of the CL emission has to be ascribed mainly to oxide-related recombination.