多光束激光干涉光刻图样

利用电磁理论,研究了多光束激光干涉图样的产生原理,结合计算机数值模拟和相关实验结果,分析了干涉图样的影响因素。研究结果表明：多光束激光干涉图样可以看成是多组余弦分布的平行线条纹的叠加;相干光束的偏振方向、入射方向、光束间相差是干涉图样的重要影响因素,改变这些因素,余弦分布的平行线条纹的振幅、置、周期和方向发生变化,图样也随之变化。     

Influences of water on photoresist surface in immersion lithography technology

In this study, we evaluated the influence of photoresist-water contact time on the quantity of the photoacid generator (PAG) leached from photoresists into pure water and alteration of the photoresist composition using LC-MS, XPS, and TOF-SIMS, by employing exposed and unexposed photoresists. As a result, the quantity of PAG leached into pure water increased as the contact time elapsed. Then, it was observed by TOF-SIMS that the quantity of the PAG on the photoresist surface decreased as the contact time elapsed. Regarding the ratio of the functional groups on the photoresist surface, the methyladamantyl group decreased but the carboxyl group increased because of exposure, respectively. On the exposed photoresist surface, the methyladamantyl group increased as the contact time elapsed. This was strongly related to the phenomenon that the quantity of methyladamantyl group was different between the inside and surface of photoresist.     

Study on wetting properties of periodical nanopatterns by a combinative technique of photolithography and laser interference lithography

This study presents the wetting properties, including hydrophilicity, hydrophobicity and anisotropic behavior, of water droplets on the silicon wafer surface with periodical nanopatterns and hierarchical structures. This study fabricates one- and two-dimensional periodical nanopatterns using laser interference lithography (LIL). The fabrication of hierarchical structures was effectively achieved by combining photolithography and LIL techniques. Unlike conventional fabrication methods, the LIL technique is mainly used to control the large-area design of periodical nanopatterns in this study. The minimum feature size for each nanopattern is 100 nm. This study shows that the wetting behavior of one-dimensional, two-dimensional, and hierarchical patterns can be obtained, benefiting the development of surface engineering for microfluidic systems.     

激光干涉光刻法制作100 nm掩模

介绍了一种利用激光干涉光刻技术得到特征图形,并通过离子束刻蚀将图形转移到铬层上,从而获得掩模的方法。针对掩模透光率以及对干涉图形对比度可能产生影响的两个参数分别进行了数值仿真,从而证明此方法的可行性和参数的优化选择。自搭干涉光刻实验系统,用257 nm的激光光源实现光刻,得到特征尺寸为100 nm的图形,再经过离子束刻蚀,最终得到周期200 nm、线宽100 nm的掩模。     

Effects of laser fluence on near-field surface nanostructuring

In this work, molecular dynamics simulation is performed to explore the long-time (up to 5 ns) behavior of argon crystal in surface nanostructuring with an extremely localized near-field laser beam. The surface nanostructuring region is limited to tens of nanometers in diameter, although the simulated systems are much larger (comprised of more than 770,000 atoms). This study focuses on the long-time solidification and crystallization procedure, which is driven by the heat conduction in the material. The effect of the computational domain on the final nanostructure is studied in detail. Different laser fluences are used in the simulation to explore how and to what extent the energy input affects the dynamic melting behavior and the final dimension and profile of the surface nanostructure. In-depth theoretical investigation gives satisfactory explanation of the effect of the laser fluence on the melting depth. Spot-like structural defects in the sub-surface region are observed and investigated until full solidification.     

Superhydrophobic surface structures in thermoplastic polymers by interference lithography and thermal imprinting

We present a method to produce superhydrophobic surfaces in thermoplastic polymer substrates. The method involves the creation of a nickel stamp using a customized laser interference lithography technique and electroplating processes. This stamp is used to emboss sub-micrometer periodic structures into the thermoplastic. The modified surface is coated with a hydrophobic plasma-polymerized hexafluoropropene layer. Surfaces with different periodicity and relief depth were created. On the surface with the highest aspect ratio, advancing water contact angles of 167° were measured with a water contact angle hysteresis of below 5°.     

Optimum design of photoresist thickness for 90-nm critical dimension based on ArF laser lithography

In this work,a 90-nm critical dimension(CD) technological process in an ArF laser lithography system is simulated,and the swing curves of the CD linewidth changing with photoresist thickness are obtained in the absence and presence of bottom antireflection coating(BARC).By analysing the simulation result,it can be found that in the absence of BARC the CD swing curve effect is much bigger than that in the presence of BARC.So,the BARC should be needed for the 90-nm CD manufacture.The optimum resist thickness for 90-nm CD in the presence of BARC is obtained,and the optimizing process in this work can be used for reference in practice.     

Research on the optical field distribution and micro-fabrication model in convex-surface laser lithography

A system of convex-surface laser lithography with diode laser is established in this paper. Based on this system, a mathematical model of optical field distribution and lithography on the photoresist layer of convex-surface substrate with diode laser is presented. According to the lithography system and model, some numerical simulations are carried out. The simulation result shows that lithographic lines on convex-surface lithography are not symmetric about the optical axis of incident laser beam. Axis of lines at different vector radius on convex-surface substrate will offset from the wavefront normal of incident laser beam. The offset distance depends on the slopes of different equivalent slants. The simulative results of lithographic model agree well with the lithographic experimental data.     

双尺度织构的激光光刻工艺

搭建了双光束激光干涉光刻系统和激光快速扫描系统。利用干涉光刻系统,实现了不同周期、不同深度、大面积的表面规则光栅织构的构筑。利用激光快速扫描器的二维扫描功能,通过控制激光功率和扫描速度,对曝光量和填充线条间距进行了优化。提出了两种双尺度复合织构的制备方法：一种是在激光快速扫描系统中对抗蚀剂表面分别进行x, y方向的扫描光刻,然后在干涉光刻系统中进行双光束干涉光刻;另一种是在激光干涉光刻系统中进行两次曝光,每次曝光的入射角不同。实验结果表明：这两种方法在制备双尺度复合织构方面具有快速、廉价、操作简易等优点。     

The theoretic analysis of maskless surface plasmon resonant interference lithography by prism coupling

The use of an attenuated total reflection-coupling mode of prism coated with metal film to excite the interference of the surface plasmon polaritons （SPPs） was proposed for periodic patterning with a resolution of subwavelength scale. High intensity of electric field can be obtained because of the coupling between SPPs and evanescence under a resonance condition, which can reduce exposure time and improve contrast. In this paper, several critical parameters for maskless surface plasmon resonant lithography are described, and the preliminary simulation based on a finite difference timedomain technique agrees well with the theoretical analysis, which demonstrates this scheme and provides the theoretical basis for further experiments.     

Impact of process parameters on pattern formation in the maskless plasmonic computational lithography

The extraordinary optical transmission through a sub-wavelength size metal-aperture and metamaterials has been tremendous interests for the untilization of the surface plasmon polariton (SPP). Its technology, however, is hard to apply for the optical lithography process. In this study, a maskless plasmonic lithography (MPL) is modeled and simulated for 15-nm critical dimension (CD). The near-field intensity with the plasmonic phenomena of aperture shapes is described due to aperture parameters by using a scattering matrix (S-matrix) analysis method and the finite difference time domain (FDTD) method. MPL parameters of bowtie structures are optimized and improved for the imperfection of the resist pattern. The most dominant parameter on CD is gap size of bowtie by Taguchi method.     

连续激光干扰效果评估方法北大核心CSCD

采用改进后的图像相关度计算方法,在精确配准干扰前后图像的基础上,以像素为单位计算图像相关度,根据人眼识别效果在评估前确定干扰阈值,计算图像有效干扰像元统计值,定量描述激光干扰效果;开展多波段激光干扰成像系统试验,采集不同干扰功率下的激光干扰图像,评估干扰效果。结果表明,该方法能精确识别图像局部变化,客观反映图像质量变化,对各波段不同功率下的激光干扰成像图像给出科学评估结果,对单对图像的处理速度优于s级,具有一定的工程应用价值。     

Comparison of the laser ablation process on Zn and Ti using pulsed digital holographic interferometry

Pulsed digital holographic interferometry has been used to compare the laser ablation process of a Q-switched Nd-YAG laser pulse (wavelength 1064 nm, pulse duration 12 ns) on two different metals (Zn and Ti) under atmospheric air pressure. Digital holograms were recorded for different time delays using collimated laser light (532 nm) passed through the volume along the target. Numerical data of the integrated refractive index field were calculated and presented as phase maps. Intensity maps were calculated from the recorded digital holograms and are used to calculate the attenuation of the probing laser beam by the ablated plume. The different structures of the plume, namely streaks normal to the surface for Zn in contrast to absorbing regions for Ti, indicates that different mechanisms of laser ablation could happen for different metals for the same laser settings and surrounding gas. At a laser fluence of 5 J/cm², phase explosion appears to be the ablation mechanism in case of Zn, while for Ti normal vaporization seems to be the dominant mechanism.     

多台阶器件结构深层表面光刻工艺优化

针对多台阶器件结构深层表面光刻工艺中存在的问题,对不同台阶高度分别测量了台阶表面及台阶底部沉积的光刻胶厚度,并对台阶高度与光刻胶厚度的关系进行数值描述与分析.基于Beer定律对薄光刻胶光吸收系数的描述,分析了通过实验得到的不同曝光时间下光刻胶的光强透过率曲线,解释了随着曝光时间的增加光刻胶光强透过率发生变化的原因,同时认为光刻胶光吸收系数与光刻胶厚度密切相关.在此基础上,确定了台阶底部堆积光刻胶完全曝光所需时间.优化平面光刻工艺,在不同台阶高度的深台阶表面及底部同时制作出窄线条的高质量图形.     

Near field properties of nanoparticle arrays fabricated by laser annealing of thin Au and Ag films

In this work we show the properties of the electromagnetic field in the vicinity of a monolayer nanoparticle array on SiO₂ substrate. The nanoparticle array is produced by a simple experimental procedure, where thin gold and silver films are deposited on a substrate by pulsed laser deposition technique and they are annealed by nanosecond laser pulses. At certain conditions the laser annealing leads to a homogeneous decomposition of the film into nanoparticles with diameters in the range of few tens of nanometers. Using FDTD simulations the near field distribution in array structures taken from SEM images are obtained. The distribution shows presence on “hot spots” where the near field intensity is enhanced more than two orders of magnitude compared to the incident one. The existence of enhanced field intensity is assumed to be the main reason on enhancement of the Raman scattering signal obtained experimentally using the produced structures as active substrates.     

激光触发真空沿面闪络开关的初步实验研究

 介绍了沿面闪络开关的发展状况和基本原理，实验研究了真空条件下激光触发介质沿面闪络特性。实验采用固体Nd:YAG纳秒激光器作为触发源，对试样施加正直流高压，电压范围1～6 kV，试样绝缘子为直径50 mm的尼龙6。通过研究不同激光能量、波长和聚焦形状对介质闪络的影响，总结出适用于沿面闪络开关的激光触发形式。实验表明：在一定电场和真空度下闪络的时延和抖动将随着输入激光能量的提高而减小，而激光可触发的电压范围将提高；激光波长减小有助于提高触发的稳定性；激光焦斑的形状是沿面闪络触发的最大影响因素，采用具有一定能量密度、焦斑横跨两电极的带状激光来触发闪络是闪络开关的理想选择。     

RIMAPS and variogram analysis of the surface topography induced by laser interference micropatterning

A micropattern induced by laser interference on the surface of a copper alloy specimen is characterized using rotated image with maximum average power spectrum (RIMAPS) technique and the variogram method. The experimental bidimensional pattern is compared to the expected ideal regular one. Results confirm that the systematic use of RIMAPS and variograms, helps to determine how far the real surface obtained in the experiment differs from ideal regular micropattern. The dimensions of irregularities that cause the discrepancy between the obtained and ideal micropattern are also quantified.     

Direct laser interference patterning of multi-walled carbon nanotube-based transparent conductive coatings

Topographical structures were created on the surface of multi-walled carbon nanotube-based coatings deposited on borosilicate glass using the direct laser interference patterning (DLIP) technique. Films made by multi-walled carbon nanotubes (MWNTs) dispersed in antimony-doped tin oxide (ATO) matrix and networks of MWNTs with both low and high adherence to the substrates were irradiated with one single laser pulse. Due to the high absorption coefficient of ATO, the film was completely removed at the interference maxima positions leading to periodic arrays of high quality on macroscopic areas. Additionally, increase of the laser fluence has produced wider ablated regions. Irradiation of high adherent networks of MWNTs produced a periodic porous structure, what has been attributed to the presence of adherence promoters in the film. On the other hand, MWNT networks with low adhesion to the substrate were strongly removed at the interference maxima positions. In this case, however, the fabricated periodic structures presented several defects that result from the poor adherence of the film to the substrate.     

Effects of laser intensity and ambient conditions on the laser-induced plume

Laser ablation presents a promising technique for material processing. The quality of products is strongly influenced by the properties of the laser-induced plume. In compressible flow, the ambient conditions can be transmitted upstream. Therefore, the laser ablation process is strongly affected by the ambient conditions. In this paper, the effects of laser intensity, back pressure and temperature on the laser-induced plume were studied using a numerical model, which calculates the density, pressure and temperature of the laser-induced plume at different laser intensity and ambient conditions. The results are in agreement with experimental results available in the literature and can be used for the optimization of the pulsed laser deposition process.     

Quantum interference and diffraction of parametric down-converted biphotons

We present two-photon diffraction and interference experiments utilizing parametric down-converted photon pairs (biphotons) and a transmission grating. The biphoton exhibits a diffraction-interference pattern equivalent to an effective single particle with half wavelength of the constituent photons.