Fabrication of PDMS microlens array by digital maskless grayscale lithography and replica molding technique

This paper presents a facile and effective method to fabricate microlens array in polydimethylsiloxane (PDMS). The microlens array model is fabricated in photoresist via digital maskless grayscale lithography technique and the replica molding technique is used to fabricate PDMS microlens array. A convex PDMS microlens array with rectangular aperture and concave PDMS microlens array with hexagonal aperture are fabricated. The morphological characteristics of the microlens arrays are measured by microscope and 3D profiler. The results indicate that the profiles of the PDMS microlens arrays are clear and distinct. This method provides a simple and low-cost approach to prepare large area, concave or convex with arbitrary shape microlens array, which has potential application in many optoelectronic devices.     

二维光子晶体的软平板印刷技术制作研究

分析了软平板印刷技术制作二维光子晶体的特点和方法.利用绝缘PDMS模板,采用软平板印刷技术制造了三角晶系结构的二维聚合物光子晶体,采用同样的技术成功制成尺寸为150~500 nm,纵横比达1.25的高密度二维光子晶体.与其他制作技术相比,平板印刷技术具有大尺寸和易于制作的优点.结果表明,制作获得的微结构有很高的保真度.     

Fabrication of CoPt magnetic nanodot arrays by electrodeposition process

We attempted to fabricate patterned media using the electrochemical deposition process along with nanopatterned substrates prepared by the electron beam lithography (EBL), UV nanoimprint lithography (UV-NIL), and spin-on-glass nanoimprint lithography (SOG-NIL) approaches. CoPt was electrodeposited into the nanopatterned substrates and chemical mechanical polishing was carried out to planarize the surface. It was clarified that CoPt nanodot arrays were successfully deposited into the patterned nanopores fabricated by UV-NIL and SOG-NIL as well as by EBL with high area selectivity and uniformity. The density of the CoPt nanodot arrays deposited into the nanopores fabricated by EBL was equal up to an areal recording density of 250 Gbit/in².     

High-power laser interference lithography process on photoresist: Effect of laser fluence and polarisation

High throughput and low cost fabrication techniques in the sub-micrometer scale are attractive for the industry. Laser interference lithography (LIL) is a promising technique that can produce one, two and three-dimensional periodical patterns over large areas. In this work, two- and four-beam laser interference lithography systems are implemented to produce respectively one- and two-dimensional periodical patterns. A high-power single pulse of ∼8 ns is used as exposure process. The optimum exposure dose for a good feature patterning in a 600 nm layer of AZ-1505 photoresist deposited on silicon wafers is studied. The best aspect ratio is found for a laser fluence of 20 mJ/cm². A method to control the width of the sub-micrometer structures based on controlling the resist thickness and the laser fluence is proposed.     

Micropatterning and transferring of polymeric semiconductor thin films by hot lift-off and polymer bonding lithography in fabrication of organic field effect transistors (OFETs) on flexible substrate

Micropatterning and transferring of polymeric semiconductor thin films by hot lift-off and polymer bonding lithography in fabrication of OFETs with polymeric dielectric on the flexible substrate was proposed. The desired polymeric semiconductor patterns were fabricated on the flat polydimethylsiloxane (PDMS) surface with a selective lift-off method we proposed previously. The isolated and well defined polymeric semiconductor patterns left on the flat PDMS surface can be further transferred to the gate polymeric dielectric surface by polymer bonding lithography due to the low interfacial energy of PDMS. The transistor fabricated with this ‘dry’ process has a higher field-effect mobility compared with that using spin coated semiconductor layer.     

Fabrication of Nanoimprint Stamp Using Interference Lithography

Interference lithography is used to fabricate a nanoimprint stamp, which is a key step for nanoimprint lithography. A layer of chromium in thickness of about 20 nm is deposited on the newly cleaned fused silica substrate by thermal evaporation, and a layer of positive resist in thickness of 150nm is spun on the chromium layer. Some patterns, including lines, holes and pillars, are observed on the photoresist film by exposing the resist to interference patterns and they are then transferred to the chromium layer by wet etching. Fused silica stamps are fabricated by reactive ion etching with CHF3/O2 as etchants using the chromium layer as etch mask. An atomic force microscope is used to analyse the pattern transfer in each step. The results show that regular hole patterns of fused silica, with average full width 143nm at half maximum （FWHM）, average hole depth of 76nm and spacing of 450nm, have been fabricated. The exposure method is fast, inexpensive and applicable for fabrication of nanoimprint stamps with large areas.     

FIB快速加工纳米孔点阵的新方法

纳米尺度的点阵在纳米器件和基础科学研究方面都具有非常重要的应用.目前普遍采用的聚焦离子束和电子束曝光技术可以很方便的在衬底上加工纳米量级的微细结构，但大面积的图形加工过程需要花费太多的机时.介绍一种利用设计图形BMP文件的像素点阵和实际加工区域之间的匹配关系，通过聚焦离子束加工获得所需要的纳米孔点阵的新方法.采用这种方法可以在短时间内获得大面积的纳米点阵结构. 关键词： 聚焦离子束 电子束曝光 纳米孔点阵     

磁性量子元胞自动机功能阵列的实验研究

采用电子束光刻、热蒸镀和剥离工艺在室温下制备了多组磁性量子元胞自动机器件功能阵列. 实验研究了曝光剂量和曝光时间对三个不同间距参数磁性量子元胞自动机阵列图案的影响, 发现100 pA电子束束流和0.38 μs曝光时间可获得理想的阵列图案. 对制备的反相器阵列结构进行了磁力显微测试, 结果显示了正确的逻辑功能, 成功实现了不同间距参数功能阵列的实验制备. 此外, 实验还发现纳磁体阵列制备中容易出现缺陷, 模拟结果表明丢失纳磁体缺陷导致了信号传递反相.     

Profile calculation of gold nanostructures by dispersed-nanosphere lithography through oblique etching for LSPR applications

Nanosphere lithography is an inexpensive method used to fabricate gold nanostructures on a substrate. Using dispersed-nanosphere lithography, in which the nanospheres are dispersed on a substrate, 2D or 3D nanostructures can be fabricated by obliquely depositing a gold film on the nanospheres and etching the gold film afterward. These nanostructures are tunable and acute, and are thus good emitting elements for the localized surface plasmon resonance applications. So far, for the fabrication of nanostructures on a substrate with dispersed nanospheres, only 2D nanostructures have been reported through perpendicular etching. We report in this paper that the 3D nanostructures fabricated by dispersed-nanosphere lithography are rigid non-conformal structures, and perpendicular gold etching can be expanded to oblique etching, which provides more possibilities for fabricating the gold nanostructures in various shapes. The profiles of gold nanostructures after several varying angle depositions, and their final profiles after perpendicular or oblique etching, are calculated in this paper. Our profile simulations are applicable for nanospheres (or microspheres) within the range of tens of nanometers to tens of micrometers, and are consistent with our fabricated nanostructures observed using scanning electron and atomic force microscopy. Electronic Supplementary Material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Anti-sticking treatment for a nanoimprint stamp

Nanoimprint lithography (NIL), as a low-cost and mass production technique, has played an important role in micro/nano fabrication. However, the sticking problem between the stamp and resist blocks its further application. In order to modify the contact surface, a molecular dynamics (MD) method was used to choose the proper material to coat on the surface of the stamp. According to the MD analysis, CF₂ was found to be a good choice for this purpose. It was applied to the nanoimprint stamp by using the gases in reactive ion etching (RIE). A self-assembly monolayer (SAM) layer was also used in the experiment to release the contact surface energy. Both dry and wet methods were demonstrated as excellent anti-sticking approaches by measuring the contact angles and calculating the surface energy. Both the stamps after anti-sticking treatment can be used more times than the untreated stamps.     

Fabrication of a 256-bits organic memory by soft x-ray lithography

This paper reports a procedure of soft x-ray lithography for the fabrication of organic crossbar structure. Electron beam lithography is employed to fabricate the mask for soft x-ray lithography, with direct writing technology to lithograph positive resist, polymethyl methacrylate on the polyimide film. Then Au is electroplated on the polyimide film. Hard contact mode exposure is used in x-ray lithography to transfer the graph from the mask to the wafer. The 256-bits organic memory is achieved with the critical dimension of 250~nm.     

Subwavelength structures for broadband antireflection application

The subwavelength structures are designed and fabricated for broadband antireflection application. Under target of zero reflectivity, the parameters of periodic 2-D continuous conical structures are analyzed by the finite-difference time-domain (FDTD) method. The corresponding conical structures are obtained with spatial period of 350 nm and structure height of 300 nm, respectively. The 2-D continuous conical structured surface is fabricated by micro-replication process combining with the originated structure fabrication realized by interference lithography, Ni mold electroplation and replication by using UV imprinting into plastics. The average reflectances of the simulation and replicated polymer prototype are about 0.50% and 0.54% within the spectral ranges of 400-650 nm, respectively. In a word, the subwavelength structured surface with low reflection is developed and proved to be highly consistent with the simulation results.     

Design and analysis of the single-step nanoimprinting lithography equipment for sub-100 nm linewidth

Nanoimprint lithography (NIL) is the cutting-edge technology to produce sub-100 nm scale features on substrates. The fundamental procedure of nanoimprint lithography is replicating the patterns defined in the stamp to any deformable materials such as photoresist spun on substrates by pressing and the physical shape of the resist is deformed during the imprinting process. In this study, for the single-step nanoimprinting process, the 4-in. imprinting head, the fabricated 4-in. mask, the alignment system for multi-layer processes, and the six-DOF compliant mechanism of a wafer stage for single-step nanoimprinting on a 4-in. wafer are proposed. Using the designed nanoimprinting equipment, the nanoscale patterns with 100 nm linewidth and 150 nm height were clearly patterned on the substrate. Finally, the nanoimprinting results show the validity of the developed equipment.     

The three-dimensional photonic crystals coated by gold nanoparticles

We report on the fabrication of metallodielectric photonic crystals by means of interference lithography and subsequent coating by gold nanoparticles. The grating is realized in a SU-8 photoresist using a He-Cd laser of wavelength 442 nm. The use of the wavelength found within the photoresist low absorption band enables fabricating structures that are uniform in depth. Parameters of the photoresist exposure and development for obtaining a porous structure corresponding to an orthorhombic lattice are determined. Coating of photonic crystals by gold nanoparticles is realized by reduction of chloroauric acid by a number of reductants in a water solution. This research shows that the combination of interference lithography and chemical coating by metal is attractive for the fabrication of metallodielectric three-dimensionally periodic microstructures.     

Macromolecular nanoelectronics

We have explored new organic materials and fabrication methods to fabricate organic photodiodes and light emitting diodes. Grafting of a fullerene derivative to a polythiophene backbone yielded an integrated acceptor-donor polymer that we used as the active material in organic photodiodes. Using a method of soft lithography, soft embossing, we fabricated submicron structures to be used as organic light emitting diodes. Employing a silicone rubber replica (stamp) of an optical diffraction grating we transferred the grating pattern to an organic resist layer by placing the stamp in conformal contact with the resist. The transferred pattern was subsequently used as an etch mask for the processing of the device. The structures were successfully utilized as light emitting diodes and photodiodes, with device characteristics influenced by the imposed structure.     

A novel hanging bowl-shaped mask for the fabrication of vertical sidewall structures

Contact exposure is expected to occur in conventional lithography, and can be a source of process deviations (such as shrinking and distortion of templates) during reactive ion etching and inductively coupled plasma etching, as these deviations are induced by ion bombardment. This typically results in undesired sidewall effects, such as lower sidewall angles. Here we report a novel hanging bowlshaped lithography mask that can effectively minimize sidewall effects in lithography applications. As a test case, standard silicon carbide pillars with vertical sidewalls are fabricated using this mask. The mask could be used for fabrication of high-aspect-ratio structures with ultra-violet lithography.     

GaN基纳米阵列LED器件制备及发光特性

为了降低GaN材料中因应变诱导的量子斯托克斯效应,增加器件有源区内的电子-空穴波函数在实空间的交叠从而提高GaN基LEDs的发光效率,采用紫外软压印技术制备了均匀的周期性纳米柱阵列结构,结合常规LED器件微加工技术获得了In GaN/GaN基蓝光与绿光纳米阵列LED器件并对其进行了表征分析。结果表明:纳米柱阵列LED器件具有均匀的发光和稳定的光电性能。纳米结构不仅有效缓解了量子阱中的应力积累(弛豫度~70%),提高了器件的辐射复合几率和出光效率,同时结合纳米柱侧壁的化学钝化处理进一步降低了器件有源区的缺陷密度,显著降低了LED器件的漏电流(~10-7),最终提高了器件的发光效率。     

电子束重复增量扫描曝光技术

 提出了电子束重复增量扫描曝光技术新概念,对吸收能量密度与深度和曝光剂量之间的关系、溶解速度与吸收能量密度之间的关系进行了理论分析,发现溶解速度随曝光剂量增加而增大。以此为依据,在SDS-3型电子束曝光机上采用20 keV能量的电子束对570 nm厚的聚甲基丙烯酸甲酯进行了7次重复增量扫描曝光实验,得到了轮廓清晰的梯锥和圆锥3维结构,证明了电子束重复增量扫描曝光技术的可行性,为电子束加工3维结构提供了新工艺。     

The future of focused electron beam-induced processing

A perspective is sketched for the field of focused electron beam-induced processing (FEBIP). The FEBIP lithography technique is compared to the very successful resist-based electron beam lithography (EBL) technique. The advantages of FEBIP over EBL are identified, the main advantage being its high spatial resolution. This will enable FEBIP to become an important lithography technique for the fabrication of devices with critical dimension in the range between 1 and 20 nm and serve as a complementary technique to EBL. It will be discussed what needs to be done to achieve this and what the potential applications are.     

Influence of un-cured PDMS chains in stamp using PDMS-based lithography

We present the compatibility of elastomeric stamp, poly(dimethylsiloxane) (PDMS), with inks for non-photolithography. This ink limitation is important in considering the lamination of hydrophilic solution on the patterned ink surface using an elastomeric stamp. We focus on an increase of the hydrophobicity of the patterned surface due to diffusion of low molecular weight (LMW) silicone polymer chains. This hydrophobicity increases inversely with the PDMS–ink interaction parameter (χ), which is correlated with the solubility parameter (δ). This study's results translate into proposed design factors for ink used in the patterned functional layer for PDMS-based lithography. Both the XPS and the contact angle measurement show that the hydrophobicity can be increased by LMW PDMS chains transfer from stamps, and this increase can cause the expansion of the free volume in PDMS pores through a swelling effect.