Direct stamp fabrication for NIL and hot embossing using HSQ

Commonly stamps or masters for nanoimprinting are made by electron beam lithography (EBL) and subsequent reactive ion etching into silicon. Here we present a single step procedure to prepare stamps suitable for nanoimprinting and hot embossing. The stamps are directly fabricated in HSQ (hydrogen silsequioxane), a negative EBL resist, which has a high lateral resolution and good mechanical properties. We demonstrate successful pattern transfer in both bulk PMMA and PCL by hot embossing with features down to 20 nm. Such pattern transfer is useful for biological applications. Also, we demonstrate that this approach can make stamps suitable for nanoimprint lithography and have achieved features as small as 35 nm. It was found that the stability and strength of the HSQ could be improved by annealing and that the application of a non-stick coating was not necessarily required although it aided the demoulding.     

Electron beam lithography at 10 keV using an epoxy based high resolution negative resist

The behaviour of a new epoxy based resist (mr-EBL 6000.1 XP) as a negative resist for e-beam lithography is presented. We demonstrate that it is possible to define sub-100 nm patterns when irradiating thin (120 nm) layers of resist with a 10 keV electron beam. The dependence of resolution and remaining thickness on electron dose, electron energy and photo acid generator (PAG) content is determined. After the electron beam lithography process, the resist is used as a mask for reactive ion etching. It presents a good etch resistance, that allows transfer of patterns to the substrate with resolution below 100 nm.     

Development of interference lithography for 22 nm node and below

An extreme ultraviolet (EUV) interference lithographic exposure tool was installed at the long undulator beamline in NewSUBARU to evaluate EUV resists for 25 nm node and below. The two-window transmission grating of 40 and 50 nm half pitch (hp) were fabricated with techniques of spattering, electron beam lithography, dry etching and wet etching. hp patterns (20 and 25 nm) of chemically amplified resist (CAR) and non-CAR were successfully replicated using the EUV interference lithographic exposure tool.     

Stencil-assisted reactive ion etching for micro and nano patterning

Stencil-assisted oxygen reactive ion etching is a low-cost and parallel process for the replication of micrometric and nanometric patterns in any organic material. This lithography process allows the patterning of organic material non sensitive to electronic or optical radiations, sensitive to solvents, or already patterned which cannot be patterned by conventional lithography methods. We demonstrate the versatility of stencil-assisted reactive ion etching though 3 examples. First to define 500 nm holes in PMMA. Secondly, the fabrication step has been integrated in a lift-off process of metal or molecular self-assembled monolayers. We finally apply stencil-assisted reactive ion etching to pattern an assembly of 100 nm latex nanoparticles.     

A General Approach to Semimetallic,Ultra‐High‐Resolution,Electron‐Beam Resists

Commercial electron‐beam resists are modified into semimetallic resists by doping with 1–3 nm metal nanoparticles, which improve the resolution, contrast, strength, dry‐etching resistance, and other properties of the resist. With the modified resists, fine resist nanopatterns from electron‐beam lithography are readily converted into 5–50 nm, high‐quality multilayers for metallic nanosensors or nanopatterns via ion‐beam etching. This method solves the problem of the fabrication of fine (<50 nm) metallic nanodevices via pattern transferring.     

Fabrication of sub-micron high aspect ratio diamond structures with nanoimprint lithography

Polycrystalline diamond with optical quality has been patterned using nanoimprint lithography. Nanoimprint lithography is a rather new method for fabrication of resist structures with features sizes down to at least 20 nm. The pattern used in this article is a grating with a period of 600 nm and a fill factor of 0.5. Using plasma etching the nanoimprinted grating is etched into a freestanding diamond substrate. We have accomplished the fabrication of 300 nm diamond features with a depth of about 2 μm, which corresponds to an aspect ratio of 7.     

Sputtered metal lift-off for grating fabrication on InP based optical devices

Sputtered metal gratings have been realized using lift-off process based on bilayer resist electron beam lithography (EBL). The lithography mask is composed of PMMA (poly(methylméthacrylate)) layer deposited under HSQ (hydrogen silsesquioxane) inorganic resist. EBL is performed in HSQ, whereas PMMA is used to ease final lift-off. We demonstrate the possibility of patterning by lift-off metals with different sputtering yields and deposition conditions. Gratings with period of 200 nm and filling factor of 50% are obtained.     

Fabricating nanoscale device features using the 2-step NERIME nanolithography process

The 2-step negative resist image by dry etching (2-step NERIME) focused ion beam (FIB) top surface imaging (TSI) process is a novel nanolithography technique for creating nanometer scale resist features using conventional DNQ/novolak resists. The 2-step NERIME process combines the advantages of FIB lithography and TSI processing, delivering high aspect ratio nanometer-scale resist critical dimensions (CDs). Previous work has reported 90 nm resist CDs over substrate topography using the 2-step NERIME process, and 80 nm etched features masked using resist patterned by the 2-step NERIME process. In this work we further extend the 2-step NERIME process, and demonstrate its potential as a low-cost and convenient nanolithography option for proof-of-concept nanoscale fabrication, through the creation of sub-100 nm titanium-nitride (TiN) device features.     

Characteristics of negative electron beam resists, ma-N2410 and ma-N2405

We have characterized the electron beam lithography (EBL) properties of the new negative tone resists, ma-N2410 and ma-N2405. These negative resists reacts under low electron dose values from 10 to 140 μC/cm², tested using 10, 20, 28 keV electron beam. There was negligible loss of pattern height, which was attributed to the combined dose of the incident electron beam and the backscattered electrons. Experimental tests were performed under various EBL writing conditions of dose value, developing time, line-width and resist thickness. Our investigation showed that these new commercially available resists have high resolution and high contrast with non-chemical amplification, useful for micro-fabrication application.     

Silated acidic copolymers for nanoimprint lithography on flexible plastic substrates

A new silated acidic polymer was developed as the resist for nanoimprint lithography on flexible substrates. This polymer was synthesized from methylmethacrylate, n-butylacrylate, methacrylic acid and 3-[tris(trimethylsiloxy)silyl]propyl methacrylate by free radical copolymerization with an azobisisobutyronitrile (AIBN) initiator at 90 °C. The resist has excellent reactive ion etching (RIE) resistability, a lower T_g (43 °C) compared to poly(methyl methacrylate) (PMMA) and good flowability. It is suitable to use on flexible plastic substrates. The resist can be easily removed by an aqueous base solution at the final stripping step, instead of using an organic solvent or RIE. A 100 nm/50 nm (line/space) feature pattern was obtained on a flexible polyethylene terephthalate (PET)/ITO substrate.     

多能点X射线透射光栅的制作技术

针对X射线自支撑透射光栅在多能点单色成像光栅谱仪中的应用,采用电子束和光学匹配曝光、微电镀和高密度等离子体刻蚀技术,成功制备了周期为500nm、金吸收体厚度为350nm、占空比接近1∶1,满足三个能点成像需求的2000lp/mm X射线自支撑透射光栅。首先利用电子束光刻和微电镀技术制备金光栅图形,然后采用紫外光刻和微电镀技术制作自支撑结构,最后通过腐蚀体硅和感应耦合等离子体刻蚀聚酰亚胺完成X射线自支撑透射光栅的制作。在电子束光刻中,采用几何校正和高反差电子束抗蚀剂实现了对纳米尺度光栅图形的精确控制。实验结果表明,同一个器件分布的三块光栅占空比合理,栅线平滑,可以满足单能点单色成像谱仪的要求。     

Surface charging suppression using PEDOT/PSS in the fabrication of three dimensional structures on a quartz substrate

Pattern writing on insulating materials (e.g. quartz) using electron beam lithography (EBL) is a challenging task and it is even more difficult when the pattern is three dimensional (3D). Surface charging trapped on insulating substrates may deflect the electron beam during electron beam pattern writing causing undesired effects.In this work, the surface charging has been suppressed by top coating with water soluble conductive polymer layer using poly (3,4-Etylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS). The 3D masking profiles are created on a negative tone photoresist (Microresist, ma-N2403) using Raith150 EBL tool with variable dose controlled beam exposure. The 3D patterns have been transferred onto the quartz substrate by single step reactive ion etching (RIE) with suitable resist to substrate selectivity.We have demonstrated the fabrication of 3D geometrical shapes such as pyramids, hemispheres, and cones with dimensions down to 300 nm using this technique without any surface charging effects.     

UV nanoimprint lithography of sub-100 nm nanostructures using a novel UV curable epoxy siloxane polymer

We reported the replication of sub-100 nm nanostructures by an ultraviolet (UV) nanoimprint lithography (NIL) technique. We used a novel UV curable epoxy siloxane polymer as the NIL resist to achieve features as small as 50 nm. The polymeric soft molds for the NIL were fabricated by casting toluene diluted poly(dimethyl-siloxane) (PDMS) on the hydrogensilsesquioxane (HSQ) hard mold. The NIL results were characterized by using a scanning electron microscope and an atomic force microscope. Our results illustrate that, with the epoxy siloxane resist, the 50 nm HSQ features on the hard mold can be successfully replicated using PDMS soft molds.     

Large area nanosize array stamp for UV-based nanoimprint lithography fabricated by size reduction process

A novel size reduction process using electron beam lithography (EBL) combining with wet etching technique is developed as a possible solution for producing large area and low cost nanopattern stamp for UV-based nanoimprint lithography (UV-NIL). In the first step, a microstructure stamp with 1.4 μm periodical pore array and aspect ratio of 1:1 was formed over a 1 inch² area on a quartz substrate. This process was carried out using common electron beam lithography (EBL) equipment, which was easily available in the modern integrated circuits (IC) semiconductor factory. Afterwards, with a controlled wet etching technique, the pore array was changed into tip patterns with the line width below 100 nm and the period keeping as before. The uniformities and nanopattern accuracies were investigated to identify its possibility as a UV-NIL stamp by AFM and SEM. Finally, as a demonstration, the as obtained stamp was used as a positive stamp to replicate the nanotips into UV-curable resist successfully by a UV-NIL process. The method developed for the mold of nanoimprint lithography would be a simple and low price approach to fabricate large area UV-NIL stamp and the nanotip array structures would be widely used in two dimensional (2D) photonic crystal application.     

A process for the fabrication of large areas of high resolution,high aspect ratio silicon structures using a negative tone Novolak based e-beam resist

The non-chemically amplified negative resist ARN 7520 produced by ALLRESIST GmbH shows excellent suitability for fabricating stamps for nanoimprinting with a pitch resolution as high as 70 nm and dense periodical structures using e-beam lithography and dry etching. Due to its chemical formulation, the resist does not swell in the developer, has good sensitivity and contrast. The adhesion of such class of resists is provided by silane containing promoters used before the spin-coating. However, for the lower exposure doses, the bonding of the nanostructures to the surface is still insufficient. Instead of the promoter, we evaporate 3–5 nm Ti layer before the resist spin-coating. This strongly improves the resist adhesion in a wide range of exposure doses, suppresses the influence of the substrate conductivity on the electron beam lithography parameters and also improves the structure profile during dry etching. Reducing ion voltage from 400 to 200 V midway through dry etching also helps to keep the structure walls more vertical. Silicon stamps with lines and spacings of 70–100 nm periods and an area of 3 × 3 mm² have been successfully fabricated.     

Fabrication and characterization of bilayer metal wire-grid polarizer using nanoimprint lithography on flexible plastic substrate

In this work, we demonstrate the fabrication of bilayer metal wire-grid polarizers and the characterization of their performance. The polarizers with 200 nm period were fabricated on flexible plastic substrates by nanoimprint lithography (NIL), followed by aluminum deposition. Transmission efficiency over 0.51 and extinction ratio higher than 950 can be achieved in the visible range when the aluminum thickness of the polarizer is 100 nm. The fabrication process only involves direct imprinting on flexible plastic substrates and aluminum deposition, without any resist spin-coating, lift-off, and etching processes, which is much simpler, less costly, and applicable to large volume production.     

Generation and characterization of polymeric tridimensional microstructures for micromachine application

In this work, we use the thick layer of polymethylmethacrylate polymer, for micromachining development. In the development of the structures, a three layer process is used. In a silicon wafer is deposited the thick layer spin coating. Over this layer is deposited a thin layer of silicon. The third layer is 1.5 μm of e-beam resist deposited by spin coating. After the deposition of the layers, we perform the e-beam lithography in the top layer resist. This pattern is transferred by plasma etching for the silicon layer. The resolution limits of this process is the resolution of the electron resist and is increased to 0.25 μm (nanometric resolution), using an electron beam spot size of 50 nm and dry development.     

高分辨率SiNx纳米压印模板的快速制备工艺

纳米压印技术是近年来国际新兴的纳米光刻技术,具有高分辨率、高效率和低成本等优点。本文结合电子束光刻技术和干法刻蚀技术开发了简洁的纳米压印SiNx光栅模板制造工艺。为提高工艺效率,引进高灵敏度的化学放大胶NEB-22胶（负性胶）作为电子光刻胶,用电子束光刻技术在NEB-22上刻出光栅图形,再利用其作为掩膜,经反应离子刻蚀后,将光栅图形转移到氮化硅上,得到所需模板。文中详细研究了NEB-22胶的电子束光刻特性及其干法刻蚀特性,指出了它作为电子束光刻胶的优点及它相对于铬掩膜而言作为干法刻蚀掩膜的不足。     

Zinc-Imidazolate Films as an All-Dry Resist Technology

Motivated by the drawbacks of solution phase processing, an all-dry resist formation process is presented that utilizes amorphous zinc-imidazolate (aZnMIm) films deposited by atomic/molecular layer deposition (ALD/MLD), patterned with electron beam lithography (EBL), and developed by novel low temperature (120 °C) gas phase etching using 1,1,1,5,5,5-hexafluoroacetylacetone (hfacH) to achieve well-resolved 22 nm lines with a pitch of 30 nm. The effects of electron beam irradiation on the chemical structure and hfacH etch resistance of aZnMIm films are investigated, and it is found that electron irradiation degrades the 2-methylimidazolate ligands and transforms aZnMIm into a more dense material that is resistant to etching by hfacH and has a C:N:Zn ratio effectively identical to that of unmodified aZnMIm. These findings showcase the potential for aZnMIm films to function in a dry resist technology. Sensitivity, contrast, and critical dimensions of the patterns are determined to be 37 mC cm⁻², 0.87, and 29 nm, respectively, for aZnMIm deposited on silicon substrates and patterned at 30 keV. This work introduces a new direction for solvent-free resist processing, offering the prospect of scalable, high-resolution patterning techniques for advanced semiconductor fabrication processes.     

Fast patterning and dry-etch of SiNχ for high resolution nanoimprint templates

We developed a simplified nanofabrication process for imprint templates by fast speed electron beam lithography (EBL) and a dry etch technique on a SiNx substrate, intended for large area manufacturing. To this end,the highly sensitive chemically amplified resist (CAR), NEB-22, with negative tone was used. The EBL process first defines the template pattern in NEB-22, which is then directly used as an etching mask in the subsequent reactive ion etching (RIE) on the SiNx to form the desired templates. The properties of both e-beam lithography and dry etch of NEB-22 were carefully studied, indicating significant advantages of this process with some drawbacks compared to when Cr was used as an etching mask. Nevertheless, our results open up a good opportunity to fabricate high resolution imprint templates with the prospect of wafer scale manufacturing.