纳米压印工艺中关键技术

纳米压印技术由于其分辨率高、工艺成本低以及适于大规模工业化生产的优点被广泛利用于纳米尺度的半导体器件的制作之中。然而,传统的硬模板压印技术存在着模板寿命短、大面积均匀性差以及易受颗粒影响的缺点。本文提出了一种高分子聚合物软模板（IPS）压印的方法来改进以上缺点,同时,本文提出在软模板制作和后续的紫外压印中采用变温变压阶梯升降压的方法来提高压印过程中胶的流动性,以提高压印图形的质量。最后,我们利用这种方法方法出了高质量的50纳米线宽的光栅图形。     

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.     

Fabrication of ordered micro- and nano-scale patterns based on optical discs and nanoimprint

A simple method to fabricate one-dimensional(1-D) and two-dimensional(2-D) ordered micro- and nano-scale patterns is developed based on the original masters from optical discs, using nanoimprint technology and soft stamps. Polydimethylsiloxane(PDMS) was used to replicate the negative image of the 1-D grating pattern on the masters of CD-R, DVD-R and BD-R optical discs, respectively, and then the 1-D pattern on one of the PDMS stamps was transferred to a blank polycarbonate(PC) substrate by nanoimprint. The 2-D ordered patterns were fabricated by the second imprinting using another PDMS stamp. Different 2-D periodic patterns were obtained depending on the PDMS stamps and the angle between the two times of imprints. This method may provide a way for the fabrication of complex 2-D patterns using simple 1-D masters.     

UV enhanced substrate conformal imprint lithography (UV-SCIL) technique for photonic crystals patterning in LED manufacturing

The global LED (light emitting diode) market reached 5 billion dollors in 2008 and will be driven towards 9 billion dollors by 2011 [1]. The current applications are dominated by portable device backlighting, e.g. cell phones, PDAs, GPS, laptop etc. In order to open the general lighting market doors the luminous efficiency needs to be improved significantly. Photonic crystal (PhC) structures in LEDs have been demonstrated to enhance light extraction efficiency on the wafer level by researchers [2]. However, there is still a great challenge to fabricate PhC structures on LED wafers cost-effectively. Nanoimprint lithography (NIL) [3] has attracted considerable attentions in this field due to its high resolution, high throughput and low cost of ownership (CoO). However, the current NIL techniques with rigid stamps rely strongly on the substrate flatness and the production atmosphere. Those factors hinder the integration of NIL into high volume production lines. UV-NIL with flexible stamps [4], e.g. PDMS stamps, allows the large-area imprint in a single step and is less-sensitive to the production atmosphere. However, the resolution is normally limited due to stamp distortion caused by imprint pressure.A novel NIL technique developed by Philips Research and Süss MicroTec, substrate conformal imprint lithography (SCIL), bridges the gap between UV-NIL with rigid stamp for best resolution and soft stamp for large-area patterning. Based on a cost-effective upgrade on Süss mask aligner, the capability can be enhanced to nanoimprint with resolution of down to sub-10 nm on an up to 6 inch area without affecting the established conventional optical lithographic processes on the machine. Benefit from the exposure unit on the mask aligners, the SCIL process is now extended with UV-curing option, which can help to improve the throughput dramatically. In this paper, the fabrication of photonic crystal structures with SCIL technique on Süss MA6 mask aligner is demonstrated. In addition, the industrialization considerations of UV-SCIL process in high volume manufacturing are briefly discussed.     

用于纳米器件的电子束与光学混合光刻技术

成功开发出了一种可用于纳米结构及器件制作的电子束与光学光刻的混合光刻工艺。通过两步光刻工艺,在栅结构层上采用大小图形数据分离的方法,使用光学光刻形成大尺寸栅引出电极结构,利用电子束直写形成纳米尺寸栅结构,并通过图形转移工艺解决两次光刻定义的栅结构的叠加问题。此混合光刻工艺技术可以解决纳米电子束直写光刻技术效率较低的问题,同时避免了电子束进行大面积、高密度图形曝光时产生严重邻近效应影响的问题。这项工艺技术已经应用于先进MOS器件的研发,并且成功制备出具有良好电学特性、最小栅长为26 nm的器件。     

The fabrication of three-dimensional nano-structures by defocused electron beam energy

We demonstrate a novel method to fabricate three-dimensional structure with various shapes using defocused electron beam lithography (DEBL) for optical elements. In this study, we experimentally analyzed the relationship between the shape profiles of exposed patterns and defocusing length by varying parameters for e-beam lithography.Through these experiments, we found out that the shape profiles of exposed patterns depended on the defocusing length at the specific conditions in the e-beam lithography. This is due to the fact that the distribution and intensity of electron beam energy are changed by the defocusing length degree in the DEBL. These results allow the fabrication of three-dimensional (3D) structures with various shapes for optical elements by varying the defocusing length under the proper conditions of e-beam lithography. Based on these results, we can fabricate the 3D patterns with hemispherical shape for nano lens array and nano cone shape for SERS (surface enhanced Raman spectroscopy) and optical diffraction grating patterns with nano scale depth and width.     

Probing individual nanoscale organic light-emitting diodes with atomic force electroluminescence microscopy and bridge-enhanced nanoscale impedance microscopy

Two recently developed atomic force microscopy (AFM) techniques are used to characterize the impedance and charge transport/emission characteristics of individually addressed micro- and nano-scale organic light-emitting diodes (OLEDs). To fabricate independent diodes at this length scale, a suspended silicon nitride membrane shadow mask scheme is employed with semiconductor processing and electron beam lithography. This approach enables the fabrication of individually addressable OLEDs ranging in size from microns down to hundreds of nanometers. Atomic force electroluminescence microscopy (AFEM) and bridge enhanced nanoscale impedance microscopy (BE-NIM) are used to characterize these devices. AFEM offers real-time nanometer-scale spatial resolution mapping of simultaneously acquired current, topography, and light emission data while BE-NIM enables real-time impedance spectroscopy studies of functioning OLEDs. These two AFM techniques are shown to be capable of analyzing device-to-device response variations across a broad range of length scales and to provide unique quantification of intra-array device variations.     

Fabrication of roll imprint stamp for continuous UV roll imprinting process

Recently, nano imprint lithography has been developed for mass production of nano-scale patterns on large-scale substrates. To achieve high throughput and cost reduction, roll-to-roll imprint lithography has been introduced. The roll-to-roll imprint is the suitable process for large area patterning, especially, flexible substrates for display devices. In this study, roll-to-roll imprint stamp is fabricated using poly-vinyl alcohol (PVA) mold and UV curable poly-dimethylsiloxanes (PDMS) resin for continuous roll imprinting process. The PVA mold was chosen since it is flexible and can be dissolved in water. Since the PDMS can form thin SiO_x layer on the surface by oxygen plasma treatment, silane based hydrophobic anti-stiction layer can be formed directly on the surface of PDMS. As a result, nano-sized patterns were successfully formed on the flexible PET films by UV roll imprinting with the fabricated roll stamp.     

MMI微压印模板的设计与研究

微纳米压印技术作为代替传统光刻的一种新兴技术,有着重要的应用潜力。近年来在直接加工微器件如微流体、微生物器件,特别是在微平面光学器件方面得到了较快的发展。采用微压印法直接加工聚合物微平面光学器件是一个具有实用价值和研究价值的课题。该文首先讨论并选取了聚甲基丙稀酸甲酯(PMMA),研究了聚合物多模干涉(MMI)耦合器器件的微压印模板的设计和加工,讨论了压印模板材料的影响。根据典型基于MMI聚合物分光器件模板的设计实例,由聚合物的光学性能和分光要求,设计出模板的几何尺寸,通过微细加工工艺加工出模板,并给出了初步的热压印实验结果。     

Fabrication of nickel stamp with improved sidewall roughness for optical devices

We proposed the simple and attractive fabrication method of nickel stamp with improved sidewall roughness for polymeric optical devices. For this, the imprinted optical devices patterns under optimum imprinting conditions were annealed to improve the sidewall roughness generated by the DRIE process in the silicon stamp fabrication. The annealed sidewall roughness is reduced to 24.6 nm, nearly decreasing by 76% compared with the result before the annealing. Then, low cost and durable nickel stamp with improved sidewall roughness was fabricated by the annealed polymeric patterns being used as original master for electroforming process. And, we verified the superiority of the improved nickel stamp by comparing the optical propagation losses for optical waveguides to be fabricated, respectively, using the nickel stamp and original silicon stamp. The optical waveguides fabricated by the imprint lithography using the improved nickel stamp was demonstrated that their optical losses were reduced as 0.21 dB/cm, which was less than the propagation loss for polymeric waveguides using the conventional original silicon stamp. This result could show the effectiveness of the fabricated nickel stamp with improved sidewall roughness. Furthermore, we were able to successfully fabricate a polymeric 1 × 8 beam splitter device using the improved nickel stamp. And, the insertion loss for eight channels obtained to be from 10.02 dB to 10.91 dB.     

Fabrication of 50 nm patterned nickel stamp with hot embossing and electroforming process

Fabrication of imprint stamp is a key issue of nanoimprint lithography. In this study, we attempt to fabricate the nickel imprint stamp using hot embossing lithography and electroforming processes. As small as 50 nm sized patterns of original silicon master were faithfully transferred to polyvinyl chloride (PVC) film. By electroforming on hot embossed PVC film, nickel stamp, which has the same patterns of original silicon master stamp, was successfully fabricated.     

Fabrication of large area nano-rings for MRAM application

We have developed lateral etch techniques to fabricate large area high density nano-scale magnetic ring arrays by deep ultraviolet lithography. Both centered and de-centered rings have been obtained. The width of the rings are controlled by the lateral etch time, and the inner ring diameter was scaled down below the lithography resolution limit. For de-centered rings, the shift between the center of inner and outer circles was easily adjustable. The characteristics of the ring arrays were characterized by SEM, AFM and SQUID.     

Imprint lithography enabling ultra-low loss coaxial interconnects

Processing techniques have been demonstrated to fabricate a novel structure with smooth transitions, metallic shielding, and encapsulated air dielectric layers using sacrificial polymers and the three-dimensional patterning capabilities of imprint lithography. This innovative structure incorporates encapsulated air dielectrics with copper shielding. A semicircular stamp was fabricated to create the circular base of the coaxial transmission line using the reflow properties of solder, and imprinting the stamp produced smooth rounded terminations. Copper shielding was electroplated and a sacrificial photosensitive polycarbonate was patterned using a unique interaction with the copper. The polycarbonate was over-coated with a epoxycyclohexyl polyhedral oligomeric silsesquioxane (POSS) layer and then thermally decomposed to form an air cavity. A center conductor was patterned using photolithography and electro-deposition. The half-coaxial line was aligned with a sample with the top portion of the copper shielding and bonded in the imprinter to complete the structure. Imprint lithography also demonstrated the capability to planarize surfaces which simplified the buildup process, and complex structures were fabricated with a comparable number of registration steps to traditional transmission lines. The mechanical integrity of the air-clad transmission lines was also evaluated using nano-indentation.     

Negative UV–NIL (NUV–NIL) – A mix-and-match NIL and UV strategy for realisation of nano- and micrometre structures

This paper presents a novel strategy for aligning patterns created with nano-imprint lithography (NIL) and UV lithography, similar to a mix-and-match process, which allows for the fabrication of large and small features in a single layer of resist. The resin used to demonstrate this new imprinting scheme is SU-8, a very widely used negative photoresist. Rapid stamp manufacturing using ma-N 2405 photoresist is also demonstrated. The processing scheme is a promising candidate for patterning of sensors featuring nanometre sized electrodes.     

Nanofabrication of gallium nitride photonic crystal light-emitting diodes

We describe a comparison of nanofabrication technologies for the fabrication of 2D photonic crystal structures on GaN/InGaN blue LEDs. Such devices exhibit enhanced brightness and the possibility of controlling the angular emission profile of emitted light. This paper describes three nano lithography techniques for patterning photonic crystal structures on the emitting faces of LEDs: direct-write electron beam lithography, hard stamp nanoimprint lithography and soft-stamp nanoimprint lithography with disposable embossing masters. In each case we describe variations on the technique as well as its advantages and disadvantages. Complete process details have been given for all three techniques. In addition, we show how high performance GaN dry etch techniques, coupled with optical process monitoring can transfer resist patterns into underlying GaN material with high fidelity.     

Embedded nano channels fabricated by non-selective reverse contact UV nanoimprint lithography technique

In this work, a novel nanofabrication technique is presented, namely “Reverse contact Ultraviolet Nanoimprint Lithography” (RUVNIL). It is based on reverse nanoimprint lithography and ultraviolet contact lithography. It provides flexibility in building complex three-dimensional structures allowing selective imprint over pre-patterned surfaces with or without residual layer in opposition to what is often encountered in the normal NIL process. We have investigated and optimized the imprinting parameters that are required for three-dimensional nanofabrication and applied it to the fabrication of nano-fluidic channels. This lithography technique is a very promising process for three-dimensional nanofabrication.     

NIL—a low-cost and high-throughput MEMS fabrication method compatible with IC manufacturing technology

Current MEMS fabrication technology cannot satisfy the simultaneous needs of 3D structure fabrication and compatibility with IC manufacturing technology, which have impeded the development of MEMS industrialization to a certain extent. Nanoimprint lithography (NIL) provides a new MEMS fabrication method that is compatible with IC manufacturing technology and bears high throughput and low cost. This paper presents an in-house prototype NIL tool with a high precision automatic alignment system based on moiré fringe signals. Some printing results of nanostructures or micro-devices using the prototype are presented, and hot embossing lithography, one typical NIL technology is depicted in detail by taking microlens array fabrication as an example. High fidelity and fine uniformity demonstrate NIL will be a new method to fabricate 3D structures of MEMS.     

X射线光刻和剥离技术制作声表面波叉指换能器

提供了采用电子束光刻、X射线光刻和金属剥离技术制作亚微米尺寸的声表面波叉指换能器的方法.首先利用电子束光刻和微电镀技术制作x射线光刻的掩模,然后利用X射线光刻和剥离技术高效地制作大面积、纳米尺电、电极陡直均匀的叉指换能器.制备出的叉指电极特征尺寸为600 nm,面积为4 mm×6 mm,断指率小于3‰,可应用于高频声表面波器件中.研究结果表明,X射线光刻结合剥离技术是一种制备高频SAW器件的优良方法.     

Roller nanoimprint lithography for flexible electronic devices of a sub-micron scale

This paper proposes a new concept of a RNIL (roller nanoimprint lithography) system. The system does not require the roll stamp that is necessary in the conventional RNIL system, and it easily transfers patterns from a hard stamp to a flexible substrate. Generally, hard stamps such as Si wafers are of a circular shape. While imprinting with a hard stamp using the RNIL system, the pressing force of the press roller in the system varies as the length of the contact line between the circular-type hard stamp and the roller changes. In this study, the contact force profile is presented and is then implemented. Micro- and nano-scale patterns are transferred from Si stamps onto thin and flexible PC (polycarbonate) substrates. Then performance of the system is the evaluated by SEM images.     

Development of metal etch mask by single layer lift-off for silicon nitride photonic crystals

We present a method for fabrication of nanoscale patterns in silicon nitride (SiN) using a hard chrome mask formed by metal liftoff with a negative ebeam resists (maN-2401). This approach enables fabrication of a robust etch mask without the need for exposing large areas of the sample by electron beam lithography. We demonstrate the ability to pattern structures in SiN with feature sizes as small as 50 nm. The fabricated structures exhibit straight sidewalls, excellent etch uniformity, and enable patterning of nanostructures with very high aspect ratios. We use this technique to fabricate two-dimensional photonic crystals in a SiN membrane. The photonic crystals are characterized and shown to have quality factors as high as 1460.