Distortion reduction by load release for imprint lithography

Due to the light source limitation and prohibitive cost inherent in conventional photolithography, various nontraditional patterning technologies, such as imprint lithography, electron beam or X-ray lithography have been attempted over the past 10 years. In this paper, a UV imprint lithography process is introduced for patterning sub-micrometer structures by using a soft PDMS mould, and an imprint experimental device with a loading mechanism driven by PZT for generating a time-variant load is described. As shown experimentally, an increased pressing load will reduce the thickness of the resist layer, leading to a reliable etching-through of the resist. It is found, however, that the mechanical pressing can generate geometrical distortion on the patterned resist mainly due to the elasticity. Incorporated with the use of a low viscosity photo-curable resist, a loading process with a load release step is proposed to reduce the geometrical distortion on the resist patterns. In the loading process, the loading force is partially released after the press peak but before the resist curing. Such a loading process can reduce the elastic distortion while attaining a thin remained resist layer. It is shown that this loading process, called Distortion Reduction by Load Release or DRLR simply can be combined with an imprint process for different patterning areas and feature sizes.     

Enhancement or reduction of catalytic dissolution reaction inchemically amplified resists by substrate contaminants

Chemical interaction of resist and substrate at the interface, which modifies the dissolution reaction, has degraded sidewall profile of resist features. Depending on the nature of the residue on the substrate, the “bottom pinching” (BP) effect and footing are observed, especially for chemically amplified (CA) resists. The BP effect is observed for CA resist on top of organic bottom antireflection coating (BARC). The BP effect is attributed to the acid generated from the underlying organic BARC. With optimization on softbake temperature of BARC, the BP effect is eliminated. On a silicon nitride surface, new chemical information has been obtained which explains “footing” and BP effects in CA resists. X-ray photoelectron spectroscopy (XPS) measurements indicate that the residual alkaline molecules on the nitride surface play a major role in the formation of footing. It appears that the organic contaminants are not responsible for footing. Less severe footing is observed if the nitride surface is plasma-deposited with a thin oxide cap, which suppresses the surface basicity. However, extended plasma deposition causes resist BP. This is ascribed to the surface acidity of a newly formed oxide cap, which enhances the CA resist development process. Results show that the N (1 s) peak, after extended plasma treatment, has shifted to a higher binding state, which suggests that the nitride surface becomes acidic, causing BP     

采用几何校正优化的轮廓波水印算法

针对目前的图像水印难以同时抵抗常规攻击和几 何攻击的不足,提出一种新的轮廓波 水印算法。水印嵌入阶段,该方法将宿主图像进行离散小波变换和非下采样轮廓波变换,并 将水印嵌入到熵值最大的高频子带,解决了将水印嵌入低频无法抵抗几何攻击及高频不能 很好抵抗滤波等常规攻击的问题。在水印嵌入前对嵌入区域进行加密处理,提高算法的安全 性。水印提取阶段,利用Zernike矩对含水印图像进行几何校正再进行提取,进一步提高了 算法的抗几何攻击能力。最后利用峰值信噪比和归一化系数对算法进行评价,验证算法的不 可感知性和鲁棒性。仿真实验结果表明,算法在不同的宿主图像和水印图像上均表现良好。 该算法在具有较好不可见性的基础上,除了对常规攻击具有很好的抵抗力,对几何攻击也具 有强鲁棒性,归一化系数(normalization coefficient,NC)均达到了0.99     

Fabrication of metallic nanocavities by soft UV nanoimprint lithography

We propose a process combining UV-assisted nanoimprint lithography (NIL) and shadow mask evaporation techniques to fabricate metallic nanoparticles with cavities. A bi-layer transparent soft stamp with a hard top layer containing the high resolution patterns was obtained by spin coating and casting methods of PDMS. Then, it was used to mold the top photo-curable resist on a thick PMMA layer. After removal of the residual NIL resist layer, high density and high aspect ratio PMMA nanopillar arrays were obtained by reactive ion etching. Afterward, a four step evaporation under oblique angle was performed to deposit the gold nanostructures at the top of nanopillars. After lift-off, uniformly sized gold nanocavities were collected. Dark-field microscopy imaging of the fabricated nanocavities shows a clear geometry dependence of the emission peak wavelength, thereby providing a novel types of bio-sensing nano-objects.     

Study of X-ray lithographic conditions for SU-8 by Fourier transform infrared spectroscopy

There is growing interest in the use of chemically-amplified resists (CARs) such as SU-8 in the field of microelectromechanical systems (MEMS) research. This is due to its outstanding lithographic performance and its ability for use in the fabrication of stable structures with very high aspect ratio. However, it is important to control the processing conditions for optimum results in the desired application. In this investigation, the thickness (10-25 μm) of SU-8 resist film, due to different spin coating speeds on silicon wafers, was measured using Fourier transform infrared (FT-IR) spectroscopy. The effect of thermal-initiated cross-linking at various temperatures (95-160 °C) for 15 min baking time on the 25 μm SU-8 resist was studied by monitoring the 914 cm⁻¹ absorption peak in the FT-IR spectrum. Results of the experiments showed that the onset of thermal-initiated cross-linking begins at about 120 °C. Furthermore, 25 μm SU-8 resist was optimized for X-ray lithographic applications by studying the cross-linking process of the resist under different conditions of post-exposure bake (PEB) temperatures. The exposure dose of soft X-ray (SXR) irradiation with energies about 1 keV from a dense plasma focus (DPF) device was fixed at 2500 mJ/cm² on the resist surface. Results showed that the optimum processing conditions consisted of an intermediate PEB at 65 °C for 5 min, with the PEB temperature ramped up to 95 °C over 1.5 min and then followed by a final PEB at 95 °C for 5 min. The scanning electron microscopy (SEM) images showed SU-8 test structures successfully imprinted, without affecting the resolution, and with aspect ratios of up to 20:1 on 25 μm SU-8 resist.     

Two-layer resist structure for electron-beam fabrication of a submicrometer gate length GaAs device

A two-layer resist structure using EBR-9 and PMMA for fabricating a fine metal line with a mushroom-like cross-sectional profile is reported. The structure provides T-shaped resist cavities with undercut profiles using electron-beam exposure. With the optimum developing condition, the bottom opening is as small as 0.1 µm, and the top opening is wide enough not to require an additional exposure in order to obtain a mushroom-like metal lift-off pattern. A Monte Carlo calculation is carried out in order to analyze the profile of the two-layer resist structure, and it is shown that an undercut T-shaped resist profile with a 0.1-µm bottom opening can be obtained using a high-sensitivity resist on a low-sensitivity resist structure. A 0.15-µn mushroom-like lift-off metal profile has been fabricated on a 0.1-µm recessed GaAs substrate by the use of this resist structure.     

栅长90nm的晶格匹配InAlAs／InGaAs／InP HEMT

文章报道了90nm栅长的晶格匹配InP基HEMT器件。栅图形是通过80kV的电子束直写的,并采用了优化的三层胶工艺。器件做在匹配的InAlAs／InGaAs／InP HEMT材料上。当Vds=1．0V时,两指75μm栅宽器件的本征峰值跨导达到720ms／mm,最大电流密度为500mA／mm,器件的阂值电压为．0．8V,截止频率达到127GHz,最大振荡频率达到152GHz。     

Numerical study on bubble trapping in UV-nanoimprint lithography

Bubble trapping in the template pattern during the resist filling process is one of the most serious issues in UV-nanoimprint lithography. The mechanism of bubble trapping is studied based on a numerical analysis of the resist flow in a simple model. Flow behavior of water-like low viscosity liquid as a resist is investigated for particular structures of the template and the contact angles for the template and the substrate. Time evolutions of the flow of the resist are simulated and the mechanism of bubble trapping is demonstrated. The results show that large contact angle between the resist and the template causes bubble trapping, however the contact angle between the resist and the substrate does not greatly influence the results.     

一种基于DWT-DCT变换域的全息水印技术

在研究傅里叶全息技术基础上,提出了一种结合离 散小波变换和离散波变换(DWT-DCT)变换的彩色图像数字水印算法,使得水印 拥有强鲁棒性和不可见性。首先,对水印信息进行傅里叶变换,并生成全息水印图; 其次,将载体图 像在RGB空间内的蓝色B分量进行小波分解,对其低频部分进行DCT;最后, 将水印全息图嵌入其高频系数 中。实验结果发现,以k=0.05的强度嵌入水印后,含水印图像的峰值 信噪比(PSNR)达到47,能有效抵抗 信号处理和裁切攻击,同时提取出的水印和原始水印的相似性(NC值)能保持在0. 75以上,说明本文水印 算法有较强的鲁棒性和不可见性。本文算法能够抵抗裁切、滤波、噪声和JPEG压缩攻击,可 用于数字图像版权保护方面。     

减小光刻中驻波效应的新方法研究

光刻过程中，抗蚀剂内部光敏混合物（PAC）浓度受光场的影响呈驻波分布，导致抗蚀剂显影后的侧壁轮廓成锯齿状。分析了后烘（PEB）对PAC浓度分布的影响，模拟了不同后烘扩散长度下的抗蚀剂显影轮廓，从模拟结果可知利用后烘可明显减小驻波效应，得到平滑的抗蚀剂显影轮廓，提高光刻质量。     

一种基于元胞自动机的显影模型

本文利用元胞自动机的方法建立电子抗蚀剂显影模型,阐述了用该模型确立电子抗蚀剂显影后轮廓的方法,在结合相应的能量沉积模型和显影速率模型后,给出了电子抗蚀剂最终显影轮廓的模拟结果,并用ZEP520电子抗蚀剂进行实验验证.     

Improving etch selectivity and stability of novolak based negative resists by fluorine plasma treatment

Fluorine plasma treatment is applied to cross-link a novolak based negative tone optical resist (maN-2400) to achieve increased dry etching selectivity. Furthermore, fluorine plasma treatment is used to strengthen the same resist to keep it in place during a second lithography step on top of the first one. Using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, cross-linking and passivation of the resist during plasma treatment is demonstrated. In contrast to the application of a baking process after resist development, AFM images show that fluorine plasma treatment preserves the intrinsic structure of the resist.     

新型悬空结构射频微电感的制作与测试

利用MEMS(Micro Electro-Mechanical System:微机电系统)工艺中的牺牲层技术制作了一种新型悬空结构微电感,在此悬空结构中,微电感的线圈制作在与衬底平行的平面上,线圈与衬底之间有立柱支撑;此新型微电感的制作工艺流程简单,与集成电路工艺相兼容,且其高频性能较好。并对此结构微电感的性能进行了测试,测试频率范围在0.05~10 GHz之间,结果表明:当悬空结构微电感的悬空高度为20 靘,工作频率在3~5 GHz范围内时,其电感量达到4 nH,其Q值最大可达到22。     

Resist pattern peeling assessment in DUV chemically amplified resist

As device size shrinks resist line peeling becomes more challenging. In this paper we studied the resist pattern peeling based on resist processing parameters and type of bottom antireflective coating (BARC), for patterning trench structures with different duty ratios, in copper and low k dual damascene process. To minimize resist poisoning in dual damascene process, acetal-based resist was used. Significant improvement in via poisoning was observed with this chemistry as compared to environmentally stable chemically amplified resist chemistry but at the cost of pattern peeling. In order to solve pattern peeling problem we tried to analyze key factors such as compatibility with BARC, post-exposure bake, BARC curing, adhesion and their effects. Pitch dependency on pattern peeling margin is observed.     

光刻中驻波效应的影响分析

驻波效应是抗蚀剂在曝光过程中的寄生现象。一般认为,驻波效应对薄胶的光刻图形有较大的影响,而对厚胶的光刻图形影响不大。根据DILL曝光模型进行了模拟计算,分析了在曝光过程中抗蚀剂折射率的改变对驻波强度和位置的影响以及驻波效应引起抗蚀剂曝光剂量分布的变化,并结合MACK显影模型分析了当抗蚀剂的厚度改变时,驻波效应对其显影轮廓的影响程度,计算分析得出了一个可以不采用后烘工序的抗蚀剂厚度值。     

Structural Transformation of Acrylic Resin upon Controlled Electron‐Beam Exposure Yields Positive and Negative Resists

Zwitter polymers are defined as polymers that undergo transformation from a linear to a crosslinked structure under electron‐beam irradiation. A resist polymer may be either linear or crosslinked, depending on electron‐beam dosage. The structural transformation of acrylic resin make it suitable for applications in positive and negative resists in the semiconductor field. The contrast ratio and threshold dose both increase with increasing resist thickness for both the positive and negative resists, while the positive resist exhibits better contrast than the negative. The intensity of the characteristic Fourier‐transform infrared absorption band at 1612 cm^–1 (vinyl group) is used to explain the phenomena behind these resist transformations. We evaluate the effects of two important processing conditions: the soft baking and post‐exposure baking temperatures. Pattern resolution decreases upon increasing the baking temperature, except for soft baking of the negative resist. The effect of electron dose on the pattern resolution is also discussed in detail for both resists. High electron‐beam exposure does not improve the etching resistance of the resist because of the porous nature of the resist that develops after high‐dosage irradiation.     

Stochastic simulation studies of molecular resists

The influence of resist molecular weight as well as its architecture becomes important in lithographic scales aiming at sub-45 nm resolution. The effects of processing and resist molecular geometry on line-edge roughness (LER) should be well understood in order to meet the ITRS lithographic specifications. In this work, two-dimensional simulations and comparisons of the LER between films of molecular resists and resist films made of oligomers with the same molecular diameter, showed that in all cases molecular resists have lower LER. Explanations of this behavior are proposed based on molecular architecture and the free volume distribution in the resist film. It was also found that the size of free volume regions is less in molecular resist than in the corresponding oligomers.     

A new method of formation of the masking image (relief) directly during the electron-beam exposure of the resist

A new method of dry electron-beam etching of some positive resists directly during exposure is proposed. It is shown that exposure of the PMMA resist (the layer 80–85 nm thick on the Si wafer) by electrons with energy of 15–20 keV in vacuum at temperatures of 115–170°C (above the glass-transition temperature of the PMMA) leads to the effective etching of the resist at relatively low exposure doses by a factor of 10–100 smaller than the exposure doses of this resist in the conventional “wet” lithography. It is assumed that the direct etching proceeds by the mechanism of the radical-chain depolymerization of the PMMA resist to a monomer. The high efficiency of the suggested method for the formation of spatial 3D structures in the PMMA resist is shown.     

Linewidth control for 0.25 micron gate patterning

Linewidth control of small lines over non-planarized topography is particularly challenging due to resist thin film interference effects and reflective notching. This paper compares the linewidth control performance of several deep-UV resist processes, using dyed resist and both top and bottom anti-reflection coatings. Only the bottom anti-reflective coating (BARC) provides adequate linewidth control for development work on 0.25 micron gate patterning. The BARC and resist coating behavior over isolation topography is characterized using atomic force microscopy and correlated to residual linewidth variation. The performance of a zero bias etch process for BARC removal is also presented.     

Fabrication of carbon nanotube arrays for field emission and sensor devices by nanoimprint lithography

This work brings forth the idea of incorporating insulation in the resist used for ultraviolet (UV) curing nanoimprint lithography (NIL). Carbon nanotubes (CNTs) are grown in the space between two insulated resist patterns on the conductive substrate to make CNTs arrays. Two imprinting processes, soft UV curing NIL with DRPPR process and novel NIL without cured residual resist, are presented to achieve the insulation patterns. First the fabricating process is performed using a polydimethylsiloxane (PDMS) stamp. Subsequently, inductively coupled plasma (ICP) is essential to wipe off the residual resist film. To avoid the ICP process, a novel UV curing NIL is presented. Its special hard quartz stamp with chrome shelter can protect the residual resist film out of curing during the UV exposure process, and the uncured resist can be easily removed by ultrasonic vibration in organic solutions. The CNT arrays are prepared on the patterned substrates by the pyrolysis of iron phthalocyanine (FePc). Field emission experiments reveal that the turn-on field of those CNTs arrays is low to 1.3 V/um.