EUV Lithography optics contamination and lifetime studies

In this paper we discuss surface phenomena leading to contamination of multilayer optics designed for Extreme Ultraviolet (EUV) lithography. Experimental data supported by calculations indicate dramatic influence of resonance structure of EUV mirror on the secondary electron yield. These low energy electrons play an important role in radiation chemistry at the mirror surface. We also discuss the dependence on the partial pressure of admitted gas of equilibrium surface coverage and contamination rate under EUV irradiation.     

极紫外光学器件辐照污染检测技术

总结并讨论了极紫外光刻技术中,有关极紫外光学器件受辐照污染的"在线"检测方法。简要介绍了极紫外光刻系统的原理、反射镜膜层结构以及表面污染产生的机理;指出光刻系统中"在线"检测的技术要求;分析了目前几种主要表面检测技术的特点;给出了每种方法在极紫外光学系统中的应用潜力;最后,指出光纤椭偏仪在极紫外光学系统的"在线"表面污染检测中具有良好的应用前景。     

Secondary electron yield measurements of carbon covered multilayer optics

Carbon contamination on extreme ultraviolet (EUV) optics has been observed in EUV lithography. In this paper, we performed in situ monitoring of the build-up and removal of carbon contamination on Mo/Si EUV multilayers by measuring the secondary electron yield as a function of primary electron energy. An electron beam with an energy of 2 keV was used to simulate the EUV radiation induced carbon contamination. For a clean EUV multilayer, the maximum secondary electron yield is about 1.5 electrons per primary electron at a primary electron energy of 467 eV. The maximum yield reduced to about 1.05 at a primary electron energy of 322 eV when the surface was covered by a non-uniform carbon layer with a maximum thickness of 7.7 nm. By analyzing the change in the maximum secondary electron yield with the final carbon layer thickness, the limit of detection was estimated to be less than 0.1 nm.     

Surface phenomena related to mirror degradation in extreme ultraviolet (EUV) lithography

One of the most promising methods for next generation device manufacturing is extreme ultraviolet (EUV) lithography, which uses 13.5 nm wavelength radiation generated from freestanding plasma-based sources. The short wavelength of the incident illumination allows for a considerable decrease in printed feature size, but also creates a range of technological challenges not present for traditional optical lithography. Contamination and oxidation form on multilayer reflecting optics surfaces that not only reduce system throughput because of the associated reduction in EUV reflectivity, but also introduce wavefront aberrations that compromise the ability to print uniform features. Capping layers of ruthenium, films ∼2 nm thick, are found to extend the lifetime of Mo/Si multilayer mirrors used in EUV lithography applications. However, reflectivities of even the Ru-coated mirrors degrade in time during exposure to EUV radiation. Ruthenium surfaces are chemically reactive and are very effective as heterogeneous catalysts. In the present paper we summarize the thermal and radiation-induced surface chemistry of bare Ru exposed to gases; the emphasis is on H₂O vapor, a dominant background gas in vacuum processing chambers. Our goal is to provide insights into the fundamental physical processes that affect the reflectivity of Ru-coated Mo/Si multilayer mirrors exposed to EUV radiation. Our ultimate goal is to identify and recommend practices or antidotes that may extend mirror lifetimes.     

Generation of extreme ultraviolet vortex beams using computer generated holograms

We fabricate computer generated holograms for the generation of phase singularities at extreme ultraviolet (EUV) wavelengths using electron beam lithography and demonstrate their ability to generate optical vortices in the nonzero diffraction orders. To this end, we observe the characteristic intensity distribution of the vortex beam and verify the helical phase structure interferometrically. The presented method forms the basis for further studies on singular light fields in the EUV frequency range, i.e., in EUV interference lithography. Since the method is purely achromatic, it may also find applications in various fields of x ray optics.     

On the possibility of applying kinoform elements in mirror projectors for EUV lithography

The potential of the technology of reflective diffraction (holographic) optical elements intended for the EUV range is considered, and their application in projection lithography is discussed.     

Nanolithography in microelectronics: A review

The current status of basic photolithographic techniques allowing researchers to achieve results that seemed to be unrealistic even a short time ago is reviewed. For example, advanced DUV photolithography makes it possible to exactly reproduce IC elements 25 times smaller in size than the wavelength of an excimer laser used as a lithographic tool. Approaches owing to which optical lithography has pushed far beyond the Rayleigh-Abbe diffraction limit are considered. Among them are optical proximity correction, introduction of an artificial phase shift, immersion, double exposure, double patterning, and others. The prospects for further advancement of photolithography into the nanometer range are analyzed, and the capabilities of photolithography are compared with those of electronolithography, EUV lithography, and soft X-ray lithography     

Wavelength separation from extreme ultraviolet mirrors using phaseshift reflection

A generic design and fabrication scheme of Mo/Si multilayer-grating phaseshift reflector systems is reported. Close to optimized extreme ultraviolet (EUV, λ=13.5 nm) reflectance values up to 64% are demonstrated, while the diffractive properties can be exploited in spectral filtering applications. The results can contribute to a wavelength-unspecific solution for the suppression of λ>100 nm out-of-band radiation in EUV lithography.     

EUV micropatterning for biocompatibility control of PET

We have investigated the influence of oriented microstructures at modified polyethylene terephthalate (PET) on the adhesion and alignment of Chinese hamster ovary (CHO) cells. For surface modification, the PET foils were exposed to the radiation of a laser-plasma extreme ultraviolet (EUV) source based on a double-stream gas-puff target. The emission of the plasma was focused onto the samples by means of a gold-plated ellipsoidal collector. The spectrum of the focused radiation covered the wavelength range from 9 to 70 nm. The PET samples were irradiated with the EUV pulses at a repetition rate of 10 Hz in a high vacuum. For control experiments, PET samples were also irradiated in air with the light of a 193 nm ArF-excimer laser. Different kinds of surface microstructures were obtained depending on the EUV or laser fluence and pulse number, including oriented wall- and ripple-type structures with lateral structure periods of a few μm. The surface morphology of polymer samples after the irradiation was investigated using a scanning electron microscope (SEM). Changes in chemical surface structure of the irradiated samples were investigated using X-ray photoelectron spectroscopy (XPS). We demonstrated that the cells show good adhesion and align along oriented wall- and ripple-type microstructures on PET surfaces produced by the EUV irradiation.     

Space solar telescope in soft X-ray and EUV band

In this paper we have reviewed our achievements in soft X-ray and extreme ultraviolet (EUV) optics. Up to now, the research system of soft X-ray and EUV optics has been established, including light sources, detectors, calibrations, optical testing and machining of super smooth mirrors, and fabrications of multilayer film mirrors. Based on our achievements, we have developed two types of solar space telescopes for the soft X-ray and EUV space solar observations. One is an EUV multilayer normal incident telescope array including 4 different operation wavelength telescopes. The operation wavelengths of the EUV telescope are 13.0, 17.1, 19.5 and 30.4 nm. The other is a complex space solar telescope, which is composed of an EUV multilayer normal incident telescope and a soft X-ray grazing incident telescope. The EUV multilayer normal incident telescope stands in the central part of the soft X-ray grazing incident telescope. The normal incident telescope and the grazing incident telescope have a common detector. The different operation wavelengths can be changed by rotating a filter wheel.     

22nm极紫外光刻物镜热和结构变形及其对成像性能影响

极紫外光刻技术(EUVL)是半导体制造实现22nm及其以下节点的下一代光刻技术。在曝光过程中,EUVL物镜的每一面反射镜吸收35%～40%的入射极紫外(EUV)能量,使反射镜发生热和结构变形,影响投影物镜系统的成像性能。基于数值孔径为0.3,满足22nm技术节点的产业化EUV投影物镜,采用有限元分析(FEA)的方法研究反射镜变形分布,再将变形导入光学设计软件CODE V中,研究反射镜变形其对成像特性的影响。研究结果表明:当达到硅片的EUV能量为321mW,产量为每小时100片时,反射镜最高升温9.77℃,通光孔径内的最大变形为5.89nm;若采用相干因子0.5的部分相干光照明,变形对22nm线宽产生6.956nm的畸变和3.414%的线宽误差。     

The structure of thin carbon films deposited at 13.5 nm EUV irradiation

In this work, the structure and chemistry of thin nm-thick carbon films deposited on a substrate using strong 13.5 nm EUV irradiation under a strong vacuum were studied. The film structure was studied by Raman spectroscopy in comparison with the Raman spectra of well-known carbon phases: diamond, single-wall nanotubes, nano- and micro-crystalline graphite and amorphous carbon. As well, FTIR spectroscopy was used to study possible IR-active chemical bonds, primarily, hydrogen bonds. It was shown that films deposited on a surface under EUV irradiation consists of amorphous sp ²-carbon. The mechanisms of deposition are discussed briefly. Knowledge about the structure and chemistry of such carbon films is very important for EUV lithography.     

Mo/Si multilayers used for the EUV normal incidence solar telescope

This paper first reviews an EUV normal incidence solar telescope that we have developed in our lab. The telescope is composed of four EUV telescopes and the operation wavelengths are 13.0 nm, 17.1 nm, 19.5 nm, and 30.4 nm. These four wavelengths, fundamental to the research of the solar activity and the atmosphere dynamics, are always chosen by the EUV normal incidence solar telescope. In the EUV region, almost all materials have strong absorption, so optics used in this region must be coated by the multila...     

基于脉冲CO2激光锡等离子体光刻光源的极紫外辐射光谱特性研究

研究了不同条件下脉冲放电CO₂激光烧蚀平板锡靶产生的等离子体极紫外辐射特性, 设计并建立了一套掠入射极紫外平焦场光栅光谱仪, 结合X射线CCD探测了光源在6.5～16.8 nm波段的时间积分辐射光谱,得到了极紫外光谱随激光脉宽, 入射脉冲能量及背景气压的变化规律。实验结果发现：入射激光脉冲能量在30～600 mJ变化时,极紫外辐射光谱的强度随辐照激光脉冲能量的增加而增加, 但并不是线性关系, 具有饱和效应, 且产生极紫外辐射的脉冲能量阈值约为30 mJ,当激光脉冲能量为425 mJ时具有最高的转换效率,此时中心波长13.5 nm处2%带宽内的转换效率约为1.2%。激光脉冲半高全宽在50～120 ns范围内变化时, 极紫外辐射光谱的峰值位置均位于13.5 nm,光谱形状几乎没有什么变化, 但是脉宽从120 ns变到52 ns后,由于激光功率密度的提高,极紫外辐射强度也随之增强了约1.6倍。极紫外光谱的强度随背景气压的增大而迅速下降, 当腔内空气气压为200 Pa时, 极紫外辐射光子几乎被全部吸收,而当缓冲氦气气压为7×104 Pa时,仍能够探测到微弱的极紫外辐射信号,计算表明100 Pa的空气对13.5 nm极紫外光的吸收系数为3.0 m-1,而100 Pa的He气的吸收系数为0.96 m-1。     

SECRAL等离子体中EUV光功率的产生

The high power EUV source is one of key issues in the development of EUV lithography which is considered to be the most promising technology among the next generation lithography.However neither DPP nor LPP seems to meet the requirements of the commercial high-volume product.Insufficiency of DPP and LPP motivate the investigation of other means to produce the EUV radiation required in lithography.ECR plasma seems to be one of the alternatives.In order to investigate the feasibility of ECR plasma as a EUV light source,the EUV power emitted by SECRAL was measured.A EUV power of 1.03W in 4~ sr solid angle was obtained when 2000W 18GHz rf power was launched,and the corresponding CE was 0.5%.Considering that SECRAL is designed to produce very high charge state ions,this very preliminary result is inspiring. Room-temperature ECR plasma and Sn plasma are both in the planned schedule.     

Pinch Plasma Radiation Sources for the Extreme Ultraviolet

Extreme ultraviolet lithography (EUVL) is under discussion to be implemented in the production of chips as early as 2005 to 2007 for reducing structures in semiconductor devices to below 70 nm. The challenging task of developing optical components and radiation sources within this short period of time is pushing technology. As discharge produced and laser produced plasmas are the main candidates for EUV‐sources, plasma technology is forced to leap forward significantly. Progress in EUV‐sources is expected to open EUV‐technology for other applications in science and technology with increased need for spatial resolution, elemental contrast or sensitivity. Various technical concepts for realising high power sources for EUV lithography are under investigation world‐wide. Laser produced and discharge produced plasmas are the most promising schemes. Discharge produced pinch plasmas in general are of special interest, because their prospected costs (esp. cost of ownership) for the demanded throughput is expected to be much lower than with laser produced plasmas. However, the discharge plasmas are of high risk, because many crucial tasks have to be solved before reaching the required power levels. Beside the optimisation of the EUV‐generation ‐ which is the key to build the most reliable device with demanded EUV power ‐ the success will depend on the individual technical aspects of each source concept. Currently investigated pinch plasma concepts are evaluated based on their potential to be upgraded to fulfil the challenging demands of EUV‐lithography.     

微纳加工技术在微纳电子器件领域的应用

微纳加工技术推动着集成电路不断缩小器件尺寸和提高集成度，光学光刻技术依然是目前的主流微纳加工技术，同时有多种替代技术如电子束直写、极紫外光刻和投影电子束技术，文章介绍了自上而下的微纳加工技术的进展及其在微纳器件研制的重要作用。     

纳米光刻技术

纳米科学技术将成为新世纪信息时代的核心。纳米量级结构作为研究微观量子世界的重要基础之一,其制作技术是整个纳米技术的核心基础,已成为当前世界科学研究急需解决的问题。文章针对上前的科技发展情况,介绍了几种纳米光刻技术的实现新途径、发展现状和关键问题。详细阐述了波前工程、电子束光刻、离子束光刻、Ｘ射线光刻原子光刻、干涉光刻、极紫外光刻以及１５７光刻的原理和实现难点。作为下一代各种光刻技术,它们都有望实现     

System for illumination of an EUV-nanolithograph mask

The system for illuminating a mask of the nanolithograph for EUV lithography at the 13.5 nm wavelength is considered. The basic elements of the system are a source of extreme ultraviolet radiation, a spherical mirror-collector, and a compound mirror (homogenizer) that consists of 25 minimirrors and provides uniform exposure of the required area of the mask. Numerical computations of minimirror parameters are given in comparison to experiments, and reflection factors of minimirrors in the vicinity of λ = 13.5 nm are presented.