EUV‐Lithographie für zukünftige IC‐Chips. EUV‐Lithography for Future IC‐Technology

In the past the overwhelming success of the semiconductor industry was based on the realisation of ever smaller structures on chips in ever shorter periods. This allowed to increase the computational speed of the processors and the amount of data that can be stored in a memory chip. This reduction of the critical dimension was mastered within optical lithography by transition to smaller wavelengths. Those lithography technologies that are currently in the development or test phase, based on 193 nm or as well 157 nm laser sources, will not achieve dimensions around 50 nm. A fundamental change of technology is thus emerging. The currently favored basis for dimensions of 50 nm and below is EUV lithography, based on an optical technology with an exposure wavelength of 13,4 nm. This substantial reduction of the wavelength also implies a radical change of the methodology used up to now.     

超微细图形加工技术进展

自1959年集成电路发明以来，它已经对人类的生产和生活方式的很多方面产生了极其重大的影响。集成电路正以线宽每年缩小30％、集成规模增长1倍、芯片价格随之下降的惊人速度发展。光刻技术的发展始终是集成电路发展的决定因素。本文综述了深亚微米光刻和纳米光刻技术。在光学光刻部分，简要描述了光刻的历史演变，较详细综述了光学光刻的最新进展，如相移掩模、离轴照明及深紫外曝光。最后介绍了电子束曝光及X射线曝光的发展状况及SIM纳米加工的发展状况。     

Functional integrated optical elements for beam shaping with coherence scrambling property, realized by interference lithography

Many applications, such as semiconductor lithography and material processing, require the shaping of laser beams to provide a homogenous field illumination. We present the conception, implementation, and experimental verification of a combined single-element homogenizer. Additionally, for excimer laser applications, the concept is associated with a coherence scrambling capability. We used the technique of holographic interference lithography to integrate the multifunctional properties in a diffractive optical element. The wavelength difference between the recording process (457.9 nm) and the application (193 nm) results in a change of the imaging properties and requires a geometrical adaptation of the optical setup. The coherence scrambling effect of the setup is based on an off-axis design, including the beam shaping diffractive structure.     

Atomic-precision multilayer coating of the first set of optics for an extreme-ultraviolet lithography prototype system

We present our results of coating a first set of optical elements for an extreme-ultraviolet (EUV) lithography system. The optics were coated with Mo-Si multilayer mirrors by dc magnetron sputtering and characterized by synchrotron radiation. Near-normal incidence reflectances above 65% were achieved at 13.35 nm. The run-to-run reproducibility of the reflectance peak wavelength was maintained to within 0.4%, and the thickness uniformity (or gradient) was controlled to within +/-0.05% peak to valley, exceeding the prescribed specification. The deposition technique used for this study is an enabling technology for EUV lithography, making it possible to fabricate multilayer-coated optics to accuracies commensurate with atomic dimensions.     

Lithography for enabling advances in integrated circuits and devices

Because the transistor was fabricated in volume, lithography has enabled the increase in density of devices and integrated circuits. With the invention of the integrated circuit, lithography enabled the integration of higher densities of field-effect transistors through evolutionary applications of optical lithography. In 1994, the semiconductor industry determined that continuing the increase in density transistors was increasingly difficult and required coordinated development of lithography and process capabilities. It established the US National Technology Roadmap for Semiconductors and this was expanded in 1999 to the International Technology Roadmap for Semiconductors to align multiple industries to provide the complex capabilities to continue increasing the density of integrated circuits to nanometre scales. Since the 1960s, lithography has become increasingly complex with the evolution from contact printers, to steppers, pattern reduction technology at i-line, 248 nm and 193 nm wavelengths, which required dramatic improvements of mask-making technology, photolithography printing and alignment capabilities and photoresist capabilities. At the same time, pattern transfer has evolved from wet etching of features, to plasma etch and more complex etching capabilities to fabricate features that are currently 32 nm in high-volume production. To continue increasing the density of devices and interconnects, new pattern transfer technologies will be needed with options for the future including extreme ultraviolet lithography, imprint technology and directed self-assembly. While complementary metal oxide semiconductors will continue to be extended for many years, these advanced pattern transfer technologies may enable development of novel memory and logic technologies based on different physical phenomena in the future to enhance and extend information processing.     

Inorganic immersion fluids for ultrahigh numerical aperture 193 nm lithography

Immersion lithography has become attractive since it can reduce critical dimensions by increasing numerical aperture (NA) beyond unity. Among all the candidates for immersion fluids, those with higher refractive indices and low absorbance are desired. Characterization of the refractive indices and absorbance of various inorganic fluid candidates has been performed. To measure the refractive indices of these fluids, a prism deviation angle method was developed. Several candidates have been identified for 193 nm application with refractive indices near 1.55, which is approximately 0.1 higher than that of water at this wavelength. Cauchy parameters of these fluids were generated and approaches were investigated to tailor the fluid absorption edges to be close to 193 nm. The effects of these fluids on photoresist performance were also examined with 193 nm immersion lithography exposure at various NAs. Half-pitch 32 nm lines were obtained with phosphoric acid as the immersion medium at 1.5 NA. These fluids are potential candidates for immersion lithography technology.     

Influence of the mask magnification on imaging in hyper-NA lithography

Argon fluoride laser (ArF) lithography using immersion technology has the potential to extend the application of optical lithography to 45 nm half-pitch and possibly beyond. By keeping the same 4x magnification factor, the dimensions of the structures on masks are becoming comparable to the exposure wavelength or even smaller. The polarization effect induced by mask features is, however, an issue. The introduction of a larger mask magnification should be strongly considered when poor diffraction efficiencies from subwavelength mask features and the resulting image degradation would be encountered in hyper-NA lithography. The dependence of the diffraction efficiencies on mask pitch and illuminating angle are evaluated. The near-field intensity and phase distributions from the mask are calculated. The imaging performance of 4x and 8x masks for the sub-45 nm node are explored. A rigorous coupled-wave analysis is developed and employed to analyze the optical diffraction from the 3D topographic periodic features.     

Forbidden pitches in sub-wavelength lithography and their implications on design

Moore’s Law has been the most important benchmark for microelectronics development over the past four decades. It has been interpreted to mean that critical dimensions (CD) of a design must shrink geometrically over time. The chip-level integration of devices has been possible through concurrent improvement in lithographic resolution. The lithographic resolution was primarily improved by moving deeper into ultraviolet spectrum of light. However, the wavelength of the optical source used for lithography has not improved for nearly a decade. This has lead to the development of sub-wavelength lithography. The diffraction effects of sub-wavelength lithography were offset by optical proximity correction (OPC), phase shift masking (PSM) and impending move to immersion lithography. Unfortunately, one time benefits from each of these resolution enhancement techniques (RET) have nearly exhausted. In this paper, we explore one important diffraction aspect of sub-wavelength lithography viz. the forbidden pitch phenomenon and its implication on future designs. We studied Forbidden pitches in context of 65 and 45 nm technologies using aerial imaging simulation. Aerial imaging simulation is computationally expensive and is not possible to perform on entire layout structures. Based on results from our simulations on selected patterns, we observe that in absence of any other resolution enhancement technique, many of the current layout patterns will be disallowed in 45 nm technology. Such restrictions significantly mitigate the benefit of migration to 45 nm technology in terms of area, power and performance of a design. We further show that even structured gate array based designs are not immune to this problem.     

Recent progress in source development for extreme UV lithography

The continuation of Moore's law for semiconductor fabrication envisages the introduction of extreme ultraviolet lithography (EUVL) based on a source wavelength of 13.5?nm for high-volume manufacturing within the next few years. While exposure tools have already been developed and the feasibility of the technology well demonstrated, the key source requirement in terms of power output remains to be achieved. Currently, sources based on laser-produced plasmas from tin droplet targets appear to be the most promising and are being deployed in manufacturing tools. Progress in CO₂ laser design aimed at increasing conversion efficiency to close to 5% should make possible the attainment of greater than 200?W of in-band optical power. Recently, research has commenced on the development of sources operating at a wavelength near 6.7?nm for beyond 13.5?nm lithography and gadolinium has been identified as the fuel of choice. The results of these experiments are described and show many similarities to the behavior of tin plasmas as essentially the same atomic and plasma processes are involved, albeit at an electron temperature close to a factor of three higher.     

半导体平面工艺在金属微细加工中的应用

借鉴半导体集成电路的制造工艺，运用制版，光刻、腐蚀等平面工艺技术，制造微型金属光栅，是在金属制造工艺方成的一种尝试，也是半导体微细加工技术在其他领域的推广应用。本文简要介绍了这种思路的引出，方案的可行性，试验结果及推广应用实例。     

Fluoride antireflection coatings for deep ultraviolet optics deposited by ion-beam sputtering

Optically high quality coatings of fluoride materials are required in deep ultraviolet (DUV) lithography. We have applied ion-beam sputtering (IBS) to obtain fluoride films with smooth surfaces. The extinction coefficients were of the order of 10(-4) at the wavelength of 193 nm due to the reduction of their absorption loss. The transmittance of the MgF2/GdF3 antireflection coating was as high as 99.7% at the wavelength of 193 nm. The surfaces of the IBS deposited films were so smooth that the surface roughness of the A1F3/GdF3 film was comparable with that of the CaF2 substrate. The MgF2/GdF3 coating fulfilled the temperature and humidity requirements of military specification. Thus, the IBS deposited fluoride films are promising candidate for use in the DUV lithography optics.     

Patterning and Templating for Nanoelectronics

The semiconductor industry will soon be launching 32 nm complementary metal oxide semiconductor (CMOS) technology node using 193 nm lithography patterning technology to fabricate microprocessors with more than 2 billion transistors. To ensure the survival of Moore's law, alternative patterning techniques that offer advantages beyond conventional top‐down patterning are aggressively being explored. It is evident that most alternative patterning techniques may not offer compelling advantages to succeed conventional top‐down lithography for silicon integrated circuits, but alternative approaches may well indeed offer functional advantages in realising next‐generation information processing nanoarchitectures such as those based on cellular, bioinsipired, magnetic dot logic, and crossbar schemes. This paper highlights and evaluates some patterning methods from the Center on Functional Engineered Nano Architectonics in Los Angeles and discusses key benchmarking criteria with respect to CMOS scaling.     

分步式压印光刻研究

针对微纳制造中光刻环节的光衍射限制，讨论了可能成为下一代光刻技术路线的压印光刻。通过对比热压印、微接触转印及常温压印的技术特点，设计了一套低成本、结构简单的紫外光固化常温压印光刻机构。其大行程纳米级定位、纳米级下压系统消除了压印过程中的机构热变形误差、驱动间隙、蠕动误差等，具有分步式纳米级驱动多场压印及纳米级下压加载能力，可实现多次重复高保真图形复制。     

Fluorescence enhancement using silver nanotriangle arrays

We describe the fabrication of silver nanotriangle array using angle resolved nanosphere lithography and utilizing the same for enhancing fluorescence. The well established nanosphere lithography is modified by changing the angle of deposition between the nanosphere mask and the beam of silver being deposited resulting in nanotriangles of varying surface area and density. The 470 nm plasmon resonance wavelength of the substrate was determined using minimum reflectivity method which closely matches with excitation wavelength of the fluorophore. Ten times enhancement in fluorescence emission intensity is obtained from fluorescein isothiocyanate coated on top of silver nanotriangle array separated by a spacer layer of poly vinyl alcohol as compared to glass. The enhanced fluorescence emission is attributed to the increase in local field enhancement.     

面向微加工的虚拟光刻系统建模与实现

提出了一种面向微加工的虚拟光刻系统Litho3D.该系统采用傅立叶光学成像模型、光刻胶曝光及显影模型,实现了投影式光学光刻的三维模拟.它拥有标准的GDSII、CIF版图格式接口和支持各种光学参数(包括数值孔径、波长、离焦量,光刻胶厚度、表面折射率等)的模拟设置.模拟结果的显示采用了体绘制与网格相结合的方法,增强了结果的可视性.此外,光刻模拟结果可以直接导入到虚拟工艺系统ZProcess中作为刻蚀工艺的掩膜输入,实现了光刻工艺与其他微机电系统(MEMS)工艺模拟的无缝集成.一系列模拟结果验证了该系统的可行性.     

Two-photon interferometry for high-resolution imaging

This paper discusses the advantages of using non-classical states of light for two aspects of optical imaging: the creation of microscopic images on photosensitive substrates, which constitutes the foundation for optical lithography, and the imaging of microscopic objects. In both cases, the classical resolution limit given by the Rayleigh criterion is approximately half of the optical wavelength. It has been shown, however, that by using multi-photon quantum states of the light field, and a multi-photon sensitive material or detector, this limit can be surpassed. A rigorous quantum mechanical treatment of this problem is given, some particularly widespread misconceptions are addressed, and turning quantum imaging into a practical technology is discussed.     

157nm紫外光刻设备用光学材料研究进展

介绍了半导体制造业专用设备，紫外光刻设备所使用的光学材料。介绍了该材料的选择，研究现状，该材料制造工艺技术的创新，以及与材料制造技术相配套的技术发展状况，同时分析了国际市场现状及该技术的发展趋势。     

Combined laser interference and photolithography patterning of a hybrid mask mold for nanoimprint lithography

A lithography technique that combines laser interference lithography (LIL) and photolithography, which can be a valuable technique for the low cost production of microscale and nanoscale hybrid mask molds, is proposed. LIL is a maskless process which allows the production of periodic nanoscale structures quickly, uniformly, and over large areas. A 257 nm wavelength Ar-Ion laser is utilized for the LIL process incorporating a Lloyd's mirror one beam inteferometer. By combining LIL with photolithography, the non-selective patterning limitation of LIL are explored and the design and development of a hybrid mask mold for nanoimprint lithography process, with uniform two-dimensional nanoscale patterns are presented. Polydimethylsiloxane is applied on the mold to fabricate a replica of the stamp. Through nanoimprint lithography using the manufactured replica, successful transfer of the patterns is achieved, and selective nanoscale patterning is confirmed with pattern sizes of around 180 nm and pattern aspect ratio of around 1.44:1.     

Near-ultraviolet zinc oxide nanowire sensor using low temperature hydrothermal growth

Two near-ultraviolet (UV) sensors based on solution-grown zinc oxide (ZnO) nanowires (NWs) which are only sensitive to photo-excitation at or below 400?nm wavelength have been fabricated and characterized. Both devices keep all processing steps, including nanowire growth, under 100?°C for compatibility with a wide variety of substrates. The first device type uses a single optical lithography step process to allow simultaneous in?situ horizontal NW growth from solution and creation of symmetric ohmic contacts to the nanowires. The second device type uses a two-mask optical lithography process to create asymmetric ohmic and Schottky contacts. For the symmetric ohmic contacts, at a voltage bias of 1?V across the device, we observed a 29-fold increase in current in comparison to dark current when the NWs were photo-excited by a 400?nm light-emitting diode (LED) at 0.15?mW?cm(-2) with a relaxation time constant (τ) ranging from 50 to 555?s. For the asymmetric ohmic and Schottky contacts under 400?nm excitation, τ is measured between 0.5 and 1.4?s over varying time internals, which is ～2 orders of magnitude faster than the devices using symmetric ohmic contacts.