Mask topography effects in projection printing of phase-shiftingmasks

Topography effects of glass edges in phase-shifting masks (PSM's) on image quality are assessed using the rigorous electromagnetic simulation program TEMPEST on three different optical systems for four PSM technologies including alternating, rim, attenuated, and chromeless. The scalar and thin mask approximations used in simulation programs such as SPLAT can be in error by as much as 20% for certain classes of shifter edges. A feature size independent bias of 0.021 λ/NA per edge is recommended for alternating masks with vertical edges because light is lost near the etched glass edges. No direct electromagnetic interaction between chromium edges and shifter edges was found for rim phase-shifting masks. The rim dimension can thus be designed solely on the basis of the sidelobe level and peak intensity. For attenuated PSM, edge effects are less severe but sidelobe problems occur. For a center to sidelobe contrast of 0.6 over a DOF of 3 RU, a lower transmission of 4% is recommended. For chromeless PSM, the imbalance in image peaks is shown to be affected by the optical stepper parameters. In any PSM technology, it appears that a 360° glass protrusion may produce a drastic drop in intensity due to resonant effects     

采用双扫描平台技术的ArF浸液式光刻

在193nm光刻中,已证明水是一种适于浸液式光刻的液体。浸液式光刻提出了一种可将传统的光学光刻拓展到45nm节点,甚至到32nm节点的潜能。另外,利用现有的透镜,浸液式光刻的选择提出了根据实际的数值孔径和特征图形可增大50%及更大的焦深范围。讨论了采用浸液式光刻获得的成像结果和套刻结果。采用一个0.75数值孔径的ArF透镜,我们用双扫描平台技术(TWINSCANTM)组装一台浸液式扫描光刻机的原理型样机。最初的浸液式曝光实验数据证明了焦深的增加较大,同时以高扫描速度保持了图像的对比度。在初期引入的生产型浸液式光刻中,将采用一个0.85数值孔径的ArF透镜。该系统的分辨率将以大于0.5μm的焦深有效地支持65nm节点半导体器件的加工。这种系统初始的成像技术数据证实有效的增大了其焦深范围。     

应用TWINSCAN平台的ArF浸没式工艺

For 193-nm lithography, water proves to be a suitable immersion fluid. ArF immersion offers the potential to extend conventional optical lithography to the 45-nm node and potentially to the 32-nm node. Additionally, with existing lenses, the immersion option offers the potential to increase the focus window with 50% and more, depending on actual NA and feature type. In this paper we discuss the results on imaging and overlay obtained with immersion. Using a 0.75 NA ArF projection lens,we have built a proto-type immersion scanner using TWINSCANTM technology. First experimental data on imaging demonstrated a large gain of depth of focus (DoF),while maintaining image contrast at high scan speed. For first pilot production with immersion, a 0.85 NA ArF lens will be used. The resolution capabilities of this system will support 65 nm node semiconductor devices with a DOF significantly larger than 0.5 um. Early imaging data of such a system confirms a significant increase in focus window.     

亚半微米光刻技术的新动向

最近几年中提出了几种用于光学光刻的新方法,包括移相掩模技术、斜向照明、环形照明、FLEX和Super-FLEX等,这些方法提高了光学投影光刻的分辨率,并改善了一定特征尺寸下的焦深,期望它们可以将现有的i线步进机的用途扩展到制造最小特征尺寸为0.3μm的半导体器件。本文介绍了这些方法的基本原理、效果和应用状况,并讨论了实用中的关键问题。     

提高光刻图形质量的双曝光技术

双曝光技术能提高图形对比度和分辨率,可改善焦深,从而提高光刻图形质量,介绍了双 曝光技术原理和几种双曝光方法,同时,提出采用双曝光技术,结合相移掩模和光学邻近效应校正来提高光刻分辨率,给出了双曝光光刻方法的实例及计算机模拟结果。     

Phase-shifting masks gain an edge

The potential, working principles, and approaches in phase shifting masks for optical lithography are discussed. The tradeoffs of each approach, and fabrication, inspection, repair, and tolerances are considered. It is feasible to use the phase shifting technology to improve optical lithography to 0.18-μm feature size with k ₁=0.35, λ=248 nm, and NA=0.5. Further resolution improvements are still possible, but much development is required for making phase shifting masks a manufacturing reality     

High-Q SAW filter and submicron process technology for timingextraction in high bit rate optical communications system

A new surface acoustic wave (SAW) filter configuration that consists of 3λ/8-wide meander-type electrodes and 3λ/8-wide excitation electrodes on ST-cut quartz was designed for use in a 2.5-Gb/s optical communications system. New submicron process techniques using the phase shifting method as well as several types of resist were investigated to fabricate this filter. It had an insertion loss of less than 14 dB and a Q of about 700, and satisfied all required system specifications over a temperature range from 0 to 60°C     

Systematic design of phase-shifting masks with extended depth offocus and/or shifted focus plane

An optimization based algorithm for designing phase-shifting masks is proposed. The approach is an extension of the previous work in the sense that the intensity image is optimized at a number of optical planes rather than just the focus plane. In addition, the algorithm can be used to design masks with shifted focus plane and/or extended depth of focus. The concept of a dual mask is introduced, and its consequences for practical phase-shifting mask design are shown. The proposed design techniques are applied to single line phase connectors, cross phase connectors, contact holes and bright lines. Simulation and experimental results verify the capability of the design technique for extending depth of focus and shift the focus plane     

A three-dimensional optical photonic crystal

We report on the successful fabrication of a working three-dimensional (3D) crystal operating at optical wavelength λ. The minimum feature size of the 3D structure is 180 nm. The 3D crystal is free from defects over the entire 6-inch silicon wafer and has an absolute photonic bandgap (PBG) centered at λ~1.6 μm. Our data provides the first conclusive evidence for the existence of a complete 3D PBG in optical λ. This development will pave the way to tinier, cheaper, more effective waveguides, optical switches and lasers     

采用梯形棱镜波前分割的激光干涉光刻技术

光学光刻技术在微细加工和集成电路(IC)制造中一直是主流技术。随着IC集成度的提高,要求越来越高的光刻分辨力,但光学光刻的分辨极限受光刻物镜数值孔径(NA)和曝光波长(λ)的限制。激光干涉光刻技术具有高分辨、大视场、无畸变、长焦深等特点,其分辨极限为λ/4,在微细加工、大屏幕显示器、微电子和光电子器件、亚波长光栅、光子晶体和纳米图形制造等领域有广阔的应用前景。阐述了激光干涉光刻技术的基本原理。提出了一种采用梯形棱镜作为波前分割元件的激光干涉光刻方法。建立了相应的曝光系统,该系统可用于双光束、三光束、四光束和五光束等多光束和多曝光干涉光刻。给出了具有点尺寸约220nm的周期图形阵列的实验结果。     

Improving resolution in photolithography with a phase-shifting mask

The phase-shifting mask consists of a normal transmission mask that has been coated with a transparent layer patterned to ensure that the optical phases of nearest apertures are opposite. Destructive interference between waves from adjacent apertures cancels some diffraction effects and increases the spatial resolution with which such patterns can be projected. A simple theory predicts a near doubling of resolution for illumination with partial incoherence σ < 0.3, and substantial improvements in resolution for σ < 0.7. Initial results obtained with a phase-shifting mask patterned with typical device structures by electron-beam lithography and exposed using a Mann 4800 10X tool reveals a 40-percent increase in usuable resolution with some structures printed at a resolution of 1000 lines/mm. Phase-shifting mask structures can be used to facilitate proximity printing with larger gaps between mask and wafer. Theory indicates that the increase in resolution is accompanied by a minimal decrease in depth of focus. Thus the phase-shifting mask may be the most desirable device for enhancing optical lithography resolution in the VLSI/VHSIC era.     

Compact range measurement systems for electrically small test zones

Traditional range requirements are evaluated for spherical and compact range measurement systems. It is shown that a compact range system is more appropriate for targets three wavelengths (λ) and larger because of the chamber size needed to meet these requirements. Commercially available compact range systems are, however, normally restricted to 10 λ or larger targets because of the excessive diffraction associated with currently available compact range reflectors. It is shown that this limitation could be overcome by using a blended rolled edge compact range reflector. For example, a 9 λ×9 λ blended rolled edge reflector can be used to measure 3 λ targets at the lowest frequency of operation. As the frequency of operation increases, the test zone of the reflector approaches one half the reflector's linear dimension, which is consistent with presently available compact range systems     

Super-resolution image reconstruction: a technical overview

A new approach toward increasing spatial resolution is required to overcome the limitations of the sensors and optics manufacturing technology. One promising approach is to use signal processing techniques to obtain an high-resolution (HR) image (or sequence) from observed multiple low-resolution (LR) images. Such a resolution enhancement approach has been one of the most active research areas, and it is called super resolution (SR) (or HR) image reconstruction or simply resolution enhancement. In this article, we use the term "SR image reconstruction" to refer to a signal processing approach toward resolution enhancement because the term "super" in "super resolution" represents very well the characteristics of the technique overcoming the inherent resolution limitation of LR imaging systems. The major advantage of the signal processing approach is that it may cost less and the existing LR imaging systems can be still utilized. The SR image reconstruction is proved to be useful in many practical cases where multiple frames of the same scene can be obtained, including medical imaging, satellite imaging, and video applications. The goal of this article is to introduce the concept of SR algorithms to readers who are unfamiliar with this area and to provide a review for experts. To this purpose, we present the technical review of various existing SR methodologies which are often employed. Before presenting the review of existing SR algorithms, we first model the LR image acquisition process.     

向50nm拓进的光学光刻技术

非光学下一代光刻技术的缓慢进展和国际半导体技术发展规划 (ITRS)的加速 ,使光学光刻肩负着IC产业的重任 ,进一步向亚波长图形领域进军。为此 ,人们开发了大量的光学光刻扩展技术。其中包括传统的缩短波长和增大数值孔径 ,以及为了扩展最小间距线间图形的分辨力而提高部分相干性。通过这些途径 ,在 1 93nm曝光中实现了 >0 .80的数值孔径和0 .85的部分相干性 ,并将进一步向 1 57nm乃止 1 2 6nm过渡。此间 ,离轴照明 (OAI)、移相掩模(PSM)和光学邻近效应校正 (OPC)等K1因子将作为分辨力提高技术的核心 ,补充到光学光刻技术范畴。此外 ,光学光刻的扩展还将通过像场尺寸缩小和倍率增大的方法使步进扫描光刻机更好地支持并可望进入至少 70nm的技术节点 ,乃至 50nm的下一代光刻。     

Interferometric chromatic dispersion measurements on short lengthsof monomode optical fiber

Chromatic dispersion measurements on short lengths of monomode optical fiber by the technique of `white light' interferometry are presented. Improved optoelectronic signal processing and rigorous data reduction techniques have resulted in a temporal resolution of ⩾7×10^-5 ps·nm^-1 in a 1-m length of fiber, equivalent to 0.06% resolution in the measurement technique. This is equivalent to a first-order chromatic dispersion coefficient ( D(λ)) resolution of 0.07 ps·nm^-1·^-1. The second-order chromatic dispersion coefficient (S(λ)) resolution was 0.02 ps·nm^-2·nm^-1. Experimental results of D(λ) and S(λ) for three different fibers are compared to theoretical calculation of material and waveguide dispersion     

白光显微干涉三维形貌测量中的移相误差校正方法

白光显微干涉术通过驱动干涉显微物镜垂直扫描移相,采集低相干干涉图序列,定位干涉包络中的零光程差位置,获取待测表面的三维形貌。微观形貌的计算由获取粗略形貌的垂直扫描（VSI）算法和获取精细形貌的移相（PSI）算法两部分组成。通常情况下,设置垂直扫描移相的步长为八分之一中心波长,但移相器误差和干涉显微物镜数值孔径效应等都会使得移相量偏离π/2。文中采用基于对比度变化重心提取的VSI算法,4M幅法和7幅法两种PSI算法,分别讨论了两种类型移相误差对形貌计算的影响。理论和数值分析结果表明,在宽带光作用下,7幅法仍对移相误差不敏感,4M幅法产生的精细相位误差形式恰好与干涉物镜数值孔径效应对条纹展宽的影响相一致,在从精细相位转换为精细形貌时相互抵消。因而,采用基于对比度变化重心提取的VSI算法和4M幅PSI算法计算形貌数据,干涉物镜数值孔径效应造成的移相误差无影响,移相器误差造成的形貌复原误差可以通过预先测量已知高度的标准台阶进行标定去除。应用上述移相误差校正方法测量了高度为460 nm的台阶,形貌测试结果正确且鲁棒。     

只读式超分辨光盘的膜层设计和分析

超分辨技术是一种无需减小记录波长或增大数值孔径而提高存储密度的方法。Ge Sb Te是一种良好的相变光存储材料 ,在超分辨光盘中可作为掩膜。利用多层膜反射率的矩阵法计算了掩膜为Ge2 Sb2 Te5薄膜的超分辨只读式光盘的光学参数与各膜层厚度之间的关系 ,最后得到了较为理想的膜层厚度匹配。采用磁控溅射法制备了只读式超分辨光盘 ,测量了光盘的光学性质。     

X-ray lithography for VLSI

In order for any lithography to become the preferred technique for the production of very large scale integrated circuit (VLSI) devices, the technique will have to 1) achieve the required resolution and registration and 2) become more cost effective in this capacity for large volume production than its competitors. The advent of advanced lithographic techniques for LSI production has been postponed by substantial advances in conventional lithography. However, integrated circuits with feature sizes of 1 µm or smaller seem to have significant performance and price advantages over current devices. Such submicron feature sizes press noncontact optical lithography up against the laws of physics. Meanwhile, advances in X-ray lithography have occurred and continue to occur at a promising rate. This paper discusses our experience with X-ray lithography at Intel. Most of our X-ray experience is with the Intel 1-Mbit bubble memory because of the small minimum feature size (1.2 µm) and the defect and alignment tolerance of this device. However, this discussion will be geared toward general VLSI applications of X-ray lithography.     

A little light magic [optical lithography]

At first glance, it appears that optical lithography has hit a dead end. Wavelengths shorter than 193 nm can't be used without a drastic redesign of lithographic systems because the shorter wavelengths are simply absorbed by the quartz lenses that direct the light onto the wafer. So is this the end? Not quite. There are a few more tricks that IC manufacturers can play. Lumped together, they are called resolution enhancement techniques (RETs), and in one way or another, they all coax the light into resolving shapes much smaller than its wavelength. The main techniques are optical proximity correction, phase-shifting masks, and modified, or "off-axis," illumination. With these tricks, the existing-and already paid for-optical lithography equipment can create patterns much smaller than the wavelength of the light used to produce them, these techniques can be easily extended to one-eighth the wavelength of the light-that is, to less than 25 nm for 193 nm light. Using these techniques, scientists at the Massachusetts Institute of Technology's (MIT's) Lincoln Laboratory, in Lexington, have built prototype transistors with a gate length of only 9 run-smaller than the smallest virus. Other tricks can also come into play. For example, by immersing the focusing lenses in a liquid with an index of refraction greater than that of air, optical lithography may be extended indefinitely. Ever since the 180 nm generation of devices, in 1999, RETs are making advanced optical lithography possible.     

Optical lithography stalls X-rays

The revival in optical lithography resulting from continuing advances in photoresists, phase-shifting masks, high-numerical-aperture step-and-repeat optical systems, multilevel-resist processing, and top-surface imaging techniques is discussed. Optical lithography is being used to make advanced IC chips, with 0.35 μm geometries in research, 0.5 μm in production. Ultraviolet (UV) light in the 200-400 nm range is the predominant system for IC manufacturing technology. Deep-UV lithography is not yet accepted for production processes, mostly due to the lack of commercially available positive and negative-tone photoresist systems for deep-UV wavelengths. In addition, negative-tone resists are temperature-sensitive and therefore hard to handle in a manufacturing environment, extensive gas-handling facilities are required for deep-UV excimer laser sources, and optical components have to be replaced often because the intense laser energy devitrifies lenses quickly