The phase-shifting mask II: Imaging simulations and submicrometer resist exposures

Submicrometer optical lithography is possible with conventional projection cameras when the mask controls the phase of the light at the object plane. Two-dimensional imaging simulations for the Mann 4800 projection camera show that the maximum spatial frequency for 60-percent contrast increases from 640 1/mm to 896 1/mm. The geometrical quality of the images of typical microcircuit patterns was shown to be acceptable for feature sizes of 0.7, 0.6, and 0.5 µ, respectively, and various parameters of the irradiance patterns were calculated. Exposures were made using a high-performance two-layer photoresist system and a mask containing patterns similar to those in the simulation. The phase-shifting mask was shown to increase exposure latitude and to produce a 95-percent yield of 833 1/mm (0.6 µ line and gap) patterns, whereas the transmission mask gave a 7-percent yield. Half micrometer features were patterned with a 22-percent yield using 0.436-µ light.     

衍射干涉光刻研究

光刻就是将掩模版上的图形转移到基底的过程,广泛应用于微电子、微机械领域。衍射现象是光刻工艺无法避免的问题,当掩模图形尺寸接近光源波长时,就会产生衍射干涉现象。利用这一现象,可以产生小于掩模图形尺寸的图形。采用严格耦合波分析算法对光刻过程中的衍射干涉做了仿真分析;并用karl suss MA6光刻机实现了基于掩模的干涉光刻实验,通过增加滤光片得到相干光源,增强光刻过程的衍射,形成衍射干涉,掩模版透光区域和部分不透光区域下方的光刻胶得到曝光,利用微米尺度的光栅图形,在光刻胶上产生亚微米的光栅;最后利用干法刻蚀工艺,在硅基底上加工出亚微米尺度光栅。     

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。     

New approach to resolution limit and advanced image formationtechniques in optical lithography

Practical resolution, the minimum feature size with a depth of focus (DOF) required for LSI fabrication process, is analyzed. Dependence of practical resolution on various factors, such as optical system parameters (exposure wavelength λ, and numerical aperture NA), resist processes, and required DOF, is investigated. It is shown that practical resolution in the sub-halfmicrometer region is not improved, and may even be degraded, with increasing NA. Furthermore, resolution improvement by increasing NA becomes less effective as λ becomes shorter. This means that the high-resolution capability of high-NA/short-wavelength optics cannot be utilized to create fine-pattern LSIs. In order to overcome this limitation, the effectiveness of advanced image formation techniques, the phase-shifting method and the FLEX method, in practical resolution enhancement is investigated. It is experimentally verified, using a phase-shifting mask and the excimer laser stepper, that a pattern feature size less than 0.2 μm can be clearly delineated with sufficient focus latitude. These advanced techniques make it possible to overcome the resolution limitation of conventional optical lithography     

Two-Laser Lithography Shrinks Transistors on the Cheap

Engineers are near the outer limits of what can be done with optical lithography, the process by which light shone through a patterned mask defines the fine structures of microprocessors and memory chips. Now three teams of optics experts have independently hit upon what could turn out to be a way to extend optical lithography?s use?and, what?s even more critical, to do it cheaply.     

Step-and-repeat X-ray/Photo hybrid lithography for 0.3-µm MOS devices

X-ray / photo hybrid lithography is proposed as a method for achieving high resolution and high throughput in sub-half-micrometer VLSI fabrication. Distortions and correction techniques are discussed for accurate registration between X-ray and photo levels. Inherent distortions caused by each type of lithography are measured in advance. These distortions are corrected by introducing a linear shrinkage factor into e-beam data preparation for X-ray mask writing. The overlay accuracy between X-ray and photo levels and also between two X-ray levels is less than 0.15 µm (σ). A three-layer resist system is introduced to fully utilize high-sensitivity and high-resolution features of an X-ray positive resist, FBM-G. An application of hybrid lithography to 0.3-µm MOS devices is presented. The results indicate that further application of X-ray / photo hybrid lithography to the sub-half-micrometer device fabrication process is feasible.     

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。     

侧墙铬衰减型新结构移相掩模的应用

提出了一种全新的移相掩模--侧墙铬衰减型移相掩模（SCAPSM) ，相对于通常的衰减型移相掩模，其制造工艺仅多两步，却可以较大幅度提高光刻分辨率. 采用PROLITH光学光刻模拟软件，参考ArF步进扫描投影光刻机TWINSCAN XT:1400E的曝光参数，对侧墙铬衰减型移相掩模的工艺进行了研究，证明SCAPSM+离轴照明的方案可以将干式193nm光学光刻的分辨率提高到50nm.     

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.     

Application of X-rays to nanolithography

The development of a successful fabrication process for electron devices with dimensions in the sub-100-nm domain will require a form of a high-resolution and high-volume patterning. In this paper we discuss the extensibility of X-ray lithography to this domain in terms of the resolution of the technique, considering in detail the effect of diffraction and photoelectrons. We show that optimized masks and exposure systems can deliver with relative ease patterning in the 70-50-nm region, while phase-shifting techniques can extend the resolution to sub-40 nm. High volume is provided by the use of the mask. The challenge remains in the fabrication of the IX mask, and in the achievement of the necessary placement accuracy     

Reduction of polarization and swing effects in a high numerical aperture exposure system by utilizing resist antireflective coatings

Exposure systems having high numerical apertures (NAs) are essential for increasing the resolution of optical lithography. The efficiency of conventional single-layer bottom antireflective coating (BARC) structures, however, degrades as the angle of incidence increases. In this paper we demonstrate a multilayer BARC structure for high-NA systems employed in ArF lithography. Because the reflection difference between transverse electric (TE or s) and transverse magnetic (TM or p) polarization at the air-resist interface results in low image contrast for high-NA exposure systems, we also describe a single-layer top antireflective coating (TARC) layer that can be used to reduce the polarization effect. By combining the optimized TARC and multilayer BARC structures, the swing effect can be alleviated and the image contrast can be improved for angles of incidence ranging from 0° to 70° (i.e., NA = ca. 0.93).     

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.     

Level-specific lithography optimization for 1-Gb DRAM

A general level-specific lithography optimization methodology is applied to the critical levels of a 1-Gb DRAM design at 175- and 150-nm ground rules. This three-step methodology-ruling out inapplicable approaches by physical principles, selecting promising techniques by simulation, and determining actual process window by experimentation-is based on process latitude quantification using the total window metric. The optimal lithography strategy is pattern specific, depending on the illumination configuration, pattern shape and size, mask technology, mask tone, and photoresist characteristics. These large numbers of lithography possibilities are efficiently evaluated by an accurate photoresist development bias model. Resolution enhancement techniques such as phase-shifting masks, annular illumination and optical proximity correction are essential in enlarging the inadequate process latitude of conventional lithography     

高分辨率投影光刻机光瞳整形技术

在高分辨光学光刻技术中,光瞳整形技术针对不同的掩模图形产生特定的光瞳光强分布模式,从而实现分辨力增强,获得更好的成像性能。概述了高分辨率投影光刻机照明系统中基于衍射光学元件(DOE)、微透镜阵列(MLA)和微反射镜阵列(MMA)的3种光瞳整形技术,并对这些技术的工作原理、设计制作方法和性能特点进行了归纳与总结。     

超精细图案光刻技术的研究与发展

根据国内外研究和发展现状，对有望突破100nm超精细图案光刻分辨率的一些关键技术进行了阐述，其中包括曝光技术、掩模技术、光学系统改进和以离轴照明、相位移掩模、多重滤光和图形演算为代表的分辨率增强技术等。     

New effects of modified illumination in optical lithography

In optical lithography the most fine and isolated dark line is obtained at the phase-shifter edge of a chromeless phase-shifting mask, but only closed-loop patterns can be formed. An easy method for eliminating the useless dark line at the phase-shifter edge by combining modified illumination technologies is proposed. Using a modified light source, which is arranged along one axis (x or y) of the light source area, the resultant optical intensity is different in the x and y directions. A fine resist pattern of 0.15 μm produce along only one direction of the phase-shifter's edge is demonstrated     

100 nm分辨率交替式移相掩模设计

讨论了100nm分辨率交替式移相掩模设计中的关键问题,以及通过对版图的拓扑分析,建立自动化的解决相位冲突的各种方法。通过比较,确立了分层叠加曝光的方案,并针对分层叠加曝光技术,进行了100nm节点中分层技术中两种关键图形的模拟。得出了分层叠加曝光在100nm技术节点中也可以实现的结论。     

New concept for applying edge line phase-shifting masks to arbitrary mask layouts

This paper explains the principle of a method which avoids printing of phantom resist lines due to undesired intensity minima appearing on Cr-less edge line phase-shifting masks. The method combines principles of grey-tone lithography and attenuated phase-shifting masks to give, what we call, a Cr-Less Attenuated Phase-shifting mask (CLAP). Rules for generating a CLAP design and a paradigm setup of a CLAP mask are presented. The capabilities and possible limitations of the CLAP method based on simulated results for a standard wafer stepper setup using the SOLID lithography simulator are being assessed.     

Direct sub-100-nm patterning of an organic low-k dielectric for electrical and optical interconnects

Low-k dielectric materials compatible with copper interconnect fabrication processes extending to the sub-50-nm technology nodes are desired for high speed integrated circuit (IC) fabrication. We demonstrate that bisbenzocyclobutene (BCB), an organic low-k dielectric material, can be patterned with sub-100-nm resolution using electron beam lithography, providing new avenues for nanoscale electrical and optical interconnect fabrication.