Rigorous electromagnetic simulation of mask magnification effects on the diffracted light for EUV binary mask

Extreme ultraviolet (EUV) lithography is expected to be the main candidate in the semiconductor manufacturing starting at 32 nm. As the CD is getting smaller, the aspect ratio of the patterns on the EUV mask is becoming larger. The shadowing effect will become much more significant when keeping the same 4× mask magnification. In this work, mask magnification effects on the diffracted light were explored with rigorous coupled-wave analysis (RCWA) for the sub-32 nm node. The simulated binary mask consists of 70-nm TaBN absorber and 2.5-nm Ru capping layer. The dependences of the diffraction efficiencies on mask pitches were calculated. The impacts of the absorber shadowing were observed from the near field distribution on the EUV mask. The aerial images formed by the diffracted light from the 4× and 8× masks were further evaluated.     

Study on critical dimension of printable phase defects using an EUV microscope

We constructed an extreme ultraviolet microscopy (EUVM) system for actinic mask inspection that consists of Schwarzschild optics and an X-ray zooming tube. This system was used to inspect finished extreme ultraviolet lithography (EUVL) masks and Mo/Si glass substrates. A clear EUVM image of a 300-nm-wide pattern on a 6025 glass mask was obtained. The resolution was estimated to be 50 nm or less from this pattern. Programmed phase defects on the glass substrate were also used for inspection. The EUV microscope was able to resolve a programmed pit defect with a width of 40 nm and a depth of 10 nm and also one with a width of 70 nm and a depth of 2 nm. However, a 75-nm-wide 1.5-nm-deep pit defect was not resolved. Thus, in this study, one critical dimension of a pit defect was estimated to be a depth of 2 nm.     

Observation of the internal defects of multilayer film

We constructed the EUV microscope (EUVM) for actinic mask inspection which consists of Schwarzschild optics (NA 0.3, 30×) and X-ray zooming tube. Using this system, EUVL finished mask and Mo/Si coated glass substrates are inspected. EUVM image of 300-nm-wide pattern of finished mask was clearly observed. Resolution can be estimated to be 50 nm or less from this pattern. The programmed phase defect on the glass substrate made by HOYA is also used for inspection. By using EUV microscope, programmed phase defect with dot patterns of over 90 nm in size and over 4 nm-height bump can be observed finely. And the programmed phase defect of 100-nm-wide and 2-nm-depth pit was also observed. Thus, in this research, observation of a programmed phase defect was advanced using the EUV microscope, in other words, it is succeeded in observation of the topological defect image inside a multilayer film. These results show that it is possible to detect internal reflectance distribution of multilayer under the EUV microscope, without being dependent on surface figure.     

极紫外光刻材料研究进展

极紫外光刻是微电子领域有望用于下一代线宽为22nm及以下节点的商用投影光刻技术,光刻材料的性能与工艺是其关键技术之一。为我国开展极紫外光刻材料研究提供参考,综述了最近几年来文献报道的研究成果,介绍了极紫外光刻技术发展历程、现状、光刻特点及对光刻材料的基本要求,总结了极紫外光刻材料的研究领域和具体分类,着重阐述了主要光刻材料的组成、光刻原理,光刻性能所达到的水平和存在的主要问题,最后探讨了极紫外光刻材料未来的主要研究方向。     

Process impact of mask grid variation

This paper will focus on the process impact of the intentional change in the mask writing grid. Grids ranging from 1 nm to 4 nm (defined at mask level) were used to investigate the effect on test structures in critical locations. The impact on optical proximity correction (OPC) to control line end pull back, corner rounding and general image fidelity will be investigated on >1 numerical aperture (NA) immersion imaging system.     

Flatness characterization of EUV mask chucks

For future extreme ultra violet (EUV) lithography at a wavelength of about 13 nm, flatness of the mask surface is an issue, since out-of-plane deviations sensitively transfer to in-plane distortions. Electrostatic clamping devices of extreme flatness and high stiffness are required. At Fraunhofer IOF, manufacturing processes for EUV mask chucks made from low thermal expansion materials are investigated. Since the chucking surface is finally structured into a pin array, flatness characterization is not trivial. The paper reports on flatness characterization of a mask chuck prototype at various stages of surface manufacturing. We present measurement results obtained with sophisticated commercial tools based on optical and tactile principles and discuss limitations encountered in both cases as well as possible strategies for improvement.     

可用于极紫外光刻的三线毛细管的概念设计

极紫外光刻(EUVL)技术是目前193 nm浸没式光刻技术的延伸,有望突破30 nm或更小技术节点而成为下一代光刻(NGL)技术的主流。毛细管放电极紫外(EUV)光源可为极紫外光刻研究提供高效、便捷的光刻源头,但光源的辐射功率较低一直制约着极紫外光刻技术的发展。三线毛细管放电极紫外光源的概念设计与常用毛细管装置有着本质的区别,它们不同的工作机制将使三线毛细管放电产生的环带状等离子体极紫外光源的辐射功率明显高于常用毛细管的情形,最佳收集角也得到相应的提高。三线毛细管概念设计方案的提出不仅从技术上开拓出一片全新的领地,为极紫外光刻研究提供所需的光源,而且从效益上看更适合于大规模工业生产。     

Analysis of pattern-dependent image placement of single-membrane stencil masks for electron-beam lithography

Large single-membrane stencil masks have been developed for electron-beam lithography. Since a large membrane induces large image placement (IP) error, which is pattern dependent, a method of correcting EB data has been studied to compensate the membrane distortion. In this study, firstly, the effect of crystal anisotropy of a Si membrane to the distortion is examined by making masks from blanks with different orientations. The influence of the anisotropy is found to be small and simulation based on isotropic modeling should be applicable. Secondly, a finite element method (FEM) called ANSYS and Pseudo-FEM are used to predict distortions for three masks with 8 mm-, 12 mm-, or 18 mm-square die of an opening ratio of 0.2 on a 24 mm-square membrane. The simulation results are compared with the results obtained in the experiment on anisotropy and a previous experiment. Qualitative agreement is observed between simulation and experiment but quantitative agreement is obtained only after introduction of adjustment factors. A suggestion is made to improve the IP correction scheme for EB data.     

Contact and proximity lithography using 193 nm Excimer laser in Mask Aligner

In this paper we describe the use of an Excimer laser for full-field lithography in a Mask Aligner. The DUV light from the Excimer laser is homogenized by using micro lens based optical integrators instead of a macro lens array. A simulation of the intensity distribution for 5 μm squares was performed to visualize the diffraction effects and to show the potential of 193 nm illumination. It is demonstrated that compared to the conventional homogenization optics the MO Exposure Optics further improves the illumination uniformity, calculated as 1.8% for MO Exposure Optics and 2.9% for the A-Optics. Moreover the improved optical setup allows a modification of the angular spectrum by using exchangeable illumination filter plates (IFP). Compared to the A-Optics the main improvement effect of MO Exposure Optics is detectable in the patterning of layouts containing critical dimension from 8 μm down to 2 μm.     

LER evaluation of molecular resist for EUV lithography

We have designed and synthesized a molecular resist material, which has no distribution of the protecting groups and have evaluated its performance as a molecular resist with EB and EUV exposure tool. The molecular resist attained a resolution of sub-45 nm patterning at an exposure dose of 12 mJ/cm². It was found that controlling the distribution of the protecting groups in a molecular resist material has a great impact on improving line edge roughness (LER). Low LER values of 3.1 nm (inspection length: L = 620 nm) and 3.6 nm (L = 2000 nm) were achieved with this molecular resist using Extreme UltraViolet (EUV) lithography tool.     

Lithography scaling issues associated with III–V MOSFETs

In this work we investigate fabrication issues associated with scaling down the gate length and source drain contact separation of a III–V MOSFET. We used high resolution electron-beam lithography and lift-off for gate and ohmic contact patterning to fabricate gate-last lithographically-aligned MOSFETs. This work considers the effect of variations in resist thickness on gate lengths and also the fabrication of long narrow gaps using electron-beam lithography. The study showed that the effect of resist thickness variation on metal linewidth is insignificant. A difference of around 2–3 nm was found between PtAu linewidths fabricated using 150 and 280 nm thick resist. A VB6 lithography tool was found to be useful for linewidth measurements. We showed that the choice of resist is critical to gap formation, and that PMMA is not well suited to this task.     

Trades-off between lithography line edge roughness and error-correcting codes requirements for NAND Flash memories

The only way to keep pace with Moore’s Law is to use probabilistic computing for memory design. Probabilistic computing is ‘unavoidable’, especially when scaled memory dimensions go down to the levels where variability takes over. In order to print features below 20 nm, novel lithographies such as Extreme Ultra Violet (EUV) are required. However, transistor structures and memory arrays are strongly affected by pattern roughness caused by the randomness of such lithography, leading to variability induced data errors in the memory read-out. This paper demonstrates a probabilistic–holistic look at how to handle bit errors of NAND Flash memory and trades-off between lithography processes and error-correcting codes to ensure the data integrity.     

Improvement of model kernel representation in process simulation by taking pattern correlation into account

In the modern photolithography simulation, the computation demand on resolution enhancement techniques (RETs) and optical proximity corrections (OPCs) is proportional to the simulation runtime of the model, which is dependant on the number of the kernels retained with the constrain of the model accuracy. Thus, it is essential to retain as few kernels as possible in the model calibration. Traditionally, the kernels are retained based upon their contribution to the aerial image, which is solely determined by the magnitudes of the eigenvalues. This method works well for arbitrary photolithography masks. However, real masks are never arbitrary and random. Instead, they have regular shapes and arrangements as governed by design rules, indicating the contributions from the retained kernels are statistically correlated to each other. By taking such correlations into account, the system representation can be improved to contain fewer kernels for a constant model accuracy. In this paper, the mathematical derivation of the pattern correlation concept is discussed and the concept is applied to a contact layer illuminated by a Quasar optical system with λ = 193 nm and NA = 0.8. Significant improvement of model kernel representation is observed, four improved kernels vs 15 original kernels, and the new methodology is justified by comparing the difference of the aerial image intensities between the full kernel representation and the retained kernels representation at sampling points.     

Patterning capability of new molecular resist in EUV lithography

We designed and synthesized a new partially-protected polyphenol, 25X-MBSA-M, for which the position and number of protected hydroxyl groups have no dispersion, and evaluated the EUV patterning performance of a chemically amplified positive-tone resist based on it. EUV imaging experiments were performed using the high-numerical-aperture (NA = 0.3), small-field EUV exposure tool (HINA) at ASET and coherent illumination (σ = 0.0). Patterning results showed the resolution of the resist to be 28 nm at an EUV exposure dose of 12.2 mJ/cm², the obtainable aspect ratio to be as high as 2, and the line-edge roughness (LER) to be small, with 3σ being 3.6 nm for 45-nm line-and-space patterns and an inspection length, L, of 2000 nm. In addition, pattern collapse was markedly suppressed.     

Low energy Xe+ ion beam machining of ULE® substrates for EUVL projection optics – Evaluation of high-spatial frequency roughness

Ion beam figuring (IBF) is a suitable technology for the final shape correction of substrates used in the projection optics of EUVL tools. In order to achieve HSFR below 0.10 nm rms, we have conducted our research on ion beam machining of the ULE® substrate by Xe⁺ ion beam with energy less than 2 keV. The HSFR of the unprocessed ULE® surface was 0.06 nm rms, whereas the HSFR of the ULE® substrate machined by under 0.7 keV Xe⁺ ion beam was less than 0.08 nm rms. This HSFR (0.08 nm rms) is lower than that (0.10 nm rms) of the ULE® substrate machined with Ar⁺ ion beam. Therefore, Xe⁺ ion beam with energy under 0.7 keV can be used for figure error correction of the ULE® substrates for projection optics used in commercially available EUVL exposure tools.     

极紫外光刻光源

分析了极紫外光刻技术作为下一代光刻技术的首选技术目前飞速发展阶段的状况,表明欧、美、日、俄等国家和地区在该领域集中了大量的人力、物力的目标是将光刻精度提高到50nm.指出了极紫外光源是极紫外光刻的核心设备,目前的主要研究方向是提高能量转换效率和输出功率,提高系统各部分的寿命,降低成本等.     

Fabrication of novel double microlens using two step soft lithography

A novel method to fabricate double layer microlens array is proposed where the second smaller microlens are imprinted on the first larger microlens by using soft lithography twice. Key step to implement this method is to imprint micron-size structures on convex surface using nano-imprinting technology. It is required to prepare thin polydimethylsiloxane (PDMS) mold for the second soft lithography and thus different thickness of PDMS molds have been tested. It is found that 870 μm thick mold is good for fine duplication and durability. We have successfully fabricated the first microlens hemisphere of 51 μm diameter and the second microlens of 3 μm diameter on top of the first. The double microlens array shows more focused light spot when viewed through optical microscope.     

硅集成电路光刻技术的发展与挑战

从微电子集成电路技术发展的趋势,介绍了集成电路技术发展对光刻曝光技术的需求,综述了当前主流的DUV光学曝光技术和新一代曝光技术中的157nm光学曝光、13nm EUV曝光、电子束曝光、X射线曝光、离子束曝光和纳米印制光刻技术的发展状况及所面临的技术挑战.同时,对光学曝光技术中采用的各种分辨率增强技术如偏轴照明(OAI)、光学邻近效应校正(OPC)、移相掩膜(PSM)、硅片表面的平整化、光刻胶修剪(resist trimming)、抗反射功能和表面感光后的多层光刻胶等技术的原理进行了介绍,并对不同技术时代可能采用的曝光技术作了展望性的评述.     

A high-bandwidth,high-precision,two-axis steering mirror with moving iron actuator

This paper focuses on the design, fabrication, assembly, and testing of high bandwidth two-axis mirror positioners for precision optical platforms, which we refer to as the Advanced Fast Steering Mirror (AFSM) and the small Advanced Fast Steering Mirror (sAFSM). These novel positioners consist of a mirror platform driven in two rotational axes by flux-steering electromagnetic actuators, and controlled via position feedback loops. The devices are designed for beam stabilization tasks in lithography, laser communication, lidar, and similar optical applications. We have experimentally demonstrated small-signal system bandwidth of 10 kHz using optical quad-cell feedback and a two-channel analog control architecture. The AFSM has a travel range of ±3.5 mrad, and a measured angular acceleration of 1 × 10⁵ rad/s².     

一种适于快速OPC的精确光刻胶剖面仿真算法

光刻仿真工具是描述实际工艺的有效工具。利用光刻仿真工具，能够准确地描述由掩模制造工艺、光刻胶曝光、显影、蚀刻所引起的光学邻近效应和畸变所导致的关键尺寸的变化。利用了改进的空间图像仿真及可变光强阈值模型来获得准确的硅片图形。改进的空间图像的基本思想是，用空间图像与一个高斯滤波器进行卷积，从而使图像较原来变得模糊，以此来模拟光刻胶的实际扩散效应。描述了一种适用于快速光学邻近校正（OPC）的准确的光刻胶剖面仿真算法。