衍射光学元件灰度掩模板激光制作系统研究

根据灰度掩模的制作理论,提出了由PP8000胶片输出仪、远心成像透镜组、平行准直He-Cd激光器构成的精缩投影曝光灰度掩模制作系统。通过灰度掩模平面不同位置处提供可变的透过率,经一次光刻后得到所需的衍射光学元件。该系统不仅可采用黑白胶片制作高分辨率灰度掩模板,还可根据彩色灰度等效理论,利用彩色等效胶片实现256灰度级的扩展细分,以进一步提高灰度掩模板制作的分辨率。对于16台阶灰度掩模,其分辨率可以从0~255扩展到0~1280灰度级。利用该系统给出了二元光栅精缩后的感光图片。     

基于DMD光刻制作微柱透镜阵列分模曝光的研究

针对无掩模光刻技术制作微柱透镜阵列的面形精度问题,对曝光方式和掩模设计进行研究,采用一种分模曝光方法,包括图形分层,掩模设计,分层掩模灰度调制,分层曝光四个步骤。在曝光前,需要对二维掩模版图按设计结构高度进行分层,以实现单层掩模在抗蚀剂上的投影成像高度不超过物镜的焦深范围。基于数字微镜阵列对灰度掩模的空间调制原理,设计出匹配的分层掩模版图,给出了图形分层原则和方法以及模板设计的原理。实验结果表明:采用该方法制作微柱透镜阵列,面形平均误差为0.54μm,相比以往单模曝光平均误差值0.79μm,平均误差减小了0.25μm,该方法弥补了由物镜焦深限制所造成的技术问题,提高了曝光质量。     

任意形状图形的灰度掩模图的设计系统研究

灰度掩模技术是制作三维微纳结构的有效方法之一,灰度掩模图设计是灰度掩模技术的重要组成部分.目前,在微机械器件制作领域中,通常只给出常用规则形状三维结构对应的灰度掩模图的设计方法,对于任意形状图形的灰度掩模图设计鲜有报道.本文综合灰度光刻技术中的编码原理和有限元法中的铺路法,提出了适合于任意形状图形的灰度掩模图设计算法,解决了误差处理和图形闭合两个关键问题,给出了算法及图形的评价方法,并利用AutoCAD二次开发工具ObjectARX研究了算法的程序实现,构建了灰度掩模图的设计系统.利用该系统设计了多幅常规规则形状和任意形状灰度掩模图,结果表明,该系统可以高效地设计任意形状图形的灰度掩模.研究工作为任意形状图形灰度掩模图的设计提供了一种新方法,可以提高灰度掩模图的设计效率,为三维微纳器件的制作提供技术积累.     

消除激光直写系统中声光调制器迟滞现象的方法

激光直写是一种适用于衍射光学器件及掩模加工的方法。利用声光调制器对曝光功率进行精确控制对所制作器件的性能是至关重要的。首先描述了声光调制器的迟滞现象及其对曝光后掩模面图开的不良影响。基于这一分析,提出了一种方法来克服声光调制器迟滞现象所带来的问题。简述了此项技术的设计原理和实现。实际制作的掩模样品图案显示了所述方法的有效性。     

误差扩散法编码设计制作微光学元件

以发展微光学元件制作新方法为目标,提出利用误差扩散编码方法设计灰阶编码掩模制作微光学元件。此方法同其他编码方法相比,具有量化效果好、衍射效率高、制作文件小、计算速度快、通用性好等优点。用此方法对制作微透镜的掩模进行了设计,利用预校正法和边缘增强法相结合的方法对掩模进行了优化,并对曝光、显影过程进行了模拟,得到了满意的结果。     

用灰度曝光技术改善数字光刻图形轮廓

基于空间光调制器(SLM)数字光刻技术可用于IC掩模制作或直接作为微结构的加工工具,但用数字投影光刻系统加工某些结构的二元图形时,往往难以获得预期的图形轮廓,即图形边缘处有一定畸变,特别是较低缩小倍率时。本文提出优化设计图形边缘灰度的方法来校正光刻图形的畸变。文中分析了数字光刻制作这些二元光刻图形时空间像畸变产生的物理机制,详细讨论了设计图形边缘灰度优化的规则,并以加工圆孔滤波器为例,模拟了它的数字光刻成像过程。结果表明,设计图形的边缘采用灰度曝光可使其空间像畸变减小约8个百分点,光场分布更为均匀。数字灰度曝光技术简单易行,可为改善光刻图形质量提供了新途径。     

反应离子束刻蚀石英同质掩模制作小阶梯光栅

离子束刻蚀作为真空技术的一种重要应用,已广泛运用于现代微电子器件和微光学器件的制作工艺中。本文结合反应离子束刻蚀与全息光刻技术,针对线密度较低的小阶梯光栅,倾斜刻蚀石英同质掩模,制作了三种在紫外光和可见光波段透射闪耀的小阶梯光栅。第一种光栅线密度为360lp/mm,闪耀角16.8°,在325nm波长的透射衍射效率为74%;第二种和第三种光栅线密度均为400lp/mm,闪耀角为34.7°和43°,其在632.8nm波长的透射衍射效率分别为63%和57%。结果表明,使用CHF_3作为刻蚀气体的反应离子束刻蚀石英同质掩模,所制作的小阶梯光栅在其工作波段透射闪耀的衍射效率为理论值的75%以上,为全息离子束制作低线密度大闪耀角的光栅提供参考。     

用于KrF准分子激光光刻的衰减相移掩模

讨论了相移掩模提高光刻分辨力的基本原理,提出了一种抗蚀剂相移器制作衰减相移掩模的新方法,利用自行设计、建立的KrF准分子激光投影光刻实验曝光系统进行了实验研究,给出了实验结果,并与传统光刻方法作了比较.     

制作光纤光栅的相移掩模-双光束干涉曝光方法

介绍将无铬相移掩模技术和双光束干涉曝光技术用于制作纳米级图形光纤光栅的基本原 理和实验系统设计。提出一种用可移动反射镜使写入光束扫描固定在一起的相移掩模和光纤组合体制作光纤光栅的方法,既便于系统调整,增强曝光能量,又可方便制作高分辨力、长尺寸光纤光栅,无论是周期光栅,还是非周期光栅。     

形成连续微光学元件的灰度掩模图形生成方法

针对利用灰度掩模制作连续微光学元件的方法 ,介绍了从元件结构到灰度图形的转换 ,灰度图形的修正 ,灰度图形的数字化以及图形编码等关键步骤。最后给出生成微透镜列阵掩模图形的实例。     

Research on digital mask fabrication technique of micro-optical element

By means of control flexibility of digital micromirrors, a digital mask fabrication system of a micro-optical element is designed. A single optical element can be obtained on the substrate after a one-time planar exposure. By using a computer to control the digital micromirrors, real-time movement and switch of the mask can be realized, and accordingly superimposed exposure of the multi-mask can be achieved. The real-time digital-mask technique, the digital-mask-movement technique and the digital-mask-fractal technique are, respectively, investigated. Theoretical analysis and experimental results show that the lost efficiency caused by the limitation of lens aperture is greatly reduced by use of the mask fractal technique. Moreover, the lithography resolution of the gray-scale mask fabricated by an electro-addressable spatial light modulator is improved and the edge acutance is perfected.     

Two-beam-current method for e-beam writing gray-scale masks and its application to high-resolution microstructures

A two-beam-current method is introduced for e-beam writing in the fabrication of gray-scale masks. Compared with the simpler single-current method, the two-beam-current method offers two important advantages: (a) it can achieve a much larger dynamic range for e-beam exposure; (b) the writing time for a gray-scale mask can be reduced when a large pattern is to be written. Here, the new method is first described in detail and its application to the fabrication of our new gray-scale mask is demonstrated. Then, the improved gray-scale masks were employed to fabricate large dynamic range, high-resolution micro-optical elements of less than a couple of micrometers depth, using deep ultraviolet lithography at 248 nm wavelength and an inductively coupled plasma reactive ion etching system.     

Gray-scale masks for diffractive-optics fabrication: I. Commercial slide imagers

Fabrication of diffractive optics with binary masks requires multiple photolithographic processes to produce high-efficiency elements. Alignment or etching errors at any stage of fabrication decrease the efficiency of the element. We developed an easily accessible procedure that reduces fabrication complexity and costs by using a single gray-scale mask. The gray-scale patterns are generated by commercial slide imagers and are then photoreduced onto low-contrast film plates. Multiple-level or continuous relief structures (kinoforms) may be constructed by use of the photoreduced gray-scale patterns as lithographic masks. Diffractive-optic lenses and blazed gratings were fabricated in photoresist with this procedure. First-order diffraction efficiencies as high as 85% were measured for the blazed gratings. The advantages and the limitations of this technique are discussed.     

Cost-effective mass fabrication of multilevel diffractive optical elements by use of a single optical exposure with a gray-scale mask on high-energy beam-sensitive glass

We present a method for reproducing diffractive optical elements in quantity. The method is compatible with VLSI microfabrication techniques and involves generating a gray-scale mask. The gray-scale mask is employed in an optical aligner to expose an analog photoresist on any environmentally durable substrate, e.g., glass, quartz, semiconductor, or metal, one exposure for each diffractive optical element. After copies of the mask on the photoresist are developed, many substrates can be processed in parallel in a chemically assisted ion-beam etcher to transfer the microstructures on the analog resists simultaneously onto the surfaces of the substrates.     

Localized self-volume growth in hybrid sol-gel glass induced by ultraviolet radiation with a gray-scale mask

UV-induced self-volume growth of the hybrid sol-gel glass was investigated for fabrication of an arbitrary-surface relief structure with a user-defined gray scale mask. The gray scale mask was generated through exposure of a high-energy beam-sensitive glass under an electron beam. Saw-tooth gratings of different periods were fabricated by a simple UV exposure through the gray-scale mask. Experimental results showed that the smaller the period is, the shallower the depth obtained owing to the self-volume growth effect is.     

Properties of DMDs for holographic displays

Digital micromirror device’s (DMD) properties as being a display device for holographic displays are investigated. High speed, a large separation between reconstructed image and reconstruction beam, two symmetric diffraction patterns, and low intensity (0,0)th-order beam at a blazed grating condition are the desired properties for the displays. The blazed grating condition of a DMD can reconstruct images with higher diffraction efficiency than the line grating condition. DMD’s high speed enables to present colors and gray levels to the reconstructed image. However, reconstructed images from a gray-level computer-generated hologram (CGH) and its binary form hologram reveal no noticeable difference between them, except the background noise in the image from the CGH.     

Diffractive optical element designed by use of an irregular etching-depth sequence

In fabricating a diffractive optical element the ratio of the etching depth between the (n - 1)th and the nth mask is usually 1/2. We found that the diffraction efficiency of a diffractive optical element can be improved by as much as 7.8% if the above ratio (1/2) is not kept constant. For achieving this improvement the difference between the desired and the actual diffraction pattern is also used as an objective function for phase quantization.     

Development of a two-dimensional phase-grating mask for fabrication of an analog-resist profile

Fabrication of a thick analog profile with photoresist is a difficult task in photolithography. We demonstrate that a binary phase-grating photomask with an appropriate period and duty cycles is capable of manipulating the exposure illumination in an analog fashion and can be used for fabrication of the desired analog micro-optics profiles on the surface of a thick photoresist. By choosing the proper period and variation of duty cycle of the phase-grating mask, one can create the desired analog intensity of exposure illumination for an optical stepper. This allows the formation of a wide range of analog micro-optics profiles with an SPR 220-7 photoresist. The numerical convolution of the diffraction efficiency curve and resist exposure characteristics is used to predict the final resist profile and also to design the appropriate duty-cycle distribution for the binary phase grating. As a demonstration of this technology, we fabricated a variety of micro-optical elements, such as a positive lens, ring lens, prism, and vortex of approximately 100-200 microm diameter, by using a phase-grating mask fabricated in a poly(methyl methacrylate) electron-beam resist.     

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.