面投影微立体光刻技术研究进展

综述了国内外最近几年面投影微立体光刻技术的研究进展.阐述了液晶动态掩膜技术和数字微反射镜动态掩膜技术的基本原理.分析了两者的技术核心并对相关参数进行了比较.最后,对该技术的发展前景作了展望.     

三维复杂微系统的微立体光刻成型工艺

介绍了一种具有更高加工分辨率且可直接成型 3维复杂微系统的一次曝光型微立体光刻成型样机 Micro SL er,及其配套专用光敏树脂 Micro SL5 2 2 0。重点给出了 Micro SL er中经薄膜晶体管阵列编址的液晶显示光阀表盘 ,也即可控透光模板的构造、性能及其对 Micro SL er层面加工分辨率和截面曝光尺寸的影响。对比了 Micro SL er的国产配套光敏树脂 Mi-cro SL5 2 2 0与国外同类产品 DSM7110型光敏树脂的各项技术指标。为证明一次曝光型微立体光刻工艺在成型 3维复杂微结构时的优越性 ,给出了经 Micro SL er成型出的微机械部件、微型件浇铸模、微流体系统部件等实物的扫描电子显微照片及相关的加工参数。探讨了现阶段的传统立体光刻工艺、小光斑立体光刻工艺及微立体光刻工艺在加工分辨率方面的差异 ,分别指出了影响这 3种立体光刻成型分辨率的关键因素     

三维复杂微器件的微立体光刻成形

介绍了一种具有更高加工分辨率且可直接成形三维复杂微型器件的一次曝光型微立体光刻成形装置。重点给出了经薄膜晶体管阵列编址的液晶显示光阀表盘，即可控透光模板的构造、性能及其对微立体光刻成形装置层面加工分辨率和截面曝光尺寸的影响。为证明微立体光刻工艺在成形三维复杂微结构时的优越性，给出了所加工出的微机械部件、微型件浇铸模、微流体系统部件等实物的扫描电子显微照片及相关的加工参数。     

立体光刻(SL)工艺研究

介绍了立体光刻工艺的成形机理和工艺特点及应用,并对成形过程进行了详细的分析.讨论了进一步提高工艺水平需要进行研究的几个方面.     

微机械制造中的三维立体光刻加工技术

文章介绍了微机械和微机电系统制造的一种重要方法-三维立体光刻技术方法的基本原理、加工技术及其应用.同时还介绍了立体光刻技术结合抗腐蚀层、牺牲层工艺加工微器件的原理、方法和应用.     

193nm光刻投影物镜的研究

为了跟踪国际光刻设备的发展,介绍了工作波长为193nm国际主流光刻机的发展现状,对光刻机的核心—投影物镜的设计原理进行了分析,针对投影物镜光学系统参数、光学结构、光学材料和机械结构进行了深入探讨,最后对中国光刻机的发展前景进行展望。     

高数值孔径投影光刻物镜的光学设计

针对45nm节点投影光刻物镜的应用,开展了工作波长为193nm的深紫外浸没式高数值孔径(NA)投影光刻物镜的研究和研制。设计了数值孔径(NA)为1.30的离轴三反射镜投影光刻物镜和NA为1.35的同轴两反射镜投影光刻物镜,并对两个设计方案的优劣进行对比分析,选择了同轴式结构作为最终的设计方案。分析了系统在不同NA情况下可变光阑与其远心度之间的关系,提出了用双可变曲面光阑的设计方案来优化系统的远心度。实验表明,应用本文设计方案,光刻物镜的波像差小于1nm,畸变小于1nm;新型的可变光阑使系统NA在0.85~1.35变化时的最大远心度由5.83~17.57mrad降低至0.26~3.21mrad。本文提出的设计方案为45nm节点高数值孔径投影光刻物镜的研制提供了有益的理论依据和指导。     

软X射线投影光刻原理装置的设计

首先介绍了投影光刻技术发展的历程、趋势和软X射线投影光刻技术的特性,其次介绍了软X射线投影光刻原理装置的研制工作.该装置由激光等离子体光源、掠入射椭球聚光镜、透射掩模、镀有多层膜的Schwarzchild微缩投影物镜、涂有光刻胶的硅片及相应的真空系统组成.0.1倍的Schwarzchild微缩投影物镜具有小于0.2μm的分辨率.     

基于光栅制造的光刻投影物镜设计

光栅尺作为位移传感器被广泛应用在精密测量体系中,随着测量趋于纳米级精度和大量程,对光栅尺的制造精度提出了更高的要求。刻线误差是影响光栅尺制造精度的重要因素,减小刻线误差能够有效提高光栅制造精度。设计了一种大孔径、低畸变的投影光刻物镜,并在Zemax光学设计软件中对物镜进行了设计及优化。结果显示,其全视场波像差小于λ/10,MTF>0.6,最大畸变<0.0037%,最大分辨率R=2μm,数值孔径NA=0.15,缩小倍率5×,最大焦深±9.73μm。对其进行公差分析,结果表明,该物镜完全满足提高光栅尺制造精度的需求。     

投影莫尔技术应用于静态物面微小变形测试的研究

物面微小变形测试在电子制造、逆工程等领域具有重要意义。本文一改传统机械式相移结构,设计了一种全新的投影莫尔三维轮廓投影成像测试系统。首次利用计算机实时控制变光源实时控制相移,大大提高了系统测试速度（全场测量：4－8sec）。采用垂直投影,对CCD倾斜成像机构,提高了光场的均匀性和可测物范围（测量面积最大可为300＊300mm^2）。另外该系统还具有光强照明均匀性好等特点。系统测量精度可达40μm。文中详细分析了系统关键技术,并给出了具体实验结果。结果表明系统的设计原理是成功的。     

Three-dimensional microstructure using partitioned cross-sections in projection microstereolithography

Microstereolithography (μSL) is similar to the conventional stereolithography process and allows the fabrication of complex microstructures with high aspect ratios. In the projection μSL process, each layer is fabricated by one irradiation of the light which has a cross-sectional shape. At this time, the fabrication range is limited by the field of view of pattern generator (LCD or DMD) and the magnification of the objective lens. In this study, we propose a partitioned cross-section method for expanding the fabrication range while maintaining the fabrication resolution in the projection μSL system. A cross-section is partitioned into several sub-sections, having required size in the pattern generator. Then, the shaped light corresponding to sub-section is irradiated at specific position on the resin surface, and cured sub-sections make completed cross-section. The procedure for generating a series of sub-sections has been presented. Using this method, some microstructures have been fabricated.     

Design of microstereolithography system based on dynamic image projection for fabrication of three-dimensional microstructures

As demands for complex microstructures with high aspect ratios have increased, the existing methods, MEMS and LIGA, have had difficulties coping with the number of masks and fabricable heights. A microstereolithography technology can meet these demands because it has no need of masks and is capable of fabricating high aspect ratio microstructures. In this technology, 3D part is fabricated by stacking layers, 2D sections, which are sliced from STL file, and the Dynamic Image Projection process enables the resin surface to be cured by a dynamic image generated with DMD™ (Digital Micromirror Device) and one irradiation. In this paper, we address optical design process for implementing this microstereolithography system that takes the light path based on DMD operation and image-formation on the resin surface using an optical design program into consideration. To verify the performance of this implemented microstereolithography system, complex 3D microstructures with high aspect ratios were fabricated.     

Mass production of 3-D microstructures using projection microstereolithography

Microstereolithography (MSL) technology is derived from the conventional stereolithography process and can meet the demands for fabricating complex 3-D microstructures with high resolution. This technology can be divided into scanning and projection methods, which have different levels of precision and fabrication speeds. Scanning MSL fabricates very fine 3-D microstructures by controlling the position of the laser spot on the resin surface. Projection MSL quickly fabricates one layer with one exposure using a mask. In this paper, we propose a projection MSL system with uniform illumination and image formation based on optical design for fabricating microstructure arrays. This system can realize mass production of 3-D microstructures in the meso-range, which falls between micro-and macro-ranges, with a resolution of a few microns. Microstructure arrays were fabricated to verify the performance of the proposed system.     

Dithering method for improving the surface quality of a microstructure in projection microstereolithography

In layered manufacturing, geometrical gap occurs between the computer-aided design (CAD) model and the fabricated, due to the stair-stepping effect. It will deteriorate the surface quality of the microstructure. By reducing the stair steps, the surface quality of a layered manufactured microstructure can be improved. In this research, dithering method is introduced to improve the surface quality of a microstructure in projection microstereolithography. The dithering method can represent grayscale effect with monochrome image, so it is applicable to the digital micromirror device for ultraviolet, which allows monochrome image as an input format. By adjusting the beam intensity using the dithered image, it is possible to control the cure depth of the resin within a layer. In a cross-section, the region to be dithered is obtained by the difference of the cross-sections between the current layer and the previous layer. It is called a compensation area (CA) in this research. The gray level to be applied is determined considering the CAD model and the curing characteristics of the resin. The dithered CA is then combined with the current cross-section. The parabola-shaped microstructures, using dithered and non-dithered cross-sectional images, have been fabricated and compared. The dithering method has shown good performance for improving surface quality and reducing the fabrication time.     

Multi-material microstereolithography

We have previously described the development of a microstereolithography (µSL) system using a Digital Micromirror Device (DMD) for dynamic pattern generation and an ultraviolet (UV) lamp filtered at 365 nm for crosslinking a photoreactive polymer solution. The µSL system was designed with x–y resolution of approximately 2 µm and a vertical (z) resolution of approximately 1 µm (with practical build limitations on vertical resolution of approximately 30 µm due to limitations on controlling UV penetration in z). The developed µSL system is capable of producing real three-dimensional (3D) microstructures, which can be employed in applications such as microfluidics, tissue engineering, and various functional microsystems. Many benefits will potentially be derived from producing multiple material microstructures in µSL, and one particular application area of interest is in producing multi-material microscaffolds for tissue engineering. In the present work, a method for multi-material µSL fabrication was developed using a syringe pump system to add a material to a small, removable vat designed specifically for the multi-material µSL system. Multi-material fabrication was accomplished using a material changeover process that included manually removing the vat, draining the current material, rinsing the vat, returning the vat to the system, and finally dispensing a prescribed volume in the vat using the syringe pump. Layer thicknesses of approximately 30 µm were achieved using this process. To demonstrate this system, several multi-material microstructures were produced to highlight the capability of this promising technology for fabricating 3D functional, multi-material microstructures with spatial control over placement of both material and structure.     

Cross-section segmentation for improving the shape accuracy of microstructure array in projection microstereolithography

Microstereolithography is a microfabrication technology done in a layer-by-layer fashion. It is useful to fabricate a microstructure with both a high aspect ratio and a complex shape. Projection microstereolithography is suitable for microstructure array fabrication due to the fast process time using patterned light irradiation. However, nonuniform light intensity on the resin surface deteriorates the fabrication precision. This research proposes the cross-section segmentation for uniform exposure energy on the resin surface. Each subsection consisting of a cross-section is separately converted into an image file. The estimated exposure time of each subsection is stored in a text file and used during the fabrication. Finally, several microstructure arrays are fabricated to verify this method.     

Multiple fabrications of sacrificial layers to enhance the dimensional accuracy of microstructures in maskless projection microstereolithography

Microstereolithography (MSL) is a promising technology for producing fully three-dimensional microstructures with overhanging features and high-aspect ratios. In conventional stereolithography (SL), a layer thickness of ≈50–100 μm is obtained by using a recoater. However, a recoater cannot be used in MSL, where the layer thickness is typically ≈10 μm or less, since resin flow may break or distort the pre-fabricated layers. In most MSL systems, the resin surface (or layer thickness) is controlled by a free surface technique that employs resin gravity to refresh the resin surface over a given settling time. In addition, a sacrificial layer must be fabricated in MSL to create a flat initial surface and provide support, just as in SL. In this paper, the fabrication methodology and functionality of the sacrificial layer is investigated for microstereolithography microstructures fabricated using the free surface technique. Experimental data are presented that indicate the greater the number of sacrificial layers, the sharper the dimensional accuracy of the microstructures in the building direction. This is because multiple fabrications of the sacrificial layer affect the resin ‘wetting’ status on the substrate or pre-cured surfaces. Several microstructures were fabricated to verify the effect of multiple fabrications of the sacrificial layer on dimensional accuracy in the building direction.     

Automatic alignment direct step-on-wafer projection system

This paper describes an automatic alignment direct step-on-wafer (dsw) projection system. Automatic alignment accuracy is better than ±0.25 μm and useful achievable resolution is 1.5 μm or better. Stepping of the stage is achieved using a record ruler (glass scale) and photoelectric microscope. Its precision is better than ±0.33 μm (3 σ). Also included in the system is a reticle box with automatic reticle detection and selection, high pressure pulsed mercury lamp and uv light integrating exposure controller as well as a closed-circuit tv viewing and display system. The fundamental design, some experimental testing data and error analysis of the machine are described briefly in this paper     

多媒体背投系统中的光学薄膜

背投技术是当今显示领域内的新秀 ,主要介绍了用于多媒体投影系统所需要的各类光学薄膜的作用、参数和光学性能 ,同时针对该领域内国内外最新研究状况进行了调研 ,给出了现在所面临的关键技术难题并对其发展前景做了预测。     

Evaluation of system models for an endoscopic fringe projection system

To be able to perform inline inspection of complex geometries, which exhibit for example undercuts or internal structures, a new endoscopic micro fringe projection system has been developed. It is designed to perform areal measurements for tool inspection inside the limited space of metal forming presses by employing flexible image fibers to couple the measurement system’s camera and projector to a compact sensor head. The projector features a laser light source and a digital micro-mirror device to generate high-contrast fringe patterns. To increase the depth of field of the sensor heads, custom gradient-index lenses have been designed as an approximation to the Scheimpflug principle. Challenges arise for both calibration and phase measuring algorithms from the optics, as well as from the reduction in resolution introduced by the fiber bundles. This paper presents an evaluation of two different system models for the endoscopic fringe projection system, which are based on the pinhole camera model and a black box model. An automated calibration process, which gathers the calibration data for two calibration algorithms that are robust to artifacts introduced by the optical path, is demonstrated. Based on a comparison of measurements, differences between the two modeling approaches are discussed. Finally, results of measurements of a demonstrational metal forming tool are shown as an application example.