下一代光刻技术——压印光刻

通过分析集成电路制造工艺中的核心环节--光刻技术,采用机械微复形原理的压印光刻技术可避免传统光学光刻的光学衍射限制,能够对最小到6 nm特征尺寸的图形进行复制.通过研究压印光刻原理,详细分析对比热压印及常温压印的工艺特点、复形面积、模具结构和阻蚀胶固化过程等,揭示出常温压印更适用于多层套刻的图形制作.针对基于紫外光固化的常温压印光刻工艺在压印过程中的关键技术:阻蚀胶成膜控制、对准、套刻、精确加载、留膜厚度控制、阻蚀胶固化控制等进行深入研究,提出释放保形软压印工艺,能够实现基于常温软模具压印的大面积亚100 nm级特征尺寸图形的复制.最后,以SIL-Ⅰ型分步式常温紫外光固化压印光刻机的研究为例,对其结构特性做出深入分析,估算出系统的精度等级;通过试验,对系统的压印复形精度做出评估.     

常温微压印中抗蚀剂流动的研究及工艺优化

为提高微压印中抗蚀剂的复型精度,利用POLYFLOW,基于流固耦合方法对常温压印过程中抗蚀剂的流动进行了有限元模拟,系统地分析了抗蚀剂的初始厚度,留膜厚度,模具的深宽比,占空比,模具下压速度等因素对抗蚀剂流动填充的影响规律。搭建了压印的可视化实验平台,通过该平台对不同工艺条件(包括抗蚀剂的初始厚度,留膜厚度以及模具的下压速度)及软模具结构(深宽比,占空比)下抗蚀剂的流动填充过程及其填充形貌进行了实时观测,并与数值计算结果进行比较。结果表明,在不影响填充效率的情况下,采用低速下压(≤1μm/s)方式,在占空比0.375,深宽比2时,填充度可达到90%以上。仿真和实验验证了优化的压印工艺条件和模具结构。另外,本文还引入了增加模板特征高度预留量的概念,可进一步提高复型精度。     

纳米压印光刻中抗蚀剂膜厚控制研究

研究了纳米压印光刻匀胶工艺中抗蚀剂膜厚与抗蚀剂粘度、匀胶转速、匀胶时间和滴胶量之间的关系。实验研究表明,抗蚀剂膜厚与抗蚀剂粘度、匀胶转速和匀胶时间均呈幂指数关系;当匀胶转速达到一定值,匀胶时间足够大时,膜厚不再随匀胶时间变化而变化,存在最小厚度,即抗蚀剂膜厚与滴胶量无关。建立了抗蚀剂膜厚与抗蚀剂粘度、匀胶转速和匀胶时间之间的量化关系公式,实现了对抗蚀剂膜厚的控制。     

纳米压印光刻模具制作技术研究进展及其发展趋势

模具是纳米压印光刻(Nanoimprint lithography,NIL)与传统光学光刻工艺最大的区别所在,模具作为压印特征的初始载体直接决定着压印图型的质量,要实现高质量的压印复型,必须要有高质量的压印模具。不同于传统光学光刻使用的掩模(4X),纳米压印光刻使用的是1X模版,它在模具制作、检查和修复技术面临更大挑战。当前,模具的制作已经成为NIL最大的技术瓶颈,而且随着纳米压印光刻研究的日益深入以及应用领域的不断扩大,NIL模具的制造将变的越来越重要并面临着更加严峻的挑战。因此,模具的制造已经成为当前纳米压印光刻一个最重要的研究热点,纳米压印光刻发展的历史也是压印模具不断发展创新的历史。综述了当前国内外各种纳米压印光刻模具制作技术研究进展,并指出三维模具、大面积模具和高分辨率模具的制作、模具缺陷的检查和修复是当前及其将来最迫切的需求、最主要的研究热点和挑战。     

压印光刻工艺中光刻胶填充流变模拟与试验研究

压印光刻工艺中,为了实现高质量的压印复型,必须能够理解和预测压印载荷作用下光刻胶的流变填充行为。根据实际采用的光刻胶的特性,建立了基于粘性流体的光刻胶流变填充有限元模型,采用体积率法对光刻胶流场的运动边界进行追踪,研究模板特征几何尺寸、胶层厚度及及尺度效应对压印填充过程的影响及其作用机理。结果表明,光刻胶流变填充以单峰或双峰两种模式进行,模式的转变点可由特征凹槽宽度和初始胶厚度的比值来预测,并受表界面效应的影响;最有利于填充的特征深宽比约为0.8;最佳初始胶层厚度约为特征深度的2倍。进行了相应的压印试验,试验结果与模拟计算的结论吻合,说明仿真结果可信,可以作为压印光刻工艺中模板图形几何特征、胶厚以及模板表面处理的工艺设计依据。     

微压印过程中抗蚀剂流动分析

为研究微压印过程中低黏度抗蚀剂流动状态对微压印成形精度的影响,对常温压印过程中抗蚀剂流动进行了有限元分析,系统研究了不同结构的模板占空比、宽厚比等压印工艺条件对抗蚀剂填充的影响,以及抗蚀剂流动对软模具的变形影响,得到了单双峰转换曲线及模具结构对抗蚀剂填充效率的影响曲线,从理论上分析了抗蚀剂流动特性,并进行了实验验证,进一步证明了仿真方法的可行性。     

一种提高压印光刻软模复制精度的方法

由于传统的光刻生产工艺有透镜光学极限性 ,压印光刻为集成电路的生产提供了一种新思路。在压印光刻中 ,模具的制造是重点。为了获得高精度的压印模具 ,在实验中着重从模具材料的选择、固化剂的添加量、真空压力大小、固化温度、固化时间等方面进行分析和研究。采用正交实验方式和数理方差分析 ,通过检测压印模具的平整度、一致性、特征尺寸及模具表面的固化收缩率等参数的变化 ,特别是模具的特征尺寸变化 ,得到了压印模具制作的最佳工艺组合     

纳米压印复合软模具建模研究

基于复合软模具纳米压印是一种高效、低成本和批量化制造大面积微纳米结构的新方法,已经被看作是最具有工业化应用前景的微纳制造技术。大尺寸复合软模具的设计和制造是当前大面积纳米压印所面临的一项挑战性难题,也是影响和制约晶圆级微纳米压印广泛工业化应用的技术瓶颈。开展了大面积纳米压印复合软模具理论分析、数值模拟和试验验证的系统研究。基于薄板弯曲理论,建立复合软模具变形理论模型。利用ABAQUS模拟软件,揭示了模具几何特征、材料属性以及压印工艺要素对于复合软模具变形的影响及其规律。提出纳米压印复合软模具设计的基本准则。该研究为大面积纳米压印复合软模具设计、优化和制造奠定了重要理论基础,并为大面积纳米压印装备开发和工艺优化提供方向性指导。     

基于非接触式热压印技术的微透镜阵列制作

为了降低热压印工艺制作微透镜阵列对模具的要求,提出了非接触式热压印工艺制作微透镜阵列,采用了自主研制的纳米压印样机与光刻工艺制作的通孔式不锈钢模具在PMMA表面压印出微透镜阵列,并分析了压印过程中温度、压力、时间等参数对微透镜阵列表面形貌的影响。研究结果表明,利用非接触式热压印工艺可以制作表面形貌好、位置精度高的微透镜阵列,压印时最佳压印温度为140℃~180℃,最佳脱模温度为80℃,最佳压力为1 500 Pa~3 500 Pa,且采用通孔式模具不需要真空,降低了对环境的要求。     

大面积纳米压印光刻晶圆级复合软模具制造

为了解决大面积纳米压印所面临的大尺寸晶圆级复合软模具低成本制造的难题,对于当前广泛使用的大尺寸晶圆级双层复合软模具开展了理论分析、数值模拟和制造方法的系统研究。提出并建立了复合软模具脱模过程和气泡缺陷理论模型;利用ABAQUS工程模拟软件,揭示了大尺寸复合软模具影响脱模的因素和内在规律;提出一种大尺寸晶圆级双层复合软模具低成本制造方法,并完成了10.16cm(4inch)满片双层复合软模具复制的实验验证。研究结果为大尺寸复合软模具制造奠定了理论基础,并提供了一种低成本高质量制造大尺寸晶圆级双层复合软模具切实可行的方法。     

Design of orientation stages for step and flash imprint lithography

This paper presents the design of orientation stages for high-resolution imprint lithography machines. These machines implement a new lithography process known as Step and Flash Imprint Lithography (SFIL) and are intended for 1) sub 100 nm imprint demonstrations on flat substrates and 2) investigation of potential defect propagation during step and repeat imprinting. SFIL is an imprint lithography process that is a combination of chemical and mechanical steps and its implementation at room temperature and low pressure makes it an attractive process as compared to other imprint techniques. A critical component of an imprint machine is the orientation stage that is required to provide uniform intimate contact between the template and substrate surfaces. The orientation stage requirements are distinct from those used in photolithography since the depth of focus of projection optics allows for larger errors in the orientation alignment. Also, due to contact between the template and substrate surfaces in imprint lithography, the separation kinematics must be carefully controlled in the SFIL process. Two different orientation stages are designed for single- and multi-imprint machines. In order to eliminate the particle contamination due to frictional contacts, all joints are made with flexure joints. Imprint experiments have been performed to demonstrate sub 100 nm imprints.     

静电场辅助的微压印光刻技术

介绍了一种静电场辅助的新型微压印光刻技术,并对其工艺过程进行了深入的理论研究。首先,采用数值仿真软件COMSOL~(TM) Multiphysics,建立了静电场辅助的压印光刻瞬态仿真分析模型,讨论了不同时域微结构的演化过程。然后,详细分析了微结构的成型与仿真实验参数的定性关系,发现:适当地减小极板间距、模板凸起结构周期,同时增加模板的凸起高度、初始聚合物薄膜厚度和电压有助于微纳结构的成型。最后,通过仿真实验参数优化,得到了带有31μm中空结构的球冠微结构。与传统压印方法相比,静电场辅助的微压印技术工艺过程简单且成本较低,能够广泛应用于微电子机械系统、光子学、遗传学和组织系统等。     

Quantitative analysis of the material flow in transitional region during isothermal local loading forming of Ti-alloy rib-web component

The material flow in transitional region plays an important role in the forming quality of transitional region in the isothermal local loading forming of titanium alloy large-scale rib-web component. To study the material flow in transitional region, the finite element (FE) model of transitional region was established based on DEFORM-2D software and validated by physical experiment. Then, a quick and easy method, which can measure the area of different local regions of forged part in DEFORM-2D via user subroutine, was proposed to achieve the quantitative analysis of material flow mechanism. This technique can also be used in the analysis of other forming process, such as the calculation of fill ratio in forging process. The material flow pattern of transitional region during local loading forming was analyzed step by step and compared with integral forming. The results show that the material flow of transitional region during local loading process can be divided into six stages according to the material flow pattern and load-time curve. Twice transverse material flow with opposite directions occurred in the first and second loading steps sequentially, which does not exist in the integral forming. Four characteristic values evaluating the transverse flow of material, which are associated with the formation of defects and their severities, are defined and quantitatively measured at various processing conditions. It is found that decreasing the spacer block thickness and increasing friction both can decrease the four characteristic values, thus weaken the transverse material flow, which are helpful to improve the forming quality in transitional region. However, the transverse flow of material is little affected by the loading speed.     

SU-8 紫外深度光刻的误差及修正

在深紫外LIGA加工中,制作高精度大高宽比的微器件是很困难的。难点在于SU-8 光刻胶对紫外光的吸收系数随着波长变短而很快变大,而且其穿透深度也相应迅速变小;同时由于紫外光的衍射效应,获得高精度的大高宽比结构并不容易。本文深入研究了影响紫外深度光刻图形转移精度的如下因素:衍射效应、曝光剂量、紫外光波长和蝇眼透镜的分布等等。建立了基于模型区域的校正系统,该校正系统采用了分类分区域的思想将掩模图形按其畸变的特点进行了分类,在校正过程中对不同的类别分别建立校正区域,在每一校正区域内进行校正优化处理和校正评价,这种基于模型的分类分区域评价思想,使得校正过程有效且实时,该校正方法不仅降低了校正的复杂性,同时提高了校正的效率。     

EXPERIMENTAL STUDY ON THE HOT EMBOSSING POLYMER MICROFLUIDIC CHIP

Experiments are used to study the fabrication of polymer microfluidic chip with hot embossing method. The pattern fidelity with respect to the process parameters is analyzed. Experiment results show that the relationship between the imprint temperature and the microchannel width is approximately exponential. However, the depth of micro channel isn＇t sensitive to the imprint temperature. When the imprint pressure is larger than 1 MPa and the imprint time is longer than 2 min, the increasing of imprint pressure and holding time has little impact on the microchannel width. So over long holding time is not needed in hot embossing. Based on the experiment analysis, a series of optimization process parameters is obtained and a fine microfluidic chip is fabricated. The electrophoresis separation experiment are used to verify the microfluidic chip performance after bonding. The results show that 100bp-ladder DNA sample can be separated in less than 5 min successfully.     

A nano-scale alignment method for imprint lithography

A novel nano-scale alignment technique based on moiré signal for room-temperature imprint lithography in the submicron realm is proposed. The moiré signals generated by two pairs of quadruple gratings on mold and wafer are optically projected onto two photo-detector arrays, then the detected moiré signals are used to estimate the alignment errors in the x and y directions. The experiment results indicate that complex differential moiré signal is sensitive to relative displacement of the mold and wafer, and the alignment accuracy obtained in the x and y directions and in ϑ are ±20 nm, ±25 nm and ±1 μrad (3σ), respectively. They can meet the requirements of alignment accuracy for submicron imprint lithography.     

Molecular dynamics study of pattern transfer in nanoimprint lithography

A molecular dynamics simulations model of nanoimprint lithography (NIL) is proposed in order to study the pattern transfer and its related phenomena. The proposed model is similar to a real NIL process imprinting an α-quartz stamp with a rectangular line pattern into an amorphous poly-(methylmethacrylate) (PMMA) film. The polymer deformation behavior and the adhesion and friction effects between the stamp and the polymer film are investigated and their dependency on the pattern aspect ratio is discussed. Force fields including bond, angle, torsion, van der Waals, and electrostatic potentials are used to describe intermolecular and intramolecular interacting forces. Nosé-Hoover thermostat is used to control the temperature of the polymer film and cell multipole method is adopted to treat long range interactions. The deformation of the polymer film is observed for two stamps having different aspect ratio patterns. The distributions of density and stress in the polymer film are calculated for the detail analysis of deformation behavior. For a high aspect ratio pattern (aspect ratio = 2.5, imprint depth = 8.0 nm), large amount of springback of the residual polymer film is observed, which is mainly due to the residual compressive stress left in the polymer film. However, for a low aspect ratio pattern (aspect ratio = 1.0, imprint depth = 3.0 nm), the springback is not observed. In addition, adhesion and friction forces are obtained by dividing the polymer film into subregions and calculating the interacting force between each subregion and the stamp. While the adhesion force is nearly constant regardless of the pattern aspect ratio, the friction force increases as the pattern aspect ratio grows, so the friction force becomes larger than the adhesion force when the pattern aspect ratio increases.     

Active wafer shape modulation using a multi-actuator chucking system

Jet and Flash Imprint Lithography has proven to be a viable alternative to optical lithography for fabrication of sub 30 nm nanostructures for large volume semiconductor manufacturing. Machine throughput, overlay and process defectivity that meet and exceed the International Technology Roadmap for Semiconductors (ITRS) are essential for commercial viability of any new lithography technology. Jet and Flash Imprint Lithography uses an inkjet head to dispense a grid of liquid drops on the wafer surface to match the volume requirements of the pattern being imprinted. Wafer shape modulation has been shown to increase imprinting speed significantly by reducing air bubble trapping in the drop interstitial sites. A wafer shape modulation chuck that can address arbitrary field locations and sizes on a wafer with a novel actuation scheme that minimizes the number of actuators while increasing imprinting speed and reducing process defects significantly is presented.     

CFD analysis of effects on fluid flow resistance of metallic wavy structures

Microscale wrinkles can be utilized to enhance the characteristics of products. For example, a shark skin having riblet surface can move faster underwater, minimizing fluid flow resistance. We introduce a novel approach to fabricate microscale metallic wrinkles using a soft lithography and electroforming process; we also evaluated the effects of wrinkles by computational fluid dynamics (CFD) analyses. For the generation of metallic wrinkles, a UV-curable resin, NOA68T was used to fabricate a master wrinkling pattern by mechanism of compressive forces on a skin of the weakly polymerized resin layer. The master pattern was molded and replicated as metallic wrinkles on a surface via soft lithography and electroforming processes. To understand the advantages of a wavy surface on reduction of flow resistance, we carried out two- and three-dimensional (2D and 3D) CFD analyses. The drag coefficient of a wrinkled 2D square model was decreased about 17.1 %, and a 3D real wrinkle model showed 4.9 to 7.3 % reduction of it compared to without wrinkle models. We believe that it is possible to reduce the fluid flow resistance using wavy surfaces that can easily be generated selectively or wholly on an arbitrary surface.