基于碲基相变材料的激光热模光刻技术研究
文献类型：学位论文
| 作者 | 魏涛 |
| 文献子类 | 博士 |
| 导师 | 张龙 |
| 关键词 | 激光热模光刻 Laser heat-mode lithography 热模光刻胶 heat-mode resists 灰度光刻 greyscale lithography 微纳结构 color printing 彩色打印 micro/nano structures |
| 其他题名 | Investigation of laser heat-mode lithography based on Te-based phase change material |
| 英文摘要 | 光刻已经广泛应用于微电子芯片和微纳结构光电子器件的制造。随着技术的发展，人们对光刻也提出了更高的要求，如更小的特征尺寸，更大的光刻面积、更高的光刻速率、更简化的工艺流程、以及满足更加个性化的设计与制造需求。目前，研究人员提出了各种各样的光刻方法，包括：1）高能束光刻（如电子束、软x射线、聚焦粒子束），优点是能实现高分辨率的图形结构，缺点是设备昂贵，真空操作，光刻速率慢和光刻面积小；2）探针光刻（如热探针/近场探针/扫描隧道探针），优点是大气中操作，得到任意高分辨率的图形结构，缺点是光刻速率极慢，难以大面积光刻；3）模板光刻（如掩模曝光光刻、纳米压印、模板自组装等）是一种低成本高效率的微纳结构刻写加工方法，但昂贵的纳米结构模板使其难以在个性化小批量的微纳结构器件制备中得到应用。 激光直写光刻由于能在大气环境中进行大面积的任意图形结构的快速加工等特点，使得在微电子掩模板、集成光学和衍射光学器件的制造中得到了较为广泛的应用。然而仍具有一些不足：1）光刻特征尺寸难以突破衍射极限；2）难以进行跨尺度(光刻特征尺寸任意可调)光刻；3）由于采用的是有机光刻胶，里面有光酸剂等物质，导致光刻前要进行前烘处理，光刻后要进行后烘及图形固化处理等，整个光刻流程复杂；4）光刻分辨率受制于分子结构尺寸，导致光刻图形的分辨率和边缘粗糙度难以达到亚纳米甚至原子级别。5）有机薄膜对光吸收具有波长选择性，导致光刻胶薄膜的波长单一性，即一种波长的光刻仪器需要研制合成相应的光刻胶。 基于激光直写的热模(heat-mode)光刻是一种光致热物理反应（包括光致热相变、热非线性、热扩散等）。其原理是激光作用于热模光刻胶薄膜，其吸收光子，光子不会直接破环热模光刻胶的价键和晶体结构，而是将吸收的光子能量进一步转化成晶格振动，导致热模光刻胶的温度升高，温度升至某种阈值（如晶化）后，热模光刻胶的价键结构或晶体结构才会发生变化，从而实现曝光。曝光之后再利用其选择刻蚀特性进行显影，从而完成整个光刻流程。其特点在于：1）热模光刻胶的吸收光谱一般都覆盖从近红外到极紫外的整个光刻曝光的波段，满足宽波段光刻要求。2）光刻特征尺寸取决于热致结构变化区域的尺寸，而该区域的尺寸既受光斑约束，又受到热致相变阈值、热致非线性以及热扩散等多重约束。3）激光光斑的强度呈高斯分布，光斑中心的温度高，沿四周扩散并逐渐降低，通过调控热扩散通道和曝光策略，能实现跨尺度光刻。4）热模光刻胶的基本组成单元是原子，因此热模光刻图形结构的分辨率和边缘粗糙度能达到亚纳米甚至原子级别。5）热模光刻胶没有交联剂和光酸剂等中间物质，光刻流程不需要前烘、后烘和固化等处理，光刻过程也不会产生气泡等副产物，光刻流程只有涂胶、曝光、显影、清洗，因此光刻工艺大为简化。由于其相变阈值特性，本论文以碲基相变材料为热模光刻胶，研究了其热模光刻特性及在图像打印和微纳结构制备中的应用前景。 首先研究了Te薄膜的灰度光刻特性，发现其具有二阶灰度特性，对Te薄膜进行结构分析表明灰度特性来源于激光诱导Te晶粒细化。由于其在多阶灰度特性上的不足，提出采用氧掺杂的Te薄膜（TeOx）作为灰度材料，研究发现其多阶灰度特性相比于Te薄膜更好，具有更丰富的灰度阶。通过调控TeOx薄膜的带隙能量，可实现灰度图像打印。但是TeOx薄膜的组成难以固定且灰度阶不够丰富，该组成的热稳定性比较差，不利于长期保存，因此我们最终选用Ge2Sb2Te5薄膜作为多阶灰度材料，并制备了多阶灰度图像，与原图几乎一致。其丰富的多阶灰度特性主要归结于Ge2Sb2Te5薄膜的不同晶化程度导致的反射率差异。基于Ge2Sb2Te5薄膜的多阶灰度特性，我们设计制备了“玻璃基片/Ge2Sb2Te5/ZnS-SiO2”样品结构，基于多层薄膜间的干涉效应成功实现激光彩色打印，得到了简单和复杂的彩色图像，色彩较丰富。这在彩色图像存储及彩色防伪领域具有重要应用价值。 研究了ZnS-SiO2薄膜的激光热模光刻特性，发现该薄膜具有正胶特性，与文献报道的相反。通过XRD和XPS表征，我们进行了详细的结构分析，解释了其正胶特性的结构根源。其刻蚀选择性解释如下：沉积态的ZnS-SiO2薄膜是由化学无序的ZnS:O晶粒和SiSnO4-n四面体组成，而激光辐射后ZnS-SiO2薄膜含有ZnO晶粒和SiSn+1O3-n四面体。在氢氟酸溶液中，ZnO晶粒和SiSn+1O3-n四面体的溶解速率高于ZnS:O晶粒和SiSnO4-n四面体。因此，ZnS-SiO2薄膜呈现正胶特性。创造性地提出了利用激光诱导相变潜热的释放，在透明ZnS-SiO2薄膜上制备出不同尺寸、不同形状的微纳结构。理论和实验表明通过调节相变潜热的释放，结构特征尺寸最小可达100nm左右。 在激光热模光刻中，热扩散对制备的微纳结构尺寸影响很大，需要严格控制热模光刻胶的热场分布。为此，研究了激光热模光刻胶的热场分布特性。提出采用热扩散系数低的光刻胶材料、添加热传导层、减小热作用时间如采用短脉冲激光及样品高速运动等方法来抑制热扩散，减小热斑尺寸，并对其进行了理论模拟与分析。; Lithography has been widely used to fabricate micro-electronic chips and photo- electronic devices. With the development of technology, one has proposed more serious requirement about lithography such as smaller feature size, larger lithographic area, higher writing speed, simple process procedure and more individual design and manufacturing. So far, all kinds of lithographic methods have been proposed, including high energy-beam lithography (such as electron beam, soft X-ray and focused ion-beam), probe-based lithography (such as thermal scanning probe, near-field probe and scanning tunnel probe) and template-based lithography (such as projection lithography, nano-imprint and chemical self-assembly). High energy-beam lithography can fabricate patterns with high resolution. However, it suffers from expensive equipment, high-vacuum environment, low writing speed and small writing area. Probe-based lithography can operate in air and fabricate arbitrary patterns with high resolution. Unfortunately, its writing speed is low and writing area is small. In addition, template-based lithography is a low-cost and efficient fabrication method. However, expensive nanoscale template limits its application in micro/nano devices with individual and low-volume fabrication. Direct laser writing can be used to fabricate large-area patterns with high speed in air. It has been widely applied in the fabrication of chip mask, integrated optics and diffractive optic devices. However, in direct laser writing, the feature size is limited by diffraction limit. It is difficult to realize multiscale lithography from nanoscale to microscale. Moreover, the lithography procedure is complex since the organic photoresist is used and the procedures of soft bake, post-exposure bake, and hard bake are required. Besides, the pattern resolution is limited by the size of large molecular structure, leading to the low resolution and high line-edge roughness. Organic photoresist is only sensitive to the light with particular wavelength. Laser heat-mode lithography is based on opto-thermal effect such as laser-induced phase-change. When laser is focused onto heat-mode resist, the resist absorbs photon energy and is heated, leading to temperature rise. The structure of the resist changes when the temperature reaches threshold (such as crystallization). Thus, the heat-mode resist is exposed. The whole lithography procedure is completed after development in solutions based on the etching selectivity. Laser heat-mode lithography has the advantages of wide exposure spectral range from infrared to violet wavelength. Moreover, the feature size is lower than the diffraction limit, and multiscale lithography from nanoscale to microscale can be realized. Since the heat-mode resist consists of atoms, the pattern resolution and line-edge roughness can reach sub-nanoscale and atom scale, respectively. In addition, the lithography procedure is greatly simple, only including thin film deposition, exposure and development. In this article, Te-based phase-change material is selected as heat-mode resist. The heat-mode lithography characteristics are investigated. The grayscale and color printing of Te-based phase- change material is also investigated. The main contents of this article are so follows: We investigated the grayscale features of Te thin films and it is found that two-level grayscale tones can be obtained. The structural analysis indicates that the grayscale tone is attributed to the grain refinement after laser irradiations. Due to poor multi-level grayscale, oxygen doped Te thin film (TeOx) is proposed and selected as grayscale materials. Our study indicates that the grayscale characteristics of TeOx thin films are better than that of Te thin films. The grayscale image printing can be achieved by tuning bandgap energy of TeOx thin films. However, it is difficult to fix the composition of TeOx thin films and the grayscale levels are still poor. At the same time, the thermal stability of TeOx thin films is not high. Therefore, Ge2Sb2Te5 thin film is selected as multi-level grayscale materials. Arbitrary grayscale images can be printed on Ge2Sb2Te5 thin film. The multi-level grayscale tones can be ascribed to the divergence of crystalline extent, resulting in the different reflectivity. We design and fabricate the sample structure “glass substrate/Ge2Sb2Te5/ZnS-SiO2” based on the multi-level grayscale features of Ge2Sb2Te5 thin film. Simple color images were printed due to the interference effect between multi-layer thin films. It has potential applications in color image storage and color security. We investigated the laser heat-mode lithography characteristics and mechanism of ZnS-SiO2 thin films. It is found that ZnS-SiO2 thin film can be selected as positive photoresist. The etching selectivity of ZnS-SiO2 thin films is so follows: Chemically disordered ZnS:O crystalline structures and SiSnO4-n networks are formed in the as-deposited ZnS-SiO2 thin films, while ZnO and SiSn+1O3-n tetrahedral networks were formed after laser irradiation. The ZnO and SiSn+1O3-n tetrahedrons have higher solubilities in hydrofluoric acid than ZnS:O and SiSnO4-n networks. Furthermore, we proposed micro/nano lithography of ZnS-SiO2 thin film through laser induced phase-change latent release. The theoretical simulation and experimental results reveal that micro/nano structures with feature size from microscale to nanoscale can be realized by tuning phase-change latent release. To obtain nanoscale pattern structures in laser heat-mode lithography, one needs to manipulate the thermal diffusion channels. We provide methods to restrain the in-plane thermal diffusion and improve the out of plane thermal diffusion. Theoretical and experimental results suggested that the size of the heat-spot can be decreased by decreasing the thickness of the heat-mode resist thin films, inserting the thermal conduction layers, and shortening the laser irradiation time. Besides, one of optimized laser writing strategies is given, where the in-plane thermal diffusion is completely restrained, and the out-of-plane thermal diffusion is improved. |
| 学科主题 | 材料学 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31032]  |
| 专题 | 中国科学院上海光学精密机械研究所 |
| 作者单位 | 中国科学院上海光学精密机械研究所 |
| 推荐引用方式 GB/T 7714 | 魏涛. 基于碲基相变材料的激光热模光刻技术研究[D]. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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