| 题名 | 飞秒激光微加工铬掩模版的实验研究 |
| 作者 | 韩泽华 |
| 学位类别 | 博士 |
| 答辩日期 | 2008 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 周常河 |
| 关键词 | 飞秒激光 微加工 铬掩模版 双脉冲 有限元方法 |
| 其他题名 | Experimental Studies on Femtosecond Laser Micromachining of Cr Mask |
| 中文摘要 | 飞秒脉冲激光在材料精细加工中变得越来越有吸引力，尤其是在微加工、微光学和微电子学领域中。相对于长脉冲激光，飞秒脉冲激光的优势在于，在脉冲持续的很短时间内电子来不及向周围的晶格传递能量，从而积聚极高的能量，并最终导致高度局域化激光破坏。利用飞秒脉冲激光进行微加工具有：热损害小，移除效率高，可加工各种材料以及精确控制加工尺寸等诸多独特优点。本论文围绕飞秒激光微加工这一主题，对金属铬掩模版的烧蚀特性进行了深入细致的理论和实验研究。在现有飞秒激光与金属材料相互作用理论模型的基础上，选择并改进了合适的理论模型来解释飞秒激光微加工金属铬掩模版过程中出现的各种现象和过程。主要内容有以下的几个方面： 分析对比了飞秒激光脉冲与物质相互作用的各种理论模型，并针对贵金属金和过渡金属铬在不同入射激光能流通量下的双温模型方程进行了数值模拟与计算，这为研究飞秒激光对金属材料的微加工提供了理论上的基础。 利用飞秒激光脉冲分别对玻璃和石英衬底的金属铬掩模版进行微加工，发现两种样品表面均有波纹状的微突起结构产生。这些微突起结构离开样品表面的高度为10-300nm不等，并且随着激光功率的增大而增加，在一定功率下达到饱和状态，它们的形貌、尺寸和高度取决于衬底材料以及入射飞秒激光的脉冲参数和能流通量。通过化学方法证明了这些微突起结构是由玻璃和石英的主要成分SiO2组成的，并非样品表面的铬元素。此外，通过适当选取飞秒激光功率和加工速度，还在金属铬掩模版上制作了两种不同周期和线宽的光栅结构。 开展了双脉冲飞秒激光微加工金属铬掩模版的研究，发现在单个脉冲强度稍低于阈值时，双脉冲飞秒激光烧蚀过程中存在着时域的烧蚀窗口效应。即当双脉冲之间的时间延迟少于400ps的量级时，对金属铬掩模版的烧蚀现象就比较明显，并且其表面的反射率会一直保持在一个较低的水平上。当双脉冲之间的时间延迟大于400ps的量级时，对金属铬掩模版的烧蚀就变得不再可能，而且其表面的反射率也急剧上升到一个较高的水平上。通过对双曲线型双温模型方程中的体激光源项进行修改，给出了双脉冲下的双温模型方程，并成功用来解释上述双脉冲飞秒激光烧蚀过程中的时域烧蚀窗口效应。 进行了偏振飞秒双脉冲微加工金属铬掩模版的研究，发现无论是线偏振还是圆偏振飞秒激光，它们在样品表面所造成的微突起结构的高度都是在1-10ps的双脉冲时延范围内呈现明显的下降，而在此时延范围之外并没有什么大的变化，这说明微突起结构的形成与偏振状态无关。而通过对双脉冲双温模型的模拟分析，发现在0-400ps的双脉冲时延范围以及10-5000Jm-2的激光能流通量范围下，实验所用铬掩模版中电子－声子相互耦合的弛豫时间都在1-10ps的范围内，这说明微突起结构的形成过程可能涉及到电子－声子的相互耦合过程，而且电子－声子的耦合过程对减少微突起结构形成的趋势起到非常重要的作用。 利用有限元方法并结合超快热弹性性模型，对飞秒激光微加工金属铬掩模版的过程进行模拟分析，很好地解释了微突起结构的形成原因。特别是在圆锥形微突起结构的形状和高度上，数值模拟与实验结果相符很好，这也从实验上证实了超快热弹性模型的合理性和有效性。 |
| 英文摘要 | Femtosecond pulsed laser is getting more and more attractive in precise material processing, especially in the fields of micromachining, microoptics and microelectronics. The advantage of femtosecond pulsed laser relative to long pulsed laser is based on the fact that the electrons can acquire significant energy from the pulse before transferring energy to the surrounding lattice, which can result in highly localized laser-induced breakdown. There are many particular merits of femtosecond pulsed laser micromachining, such as: negligible thermal damage, high cutting effiency, nearly ablation of all kinds of materials and precise control of machining sizes. Surrounding the subject of femtosecond laser micromachining, ablation characteristics of chromium mask were studied on both theories and experiments deeply and elaborately. Based on the existed models of the interaction between femtosecond laser and metal materials, appropriate theoretical models were selected and improved to explain the various phenomena and processes during femtosecond laser micromachining of chromium mask. The main content of this dissertation includes the following aspects: Firstly, different theoretical models of the interaction between femtosecond laser pulses and matter were analysed and compared. The two-temperature model equations of the noble metal Au and the transition metal Cr were numerically simulated at different laser fluence particularly, which provides the theoretical bases of femtosecond laser micromachining of metal materials. Secondly, micromachining of chromium masks on the substrates of glass and fused silica were carried out with femtosecond laser pulses, and it is found that periodic microripple structures were formed on the sample surface in both cases. The heights of these microripple structures varied from 10nm to 300nm by increasing the laser power and saturated at a higher laser power. The morphology, sizes and heights of theses microstructures depend on the substrate materials, the parameters and the fluence of irradiated femtosecond laser pulses. Chemical methods proved that the microripple structures are composed of not the chromium but the main component of the glass and fused silica substrates SiO2. Furthmore, two kinds of gratings were fabricated on chromium mask with different periods and linewidths by selecting the laser power and micromachining speed properly. Thirdly, femtosecond laser micromachining of chromium mask were investigated by using double-pulse method. Experimental results show that there exists a temporal ablation window effect with each of the double pulses adjusted just smaller than the threshold. When the delay between the double pulses is within the order of 400ps, the ablation of chromium mask could happen and the reflectivity from the sample surface retains at a lower level. When the delay between the double pulses is beyond the order of 400ps, the ablation of chromium mask could not happen and the reflectivity from the sample surface shows a sharp rise at the same time. By correcting the volumetric laser source term in the hyperbolic two-temperature model, the two-temperature model was developed into the form of double pulses and was applied to explain the above temporal ablation window effect during double-pulse femtosecond laser ablation process successfully. Fourthly, micromachining of chromium mask were investigated by polarized femtosecond double pulses, and microbump structures were formed on the sample surface for both linearly and circularly femtosecond double pulses. It is found that the heights of the microbumps exhibit an obvious drop between the 1-10ps of double pulses delay and have no obvious variation bejond this delay range in both cases, which demonstrates the formation of the microbump structures is independent of the polarized state. The electron-phonon relaxation time in chromium mask irradiated with femtosecond double pulses covers 1-10ps for a widely delay range of 0-400ps and fluence range of 10-5000Jm-2 according to the two-temperature model of double pulses calculations, which revealed that the electron–phonon coupling process may be involved in the formation of the microbump structures and plays an important role in reducing the tendency of their formation. Finally, finite element method and ultrafast thermoelasticity model were combined to simulate the process of femtosecond laser micromachining of chromium mask, which provide a good explanation of the microbump structures formation. Numerical results exhibited excellment good agreements with the experimental results in both the shape and height of the conical microbump structures, which verified the reasonableness and effectiveness of the ultrafast thermoelasticity model in experiments. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15228]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 韩泽华. 飞秒激光微加工铬掩模版的实验研究[D]. 中国科学院上海光学精密机械研究所. 2008. |
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