飞秒激光与氮化硅晶体相互作用的研究

【作者】 张文涛；

【导师】 白晋涛； 王凯歌；

【作者基本信息】 西北大学 ， 光学， 2009， 硕士

【摘要】 氮化硅晶体薄膜在微电子工业、光电子工业、机械工业等方面具有广泛的应用。研究飞秒激光跟氮化硅晶体薄膜的相互作用,既能发展飞秒激光与电介质材料相互作用的有关理论,为研究飞秒激光与其它电介质材料相互作用提供借鉴,又可以拓展氮化硅晶体薄膜在微电子、光电子及纳米材料器件方面的应用范围。本论文对飞秒激光与β相氮化硅晶体薄膜相互作用的机理进行了一定的理论研究。主要工作包含以下几个方面:一.依据飞秒激光与电介质材料相互作用的相关理论探讨了飞秒激光与氮化硅材料相互作用机理。通过理论分析得出本文参数下的飞秒激光与氮化硅材料相互作用的主要非线性效应是多光子离化和雪崩离化;飞秒激光与氮化硅材料相互作用的两个具体过程是:首先通过多光子离化和雪崩离化使材料内部电子电离,并最终在材料内部形成等离子体状态,之后等离子体强烈吸收激光能量直至氮化硅晶体材料被去除。二.依据飞秒激光与电介质材料相互作用的福克-普朗克(F-P)动力学方程,通过数值计算分析讨论了飞秒激光对β相氮化硅晶体薄膜的损伤情况。首先计算了不同激光参数下氮化硅晶体薄膜的多光子离化系数和雪崩离化系数。然后通过MATLAB软件编写程序,求解飞秒激光与氮化硅晶体薄膜相互作用的F-P方程。计算出三种不同激光参数下氮化硅晶体薄膜的损伤阈值,损伤形貌,给出电子数密度、光强、表面反射率等参数随脉冲持续时间变化的图示关系等。三种激光参数分别为波长780nm,脉冲宽度100fs以上;波长800nm,脉冲宽度100fs左右;波长800nm,脉冲宽度15fs。计算过程中均考虑了不同的激光功率密度和激光半径。三.从脉冲激光的时间和空间分布出发,参照Docchio改进后的损伤模型分析计算了长脉冲(纳秒、皮秒)作用材料时的损伤位置,损伤时间以及等离子体吸收能量等情况。然后依据Fan改进后的模型分析计算飞秒激光与氮化硅晶体相互作用过程中,最先产生损伤的时间、位置等情况。通过比较分析得出,最先产生损伤的位置主要与激光脉冲宽度和激光腰斑半径有关。更多还原

【Abstract】 The silicon nitride crystal film（β- Si₃N₄） be widely used in micro-electronic industry, photo-electronic industry, machinery industry, etc. Studying the interaction between femtosecond laser and Si₃N₄ crystal film can not only extend the theory of interaction between femtosecond pulse and the dielectric, provide reference for other insulating materials, but also extend the use of silicon nitride crystal film in micro-electronic, photo-electronic and nanometer materials device.In this paper, some results of theoretical studies and numerical calculations about the interaction between femtosecond laser andβ-Si₃N₄ crystal film are presented. The main contents are classified as follows:Firstly, the process of the interaction between femtosecond laser andβ- Si₃N₄ crystal film is described according to the theory of the interaction between femtosecond laser and insulating materials. Multiphoton ionization and impact ionization are two primary nonlinear effects in the process. There are two processes in the process of the interaction between femtosecond laser andβ- Si₃N₄ crystal film, the first one is that electron ionized through multiphoton ionization and impact ionization ,and produced plasma in the material. After that plasma absorbed laser energy greatly untilβ-Si₃N₄ is evaporated.Secondly, the interaction between femtosecond laser and silicon nitride crystal film （β-Si₃N₄） is analyzed and numerical studied in detail with Fokker-Planck （F-P） equation. First, we get the multiphoton ionization coefficient and impact ionization coefficient in different laser parameters . Then we evaluate F-P equation in detail with MATLAB programmer, and get the damage threshold ,crater shape, the verse of the electronic density, the verse of laser fluence,the verse of reflectivity of Si₃N₄ film in three different laser parameters, which are 780nm, pulse width greater than 100fs; 800nm, pulse width greater than or equal 100fs; 800nm, 15fs. we also consider different laser intensity and laser radius.Finally, considering laser intensity distributing in time and space, we calculate the breakdown point, the earliest damage time and plasma absorption etc, with the moving breakdown model which improved by Docchio, when long laser pulse ablation silicon nitride crystal film. we calculate the breakdown point and the earliest damage time etc, with the breakdown model which improved by Fan, when femtosecond ablations silicon nitride crystal film. We get the conclusion that the first breakdown point in the medium is mainly determined by pulse width and the laser radius.更多还原