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题名	短脉冲激光对硅及硅基光电器件的损伤效应与机理
作者	邵俊峰
学位类别	博士
答辩日期	2015-05
授予单位	中国科学院大学
导师	郭劲
关键词	晶体硅 超短脉冲激光 激光辐照效应 双温模型 器件损伤机理
其他题名	Short-Pulsed Laser Induced Ablation Effects and Mechanism of Silicon and Silicon-based EO Devices
学位专业	光学工程
中文摘要	本论文拟开展短脉冲激光对硅材料及硅基光电器件的损伤效应和机理研究，并对损伤过程和机理形成一个系统而完整的认识，从而为激光加工、激光防护以及相关工程应用提供依据。论文首先在绪论中讨论了超短脉冲激光技术、硅材料应用以及硅基器件的进展，并较为详细地综述了激光辐照效应研究领域的进展，然后从激光辐照材料到辐照结构的基本思路展开相关研究。解决了超短脉冲与晶体硅的相互作用问题，进而在材料损伤机理清晰的情况下分析了硅基器件的损伤过程及机理。详细工作内容如下： 1）首先，理论上推导了基于密度泛函理论的超快激光与硅的半经典相互作用模型，并结合宏观的介电常数变化特性分析了飞秒激光损伤硅的物理过程。进一步采用基于电子激发、俄歇复合以及双光子吸收等过程的双温模型唯象理论研究了皮秒、飞秒脉冲激光与晶体硅的相互作用过程。着重分析了“非热损伤”的过程及机理，获得了晶体硅的热损伤、“非热”损伤过程，最后讨论了多脉冲积累损伤过程。“非热”损伤机理可理解为过量激发载流子造成的半导体金属化相变过程。在100fs、800nm单脉冲辐照条件下的损伤阈值约0.25J/cm2，热损伤贡献率远高于非热损伤贡献率。入射激光能量密度高于0.53J/cm2时“非热”损伤贡献为主，此时损伤过程从皮秒降低到100fs内完成，与热损伤的电子、晶格时间演化过程显著不同。进一步研究了脉冲宽度、多脉冲积累等因素对损伤效果的影响。当两个激光脉冲间隔小于100ns时会发生热积累效应，并显著降低激光损伤阈值。第一个激光脉冲引起的电子密度变化对损伤贡献较小；而第一个激光脉冲导致的晶格温升将进一步导致高密度电子激发以及晶格的进一步温升，对损伤起主要贡献。所获得的理论分析结果与公开报道的反射率实验结论一致。 2）利用光谱仪对激光损伤材料表面产生的荧光进行光谱分析，得到材料的损伤阈值。利用飞秒激光诱导硅等离子体光谱讨论了损伤阈值和多脉冲损伤机理两个问题。利用飞秒单脉冲激光照射Si和SiO2/Si两种样品，探测的波长为Si(I)390.55 nm谱线，获得了这两种样品在烧蚀阈值附近光谱的辐射强度随着激光能量密度的变化关系，并对光谱的辐射强度进行线性拟合，近似地得到了Si和SiO2/Si两种样品在飞秒激光照射下的损伤阈值分别为0.86 J/cm2和1.11 J/cm2。利用双波长飞秒双脉冲激光诱导硅产生等离子体辐射，发现产生的硅等离子体辐射强度随着双脉冲时间间隔的变化而变化。与同一波长的飞秒激光双脉冲作用下不同，在坐标轴两边达到最大辐射强度的时间是不同的。当400 nm的激光早于800 nm的光到达样品表面时，辐射强度的增加是迅速的，同时辐射强度的衰减也是比较快的。对于较长的时间间隔(±300 ps)，加强比为0.5，双波长的飞秒双脉冲激光对产生的等离子体辐射加强率更低。 3）较为系统地开展了重频、短纳秒/皮秒激光对行间转移型电荷耦合器件的损伤实验研究。实验方法采取器件直接读出、扫描电镜以及电子学等途径结合硅材料的损伤机理和过程分析器件损伤效应。实验中引入可激光光斑测量的二阶矩理论提高损伤阈值测量精度。并利用转台控制到达光电探测器件的脉冲数量和脉冲之间的时间间隔精确控制多脉冲积累过程。最后综合利用损伤效应实验结果分析了损伤机理。1.5ns、400ps千赫兹激光条件下，器件功能性损伤阈值为13.6~121mJ/cm2，显著小于单脉冲损伤阈值263~1146mJ/cm2。实验表明存在两种显著不同的损伤机理。其一、多个脉冲到达CCD靶面同一位置的损伤或致盲具有积累效应，多个脉冲积累损伤能够显著降低线损伤和全靶面损伤阈值，降低程度与脉冲个数、激光到靶能量密度有关。在积累脉冲个数达到100个时，多脉冲点损伤积累成线损伤的阈值与单脉冲线损伤阈值相比可显著降低至其约1/3水平。多脉冲激光致盲机理与单脉冲致盲机理相同，均表现为器件垂直转移电路间及地间的短路；其二、激光脉冲串到达CCD靶面的不同位置也能够实现器件的功能性失效，而这种器件功能性失效机理与单脉冲损伤显著不同，仅表现为线损伤的叠加，并未造成器件的串行读出电路短路或紊乱，功能性损伤阈值即对应线损伤阈值(0.66 J/cm2)，而显著小于单次致盲阈值(1.5J/cm2~2.2J/cm2)。 本文开展了超短脉冲激光与硅材料及硅基器件的相互作用理论和实验研究，在理论方面采用了较为先进的基于密度泛函理论的半经典近似理论、改进双温模型理论，较系统地阐述了超短脉冲激光与硅的相互作用过程，在量子分子动力学计算、唯象双温理论方法上取得一定创新；在材料损伤和器件损伤实验中，采用了目前较前沿的泵浦探测技术分析动态微观测试技术，实验手段上有一定进展，在材料多层膜系界面损伤和多脉冲损伤机理方面有新的成果。在短脉冲激光对电荷耦合器件的多脉冲损伤效应和机理研究方面，通过材料学和电子学方法分析了器件损伤的机理，在前人研究基础上重点分析了多脉冲、短脉宽激光损伤机理，具有较为明确的应用价值。该研究对激光辐照效应及理论研究方面有了较为深入的认知，并可为激光加工以及相关光电工程应用研究提供借鉴和参考。
英文摘要	This thesis is focused on short pulse laser interaction with silicon and silicon-based EO device.The major objectives of this research is to obtain an unified and complete understanding of the laser damage effect and mechanism to bring solid ground for laser ablation, machinery, laser protection and other engineering applications. In the introduction part, closely related technology progress in recent years about short and ultrashort/ultrafast lasers, silicon and its applications are comprehensively summarized briefly. Also, the progress in laser interaction with matter are also discussed.Then the research is carried out from simple single materials to complex film materials step by step, which means the interaction of short laser pulses with crystal silicon is studied in the first place, then the damage mechanism of EO devices under laser pulse irradiation. The contents of the thesis shall include: 1）Firstly, DFT-based semi-classical laser interaction with silicon theory is deduced. The imaginery part of dielectric constant is used as a microscopical tool to study the physical processes since this parameter have macroscopical meaning as well.Then it is introduced with band electron excitation, Auger recombination effect and two photon excitation etc. to modify original Two-Temperature Model to adapt for the short pulse laser interaction with silicon. Then, the damage threshold is given and the thermal and non-thermal damage contributions are analyzed. Finally, two-pulse laser interaction with silicon is discussed. Also, several key parameters such as electron density and lattice temperature influence for heat accumulation effect are compared. Non thermal process is defined a semiconductor-to-metal transitions. With a laser of 800nm wavelength and 100fs, the laser damage fluence is about 0.25J/cm2. At this fluence level, thermal contribution dominates the process, which is identical to experiments. With a laser fluence larger than 0.53 J/cm2 non-thermal damage mechanism prevails. With two pulses shooting, the heat accumulation effect is predicted, which shows that a time span between two pulses smaller than 100ns cannot be ignored and it can reduce the damage threshold significantly. It is identified an electron density after the first pulse does not significantly change the heating process. However, the lattice temperature after the first pulse (higher than 800K) can cause serious electron excitation.The theoretical study results can be confirmed with refelction experiment mutually. 2）The optical spectrum analyzer is used to study the fluorescence of femtosecond laser ablation of silicon surface, and the damage threshold are analytically fitting. Femtosecond laser induced plasma spectrum method is applied to analyze damage threshold and multiple pulses damage mechanism. Single pulse femtosecond laser is shot on Si and SiO2/Si samples. The detection wavelength is Si(I) 390.55 nm line. The plasma radiations near damage threshold of both samples are acquired to build relations between laser fluences and spectrum intensities. The damage thresholds are found to be 0.86 J/cm2 and 1.11 J/cm2 for Si and SiO2/Si,respectively. With duo different wavelength laser pulses irradiation on silicon samples, the plasma radiation intensity is highly correlated with pulse spacing. Different from that of identical wavelength pulse process, the intensity peaks are found to be different. As 400nm wavelength ahead of 800 wavelength pulse reaches the surface, the increasement of radiation intensity is sharp while the declining is also fast. For longer time spaces (±300 ps), the increasing ratio reaches 0.5.With two different wavelength laser pulses irradiation on silicon samples, the radiation increasement ration is much lower. 3）Systematic experimental damage effects of single and multiple pulse picosecond laser interaction with interline charged coupled device is studied. Experimental methods are used including video output, SEM and electrical test, etc. The camera is installed on electric revolving stage to control laser and the test subject intersecting time and pulse numbers to manipulate multiple pulses impinging conditions. A secondary moment method is employed to obtain the laser diameters on CCD surface. Bearing the damage effects data a unified picture of EO device malfunction mechanism is induced. The experiment finds that the functional damage threshold of multiple-pulse damage is about 24~84.5mJ/cm2, which is severely lower than that of single-pulse ablation for 1.5ns and 400 ps kilohertz-repetition-rate lasers, approximating 470~800mJ/cm2. Two vast different CCD device malfunctioning mechanisms are presented. With multiple pulses reach the same pixel on CCD surface, the laser damage threshold is declined sharply, which is closely related with pulse numbers and laser fluencies. For instance, with 100 pulses the damage shreshold only amouts to 1/3 of the single-shot value. In this case, multiple pulse damage mechanism is found to be identical to sing-shot case. With multiple pulses reach different pixels, the situation is quite different which attributes only to multiple vertical line damage superposed effect without vertical transfer clock lines short circuit effect. In this thesis, short and ultrashort/ultrafast laser interaction with silicon and silicon-based EO devices are studied both from theoretical and experimental methods. In theorm aspects, advanced Density Functional Theory (DFT) based semi-classical approximation theory and improved Two Temperature Model(TTM) are adopted to study the instantaneous process between carriers and lattice, including temperature, carrier density and space-time evolution. The semi classical DFT theory and phenomenological methods used here are newly created. In the experiment part, advanced pumped detection method and instantaneous spectrum measurement are used to dynamically study the micro level processes. In multiple materials surface and multiple pulses damage mechanism research new results are given. Finally, multiple pulses damage Charged Coupled Devices(CCDs) are studied,and the damage mechanism under are analyzed from material and electronical levels. The research is probably useful for laser ablation, machinery, laser protection and other engineering applications.
公开日期	2015-12-24
内容类型	学位论文
源URL	[http://ir.ciomp.ac.cn/handle/181722/48890]
专题	长春光学精密机械与物理研究所_中科院长春光机所知识产出
推荐引用方式 GB/T 7714	邵俊峰. 短脉冲激光对硅及硅基光电器件的损伤效应与机理[D]. 中国科学院大学. 2015.

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