脉冲紫外激光刻蚀聚合物薄膜的发射光谱和形貌学研究

用聚焦的紫外XeCl准分子激光器轰击高分子聚合物薄膜(涤纶薄膜),由OMA系统接收其发射光谱.发现谱线主要为C_2的Swan带和CN的红带,并与高压汞灯照射后的聚合物薄膜的发射谱进行了比较,在我们的实验精度内,没有发现区别.实验显示,每个光脉冲能刻蚀掉几分之一到几个微米的薄膜.激光的刻蚀效应存在波长和能量密度两个阈值.对于涤纶薄膜,能量密度的阈值约为40mJ/cm~2.同时还作了紫外吸收光谱和SEM照片的分析.     

酸蚀与紫外激光预处理结合提高熔石英损伤阈值

采用HF酸刻蚀和紫外激光预处理相结合的方式提升熔石英元件的负载能力,用质量分数为1%的HF缓冲溶液对熔石英刻蚀1~100 min,综合透过率、粗糙度和损伤阈值测试结果,发现刻蚀时间为10min的熔石英抗损伤能力最佳。采用355 nm紫外激光对HF酸刻蚀10 min的熔石英进行预处理,结果表明:紫外预处理能量密度在熔石英零损伤阈值的60%以下时,激光损伤阈值单调递增;能量到达80%时,阈值反而低于原始样片的损伤阈值。适当地控制酸蚀时间和紫外激光预处理参数能有效提高熔石英的抗损伤能力。     

非晶硅薄膜太阳能电池的紫外激光刻蚀工艺

为提高电池的光电转换效率,通过改善激光刻蚀工艺,采用355 nm紫外纳秒激光分别进行了ZnO:Al薄膜（AZO）刻蚀（P1）、非晶硅薄膜（-Si）刻蚀（P2）和背电极刻蚀（P3）研究。采用万用表测量P1隔离电阻,采用电子扫描显微镜（SEM）和三维激光扫描仪测量刻槽的微结构和三维成像,激光拉曼散射光谱检测非晶硅薄膜刻蚀边缘的晶化。实验结果表明,当刻蚀速度600 mm/s,重复频率40 kHz,功率1.74 W的紫外激光刻蚀ZnO:Al薄膜时,刻槽的隔离效果最佳,达20 M; 紫外激光刻蚀能够有效地减小激光热效应引起的热影响和刻槽边缘的晶化范围,提高非晶硅薄膜电池的性能。     

平顶激光束诱导薄膜损伤阈值测量系统

为了满足快速、精确、定量地测量薄膜激光损伤阈值的要求,设计了平顶激光束诱导薄膜损伤阈值测量系统.介绍了损伤阈值测量的原理和方法,提出二分查找与顺序查找相结合的能量密度查找方式;根据分光镜的分光比及能量探测器示值求解辐照激光能量,用CCD成像法精密测量了作用在薄膜表面的激光光斑面积;基于小波变换法,通过图像处理精确识别了薄膜的损伤;建立能量密度与损伤几率坐标并进行最小二乘法拟合,对损伤阈值进行了标定.对45°高反射膜分别进行了高斯光束辐照和平顶光束辐照的测量实验,结果表明:高斯光束辐照测量的损伤阈值为9.95J/cm~2,平顶光束辐照测量的损伤阈值为13.98J/cm~2,平顶光束诱导比高斯光束诱导的损伤阈值高40.5%.     

表面态调控对GaN荧光光谱的影响

采用高阻本征GaN薄膜,通过H3PO4刻蚀和SiOxNy薄膜钝化方法对GaN薄膜进行表面态调控,研究了表面态调控对GaN薄膜光致荧光光谱的影响.研究发现,H3PO4刻蚀对改善GaN薄膜的紫外荧光发射作用不大,但显著增加可见荧光的强度;经SiOxNy薄膜表面钝化的GaN紫外荧光量子效率增加12—13倍,同时对可见荧光有明显增加.通过比较H3PO4刻蚀和SiOxNy薄膜钝化的室温和低温荧光光谱,探讨了表面态调控对GaN紫外荧光、蓝带荧光和黄带荧光的影响及相关物理机理.     

短脉冲激光打靶用溅射防护薄膜的光学性质

针对短脉冲激光打靶用溅射防护聚合物薄膜做了初步研究。研究了氟化乙丙共聚物(FEP)、全氟烷氧基共聚物和乙烯-四氟乙烯共聚物三种厚度均为25μm的聚合物薄膜的透过率,结果表明FEP薄膜在355nm处光透过率达93%,有望用于激光打靶的溅射防护。进一步对FEP聚合物薄膜的波前畸变、激光损伤阈值进行了研究,结果表明φ80mm的聚合物薄膜在632.8nm处的透射波前畸变的峰谷值(PV值)为波长的1.006倍;在采用输出波长355nm,脉冲宽度9.3ns的Nd:YAG激光为照射光源波长处,薄膜零损伤概率时的最高激光能量密度为10.35J/cm2,100%损伤概率时的最低激光能量密度为11.48J/cm2。     

脉冲激光晶化非晶硅薄膜的有限差分模拟

 根据热传导原理,建立了脉冲激光晶化非晶硅薄膜的理论模型。运用有限差分方法研究了不同激光波长、能量密度等因素对薄膜温度变化及相变过程的影响。计算了不同波长激光器对厚度500 nm非晶硅晶化的阈值能量密度。结果发现,准分子晶化的阈值能量密度最低,但是在同样的能量密度下,熔融深度却不及使用更长波长的激光器。计算并分析了升高衬底温度对结晶速度和晶粒尺寸的影响,模拟结果较好地验证了实验结论和规律。     

激光预处理中缺陷上的激光能量覆盖

分析了不同预处理方式下缺陷上的激光能量的覆盖特点。理论分析表明,相同预处理效率下,单步预处理缺陷上激光能量覆盖率优于多步预处理。实验研究了电子束蒸发制备的HfO2/SiO2多层高反膜的激光预处理,结果发现单步预处理后薄膜的单脉冲激光损伤阈值比相同效率的4步预处理后薄膜的单脉冲激光损伤阈值要好。采用最高能量密度为112%激光损伤阈值的5步预处理后,光学薄膜的激光损伤阈值提高了83.5%。     

HfO_2/SiO_2高反射膜的缺陷及其激光损伤

用原子力、Normaski和扫描电子显微镜等分析仪器 ,对高损伤阈值薄膜常采用的 Hf O2 /Si O2 薄膜进行了表面显微图象研究 ,分析了薄膜常见的表面缺陷 ,如节瘤 ,孔洞和划痕等。薄膜表面缺陷的激光损伤实验表明 ,不同缺陷的抗激光损伤能力大不相同 ,节瘤缺陷最低 ,约为 1 5 J/ cm2 ,薄膜的损伤阈值主要由其决定 ,孔洞的激光损伤能力与节瘤相比较高 ,约为节瘤的 2～ 3倍。节瘤缺陷在低能量密度的激光损伤所形成的孔洞 ,与镀制过程中形成的孔洞形貌相似 ,激光再损伤能力也相似。低能量密度的激光把节瘤缺陷变为孔洞缺陷是激光预处理提高薄膜损伤阈值的原因之一     

基频HfO2/SiO2高反射薄膜激光损伤生长特性

以1064 nm波长作用下的HfO2/SiO2高反射薄膜为研究对象,研究了高反射薄膜在损伤生长过程中分层剥落初始损伤结构的变化规律、损伤形貌特征和损伤生长阈值等特性。实验结果表明:分层剥落初始损伤结构的横向尺寸随激光能量密度的增加呈分段线性增长,破斑沿纵向拓展的损伤生长阈值是沿横向拓展的损伤生长阈值的2倍以上,初始损伤结构横向尺寸的生长率与能量密度呈指数关系,且生长阈值随着辐照次数的增加显著降低。     

脉宽对中红外激光带内损伤HgCdTe材料的影响

研究了脉宽对于中红外脉冲激光带内损伤碲镉汞（HgCdTe）材料阈值的影响,使用一维自洽模型对激光辐照HgCdTe材料程中的载流子数密度,载流子对数目流,载流子对能流,载流子温度和材料晶格温度等相关参数进行仿真计算。仿真结果表明,波长2.85 μm,脉宽30 ps～10 ns单脉冲激光带内辐照HgCdTe材料的损伤阈值为200～500 mJ/cm2。其中,300 ps～3 ns脉冲激光的损伤阈值相近,均为200 mJ/cm2且低于其他脉宽激光的损伤阈值。搭建实验光路并进行相关实验验证仿真模型的正确性。实验发现,波长2.85 μm、脉宽300 ps的单脉冲激光带内辐照HgCdTe材料的损伤阈值在200 mJ/cm2左右。相同条件下,10 ns单脉冲激光带内辐照HgCdTe材料的损伤阈值约474 mJ/cm2。百皮秒脉冲激光对HgCdTe材料的损伤过程结合了热击穿和光学击穿效应,其独特的毁伤机理加剧了材料的损伤。     

飞秒激光烧蚀镍钛形状记忆合金的蚀除机理

结合双温模型的分子动力学模拟方法,研究了飞秒激光脉冲辐照B2结构镍钛合金时烧蚀阈值附近的靶材蚀除机制,数值模拟了中心波长为800nm,脉宽为100fs,能量密度为25~50mJ/cm2的激光与90nm厚B2结构镍钛合金薄膜相互作用过程。确定了脉宽为100fs的脉冲激光与镍钛形状记忆合金相互作用的烧蚀阈值,发现烧蚀阈值条件下,靶材的蚀除机制是单纯基于应力作用的机械破碎;烧蚀阈值附近,未蚀除靶材受热影响发生无序化相变的区域较小,且随激光能量密度的降低而减小。提高激光功率密度,烧蚀同时呈现热机械蚀除和机械破碎机制。     

Direct observation of laser-induced crystallization of a-C:H films

The post-growth modification of diamond-like amorphous hydrogenated carbon a-C:H films by laser treatment has been studied by transmission electron microscopy and Raman spectroscopy. a-C:H films grown on Si substrates by benzene decomposition in a rf glow discharge were irradiated with 15 ns pulses of a KrF-excimer laser with fluences in the range of E=50–700 mJ/cm². At fluences below 100 mJ/cm² an increase in the number of graphitic clusters and in their ordering was evidenced from Raman spectra, while the film structure remained amorphous according to electron microscopy and electron diffraction observations. At higher fluences the appearance of diamond particles of 2–7 nm size, embedded into the lower crystallized graphitic matrix, was observed and simultaneously a progressive growth of graphite nanocrystals with dimensions from 2 nm to 4 nm was deduced from Raman measurements. The maximum thickness of the crystallized surface layer (400 nm) and the degree of laser annealing are limited by the film ablation which starts at E>250 mJ/cm². The laser-treated areas lose their chemical inertness. In particular, chemical etching in chromium acid becomes possible, which may be used for patterning the highly inert carbon films.     

C60/PMMA复合材料的反饱和吸收与光限幅特性研究

本文报导C₆₀/PMMA复合材料的制备方法,并采用调QNd:YAG倍频脉冲激光照射C₆₀/PMMA夏合材料,研究了其反饱和吸收与光限幅将性。在线性透射率为46%条件下,光限幅阈值能量密度为65mJ/cm²,材料破坏能量密度阈值为600mJ/cm².与C₆₀甲苯溶液相比具有一定的优点。     

Influence on the laser induced backside dry etching of thickness and material of the absorber, laser spot size and multipulse irradiation

Laser induced backside dry etching method (LIBDE) was developed - analogously to the well-known laser induced backside wet etching (LIBWE) technique - for the micromachining of transparent materials. In this procedure, the absorbing liquid applied during LIBWE was replaced with solid metal layers. Fused silica plates were used as transparent targets. These were coated with 15-120 nm thick layers of different metals (silver, aluminium and copper). The absorbing films were irradiated by a nanosecond KrF excimer laser beam through the quartz plate. The applied fluence was varied in the 150-2000 mJ/cm² range, while the irradiated area was between 0.35 and 3.6 mm². At fluences above the threshold values, it was found that the metal layers were removed from the irradiated spots and the fused silica was etched at the same time. In our experiments, we investigated the dependence of the main parameters (etch rate and threshold) of LIBDE on the absorption of the different metal layers (silver, copper, aluminium), on the size of the irradiated area, on the film thickness and on the number of processing laser pulses.     

Effect of spot size on cone formation in a XeCl laser ablation of polyethersulfone films

Radiation from the UV excimer lasers, with the fluence above the ablation threshold, can etch the polymer surfaces by photoablation. In some cases different microstructures may appear on the surface during the laser ablation. In this paper the effect of the laser spot size on the cone formation on polyethersulfone films has been investigated. The experiments have been performed with a XeCl laser at the wavelength of 308 nm and at the fluences of 70 and 100 mJ/cm² at air. For the investigation of the effect of the laser spot size on cone formation, the samples were irradiated at two different laser spot sizes of w₁ and w₂ = 0.1 w₁. The morphology of the processed surface was studied by scanning electron microscopy (SEM). It has shown that the shape, size and density of cones change with the change of the laser spot size. Also, the number of pulses and the pulse repetition rate which are needed for threshold of cone formation are affected by the laser beam spot size on the surface.     

Thresholds of plasma formation in silicon identified by optimizing the ablation laser pulse form

Using an evolutionary algorithm combined with pulse shaping, we have identified that rapid plasma formation in Silicon can occur already at a fluence of about 150 mJ/cm2 if a substantial part of the laser energy is deposited efficiently around 200 fs after an exciting laser pulse. Nonthermal solid-to-liquid phase transition leads to the increase of the deposited energy in the material. Highly charged ions have been observed in the mass spectrum. While the pulse optimization procedure allowed us to identify the plasma formation, further experiments where the influence of the laser pulse width on the ablation yield was studied and Two-Pulse-Correlation experiments provided additional proof for the appearance of rapid plasma formation.     

532 nm激光辐照下ZnSe薄膜光学特性研究

采用电子束热蒸发技术制备了ZnSe薄膜,研究了532 nm波长的不同能量(2.0 mJ、2.5 mJ、3.0 mJ)、不同脉冲数(3、10、15)激光诱导前后,ZnSe薄膜的透射率、折射率、消光系数、损伤阈值(LIDT)的变迁。研究结果显示,在能量为2.0 mJ激光辐照后,ZnSe薄膜折射率提高,透射率下降。相比较能量为2.5 mJ、3.0 mJ激光辐照,在能量为2.0 mJ激光辐照后折射率提高最明显,由2.489 4提高到2.501 6。薄膜损伤阈值从0.99 J/cm2提高到1.39 J/cm2(10脉冲辐照);薄膜的损伤经过了无损伤到严重损伤突变的损伤演变过程。采用原子力显微镜对预处理后薄膜表面粗糙度进行检测,发现激光预处理后的薄膜表面粗糙度Ra有所下降,从0.563 nm降低到0.490 nm(15脉冲激光辐照)。     

Laser-assisted etching of gallium arsenide in chlorine at 308 nm

Xenon chloride (308 nm) excimer laser-assisted etching of GaAs (100) in Cl₂ was demonstrated and characterized with respect to laser and gas parameters. The etch rate increased linearly with laser fluence from thresholds in the range of 50 to 75 mJ/cm² to the highest fluence studied, 650 mJ/cm². For a laser fluence of 370 mJ/cm², the etch rate varied with Cl₂ pressure reaching a maximum at a Cl₂ pressure of about 2 Torr. The etch rate decreased monotonically with Ar buffer gas pressure because of redeposition of GaCl₃ products into the etched channel. The redeposited GaCl₃ affected the etch rate and the etch morphology. The etch rate and morphology also varied with laser repetition rate. The mobility of chlorine on the surface also plays an important role in the etching mechanism.