Laser surface cleaning of organic contaminants

Laser surface cleaning process has been a useful and efficient technique for various industrial applications. The removal of photoresist contaminants on silicon wafers was investigated with a krypton fluoride (KrF) excimer laser, and the irradiated area was characterized using a profilometer, a scanning electronic microscopy (SEM), an Auger electron spectroscopy (AES) and a Fourier transition infrared spectroscopy (FT-IR). It was found that there exist an optimal number of pulses to remove the contaminant from the substrate surface without any laser-induced damage, depending on the laser density on the surface. A model to predict the optimal number of pulses, which agrees well with Beer–Lambert's law, is proposed and proved to be operable.     

Laser surface cleaning, de-rusting, de-painting and de-oxidizing

Many materials have been tested as substrates and surface products. Typically ferrous (Carbon Steels and Stainless Steels) and non-ferrous (Al and Cu metals and its alloys) materials have been employed. Some epoxy, polyurethane, polyester and acrylic paints with different thickness and colour have been tested. Many types of surface rust and oxide on different bulk material have been undertaken to test. Similarly, some different types of oils and greases commonly used in industry to prevent oxidation, have been studied. Different types of laser sources have been employed: an axial fast flow, 1.5 kW CO₂ c.w. and pulsed laser source emitting a 10.6 7m beam; and a portable Nd:YAG laser, Q-switchedand normal-mode source: 1st harmonic 1.064 7m (6 ns pulse duration), 2nd harmonic 532 nm (120 7s duration pulse, 1 J max per pulse) wavelengths, multi-articulated seven mirror beam guiding device, 20 Hz repetition rate. This provides shots with 600 mJ maximum energy per pulse and 100 MW peak power per pulse with very low beam divergence: 0.5 mrad at full angle.     

光学元件超声清洗工艺研究

系统开展了光学元件超声清洗工艺的实验研究。通过研究超声清洗剂、清洗温度等工艺参数的优化,找到了能够有效祛除元件表面无机污染物和有机污染物的较佳超声清洗工艺,且超声清洗没有对光学元件表面产生损伤,清洗后的光学元件接触角小于6,并不残留大于1 m的颗粒,超声清洗对光学元件表面污染物的祛除能力远胜于手工清洗。     

光学元件超声清洗工艺研究

系统开展了光学元件超声清洗工艺的实验研究。通过研究超声清洗剂、清洗温度等工艺参数的优化,找到了能够有效祛除元件表面无机污染物和有机污染物的较佳超声清洗工艺,且超声清洗没有对光学元件表面产生损伤,清洗后的光学元件接触角小于6,并不残留大于1 m的颗粒,超声清洗对光学元件表面污染物的祛除能力远胜于手工清洗。     

Laser cleaning on Roman coins

Ancient metal objects react with moisture and environmental chemicals to form various corrosion products. Because of the unique character and high value of such objects, any cleaning procedure should guarantee minimum destructiveness. The most common treatment used is mechanical stripping, in which it is difficult to avoid surface damage when employed. Lasers are currently being tested for a wide range of conservation applications. Since they are highly controllable and can be selectively applied, lasers can be used to achieve more effective and safer cleaning of archaeological artifacts and protect their surface details. The basic criterion that motivated us to use lasers to clean Roman coins was the requirement of pulsed emission, in order to minimize heat-induced damages. In fact, the laser interaction with the coins has to be short enough, to produce a fast removal of the encrustation, avoiding heat conduction into the substrate. The cleaning effects of three lasers operating at different wavelengths, namely a TEA CO₂ laser emitting at 10.6 m, an Er:YAG laser at 2.94 m, and a 2-Nd:YAG laser at 532 nm have been compared on corroded Romans coins and various atomic and nuclear techniques have also been applied to evaluate the efficiency of the applied procedure. PACS 42.55.-f; 42.55.Ah; 81.05.Bx.     

大气常压等离子射流清洗溶胶-凝胶SiO_2膜表面油脂污染物

采用大气常压等离子射流技术对溶胶-凝胶SiO2膜表面的油脂污染物进行清洗。利用分光光度计、扫描电子显微镜、红外光谱仪对溶胶-凝胶SiO2膜透过率、表面形貌、化学结构进行表征,并分析清洗前后溶胶-凝胶SiO2膜的激光损伤阈值变化。损伤阈值测试表明,1064nm波长的激光损伤阈值由污染后的16.08J/cm2上升到24.41J/cm2,与污染前24.72J/cm2的损伤阈值相当。同时还获取清洗的最佳时间为10s。清洗前后,溶胶-凝胶SiO2膜保持完好,且未产生新的有机污染物。研究结果表明:大气常压等离子射流技术可对溶胶-凝胶SiO2膜表面的油脂污染物进行有效地清洗,从而提高溶胶-凝胶SiO2膜的透过率和激光损伤阈值,为高功率激光装置的稳定运行提供保障。     

Laser cleaning of glass

The pulse lasers, YAG-, CO₂-, and N₂-lasers, are examined for use in the cleaning of glass. Cleaning is found to be due to the evaporation and sputtering of stains on the glass by the heat energy of the laser light. Only the N₂ laser can be used for the cleaning of the exit surface of the glass (the opposite side to the laser). A laser with a high peak power of about 10⁶J/s and short-pulse duration below 100 ns is found to be necessary in practice.     

Plasma cleaning of multilayer mirrors in EUV lithography from amorphous carbon contaminations

The feasibility of plasma cleaning of the multilayer mirrors used in 13.5-nm EUV lithography from carbon contaminations is studied. Experiments conducted in electrodeless plasma of the surface-wave low-pressure discharge in helium and hydrogen demonstrated the high rate, efficiency, and selectivity of this cleaning without any damage of the mirror’s upper protection layer, even at the atomic level. The optimal working parameters of plasma cleaning are determined and its possible mechanism is discussed.     

光学元件激光预处理技术

国外学者用1064 nm激光对pickoff镜进行预处理,发现损伤阈值平均提高38.8%。国内研究者用CO2激光中度抛光后,熔石英基片的损伤阈值提到了30%左右,激光波长、扫描方式等对处理效果影响也比较明显。介绍了三种公认的预处理机制,将离线与在线处理方式做了简单地比较,并对国内外激光预处理技术的发展和前景进行了展望。     

Laser cleaning of polymer surfaces

We have investigated the removal of small spherical particles from polymer surfaces by means of 193-nm ArF and 248-nm KrF laser light. Polystyrene (PS) particles with diameters in the range of 110 nm to 1700 nm and silica particles (SiO₂) with sizes of 400 nm and 800 nm are successfully removed from two different substrates, polyimide (PI) and polymethylmethacrylate (PMMA). Experiments were performed in air (23 °C, relative humidity 24–28%) and in an environment with a relative humidity (RH) of about 90%. Received: 13 July 2000 / Accepted: 14 July 2000 / Published online: 9 November 2000     

飞秒非线性光学的最新进展——几个周期超短超强激光脉冲的非线性光学

本文介绍了飞秒非线性光脉冲研究的最新进展。超快技术的发展已经能够产生仅含几个振荡周期的超强脉冲,其强度梯度使电子可以存在于比库仑束缚场高许多倍的外场产生的原子束缚态,并产生了同光频相差不大的电离率,从而导致了非线性光学的一些新的特点。     

飞秒非线性光学的最新进展——几个周期超短超强激光脉冲的非线性光学

 本文介绍了飞秒非线性光脉冲研究的最新进展。超快技术的发展已经能够产生仅含几个振荡周期的超强脉冲,其强度梯度使电子可以存在于比库仑束缚场高许多倍的外场产生的原子束缚态,并产生了同光频相差不大的电离率,从而导致了非线性光学的一些新的特点。     

玻璃质光学元件表面微裂纹的研究

研究了影响玻璃质光学元件表面质量的主要因素,认为表面微裂纹是表面强度改变的主要原因。用机械磨削初成形工艺方法分析研究了表面微裂纹产生的原因;通过裂纹尖端应力集中及Griffith能量平衡理论,分析了裂纹扩展方式;结合表面结构缺陷理论及研磨处理表面微缺陷工艺,阐述了HF腐蚀法对微裂纹的去除机理及效果;最后,综述了通过生产工艺提高玻璃强度的方法,重点讨论了离子交换法,镀膜法和HF腐蚀法等表面处理技术,指出使用HF腐蚀法去除表面微裂纹更适用于玻璃质光学元件的表面加工。     

高功率激光装置大口径光学元件侧面清洗实验

针对高功率激光装置内部最易产生受激布里渊散射(SBS)效应的大口径取样光栅(BSG)元件,测试了经过化学刻蚀、紫外激光清洗作用处理后,大口径光学元件BSG侧面在355 nm激光辐照下的损伤阈值、损伤形态以及产生的石英颗粒气溶胶对环境污染程度的分析。结果表明：经过化学刻蚀,BSG侧面的损伤阈值提高78%,基本与通光面的损伤阈值相当,而经过紫外激光处理后的损伤阈值提升不高,仅为通光面损伤阈值的56%。侧面对比分析了相同激光能量辐照下样片侧面产生的气溶胶污染状况,结果表明紫外激光处理同样可以提高光学元件侧面产生污染物的阈值,且对光学元件性能没有影响。通过微观形貌和对通光口径影响分析表明,紫外激光清洗处理比化学刻蚀具有更好的安全性和适用性。     

高功率激光装置大口径光学元件侧面清洗实验

针对高功率激光装置内部最易产生受激布里渊散射(SBS)效应的大口径取样光栅(BSG)元件,测试了经过化学刻蚀、紫外激光清洗作用处理后,大口径光学元件BSG侧面在355 nm激光辐照下的损伤阈值、损伤形态以及产生的石英颗粒气溶胶对环境污染程度的分析。结果表明:经过化学刻蚀,BSG侧面的损伤阈值提高78%,基本与通光面的损伤阈值相当,而经过紫外激光处理后的损伤阈值提升不高,仅为通光面损伤阈值的56%。侧面对比分析了相同激光能量辐照下样片侧面产生的气溶胶污染状况,结果表明紫外激光处理同样可以提高光学元件侧面产生污染物的阈值,且对光学元件性能没有影响。通过微观形貌和对通光口径影响分析表明,紫外激光清洗处理比化学刻蚀具有更好的安全性和适用性。     

Spatial resolution of imaging contaminations on the GaAs surface by scanning tunneling microscope-cathodoluminescence spectroscopy

We obtained the luminescence image of the GaAs (1 1 0) surface by scanning tunneling microscope-cathodoluminescence (STM-CL) spectroscopy, where low-energy (∼100 eV) electrons field emitted from the STM tip were used as a bright excitation source. The STM-CL image with high photon signal (1.25 × 10⁴ cps) showed the dark image corresponding to the surface contamination in the STM image working as the nonradiative recombination centers of carriers. This dark image demonstrated the spatial resolution of about 100 nm in STM-CL spectroscopy of the GaAs (1 1 0) surface, which was determined by the field-emitted electron beam diameter.     

The physical optics integral on the scatterer's unlit surface

The scattering integrals of the modified theory of physical optics are redefined according to the illuminated and unlit surfaces of the scattering object. With this aim the canonical problem of wedge diffraction is taken into account. It is shown that the new scattering integral contain two geometrical optics and diffracted fields. One of the geometrical optics waves is the reflected field component that propagates in the real space. The other one transmits to an imaginary space through the scattering surface and does not have any influence in the real space. The diffracted waves exist in the real space and satisfy the related boundary condition on the scattering surfaces. The resultant field expressions are compared with the exact series solution of the problem numerically.     

Laser cleaning of artificially aged textiles

In order to analyse ancient textiles to identify the fibre, a proper cleaning of the sample is necessary. The anaerobic environment (i.e., the peatery), aiding the preservation of handmade textiles, often impregnates the textiles in such a way that the usual chemical procedures for cleaning are not sufficient while making the sample brittle. The use of laser pulses may offer an alternative method of cleaning. Four different textiles (wool, silk, flax, and cotton) have been investigated. As a first step we used laser irradiation on untreated samples to investigate the laser induced effects on textile materials. As a second step, consolidated samples, samples artificially aged (i.e., samples exposed to a lacustrine environment), and samples both artificially aged and consolidated were irradiated. Several combinations of the main laser parameters (energy density and number of pulses) were tested in order to find the best irradiation conditions. Scanning electron microscopy (SEM) was used to analyze the induced morphological changes. The obtained results are well reproducible while proving the very high efficiency in material removal of the laser pulses: in the four investigated textiles, the laser cleaning procedure permitted the identification of the fibres. PACS 79.20.Ds; 61.80.Bd     

Simulation study and experiment on laser-ablation surface cleaning

A study of the ablation effects of an ultra-short pulsed Nd : YAG laser was carried out. Using a 21 μm Zn-coated carbon steel plate as the target, the relationship between ablation rate and laser fluence was investigated through computer simulation and experiment, and the optimal processing conditions were determined. The tendency of the scanning operation curve was confirmed and the data obtained were taken as a guide for the practical utilization of this technique. Finally, a decontamination factor was introduced and satisfactory cleaning was obtained.     

Effect of silicon surface cleaning procedures on oxidation kinetics and surface chemistry

The effect of surface cleaning procedures on the kinetics of thermal oxide growth on silicon is presented. The goal is to relate the properties of the cleaned surface (composition, chemistry, impurity content) to the changes in oxide growth mechanisms. Experimentally, silicon (100) wafers were given different variations of an RCA clean, and then oxidized in dry O₂ at 900°C producing oxides with thicknesses between 170 and 3900 Å. The results, in general agreement with earlier studies, show that the percentage difference in thickness is strongly dependent on oxide thickness. The data, which are explained in terms of the predictions of a linear-parabolic and a parallel oxidation model, suggest that the surface cleans do not alter the diffusion of molecular oxygen in the oxide. Auger analysis of the surfaces shows that there is a substantial carbon contamination on the HF stripped wafer which is considerably reduced after a 5 min N₂ anneal.