Thermophoretic Control of Submicron-sized Particulate Recontamination

Thermophoresis is the movement of particles in a thermal gradient. It has the advantages of being simple to set up and to carry out. Here, it is used to prevent the recontamination of emitted particles smaller than 0.5 μm during the dry laser cleaning of particles not chemically bound to the substrate. Its use permits the efficiency of such dry laser cleaning to be greatly improved. A comparison between the thermophoretic and laminar flow techniques is carried out, showing that thermophoresis is more efficient.     

Excimer Laser Induced Removal of Particles from Hydrophilic Silicon Surfaces

A pulsed KrF excimer laser was used to remove several types of submicron-sized particles from silicon surfaces. Polystyrene latex particles, 0.1 μm and larger, were removed from silicon surfaces by dry laser cleaning (no water layer condensed on the surface) but SiO₂ particles could not be so removed. However, during steam laser cleaning, in which a thin film of water is deposited on the surface as both an energy transfer medium and an adhesion force reduction agent, these 0.1-0.2 μm SiO₂ particles were almost entirely removed. Calculations of the various forces contributing to adhesion indicate that hydrogen bonds are the major contributor to the adhesion of inorganic particles to substrate surfaces. Photoacoustic detection, using piezoelectric transducers, monitored the surface vibrations induced by the laser pulses.     

Excimer Laser Induced Removal of Particles from Hydrophilic Silicon Surfaces

A pulsed KrF excimer laser was used to remove several types of submicron-sized particles from silicon surfaces. Polystyrene latex particles, 0.1 μm and larger, were removed from silicon surfaces by dry laser cleaning (no water layer condensed on the surface) but SiO₂ particles could not be so removed. However, during steam laser cleaning, in which a thin film of water is deposited on the surface as both an energy transfer medium and an adhesion force reduction agent, these 0.1–0.2 μm SiO₂ particles were almost entirely removed. Calculations of the various forces contributing to adhesion indicate that hydrogen bonds are the major contributor to the adhesion of inorganic particles to substrate surfaces. Photoacoustic detection, using piezoelectric transducers, monitored the surface vibrations induced by the laser pulses.     

激光干式除锈

无论是在生产还是在科研中,有效地去除金属锈蚀一直是人们极为关注的一个领域。我们对一种新式除锈方法——激光干式除锈法的原理、特点和基本结构进行了详细介绍,在实验室内对不同程度的铁锈进行了激光清洗试验,初步得到了激光清洗阈值、清洗效率、清洗成本、清洗效果等数据,将这些数据与其它除锈方法进行比较,表明激光干式除锈是比较理想的除锈方法,有望因其成本低、污染少、效果好等优点而广泛应用于工业除锈。     

激光清洗技术及应用

介绍了激光清洗的两种机理．一是基体与污物对某一波长的激光吸收系数差别很大,或两者溶、沸点相差悬殊,污物吸收激光能量后汽化挥发,或受热膨胀脱离基体表面;二是基体与污物性能差异不大,在高能量密度、高频率的脉冲激光作用下,污物层内产生分裂应力而与基体脱离．同时介绍了一些激光清洗技术的应用．     

Surface Cleaning by Electrostatic Removal of Particles

Contamination of product surfaces by particles during microelectronics manufacturing can lead to significant losses of product yield and reliability. In many cases, cleaning by an effective dry process would be preferable to cleaning by an equally effective wet process. A new dry process for cleaning is described. The product surface to be cleaned is grounded or placed on a grounded surface. An insulating film, approximately 20 μm thick, is placed on the contaminated product surface. A counterelectrode is placed on the film, with enough direct current voltage, typically kilovolts, to create fields of approximately 1 MV/cm. When the film is removed from the contaminated product surface, particles as small as 1 μm are removed with the film. Particles deposited dry are substantially easier to remove than particles deposited wet and allowed to dry. Also very difficult to remove are particles that melt and then solidify on a surface. Various insulating films have shown successful particle removal, but all films tested have also deposited some new particles onto the surface being cleaned, in addition to removing old particles.     

Nanoparticle removal from substrates with pulsed-laser induced plasma and shock waves

Removing particles with nanometer scale diameters from substrates is a challenging task with numerous critical applications. A novel removal method for nanoparticles is developed and tested. The technique, which is dry and non-contact, takes advantages of shock wavefronts initiated by plasma formation under a focused laser beam pulse and its interaction with the substrate. Experimental results indicate that silica particles down to 500 nm on silicon wafers can be removed without substrate damage. In the reported experiments, a Q-switched Nd : YAG pulsed laser with a 5-ns pulse width and 360-mJ pulse energy at 1064 nm wavelength is employed as a plasma generation source. It is reported that the traditional dry laser cleaning method based on the rapid thermal expansion under direct laser irradiation often results in surface damage in the nanometer scale due to light diffraction around nanoparticles and/or stress localization in the thermal skin. This occurs when the characteristic dimensions of the particles are comparable to the wavelength of incident beam. In the laser plasma method, various mechanisms are responsible for the removal effect. The strong shock wave in air generates complex pressure wavefields resulting in both drag/lift on the particle and acceleration of the substrate. However, shock waves are not transmitted to the solid substrate due to a large difference between the relevant wave phase speeds in the two media. The effects of the number of shots and the distance between the surface and the plasma boundary on the removal efficiency are reported.     

轮胎模具的清洗技术

简单介绍轮胎模具传统清洗方法,重点介绍激光清洗技术和干冰清洗技术,并进行了比较。     

蒸气式激光清洗

介绍了蒸气式（湿式）激光清洗,对基底强吸收、基底与液膜共同吸收、液膜强吸收的3种情况给予了分析讨论。给出了实验装置示意图,还介绍了蒸气式激光清洗中的一些理论问题,如峰值温度和瞬态力的估算。最后对干式和湿式激光清洗进行了简单比较。     

Principles and mechanisms of sub-micrometer particle removal by CO2 cryogenic technique

The removal of sub-micrometer particles from surfaces is critical in different manufacturing processes requiring precision cleaning, such as in integrated devices, microsystems, read/write head, magnetic recording media, etc. Defects caused by small particles can adversely affect device performance and yields. The efficiency required in removing increasingly small particles without affecting underlying film integrity is a major challenge in standard wet cleaning. This paper describes the theory and mechanism of a dry, non-etching cleaning method in the form of CO₂ cryogenic aerosol. A theoretical model of particle removal is presented along with discussions on the forces of particle-substrate adhesion in air. Results of cleaning experiments using standard polydisperse particles and slurries provide the validity of the cleaning model.     

激光和干冰清洗轮胎模具技术与应用

介绍轮胎模具清洗新技术——激光和干冰清洗技术的工作原理、技术特点和应用。激光清洗通过控制能量密度和波长等激光工艺参数,不损伤模具,清除的废料可回收,清洗过程实现自动化控制,劳动强度小,清洗效率高,且清洗设备使用寿命长,运行成本低,尽管首期投资大,但推广应用前景广阔。干冰清洗技术在轮胎模具上已成功应用,可以直接清洗硫化后的高温模具,不损伤模具,不污染环境,不留下任何残留物,且可以清洗细小排气孔,但运行成本高,噪声和劳动强度大。     

Effect of Particle Impact on Surface Cleaning Using Dry Ice Jet

The removal of particulate contaminants adhering to a surface has been investigated using a dry ice blasting system. Monosized spherical latex particles of micron and submicron sizes were used as particulate contaminants, while the dry ice jet was produced by the thermal expansion of liquid carbon dioxide (CO₂). Removal of the contaminants was observed in situ using a high-speed microscope camera and quantified through digital image analysis. The experimental results showed that dry ice blasting performs well for surface cleaning, which is attributed to the collision of the dry ice particles with the contaminants. For submicron-sized contaminants, a lower temperature jet was required in order to produce a larger number of dry ice particles to enhance the removal efficiency. The removal efficiency increased with an increase of the jet pressure on the surface. In addition, a theoretical analysis of the moments of forces caused by particle impact and aerodynamic drag showed that particle impact is primarily responsible for removal. Furthermore, the effect of the dry ice cleaning was visually observed by applying it to the removal of a film resin covering a surface.     

Liquid Explosive Evaporative Removal of Submicron Particles from Hydrophilic Oxidized Silicon Surfaces

A pulsed CO₂ laser-based system, operating at a wavelength of 10.6 μm, was used as a cleaning tool to remove particles as small as 0.1 μm from hydrophilic, oxidized silicon surfaces. The laser beam served as a fast heating source to induce the explosive evaporation of a water film deposited on the particle-contaminated surface. The resulting explosive forces were high enough to expel particles from the surface efficiently. The contaminant particles used were 0.1 μm alumina, 0.1–0.2 μm silica, and 0.1 μm polystyrene latex.

For each of these, the cleaning efficiency was monitored as a function of the laser fluence, the thickness of the deposited water film and the number of cleaning cycles. Whatever the nature of the particles, the cleaning efficiency was characterized by an upper limit of the energy density, determined to be 1.5 J/cm², at which substrate damage occurred. At all lower laser fluences, the removal efficiency was particle-dependent.

The thickness of the deposited water film was varied by changing the time of exposure of the surface to water vapor, the vapor flow being fixed at 4700 ml/min. An exposure time of 1.5 s was found to be the most effective. Increasing the number of cleaning cycles permitted the evaluation of the effect of the zeta potentials of the particles with respect to that of the surface.     

Liquid Explosive Evaporative Removal of Submicron Particles from Hydrophilic Oxidized Silicon Surfaces

A pulsed CO₂ laser-based system, operating at a wavelength of 10.6 μm, was used as a cleaning tool to remove particles as small as 0.1 μm from hydrophilic, oxidized silicon surfaces. The laser beam served as a fast heating source to induce the explosive evaporation of a water film deposited on the particle-contaminated surface. The resulting explosive forces were high enough to expel particles from the surface efficiently. The contaminant particles used were 0.1 μm alumina, 0.1-0.2 μm silica, and 0.1 μm polystyrene latex.

For each of these, the cleaning efficiency was monitored as a function of the laser fluence, the thickness of the deposited water film and the number of cleaning cycles. Whatever the nature of the particles, the cleaning efficiency was characterized by an upper limit of the energy density, determined to be 1.5 J/cm², at which substrate damage occurred. At all lower laser fluences, the removal efficiency was particle-dependent.

The thickness of the deposited water film was varied by changing the time of exposure of the surface to water vapor, the vapor flow being fixed at 4700 ml/min. An exposure time of 1.5 s was found to be the most effective. Increasing the number of cleaning cycles permitted the evaluation of the effect of the zeta potentials of the particles with respect to that of the surface.     

激光清洗及其应用进展

激光清洗作为一种新型的清洗方法如今已经被广泛应用。它是通过激光分解及激光剥离的原理使得污染物脱离物体表面从而达到清洗的目的。由于激光清洗的方法简便,不产生固体、液体和气体的污染物,所以其被研究用于很多方面。而其在激光脱漆、微电子器件清洗、橡胶模具清洗、胶粘剂残留物脱除、浮油去除、古建筑和艺术品修复等方面的应用尤为突出。虽然目前激光清洗还无法取代传统清洗技术,但随着世界对环保要求的逐渐提高,激光清洗会克服种种弊端在各领域成为高效清洗的技术手段。     

国内选净最新技术——干式选净理论和实践初探

选净与选别不同，选净主要要求物料颗粒表面的洁净。本文旨在探索干式选净设备的设计、制造的理论和实践问题。尽管设计已在实践中获得成功，理论依据已得到工业试验的印证，但是由于干式选净技术目前在国内尚属新技术，还有待于进一步开展研究工作。     

橡胶模具激光清洗的工艺研究

激光清洗模具的原理是利用模具基体物质与表面附着的污垢对某一频率的激光能量吸收系数的差别,使激光能量充分被表面附着的污垢所吸收,从而受热膨胀直至气化,所形成的气体被吸收利用而不损伤模具甚至强化模具基体,以达到绿色清洗的目的。本文从橡胶模具表面颗粒受力、激光清洗的机理与主要性能参数及其光路控制,对激光加工技术的应用进行了探讨。     

Removal of Fine Particles from Smooth Flat Surfaces by Consecutive Pulse Air Jets

In order to develop an effective dry surface cleaning method, removal of fine particles by pulse air jets was experimentally investigated. A dimensionless resuspension parameter, F*, which is the ratio of drag force on particles to van der Waals adhesion force, was introduced to correlate the removal efficiency. Resuspension experiments were carried out with monodisperse PSL particles and wax particles with diameter between 0.25 and 1.1 μm on silicon wafer and glass plate. As a result, it was found that deposition process of particles on the surface (gravitational settling and impaction at a relatively low impaction velocity) has little effect on the removal efficiency and that consecutive pulse air jet is effective in the removal of fine particles. Further, F* is the key parameter in determining the removal efficiency. The prediction method for the removal efficiency by pulse air jets with F* is proposed.     

Efficiency studies of particle removal with pulsed-laser induced plasma

The detachment and removal of micro- and nanoparticles from surfaces is of importance in many industries. The cleaning of silicon wafers is of great interest in the semiconductor, microelectronics, and optics industries. The development and adoption of dry, rapid, non-contact, and non-damaging particle removal technologies is a critical process. The proposed laser-induced plasma (LIP) removal technique is a novel method for detaching and removing fine particles from substrates. The current technique is a dry, non-contact method that takes advantage of the strong shock wavefront from expanding plasma, created by focusing a laser pulse in air above the substrate. The transient pressure field acts on the target particles to produce a rotational moment and a rolling mode of detachment from the substrate. In the current study, the LIP removal technique is employed repeatedly to remove particles over an area of a silicon wafer, and a systematic efficiency study for the removal effectiveness is performed. A Q-switched Nd:YAG pulsed laser operating at 1064 nm with a 370 mJ pulse energy and 5 ns pulse length is used in experiments. 0.99 μm diameter silica spheres and 3.063 μm diameter polystyrene spheres were successfully detached and removed with no substrate damage. The removal efficiency at various gap distances between plasma core and substrate is determined and reported. This work is the first laboratory demonstration of the LIP technique over an extended area. The reported results substantiate the LIP removal technique as a serious option for particle detachment and removal from extended areas.     

利用均匀设计法制备撕剥型干洗剂及性能分析

为开发环保无毒和无粉尘的便携干洗剂,选用聚乙烯醇(PVA)、水、乙醇、D-柠檬烯、硅胶和羧甲基纤维素(CMC)采用控制变量法初步制备了撕剥型干洗剂。以PVA、CMC、硅胶和D-柠檬烯的质量分数为自变量因素,去污效率为表征指标,取4因素7水平设计均匀实验。再以SPSS软件对结果进行回归分析得到数学模型,以MATLAB软件对模型进行计算,得到优化配比(质量分数,以体系总质量为基准):PVA 2488(牌号)为4.5%、CMC为1.5%、800目硅胶为7.5%、D-柠檬烯为11%。该配方去污效率可达97.08%。通过FTIR和SEM对干洗剂所得薄膜及织物进行结构表征和去污原理分析,并对织物的物理性能进行测试。结果表明,干洗剂对粉尘微粒与油渍的去污效果很好,织物上残留很少,织物仍保留着较好的服用性能。