Abstract.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 (SiO 2 ) 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%. PACS: 42.62.CfLaser cleaning of surfaces from particles with diameters in the range from 100 nm to several microns has become increasingly important in lithography [1], semiconductor device fabrication [2-6], micromechanics, optics, telecommunications, etc.Conventional techniques such as ultrasonic and megasonic cleaning, wiping and scrubbing, high-pressure jet spraying, etching, plasma cleaning, etc., are often inadequate for the removal of particulate contaminants of micron and submicron size. The problems with these techniques include ineffectiveness, addition of contaminants, damage of prefabricated parts, etc. It has been demonstrated that laser cleaning can be used to efficiently remove micron and submicron particles from solid surfaces. Such particulates adhere with relatively strong forces [7] that are difficult to overcome with the traditional cleaning techniques. Laser cleaning based on the absorption of pulsed-laser radiation by the substrate and/or the particulates is denoted as dry laser cleaning (DLC) [6,8]. If the removal of particulates is related to the superheating and explosive evaporation of an auxiliary thin liquid film, the technique is denoted as steam laser cleaning (SLC) [4,5].Since 1991 of the particles from the surface and their spatial distribution after leaving the substrate in relation to the surface roughness [9]. In recent publications there has been a significant increase in the use of polymer science in the fields of microelectronics and sensor technology [10]. From polymers used in packaging to polymers used as electrets, polymers will soon be facing the same cleaning difficulties as conventional semiconductor materials. Only a few existing papers [11,12] describe the removal of residues of polymers from polymers. Nonetheless, to the authors' knowledge, no papers have dealt with laser-induced removal of particles from polymer substrates.In this paper we investigate laser cleaning of PI (polyimide) and PMMA (polymethylmethacrylate) from PS (polystyrol) and SiO 2 (silica) microspheres of different sizes. Experimental procedureThe experimental setup consists of a KrF excimer laser (Lambda Physik LPX 205), which provides at λ = 248 nm a maximum pulse energy of E ≈ 470 mJ (at a ν r = 1 Hz repetition rate). Its pulse length is τ (FWHM) ≈ 31 ns and its repetition rate is between 1 Hz and 30 Hz. The pulse energy is computer-controlled by an external adjustable tunable dielectric attenuator.The output from a circular aperture was imaged using a lens onto the polymer target...

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The cleaning of silicon surfaces from submicron dust particles has been studied by means of the "Steam Laser Cleaning" (SLC) process and compared to "Dry Laser Cleaning" (DLC) which is used nowadays in many applications. For SLC a thin liquid layer (e.g. a water-alcohol mixture) is condensed onto the substrate, and is subsequently evaporated by irradiating the surface with a short laser pulse. The DLC process, on the other hand, only relies on the laser pulse, without application of a vapor jet. We have systematically investigated the efficiency of these two processes for the removal of well-characterized polymer, silica and alumina particles of various sizes down to 60 nm in diameter, and have also studied the influence of light wavelength and laser pulse duration for nanosecond and picosecond pulses. The results demonstrate that for the gentle cleaning of silicon wafers SLC is a very efficient method and is superior to DLC. An effect which so far has only rarely been taken into account for laser cleaning is the field enhancement under the particles, which can give rise to serious surface damage, in particular when cleaning pulses in the picosecond and femtosecond range in the DLC are applied.

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