Experiments and numerical calculations for the interpretation of the backside wet etching of fused silica

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Abstract

Experimental investigations and thermal calculations of laser induced backside wet etching (LIBWE) of fused silica are presented. Fused silica plates having 1 mm thickness were irradiated by an ArF excimer laser in the presence of liquid absorber. The absorbing liquids were naphthalene-methyl-methacrylate solutions with different concentrations (0, 0.21, 0.43, 0.85 and 1.71 mol/dm3). The absorption coefficients (α) of these solutions at the applied wavelength were determined using a plano-concave microcuvette. It was found that the value of α could be varied in the range of 39400-62300 cm-1 by the change of the naphthalene content. The dependence of the etch rate on both the absorption coefficient of the liquid absorbers and the applied fluence was studied. The etch depths were measured by an atomic force microscope. At 450 mJ/cm2 laser fluence, the etch rates were found to be between 13.3 and 22.2 nm/pulse depending on the actual absorption coefficient. In the next experiment the laser fluence was varied from 110 to 860 mJ/cm2 and the etch rate was found to vary between 4.7 and 49.5 nm/pulse when the concentration of the applied solution was constant 0.85 mol/dm3. The mechanism of the LIBWE can be explained in the first approximation by thermal effects and their consequences. We calculated the maximal depth of melted fused silica layer by numerical solution of the one-dimension heat flow equation taking into account the phase transformations of the liquid reagents and the fused silica target. These calculations proved that the thickness of the melted quartz layer depends linearly on both of the absorption coefficient of the liquid and the laser fluence. Our calculations give an upper estimation of the etch rate. On the basis of our results a possible interpretation of the LIBWE was suggested.

Original languageEnglish
Pages (from-to)121-126
Number of pages6
JournalThin Solid Films
Volume453-454
DOIs
Publication statusPublished - Apr 1 2004
EventProceedings of Symposium H on Photonic Processing of Surfaces - Strasbourg, France
Duration: Jun 10 2003Jun 13 2003

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Keywords

  • Absorption coefficient measurement
  • Excimer laser
  • Fused silica
  • Plano-concave microcuvette
  • Wet etching

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Metals and Alloys
  • Materials Chemistry

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