Reaction of silicon with chlorine and ultraviolet laser induced chemical etching mechanisms

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  • W. Sesselmann
    Siemens AG, Corporate Production and Logistics, Otto-Hahn-Ring 6, D-8000 Munich 83, Federal Republic of Germany
  • E. Hudeczek
    Siemens AG, Corporate Production and Logistics, Otto-Hahn-Ring 6, D-8000 Munich 83, Federal Republic of Germany
  • F. Bachmann
    Siemens AG, Corporate Production and Logistics, Otto-Hahn-Ring 6, D-8000 Munich 83, Federal Republic of Germany

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<jats:p>The reaction of 〈100〉Si with Cl2 and the excimer laser induced chemical etching process using 308 and 248 nm radiation have been investigated. Our results show that even at high Cl2 pressures, only a thin passivating chlorinated surface layer is built up which impedes further reaction. Pulsed excimer laser etching at high energy fluences is dominated by thermal evaporation. At lower energy fluences the melt depth decreases and good etch profiles with excellent spatial resolution are observed. At the lowest laser fluences nonthermal, wavelength dependent etching occurs. The laser etching at 308 nm is based on locally enhanced surface chlorination due to effective photodissociation of Cl2 in the gas phase. Photoinduced desorption, most likely due to nonradiative electron-hole recombination, leads to etching. Conversely, at 248 nm, negligible gas phase photodissociation occurs and the surface reaction of Cl2 molecules limits the etch rate. However, the higher photon energy (5.0 eV for 248 nm) leads to efficient photodesorption of surface atoms and molecules by direct bond breaking which can give rise to higher etch rates than at 308 nm. Depending on the actual conditions, etching at 308 or 248 nm is more efficient. High etch rates can be achieved by combining the effective photodesorption process at 248 nm with a high degree of surface chlorination due to generation of chlorine gas phase radicals in a microwave discharge. In addition, the spatial resolution capability for direct pattern transfer by excimer laser induced chemical etching has been analyzed as a function of energy fluence, gas pressure, and gas phase radical concentration.</jats:p>

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