Surface acceleration during dry laser cleaning of silicon

We report on measurements of the surface acceleration for the application o f dry laser cleaning. For that purpose, industrial silicon samples were irr adiated by a frequency-doubled Q-switched Nd:YAC laser. The surface displac ement was measured by a heterodyne interferometer and recorded by a digital storage oscilloscope. Several hundreds of shots were averaged to give smoo th displacement curves which could be derived numerically. The experiments show that the highest accelerations, which are thought to be responsible fo r the cleaning, occur on the time scale of the laser pulse. Simple theoreti cal models are in good agreement with the experimental data. The maximal di splacement depends only on the deposited energy, while the maximal accelera tion shows also a strong dependence from the temporal pulse shape. This kno wledge allows one to optimize the pulse shape for the cleaning process.