Electrical and micromechanical performance of ultrasonically cleaned silicon wafers

The evolution of the electrical and micromechanical properties of Si wafers subjected to a kHz-frequency ultrasonic treatment in a water-containing ultrasonic cleaning bath is reported. The cleaning stages observed with varying treatment time are discussed. It is believed that, wafer treating during the first ≈ 60 min is capable of removing contaminating particulates from the wafer surface and actives interface dangling bonds. These are leading to a decrease of subsurface resistance towards dislocation displacements as observed by the micro-hardness decrease, affect free carrier migration barriers seen in variations of the I-V barrier heights, and acts as recombination centers resulting in accelerated photovoltage decays. Although an exact mechanism is not yet clarified, a partial healing of the bonds may occur at longer excitation times (≈ 60-120 min) thus partially reversing the observed changes.