PHOTOTHERMAL PROBE-BEAM DEFLECTION MEASUREMENT OF MOISTURE ADSORPTION ON A SILICON SURFACE UNDER ATMOSPHERIC CONDITIONS.

Abstract

Photothermal desorption from a surface in atmospheric conditions utilizing a probe-beam deflection technique is demonstrated for the case of adsorbed water on a silicon wafer with normal surface oxide. In one atmosphere of nitrogen mixed with 20 Torr of water vapor, the desorption of water molecules by pulsed photothermal heating produces a characteristic delayed peak in the signal, which can be used to estimate the amount of desorbed molecules and the readsorption time. The behavior is observed to be very similar when the nitrogen atmosphere is replaced by oxygen, argon, helium, or freon gases at one atmosphere. A probe beam that is focused vertically above the pulsed laser spot is used to detect the shape of the pressure pulse produced at the Si surface.