Surface temperature measurements using pyrometry during excimer laser pulsed etching of silicon in a Cl 2 environment

Abstract

It appears from angular-resolved time-of-flight (TOF) studies, performed on the products desorbed during nanosecond pulsed excimer laser etching of silicon in a low pressure chlorine environment, that the mean energy of the desorbed particles is dependent on the chlorine surface coverage (θ). Monte-Carlo simulations of the desorption process have shown that all of the results of the TOF experiments can be explained by assuming that the maximum surface temperature T s reached during the laser pulse depends on θ. For the laser fluence used, T s varies from 1600 K at θ ≈ 0.01 up to 3500 K at full monolayer coverage. In this study we present time-resolved emission spectrometry of a silicon surface during laser irradiation, in order to elucidate the role of the surface temperature in the etching mechanism. The emission of the irradiated spot is measured as a function of laser fluence and chlorine coverage. The measured emission can be interpreted as thermal emission at the surface temperature. The temperature obtained from the emission measurements is in good agreement with that derived from the TOF experiments. The influence of the adsorbed chlorine on the surface temperature is discussed in the light of possible models.