Development of Localized Plasma Etching System for Failure Analyses in Semiconductor Devices: (4)Precise Temperature Measured during Plasma Etching

Abstract

Temperature measurement of Si surfaces being etched by an inward plasma technique was performed with a sampling period of 0.1 s. A band edge thermometer was employed, which is based on the temperature dependence of the absorption edge of silicon. The temperature rise associated with the inward plasma etching was demonstrated to be smaller than that with an outward technique. Time dependence of the temperature and optical emission intensities from the plasma were measured simultaneously. As plasma was ignited and the discharge glowed, the temperature rose abruptly in the time domain within 3 s, after which it approached a linear dependence. The transition in temperature change from an initial abrupt one to a linear manner coincided with the maxima of the optical emission intensity of F atoms as well as total emission intensity integrated between 200 and 1000 nm. The magnitude of the initial temperature change linearly correlated with the intensity of the optical emission line by F atoms, i.e., the number of F radicals, while its correlation with the total intensity was obscured. It was therefore concluded that light absorption is not sufficient to explain the initial temperature change. Other effects including heat conduction of the etching gas to the surface and reaction heat associated with etching should be included.