Etching organic low dielectric film in ultrahigh frequency plasma using N2/H2 and N2/NH3 gases

Abstract

The behavior of species in the gas phase and their effects on the etching characteristics of organic film with the lower dielectric constant (low-k) were investigated in 500 MHz ultrahigh frequency (UHF) plasma using N2/H2 and N2/NH3 gases. The absolute H and N radical densities and NH3 molecule density in etching plasmas were evaluated by the vacuum ultraviolet absorption spectroscopy and the infrared diode laser absorption spectroscopy technique, respectively. The effects of frequency that excited the plasma in the production of H and N radicals were clarified by comparing the behavior of radicals in the UHF plasma with that in the inductively coupled plasma (ICP) exciting at the frequency of 13.56 MHz reported in the previous study. H radicals were produced more efficiently from NH3 gas and N radicals more efficiently from N2 gas in the UHF plasma than in the ICP. H radicals were generated not only through the dissociation of the H2 molecule but also from NH3 molecules produced in the N2/H2 plasma. On the other hand, the N radical density was lower by one order of magnitude than the H radical density, and was seldom produced from the NH3 molecule. It was found that the etch rate and etched profile could be controlled with an internal plasma parameter of the ratio of the H and N radical densities under the constant electron density in the plasma gas chemistry of both N2/H2 and N2/NH3. The optimal conditions for the anisotropic profile and high etch rate were well determined by the ratio of the H and N radical densities and the substrate temperature. The results of this study are very useful not only for understanding the fundamental process of organic low-k film etching but also for precisely controlling the etching process.