Low dielectric constant materials (low-k) are used as interlevel dielectrics in integrated circuits. This paper concerns the etching process of these materials in high density plasma with the aim to provide some insights concerning the etch mechanisms. Materials studied are methylsilsesquioxane (MSQ) polymers, either dense (SiOC) or containing 40% of porosity (porous SiOC). Amorphous hydrogenated silicon carbide (SiC) material, used as hard mask and/or etch stop layer, is also investigated. Etch is performed in an inductively coupled reactor using fluorocarbon gases, which have proven to be very successful in the etch of conventional SiO2. First, etching with hexafluoroethane (C2F is performed. Although etch rates are high, etch selectivities with respect to SiC are weak. So, oxygen, argon, and hydrogen are added to C2F6 with the aim of improving selectivities. The best selectivity is obtained for the C2F6/H2 (10%–90%) mixture. To understand etch rate and selectivity variations, plasma analyses by optical emission spectroscopy are correlated to surface analysis using X-Ray Photoelectron Spectroscopy (XPS). In general, atomic fluorine concentration in the plasma explains the etch rate, while the presence of a fluorocarbon layer on the surface is well correlated to the selectivity. To ensure that the etch process does not affect materials properties, and particularly their dielectric constant, bulk analysis by Fourier Transformed Infra-Red spectroscopy and images by Scanning Electron Microscopy have also been carried out.
Copolymers containing polyhedral oligomeric silsesquioxane (POSS) pendant groups and various acrylate type monomers are studied by x-ray photoelectron spectroscopy. These copolymers have potential application as bilayer resist material for next generation lithography. Two methods are used in order to characterize resist surfaces, angular resolved XPS and inelastic background signal quantification (Tougaard method). The existence of a surface layer rich in POSS is proven. About 1.5nm thick, this layer stands above a material with uniform POSS concentration. Evaluation of POSS concentration depth profiles shows that surface segregation depends on the polymer comonomers and on the silicon content.
