I n s i t u ellipsometry during plasma etching of SiO2 films on Si

The etching of SiO2 films on a Si substrate in an rf plasma in CF4 has been studied with in situ ellipsometry. The etch rate was measured as a function of flow, rf power and pressure. An accurate analysis of the experimental data using numerical simulations based on multilayer models has yielded information both on the refractive index of the etched SiO2 film and on the existence of a top layer. It could be established that a layer is present on top of the SiO2 during etching, which is probably caused by roughening of the SiO2 layer. Furthermore at high pressures (>8 Pa) it was demonstrated that after the complete removal of the SiO2 film a polymer layer starts growing on the Si substrate.