A Multi-scale Study On Silicon-oxide Etching Processes In C₄F₈/Ar Plasmas

Plasma etching has been widely used in micro-electronics fabrication because of the high selectivity and controllability. C4F8/Ar gas mixtures are commonly used to etch oxide with good etching selectivity at acceptable etching rate. Further understanding of the etching progress for better trench profile is required, since the micro- and nano-electronic devices need to decrease the critical dimension in the integrated circuit fabrication. Thus numerical simulations have been an effective tool to realize better understandings, optimizations of processing and low cost reactor designs.A numerical method to simulate SiO2 dry etching with inductively coupled C4F8/Ar plasma has been constructed using a hybrid model, which coupled the reactor, sheath and trench model. Firstly, ion and neutral particle densities and fluxes in reactor are decided using the commercial CFD-ACE+ model of inductively coupled plasma, which is more accurate than the global model coefficients. Secondly, sheath model include ratio frequency, pulsed radio frequency. Set the ion densities as the sheath boundary conditions, the CFD-ACE+ model and the sheath model are coupled to obtain the fluxes, energy and angular distributions for reactants arriving at the substrate at different external discharge parameters. And then, the transports of reactant particles including ions and neutrals in both sheath and trench are considered when the trench profile evolution. Finally, the profile evolution under different discharge parameters for etching of SiO2 in C4F8/Ar plasmas by combining a surface reaction model including the consideration of the neutral coverage with a cell removal method.Results show that CFx+, C2Fx+, C+, Ar+, F+ are dominant ions in the SiO2 etching progress in the C4F8/Ar plasma. And all these ions in the center of the chamber are much more than at the edges. Besides, all of the ion fluxes become larger with the pressure and power increase. At the same time, the discharge parameters, including discharge pressure, rf power, gas mixture ratio, bias voltage and frequency, duty ratio, have synergistic influences upon ion angular distributions (IADs) and ion energy distributions (IEDs), thus further affecting the trench profiles evolution. As the time forwarding, the aspect ratio increases with the increase of the trench depth, the trench becomes shaper. It is worthy to note that, both photoresist thickness and photoresist profile slope have decisive affections on the pattern profile.