Recipes for Plasma Atomic Layer Etching

Summary form only given. The development of robust processes for gate plasma etching to produce desired profiles and sidewall angles is critical to future technological nodes. The gradual decrease in equivalent gate oxide thickness at future technology nodes (les 100 nm node) has necessitated process control at the atomic level. To insure this level of control, it is desirable to use a self-limiting process which is independent of the processing time. In plasma atomic layer etching (PALE), the formation of a monolayer of reactants or passivation is followed by the removal of the layer which also removes a single laver of the underlving material and so self terminates the process. A challenge of utilizing PALE is the high cost of specialized beam equipment and slow processing speed. The feasibility of using conventional plasma equipment for PALE processes was previously computationally demonstrated for Si [in Ar/Cl₂ (passivation) followed by Ar (etch)] and SiO₂ [in Ar/C₄F₈ (passivation) followed by Ar (etch)]. The Hybrid Plasma Equipment Model (HPEM) and the Monte Carlo feature profile model (MCFPM) were modified to have pulse periodic capability as required for PALE, and to kinetically resolve ion energy distributions to finely resolve threshold energies. The speed of PALE processes is limited by having to purge the different gas mixtures being employed to perform the individual steps during one cycle which removes a monolayer. Eliminating the purge step can greatly increase the speed of the process. This can be achieved if by using a single gas mixture one can perform both the passivation and etching steps with similar precision and control. In this presentation, results from a computational investigation of etching recipes are discussed. Methods are demonstrated whereby a single gas mixture (that is, no purging steps) can be used for PALE by controlling the shape of the ion energy distribution (IED). This latter control is obtained through the use of non-sinusoidal waveforms in which the IED can be narrowed to discriminate between etching thresholds.