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Gate spacers etching of Si3N4 using cyclic approach for 3D CMOS devices

In this work, we optimize a CH3F/O2/He/SiCl4 chemistry to etch silicon nitride gate spacers for 3D CMOS devices in a 300 mm inductively coupled plasma reactor. The chemistry has high directivity and high selectivity to Si and SiO2. A cyclic approach, which alternates this chemistry with a CH2F2/O2/CH4/He plasma, is investigated. Using quasi in situ x-ray photoelectron spectroscopy and ellipsometry measurements, etching mechanisms are proposed to explain the results obtained. As a result of process optimization, silicon nitride spacers with vertical profile and a small critical dimension loss of 3 nm as well as complete spacers removal on sidewalls of the active area are obtained on 3D patterns, confirming the advantages of this approach.