SiO2 etch-damage mitigation in fluorocarbon C4F8 plasma: CFx polymer deposition and polyatomic ion effects

Fluorocarbon plasma etching is studied in terms of damage mitigation in a SiO₂/Si (silicon dioxide/silicon) stack. The SiO₂ etch is performed by C${}_4$F${}_8$ or CF${}_4$ plasma, generated by low-pressure capacitively-coupled discharge. The etch damage is characterized as the SiO₂/Si interface defects, which are examined through the carrier lifetime of Si. The damage is mitigated for the C${}_4$F${}_8$ plasma etching, where CF${}_x$ polymer deposition on the etch surface plays an important role. Besides, polyatomic ions, i.e., C${}_x$F${}_y^{+}$, are considered to play a role in the damage mitigation, since they are limited to penetrate into the SiO₂ layer, deeply. The damage recovery is also studied in hydrogen (H${}_2$) annealing. The recovery is limited for the CF${}_4$ plasma etching, where the F-atom residues are considered to react with hydrogen, preventing the damage recovery.