Reducing CFx residue from Etching Process by Optimizing Post Plamsa Treatment

Fluorocarbon (CF
x
) and its hydrogenated forms (CH
x
F
y
) play important roles in fabricating high aspect ratio pattern in etching process. However, their chemical and thermal stability hinder removal of remaining residue. In this paper, we studied efficient removing of CF
x
residue by adopting N
2
post etch treatment. Typically in our platform, reacting with subsequent hydrofluoric acid (HF) cleaning, the remaining CF
x
residue possibly forms a sub-micro size particle, which drops manufacturing yield. By changing post plasma treatment gas from Ar to N
2
, F anion on the wafer surface was reduced by 79% (HPIC) and 44% within sub-layer (tof-SIMS), thereby CF
x
particle formation was completely suppressed. Controlling post etch treatment time and partial pressure of N
2
gas also revealed that chemical reaction between CF
x
residue and N* radical is the major removing factor, whereas plasma washing from ion bombardment is subsidiary. Increasing Cl
2
gas concentration in the main etching process also exhibited CF
x
removing effect, however, the particle formation was not fully reduced. In addition, we could demonstrate that controlling humidity in etching machine also affects subsequent wet cleaning efficiency of CF
x
residue.