Abstract: A method of reducing the critical dimension (CD) of a hard mask by a wet etch method is described. An oxide hard mask is treated with a H2SO4/H2O2 (SPM) solution followed by treatment with a NH4OH/H2O2/H2O (APM) solution to trim the CD by 0 to 20 nm. With nitride or oxynitride hard masks, a buffered HF dip is inserted prior to the SPM treatment. For oxide hard masks, the SPM solution performs the etch while APM solution assists in removing plasma etch residues. With oxynitride hard masks, the APM performs the etch while BHF and SPM solutions remove plasma etch residues. The hard mask pattern can then be transferred with a dry etch into an underlying polysilicon layer to form a gate length of less than 150 nm while controlling the CD to within 3 to 5 nm of a targeted value.