The present invention relates to a compound that is useful as an additive for improving post exposure delay stability in a photoresist composition, and a photoresist composition containing the same. In particular, it has been found that a compound of the formula: where A, R1 to R3 are defined herein, can efficiently prevent or reduce the phenomenon of a lack of pattern formation and T-topping resulting from post exposure delay (PED) by reducing influences of environmental amine compounds. PED is a disadvantage of alicyclic compounds used in the lithography process using light sources such as KrF, ArF, VUV, E-beam, ion beam and EUV.