The present invention relates to a cross-linker for use in a photoresist which is suitable for a photolithography process using KrF (248 ru), ArF (193 nm), E-beam, ion beam or EUV light source. According to the present invention, preferred cross-linkers comprise a copolymer having repeating units derived from: (i) a compound represented by following Chemical Formula 1 and/or (ii) one or more compound(s) selected from the group consisting of acrylic acid, methacrylic acid and maleic anhydride. wherein, R1, R2 and R individually represent straight or branched C1-10 alkyl, straight or branched C1-10 ester, straight or branched C1-10 ketone, straight or branched C1-10 carboxylic acid, straight or branched C1-10 acetal, straight or branched C1-10 alkyl including at least one hydroxyl group, straight or branched C1-10 ester including at least one hydroxyl group, straight or branched C1-10 ketone including at least one hydroxyl group, straight or branched C1-10 carboxylic acid including at least one hydroxyl group, and straight or branched C1-10 acetal including at least one hydroxyl group; R3 represents hydrogen or methyl; m represents 0 or 1; and n represents a number of 1 to 5.