Uniform light exposure of positive photoresist for replicating spiral groove in plastic substrate

In a method for replicating a spiral groove pattern comprising the steps of:

• optical or electron beam recording the pattern in a positive photoresist layer;
• developing the photoresist layer by removing areas of said layer which have been optically or electron beam exposed so that the recorded pattern is reproduced in the photoresist layer;
• transferring the pattern to a metal layer;
• and
• forming the pattern in the surface of a plastic substrate;
• the improvement which comprises the additional steps prior to transferring the pattern to the metal layer of:
• uniformly irradiating the photoresist surface layer with light for sufficient time so that the surface layer of photoresist becomes soluble in a solvent developer;
• and
• removing the irradiated photoresist surface layer so that undercutting and formation of a cusp between the photoresist walls and the photoresist top surface are substantially prevented.