The behavior of reaction products during puddle development was investigated in ultralarge-scale integration (ULSI) lithography. The concentration of reaction products originating from novolak photoresist was optically measured. Reaction products during puddle development migrated with time and gathered into cell-like structures. After 5 min from the developer puddle formation, the dissolution rate of photoresist at the cellular structures was about 10% lower than that in other areas. We examined two modified methods of puddle development in order to control the gathering phenomenon of reaction products: one is a method of agitating the reaction product by rocking the wafer, and the other is a method of heating the upper side of the developer solution. The distributions of the dissolution rate (3) for the former and latter methods were 5.9 and 5.3 nmmin, respectively. Compared with the distribution of the dissolution rate of 9.9 nmmin for conventional puddle development, both modified methods can improve the distribution of the dissolution rate. The migration of reaction products was large when the wafer temperature was high, and the Marangoni number was consistent with the critical value. Therefore, the cellular structures seem to be caused by Marangoni convection.
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