Systems of re-entrant nature are further classified into re-entrant job shop, re-entrant flow shop, and re-entrant flow shop with permutation [4-6]. Based on this classification, semiconductor manufacturing systems are classified as re-entrant flow shops; where, every job in the line is processed on machines in the same order Mt,M2, •••Mm, M1,M2, •••Mm, M1,M2, •••Mm•