A mixed dispatching rule for semiconductor wafer fabrication

The critical ratio (CR) is often used as the dispatching rule for semiconductor wafer fabrication in integrated circuit (IC) foundries, although this not consider the fact that different products may have different processing times. In general, products with long processing time ought to be prioritised. However, CR would give various products the same priority, which may cause the problem that some products cannot be delivered on time. This study thus proposes a mixed dispatching rule in prioritising the work in process for wafer fabrication, which uses historical production data to classify products first, and then employs CR to give different weights to products based on their lengths of processing time, to optimally utilise production resources and thus enhance order fulfilment. The empirical results show that the mixed dispatching rule, which considers both the delivery and processing times of products, outperforms the first in first out, earliest due date, and CR dispatching rules.