Capacity allocation model for photolithography workstation with the constraints of process window and machine dedication

As semiconductor process technology progresses, a more rigid process requirement emerges. Process window, also known as process capability, means that a wafer needs to be processed on the machines that can satisfy its process specification. Machine dedication, means that after the first critical layer of a wafer lot is processed on a certain machine, the subsequent critical layers of this lot must be processed on the same machine, to ensure final products of a good quality. The interaction of the two characteristics makes the production plan, based on the overall capacity of workstations, very hard to implement in the real production environment. This paper, therefore, proposes an integer programming model to solve the capacity allocation problem. With the objective of load levelling, the proposed model will assign the load of each layer, of each order, to each machine, with considerations of process window and machine dedication constraints. The model can be used in practice, and the loading allocation results can be a reference for controlling load levelling and setting the release time, in a wafer fabrication plant.