Integer programming-based real-time dispatching (i-RTD) heuristic for wet-etch station at wafer fabrication

A real-time dispatching heuristic derived from an optimal binary integer programming model (i-RTD) to minimise the makespan of the automatic wet-etch station (AWS) scheduling problem with a chemical draining constraint is presented. Each chemical bath is drained and refilled every several days. This draining process, known as chemical dumping in the industry, occurs during the middle of a process and interrupts production. This chemical draining event creates a need for intelligent flow shop scheduling so that all baths are optimally utilised and so that jobs can skip a bath being drained and move to the next bath without interruption. The production losses from these interruptions can be minimised by optimally sequencing jobs before they enter the AWS. This paper first creates the binary integer programming (BIP) model to exactly describe the AWS scheduling problem, which later forms the basis for the i-RTD model to generate an efficient solution in real time. This unique heuristic accounts for the chemical draining constraint, time window constraint, zero wait constraint, and real-time constraint and represents a new dispatching paradigm of considerable practical interest.