In semiconductor industry, cluster tools are widely used in wafer manufacturing, especially in wafer fabrication. Many previous researches have dealt with conventional architecture of cluster tools, which are single-arm and dual-arm. Recently, a new cluster tool architecture has been introduced to improve productivity and quality of wafers. The new architecture is called independent dual-arm.
In previous researches, conceptual design of independent dual-arm is proposed as well as new sequences, which are transformed versions of conventional sequences. The sequences are Modified Swap and Dual-backward sequences. By utilizing independent dual-arm with proposed sequences, improvement in performance has been observed. However, when wafer delay constraints are given, scheduling gets more complex and the sequences may not be feasible. Wafer delay is caused when a processed wafer is left not taken by a robot arm, and residual heat, gas, and particles inside the process chamber may deteriorate the wafer’s quality. Thus, wafer delay is an essential quality factor which should be decreased, or more preferably, minimized.
In this thesis, to reconcile the issue of wafer delay constraints in cluster tools with independent dual-arm, we propose a new sequence called Disjunct Backward sequence. The sequence is based on conventional sequence, with disjoint robot tasks in a wafer flow. We also present feasibility of Disjunct Backward sequence compared to those of existing sequences. Lastly, the performance of the sequence is compared with the optimal result given by MIP model.