Scheduling Single-Armed Cluster Tools With Chamber Cleaning Operations

Abstract

As wafer circuit widths shrink down, wafer fabrication processes require stringent quality control. Therefore, fabs recently tend to clean a chamber after processing each wafer, in order to remove chemical residuals within the chamber. Such chamber cleaning, called purge operation, increases scheduling complexity in robotized cluster tools. In this paper, we examine scheduling problems of single-armed cluster tools with purge operations for series-parallel chambers. By extending the wellknown backward sequence, we propose a backward(z) sequence that allows partial loading for parallel chambers, where vector z specifies how many chambers z i of each process step i are kept empty for cleaning. We then propose a way of finding optimal vector z * and identify when backward(z * ) achieves the minimum cycle time among all possible sequences. We present experimental results on the accuracy of backward(z * ).Note to Practitioners-Wafer processing of circuits with extremely small circuit widths is subject to contamination by residual chemicals within chambers. Therefore, in leading fabs, 50%∼80% of cluster tools for etching, wafer cleaning, chemical vapor deposition, and physical vapor deposition processes clean chambers each time a wafer is processed. Such cleaning operation complicates tool operation and hence makes conventional scheduling rules inefficient. Our proposed simple modifications of the conventional backward sequence significantly improve the throughput rate of cluster tools. They are easy to implement.

Scheduling of Single-Arm Cluster Tools with Residency Time Constraints and Chamber Cleaning Operations

“…This work deals with a scheduling problem for SACTs with WRTCs and chamber cleaning operations which are commonly seen requirements in real semiconductor manufacturing. Different from the studies on scheduling SACTs with purge operations in [22], this work focuses on a more general case in which a chamber at a PM may process more than one wafer before a cleaning operation is required. To do so, this work presents a virtual wafer-based method such that a PM processes either a real wafer or a virtual wafer at a time.…”

“…Thus, if V = 2 holds after Statement ( 18) is performed, R and V are updated by Statements (20) and (21), respectively. In addition, V 0 is updated to be one by Statement (22). By Statement (23), if V 0 = 0, it means that there does not exist two virtual wafers to be consecutively processed by a PM during two adjacent wafer loading sequences so as to meet the chamber cleaning requirement for the PM.…”

“…Chamber cleaning is necessary for wafer quality, but this makes the scheduling problem more challenging. Yu et al [22,23] present an interesting idea of partially loading wafers into parallel PMs at a step for SACTs and DACTs with chamber cleaning requirements. By doing so, parallel PMs can be alternately cleaned.…”

“…However, it is also important to consider a more general case in which a chamber in a PM is required to be cleaned after a specified quantity of wafers is consecutively processed, which arises from practical wafer fabrication cases. For such a case with WRTCs being considered at the same time, the existing method in [22,23] is no longer applicable. Thus, this work aims to solve such a new and challenging problem for SACTs with WRTCs and chamber cleaning operations by proposing a virtual wafer strategy.…”

Efficient Approach to Cyclic Scheduling of Single-Arm Cluster Tools With Chamber Cleaning Operations and Wafer Residency Time Constraint

“…It is known that, in a leading fab, purge is adopted for 50%80% of the tools that are used for etching and chemical/physical vapor deposition. The purge takes time from 30300 seconds [36].…”