ChunRong Pan

Response Policies to Process Module Failure in Single-Arm Cluster Tools Subject to Wafer Residency Time Constraints

In semiconductor manufacturing, wafer residency time constraints make the scheduling problem of cluster tools complicated. A process module (PM) in cluster tools is prone to failure. It is crucial to deal with any such failure in a proper and timely manner. If there are feasible periodic schedules in operating a cluster tool before and after a PM failure, it is desired to make it operate continuously when such a failure occurs. However, due to wafer residency time constraints, it is highly challenging to control a tool such that it can be correctly transferred from a feasible schedule before failure to another after it. To solve this problem, a Petri net model is developed to describe the dynamic behavior of a single-arm cluster tool and failure response policies are proposed. The proposed policies are formulated via simple control laws for their easy implementation. Examples are given to show them. Note to Practitioners-For single-arm cluster tools with wafer residency constraints, this work proposes the response policies when a PM fails in wafer fabrication. With a Petri net model, when there are feasible cyclic schedules for both before and after failure, policies are presented to respond to a PM failure such that the wafers in a tool can be completed in a feasible way. The policies require polynomially complex calculation and can be implemented on-line to satisfy the real-time requirements. Therefore, they are applicable to practical semiconductor manufacturing systems.

How to Respond to Process Module Failure in Residency Time-Constrained Single-Arm Cluster Tools

Cyclic scheduling and operation of a residency time-constrained single-arm cluster tool with failure-prone process modules are highly challenging. In some cases, when a failure occurs, there still exists a feasible cyclic schedule for the performance-degraded tool. In other cases, such a schedule no longer exists. For the latter, it is highly desired to respond to a process module failure properly such that the tool can continue working and the wafers in the tool can be completed in a feasible way. This work is the first one to study this important issue. The idea is to apply Petri nets to describe the dynamic behavior of a single-arm cluster tool. With the developed Petri net model, this paper formulates failure response policies to control the cluster tool such that it can keep working without violating any residency time constraint. The failure response policies are implemented via efficient real-time control laws. Illustrative examples are presented to show their usage.

A Novel Algorithm for Wafer Sojourn Time Analysis of Single-Arm Cluster Tools With Wafer Residency Time Constraints and Activity Time Variation

This paper addresses the scheduling problem of single-arm cluster tools with both wafer residency time constraints and activity time variation in semiconductor manufacturing. Based on a Petri net model developed in our previous work, polynomial algorithms are proposed to obtain the exact upper bound of the wafer sojourn time delay for the first time. With the obtained results, one can check the feasibility of a given schedule or find a feasible and optimal one if it exists. Illustrative examples are given to show the applications of the proposed method.

Scheduling Cluster Tools in Semiconductor Manufacturing: Recent Advances and Challenges

Cluster tools are automated robotic manufacturing systems containing multiple computer-controlled process modules. They have been increasingly used for wafer fabrication. This paper reviews the modeling and scheduling methods for cluster tools with both nonrevisiting and revisiting processes. For nonrevisiting processes, we focus on the modeling and scheduling problems of cluster tools with different constraints. Then, their solution methods are reviewed and compared. For revisiting processes, this paper first discusses the scheduling problem of some general manufacturing systems with revisiting. Then, the modeling and scheduling methodologies used to solve the scheduling problems of cluster tools with revisiting processes are reviewed. Future research directions and conclusions are finally discussed.Note to Practitioners—Semiconductor manufacturing systems are among the most advanced and complicated manufacturing systems. Their key equipment is highly automated robot-based cluster tools. With wafer residency time constraints, wafer revisiting, activity time variation, chamber cleaning requirements, and failure-prone process modules (PMs), it is very challenging to schedule and control them. This paper surveys their modeling and scheduling methods. Scheduling them requires one to schedule their robot tasks and processing activities simultaneously. Owing to wafer residency time constraints and the lack of buffers among PMs, it is difficult to conduct their optimal scheduling. This paper presents a thorough review of the state-of-the-art research results about modeling and optimal scheduling of clusters tools and indicates the future research directions.

Modeling and scheduling of cluster tools dealing with wafer revisiting: A brief review

For some fabrication processes, such as atomic layer deposition, wafers need to visit some process modules for a number of times, instead of once, thus leading to a revisiting process. It is complicated to schedule cluster tools with wafer revisit in semiconductor fabrication. This paper briefly discusses the modeling and scheduling issues for cluster tools dealing with a revisiting process. Then, we review and compare the methods for their modeling and scheduling. Finally, future research directions and conclusions with a revisiting process are finally given.

Schedulability analysis for dual-armed cluster tools with mixed-processing of multi-variety wafers

Wafer fabrication tends to small batch, and single wafer processing is effective in cluster tools. With the decrease of processes, redundant processing modules are adopted to improve the utilization of cluster tools. The scheduling of mixed-processing of multi-variety wafers should be developed for dual-armed cluster tools. Based on resource oriented Petri net model, we analyze the process by the traditional swap strategy, then wafer processing cycle time and robot cycle time are obtained. A theorem of the schedulability is achieved by analyzing the processing parameters of multi-variety wafers. The schedule is obtained by a scheduling determining programming. Finally, illustrative examples are presented to show the usage of the programming.

How to start-up dual-arm cluster tools involving a wafer revisiting process

For some wafer fabrication processes, e.g., atomic layer deposition, wafers need to visit some process modules for a number of times instead of once, which leads to a revisiting process. It is complicated to schedule cluster tools with wafer revisiting in semiconductor fabrication. Most studies on cluster tool scheduling aim to find the optimal steady state schedule. However, the recent trend to run small batches of different wafers has raised more needs for efficient start-up and close-down processes of cluster tools with wafer revisiting. This paper introduces two scheduling strategies to schedule the start-up transient process. After the tool finishes it from the idle state, it reaches a required steady state from which an optimal one-wafer cyclic schedule can be put into use. An industrial case is given to show the applications of the obtained results.

Simulation modeling and visualization of start-up transient processes of dual-arm cluster tools with wafer revisiting

The trends of increasing wafer diameter and smaller lot sizes from 25 wafers to a few wafers have led to more transient periods in wafer fabrication, thereby requiring more research on the optimal execution of transient processes. For some wafer fabrication processes, such as atomic layer deposition (ALD), wafers need to visit some process modules for a number of times, instead of once, thus leading to a so-called revisiting process. Research on transient processes of dual-arm cluster tools with wafer revisit processes becomes urgently needed for high-performance wafer fabrication. A cluster tool has no buffer except its robot, which makes its scheduling difficult. Thus, in order to study a cluster tool with revisiting process, a simulation system is helpful. This work develops a simulation model and system for a dual-arm cluster tool with a wafer revisit by using eM-Plant as a simulation platform. The resultant simulation system can be used for analysis and optimization of transient processes. An illustrative example is given to show its applications.

Petri net-based response policies to process module failure in time-constrained single-arm cluster tools

For wafer fabrication, a process module (PM) in cluster tools is prone to failure. It is crucial to deal with such failure in a proper and timely manner. With residency time constraints, if there are feasible periodic schedules in operating a cluster tool before and after a PM failure, it is desired to make it operate continuously when such a failure occurs. A Petri net model is developed to describe the dynamic behavior of a single-arm cluster tool and failure response policies are proposed to deal with a failure. The proposed policies are formulated via simple control laws for their real-time and on-line implementation. An example is presented to show their application.