e-journal

Scheduling Cluster Tools for Concurrent Processing of Two Wafer Types

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We examine a scheduling problemof cluster tools that concurrently process two wafer types in a cyclic operational sequence. Whereas the process steps for different wafer types are assigned to different processing modules (PMs), the wafer loading and unloading tasks at the PMs are performed by a single robot. For a given cycle plan, which is a mix of different wafers for each cycle, we wish to determine the robot task sequence so as to minimize the tool cycle time. When a single wafer type is processed, the backward and swap sequences are optimal for single-armed and dual-armed tools, respectively. They are being prevalently used because of their simplicity and robustness. To maintain such advantages
in concurrent processing, we introduce and define the concurrent backward and swap sequences (CBSs and CSSs, respectively). We then develop conditions on process times, robot task times, and the number of wafers produced in a cycle for which such CBSs and CSSs are still optimal for concurrent processing.
We also show that, for some special cases, the two wafer types can achieve their maximum throughput rates as if each wafer type exclusively uses the tool regardless of other wafer types in progress.
When the developed conditions do not hold, an effective mixed integer programming (MIP) model based on the CBSs and CSSs is used for robot task sequencing. Finally, we experimentally verify its efficiency and effectiveness by comparing to the existing scheduling methods for optimal scheduling of cluster tools.
Note to Practitioners—A cluster tool consists of several processing chambers, typically six or more, and a single wafer handling robot. It has complex robot task scheduling issues because of its configuration. Cluster tools use simple scheduling rules such as the backward and swap sequences that are developed for processing identical wafers. Recent fabs increasingly use only two or three process steps for processing wafers of an identical type while there are six to eight chambers in a tool. Therefore, they tend to process several different wafer types concurrently in a tool in order to better utilize the chambers. Since tools mostly use the simple backward or swap sequence, we wish to know whether they are still optimal for concurrent processing. We present conditions on process times, robot task times, and the number of wafers produced in a cycle for which the backward and swap sequences
are still optimal. The conditions also suggest how many wafers of each type in a cycle should be produced to maximize the utilization of a tool. When the conditions are not met, we develop an efficient
MIP model based on the backward and swap sequences.With this MIP, most practical problems can be solved instantaneously as compared to the existing methods.
Index Terms—Cluster tools, concurrent processing, cyclic scheduling, mixed integer programming, two wafer types.

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Informasi Detail

Judul Seri

IEEE TRANSACTIONS ON AUTOMATION SCIENCE AND ENGINEERING

No. Panggil

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Penerbit

New York : IEEE., 2014

Deskripsi Fisik

IEEE TRANSACTIONS ON AUTOMATION SCIENCE AND ENGINEERING, VOL. 11, NO. 2, APRIL 2014

Bahasa

English

ISBN/ISSN

1545-5955

Klasifikasi

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Tipe Isi

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Tipe Media

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Tipe Pembawa

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Edisi

VOL. 11, NO. 2, APRIL 2014

Subjek

TEKNIK

Info Detail Spesifik

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Pernyataan Tanggungjawab

Yuli/Agus

Versi lain/terkait

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