Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1998-11-09
2001-06-05
Grant, William (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S097000
Reexamination Certificate
active
06243612
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a processing system and more particularly relates to a processing system, such as a semiconductor manufacturing system, that includes a scheduling system for scheduling processing of lots based on a composite ratio which focuses on selected process scheduling factors such as, processing system efficiency, such as, providing continuous work to constraint resources in the processing system, and on other process scheduling factors such as customer factors and market factors which may influence scheduling of processes.
2. Description of the Related Art
Processing systems such as manufacturing systems often utilize one or more manufacturing lines or process paths, each having a variety of equipment stations to convert lots of material into useful articles. The lots of material may be any raw material, processed material, components, or other tangible item. Typically, each lot is transported to stations, and each piece of equipment at each station carries out a specific operation or process on the lots. In a reentrant processing system, one or more process paths proceed from a station and reenter or return to that station at some later time for further processing subsequent to processing at that station or at another station. For example, in a semiconductor manufacturing system, lots, which in such case are generally silicon based wafers, may flow along a process path of a cleaning equipment station, photo lithographer equipment station, to an etching equipment station, to an implanter equipment station, return to the cleaning equipment station, return to the photo lithographer equipment station, and so on until a complete integrated circuit is manufactured.
Careful scheduling of process operations at stations in process paths is generally essential to such a system operating efficiently. Processing systems such as semiconductor manufacturing facilities and other facilities where process paths include multiple equipment resources are generally especially sensitive to lot processing scheduling issues. Thus, industries have expended a tremendous amount of effort in extensively utilizing resource planning to increase processing efficiency by appropriately scheduling processing of lots.
Some sophisticated scheduling systems coordinate facility wide planning by globally defining the manufacturing process. Such facility wide planning typically includes identifying constraint resources, also commonly referred to as bottleneck operations. An equipment station is considered a constraint resource if its remaining available production capacity is relatively small such as less than about five per cent (5%). It is a generally accepted theory that manufacturing efficiency and thus overall manufacturing system capacity is determined by constraint resources. The need to avoid starvation, i.e. idle time or queue depletion, of a constraint resource, is discussed in Goldratt, Eliahu, “Theory of Constraints”. Thus, an overall approach to increasing the efficiency of a manufacturing system attempts to ensure that constraint resources are “fed”, i.e. lots are provided to the constraint resource, by ensuring that queues of lots are replenished at the constraint resource so as to keep usage of the constraint resource as close to one hundred per cent (100%) as possible.
In the manufacturing process, queues of lots are distributed among various equipment resource stations in accordance with the process stage of each particular lot. The process scheduling of such lots are often driven solely by customer due dates. However, dispatching of lots at the stations for processing by the respective stations solely in accordance with customer due dates does not always result in optimal constraint resource utilization especially in a highly reentrant processing system. Additionally, conventional scheduling systems especially in highly reentrant processing environments, have typically proved inadequate in maintaining high usage of constraint resources.
SUMMARY OF THE INVENTION
In one embodiment of the present invention, a processing system includes a scheduling system which schedules processing of lots at stations in the processing system based on a composite ratio for each lot of process scheduling factors. The composite ratio of each lot, in one embodiment, provides a single measure for each lot that is based on multiple process scheduling factors such as manufacturing efficiency, customer delivery due dates, and other relevant process scheduling factors such as market factors.
In one embodiment, a scheduling system utilizes a composite ratio for each lot which is a function of respective process scheduling influencing factors that determine a process scheduling order for the lots on a station by station basis. One such factor is, for example, a measure referred to as a ‘hunger ratio’ which relates to processing system efficiency. The hunger ratio of each lot is utilized by a scheduling system to facilitate processing system efficiency by driving lots of inventory to all occurrences of a defined constraint resource(s) in the processing system to prevent starvation of the constraint resource(s). Another illustrative factor is a ‘critical ratio’ of each lot. The critical ratio focuses on a due date for the completion of all processing on a lot, and, thus, drives lot process scheduling toward such completion due dates. Another illustrative factor is a ‘market factor’ for each lot. The market factor influenced the scheduling system to drive lot process scheduling based on market factors such as relative customer importance and market sales price.
In one embodiment of the present invention, a scheduling system combines the hunger ratio with at least one other process scheduling influencing factor such as the critical ratio and/or market factor of each lot to generate respective composite ratios which are used to determine the processing order of lots queued among stations in a processing system. Each scheduling influencing factor may be weighted to assign the desired influence of each process scheduling factor on the composite ratio., The composite ratio, in one embodiment, provides a scaleable measure upon which to base lot processing scheduling.
In one embodiment, the hunger ratio is generally defined as a ratio of the time, TNBNLy, in which a lot Ly will be needed at the next constraint resource in the lot's process path to the time expected for a select lot to arrive at the next constraint resource based on the select lot's current stage on the process path. TNBNLy is, in one embodiment, defined by the aggregate processing times by the next constraint resource of lot Ly of all lots proceeding to the same next constraint resource as lot Ly that have a planned cycle time which is less than the planned cycle time of the select lot. In one embodiment, the planned cycle time of lot Ly is the estimated time needed for lot Ly to proceed from the lot's current station after processing by the station until lot Ly arrives at the next constraint resource. Other processing stations may be interposed between the lot Ly's current station and the next constraint resource. Additionally, TNBNLy may be reduced by a time safety buffer of the next constraint resource of lot Ly by, for example, subtracting the time safety buffer from TNBNLy. The ‘select lot’ is determined in one embodiment by the desired inclusion of lots in determining the hunger ratio. In one embodiment, the select lot is lot Ly and, in another embodiment the select lot is a lot queued at the same station as lot Ly and having the greatest planned cycle time to the select lot's next constraint resource.
In one embodiment of the present invention, a method of scheduling processing of lots queued at stations including constraint resources in a processing system includes the step of scheduling processing of the lots by the stations at which the lots are queued, wherein a process scheduling order of the lots is influenced by respective hunger ratios of each lot, wh
Baker Anthony R.
Krishnaswamy Shekar
Palmeri Victor
Patel Nipa
Rippenhagen Clay L.
Advanced Micro Devices , Inc.
Cabrera Zoila
Grant William
Skjerven Morrill & MacPherson LLP
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