TRANSPORT SYSTEM DESCRIPTION - 晶圓廠自動化物料搬運系統之搬運策略模擬研究

3.1 Transport Facility

Generally, the 300mm AMHS is implemented as many separate loops and spreading up from a centre loop. In which the separate loops, intrabay systems take charge within bay transportation, and the centre loop, interbay system is responsible for transporting wafer between different bays.

All loops are located overhead to attain zero footprints in transport and minimise the fab footprint.

The wafer carrier, or front-opening unified pod (FOUP), is a kind of closed carrier with an automated door at the front side, and the vehicle, an overhead hoist transporter (OHT), is capable of carrying one FOUP at a time and has a hoisting mechanism to automatically load/unload one FOUP.

Three kinds of combination of interbay and intrabay were represented in Figure 3.1. In Figure 3.1(a), these two systems were separated loops and the tasks between different bays involved transferring by stocker. In Figure 3.1(b), these tracks were connected in front of each bay, and the return track made the within-bay transport more efficient. In Figure 3.1(c), the tracks were connected in front of each bay by turntable, but this turntable is a kind of resource restriction, because there might be some vehicles waiting for a turntable to move to interbay or intrabay, or even wait for a straight move in interbay or return to intrabay. Hence, traffic congestion occurs.

Under above combination layouts, not only can the wafer be delivered without labour for transport loading, but also that the mishandling, particle contamination and vibration shocks to the wafers can be reduced. Especially in Figure 3.1(b) and (c), FOUP can be delivered directly tool-to-tool without transferring by stocker and so decreasing delivery variation. In this research, the configuration of Figure 3.1(b) is the object of study, and the simplified layout of the object system is displayed in Figure 1.1.

OHT

(a) Separated OHT track

OHT

(b) Connected OHT track withreturn trackreturn track

return track

turn table

turn table ^OHT^OHT

Track for OHT Track direction

Load/unload direction of OHT

OHT FOUP

Port (interface) for OHT and tool/stocker

Figure 3.1 Configurations of the 300mm AMHS

The interface for vehicle to input and retrieve FOUP through stocker in the Figure 3.1(b) configuration is displayed in Figure 3.2. It shows that the transport can be flexibly operated for handling different transport requirement. For instance, vehicle A will unload one FOUP to stocker A.

It can travel on interbay track to unload that FOUP on port b, or go through intrabay track to unload on port c. The terminal port and travel path are determined based on the transport strategy.

OHT

Figure 3.2 Interface of OHT and stocker

3.2 Transport Operation

The four types of the tool-to-tool transport operation between different bays utilising different facilities are shown in Figure 3.3. The suffix number in OHT refers to the vehicle used in transporting. Which type of operation would be used is determined based on the transport strategy.

The more times to transfer FOUP through stocker, the more time are required to complete the tool-to-tool transport. And also, all types, except type 4, involve another complex stocker selection issue. However, alothought the type 4 transport needs not transfer the FOUP by stocker; the directly tool-to-tool transport requires detecting the status of both source and destination tools and the transport will be happened while destination tool requests/pulls the next one FOUP to process from source tool when it just becomes idle, which likes the JIT (Just in Time) concept. In this research, only type 4 will be considered in Search Range (SR) assignment issue, while type 3 and type 4 are considered in Integrated Dispatching (ID) issue for focusing the studies.

S o u rc e to o l

intrabay interbay intrabay

S SS

S S

D es tin a tio n to o l

(2) FSS deals with the selection of a stocker for temporarily storage due to FOUP’s next step tool, which is blocking, or the selection of an appropriate stocker for batch collection.

(3) TSF deals with the selection ofaspecificFOUP from asetofwaiting FOUP asatool’snext task.

(4) FSV deals with the selection of a vehicle from a set of available vehicles to transport a FOUP which requests to move.

(5) VSF deals with the selection of a FOUP from a set of waiting FOUP as avehicle’snextdelivery task when the vehicle just completed a task.

The dispatching operations in this study are foused on FSV and VSF, in which FSV resembles work-centre-initiated task assignment and VSF resembles vehicle-initiated task assignment in Egbelu and Tanchoco [16]. The descriptions please see Figure 3.4.

Some definitions of VD are: (1) FSV successfully means that when FSV occurs, the FOUP finds an appropriate IV and assigns it to transport. On the contrary is FSV unsuccessfully; (2) VSF successfully means when VSF occurs, the vehicle finds an appropriate WF and assigns it for the next task. On the contrary is VSF unsuccessfully. Furthermore, the statuses of vehicles include: (1) idle, which has no FOUP to transport and waits for assignment; (2) empty, which has assigned by a FOUP and just moves to pick up that FOUP; (3) loaded, which has assigned by a FOUP and is executing the transport now.

(a) FOUP-Searches-Vehicle (FSV) (b) Vehicle-Searches-FOUP (VSF)

Fa Ta Vb

Initial-FOUP Idle Vehicle (IV) Track direction Assigned vehicle Initial-FOUP Idle Vehicle (IV) Track direction Assigned vehicle

Initial-vehicle Waiting FOUP (WF) Track direction Assigned FOUP Initial-vehicle Waiting FOUP (WF) Track direction Assigned FOUP

Which IV ? Which WF ?

(1) FOUP Fa has finished the process step (2) The next step of Fa is scheduled to tool Ta (3) Which one idle vehicle to transport it to Ta ?

(1) Vehicle Vb has completed one task (2) Vb becomes available

(3) Which one waiting FOUP for the next task ?

Figure 3.4 Definition of vehicle dispatching operations

3.4 System Problem Descrition

In the literatures, the range of search to find the FOUP or vehicle for service is only in the one loop where the transport request initial, like Figure 3.5(a), (b) and (c). What the range of search when dispatching occurs in the environment likes Figure 3.5 (d) is the first issue required to treatment.

(a) Interbay study (b) Intrabay study

(d) Connected Interbay

& Intrabay study

? ?

^Stocker^Tool

Transport system for study Search Range for dispatching Stocker

Tool

Transport system for study Search Range for dispatching

Figure 3.5 Range of search in vehicle dispatching studies

Further, as the close interactions between production and transport in the fully-auto manufacturing environment, the functions of transport are not only to give service to the production requests, like moving FOUP to its downstream tool, but should carry out some activities to smooth the production for fully-supporting. Thus, it is necessary to identify the interactions between TD and VD, and to develop a transport strategy that will evaluate atool’scapability and then adjust the FOUP’stransportpriority when executing VD for better vehicle allocation.

The dispatching behavior and boundry considered in above two problems are shown in Figure 1.3, and the details please see the following sections.

在文檔中晶圓廠自動化物料搬運系統之搬運策略模擬研究 (頁 38-44)