Powerful. Efficient. Smart.
Scheduling is here
In the early days of semiconductor manufacturing, "Scheduling" meant teams of people poring over lot lists and routes and discussing how to run WIP for the day. As factories grew in size, such an approach became impractical, necessitating technological help. The development of dispatch logic provided a stopgap solution to the scale problem. With dispatch logic, operations could forget about the complexity of the rest of the factory and focus on defining optimal local rules for running the WIP at station. The computational power and data repository hardware required to do more than this well was lacking at the time.
Until now. The FPS Scheduler uses advanced algorithms leveraging practical constraints and real time information to make a schedule based on current conditions and priorities. The schedule updates every few minutes, guaranteeing continuously relevant results amidst the dynamic conditions of the Fab.
FPS schedules more than 1,000,000 wafers per day in semiconductor factories AROUND the world.
Scheduling is not Dispatch
Dispatch rules have worked well. When maintained by skilled programmers and operators, they provide impressive efficiency. They are generally fast to execute, comprehend local priorities, and provide more consistent behavior than purely manual decisions. However, their drawbacks are considerable:
- Dispatch rules do not forecast results. If I run this lot now, will it be able to finish its queue timer 6 steps from now?
- Each local step must have its own logic, which can be out of sync or in conflict with upstream or downstream rules.
- Rules are difficult to quickly adjust to changing needs
- Global business goals are difficult to formulate in the language of local dispatch rules
- Rules typically only consider lots at station, and not those arriving soon or downstream.
- The results of changing dispatch rules are very hard or impossible to test in advance
- Look ahead. A scheduler will stop a lot if a queue timer will expire.
- See the whole line. Factors like line balance, down toolsets, WIP holding are comprehended.
- Incorporate setup changes, reticle switches, movement penalties, etc.
- Comprehend upcoming maintenance events
- Provide true balancing of local and global priorities
- Facilitate centralized business logic, and give Fab managers the controls
- Allow changes to be tested hypothetically, without affecting production
- Open up smart manufacturing integration opportunities - A system that "knows" where WIP will be creates opportunities for managing pumps, abatement units, etc.
Facility and Area Scheduling
For small fabs, a single Area Scheduler can be powerful enough to schedule all the WIP in the facility.
For most high volume fabs, FPS will install a group of several Area Schedulers working together. Area Schedulers feature modular logic to accommodate the specific complexities of the area being scheduled - Lithography, Diffusion, Implant, etc. They also talk to each other to produce behavior requiring multi-area and global priorities.
The end result is that you are able to see where any lot will process, based on real time tool status, recipe qualifications, and lot status, over the next 12 hours.
The Scheduler Gantt Chart shows when and where lots will run, but equally importantly, it shows how the decision was made.
The UI will display the reasons that led to the placement of the lot on the schedule, broken down by the importance of each priority. If you disagree with the Scheduler's decision, you can see how to adjust priorities in order to change it.
Intuitive Controls, Easy Testing
Scheduling priorities are set with a simple UI with clear explanations, The UI includes a full sandbox to test the effects of changing priorities. Compare this to the problem of quantifying the effects of changing dispatch rules. It has truly never been this easy.
Not just a replacement, but something new
FPS Schedulers open up entirely new factory capabilities. Consider an example of a tool with an expensive abatement system that Fab managers have targeted for cost reduction. The system has a warm down mode which reduces the cost of operation by 95%, but that is only used during tool PMs. The FPS Scheduler can schedule around the tool when possible and with the right system integration can automatically trigger the abatement warm down when the tool is not needed. Like turning off the lights when leaving a room - big, expensive, environmentally unfriendly lights.
Bottom line: the opportunities created by FPS Schedulers showcase the next generation of factory technology.
When was the last time you had a strong lever for line balance? Or a quick way to stop a WIP bubble from forming due to an unexpected bottleneck tool downtime? Or an easy way to run your tool that requires a particular pattern of lots?
We have seen impressive achievements with variations on dispatch logic, and there is no question that full factory scheduling is a difficult problem requiring a lot of hard work. However, this is all the more reason to choose the right tool to invest the time in. Installing FPS schedulers in a large Fab can take up to a year. But that year of time pales in comparison to the equivalent years spent updating and maintaining less powerful solutions only to deliver less optimal results.