Batch processing is only as efficient as the ability to make the necessary lots available to the operators at batch tools. Commonly, operators at batch tools request lots to be pulled from upstream operations or simply wait until they have the correct lots at the batch tool to create a batch before processing. Providing equipment operators with the ability to see available upstream lots, along with the ability to pull the specific batch lots they need into their tool for processing, maximizes operator efficiency at batch processing steps.
Example Batch Reservation Scenario Using an Automated Dispatching System
Consider a simplified scenario as illustrated in Figure 1 where squares, circles and triangles represent lot types. The batch tool needs two additional square lots to complete a batch reservation. The equipment operator sees all available lots in the line and adds the required number of square lots to the reservation list to complete this batch, even though the additional (prioritized) square lots have yet to arrive at the batch step.
An automated dispatcher can prioritize square lots at upstream dispatch lists in order to fulfill the reservation request of the downstream batch tool. When all reserved lots for the batch arrive at the batch tool, the dispatching system orders the list of available batches so that complete batches appear at the top of its dispatch list while partial batches are displayed below.
This reservation process can also help ensure that non-production “filler lots” are available to meet minimum batch load size requirements. Furnaces, for example, often require a full “tube” in order to maintain uniformity across all wafers. Filler wafers are often used when production wafers alone don’t fill the furnace. These filler wafers are reusable and require regular cleaning which may mean the quantity of available filler wafers at the batch step can fluctuate. In order to ensure these filler lots are always available, defined inventory levels may be used to increase the priority of upstream filler lots being cleaned when inventory levels at the batch tools for filler lots are low or de-prioritize filler lots when levels are acceptable.
The Value of an Automated Dispatching System
Automated dispatching systems allow equipment operators to focus on critical tasks by automating the communication processes required to keep all tools, including batch tools, fed. This is of particular value when considering the efficiencies that can be achieved when high priority lots can be batched and processed quickly. Ultimately, automated dispatching systems minimize planning efforts and maximize process flow into, through, and out of batch tool (and other tool) areas.