Wafer Dispatch Randomization for Defect Reduction
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Solution Overview
Problem
In semiconductor fabrication facilities, the transition to single wafer processing has rendered traditional lot-based organizational techniques and dispatch rules less effective, leading to potential bottlenecks and increased likelihood of defects due to fixed processing order, especially with wafer sorters being limited resources.
Innovation Solution
A method and system for randomly selecting wafers for processing based on their queue time, using a time window technique or weighted random selection to reduce the introduction and magnification of defects, while allowing for integration of priority considerations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional FIFO dispatch rules are used for single wafer processing, then queue management is simplified, but defects compound due to fixed processing order and position-oriented defects are introduced
Solution Approach 1:
The patent applies dynamics by transitioning from static FIFO dispatch rules to dynamic randomization of wafer dispatch order. The system randomly selects wafers from the queue for processing, making the dispatch order variable rather than fixed. This dynamic approach prevents position-oriented defects from compounding while still maintaining manageable queue control through the random selection mechanism.
2Reliability
If wafer sorters are used frequently for randomization, then defect introduction is reduced, but bottlenecks occur due to limited sorter resources
Solution Approach 1:
The patent extracts the randomization function from the physical wafer sorter hardware and implements it through software-based random selection in the dispatch system. By taking out the randomization capability from the limited sorter resource and embedding it in the workflow management software, the system achieves defect reduction without being constrained by sorter availability, thus avoiding bottlenecks.
Solution Approach 2:
The patent introduces software-based random selection as an intermediary between the wafer queue and the processing tool. This intermediary layer performs the randomization function that would otherwise require physical wafer sorters, allowing the system to achieve the same defect-prevention effect without relying on limited sorter resources.
3Productivity
If lot-based organizational techniques are used, then batch processing efficiency is maintained, but single wafer processing requirements are not met
Solution Approach 1:
The patent changes the organizational parameter from lot-based grouping to individual wafer-based management. Instead of processing wafers in fixed lots, the system manages and dispatches individual wafers independently, selecting random wafers from the queue for processing. This parameter change enables adaptation to single wafer processing requirements while maintaining efficient resource utilization.
Data Source
AI summary
A method for dispatching wafers for processing in a tool includes identifying a queue of wafers available to be processed in the tool. One of the wafers is randomly selected based at least in part on a length of time each wafer has been in the queue. The selected wafer is dispatched for processing in the tool.