critical queue time

**Critical queue time** is the **high-priority waiting-time window where approaching expiration requires immediate scheduling escalation to avoid process violation** - it represents near-term risk state for time-sensitive lots. **What Is Critical queue time?** - **Definition**: Queue-time condition where remaining allowable wait margin is low and urgent action is needed. - **Risk Signal**: Lot transitions from normal priority to elevated priority as deadline proximity increases. - **Scheduling Role**: Drives dispatch override logic and contingency routing decisions. - **Operational Context**: Common in clean-to-furnace, etch-to-clean, and other sensitive sequence loops. **Why Critical queue time Matters** - **Violation Prevention**: Early escalation reduces probability of max-queue breaches. - **Yield Protection**: Avoids quality loss from aging-sensitive intermediate states. - **Flow Coordination**: Forces alignment between upstream start decisions and downstream capacity. - **Resource Prioritization**: Focuses attention on lots with highest immediate quality risk. - **Excursion Control**: Prevents clustered failures when bottlenecks disrupt time-critical routes. **How It Is Used in Practice** - **Risk Tiering**: Define warning bands based on remaining queue-time margin. - **Dispatch Escalation**: Promote critical lots to priority classes with protected transport and tool access. - **Precheck Rules**: Block upstream release when downstream readiness cannot support time-window compliance. Critical queue time is **an essential real-time risk signal for fab scheduling** - proactive escalation around shrinking queue margins is necessary to maintain quality and flow reliability.