Wafer Excursion OCAP Response Template
An OCAP, or out of control action plan, tells the operator and engineer what to do the moment an SPC chart signals. This template documents one excursion from trigger through containment, cause and tool return to production.
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Wafer Excursion OCAP Response Template
Excursion Summary
Excursion ID: EXC-2026-0417 Area: Etch Tool / chamber: ETCH-07 / Chamber B Chart: Post-etch CD, Xbar-R, product PMIC-180-R2 Trigger: 8 points one side of the center line Detected on: 2026-10-19
Immediate Actions (first hour)
| Action | Done | By | Time |
|---|---|---|---|
| Stop tool from processing production lots | |||
| Place affected lots on MES hold | |||
| Notify process, equipment and area manager | |||
| Preserve tool logs and sensor data | |||
| Identify lots processed since last good point |
Lots at Risk
A24Q1187.1, A24Q1188.2, A24Q1190.1 on hold. Four lots in queue before ETCH-07 diverted.
Root Cause Investigation
Suspected root cause: Chamber B pressure controller drift after PM on 2026-10-15. Suspect throttle valve calibration offset.
Evidence reviewed (PM history, alarm log, recipe change log, material change): ______________________________________________
Corrective and Preventive Action
Corrective action: Recalibrate throttle valve, run qualification wafers, confirm CD and uniformity back within limits before releasing the tool.
Action owner: Etch equipment engineer
Preventive action (chart rule change, PM checklist update, interlock): ______________________________________________
Tool Return to Production
| Requirement | Result | Verified by |
|---|---|---|
| Qualification wafers within limits | ||
| Monitor chart back in control | ||
| Lot dispositions complete |
Approvals
OCAP structure varies by fab. Use this as a starting layout and align the trigger list with the rules in your SPC system. It is a documentation aid, not a replacement for your site excursion procedure.
Connect excursion data to your ERP and MES
Optional: discuss querying SPC, MES and maintenance history together, privately.
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How to use the OCAP template
Start the form the moment a chart violates a rule, not after the investigation. Capture the tool, chamber, parameter and the exact rule that fired. Work the immediate actions table first: stop the tool, hold the lots, notify, preserve data. Then fill in lots at risk, suspected cause and corrective action. Export to PDF or Word for the excursion file. The tool return table forces an explicit condition for putting the equipment back into production, which is often missing when engineers rely on memory.
- Open the form when the alarm fires
- Name the rule violated, not just the chart
- Preserve tool logs before they roll over
- Define return-to-production criteria in writing
Rules that trigger an OCAP
Most fabs use a subset of the Western Electric or Nelson rules on monitor and product charts: one point beyond three sigma, two of three beyond two sigma, eight points on one side of the center line, or a run of six rising or falling points. Spec limit violations and probe yield drops are treated separately and often escalate faster. The template lists these so the trigger is recorded precisely. Choosing the wrong rule set causes either alarm fatigue or missed drifts, so review which rules your SPC system enforces and keep this list in sync.
Finding the lots at risk
The costly question in any excursion is which wafers ran since the process was last known good. Work backwards from the alarm to the last in-control monitor, then list every lot processed by that tool and chamber in between. Include lots currently in queue so they can be diverted. Compare this with what has already moved downstream, because some lots will be past the next metrology step and need inline inspection or probe data to confirm. Record the count and hold status for each lot in the lots at risk field.
Common mistakes
Engineers often fix the symptom and skip the preventive step, so the same drift returns after the next PM. Others release the tool on a single passing wafer instead of the qualification plan. Another frequent miss is failing to ask whether a recent PM, recipe edit or consumable change coincides with the start of the shift in the chart. Use the root cause evidence prompt to list these changes. If an excursion repeats, open a full 8D rather than extending the OCAP.
Frequently Asked Questions
What does OCAP stand for?
OCAP stands for out of control action plan. It is the predefined set of actions an operator or engineer takes when a process control chart signals, covering containment, investigation and the conditions to resume production.
Is an OCAP the same as an 8D?
Not exactly. An OCAP is a fast, structured response tied to an SPC trigger and is usually closed within hours or days. An 8D is a deeper team problem-solving report used for recurring or customer-impacting problems. Many fabs escalate from one to the other.
How long should an excursion form be kept?
Keep it as long as your quality system or customer agreements require for process records. Automotive and aerospace customers often expect several years of retention, so follow your own retention schedule.
Can I use this for assembly or test excursions?
Yes. Change the area to wire bond, die attach, molding or final test, and the chart field to the relevant parameter such as pull strength or test yield. The containment and return-to-production logic is identical.
If excursion history sits across MES, SPC and ERP maintenance records, Netray can help you query it in plain language on your own infrastructure.
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