disposition decision

**Disposition Decision** is the **formal engineering and quality judgment that determines the fate of non-conforming semiconductor material** — evaluating whether held wafer lots should be released as acceptable, reworked to correct the defect, scrapped as unrecoverable, or downgraded to a lower product specification, based on technical analysis of deviation magnitude, device margin, reliability risk, and economic value. **The Four Disposition Outcomes** **Release — Use As Is (UAI)** The held material is released for continued processing or shipment despite the known deviation. Justified when technical analysis demonstrates the deviation falls within the design margin not captured in the original specification. A formal deviation justification document records the technical rationale, the responsible engineers who approved it, and any lot monitoring requirements (e.g., "require 1000-hour HTOL reliability test on 5 units from this lot"). **Rework** The defective layer or process step is reversed and repeated to bring the wafer back into specification. Viable only for reversible process steps: Reworkable: Photolithography (strip photoresist and re-coat/expose/develop), wet cleans (clean again), some thin film depositions (strip and re-deposit if substrate is not damaged). Not reworkable: Implantation (cannot remove dopants), thermal oxidation, most etches (removed material cannot be restored), anything that diffuses into the crystal lattice. Rework authorization requires analysis of rework impact, not just the original excursion impact. **Scrap** The wafers are permanently removed from production — economically the worst outcome. Scrap is the disposition when: the deviation is irreversible, device impact assessment shows unacceptable yield or reliability risk, or the cost of analysis and rework exceeds the material's remaining value. Scrap decisions at high accumulated process value require senior management approval. **Downgrade** Rather than scrapping lots that fail primary product specifications, material may be sold at a lower price point as a binned product with reduced performance specifications (lower speed, higher power), or used for test/qualification purposes internally. **Disposition Authority Matrix** Fabs define an authority hierarchy matching decision impact to authorization level: an engineer may approve UAI for 1–5 wafers with minor deviation; a senior engineer or manager for 6–25 wafers; a director and MRB for >25 wafers or high-severity deviations; executive sign-off for catastrophic excursions with major customer impact. **Disposition Decision** is **the verdict on non-conforming material** — the structured, documented, multi-disciplinary technical judgment that determines whether held wafers are safe to ship, salvageable through rework, or must be written off as lost yield.