1. Purpose of the gate
First wafers are a short review with a clear purpose: confirm the wafers are the ones the plan needs, see the first wafer-level results, and confirm the lab is ready to characterise them safely and correctly. Measurements of power devices at high voltage and current are only as good as the benches and fixtures used, so readiness matters as much as the wafers.
Wafer-level results give the first view of yield, threshold, leakage, on-resistance and breakdown distributions and how they link to material defect maps. Surprises here, such as a broad threshold distribution or low breakdown at the wafer edge, change the characterisation plan and may trigger process investigations before samples are built.
The gate criteria are wafers received, wafer-level parametric results and the characterisation plan and fixtures ready. No key decision is frozen here.
The review also sets expectations for what the first wafers can and cannot prove. They show whether the frozen baseline builds the intended device and give a first view of spread, but they come from a small number of lots, often from one material lot, so they cannot yet support guaranteed datasheet limits or qualification. The characterisation plan should say how later lots, ideally from different material lots and fab runs, will be added before limits are set, and which early results will be treated as learning only.
Safety is part of readiness. Power device benches store energy in capacitor banks and apply voltages that are lethal, and destructive ruggedness tests can make devices fail violently. The review confirms that interlocks, enclosures, discharge procedures and trained operators are in place for every bench the plan uses, including any external lab.
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