1. Purpose of the gate
A move to a larger wafer, such as from 150 mm to 200 mm silicon carbide, is one of the largest cost levers a power device maker has, and one of the largest commitments. It needs capital for new or converted tools, a new material qualification, process transfer and matching, an equivalence argument, possibly requalification, and the approval of every customer who has approved the device. Public analysis, such as McKinsey on Semiconductors, describes the industry making this move for silicon carbide and the role of better wafering methods in getting more wafers from each crystal; each company still has to show the move pays for its own products.
This gate decides whether to start the transition and on what terms. It tests the business case, including yield assumptions for early larger material, which is often worse than mature smaller material at first; the plan, including which devices move, in what order and on which tools; and the qualification and notification route, which decides how long it will be before larger-wafer parts can ship to each customer.
The gate criteria are an approved wafer size business case, an agreed transition plan with its qualification scope and an agreed customer notification approach. The wafer diameter and transition scope decision is taken here and frozen at Larger wafer equivalence shown.
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