1. Purpose and scope
A larger wafer carries more dies for roughly the same processing effort, so moving up a diameter is one of the main levers on cost for silicon carbide. Public analysis, such as McKinsey on Semiconductors, describes the industry moving silicon carbide from 150 mm to 200 mm substrates and notes that newer wafering methods such as laser cutting can produce more wafers from each crystal. The move is not free: larger crystals are harder to grow with low defect density, epitaxy uniformity must hold across a larger area, many tools must be converted or replaced, and every customer who has approved the device must be convinced that nothing has changed that matters to them.
The purpose of this stage is to make the move with evidence. It plans the transition, qualifies larger substrates and epitaxy, transfers and matches the process, and shows equivalence of parametrics, yield and reliability between the original and larger wafers against limits set before the data arrives. Depending on the agreement with quality and customers, qualification is then read across or repeated.
The stage appears after the production ramp in the lifecycle because the move is usually made for a product or platform already in volume, under the change control of Cost-down & Sustaining, although it can also be planned during development of a new platform. In scope: the wafer size business case, the transition plan, larger-diameter substrate qualification, process equivalence, equivalence characterisation and the customer notification approach. Out of scope: the full requalification itself, which uses the methods of the qualification stage.
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