TSMC experimenting with rectangular wafers vs. round for more chips per wafer
TSMC is reportedly exploring rectangular silicon wafers or panels to pack more chips or interposers into each unit, challenging the long‑standing reliance on circular wafers grown from cylindrical ingots. Commenters weigh the potential gains in usable area, simpler lithography staging, and reduced edge-waste against major process hurdles such as spin coating uniformity, equipment retooling, and the entrenched 300 mm round‑wafer ecosystem. There is broad agreement that raw silicon cost is now minor compared to fabrication complexity, so any shift would hinge on whether new shapes deliver enough yield and packaging advantages to justify overhauling existing tools and standards.
Rectangular vs. Round Wafers
- Several comments note silicon ingots are drawn as cylinders, so wafers are naturally round; making rectangles means squaring the boule or cutting rectangles from circular wafers.
- Some argue this is still advantageous: squaring the boule yields large, pure silicon offcuts that can be recycled, while partial chips on circular edges are contaminated and harder to reuse.
- Rectangular wafers align better with existing X/Y positioning stages and rectangular chip layouts, potentially improving clamping, reducing acceleration stresses, and simplifying lithography modeling.
- Others point out that many process steps, especially spin coating and optics, are optimized for circular wafers; uniform coating on rectangles is called “sucks” and non‑trivial.
Cost, Waste, and Value
- Multiple posts emphasize that raw silicon cost is negligible compared to finished chip value.
- Example figures in the thread: tens of dollars for 200–300 mm blank wafers vs. hundreds of thousands to around a million dollars of value per 300 mm wafer for high‑end GPUs.
- Therefore, improving usable die count (especially avoiding edge partial dies) matters far more than saving raw silicon.
Interposers and Panels
- One clarification: this move may be about large rectangular panels for interposers, not traditional chip wafers.
- Interposers are now bigger than individual chips; using circular wafers leads to significant wasted edge area.
- For interposers, ultra‑perfect silicon isn’t required; continuous ribbons like those used for solar cells could be sliced into rectangular panels and then finished with a thin high‑quality surface.
Alternative Shapes (Hexagons, Triangles, 3D)
- Hexagonal wafers or chips are discussed but generally dismissed:
- Hard to dice with long straight cuts; require complex, multi‑direction cuts across a fragile wafer.
- Triangular chips tessellate but give no clear advantage and complicate design and tooling.
- Some speculative 3D concepts (cube chips with coolant channels, “shells” nesting into spheres) run into heat dissipation and manufacturing complexity concerns.
Process and Industry Inertia
- Round process chambers (etch, deposition) are valued for uniformity; square chambers are expected to pose challenges.
- The industry’s deep investment in 300 mm circular wafers is seen as a major barrier to change.
- A lithography engineer notes only upsides for rectangles in their domain but doubts widespread adoption will be fast.
Economics and Foundry Relationships
- Comments suggest large customers (e.g., major device and GPU makers) prepay or co‑invest in fab capacity and sometimes even own specific machines, helping fund radical equipment changes.