TSMC experimenting with rectangular wafers vs. round for more chips per wafer

Original Article ↗ Hacker News Discussion ↗

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.