CMP and cleaning

What is the role of the retaining ring that surrounds the wafer in a CMP polishing head?

  1. ATo cool the wafer
  2. BTo color the slurry
  3. CTo hold the wafer so it does not slip out during polishing and to reduce polishing variation at the wafer edge
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Answer: C. To hold the wafer so it does not slip out during polishing and to reduce polishing variation at the wafer edge

The retaining ring surrounds the edge of the wafer held in the polishing head. It prevents the wafer from slipping out sideways during polishing and presses down on the pad to limit pad deformation at the wafer edge, reducing variation in removal near the edge.

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More CMP and cleaning questions

  1. Why are particles, once detached, unlikely to redeposit in alkaline cleaning solutions such as SC-1?
  2. What problems are caused by metal contamination such as iron and copper on the wafer surface?
  3. What is the main cause of fine scratches on the wafer surface in CMP?
  4. To prevent fine structures from collapsing, which method removes native oxide and the like without using liquids?
  5. Which combination correctly lists processes in which CMP is used?