Step 4 of 17Material preparation
Wafer
Slicing and polishing the substrate.
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At a glance
Inputs
- Silicon ingot
- Slurry and polishing pads
- Ultra-pure water
ProcessWafer
Outputs
- Polished, cleaned single-crystal wafers
What is it?
Conversion of the cylindrical ingot into thin, flat, mirror-polished wafers that serve as the substrate for all subsequent processing.
Why is it needed?
The wafer surface must be atomically flat and defect-free — lithography later focuses features onto it with nanometre precision, and any waviness or damage degrades every device built on it.
How does it work?
The ingot is ground to a precise diameter, then sliced into thin discs with a wire saw. Slicing leaves surface damage that must be removed.
Wafers are lapped and etched to remove saw damage, then chemically-mechanically polished to a mirror finish on the device side, cleaned, and inspected.
Critical parameters
- Thickness uniformity
- Total thickness variation (TTV)
- Surface flatness / warp
- Particle count
Typical defects
- Micro-scratches
- Saw-mark residue
- Edge chips
- Particulate contamination
Equipment involved
- Wire saw
- Lapping and CMP polishers
- Wafer cleaning stations
Materials involved
- Polishing slurry
- Ultra-pure water
- Cleaning chemistries