UNIT 5 • INGOT TO WAFER

From ingot to wafers

The ingot is trimmed, ground to an exact diameter, marked with a notch, and sliced into thin discs by a diamond-coated wire saw. Each slice becomes one wafer.

One ingot yields hundreds of wafers.

THE FINISHING LINE

A typical order of steps

Crop and test Remove the ends and check resistivity and crystal quality

Grind and mark Grind to exact diameter and add the notch

Slice A diamond wire saw cuts the ingot into wafers

Round and lap Round the edges to prevent chipping, then lap flat

Etch Chemistry removes the damaged surface layer

Polish Chemical-mechanical polishing gives a mirror finish

Clean and inspect Remove particles and check flatness and defects

Each step removes damage caused by the one before it.

NOTCH AND FLATS

A mark that says which way is up

notch → orientation

300 mm wafers carry a tiny notch that tells equipment how the crystal lattice is oriented; smaller wafers use a flat edge instead. Tools use it to align each wafer so that layers and cuts line up with the crystal.

Every wafer, in every tool, is aligned to its notch.

WAFER SIZES

Bigger wafers, more chips

150 mm · 6 inch About 675 µm thick

200 mm · 8 inch About 725 µm thick

300 mm · 12 inch About 775 µm thick

Area jump A 300 mm wafer has about 2.25 times the area of a 200 mm wafer

450 mm Proposed, but the industry never adopted it

Thickness grows with diameter so the wafer stays strong enough to handle.

SPECIAL WAFERS

Not every wafer is plain

💿

Polished (prime)

The standard starting wafer: polished and cleaned, ready for the fab

🌱

Epitaxial

A thin, extra-perfect crystal layer grown on top, for demanding devices

🥪

SOI

Silicon on insulator: a buried oxide layer under a thin silicon film, to cut leakage

The starting wafer can already contain a layer that helps the device.

HOW FLAT IS FLAT?

Smooth beyond belief

sub-nanometer smooth

A polished wafer is smooth to well under a nanometer, and flat to within a tiny fraction of a micrometer across each exposure site. Lithography focuses light very precisely, so any bump would blur the pattern.

Flatness isn't cosmetic: it's what lets tiny patterns print sharply.

UNIT 5 STUDY COMPLETE

💿

Ready for the Fab Challenge?

You can trace an ingot through slicing, lapping, polishing, and inspection.