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IC manufacturing, alignment and exposure

Short answer

IC fabrication steps: wafer prep, oxidation/deposition, photolithography, etching, doping, metallisation and testing. In photolithography, alignment marks are matched optically; exposure uses contact, proximity or projection (stepper/scanner) printing with short-wavelength UV/EUV to achieve fine resolution.

What are IC manufacturing steps in semiconductor industries? Describe the alignment and exposure techniques in photolithographic process in IC fabrications.

IC manufacturing steps

  1. Wafer preparation: silicon is purified, grown into a single-crystal ingot, sliced, polished and cleaned.
  2. Oxidation / film deposition: SiO2 is grown, or poly-Si or metal is deposited by CVD or sputtering.
  3. Photolithography: photoresist is coated, exposed through a mask and developed to define the pattern.
  4. Etching: wet or dry etching removes the exposed film.
  5. Doping: diffusion or ion implantation forms n and p regions (wells, source/drain).
  6. Metallisation and interconnect: aluminium or copper wires and contacts connect the devices, with insulating layers between them.
  7. Planarisation and repeat: steps 2-6 repeat for each mask layer (20-40 times).
  8. Wafer test: each die is tested with a probe card.
  9. Dicing, packaging and final test: the wafer is cut into dies, which are mounted in packages, wire-bonded, sealed and tested.

Alignment and exposure

The mask must be aligned exactly with the pattern already on the wafer; then the resist is exposed to light.

  • Alignment: special alignment marks on the mask and on the wafer are viewed through a microscope or detected optically; the stage moves and rotates the wafer until they overlap. The overlay error must be a small fraction of the minimum feature size.
  • Contact printing: the mask touches the resist; high resolution, but the mask gets damaged and contaminated.
  • Proximity printing: the mask is held 10-25 µm above the wafer; no damage, but diffraction reduces resolution.
  • Projection printing: a lens (or mirror) system projects the mask image onto the wafer.
    • 1:1 scanning projection (early scanners): the wafer is exposed through a narrow slit while the mask and wafer scan together, with no reduction.
    • Step-and-repeat (stepper): exposes one die area at a time at 4x-5x reduction, so the mask features can be larger than on the wafer.
    • Step-and-scan (scanner): combines both; each field is exposed through a slit while the mask and wafer move in sync, at 4x reduction. It is used in advanced fabs.
  • Light source: mercury g-line (436 nm), i-line (365 nm), KrF laser (248 nm), ArF laser (193 nm, with immersion) and EUV (13.5 nm); a shorter wavelength gives finer resolution, R = k1·λ/NA.
  • The exposure time/dose must be controlled so that the resist is fully exposed and the edges are sharp.

✓ Answer checked by Claude Opus 5.5 (high effort)

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