Lithography

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Lecture 14
Lithography

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Three Basic Exposure Methods
11 Exposure
11 Exposure
51 Exposure
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• Contact printing capable of high resolution but
  has unacceptable defect densities. May be used in
  Development.
• Proximity printing cannot easily print features
  below a few mm in line width. Used in
  nano-technolgy.
• Projection printing provides high resolution and
  low defect densities and dominates today.
  Typical projection systems use reduction optics
  (2X - 5X), step and repeat or step and scan.
  They print 50 wafers/hour and cost 5 - 10M.

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Steps in Lithography Process
Lithography has three parts (1) Light source,
(2) Wafer exposure (3) Resist
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Light Sources

• Decreasing feature sizes requires shorter ?.
• Hg vapor lamps Hg plasma inside glass lamp
• Produces multiple wavelengths
• Limited in intensity
• g line ? 436 nm (used to mid 1980s)
• I line ? 365 nm (early 1990s, gt0.3 µm)
• Deep UV by excimer lasers
• Kr NF3 (energy) ? KrF (photon emission)
• KrF ? 248 nm (used for 0.25 µm)
• ArF ? 193 nm (used for 0.12 µm)