SOURCE SYSTEM

Consists of:

• Light source - intense source (for short exposure time) with short wavelength (for high resolution)
  • High pressure arc mercury lamp
    • 2 electrodes in a high pressure mercury vapor
    • High voltage applied to accelerate electrons; Hg atoms excited by collisions with electrons, deexcite by emitting a photon
    • Wavelength depends on the energy state of the excited atom - i-line (at 365 nm) is the strongest, h-line (405 nm), g-line (436 nm)
  • Excimer laser (discussed later)
  • Advanced (X-ray, electrons, ions)
• Reflecting/refracting optics - pupose: colect, collimate, filter, focus the light
  • Collect - lamp in focal point of mirror, in order to collect almost all the emitted light
  • Colimate - produces parallel beams of light
  • Filter - in order to use only one line from the emited spectra
  • Uniformise the light intensity over the wafer by decollimating and reshaping it