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Definition: ultraviolet light

An invisible band of radiation at the upper end of the visible light spectrum. With wavelengths from 10 to 400 nm, ultraviolet (UV) starts at the end of visible light and ends at the beginning of X-rays. The primary source of ultraviolet light is the sun, and most of the UV that reaches earth is in the lower-frequency, longer-wavelength Ultraviolet "A" region (see below).

Although ultraviolet (UV) light is widely known as a disinfectant, it was also used to erase EPROM chips. After several minutes of exposure to UV light, the chip could be programmed again (see EPROM).

Ultraviolet for Chip Making
Chips are made by using lithography to create silicon layers. Each layer is exposed to light through a pattern (mask), and for a long time, far ultraviolet (FUV) was the light source. However, because light cannot create a pattern smaller than its own wavelength, several photomasks are used, and complex chips require dozens of lithography steps.

In order to make the transistor elements even smaller, extreme ultraviolet (EUV) became the next-generation light source (see table below). See process technology.

                           from 10 to
  Ultraviolet Region     400 nanometers

  UVA  Long-wave "A"       315-400
  UVB  Medium-wave "B"     280-315
  UVC  Short-wave "C"      100-280

  NUV  Near ultraviolet    300-400
  MUV  Middle ultraviolet  200-300
  FUV  Far ultraviolet     122-200
  EUV  Extreme ultraviolet  10-121

  Lyman Alpha               121.6
   (hydrogen fingerprint)

  VUV  Vacuum ultraviolet  Less than 200
  DUV  Deep Ultraviolet    Less than 300

Ultraviolet in the Spectrum
The ultraviolet band is between visible light and X-rays.