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The charge couple device(CCD) used in spectroscopy requests good response to the wave bands between 190-1000 nm.
The common measure to carry out UV response is phosphor coatings or back illuminated. Among them, phosphors are
wavelength converters that convert short-wavelength light into the visible spectral region. This technology needs adding
special process which not only raises cost, reduces yield, but also reduces the resolution of the image. Back illuminated
is reducing CCD thickness to 15um which is thinner than the normal paper by mechanical polishing and chemical
corrosion after completing the front processes of CCD. This technology needs special instrument, complex process , and
the yield is also low. Both phosphor coatings and back illuminated have some disadvantages such as low space
resolution, complex process, low yield, high cost etc.
The CCD of traditional structure has no response to the wavelength less than 350nm, the reason is that the length of UV
penetrating through Si is shallow, the penetrating length is only 6.5nm of 300nm UV, the shorter wavelength UV, the
shallower penetrating length. The junction depth of normal CCD process is above 200nm, some realize shallow junction
through molecular beam epitaxy, but the instrument is expensive and the cost is high. The photosensitive area of
normal structure CCD adopting portrait P-N junction, light incidences from N area, N area can't be completely depleted
because of the restrict of physics, photon can't arrive depletion area directly.
On the basis of thorough analysis traditional UV CCD, horizontal P-N junction structure of Photosensitive area is put
forward, whose depletion can reach the surface, the photon falls depletion area directly, which can effectively carry out
the absorption of the UV light and the collection of photoelectron. As the latent absorption of Si3N4 to UV with less than
248nm wavelength, the Si3N4 passivation on the photosensitive area is take out. The improved 2048 elements linear
CCD achieves excellent wide spectral response, the maximum quantum efficiency comes to 65% in the ultraviolet band
and the average quantum efficiency comes to 40% between 190nm and 1000nm wave band.
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