The photolithography
has its resolution limited by diffraction effects. To improve the
resolution, therefore, the diffraction effects are reduced by reducing
the wavelength. However, if the wavelength is reduced further, all
optical materials become opaque because of the fundamental absorption,
but transmission increases again in the X-ray region. This led to the
requirement of X-rays for lithography purpose.
In X-ray lithography
an X-ray source illuminates a mask, which casts shadows on to a
resist-covered wafer. The mask and resist material for X-ray lithography
are mainly determined by the absorption spectra of these materials in
the X-ray region.
