Evaporated AgBr as an x-ray sensitive layer in a two-layer resist system for x-ray lithography

Exposure of 2000 Å films of evaporated AgBr to 7 Å x-rays produced developable Ag images with 5 µJ/cm²of x-ray energy. The optical density of developed AgBr films vs. x-ray intensity produced a log-linear dependence in the range of 10 to 5000µJ/cm²with a gamma of 0.18. The extraordinary x-ray speed of evaporated AgBr stems both from photographic development, which multiplies the Ag latent image by a factor of ∼10⁵, and by virtue of the relatively heavy atoms which provide a calculated mass absorption coefficient of 32% from a 2000 å film. We have also exposed a special two-layer resist system consisting of AgBr/polymer on Si through an x-ray mask consisting of Ti membrane with Au as the opaque material. In previous work (1), we have shown that the photographically generated Ag image provides a very good mask for plasma etching polymer.