Proximity effect (electron beam lithography)

When an electron beam is incident on a material, the electrons are not destroyed but are scattered both elastically (with angle changes but without energy loss) and inelastically (with energy loss). The elastically scattered electrons generally have sufficient energy to travel a large distance. Those which head back toward the source are called the back-scattered electrons. The inelastically scattered electrons generate additional radiation quanta through their energy loss, including X-rays, Auger electrons, and low-energy ejected electrons (also called secondary electrons). The range of the back-scattered electrons is much larger than the range of the secondary or Auger electrons due to their higher energy.

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Back-scattered electrons often cause features written by electron beam lithography to be wider in densely patterned areas. Most electron-beam lithography systems compensate for this pattern dependence by reducing the dose in densely patterned regions compared to isolated features. The compensation cannot completely remove the fundamentally large difference in dose sensitivity between isolated and nested features.