Proximity Effect

The proximity effect is a major challenge for electron beam lithography. Patterns in electron sensitive resists are created by exposing the resist to a beam of energetic electrons, typically 25 [keV] to 100 [keV]. The exposed regions in the resist become more or less soluble when the resist is immersed in a developer. When an electron beam strikes the resist, it forward scatters, exposing a cone into the resist rather than an infinitely narrow well. After it passes through the resist, it can back scatter off the substrate and head towards the resist again at large angles. Finally, after the electron escapes the resist, it may strike the ceiling of the chamber, back scatters and strike the resist somewhere far from the original beam position. This additional exposure is undesirable, limits the resolution of electron beam lithography, and makes high density pattern very challenging.