Among the first resists used (since about 1980) and still applied in many cases are short-chain (50.000 g/mol (50k)) as well as long-chain (950.000 g/mol (950k)) poly(methyl methacrylate) (PMMA resist, sensitivity at 100 keV approximately 250 – 500 µC/cm2).
Significant components of electron beam lithography systems are the electron source, the electro-optical system and the focusing system (deflection or respectively projection unit). Hot cathodes are used for equipment with lower resolution, devices with higher resolution, however, preferably need thermic field emission sources.
Alongside the occuring elastic scattering effects at a collision with other electrons or atoms, incoming primary electrons can also be scattered inelastically when entering or traversing resist layers.
There are both mask-based and maskless writing procedures in electron beam lithography. More up-to-date systems use defined beams with, by the application of masks, selectively adjusted geometrical cross sections or respectively profiles, which are deflected upon the various positions (vector scan mode).
Polymer resists (layer builders)
Other resist components (adhesion promoter, tenside, solvent, colorant)
Process information such as: Cleaning of substrates, adhesive strength, dilution of resists, yellow light, softbake, rehydration, exposure and storage
Process procedures such as: Lift-off procedures, wet-chemical etching, dry-chemical etching, UV-curing, lithographic procedures and stabilization/curing of resist layers
See Photo resists: General
Electron beam lithography is a special procedure for the structuring of electron beam sensitive resist layers in order to produce microelectronic circuits and photomasks used in photolithography.
If an electron beam with high energy is channeled onto a resist layer (5- 100 keV), forward scattering ( 90° in direction of arrival). The deflection causes the electron beam to widen, thus reducing resolution.
The minimum necessary exposure time for a certain area, at a given exposure dose, can be calculated by the following correlation: Area * dose = Duration of exposure * beam current.
A further mask-based technology is SCALPEL (Scattering with Angular Limitation Projection Electron-beam Lithography). Due to the interposed mask, certain parts of the electron beam are shadowed. The scattering layer strongly deflects incident electrons. A great advantage of this procedure as compared to electron absorption is less loading and less heating of the mask.
Raster scan principle is a procedure in which the electron beam is led line by line over the exposure area, comparable to the beam guidance in an electron microscope. The structures are exposed by switching the electron beam on and off while continuously moving the substrate (XY regulation).