An electron beam processing apparatus for treating a substrate is provided. The apparatus has an electron beam generating assembly housed in a chamber that includes a filament for generating a plurality of electrons upon heating. The apparatus may also have a foil support assembly that is configured to direct the plurality of electrons through a thin foil out of the chamber. The apparatus may further have a processing assembly that is configured to pass the substrate by the thin foil so that the plurality of electrons penetrates the substrate and cause a chemical reaction. A distance of an air gap between the thin foil and the substrate may be adjustable.