Electron scattering and related phenomena in scattering with angular limitation projection electron lithography (SCALPEL*)

Scattering with angular limitation projection electron lithography (SCALPEL) is a unique charged-particle projection imaging technique that employs a scattering mask with the pattern segmented between supporting struts. An aperture installed in the back-focal plane of the projection lens filters out the electrons scattered at large angles in the patterned area of the mask producing a high contrast aerial image. Various scattering phenomena involved with the energetic (100 keV) electrons carrying the mask pattern information to the wafer through the projection optics are responsible for the aerial image formation in SCALPEL. These phenomena can be grouped into three major categories: (i) electron elastic scattering in the mask responsible for the aerial image intensity and contrast. (ii) electron inelastic scattering in the mask-membrane that might have negative effects, such as membrane charging, beam chromatic blur generation, mask heating, etc.. (iii) Coulomb interactions of electrons in the beam (space charge effect) generating a beam blur that links the system throughput and resolution. Analytical models developed to describe and quantitatively evaluate these phenomena are briefly reviewed. The implication of these models to the design and optimization of the electron projection lithography systems are discussed.