Electron-beam interactive oxide films for nanometer-scale lithography

A number of oxide thin films produced by rf sputtering have been found to show high resolution lithographic characteristics when exposed under high dose rate conditions in a scanning transmission electron microscope. Holes and lines less than 10 nm in dimensions have been formed in amorphous films of Al2O3, Y2O3, Sc2O3, 3Al2O3·2SiO2 and MgO·Al2O3 through the direct removal of material during exposure. Complete exposure in these films was produced in less than 80 ms using a dose rate of 1 x 105 A/cm2. In addition to the requirement of amorphous film structure the material characteristics found to be important in determining film response included high ionic character, high heat of formation and incorporation of inert gas into the structure. The high resolution characteristics in amorphous Al2O3 films allowed the production of 5.0 nm holes with a minimum center-to-center spacing of 8.9 nm. The effects of film thickness, inert gas incorporation and exposure parameters were studied using amorphous Al2O3 films. An optimum thickness was found to occur at approximately 90 nm where the dose required for exposure was 25 x 102 C/cm2 (∼ 25 ms). Argon concentrations could be controlled over the range of approximately 1.0-2.5 At.% and films containing larger amounts of Ar showed improved sensitivity. Increasing the dose rate of exposure resulted in decreased time and increased total dose requirements for exposure. No threshold current densities for material removal were observed above 1 x 103 A/cm2. A qualitative model of the exposure process has been developed which describes material removal as a sequence of events