Comparative study of sputtered and spin-coatable aluminum oxide electron beam resists

The electron beam exposure characteristics of sputtered ${\mathrm{AlO}}_x$ and spin-coatable ${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ resists are compared and contrasted. When exposed to an electron beam, sputtered ${\mathrm{AlO}}_x$ resists on a silicon substrate undergo an intense mass loss. However, electron energy loss spectroscopy shows that even after a prolonged exposure some aluminum and oxygen remains on the silicon surface. Spin-coatable ${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ resist was prepared by reacting aluminum tri-sec-butoxide, ${\mathrm{Al(OBu}}^s{)}_3,$ with acetylacetone (AcAc) in isopropyl alcohol. These are negative tone resists and they are ${\text{>10}}^6$ times more sensitive to an electron beam than the sputtered ${\mathrm{AlO}}_x,$ bringing its sensitivity very close to high resolution organic resists such as calixarene. The exposure properties of spin-coatable and sputtered aluminum oxide resists are discussed together with their sensitivity, damage mechanisms, line edge roughness, and etching characteristics. A brief note on the change of methodology of resist design is added when inorganic resists are to be used in high resolution electron beam nanolithography.