Selective ion beam etching of Al2O3 films

The reactive ion beam etching of alumina with a photoresist mask was examined using fluorohydrocarbon gases to achieve high selectivity and accurate Al2O3 pattern size. The etching rate of Al2O3 decreased with larger numbers of hydrogen atoms in the gas molecule from CHF3 to CH3F. In both CH2F2 and CH3F ion beams, photoresist was not etched because of polymer formation. The mixed 37% CH2F2 + CHF3 and 18% CH3F + CHF3 gases realised fast Al2O3 etching with larger selectivity. The etched Al2O3 pattern has a steep sidewall taper angle and no width reduction during etching. Studies of the photoresist surface after etching revealed that the deposited polymer using CH3F contained fewer C-F bonds than the damaged layer exposed to CHF3 ion beam. The etching rate of Al2O3 was dominated by sputtering of nonvolatile reaction products formed on the etched Al2O3 surface. 10 refs.