Improved step coverage by ion beam resputtering

Abstract

Coverage of steps by ion beam sputtered SiO2 films is greatly improved by bombarding the growing film with an ion beam. Cracks are eliminated at step edges, and step coverage profiles can be controlled by varying the degree of resputtering, as has been observed in rf bias sputtering. Using an ion beam of well-defined energy, flux, and angle, the resputtering process is under direct control. In a dual ion beam system, we examined the step coverage profiles of SiO2 films deposited under 500 eV argon ion bombardment to produce resputtering fractions of 0%, 17%, and 42%. Films deposited with no resputtering show overhanging step profiles, while those deposited with 17% resputtering give smooth sloping profiles with good coverage even with film thicknesses less than the step height. Successful lift-off patterning is also achieved with 17% resputtering. Films deposited with 42% resputtering have sloping profiles but do not fully cover step edges. We conclude that step coverage can be greatly improved using resputtering fractions of less than 20%. This level of resputtering does not degrade other film properties, and is compatible with lift-off processing.