Thin RF sputtered and thermal Ta_2O_5 on Si for hihg density DRAM application

摘要

Tantalum pentoxide thin films on Si prepared by two conventional for modern microelectronics methods (RF sputtering of Ta in Ar ＋ O_2 mixture and thermal oxidation of tantalum layer on Si) have been investigates with resspect to their dielectric, structural and electric properties. It has been found that the formation of ultra thin SiO_2 film at the interface with Si, during fabrication implementing the methods used, is unavoidable as both, X-ray photoelectron spectroscopy and electricla measurements, have indicated. The initial films (as-deposited and asgrown) are not perfect and contain suboxides of tantalum and silicon which act as electricla active centers in the form of oxide charges and interface states. Conditions which guarantee obtaining hihg quality tantalum oxide with dielectric constant of 32-37 and leakage current density less than 10~-7 A/cm~2 at 1.5 V applied voltage (Ta_2O_5 thickness equivalent to about 3.5 nm of SiO_2) have been established. These specifications make the layers obtained suitable alternative to SiO_2 for high density DRAM application.