Study Of Ta₂O₅ Based MOS Capacitors, With Tantalum Oxidized In O₂:NH₃ Ambient.

Abstract

Tantalum Pentaoxide, an alternative to SiO₂, as a high-k dielectric for DRAM and MOS applications, faces the problem of interface mismatch at silicon. SiO₂ or Si₃N₄ interfacial layer could help in overcoming this problem. The higher band offsets of these materials also help in the reduction of leakage currents at low electric fields. Here we study the physical and electrical characteristics of Ta, oxidized in O₂:NH₃ ambient, and without any other interface layer. This is done to check if N/H moves to the interface, and thus improves the electrical properties. XRD studies of the film, showed the presence of Ta₂O₅. Peaks corresponding to TaSi₂, un-oxidized tantalum and TaN were also found in the film. But the intensity of these peaks decreased with the reduction of NH₃ content. Thus a higher oxygen content could reduce the content of TaN and unoxidized tantalum. FTIR analysis however showed strong Ta=O and Si-O peaks. For the MOS capacitors, due to the presence of resistive components, the maximum capacitance was reduced, compared to that of pure Ta₂O₅ films. Oxide charges in the films were observed to be around 1.9E10 ^cm-2. But the traps in these films were found to be almost negligible as observed from the negligible hysteresis in the C-V characteristics. Films with N/H showed lesser oxide charges by an order of magnitude, as compared to pure Ta₂O₅ films.