Thermal annealing of Nb2O5 and Ta2O5 thin films for CMOS based chemical sensors

Thin films of niobium pentoxide (Nb2O5) and tantalum pentoxide (Ta2O5) have many applications in microelectronics as gate dielectrics for field-effect transistors (FETs) and metal-insulator-semiconductor (MIS) structures, due to their high dielectric permittivity. Their structural properties and chemical stability also allow for uses in chemical sensing, especially those based on FETs and electrolyte-insulator-semiconductor (EIS) structures. In order to achieve the electrical and chemical properties necessary for long-term stability, the films require thermal annealing after deposition. In this work, thin films of Ta2O5 and Nb2O5 were separately deposited by r.f. sputtering of high purity ceramic targets in Ar/O2 atmosphere on 200 mm n-type (100) Si-wafers, with the wafers having a dry thermal oxide layer of about 65 nm. The Ta2O5 and Nb2O5 films show amorphous properties as deposited. The morphology of the films was then investigated after rapid thermal annealing (RTA) between 500-950 deg C, in order to characterize the crystallinity and the stoichiometry of the films. RTA was performed in O2 and followed by switching in situ into Ar atmosphere.