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

Thin films of niobium pentoxide (Nb<inf>2</inf>O<inf>5</inf>) and tantalum pentoxide (Ta<inf>2</inf>O<inf>5</inf>) 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 Ta<inf>2</inf>O<inf>5</inf> and Nb<inf>2</inf>O<inf>5</inf> were separately deposited by r.f. sputtering of high purity ceramic targets in Ar/O<inf>2</inf> atmosphere on 200 mm n-type (100) Si-wafers, with the wafers having a dry thermal oxide layer of about 65 nm. The Ta<inf>2</inf>O<inf>5</inf> and Nb<inf>2</inf>O<inf>5</inf> films show amorphous properties as deposited. The morphology of the films was then investigated after rapid thermal annealing (RTA) between 500-950 °C, in order to characterize the crystallinity and the stoichiometry of the films. RTA was performed in O<inf>2</inf> and followed by switching in situ into Ar atmosphere.