Microwave irradiation impact on Ta₂O₅stack capacitors with different gates

Abstract

The effect of microwave radiation at room temperature on the characteristics of Ta 2 O 5 (7-25 nm)-based capacitors with various gates (Al, W, TiN) has been investigated. The variation of the parameters upon treatment is a function of the initial properties of the devices. The permittivity of the stacks slightly increases, and both oxide charges and interface states density decrease after ∼5-10 s of irradiation. The parameter, however, that is definitely sensitive to the exposure is the leakage current-a current reduction, up to ∼2 orders of magnitude-and an improvement of the breakdown fields has been found for irradiated samples. The process is not accompanied either by additional oxidation of Si or by crystallization effects in the films. The current improvement is addressed to the annealing of gate-deposition-induced defects and defects due to reactions at the gate/Ta 2 O 5 interface rather than to annealing of poor-oxidation-related defects. The radiation-induced change of the mechanisms governing the conductivity in the stacks is discussed in terms of partial annealing of pre-existing electron traps. An Auger electron spectroscopy detectable variation in the composition of the films has not been observed within exposure times for which a change of the electrical characteristics has been established. Considering that the combination of metal gates with high-k layers is the solution for the further scaling of top-down microelectronic devices, short-time microwave radiation appears to be a promising way for leakage current reduction in Ta 2 O 5 stacks with metal gates, to a level adequate for the storage capacitor application.

Conductive-atomic force microscopy characterization of Ta2O5/SiO2stacks and the effect of microwave irradiation

“…According to the previous macroscopic I -V data [21][22][23] the short time (∼10-15 s) microwave irradiation at room temperature reduces significantly (up to four decades) the leakage current in both pure and Ti-doped Ta 2 O 5 stack capacitors. To study how the microwave irradiation affects the electrical conduction of the stack at the nanometre scale we made the corresponding measurements with C-AFM.…”

“…Fabrication conditions providing films with high dielectric constant (∼37) and leakage current below 10 −9 A cm −2 at 1 MV cm −1 have been optimized. We have also shown [21][22][23] that microwave radiation for several seconds could be used as a room temperature alternative to high-temperature annealing processes for improving the electrical parameters of Ta 2 O 5 films on Si. The purpose here is to characterize topographically and electrically the ultrathin Ta 2 O 5 with nanometric resolution and its local response to microwave irradiation.…”

“…d is the total thickness of the film including the interfacial lower-k layer. To evaluate the effect of microwave irradiation, the films were exposed in a magnetron (2.45 GHz, power density of 1.5 W cm −2 ) for 10 s. This exposure time was established previously [21,23] as the optimal one in terms of leakage current and dielectric constant of ultrathin Ta 2 O 5 MOS capacitors. The temperature of the samples during irradiation was close to room temperature.…”