Insulating properties of tantalum pentoxide capacitor films obtained by annealing in dry ozone

Abstract

Highly insulating tantalum pentoxide (Ta2O5) capacitor films were obtained by dry O3 annealing at low temperatures ranging from 350 to 500 °C. Typical leakage current density and resistivity of a 10-nm-thick Ta2O5 film measured at 2 MV/cm were 2.5×10−8 A/cm2 and 4.8×1013 Ω cm, respectively, obtained by dry O3 annealing at 450 °C, while leakage current density of the as-deposited film was about 10−1 A/cm2. It was confirmed that the mechanism which improves the insulating properties after dry O3 annealing involves the reduction of the leakage current due to the reduction of the concentration of such impurities as hydrogen and carbon, and the reduction of oxygen vacancies in Ta2O5 films. In addition, amorphous Ta2O5 films annealed in dry O3 show much better insulating properties than polycrystalline films. This can be attributed to the suppression of leakage current at the grain boundaries. Regarding dielectric properties, Ta2O5 films have an average dielectric constant of 28, and the typical SiO2 equivalent thickness of a 10-nm-thick Ta2O5 film was 2.4 nm. Results of the time dependent dielectric breakdown measurement, the calculation of the storage node height of a capacitor, and the frequency dependence of the capacitance value suggest that the above Ta2O5 film is applicable to an integrated capacitor for next generation devices, replacing conventional capacitor films.

Electrical characteristics of thin Ta2O5 films deposited by reactive pulsed direct-current magnetron sputtering

“…8 Several efforts were made to improve the electrical properties of CVD Ta 2 O 5 films. For examples, a two-step thermal annealing technique using dry ozone 11 and a nitrogen plasma treatment 12 were shown to improve the film properties. Sometimes it is desirable to prepare Ta 2 O 5 films at low substrate temperatures because of a strict thermal budget.…”

Dielectric function of amorphous tantalum oxide from the far infrared to the deep ultraviolet spectral region measured by spectroscopic ellipsometry

“…Postannealing of the amorphous samples at elevated temperatures above 700°C causes crystallization. 16 Depending on the annealing history, a͒ Electronic mail: franke@engrs.unl.edu either orthorhombic 6,8,15,29 or hexagonal 14 phases can be obtained.…”

“…3 Thin films of tantalum oxide are also employed as an ion conductor in electrochromic devices. 4,5 Known as a material with high static dielectric constant and with good electrical insulating properties, tantalum oxide has the potential for microelectronic applications as a capacitor and gate material, thereby replacing silicon dioxide in metal-insulator-metal [6][7][8][9][10][11] or metal-insulator-semiconductor [6][7][8][9][10][12][13][14][15][16][17] structures as well as in large-scale integrated circuits for dynamic random access memories. 6 Sputter-deposited thin films tend to show film porosity, which affects electrical or optical properties.…”

4H-SiC MIS structures using oxidized Ta2Si as high-k dielectric

“…Using X-ray diffraction analysis, Ta 2 O 5 peaks are clearly evidenced implying an hexagonal δ-Ta 2 O 5 (ε r =25-57) [7][8][9][10][11] phase on p-Si (figure 1) and n-type 4H-SiC (figure. 2) substrates.…”