Properties of Zr Silicate and Zr-Si Oxynitride High-k Dielectric Alloys for Advanced Microelectronic Applications; Chemical and Electrical Characterizations

Abstract

As the microelectronic devices are aggressively scaled down to the 1999 International Technology Roadmap, the advanced complementary metal oxide semiconductor (CMOS) is required to increase packing density of ultra-large scale integrated circuits (ULSI). However, SiO2 or Si oxynitride (SiOxNy) films which is a traditional gate oxide materials shows its limitations in direct tunneling current density at the below about 3nm thickness, and moreover, the priority of leakage current is ranked high in device performance and reliability as the portable device prevails. High-k alternative dielectrics can provide the required levels of EOT for device scaling at larger physical thickness, thereby providing a materials pathway for reducing the tunneling current.

Zr silicates and its end members (SiO2 and ZrO2) and Zr-Si oxynitride films, (ZrO2)x(Si3N4)y(SiO2)z, have been deposited using a remote plasma-enhanced chemical vapor deposition (RPECVD) system. After deposition of Zr silicate, the films were exposed to He/N2 plasma to incorporate nitrogen atoms into the surface of films. The amount of incorporated nitrogen atoms was measured by on-line Auger electron spectrometry (AES) as a function of silicate composition and showed its local minimum around the 30% silicate. Characterization by AES and x-ray photoelectron spectroscopy (XPS) indicated that the nitrogen atoms were substituted for the oxygen atoms' position and made a bond with Si and Zr depending on the silicate composition. The effect of nitrogen atoms on capacitance-voltage (C-V) and leakage-voltage (J-V) were also investigated by fabricating metal-oxide-semiconductor (MOS) capacitors. Results suggested that incorporating nitrogen into silicate decreased the leakage current in SiO2-rich silicate, whereas the leakage increased in the middle range of silicate.

The pseudo-ternary alloy composition was determined by Rutherford back scattering (RBS) that was calibrated by on-line Auger electron spectroscopy (AES) and showed the composition's thermodynamically stable boundary composition in ternary phase diagrams. Zr-Si oxynitride was a pseudo-ternary alloy and no phase separation was detected by x-ray photoelectron spectroscopy (XPS) analysis up to 1100°C annealing. The leakage current of Zr-Si oxynitride films showed two different temperature dependent activation energies, 0.02 eV for low temperature and 0.3 eV for high temperature. Poole-Frenkel emission was the dominant leakage mechanism.

Zr silicate alloys with no Si3N4 phase were chemically separated into the SiO2 and ZrO2 phase as annealed above 900°C. While chemical phase separation in Zr silicate films with Si3N4 phase (Zr-Si oxynitride) were suppressed as increasing the amount of Si3N4 phase due to the narrow bonding network in Si3N4 phase. (3.4 bonds/atom for Si3N4 network, 2.67 bonds/atom for SiO2 network)