High Quality of Ultra-Thin SiO_xN_y Films Prepared in Nitrous Oxide Ambients Using Thermal Low-Pressure Oxynitridation

Abstract

The thermal low-pressure oxynitridation of Si(100) in N₂O has been studied for ultra-thin (<5 nm) SiO _x N _y films. The nitrogen concentration and depth profiles were accurately determined by secondary ion mass spectrometry. It has been found that small amounts of nitrogen uniformly distribute in the dielectrics, and the kinetics of the oxynitridation (i.e., thickness vs. time) can be accurately expressed as a logarithmic equation. Meanwhile, the electrical properties of the oxynitride films: the average breakdown equivalent fields of dioxide (E_BD), the breakdown time (T_BD), the fixed charge (Q_f), and the interface state density (D_it) have been characterized and analyzed by the current–voltage (I–V), the time-dependent dielectric breakdown, the capacitance–voltage (C–V), and the conductance–frequency (G–W), respectively. The oxynitride films with E_BD ≈ 15.46 MV cm⁻¹ and T_BD ≈ 2.39 E⁴ ms were prepared successfully by processing optimization. The result reveals that the thermal low-pressure oxynitridation is helpful to obtain excellent gate dielectrics with low interface state density (D_it with an order from 2.0 E⁹ to 3.0 E¹⁰ ev⁻¹ cm⁻²). Such a result can be attributed to nitrogen incorporation and slow growth rate during low-pressure processes. It is concluded that the characteristics of the oxynitride films are suitable for applications in metal-oxide-semiconductor and nonvolatile memory devices.

Keywords:

• Nitrous oxide (N₂O)
• Oxynitride
• SIMS
• TDDB