Electrical properties of rapid thermally annealed SiNx : H/Si structures characterized by capacitance-voltage and surface photovoltage spectroscopy

Abstract

A comparative investigation of the characteristics of the SiNx:H/Si interface has been undertaken by capacitance-voltage measurements and surface photovoltage spectroscopy. By each of these techniques, we have determined the distribution of the interface trap density within the silicon bandgap. The samples were grown by the electron-cyclotron resonance plasma method starting from SiH4 and N-2 as precursor gases whose flow ratio was varied to produce films of three different compositions: silicon rich, near stoichiometric and nitrogen rich. Post-deposition rapid thermal annealing treatments were applied to observe the evolution of interface properties with the annealing temperature in the range from 300 to 1050 degreesC. For thin dielectrics, the interface state density has a U-shaped distribution dominated by hand-tail states. The minimum of this distribution decreases significantly and shifts to midgap for moderate annealing temperatures. For higher annealing temperatures, the trend is reversed. In the silicon-rich films, the percolation of rigidity caused by the chains of Si-Si bonds impedes the initial decrease of the defect density. For thicker films, the strain of the: SiNx:H film produces a higher density of defects that results in increased levels of leakage currents and poorer electrical characteristics.