The effect of Fowler–Nordheim tunneling current on thin SiO2 metal-oxide-semiconductor capacitors

Abstract

p-type metal-oxide-semiconductor (MOS) capacitors with various oxide thickness (less than 200 Å) are stressed by Fowler–Nordheim (F–N) tunneling constant current with negative gate bias, and high frequency and low frequency capacitance-voltage (C-V) characteristics have been used to investigate the charge trapping phenomenon in thermally grown thin SiO2 films. Under constant current stress, high frequency C-V curve shifts negatively, and flatband votage shifts ΔVFB don’t saturate even at large injected charge F. In order to explain this behavior, we propose the expression, ΔVFB =A[1− exp(−σF)]+KF. The first term indicates hole trapping by the preexisting traps and the second term means the generation factor due to traps generated under stress. A fitting parameter A is nearly in proportion to the square of SiO2 thickness. This can be interpreted with the uniform distribution of bulk hole traps throughout the SiO2. Both capture cross section σ and generation factor K rapidly decrease with decreasing SiO2 thickness. From the results of low frequency C-V characteristics, the interface states with very high density of the order of 1013/cm2 eV are generated over a wide range of band gap.