Effect of plasma treatment on the density of defects at an amorphous Si:H-insulator interface

Abstract

Interface state density between a-Si:H and an insulating film (a-SiN 1.7 :H or a-SiO 2.0) was measured by photothermal deflection ͑PD͒ spectroscopy and electron spin resonance. While the interface state density in a-SiN 1.7 :H on a-Si:H structure was smaller than the free surface state density on a-Si:H, that in a-SiO 2.0 :H on a-Si:H structure was larger than the free surface state density of a-Si:H. The difference in the surface state density between these specimens was discussed in terms of plasma surface reaction. The effect of plasma reaction was examined by treating the surface of the a-Si:H layer by the plasma of NH 3 or N 2 O gas which were dominant constituents of the source gases used to deposit the insulating layers. The PD spectral shape of a-SiO 2.0 on a-Si:H was similar to N 2 O plasma-treated a-Si:H and that of the a-SiN 1.7 :H on a-Si:H structure was similar to NH 3 plasma-treated a-Si:H. These results indicate that the interface defects in the a-SiO 2.0 on a-Si:H structure were induced by the plasma reaction of the source gas with the surface of a-Si:H at the initial stage of deposition. The interface state densities in a-Si:H on a-SiN 1.7 :H and a-Si:H on a-SiO 2.0 interfaces were smaller than those of a-SiN 1.7 :H on a-Si:H and a-SiO 2.0 on a-Si:H, respectively. These differences in the interface defect density were due to the difference in the precursor used to deposit the upper layer. Chemical reaction on the surface of a-Si:H with a source gas induces interface defects at the initial stage of the deposition of the insulating layer. This surface chemical reaction was investigated by varying the condition of plasma species at the surface of a-Si:H.

Integrated amorphous and polycrystalline silicon thin-film transistors in a single silicon layer

“…On the other hand, TFTs with SiN as the gate dielectric, deposited at 300 C by PECVD, using SiH , H and NH , and at a rf power of 0.09 W/cm had of 9 cm /Vs (sample 3). Although the SiO / -Si : H interface state densities are higher than that of the SiN / -Si : H interface [23], the leakage currents were not significantly increased when SiO was used as the gate dielectric instead of SiN for the -Si : H TFTs. But, the and hence were also higher (0.5-1 cm /Vs compared to 0.2 cm /Vs) with of only 10-50 fA/ m, when SiO was the gate dielectric instead of SiN .…”