Impact of source/drain contacts formation of self-aligned amorphous-IGZO TFTs on their negative-bias-illumination-stress stabilities

In this study, we have compared the performance of self-aligned a-IGZO thin-film transistors (TFTs) whereby the source/drain (S/D) region's conductivity enhanced in three different ways, that is, using SiNx interlayer plasma (hydrogen diffusion), using calcium (Ca as reducing metal) and using argon plasma (changing the atomic ratio). All these TFTs show comparable characteristics such as field-effect mobility (μFE) of over 10.0 cm2/(V.s), sub-threshold slope (SS-1) of 0.5 V/decade, and current ratio (ION/IOFF) over 108. However, under negative-bias-illumination-stress (NBIS), all these TFTs showed strong degradation. We attributed this NBIS stability issue to the exposed S/D regions and changes in the conductivity of S/D contact regions. The hydrogen plasma-treated TFTs showed the worst NBIS characteristics. This is linked to increased hydrogen diffusion from the S/D contact regions to the channel. In this study, we observed that the negative-bias-illumination-stress stabilities of self-aligned a-IGZO thin-film transistors are strongly dependent upon the source/drain (S/D) region's direct exposure to stress light. Among few different techniques for S/D conductivity enhancements such as metal reduction (Ca metal), Ar plamsa, and SiNx plasma (hydrogen diffusion), the SiNx plasma-treated thin-film transistors showed the worst negative-bias-illumination-stress suitabilities. This is linked to increased hydrogen diffusion from the S/D contact regions to the channel. cop. 2015 Society for Information Display.