Mechanism of electrical performance deterioration in a-Si:H TFTs caused by source/drain Decap treatment

During the fabrication process of the display industry, the Decap treatment is usually employed as a means to reuse semiconductor materials of thin film transistors (TFTs), but the influence and mechanism of Decap process on the properties of the decapped samples is unknown. To elucidate this occurrence, the electrical characteristics of the channel layer, as well as the microstructure and components at the interface between the Source/Drain (S/D) and the channel layer were examined. It reveals that the infiltration of impurity ion (O and Mo) has significant impact on the deterioration of device performance for a-Si:H TFTs with a Mo/Al/Mo stacked S/D electrode structure. More specifically, oxygen's intrusion leads to the formation of SiOX and the alterations of the surface energy levels and charge distribution of Si, thus introduces an interface trap states between channel layer and S/D electrodes to scatter and capture of interface carriers. And Mo's intrusion may induce the come into being of MoSi or MoP chemical states, causing the decrease of the doping efficiency of phosphorus and the reduction of carrier concentration (from 5.52 × 1016 cm−3 to 4.44 × 1016 cm−3) of a-Si:H channel layer. The combined effect of these two factors results in the decline of electrical performance of S/D decapped a-Si:H TFTs.