(Invited) Reliability of Ultra Nano-sheet InWO Thin Film Transistor for Back-end of Line Applications

Abstract

The amorphous indium-tungsten oxide (a-IWO) ultra nano-sheet (UNS) thin-film transistor (TFT) has been developed successfully and exhibited high device performance. It is also suitable for the back end of line (BEOL) technologies due to its superior electrical characteristic and low operation voltage[1, 2]. In this work, we study the reliability of TFT with nano-sheet IWO as channel layer for BEOL applications. The backchannel passivation with an organic layer was proposed to effectively isolate the humidity in the atmosphere. Experimental results have shown that the a-IWO nano-sheet TFT can exhibit the great potential and excellent reliability for BEOL IC applications. Experiment The bottom gate structure was used. A Mo films was deposited by DC sputter as gate electrode. Then, a layer of HfO2 film was deposited through the atomic layer deposition (ALD). Next, the 4nm-thick nano-sheet a-IWO thin film was deposition as the channel layer by RF sputter. The Mo source/drain contacts were deposited by DC sputter. Finally, the organic passivation layer covered on the device with spin coating method. The conditions of thermal annealing process were studied for the optimization of the interface quality between IWO nano-sheet backchannel and organic passivation layer. Result and discussion The amorphous oxide semiconductor (AOS) channel layer is easily affected by the atmosphere from the environments, like oxygen and moisture causing the electrical degradation [3, 4]. Therefore, the passivation effectively avoids the degradation of device features under positive bias thermal stress (PBTS) measurement, as shown in Fig. 1. The passivation layer can effectively improve the TFT device reliability and reduce the positive shift of threshold voltage. Reference [1] P. Y. Kuo, C. M. Chang, and P. T. Liu, pp. 21-22.[2] P. Y. Kuo, C. M. Chang, I. H. Liu, and P. T. Liu, Scientific reports, vol. 9, no. 1, pp. 1-7, 2019.[3] J. Yao, N. Xu, S. Deng, J. Chen, J. She, H. P. D. Shieh, P. T. Liu, and Y. P. Huang, IEEE Transactions on Electron Devices, vol. 58, no. 4, pp. 1121-1126, 2011.[4] P. T. Liu, Y. T. Chou, and L. F. Teng, Applied Physics Letters, vol. 95, no. 23, pp. 233504, 2009. Figure 1