Performance Improvement of Aluminum doped MOHOS Total Dose Radiation Sensor Device by Fluorine Plasma Treatment

        Aluminum doped titanium nitride–silicon oxide–hafnium oxide–silicon oxide–silicon device with Fluorine plasma treatment (hereafter F-Al-MOHOS) can be a candidate for total ionization dose (TID) radiation sensor application. In this report, the performance improvement in terms of gamma TID radiation induced charge generation effect and charge-retention characterization for F-Al-MOHOS (SONOS-type Hf-based high K device) is the main subject of this study. F-Al-MOHOS devices with various Aluminum compositions in the HfO₂ charge-trapping layer tuned by metal organic chemical vapor deposition (MOCVD) system and with various Fluorine plasma treatment deposited by plasma-enhanced chemical vapor deposition (PECVD) system are to be used for comparison.

       Results indicate that better TID radiation induced charging effect is achieved with 20% Al content in the HfO₂ trapping layer in this study. The radiation induced trap density of the HfO₂ trapping layer can be increased by tuning a suitable Al ratio in HfO₂. But the charge retention performance of Al-MOHOS can be increased by increasing the Al doping ratio. Doping high ratio Al into pure HfO₂ film can enhance the crystallization temperature of Al-HfO₂ compound and improve the charge retention characteristic of Al-MOHOS device with high temperature S/D annealing process [1]. However, due to the fluorine incorporation into HfO₂ trapping layer by F plasma treatment pre and post HfO₂ deposition (hereafter pre post F treatment), radiation induced charge generation efficiency for F-MOHOS is also enhanced. Meanwhile, the charge-retention characteristic of F plasma treatment MOHOS device has also been significantly improved. It shows that the charge-retention performance of the F-MOHOS device with negative gate bias stress (NVS) after 10Krad TID radiation exposure, the condition of pre-HfO₂ F plasma treatment one is better than the post-HfO₂ F treatment condition. But the charge-retention performance of the F-MOHOS device with NVS for 5Mrad TID radiation exposure condition, the post-HfO₂ F plasma treatment is better than pre-treatment condition. The result obviously indicates that F plasma treatment is helpful to passivate the HfO₂-SiO₂ interface, eliminate shallow trap effectively and result in deep charge trap level [2] .

     The experimental results show that radiation induced charge density of F-Al-MOHOS device with 20% Al doping  and pre post F treatment HfO₂ is 6 times larger than that of MONOS device. In brief, the significant improvements in terms of radiation induced charging effect and charge-retention characterization of F-Al-MOHOS device may be achieved by doping suitable Al content and pre post F passivation for the HfO₂ charge-trapping layer, which can be attributed to the radiation induced high density deep trapped charges for F-Al-MOHOS radiation sensor device. The F-Al-MOHOS reported in this study has demonstrated their potential application for non-volatile TID radiation sensing application in the future.