Study On The Radiation Effect Of SIMOX SOI Materials

The SOI, which is the silicon material on insulator, structure is usually the topsilicon-buried insulator-silicon substrate. Compared to traditional bulk silicon materials, Theexistence of insulating buried layer, completely isolated the top silicon with silicon substrate,make the devices and circuits based on SOI technology have a lower power, higher speed,higher integration level, higher temperature resistance, a larger resistance to single particleincident and transient radiation effect, Therefore，SOI technology is praised as a siliconintegrated circuit technology in the21st century.The existence of buried layer also makes the SOI devices and circuits more sensitive to totaldose radiation. In the ionizing radiation environment, the hole trap in the buried layer cancapture the hole generated by radiation and accumulate in the buried layer, so that to causing achance in characteristics of the devices and circuits or destroy them. This research work use thenitrogen-fluorine compound implantation process to inject the nitrogen and fluorine ions intothe buried layer of SIMOX (SIMOX: Separation by Implanted Oxygen) SOI materials tochance the material’s characteristics, in order to explore effective ways to improve thecharacteristics of SOI material total dose radiation.The thickness of top silicon and buried layer of SIMOX SOI materials used in our work is190nm and150nm, respectively. And the initial wafer is <100> p-type silicon. In theexperiment, nitrogen ions were implanted into the buried oxide with a dose of1016cm-2, andoptimized implantation energy90keV was adopted. The subsequent annealing was performedat1100℃for0.0,0.5,1.0,1.5,2.5h, respectively. And then, fluorine ions were implanted intothe buried oxide with a dose of1016cm-2and energy of120kev, the subsequent annealing wasperformed in the nitrogen environment at900℃for2h. Finally, in order to characterize theradiation effects of the materials by the high frequency voltage-capacitance(C-V), the ReactiveIon Etching (RIE) method is used to remove the top silicon to fabricate the capacitors of PBS(Polysilicon-Buried oxide-Silicon substructure).Firstly, the effect of fluoride injection on the positive density in the buried oxide of SIMOXSOI materials is researched. Researcher find that the fluoride injection can effectively suppressthe increase of fixed positive charge density in the buried oxide by the high dose of nitrogen injection, and the annealing time have a huge impact on the reduce of the positive density in theburied oxide after nitrogen-fluorine compound implantation. Analysts believe that the mainreason of the decrease of positive charge density is the electron trap in the buried oxide wasproduct by fluoride injection.The high frequency (1MHz) voltage-capacitance(C-V) of PBS capacitance before and afterirradiation were measured to study the influence of the nitrogen-fluorine compoundimplantation to the irradiation effect of the PBS, and the PBS capacitances were irradiated withCo-60γ-ray source at a dose of100rad (Si)/s. The results show that compared to beforeirradiation, all of the PBS capacitor C-V curves after irradiation have an negative drift, whichmeans the density of positive charge in the buried oxide is increase after a certain dose ofradiation. However, the difference of total dose radiation effect between nitrogen implantedPBS and nitrogen-fluoride implanted PBS is exited. Compared to nitrogen implanted PBS with1.5h annealing time, the nitrogen-fluorite implanted PBS capacitor with the correspondingmodification have an smaller negative C-V drift after a dose of700krad(Si) radiation, whichmeans that the resistance of nitrogen implanted buried oxide to total dose radiation can beimproved with a appropriate fluoride injection process.The twice annealing was experimented which is performed at120℃for15min wereexperienced by the PBS capacitance after700krad(Si) dose radiation and the annealingbehavior were observed and characterized by C-V technology to study the annealing effect ofPBS capacitor after radiation. The experimental results show that the PBS capacitors afterirradiation have no obvious annealing behavior in that annealing condition.For the study of the effect of high-dose radiation effect of nitrogen-fluoride compoundimplanted materials, the PBS capacitors were irradiated total doses of3×105,5×105,7×105and1×106rad(Si)/s with Co-60γ-ray source at a dose of100rad (Si)/s. The results show that, inmost cases, compared to the PBS capacitors before annealing with different radiation dose, theflat-band voltage negative drift with the same radiation dose is smaller, which due to theirradiation effects after annealing is the cumulative effect of the radiation dose before and afterannealing. The re-irradiation after annealing is difficult to achieve the damage level beforeannealing with the same dose of radiation in the condition of some parts of hole trap in theburied oxide capture the hole because of the radiation before annealing. In addition, the results also show that the flat-band voltage shift with different dose of radiation is complex, and we tryto make the preliminary interpretation about them.Finely, the process of nitrogen and fluoride implanted into buried oxide of SIMOX SOImaterials was simulated by computer to understand the implantation technology and relatedexperimental result.