Influence of high-energy Beamstrahlung gamma-radiation on MNIS-structure parameters

Full text: It is known, that MNIS- structures and devices on their basis are rather sensitive to influence of radiation, and irradiation of these structures by electrons, gamma-quanta, neutrons, etc. leads to degradation of their parameters [1]. The degradation is observable in insulator and at the insulator - semiconductor interface. In the given work influence of high-energy Bremsstrahlung gamma-radiation from betatron and 60Co gamma-quanta on characteristics of silicon MNIS- structures was investigated. Samples of Al-Si3N4-SiO2-Si type MNIS- structures were used. The samples were irradiated at betatron SB-50 with the intrachamber technique at the maximal energy of -quanta of Bremsstrahlung spectra 30 MeV at the doze rate 350 rad/s in the doze range of 104 -107 rad. The irradiation temperature did not exceed 30 C. There was no voltage on the shutter during the irradiation. It was revealed, that high-frequency C-V-characteristics of Al-Si3N4-SiO2-Si structures after such irradiation to the doze 7.106 rad move towards negative displacement with slight slope change, and in the case of 60Co gamma-irradiation the shift is significant. It was supposed, that the C-V-curve shift after the irradiation is due to accumulation of the volumetric positive charge generated by the radiation in the oxide layer of the structure. The observed value of radiation induced shift is obviously connected with the amount of the accumulated positive charge. It was found, that the volumetric positive charge induced by 60Co gamma-irradiation is larger, than that generated by the high-energy Bremsstrahlung gamma-radiation. This effect is caused, possibly, by the energy dependence of the interaction of radiation with substance. Photonuclear reactions induced by the high-energy Bremsstrahlung -gamma radiation (the maximal energy of gamma-quanta 30 MeV) in SiO2 layer [2,3] generate aluminium and nitrogen radionuclides which, according to [4], act as electron traps that results in radiation stability increase. Probably thereof the shift of high-frequency C-V-characteristic curves, the threshold voltage change and the flat zones voltage are considerably less than those for 60Co gamma-irradiation case. The energy spectra of fast surface states created after the irradiation of MNIS- structures by the high-energy Bremsstrahlung and 60Co gamma-radiations were calculated from the measured high-frequency C-V-characteristics. The obtained energy distributions of surface states (SS) before and after the irradiations have shown, that after 60Co gamma-irradiation the number of states Nss is 2-3 times more, than that after the high-energy Bremsstrahlung gamma-irradiation. At presence of metal electrode on the insulator surface the observed increase in the Ss number, according to [4], is due to either capture of the hot holes generated on the semiconductor surface or to diffusion of the holes generated near to transit area from oxide to semiconductor. The observed difference in Nss (E) change at different irradiations is, probably, connected with various ionizing ability of radiations, in particular, with formation of Al and N nuclides in the SiO2 layer and at the oxide -semiconductor interface as a result of photonuclear reactions [2,3]. In opinion of authors [4], aluminum and nitrogen radio nuclides can trap electrons and prevent diffusion of holes from oxide to the interface. Apparently, it also causes a smaller Nss(E) change observed by us at irradiation of the studied MNIS- structures by the high-energy Bremsstrahlung gamma-radiation, in comparison with that at 60Co gamma-quanta. References: 1. Mitchell Dzh., Wilson D. Surface effects in semiconductor devices caused by irradiation, 1970, 59 c.; 2. Akulovich I.I., Zhitkovskij V.D., Korshunov F.P., Petrenko V.V. Materials of All-Union Conference, 1987, c.333-335.; 3. Revesz A.G., Zaininger K.H., Evans R.J. // J. Electrochemical Soc., 1969, v.116, N8, p.1146-1148.; 4. Pershenkov V.S., Priests B.D Surface radiation effects in IMS, 1988, 67 P. (authors)