First, the flux of the BL21B beam line must be measured by using photodiode to calculate the actual dose rate.
According to the EUV irradiation induced damages on the memory characteristics discussed in Chap 3, it is clear that the most critical issue is the severely degraded blocking layer in the TFT-SONOS memory. Therefore, improving the EUV irradiation immunity to the blocking layer is needed. Since SiO2 is stronger than most of the dielectric used in IC industry to resist the high energy radiation [55], SiO2 should be the best candidate of the blocking layer. In this case, those radiation hardness techniques which have been reported would be helpful.
In addition, decreasing the program/erase (P/E) voltages is another possible solution to improve the endurance characteristic. Using high dielectric constant material as blocking layer can improve the gate coupling efficiency so that the operation voltage can be lowered. Using high-k blocking layer can also reduce the electric field intensity in the blocking layer, which is also helpful to improve the endurance characteristic. The Al2O3 used in the TiN NC memory in this thesis is promising. Another high-k materials are worthy for investigation.
In this thesis, poly-Si SONOS memory prepared in academic laboratory was
used. It is acknowledged that the device performance of our devices is not as good as that of the SONOS memory fabricated by industry. The response of the high performance SONOS memory to the EUV irradiation should be examined.
For the multi-gate TiN NC memory, the memory characteristics before EUV irradiation are not good enough, especially the retention characteristic. Samples with better performance would be more sensitive to radiation damages. Therefore, the immunity to EUV irradiation of the NC memory should be reconfirmed by using other sample which has better performance.
Fig. 4-1: The observed phenomena of the TFT-SONOS memory after EUV irradiation.
Fig. 4-2: The observed phenomena of the multi-gate TiN NC memory after EUV irradiation.
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