1. Total Dose Response of HfSiON MOS Capacitors
D. K. Chen, F. E. Mamouni, R. D. Schrimpf, D. M. Fleetwood, and K. F. Galloway
Department of Electrical Engineering and Computer Science,
Vanderbilt University, Nashville, TN
G. Lucovsky and S. Lee
Dept of Physics and Material Science,
North Carolina State University
B. Jun and J. D. Cressler
Dept of Electrical Engineering and Computer Science,
Georgia Institute of Technology

2. Introduction Quantum mechanical tunneling significant in SiO2
Charge trapping in HfSiON (Amorphous and Crystalline HfO2) [G. Lucovsky et al., IEEE Trans. Nucl. Sci., vol. 53, pp , 2006.]
Total dose irradiation and constant voltage stress
TID-induced charge trapping compared to previous Hf silicate devices

3. Device Description
HfSiON
Al Gate
Silicon Substrate
Al Substrate Contact Vg
FOX
SiON
(HfO2)0.4(SiO2)0.4(Si3N4)0.2 Low-Si3N4 K = 14.6 tox = 15 nm
(HfO2)0.3(SiO2)0.3(Si3N4)0.4 High-Si3N4 K = 12.7 tox = 13 nm
Equivalent oxide thickness ~ 4 nm
The samples were prepared by remote plasma enhanced chemical vapor deposition (RPECVD), with ~0.6 nm SiON layer; Rapid thermal anneal done at 900 oC

4. Experimental Details
1-MHz C-V measurement at a rate of 0.05 V/s; Irradiated with 10 keV X-ray at a rate of 31.5 krad(SiO2)/min
Interface trapped charge density (Nit) unchanged after radiation; prerad Nit ~ 3.8 x 1012 cm-2
Relatively small gate leakage current (<10 Vfb + 1 V) unaffected by radiation

5. Improvement Relative to Hf Silicate Devices
TID-induced charge trapping factor of 17 less relative to previous Hf silicate devices [J. A. Felix et al., IEEE Trans. Nucl. Sci., vol. 49, pp , 2002]

6. Midgap Voltage Shifts Weak bias dependence
Relative low mobility of holes in HfSiON similar to hafnium silicates [J. A. Felix et al., IEEE Trans. Nucl. Sci., vol. 49, pp , 2002]
Electron trapping
TID-induced and substrate injection at large positive biases

7. Comparison of Low- and High-Si3N4 Devices
Crystalline HfO2 in the low-Si3N4 film contains grain boundaries
Negative gate bias show similar charge trapping levels

8. Constant Voltage Stress (Substrate Injection)
O vacancies and interstitials in the Low-Si3N4 film favorable for electron trapping from substrate injection
Defects located near the interface an important source for electron trap sites

9. Constant Voltage Stress (Gate Injection)
Level of charge trapping much less compared to substrate injection
Saturation occurs much earlier than substrate injection case
Electron injection from the gate and movement of charge centroid

10. Comparison to Hf Silicate Devices
Electron injection balances positive charge trapping for positive and negative biases
∆Not ~ factor of 17 smaller at 1 Mrad(SiO2)
1.2 x 1012 cm-2 Hf silicate
7.1 x 1010 cm-2 HfSiON
Reduced charge trapping indicates superior HfSiON film qualities (smaller bulk trap density) and improvements in processing

11. Conclusions
HfSiON show drastic improvements in total dose irradiation hardness relative to Hf silicate devices
Crystallization creates grain boundary defects especially vulnerable to stress-induced electron trapping
Reduced charge trapping indicates smaller bulk defect density in HfSiON film relative to Hf silicates

12. Acknowledgements
Dr. Lucovsky’s group at NC State University for providing the samples
Air Force Office of Scientific Research (AFOSR) for supporting this work