Effects of Device Aging on Microelectronics Radiation Response and Reliability D. M. Fleetwood, M. P. Rodgers, L. Tsetseris, X. J. Zhou, I. Batyrev, S. Wang, R. D. Schrimpf, and S. T. Pantelides Vanderbilt University, Nashville, TN Work supported in part by AFOSR MURI and US Navy 2 Outline Previous Work Effects of burn-in, pre-irradiation temperature stress Aging and baking effects on unpassivated capacitors Aging effects on transistors Parts stored in a non-hermetic environment Parts stored hermetically sealed Humidity testing Density functional theory calculations Hardness assurance implications 3 Effects of pre-irradiation elevated temperature stress M. R. Shaneyfelt, et al., IEEE Trans. Nucl. Sci. vol. 41, 2550 (1994) M. R. Shaneyfelt, et al., IEEE Trans. Nucl. Sci., vol. 43, 865, Example of burn-in reducing interface traps in gate oxide Example of pre-rad temperature stress reducing oxide traps in field oxide 4 Aging effects in unpassivated, Al gate capacitors N ot (10 12 cm -2 ) Unbaked baked Unbaked baked 1986 Dose [krad(SiO 2 )] N it (10 12 cm -2 ) N ot (10 12 cm -2 ) A. P. Karmarkar, B. K. Choi, R. D. Schrimpf, and D. M. Fleetwood, IEEE Trans. Nucl. Sci., vol. 48, pp , t ox = 33 nm; bias during rad = 5 V; bias during bake = 0 V 5 Experimental Details: Aging Study Fully processed and passivated poly-Si gate MOS transistors 32 nm, stored non-hermetically 60 nm, stored hermetically 60 nm, stored non-hermetically Parts from same lot well characterized in keV X-ray irradiation at dose rates of 100 and 850 rad(SiO 2 )/s for 60 and 32 nm, parts respectively 6 V bias applied to all nMOS gates with all other pins held at ground, for rad + anneal Midgap method of Winokur and McWhorter used to estimate V ot and V it D. M. Fleetwood et al. IEEE TNS Vol. 35, No. 6, 1497, Dec WINOKUR etal. 1987 6 Test Procedure: 32 nm, non-hermetically stored Parts were stored Parts were packaged & hermetically sealed in of the 6 parts were 200 C with all pins grounded prior to irradiation (PETS) Half of the parts were not baked Parts were irradiated to 500 krad(SiO 2 ) Parts were delidded Parts were stored (not hermetically sealed) Data recorded throughout the postirradiation anneal. (room temperature) Parts were irradiated to 500 krad(SiO 2 ) 2 months after irradiation parts subjected to a high temperature anneal 100 C 7 32 nm devices, non-hermetic: V th 500 krad(SiO 2 ) M. P. Rodgers, D. M. Fleetwood, R. D. Schrimpf, I. G. Batyrev, S. Wang, and S. T. Pantelides, IEEE Trans. Nucl. Sci. 52, (2005). 8 500 krad(SiO 2 ) M. P. Rodgers, D. M. Fleetwood, R. D. Schrimpf, I. G. Batyrev, S. Wang, and S. T. Pantelides, IEEE Trans. Nucl. Sci. 52, (2005). 32 nm devices, non-hermetic: V it 9 32 nm devices, non-hermetic: V ot 500 krad(SiO 2 ) M. P. Rodgers, D. M. Fleetwood, R. D. Schrimpf, I. G. Batyrev, S. Wang, and S. T. Pantelides, IEEE Trans. Nucl. Sci. 52, (2005). 10 Parts were stored Parts were delidded & irradiated to 100 krad(SiO 2 ) Data recorded throughout the postirradiation anneal. (room temperature) Parts were delidded Parts were packaged & hermetically sealed in 1987 Half of the parts were 200 C with all pins grounded prior to irradiation (PETS) Half of the parts were not baked Parts were irradiated to 100 krad(SiO 2 ) 2 months after irradiation parts subjected to a high temperature anneal 100 C Test Procedure: 60 nm, hermetically stored 11 60 nm devices, hermetic: V th 100 krad(SiO 2 ) M. P. Rodgers, D. M. Fleetwood, R. D. Schrimpf, I. G. Batyrev, S. Wang, and S. T. Pantelides, IEEE Trans. Nucl. Sci. 52, (2005). 12 32 nm devices, non-hermetic: V it 100 krad(SiO 2 ) M. P. Rodgers, D. M. Fleetwood, R. D. Schrimpf, I. G. Batyrev, S. Wang, and S. T. Pantelides, IEEE Trans. Nucl. Sci. 52, (2005). 13 32 nm devices, non-hermetic: V ot 100 krad(SiO 2 ) M. P. Rodgers, D. M. Fleetwood, R. D. Schrimpf, I. G. Batyrev, S. Wang, and S. T. Pantelides, IEEE Trans. Nucl. Sci. 52, (2005). 14 60 nm devices: stored non-hermetically Dose: 100 krad(SiO 2 ); 6V bias Similar enhancement in interface-trap buildup to 32 nm devices, stored non-hermetically 15 Source of extra hydrogen Left: Water complex consisting of two SiOH (silanol) groups and a broken ring [energy = +( ) eV] Right: Water complex consisting of two SiOH groups and no broken ring [energy = -0.3 eV]. Water that diffuses into SiO 2 naturally dissociates, providing extra H + to enhance interface-trap formation M. P. Rodgers, et al., IEEE Trans. Nucl. Sci. 52, (2005). 16 Supporting evidence: humidity testing 130 C at 85% Relative Humidity; 0 V Rad: 100k, 6V Anneal, 6V Enhancement due to increased interface-trap buildup during post-irradiation anneal 17 Implications for hardness assurance 50% margin in irradiation not sufficient to describe aging- induced increase in for non- hermetically stored devices Exposing parts to PETS does not simulate the aging effects observed in these parts Additional margins required in hardness assurance testing for parts susceptible to enhanced interface-trap buildup during aging Combining the aging and PETS effects shown may explain previous complications in low- dose-rate response of MOS and bipolar devices Irradiate to spec level rad(Si)/s Electrical Test < 2 hr Pass ? Biased Anneal C Irradiate to 0.5x spec rad(Si)/s Biased T=25 C Reject Parts Reject Parts OK Pass ? Electrical Test < 2 hr No Yes 18 Conclusions Radiation response of MOS devices can change significantly with aging time after processing and/or packaging. Effects are most significant for interface trap buildup during post- irradiation annealing. Theory, as supported by the results of humidity tests, suggests that the increase in degradation is associated with H 2 O or other H-containing complexes. Non-hermetic environments are especially challenging. How hermetic is hermetic enough? Some effects seen even for hermetic environments, likely due to on-chip sources of hydrogen. Extra margins required in lot acceptance testing for sensitive devices/environments.