The Effect of Defects on Time Dependent Dielectric Breakdown Acceleration in TiN/ZrO2/Al2O3/p-Ge Gate Stacks

Monday, 29 May 2017: 11:20
Churchill B2 (Hilton New Orleans Riverside)
Y. Ding, D. Misra (New Jersey Institute of Technology), K. Tapily (TEL Technology Centre, America, LLC), R. D. Clark (TEL Technology Center, America, LLC), S. Consiglio (TEL Technology Center), C. S. Wajda, and G. J. Leusink (TEL Technology Center, America, LLC)
Introduction of a thin GeO2 as the interfacial layer (IL) seems to be beneficial for formation of high-k gate stacks on germanium substrate. The thickness of GeO2/GeOx impacts the overall equivalent oxide thickness (EOT) because of its low dielectric constant compared to high-k layer. Current trends indicate that the formation of appropriate thickness of GeOx or GeO2 between high-k and Ge substrate seems to have low interface state density (Dit). Since ZrO2 showed lower leakage current than HfO2 with similar dielectric high-k stack, ZrO2/Al2O3 bilayer as gate dielectric is becoming popular. Even though excellent gate stacks on germanium substrate has been demonstrated the reliability and the impact of interfacial layer is still unknown.

This work investigates the p-Ge/Al2O3/ZrO2/TiN gate stacks with thin GeO2 or GeOx layer, formed when the gate stack was exposed to pre- or post-deposition slot plane antenna plasma oxidation (SPAO). The post Al2O3/ZrO2 deposition SPAO forms relatively thicker GeO2 and post Al2O3 deposition SPAO forms thinner GeO2 whereas pre-deposition SPAO forms thin fragmented GeOx layer at the interface. We have observed that the relatively thicker GeO2 interfacial layer formed after the post Al2O3/ZrO2 deposition SPAO degraded faster during time dependent dielectric breakdown (TDDB) measurements on substrate injection mode compared to the thin GeO2 or GeOx interfacial layers (Fig. 1). The improvement in TDDB degradation for thinner interfacial layer thickness suggests that electrons tunnel through the thinner GeOx IL, and TDDB measured the quality of Al2O3 rather than IL.

The TDDB characteristics in gate injection mode suggests that the SPAO can significantly affect the TDDB characteristics GEI mode (Fig. 1). The SPAO treatment effectively removes the trap centers in ZrO2 and Al2O3 layers when SPAO was performed after the gate stack deposition. By employing carrier transport mechanisms as a function of temperature in both gate and substrate injection mode we were able to identify the traps that contributes to the TDDB degradation. The trap center (ft1 = 0.13 eV) observed in the ZrO2 when ZrO2 is not subjected to the SPAO, i.e. pre-deposition SPAO. This trap ft1 (0.13 eV) was eliminated for post Al2O3/ZrO2 deposition SPAO. While defects in the ZrO2 layer determines the TDDB characteristics in gate injection mode the GeO2 or GeOx interfacial layer thickness determines the TDDB degradation in substrate injection mode.