S-Space College of Engineering/Engineering Practice School (공과대학/대학원) Dept. of Material Science and Engineering (재료공학부) Theses (Ph.D. / Sc.D._재료공학부)
Characterization of Atomic Layer Deposited Lanthanum Silicate Films for a Gate Oxide of Si and Ge Devices
- 공과대학 재료공학부
- Issue Date
- 서울대학교 대학원
- high-κ; ALD; La-silicate; La2O3; Al2O3; SiO2; Si; Ge; deposition behavior; Ozone; leakage current mechanism; XPS
- 학위논문 (박사)-- 서울대학교 대학원 : 재료공학부, 2014. 2. 김형준.
- The effect of oxygen sources, i.e. O3 or H2O, on chemical composition, dielectric constant and leakage current density of atomic-layer-deposited La-silicate films on Si substrate was examined. The dielectric constant of La-silicate films grown on Si substrate using O3 was ~ 8.0, which was lower than that of La-silicate films grown using H2O, ~ 11.7 due to the higher Si concentrations. However, leakage current density of La-silicate films grown using O3 was about 3 orders of magnitude lower than that of La-silicate films grown using H2O at an identical capacitance-equivalent-thickness (but almost half the physical thickness), due to the higher Si concentrations and less La-carbonate formation.
We have investigated the effects of Si concentrations in La-silicate film formed by ALD on Ge substrate of the electric property especially in reduction of C-V hysteresis. La-silicate film with Si concentration increment (~ 25 % to ~ 35 %) on Ge substrate effectively reduced C-V hysteresis due to suppression of Ge sub-oxide generation calculated from XPS analysis.
La-silicate film with very thin Al2O3 interface passivation layer on Ge substrate obtained smaller C-V hysteresis as ~238 mV due to lower interface state density by suppression of Ge sub-oxide formation. BEMAS-SiO2 capping La-silicate film with Al2O3 interface passivation layer showed smaller Ge sub-oxide formation as smaller C-V hysteresis shown.
Al2O3 interface passivation La-silicate film and SiO2 capping La-silicate film with Al2O3 interface passivation layer has tendency of low leakage current density. It is also found that the Al2O3 thickness of 1– 2 monolayer and SiO2 capping is critical for the reduction of the interface state density.
In conclusion, the ALD-Al2O3 interfacial passivation layer and SiO2 capping, whose thickness can be precisely controlled, is effective for controlling the formation of Ge oxides at high-k/Ge interfaces.