Updates of Iowa State University S. Dumpala, S. Broderick and K. Rajan Sep – 18, 2013 Summary • Refinements in Environmental chamber set up for in-situ gas reactions • Oxidation studies of Al using new set up of E-cell • Preliminary analysis of silicon oxidation results in comparison with ReaxFF simulations (Adri’s papers) • Further analysis of silicon oxidation growth mechanisms and sub oxide species at different temperatures • Study of Si tips from Maryland using APT Aluminum Oxidation E-Cell APT Results Bulk Alumina Phase 3D atomic scale interfacial analysis (structural and chemical) Stoichiometry of different phases observed Inter-diffusional characteristics of elements Bulk Al Phase Reduced Contamination with In-situ E-Cell Oxidation Ex-situ Oxidation Unkown peaks. In-situ E-cell Oxidation • Numerous additional peaks representing contamination that were detected in ex-situ oxidation were absent in in-situ oxidation results. Increased Mass Resolution with In-situ E-Cell Oxidation Ex-situ Oxidation In-situ E-cell Oxidation Unkown peaks. • Lower mass resolution with longer tails of the peaks were seen in ex-situ APT of Si Tips from Maryland : Anode Voltage: 250 V of Argon exposure Bare Si Tip 50 monolayers 150 monolayers • Laser APT – 1nj (laser power) • Higher Ar content in beam exposed tips compared to bare Si tip Bare Si Tip Mass Spectra 50 monolayers 1. Small peak of Ar 150 monolayers 2. Check other condition tips (Different beam currents) 3. Different deposition thickness of monolayers 4. FIM studies Oxidation of Silicon ReasFF Simulations APT- Experimental • Hyper thermal oxidation (atomic and molecular oxygen beam source) • Plasma oxidation (ambient oxygen) • Dynamic study • Static study (post deposition study) • Smaller time scales (3pc) • Longer time scales (minutes) • Monolayer detection • Sub nano scale detection Interfacial Diffusion – Interfacial Width 383 K 100 548 K 2 nm 90 90 80 Concentration (at%) Concentration (at%) 2.5 nm 100 70 60 50 40 30 20 10 80 70 60 50 40 30 20 10 0 0 -5 -4 -3 -2 -1 0 1 Distance (nm) -4 -2 0 2 3 2 4 5 -5 4 -4 -4 -3 -2 -2 -1 0 1 Distance (nm) 0 2 2 3 4 4 5 -2 -2 0 0 2 2 Diffusion Profiles – Sub Oxides 100 90 Region II Region I Concentration (at%) Region III 70 60 50 40 30 20 80 2.5 nm 548 K 50 40 30 20 0 0 -3 25 -2 -1 0 1 2 3 4 Region I Region II 60 10 -4 Region III 70 10 -5 -5 5 -4 -3 -2 -1 0 1 2 3 4 5 Distance (nm) Distance (nm) 20 Si2O % 20 SiO 15 SiO2 10 5 Concentration (at%) Concentration (at%) 100 90 80 Concentration (at%) 2 nm 383 K 18 16 Si2O % 14 SiO 12 SiO2 Si2O % 10 SiO2 SiO 8 6 4 2 0 0 -5 -4 -3 -2 -1 0 1 Distance (nm) 2 3 4 5 -5 -4 -3 -2 -1 0 1 Distance (nm) 2 3 4 5 Analysis of Interfacial Sub Oxides – Comparison of Simulations with APT Average Concentration (at%) ReaxFF Simulation 6 Atom Probe (Interfacial Region) Si2O 5 SiO 4 SiO2 3 Si2 SiO 2 1 0 • Interface region – Between bulk Si, and bulk silica (region II from proxigrams) • The total number of sub oxide species Region II Region III increase with increase temperature, observed similar trend in APT results • Relative amounts/ratio of Si+1 (Si2O), Si+2 (SiO) at two different temperatures agrees with simulations • Silica layer – 1. Surface, 2. Bulk (Si+4 components in interface) Average Concentration (at%) 383 K 8 Si2O 7 SiO 6 5 548 K SiO2 4 3 2 1 0 383 K 548 K Analysis of Si+4 (SiO2) Oxides – Comparison of Simulations with APT 16 Average Concentration (at%) ReaxFF Simulation Atom Probe (Silica Region) 14 Si2O 12 SiO 10 SiO2 8 6 4 2 0 383 K • 548 K For 8 ML, the number of Si4+ components is much higher at low temperatures than at high temperatures, indicating that the initial growth of the silica (SiO2) Region II Region layer occurs much faster at low thanIIIat high temperature • After 32 ML, number of Si4+ components is almost same at all temperatures indicating that the silica layer now grows faster at higher temperatures, but its nucleation started later • APT results also indicate the presence of almost same number of Si4+(SiO2) components at both the temperatures Growth Mechanism - Low Temperature ReaxFF - 300 K 500 450 400 350 APT 300 - 383 K 25 100 Region II Region I 70 200 60 50 40150 30 20 100 20 15 Average Concentration (at%) Region III 80 Concentration (at%) 90250 Concentration (at%) 14 2 nm Si2O % 12 SiO 10 SiO2 10 5 10 0 -5 50 • • -4 -3 -2 -1 0 Distance (nm) 1 2 3 4 5 Si2O SiO SiO2 8 Si2O % SiO2 6 SiO 4 2 0 0 -5 -4 -3 -2 -1 0 1 2 3 4 5 Region I Region II Region III Distance (nm) 0 Stage I - Growth of sub oxides and an incipient silica layer growth I Region II III Stage II -1)Region Continued growth of sub oxides and alsoRegion growth of silica observed, 2) Inward growth rate of sub oxides drops (high activation energy) (mainly Si2O) due to fast -3 -2 -1 0 1 2 3 4 5 conversion of Si+1 Si+2 Si+4 • Stage III, IV - Growth of sub oxides and silica slowed down Growth Mechanism - High Temperature ReaxFF - 1300 K 500 450 400 350 APT300- 548 K 80 Region III 200 70 Region I Region II 60 50 150 40 30 100 20 14 18 Si2O % 12 16 10 SiO 14 12 SiO2 10 8 6 4 2 10 -5 -4 -3 -2 -1 0 1 2 3 4 -5 5 SiO SiO2 S 8 Si2O % S SiO S 6 SiO2 4 2 -4 -3 -2 -1 0 1 2 3 4 5 Region I Region II Region III Distance (nm) Distance (nm) 20 Si2O 0 0 50 0 • • Average Concentration (at%) 90 Concentration (at%) 2.5 nm 250 Concentration (at%) 100 16 20 0 18 Concentration (at%) Regionof I sub oxides and Region Region III growth Stage I - Growth anII incipient silica layer Si2O % 14 SiO Stage II -1) Continued growth of sub oxides and also growth of silica observed, 2) Inward 12 SiO2 -310 growth -2 rate-1of sub 0 oxides 1 2 3 does 4 not drop 5 still continues as in lower temperature case • 8 Stage III, IV – 1) Continued growth of sub oxides (interstitial neutral oxygen atoms 6 4 surmount the activation energy barrier at threshold T of 500 K), 2) Interface (consisting of 2 sub oxides) is thicker than low T and 3) Inward growth of silica slows down 0 16 Si2O % SiO SiO2 Effect of Temperature on Growth Mechanism 500 ReaxFF 450 400 350 300 - 383 K APT 25 Region III 80 Region II 500 70 Concentration (at%) 250 90 Concentration (at%) 14 2 nm Region I 200 60 50 450 150 40 30 20 100 10 0 -5 -4 50 400 350 -3 Si2O % 20 12 10 SiO 15 Average Concentration (at%) 100 SiO2 Si2O % -1 0 1 2 3 4 SiO 5 -4 -3 -2 -1 0 1 2 3 4 20 Region I 2.5 nm -1 Region II 0 Region I 1 150 40 30 100 20 Region II Region III 18 60 50 Region I 2 3 16 4 14 Si2O % 12 5 SiO 14 12 SiO2 10 8 6 4 10 2 10 -5 -4 -3 -2 Region II Region III -1 0 Distance (nm) 1 2 3 4 5 Si2O SiO SiO2 8 Si2O % SiO 6 SiO2 4 2 0 0 50 0 2 5 Average Concentration (at%) 70 -2 Region III 200 4 16 Concentration (at%) Concentration (at%) 90 -3 80 6 Distance (nm) Distance (nm) 250 SiO2 8 0 -5 5 300 APT 0 - 548 K 100 SiO SiO2 10 0 -2 Si2O -5 -4 -3 -2 -1 0 1 Distance (nm) 2 3 4 5 Region I Region II Region III Future • Study of thermal oxidation (silicon) case • Analysis of bonding information in different regions (bulk, interface) from APT data that could offer complimentary information to the bond length and bong angle analysis by ReaxFF.