Limits...
Trimethylaluminum and Oxygen Atomic Layer Deposition on Hydroxyl-Free Cu(111).

Gharachorlou A, Detwiler MD, Gu XK, Mayr L, Klötzer B, Greeley J, Reifenberger RG, Delgass WN, Ribeiro FH, Zemlyanov DY - ACS Appl Mater Interfaces (2015)

Bottom Line: TMA did not adsorb on the Cu(111) surface, a result consistent with density functional theory (DFT) calculations predicting that TMA adsorption and decomposition are thermodynamically unfavorable on pure Cu(111).On the other hand, TMA readily adsorbed on the Cu2O/Cu(111) surface at 473 K resulting in the reduction of some surface Cu(1+) to metallic copper (Cu(0)) and the formation of a copper aluminate, most likely CuAlO2.O2 half-cycles at 623 K were more effective for carbon removal than O2 half-cycles at 473 K or water half-cycles at 623 K.

View Article: PubMed Central - PubMed

Affiliation: †School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907, United States.

ABSTRACT
Atomic layer deposition (ALD) of alumina using trimethylaluminum (TMA) has technological importance in microelectronics. This process has demonstrated a high potential in applications of protective coatings on Cu surfaces for control of diffusion of Cu in Cu2S films in photovoltaic devices and sintering of Cu-based nanoparticles in liquid phase hydrogenation reactions. With this motivation in mind, the reaction between TMA and oxygen was investigated on Cu(111) and Cu2O/Cu(111) surfaces. TMA did not adsorb on the Cu(111) surface, a result consistent with density functional theory (DFT) calculations predicting that TMA adsorption and decomposition are thermodynamically unfavorable on pure Cu(111). On the other hand, TMA readily adsorbed on the Cu2O/Cu(111) surface at 473 K resulting in the reduction of some surface Cu(1+) to metallic copper (Cu(0)) and the formation of a copper aluminate, most likely CuAlO2. The reaction is limited by the amount of surface oxygen. After the first TMA half-cycle on Cu2O/Cu(111), two-dimensional (2D) islands of the aluminate were observed on the surface by scanning tunneling microscopy (STM). According to DFT calculations, TMA decomposed completely on Cu2O/Cu(111). High-resolution electron energy loss spectroscopy (HREELS) was used to distinguish between tetrahedrally (Altet) and octahedrally (Aloct) coordinated Al(3+) in surface adlayers. TMA dosing produced an aluminum oxide film, which contained more octahedrally coordinated Al(3+) (Altet/Aloct HREELS peak area ratio ≈ 0.3) than did dosing O2 (Altet/Aloct HREELS peak area ratio ≈ 0.5). After the first ALD cycle, TMA reacted with both Cu2O and aluminum oxide surfaces in the absence of hydroxyl groups until film closure by the fourth ALD cycle. Then, TMA continued to react with surface Al-O, forming stoichiometric Al2O3. O2 half-cycles at 623 K were more effective for carbon removal than O2 half-cycles at 473 K or water half-cycles at 623 K. The growth rate was approximately 3-4 Å/cycle for TMA+O2 ALD (O2 half-cycles at 623 K). No preferential growth of Al2O3 on the steps of Cu(111) was observed. According to STM, Al2O3 grows homogeneously on Cu(111) terraces.

No MeSH data available.


Related in: MedlinePlus

STM images after first O2 half-cycle(4500 L O2 at 623 K) (a) 200 nm × 200 nm, (b) 50 nm× 50 nm, and (c) 25 nm × 25 nm. (d) Line profile along thesolid white line indicated in image c. It = 1.0 nA, Ut = −0.75 V.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4528256&req=5

fig10: STM images after first O2 half-cycle(4500 L O2 at 623 K) (a) 200 nm × 200 nm, (b) 50 nm× 50 nm, and (c) 25 nm × 25 nm. (d) Line profile along thesolid white line indicated in image c. It = 1.0 nA, Ut = −0.75 V.

Mentions: Curve-fitting of theO 1s peak revealed two components: the component at 529.9 eV representsCu2O (19% of the total O 1s area) and the second componentat 530.8 eV is from oxygen in the copper aluminate (81% of the totalO 1s area) (Figure 5). An O 1s BE of 531.2 eV has been reported previously for thin filmalumina on Pt(111).29 The slight Cu 2p2/3 peak shoulder reappeared at ca. 936.0 eV, consistent withthe formation of some CuO (see Supporting Information Figure S1). Cu2O was also formed, as evidenced by long-rangeorder observed in STM images (Figure 10b,c). The Al 2s peak is distinguishable from the shoulderof Cu 3s at 118.7 eV (Figure 5). Al 2s shifted by −0.8 eV to 118.7 eV following O2 exposure. Lower Al 2p binding energies for aluminum oxideshave been attributed to the presence of Al3+ coordinatedtetrahedrally52−55 (see discussion in reference (29)). In this case, the Al 2p and Cu 3p peaks overlap, butthe Al 2s and Al 2p peaks should exhibit a similar chemical shiftin XPS. Here, the shift to lower BE is consistent with the formationof alumina with an increased Altet/Aloct ratiofollowing the O2 half-cycle. A hydroxide-containing speciescan cause a similar shift of the O 1s and Al 2p (Al 2s) peaks;56−58 however, no O–H stretching vibrations were detected by HREELSafter TMA or O2 half-cycles at ca. 3300–3700 cm–1. The Al:O ratio after the first O2 half-cyclewas approximately 0.53, nearly unchanged from after the first TMAcycle. The resulting Al:O atomic percentage ratios after each O2 half-cycle are plotted in Figure 8.


Trimethylaluminum and Oxygen Atomic Layer Deposition on Hydroxyl-Free Cu(111).

Gharachorlou A, Detwiler MD, Gu XK, Mayr L, Klötzer B, Greeley J, Reifenberger RG, Delgass WN, Ribeiro FH, Zemlyanov DY - ACS Appl Mater Interfaces (2015)

STM images after first O2 half-cycle(4500 L O2 at 623 K) (a) 200 nm × 200 nm, (b) 50 nm× 50 nm, and (c) 25 nm × 25 nm. (d) Line profile along thesolid white line indicated in image c. It = 1.0 nA, Ut = −0.75 V.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4528256&req=5

fig10: STM images after first O2 half-cycle(4500 L O2 at 623 K) (a) 200 nm × 200 nm, (b) 50 nm× 50 nm, and (c) 25 nm × 25 nm. (d) Line profile along thesolid white line indicated in image c. It = 1.0 nA, Ut = −0.75 V.
Mentions: Curve-fitting of theO 1s peak revealed two components: the component at 529.9 eV representsCu2O (19% of the total O 1s area) and the second componentat 530.8 eV is from oxygen in the copper aluminate (81% of the totalO 1s area) (Figure 5). An O 1s BE of 531.2 eV has been reported previously for thin filmalumina on Pt(111).29 The slight Cu 2p2/3 peak shoulder reappeared at ca. 936.0 eV, consistent withthe formation of some CuO (see Supporting Information Figure S1). Cu2O was also formed, as evidenced by long-rangeorder observed in STM images (Figure 10b,c). The Al 2s peak is distinguishable from the shoulderof Cu 3s at 118.7 eV (Figure 5). Al 2s shifted by −0.8 eV to 118.7 eV following O2 exposure. Lower Al 2p binding energies for aluminum oxideshave been attributed to the presence of Al3+ coordinatedtetrahedrally52−55 (see discussion in reference (29)). In this case, the Al 2p and Cu 3p peaks overlap, butthe Al 2s and Al 2p peaks should exhibit a similar chemical shiftin XPS. Here, the shift to lower BE is consistent with the formationof alumina with an increased Altet/Aloct ratiofollowing the O2 half-cycle. A hydroxide-containing speciescan cause a similar shift of the O 1s and Al 2p (Al 2s) peaks;56−58 however, no O–H stretching vibrations were detected by HREELSafter TMA or O2 half-cycles at ca. 3300–3700 cm–1. The Al:O ratio after the first O2 half-cyclewas approximately 0.53, nearly unchanged from after the first TMAcycle. The resulting Al:O atomic percentage ratios after each O2 half-cycle are plotted in Figure 8.

Bottom Line: TMA did not adsorb on the Cu(111) surface, a result consistent with density functional theory (DFT) calculations predicting that TMA adsorption and decomposition are thermodynamically unfavorable on pure Cu(111).On the other hand, TMA readily adsorbed on the Cu2O/Cu(111) surface at 473 K resulting in the reduction of some surface Cu(1+) to metallic copper (Cu(0)) and the formation of a copper aluminate, most likely CuAlO2.O2 half-cycles at 623 K were more effective for carbon removal than O2 half-cycles at 473 K or water half-cycles at 623 K.

View Article: PubMed Central - PubMed

Affiliation: †School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907, United States.

ABSTRACT
Atomic layer deposition (ALD) of alumina using trimethylaluminum (TMA) has technological importance in microelectronics. This process has demonstrated a high potential in applications of protective coatings on Cu surfaces for control of diffusion of Cu in Cu2S films in photovoltaic devices and sintering of Cu-based nanoparticles in liquid phase hydrogenation reactions. With this motivation in mind, the reaction between TMA and oxygen was investigated on Cu(111) and Cu2O/Cu(111) surfaces. TMA did not adsorb on the Cu(111) surface, a result consistent with density functional theory (DFT) calculations predicting that TMA adsorption and decomposition are thermodynamically unfavorable on pure Cu(111). On the other hand, TMA readily adsorbed on the Cu2O/Cu(111) surface at 473 K resulting in the reduction of some surface Cu(1+) to metallic copper (Cu(0)) and the formation of a copper aluminate, most likely CuAlO2. The reaction is limited by the amount of surface oxygen. After the first TMA half-cycle on Cu2O/Cu(111), two-dimensional (2D) islands of the aluminate were observed on the surface by scanning tunneling microscopy (STM). According to DFT calculations, TMA decomposed completely on Cu2O/Cu(111). High-resolution electron energy loss spectroscopy (HREELS) was used to distinguish between tetrahedrally (Altet) and octahedrally (Aloct) coordinated Al(3+) in surface adlayers. TMA dosing produced an aluminum oxide film, which contained more octahedrally coordinated Al(3+) (Altet/Aloct HREELS peak area ratio ≈ 0.3) than did dosing O2 (Altet/Aloct HREELS peak area ratio ≈ 0.5). After the first ALD cycle, TMA reacted with both Cu2O and aluminum oxide surfaces in the absence of hydroxyl groups until film closure by the fourth ALD cycle. Then, TMA continued to react with surface Al-O, forming stoichiometric Al2O3. O2 half-cycles at 623 K were more effective for carbon removal than O2 half-cycles at 473 K or water half-cycles at 623 K. The growth rate was approximately 3-4 Å/cycle for TMA+O2 ALD (O2 half-cycles at 623 K). No preferential growth of Al2O3 on the steps of Cu(111) was observed. According to STM, Al2O3 grows homogeneously on Cu(111) terraces.

No MeSH data available.


Related in: MedlinePlus