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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: 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.According to STM, Al2O3 grows homogeneously on Cu(111) terraces.

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.


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STM images(a) 200 nm × 200 nm and (b) 50 nm × 50 nm obtained afterthe second TMA half-cycle (2000 L TMA at 473 K). (c) Zoom-in regionof the highlighted section in image b and the line profile along thesolid line indicated in the image. The tunneling current was 0.5 nA;the bias voltage was −0.9 V.
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fig11: STM images(a) 200 nm × 200 nm and (b) 50 nm × 50 nm obtained afterthe second TMA half-cycle (2000 L TMA at 473 K). (c) Zoom-in regionof the highlighted section in image b and the line profile along thesolid line indicated in the image. The tunneling current was 0.5 nA;the bias voltage was −0.9 V.

Mentions: Figure 11 shows STM images obtainedafter the second TMA half-cycle. Numerous holes were seen on terracesand islands. Terraces were covered with islands having sharp boundariesand a ridge-like structure (marked by a rectangle in Figure 11b,c). These morphologicalchanges reflected the transition from monolayer alumina islands afterthe first TMA half-cycle (Figure 9) to multilayer islands, as the ridge structure islikely the second alumina layer and/or CuAlO2. The ridgeshave an apparent height of about 0.17 nm (Figure 11b), close to the average height for thealumina islands (0.19 nm) after the first TMA half-cycle observedin Figure 9.


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(a) 200 nm × 200 nm and (b) 50 nm × 50 nm obtained afterthe second TMA half-cycle (2000 L TMA at 473 K). (c) Zoom-in regionof the highlighted section in image b and the line profile along thesolid line indicated in the image. The tunneling current was 0.5 nA;the bias voltage was −0.9 V.
© Copyright Policy
Related In: Results  -  Collection

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

fig11: STM images(a) 200 nm × 200 nm and (b) 50 nm × 50 nm obtained afterthe second TMA half-cycle (2000 L TMA at 473 K). (c) Zoom-in regionof the highlighted section in image b and the line profile along thesolid line indicated in the image. The tunneling current was 0.5 nA;the bias voltage was −0.9 V.
Mentions: Figure 11 shows STM images obtainedafter the second TMA half-cycle. Numerous holes were seen on terracesand islands. Terraces were covered with islands having sharp boundariesand a ridge-like structure (marked by a rectangle in Figure 11b,c). These morphologicalchanges reflected the transition from monolayer alumina islands afterthe first TMA half-cycle (Figure 9) to multilayer islands, as the ridge structure islikely the second alumina layer and/or CuAlO2. The ridgeshave an apparent height of about 0.17 nm (Figure 11b), close to the average height for thealumina islands (0.19 nm) after the first TMA half-cycle observedin Figure 9.

Bottom Line: 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.According to STM, Al2O3 grows homogeneously on Cu(111) terraces.

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