Specific Process Knowledge/Thin film deposition/Deposition of Gold/Adhesion layers: Difference between revisions
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The first analysis was performed to clarify if oxygen was originating from source i). To rule out possible oxygen migration from the oxygen-rich SiO2 substrate, the metal thin-films were deposited on amorphous Si3N4. For both samples, after Ar ion milling of 20 nm of Au, the Au 4f signal intensity decreased and Cr 2p and Ti 2p signals started to appear together with the O 1s signal (Fig. 10a for Ti and 10b for Cr, respectively). | The first analysis was performed to clarify if oxygen was originating from source i). To rule out possible oxygen migration from the oxygen-rich SiO2 substrate, the metal thin-films were deposited on amorphous Si3N4. For both samples, after Ar ion milling of 20 nm of Au, the Au 4f signal intensity decreased and Cr 2p and Ti 2p signals started to appear together with the O 1s signal (Fig. 10a for Ti and 10b for Cr, respectively). | ||
[[File:Picture13.png| | [[File:Picture13.png|450px|center|thumb|Fig. 10: XPS depth profiling of 2nm Ti/20nm Au (a) and 2nm Cr/20nm Au (b) samples deposited on Si3N4 substrate. Both samples show the presence of a Au 4f signal from the surface to a depth of 20 nm. For a depth deeper than 20 nm, both Ti 2p and Cr 2p signals appear together with the O 1s signal.]] | ||
Peak fits for the Ti and Cr signals were performed, and are reported in Fig. 11. The Ti 2p peak is a convolution of three components: a TiN doublet at 455.0 and 461.1 eV, a TiO2 doublet at 457.7 and 464.0 eV and a TiOx signal, which forms the descending background tail. The fit gives the following information: 1) Ti has formed Ti-N bonds with the Si3N4 substrate; 2) the adhesion layer was partially oxidized during deposition and not from source i). Metallic Ti could not be detected, but its presence cannot be excluded: metallic Ti is highly reactive with respect to oxygen and nitrogen, and the destructive sputtering process used for the depth profiling could have enhanced the mixing between Ti, O and N, catalyzing the reaction of the metallic Ti bound to Au to form an oxide or a nitride. The Cr 2p peak fit is formed by three components: a metallic Cr doublet at 574.4 and 583.6 eV, a Cr2O3 doublet at 576.3 and 585.6 eV and a CrO3 doublet at 580 and 589.2 eV. The result of the fit indicates a partial oxidation of Cr, as in the Ti case. | Peak fits for the Ti and Cr signals were performed, and are reported in Fig. 11. The Ti 2p peak is a convolution of three components: a TiN doublet at 455.0 and 461.1 eV, a TiO2 doublet at 457.7 and 464.0 eV and a TiOx signal, which forms the descending background tail. The fit gives the following information: 1) Ti has formed Ti-N bonds with the Si3N4 substrate; 2) the adhesion layer was partially oxidized during deposition and not from source i). Metallic Ti could not be detected, but its presence cannot be excluded: metallic Ti is highly reactive with respect to oxygen and nitrogen, and the destructive sputtering process used for the depth profiling could have enhanced the mixing between Ti, O and N, catalyzing the reaction of the metallic Ti bound to Au to form an oxide or a nitride. The Cr 2p peak fit is formed by three components: a metallic Cr doublet at 574.4 and 583.6 eV, a Cr2O3 doublet at 576.3 and 585.6 eV and a CrO3 doublet at 580 and 589.2 eV. The result of the fit indicates a partial oxidation of Cr, as in the Ti case. | ||
[[File:Picture14.png| | [[File:Picture14.png|450px|center|thumb|Fig. 11: Left: Ti 2p XPS peak fit of the 2-Ti/20-Au sample. Right: Cr 2p XPS peak fit of the 2-Cr/20-Au sample.]] | ||
The second analysis was performed to understand whether the oxygen was originating from source ii) or iii). A 2-Ti/20-Au/2-Ti/20-Au sandwich structure was deposited and analyzed. Both layers of Ti were partially oxidized: the Ti 2p peak signals (Fig. 5.13a) are present at the same depth together with the O 1s signals (Fig. 5.13b). The O 1s signal in the Ti layer in contact with the Si3N4 substrate has higher intensity than the one of the Ti layer between the Au layers. Hence, the Ti layer in contact with the substrate is more oxidized, which suggests that Ti reacted with water adsorbed on the substrate surface. The conclusion is that the oxygen originated from sources ii) and iii). | The second analysis was performed to understand whether the oxygen was originating from source ii) or iii). A 2-Ti/20-Au/2-Ti/20-Au sandwich structure was deposited and analyzed. Both layers of Ti were partially oxidized: the Ti 2p peak signals (Fig. 5.13a) are present at the same depth together with the O 1s signals (Fig. 5.13b). The O 1s signal in the Ti layer in contact with the Si3N4 substrate has higher intensity than the one of the Ti layer between the Au layers. Hence, the Ti layer in contact with the substrate is more oxidized, which suggests that Ti reacted with water adsorbed on the substrate surface. The conclusion is that the oxygen originated from sources ii) and iii). | ||