Soft X‐ray characterization of ion beam sputtered magnesium oxide (MgO) thin film

Abstract

In the present study, surface and interface characterization of magnesium oxide (MgO) thin film is carried out by using non‐destructive soft X‐ray reflectivity and absorption technique. To get a further insight about the in‐depth and surface composition, secondary ion mass spectroscopy measurement is also carried out. The analysis of the reflectivity data indicates the presence of Mg‐Si‐O layer between the principal layer (MgO) and Si substrate interface. The secondary ion mass spectroscopy spectra corroborate well with the model assumed in the analysis of the reflectivity data. Combined soft X‐ray reflectivity‐total electron yield result confirms the presence of low‐density MgO on top of principal MgO layer. Total electron yield result confirms the rocksalt structure of the film and provides a glimpse of the electronic structure near the O‐K absorption edge.

Non‐Oxidative Mechanism in Oxygen‐Based Magneto‐Ionics

“…Moving toward higher sputtering times, the signal decreases up to the point where the 30 Si signal increases, marking the vicinity of the Ta/SiO 2 interface. Similarly, by moving from the center of the CoFeB layer toward lower sputtering times an increase in the MgO and 18 O signals is evidenced, which indicates the vicinity of the CoFeB(Pt)/MgO interface. The shaded area between 80 s and 42 s indicates the approximate position of the MgO layer, the upper limit of 42 s is chosen based on the change of slope seen in the profiles of OH, MgO, and 18 O below 50 s. The 18 O and MgO profiles, shown in Figure 5b,c, respectively, are convoluted with the SiO 2 and SiC signals at high sputtering times due to mass interference, and do not evolve significantly after gating with negative voltages.…”

“…Similarly, by moving from the center of the CoFeB layer toward lower sputtering times an increase in the MgO and 18 O signals is evidenced, which indicates the vicinity of the CoFeB(Pt)/MgO interface. The shaded area between 80 s and 42 s indicates the approximate position of the MgO layer, the upper limit of 42 s is chosen based on the change of slope seen in the profiles of OH, MgO, and 18 O below 50 s. The 18 O and MgO profiles, shown in Figure 5b,c, respectively, are convoluted with the SiO 2 and SiC signals at high sputtering times due to mass interference, and do not evolve significantly after gating with negative voltages. Interestingly, the OH profile evolves independently of the 18 O and MgO profiles, showing a clear decrease in content in the region corresponding to the position of the MgO layer after gating with negative voltages as shown in Figure 5a.…”

“…[7,16,17] Pre-edge features have also been detected in MgO thin films and substrates, which was correlated to the crystalline structure. [18] HfO 2 films can also present pre-edge features related to the presence of oxygen vacancies. [19] This makes the analysis of the Oxygen K-edge structure in this system a very complex task.…”

“…The shaded area between 80 s and 42 s indicates the approximate position of the MgO layer, the upper limit of 42 s is chosen based on the change of slope seen in the profiles of OH, MgO, and 18 O below 50 s. The 18 O and MgO profiles, shown in Figure 5b,c, respectively, are convoluted with the SiO 2 and SiC signals at high sputtering times due to mass interference, and do not evolve significantly after gating with negative voltages. Interestingly, the OH profile evolves independently of the 18 O and MgO profiles, showing a clear decrease in content in the region corresponding to the position of the MgO layer after gating with negative voltages as shown in Figure 5a. This further supports the idea of a gate induced loss of hydroxyl groups, which can be related with the dehydration of regions in the MgO layer that are rich in Mg(OH) 2 .…”

“…Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS): ToF-SIMS depth profiles were collected in an upgraded ION-TOF IV instrument (ION-TOF GmbH) using 500 eV Cs+ ions for sputtering a 300 μm × 300 μm area and 25 keV Ga+ ions with an energy of 25 keV for the analysis of a 50 μm × 50 μm area at the center of the sputtered region, operating in interlaced mode. Secondary ions were collected in negative polarity and the collected intensities normalized to the signal of 18 Oin the middle of the HfO 2 layer. 18 O was selected as a robust signal to probe Oxygen because its natural abundance ( 0.2%) allowed to avoid saturation in detection in oxide layers, such as HfO 2 and MgO, a situation occurring if 16 O, the most abundant Oxygen isotope, would be considered.…”