Introduction
We Hualincona studied the effect of the wet cleaning process of solvents and cleaning agents on the chemical properties of the substrate surface of the deposited magnesium oxide (001). Six different wet cleaning processes using solvents and detergents were compared. The effect on film growth was studied by the example system ScN. The surface chemistry of the cleaning surface was studied using X-ray photoelectron spectroscopy, and the film/substrate interface after film growth was studied using time-of-flight secondary ion mass spectroscopy. The composition of the surface depends on the wet cleaning process. Sonication before solvent in detergent produces pure oxide surfaces compared to hydroxide/carbonate contaminated surfaces in all other processes. The annealing step is effective for removing carbon pollutants as well as most hydroxides or carbonates. Research on film/substrate interfaces has shown that the wet cleaning process significantly affects the final interface and film quality. The substrate that is cleaned with detergent and then cleaned with solvent shows the cleanest substrate surface before annealing and after annealing, and also shows the clearest film/substrate interface.
Experiment
Preparation of samples
Before any experiment, the MgO substrate and substrate with size 10 × 10 mm2 were sealed separately and stored in a desiccator. Reference samples marked REF were purged with nitrogen only. Different ultrasonic treatments in the solvent were used in the wet cleaning process and dried under a nitrogen stream, and finally: acetone (10 minutes) + isopropanol (10 minutes)
(labeled as AI); acetone (10 minutes) + ethanol (10 minutes) (labeled as AE); heptane (10 minutes) + acetone (10 minutes) + ethanol (10 minutes) (labeled as HAE). The soap/cleaner used in this study was diluted II in the recommended ratio (2 vol.%). A II alkaline concentrated detergent (K3PO4 15-30%, anionic surfactant 15%, non-anionic surfactant 5%) is a commercial cleaning solution for cleaning test tubes and is widely used for cleaning glass substrates. Detergents with similar ingredients or sold for the same purpose should produce similar effects as those observed in this study. The substrate was washed in detergent with ultrasonic wave for 3 minutes, followed by rinsing in deionized water twice (labeled D). Finally, a combination of detergent and solvent is used in the detergent "method", followed by acetone for 10 minutes, followed by ethanol for 10 minutes (labeled as DAE). In a deposition chamber with a substrate pressure of 10-8 Torr, the same wet cleaning procedure was used before the annealing step of 700°C/2h. To evaluate the effect on film growth, a 150-nanometer thick silicon nitride film was deposited on a magnesium oxide (001) substrate by DC magnetron sputtering at a substrate temperature of 120 watts, 0.27 Pa (2 mTorr) total pressure, 25% N2 and 950°C for 75 minutes. Prior to deposition, the substrate is cleaned by the different wet cleaning procedures described above and then annealed in situ at 700°C/2h under vacuum (10-8 Torr). For simplicity and readability, 18 samples were used in abbreviation, listed in Table 2. Cleaning of samples was performed before different characterizations, with the shortest time between cleaning and insertion of XPS and ToF-Sims chambers or contact angle measurements (the sample remains sealed in the box for transport). To maintain the time limit between cleaning and analysis and to avoid any more contamination on the surface, a new substrate was adopted and repeated cleaning of the three parts of the study (wet cleaning/annealing/deposition).
Time of Flight Secondary Ion Mass Spectrometry (ToF-Sims) The element distribution in the
membrane was measured by the time of Flight Secondary Ion Mass Spectrometry (ToF-Sims) using ToF. Sims V Instrument (German Ion Time of Flight Co., Ltd.). The double beam depth distribution is completed in positive and negative secondary ion mode by alternately applying the analysis beam and the sputtering beam (non-interleaved). Here, as a function of sputtering time, the selected positive corresponding negative secondary ion species are monitored. During cross-sectional measurements, low-energy electron injection is used for charge compensation.
Discussion on wet cleaning treatment of
magnesium oxide (001) substrate. In-situ annealing treatment of MgO (001) substrate after wet cleaning. Deposition of ScN film on magnesium oxide substrate. Result
Recommended cleaning process depends on the requirements of film deposition and application. However, using a cleaning process of sonication in detergents, followed by sonication in acetone and ethanol, the cleanest surface with pure oxides is produced after wet cleaning.This process is also the only process that presents a pure oxide surface after annealing, while another process results in the cleanest surface with a single layer of hydroxide on the surface. Finally, in the case of ScN film deposition, sonication in the detergent and subsequent sonication in the solvent leads to the sharpest membrane/substrate interface in the case of ScN film deposition.
