| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 99 === The objective of this study is to prepare different Cr-N-O thin films by using air as a reactive gas instead of conventional used nitrogen and oxygen gas. The process was conducted at high base pressures (low vacuum), which could substantially reduce the pumping time to achieve the aims of lowering manufacturing cost and saving energy in industrial applications. The deposition was conducted by DC magnetron sputtering at air/Ar flow ratios varying from 0 to 2.00; two sputtering powers of 100 W and 400 W were selected; the base pressure was 1.3×10-2 Pa; the working pressure was varied in the range of 0.21–0.36 Pa; the bias voltage was kept at -50 V; the sputtering time was fixed at 20 minutes. The crystal structures, chemical compositions, resistivity, hardness, and optical band gap of the deposited films at different air/Ar flow ratios and sputtering power were investigated.
As the sputtering power was 400 W and air/Ar ratio was 0–0.05, the films were identified to be the body-centered cubic Cr structure by X-ray diffraction (XRD). The resistivities of the films measured by a four probe system were about 31–75 μΩ–cm. The obtained films were Cr. When the air/Ar ratios were in the range of 0.10–0.35, the resistivities of the films were between 102 and 260 μΩ–cm, and the hardnesses obtained by using a nanoindentor were 19.2–21.2 GPa. Furthermore, the films possessed mixed phase structures, which were revealed by a broad diffraction peak around 42°–46°(2θ). Based on above analyses, the films consisted of Cr/Cr2N/CrN/CrNxOy. As the air/Ar ratio rose to 0.40–0.50, the deposited films had a CrN rock-salt structure. X-ray photoelectron spectroscopy (XPS) analysis indicated that the N/Cr ratios of the films were 0.38–0.46 with 19.7–30.8 at% of oxygen. The resistivities and hardnesses of the films were 326–4.2×105 μΩ–cm and 17.0–24.0 GPa, respectively. The films possessed crystalline CrNxOy. When the air/Ar ratio increased to 0.55–0.60, the obtained films were amorphous. The hardnesses of the films were about 20.9–24.0 GPa. The N/Cr ratio of the films decreased to 0.21–0.23 while the oxygen of the films increased up to 42.5–45.1 at%, thus the measured resistivitiy was out of the scale. The results indicated that the CrNxOy films could transform from crystalline into amorphous. Moreover, the structure of the films changed to N-doped CrOx phase as the air/Ar ratio reached 0.80–2.00. Because the N/Cr ratios of the films declined 0.05–0.07 and the O/Cr ratios of the films were up to 1.20–1.27. The optical band gaps of the films that calculated from UV-Vis spectra were in the range of 3.10–3.31 eV.
When the sputtering power of 100 W was applied and only Ar was used, the deposited films also exhibited a body-centered cubic structure. The resistivity of the films was 161 μΩ–cm. The obtained films were Cr. As the air/Ar ratio reached 0.02–0.10, the resistivities of the films were in the range of 180–554 μΩ–cm. The broad peak of each specimen utilizing XRD was in the neighborhood of 42°–46°(2θ). According to the results, the films exhibited mixed Cr/Cr2N/CrN/CrNxOy phases. Moreover, amorphous N-doped CrOx films could be obtained at the air/Ar ratios of 0.15–2.00, and the optical band gaps of the films were varied from 2.98–3.29 eV.
The process windows of the Cr-N-O thin films at various air/Ar flow ratios as well as the sputtering powers were investigated. Therefore, the structures of Cr-N-O thin films at different air/Ar ratios could be successfully identified. Moreover, the formation of the films predominated by two mechanisms: kinetics and thermodynamics, which depend on the air/Ar flow ratios. Results indicated that the film deposition was predominated by the kinetics mechanism at lower air/Ar flow ratios, which resulted in the different structures of Cr, mixed Cr/Cr2N/CrN/CrNxOy, crystalline and amorphous CrNxOy observed in the films. On the other hand, the films became N-doped CrOx as the air/Ar flow ratio was relatively high, which is due to the thermodynamics governed formation.
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