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Effect of annealing temperature on properties of Al–Cu–N thin films deposited by DC magnetron sputtering
Surface & Coatings Technology 201 (2007) 5570 – 5573 www.elsevier.com/locate/surfcoat
Effect of annealing temperature on properties of Al–Cu–N thin films deposited by DC magnetron sputtering M. Shariati ⁎, M. Ghoranneviss, H. Hosseini, M.R. Hantehzadeh Plasma Physics Research Center, Science and Research Campus, Islamic Azad University, Tehran, Iran Available online 10 August 2006
Abstract Al–Cu–N films have been deposited on steel substrate by DC magnetron sputtering. These samples were annealed at 200, 400, 600 and 800 °C under vacuum condition. The effects of annealing temperature on structure, morphology and optical properties of Al–Cu–N films were investigated. By means of X-ray diffraction (XRD) the phase composition was characterized. Atomic Force Microscopy (AFM) was used to evaluate and compare the surface roughness before and after annealing. Also UV–Vis–NIR spectrophotometer was used to investigate the optical properties of the samples. The results show that with increasing in the annealing temperature the intensity of the peaks gradually increased and the full width at half maximum (FWHM) of the peaks gradually decreased and also increasing in the grain size and the amount of the samples roughness during the annealing process are observed. It demonstrates that desirable reflectance and roughness of Al–Cu–N films deposited by DC reactive magnetron sputtering can be obtained by controlling the annealing temperature. © 2006 Elsevier B.V. All rights reserved. PACS: 68.55.-a; 81.15.Cd; 81.40.Ef; 78.68.+m Keywords: Al–Cu–N films; Annealing temperature; DC magnetron sputtering; XRD; AFM; Spectrophotometer
1. Introduction In recent years, much attention has been given to III-V semiconductors. Aluminum Nitride (AlN) with wurtzite hexagonal structure is one of the famous semiconductors in this group, which has wide applications for many acoustic and optical applications [1–3]. In parallel to these researches, new works have been done to add new elements to these families of semiconductors to produce new materials with new properties. Al–Cu–N, a nano-composite film, is produced by reactive sputtering technique which is a process that can work under low temperature. This nano-composite is a hard and super hard film (N40 GPa), composed of one hard and one soft phase [4]. It is well known that texture or preferred crystallographic orientation of materials strongly affects their properties. Also mechanical and thermal treatments influence the preferred orientation. ⁎ Corresponding author. Plasma Physics Research Center, Science and Research Campus, Islamic Azad University, P.O. Box: 14665-678, Tehran, Iran. Tel.: +98 21 44815921; fax: +98 21 44817165. E-mail address: [email protected] (M. Shariati). 0257-8972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.07.151
The purpose of this paper is to investigate the effect of annealing temperature on structure, morphology and optical properties of Al–Cu–N thin films. Steel has been chosen as a substrate because of its wide application in industry. Properties like corrosion resistance and oxidation resistance are some
Fig. 1. Schematic of the system.
M. Shariati et al. / Surface & Coatings Technology 201 (2007) 5570–5573 Table 1 Deposition condition Substrate-to-target distance Substrate Base pressure Final pressure Current Deposition time
30 mm Stainless steel (grade 304) 4.7 × 10− 5 Torr 2 × 10− 2 Torr 100 mA 1h
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Table 2 FWHM of the Al2Cu3 and Cu3N as-grown and annealed at 200, 400, 600 and 800 °C Sample
Al2Cu3
Cu3N
As-grown 200 °C 400 °C 600 °C 800 °C
0.5148 0.5034 0.4857 0.4649 0.4116
0.5832 0.5641 0.5430 0.5334 0.4202
characteristics which encourage researchers to use this alloy as a substrate. 2. Experimental The Al–Cu–N films were deposited by a reactive DC magnetron sputtering (Fig. 1). This system consists of two coaxial cylinders as cathode (inner one) and anode (outer one). The diameters of the outer and the inner cylinders are 10 cm and 3 cm, respectively and the height of the inner and the outer cylinders are 20 cm. In this experiment, it was used a composed target, a cylindrical Al with 3 cm diameter and a fine Cu wire which was twisted round to the Al target. Working gas is a mixture of Ar + N2 in the deposition chamber. Films were deposited under the condition which is presented in Table 1. The Al–Cu–N films were deposited on to polished and ultrasonically pre-cleaned AISI304 stainless steel substrates. The typical thickness of sputtered films was approximately 200 nm. The films thickness was measured with a Surface Profile Meter, Hommel Werke T-8000. The samples were annealed at 200, 400, 600 and 800 °C for 1 h in vacuum (P ≤ 10− 2 Torr). The structure of the films were characterized by X-ray diffraction using a SEIFERT XRD 3003 PTS which uses Cu kα (λ = 0.154 nm) radiation. The surface morphologies were observed by Atomic Force Microscopy, Park Scientific Instrument, Auto probe CP.
Fig. 2. XRD pattern of the films as-grown and annealed at 200, 400, 600 and 800 °C.
The optical reflectance measurements were performed using a UV–Vis–NIR Spectrophotometer, Varian, Cary 500. 3. Results and discussion The XRD pattern for the samples as-grown and annealed at 200, 400, 600 and 800 °C for stainless steel substrates are shown in Fig. 2. As the Fig. 2 shows, there are 2 peaks of Cu3N (300) and Al2Cu3 (200) for all samples. The observation of peaks revealed that with increasing the annealing temperature the intensity of the peaks gradually increased and the full width at half maximum (FWHM) of the peaks gradually decreased according to the Table 2 which indicates an increase in the crystallite sizes. The crystallite sizes were estimated by the Scherrer formula [5]. Crystallite size ¼ K k=ðFWHM coshÞ Fig. 3 shows the dependence of crystallite size on the annealing temperature, which exhibit that with increasing the annealing temperature, the crystallite sizes gradually increase. Fig. 4 shows the AFM images (1 μm × 1 μm) of the Al–Cu–N films as-grown and annealed at 200, 400, 600 and 800 °C, respectively. These images show that the grain size of the films clearly increase as the annealing temperature rises, which is consistent with the XRD results. Investigation of the AFM images demonstrates that at the beginning of growth, the grain sizes are small (Fig. 4a). By annealing the sample, these small grains gradually combine and make bigger grains (Fig. 4b). With increasing the annealing temperature to 400 °C, the grains become bigger (Fig. 4c) and at last it can cause to create clusters (Fig. 4d). Finally, with
Fig. 3. Crystallite size (Å) of the Al2Cu3 and Cu3N as-grown and annealed at 200, 400, 600 and 800 °C.
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Fig. 4. AFM images (1 μm × 1 μm) of samples as-grown and annealed at 200, 400, 600 and 800 °C, respectively.
M. Shariati et al. / Surface & Coatings Technology 201 (2007) 5570–5573
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When the roughness rise, the surface loose its smoothness, thus the incident beam diffuse from the surface and the specular reflectance decrease. The amount of diffusion has a direct relation to increase in the roughness. If the roughness of the sample increases, diffusion from the sample surface will rise. So in higher annealing temperature, more diffusion and less reflectance are observed. 4. Conclusion
Fig. 5. Dependence of the roughness (Å) on the annealing temperature (°C).
In this experiment the effect of annealing process (up to 800 °C) has been investigated on the characteristics of Al–Cu–N films, deposited on steel substrates. Morphology analysis shows that during the annealing process, the grains size increase which is consistent with the XRD results. As the grains size rise, the sample roughness also increases. On the contrary, with increasing in the amount of roughness, the specular reflectance of the samples surface decreases. The results demonstrate that desirable characteristics such as reflectance or roughness of Al–Cu–N films deposited by DC reactive magnetron sputtering can be obtained by controlling the annealing temperature. Acknowledgments
Fig. 6. Reflectance spectra of the films as-grown and annealed at 200, 400, 600 and 800 °C.
The authors would like to thank Dr. A. Shafiekhani of Alzahra University for annealing the samples, Mrs. P. Amiri for XRD analyze and also Ms. Sh. Milani for her help. References
increasing the annealing temperature to 800 °C, these clusters combine and create big grains which are shown in Fig. 4e. The samples roughness also increases during the annealing process. Fig. 5 shows the dependence of roughness on the annealing temperature. Fig. 6 shows the reflectance spectra of the films as-grown and annealed at 200, 400, 600 and 800 °C. As the figure shows by annealing the reflectance of the samples gradually decrease.
[1] [2] [3] [4]
D. Liufu, K.C. Kao, J. Vac. Sci. Technol., A 16 (1998) 2360. M.-A. Dubois, P. Muralt, Appl. Phys. Lett. 74 (1999) 3032. M.T. Wauk, D.K. Winslow, Appl. Phys. Lett. 13 (1968) 286. J. Musil, H. Hruby, P. Zeman, H. Zeman, R. Cerstvy, P.H. Mayrhofer, C. Mitterer, Surf. Coat. Technol. 142–144 (2001) 603. [5] B.D. Cullity, Elements of X-ray Diffractions, Addition- Wesley, Reading, MA, 1978, p. 102.
Effect of annealing temperature on properties of Al–Cu–N thin films deposited by DC magnetron sputtering M. Shariati ⁎, M. Ghoranneviss, H. Hosseini, M.R. Hantehzadeh Plasma Physics Research Center, Science and Research Campus, Islamic Azad University, Tehran, Iran Available online 10 August 2006
Abstract Al–Cu–N films have been deposited on steel substrate by DC magnetron sputtering. These samples were annealed at 200, 400, 600 and 800 °C under vacuum condition. The effects of annealing temperature on structure, morphology and optical properties of Al–Cu–N films were investigated. By means of X-ray diffraction (XRD) the phase composition was characterized. Atomic Force Microscopy (AFM) was used to evaluate and compare the surface roughness before and after annealing. Also UV–Vis–NIR spectrophotometer was used to investigate the optical properties of the samples. The results show that with increasing in the annealing temperature the intensity of the peaks gradually increased and the full width at half maximum (FWHM) of the peaks gradually decreased and also increasing in the grain size and the amount of the samples roughness during the annealing process are observed. It demonstrates that desirable reflectance and roughness of Al–Cu–N films deposited by DC reactive magnetron sputtering can be obtained by controlling the annealing temperature. © 2006 Elsevier B.V. All rights reserved. PACS: 68.55.-a; 81.15.Cd; 81.40.Ef; 78.68.+m Keywords: Al–Cu–N films; Annealing temperature; DC magnetron sputtering; XRD; AFM; Spectrophotometer
1. Introduction In recent years, much attention has been given to III-V semiconductors. Aluminum Nitride (AlN) with wurtzite hexagonal structure is one of the famous semiconductors in this group, which has wide applications for many acoustic and optical applications [1–3]. In parallel to these researches, new works have been done to add new elements to these families of semiconductors to produce new materials with new properties. Al–Cu–N, a nano-composite film, is produced by reactive sputtering technique which is a process that can work under low temperature. This nano-composite is a hard and super hard film (N40 GPa), composed of one hard and one soft phase [4]. It is well known that texture or preferred crystallographic orientation of materials strongly affects their properties. Also mechanical and thermal treatments influence the preferred orientation. ⁎ Corresponding author. Plasma Physics Research Center, Science and Research Campus, Islamic Azad University, P.O. Box: 14665-678, Tehran, Iran. Tel.: +98 21 44815921; fax: +98 21 44817165. E-mail address: [email protected] (M. Shariati). 0257-8972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.07.151
The purpose of this paper is to investigate the effect of annealing temperature on structure, morphology and optical properties of Al–Cu–N thin films. Steel has been chosen as a substrate because of its wide application in industry. Properties like corrosion resistance and oxidation resistance are some
Fig. 1. Schematic of the system.
M. Shariati et al. / Surface & Coatings Technology 201 (2007) 5570–5573 Table 1 Deposition condition Substrate-to-target distance Substrate Base pressure Final pressure Current Deposition time
30 mm Stainless steel (grade 304) 4.7 × 10− 5 Torr 2 × 10− 2 Torr 100 mA 1h
5571
Table 2 FWHM of the Al2Cu3 and Cu3N as-grown and annealed at 200, 400, 600 and 800 °C Sample
Al2Cu3
Cu3N
As-grown 200 °C 400 °C 600 °C 800 °C
0.5148 0.5034 0.4857 0.4649 0.4116
0.5832 0.5641 0.5430 0.5334 0.4202
characteristics which encourage researchers to use this alloy as a substrate. 2. Experimental The Al–Cu–N films were deposited by a reactive DC magnetron sputtering (Fig. 1). This system consists of two coaxial cylinders as cathode (inner one) and anode (outer one). The diameters of the outer and the inner cylinders are 10 cm and 3 cm, respectively and the height of the inner and the outer cylinders are 20 cm. In this experiment, it was used a composed target, a cylindrical Al with 3 cm diameter and a fine Cu wire which was twisted round to the Al target. Working gas is a mixture of Ar + N2 in the deposition chamber. Films were deposited under the condition which is presented in Table 1. The Al–Cu–N films were deposited on to polished and ultrasonically pre-cleaned AISI304 stainless steel substrates. The typical thickness of sputtered films was approximately 200 nm. The films thickness was measured with a Surface Profile Meter, Hommel Werke T-8000. The samples were annealed at 200, 400, 600 and 800 °C for 1 h in vacuum (P ≤ 10− 2 Torr). The structure of the films were characterized by X-ray diffraction using a SEIFERT XRD 3003 PTS which uses Cu kα (λ = 0.154 nm) radiation. The surface morphologies were observed by Atomic Force Microscopy, Park Scientific Instrument, Auto probe CP.
Fig. 2. XRD pattern of the films as-grown and annealed at 200, 400, 600 and 800 °C.
The optical reflectance measurements were performed using a UV–Vis–NIR Spectrophotometer, Varian, Cary 500. 3. Results and discussion The XRD pattern for the samples as-grown and annealed at 200, 400, 600 and 800 °C for stainless steel substrates are shown in Fig. 2. As the Fig. 2 shows, there are 2 peaks of Cu3N (300) and Al2Cu3 (200) for all samples. The observation of peaks revealed that with increasing the annealing temperature the intensity of the peaks gradually increased and the full width at half maximum (FWHM) of the peaks gradually decreased according to the Table 2 which indicates an increase in the crystallite sizes. The crystallite sizes were estimated by the Scherrer formula [5]. Crystallite size ¼ K k=ðFWHM coshÞ Fig. 3 shows the dependence of crystallite size on the annealing temperature, which exhibit that with increasing the annealing temperature, the crystallite sizes gradually increase. Fig. 4 shows the AFM images (1 μm × 1 μm) of the Al–Cu–N films as-grown and annealed at 200, 400, 600 and 800 °C, respectively. These images show that the grain size of the films clearly increase as the annealing temperature rises, which is consistent with the XRD results. Investigation of the AFM images demonstrates that at the beginning of growth, the grain sizes are small (Fig. 4a). By annealing the sample, these small grains gradually combine and make bigger grains (Fig. 4b). With increasing the annealing temperature to 400 °C, the grains become bigger (Fig. 4c) and at last it can cause to create clusters (Fig. 4d). Finally, with
Fig. 3. Crystallite size (Å) of the Al2Cu3 and Cu3N as-grown and annealed at 200, 400, 600 and 800 °C.
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Fig. 4. AFM images (1 μm × 1 μm) of samples as-grown and annealed at 200, 400, 600 and 800 °C, respectively.
M. Shariati et al. / Surface & Coatings Technology 201 (2007) 5570–5573
5573
When the roughness rise, the surface loose its smoothness, thus the incident beam diffuse from the surface and the specular reflectance decrease. The amount of diffusion has a direct relation to increase in the roughness. If the roughness of the sample increases, diffusion from the sample surface will rise. So in higher annealing temperature, more diffusion and less reflectance are observed. 4. Conclusion
Fig. 5. Dependence of the roughness (Å) on the annealing temperature (°C).
In this experiment the effect of annealing process (up to 800 °C) has been investigated on the characteristics of Al–Cu–N films, deposited on steel substrates. Morphology analysis shows that during the annealing process, the grains size increase which is consistent with the XRD results. As the grains size rise, the sample roughness also increases. On the contrary, with increasing in the amount of roughness, the specular reflectance of the samples surface decreases. The results demonstrate that desirable characteristics such as reflectance or roughness of Al–Cu–N films deposited by DC reactive magnetron sputtering can be obtained by controlling the annealing temperature. Acknowledgments
Fig. 6. Reflectance spectra of the films as-grown and annealed at 200, 400, 600 and 800 °C.
The authors would like to thank Dr. A. Shafiekhani of Alzahra University for annealing the samples, Mrs. P. Amiri for XRD analyze and also Ms. Sh. Milani for her help. References
increasing the annealing temperature to 800 °C, these clusters combine and create big grains which are shown in Fig. 4e. The samples roughness also increases during the annealing process. Fig. 5 shows the dependence of roughness on the annealing temperature. Fig. 6 shows the reflectance spectra of the films as-grown and annealed at 200, 400, 600 and 800 °C. As the figure shows by annealing the reflectance of the samples gradually decrease.
[1] [2] [3] [4]
D. Liufu, K.C. Kao, J. Vac. Sci. Technol., A 16 (1998) 2360. M.-A. Dubois, P. Muralt, Appl. Phys. Lett. 74 (1999) 3032. M.T. Wauk, D.K. Winslow, Appl. Phys. Lett. 13 (1968) 286. J. Musil, H. Hruby, P. Zeman, H. Zeman, R. Cerstvy, P.H. Mayrhofer, C. Mitterer, Surf. Coat. Technol. 142–144 (2001) 603. [5] B.D. Cullity, Elements of X-ray Diffractions, Addition- Wesley, Reading, MA, 1978, p. 102.