- Email: [email protected]
AlN multilayers coating
Surface & Coatings Technology 200 (2005) 94 – 99 www.elsevier.com/locate/surfcoat
Study of the moisture and thermal resistance of AlN/ZrN/AlN multilayers coating M. Del ReT, J.-P. Dauchot, M. Hecq Laboratoire de Chimie Inorganique et Analytique Universite´ de Mons-Hainaut, Parc Initialis, Av. Copernic 7000 Mons, Belgium Available online 9 April 2005
Abstract The moisture and thermal resistances of AlN/ZrN/AlN multilayers deposited by magnetron sputtering onto borosilicate glass wafers were investigated. This kind of multilayers has a great reflectivity in the IR range and a good transmission in the visible range. Two deposition parameters (substrate temperature and substrate bias) were varied. The as-deposited coatings were annealed in an oven at different temperatures for 10 min and/or exposed to a corrosive atmosphere (200 ml SO2 into 2 l of water heated at 40 8C) for three cycles of 8 h. The degraded films were characterised by different techniques. Spectrophotometry in the UV–Vis–IR range (300 to 2500 nm) was used to measure the optical properties (Transmission, Reflection). X-ray photoelectron spectroscopy (XPS) was used to measure the films stoichiometry and to characterize the humidity migration into the layers. The substrate RF bias has a great influence on the coating stability. The ZrN layer oxidation occurs during the moisture and thermal tests when the layers were deposited with a bias below 35 W and the optical properties of the coatings are degraded. Above this value, the ZrN layer is well protected from humidity diffusion. This behaviour is certainly due to the porosity decrease of the films when bias is added. These results confirm the necessity of a bias during deposition to increase the coating durability. D 2005 Elsevier B.V. All rights reserved. Keywords: Optical properties; Reactive magnetron sputtering; ZrN
1. Introduction
2. Experimental details
The thermal insulation techniques of windows have been enhanced due to the development of thin films sputter deposition. ZrN is known to be a good reflective material in the IR wavelength range [1]. It is due to the metallic structure of the stoichiometric ZrN. This property is interesting for applications in thermal insulation coatings. Previous works show that AlN/ZrN/AlN multilayers have the optical properties required by a low-e coating [2]. Thin films are deposited by various methods: evaporation, spray pyrolysis, chemical vapour deposition, and sputtering. In the present work, we study the sputtering of a zirconium and an aluminium targets in Ar/N2 direct current magnetron discharges. We investigate the moisture and thermal resistance of this multilayer by XPS and spectrophotometry in the UV–Visible–IR range.
The ZrN and AlN films are deposited by d.c. reactive magnetron sputtering. The target-substrate distance is 15 cm. The substrate is a borosilicate glass of 1 cm2 cleaned
T Corresponding author. Tel.: +32 65 37 38 51; fax: +32 65 37 38 41. E-mail address: [email protected] (M. Del Re). 0257-8972/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2005.02.155
Table 1 Experimental conditions for optical properties investigations Sample
Bias AlN (W)
Bias ZrN (W)
Substrate temperature
Annealing temperature (8C)
Chemical degradation
1 2 3 4 5 6 7 8 9 10
35 35 35 35 50 35 0 35 0 35
50 50 50 50 50 35 0 50 0 50
room room 500 8C 500 8C room room 500 8C room 500 8C 500 8C
150 400 600 600 600 600
yes yes yes yes yes yes yes yes yes yes
M. Del Re et al. / Surface & Coatings Technology 200 (2005) 94–99
95
100 90 after chemical degradation
80
after annealing at 400°C as-deposited
70 T curves
T,R (%)
60 50 R curves
40 30 20 10 0 300
500
700
900
1100
1300
1500
1700
1900
Wavelength (nm) Fig. 1. Optical properties of sample 2.
strate temperature (ambient or 500 8C) and different RF substrate bias (0, 35, or 50 W) after the thermal and chemical degradations. Table 1 resumes the experimental conditions. Figs. 1–8 show the recorded T and R of each sample as-deposited and after annealing and/or chemical exposure. Samples 1 to 5 and 10 show no significant variations of their optical properties. It is due to the high bias applied on the substrate during the ZrN deposition. This bias increases the ions energy arriving on the sample surface. The surface mobility of the sputtered atoms arriving from the target is thus increased and the layer porosity decreases. The ZrN layer annealing resistance increases and the optical properties are stabilized. Samples 6 to 9 loose the required properties in the IR range, the
with a Balzers substrate cleaners 1 and 2. The experimental system has already been described elsewhere [2,3]. The asdeposited coatings were annealed in an oven at different temperatures (150 to 600 8C) for 10 min and/or exposed to a corrosive atmosphere (200 ml SO2 into 2 l of water heated at 40 8C) for three cycles of 8 h each.
3. Results and discussion 3.1. Optical properties We have studied the behaviour of the optical properties of AlN/ZrN/AlN multilayers deposited at different sub100 90
after chemical degradation
80 as-deposited
70
after annealing at 600°C
T,R (%)
60 50 40 30 20 10 0 300
500
700
900
1100
1300
Wavelength (nm) Fig. 2. Optical properties of sample 3.
1500
1700
1900
96
M. Del Re et al. / Surface & Coatings Technology 200 (2005) 94–99 100 90 after chemical degradation
80 as-deposited
70 after annealing at 600°C
T,R (%)
60 50 40 30 20 10 0 300
500
700
900
1100
1300
1500
1700
1900
Wavelength (nm) Fig. 3. Optical properties of sample 5.
2 at 400 8C has modified his resistance against chemical degradation. Further investigations will be done to find an explanation of this behaviour.
reflectivity decreases dramatically after annealing and/or chemical degradation. The low substrate bias during the ZrN deposition for sample 6, 7, and 9 explains this behaviour [4]. Oxygen diffuses into the layer and the ZrN becomes oxidised and looses the metallic like optical properties. Sample 8 is different. This sample is deposited in the same conditions as sample 2. We have shown that sample 2 is not degraded under chemical exposure. So, the sample 8 should behave in the same manner. The Fig. 6 shows that the reflection after chemical exposure has decreased. The difference between these two samples is the annealing effect. It seems that the annealing of sample
3.2. XPS profiles In order to correlate the optical properties to the oxygen concentration in the ZrN layer, XPS profiles have been done for samples 4 and 7 as deposited and after annealing and/or chemical degradation. A study of the annealing effect by XPS has already been done [2]. Fig. 8 shows the results for sample 4 after annealing at 600 8C.
100 90 after chemical degradation
80 as-deposited
70
after annealing at 600°C
T,R (%)
60 50 40 30 20 10 0 300
500
700
900
1100
1300
Wavelength (nm) Fig. 4. Optical properties of sample 6.
1500
1700
1900
M. Del Re et al. / Surface & Coatings Technology 200 (2005) 94–99
97
100 90 after chemical degradation
80 as-deposited
70
T,R (%)
60 50 40 30 20 10 0 300
500
700
900
1100
1300
1500
1700
1900
Wavelength (nm) Fig. 5. Optical properties of sample 7.
the optical properties of the multilayer after degradations. The substrate temperature improves the reflectivity but is not an influent factor in the improvement of the oxidation resistance. The XPS profiles have correlated the oxygen concentration in the ZrN layer to the optical properties after degradations.
Oxygen concentration in the ZrN layer is below 2% and inexistent near the middle of the layer. This poor oxygen concentration explains the good optical properties of this sample after annealing. The sample 7 ZrN layer contains near 20% of oxygen (Fig. 9). The oxidation of the ZrN layer conducts to a global degradation of the multilayer optical properties.
Acknowledgments 4. Conclusions M. Del Re thanks the Fonds pour la Recherche dans l’Industrie et l’Agriculture (FRIA, Brussels) for financial support.
We have demonstrated that the RF substrate bias applied during the ZrN deposition is the key to keep
100 90 after chemical degradation
80 as-deposited
70
T,R (%)
60 50 40 30 20 10 0 300
500
700
900
1100
1300
Wavelength (nm) Fig. 6. Optical properties of sample 8.
1500
1700
1900
98
M. Del Re et al. / Surface & Coatings Technology 200 (2005) 94–99 100 90 after chemical degradation
80 as-deposited
T,R (%)
70 60 50 40 30 20 10 0 300
500
700
900
1100
1300
1500
1700
1900
Wavelength (nm) Fig. 7. Optical properties of sample 10.
70 60 50
%
40 30
Al N O C Zr Si
20 10 0
0
500
1000
1500
2000
2500
3000
3500
4000
sputtering time (sec) Fig. 8. XPS profile for sample 4.
60
50
%
40
30
Al N O C Zr Si
20
10
0
0
500
1000
1500
2000
2500
sputtering time (sec) Fig. 9. XPS profile for sample 7.
3000
3500
4000
M. Del Re et al. / Surface & Coatings Technology 200 (2005) 94–99
References [1] L. Pichon, T. Girardeau, A. Straboni, F. Lignou, P. Gue´rin et, J. Perrie`re, Appl. Surf. Sci. 150 (1999) 115. [2] M. Del Re, R. Gouttebaron, J.P. Dauchot, M. Hecq, Surf. Coat. Technol. 180–181 (2004 March) 488.
99
[3] V. Vancoppenolle, P.-Y. Juan, M. Wautelet, M. Hecq, J. Vac. Sci. Technol., A 17 (6) (1999 Nov./Dec.) 3317. [4] M. Del Re, R. Gouttebaron, J.P. Dauchot, M. Hecq, Surf. Coat. Technol. 174–175 (2003) 240.
Study of the moisture and thermal resistance of AlN/ZrN/AlN multilayers coating M. Del ReT, J.-P. Dauchot, M. Hecq Laboratoire de Chimie Inorganique et Analytique Universite´ de Mons-Hainaut, Parc Initialis, Av. Copernic 7000 Mons, Belgium Available online 9 April 2005
Abstract The moisture and thermal resistances of AlN/ZrN/AlN multilayers deposited by magnetron sputtering onto borosilicate glass wafers were investigated. This kind of multilayers has a great reflectivity in the IR range and a good transmission in the visible range. Two deposition parameters (substrate temperature and substrate bias) were varied. The as-deposited coatings were annealed in an oven at different temperatures for 10 min and/or exposed to a corrosive atmosphere (200 ml SO2 into 2 l of water heated at 40 8C) for three cycles of 8 h. The degraded films were characterised by different techniques. Spectrophotometry in the UV–Vis–IR range (300 to 2500 nm) was used to measure the optical properties (Transmission, Reflection). X-ray photoelectron spectroscopy (XPS) was used to measure the films stoichiometry and to characterize the humidity migration into the layers. The substrate RF bias has a great influence on the coating stability. The ZrN layer oxidation occurs during the moisture and thermal tests when the layers were deposited with a bias below 35 W and the optical properties of the coatings are degraded. Above this value, the ZrN layer is well protected from humidity diffusion. This behaviour is certainly due to the porosity decrease of the films when bias is added. These results confirm the necessity of a bias during deposition to increase the coating durability. D 2005 Elsevier B.V. All rights reserved. Keywords: Optical properties; Reactive magnetron sputtering; ZrN
1. Introduction
2. Experimental details
The thermal insulation techniques of windows have been enhanced due to the development of thin films sputter deposition. ZrN is known to be a good reflective material in the IR wavelength range [1]. It is due to the metallic structure of the stoichiometric ZrN. This property is interesting for applications in thermal insulation coatings. Previous works show that AlN/ZrN/AlN multilayers have the optical properties required by a low-e coating [2]. Thin films are deposited by various methods: evaporation, spray pyrolysis, chemical vapour deposition, and sputtering. In the present work, we study the sputtering of a zirconium and an aluminium targets in Ar/N2 direct current magnetron discharges. We investigate the moisture and thermal resistance of this multilayer by XPS and spectrophotometry in the UV–Visible–IR range.
The ZrN and AlN films are deposited by d.c. reactive magnetron sputtering. The target-substrate distance is 15 cm. The substrate is a borosilicate glass of 1 cm2 cleaned
T Corresponding author. Tel.: +32 65 37 38 51; fax: +32 65 37 38 41. E-mail address: [email protected] (M. Del Re). 0257-8972/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2005.02.155
Table 1 Experimental conditions for optical properties investigations Sample
Bias AlN (W)
Bias ZrN (W)
Substrate temperature
Annealing temperature (8C)
Chemical degradation
1 2 3 4 5 6 7 8 9 10
35 35 35 35 50 35 0 35 0 35
50 50 50 50 50 35 0 50 0 50
room room 500 8C 500 8C room room 500 8C room 500 8C 500 8C
150 400 600 600 600 600
yes yes yes yes yes yes yes yes yes yes
M. Del Re et al. / Surface & Coatings Technology 200 (2005) 94–99
95
100 90 after chemical degradation
80
after annealing at 400°C as-deposited
70 T curves
T,R (%)
60 50 R curves
40 30 20 10 0 300
500
700
900
1100
1300
1500
1700
1900
Wavelength (nm) Fig. 1. Optical properties of sample 2.
strate temperature (ambient or 500 8C) and different RF substrate bias (0, 35, or 50 W) after the thermal and chemical degradations. Table 1 resumes the experimental conditions. Figs. 1–8 show the recorded T and R of each sample as-deposited and after annealing and/or chemical exposure. Samples 1 to 5 and 10 show no significant variations of their optical properties. It is due to the high bias applied on the substrate during the ZrN deposition. This bias increases the ions energy arriving on the sample surface. The surface mobility of the sputtered atoms arriving from the target is thus increased and the layer porosity decreases. The ZrN layer annealing resistance increases and the optical properties are stabilized. Samples 6 to 9 loose the required properties in the IR range, the
with a Balzers substrate cleaners 1 and 2. The experimental system has already been described elsewhere [2,3]. The asdeposited coatings were annealed in an oven at different temperatures (150 to 600 8C) for 10 min and/or exposed to a corrosive atmosphere (200 ml SO2 into 2 l of water heated at 40 8C) for three cycles of 8 h each.
3. Results and discussion 3.1. Optical properties We have studied the behaviour of the optical properties of AlN/ZrN/AlN multilayers deposited at different sub100 90
after chemical degradation
80 as-deposited
70
after annealing at 600°C
T,R (%)
60 50 40 30 20 10 0 300
500
700
900
1100
1300
Wavelength (nm) Fig. 2. Optical properties of sample 3.
1500
1700
1900
96
M. Del Re et al. / Surface & Coatings Technology 200 (2005) 94–99 100 90 after chemical degradation
80 as-deposited
70 after annealing at 600°C
T,R (%)
60 50 40 30 20 10 0 300
500
700
900
1100
1300
1500
1700
1900
Wavelength (nm) Fig. 3. Optical properties of sample 5.
2 at 400 8C has modified his resistance against chemical degradation. Further investigations will be done to find an explanation of this behaviour.
reflectivity decreases dramatically after annealing and/or chemical degradation. The low substrate bias during the ZrN deposition for sample 6, 7, and 9 explains this behaviour [4]. Oxygen diffuses into the layer and the ZrN becomes oxidised and looses the metallic like optical properties. Sample 8 is different. This sample is deposited in the same conditions as sample 2. We have shown that sample 2 is not degraded under chemical exposure. So, the sample 8 should behave in the same manner. The Fig. 6 shows that the reflection after chemical exposure has decreased. The difference between these two samples is the annealing effect. It seems that the annealing of sample
3.2. XPS profiles In order to correlate the optical properties to the oxygen concentration in the ZrN layer, XPS profiles have been done for samples 4 and 7 as deposited and after annealing and/or chemical degradation. A study of the annealing effect by XPS has already been done [2]. Fig. 8 shows the results for sample 4 after annealing at 600 8C.
100 90 after chemical degradation
80 as-deposited
70
after annealing at 600°C
T,R (%)
60 50 40 30 20 10 0 300
500
700
900
1100
1300
Wavelength (nm) Fig. 4. Optical properties of sample 6.
1500
1700
1900
M. Del Re et al. / Surface & Coatings Technology 200 (2005) 94–99
97
100 90 after chemical degradation
80 as-deposited
70
T,R (%)
60 50 40 30 20 10 0 300
500
700
900
1100
1300
1500
1700
1900
Wavelength (nm) Fig. 5. Optical properties of sample 7.
the optical properties of the multilayer after degradations. The substrate temperature improves the reflectivity but is not an influent factor in the improvement of the oxidation resistance. The XPS profiles have correlated the oxygen concentration in the ZrN layer to the optical properties after degradations.
Oxygen concentration in the ZrN layer is below 2% and inexistent near the middle of the layer. This poor oxygen concentration explains the good optical properties of this sample after annealing. The sample 7 ZrN layer contains near 20% of oxygen (Fig. 9). The oxidation of the ZrN layer conducts to a global degradation of the multilayer optical properties.
Acknowledgments 4. Conclusions M. Del Re thanks the Fonds pour la Recherche dans l’Industrie et l’Agriculture (FRIA, Brussels) for financial support.
We have demonstrated that the RF substrate bias applied during the ZrN deposition is the key to keep
100 90 after chemical degradation
80 as-deposited
70
T,R (%)
60 50 40 30 20 10 0 300
500
700
900
1100
1300
Wavelength (nm) Fig. 6. Optical properties of sample 8.
1500
1700
1900
98
M. Del Re et al. / Surface & Coatings Technology 200 (2005) 94–99 100 90 after chemical degradation
80 as-deposited
T,R (%)
70 60 50 40 30 20 10 0 300
500
700
900
1100
1300
1500
1700
1900
Wavelength (nm) Fig. 7. Optical properties of sample 10.
70 60 50
%
40 30
Al N O C Zr Si
20 10 0
0
500
1000
1500
2000
2500
3000
3500
4000
sputtering time (sec) Fig. 8. XPS profile for sample 4.
60
50
%
40
30
Al N O C Zr Si
20
10
0
0
500
1000
1500
2000
2500
sputtering time (sec) Fig. 9. XPS profile for sample 7.
3000
3500
4000
M. Del Re et al. / Surface & Coatings Technology 200 (2005) 94–99
References [1] L. Pichon, T. Girardeau, A. Straboni, F. Lignou, P. Gue´rin et, J. Perrie`re, Appl. Surf. Sci. 150 (1999) 115. [2] M. Del Re, R. Gouttebaron, J.P. Dauchot, M. Hecq, Surf. Coat. Technol. 180–181 (2004 March) 488.
99
[3] V. Vancoppenolle, P.-Y. Juan, M. Wautelet, M. Hecq, J. Vac. Sci. Technol., A 17 (6) (1999 Nov./Dec.) 3317. [4] M. Del Re, R. Gouttebaron, J.P. Dauchot, M. Hecq, Surf. Coat. Technol. 174–175 (2003) 240.