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Chemical compositions and optical properties of HfOxNy thin films at different substrate temperatures
ARTICLE IN PRESS
Materials Science in Semiconductor Processing 9 (2006) 876–879
Chemical compositions and optical properties of HfOxNy thin films at different substrate temperatures M. Liua,, Q. Fanga,b, G. Hea, L.Q. Zhua, S.S. Pana, L.D. Zhanga a
Key Laboratory of Materials Physics, Anhui Key Laboratory of Nanomaterials and Nanostructure, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, PR China b Electronic and electrical Engineering, University College London, Torrington Place, London WCIE 7JE, UK Available online 7 November 2006
Abstract High-k HfOxNy thin films have been grown by radio frequency (rf) reactive sputtering of metal Hf target in N2/Ar/O2 ambient at different substrate temperatures. The chemical compositions of the films have been investigated as a function of substrate temperature by X-ray photoelectron spectroscopy (XPS). XPS measurements showed that nitrogen concentration increases with an increase in substrate temperature. Room-temperature spectroscopic ellipsometry (SE) with photon energy 0.75–6.5 eV was used to investigate the optical properties of the films. SE results demonstrated that refractive index n increases with an increase in substrate temperature. Based on TL parameters which were obtained from the best fit results used in a simulation of the measured spectra, meanwhile, we conclude that the energy band gap (Eg) decreases with an increase in substrate temperature. r 2006 Elsevier Ltd. All rights reserved. PACS: 77.55.+f; 77.84.Bw; 78.20.Ci Keywords: High-k; Optical properties; Band gap; HfOxNy thin films
1. Introduction High-k gate dielectrics such as HfO2, ZrO2 and TiO2 have been investigated as alternative gate dielectrics to replace conventional SiO2 or oxynitrides. Among these high-k materials, HfO2 has emerged as one of the most promising candidates for its relatively high dielectric constant and thermodynamic stability when in direct contact with Si [1–2]. However, it is known that the crystallization temperature of HfO2 is low, leading Corresponding author. Tel.: +86 551 5591465; fax: +86 551 5591434. E-mail address: [email protected] (M. Liu).
1369-8001/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.mssp.2006.10.004
to the formation of grain boundaries, which can act as a path for oxygen or dopant diffusion into the gate dielectric. The high oxygen and impurity penetration and boron diffusion into the gate dielectric should be suppressed to maintain low equivalent oxide thickness (EOT), decrease leakage current and reduce flatband voltage fluctuations [3]. Recently, incorporating N into binary metal oxides has been broadly investigated in order to increase the crystallization temperature, improve electric properties and suppress oxygen and/or boron diffusion through such high-k gate dielectric as TiOxNy, HfSixOyNz, HfOxNy and ZrOxNy [4–7]. In our previous work, optical properties of HfO2 films with incorporated nitrogen and the effect of the
ARTICLE IN PRESS M. Liu et al. / Materials Science in Semiconductor Processing 9 (2006) 876–879
2. Experimental details The n-type Si (1 0 0) substrates with a resistivity of 2–5 O cm were pre-cleaned by a standard RCA (Radio corporation of American) processing [11]. The substrates were then immersed in dilute HF (10%) solution for 10 s to remove any native oxide. The silicon dangling bonds were passivated with hydrogen atom by rinsing in deionized water. Wafers were then loaded into the chamber of a magnetron sputtering system. HfOxNy thin films were deposited by rf magnetron sputtering of metal Hf target with Ar/ N2/O2 mixtures at flow rates of 30/20/5 sccm. The deposition power was kept at 100 W. In this way, we obtained films with thickness of about 20 nm. The chamber pressure during deposition was constant at 0.2 Pa. Deposition was performed at three substrate temperatures: 100, 200 and 300 1C. The surface chemical bonding states were measured by X-ray photoelectron spectroscopy using the ESCALAB MK II (VG UK) system, equipped with MgKa radiation source (1253.6 eV). The optical properties of HfOxNy films at different substrate temperatures were determined by means of an ex-situ spectroscopic ellipsometry in the spectral range of 0.75–6.5 eV with a step of 0.05 eV at an incident angle of 701.
been performed. N1s XPS spectrum of a film deposited at 100 1C substrate temperature is shown in Fig. 1. The result shows N1s peak at 396.0 eV, associated with N–Hf bonds [12]. Through area calculation, we determine that the film stoichiometry expressed as the N/Hf integrated signal ratio changes with the substrate temperature from 0.24 at 100 1C through 0.31 at 200 1C to 0.35 at 300 1C. This indicates that nitrogen concentration increases with an increase in substrate temperature. Fig. 2 presents the Hf4f XPS spectra at different substrate temperatures. The observed Hf4f5/2 and Hf4f7/2 peaks shift to a lower binding energy with an increase in substrate temperature. Chio et al. [13] showed that the Hf4f5/2 and Hf4f7/2 peaks of samples containing nitrogen shift towards lower binding energy compared to the HfO2 films. All the above-mentioned results suggest that with an increase in substrate temperature, the nitrogen concentration increases. When the substrate temperature is higher, the atoms arriving at the substrate are more active and react more easily with Hf atoms to form N–Hf bonds. Therefore, the nitrogen concentration of HfOxNy thin films is higher at a higher substrate temperature. In order to further study the effect of substrate temperature on the physics properties of HfOxNy thin films, the optical constants of the films were determined with ex situ spectroscopic ellipsometry (SE). It should be noted that discussion here is associated with high-frequency dielectric constant which is solely due to electronic transitions and therefore should not be confused with the dielectric constant that determines the capacitance of MOS or
N1s
Intensity (counts)
annealing temperature on the optical properties of HfOxNy thin films have already been investigated [8,9]. It is well known that deposition conditions such as substrate temperature and deposition pressure have a strong effect on the properties of high-k gate dielectric. For example, the effect of substrate temperature on the thermodynamic stability property of LaAlO3 (LAO) high-k film have been shown by Lu et al., and their studies demonstrated that the interfacial reaction between the LAO film and the silicon substrate is strongly correlated to the substrate temperature [10]. Up to our knowledge, there have been few reports on the effect of the substrate temperature on the optical properties of HfOxNy thin films during deposition. Therefore, we focus here on the effect of the substrate temperature on these properties. The chemical compositions of the HfOxNy thin films are discussed as well.
390
3. Results and discussion In order to investigate the film compositions and chemical bonding states, ex situ XPS analysis has
877
395
400
405
410
Binding energy (eV) Fig. 1. A typical N1s XPS spectra of as-deposited HfOxNy film with the substrate temperature of 100 1C. The pronounced N1s peak indicates that the nitrogen is present in the HfOxNy films.
ARTICLE IN PRESS M. Liu et al. / Materials Science in Semiconductor Processing 9 (2006) 876–879
Hf4f2 / 7
Hf4f
100°C 200°C 300°C
1.0
0.5
0.5
0.0
0.0
-0.5
-0.5
Is
Intensity (counts)
Hf4f2 / 5
1.0
Ic
878
2
10
12
14
16
18
20
22
24
4 3 5 Photon Energy (eV)
6
Fig. 3. Experimental (open circles) and best fit (solid lines) spectroscopic ellipsometric data for the film deposited at 200 1C.
Binding energy (eV) Fig. 2. Hf4f XPS spectra of HfOxNy film at different substrate temperatures. The decrease of the Hf4f peak indicates the increase of the nitrogen content with increasing substrate temperature.
Z
1 Eg
x2 ðxÞ dx. x2 E 2
4.0
3.9
3.8 100
(2)
Eqs. (1) and (2) as a function of the photon energy E are uniquely defined by four parameters: A (transition matrix element) related to the film density [16], E0 (peak transition energy), C (broadening term), and Eg (band gap). A simple model of four-phase structure (substrate/interfacal layer/ HfOxNy thin film/HfOxNy thin film+void) has been established for the simultaneous fitting of the measured parameters Is and Ic of SE, here Is and Ic are the experimental SE data. Fig. 3 shows the experimental (open circles) and fitted (solid lines) spectra of a HfOxNy thin film at 200 1C substrate temperature. It can be seen that an excellent fit has been obtained indicating that the optical constants of the films can be exactly determined in this way. Using the four-phase model structure which has been mentioned above, the energy band gap (Eg) at different substrate temperatures were obtained from the best fit parameters. Fig. 4 shows Eg as a function of substrate temperature. The gap Eg changes from 4.09 through 3.84 to 3.79 as the substrate temperature changes from 100 through 200 to 300 1C,
200
300
Substrate temperature (°C) Fig. 4. The energy band gap (Eg) as a function of the substrate temperature. The values of Eg have been obtained from the best fit parameters of the measured spectra.
2.6
Refractive index (n)
2 1 ðEÞ ¼ 1 þ P p
Energy band gap (Eg)
MIM structures. To characterize the dielectric function, we adopt the Tauc–Lorentz (TL) dispersion function [14,15], which is expressed as following: 8 2 0 CðEE g Þ 1 < AE ðE4E g Þ ðE 2 E 20 Þ2 þC 2 E 2 E ; (1) 2 ðEÞ ¼ :0 ðEpE g Þ
4.1
2.4
2.2
2.0
300°C 200°C
1.8
100°C 2
3 4 Photon energy (eV)
5
Fig. 5. The refractive index n as a function of energy for HfOxNy films grown at various substrate temperature. The refractive index increases with increasing substrate temperature.
ARTICLE IN PRESS M. Liu et al. / Materials Science in Semiconductor Processing 9 (2006) 876–879
879
Table 1 Parameter values of the fitting results obtained form all samples using TL model dispersions Substrate temp (1C)
t (nm)
Eg (eV)
eN
A
E0 (eV)
C
100 200 300
16.8870.44 18.7770.40 19.3370.21
4.0970.06 3.8470.05 3.7970.02
4.0970.12 2.0970.18 2.8670.12
133.2378.25 190.85710.33 206.0174.99
5.9470.32 5.4770.21 5.3470.13
9.1270.59 7.9270.31 7.8070.19
respectively, indicating that Eg value decreases with an increase in substrate temperature. In the previous section, we have already shown that with an increase in substrate temperature the nitrogen concentration increases. Therefore, Eg decreases with the increase of nitrogen concentration. These results are in agreement with the results of Asahi et al. that substitutional doping of N into TiO2 leads to the decrease of the band gap [17]. In our case, the nitrogen concentration increases with an increase in substrate temperature, leading to increased N 2p XPS signal; this means that the band gap decreases due to the increased mixing of N 2p states with O 2p states. Fig. 5 demonstrates the variation of the refractive index n as a function of energy at different substrate temperatures. It can be seen that the refractive index n of HfOxNy samples increases with an increase in substrate temperature. The reason for this behavior may be that when the films are deposited at higher substrate temperature, the higher mobility of the atoms arriving at the substrate favors formation of more closely packed HfOxNy thin films. Table 1 displays all the TL parameters obtained from the best fit to the measured spectra. The parameter A increases with an increase in substrate temperature indicating that the film deposited at a higher substrate temperature has a higher density. It has been proved that the increasing packing density leads to a higher refractive index [18]. Therefore, the higher substrate temperature, the more closely packed is the film and, as a result, the higher is the refractive index. 4. Conclusion The effect of substrate temperature on the optical properties of HfOxNy thin films has been investigated using SE with photon energy 0.75–6.5 eV at room temperature. The chemical composition of the films have has also been investigated. The nitrogen content increases with an increase in substrate
temperature, while the energy band gap (Eg) decreases with an increase in substrate temperature. The changes of the refractive index n with substrate temperature have also been discussed in detail. Acknowledgments This work was supported by National Major Project of Fundamental Research for Nanomaterials and Nanostructures (Grant no. 2005CB623603). References [1] Wilk GD, Wallace RM, Anthony JM. J Appl Phys 2001;89:5243. [2] Lee B-H, Kang L, Neih R, Qi W, Lee JC. Appl Phys Lett 2000;76:1926. [3] Cao M, Voorde PV, Cox M, Greene W. IEEE Electron Dev Lett 1998;19:291. [4] Mohamed SH, Kappertz O, Niemeier T, Drese R, Wakkad MM, Wuttig M. Thin Solid Films 2004;468:48. [5] Quevedo-Lopez MA, El-Bouanani M, Kim MJ, Gnade BE, Wallace RM, Visokay MR, et al. Appl Phys Lett 2003;82:4669. [6] Lee M, Lu Z-H, Ng W-T, Landeer D, Wu X, Moisa S. Appl Phys Lett 2003;83:2638. [7] Nieh RE, Kang CS, Cho H-J, Onishi K, Choi R, Krishnan S, et al. IEEE Trans Electron Dev 2003;50:333. [8] He G, Zhang LD, Li GH, Liu M, Zhu LQ, Pan SS, et al. Appl Phys Lett 2005;86:232901. [9] Liu M, Fang Q, He G, Li L, Zhu LQ, Li GH, et al. Appl Phys Lett 2006;88:192904. [10] Lu XB, Zhang X, Huang R, Lu HB, Chen ZH, Xiang WF, et al. Appl. Phys Lett 2004;84:2620. [11] Kern W, Poutinen DA. RCA Rev 1970;31:187. [12] Kang CS, Cho HJ, Onishi K, Nieh R, Choi R, Gopanlan S, et al. Appl Phys Lett 2002;81:2593. [13] Chio KJ, Kim JH, Yoon SG, Shin WC. J Vac Sci Technol B 2004;22:1755. [14] Jellison Jr. GE, Modine FA. Appl Phys Lett 1996;69:371. [15] Jellison Jr. GE, Modine FA. Appl Phys Lett 1996;69:2137. [16] Morral AFI, Cabarrocas PRI, Clerc C. Phys Rev B 2004;69:125307. [17] Asahi R, Morikawa T, Ohwaki T, Aoki K, Taga Y. Science 2001;293:269. [18] Hu H, Zhu CX, Lu YF, Wu YH, Liew T, Li MF, et al. J Appl Phys 2003;94:551.
Materials Science in Semiconductor Processing 9 (2006) 876–879
Chemical compositions and optical properties of HfOxNy thin films at different substrate temperatures M. Liua,, Q. Fanga,b, G. Hea, L.Q. Zhua, S.S. Pana, L.D. Zhanga a
Key Laboratory of Materials Physics, Anhui Key Laboratory of Nanomaterials and Nanostructure, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, PR China b Electronic and electrical Engineering, University College London, Torrington Place, London WCIE 7JE, UK Available online 7 November 2006
Abstract High-k HfOxNy thin films have been grown by radio frequency (rf) reactive sputtering of metal Hf target in N2/Ar/O2 ambient at different substrate temperatures. The chemical compositions of the films have been investigated as a function of substrate temperature by X-ray photoelectron spectroscopy (XPS). XPS measurements showed that nitrogen concentration increases with an increase in substrate temperature. Room-temperature spectroscopic ellipsometry (SE) with photon energy 0.75–6.5 eV was used to investigate the optical properties of the films. SE results demonstrated that refractive index n increases with an increase in substrate temperature. Based on TL parameters which were obtained from the best fit results used in a simulation of the measured spectra, meanwhile, we conclude that the energy band gap (Eg) decreases with an increase in substrate temperature. r 2006 Elsevier Ltd. All rights reserved. PACS: 77.55.+f; 77.84.Bw; 78.20.Ci Keywords: High-k; Optical properties; Band gap; HfOxNy thin films
1. Introduction High-k gate dielectrics such as HfO2, ZrO2 and TiO2 have been investigated as alternative gate dielectrics to replace conventional SiO2 or oxynitrides. Among these high-k materials, HfO2 has emerged as one of the most promising candidates for its relatively high dielectric constant and thermodynamic stability when in direct contact with Si [1–2]. However, it is known that the crystallization temperature of HfO2 is low, leading Corresponding author. Tel.: +86 551 5591465; fax: +86 551 5591434. E-mail address: [email protected] (M. Liu).
1369-8001/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.mssp.2006.10.004
to the formation of grain boundaries, which can act as a path for oxygen or dopant diffusion into the gate dielectric. The high oxygen and impurity penetration and boron diffusion into the gate dielectric should be suppressed to maintain low equivalent oxide thickness (EOT), decrease leakage current and reduce flatband voltage fluctuations [3]. Recently, incorporating N into binary metal oxides has been broadly investigated in order to increase the crystallization temperature, improve electric properties and suppress oxygen and/or boron diffusion through such high-k gate dielectric as TiOxNy, HfSixOyNz, HfOxNy and ZrOxNy [4–7]. In our previous work, optical properties of HfO2 films with incorporated nitrogen and the effect of the
ARTICLE IN PRESS M. Liu et al. / Materials Science in Semiconductor Processing 9 (2006) 876–879
2. Experimental details The n-type Si (1 0 0) substrates with a resistivity of 2–5 O cm were pre-cleaned by a standard RCA (Radio corporation of American) processing [11]. The substrates were then immersed in dilute HF (10%) solution for 10 s to remove any native oxide. The silicon dangling bonds were passivated with hydrogen atom by rinsing in deionized water. Wafers were then loaded into the chamber of a magnetron sputtering system. HfOxNy thin films were deposited by rf magnetron sputtering of metal Hf target with Ar/ N2/O2 mixtures at flow rates of 30/20/5 sccm. The deposition power was kept at 100 W. In this way, we obtained films with thickness of about 20 nm. The chamber pressure during deposition was constant at 0.2 Pa. Deposition was performed at three substrate temperatures: 100, 200 and 300 1C. The surface chemical bonding states were measured by X-ray photoelectron spectroscopy using the ESCALAB MK II (VG UK) system, equipped with MgKa radiation source (1253.6 eV). The optical properties of HfOxNy films at different substrate temperatures were determined by means of an ex-situ spectroscopic ellipsometry in the spectral range of 0.75–6.5 eV with a step of 0.05 eV at an incident angle of 701.
been performed. N1s XPS spectrum of a film deposited at 100 1C substrate temperature is shown in Fig. 1. The result shows N1s peak at 396.0 eV, associated with N–Hf bonds [12]. Through area calculation, we determine that the film stoichiometry expressed as the N/Hf integrated signal ratio changes with the substrate temperature from 0.24 at 100 1C through 0.31 at 200 1C to 0.35 at 300 1C. This indicates that nitrogen concentration increases with an increase in substrate temperature. Fig. 2 presents the Hf4f XPS spectra at different substrate temperatures. The observed Hf4f5/2 and Hf4f7/2 peaks shift to a lower binding energy with an increase in substrate temperature. Chio et al. [13] showed that the Hf4f5/2 and Hf4f7/2 peaks of samples containing nitrogen shift towards lower binding energy compared to the HfO2 films. All the above-mentioned results suggest that with an increase in substrate temperature, the nitrogen concentration increases. When the substrate temperature is higher, the atoms arriving at the substrate are more active and react more easily with Hf atoms to form N–Hf bonds. Therefore, the nitrogen concentration of HfOxNy thin films is higher at a higher substrate temperature. In order to further study the effect of substrate temperature on the physics properties of HfOxNy thin films, the optical constants of the films were determined with ex situ spectroscopic ellipsometry (SE). It should be noted that discussion here is associated with high-frequency dielectric constant which is solely due to electronic transitions and therefore should not be confused with the dielectric constant that determines the capacitance of MOS or
N1s
Intensity (counts)
annealing temperature on the optical properties of HfOxNy thin films have already been investigated [8,9]. It is well known that deposition conditions such as substrate temperature and deposition pressure have a strong effect on the properties of high-k gate dielectric. For example, the effect of substrate temperature on the thermodynamic stability property of LaAlO3 (LAO) high-k film have been shown by Lu et al., and their studies demonstrated that the interfacial reaction between the LAO film and the silicon substrate is strongly correlated to the substrate temperature [10]. Up to our knowledge, there have been few reports on the effect of the substrate temperature on the optical properties of HfOxNy thin films during deposition. Therefore, we focus here on the effect of the substrate temperature on these properties. The chemical compositions of the HfOxNy thin films are discussed as well.
390
3. Results and discussion In order to investigate the film compositions and chemical bonding states, ex situ XPS analysis has
877
395
400
405
410
Binding energy (eV) Fig. 1. A typical N1s XPS spectra of as-deposited HfOxNy film with the substrate temperature of 100 1C. The pronounced N1s peak indicates that the nitrogen is present in the HfOxNy films.
ARTICLE IN PRESS M. Liu et al. / Materials Science in Semiconductor Processing 9 (2006) 876–879
Hf4f2 / 7
Hf4f
100°C 200°C 300°C
1.0
0.5
0.5
0.0
0.0
-0.5
-0.5
Is
Intensity (counts)
Hf4f2 / 5
1.0
Ic
878
2
10
12
14
16
18
20
22
24
4 3 5 Photon Energy (eV)
6
Fig. 3. Experimental (open circles) and best fit (solid lines) spectroscopic ellipsometric data for the film deposited at 200 1C.
Binding energy (eV) Fig. 2. Hf4f XPS spectra of HfOxNy film at different substrate temperatures. The decrease of the Hf4f peak indicates the increase of the nitrogen content with increasing substrate temperature.
Z
1 Eg
x2 ðxÞ dx. x2 E 2
4.0
3.9
3.8 100
(2)
Eqs. (1) and (2) as a function of the photon energy E are uniquely defined by four parameters: A (transition matrix element) related to the film density [16], E0 (peak transition energy), C (broadening term), and Eg (band gap). A simple model of four-phase structure (substrate/interfacal layer/ HfOxNy thin film/HfOxNy thin film+void) has been established for the simultaneous fitting of the measured parameters Is and Ic of SE, here Is and Ic are the experimental SE data. Fig. 3 shows the experimental (open circles) and fitted (solid lines) spectra of a HfOxNy thin film at 200 1C substrate temperature. It can be seen that an excellent fit has been obtained indicating that the optical constants of the films can be exactly determined in this way. Using the four-phase model structure which has been mentioned above, the energy band gap (Eg) at different substrate temperatures were obtained from the best fit parameters. Fig. 4 shows Eg as a function of substrate temperature. The gap Eg changes from 4.09 through 3.84 to 3.79 as the substrate temperature changes from 100 through 200 to 300 1C,
200
300
Substrate temperature (°C) Fig. 4. The energy band gap (Eg) as a function of the substrate temperature. The values of Eg have been obtained from the best fit parameters of the measured spectra.
2.6
Refractive index (n)
2 1 ðEÞ ¼ 1 þ P p
Energy band gap (Eg)
MIM structures. To characterize the dielectric function, we adopt the Tauc–Lorentz (TL) dispersion function [14,15], which is expressed as following: 8 2 0 CðEE g Þ 1 < AE ðE4E g Þ ðE 2 E 20 Þ2 þC 2 E 2 E ; (1) 2 ðEÞ ¼ :0 ðEpE g Þ
4.1
2.4
2.2
2.0
300°C 200°C
1.8
100°C 2
3 4 Photon energy (eV)
5
Fig. 5. The refractive index n as a function of energy for HfOxNy films grown at various substrate temperature. The refractive index increases with increasing substrate temperature.
ARTICLE IN PRESS M. Liu et al. / Materials Science in Semiconductor Processing 9 (2006) 876–879
879
Table 1 Parameter values of the fitting results obtained form all samples using TL model dispersions Substrate temp (1C)
t (nm)
Eg (eV)
eN
A
E0 (eV)
C
100 200 300
16.8870.44 18.7770.40 19.3370.21
4.0970.06 3.8470.05 3.7970.02
4.0970.12 2.0970.18 2.8670.12
133.2378.25 190.85710.33 206.0174.99
5.9470.32 5.4770.21 5.3470.13
9.1270.59 7.9270.31 7.8070.19
respectively, indicating that Eg value decreases with an increase in substrate temperature. In the previous section, we have already shown that with an increase in substrate temperature the nitrogen concentration increases. Therefore, Eg decreases with the increase of nitrogen concentration. These results are in agreement with the results of Asahi et al. that substitutional doping of N into TiO2 leads to the decrease of the band gap [17]. In our case, the nitrogen concentration increases with an increase in substrate temperature, leading to increased N 2p XPS signal; this means that the band gap decreases due to the increased mixing of N 2p states with O 2p states. Fig. 5 demonstrates the variation of the refractive index n as a function of energy at different substrate temperatures. It can be seen that the refractive index n of HfOxNy samples increases with an increase in substrate temperature. The reason for this behavior may be that when the films are deposited at higher substrate temperature, the higher mobility of the atoms arriving at the substrate favors formation of more closely packed HfOxNy thin films. Table 1 displays all the TL parameters obtained from the best fit to the measured spectra. The parameter A increases with an increase in substrate temperature indicating that the film deposited at a higher substrate temperature has a higher density. It has been proved that the increasing packing density leads to a higher refractive index [18]. Therefore, the higher substrate temperature, the more closely packed is the film and, as a result, the higher is the refractive index. 4. Conclusion The effect of substrate temperature on the optical properties of HfOxNy thin films has been investigated using SE with photon energy 0.75–6.5 eV at room temperature. The chemical composition of the films have has also been investigated. The nitrogen content increases with an increase in substrate
temperature, while the energy band gap (Eg) decreases with an increase in substrate temperature. The changes of the refractive index n with substrate temperature have also been discussed in detail. Acknowledgments This work was supported by National Major Project of Fundamental Research for Nanomaterials and Nanostructures (Grant no. 2005CB623603). References [1] Wilk GD, Wallace RM, Anthony JM. J Appl Phys 2001;89:5243. [2] Lee B-H, Kang L, Neih R, Qi W, Lee JC. Appl Phys Lett 2000;76:1926. [3] Cao M, Voorde PV, Cox M, Greene W. IEEE Electron Dev Lett 1998;19:291. [4] Mohamed SH, Kappertz O, Niemeier T, Drese R, Wakkad MM, Wuttig M. Thin Solid Films 2004;468:48. [5] Quevedo-Lopez MA, El-Bouanani M, Kim MJ, Gnade BE, Wallace RM, Visokay MR, et al. Appl Phys Lett 2003;82:4669. [6] Lee M, Lu Z-H, Ng W-T, Landeer D, Wu X, Moisa S. Appl Phys Lett 2003;83:2638. [7] Nieh RE, Kang CS, Cho H-J, Onishi K, Choi R, Krishnan S, et al. IEEE Trans Electron Dev 2003;50:333. [8] He G, Zhang LD, Li GH, Liu M, Zhu LQ, Pan SS, et al. Appl Phys Lett 2005;86:232901. [9] Liu M, Fang Q, He G, Li L, Zhu LQ, Li GH, et al. Appl Phys Lett 2006;88:192904. [10] Lu XB, Zhang X, Huang R, Lu HB, Chen ZH, Xiang WF, et al. Appl. Phys Lett 2004;84:2620. [11] Kern W, Poutinen DA. RCA Rev 1970;31:187. [12] Kang CS, Cho HJ, Onishi K, Nieh R, Choi R, Gopanlan S, et al. Appl Phys Lett 2002;81:2593. [13] Chio KJ, Kim JH, Yoon SG, Shin WC. J Vac Sci Technol B 2004;22:1755. [14] Jellison Jr. GE, Modine FA. Appl Phys Lett 1996;69:371. [15] Jellison Jr. GE, Modine FA. Appl Phys Lett 1996;69:2137. [16] Morral AFI, Cabarrocas PRI, Clerc C. Phys Rev B 2004;69:125307. [17] Asahi R, Morikawa T, Ohwaki T, Aoki K, Taga Y. Science 2001;293:269. [18] Hu H, Zhu CX, Lu YF, Wu YH, Liew T, Li MF, et al. J Appl Phys 2003;94:551.