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Effects of substrate bias and growth temperature on properties of aluminium oxide thin films by using filtered cathodic vacuum arc
Surface & Coatings Technology 198 (2005) 94 – 97 www.elsevier.com/locate/surfcoat
Effects of substrate bias and growth temperature on properties of aluminium oxide thin films by using filtered cathodic vacuum arc B.K. Tay*, Z.W. Zhao, C.Q. Sun School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, 639798, Singapore Available online 26 November 2004
Abstract Two sets of aluminium oxide thin films were deposited using off-plane filtered cathodic vacuum arc (FCVA) at the working pressure of 6104 Torr under various substrate biases (60 to 140 V) and substrate temperatures (120–600 8C), respectively. Optical and mechanical properties, such as refractive index, residual stress, hardness and Young’s modulus, of the films were investigated. It has been found that both the refractive index and the residual compressive stress of the films increase with increasing substrate bias, while no significant changes in the hardness and Young’s modulus could be noted. For the films grown at various growth temperatures, a transition temperature of 300 8C was found. A sharp increase in refractive index is observed as the substrate temperature varies from 200 to 300 8C. Beyond this temperature, no much significant changes in refractive index could be found. Hardness and Young’s modulus follow similar trend to that of refractive index, while the residual compressive stress in the films behaves inversely. D 2004 Elsevier B.V. All rights reserved. Keywords: FCVA; Aluminium oxide; Optical properties; Mechanical properties
1. Introduction Aluminium oxide thin films have received an increasing interest due to their wide applications as optical coatings, dielectric layers, wear-resistant coatings, and protective coatings [1–4]. Various techniques have been used to deposit aluminium oxide thin films, such as magnetron sputtering [3,5], plasma-enhanced chemical vapour deposition [2], metal organic chemical vapour deposition [6,7], dual ion beam sputtering [8]. Besides, vacuum arc has been used to form metal oxide and nitride thin films [9–15] due to its characteristics of high ionization ratio, high ion energy (50–150 eV) and high deposition rate. However, the generation of macro particles during film deposition is the drawback of the vacuum arc, limiting the use of such technique to grow high quality films for optical applications [16]. Filtered cathodic vacuum arc (FCVA) technique is a promising * Corresponding author. Tel.: +65 67904533; fax: +65 67933318. E-mail address: [email protected] (B.K. Tay). 0257-8972/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2004.10.049
method by employing electromagnetic and mechanical filtering technique to eliminate unwanted macro particles and neutral atoms [17]. In particular, a novel ring [18] was used to introduce reactive gas into FCVA system resulting in better ionization. Several reports in the literature have discussed the formation of aluminium oxide thin films by FCVA [9–11]. Improved protection from corrosion and environmental effects of aluminium oxide thin films as well as the stability have been studied in the literature [9,11]. In addition, high deposition rate of aluminium oxide thin films had been presented by other researchers [10,18]. However, few reports describe the effects of substrate bias and growth temperature on the properties of aluminium oxide thin films. Thus, in this work, aluminium oxide thin films were deposited by FCVA under various substrate biases and temperatures, respectively. The aim is to investigate the variations of some optical and mechanical properties (e.g. refractive index, residual stress, hardness and Young’s modulus) of the deposited films under various growth conditions.
B.K. Tay et al. / Surface & Coatings Technology 198 (2005) 94–97
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2. Experimental details Aluminum oxide thin films were deposited by the FCVA as described elsewhere [19]. An aluminum cathode with a purity of 99.98% was operated at an arc current of 125 A to obtain the plasma. The base pressure of the system was evacuated to a base pressure of 106 Torr. A ring method was used to introduce reactive gas into the chamber leading to better ionization. Two series of deposition were conducted. In the first set, various negative DC voltages, V b, ranged from 60 to 140 V were applied to the substrates during the film growth. In the second set, aluminum oxide thin films were deposited with varying the temperature from 120 to 600 8C. During all the depositions, working pressure was kept at 6104 Torr and n-type Si(100) was used as substrate. The phase and crystal structures of deposited thin films were identified by X-ray diffraction (XRD) with a Cu Ka source. Optical constants and film thickness were both obtained by using UVISEL spectroscopic phase-modulated ellipsometer in the spectral range of 300–900 nm. The residual stress of grown films was obtained using the radiusof-curvature technique by the Tencor P-10 Surface Profiler. Both film hardness and Young’s modulus were characterized using nanoindentation techniques (Nanoindenter II, Nano Instruments) [20].
3. Results and discussion 3.1. Effects of substrate bias (V b) XRD profiles show that the films deposited at V b ranged between 60 and 140 V with a constant working pressure of 6104 Torr were all amorphous in structure. Refractive index for the films deposited at various V b were obtained by fitting the ellipsometric measurements to a Sellmeier dispersion model, which is shown to be appropriate for transparent materials. Fig. 1 shows the dispersion of refractive index at various substrate biases. It is noted that the higher refractive index could be reached when a higher negative bias was applied to the substrate during the process of film deposition. It is widely known that substrate bias voltage and process pressure relate directly to the ion energy. Bubenzer proposed that ion energy could be expressed with the following relation [21]: E ¼ KVb =Pm ;
0VmV1;
ð1Þ
where K is a constant, V b is the bias voltage, P is the pressure and m is a coefficient. According to this expression, the ion energy would be proportional to the V b when other parameters keep constant during film growth. In the present case, the deposition pressure was kept constant. When the film surface was bombarded by the arriving ions during film growth, the interaction ions would
Fig. 1. Dispersive curves of refractive index for the films deposited at various substrate bias.
produce phonons, vacancies, the knock-on atoms, and electronic excitations. With increasing V b, knock-on atoms may penetrate into the film more deeply and then are trapped as interstitials, preferentially in quenched vacancy sites. Vacancies near the surface that are produced by bombarding ions are partially refilled by newly arriving ions, which results in downward packing of materials such that films grow in a more densely packed structure [16]. It is well known that the film refractive index is correlated to the film packing density and proportional to it. Thus, the higher density contributes to the increase of refractive index at higher V b. The stress in the films was evaluated using Stoney’s equation by measuring the radii of curvature of the filmsubstrate composite and bare substrate [22]. Fig. 2 shows the residual compressive stress of aluminium oxide thin films against various V b. In general, the film residual compressive stresses increase slowly with the V b. The residual stresses in the films include the thermal stresses and intrinsic stresses. Because no heating was applied during the film growth, the thermal stress induced by the mismatch of thermal expansion coefficient between film and substrate can be negligible. The residual compressive stress originated mainly from the intrinsic stress formed during the film growth. As V b increases, the particles impinging on the surface of the growing film can move to more energetically favored sites such as vacancies. Higher density of the grown films promoted the increase in the compressive stress [23]. Hardness and Young’s modulus of aluminium oxide thin films are about 15 and 200 GPa (not shown). There is almost no variation of hardness and Young’s modulus with substrate bias voltage. 3.2. Effects of growth temperature Refractive index of the second set of samples was obtained using same method as described above. Dispersive curves of refractive index of the grown films were plotted
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B.K. Tay et al. / Surface & Coatings Technology 198 (2005) 94–97
Fig. 2. Distribution of residual compressive stress in the films grown under different substrate bias.
Fig. 4. Distribution of residual compressive stress in the films grown at different temperatures.
in Fig. 3. For the films deposited at 120 and 200 8C, no obvious deviation in the refractive index between the curves could be found, especially in the longer wavelength range. A sudden shift in the refractive index is observed when the film deposited at 300 8C. Beyond 300 8C, no difference in refractive index among the curves could be observed. This implies that the growth temperature of 300 8C was a transition temperature, where a high film packing density could be achieved and thereby result in higher refractive index. The residual compressive stress in the films deposited at various growth temperatures was plotted in Fig. 4. For the films grown at 100 and 200 8C, no much change could be observed. At 300 8C, the residual compressive stress in the film decreases and remains stable beyond the growth temperature of 300 8C. Fig. 5 shows the dependence of hardness and Young’s modulus on the growth temperature. At low growth temperatures, neither hardness nor Young’s modulus shows significant changes, such as 100 and 200 8C. As increasing the growth temperature, both hardness and Young’s modulus increase compared with those at 100 and 200 8C,
The effects of bias substrate and growth temperature on the properties of the films deposited at 6104 Torr by FCVA were examined. When negative bias voltage was supplied to the substrate during film growth, the films were amorphous in nature. The film refractive index increases as increasing growth
Fig. 3. Dispersive curves of refractive index for the films deposited at various growth temperatures.
Fig. 5. Hardness and Young’s modulus of aluminium oxide thin films deposited at various substrate temperatures.
respectively. No significant changes of hardness and Young’s modulus could be observed when the growth temperature exceeded 300 8C. From the results above, the variations of residual compressive stress, hardness and Young’s modulus with the growth temperature show a rapid change in the same temperature of 300 8C. Similar behaviour happens to the variation of refractive index with the growth temperature as indicated in Fig. 4, suggesting the temperature of 300 8C is a critical point, exceeding which the changes in the properties of grown films would occur.
4. Conclusions
B.K. Tay et al. / Surface & Coatings Technology 198 (2005) 94–97
temperature as well as the residual compressive stress. Both of hardness and Young’s modulus of the grown films were kept constant. Effects of growth temperature on film properties were studied. A transition temperature of 300 8C was observed. A sharp increase in refractive index is observed as the growth temperature varies from 200 8C to 300 8C. Beyond this temperature, no much significant changes in refractive index could be found. Both of hardness and Young’s modulus follow similar trend to that of refractive index, while the residual compressive stress in the films behaves inversely.
References [1] M. Aguilar-Frutis, M. Garcia, C. Falcony, Appl. Phys. Lett. 72 (1998) 1700. [2] C.H. Lin, H.L. Wang, M.H. Hon, Thin Solid Films 283 (1996) 171. [3] P.J. Kelly, R.D. Arnell, J. Vac. Sci. Technol., A, Vac. Surf. Films 17 (1999) 945. [4] C.S. Bhatia, G. Guthmiller, A.M. Spool, J. Vac. Sci. Technol., A, Vac. Surf. Films 7 (1989) 1298. [5] W.D. Sproul, M.E. Graham, M.S. Wong, S. Lopez, D. Li, R.A. Scholl, J. Vac. Sci. Technol., A, Vac. Surf. Films 13 (1995) 1188. [6] E. Ciliberto, I. Fragala, R. Rizza, G. Spoto, G.C. Allen, Appl. Phys. Lett. 67 (1995) 1624. [7] T.W. Kim, S.S. Yom, W.N. Kang, Y.S. Yoon, C. Kim, S. Kim, I.S. Yang, Y.J. Wee, Appl. Surf. Sci. 65/66 (1993) 854.
97
[8] G. Emiliani, S. Scaglione, J. Vac. Sci. Technol., A, Vac. Surf. Films 5 (1987) 1824. [9] S. Anders, A. Anders, M. Rubin, Z. Wang, S. Raoux, F. Kong, I.G. Brown, Surf. Coat. Technol. 76–77 (1995) 167. [10] H. Randhawa, J. Vac. Sci. Technol., A, Vac. Surf. Films 7 (1989) 2346. [11] H. Bolt, F. Koch, J.L. Rodet, D. Karpov, S. Menzel, Surf. Coat. Technol. 116–119 (1999) 956. [12] A. Bendavid, P.J. Martin, X. Wang, M. Wittling, T.J. Kinder, J. Vac. Sci. Technol., A, Vac. Surf. Films 13 (1995) 1658. [13] H. Takikawa, K. Kimura, R. Miyano, T. Sakakibara, Thin Solid Films 377–378 (2000) 74. [14] T. Zhang, J.H. Song, X.B. Tian, P.K. Chu, I.G. Brown, J. Vac. Sci. Technol., A, Vac. Surf. Films 19 (2001) 2048. [15] Y.H. Cheng, B.K. Tay, S.P. Lau, X. Shi, J. Vac. Sci. Technol., A, Vac. Surf. Films 19 (2001) 736. [16] R.L. Boxman, D.M. Sanders, P.J. Martin, Handbook of Vacuum Arc Science and Technique: Fundamentals and Applications, Noyes, Par Ridge, NJ, 1995. [17] B.K. Tay, X. Shi, D.I. Flynn, Surf. Eng. 13 (1997) 213. [18] Y.S. Choong, B.K. Tay, S.P. Lau, X. Shi, Y.H. Cheng, Thin Solid Films 386 (2001) 1. [19] X. Shi, B.K. Tay, H.S. Tan, Filtered Cathodic Arc Source, Patent (PCT/GB96/00389), 20 Feb (1995). [20] W.C. Olive, G.M. Pharr, J. Mater. Res. 7 (1992) 1564. [21] A. Bubenzer, B. Dischler, G. Brandt, P. Koidl, J. Appl. Phys. 54 (1983) 4590. [22] G.G. Stoney, Proc. R. Soc. Lond. Ser. A82 (1909) 172. [23] A. Bendavid, P.J. Martin, H. Takikawa, Thin Solid Films 360 (2000) 241.
Effects of substrate bias and growth temperature on properties of aluminium oxide thin films by using filtered cathodic vacuum arc B.K. Tay*, Z.W. Zhao, C.Q. Sun School of Electrical and Electronic Engineering, Nanyang Technological University, Nanyang Avenue, 639798, Singapore Available online 26 November 2004
Abstract Two sets of aluminium oxide thin films were deposited using off-plane filtered cathodic vacuum arc (FCVA) at the working pressure of 6104 Torr under various substrate biases (60 to 140 V) and substrate temperatures (120–600 8C), respectively. Optical and mechanical properties, such as refractive index, residual stress, hardness and Young’s modulus, of the films were investigated. It has been found that both the refractive index and the residual compressive stress of the films increase with increasing substrate bias, while no significant changes in the hardness and Young’s modulus could be noted. For the films grown at various growth temperatures, a transition temperature of 300 8C was found. A sharp increase in refractive index is observed as the substrate temperature varies from 200 to 300 8C. Beyond this temperature, no much significant changes in refractive index could be found. Hardness and Young’s modulus follow similar trend to that of refractive index, while the residual compressive stress in the films behaves inversely. D 2004 Elsevier B.V. All rights reserved. Keywords: FCVA; Aluminium oxide; Optical properties; Mechanical properties
1. Introduction Aluminium oxide thin films have received an increasing interest due to their wide applications as optical coatings, dielectric layers, wear-resistant coatings, and protective coatings [1–4]. Various techniques have been used to deposit aluminium oxide thin films, such as magnetron sputtering [3,5], plasma-enhanced chemical vapour deposition [2], metal organic chemical vapour deposition [6,7], dual ion beam sputtering [8]. Besides, vacuum arc has been used to form metal oxide and nitride thin films [9–15] due to its characteristics of high ionization ratio, high ion energy (50–150 eV) and high deposition rate. However, the generation of macro particles during film deposition is the drawback of the vacuum arc, limiting the use of such technique to grow high quality films for optical applications [16]. Filtered cathodic vacuum arc (FCVA) technique is a promising * Corresponding author. Tel.: +65 67904533; fax: +65 67933318. E-mail address: [email protected] (B.K. Tay). 0257-8972/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2004.10.049
method by employing electromagnetic and mechanical filtering technique to eliminate unwanted macro particles and neutral atoms [17]. In particular, a novel ring [18] was used to introduce reactive gas into FCVA system resulting in better ionization. Several reports in the literature have discussed the formation of aluminium oxide thin films by FCVA [9–11]. Improved protection from corrosion and environmental effects of aluminium oxide thin films as well as the stability have been studied in the literature [9,11]. In addition, high deposition rate of aluminium oxide thin films had been presented by other researchers [10,18]. However, few reports describe the effects of substrate bias and growth temperature on the properties of aluminium oxide thin films. Thus, in this work, aluminium oxide thin films were deposited by FCVA under various substrate biases and temperatures, respectively. The aim is to investigate the variations of some optical and mechanical properties (e.g. refractive index, residual stress, hardness and Young’s modulus) of the deposited films under various growth conditions.
B.K. Tay et al. / Surface & Coatings Technology 198 (2005) 94–97
95
2. Experimental details Aluminum oxide thin films were deposited by the FCVA as described elsewhere [19]. An aluminum cathode with a purity of 99.98% was operated at an arc current of 125 A to obtain the plasma. The base pressure of the system was evacuated to a base pressure of 106 Torr. A ring method was used to introduce reactive gas into the chamber leading to better ionization. Two series of deposition were conducted. In the first set, various negative DC voltages, V b, ranged from 60 to 140 V were applied to the substrates during the film growth. In the second set, aluminum oxide thin films were deposited with varying the temperature from 120 to 600 8C. During all the depositions, working pressure was kept at 6104 Torr and n-type Si(100) was used as substrate. The phase and crystal structures of deposited thin films were identified by X-ray diffraction (XRD) with a Cu Ka source. Optical constants and film thickness were both obtained by using UVISEL spectroscopic phase-modulated ellipsometer in the spectral range of 300–900 nm. The residual stress of grown films was obtained using the radiusof-curvature technique by the Tencor P-10 Surface Profiler. Both film hardness and Young’s modulus were characterized using nanoindentation techniques (Nanoindenter II, Nano Instruments) [20].
3. Results and discussion 3.1. Effects of substrate bias (V b) XRD profiles show that the films deposited at V b ranged between 60 and 140 V with a constant working pressure of 6104 Torr were all amorphous in structure. Refractive index for the films deposited at various V b were obtained by fitting the ellipsometric measurements to a Sellmeier dispersion model, which is shown to be appropriate for transparent materials. Fig. 1 shows the dispersion of refractive index at various substrate biases. It is noted that the higher refractive index could be reached when a higher negative bias was applied to the substrate during the process of film deposition. It is widely known that substrate bias voltage and process pressure relate directly to the ion energy. Bubenzer proposed that ion energy could be expressed with the following relation [21]: E ¼ KVb =Pm ;
0VmV1;
ð1Þ
where K is a constant, V b is the bias voltage, P is the pressure and m is a coefficient. According to this expression, the ion energy would be proportional to the V b when other parameters keep constant during film growth. In the present case, the deposition pressure was kept constant. When the film surface was bombarded by the arriving ions during film growth, the interaction ions would
Fig. 1. Dispersive curves of refractive index for the films deposited at various substrate bias.
produce phonons, vacancies, the knock-on atoms, and electronic excitations. With increasing V b, knock-on atoms may penetrate into the film more deeply and then are trapped as interstitials, preferentially in quenched vacancy sites. Vacancies near the surface that are produced by bombarding ions are partially refilled by newly arriving ions, which results in downward packing of materials such that films grow in a more densely packed structure [16]. It is well known that the film refractive index is correlated to the film packing density and proportional to it. Thus, the higher density contributes to the increase of refractive index at higher V b. The stress in the films was evaluated using Stoney’s equation by measuring the radii of curvature of the filmsubstrate composite and bare substrate [22]. Fig. 2 shows the residual compressive stress of aluminium oxide thin films against various V b. In general, the film residual compressive stresses increase slowly with the V b. The residual stresses in the films include the thermal stresses and intrinsic stresses. Because no heating was applied during the film growth, the thermal stress induced by the mismatch of thermal expansion coefficient between film and substrate can be negligible. The residual compressive stress originated mainly from the intrinsic stress formed during the film growth. As V b increases, the particles impinging on the surface of the growing film can move to more energetically favored sites such as vacancies. Higher density of the grown films promoted the increase in the compressive stress [23]. Hardness and Young’s modulus of aluminium oxide thin films are about 15 and 200 GPa (not shown). There is almost no variation of hardness and Young’s modulus with substrate bias voltage. 3.2. Effects of growth temperature Refractive index of the second set of samples was obtained using same method as described above. Dispersive curves of refractive index of the grown films were plotted
96
B.K. Tay et al. / Surface & Coatings Technology 198 (2005) 94–97
Fig. 2. Distribution of residual compressive stress in the films grown under different substrate bias.
Fig. 4. Distribution of residual compressive stress in the films grown at different temperatures.
in Fig. 3. For the films deposited at 120 and 200 8C, no obvious deviation in the refractive index between the curves could be found, especially in the longer wavelength range. A sudden shift in the refractive index is observed when the film deposited at 300 8C. Beyond 300 8C, no difference in refractive index among the curves could be observed. This implies that the growth temperature of 300 8C was a transition temperature, where a high film packing density could be achieved and thereby result in higher refractive index. The residual compressive stress in the films deposited at various growth temperatures was plotted in Fig. 4. For the films grown at 100 and 200 8C, no much change could be observed. At 300 8C, the residual compressive stress in the film decreases and remains stable beyond the growth temperature of 300 8C. Fig. 5 shows the dependence of hardness and Young’s modulus on the growth temperature. At low growth temperatures, neither hardness nor Young’s modulus shows significant changes, such as 100 and 200 8C. As increasing the growth temperature, both hardness and Young’s modulus increase compared with those at 100 and 200 8C,
The effects of bias substrate and growth temperature on the properties of the films deposited at 6104 Torr by FCVA were examined. When negative bias voltage was supplied to the substrate during film growth, the films were amorphous in nature. The film refractive index increases as increasing growth
Fig. 3. Dispersive curves of refractive index for the films deposited at various growth temperatures.
Fig. 5. Hardness and Young’s modulus of aluminium oxide thin films deposited at various substrate temperatures.
respectively. No significant changes of hardness and Young’s modulus could be observed when the growth temperature exceeded 300 8C. From the results above, the variations of residual compressive stress, hardness and Young’s modulus with the growth temperature show a rapid change in the same temperature of 300 8C. Similar behaviour happens to the variation of refractive index with the growth temperature as indicated in Fig. 4, suggesting the temperature of 300 8C is a critical point, exceeding which the changes in the properties of grown films would occur.
4. Conclusions
B.K. Tay et al. / Surface & Coatings Technology 198 (2005) 94–97
temperature as well as the residual compressive stress. Both of hardness and Young’s modulus of the grown films were kept constant. Effects of growth temperature on film properties were studied. A transition temperature of 300 8C was observed. A sharp increase in refractive index is observed as the growth temperature varies from 200 8C to 300 8C. Beyond this temperature, no much significant changes in refractive index could be found. Both of hardness and Young’s modulus follow similar trend to that of refractive index, while the residual compressive stress in the films behaves inversely.
References [1] M. Aguilar-Frutis, M. Garcia, C. Falcony, Appl. Phys. Lett. 72 (1998) 1700. [2] C.H. Lin, H.L. Wang, M.H. Hon, Thin Solid Films 283 (1996) 171. [3] P.J. Kelly, R.D. Arnell, J. Vac. Sci. Technol., A, Vac. Surf. Films 17 (1999) 945. [4] C.S. Bhatia, G. Guthmiller, A.M. Spool, J. Vac. Sci. Technol., A, Vac. Surf. Films 7 (1989) 1298. [5] W.D. Sproul, M.E. Graham, M.S. Wong, S. Lopez, D. Li, R.A. Scholl, J. Vac. Sci. Technol., A, Vac. Surf. Films 13 (1995) 1188. [6] E. Ciliberto, I. Fragala, R. Rizza, G. Spoto, G.C. Allen, Appl. Phys. Lett. 67 (1995) 1624. [7] T.W. Kim, S.S. Yom, W.N. Kang, Y.S. Yoon, C. Kim, S. Kim, I.S. Yang, Y.J. Wee, Appl. Surf. Sci. 65/66 (1993) 854.
97
[8] G. Emiliani, S. Scaglione, J. Vac. Sci. Technol., A, Vac. Surf. Films 5 (1987) 1824. [9] S. Anders, A. Anders, M. Rubin, Z. Wang, S. Raoux, F. Kong, I.G. Brown, Surf. Coat. Technol. 76–77 (1995) 167. [10] H. Randhawa, J. Vac. Sci. Technol., A, Vac. Surf. Films 7 (1989) 2346. [11] H. Bolt, F. Koch, J.L. Rodet, D. Karpov, S. Menzel, Surf. Coat. Technol. 116–119 (1999) 956. [12] A. Bendavid, P.J. Martin, X. Wang, M. Wittling, T.J. Kinder, J. Vac. Sci. Technol., A, Vac. Surf. Films 13 (1995) 1658. [13] H. Takikawa, K. Kimura, R. Miyano, T. Sakakibara, Thin Solid Films 377–378 (2000) 74. [14] T. Zhang, J.H. Song, X.B. Tian, P.K. Chu, I.G. Brown, J. Vac. Sci. Technol., A, Vac. Surf. Films 19 (2001) 2048. [15] Y.H. Cheng, B.K. Tay, S.P. Lau, X. Shi, J. Vac. Sci. Technol., A, Vac. Surf. Films 19 (2001) 736. [16] R.L. Boxman, D.M. Sanders, P.J. Martin, Handbook of Vacuum Arc Science and Technique: Fundamentals and Applications, Noyes, Par Ridge, NJ, 1995. [17] B.K. Tay, X. Shi, D.I. Flynn, Surf. Eng. 13 (1997) 213. [18] Y.S. Choong, B.K. Tay, S.P. Lau, X. Shi, Y.H. Cheng, Thin Solid Films 386 (2001) 1. [19] X. Shi, B.K. Tay, H.S. Tan, Filtered Cathodic Arc Source, Patent (PCT/GB96/00389), 20 Feb (1995). [20] W.C. Olive, G.M. Pharr, J. Mater. Res. 7 (1992) 1564. [21] A. Bubenzer, B. Dischler, G. Brandt, P. Koidl, J. Appl. Phys. 54 (1983) 4590. [22] G.G. Stoney, Proc. R. Soc. Lond. Ser. A82 (1909) 172. [23] A. Bendavid, P.J. Martin, H. Takikawa, Thin Solid Films 360 (2000) 241.