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The evolution of preferred orientation and morphology of AlN films under various RF sputtering powers
Surface and Coatings Technology 167 (2003) 297–301
The evolution of preferred orientation and morphology of AlN films under various RF sputtering powers Hao Cheng*, Peter Hing Advanced Materials Research Center (AMRC), School of Materials Engineering, Nanyang Technological University, Singapore 639798, Singapore
Abstract Wurtzite AlN films were deposited by RF reactive sputtering technique in argon and nitrogen gas mixtures. The evolution of preferred orientation and morphology of AlN films with the change in RF power was studied. X-ray diffraction (XRD), field emission scanning electron microscopy and scanning probe microscopy were employed to characterize the deposited films. It was found that at low RF powers, the preferred orientation was not distinct: (1 0 0), (0 0 2) and (1 0 1) peaks appeared in the u–2u XRD pattern. Increasing the RF power to 500 W led to the development of (1 0 1) preferred orientation. The grain morphology of the deposited films changed from pebble-like to pyramid cones with the increase in RF power, leading to the roughening of the film surface. 䊚 2003 Elsevier Science B.V. All rights reserved. Keywords: AlN film; RF sputtering; Preferred orientation; Morphology; Roughness
1. Introduction Because of its excellent thermal conductivity (3.2 Wy mK), chemical stability, high hardness, high acoustic velocity, large electromechanical coupling coefficient and a wide band gap (6.2 eV), AlN thin film received great interest as a promising candidate for electronic material for thermal dissipation, dielectric and passivation layers, surface acoustic wave devices and photoelectric devices w1–4x. Many techniques, such as DCy RF sputtering w5,6x, chemical vapor deposition w7x, laser chemical vapor deposition w8x, pulsed laser ablation and molecular beam epitaxial w9x, have been used to fabricate AlN thin films on various substrates. In most cases mentioned above, the deposition temperatures are quite high. High temperature deposition has the disadvantages of the degradation of the substrate and the AlN thin films during deposition due to thermal damage. Hence, deposition of AlN thin films at low temperature has become increasingly important and valuable w10x. Sputtering technique is promising under circumstances where low temperature deposition and conformal coatings are needed w11x. *Corresponding author. Tel.: q65-7904614; fax: q65-7900920. E-mail address: [email protected] (H. Cheng).
The performance of an AlN film is greatly influenced by its microstructure. For example, films with various preferred orientation will show different piezoelectric behavior, (0 0 2) preferred orientation is shown to be better (with the highest piezoelectric stress constant) w12x. For future application in high temperature, high energy devices with reduced device feature size, the heat dissipation capacity of AlN films becomes more and more important. The microstructure factors such as morphology, interface roughness and anisotropic structure play important roles in phonon scattering procedure in AlN films at certain temperature ranges, and thus will influence heat transport properties of the deposited films w13,14x. The fact that the microstructure of sputtered films is greatly influenced by the deposition condition necessitates the effort to study the evolution of microstructure and morphology of AlN films under various deposition conditions. Yet information on the influence of RF power is still lacking. In this work, we present our experimental results on the evolution of morphology and microstructure of AlN films with the change in RF power. 2. Experimental AlN films were deposited with a 99.99% pure Al
0257-8972/03/$ - see front matter 䊚 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0257-8972(02)00923-4
298
H. Cheng, P. Hing / Surface and Coatings Technology 167 (2003) 297–301
Table 1 Deposition conditions Substrate Substrate temperature Substrate-to-target distance Targets Sputtering gas Residual pressure RF power (W) Pre-sputtering pressure (mTorr) Pre-sputtering power (W) Sputtering pressure (mTorr) Gas flow rate
2=2 cm2 (1 0 0) Si 350 8C 14 cm 3 inch 99.99% pure Al AryN2 mixture 75% N2 -5=10y6 Torr 100, 200, 300, 500 20 300 5 12 sccm
AlN films have a wurtzite structure and no metastable cubic phase was found, as shown in Fig. 1a. At low RF powers, the formation of preferred orientation was less distinct as (1 0 0), (0 0 2) and (1 0 0) peaks appeared in the XRD pattern, as shown in Fig. 1b. With increasing RF power, the development of (1 0 1) preferred orien-
target and in 99.9995% nitrogen and argon mixture. A planar magnetron sputtering system supplied by Coaxial, UK was used for film deposition. The sputtering system consists of a cylindrical chamber approximately 65 cm in diameter and two 3-inch water-cooled target holders tilted at approximately 308 with respect to the normal of the horizontal substrate holder. The target–substrate distance is 14 cm. An impedance-matching network was used to control the RF power input. 2=2 cm2 (1 0 0) silicon wafers were used as substrates in this work. Before the deposition, the substrates were cleaned with 5% HF solution for 3 min, followed by rinsing in acetone and distilled water in ultrasonic bath. High-purity Ar gas was introduced into the chamber after the chamber was evacuated to below 5=10y6 Torr. Then the pure Al target was pre-sputtered for 10 min. During pre-sputtering the RF power and Ar pressure were fixed at 300 W and 20 mTorr, respectively. Then nitrogen gas was introduced into the chamber and reactive sputtering started. The RF power was changed from 100 to 500 W for different batches, while all the other parameters were kept constant. The detailed deposition parameters were summarized and listed in Table 1. Grazing incidence X-ray diffraction (GIXRD) scan was used for phase identification. The incidence angle a was fixed at 0.58 for all the measurements. Conventional u–2u XRD scan was used to study the preferred orientation of AlN films. All the measurements were carried out using a Shimadzu 6000 XRD instrument with Cu Ka radiation. JSM-6340F field emission scanning electron microscopy (FESEM) and Dimensional娃 3100 series scanning probe microscopy (SPM) worked at tapping mode were used to study the surface morphology of the deposited AlN films. The thicknesses of the deposited films were measured by cross-sectional FESEM images and by an alpha-step 500 type surface profiler. 3. Results and discussion The GIXRD result indicates that all the deposited
Fig. 1. XRD patterns of AlN films deposited at various N2 concentrations.
H. Cheng, P. Hing / Surface and Coatings Technology 167 (2003) 297–301
tation was observed, as shown in the films deposited at 450–500 W. It is well known that two kinds of Al–N bond exist in wurtzite AlN, named as B1 and B2. {1 0 0} planes consist of only B1 bond, while {0 0 2} and {1 0 1} planes consist of B1 and B2 bonds together. The formation energy of B2 bond is larger than that of B1. Thus, adatoms with higher energies are energetically favorable for the formation of (0 0 2) and (1 0 1) surface planes w15x. With an increase in RF power both the sputtering yield and the incident particle kinetic energy near the substrate surface will be increased w16x. Hence, high RF power is energetically favorable for the formation of surface planes with higher formation energy. Our result agrees well with this prediction. One possible reason for the formation of AlN films with mixed orientation in this work is that the kinetic energies of adatoms at these RF powers fell between the low and high energy that are energetically favorable for the formation of (1 0 0) and (0 0 2) preferred orientation, respectively, w15x. The fact that (1 0 1) instead of (0 0 2) preferred orientation was formed at high RF powers can be attributed to the difference in growth rate on {1 0 1} and {0 0 2}. {0 0 2} planes were found to grow at a slow rate w17x. As is shown later in the deposition rateRF power curve (Fig. 4), the films with (1 0 1) preferred orientation deposited at high powers grow much faster. According to the Van Der Drift model, in the formation of columnar structure, crystal grains oriented with their slower growing direction normal to the surface are terminated while faster growing directions are preserved as they intersect the grain boundaries w18x. Low sputtering yields and adatom kinetic energies introduced by low RF powers result in low deposition rate and surface mobility of the adatoms. Hence, a small grain size and a smooth surface were observed in the AlN film deposited at 100 W, as shown in Fig. 2a. With increasing RF power, a continuous growth in grain size was found, as shown in Fig. 2b–e—which indicates better surface mobility of the adatoms at high RF power. A coincidence in preferred orientation and surface morphology was also observed. Pyramid cone structure was found in films deposited at RF power larger than 300 W, where (1 0 1) preferred orientation was distinct, as shown in Fig. 2c–e. This result agrees well with former experimental work on AlN films deposited at various sputtering pressures w19x and is further confirmed by our results on AlN films deposited at various deposition conditions w20x. Further increasing the RF power to 500 W, results in the roughening of the film surface as the facet character of grains became less obvious, as shown in Fig. 2e. This can be attributed to the improved surface mobility of adatoms at larger RF powers, where adatoms are able to diffuse from grain boundaries to lower energy positions with the introduction of vacancies and voids at the grain interfaces w21x. A typical cross-sectional
299
Fig. 2. Surface morphology of AlN films deposited at different RF power.
micrograph is also shown in Fig. 2f, where the formation of columnar grains is clearly shown. The surface roughness of the deposited films was studied using a SPM worked at atomic force microscopy (AFM) mode. Fig. 3 shows the AFM micrographs of AlN films deposited at various RF powers. Continuous increases in grain size and surface roughness were again observed. The measured deposition rates and surface roughness values are summarized in Fig. 4, where Rq and Ra are root-mean-square and arithmetic mean surface roughness, respectively. As shown in this figure, an increase in RF power resulted in not only higher deposition rate and larger grain size but also a greatly roughened surface. Larger grains have been shown to reduce the phonon scattering at grain boundaries hence improve the heat transport properties of AlN films, while rougher surfaces have been shown to increase phonon scattering at surface boundaries hence degrade the thermal transport properties of the deposited films. Thus, RF power should be properly chosen to optimize the thermal transport property of the deposited AlN films.
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Fig. 3. AFM photos of the deposited AlN films.
4. Conclusion The evolution of preferred orientation and surface morphology with the change in RF power was studied
in this work. It was found that at low RF power, the deposited AlN films showed mixed orientation with (1 0 0), (0 0 2) and (1 0 1) peaks all appear in the XRD pattern. High RF power is favorable for depositing AlN films with (1 0 1) preferred orientation. A correlation between preferred orientation and morphology of the deposited films was also observed as pyramid cone structure was found in films with (1 0 1) preferred orientation. The increase in RF power results in not only a higher deposition rate and a larger grain size but also a rougher surface. References
Fig. 4. Evolution of surface roughness and deposition rate with the change in RF power.
w1x A. Kumar, H.L. Chan, J.J. Weimer, L. Sanderson, Thin Solid Films 308–309 (1997) 406–409. w2x A. Giardini, A. Mele, T.M. DiPalma, C. Flamini, S. Orlando, R. Teghil, Thin Solid Films 295 (1997) 77–82. w3x N. Tanaka, H. Okano, T. Usuki, K. Shibata, Jpn. J. Appl. Phys. 33 (1994) 5249–5254. w4x J.H. Edgar, C.A. Carosella, C.R. Eddy Jr., D.T. Smith, J. Mater. Sci.-Mater. Electron. 7 (1996) 247–253.
H. Cheng, P. Hing / Surface and Coatings Technology 167 (2003) 297–301 w5x S. Muhl, J.A. Zapien, J.M. Mendez, E. Andrade, J. Phys. D: Appl. Phys. 30 (1997) 2147–2155. w6x G. Carlotti, G. Gbbiotti, F.S. Hickernell, H.M. Liaw, G. Socino, Thin Solid Films 310 (1997) 34–38. w7x A.V. Dobrynin, J. Appl. Phys. 85 (1999) 1876–1882. w8x G. Radhakrishnan, J. Appl. Phys. 78 (1995) 6000–6005. w9x S. Tanaka, R.S. Kern, J. Bentley, R.F. Davis, Jpn. J. Appl. Phys. 35 (1996) 1641–1647. w10x M. Ishihara, K. Yamamoto, F. Kokai, Y. Koga, Jpn. J. Appl. Phys. 40 (2001) 2413–2416. w11x R. Bathe, R.D. Vispute, D. Habersat, et al., Thin Solid Films 398–399 (2001) 575–580. w12x R.S. Naik, R. Reif, J.J. Lutsky, C.G. Sodini, J. Electrochem. Soc. 146 (1999) 691–696. w13x M. Asheghi, Y.K. Leung, S.S. Wong, K.E. Goodson, Appl. Phys. Lett. 71 (1997) 1798–1800.
301
w14x A.D. McConnell, S. Uma, K.E. Goodson, in: G.P. Celata et al., (Eds.), Proceedings of the International Conference on Heat Transfer and Transport Phenomena in Microscale, Begell House, New York, 2000, pp. 413–419. w15x X.H. Xu, H.S. Wu, C.J. Zhang, Z.H. Jin, Thin Solid Films 388 (2001) 62–67. w16x W. Zou, Ph.D. Thesis, University of Virginia, 2001. w17x G.Y. Meng, S. Xie, D.K. Peng, Thin Solid Films 334 (1998) 145–150. w18x B. Rauschenbach, J.W. Gerlach, Cryst. Res. Technol. 35 (2000) 675–688. w19x B. Wang, Y.N. Zhao, Z. He, Vacuum 48 (1997) 427–429. w20x H. Cheng, P. Hing, The Influence of Deposition Conditions on Structure and Morphology of AlN Films Deposited by RF Reactive Sputtering, submitted for publication. w21x J. Yun, D.S. Dandy, Diamond Relat. Mater. 9 (2000) 439–445.
The evolution of preferred orientation and morphology of AlN films under various RF sputtering powers Hao Cheng*, Peter Hing Advanced Materials Research Center (AMRC), School of Materials Engineering, Nanyang Technological University, Singapore 639798, Singapore
Abstract Wurtzite AlN films were deposited by RF reactive sputtering technique in argon and nitrogen gas mixtures. The evolution of preferred orientation and morphology of AlN films with the change in RF power was studied. X-ray diffraction (XRD), field emission scanning electron microscopy and scanning probe microscopy were employed to characterize the deposited films. It was found that at low RF powers, the preferred orientation was not distinct: (1 0 0), (0 0 2) and (1 0 1) peaks appeared in the u–2u XRD pattern. Increasing the RF power to 500 W led to the development of (1 0 1) preferred orientation. The grain morphology of the deposited films changed from pebble-like to pyramid cones with the increase in RF power, leading to the roughening of the film surface. 䊚 2003 Elsevier Science B.V. All rights reserved. Keywords: AlN film; RF sputtering; Preferred orientation; Morphology; Roughness
1. Introduction Because of its excellent thermal conductivity (3.2 Wy mK), chemical stability, high hardness, high acoustic velocity, large electromechanical coupling coefficient and a wide band gap (6.2 eV), AlN thin film received great interest as a promising candidate for electronic material for thermal dissipation, dielectric and passivation layers, surface acoustic wave devices and photoelectric devices w1–4x. Many techniques, such as DCy RF sputtering w5,6x, chemical vapor deposition w7x, laser chemical vapor deposition w8x, pulsed laser ablation and molecular beam epitaxial w9x, have been used to fabricate AlN thin films on various substrates. In most cases mentioned above, the deposition temperatures are quite high. High temperature deposition has the disadvantages of the degradation of the substrate and the AlN thin films during deposition due to thermal damage. Hence, deposition of AlN thin films at low temperature has become increasingly important and valuable w10x. Sputtering technique is promising under circumstances where low temperature deposition and conformal coatings are needed w11x. *Corresponding author. Tel.: q65-7904614; fax: q65-7900920. E-mail address: [email protected] (H. Cheng).
The performance of an AlN film is greatly influenced by its microstructure. For example, films with various preferred orientation will show different piezoelectric behavior, (0 0 2) preferred orientation is shown to be better (with the highest piezoelectric stress constant) w12x. For future application in high temperature, high energy devices with reduced device feature size, the heat dissipation capacity of AlN films becomes more and more important. The microstructure factors such as morphology, interface roughness and anisotropic structure play important roles in phonon scattering procedure in AlN films at certain temperature ranges, and thus will influence heat transport properties of the deposited films w13,14x. The fact that the microstructure of sputtered films is greatly influenced by the deposition condition necessitates the effort to study the evolution of microstructure and morphology of AlN films under various deposition conditions. Yet information on the influence of RF power is still lacking. In this work, we present our experimental results on the evolution of morphology and microstructure of AlN films with the change in RF power. 2. Experimental AlN films were deposited with a 99.99% pure Al
0257-8972/03/$ - see front matter 䊚 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0257-8972(02)00923-4
298
H. Cheng, P. Hing / Surface and Coatings Technology 167 (2003) 297–301
Table 1 Deposition conditions Substrate Substrate temperature Substrate-to-target distance Targets Sputtering gas Residual pressure RF power (W) Pre-sputtering pressure (mTorr) Pre-sputtering power (W) Sputtering pressure (mTorr) Gas flow rate
2=2 cm2 (1 0 0) Si 350 8C 14 cm 3 inch 99.99% pure Al AryN2 mixture 75% N2 -5=10y6 Torr 100, 200, 300, 500 20 300 5 12 sccm
AlN films have a wurtzite structure and no metastable cubic phase was found, as shown in Fig. 1a. At low RF powers, the formation of preferred orientation was less distinct as (1 0 0), (0 0 2) and (1 0 0) peaks appeared in the XRD pattern, as shown in Fig. 1b. With increasing RF power, the development of (1 0 1) preferred orien-
target and in 99.9995% nitrogen and argon mixture. A planar magnetron sputtering system supplied by Coaxial, UK was used for film deposition. The sputtering system consists of a cylindrical chamber approximately 65 cm in diameter and two 3-inch water-cooled target holders tilted at approximately 308 with respect to the normal of the horizontal substrate holder. The target–substrate distance is 14 cm. An impedance-matching network was used to control the RF power input. 2=2 cm2 (1 0 0) silicon wafers were used as substrates in this work. Before the deposition, the substrates were cleaned with 5% HF solution for 3 min, followed by rinsing in acetone and distilled water in ultrasonic bath. High-purity Ar gas was introduced into the chamber after the chamber was evacuated to below 5=10y6 Torr. Then the pure Al target was pre-sputtered for 10 min. During pre-sputtering the RF power and Ar pressure were fixed at 300 W and 20 mTorr, respectively. Then nitrogen gas was introduced into the chamber and reactive sputtering started. The RF power was changed from 100 to 500 W for different batches, while all the other parameters were kept constant. The detailed deposition parameters were summarized and listed in Table 1. Grazing incidence X-ray diffraction (GIXRD) scan was used for phase identification. The incidence angle a was fixed at 0.58 for all the measurements. Conventional u–2u XRD scan was used to study the preferred orientation of AlN films. All the measurements were carried out using a Shimadzu 6000 XRD instrument with Cu Ka radiation. JSM-6340F field emission scanning electron microscopy (FESEM) and Dimensional娃 3100 series scanning probe microscopy (SPM) worked at tapping mode were used to study the surface morphology of the deposited AlN films. The thicknesses of the deposited films were measured by cross-sectional FESEM images and by an alpha-step 500 type surface profiler. 3. Results and discussion The GIXRD result indicates that all the deposited
Fig. 1. XRD patterns of AlN films deposited at various N2 concentrations.
H. Cheng, P. Hing / Surface and Coatings Technology 167 (2003) 297–301
tation was observed, as shown in the films deposited at 450–500 W. It is well known that two kinds of Al–N bond exist in wurtzite AlN, named as B1 and B2. {1 0 0} planes consist of only B1 bond, while {0 0 2} and {1 0 1} planes consist of B1 and B2 bonds together. The formation energy of B2 bond is larger than that of B1. Thus, adatoms with higher energies are energetically favorable for the formation of (0 0 2) and (1 0 1) surface planes w15x. With an increase in RF power both the sputtering yield and the incident particle kinetic energy near the substrate surface will be increased w16x. Hence, high RF power is energetically favorable for the formation of surface planes with higher formation energy. Our result agrees well with this prediction. One possible reason for the formation of AlN films with mixed orientation in this work is that the kinetic energies of adatoms at these RF powers fell between the low and high energy that are energetically favorable for the formation of (1 0 0) and (0 0 2) preferred orientation, respectively, w15x. The fact that (1 0 1) instead of (0 0 2) preferred orientation was formed at high RF powers can be attributed to the difference in growth rate on {1 0 1} and {0 0 2}. {0 0 2} planes were found to grow at a slow rate w17x. As is shown later in the deposition rateRF power curve (Fig. 4), the films with (1 0 1) preferred orientation deposited at high powers grow much faster. According to the Van Der Drift model, in the formation of columnar structure, crystal grains oriented with their slower growing direction normal to the surface are terminated while faster growing directions are preserved as they intersect the grain boundaries w18x. Low sputtering yields and adatom kinetic energies introduced by low RF powers result in low deposition rate and surface mobility of the adatoms. Hence, a small grain size and a smooth surface were observed in the AlN film deposited at 100 W, as shown in Fig. 2a. With increasing RF power, a continuous growth in grain size was found, as shown in Fig. 2b–e—which indicates better surface mobility of the adatoms at high RF power. A coincidence in preferred orientation and surface morphology was also observed. Pyramid cone structure was found in films deposited at RF power larger than 300 W, where (1 0 1) preferred orientation was distinct, as shown in Fig. 2c–e. This result agrees well with former experimental work on AlN films deposited at various sputtering pressures w19x and is further confirmed by our results on AlN films deposited at various deposition conditions w20x. Further increasing the RF power to 500 W, results in the roughening of the film surface as the facet character of grains became less obvious, as shown in Fig. 2e. This can be attributed to the improved surface mobility of adatoms at larger RF powers, where adatoms are able to diffuse from grain boundaries to lower energy positions with the introduction of vacancies and voids at the grain interfaces w21x. A typical cross-sectional
299
Fig. 2. Surface morphology of AlN films deposited at different RF power.
micrograph is also shown in Fig. 2f, where the formation of columnar grains is clearly shown. The surface roughness of the deposited films was studied using a SPM worked at atomic force microscopy (AFM) mode. Fig. 3 shows the AFM micrographs of AlN films deposited at various RF powers. Continuous increases in grain size and surface roughness were again observed. The measured deposition rates and surface roughness values are summarized in Fig. 4, where Rq and Ra are root-mean-square and arithmetic mean surface roughness, respectively. As shown in this figure, an increase in RF power resulted in not only higher deposition rate and larger grain size but also a greatly roughened surface. Larger grains have been shown to reduce the phonon scattering at grain boundaries hence improve the heat transport properties of AlN films, while rougher surfaces have been shown to increase phonon scattering at surface boundaries hence degrade the thermal transport properties of the deposited films. Thus, RF power should be properly chosen to optimize the thermal transport property of the deposited AlN films.
300
H. Cheng, P. Hing / Surface and Coatings Technology 167 (2003) 297–301
Fig. 3. AFM photos of the deposited AlN films.
4. Conclusion The evolution of preferred orientation and surface morphology with the change in RF power was studied
in this work. It was found that at low RF power, the deposited AlN films showed mixed orientation with (1 0 0), (0 0 2) and (1 0 1) peaks all appear in the XRD pattern. High RF power is favorable for depositing AlN films with (1 0 1) preferred orientation. A correlation between preferred orientation and morphology of the deposited films was also observed as pyramid cone structure was found in films with (1 0 1) preferred orientation. The increase in RF power results in not only a higher deposition rate and a larger grain size but also a rougher surface. References
Fig. 4. Evolution of surface roughness and deposition rate with the change in RF power.
w1x A. Kumar, H.L. Chan, J.J. Weimer, L. Sanderson, Thin Solid Films 308–309 (1997) 406–409. w2x A. Giardini, A. Mele, T.M. DiPalma, C. Flamini, S. Orlando, R. Teghil, Thin Solid Films 295 (1997) 77–82. w3x N. Tanaka, H. Okano, T. Usuki, K. Shibata, Jpn. J. Appl. Phys. 33 (1994) 5249–5254. w4x J.H. Edgar, C.A. Carosella, C.R. Eddy Jr., D.T. Smith, J. Mater. Sci.-Mater. Electron. 7 (1996) 247–253.
H. Cheng, P. Hing / Surface and Coatings Technology 167 (2003) 297–301 w5x S. Muhl, J.A. Zapien, J.M. Mendez, E. Andrade, J. Phys. D: Appl. Phys. 30 (1997) 2147–2155. w6x G. Carlotti, G. Gbbiotti, F.S. Hickernell, H.M. Liaw, G. Socino, Thin Solid Films 310 (1997) 34–38. w7x A.V. Dobrynin, J. Appl. Phys. 85 (1999) 1876–1882. w8x G. Radhakrishnan, J. Appl. Phys. 78 (1995) 6000–6005. w9x S. Tanaka, R.S. Kern, J. Bentley, R.F. Davis, Jpn. J. Appl. Phys. 35 (1996) 1641–1647. w10x M. Ishihara, K. Yamamoto, F. Kokai, Y. Koga, Jpn. J. Appl. Phys. 40 (2001) 2413–2416. w11x R. Bathe, R.D. Vispute, D. Habersat, et al., Thin Solid Films 398–399 (2001) 575–580. w12x R.S. Naik, R. Reif, J.J. Lutsky, C.G. Sodini, J. Electrochem. Soc. 146 (1999) 691–696. w13x M. Asheghi, Y.K. Leung, S.S. Wong, K.E. Goodson, Appl. Phys. Lett. 71 (1997) 1798–1800.
301
w14x A.D. McConnell, S. Uma, K.E. Goodson, in: G.P. Celata et al., (Eds.), Proceedings of the International Conference on Heat Transfer and Transport Phenomena in Microscale, Begell House, New York, 2000, pp. 413–419. w15x X.H. Xu, H.S. Wu, C.J. Zhang, Z.H. Jin, Thin Solid Films 388 (2001) 62–67. w16x W. Zou, Ph.D. Thesis, University of Virginia, 2001. w17x G.Y. Meng, S. Xie, D.K. Peng, Thin Solid Films 334 (1998) 145–150. w18x B. Rauschenbach, J.W. Gerlach, Cryst. Res. Technol. 35 (2000) 675–688. w19x B. Wang, Y.N. Zhao, Z. He, Vacuum 48 (1997) 427–429. w20x H. Cheng, P. Hing, The Influence of Deposition Conditions on Structure and Morphology of AlN Films Deposited by RF Reactive Sputtering, submitted for publication. w21x J. Yun, D.S. Dandy, Diamond Relat. Mater. 9 (2000) 439–445.