INFLUENCE OF MOLYBDENUM IN STRUCTURAL AND ...
INFLUENCE OF MOLYBDENUM IN STRUCTURAL AND ELECTRICAL PROPERTIES OF AlN THIN FILMS DEPOSITED BY DC MAGNETRON SPUTTERING G.W.A. Cardoso1*; G. Leal1; T.S. Braga2; A.S. da Silva Sobrinho2; M. Massi1,2 Science and Technology Institute, Federal University of São Paulo, 12231-280, São José dos Campos, SP, Brazil 2 Plasma and Process Laboratory, Technological Institute of Aeronautics, 12228-900, São José dos Campos, SP, Brazil 1
Aluminum nitride thin films have high thermal and chemical stabilities that make it a promissory material to be used in MEMS. The addition of metallic nanoparticles into the film matrix can reduce the value of resistivity, and then, qualify the material to be used in piezoresistivity devices. In this work, Mo-AlN thin films were deposited on Si (100) substrate by DC magnetron sputtering. The films were characterized by mechanical profilometry, 4-points probe, X-ray diffraction and Rutherford backscattering spectroscopy (RBS). The results indicate that intrinsic AlN films presented, as expected, insulator characteristics, while the doped films (about 6% of Mo), presented a reduction in the resistivity values up to 10Ω.cm. The RBS results indicates the presence of oxygen in the films deposited at higher work pressure (10mTorr) that was confirmed by the XRD peaks of AlON at 2θ=52.7º and the increase of resistivity.
Keywords: Mo-AlN, Mo-AlNO, Thin films, DC Magnetron Sputtering
Introduction Aluminum nitride thin films have high thermal and chemical stabilities that make it a promissory material to be used in MEMS [Zuo et al., 2010]. However, its electrical resistivity is not adequate for some applications, such as in pressure sensors. The addition of metallic nanoparticles into the film matrix can reduce the value of this property, and then, qualify the material to be used in piezoresistivity devices. Molybdenum was chosen due to excellent corrosion resistance at high temperatures and to be widely used to protect refractory metals against oxidation in oxygen-containing media. Among its principal properties of the Molybdenum can highlight: high melting point (2883 K), high thermal conductivity (138 Wm-1K-1), good electrical properties and thermal expansion coefficient close to AlN (~7x10-6 K-1 between 300 and 1200 K, against ~6.5x10-6 K-1 for pure AlN in the same range of temperature) [Zhang et al., 2009]. Experimental part DC magnetron sputtering technique was used to deposit Mo-AlN thin films on Si (100) p-type substrates with resistivity about 1-10 Ω.cm. The silicon substrates were previously cleaned with a solution of H2SO4 - H2O2 (4:1) and then with H2O - HF (20:1). In order to remove the target oxide layer, 10 min of a pre-sputtering in argon atmosphere was done. Mo-AlN thin films were deposited with a fixed power (100W) applied to an Al target with a molybdenum tape (5mmx1mmx102mm) placed in front of it, for 60min. A gas mixture of Ar (4.0 sccm) and N2 (between 1.0 and 2.0 sccm) was used and the substrate temperature kept at 400ºC. The target-substrate distance and work pressure were varied in the ranges 60-90 mm and 3-10 mTorr, respectively (Table 1). The same parameters were used without tape Mo for the production of thin films of AlN intrinsic (samples A09 and A10). The films were characterized by 4-points probe, mechanical profilometry, Rutherford backscattering spectroscopy (RBS) and X-ray diffraction.
Results and discussion Changing the deposition parameters was observed that higher rate deposition can be obtained decreasing the target-substrate distance or N2 flow (Table 2). Intrinsic AlN films presented insulator characteristics, while the doped films with Mo presented a reduction in the resistivity values below 100 Ω.cm. The RBS results (Fig. 1) indicate the presence of oxygen in the films deposited at higher work pressure (10 mTorr) that was confirmed by the XRD peaks (Fig. 2) of AlON at 2θ=52.7º and the increase of resistivity. Table 1 - Deposition parameters Samples A01 A02 A03 A04 A05 A06 A07 A08 A09 A10
Distance Pressure Flow N2 (mm) (mTorr) (sccm) 60 3 1 60 3 2 60 10 1 60 10 2 90 3 1 90 3 2 90 10 1 90 10 2 60 3 1 60 3 2
Samples
Deposition rate nm/min 16.2 8.5 6.6 4.3 8.5 4.2 4.2 3.2 6.4 2.9
A01 A02 A03 A04 A05 A06 A07 A08 A09 A10
resistivity (Ω.cm) 67.193 0.004 0.010 0.148 0.993 0.134 0.360 0.006 ---
Al N Mo O
50 40
A08 A07
Intensity (a.u.)
Composition (%)
Table 2 - Thickness and resistivity results
30 20
A06 A05 A04 A03 A02
10
A01 0 A01
A02
A03
A04
A05
A06
A07
A08
20
30
40
50
60
70
80
90
2
Samples Mo-AlN
Fig. 1 – RBS
Fig. 2 - XRD Samples Mo-AlN
Conclusions The results indicate that intrinsic AlN films presented, as expected, insulator characteristics, while the doped films (about 6% of Mo), presented a reduction in the resistivity values up to 10 Ω.cm. Analyzing the RBS spectra, was observed that films deposited at higher work pressure (10mTorr) presented more oxygen contamination in its composition, which resulted in AlON crystalline peaks at 2θ=52.7º. References [1] Zuo, C.; Sinha, N.; Piazza, G., 2010. Very High Frequency Channel-Select MEMS Filters based on Self-Coupled Piezoelectric AlN Contour-Mode Resonators. Sensors and Actuators A: Physical, v. 160, n. 1–2, p. 132-140. [2] Zhang, Y., Yang, Z., Ma, H., Duyan, J., 2009. Influence of Mo addition on dielectric properties of AlN ceramic matrix composites. Journal of Physics: Conference Series, v. 152, n. 1, p. 012063. Acknowledgement The authors thank for LAMFI-USP and LNNano laboratories for the use of characterization equipments. They also thank the financial support of AEB, CAPES and FAPESP (Grants 2011/50773-0 and 2013/17045-7).
Aluminum nitride thin films have high thermal and chemical stabilities that make it a promissory material to be used in MEMS. The addition of metallic nanoparticles into the film matrix can reduce the value of resistivity, and then, qualify the material to be used in piezoresistivity devices. In this work, Mo-AlN thin films were deposited on Si (100) substrate by DC magnetron sputtering. The films were characterized by mechanical profilometry, 4-points probe, X-ray diffraction and Rutherford backscattering spectroscopy (RBS). The results indicate that intrinsic AlN films presented, as expected, insulator characteristics, while the doped films (about 6% of Mo), presented a reduction in the resistivity values up to 10Ω.cm. The RBS results indicates the presence of oxygen in the films deposited at higher work pressure (10mTorr) that was confirmed by the XRD peaks of AlON at 2θ=52.7º and the increase of resistivity.
Keywords: Mo-AlN, Mo-AlNO, Thin films, DC Magnetron Sputtering
Introduction Aluminum nitride thin films have high thermal and chemical stabilities that make it a promissory material to be used in MEMS [Zuo et al., 2010]. However, its electrical resistivity is not adequate for some applications, such as in pressure sensors. The addition of metallic nanoparticles into the film matrix can reduce the value of this property, and then, qualify the material to be used in piezoresistivity devices. Molybdenum was chosen due to excellent corrosion resistance at high temperatures and to be widely used to protect refractory metals against oxidation in oxygen-containing media. Among its principal properties of the Molybdenum can highlight: high melting point (2883 K), high thermal conductivity (138 Wm-1K-1), good electrical properties and thermal expansion coefficient close to AlN (~7x10-6 K-1 between 300 and 1200 K, against ~6.5x10-6 K-1 for pure AlN in the same range of temperature) [Zhang et al., 2009]. Experimental part DC magnetron sputtering technique was used to deposit Mo-AlN thin films on Si (100) p-type substrates with resistivity about 1-10 Ω.cm. The silicon substrates were previously cleaned with a solution of H2SO4 - H2O2 (4:1) and then with H2O - HF (20:1). In order to remove the target oxide layer, 10 min of a pre-sputtering in argon atmosphere was done. Mo-AlN thin films were deposited with a fixed power (100W) applied to an Al target with a molybdenum tape (5mmx1mmx102mm) placed in front of it, for 60min. A gas mixture of Ar (4.0 sccm) and N2 (between 1.0 and 2.0 sccm) was used and the substrate temperature kept at 400ºC. The target-substrate distance and work pressure were varied in the ranges 60-90 mm and 3-10 mTorr, respectively (Table 1). The same parameters were used without tape Mo for the production of thin films of AlN intrinsic (samples A09 and A10). The films were characterized by 4-points probe, mechanical profilometry, Rutherford backscattering spectroscopy (RBS) and X-ray diffraction.
Results and discussion Changing the deposition parameters was observed that higher rate deposition can be obtained decreasing the target-substrate distance or N2 flow (Table 2). Intrinsic AlN films presented insulator characteristics, while the doped films with Mo presented a reduction in the resistivity values below 100 Ω.cm. The RBS results (Fig. 1) indicate the presence of oxygen in the films deposited at higher work pressure (10 mTorr) that was confirmed by the XRD peaks (Fig. 2) of AlON at 2θ=52.7º and the increase of resistivity. Table 1 - Deposition parameters Samples A01 A02 A03 A04 A05 A06 A07 A08 A09 A10
Distance Pressure Flow N2 (mm) (mTorr) (sccm) 60 3 1 60 3 2 60 10 1 60 10 2 90 3 1 90 3 2 90 10 1 90 10 2 60 3 1 60 3 2
Samples
Deposition rate nm/min 16.2 8.5 6.6 4.3 8.5 4.2 4.2 3.2 6.4 2.9
A01 A02 A03 A04 A05 A06 A07 A08 A09 A10
resistivity (Ω.cm) 67.193 0.004 0.010 0.148 0.993 0.134 0.360 0.006 ---
Al N Mo O
50 40
A08 A07
Intensity (a.u.)
Composition (%)
Table 2 - Thickness and resistivity results
30 20
A06 A05 A04 A03 A02
10
A01 0 A01
A02
A03
A04
A05
A06
A07
A08
20
30
40
50
60
70
80
90
2
Samples Mo-AlN
Fig. 1 – RBS
Fig. 2 - XRD Samples Mo-AlN
Conclusions The results indicate that intrinsic AlN films presented, as expected, insulator characteristics, while the doped films (about 6% of Mo), presented a reduction in the resistivity values up to 10 Ω.cm. Analyzing the RBS spectra, was observed that films deposited at higher work pressure (10mTorr) presented more oxygen contamination in its composition, which resulted in AlON crystalline peaks at 2θ=52.7º. References [1] Zuo, C.; Sinha, N.; Piazza, G., 2010. Very High Frequency Channel-Select MEMS Filters based on Self-Coupled Piezoelectric AlN Contour-Mode Resonators. Sensors and Actuators A: Physical, v. 160, n. 1–2, p. 132-140. [2] Zhang, Y., Yang, Z., Ma, H., Duyan, J., 2009. Influence of Mo addition on dielectric properties of AlN ceramic matrix composites. Journal of Physics: Conference Series, v. 152, n. 1, p. 012063. Acknowledgement The authors thank for LAMFI-USP and LNNano laboratories for the use of characterization equipments. They also thank the financial support of AEB, CAPES and FAPESP (Grants 2011/50773-0 and 2013/17045-7).
