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Properties of ZrO2 thin films prepared by laser ablation
Materials Science in Semiconductor Processing 5 (2003) 253–257
Properties of ZrO2 thin films prepared by laser ablation I. Vrejoiua,1, D.G. Mateia, M. Morara, G. Epurescua, A. Ferrarib, M. Balucanib, G. Lamedicab, G. Dinescua, C. Grigoriua, M. Dinescua,* a
National Institute for Laser, Plasma and Radiation Physics, P.O. Box MG–36 Magurele, Bucharest 76900, Romania b INFM, Unit E6, University ‘‘La Sapienza’’, Rome, Italy
Abstract ZrO2 thin films have been prepared by laser ablation of Zr or ZrO2 targets in oxygen reactive atmosphere. The influence of the deposition parameters as oxygen pressure and target composition on the structure and morphology of the deposited layers has been studied. Scanning electron microscopy, secondary ion mass spectroscopy and dielectric constant measurements have been performed to characterize the deposited layers. Dielectric constant values in the range 15–20 and low losses were evidenced for samples prepared in a narrow range of experimental conditions. r 2002 Elsevier Science Ltd. All rights reserved. PACS: 77.84; 79.20.D; 78.20.C; 68.37.P; 81.15.F Keywords: ZrO2; Laser ablation; Dielectric constant; Microscopy; Ablation film deposition
1. Introduction The physical properties of zirconium oxide (or zirconia)—high dielectric constant and, strength, stability at high temperatures—make it useful for applications involving gas sensors [1], corrosion or heatresistant mechanical parts, high refractive index optical coatings. Of particular interest is its use as an alternative gate dielectric in metal-oxide semiconductor (MOS) devices or capacitor in dynamic random access memory chips [2]. At the present time, the gate dielectric widely used in MOS transistors is SiO2, mainly due to the quality of the interface with the Si wafer. The dielectric’s thickness in integrated circuits has been downscaled to 2–3 nm in order to achieve smaller physical dimensions, higher operation speed, and lower driving voltage. A further reduction in the oxide thickness would impose several problems, including a high level of the leakage current [3,4], a large degree of dopant (boron) diffusion *Corresponding author. Tel.: +40-1-4231226; fax: +40-14231791. E-mail address: dinescum@ifin.nipne.ro (M. Dinescu). 1 Present address: Institute of Angewandte Physik, Johannes Kepler University Linz, A-400 Linz, Austria.
in the gate oxide and nonuniformity of the thin film. These problems arrive because of the low dielectric constant (eB3:5) of SiO2. Some of the high e candidates are TiO2, Al2O3, Ta2O5 [5,6], Hf1xSixO2, Zr1xSixO2 [7], ZrO2. Among these, zirconia is remarkable because of its dielectric constant of B20, good thermodynamic stability with the Si wafer, low-leakage-current level, high thermal stability [8–10]. Several techniques have been used to obtain thin films of ZrO2: Metalo-organic chemical vapour deposition [11,12], Radio-frequency sputtering [13], ALCVD [14], ultraviolet ozone oxidation [15–17], pulsed laser deposition (PLD) [18], photo-chemical vapour deposition [19], etc. In the present study, the electrical and morphological properties of zirconia thin films obtained by PLD in different conditions are analysed.
2. Experimental The targets used for ablation were sintered ZrO2 ceramic and Zr/Nb (2.5 wt% Nb) metallic samples. The beam of a frequency-tripled SURELITE II Nd:YAG laser (wavelength 355 nm, pulse length 5 ns, repetition
1369-8001/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII: S 1 3 6 9 - 8 0 0 1 ( 0 2 ) 0 0 0 8 3 - 5
254
I. Vrejoiu et al. / Materials Science in Semiconductor Processing 5 (2003) 253–257
(a)
(b)
(c)
(d)
Fig. 1. SEM images of ZrO2 films prepared starting from a ZrO2 sintered ceramic target, at a laser fluence of 3 J/cm2 and the oxygen pressure of 103 mbar (a and b) and 102 mbar (c and d).
(a)
(b)
Fig. 2. (a and b) SEM images of a film prepared starting from a ZrO2 sintered ceramic target at a laser fluence of 5.4 J/cm2 and the oxygen pressure of 103 mbar.
I. Vrejoiu et al. / Materials Science in Semiconductor Processing 5 (2003) 253–257
pressure from the same type of target. In Fig. 1 the SEM images of the surface of two films prepared in same experimental conditions except the oxygen pressure: p ¼ 103 (Fig. 1a and b) and 102 mbar (Fig. 1c and d) are presented. Films prepared at lower oxygen pressure exhibit a compact, dense and uniform ceramic structure with no cracks or pores. Increasing the pressure, the film surface gets covered with ‘‘mushroom’’-like structures, the appearance of pores and less compact aspect is evidenced. A similar but stronger effect was observed for films prepared at low pressure (103 mbar), but at higher 22.8
ε' tanδ
0.04
22.6 0.03
ε'
22.4 0.02
22.2
tanδ
rate 10 Hz) was focused through a spherical lens on the target at 451 incidence. The fluences were in the range 3– 6 J/cm2. In order to achieve uniform ablation, the target was simultaneously rotated and translated [20]. As substrate, (1 0 0)-silicon was used, with Pt coating as bottom electrode for further electrical measurements. The substrate was positioned at 5 cm in front of the target, parallel to it, and was kept at room temperature throughout all experiments. All the depositions were performed in oxygen reactive atmosphere, with pressures ranging from 103 to 0.1 mbar. The film thickness was measured using a tali-step profilometer. Secondary ions mass spectroscopy (SIMS), scanning electron microscopy (SEM) and electrical measurement have been done for samples characterization. Dielectric characteristics and temperature dependence studies were performed in order to characterize the dielectric behaviour of the samples. Circular aluminium top electrodes of 1.5 mm diameter were deposited through a mask. For the low-frequency range 20 Hz–1 MHz a Hewlett Packard 4284A Precision LCR-meter was used, while for frequencies up to 30 MHz an Agilent 4285A Precision LCR-meter was employed.
255
0.01
22.0
21.8 10
100
1000 10000 frequency [Hz]
100000
0.00 1000000
3. Results and discussions 30
Films with thickness in the range 200–500 nm have been deposited as a result of 2–4 105 laser pulses. A ( deposition rate of 0.2–0.3 A/pulse was recorded for films prepared starting from the ceramic ZrO2 target and less ( than 0.15 A/pulse for those prepared starting from the metallic one. SEM studies evidenced big differences between films prepared starting from metallic and ceramic targets, but also between films prepared at different oxygen reactive
ε' tanδ
200
20 150 10 ε'
tanδ
100 0 50
-10 0 -20 -50 100000
1000000 frequency [Hz]
1E7
Y= B + iG is the 1/Z, Z being the complex impedance
0.010
0.015
0.005 resonance frequencyat 14.3 MHz 0.000
0.005
B [µS]
G [µS]
0.010
B susceptance (related to real part of dielectric function) G contuctance (related to imaginary part of dielectric function)
-0.005 0.000 -0.010 100000
Fig. 3. SEM image of a film prepared starting from a Zr metallic target at a laser fluence of 6 J/cm2 and the oxygen pressure of 5 102 mbar.
1000000 frequency [Hz]
1E7
Fig. 4. Dielectric constant dispersion measurements for a ZrO2 film prepared starting from a Zr metallic target at a laser fluence of 6 J/cm2 and oxygen pressure of 5 102 mbar; the film thickness 300 nm.
I. Vrejoiu et al. / Materials Science in Semiconductor Processing 5 (2003) 253–257
256
laser fluence 5.4 J/cm2 with respect to 3 J/cm2 (Fig. 2a and b). Pores with hundreds of nanometers diameter are observed, together with more dense and bigger ‘‘mushroom-islands’’. A completely different aspect was achieved for films deposited starting from Zr metallic target. Smooth surface, with small and rare droplets (droplet free over a large area) have been obtained for films prepared for a narrow range of experimental conditions: p ¼ 5 102 mbar and laser fluence around 6 J/cm2 (Fig. 3). Regarding film composition, SIMS spectra evidenced a uniform distribution of both Zr and O in the deposited layer. Samples deposited from metallic target in 0.05 mbar oxygen and at 6 J/cm2 laser fluence showed the lowest
0.30
19 ε'
tanδ
18
0.25
17
0.20
ε'
0.15 15
tanδ
16
frequency dispersion and smallest losses (tan d) (Fig. 4). The real part of dielectric function (e0 ) had a value close to 22 for all the frequencies in the range from 20 Hz up to 2 MHz, while tan d did not exceed 0.06 The resonances from frequencies bigger than 10 MHz (14.7 MHz and 17.5 MHz), shown in Figs. 4 and 5 are artefacts introduced by the set-up. Samples deposited from ZrO2 target in 0.001 mbar oxygen and 3 J/cm2 laser fluence exhibited bigger losses for frequencies below 1 kHz, and also a smaller dielectric constant (around 14) for the frequency range 1 kHz—1 MHz (Fig. 5). The temperature dependence was studied by in situ measuring the dielectric function at two frequencies (1 kHz or 1 MHz), while sample heating was performed. For both type of samples, the dielectric constant and tan d measured at 1 kHz, slightly increased (o10%) by heating up to 1501C (as in Figs. 6 and 7). One can observe a more pronounced increase for the samples deposited from ZrO2 target (Fig. 7). Apparently, a higher oxygen pressure (0.1 mbar) did not lead to better dielectric properties for the samples deposited from bare Zr targets, because they showed significantly higher dielectric losses for the whole investigated frequency range. Also, the above
0.10
14
0.05
13 12 100
10
1000 10000 frequency [Hz]
0.08
26
ε'
measured at 1 kHz
0.00 100000 1000000
tan δ
25
0.06
24
0.04
23
0.02
10
ε'
5 0
10
-5 5 -10 0
tanδ
ε'
tan δ
tanδ
ε'
15
-15
-5
0.00
22 50
-20
100
150
2 00
ο
temperature [ C]
-25 100000
1000000 frequency [Hz]
1E7
22.8
0 .075
ε'
measured at 1 MHz
tan δ
22.6
4.00E-009
4.00E-009
0 .070
Y=B + iG is the 1/Z, Z being the complex impedance 22.4
3.00E-009
3.00E-009
B
0 .065
G [S]
resonance frequency at 17.5MHz
1.00E-009
ε' B [S]
2.00E-009
tan δ
22.2
2.00E-009
22.0
0 .060
21.8
1.00E-009 0.00E+000
G
0 .055 21.6
0.00E+000
-1.00E-009 0 .050
21.4
100000
1000000 frequency [Hz]
1E7
Fig. 5. Dielectric constant dispersion measurements for a ZrO2 film prepared starting from a ZrO2 sintered ceramic target at a laser fluence of 3 J/cm2 and oxygen pressure of 103 mbar.
50
100
150
200
temperature [οC]
Fig. 6. Temperature behaviour of the dielectric constant for a ZrO2 film prepared starting from a Zr metallic target at a laser fluence of 6 J/cm2 and oxygen pressure of 5 102 mbar.
I. Vrejoiu et al. / Materials Science in Semiconductor Processing 5 (2003) 253–257
257
each type of target, a range of experimental conditions has been identified in order to obtain smooth films. The best surface morphology was obtained for ablation of a Zr target in an atmosphere of O2 at 5 102 mbar pressure and a fluence of 6 J/cm2. The dielectric constant value was in the range 12–24 over a wide range of frequencies and temperature, 20 Hz–2 MHz, respectively, 20–1501C.
Acknowledgements Some of the authors (D.G.M., M.M., G.E., G.D., C.G., M.D.) gratefully acknowledge the financial support from NATO SfP 97-1934 Project.
References
Fig. 7. Temperature behaviour of the dielectric constant for a ZrO2 film prepared starting from a ZrO2 sintered ceramic target, at a laser fluence of 3 J/cm2 and oxygen pressure of 103 mbar.
observation holds for the samples deposited from ZrO2 targets. By increasing the oxygen pressure from 0.001 to 0.01 mbar, the films morphology changed (holes formed), a fact that had severe consequences for the dielectric behaviour. The increase of the laser fluence from 3 to 5.4 J/cm2 did not result in any change of the dielectric behaviour when the oxygen pressure was kept constant at 0.001 mbar and led to a higher density of droplets and outgrowths on the film surface, as proved by SEM investigations.
4. Conclusions ZrO2 thin films (200–500 nm thick) have been deposited by laser ablation in oxygen reactive atmosphere (103–0.1 mbar), using a ZrO2 or Zr target. For
[1] Niranjan RS, Sathaye SD, Mulla IS. Sensors Actuators 2001;64:B81. [2] Kingon AI, Maria JP, Streiffer SK. Nature 2000;406:1032. [3] Buchanan DA, Lo SH. Microelectron Eng 1997;36:13. [4] Heiser G, Schenk A. J Appl Phys 1997;81:7900. [5] Alers GB, Werder DJ, Chabal Y, Lu HC, Gusev EP, Garfunkel E, Gustafsson T, Urdahl RS. Appl Phys Lett 1998;73:1517. [6] Grahn JV, Hellberg PE, Olsson E. J Appl Phys 1998; 84:1632. [7] Wilk GD, Wallance RM, Anthony JM. J Appl Phys 2000; 87:484. [8] Wilk GD, Wallance RM, Anthony JM. J Appl Phys 2001; 89:5243. [9] Sasaki K, Maier J. Solid State Ionics 2000;134:303. [10] Qi W, Nich R, Lee B, Kang L, Jeon Y, Lee JC. Appl Phys Lett 2000;77:3269. [11] Shappir J, Anis A, Pinsky I. IEEE Trans Electron Devices 1986;ED-33:442. [12] Garcia G, Casado J, Llibre J, Figueras A. J Crystal Growth 1995;156:426. [13] Tomaszewski H, Haemers J, Denul J, DeRoo N, De-Gryse R. Thin Solid Films 1996;287:104. [14] Copel M, Gribelyuk MA, Gusev E. Appl Phys Lett 2000; 76:436. [15] Ramanathan S, Wilk GD, Muller DA, Park CM, McIntyre PC. Appl Phys Lett 2001;79:2621. [16] Ramanathan S, McIntyre PC. Appl Phys Lett 2002; 80:3793. [17] Ramanathan S, Muller DA, Wilk GD, Park CM, McIntyre PC. Appl Phys Lett 2001;79:3311. [18] Delgado JC, S!anchez F, Aguiar R, Maniette Y, Ferrater C, Varela M. Appl Phys Lett 1996;68:1048. [19] Yu JJ, Boyd IW. Appl Phys A 2002;75:489. [20] Arnold N, B.auerle D. Appl Phys A 1999;68:363.
Properties of ZrO2 thin films prepared by laser ablation I. Vrejoiua,1, D.G. Mateia, M. Morara, G. Epurescua, A. Ferrarib, M. Balucanib, G. Lamedicab, G. Dinescua, C. Grigoriua, M. Dinescua,* a
National Institute for Laser, Plasma and Radiation Physics, P.O. Box MG–36 Magurele, Bucharest 76900, Romania b INFM, Unit E6, University ‘‘La Sapienza’’, Rome, Italy
Abstract ZrO2 thin films have been prepared by laser ablation of Zr or ZrO2 targets in oxygen reactive atmosphere. The influence of the deposition parameters as oxygen pressure and target composition on the structure and morphology of the deposited layers has been studied. Scanning electron microscopy, secondary ion mass spectroscopy and dielectric constant measurements have been performed to characterize the deposited layers. Dielectric constant values in the range 15–20 and low losses were evidenced for samples prepared in a narrow range of experimental conditions. r 2002 Elsevier Science Ltd. All rights reserved. PACS: 77.84; 79.20.D; 78.20.C; 68.37.P; 81.15.F Keywords: ZrO2; Laser ablation; Dielectric constant; Microscopy; Ablation film deposition
1. Introduction The physical properties of zirconium oxide (or zirconia)—high dielectric constant and, strength, stability at high temperatures—make it useful for applications involving gas sensors [1], corrosion or heatresistant mechanical parts, high refractive index optical coatings. Of particular interest is its use as an alternative gate dielectric in metal-oxide semiconductor (MOS) devices or capacitor in dynamic random access memory chips [2]. At the present time, the gate dielectric widely used in MOS transistors is SiO2, mainly due to the quality of the interface with the Si wafer. The dielectric’s thickness in integrated circuits has been downscaled to 2–3 nm in order to achieve smaller physical dimensions, higher operation speed, and lower driving voltage. A further reduction in the oxide thickness would impose several problems, including a high level of the leakage current [3,4], a large degree of dopant (boron) diffusion *Corresponding author. Tel.: +40-1-4231226; fax: +40-14231791. E-mail address: dinescum@ifin.nipne.ro (M. Dinescu). 1 Present address: Institute of Angewandte Physik, Johannes Kepler University Linz, A-400 Linz, Austria.
in the gate oxide and nonuniformity of the thin film. These problems arrive because of the low dielectric constant (eB3:5) of SiO2. Some of the high e candidates are TiO2, Al2O3, Ta2O5 [5,6], Hf1xSixO2, Zr1xSixO2 [7], ZrO2. Among these, zirconia is remarkable because of its dielectric constant of B20, good thermodynamic stability with the Si wafer, low-leakage-current level, high thermal stability [8–10]. Several techniques have been used to obtain thin films of ZrO2: Metalo-organic chemical vapour deposition [11,12], Radio-frequency sputtering [13], ALCVD [14], ultraviolet ozone oxidation [15–17], pulsed laser deposition (PLD) [18], photo-chemical vapour deposition [19], etc. In the present study, the electrical and morphological properties of zirconia thin films obtained by PLD in different conditions are analysed.
2. Experimental The targets used for ablation were sintered ZrO2 ceramic and Zr/Nb (2.5 wt% Nb) metallic samples. The beam of a frequency-tripled SURELITE II Nd:YAG laser (wavelength 355 nm, pulse length 5 ns, repetition
1369-8001/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII: S 1 3 6 9 - 8 0 0 1 ( 0 2 ) 0 0 0 8 3 - 5
254
I. Vrejoiu et al. / Materials Science in Semiconductor Processing 5 (2003) 253–257
(a)
(b)
(c)
(d)
Fig. 1. SEM images of ZrO2 films prepared starting from a ZrO2 sintered ceramic target, at a laser fluence of 3 J/cm2 and the oxygen pressure of 103 mbar (a and b) and 102 mbar (c and d).
(a)
(b)
Fig. 2. (a and b) SEM images of a film prepared starting from a ZrO2 sintered ceramic target at a laser fluence of 5.4 J/cm2 and the oxygen pressure of 103 mbar.
I. Vrejoiu et al. / Materials Science in Semiconductor Processing 5 (2003) 253–257
pressure from the same type of target. In Fig. 1 the SEM images of the surface of two films prepared in same experimental conditions except the oxygen pressure: p ¼ 103 (Fig. 1a and b) and 102 mbar (Fig. 1c and d) are presented. Films prepared at lower oxygen pressure exhibit a compact, dense and uniform ceramic structure with no cracks or pores. Increasing the pressure, the film surface gets covered with ‘‘mushroom’’-like structures, the appearance of pores and less compact aspect is evidenced. A similar but stronger effect was observed for films prepared at low pressure (103 mbar), but at higher 22.8
ε' tanδ
0.04
22.6 0.03
ε'
22.4 0.02
22.2
tanδ
rate 10 Hz) was focused through a spherical lens on the target at 451 incidence. The fluences were in the range 3– 6 J/cm2. In order to achieve uniform ablation, the target was simultaneously rotated and translated [20]. As substrate, (1 0 0)-silicon was used, with Pt coating as bottom electrode for further electrical measurements. The substrate was positioned at 5 cm in front of the target, parallel to it, and was kept at room temperature throughout all experiments. All the depositions were performed in oxygen reactive atmosphere, with pressures ranging from 103 to 0.1 mbar. The film thickness was measured using a tali-step profilometer. Secondary ions mass spectroscopy (SIMS), scanning electron microscopy (SEM) and electrical measurement have been done for samples characterization. Dielectric characteristics and temperature dependence studies were performed in order to characterize the dielectric behaviour of the samples. Circular aluminium top electrodes of 1.5 mm diameter were deposited through a mask. For the low-frequency range 20 Hz–1 MHz a Hewlett Packard 4284A Precision LCR-meter was used, while for frequencies up to 30 MHz an Agilent 4285A Precision LCR-meter was employed.
255
0.01
22.0
21.8 10
100
1000 10000 frequency [Hz]
100000
0.00 1000000
3. Results and discussions 30
Films with thickness in the range 200–500 nm have been deposited as a result of 2–4 105 laser pulses. A ( deposition rate of 0.2–0.3 A/pulse was recorded for films prepared starting from the ceramic ZrO2 target and less ( than 0.15 A/pulse for those prepared starting from the metallic one. SEM studies evidenced big differences between films prepared starting from metallic and ceramic targets, but also between films prepared at different oxygen reactive
ε' tanδ
200
20 150 10 ε'
tanδ
100 0 50
-10 0 -20 -50 100000
1000000 frequency [Hz]
1E7
Y= B + iG is the 1/Z, Z being the complex impedance
0.010
0.015
0.005 resonance frequencyat 14.3 MHz 0.000
0.005
B [µS]
G [µS]
0.010
B susceptance (related to real part of dielectric function) G contuctance (related to imaginary part of dielectric function)
-0.005 0.000 -0.010 100000
Fig. 3. SEM image of a film prepared starting from a Zr metallic target at a laser fluence of 6 J/cm2 and the oxygen pressure of 5 102 mbar.
1000000 frequency [Hz]
1E7
Fig. 4. Dielectric constant dispersion measurements for a ZrO2 film prepared starting from a Zr metallic target at a laser fluence of 6 J/cm2 and oxygen pressure of 5 102 mbar; the film thickness 300 nm.
I. Vrejoiu et al. / Materials Science in Semiconductor Processing 5 (2003) 253–257
256
laser fluence 5.4 J/cm2 with respect to 3 J/cm2 (Fig. 2a and b). Pores with hundreds of nanometers diameter are observed, together with more dense and bigger ‘‘mushroom-islands’’. A completely different aspect was achieved for films deposited starting from Zr metallic target. Smooth surface, with small and rare droplets (droplet free over a large area) have been obtained for films prepared for a narrow range of experimental conditions: p ¼ 5 102 mbar and laser fluence around 6 J/cm2 (Fig. 3). Regarding film composition, SIMS spectra evidenced a uniform distribution of both Zr and O in the deposited layer. Samples deposited from metallic target in 0.05 mbar oxygen and at 6 J/cm2 laser fluence showed the lowest
0.30
19 ε'
tanδ
18
0.25
17
0.20
ε'
0.15 15
tanδ
16
frequency dispersion and smallest losses (tan d) (Fig. 4). The real part of dielectric function (e0 ) had a value close to 22 for all the frequencies in the range from 20 Hz up to 2 MHz, while tan d did not exceed 0.06 The resonances from frequencies bigger than 10 MHz (14.7 MHz and 17.5 MHz), shown in Figs. 4 and 5 are artefacts introduced by the set-up. Samples deposited from ZrO2 target in 0.001 mbar oxygen and 3 J/cm2 laser fluence exhibited bigger losses for frequencies below 1 kHz, and also a smaller dielectric constant (around 14) for the frequency range 1 kHz—1 MHz (Fig. 5). The temperature dependence was studied by in situ measuring the dielectric function at two frequencies (1 kHz or 1 MHz), while sample heating was performed. For both type of samples, the dielectric constant and tan d measured at 1 kHz, slightly increased (o10%) by heating up to 1501C (as in Figs. 6 and 7). One can observe a more pronounced increase for the samples deposited from ZrO2 target (Fig. 7). Apparently, a higher oxygen pressure (0.1 mbar) did not lead to better dielectric properties for the samples deposited from bare Zr targets, because they showed significantly higher dielectric losses for the whole investigated frequency range. Also, the above
0.10
14
0.05
13 12 100
10
1000 10000 frequency [Hz]
0.08
26
ε'
measured at 1 kHz
0.00 100000 1000000
tan δ
25
0.06
24
0.04
23
0.02
10
ε'
5 0
10
-5 5 -10 0
tanδ
ε'
tan δ
tanδ
ε'
15
-15
-5
0.00
22 50
-20
100
150
2 00
ο
temperature [ C]
-25 100000
1000000 frequency [Hz]
1E7
22.8
0 .075
ε'
measured at 1 MHz
tan δ
22.6
4.00E-009
4.00E-009
0 .070
Y=B + iG is the 1/Z, Z being the complex impedance 22.4
3.00E-009
3.00E-009
B
0 .065
G [S]
resonance frequency at 17.5MHz
1.00E-009
ε' B [S]
2.00E-009
tan δ
22.2
2.00E-009
22.0
0 .060
21.8
1.00E-009 0.00E+000
G
0 .055 21.6
0.00E+000
-1.00E-009 0 .050
21.4
100000
1000000 frequency [Hz]
1E7
Fig. 5. Dielectric constant dispersion measurements for a ZrO2 film prepared starting from a ZrO2 sintered ceramic target at a laser fluence of 3 J/cm2 and oxygen pressure of 103 mbar.
50
100
150
200
temperature [οC]
Fig. 6. Temperature behaviour of the dielectric constant for a ZrO2 film prepared starting from a Zr metallic target at a laser fluence of 6 J/cm2 and oxygen pressure of 5 102 mbar.
I. Vrejoiu et al. / Materials Science in Semiconductor Processing 5 (2003) 253–257
257
each type of target, a range of experimental conditions has been identified in order to obtain smooth films. The best surface morphology was obtained for ablation of a Zr target in an atmosphere of O2 at 5 102 mbar pressure and a fluence of 6 J/cm2. The dielectric constant value was in the range 12–24 over a wide range of frequencies and temperature, 20 Hz–2 MHz, respectively, 20–1501C.
Acknowledgements Some of the authors (D.G.M., M.M., G.E., G.D., C.G., M.D.) gratefully acknowledge the financial support from NATO SfP 97-1934 Project.
References
Fig. 7. Temperature behaviour of the dielectric constant for a ZrO2 film prepared starting from a ZrO2 sintered ceramic target, at a laser fluence of 3 J/cm2 and oxygen pressure of 103 mbar.
observation holds for the samples deposited from ZrO2 targets. By increasing the oxygen pressure from 0.001 to 0.01 mbar, the films morphology changed (holes formed), a fact that had severe consequences for the dielectric behaviour. The increase of the laser fluence from 3 to 5.4 J/cm2 did not result in any change of the dielectric behaviour when the oxygen pressure was kept constant at 0.001 mbar and led to a higher density of droplets and outgrowths on the film surface, as proved by SEM investigations.
4. Conclusions ZrO2 thin films (200–500 nm thick) have been deposited by laser ablation in oxygen reactive atmosphere (103–0.1 mbar), using a ZrO2 or Zr target. For
[1] Niranjan RS, Sathaye SD, Mulla IS. Sensors Actuators 2001;64:B81. [2] Kingon AI, Maria JP, Streiffer SK. Nature 2000;406:1032. [3] Buchanan DA, Lo SH. Microelectron Eng 1997;36:13. [4] Heiser G, Schenk A. J Appl Phys 1997;81:7900. [5] Alers GB, Werder DJ, Chabal Y, Lu HC, Gusev EP, Garfunkel E, Gustafsson T, Urdahl RS. Appl Phys Lett 1998;73:1517. [6] Grahn JV, Hellberg PE, Olsson E. J Appl Phys 1998; 84:1632. [7] Wilk GD, Wallance RM, Anthony JM. J Appl Phys 2000; 87:484. [8] Wilk GD, Wallance RM, Anthony JM. J Appl Phys 2001; 89:5243. [9] Sasaki K, Maier J. Solid State Ionics 2000;134:303. [10] Qi W, Nich R, Lee B, Kang L, Jeon Y, Lee JC. Appl Phys Lett 2000;77:3269. [11] Shappir J, Anis A, Pinsky I. IEEE Trans Electron Devices 1986;ED-33:442. [12] Garcia G, Casado J, Llibre J, Figueras A. J Crystal Growth 1995;156:426. [13] Tomaszewski H, Haemers J, Denul J, DeRoo N, De-Gryse R. Thin Solid Films 1996;287:104. [14] Copel M, Gribelyuk MA, Gusev E. Appl Phys Lett 2000; 76:436. [15] Ramanathan S, Wilk GD, Muller DA, Park CM, McIntyre PC. Appl Phys Lett 2001;79:2621. [16] Ramanathan S, McIntyre PC. Appl Phys Lett 2002; 80:3793. [17] Ramanathan S, Muller DA, Wilk GD, Park CM, McIntyre PC. Appl Phys Lett 2001;79:3311. [18] Delgado JC, S!anchez F, Aguiar R, Maniette Y, Ferrater C, Varela M. Appl Phys Lett 1996;68:1048. [19] Yu JJ, Boyd IW. Appl Phys A 2002;75:489. [20] Arnold N, B.auerle D. Appl Phys A 1999;68:363.