- Email: [email protected]
Influence of vacuum rapid thermal annealing on the properties of Al and Ag films on quartz
Vacuum/volume
47/number Illpages 1329 to 1331/1996 Copyright Q 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0042-207X/56 $15.00+.00
Pergamon PII: SOO42-207X(96300167-X
Influence of vacuum rapid thermal annealing on the properties of Al and Ag films on quartz* V Lasarova, G Beshkov and L Spassov, Instituteof Solid Srare Physics, Tzarigradsko Chaussee Blvd., 7784 Sofia, Bulgaria
Bulgarian
Academy
of Sciences,
72
received in final revised form 70 April 1996
The influence of rapid thermal annealing of 700°C and 800°C in 5x 10e5 mbar vacuum on the structure and morphology of aluminum and silver thin films, deposited on quartz substrates is investigated. The metal films studied have thicknesses of 200 nm and 120 nm for AI and Ag, respectively, when the annealing rime ranges from 5 to 180 s. A recrystallization process in the Al films is observed. A correlation between the annealing rime and the equivalent parameters’ change of the quartz resonators with silver electrodes is also found. Copyright 0 1996 Elsevier Science Ltd
Introduction
Aluminium films have a large application in microelectronics for metalization. There are data reported’ for Al contacts in Shottky diodes on polycrystalline diamond layer basis. These structures are studied with respect to Z-V characteristics as well as mechanical stresses based defects, the adhesion between various layers used in the devices for chemical and military industries and space techniques application2 Intensive investigations of Al contacts with different dopants have been made for improving their life time.3x4The strong influence of the substrate surface on the properties of the metal films has been studied by other authors.’ TEM investigations show various defects such as dislocation, vacancies and clusters, appearing in the films during the low-temperature treatment.‘j The subject of the present article is the investigation of the structural and morphological from rapid thermal annealing of Al and Ag films, deposited on quartz substrates; this film substrate structure is the base of the acoustoelectronics devices, so it is very important to study it in detail. To the authors knowledge such investigations have not been published up to now.
The silver films with thickness of 120 nm were deposited on at 2 x iO-‘j mbar. After deposition the films were treated by RTA in vacuum 5 x lo-’ mbar. The time for reaching the RTA temperature was 0.2s. RTA treatments were done at 700°C and 800°C for the system quartz-Al and at 800°C for the quartz-Ag system; the treatment times were 5 s, 15 s, 30 s, 1 min and 3 min. Structural and morphological investigations before and after RTA treatment were made by SEM and TEM techniques. Also, resonators with silver electrodes with a frequency of 10.8, 11 and 18 MHz were RTA treated. The devices were made of 8 mm diameter two-side lapped quartz substrates, with Ag-electrodes of 4 mm diameter. The investigations show that before RTA all Al films were amorphous. A typical diffraction pattern of a non-treated Al film is shown in Figure 1. After RTA at 700°C for 5 s a recrystallization process starts in the Al film as it can be seen from the appearance of Debye lines (Figure 2), which become better expressed with increasing annealing time (Figure 3, 1min; Figure 4, 3 min). 8 mm quartz plates by vacuum evaporation
Experimental results and discussion
The aluminum films were deposited on one-side polished 10 x 20 mm quartz substrates after a standard chemical cleaning. The films were deposited by DC magnetron sputtering at 3 x 10m3 mbar and 7 kW at a deposition rate of 71 nm/min; the final films thickness was 200 nm.
*Paper based on that given to 9th International Electron Bulgaria.
and
Ion
Technologies,
14-17
School on Vacuum September 1995, Sozopol, Figure 1. Electronograph
picture
of Al thin film before RTA trea 1329
V Lasarova et al: Vacuum rapid thermal annealing
Figure 2. Electronograph picture of Al thin film after RTA treatment (t = 700°C. 5 = 5 s).
Figure 3. Electronograph picture of Al thin film before RTA treatment (1 = 70@-C,t = 1min).
Figure 4. Electronograph (t = 7OO”C,5 = 3 min).
picture of Al thin film after RTA treatment
Figure 6. Electronograph (t = 8OO”C,7 = 1 min).
picture of Al thin film after RTA treatment
picture of Al thin film after RTA treatment
When the time of RTA was raised to 3 min no further changes were observed. This shows that the recrystallization process is accomplished. RTA treatment at 800°C shows that the recrystallization process for 5 s is comparable with RTA at 700°C for 1 min (Figures 5 and 3). In contrast the processes at 700°C for 3 min are comparable with the ones at 800°C for 1 min, afterwards no changes are observed (Figures 4 and 6). The surface morphology of Al films is not influenced by the RTA treatments (Figure 7). The sheet resistivity pS of the Al films is measured before and after RTA by a four point probe technique and the results are shown in Table 1. It is found that a tendency to increase pS for the Al film annealed at 700°C and 800°C. This tendency is stronger for 700°C treated films. No structural and morphological changes are observed in Ag films after RTA treatment. Probably this is because of the higher 1330
Figure 5. Electronograph (t = 8OO”C,T = 5 s).
Figure 7. Electron microscope picture of Al film after RTA treatment.
melting temperature of silver. Figure 8 shows a typical surface morphology of Ag film. Nevertheless the resonators with Ag electrodes change their parameters after RTA treatment. In Table 2 the data are shown for the resonance frequency, equivalent dynamic resistivity R,T, static capacity C,, equivalent capacitivity C,, equivalent inductivity L, and the qualitative factor Q of quartz resonators before and after RTA treatments. For RTA from 5 to 15 s and increase of the equivalent dynamic resistivity R, and a decrease of the
VLasarova
eta/:Vacuum
rapidthermalannealing
Table 1. Dependence of Al films sheet resistivity of RTA parameters Sheet resistivity
RTA-parameters
t[“c1
+I
Vacuum
PSWO Before RTA process
After RTA process
700 700 700 700 800 800
5 15 30 60 5 60
5x1o-5 5x1o-5 5x10m5 5xlo-5 5x1o-5 5x10m5
158 158 158 158 158 158
158 178 186 193 182 192
30%. The equivalent dynamic induction increases as well. The parameters do not change remarkably at treatment time over 30s. In our opinion all changes of the resonators’ parameters are caused by the quartz crystal lattice influence by the RTA treatment. Comparing the resonators’ equivalent parameters before and after RTA it can be concluded that the longer RTA treatment decreases the residual mechanical stresses in the crystal lattice and thus improves the device parameters. Also quartz substrates keep their orientation and structure after phase transition between p and c[ modification at 573°C (the Curie point for quartz) during the heating and cooling. Conclusions
It is found out that a recrystallization process appears in Al films after RTA treatment in vacuum. The microstructure starts to change from amorphous to crystalline after 5 s RTA treatment. The process finishes in 3 min at 700°C and 1 min at 800°C. No structural and morphological changes are observed in Ag films at the same conditions. At the same time the resonators with Ag electrodes change their equivalent parameters. The final improvement of the parameters is probably caused by quartz crystal lattice relaxation. References 1. C Zhao and E M Charlson, Proc of Int Conf
of Carbon Films, 27
April-l May 1992, San Francisco (1992) p 431436. 2. W Zhu, R C McCune, J N de Vxies, M A Tamor and K J Simon, Fig,ure8. Electron microscope picture of Ag film after RTA treatment
qualitative factor Q occur. The changes are bigger for the shorter RTA treatment duration (5 s) and smaller for 15 s (Table 2, samples B, and B2). At longer RTA durations the opposite effect is observed - the resonators’ parameters improved: the equivalent resistivity R, decreases by about 20% and the Q-factor increases by about
Table 2. Influence MHz
of RTA-process
on the equivalent
Equivalent
parameters
parameters
of quartz
.fSW
of quartz
resonators
&PI
Diamond Related Mater, 4/3,220-233 (1995). 3. J Yamada, T Shibo, N Hosako and T Toyama, IEEE 1986 Ultrasonics Symp Proc (1986) p 267-272 4. Y Kinoshika, A Nakagoshi, M Kojimo and M Hikito, IEEE 1983 Ultrasonics Symp Proc (1983) p 83. 5. C A Ross and J J Barrese, Abstracts of Materiuls Research Society Fall Meeting, 27 November-2 December 1994, Boston (1994) p 107. 6. V N Matyeev and 0 V Kononenko, Abstracts of Materials Research Society Fall Meeting, 27 November-2 December 1994, Boston (1994)
p 71.
resonators
with Ag electrode
and resonance
frequencies
before and after RTA
C,[fFl
CJPFI
WI
dsl
Before RTA
After RTA
Before RTA
After RTA
Before RTA
After RTA
Before RTA
After RTA
Before RTA
B,
800 800 800 800 800
5 15 30 60 180
10809110 11071324 18160873 10797930 18093751
10808936 11071799 18160777 10805260 18094357
31.7 23.2 9.4 47.1 11.8
76.5 34.7 7.5 37.3 9.0
4.024 4.000 6.270 4.010 6.470
4.012 3.977 6.080 3.970 6.270
18.44 18.39 25.45 17.91 23.16
45.07 18.03 24.98 17.87 22.75
11.76 11.24 3.02 12.14 3.34
B2 B,, BS B,,
Q* 10’
L,[mHl
No.
RTA parameters
10.8, 11 .O and 18.0
After RTA 4.83
11.47 3.07 12.15 3.40
Before RTA
After RTA
25.2 33.7 36.6 17.5 32.2
0.4 23.0 46.7 22. I 42.9
1331
47/number Illpages 1329 to 1331/1996 Copyright Q 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0042-207X/56 $15.00+.00
Pergamon PII: SOO42-207X(96300167-X
Influence of vacuum rapid thermal annealing on the properties of Al and Ag films on quartz* V Lasarova, G Beshkov and L Spassov, Instituteof Solid Srare Physics, Tzarigradsko Chaussee Blvd., 7784 Sofia, Bulgaria
Bulgarian
Academy
of Sciences,
72
received in final revised form 70 April 1996
The influence of rapid thermal annealing of 700°C and 800°C in 5x 10e5 mbar vacuum on the structure and morphology of aluminum and silver thin films, deposited on quartz substrates is investigated. The metal films studied have thicknesses of 200 nm and 120 nm for AI and Ag, respectively, when the annealing rime ranges from 5 to 180 s. A recrystallization process in the Al films is observed. A correlation between the annealing rime and the equivalent parameters’ change of the quartz resonators with silver electrodes is also found. Copyright 0 1996 Elsevier Science Ltd
Introduction
Aluminium films have a large application in microelectronics for metalization. There are data reported’ for Al contacts in Shottky diodes on polycrystalline diamond layer basis. These structures are studied with respect to Z-V characteristics as well as mechanical stresses based defects, the adhesion between various layers used in the devices for chemical and military industries and space techniques application2 Intensive investigations of Al contacts with different dopants have been made for improving their life time.3x4The strong influence of the substrate surface on the properties of the metal films has been studied by other authors.’ TEM investigations show various defects such as dislocation, vacancies and clusters, appearing in the films during the low-temperature treatment.‘j The subject of the present article is the investigation of the structural and morphological from rapid thermal annealing of Al and Ag films, deposited on quartz substrates; this film substrate structure is the base of the acoustoelectronics devices, so it is very important to study it in detail. To the authors knowledge such investigations have not been published up to now.
The silver films with thickness of 120 nm were deposited on at 2 x iO-‘j mbar. After deposition the films were treated by RTA in vacuum 5 x lo-’ mbar. The time for reaching the RTA temperature was 0.2s. RTA treatments were done at 700°C and 800°C for the system quartz-Al and at 800°C for the quartz-Ag system; the treatment times were 5 s, 15 s, 30 s, 1 min and 3 min. Structural and morphological investigations before and after RTA treatment were made by SEM and TEM techniques. Also, resonators with silver electrodes with a frequency of 10.8, 11 and 18 MHz were RTA treated. The devices were made of 8 mm diameter two-side lapped quartz substrates, with Ag-electrodes of 4 mm diameter. The investigations show that before RTA all Al films were amorphous. A typical diffraction pattern of a non-treated Al film is shown in Figure 1. After RTA at 700°C for 5 s a recrystallization process starts in the Al film as it can be seen from the appearance of Debye lines (Figure 2), which become better expressed with increasing annealing time (Figure 3, 1min; Figure 4, 3 min). 8 mm quartz plates by vacuum evaporation
Experimental results and discussion
The aluminum films were deposited on one-side polished 10 x 20 mm quartz substrates after a standard chemical cleaning. The films were deposited by DC magnetron sputtering at 3 x 10m3 mbar and 7 kW at a deposition rate of 71 nm/min; the final films thickness was 200 nm.
*Paper based on that given to 9th International Electron Bulgaria.
and
Ion
Technologies,
14-17
School on Vacuum September 1995, Sozopol, Figure 1. Electronograph
picture
of Al thin film before RTA trea 1329
V Lasarova et al: Vacuum rapid thermal annealing
Figure 2. Electronograph picture of Al thin film after RTA treatment (t = 700°C. 5 = 5 s).
Figure 3. Electronograph picture of Al thin film before RTA treatment (1 = 70@-C,t = 1min).
Figure 4. Electronograph (t = 7OO”C,5 = 3 min).
picture of Al thin film after RTA treatment
Figure 6. Electronograph (t = 8OO”C,7 = 1 min).
picture of Al thin film after RTA treatment
picture of Al thin film after RTA treatment
When the time of RTA was raised to 3 min no further changes were observed. This shows that the recrystallization process is accomplished. RTA treatment at 800°C shows that the recrystallization process for 5 s is comparable with RTA at 700°C for 1 min (Figures 5 and 3). In contrast the processes at 700°C for 3 min are comparable with the ones at 800°C for 1 min, afterwards no changes are observed (Figures 4 and 6). The surface morphology of Al films is not influenced by the RTA treatments (Figure 7). The sheet resistivity pS of the Al films is measured before and after RTA by a four point probe technique and the results are shown in Table 1. It is found that a tendency to increase pS for the Al film annealed at 700°C and 800°C. This tendency is stronger for 700°C treated films. No structural and morphological changes are observed in Ag films after RTA treatment. Probably this is because of the higher 1330
Figure 5. Electronograph (t = 8OO”C,T = 5 s).
Figure 7. Electron microscope picture of Al film after RTA treatment.
melting temperature of silver. Figure 8 shows a typical surface morphology of Ag film. Nevertheless the resonators with Ag electrodes change their parameters after RTA treatment. In Table 2 the data are shown for the resonance frequency, equivalent dynamic resistivity R,T, static capacity C,, equivalent capacitivity C,, equivalent inductivity L, and the qualitative factor Q of quartz resonators before and after RTA treatments. For RTA from 5 to 15 s and increase of the equivalent dynamic resistivity R, and a decrease of the
VLasarova
eta/:Vacuum
rapidthermalannealing
Table 1. Dependence of Al films sheet resistivity of RTA parameters Sheet resistivity
RTA-parameters
t[“c1
+I
Vacuum
PSWO Before RTA process
After RTA process
700 700 700 700 800 800
5 15 30 60 5 60
5x1o-5 5x1o-5 5x10m5 5xlo-5 5x1o-5 5x10m5
158 158 158 158 158 158
158 178 186 193 182 192
30%. The equivalent dynamic induction increases as well. The parameters do not change remarkably at treatment time over 30s. In our opinion all changes of the resonators’ parameters are caused by the quartz crystal lattice influence by the RTA treatment. Comparing the resonators’ equivalent parameters before and after RTA it can be concluded that the longer RTA treatment decreases the residual mechanical stresses in the crystal lattice and thus improves the device parameters. Also quartz substrates keep their orientation and structure after phase transition between p and c[ modification at 573°C (the Curie point for quartz) during the heating and cooling. Conclusions
It is found out that a recrystallization process appears in Al films after RTA treatment in vacuum. The microstructure starts to change from amorphous to crystalline after 5 s RTA treatment. The process finishes in 3 min at 700°C and 1 min at 800°C. No structural and morphological changes are observed in Ag films at the same conditions. At the same time the resonators with Ag electrodes change their equivalent parameters. The final improvement of the parameters is probably caused by quartz crystal lattice relaxation. References 1. C Zhao and E M Charlson, Proc of Int Conf
of Carbon Films, 27
April-l May 1992, San Francisco (1992) p 431436. 2. W Zhu, R C McCune, J N de Vxies, M A Tamor and K J Simon, Fig,ure8. Electron microscope picture of Ag film after RTA treatment
qualitative factor Q occur. The changes are bigger for the shorter RTA treatment duration (5 s) and smaller for 15 s (Table 2, samples B, and B2). At longer RTA durations the opposite effect is observed - the resonators’ parameters improved: the equivalent resistivity R, decreases by about 20% and the Q-factor increases by about
Table 2. Influence MHz
of RTA-process
on the equivalent
Equivalent
parameters
parameters
of quartz
.fSW
of quartz
resonators
&PI
Diamond Related Mater, 4/3,220-233 (1995). 3. J Yamada, T Shibo, N Hosako and T Toyama, IEEE 1986 Ultrasonics Symp Proc (1986) p 267-272 4. Y Kinoshika, A Nakagoshi, M Kojimo and M Hikito, IEEE 1983 Ultrasonics Symp Proc (1983) p 83. 5. C A Ross and J J Barrese, Abstracts of Materiuls Research Society Fall Meeting, 27 November-2 December 1994, Boston (1994) p 107. 6. V N Matyeev and 0 V Kononenko, Abstracts of Materials Research Society Fall Meeting, 27 November-2 December 1994, Boston (1994)
p 71.
resonators
with Ag electrode
and resonance
frequencies
before and after RTA
C,[fFl
CJPFI
WI
dsl
Before RTA
After RTA
Before RTA
After RTA
Before RTA
After RTA
Before RTA
After RTA
Before RTA
B,
800 800 800 800 800
5 15 30 60 180
10809110 11071324 18160873 10797930 18093751
10808936 11071799 18160777 10805260 18094357
31.7 23.2 9.4 47.1 11.8
76.5 34.7 7.5 37.3 9.0
4.024 4.000 6.270 4.010 6.470
4.012 3.977 6.080 3.970 6.270
18.44 18.39 25.45 17.91 23.16
45.07 18.03 24.98 17.87 22.75
11.76 11.24 3.02 12.14 3.34
B2 B,, BS B,,
Q* 10’
L,[mHl
No.
RTA parameters
10.8, 11 .O and 18.0
After RTA 4.83
11.47 3.07 12.15 3.40
Before RTA
After RTA
25.2 33.7 36.6 17.5 32.2
0.4 23.0 46.7 22. I 42.9
1331