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Interface structure and adhesion of sputtered Ti layers on Si: the effect of heat treatment
236
Thin Solid Films, 236 (1993) 236-239
Interface structure and adhesion of sputtered Ti layers on Si: the effect of heat treatment I. K o n d o ,
T. Yoneyama,
K. Kondo
and O. Takenaka
Production Engineering Research and Development, Nippondenso Co. Ltd., I-1 Kariya 448 (Japan)
A. Kinbara Department of Applied Physics, The University of Tokyo, Tokyo 113 (Japan)
Abstract Interface structure and adhesion of the Ti films on Si substrates pretreated by an Ar ion bombardment have been investigated by high resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron diffraction and Auger electron spectroscopy (AES). Two extra layers were observed between the Ti layer and Si substrate in the as-deposited condition. One was an amorphous Si (a-Si) layer about 2 nm thick which contain Ar atoms on the single-crystal Si surface, and the other is an amorphous Ti-Si (a-Ti-Si) mixed layer about 3 nm thick on the a-Si layer. A peeling test indicates that complete detachment occurred at the interface between the a-Si and the a-Ti-Si mixed layer. However, the adhesion was increased by the heat treatment at 723 K for 30 min, and peeling ratio was reduced to about 10%. Ar atoms distributed at the interface seem to cause the reduction of the adhesion. The heat treatment changed the distribution of Ar atoms at the interface. The profile of the interface was also changed to increase the area of direct contact between the Ti-Si mixed layer and the Si substrate. Both effects seem to enhance the adhesion.
1. Introduction
TABLE 1. The experimental conditions of Si surface pretreatments
Ti films have been used as electrodes for Si devices because of their low resistivity and high thermal stability [1, 2]. However, the adhesion of Ti films on Si substrates has not been investigated sufficiently in spite of the requirement for the high reliability of these films in industry [3]. In previous reports [4, 5], we investigated the interface structure between Ti and Si, and also the adhesion of the Ti films to Si after an Ar ion b o m b a r d m e n t of the Si surface. It was suggested that Ar atoms incorporated in the Si substrate during the Ar b o m b a r d m e n t caused the decrease in adhesion because of the precipitation of Ar atoms at the interface. In the present study, we have investigated the effect of heat treatment on the Ti film adhesion after Ti film deposition on the Si substrate. The role of Ar atoms in adhesion and silicide formation at the interface has been particularly emphasized in detail.
Pretreatment
Condition
Etching time
Chemical etching Ar ion bombardment
Solutionof 1% HF (298 K) Cathodicvoltage, 400 V
30 s 180 s
2. Experimental details A d.c. planar magnetron sputtering apparatus was used for deposition of Ti on the Si(100) wafer (mirrorpolished surface, 127 m m in diameter, 0.6 m m in thickness) successively followed by Ni deposition on an Ar
0040-6090/93/$6.00
atmosphere. The sputtering chamber was first evacuated to 1.3 x 10-SPa before the deposition, and then Ar gas of 99.999% purity_ was introduced and kept at 2.67 Pa during deposition. The Si(100) wafer substrate was cleaned by an Ar ion b o m b a r d m e n t or a chemical pretreatment. The experimental conditions o f the pretreatment are listed in Table 1. Deposition rates of Ti 99.9% in purity and Ni 99.9% in purity were 4.0 nm s - ' and 5.0 nm s-1 respectively. The temperature of the Si substrate during deposition was about 523 K. The heat treatment has been carried out in an electric furnace at various temperatures for 30 min in a forming gas (90 vol.% N2 + 10 vol.% H2). The adhesion of deposited films was evaluated by the tape test, and the peeling-off area was measured after testing with the adhesive tape. The stress applied to the adhesive tape was about 0.9 MPa. The percentage peeled-off area P (peeling ratio) was obtained using the formula
© 1993 - - Elsevier Sequoia. All rights reserved
L Kondo et aL/ Sputtered 77 layers on Si
p =
237
peeled-off area sample size (25 mm 2)
where the sample size is 5 roan x 5 mm, and we measured I0 samples prepared under the same deposition conditions. A force originating from the internal stress in the Ni film is spontaneously applied to the Ti film in addition to the adhesive tape. The above-mentioned force (here we call it the internal force) calculated from the wafer bending was defined by the internal stress multiplied by the Ni film thickness. To control the internal force, we changed the Ni film thickness. The heat-treated specimens and both surfaces after the peeling at the interface (film side and substrate side) were investigated by high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDS), electron diffraction (ED), optical microscopy (OM) and Auger electron spectroscopy (AES).
(a)
400/z rn I
(b)
I
Fig. 2. Photographs (OM) of a peeled-off surface. (a) Heat treatment was at 723 K for 30 min. Peeling of the film was observed. (b) Heat treatment was at 773 K for 30 min. The peeling was mainly a cracking in the Si substrate.
substrate appeared in at 773 K. This result shows that the adhesion force of Ti on Si annealed at 773 K was higher than the cohesive force of Si.
3.2. Examination of the peeled-off surface 3. Results
3.1. Adhesion properties The results obtained from the tape test are shown in Fig. 1. Although peeling occurred at an internal force lower than 1 4 0 N m -1 for the sample without heat treatment, the adhesion increased and the peeling did not occur up to an internal force of 220 N m -1 after a heat treatment at 673 K for 30 min. With the increase in heat temperature, the adhesion increased and the peeling ratio was reduced. Figure 2 shows OM photographs of a peeled-off surface in the corner. It was found that the peeling of the film was observed at 723 K but cracking of the Si
I
I00 ~,
I
I
O
A 673 K, 30 min 723 K, 30 r n i n
80
773 K, 30min
No Heat Treatment
chemicaJ pneltealeeaIItef
¢o1
"g
60
•"
40
~,
20
i,..
I
In order to make clear the location where the peeling occurs, the surfaces of both the film side and the substrate side were investigated by AES. Figure 3 shows the AES results for the samples without the heat treatment and with the treatment at 723 K. From the Ni/Ti side, the AES spectra revealed the existence of a Ti-Si mixed layer [4-7] and O, while from the Si side, Si and O were found. Only in the case without heat treatment Ar was detected from the Si side. Figure 4 shows the AES depth profiles of the peeledoff surface of the Ni/Ti side. In general [4, 8], it has been considered that Si atoms diffuse into the Ti layer at the interface by the heat treatment. We could confirm it from these AES results, because the intensity of the Si in Ti increased with the increase in the temperature. As a result, we conclude that the number of Si atoms in the Ti-Si mixed layer and the thickness
0
.-.,J J,
t00
~I
200
.
~
I -
300
]
,5 400
Kinetic Energy CnV)1000
-( 2 3 K .
30mi n
Kinetic [ncttl~' (IV) 1000
500
Internal force (N/m) Fig. 1. Internal force of Ni/Ti films vs. percentage peeled area between the Ti films and the Si substrates. The Si substrates were bombarded by Ar ions and heated at different temperatures. With increase in heat treatment temperature, the percentage peeled-off area was reduced.
0 I(inn~ic Energy fO)I000
0 Kinetic Energy (eV) r000
Fig. 3. AES spectra of detached Ti film and Si substrate. The peeling occurred at the interface between the Ti-Si mixed layer and Si substrate. Ar was not detected from the Si side at 723 K.
L Kondo et al. / Sputtered Ti layers on Si
238
leleg
673K, 30men
Ioooo
HIU
Ti
.=
=
]eeel
15ell
no heat ireatment
911
=
723K, 30min iloeo
Si
IIII
= 5000 ~,
Sputtering time (rain) ISEO
Sputtering time (men)
773 K, 3Omen
Si
IHOI
=
~tll
Sputtering time (min) 15100
laOe|
,J
chemical pretreatmentIref,)
TiSiz(ref'. )
leoIo
,,,
5001
Si
leell "S.,
= 5e;!
"$i
Ti
0 ......................
1. . . . . . . . . . . . . . . . . . . . . . . . .
10
Sputtering time (men)
Sputtering time
(mi~)
Sputtering time (min)
Fig. 4. AES depth profiles of the peeled-off surface of the Ti side. The amount of Si at the interface and the thickness of the Ti-Si mixed layer increased with the increase in the temperature.
of the Ti-Si mixed layer were increased by the heat treatment. 3.3. Interface structure Figure 5 shows an HRTEM photograph showing the interface structure, where EDS and ED data are also displayed. Before the heat treatment at 723 K, there were two extra layers between the Ti layer and the Si substrate. One was an amorphous Si (a-Si) layer ( ~ 2 nm) formed on the single-crystal Si surface which contains Ar atoms and the other an amorphous Ti-Si mixed layer (,~ 3 nm) on the amorphous Si layer, and the interface was even on an atomic scale [4-7]. However, after the heat treatment at 723 K, it is observed
~;s
EDS T[
Fig. 5. TEM observation of the interface between Ti film and Ar ion bombarded Si(100) surface after heat treatment at 723 K for 30 men. The interface between the Ti-Si mixed layer and Si substrate was wavy, and Ar atoms were segregated at the protrusions.
that the interface layer was only a Ti-Si mixed layer (10 nm), and the interface between the Ti-Si layer and Si substrate was uneven. By the use of EDS, 4.3 at.% Ar was detected at the protrusions on the uneven interface, and there was less than 0.9 at.% Ar at the bottoms of the protrusions. The results of ED reveal the existence of small crystallites in the Ti-Si mixed layer. The interplanar spacing was estimated to be 2.30/~, and hence it is considered that the crystallites of TiSi2 were formed in the layer [9-11].
4. Discussion Adhesion between Ti and Si has been considered to be influenced by the Ar atoms implanted during the Ar ion bombardment [4], and here the behaviour of the Ar atoms and the adhesion change caused by the heat treatment are discussed. Figure 6 shows a model for the increase in adhesion caused by the heat treatment. Ar is incorporated in the Si surface during Ar ion bombardment. With the Ar incorporation, the Si surface is damaged and becomes amorphous. When the Ti layer is deposited onto the a-Si, the incorporated Ar atoms concentrate around the interface between the amorphous Si layer and the amorphous Ti-Si mixed layer [4-7]. As a result of the heat treatment at 723 K for 30 men, Si atoms diffuse into the Ti layer to form the Ti-Si mixed layer, and the Ar atoms contained in the amorphous Si layer are excluded from the layer to form lumps at the protrusions on the interface. Consequently, the area of direct contact of the Ti-Si layer and the Si substrate increases, and
L Kondo et al. / Sputtered Ti layers on Si
723 K Ar ion
bombardment
,r
*~
//
:°°°':°°,
Ti deposition
I
,,
I
T~~
30 min t.
,
$i
,
_ a-T i ' $_i _
Ar segregation
Ar concentration
............
l
a-Ti .$i Ar incorporation
30 min I " $i
239
Ar atoms incorporated in the Si surface during Ar ion bombardment caused the decrease in adhesion at the interface. However, the adhesion was enhanced by the heat treatment at 723 K for 30 min. This enhancement was related to the segregation of Ar atoms at the interface. The heat treatment at 773 K for 30 min makes the adhesion much higher because of the formation of the TiSi2 phase at the interface.
|
Acknowledgments Ar segregation Formation of TiSi2
Fig. 6. Model of the increase in adhesion caused by heat treatment.
The authors wish to thank M. Nagata and Y. Inaguma of Nippondenso for the AES analysis.
The heat treatment changes the Ar concentration and the profile of the interface, which enhances the adhesion of the Ti films.
References enhancement of the adhesion is observed. From the ED results, it should be noted that small TiSi2 crystallites were formed at 723 K. The first silicide phase nucleated in the amorphous Ti-Si mixed layer is assumed to be TiSi2, since it has a low activation energy of nucleation from the T i - S i amorphous mixed layer [11, 12]. In the case of 773 K, the TiSi2 compound phase was clearly formed. The AES intensity ratio of the Si atoms and the Ti atoms at the interface was about the same as for the reference sample of TiSi2. The TiSi2 phase formed at the boundary of the crystalline Si seems to be effective in increasing adhesion between Ti films and the Si substrate.
5. Conclusions The interface structure of Ti films on Si substrates and their adhesion characteristics after Ar ion bombardment and heat treatment have been investigated.
1 M. A. Nicolet and S. S. Lau, in N. G. Einspruch and G. B. Larrabee (eds.), VLSI Electronics, Vol. 6, Academic Press, New York, 1983, p. 453. 2 S. P..Muraka, M. H. Read, C. J. Doherty and D. B. Fraser, J. Electrochem. Soc., 129 (1982) 293. 3 T. Yoneyama, I. Kondo, O. Takenaka and M. Yamaoka, Thin Solid Films, 193-194 (1990) 1056. 4 I. Kondo, T. Yoneyama, K. Kondo, O. Takenaka and A. Kinbara, J. Vac. Sci. Technol. A, 10 (1992) 3166. 5 I. Kondo, T. Yoneyama, K. Kondo, O. Takenaka and A. Kinbara, d. Vac. Sci. Technol. A, 11 (1993) 319. 6 S. Ogawa, T. Kouzaki, T. Y0shida and R. Sinclair, Mater. Res. Soc. Symp. Proc., 181 (1990) 139. 7 S. Ogawa, T. Yoshida and R. Sinclair, Extended Abstr. Conf. on Solid State Devices and Materials, Sendal, Japan, Business Center for Acad. Sci., Bunkyo-ku, Tokyo, 1990, p. 429. 8 T. Yamauchi, Ph.D. Thesis, Nagoya University, 1992. 9 R. Beyers and R. Sinclair, J. Appl. Phys., 57 (12) (1985) 5240. 10 Powder Diffraction File, ASTM, Philadelphia, Card 2-1120. 11 S. F. Gong, A. Robertsson, H. T. G. Hentzell and X. H. Li, J. Appl. Phys., 68 (9) (1990) 4535. 12 S. F. Gong and H. T. G. Hentzell, J. AppL Phys., 68 (9) (1990) 4542.
Thin Solid Films, 236 (1993) 236-239
Interface structure and adhesion of sputtered Ti layers on Si: the effect of heat treatment I. K o n d o ,
T. Yoneyama,
K. Kondo
and O. Takenaka
Production Engineering Research and Development, Nippondenso Co. Ltd., I-1 Kariya 448 (Japan)
A. Kinbara Department of Applied Physics, The University of Tokyo, Tokyo 113 (Japan)
Abstract Interface structure and adhesion of the Ti films on Si substrates pretreated by an Ar ion bombardment have been investigated by high resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron diffraction and Auger electron spectroscopy (AES). Two extra layers were observed between the Ti layer and Si substrate in the as-deposited condition. One was an amorphous Si (a-Si) layer about 2 nm thick which contain Ar atoms on the single-crystal Si surface, and the other is an amorphous Ti-Si (a-Ti-Si) mixed layer about 3 nm thick on the a-Si layer. A peeling test indicates that complete detachment occurred at the interface between the a-Si and the a-Ti-Si mixed layer. However, the adhesion was increased by the heat treatment at 723 K for 30 min, and peeling ratio was reduced to about 10%. Ar atoms distributed at the interface seem to cause the reduction of the adhesion. The heat treatment changed the distribution of Ar atoms at the interface. The profile of the interface was also changed to increase the area of direct contact between the Ti-Si mixed layer and the Si substrate. Both effects seem to enhance the adhesion.
1. Introduction
TABLE 1. The experimental conditions of Si surface pretreatments
Ti films have been used as electrodes for Si devices because of their low resistivity and high thermal stability [1, 2]. However, the adhesion of Ti films on Si substrates has not been investigated sufficiently in spite of the requirement for the high reliability of these films in industry [3]. In previous reports [4, 5], we investigated the interface structure between Ti and Si, and also the adhesion of the Ti films to Si after an Ar ion b o m b a r d m e n t of the Si surface. It was suggested that Ar atoms incorporated in the Si substrate during the Ar b o m b a r d m e n t caused the decrease in adhesion because of the precipitation of Ar atoms at the interface. In the present study, we have investigated the effect of heat treatment on the Ti film adhesion after Ti film deposition on the Si substrate. The role of Ar atoms in adhesion and silicide formation at the interface has been particularly emphasized in detail.
Pretreatment
Condition
Etching time
Chemical etching Ar ion bombardment
Solutionof 1% HF (298 K) Cathodicvoltage, 400 V
30 s 180 s
2. Experimental details A d.c. planar magnetron sputtering apparatus was used for deposition of Ti on the Si(100) wafer (mirrorpolished surface, 127 m m in diameter, 0.6 m m in thickness) successively followed by Ni deposition on an Ar
0040-6090/93/$6.00
atmosphere. The sputtering chamber was first evacuated to 1.3 x 10-SPa before the deposition, and then Ar gas of 99.999% purity_ was introduced and kept at 2.67 Pa during deposition. The Si(100) wafer substrate was cleaned by an Ar ion b o m b a r d m e n t or a chemical pretreatment. The experimental conditions o f the pretreatment are listed in Table 1. Deposition rates of Ti 99.9% in purity and Ni 99.9% in purity were 4.0 nm s - ' and 5.0 nm s-1 respectively. The temperature of the Si substrate during deposition was about 523 K. The heat treatment has been carried out in an electric furnace at various temperatures for 30 min in a forming gas (90 vol.% N2 + 10 vol.% H2). The adhesion of deposited films was evaluated by the tape test, and the peeling-off area was measured after testing with the adhesive tape. The stress applied to the adhesive tape was about 0.9 MPa. The percentage peeled-off area P (peeling ratio) was obtained using the formula
© 1993 - - Elsevier Sequoia. All rights reserved
L Kondo et aL/ Sputtered 77 layers on Si
p =
237
peeled-off area sample size (25 mm 2)
where the sample size is 5 roan x 5 mm, and we measured I0 samples prepared under the same deposition conditions. A force originating from the internal stress in the Ni film is spontaneously applied to the Ti film in addition to the adhesive tape. The above-mentioned force (here we call it the internal force) calculated from the wafer bending was defined by the internal stress multiplied by the Ni film thickness. To control the internal force, we changed the Ni film thickness. The heat-treated specimens and both surfaces after the peeling at the interface (film side and substrate side) were investigated by high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDS), electron diffraction (ED), optical microscopy (OM) and Auger electron spectroscopy (AES).
(a)
400/z rn I
(b)
I
Fig. 2. Photographs (OM) of a peeled-off surface. (a) Heat treatment was at 723 K for 30 min. Peeling of the film was observed. (b) Heat treatment was at 773 K for 30 min. The peeling was mainly a cracking in the Si substrate.
substrate appeared in at 773 K. This result shows that the adhesion force of Ti on Si annealed at 773 K was higher than the cohesive force of Si.
3.2. Examination of the peeled-off surface 3. Results
3.1. Adhesion properties The results obtained from the tape test are shown in Fig. 1. Although peeling occurred at an internal force lower than 1 4 0 N m -1 for the sample without heat treatment, the adhesion increased and the peeling did not occur up to an internal force of 220 N m -1 after a heat treatment at 673 K for 30 min. With the increase in heat temperature, the adhesion increased and the peeling ratio was reduced. Figure 2 shows OM photographs of a peeled-off surface in the corner. It was found that the peeling of the film was observed at 723 K but cracking of the Si
I
I00 ~,
I
I
O
A 673 K, 30 min 723 K, 30 r n i n
80
773 K, 30min
No Heat Treatment
chemicaJ pneltealeeaIItef
¢o1
"g
60
•"
40
~,
20
i,..
I
In order to make clear the location where the peeling occurs, the surfaces of both the film side and the substrate side were investigated by AES. Figure 3 shows the AES results for the samples without the heat treatment and with the treatment at 723 K. From the Ni/Ti side, the AES spectra revealed the existence of a Ti-Si mixed layer [4-7] and O, while from the Si side, Si and O were found. Only in the case without heat treatment Ar was detected from the Si side. Figure 4 shows the AES depth profiles of the peeledoff surface of the Ni/Ti side. In general [4, 8], it has been considered that Si atoms diffuse into the Ti layer at the interface by the heat treatment. We could confirm it from these AES results, because the intensity of the Si in Ti increased with the increase in the temperature. As a result, we conclude that the number of Si atoms in the Ti-Si mixed layer and the thickness
0
.-.,J J,
t00
~I
200
.
~
I -
300
]
,5 400
Kinetic Energy CnV)1000
-( 2 3 K .
30mi n
Kinetic [ncttl~' (IV) 1000
500
Internal force (N/m) Fig. 1. Internal force of Ni/Ti films vs. percentage peeled area between the Ti films and the Si substrates. The Si substrates were bombarded by Ar ions and heated at different temperatures. With increase in heat treatment temperature, the percentage peeled-off area was reduced.
0 I(inn~ic Energy fO)I000
0 Kinetic Energy (eV) r000
Fig. 3. AES spectra of detached Ti film and Si substrate. The peeling occurred at the interface between the Ti-Si mixed layer and Si substrate. Ar was not detected from the Si side at 723 K.
L Kondo et al. / Sputtered Ti layers on Si
238
leleg
673K, 30men
Ioooo
HIU
Ti
.=
=
]eeel
15ell
no heat ireatment
911
=
723K, 30min iloeo
Si
IIII
= 5000 ~,
Sputtering time (rain) ISEO
Sputtering time (men)
773 K, 3Omen
Si
IHOI
=
~tll
Sputtering time (min) 15100
laOe|
,J
chemical pretreatmentIref,)
TiSiz(ref'. )
leoIo
,,,
5001
Si
leell "S.,
= 5e;!
"$i
Ti
0 ......................
1. . . . . . . . . . . . . . . . . . . . . . . . .
10
Sputtering time (men)
Sputtering time
(mi~)
Sputtering time (min)
Fig. 4. AES depth profiles of the peeled-off surface of the Ti side. The amount of Si at the interface and the thickness of the Ti-Si mixed layer increased with the increase in the temperature.
of the Ti-Si mixed layer were increased by the heat treatment. 3.3. Interface structure Figure 5 shows an HRTEM photograph showing the interface structure, where EDS and ED data are also displayed. Before the heat treatment at 723 K, there were two extra layers between the Ti layer and the Si substrate. One was an amorphous Si (a-Si) layer ( ~ 2 nm) formed on the single-crystal Si surface which contains Ar atoms and the other an amorphous Ti-Si mixed layer (,~ 3 nm) on the amorphous Si layer, and the interface was even on an atomic scale [4-7]. However, after the heat treatment at 723 K, it is observed
~;s
EDS T[
Fig. 5. TEM observation of the interface between Ti film and Ar ion bombarded Si(100) surface after heat treatment at 723 K for 30 men. The interface between the Ti-Si mixed layer and Si substrate was wavy, and Ar atoms were segregated at the protrusions.
that the interface layer was only a Ti-Si mixed layer (10 nm), and the interface between the Ti-Si layer and Si substrate was uneven. By the use of EDS, 4.3 at.% Ar was detected at the protrusions on the uneven interface, and there was less than 0.9 at.% Ar at the bottoms of the protrusions. The results of ED reveal the existence of small crystallites in the Ti-Si mixed layer. The interplanar spacing was estimated to be 2.30/~, and hence it is considered that the crystallites of TiSi2 were formed in the layer [9-11].
4. Discussion Adhesion between Ti and Si has been considered to be influenced by the Ar atoms implanted during the Ar ion bombardment [4], and here the behaviour of the Ar atoms and the adhesion change caused by the heat treatment are discussed. Figure 6 shows a model for the increase in adhesion caused by the heat treatment. Ar is incorporated in the Si surface during Ar ion bombardment. With the Ar incorporation, the Si surface is damaged and becomes amorphous. When the Ti layer is deposited onto the a-Si, the incorporated Ar atoms concentrate around the interface between the amorphous Si layer and the amorphous Ti-Si mixed layer [4-7]. As a result of the heat treatment at 723 K for 30 men, Si atoms diffuse into the Ti layer to form the Ti-Si mixed layer, and the Ar atoms contained in the amorphous Si layer are excluded from the layer to form lumps at the protrusions on the interface. Consequently, the area of direct contact of the Ti-Si layer and the Si substrate increases, and
L Kondo et al. / Sputtered Ti layers on Si
723 K Ar ion
bombardment
,r
*~
//
:°°°':°°,
Ti deposition
I
,,
I
T~~
30 min t.
,
$i
,
_ a-T i ' $_i _
Ar segregation
Ar concentration
............
l
a-Ti .$i Ar incorporation
30 min I " $i
239
Ar atoms incorporated in the Si surface during Ar ion bombardment caused the decrease in adhesion at the interface. However, the adhesion was enhanced by the heat treatment at 723 K for 30 min. This enhancement was related to the segregation of Ar atoms at the interface. The heat treatment at 773 K for 30 min makes the adhesion much higher because of the formation of the TiSi2 phase at the interface.
|
Acknowledgments Ar segregation Formation of TiSi2
Fig. 6. Model of the increase in adhesion caused by heat treatment.
The authors wish to thank M. Nagata and Y. Inaguma of Nippondenso for the AES analysis.
The heat treatment changes the Ar concentration and the profile of the interface, which enhances the adhesion of the Ti films.
References enhancement of the adhesion is observed. From the ED results, it should be noted that small TiSi2 crystallites were formed at 723 K. The first silicide phase nucleated in the amorphous Ti-Si mixed layer is assumed to be TiSi2, since it has a low activation energy of nucleation from the T i - S i amorphous mixed layer [11, 12]. In the case of 773 K, the TiSi2 compound phase was clearly formed. The AES intensity ratio of the Si atoms and the Ti atoms at the interface was about the same as for the reference sample of TiSi2. The TiSi2 phase formed at the boundary of the crystalline Si seems to be effective in increasing adhesion between Ti films and the Si substrate.
5. Conclusions The interface structure of Ti films on Si substrates and their adhesion characteristics after Ar ion bombardment and heat treatment have been investigated.
1 M. A. Nicolet and S. S. Lau, in N. G. Einspruch and G. B. Larrabee (eds.), VLSI Electronics, Vol. 6, Academic Press, New York, 1983, p. 453. 2 S. P..Muraka, M. H. Read, C. J. Doherty and D. B. Fraser, J. Electrochem. Soc., 129 (1982) 293. 3 T. Yoneyama, I. Kondo, O. Takenaka and M. Yamaoka, Thin Solid Films, 193-194 (1990) 1056. 4 I. Kondo, T. Yoneyama, K. Kondo, O. Takenaka and A. Kinbara, J. Vac. Sci. Technol. A, 10 (1992) 3166. 5 I. Kondo, T. Yoneyama, K. Kondo, O. Takenaka and A. Kinbara, d. Vac. Sci. Technol. A, 11 (1993) 319. 6 S. Ogawa, T. Kouzaki, T. Y0shida and R. Sinclair, Mater. Res. Soc. Symp. Proc., 181 (1990) 139. 7 S. Ogawa, T. Yoshida and R. Sinclair, Extended Abstr. Conf. on Solid State Devices and Materials, Sendal, Japan, Business Center for Acad. Sci., Bunkyo-ku, Tokyo, 1990, p. 429. 8 T. Yamauchi, Ph.D. Thesis, Nagoya University, 1992. 9 R. Beyers and R. Sinclair, J. Appl. Phys., 57 (12) (1985) 5240. 10 Powder Diffraction File, ASTM, Philadelphia, Card 2-1120. 11 S. F. Gong, A. Robertsson, H. T. G. Hentzell and X. H. Li, J. Appl. Phys., 68 (9) (1990) 4535. 12 S. F. Gong and H. T. G. Hentzell, J. AppL Phys., 68 (9) (1990) 4542.