- Email: [email protected]
Si contact properties with C-implantation
Microelectronic Engineering 82 (2005) 479–484 www.elsevier.com/locate/mee
Improvement in NiSi/Si contact properties with C-implantation Osamu Nakatsuka a
a,b,*
, Kazuya Okubo b, Akira Sakai b, Masaki Ogawa a, Yukio Yasuda b,1, Shigeaki Zaima b
EcoTopia Science Institute, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan b Department of Crystalline Materials Science, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan Available online 18 August 2005
Abstract We have investigated effects of C+ ion implantation into Si substrates on electrical properties of NiSi/Si(0 0 1) contacts. Increase in sheet resistance of a NiSi layers on Si was effectively suppressed by the C implantation, which is due to preventing the agglomeration of polycrystalline NiSi grains. The contact resistance of NiSi/p+–Si contacts with C implantation is formed to be lower than that without C, while that of NiSi/n+–Si contacts is not influenced by C. The pile-up of B atoms at the NiSi/Si interface after silicidation of Ni/Si systems with C implantation accounts for this phenomenon. 2005 Elsevier B.V. All rights reserved. Keywords: Nickel; Silicide; Carbon; Contact resistance; Ion implantation; Thin film
1. Introduction NiSi is a promising candidate for contact materials in next-generation ULSI devices, because of its low resistivity, low process temperature, and * Corresponding author. Tel.: +81 52 789 3819; fax: +81 52 789 2760. E-mail address: [email protected] (O. Nakatsuka). 1 Present address: Research Institute of KUT, Kochi University of Technology.
low Si consumption in silicidation [1–3]. However, its poor thermal stability is a serious problem for application to contact materials. Agglomeration of polycrystalline NiSi occurs over 650 C, which leads to increasing sheet resistance [3,4]. In order to stabilize NiSi, the incorporation processes of the third elements such as Pt, Pd, Ti, N and SiO2 into Ni/Si system were reported [5–9]. On the other hand, incorporation of C into Si promises several advantages for Si devises, such as energy band engineering [10], controlling impurity diffusion in
0167-9317/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2005.07.046
480
O. Nakatsuka et al. / Microelectronic Engineering 82 (2005) 479–484
at 1100 C for 30 s in a N2 ambient for recrystallization and defect annihilation. After etching a SiO2 layer and chemical cleaning, a Ni layer with thickness of 20 or 10 nm was deposited in an ultra-high vacuum (UHV) chamber hose base pressure was below 2 · 107 Pa. Then, the samples were successively annealed at 350 C for 30 min in the same UHV chamber. Some samples were additionally annealed at a temperature ranging from 550 to 850 C for 30 s in a N2 ambient with a RTA system. The obtained Ni silicide/Si structures were analyzed by glancing angle X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and secondary ion mass spectroscopy (SIMS). The sheet resistance of silicide layers and the contact resistance were also measured by a four point probe method and a four terminal Kelvin method, respectively.
Si and SiGe substrates [11], and the introduction of the tensile-strain in a Si channel [12]. We have previously reported that the incorporation of a very small amount of C into Si substrate is effective in suppressing the agglomeration of NiSi grains [13]. Therefore, it is important to understand effects of C on the formation of NiSi/Si contacts and the thermal stability of NiSi layers in order to establish the C engineering for Si devices. In this study, we focused on C+ ion implantation into Ni/ Si system, which promises process compatibility and precise control of C distribution in shallow junctions. We investigated effect of C implantation into Si substrates on thermal stability and electrical properties of NiSi/Si contacts.
2. Experiments Both n- and p-type Si(0 0 1) substrates were used. After the formation of a 70 nm-thick SiO2 layer with dry oxidation, C+ ions were implanted into Si substrates at an implantation energy of 30 keV at a dose ranging from 3 · 1014 to 3 · 1015 cm2. C+ ions were supplied by ionizing a mixed gas of CO2 and Ar. B+ or P+ ions were also implanted at a dose of 3 · 1015 cm2 to measure contact resistance. Implantation energy of B+ and P+ ions were 30 and 85 keV, respectively. Rapid thermal annealing (RTA) was performed
Sheet resistance ( Ω /sq.)
b
NiSi2
NiSi
8
NiSi2
4 NiSi
2
0 300
400
500
600
700
800
Annealing temperature (oC)
NiSi2
NiSi
80
Without C C: 3x1015 cm-2
6
Figs. 1(a) and (b) show annealing temperature dependence of sheet resistances for samples with 20-nm- and 10-nm-thick Ni layers, respectively, with and without C implantation at a dose of 3 · 1015 cm2. Major reaction products after annealing determined by XRD and TEM observation were also shown in the figure. After annealing
900
Sheet resistance (Ω /sq.)
a
3. Results and discussion
Without C C: 3x1015 cm-2
60
40
20 NiSi2 NiSi
0 300
400
500
600
700
800
900
Annealing temperature (oC)
Fig. 1. Sheet resistances of: (a) Ni(20 nm)/Si and (b) Ni(10 nm)/Si samples with and without C implantation as a function of annealing temperature.
O. Nakatsuka et al. / Microelectronic Engineering 82 (2005) 479–484
at 350 C, the sheet resistance of silicide layers corresponds to the intrinsic value of NiSi regardless of the C implantation. In the samples without C, the sheet resistance gradually increases with the annealing temperature over 650 C. Note that a significant increase is observed in the sample with 10-nm-thick Ni layers after annealing at 750 C compared to that with thicker Ni layers (20 nm). The increase in the sheet resistance is caused by the agglomeration of the NiSi layer due to annealing [4] and the NiSi agglomeration becomes prominent with decreasing the NiSi thickness. On the other hand, in samples with C implantation, the increasing in sheet resistance is effectively suppressed even for the sample with thinner NiSi layers after annealing at 750 C. Fig. 2(a) shows a SEM image of the Ni(20 nm)/ Si sample after annealing at 750 C without C implantation. Fig. 2(b) and (c) also show those of Ni(20 nm)/Si samples with C implantation at doses of 3 · 1014 to 3 · 1015 cm2, respectively.
481
Agglomeration of NiSi and Si exposed area corresponding to dark regions are clearly observed in the sample without C [4]. On the other hand, Si exposed regions become smaller with increasing the implantation density of C. In the sample with C implantation at a dose of 3 · 1015 cm2, Si exposed region is hardly observed and the surface morphology is very smooth. Fig. 3(a) and (b) show cross-sectional TEM images of samples after 750 C annealing without and with C implantation at a dose of 3 · 1015 cm2, respectively. In the sample without C, NiSi grains have a hemispherical shape due to the agglomeration and reducing the area of NiSi/NiSi boundaries, as shown in Fig. 3(a). On the contrary, in the sample with C implantation, grain boundaries between NiSi grains are clearly observed, and plane NiSi/Si interface structure is maintained. These results demonstrate the suppression of NiSi agglomeration due to the C implantation, i.e., a polycrystalline NiSi layer formed on Si with C implantation
Fig. 2. SEM images of Ni/Si samples: (a) without C and (b) with C implantation at a dose of 3 · 1014 cm2, and (c) 3 · 1015 cm2. All samples were annealed at 750 C for 30 s.
Fig. 3. Cross-sectional TEM images of Ni/Si samples: (a) without C and (b) with C implantation at a dose of 3 · 1015 cm2. These samples were annealed at 750 C for 30 s.
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O. Nakatsuka et al. / Microelectronic Engineering 82 (2005) 479–484
shows high thermal robustness for annealing at 750 C. That leads to suppressing the increase in the sheet resistance of NiSi layers after annealing over 650 C. Fig. 4 shows contact resistance of NiSi/n+–Si and p+–Si contacts, respectively, with and without C implantation at a dose of 3 · 1015 cm2. NiSi/Si contacts for these samples were formed by annealing Ni(20 nm)/Si samples at 350 C for 30 min. In the case of NiSi/n+–Si, there are no significant differences of the contract resistances between samples with and without C implantation. On the other hand, in the case of NiSi/p+–Si, the contact resistances of samples with C implantation are lower, about one third compared to that without C. Figs. 5(a) and (b) show SIMS depth profiles around the NiSi/p+–Si interface for samples without and with C implantation at a dose of 3 · 1015 cm2, respectively, after 350 C silicidation. The secondary ions of B+ and other elements + were detected using Oþ primary ions, 2 and Cs respectively. As shown in Fig. 5(a), B atoms diffuse from the NiSi layer into the Si substrate after annealing for the NiSi formation. Note that a plateau of B profile with low concentration appears in the NiSi layer of the sample without C. On the other hand, in the sample with C implantation, B atoms remain in the NiSi layer. Instead, there is a
10
a plateau region of C profile in the NiSi layer near the NiSi/Si interface. This result indicates that C implantation restrains the diffusion of B atoms near the NiSi/Si interface into the Si substrate and causes pile-up of B atoms at the interface during the NiSi formation. Low contact resistance obtained for the sample with C implantation is possible attributed to this higher concentration of B at the NiSi/p+–Si interface [14]. Now, we deduce behavior of C atoms during NiSi formation and effects of C on the properties of NiSi/Si contacts. Considering that the solubility of C in Ni and Si is very low [15], C atoms surely segregate to the NiSi grain boundary and the NiSi/ Si interface during the NiSi formation. The plateau of C profile shown in Fig. 5(b) likely indicates homogeneous distribution of segregated C atoms at the NiSi grain boundary. Segregated C atoms at the boundary should reduce the interfacial energy between NiSi grains, which leads to suppressing the agglomeration of NiSi. Additionally, the preferential segregation of C atoms to the NiSi grain boundary probably prevents the diffusion of B from NiSi grains during silicidation, which leads to the pile-up of B atoms at the NiSi/Si interface. However, local distribution of C and B atoms in a polycrystalline NiSi layer and the NiSi/Si interface have to be investigated in the future. b
3
103
10
2
10
1
10
0
with C w/o C Contact resistance (Ω)
Contact resistance (Ω)
with C w/o C
-1
10 -8 10
10
-7
Contact area
10
-6
(cm2)
-5
10
102
101
100
10-1 10-8
10-7
10-6
10-5
Contact area (cm2)
Fig. 4. Contact resistances of: (a) NiSi/n+–Si and (b) NiSi/p+–Si samples with and without C implantation as a function of contact area.
O. Nakatsuka et al. / Microelectronic Engineering 82 (2005) 479–484
B and C concentration (cm-3)
Si 104 1021 103 1020
B
102
Ni
1019 101
C 1018 0
20
40
60
80
b
105
100 100
1022
NiSi
Si
105
Si 104 1021
C
103
B
1020
102
Ni
1019
101
1018 0
Depth (nm)
Si and Ni secondary ion intensity (cps)
Si
B and C concentration (cm-3)
NiSi
1022
Si and Ni secondary ion intensity (cps)
a
483
100 20
40
60
80
100
Depth (nm) +
Fig. 5. SIMS depth profiles around the NiSi/p –Si interface for samples: (a) without and (b) with C implantation after annealing at 350 C. Ion implantation was performed at a dose of 3 · 1015 cm2 for both B and C.
4. Conclusion We have investigated effects of C implantation on electrical properties of NiSi/Si contacts. Increase in the sheet resistance of NiSi layers after annealing over 650 C is suppressed due to preventing the agglomeration of the polycrystalline NiSi layer. Higher implantation density of C is more effective to suppress the NiSi agglomeration. While the contact resistance of the NiSi/n+–Si samples is not influenced by C implantation, that of the NiSi/p+–Si samples can be reduced compared to that without C. The reduction of contact resistance in the NiSi/p+–Si sample is due to the pile-up of B atoms at the interface, which is likely caused by preferential segregation of C to NiSi grain boundaries. Implantation of a small amount of C less than 3 · 1015 cm2 into Ni/Si systems promises high thermal robustness and low resistance of NiSi/Si contacts. Acknowledgement This work is partly supported by the Grant-inAid for Scientific Research (A) (No. 15206004)
from the Ministry of Education, Culture, Sports, Science and Technology. References [1] A. Lauwers, A. Steegen, M. de Potter, R. Lindsay, A. Satta, H. Bender, K. Maex, J. Vac. Sci. Technol. B 19 (6) (2001) 2026–2037. [2] C. Lavoie, F.M. dÕHeurle, C. Detavernier, C. Cabral, Microelectron. Eng. 70 (2–4) (2003) 144–157. [3] Y. Tsuchiya, A. Tobioka, O. Nakatsuka, H. Ikeda, A. Sakai, S. Zaima, Y. Yasuda, Jpn. J. Appl. Phys. 41 (4B) (2002) 2450–2454. [4] K. Okubo, Y. Tsuchiya, O. Nakatsuka, A. Sakai, S. Zaima, Y. Yasuda, Jpn. J. Appl. Phys. 43 (4B) (2004) 1896–1900. [5] P.S. Lee, K.L. Pey, D. Mangelinck, J. Ding, D.Z. Chi, L. Chan, IEEE Electr. Dev. Lett. 22 (12) (2001) 568–570. [6] C.J. Tsai, P.L. Chung, K.H. Yu, Thin Solid Films 365 (1) (2000) 72–76. [7] T.-H. Hou, T.-F. Lei, T.-S. Chao, IEEE Electr. Dev. Lett. 20 (11) (1999) 572–573. [8] L.W. Cheng, S.L. Cheng, J.Y. Chen, L.J. Chen, B.Y. Tsui, Thin Solid Films 355–356 (1999) 412–416. [9] C.-J. Choi, Y.-W. Ok, T.-Y. Seong, H.-D. Lee, Jpn. J. Appl. Phys. 41 (4A) (2002) 1969–1973. [10] H.J. Osten, J. Appl. Phys. 84 (5) (1998) 2716–2721. [11] L.D. Lanzerotti, J.C. Sturm, E. Stach, R. Hull, T. Buyuklimanli, C. Magee, Appl. Phys. Lett. 70 (23) (1997) 3125–3127.
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O. Nakatsuka et al. / Microelectronic Engineering 82 (2005) 479–484
[12] K.W. Ang, K.J. Chui, V. Bliznetsov, A. Du, N. Balasubramanian, M.F. Li, G. Samudra, Y.-C. Yeo, IEDM Tech. Dig. (2004) 1069–1071. [13] S. Zaima, O. Nakatsuka, A. Sakai, J. Murota, Y. Yasuda, Appl. Surf. Sci. 224 (1–4) (2004) 215–221.
[14] S.M. Sze, Physics of Semiconductor Devices, second ed., John Wiley & Sons, New York, 1988, pp. 245– 311. [15] P. Villars et al. (Eds.), Pauling File: Inorganic Materials Database, ASM International, USA, 2002.
Improvement in NiSi/Si contact properties with C-implantation Osamu Nakatsuka a
a,b,*
, Kazuya Okubo b, Akira Sakai b, Masaki Ogawa a, Yukio Yasuda b,1, Shigeaki Zaima b
EcoTopia Science Institute, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan b Department of Crystalline Materials Science, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan Available online 18 August 2005
Abstract We have investigated effects of C+ ion implantation into Si substrates on electrical properties of NiSi/Si(0 0 1) contacts. Increase in sheet resistance of a NiSi layers on Si was effectively suppressed by the C implantation, which is due to preventing the agglomeration of polycrystalline NiSi grains. The contact resistance of NiSi/p+–Si contacts with C implantation is formed to be lower than that without C, while that of NiSi/n+–Si contacts is not influenced by C. The pile-up of B atoms at the NiSi/Si interface after silicidation of Ni/Si systems with C implantation accounts for this phenomenon. 2005 Elsevier B.V. All rights reserved. Keywords: Nickel; Silicide; Carbon; Contact resistance; Ion implantation; Thin film
1. Introduction NiSi is a promising candidate for contact materials in next-generation ULSI devices, because of its low resistivity, low process temperature, and * Corresponding author. Tel.: +81 52 789 3819; fax: +81 52 789 2760. E-mail address: [email protected] (O. Nakatsuka). 1 Present address: Research Institute of KUT, Kochi University of Technology.
low Si consumption in silicidation [1–3]. However, its poor thermal stability is a serious problem for application to contact materials. Agglomeration of polycrystalline NiSi occurs over 650 C, which leads to increasing sheet resistance [3,4]. In order to stabilize NiSi, the incorporation processes of the third elements such as Pt, Pd, Ti, N and SiO2 into Ni/Si system were reported [5–9]. On the other hand, incorporation of C into Si promises several advantages for Si devises, such as energy band engineering [10], controlling impurity diffusion in
0167-9317/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2005.07.046
480
O. Nakatsuka et al. / Microelectronic Engineering 82 (2005) 479–484
at 1100 C for 30 s in a N2 ambient for recrystallization and defect annihilation. After etching a SiO2 layer and chemical cleaning, a Ni layer with thickness of 20 or 10 nm was deposited in an ultra-high vacuum (UHV) chamber hose base pressure was below 2 · 107 Pa. Then, the samples were successively annealed at 350 C for 30 min in the same UHV chamber. Some samples were additionally annealed at a temperature ranging from 550 to 850 C for 30 s in a N2 ambient with a RTA system. The obtained Ni silicide/Si structures were analyzed by glancing angle X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and secondary ion mass spectroscopy (SIMS). The sheet resistance of silicide layers and the contact resistance were also measured by a four point probe method and a four terminal Kelvin method, respectively.
Si and SiGe substrates [11], and the introduction of the tensile-strain in a Si channel [12]. We have previously reported that the incorporation of a very small amount of C into Si substrate is effective in suppressing the agglomeration of NiSi grains [13]. Therefore, it is important to understand effects of C on the formation of NiSi/Si contacts and the thermal stability of NiSi layers in order to establish the C engineering for Si devices. In this study, we focused on C+ ion implantation into Ni/ Si system, which promises process compatibility and precise control of C distribution in shallow junctions. We investigated effect of C implantation into Si substrates on thermal stability and electrical properties of NiSi/Si contacts.
2. Experiments Both n- and p-type Si(0 0 1) substrates were used. After the formation of a 70 nm-thick SiO2 layer with dry oxidation, C+ ions were implanted into Si substrates at an implantation energy of 30 keV at a dose ranging from 3 · 1014 to 3 · 1015 cm2. C+ ions were supplied by ionizing a mixed gas of CO2 and Ar. B+ or P+ ions were also implanted at a dose of 3 · 1015 cm2 to measure contact resistance. Implantation energy of B+ and P+ ions were 30 and 85 keV, respectively. Rapid thermal annealing (RTA) was performed
Sheet resistance ( Ω /sq.)
b
NiSi2
NiSi
8
NiSi2
4 NiSi
2
0 300
400
500
600
700
800
Annealing temperature (oC)
NiSi2
NiSi
80
Without C C: 3x1015 cm-2
6
Figs. 1(a) and (b) show annealing temperature dependence of sheet resistances for samples with 20-nm- and 10-nm-thick Ni layers, respectively, with and without C implantation at a dose of 3 · 1015 cm2. Major reaction products after annealing determined by XRD and TEM observation were also shown in the figure. After annealing
900
Sheet resistance (Ω /sq.)
a
3. Results and discussion
Without C C: 3x1015 cm-2
60
40
20 NiSi2 NiSi
0 300
400
500
600
700
800
900
Annealing temperature (oC)
Fig. 1. Sheet resistances of: (a) Ni(20 nm)/Si and (b) Ni(10 nm)/Si samples with and without C implantation as a function of annealing temperature.
O. Nakatsuka et al. / Microelectronic Engineering 82 (2005) 479–484
at 350 C, the sheet resistance of silicide layers corresponds to the intrinsic value of NiSi regardless of the C implantation. In the samples without C, the sheet resistance gradually increases with the annealing temperature over 650 C. Note that a significant increase is observed in the sample with 10-nm-thick Ni layers after annealing at 750 C compared to that with thicker Ni layers (20 nm). The increase in the sheet resistance is caused by the agglomeration of the NiSi layer due to annealing [4] and the NiSi agglomeration becomes prominent with decreasing the NiSi thickness. On the other hand, in samples with C implantation, the increasing in sheet resistance is effectively suppressed even for the sample with thinner NiSi layers after annealing at 750 C. Fig. 2(a) shows a SEM image of the Ni(20 nm)/ Si sample after annealing at 750 C without C implantation. Fig. 2(b) and (c) also show those of Ni(20 nm)/Si samples with C implantation at doses of 3 · 1014 to 3 · 1015 cm2, respectively.
481
Agglomeration of NiSi and Si exposed area corresponding to dark regions are clearly observed in the sample without C [4]. On the other hand, Si exposed regions become smaller with increasing the implantation density of C. In the sample with C implantation at a dose of 3 · 1015 cm2, Si exposed region is hardly observed and the surface morphology is very smooth. Fig. 3(a) and (b) show cross-sectional TEM images of samples after 750 C annealing without and with C implantation at a dose of 3 · 1015 cm2, respectively. In the sample without C, NiSi grains have a hemispherical shape due to the agglomeration and reducing the area of NiSi/NiSi boundaries, as shown in Fig. 3(a). On the contrary, in the sample with C implantation, grain boundaries between NiSi grains are clearly observed, and plane NiSi/Si interface structure is maintained. These results demonstrate the suppression of NiSi agglomeration due to the C implantation, i.e., a polycrystalline NiSi layer formed on Si with C implantation
Fig. 2. SEM images of Ni/Si samples: (a) without C and (b) with C implantation at a dose of 3 · 1014 cm2, and (c) 3 · 1015 cm2. All samples were annealed at 750 C for 30 s.
Fig. 3. Cross-sectional TEM images of Ni/Si samples: (a) without C and (b) with C implantation at a dose of 3 · 1015 cm2. These samples were annealed at 750 C for 30 s.
482
O. Nakatsuka et al. / Microelectronic Engineering 82 (2005) 479–484
shows high thermal robustness for annealing at 750 C. That leads to suppressing the increase in the sheet resistance of NiSi layers after annealing over 650 C. Fig. 4 shows contact resistance of NiSi/n+–Si and p+–Si contacts, respectively, with and without C implantation at a dose of 3 · 1015 cm2. NiSi/Si contacts for these samples were formed by annealing Ni(20 nm)/Si samples at 350 C for 30 min. In the case of NiSi/n+–Si, there are no significant differences of the contract resistances between samples with and without C implantation. On the other hand, in the case of NiSi/p+–Si, the contact resistances of samples with C implantation are lower, about one third compared to that without C. Figs. 5(a) and (b) show SIMS depth profiles around the NiSi/p+–Si interface for samples without and with C implantation at a dose of 3 · 1015 cm2, respectively, after 350 C silicidation. The secondary ions of B+ and other elements + were detected using Oþ primary ions, 2 and Cs respectively. As shown in Fig. 5(a), B atoms diffuse from the NiSi layer into the Si substrate after annealing for the NiSi formation. Note that a plateau of B profile with low concentration appears in the NiSi layer of the sample without C. On the other hand, in the sample with C implantation, B atoms remain in the NiSi layer. Instead, there is a
10
a plateau region of C profile in the NiSi layer near the NiSi/Si interface. This result indicates that C implantation restrains the diffusion of B atoms near the NiSi/Si interface into the Si substrate and causes pile-up of B atoms at the interface during the NiSi formation. Low contact resistance obtained for the sample with C implantation is possible attributed to this higher concentration of B at the NiSi/p+–Si interface [14]. Now, we deduce behavior of C atoms during NiSi formation and effects of C on the properties of NiSi/Si contacts. Considering that the solubility of C in Ni and Si is very low [15], C atoms surely segregate to the NiSi grain boundary and the NiSi/ Si interface during the NiSi formation. The plateau of C profile shown in Fig. 5(b) likely indicates homogeneous distribution of segregated C atoms at the NiSi grain boundary. Segregated C atoms at the boundary should reduce the interfacial energy between NiSi grains, which leads to suppressing the agglomeration of NiSi. Additionally, the preferential segregation of C atoms to the NiSi grain boundary probably prevents the diffusion of B from NiSi grains during silicidation, which leads to the pile-up of B atoms at the NiSi/Si interface. However, local distribution of C and B atoms in a polycrystalline NiSi layer and the NiSi/Si interface have to be investigated in the future. b
3
103
10
2
10
1
10
0
with C w/o C Contact resistance (Ω)
Contact resistance (Ω)
with C w/o C
-1
10 -8 10
10
-7
Contact area
10
-6
(cm2)
-5
10
102
101
100
10-1 10-8
10-7
10-6
10-5
Contact area (cm2)
Fig. 4. Contact resistances of: (a) NiSi/n+–Si and (b) NiSi/p+–Si samples with and without C implantation as a function of contact area.
O. Nakatsuka et al. / Microelectronic Engineering 82 (2005) 479–484
B and C concentration (cm-3)
Si 104 1021 103 1020
B
102
Ni
1019 101
C 1018 0
20
40
60
80
b
105
100 100
1022
NiSi
Si
105
Si 104 1021
C
103
B
1020
102
Ni
1019
101
1018 0
Depth (nm)
Si and Ni secondary ion intensity (cps)
Si
B and C concentration (cm-3)
NiSi
1022
Si and Ni secondary ion intensity (cps)
a
483
100 20
40
60
80
100
Depth (nm) +
Fig. 5. SIMS depth profiles around the NiSi/p –Si interface for samples: (a) without and (b) with C implantation after annealing at 350 C. Ion implantation was performed at a dose of 3 · 1015 cm2 for both B and C.
4. Conclusion We have investigated effects of C implantation on electrical properties of NiSi/Si contacts. Increase in the sheet resistance of NiSi layers after annealing over 650 C is suppressed due to preventing the agglomeration of the polycrystalline NiSi layer. Higher implantation density of C is more effective to suppress the NiSi agglomeration. While the contact resistance of the NiSi/n+–Si samples is not influenced by C implantation, that of the NiSi/p+–Si samples can be reduced compared to that without C. The reduction of contact resistance in the NiSi/p+–Si sample is due to the pile-up of B atoms at the interface, which is likely caused by preferential segregation of C to NiSi grain boundaries. Implantation of a small amount of C less than 3 · 1015 cm2 into Ni/Si systems promises high thermal robustness and low resistance of NiSi/Si contacts. Acknowledgement This work is partly supported by the Grant-inAid for Scientific Research (A) (No. 15206004)
from the Ministry of Education, Culture, Sports, Science and Technology. References [1] A. Lauwers, A. Steegen, M. de Potter, R. Lindsay, A. Satta, H. Bender, K. Maex, J. Vac. Sci. Technol. B 19 (6) (2001) 2026–2037. [2] C. Lavoie, F.M. dÕHeurle, C. Detavernier, C. Cabral, Microelectron. Eng. 70 (2–4) (2003) 144–157. [3] Y. Tsuchiya, A. Tobioka, O. Nakatsuka, H. Ikeda, A. Sakai, S. Zaima, Y. Yasuda, Jpn. J. Appl. Phys. 41 (4B) (2002) 2450–2454. [4] K. Okubo, Y. Tsuchiya, O. Nakatsuka, A. Sakai, S. Zaima, Y. Yasuda, Jpn. J. Appl. Phys. 43 (4B) (2004) 1896–1900. [5] P.S. Lee, K.L. Pey, D. Mangelinck, J. Ding, D.Z. Chi, L. Chan, IEEE Electr. Dev. Lett. 22 (12) (2001) 568–570. [6] C.J. Tsai, P.L. Chung, K.H. Yu, Thin Solid Films 365 (1) (2000) 72–76. [7] T.-H. Hou, T.-F. Lei, T.-S. Chao, IEEE Electr. Dev. Lett. 20 (11) (1999) 572–573. [8] L.W. Cheng, S.L. Cheng, J.Y. Chen, L.J. Chen, B.Y. Tsui, Thin Solid Films 355–356 (1999) 412–416. [9] C.-J. Choi, Y.-W. Ok, T.-Y. Seong, H.-D. Lee, Jpn. J. Appl. Phys. 41 (4A) (2002) 1969–1973. [10] H.J. Osten, J. Appl. Phys. 84 (5) (1998) 2716–2721. [11] L.D. Lanzerotti, J.C. Sturm, E. Stach, R. Hull, T. Buyuklimanli, C. Magee, Appl. Phys. Lett. 70 (23) (1997) 3125–3127.
484
O. Nakatsuka et al. / Microelectronic Engineering 82 (2005) 479–484
[12] K.W. Ang, K.J. Chui, V. Bliznetsov, A. Du, N. Balasubramanian, M.F. Li, G. Samudra, Y.-C. Yeo, IEDM Tech. Dig. (2004) 1069–1071. [13] S. Zaima, O. Nakatsuka, A. Sakai, J. Murota, Y. Yasuda, Appl. Surf. Sci. 224 (1–4) (2004) 215–221.
[14] S.M. Sze, Physics of Semiconductor Devices, second ed., John Wiley & Sons, New York, 1988, pp. 245– 311. [15] P. Villars et al. (Eds.), Pauling File: Inorganic Materials Database, ASM International, USA, 2002.