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Si contact system
Microelectronic Engineering 71 (2004) 69–75 www.elsevier.com/locate/mee
High temperature stability of Zr–Si–N diffusion barrier in Cu/Si contact system Ying Wang b
a,*
, Changchun Zhu a, Zhongxiao Song b, Ying Li
c
a School of Electronics and Information Engineering, Xi’an Jiaotong University, Xi’an 710049, China State-Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China c Research Institute of Polymer Materials, Shanghai Jiaotong University, Shanghai 200240, China
Received 18 July 2003; received in revised form 18 July 2003; accepted 15 September 2003
Abstract Zr–Si–N thin films were deposited on silicon substrates by radio frequency reactive magnetron sputtering (RFMS) technique. Subsequently, Cu films were sputtered on the Zr–Si–N thin films by direct current-pulse magnetron sputtering (DCPMS). The Zr–Si–N films and Cu/Zr–Si–N/Si contact systems were analyzed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), four-point probe sheet resistance measurements, scanning electron microscopy (SEM) and Auger electron spectroscopy (AES), respectively. It was found that the sheet resistances of Cu/Zr–Si–N/Si contact systems annealed in H2 /N2 gas mixture were lower than those of asdeposited specimens even after annealing at 800 °C for 1 h. Zr–Si–N thin film showed excellent barrier property so that the Cu/Zr–Si–N/Si contact systems keep the structures unchanged and Cu3 Si phase could not be detected. Amorphous Zr–Si–N thin film was considered to be a promising candidate in Cu diffusion barrier due to its high thermal stability. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Diffusion barrier; Cu metallization; Zr–Si–N; Sputtering
1. Introduction Copper metallization has become very popular in the Si industry. Compared with aluminum alloy, the use of copper as the metallization for transmission lines and ground plane metallization provides a lower bulk resistivity, higher electromigration, stress migration resistance, higher
*
Corresponding author. Tel.: +86-29-2668644; fax: +86-292663957. E-mail address: [email protected] (Y. Wang).
melting point, higher thermal conductivity and lower reactivity with commonly used diffusion barrier materials [1–3]. Because of the high mobility of Cu in metals and semiconductors very effective diffusion barriers are necessary to prevent Cu diffusing into the silicon [4,5]. Cu in silicon will form deep acceptor levels that act as generationrecombination centers or traps and alter the density and lifetime of the non-equilibrium minor carriers. Cu diffusing into dielectric and subsequently into silicon regions underneath is fatal because it can deteriorate the device operation [6]. To counter this rapid diffusion of copper,
0167-9317/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2003.09.002
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Y. Wang et al. / Microelectronic Engineering 71 (2004) 69–75
amorphous alloys with high crystallization temperature are appealing candidates for diffusion barriers because they lack grain boundaries that can act as diffusion paths [7]. It is well known that ternary amorphous thin films generally show excellent barrier properties due to their high crystallization temperatures. Recently, ternary amorphous thin films such as Ti–Si–N, Mo–Si–N, W–Si–N, Ta–Si–N have been studied extensively as suitable diffusion barriers for Cu metallization [8–10]. In this article, we introduced a new ternary amorphous thin film – Zr–Si–N as Cu diffusion barrier and focus on investigating thermal stability of the thin film under high annealing temperature.
2. Experimental Substrates of n-type (1 1 1) Si were cleaned in a dilute HF solution (HF:H2 O ¼ 1:20) for 60 s and rinsed in de-ionized water. The base pressure of the vacuum chamber was 2 105 Pa and the substrates were cleaned by bombardment of Ar ion prior to the depositing the diffusion barrier. Zr–Si–N films approximately 100 nm in thickness were deposited on the Si substrates by radio frequency reactive magnetron sputtering (RFMS) using the targets consisting of zirconium (99.9% purity) plate (£ 75 mm 5 mm) and silicon (99.999% purity) plate (10 mm 10 mm 0.6 mm) in a mixture of argon and nitrogen, both of 99.999% purity. During depositing Zr–Si–N diffusion barrier the pressure in the vacuum chamber was 0.3 Pa and the gas flow rate of N2 /Ar was 4 sccm/16 sccm. The sputtering power was 300 W and the substrate bias voltages were )100 and )200 V, respectively. Subsequently, Cu films with the thickness of approximately 300 nm were sputtered by direct current-pulsed magnetron sputtering (DC-PMS) from a copper target (99.9% purity) in pure Ar without breaking vacuum. The chamber pressure was 0.1 Pa and the power was 200 W. The Cu/Zr–Si–N/Si specimens were annealed at 800 °C for 1 h in H2 (10%) and N2 (90%) gas mixture. The specimens were analyzed by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), four-point probe sheet resistance mea-
surements, scanning electron microscopy (SEM) and Auger electron spectroscopy (AES), respectively.
3. Results and discussion Fig. 1 shows the XRD patterns obtained from as-deposited Zr–Si–N films. The patterns only show diffraction peaks assigned to crystalline ZrN. However, other crystalline phase like Si3 N4 or Zr silicide cannot be observed. This result implies that Si is present in an amorphous phase of either Si3 N4 or Si. With the substrate bias decreasing from )200 to )100 V, the (1 1 1) peak becomes weak and the intensity of the (2 2 0) peak decreases significantly. The most important contribution to XRD peak broadening originates from particle size and micro-stress-induced alteration of the lattice. The chemical state of the Zr–Si–N films sputtered with bias )100 and )200 V were analyzed by XPS. As shown in Fig. 2, the bonding energies of N1s and Zr3d indicate the existence of ZrN. The bonding energies of Si2p and N1s peaks closely match those of Si3 N4 . But this compound phase is not detected by XRD due to its weak intensity. It is thought that the existing states of Si and Zr in the films are Si3 N4 -like phase and ZrN phase in
Fig. 1. XRD spectra of as-deposited Zr–Si–N films for substrate bias voltages of )100 and )200 V.
Y. Wang et al. / Microelectronic Engineering 71 (2004) 69–75
Fig. 2. XPS spectra of: (a) N1s, (b) Si2p, (c) Zr3d for Zr–Si–N films.
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Zr–Si–N films. This kind of structure contributes to the excellent barrier property of Zr–Si–N films. The film morphology was examined using AFM. Fig. 3 shows the AFM images of Zr–Si–N films deposited on Si substrates with bias of )100 and )200 V, respectively, over a 10 10 lm area. A fairly smooth surface with a root mean square (RMS) value of 0.689 nm is obtained for the Zr– Si–N ()100 V) specimen as shown in Fig. 3(a). Furthermore, RMS of 1.026 nm is obtained for Zr–Si–N ()200 V) specimen as shown in Fig. 3(b). The difference between RMS surface roughness of the films suggests that high bias can roughen the surface of Zr–Si–N film. The sheet resistances of specimens were determined using the four-point probe technique. The variation of Cu sheet resistance is commonly used to examine the capability of diffusion barrier against Cu diffusion. It is well known that Cu diffuses fast in Si and forms Cu–Si compounds at a temperature as low as 200 °C [11]. The formation of Cu–Si compounds results in the increase of sheet resistances of Cu/Si contacts. Table 1 shows the sheet resistances of the Cu/Zr–Si–N/Si contact systems before and after annealing at 800 °C. It is found that the sheet resistances of specimens annealing in H2 /N2 gas mixture is still lower than those of as-deposited specimens at the same substrate bias after annealing at 800 °C. The sheet resistances can also be used to estimate the degree of intermixing reactions and changes of integrity across the metallization layer. The sheet resistance of the specimen rises abruptly indicating a severe intermixing or interfacial reactions occurred across all the Cu films. As can be seen from Table 1, no evidence for copper silicide formation is found for the specimen after annealing at 800 °C. In addition, it seems that the oxidation of Cu film is prevented in H2 /N2 gas mixture annealing which contributes to the decrease of the sheet resistances. X-ray diffraction spectra of Cu/Zr–Si–N/Si specimens before and after annealing were investigated. Fig. 4 shows the XRD patterns obtained from the as-deposited contact system and those annealed at 800 °C. In the spectrum from the asdeposited contact, the predominant reflection line from Cu (1 1 1) and those from Cu (2 0 0) with very weak intensity are observed, which indicates that
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Fig. 3. AFM micrographs of as-deposited Zr–Si–N films for substrate bias voltages of: (a) )100 V and (b) )200 V.
Cu film posses (1 1 1) texture. Sharpened (1 1 1) and (2 0 0) peaks of annealed-Cu films indicate the growth of Cu crystalline occurring during annealing, but other crystalline phase like Cu silicide or Zr silicide cannot be observed up to 800 °C. On the other hand, it has been reported that Cu (1 1 1)
provided higher electro-migration resistance than that of Cu (2 0 0) [12]. In the present experiment, the intensities of Cu (1 1 1) peak are larger than those of Cu (2 0 0) peaks for all specimens (the ratio of the intensities of Cu (1 1 1) to those of Cu (2 0 0) are 35 and 56 for Cu/Zr–Si–N()100 V)/Si and Cu/
Table 1 The sheet resistances of the Cu/Zr–Si–N/Si contacts before and after annealing at 800 °C Substrate bias (V) Annealing ambient Sheet resistance ðX=Þ
)100 As-deposited 0.029
Annealed 0.021
)200 As-deposited 0.028
Annealed 0.016
Y. Wang et al. / Microelectronic Engineering 71 (2004) 69–75
Fig. 4. XRD spectra of: (a) Cu/Zr–Si–N()100 V)/Si and (b) Cu/ Zr–Si–N()200 V)/Si contact systems annealed at 800 °C.
Zr–Si–N()200 V)/Si specimens, respectively, in which )100 and )200 V are the substrate bias voltages when depositing Zr–Si–N diffusion barriers). These results indicate that Zr–Si–N barrier can favor Cu (1 1 1) texture that contributes to the electro-migration resistance performances.
73
The surface morphology of the annealed Cu/Zr– Si–N()200 V)/Si multiplayer structure shown in Fig. 5 was obtained by employing SEM. It is evident that after annealing at 800 °C, the surface of Cu/Zr– Si–N/Si structure shows an increased average grain size. In the copper layer, annealing produces voids that expose the Zr–Si–N layer underneath, but the presence of the voids does not cause the barrier to fail. The origin of the voidsÕ formation is not connected with a Si–Cu interaction, but results from thermal stress in the Cu film itself. In order to inspect interfacial reaction of Cu/ Zr–Si–N/Si systems in detail, the depth profiles of AES were carried out. Fig. 6 shows that AES depth profiles of the Cu/Zr–Si–N()200 V)/Si specimens as-deposited and annealed at 800 °C. As shown in Fig. 6(a), the depth profile from the asdeposited contact system exhibits a well-separated stacked structure with a sharp transition of all elements at each interface. The depth profile of the as-deposited Cu/Zr–Si–N()100 V)/Si specimen is not shown in this article, but exhibits similarity to that of the as-deposited Cu/Zr–Si–N()200 V)/Si specimen. In the case of specimens annealed at 800 °C shown in Figs. 6(b) and (c), depth of profiles
Fig. 5. SEM micrographs of Cu/Zr–Si–N()200 V)/Si contact system after annealing at 800 °C.
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Y. Wang et al. / Microelectronic Engineering 71 (2004) 69–75
are similar and have no intermixing evidence at interfaces of Cu/Zr–Si–N and Zr–Si–N/Si. In addition, the scarce change in structure upon annealing indicates that the Zr–Si–N film be an excellent diffusion barrier, the diffusion of Cu and/ or Si through Zr–Si–N film is inhibited effectively. As is expected from the XRD spectra and the sheet resistance measurements, any noticeable change is not found even after annealing at 800 °C. 4. Conclusions In this investigation, we have examined the Zr– Si–N thin film as a barrier in Cu/Si contact. Amorphous Zr–Si–N films approximately 100 nm in thickness were deposited onto (1 1 1) Si substrates using radio frequency reactive magnetron sputtering from Zr and Si target materials in a mixture of argon and nitrogen. It is observed that the sheet resistances of Cu/Zr–Si–N/Si contact system annealing in H2 /N2 gas mixture is lower than those of as-deposited specimens even after annealing at 800 °C. Zr–Si–N thin films show excellent barrier property so that Cu–Si phase could not be detected in any of the specimens after annealing. In addition, the Cu/Zr–Si–N/Si contact systems keep structures unchanged after annealing at 800 °C for 1 h. These results imply that Zr–Si–N is a suitable diffusion barrier for the Cu metallization system from the views of expected electromigration resistance and thermal stability.
Acknowledgements This work was supported by the National Science Foundation (60036010 and 60176020) and Key Project Foundation of 863 (2001AA313090) of PR China.
References
Fig. 6. AES depth profiles of specimens: (a) as-deposited Cu/ ZrSiN()200 V)/Si, (b) Cu/ZrSiN()100 V)/Si annealed at 800 °C and (c) Cu/ZrSiN()200 V)/Si annealed at 800 °C.
[1] C.J. Chang, C.M. Chieh, Thin Solid Films 335 (1998) 146. [2] Y.W. Luh, W.W. Fa, L.D. Gey, W.C. Chang, O.K. Liang, Solid-State Electron. 45 (2001) 149. [3] L.K. Maung, Y.K. Lee, Li, S.T. Osipowicz, H.L. Seng, Mater. Sci. Eng. B 84 (2001) 217.
Y. Wang et al. / Microelectronic Engineering 71 (2004) 69–75 [4] A. Cros, M.O. Aboelfotoh, K.N. Tu, J. Appl. Phys. 67 (1990) 3328. [5] C.A. Chang, J. Appl. Phys. 67 (1990) 566. [6] Y.K. Lee, M. Latt, K. Jaehyung, K. Lee, Kangsoo, Mater. Sci. Semicond. Process 3 (2000) 179. [7] L.S. Hung, F.W. Saris, S.Q. Wang, J.W. Mayer, J. Appl. Phys. 59 (1986) 2416. [8] J.S. Reid, X. Sun, E. Kolawa, M.A. Nicolet, IEEE Electron Device Lett. 15 (1994) 298.
75
[9] E. Blanquet, A.M. Dutron, V. Ghetta, C. Bernard, R. Madar, Microelectron. Eng. 37-38 (1997) 189. [10] R.S. Liu, C.C. You, M.S. Tsai, S.F. Hu, Y.H. Li, C.P. Lu, Solid State Commun. 125 (2003) 445. [11] R.A. Donaton, B. Coenegrachts, M. Maenhoudt, I. Pollentier, H. Struyf, Microelectron. Eng. 55 (2001) 277. [12] K. Abe, Y. Harada, H. Onoda, J. Vac. Sci. Technol. B 17 (1999) 1464.
High temperature stability of Zr–Si–N diffusion barrier in Cu/Si contact system Ying Wang b
a,*
, Changchun Zhu a, Zhongxiao Song b, Ying Li
c
a School of Electronics and Information Engineering, Xi’an Jiaotong University, Xi’an 710049, China State-Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China c Research Institute of Polymer Materials, Shanghai Jiaotong University, Shanghai 200240, China
Received 18 July 2003; received in revised form 18 July 2003; accepted 15 September 2003
Abstract Zr–Si–N thin films were deposited on silicon substrates by radio frequency reactive magnetron sputtering (RFMS) technique. Subsequently, Cu films were sputtered on the Zr–Si–N thin films by direct current-pulse magnetron sputtering (DCPMS). The Zr–Si–N films and Cu/Zr–Si–N/Si contact systems were analyzed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), four-point probe sheet resistance measurements, scanning electron microscopy (SEM) and Auger electron spectroscopy (AES), respectively. It was found that the sheet resistances of Cu/Zr–Si–N/Si contact systems annealed in H2 /N2 gas mixture were lower than those of asdeposited specimens even after annealing at 800 °C for 1 h. Zr–Si–N thin film showed excellent barrier property so that the Cu/Zr–Si–N/Si contact systems keep the structures unchanged and Cu3 Si phase could not be detected. Amorphous Zr–Si–N thin film was considered to be a promising candidate in Cu diffusion barrier due to its high thermal stability. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Diffusion barrier; Cu metallization; Zr–Si–N; Sputtering
1. Introduction Copper metallization has become very popular in the Si industry. Compared with aluminum alloy, the use of copper as the metallization for transmission lines and ground plane metallization provides a lower bulk resistivity, higher electromigration, stress migration resistance, higher
*
Corresponding author. Tel.: +86-29-2668644; fax: +86-292663957. E-mail address: [email protected] (Y. Wang).
melting point, higher thermal conductivity and lower reactivity with commonly used diffusion barrier materials [1–3]. Because of the high mobility of Cu in metals and semiconductors very effective diffusion barriers are necessary to prevent Cu diffusing into the silicon [4,5]. Cu in silicon will form deep acceptor levels that act as generationrecombination centers or traps and alter the density and lifetime of the non-equilibrium minor carriers. Cu diffusing into dielectric and subsequently into silicon regions underneath is fatal because it can deteriorate the device operation [6]. To counter this rapid diffusion of copper,
0167-9317/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2003.09.002
70
Y. Wang et al. / Microelectronic Engineering 71 (2004) 69–75
amorphous alloys with high crystallization temperature are appealing candidates for diffusion barriers because they lack grain boundaries that can act as diffusion paths [7]. It is well known that ternary amorphous thin films generally show excellent barrier properties due to their high crystallization temperatures. Recently, ternary amorphous thin films such as Ti–Si–N, Mo–Si–N, W–Si–N, Ta–Si–N have been studied extensively as suitable diffusion barriers for Cu metallization [8–10]. In this article, we introduced a new ternary amorphous thin film – Zr–Si–N as Cu diffusion barrier and focus on investigating thermal stability of the thin film under high annealing temperature.
2. Experimental Substrates of n-type (1 1 1) Si were cleaned in a dilute HF solution (HF:H2 O ¼ 1:20) for 60 s and rinsed in de-ionized water. The base pressure of the vacuum chamber was 2 105 Pa and the substrates were cleaned by bombardment of Ar ion prior to the depositing the diffusion barrier. Zr–Si–N films approximately 100 nm in thickness were deposited on the Si substrates by radio frequency reactive magnetron sputtering (RFMS) using the targets consisting of zirconium (99.9% purity) plate (£ 75 mm 5 mm) and silicon (99.999% purity) plate (10 mm 10 mm 0.6 mm) in a mixture of argon and nitrogen, both of 99.999% purity. During depositing Zr–Si–N diffusion barrier the pressure in the vacuum chamber was 0.3 Pa and the gas flow rate of N2 /Ar was 4 sccm/16 sccm. The sputtering power was 300 W and the substrate bias voltages were )100 and )200 V, respectively. Subsequently, Cu films with the thickness of approximately 300 nm were sputtered by direct current-pulsed magnetron sputtering (DC-PMS) from a copper target (99.9% purity) in pure Ar without breaking vacuum. The chamber pressure was 0.1 Pa and the power was 200 W. The Cu/Zr–Si–N/Si specimens were annealed at 800 °C for 1 h in H2 (10%) and N2 (90%) gas mixture. The specimens were analyzed by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), four-point probe sheet resistance mea-
surements, scanning electron microscopy (SEM) and Auger electron spectroscopy (AES), respectively.
3. Results and discussion Fig. 1 shows the XRD patterns obtained from as-deposited Zr–Si–N films. The patterns only show diffraction peaks assigned to crystalline ZrN. However, other crystalline phase like Si3 N4 or Zr silicide cannot be observed. This result implies that Si is present in an amorphous phase of either Si3 N4 or Si. With the substrate bias decreasing from )200 to )100 V, the (1 1 1) peak becomes weak and the intensity of the (2 2 0) peak decreases significantly. The most important contribution to XRD peak broadening originates from particle size and micro-stress-induced alteration of the lattice. The chemical state of the Zr–Si–N films sputtered with bias )100 and )200 V were analyzed by XPS. As shown in Fig. 2, the bonding energies of N1s and Zr3d indicate the existence of ZrN. The bonding energies of Si2p and N1s peaks closely match those of Si3 N4 . But this compound phase is not detected by XRD due to its weak intensity. It is thought that the existing states of Si and Zr in the films are Si3 N4 -like phase and ZrN phase in
Fig. 1. XRD spectra of as-deposited Zr–Si–N films for substrate bias voltages of )100 and )200 V.
Y. Wang et al. / Microelectronic Engineering 71 (2004) 69–75
Fig. 2. XPS spectra of: (a) N1s, (b) Si2p, (c) Zr3d for Zr–Si–N films.
71
Zr–Si–N films. This kind of structure contributes to the excellent barrier property of Zr–Si–N films. The film morphology was examined using AFM. Fig. 3 shows the AFM images of Zr–Si–N films deposited on Si substrates with bias of )100 and )200 V, respectively, over a 10 10 lm area. A fairly smooth surface with a root mean square (RMS) value of 0.689 nm is obtained for the Zr– Si–N ()100 V) specimen as shown in Fig. 3(a). Furthermore, RMS of 1.026 nm is obtained for Zr–Si–N ()200 V) specimen as shown in Fig. 3(b). The difference between RMS surface roughness of the films suggests that high bias can roughen the surface of Zr–Si–N film. The sheet resistances of specimens were determined using the four-point probe technique. The variation of Cu sheet resistance is commonly used to examine the capability of diffusion barrier against Cu diffusion. It is well known that Cu diffuses fast in Si and forms Cu–Si compounds at a temperature as low as 200 °C [11]. The formation of Cu–Si compounds results in the increase of sheet resistances of Cu/Si contacts. Table 1 shows the sheet resistances of the Cu/Zr–Si–N/Si contact systems before and after annealing at 800 °C. It is found that the sheet resistances of specimens annealing in H2 /N2 gas mixture is still lower than those of as-deposited specimens at the same substrate bias after annealing at 800 °C. The sheet resistances can also be used to estimate the degree of intermixing reactions and changes of integrity across the metallization layer. The sheet resistance of the specimen rises abruptly indicating a severe intermixing or interfacial reactions occurred across all the Cu films. As can be seen from Table 1, no evidence for copper silicide formation is found for the specimen after annealing at 800 °C. In addition, it seems that the oxidation of Cu film is prevented in H2 /N2 gas mixture annealing which contributes to the decrease of the sheet resistances. X-ray diffraction spectra of Cu/Zr–Si–N/Si specimens before and after annealing were investigated. Fig. 4 shows the XRD patterns obtained from the as-deposited contact system and those annealed at 800 °C. In the spectrum from the asdeposited contact, the predominant reflection line from Cu (1 1 1) and those from Cu (2 0 0) with very weak intensity are observed, which indicates that
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Y. Wang et al. / Microelectronic Engineering 71 (2004) 69–75
Fig. 3. AFM micrographs of as-deposited Zr–Si–N films for substrate bias voltages of: (a) )100 V and (b) )200 V.
Cu film posses (1 1 1) texture. Sharpened (1 1 1) and (2 0 0) peaks of annealed-Cu films indicate the growth of Cu crystalline occurring during annealing, but other crystalline phase like Cu silicide or Zr silicide cannot be observed up to 800 °C. On the other hand, it has been reported that Cu (1 1 1)
provided higher electro-migration resistance than that of Cu (2 0 0) [12]. In the present experiment, the intensities of Cu (1 1 1) peak are larger than those of Cu (2 0 0) peaks for all specimens (the ratio of the intensities of Cu (1 1 1) to those of Cu (2 0 0) are 35 and 56 for Cu/Zr–Si–N()100 V)/Si and Cu/
Table 1 The sheet resistances of the Cu/Zr–Si–N/Si contacts before and after annealing at 800 °C Substrate bias (V) Annealing ambient Sheet resistance ðX=Þ
)100 As-deposited 0.029
Annealed 0.021
)200 As-deposited 0.028
Annealed 0.016
Y. Wang et al. / Microelectronic Engineering 71 (2004) 69–75
Fig. 4. XRD spectra of: (a) Cu/Zr–Si–N()100 V)/Si and (b) Cu/ Zr–Si–N()200 V)/Si contact systems annealed at 800 °C.
Zr–Si–N()200 V)/Si specimens, respectively, in which )100 and )200 V are the substrate bias voltages when depositing Zr–Si–N diffusion barriers). These results indicate that Zr–Si–N barrier can favor Cu (1 1 1) texture that contributes to the electro-migration resistance performances.
73
The surface morphology of the annealed Cu/Zr– Si–N()200 V)/Si multiplayer structure shown in Fig. 5 was obtained by employing SEM. It is evident that after annealing at 800 °C, the surface of Cu/Zr– Si–N/Si structure shows an increased average grain size. In the copper layer, annealing produces voids that expose the Zr–Si–N layer underneath, but the presence of the voids does not cause the barrier to fail. The origin of the voidsÕ formation is not connected with a Si–Cu interaction, but results from thermal stress in the Cu film itself. In order to inspect interfacial reaction of Cu/ Zr–Si–N/Si systems in detail, the depth profiles of AES were carried out. Fig. 6 shows that AES depth profiles of the Cu/Zr–Si–N()200 V)/Si specimens as-deposited and annealed at 800 °C. As shown in Fig. 6(a), the depth profile from the asdeposited contact system exhibits a well-separated stacked structure with a sharp transition of all elements at each interface. The depth profile of the as-deposited Cu/Zr–Si–N()100 V)/Si specimen is not shown in this article, but exhibits similarity to that of the as-deposited Cu/Zr–Si–N()200 V)/Si specimen. In the case of specimens annealed at 800 °C shown in Figs. 6(b) and (c), depth of profiles
Fig. 5. SEM micrographs of Cu/Zr–Si–N()200 V)/Si contact system after annealing at 800 °C.
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Y. Wang et al. / Microelectronic Engineering 71 (2004) 69–75
are similar and have no intermixing evidence at interfaces of Cu/Zr–Si–N and Zr–Si–N/Si. In addition, the scarce change in structure upon annealing indicates that the Zr–Si–N film be an excellent diffusion barrier, the diffusion of Cu and/ or Si through Zr–Si–N film is inhibited effectively. As is expected from the XRD spectra and the sheet resistance measurements, any noticeable change is not found even after annealing at 800 °C. 4. Conclusions In this investigation, we have examined the Zr– Si–N thin film as a barrier in Cu/Si contact. Amorphous Zr–Si–N films approximately 100 nm in thickness were deposited onto (1 1 1) Si substrates using radio frequency reactive magnetron sputtering from Zr and Si target materials in a mixture of argon and nitrogen. It is observed that the sheet resistances of Cu/Zr–Si–N/Si contact system annealing in H2 /N2 gas mixture is lower than those of as-deposited specimens even after annealing at 800 °C. Zr–Si–N thin films show excellent barrier property so that Cu–Si phase could not be detected in any of the specimens after annealing. In addition, the Cu/Zr–Si–N/Si contact systems keep structures unchanged after annealing at 800 °C for 1 h. These results imply that Zr–Si–N is a suitable diffusion barrier for the Cu metallization system from the views of expected electromigration resistance and thermal stability.
Acknowledgements This work was supported by the National Science Foundation (60036010 and 60176020) and Key Project Foundation of 863 (2001AA313090) of PR China.
References
Fig. 6. AES depth profiles of specimens: (a) as-deposited Cu/ ZrSiN()200 V)/Si, (b) Cu/ZrSiN()100 V)/Si annealed at 800 °C and (c) Cu/ZrSiN()200 V)/Si annealed at 800 °C.
[1] C.J. Chang, C.M. Chieh, Thin Solid Films 335 (1998) 146. [2] Y.W. Luh, W.W. Fa, L.D. Gey, W.C. Chang, O.K. Liang, Solid-State Electron. 45 (2001) 149. [3] L.K. Maung, Y.K. Lee, Li, S.T. Osipowicz, H.L. Seng, Mater. Sci. Eng. B 84 (2001) 217.
Y. Wang et al. / Microelectronic Engineering 71 (2004) 69–75 [4] A. Cros, M.O. Aboelfotoh, K.N. Tu, J. Appl. Phys. 67 (1990) 3328. [5] C.A. Chang, J. Appl. Phys. 67 (1990) 566. [6] Y.K. Lee, M. Latt, K. Jaehyung, K. Lee, Kangsoo, Mater. Sci. Semicond. Process 3 (2000) 179. [7] L.S. Hung, F.W. Saris, S.Q. Wang, J.W. Mayer, J. Appl. Phys. 59 (1986) 2416. [8] J.S. Reid, X. Sun, E. Kolawa, M.A. Nicolet, IEEE Electron Device Lett. 15 (1994) 298.
75
[9] E. Blanquet, A.M. Dutron, V. Ghetta, C. Bernard, R. Madar, Microelectron. Eng. 37-38 (1997) 189. [10] R.S. Liu, C.C. You, M.S. Tsai, S.F. Hu, Y.H. Li, C.P. Lu, Solid State Commun. 125 (2003) 445. [11] R.A. Donaton, B. Coenegrachts, M. Maenhoudt, I. Pollentier, H. Struyf, Microelectron. Eng. 55 (2001) 277. [12] K. Abe, Y. Harada, H. Onoda, J. Vac. Sci. Technol. B 17 (1999) 1464.