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A method for AlCu interconnect electromigration performance predicting and monitoring
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Microelectronic Engineering 85 (2008) 577–581 www.elsevier.com/locate/mee
A method for AlCu interconnect electromigration performance predicting and monitoring Wenjie Zhang a
a,b,c,*
, Leeward Yi
a,b,c
, Pingyi Chang c, Jin Wu
c
Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, China b Graduate School of Chinese Academy of Sciences, Beijing, China c Grace Semiconductor Manufacturing Corporation, Thin Film Department, Guoshoujing Road 818#, Zhangjiang Hi-Teck Park, Shanghai 201203, China Received 23 January 2006; accepted 23 October 2007 Available online 30 October 2007
Abstract The physical properties of (bottom)Si/SiO2/Ti(top) and (bottom)Si/SiO2/Ti/TiN/Al(0.5 wt.% Cu)(top) structures by different processes were compared and studied. The resistivities of thin Ti films and the reflectivities of thin Al alloy films were found to correlate to their microstructure as well as the mean time to fail (MTTF) in electromigration (EM) testing. A method to predict and monitor the EM performance of the AlCu interconnects was proposed. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Electromigration; Resistivity; Reflectivity
1. Introduction Thin AlCu films with Ti and TiN underlayers are still widely used in silicon very large scale integration (VLSI) technology as interconnects for its certain advantages in lithographic processing and the good adhesion to the SiO2 surface [1]. However, with the critical dimension shrinking to sub quarter-micron, the electrical current density is large enough to induce serious electromigration (EM) failures. In order to get a robust AlCu interconnect to resist the EM failures, the industry and academe have been making huge effort to find out better manufacturing processes to prolong the mean-time-to-fail (MTTF) of EM failures [2,3]. As early as 1980s, the microstructures of the interconnects had been found to dominate the interconnect EM performance [4]. After that, lots of work proved that the AlCu film texture was one of the most * Corresponding author. Address: Grace Semiconductor Manufacturing Corporation, Thin Film Department, Guoshoujing Road 818#, Zhangjiang Hi-Teck Park, Shanghai 201203, China. E-mail address: [email protected] (W. Zhang).
0167-9317/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2007.10.003
important factors [5,6]. While for interconnects manufacturing, because of the long cycles of the EM testing, to obtain a method with quick turn between interconnect properties with finial EM performance is always wanted. Here, we tried to find out the relationship between the interconnect microstructures, such as the texture, and normal physical properties, such as the film resistivity and the reflectivity. The normal physical properties are the best vehicle for monitoring and predicting the interconnect EM performance for its quick measurement procedure and very convenient execution. In this work, we studied single Ti films and Al(0.5 wt.% Cu) films on Ti/TiN underlayers. Ti films deposited by ionized-metal-plasma (IMP) sputtering method compared with Ti films by conventional direct-current (DC) magnetron sputtering. The effect of different Ti underlayers on the texture and EM lifetime of AlCu interconnects was confirmed. To find a quick monitor scheme of AlCu interconnects, the relationship of the surface roughness, reflectivity, resistivity and crystalline textures as well as the grain size distribution of AlCu films or Ti films were investigated systematically in detail. Reflectivity of (bottom)Si/
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W. Zhang et al. / Microelectronic Engineering 85 (2008) 577–581
SiO2/Ti/TiN/AlCu(top) and resistivity of (bottom)Si/SiO2/ Ti(top) were found to be capable to predict Al(1 1 1) and Ti(0 0 2) texture. Based on the correlation between the reflectivity and MTTF, a quick method for the EM performance predicting and monitoring was proposed. 2. Experiments In this work, we used three kinds of film stacks: (A) Si/ SiO2/Ti; (B) Si/SiO2/Ti/TiN/AlCu; (C) Si/SiO2/Ti/TiN/ AlCu/TiN. In these three structures, from left to right, the films are layered from bottom to the top. The former two structures were for physical properties study and the last structure for EM testing. At first, 100 nm SiO2 was deposited onto 8-inch silicon wafers by plasma enhanced chemical vapor deposition (PE-CVD). Then three kinds of Ti films were prepared for structure (A): standard Ti (named as s-Ti) film processed by standard DC magnetron sputtering with a nitrogen contaminated Ti target, pure Ti (p-Ti) processed by the same method but with a pure target, and i-Ti film by IMP sputtering. All the Ti films were kept at a same thickness of 30 nm. For structure (B), 20 nm TiN film and 400 nm Al (0.5 wt.% Cu) film were sputtered in succession within the same system by DC magnetron sputtering without vacuum-break. For structure (C), 50 nm TiN were also sputtered sequentially to cap the AlCu film surface and the whole stack was processed interconnect patterning, packaging and final EM testing. For structure (A) and (B), single 30 nm-Ti films and stack of 30 nm-Ti/20 nm-TiN/400 nm-AlCu were comparatively investigated as deposited with the following metrological techniques: reflectivity measurement at the wavelength of 463 nm, surface roughness measurement by scanning probe microscopy (SPM), the texture analysis by x-ray diffraction (XRD) and AlCu grain contrast images by focused-ion-beam (FIB). The textures of the AlCu and Ti film were examined by the XRD rocking curves of the Al(1 1 1) and Ti(0 0 2) planes. The full-width at half-maximum (FWHM) of the rocking curve were compared as the index of texture. The surface roughness was evaluated by the root-mean-square (RMS) of the surface height. AlCu grain size distributions of the structure (B) were analyzed by taking each grain as a circle and its diameter as the grain size. 3. Results and discussion 3.1. AlCu properties with different Ti underlayers Fig. 1a shows the rocking curves of Al(1 1 1) plane on different Ti/TiN underlayers. Fig. 1b shows the FWHM of Ti(0 0 2) and Al(1 1 1) planes with the different Ti/ TiN underlayers. From the two figures, we can find a strong correlation between the texture of Al(1 1 1) and Ti(0 0 2). And i-Ti improved Al(1 1 1) texture formation because of the better Ti(0 0 2) texture compared to s-Ti and p-Ti. This means that the Ti film texture controls
Fig. 1. Ti texture and AlCu texture with different Ti deposition processes: (a) rocking curves of Al(1 1 1) in structure (B); (b) Al(1 1 1) and Ti(0 0 2) FWHM in structure (A) and (B).
the AlCu film texture formation, which is consistent with others’ work [6]. Interestingly, the roughness of AlCu surface in structure (B) shows a strong correlation with the Al(1 1 1) texture and surface reflectivity, see Fig. 2a. Because the Ti layer thickness is relatively thin, its reflectivity is dominated by the thickness, see Fig. 3a. But the resistivities of the thin Ti layers in structure (A) had correlations to Ti(0 0 2) texture, see Fig. 3b. The roughness and reflectivity correlation of AlCu films is apparent. The correlation between roughness and texture can be explained by the structure evolution during processing polycrystalline films. During Al deposition, the grain boundaries are mobile and the grain structure evolves during the coalescence process and continues to evolve during film thickening [7]. Furthermore, the process temperature is relatively high (300 °C) and film is thick enough. So different crystalline planes with different growth rates is adequately exhibited. If more Al grains have (1 1 1) texture, more Al atoms will be deposited with the same growth rate
W. Zhang et al. / Microelectronic Engineering 85 (2008) 577–581
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Fig. 3. Relationship of the reflectivity, thickness and texture of Ti: (a) Ti reflectivity and thickness in structure (A); (b) Ti resistivity and (0 0 2) FWHM in structure (A).
Fig. 2. Relationship of the roughness, reflectivity and texture of AlCu: (a) Al(1 1 1) FWHM, surface roughness and reflectivity of structure (B); (b) SPM images of structure (B) with i-Ti underlayer; (c) SPM images of structure (B) with p-Ti underlayer.
parallel to the surface. Thus, a smoother surface will be showed. Fig. 2b and c show the AlCu surface roughness of structure (B) by SPM with i-Ti and p-Ti underlayers. But for Ti films, the roughness or reflectivity have no correlation with texture. A very possible causation is the immobile grain boundaries of Ti films [7]. Moreover, the process temperature of Ti deposition (100 °C) is much lower than Al and the Ti film is very thin. So the grain size and orientation distributions of Ti films are worse than that of Al films. The transmition electron microscopy (TEM) images in Fig. 4 confirmed that Ti has much smaller grains
Fig. 4. TEM images of structure (B) with i-Ti underlayer.
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than AlCu in structure (B). That is why the Ti has much larger FWHM than Al in overall, and shows no correlation between roughness and texture as AlCu does. If Ti films have better (0 0 2) texture, more Ti grains will have parallel crystalline planes distribution and the film has relatively less defects such as the impurities. This will reduce the electron scattering and result low resistivity. 3.2. Correlation of AlCu reflectivity and MTTF of EM To confirm the texture impact on EM lifetime, package level data were collected. AlCu interconnects were processed by using structure (C) with different Ti underlayers : s-Ti, p-Ti and i-Ti. Two 8-inch wafers were used for each condition. All six wafers were synchronously processed the interconnect fabrication. The EM testing was carried with the same temperatures of 240 °C and the current density of 1 MA/cm2 for a metal line with width and length of 2.5 lm and 800 lm. Twenty samples were randomly chosen from each wafer. The MTTF distribution was plotted in Fig. 5. The structure (C) with p-Ti underlayer had much longer MTTF than s-Ti as underlayer, but the structure with i-Ti did not fail any one sample within the whole 1000 h testing which means much longer MTTF than the other two structures. The average and standard deviation of the grain size were listed in Table 1, and the ratio of the mean value to square of the sigma as well as the MTTFs were also calculated. The Al(1 1 1) texture and the grain size distribution were both the contributors to the results according to the conclusions in [4], however, the MTTF of i-Ti based AlCu interconnect indicates the texture of Al(1 1 1) is the major factor. The EM results showed that higher reflectivity resulting a longer MTTF. Given the relationship in Fig. 2, the results show that the
Table 1 Grain size data of structure (B) with different underlayers Underlayer type
S-Mean (lm)
r-Sigma (lm)
S/r2 (lm 1)
MTTF (hours)
s-Ti p-Ti i-Ti
0.94 0.75 0.66
0.70 0.51 0.41
1.9 2.9 3.9
21 317 >1000
reflectivity of Al films with Ti/TiN underlayers can be used as a quick monitor scheme for EM MTTF evaluation. 3.3. Quick method for EM performance prediction and monitoring The above results showed that we can use the AlCu reflectivity in structure (B) to predict and monitor the AlCu interconnect microstructure and the final EM performance. In the technology development phase, this is a quick method for AlCu interconnect EM reliability prediction. We can choose many process conditions and take the reflectivity of AlCu in structure (B) as the first-priority criteria. Then pick out the conditions which have large reflectivity to do further reliability and physical measurement. The reflectivity measurement is a standard requirement in all interconnect fabs and itself a very quick process, and this measurement can tell the with-in-wafer uniformity. Most important, this method could save much time because the long cycles of EM testing. Also, in the production phase, the reflectivity of structure (B) is a good item to monitor the interconnect quality. In the other hand, if the study starts from the Ti underlayer in Ti/TiN/AlCu structures, the resistivity of single Ti films can be used as the initial filter for better processes. In summary, we think that using the reflectivity to predict and monitor the intercon-
Fig. 5. EM MTTF results of structure (C) with i-Ti, p-Ti and s-Ti underlayers.
W. Zhang et al. / Microelectronic Engineering 85 (2008) 577–581
nect EM performance is a promising method, and its feasibility and precision are under further investigation. 4. Conclusions The physical properties including the reflectivity, resistivity, surface roughness and texture as well as cross-section topography of different Si/SiO2/Ti and Si/SiO2/Ti/ TiN/AlCu films were studied. The following results were found:
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Acknowledgements The authors would like to thank Prof. Shi of Fudan University for her help in XRD measurement and Mrs. Wendy Chen, Mr. Jerry Li as well as Dr. Jiang Bin, Mr. Sandy Zhang, Dr. Hongwei Huang and Mrs. Rita Hou of QRA Department of Grace Semiconductor Manufactory Company for their FIB and TEM analysis in this work. References
1. AlCu interconnect texture is controlled by the substrate texture. i-Ti is the best for excellent Al(1 1 1) texture comparing with s-Ti and p-Ti. AlCu films texture is correlated to its reflectivity and Ti film texture is correlated to the resistivity. 2. AlCu interconnect EM MTTF correlates to the reflectivity of AlCu films on Ti/TiN underlayers and resistivity of Ti underlayers. The reflectivity of AlCu and resistivity of Ti can be used as quick feedback to predict and monitor the AlCu interconnect EM performance.
[1] K.N. Tu, J. Appl. Phys. 94 (2003) 5451–5473. [2] C.K. Hu, K.P. Rodbell, T.D. Sullivan, K.Y. Lee, D.P. Bouldin, IBM J. Res. Develop. 39 (1995) 465–497. [3] R.G. Filippi et al., Thin Solid Film 388 (2001) 303–314. [4] S. Vaidya, A.K. Sinha, Thin Solid Films 75 (1981) 253. [5] D.B. Knorr, D.P. Tray, Appl. Phys. Lett. 59 (1991) 3241–3243. [6] R. Jaiswal et al., Proc. Adv. Metal. Conf. (1999) 735–739. [7] C.V. Thompson, Annu. Rev. Mater. Sci. 30 (2000) 159–190.
Microelectronic Engineering 85 (2008) 577–581 www.elsevier.com/locate/mee
A method for AlCu interconnect electromigration performance predicting and monitoring Wenjie Zhang a
a,b,c,*
, Leeward Yi
a,b,c
, Pingyi Chang c, Jin Wu
c
Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, China b Graduate School of Chinese Academy of Sciences, Beijing, China c Grace Semiconductor Manufacturing Corporation, Thin Film Department, Guoshoujing Road 818#, Zhangjiang Hi-Teck Park, Shanghai 201203, China Received 23 January 2006; accepted 23 October 2007 Available online 30 October 2007
Abstract The physical properties of (bottom)Si/SiO2/Ti(top) and (bottom)Si/SiO2/Ti/TiN/Al(0.5 wt.% Cu)(top) structures by different processes were compared and studied. The resistivities of thin Ti films and the reflectivities of thin Al alloy films were found to correlate to their microstructure as well as the mean time to fail (MTTF) in electromigration (EM) testing. A method to predict and monitor the EM performance of the AlCu interconnects was proposed. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Electromigration; Resistivity; Reflectivity
1. Introduction Thin AlCu films with Ti and TiN underlayers are still widely used in silicon very large scale integration (VLSI) technology as interconnects for its certain advantages in lithographic processing and the good adhesion to the SiO2 surface [1]. However, with the critical dimension shrinking to sub quarter-micron, the electrical current density is large enough to induce serious electromigration (EM) failures. In order to get a robust AlCu interconnect to resist the EM failures, the industry and academe have been making huge effort to find out better manufacturing processes to prolong the mean-time-to-fail (MTTF) of EM failures [2,3]. As early as 1980s, the microstructures of the interconnects had been found to dominate the interconnect EM performance [4]. After that, lots of work proved that the AlCu film texture was one of the most * Corresponding author. Address: Grace Semiconductor Manufacturing Corporation, Thin Film Department, Guoshoujing Road 818#, Zhangjiang Hi-Teck Park, Shanghai 201203, China. E-mail address: [email protected] (W. Zhang).
0167-9317/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2007.10.003
important factors [5,6]. While for interconnects manufacturing, because of the long cycles of the EM testing, to obtain a method with quick turn between interconnect properties with finial EM performance is always wanted. Here, we tried to find out the relationship between the interconnect microstructures, such as the texture, and normal physical properties, such as the film resistivity and the reflectivity. The normal physical properties are the best vehicle for monitoring and predicting the interconnect EM performance for its quick measurement procedure and very convenient execution. In this work, we studied single Ti films and Al(0.5 wt.% Cu) films on Ti/TiN underlayers. Ti films deposited by ionized-metal-plasma (IMP) sputtering method compared with Ti films by conventional direct-current (DC) magnetron sputtering. The effect of different Ti underlayers on the texture and EM lifetime of AlCu interconnects was confirmed. To find a quick monitor scheme of AlCu interconnects, the relationship of the surface roughness, reflectivity, resistivity and crystalline textures as well as the grain size distribution of AlCu films or Ti films were investigated systematically in detail. Reflectivity of (bottom)Si/
578
W. Zhang et al. / Microelectronic Engineering 85 (2008) 577–581
SiO2/Ti/TiN/AlCu(top) and resistivity of (bottom)Si/SiO2/ Ti(top) were found to be capable to predict Al(1 1 1) and Ti(0 0 2) texture. Based on the correlation between the reflectivity and MTTF, a quick method for the EM performance predicting and monitoring was proposed. 2. Experiments In this work, we used three kinds of film stacks: (A) Si/ SiO2/Ti; (B) Si/SiO2/Ti/TiN/AlCu; (C) Si/SiO2/Ti/TiN/ AlCu/TiN. In these three structures, from left to right, the films are layered from bottom to the top. The former two structures were for physical properties study and the last structure for EM testing. At first, 100 nm SiO2 was deposited onto 8-inch silicon wafers by plasma enhanced chemical vapor deposition (PE-CVD). Then three kinds of Ti films were prepared for structure (A): standard Ti (named as s-Ti) film processed by standard DC magnetron sputtering with a nitrogen contaminated Ti target, pure Ti (p-Ti) processed by the same method but with a pure target, and i-Ti film by IMP sputtering. All the Ti films were kept at a same thickness of 30 nm. For structure (B), 20 nm TiN film and 400 nm Al (0.5 wt.% Cu) film were sputtered in succession within the same system by DC magnetron sputtering without vacuum-break. For structure (C), 50 nm TiN were also sputtered sequentially to cap the AlCu film surface and the whole stack was processed interconnect patterning, packaging and final EM testing. For structure (A) and (B), single 30 nm-Ti films and stack of 30 nm-Ti/20 nm-TiN/400 nm-AlCu were comparatively investigated as deposited with the following metrological techniques: reflectivity measurement at the wavelength of 463 nm, surface roughness measurement by scanning probe microscopy (SPM), the texture analysis by x-ray diffraction (XRD) and AlCu grain contrast images by focused-ion-beam (FIB). The textures of the AlCu and Ti film were examined by the XRD rocking curves of the Al(1 1 1) and Ti(0 0 2) planes. The full-width at half-maximum (FWHM) of the rocking curve were compared as the index of texture. The surface roughness was evaluated by the root-mean-square (RMS) of the surface height. AlCu grain size distributions of the structure (B) were analyzed by taking each grain as a circle and its diameter as the grain size. 3. Results and discussion 3.1. AlCu properties with different Ti underlayers Fig. 1a shows the rocking curves of Al(1 1 1) plane on different Ti/TiN underlayers. Fig. 1b shows the FWHM of Ti(0 0 2) and Al(1 1 1) planes with the different Ti/ TiN underlayers. From the two figures, we can find a strong correlation between the texture of Al(1 1 1) and Ti(0 0 2). And i-Ti improved Al(1 1 1) texture formation because of the better Ti(0 0 2) texture compared to s-Ti and p-Ti. This means that the Ti film texture controls
Fig. 1. Ti texture and AlCu texture with different Ti deposition processes: (a) rocking curves of Al(1 1 1) in structure (B); (b) Al(1 1 1) and Ti(0 0 2) FWHM in structure (A) and (B).
the AlCu film texture formation, which is consistent with others’ work [6]. Interestingly, the roughness of AlCu surface in structure (B) shows a strong correlation with the Al(1 1 1) texture and surface reflectivity, see Fig. 2a. Because the Ti layer thickness is relatively thin, its reflectivity is dominated by the thickness, see Fig. 3a. But the resistivities of the thin Ti layers in structure (A) had correlations to Ti(0 0 2) texture, see Fig. 3b. The roughness and reflectivity correlation of AlCu films is apparent. The correlation between roughness and texture can be explained by the structure evolution during processing polycrystalline films. During Al deposition, the grain boundaries are mobile and the grain structure evolves during the coalescence process and continues to evolve during film thickening [7]. Furthermore, the process temperature is relatively high (300 °C) and film is thick enough. So different crystalline planes with different growth rates is adequately exhibited. If more Al grains have (1 1 1) texture, more Al atoms will be deposited with the same growth rate
W. Zhang et al. / Microelectronic Engineering 85 (2008) 577–581
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Fig. 3. Relationship of the reflectivity, thickness and texture of Ti: (a) Ti reflectivity and thickness in structure (A); (b) Ti resistivity and (0 0 2) FWHM in structure (A).
Fig. 2. Relationship of the roughness, reflectivity and texture of AlCu: (a) Al(1 1 1) FWHM, surface roughness and reflectivity of structure (B); (b) SPM images of structure (B) with i-Ti underlayer; (c) SPM images of structure (B) with p-Ti underlayer.
parallel to the surface. Thus, a smoother surface will be showed. Fig. 2b and c show the AlCu surface roughness of structure (B) by SPM with i-Ti and p-Ti underlayers. But for Ti films, the roughness or reflectivity have no correlation with texture. A very possible causation is the immobile grain boundaries of Ti films [7]. Moreover, the process temperature of Ti deposition (100 °C) is much lower than Al and the Ti film is very thin. So the grain size and orientation distributions of Ti films are worse than that of Al films. The transmition electron microscopy (TEM) images in Fig. 4 confirmed that Ti has much smaller grains
Fig. 4. TEM images of structure (B) with i-Ti underlayer.
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W. Zhang et al. / Microelectronic Engineering 85 (2008) 577–581
than AlCu in structure (B). That is why the Ti has much larger FWHM than Al in overall, and shows no correlation between roughness and texture as AlCu does. If Ti films have better (0 0 2) texture, more Ti grains will have parallel crystalline planes distribution and the film has relatively less defects such as the impurities. This will reduce the electron scattering and result low resistivity. 3.2. Correlation of AlCu reflectivity and MTTF of EM To confirm the texture impact on EM lifetime, package level data were collected. AlCu interconnects were processed by using structure (C) with different Ti underlayers : s-Ti, p-Ti and i-Ti. Two 8-inch wafers were used for each condition. All six wafers were synchronously processed the interconnect fabrication. The EM testing was carried with the same temperatures of 240 °C and the current density of 1 MA/cm2 for a metal line with width and length of 2.5 lm and 800 lm. Twenty samples were randomly chosen from each wafer. The MTTF distribution was plotted in Fig. 5. The structure (C) with p-Ti underlayer had much longer MTTF than s-Ti as underlayer, but the structure with i-Ti did not fail any one sample within the whole 1000 h testing which means much longer MTTF than the other two structures. The average and standard deviation of the grain size were listed in Table 1, and the ratio of the mean value to square of the sigma as well as the MTTFs were also calculated. The Al(1 1 1) texture and the grain size distribution were both the contributors to the results according to the conclusions in [4], however, the MTTF of i-Ti based AlCu interconnect indicates the texture of Al(1 1 1) is the major factor. The EM results showed that higher reflectivity resulting a longer MTTF. Given the relationship in Fig. 2, the results show that the
Table 1 Grain size data of structure (B) with different underlayers Underlayer type
S-Mean (lm)
r-Sigma (lm)
S/r2 (lm 1)
MTTF (hours)
s-Ti p-Ti i-Ti
0.94 0.75 0.66
0.70 0.51 0.41
1.9 2.9 3.9
21 317 >1000
reflectivity of Al films with Ti/TiN underlayers can be used as a quick monitor scheme for EM MTTF evaluation. 3.3. Quick method for EM performance prediction and monitoring The above results showed that we can use the AlCu reflectivity in structure (B) to predict and monitor the AlCu interconnect microstructure and the final EM performance. In the technology development phase, this is a quick method for AlCu interconnect EM reliability prediction. We can choose many process conditions and take the reflectivity of AlCu in structure (B) as the first-priority criteria. Then pick out the conditions which have large reflectivity to do further reliability and physical measurement. The reflectivity measurement is a standard requirement in all interconnect fabs and itself a very quick process, and this measurement can tell the with-in-wafer uniformity. Most important, this method could save much time because the long cycles of EM testing. Also, in the production phase, the reflectivity of structure (B) is a good item to monitor the interconnect quality. In the other hand, if the study starts from the Ti underlayer in Ti/TiN/AlCu structures, the resistivity of single Ti films can be used as the initial filter for better processes. In summary, we think that using the reflectivity to predict and monitor the intercon-
Fig. 5. EM MTTF results of structure (C) with i-Ti, p-Ti and s-Ti underlayers.
W. Zhang et al. / Microelectronic Engineering 85 (2008) 577–581
nect EM performance is a promising method, and its feasibility and precision are under further investigation. 4. Conclusions The physical properties including the reflectivity, resistivity, surface roughness and texture as well as cross-section topography of different Si/SiO2/Ti and Si/SiO2/Ti/ TiN/AlCu films were studied. The following results were found:
581
Acknowledgements The authors would like to thank Prof. Shi of Fudan University for her help in XRD measurement and Mrs. Wendy Chen, Mr. Jerry Li as well as Dr. Jiang Bin, Mr. Sandy Zhang, Dr. Hongwei Huang and Mrs. Rita Hou of QRA Department of Grace Semiconductor Manufactory Company for their FIB and TEM analysis in this work. References
1. AlCu interconnect texture is controlled by the substrate texture. i-Ti is the best for excellent Al(1 1 1) texture comparing with s-Ti and p-Ti. AlCu films texture is correlated to its reflectivity and Ti film texture is correlated to the resistivity. 2. AlCu interconnect EM MTTF correlates to the reflectivity of AlCu films on Ti/TiN underlayers and resistivity of Ti underlayers. The reflectivity of AlCu and resistivity of Ti can be used as quick feedback to predict and monitor the AlCu interconnect EM performance.
[1] K.N. Tu, J. Appl. Phys. 94 (2003) 5451–5473. [2] C.K. Hu, K.P. Rodbell, T.D. Sullivan, K.Y. Lee, D.P. Bouldin, IBM J. Res. Develop. 39 (1995) 465–497. [3] R.G. Filippi et al., Thin Solid Film 388 (2001) 303–314. [4] S. Vaidya, A.K. Sinha, Thin Solid Films 75 (1981) 253. [5] D.B. Knorr, D.P. Tray, Appl. Phys. Lett. 59 (1991) 3241–3243. [6] R. Jaiswal et al., Proc. Adv. Metal. Conf. (1999) 735–739. [7] C.V. Thompson, Annu. Rev. Mater. Sci. 30 (2000) 159–190.