The demonstration of low-temperature (350 °C) grown carbon nano-tubes for the applications of through silicon via in 3D stacking and power-via

Low temperature Carbon Nano-tubes (CNTs) growth technology is developed in this work with the insert of Al (Aluminum) between Ni (Nickel) and Ti (Titanium) as the reactant. The optimized Al thicknesses are also investigated. CNTs growth at the low temperature below 400 °C is the key factor for the back end of line compatible process integration. In this work, we grow the CNTs by thermal chemical vapor deposition process at 350 and 400 °C. The low ratio of peak ID/IG in Raman spectra and scanning electron microscope images proves the CNTs material quality. On the other hand, the high thermal conductivity (k) value of ∼50 W m − 1 K − 1 is also demonstrated. Both high material quality and k value on our low temperature grown CNTs show promising opportunities for the integration of semiconductor three dimensional packages and power-via related applications.

Carbon Nano-tubes (CNTs) are well-known materials for their excellent thermal and electrical properties.
1,21. P. Kim, L. Shi, A. Majumdar, and P. L. McEuen, “ Thermal transport measurement of individual multiwalled nanotubes,” Phys. Rev. Lett. 87, 215502 (2001). https://doi.org/10.1103/PhysRevLett.87.2155022. B. Q. Wei, R. Vajtai, and P. M. Ajayan, “ Reliability and current carrying capacity of carbon nanotubes,” Appl. Phys. Lett. 79, 1172 (2001). https://doi.org/10.1063/1.1396632 In our previous work,33. P.-Y. Lu, C.-M. Yen, S.-Y. Chang, Y.-J. Feng, C. Lien, C.-W. Hu, C.-W. Yao, M.-H. Lee, and M.-H. Liao, “ The demonstration of Carbon Nano-Tubes (CNTs) as a promising high Aspect Ratio (>25) Through Silicon Vias (TSVs) material for the vertical connection in the high dense 3DICs,” in International Electron Devices Meeting (IEDM), San Francisco, CA, 2020. we incorporated the growth of high-quality CNTs at ∼550 °C through the thermal chemical vapor deposition (TCVD) process using ferrocene precursors, into through silicon vias (TSVs) with excellent electrical and thermal properties, suitable for use in three-dimensional integrated circuits (3DICs). However, most of the works focus on the CNTs grown at high temperatures with better density, and there is very little literature that demonstrates the growth of CNTs at low temperatures below 400 °C and their possible application in advanced 3D packaging technology. In this work, we grow CNTs at temperatures as low as 350 and 400 °C and also investigate the metal thickness of the catalytic Al underlayer, to grow CNTs with good material quality and high thermal conductivity (k). Both of these properties prove the CNTs grown in this work to be perfectly suitable for the 3DICs, not only for TSVs but also for power via. Several works have reported the use of metal catalytic underlayer for the growth of CNTs under lower temperatures.4–9,11–144. N. Chiodarelli, Y. Li, D. J. Cott, S. Mertens, N. Peys, M. Heyns, S. D. Gendt, G. Groeseneken, and P. M. Vereecken, “ Integration and electrical characterization of carbon nanotubes via interconnects,” Microelectron. Eng. 88(5), 837–843 (2011). https://doi.org/10.1016/j.mee.2010.06.0175. M. Ahmad, J. V. Anguita, V. Stolojan, T. Corless, J.-S. Chen, J. D. Carey, and S. R. P. Silva, “ High quality carbon nanotubes on conductive substrates grown at low temperatures,” Adv. Funct. Mater. 25(28), 4419–4429 (2015). https://doi.org/10.1002/adfm.2015012146. Y. Xiao, Z. Ahmed, Z. Ma, C. Zhou, L. Zhang, and M. Chan, “ Low temperature synthesis of high-density carbon nanotubes on insulating substrate,” Nanomaterials 9, 473 (2019). https://doi.org/10.3390/nano90304737. H. Sugime, S. Esconjauregui, L. D'Arsie, J. Yang, A. W. Robertson, R. A. Oliver, S. Bhardwaj, C. Cepek, and J. Robertson, “ Low-temperature growth of carbon nanotube forests consisting of tubes with narrow inner spacing using Co/Al/Mo catalyst on conductive supports,” ACS Appl. Mater. Interfaces 7, 16819–16827 (2015). https://doi.org/10.1021/acsami.5b048468. Y.-M. Liu, Y. Sung, T.-T. Chen, H.-T. Wang, and M.-D. Ger, “ Low temperature growth of carbon nanotubes by thermal chemical vapor deposition using non-isothermal deposited Ni–P–Pd as co-catalyst,” Mater. Chem. Phys. 106(2–3), p 399–405 (2007). https://doi.org/10.1016/j.matchemphys.2007.06.0209. O. V. Yazyev and A. Pasquarello, “ Effect of metal elements in catalytic growth of carbon nanotubes,” Phys. Rev. Lett. 100, 156102 (2008). https://doi.org/10.1103/PhysRevLett.100.15610211. M. Cantoro, S. Hofmann, S. Pisana, V. Scardaci, A. Parvez, C. Ducati, A. C. Ferrari, A. M. Blackburn, K.-Y. Wang, and J. Robertson, “ Catalytic chemical vapor deposition of single-wall carbon nanotubes at low temperatures,” Nano Lett. 6(6), 1107–1112 (2006). https://doi.org/10.1021/nl060068y12. S. Esconjauregui, R. Xie, M. Fouquet, R. Cartwright, D. Hardeman, J. Yang, and J. Robertson, “ Measurement of area density of vertically aligned carbon nanotube forests by the weight-gain method,” J. Appl. Phys. 113, 144309 (2013). https://doi.org/10.1063/1.479941713. M. Chhowalla, K. B. K. Teo, C. Ducati, N. L. Rupesinghe, G. A. J. Amaratunga, A. C. Ferrari, D. Roy, J. Robertson, and W. I. Milne, “ Growth process conditions of vertically aligned carbon nanotubes using plasma enhanced chemical vapor deposition,” J. Appl. Phys. 90, 5308 (2001). https://doi.org/10.1063/1.141032214. S. Vollebregt, F. D. Tichelaar, H. Schellevis, C. I. M. Beenakker, and R. Ishihara, “ Carbon nanotube vertical interconnects fabricated at temperatures as low as 350 °C,” Carbon 71, 249–256 (2014). https://doi.org/10.1016/j.carbon.2014.01.035 In this work, we used Ni/Al/Ti as the metal underlayers for providing the appropriate amount of activation energy (Ea) for the synthesis of the CNTs. In another work,66. Y. Xiao, Z. Ahmed, Z. Ma, C. Zhou, L. Zhang, and M. Chan, “ Low temperature synthesis of high-density carbon nanotubes on insulating substrate,” Nanomaterials 9, 473 (2019). https://doi.org/10.3390/nano9030473 Xiao et al. used a similar combination of Ni/Al/Ni metal multilayer as the catalyst for the growth of the CNTs; but in their work, the reported Raman spectra values of peak (ID/IG) intensity, indicating the defect level, are high compared to our work. We demonstrate the composition of different structures and found that adding an Al layer77. H. Sugime, S. Esconjauregui, L. D'Arsie, J. Yang, A. W. Robertson, R. A. Oliver, S. Bhardwaj, C. Cepek, and J. Robertson, “ Low-temperature growth of carbon nanotube forests consisting of tubes with narrow inner spacing using Co/Al/Mo catalyst on conductive supports,” ACS Appl. Mater. Interfaces 7, 16819–16827 (2015). https://doi.org/10.1021/acsami.5b04846 or Pd layer88. Y.-M. Liu, Y. Sung, T.-T. Chen, H.-T. Wang, and M.-D. Ger, “ Low temperature growth of carbon nanotubes by thermal chemical vapor deposition using non-isothermal deposited Ni–P–Pd as co-catalyst,” Mater. Chem. Phys. 106(2–3), p 399–405 (2007). https://doi.org/10.1016/j.matchemphys.2007.06.020 has the opportunity to grow CNTs at low temperatures. In Ref. 77. H. Sugime, S. Esconjauregui, L. D'Arsie, J. Yang, A. W. Robertson, R. A. Oliver, S. Bhardwaj, C. Cepek, and J. Robertson, “ Low-temperature growth of carbon nanotube forests consisting of tubes with narrow inner spacing using Co/Al/Mo catalyst on conductive supports,” ACS Appl. Mater. Interfaces 7, 16819–16827 (2015). https://doi.org/10.1021/acsami.5b04846, Sugime et al. presented the effect on the CNT growth height compared to the change made in the Al metal layer thickness. The role of the Al layer is to prevent the interaction between the top and the bottom metal layers. In Ref. 99. O. V. Yazyev and A. Pasquarello, “ Effect of metal elements in catalytic growth of carbon nanotubes,” Phys. Rev. Lett. 100, 156102 (2008). https://doi.org/10.1103/PhysRevLett.100.156102, the authors present the concept behind the influence of different metal layers in the catalytic growth of CNTs, and it is shown that the lower value of the adatom diffusion barrier helps in providing high Ea for the CNT growth. The authors present the adatom diffusion barrier for Ni, Cu, and Ag as 0.39, 0.07, and 0.20 eV and conclude that the Cu metal is the most suitable catalyst for the growth in their work. In this work, we incorporate the knowledge from Ref. 99. O. V. Yazyev and A. Pasquarello, “ Effect of metal elements in catalytic growth of carbon nanotubes,” Phys. Rev. Lett. 100, 156102 (2008). https://doi.org/10.1103/PhysRevLett.100.156102 and found that Al has a lower adatom diffusion barrier value of 0.02 eV,1010. S. Valkealahti and M. Manninen, “ Diffusion on aluminum-cluster surfaces and the cluster growth,” Phys. Rev. B 57, 15533 (1998). https://doi.org/10.1103/PhysRevB.57.15533 much lower than that of Cu as reported in Ref. 99. O. V. Yazyev and A. Pasquarello, “ Effect of metal elements in catalytic growth of carbon nanotubes,” Phys. Rev. Lett. 100, 156102 (2008). https://doi.org/10.1103/PhysRevLett.100.156102.

The substrate area of 2 × 2 cm2 p-type Si (100) wafers was used in this work. In order to maintain the integrity of the experiment, the surface of the silicon wafer was cleaned thoroughly in ultrasonic cleaner with acetone, isopropanol, and DI water in the mentioned order. Next, we put the substrate die on the heater to heat for 5 min to dry off the excess water. A metal stack consisting of 100 nm Ti, 8–12 nm Al/10 nm Pd, and 2 nm Ni was sputtered in the order with a direct current (DC) power supply. The next step is the growth of CNT in a commercially available TCVD furnace. In the heating stage using 500/30 standard cubic centimeters per minute (s.c.c.m) of Ar/H2, followed by CNT growth using 180 s.c.c.m of C2H2, the flow rate is not varied for the growth, and the temperatures range from 350 to 400 °C. CNT growth time is 30 min for all the samples fabricated in this work. The grown CNT samples were characterized using a JSM-6390 scanning electron microscope (SEM), Hitachi H-7100 Transmission Electron Microscope (TEM), and Raman spectroscope with a 532 nm Ar+ laser. The thermal conductivity (k) value is measured by the 3-ω thermal conductivity value measurement system.

CNTs growth is carried out on p-Si substrate coated with Ti (100 nm), Al/Pd, and Ni (2 nm) [as shown in Fig. 1(a)], and the thickness of the Al film is varied from 8 to 12 nm on different samples. We compared the structure with and without the addition of the intermediate layer at 400 °C (the thickness of the intermediate layer is 10 nm), and it can be found that the height of the CNT with the addition of the Al layer is the highest [Fig. 1(b)]. Because the Al layer can reduce the sintered particles of the catalytic layer,11,1211. M. Cantoro, S. Hofmann, S. Pisana, V. Scardaci, A. Parvez, C. Ducati, A. C. Ferrari, A. M. Blackburn, K.-Y. Wang, and J. Robertson, “ Catalytic chemical vapor deposition of single-wall carbon nanotubes at low temperatures,” Nano Lett. 6(6), 1107–1112 (2006). https://doi.org/10.1021/nl060068y12. S. Esconjauregui, R. Xie, M. Fouquet, R. Cartwright, D. Hardeman, J. Yang, and J. Robertson, “ Measurement of area density of vertically aligned carbon nanotube forests by the weight-gain method,” J. Appl. Phys. 113, 144309 (2013). https://doi.org/10.1063/1.4799417 the height of the CNT is higher than the others. Through the abovementioned results, it was found that CNT can be grown at temperatures as low as 350 °C with the addition of an Al underlayer. In addition, the thickness should be optimized because the size of the thickness in the multi-layer structure will affect the interaction between the various metal layers during the growth of carbon nanotubes.77. H. Sugime, S. Esconjauregui, L. D'Arsie, J. Yang, A. W. Robertson, R. A. Oliver, S. Bhardwaj, C. Cepek, and J. Robertson, “ Low-temperature growth of carbon nanotube forests consisting of tubes with narrow inner spacing using Co/Al/Mo catalyst on conductive supports,” ACS Appl. Mater. Interfaces 7, 16819–16827 (2015). https://doi.org/10.1021/acsami.5b04846 In Fig. 2, we show the optimized thickness of the Al underlayer, which is suitable for the growth of CNT with good quality at a low temperature, and the CNT height is found to be the highest when the Al thickness is 10 nm.In Fig. 3, electron microscopy images (90° tilted) of CNTs grown on substrate temperature of 400 °C for different thicknesses of Al layers are shown. The images of the vertically aligned CNTs grow to a height of 320 nm. It can be seen from the SEM images that the arrangement is neat and dense, and it can be observed from the inset display of a typical Transmission Electron Microscopy (TEM) image from CNT grown at 400 °C, that the CNTs appear to be hollow. For our sample, the average diameter was found to be around 10 nm, with the smallest observed tubes being 8 nm and the largest around 12 nm.Figure 4 shows the ID/IG ratio from the Raman Spectra of CNT growth with Ni/Al/Ti (2/10/100 nm) metal underlayer, with different growth temperatures from 350 to 400 °C. As can be seen from the figure, the Raman intensity at 350 °C is the lowest. The lower values of the ID/IG ratio are related to the higher structural quality of CNTs.1313. M. Chhowalla, K. B. K. Teo, C. Ducati, N. L. Rupesinghe, G. A. J. Amaratunga, A. C. Ferrari, D. Roy, J. Robertson, and W. I. Milne, “ Growth process conditions of vertically aligned carbon nanotubes using plasma enhanced chemical vapor deposition,” J. Appl. Phys. 90, 5308 (2001). https://doi.org/10.1063/1.1410322 Thus, a corresponding ID/IG ratio of 0.78 represents high quality CNTs grown at 350 °C. In Fig. 5, the ID/IG ratio is compared with values obtained from the works of literature.5–7,14–165. M. Ahmad, J. V. Anguita, V. Stolojan, T. Corless, J.-S. Chen, J. D. Carey, and S. R. P. Silva, “ High quality carbon nanotubes on conductive substrates grown at low temperatures,” Adv. Funct. Mater. 25(28), 4419–4429 (2015). https://doi.org/10.1002/adfm.2015012146. Y. Xiao, Z. Ahmed, Z. Ma, C. Zhou, L. Zhang, and M. Chan, “ Low temperature synthesis of high-density carbon nanotubes on insulating substrate,” Nanomaterials 9, 473 (2019). https://doi.org/10.3390/nano90304737. H. Sugime, S. Esconjauregui, L. D'Arsie, J. Yang, A. W. Robertson, R. A. Oliver, S. Bhardwaj, C. Cepek, and J. Robertson, “ Low-temperature growth of carbon nanotube forests consisting of tubes with narrow inner spacing using Co/Al/Mo catalyst on conductive supports,” ACS Appl. Mater. Interfaces 7, 16819–16827 (2015). https://doi.org/10.1021/acsami.5b0484614. S. Vollebregt, F. D. Tichelaar, H. Schellevis, C. I. M. Beenakker, and R. Ishihara, “ Carbon nanotube vertical interconnects fabricated at temperatures as low as 350 °C,” Carbon 71, 249–256 (2014). https://doi.org/10.1016/j.carbon.2014.01.03515. Y. Xiao, S. Li, C. Prawoto, and M. Chan, “ Synthesis of carbon nanotube in sub-100 nm vias on Ni silicide,” in IEEE International Conference on Electron Devices and Solid State Circuits (EDSSC), 2018.16. Q. Wang, Y. Zheng, C. Zhou, M. Chan, and C. Y. Yang, “ Low-temperature grown vertically aligned carbon nanotube array for an optimal infrared bolometer,” Nanotechnology 32, 505719 (2021). https://doi.org/10.1088/1361-6528/ac28dc It can be seen from the distribution in the figure that at low growth temperatures, the values of CNT grown in this work are relatively low, and, hence, it can be proved that the quality is high and promising.At the last, in order to understand the heat dissipation performance of CNTs, we conducted analog measurements through the 3-omega thermal conductivity measurement system. We found that the k value was 54.6 and 21.6 (W/mK) on the samples with 400 and 350 °C processing (Fig. 6), respectively. In comparison to the k reported by Sugime et al. in their work,77. H. Sugime, S. Esconjauregui, L. D'Arsie, J. Yang, A. W. Robertson, R. A. Oliver, S. Bhardwaj, C. Cepek, and J. Robertson, “ Low-temperature growth of carbon nanotube forests consisting of tubes with narrow inner spacing using Co/Al/Mo catalyst on conductive supports,” ACS Appl. Mater. Interfaces 7, 16819–16827 (2015). https://doi.org/10.1021/acsami.5b04846 we have achieved a higher k value, which proves that the CNT grown in this work is best-suitable for heat dissipation in the integrated systems. Our 3-omega thermal conductivity measurement system has been calibrated with other commercial system well.

The growth of high quality multi-walled carbon nanotubes on conducting metallic layers at substrate temperatures of 350 °C is demonstrated. The addition of the Al layer plays an important role in this low temperature growth work, and the highest quality (ID/IG = 0.78 in Raman spectra) of carbon nanotubes is achieved using a 10 nm Al layer. The key to material quality is the ability to control the energy coupled to the catalyst particles. Finally, the k value of the grown CNT is relatively high (54.6 W/mK for CNT grown at 400 °C and 21.6 W/mK for CNT grown at 350 °C), which indicates the better heat dissipation performance for future applications of advanced packages and power via.

This work was supported by the Ministry of Science and Technology (MOST), Taiwan, under Grant Nos. 109-2628-E-002-003-MY3 and 110-2218-E-002-042-MBK. This work was also supported by the Ministry of Education, Taiwan, under Grant Nos. 110L892605, 110L7728, and 110HT512004. The discussion and the project funding support from industries (Intel and PSMC) are also highly appreciated.

Conflict of Interest

The authors have no conflicts to disclose.

Author Contributions

H.-Y. Lin: Data curation (lead); Methodology (lead); Writing – original draft (lead). Nilabh Basu: Formal analysis (lead); Writing – review & editing (lead). Sheng-Chi Chen: Project administration (supporting); Resources (supporting). Min-Hung Lee: Funding acquisition (supporting); Project administration (supporting); Resources (supporting). Ming-Han Liao: Conceptualization (lead); Project administration (lead); Resources (lead); Supervision (lead); Writing – review & editing (supporting).

The data that support the findings of this study are available from the corresponding author upon reasonable request.

REFERENCES

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