Surface Activated Bonding (SAB)

www.3dic.org/Surface activated bonding (SAB)

Surface activated bonding (SAB) is a low temperature wafer bonding technology with atomically clean and activated surfaces. Surface activation prior to bonding by using Ar beam bombardment is typically employed to clean and activate the surfaces. High strength bonding of semiconductor, metal, and dielectric can be obtained at <200°C or even at room temperature.

Overview

In the standard SAB method, wafer surfaces are activated by Ar atom bombardment in ultra-high vacuum (UHV) of 10−4–10−7 Pa. The bombardment removes adsorbed contaminants and native oxides on the surfaces. The activated surfaces are atomically clean and reactive for formation of direct bonds between wafers when they are brought into contact even at room temperature.


Standard SAB

Table I. Studies of standard SAB for various materials
Si Ge GaAs SiC Cu Al2O3 SiO2
Si [1] [2] [3] [3]
Ge [4]
GaAs [2] [5]
SiC [5] [6]
Cu [7]
Al2O3 [3] [3]
SiO2 Failure[3]

Modified SAB using Si intermediate layer

The standard SAB failed to bond some merterials such as SiO2 and polymer films. The modified SAB was developed to solve this problem, by using a sputtering deposted Si intermediate layer to improve the bond stregnth.

Table II. Modified SAB with Si intermediate layer
Bonding intermediate layer References
SiO2-SiO2 Sputtered Fe-Si on SiO2 [8]
Polymer films Sputtered Fe-Si on both sides [9]
Si-SiC Sputtered Si on SiC [10]
Si-SiO2 Sputtered Si on SiO2 [11]

Combined SAB for Cu/SiO2 hybrid bonding

The combined surface activated bonding (SAB) technique is developed for Cu/SiO2 hybrid bonding without any intermediate layer. This technique employs a combination of surface irradiation using a Si-containing Ar beam and prebonding attach-detach procedure prior to bonding in vacuum, followed by postbonding annealing in ambient pressure. The bonding method has also been found effective for SiO2-SiO2, SiO2-SiNx, and Cu-Cu bonding at 200°C. [12][13] The benefits of the combined SAB are low bonding temperature, excellent bond strength of dielectric-dielectric (SiO2-SiO2 and SiO2-SiNx) and Cu-Cu bonds for Cu/dielectric hybrid bonding, and absence of any deposited intermediate layer.

Table III. Combined SAB
Bond interface References
SiO2-SiO2 direct bond interface [12]
SiO2-SiNx direct bond interface [13]
Cu-Cu direct bond interface [13]

References

  1. H. Takagi, K. Kikuchi, R. Maeda, T. R. Chung, and T. Suga, “Surface activated bonding of silicon wafers at room temperature,” Applied Physics Letters, vol. 68, no. 16, pp. 2222–2224, Apr. 1996. Available: http://dx.doi.org/10.1063/1.115865
  2. 2.0 2.1 J. Liang, T. Miyazaki, M. Morimoto, S. Nishida, N. Watanabe, and N. Shigekawa, “Electrical Properties of p-Si/n-GaAs Heterojunctions by Using Surface-Activated Bonding,” Appl. Phys. Express, vol. 6, no. 2, p. 021801, Feb. 2013. Available: http://dx.doi.org/10.7567/APEX.6.021801
  3. 3.0 3.1 3.2 3.3 3.4 H. Takagi, J. Utsumi, M. Takahashi, and R. Maeda, “Room-Temperature Bonding of Oxide Wafers by Ar-beam Surface Activation,” ECS Trans., vol. 16, no. 8, pp. 531–537, Oct. 2008. Available: http://dx.doi.org/10.1149/1.2982908
  4. E. Higurashi, Y. Sasaki, R. Kurayama, T. Suga, Y. Doi, Y. Sawayama, and I. Hosako, “Room-temperature direct bonding of germanium wafers by surface-activated bonding method,” Jpn. J. Appl. Phys., vol. 54, no. 3, p. 030213, Mar. 2015. Available: http://dx.doi.org/10.7567/JJAP.54.030213
  5. 5.0 5.1 E. Higurashi, K. Okumura, K. Nakasuji, and T. Suga, “Surface activated bonding of GaAs and SiC wafers at room temperature for improved heat dissipation in high-power semiconductor lasers,” Jpn. J. Appl. Phys., vol. 54, no. 3, p. 030207, Mar. 2015. Available: http://dx.doi.org/10.7567/JJAP.54.030207
  6. F. Mu, K. Iguchi, H. Nakazawa, Y. Takahashi, M. Fujino, and T. Suga, “Direct Wafer Bonding of SiC-SiC by SAB for Monolithic Integration of SiC MEMS and Electronics,” ECS J. Solid State Sci. Technol., vol. 5, no. 9, pp. P451–P456, Jul. 2016. Available: http://dx.doi.org/10.1149/2.0011609jss
  7. T. H. Kim, M. M. R. Howlader, T. Itoh, and T. Suga, “Room temperature Cu–Cu direct bonding using surface activated bonding method,” Journal of Vacuum Science & Technology A, vol. 21, no. 2, pp. 449–453, Mar. 2003. Available: http://dx.doi.org/10.1116/1.1537716
  8. R. Kondou and T. Suga, “Room temperature SiO2 wafer bonding by adhesion layer method,” presented at the Electronic Components and Technology Conference (ECTC), 2011 IEEE 61st, 2011, pp. 2165–2170. Available: http://dx.doi.org/10.1109/ECTC.2011.5898819
  9. T. Matsumae, M. Fujino, and T. Suga, “Room-temperature bonding method for polymer substrate of flexible electronics by surface activation using nano-adhesion layers,” Japanese Journal of Applied Physics, vol. 54, no. 10, p. 101602, Oct. 2015. Available: http://dx.doi.org/10.7567/JJAP.54.101602
  10. F. Mu, K. Iguchi, H. Nakazawa, Y. Takahashi, M. Fujino, and T. Suga, “Room-temperature wafer bonding of SiC–Si by modified surface activated bonding with sputtered Si nanolayer,” Japanese Journal of Applied Physics, vol. 55, no. 4S, p. 04EC09, Apr. 2016. Available: http://dx.doi.org/10.7567/JJAP.55.04EC09
  11. K. Tsuchiyama, K. Yamane, H. Sekiguchi, H. Okada, and A. Wakahara, “Fabrication of Si/SiO2/GaN structure by surface-activated bonding for monolithic integration of optoelectronic devices,” Japanese Journal of Applied Physics, vol. 55, no. 5S, p. 05FL01, May 2016. Available: http://dx.doi.org/10.7567/JJAP.55.05FL01
  12. 12.0 12.1 R. He, M. Fujino, A. Yamauchi, and T. Suga, “Combined surface-activated bonding technique for low-temperature hydrophilic direct wafer bonding,” Japanese Journal of Applied Physics, vol. 55, no. 4S, p. 04EC02, Apr. 2016. Available: http://dx.doi.org/10.7567/JJAP.55.04EC02
  13. 13.0 13.1 13.2 R. He, M. Fujino, A. Yamauchi, Y. Wang, and T. Suga, “Combined Surface Activated Bonding Technique for Low-Temperature Cu/Dielectric Hybrid Bonding,” ECS Journal of Solid State Science and Technology, vol. 5, no. 7, pp. P419–P424, 2016. Available: http://dx.doi.org/10.1149/2.0201607jss