Surface activated bonding

'''Surface activated bonding''' ('''SAB''') is a non-high-temperature wafer bonding technology with atomically clean and activated surfaces. Surface activation prior to bonding by using fast atom bombardment is typically employed to clean the surfaces. High-strength bonding of semiconductors, metals, and dielectrics can be obtained even at room temperature.<ref>{{Cite web|url=https://www.mhi-machinetool.com/en/products/detail/wafer_bonding_machine.html|title=Room Temperature Wafer Bonding Machine BOND MEISTER｜Mitsubishi Heavy Industries Machine Tool Co., Ltd.|website=www.mhi-machinetool.com}}</ref><ref>{{Cite web|url=https://www.mhi.com/news/story/1201161491.html|title=MHI Develops World's First 12-inch Wafer Bonding Machine | Mitsubishi Heavy Industries, Ltd. Global Website|first=Mitsubishi Heavy Industries|last=Ltd|website=Mitsubishi Heavy Industries, Ltd.|date=16 January 2012 }}</ref>

== Overview == In the standard SAB method, wafer surfaces are activated by argon fast 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.<ref>{{Cite book |last=Tu |first=Yuan |title=Insights into Semiconductor Technologies: Transistor, Interconnect, Packaging, Lithography and Memory |date=2026 |publisher=Springer Nature Switzerland |isbn=978-3-032-03999-6 |edition=1st ed. 2026 |series=Synthesis Lectures on Engineering, Science, and Technology |location=Cham |pages=109 |language=en}}</ref>

==Researches on SAB== The SAB method has been studied for bonding of various materials, as shown in Table I. {| class="wikitable" |+Table I. Studies of standard SAB for various materials ! !Si !Ge !GaAs !SiC !Cu !Al2O3 !SiO2 |- |Si |<ref name=":1" /><ref name=":2" /> | |<ref name=":14">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 {{doi|10.7567/APEX.6.021801}}</ref> |<ref name=":3" /> | |<ref name=":0">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 {{doi|10.1149/1.2982908}}</ref><ref name=":15">{{Cite journal|last1=Ichikawa|first1=Masatsugu|last2=Fujioka|first2=Akira|last3=Kosugi|first3=Takao|last4=Endo|first4=Shinya|last5=Sagawa|first5=Harunobu|last6=Tamaki|first6=Hiroto|last7=Mukai|first7=Takashi|last8=Uomoto|first8=Miyuki|last9=Shimatsu|first9=Takehito|title=High-output-power deep ultraviolet light-emitting diode assembly using direct bonding|journal=Applied Physics Express|volume=9|issue=7|article-number=072101|doi=10.7567/apex.9.072101|bibcode=2016APExp...9g2101I|year=2016|s2cid=100054996 }}</ref> | |- |Ge | |<ref name=":4" /> | | | | | |- |GaAs |<ref name=":14" /> | | |<ref name=":5" /> | | | |- |SiC |<ref name=":3" /> | |<ref name=":5" /> |<ref name=":6" /> | | | |- |Cu | | | | |<ref name=":7" /><ref name=":8" /> | | |- |Al2O3 |<ref name=":0" /><ref name=":15" /> | | | | |<ref name=":0" /> | |- |SiO2 | | | | | | |Failure<ref name=":0" /> |} The standard SAB, however, failed to bond some materials such as SiO2 and polymer films. The modified SAB was developed to solve this problem, by using a sputtering deposited Si intermediate layer to improve the bond strength. {| class="wikitable" |+Table II. Modified SAB with Si intermediate layer ! !Bonding intermediate layer !References |- |SiO2-SiO2 |Sputtered Fe-Si on SiO2 |<ref>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 {{doi|10.1109/ECTC.2011.5898819}}</ref> |- |Polymer films |Sputtered Fe-Si on both sides |<ref>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 {{doi|10.7567/JJAP.54.101602}}</ref><ref name=":9" /><ref name=":10" /> |- |Si-SiC |Sputtered Si on SiC |<ref name=":11" /> |- |Si-SiO2 |Sputtered Si on SiO2 |<ref>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 {{doi|10.7567/JJAP.55.05FL01}}</ref> |} The combined SAB has been developed for SiO2-SiO2 and Cu/SiO2 hybrid bonding, without use of any intermediate layer. {| class="wikitable" |+Table III. Combined SAB using Si-containing Ar beam ! !Bond interface !References |- |SiO2-SiO2 |Direct bond interface |<ref name=":12" /> |- |Cu-Cu, SiO2-SiO2, SiO2-SiNx |direct bond interface |<ref name=":13" /> |}

== Technical specifications == {| class="wikitable" width="80%" |- | style="background:#CEE3F6" | Materials || * Semiconductor: Si-Si,<ref name=":1">{{Cite journal|last1=Takagi|first1=H.|last2=Kikuchi|first2=K.|last3=Maeda|first3=R.|last4=Chung|first4=T. R.|last5=Suga|first5=T.|date=1996-04-15|title=Surface activated bonding of silicon wafers at room temperature|journal=Applied Physics Letters|volume=68|issue=16|pages=2222–2224|doi=10.1063/1.115865|bibcode=1996ApPhL..68.2222T|issn=0003-6951}}</ref><ref name=":2">{{Cite journal|last1=Wang|first1=Chenxi|last2=Suga|first2=Tadatomo|date=2011-05-01|title=Room-Temperature Direct Bonding Using Fluorine Containing Plasma Activation|journal=Journal of the Electrochemical Society|language=en|volume=158|issue=5|pages=H525–H529|doi=10.1149/1.3560510|s2cid=97977240 |issn=0013-4651|url=http://jes.ecsdl.org/content/158/5/H525.full.pdf}}</ref> Ge-Ge,<ref name=":4">{{Cite journal|last1=Higurashi|first1=Eiji|last2=Sasaki|first2=Yuta|last3=Kurayama|first3=Ryuji|last4=Suga|first4=Tadatomo|last5=Doi|first5=Yasuo|last6=Sawayama|first6=Yoshihiro|last7=Hosako|first7=Iwao|date=2015-03-01|title=Room-temperature direct bonding of germanium wafers by surface-activated bonding method|journal=Japanese Journal of Applied Physics|language=en|volume=54|issue=3|article-number=030213|doi=10.7567/jjap.54.030213|bibcode=2015JaJAP..54c0213H|doi-access=free}}</ref> GaAs-SiC,<ref name=":5">{{Cite journal|last1=Higurashi|first1=Eiji|last2=Okumura|first2=Ken|last3=Nakasuji|first3=Kaori|last4=Suga|first4=Tadatomo|date=2015-03-01|title=Surface activated bonding of GaAs and SiC wafers at room temperature for improved heat dissipation in high-power semiconductor lasers|journal=Japanese Journal of Applied Physics|language=en|volume=54|issue=3|article-number=030207|doi=10.7567/jjap.54.030207|bibcode=2015JaJAP..54c0207H|doi-access=free}}</ref> SiC-SiC,<ref name=":6">{{cite journal|last1=Mu|first1=F.|last2=Iguchi|first2=K.|last3=Nakazawa|first3=H.|last4=Takahashi|first4=Y.|last5=Fujino|first5=M.|last6=Suga|first6=T.|title=Direct Wafer Bonding of SiC-SiC by SAB for Monolithic Integration of SiC MEMS and Electronics|journal=ECS Journal of Solid State Science and Technology|date=30 June 2016|volume=5|issue=9|pages=P451–P456|doi=10.1149/2.0011609jss}}</ref> Si-SiC,<ref name=":3">{{Cite journal|last1=Liang|first1=J.|last2=Nishida|first2=S.|last3=Arai|first3=M.|last4=Shigekawa|first4=N.|date=2014-04-21|title=Effects of thermal annealing process on the electrical properties of p+-Si/n-SiC heterojunctions|journal=Applied Physics Letters|volume=104|issue=16|page=161604|doi=10.1063/1.4873113|bibcode=2014ApPhL.104p1604L|s2cid=56359750|issn=0003-6951|url=http://dlisv03.media.osaka-cu.ac.jp/contents/osakacu/kiyo/10773118-104-16-161604.pdf }}</ref><ref name=":11">{{Cite journal|last1=Mu|first1=Fengwen|last2=Iguchi|first2=Kenichi|last3=Nakazawa|first3=Haruo|last4=Takahashi|first4=Yoshikazu|last5=Fujino|first5=Masahisa|last6=Suga|first6=Tadatomo|date=2016-04-01|title=Room-temperature wafer bonding of SiC–Si by modified surface activated bonding with sputtered Si nanolayer|journal=Japanese Journal of Applied Physics|language=en|volume=55|issue=4S|article-number=04EC09|doi=10.7567/jjap.55.04ec09|bibcode=2016JaJAP..55dEC09M|s2cid=124719605 }}</ref> etc. * Metal: Al-Al, Cu-Cu,<ref name=":7">{{Cite journal|last1=Kim|first1=T. H.|last2=Howlader|first2=M. M. R.|last3=Itoh|first3=T.|last4=Suga|first4=T.|date=2003-03-01|title=Room temperature Cu–Cu direct bonding using surface activated bonding method|journal=Journal of Vacuum Science & Technology A|volume=21|issue=2|pages=449–453|doi=10.1116/1.1537716|bibcode=2003JVST...21..449K|s2cid=98719282|issn=0734-2101}}</ref><ref name=":8">{{Cite journal|last1=Shigetou|first1=A.|last2=Itoh|first2=T.|last3=Matsuo|first3=M.|last4=Hayasaka|first4=N.|last5=Okumura|first5=K.|last6=Suga|first6=T.|date=2006-05-01|title=Bumpless interconnect through ultrafine Cu electrodes by means of surface-activated bonding (SAB) method|journal=IEEE Transactions on Advanced Packaging|volume=29|issue=2|pages=218–226|doi=10.1109/TADVP.2006.873138|s2cid=27663896|issn=1521-3323}}</ref> etc. * Dielectric: Polymer films,<ref name=":9">{{Cite journal|last1=Matsumae|first1=Takashi|last2=Nakano|first2=Masashi|last3=Matsumoto|first3=Yoshiie|last4=Suga|first4=Tadatomo|date=2013-03-15|title=Room Temperature Bonding of Polymer to Glass Wafers Using Surface Activated Bonding (SAB) Method|journal=ECS Transactions|language=en|volume=50|issue=7|pages=297–302|doi=10.1149/05007.0297ecst|bibcode=2013ECSTr..50g.297M |issn=1938-6737}}</ref><ref name=":10">{{Cite book|last1=Takeuchi|first1=K.|last2=Fujino|first2=M.|last3=Suga|first3=T.|last4=Koizumi|first4=M.|last5=Someya|first5=T.|title=2015 IEEE 65th Electronic Components and Technology Conference (ECTC) |chapter=Room temperature direct bonding and debonding of polymer film on glass wafer for fabrication of flexible electronic devices |date=2015-05-01|pages=700–704|doi=10.1109/ECTC.2015.7159668|isbn=978-1-4799-8609-5|s2cid=11395361}}</ref> SiO2,<ref name=":12">{{Cite journal|last1=He|first1=Ran|last2=Fujino|first2=Masahisa|last3=Yamauchi|first3=Akira|last4=Suga|first4=Tadatomo|date=2016-04-01|title=Combined surface-activated bonding technique for low-temperature hydrophilic direct wafer bonding|journal=Japanese Journal of Applied Physics|language=en|volume=55|issue=4S|article-number=04EC02|doi=10.7567/jjap.55.04ec02|bibcode=2016JaJAP..55dEC02H|s2cid=123656692 }}</ref><ref>{{Cite journal|last1=He|first1=Ran|last2=Fujino|first2=Masahisa|last3=Yamauchi|first3=Akira|last4=Suga|first4=Tadatomo|date=2015-03-01|title=Novel hydrophilic SiO2 wafer bonding using combined surface-activated bonding technique|journal=Japanese Journal of Applied Physics|language=en|volume=54|issue=3|article-number=030218|doi=10.7567/jjap.54.030218|bibcode=2015JaJAP..54c0218H|s2cid=119520218 |doi-access=free}}</ref> etc. * Cu/Dielectric Hybrid: Cu/SiO2 and Cu/SiO2/SiNx<ref name=":13">{{Cite journal|last1=He|first1=Ran|last2=Fujino|first2=Masahisa|last3=Yamauchi|first3=Akira|last4=Wang|first4=Yinghui|last5=Suga|first5=Tadatomo|date=2016-01-01|title=Combined Surface Activated Bonding Technique for Low-Temperature Cu/Dielectric Hybrid Bonding|journal=ECS Journal of Solid State Science and Technology|language=en|volume=5|issue=7|pages=P419–P424|doi=10.1149/2.0201607jss|s2cid=101149612|issn=2162-8769}}</ref> |- | style="background:#CEE3F6" | Advantages || * Low process temperature: room temperature–200 °C * No concerns of thermal stress and damages * High bonding quality * Semiconductor and metal bonding interfaces without oxides * Completely dry process without wet chemical cleaning * Process compatibility to semiconductor technology |- | style="background:#CEE3F6" | Drawbacks || * High vacuum level (10−4–10−7 Pa) |}

==References== {{reflist}}

Category:Wafer bonding Category:Semiconductor technology Category:Electronics manufacturing Category:Packaging (microfabrication) Category:Semiconductor device fabrication Category:Microelectronic and microelectromechanical systems