75 Wafer Bonding

Fig. 2.75 The wafer bonding process. Reprinted from Kan-dlikar and Grande (2002) with permission...

Tong, Q.-Y. Gosele, U. 1999. Semiconductor Wafer Bonding Science and Technology. John Wiley, New York. 

Schmidt, M. A. 1998. Wafer-to-wafer bonding for microstructure formation. Proc. IEEE 86 1575-1585. 

Tishinin, D.V., Dapkus, P.D., Bond, A.E., Kim, L, Lin, C.K., and O Brien, J., 1999, Vertical resonant couplers with precise coupling efficiency control fabricated by wafer bonding, IEEE Photon. Technol. Lett. 11(8) 1003-1005. 

The samples were pn junction diodes formed on an SOI wafer fabricated by wafer bonding technique. The thicknesses of the n-type top Si layer with resistivity of 2-4 fl cm, the oxide layer, and the n-type Si substrate with resistivity of 1-50 H cm are 5.7, 0.48, and 630 pm, respectively. The p region, which is 50 pm in diameter and 0.5 pm in depth, was... 

Mehra, A., Ayon, A. A., Microfabrication of high-temperature silicon devices using wafer bonding and deep reactive ion etching, IEEE J. Microelectromech. Syst. 1999, 8, 152-160. 

To form effective bonding between these wafers, very smooth surfaces are required, which are produced by means of CMP. After the wafer bonding and singulation of the dies, the fragile structures are protected, sometimes even under high-vacuum conditions, and can then be integrated into the system. 

Roughness Somenm lOnm Relaxed Exception wafer bonding w0.5nm... 

Particle density <0.02/cm2 Die-size dependent Relatively uncritical Exception wafer bonding < 1 /cm ... 

Surface contamination <1 X 10 /cm CMOS <5xl0/cm Mechanical devices product specific Uncritical Wafer bonding and BioMEMS need clean surface ... 

Residue particle density Advanced post-CMP cleaning processes typically fulfill the killer defect density requirements of <0.02/cm for microelectronic applications [14]. The defect density in microfabrication is relatively uncritical with the exception of wafer bonding, where a particle density [Pg.410]

Another approach to 3D integration is to use wafer bonding to stack die before singulation this approach is referred to as wafer-level 3D. There have been a variety of approaches to wafer-level 3D that have been demonstrated, which can be categorized by the wafer-bonding approach used oxide-to-oxide, copper-to-copper, polymer-to-polymer (or adhesive bonding), and mixtures of these approaches (such as redistribution layer bonding). Each of these four approaches will be introduced in this section, with emphasis placed on their application to 3D. The bond unit processes are described further in Section 15.4.2, and their associated CMP issues are discussed in detail in Section 15.5. 

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