Wafer Bonding Techniques

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... 

Bulk micromachining relies on several etching techniques and creates projections of planar photolithographic masks in 3 dimensions. Surface micromachining relies on sacrificial layer and wafer bonding techniques. It creates true 3D structures as a stack of 2D patterned layers. Hence, it is more correct to refer to both micromachining techniques as two and a half dimensional (2% D). 

Wafer bonding techniques are developed to allow building of more complex 3D structures and to perform micropackaging on the wafer level. 

A. Cozma, Development of wafer bonding techniques with application to self-testable silicon pressure sensors, unpublished, Ph.D. Thesis, K. Univ. Leuven, Belgium, 1998. 

N. Miki, Wafer bonding techniques for MEMS, Sensor Letters, 3(4), 11, 2005. 

The fabrication uses the parylene-C wafer bonding technique at a low temperature of 280 °C. Here, an oxygen plasma-treated parylene-C can bond directly to SisN4 with an average bonding strength of 23 MPa. 

The wafer bonding technique has been used to encapsulate MEMS devices before the dicing process. Wafers (silicon or glass) with recessed microcavities are used to bond to the MEMS device wafer. The microcavity provides a protection cap to the micromechanical component. The hermetic sealing between the bonded wafers will prevent water (during dicing operation) from coming into the cavity. It will also delay moisture diffusion from the envi-... 

Figure 5.1.12 shows a typical bulk-micromachined structure fabricated on an SOI wafer by use of the previously described etching and bonding techniques. 

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