Generalized bonding

Summary form only given. The bonding and etchback approach to SOI (BESOI) can be used to combine several different semiconductors on a single monolithically integrated substrate and to bond high-quality transparent substrates for display devices, piezoelectric substrates for surface acoustic wave devices, etc. The bonding and etch-back technique for silicon SOI structures utilizes thermally grown SiO₂ as the insulating layer and the bonding interfaces. Typically, a bonding temperature of at least 800°C is required to obtain bond strength sufficient to survive subsequent processing. Thus, bonding with a reactivity sputter deposited SiO₂ layer is suggested. The surface reactivity of the sputter SiO₂ can be made high enough to achieve bond energies at 165°C sufficient to permit mechanical polishing and subsequent chemical polishing to a couple of microns in thickness. Then the structure can be processed at much higher temperature without serious stress problems. Certain materials (such as Ge) do not have good adhesion to SiO₂. In such cases, it is expected that the use of a few monolayers of an appropriate adhesion material or another insulator with the desired adhesion may still permit bonding with an isolation layer. This has been demonstrated using a thin Si layer on a Ge crystal to promote adhesion of a sputter deposited SiO ₂ bonding layer. Finally, with bias sputtering, surface smoothness can be improved so substrates with surface morphologies somewhat too rough for direct bonding can still be bonded. These concepts have been demonstrated by successfully bonded and lapping Ge to Si, and Si to fused quartz