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Heterointegration
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Heterointegration is the assembling of devices realized from different materials with specific functionalities on a single substrate for complex system-on-a-chip solutions. In general, there are three different heterointegration approaches: # epitaxy, # wafer bonding, and # hybrid (i.e., using both epitaxy and wafer bonding). Packaging architecture Heterointegration urges the system designer to combine digital, analog, and radio-frequency (RF) components in a single system and to shrink down the geometry so that systems are integrated on a package environment. The principle of heterointegration of different technologies in a layer by layer approach leads to a cost effective merge of different component technologies enabling multifunctional systems. Most compound semiconductors (CS)s exhibit a strong lattice and thermal mismatch with silicon (Si).<ref nameGosele/> “These incompatibilities strongly limit the quality of CS epitaxial layers grown on Si substrates.”<ref nameGosele/> A large density of dislocations, many antiphase domains, and autodoping effects can affect both the carrier mobility and the leakage current in the devices.<ref nameGosele/> Growth of a metamorphic composite buffer leads to relatively higher quality CS layers because there is a reduction in antiphase domains, a bridge between widely differing lattice constants, and a relaxing of strain energy and gliding dislocations.<ref nameGosele/> Wafer bonding Wafer bonding and layer transfer technologies can realize the combination of dissimilar semiconductor materials without the need for direct epitaxy.<ref nameGosele/> Initially, the donor and host wafers can be tightly joined to form a single entity,<ref nameGosele/> or they can be bond with an intermediate layer to form a single entity.<ref name=Gosele/> The second step consists of releasing a thin layer from the donor wafer after the bonding process.<ref nameGosele/> This can be done by mechanical grinding, lapping, and polishing, or by selective etching with an acid water mixture. An obvious drawback is the cost involved in possibly losing the complete starting CS wafer.<ref nameGosele/> This can also be accomplished by mechanical lateral cleaving from the donor wafer after bonding to the host wafer.<ref nameGosele/> The seed substrate can then be reused to make another wafer.<ref nameGosele/> Alternately, selective lateral chemical etching may be performed of a sacrificial layer introduced between the substrate and the layer to be transferred.<ref name=Gosele/> Lastly, cleaving a semiconductor thin layer of the wafer is performed by ion implantation of hydrogen and/or helium energetic ions laterally to create a mechanically weak zone a few hundred nanometers below the surface of the donor wafer. The donor and host wafers with an intermediate layer are bonded tightly together and subjected to a low temperature anneal at a temperature in the 200-500°C range.<ref nameGosele/> This forms lateral microcracks parallel to the boding surface and produces direct splitting of the donor wafer.<ref nameGosele/> The process is termed ‘ion-cutting’, or the ‘ion-cut process’.<ref name=Gosele/> 
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