Construction of Microelectronic Devices

Details of building specific types of microelectronic devices are well described by Grovenor as an illustration, we consider only the chemical techniques involved in making a metallic contact to a silicon wafer surface. Preparation of a wafer of Si or other material and application of epitaxial layers of semiconducting or insulating materials, if required, were outlined in Section 19.2.1. The construction of shaped features on the wafer is usually done by photolithography, or ion- or electron-beam variants thereof. 

A positive photoresist is one that becomes more soluble in the developing fluid as a result of exposure to light, and so dissolves away leaving the desired pattern in the form of undissolved resist a negative resist becomes less soluble on irradiation, so that it is then the illuminated areas that remain. 

Organosilanes are particularly effective as positive ultraviolet photoresists (Section 3.5.1). The oxide layer exposed where the resist has been removed may then be etched with an appropriate solution (buffered aqueous HF in the case of a silica layer) to expose the silicon underneath. Application of the desired metal over the whole surface is then followed by removal of the remaining photoresist, taking the unwanted parts of the metal layer with it and leaving the metal contact on the Si that had been exposed by etching. Variations on this approach can be used to attach shaped deposits of other electronically active materials. 

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