Lithography in Integrated Circuit Device Fabrication

To see a world in a grain of sand And a heaven in a wild flower Hold infinity in the palm of your hand And eternity in an hour. 

There are a variety of ways transistors can be categorized, including the following  

The main difference between the JFET and the MOSFET is that the gate on the MOSEET, which is the input to the FET, is insulated by a thin dielectric material (silicon dioxide, referred to as gate oxide) from the other two electrodes of the transistor. In contrast, the gate of the JFET forms a physical p-n junction with the other electrodes of the transistor. JFETs are used extensively in GaAs integrated circuits.  

MOSEETs gained wide acceptance in logic applications in the 1970s and have since remained the workhorse transistor in IC products. They are of two types. 

The gate is the input electrode in each MOSFET. The source and the drain electrodes are heavily doped with u-type or p-type dopants, respectively, consistent with the type of the transistor. These two electrodes supply the majority current carriers in the transistor. Because the nMOSFET uses electrons as the primary carriers, its channel is termed u-type. In contrast, the pMOSFET has a p-channel, formed hy holes from the source to the drain. The n-channel MOSFET is fabricated inside a p-well, while the p-channel MOSFET is fabricated inside an u-well.  

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The ability to make ever smaller solid-state devices by improved lithography techniques has led to the development of so-called beam lead Schottky-barrier diode detectors and mixers in which diodes are fabricated by the same techniques used to make integrated circuits, and for this reason, they can be included in these circuits. Figure 7 shows such a beam-lead detector/mixer made by Virginia Diodes of Charlottesville, VA [15]. This same configuration is used in fabricating the varactor devices used for frequency multiplication discussed in the preceding section. 

Epitaxy—The growth of crystalline layers of semiconducting materials in a layered structure. Integrated circuits—Complex electronic circuits fabricated using multiple growth and lithography/ pattern transfer stages to produce many miniature electronic elements on a monolithic device. 

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