Lithography

The field of lithography is vitally important to the electronics industry.  It is the only process that can mass-produce microchips and other complex semiconductor devices.  Like many other semiconductor processes, it's found a use in making nanostructures out of semiconductor materials.

Lithography is actually just one step in the semiconductor fabrication process.  However, it is the only step that can effectively guide the other steps that are required.  The technique is all about patterning a substrate (or wafer) with a desired layout.  To begin, you need to coat the substrate with photoresist.  Next, the substrate has to be carefully aligned with its 'mask'.  The mask holds the key to the patterning process.  By selectively allowing light to pass through, only designated sections of the substrate are exposed.  The light will either break down the layer of photoresist or harden it.  The portions of photoresist that are weakened as a result can be removed with acid or other volatile substances.  Any photoresist that remains will act as a barrier for any subsequent process like epitaxy, doping, or etching.  It is with these sequences of photoresist layering, masking, exposure, photoresist removal, and semiconductor processing that makes up the semiconductor fabrication process.

On a given wafer, dozens or hundreds of chips can be made at the same time.  The technique is so thoroughly perfected that major chipmakers like Intel and AMD can churn out high-yields at quick speeds.

In nanotechnology, lithography has proven extremely useful in patterning a substrate for selective growth of nanostructures.  For instance you can prepare a substrate so that it will grow nanowires and quantum dots in only the selected areas.  Lithography can also pave the way for a number of other structures.

Unfortunately, there are limits to the smallest feature size that is possible with lithography.  That's because the light that is used to pass through the mask has a fundamental restriction known as the 'diffraction limit of light'.  Many industry experts are worried about this as the demand for faster computer chips grows.  Already, modern manufacturers are using high-power lithography to push the limits of the technique.  Using extreme ultraviolet rays, it's possible to have feature sizes on the order of 90 nm.  While it is possible to create lithographic machines that can go smaller, prohibitive costs are preventing all but the most powerful chipmakers to pursue the research. 

Because of this, lithography will never be able to make nanostructures directly.  This is also the reason why nanotechnology is so important for the future of electronics.  It's one of the only known ways that future miniaturization of electronics can proceed further beyond the fundamental limits of lithography.