See Also: Intel Microprocessor Evolution, Microprocessor
One of the primary information sources we used on this topic is Info @ Intel, March, 1996.
Today’s microprocessors are constructed like multi-story buildings, with many
different layers of material combining to create a single, complex unit. Much like a
negative in photography, photolithography is used to create these layers by
imprinting the Transistor and Electric Circuit designs onto the Silicon wafer. The Intel Pentium processor contains 20 micro-thin layers of
materials such as Silicon dioxide, Aluminum, and Tungsten - all built up on a wafer using a process that requires more than 250
manufacturing steps. Each of these layers has its own unique pattern which, combined
with the other layers on the device, packs together the millions of individual
circuits that comprise the finished microprocessor.
Over Time, the line widths of circuits deposited on silicon have shrunk consistently.
Measured in Microns these line widths were along the order of 10 microns for the first Intel
processor. It was predicted at the time that it would be difficult to break the
1-micron barrier. By the end of 1996 the Intel Pentium Pro processor will be
produced in volume using a 0.35-micron process.
As you try to go below 0.2 microns photolithography issues such as Light Wavelengths and depth of field are formidable obstacles. For example, lithographers
must confront the task of building structures smaller than the wavelength of light
- a challenge similar to trying to paint a line narrower than the width of the
paintbrush being used. Simultaneously, in much the same way that a
photographer’s depth of field decreases as a wider lens increases resolution, the focus of
a photolithographer’s projected image begins to fade at distances well below a micron.