Fabrication Process and its Impact on Physical Design

Abstract

The biggest driving force behind growth in the semiconductor, computer, networking, consumer electronics, and software industries in the last half century has been the continuous scaling, or miniaturization, of the transistor. Computers and other electronic devices have become smaller, more portable, cheaper, easier to use, and more accessible to everyone. As long as we can make the transistor faster and smaller, make the wires that interconnect them less resistive to electrical current, and make each chip denser, the digital revolution will continue. The manufacture of ICs, like any other high volume manufacturing business, is very cost sensitive. The yield of the fab must be very high to be profitable. So in any given process generation, semiconductor manufacturers use process equipment and critical dimensions that allow them acceptable yields. As more and more chips are manufactured and tested in a process, the process matures and the yield of the process increases. When the yield increases, more aggressive (that is, smaller) critical dimensions can be used to shrink the layout. This process of shrinking the layout, in which every dimension is reduced by a factor is called scaling. In general, scaling refers to making the transistors, and the technology that connects them, smaller. As a transistor becomes smaller, it becomes faster, conducts more electricity, and uses less power, the cost of producing each transistor goes down, and more of them can be packed on a chip. If a chip is scaled, it leads to a smaller die size, increased yield, and increased performance. Suppose a chip in 0.25 micron process generation is x microns wide and x microns high. Assume a shrink factor of 0.7 from 0.25 to 0.18 micron process. Therefore, on 0.18 process, we can essentially produce a 0.7x micron wide and 0.7x micron high chip. That is, the scaled chip is half the size of the original chip, in terms of area. It will have better yield, due to smaller die size and it will have better performance due to faster transistors and shorter interconnect.