Essential Guide to Semiconductors, The

Let's Get Small

What exactly are these engineers measuring with their very small rulers? They measure something they call effective length, often abbreviated L_eff in engineering lingo. Broadly speaking, the effective length is the thickness of the thinnest thing that can be manufactured reliably. Effective length depends very much on the maturity of the fab and its equipment, the experience of the technicians in the clean room, the company's tolerance for risk versus aggressiveness, and the amount of money it's willing to invest in the process. The best (i.e., the smallest) effective length achievable varies from company to company, and even from fab to fab within a company. Some large companies operate a few fabs on the cutting edge of current ...