10 - Semiconductor technology

Abstract

This chapter highlights some unparalleled advances in the semiconductor industry of the past decade. Memory densities have increased by over a thousand times, the simple 8 bit microprocessors of the late 1970s have matured into 1 million transistor plus processors such as the MC68040, current handling and switching speeds have increased from a few milliamps to tens of amps and from a few kilohertz to over 200 MHz. Integrated circuits are fabricated by taking monocrystalline wafers of silicon and diffusing impurities into them under controlled conditions to form semiconducting structures within the material. These are then connected together using aluminum metallization or conductive polysilicon tracks. The tracks and diffusions are selectively performed using a photoresist coating, exposing it to a patterned mask, developing the resist to remove the unexposed resist and, thus, the silicon. Diffusions are achieved using heating within a gaseous atmosphere or by direct ion implantation. These processes are carried out on a very small and continually decreasing scale. The metallization tracks used in devices of 10 to 15 years ago were about 10–20 microns in width. This may be thinner than a human hair but is many times larger than the submicron widths appearing today.