9 - Semiconductor technology

Abstract

This chapter provides an overview of the semiconductor technology. Integrated circuits are fabricated by taking monocristaline wafers of silicon and diffusing impurities into them under controlled conditions to form semiconducting structures within the material. These are then connected together using aluminium metallization or conductive polysilicon tracks. The tracks and diffusions are performed selectively 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 10–15 years ago were about 10–20 μm in width. Semiconductor structures are formed around P and N types of diffusions caused by a lack or excess of electrons within the crystal lattice. With these basic blocks, capacitors, transistors, diodes, and resistors can be fabricated and connected in a way similar to that in which discrete components are utilized on a printed circuit board. There are two types of transistor that can be made in this way. The first type is the bipolar transistor whose structure is shown in. It consists of three semiconductor diffusions to form an N–P–N or a P–N–P sandwich. The second type is the MOS transistor, which is small, with reasonable switching capability but with reduced current capability.