Essential Guide to Semiconductors, The

Building the Layer Cake

After a wafer is polished, it's time to start building up the layers of material that will become the transistors on our chip. A wafer is pure silicon, but it takes more than silicon to make a chip work. There are the metal wires, of course, but those will be added later. At this stage, we need to build up a few layers of silicon (which conducts electricity) alternating with a few layers of an insulator (which doesn't conduct electricity). These two types of material will be stacked, like layers of frosting between layers of cake. Later, we'll etch away some of this insulator (most of it, actually), leaving a carefully planned-out three-dimensional pattern of silicon and other materials that channel electricity in exactly ...