Early in the days of electronics, the different components used in building circuits were discrete. Capacitors, inductors and resistors were soldered in place to connect them to other components in the circuit forming printed circuit boards. This approach was effective but included many inefficiencies. The discrete components wasted large amounts of material and by having conductor traces that covered large areas the opportunities for broken solder joints or errors in connections created problems.
The industry addressed these issues over time by advancing the methods by which complex circuits are built on semiconductor material. Many transistors can be fashioned by various means, like lithography, on silicon wafers. This approach of producing many identical circuits on a single substrate of silicon improved quality and quantity. Using this technique and silicon wafer dicing has produced very inexpensive methods by which complex circuits are made today. Building circuits on wafers involves masking, irradiation and doping.
The final circuit design is created using design software and the circuit is built up in layers on the silicon substrate. Each layer is constructed by covering parts of the substrate with photo resistive masking then exposing the surface to a specific radiation source. Masks are designed to limit exposure to very select areas. Between each exposure, other processes either remove or add material based on the pattern created by the mask.
Sources of radiation include ultraviolet light and x-rays with short wavelengths that accurately replicate the masks pattern. Photolithography is the process by which irradiated areas are affected. Following irradiation sometimes chemical washes are used to remove materials. Other times material is added by different means.
The application of different substances to the silicon, after masking, creates areas with varying electrical properties necessary for circuit operation. Methods such as atomic diffusion or ion implantation accomplish the doping process.
Successive layers of circuitry are built using these and other steps. The final wafer typically contains multiple copies of identical integrated circuits. The wafer can then be cut up into individual dies that are inserted into electronic equipment. The fascinating process of creating integrated circuitry on chips has enabled much of the progress in today’s technologies. These processes are constantly being improved to fuel advances in the semiconductor industry.