We saw that material can be deposited on the silicon wafer by various techniques such as PVD, CVD etc. The methods which modify the silicon wafer are also needed for IC manufacturing and they are ion implantation, diffusion and oxidation. We saw the details of diffusion earlier.  In this section, we will learn about the ion implantation technique.

Basics: Silicon, phosphorous and boron and solids. They can be added by diffusion, which is a relatively less expensive process. However, the depth of doping and the quantity of doping is not precisely controllable. Hence the transistor dimensions would not be very precise.  When the transistor dimensions were 10 micron (i.e.10,000 nm)or so, if the variability in doping level is 100 nm, it was acceptable because it was only 1%. When the transistor size itself is 100 nm, this much variability is not acceptable. For the ICs with small transistors, ion implantation is used. In ion implantation, the phosphorous (or boron) must be first ionized.  Then they must be accelerated and made to impinge on the wafers. Then they will penetrate into the wafer. This is similar to firing bullets into a solid wooden door. The bullets will get embedded into the wood.