This concentration gradient is a function of the distance between the source and silicon, the temperature of the pre-deposition, and the composition of the gas ambient (oxidizing or non-oxidizing, presence of H₂O, etc.). Ideally, however, it is not a function of gas flow rate, which is low enough so that the gas between source and wafer is essentially stagnant. The concentration gradient results in the transfer of B₂O₃ to the silicon surface, and so produces a very thin, very highly doped region at the silicon wafer surface. The final level of doping and resulting sheet resistance is determined by time and the size of the concentration gradient. Note, however, that the pre-deposition temperature is so low that very little boron diffusion into the silicon actually takes place.

After the predeposition diffusion the dopants are situated close to the surface of the wafer. However, they must diffuse even farther to lower the overall concentration in order for some of the devices to work properly. In addition, oxygen and water vapor are introduced during the drive diffusion to grow a new oxide over the areas which were exposed to bare silicon during the photolithography process. This new oxide can be patterned again so that other selective diffusion processes can be performed to create other types of devices.