Equipment: Usually, large chambers that can hold many wafers are used to conduct the diffusion process. The doping source is usually in gas or liquid phase. When it is a liquid source, it is typically carried out using nitrogen in gaseous form; that is, the carrier gas will be bubbled through the liquid source. Sometimes even for solid source the carrier gas may pass over a heated solid source. The inert gas is used so that it can provide enough volume and maintain a laminar flow. Even though liquid or gas sources are used, finally they are all converted to solid source. For example, if phosphorus oxy-chloride is used as a source, it will react with oxygen and form phosphorus pentoxide, which will be deposited on top of the wafer. If phosphine is used, that will also be reacted with oxygen, so that phosphorus pentoxide can form on the wafer.
When a solid source is used, the source will be in the form of slugs, which will be kept between the wafers. There are some advantages and disadvantages. The advantage is that these are safer to handle. There is no toxic wafer, at least at room temperature. The disadvantage is that cleaning is an issue; the slugs can break down, in which case, cleaning is an issue. The other disadvantage is the throughput is low; that is, the number of wafers that can be doped in unit time is lower in this method.