Liquid Source diffusion system:

The figure shows thermal diffusion setup with a liquid dopant source.

A carrier gas like nitrogen is bubbled through the dopant liquid and the vapor is carried into the furnace.

Oxygen is also used when an oxide surface needs to be created along with doping.

Liquid sources are extremely convenient since the doping process can be readily initiated or terminated by controlling gas source through bubbler.

Amount of dopant transported to slice is controlled by adjusting the temperature of bubbler.

As liquid sources boron bromide BBr3 or phosphoryl chloride POCl3 can be used.

Since many wafers can be processed simultaneously, this method is quite favorable.

Gaseous Source diffusion system:

The above diagram shows the gas manifold system for a thermal diffusion system.

A carrier gas (nitrogen, argon, etc) is enriched with the desired dopant (also in gaseous form, e.g. phosphine $PH_3$ or diborane $B_2H_6$) and led to the silicon wafers, on which the concentration balance can take place.

There is also a reaction gas, like oxygen, if an oxide layer also needs to be formed.

Gaseous sources are even more convenient than the liquid.

It is a common practice to use excess dopant gas concentration to make system relatively insensitive t gas flow rate.

A chemical trap is made is used to dispose unreacted dopant gases which are usually dangerous.