Diffusion furnaces are used for applications that require sustained, high temperatures at moderate vacuum. This could include thermal oxide growth, doping, and dopant diffusion. Typically, these furnaces are quite large and can accommodate a large quantity of substrates. Thermal oxide growth on silicon is carried out at very high temperatures accompanied by the flow of oxygen containing gas. Oxides grown this way are very high quality in terms of dielectric and morphological properties.

Wafers can also be doped in diffusion furnaces by exposing them to a flux of dopant atoms by sublimation/evaporation from a solid/liquid source or by a gas source. Further to this, dopant diffusion may be carried out by heating wafers for a time necessary to achieve the desired doping profile.