FTP / Furnace Thermal Processing

Furnace Thermal Processing refers to thermal treatments performed at atmospheric pressure in a hot-walled quartz tube furnace under (1) oxidizing or (2) neutral/forming gas ambient.

The former case (also called thermal oxidation) is widely used for the growth of silicon dioxide (SiO₂) layers on Si substrates through the chemical reaction of Si with an oxidant gas like O₂, N₂O or water vapour (H₂O). The wet oxidation process (H₂O) is faster than the dry oxidation process (O₂, N₂O) leading to SiO₂ layers thicker but of lower density than the latter. In both cases the growth kinetics and thereby the resulting oxide thicknesses depend on the crystallographic orientation of the substrate. Typically, wet oxides are in the 0.2 to 1μm range in thickness and serve as masks against dopant implantation or isolation dielectrics (e.g., as field oxides in IC processing), while dry oxide films (3 to 100nm in thickness) are commonly used as gate insulators in CMOS technology.

Annealing is a thermal process where the substrate is exposed to temperatures in the 300 to 1100^oC range for a specific period of time in neutral (typically under N₂ flow) or forming gas (N₂/H₂) ambient. Temperature could be increased to the target temperature within a few minutes to a few hours depending on the application. Annealing in neutral ambient is commonly used for post-implantation dopant activation while annealing in forming gas serves as a post-metallization step.