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Why Use a Diffusion Furnace?

Diffusion Furnace

What is diffusion?

Diffusion is the process of molecules moving from an area of high concentration to a low one. This occurs routinely within and between liquids, gases and solids in daily life. This process is exploited by diffusion furnaces. Furnaces elevate the temperature of workpieces and introduce gaseous elements to encourage solid state diffusion.

Solid state diffusion happens when the molecules of a substance mix with a host solid at the atomic level.

Diffusion Furnace

A diffusion furnace is a thermal processing unit with a cylindrical heating chamber that can be oriented either vertically or horizontally. This enables workpieces that are circular to be processed with perfect thermal uniformity. These workpieces can also function under partial vacuum conditions to ensure tight atmospheric control throughout operation.

Dopants and Semiconductors

When a semiconductor wafer is treated in a diffusion furnace, it is heated to within a setpoint temperature and subjected to a flow of gaseous molecules known as the vapor-phase. This phase diffuses into the solid substrate at the atomic level, this process is known as doping.  

Semiconductors, like silicon, display unique electronic properties between those of an insulator and a conductor. When dopants are introduced, they modulate those electronic properties and make them suitable for semiconductor device fabrication. They diffuse into the crystal lattice and become immobilized within the atomic structure, creating either an excess or deficiency of electron or electron holes. This is what alters the conductivity of the semiconducting wafer!

In order to increase the number of free electrons in the wafer´s atomic structure, elements such as phosphorus are used. In order to introduce an electro acceptor which creates extra electron-hole energy levels, gallium is used.