How the Annealing Furnace Works

The annealing furnace involves a process used in semiconductor device fabrication that consist of heating multiple semiconductor wafers in order to affect their electrical properties. Heat treatments are designed for different effects. Wafers can be heated in order to activate dopants, change film to film or film to wafer substrate interfaces; density deposited films, change states of grown films, repair damage from implants, move dopants or drive dopant from one film into another.

Annealing Properties
Annealing, in metallurgy and materials science, is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness, making it more workable. It involves heating a material to above its recrystallization temperature, maintaining a suitable temperature, and then cooling. In annealing, atoms migrate in the crystal lattice, and the number of dislocations decreases, leading to the change in ductility and hardness.

Annealing Function
In the cases of copper, steel, silver, and brass, this process is performed by heating the material (generally until glowing) for a while and then slowly letting it cool to room temperature in still air. Copper, silver and brass can be cooled slowly in air, or quickly by quenching in water, unlike ferrous metals, such as steel, which must be cooled slowly to anneal. In this fashion, the metal is softened and prepared for further work.

Annealing Equipment
An annealing furnace may be integrated into other furnace processing steps, such as oxidations, or may be processed on their own. Furnace anneals performed by equipment especially built to heat semiconductor wafers. Furnaces are capable of processing lots of wafers at a time, but each process can last between several hours and a day.

Annealing Process
Typically, large ovens are used for the annealing process. The inside of the oven is large enough to place the workpiece in a position to receive maximum exposure to the circulating heated air. For high volume process annealing, gas fired conveyor furnaces are often used. For large workpieces or high quantity parts, car bottom furnaces are used so workers can easily move the parts in and out. Once the annealing process is successfully completed, workpieces are sometimes left in the oven.


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