EFG Process. Photo: Schott Solar
EFG Process. Photo: Schott Solar

EFG process - Edge-defined Film-fed Growth

The search for a more cost and material efficient production methode lead to the development of the EFG process. In 1965 sientists at Tyco Laboratories, Inc. invented the EFG process which was further developed (1971) into a process to produce photovoltaic silicon.

 

In the EFG process (edge-defined film-fed growth), an octagonal silicon pipe is directly pulled out of the cast and is then cut into slices by a laser.

 

This production method is based on the capillary action of liquid silicon.

Within a silicon melt a molded part made of graphite containing an octagonal gap is located. Capillary action causes the liquid silicon to rise in the gap. A film brought close to the gap catches the liquid silcone. Now the film is pulled up at a speed of approximately 1 - 2 cm/min.

The liquid silicon sets to an octagon at the bottom side of the film with a wall thickness of around 300 μm and an edge length of 125 mm. A laser cuts the tube into 125 by 125mm wafers.