Alumina Coated Sources

Aluminum oxide coated evaporation sources were developed to replace alumina crucible boats for some specific applications. Advantages of this evaporation source include good heat transfer and inertness of alumina (AO) with most metals. Additionally, the evaporant does not wet the alumina resulting in no resistance change of the boat when the material melts. Due to alumina’s non-wetting characteristics, the evaporant forms a sphere when melted, resulting in a point source.

Properties of Alumina

This type of evaporation source will give long life compared to the non-protected sources. Coated sources will require from thirty to fifty percent more power to affect an evaporation due to the difference in heat conduction. The aluminum oxide is semiconductor grade and is applied to the boat or basket by a plasma spray technique. Temperatures of 1850°C should be avoided, and when an evaporation is effected the power should be reduced slightly to avoid overheating.

Tungsten & Molybdenum Boats with Alumina Barriers

This type of source has been designed to give the benefit of a refractory metal boat and a ceramic barrier. The exposed metal area in the bottom of the boat allows the evaporant to be in good thermal contact with the source. The alumina barrier will inhibit the evaporant from creeping toward the heat sink or from wetting the entire boat.