Thermally evaporating aluminum presents several challenges due to incompatibilities with the materials that commonly comprise deposition boats/crucibles. During the initial melt of aluminum, the surface tension of the liquid metal will cause it to wet the ceramic walls and ‘wick’ up the crucible or boat. After deposition – as the molten aluminum cools – the lower surface tension of the solid metal causes it to recede, stressing the walls of the crucible and often causing it to crack. One common method of preventing crucible cracking is to empty the source of all molten aluminum by evaporating it dry after each deposition; however, this requires a vent and material loading cycle after each aluminum layer, which is not suitable for load-lock or cluster integrated systems, and is very time consuming.
Beyond this, Aluminum can actually wick all the way to the copper posts causing a short. When the boat being used is made from refractory metals, the aluminum alloys to form brittle compounds that crack easily. It is common to see metal boats break after only 1-3 depositions. For standalone systems without a load lock, Angstrom has developed a proprietary evaporation source capable of up to about 100 aluminum depositions without degradation of the source or film performance. You can find more information on this source here.
For cluster or load lock integrated systems, Angstrom has developed a solution using an automated material dispensing system. To learn more about our aluminum evaporation solutions, or to see a demonstration, please contact us.
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