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Particulates in e-beam deposited films

Most users get a fine film quality for their application using the Temescal and Wordentec e-beam evaporators without having to worry about optimizing it. However, some applications are extra sensitive to the film quality. For instance to make contacts to graphene it has been helpful for some users to pump the system down overnight to reduce the amount of adsorbed molecules that can interfere with the essentially 1D interface between graphene and metal contacts.

On this page we look at another issue that has bothered some users, namely particulates, especially in Au films.

Comparison of particulates in TiAu, Al, and Ag films from Temescal and Wordentec

Testing November/December 2018 by Rebecca Ettlinger and Evgeniy Shkondin

The number of particles that end up on the film depends on the material being deposited and the deposition parameters as well as the cleanliness of the wafer and the chamber. We have done some tests to compare particulates on the films in the Temescal and the Wordentec for different materials and process conditions.

Main conclusions:

A lower deposition rate gave fewer particles for both TiAu films and Al films (comparison of 10 Å/s and 2 Å/s).
Optimizing the deposition parameters (the soak and rise times and perhaps power level) can reduce the number of particles. If you would like to optimize the process for a material that you are working with, please contact the process responsible staff.
For TiAu layers, there are relatively many particles compared to, e.g., Al or Ni. Specifically for Au, this is apparently due to carbon contamination of the target material, which is reduced by long soaking times before the deposition starts.
There will be more particles on the film if the loading of the wafer does not go smoothly, so it is worthwhile to be careful and use the vacuum tweezers if possible.
There are fewer particles from just loading/pumping/venting/unloading wafers with no processing in the Wordentec than the Temescal, at least when tested in Nov/Dec 2018.

The full results of the testing can be found here: File:particles-pinholes test Temescal.pptx.

Reducing the particulates in TiAu films

Testing July/August 2019 by Evgeniy Shkondin and Patama Pholprasit

Deposition of Ti/Au revealed a big number of particles on the wafers. The amount has been heavily reduced by optimizing deposition conditions and choosing the right crucible. The particles are in fact gold droplets of various size ejected from the melt.

Main guidance and conclusions:

Ensure the chamber, shutters etc. are properly cleaned.
Use as pure Au target as possible.
Do not use ceramic crucible, put Au pellets directly into the dedicated Cu heart pocket. W-crucible can be considered (but so far we did not tested it).
Sweep pattern needs to be optimized so it coveres the bigger area of the target but avoid getting the beam to close to the edges.
Optimize soak/rise powers and times.
Use deposition rate of 2 Å/s. Ensure that the rise2 power is adequate for that rate.
Ensure appropriate PID values, since the deposition rate has to be stable during the evaporation.

The full results of the testing can be found here: Media:Au issues with Temescal.pptx.

Reducing the particulates in TiAu films

Testing spring 2021 by Evgeniy Shkondin

Deposition of Ti/Au revealed a big number of particles on the wafers. This issue keeps appearing. In spring 2021 we decided to monitor the particles each week to see if we overlooked something. The particles are in fact gold droplets of various size ejected from the melt.

No new factors were discovered. No relation between gold target mass and particles was found.

The full results of the testing in 2021 can be found here: Media:Au target monitoring.pptx.