I recently deposited LiF on the surface of my silicon detector made of a silicon semiconductor substrate. The top contact is aluminium and that is where the LiF was deposited on.
After deposition, I observed some cracks which led to some of the LiF come off the surface.
I normally use Edwards E306A Thermal Evaporator to perform the deposition process. The thickness of LiF deposited is about 6um.
Can anyone advise me on the best way to perform the deposition without have cracks after deposition? This can be from the viewpoint of pre-deposition, during or after the deposition.
Without knowing anything else, my first guess would be a difference in thermal expansion between film and deposit - is your substrate heated? it can be thickness-dependent whether the film delaminates or not, even if you use the same temperatures.
If it was a one-off observation, try again on a different substrate. Check your vacuum - if the aluminium oxidises, it might push LiF off. Or, even more simply, you might have incorporated defects into your film which lead to stress concentrations and cracking of the film. Have you checked EDX or SEM with Backscattered electron imaging for impurities?
If the deposition is not too time-consuming, it might be best to try again on a different substrate and if it works and the cracking does not happen again, it might just have been contamination of some kind.
I have to agree to Cornelia. Thermal Expansion might be the Problem. 6µm is quite thick. Are you very Close to the Evaporation source ? I guess that thickness takes some time. Thermal Management could help (cooling, longer and slower Deposition, higher distance to the Evaporator). Cleanliness of the surface is allwas a Topic (corona discharge).
Hi Thomas and Cornelia,
Thank you very much for your responses.
With regards to thermal expansion, it is possible and may not be easily overruled. Also the issue of defects or surface cleaning are good options.
In addition, i realised that, i might have been doing the deposition at higher rate and/or low vacuum.
It normally takes long time to do the deposition; typically 3-4 hours per sample, under normal circumstances.
Thank you all for your wonderful contributions
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