I deposited Ga2O3 thin film on fused quartz substrate at 500oc in Ar ambient by RF sputtering and then annealed at 900oc (very slow heating and very slow cooling i.e 1oc/min) in air ambient for 1 hour . Then I can see cracks on the film by optical microscope. But there was no cracks after deposition. How can I get crack-free film?
Shantanu Jana Hello!
I hope you are doing well.
Ga2O3 has several crystalline modifications. You can observe a polymorphic transition in the temperature range from 650 to 900 degrees (from ε to β-phase). This transition accompanied by a change in volume (probable cause of cracks...).
I'm afraid that it will not be possible to avoid cracks in this design. But you can try to select appropriate intermediate layer between Ga2O3 and substrate.
I hope my thoughts will be useful!
Andrei A. Kozlov Thank you for your valueable answer.
I want to clarify that I am using the target for sputtering which was already in beta phase of Ga2O3. So, I think transition may not be possible.
Shantanu Jana
Thomas Breuer gave the excellent explanation above. There is no crystall structure transfer in RF magnetron sputtering process. The resulting structure is formed through the process of atomic growth. Moreover, you can observe non-stoichiometric compound, for example Ga1.9O3.1 (oxygen-rich compound).
In other words, the similarity of the target material and film is only in chemical composition, but not in phase.
Your process condition may not be favorable to form beta phase in growth process.
To make sure you can do XRD analyses after deposition and after annealing process.
Best wishes, Andrei
Thank you all for your valueable answers. It is very helpful to me. Thank you again. Andrei A. Kozlov Thomas Breuer