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hypothetical example simulating deposition
Posted Apr 13, 2015, 3:45 a.m. EDT Version 5.0 1 Reply
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I'm trying to simulate the thermal stresses after a fabrication process in which I'm depositing one domain at a certain temperature, change the temperature, deposit another domain, change the temperature again, deposit another domain,... and then finally bring the whole structure to a final temperature.
I found a tutorial which I think may be pretty helpful for this.
www.comsol.com/model/thermal-stresses-in-a-layered-plate-273
I simulated the above scenario okay but I am having trouble doing so in 3D.
According to the simulation, the stress is non-constant only in the domain present initially and in the firsly deposited domain. in the domains that are deposited later, the stress is perfectly constant throughout the entirety of the domains. This does not seem correct to me (or is it?). Does anyone have a suggestion for how to improve my simulation? The only major change I think I did compared to the tutorial was I changed the matrix for the initial stress conditions (from 2D to 3D) and my boundary conditions are rollers where as the boundary conditions in the tutorial were for points and of the y-displacement-type.
File is attached.
Any help or suggestions would be greatly appreciated.
Thank you.
I found a tutorial which I think may be pretty helpful for this.
www.comsol.com/model/thermal-stresses-in-a-layered-plate-273
I simulated the above scenario okay but I am having trouble doing so in 3D.
According to the simulation, the stress is non-constant only in the domain present initially and in the firsly deposited domain. in the domains that are deposited later, the stress is perfectly constant throughout the entirety of the domains. This does not seem correct to me (or is it?). Does anyone have a suggestion for how to improve my simulation? The only major change I think I did compared to the tutorial was I changed the matrix for the initial stress conditions (from 2D to 3D) and my boundary conditions are rollers where as the boundary conditions in the tutorial were for points and of the y-displacement-type.
File is attached.
Any help or suggestions would be greatly appreciated.
Thank you.
Attachments:
1 Reply Last Post Apr 19, 2015, 8:46 p.m. EDT
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Posted:
10 years ago
I agree -- this seems incorrect to me. But reality is complicated.
Consider two cases: epitaxial and amorphous deposition. In the epitaxial case, the final stress of the system is independent of deposition history. There is only one pseudomorphic arrangement of atoms, and the final stress field will be the one which minimizes the free energy of these bonds consistent with the boundary conditions. The deposition temperature is irrelevant.
But if the deposition is amorphous, then the stress state of the underlying substrate is irrelevant. The film will always be deposited, in the ideal case, at zero stress for the present temperature. Meanwhile the system is dynamically relaxing to at each moment in time minimize the free energy. This will yield stress gradients everywhere at all times. Then if the system returns to the room temperature there will be an additional stress associated with thermal mismatch, which consistent with boundary conditions will also be spatially dependent.
I've not looked at the example (it's a bit of a hassle for me to do so right now) but I completely agree with you that uniform stress in the deposited layer, except under very specific conditions, makes no sense.
Consider two cases: epitaxial and amorphous deposition. In the epitaxial case, the final stress of the system is independent of deposition history. There is only one pseudomorphic arrangement of atoms, and the final stress field will be the one which minimizes the free energy of these bonds consistent with the boundary conditions. The deposition temperature is irrelevant.
But if the deposition is amorphous, then the stress state of the underlying substrate is irrelevant. The film will always be deposited, in the ideal case, at zero stress for the present temperature. Meanwhile the system is dynamically relaxing to at each moment in time minimize the free energy. This will yield stress gradients everywhere at all times. Then if the system returns to the room temperature there will be an additional stress associated with thermal mismatch, which consistent with boundary conditions will also be spatially dependent.
I've not looked at the example (it's a bit of a hassle for me to do so right now) but I completely agree with you that uniform stress in the deposited layer, except under very specific conditions, makes no sense.