Dear Dr. Prachi Arora ,
I suggest you to have a look at the following papers regarding the function of surface roughness:
-Effect of deposition rate on structure and surface morphology of thin evaporated Al films on dielectrics and semiconductors
Kirill Bordo, Horst-Günter Rubahn
Materials Science, 18(4) (2012)
Available, on RG, at: https://www.researchgate.net/publication/272702043_Effect_of_Deposition_Rate_on_Structure_and_Surface_Morphology_of_Thin_Evaporated_Al_Films_on_Dielectrics_and_Semiconductors
-Role of ionization fraction on the surface roughness, density, and interface mixing of the films deposited by thermal evaporation, dc magnetron sputtering, and HiPIMS: An atomistic simulation
Movaffaq Kateb, Hamidreza Hajihoseini, Jon Tomas Gudmundsson, Snorri Ingvarsson
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films, 37(3):338903JVA (2019)
Available, on RG, at: https://www.researchgate.net/publication/332461959_Role_of_ionization_fraction_on_the_surface_roughness_density_and_interface_mixing_of_the_films_deposited_by_thermal_evaporation_dc_magnetron_sputtering_and_HiPIMS_An_atomistic_simulation
About the function of backing system in PVD technique could be due that the presence of background gases in the deposition chamber may contaminate the deposited thin film. For example, the presence of a small amount of oxygen or moisture during thermal evaporation in the process of Organic Light-Emitting Diode (OLED) and organic photovoltaic devices fabrication, makes the active functional parts of these devices inefficient.
Best regards, Pierluigi Traverso.
Hello
please read from
https://www.normandale.edu/departments/stem-and-education/vacuum-and-thin-film-technology/learning-in-a-vacuum---what-to-expect/articles/how-to-choose-a-roughing/backing-pump-for-the-turbo-and-drag-family
In general if the roughing and backing is not properly done, you may loose your turbopump
1. Roughing is used to pump down the pressure of the chamber usually by rotor/stator motor to a level from where high vacuum pump can be operated.
2. Backing is used to create low pressure in the High vacuum line so that the high vacuum pump (TMP) can be operated in the chamber..
When the thermal evaporator is started, initially the pump line is disconnected from the chamber. So, the pump line including the diffusion pump (if exist) should vacuum into a certain level. So that the oil in the diffusion pump is de-gassed and the pump line is vacuumed. This is called Backing.
Then the chamber should be vacuumed to a certain level by a rotary pump so that the difference of vacuum in the diffusion pump and the chamber is very low. This is called roughing.
Finally, the high vacuum valve will open which connects the chamber and the diffusion pump, and further, it will vacuum. This is called fine pumping.
Best Regards.
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