In our research, we found out that polystyrene will operate better in Reactive Ion Etching after over exposure of Electron Beam or Laser Irradiation. Polystyrene seems to change its chemical structure and we are puzzled, which part of the molecular structure interacts with the irradiation source?
How do we control the the effect, so that we might understand when the polymer such as polystyrene starts to change it chemical structure, thus change from negative resistance to positive resistance.
We know that radiation do altered polymer structure, but how much and when or the energy of the electrons in the electron beam or photon...or still, how deep can photons penetrate into polymers?
Electron beam modification of polymer nanospheres.
Authors: M A Agam, Q Guo
Journal of nanoscience and nanotechnology. 11/2007; 7(10):3615-9.
This is my paper, which look at polystyrene nanospheres...bombarded with electrons. The polystyrene nanospheres become more carbonaceous and resistant toward Reactive ion Etching or organic solvent. When my student used laser to irradiate the same Polystyrene Nanospheres, the same effect happened and later we found a paper by Buvana that suggested zwitter charactheristic...the changes from negative resist to positive resist due to over exposure of polymer resists. The question now...is when is the critical factors that the ever exposure of polymer resists to irradiation source? Does different radiation type gave different critical point? Anybody care to answer this...because once we know the exact dosages of radiation, we can play around with the polymer resists for better pattern transfer for IC fabrication.
We can have the idea of removal content of CO2 or other groups from polymer during Irradiation. Did you tried in-situ mass spectroscopy. Additionally, If you are dealing with electron or photons to interact with polymer, then thickness may have important factor because these beams can modify the surface only, the penetration depth is not much higher and in the order of few micron.
Electron beam or laser Irradiation may cause polymer crosslinking and properties of the network differ a lot from those of uncrosslinked material.
TQ guys. I did on 500 nm polystyrene nanospheres. I know the polymer can crosslink, but as we know negative resist could let the molecular of the polymer been cut into small pieces and can be dissolved with organic solvent, but when you overexposure either laser or electron beam to the polymer, the polymer will change from negative to positive resist...which could be interpret as more binding or crosslinking taking place, thus creating more dense carbonaceous materials, which later become more resistant toward reactive ion etching or organic solvent. I would like to have comment from Chemist people...any comment.
The zwitter charactheristic is somehow can be said the interaction of radiation to polymer molecule, where simultaneous cutting and crosslinking of molecule happened. In basic polystyrene molecule, as there are only c-H and C-O, C=O are involved, therefore the rate for crosslingking and scissoring of the polymer resist due to irradiation are somehow can be looked at the C-O and C=O bond. Now, as we have investigated the fluctuation of C-O and C=O formation, I believe we are looking at the back bone chain of the polymer and the benzene ring. Benzene ring has the c=O bond, not at the back bone chain, where it has only C-C and C-H bonding. Therefore, I am speculating that the benzene ring could be the one become the main factor of the formation of C=O or C-O. Nevetheless, Benzene ring was found to be more stable ...need to check this. Now the question is...which part of the polymer of polystyrene that become the main factor to create the C=O and C-O formation during laser or electron beam irradiation?
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