The document discusses two potential mechanisms for acid generation in photoresists: intramolecular and intermolecular. The intramolecular mechanism involves a single molecule absorbing a photon, exciting an electron and breaking an A-H bond to generate H+ and A-. The intermolecular mechanism involves multiple nearby molecules where a high-energy impact causes ionization and dissociation, producing H+ and electrons that can be captured by the acid generator molecule. However, the document argues that in condensed materials there is no clear distinction between intra- and intermolecular processes, as energy deposition can disturb large volumes, and the mechanisms are effectively the same.

1. To the CAR generic
mechanism(s)
Hopefully, it is not oversimplified
Yehiel Gotkis

2. Two mechanisms of acid generation could be
anticipated
Itramolecular –
Acid yielding AG transformations triggered by photon (single or multi-) absorption proceeding all within the same AG
molecule, C+(AH)- :
C+(HA)- + hν -> C0---H+ A-
It must be a closely resonant process because the photon has to be absorbed entirely.
One of the electrons localized at the A - H bond is excited to a delocalized orbital, and it either recombines back to the
same orbital or finds its way to another potential energy minimum, which is highly likely to be located at the positively
charged C+, and neutralize its charge converting it to C0.
The intramolecular distance C0---AH0 , being the most probable bond to absorb the excessive energy, extensively
elongates leaving the delocalized electron, when it is located on the C0, no chance to return back.
At the same time the covalently bonded neutral AH fragment undergoes its own electron density and geometry
restructuring, converting the covalent bond to an ionic one becoming an acid:
HA -> H+ A-
Ultimately, it is the same story we discussed before, namely, the excitation promotes
transfer of one of the A-H electrons to the cation localized orbitals, neutralizing its
charge and field. The covalent A-H bond is converted to an ionic bond making the
---H+ A- to act as a strong acid.

3. Two mechanisms of acid generation could be
anticipated
Itermolecular –
Acid yielding AG transformation triggered by an impact of a highly energetic incident object(s) (photon(s), electron, I believe, even ion)
affecting an extended ensemble of AG and its neighboring species.
In this case, the high amount of energy, carried by the impacting object, produces more extended bonding “demolition”, including
numerous molecular and dissociative ionization events, charge transfers, geometry restructuring and so on. Among them, the
processes of interest are
General ionization, producing low energy electrons
M -> M+ + e
Specific dissociative ionization of species containing terminal C-H bonds, producing H+, like, for example, - CH2 – polymer sections:
- CH2 – -> = CH – + H+ + e
This kind of processes result in formation of the both species necessary to promote the AG acidification- low energy electrons to
neutralize the cation and protons to electrostatically stick to the anion forming the acid.
C+(HA)- + H+ + e -> C0---(AH)-H+
Ultimately we see the same story again, namely, excitation promotes transfer of the resist’s electrons to
anti- or highly excited orbitals allowing the AG to capture it, neutralize its cation and “provide” the anion
freedom to expand its electrostatic field around and lure a proton.

4. Are the two discussed acid generation
mechanisms really different? I think that NO.
• Dealing with condensed phase materials we should not forget that, in general, being
condensed, individual molecules lose their individuality - there are no individual
molecules in the bulk. A piece of condensed material is a single big molecule, with some
bonds of it being covalent and others ionic, some are strong multiple bonds and others
are weak (Van-der-Waals bonding) and so on.
• As a result, an impacting object, (multi-)photon, electron, ion etc. deposits its energy
reasonable locally. However, thanks to the energy dissipation phenomenon, the
associated destabilization, may extend pretty far from the incident location, depending
on the amount of energy deposited, the density of states involved in energy transfer and
their coupling.
• For the same material the higher the energy deposit, the larger the material volume
disturbed.
• In the DUV we are shouting single bullets (low energy photons) into the resist, hoping that at least
some of them will hit the AG and trigger the targeted acidic transformation.
• In highly energetic activation, e-beam, EUV, Soft X-ray, ions etc. we drop an “heavy bomb” which
explodes a huge volume of material, and we believe that the AG molecule will selectively pick up
from the mess formed, the necessary stuff to finally convert itself to an acid.