Electron Impact Reactions (slide 1) convert relatively inert molecules into very reactive radicals. The role of reactive radicals is very important in plasma etching: most of the plasma surface chemistry is achieved thanks to radicals. The role of radicals depends also on the plasma density: in low density RIE discharges, they play a fundamental role whereas ions may be strongly involved in the chemistry in high density plasmas.
Electron Impact Ionizations (slide 2) transform atoms and molecules into ions. Dissociation and ionization may often simultaneously occur: this process is called Dissociative Ionization.
Some molecules tend to capture low energy electrons and form negative ions. This process is called Electron Attachment (slide 3). It produces negative ion fragments as well as neutrals and leads to lower plasma densities. The energy acquired by the molecule in the capture process can cause the molecule to dissociate. This process is called Dissociative Electron Attachment.
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