Specifically, in the context of photolithographic processes,
Case 1: positive photoresist. What is the chemical reaction promoted by the UV light? The kind of chemistry is used for positive photoresists is the same no matter what is the specific positive photoresist? I read somewhere that the main kind of UV promoted reaction would be some structural changes in the polymers so the spun layer changes its solubility … is this true each time?
Case 2: the same question as in the case 1 but about the negative photoresist. I read somewhere that in this case the main kind of reaction used is radical based processes … is this true each time?
General question: if a photoresist is spun down to a surface decorated wafer, the UV treatment would degrade the surface decoration at the wafer-photoresist layer interface?
Traditional photoresists such as the AZ series from Shipley and many others that followed have a photoinitiator active in the UV (405nm, 365nm) and upon exposure it decomposes to indene carboxilic acid which is soluble in a baisc devloper. Thus the exposed regions are washed away during development along with the polymer; the unexposed regions are not.
Negative photoresists crosslink upon exposure to UV light and thus the exposed regions are less soluble in a solvent such as toluene compared to the unexposed regions. The reolution of negative photoresists by definition is poorer than those of positive resists.
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