The stripping of photoresists from a silicon wafer using an rf oxygen plasma has been monitored using the optical emission from electronically excited OH and CO species in the ultraviolet region of the spectrum. The band systems at 283.0 nm (CO*, OH*), 297.7 nm (CO*), and 308.9 nm (OH*) are intense and spectrally isolated from other systems and arise from plasma-induced oxidation of the polymeric photoresist material. The endpoint of plasma stripping and the amount of stripped material is easily determined quantitatively. In addition, variations in stripping rate of photoresist as a function of wafer position in the reaction chamber can be detected.
A new photoresist stable to 500°C has been developed. The addition of potassium dichromate to a polyamic acid, believed to be the condensation product of pyromellitic dianhydride and 4,4′‐diaminodiphenylether, results in a photosensitive polymer which can be cast or spun. The resultant film after exposure, development and post‐bake is a crosslinked aromatic polyimide. An efficient developing solution consisting of a 5:1 mixture of hexamethylphosphoramide and dimethylsulfoxide has been discovered. The system has been fully characterized in terms of composition, film formation, exposure, development, hardening and removal. This material has already proven useful as an area‐controlled, thermally stable dielectric and as a sputter‐etch resist. It has been demonstrated that under the conditions of sputter‐etching (bombardment of substrate with Ar, Ar+ species with energies from 1–300 eV) commercial photoresists, of the polyisoprene variety, char to the extent of being ineffective as a masking material. Under these same conditions, the thermally stable resist retains its film integrity and uniform sputter‐etch rate. An exemplary processing sequence is included as an appendix.
Plasma‐developed negative photoresists with good sensitivity and at least 1 μm resolution have been developed by the addition of quinone sensitizers such as phenanthrenequinone to a plasma‐developed x‐ray resist comprised of poly(2,3‐dichloro‐1‐propyl acrylate) and N‐vinyl carbazole. The sensitivity is optimum in the 290–350 nm range. Locking of the carbazole by cationic polymerization is presumably accomplished via cation radical intermediates produced upon quenching N‐vinyl carbazole excited states with quinones that are excellent electron acceptors.
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