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.
Water rinse of aluminum metallized integrated circuits must be carefully monitored because the A1 can oxidize rapidly under certain conditions. A1 oxidation in 10 IVIft deionized water was therefore studied using Auger spectroscopy, and transmission and scanning electron microscopies, to investigate the oxide growth as a function of water temperature and rinse time, use of photolithography, and Cu-doping of the AI. A1 oxide thicknesses were 20-30A before any treatment and were 35, 70, and ---~3000A after 5 rain rinses in 40 ~ 60 ~ and 80~ water, respectively. Photolithography and Cu doping induced no large effects. In 40~ water, little oxidation occurred for 20 rain and rapid oxidation began after 40 rain, especially at nucleation sites with C and Si contamination. The oxide grown in water has a porous structure, is nearly amorphous, and contains gamma-alumina and hydrated oxides. Near 80~ several thousand angstroms of oxide can grow in minutes.
Fabrikationsbedingtes Spülen von mit Al metallisierten integrierten Schaltkreisen kann unter bestimmten Bedingungen zu rapider Oxidation des Al Anlaß geben.
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