A method of making etch-resistant masks

摘要

1,147,490. Etching. INTERNATIONAL BUSINESS MACHINES CORP. 5 Oct., 1967 [13 Jan., 1967], No. 45428/67. Heading B6J. [Also in Division H5] An etch resistant mask is prepared by coating a substrate with a polymeric film, exposing selected portions of this film to electron beam radiation, the film and the exposure being such that the degree of polymerization of the whole of the thickness of the exposed areas is reduced and dissolving the exposed areas in a developing solution in which the unexposed areas are substantially insoluble. Preferably the thickness of the polymeric film is not greater than 25 microns and the charge density of the electron beam is in the range 10-5 to 2 x 10-3 coulomb/ cm2 and the accelerating potential of the beam is in the range 5 to 30 kV. The developing solution may consist of a first liquid capable of dissolving the polymeric film whatever its degree of polymerization and a second liquid which is incapable of dissolving the polymeric film, the proportions of the two liquids being such that the mixture is just able to dissolve the exposed areas of film but is incapable of dissolving the unexposed areas. Preferred film forming materials are cellulose derivatives e.g. cellulose ether or ester, cellulose acetate, cellulose acetate-butyrate, or cellulose propionate; vinyl type polymers or copolymers in which one half of the carbon atoms are quaternary and wherein the repeat units of the polymer preferably have the formula where R 1 and R 2 can be any one of the groups CH 3 , C 6 H 5 , -COOCH 3 , and -COOÀC 2 H 4 ÀOH. Preferred polymers are given as polyisobutylene, poly(α-methylstyrene), methyl methacrylate, and a copolymer methyl methacrylate/2 hydroxy ethyl methacrylate. Particular solvent mixtures for the specified polymers are given in the Specification. The average molecular weight of the polymer used is given as 6,000 to 20,000. Prior to exposure to radiation the filmmay be baked e.g. at 150‹ C. to 180‹ C. for about 30 mins, to improve its adhesion to the substrate. After the exposed portions have been dissolved, the polymeric film may be baked e.g. at a temperature below the softening point of the film, to reduce or eliminate any undercutting of the etched pattern due to the lateral spread of the radiation during exposure. The width of the electron beam used is given as 2000Š and the resolution obtained is 0À8 to 2À0 microns. The development time used in treating the irradiated film using the materials listed in the Specification never exceeds 1 min.