Patent ID: 7073518

Claim:
A cleaning method for a mask used in a vacuum vapor deposition step in the production of a low molecular weight organic electro luminescence (EL) device, comprising cleaning the mask, wherein said cleaning is carried out by immersion or jet flow, with a solution consisting of N-methyl-2-pyrrolidinone and one or more aprotic polar solvents selected from the group consisting of N,N-dimethylformamide, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,4-dioxane, and cyclohexanone, or consisting of one or more aprotic polar solvents selected from the group consisting of N,N-dimethylformamide, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,4-dioxane, and cyclohexanone.