PURPOSE: To perform good annealing even when requiring no spacer, by applying rust prevention on etched flat mask using alkaline solution then neutralizing the residual alkaline solution on the mask surface with organic acid.

CONSTITUTION: Rusted flat mask having opening for passing many electron beam formed by etching is applied with rust prevention through alkaline bathing added with chelate agent. After mash water it is immersed in organic acid having high neutralizing ability such as 1W10vol.% of malic acid, citric acid, succinic acid, etc. to neutralize the residual alkaline solution on the surface of mask, then it is washed in water and applied with rust prevention using morpholine (trade name) or thin alkaline liquid of pH8W9. Since residual alkaline component on the mask is neutralized, cleaned and removed, good annealing where masks are not contacted tightly is achieved even when annealing requiring no spacer is applied as it is under same condition with mask not applied with rust prevention.