| abstract |
An object of the present invention is to ensure the flatness of the underlying layer after removing the porous layer. As a solution to this, in the first step, the pretreatment liquid (for example, water) is allowed to soak into the porous layer, and in the second step, the pretreatment liquid that has soaked into the porous layer is replaced with an etching solution (for example, hydrofluoric acid). By this method, the time which infiltrates an etching liquid into a porous layer is shortened, and the deviation of the progress of etching liquid is suppressed. |