Separation method, display device, display module, and electronic device

A method for manufacturing a semiconductor device comprising the steps of:

• forming a first resin layer comprising a resin or a resin precursor over a substrate;
• performing a prebaking treatment on the first resin layer to form a second resin layer;
• removing a part of the second resin layer to form a third resin layer after performing the prebaking treatment;
• performing a first heat treatment on the third resin layer in an atmosphere comprising an oxygen gas;
• forming an insulating layer to cover an end portion of the third resin layer and in contact with the substrate;
• performing a second heat treatment on the insulating layer;
• and
• separating the insulating layer from the substrate,
• wherein the first resin layer has a thickness of 2.0 μm before the prebaking treatment.