Method for Forming Mask Pattern, Thin Film Transistor and Method for Forming the Same, and Display Device

A method for forming a mask pattern, comprising:

• forming a negative photoresist on a substrate, the negative photoresist having the following properties:
• after the negative photoresist is exposed in an environment without oxygen, an exposed portion is cured;
• after the negative photoresist is exposed in an environment with oxygen, a surface part of an exposed portion is not cured, while other part of the exposed portion than the surface part is cured;
• in an environment without oxygen, performing a first exposure on the negative photoresist by use of a first ordinary mask plate, so that a fully-cured portion of the negative photoresist is exposed to light and a semi-cured portion and a removed portion of the negative photoresist are not exposed to light;
• in an environment with oxygen, performing a second exposure on the negative photoresist with s second ordinary mask plate, so that the semi-cured portion of the negative photoresist is exposed to light and the removed portion of the negative photoresist is not exposed to light;
• and
• removing the uncured negative photoresist and forming the mask pattern.