Method of fabricating metal mask

A method of fabricating a metal mask, comprising:

• receiving a conductive substrate, wherein the conductive substrate comprises:
• a first surface;
• a second surface, opposite to the first surface;
• a third surface, connecting the first surface and the second surface;
• a fourth surface, opposite to the third surface and connecting the first surface and the second surface;
• forming a plurality of trenches in a direction from the first surface to the second surface and a plurality of protrusions in the conductive substrate, wherein the plurality of the trenches and the plurality of the protrusions are alternately arranged;
• filling the plurality of the trenches with a first insulation material, wherein the first insulation material covers a first area of the plurality of the protrusions;
• forming a metal layer on the conductive substrate, wherein the metal layer overlies a second area of the plurality of the protrusions, and the second area is different from the first area;
• removing the first insulation material;
• and
• removing the conductive substrate such that the metal layer becomes a metal mask with a three-dimensional structure, wherein the metal mask with the three-dimensional structure comprises a plurality of strip-shaped structures.