Patent ID: 7820366

Claim:
A method of writing identifying information on a wafer, wherein the identifying information is written through the use of at least one patterned resist layer on the wafer used for forming thin-film elements, the method comprising: a step of forming two resist layers on the wafer, the two resist layers consisting of a lower resist layer and an upper resist layer, the lower resist layer being soluble in a developer, the upper resist layer being formed of a positive resist and being photosensitive; a first exposure step of exposing the two resist layers based on a first pattern for an alignment mark by projecting the first pattern onto the two resist layers; a first development step of partially developing the upper resist layer to form a pattern to be a reference of a location in the upper resist layer, the first development step being performed after the first exposure step and performed such that a portion of the exposed upper resist layer exposed in the first exposure step is partially removed, but the portion is not completely removed down to the lower resist layer, a second exposure step of exposing the two resist layers based on a second pattern for the identifying information by projecting the second pattern onto the two resist layers, using the pattern formed in the upper resist layer in the first development step as the reference of the location; a second development step of developing the two resist layers to form two patterned resist layers after the second exposure step, the two patterned resist layers in combination having a shape with undercuts; a patterned film forming step of forming a patterned film for the alignment mark that is patterned based on the first pattern and a patterned film for the identifying information that is patterned based on the second pattern, using the two patterned resist layers; and removing the two patterned resist layers.