Inspection method, template substrate, and focus offset method

An inspection method for inspecting a substrate to detect a defect using an optical image obtained by irradiating a substrate with light emitted from a light source through an optical system, and causing the light reflected by the substrate to be incident to a sensor through the optical system,

• wherein the substrate includes a first pattern constructed with a repetitive pattern that is not resolved by a wavelength of the light source, and
• at least one alignment mark that is arranged on the same plane as the first pattern,
• wherein the alignment mark includes a second pattern constructed with a repetitive pattern that is not resolved by the wavelength of the light source;
• and
• a programmed defect that is provided in the second pattern and not resolved by the wavelength of the light source, the inspection method comprising:
• adjusting a focus offset such that a strongest signal of the programmed defect is obtained with respect to a base value of a gradation value in an optical image of the programmed defect by capturing the optical image while changing a focal distance between the surface in which the first pattern is provided and the optical system;
• detecting a defect of the first pattern by capturing an optical image of the first pattern after the focus offset is adjusted.