Patent ID: 9557523
Date: 2017-01-31
CPC Classifications: G02B

Claim:
1. A method of focusing an optical system on a second surface of a target object having an upper surface including a first surface and the second surface located below the first surface, wherein the target object has a step between the first surface and the second surface, the apparatus comprising: a first step of projecting oblique incidence light to the first surface at a first incident angle which forms a first angle with respect to a first direction parallel to an optical axis of the optical system, and receiving the light reflected by the first surface to measure a surface position of the first surface; a second step of projecting oblique incidence light to the second surface at a second incident angle which forms a second angle smaller than the first angle with respect to the first direction, and receiving the light reflected by the second surface to measure a surface position of the second surface, wherein the second incident angle is determined so as to prevent the light reflected by the second surface from being reflected by the step between the first surface and the second surface; a third step of obtaining, based on a measurement result of the surface position of the first surface, an in-focus condition in which the optical system is focused on the first surface; a fourth step of obtaining information about a step amount between the first surface and the second surface based on the measurement result of the surface position of the first surface and a measurement result of the surface position of the second surface; and a fifth step of focusing the optical system on the second surface based on the in-focus condition and the information about the step amount.