Calculation method, image-capturing method, and image-capturing apparatus

An image-capturing method comprising:

• calculating step of calculating a shear amount produced by a predetermined optical element which is arranged on an optical path of an interference optical system;
• a step of adjusting a position of the predetermined optical element, by moving at least in a direction crossing the optical axis of the interference optical system, based on the shear amount calculated in the step of the calculating such that a path difference between two rays of light divided by the interference optical system becomes a predetermined value;
• and
• a step of capturing an interference contrast image of a sample by the interference optical system after the step of adjusting, wherein
• the step of calculating comprises:
• a step of capturing an interference contrast image of a quadric surface included in an object surface by the interference optical system;
• a step of measuring a fringe interval of interference fringes included in the interference contrast image;
• and
• a step of calculating the shear amount based on a constant in a formula expressing the quadric surface and the fringe interval,
• the shear amount is the lateral shift between the two parallel light beams of illumination light transmitted through the predetermined optical element,
• the quadric surface is at least one of a surface of a spherical body, a surface of a circular column, or a parabolic surface, and
• the formula expressing the surface of the spherical body is x2+y2+z2=R2, the formula expressing the surface of the circular column is s2+z2=R2, the formula expressing the parabolic surface is z=as2, z denotes a position in the height direction, x and y denote horizontal positions, s denotes a position in the shear direction, and R and a denote constants.

An image-capturing apparatus comprising:

• an interference optical system;
• a predetermined optical element being arranged on an optical path of the interference optical system;
• and
• a processing unit configured to execute:
• a process of capturing an interference contrast image of a quadric surface included in an object surface by the interference optical system;
• a process of calculating a shear amount of the predetermined optical element based on a fringe interval of interference fringes included in the interference contrast image and a constant in a formula expressing the quadric surface;
• and
• a process of adjusting a position of the predetermined optical element, by moving at least in a direction crossing the optical axis of the interference optical system, based on the shear amount calculated in the calculating process such that a path difference between two rays of light divided by the interference optical system becomes a predetermined value,
• wherein
• the shear amount is the lateral shift between two parallel light beams of illumination light transmitted through the predetermined optical element,
• the quadric surface is at least one of a surface of a spherical body, a surface of a circular column, or a parabolic surface,
• the formula expressing the surface of the spherical body is x2+y2+z2=R2, the formula expressing the surface of the circular column is s2+z2=R2, the formula expressing the parabolic surface is z=as2, z denotes a position in the height direction, x and y denote horizontal positions, s denotes a position in the shear direction, and R and a denote constants, and
• the shear amount is calculated based on the interference fringes obtained by illuminating the object having the quadric surface placed on a stage with ordinary light and extraordinary light that are the two parallel light beams.