Patent ID: 8432554

Claim:
A surface position detecting apparatus, comprising: a light projection system which projects a light from an oblique direction onto a detection target surface; and a light reception system which receives the light reflected on the detection target surface, said surface position detecting apparatus being adapted to detect a surface position of the detection target surface on the basis of an output from the light reception system, wherein at least one of the light projection system and the light reception system comprises a total reflection prism member including an internal reflection surface which totally reflects the light, and wherein an amount of a relative positional deviation between polarization components of the light totally reflected on the internal reflection surface satisfies the following relation: [ Math ⁢ ⁢ 16 ] λtanθ π ⁢ n 2 ⁢ sin 2 ⁢ θ - 1 ⁢ ( 1 n 2 ⁢ sin 2 ⁢ θ + sin 2 ⁢ θ - 1 - 1 ) · cos ⁢ ⁢ θ ≤ 0.3 ⁢ ⁢ ( µm ) where λ (μm) is a wavelength of the light, n is a refractive index of an optical material forming the total reflection prism member, and θ (0°≦θ≦90°) is an angle of incidence of a ray along an optical axis in the light incident to the internal reflection surface of the total reflection prism member.