Patent ID: 6947121

Claim:
A projection optical system for projecting onto a workpiece a reduced image pattern arranged on a mask based on the exposure light of a predetermined wavelength, comprising: a plurality of optical elements arranged to each receive the exposure light, each of the plurality of optical elements being shaped and positioned such that both sides of the mask and the workpiece are set to be telecentric; wherein the plurality of optical elements comprises: a first lens group arranged between a first object and a second object; a second lens group having a negative power, and arranged between the first lens group and the second object; a third lens group having a positive power and arranged between the second lens group and the second object; a fourth lens group having a negative power and arranged between the third lens group and the second object; a fifth lens group having a positive power and arranged between the fourth lens group and the second object; wherein two lens surfaces of the first lens group satisfy the condition φ 1 /φ exp ≦3.5, the first material satisfies the condition n 1 ≦1.57, the projection optical system including a second lens made of a second material, two lens surfaces of the second lens satisfy the condition φ 1 /φ exp >3.5, and the second material satisfies the condition n 2 >1.57, where φ exp is designated as a diameter of an exposure area on the second object, φ 1 is designated as a diameter of a clear aperture of the two lens surfaces of the first lens group, φ 2 is designated as a diameter of a clear aperture of the two lens surfaces of the second lens, and n 1 is designated as a refractive index of the first lens, and n 2 represents a refractive index of the second lens; and wherein the projection optical system includes an image circle having a diameter of at least 42 mm and a maximum value of a numerical aperture at a side of the workpiece is determined to be greater than or equal to 0.5.