Projection objective lens system

1. A projection objective lens system comprising, from an object plane to an image plane:

a first lens group having a positive refractive power;

a second lens group having a negative refractive power;

a third lens group having a positive refractive power;

a fourth lens group having a negative refractive power;

a fifth lens group having a positive refractive power and including a first sub-lens group and a second sub-lens group; and

an aperture stop positioned between the first sub-lens group and the second sub-lens group;

wherein the projection objective lens system includes at least two types of optical materials including high refractive index materials having a refractive index of greater than 1.6 at a working wavelength and low refractive index materials having a refractive index of smaller than 1.6 at a working wavelength;

wherein all lenses of the first sub-lens group are positive lenses formed of low refractive index materials;

wherein the second sub-lens group includes a negative lens which has an aspheric rear surface and is formed of a high refractive index material; and

wherein the following formula is satisfied:

ΔR/R<1%,

where ΔR represents a difference between a radius at the aperture stop of a marginal field beam bundle and a radius at the aperture stop of a central field beam bundle, and R represents a radius at the aperture stop of a central field beam bundle.

2. The projection objective lens system according to claim 1 , wherein the first lens group includes: a first sub-lens group having a negative refractive power and including at least one negative lens with an aspheric front surface; and a second sub-lens group having a positive refractive power and including at least three lenses.

3. The projection objective lens system according to claim 2 , wherein the negative lens of the first sub-lens group of the first lens group is made of a low refractive index material, and the second sub-lens group of the first lens group includes at least one lens made of a high refractive index material.

4. The projection objective lens system according to claim 1 , wherein the second lens group includes at least three negative lenses.

5. The projection objective lens system according to claim 4 , wherein at least two of the negative lenses of the second lens group are made of high refractive index materials.

6. The projection objective lens system according to claim 1 , wherein the third lens group includes at least three positive lenses.

7. The projection objective lens system according to claim 6 , wherein at least one of the positive lenses of the third lens group is made of a high refractive index material.

8. The projection objective lens system according to claim 1 , wherein the fourth lens group includes at least three negative lenses; and a last lens of the fourth lens group has an aspheric rear surface.

9. The projection objective lens system according to claim 8 , wherein at least two of the negative lenses of the fourth lens group are made of high refractive index materials.

10. The projection objective lens system according to claim 1 , wherein a positive lens of the first sub-lens group of the fifth lens group disposed closest to the aperture stop has: a front surface bending away from the aperture stop, an apex of the front surface being far apart from the aperture stop, a radius of curvature of the front surface being positive; and a rear surface bending away from the aperture stop, an apex of the rear surface being far apart from the aperture stop, a radius of curvature of the rear surface being greater than that of the front surface.

11. The projection objective lens system according to claim 1 , further comprising: a first flat plate disposed between the object plane and the first lens group; a second flat plate disposed between the aperture stop and the first sub-lens group of the fifth lens group; and a third flat plate disposed between the fifth lens group and the image plane.

12. The projection objective lens system according to claim 11 , wherein the first and third flat plates provide cover glasses for protecting the internal optical lenses from external impacts, and the second flat plate serves as a compensating element which can be polished to compensate the imaging quality of the system that has been affected by other optical elements.

13. The projection objective lens system according to claim 1 , wherein a free diameter of the negative lens of the second sub-lens group of the fifth lens group that has an aspheric surface is no smaller than 0.9 Dmax, where Dmax is a greatest free diameter of all lenses.

14. The projection objective lens system according to claim 1 , wherein the system has an object-side working distance that is greater than 40 mm, an image-side working distance that is greater than 10 mm, and an image-side numerical aperture that is greater than 0.5.

15. The projection objective lens system according to claim 1 , wherein the system has an object-side working distance that is greater than 45 mm, an image-side working distance that is greater than 12 mm, an angle between an image formed and an optical axis that is smaller than 1 mrad, a ratio of a distance between the object and image planes to an effective focal length of the projection objective lens system that is within the range of 0.15 to 0.3, a ratio of a difference between radii at the aperture stop of a marginal field beam bundle and a central field beam bundle to a radius at the aperture stop of a central field beam bundle that is smaller than 0.5%, and an image-side numerical aperture that is greater than 0.65.

16. A micro-lithography system employing the projection objective lens system according to claim 1 .