A method of designing an extreme ultraviolet lithography projection objective, wherein the projection objective is disposed between a mask and a wafer plane, the objective comprising six lenses and an aperture diaphragm positioned from the mask along a beam propagation direction to the wafer plane in the order of:
- a first lens (M1), the aperture diaphragm disposed on a second lens (M2), the second lens, a third lens (M3), a fourth lens (M4), a fifth lens (M5), and a sixth lens (M6), said method comprising the steps of:
- determining a set of optical parameters of the projection objective comprising:
- object side numerical aperture (NAO), magnification of the objective (M), image side numerical aperture (NAI), object field height (YOB), image field height (YIM);
- and incidental angle of chief ray on object side (CA) based on NAO;
- determining a ratio of the object field height YOB to the distance between the mask and the first lens M1 (ratio1), a ratio of the distance between the first lens M1 and the second lens M2 to the distance between the mask and the first lens M1 (ratio2), a clear unobstructed space between the first lens M1 and the ray beam emerged from M2 (CLEAPE1), a working distance between the wafer and the sixth lens M6 (WDI), a ratio of WDI to the distance between the fifth lens M5 and the sixth lens M6 (ratio3), a clear unobstructed space between the sixth lens M6 and an incidental ray beam onto the fifth lens M5 (CLEAPE6), and a clear obstructed space between the fifth lens M5 and an emerged ray beam from M6 (CLEAPE5);
- determining a distance between the mask and the first lens M1 as −l1, wherein |−l1|=YOB/ratio1, and determining a distance between the first lens M1 and the second lens M2 as −d1, wherein |−d1|=YOB/ratio1·ratio2;
- determining the radius of the first lens M1 as r1, wherein
- r
- 1
- =
- h
- z
-
-
- 1
- /
- sin
-
- (
- arctan
-
- (
- h
- z
-
-
- 1
- /
- (
- -
- d
- 1
- +
- z
- z
-
-
- 1
- )
- )
- 2
- -
- CA
- 2
- )
- where hz1 denotes the height of chief ray (RAY1) on the first lens M1, and zz1 denotes the axial distance of an incidental point of chief ray RAY1 on the first lens M1 to the vertex of the first lens M1;
- determining the radius of the second lens M2 as r2, wherein
- r
- 2
- =
- h
- a
-
-
- 2
- /
- sin
- (
- U
- a
-
-
- 2
- 2
- -
- arctan
-
- (
- h
- b
-
-
- 1
- -
- CLEAPE
-
-
- 1
- -
- h
- a
-
-
- 2
- -
- d
- 1
- )
- 2
- )
- where Ua2 denotes the slope angle of an upper marginal ray (RAY2) on the first lens M1, ha2 denotes the height of an upper marginal ray (RAY2) on the second lens M2, and hb1 denotes the height of a lower marginal ray (RAY3) on the first lens M1;
- determining the distance between the fifth lens M5 and the sixth lens M6 as d5, wherein |d5|=WDI·ratio3;
- defining a virtual plane D1 in the light path of the objective at the same position as that of the fifth lens M5, aligning the incidental chief ray RAY1 on the sixth lens M6 parallel to an optical axial OA, and determining the radius of the sixth lens M6 as r6, wherein
- r
- 6
- =
- h
- b
-
-
- 6
- /
- sin
-
- (
- arctan
-
- (
- (
- h
- b
-
-
- 6
- -
- (
- h
- b
-
-
- D
-
-
- 1
- -
- CLEAPE
-
-
- 5
- )
- )
- /
- (
- -
- d
- 5
- -
- z
- b
-
-
- 6
- )
- )
- 2
- +
- U
- b
-
-
- 6
- ′
- 2
- )
- where hb6 denotes the height of the lower marginal ray RAY3 on the sixth lens M6, hbD1 denotes the height of the lower marginal ray RAY3 on the virtual plane D1, zb6 denotes the axial distance between incidental point of the lower marginal ray on the sixth lens M6 and the vertex of the sixth lens M6, and U′b6 denotes the slope angle of the lower marginal ray RAY3 on the sixth lens M6;
- determining the radius of the fifth lens M5 as r5, wherein
- r
- 5
- =
- h
- b
-
-
- 5
- /
- sin
-
- (
- arctan
-
- (
- (
- h
- b
-
-
- 5
- -
- (
- h
- a
-
-
- 6
- -
- CLEAPE
-
-
- 6
- )
- )
- /
- (
- -
- d
- 5
- -
- z
- a
-
-
- 6
- )
- )
- 2
- +
- U
- b
-
-
- 5
- ′
- 2
- )
- where hb5 denotes the height of lower marginal ray RAY3 on the fifth lens M5, ha6 denotes the height of lower marginal ray RAY3 on the sixth lens M6, U′b5 denotes the slope angle of the lower marginal ray RAY3 on the fifth lens M5, za6 denotes the axial distance between an incidental point of the upper marginal ray RAY2 on the sixth lens M6 and the vertex of the sixth lens M6, and U′b5 denotes the slope angle of the lower marginal ray RAY3 on the fifth lens M5;
- and
- determining the radius of the third lens M3 as r3 according to an object-image conjugation relationship, a magnification relationship, a pezval sum condition and a conjugation relationship of entrance and exit pupil, the radii of and distances between the first lens M1, the second lens M2, the fifth lens M5, and the sixth lens M6, the radius of the fourth lens M4 as r4 based on a paraxial iterative algorithm, and the distance between the third lens M3 and the fourth lens M4 as d3, the distance between the second lens M2 and the third lens M3 as l3, and the distance between the fourth lens M4 and the fifth lens M5 as d5, and the image distance of the fourth lens M4 as l′4.