1. A method of fabricating an extreme ultraviolet photomask, comprising:
providing a mask comprising, in order, a substrate, a reflective layer, and a capping layer;
forming an opening in the capping layer and at least a portion of the reflective layer;
forming an absorber layer in the opening and over a top surface of the capping layer; and
removing at least a portion of the absorber layer, while leaving another portion of the absorber layer to form an absorber, wherein the absorber has a top surface lower than a top surface of the capping layer.
2. The method of claim 1, wherein the absorber has the top surface lower than a top surface of the reflective layer.
3. The method of claim 1, wherein a height difference of the top surface of the absorber and the top surface of the capping layer ranges between about 20 nm and about 50 nm.
4. The method of claim 1, wherein the reflective layer comprises alternating Mo and Si layers ranging between about 20 pairs and about 80 pairs.
5. The method of claim 1, further comprising:
forming an underlying reflective layer over the substrate; and
forming an intervening layer between the underlying reflective layer and the reflective layer.
6. The method of claim 5, wherein the intervening layer includes Cr, Ru, or a combination thereof.
7. The method of claim 5, wherein the absorber is formed on the intervening layer.
8. The method of claim 5, wherein the underlying reflective layer comprises alternating Mo and Si layers ranging between about 20 pairs and about 40 pairs.
9. The method of claim 5, wherein a thickness ratio of the reflective layer to the underlying reflective layer ranges between about 0.25 and about 1.
10. The method of claim 1, further comprising forming a planarization layer over the absorber layer.
11. The method of claim 10, wherein the planarization layer is Ag2O3, Si-containing layer, Carbon-containing layer, or combinations thereof.
12. The method of claim 10, further comprising removing the planarization layer before removing the at least a portion of the absorber layer.
13. The method of claim 1, wherein the absorber layer is TaSi, TaBN, TaN, TaSiON, TaBO, or TaON.
14. The method of claim 1, wherein the absorber has a thickness ranging between about 20 nm and about 150 nm.
15. The method of claim 1, further comprising forming a hard mask layer over the capping layer.
16. The method of claim 15, further comprising removing the hard mask after forming the absorber.
17. The method of claim 1, wherein the step of removing includes a CMP process andor a dry etching process.
18. An extreme ultraviolet photomask, comprising:
a reflective layer over a substrate;
a capping layer over the reflective layer; and
an absorber in the capping layer and the reflective layer, wherein a top surface of the absorber is lower than a top surface of the capping layer.
19. A method for forming an integrated circuit comprising:
forming a photomask by
forming a reflective layer over a substrate;
forming a capping layer over the reflective layer; and
forming an absorber in the capping layer and the reflective layer, wherein a top surface of the absorber is lower than a top surface of the capping layer;
forming a layer on a substrate; and
patterning the layer using the photomask in a photolithography step.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A wide-angle photographic lens system enabling correction of distortion, comprising: a first lens, an iris, a second lens and a third lens sequentially arranged along an optical axis from an object, wherein
the first lens has weak refractivity, the second lens has strong positive refractivity, and the third lens has negative refractivity, wherein the lens system satisfies relations,
|f1f|>2.8, f2f<1, and tetc<0.4,
wherein f1 is a focal length of the first lens, f is a total focal length of all the lenses, f2 is a focal length of the second lens, te is a lens thickness on an effective diameter of a rear surface of the second lens, and tc is a center thickness of the second lens.
2. The wide-angle photographic lens system enabling correction of distortion as set forth in claim 1, wherein incidence angles of a main beam of light in a field not less than 60% of a maximum image height in the lens system satisfy a relation,
A\u2014fr<A\u2014s,
wherein A_fr is an incidence angle of the main beam of light received on a tangent of a center of a front surface of the first lens, and A_s is an incidence angle of the main beam of light received on the iris.
3. The wide-angle photographic lens system enabling correction of distortion as set forth in claim 1 or 2, satisfying a relation,
|R\u2014L1S1f|>3.5,
wherein R_L1S1 is a radius of curvature of a front surface of the first lens.
4. The wide-angle photographic lens system enabling correction of distortion as set forth in claim 1 or 2, satisfying a relation,
h\u2014L1S1<h\u2014L3S2,
wherein h_L1S1 is an effective diameter of a front surface of the first lens, and h_L3S2 is an effective diameter of a rear surface of the third lens.
5. The wide-angle photographic lens system enabling correction of distortion as set forth in claim 1 or 2, satisfying a relation,
t34t>0.09,
wherein t34 is an interval between a rear surface of the first lens and a front surface of the second lens, and t is a total length of the lens system which is a distance from a front surface of the first lens to an image surface.
6. The wide-angle photographic lens system enabling correction of distortion as set forth in claim 1 or 2, satisfying a relation,
f23f>0.8,
wherein f is the total focal length of all the lenses, and f23 is a sum of focal lengths of the second lens and the third lens.
7. The wide-angle photographic lens system enabling correction of distortion as set forth in claim 1 or 2, wherein the first lens has aspheric surfaces on opposite surfaces, the second lens has an aspheric surface on at least one surface, and the third lens has aspheric surfaces on opposite surfaces.
8. The wide-angle photographic lens system enabling correction of distortion as set forth in claim 1 or 2, wherein any one or more of the first lens, the second lens and the third lens are made of a material different from a material of remaining lenses.
9. A wide-angle photographic lens system enabling correction of distortion, comprising: a first lens, an iris, a second lens and a third lens sequentially arranged along an optical axis from an object, wherein
the first lens has weak refractivity, the second lens has strong positive refractivity, and the third lens has negative refractivity, wherein incidence angles of a main beam of light in a field not less than 70% of a maximum image height in the lens system satisfy a relation,
A\u2014fr<A\u2014s,
wherein A_fr is an incidence angle of the main beam of light received on a tangent of a center of a front surface of the first lens, and A_s is an incidence angle of the main beam of light received on the iris.
10. The wide-angle photographic lens system enabling correction of distortion as set forth in claim 9, satisfying relations, |f1f|>2.8, f2f<1, and tetc<0.4,
wherein f1 is a focal length of the first lens, f is a total focal length of all the lenses, f2 is a focal length of the second lens, te is a lens thickness on an effective diameter of a rear surface of the second lens, and tc is a center thickness of the second lens.
11. The wide-angle photographic lens system enabling correction of distortion as set forth in claim 9 or 10, satisfying a relation,
|R\u2014L1S1f|>3.5,
wherein R_L1S1 is a radius of curvature of the front surface of the first lens.
12. The wide-angle photographic lens system enabling correction of distortion as set forth in claim 9 or 10, satisfying a relation,
h\u2014L1S1<h\u2014L3S2,
wherein h_L1S1 is an effective diameter of the front surface of the first lens, and h_L3S2 is an effective diameter of a rear surface of the third lens.
13. The wide-angle photographic lens system enabling correction of distortion as set forth in claim 9 or 10, satisfying a relation,
t34t>0.09,
wherein t34 is an interval from a rear surface of the first lens to a front surface of the second lens, and t is a total length of the lens system which is a distance from the front surface of the first lens to an image surface.
14. The wide-angle photographic lens system enabling correction of distortion as set forth in claim 9 or 10, satisfying a relation,
f23f>0.8,
wherein f is a total focal length of all the lenses, and f23 is a sum of focal lengths of the second lens and the third lens.
15. The wide-angle photographic lens system enabling correction of distortion as set forth in claim 9 or 10, wherein the first lens has aspheric surfaces on opposite surfaces, the second lens has an aspheric surface on at least one surface, and the third lens has aspheric surfaces on opposite surfaces.
16. The wide-angle photographic lens system enabling correction of distortion as set forth in claim 9 or 10, wherein any one or more of the first lens, the second lens and the third lens are made of a material different from a material of remaining lenses.