Patent Number: 
Section: claims

1. A lithographic projection apparatus comprising: a radiation system to provide a projection beam of radiation;  a support structure adapted to support patterning structure which can be used to pattern the projection beam according to a desired pattern;  a substrate table to hold a substrate;  a projection system to project the patterned beam onto a target portion of the substrate,  wherein said projection system includes precisely four imaging mirrors in the optical path of the projection beam and has an incidence angle classification, C, of 2(xe2x88x92), 6(xe2x88x92), or 9(xe2x88x92), where:  a i =1 if an angle of incidence of a chief ray at mirror i is negative,  a i =0 if the angle of incidence of the chief ray at mirror i is positive,  M is a magnification of the projection system, and  the index i numbers the mirrors from object to image. 2. Apparatus according to  claim 1  wherein said projection system has a stop on one of a second mirror of the four imaging mirrors and a third mirror of the four imaging mirrors. claim 1 3. Apparatus according to  claim 1  wherein said projection system has an intermediate image located at one of between first and second ones of the mirrors, between second and third ones of the mirrors and between third and fourth ones of the mirrors. claim 1 4. A lithographic projection apparatus comprising: a radiation system to provide a projection beam of radiation;  a support structure adapted to support patterning structure which can be used to pattern the projection beam according to a desired pattern;  a substrate table to hold a substrate;  a projection system to project the patterned beam onto a target portion of the substrate,  wherein said projection system has precisely six imaging mirrors in the optical path of the projection beam and has an incidence angle classification, C, of 5(+), 6(xe2x88x92), 9(+), 13(+), 18(xe2x88x92), 21(+), 22(xe2x88x92), 25(+), 29(+), 34(xe2x88x92), 37(+), 38(xe2x88x92), 42(xe2x88x92), or 54(xe2x88x92), where:  a i =1 if an angle of incidence of a chief ray at mirror i is negative,  a i =0 if the angle of incidence of the chief ray at mirror i is positive,  M is a magnification of the projection system, and  the index i numbers the mirrors from object to image. 5. Apparatus according to  claim 4 , wherein said projection system has a stop located on one of second, third, fourth and fifth ones of the mirrors. claim 4 6. Apparatus according to  claim 4 , wherein said projection system has an intermediate image between the second and fifth mirror. claim 4 7. Apparatus according to  claim 4  wherein said projection system has the smallest deviation from telecentricity while still enabling obscuration-free illumination of the mask such that, for each point on the object, in a pencil of rays leaving an object, a ray forming the smallest angle with an optical axis forms an angle not larger than 10xc2x0 to the optical axis. claim 4 8. Apparatus according to  claim 4  wherein said projection is substantially telecentric on the image side such that for each point on an object, the ray passing through the center of the aperture stop forms in an image space an angle with an optical axis not larger than 1xc2x0. claim 4 9. Apparatus according to  claim 4  wherein each mirror in said projection system is substantially rotationally symmetric about an optical axis. claim 4 10. Apparatus according to  claim 4  wherein said projection system has a magnification whose absolute value is in the range of from ⅓ to {fraction (1/10)}. claim 4 11. Apparatus according to  claim 10  wherein said magnification has an absolute value substantially equal to one of xc2xc and ⅕. claim 10 12. Apparatus according to  claim 4  wherein said projection beam comprises extreme ultraviolet radiation having a wavelength in the range of from 8 to 20 nm. claim 4 13. Apparatus according to  claim 12  wherein said projection beam comprises extreme ultraviolet radiation having a wavelength in the range of from 9 to 16 nm. claim 12 14. An apparatus according to any  claim 4 , wherein the support structure comprises a mask table for holding a mask. claim 4 15. An apparatus according to  claim 4 , wherein the radiation system comprises a radiation source. claim 4 16. A device manufacturing method comprising: projecting the patterned beam onto a target portion of the substrate, wherein said projection system has precisely six imaging mirrors in the optical path of the projection beam and has an incidence angle classification, C, of 5(+), 6(xe2x88x92), 9(+), 13(+), 18(xe2x88x92), 21(+), 22(xe2x88x92), 25(+), 29(+), 34(xe2x88x92), 37(+), 38(xe2x88x92), 42(xe2x88x92), or 54(xe2x88x92), where:  a i =1 if an angle of incidence of a chief ray at mirror i is negative,  a i =0 if the angle of incidence of the chief ray at mirror i is positive,  M is a magnification of the projection system, and  the index i numbers the mirrors from object to image. 17. A lithographic projection apparatus comprising: a radiation system to provide a projection beam of radiation;  a support structure adapted to support patterning structure which can be used to pattern the projection beam according to a desired pattern;  a substrate table to hold a substrate;  a projection system to project the patterned beam onto a target portion of the substrate,  wherein said projection system has precisely eight imaging mirrors in the optical path of the projection beam and has an incidence angle classification, C, of 2(+), 5(+), 9(+), 12(+), 13(+), 18(+), 18(xe2x88x92), 19(+), 20(+), 21(+), 22(+), 23(+), 25(+), 26(+), 34(xe2x88x92), 36(+), 37(+), 38(xe2x88x92), 45(+), 46(+), 49(+), 52(+), 53(+), 54(+), 54(xe2x88x92), 55(xe2x88x92), 59(xe2x88x92), 68(+), 69(+), 73(+), 74(+), 77(+), 82(+), 82(xe2x88x92), 85(+), 88(+), 89(+), 90(xe2x88x92), 92(+), 93(+), 97(+), 100(xe2x88x92), 101(+), 102(xe2x88x92), 104(+), 105(+), 106(+), 106(xe2x88x92), 107(+), 108(+), 109(+), 109(xe2x88x92), 110(+), 110(xe2x88x92), 111(+), 113(+), 116(+), 117(+), 118(+), 118(xe2x88x92), 120(+), 121(+), 122(xe2x88x92), 123(xe2x88x92), 132(+), 133(+), 134(xe2x88x92), 137(+), 138(+), 141(+), 145(+), 145(xe2x88x92), 146(+), 146(xe2x88x92), 147(+), 148(+), 148(xe2x88x92), 149(+), 150(+), 150(xe2x88x92), 151(+), 151(xe2x88x92), 152(xe2x88x92), 153(+), 154(+), 154(xe2x88x92), 155(+), 155(xe2x88x92), 156(+), 157(+), 159(+), 161(+), 162(xe2x88x92), 163(xe2x88x92), 164(+), 165(+), 166(+), 166(xe2x88x92), 167(+), 168(+), 169(+), 170(+), 170(xe2x88x92), 171(+), 172(+), 173(+), 174(+), 175(+), 176(+), 177(+), 178(xe2x88x92), 179(+), 180(+), 180(xe2x88x92), 181(+), 181(xe2x88x92), 182(+), 182(xe2x88x92), 183(+), 183(xe2x88x92), 184(+), 185(+), 185(xe2x88x92), 186(xe2x88x92), 187(+), 187(xe2x88x92), 188(xe2x88x92), 189(+), 196(+), 197(+), 201(+), 203(+), 205(+), 209(+), 214(xe2x88x92), 216(+), 217(+), 218(+), 218(xe2x88x92), 225(+), 228(+), 229(+), 230(+), 232(+), 233(+), 235(+), 236(+), 237(+), 238(xe2x88x92), 243(+), 246(+), 247(+), 248(+), 250(xe2x88x92), where:  a i =1 if an angle of incidence of a chief ray at mirror i is negative,  a i =0 if the angle of incidence of the chief ray at mirror i is positive,  M is a magnification of the projection system, and  the index i numbers the mirrors from object to image. 18. Apparatus according to  claim 1  wherein said projection system has the smallest deviation from telecentricity while still enabling obscuration-free illumination of the mask such that, for each point on the object, in a pencil of rays leaving an object, a ray forming the smallest angle with an optical axis forms an angle not larger than 10xc2x0 to the optical axis. claim 1 19. Apparatus according to  claim 1  wherein said projection is substantially telecentric on the image side such that for each point on an object, the ray passing through the center of the aperture stop forms in an image space an angle with an optical axis not larger than 1xc2x0. claim 1 20. Apparatus according to  claim 1  wherein each mirror in said projection system is substantially rotationally symmetric about an optical axis. claim 1 21. Apparatus according to  claim 1  wherein said projection system has a magnification whose absolute value is in the range of from ⅓ to {fraction (1/10)}. claim 1 22. Apparatus according to  claim 21  wherein said magnification has an absolute value substantially equal to one of xc2xc and ⅕. claim 21 23. Apparatus according to  claim 1  wherein said projection beam comprises extreme ultraviolet radiation having a wavelength in the range of from 8 to 20 nm. claim 1 24. Apparatus according to  claim 23  wherein said projection beam comprises extreme ultraviolet radiation having a wavelength in the range of from 9 to 16 nm. claim 23 25. An apparatus according to any  claim 1 , wherein the support structure comprises a mask table for holding a mask. claim 1 26. An apparatus according to  claim 1 , wherein the radiation system comprises a radiation source. claim 1 27. Apparatus according to  claim 17  wherein said projection system has the smallest deviation from telecentricity while still enabling obscuration-free illumination of the mask such that, for each point on the object, in a pencil of rays leaving an object, a ray forming the smallest angle with an optical axis forms an angle not larger than 10xc2x0 to the optical axis. claim 17 28. Apparatus according to  claim 17  wherein said projection is substantially telecentric on the image side such that for each point on an object, the ray passing through the center of the aperture stop forms in an image space an angle with an optical axis not larger than 1xc2x0. claim 17 29. Apparatus according to  claim 17  wherein each mirror in said projection system is substantially rotationally symmetric about an optical axis. claim 17 30. Apparatus according to  claim 17  wherein said projection system has a magnification whose absolute value is in the range of from 1/3 to 1/10. claim 17 31. Apparatus according to  claim 2  wherein said magnification has an absolute value substantially equal to one of xc2xc and ⅕. claim 2 32. Apparatus according to  claim 17  wherein said projection beam comprises extreme ultraviolet radiation having a wavelength in the range of from 8 to 20 nm. claim 17 33. Apparatus according to  claim 32  wherein said projection beam comprises extreme ultraviolet radiation having a wavelength in the range of from 9 to 16 nm. claim 32 34. An apparatus according to any  claim 17 , wherein the support structure comprises a mask table for holding a mask. claim 17 35. An apparatus according to  claim 17 , wherein the radiation system comprises a radiation source. claim 17 36. A device manufacturing method comprising: projecting a patterned beam of radiation onto a target portion of a layer of radiation-sensitive material on a substrate using an imaging system including precisely four imaging mirrors in the optical path of the projection beam and has an incidence angle classification, C, of 2(xe2x88x92), 6(xe2x88x92), or 9(xe2x88x92), where:  a i =1 if an angle of incidence of a chief ray at mirror i is negative,  a i =0 if the angle of incidence of the chief ray at mirror i is positive,  M is a magnification of the projection system, and  the index i numbers the mirrors from object to image. 37. A device manufactured in accordance with the method of  claim 36 . claim 36 38. A device manufacturing method comprising: projecting the patterned beam onto a target portion of the substrate, wherein said projection system has precisely eight imaging mirrors in the optical path of the projection beam and has an incidence angle classification, C, of C, of 2(+), 5(+), 9(+), 12(+), 13(+), 18(+), 18(xe2x88x92), 19(+), 20(+), 21(+), 22(+), 23(+), 25(+), 26(+), 34(xe2x88x92), 36(+), 37(+), 38(xe2x88x92), 45(+), 46(+), 49(+), 52(+), 53(+), 54(+), 54(xe2x88x92), 55(xe2x88x92), 59(xe2x88x92), 68(+), 69(+), 73(+), 74(+), 77(+), 82(+), 82(xe2x88x92), 85(+), 88(+), 89(+), 90(xe2x88x92), 92(+), 93(+), 97(+), 100(xe2x88x92), 101(+), 102(xe2x88x92), 104(+), 105(+), 106(+), 106(xe2x88x92), 107(+), 108(+), 109(+), 109(xe2x88x92), 110(+), 110(xe2x88x92), 111(+), 113(+), 116(+), 117(+), 118(+), 118(xe2x88x92), 120(+), 121(+), 122(xe2x88x92), 123(xe2x88x92), 132(+), 133(+), 134(xe2x88x92), 137(+), 138(+), 141(+), 145(+), 145(xe2x88x92), 146(+), 146(xe2x88x92), 147(+), 148(+), 148(xe2x88x92), 149(+), 150(+), 150(xe2x88x92), 151(+), 151(xe2x88x92), 152(xe2x88x92), 153(+), 154(+), 154(xe2x88x92), 155(+), 155(xe2x88x92), 156(+), 157(+), 159(+), 161(+), 162(xe2x88x92), 163(xe2x88x92), 164(+), 165(+), 166(+), 166(xe2x88x92), 167(+), 168(+), 169(+), 170(+), 170(xe2x88x92), 171(+), 172(+), 173(+), 174(+), 175(+), 176(+), 177(+), 178(xe2x88x92), 179(+), 180(+), 180(xe2x88x92), 181(+), 181(xe2x88x92), 182(+), 182(xe2x88x92), 183(+), 183(xe2x88x92), 184(+), 185(+), 185(xe2x88x92), 186(xe2x88x92), 187(+), 187(xe2x88x92), 188(xe2x88x92), 189(+), 196(+), 197(+), 201(+), 203(+), 205(+), 209(+), 214(xe2x88x92), 216(+), 217(+), 218(+), 218(xe2x88x92), 225(+), 228(+), 229(+), 230(+), 232(+), 233(+), 235(+), 236(+), 237(+), 238(xe2x88x92), 243(+), 246(+), 247(+), 248(+), 250(xe2x88x92), where:  a i =1 if an angle of incidence of a chief ray at mirror i is negative,  a i =0 if the angle of incidence of the chief ray at mirror i is positive,  M is a magnification of the projection system, and  the index i numbers the mirrors from object to image.