EP0888570A1

EP0888570A1 - Reticular objective for microlithography-projection exposure installations

Info

Publication number: EP0888570A1
Application number: EP97952867A
Authority: EP
Inventors: Jörg SCHULTZ; Johannes Wangler; Karl-Heinz Schuster
Original assignee: Carl Zeiss AG
Current assignee: Carl Zeiss SMT GmbH
Priority date: 1996-12-21
Filing date: 1997-12-03
Publication date: 1999-01-07
Also published as: JP2000505916A; US6366410B1; JP4044146B2; KR100524662B1; WO1998028644A1; DE19653983A1; TW388798B; KR19990087107A

Abstract

A reticular objective is realized by introduction of a few (3-5 units) aspherical lenses (7, 11, 17) of high-quality correction with a low number of lenses (few that 10), and low path in glass (maximum 25-30 % of the object-reticle distance), thus enhancing efficiency.

Description

Description :

REMA lens for microlithography processing projections

The invention relates to a REMA lens. This is a lens with which a reticle masking device (REMA) is imaged in the plane of the reticle that carries the structured mask for the lithography. The area illuminated on the reticle is thus sharply outlined. The reticle masking device is usually constructed with adjustable cutting edges. The picture is usually magnifying.

A REMA lens is used in microlithography projection exposure systems (steppers or scanners).

From DE-U 94 09 744 an illumination device for a microlithographic projection exposure system is known, in which the following are provided: light source, shutter, coupling lens (zoom axicon), glass rod as integrator, reticle masking system, REMA lens for imaging the intermediate field level lying in the reticle masking system onto the reticle, containing a first lens group, an intermediate pupil level, a second lens group, a deflecting mirror, a third lens group and the reticle level with the reticle. This is followed by a projection lens, which is normally reduced in size and - for example with a non-telecentric entrance - contains an internal pupil plane, then the afer in the image plane.

In the system according to EP 0 526 242 AI, a projection objective is provided after the integrator, here a honeycomb condenser, before the reticle masking system follows. The reticle masking system is optically conjugated to the reticle plane via two lens groups and mirrors, i.e. is imaged. At the same time, the aperture at the exit of the integrator - the secondary light source - through the two lens groups and parts of the projection lens onto the pupil of the projection Lens shown. Nothing is said about image errors.

WO 95/32446 by the applicant describes a high-aperture catadioptric reduction lens for microlithography, the embodiment of a REMA lens shown here being exactly suitable for the embodiment according to FIG. 3 and Table 2.

The patent application DE-A 195 48 805 from December 27, 1995, which was published only after the priority date, describes REMA lenses with exclusively spherical lens surfaces. The exemplary embodiment there has 13 lenses and is very similar in its optical properties to the exemplary embodiment shown here (FIG. 1). With regard to their pupil function, both REMA lenses fit perfectly to the projection lens of WO 95/32446.

The aforementioned WO document such as DE-A 195 48 805 and DE-U are therefore expressly part of the disclosure of this patent application.

The object of the invention is to provide a REMA lens which has considerably fewer interfaces - at which reflection losses occur - and considerably less glass path - in which absorption takes place - and thus has a significantly improved transmission efficiency. No compromise can be made on the optical properties.

This problem is solved by a REMA objective with a few, at most four to five, aspheres according to one of the independent claims 1 or 2 and by a complete projection exposure system according to claim 16.

It is known per se that aspheres open up new correction possibilities and lenses can thus be saved. But it is also clear that aspheres drastically increase the manufacturing and quality inspection effort, so that they are their number and their deviation from the spherical shape must be used sparingly.

Surprisingly, it was possible to reduce the number of lenses and the glass path to less than 60% with only three to four, at most five, aspheres, the deviations of which are moderate from the sphericity. The high requirements for a REMA lens are still met, but the efficiency (transmission) is significantly increased.

Claim 1 makes this relationship clear. Claim 2 is based on the structure, with condenser, intermediate and field lens part.

The sub-claims 3 to 15 relate to advantageous execution forms.

Claim 3 quantifies the reduced glass path to below 30%, preferably below 25%, of the object-reticle distance.

Claims 7 and 8 relate to the adaptation to the special preferred environment with REMA at the exit of a glass rod or with a reducing catadioptric projection object.

Claim 15 describes the adaptation to the pupil function of a projection lens with very good telecentricity with very small deviations. The small deviations of the main rays of the projection lens from the parallelism are very well hit by the REMA lens.

Independent claim 16 takes up this good adaptation of the REMA objective with the few elements described to the associated projection objective for an entire microlithography projection exposure system.

The invention is explained in more detail with reference to the drawings. FIG. 1 shows the lens section of a REMA objective with three aspheres;

FIG. 2 schematically shows a microlithography projection exposure system;

Figure 3 shows a given pupil function;

FIG. 4 shows in the example deviations of the pupil function from FIG. 3; and

FIG. 5 shows the lens section of another embodiment with four aspheres.

The exemplary embodiment of a REMA objective with the lens section of FIG. 1 has the data in Table 1. It consists of a condenser part 100, designed as a partial objective, in front of the aperture diaphragm 8, an intermediate part 200 and a field lens part 300. In each of these parts there is an asphere 7, 11, 17 provided. So the REMA lens has only seven lenses. The flat surfaces 9 and 14 only have a placeholder function. A deflecting mirror (240 in FIG. 2) can be arranged in the region of 14.

The aspherical surfaces are described according to the formula: p (h) = (h ² / R + V ^" R ² - (l + k) h ² ) + cl h ⁴ + .. + cn h ^{2n + 2} p the arrow height, h the distance to the optical axis, R the apex radius, k the conical constant and cl to cn are the aspherical constants.Aspherical surfaces are all optical surfaces with a rotationally symmetrical deviation from the best-matched sphere above approx. 5 micrometers The useful asphericities are predominantly of the order of 0.1 to 1 mm (typically up to 2 mm).

The objective forms the object plane 1, in which the reticle masking system is arranged, with the object-image distance of 1200 mm on the reticle level 19. The air spaces at the object level 1, at the aperture level 8, between the intermediate part 200 and the field lens portion 300, and at the reticle level 19 are generously dimensioned so that the parts to be arranged there - the REMA system 90, correction elements in the aperture level, a deflecting mirror 240 and the handling system 330 (see FIG. 2) for the reticle - can be accommodated without problems.

The main function of a REMA objective, the imaging of a light-dark edge (cutting edge of the REMA diaphragm) from the object plane 1 to the reticle plane 19 with an edge profile whose brightness values are 5% and 95% by less than 5%, preferably less than 0.5% of the field of view diameter are spaced apart:

The distance is 0.4% of the image field diameter of 42.1 mm. This information provides an integral measure of all image defects in the entire image field, which is directly based on the function of the REMA lens.

This good correction is difficult because the REMA lens has the considerable light conductance of 11.4 mm (product of the object field diameter 19 mm and the object-side numerical aperture NAO = 0.6). In general, light conductance values greater than 10 mm are required for such lenses.

The magnification of the REMA lens is 4.444: 1.

Another core function of the REMA lens is that the incoming main beam, ie the heavy beam of the incident light cone, differs only slightly from the specified main beam of a subsequent projection lens at every point of the image plane 19, namely by less than 3 mrad. This is equivalent to the requirement that a given pupil function - see FIG. 3 - must be reproduced with the smallest deviations in the reticle plane 19. As FIG. 4 shows, this is achieved perfectly. In Figure 3, the sine of the main beam angle sin (i) is shown as a function of the image height YB in the reticle plane 19, in Figure 4, the deviation sin (i), which is in a band of +/- 0.11 mrad around zero .

Adaptation to double-eccentric projection lenses is assumed, so that the REMA lens is also high-quality telecentric on the image side. It is also absolutely telecentric on the object side.

The design of the field lens group 300 is decisive for the adaptation. In the example, it is reduced to the minimum of two lenses, the converging lens 15, 16 and the diverging lens 17, 18. The asphere required here - otherwise many spherical elements would be required - is the Area 17. In this area the main jet heights are greater than the marginal jet heights.

One of the surfaces, preferably the last surface 18, can also be made flat so that it is suitable for carrying a gray filter as a thin layer to control the intensity distribution on the reticle.

The condenser part 100 is designed as a partial objective whose object plane is at infinity. The aperture lies in the object plane 1 of the overall lens and the image plane in the aperture 8 of the overall lens. The marginal rays of the partial objective thus correspond to telecentric main rays of the overall objective, the main rays of the partial objective correspond to the marginal rays of the overall objective.

The image of this partial objective (condenser part 100) in the plane of the diaphragm 8 should be corrected as well as possible, since 8 correction elements can be accommodated in this plane and a clean diaphragm function is achieved. Accordingly, the coma, expressed as the transverse deviation, is made in its maximum value less than 1%, preferably less than 0.2%, of the image field diameter of this partial image. For example 0.08% are achieved. For this purpose, the condenser part contains at least one hollow surface that is curved toward the object 1, for which the opening ratio of the radius of curvature to the lens diameter is close to the minimum of 0.5 for the hemisphere. In the example, the value on area 2 is 0.554. In general, it should be chosen less than 0.65.

When using one (as in FIG. 1) asphere 7 to two aspheres, three (2/3, 4/5, 6/7) to four lenses are now sufficient to implement these functions of the condenser part 100.

The intermediate part 200 also has an asphere 11. He now manages with a pair of lenses 10/11, 12/13, surface 13 fulfilling the following condition:

It is a curved hollow surface with | sin (iR _anc j) | ≥ 0.8 NAO. This surface 13 thus causes a strong refraction in the edge area. For the REMA lens according to the invention, this edge beam angle is in any case greater than 0.6 NAO.

The REMA lens according to the invention thus has all the functions of the REMA lens according to DE 195 48 805.9; the embodiment of the example according to FIG. 1 can directly replace the exemplary embodiment of FIG. 1 there. The effect of the few aspheres 7, 11, 17 is drastic:

The condenser part 100 shrinks from 5 to 3 lenses, the intermediate part 200 only needs 2 to 4 lenses, and in the field lens part 300 the number of lenses is also halved to 2. In this example there are only 7 lenses left (a maximum of 10 for others Versions).

The glass path, that is the sum of all glass thicknesses of the lenses on the optical axis, amounts to only 235 mm here compared to 396 mm in the earlier application, with a lens-image distance 1-19 of 1200 mm in both cases. The glass path is therefore reduced by over 40%, the proportion of the cutting width is only 20%, and in other versions only up to 25-30% of the cutting width. The transmission of high quality quartz glass at 248 nm is approx. 99.9% / cm. Aging processes (radiation damage, color center formation) reduce the value during operation. At the glass-air boundary layers, high-quality antireflection layers at 248 nm can achieve transmission levels of approx. 99.5%.

While the REMA lens according to DE 195 48 805.9 thus achieves a maximum of 84.4% transmission efficiency, the value in the example in FIG. 1 is at least 91.1%.

This improvement in the transmission efficiency becomes even more important in systems for lower wavelengths, for example 193 nm, since there the transmission of quartz (and also possible alternatives) drops significantly and the implementation of antireflection layers is more difficult. At the same time, the material costs are even more important and the laser power becomes more expensive and thus the light losses become more expensive.

Since the present design can be adapted to the conditions at other, especially lower, wavelengths taking into account the changed refractive index, the invention is particularly valuable for this development towards lower wavelengths.

FIG. 2 shows a schematic overview of the optical part of an entire projection exposure system (wafer stepper), in which the REMA lens 123 according to the invention is integrated.

A KrF excimer laser 50 with a wavelength of 248 nm serves as the light source. A device 60 is used for beam shaping and coherence reduction. A zoom axicon lens 70 enables different types of lighting to be set as required. It is like the entire arrangement (apart from the features of the REMA lens 123 according to the invention), for example, from the EP-A 0 687 956 or from DE-U 94 09 744 (both by the applicant) are known. The light is coupled into the glass rod 80, which is used for mixing and homogenization.

The reticle masking system 90, which lies in the object plane 1 of the REMA objective 123, immediately follows. This consists of the first lens group 100, the pupil plane (diaphragm plane) 14, the second lens group 200, the deflecting mirror 240, the third lens group 300 and the image plane 33. The reticle 330 is arranged here, which is precisely positioned by the changing and adjusting unit 331 becomes. This is followed by the catadioptric projection lens 400 according to WO 95/32446 with the pupil plane 410. In the exemplary embodiment of Tables 1 and 2, however, the entrance pupil is almost infinite in front of the projection lens. The wafer 500 is arranged in the image plane.

Figure 5 shows the lens section of another embodiment with 4 aspheres 505, 509, 514, 520 and a total of 18 interfaces of 8 lenses and a flat plate 521, 522. Table 2 gives the dimensions. Areas 511 and 516 only serve as governors. Image scale (4.730: 1) and image field (diameter 127 mm) do not differ significantly from the example in Figure 1. However, the light conductance is larger at 16.2 mm.

Here, too, the number of lenses and the glass path are drastically reduced with 22% of the object-image distance compared to a purely spherical design. As the comparison with FIG. 1 shows, the condenser part 550 with 4 lenses here, including 2 aspheres 505, 509, still has room for improvement. Nevertheless, the improvement compared to the purely spherical REMA lens is considerable, with moderate use of aspheres. Table 1

Scale: 4,444: 1 wavelength: 248.33 nm

Radius thickness material

1 55.240 2 -38.258 46.424 quartz 3 -66.551, 633 4 881.696 45.341 quartz 5 -190.791, 924

374.111 47.958 quartz

7 -287.518 222.221 8 aperture 17, 900 9 00 79.903 10 164.908 52.350 quartz 11 • 1246.141 27.586 12 280.226 19.580 quartz 13 114.495 133.941 14 oo 365.253 15 -216.480 12.551 quartz 16 -113.446 1.399 17 -329, 056 10.797 quartz 18 - 552,687 60,000 19,000

Area Aspherical Constants

7 K = -, 00640071 Cl =, 347156E-07 C2 =, 802432E-13 C3 = -, 769512E-17 C4 =, 157667E-21

11 K = +, 00104108 Cl =, 431697E-07 C2, 564977E-13 C3 = -, 125201E-16 C4 =, 486357E-21

17 K = +, 00121471 Cl = -, 991033E-07 C2 = -, 130790E-11 C3 = -, 414621E-14 C4 =, 200482E-17 C5 = -, 392671E-21 Table 2

Scale: 4, 730 Wavelength: 248, 33 nm

Radius thickness material

501 00 49.615

502 -36.076 39.343 quartz

503 -58.772 7.280

504 769.933 46.491 quartz

505 -154.827 24, 882

506 251.853 42.379 quartz

507-5038.206 177.092

508 1206.092 26.134 quartz

509 -382.601 2.521

510 aperture 16,000

511 00 48.808

512 220.678 54.515 quartz

513 -329.344 23.787

514 -2544.603 12.265 quartz

515 107,244 178, 887

516 00 312.788

517 -634.092 24.232 quartz

518 -177.052 24.158

519 -1168.238 15.641 quartz

520 -3520.690 9.182

521 00 4,000 quartz

522 00 60,000

523 00,000

Area Aspherical Constants

505 K = -, 11512040 Cl =, 36489383E-07 C2 =, 16169445E-11 C3 = -, 70228033E-16 C4 =, 36695356E-20

509 K = -, 01464591 Cl =, 37060030E-07 C2 =, 92577260E-12 C3 = -, 10037407E-16 C4 =, 29843433E-20

514 K = +, 00003903 Cl = -, 13705523E-08 C2 = -, 90824867E-12 C3 =, 81297785E-16 C4 = -, 56418498E-20

520 K = -, 000150010 Cl =, 17085177E-07 C2 =, 18373060E-10 C3 = -, 49871601E-14 C4 =, 61193181E-18 C5 = -, 23186913E-22

Claims

Claims:

1. REMA lens with three to eight times magnification, a light conductance greater than 10 mm, in which the imaging of a light-dark edge from the object plane (1) to the reticle plane (19) results in an edge profile whose brightness values are 5% and 95% apart by less than 2%, preferably less than 0.5%, of the image field diameter, characterized in that no more than 10 lenses, 1 to 5, preferably 3 to 4, aspherical surfaces (7, 11, 17), are provided.

2. REMA objective, which images an object plane (1) lying at a finite distance on a reticle plane (19), with a condenser part (100), designed as a front partial objective, the image plane of which is at infinity, the diaphragm in the object plane (1) of the entire REMA objective, with an intermediate part (200) and with a field lens part (300), characterized in that the condenser part (100), intermediate part (200) and field lens part (300) each have one or two aspherical lens surfaces (7, 11, 17), with a total of no more than five, preferably no more than four, aspherical surfaces (7, 11, 17), and that the total number of lenses is a maximum of 10.

3. REMA lens according to at least one of claims 1 or 2, characterized in that the glass path in the lenses is a maximum of 30%, preferably a maximum of 25%, of the distance from the object plane (1) and reticle plane (19).

4. REMA lens according to claim 1, 2 or 3, characterized in that at least one optical surface with a largest amount of the sine of the angle of incidence against the surface normal of an edge beam in air (| sin (iR ndH) greater than 0.6 times, preferably greater than 0.8 times the object-side numerical aperture (NAO) is present.

5. REMA lens according to at least one of claims 1-4, characterized in that it contains a partial lens (100) which generates a pupil plane (14) corrected with respect to the coma.

6. REMA objective according to claim 5, characterized in that the partial objective (100) has at least one hollow surface (4) which is curved towards the object plane (1) and on which the aperture ratio of the radius of curvature to the lens diameter is less than 0.65.

7. REMA lens according to at least one of claims 1-6, characterized by the use in a microlithography projection exposure system, in which the reticle masking (90) is arranged at the output of a glass rod (80).

8. REMA lens according to at least one of claims 1-7, characterized by the use in a microlithography projection exposure system in which the projection lens (400) is a miniaturizing catadioptric lens.

9. REMA lens according to claim 1, characterized in that it consists of a condenser part (100), formed as a front partial lens, the image plane of which is at infinity, the aperture in the object plane (1) of the entire REMA lens, an intermediate part ( 200) and a field lens part (300) is constructed.

10. REMA lens according to claim 2, characterized in that it has three to eight times magnification.

11. REMA lens according to claim 2, characterized in that it has an image field diameter greater than 80 mm.

12. REMA lens according to claim 2, characterized in that it has an image-side numerical aperture of over 0.10.

13. REMA lens according to claim 2, characterized in that it has a light conductance greater than 10 mm.

14. REMA lens according to claim 2, characterized in that the imaging of a light-dark edge of the object plane

(1) on the reticle plane (19) produces an edge profile whose brightness values are 5% and 95% apart by less than 2%, preferably less than 0.5%, of the image field diameter.

15. REMA lens according to at least one of claims 1-14, characterized in that it reproduces a predetermined pupil function with values of sin (i) in the range ± 10 mrad with deviations below + 1 mrad, in particular below ± 0.3 mrad.

16. Microlithography projection exposure system with a lighting device containing an enlarging REMA lens (123) and with a reducing projection lens (400), the pupil plane (12) of the REMA lens (123) into the pupil plane (410) of the

Projection objective (400) is imaged and in each point of the reticle plane (330) the incoming main beam of the REMA objective (123) deviates only less than 3 mrad, preferably less than 0.3 mrad, from the main beam of the projection objective (400), characterized that the REMA lens (123) has a maximum of 10 lenses with a maximum of 5, preferably a maximum of 4, aspherical surfaces.