DE19929701A1 - Lens with crystal lenses - Google Patents

Abstract

A lens with lenses of two different crystals, in particular CaF¶2¶ and BaF¶2¶, is particularly suitable as a refractive projection objective of microlithography at 157 nm. Such projection lenses for 193/248 nm with quartz glass and achromatization with CaF¶2¶ be with BaF¶2¶ Compaction-resistant. With other fluorides and partially catadioptric lenses microlithography projection exposure systems in the wavelength range 100-200 nm possible.

Description

The invention relates to a lens with crystal lenses. Such lenses have been known for over a hundred years as Apochromat microscope lenses from Carl Zeiss with fluorspar (CaF ₂ ) lenses.

More recently, refractive projection lenses for microlithography have been realized in DUV at 248 or 193 nm wavelengths containing quartz glass and CaF ₂ lenses.

DD 222 426 B5 discloses an optical system with optical glasses and BaF ₂ single crystal as optical media, which can be used for wavelengths of 150 to 10 ⁴ nm. The embodiment is a planapochromate for 480 to 800 nm with several different glasses and BaF ₂ .

The choice of materials for UV microlithography lenses - focusing on the Wavelength 248 nm - is described in G. Roblin, J. Optics (Paris), 15 (1984) pp. 281-285 described.

As a result, only combinations of quartz glass with CaF ₂ or LiF are considered useful.

In U. Behringer, F + M (Munich) 107 (1999), 57-60 fluorides such as CaF ₂ , M _g F ₂ and LiF are described as suitable for 157 nm microlithography, with reservations because of the birefringence of MgF ₂ and because the handling of LiF.

KF Walsh et al., SPIE Vol. 774 (1987), 155-159, inter alia, the excimer lasers for 248, 193 and 157 nm wavelength are presented and for 248 nm quartz glass, CaF ₂ , BaF ₂ and M _g F ₂ as named only useful lens materials. For wavelengths below 248 nm, quartz glass is expected to be the only usable material.

In US 5,031,977 a catadioptric 1: 1 projection lens for microlithography at 248 nm is described, which contains a concave mirror, a quartz glass lens, a LiF lens and two deflection prisms of CaF ₂ . Arguments for material selection are just as little given as references to modifications of the specific construction.

However, close to 157 nm is the absorption edge of quartz glass. CaF _{2 still} transmits at 157 nm, but has too high a dispersion for a pure CaF ₂ objective of microlithography, even for a spectrally narrowed F ₂ excimer laser. So far, therefore, lenses for wavelengths below 193 nm only as katadioptrische-. DE 196 39 586 A of the same inventor and applicant and US Prov. Appln. Ser. No. 60 / 094,579 of 29 July 1998 by the same applicant - or catadioptric - cf. US 5,686,728 systems known. US 5,686,728 is a pure mirror objective for VUV microlithography with, for example, 126 nm, 146 nm or 157 nm excimer laser.

The object of the invention is to specify an alternative lens concept with a Material composition, the new applications, especially in the Microlithography at low wavelengths opened.

This object is achieved by a lens according to claim 1, a projection lens The microlithography of claim 4, or 9, 11, 12 and a Projection exposure apparatus according to claim 16, 17 or 18. Advantageous Embodiments are subject of the dependent claims 2, 3, 5-8, 10, 14-16, 19-21 and 23rd

A sub-aspect is specified in claim 13.

A method for producing microstructured components according to claim 22 provides in that a substrate provided with a photosensitive layer is provided by means of a mask and a projection exposure apparatus according to at least one of claims 17 to 21 - and  thus with a lens according to one of the preceding claims - by ultraviolet Is exposed to light and optionally after developing the photosensitive layer is patterned according to a pattern contained on the mask.

The invention is based on the recognition that it is possible to provide novel lens properties by using two different crystals in one lens. In particular, this includes the possibility of achromatization at low wavelengths, in which any known glass, including quartz glass, strongly absorbs. The reservations made in microlithography against BaF ₂ refer to 248 nm and quartz glass as partners.

Alkali and alkaline earth halides, especially their fluorides, as well as other fluorides are as Optics material known. Their sometimes difficult material properties have so far led to their excellent transmission properties in deep UV only used to some extent. According to the invention it has been shown that with these and similar materials optical microlithography up to about 100 nm wavelength after can be stretched down.

With the pairing of two fluoride crystals, in particular of CaF ₂ , BaF ₂ , SrF ₂ LiF, NaF, or KF, but also of mixed crystal fluorides, a pair of materials for the achromatization of 157 nm optics can be specified for the first time. The materials are already known in optics manufacturing, as evidenced by the cited prior art. Barium fluoride, strontium fluoride or sodium fluoride is preferably used according to claim 6 for negative lenses, and only for individuals, because that may suffice.

Calcium fluoride is then found according to claim 7 not only for the positive lenses, but also for the remaining negative lenses use.

It is particularly advantageous according to claim 8, that numerical apertures above 0.5, also at 157 nm. The following example with the numerical aperture of 0.8 proves this clearly. This becomes the resolution advantage of EUV microlithography partially compensated by about 1/10 of the wavelength, since about reaches the triple NA  becomes. Compared to 193 nm, however, the resolution can be almost halved at 109 nm, since the Level of NA is maintained. For the machining accuracy has ten times Wavelength compared to EUVL drastic advantages.

The stitching method (line by line exposure of the chip) according to claim 20, which recently got into conversation in microlithography at very low wavelengths, allows reduced image fields as rectangles with moderate aspect ratio and thus ensures for a drastic reduction of the lenses. The latter relaxes the Manufacturing problems for the lens crystals drastically.

A quite different embodiment of the invention according to claims 9 and 10 has surprisingly been found:
In DUV microlithography at 248 nm or 193 nm, an aging process known as "compaction" occurs in quartz glass, through which the material is compacted and consequently the refractive index and shape of the lens are changed. Of course, this degrades the imaging performance of the lens. In addition to the compensation by adjustable members it was recognized that the most heavily loaded and affected image-side lenses instead of quartz glass of crystal, namely preferably CaF ₂ , SrF ₂ or BaF ₂ can be made, which are much more stable to UV radiation.

In the patent application DE 198 55 157.6 of the applicant of the same filing date are several embodiments with such use of calcium fluoride lenses included, which should be part of the disclosure of this application.

In this case, BaF _2, like SrF ₂ at this point according to claim 9, has the advantage, which is disadvantageous in the context of achromatization, of being substantially less different from quartz glass in its optical properties than CaF ₂ (see Roblin at the given location). The design changes of a projection lens when replacing quartz lenses with BaF ₂ or SrF ₂ lenses close to the image are therefore minimal. The projection lens is thus optimized by the use of two crystalline materials - CaF ₂ for achromatization, BaF ₂ or SrF ₂ against the compaction.

For a 157 nm objective, purely refractive and made of one material, ie CaF ₂ , laser band widths down to 0.1 μm would be necessary, depending on the aperture and image field size.

It is not expected that these values can be easily achieved when changing from 193 to 157 nm. Everything becomes even more demanding, material permeability, Layer availability, grating for the laser components.

According to the invention, a material was found with BaF ₂ which is transparent and isotropic at 157 nm, which has a markedly higher dispersion at 157 nm than CaF ₂ and can be supplemented with this for the achromat. BaF ₂ absorbs completely only at about 130 nm. The proximity of the absorption edge to 157 nm is responsible for the rapid progression of the refractive index change (strong dispersion) at 157 nm. The same applies to other fluorides such as SrF ₂ .

At 193 nm, achromatization is established by the combination of CaF ₂ and quartz glass. BaF ₂ has only a slightly higher dispersion than CaF ₂ and, as it were, is useless in the dispersion between the dispersion of CaF ₂ and quartz glass.

For 157 nm, the situation changes because fused silica shows increased absorption. According to general opinion, there was no suitable partner for achromatization for CaF ₂ .

This is not the case: Although the dispersion distance between CaF ₂ and BaF ₂ at 157 nm is smaller than between CaF ₂ and quartz glass at 193 nm, it can still be very well partially chromatized under moderate use of BaF ₂ , at a similar level as at 193 nm, z. B. 50% color longitudinal error reduction.

At 193 nm, only partial achromatization is generally performed to minimize the CaF ₂ volume employed for reasons of cost, availability, and material properties. At 157 nm, one would like to keep the partner BaF ₂ small in volume, since it has a higher specific gravity and thus the BaF ₂ lenses bend more under gravity.

At 193 nm, one would like to make everything out of quartz glass, if possible at 157 nm everything from CaF ₂ . Since the number of positive lenses in the refractive lithography lens is significantly larger than that of the negative ones, it would be advantageous at 193 nm if fused quartz had a small dispersion. But conversely, CaF ₂ has the smaller dispersion and can not or should not be used in all positive lenses. Thus, positive lenses are made of quartz glass, which expresses the degree of achromatization.

At 157 nm, it is also desirable that the preferred material, here CaF ₂ , has a smaller dispersion than the partner.

In contrast to 193 nm, this is the case at 157 nm with BaF ₂ . Almost all lenses, certainly all positive lenses, can be from the crown, namely CaF ₂ . A few negative lenses are made of BaF ₂ , alternatively of SrF ₂ , because qualitatively the same applies as for BaF ₂ .

Of course, the above statements also apply to lenses in a catadioptric lens, especially for refractive partial lenses used for this purpose. The invention Lens can therefore also be catadioptric. The important thing is that lenses, and not only optical auxiliary elements such as deflection prisms or plane plates made of crystal.

One would like to lithography with a shorter wavelength than 157 nm and at the same time with operate very high numerical aperture, one encounters a wealth already known Problems in a tightened form. First, one must be aware that only at Excimer laser wavelengths suitable bandwidth and output power of the Light source is expected. The spectra of the noble gases also emit from about 60 nm, only these are very broadband and thus accessible only to pure mirror systems. Pure mirror systems with really extended field between 10 and 26 mm have up to now no aperture greater NA = 0.6.  

Excimer lasers can operate at the following wavelengths below 157 nm become:

NeF 109 nm Ar2 126 nm ArKr 134 nm Kr2 147 nm

In terms of material, a well-known candidate with very good transmission for 134 and 147 nm is CaF ₂ . For 134 and 147 nm catadioptric lenses with only CaF ₂ as the lens material are conceivable and thus do not represent anything new. If refractive lenses with more apertures are to be obtained, such as 0.80 / 0.85 / 0.90, the wavelength is 147 nm by the material system given above for 157 nm: positive lenses predominantly of CaF ₂ , some negative lenses of BaF ₂ . Since the absorption edge of BaF _{2 is} about 134.5 nm, it is still about 13 nm at 147 nm. This means increased absorption, but allows a more relaxed longitudinal chromatic aberration correction, since BaF ₂ now has a stronger dispersion at 147 nm than at 157 nm, with a higher increase than CaF ₂ , since the absorption edge of CaF ₂ is 125 nm.

In other words: with equally good bandwidth of the lasers of 157 nm and 147 nm, a material pair CaF ₂ and BaF ₂ at 147 nm gives the better result with regard to color correction in the case of a purely refractive objective. The absorption losses are, however, higher.

Even at 134 nm, no pair of materials for achromatization of purely refractive systems has been reported so far. According to the invention, this was found in the material pair CaF ₂ -SrF ₂ . The distance to the absorption edge of SrF ₂ at 130 mn must be classified as very low. The increased absorption makes the crystal appear reasonable only for very thin and small negative lenses. Therefore, such a system will be realistic only for smaller fields of view, such as a half field system (stitching).

At 126 nm, CaF ₂ precipitates completely, since the distance to the absorption edge is only 1 nm.

There remain as known materials MgF ₂ and LiF. MgF ₂ is also highly birefringent at 126 nm and thus unsuitable. Although LiF is permeable at 126 nm, it is unsuitable for smaller diameters since the radiation load increases and the material thereby changes inadmissibly (transmission and refractive index). Even a catadioptric system does not get through in the area of the highest aperture (in front of the image plane) without material in the passage. Thus, one would not be able to build a high-open lithography lens with a large field at 126 nm.

According to the invention, a further material can now be specified especially for the highly loaded small diameters. The configuration at 126 nm consists of a catadioptric lithography objective, which consists mainly of LiF. However, in the high-intensity irradiated lenses, it is the isotropic amorphous form of BeF ₂ . The crystalline form is birefringent similar to the crystalline quartz. The glassy solidified form, similar to quartz glass, is isotropic when prepared accordingly. Since BeF _{2 is} significantly more laser-resistant at 126 nm than LiF, it is the appropriate material in a few lenses either in a beam waist or at several beam waists and / or at the image end of the lens. The low number of BeF ₂ lenses is ultimately desirable, since BeF ₂ must be classified as a strong respiratory poison and weaker contact poison. For the infrared range, there are already long production lines that handle the handling of toxic optical components. Nevertheless, it is advantageous to limit the number of BeF ₂ lenses to the bare minimum. It is therefore a refractive or catadioptric lithography objective made of at least one crystalline and one glassy fluoride.

BeF ₂ must be prepared and processed anhydrous, since it tends to H ₂ O uptake and the H ₂ O immediately blocks the wavelength 126 nm.

In particular, H ₂ O-anne BeF ₂ production also makes the HeF laser wavelength accessible at 109 nm. Both components in highly pure form, LiF and BeF ₂ , enable a catadioptric objective at 109 nm.

Large dispersion optical materials are conventionally referred to as flint (glass) low dispersion referred to as crown (glass).

For the various DUV to VUV wavelengths are in accordance with the above proposed following compactly presented material combinations:

AL = L <- 193 nm: - CaF ₂ Kron KF Flint - CaF ₂ Kron KF + SiO ₂ glass flint - LiF +, CaF ₂ Kron KF Flint - LiF +, CaF ₂ Kron KF + SiO ₂ glass flint AL = L CB = 2 <-157 + 147 nm: @ CaF ₂ and / or LiF Kron NaF, BaF ₂ , and / or SrF ₂ Flint AL = L CB = 2 <- 134 nm: @ - CaF ₂ Kron SrF ₂ flint - CaF ₂ Kron NaF flint - LiF Kron SrF ₂ flint - LiF Kron NaF flint - LiF Kron NaF + SrF ₂ flint

while SrF ₂ for small diameter, as more radiation resistant than NaF

The above-mentioned systems can be coated with MgF ₂ and LaF ₃ thin-film systems. In addition, SiO ₂ and Al ₂ O ₃ are also suitable as antireflection layers for 193 nm.

This option of antireflection coating is an important requirement for the Realizability of multi-unit refractive lenses, otherwise per lens surface about 10% reflection loss occurs.

Since no antireflection layers are known for 126 nm and 109 nm, this is another Reason why catadioptric systems with few (eg 3-5) lenses are preferable here are according to claim 12.

When achromatizing with LiF and NaF, there is a possibility of interfaces Save crystal gas, thus also anti-reflection layers or reflection losses, according to Claims 13 and 14.

The thermal conductivity and the thermal expansion of both substances are very similar:

thermal conductivity expansion LiF 4.01 W / m / K 37,0.10 ^-6 / C NaF 3.75 W / m / K 36,0.10 ^-6 / C

Thus, a "cemented" can be created by wringing, each a + and -Linse or two + and one-lens. Since the refractive indices of both crystals are very low and the anti-reflection therefore difficult, this Kittgliedbildung is particularly helpful.

Apart from individual such cemented components, the objective could otherwise consist of CaF ₂ lenses.

Also blasted limbs of CaF ₂ and BaF ₂ are possible:

thermal conductivity expansion CaF ₂ 19.71 W / m / K 18.8.10 ^-6 / C BaF ₂ 11.72 W / m / K 18,1.10 ^-6 / C

Only the excellent thermal conductivity of the crystals over glasses leaves such bleaching appear safe, especially with different absorption (and thus warming).

As further crystals especially mixed crystals of fluorine are suitable, including those with Alkali or alkaline earth and other elements such as tin, zinc or aluminum. Height Dispersion and good light stability with high transmission in the VUV are the Selection criteria, avoiding birefringence.

Of course, the above statements also apply to lenses in a catadioptric lens, especially for refractive partial lenses used for this purpose. The invention Lens can therefore also be catadioptric. The important thing is that lenses, and not only optical auxiliary elements such as deflection prisms or plane plates made of crystal.

The invention will be explained in more detail with reference to the drawing, whose

Fig. 1 shows a lens section of a 157 nm microlithography projection objective with BaF ₂ lenses;

Fig. 2 shows a lens section of a 157 nm microlithography projection objective with NaF lenses and aspheres;

Fig. 3 shows a qualitative image of a projection exposure apparatus of microlithography;

Fig. 4 shows schematically a projection lens with cemented element; and

Fig. 5 shows schematically a catadioptric projection lens.

For the exemplary embodiment shown in the lens section in FIG. 1, Table 1 indicates the data.

It is a microlithography projection objective for the F ₂ excimer laser at 157 nm. By using CaF ₂ and BaF ₂ (for the lenses 17 , 18 , 21 , 24 , 26 , 28 , 30 ) it was possible to with a bandwidth of 0.5 μm, a stitching-compatible image field of 8.0 × 13.0 mm ² , a reduction factor of 4.0: 1, a distance object Ob to image Im of 1000 mm and with two-sided telecentric a numerical Aperture of 0.8 to realize. A further increase in the numerical aperture is quite possible. The color longitudinal error is reduced by a factor of 3 compared to a pure CaF ₂ objective. It is still CHL (500 pm) = 0.095 mm. This factor can be increased by additional CaF ₂ -BaF ₂ lens pairs. The total RMS error of the wavefront in image IM lies at RMS <13 m λ for all image heights, whereby the clearly reduced wavelength serves as a reference measure λ.

The refractive indices at the main wavelength λ ₀ = 157.63 nm of the F ₂ excimer laser and in 500 μm distance at λ ₁ = 158.13 nm

n ₀ = 1.5584 n ₁ = 1.5571 for CaF ₂ n ₀ = 1.6506 n ₁ = 1.6487 for BaF ₂ n ₀ = 1.5102 n ₁ = 1.5097 for SrF ₂ n ₀ = 1.4781 n ₁ = 1.4474 for LiF n ₀ = 1.4648 n ₁ = 1.4629 for NaF n ₀ = 1.5357 n ₁ = 1.5328 for KF

This results in an Abbe number (inverse to the dispersion):
CaF ₂ = 1219, BaF ₂ = 874, SrF ₂ = 392,
LiF = 674, NaF = 242, KF = 184.

Thus, at 157 nm BaF _{2 has} a 40% higher dispersion than CaF ₂ . In comparison, at 193 nm quartz glass has a 54% dispersion as CaF ₂ .

The projection objective of Fig. 1 and Table 1 has a total of 39 lenses and a plane-parallel termination plate P. Seven negative lenses 17 , 18 , 21 , 24 , 26 , 28 and 30 are made of BaF ₂ for achromatization. The construction is directly related to the above-described non-prepublished patent application DE 198 55 157.6 (the content of which is also intended to be part of this application) described design.

In the area of the system diaphragm AS, a third waist T3, which is not strongly constricted, is formed on the lens 26 , following the already classic sequence of abdomen B1 on lens 5 , waist T1 on lens 10 , abdomen B2 on lens 15 , waist T2 on lens 18 and abdomen B3 on lens 22 , as well as followed by abdomen B4. Particularly sophisticated is the lens group of lenses 20 to 39 with the double abdomen B3, B4.

Several spherical corrective air through spaces of greater thickness in the middle than at the edge are provided in the region of the aperture AS between the lenses 23/24, 26/27 and 29/30, 30/31 as a key correction means. This design limits the lens diameter even with the largest numerical aperture. The lens radii given in Table 1 - corresponding to the respective largest beam heights - show that the lens diameter is a maximum of 190 mm at the belly B4. Also, the lens diameters are distributed fairly uniformly, from lens 13 in the region of the second surface B2 to lens 34 near the image IM, all lens diameters are between 140 mm and 190 mm.

The negative BaF ₂ lenses 21 , 24 , 26 , 28 , 30 are arranged in classic + - pairs with positive CaF ₂ lenses 22 , 23 , 25 , 27 , 29 alternately in the region of the double abdomen B3, B4 predominantly in front of the diaphragm AS and are supplemented by two negative BaF ₂ lenses 17 , 18 in the region of the second waist T2. This results in a very effective use of the second crystal material for achromatization.

The use of two crystal lens materials according to claims 9 or 10 results from the lens designs known for example from the patent applications DE 198 55 108.8 and DE 198 55 157.6 of the same filing date and from other sources, characterized in that in a DUV lens ( 300-180 nm) with predominantly quartz glass lenses and predominantly close-glare, the achromatization serving CaF ₂ lenses the image IM next lenses - corresponding in Fig. 1 lenses 39 , 38 , etc. - made of quartz glass or CaF ₂ , now by BaF ₂ - or SrF ₂ lenses are replaced. The little different optical properties of BaF ₂ and SrF ₂ over quartz glass require only routine design changes with an optical design program. Of course, the plane plate P can be useful made of BaF ₂ . However, if it is changed more frequently, as a wear and protection element, it can also remain made of quartz glass (in the abovementioned wavelength range).

The exemplary embodiment of FIG. 2 shows a 157 nm full-field scanner projection lens based on CaF ₂ lenses, which is produced by the use of a total of five negative lenses 218 , 219 , 220 , 221 ; 232 , 233 , 234 , 235 ; 236 , 237 ; 249 , 250 ; 257 , 258 of NaF in the two waists, in the aperture space and in the convergent beam path in front of the image plane in the achromatized.

A total of three aspheric lens surfaces 211 , 221 , 257 , two of them on NaF, contribute to the good correction with a compact, material-saving construction of the objective.

Image scale 1: 4, image field diameter 27.2 mm for an 8 × 26 mm scanner full field and image-side numerical aperture of NA = 0.77 are essential characteristics of the lens whose RMS image error is below 16 mλ across all image heights in a laser Bandwidth of Δλ = ± 0.2 pm. The longitudinal chromatic aberration for the comparison value Δλ = 500 pm is CHL (500 pm) = 0.153 mm. The individual geometry data are summarized in Table 2. The largest used lens diameter is 46 mm at the lens 247 , 248 .

The design and use of the aspheres is done according to the principles of Patent application DE 199 22 209.6 of 14 May 1999 of the same inventor and Applicant, which is to be considered as part of the disclosure of this application.  

The projection exposure apparatus of microlithography shown schematically in FIG. 3 comprises an excimer laser as light source 301 , a device 302 for bandwidth reduction, which can also be integrated in the laser, an illumination system 303 with homogenization and field diaphragm device, etc., a mask holder 304 with positioning and mover 314 . A projection objective 305 according to the invention comprises lenses 315 , 325 made of different crystals or fluorides. In the image plane, the object is provided on an object holder 306 with positioning and moving device 316 . In the version as a scanner, mask and object holders are moved synchronously in different speeds at the imaging scale. Of course, the facilities of a projection exposure system, not shown here, such as control and regulating systems, autofocus, wafer and mask changing systems, and air conditioning also belong to this category.

Fig. 4 shows an objective lens 400 with a "lens component" 401, ie, without an air gap repaid lens group is held in this deep UV region by wringing, since no radiation-resistant mastic / glue is available. As stated above, such members with positive LiF and negative NaF lenses are useful or with BaF ₂ and CaF ₂ . Further lenses 402 in the lens 400 are then z. B. made of CaF ₂ or another of the materials described above.

Fig. 5 shows schematically a catadioptric objective according to the invention, as proposed for 126 nm or 109 nm lithography.

The object Ob is imaged onto the image plane Im by means of 4 mirrors M1 to M4 and 4 lenses L1 to L4. A lens L1 is combined with the mirror M1 to a mangin level. This facilitates manufacturing and reduces reflection losses and disturbances. The lenses L1, L3, L4, in which the radiation beam has a large cross-section and thus low intensity, are made of LiF. However, the image-near lens L2, which is used to increase the numerical aperture, is exposed to concentrated radiation. For this amorphous BeF _{2 is} used because of its higher radiation resistance.

The catadioptric lens is due to the absorption and the relatively difficult production of the lens materials only a few lenses, ie 1 to 10, included. Such microlithography projection lenses are z. B. known for 193 nm, cf. US 4,701,035 Fig. 12 and US 5,815,310 Fig. 3 with NA = 0.6 and quartz glass as a lens material. Starting from such systems, concrete embodiments of the invention can be derived, specifying the optical properties of the newly specified materials.

For the other lens designs of the invention is basically the Derive detailed design using design programs from existing designs. For this, the refractive index and dispersion of the materials at the respective Use operating wavelengths.

From "Handbook of Optics", McGraw-Hill 1995, Ch. 33 Properties of Crystals and Glasses, p. 33.64, ref. [125] are, for example, the dispersion curves of
LiF from 100 nm
NaF from 150 nm, with extrapolation from 130 nm
KF from 150 nm, with extrapolation from 130 nm
known.

The absorption edges of BaF ₂ , CaF ₂ , MgF ₂ , SrF ₂ and LiF ₂ can be found in GB 1 276 700 concerning a bandpass filter at 130 nm.

Optical constants of the mentioned antireflection layers can be found for example in M. Zukic et al. Applied Optics 29 no. 28, Oct. 1980, p 4284-4292.

The cited references are of course only examples. In addition, the precise optical properties also by measuring samples with a UV Spectrometers are obtained.  

Table 3a gives the Abbezahlen some fluoride and for comparison of quartz glass for the wavelengths of the ArF and the F ₂ -Excimerlasers.

Derived therefrom are the quotients of the Abbe numbers in Table 3b for different Kron / Flint combinations given at 157 nm. Big quotient means strong Color error correction with little flint.

Accordingly, the combination Kron LiF, Flint KF would be ideal. The difficult properties from KF speak against it (absorption, water sensitivity).

However, only the combination with NaF can compete with the Kron CaF ₂ over the combinations with LiF as Kron.

As soon as the production of lenses made of LiF is comparable to that of CaF ₂ lenses, lens constructions with LiF as crown are preferable, in combination with BaF ₂ or NaF, for example.

The inventive use of crystal lenses also brings catadioptric Systems in the wavelength range 130 to 200 nm have the same advantages.

A projection exposure apparatus with an objective according to the invention corresponds to For example, those known from the cited patent applications and other sources Superstructures, but now with the objective according to the invention.

For 157 nm systems is a F ₂ -Excimer laser with moderate effort to limit bandwidth, a matched lighting system z. B. according to the patent application DE 198 55 106, at least with fluoride and / or mirror optics, but also z. B. with inventive lens to provide. These are mask and wafer positioning and handling systems, etc. to the projection lens according to the invention.

The aspherical surfaces are given by the equation:

where P is the arrow height as a function of the radius h (height to the optical axis 7 ) with the aspheric constants C ₁ to C _n given in the tables. R is the peak radius specified in the tables.

Table 1

Table 2

Table 3a

pay off

Table 3b

Dispersion comparison 157 nm

Claims (18)

1. Lens with lenses of at least two different crystals. 2. Lens according to claim 1, characterized in that the lenses consist of at least two different fluorides, in particular of CaF ₂ , BaF ₂ , SrF ₂ , LiF, NaF, KF. 3. Lens according to claim 1 or 2 with additional lenses of vitreous material, in particular quartz glass or amorphous BeF _second 4. projection lens of microlithography, corrected for illumination with a F ₂ excimer laser at 157 nm, characterized in that it is purely refractive and contains lenses of BaF ₂ , SrF ₂ , NaF, LiF or KF. 5. Projection objective according to claim 4, characterized in that CaF _{2 is} used as a further crystal lens material. 6. projection lens according to claim 4 or S. characterized in that individual negative lenses are made of BaF ₂ or SrF ₂ or NaF. 7. projection lens according to claim 5 or 6, characterized in that all positive lenses and individual negative lenses are made of CaF ₂ . 8. projection lens according to at least one of claims 4 to 7, characterized characterized in that the image-side numerical aperture over 0.5, preferably over 0.6, is.   9. Refractive projection lens of microlithography, corrected for the illumination with wavelengths below 360 nm, containing lenses of quartz glass, characterized in that at least one of the two of the image plane of the lens next lenses made of crystal, preferably CaF ₂ , SrF ₂ or BaF ₂ executed is. 10. Lens according to claim 3 or 9, characterized in that it is a microlithographic projection lens, corrected for the laser illumination with a wavelength below 360 nm, and most lenses made of quartz glass, several positive lenses preferably near the lens, for achromatization of CaF ₂ and one or more object-side lenses for preventing the compaction influence from BaF ₂ or another fluoride, in particular SrF ₂ , are made. 11. Projection objective of microlithography with a working wavelength of 100-180 nm with lenses of at least two of the crystal materials CaF ₂ , BaF ₂ , LiF, NaF, SrF, KF or the amorphous BeF ₂ . 12. Projection objective of microlithography, designed as a catadioptric objective with a working wavelength of 100-130 nm containing lenses made of LiF and / or amphoric BeF ₂ . 13. achromatic lens group consisting of contiguous lenses of different fluorides, in particular NaF and LiF or CaF ₂ and BaF ₂ . 14. Projection objective with at least one achromatic lens group according to claim 13. 15. Lens according to at least one of claims 1 to 14, characterized in that at least one lens has an aspherical surface. 16. Lens according to at least one of claims 1 to 15, characterized in that lenses carry a thin-film coating of MgF ₂ and / or LaF ₃ . 17. Projection exposure machine with 157 nm light source and refractive Projection lens. 18. Projection exposure system of microlithography

• with a light source containing an excimer laser with 100-160 nm, preferably 100-150 nm wavelength,
• with an illumination system containing refractive optical elements of one or more fluorides, in particular alkali metal or alkaline earth fluorides,
• a reticle positioning and movement system
• with a projection objective with lenses made from at least two of the crystal materials CaF ₂ , BaF ₂ , LiF, NaF, SrF, KF or the amorphous BeF ₂ .
• - with an object positioning and movement system.
• - Projection exposure apparatus, in particular according to claim 17 or 18, characterized in that the projection lens is designed according to at least one of claims 1 to 15.
• - Projection exposure apparatus according to at least one of claims 17 to 19, characterized in that it is designed for the stitching method.
• - Projection exposure apparatus according to at least one of claims 18 to 20, characterized in that an excimer laser with 109, 126, 134, 146 or 157 nm wavelength is used as the light source.
• Method for producing microstructured components, in which a substrate provided with a photosensitive layer is exposed by means of a mask and a projection exposure apparatus according to at least one of claims 17 to 21 by ultraviolet laser light and a pattern of a pattern contained on the mask is patterned.
• - Lens according to claim 1, characterized in that in at least one diverging lens, a material is used, the refractive index of which is lower than the average refractive index of the materials used in the converging lenses.