|Publication number||USRE42570 E1|
|Application number||US 11/247,002|
|Publication date||Jul 26, 2011|
|Filing date||Oct 7, 2005|
|Priority date||Sep 26, 1996|
|Publication number||11247002, 247002, US RE42570 E1, US RE42570E1, US-E1-RE42570, USRE42570 E1, USRE42570E1|
|Inventors||Karl Heinz Schuster|
|Original Assignee||Carl Zeiss Smt Gmbh|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (22), Classifications (25), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a reissue of U.S. Pat. No. 6,631,036 which is a continuation-in-part application of patent application Ser. No. 09/263,788, filed Mar. 5, 1999, which, now U.S. Pat. No. 6,169,627, in turn, is a continuation-in-part application of patent application Ser. No. 08/936,537, filed Sep. 24, 1997, now abandoned.
The invention relates to catadioptric objective and the use thereof in a microscope or a microlithographic projection exposure apparatus. The catadioptric objective includes spherical and aspherical lens elements and two concave mirrors which face each other. All components of the catadioptric objective, including also the object field and the image field, are arranged centered to a linear optical axis. This class of catadioptric objectives has a central aperture obscuration.
At wavelengths in the deep ultraviolet range, that is, wavelengths less than 250 nm, mirrors having a positive refractive power are used in combination with lenses of negative refractive power as suitable means for color correction.
A catadioptric microscope objective having two concave mirrors facing each other is disclosed in Russian patent publication 124,665. The 60× magnification of the catadioptric microscope objective is achieved without intermediate imaging. Because of the low field size, only a few spherical lenses are needed for correction. A composite lens is used in addition to the mirrors for color correction. This correction means is, however, no longer available in the deep ultraviolet wavelength range.
Catadioptric objectives for microlithography having only one concave mirror are known from U.S. Pat. No. 5,691,802 or European patent publication 0,475,020. In these systems, the optical axis must be bent at least once. If reticle and wafer are to be mounted parallel to each other, then a two-fold beam deflection is required. This leads to significant complexity with respect to construction. If, in addition, a purely reflective beam splitter is used, such as disclosed in U.S. Pat. No. 5,691,802, then only off-axis object fields can be imaged. The lenses of the objective near to the field are non-symmetrically illuminated whereby asymmetrical thermal deformations and therefore imaging errors which are difficult to correct occur because of the absorption of the lenses. A centered arrangement of the optical components on a linear optical axis having two concave mirrors facing each other as shown in
The effects of an aperture obscuration on the contrast transmission function is investigated in the article of S. T. Yang et al entitled “Effect of Central Obscuration on Image Formation in Projection Lithography” (SPIE Volume 1264, Optical/Laser Microlithography III (1990), pages 477 to 485. For incoherent illumination, the contrast is reduced for low spatial frequencies in comparison to an unvignetted system. The acceptance of obscured objectives can therefore be significantly increased when the aperture obscuration is further reduced. In addition, a reduction of the contrast transmission function must not necessarily lead to a reduction of the resolution capacity because of the nonlinear response function of the photoresist. By suitably selecting the photoresist, the break in the contrast transfer function continues to lie above the exposure threshold of the photoresist.
It is an object of the invention to further reduce the aperture obscuration and the lens diameters in objectives of the kind described above. It is a further object of the invention to provide excellent imaging and color correction for the field sizes typical for microlithography and an increase of the image end aperture compared to the state of the art with the least possible use of material.
The catadioptric objective of the invention transmits a light beam along a light path and defines an optical axis. The catadioptric objective includes in sequence of the travel of the light beam: a first lens group having a negative refractive power and arranged centered on the optical axis; a first concave mirror having a central cutout and being arranged centered on the optical axis downstream of the first lens group; a second concave mirror having a central cutout and being arranged centered on the optical axis downstream of the first concave mirror; the first and second concave mirrors being disposed so as to face each other; a second lens group having a negative refractive power and being arranged centered on the optical axis downstream of the second concave mirror; the first lens group having a first plurality of lenses arranged upstream of the first concave mirror; the second lens group having a second plurality of lenses arranged downstream of the second concave mirror; and, one of the first and second plurality of lenses having at least one aspheric lens surface.
The catadioptric objective of the invention is normally combined as a partial objective with at least one dioptric (purely refractive) partial objective to form a reduction objective. The combination of a catadioptric component objective with at least one dioptric partial objective and the use in a microscope or in a microlithographic projection exposure apparatus is also described.
In the catadioptric objective, the light rays starting from the object plane first pass through a first lens group having a negative refraction power and then impinge on a first concave mirror which has a hole at its center. This concave mirror is mounted concavely to the object plane. The light is reflected back and impinges on the second concave mirror which likewise has a central hole. This second concave mirror is mounted concavely to the image plane. In this way, the two concave mirrors face each other. The light rays are reflected back from this second concave mirror and pass through a second lens group having a negative refractive power before they impinge on the image plane of this catadioptric partial objective.
The cutouts in the mirrors make a continuous ray trace possible but lead to a central obscuration in the illumination of the diaphragm plane. All rays which would impinge in the region of the mirror cutouts when reflected at the concave mirrors do not contribute to imaging and have to be vignetted via suitable measures. An obscuration of the aperture rays occurs. The rays which proceed from an object point are characterized as aperture rays and these rays lie within a bundle of rays delimited by the system diaphragm.
The first lens group, the two concave mirrors and the second lens group are arranged centered on a common optical axis defining a straight line. The aperture obscuration and the use of material for the lenses is further reduced because of the targeted use of aspheric surfaces.
By using with one or several partial objectives, the intermediate image, which is generated by this catadioptric objective, shows intense aberrations which are then compensated with the additional objectives in the total image. The catadioptric objective is to exhibit a chromatic overcorrection and/or overcorrection of the Petzval sum as a compensation for combination with dioptric partial objectives.
It is especially advantageous when the lens elements directly forward of the first concave mirror and/or the lens elements directly after the second concave mirror have an intense negative refractive power. The lens elements can be individual negative lenses or can be several lens elements which, however, have to exhibit an overall negative refractive power. It is advantageous when these lenses having negative refractive power or adjacent lenses have aspheric lens surfaces. These lenses with negative refractive power generate a chromatic overcorrection. The amount of the chromatic axial aberration for lenses having a refractive power Φ and a marginal ray height hRD is proportional to hRD 2·Φ and the lenses having negative refractive power close to the mirror have a low marginal ray height because of the required low aperture obscuration. For this reason, the refractive power of the lenses has to be that much higher in order to achieve an adequate chromatic overcorrection.
It is advantageous when the lenses of the object end field lens group and/or the image end field lens group have at least one aspheric surface in order to influence the chief ray angle in the object plane and the image plane. All those lenses are counted to the field lens group within which the marginal ray of an object point of the optical axis runs between the optical axis and the chief ray of the outermost field point.
A further feature of the invention is that the first lens group can be subdivided into three subgroups. The center subgroup has a positive refractive power; whereas, the first and third subgroups have negative refractive powers. For the correction, it advantageous when a lens of the center subgroup has an aspherical surface.
To hold the lens diameter small, the lenses of the first and second lens group advantageously are passed through only in one direction. Lenses, which are run through a multiple number of times, should be in the light path between the concave mirrors and have correspondingly large diameters. However, this does not preclude that the first and/or second lens group extend partially into the space between the mirrors.
If the absolute value of the magnification ratio of this catadioptric objective lies approximately between 0.70 and 1.30, then an assembly symmetrical to the diaphragm plane can be achieved for the concave mirrors and their central cutouts. In this way, the diameters of the cutouts and therefore their contributions to the aperture obscuration are similarly large. If the magnification ratio does not lie in this region, then the first and second lens group have different focal lengths and it is significantly more difficult to maintain the diameters of the cutouts the same size. A further advantage of an absolute value of the magnification ratio between 0.7 and 1.3 and of a configuration symmetrical to the diaphragm plane is the fact that asymmetrical imaging errors such as coma can be well controlled in a low order.
The minimum aperture obscuration is achieved when the last lens of the first lens group and the first lens of the second lens group are each arranged in the region of a mirror cutout. It is therefore advantageous when individual lenses or at least lens parts are located in the geometric space between the first and second concave mirrors.
A concave surface which comes close to a hemisphere is advantageously provided in the first and/or second lens group. The ratio of half a lens diameter to the radius of the surface is greater than 0.70 for these surfaces. The concave surface of the first lens group then faces toward the object plane and the concave surface of the second lens group faces toward the image plane. The aperture obscuration can be held very low because of these very intense diverging surfaces close to the concave mirrors.
It is advantageous that the lens having the concave surface or an adjacent lens has an aspherical lens surface. The aperture obscuration can be further reduced with the aspherical surface in the proximity of a lens having a high negative refractive power.
The maximum deflection of the marginal ray within the first lens group and/or within the second lens group can be achieved with low aperture obscuration when a lens surface is provided in close proximity to the concave mirrors so that the angles of incidence of the marginal rays referred to the surface normal assume maximum values at the particular passthrough point. The angles of incidence are limited upwardly only by the necessity of an antireflecting coating, which is adapted for the particular working wavelength, and unwanted polarization effects for angles of incidence close to the Brewster angle. In this way, the sines of the angles of incidence for these lens surfaces result which, in any event, are greater than the object end numerical aperture by a factor of three.
It is advantageous when the lens has a surface, which has high angles of incidence, or an adjacent lens has an aspherical surface. In this way, aberrations can be compensated which are caused by the surface having high angles of incidence.
It is possible to reduce the aperture obscuration to values below 35% and even down to 20% with the aspheric surfaces and the lenses having high negative refractive power in the proximity of the concave mirrors. The aperture obscuration is defined as a percent ratio of the sine of the ray angle of a ray which proceeds from an object point on the optical axis and is targeted to the edge of the mirror hole and the sine of the ray angle of the marginal ray of the same object point. The ray angles are determined with respect to the optical axis.
If the concave mirrors are arranged forward and rearward of the diaphragm plane, then the holes of the mirrors are almost symmetrical to the diaphragm plane. With this measure, the field-dependent aperture obscuration can be minimized. With the diaphragm plane between the concave mirrors, the chief rays intersect the optical axis after the reflection at the first concave mirror and forward of the reflection at the second concave mirror.
The catadioptric objective is so configured that a ray trace, which is substantially symmetrical to the diaphragm plane, results between the first and second lens groups so that the ray height of the marginal ray, which proceeds from an object point on the optical axis, at the last surface of the first lens group differs from the ray height of the same marginal ray at the first surface of the second lens group by a maximum of 20%.
A large aperture expansion is required in order to hold the aperture obscuration as low as possible and to reduce the structural length of the objective. If one looks at a ray, which intersects the optical axis in the object plane, then the aperture expansion can be defined as the ratio of the sine of the angle i2 of this ray after the first lens group to a sine of the angle i1 of the same ray forward of the first lens group. The angles are then each determined with respect to the optical axis. With a negative refractive power of the first lens group, the aperture expansion
is adjusted to greater than 2.0.
With aspheric surfaces, it is possible to control the aperture expansion in dependence upon the angle of the ray impinging upon the first lens group. With very high values for the aperture expansion and lenses having high negative refractive power, a significantly higher aperture expansion results for purely spherical lens surfaces for the marginal rays than, for example, for a paraxial ray. The increase of the aperture expansion with increasing ray angle leads to larger mirror diameters and therefore to an increase of the objective dimensions. With aspherical lens surfaces forward and rearward of the concave mirrors, the aperture expansion can be influenced in dependence upon angle. The object is that the ratio mR/mP is less than 1.1 and preferably less than 1.05 for the aperture expansion mR for a marginal ray and for the aperture expansion mP for a paraxial ray. The aspherical surfaces forward and rearward of the concave mirrors are so configured that the effect, which is generated by the aspherical surface of the first lens group, is compensated to a large extent by the aspherical surface of the second lens group. The action of the aspherical surfaces cannot be viewed completely in isolation but only in combination with the neighboring system surfaces.
The lens diameters can be greatly reduced in comparison to the mirror diameters with the intense aperture expansion of the first lens group and the corresponding aperture reduction of the second lens group. Material which is transparent in the low ultraviolet range and has large diameters is very expensive and is only available to a limited extent. For this reason, it is advantageous when the maximum lens diameters amount to only 20% to 25% of the mirror diameters.
For coupling the catadioptric objective to the illuminating system, it is advantageous when the catadioptric objective has an almost homocentric entrance pupil. The deviation of the object end pupil function from a line fit through this pupil function can serve as an index. The object end pupil function is understood to mean the trace of the tangent values of the chief ray angles in the object plane over the intersect heights of the chief rays in the object plane. An objective having a homocentric entry pupil would exhibit a linear pupil function. The compensating line is determined from all ray-angle ray-height value pairs in the region from −Ymax to +Ymax wherein Ymax is the maximum possible object height of the circular-shaped object field. The deviation of the pupil function from the line fit should and can be maximally ±10 mrad, preferably maximally ±5 mrad.
It is possible that all lenses are of the same material because of the color correction with the aid of both concave mirrors and the mirror-near lenses having high negative refractive power.
With wavelengths ≦250 nm, preferably the fluoride crystals CaF2, BaF2, SrF2, LiF, NaF, KF can, inter alia, be used in addition to special quartz glasses and mixed crystals.
In the intermediate spaces between the lenses, a gas is advantageously provided which exhibits only a slight absorption in the region of the working wavelength. The gas charge can be provided with synthetic air, N2 or rare gases in dependence upon working wavelength. Large light paths occur in the space between the concave mirrors and disturbances because of refractive index fluctuations and pressure fluctuations have a great influence. For this reason, the space between the concave mirrors is preferably filled with a gas whose refractive index exhibits a lower temperature dependency and pressure dependency than nitrogen. Helium is ideally suited.
It is purposeful to couple the described catadioptric objective with a refractive objective in a reduction objective. The catadioptric objective of the invention defines a first partial objective which images the object plane into an intermediate image plane. The intermediate image plane is imaged to demagnified with a refractive second objective on the image plane. The magnification ratio of the reduction objective typically lies in the range from −0.1 to −0.5. The sequence of catadioptric and refractive component partial objectives can also be reversed. In the catadioptric partial objective, the chromatic axial aberration and the image field curvature are so overcorrected by the lenses, which are adjacent to the concave mirrors having intense negative refractive powers so that a corrected image results in the image plane of the reduction objective with reference to chromatic aberration and image field curvature. The lenses of the refractive partial objective correct the image errors spherical aberration, oblique spherical aberration and coma for an image field greater than 20 mm and an image end aperture greater than NA=0.7.
The intermediate image by the catadioptric partial objective is only inadequately corrected. Aberrations such as a large inner coma are present in the intermediate image because of the intense aperture expansion and the lenses having high negative refractive power. To correct these aberrations, which are introduced by the catadioptric partial objective, and to provide adequate correction of the large image field and the high numerical aperture, it is advantageous when the refractive partial objective has at least one aspherical surface.
Two aspherical lens surfaces are arranged symmetrically to the diaphragm plane and permit a correction of the spherical aberration as well as the correction of the field-dependent aperture aberration such as coma and oblique spherical aberration. The two aspherical lens surfaces are arranged in such a manner that a chief ray has at both surfaces a similarly large ray height with respect to magnitude and the difference in the ray heights amounts to maximally 30% and preferably less than 20%.
In these and other objectives, it is advantageous to provide two mutually adjacent aspherical surfaces to correct the spherical aberration and the sine condition. The two aspherical surfaces can define the two sides of a lens or they can be provided on two lenses and lie separated from each other by an air space. These double aspheres close to the diaphragm plane are especially effective so that the ray heights of the chief ray of the outermost field point at the adjacent aspherical surfaces are maximally 15%, preferably maximally 10% of the diameter of the diaphragm.
If the refractive partial objective is disposed forward of the image plane of the entire objective, then it is advantageous to provide an aspheric surface in the field lens group next to the intermediate image plane in order to influence the chief ray angles in such a manner that a telecentric trace of the chief rays results at the image end. The chief ray angles with reference to the image plane should lie within the entire image field in the range of ±5 mrad. The object end field lens group of the refractive partial objective includes all the lenses within which the marginal ray of an object point of the optical axis runs between the optical axis and the chief ray of the outermost field point.
Because of the chromatic overcorrection of the catadioptric partial objective, it is possible to utilize only lenses made of one material in the refractive partial objective even for a bandwidth of the light source of several pikometers (up to 10 pm).
The reduction objective is formed from the catadioptric partial objective and the refractive partial objective and can be used also in a microscope because of the high numerical aperture of NA>0.70. In the reduction objective, the object plane and the image plane are to be exchanged, that is, the objective is to be operated in the opposite direction. A further increase of the aperture can be achieved with a reduction of the field size.
The objective can be used for the inspection of wafers with small fields, very high apertures and wavelengths less than 250 mm. This can take place in the context of a narrow wavelength band or a broad wavelength band.
Usually, this class of catadioptric reduction objectives is used in microlithography. The objective is then a component of the microlithographic projection exposure system. The following lasers can be used as light sources in the DUV/VUV wavelength range: ArF laser for 193 nm, F2 laser for 157 nm, Ar2 laser for 126 nm and NeF laser for 109 nm. An illuminating system ensures the homogeneous illumination of the structure mask. The field lens group of the illuminating system functions to adapt the exit pupil of the illuminating system to the entrance pupil of the projection objective. The illuminating system additionally includes means for controlling the partial coherence and for field masking the structural mask.
Microstructural components having structural sizes even below 0.1 μm can be produced with a microlithographic projection exposure system of the above kind.
The invention will now be described with reference to the drawings wherein:
The lens section view shown in
An intermediate image plane Z is realized between the surfaces 29′ and 30′ and meniscus lenses (46′, 47′; 48′, 49′) and (53′, 54′) are provided at the additional pupil P corresponding thereto. These meniscus lenses optimally correct image errors generated by the mirrors (21′, 23′) and especially off-axis image errors.
A planar plate (50′/51′) is provided between the meniscus lenses directly in the region of the pupil P. During manufacture of these objectives, this planar plate (50′/51′) can be used for the purpose of correcting residual errors of the objectives via small form corrections which can, for example, be generated by ion ray etching thus making a nonspherical, nonplanar surface but retaining the overall planar shape.
The object-end lens group (1′ to 20′) is a wide angle retrofocus objective. The lens group (24′ to 29′) is mirrored with respect to function to the lens group (1′ to 20′) and is forward of the intermediate image Z of this type. The meniscus lenses (19′, 20′ and 24′, 25′) cause the light beam to diverge greatly at the mirror end and thereby result in the small central bore. The two lens groups (1′ to 20′) and (24′ to 29′) extend into the mirror arrangement (21′, 23′). It is an important function of the meniscus lenses (19′, 20′) and (24′, 25′) to create a large axial chromatic aberration. This aberration is compensated by all of the remaining lenses.
The greatly convex surface 57′ in combination with the glass thickness of the corresponding lens up to the surface 60′ is significant for the here-described objective class and is similarly conventional for microscope objectives.
All lenses are spherical and are made of quartz glass. Other materials (calcium fluoride) can be provided for the operation at lower wavelengths such as 157 nm.
The mirrors are aspherical in accordance with the known power series expansion:
P(h)=(½R)h2+c1h4+. . . +cnh2n+2
wherein: P is the sagitta as a function of the radius h (elevation to the optical axis) with the aspheric constants c1 to cn presented in Table 1. R is the vertex radius from Table 1. The deviations of the mirror surfaces from the spherical are moderate and can be controlled during manufacture. The type of glass listed in Table 1 is SUPRA1 or quartz.
The manufacture of such aspherical mirrors in the diameter range of 0.5 to 1 meter is known from the area of astronomic instruments. For assembly-line manufacture, shaping techniques such as galvano forming can be applied. The manufacturing accuracy does not have to be too great because conjugated corrective surfaces are available on the above-mentioned planar plate (50′/51′) or on one of the adjacent meniscus lens surfaces 48′, 49′, 53′ or 54′.
An optical element (50′, 51′) is arranged in the region of the pupil (P) following the intermediate image (Z). This optical element (50′, 51′) has non-spherical corrective surfaces.
It is also possible to provide elastic mirrors. As a departure from the known alignment cementing, these mirrors can be adjusted in an assembly phase utilizing actuators and can then be fixed on a rigid carrier. On the other hand, these mirrors can be controlled in optimal form during operation on line with, for example, piezoelectric actuators in order to compensate, for example, for thermal lens effects.
A projection exposure system is shown in
The object is identified by reference numeral 205 and can be, for example, a semiconductor wafer or LCD panel. The object 205 is held by an object holder and operating system 250.
The catadioptric reduction objective shown in
To correct residual errors, non-spherical corrective surfaces are provided in the vicinity of the diaphragm plane following the intermediate image plane. The form of the corrective surfaces is dependent upon the residual errors of the individual sample so that the aspherical corrective surfaces are not part of the objective design.
At wavelengths less than 200 nm, normal quartz glass is not suitable; however, fluoride crystals (for example, CaF2) can be used but these materials are available only to a limited extent in the required quality and size. For this reason, it is desirable to provide a design wherein the lens diameters are still further reduced so that a lesser amount of expensive fluoride material need be used.
Finally, it is better for the size of the aperture obscuration to omit the lenses of the first lens group located between the two concave mirrors.
The catadioptric reduction objective includes a catadioptric first partial objective L1 having surfaces 2 to 48 and a refractive second partial objective L2 having the surfaces 50 to 84. The catadioptric first partial objective L1 images the object plane OB slightly demagnified on the intermediate image plane IMI with a magnification ratio βL1=−0.76. The intermediate image plane IMI is imaged by the refractive second partial objective L2 on the image plane IM significantly demagnified with a magnification ratio of βL2=−0.33. In this way, the total magnification ratio β of the object plane OB in the image plane IM is β=−0.25. The circularly-shaped object field OB has a diameter of 91.2 mm and the corresponding image field IM has a diameter of 22.8 mm. If the catadioptric reduction objective is used in lithography, then object field and image field are rectangularly shaped. For example, a rectangularly-shaped field having the X-Y dimensions 22 mm×6 mm can be placed in the circular-shaped image field as would be suitable for a wafer scanner. The image end numerical aperture is NA=0.8 in the first embodiment. A numerical aperture this high in combination with a large image field has only recently been presented for projection objectives.
All lenses of this catadioptric reduction objective are made of the same material, in this case, CaF2. CaF2 has a refractive index of 1.55841 at the working wavelength of λ=157.3 nm. If one has the possibility in the wavelength region less than 250 nm to use a second material having higher dispersion in lenses having negative refractive power, then the color correction can be further improved. For example, sodium fluoride NaF as a counterpart to CaF2 is, for example, conceivable.
At wavelengths λ<200 nm, oxygen O2 is absorbent so that a gas charge with N2 or a suitable rare gas is provided. In the first embodiment, the lens intermediate spaces are filled with N2.
The catadioptric partial objective L1 comprises a first lens group G11 having surfaces 2 to 27, a first concave mirror M1 having a central cutout B1, a first pupil plane AS1, a second concave mirror M2 having a central cutout B2 and a second lens group G12 having surfaces 33 to 48. These optical components are passed through by the light rays in the sequence indicated. In
The two concave mirrors M1 and M2 facing each other fulfill two significant tasks in the catadioptric partial objective L1: the concave mirrors together with the neighboring lenses of negative refractive power generate the overcorrection of the axial chromatic aberration and the field curvature. As concave mirrors, they have a large positive refractive power but do not introduce any chromatic image errors. For chromatic overcorrection in the intermediate image plane IMI, the first lens group G11 and the second lens group G12 have a high negative refractive power whose diverging action is again compensated by the concave mirrors so that the first partial objective L1 generates a real image. Simultaneously, the lenses having negative refractive power with low marginal ray heights in combination with mirrors of positive refractive power with high marginal ray heights are the ideal correction means for field flattening. With the catadioptric partial objective L1, the field curvature in the intermediate image plane IMI can be overcorrected so that a planar image field results in the image plane IM after the imaging with the refractive partial objective L2 without additional corrective means for field flattening being needed in the refractive partial objective 12.
The mirror hole B1 of the concave mirror M1 and the mirror hole B2 of the concave mirror M2 lead to an obscuration in the pupil illumination. Specific aperture regions cannot be transmitted with this class of objectives. In the first embodiment, for an object point on the optical axis, the sine of the marginal ray angle is sine(iMax)=0.2 and the sine of the minimum possible aperture angle is sine (iMin)=0.0369. The aperture obscuration is computed at 18.5%.
A corresponding masking device is provided in the pupil plane AS1 in order to shade the rays which would impinge on the cutout B1 of the first concave mirror M1 and have an aperture angle of less than iMin. This masking device is so selected that the aperture obscuration is of the same size for all object points and lies centered to the chief ray. The minimally possible aperture obscuration of 18.5% for a point on the optical axis is increased to 20% when considering all object points. This masking device can, for example, be a circular absorbing disc which is arranged centered to the optical axis. A rod can serve as a holder which extends along the optical axis and is attached to the lens surfaces 27 and 33. In both lens surfaces, a recess can be machined (for example, with a diamond) in which the holding rod can be seated. The region about the optical axis in the vicinity of the pupil plane AS1 is not in the imaging beam path. For this reason, the holding device can be so designed that there is no effect on the imaging. A holder of the masking device having spokes or the like extending from the lens holder or mirror holder would lead to diffraction and thereby lead to a reduction of the resolution capacity.
The aperture obscuration affects the contrast transmission function of this class of objectives. For this reason, it is advantageous when the aperture obscuration is held as small as possible. All optical components of the catadioptric partial objective L1 are therefore so designed that the aperture obscuration remains limited to a minimum possible value.
It is necessary that the lenses next to the concave mirror have a large negative refractive power in order to hold the aperture obscuration small. In the embodiment, these are the lenses having the surface number 24/25, 26/27 and 33/34, 35/36. In the first lens group G11, the lenses contain concave surfaces 24 and 26, which are concave to the object plane OB and, in the second lens group G12, the lenses have concave surfaces 34 and 36 concave to the intermediate image plane IMI with very high values for the aperture ratio of lens height hmax to lens radius R. Thus, for surface 24, h24 max/R24=0.72 and for surface 36, h36 max/R36=0.75. The aperture ratio of the concave surfaces for these negative lenses close to the mirrors is therefore significantly greater than 0.7.
The last lens 26/27 of the first lens group G11 is designed as a biconcave lens in order to obtain the maximum expansion of the aperture rays after the lens group G11. The angles of incidence of the aperture rays in the optically thinner medium (that is, with a refractive index less than 1.1) on the lens side 27, which faces toward the concave mirror M1, assume the largest possible values. In the present example, the sine of the incident angle with respect to the surface normal in the optically thinner medium for the marginal ray on the surface 27 for an object point on the optical axis is sine(i27 RD)=0.779. Correspondingly, the first lens 33/34 of the second lens group G12 is a biconcave lens and the lens surface 33 is a surface where high angles of incidence are present. Accordingly, the sine of the angle of incidence in the optically thinner medium with respect to the surface normal for the same marginal ray is sine(i33 RD)=0.722.
It is possible to greatly expand the aperture rays with the negative refractive power of the first lens group G11. Thus, the sine of the angle of the marginal ray of an object point on the optical axis is 0.200 forward of the first lens group G11 and 0.706 after the first lens group G11 with respect to the optical axis. The aperture expansion for this marginal ray therefore is 3.532. Because of the negative refractive power of the second lens group G12, the sine of the angle of the same marginal ray with respect to the optical axis reduces from 0.676 forward of the second lens group G12 to 0.304 after the second lens group G12, that is, by the factor 1/2.254.
The aperture expansion is dependent upon the magnitude of the aperture angle i1 forward of the first lens group G11. With a very great ray deflection with only a few spherical lens elements, an increase of the aperture expansion with an increasing aperture angle i1 would occur which, in the following, is identified as a positive distortion of the aperture expansion. This distortion is unwanted because it leads to an increase in the mirror diameters without being able to thereby reduce the aperture obscuration. In order to reduce the positive distortion of the aperture expansion with purely spherical lens surfaces, the negative refractive power of the lenses 24/26 and 26/27 would have to be distributed to additional lenses in order to reduce the angle of incidence of the diverging surfaces. Additional lenses would, however, lead to an increase of the structural length and to further transmission losses.
The distortion of the aperture expansion can be corrected without additional lens elements when an aspherical lens surface 27 is provided in the lens group having negative refractive power (surfaces 24 to 27). It is advantageous when the last lens surface 27 of the first lens group G11 is aspheric because, in this way, the dispersion of the ray angles directly forward of the first concave mirror M1 can be influenced. The object is to reduce the positive distortion of the aperture expansion and, in the ideal case, reverse into a negative distortion. With a reduction of the aperture expansion for increasing aperture angles i1, the mirror diameters can be reduced with the aperture obscuration remaining the same. In the present example, the aperture expansion mR=3.532 for a marginal ray having i1 R=0.2. The aperture expansion mP=3.465 for a paraxial ray having i1 P=0.002. The paraxial ray would not exhibit a throughgoing ray trace because of the aperture obscuration in the real system; however, it is viewed here as a fictitious system without mirror cutouts. The ratio of the aperture expansion mR for the marginal ray and mP for the paraxial ray is mR/mP=1.019. The positive distortion of the aperture expansion lies only at 2% with the aspherical lens surface 27. The first surface 33 of the second lens group G12 is likewise aspherical in order to compensate the distortion of the aperture expansion introduced by the aspherical surface 27. The surfaces 27 and 33 are next to the concave mirrors and are aspheric as are the concave mirrors M1 and M2. For this reason, the aperture rays between the first and second lens groups G11 and G12 are guided in such a manner that the mirror diameters can be reduced with aperture obscuration being constant.
To minimize the aperture obscuration further, the two concave mirrors M1 and M2 and the lenses 26/27 and 33/34, which are close to the mirrors, are arranged almost symmetrically to the pupil plane AS1. The distances of the concave mirrors M1 and M2 as also of the lens surfaces 27 and 33 to the pupil plane AS1 each are 189.73 mm. The two mirrors are arranged concave to the diaphragm plane and have similar curvatures. The negative lenses 26/27 and 33/34 are biconcave lenses. The weaker curved surfaces each face the pupil plane AS1. With this assembly, a beam trace, which is substantially symmetrical to the pupil plane AS1 results between the surfaces 27 and 33. Accordingly, a marginal ray from an object point on the optical axis has approximately the same ray elevation at the last surface 27 of the first lens group G11 and at the first surface 33 of the second lens group G12. At surface 27, the beam height hG11=40.66 mm and at surface 33, the ray height hG12=40.56 mm. With this assembly, which is symmetric to the pupil plane AS1, the contribution of the mirror holes B1 and B2 to the aperture obscuration is almost the same.
In the first embodiment, at least the peripheral regions of the lens 26/27 and the lens 33/34 are disposed in the space between the concave mirrors M1 and M2. In this way, one achieves that, on the one hand, the spacing of the lens 26/27 to the concave mirror M1 and the spacing of the lens 33/34 to the concave mirror M2 is as small as possible. On the other hand, the beam path between the concave mirrors M1 and M2 may only be minimally vignetted because of the last lens 26/27 of the first lens group G11 and the first lens 33/34 of the second lens group.
It is advantageous when the catadioptric reduction objective has an approximately homocentric entrance pupil. That means that the chief rays, which extend up to the optical axis, should intersect at one point on the optical axis.
The object end field lens group FL1 having the surfaces 2 to 17 has an aspheric surface 12 in order to be able to influence the object end pupil function. To provide a pupil function having a dominant linear component with an object diameter of 91.2 mm and an object end numerical aperture of NAO=0.2 would, without the aspherical surface 12, require additional lenses.
To control the pupil function, the field lens group FL11 is assembled from a first subgroup G111 having the surfaces 2 to 5 and a second subgroup G112 having the surfaces 6 to 19. Here, the first subgroup G111 has a negative refractive power and the second subgroup G112 has a positive refractive power. To mount the aspheric surface 12 in the second subgroup G112 having positive refractive power has the advantage that the amounts of higher order of the aspheric surface do not operate directly on the pupil function because of the distance to the object plane. In addition, the splitting of the beams was increased by the negative refractive power of the first subgroup G111. The lenses having the surfaces 20 to 27 form a third subgroup G113 having negative refractive power which already serves to expand the beam.
The field lens groups FL12 (having the surfaces 41 to 48) and FL21 (having the surfaces 50 to 55) are next to the intermediate image plane IMI and likewise have aspheric surfaces 48 and 53 which, in this case, influence the image end pupil function and the distortion in the image plane IM. In the image plane IM, the distribution of the chief ray angle should be as telecentric as possible. Thus, the image end pupil function for the embodiment of Table 2 runs between ±3.6 mrad. For use in microlithography, it is adequate when the image end pupil function has values between ±10 mrad.
With the overcorrection of the image field curvature with the catadioptric partial objective L1, it is not necessary to provide a narrowed beam path for Petzval correction within the dioptric partial objective L2. In this way, the lens diameters remain limited. The maximum lens diameters in the partial objective L2 is 116.5 mm at surface 62. In the first partial objective L1 too, the lens diameters are low in order to reduce the aperture obscuration. The largest lens in the catadioptric partial objective L1 is in the lens group G112 with a diameter of 130.4 mm. The mirror diameters can be held to less than 700 mm via the aspheric surfaces 27 and 33, which are close to the mirror, with an aperture obscuration of 20%. In this way, the concave mirror M1 has a diameter of 691.5 mm and the concave mirror M2 has a diameter of 663.0 mm.
The lateral aberrations of the aperture rays are only inadequately corrected with the intermediate imaging of the catadioptric partial objective L1. The large inner coma is clearly visible in
For a small aperture obscuration, the image field can be very well corrected with the combination of the catadioptric partial objective L1 and the refractive partial objective L2 and with the targeted use of aspherical surfaces. As an index for the quality of the objective, the wavefront can be considered within the image field of 22.8 mm diameter and with the image end numerical aperture of NA=0.8 with the aid of a polychromatic simulation. The root mean square (RMS) values of the wavefront deviations for a light source at 157.63 nm with a bandwidth of 1.2 pm are less than 8 mλ within the entire image field. These slight wavefront deviations can, inter alia, be explained with the excellent correction of image focal surface and spherical aberration.
To achieve a field-independent aperture obscuration, it is advantageous to provide a masking device also in the refractive partial objective L2. The pupil plane AS2 in the refractive partial objective L2 has a positive curvature and the chief rays intersect the optical axis between surfaces 69 and 70. For this reason, the masking device should be placed between surfaces 69 and 70. The size of the masking device is to be so selected that the aperture obscuration, which is caused by the mirror holes, is increased only so far that, for each field point, an aperture obscuration results which is the same size and centered to the chief ray. A rod can serve as a holder for the masking device. The rod runs along the optical axis and is attached to the lens surfaces 69 and 70. It is also possible to apply the masking directly to a lens surface which is close to the intersect point of the chief rays with the optical axis such as surface 70.
The lens and mirror intermediate spaces are flushed with helium in the second embodiment. The gas charge with helium affords the advantage that the pressure and temperature dependency of the refractive index with helium in comparison to nitrogen is less by a factor of 10. Thus, the temperature coefficient of the refractive index dn/dT at λ=157.6 nm, T=0° C. and p=1013 mbar for nitrogen is −1.2·10−6/K and for helium is −0.14·10−6/K, the pressure coefficient of the refractive index dn/dp for nitrogen is −0.34·10−6/mbar and, for helium, is −0.036·10−6/mbar. In the large volumes between the concave mirrors M1′ and M2′, temperature gradients, which occur during the irradiation, lead to convection. For materials with temperature-dependent refractive indices, convection causes a time-dependent deformation of the wavefronts which cannot be corrected. It is therefore advantageous to fill the space between the mirrors with a gas having minimal temperature dependency of the refractive index.
The number of lenses is to be held as low as possible in order to prevent transmission losses because of reflections at the lens surfaces. Thus, in the second embodiment, the two lenses of negative refractive power (24/25, 26/27, 33/34 and 35/36) before and after the concave mirrors of the first embodiment can be combined to one negative lens (126/127 and 133/134) each before and after the mirrors. The negative refractive power of these lenses (126/127 and 133/134) must be increased in order to obtain a ray expansion of 3.567 for the marginal ray and an aperture obscuration for an object point on the optical axis of 18%. This is, on the one hand, possible with a larger aperture ratio of lens height hmax to lens radius R. Thus, for surface 126, the quotient h126 max/R126=0.814 and, for surface 134, the quotient is h134 max/R134=0.800. On the other hand, the angle of incidence at the lens surfaces 127 and 133, which face toward the mirrors, was increased. In the second embodiment, the sine of the angle of incidence with respect to the surface normal in the optically thinner medium for the marginal ray for an object point on the optical axis on the surface 127 is sine(i127 RD)=0.802 and, on the surface 133, sine(i133 RD)=0.748.
It is advantageous in the refractive partial objective L2′ to provide a double asphere on the surfaces 172 and 173 in order to obtain a similarly good wavefront correction within the image field for the second embodiment as in the first embodiment. With the adjacent aspheric surfaces in proximity to the system pupil plane AS2′, the spherical aberration and the sine condition can be well corrected simultaneously. The double aspheres as a correction means can be used also in purely refractive and catadioptric objectives having a non-centered arrangement. The two aspheric surfaces can even form the forward side and the rear side of an individual lens. For manufacturing reasons, it is however advantageous to arrange two lenses each having an aspheric surface so that the aspheric surfaces are adjacent.
With the double asphere (172, 173) and the aspheric surfaces 164 and 176 arranged forward and rearward of the aperture stop AS2′, adequate correction means are available in order, with a modest use of material, to correct the wavefront deviation within an image field of 22.8 mm diameter and for an image end numerical aperture of NA=0.8 to less than 8 mλ. The polychromatic simulation was carried out with a light source at 157.6 nm and a bandwidth of 1.2 pm.
The examples show the combination of a coaxial catadioptric objective with a dioptric partial objective. Other combinations such as with two dioptric partial objectives forward and rearward of the catadioptric partial objective are also possible in the context of the invention.
The schematic representation of
A microlithographic projection exposure apparatus for producing microstructured components is shown schematically in
It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.
C 1 =
C 2 =
C 3 =
C 4 =
C 5 =
C 6 =
C 7 =
C 1 =
C 2 =
C 3 =
C 4 =
C 5 =
C 6 =
C 7 =
SUPRA1 = Quartz
TABLE 2 Surface Radius Asphere Mirror Thickness Material Diameter OB INFINITE 26.122 N2 100.0 2 −226.258 4.000 CAF2 99.7 3 1694.910 7.361 N2 104.1 4 −210.020 4.023 CAF2 104.1 5 −4263.571 0.750 N2 110.8 6 353.550 30.488 CAF2 117.3 7 −137.865 0.750 N2 122.7 8 116.889 15.735 CAF2 130.4 9 177.655 5.923 N2 127.8 10 118.343 32.491 CAF2 126.6 11 −373.347 2.660 N2 122.1 12 −231.515 A 7.862 CAF2 122.1 13 88.994 0.864 N2 107.7 14 77.637 8.155 CAF2 108.4 15 81.208 20.608 N2 105.4 16 221.890 9.012 CAF2 105.5 17 163.578 2.429 N2 103.7 18 110.213 27.605 CAF2 104.6 19 −1324.253 9.444 N2 100.5 20 97.719 4.000 CAF2 89.4 21 64.603 14.158 N2 83.4 22 684.267 A 5.079 CAF2 83.4 23 216.155 24.074 N2 82.3 24 −57.188 2.000 CAF2 82.3 25 −92.747 5.064 N2 87.8 26 −72.557 2.000 CAF2 88.3 27 344.860 A 189.734 N2 105.0 M1 −813.737 A S −189.734 N2 691.5 AS1 INFINITE −189.734 N2 677.8 M2 910.975 A S 189.734 N2 663.0 33 −416.373 A 2.000 CAF2 106.4 34 65.887 4.948 N2 87.8 35 80.253 2.000 CAF2 87.3 36 54.610 31.217 N2 81.7 37 −84.333 7.747 CAF2 81.6 38 −75.708 0.750 N2 83.7 39 −1017.773 27.565 CAF2 81.7 40 −155.591 5.282 N2 79.9 41 −81.310 8.228 CAF2 79.9 42 −68.211 1.949 N2 80.7 43 −78.791 6.095 CAF2 77.1 44 −108.111 2.600 N2 77.2 45 −81.487 21.352 CAF2 77.2 46 −143.068 0.938 N2 80.4 47 199.620 40.095 CAF2 79.0 48 −145.642 A 20.000 N2 71.9 IM1 INFINITE 44.528 N2 67.0 50 −75.128 4.117 CAF2 69.0 51 −90.888 0.971 N2 72.4 52 −632.737 22.418 CAF2 76.6 53 408.536 A 0.900 N2 87.2 54 147.577 23.337 CAF2 91.9 55 −284.699 1.148 N2 94.9 56 544.076 28.648 CAF2 96.3 57 −917.060 10.169 N2 97.7 58 1123.355 15.459 CAF2 98.1 59 2847.866 22.266 N2 98.0 60 −84.178 4.000 CAF2 98.0 61 −351.550 0.750 N2 105.7 62 131.866 26.379 CAF2 116.5 63 −235.338 2.325 N2 116.4 64 222.992 31.521 CAF2 111.2 65 38305.126 9.715 N2 101.7 66 −2322.734 A 22.353 CAF2 96.4 67 1104.047 13.909 N2 88.6 68 −81.868 7.918 CAF2 88.6 69 −177.471 8.961 N2 91.5 70 −86.806 6.077 CAF2 91.5 71 −96.333 1.537 N2 94.4 AS2 INFINITE 0.750 N2 95.3 73 130.184 4.810 CAF2 103.5 74 97.753 2.761 N2 104.4 75 116.560 23.022 CAF2 104.4 76 −270.739 0.750 N2 105.5 77 194.680 18.881 CAF2 107.1 78 −210.640 A 0.750 142 106.4 79 55.466 43.620 CAF2 92.6 80 50.189 2.182 N2 59.6 81 37.769 13.715 CAF2 55.3 82 77.000 1.188 N2 47.9 83 60.105 8.895 CAF2 44.7 84 185.707 5.644 N2 36.9 IM INFINITE N2 22.8
ASPHERE AT SURFACE 12
RADIUS = 231.51455
MAXIMUM HEIGHT = 61.10
EX = −2.3650089000
C 1 = .4794899400E−07
C 2 = .6604175100E−11
C 3 = −.7562978300E−15
C 4 = .6805192600E−19
C 5 = −.2666129900E−23
ASPHERE AT SURFACE 22
RADIUS = 684.26729
MAXIMUM HEIGHT = 41.80
EX = .0000000000
C 1 = .1509596800E−06
C 2 = −.5120549400E−10
C 3 = −.5610431800E−14
C 4 = −.1117020200E−16
C 5 = .2518000300E−20
C 6 = −.1694764600E−23
ASPHERE AT SURFACE 27
RADIUS = 344.85984
MAXIMUM HEIGHT = 52.50
EX = 7.0085930000
C 1 = −.5923208000E−07
C 2 = .1890459800E−10
C 3 = −.4378968800E−15
C 4 = −.5239005100E−18
C 5 = .1912278200E−21
ASPHERE AT SURFACE 29
RADIUS = −813.73677
MAXIMUM HEIGHT = 345.80
EX = 1.0459455000
C 1 = −.4485550100E−10
C 2 = −.1176505800E−15
C 3 = −.1049527100E−20
C 4 = −.8619328500E−26
C 5 = −.2274167800E−31
C 6 = −.3345014000E−37
C 7 = −.3286498200E−43
ASPHERE AT SURFACE 31
RADIUS = 910.97468
MAXIMUM HEIGHT = 331.50
EX = .9036275200
C 1 = .6193779100E−10
C 2 = −.1344616200E−15
C 3 = −.1509012800E−20
C 4 = −.7421992700E−26
C 5 = −.4535969900E−31
C 6 = .1986463200E−36
C 7 = −.1449901900E−41
ASPHERE AT SURFACE 33
RADIUS = −416.37282
MAXIMUM HEIGHT = 53.30
EX = 13.3142580000
C 1 = .6027181300E−07
C 2 = .2450300200E−10
C 3 = −.4142498400E−14
C 4 = .3917454300E−18
C 5 = −.1088457000E−25
ASPHERE AT SURFACE 48
RADIUS = −145.64247
MAXIMUM HEIGHT = 36.00
EX = −.4376678300
C 1 = −.2590488300E−07
C 2 = .4696937200E−12
C 3 = .7666469100E−16
C 4 = .8507764300E−21
C 5 = −.1186245400E−25
ASPHERE AT SURFACE 53
RADIUS = 408.53641
MAXIMUM HEIGHT = 43.60
EX = −14.2359470000
C 1 = .9773912300E−07
C 2 = −.6627558800E−11
C 3 = −.2537861300E−15
C 4 = −.1281961700E−18
C 5 = −.1182417800E−25
ASPHERE AT SURFACE 66
RADIUS = −2322.73355
MAXIMUM HEIGHT = 48.20
EX = −504.9485600000
C 1 = −.2616677600E−07
C 2 = −.3063442300E−10
C 3 = .3964984700E−14
C 4 = −.1714421100E−17
C 5 = −.1187390103E−25
ASPHERE AT SURFACE 78
RADIUS = −210.64008
MAXIMUM HEIGHTS = 53.20
EX = 6.3257878000
C 1 = .4095943500E−07
C 2 = .1712273600E−12
C 3 = .9639448600E−15
C 4 = −.2847604400E−18
C 5 = .7274168800E−23
TABLE 3 Surface Radius Asphere Minor Thickness Material Diameter OB′ INFINITY 26.122 He 50.0 102 −204.364 4.000 CaF2 49.7 103 −13179.432 7.350 He 51.9 104 −184.672 4.011 CaF2 51.9 105 −1226.241 0.753 He 55.3 106 259.607 26.956 CaF2 60.1 107 −147.776 0.750 He 61.4 108 125.704 11.380 CaF2 63.6 109 178.234 0.750 He 62.7 110 111.880 29.403 CaF2 62.4 111 −380.095 3.030 He 60.9 112 −235.417 A 17.184 CaF2 60.9 113 82.808 0.750 He 51.7 114 67.123 8.979 CaF2 52.5 115 69.627 17.234 He 50.6 116 281.120 6.567 CaF2 50.6 117 272.393 0.758 He 50.2 118 115.088 36.934 CaF2 50.2 119 389.484 0.750 He 45.5 120 88.823 4.097 CaF2 43.6 121 73.172 15.989 He 41.7 122 −1528.771 10.066 CaF2 41.4 123 217.517 13.370 He 40.3 124 −89.601 7.977 CaF2 40.3 125 −76.531 9.154 He 41.2 126 −50.697 4.001 CaF2 41.2 127 259.195 A 189.734 He 52.7 M1′ −814.100 A S −189.734 He 349.3 AS1′ INFINITY −189.734 He 342.6 M2′ 911.247 A S 189.734 He 335.0 133 −276.266 A 4.000 CaF2 54.0 134 52.152 32.685 He 41.7 135 −80.264 6.728 CaF2 41.7 136 −77.215 0.850 He 42.8 137 −1419.828 32.679 CaF2 41.9 138 −147.648 5.801 He 41.0 139 −78.453 7.489 CaF2 41.0 140 −70.298 0.750 He 41.5 141 −84.334 6.166 CaF2 40.2 142 −98.563 2.147 He 40.3 143 −80.891 21.397 CaF2 40.3 144 −151.520 0.750 He 42.0 145 242.014 45.863 CaF2 41.3 146 −145.419 A 22.791 He 37.5 IMI′ INFINITY 43.060 He 33.2 148 −77.276 4.000 CaF2 34.7 149 −95.689 0.751 He 36.4 150 −894.688 22.703 CaF2 38.6 151 427.406 A 0.750 He 43.9 152 143.694 24.676 CaF2 46.4 153 −346.670 2.353 He 47.9 154 347.126 29.393 CaF2 48.8 155 −10246.191 11340 He 49.1 156 479.165 15.800 CaF2 49.3 157 634.264 23.350 He 48.8 158 −81.257 4.000 CaF2 48.8 159 −299.826 0.750 He 52.8 160 128.827 26.561 CaF2 58.6 161 −250.110 0.783 He 58.5 162 213.461 33.162 CaF2 56.1 163 −4384.454 9.042 He 51.0 164 −1171.671 A 24.405 CaF2 48.4 165 1409.721 14.203 He 44.3 166 −79.418 7.954 CaF2 44.3 167 −174.125 8.406 He 45.9 168 −85.986 6.344 CaF2 45.9 169 −94.556 0.750 He 47.5 AS2′ INFINITY 0.750 He 48.0 171 128.150 4.001 CaF2 52.4 172 99.397 A 2.565 He 52.8 173 116.720 A 23.743 CaF2 52.8 174 −265.459 0.750 He 53.3 175 220.793 18.648 CaF2 53.8 176 −192.915 A 0.751 He 53.4 177 55.415 43.719 CaF2 46.3 178 48.232 2.666 He 29.6 179 37.843 13.583 CaF2 27.5 180 77.482 0.896 He 23.8 181 61.588 9.014 CaF2 22.5 182 233.027 5.544 He 18.7 IM′ INFINITY He 11.6
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|U.S. Classification||359/726, 359/731, 359/729, 359/364, 359/728, 359/727|
|International Classification||G02B17/00, G02B17/08, G02B13/18, G02B13/14, G03F7/20|
|Cooperative Classification||G03F7/70241, G02B13/143, G03F7/70275, G02B13/18, G03F7/70225, G02B17/0808, G02B17/0892|
|European Classification||G02B13/14B, G02B17/08A1, G02B17/08U, G02B13/18, G03F7/70F2, G03F7/70F12, G03F7/70F6|
|Jan 18, 2011||AS||Assignment|
Owner name: CARL ZEISS SMT GMBH, GERMANY
Free format text: A MODIFYING CONVERSION;ASSIGNOR:CARL ZEISS SMT AG;REEL/FRAME:025763/0367
Effective date: 20101014
|Oct 11, 2011||CC||Certificate of correction|
|Apr 2, 2015||FPAY||Fee payment|
Year of fee payment: 12