DE102010029050A1 - Magnifying imaging lens for use in aerial image metrology system for e.g. simulation of effects of characteristics of lithography masks used for manufacturing semiconductor elements, has image plane representing lens field plane - Google Patents

Abstract

The lens (1) has a mirror group with two mirrors (M1, M2) and a diffractive optical element (11) i.e. zone plate, for imaging an object field (2) in an object plane (3) in an image field (4) in an image plane (5). The image plane represents a lens field plane after the object field. A spatial distance (A) between one of the mirrors, which is arranged spatially nearest to the image field, and the image field is smaller than a spatial distance (B) between the element and the image field. The object field and the image field are arranged in center relative to an optical axis (oA) of the lens. An independent claim is also included for a metrology system for inspecting objects.

Description

The invention relates to a magnifying imaging optics and a metrology system with such imaging optics.

A magnifying imaging optics of the type mentioned above is used to analyze effects of properties of masks for microlithography from the DE 102 20 815 A1 . DE 102 20 816 A1 , of the US Pat. No. 6,894,837 B2 as well as the technical articles "EUV microscopy with a Schwarzschild objective and adapted zone plate lens", L. Juschkin et al., Proceedings of SPIE, Vol. 7360, 736005-1 to -8 , and Brizuela et al., Optics Letters 2009, Vol. 34, No. 2, "Microscopy of extreme ultraviolet lithography masks with 13.2 nm tabletop laser illumation". 3, pages 271 to 273 , known.

It is an object of the present invention to develop an imaging optics of the type mentioned above such that their handling is improved with the best possible image quality.

The object is achieved by an imaging optics with the in claim 1 and an imaging optics with the features specified in claim 2.

In the imaging optics according to a first aspect of the invention according to claim 1 no intermediate image between the object field and the image field takes place. The imaging optics can therefore be readily designed so that the mirrors of the at least one mirror group are not arranged close to the field. This avoids manufacturing problems that exist in practice in the fabrication of near-field mirrors.

The imaging optics according to a second aspect of the invention according to claim 2 can be designed with advantageously short overall length, since the diffractive optical element can be spatially accommodated between the mirrors of the mirror group. The overall length is the distance between the two components of the imaging optic which are arranged furthest apart from one another, whereby the object field and / or the image field are understood as components in this context. As a rule, the overall length is the distance between the object field and the image field. For example, if, for example, one of the mirrors is farther from one of the panels than the two panels are spaced apart, it may also be the distance between one of the panels and the component farthest therefrom. The overall length always refers to an unfolded beam path, d. H. on an imaging optics without beam deflection by plane mirror.

The advantages of magnifying imaging optics according to claim 3 correspond to a combination of the above-explained advantages of the two aspects of the magnifying imaging optics.

The magnifying imaging optics can have exactly two mirrors. The magnifying imaging optics can have exactly one mirror group. Of course, the imaging optics can also be used as a downsizing imaging optic, whereby the object field and image field exchange their function and the relationship between object size and image size is used as a magnification.

An embodiment of the diffractive optical element as a zone plate leads to advantageous design degrees of freedom in the design of the magnifying imaging optics. A zone plate design is particularly advantageous in the context of imaging light at a wavelength less than 100 nm.

A magnification according to claim 5 leads to a good suitability of the imaging optics in the context of a metrology and inspection system. The magnification may be greater than 530, may be greater than 600, may be greater than 750, may be greater than 1,000, may be greater than 1,500, and may be greater than 2,000.

An object-side numerical aperture according to claim 6 is well adapted to the imaging ratios of projection lenses of projection exposure equipment for EUV microlithography for the production of micro- or nanostructured components. The object-side numerical aperture may be at least 0.0825 and may be at least 0.125. The imaging optics can be designed so that it is possible to change between these numerical apertures with the aid of an aperture stop.

An object-side main beam angle according to claim 7 is also adapted to the conditions in the EUV projection exposure. The object-side main beam angle can also be 8 °. The pictorial Optics can be designed for multiple main beam angles, which can be switched between using an aperture stop. This may be the same aperture stop with which, if necessary, the object-side numerical aperture is adjustable.

An on-axis field according to claim 8 is particularly suitable for imaging a rotationally symmetrical, square or rectangular field.

An off-axis field according to claim 9 is particularly suitable for imaging an arcuate field.

A field size according to claim 10 leads to the possibility to examine a spatially extended object. The size of the object field can be at least 7.5 μm × 7.5 μm, at least 10 μm × 10 μm, at least 15 μm × 15 μm and can be 20 μm × 20 μm or even larger.

An aspherical mirror according to claim 11 again increases the degrees of freedom in the design of the imaging optics. This first mirror can be designed as a concave mirror, regardless of its possible aspherical design. The aspheric mirror can be embodied as a conical mirror, that is to say as a mirror, in which in an aspherical equation only the coefficient K, ie the conical constant, is different from zero. This facilitates the production of this mirror.

The advantages of a metrology or inspection system according to claim 12 correspond to those which have already been explained above with reference to the imaging optics.

Embodiments of the invention will be explained in more detail with reference to the drawing. In this show:

1 a meridional section through a first embodiment of a magnifying imaging optics for use in a metrology system for simulating and analyzing effects of properties of lithographic masks on an optical image within a projection optics of a projection exposure apparatus for microlithography;

2 in one too 1 similar representation of another embodiment of the imaging optics and

3 highly schematic and with respect to the beam path shown not to scale a metrology system in which the magnifying imaging optics can be used.

A magnifying imaging optics 1 in the 1 is used in a metrology system for analyzing an aerial image metrology system (AIMS) and serves to simulate and analyze the effects of properties of lithographic masks, which in turn are used in the projection exposure for the production of semiconductor devices, to which optical imaging of projection optics within the projection exposure apparatus. AIMS systems are from the DE 102 20 815 A1 (compare there 9 ) and the DE 102 20 816 A1 (compare there 2 ) known.

The imaging optics 1 forms an object field 2 in an object plane 3 with a magnification factor (magnification β) of 750 in an image field 4 in an image plane 5 from. In the object field 2 For example, the lithography mask to be measured, which is also called a reticle, can be arranged. In the picture field 4 For example, a CCD chip of a CCD camera can be arranged to analyze the generated, enlarged image.

To facilitate the representation of positional relationships, a Cartesian xyz coordinate system is used below. The x-axis runs in the 1 perpendicular to the drawing plane into this. The y-axis runs in the 1 up. The z-axis runs in the 1 to the right.

Shown in the 1 the course of main rays 6 as well as coma rays 7 . 8th which emanate from a plurality of superimposed object field points in the y direction. The main rays 6 on the one hand and the coma rays 7 . 8th On the other hand, hereinafter also referred to as imaging beams.

The object field 2 on the one hand and the image field 4 on the other hand lie in mutually spaced xy planes.

The main rays 6 go in the imaging beam path between the object field 2 and the image field 4 from the object field 2 with a main beam angle α of 8 ° to a normal in the z-direction normal 9 on a central object field point of the object plane 3 out.

An object-field-side numerical aperture of the imaging optics 1 NAO = 0.125. Using a decentrable aperture diaphragm 10 For example, the object-field-side numerical aperture can be reduced to NA0 = 0.0625 or NA0 = 0.0825, whereby at the same time a main beam angle α of 6 ° can be realized.

In the picture plane 5 meet the picture rays 6 to 8th almost perpendicular to the image plane 5 and almost parallel to each other on the image field 4 ,

In the imaging beam path between the object field 2 and the image field 4 has the imaging optics 1 exactly two mirrors, which are referred to in the order of their arrangement in the imaging beam path below with M1 and M2. The two mirrors M1, M2 represent the only mirror group of the imaging optics 1 The first mirror M1 in the beam path after the object field 2 is concave and aspheric. The subsequent in the beam path second mirror M2 is designed spherical and convex.

Shown in the 1 the sectional curves of parent surfaces used for the mathematical modeling of reflection surfaces of mirrors M1 and M2. Actually physically present in the illustrated section plane are those regions of the reflection surfaces of the mirrors M1 and M2, that of the coma rays 7 . 8th and between the coma rays 7 . 8th be actually acted upon with imaging radiation.

A common rotational symmetry axis of the reflection surfaces of the imaging optics 1 , So the mirror M1 and M2, which is also referred to as optical axis oA, coincides with the normal 9 on the central object field point together. The object field 2 the imaging optics 1 to 1 and the picture box 4 are centered on the optical axis oA (on-axis).

In the imaging beam path between the object field 2 and the image field 4 the mirror M2 is a diffractive optical element 11 arranged downstream in the form of a zone plate. The zone plate 11 together with the mirror group M1, M2 ensures the image of the object field 2 in the picture field 4 ,

The picture plane 4 represents in the imaging beam path of the imaging optics 1 the after the object field 2 first field level of the imaging optics 1 dar. The imaging optics 1 So there is no intermediate picture.

A spatial distance A between the image field 4 spatially closest mirror M1 of the mirror group M1, M2 and the image field 4 is smaller than a spatial distance B between the diffractive optical element 11 and the image field 4 , In the execution after 1 the ratio A / B is about 1/9. Other distance ratios A / B in the range between 1 / 1.1 and 1/20, in particular 1 / 1.5, 1/2, 1/3, 1/4, 1/5, 1/6, 1/7 , 1/8, 1/10, 1/12 or 1/15 or intermediate values are possible.

The imaging optics 1 is designed for an operating wavelength of 13.5 nm.

Optical data of the imaging optics 1 to 1 are reproduced below using a table. This table shows in the column "radius" in each case the radius of curvature of the mirrors M1 and M2. The third column (thickness) describes the distance, starting from the object plane 3 , in each case to the following surface in the z-direction. Insofar as the following figures are lengths and unless otherwise stated, the unit mm shall be used. area radius thickness operation mode object infinitely 169.519947 aperture infinitely 818.402049 M1 -818.07818 -695.553966 REFL M2 -5.06502 257.631970 REFL zone plate infinitely 500.000000 image infinitely 0,000

At the zone plate 11 the first diffraction order of the imaging rays is used.

The arrangement of the diffractive structures on the zone plate 11 can be modeled by a description based on the interference of two spherical waves. A corresponding model description is disclosed in Code V 10.2 Reference Manual, pages 4-135 to 4-138 , For the realization of the zone plate 11 the following parameter values are to be inserted in the description given there:
HV1: VIR
HV2: REA
HOR: 1,000000
HX1 = HY1 = HX2 = HY2 = 0
HZ1: -0.674846E + 02
HZ2: -0,10000E-21
HWL: 13.50
HCT: R
BLT: Ideal

The phase function used in the model description has the form of a rotationally symmetric (even) polynomial according to the following formula:

In this formula, only the coefficients C ₂ , C ₃ and C _{4 are} different from zero and have the following values:
C ₂ : 7,0454E-06
C ₃ : -2,1503E-05
C ₄ : 1,7167E-05

The aperture stop 10 is not offset from the optical axis oA in the x-direction and offset by -23.903602 in the y-direction.

The exact surface shape of the reflecting surfaces of the mirror M1 is described by the following aspherical equation for the arrow height z (h):

h hereby represents the distance to the optical axis, ie to the normal 9 , the imaging optics 1 Thus h ² = x ² + y ² . For c, the inverse of "radius" is used in the equation.

In the aspheric surface description of the reflection surface of the mirror M1, only the conical constant K is different from zero and has the value K = -0.028827.

An overall length T, ie a distance between the object plane 3 and the picture plane 5 , is 1 050 mm.

A field size in the object plane 3 is 20 microns × 20 microns. Within this field size is the object field 2 so aberration corrected. The picture field is corresponding 4 then aberration corrected within a radius of 15mm.

The imaging optics 1 is part of a metrology system 12 (see. 3 ). To this metrology system 12 still belong to a light source 13 and an illumination optics for illuminating a reticle 14 within the object field 2 and in the context of the image field 4 already mentioned CCD chip 15 which is part of a detection device of the metrology system. The reticle 14 does that with the metrology system 12 to be examined object.

The sources of light used are the EUW light sources which are also customary for lithography systems 13 in question, for example, laser plasma sources (LPP) or discharge produced plasma (DPP).

Based on 2 Below is another embodiment of an imaging optics 16 described in place of the imaging optics 1 to 1 can be used. Components and functions corresponding to those described above with reference to FIGS 1 already described, bear the same reference numbers and will not be discussed again in detail.

In the imaging optics 16 are the object field 2 and the picture box 4 in terms of the optical axis 9 decentered (off-axis) arranged. A field decentering y _{DE of} the object field 2 has in the imaging optics 16 an absolute value of 50 μm. Also the imaging optics 16 has an enlarged magnification β of 750. A field decentering y _{DE of} the image field 4 is at the imaging optics 16 So 37.5 mm.

The optical data of the imaging optics 16 to 2 are reproduced below with reference to a table, which is structurally the table of the imaging optics 1 to 1 equivalent. area radius thickness operation mode object infinitely 192.483390 aperture infinitely 847.51610 M1 -859.07424 -726.972232 REFL M2 -9.70337 390.313565 REFL zone plate infinitely 500.000000 image infinitely 0,000

At the zone plate 11 the first diffraction order of the imaging rays is used.

The arrangement of the diffractive structures on the zone plate 11 can be modeled by a description based on the interference of two spherical waves. A corresponding model description is disclosed in Code V 10.2 Reference Manual, pages 4-135 to 4-138 , For the realization of the zone plate 11 the following parameter values are to be inserted in the description given there:
HV1: VIR
HV2: REA
HOR: 1,000000
HX1 = HY1 = HX2 = HY2 = 0
HZ1: -0.460981E + 02
HZ2: -0,10000E + 21
HWL: 13.50
HCT: R
BLT: Ideal

The phase function used in the model description has the form of a rotationally symmetric (even) polynomial according to the following formula:

In this formula, only the coefficients C ₂ , C ₃ and C _{4 are} different from zero and have the following values:
C ₂ : -2,813E-06
C ₃ : 1,1379E-07
C ₄ : -2.5442E-09

In the imaging optics 16 is the aperture stop 10 decentered by a y value of -27.191627.

Even with the imaging optics 16 the mirror M1 is a conically aspherical concave mirror whose reflection surface can in turn be described with the aspherical equation already given above. Except for the conic constant K, the surface description of the mirror M2 is in the imaging optics 16 again all other constants are zero. The conic constant K has in the surface description of the mirror M1 of the imaging optics 16 the value K = -0.028923.

The following table shows some parameters of the two imaging optics 1 and 16 summarized. Imaging optics 1 Imaging optics 16 Length [mm] 1050 1203 NAO 0125 0125 magnification 750 750 CRAO [°] 8th 8th Field size [μm × μm] 20 × 20 20 × 20 Field decentration [μm] 0 50 Diameter M1 [mm] 240 251 Diameter M2 [mm] 0.86 1.67 Diameter ZPL [mm] 1.61 1.31 Asphericity M1 [μm] 7.2 7.7 Radius M2 [mm] 5.1 9.7 Wavefront error rms [mλ] 2.2 8.9 Distortion [μm] <1 <1

CRAO denotes the main beam angle, starting from the object field 2 , The value "field size" gives the size of the respective object field 2 at. The field decentration affects the respective object field 2 and is measured in the y direction. The diameter values for the mirrors M1, M2 indicate the diameters of the optically used reflection surface. The value "diameter ZPL" indicates the optically used diameter of the zone plate 11 at.

The value asphericity describes the maximum shape deviation of an aspheric surface from a best-fitting spherical surface. This size then depends on the aspheric parameters, that is also on the conical constant, but also on the optically used area of the surface.

The values "wavefront error" and "distortion" refer to the entire respective object field 2 ,

The length 5 the respective imaging optics 1 . 16 always refers to an unfolded design of the imaging optics 1 . 16 So on a design without purely deflecting acting intermediate plane mirror. The length 5 is determined either by the distance between the object field 2 and the image field 4 , defined by the distance between the object field and the most distant optical component or by the distance between the image field and the most distant optical component.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10220815 A1 [0002, 0022]
• DE 10220816 A1 [0002, 0022]
• US 6894837 B2 [0002]

Cited non-patent literature

• "EUV microscopy with a Schwarzschild objective and adapted zone plate lens", L. Juschkin et al., Proceedings of SPIE, Vol. 7360, 736005-1 to -8 [0002]
• Brizuela et al., Optics Letters 2009, Vol. 34, No. 2, "Microscopy of extreme ultraviolet lithography masks with 13.2 nm tabletop laser illumation". 3, pages 271 to 273 [0002]
• Code V 10.2 Reference Manual, pages 4-135 to 4-138 [0039]
• Code V 10.2 Reference Manual, pages 4-135 to 4-138 [0054]

Claims (12)

Magnifying imaging optics ( 1 ; 16 ) - having at least one mirror group (M1, M2) with at least two mirrors (M1, M2) and at least one diffractive optical element ( 11 ) for mapping an object field ( 2 ) in an object plane ( 3 ) in an image field ( 4 ) in an image plane ( 5 ), - where the image plane ( 5 ) which after the object field ( 3 ) first field plane of the imaging optics ( 1 ; 16 ). Magnifying imaging optics ( 1 ; 16 ) - having at least one mirror group (M1, M2) with at least two mirrors (M1, M2) and at least one diffractive optical element ( 11 ) for mapping an object field ( 2 ) in an object plane ( 3 ) in an image field ( 4 ) in an image plane ( 5 ), - wherein the diffractive optical element ( 11 ) of the mirror group (M1, M2) in the beam path between the object field ( 2 ) and the image field ( 4 ), wherein a spatial distance (A) between one of the image field ( 4 ) spatially closest mirror (M1) of the mirror group (M1, M2) and the image field ( 4 ) is smaller than a spatial distance (B) between the diffractive optical element ( 11 ) and the image field ( 4 ). Magnifying imaging optics ( 1 ; 16 ) according to claim 1 and 2. Imaging optics according to one of claims 1 to 3, characterized in that the diffractive optical element ( 11 ) is designed as a zone plate. Imaging optics according to one of claims 1 to 4, characterized by a magnification which is greater than 500. Imaging optics according to one of claims 1 to 5, characterized by an object-side numerical aperture of at least 0.0625. Imaging optics according to one of claims 1 to 6, characterized by an object-side main beam angle of at least 6 °. Imaging optics according to one of claims 1 to 7, characterized in that the object field ( 2 ) and the image field ( 4 ) with respect to an optical axis (oA) of the imaging optics (oA) 1 ) are arranged centered. Imaging optics according to one of claims 1 to 7, characterized in that the object field ( 2 ) and the image field ( 4 ) with respect to an optical axis (oA) of the imaging optics (oA) 16 ) are arranged decentered. Imaging optics according to one of claims 1 to 9, characterized by a size of the object field ( 2 ) of at least 5 μm × 5 μm. Imaging optics according to one of claims 1 to 10, characterized in that one in the beam path the object field ( 2 ) is arranged downstream of the first mirror (M1) of the mirror group (M1, M2) as an aspherical mirror. Metrology system for the examination of objects - with an imaging optic ( 1 ; 16 ) according to one of claims 1 to 11, - with a light source ( 13 ) for illuminating the object field ( 3 ), - with one the image field ( 4 ) detecting spatially resolving detection device ( 15 ).

Images