DE102011084255A1 - Imaging lens for use in metrology system that is utilized during manufacturing of semiconductor components, has mirrors for reproducing object field, where ratio between dimensions of imaging field and user surface is larger than three - Google Patents

Abstract

The lens (1) has first, second and third mirrors (M1-M3) for reproducing an object field (2) in an object plane (3) into an imaging field (4) in an imaging plane (5), where ratio between transverse dimension of the imaging field and transverse dimension of a user surface of the third mirror in front of the imaging field is larger than 3. An exchangeable aperture diaphragm (S) is arranged in an installation area between the object plane and the second mirror in an optical path that is formed between the object field and the first mirror, where the third mirror is designed convexly. An independent claim is also included for a metrology system comprising an imaging lens.

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 simulate and analyze the effects of microlithography mask characteristics DE 102 20 815 A1 known. Other imaging optics are known from the US 6,894,834 B2 , of the WO 2006/0069725 A1 and the US 5,071,240 ,

It is an object of the present invention to further develop an imaging optics of the type mentioned above such that requirements for a mirror quality of the imaging optics are reduced.

The object is achieved according to a first aspect of the invention by an imaging optics having the features specified in claim 1 and according to another aspect of the invention by an imaging optics with the features specified in claim 2.

According to the invention, it has been recognized that a design of the magnifying imaging optics with exactly three mirrors and a mirror with a small required effective area that is the last in relation to the image field dimension reduces the quality requirements in the production of this last mirror. It is not necessary to precisely polish this last mirror over a large area. The transverse dimension ratio between the image field dimension and the useful surface dimension of the last mirror may be greater than 5, may be greater than 10, may be greater than 20, and may be, for example, 20.16 or 28.68.

A shape sequence concave / concave / convex according to the further aspect has been found to be particularly suitable in the imaging optics. Such a shape sequence favors a design of an imaging beam path in which individual field point contributions on the mirrors of the imaging optics mix well. This reduces the manufacturing quality requirements as well as the operating requirements for the mirrors of the imaging optics. The convex mirror promotes a divergent from this mirror course of the main rays, ie a fanning of the imaging beam path. This makes it possible to increase the diameter of the imaging beam path where this is necessary, in particular close to the field of view, wherein the imaging beam path can advantageously be designed with a small diameter in the region of the mirror guiding the imaging beam path. Each of the mirrors of the magnifying imaging optics according to the further aspect is subjected to imaging beams just once. This increases flexibility of the structure of the magnifying imaging optics, in particular an adjustment flexibility, since each reflective surface in the imaging beam path can be arranged and in particular adjusted independently of the reflective surfaces of reflective surfaces located in front or behind the beam path.

A transverse dimension ratio between a useful surface dimension of the last mirror and a subaperture diameter on this last mirror according to claim 3 reduces the cleanliness requirements in the production and operation of the last mirror of the imaging optics, since the individual field point contributions on the last mirror due to this Mix dimension ratio well. The subaperture is that part of the entire imaging beam path which is assigned to exactly one field point in each case. In a pupil plane, the subaperture is the same size as the pupil itself. In a field plane, the subaperture has the diameter 0, so it is punctiform. The transverse dimension ratio of the effective area of the last mirror and the subaperture diameter may be less than 10, may be less than 5, may be 4.43, may be less than 2, and may be 1.98. The above-mentioned transverse dimension ratios utility area dimension / subaperture diameter can be fulfilled in all mirrors of the magnifying imaging optics.

An intermediate image according to claim 4 leads in the vicinity of the intermediate image plane to a compact beam path and thus facilitates a compact design of the imaging optics. The imaging optics can have exactly one intermediate image between the object field and image field.

A maximum angle of incidence according to claim 5 allows an embodiment of the imaging optics with a highly reflective multi-layer (multilayer) coating to optimize a useful light throughput of the imaging optics.

A magnification according to claim 6 leads to a good suitability of the imaging optics in the context of a metrology and inspection system. The magnification can be 750.

An object field size according to claim 7 leads to a good suitability of the magnifying imaging optics in a metrology system.

An object-side numerical aperture according to claim 8 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 can be 0.118. The imaging optics can be designed so that it is possible to change between different object-side numerical apertures with the aid of an aperture stop.

A decenterable aperture diaphragm can also be used for setting, for example, a main beam angle of the imaging beams emanating from the object field. The decenterable aperture diaphragm can be decentered in the diaphragm plane and at the same time in a meridional plane of the imaging optics. Alternatively or additionally, the decenterable aperture diaphragm can be decentered in the diaphragm plane and perpendicular to the meridional plane. The centerable aperture diaphragm can be elliptical and can be designed to be rotatable about an axis guided parallel to the optical axis of the imaging optical system through the aperture ellipse center.

The aforementioned object is achieved according to a further aspect of the invention by an imaging optics with the features specified in claim 9.

The advantages of the imaging optics according to this further aspect correspond to those which have been explained above in connection with the imaging optics according to the first aspect.

The features of the above-explained aspects of the imaging optics may also be present in combination with each other.

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. When referring to object-side components of the imaging optics below, those components on the high-aperture side of the imaging optics are meant. When referring to image-side components of the imaging optics, the components on the low-aperture side are meant. When the imaging optic is used as a decreasing imaging optic, the light path of imaging light goes from the low-aperture side to the high-aperture side of the imaging optic. The two in the imaging beam path field next mirror on the high-aperture side of the imaging optics can be concave. This leads to the possibility of a well-corrected design of the imaging optics.

The advantages of a metrology or inspection system according to claim 11 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 Meridionalschnitt by 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 and for large-scale detection of mask defects;

2 and 3 each in one too 1 similar representation of a further embodiment of the imaging optics; and

4 schematically the course of Subaperturen between a field plane and a pupil plane.

A magnifying imaging optics 1 in the 1 is used in a metrology system for analyzing a lithography mask after patterning errors. The structuring error can be examined by means of an analysis of an aerial image metrology system (AIMS). The metrology system is used to simulate and analyze the effects of properties of lithographic masks, which in turn are used in projection exposure for the production of semiconductor devices, on the optical imaging of projection optics within the projection exposure apparatus. AIMS systems are from the DE 102 20 815 A1 known.

The imaging optics 1 forms an object field 2 in an object plane 3 with a magnification factor 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 camera sensitive to the imaging wavelength may 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 for the visualization of an imaging beam path of the imaging optics 1 the course of main rays 6 as well as coma rays 7 . 8th that emanate from three 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 object field 2 has in each case an extent (transverse dimension) of 20 μm in the x-direction and in the y-direction, ie has a field size of 20 × 20 μm ² .

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. Other main beam angles α, in particular a smaller main beam angle α of 6 °, are possible depending on the selected aperture.

An object-field-side numerical aperture of the imaging optics 1 NAO = 0.118. By means of a decentrable aperture diaphragm S, the object-field-side numerical aperture can be reduced to NA0 = 0.0825, whereby at the same time a main beam angle α of 6 ° can be realized. The aperture diaphragm S can be decentered in the y-direction and / or in the x-direction. The aperture diaphragm S can be designed with an elliptical diaphragm opening. In this case, the aperture diaphragm S may be one to the optical axis of the imaging optics 1 be guided in parallel through the aperture diaphragm ellipse center axis, in particular by means of a drive motor, executed.

In the picture plane 5 the picture rays meet 6 to 8th almost perpendicular to the image plane 5 each in an image field point of the image field 4 , The main rays 6 that belong to each of the image field points are divergent to each other. This causes the image field 4 is significantly larger than the last mirror M3.

In the imaging beam path between the object field 2 and the image field 4 has the imaging optics 1 exactly three mirrors, which are designated in the order of their arrangement in the imaging beam path below with M1, M2 and M3. The three mirrors M1 to M3 represent three separate optical components.

The decentralized and exchangeable aperture diaphragm S is in the space between the object plane 3 and the mirror M2 in the beam path between the object field 2 and the mirror M1.

The one in the beam path between the object field 2 and the image field 4 first mirror M1 is aspherical and the further mirrors M2 and M3 are spherical.

Shown in the 1 the sectional curves of parental surfaces, which are used for the mathematical modeling of the reflection surfaces of mirrors M1 to M3. Actually physically present in the illustrated section plane are those regions of the reflection surfaces of the mirrors M1 to M3 that are separated from the coma rays 7 . 8th and between the coma rays 7 . 8th be actually acted upon with imaging radiation.

In the imaging beam path between the mirrors M1 and M2 is an intermediate image 10 ,

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 two tables. The first table shows in the column "radius" in each case the radius of curvature of the mirrors M1 to M3. The third column (thickness) describes the distance, starting from the object plane 3 , in each case to the following surface in the z-direction.

h stellt hierbei den Abstand zur optischen Achse, also zur Normalen 9, der abbildenden Optik 1 dar. Es gilt also h² = x² + y². Für c wird in die Gleichung der Kehrwert von „Radius” eingesetzt. Fläche Radius Dicke Betriebsmodus Objekt Unendlich 257.878 Blende Unendlich 891.940 M1 –952,018 –861.937 REFL M2 94.260 912.119 REFL M3 30.892 –862.121 REFL Bild Unendlich 0.000 Fläche K A B M1 0.000000E+00 5.968375E–12 6.442743E–18 Fläche C D E M1 6.234558E–24 8.904749E–30 0.000000E+00 The second table describes the exact aspherical surface shape of the reflecting surfaces of the mirror M1, wherein the constants K and A to E are to be used in the following equation for the arrow height:

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. area radius thickness operation mode object infinitely 257878 cover infinitely 891940 M1 -952.018 -861937 REFL M2 94260 912119 REFL M3 30892 -862121 REFL image infinitely 0000 area K A B M1 0.000000E + 00 5.968375E-12 6.442743E-18 area C D e M1 6.234558E-24 8.904749E-30 0.000000E + 00

The following table gives the angles of incidence of the main ray 6 of the central object field point on the individual mirrors M1 to M3 again: Angle of incidence of the principal ray of the central field point M1 1.5 ° M2 5.5 ° M3 10

The maximum angle of incidence is so small that it is sufficient to apply the mirrors M1 to M3 for the operating wavelength at 13.5 nm with a multilayer coating with a single layer thickness constant over the reflection surface of the mirrors M1 to M3 used. With comparatively simple production, this results in high reflectivities of the mirrors M1 to M3 and a correspondingly high throughput of the imaging optics 1 for the operating wavelength of 13.5 nm.

An overall length T, ie a distance between the object plane 3 and the farthest in the z-direction mirror M3, is 1,200 mm. A ratio of the length T and the magnification β is 1,200 mm / 750 = 1.6 mm.

The image field 4 has in each case an extension of 15 mm in the x-direction and in the y-direction. A transverse dimension of the image field measured in the meridional plane 1 , ie along the y-direction, is therefore 15 mm. In the same direction, a transverse dimension of a usable area of the last mirror M3 is 0.523 mm. A relationship between a transverse dimension of the image field 4 and a measured in the same direction transverse dimension of the effective area of the last mirror M3 is thus 28.68.

In the case of the transverse dimension, the described embodiments therefore each involve the y-direction.

A subaperture of the imaging beam path has a diameter of 0.264 mm on the last mirror M3. The subaperture is that part of the entire imaging beam path between the object field 2 and the image field 4 , which is assigned to exactly one field point. In a pupil plane of the the subaperture is the same size as the pupil itself. In a field plane of the imaging beam path, the subaperture has the diameter 0, so it is punctiform.

A ratio between the transverse dimension of the effective area of the last mirror M3 in the meridional plane (0.523 mm) and the diameter of the subaperture on this last mirror M3 (0.264 mm) is 1.98.

The main rays 6 different field points between the last mirror M3 and the image field 4 run divergent.

The imaging optics 1 is part of a metrology system. This metrology system also includes a light source 10a , which provides illumination light with the operating wavelength of 13.5 mm, as well as an illumination optics 10b for illuminating the object field 2 and in the context of the image field 4 already mentioned CCD chip 10c which is part of a detection device of the metrology system.

Suitable light sources are the light sources customary also for lithography systems, for example laser plasma sources (LPP) or discharge produced plasma (DPP). Compared to the light sources for lithography systems, the light sources for the metrology system require a significantly lower swelling power due to the small object field size.

Based on 2 Below is another embodiment of an imaging optics 11 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. The differences to the previous embodiment will be discussed below.

A difference in the imaging beam path between the imaging optics 1 and 11 consists in the beam guidance between the mirror M3 and the image field 4 , The incident angle of the principal ray of the central field point is on the mirror M3 in the imaging optics 11 about 4 °, so it is much larger than the imaging optics 1 , This results in a clear separation of the imaging beam path on the one hand between the mirrors M2 and M3 and on the other hand between the mirror M3 and the image field 4 , This allows the distance between the last mirror M3 and the image field 4 with the there arranged CCD chip with respect to the arrangement according to 1 significantly reduce. A distance between the mirror M3 and the image field 4 is little more than 60% of the distance between mirrors M2 and M3.

The optical data of the imaging optics 11 to 2 are reproduced below with reference to two tables, which are structurally the tables of the imaging optics 1 to 1 correspond. area radius thickness operation mode object infinitely 250843 cover infinitely 919336 M1 -966609 -845204 REFL M2 42,650 895217 REFL M3 45098 -545217 REFL image infinitely 0000 area K A B M1 0.000000E + 00 4.912195E-12 5.176188E-18 area C D e M1 4.855906E-24 6.801811E-30 0.000000E + 00

The effective area of the mirror M3, measured in the meridional plane 2 , has a transverse dimension of 0.744 mm. The relationship between the transverse dimension of the image field 4 (15 mm) and this effective area transverse dimension is in the imaging optics 11 So 20:16.

A subaperture diameter on the last mirror M3 is 0.168 mm. A ratio of the usable surface transverse dimension of the mirror M3 in the meridional plane 2 and the subaperture diameter is thus 4.43.

Based on 3 Below is another embodiment of an imaging optics 12 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. The differences to the previous embodiment will be discussed below.

The imaging optics 12 has exactly four mirrors M1 to M4. The four mirrors M1 to M4 represent four separate optical components. From the basic arrangement, the mirror M4 is arranged approximately where in the imaging optics 1 to 1 the image field 4 is arranged. The angles of incidence of the principal ray of the central field point correspond for the mirrors M1 to M3 to those described above in connection with the imaging optics 1 to 1 were called. The angle of incidence of the principal ray of the central field point on the mirror M4 is 1.5 °.

The mirror M4 is spherical and convex in shape.

A usable area of the last mirror M4 of the imaging optics 12 has measured in the meridional plane 3 , a transverse dimension of 4,238 mm. A ratio between the transverse dimension of the image field (15 mm) and the usable surface transverse dimension of the mirror M4 (4.238 mm) is in the imaging optics 12 So 3.54. A subaperture has a diameter of 0.218 mm on the last mirror M4. A ratio between the effective area transverse dimension of the mirror M4 (4.238 mm) and the subaperture diameter (0.218 mm) is in the imaging optics 12 thus 19:44.

The imaging optics 12 has between the object plane 3 and the picture plane 5 a length of 1,000 mm.

A ratio of the length T and the magnification β is 1,000 mm / 750 = 1.333.

The optical data of the imaging optics 12 to 3 are reproduced below with reference to two tables, which are structurally the tables of the imaging optics 1 to 1 correspond. area radius thickness operation mode object infinitely 137852 cover infinitely 761737 M1 -746256 -646241 REFL M2 17169 696574 REFL M3 850000 -666574 REFL M4 -731268 716651 REFL image infinitely 0000 area K A B M1 0.000000E + 00 9.553424E-12 1.675218E-17 area D e F M1 3.069954E-23 1.504440E-29 2.323575E-34

The overall length T always refers to an unfolded configuration of the imaging optics, that is, to a configuration without purely deflecting acting intermediate plane mirror. The length T is defined either by the distance between the object field and the image field, 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.

The following table again summarizes some characteristic sizes of the imaging optics 1 . 11 and 12 together: E1 E2 E3 Diameter last mirror in the meridional plane [mm] 0523 0744 4238 Subaperture (SA) diameter last mirror [mm] 0264 0168 0218 Ratio: diameter of the last mirror / SA diameter [mm] 1.98 4:43 19:44 Diameter of the image field (meridional plane) 15:00 15:00 15:00 Ratio diameter image field / diameter last mirror 28.68 20:16 3:54

4 illustrates the subaperture diameter between the object plane 3 and a pupil plane P. are shown in the 4 only the coma rays 7 . 8th that originate from three object field points and delimit the subapertures. In the object field 3 the subapertures have a diameter of 0. In the pupil plane P, those of the coma rays 7 . 8th spanned Subaperturen a diameter corresponding to the pupil diameter PD. In an exemplified intermediate level ZE between the object plane 3 and the pupil plane P, the sub-apertures have a diameter which corresponds approximately to half the total diameter of the imaging beam path. If a mirror were arranged in the intermediate plane ZE, there would be the relationship between a transverse dimension of the mirror effective area and the diameter of the subaperture 2 ,

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, 0023]
• US 6894834 B2 [0002]
• WO 2006/0069725 A1 [0002]
• US 5071240 [0002]

Claims (11)

Magnifying imaging optics ( 1 ; 11 ) - with exactly three mirrors (M1 to M3) containing an object field ( 2 ) in an object plane ( 3 ) in an image field ( 4 ) in an image plane ( 5 ), wherein a ratio between a transverse dimension of the image field ( 4 ) and a transverse dimension, measured in the same direction, of a usable area of the last mirror (M3) in front of the image field ( 4 ) is greater than 3. Magnifying imaging optics ( 1 ; 11 ) - with exactly three mirrors (M1 to M3) containing an object field ( 2 ) in an object plane ( 3 ) in an image field ( 4 ) in an image plane ( 5 ), - wherein a first mirror (M1) in the beam path after the object field ( 2 ) concave, a second mirror (M2) in the beam path after the object field ( 2 ) concave and a third mirror (M3) in the beam path after the object field ( 2 ) is convex. Imaging optics according to claim 1 or 2, characterized in that a ratio between a transverse dimension of a useful area of a in the beam path between the object field ( 2 ) and the image field ( 4 ) last mirror (M3) and a diameter of a subaperture on the last mirror (M3) is less than 20. Imaging optics according to one of claims 1 to 3, characterized by at least one intermediate image ( 10 ) between the object field ( 2 ) and the image field ( 4 ). Imaging optics according to one of claims 1 to 4, characterized in that an angle of incidence of imaging beams ( 6 ) on the last mirror (M3) in front of the image field ( 4 ) is less than 15 °. Imaging optics according to one of claims 1 to 5, characterized by a magnification of at least 500. Imaging optics according to one of claims 1 to 6, characterized by a size of the object field ( 2 ) of at least 20 μm × 20 μm. Imaging optics according to one of claims 1 to 7, characterized by an object-side numerical aperture of at least 0.1. Magnifying imaging optics ( 12 ), - with at least three mirrors (M1 to M4), an object field ( 2 ) in an object plane ( 3 ) in an image field ( 4 ) in an image plane ( 5 ), - wherein a first mirror (M1) in the beam path after the object field ( 2 ) concave, a second mirror (M2) in the beam path after the object field ( 2 ) concave and a third mirror (M3) in the beam path after the object field ( 2 ) is convex, - wherein an angle of incidence of imaging rays ( 6 ) on the last mirror (M4) in front of the image field ( 4 ) is smaller than 15 °, - where a ratio between a transverse dimension of the image field ( 4 ) and a measured in the same direction transverse dimension of a usable area of the last mirror (M4) in front of the image field ( 4 ) is greater than 3. Imaging optics according to claim 9, characterized in that a ratio between a transverse dimension of a useful surface of a in the beam path between the object field ( 2 ) and the image field ( 4 ) last mirror (M4) and a diameter of a subaperture on the last mirror (M4) is less than 20. Metrology system for the examination of objects - with an imaging optic ( 1 ; 11 ; 12 ) according to one of claims 1 to 10, - with a light source ( 10a ) for illuminating the object field ( 2 ), - with one the image field ( 4 ) detecting spatially resolving detection device ( 10c ).

Images