The disclosure relates to a projection objective for microlithography with an obscurated pupil. The projection objective includes a first optical surface, which has a first region provided for application of useful light. The projection objective also includes at least one second optical surface, which has a second region provided for application of useful light. A beam envelope of the useful light extends between the first region and the second region during the operation of the projection objective.
A projection objective for microlithography is known from the document WO 2006/069725 A1.
Projection objectives are used in microlithography in projection exposure apparatuses for the production of semiconductor components and other finely structured components. In this case, the projection objectives serve to project patterns of photomasks or optical reticles, also referred to generally as masks or reticles, onto an object coated with a light-sensitive layer with maximum resolution on a reduced scale.
In this case, in order to produce ever finer structures it is often desirable to increase the image-side numerical aperture (NA) of the projection objective and to use ever shorter wavelengths. In some cases, wavelengths of less than 20 nm, that is to say in the extreme ultraviolet (EUV), are used.
In the EUV wavelength range, only materials whose transparency is not very adequate may be available for the production of optical components. Accordingly, in general, projection objectives for EUV lithography have exclusively reflective optical elements. Such projection objectives are correspondingly referred to as catoptric.
WO 2006/069725 proposes, in order to obtain a high image-side numerical aperture, obscurating the pupil of the projection objective by providing one or a plurality of the optical surfaces, mirrors in that case, with through holes through which the useful light passes. In that case, the through holes lie approximately on the optical axis.
In the case of such obscurated projection objectives, it can be important for the imaging quality that the useful light is applied to all the optical surfaces of the projection objective which are provided for application of the useful light in the correct order and without omitting one or more of the optical surfaces before it passes into the image plane.
Precisely in the case of obscurated projection objectives, however, it can happen that scattered light passes through the through holes in the optical surfaces directly into the image plane without previously impinging on all the regions of the optical surfaces which are provided for application of useful light.
Within the meaning of the present disclosure, “scattered light” is understood to be not only that light which arises as a result of undesirable reflections at the optical surfaces, but also so-called over-apertured light, that is to say those light beams which have a larger aperture than the system aperture.
Within the meaning of the present disclosure, “beam envelope” of the useful light should be understood to be the totality of the marginal rays of the useful light bundle or in other words the envelope of the useful light beam.
The reason why scattered light passes through the through holes in the optical surfaces directly into the image plane whilst omitting specific optical surfaces may be due to the fact that the scattered light passes through the through holes at an angle of incidence that deviates from the angular range which the useful light exhibits upon passing through the through holes.
In some embodiments, the disclosure provides a projection objective with an obscurated pupil for microlithography in which the imaging properties are improved by more effective suppression of scattered light.
In certain embodiments, at least one tube open on the input side and on the output side in the light propagation direction and serving for screening scattered light is arranged between the first optical surface and the second optical surface. The tube extends in the propagation direction of the useful light over at least a partial length of the beam envelope and circumferentially surrounding the beam envelope.
In a projection objective, the beam envelope of the useful light between two optical surfaces is enclosed by a tube which is circumferentially closed but open at the ends. The fact that the beam envelope is enclosed by the at least one tube means that the useful light can pass undisturbed through the tube, whereas scattered light, that is to say that light which arises as a result of undesirable reflections, or over-aperture light, having a different propagation direction with respect to the beam envelope of the useful light, is effectively screened by the tube. For this purpose, the at least one tube can be absorbent on the inside and/or on the outside.
In one exemplary configuration, the beam envelope of the useful light between the first optical surface and the second optical surface is a first beam envelope and is overlapped by a second beam envelope of the useful light over a partial length of the first beam envelope. The tube extends over at least a partial length of the overlap-free partial region of the first beam envelope.
In this case, it is advantageous that the at least one tube ensures the undisturbed propagation of the useful light in the overlap region of the two beam envelopes.
In this case, it is desirable for the tube to extend over the entire length of the overlap-free partial region of the first beam envelope.
In this case, it is advantageous that the scattered light suppression by the at least one tube is particularly effective because the beam envelope of the useful light is enclosed over the maximum possible length in the light propagation direction.
It generally holds true that the at least one tube ensures an optimum scattered light suppression if it surrounds the beam envelope of the useful light between the two optical surfaces over at least 50% of the beam envelope length, such as over the entire beam envelope length.
In a further exemplary configuration, the tube surrounds the beam envelope at a minimal distance, for example at a distance of less than 2 mm (e.g., less than 1 mm, less than 0.2 mm) but contactlessly.
If the tube surrounds the beam envelope contactlessly, this prevents the tube from disturbing the propagation of the useful light. The smaller the distance between the tube and the beam envelope of the useful light, the more effective the scattered light screening by the tube is, too, because even that scattered light whose propagation direction deviates only slightly from that of the beam envelope is effectively prevented from propagating by the tube.
In a further exemplary configuration, an intermediate image is generated between the first optical surface and the second optical surface, and the tube is arranged at least in proximity to the intermediate image.
The beam envelope of the useful light has the smallest circumference in the region of an intermediate image, such that the region of the intermediate image is particularly well suited to the arrangement of the at least one tube because the at least one tube can likewise be formed with a small circumference, such that the at least one tube does not occupy a large structural space within the projection objective.
In a further exemplary configuration, the geometrical shape of the interior of the tube is adapted to the shape of the beam envelope.
This measure is advantageous particularly in conjunction with one of the measures mentioned above according to which the tube surrounds the beam envelope of the useful light at a minimal distance, because, as a result of the adaptation of the geometrical shape of the interior of the tube to the shape of the beam envelope, the minimal distance is complied with over the entire circumference of the beam envelope and over the entire length over which the tube extends.
In one exemplary practical configuration, if the beam envelope is truncated cone shaped, the tube is likewise formed in truncated-cone-shaped fashion.
If the beam envelope is double truncated cone shaped, the tube can be formed in double-truncated-cone-shaped fashion or at least two truncated-cone-shaped tubes surround the beam envelope.
A double-truncated-cone-shaped form of the beam envelope of the useful light is advantageous in particular at an intermediate image since the beam envelope of the useful light both upstream of the intermediate image and downstream of the intermediate image is circumferentially enclosed by the one double-truncated-cone-shaped tube or the two truncated-cone-shaped tubes.
In a further exemplary configuration, a third optical surface provided with a through hole is arranged between the first optical surface and the second optical surface. The through hole serves for the passage of the useful light, and the tube is arranged in or in the region of the through hole.
This measure has the further advantage that the propagation of scattered light through the through hole in an optical surface can be effectively suppressed, while the useful light passes unimpeded through the through hole, to be precise through the tube. The present disclosure can advantageously be applied to catoptric projection objectives with an obscurated pupil, in particular to projection objectives for EUV microlithography.
However, the present disclosure is not restricted to catoptric projection objectives in the EUV range, but rather can also be used for projection objectives used in the longer-wavelength range.
Further advantages and features will become apparent from the description below and the accompanying drawing. It goes without saying that the features mentioned above and those explained below can be used not only in the combination respectively specified, but also in other combinations or by themselves, without departing from the scope of the present dislcosure. Exemplary embodiments of the disclosure are illustrated in the drawing and are described below with reference to the drawing, in which:
An optical axis of the projection objective 10 is designated by OA.
The optical surfaces S1 to S6 each have a region provided for application of useful light.
An intermediate image Z is furthermore situated between the optical surfaces S4 and S5. On account of the intermediate image Z, the beam envelope SH of the useful light between the optical surfaces S4 and S5 has the shape of a double cone or double truncated cone, the circumferentially narrowest location of which lies in the intermediate image Z.
The optical surface S5 has a through hole A1 and the optical surface S6 has a through hole A2, through which the useful light passes in each case. The useful light passes through the through hole A2 on the way from the optical surface S4 to the optical surface S5, and the useful light passes through the through hole A1 proceeding from the optical surface S6 to the image plane B.
In order, then, to prevent scattered light—which is generated for example at one of the optical surfaces S1, S2, S3 or S4 or which includes over-aperture light—from passing through the through hole A2 and through the through hole A1 directly into the image plane B, the beam envelope SH of the useful light between the optical surfaces S4 and S5 is surrounded by a tube 12 over a partial length of the beam envelope SH, the tube screening scattered light or preventing it from propagating.
The tube 12 is illustrated by itself in
The tube 12 has a circumferential wall 18, which, by contrast, is fully circumferentially closed and optionally absorbent on the inside and/or on the outside.
In accordance with
For better utilization of the overlap-free region of the beam envelopes, the tube 12 can also have a shape such as is supplemented by interrupted lines in
In this case, therefore, the tube 12 extends over the entire length of the beam envelope of the useful light between the optical surfaces S4 and S5 in which the beam envelope does not overlap the beam envelopes between the optical surfaces S3 and S4, or S5 and S6, or S6 and the image plane.
In the exemplary embodiment in accordance with
The tube 12 surrounds the beam envelope of the useful light between the optical surfaces S4 and S5 at as minimal a distance as possible, but without touching the beam envelope SH.
In the projection objective 10, the tube 12 is arranged in the vicinity of the intermediate image Z, but cannot reach as far as the intermediate image Z for structural reasons owing to the optical surface S3.
The projection objective 20 has eight optical surfaces S1 to S8 between an object plane O and an image plane B in the sequence of light propagation, the optical surface S6 having a through hole A1, the optical surface S5 having a through hole A2, the optical surface S8 having a through hole A3 and the optical surface S7 having a through hole A4.
The optical surfaces S1 to S8 are all realized by mirrors, such that the projection objective 20 is a catoptric projection objective. In contrast to the illustration in accordance with
The arrangement of the optical surfaces S1 to S8 generates a first intermediate image at Z1 and a second intermediate image at Z2.
A tube 22 is arranged between the optical surfaces S4 and S5. The tube circumferentially surrounds the beam envelope of the useful light between the optical surfaces S4 and S5. The tube 22 extends over a partial length of the beam envelope of the useful light between the optical surfaces S4 and S5 in which the useful light does not overlap the useful light between the optical surfaces S3 and S4 and S5 and S6 and between the optical surface S6 and the image plane.
The tube 22 surrounds the beam envelope of the useful light in the intermediate image Z1 and on both sides of the intermediate image Z1, as revealed in
Furthermore, the tube 22 passes through the through hole A1 in the optical surface S6, which makes it possible for the tube 22 to be mechanically fixed in particular to the through hole A1.
Since the beam envelope of the useful light on both sides of the intermediate image Z1 has the shape of a double truncated cone, the tube 22 is advantageously likewise formed as a double truncated cone.
Like the tube 12, the tube 22 is open at its longitudinal ends 24 and 26 and has a wall 28 that is opaque to light in the wavelength range of interest and is optionally absorbent on the inside and/or on the outside.
Instead of the double-truncated-cone-shaped tube 22, it is also possible to arrange two tubes in accordance with
The projection objective 30 has a total of ten optical surfaces S1 to S10 between an object plane O and an image plane B, the optical surfaces being realized as mirrors, such that the projection objective 30 is catoptric.
The projection objective 30 generates three intermediate images at Z1, Z2 and Z3. As in
In the projection objective 30, the beam envelope of the useful light in the region of the intermediate image Z1 between the optical surfaces S4 and S5 is surrounded by a tube 32 over a partial length that is free of overlaps with adjacent beam envelopes of the useful light, and, in addition, the beam envelope of the useful light between the optical surfaces S6 and S7 is surrounded by a second tube 34.
The tubes 32 and 34 essentially correspond to the tube 22 in accordance with the exemplary embodiment in
In the region of the intermediate image Z2, the optical surface S8 has a through hole A1, in which the tube 34 is advantageously arranged. Further through holes are situated at the optical surfaces S7, S9 and S10, the through holes being designated by A2, A3 and A4.
The projection objectives 10, 20 and 30 described above are suitable in particular for use in EUV lithography.
Number | Date | Country | Kind |
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10 2007 046 398.9 | Sep 2007 | DE | national |
This application is a continuation of, and claims benefit under 35 USC 120 to, international application PCT/EP2008/007807, filed Sep. 18, 2008, which claims benefit of German Application No. 10 2007 046 398.9, filed Sep. 21, 2007 and U.S. Ser. No. 60/974,171, filed Sep. 21, 2007. International application PCT/EP2008/007807 is hereby incorporated by reference in its entirety.
Number | Date | Country | |
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60974171 | Sep 2007 | US |
Number | Date | Country | |
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Parent | 12723456 | Mar 2010 | US |
Child | 15894293 | US |
Number | Date | Country | |
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Parent | PCT/EP2008/007807 | Sep 2008 | US |
Child | 12723456 | US |