This application claims benefit under 35 U.S.C. §119 to German Application No. 10 2010 061 820.9, filed Nov. 24, 2010. The contents of both of these applications are hereby incorporated by reference in its entirety.
The disclosure relates to an optical assembly for projection lithography, in other words for lithography using the imaging of structures on a lithography mask or a reticle, wherein the optical assembly has an optical component to guide imaging or illumination light. The disclosure also relates to a method for at least locally measuring the temperature of a substrate of an optical component for projection lithography, an illumination optical system with such an optical assembly, a projection optical system with such an optical assembly, a projection exposure system with such an illumination optical system, a projection exposure system with such a projection optical system, a production method for microstructured or nanostructured components using such a projection exposure system, and a microstructured or nanostructured component produced by such a production method.
Optical components for guiding imaging or illumination light within a projection exposure system are known, for example from WO 2009/100856 A1.
The present disclosure provides an optical assembly for projection lithography, in which a temperature or temperature distribution of the substrate of the optical component can be detected with a high degree of precision.
The optical fluorescence measurement according to the disclosure allows contactless temperature measurement of the substrate of the optical component. Oscillation or contact problems during the temperature measurement are dispensed with. The excitation optical system and the fluorescence optical system may coincide, at least in portions, in other words use shared optical components. The excitation optical system and the fluorescence optical system may, however, also be designed to be completely separate from one another, which can help to improve an optical resolution of the temperature measurement. Using the optical fluorescence measurement according to the disclosure, the temperature or the temperature distribution can also be measured deep within the substrate as long as the substrate has adequate transparency for the fluorescence excitation light and the fluorescent light. Typical optical glass materials and in particular ULE® or Zerodur® can be used as the substrate. The temperature measurement can take place without background disturbances (such as may be present, for example, in pyrometry owing to radiant background components). Using the fluorescence temperature measurement, a temperature precision that is adequate for the purposes of projection exposure of 0.1 K or an even higher temperature precision can be achieved. The optical component of the optical assembly may be a component of the illumination optical system, a component of the projection optical system, an EUV collector, or a projection lithography reticle. The fluorescence temperature measurement is not limited to EUV lithography, but can also be used in projection exposure systems working with other wavelengths. The reflective substrate reflects the imaging and/or illumination light. The fluorescent component may be arranged in the interior of the substrate. The fluorescent component may at least in part be arranged spaced apart from a substrate surface.
Erbium as the fluorescent component can allow a precise temperature measurement. A temperature measurement on the basis of a fluorescence intensity measurement is described in the specialist article by A. Pollman et al., Appl. Phys. Lett. 57 (26), 1990. An optical fluorescence temperature measurement based on a decay time of the fluorescence signal is described in a specialist article by Z. Y. Zhang et al., Rev. Sci. Instrum. 68 (7), 1997.
An optical fibre as a component of the excitation optical system or the fluorescence optical system makes it possible to arrange the excitation light source and the fluorescent light detector where installation space is available.
A confocal lens can allow good spatial resolution of the volume fraction in the substrate to be measured with regard to its temperature. If the confocal lens is used with an optical fibre in the excitation optical system or the fluorescence optical system, a fibre end can be imaged with the confocal lens on the volume fraction to be measured. If both the excitation optical system and the fluorescence optical system have their own confocal lens, this leads to the possibility of a very high spatial resolution.
A wavelength of the fluorescence excitation light of 980 nm can be produced, and a detected wavelength of the fluorescent light in the range of 1550 nm can be detected with conventional laser technology, for example with laser diodes, as 1550 nm is a standard telecommunication wavelength.
Advantages of a method for temperature measurement can correspond to those which have already been described above in connection with the optical assembly. When ensuring the presence of the fluorescent component, it can be ensured, in particular, that the fluorescent component is present in the interior of the optical component. A local volume fraction, which is spaced apart from a surface of the substrate, can be measured in the interior of the substrate during the temperature measurement.
The variants of an intensity measurement, a decay time measurement and a wavelength measurement can be used as an alternative to one another or else in combination with one another and allow a precise temperature measurement. During the wavelength measurement, the wavelength of a maximum of a fluorescent light spectrum or else the half-value width of a fluorescence spectrum can be measured in each case with respect to its temperature dependency.
The advantages of an illumination optical system, a projection optical system, a projection exposure system, a production method, and a component according to a production method can correspond to those which have already been discussed above with reference to the optical assembly and the temperature measuring method.
The temperature measuring result with respect to local substrate temperatures or substrate temperature distributions can be used as the actual temperature value for a subsequent temperature control of the optical component.
Embodiments of the disclosure will be described in more detail below with the aid of the drawings, in which:
The useful radiation bundle 3 is collected by a collector 4. Corresponding collectors are known, for example, from EP 1 225 481 A, US 2003/0043455 A and WO 2005/015314 A2. After the collector 4 and grazing incidence reflection on a spectral filter 4a, the useful radiation bundle 3 firstly propagates through an intermediate focus plane 5 with an intermediate focus Z and then impinges on a field facet mirror 6. After reflection on the field facet mirror 6, the useful radiation bundle 3 impinges on a pupil facet mirror 7.
After reflection on the pupil facet mirror 7, the useful radiation bundle 3 is firstly reflected on two further mirrors 8, 9. After the N2 mirror, the useful radiation bundle 3 impinges on a grazing incidence mirror 10.
Together with the pupil facet mirror 7, the further mirrors 8 to 10 image field facets of the field facet mirror 6 in an object field 11 in an object plane 12 of the projection exposure system 1. A surface portion to be imaged of a reflective reticle 13 is arranged in the object field 11.
The mirrors 6 to 10, and in a wider sense, also the collector 4, belong to an illumination optical system 14 of the projection exposure system 1.
A projection optical system 15 images the object field 11 in an image field 16 in an image plane 17. A wafer 18 is arranged there. The reticle 13 and the wafer 18 are carried by a reticle holder 19 and a wafer holder 20. The pupil facet mirror 7 lies in an optical plane, which is optically conjugated with a pupil plane of the projection optical system 15.
The object field 11 is arcuate, the meridional section of the illumination optical system 14 shown in
Perpendicular to the plane of the drawing of
The projection optical system 15 is a mirror optical system with six mirrors M1 to M6, which are numbered consecutively in
Each of the mirrors 6 to 10 of the illumination optical system 14 and M1 to M6 of the projection optical system 15 is an optical component with an optical face which can be impinged upon by the useful radiation bundle 3. The reticle 13 is also an optical component of this type.
The light source 2, the collector 4 and the spectral filter 4a are accommodated in a source chamber 21, which can be evacuated. The source chamber 21 has a through-opening 22 for the useful radiation bundle 3 in the region of the intermediate focus Z. Accordingly, the illumination optical system 14 following the intermediate focus Z, and the projection optical system 15 and the reticle holder 19 and the wafer holder 20 are housed in an illumination/projection optical system chamber 23, which can also be evacuated and of which
The temperature measuring device 27 has an excitation light source 29 to produce fluorescence excitation light. The excitation light source 29 is shown schematically in
A fluorescent component contained in the mirror substrate 24 is excited to fluorescence by the fluorescence excitation light focused in the volume fraction 28. Components of the substrate 24 that are already present in any case in the mirror material of the substrate 24 can be used to excite fluorescence. Alternatively, a fluorescent doping may be introduced into the material of the substrate 24. This may be erbium. A concentration of the fluorescent component may be 100 ppm or more.
The optical fibre 31 and the lens 33 are an excitation optical system 35 to guide the fluorescence excitation light to the volume fraction 28 to the fluorescent component of the substrate 24.
The fluorescent light has a wavelength of 1550 nm.
The fluorescent light produced is in turn guided via the beam path 32, the lens 33 and the optical fibre 31. Once the fluorescent light has left the optical fibre 31, the fluorescent light is outcoupled at the optical outcoupling component 30, in other words separated from the incident beam path of the fluorescence excitation light. After the outcoupling at the optical outcoupling component 30, the fluorescent light produced impinges on a fluorescent light detector 36.
The lens 33, the optical fibre 31 and the optical outcoupling element 30 are components of a fluorescence optical system 37 to guide the fluorescent light from the volume fraction 28 to the fluorescent light detector 36.
The lens 33 and the optical fibre 31 in the embodiment according to
Because of the confocal arrangement of the lens 23, a high spatial resolution of the fluorescent light detection is produced. The volume fraction 28, within which the fluorescence excitation takes place and within which a fluorescent light scanning takes place, is correspondingly small.
For at least local measurement of the temperature of the substrate 24, the procedure is as follows: it is firstly ensured that the substrate 24 contains a fluorescent component. This fluorescent component may, for example, be present in any case in the material of the substrate 24 in the form of an impurity or be introduced deliberately. It is then predetermined how large the volume fraction 28 is to be, within which a fluorescence excitation is to take place. The excitation optical system 35 and the fluorescence optical system 37 and also the excitation light source 29 are then provided in a configuration ensuring that a fluorescent light detection takes place in the volume fraction 28 in a size corresponding to the predetermined volume fraction size, in other words the predetermined spatial resolution of the detection. The fluorescent component in the volume fraction 28 is then excited to fluorescence with the fluorescence excitation light and the fluorescent light produced in the volume fraction 28 is detected by the fluorescent light detector 36.
This measuring method can firstly take place at a series of known temperatures of the substrate 24 in the temperature range to be measured. The temperature measuring device 27 is calibrated in this manner. A temperature-dependent variation of an intensity of the detected fluorescent light, a decay time of the detected fluorescent light or a wavelength of the detected fluorescent light can be used as the measuring variable.
During the intensity measurement, the intensity of the fluorescent light is detected by the fluorescent light detector 36. Very sensitive intensity detectors exist for a fluorescent light wavelength in the near infrared (NIR) range, in other words, for example in the range of 1550 nm.
To detect a decay time of the fluorescent light, the excitation of the volume fraction 28 takes place with a temporally limited fluorescence excitation light pulse. Depending on the time course of the fluorescence excitation, a fluorescent light response of the fluorescence excitation is then measured with the fluorescent light detector 36 with time resolution and a decay time constant of the fluorescent light is determined therefrom. This decay time also has a temperature dependency, which can firstly be determined by a calibration and then used for temperature measurement.
If the wavelength of the fluorescent light is detected for temperature measurement, the fluorescent light detector 36 has a spectral sensitivity. This can be produced by a spectral filtering or by a unit spectrally separating the fluorescent light, for example a grating or a dispersive element. The wavelength of the fluorescent light, at a fixed wavelength of the fluorescence excitation light, is temperature-dependent. After a corresponding calibration of the temperature dependency of a wavelength displacement of the fluorescent light, a temperature measurement can in turn take place based on the measured fluorescent light wavelength. Accordingly, a temperature measurement can also take place based on a temperature dependency of a half-value width of a fluorescence spectrum.
In the temperature measuring device 39, an excitation optical system 40 and a fluorescence optical system 41 are designed to be separate from one another. The two optical systems 40, 41 in each case have an optical fibre 42, 43 and a confocally arranged lens 44, 45 in accordance with the structure of the excitation optical system 35 of the configuration according to
A temperature measuring method using the temperature measuring device 39 corresponds to that which was already described above in conjunction with the temperature measuring device 27.
The substrate 24 can be measured at various points with a plurality of the above-described temperature measuring devices 27 and/or 39. It is possible via a combination of this type of measuring devices to measure a temperature distribution within the substrate 24.
A resolution of the temperature measurement in the region of 0.1 K or else a still better temperature resolution can be achieved with the temperature measuring devices 27, 39. The volume fractions 28, 28′, as shown in
During the projection exposure, the reticle 13 and the wafer 18, which carries a coating which is light-sensitive to the EUV illumination light 3, are provided. At least one portion of the reticle 13 is then projected on to the wafer 18 with the aid of the projection exposure system 1. Finally, the light-sensitive layer exposed by the EUV illumination light 3 is developed on the wafer 18. The microstructured or nanostructured component, for example a semiconductor chip, is produced in this manner.
The embodiments described above were described with the aid of EUV illumination. As an alternative to EUV illumination, UV illumination or VUV illumination can also be used, for example with illumination light with a wavelength of 193 nm.
Number | Date | Country | Kind |
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10 2010 061 820.9 | Nov 2010 | DE | national |