DE102022209922A1 - REFLECTOMETER DEVICE, MEASURING ARRANGEMENT, METHOD FOR PRODUCING AN OPTICAL REFERENCE ELEMENT AND METHOD FOR MEASURING A SAMPLE OF A LITHOGRAPHY SYSTEM - Google Patents

Abstract

A reflectometer device (24) for measuring a sample (25) of a lithography system (1) using a measuring radiation (26), having an optical reference element (27) in a beam path (28) of the measuring radiation (26), which has a beam splitter layer (29 ) for reflecting a portion (30) of the measuring radiation (26) onto the sample (25) and for transmitting a further portion (31) of the measuring radiation (26) and a detector layer (32) for detecting the transmitted portion (31) of the measuring radiation ( 26) includes.

Description

The present invention relates to a reflectometer device, a measuring arrangement with such a reflectometer device, a method for producing an optical reference element of such a reflectometer device and a method for measuring a sample of a lithography system by means of such a reflectometer device.

Microlithography is used to produce microstructured components, such as integrated circuits. The microlithography process is carried out using a lithography system which has an illumination system and a projection system. The image of a mask (reticle) illuminated by the illumination system is projected by means of the projection system onto a substrate, for example a silicon wafer, which is coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection system, in order to project the mask structure onto the light-sensitive coating of the substrate transferred to.

Driven by the pursuit of ever smaller structures in the production of integrated circuits, EUV lithography systems are currently being developed which use light with a wavelength in the range from 0.1 nm to 30 nm, in particular 13.5 nm. Since most materials absorb light of this wavelength, reflective optics, i.e. mirrors, must be used in such EUV lithography systems instead of - as before - refracting optics, i.e. lenses.

In the manufacturing process and in the operation of lithography systems, reflectometers are usually used to measure optical elements of the lithography system. For example, a reflection behavior of an optical element and a layer thickness of a coating applied to the optical element are examined using reflectometry. Reflectometric measurements in the EUV wavelength range are difficult due to the high absorption of EUV radiation by matter.

Against this background, an object of the present invention is to provide an improved reflectometer device for a lithography system.

Accordingly, a reflectometer device for measuring a sample of a lithography system using measuring radiation is proposed. The reflectometer device has an optical reference element in a beam path of the measuring radiation. The optical reference element comprises a beam splitter layer for reflecting a portion of the measuring radiation onto the sample and for transmitting a further portion of the measuring radiation and a detector layer for detecting the transmitted portion of the measuring radiation.

By using the beam splitter layer, the measuring beam can be split into several parts. Thus, a portion of the measurement radiation can be used to irradiate the sample and another portion of the measurement radiation can be used for a reference measurement. Through the reference measurement, information about the measurement radiation, such as an intensity of the measurement radiation, can be recorded and taken into account when evaluating the measurement radiation reflected by the sample. Consequently, measurement of a reflectivity of the sample can be carried out more accurately. For example, a measurement radiation reflected by the sample can be examined with regard to its intensity, its wavelength(s) and/or its wavelength spectrum (wavelength-dependent intensity distribution).

The beam splitter layer is set up in particular for physical beam splitting of the measuring beam. With physical beam splitting, the beam splitting (in contrast to geometric beam splitting) occurs evenly over the entire cross section of the incident radiation through a partially transparent mirror surface in accordance with its transmittance and reflectance, and a beam cross section of the radiation remains unchanged.

By using a beam splitter layer for physical beam splitting instead of a geometric beam splitter, disadvantages associated with geometric beam splitters can be avoided. An example of a geometric beam splitter is a comb structure whose tines reflect some of the incident radiation, with the gaps allowing another portion of the incident radiation to pass through. A disadvantage of a geometric beam splitter is that the splitting ratio depends on a position, a size, a shape and an intensity distribution of the incident radiation. In addition, with a geometric beam splitter, a halo can occur due to scattered light at the edges of the beam splitter. By using the physical beam splitter layer, the dependence of the splitting ratio on the incident radiation and scattered light can be avoided.

The beam splitter layer has, for example, a material that includes ruthenium (Ru), germanium (Ge), silicon (Si), molybdenum (Mo) and/or another suitable material. The beam splitter layer can, for example, consist of a single one Be made of material from the group that includes ruthenium, germanium, silicon, molybdenum and / or another suitable material. Alternatively, the beam splitter layer may also comprise more than one material from the group including ruthenium, germanium, silicon, molybdenum and/or another suitable material.

For example, the beam splitter layer can also have a layer structure whose two or more layers differ in material composition. For example, a respective layer of the layer structure may have a material composition comprising one or more of the materials from the group consisting of ruthenium, germanium, silicon, molybdenum and/or another suitable material. An example of a layer structure of the beam splitter layer is a sequence of molybdenum and silicon layers. For example, the beam splitter layer comprises a molybdenum layer on which a silicon layer is arranged. Optionally, the beam splitter layer includes e.g. B. also a further molybdenum layer which is arranged on the silicon layer, and a further silicon layer which is arranged on the molybdenum layer.

An angle of incidence of radiation incident on the beam splitter layer is, for example, between 70° and 90°, 80° and 85°, 80°, 82° and/or 85°. The angle of incidence is in particular an angle between the radiation incident on the beam splitter layer of the optical reference element and a plumb line on the optical reference element.

Because the optical reference element has the beam splitter layer and the detector layer, a beam splitter device separate from the optical reference element and a detector device separate from the optical reference element for detecting the reference radiation are not required. In other words, the beam splitter layer and the detector layer are integrated into the optical reference element. The reflectometer device can thus be simplified.

The optical reference element has, for example, a carrier substrate on which the beam splitter layer and the detector layer are attached. The carrier substrate supports in particular the beam splitter layer, so that deformation of the beam splitter layer can be avoided, even if the beam splitter layer is thin. The beam splitter layer is designed, for example, as a coating of the carrier substrate. In particular, the carrier substrate in the present case can be designed to be stable, for example with a relatively large thickness, since the measuring radiation does not penetrate the carrier substrate.

The detector layer is in particular a radiation detector designed as a layer for detecting the portion of the measurement radiation transmitted through the beam splitter layer. The detector layer can measure the transmitted portion of the measurement radiation based on various physical processes, in particular those that involve an interaction between radiation and matter, and/or based on the measurement of various quantities, such as a current measurement, a voltage measurement, a measurement of an electric field and /or a temperature measurement.

The reflectometer device can be used to measure a sample of a lithography system (projection exposure system) using the measuring radiation, e.g. B. can be used in the production of the lithography system or in the operation of the lithography system. The sample of the lithography system is, for example, an optical element of the lithography system. The sample of the lithography system is, for example, a mirror of the lithography system. The sample is, for example, an optical element of an illumination optics and/or a projection optics of the lithography system. The sample can, for example, also be a collector (e.g. collector mirror) which is designed to concentrate illumination radiation from a light source of the lithography system. The lithography system (projection exposure system) can be an EUV lithography system. EUV stands for “Extreme Ultraviolet” and describes a wavelength of working light between 0.1 nm and 30 nm. The lithography system (projection exposure system) can also be a DUV lithography system. DUV stands for “Deep Ultraviolet” and describes a wavelength of work light between 30 nm and 250 nm.

According to one embodiment, the beam splitter layer has a partially transparent layer with a partially transparent material and a reflective surface.

The partially transparent layer is, for example, a semi-transparent layer. The reflective surface is, for example, a partially reflective surface.

According to a further embodiment, the optical reference element comprises a carrier substrate, wherein the carrier substrate has a front surface with respect to the incident measurement radiation, the detector layer is arranged in front of the front surface of the carrier substrate with respect to the incident measurement radiation, and the beam splitter layer with respect to the incident measuring radiation is arranged in front of the detector layer.

The detector layer is arranged in particular between the carrier substrate and the beam splitter layer.

The beam splitter layer is arranged, for example, in direct contact with the detector layer. In other words, the beam splitter layer is, for example, a coating applied directly to the detector layer.

According to a further embodiment, the reflectometer device further has a light source for emitting the measuring radiation, a holder for holding and/or moving the sample, and/or a detector device for detecting a measuring radiation reflected by the sample.

With the holder, the sample can be arranged in the measuring beam path of the reflectometer device, so that the portion of the measuring radiation reflected by the optical reference element of the reflectometer device can irradiate the sample. The holder can, for example, also be set up to move the sample or to position the sample in different orientations relative to the measuring beam path. For this purpose, the holder can, for example, have one or more actuators, a robotic unit, a robotic arm, a goniometer, a motor and/or a control unit.

The light source of the reflectometer device is set up, for example, to emit a measuring radiation with a wavelength range that includes a wavelength of a working light of the lithography system. A wavelength range of the measuring radiation of the reflectometer device is, for example, broader than a wavelength range/wavelength of the working light of the lithography system.

According to a further embodiment, the reflectometer device is set up for measuring a sample of an EUV lithography system using EUV radiation as measuring radiation, and/or the reflectometer device comprises an EUV light source for emitting the measuring radiation.

For example, the detector layer of the reflectometer device is set up to detect EUV radiation.

The reflectometer device is in particular an EUV reflectometer device, which uses measuring radiation in the EUV range to measure the sample. This means that it can be used to measure a sample, such as a mirror, of an EUV lithography system in order to examine the reflectivity of the sample in the EUV range.

EUV stands for “Extreme Ultraviolet” and describes a wavelength of the working light between 0.1 nm and 30 nm. The wavelength of the working light of the EUV lithography system is therefore between 0.1 nm and 30 nm and in particular 13.5 nm. Furthermore, has the measuring radiation of the reflectometer device also has a wavelength range between 0.1 nm and 30 nm. For example, the EUV light source of the reflectometer device emits a measuring radiation with a wavelength range of 10 to 20 nm or 12.4 to 16 nm.

In other embodiments, the reflectometer device can also be set up to measure a sample of a DUV lithography system using DUV radiation as measuring radiation. DUV stands for “Deep Ultraviolet” and describes a wavelength of work light between 30 nm and 250 nm.

According to a further embodiment, the beam splitter layer is set up to reflect and transmit EUV radiation, and/or a thickness of the beam splitter layer is 1 μm or smaller, 100 nm or smaller, 50 nm or smaller, 10 nm or smaller, 5 nm or smaller, 1 nm or smaller and/or 0.1 nm or smaller.

By forming a particularly thin beam splitter layer, the absorption of the EUV radiation in the beam splitter layer can be kept relatively low.

According to a further embodiment, the detector layer has a photodiode and/or a semiconductor photodiode.

As a result, the portion of the measuring radiation transmitted through the beam splitter layer can be recorded as a (photo-)electric signal in an electrical measuring circuit of the photodiode. For example, the transmitted portion of the measuring radiation can lead to a change in an electrical current, an electrical voltage and/or an electrical resistance in the measuring circuit of the photodiode by impinging on the photodiode of the detector layer. For example, an intensity of the measuring radiation striking the photodiode of the detector layer is proportional to a change in the electrical current, the electrical voltage and/or the electrical resistance in the measuring circuit.

The detector layer has, for example, an EUV-sensitive (semiconductor) photodiode.

According to a further embodiment, the detector layer comprises a P-doped layer, an N-doped layer and a PN junction. The optical reference element also includes a first and second electrically conductive contact element, which are in electrical contact with the P-doped layer and the N-doped layer, respectively. Furthermore, the optical reference element comprises a current and/or voltage measuring device, and the first and second contact elements are electrically connected to one another via the current and/or voltage measuring device.

As a result, the transmitted portion of the measurement radiation can be detected using a current measurement and/or voltage measurement between the first and second contact elements.

The P-doped layer is in particular a P-doped semiconductor layer in which foreign atoms (e.g. boron, indium, aluminum or gallium) have been introduced as acceptors into a base material (e.g. silicon or germanium), so that freely movable positive charge carriers (i.e. so-called gaps, holes or holes) are present.

The N-doped layer is in particular an N-doped semiconductor layer in which foreign atoms (e.g. phosphorus, arsenic or antimony) have been introduced as donors into a base material (e.g. silicon or germanium), so that freely movable negative charge carriers (i.e. electrons) are present.

The PN junction of the detector layer is the transition from the P-doped layer to the N-doped layer. For example, the P-doped layer and the N-doped layer in the PN junction are in direct contact with each other. Alternatively, a so-called PiN diode can also be present, in which an undoped material is arranged in the PN junction between the P- and N-doped layer, whereby the space charge zone is enlarged. In the PN junction, electrons diffuse from the N-doped layer into the P-doped layer and recombine there, and holes (holes) diffuse from the P-doped layer into the N-doped layer and recombine there. As a result, an electric field builds up at the PN junction (so-called space charge zone or barrier layer), which counteracts the diffusion movement of electrons and holes. In addition, an area is formed that is depleted of free charge carriers (depletion zone).

By applying an external voltage in the reverse direction to the detector layer (i.e. negative terminal of a voltage source is electrically connected to the P-doped layer and positive terminal of the voltage source is electrically connected to the N-doped layer), the electric field of the barrier layer can be increased and it only flows a very low current (blocking current). For this purpose, the optical reference element includes, for example, a voltage source. In this case, the first and second contact elements are electrically connected to one another via the current and/or voltage measuring device and the voltage source.

If the measuring radiation transmitted through the beam splitter layer hits the detector layer, the photons of the measuring radiation are absorbed in the barrier layer of the semiconductor photodiode and electron-hole pairs are generated (internal photoelectric effect, lifting electrons into the conduction band of the semiconductor). The photoelectrically generated electron-hole pairs are separated by the prevailing electric field in the barrier layer and can be detected as a flowing charge (e.g. due to detection of a change in the barrier current) via the first and second contact elements.

The first and/or second electrically conductive contact element can be designed as a layer which is in (large) area electrical contact with the P-doped layer and/or the N-doped layer. For example, a first and/or second electrically conductive contact element designed as a layer can correspondingly cover the P-doped layer and/or the N-doped layer largely (more than 50%) and/or completely.

Alternatively, the first and/or second electrically conductive contact element can be in electrical contact with the P-doped layer and/or the N-doped layer only in an edge region of the corresponding layer. In particular, if the doping of the corresponding P-doped and/or N-doped layer is so high that the top and bottom of the diode also become electrically conductive, contacting only at the edge may be sufficient.

The first and/or second electrically conductive contact element has a material that includes, for example, ruthenium, molybdenum and/or nickel.

According to another embodiment
one of the first and second contact elements is designed as a contact layer, which is arranged between a carrier substrate of the optical reference element and the detector layer,
the other of the first and second contact elements is arranged on a front surface of the detector layer with respect to the incident measuring radiation, and/or
the beam splitter layer forms the other of the first and second contact elements.

For example, one of the first and second contact elements is arranged directly on a front surface of the carrier substrate with respect to the incident measuring radiation. For example, one of the first and second contact elements is formed as a coating of the front surface of the carrier substrate.

For example, the detector layer is arranged directly on a front surface of one of the first and second contact elements with respect to the incident measuring radiation. For example, the detector layer is formed as a coating of the front surface of one of the first and second contact elements.

For example, the beam splitter layer and/or the other of the first and second contact elements is arranged directly on a front surface of the detector layer with respect to the incident measurement radiation. For example, the beam splitter layer and/or the other of the first and second contact elements are formed as a coating of the front surface of the detector layer.

According to a further embodiment, the front surface of the detector layer has a first region in which the beam splitter layer is arranged and a second region in which the other of the first and second contact elements is arranged.

As a result, a front side contact (front side in relation to the incident measuring radiation) of the detector layer can be arranged in such a way that the beam splitter layer is exposed for the incident measuring radiation.

According to a further embodiment, the reflectometer device has a secondary electron detector for detecting the transmitted portion of the measurement radiation, wherein the secondary electron detector is set up to detect secondary electrons emerging from the detector layer and/or a charge of the optical reference element due to secondary electrons emerging from the detector layer.

Secondary electrons can be released from the detector layer by the measurement radiation (in particular an EUV measurement radiation and/or a DUV measurement radiation).

For example, an electrical charge of the optical reference element due to secondary electrons emerging from the detector layer is detected in that the optical reference element is electrically insulated with the detector layer and becomes positively charged by the detachment of the secondary electrons. This positive charge of the optical reference element can then be detected, for example by measuring an amount of current required to electrically neutralize the optical reference element. For this purpose, the reflectometer device in particular has a current measuring device. This current measuring device is set up, for example, to measure current with an accuracy in the femtoampere range.

According to a further embodiment, the detector layer comprises a fluorescent layer for exciting fluorescence through the transmitted portion of the measurement radiation and for emitting fluorescent radiation. Furthermore, the reflectometer device and/or the detector layer comprises a fluorescence radiation detector unit for detecting the fluorescence radiation.

Because the detector layer has a fluorescent layer, the radiation incident on the detector layer can be converted into fluorescent radiation and detected by detecting the fluorescent radiation. In particular, the transmitted measuring radiation represents an excitation radiation which, when it hits the fluorescent layer, stimulates it to emit the fluorescent radiation. For example, the fluorescence radiation is then detected via the formation of electron-hole pairs in a semiconductor photodiode.

For example, the measurement radiation (excitation radiation) has a first wavelength range. Furthermore, the excitation radiation striking the fluorescent layer stimulates the fluorescent layer to emit the fluorescent radiation in a second wavelength range. The first wavelength range of the measurement radiation (excitation radiation) is, for example, different from the second wavelength range of the fluorescence radiation. The second wavelength range is, for example, shifted to longer wavelengths relative to the first wavelength range. The second wavelength range can, for example, partially overlap with the first wavelength range, or the first and second wavelength ranges can be disjoint to one another.

For example, measurement radiation in the EUV range is converted into fluorescent radiation in the longer-wave UV range or in the visible wavelength range.

Furthermore, the detector layer can be designed as the fluorescence radiation detector unit. In this case, the measurement radiation transmitted through the beam splitter layer and in the Fluo Radiation converted into fluorescence radiation is detected in the detector layer.

Alternatively, the reflectometer device can have a fluorescence radiation detector unit that is separate from the detector layer and/or the optical reference element. In this case, the measurement radiation transmitted through the beam splitter layer and the radiation converted into fluorescence radiation in the fluorescence layer is again transmitted through the beam splitter layer or through the substrate and detected in an external fluorescence radiation detector unit.

According to a second aspect, a reflectometer device for measuring a sample of a lithography system using measuring radiation is proposed. The reflectometer device comprises an optical reference element in a beam path of the measuring radiation, which comprises a reflection layer for reflecting a portion of the measuring radiation onto the sample and for absorbing a further portion of the measuring radiation and a secondary electron detector for detecting the absorbed portion of the measuring radiation, the secondary electron detector for this purpose is set up to detect secondary electrons emerging from the reflection layer and / or a charge of the optical reference element due to secondary electrons emerging from the reflection layer.

According to a third aspect, a measuring arrangement for a lithography system is provided. The measuring arrangement includes an optical element for the lithography system as a sample and a reflectometer device as described above or below for measuring the sample.

According to a fourth aspect, a lithography system is provided. The lithography system includes a measuring arrangement as described above.

The reflectometer device is used, for example, to monitor an exposure energy of the optical element during operation of the lithography system. The optical element is z. B. an optical element of the lighting optics or the projection optics of the lithography system.

• a1) Aufbringen einer Detektorschicht auf einem Trägersubstrat, und
• b1) Aufbringen einer Strahlteiler-Schicht auf der Detektorschicht.

According to a fifth aspect, a method for producing an optical reference element of a reflectometer device for measuring a sample of a lithography system is provided. The manufacturing process includes the steps:

• a1) Applying a detector layer to a carrier substrate, and
• b1) Application of a beam splitter layer on the detector layer.

For example, the carrier substrate is coated with the detector layer in a coating process. For example, the detector layer is coated with the beam splitter layer in a coating process.

In embodiments, the manufacturing method according to the fifth aspect can have a step of applying a first electrically conductive contact layer to the carrier substrate before step a1). In this case, the detector layer is applied to the first contact layer in step a1).

The manufacturing method according to the fifth aspect can, in embodiments, after step b 1) have a step of applying a second contact element/a second contact layer on the detector layer.

In embodiments, the manufacturing method according to the fifth aspect may include electrically connecting the first electrically conductive contact layer and/or the second electrically conductive contact layer to a readout unit.

In embodiments, the manufacturing method according to the fifth aspect can include polishing the detector layer after step a1).

• a2) Einstrahlen einer Messstrahlung auf eine Strahlteiler-Schicht eines optischen Referenzelements der Reflektometervorrichtung,
• b2) Reflektieren eines Anteils der Messstrahlung mittels der Strahlteiler-Schicht auf die Probe,
• c2) Transmittieren eines weiteren Anteils der Messstrahlung durch die Strahlteiler-Schicht hindurch zu einer Detektorschicht des optischen Referenzelements, und
• d2) Erfassen des transmittierten Anteils der Messstrahlung mittels der Detektorschicht.

According to a sixth aspect, a method for measuring a sample of a lithography system using a reflectometer device is provided. The survey procedure includes the steps:

• a2) irradiating a measuring radiation onto a beam splitter layer of an optical reference element of the reflectometer device,
• b2) reflecting a portion of the measuring radiation onto the sample using the beam splitter layer,
• c2) transmitting a further portion of the measurement radiation through the beam splitter layer to a detector layer of the optical reference element, and
• d2) Detecting the transmitted portion of the measurement radiation using the detector layer.

According to a seventh aspect, a reflectometer device for measuring a sample of a lithography system using measuring radiation is proposed. The reflectometer device according to the seventh aspect has an optical reference element in a beam path of the measuring radiation, which has a reflection layer Reflecting a portion of the measurement radiation onto the sample and for absorbing a further portion of the measurement radiation and a detector layer for detecting the absorbed portion of the measurement radiation.

Compared to a reflectometer device with a beam splitter layer (first aspect), in the reflectometer device according to the seventh aspect, a larger proportion of the incident radiation can be used to measure the sample. For example, the incident radiation can be used almost entirely to measure the sample. The reflected portion of the radiation is passed on to the sample, the absorbed radiation is detected and the transmitted portion is zero due to total reflection.

The reflection layer includes e.g. B. Copper. Copper offers the advantage of uniform reflection over the desired wavelength range.

According to an embodiment of the seventh aspect, the detector layer for detecting the absorbed portion of the measurement radiation has a pyroelectric material, and/or the detector layer for detecting the absorbed portion of the measurement radiation is set up to detect a temperature change of the reflection layer and/or the detector layer .

The pyroelectric material includes e.g. B. sodium nitrite (NaNO ₂ ).

In the present case, “on” is not necessarily to be understood as limiting it to exactly one element. Rather, several elements, such as two, three or more, can also be provided. Any other counting word used here should not be understood to mean that there is a limitation to exactly the number of elements mentioned. Rather, numerical deviations upwards and downwards are possible, unless otherwise stated.

The embodiments and features described for the reflectometer device apply accordingly to the proposed measuring arrangement and the proposed methods and vice versa.

Further possible implementations of the invention also include combinations of features or embodiments described above or below with regard to the exemplary embodiments that are not explicitly mentioned. The person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

• 1 zeigt einen schematischen Meridionalschnitt einer Projektionsbelichtungsanlage für die EUV-Projektionslithographie;
• 2 zeigt eine Messanordnung mit einer Reflektometervorrichtung zur Vermessung eines optischen Elements der Projektionsbelichtungsanlage aus 1 gemäß einer ersten Ausführungsform;
• 3 zeigt ein optisches Referenzelement der Reflektometervorrichtung aus 2;
• 4 zeigt ein optisches Referenzelement einer Reflektometervorrichtung gemäß einer zweiten Ausführungsform;
• 5 zeigt ein optisches Referenzelement einer Reflektometervorrichtung gemäß einer dritten Ausführungsform;
• 6 zeigt ein optisches Referenzelement einer Reflektometervorrichtung gemäß einer vierten Ausführungsform;
• 7 zeigt ein Flussablaufdiagramm eines Verfahrens zum Herstellen eines optischen Referenzelements einer Reflektometervorrichtung zur Vermessung einer Probe einer Lithographieanlage;
• 8 zeigt ein Flussablaufdiagramm eines Verfahrens zum Vermessen einer Probe einer Lithographieanlage mithilfe einer Reflektometervorrichtung; und
• 9 zeigt ein optisches Referenzelement einer Reflektometervorrichtung gemäß einer fünften Ausführungsform, wobei ein optisches Referenzelement der Reflektometervorrichtung eine pyroelektrische Dektorschicht aufweist.

Further advantageous refinements and aspects of the invention are the subject of the subclaims and the exemplary embodiments of the invention described below. The invention is further explained in more detail using preferred embodiments with reference to the accompanying figures.

• 1 shows a schematic meridional section of a projection exposure system for EUV projection lithography;
• 2 shows a measuring arrangement with a reflectometer device for measuring an optical element of the projection exposure system 1 according to a first embodiment;
• 3 shows an optical reference element of the reflectometer device 2 ;
• 4 shows an optical reference element of a reflectometer device according to a second embodiment;
• 5 shows an optical reference element of a reflectometer device according to a third embodiment;
• 6 shows an optical reference element of a reflectometer device according to a fourth embodiment;
• 7 shows a flowchart of a method for producing an optical reference element of a reflectometer device for measuring a sample of a lithography system;
• 8th shows a flowchart of a method for measuring a sample of a lithography system using a reflectometer device; and
• 9 shows an optical reference element of a reflectometer device according to a fifth embodiment, wherein an optical reference element of the reflectometer device has a pyroelectric detector layer.

In the figures, identical or functionally identical elements have been given the same reference numerals, unless otherwise stated. Furthermore, it should be noted that the representations in the figures are not necessarily to scale.

1 shows an embodiment of a projection exposure system 1 (lithography system), in particular an EUV lithography system. One embodiment of a lighting system 2 of the projection exposure system 1 has, in addition to a light or radiation source 3, lighting optics 4 for illuminating an object field 5 in an object plane 6. In an alternative off For guidance, the light source 3 can also be provided as a module separate from the other lighting system 2. In this case, the lighting system 2 does not include the light source 3.

A reticle 7 arranged in the object field 5 is exposed. The reticle 7 is held by a reticle holder 8. The reticle holder 8 can be displaced via a reticle displacement drive 9, in particular in a scanning direction.

In the 1 For explanation purposes, a Cartesian coordinate system with an x-direction x, a y-direction y and a z-direction z is shown. The x-direction x runs perpendicularly into the drawing plane. The y-direction y is horizontal and the z-direction z is vertical. The scanning direction is in the 1 along the y-direction y. The z direction z runs perpendicular to the object plane 6.

The projection exposure system 1 includes projection optics 10. The projection optics 10 is used to image the object field 5 into an image field 11 in an image plane 12. The image plane 12 runs parallel to the object plane 6. Alternatively, an angle other than 0 ° is also between the object plane 6 and the Image level 12 possible.

A structure on the reticle 7 is imaged on a light-sensitive layer of a wafer 13 arranged in the area of the image field 11 in the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be displaced in particular along the y-direction y via a wafer displacement drive 15. The displacement, on the one hand, of the reticle 7 via the reticle displacement drive 9 and, on the other hand, of the wafer 13 via the wafer displacement drive 15 can take place in synchronization with one another.

The light source 3 is an EUV radiation source. The light source 3 emits in particular EUV radiation 16, which is also referred to below as useful radiation, illumination radiation or illumination light. The useful radiation 16 in particular has a wavelength in the range between 5 nm and 30 nm. The light source 3 can be a plasma source, for example an LPP source (Laser Produced Plasma, plasma generated with the help of a laser) or a DPP source (Gas Discharged Produced Plasma). It can also be a synchrotron-based radiation source. The light source 3 can be a free electron laser (FEL).

The illumination radiation 16, which emanates from the light source 3, is focused by a collector 17. The collector 17 can be a collector with one or more ellipsoidal and/or hyperboloid reflection surfaces. The at least one reflection surface of the collector 17 can be in grazing incidence (GI), i.e. with angles of incidence greater than 45 °, or in normal incidence (English: Normal Incidence, NI), i.e. with angles of incidence smaller than 45 ° , with the lighting radiation 16 are applied. The collector 17 can be structured and/or coated on the one hand to optimize its reflectivity for the useful radiation and on the other hand to suppress false light.

After the collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focus plane 18. The intermediate focus plane 18 can represent a separation between a radiation source module, having the light source 3 and the collector 17, and the illumination optics 4.

The lighting optics 4 comprises a deflection mirror 19 and, downstream of it in the beam path, a first facet mirror 20. The deflection mirror 19 can be a flat deflection mirror or alternatively a mirror with an effect that influences the bundle beyond the pure deflection effect. Alternatively or additionally, the deflection mirror 19 can be designed as a spectral filter which separates a useful light wavelength of the illumination radiation 16 from false light of a wavelength that deviates from this. If the first facet mirror 20 is arranged in a plane of the illumination optics 4, which is optically conjugate to the object plane 6 as a field plane, it is also referred to as a field facet mirror. The first facet mirror 20 includes a large number of individual first facets 21, which can also be referred to as field facets. Of these first facets 21 are in the 1 just a few are shown as examples.

The first facets 21 can be designed as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or part-circular edge contour. The first facets 21 can be designed as flat facets or alternatively as convex or concave curved facets.

Like, for example, from the DE 10 2008 009 600 A1 is known, the first facets 21 themselves can also each be composed of a large number of individual mirrors, in particular a large number of micromirrors. The first facet mirror 20 can in particular be used as a microelectromechanical system (MEMS system). be trained. For details see the DE 10 2008 009 600 A1 referred.

Between the collector 17 and the deflection mirror 19, the illumination radiation 16 runs horizontally, i.e. along the y-direction y.

A second facet mirror 22 is located downstream of the first facet mirror 20 in the beam path of the illumination optics 4. If the second facet mirror 22 is arranged in a pupil plane of the illumination optics 4, it is also referred to as a pupil facet mirror. The second facet mirror 22 can also be arranged at a distance from a pupil plane of the lighting optics 4. In this case, the combination of the first facet mirror 20 and the second facet mirror 22 is also referred to as a specular reflector. Specular reflectors are known from US 2006/0132747 A1 , the EP 1 614 008 B1 and the US 6,573,978 .

The second facet mirror 22 comprises a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets.

The second facets 23 can also be macroscopic facets, which can have, for example, round, rectangular or even hexagonal edges, or alternatively they can be facets composed of micromirrors. In this regard, reference is also made to the DE 10 2008 009 600 A1 referred.

The second facets 23 can have flat or alternatively convex or concave curved reflection surfaces.

The lighting optics 4 thus forms a double faceted system. This basic principle is also known as the honeycomb condenser (Fly's Eye Integrator).

It may be advantageous not to arrange the second facet mirror 22 exactly in a plane that is optically conjugate to a pupil plane of the projection optics 10. In particular, the second facet mirror 22 can be arranged tilted relative to a pupil plane of the projection optics 10, as is the case, for example, in FIG DE 10 2017 220 586 A1 is described.

With the help of the second facet mirror 22, the individual first facets 21 are imaged into the object field 5. The second facet mirror 22 is the last beam-forming mirror or actually the last mirror for the illumination radiation 16 in the beam path in front of the object field 5.

In a further embodiment of the illumination optics 4, not shown, transmission optics can be arranged in the beam path between the second facet mirror 22 and the object field 5, which contributes in particular to the imaging of the first facets 21 into the object field 5. The transmission optics can have exactly one mirror, but alternatively also two or more mirrors, which are arranged one behind the other in the beam path of the lighting optics 4. The transmission optics can in particular include one or two mirrors for perpendicular incidence (NI mirror, normal incidence mirror) and/or one or two mirrors for grazing incidence (GI mirror, gracing incidence mirror).

The lighting optics 4 has the version in the 1 is shown, after the collector 17 exactly three mirrors, namely the deflection mirror 19, the first facet mirror 20 and the second facet mirror 22.

In a further embodiment of the lighting optics 4, the deflection mirror 19 can also be omitted, so that the lighting optics 4 can then have exactly two mirrors after the collector 17, namely the first facet mirror 20 and the second facet mirror 22.

The imaging of the first facets 21 into the object plane 6 by means of the second facets 23 or with the second facets 23 and a transmission optics is generally only an approximate image.

The projection optics 10 comprises a plurality of mirrors Mi, which are numbered consecutively according to their arrangement in the beam path of the projection exposure system 1.

At the one in the 1 In the example shown, the projection optics 10 includes six mirrors M1 to M6. Alternatives with four, eight, ten, twelve or another number of mirrors Mi are also possible. The projection optics 10 is a double obscured optics. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 16. The projection optics 10 has an image-side numerical aperture that is larger than 0.5 and which can also be larger than 0.6 and, for example, 0.7 or can be 0.75.

Reflection surfaces of the mirrors Mi can be designed as free-form surfaces without an axis of rotational symmetry. Alternatively, the reflection surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface shape. The mirrors Mi can, just like the mirrors of the lighting optics 4, have highly reflective coatings for the lighting radiation 16. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

The projection optics 10 has a large object image offset in the y direction y between a y coordinate of a center of the object field 5 and a y coordinate of the center of the image field 11. This object image offset in the y direction y can be in be approximately as large as a z-distance between the object plane 6 and the image plane 12.

The projection optics 10 can in particular be anamorphic. In particular, it has different imaging scales ßx, By in the x and y directions x, y. The two imaging scales ßx, By of the projection optics 10 are preferably (ßx, ßy) = (+/- 0.25, +/- 0.125). A positive magnification B means an image without image reversal. A negative sign for the image scale B means an image with image reversal.

The projection optics 10 thus leads to a reduction in size in the x direction x, that is to say in the direction perpendicular to the scanning direction, in a ratio of 4:1.

The projection optics 10 leads to a reduction of 8:1 in the y direction y, that is to say in the scanning direction.

Other image scales are also possible. Image scales of the same sign and absolutely the same in the x and y directions x, y, for example with absolute values of 0.125 or 0.25, are also possible.

The number of intermediate image planes in the x and y directions x, y in the beam path between the object field 5 and the image field 11 can be the same or, depending on the design of the projection optics 10, can be different. Examples of projection optics with different numbers of such intermediate images in the x and y directions x, y are known from US 2018/0074303 A1 .

One of the second facets 23 is assigned to exactly one of the first facets 21 to form an illumination channel for illuminating the object field 5. This can in particular result in lighting based on Köhler's principle. The far field is broken down into a large number of object fields 5 using the first facets 21. The first facets 21 generate a plurality of images of the intermediate focus on the second facets 23 assigned to them.

The first facets 21 are each imaged onto the reticle 7 by an assigned second facet 23, superimposed on one another, in order to illuminate the object field 5. The illumination of the object field 5 is in particular as homogeneous as possible. It preferably has a uniformity error of less than 2%. Field uniformity can be achieved by overlaying different lighting channels.

By arranging the second facets 23, the illumination of the entrance pupil of the projection optics 10 can be geometrically defined. By selecting the illumination channels, in particular the subset of the second facets 23 that guide light, the intensity distribution in the entrance pupil of the projection optics 10 can be adjusted. This intensity distribution is also referred to as the lighting setting or lighting pupil filling.

A likewise preferred pupil uniformity in the area of defined illuminated sections of an illumination pupil of the illumination optics 4 can be achieved by redistributing the illumination channels.

Further aspects and details of the illumination of the object field 5 and in particular the entrance pupil of the projection optics 10 are described below.

The projection optics 10 can in particular have a homocentric entrance pupil. This can be accessible. It can also be inaccessible.

The entrance pupil of the projection optics 10 cannot regularly be illuminated precisely with the second facet mirror 22. When imaging the projection optics 10, which images the center of the second facet mirror 22 telecentrically onto the wafer 13, the aperture rays often do not intersect at a single point. However, an area can be found in which the pairwise distance of the aperture beams becomes minimal. This surface represents the entrance pupil or a surface conjugate to it in local space. In particular, this surface shows a finite curvature.

It may be that the projection optics have 10 different positions of the entrance pupil for the tangential and sagittal beam paths. In this case, an imaging element, in particular an optical component of the transmission optics, should be provided between the second facet mirror 22 and the reticle 7. With the help of this optical element the under different positions of the tangential entrance pupil and the sagittal entrance pupil must be taken into account.

At the in the 1 As shown in the arrangement of the components of the illumination optics 4, the second facet mirror 22 is arranged in a surface conjugate to the entrance pupil of the projection optics 10. The first facet mirror 20 is tilted relative to the object plane 6. The first facet mirror 20 is arranged tilted to an arrangement plane that is defined by the deflection mirror 19. The first facet mirror 20 is arranged tilted to an arrangement plane that is defined by the second facet mirror 22.

When producing optical elements in 1 In the projection exposure system 1 (lithography system) shown, the reflectivity of these optical elements is measured using a reflectometer device 24, as shown, for example, in 2 is shown, measured. Such a reflectometer device 24 can also be used when the lithography system 1 is in operation. The reflectometer device 24 is used to measure a sample 25 of the lithography system 1. The sample 25 is, for example, one of the optical elements in FIG 1 projection exposure system 1 (lithography system) shown, such as the collector 17 or one of the mirrors 19, 20, 22 and M1-M6.

The sample 25 is in particular using a measuring radiation 26 ( 2 ) measured. The measurement radiation 26 is, for example, EUV radiation. The measuring radiation 26 has, for example, a wavelength range of 10 - 20 nm or 12.4 to 16 nm. The reflectometer device 24 is, for example, an EUV reflectometer device.

As in the first embodiment in 2 shown, the reflectometer device 24 includes an optical reference element 27 in a beam path 28 of the measuring radiation 26. The optical reference element 27 has a beam splitter layer 29. The beam splitter layer 29 serves to reflect a portion 30 (partial beam 30) of the measuring radiation 26 onto the sample 25 and to transmit a further portion 31 (further partial beam 31) of the measuring radiation 26 through the beam splitter layer 29. An angle of incidence of the measuring radiation 26 when incident on the optical reference element 27 or on the beam splitter layer 29 is marked with the reference symbol α.

The optical reference element 27 also has a detector layer 32 for detecting the transmitted portion 31 of the measuring radiation 26.

The measuring radiation 30 reflected by the beam splitter layer 29 is radiated onto the sample 25 in order to examine the reflectivity of the sample 25 using a measuring radiation 33 reflected by the sample 25.

As in 2 shown, the reflectometer device 24 can, for example, also have a light source 34 for emitting the measuring radiation 26. The light source 34 is, for example, an EUV light source. The light source 34 is, for example, a (e.g. broadband) EUV light source, which produces measurement radiation in a spectral range of 2 nm to 120 nm, 5 nm to 40 nm, 10 nm to 20 nm, 12.4 nm to 16 nm and/or emits with a wavelength of 13.5 nm. The light source 34 is, for example, a laser plasma source with a gold target. The light source can, for example, continuously emit radiation or can, for example, emit pulsed radiation. A pulsed radiation is, for example, pulsed at 100 kHz, 40 Hz, 20 Hz, or at 10 Hz. The light source 34 can also be another type of light source.

In particular, for example, the light source 34 itself can be set up to emit light with wavelengths in the above-mentioned spectral ranges. Alternatively, a monochromator can be arranged in the beam path of the radiation emitted by the light source, which selects a wavelength range and/or a wavelength from a broadband light source. The monochromator can be set up, for example, to select the above-mentioned spectral ranges. A size of the spectral range transmitted by the monochromator can, for example, be one thousandth of a size of the wavelength range emitted by the light source (the monochromacy is 1000 in this case). The monochromacy can also be 750, 300, or 100, for example. Because a wavelength and/or a wavelength range of the radiation 26 incident on the beam splitter layer 29 can be adjusted, it is possible to measure the reflection of the beam splitter layer 29 as a function of the wavelength (i.e. as a reflection spectrum).

The reflectometer device 24 can, for example, also include a holder 35 for holding and/or moving the sample 25, as shown schematically in 2 illustrated. With the holder 35, the sample 25 can be arranged in the measuring beam path of the measuring radiation 30 reflected by the optical reference element 27. Although in 2 not shown, the holder 35 can, for example, also have one or more actuators, a robotic unit, a robotic arm, a goniometer, a motor and/or a control unit. This allows the sample 25 to be moved and, for example, positioned in different orientations relative to the measuring beam path 30.

To detect the measuring radiation 33 reflected by the sample 25, the reflectometer device 24 can also include, for example, a detector device 36, as in 2 shown.

By using the beam splitter layer 29, part of the measurement radiation 26 incident on the optical reference element 27 is reflected (reflected measurement radiation 30) and used to irradiate the sample 25. In addition, by using the beam splitter layer 29, a further portion of the measurement radiation 26 incident on the optical reference element 27 is transmitted (transmitted measurement radiation 31) and used for a reference measurement. Through the reference measurement based on the transmitted measurement radiation 31, information from the measurement radiation 26, such as an intensity of the measurement radiation 26, can be recorded and taken into account when evaluating the measurement radiation 33 reflected by the sample 25. This allows, for example, the intensity of the measuring radiation 26 to be taken into account when measuring the reflectivity of the sample 25. For example, the intensity of the measuring radiation 26 can be detected at the same time as detecting the measuring radiation 33 reflected by the sample 25.

In 3 is the optical reference element 27 2 shown enlarged. The beam splitter layer 29 of the optical reference element 27 is set up in particular for physical beam splitting of the measurement radiation 26. The beam splitter layer 29 in particular comprises a partially transparent and/or semi-transparent material 37 ( 3 ) and a reflective surface 38. The beam splitter layer 29 can have one or more individual layers. In order to be partially transparent to EUV radiation, a thickness D of the beam splitter layer 29 is, for example, only a few nanometers thick.

The beam splitter layer 29 is advantageously arranged on a carrier substrate 39 of the optical reference element 27, which supports the beam splitter layer 29 and protects it from deformation.

The carrier substrate 39 has a front surface 40 and a rear surface 41 with respect to the incident measuring radiation 26 ( 3 ). The front surface 40 faces the incident measuring radiation 26, while the rear surface 41 faces the front surface 40 and faces away from the incident measuring radiation 26.

The detector layer 32 is arranged in particular in front of the front surface 40 of the carrier substrate 39 with respect to the incident measuring radiation 26. The detector layer 32 can, for example, be arranged directly on the front surface 40 of the carrier substrate 39. In other embodiments ( 4 ), however, one or more further layers can also be arranged between the carrier substrate 39 and the detector layer 32.

The detector layer 32 has a front surface 42 with respect to the incident measuring radiation 26. Furthermore, the beam splitter layer 29 is arranged in front of the front surface 42 of the detector layer 32 with respect to the incident measuring radiation 26. The beam splitter layer 29 may, for example, be arranged and attached directly to the front surface 42 of the detector layer 32.

One in 2 shown embodiment of a measuring arrangement 43 for the lithography system 1 1 comprises the sample 25, which is, for example, one of the optical elements of the lithography system 1, and the reflectometer device 24 for measuring the sample 25.

For example, in a first configuration, the beam splitter layer 29 is a ruthenium layer with a thickness D of 1 nm, the detector layer 32 is a Si diode layer and the angle of incidence α is 85°. Such a configuration allows radiation losses to be kept low. However, with such a configuration there is a hard cut-off at just under 14 nm, so that for measurements above this wavelength, e.g. B. retractable, additional beam splitter may be required.

In another example (second configuration), an angle of incidence α of 80° is selected for a ruthenium layer with a thickness D of 1 nm as the beam splitter layer 29 and a Si diode layer as the detector layer 32. This configuration has the advantage that the cut-off shifts to around 17 nm.

In the above configuration examples (first and second configurations), the reflection can be enhanced by increasing the thickness D of the ruthenium layer (beam splitter layer 29), but this also increases the absorption losses in the layer. These can neither be measured as a reference signal nor does the lost intensity reach the sample in order to then be measured.

In a third configuration, the beam splitter layer 29 has a layer structure of two silicon layers and two molybdenum layers arranged alternately so that a first molybdenum layer is arranged on the detector layer 32. The silicon and molybdenum individual layers each have a thickness of 2 nm, so that the total thickness of the beam splitter layer 29 is 8 nm. The detector layer 32 is also in this Configuration of a Si diode layer and the angle of incidence α is 80°. The advantages of this configuration are that the cut-off also only occurs at 17 nm and a splitting ratio of the beam splitter layer 29 is closer to 1 compared to the second configuration. However, more radiation losses occur here due to absorption.

In a fourth configuration, the beam splitter layer 29 is a molybdenum layer with a thickness D of 1 nm, the detector layer 32 is a Ge diode layer and the angle of incidence α is 82°. Advantageously, in this configuration there is no cut-off wavelength and there is a relatively uniform distribution of the division ratio over the wavelength. However, there are more absorption losses compared to the second configuration.

In 4 a second embodiment of an optical reference element 44 of a reflectometer device 45 is shown. The following essentially describes differences from the first embodiment of the optical reference element 27 ( 2 and 3 ).

Similar to the reflectometer device 24 according to the first embodiment ( 2 and 3 ), the optical reference element 44 of the reflectometer device 45 according to the second embodiment ( 4 ) also has a carrier substrate 46, a beam splitter layer 47 and a detector layer 48. An incident measuring radiation 26' (similar to the measuring radiation 26 in 2 and 3 ) is partially directed by the beam splitter layer 47 towards the sample 25 ( 2 ) reflected (reflected measurement radiation 30' in 4 ) and partially transmitted to the detector layer 48 (transmitted measurement radiation 31 ').

The detector layer 48 of the optical reference element 44 of the reflectometer device 45 according to the second embodiment has a semiconductor photodiode 49. The semiconductor photodiode 49 includes a P-doped semiconductor layer 50 (short: P layer 50) and an N-doped semiconductor layer 51 (short: N layer 51). The P layer 50 includes a semiconductor base material such as silicon or germanium. In the semiconductor base material of the P layer 50, foreign atoms, such as boron, indium, aluminum or gallium, are introduced as acceptors, which provide freely movable positive charge carriers (i.e. gaps, holes or holes). The N layer 51 comprises a semiconductor base material such as silicon or germanium. In the semiconductor base material of the N layer 51, foreign atoms, such as phosphorus, arsenic or antimony, are introduced as donors, which provide freely movable negative charge carriers (i.e. electrons).

In the in 4 In the example shown, the N layer 51 is arranged in front of the P layer 50 with respect to the incident measuring radiation 26 '(ie in the orientation of 4 the N layer 51 is arranged above the P layer 50). In other examples, however, the P layer 50 can also be arranged in front of the N layer 51 with respect to the incident measuring radiation 26 '(ie in the orientation of 4 In this case, the P layer 50 is arranged above the N layer 51).

In the transition 52 (PN junction 52) between the P layer 50 and the N layer 51, electrons diffuse from the N layer 51 into the P layer 50 and recombine there with holes in the P layer 50. In addition, defect electrons (holes) in the P layer 50 diffuse into the N layer 51 and recombine there with electrons in the N layer 51. This creates an electric field E at the PN junction 52 in the area of a so-called space charge zone 53, that of the diffusion movement which counteracts electrons and holes. In addition, an area is formed that is depleted of free charge carriers, the so-called depletion zone 54. The space charge zone 53 or depletion zone 54 represents a so-called barrier layer 55 of the semiconductor photodiode 49 (in 4 drawn with a dashed line).

The optical reference element 44 further comprises a first and second electrically conductive contact element 56, 57. The first electrically conductive contact element 56 is in electrically conductive contact with the P layer 50, for example. The second electrically conductive contact element 57 is in electrically conductive contact with the N layer 51, for example. In the case in which the P and N layers 50, 51 are arranged the other way around with respect to the incident measuring radiation 26 ', the first electrically conductive contact element 56 can also be connected to the N layer 51 and the second electrically conductive contact element 57 can also be arranged the P layer 50 be in electrically conductive contact. A material of the first and/or second electrically conductive contact element 56, 57 includes, for example, molybdenum, nickel and/or aluminum.

The detector layer 48 can, for example, also be designed as an optical position sensor (“Position Sensitive Device/Detector/Diode”, PSD). An optical position sensor is set up in particular to measure the (e.g. one- or two-dimensional) position and intensity of the incident radiation 26. An optical position sensor includes in particular a PiN diode.

In the example of 4 the first electrically conductive contact element 56 is designed as a layer 58, which is on a front surface 59 of the carrier substrate 46 and in direct physical is arranged in contact with the front surface 59. In other examples, the first electrically conductive contact element 56 can also be designed differently or arranged differently than in 4 shown.

Furthermore, in the example of 4 the second electrically conductive contact element 57 in the orientation of 4 arranged next to the beam splitter layer 47. In particular, the front surface 60 of the detector layer 48 has a first region 61 in which the beam splitter layer 47 is arranged. In addition, the front surface 60 of the detector layer 48 has a second region 62 in which the second electrically conductive contact element 57 is arranged. In this case, in which the second electrically conductive contact element 57 is arranged only in the edge region 62 of the front surface 60 of the detector layer 48, it is advantageous if the N layer 51 has a high concentration of foreign atoms as donors.

Different from that in 4 However, in the example shown, the beam splitter layer 47 itself can form the second electrically conductive contact element, so that no separate second electrically conductive contact element such as the contact element 57 is necessary. In this case, the beam splitter layer 47 may be formed over the entire surface 60 of the detector layer 48 including the regions 61 and 62.

The first and second electrically conductive contact elements 56, 57 are electrically connected to one another via a circuit 63. In particular, a measuring device 64 is arranged in the circuit 63. The measuring device 64 is, for example, an ammeter. In other examples, the measuring device 64 can also be a voltage measuring device.

The optical reference element 44 can also include a voltage source 65, for example. The voltage source 65 is arranged in particular in the circuit 63 in electrical contact with the first and second electrically conductive contact elements 56, 57. Using the voltage source 65, an external voltage in the reverse direction can be applied to the detector layer 48 or the semiconductor photodiode 49. Applying an external voltage in the reverse direction means that the negative pole of the voltage source 65 is electrically connected to the P layer 50 and the positive pole of the voltage source 65 is electrically connected to the N layer 51. The applied external voltage increases the electric field E of the barrier layer 55 and only a very small current (blocking current) flows in the circuit 63 and through the measuring device 64. In particular, the applied external voltage increases the depletion zone and makes the detector layer 48 more sensitive .

The measuring radiation 26′ incident on the optical reference element 44 is partially transmitted through the beam splitter layer 47 and the transmitted measuring radiation 31′ is absorbed in the barrier layer 55 of the detector layer 48. The internal photoelectric effect creates 55 electron-hole pairs in the barrier layer. The electric field E prevailing in the barrier layer 55 separates the electron-hole pairs and can be detected as a flowing charge in the measuring device 64 of the circuit 63 via the first and second contact elements 56, 57.

In 5 a third embodiment of an optical reference element 66 of a reflectometer device 67 is shown. Essential differences to the second embodiment of the optical reference element 44 ( 4 ).

The optical reference element 66 of the reflectometer device 67 according to the third embodiment ( 5 ) has a carrier substrate 68 and a reflection layer 69. An incident measuring radiation 26" (similar to the measuring radiation 26 in 2 and 3 ) is (partially) directed by the reflection layer 69 towards the sample 25 ( 2 ) reflected (reflected measurement radiation 30" in 5 ) and partially absorbed in the reflection layer 69 (absorbed measurement radiation 70).

The absorbed measuring radiation 70 causes secondary electrons 71 to be released from the reflection layer 69. For example, electrons 71 can be released from the reflection layer 69 (e.g. by an external photo effect) by the incident radiation 26". By releasing the secondary electrons 71, the optical reference element 66 becomes electrically positively charged. The electrical charge of the optical Reference element 66 can be detected, for example, by mounting the optical reference element 66 in an electrically insulated manner (not shown) and measuring a quantity of current required for electrically neutralizing the optical reference element 66. For this purpose, the reflectometer device 67 in particular has a circuit 72, a current source 73 and a Current measuring device 74. The current measuring device 74 and / or the circuit 72, the current source 73 and the current measuring device 74 in particular form a secondary electron detector. Since the amounts of current required to electrically neutralize the optical reference element 66 are very small, the current measuring device 74 is designed in particular to measure current with an accuracy in the femtoampere range rich to measure. Instead of the in 5 In the circuit shown, alternative circuits are also possible, in which the reference element 66 z. B. is connected to ground potential via a measuring device without a voltage source.

Alternatively, the reflectometer device 67 can also have a separate secondary electron detector 74 ' (dashed line in 5 ), which is arranged in front of the optical reference element 66 with respect to the incident measuring radiation 26".

The reflectometer device 67 can optionally, for example, also have a device 75 for collecting the detached secondary electrons 71 opposite the optical reference element 66. At the facility 75, the in 5 is only indicated schematically, it can be, for example, a plate of a plate capacitor, which is electrically positively charged to electrically attract the secondary electrons 71. Instead of the in 5 In the circuit shown, the device 75 can also be connected to a ground potential via a measuring device without a voltage source.

In 6 a fourth embodiment of an optical reference element 76 of a reflectometer device 77 is shown. Essential differences to the second embodiment of the optical reference element 44 ( 4 ).

Similar to the reflectometer device 45 according to the second embodiment ( 4 ), the optical reference element 76 of the reflectometer device 77 according to the fourth embodiment ( 6 ) also has a carrier substrate 78, a beam splitter layer 79 and a detector layer 80. Deviating from the second embodiment, the detector layer 80 of the optical reference element 76 according to the fourth embodiment has a fluorescent layer 81.

An incident measuring radiation 26''' (similar to the measuring radiation 26 in 2 and 3 ) is partially directed by the beam splitter layer 79 towards the sample 25 ( 2 ) reflected (reflected measurement radiation 30''' in 6 ) and partially transmitted to the detector layer 80 (transmitted measurement radiation 31'''). The transmitted measurement radiation 31''' excites fluorescence in the fluorescence layer 81 and is converted into fluorescence radiation 82.

The reflectometer device 77 according to the fourth embodiment has a fluorescent radiation detector 83 for detecting the fluorescent radiation 82. The fluorescent radiation detector 83 is in particular set up to detect radiation in a wavelength range of the fluorescent radiation 82. The wavelength range of the fluorescence radiation 82 can be different from a wavelength range of the measurement radiation 26''', 31'''.

In the in 6 In the example shown, the fluorescence radiation detector unit 83 is designed as a layer arranged on the carrier substrate 78. For example, the fluorescent radiation detector unit 83 formed as a layer has a semiconductor photodiode (similar to the semiconductor photodiode 49 in 4 ) and the fluorescence radiation 82 is detected via the formation of electron-hole pairs in the semiconductor photodiode of the fluorescence radiation detector unit 83.

In other examples, however, a fluorescence radiation detector unit can also be designed as a separate detector unit 83 'instead of as a layer of the optical reference element 76. Such a separate detector unit 83 'is a component separate from the optical reference element 76, which is arranged in front of the optical reference element 76 with respect to the measuring radiation 26''' incident on the optical reference element 76. In 6 Such a separate detector unit 83 ', which would replace the layer 83, is shown in dashed lines.

The fluorescent layer 81 excites the incident measurement radiation 31''', for example to emit the fluorescence radiation 82 in a wavelength range different from a wavelength range of the incident measurement radiation 31'''. For example, a measurement radiation 31''' in the EUV range is converted into a fluorescent radiation 82 in the longer-wave UV range or in the visible wavelength range.

The following is with reference to 7 a method for producing an optical reference element 27, 44, 76 of a reflectometer device 24, 45, 77 for measuring a sample 25 of a lithography system 1 is described.

In a first step S1 of the manufacturing process, a detector layer 32, 48, 80 is applied to a carrier substrate 39, 46, 78.

Optionally, the detector layer 32, 48, 80 can then be overpolished in order to achieve better optical quality.

In a second step S2 of the manufacturing process, a beam splitter layer 29, 47, 79 is applied to the detector layer 32, 48, 80.

In embodiments, the manufacturing method may include a step before step S1 bringing a first electrically conductive contact layer 56 on the carrier substrate 39, 46, 78. In this case, the detector layer 32, 48, 80 is applied to the first contact layer 56 in step S1.

In embodiments, the manufacturing method can further comprise a step of applying a second contact element 57 and/or a second contact layer 57 on the detector layer 32, 48, 80 after step S2.

In embodiments, in the manufacturing method, step S2 can be carried out before step S1, so that a beam splitter layer 29, 47, 79 is first applied to the detector layer 32, 48, 80. In step S1 carried out after step S2, the detector layer 32, 48, 80 with the beam splitter layer 29, 47, 79 is then applied to a carrier substrate 39, 46, 78 (for example a plane ellipsoid).

The following is with reference to 8th a method for measuring a sample 25 of a lithography system 1 using a reflectometer device 24, 45, 77 is described.

In a first step S 1 'of the measurement method, a measuring radiation 26, 26', 26''' is irradiated onto a beam splitter layer 29, 47, 79 of an optical reference element 27, 44, 76 of the reflectometer device 24, 45, 77.

In a second step S2' of the measurement method, a portion 30, 30', 30''' of the measurement radiation 26, 26', 26''' is reflected onto the sample 25 by means of the beam splitter layer 29, 47, 79.

In a third step S3' of the measurement method, a further portion 31, 31', 31''' of the measuring radiation 26, 26', 26''' is passed through the beam splitter layer 29, 47, 79 to a detector layer 32, 48, 80 of the optical reference element 27, 44, 76 is transmitted.

In a fourth step S4' of the measurement method, the transmitted portion 31, 31', 31''' of the measurement radiation 26, 26', 26''' is detected by means of the detector layer 32, 48, 80.

For example, before step S4', the method has a calibration step to determine a splitting ratio of the beam splitter layer 29, 47, 79. By determining the division ratio of the beam splitter layer 29, 47, 79, a reflection value for the sample 25 can be determined from the ratio of the measured reflected radiation and the measured transmitted radiation.

9 shows a reflectometer device 124 according to a fifth embodiment. In contrast to the reflectometer devices 24, 45, 77 in the 2 until 4 and 6 , the reflectometer device 124 does not have a beam splitter layer.

Furthermore, a detector layer 132 of the reflectometer device 124 is set up to detect absorbed radiation 131 instead of detecting radiation transmitted through a beam splitter layer.

The reflectometer device 124 in 9 also serves to measure a sample 25 ( 2 ) of a lithography system 1 ( 1 ) using a measuring radiation 126. For this purpose, the reflectometer device 124 includes an optical reference element 127 in a beam path of the measuring radiation 126. The optical reference element 127 has a reflection layer 129 for reflecting a portion 130 of the measuring radiation 126 onto the sample 25. Since it is the If layer 129 is a reflection layer but not a beam splitter layer, a proportion of transmitted radiation is zero. This means that the incident radiation 126 can be used almost entirely to measure the sample 25. The reflection layer 129 is set up to absorb a further portion 131 of the measurement radiation 126, which is in particular a very small portion. In 9 is an absorption of a part 131 of the measuring radiation 126, which is z. B. in a temperature change of the reflection layer 129, only indicated schematically and provided with the reference number 131. The optical reference element 127 also has a detector layer 132 for detecting the absorbed portion 131 of the measuring radiation 126. The detector layer 132 is set up, for example, to detect a temperature change of the reflection layer 129, the detector layer 132 and/or a carrier substrate 139 of the optical reference element 127.

The detector layer 132 includes, for example, a pyroelectric material 137 such as sodium nitrite. The detector layer 132 is in particular designed to detect the absorbed portion 131 of the measurement radiation 126 by detecting a temperature change of the reflection layer 129, the detector layer 132 and/or the carrier substrate 139.

The reflection layer 129 includes e.g. B. Copper. A thickness of the reflection layer 129 is, for example, a few nanometers to several tens of nanometers (e.g. 40 nm). A thickness of the detector layer 132 is, for example, a few micrometers to several tens of micrometers (e.g. 40 μm). A A Fall angle of the incident radiation 126 is z. B. 80° or 85°.

The reflection layer 129 has a reflective surface 138. The reflection layer 129 is advantageously arranged on a carrier substrate 139 of the optical reference element 127, which supports the reflection layer 129 and protects it from deformation.

The carrier substrate 139 has a front surface 140 and a rear surface 141 with respect to the incident measuring radiation 126. The front surface 140 faces the incident measuring radiation 126, while the rear surface 141 faces the front surface 240 and faces away from the incident measuring radiation 126.

The detector layer 132 is arranged in particular in front of the front surface 140 of the carrier substrate 139 with respect to the incident measuring radiation 126. The detector layer 132 can, for example, be arranged directly on the front surface 140 of the carrier substrate 139. In other embodiments, however, one or more further layers can also be arranged between the carrier substrate 139 and the detector layer 132.

The detector layer 132 has a front surface 142 with respect to the incident measuring radiation 126. Furthermore, the reflection layer 129 is arranged in front of the front surface 142 of the detector layer 132 with respect to the incident measuring radiation 126. The reflection layer 129 can, for example, be arranged and attached directly to the front surface 142 of the detector layer 132.

Although in 9 not shown, a gold passivation layer can be arranged above the reflection layer 129, ie on the reflecting surface 138. An advantage of a gold passivation layer is that the reflection layer 129 is protected from contact with oxygen, the reflection is more stable over time and the reflection or the ratio of reflection and absorption remains in an even narrower range over the desired wavelength range.

The reflectometer devices 24, 45, 67, 77, 124 described above, the manufacturing process and the measurement process can also be used, for example, for a DUV lithography system.

Although the present invention has been described using exemplary embodiments, it can be modified in many ways.

REFERENCE SYMBOL LIST

1

Projection exposure system

2

Lighting system

3

light source

4

Illumination optics

5

Object field

6

Object level

7

Reticule

8th

Reticle holder

9

Reticle displacement drive

10

Projection optics

11

Image field

12

Image plane

13

wafers

14

wafer holder

15

Wafer displacement drive

16

Illumination radiation

17

collector

18

Intermediate focal plane

19

Deflecting mirror

20

first facet mirror

21

first facet

22

second facet mirror

23

second facet

24

Reflectometer device

25

sample

26, 26', 26'', 26''

Measuring radiation

27

optical reference element

28

beam path

29

Beam splitter layer

30, 30', 30'', 30'''

Share (reflected measurement radiation)

31, 31', 31'''

Share (transmitted measurement radiation)

32

detector layer

33

reflected measurement radiation

34

light source

35

bracket

36

Detector device

37

material

38

surface

39

Carrier substrate

40

surface

41

surface

42

surface

43

Measuring arrangement

44

optical reference element

45

Reflectometer device

46

Carrier substrate

47

Beam splitter layer

48

detector layer

49

semiconductor photodiode

50

P-doped semiconductor layer

51

N-doped semiconductor layer

52

PN junction

53

Space charge zone

54

Depletion zone

55

barrier layer

56

Contact element

57

Contact element

58

layer

59

surface

60

surface

61

Area

62

Area

63

circuit

64

measuring device

65

voltage source

66

optical reference element

67

Reflectometer device

68

Carrier substrate

69

Beam splitter layer

70

Proportion (absorbed measurement radiation)

71

secondary electron

72

circuit

73

power source

74.74'

Current measuring device

75

Furnishings

76

optical reference element

77

Reflectometer device

78

Carrier substrate

79

Beam splitter layer

80

detector layer

81

Fluorescent layer

82

Fluorescent radiation

83.83'

Detector unit

124

Reflectometer device

126

Measuring radiation

127

optical reference element

129

Beam splitter layer

130

Share (reflected measurement radiation)

131

Proportion (absorbed measurement radiation)

132

detector layer

137

material

138

surface

139

Carrier substrate

140

surface

141

surface

142

surface

α

angle

D

thickness

E

electric field

M1

Mirror

M2

Mirror

M3

Mirror

M4

Mirror

M5

Mirror

M6

Mirror

S1-S2

Procedural steps

S1'-S4'

Procedural steps

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was 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 102008009600 A1 [0091, 0095]
• US 20060132747 A1 [0093]
• EP 1614008 B1 [0093]
• US 6573978 [0093]
• DE 102017220586 A1 [0098]
• US 20180074303 A1 [0112]

Claims (18)

Reflectometer device (24) for measuring a sample (25) of a lithography system (1) using a measuring radiation (26), having an optical reference element (27) in a beam path (28) of the measuring radiation (26), which has a beam splitter layer (29) for reflecting a portion (30) of the measuring radiation (26) onto the sample (25) and for transmitting a further portion (31) of the measuring radiation (26) and a detector layer (32) for detecting the transmitted portion (31) of the measuring radiation (26 ). Reflectometer device Claim 1 , wherein the beam splitter layer (29) has a partially transparent layer with a partially transparent material (37) and a reflective surface (38). Reflectometer device Claim 1 or 2 , wherein the optical reference element (27) comprises a carrier substrate (39), the carrier substrate (39) has a front surface (40) with respect to the incident measuring radiation (26), the detector layer (32) with respect to the incident measuring radiation (26 ) is arranged in front of the front surface (40) of the carrier substrate (39), and the beam splitter layer (29) is arranged in front of the detector layer (32) with respect to the incident measuring radiation (26). Reflectometer device according to one of the Claims 1 - 3 , further comprising a light source (34) for emitting the measuring radiation (26), a holder (35) for holding and / or moving the sample (25), and / or a detector device (36) for detecting one of the sample (25) reflected measurement radiation (33). Reflectometer device according to one of the Claims 1 - 4 , wherein the reflectometer device (24) is set up to measure a sample (25) of an EUV lithography system (1) using EUV radiation as measuring radiation (26), and / or the reflectometer device (24) has an EUV light source (34). Emitting the measuring radiation (26). Reflectometer device according to one of the Claims 1 - 5 , wherein the beam splitter layer (29) is set up to reflect and transmit EUV radiation (26), and / or a thickness (D) of the beam splitter layer (29) 1 µm or smaller, 100 nm or smaller, 50 nm or smaller, 10 nm or smaller, 5 nm or smaller, 1 nm or smaller and/or 0.1 nm or smaller. Reflectometer device according to one of the Claims 1 - 6 , wherein the detector layer (48) has a photodiode and / or a semiconductor photodiode (49). Reflectometer device Claim 7 , wherein the detector layer (48) comprises a P-doped layer (50), an N-doped layer (51) and a PN junction (52), the optical reference element (44) has a first and second electrically conductive contact element (56, 57), which are in electrical contact with the P-doped layer (50) and the N-doped layer (51), the optical reference element (44) comprises a current and/or voltage measuring device (64), and the first and second contact elements (56, 57) are electrically connected to one another via the current and/or voltage measuring device (64). Reflectometer device Claim 8 , wherein one of the first and second contact elements (56, 57) is designed as a contact layer (58) which is arranged between a carrier substrate (46) of the optical reference element (44) and the detector layer (48), the other of which The first and second contact elements (56, 57) are arranged on a front surface (60) of the detector layer (48) with respect to the incident measuring radiation (26 '), and / or the beam splitter layer (47) is the other of the first and the second contact element (56, 57). Reflectometer device Claim 9 , wherein the front surface (60) of the detector layer (48) has a first region (61) in which the beam splitter layer (47) is arranged, and a second region (62) in which the other of the first and the second contact element (56, 57) is arranged. Reflectometer device according to one of the Claims 1 - 10 , wherein the detector layer (80) comprises a fluorescence layer (81) for exciting fluorescence through the transmitted portion (31''') of the measuring radiation (26''') and for emitting fluorescence radiation (82), and wherein the reflectometer device (77 ) and/or the detector layer (80) comprises a fluorescent radiation detector unit (83, 83') for detecting the fluorescent radiation (82). Reflectometer device (67) for measuring a sample (25) of a lithography system (1) using a measuring radiation (26''), having an optical reference element (66) in a beam path (28) of the measuring radiation (26''), which has a reflection Layer (69) for reflecting a portion (30'') of the measuring radiation (26'') onto the sample (25) and for absorbing a further portion (70) of the measuring radiation (26'') and a secondary electron detector (74, 74') for detecting the absorbed portion (70) of the measuring radiation (26''), the secondary electron detector (74 , 74') is set up to detect secondary electrons (71) emerging from the reflection layer (69) and/or a charge of the optical reference element (66) due to secondary electrons (71) emerging from the reflection layer (69). Measuring arrangement (43) for a lithography system (1) with an optical element (17, 19, 20, 22, M1, M2, M3, M4, M5, M6) for the lithography system (1) as a sample (25) and a reflectometer device (24, 45, 67, 77, 124) according to one of the Claims 1 - 12 , 17 or 18 for measuring the sample (25). Lithography system (1) with a measuring arrangement (43). Claim 13 . Method for producing an optical reference element (27, 44, 76) of a reflectometer device (24, 45, 77) for measuring a sample (25) of a lithography system (1), with the steps: a1) applying (S1) a detector layer (32, 48, 80) to a carrier substrate (39, 46, 78), and b1) Application (S2) of a beam splitter layer (29, 47, 79) on the detector layer (32, 48, 80). Method for measuring a sample (25) of a lithography system (1) using a reflectometer device (24, 45, 77), with the steps: a2) irradiating (S1') a measuring radiation (26, 26', 26''') onto a beam splitter layer (29, 47, 79) of an optical reference element (27, 44, 76) of the reflectometer device (24, 45, 77 ), b2) reflecting (S2') a portion (30, 30', 30''') of the measuring radiation (26, 26', 26''') onto the sample (25) by means of the beam splitter layer (29, 47, 79). ), c2) transmitting (S3') a further portion (31, 31', 31''') of the measuring radiation (26, 26', 26''') through the beam splitter layer (29, 47, 79) to a detector layer (32, 48, 80) of the optical reference element (27, 44, 76), and d2) Detecting (S4') the transmitted portion (31, 31', 31''') of the measuring radiation (26, 26', 26''') by means of the detector layer (32, 48, 80). Reflectometer device (124) for measuring a sample (25) of a lithography system (1) using a measuring radiation (126), having an optical reference element (127) in a beam path of the measuring radiation (126), which has a reflection layer (129) for reflecting a Portion (130) of the measuring radiation (126) on the sample (25) and for absorbing a further portion (131) of the measuring radiation (126) and a detector layer (132) for detecting the absorbed portion (131) of the measuring radiation (126). Reflectometer device (124). Claim 17 , wherein the detector layer (132) for detecting the absorbed portion (131) of the measuring radiation (126) has a pyroelectric material, and / or the detector layer (132) is set up to detect the absorbed portion (131) of the measuring radiation (126), to detect a temperature change of the reflection layer (129) and/or the detector layer (132).

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