KR20230165243A - Mirrors, laser beam systems, EUV radiation sources and lithographic devices for performing metrology in laser beam systems - Google Patents

Abstract

A mirror for performing metrology of a laser beam system in an EUV light source is described, the mirror comprising: a mirror layer having a front surface configured to receive and reflect a laser beam of the laser beam system; - a metrology layer arranged on the rear surface of the mirror layer, the metrology layer comprising a resistance grid comprising a plurality of conductive segments and a plurality of electrical contacts configured to be connected to a metrology instrument.

Description

Mirrors, laser beam systems, EUV radiation sources and lithographic devices for performing metrology in laser beam systems

Cross-reference to related applications

This application claims priority from EP Application No. 21167393.4, filed April 8, 2021, and EP Application No. 21169691.9, filed April 21, 2021, which are hereby incorporated by reference in their entirety.

The present invention relates to a mirror for performing metrology as can be used in a laser beam system for an EUV radiation source. In particular, the mirror can be applied to determine or estimate the power distribution of the laser beam received by the mirror.

A lithographic apparatus is a machine configured to apply a desired pattern onto a substrate. Lithographic devices can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern in a patterning device (eg, a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate.

A lithographic apparatus may use electromagnetic radiation to project a pattern onto a substrate. The wavelength of this radiation determines the minimum size of a feature that can be formed on the substrate. Lithographic devices using extreme ultraviolet (EUV) radiation in the range of 4 to 20 nm, for example with a wavelength of 6.7 nm or 13.5 nm, have a smaller It can be used to form features on a substrate.

In order to generate the required EUV radiation for patterning the substrate, an EUV radiation source is often applied. Such EUV radiation sources may comprise, for example, a laser beam system, for example a system comprising a CO ₂ laser arranged to deposit energy via the laser beam in a fuel such as tin (Sn). To ensure effective conversion of stored energy into EUV radiation, accurate knowledge of laser beam parameters such as power, power distribution, and position may be desirable. Known solutions for determining these parameters may adversely affect the power or power distribution of the laser beam.

The object of the present invention is to provide an improved way to determine laser beam parameters in order to better quantify the laser beam of a laser beam system, such as a laser beam system for use in EUV radiation sources.

Accordingly, according to a first aspect of the invention, there is provided a mirror for performing metrology of a laser beam system within an EUV light source, the mirror comprising:

a mirror layer having a front surface configured to receive and reflect a laser beam of the laser beam system;

a metrology layer arranged on the rear surface of the mirror layer, wherein the metrology layer

- a resistive grid comprising a plurality of conductive segments and a plurality of electrical contacts, or

- comprising a resistive layer and a plurality of electrical contacts,

The plurality of electrical contacts of the resistive grid or resistive layer are thereby configured to be connected to a measuring instrument.

According to a second aspect of the present invention, a metrology system is provided, the metrology system comprising:

Mirror according to the invention; and

and a measurement system configured to determine the resistance value of one or more conductive segments of the resistance grid.

According to a third aspect of the invention, a laser beam system for an EUV radiation source is provided, the laser beam system comprising a laser beam source and at least one metrology system according to the invention.

According to a fourth aspect of the invention, an EUV radiation source is provided, the EUV radiation source comprising a laser beam system according to the invention.

According to a fifth aspect of the invention, a lithography system comprising an EUV radiation source and a lithography apparatus according to the invention is provided.

Embodiments of the invention will now be described by way of example only with reference to the accompanying schematic diagrams, in which:
Figure 1 shows a lithographic system comprising a lithographic apparatus and a radiation source according to the invention.
Figure 2 schematically shows a cross-sectional view of a first mirror for performing measurements, according to an embodiment of the present invention.
Figure 3 schematically shows a cross-sectional view of a second mirror for performing measurements, according to an embodiment of the present invention.
Figures 4a-4c schematically show top views of portions of a metrology layer as applied in an embodiment of the invention.
Figures 5a and 5b schematically show top views of a portion of a mirror for performing measurements, according to an embodiment of the invention.
6A, 6B and 7 schematically show a resistive grid as may be applied in embodiments of the present invention.
Figure 8 schematically shows a measurement system according to an embodiment of the present invention.
Figure 9 schematically shows a resistive grid as may be applied in embodiments of the present invention.
Figure 10 schematically shows a laser beam system according to an embodiment of the present invention.

Figure 1 shows a lithographic system comprising a radiation source (SO), eg an EUV radiation source according to the invention, and a lithographic apparatus (LA). The radiation source SO is configured to generate an EUV radiation beam B and to supply the EUV radiation beam B to the lithographic apparatus LA. The lithographic apparatus (LA) includes an illumination system (IL), a support structure (MT) configured to support a patterning device (MA) (e.g. a mask), a projection system (PS) and a substrate configured to support the substrate (W). Includes table (WT).

The illumination system IL is configured to condition the EUV radiation beam B before it is incident on the patterning device MA. In this regard, the lighting system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11 . The faceted field mirror device 10 and the faceted pupil mirror device 11 together provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may comprise other mirrors or devices in addition to or instead of the faceted field mirror device 10 and the faceted pupil mirror device 11 .

After being thus adjusted, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam (B') is produced. The projection system PS is configured to project the patterned EUV radiation beam B' onto the substrate W. For this purpose, the projection system PS comprises a plurality of mirrors 13, 14 configured to project the patterned EUV radiation beam B' onto the substrate W held by the substrate table WT. can do. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B', thus forming an image with smaller features than the corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although in Figure 1 the projection system PS is shown as having only two mirrors 13 and 14, the projection system PS may comprise a different number of mirrors (e.g. 6 or 8 mirrors). there is.

Substrate W may include a previously formed pattern. In this case, the lithographic apparatus LA aligns the image formed by the patterned EUV radiation beam B' with a pattern previously formed on the substrate W.

A small amount of gas (for example hydrogen) in a relative vacuum, i.e. at a pressure well below atmospheric pressure, may be provided to the radiation source SO, to the illumination system IL and/or to the projection system PS.

The radiation source SO shown in Figure 1 is of a type that may be referred to for example as a laser produced plasma (LPP) source. The laser system 1, which may for example comprise a CO ₂ laser, for example a laser system according to the invention, provides tin (Sn) via a laser beam 2, for example from a fuel emitter 3. ) are arranged to accumulate energy from fuels such as Although noted in the following description, any suitable fuel may be used. The fuel may, for example, be in liquid form and may also be, for example, a metal or alloy. The fuel emitter 3 may comprise a nozzle configured to direct tin, for example in the form of droplets, along a trajectory to the plasma formation area 4 . The laser beam 2 is incident on the tin in the plasma formation area 4. In an embodiment, the laser system 1 may comprise one or more mirrors for metrology according to the invention for the purpose of determining the properties of the laser beam 2. Deposition of laser energy into tin generates tin plasma 7 in plasma formation region 4. Radiation, including EUV radiation, is emitted from the plasma 7 during de-excitation and recombination of electrons and ions in the plasma.

EUV radiation from the plasma is collected and focused by the collector 5. The collector 5 comprises, for example, a near normal incidence radiation collector 5 (sometimes more generally referred to as a normal incidence radiation collector). The collector 5 may have a multilayer mirror structure arranged to reflect EUV radiation (eg EUV radiation with a desired wavelength such as 13.5 nm). The collector 5 may have an elliptical configuration with two foci. As discussed below, a first of the foci may be at the plasma formation region (4) and a second of the foci may be at the intermediate focus (6).

The laser system 1 can be spatially separated from the radiation source SO. In this case, the laser beam 2 is directed from the laser system 1, for example with the help of a beam delivery system (not shown) comprising suitable directing mirrors and/or beam expanders and/or other optics. You can proceed to the radiation source (SO). The laser system 1, radiation source SO, and beam delivery system may be considered together as a radiation system.

The radiation reflected by the collector 5 forms an EUV radiation beam B. The EUV radiation beam B is focused at an intermediate focus 6 to form an image at the intermediate focus 6 of the plasma present in the plasma formation region 4 . The image at the intermediate focus 6 serves as a virtual radiation source for the illumination system IL. The radiation source SO is arranged so that the intermediate focus 6 is located at or close to the opening 8 of the enclosure structure 9 of the radiation source SO.

1 shows the radiation source (SO) as a laser-generated plasma (LPP) source, but any suitable source, such as a discharge-generated plasma (DPP) source or a free electron laser (FEL), may be used to generate EUV radiation. there is.

Figure 2 schematically shows a cross-sectional view of a mirror 200 for performing measurement according to an embodiment of the present invention.

The mirror 200 can be applied, for example, to a laser beam system, for example a laser beam system of an EUV radiation source.

In the embodiment as shown, mirror 200 includes a mirror layer 210 having a front surface 210.1 and a back surface 210.2. According to the invention, the front surface 210.1 of the mirror layer 210 is configured to receive (arrow 250) and reflect (arrow 252) the laser beam of the laser beam system. Within the meaning of the invention, the front surface of the mirror layer is assumed to be the surface of the mirror that faces the laser beam during use. Expressed differently, the front surface of the mirror layer as applied to the mirror according to the invention is considered to be in the optical path of the laser beam during use. In contrast, the rear surface of the mirror layer of the mirror according to the invention refers to the surface that does not face the laser beam 250. The back surface 210.2 of the mirror layer 210 may also be considered the surface opposite the front surface 210.1 of the mirror layer 210. Mirror 200 further includes a metrology layer or metrology structure 220 arranged on the rear surface 210.2 of mirror layer 210. By arranging the metrology layer 220 on the rear surface 210.2 of the mirror layer 210, the metrology layer 220 will not affect the reflection of the laser beams 250, 252. In particular, adverse effects such as glint or reduced reflectivity are advantageously eliminated. According to the invention, the metrology layer 220 as applied to the mirror 200 according to the invention comprises a resistive grid 230, which comprises a plurality of conductive segments 230.1 and a plurality of electrical Includes contacts (230.2). According to the invention, electrical contact 230.2 is configured to be connected to a metrology instrument or measurement system. A location where two or more conductive segments 230.1 are connected may be referred to as a node 230.3. Note that electrical contact 230.2 may also be referred to as a node of resistive grid 230.

In an embodiment of the invention, which will be described in more detail below, the resistive grid 230 of the mirror 200 according to the present invention is configured such that the resistance value of the conductive segment 230.2 of the resistive grid 230 during use of the mirror 200 is And it can be connected to a measurement device configured to determine the temperature distribution of the resistance grid 230 based on the resistance value. Based on the temperature distribution, operating parameters of the received laser beam 250 can be derived. These operating parameters may include, for example, the power of the received laser beam 250, the power distribution of the received laser beam 250, the position of the received laser beam 250, or a combination thereof.

Within the meaning of the present invention, a layer refers to a relatively thin structure or part of a structure; That is, the thickness of the layer, for example the thickness Tm of the mirror layer 210, is small compared to the dimension of the layer in the direction perpendicular to the thickness, for example in the indicated X-direction. Within the meaning of the present invention, a layer may also be referred to as a stratum or substrate. Additionally, in embodiments, the thickness Tm may be small compared to the laser beam of the laser beam system being measured. The thickness of the layer may be, for example, ˜100 μm or a few mm. The width W of the mirror 200 may be, for example, several cm, greater than 10 cm, or greater than 20 cm. Depending on the desired function of mirror 200, the front surface 210.1 of mirror layer 210, i.e., the surface facing laser beam 250 during use, may be a substantially flat surface or a curved surface. Surface 210.1 may have various shapes, for example rectangular or circular.

The layers of mirror 200 , such as mirror layer 210 and metrology layer 220 , may be manufactured as separate components and then assembled to implement mirror 200 . Mirror layer 210 may be, for example, a foil-like structure glued onto the top surface or front surface 220.1 of metrology layer 220. Alternatively, the layers can be fabricated sequentially, for example, starting from a base substrate and by various techniques such as etching, deposition, etc. Note that, in a similar manner as discussed above for metrology layer 210, front surface 220.1 of metrology layer 220 refers to the surface of metrology layer 220 that faces laser beam 250 during use. . However, it is understood that the laser beam 250 does not reach the metrology layer 220 but is substantially reflected by the mirror layer 210 .

In the embodiment as shown, electrical contact 230.2 is visible at the side surface of metrology layer 220. As will be appreciated, electrical contacts 230.2 may also be provided at other locations where the electrical contacts can be accessed to access a metrology instrument or metrology tool.

The resistive grid 230 as schematically shown in Figure 2, and in particular the conductive segments of the resistive grid, may be made of various materials and manufactured by various manufacturing techniques.

In embodiments, resistive grid 230 may be realized by printing the desired pattern onto the surface of the metrology layer. In this embodiment, ink containing conductive material may be printed onto the surface of the metrology layer. For example, ink containing Ag particles can be applied.

In embodiments, the grid may be realized by etching the desired pattern into the surface of the metrology layer, thereby forming a pattern of trenches into the surface. To realize a resistive grid, the trench can then be filled with a conductive material.

Examples of conductive materials that can be applied in the present invention to implement the resistive grid 230 of the metrology layer 220 of the mirror 200 according to the present invention include Ag, Au, Pt, Cu, Al, Fe, W, Ni , Mo, Sn, Zn. Another example of a material for realizing a resistive grid is a semiconductor material. In embodiments, the resistive grid may be made of a locally doped semiconductor structure. In embodiments, segments of the resistive grid may include NTC or PTC elements or materials. In a preferred embodiment, the material applied for the production of the conductive segments 230.1 of the electrical grid 230 has a high coefficient of thermal resistance α, for example greater than 0.035/°C. In an embodiment, the material as applied to fabricate the segments 230.1 of the resistive grid has a conductivity that is at least two orders of magnitude higher than the conductivity of the material of the metrology layer 220 itself. In an embodiment, metrology layer 220 may be made of Si or Ge, for example.

In an embodiment, resistive grid 230 is embedded in metrology layer 220 of mirror 200. To do this, metrology layer 220 may include a cover layer, also referred to as a capping layer applied onto resistance grid 230 . By doing this, contact between the resistance grid 230 and the mirror layer 210 can be prevented. In embodiments, the cover layer or capping layer is made of the same material as the metrology layer. A cover layer can be deposited onto the grid surface using deposition techniques such as ALD, vaporization, etc. In an embodiment, SiO ₂ may be used as a material for the cover layer. In an embodiment, metrology layer 220 may be fabricated from an SOI substrate, where the oxide forms a barrier and a resistive grid is formed on the semiconductor. Alternatively, germanium on an insulating substrate may be applied.

In an embodiment of the invention, mirror layer 210 includes multiple layers. Mirror layer 210 may include a stack of layers made of different materials, for example. As an example, mirror layer 210 may include a stack of alternating layers of first material and layers of second material. In an embodiment, the first or second material includes Ge and/or ZeSn.

In the embodiment as shown, the resistance grid 230 is arranged near the front surface 220.1 of the metrology layer 220. Alternatively, the resistive grid 230 may also be arranged closer to the bottom surface 220.2 of the metrology layer 220.

In the embodiment as shown, the width W of metrology layer 220 is shown to be equal to the width of mirror layer 210. It may be pointed out that this is not necessary. Metrology layer 220 may also be wider or narrower than mirror layer 210. The shape of the metrology layer 220, and in particular the shape of the front surface 220.1 of the metrology layer 220, need not have the shape of the bottom surface of the mirror layer 210.

In an embodiment of the invention, a metrology layer, such as metrology layer 220 shown in Figure 2, includes more than one resistive grid.

Figure 3 schematically shows this embodiment. Figure 3 schematically shows a mirror 300 for performing measurement according to the present invention. The mirror 300 for performing measurement includes a mirror layer 310 and a measurement layer 320, and the measurement layer 320 includes two resistive grids 332 and 334. In the embodiment as shown, the positive resistive grid is embedded in metrology layer 320. Each of the resistive grids 332 and 334 as shown includes, for example, a plurality of conductive segments 332.1, 334.1 and a plurality of conductive contacts 332.2, 334.2 connected to a metrology instrument. In embodiments, a mirror for performing metrology according to the present invention may include multiple metrology layers, whereby each metrology layer includes a resistive grid or resistive layer. In these embodiments, each resistance grid may be embedded in a different metrology layer or substrate, stratum, or disk. In this case, if one of the resistance grids is defective, it can be replaced by replacing the measurement layer containing it.

It may be noted that the layout of resistance grids 332, 334 may be different. Examples of the layout of these grids are given below.

In the embodiment as shown, the mirror 300 for performing metrology has a cooling layer or cooling structure 340 configured to cool the mirror layer 310 that receives and reflects the laser beams 350, 352 during use. Includes more. In this connection, it may be noted that the mirror according to the invention, in particular the mirror layer of the mirror according to the invention, may heat up during operation. To explain this, the application of a mirror in a 30 kW laser system can be considered. Even though the mirror for performing measurements as applied to the optical path of a laser system has a reflectivity of 99%, approximately 300 W will still be dissipated by the mirror. If proper cooling measures are not taken, this can lead to unwanted or unacceptable heating of the mirror.

The cooling layer or cooling structure 340 as applied in embodiments according to the present invention may be made of, for example, a material with good thermal conductivity, for example Cu or Al, and may also have a plurality of cooling channels 340.1. and a cooling fluid, for example water, may flow through the cooling channel. Alternatively or additionally, depending on the cooling effort required, the cooling layer may also have one or more cooling fins that can be cooled by gas flow or liquid flow. The cooling layer 340 as applied in embodiments of the invention may be mounted, for example, on the lowermost surface 320.2 of the metrology layer 320 of the mirror 300 for performing measurements. Note that the mirror 200 for performing measurements as shown schematically in FIG. 2 may also be equipped with a cooling layer or cooling structure similar to cooling layer or cooling structure 340 . In embodiments, metrology layer 320 may be deposited directly on cooling layer or cooling structure 340 or may be attached to the cooling layer or cooling structure using chemicals or adhesives or by physical means such as clamping. You can.

4a, 4b and 4c show top views of parts of a mirror for performing metrology according to the invention, in particular parts of the metrology layer 420 as may be applied to a mirror for performing metrology according to the invention. It is shown schematically. In the arrangement as shown, metrology layer 420 as shown includes a resistive grid 432, 434, 436, where the resistive grid includes a plurality of conductive segments and a plurality of contacts. As mentioned above, various manufacturing techniques can be applied to realize the resistive grid. In FIG. 4A , resistive grid 432 may be assumed to be printed onto the surface of metrology layer 420 . The resistive grid thus forms a thin layer of conductive material deposited, for example by printing, on the top or front surface 420.2 of metrology layer 420, which thin layer forms conductive segments 432.1. In a similar manner, electrical contacts 432.2 may be printed onto front surface 420.2.

4B, resistive grid 434 includes conductive segments 434.1 embedded in trenches 434.3 etched into front surface 420.2 of metrology layer 420. In a similar manner, electrical contact 434.2 can be realized by etching a protrusion into the front surface and filling the protrusion with a conductive material.

In Figure 4C, the trench 436.3 used to create the conductive segment 434.1 of the resistive grid 436 extends to the edge or side surface 420.3 of the metrology layer 420. Electrical contacts 436.2 may then be formed at side surfaces 420.3 on the termination surfaces of the material embedded in trench 436.3.

In embodiments, the metrology layer may be made of, for example, a silicone substrate. This substrate may be, for example, 1 to 10 mm thick. Starting from this substrate, the resistive grid as applied can be printed or etched and deposited on the top or front surface of the substrate.

Once the resistance grid 430 is created, the substrate may then be covered with a cover layer or capping layer that serves as an insulating layer to electrically insulate the resistance grid. If the resistance grid 430 is covered with an insulating layer, care must be taken to ensure that the electrical contacts remain accessible for connection to the measuring instrument. To do this, the metrology layer can be provided with conductors, for example conductive wires, which are connected to electrical contacts and accessible to the metrology instrument. To achieve this connection, the metrology layer as applied comprises, for example, vias for connecting electrical wires to electrical contacts. In an embodiment, the size of the cover layer or capping layer is smaller than that of the metrology layer, so that the electrical contacts, which may be arranged along the contour or perimeter of the resistance grid, are easily accessible. The electrical contacts may be positioned between the back surface of the mirror layer and the metrology layer and/or at the same level as the capping layer or cover layer. By doing this, the resistive grid remains uncovered outside the cover or capping layer. In this embodiment, the mirror layer may be arranged on the cover layer and may have the same size or smaller than the cover layer.

FIG. 5A is a top view of a portion of a mirror 500 for performing metrology according to the present invention including metrology layer 420, mirror layer 510 and cooling layer or cooling structure 530 as shown in FIG. 4C. is shown schematically. Note that the gaps between mirror layer 510 and metrology layer 420 and cooling layer 530 are applied for clarity purposes only. Additionally, the metrology layer 420 has a cover layer 422 so that the resistive grid remains covered and insulated from the mirror layer 510 when the mirror layer 510 is mounted on the metrology layer 420. It can be pointed out. The cooling layer 530 as schematically shown includes cooling channels 530.1 configured to receive a cooling fluid for cooling the mirror layer 510 of the mirror 500 according to the invention. In the embodiment of the invention shown schematically in Figure 5B, the metrology layer 420 further includes one or more RFID tags 550, e.g., passive or active RFID tags 550, which perform metrology during use. and configured to emit or transmit measurement data retrieved from electrical contacts of the resistance grid of layer 420. This RFID tag or tags are embedded, for example, in a metrology layer, for example under or adjacent to a resistive grid. By using these RFID tags, wiring between electrical contacts and measuring instruments is no longer required. In this embodiment, the electrical contacts of the resistance grid are thus configured to be connected to the measuring instrument in a wireless manner. Alternative means for wirelessly connecting the electrical contacts of the resistance grid to the measurement instrument may also be considered.

Figure 6a schematically shows a first possible layout of a resistive grid 630 as could be applied to a mirror for performing measurements according to the invention. Figure 6A is a schematic front or top view of a resistive grid 630 as may be applied to the metrology layer of a mirror for performing metrology according to the present invention. In the embodiment as shown, resistive grid 630 includes a plurality of conductive segments 630.1 and a plurality of electrical contacts 630.2. In the embodiment as shown, electrical contacts 630.2 are arranged along the contour or perimeter of the resistive grid. In the embodiment as shown, a total of 24 electrical contacts are shown, four of which are identified as N0, N6, N12, and N18. Electrical contacts 630.2 and interconnections or intersections of two or more conductive segments 630.1 may also be referred to as nodes of resistance grid 630. The nodes of the resistance grid may be subdivided into a first group or subset of external or accessible nodes and a second group or subset of internal or inaccessible nodes. These may be considered the first group of nodes as the electrical contacts of the resistive grid may be accessible for connection to a measurement instrument or device. In the embodiment as shown, the resistive grid is a substantially rectangular grid comprising conductive segments extending along the X or Y axis. In an embodiment, the resistive grid has 16 electrical contacts. Note that this is just an example and the number of electrical contacts could be larger or smaller.

FIG. 6B schematically shows an alternative substantially rectangular grid that also has a total of 24 electrical contacts or nodes distributed along the outline or perimeter of the resistive grid 680. In the embodiment as shown, resistive grid 680 includes a plurality of conductive segments 680.1 and a plurality of electrical contacts 680.2.

Figure 7 schematically shows an alternative layout of a resistive grid 730 as could be applied to the metrology layer of a mirror for performing measurements according to the invention. In the embodiment as shown, resistive grid 730 includes a plurality of conductive segments 730.1 and a plurality of electrical contacts 730.2. In the embodiment as shown, eight electrical contacts can be seen, numbered N0 through N8. This resistive grid may be referred to as a substantially radial grid with arc-shaped segments and segments extending radially outward.

According to an aspect of the invention, the metrology layer as applied to the mirror for performing the metrology according to the invention may be used to determine the operating parameters, or characteristics, of the received laser beam, for example the power or power of the laser beam as received. It can be used to determine the distribution or position of a laser beam as received. This aspect of the invention can be implemented, for example, in a metrology system. In an embodiment of the invention, a metrology system is provided, the metrology system comprising a mirror and a measurement system for performing measurements according to the invention.

Figure 8 schematically shows such a measurement system 800 according to the invention. Measurement system 800 as shown includes a mirror 810 and a measurement system 820 for performing measurements according to the present invention. In the embodiment as shown, the mirror 810 for performing metrology includes a mirror layer 810.1, a metrology layer 810.2 comprising a resistive grid 812 with electrical contacts 814, and a cooling structure 810.3. ) is included. According to the present invention, the measurement system 820 of the measurement system 800 is configured, during use, to determine the characteristics of a laser beam applied to the mirror 810 for performing measurements. In particular, the measurement system 820 as applied determines the power of the laser beam as received by the mirror 810, the power distribution of the laser beam as received by the mirror 810, or the power distribution of the laser beam as received by the mirror 810. Can be used to determine location.

To do this, the measurement system or instrument 820 as applied in embodiments of the invention, during use, has a resistive grid applied to the metrology layer 810.2 of the mirror 810 for performing measurements of the metrology system 800. and configured to determine the resistance value of one or more conductive segments of 812. This may also be referred to as determining the resistance distribution of the resistance grid.

Based on the resistance value or resistance values, or resistance distribution as determined, measurement system 820 can then determine the corresponding temperature of the conductive segment. To do this, use can be made, for example, from the following equation:

here:

R _T =resistance of the conductive segment at temperature T,

R _T0 =resistance of the conductive segment at reference temperature T0,

α=coefficient of thermal resistance of the conductive segment.

Once the temperature of one or more conductive segments of resistive grid 812 is known, this temperature or temperature distribution can be considered indicative of the operating characteristics of the laser beam received by mirror 810.

In order to determine the resistance value of one or more conductive segments of the applied resistance grid, the measurement system 820 of the metrology system 800 according to the invention, in an embodiment, connects the electrical contacts of the resistance grid of the mirror for performing the measurement. It may be configured to apply a voltage or current to one or more of the contacts and measure the voltage at one or more of the remaining contacts. This measurement can be realized for example using a connection 830 arranged between the metrology layer 810.2 of the mirror 810 and the measurement system 820, for example a multi-wire cable. To apply a voltage or current to one or more electrical contacts, measurement system 820 may include a power source, for example a voltage source or a current source.

As an example, referring to Figure 7, a measurement system or instrument 820 as applied to a measurement system according to the present invention may be configured to apply a voltage V0 to node N0, a voltage of 0 volts to apply to node N4, and the remaining contacts. It may be configured to measure the voltage at one or more of nodes, for example, nodes N1, N2, N3, N5, N6, N7. Voltage V0 may also be referred to as the voltage difference applied to nodes N0 and N4.

In order to accurately determine the temperature distribution of the mirror layer of the mirror for performing measurements as applied, it is desirable to determine the resistance value of a significant portion or all of the conductive segments of the resistive grid, e.g., resistive grid 730. something to do. Considering the layout of the resistance grid as shown, the skilled person will understand that this involves determining a number of unknowns.

In order to arrive at sufficient information to determine the plurality of unknowns, the measurement system according to the invention may, in an embodiment, be configured to perform a plurality of measurements on the metrology layer, in particular on the resistance grid of the metrology layer. there is.

If the resistive grid contains N electrical contacts, there are N contacts to which voltage V0 can be applied. Once voltage V0 is applied to a particular node, a zero voltage or ground connection can be applied to any of the N-1 remaining contacts. Likewise, for a grid with N electrical contacts, there is an N*(N-1) method of applying a voltage difference between two electrical contacts of the grid. Alternatively or additionally, the measurement may be performed by injecting current into multiple, for example more than two, electrical contacts and collecting current from one or more electrical contacts. As such, more than N*(N-1) measurements may be available.

Thus, based on a plurality of measurements as performed, a set of equations are derived and solved using Ohm's law and Kirchhoff's law to give the values for the resistance of the conductive segments of the resistive grid. can be reached. Mathematical techniques such as least squares estimation and covariance matrix propagation methods can also be applied to retrieve unknown values for the resistance of a segment.

It may also be pointed out that the problem of how to determine the resistance value of the conductive segments of a resistive grid has some similarities with solving the electrical impedance tomography equation. In electrical impedance tomography, the impedance distribution inside a volume is found by applying a current at some surface electrodes and taking voltage measurements at other electrodes. This impedance distribution can be determined using, for example, boundary element methods.

If the resistive grid, as applied to the mirror for performing measurements according to the invention, is very dense or fine-grained, i.e. has a large number of relatively small segments, a similar mathematical method can be applied to derive the resistance distribution of the resistive grid. there is.

Figure 9 schematically shows this dense resistive grid 900 with a rectangular grid of small conductive segments 910 and a number of electrical contacts 920 arranged along the outline or perimeter of the grid 900.

If the boundary element method, etc. is applied to determine the resistance or resistance distribution of the resistance grid, the resistance grid may also be made of a uniform conductive layer or sheet, for example Ag, Au, Pt, Cu, Al, Fe, W, or It may be formed as a layer or sheet comprising or made of conductive ink or any other material having a sufficiently high thermal conductivity coefficient. In this embodiment of the invention, the resistive grid as applied to the mirror for performing measurements is therefore a resistive layer. Therefore, rather than having separate conductive segments, the metrology layer of the mirror comprises a resistive layer, for example a conductive sheet such as a Cu- or Al-sheet, which is connected, for example along the contour or perimeter of the resistive layer. It has a plurality of electrical contacts. Referring to Figure 9, this embodiment may therefore include a resistive layer, i.e. a continuous sheet or layer of conductive material, instead of a dense resistive grid 900.

In an embodiment, the measuring system as applied to the measuring system according to the invention is configured to determine or calculate, at a rate of 1 Hz, the value for the resistance of the conductive segment or the value for the resistance distribution, or any operating characteristic derived therefrom. It can be configured.

According to a further aspect of the invention, a laser beam system for an EUV radiation source is provided, the laser beam system comprising a laser beam source and at least one mirror for metrology according to the invention or at least one metrology system according to the invention.

Figure 10 schematically shows an embodiment of a laser beam system 1000 according to the present invention. In the embodiment as shown, the laser beam system 1000 includes a laser beam source 1010, two mirrors 1020 and 1030 for metrology, and, during use, a resistor applied to the metrology layer of the mirrors 1020 and 1030. and a measurement system 1040 configured to determine the resistance value of one or more conductive segments of the grid. Accordingly, the functionality of measurement system 1040 is similar to the functionality of measurement system 820 shown in FIG. 8. However, measurement system 1040 is configured to determine the resistance value of the conductive segment for two mirrors, mirrors 1020 and 130, rather than just one. However, as an alternative, each mirror or mirrors 1020, 1030 may be equipped with its own measurement system for determining the resistance value, resistance distribution or temperature distribution of the mirror's resistance grid, or the operating characteristics of the laser beam as received by the mirror. It can be pointed out that this is possible. Connections 862 and 864 schematically depict the wiring from measurement system 1040 to the resistive grids of mirrors 1020 and 1030 to perform the required measurements as described above. In the embodiment as shown, mirrors 1020 and 1030 are arranged in the optical path of laser beam 1050 and can therefore be used to deflect laser beam 1050. In the embodiment as shown, the measurement system 1040 thus measures the laser beam 1050 received by each of the two mirrors 1020, 1030, i.e. at different positions along the optical path of the laser beam 1050. It may be configured to determine operating characteristics.

If the operating characteristics of the laser beam 1050 produced by the laser beam source 1010 of the laser beam system 1000 are determined at different locations along the optical path, the information may also be used in the mirror as applied to the laser beam system 1000. It can be used to determine or evaluate the operating characteristics of. In particular, if measurement system 1040 is configured to perform measurements on two consecutive mirrors along the optical path, anomalies in the measurements can be used to evaluate the operation of mirrors 1020 and 1030. In particular, any anomalies observed between measurement data or properties derived therefrom of different mirrors, for example successive mirrors along the optical path, may be an indication of the mirror's operating state or operating condition. As such, in an embodiment, the measurement system 1040 as applied to a laser beam system according to the invention may be configured to determine the measurement of the laser system as received by each of the mirrors or based on a comparison of measurements for the mirrors. Based on a comparison of the determined operating characteristics, it may be configured to determine operating characteristics of a mirror of the laser beam system.

As an example, it is assumed that a defect has occurred in the mirror 1020 that causes deterioration of the reflection characteristics of the mirror 1020. For example, assume that the reflectivity of mirror 1020 is reduced from a nominal value of 99% to 98%, while the reflectivity of mirror 1030 is maintained at its nominal value, i.e., 99%.

As described above, the measurement system 1040 as applied in the present invention may be configured to determine the power or power distribution of the received laser beam, for example based on a determined temperature distribution of the mirror layer of the mirror; , whereby the temperature distribution is derived from the resistance value of the conductive segments of the resistance grid of the mirror or from the resistance distribution of the resistance grid. For the given example, the calculation of the power of the received laser beam will therefore be based on the temperature of the mirror, which in turn is based on the dissipation of the mirror. Since a decrease in reflectivity will cause an increase in the dissipation of the mirror, this decrease will cause an incorrect calculation of the power of the received laser beam. In particular, the reduced reflectivity of mirror 1020 will result in the calculated power of the laser beam as received by mirror 1030 being higher than the calculated power of the laser beam as received by mirror 1030. . Because mirror 1030 is upstream of mirror 1020, this calculation may not be accurate and may indicate an anomaly in the operation of one of the mirrors. By comparing the measured data or its derived properties, the operating characteristics of the applied mirror, such as the likelihood of defects, deterioration state or reflectivity, can be determined or estimated.

Such information may be useful, for example, to determine whether to perform preventive maintenance or repair of components of laser beam system 1000.

In the embodiment as shown in FIG. 10 , the laser beam system 1000 further includes a control system 1060 configured to control the operation of the laser beam source 1010, and in particular to control the generation of the laser beam 1050. do. Control system 1060 may be configured to determine a control signal 1070 to control laser beam source 1010 in this regard. In an embodiment of the invention, the measurement data acquired by the measurement system 1040 or any operating characteristics derived therefrom are used as feedback to the control system 1070 of the laser beam system, as represented by the data signal 1080. can be provided. Based on the data, the control system 1060 of the laser beam system can adjust the operation of the laser beam system, particularly the operating characteristics of the laser beam 1050 as produced by the laser beam source 1010. For example, based on measurement data acquired by measurement system 1040, a drift or displacement of laser beam 1050 may be detected, resulting in mirror steering of laser beam system 1000 to realign the laser beam. The (steering) system may be configured to steer one or more mirrors of the laser beam system. It is noted that the one or more mirrors that can be steered by this mirror steering system may include one or more of mirrors 1020, 1030 and/or may include additional mirrors of the laser beam system as applied. It can be.

According to a further aspect of the invention, an EUV radiation source is provided, the EUV radiation source comprising a laser beam system according to the invention. This EUV radiation source can advantageously be applied in a lithographic system according to the invention, which system comprises an EUV radiation source according to the invention and a lithographic apparatus. This EUV radiation source and lithographic apparatus is schematically described with reference to FIG. 1 .

Although specific reference may be made herein to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Other possible applications include the fabrication of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

Although specific reference may be made herein to embodiments of the invention in the context of lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection device, metrology device, or any device that measures or processes objects such as wafers (or other substrates) or masks (or other patterning devices). These devices may be generally referred to as lithography tools. These lithography tools can utilize vacuum conditions or ambient (non-vacuum) conditions.

Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, the invention is not limited to optical lithography and may be used in other applications, such as imprint lithography, where the context allows. It will be recognized that there is.

Where the context allows, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium that can be read and executed by one or more processors. Machine-readable media can include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, machine-readable media may include read only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory device; It may include electrical, optical, acoustic, or other types of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.). Additionally, firmware, software, routines, and instructions may be described herein as performing specific operations. However, it should be noted that this description is for convenience only and that such operation is in fact due to a computing device, processor, controller, or other device executing firmware, software, routines, instructions, etc., and that doing so does not place the actuator or other device in the physical world. It must be recognized that it allows interaction with .

Although specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The above description is intended to be illustrative and not limiting. It will therefore be clear to those skilled in the art that modifications may be made to the invention as described without departing from the scope of the provisions set forth below;

1. A mirror for performing metrology of a laser beam system in an EUV light source includes a mirror layer having a front surface configured to receive and reflect a laser beam of the laser beam system; a metrology layer arranged on the rear surface of the mirror layer, the metrology layer comprising a resistive grid comprising a plurality of conductive segments and a plurality of electrical contacts, or a resistive layer comprising a plurality of electrical contacts, thereby providing a resistance The plurality of electrical contacts of the grid or resistive layer are configured to be connected to a measurement instrument.

2. In a mirror according to clause 1, the resistive grid comprises a plurality of nodes, and each conductive segment forms a connection between a pair of nodes among the plurality of nodes.

3. In a mirror according to clause 2, the plurality of electrical contacts are provided by a subset of the plurality of nodes.

4. A mirror according to any one of clauses 1 to 3, wherein the metrology layer comprises a substrate layer.

5. In the mirror according to clause 4, the substrate layer comprises silicon.

6. In the mirror according to clause 4 or 5, the resistive grid is formed by printing a corresponding pattern onto the surface of the substrate layer using conductive ink.

7. In the mirror according to clause 4 or 5, in order to form a plurality of conductive segments and a plurality of electrical contacts, a resistive grid is formed by etching a trench in the surface of the substrate layer and providing a conductor in the trench.

8. In the mirror according to any one of clauses 1 to 7, the surface of the metrology layer is covered with a protective layer.

9. A mirror according to any one of clauses 4 to 8, wherein the surface of the substrate layer with the resistive grid faces the rear surface of the mirror layer.

10. In a mirror according to any one of clauses 1 to 9, the electrical contacts are arranged along the contour or perimeter of the resistive grid.

11. Mirror according to any one of clauses 1 to 10, wherein the mirror comprises a stack of metrology layers arranged on the rear surface of the mirror layer.

12. The mirror according to any one of clauses 1 to 11 further comprises a cooling layer configured to cool the mirror layer.

13. A mirror according to clause 12, wherein the cooling layer comprises one or more cooling channels configured to receive a cooling fluid.

14. In the mirror according to clause 12 or 13, the cooling layer is arranged on the rear surface of the metrology layer.

15. A mirror according to any one of clauses 1 to 14, wherein the resistive grid is a substantially rectangular grid or a substantially radial grid.

16. The measurement system is,

a mirror according to any of clauses 1 to 15, and

A measurement system configured to determine the resistance value of one or more conductive segments of the resistance grid.

17. In a metrology system according to clause 16, the measurement system shall be:

connect one or more of the electrical contacts to a power source;

to measure voltage or current on one or more of the electrical contacts that are not connected to a power source;

It is configured to determine the resistance value of one or more conductive segments among the plurality of conductive segments based on the measured voltage or current.

18. In the measurement system according to clause 16 or 17, the measurement system is further configured to estimate the temperature distribution of the mirror layer based on the determined resistance value.

19. In the measurement system according to clause 18, the measurement system is further configured to determine, during use, the operating characteristics of the laser beam received by the mirror.

20. In a metrology system according to clause 19, the operating characteristics include the power of the laser beam, the power distribution of the laser beam or the position of the laser beam.

21. The laser beam system for EUV radiation source is:

a laser beam source, and

comprising one or more metrology mirrors according to any one of clauses 1 to 15 or one or more metrology systems according to any of clauses 16 to 20.

22. In a laser beam system according to clause 21, one or more mirrors or one or more metrology systems are arranged in the optical path of the laser beam of the laser beam system.

23. A laser beam system according to clause 22 comprises two or more measurement systems, the two or more measurement systems configured to determine the operating characteristics of the laser beam received by each of the two or more mirrors of the two or more measurement systems. do.

24. In a laser beam system according to clause 23, the measuring system of two or more metrology systems is based on a comparison of the determined operating characteristics of the laser beam as received by each of the two or more mirrors of the two or more metrology systems. , is configured to determine the operating characteristics of the mirrors of two or more measurement systems.

25. In laser beam systems according to clause 24, the operating characteristics of the mirrors include the possibility of defects, deterioration state or reflectivity.

26. The EUV radiation source comprises a laser beam system according to any one of clauses 21 to 25.

27. The lithographic system comprises an EUV radiation source and a lithographic apparatus according to clause 26.

Claims (15)

A mirror for performing metrology of a laser beam system within an EUV light source, comprising:
a mirror layer having a front surface configured to receive and reflect a laser beam of the laser beam system; and
a metrology layer arranged on a rear surface of the mirror layer, the metrology layer comprising:
° a resistive grid comprising a plurality of conductive segments and a plurality of electrical contacts, or
° comprising a resistive layer containing a plurality of electrical contacts,
whereby the plurality of electrical contacts of the resistive grid or the resistive layer are configured to be connected to a metrology instrument. 2. The method of claim 1, wherein the resistance grid includes a plurality of nodes, each conductive segment forming a connection between a pair of nodes of the plurality of nodes, and the plurality of electrical contacts are a subset of the plurality of nodes. A mirror for performing measurements, provided by . 3. The mirror of claim 2, wherein the metrology layer includes a substrate layer, and the resistance grid is formed by printing a corresponding pattern onto the surface of the substrate layer using a conductive ink. 3. The method of claim 2, wherein the metrology layer includes a substrate layer, whereby the resistive grid etches a trench in the surface of the substrate layer to form the plurality of conductive segments and the plurality of electrical contacts and A mirror for performing measurements, formed by providing a conductor. 5. Mirror according to any one of claims 1 to 4, wherein the surface of the measurement layer is covered with a protective layer. 6. The method according to any one of claims 1 to 5, wherein the metrology layer comprises a substrate layer, the surface of the substrate layer with the resistance grid facing the rear surface of the mirror layer. mirror. 7. A mirror according to any preceding claim, wherein the mirror comprises a stack of metrology layers arranged on the rear surface of the mirror layer. 8. The method according to any one of claims 1 to 7, wherein the mirror further comprises a cooling layer configured to cool the mirror layer, the cooling layer arranged on the rear surface of the metrology layer, to perform metrology. Mirror to do it. In a measurement system,
- a mirror according to any one of claims 1 to 8; and
- a metrology system comprising a measurement system configured to determine the resistance value of one or more conductive segments of said resistance grid. The method of claim 9, wherein the measurement system
a. connect one or more of the electrical contacts to a power source;
b. measure voltage or current at one or more of the electrical contacts not connected to the power source;
c. A measurement system configured to determine a resistance value of the one or more conductive segments among the plurality of conductive segments based on the measured voltage or current. 11. The method of claim 9 or 10, wherein the measurement system is further configured to estimate the temperature distribution of the mirror layer based on the determined resistance value, wherein the measurement system is configured to, during use, determine the temperature distribution of the laser beam received by the mirror. A metrology system further configured to determine operating characteristics, wherein the operating characteristics include power of the laser beam, power distribution of the laser beam, or position of the laser beam. In the laser beam system for EUV radiation source,
laser beam source; and
A laser beam system comprising at least one metrology mirror according to any one of claims 1 to 8 or at least one metrology system according to any one of claims 9 to 11. 13. The laser beam system of claim 12, wherein the laser beam system includes two or more metrology systems and two or more mirrors, wherein the two or more metrology systems are received by each of the two or more mirrors of the two or more metrology systems. A laser beam system configured to determine the operating characteristics of a laser beam. 14. The method of claim 13, wherein the measurement system of the two or more metrology systems is based on a comparison of determined operating characteristics of the laser beam as received by each of the two or more mirrors of the two or more metrology systems. A laser beam system comprising at least one metrology system configured to determine operating characteristics of mirrors, wherein the operating characteristics of the mirrors include defect probability, deterioration state, or reflectivity. EUV radiation source comprising a laser beam system according to any one of claims 12 to 14.