NL2012093C2

NL2012093C2 - Improved extreme ultra violet light source.

Info

Publication number: NL2012093C2
Application number: NL2012093A
Authority: NL
Inventors: Fokko Marten Mulder
Original assignee: Univ Delft Tech
Priority date: 2014-01-16
Filing date: 2014-01-16
Publication date: 2015-07-20
Also published as: WO2015108420A1

Abstract

The present invention relates to an Extreme Ultra Violet light source, to a trap for use in such a light source, to a multilayer mirror for use in such a light source, to a grazing incident mirror for use in such a light source, and to a multi- layer for use in the multilayer mirror. Such a light source may for instance be used in lithography, such as used in semiconductor integrated circuit production.

Description

Improved Extreme Ultra Violet light source

FIELD OF THE INVENTION

The present invention relates to an Extreme Ultra Violet light source, to a trap for use in such a light source, to a multilayer mirror for use in such a light source, to a grazing incident mirror for use in such a light source, and to a multilayer for use in the multilayer mirror. Such a light source may for instance be used in lithography, such as used in semiconductor integrated circuit production.

BACKGROUND OF THE INVENTION

An Extreme Ultra Violet light (EUVL) light source relates to a complex system.

In terms of a source of radiation it is noted that neutral atoms or condensed matter cannot emit EUV radiation. For matter to emit it, ionization must take place first. In view of energy involved, EUV light can only be emitted by electrons which are bound to multicharged (Mn+) positive ions.

Such electrons are more tightly bound than typical valence electrons. A thermal production of multicharged positive ions is typically only possible in a hot dense plasma, which itself strongly absorbs EUV. As possible elements Xe and Sn are considered. The Xe or Sn plasma sources for EUV lithography may be discharge-produced or laser-produced. Discharge-produced plasma is made by lightning in e.g. a tin vapor. Laser-produced plasma is made by microscopic droplets of molten tin heated by powerful laser. Laser-produced plasma sources are considered to outperform discharge-produced plasma sources. An EUVL output power exceeding 100 W is a requirement for enabling sufficient throughput of a lithography system that utilises EUV. While state-of-the-art 193 nm ArF ex-cimer lasers offer intensities of 200 W/cm2, lasers for producing EUV-generating plasmas need to be much more intense, on the order of 1010 W/cm2; in other words very high energy levels per unit surface. A further characteristic of the plasma-based EUV sources under development is that they are not coherent, unlike lasers used for prior art optical lithography. A further issue relates to dosing of EUV light and calibration of an EUV dosimeter, which is a nontrivial unsolved issue. The secondary electron number variability is a well-known root cause of noise in avalanche photodiodes.

It is noted that EUVL differs significantly from deep ultraviolet lithography. Unfortunately all matter absorbs EUV radiation. In order to overcome this problem at least partially EUV lithography needs to take place in a vacuum (or at least reduced pressure). Optical elements used in lithography, including a photomask, must make use of advanced multilayers. These multilayers must be largely defect-free, in order to minimize side effects, such as absorption of light. An example of such a multilayer is a Mo/Si multilayer which reflects light by means of interlayer interference; unfortunately these mirrors will still absorb a significant amount the incident light («30%).

Typically EUVL systems contain a significant amount of mirrors, such as at least two condenser multilayer mirrors, six projection multilayer mirrors, and a multilayer object (mask). A disadvantage of the present optics is that these absorb a large fraction («96%) of available EUV light; therefore a EUV source will need to be sufficiently bright amongst others for compensating absorption losses. EUV source development has focused on plasmas generated by laser or discharge pulses. A mirror for collecting the light is unfortunately directly exposed to the plasma; it is therefore vulnerable to damage from the high-energy ions and other debris from the plasma. This damage associated with the high-energy process of generating EUV radiation has hindered implementation of EUV light sources for lithography.

It is noted that various other issues are associated with use of EUVL in lithography, such as flare, heating per feature volume, and increased heating due to the vacuum environment .

Heating is also a particularly serious issue for multilayer mirrors used, because, as EUV is absorbed within a thin distance from the surface, the heating density is higher. As a result, water cooling is expected to be used for the high heating load; however, the resulting vibration of cooling is a concern.

Also multilayer optics contamination is a concern.

It is noted that as EUV is highly absorbed by all materials, EUV optical components used inside a lithography tool are susceptible to damage, mainly manifest as observable ablation. Such damage is a new concern specific to EUV lithography, as conventional optical lithography systems use mainly transmissive components and electron beam lithography systems do not put any component in the way of electrons, although these electrons end up depositing energy in the exposed sample substrate. A further problem is that elements used in an EUV light source tend to degrade. In an example thereof multilayers used tend to delaminate. Also elements are vulnerable to contamination, such as from the multicharged ions (e.g. Sn) in the EUV emitting plasma. Thereto in principle unwanted species, such as hydrogen, are introduced, in order to capture the multicharged ions and also to chemically remove debris from the plasma con-densed on the optical components (e.g.

Sn). However, hydrogen gas as well as ionised hydrogen in the plasma also interacts with optical and construction elements used, which is in principle unwanted.

The present invention therefore relates to an improved EUV light source and further details thereof, which overcome one or more of the above disadvantages, without compromising functionality and advantages.

SUMMARY OF THE INVENTION

It is an object of the invention to overcome one or more limitations of EUV light sources of the prior art and at the very least to provide an alternative thereto.

In a first aspect, the invention relates to an EUV light sources according to claim 1, comprising one or more improvements .

The present EUV light source preferably comprises enough mirrors for reflection and condensing, such as at least two condenser multilayer mirrors and six projection multilayer mirrors . A mirror, such as a grazing incidence mirror, may comprise a supporting layer, such as a Mo layer. In view of Mo, it is preferred to use another material, such as Ni. It may further comprise one or more EUV-light reflecting layers. Another type of mirror (for use in reflecting higher angle up to perpendicular incidence rays) may also contain a series of further layers, such as at least one Mo-Si double layer.

It is preferred that the present material (and layer thereof) match with further layers being provided, such as the above one or more reflecting layers, and a supporting underground. In an example of a grazing incidence mirror, specifically the present material matches with a reflecting layer, e.g. in terms of lattice constant, option of forming an alloy therewith, etc.

For the present mirrors the material is preferably not absorbing EUV light, such as 50% or more is reflected by the (thin) layers. It is also preferably capable of absorbing, transferring and releasing hydrogen. The layer preferably does not expand more than a few percent, preferably less than 2% (at operating temperature and hydrogen pressure).

It is noted that at least some of the present elements of the claims are somewhat functional of nature. However, said functionality is considered in view of specific circumstances, such as given boundary conditions. In view of the enthalpy of formation and hydrogen equilibrium pressure, as well as an average plasma potential, it is noted that these are taken at the given boundary conditions, e.g. operating temperature. For the rotating foil trap such an operating temperature is typically from 1000 -1500 K, and for the multilayer mirror and grazing incident mirror it typically is 273-375 K. The hydrogen pressure is from about 5 Pa - 300 Pa, whereas an average plasma potential ranges from 0.1-5 V, e.g. depending on an average plasma temperature. In view of the plasma potential it is noted that it has been found that a difference in average plasma potential at a surface of e.g. a mirror, of e.g. 0.1 V may have as a result a change in hydrogen equilibrium pressure of 108 Pa, and a difference of 0.2 V may already result in a change in hydrogen equilibrium pres sure of 1016 Pa. So despite modest changes in average potential, a relative huge change in hydrogen equilibrium pressure may occur. Of course exact equilibrium pressures depend on materials used as well as the (average) plasma potential.

It is noted that the given boundary conditions can be established quite accurately, upon construction and use of a light source. As a result the characteristics of the present mirrors and trap can be adapted quite easy.

In this respect it is noted that in order to capture debris and particles, emitted by the emission source and plasma, various measures are considered. One of these measures is to capture debris and particles by a trap, such as a rotating trap. A further option is to reduce particles and debris to relatively innocent species, such as by chemically reacting particles and debris. An example of such a chemical reaction relates to hydrogen (H2) or protons, which e.g. react with Sn to form SnH4.

The removal of debris from the pulsed light source, including condensed Sn may be assisted by the installation of a microwave assisted continuous plasma. This is considered to induce a continuously present hydrogen plasma with a not so high plasma temperature and potential, which then can continuously remove the debris in addition to the very hot pulsed plasma from the pulsed EUV source itself. The hydrogen pressure in the vacuum chamber may then be reduced since the continuously present plasma can work effectively with lower hydrogen pressure. The lower hydrogen pressure helps to reduce the hydrogen implantation during the high plasma potential pulses of the EUV source. To stop the debris from the EUV source preferably still a sufficient gas pressure is present; however, this may be a low pressure hydrogen or a low pressure mixture of hydrogen and argon.

The materials used in the present light source experience a high dose of atomic H+ implantation as a result of the hydrogen containing plasma. It has been found that such implantation leads to significant damage to the materials used. The damage leads over time to blister formation and degradation of the specifications of the materials, and a reduced lifetime .

Present inventors have examined an origin of the damage in the materials used. The results of these examinations are used to enable mitigation of damage by suitable materials modification, by modified operating methods, and/or by modified design rules for the materials and components. Some specifications of components typically considered are given in the examples below.

It has been found that especially the prior art metals Ru and Mo are considered relatively unsuited for use in the present EUV light source. Especially presence of hydrogen plasma is a concern. It has been found that hydrogen will build up a high hydrogen pressure in defects or at interfaces of the materials (c.q. layers), resulting in damaging of the material, such as by blister formation. The effect of this damage of the materials is that these do not fulfil specifications any more.

When considering hydrogen and e.g. metals the following is considered.

The presence of an electrical potential on a conductive hydrogen and protons containing medium (the plasma) is considered to cause a change in the thermodynamic equilibrium hydrogen content inside a material, as is detailed below.

In general hydrogen reacts with metals in a reaction:

M + V2H2 <-> MH

The equilibrium hydrogen gas pressure is considered to follow the van 't Hoff equation:

with AHf’"Jthe enthalpy of formation in kJ/mole H of the metal hydride, and AS0 the entropy change in the reaction above. Electrochemical insertion of hydrogen in a metal is considered to follow, the relation:

where Pref is 1CT Pa, and F is the Faraday constant of 96485.34 C/mol.

These equations relate the alterations in hydrogen equilibrium pressure when an electrical potential is applied between the metal and a reference electrode with a proton con- ducting electrolyte in between.

From the equations above it can be concluded that: RTlny2- = -2F(Emh -E0) = 2AHf -2TAS0 which indicates that under an applied potential the equilibrium pressure behaves as if the metal hydride has an altered AHf (assuming that ASo essentially remains constant).

The plasma generates a plasma potential Φ that is considered to depend on the plasma electron temperature Te: Λ 1 kTe φ =---e~ 2 e

The resulting potential Φ = EMH - Ea will thus drive the insertion of hydrogen in the metal facing the plasma.

The plasma is pulsed, leading to high pulses of the potential and intermediate return to (close to) zero potential difference. On average there results a negative potential however, that will on average alter the hydrogen equilibrium pressure and the hydrogen content in the material.

It has been found that the present material is capable to accept hydrogen inserted from the plasma, and it is capable of releasing it again to the plasma, at present conditions of about 5 Pa and also at future conditions of 200 Pa hydrogen pressure. It has been found that as a result of the selection of the present material that if H would diffuse to an underlying material that cannot accept the H and/or there is a defect, the pressure in the defect will essentially not go above the H2 equilibrium pressure; thereby damage caused by hydrogen pressure build-up is prevented.

Typically characteristics of a metal are that they may oxidize, may form a cation, are an electrical conductor, etc. The present alloys and intermetallic compounds have an equilibrium pressure (Pa) for hydrogen absorption. Such an equilibrium pressure per se can be measured with means known to a person skilled in the art. An example of such a measurement is making use of X-rays in view of material structure. Typically it is measured at ambient temperature (273 K).

In table 1 various metals and equilibrium pressures (Pa, @273 K)(as calculated/estimated) are given.

Mg 1.1*10°

Ti 6 .1 * 10~15

Zr 1.2* 1CT23

Hf 1*1CT5 Ta 1*1CT13

It is noted that hydrogen is typically provided to remove the debris of the emission source, such as Sn. Specifically a thin layer of e.g. Sn is in operation deposited on e.g. a mirror; the thin layer can largely be removed by providing hydrogen, typically in a continuous mode.

The present equilibrium pressure is taken such that at the one hand the present material can absorb hydrogen at given boundary conditions, and at the other hand can release hydrogen, for instance at room temperature.

As a result of the above selection of materials, in view of given boundary conditions, the present light source provides an extended life time, with no or limited degradation of components, such as rotating foil trap, multilayer mirrors and grazing incident mirror. Blister formation, delamination of layers and the like is largely prevented.

It is noted that a term as "on top" or "above" may relate to a sequence of e.g. layers, a first layer covering a second layer. The layer may also partly be on top, i.e. a first layer covering a part of a second layer. In view of the present application such terminology is mainly functional of nature .

The present invention provides a solution to one or more of the above mentioned problems and overcomes drawbacks of the prior art.

Advantages of the present description are detailed throughout the description.

DETAILED DESCRIPTION OF THE INVENTION

In a first aspect the present invention relates to an improved extreme ultraviolet light (EUV) source for use in nanolithography according to claim 1, wherein the trap, the optional grazing incidence mirror and the at least one multilayer mirror top layer comprise a material which material comprises at least one metal and has

Rla)a negative enthalpy of MH formation (Δη<0 material + hydrogen <-» Metal-hydride) and

Rib) a hydrogen equilibrium pressure at an operating temperature Toper of the material of 0.1 Pa-108 Pa, allowing absorption of hydrogen.

In an example of the present light source the boundary conditions further comprise an average plasma potential. The boundary conditions are taken into account, e.g. when deter-mining/calculating requirements for the present material.

It is noted that plasma facing materials experience an electrochemical proton potential that also depends on a plasma temperature. As a result also the hydrogen equilibrium pressures will be influenced significantly by the presence of the plasma. This is considered a significant complication that is present, and in addition the plasma is pulsed in time. In a first order approximation it has been found sufficient to work with the time averaged plasma potential as a driving force for the hydrogen equilibrium pressures. This may however not be the case when the protons diffuse rapid enough between the pulses and react instantaneously to the varying potential; in this case an advanced approximation may be required.

In an example of the present light source the hydrogen equilibrium pressure at given boundary conditions of the material is in a range from 1 Pa-107 Pa, preferably from 100 Pa-5*106 Pa, such as from 300 Pa-106 Pa. It has been found that the hydrogen equilibrium pressure is preferably not too small; sufficiently high to be above the applied hydrogen pressure in the light source, but also limited to some extent, in order to prevent e.g. blister formation. The hydrogen equilibrium pressure is preferably not too large, in order to allow (re-) absorption from high pressure defects.

In an example of the present light source (R2) the hydrogen equilibrium pressure at given boundary conditions when the plasma is applied is in a range from 10 Pa-107 Pa, preferably from 50 Pa-5*106 Pa, such as from 200 Pa-106 Pa. It is preferably somewhat higher than the hydrogen pressure of the light source, e.g. larger than 5 Pa for a prior art system and larger than 200 Pa for an advanced system. In the first case >20 Pa is preferred, in the second case > 300 Pa is pre- ferred.

In an example of the present light source the at least one multilayer mirror comprises a sequence of layers ie[2;n], wherein a layer closer to a (plasma facing) surface of the mirror, the surface reflecting EUV light, has a lower hydrogen equilibrium pressure at given boundary conditions of the material than a subsequent layer (P[H2]i(@T)< P [H2] i+i ( @T) ) . The hydrogen equilibrium pressures of subsequent layers preferably differ by at least a factor 2, more preferably at least a factor 5, even more preferably at least a factor 10. As accelerated protons coming from the plasma may be inserted up to a few layers deep in the multilayer mirror, these protons are inherently transferred back through a sequence of layers from a deeper layer (i+1) to a less deep layer (i), and revolve as hydrogen molecules in the vacuum chamber. It has been found that this elegant solution mitigates problems caused by hydrogen absorption and high pressure hydrogen trapped in defects to a large extent.

In an example of the present light source (R0) a melt temperature Tmeit of the material is more than 100 K higher than an operating temperature (Tmeit > Toper + 100 K) . Such is in particular relevant for the rotating foil trap, as this trap is operated at relatively high temperatures. It is preferred that the melt temperature is more than 250 K higher, such as more than 400 K higher. It has been found that such a melt temperature is sufficient to provide a durable light source.

In an example of the present light source the rotating foil trap comprises a material with (mechanical properties) (ROa) a hardness of > 4 Moh, preferably > 5 Moh, and/or (ROb) a tensile strength of > 500 MPa, and/or (ROc) an elastic modulus of > 100 Gpa. The hardness can be determined as in mineralogy, using the so called Mohs scale. The tensile strength is considered a maximum stress that a material can withstand while being stretched or pulled before failing or breaking. It can be measured with a tensom-eter under standard conditions, such as ASTM conditions.

These conditions may vary somewhat, from material to material. The elastic modulus relates to a mathematical descrip tion of an object or substance's tendency to be deformed elastically. Here specifically the Young's modulus (E) is considered. The Young's modulus (E) describes tensile elasticity, or the tendency of an object to deform along an axis when opposing forces are applied along that axis; it is defined as the ratio of tensile stress to tensile strain. It is often referred to simply as the elastic modulus.

Prior art systems use e.g. Mo or alloys thereof as a material, having for a defect free Mo material an elastic modulus of about 330 Gpa, a tensile strength of about 650 Mpa, and a Mohs value of 5.5, which values are considered good enough.

It is noted that for a manufactured and processed foil trap there are normally imperfections because of the difficult workability of the Mo material. This reduces the actual strength of the prior art systems.

For the tensile strength a value of > 300 Mpa is preferred, preferably > 500 Mpa. For the elastic modulus a value of > 200 GPa is preferred.

In an example of the present light source a surface voltage compensator is provided for the at least one mirror and/or for the rotating foil trap, preferably a voltage compensator comprising one or more of a surface potential detector, an oscillating voltage compensator, a surface temperature sensor, an ampere measurer, a power supply and a controller. The surface voltage compensator is adapted to compensate for a plasma induced (electrical) potential on a surface of the present mirror or rotating foil trap. Such a compensation can be provided in relation to the plasma potential, being present in operation of the light source. It is preferred to compensate actively, in response to and to (partially) counteract a (varying) plasma potential. Thereto a surface potential detector is provided, for determining a real time surface potential. Preferably also a surface temperature is determined real time, in order to compensate for a varying temperature, if present. Likewise an ampere measurer and a power supply are present. A controller may actively provide output, based on determined parameters, to the oscillating voltage compensator. The controller preferably comprises software for predicting changes in the potential, based on measurements.

In an example of the present light source the rotating foil trap is made of an alloy or intermetallic compound comprising AaBb, wherein A is selected from Nb, B is selected from V, Ir, Os, Pt, Pd, Au, Mo, Ti, and Zr, ae [ 0, 75; 0,99 ] , and be [ 0,01;0,25], preferably be [ 0,02;0,10] . It is noted that a component A is selected such that it is not equal to a component B. It is found that especially Nb comprising materials are particularly suited. Albeit the Nb being somewhat less suited than Mo in terms of mechanical properties, the hydrogen behaviour is much better. Also a product such as rotating foil trap Nb can be produced much easier. The Nb preferably comprises a small amount of alloying metals. It has been found that the second metal improves mechanical properties significantly. Preferred second metals are Zr, Mo, Ti and V. Preferred alloys are NbZr and NbV, such as NbV0.05Mo0.05Zr0.01 and NbVo. 04 ·

For all alloys/compounds mentioned also combinations of elements mentioned are envisaged

Especially Nb-V alloys have been found to have very good workability and mechanical properties at higher operating temperatures, enabling thinner lamellae with closer spacings to be made, that in turn make the reduction of the rotation speed possible. Next to the lower rotation speed also the lower density of Nb compared to Mo reduces the forces exerted on the lamellae. These factors make that the smaller strength of the Nb-V alloy are even more than compensated. In the presence of hydrogen for these alloys it is of importance that their temperature is always kept near the normal high operating temperatures of the source, since then the equilibrium pressure is high and the hydrogen will not be absorbed.

In an example of the present light source the grazing incidence mirror comprises a layer of an alloy or intermetallic compound CcDdEe. The layer is preferably thick enough, such as 10-500 nm, preferably 100-300 nm, in order to stop protons entering from the plasma into the (underlying) layer.

Herein C is selected from Zr, Mo, and Nb, D is selected from

Rh, Mo, Ru, Zr, Nb, Sc, Ti, Mg, Ni, Co, Zn, Cu, Fe, Cr, Mn,

Hf, La, Ta, Ir, Os, Pt, Pd, Au, and V, E is selected from Rh,

Mo, Ru, Zr, Nb, Sc, Ti, Mg, Ni, Co, Zn, Cu, Fe, Cr, Mn, Hf,

La, Ta, Ir, Os, Si, H, Re and V, ce[0,30;0,95] , de [ 0,05;0,70], and ee [ 0,00;0,35] . It is noted that a component C is selected such that it is not equal to a component D or E, and a component D is selected such that it is not equal to a component E. Preferred compositions of the reflecting layer are ZrMoH, such as ZrMo2H0-o.i, ZrRuH, such as ZrRu2H0-o.ir and ZrRuPd, such as ZrRui.9Pd0.i. The layer may be coated on a construction made out of Ni metal.

In an example of the present light source the at least one multilayer mirror comprises at least two layers, wherein a first layer has a lower EUV light scattering density, compared to a second layer with a higher EUV light scattering density, and wherein a layer has metallic or non-metallic properties. It has been found that multi layers can reach a reflectivity of 60-70% of the EUV light.

In an example of the present light source the above high density layer comprises an alloy or intermetallic compound FfGgJj, wherein F is selected from Zr, Mo, and Nb, G is selected from Rh, Mo, Ru, Zr, Nb, Sc, Ti, Mg, Ni, Co, Zn, Cu,

Fe, Cr, Mn, Hf, La, Ta, Ir, Os, N, Pt, Ir, Os, Pt, Pd, Au and V, J is selected from Rh, Mo, Ru, Zr, Nb, Sc, Ti, Mg, Ni, Co, Zn, Cu, Fe, Cr, Mn, Hf, La, Ta, Ir, Os, Si, Η, B, O, Al, N,

Re and V, be[0,16;0,99], ge[0,05;0,45], and je[0,00;0,70], wherein the alloy or intermetallic compound has a EUV-light transmittance (@ 13 nm) of >0,7. It is noted that a component F is selected such that it is not equal to a component G or J, and a component G is selected such that it is not equal to a component J. The thin layers of the materials preferably have a sufficient EUV-light transmittance.

In view of hydrogen absorption behaviour the above mentioned metals are considered specifically. Preferred compositions of the high density layer are ZrMoH, such as ZrMo2H0-o.ii ZrRuH, such as ZrRu2H0-o.i/· and ZrRuPd, such as ZrRui.9Pd0.i. Each individual layer may be adapted to requirements. Typically a layer thickness is from 1-20 nm, such as from 5-10 nm. For the deepest layers there will be no penetration of protons from the plasma anymore and the normally chosen Si layers can be used.

In an example of the present light source the low density layer comprises a compound K^L^M^ where K is selected from Si, Al, Mg, L is selected from B, C, N, 0, Mg, Al, P, and M is selected from Η, B, C, N, 0, Mg, Al, P, kG[0,25;0,99], le [ 0,0;0,7], me [ 0,0;0,7] . It is noted that a component k is selected such that it is not equal to a component L or M, and a component L is selected such that it is not equal to a component M. Preferred compositions are SiMgH, such as SiMg0.iHx, MgSiN, such as MgSiN2_x, SiMgAl, such as SiMg0.2Al0.i, and MgAlO, such as MgAl204_x.

In an example of the present light source a layer thickness is from 0.5-30 nm. Each individual layer may be adapted to requirements. Typically a layer thickness is from 1-20 nm, such as from 5-10 nm. It is considered that for the deep-est/deeper layers there will be no penetration of protons from the plasma anymore and Si layers can be used.

In a second aspect the present invention relates to a foil trap for use in a light source according to the invention, wherein the rotating foil trap comprises a material which material comprises at least one metal and has,

Rib) a hydrogen equilibrium pressure of 0.1 Pa-108 Pa, allowing absorption of hydrogen. Advantages of the present rotating foil trap are amongst others given throughout the description .

In a third aspect the present invention relates to a multilayer mirror or grazing incident mirror for use in a light source according to the invention, wherein the mirror comprises a sequence of layers ie[2;n], wherein a layer closer to a surface of the mirror, the surface reflecting EUV light, has a lower hydrogen equilibrium pressure at given boundary conditions, the boundary conditions comprising operating temperature Toper, than a subsequent layer (P[H2]i(@T)< P [H2] i+i ( @T) ) . Advantages of the present mirrors are amongst others given throughout the description.

In a fourth aspect the present invention relates to a multilayer for use in multilayer mirror according to the invention comprising a sequence of layers ie[2;n], wherein a layer closer to a surface of the multilayer, the surface being capable of reflecting light, such as EUV light, has a lower hydrogen equilibrium pressure at given boundary conditions, the boundary conditions comprising operating temperature Toperi than a subsequent layer (Ρ[Η2]ι(@Τ)< P [H2] i+i ( @T) ) . Advantages of the present multilayer are amongst others given throughout the description. One of the advantages is that now a hydrogen adsorption behaviour of each individual layer can be adapted and controlled. As such the multilayer can be adapted easily to e.g. requirements of a light source, or any other application. As such the multilayer can be used to adapt and control absorption of hydrogen.

The invention will hereafter be further elucidated through the following examples which are exemplary and explanatory of nature and are not intended to be considered limiting of the invention. To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims.

FIGURES

Figure 1 is a schematic representation of a multilayer, having layers 1, i+1 and i+2. DETAILED DESCRIPTION OF FIGURES Figure 1 is a schematic representation of a multilayer, having layers 1, i+1 and i+2. Therein an optional top layer (ZrN) is shown, having a thickness of 10 nm. The ZrN layer is followed by a 15 nm thick ZrRu2H0-o.i layer. Then a sequence of layers is provided, for instance having as layer I ZrMo2H0-o.i of 5 nm, and followed by further ZrMoH layers of 5 nm thick, respectively. Then a SiMo sequence of layers of e.g. 4 layers is provided, each having a thickness of 10 nm. A supporting structure is provided.

In an example a sequence of alternating layers of denser and less dense materials are provided, such as 5 nm ZrN, 5nm

MgSi, 5 nm ZrRuH, 5 nm MgSi, 5 nm ZrMoH0-o.if and then Si/Mo layers. A thickness of the layers mentioned specifically is in the example in the same order of magnitude, or the same.

In the figure also a voltage compensator 21 is shown schematically .

EXAMPLES 1 Specifics of the components RFT (Rotating Foil Trap)

- Operating temperature: 1100 - 1500K - High rotation speed - Thin lamellae, high strength required - Prior art material: Mo based, with small additions of e.g. Ti-Zr - Examples of present Material: Nb0.96V0.04· This alloy has a high enough hydrogen equilibrium pressure at the high operating temperatures. As a matter of precaution hydrogen preferably only reaches it at the high operating temperature and is removed when cooling down. Otherwise the H2 will be absorbed in the alloy and may deform it.

This alloy has very good formability but is less strong than the currently used Mo. However, the lower density and the better formability enable the appropriate performance compared to current Mo. A further example is Nbo.95Zro.05 which takes up H under pressure forming (Nbo.95Zro.05) HO . 01 . MM (Multilayer Mirrors) - Operating T: water cooled, so not high - Prior art material: Mo and Si multilayers - Typically comprising a protection layer, such as a lOnm ZrN toplayer. This should be EUV transparent while protecting multilayers from H implantation by having a high stopping power GM (Grazing incidence Mirror) - Operating T: cooled, so not too high

- Ru toplayer for high EUV reflectivity, limited EUV absorption - Prior art Material base is Mo

Plasma - High plasma T,

Pulsed @80 kHz, fast decay between pulses - Hydrogen pressure from 5 to 200 Pa

Substrate preparation

Thin films with a thickness of 10 nm were deposited at room temperature substrates in an ultrahigh-vacuum (UHV) DC/RF magnetron sputtering system (base pressure 10~8 mbar, Ar deposition pressure 0.003 mbar).

Alloy thin films with a thickness of 5 nm were codeposited in a similar DC magnetron sputter system using quartz substrates. On deposition the films are crystalline, which decays on cycling with hydrogen.

Claims

An improved extreme ultraviolet light (EUV) source for use in nanolithography comprising at least one vacuum chamber, an emission source, the emission source producing EUV light upon activation, for example, by laser excitation of Sn, or Xe, a hydrogen source, such as a hydrogen plasma, such as a hydrogen discharge plasma and a laser-induced plasma, at least one multi-layer mirror for reflecting and directing EUV light, wherein the at least one multi-layer mirror has interlayer interference and comprises a mirror top layer, optionally a means for forming at least partially coherent EUV light, optionally a shaving incident mirror, at least one means for capturing particles from the emission source, the at least one means being selected from a trap, such as a rotating foil trap, a microwave supported plasma, and a chemical species that forms a chemical compound with the emission source, such as SnH4, characterized in that the roter and the foil trap, the optional shearing raid mirror and at least one multi-layer mirror top layer comprise a material which comprises at least one metal and has, under given preconditions, the preconditions comprising the operating temperature Toper, Rla) a negative enthalpy of MH formation (ΔΗ < 0 material + hydrogen < - »metal hydride) and Rib) a hydrogen equilibrium pressure at a working temperature Toper of the material from 0.1 Pa-108 Pa, which makes absorption of hydrogen possible.

A light source according to claim 1, wherein boundary conditions comprise an average plasma potential.

A light source according to any one of the preceding claims, wherein the hydrogen equilibrium pressure at given boundary conditions of the material is in a range of 1 Pa-107 Pa, preferably 100 Pa-5 * 106 Pa, such as from 300 Pa-106 Pa

A light source according to any one of the preceding claims, wherein (R2) is the hydrogen equilibrium pressure at given boundary conditions when the plasma is applied in a range of 10 Pa-107 Pa, preferably of 50 Pa-5 * 106 Pa, such as 200 Pa-106 Pa.

A light source according to any one of the preceding claims, wherein the at least one multi-layer mirror comprises a sequence of layers ie [2; n], a layer closer to the surface of the mirror, the surface reflecting EUV light, a lower hydrogen equilibrium pressure at given preconditions of the material then has a following layer (P [H2] i (@ T) < P [H2] i + 1 (@ T)).

A light source according to any one of the preceding claims, wherein (R0) a melting temperature Tmeit of the material is more than 100 K higher than a working temperature (Tmeit > Toper + 100 K).

A light source according to any one of the preceding claims, wherein the rotating foil step comprises a material with (ROa) a hardness of > 4 Moh, preferably > 5 Moh, and / or (ROb) a tensile strength of > 300 MPa, and / or (R0C) an elastic modulus of > 100 Gpa.

A light source according to any one of the preceding claims, wherein a surface tension compensator is provided for the at least one mirror and / or the rotating foil trap, preferably a tension compensator comprising one or more of a surface potential detector, an oscillating voltage compensator, a temperature sensor, an ammeter, a power supply and a controller.

A light source according to any one of the preceding claims, wherein the rotating foil trap is made of an alloy or intermetallic compound comprising AaBb, wherein A is selected from Nb, B is selected from V, Ir, Os, Pt, Pd, Au, and Zr , an ae [0.75; 0.99], and [0.01; 0.25], preferably be [O, 02; O, 10].

A light source according to any one of the preceding claims, wherein the shearing incident mirror comprises a layer of an alloy or intermetallic compound CcDdEe, wherein C is selected from Zr, Mo, and Nb, D is selected from Rh, Mo, Ru, Zr, Nb , Sc, Ti, Mg, Ni, Co, Zn, Cu, Fe, Cr, Mn, Hf, La, Ta, Ir, Os, Pt, Pd, Au and V, E are selected from Rh, Mo, Ru, Zr , Nb, Sc, Ti, Mg, Ni, Co, Zn, Cu, Fe, Cr, Mn, Hf, La, Ta, Ir, Os, Si, H, Re and V, ce [0.30; 0.95 ], the [0.05; 0.70], and ee [0.00; 0.35].

A light source according to any one of the preceding claims, wherein the at least one multi-layer mirror comprises at least two layers, wherein a first layer has a different density and thus EUV scattering density compared to a second layer, and wherein a layer of metallic or non-metallic properties has.

A light source according to claim 11, wherein the metallic layer comprises an alloy or intermetallic compound FfGgJj, wherein V is selected from Zr, Mo and Nb, G is selected from Rh, Mo, Ru, Zr, Nb, Sc, Ti, mg , Ni, Co, Zn, Cu, Fe, Cr, Mn, Hf, La, Ta, Ir, Os, N, Pt, Ir, Os, Pt, Pd, Au and V, J are selected from Rh, Mo, Ru , Zr, Nb, Sc, Ti, Mg, Ni, Co, Zn, Cu, Fe, Cr, Mn, Hf, La, Ta, Ir, Os, Si, Η, B, O, Al, N, Re and V , fG [0.16; 0.99], ge [0.05; 0.45], and je [0.00; 0.70], in which the alloy or intermetallic compound has an EUV light transmittance (@ 13 nm ) has from > 0.7, and / or wherein the non-metallic layer comprises a compound KkLiMm where K is selected from Si, L is selected from B, C, N, O, Mg, Al, P and M is selected from Η, B, C, N, O, Mg, Al, P, kG [0.25; 0.99], ie [0.0; 0.7], me [0.0; 0.7].

A light source according to any one of the preceding claims, where a layer thickness is 0.5-30 nm.

A rotating foil trap for use in a light source according to any one of the preceding claims, wherein the rotating foil stage comprises a material which has at least one metal and, at given boundary conditions, the boundary conditions comprising the operating temperature Toper, R1a) a negative enthalpy of MH formation (ΔΗ < 0 material + hydrogen < - »metal hydride) and Rib) a hydrogen equilibrium pressure at a working temperature Toper of the material from 0.1 Pa-108 Pa, which makes absorption of hydrogen possible.

A multi-layer mirror or shaving incident mirror for use in a light source according to any one of claims 1-14, wherein the mirror comprises a sequence of layers ie [2; n], a layer closer to the surface of the mirror, the surface EUV reflects light, a lower hydrogen equilibrium pressure at given boundary conditions of the material then has a subsequent layer (P [H2] i (@T) < P [H2] i + i (@T)), and optionally including a protective layer.

A multi-layer for use in a multi-layer mirror according to claim 15, comprising a sequence of layers ie [2; n], wherein a layer closer to the surface of the mirror, the surface reflecting EUV light, a lower hydrogen equilibrium pressure at given boundary conditions of the material then has a following layer (P [H2] i (@T) < P [H2] i + 1 (@T)).