DE102004027347B4 - Wavelength selector for the soft X-ray and the extreme ultraviolet range - Google Patents

Abstract

Wavelength selector for the soft X-ray range and / or EUV range, wherein the wavelength selector comprises at least two reflectors which are optically connected in series such that an incident beam incident on the first reflector extends in a substantially fixed angular relationship to the beam reflected by the last reflector .
characterized,
that
At least one of the reflectors (M1, M2, M3, M4) has a wavelength-selective region dependent on its angle of incidence (α) and the angle of incidence (α, α + θ) of at least two of the reflectors (M1, M2, M3, M4) for wavelength selection is changeable and
- To change the line width of the last reflector (M4) reflected beam (2) at least
- Two reflectors having a wavelength selective range (M1, M2, M3, M4) are provided, which are optimized for different wavelengths and / or
- Two reflectors having a wavelength selective area (M2, M3) are provided, the angle of incidence differing from each other (α + θ + ε, α + θ ...

Description

The The invention relates to a wavelength selector for the soft x-ray range and the extreme ultraviolet region according to the preamble of the claim 1.

For the lithographic Structuring of dimensions below 50 nm is the extreme ultraviolet lithography (EUVL) Technology with wavelengths from 10 nm-15 nm developed. For the use in metrology devices for the EUV lithography, for example for verification of EUV masks, it is beneficial to the wavelength the EUV radiation over change a range of a few nm to be able to. Also outside EUV lithography are inexpensive and tunable soft X-ray sources significant.

So far such are in a wider range tunable X-ray sources only in the range of high resolution Monochromators at synchrotron radiation sources to disposal. However, the beam times of synchrotron radiation sources are very high expensive. For many applications will as well the achievable high resolution not required.

The solutions previously used in the laboratory are static solutions, where the wavelength range can not be continuously tuned, but only different filters or grids can be replaced.

The US 5 173 930 A describes an X-ray monochromator, ie a wavelength selector for X-rays, in which a plurality of mirror pairs are arranged in a housing, wherein the individual mirrors of each pair of mirrors are provided with a specific coating forming a Bragg reflector. The individual mirrors of each mirror pair have the same coating, while the respective different pairs of mirrors are provided with different coatings. The mirror pairs are designed so that they are optimal for each wavelength range and can be selected by pivoting the mirror a certain wavelength.

From the DE 694 29 598 T2 For example, a crystal monochromator and a crystal analyzer for use in an X-ray analyzer are each constructed of four germanium single crystals, the reflecting surface of each single crystal being not parallel to the diffracting crystal lattice plane, but having an angle in the range of 15 ° to 10 ° with the crystal lattice planes 23 ° forms. The use of such single crystals offers the advantage that it is possible to use both 220 reflections and 440 reflections by changing the angle of incidence of the incident x-ray beam by rotating the single crystals between two discrete positions. The 220 reflection results in a high radiation intensity, while the 440 reflection causes a high resolution.

From the DE 103 05 813 A1 An X-ray monochromator is known in which X-rays are monochromatized by reflection on a single substrate provided with a plurality of multilayer films, the period length of the film-forming layers consisting of a reflection layer and a spacer layer being different and becoming smaller towards the substrate ,

task The present invention is therefore a wavelength selector for the soft x-ray range (0.12 nm to 5 nm, 250 eV to 10 keV) or extreme UV range (5 nm to 41 nm; 30 eV and 250 eV), which require the provision of Tunable radiation easily and inexpensively.

The Task is by a wavelength selector solved with the features of claim 1.

in this connection At least two reflectors are provided, which are so optically are connected in series that an incident on the first reflector incident beam in a substantially fixed angular relationship to that of the last one Reflector reflected beam passes. According to the invention at least one of the reflectors is dependent on the angle of incidence, wavelength selective Range on and the angle of incidence of at least two of the reflectors is for wavelength selection variable.

By the wavelength selective Areas of the at least one reflector is the tuning of Soft X-ray radiation impinging on this reflector within one certain wavelength range possible. In that the angle of incidence of at least two of the reflectors for wavelength selection variable is achieved and at the same time that the incident beam and the reflected from the last reflector beam in a fixed angular relationship stand each other, it is possible the inventive wavelength selector to insert into an existing laboratory setup. Incidence beam and the The reflected beam from the last reflector changes during the Tuning the wavelength selector not, so that the wavelength selector according to the invention can be easily inserted into an existing beam path.

The wavelength-selective region exhibits Advantage of multibeam interference on. Such a wavelength-selective region can be designed, for example, as a multilayer mirror, as a reflection grating or as a Bragg reflector.

One Such multi-beam interference having wavelength-selective Range reflects dependent different wavelengths from the respective angle of incidence, wherein the rest Overlay beam components with other wavelengths destructively. Such a multi-beam interference having wavelength-selective Range therefore serves as a wavelength selector.

The wavelength selective Areas are advantageous for the wavelength range from 10-15 nm optimized.

With Advantage can change the angle of incidence of all reflectors, so that guarantees on the one hand is that the incident beam and the reflected from the last reflector Beam always have the same angular relationship to each other and the others a tuning over a big Wavelength range, for example, 10 nm can be achieved. It is suitable at, the angles of incidence of the reflectors simultaneously by the same angle to change.

In a particularly advantageous embodiment of the invention are the Angle of incidence of the reflectors changeable such that the incident beam on the first reflector always collinear or parallel to the reflected Beam of the last reflector runs. This is the arrangement of the wavelength selector at any point in the beam path of the laboratory application possible, because in a collinear arrangement entrance ray and reflected Beam lie on the same optical axis.

The Adjustment of the angle of incidence of the reflectors is advantageous over at least an adjusting means, in particular an adjusting motor, made, wherein the adjusting means over a central control unit, in particular a computer, with each other can be coordinated.

Around a simple integration of the wavelength selector in a beam path to enable an existing laboratory application, It makes sense to arrange the reflectors such that the through the change the angle of incidence of a first reflector caused distraction of the Beam path through change the angle of incidence of at least one second reflector canceled becomes. The reflectors can be arranged so that they are in itself a beam displacement element form.

at Using four reflectors can be so two optically in series switched beam displacement elements are arranged, which are arranged so that the beam offset cancel each other out. This will achieved that the entrance beam and the last reflector reflected beam on a common optical axis, ie collinear.

Around the line width of the wavelength distribution of the selected beam and in particular to be able to reduce be in a development of the invention at least two each a wavelength selective Area-used reflectors optimized for different wavelengths are. Through this targeted "detuning" of the two wavelength-selective Areas against each other, a reduction in the line width is achieved. This is inevitable at the expense of intensity, because the appropriate outdoor areas of the respective wavelength spectrum destructively interfere with each other. This loss of intensity can but tolerated within a certain wavelength range, because he almost neglects here is.

These Detuning the wavelength-selective Areas against each other can be formed by at least two multilayer mirrors are provided, and at least two of the Multi-layer mirrors differing layer thicknesses exhibit. The respective reflected wavelengths of the two different ones Multi-level mirror for a given angle therefore differ slightly, thereby the detuning is achieved.

The Detuning the at least two different wavelength-selective ones Areas can also be defined by at least two different Bragg reflectors or reflection grating can be achieved, in which case at least two Bragg reflectors or two reflection grating different lattice constants exhibit.

In a further development of the invention, it is provided for changing and in particular reducing the line width that at least two reflectors with wavelength-selective areas are provided, which are arranged in such a way that they have incidence angles differing from one another. As a result, a slight detuning of the two reflectors is achieved against each other, resulting in a reduction in the line width of the reflected beam from the last reflector. In this development, two substantially identical wavelength-selective reflectors can be used, which then each only have to have different angles of incidence. The angles of incidence advantageously differ by a maximum of three degrees. This will on the one hand a sufficient reduction of On the other hand, the intensity loss due to such a slight detuning is not too great.

Around a wavelength selection for far to reach apart, different wavelength ranges, the reflectors with the wavelength-selective regions are advantageous interchangeable. Through different sets of wavelength-selective Reflectors can be achieved so that different Areas of x-radiation in the soft X-ray range be tuned and selected.

The Invention will be described below with reference to the drawings of the figures. Show it:

1 a wavelength selector with four reflectors;

2 a diagram of the reflectivity of a wavelength-selective reflector with variation of the angle of incidence;

3 a diagram of the reflectivity of a wavelength selector with a reflector, the in 2 has shown properties, and a structure according to the 1 ;

4 a diagram of the reflectivity of a wavelength selector according to 1 in which the reflector is designed as a multilayer mirror and the individual reflectors are detuned by changing the layer thickness against each other;

5 a diagram of the variation of the line width at detuning the in 1 shown reflectors M2 and M3 by one angle + ε and -ε; and

6 a wavelength selector according to 1 , in which the reflectors M2 and M3 are detuned from each other by an angle ε.

In 1 a wavelength selector with four reflectors M1 to M4 is shown, wherein two pairs of wavelength selectors M1 and M2, and M3 and M4 each form a beam displacement element SV1 and SV2. The two beam displacement elements SV1 and SV2 are optically connected in series and arranged so that the incident on the first reflector M1 incident beam 1 and the beam reflected from the last mirror M4 2 on a common optical axis 100 are located. The incident beam 1 and the beam reflected from the last mirror M4 2 thus have a fixed angular relationship to each other, because they are collinear.

The in the wavelength selector of 1 Optically arranged in series reflectors M1 to M4 are each formed as a wavelength-selective mirror. These are multilayer mirrors for the extreme ultraviolet range.

at a multilayer mirror undergoes this wavelength selectivity Multibeam interference achieved. Of course it is also possible instead a multilayer mirror, a Bragg reflector or a reflection grating to use or any other reflective, multi-beam interference having to use reflective arrangement. The reflectors used are there for optimized wavelength range between 10-15 nm.

By change of the angle of incidence α on a such wavelength-selective Reflector is achieved that the maximum intensity of each reflected Beam along the wavelength range shifts. In other words, as the angle of incidence changes, So by pivoting the wavelength-selective reflector, a Selection of a specific wavelength range allows.

In 1 are all, each having wavelength-selective areas having reflectors M1 to M4 arranged pivotably, so that the respective angle of incidence α of each reflector M1 to M4 can be changed. For the purpose of pivoting the reflectors M1 to M4, adjusting means M1.1, M2.1, M3.1 and M4.1 are provided for this purpose, each of which is in operative connection with the reflectors M1 to M4. These adjustment means M1.1, M2.1, M3.1 and M4.1 can be coordinated via a common control unit.

In 1 two different beam paths are shown. A first beam path in a first orientation of the reflectors M1 to M4 is a solid line 10 shown. The respective normals on the reflectors M1 to M4 are shown in solid lines for this beam path. A second beam path 10 ' is shown in dashed lines.

First, the solid beam path will now be described. An input beam 1 meets the first reflector M1 at an angle of incidence α and is correspondingly reflected at the same angle of reflection to the reflector M2, to the reflector M3 and then to the reflector M4, from where it is reflected by the last reflector M4 2 leaves the wavelength selector. input beam 1 and beam reflected from the last reflector M4 2 lies, as already described above, on a common optical axis 100 , Since the reflectors M1 and M2 and also M3 and M4 are aligned parallel to one another and the reflectors M2 and M3 enclose an angle of 90 °, the incidence angles and angle of reflection of all reflectors M1 to M4 in the size of α.

The second dashed line 10 ' is achieved by pivoting the reflectors M1 to M4 by an angle θ. The change of the angle of incidence by the angle θ is carried out simultaneously or simultaneously by all the reflectors M1 to M4. The pivoting of the reflectors M1 and M2 takes place in the same direction, as well as the pivoting of the reflectors M3 and M4, wherein the reflectors M1 and M2 and the reflectors M3 and M4 are pivoted in opposite directions. The situation of the pivoted reflectors is in the 1 dashed lines. As a beam path then results that the incident beam 1 now impinges on the first reflector M1 at an angle α + θ, accordingly by an angle changed by 20 with respect to the original beam 10 is reflected to the second reflector M2, also in this incident at an angle of incidence of α + θ, since also the reflector M2 has been pivoted by an angle θ. Due to the pivoting of the reflector M3 likewise by an angle θ, the beam reflected by the reflector M2 also impinges on the reflector M3 at an angle of incidence α + θ. Accordingly, the beam path then passes to the reflector M4, where it due to the pivoting of the reflector M4 by the angle θ then back into the original from the last reflector M4 reflected beam 2 running back.

The Arrangement is here in principle axisymmetric to an axis, parallel to the through the pivot axes of the reflectors M1 and M2 or M3 and M4 lying axis.

By the arrangement of the reflectors as two beam displacement elements SV1, SV2 in which the beam offset achieved by the first beam displacement element SV1 undone by the second beam offset element SV2 , this wavelength selector can simply in an already existing beam path, for example a laboratory device, added become.

By the pivoting of the reflectors M1 to M4 is then achieved that the angle of incidence of the rays on the respective reflector M1 to M4 changes and accordingly a different wavelength is selected, which then from the last reflector M4 back into the existing beam path is fed.

In 2 is the reflectivity of a multilayer mirror, which is designed here for example as Mo / Si multilayer stack with 40 double layers and an optimization for 45 ° angle of incidence at a double-layer thickness of about 9.8 nm shown. It can be seen that the reflectivity in the respective maxima of the individual reflectivity curves, which were varied here for angles of incidence of 40 ° to 55 ° in steps of 1 °, in a wavelength range of approximately 12.5 nm to 15.5 nm only varies slightly. Within this range of about 3 nm, therefore, the respective wavelength can be set with the corresponding multilayer mirror without disproportionately large intensity losses occurring here.

In the 2 In this case, the reflection for a mirror is shown at different angles of incidence. If another wavelength range is of interest, then a corresponding multilayer mirror can be produced either by changing the double-layer thickness or by selecting a different combination of materials, for example Mo / Be.

In 3 Again, the reflectivity is plotted against the wavelength, in which case an arrangement according to the 1 is shown with four wavelength-selective reflectors, each one of the reflectors having the characteristics of in 2 has shown multilayer mirror. Here again a wavelength selection by variation of the respective angle of incidence in the range of 40 ° to 55 ° is shown.

The in the 1 Arrangement shown thus allows the tuning of the wavelength in a wavelength range of about 12.5 nm to 15.5 nm, ie over a range of 3 nm, each having a line width of about 1 nm.

To reduce the line width can be achieved by targeted detuning of the mirror, ie by a targeted optimization of the mirror for different wavelength ranges, a reduction of the line areas. In the arrangement of 1 For example, the reflectors M2 and M3 are designed as double-layer mirrors with a double-layer thickness of a slightly different value.

In 4 the reflectivity of a corresponding arrangement is shown. Here, two of the four mirrors are formed with a double layer thickness of 9.8 nm and two of the mirrors with a double layer thickness of 9.4 nm. The resulting line widths are significantly lower in this arrangement than those in the 3 shown.

The in the 4 said detuning of two of the four reflectors can be achieved by using a Bragg grating or by using a reflection grating also by changing the lattice constants of any two of the four reflectors.

A second way to reduce the line width is in 6 shown. Here's how in turn, the arrangement of 1 shown. However, the reflectors M2 and M3 are each detuned by an angle ε against each other. During the pivoting of the reflectors, the pivoting of the reflectors M2 and M3 is therefore provided by an angle θ-ε or θ + ε respectively when the reflector M1 and M4 are pivoted by an angle θ.

By This measure is a detuning of the reflectors M2 and M3 over the Reflectors M1 and M4 reached, also select the reflectors M1 and M4 then slightly different Wavelength range, as the reflectors M2 and M3. This in turn is a reduction of Line width reached.

In 5 the corresponding reduction of the line widths is shown. The angle α is held firmly at 45 °.

Shown is a detuning of the reflectors M2 and M3 by + ε and -ε. The intensities. the individual Curves are normalized to the respective maximum. Significantly too can be seen that at a detuning of the reflectors M2 and M3 by an angle of ε = 2 ° or ε = 3 ° one essential smaller line width results. However, the intensity decreases at this Detuning and is in the example shown for ε = 3 ° at about 70% of the value of ε = 0.

You want a larger wavelength range select or select a different wavelength range, so can the reflectors M1 to M4 are replaced by another set, the for each other wavelength ranges optimized is. The price for several reflector sets for Cover a wider wavelength range are still low compared to synchrotron beam time costs.

The wavelength selectors of the type proposed are suitable for in situ metrology for EUV lithography, in particular in-situ analysis of the wavelength spectrum of EUV lithography sources in the soft X-ray range.

Of the inventive wavelength selector is not for use in the wavelength range between 10 nm limited to 15 nm. By selecting the materials for The multilayer mirrors are all wavelength ranges in the soft X-ray range and the extreme ultraviolet region for wavelength selection by a wavelength selector according to the invention accessible. With that could z. B. tunable light sources for biological applications in Soft X-ray range realized become.

Claims (16)

Wavelength selector for the soft X-ray range and / or EUV range, wherein the wavelength selector comprises at least two reflectors which are optically connected in series such that an incident beam incident on the first reflector extends in a substantially fixed angular relationship to the beam reflected by the last reflector , characterized in that - at least one of the reflectors (M1, M2, M3, M4) has a wavelength-selective range dependent on its angle of incidence (α) and the angle of incidence (α, α + θ) of at least two of the reflectors (M1, M2 , M3, M4) for wavelength selection is changeable and - for changing the line width of the last reflector (M4) reflected beam ( 2 ) at least - two wavelength selective area having reflectors (M1, M2, M3, M4) are provided, which are optimized for different wavelengths and / or - two wavelength selective area having reflectors (M2, M3) are provided, the angle of incidence differing from each other (α + θ + ε, α + θ - ε). wavelength according to claim 1, characterized in that the wavelength-selective Area formed as a multi-beam interference exhibiting area is. wavelength according to claim 1 or 2, characterized in that the wavelength-selective Area a multilayer mirror, a reflection grille and / or a Bragg reflector is. wavelength according to one of the preceding claims, characterized that the wavelength selective Range for wavelength selection in a wavelength range from 10-15 nm serves. wavelength according to one of the preceding claims, characterized that the angle of incidence (α, α + θ) of all Reflectors (M1, M2, M3, M4) changeable is. wavelength according to claim 5, characterized in that the angles of incidence (α, α + θ) of the reflectors for wavelength selection simultaneously changeable by the same angle (θ). Wavelength selector according to claim 5 or 6, characterized in that the angles of incidence (α, α + θ) of the reflectors (M1, M2, M3, M4) are variable such that the incident beam ( 1 ) on the first reflector (M1) always collinear or parallel to reflected beam ( 2 ) of the last reflector (M4). wavelength according to one of the claims 5 to 7, characterized in that each reflector (M1, M2, M3, M4) with at least one adjusting agent (M1.1, M2.1, M3.1, M4.1) for the adjustment of its angle of incidence (α, α + θ) is in operative connection. wavelength according to at least one of the preceding claims, characterized that through change of the angle of incidence (α, α + θ) at least a first reflector (M1, M2) caused deflection of the beam path through change of the angle of incidence (α, α + θ) at least of a second reflector (M3, M4) is canceled. wavelength according to one of the preceding claims, characterized the reflectors (M1, M2, M3, M4) are arranged such that they form a beam displacement element (SV1, SV2). wavelength according to one of the preceding claims, characterized that four reflectors (M1, M2, M3, M4) are arranged such that they comprise two optically series-connected beam displacement elements (SV1, SV2). wavelength according to claim 11, characterized in that the beam offset of the two beam offset elements (SV1, SV2) cancel each other. wavelength according to one of the claims 1 to 12, characterized in that the wavelength-selective Areas are formed by multilayer mirrors (M1, M2, M3, M4) and at least two of the multilayers are different from each other Have layer thicknesses. wavelength according to one of the claims 1 to 12, characterized in that the wavelength-selective Regions formed as Bragg reflectors or reflection grating are and at least two Bragg reflectors or reflection gratings differing lattice constants exhibit. wavelength according to one of the preceding claims, characterized that two substantially identical wavelength-selective reflectors (M2, M3) have different angles of incidence (α + θ + ε, α + θ - ε). wavelength according to one of the preceding claims, characterized that the angle of incidence by max. Distinguish 3 °.