PELLICLE MEMBRANE FOR A LITHOGRAPHIC APPARATUS

Abstract

A pellicle membrane for a lithographic apparatus, the membrane including a matrix including a plurality of inclusions distributed therein. A method of manufacturing the pellicle membrane, a lithographic apparatus including the pellicle membrane, a pellicle assembly for use in a lithographic apparatus including the membrane, as well as the use of the pellicle membrane in a lithographic apparatus or method.

Claims

1. A pellicle membrane for a lithographic apparatus, the membrane comprising a matrix including a plurality of inclusions distributed therein.

2. The pellicle membrane according to claim 1, wherein the plurality of inclusions comprises a plurality of crystals.

3. The pellicle membrane according to claim 1, wherein the inclusions comprise a first material and the matrix comprises a second material, the emissivity of the first material being greater than the emissivity of the second material.

4. The pellicle membrane according to claim 1, wherein the inclusions comprise molybdenum silicide, zirconium silicide, ruthenium silicide, tungsten silicide, or a combination selected therefrom thereof.

5. The pellicle membrane according to claim 1, wherein the matrix comprises silicon.

6. The pellicle membrane according to claim 5, wherein the matrix comprises silicon nitride and/or silicon carbide.

7. The pellicle membrane according to claim 5, wherein the silicon comprises any one of p-Si, a-Si, nc-Si, mono-Si, or a combination selected therefrom.

8. The pellicle membrane according to claim 1, wherein the membrane does not include a metallic coating and/or wherein the matrix material does not comprise carbon.

9. The pellicle membrane according to claim 1, wherein the membrane has a thickness of from about 10 nm to about 50 nm.

10. (canceled)

11. The pellicle membrane according to claim 1, wherein the membrane does not comprise multiple stacked layers.

12. The pellicle membrane according to claim 1, wherein the inclusions comprise molybdenum silicide, zirconium silicide, ruthenium silicide, tungsten silicide, or a combination selected therefrom and wherein the molybdenum, zirconium, tungsten, and/or ruthenium is present in the pellicle membrane in an amount of from about 2% to about 40% (atomic %), or wherein the pellicle membrane has a composition of from around 10 to around 60 vol% of the inclusion material.

13. (canceled)

14. The pellicle membrane according to claim 1, wherein the matrix material is non filamentary.

15-18. (canceled)

19. A pellicle assembly for use in a lithographic apparatus, the pellicle assembly comprising the pellicle membrane according to claim 1.

20. (canceled)

21. A method of controlling a composition of a pellicle membrane, the method comprising providing a sputtering target, and adjusting power provided to the sputtering target to adjust the composition of the pellicle membrane.

22. The method according to claim 21, comprising providing a first sputtering target and a second sputtering target, and adjusting the power provided to one or both of the first and second sputtering targets to adjust the composition of the pellicle membrane.

23. The method of claim 22, wherein the first sputtering target comprises a matrix material.

24. The method of claim 22, wherein the second sputtering target comprises an inclusion material.

25. (canceled)

26. The method according to claim 21, wherein the power is within the range of from 50 to 1000 W.

27. The method according to claim 21, comprising providing power within the range of from 50 W to around 300 W to the sputtering target to provide a pellicle membrane having a vol% of inclusion material of from 10 to 60 vol%.

28. A method of designing a membrane for a lithographic apparatus, the membrane comprising a matrix including a plurality of inclusions distributed therein and the membrane being characterized by an output property which is at least partially dependent on an input property, the method comprising: receiving a set of input values associated with the input property; generating, using semi-empirical thermodynamic modelling, a set of modelled membranes, each modelled membrane being modelled based on an input value of the set of input values associated with the input property; predicting, based on the model, an output value associated with the output property for each membrane of the set of modelled membranes; selecting one or more membranes from the set of modelled membranes based on the predicted output values; outputting one or more input values from the set of input values based on the selected one or more membranes.

29-39. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawing in which corresponding reference symbols indicate corresponding parts, and in which:

[0070] FIG. 1 depicts a lithographic apparatus according to an embodiment of the invention.

[0071] The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements.

DETAILED DESCRIPTION

[0072] FIG. 1 shows a lithographic system including a pellicle 15 (also referred to as a membrane assembly) according to the present invention. The lithographic system comprises a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an extreme ultraviolet (EUV) radiation beam B. The lithographic apparatus LA comprises 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 table WT configured to support a substrate W. The illumination system IL is configured to condition the radiation beam B before it is incident upon the patterning device MA. The projection system is configured to project the radiation beam B (now patterned by the mask MA) onto the substrate W. The substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus aligns the patterned radiation beam B with a pattern previously formed on the substrate W. In this embodiment, the pellicle 15 is depicted in the path of the radiation and protecting the patterning device MA. It will be appreciated that the pellicle 15 may be located in any required position and may be used to protect any of the mirrors in the lithographic apparatus.

[0073] The radiation source SO, illumination system IL, and projection system PS may all be constructed and arranged such that they can be isolated from the external environment. A gas at a pressure below atmospheric pressure (e.g. hydrogen) may be provided in the radiation source SO. A vacuum may be provided in illumination system IL and/or the projection system PS. A small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure may be provided in the illumination system IL and/or the projection system PS.

[0074] The radiation source SO shown in FIG. 1 is of a type which may be referred to as a laser produced plasma (LPP) source. A laser, which may for example be a CO.sub.2 laser, is arranged to deposit energy via a laser beam into a fuel, such as tin (Sn) which is provided from a fuel emitter. Although tin is referred to in the following description, any suitable fuel may be used. The fuel may for example be in liquid form, and may for example be a metal or alloy. The fuel emitter may comprise a nozzle configured to direct tin, e.g. in the form of droplets, along a trajectory towards a plasma formation region. The laser beam is incident upon the tin at the plasma formation region. The deposition of laser energy into the tin creates a plasma at the plasma formation region. Radiation, including EUV radiation, is emitted from the plasma during de-excitation and recombination of ions of the plasma.

[0075] The EUV radiation is collected and focused by a near normal incidence radiation collector (sometimes referred to more generally as a normal incidence radiation collector). The collector may have a multilayer structure which is arranged to reflect EUV radiation (e.g. EUV radiation having a desired wavelength such as 13.5 nm). The collector may have an elliptical configuration, having two ellipse focal points. A first focal point may be at the plasma formation region, and a second focal point may be at an intermediate focus, as discussed below.

[0076] The laser may be separated from the radiation source SO. Where this is the case, the laser beam may be passed from the laser to the radiation source SO with the aid of a beam delivery system (not shown) comprising, for example, suitable directing mirrors and/or a beam expander, and/or other optics. The laser and the radiation source SO may together be considered to be a radiation system.

[0077] Radiation that is reflected by the collector forms a radiation beam B. The radiation beam B is focused at a point to form an image of the plasma formation region, which acts as a virtual radiation source for the illumination system IL. The point at which the radiation beam B is focused may be referred to as the intermediate focus. The radiation source SO is arranged such that the intermediate focus is located at or near to an opening in an enclosing structure of the radiation source.

[0078] The radiation beam B passes from the radiation source SO into the illumination system IL, which is configured to condition the radiation beam. The illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. The faceted field mirror device 10 and faceted pupil mirror device 11 together provide the radiation beam B with a desired cross-sectional shape and a desired angular distribution. The radiation beam B passes from the illumination system IL and is incident upon the patterning device MA held by the support structure MT. The patterning device MA reflects and patterns the radiation beam B. The illumination system IL may include other mirrors or devices in addition to or instead of the faceted field mirror device 10 and faceted pupil mirror device 11.

[0079] Following reflection from the patterning device MA the patterned radiation beam B enters the projection system PS. The projection system comprises a plurality of mirrors 13, 14 which are configured to project the radiation beam B onto a substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the radiation beam, forming an image with features that are smaller than corresponding features on the patterning device MA. A reduction factor of 4 may for example be applied. Although the projection system PS has two mirrors 13, 14 in FIG. 1, the projection system may include any number of mirrors (e.g. six mirrors).

[0080] The radiation sources SO shown in FIG. 1 may include components which are not illustrated. For example, a spectral filter may be provided in the radiation source. The spectral filter may be substantially transmissive for EUV radiation but substantially blocking for other wavelengths of radiation such as infrared radiation.

[0081] In an embodiment the membrane assembly 15 is a pellicle for the patterning device MA for EUV lithography. The membrane assembly 15 of the present invention can be used for a dynamic gas lock or for a pellicle or for another purpose. In an embodiment the membrane assembly 15 comprises a membrane formed from the at least one membrane layer configured to transmit at least 90% of incident EUV radiation. In order to ensure maximized EUV transmission and minimized impact on imaging performance it is preferred that the membrane is only supported at the border.

[0082] If the patterning device MA is left unprotected, the contamination can require the patterning device MA to be cleaned or discarded. Cleaning the patterning device MA interrupts valuable manufacturing time and discarding the patterning device MA is costly. Replacing the patterning device MA also interrupts valuable manufacturing time.

[0083] In the method according to the sixth aspect of the present invention, the ratio (atomic or mass) of the matrix material to the inclusion material may be adjusted by adjusting the power applied to a sputtering target comprising the matrix material and/or adjusting the power applied to a sputtering target. The following description refers to a silicon matrix and molybdenum silicide crystal inclusions, but it will be appreciated that this is for example only and it is equally applicable to any combination of matrix material and inclusion material described herein.

[0084] Table 1 below demonstrates the difference in the amount of molybdenum silicide in a pellicle membrane and how it depends on the power applied to the molybdenum silicide target.

[0085] As can be seen from Table 1 below, by increasing the power applied to the molybdenum silicide target, it is possible to increase the density of the ultimate pellicle membrane and to also increase the vol% of molybdenum silicide in the pellicle membrane. The power applied to the silicon target is maintained, although it will be appreciated that the silicon target power may also be adjusted in other embodiments of the method.

TABLE-US-00001 MoSi.sub.2 target Power Si target power Density vol% MoSi.sub.2 75 W 500 W 3.06 g/cm.sup.3 18.5 100 W 500 W 3.28 g/cm.sup.3 24.0 125 W 500 W 3.46 g/cm.sup.3 28.7 250 W 500 W 4.02 g/cm.sup.3 43.0

The membrane created by the co-sputtering may be subjected to further processing steps as required, including but not limited to annealing. The method of co-sputtering the two target materials allows for the creation of deposited layer which has a residual stress after annealing of less than 1 GPa. As such, such a membrane is able to function as a free-standing pellicle membrane. This has not previously been possible with other methods.

EXAMPLES

[0086] The following examples provide specific embodiments of the present invention. These examples are not intended to be limiting to the scope of the invention.

Example 1 - MoSi Crystals in an Amorphous SiN Matrix

[0087] This pellicle membrane may be manufactured through reactive physical vapour deposition of a MoSi.sub.2 target in a nitrogen-rich environment. The membrane is subsequently annealed at a high temperature, particularly over at least 700° C. The annealing may take place at temperatures up to 1200° C., up to 1100° C., up to 1000° C., or up to 900° C. It will be appreciated that higher annealing temperatures could be used if required. The annealing step provides the membrane with its final density and forms the molybdenum silicide crystals which are randomly scattered within the SiN matrix. The SiN lowers the coefficient of thermal expansion (CTE) of the membrane such that during the annealing step, the difference in the CTE between the membrane and the silicon substrate wafer on which it is made is lowered. This results in the required amount of pre-stress in the membrane. The molybdenum silicide crystals provide the membrane with emissive properties which lower the operating temperature of the pellicle membrane in use. In this way, a membrane with a thickness of less than 25 nm can be provided which has an EUV transmissivity approaching 90% and which is able to withstand exposure to EUV radiation, hydrogen plasma and temperatures seen in scanner conditions using 600W power sources. Alternatively, the pellicle membrane is manufactured through co-sputtering of a molybdenum silicide target and a silicon nitride target, with the power applied to each target being adjusted to change the relative ratio of silicon nitride and molybdenum silicide in the ultimate membrane. As with the pellicle membrane manufactured through reactive physical vapour deposition, there may be a subsequent annealing step.

Example 2 - MoSi Crystals in a Polycrystalline Silicon (p-Si) Matrix

[0088] This pellicle membrane may be manufactured through co-sputtering (physical vapour deposition with multiple targets) using a molybdenum and a silicon target. It will be appreciated that it is also possible to use a molybdenum silicide target and a silicon target. It will be appreciated that it is also possible to use a single target containing molybdenum and silicon in a given ratio. The power provided to the targets may be selected to provide a silicon-rich deposition. After annealing, the molybdenum forms molybdenum silicide while the surplus of silicon forms p-Si resulting in the composite material. P- Si is highly transparent to EUV radiation, so it is possible to increase the thickness of the membrane to make it more physically robust with only a small sacrifice in EUV transmissivity. In this way, a membrane with a thickness of around 20 nm can be manufactured which has an EUV transmissivity of over 90%. If required, a slightly thicker membrane of around 40 nm in thickness can be produced, which still has an EUV transmissivity of around 90%. The thicker membrane requires a lower level of pre-stress in order to prevent sagging of the pellicle membrane.

Example 3 - MoSi Crystals in a SiC Matrix

[0089] The advantage of this combination is mainly EUV transmission. Carbon absorbs less EUV than Nitrogen and should give a ~3% EUVT benefit over MoSiN if all Nitrogen is replaced by Carbon.

Selection of Membrane Properties

[0090] The pellicle membrane can be characterised using a number of properties, for example: matrix density, matrix composition, inclusion concentration (e.g. vol% within matrix, and/or relative concentration of materials within the inclusions), inclusion composition, inclusion distribution, membrane thickness, membrane thickness variation, membrane porosity, amount of membrane pre-stress, membrane emissivity, membrane transmissivity, membrane sensitivity (e.g. sensitivity to temperature, pressure). External properties may also affect properties of the pellicle membrane, for example: fabrication method, and properties associated with the fabrication method e.g. the power applied to a sputtering target in a sputtering or co-sputtering method, annealing method (e.g. electron beam annealing, rapid thermal annealing), and properties associated with the annealing method e.g. annealing temperature, annealing heating gradient, properties associated with other processing steps, and the gas atmosphere in which a fabrication annealing, or other processing step takes place. Annealing may be considered a processing step.

[0091] Some properties, referred to herein as input properties, do not significantly depend on other properties. Input properties may be selected by a user as an input to the fabrication of a pellicle membrane. That is, input properties are independent variables relevant to the fabrication of a pellicle membrane. The input properties may be referred to as independent variables. Examples of input properties are matrix composition, inclusion composition, fabrication method.

[0092] Some properties, referred to herein as output properties, depend, at least partially, upon other properties. That is, output properties are dependent variables and may be referred to as such. Output properties thus cannot be directly selected, but may be achieved through selection of input properties. Output properties may depend on input properties only, may depend on other output properties only, or may depend on a combination of input and output properties. Examples of output properties are matrix density (which may depend at least on the power applied to a sputtering target) and pellicle transmissivity (which may depend on at least matrix density, matrix composition, membrane thickness). Output properties comprise properties of the membrane itself and can be referred to as membrane properties.

[0093] Input properties of the pellicle membrane can be selected so as to optimise the output properties of a pellicle membrane for a given application. Given the large range of properties, and the range of values each property may take, it is not practical to manufacture a pellicle membrane for each combination of properties and values thereof. Instead, modelling the properties of a membrane allows for the selection of an optimal set of properties for pellicle membrane for a given application. Using thermodynamic modelling, a large range of pellicle membranes may be virtually tested. That is, properties of membranes may determined without necessitating the entire process of fabrication and testing of such a membrane. Such a process of fabrication and testing of a membrane may be costly and/or time consuming (e.g. on the order of months). As a result, fabricating and testing membranes with different properties is even more costly and/or time consuming. By iteratively performing virtual testing, a large solution space may be scanned in order to determine an optimal set of properties for a given application, at a greatly reduced cost and/or duration. The determination of an optimal set of properties for a membrane may be referred to as designing a membrane.

[0094] Thermodynamic modelling, in particular semi-empirical thermodynamic modelling, can be used. Semi-empirical methods use some experimental data to validate thermodynamic calculations. The experimental data may comprise, for example, a single point of experimental data. Alternatively or additionally, the experimental data may comprise data from a catalogue or database of measured properties of a material e.g. a Gibbs energy database.

[0095] In a specific example, the CALculation of PHAse Diagrams (CALPHAD) is used. The CALPHAD methodology models the properties of constituent parts of a system and uses these to predict properties of the entire system. A CALPHAD software package is available at https://gtt-technologies.de/.

[0096] In an example method, an input property is scanned (that is, a parameter associated with an input property is varied incrementally from a first value to a second value) and an output parameter predicted for each value of said input property. For example, using the example of a pellicle membrane according to example 2 above (comprising MoSi crystals in a polycrystalline silicon (p-Si) matrix), the temp. The model outputs data comprising a predicted temperature sensitivity for each annealing temperature tested. From the output data, an optimal temperature sensitivity (e.g. the lowest predicted temperature sensitivity) may be identified, and thus an optimal annealing temperature associated with the optimal 3temperature sensitivity identified. This optimal annealing temperature may then be used in future fabrication processes in order to make a pellicle membrane with reduced temperature sensitivity.

[0097] The above method is a single input, single output modelling method. In another method, multiple outputs may be predicted. For example, the above described model may output data comprising a predicted temperature sensitivity for each annealing temperature and a predicted pellicle membrane transmissivity for each annealing temperature. That is, the output data is a multi-dimensional matrix of values. An optimal temperature sensitivity and/or an optimal transmissivity may be identified, and one or more corresponding optimal annealing temperatures may therefore be identified. One or more annealing temperatures may be identified which yield an acceptable temperature sensitivity and acceptable transmissivity. That is, a range of input values may be identified which yield an acceptable combination of output values.

[0098] The above method is a single input, multiple output modelling method. In another example, multiple inputs may be used. For example, using the same example of a pellicle membrane according to example 2, the temperature sensitivity of the pellicle is predicted for a range values of a set of input properties: annealing temperatures in the range 500 to 1000° C., heating gradients in the range 1° C. s.sup.-1 to 5° C. s.sup.-1, cooling gradient in the range 1° C. s.sup.-1 to 5° C. s.sup.-1 and different gas environments (hydrogen, nitrogen). The model outputs data comprising a predicted temperature sensitivity for each combination of values of each input property. That is, the output data is a multi-dimensional matrix of values. An optimal temperature sensitivity (e.g. the lowest predicted temperature sensitivity) may be identified from the output data, and thus optimal values of the set of input properties associated with the optimal temperature sensitivity identified.

[0099] Correspondingly, multiple input, multiple output modelling methods may be used. For example, using an example of a pellicle membrane comprising MoSiN (nitrogen doped MoSi) crystals in a matrix, the temperature sensitivity and pressure sensitivity (e.g. gas pressure) is predicted for a set of input properties: doping methods (e.g. co-sputtering, diffusion from sacrificial layers, implantation) and dopant concentrations (e.g. 0% to 5%). The output is a multi-dimensional matrix of values, from which an optimal set of input and output values or acceptable range of input and output values may be identified.

[0100] By outputting optimal input values, said outputted input values can be provided to a fabrication process, for example a membrane can be fabricated using said outputted input values. In this way, an optimised membrane may be fabricated using the design process described above. Alternatively, the outputted input and/or output values may be stored, or may be used as inputs to future design processes.

[0101] The above described modelling methods (i.e. design processes) are of particular use for the following use cases.

[0102] Sensitivity analysis. Pellicle membranes are typically sensitive to temperature and/or gas pressure. By modelling pellicle membranes with various properties, one or more optimal sets of input properties may be identified which may be used to generate a pellicle membrane with optimised (i.e. reduced) sensitivity. In particular, the following input properties are input to the model: inclusion composition and dopant concentration (e.g. relative concentration of N, Mo and Si in a pellicle membrane comprising MoSiN crystals in a matrix), annealing temperature, annealing gradient, annealing type, annealing atmosphere, pellicle membrane thickness, inclusion distribution (e.g. point defect engineering).

[0103] Identifying material combinations. A variety of materials can be used for the inclusions and/or matrix. Modelling as described above can be used to identify optimal combinations of materials. Optimal combinations are determined based on one or more optimal output properties or acceptable ranges of output properties, e.g. membrane transmission and/or stability characteristics. In particular, the following input properties are input to the model: inclusion composition (e.g. inclusion material such as C, Si, Mo, Ru, N, O, B, Hf, Zr, Nb, Y and relative concentrations therof), dopant concentration, fabrication method, doping method.

[0104] Optimising fabrication methods. By modelling properties of a pellicle membrane associated with a range of fabrication and/or processing methods, fabrication and processing methods (and optimal properties thereof) may be identified which optimise one or more properties of a pellicle membrane, without physically fabricating a large set of pellicles. In particular, the following input properties are input to the model: fabrication method, doping method, annealing method, annealing temperature, annealing gradient, gas atmosphere.

[0105] Considering the selection of an optimal property (or an acceptable property), an optimal or acceptable property may be determined in a number of ways. An optimal property may be determined by comparing the set of output properties predicted by the method, and selecting the optimal (for example largest or smallest) value. An optimal or acceptable property may be determined by comparing the set of output properties predicted by the model to a threshold value, and selecting all predicted output properties which exceed the threshold value.

[0106] Where reference is made to the prediction of an output property, it should be understood that the prediction may be a prediction of a value associated with the output property. Similarly, the provision of, or receipt of, an input property, this may comprise the provision or receipt of a value associated with the input property.

[0107] The modelling methods described herein may be implemented as instructions in a computer program. That is, the modelling methods may be computer-implemented. Such a computer program may be stored on a computer storage medium.

[0108] Although specific reference may be made in this text 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, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

[0109] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0110] The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.