MATERIAL

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 22181351.2 which was filed on June 27, 2022 and which is incorporated herein in its entirety by reference.

FIELD

[0002] The present invention relates to materials, methods and apparatuses for forming a patterned layer of 2D material.

BACKGROUND

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate.

[0004] To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.

[0005] There is a general desire to use 2D materials in ICs and this requires improvements to known techniques for forming 2D materials.

SUMMARY

[0006] According to a first aspect of the invention, there is provided a material for depositing on a substrate, the material comprising: an oxide of Tellurium, Transition metal telluride, and/or Transition metal dichalcogenide; and ligands for forming crosslinks in response to illumination by radiation.

[0007] According to a second aspect of the invention, there is provided a system for forming a pattern of 2D material on a surface, the system comprising one or more apparatuses configured to: deposit a precursor material on a surface, wherein the precursor material comprises one or more constituents for forming a 2D material on the surface and one or more constituents for forming crosslinks in response to illumination by radiation; illuminate the deposited precursor material with patterned radiation such that crosslinks form in the illuminated precursor material; perform a development process for removing precursor material that does not comprise crosslinks; perform one or more processes for removing constituents of the precursor material such that substantially only the one or more constituents for forming the 2D material remain; and perform a crystallization process for forming the 2D material on the surface.

[0008] According to a third aspect of the invention, there is provided a method of forming a pattern of 2D material on a surface, the method comprising: depositing a precursor material on a surface, wherein the precursor material comprises one or more constituents for forming a 2D material on the surface and one or more constituents for forming crosslinks in response to illumination by radiation; illuminating the deposited precursor material with patterned radiation such that crosslinks form in the illuminated precursor material; performing a development process for removing precursor material that does not comprise crosslinks; performing one or more processes for removing the constituents of the precursor material such that substantially only the one or more constituents for forming the 2D material remain; and performing a crystallization process for forming the 2D material on the surface.

[0009] According to a fourth aspect of the invention, there is provided a device comprising one or more layers of 2D material, wherein the device is manufactured according to the method of the third aspect.

[00010] According to a fifth aspect of the invention, there is provided a substrate at least partially coated with the material according to the first aspect.

[00011] According to a sixth aspect of the invention, there is provided a substrate with a 2D material formed thereon, wherein the 2D material is formed according to the method of the third aspect.

[00012] According to a seventh aspect of the invention, there is provided a substrate with a 2D material formed thereon, wherein the 2D material comprises Tellurium.

[00013] According to an eighth aspect of the invention, there is provided a substrate with a 2D material formed thereon, wherein the 2D material comprises one or more of Tellurene or atoms of a transition metal, M, covalently bonded with atoms of a chalcogen, Q, in the MQ2 form, such as MoTe2, M0S2, PtTe ₂ , WTe ₂ , WS ₂ , or WSe ₂ .

BRIEF DESCRIPTION OF THE DRAWINGS

[00014] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

- Figure 1 depicts a lithographic system comprising a lithographic apparatus and a radiation source;

- Figure 2A schematically shows a metal oxide nanocluster;

- Figure 2B schematically shows a metal oxide nanocluster during, or soon after, an EUV exposure process;

- Figure 2C schematically shows a plurality of metal oxide nanoparticles and ligands after a plurality of exposed metal oxide nanoclusters have condensed;

- Figure 3 schematically shows a MOSFET with the channel of the MOSFET made from a 2D material;

- Figure 4A schematically shows a substrate, with a patterned arrangement of structures, that has been coated with a precursor material; - Figure 4B schematically shows an EUV exposure process being performed;

- Figure 4C schematically shows remaining precursor material after a development process has been performed;

- Figure 4D schematically shows remaining constituents after the precursor material has been stripped;

- Figure 4E schematically shows constituents of 2D material after insertion and/or replacement processes have been performed;

- Figure 4F schematically shows a crystallized 2D material;

- Figure 5 schematically shows an exposure process arrangement for using a kinetic plasma to perform a crystallization process; and

- Figures 6A-6C schematically shows a number of different waveforms may be applied during the crystallization process.

DETAILED DESCRIPTION

[00015] Figure 1 shows a lithographic system comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and to supply the EUV radiation beam B to the lithographic apparatus LA. The lithographic apparatus LA 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.

[00016] The illumination system IL is configured to condition the EUV radiation beam B before the EUV radiation beam B is incident upon the patterning device MA. Thereto, 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 EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. 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.

[00017] After being thus conditioned, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B’ is generated. The projection system PS is configured to project the patterned EUV radiation beam B’ onto the substrate W. For that purpose, the projection system PS may comprise a plurality of mirrors 13,14 which are configured to project the patterned EUV radiation beam B’ onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B’, thus forming an image with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is illustrated as having only two mirrors 13,14 in Figure 1, the projection system PS may include a different number of mirrors (e.g., six or eight mirrors). [00018] The substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus LA aligns the image, formed by the patterned EUV radiation beam B’, with a pattern previously formed on the substrate W.

[00019] A relative vacuum, i.e. a small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, in the illumination system IL, and/or in the projection system PS.

[00020] The radiation source SO shown in Figure 1 is, for example, of a type which may be referred to as a laser produced plasma (LPP) source. A laser system 1, which may, for example, include a CO2 laser, is arranged to deposit energy via a laser beam 2 into a fuel, such as tin (Sn) which is provided from, e.g., a fuel emitter 3. 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 3 may comprise a nozzle configured to direct tin, e.g. in the form of droplets, along a trajectory towards a plasma formation region 4. The laser beam 2 is incident upon the tin at the plasma formation region 4. The deposition of laser energy into the tin creates a tin plasma 7 at the plasma formation region 4. Radiation, including EUV radiation, is emitted from the plasma 7 during deexcitation and recombination of electrons with ions of the plasma.

[00021] The EUV radiation from the plasma is collected and focused by a collector 5. Collector 5 comprises, for example, a near-normal incidence radiation collector 5 (sometimes referred to more generally as a normal-incidence radiation collector). The collector 5 may have a multilayer mirror structure which is arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 may have an ellipsoidal configuration, having two focal points. A first one of the focal points may be at the plasma formation region 4, and a second one of the focal points may be at an intermediate focus 6, as discussed below.

[00022] The laser system 1 may be spatially separated from the radiation source SO. Where this is the case, the laser beam 2 may be passed from the laser system 1 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 system 1, the radiation source SO and the beam delivery system may together be considered to be a radiation system.

[00023] Radiation that is reflected by the collector 5 forms the EUV radiation beam B. The EUV radiation beam B is focused at intermediate focus 6 to form an image at the intermediate focus 6 of the plasma present at the plasma formation region 4. The image at the intermediate focus 6 acts as a virtual radiation source for the illumination system IL. The radiation source SO is arranged such that the intermediate focus 6 is located at or near to an opening 8 in an enclosing structure 9 of the radiation source SO.

[00024] Although Figure 1 depicts the radiation source SO as a laser produced plasma (LPP) source, any suitable source such as a discharge produced plasma (DPP) source or a free electron laser (FEL) may be used to generate EUV radiation. [00025] The process of manufacturing semiconductors comprises coating a surface of the substrate with a resist. An exposure process may then be performed in which the surface coated by the resist is irradiated by the patterned EUV radiation beam. Photons in the patterned EUV radiation beam react with the resist to induce a change in the irradiated parts of the resist. A development process may then be performed in which either only the changed parts of the resist, or only the unchanged parts of the resist, are removed so that the surface of the substrate is coated with resist with a pattern that is dependent on the pattern of the EUV radiation beam. Further processes may then be performed to manufacture semiconductors in dependence on the pattern of the resist on the surface of the substrate. [00026] A known resist suitable for use with lithography is a chemically amplified resist (CAR) and may be based on polymers. Upon exposure to electromagnetic radiation, the polymers in the CAR absorb photons and secondary electrons may be generated. The generation of secondary electrons in the resist is how a high-energy photon loses most of its energy. The secondary electrons in the resist diffuse and may generate further secondary electrons with lower energies until the energy of the secondary electrons is lower than that required to break bonds in the CAR. The electrons generated excite photo-acid generators (PAGs) which subsequently decompose and can catalyse a de-blocking reaction that occurs on the polymer. This leads to a change in solubility of the CAR.

[00027] Alternative resists for use in lithography, in particular EUV lithography, comprise metal oxide nanoclusters. These resists comprise metal oxide nanoparticles which are prevented from clustering together by each metal oxide nanoparticle having a ligand shell. Upon EUV exposure, photons are absorbed by the nanoparticles and secondary electrons are generated that cause the metal oxide nanoparticles to cluster together. This changes the solubility of the exposed parts of the resist. A development process may then remove only the unexposed parts of the resist, or only the exposed parts of the resist. A metal oxide nanoparticle has a higher EUV absorption cross-section than the carbon atoms in a CAR and there is therefore a greater likelihood of EUV photons being absorbed. Accordingly, metal oxide based resists require a less intense EUV beam and/or a shorter exposure time. Furthermore, the different conversion mechanism has potentially lower chemical noise than CAR resist system.

[00028] The exposure process of a metal oxide resist is explained in more detail with reference to Figures 2A to 2C.

[00029] Figure 2A schematically shows a metal oxide nanocluster. The metal oxide cluster comprises a metal oxide nanoparticle 201 that is surrounded by ligands 202. The ligands 202 form a shell around the metal oxide nanoparticle 201. The metal oxide nanoparticle 201 may be, for example, tin oxide. Each ligand may be a polymer structure.

[00030] Figure 2B schematically shows the metal oxide nanocluster 201 during, or soon after, an EUV exposure process. A metal oxide nanoparticle 201 has absorbed an EUV photon and this has caused a photoelectron to be generated. The photoelectron further collides with atoms and has caused secondary electrons to be generated. The secondary electrons have caused the dissociation of at least one of the ligands 202 of a metal oxide nanoparticle 201 and an active site 203 has formed due to the dissociation. [00031] Figure 2C schematically shows a plurality of metal oxide nanoparticles 201 and ligands 202 after a plurality of exposed metal oxide nanoclusters have condensed. Oxygen bonds 204 may have formed between the active sites 203 so as to bond a plurality of metal oxide nanoclusters together. The plurality of bonded together metal oxide nanoclusters shown in Figure 2C may have a different solubility to the unexposed metal nanoclusters as shown in in Figure 2A. In particular, the plurality of bonded together metal oxide nanoclusters shown in Figure 2C may be insoluble in development fluid and therefore remain during a subsequently performed development process. However, unexposed metal nanoclusters may be soluble in development fluid and therefore removed during the development process.

[00032] To achieve the general goal of further scaling down the size of manufactured structures and components, 2D materials may be used. 2D materials are atomically thin flat layers and therefore have a very low height above the surface that they are formed on. A monolayer of a 2D material typically has a sub-nanometer thickness.

[00033] A potential use of 2D materials is as the channel of a MOSFET. A problem with the standard non-2D materials used for the channel of a MOSFET is that short channel effects, such as leakage due to tunneling, impose a limit to the minimum channel length. Forming the MOSFET channel from 2D materials enables channel lengths smaller than the limits imposed by conventional semiconductors, such as silicon.

[00034] Figure 3 schematically shows a MOSFET with the channel of the MOSFET made from a 2D material. The MOSFET comprises a substrate 301, 302. The substrate may comprise a layer of Silicon dioxide, SiO2, 302 on a layer of Silicon 301. Formed on the substrate 301, 302 may be the source 303 and drain 306 of the MOSFET, both of which may be metal layers. Also formed on the substrate 301, 302, between the source 303 and drain 306, is the channel 307 of the MOSFET. The channel 307 of the MOSFET is a layer of 2D material. An oxide layer 304 may be formed on the channel 307. The oxide layer 304 may be, for example, Hafnium dioxide, HfO2. Formed on the oxide layer 304 may be the gate 305 of the MOSFET, which is typically poly-Si or any conducting material. There are many other designs of MOSFET that may also use 2D materials. For example, di-electric may be provided on both sides of the channel and the die-electric may also be a 2D material, such as hBN.

[00035] The 2D material used for the channel of the MOSFET may be, for example, Molybdenum disulfide, M0S2. A single layer of M0S2 is a crystalline structure with a single layer of Molybdenum atoms arranged between two single layers of sulfur atoms. The height of the single layer of M0S2 may be about 0.65nm to Inm. Such a 2D material has semiconductor properties, a low relative dielectric constant and other properties that make it suitable for use as the channel of the MOSFET. When the channel of the MOSFET is made from a 2D material, the channel may be shorter than if standard non- 2D materials are used. Many other 2D materials may be used for the channel due to their semiconductor bandgap. For example, the 2D material may be WS2, WSe2, MoTe2, or other 2D materials.

[00036] A problem with the use of 2D materials in structures such as that shown in Figure 3 is that it is difficult to correctly form a patterned layer of 2D material. 2D materials are very sensitive and may be damaged by the standard patterning processes such as resist coating, lithography, etch and resist stripping.

[00037] WO2019166318A1 discloses resist-less direct patterned EUV deposition of 2D materials. However, a problem with the techniques described therein is that a very high EUV dose is required. The required EUV dose may be a lot larger than 100mJ/cm ² .

[00038] Although Chemical Vapor Deposition (CVD) may be used to grow 2D materials, the required temperature is too high for it to be compatible with other material processing steps in CMOS technology.

[00039] It is known for the crystal structure of a 2D material to be grown on a first substrate at high temperature and then for an exfoliation process to be performed so that the layer of 2D material is transferred to the surface of second substrate. However the exfoliation and transfer processes are slow, the required chemicals are expensive, the yield is low, and a lot of defects are introduced due to the low maturity level of the technology.

[00040] W02020207759A1 discloses a technique of direct EUV induced deposition. However, a large EUV exposure dose is still required. The EUV exposure dose may be at least 1.5 to 2 J/cm ² to deposit a monolayer of 2D material.

[00041] Embodiments solve at least some of the above problems by providing a new approach to forming 2D materials on surfaces such as a substrate.

[00042] Embodiments comprise including one or more constituents of a 2D material in a solid precursor material. The precursor material may be referred to as a resist matrix. The precursor material is a resist-type material and it adsorbs EUV photons in its bulk. The precursor material may be deposited, in a similar way to known techniques with a resist, on a surface, such as the surface of a substrate. The precursor material may then be patterned with EUV radiation. A development process may then be performed for removing the regions of the precursor material that were not illuminated by the EUV radiation. This leaves a patterned arrangement of remaining precursor material. An etch process may then be performed for removing the constituents of the remaining precursor material other than the desired one or more constituents for forming the 2D material. Insertion and/or replacement processes may then be performed to provide all of the required constituents of the 2D material. A process may then performed for crystallizing the constituents of the 2D material. A pattern of 2D material is thereby formed on a surface.

[00043] Advantageously, the required EUV dose may be no more than that required for standard EUV resist patterning. That is to say, the required EUV dose may be similar to that needed to pattern a metal oxide based resist. The required EUV dose may be less than or equal to about 100 mJ/cm ² . [00044] Embodiments are described in more detail below with reference to Figures 4A to 4F.

[00045] Figure 4 A schematically shows a substrate 401, W that has already had a patterned arrangement of structures 403 formed on it according to known techniques. The structures 403, and unpatterned regions of the substrate 401, W have been coated with a precursor material 402a. The precursor material 402a may have been deposited by, for example, chemical vapor deposition, CVD, AED, spin coating or other known techniques for depositing a resist.

[00046] The precursor material 402a may be a nanocluster with a similar, or the same, structure as the metal oxide nanocluster as described earlier with reference to Figures 2A to 2C. That is to say, the precursor material 402a may have a core 201, that may be a metal comprising core 201, that is surrounded by ligands 202. The ligands 202 form a shell around the core 201. Each ligand may be a polymer structure.

[00047] The core 201 may comprise, for example, one or more of an oxide of Tellurium (such as Tellurium oxide, Tellurium trioxide or, preferably, Tellurium dioxide), Transition metal telluride, or Transition metal dichalcogenide. Advantageously, the absorption of EUV photons by Tellurium is relatively high. A further advantage of using Tellurium in the core 201 is that the Tellurium may form part of the 2D material that is eventually produced. The 2D material may be, for example, MoTe2, WTe2, PtTe2 or Tellurene.

[00048] Figure 4B schematically shows an EUV exposure process being performed. During the EUV exposure process, the precursor material 402a is illuminated by patterned EUV radiation 404. The illuminated precursor material 402a absorbs EUV photons. This causes photoelectrons to be generated and the collision between photoelectrons and atoms causes secondary electrons to be generated. The secondary electrons cause the dissociation of the ligands 202 so that active sites 203 are formed in a process that is similar to, or the same as, the process shown in Figure 2B.

[00049] A plurality of the nanoclusters may then condense to form condensed precursor material 402b. The condensation process may be similar to, or the same as, the process shown in Figure 2C. The condensation process may comprise bonds 204 forming between the active sites 203 so as to bond a plurality of nanoclusters together. Each bond may be, for example, an Oxygen bond or a Tellurium bond.

[00050] A development process may then be performed. The condensed precursor material 402b may have a different solubility to the unexposed regions of precursor material 402a. In particular, the condensed precursor material 402b may be insoluble in development fluid and therefore not removed by the development process. The unexposed precursor material 402a may be soluble in development fluid and therefore removed during the development process. Figure 4C schematically shows the remaining precursor material 402b after the development process has been performed. The development process may be a wet development process.

[00051] Accordingly, an EUV induced deposition process may be used to form a pattern of the precursor material 402b. The content of each core 201 and/or the elements that bond the nanoclusters together following the condensation process may be substantially the only differences between the provision of a patterned precursor material 402b according to embodiments and the resist patterning techniques as described with reference to Figures 2A to 2C.

[00052] A process may then be performed for stripping the precursor material 402c so that substantially only the constituents that are required by the further processes for forming the 2D material remain. Figure 4D schematically shows the remaining constituents 402c after the precursor material 402b has been stripped. The remaining constituents 402c may be transition metal precursors or transition metal dichalcogenide precursors. The process for stripping the precursor material 402b may be an etching process and is preferably a selective dry etch process. The etching process may be radical based and comprise only chemical etching. There may be no bias voltage applied during the etching process so that there is no ion based etching.

[00053] One or more processes may then be performed for providing all of the constituents that are required for forming the 2D material. In particular, one or more processes may be performed for inserting a chalcogen. Each process for inserting a chalcogen may be a CVD process. The inserted chalcogen may be any of the elements in group 16 of the periodic table. For example, the inserted chalcogen may be Sulfur, Selenium or Tellurium. The chalcogen insertion process may not be required if the desired chalcogen for the 2D material was a constituent of the precursor material 402a. Additionally, or alternatively, one or more processes may be performed for replacing a constituent of the remaining precursor material 402c. Each process for replacing a constituent may be a CVD process. The metal inserted by the replacement process may, for example, any of Molybdenum, Tungsten, Palladium, Platinum, Zirconium or Tin. For example, if the remaining precursor material 402c comprises Tin, that may be in the form of Tin oxide, a process may be performed for replacing the Tin with Molybdenum.

[00054] Figure 4E schematically shows the constituents of the 2D material 402d after the above described insertion and/or replacement processes have been performed. The constituents of the 2D material 402d may not currently be in a crystalline form. A further process may therefore be performed for re-arranging the constituents of the 2D material 402d into a crystalline structure so as to form crystallized 2D material 402e as schematically shown in Figure 4F.

[00055] A number of different processes may be performed for forming the 2D material into a crystalline structure. For example, a temperature based crystallization process, such as annealing, may be performed.

[00056] Preferably, the crystallization process is performed by using a kinetic plasma with ion energy control provided by a tailored waveform.

[00057] Figure 5 schematically shows the configuration of an exposure process arrangement for using a kinetic plasma to perform the crystallization process.

[00058] The exposure process arrangement comprises a substrate W. The substrate W comprises a substrate body 505. The substrate body 505 may have on it a patterned layer 504 of the constituents of the 2D material 402d that are initially not in a crystallized form. The substrate body 505 may be secured to a substrate table 507 by an electrostatic clamp 506.

[00059] The patterned layer 504 of the constituents of the 2D material 402d may be arranged so that at least part of it may be illuminated by EUV radiation. The path of the EUV radiation may be orthogonal to the major surfaces of the substrate W. An illumination region 502 may be defined between a grounded wall 501 and the exposed major surface of the substrate W. When the exposed major surface of the substrate W is illuminated, EUV radiation may pass through one or more openings in the grounded wall 501 and through the illumination region 502.

[00060] The exposure process arrangement may further comprise a matching box 508 and a power supply arrangement 514. The power supply arrangement 514 may comprise a switch 509, a ground terminal 510, a sinusoidal waveform generator 511 and a flexible waveform generator 512. The switch 509 may control the type of waveform that is output by the power supply arrangement 514. When the switch 509 is applied to the sinusoidal waveform generator 511 or the flexible waveform generator 512, the output of the power supply arrangement 514 may be an AC voltage. An AC voltage output from the power supply arrangement 514 may generate an alternating electric field 513 in the patterned layer 504 of the constituents of 2D material 402d. The direction of the alternating electric field 513 in the patterned layer 504 of the constituents of 2D material 402d may be substantially orthogonal to the major surfaces of the substrate W. The direction of the alternating electric field 513 in the patterned layer 504 of the constituents of 2D material 402d may therefore be substantially in line with, or parallel to, the path of the EUV radiation that illuminates the exposed major surface of the substrate W.

[00061] The alternating electric field 313 in the patterned layer 504 of the constituents of 2D material 402d may cause the 2D material to crystallize into a layer of crystallized 2D material 402e.

[00062] A number of different waveforms may be applied to generate the alternating electric field 313. Figures 6A and 6B show sinusoidal waveforms with different frequencies that may be applied. Preferably, a tailored waveform such as that shown in Figure 6C is applied. Such a tailored waveform may be configured to apply an appropriate energy for re-arranging atoms so as to appropriately form the crystallized 2D material 402e.

[00063] The above described exposure process arrangement, that is shown in Figure 5, and the use of the waveforms shown in Figure 6A to 6C have already been described in a document published by QUESTEL RESEARCH DISCLOSURE. The document published by QUESTEL RESEARCH DISCLOSURE, which is incorporated herein in its entirety by reference, is titled ANISOTROPIC RESIST PATTERNING, the database number is 696059, the digital publication date is 15 March 2022, and the time stamp is 758220ea9fc74fcd8b575d26da52c3ea222304b25153c8e7cl76308ceebf lc57. A link to the document is: https://www.researchdisclosure.com/database/RD696059 (as viewed on 13 June 2022).

[00064] Accordingly, embodiments provide a new technique for forming a patterned layer of a 2D material on a surface, such as the surface of a substrate 401, W. Advantageously, the required EUV dose may be substantially less than that required by known EUV based techniques for forming patterned 2D materials.

[00065] The formed 2D material may comprise atoms of a transition metal, M, and atoms of a chalcogen, Q. M may be from any of groups IV, V or VI of the periodic table. Q may be any chalcogen, such as Sulfur, Selenium and Tellurium. The M and Q atoms may form a covalently bonded 2D layer of the MQ2 type with a hexagonal lattice.

[00066] Embodiments include a number of modifications and variations to the above-described techniques.

[00067] Embodiments include more than one apparatus, or tool, being used in the formation of the 2D material. In particular, the process for crystallizing the constituents of the 2D material may be performed in a separate apparatus, or separate tool, from the apparatus, or tool, that illuminates the deposited precursor material with patterned radiation.

[00068] In the above described embodiments, EUV radiation is used to illuminate the deposited precursor material. Embodiments also include radiation with wavelengths other than EUV being used in the formation the 2D material. For example, embodiments include illuminating the precursor material with DUV radiation. The type of precursor material that is used may be dependent on the wavelength of the radiation that illuminates it. Accordingly, the precursor material used with DUV radiation may be different from that used with EUV radiation, so that the bulk of the precursor material efficiently absorbs the DUV radiation. Similarly, different development and/or stripping processes may be performed that are appropriate for the used precursor material.

[00069] In the above-described embodiments, only the precursor material that has been illuminated remains after the development process. Embodiments also include using a different precursor material such that the regions of the precursor material that were illuminated are removed the development process, and the regions of the precursor material that were not illuminated are not removed by the development process.

[00070] Embodiments have described the formation of a single layer of 2D material. Embodiments also include the described techniques being used to form a multi-layer material and/or a plurality of overlapping layers of 2D material.

[00071] Embodiments are not restricted to forming a pattern with a specific type of 2D material, or for the patterned 2D material being for the specific purpose of providing the channel of a MOSFET. Embodiments include the formation of a patterned arrangement of a number of different types of 2D material for any purpose. For example, embodiments include forming patterned arrangements of 2D materials for use as metal caps or diffusion barrier interconnectors. There are a number of different types of 2D material that include electrical insulators, semiconductors, half-metals, semi-metals, metals, and superconductors. Embodiments include forming a pattern of any type of 2D material as is required given the purpose of the 2D material in the manufactured device. [00072] Figures 4A to 4F show the formation of a layer of 2D material on a substrate 401, W that already has a patterned arrangement of structures formed on it. Embodiments also include forming a layer of 2D material on the surface of a substrate that does not already have structures formed on it.

[00073] Embodiments include the core 201 of the precursor material alternatively, or additionally, comprising one or more of Molybdenum, Tungsten, Palladium, Platinum, Zirconium, Tin or oxides thereof. The core 201 may alternatively, or additionally, comprise other transition metals and/or oxides thereof.

[00074] Embodiments include the following numbered clauses:

1. A material for depositing on a substrate, the material comprising: an oxide of Tellurium, Transition metal telluride, and/or Transition metal dichalcogenide; and ligands for forming crosslinks in response to illumination by radiation.

2. The material according to clause 1, wherein the ligands form crosslinks in response to illumination by extreme ultraviolet, EUV, radiation.

3. The material according to clause 1 or 2, wherein the Transition metal telluride comprises one or more of Molybdenum telluride, Tungsten telluride or Platinum telluride.

4. A system for forming a pattern of 2D material on a surface, the system comprising one or more apparatuses configured to: deposit a precursor material on a surface, wherein the precursor material comprises one or more constituents for forming a 2D material on the surface and one or more constituents for forming crosslinks in response to illumination by radiation; illuminate the deposited precursor material with patterned radiation such that crosslinks form in the illuminated precursor material; perform a development process for removing precursor material that does not comprise crosslinks; perform one or more processes for removing constituents of the precursor material such that substantially only the one or more constituents for forming the 2D material remain; and perform a crystallization process for forming the 2D material on the surface.

5. The system according to clause 4, wherein the one or more constituents of the precursor material for forming crosslinks form crosslinks in response to illumination by extreme ultraviolet, EUV, radiation; and the one or more apparatuses are configured to illuminate the deposited precursor material with patterned EUV radiation such that crosslinks form in the illuminated precursor material.

6. The system according to clause 4 or clause 5, wherein, before the crystallization process is performed, an apparatus of the system is configured to further perform an insertion process for inserting a constituent of the 2D material to be formed on the surface.

7. The system according to clause 6, wherein system comprises a chemical vapor deposition, CVD, apparatus configured to perform the insertion process. 8. The system according to any of clauses 5 to 7, wherein, before the crystallization process is performed, an apparatus of the system is configured to further perform a replacement process for replacing one or more of the constituents for forming the 2D material.

9. The system according to clause 8, wherein system comprises a chemical vapor deposition, CVD, apparatus configured to perform the replacement process.

10. The system according to any of clauses 5 to 9, wherein the system comprises a wet development process apparatus configured to remove the precursor material that does not comprise crosslinks.

11. The system according to any of clauses 5 to 10, wherein the system comprises a dry etching apparatus and/or a chemical etching apparatus configured to remove constituents of the precursor material such that substantially only the one or more constituents for forming the 2D material remain.

12. The system according to any of clauses 5 to 11, wherein the system comprises an apparatus configured to perform temperature based crystallization for forming the 2D material.

13. The system according to any of clauses 5 to 12, wherein the system comprises an apparatus configured to use a kinetic plasma with ion energy control to crystallize the 2D material.

14. The system according to any of clauses 5 to 13, wherein the deposited precursor material comprises an oxide of Tellurium, Transition metal telluride, and/or Transition metal dichalcogenide.

15. The system according to clause 14, wherein the Transition metal telluride is Molybdenum telluride, Tungsten telluride or Platinum telluride.

16. The system according to any of clauses 5 to 15, wherein the deposited precursor material is the material according to any of clauses 1 to 3.

17. The system according to any of clauses 5 to 16, wherein the formed 2D material comprises atoms of a transition metal, M, and atoms of a chalcogen, Q.

18. The system according to clause 17, wherein the M and Q atoms form a covalently bonded 2D layer of the MQ2 type.

19. A method of forming a pattern of 2D material on a surface, the method comprising: depositing a precursor material on a surface, wherein the precursor material comprises one or more constituents for forming a 2D material on the surface and one or more constituents for forming crosslinks in response to illumination by radiation; illuminating the deposited precursor material with patterned radiation such that crosslinks form in the illuminated precursor material; performing a development process for removing precursor material that does not comprise crosslinks; performing one or more processes for removing the constituents of the precursor material such that substantially only the one or more constituents for forming the 2D material remain; and performing a crystallization process for forming the 2D material on the surface.

20. The method according to clause 19, wherein the one or more constituents of the precursor material for forming crosslinks form crosslinks in response to illumination by extreme ultraviolet, EUV, radiation; and the illumination of the deposited precursor material is with patterned EUV radiation such that crosslinks form in the illuminated precursor material.

21. The method according to clause 20, wherein, before performing the crystallization process, the method further comprises performing an insertion process for inserting a constituent of the 2D material to be formed on the surface.

22. The method according to clause 21, wherein the insertion process is a chemical vapor deposition, CVD, process.

23. The method according to any of clauses 19 to 22, wherein, before performing the crystallization process, the method further comprises performing a replacement process for replacing one or more of the constituents for forming the 2D material.

24. The method according to clause 23, wherein the replacement process is a chemical vapor deposition, CVD, process.

25. The method according to any of clauses 19 to 24, wherein the development process for removing precursor material that does not comprise crosslinks is a wet development process.

26. The method according to any of clauses 19 to 25, wherein the one or more processes for removing the constituents of the precursor material such that substantially only the one or more constituents for forming the 2D material remain comprises a dry etching process and/or a chemical etching process.

27. The method according to any of clauses 19 to 26, wherein performing a crystallization process for forming the 2D material on the surface comprises performing a temperature based crystallization process.

28. The method according to any of clauses 19 to 27, wherein performing a crystallization process for forming the 2D material on the surface uses a kinetic plasma with ion energy control.

29. The method according to any of clauses 19 to 28, wherein the deposited precursor material comprises an oxide of Tellurium, Transition metal telluride and/or Transition metal dichalcogenide.

30. The method according to clause 29, wherein the Transition metal telluride is Molybdenum telluride, Tungsten telluride or Platinum telluride.

31. The method according to any of clauses 19 to 30, wherein the deposited precursor material is the material according to any of clauses 1 to 3.

32. The method according to any of clauses 19 to 31, wherein the formed 2D material comprises atoms of a transition metal, M, and atoms of a chalcogen, Q.

33. The method according to clause 32, wherein the M and Q atoms form a covalently bonded 2D layer of the MQ2 type.

34. A device comprising one or more layers of 2D material, wherein the device is manufactured according to the method of any of clauses 19 to 33.

35. A substrate at least partially coated with the material according to any of clauses 1 to 3.

36. A substrate with a 2D material formed thereon, wherein the 2D material is formed according to the method of any of clauses 19 to 33. 37. The substrate according to clause 36, wherein the formed 2D material comprises atoms of a transition metal and atoms of a chalcogen.

38. The substrate according to clause 36 or 37, wherein the formed 2D material comprises one or more of Tellurene or atoms of a transition metal, M, covalently bonded with atoms of a chalcogen, Q, in the MQ2 form, such as MoTe2, M0S2, PtTe2, WTe2, WS2, or WSe2.

39. A substrate with a 2D material formed thereon, wherein the 2D material comprises Tellurium.

40. The substrate according to clause 39, wherein the 2D material is formed according to the method of any of clauses 19 to 33.

41. A substrate with a 2D material formed thereon, wherein the 2D material comprises one or more of Tellurene or atoms of a transition metal, M, covalently bonded with atoms of a chalcogen, Q, in the MQ2 form, such as MoTe2, M0S2, PtTe2, WTe2, WS2, or WSe2.

42. The substrate according to clause 41, wherein the 2D material is formed according to the method of any of clauses 19 to 33.

[00075] 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. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquidcrystal displays (LCDs), thin-film magnetic heads, etc.

[00076] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. 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.