GRAPHENE PELLICLE LITHOGRAPHIC APPARATUS

Abstract

A catalyst including: a first layer including a transition metal; a base layer; and an interlayer, wherein the interlayer is disposed between the base layer and the first layer is disclosed. Also disclosed are methods for preparing a catalyst as well as for synthesizing graphene, a pellicle produced using the catalyst or methods disclosed herein, as well as a lithography apparatus including such a pellicle.

Claims

1. A catalyst comprising: (i) a first layer comprising a transition metal; (ii) a base layer; and (iii) an interlayer, wherein the interlayer is disposed between the base layer and the first layer.

2. The catalyst according to claim 1, wherein the transition metal in the first layer is selected from Mo, W, Pt, Cu or Ni.

3. The catalyst according to claim 1, wherein the interlayer comprises a metal oxide and/or a metal silicide and/or carbon.

4. The catalyst according to claim 3, wherein the interlayer comprises a metal oxide and the metal oxide is zirconium dioxide or wherein the interlayer comprises a metal silicide and the metal silicide comprises molybdenum silicide.

5.-7. (canceled)

8. The catalyst according to claim 1, wherein the first layer comprises elemental molybdenum and/or molybdenum carbide.

9. A method of preparing a catalyst, the method comprising: (i) providing an interlayer comprising a metal oxide, metal silicide, and/or carbon on a base layer; and (ii) providing a first layer comprising a transition metal.

10.-12. (canceled)

13. A method of synthesising graphene, the method comprising: (i) depositing carbon onto a surface of the catalyst according to claim 1; and (ii) forming a graphene layer on the catalyst.

14.-29. (canceled)

30. A method comprising synthesising graphene and using the catalyst according to claim 1 in the synthesis of the graphene.

31. (canceled)

32. A multi-layered pellicle stack comprising layers of amorphous carbon, graphene, a carbide of a transition metal, SiO.sub.2 and c-Si.

33. The multi-layered pellicle stack according to claim 32, wherein the transition metal is selected from Mo, W, Pt, Cu or Ni.

34. The multi-layered pellicle stack according to claim 32, further comprising a capping layer.

35. The multi-layered pellicle stack according to claim 34, wherein the capping layer comprises at least one of: molybdenum, aluminium, ruthenium and molybdenum, molybdenum and boron, zirconium and boron, yttrium and boron, lanthanum and boron, zirconium boride, molybdenum boride, yttrium boride, molybdenum silicide, yttrium silicide, zirconium dioxide, molybdenum oxide, yttrium oxide, diamond-like carbon, niobium oxide, carbon nitride, silicon nitride, molybdenum carbide, zirconium carbide, yttrium carbide, silicon carbide, zirconium nitride, or aluminium oxide.

36. The multi-layered pellicle stack according to claim 34, wherein the layer of graphene is below the capping layer.

37. A pellicle comprising graphene produced according to the method according to claim 13.

38. The pellicle according to claim 37, further comprising a capping layer and a pellicle core.

39. The pellicle according to claim 38, wherein the capping layer comprises at least one of: molybdenum, aluminium, ruthenium and molybdenum, molybdenum and boron, zirconium and boron, yttrium and boron, lanthanum and boron, zirconium boride, molybdenum boride, yttrium boride, molybdenum silicide, yttrium silicide, zirconium dioxide, molybdenum oxide, yttrium oxide, diamond-like carbon, niobium oxide, carbon nitride, silicon nitride, molybdenum carbide, zirconium carbide, yttrium carbide, silicon carbide, zirconium nitride, or aluminium oxide.

40. The pellicle according to claim 38, wherein the capping layer comprises one or more of: ruthenium, molybdenum, boron, yttrium, lanthanum, boron, zirconium, carbon, niobium, silicon, aluminium, nitrogen, or oxygen.

41. The pellicle according to claim 40, wherein the capping layer is selected from one or more of: ruthenium, aluminium, ruthenium and molybdenum, molybdenum and boron, zirconium and boron, yttrium and boron, or lanthanum and boron.

42.-44. (canceled)

45. The pellicle according to claim 37, wherein the pellicle core comprises graphene produced according to the method of claim 13.

46. A lithography apparatus comprising the pellicle according to any claim 37.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0060] FIG. 1 depicts a lithographic system comprising a lithographic apparatus and a radiation source;

[0061] FIG. 2 depicts a schematic cross section through a catalyst according to the present invention showing an interlayer;

[0062] FIGS. 3a and 3b show a comparison of the surface of a multilayer graphene layer produced using a catalyst of the prior art and a catalyst according to the present invention; and

[0063] FIG. 4 depicts a schematic cross section through a catalyst comprising an amorphous carbon layer according to the present invention.

DETAILED DESCRIPTION

[0064] FIG. 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.

[0065] 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.

[0066] 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 FIG. 1, the projection system PS may include a different number of mirrors (e.g. six or eight mirrors).

[0067] 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.

[0068] 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.

[0069] The radiation source SO may be a laser produced plasma (LPP) source, a discharge produced plasma (DPP) source, a free electron laser (FEL) or any other radiation source that is capable of generating EUV radiation.

[0070] Although EUV reticles are referred to in the following description, any suitable patterning device MA may be used.

[0071] Example of stacks preparation according to the invention:

p-type Si (100) wafers having resistivity between 20-30 cm covered with a film of thermally grown SiO.sub.2 with thickness of 500 nm were used as base substrate. On top of the Si wafers, a double layer, either Mo on top of a-C or a-C on Mo, was deposited resulting in 4 samples. Samples 1 and 2 had Mo on top of the a-C layer. Sample 1 had a carbon layer of 500 nm and a Mo layer of 20 nm. Sample 2 had a carbon layer of 40 nm and a Mo layer of 20 nm. The order of layers in the stack of samples 1 and 2 was: Mo, a-C, SiO2, c-Si. Samples 3 and 4 had a-C on top of Mo. Sample 3 had a carbon layer of 500 nm and a Mo layer of 50 nm. Sample 4 had a carbon layer of 40 nm and a Mo layer of 50 nm. The order of layers in the stack of samples 3 and 4 was: a-C, Mo, SiO2, c-Si. The Mo and a-C layers were sputtered at room temperature from targets having purity equal to 6N5 and 4N for Mo and C, respectively. To grow graphene, a thermal anneal up to 915 C. was performed. The anneal gas consisted of an Ar and H.sub.2 mixture at a pressure of 25 mbar.

[0072] The temperature profile had a ramp profile in three stages and started with a first stage slow ramp up to 915 C. in order to reduce thermal stress in the Si and Mo layers. The first stage was the fastest one with a rate of 200 C./min, rising from room temperature to 525 C. It was followed by a second stage having a slower ramp rate (50 C./min) till 725 C. The third ramp up rate was 30 C./min and lasted until the final temperature (915 C.) was reached. A 1 minute interval for temperature stabilization was included in between ramp up stages. The growth was performed at 915 C. for different time windows. The cooling down consisted of a rate of a controlled cooling rate of 25 C./min till 525 C. before completely switching off the heater. Because of the thermal inertia, the cooling down had an exponential profile. The annealing was carried out in a mixture of Ar and H.sub.2. By varying the ratio of the two gases and/or the growth time, the influence of the gas atmosphere on the growth process was investigated. Table 1 shows the corresponding recipes.

[0073] It has been observed for all four samples that graphene growth happens with the catalyst layer sputtered either above or below an a-C layer. The growth mechanism consisted of the diffusion of a-C inside the catalyst layer, followed by C segregation and graphene formation on top of Mo layer. For samples 1 and 2 which started with the Mo layer on top of the a-C layer, after annealing the order of layers in the stack became: graphene, Mo.sub.2C, a-C, SiO.sub.2, c-Si. For samples 3 and 4 which started with the Mo layer beneath the a-C layer, after annealing the order of layers in the stack became: a-C, graphene, Mo2C, SiO2, c-Si.

TABLE-US-00001 TABLE 1 Recipes for graphene growth Composition of Ar/H.sub.2 Growth temperature Growth time atmosphere Recipe [ C.] [min] [sccm] 1 915 90 960/40 2 915 60 960/40 3 915 30 960/40 4 915 90 0/1000 5 915 60 0/1000 6 915 30 0/1000 7 915 90 1000/0

[0074] The highest quality of graphene, proved through Raman spectroscopy and cross-sectional transmission electron microscopy TEM, was obtained for sample 1 with a 20 nm-thick Mo layer deposited on a 500 nm-thick a-C film. Based on Raman spectroscopy results it was found that the quality of the graphene layers was at least as good as that obtained in conventional CVD deposition with gaseous hydrocarbon sources. The minimum temperature used to grow graphene was around 900 C.

[0075] In a further embodiment of the invention, it was found advantageous to grow graphene using an intermediate anneal step, thereby splitting the anneal process in two stages: 1) a first anneal step of the stack of layers at a temperatures of around 700 C. in order to create a carbide of the transition metal catalyst; and thereafter 2) a second anneal step for growing the graphene layer by annealing the stack of layers at around 900 C. It is presumed that such an intermediate anneal step (the first anneal step) allows a better redistribution of the stresses in the stack layers.

[0076] FIG. 2 depicts a schematic illustration of a catalyst according to the present invention. The catalyst comprises a base layer 15, an interlayer 16 and a first layer 17. The interlayer 16 is deposited between the base layer 15 and the first layer 17 such that interlayer 16 is disposed between the base layer 15 and the first layer 17.

[0077] The base layer 15 may be any suitable material, but preferably comprises silicon and more preferably is a silicon wafer. The base layer 15 may comprise a silicon dioxide layer (not shown), which may be referred to as a thermal oxide layer. The interlayer 16 and the thermal layer are preferably different.

[0078] In use, a carbon source is provided and the catalyst is heated to a temperature required to carbonise or graphitize the carbon source. As the carbon is deposited on the surface of the catalyst, it forms graphene layers. The length of time can be adjusted to result in thicker or thinner graphitic layers.

[0079] FIG. 3a shows an optical microscope image at 100 magnification of a graphene layer produced using a known catalyst without an interlayer and FIG. 3b shows an optical microscope image at 100 magnification of a graphene layer produced using a catalyst of the present invention comprising an interlayer. It is clear that the graphene produced according to the present invention shows much greater uniformity. In addition, the graphene layer is produced much more quickly than when using a catalyst of the prior art, which leads to shortened production time and decreased thermal energy requirements.

[0080] FIGS. 4a and 4b show two options for depositing amorphous carbon on a catalyst. In particular, FIG. 4a shows the embodiment in which the amorphous carbon 18 is deposited on top of a molybdenum layer 19. The molybdenum may be supported on a base layer 20 and there may be an interlayer (not shown) between the base layer 20 and the molybdenum layer 19. There may also be a thermal oxide (silicon dioxide layer) (not shown) on the surface of the base layer 20. FIG. 4b shows the embodiment in which the amorphous carbon 18 is disposed between the molybdenum layer 19 and the base layer 20, which may comprise silicon. The catalyst may be the catalyst according to any aspect of the present invention.

[0081] In use, amorphous carbon is deposited by any suitable means, such as sputtering. The catalyst comprising the amorphous carbon is heated for a period of time sufficient to result in conversion of at least a portion of the amorphous carbon into graphene.

[0082] It was found furthermore that for the graphene growth method according to the invention other transition metals, such as W, Pt, Cu and Ni, were also suitable as catalyst layers. From the point of view of graphene quality and for the pellicle fabrication process flow it was found that Mo catalysts provided especially good results.

[0083] Even more surprisingly, it was also found that in the method according to the invention it was possible to first deposit a capping layer (e.g. SiC) on the top of the stack of layers comprising a-C/Mo and then grow graphene without CVD under the capping layer. Such approach allowed eliminating the influence of the atmosphere in the deposition chamber on graphene growth. This allowed to avoid damaging of the graphene layer that could occur by deposition of the capping layer (i.e. when the capping layer would be deposited after the graphene growth). Although not yet fully understood in terms of the reaction mechanism, it was found that graphene grown under the capping layer using the method of this invention shows a higher quality, which is detected by a lower defect peak in Raman spectra. Examples of capping layers that may be applied according to the present invention include, but are not limited to capping layers comprising zirconium boride, molybdenum boride, yttrium boride, molybdenum silicide, yttrium silicide, zirconium dioxide, molybdenum oxide, yttrium oxide, diamond-like carbon, niobium oxide, carbon nitride, silicon nitride, molybdenum carbide, zirconium carbide, yttrium carbide, silicon carbide, zirconium nitride, or aluminium oxide.

[0084] 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. In particular, features disclosed in respect of one aspect of the present invention may be combined with any other aspect of the present invention.

[0085] Although specific reference may be made in this text to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or mask (or other patterning device). These apparatus may be generally referred to as lithographic tools. Such a lithographic tool may use vacuum conditions or ambient (non-vacuum) conditions.

[0086] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention, where the context allows, is not limited to optical lithography and may be used in other applications, for example imprint lithography.