System and method for generation of lithography patterns

Abstract

A lithography pattern generation system (1) and method configured to generate a pattern (51) of features (f) on a pattern target (5), wherein the system (1) comprises; - a mask (4) comprising through holes (3) configured to be arranged in an incoming particle beam (21), wherein the lithography pattern generation system (1) is configured to generate the pattern (51) a target distance (L2) from the mask (4) on the opposite side of the incoming particle beam (21), wherein the target distance L2 is sufficiently small to allow a majority of the intensity from transmitted beam fractions from one or more of the holes (3) to participate in creation of the features (f).

Description

SYSTEM AND METHOD FOR GENERATION OF LITHOGRAPHY PATTERNSTECHNICAL FIELD

[0001] The present invention relates to microlithography and the manufacture of integrated circuits and other devices, for example quantum devices which cannot be mass produced with existing technology. More specifically it is related to exposing a mask with a particle beam, generating a particle pattern based on the information coded into the mask and exposing a target, such as a resist on a silicon wafer with the particle pattern.BACKGROUND

[0002] The fabrication of integrated circuits is currently based on pattern generation using mask-based photolithography: An enlarged version of the desired chip pattern or part of the desired chip pattern is printed on a substrate (photomask). The pattern on the mask may be distorted compared to the target pattern to account for aberration effects, optical proximity corrections etc.. Light (photons) are transmitted through or reflected off the photomask using optical components (refractive or reflective lenses) to create a demagnified image of the target pattern on a silicon wafer. The silicon wafer is coated with a photosensitive material (resist), which reacts with the photons thus creating a permanent imprint of the image in the resist. This is then used as a physical mask in the following fabrication steps. The two main light sources used in the semiconductor industry today are Deep Ultraviolet Light (DUV) which has a wavelength of 193 nm and Extreme Ultraviolet Light (EUV) which has a wavelength of 13.5 nm.

[0003] The standing aim is to create patterns with smaller and smaller feature sizes at higher and higher information densities, commonly referred to as minimum pitch - the smallest distance between the centres of two features. For a standard optical system, the smallest pitch that can be obtained is half the wavelength of the projecting beam, when the process is performed in air or vacuum (refractive index 1, the Abbe criterion). The performance of DUV is further pushed by using wavefront engineering techniques such as phase shifting masks, off-axis illumination, or optical proximity correction, achieving a minimum pitch of ~30% of the wavelength. The ultimate pitch in DUV lithography is achieved using the Immersion Lithography technique, where a high- refractive index fluid is introduced between the final lens and the wafer. Combining these techniques allows DUV to operate at an effective wavelength of ~135 nm, leading to a minimum pitch of around 38 nm. Additional pitch reduction requires multiple exposures to create one chip pattern, thus decreasing throughput and increasing complexity.

[0004] The state-of-the-art is extreme ultraviolet (EUV) photolithography, which, with photons (electromagnetic waves) of a wavelength of 13.5 nm, should be able to produce patterns with a minimum pitch or minimum feature size of around 6.75 nm according to the Abbe criterion with a refractive index of 1 (vacuum).

[0005] However, due to the high energy of the photons in EUV lithography, the pattern generation process in the resist is mediated by photo-generated secondary electrons, which can travel for several nm before inducing a reaction. Current experiments and theory indicate that the secondary electron blur radius for EUV is around 3 nm, which would limit the feature size that can be achieved to around 6 nm. This means that quantum devices based on small quantum dots and individual atoms and molecules cannot be produced with EUV. Moving to wavelengths even shorter than 13.5 nm, would just exacerbate the secondary electron issue.

[0006] In Berggren, K.K., Bard, A., Wilbur, J.L., Gillaspy, J.D., Helg, A.G., McClelland, J. J., Rolston, S.L., Phillips, W.D., Prentiss, M., Whitesides, G.M. : Microlithography by Using Neutral Metastable Atoms and Self-Assembled Monolayers. Science 269(5228), 1255-1257 (1995) https:Z7arxiv.Org / abs / htps: / / www.science.org / doi / pdf / 10.1126 / science.7652572. https: / / doi.org / 10.1126 / sdence.7652572, lithography with metastable atoms is proposed as an alternative to photolithography. Pattern generation in a thiol-based resist is demonstrated in a proximity lithography setup using a beam of metastable argon atoms transmitted through a grating supported on the substrate. In other experiments patterns have been generated with metastable atoms using light masks, in some case with the atoms being directly deposited onto a substrate. However, it has not been demonstrated that atomic beams can be used to generate any desired, complex pattern with a small minimum pitch.

[0007] some experiments have been performed to focus atomic beams to a small point with solid state lenses or mirrors or fields. However, this can only be applied for serial writing and is thus unsuitable for mass production.

[0008] In Fujita, J., Morinaga, M., Kishimoto, T., Yasuda, M., Matsui, S., Shimizu, F. : Manipulation of an atomic beam by a computer-generated hologram. Nature 380(6576), 691-694 (1996). https: / / doi.org / 10.1038Z380691a0 a desired pattern with metastable neon atoms is generated on a screen, by transmitting the atom beam through a solid mask consisting of a distribution of approximately circular through holes of 30 nm in diameter etched into a silicon nitride membrane. The openings are all of the same size and placed on the membrane at positions defined by a regular, square grid structure. We refer to this approach as grid-based binary holography. The setup operates with all system dimensionswithin the Fraunhofer regime (far-field) where the Fresnel number F « 1. The mask is designed using a Fourier transform of the desired pattern, so that the diffraction process which takes place during the transmission through the mask, leads to the desired pattern appearing in multiple copies on each side of the 0-order peak. The pattern copies on one side of the 0-order peak are rotated 180° relative to the pattern copies on the other side of the 0-order peak (see figure 4 in the original article).Nesse, T., Simonsen, I., Holst, B. : Nanometer-Resolution Mask Lithography with Matter Waves: Near-Field Binary Holography. Phys. Rev. Applied 11, 024009 (2019). https: / / dai.Qrg / 10.1103 / PhysRsvApphed. ll .024009 disclosed theoretical work on grid based binary holography with the application of small masks with square and hexagonal grid structures, a distance between the mask and the pattern plane of only 40pm and very small holes, less than 1 nm.Fiedler, J., Holst, B. : An atom passing through a hole in a dielectric membrane: Impact of dispersion forces on mask-based matter-wave lithography. Journal of Physics B, Atomic Molecular and Optical Physics, Institute of Physics Publishing, Bristol, GB, vol 55, no. 2 2022-02-10, discloses how dispersion forces interact with atom passing through a hole.

[0009] Prior art grid based binary holography, disclosed in some of the publications above and illustrated in Fig. 1 is not suitable for fast generation of patterns with feature sizes below the current state of the art. In particular it is not suitable for creating small features with large masks required for the large write-fields used in the semiconductor industry (typically 29mmx33mm).SHORT SUMMARY OF THE INVENTION

[0010] Fast generation of patterns with feature size below the limitations of prior art technology is needed to improve the performance of semiconductor devices and enable mass production of a range of quantum devices.

[0011] A goal of the present invention is to disclose a system and method for fast generation of patterns with feature sizes down to the nm range.

[0012] One of the main advantages of the invention over prior art is that nm features can be generated with nm pitch over large write fields, something which is not possible with prior art technology. Furthermore, nm features can be written using through holes or openings that are bigger than the feature sizes, which has not been demonstrated with binary holography. This may ease production of the masks.

[0013] Further advantages of the invention may be that the exposure time can be defined more precisely than in grid based binary holography since the intensity of the patterns in grid based binary holography is not uniformly distributed across and between the patterns. Furthermore, in the invention only one copy of the desired pattern is produced in an exposure, which simplifies the production process before and after pattern generation.

[0014] When feature sizes in the nm-range are achieved as a result of the invention, a challenge is that the density of holes in the mask increase and hole size decrease, which makes mask more difficult to produce and align. According to some embodiments of the invention, mask and hole size can be increased to ease mask production.

[0015] Thus, the lithography pattern generated may be denser than prior art lithography systems, which in turn makes it possible to produce microchips that have a better performance and a smaller size than prior art microchips. Further, throughput in production may be improved.

[0016] In some embodiments the invention may allow reduction of the size of the features printed on the wafer compared to the features printed on the mask without using demagnifying elements, in some instances even providing smaller feature sizes in the pattern target than the corresponding mask features.

[0017] The invention with the above-mentioned advantages, is a lithography pattern generation system and a method for generating a pattern by lithography according to the independent claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and further advantages of the systems and methods provided in accordance with the invention will now be explained in further detail by way of examples and with reference to the accompanying drawings. The drawings are not necessarily to scale. Instead, certain features may be shown exaggerated in scale or in a somewhat simplified or schematic manner, wherein certain conventional elements may have been left out in the interest of exemplifying the principles of the invention rather than cluttering the drawings with details that do not contribute to the understanding of these principles.

[0019] Fig. 1 illustrates pattern generation based on prior art grid based binary holography. Multiple copies of a target pattern 510A, 510B are generated by the diffraction of an atomic wave 210 passing through a binary holographic mask 400 with holes 300 all of the same size. The open holes are placed at positions corresponding to a grid structure. The grid has a pixel-like structure, e.g., 512x512 pixels, where each pixel point may be fully or partially open through hole or fully closed, the periodicity of the grid structure,leads to the generation of several copies of two rotated versions of the target pattern of varying intensity at a pattern target distance L2 behind the mask.

[0020] Fig. 2 illustrates schematically a lithography pattern generation system 1 according to an embodiment of the invention. The lithography pattern generation system 1 comprises one or more incoming particle beam(s) 21 with most probable wavelengths Ai from one or more particle sources 2 and a mask 4 arranged in the incoming particle beam(s) 21 between the particle source 2 and a pattern target 5. A generated pattern 51 on the pattern target results from the particles penetrating the mask 4. The source distance LI and the pattern target distance L2 from the particle source(s) 2 to the mask 4 and from the mask 4 to the pattern target 5, respectively, are indicated. Further, the mask 4 comprises through holes or openings 3 with a hole width w and a mask extension a, i.e., the maximum distance between through holes 3 that are exposed to the incoming particle beam(s) 21.

[0021] Fig. 3 illustrates schematically the main components and parameters of a lithography pattern generation system 1 according to an embodiment of the invention in one dimension. P is the period of the mask and d is the source diameter. Other references are similar to the ones used in Fig. 2.

[0022] Fig. 4 illustrate graphically the Fraunhofer diffraction patterns for a light wave A and a metastable helium matter wave B with the same wavelength through the same SiN double-slit mask of 5 nm thickness with 8 nm openings separated by an 8 nm wall. The vertical axis is the normalized intensity while the horizontal axis is the position in m). The matter wave has a dispersion force interaction with the dielectric mask, which is not applicable for light waves, resulting in a broadened diffraction pattern with much higher population of higher diffraction orders.

[0023] Fig. 5.1, 5.1, 5.3, 5.4, 5.5 and 5.6 illustrate in the vertical direction the atomic flux [atoms / s / m2] in one dimension for each of the sequentially corresponding examples of Table 1 and Table 2 below. The horizontal axis is the position in [nm]. The lower graphs show the flux where the dispersion forces Di have been taken into account, while the upper graphs do not consider these forces and thus correspond to the pattern that would be seen if the mask were illuminated with a light beam of similar wavelength to the atom beam. It can be seen that for the atom beam a strong reduction of the 0-order background as well as a higher contrast in the features may be obtained by selecting appropriate system parameters to tune the dispersion forces as further explained below.

[0024] Fig. 6a, 6b and 6c illustrate in sectional views three examples of 2D generated patterns and the mask applied to the right of each respective pattern. The scales in bothhorizontal and vertical directions are in nm. The feature-size obtained is 1.9 nm in Fig. 6a, 2.5 nm in Fig. 6b and 1.1 nm in Fig. 6c.

[0025] Fig. 7 illustrates an example of a mask with a mask material indicated by the black square. The hatched areas are the absorption regions of the physical through holes where the particles are not transmitted, as explained below. Only the remaining white areas contribute to the diffraction pattern. The drawing corresponds to the situation where the centre of the mask and the centre of the source opening are aligned.

[0026] Fig. 8 illustrates in a simplified sketch different target distances L2 away from the mask 4 for the purpose of the invention. The different distances are named A, B, C and D, where D is the most distant from the mask. A is close to the mask 4 but not in physical contact. The A to C range is called the proximity range. In this range the features in the target correspond directly to features or holes in the mask. In fact, L2 = 0 could also be said to be in the proximity range, but it has not been included here since physical contact between mask and substrate has some disadvantages mentioned elsewhere in this document. The proximity range may be further split into close and far proximity subranges from A to B and from B to C, respectively, wherein the close proximity sub-range, the feature sizes in the target are smaller than the hole width w, and in the far proximity sub-range, they are larger than the hole width. Further, the range between C and D is termed the intermediate range where the beams interfere and the features in the target are a result of interference and no longer corresponding directly to the holes in the mask. A far field involving interference exists beyond D, but this is not part of the invention and will not have the same advantages as the invention. The actual distances will vary depending on a number of factors, such as mask properties, described later in the document, and it should be noted that the ranges are dependent on the actual hole reduction, which is different from the optical regime. The distances are not to scale.EMBODIMENTS OF THE INVENTION

[0027] In the following description, various examples and embodiments of the invention are set forth in order to provide the skilled person with a more thorough understanding of the invention. The specific details described in the context of the various embodiments and with reference to the attached drawings are not intended to be construed as limitations. Rather, the scope of the invention is defined in the appended claims.

[0028] The terminology used in the description is intended to be interpreted in its broadest reasonable manner, even though it is being used in conjunction with a detailed description of certain specific implementations of the invention.

[0029] For clarity, the terminology used in the document is specified below:- Binary hologram and binary holography: Traditionally a binary hologram refers to a hologram with areas openings that are either fully transparent or fully opaque to the incoming optical scalar wave beam. For matter waves the situation is a bit different, since dispersion forces between the matter waves and a dielectric mask may prevent part or all of the matter waves to penetrate the through holes in the mask. Furthermore, the phase is perturbed across the openings. For the purpose of this document, the terms binary holograms and binary holography are also applied for such holograms masks when they are exposed by matter waves. In the previous literature on binary holography theoretical and experimentally the dispersion force interaction was not taken into consideration. The experimental paper in NATURE cited above had a target pattern with such big features that the effect of the dispersion forces are not evident.- Contrast c: Imax-Ibackground) / (Imax+Ibackground), where Imax and Ibackground represent the highest and lowest intensity.- Feature f: The smallest piece of information in the pattern. In lithography it is typically an identifiable object in the pattern, such as a line or a dot.- Feature size: The size of the feature. The feature size may be different in different directions, but in the context of this document the minimum feature size is the most important. a- Fresnel number F: where F = —2L2X .- Full width half maximum (dl / 2): The distance between points where the intensity reaches half its maximum value.- Grid period g: The minimum distance between two through holes or openings in grid based binary holography. The Grid period will be equal to or larger than the minimum hole / opening width.- Mask extension a: The maximum distance between two through holes 3 in the mask 4 plane.- Hole width w: The width of a through hole 3 in the mask 4.- Minimum hole width w: The minimum width of a through hole or opening 3 in the mask4. Through holes or openings 3 may optionally have different shapes and sizes.- Opening diameter da: The diameter of the opening of the particle source 2), defined for a supersonic source as the fraction of the virtual source retained by a collimating aperture. The virtual source is defined in the literature as the intensity distribution which can be obtained by backtracking the atoms leaving the quitting surface to a minimum area. The quitting surface is the point at which the particles can be said to move in free molecular flow, not interacting with each other. See for example: ; https: / / www.researchgate.net / publication / 356510630_Neutral_Helium_Microscopy_SHeM_ A_Review. For an effusive source, the opening of the particle source is simply the hole between the particle reservoir and the vacuum, or a collimating aperture placed downstream from that hole.- Pattern target 5: An object arranged in the diffracted particle pattern opposite the particle source 2 with regards to the mask 4. For integrated circuit production this could typically be a silicon wafer coated with resist. Formulation for resists suitable for helium atoms are presented in the literature, for example in the Berggren et al paper cited above.- Pitch: The distance between the centres of two adjacent features.- Resolution: The minimum pitch that can be transferred to the substrate.- Source distance LI: The distance between the particle source(s) 2 and the mask 4. More specifically it can be said to be the distance from the particle source(s) 2 opening to the front of the holography mask 4.- Pattern Target distance L2: The distance from the mask 4 to the pattern target 5. More specifically it can be specified as the distance from the back of the mask 4 to the pattern target 5.- Throughput: is the number of substrates or wafers that can be exposed per hour and is thus a measure of the efficiency of the lithographic process.- Wavelength A: The most probable wavelength of the particles in the incoming particle beam(s) 21 from the particle source(s) 2. The particle source(s) may have a skewed wavelength distribution.

[0030] Prior art conventional binary holography used with atomic beams mentioned initially and illustrated in Fig.l, is based on a holographic mask with uniformly sized holes arranged according to an underlying grid structure. This has several implications on the generated pattern.

[0031] First of all, different diffraction orders have different intensities, determined by the size and shapes of the through holes and the grid period, which means that the exposure time cannot be optimized for all parts of the generated pattern(s).

[0032] Secondly, the target patterns 510A, 510B as illustrated in Fig. 1 are oriented differently, which complicates production steps before, during and after pattern generation.

[0033] Third, the pattern target distance L2 of prior art must be sufficiently large to prevent the 0-order beam and the target patterns from overlapping.

[0034] The minimum pattern target distance L2 may be derived from the angular position, 0 of the first-order peak in the pattern target plane, relative to the centre of the first order peak determined by the underlying grid structure. The angle 0 is measured relative to the surface normal of the mask plane, see Fig. 1. sin 0 = A / g

[0035] The centre position of the target pattern closest to the 0-order peak (the centre position of the first-order peak) in the pattern target plane is (here the small angle approximation has been applied):(A / g)L2

[0036] For the first-order diffraction not to overlap with the 0-order diffraction, the centre of the 1-order peak must be at a distance a from the centre, (in order not to overlap with the 0-order peak which will have the mask extension a), regardless of the distance to the mask, because it consists of all the atoms that go straight through. We thus have that(A / g)L2 > a— ► L2 > ga / A > wa / A

[0037] We see that the larger the mask, the larger the minimum pattern target distance L2 has to be.

[0038] There are several problems related to the 0-order fraction in prior art.

[0039] First of all, the 0-order fraction may have a large intensity compared to the diffracted orders, and a large part of the pattern target hit by the 0-order will be unavailable for patterning. The unavailable area is in the centre of the pattern target, making it even more challenging to reduce the impact on other parts of the pattern and to generate meaningful patterns in these areas.

[0040] Blocking of the 0-order might be possible, but this would add to the complexity of the system. Further, whether blocked or not, the 0-order fraction in prior art contributes to a system with reduced efficiency in terms of the fraction of particles from the particle source that actually contributes to pattern generation.

[0041] In the invention as claimed however, the disadvantages of the 0-order have been turned into advantages.

[0042] When the pattern is arranged at the target distance L2 < wa / A, illustrated as the region between 0 and D in Fig. 8, a major part of the transmitted beam contributes positively to the intensity needed to generate the pattern target. Note that the condition that L2 < wa / A is different from the condition for Fraunhofer regime, given by the Fresnel number. This has the surprising effect that the 0-order, instead of being an obstacle for patterning, now strongly contributes to the generation of the pattern in the whole range. For dense pattern generation this is of uttermost importance since the whole target pattern area can be utilized, which again allows a larger write field during chip production.

[0043] A further advantage of the 0-order contributing directly to the pattern generation, is that the efficiency of the system improves drastically. A much larger portion of the particles that penetrate the mask will contribute to the generation of the pattern for target distances exceeding beyond the proximity range, which again results in higher contrast in the features of the pattern and smaller feature sizes. As a side effect, shorter exposure time and more throughput in production may also be achieved.

[0044] An objective of the invention is to provide a system and method with high throughput, i.e. the number of wafers produced per unit time. In addition to the time required for exposing the substrate arranged in the pattern target, the time for changing and aligning substrates contributes to production time. Furthermore, masks and substrates may bend or vary in size if environmental conditions change, such as e.g. temperature variations during exposure. Securely aligning the substrates with nm precision with regards to the mask is therefore important.

[0045] Due to the easily achievable very small wavelength of a particle beam (0.05 nm for a room temperature helium beam) the distance between the mask and the substrate, L2, can be increased compared to e.g., light proximity lithography carried out with the typical DUV and EUV wavelengths of 192 nm or 13.5 nm, without compromising the resolution. Furthermore, the distance does not need to be determined as accurately as for light. Both points are advantageous for fast wafer handling and corresponding fast throughput.

[0046] In an embodiment the substrate and mask are therefore physically separated in order to allow the substrates to be replaced without affecting the mask, and to prevent material deformations in the mask or the substrate to affect each other. Thus, in combined with the maximum distance above, the proposed target distance in this case is 0 < L2 < wa / A, illustrated in Fig. 8 as the region from A to D.

[0047] Within the target distance 0 < L2 < wa / A, ranges may be selected in order to obtain additional advantages. Two main ranges may be defined; proximity range and interference range, illustrated as A to C and C to D in Fig. 8, respectively.

[0048] In the proximity range, the majority of the features f on the target pattern 5 correspond directly to corresponding through holes or openings 3 in the mask 4. I.e., a through hole in the mask will result in a corresponding feature in the target pattern. This is achieved by ensuring that the target distance L2 is sufficiently small to prevent wave pattern interference between the openings in the target pattern 5. In the proximity range the mask 4 can therefore be seen as a stencil, since the features of the mask are recreated in the target plane but with the option of selecting a region where the size of each feature is reduced compared to eh features in the masks, due to the dispersive force interaction.

[0049] The criterion for proximity is related both to the distance between the holes and their size.

[0050] The dispersion force interaction between the mask and the particles will result in a reduction of the effective hole diameter. The strength of this force depends on the mask material (stronger for conducting and weaker for insulating materials) and particle species of the beam, both expressed in the C3-coefficient, and the mask thickness d, as well as thewavelength (particle's velocitydB= with the particle's mass m and Planck's constant h, respectively the reduced Planck constant, respectively the reduced Planck constant h= h / (2n)). The diffraction at a single circular hole (opening) with radius R can be approximated via Kirchhoff's diffraction formula and can be written as an integral dA over the normalised radial component of the aperture (opening) A= r / R as the superposition of propagating spherical waves (Bessel function A= r / R as the superposition of propagating spherical waves (Bessel function y0(%)) with a complex phase shift imprinted in the wave due to the dispersion interactionBased on Equation (22) in the Fiedler J. et al paper cited under background art, with the elliptic integrals E(x) and K(x), the phase's magnitudeand the dimensionless radial position (tilde indicates dimensionless, the real coordinate is p) at the detectorwith the wavevector kQ= 2n / AdBfthe distance between the mask and the detector L2and R the normalised hole reduction E= — . Thus, the diffraction integral (Equivalent to Eq. (3) R but all irrelevant constants have been removed)can be solved numerically for the rescaled spatial coordinate p depending on the generalised phase parameter and cutoff s. Thus, the wave at the detector only depend on these three parameters = i]j(p;E,<p) By solving this equation, a beam waist can be determined via the half-width-half-maximum (indicated by the lower index 1 / 2) of the zeroth order distribution (the intensity is determined by the absolute value square of the wave function)leading a relation that the beam width after passing the hole only depends on the hole reduction E and the phase magnitude <p, p1 / 2= P1 / 2(E, <P). Note, the tilde denotes the dimensionless beam spread, which needs to be rescaled according to Eq 5, to a physical beam spreadConsequently, a beam spread angle can be defined via

[0051] To ensure non-overlapping diffraction orders, the separation between two holes a has to be larger than twice the beam waist a » 2p1 / 2(e, <p) , (10) leading towith the hole width, or diameter w = 2R and the de-Broglie wavelength A = 2n / k0. Equation 12 is a "generalised" Fresnel number specifying the aperture a'2as the product of hole width w and separation a and introducing a correction for the dispersion interaction.

[0052] The dimensionless beam spread p1 / 2can be evaluated independently from the considered setup due to generalised parameters, normalised hole reduction E and the phase's magnitude <p. By solving Eq 7 numerically, the result can be fitted numericallyPi / 2 = PoowithPoo=1-8562, p10= 30.8597, p01= 0.6884, p20= —105.9441, p1±= —11.6529 and P02=0.0430.

[0053] If Eq 12 is solved with respect to L2, L2 can be seen as the maximum target distance for the proximity range where features corresponding directly to holes are barely detectable. However, it may also define the border between the proximity range and the interference range, which means that interference is also present to some extent.

[0054] Due to the hole reduction effect, the beam width and corresponding feature size will be smaller than the hole width in the range closest to the mask or stencil, i.e., the close proximity sub-range. However, the beam width increases further away from the mask and at a certain target distance L2 = B in Fig. 8, the feature size is equal to the hole width.

[0055] When the target distance L2 is in the far proximity sub-range between B and C in Fig. 8, the feature size in the target pattern is larger than the hole size.

[0056] In the intermediate range, in the region between C and D in Fig. 8, features in the target pattern will be a result of interference from the contributions from the different holes in the mask. A mask 4 may have a large number of holes. This means that some holes are much closer than other holes. Holes with larger separation may actually be in the proximity range, while closer holes may be in the interference range.

[0057] In the following, some specific embodiments of the invention will be described.

[0058] In a first independent system embodiment ES1-1, the invention is a lithography pattern generation system 1 configured to generate a pattern (51) of features (f) on a pattern target (5), wherein the system (1) comprises;- a mask (4) comprising through holes or openings (3) configured to be arranged in an incoming particle beam (21), wherein the lithography pattern generation system (1) is configured to generate the pattern (51) a target distance (L2) from the mask (4) on the opposite side of the incoming particle beam (21), wherein the target distance L2 is sufficiently small to allow a majority of the intensity from transmitted beam fractions from one or more of the holes or openings (3) to participate in creation of the features (f).

[0059] The terms holes and openings have the same meaning in this document. Holes or openings may have different shapes, such as e.g., circular, straight and curved lines etc. completely through the mask to allow particles to penetrate.

[0060] The above condition requires the 0-order of the beams to participate in the generation of the features of the pattern, which in turn means that the target distance (L2) must be equal to or smaller than D in Fig. 8, as explained above.

[0061] ES2-1 : The lithography pattern generation system (1) of ES1-1, wherein the through holes (3) have a minimum hole width (w) and the mask (4) has a mask extension (a) which is the maximum distance between two through holes in the mask (3) exposed by the incoming particle beam (21), wherein L2 <

[0062] ES2-2: The lithography pattern generation system (1) of ES1-1 or ES2-1, wherein L2 is sufficiently large to allow a majority of the transmitted beams from one or more of the holes (3) to interfere with each other.

[0063] ES2-3: The lithography pattern generation system (1) of any of ES1-1 to ES2-2, wherein, „ awn

[0064] L2 > — — — , wherein2Api / 2P1 / 2=1-8562 + 30.8597<p + 0.6884e — 105.9441<p2— 11.6529<pe + 0.0430e2, where £ is a normalised hole reduction for the hole (3) and (f> is a magnitude of the phase.

[0065] ES2-2 and ES2-3 correspond to L2 > C in Fig. 8.

[0066] ES3-1 : The lithography pattern generation system (1) of ES1-1, wherein L2 is sufficiently small to allow a majority of the transmitted beams from one or more of the holes (3) not to interfere with each other.

[0067] ES3-2: The lithography pattern generation system (1) of ES3-1, wherein

[0068] ES3-1 and ES3-2 correspond to L2 < C in Fig. 8.

[0069] ES4-1 : The lithography pattern generation system (1) of ES1-1, wherein L2 is sufficiently small to allow a majority of the hole widths (w) of the holes (3) to be larger than their corresponding feature sizes (f) in the pattern target (5).

[0070] ES4-2: The lithography pattern generation system (1) of ES4-1, wherein L2 < w0.01 —2.A

[0071] ES4-1 and ES4-2 correspond to L2 < B in Fig. 8.

[0072] ES5-1 : The lithography pattern generation system (1) of ES3-1 or ES3-2, wherein L2 is sufficiently large to allow a majority of the hole widths (w) of the holes (3) to be smaller than their corresponding feature sizes (f) in the pattern target (5).

[0073] ES5-2: The lithography pattern generation system (1) of claim ES5-1, wherein wL2 > 0.01—2.A

[0074] ES6-1. The lithography pattern generation system (1) of any of ES1-1 to ES5-2, wherein L2 > 0.

[0075] This requires the mask not to be in physical contact with the target, e.g., the wafer itself or a resist on the wafer, which will be advantageous for handling of both masksand wafers, as well as the overall throughput of the lithography pattern generation system (1).

[0076] In a first independent method embodiment EM 1-1, the invention is a method for generating a pattern (51) of features (f) on a pattern target (5), comprising;- arranging a mask (4) with through holes (3),- arranging the pattern target (5) a target distance (L2) from the mask (4),- exposing the mask (4) with an incoming particle beam (21) from the opposite side of the mask with respect to the pattern target (5), wherein the target distance L2 is sufficiently small to allow a major part of the intensity from transmitted beam fractions from one or more of the holes (3) to participate in creation of the features (f).

[0077] EM 1-1 : The method of EM 1-1, comprising any of the features described in the lithography pattern generation system (1) embodiments ES1-1 to ES6-1 above.

[0078] In a second independent method embodiment EM2-1, the invention is a method for generating a pattern (51) of features (f) on a pattern target (5), comprising;- defining a mask (4) with through holes (3), wherein a majority of the through holes correspond one-by-one to corresponding features (f),- defining mask parameters of the mask (4),- exposing the mask (4) with an incoming particle beam (21) from the opposite side of the mask with respect to the pattern target (5),- wherein the mask parameters (4) of the mask, and a target distance between the mask (4) and the pattern target (5) are chosen to allow hole sizes (w) of the holes (3) to be larger than the corresponding feature sizes (f).

[0079] EM2-2: The method of EM2-1, wherein the mask parameters comprise any of mask thickness and mask material.

[0080] EM2-3: The method of any of EM2-1 or EM2-2, wherein the step of defining mask parameters comprises doping, with any of neutral particles, ions and electrons.

[0081] EM2-4: The method of any of EM2-1 to EM2-3, wherein the step of defining the mask parameters comprises modifying dispersion forces interaction between the incoming particle beam and (21) the mask (4).

[0082] E-l: The system or method of any of ES1-1 to ES6-1 and EMI-1 to EM2-4, wherein the particle beam (21) comprises metastable atoms or molecules.

[0083] E-2: The system or method of any of ES1-1 to ES6-1 and EMI-1 to EM2-4, wherein wherein the particle beam (21) comprises noble gas atoms.

[0084] E-3: The system or method of any of ES1-1 to ES6-1 and EMI-1 to EM2-4, wherein the particle beam (21) comprises noble gas atoms.

[0085] E-4: The system or method of any of ES1-1 to ES6-1 and EMI-1 to EM2-4, wherein the particle beam (21) comprises helium atoms.

[0086] E-5: The system or method of any of ES1-1 to ES6-1, EMI-1 to EM2-4 and El to E4, wherein the wavelength (A) is smaller than any of the minimum feature-size (df), minimum pitch, minimum hole width (w) and mask thickness.

[0087] A specific independent embodiment of the invention will now be disclosed with reference to Fig. 2.

[0088] In this embodiment the invention is a lithography pattern generation system 1 comprising an incoming metastable helium atom beam 21 with a most probable wavelength A from a particle source 2 and a mask 4 comprising through holes 3 arranged in the incoming particle beam 21.

[0089] Contrary to the mask 400 in Fig. 1 for prior art lithography pattern generation systems, where the through holes 300 are arranged according to a pre-defined underlying grid structure, independent of the target pattern, the through holes 3 according to the invention are not arranged on the mask according to a pre-defined underlying grid structure 4. Further, the holes 3 may have different shapes and different minimum hole widths w. A single pattern with minimum feature size down to 1 nm or less is generated on a pattern target 5 arranged at a target distance L2 > 0 from the mask 4.

[0090] The invention takes advantage of the perturbation of the particle wave by the dispersion forces interaction between the dielectric mask and the particle itself when it passes through a hole in the mask. The dispersion forces, in particular the Casimir-Polder forces, are caused by the quantum-mechanical ground-state fluctuations of the electromagnetic field in the absence of charges. Due to the field fluctuations, the metastable helium atoms will be polarized for a short amount of time. The resulting induced dipole moment then interacts with the mask via dipole-dipole interactions. These forces decay with the distance, r“3-power law, but play a significant role on the nanometre length scale. The interaction is stronger closer to the edge of the hole and weaker towards the middle. This leads to a reduction of the number of atoms going straight through. In the Fraunhofer diffraction regime this has the effect of a reduced 0-order d peak and a broadened diffraction pattern as illustrated in Fig. 4.

[0091] In this embodiment metastable helium atoms passes through holes in the mask which is a silicon nitride membrane. The dispersion forces prevent a very large fraction ofthe metastable helium atoms with a wavelength of 0.1 nm to penetrate holes with a hole width less than 2nm in 5 nm thick silicon nitride masks.

[0092] The dispersion force interaction has a positive effect of the contrast of the generated patterns.

[0093] The difference in contrast may be exemplified by looking at a one-dimensional set of key system parameters. Table 1 below shows examples of parameter values for a system realisation taking dispersion forces into account assuming metastable helium and a 5 nm thick silicon nitride mask), and for a scalar wave system realisation). Table 2 shows the resulting parameter values for the two systems. It is worth noting from Table 1 that all examples are within in the range of L2 < wa / A, where first-order diffraction overlap with the 0-order diffraction for prior art.Table 1 : Parameters used to compare feature sizes of a system taking the dispersion forces into account, and a system not taking these features into account. A dispersion force profile for a standard 5 nm thick SiN wafer and metastable helium atoms is used. The patterns are three slits one at each edge of the mask and one in the middle. In addition, although the Fresnel number varies considerably, for all examples the condition L2 < wa / A is fulfilled as can be seen from the last column.Table 2: Results of the parameters for the system of Table 1, for full width half maximum: dl / 2 (-), and Contrast c (-) without dispersion forces and corresponding parameters dl / 2 (Di), and c (Di) with the dispersion forces.

[0094] It is worth looking specifically at the two columns for contrast. It can be seen that the contrast has increased considerably for all examples with comparable feature-sizeswhen the dispersion forces are taken into account. These results are also illustrated graphically in Fig. 5.1 to F.6.

[0095] The invention allows the most probable A of the particles in the incoming particle beam to be small compared to other critical dimensions such as e.g., feature size df, minimum distance between features dl / 2, mask extension a as well as source and pattern target distance LI, L2.

[0096] Since the most probable wavelength A can be chosen to be small compared to the desired feature size df, the pattern can be generated using a beam with the velocity spread of a supersonic or effusive source. The slight blur this introduces in the pattern is not a problem. The wavelength is given by the velocity and vice versa through the de Broglie equation.

[0097] The contrast in the diffraction pattern can be modified by changing the dispersion force influence through one of the following means: Changing the size of the holes, changing the shape of the hole changing the thickness of the mask material the membrane), changing the material of the mask, doping the mask by electron or ion implantation or surface functionalization or changing the metastable atom or molecule.

[0098] Fig. 6a, 6b and 6c illustrate in an embodiment of the invention sections of three 2D patterns generated in the setups listed in Example 1, 2 and 3 in Table 3 below. To the right of each figure is an illustration of the mask applied, where the size of the mask is lOpmxlOpm with lOnm circular through holes. A dispersion force profile for a standard 5 nm thick SiN wafer and metastable helium atoms is used. The repetitive patterns are generated by through holes arranged in a 3x3 grid with a hole spacing of 6pm. It is worth noting that the hole width w in the mask are from 4 to 9 times larger than the features sizes in the generated pattern.Table 3: Information about the setup and the features of the 2D pattens generated in the examples illustrated in Fig. 6a, 6b and 6c. The parameters are the same as in Table 1 and 2.

[0099] The desired 2D patterns are here periodic, which gives a periodic mask structure as seen in in Fig. 6a, 6b and 6c.

[0100] The diffraction pattern is determined by Kirchhoff's diffraction formula with the transmission function for neutral matter waves

[0101] with the wave's amplitude and the wave propagators gx(r2- r from the source point rr= s, smto the final point r2= sm,r along the distance x = L1, L2 . This equation has to be read from right to left: the matter wave propagates from a point in the source plane sto a point in the mask plane smalong the distance Ll , where it collects phase shifts across the wavefront due to the dispersion forces, here the Casimir-Polder interaction in the nonretarded limit, which depends on the interaction strength C3between the mask material and the particle, the mass of the beam particle m , the wavelength Ao, the mask's thickness d , the Planck constant h , and the mask's shape expressed by the integral over the mask's surface; afterwards the propagation continues to a point in the pattern target plane r along the propagation length L2 . The interference is described by the superposition of all optical paths from the source s to the pattern target r determined by the square of the absolute value. As each particle interferes only with itself, different initial conditions, such as other source points s or with a different wavelength respectively particle's velocity), will yield an incoherent superposition. Thus, the interference of all states have to be averaged incoherently leading to the integral over the source area and over the wavelength distribution / (A0;A,AA) with the most probable wavelength A and wavelength distribution AA .The formula above needs to be modified to account for tilted or curved mask and / or pattern target.

[0102] There are two integrals inside the mask plane: one for the coherent superposition smand one for the phase shift sm>. The first integral over smdescribes the optical paths and is over the hole's area. The other one over sm> describes the interaction with the mask material and, thus, represents the bulk material. Fig. 7 illustrates these two different areas for a section of a mask with regular spherical holes. The mask material is depicted by the dark area and denotes the area for the phase shift integral sm>. The physical holes are the white and grey areas, where the latter is the absorption region, defined as the region where the atoms are not transmitted, and thus, does not contribute to the optical paths. Only the white area is relevant for the coherent superposition.

[0103] Kirchhoff's diffraction formula describes the most general case of interference. There are different approximations for the propagator leading to simplifications valid in different regimes. They are summarized in table 4. It can be seen that the propagator simplifies to the Fourier transform in the Fraunhofer and Fresnel regimes due to the cancelation of the dependencies in the denominator, used for all previous publications on matter-wave lithography. We consider the wave propagator between the mask and the target gi_2 to achieve the resolution and the Fraunhofer regime between the source and the mask gLito achieve the stability concerning source extension and wavelength variations.Table 4: Overview of the wave propagators for the different regimes Fraunhofer regime, Fresnel regime, wave propagator).

[0104] The properties of the mask 4), such as hole width w), mask extension a), hole arrangement and mask material and thickness will determine the generated pattern. However, the generated pattern, or desired pattern, will in real life situations be determined by the circuit design of the manufactured items, such as e.g. integrated circuits. It is therefore necessary to produce the mask based on the desired pattern. This is often referred to as the inverse problem.

[0105] As discussed above, existing binary holography theory for scalar waves, uses a grid of holes with equal size as the base for the masks and assumes system dimensions and wavelength that fulfil the well-known optics condition of Fraunhofer approximation. In the Fraunhofer approximation the inverse problem is reduced to a Fourier transform of the desired pattern, which yields the required mask. Sampling the mask according to the Nyquist-Shannon sampling theorem provides its mode's bandwidth and thus the possible minimum pitch. In one dimension, this can be done analytically as described in prior art.This may to also work for matter waves if the holes in the mask are so large that the dispersion force interaction is negligible.

[0106] However, the above cannot be adapted to matter waves and masks with smaller holes required for small pitch, because the dispersion force interaction between the particles and the diffraction object induces a complex phase distribution of the matter wave as explained above, which is not accounted for in the prior art mask generation theories.

[0107] In the exemplary embodiments, various features and details are shown in combination. The fact that several features are described with respect to a particular example should not be construed as implying that those features by necessity have to be included together in all embodiments of the invention. Conversely, features that are described with reference to different embodiments should not be construed as mutually exclusive. As those with skill in the art will readily understand, embodiments that incorporate any subset of features described herein and that are not expressly interdependent have been contemplated by the inventor and are part of the intended disclosure. However, explicit description of all such embodiments would not contribute to the understanding of the principles of the invention, and consequently some permutations of features have been omitted for the sake of simplicity or brevity.

Claims

CLAIMS1. A lithography pattern generation system (1) configured to generate a pattern (51) of features (f) on a pattern target (5), wherein the system (1) comprises;- a mask (4) comprising through holes (3), configured to be arranged in an incoming particle beam (21), wherein the lithography pattern generation system (1) is configured to generate the pattern (51) a target distance (L2) from the mask (4) on the opposite side of the incoming particle beam (21) with a wavelength (A), wherein the target distance L2 is sufficiently small to allow a major part of the intensity from transmitted beam fractions from one or more of the holes (3) to participate in creation of the features (f).

2. The lithography pattern generation system (1) of claim 1, wherein the through holes (3) have a minimum hole width (w) and the mask (4) has a mask extension (a) which is the maximum distance between two through holes in the mask (3) exposed by the incoming wa particle beam (21), wherein L2 < — .A3. The lithography pattern generation system (1) of claim 1 or 2, wherein L2 is sufficiently large to allow a majority of the transmitted beams from one or more of the holes (3) to interfere with each other.

4. The lithography pattern generation system (1) of claim 3, wherein whereinp1 / 2= 1.8562 + 30.8597<p + 0.6884E - 105.9441<p2- 11.6529<pE + 0.0430E2, where E is a normalised hole reduction for the hole (3) and (f> is a magnitude of the phase.

5. The lithography pattern generation system (1) of claim 1, wherein L2 is sufficiently small to allow a majority of the transmitted beams from one or more of the holes (3) not to interfere with each other. awn6. The lithography pattern generation system (1) of claim 5, wherein L2 < - .2Ap1 / 27. The lithography pattern generation system (1) of claim 1, wherein L2 is sufficiently small to allow a majority of the hole widths (w) of the holes (3) to be larger than their corresponding feature sizes (f) in the pattern target (5). w28. The lithography pattern generation system (1) of claim 7, wherein L2 < 0.01 — .A.

9. The lithography pattern generation system (1) of claim 5 or 6, wherein L2 is sufficiently large to allow a majority of the hole widths (w) of the holes (3) to be smaller than their corresponding feature sizes (f) in the pattern target (5). w210. The lithography pattern generation system (1) of claim 9, wherein L2 > 0.01 —.A.

11. The lithography pattern generation system (1) of any of the claims above, wherein L2 > 0.

12. A method for generating a pattern (51) of features (f) on a pattern target (5), comprising;- arranging a mask (4) with through holes (3),- arranging the pattern target (5) a target distance (L2) from the mask (4),- exposing the mask (4) with an incoming particle beam (21) from the opposite side of the mask with respect to the pattern target (5), wherein the target distance L2 is sufficiently small to allow a major part of the intensity from transmitted beam fractions from one or more of the holes (3) to participate in creation of the features (f).

13. A method for generating a pattern (51) of features (f) on a pattern target (5), comprising;- defining a mask (4) with through holes (3), wherein a majority of the through holes correspond one-by-one to corresponding features (f),- defining mask parameters of the mask (4),- exposing the mask (4) with an incoming particle beam (21) from the opposite side of the mask with respect to the pattern target (5),- wherein the mask parameters (4) of the mask, and a target distance between the mask (4) and the pattern target (5) are chosen to allow hole sizes (w) of the holes (3) to be larger than the corresponding feature sizes (f).

14. The method of claim 13, wherein the mask parameters comprise any of mask thickness and mask material.

15. The method of any of claims 13 to 14, wherein the step of defining mask parameters comprises doping with any of neutral particles, ions and electrons.

16. The method of any of claims 13 to 15, wherein the step of choosing or defining the mask parameters comprises modifying dispersion forces interaction between the incoming particle beam and (21) the mask (4).

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