RU2446863C1 - Method of producing membrane filter - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to micro structure technologies. Method of producing membrane filter with pore identical sizes and shape comprises irradiating polymer film and etching of material destruction products from polymer film irradiated areas. Irradiation causes local chemical destruction of polymer film material. Polymer film is subjected to synchrotron radiation. Said radiation is structurally ordered by multi-beam lattice interference lithography. Irradiation is carried out in chamber filled with gaseous hydrogen. Hydrogen reacts photochemically with polymer film material on irradiated film sections to produce volatile products removed in irradiation.

EFFECT: membrane filter porosity of up to 0,6, ordered identical-size (from 1 nm and lather) pores, round or elliptical in crosswise and conical in lengthwise sections.

14 cl, 15 dwg, 5 tbl

Description

The invention relates to microstructural technologies and can be applied in nanotechnology, medicine, chemistry, molecular biology and optics.

Membrane filters are one means of isolating and separating nanosized particles (e.g., proteins, nucleic acids, cells, and subcellular structures). Membrane filters are porous septa with micron and submicron pores through which the filtered medium passes under the influence of pressure or concentration (diffusion), and particles larger than the pore size remain on the septum.

The most common membrane filters are obtained from cellulose ethers (nitrates and acetates) using a complex technology. In a certain way, the prepared colloidal solutions of cellulose ethers are applied in a thin layer on a smooth substrate, the solvents evaporate in a certain mode, and a fine-mesh structure is obtained. The characteristics of this structure depend on the composition of the initial solutions and the evaporation mode. Thus, membranes with pore sizes of 10-100 nm (for ultrafiltration), 1-10 nm (for nanofiltration), 0.1 nm (for reverse osmosis) are obtained. Membranes made in this way, with pores smaller than 0.1 μm in size, used to remove the smallest particles from water, from large organic molecules to ions of dissolved substances, have a small cross section, relatively high hydraulic resistance (for example, operating pressure of reverse osmosis 1- 10 MPa (10-100 atm)), and therefore, to ensure a given performance, large filtration areas are required. Pores have an irregular shape and a large scatter in pore sizes, which is why such membranes are more suitable for cleaning media from nano- and microparticles than as sieves (a sieve is a filter from which it is possible to easily separate sediment extracted from a filtered medium - liquid gas), as particles get stuck to a large extent in larger mesh cells.

Closest to the claimed technical solution is a method of obtaining the so-called. "Nuclear" or "track" membranes. To a large extent, this “screening restriction” is not characteristic of them. They are made by irradiating polymer films with a thickness of 1 to 15 microns from either polyethylene terephthalate (lavsan), or polycarbonates or nuclear fission fragments (the so-called "nuclear membranes"), or argon ions in a particle accelerator (the so-called "track membranes" "). When a particle passes through a film of polymer material, a trace (track) is formed in it in the form of a destroyed polymer. Then these tracks are etched (removed the destroyed polymer) with acid or alkali and get in the film the correct cylindrical holes of the same diameter in the range from 30 nm to 8 μm (T. Brock, Membrane filtration, M., Mir, 1987, pp. .9, 59-61). The most significant drawback of this method is the impossibility of obtaining an ordered spatial structure of pores due to the disordered spatial distribution of ions in the beam and, accordingly, tracks in the polymer film. This fact is a disadvantage of the method, because it causes a lack of the final product - a membrane filter. Thus, the spatial disorder of the obtained pore structure allows one to obtain membranes with a small (0.07–0.1) porosity (the ratio of the passage pore cross-sectional area to the total filter area), because an increase in the density of pores on the membrane leads to their overlapping and the formation of holes larger than a given size. Inadequate porosity, in turn, impairs the flow rate characteristic of the membrane (flow rate versus pressure). Also, the known method allows to obtain pores only cylindrical, round in cross section and does not allow to obtain elliptical in cross and conical in longitudinal section. Meanwhile, it is believed that the conical in the longitudinal and elliptical (“slotted”) pores in the cross section are less prone to “clogging” by particles during operation. Finally, this known method does not allow to obtain nanopores with a diameter of less than 30 nm.

The aim of this invention is a method of manufacturing a membrane filter of high porosity (up to 0.5 ÷ 0.6) with pores of the same size from 1 nm or more or round, or elliptical in the transverse and conical in longitudinal section.

The technical result achieved by this proposal consists in a method of manufacturing a membrane filter of large (0.5-0.6) porosity with pores of the same size from 1 nm and larger or round, or elliptical in transverse and conical in longitudinal section.

The specified technical result is achieved by the fact that in the known method, including irradiating the polymer film with radiation, causing local chemical destruction of the polymer and etching (removal) of degradation products from the irradiated sections of the film,

irradiation is carried out by structurally ordered synchrotron radiation using a lattice interference lithography system

(HHSolak, C. David, J. Gobrecht, V. Golovkina, F. Kerrina, SOKim, PF Nealey, Sub-50 nm period patterns with EUV interference lithography. Microelectronic Engineering, v. 67-68 (2003), pp .56-62;

Beyer O., Nee I., Havermeyer F., Buse K. Applied Optics. 2003. Vol. 42. N1. P.30-37; Cai L.Z., Yang X.L. Optical and Laser Technology. 2002. Vol. 34. P.671-674; Egglet B.J. IEEE Journal of Selected Topics in Quantum Electronics. 2001. Vol. 7. N.13. P.409-423; Harun H. Solak Laboratory for Micro and Nanotechnology, Paul Scherrer Institute, Switzerland Pushing the Limits of Nano-patterning with Extreme Ultraviolet Interference Lithography, http://lmn.web.psi.ch/xil/xil_pres.pdf)

in a chamber filled with gaseous hydrogen, due to which the etching (removal) of the material of the irradiated areas, leading to the formation of pores in the film of the polymer material, occurs during irradiation due to the formation of volatile products as a result of the photochemical reaction between the film material and hydrogen (hereinafter this process we will call “photo-etching”).

The high porosity of the membrane filter in the proposed method is achieved due to the ordered regular arrangement of the resulting pores in the membrane, corresponding to the ordered structure of the interfering radiation beams (hereinafter referred to as the "interference pattern") after the grating interference lithography system; the ellipticity of the pore cross section is achieved by choosing pairs of diffraction gratings with a different period (pores round in the cross section are obtained with the same period), and the conicity of the longitudinal pore cross section is ensured by the specific inhomogeneous distribution of the radiation flux density in the interfering radiation beams after the grating interference lithography system, which causes different photo-etching rates the material of the polymer film in the cross section of each of said radiation beams.

Figure 1 shows a diagram of a four-beam grating interference lithography.

Figure 2 shows the interference pattern of radiation beams from two diffraction gratings.

Figure 3 shows the distribution of the radiation flux density over the surface of a film of polymer material after a four-beam system of lattice interference lithography (hereinafter “interference pattern”) with pairs of diffraction gratings with different periods.

Figure 4 shows the structure of the interference pattern obtained from pairs of diffraction gratings with the same periods on the surface of the film of polymer material in a 4-beam system of patternless interference lithography with the same periods of the pairs of diffraction gratings.

Figure 5 shows the distribution of the radiation flux density in a separate cell of the periodic structure of the interference pattern obtained from pairs of diffraction gratings with the same period.

Figure 6 shows the dependence of the radiation flux density on the distance from the center of the cell of the periodic structure of the interference pattern obtained from pairs of diffraction gratings with the same period.

Figure 7 shows the dependence of the photoetching rate for different polymeric materials on the radiation flux density.

On Fig shows the dependence of the longitudinal profile of the pores of the membrane filter from the time of photo-etching.

Figure 9 shows the dependence of the radius of the pore through hole on the time of photo-etching.

Figure 10 shows the dependence of the porosity of the membrane filter on the radius of the bore of the pore.

11 shows the structure of the interference pattern on a polymer film for a different period of the pairs of diffraction gratings of the grating interference lithography system.

On Fig shows the cell structure of the periodic structure of the interference pattern on a polymer film obtained with different periods of the diffraction gratings.

On Fig shows an example of a technological scheme for manufacturing a membrane filter of a polymeric material reinforced with a microporous silicon structure.

On Fig shows an example of a technological scheme for manufacturing a membrane filter from an inorganic material reinforced with a silicon microporous structure.

On Fig shows an example of a technological scheme for manufacturing a membrane all-metal filter.

The method is carried out as follows.

The ordered pore structure in the proposed method for manufacturing a membrane filter is obtained by irradiating (exposing) a thin polymer film with narrow-band (Δλ / λ = 2.5%) coherent synchrotron radiation (SI) with a working wavelength in the range of 5 ÷ 100 nm. Such radiation is generated by a specialized multipolar undulator. Spatial structuring of radiation on the processed (exposed) polymer film 1 is carried out using an optical system of 4-beam grating interference lithography (scheme in Fig. 1), including a quasi-pattern 2, in which there are two mutually perpendicular pairs of diffraction gratings 3 and 4 with periods of PX and PY respectively. The interference of 4 first-order beams diffracted on these gratings leads to the formation of a standing electromagnetic field 5 (interference pattern) on the surface and in the bulk of film 1, which is periodic in X and Y coordinates with periods DX and DY and uniform in Z coordinate at distances of the order of the depth of field (GR) of the interference pattern. In more detail, the pattern of formation of interference pattern 5 in the method of lattice interference lithography is illustrated in FIG. 2 by the example of interference of two beams of synchrotron radiation of the first diffraction order (+1 and -1), transmitted, for example, through a pair of gratings 3 (gratings 4 are assumed to be closed from radiation). In Fig.2, for the main components of the system, the same notation is used as in Fig.1. In addition, the following notation is introduced:

θ is the angle between the interfering beams +1 and -1;

α is the diffraction angle of the beams +1 and -1 on the gratings;

1/2 GR - half the depth of field of the interference pattern.

A feature of interference pattern 5 is a large depth of field (GR) of about 100 μm (Fig. 2), which allows the process of photochemical etching without dynamic focusing, which is necessary when using other projection lithographic systems.

Another important feature of the lattice interference lithography system for the implementation of the proposed method is its complete achromaticity, i.e. independence of the dimensional parameters of the generated electromagnetic field (interference pattern) from the wavelength. This feature makes it possible to use the optimal wavelength for the implementation of the photochemical reaction in the working range of 5-100 nm without depending on the wavelength of the pores in the formed filter (of course, with a certain limitation of the period of diffraction gratings, which cannot be less than half the wavelength).

The mentioned achromaticity is due to the fact that a change in the diffraction angle of the beams α on the gratings 3 with a change in the wavelength λ leads to such a change in the angles θ (Fig. 2) between the interfering beams, at which the resulting interference pattern remains unchanged. For example, two first-order diffraction beams formed by gratings 3 (Fig. 2) make an angle α with a normal to gratings 3, and

where PX is the period of the gratings in pair 3, λ is the radiation wavelength. Therefore, these beams make an angle θ = 2α between themselves. If the interference of only these two beams were considered, then they would form a one-dimensional interference pattern (along the X axis) with a period

Taking into account relation (1), we obtain the period of the diffraction pattern

those. irrespective of the wavelength, a one-dimensional standing electromagnetic field would form, the period of which is half the period of the gratings in this pair. When using diffraction beams of the 2nd order

Formulas (1) - (4) accurately describe the two-beam interference, which is considered here to illustrate the main features of the lattice interference lithography method. In addition, double-beam interference lithography is used in the proposed method for the manufacture of diffraction gratings with the desired period by repeatedly sequentially reducing the period of existing gratings (HHSolak, C. David, J. Gobrecht, V. Golovkina, F. Kerrina, SOKim, PFNealey, Sub-50 nm period patterns with EUV interference lithography, Microelectronic Engineering, v. 67-68 (2003), pp. 56-62).

In a really used optical system of two mutually perpendicular pairs of diffraction gratings 3 and 4 (Fig. 1) with periods PX and PY, 4 secondary diffraction beams immediately interfere. They create a standing electromagnetic field (interference pattern) with a periodic two-dimensional distribution of the relative radiation flux density W / W0 in the plane of the film 1 (Fig. 3), and for the first-order diffraction beams, periods DX and DY of the interference pattern along the X and Y axes in In this case, the respective periods of PX and PY of the pairs of diffraction gratings are equal (not PX / 2 and PY / 2, as in the case of two-beam interference on a separate pair of gratings) and also are independent of the wavelength.

The three-dimensional graph of FIG. 3 shows interference pattern 5 for a particular case, as an example, when the period of diffraction gratings 4 is twice as large as the period of gratings 3: PY = 2PX, i.e. for DY = 2DX, in three-dimensional space, where the X and Y coordinates specify the surface point of the polymer film 1, and the value of the corresponding coordinate Z = Z (X, Y) is the normalized flux density W / W0 at this point of the film, where W0 is the maximum flux density value. In Fig.3, the dimensions of the interference pattern along the X and Y axes are normalized to the value of the PX period.

The two-dimensional graph of Fig. 4 shows the same distribution for a particular case of identical steps of pairs of diffraction gratings PX = PY, represented by lines 6 of the same density W / W0 of the radiation flux (indicated by the number in the line break) in the projection onto the surface of the polymer film (by analogy with lines of the same height - “horizontals” in cartography). When using pairs of diffraction gratings with equal periods PX = PY = P, the periods DX and DY of the two-dimensional diffraction pattern are the same: DX = DY = D, moreover, when the first-order beams interfere, D = P (when the second-order interference D = P / 2), and lines of equal radiation flux density 6 form concentric quasicircles arranged in a checkerboard pattern (figure 4). These concentric quasi-circles 6 actually appear to be ordered in a periodic structure of square cells 7, in the coordinate system (x, y), rotated by an angle of 45 ° relative to the original axes X and Y, with a period that we denote as 2r0. As can be seen from figure 4,

and when the interference of beams of the second order D = P / 2 and

Parameter 2r0 determines the size of a square cell 7 of the periodic structure of interference pattern 5 and, therefore, the maximum theoretically possible transverse pore size when using diffraction gratings with a given period P. Thus, the order of pore size in the proposed method is determined by the period of applied diffraction gratings P by the formulas (5 ) and (6). The distribution of the radiation flux density W / W0 in a separate cell 7 of this structure is shown in FIG. 5, where

r is the distance from the center of the cell 7, or the radius of the circle formed by a line equal to the radiation flux density 6,

r / r0 is the normalized (for general consideration) distance from the center of the cell 7 by ½ the length of the side of the cell.

For large values of the flux density (near the center of the cell), lines of density 6 are circles with great accuracy. As you move away from the center of the cell, the shape of these lines deviates slightly from the shape of the circle. Figure 6 shows the change in the normalized radiation flux density W / W0 from the value of the normalized radius r / r0 in the direction parallel to the side of the cell 7 - r and at an angle of 45 ° to it - r45.

The difference in the curves in the graph of FIG. 6 becomes noticeable only at the edges of the cell at W / W0 <0.2. This region, as a rule, will be located outside the region of the hole being formed in the cell (of an individual pore), therefore, for most practical applications, it is possible to approximate the shape of lines of equal flux density 6 with a circle of radius r.

In this case, the radiation flux density can be considered as a function of one variable - the radius of the corresponding approximating circle in the cell:

W = W (r).

The process of photochemical formation of a membrane filter is as follows. A film of a polymer material 1, for example, such as either polyethylene terephthalate (PET), or polyimide, or polycarbonate, or polysiloxane, or carbon, is placed in the focus of an optical interference lithography system (Fig. 1). Let the radiation wavelength λ, the maximum radiation flux density W0 be given, and the dependence of the photoetching rate R on the radiation flux density W for the selected film material and the radiation wavelength be known or previously experimentally determined (for example, see Fig. 7), the periods of the diffraction gratings and PY are selected according to the type and target dimensional parameters of the fabricated membrane filter. The chamber is filled with reaction gas, preferably hydrogen, forming volatile substances with the film material under the action of radiation. It is possible to use for this some other gases, for example oxygen, chlorine, fluorine. However, hydrogen is preferred due to the smallest molecular weight. Its molecules have the highest speed of thermal motion (1700 m / s under normal conditions, and oxygen molecules - only 425 m / s), which ensures faster transport to the reaction zone. In addition, in the photoreaction with polymers, hydrogen forms substances with a lower molecular weight: methane -CH ₄ (M.w. = 16), water -H ₂ O (M.w.m18), ammonia -NH ₃ (M.w. = 17), silane-SiH ₄ (M.w. = 32), which ensures their faster transport from the reaction zone.

For example, the gross reactions of photo-etching of polymers (based on the monomer unit of the polymer) in a hydrogen atmosphere are given below:

polyethylene terephthalate (lavsan) - C ₁₀ H ₈ O ₄ + 20H ₂ = 10CH ₄ + 4H ₂ O;

polycarbonate (bisphenol ether A) - C ₁₆ H ₁₄ O ₃ + 28H ₂ = 16CH ₄ + 3H ₂ O;

polyimide - C ₁₆ H ₁₄ O ₄ N ₂ + 32H ₂ = 16CH ₄ + 4H ₂ O + 2NH ₃ ;

polymethylphenylsiloxane - C ₇ H ₈ OSi + 12H ₂ = 7CH ₄ + H ₂ O + SiH ₄ ;

carbon - C + 2H ₂ = CH ₄ .

While, for example, in the reaction with oxygen, a lot of carbon dioxide CO ₂ would form (MW = 44), and photo-etching of polymethylphenylsiloxane would lead to the formation of silicon dioxide - the product is by no means volatile. Finally, it is very important that hydrogen is much less than other gases that absorbs radiation in the range of 5-100 nm, which ensures the practical absence of radiation flux loss in the chamber.

The working pressure of hydrogen is chosen so that, first of all, it is provided with an excess of its supply to the reaction zone to provide a hydrogenation reaction when chemical bonds in the polymer are broken under the action of radiation. Therefore, the necessary hydrogen flow into the reaction zone will depend on the radiation flux density W: the higher the radiation flux density, the greater the rate of polymer bond breaking and the more hydrogen is needed to saturate them. With a sufficient amount of hydrogen, which completely ensures saturation of the broken bonds (zero order hydrogen reaction), the spatial distribution of the polymer photo-etching rate in the film plane will be proportional to the distribution of the radiation flux density:

Where

R (r) is the distribution along the radius r (see Fig. 5) of the photo-etching rate of the polymer in the plane of the film 1;

A is a constant depending on the material of the film (see Fig.7);

W (r) is the distribution along the radius r of the radiation flux density (see Fig.6).

The required hydrogen pressure is preferably calculated on the basis of the molecular-kinetic theory of gases, and for real radiation densities in the range W0 = 50 ÷ 500 mW / cm ² (in a real interference lithography system), the hydrogen pressure can be 0.5 ÷ 2 Pa. At such pressures, the effect of absorption of radiation by hydrogen on the photo-etching rate of the polymer in the working wavelength range is negligible. The chamber is preferably flow-through, with constant pumping and inlet of hydrogen to remove reaction products from the chamber and maintain the hydrogen concentration constant.

Photo etching occurs according to the laws of isotropic etching. At each moment of time, the rate of further propagation of the etching front at each point r of the current front is determined by the local speed R (r). The profiles (longitudinal sections) of the formed pore (Fig. 8) in a separate cell are obtained by numerically solving the wavefront propagation equation - an analogue of the eikonal equation that describes the propagation of a light wave front in a medium with a variable refractive index (V. Lavruk, V. Manuilov ., Matveev VM, Models of the manifestation of X-ray resistors, Electronic Technology, Series 3. Microelectronics, issue 1 (140), 1991, pp. 35-38), and are presented in Fig. 8.

On Fig introduced notation:

h0 is the thickness of the polymer film;

Z / h0 is the current coordinate along the Z axis (in Fig. 1), measured from the lower surface of the polymer film and normalized to the film thickness (on the lower surface of the film Z / h0 = 0, on the upper - Z / h0 = 1);

lowercase letters a – d mark the nanopore profiles during photo-etching for specific instants of time t normalized to the etching time t0 of the film over the entire thickness h0 in the center of the cell, where the etching rate is maximum:

a - t / t0 = 1.1, b - t / t0 = 1.2; c - t / t0 = 1.3; g - t / t0 = 1.4, d - t / t0 = 1.5.

The time t0 is determined by dividing the thickness of the polymer film h0 by the known in advance (for example, from Fig. 7) etching rate for a given material of the polymer film 1 at the existing maximum radiation flux density W0 corresponding to the center of the cell:

From Fig. 8 it can be seen that the resulting pores expand to different degrees at different photo-etching times t / t0 from the lower surface of the polymer film to the upper one and can be conditionally considered conical.

From Fig. 8 it can be seen that the passage radius of the formed pore, i.e. the pore radius at the lower boundary of the film, denoted in the normalized form as rQ / r0 (it is indicated for profile a), which determines the porosity Q of the fabricated membrane filter, is set by the appropriate choice of the normalized photo-etching time t / t0. The time dependence of this radius rQ / r0 = rQ / r0 (t / t0) obtained by the same numerical methods as the photo-etched profiles in Fig. 8 is presented in Fig. 9.

Thus, in the polymer film 1, an ordered pore structure of the membrane filter is formed, corresponding to the structure of the interference pattern 5 (see, for example, FIG. 4) formed by the grating interference lithography system (see FIG. 1).

In this ordered pore structure, porosity is defined as the ratio of the area of the passage of the pore to the area of the cell:

where Q is the porosity;

rQ is the radius of the pore through hole (see Fig. 8);

2r0 — cell side 7 or period of the periodic structure (see FIG. 4);

π (rQ) ² is the area of the pore through passage;

(2r0) ² is the area of cell 7 (see Fig. 5):

After simplifying equation (9)

This dependence is shown in the graph of figure 10.

The limiting value of porosity (at rQ = r0) in the system of round pores is

Thus, the porosity in the proposed method for pores with a round cross-section (for identical periods of pairs of diffraction gratings) is determined by the radius of the pore through hole, which is obtained by choosing the appropriate photo-etching time (with a known dependence of the photo-etching rate for a given polymer on the radiation flux density).

We considered the preparation of a membrane filter with round cross-sectional pores using a grating interference lithography system with pairs of diffraction gratings (3 and 4 in FIG. 1) with the same period. Using lattices with different periods, one can similarly obtain pores of a quasi-elliptic cross section. For example, figure 11 shows the structure of the interference pattern 5 for the case of the use of pairs of gratings 3 and 4 with periods PY = 2PX (the notation is similar to the notation in figure 4).

In this case, the periodic structure of interference pattern 5 shown in Fig. 11 (Fig. 1), similar to the case considered above (Fig. 4) using pairs of diffraction gratings with equal periods, is also formed.

But in this case, the cells 7 (Fig. 11) of the periodic structure of the interference pattern are rhombs with a side equal to 2r0, it is also the period of the ordered structure of the interference pattern 5. The lines of equal flux density 6 (only one line per cell is shown) form concentric ellipses (more precisely, quasi-ellipses, similar to quasi-circles in Fig. 4).

12 shows cell 7 of the periodic structure of interference pattern 5, where 8 is an ellipse inscribed in cell 7, 6 is one of the ellipses of equal radiation density, 2r0 is the side of the cell, or the period of the periodic structure of interference pattern 5 (Fig. 1), r is the distance from the center of the cell to the point of intersection with an ellipse of equal radiation density (rQ is to the intersection with the edge of the passage hole of the elliptical pore) along the line r0, a0, b0 is the semiaxis of the ellipse 8 inscribed in the cell 7, and a and b, respectively, are the semiaxes of an arbitrary ellipse 6 equal density values, aQ and bQ are the semiaxes of the pore through hole. The values of r and r0 in the case of obtaining elliptical pores are used to determine the characteristics in the same way as previously for the case of round ones (Figs. 8, 9, 10).

However, if the passage hole of the round pore has one characteristic - the diameter is 2rQ or the radius rQ, then the elliptic has two - the major and minor axis - aQ and bQ. Therefore, it becomes necessary to express them in terms of r and r0. For such a connection, we use the second Apollonius theorem (http://www.pm298.ru/ellips18.php). which states that the area of the rhombus S, for example, cell 7 in FIG. 12, describing an ellipse, for example ellipse 8, with half axes a0 and b0

S = 4a0b0. On the other hand, the area of rhombus 7 is equal to half the product of its diagonals:

S = PxPy / 2,

where Px Py are the periods of diffraction gratings in the case of using 1st-order interference (in the case of 2nd-order interference, substitute Px, Py-Px / 2, Py / 2 in the expression).

Equating the values of the areas of the rhombus 7

,

,

On the other hand, from Fig. 11 by the Pythagorean theorem it can be seen:

Dividing equation (13) by equation (12) and performing simple transformations, we obtain

Equation 14 establishes the relationship between the half-axes and the half-length of the cell side, and more simply, between the axes of the ellipse 8 - 2a0, 2b0 inscribed in the cell 7 and the cell side 2r0 of the periodic structure, taking into account that the ratio of the axes of the ellipse is given by the ratio of the periods of the diffraction gratings Px and Py.

According to the principle of similarity for an arbitrary ellipse 6 of equal radiation density (Fig)

Where

a, b are the semiaxes of the ellipse equal to the radiation flux density,

r is the distance from the center of the cell of the periodic structure to the middle of the side of the rhombus, which describes an ellipse of equal radiation density with half axes a and b, and for the passage opening of the pore

Using the above Apollonius theorem for the area of a rhombus describing an ellipse and the well-known formula for the area of an ellipse, we can determine the maximum possible porosity of a filter with elliptical pores:

where Q _max - the maximum possible porosity of the filter,

a0, b0 — semiaxes of the ellipse 8 inscribed in the cell of the periodic structure 7;

π · a0 · b0 is the area of the ellipse 8 inscribed in the cell of the periodic structure;

4a0 · b0 is the area of the rhombus describing the ellipse 8 with the semi-axes a0, b0 according to the above Apollonius theorem. Thus, the maximum achievable porosity is the same for a filter with round and elliptical pores and does not depend on the ratio of the axes of the latter.

The performed calculations allow the implementation of the proposed method in the case of elliptical pores to apply the parameters t / t0, rQ / r0 above in Figs. 8, 9, 10 for round pores.

When exposing the polymer film 1 in a hydrogen atmosphere, an ordered structure of elliptical pores in the membrane filter is obtained, corresponding to the structure of the interference pattern 5 on the polymer film 1 formed by a grating interference lithography system (Fig. 1). The possibility of manufacturing the proposed method of a membrane filter with elliptical pores related to the so-called "slot" is a very useful technical result, because it is known that pores of this shape clog less during filtration due to the fact that the probability of a particle completely overlapping the pore cross section in the case of a slit pore is much less than in the case of a round one. In addition, such “elliptical” filters (sieves) can be an effective means of separating in shape (centrosymmetric and axisymmetric) nanoparticles of similar size.

A necessary condition for the implementation of the proposed method for the manufacture of membrane filters using lattice interference lithography is a high degree of coherence of undulator radiation (close to 100%). Since the degree of coherence decreases with decreasing wavelength, for the best modern sources, an acceptable range of wavelengths begins with 5 nm. The upper limit of the operating range cannot be greater than 100 nm due to a sharp increase in the absorption of radiation in the components of the system with a further increase in the wavelength. In addition, the shorter the radiation wavelength, the larger the pore size range of the membrane filter can be obtained on it due to the limited step size of the interference gratings, which cannot be less than half the wavelength. The preferred wavelength is near 10 nm. In particular, it is advisable to use a wavelength of 13.4 nm, at which the best Mo / Si multilayer interference mirrors operate. In specific implementations of the proposed method, such mirrors may be needed to control radiation beams (in addition, at this wavelength, in principle, it is possible to implement not only a lattice, but also a mirror interference lithography system).

Nanoporous filters are characterized by a large filtration resistance, the overcoming of which requires a pressure of tens of atmospheres. This resistance is proportional to the pore length (filter thickness) and inversely proportional to the square of the pore diameter. Under these conditions, it is advisable to make it as thin as possible to reduce the resistance of the membrane filter. The minimum possible thickness of a membrane filter is determined by the technological capabilities of manufacturing a film of a minimum thickness, which is currently significantly less than 100 nm, both for polymers and metals, and for inorganic materials. However, the practical use of filters of such a thickness seems unrealistic both in terms of the possibility of technological manipulation of such a thin film, and in terms of the possibility of its use (due to the low intrinsic strength) for filtration at real pressure.

Therefore, the proposed method implements the concept of a reinforced membrane filter 9 (see Fig. 13) with nanopores 10 made of, for example, a thin (less than 100 nm) polymer film 1, mounted on a reinforcing structure 11 of a sufficiently large thickness (of the order of 10 to 50 μm) with an ordered pore structure of 12 microns in size (for example, with a diameter of 10 to 100 μm). Upon further consideration of the reinforced membrane filters, for convenience of distinguishing, we will call the film part of it 9 “a nanoporous membrane filter”, pores 10 in it are “nanopores”, and pores 12 in the reinforcing structure 11 are “micropores” in accordance with their characteristic sizes. The technological scheme for the manufacture of similar microporous structure-reinforced membrane nanoporous filters from inorganic materials and metals is shown in Figs. 14 and 15.

The reinforcing structure 11 of the micropores 12 (see, for example, Fig. 13) provides a multiple increase in the strength of the membrane nanoporous filter 9. The pressure drop that it maintains is now determined by the strength of the membrane from a thin polymer film in a separate micropore 12 of the reinforcing structure 11. For example, for a round micropore 12 with a diameter d and a membrane with thickness h0 on it, the relationship between the pressure drop p on the membrane, the deflection of the membrane s and the total stress σ in the membrane material is determined by well-known formulas (Effect of stress on the stability of X-ray masks. M. Karnezos. J. Vac. Sci. Nechnol., B 4 (1), 1986)

where σ0 is the initial stress in the membrane (depends on technology and operating temperature),

E = 8 · E0 / 3 (1-ν) is the effective modulus of elasticity of a round membrane,

E0 and ν are Young's modulus and Poisson's ratio of the membrane material, respectively. Excluding s from (18a) and (18b), we obtain

Thus, the maximum pressure maintained by the membrane is inversely proportional to the diameter d of the micropore 12.

To determine the maximum possible pressure difference across the membrane, it is necessary to substitute in (18) the breaking stress of the membrane material (for example, a polymer film). For example, for a polyimide film with a thickness of 50 nm on a micropore with a diameter of 10 μm for typical values of E ₀ = 4000 MPa, ν = 0.4 and tensile stress σ = 100 MPa at zero initial stress σ _0, we obtain

p = 60 MPa = 600 atm.

Initial stresses lead to a decrease in the maximum possible pressure. But if the initial voltage is even 50% of the breaking voltage (the actual initial stresses are in most cases much less), then the maximum allowable pressure drop decreases by only 1.4 times.

The scalability of the result defined by formula (18) with changes in h0 and d is obvious. Therefore, for example, we can conclude that the working pressure drop p = 100 atm will be maintained with a 6-fold increase in the diameter d of micropores in the reinforcing microporous structure (up to 60 μm). On the other hand, it is possible to reduce the thickness of the film h0, while maintaining strength, to about a few nanometers, reducing the diameter of the micropore d on which it is placed.

Thus, it is seen that a membrane several tens of nanometers thick, mounted on a micropore with a diameter of several tens of microns, can withstand quite significant pressures, of the order of tens of atmospheres. Therefore, there is no need for this embodiment of the membrane filter to produce it from films thicker than 100 nm (the conventional range of sizes of nano-objects). Such nanoporous membrane filters reinforced with microporous structures are manufactured by the proposed method in combination with known methods used in silicon microelectronics technology and the LIGA process (see below).

An example of a technological scheme for manufacturing a silicon nanoporous membrane reinforced with a silicon microporous structure is shown in Fig. 13 (note: size proportions are not met, a fine pore structure, for example, taper, is not shown, the orientation of the plate in the diagram does not always correspond to the real one in the process, structures are shown in section a plane passing through the longitudinal axis of the pores), where:

13 - silicon wafer (diameter from 100 to 200 mm, thickness from 380 to 1000 microns),

1 - a polymer film (less than 100 nm thick) from, for example, either polyimide, or polyethylene terephthalate, or polycarbonate, or polysiloxane, or carbon,

11 - reinforcing microporous structure of silicon;

12 - micropore reinforcing structure of silicon in size (diameter for round, side of the rectangle for rectangular pores) from 10 to 100 microns,

9 - membrane nanoporous filter obtained from a polymer film 1;

10 - nanopore size (diameter for round, axis of the ellipse for elliptical pores) from 1 nm or more;

A - the operation of applying the polymer film 1 (hereinafter, the arrow indicates the side of the plate on which the operation is performed) on the surface of the silicon wafer 13 using one of the known methods

(e.g. Juan Schneider, Ultra Thin Polimer Films for photolithographic Applications, Nanometrix, March 2005, Internet version

http://www.nanometrix.com/pdf/Ultra%20Thin%20Polymer%20Films%20for%20photolithography.pdf; Laermer F., Urban A. Microelectronic Engineering, 2003, V.67, P.349; Rangelov I.W. Journal of Vacuum Science and Technology. 2003.V.A21. No. 4. P.1550)

B - etching of a silicon wafer 13 from the reverse side to a thickness of 50 μm by the method of plasma-chemical etching (VLSI technology. In 2 books. Transl. From English. Edited by S.Z. M .: Mir. 2006),

B - lithography (for example, Chernyaev VN Technology for the production of integrated circuits and microprocessors. A textbook for universities. M: Radio and communications. 2007; Rangelov IW Journal of Vacuum Science and Technology. 2003. V.A21. No. 4. P.1550) on the back of the plate 13 for opening micropores 12,

G - lattice interference lithography on a polymer film 1 or on the front side of the plate 13 of the proposed method, as shown by the arrow in Fig. 13, or on the opposite side, through micropores 12, which allows the previously mentioned large depth of field of the interference pattern (GR in figure 2 )

A polymer film 1 is applied to the silicon wafer 13 in a known manner (operation A). The choice of a silicon wafer for the manufacture of a reinforcing microporous structure 11 is preferable due to the refinement of all applicable known operations (A, B, C) for silicon in microelectronics. In principle, it is possible to use a plate of many other materials, if developed for them, or to develop the applicable technological operations of deposition, photolithography, etching. Pit the silicon wafer 13 on the other hand to a thickness of 50 ÷ 100 μm (B). The thinning of the wafer is necessary for the following operation (B) to be successfully carried out (B): the formation of micropores 12 in the silicon wafer 13 by a known photolithography method, obtaining a reinforcing microporous silicon structure 11. The micropores 12 in the silicon wafer are made round or rectangular. Preferably rectangular, in order to achieve greater porosity of the reinforcing microporous structure 11, because it was shown above that the maximum attainable porosity of an ordered structure with round or elliptical pores is -0.785, while it is obvious that the maximum attainable porosity of rectangular pores is -1.0. It is easy to show that the real porosity of the structure of rectangular pores with a wall thickness between pores of 0.1 from the micropore side is about 0.8. It makes sense to fight for the maximum porosity of the reinforcing microporous structure 11 because the resulting porosity of the reinforced nanoporous filter is equal to the product of the porosities of the membrane nanoporous filter 9 and the reinforcing microporous structure 11, so the resulting porosity of the reinforced membrane filter can be approximately 0.6 × 0.8 = 0.48. The pore size of the reinforcing structure 11 is selected taking into account the above estimates (formula (18)) of the strength of the formed nanoporous membrane filter 9. Then, by the proposed method, lattice interference lithography is performed on a film 1 placed on a reinforcing microporous structure 11 (operation D in Fig. 13), and a nanoporous membrane filter 9 is obtained from a polymer film reinforced with a microporous silicon structure 11.

An example of a technological scheme for manufacturing a nanoporous filter from an inorganic film or from a two-layer organic and inorganic film reinforced with a microporous silicon structure is shown in Fig. 14 (size proportions not observed, fine pore structure, for example, taper, not shown, plate orientation in the diagram does not always correspond real in the technological process, the structures are shown in section by a plane passing through the longitudinal axis of the pores), where:

13 - silicon wafer (diameter from 100 to 200 mm, thickness from 380 to 1000 microns),

14 is a film of a thickness of less than 100 nm from an inorganic material, for example, either silicon nitride or silicon carbide, or boron carbide, or boron nitride, or titanium nitride, or a metal (for example, either gold, or titanium, or platinum, or palladium, or zirconium, or their alloys, including with other metals),

11 - reinforcing microporous structure of silicon;

12 - micropore size (either round diameter or side of the rectangle) from 10 to 100 microns,

1 - a polymer film with a thickness of less than 100 nm from, for example, either polyimide, or polyethylene terephthalate, or polycarbonate, or polysiloxane, or carbon,

9 - membrane nanoporous filter from a polymer film;

10 - nanopore in a polymer film 1 size (diameter for round, axis of the ellipse for elliptical pores) from 1 nm or more,

15 - nanoporous filter of inorganic material;

16 - nanopore in a film of inorganic material 14 size (diameter for round, axis of the ellipse for elliptical pores) from 1 nm or more,

And - applying a film 14 of inorganic material in a known manner (for example, J.P. Li et al., Appl. Phys. Lett. 62 (24), 1993; B.I. Kim et al., JEDM 97-463-466),

B - etching in a known manner (for example, Chernyaev VN Technology for the production of integrated circuits and microprocessors. A textbook for universities. M: Radio and communications. 2007) silicon wafer 13 from the back to a thickness of 50-100 microns,

In - photolithography in a known manner (for example, Chernyaev VN Technology for the production of integrated circuits and microprocessors. A textbook for universities. M: Radio and communications. 2007) from the back of the plate 13 to open micropores 12 in silicon to a film of inorganic material,

D is a deposition operation in a known manner (see references to operation A in FIG. 13) of a polymer film 1 onto a surface of a film of inorganic material 14,

G - interference lithography on a polymer film 1 of the proposed method,

E - chemical etching in a known manner (Egglet BJ, IEEE Journal of Selected Topics in Quantum Electronics. 2001. Vol.7. N.13. P.409-423) of an inorganic film 14 through a membrane filter from a polymer film 9 as a mask, manufacturing a two-layer membrane nanoporous filter of a polymer film 9 and an inorganic film 15 reinforced with a silicon microporous structure 11,

G - removal of a nanoporous membrane filter from a polymer film 9 in a known manner (Poltavtsev Yu.G., Knyazev A.S. Technology of surface treatment in microelectronics. Kiev: Technique. 1990), manufacture of a nanoporous membrane filter 15 from an inorganic film 14 with nanopores 16 in size (diameter of round or elliptical axis) pores from 1 nm or more.

On a silicon wafer 13, a film of inorganic material 14 is applied in a known manner (operation A, Fig. 14), etch the silicon wafer 13 on the other hand to a thickness of 50 ÷ 100 μm (B), photolithography is carried out on this side in a known manner, by etching micropores in silicon with a size of 10-100 μm to a film of inorganic material 14 (operation B in Fig. 14), is applied in a known manner to a film of inorganic material 14, a polymer film 1 (operation D in Fig. 14), interference lithography is performed on it by the proposed method ( opera Ya G in Fig. 14), through the mask 9 thus obtained, chemical etching of the film of inorganic material 14 is carried out to obtain a nanoporous filter 15 with nanopores 16. A two-layer nanoporous filter of inorganic material 15 is obtained, coated with a membrane nanoporous filter of polymer material 9. Thus In this way, a two-layer nanoporous filter can be obtained from inorganic material 15 coated with a polymer material 9, reinforced with a silicon microporous structure 11. A mask filter from a polymer film 9 can o remove in a known manner and get a membrane nanoporous filter of inorganic material 15, reinforced with a silicon microporous structure 11.

In this embodiment, the implementation of a membrane filter of inorganic film at the stage of chemical etching, there is a restriction on the minimum possible pore size due to the limitation of the technology of chemical etching, which consists in the fact that etching the holes is chemically possible only with the so-called “Aspect ratio” (ratio of pore diameter to film thickness) not more than 1: 5. Thus, the thickness of the inorganic film determines the possible minimum pore size: it cannot be obtained less than 1/5 of the film thickness of the inorganic material. That is, for example, a pore diameter of 1 nm can be obtained only if it is possible to obtain a film of inorganic material with a thickness of 5 nm. Such technologies already exist (for example, Rangelov I.W. Journal of Vacuum Science and Technology. 2003. V.A21. No. 4. P.1550).

An example of a technological scheme for manufacturing an all-metal nanoporous filter is shown in Fig. 15 (notes: size proportions are not met, the fine structure of the pores is not shown, the orientation of the plate in the diagram and in the real process does not always coincide, the letters indicate technological operations, arrows indicate the side of the plate to be processed, structures are shown in section by a plane passing through the longitudinal axis of the pores), where:

13 - silicon wafer,

14 - a film of a metal, for example, gold, or platinum, or palladium, or titanium, or zirconium, or their alloys, including with other metals, less than 100 nm thick, deposited on the surface of the silicon wafer 13,

17 - photoresist layer with a thickness of 1 to 10 microns,

18 is a latent image of the structure of micropores in the photoresist,

19 is a mask of photoresist for electroforming micropores of the reinforcing structure 11,

11 - reinforcing metal microporous structure with a thickness of 1 to 10 microns,

12 - micropore with a size (diameter for round, side for a rectangular pore) from 10 to 100 microns,

1 - polymer film with a thickness of less than 100 nanometers,

9 - nanoporous filter from a polymer film 1, used as a mask for chemical etching;

10 - nanopore in a polymer film 1,

15 is a metal membrane nanoporous filter,

16 - nanopore metal membrane filter 15 with a size (diameter for round, axis of the ellipse for elliptical pores) from 1 nm or more,

11 in conjunction with 15 - all-metal membrane filter,

A - application in a known manner (Tarui Ya. Fundamentals of VLSI technology. Translated from Japanese. M: Radio and communication. 1985; VLSI technology. In 2 books. Translated from English. Edited by C. Z. M.: Mir . 2006; Laermer P., Urban A. Microelectronic. Engineering. 2003. V.67. P.349; Rangelov IW Journal of Vacuum Science and Technology. 2003. V.A21. No.4. P. 1550) metal film 14 onto the silicon wafer 13,

B - application in a known manner (VLSI technology. In 2 books. Transl. From English. Edited by C. Z. M .: Mir. 2006; Laermer P., Urban A. Microelectronic. Engineering. 2003. V.67. P .349; Rangelov IW Journal of Vacuum Science and Technology. 2003. V.A21. No. 4. P.1550) a photoresist layer 17 with a thickness of 1 to 10 μm on the surface of a metal film 14,

B - exposure of the photoresist (VLSI technology. In 2 books. Transl. From English. Edited by S.Z. M .: Mir. 2006) 17 through the photomask of the micropore structure (not shown), obtaining a latent image of micropores 18,

G is the manifestation of photoresist 17, obtaining a mask 19 for electrodeposition of a metal in a known manner (L. Singleton, J. of Photopolimer Sci. And Tech., V.16, N3 (2003), 413-422),

D - electroforming in a known manner (L. Singleton, J. of Photopolimer Sci. And Tech., V.16, N3 (2003), 413-422) of a reinforcing metal microporous structure 11,

E - removal in a known manner (L. Singleton, J. of Photopolimer Sci. And Tech., V.16, N3 (2003), 413-422) of the photoresist structure 18 and silicon wafer 13, obtaining a reinforcing metal microstructure 11 with micropores 12,

G - deposition of a polymer film 1 (the same links as in step A in the description of the technological scheme for manufacturing a membrane filter reinforced with a silicon structure in Fig. 13, p. 18) on the surface of the metal film 14 that was released after removal of the silicon wafer 13,

C - lattice interference lithography of the proposed method for a polymer film 1, obtaining a nanoporous polymer filter 9 with nanopores 10,

And - etching in a known manner (Akimenko S.P., Mamonova T.I., Orelovich O.L. Membranes. 2002. No. 15, p.21-28; Poltavtsev Yu.G., Knyazev A.S. Surface treatment technology in microelectronics. Kiev: Technics. 1990; Ryndin EA Designing specialized VLSI. Taganrog: TRTU. 1999) of a metal film 8, through a nanoporous membrane filter from a polymer film 9 as a mask, obtaining a two-layer (9 - polymer, 15 - metal ) a nanoporous filter reinforced with a metal microporous structure 11,

To - the removal of the polymer nanoporous filter 9 in a known manner (Danilin BS, Kireev V.Yu. Application of low-temperature plasma for cleaning and etching of materials. M .: Energoatomizdat. 1987), obtaining a metal nanoporous filter 15 reinforced with a metal microporous structure 11, those. all-metal nanoporous filter.

An all-metal membrane filter is manufactured by the proposed method using well-known operations of microelectronics technology (for example, VLSI technology. In 2 books. Transl. From English. Edited by S.Z. M .: Mir. 2006) and LIGA technologies (for example, L. Singleton, J. of Photopolimer Sci. And Tech., V.16, N3 (2003), 413-422).

A - on a silicon wafer 13 a metal film 14 is applied in a known manner;

B - a layer of photoresist 17 is applied to a metal film 14 in a known manner;

In - expose the photoresist through the photomask structure of micropores (not shown), get a latent image of micropores 18;

G - show a latent image of micropores 18 and get a mask for electrodeposition 19;

D - conduct electrodeposition through the mask 19 in a known manner and get a reinforcing metal microporous structure 11;

E - remove the photoresist 18 from micropores of a reinforcing metal microporous structure 11 and a silicon wafer 13 in a known manner, obtain a purified metal microporous (micropores are covered by a metal film 14) reinforcing structure 11;

G - on the surface of the metal film 14 released after removal of the silicon wafer 13, the polymer film 1 is applied in a known manner;

C - on the film 1 conduct lattice interference lithography of the proposed method, get a nanoporous filter from a polymer film 9 with nanopores 10;

And - etching of the metal film 14 through a nanoporous polymer filter 9 as a mask is carried out in a known manner, a metal nanoporous filter 15 with nanopores 16 is obtained (note: since chemical etching of a metal film cannot produce pores with an aspect ratio of more than 5, with a minimum thickness of the metal film 14 in 30 ÷ 100 nm, the minimum achievable pore size 16 in the metal nanoporous filter 15 is 6 ÷ 20 nm depending on the thickness of the metal film 14. To obtain nanopores with a size of the order of 1 nm metal film thickness should be less than 5 nm). The resulting structure can already be used as a nanoporous filter in accordance with operating conditions. But you can do the operation

K is a polymer nanoporous filter 9 in a known manner removed from the surface of a metal nanoporous filter 15 and get a reinforced all-metal nanoporous filter, consisting of a metal nanoporous filter 15, mounted on a metal microporous reinforcing structure 11. Obtaining a metal nanoporous filter by the described method leads to additional technical results: all-metal nanoporous filters made from these noble or chemically resistant metal c, are distinguished by chemical, thermal, radiation resistance and biochemical inertness, they are flexible in contrast to the nanoporous filters described above, for example, on a silicon reinforcing structure, which makes it possible to form, for example, cartridge filters, allowing to reduce the overall dimensions of the final product, which is relevant in case of use in medicine. An additional technical result is the possibility of using the described metal nanoporous filters as cutoffs of the long-wavelength part of the spectrum of soft x-ray and hard ultraviolet radiation with good, due to the large porosity, transmittance of the short-wavelength part of the spectrum of these radiation.

In this embodiment, it is possible to use other metals other than those listed if their physicochemical properties correspond to specific operating conditions.

The implementation of the proposed method of manufacturing a membrane filter is illustrated by the following examples.

Example 1 of the manufacture of a membrane filter from polymer films with a thickness of 5 μm (commercially available polyethylene terephthalate, polyimide, polycarbonate from 1 μm, for example, http://www.elec.ru/market/offer-172195847.html) with round pores with a diameter of about 30 nm

Preset conditions:

Pairs of gratings 3 and 4 in FIG. 1 with the same period P = 60 nm, undulator radiation λ = 13.5 nm, maximum radiation flux density W0 = 150 mW / cm ² , film thickness h0 = 5 μm, first-order interference, pressure in a hydrogen chamber 1 Pa, the dimensions of the interference pattern 5 (Fig. 1) are 5 × 5 mm.

For the indicated pairs of gratings, the period of the interference pattern upon first-order interference according to formula (5):

Table 1 shows the values of the following variables and process parameters:

R (W0) is the photo-etching rate of the polymer film at the maximum flux density, determined by the schedule in Fig. 7, nm / s,

t0 is the etching time (s) of the polymer film with a thickness h0 at the maximum photo etching rate, determined by dividing the film thickness h0 by the photo etching rate R (W0),

t is the absolute time of photoetching, s, t> t0

and end results:

rQ / r0, the ratio of the size of the pore through hole to the interference pattern parameter, determined by t / t0 according to the graph in FIG. 9,

rQ is the size of the pore through hole, nm, is determined from the ratio rQ / r0 defined above,

Q is the porosity of the membrane filter, determined according to the graph in figure 10 according to the ratio rQ / r0 defined above.

It is easy to see from Table 1 that, by choosing the relative photo-etching time t / t0 appropriately, for given radiation flux density W0 and the period of the pairs of diffraction gratings P, we can obtain the passage pore sizes rQ (from 7 to 19 nm - a change of 2.7 times) and porosity from 0.07 to 0.62 (8-fold change) of the membrane filter.

The scalability of the pore size rQ over the period of diffraction grating pairs P, film thickness h0, film etching rate R (W0), maximum radiation flux density W0, and interference order is evident from formula 5 and table 1. The polymer film is fixed on the registration and multiplication unit table , placed in the focus of the lattice interference lithography system in a chamber filled with hydrogen, choose based on the desired porosity or porosity Q or pore size rQ of the membrane filter pore rQ, exposure time t from table 1 and start the exposure process.

Example 2. The manufacture of a membrane filter from polymer films with a thickness h0 = 5 μm with elliptical pores with an axis ratio of 1: 2

The conditions for performing lattice interference lithography: pairs of gratings 3 and 4 in Fig. 1 with periods of 60 and 30 nm, undulator radiation λ = 13.5 nm, maximum radiation flux density W0 = 150 mW / cm ² , film thickness h0 = 5 μm, interference 1 -th order, the pressure in the hydrogen chamber is 1 Pa, the dimensions of the interference pattern 5 (Fig. 1) are 5 × 5 mm.

The parameter 2r0 of the interference pattern in this case according to formula (13):

,

,

,

,

r0 = 16.8. Then, in table 2, only one variable, rQ, is changed compared to table 1, and the semiaxes of the elliptical pore aQ and bQ are added (see Fig. 12).

the semiaxes of the elliptical passage hole according to the formula (16):

,

,

or after substitution of specific values of PX and PY

aQ bQ = 0.8 (rQ) ² .

Using the calculated rQ and the ratio of the semiaxes of the bore aQ = 2bQ, the values of the semiaxes are calculated.

As in the case of round pores, the scalability of the pore size over the film thickness, radiation flux density, photo-etching rate, periods of diffraction gratings, and the order of interference is obvious.

The film is processed in the same way as in example 1.

Example 3a The manufacture of a membrane filter from polymeric materials reinforced with a silicon microporous structure.

The conditions of lattice interference lithography: the thickness of the polymer film is h0 = 50 nm, the periods of the pairs of diffraction gratings are the same and equal to 20 nm, the first-order interference, the maximum radiation flux density is W0 = 250 mW / cm ² , the wavelength is 13.5 nm, the hydrogen pressure is 1.2 Pa.

According to formula (5), the interference pattern parameter is 2r0 = 14.3 nm (r0 = 7.1 nm).

Table 3 presents the variables and process parameters similar to example 1, but for these conditions, and additionally the resulting porosity of the reinforced filter Q ".

The technological scheme of manufacturing a membrane filter from a polymer film reinforced with a silicon microporous structure is shown in Fig. 13, and the explanations for it above. A polymer film 1 prepared by known methods on a reinforcing silicon structure 11 (after step B) with square (side of a square 50 μm, wall thickness between micropores 10 μm) micropores 12 (porosity of this reinforcing microporous structure Q 0.7 0.7) is placed on a combination and multiplication unit placed in the focus of the lattice interference lithography system in a chamber filled with hydrogen, choose, based on the desired or porosity or pore size of the membrane filter, the exposure time t from table 3a and start the exposure process. Obviously, the resulting porosity of the nanoporous filter 9 reinforced with a silicon structure 11 is equal to the product of the porosity of the nanoporous membrane filter 9 by the porosity Q 'of the reinforcing structure 11: Q "= Q × Q' and are shown in table 3.

It is appropriate to evaluate the achieved technical result in comparison with the prototype. The performance of the membrane filter (filtration rate per unit area of the filter at a certain pressure drop) is generally proportional to its porosity and inversely proportional to the thickness of the membrane. From table 3 it is seen that the proposed method can be obtained porosity of about 6 times more than in the known method (0.43 / 0.07 = 6) with a membrane thickness less than 200 times (10000 nm / 50 nm = 200). Thus, productivity is more than 6 × 200 = 1200 times. This allows a corresponding reduction in the total area of the membrane filter, which is especially important for medical applications, in particular for hemodialysis.

Example 3b The same as in example 3a, except that they use second-order interference, whence W0 = 125 mW / cm ² , and the interference pattern parameter according to formula (6) is 2r0 = 7.1 nm (r0 = 3.5 nm)

From the above examples (tables 1-3b), it can be seen that the technical result (pore size and porosity of the membrane filter) is determined:

1) given conditions: the maximum radiation flux density W0 of the available source, the film material that determines the photo-etching rate R (W0), the film thickness h0, which determines the etching time t0;

2) operational variables set by the operator to obtain certain values of pore size rQ and porosity Q: absolute photo-etching time t and periods PX, PY of pairs of diffraction gratings that determine the parameter r0 of interference pattern 5 and the order of interference;

3) the relationship of the given conditions, operational variables, and pore size rQ, determined by a system of rigidly interconnected dimensionless and independent of the given conditions and operational variable parameters: t / t0, rQ / r0, Q. The applied parametric description of the process is productive for manufacturing a filter with given porosity Q and pore size rQ, an example of which is given in the following example.

Example 4. It is required to fabricate a membrane filter reinforced with a silicon microporous structure, as in example 3b, from a film of polyethylene terephthalate (PET) with a thickness h0 = 100 nm, a radiation flux density of W0 = 125 mW / cm ² , second-order interference, etching rate ( according to the graph of Fig. 7) R (W0) = 31 nm / s.

The required passage pore size rQ = 5 nm, porosity 0.51.

We define t0 = h0 / R (W0) = 3.22 s, from any table 1-3b for porosity 0.51 - t / t0 = 1.5, whence the exposure time t = 1.5 × 3.22 = 4.83 s, and rQ / r0 = 0.8, whence r0 = rQ / 0.8 = 5 / 0.8 = 6.25 nm.

From the formula (6)

,

,

P = 35 nm. Thus, for the manufacture of this filter, pairs of diffraction gratings 3 and 4 (Fig. 1) with periods PX = PY = 35 nm are installed in a four-beam grating interference lithography system, and a polymer film 1 prepared as in Example 3a is placed in a chamber filled hydrogen in the focus of the lattice interference lithography system, and exhibit 4.83 s.

Example 5. Evaluation of the minimum achievable by the proposed method the size of the through hole of the pores of the membrane filter.

From the restriction of undulator radiation that coherence can be obtained only at λ> 5 nm, it follows that the allowable minimum period of diffraction gratings is 2.5 nm. Such gratings can be manufactured according to a technological scheme, for example, a similar scheme in Fig. 14, using successively diffraction gratings with large periods (see above, Fig. 2). To do this, you can take, for example, gratings with a period of 20 nm and using a two-beam grating interference lithography with second-order interference to obtain a linear interference pattern (see figure 2) with a period according to formula (4) P = 20/4 = 5 nm using radiation, for example, 13.5 nm. Then, using these gratings in 1st-order 2-beam grating lithography with radiation λ <10 nm using formula (3), we can obtain the desired diffraction grating with a period of 2.5 nm. It should only be kept in mind that due to the limitations of the chemical etching method in terms of the “aspect ratio” (see above), the thickness of the metal layer to obtain such a lattice should be no more than about 10 nm.

The interference pattern parameter for interference (λ = 5 nm) on such second-order gratings will be r0 = 0.45 nm. We take the values of the parameters t / t0, rQ / r0, Q from any table 1-3b:

Table 4 The minimum achievable by the proposed method, the size of the through hole pore rQ of the membrane filter t / t0 rQ / r0 rQ, nm Q 1.1 0.33 0.15 0.07 1.2 0.57 0.26 0.27 1.3 0.68 0.31 0.36 1.4. 0.75 0.34 0.44 1.5 0.80 0.36 0.51 2.0 0.90 0.4 0.62

Thus, the declared porosity from 0.07 to 0.6 in the limit determined by the radiation coherence condition only at λ> 5 nm can be obtained with pore diameters (2rQ) of pores from 0.3 to 0.8 nm. However, when the pore opening diameter is close to 1 nm, some difficulties should be expected with the transport of hydrogen molecules into the reaction zone and the reverse flow of reaction products, since the pore diameter becomes comparable with the diameter of the molecules (for example, Н ₂ 0.22, H ₂ O 0.3, CH ₄ 0.33, NH ₃ 0.25 nm). Given this circumstance, one can apparently take conditionally the smallest achievable by the proposed method pore size (2rQ) of 0.8 nm with a porosity of 0.62, and rounded 2rQ = 1 nm and a porosity of Q = 0.6. At the same time, it should be noted that the minimum achievable size of the pore openings per se, without reference to high porosity, has no limitations (see the graph in Fig. 10), where it can be seen that at photo etching times t close to time etching the film t0, one can obtain an arbitrarily small size of the passage hole rQ, however, at a low porosity Q. In this case, the process should be carried out with the interference pattern parameters 2r0> 1 nm in order to avoid the mentioned possible complications with the transport of hydrogen molecules into the stocks (see Fig. 8).

Example 6. The manufacture of a membrane filter from inorganic materials reinforced with a silicon microporous structure.

Requirements for the technical result: to make a membrane filter reinforced with a silicon microporous structure (see Fig. 14) from a film or silicon nitride or silicon carbide or boron carbide or boron nitride or titanium nitride or metal (for example, or gold or titanium, or platinum, or palladium, or zirconium) 30 nm thick with round pores with a diameter of 2rQ = 7 nm and porosity Q = 0.6 (here is the porosity of the filter itself from the inorganic film 15, without taking into account the contribution to the porosity of the reinforcing structure 11 in FIG. .fourteen).

Available conditions: radiation flux density W0 = 125 mW / cm ² , 2nd order interference, radiation wavelength λ = 13.5 nm, hydrogen pressure 1 Pa, material for the manufacture of a mask for chemical etching - polyimide 100 nm thick (R (W0) = 26 nm / s, the etching time of the film is t0 = 100/26 = 3.8 s). Dimensions of the interference pattern (frame size) 5 × 5 mm.

Determination of operational variables - exposure time t and period of diffraction gratings R.

From any table 1-4 (it is possible, of course, also from formulas and graphs, as in example 1) for the porosity 0.6, the values of the parameters t / t0 = 2, rQ / r0 = 0.9 are determined, and the necessary photo-etching time t = 2t0 = 7.6 s, and the necessary parameter of the interference pattern is r0 = rQ / 0.9 = 3.5 / 0.9 = 3.9 nm and, according to formula (6), the necessary period of diffraction gratings is P = 21.8 nm.

Manufacturing progress

The flow chart of the manufacture of a membrane filter from an inorganic film reinforced with a silicon microporous structure is shown in Fig. 14, and its description above. On a film of one of the inorganic materials 14 reinforced with a silicon microporous structure 11 in operations A, B, C (Fig. 14) carried out by known methods, a polyimide 1 film 100 nm thick is applied in a known manner (operation D). The resulting composition is placed on the table of the well-known system of combining and multiplying, in the focus of the lattice interference lithography system with 2 pairs of diffraction gratings 3 and 4 (Fig. 1) with the same periods P = 21.8 nm, the exposure time is set in the chamber filled with hydrogen ( frame) t = 7.6 s and interference lithography (G) is performed, obtaining a membrane filter 9 with pores 10 having a through hole with a size of 2rQ = 7 nm and porosity Q = 0.6, mounted on an inorganic film 14. Then, the inorganic film is etched chemically -ethnic material 14 in a known manner (E, 14) using a membrane filter 9 as a mask. As a result, holes 16 with a size of approximately 2rQ = 7 nm are etched under the pores 10 of the membrane filter from the polymer film in the inorganic film 14. The resulting porosity of the filter reinforced by the silicon structure 11 will be equal to the product of the porosity of the membrane nanoporous filter 9 - Q = 0.6 by the porosity of the reinforcing structure (let's say the same as in example 3a - Q '= 0.7), i.e. Q "= 0.42. After this, you can remove the membrane filter mask 9 in a known manner from the surface of the membrane filter from inorganic material 15, but you can, if appropriate, of some kind, leave it as it is - a two-layer membrane filter.

In the manufacture of a membrane filter of inorganic material with a pore opening size approaching a limit of the order of 1 nanometer, one should bear in mind the above mentioned “aspect ratio” limitation (no more than 5) for the chemical etching process. From this limitation it follows the need to apply a layer of inorganic material 14 of extreme fineness, for example, for a pore through hole of 1 nm, the thickness of this layer should be no more than 5 nm. This film thickness of the inorganic material 14 should be coordinated with the size of the micropores 12 of the reinforcing microporous structure 11 to ensure sufficient strength (see formula (18)) of the membrane filter at a given working pressure, it may be necessary to reduce the size of the micropores up to 1 μm, if necessary.

Example 7. The manufacture of all-metal membrane filter.

Requirements for the technical result: to make a membrane filter from, for example, either gold, or titanium, or platinum, or palladium, or zirconium, or their alloys, including with other metals, 30 nm thick, reinforced with microporous structure 11 (see Fig. .15) of the same metal. Pores with a diameter of 2rQ = 7 nm, porosity Q = 0.6 (here, the porosity of the filter itself from the metal film 15, which we called the "nanoporous membrane filter", without taking into account the contribution to the porosity of the reinforcing structure 11 in Fig. 15).

Available conditions: maximum radiation flux density W0 = 125 mW / cm ² , 2nd order interference, radiation wavelength λ = 13.5 nm, hydrogen pressure 1 Pa, material for the manufacture of a mask for chemical etching - polyimide with a thickness h0 = 100 nm (speed photo etching R (W0) = 26 nm / s, film etching time t0 = 100/26 = 3.8 s). Dimensions of interference pattern 5 (frame size) 5 × 5 mm.

Determination of operational variables - exposure time t and period of diffraction gratings R.

From any table 1-4 (it is possible, of course, also from formulas and graphs, as in example 1) for the porosity Q = 0.6, the values of the parameters t / t0 = 1, rQ / r0 = 0.9 are determined, and the necessary photo-etching time t = 2t0 = 7.6 s, and the necessary parameter of the interference pattern r0 = rQ / 0.9 = 3.5 / 0.9 = 3.9 nm and, according to formula (6), the necessary period of diffraction gratings is P = 21.8 nm.

Production progress. The technological scheme of manufacturing a membrane all-metal filter is shown in Fig, and its description above. A film of one of the aforementioned metals 14, reinforced with a microporous structure 11 of the same metal, obtained by known methods (after step E in FIG. 15), is applied in a known manner to a polyimide 1 film of thickness h0 = 100 nm (step G). The resulting composition is placed on the table of the well-known system of combining and multiplying, in the focus of the grid interference lithography system with 2 pairs of diffraction gratings 3 and 4 (Fig. 1) with the same periods P = 21.8 nm, the exposure time is set in the chamber filled with hydrogen ( frame) t = 7.6 s and interference lithography is performed (operation 3, Fig. 15), obtaining a nanoporous membrane filter from a polymer film 9 with pores 10 having a through hole with a size of 2rQ = 7 nm and porosity Q = 0.6, mounted on a metal film 14 a with a reinforced metal microporous structure 11, then chemical etching of the metal film 14 is carried out in a known manner (step I, FIG. 15) using a membrane nanoporous filter from the polymer film 9 as a mask. As a result, holes 16 with a size of approximately 2rQ = 7 nm are etched under the pores 10 of the membrane nanoporous filter from the polymer film 9 in the metal film 14, forming a membrane nanoporous filter from the metal film 15 reinforced with a metal microporous structure 11 of the same metal. The resulting porosity of the all-metal filter reinforced with the metal structure 11 will be equal to the product of the porosity of the membrane nanoporous filter 15 - Q = 0.6 by the porosity of the reinforcing structure (suppose the same as in example 3a - Q '= 0.7), i.e. Q "= 0.42. After this, you can remove the membrane nanoporous filter mask 9 in a known manner from the surface of the membrane nanoporous filter of metal 15, but you can, if appropriate, of some kind, leave it as it is - a two-layer membrane filter.

We gave examples of the production of a membrane filter of large porosity with pores of the smallest size. There are no physical and technological limitations to obtain membrane filters with larger pores by the proposed method. However, it seems that it is advisable to apply the proposed method up to a 2rQ pore opening size of 300-500 nm due to the fact that for large pore sizes a method using template photolithography is known (Timchenko N.A., 2004, Vacuum ultraviolet spectroscopy of solids Synchrotron “Sirius”, A.D. diss. Dr. med. Sci., Moscow, Moscow State University, Scientific Research Institute of Nuclear Physics named after D.V.Skobeltsin), which seems more simple. On the other hand, the above-described efforts to manufacture a membrane filter by the proposed method can be justified for use only in narrow specific areas where a combination of large porosity and small pore size is essential, and the price is not critical. This, for example, hemodialysis (creating a compact artificial kidney) in medicine, where filters for effective nanofiltration (1 ÷ 10 nm) are in demand. Therefore, at present, it seems that the manufacture of the membrane filters of this particular range of pore sizes by the proposed method has the greatest practical interest.

Using the proposed method for producing a membrane filter with an ordered pore structure, it is possible to obtain an additional technical result consisting in the possibility of forming a nanoporous surface structure of implants in medicine. Known (e.g., Kutty MG, Bhaduri S., Bhaduri SB Gradient surface porosity in titanium dental implants: relation between processing parameters and microstructure. J Mater Sci Mater Med. 2004. Feb; 15 (2): 145-50; Norton MR Marginal bone levels at single tooth implants with a conical fixture design. The influence of surface macro- and microstructure. Clin Oral Implants Res. 1998. Apr; 9 (2): 91-9; Picha GJ, Drake RF Pillared-surface microstructure and soft -tissue implants: effect of implant site and fixation. J Biomed Mater Res. 1996. Mar; 30 (3): 305-12) that the micro- and nanostructure of the implant surface are important for the successful integration of the implant into the connective or bone tissue .

Claims (13)

1. A method of manufacturing a membrane filter with the same pore size and shape, comprising irradiating the polymer film with radiation causing local chemical degradation of the polymer film material, and etching the degradation products of the material of the irradiated sections of the polymer film, which ensures the formation of pores in the polymer film, characterized in
that the polymer film is irradiated by synchrotron radiation, structurally ordered using a multi-beam grating interference lithography system, in a chamber filled with gaseous hydrogen, which, in the irradiated sections of the polymer film, undergoes a photochemical reaction with the polymer film material to form volatile products that are removed during irradiation. 2. The method according to claim 1, characterized in that synchrotron radiation from the undulator is used for irradiation in the wavelength range from 5 to 100 nm. 3. The method according to claim 2, characterized in that the use of radiation with a wavelength of 13.5 nm. 4. The method according to claim 1, characterized in that the hydrogen pressure in the chamber is used from 0.5 to 2 Pa. 5. The method according to claim 1, characterized in that a four-beam system of interference lattice lithography is used either with the same pore for producing round pores in the cross section or different for producing a period of pairs of diffraction gratings elliptical in the pore cross section. 6. The method according to claim 1, characterized in that the membrane filter with a given size of the passage openings of the pores and with a given value of porosity is produced using pairs of diffraction gratings with appropriate periods and an appropriate exposure time, with a known distribution of flux density over the surface of the polymer film radiation after a system of lattice interference lithography and a predetermined dependence of the photoetching rate of the polymer film material on the radiation flux density. 7. The method according to claim 1, characterized in that the material of the polymer film is either polyethylene terephthalate, or polyimide, or polycarbonate, or polysiloxane, or carbon. 8. The method according to claim 1, characterized in that in the particular case of manufacturing a membrane filter from a polymer film with a thickness of less than 100 nm, the latter is applied to the surface of a silicon wafer with a thickness of 50 to 100 μm, on the other hand of which is then performed by template lithography and silicon etching in holes through to a polymer film with a size of 10 to 100 μm, appropriately selecting the size of these holes to ensure the strength of the membrane filter at a given working filter pressure, and conduct through the polymer film grating interference lithography. 9. The method according to claim 1, characterized in that in the particular case of the manufacture of a membrane filter from a film of inorganic material, a polymer film of a thickness of less than 100 nm is applied to a film of inorganic material with a thickness of less than 100 nm, previously applied to the surface of a silicon wafer with a thickness of 50 to 100 μm on the other hand, by using template photolithography and etching of silicon, holes with a size from 10 to 100 μm are made through it to a film of inorganic material, appropriately choosing the size of these holes for echeniya strength of the membrane filter of an inorganic material at a predetermined working pressure filtration is carried out on the polymer film lattice interference lithography and through the thus obtained mask is chemically etched in the pores of the inorganic material film. 10. The method according to claim 9 or 10, characterized in that the holes in the silicon wafer perform either round or rectangular cross-section. 11. The method according to claim 10, characterized in that either silicon nitride or silicon carbide or boron nitride or boron carbide or titanium nitride or metals such as gold or platinum or palladium or titanium are used as said inorganic material , or zirconium, or their alloys, including with other metals. 12. The method according to claim 1, characterized in that in the particular case of manufacturing an all-metal membrane filter, a metal layer with a thickness of less than 100 nm is applied to the silicon wafer, a photoresist layer from 50 to 100 μm thick is applied to this metal layer, and template photolithography is performed on it with by producing rectangular or round cross-sectional columns with a transverse size of 10 to 100 μm of a photoresist insoluble in the developer, the metal layer is thickened with electroplating on the surface that has become free after the development of the photoresist before splines from 1 to 10 μm, the photoresist columns are removed, the silicon wafer is removed, a polymer film with a thickness of less than 100 nm is applied to the surface of the metal layer that has freed up after removal of the silicon wafer, grating interference lithography is carried out through it, and the metal layer is chemically etched for the education in it then. 13. The method according to p. 13, characterized in that the metal used is either gold, or platinum, or palladium, or titanium, or zirconium, or chromium, or their alloys, including with other metals.

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