SE522780C2 - Nano-fabrication method using patterned punch to contact target surface, has target surface covered with individual particles bonded to it by adhesive forces - Google Patents

Abstract

The particles (7) used to form the pattern are individual particles bonded to the target surface (5) by adhesive forces such as electrostatic, magnetic, hydrophobic, capillary or Van der Waals forces, or covalent bonds. A method for providing surfaces with patterns on the nanometer scale or on a larger scale comprises contacting a patterned punch (3) with the target surface, the latter being covered with particles intended for building up the desired end pattern (8). Contact of the punch with the target surface will cause some of these particles to be removed, leaving the punch pattern imprinted on the target surface. The particles used to form the pattern are individual particles which are fixed to the surface in a given position by adhesive forces such as electrostatic, magnetic, hydrophobic, capillary or Van der Waals forces, or covalent bonds. Independent claims are also included for devices with a surface pattern prepared by this method.

Description

20 25 30 35 S22 780 _ 2 _ special processes have been developed, for example in the semiconductor industry, for the production of smaller and denser packed circuits. Other examples are biochemical sensors with active structures down to molecular size, optical elements for photon structures, controlled nanocatalysic materials and functional biomaterials that can affect the biological response on the nanometer scale. Due to the many potential applications, there has been rapid growth in the field of nanometer technology in recent years.

There are a wide range of techniques for controlling the topography (structure) of surfaces in the size range 10 nm and up. The larger the structures, the more methods there are and the greater the control and the possibilities for variation.

The mechanical manufacturing methods such as cutting and blasting of the surface are normally less well controlled than the chemical, electrochemical or laser-based methods. The most controllable methods are the lithographic (electron and photolithographic) or derivatives of these methods, for example stamping, with which one can apply in order well-ordered small structures with high accuracy and thus control pattern size, pattern depth mm. These methods usually use some type of etching technique (dry chemical, electrochemical or wet chemical) to produce the desired structure or stamps produced by lithographic technique.

In the photolithographic methods, the size of the individual details in the pattern is limited by the wavelength of the light. In the microelectronics industry today, 250 nm UV light is used, which limits the size of the pattern details to 180 nm, see for example The National Technology Roadmap for Semiconductors.

Semiconductor Industry Association, San José Calif., 1994.

Electron or ion beam lithographic methods have shorter wavelengths but are in practice too slow to pattern larger areas.

For the production of structures where the individual parts have a size of greater than 200 nm, another lithographic technique is therefore used today, namely the stamping method "soft lithography". "Soft lithography" is a collective term for several closely related techniques that involve surface by means of a polymeric stamp, and includes, among other things, so-called microcontact printing (yCP). are so-called self-organizing molecules that form monolayers on the surface, SAM (self-assembled monolayers) .Examples of SAM materials are thiols on gold or silver, respectively silanes on glass, SiO2. stamped directly on glass surfaces.

The principles of so-called microcontact printing were already described in 1993-1994 by Kumar and Whitesides at Harvard University: Kumar, A. and Whitesides, GM, Features of Gold Having Micrometer to Centimeter Dimensions Can Be Formed Through a Combination of Stamping With an Elastomeric Stamp and an Alkanethiol Ink Followed By Chemical Etching.

Applied Physics Letters, 1993, 63 (14): p. 2002, and Kumar, A., Biebuyck, H.A. and Whitesides, G.M., Pat- terning Self-Assembled Monolayers - Applications in Materials Science. Langmuir, 1994, 10 (5): pp. 1498.

They presented a method that was simple and comparatively inexpensive and that made it possible to produce patterns in the order of 0.2-100 microns on gold. Thiols known to form so-called "self-assembled monolayers" (SAM) on gold were applied to the surface by means of a polymeric stamp. The advantages over conventional photolithography are that the method does not routinely require clean rooms and that large areas can be patterned quickly and accurately. Since then, the method has been developed and can today be used for the production of patterns where the smallest individual details have a size of about 30 nm.

The technology is also patented in several versions: US 5,512,131; US 5,669,303; US 5,776,748; US 5,937,758; US 5,925,259; US 5,976,826; US 6,060,121; US 6,096,386; A difficulty in connection with the microcontact printing method is the master that must be manufactured for the polymeric stamp. The master is produced by photo or electron beam lithography. The master thus produced is then most often used to transfer the pattern to a photoresist on a so-called Si-wafer, which is then in turn used as a master for the polymeric stamp. This is a reliable procedure in itself, but time-consuming and expensive.

It is also previously known to use so-called colloidal lithography to produce patterned surfaces. The colloidal particles used have a typical size of 1 nm to 1 μm, which makes them particularly suitable for use in nanofabrication. The technique is described in the aforementioned U.S. Patent 6, oso, 121 and in Hanarp, P. Nanofabrication with colloidal particles.

Licentiate Thesis. Chalmers University of Technol09Y, Gothenburg, Sweden, 2000, "Soft lithography" also includes the techniques MIMIC (micro-molding in capillaries) and pTM (micro transfer molding), see for example Xia et al. Unconventional methods for fabricating and patterning nanostructures. Chem Rev. 99: 1823-1848, and 10 15 20 25 30 35 522 780 _ 5 _ - a v -. s 4: Xia, Y. and Whitesides, G.M.

Chem. Int. Oath. 1998, 37, 550-575.

Soft lithography. Angew.

In these works, a systematic review is made of various methods for patterning surfaces with structures within the nanometer range. It appears that even in the latter two methods, a PDMS stamp is used to stamp material against the substrate surface.

A disadvantage of the methods described above is that they only work when the material or particles used for the patterning bind to the substrate surface rather than to the stamp. This limits the choice of particles for specific surfaces. Another disadvantage of the described methods is the risk that the order and orientation of the particles is disturbed during the transfer step.

In many contexts, there is also a need to superimpose several patterns on each other and then there is a risk that the stamp disturbs the order of the underlying pattern when the new pattern is stamped against the surface.

SUMMARY OF THE INVENTION An object of this invention is to provide a method for patterning a surface within the size range of nanometers or larger by means of a polymeric stamp where the order and orientation of the particles are not disturbed at the transfer moment.

A further object of the invention is to provide a method which with cheaper technology enables patterning of individual details, structures (pits, pores, elevations) in the pattern down to the order of 1 nm.

According to the invention, a stamp is used, preferably a polymeric so-called PDMS stamp which is provided with the current pattern.

Instead of preparing the stamp with material (batch ready) which is to form the pattern on the surface, the surface is coated (particles) with particles, after which the stamp is brought into contact with the so-called prepared surface and removes particles from the surface and / or affects the particles in accordance with the pattern of the stamp, ie contact stripping instead of contact pointing. The end result is that the pattern of the stamp is superimposed on the surface with the particles.

As already mentioned, the advantage of this procedure is that the order of the particle film left on the surface remains undisturbed by the stamp and thus several patterns can be superimposed on the particle layer.

S.k. "blotting" or "stripping" by means of polymeric stamp is a per se known method used to lift lipid attachments from a surface in order to create various membrane-associated components, see Hovis, J. and Boxer, S .Patterning barriers to lateral diffusion in supported lipid bilayer membranes by blotting and stamping. Langmuir. 2000, 16: 894-897, and Kung et al. Patterning hybrid surfaces of proteins and supported lipid bilayers. Langmuir. 2000, l6: 6773-6776.

However, the present invention differs in principle from these stripping methods both in purpose and function, since the invention relates to "stripping" of particulate films built up of individual details in the nanometer range, ie in the order of 1-100 nm, "RSA ordered films" or colloidal particle layers, while the lipid bilayers are in aqueous solution ("The bilayer is separated from the glass support by a 10-20 Å layer of water").

According to an exemplary embodiment, the particles on the surface form a fully or partially coherent particle film. According to a further exemplary embodiment, the particles are applied to the surface by means of colloidal lithography, the colloidal particles having a typical size of 1 nm-1 μm.

BRIEF DESCRIPTION OF THE INVENTION In the following, the invention will be described in more detail with reference to the accompanying drawings, in which Figure 1 shows the principle of microcontact printing (prior art), Figure 2 schematically shows the principle of the invention, Figure 3 shows an experimental embodiment for surface patterning, and Figure 4 shows some SEM images with particle patterns prepared according to the invention.

DESCRIPTION OF AN EMBODIMENT In so-called microcontact printing (soft lithography) a polymer 1 is cast on a template 2 with the inverted pattern, see figure 1. The polymer stamp 3 thus produced, preferably of polydimethylsiloxane (PDMS), is dyed with some molecule 4 and then these molecules are stamped against the substrate surface 5. The molecules that are stamped can be so-called self-organizing molecules (self = assembled monolayers, SAM) which form a monolayer 6 on the surface, for example thiols on gold or silver or silanes on glass. There are also examples of proteins being stamped directly on glass surfaces.

Provided that the particles bind to the surface rather than to the stamp, a pattern of particles, corresponding to the pattern of the stamp, will remain on the surface. This is an example of a method used today for patterning surfaces. Figure 15 schematically shows the new method according to the invention. Here, too, a polymer 1 is cast on a template 2 with the inverted pattern. The polymeric PDMS stamp 3 thus produced is then brought into contact with a particle film, monolayer, consisting of individual particles 7, which are applied to the surface 5 to be patterned. Parts of the particle film are peeled off with the patterned stamp 3, "contact stripping", after which the remaining parts of the particle film form a pattern 8 on the surface 5.

By contact in this context is meant not only purely physical contact but also the fact that the stamp comes close enough to the surface for it to be able to pull off particles according to the pattern or otherwise affect the particles on the surface to be patterned.

Preferably, the particle film has been applied to the surface 5 by means of so-called colloidal lithography. Colloidal particles 7 are used which have a typical size of 1 nm to 1 μm, which makes them particularly suitable for use in nanofabrication. The technique is described in the above-mentioned licentiate work by P. Hanarp. The ability of the colloidal particles to self-organize and be electrostatically adsorbed makes it possible to prepare larger surface units (cmz) with one or more layers of well-defined nanoparticles on the individual particles and spacing.

This distance can be varied so that the proportion of the surface covered by dots is different in size but known and reproducible. Colloidal particles come in many different materials, sizes and shapes. In this context, special reference is made to polystyrene latex particles which are available in various dispersion media, sizes and charges.

The technique used to bind the colloidal particles to the surface is relatively simple. By so-called ESA technology (electrostatic self-assembly), a substrate surface with, for example, positive charge is exposed to a solution which contains negatively charged colloidal particles, ua-av 10 15 20 25 30 35 522 780 _ 9 _ which are then adsorbed on the surface . By using different charges, more complex nanostructures can be built up. Reference is also made to the so-called RSA model (random sequential adsorption) where a particle film, monolayer, is formed sequentially by positioning the individual particles 7 randomly and irreversibly to the surface in a first step, that in the next step new particles either binds to the surface in the spaces between the already adsorbed particles, or is repelled by the already adsorbed particles if they hit them during application. Through such a repeated procedure, a larger surface can be covered quickly with a dense structure of a well-organized nanoparticle layer. In practice, the particles are adsorbed in parallel over the entire surface.

The advantage of the particles 7 being peeled off from the surface by means of the stamp 3 is that the order of the particle film left behind remains undisturbed by the stamp. The distribution, the particle order, of the remaining portions of the particle film remains the same and is controlled by the colloidal lithography method - unlike conventional stamping where the particle order is controlled by the distribution on the stamp and disturbances that may occur when the stamp is pressed against the substrate. . This increases the accuracy of the nanofabricated pattern. Particles (7) with different sizes within the typical size range can be used for the pattern.

The size of individual pattern details, structures, of the stamp 3, and thus of the patterned surface, can be in the range 1 nm-1 cm. This may be a topographical and / or chemical pattern. The individual details of the pattern may consist of irregularities in the surface such as depressions (pits, pores) elevations, longitudinal, transverse, diagonal or intersecting grooves and other cavities. Even more complicated shapes can be considered, for example rectangular or star-shaped elevations or depressions. Common to these irregularities is that they should have a discrete, reproducible form, they should be included in a pattern and may recur with a certain periodicity (periodic pattern). Characteristic units of the nanometer pattern may also consist of material islands, islands of proteins, biomolecules, etc. The units may consist of "islands" or discrete areas which may themselves form a pattern or configuration superimposed on an underlying pattern structure. Furthermore, the chemistry can be optimized for adhesion of specific particles.

In "stripping", it is the inverse pattern that remains on the surface, ie the configuration that exists between the protruding parts 3 'in the stamp, ie the spaces 3 "between the individual pattern details.

Typical particle types 7 that can be used for the particle film are colloidal particles of various kinds, as discussed above, for example organic and / or inorganic particles of polymer, silica, Au, Ag, Pt, etc., or macromolecules such as proteins, nanoparticles, polyelectrolytes such as lions, amphilphilous aggregates such as vesicles, micelles, etc.

The particle size is in the range 1 nm-10 μm.

To control the pattern structure, the chemistry of specific particles can be optimized for adhesion either on the stamp or on the surface. The order, the distribution of the particles, can be random or ordered, compare above. The scheme can be stochastic, e.g. random sequential adsorption (RSA) as described above, or according to a ballistic model (BM), or according to any lattice structure (fcc, bcc, hcp etc). The particle film can have several layers, whereby one layer does not have to be complete, and consist of different materials.

The substrate surface 5 can be smooth or structured and again the chemistry can be optimized for less adhesion of specific particles. Furthermore, the surface / stamp may be of such a nature that all particles which come into contact with the patterned area are removed from the surface, or only only certain particles are clear based on size or chemistry. Instead of the particles being physically removed from the surface, the inventive concept also includes the case that properties of particles that come into contact with the patterned area change with respect to orientation, conformation and function or that the particles divide.

Figure 3a shows how a stamp 3 is brought into contact with a surface 5 coated with a film of individual particles 7. The stamp is then removed from the surface and at the same time takes particles from the surface in accordance with the topographical pattern of the stamp. The remaining patterned particle film has been indicated by 5 'in the figure. Figure 3b shows a patterned substrate surface 5 with particle-covered windows 8 'which may, for example, have enhanced optical activity. Different boxes can be given different functions, such as different DNA sequences. This can be used to advantage when you need high sensitivity in a sensor. The individual particles may be spherical 7a, hemispherical 7b or cylindrical 7c as shown in the figure.

The stamping can be performed in vacuum, gas or liquid phase.

The process can be controlled with respect to pressure and temperature. The stamping can be repeated so that particles are pulled off one or more times. The invention can be combined with other lithography, such as UCP, photolithography and the like.

Figure 4 shows a pair of scanning electron microscopes (SBM) images of substrate surfaces patterned according to the contact stripping method. The substrate surface was coated with polystyrene latex particle clear with a diameter size of 110 nm. Thereafter, a PDMS stamp has been brought into contact with the particle surface and "stripped" the particles according to the topographic pattern of the stamp. The pattern on the stamp to provide the surface of Figure 4a had grooves with a depth of 10 μm, a width of 15 μm and a distance between the grooves of 15 μm. The pattern for creating the surface of Figure 4b had square depressions (5x5 μm) and a distance between the depressions of 15 μm.

Areas of application for the invention are, for example, biomaterials, sensors, medical diagnostics, coatings, etc.

In particular, the invention can be used to pattern signal substances for cell differentiation (or other functions) on a surface of any material (metal, polymer) to control primarily stem cell development to one or the other alternative (a stem cell is an "immature" cell that can develop into at least two different cell types).

Other areas of use may be surfaces modified with a chemical pattern on a nanometer scale with properties of interest for friction, protein and organism adsorption in other contexts than just medical, such as boat hulls, tanks for liquid food (milk), etc. Another possible area of application may be interior surfaces of pipes prepared with a pattern to prevent turbulence in the pipe during liquid flow.

The invention is not limited to the examples shown above but can be varied within the scope of the appended claims.

Claims (21)

10 15 20 25 30 35 522 780 ø ø | ø .n ~ - ~ -.;.: _; _ 3_ PATENTKRÄV A method for patterning surfaces within the size range nanometer or larger by means of a patterned stamp (3), wherein the stamp is brought into contact with the surface (5) to be patterned for transferring the pattern of the stamp to the surface, the surface (5) being coated. particles (7) which are to build up the pattern on the surface and that the stamp (3) on contact with the surface so prepared is arranged to pull off particles (7) so that the pattern of the stamp is superimposed on the surface with the particles characterized in that the particles which are to build up the pattern on the surface consist of individual particles (7) which during application are fixed to the surface in a certain position by means of adhesion forces, such as electrostatic, magnetic, hydrophobic, capillary, van der Waalska, or covalent bonding. Method according to claim 1, characterized in that the stamp (3) consists of a polymeric stamp, preferably a so-called PDMS stamp. Method according to claim 1, characterized in that the pattern configuration of the stamp (pattern 1) upon contact with the prepared surface (5) is superimposed on one of the patterns (7) existing on the surface (pattern 2). A method according to claim 1, characterized in that the particles (7) on the surface (5) form a non-continuous layer. 5. A method according to claim 1, characterized in that the particles consist of colloidal particles (7) with a typical size of 1 nm-1 μm. 6. A method according to claim 5, characterized in that the 15 15 i 25 ° 35 i i - ° ': .. "' I. o.-o." '' '' 'I -u nn I v: uø-. '' 'f u. , n. n! |. , .I u u. ",, Z u u n." 'I o. I o »f n now 1 a v that the particles (7) have the same size, or different sizes, within said size range. A method according to claim 5, characterized in that the particles (7) have a random or ordered distribution over the surface (5). Method according to Claim 5, characterized in that the particles (7) have a well-defined shape, for example spherical, hemispherical or cylindrical. A method according to claim 5, characterized in that the particles (7) consist of organic and / or inorganic particles. Process according to Claim 9, characterized in that the particles (7) consist of polystyrene latex, polymer, silica, An, Ag, Pt particles, etc., macromolecules such as proteins, nanoparticles, polyelectrolytes such as polyions, amphiphiles. aggregates such as vesicles, micelles, etc. Method according to claim 1, characterized in that the size of individual pattern details, structures, units on the patterned surface (8) is in the range 1 nm-1 cm. Method according to claim 11, characterized in that the pattern is topographical and / or chemical. A method according to claim 12, characterized in that the individual pattern details of the stamp (3) consist of irregularities in the surface such as depressions, pits, pores, ridges, longitudinal, transverse diagonal or intersecting grooves. 14. A method according to claim 1, characterized in that it takes place in a vacuum, gas or liquid phase. 10 15 20 25 30 35 I vu: ng ,, o ,, w aa nn _ f I »1 * vz: zt-« "u: f,,:, _ * I o.,, .. ~ ~. N , '. z, nu »... § IS 5 Method according to claim 1, characterized in that the chemistry of the stamp (3) and / or the surface (5) is optimized for adhesion of specific particles (7). Device comprising a surface patterned within the size range of nanometers or larger, characterized in that the pattern (8) of the surface is produced according to one of the preceding claims. Device according to claim 16, characterized in that it consists of an implant, the patterned surface (8) being made of a biocompatible material. Device according to claim 16, characterized in that it consists of or comprises sensor means for, for example, medical diagnostics, wherein the patterned surface (8) can be made with biochemically active structures for influencing biological response on the nanometer scale. Device according to claim 18, characterized in that the patterned surface (8) comprises signal substances for cell differentiation, or other functions, on a surface of any material in order to control the development of cells. Device according to claim 16, characterized in that it consists of or comprises sensor means wherein the patterned surface (8) is designed to detect or control properties in connection with liquid flow, such as friction, turbulence, protein and organism adsorption, at boat hull, in tanks, containers, pipes, etc. Device according to claim 16, characterized in that it consists of or comprises a surface coating with the patterned surface (8) for use in connection with liquid flow at, for example, boat hulls, tanks, containers, pipes, etc.