EP2529273A2

EP2529273A2 - Mold for nanoprinting lithography, and methods for producing same

Info

Publication number: EP2529273A2
Application number: EP11701139A
Authority: EP
Inventors: Stéfan LANDIS
Original assignee: Commissariat a lEnergie Atomique CEA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2010-01-28
Filing date: 2011-01-27
Publication date: 2012-12-05
Also published as: WO2011092241A2; FR2955520A1; US20120301608A1; FR2955520B1; WO2011092241A3

Abstract

The invention relates to a mold for nanoprinting lithography as well as the methods for producing same. Said mold comprises a surface which includes n structured area(s) with micrometric or nanoscale patterns, n being an integer greater than or equal to 1. Said structured surface belongs to a first layer which is supported by a second layer, the first layer being made of a rigid material and the second layer being made of a flexible material. Said mold can further include n intermediate layers arranged between the first layer and the second layer, n being an integer greater than or equal to 1, and wherein modulus of elasticity of the second layer is less than the modulus of elasticity of the nth intermediate layer adjacent to the second layer, and if n is greater than 1, the modulus of elasticity of the (i)th intermediate layer is greater than the modulus of elasticity of the (i + 1)th intermediate layer, with i = 1 to (n-1).

Description

MOLD FOR NANO-PRINTING LITHOGRAPHY AND METHODS OF MAKING SAME

DESCRIPTION

TECHNICAL AREA

The invention relates to a nano - impression lithography mold, as well as methods for producing such a mold.

STATE OF THE PRIOR ART

There are two types of nano-printing lithography:

- nano-assisted wavelength printing;

- thermal nano-printing.

In the case of thermal nano-printing, nano-printing lithography consists in duplicating patterns by hot pressing of a mold in a polymer film placed on a substrate to be printed or, in the case of a wavelength-assisted nano-printing, duplicating patterns by pressing a mold, transparent to the wavelength of use of the mold, in a photosensitive polymer film disposed on a substrate and applying radiation use wavelength (e.g., UV radiation) through the mold. The patterns reproduced in the polymer film are then etched in the printing substrate underlying the polymer film. It is specified that nano-printing refers to the printing of patterns whose size (length, width and / or diameter) is between a few nanometers and several hundred micrometers.

Typically, the mold used to shape the polymer film is a rigid mold.

Most often, the rigid mold is made in a substrate of easily structural material, for example silicon, and is obtained by standard lithography and etching techniques. It is thus possible to obtain molds of large areas (several hundred cm ² ).

However, it is sometimes necessary to use a material that proves to be difficult to structure, such as silica or quartz, for example when it is desired to obtain a UV-transparent mold. In this case, the production of the mold by lithography and etching becomes problematic as the resolution increases (resolutions less than or equal to a few tens of nanometers).

On the other hand, the use of a rigid mold makes it very difficult or impossible to print patterns with satisfactory homogeneity: the more rigid the mold, the more difficult it becomes to obtain a homogeneous contact (or contact in conformity ) at any point between a rigid mold and the substrate to be etched. Indeed, as the surfaces to be in contact are never perfectly flat, it is necessary for there to be contact on the entire surface between the mold and the substrate. print, or that the mold can be deformed, which is possible only if the mold is not too rigid, or to reduce the surface of the mold to increase its flatness. Therefore, the maximum area that can be printed in a single step using a rigid quartz mold in the context of a UV assisted nano-printing lithography is typically a few cm ² , while it is possible to print several hundred cm ² using a silicon mold in the context of thermal nano-printing lithography.

Thus, in order, on the one hand, to avoid a contact which could be destructive between the rigid mold and the substrate to be printed, and on the other hand, to homogenize the pressing of the mold on the polymer film, it is known to retain a thin residual layer of polymer at the bottom of the duplicated patterns in the polymer film. The residual thickness is subsequently removed by an oxygen plasma and the mold patterns are transferred to the underlying substrate by etching.

The disadvantage of this solution is that it requires a uniform residual thickness to obtain a pattern transfer while maintaining the lateral dimensions of the patterns. However, during the printing of the patterns, there is the appearance of a local uniformity of the residual thickness near the edges of the mold, which is caused by the passage of a dense patterned area to a zone without patterns . In order to minimize the number of these local uniformities, it is therefore preferable to use a large-area mold rather than several small molds. However, we have just demonstrated that the maximum surface of a mold was limited by its rigidity.

Furthermore, it is known to use a flexible mold (that is to say, low Young's modulus) PolyDiMethylSiloxane (PDMS). The elasticity of a PDMS mold makes it possible to obtain a conformal contact between the mold and the substrate to be printed. However, the resolution of such a mold is limited to 0.5 micrometer because of the problems of mechanical stability of the mold during pressing: the small size patterns (typically less than 500 nm) do not have sufficient mechanical stability to resist during pressing, which causes several types of mechanical deformation of the mold, thereby limiting the potential resolution of the mold. A PDMS mold can not therefore be used to produce structures having resolutions of a few nanometers, or even a few tens of nanometers.

It has been envisaged to modify the chemical formulation of the PDMS in order to improve its mechanical properties (see document [1] referenced at the end of the description). The study of the collapse of a PDMS mold as a function of the PDMS polymerization time makes it possible to assume that the printing of finer patterns is possible with a mold having a greater elastic modulus and surface hardness. However, too much rigidity or elastic modulus can make the material fragile and limit its ability to generate contact consistent with the substrate to be printed. In addition, the implementation of PDMS by thermal crosslinking remains an intrinsic limit for the manufacture of mold having a very high resolution. Indeed, the cooling cycle of the PDMS can induce mechanical stresses in the material and consequently limit its resolution. As a result, since it is desired to obtain patterns having a size less than 100 nm, it is necessary to use molds of rigid material.

In view of the problems posed by the molds of the prior art, the inventor has set himself the goal of designing a mold for nano-printing lithography which makes it possible to minimize the defects created during the printing step, and in particular, to minimize the residual thickness distribution, by making it possible to obtain a conformal contact between the mold and the substrate to be printed, the mold possibly having patterns whose size is between a few nanometers and several microns and this the mold is adapted to a nano-thermal or wavelength-assisted (for example UV) lithography.

STATEMENT OF THE INVENTION

This object is achieved by means of a mold for nano-printing lithography having a first structured face comprising n structured zone (s) with micrometric or nanometric size patterns, n being an integer greater than or equal to 1, characterized in that said first structured face belongs to a first layer which is supported by a second layer, the first layer being of a rigid material and the second layer being of a flexible material.

In what precedes and what follows, the expression "structured with patterns of micrometric or nanometric size", applied to a face or a layer, means that the face or layer in question comprises patterns of which at least one dimension selected from the length, width and diameter is less than 1 mm and greater than lym, in the case of micrometric size patterns, and is greater than or equal to 1 nanometer and less than 1000 nanometers in the case of nanometric size patterns .

In the context of the invention, the patterns may be embossed or recessed (hollow). They can be dispersed homogeneously in the n zones, and are preferably equidistant within the same zone. Advantageously, the patterns are identical (they have the same dimensions and the same shape). Advantageously, the n structured zones are identical.

In what precedes and what follows, the term "rigid", applied to a layer, means that this layer has a bending deformation (arrow) lower than a determined limit value when a determined pressure is applied on the surface of this layer. layer.

Similarly, in what precedes and what follows, the term "flexible", applied to a layer, means that this layer has a deformation in bending greater than or equal to a determined limit value when a specific pressure is applied on the surface of this layer.

To determine the limit value, it is necessary to carry out some simple calculations. For example, consider the case of a silicon and quartz mold with the following characteristics:

E _si = 130 GPa E _si0 2 = 71.7 GPa

_If V = 0.28 V = 0.16 _SL02

where E is the modulus of Young, V is the Poisson's ratio and h is the height of the layer concerned.

The bending stiffness of a part is given by the following formula:

EX h ³

~ 12x (l - V ² )

For a square plate of side a, having a thickness h, the maximum deflection generated (in bending) w is approximately equal to:

Pxa ⁴

w

D

So, if in the example above the pressure exerted uniformly on the mold is equal to 2.10 ⁵ Pa and the side has plates has a value of 20.10 ^-3 m, then we have:

w _si0 2 = 25 μπι

By these calculations, we obtained the arrow of each layer taken individually. To obtain the limit value for considering that a layer is flexible or rigid, it is necessary to compare the value of the calculated arrow and the value of the surface roughness (or topography) of the substrate that one wishes to print using the mold. . Indeed, when making an impression, it is necessary to have an intimate contact (also called "compliant" contact) between the mold and the substrate to be printed; it is therefore necessary that the entire surface of the mold is in direct contact with the entire surface of the substrate to be printed.

For example, a substrate consisting of a silicon wafer 200 mm in diameter has a roughness of 50 μτα (data provided by the supplier of the silicon wafer). Also, if the layer of the mold has an arrow greater than or equal to the roughness value of the substrate to be printed given by the manufacturer, namely 50 μιη, this layer will be considered as being made of a flexible material with respect to the substrate which is try to print. On the other hand, if the value of the deflection of the mold layer is less than the roughness value of the substrate to be printed, the layer will be considered as being a rigid material.

Thus, in our example, the silicon layer (w _S i ~ 500 μιη) is considered to be flexible, while the quartz layer (w _S io2 ~ 25 μι ^η ) is considered to be rigid.

Advantageously, the mold further comprises p intermediate layers disposed between the first layer and the second layer, p being an integer greater than or equal to 1, and wherein the Young's modulus of the second layer is lower than the Young's modulus of the p ^th intermediate layer adjacent the second layer, and if p is greater than 1, the Young's modulus of the (j_) ^th intermediate layer is greater than the Young's modulus of the (i + l) ^th interlayer, With i = 1 to (p-1) · Preferably, the Young's modulus of the first layer is greater than or equal to the Young's modulus of the ^1st intermediate layer. There is thus a gradient in Young's modulus, which makes it possible to avoid sudden transitions between the rigid layer and the flexible layer and to prevent the structure from breaking. This also makes it possible to reduce the thickness of the first rigid layer. This allows a better distribution in the structured face of the force applied to the opposite face of the mold.

It should be noted that the layers included in the mold have a thickness of between a few hundred micrometers and a few millimeters.

Advantageously, the second layer of the mold is itself supported by a support made of rigid material. The support may be a substrate or a layer of rigid material. The addition of this support helps strengthen the mold and reduce its fragility. This makes it possible to press the rigid support during handling without damaging the second layer. According to one variant, the support made of rigid material is a cylindrical element, the second layer being supported by the cylindrical part of the support. The use of a cylindrical shaped element as a support makes it possible, for example, to produce a roller print ("roller print" in English). Advantageously, the mold further comprises a second structured face comprising m zone (s) structured (s) with patterns of micrometric or nanometric size, m being an integer greater than or equal to 1, said second face belonging to a third layer, which is made of a rigid material, the first and second structured faces being situated on either side of the second layer of flexible material. This particular arrangement has the advantage of making it possible to double the printing rate by using such a mold.

Advantageously, at least one face of the first structured face and the second structured face comprises a single structured zone (that is to say n = 1 and / or m = 1), said structured zone occupying the entire surface. of said at least one face. In other words, the structuring is not localized in certain parts of the face, but extends over the whole of the face.

According to a particular variant, the mold may furthermore comprise a layer interposed between the first layer and the second layer, the said interleaved layer being made of a rigid material, the face of the interposed layer which is opposite to the first layer being structured according to n cavities disposed opposite the n structured areas of the first layer and being covered by the second layer so that the n cavities are filled with a flexible material. It is quite possible that this interlayer and the first layer are made of an identical material; it comes down to having, instead of a first layer and an interlayer, a single layer (the first layer), this single layer having on one side the n structured areas and on its opposite side n cavities opposite the n structured areas.

In general, the mold according to the invention can be used for any shaping technology of a material requiring a mold, and in particular for making a microcontact printing.

The mold can also be adapted to a particular use, such as nano-printing assisted at a particular wavelength or thermal nano-printing, depending on the constituent materials of the mold.

Thus, all the layers constituting the mold, as well as the support if it is present, can advantageously be made of transparent materials at a wavelength λ located in the range of UV wavelengths, that is, that is to say at a wavelength between 193 nm and 400 nm, or in transparent materials at a wavelength λ located in the wavelength range of the visible light, that is to say at a wavelength between 400 nm and 800 nm. This produces a mold that can be used to perform UV-assisted nano-printing or visible light-assisted nano-printing, respectively.

Alternatively, the support may be quartz or silica, the first layer of silica and the second layer of polydimethylsiloxane (PDMS) or silicone. Advantageously, all the layers constituting the mold, as well as the support if it is present, are made of thermally conductive materials, that is to say materials having a thermal conductivity greater than a few tens of Wm ^_1 .K ^_1 . We then have a mold that can be used to perform a thermal printing.

It is quite possible for one or more of the layers constituting the mold, and possibly the support, to be made of a material that is both transparent at a wavelength λ and thermally conductive.

On the other hand, the invention relates to a first method of producing a mold for nano-printing lithography comprising a structured face having n structured areas with micrometric or nanometric size patterns, the method comprising the following steps:

a) providing an initial substrate;

b) structuring a face of said initial substrate, called the front face, in a pattern representing the negative imprint of the n structured areas that one wishes to obtain on the structured face of the mold;

c) depositing a first layer on the front face of the initial substrate so as to cover the relief formed in the structuring step b), the first layer and the initial substrate being made of different materials and the first layer being in one rigid material; d) depositing a second layer on the first layer, the second layer being made of a flexible material;

e) removal of the initial substrate.

The expression "negative imprint" is understood to mean the production of a relief that perfectly fits into the relief that one wishes to obtain, namely the n structured zones of the front face of the mold.

Advantageously, the first embodiment further comprises, between step c) and step d), a step c ') of structuring the first layer so as to obtain n cavities opposite the n structured areas present on the opposite side of the first layer.

Advantageously, the first embodiment method further comprises, between step c) and step d), or between step c ') and step d), a step of depositing p intermediate layers on the first layer, p being an integer greater than or equal to 1, and wherein the Young's modulus of the ^ith intermediate layer, intended to be adjacent to the second layer to be deposited in step d), is greater than the module of Young of said second layer, and if p is greater than 1, the Young's modulus of the (i) ^th intermediate layer is greater than the Young's modulus of the (i + 1) ^th intermediate layer, with i = l to (p-1). Preferably, the Young's modulus of the first layer is greater than or equal to the Young's modulus of the ^1st intermediate layer. This gives a gradient flexibility between the first layer and the second layer.

Advantageously, step b) of the method comprises the following steps:

depositing a layer of photoresist on one face of the initial substrate;

insolation of the photosensitive resin layer according to the pattern representing the negative imprint of the n structured zones that one wishes to obtain on the structured face of the mold;

- etching of the insolated resin layer;

etching of the face of the initial substrate not covered by the resin layer.

According to a first variant, step e) of the method is obtained by performing a selective etching of the initial substrate. In this case, the material of the first layer and the material of the initial substrate are chosen so that it is possible to selectively etch the initial substrate without etching the first layer. The selective etching may for example be a wet etching.

According to a second variant, step e) of the method comprises machining the rear face of the initial substrate, followed by selective etching of the initial substrate.

Advantageously, said first embodiment method further comprises, after step d) and before or after step e), a step of depositing a support of rigid material on the second layer. The deposition of the support can thus be done before or after the removal of the initial substrate. The invention also relates to a second method for producing a mold for nanoimprint lithography comprising a structured face having n structured areas with micrometric or nanometric size patterns, the method comprising the following steps:

j) providing a substrate of rigid material;

k) structuring a face of the substrate, called the front face, so as to obtain the n structured areas;

1) thinning of the substrate by etching the rear face of said substrate;

m) depositing a layer of flexible material on the rear face of the substrate.

According to a variant, step 1) is replaced by a structuring step 1) of the rear face of the substrate so as to obtain n cavities located opposite the n structured areas of the front face.

Advantageously, the substrate is a stack of layers comprising, in order, a layer of first material, a layer of second material and a layer of third material, the first and third materials being rigid materials and in which the layer of second material serves as a stop layer for the structuring carried out in step k) and / or for the structuring carried out in step l '). For example, the structuring in step 1 ') can be carried out until reaching the layer of second material. If the structuring is obtained by etching, the second material layer may be of a material capable of stopping the etching. The stack may for example be an SOI substrate.

Advantageously, said second embodiment method further comprises, between step 1) and step m), or between step l ') and step m), a step of depositing p intermediate layers on the face back of the substrate, p being an integer greater than or equal to 1, and wherein the Young's modulus of the p ^th intermediate layer, intended to be adjacent to the layer of flexible material to be deposited in step m), is greater than the Young's modulus of said layer of flexible material which will be deposited in step m), and if p is greater than 1, the Young's modulus of the (j_) ^th intermediate layer is greater than the modulus of Young of the (i + l) ^ith interlayer, with i = 1 to (p-1).

Advantageously, said second embodiment further comprises, after step m), a step of depositing a support of rigid material on the layer of flexible material deposited in step m).

Advantageously, step k) comprises the following steps:

depositing a layer of photoresist on the front face of the substrate;

insolation of the photosensitive resin layer in a pattern representing the positive imprint of the n structured zones that one wishes to obtain on the front face of the substrate;

- etching of the insolated resin layer; etching of the front face of the substrate not covered by the resin layer.

The expression "positive imprint" is understood to mean the production of a relief identical to the relief that is to be obtained.

Advantageously, step l ') comprises the following steps:

depositing a layer of photosensitive resin on the rear face of the substrate;

insolation of the photosensitive resin layer in a pattern representing the positive cavity of the n cavities that it is desired to obtain on the rear face of the substrate;

- etching of the insolated resin layer; etching of the rear face of the substrate not covered by the resin layer.

In the first and second embodiments of the invention, the set of layers constituting said mold, as well as the support in rigid material if it is present, are advantageously made of transparent materials at a wavelength λ located in the range of UV wavelengths, in the wavelength range of visible light and / or are in thermally conductive materials.

The two production methods according to the invention make it possible to obtain molds having micrometric or nanometric size patterns on the surface, while using simple lithography and etching processes, which are well known and mastered by the skilled person. In particular, the processes for producing a mold according to the invention are compatible with the methods usually used in microelectronics and in the field of microtechnologies.

Moreover, while it was necessary in the prior art to etch substrates several hundred microns thick, sometimes in very rigid materials of the silica or quartz type, very difficult to etch, especially to obtain patterns of size less than 100 nm, it is now possible to structure the mold in a layer of a readily structural material, such as a silicon layer, without being limited by the fact that the material must be transparent or opaque. It is thus possible to structure a silicon layer to produce a UV-assisted nano-impression mold. The manufacture of the molds is thus considerably simplified and the production costs are at the same time lowered.

It is recalled that a material is said to be opaque when it does not allow, or little, to pass light. In fact, it will be considered that a material having a thickness X is opaque when its transmittance is less than or equal to 0.2. Similarly, a material is said to be transparent when it allows light to pass through; it will be considered that a material having a thickness X is transparent when its transmittance is greater than or equal to 0.85. On the other hand, it is recalled that the transmittance of a material is the ratio of the energy transmitted through this material to the incident energy. For a given substance, at a defined thickness and wavelength, transmittance is a constant.

The mold according to the invention also makes it possible to obtain a conformal contact between the mold and the substrate to be printed when they come into contact thanks to the presence of at least one layer of flexible material, which makes it possible to standardize the pressure. applied on the mold during printing. The mold according to the invention therefore has both a mechanical rigidity sufficient to perform pattern printing of a few nanometers, while having a certain flexibility (adjusted according to the flexible layer (s) used (s) )). It is thus possible to solve simultaneously the problems related to the resolution of the patterns and that related to the uniformity of pressing during the printing.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and other advantages and particularities will appear on reading the following description, given by way of non-limiting example, accompanied by the appended drawings among which:

FIG. 1 represents an example of a mold according to the invention,

FIG. 2 represents another example of a mold according to the invention,

FIG. 3 represents yet another example of a mold according to the invention,

FIG. 4 represents another example of a mold according to the invention, FIG. 5 represents another example of a mold according to the invention,

FIGS. 6a to 6h show the steps of a method for producing a mold according to the invention,

FIGS. 7a to 7g show the steps of another method of producing a mold according to the invention.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

The mold according to the invention comprises on at least one of its faces patterns in two or three dimensions of micrometric or nanometric size made in a layer of rigid material supported by at least one layer of flexible material. This combination of a rigid layer and at least one flexible layer makes it possible to reproduce, on the one hand, patterns of nanometric size, and to obtain, on the other hand, a conformal contact between the mold and the substrate to be print when they are put in contact.

The mold 1 according to the invention may consist of a single layer of rigid material 2 having patterns 3 of micrometric or nanometric size, and a layer of flexible material 4, supporting the layer of rigid material, as shown in Figure 1.

The mold according to the invention may also comprise several layers of flexible material. For example, in FIG. 2, five layers of flexible material, called interlayer layers 5i, 52, ₃ , ₄ , ₅ , are disposed between the layer of rigid material 2 forming the front face of the mold 1 and the layer of flexible material 4 forming the rear face of the mold. The interlayer layers are chosen so as to progressively adjust the mechanical properties between the layer of rigid material of the front face and the layer of flexible material of the rear face of the mold: there is then a gradient of mechanical properties between the layer of rigid material of the front face and the layer of flexible material of the rear face of the mold. The intermediate layers are therefore placed in order of increasing Young's modulus, the intermediate layer of greater Young's modulus 5s being placed adjacent to the flexible material layer 4 of the rear face of the mold and having a lower Young's modulus. to the module of said layer of flexible material.

The mold according to the invention may also comprise two faces having micrometric or nanometric size patterns. As illustrated in FIG. 3, the mold 1 may comprise two layers of rigid material 2 and 6 structured with patterns 3 of micrometric or nanometric size and disposed on either side of a layer of flexible material 4.

Optionally, the mold 1 according to the invention may further comprise a support 7 of rigid material, disposed on the flexible layer 4 (Figure 4) to consolidate the mold and make it less fragile or to adapt the mold to specific applications, as for example "roller imprint" applications, by transferring the flexible layer of the mold to a support having a cylindrical shape.

In Figures 1, 2, 4 above, the entire surface of the first layer of rigid material is structured. But it is possible also that only one or more areas of the surface of the layer are structured. For example, in Figure 5 is shown a mold comprising a rigid layer 2 having a plurality of zones comprising patterns. The representation of the mold in a sectional view allows us to deduce that this mold comprises at least two zones 30 having patterns 3. The mold shown in FIG. 5 further comprises, between the layer of rigid material 2 and the layer of material flexible 4, an interlayer 11 of rigid material whose opposite face to the layer of rigid material 2 comprises cavities arranged facing the patterned zones of the layer of rigid material 2. Here, according to the sectional representation, we see that the interlayer 11 has two cavities located opposite the two structured areas. The layer of flexible material 4 comes to cover the interlayer 11 by filling completely the cavities (the relief of the interlayer is completely covered). The interlayer and the layer of rigid material 2 may optionally be of the same material. The fact that the interposed layer has different thicknesses makes it possible to simply adjust the mechanical behavior of the mold above the structured zones.

The materials of the layers forming the mold are chosen according to their Young's coefficient, preferably as a function of their ability to be structurable by lithography and etching steps, and possibly according to their ability to be transparent to a length of time. particular wave or thermally conductive, depending on the application that one wish to give to the mold. For example, the layers of a mold for UV-assisted nano-printing lithography will be in UV-transparent materials.

Thus, rigid and UV-transparent materials may, for example, be selected from silica, quartz or sapphire.

The rigid materials and transparent to visible light may, for example, be selected from silica, quartz or sapphire.

It turns out that silica, quartz and sapphire are rigid materials that are transparent both in the visible and in the UV. They can therefore be used indifferently in the visible or in the UV. However, it is quite possible to choose rigid materials that are only transparent in the UV or in the visible.

The flexible materials and transparent to UV can, for example, be selected from silicones, polycarbonates, polyethylene, organic materials transparent to UV.

The soft materials and transparent to visible light may, for example, be selected from silicones, polycarbonates, polyethylene, organic materials transparent to visible light.

As the previous remark, it is found that silicones, polycarbonates, polyethylene and organic materials are flexible materials and transparent both in the visible and in the UV and can therefore be used indifferently in the visible or in the UV, but it is quite possible to use flexible materials that are transparent only in the visible or in the UV.

The rigid and thermally conductive materials may, for their part, be chosen, for example, from silicon, silicon nitrides, carbides or metals.

The flexible and thermally conductive materials may, for example, be selected from silicones or polycarbonates.

We will now describe an embodiment of a mold according to the invention. In particular, we will make a mold completely transparent to UV, comprising a layer of rigid material whose entire surface comprises patterns of micrometric and / or nanometric size, a layer of flexible material and a support.

First of all, a structuring of the front face of an initial substrate 13 is carried out, for example by lithography (electronic lithography, EUV, X optics, by FIEL) and by etching (reactive ionic dry etching, ionic machining, wet etching). ...). For this, depositing a resin layer 14 on one side of a silicon substrate or any other material usually used in micro and nano fabrication processes well controlled for the manufacture of microelectronic components (Figure 6a), this layer is insulated of resin in a pattern representing the inverted image (negative imprint) of the pattern that is desired on the face of the mold (FIG. 6b), the layer of insolated resin 14 and the parts not covered by the resin (Figure 6c). For example, if it is desired to obtain n relief zones on the future mold, these n recessed areas are engraved on the initial substrate. In our example, it is chosen to use a silicon substrate because the silicon enables etching with resolutions less than 10 nm and aspect ratios (height / width) greater than 10.

A layer is then deposited in a rigid material 2 and UV-transparent on the structured face of the substrate, for example a silicon oxide layer (FIG. 6d). The thickness of the deposited layer 2 must be greater than the height of the patterns made in the initial substrate 13. On the other hand, the deposit must be made so as to suitably fill the relief of the initial substrate.

Then, a layer of a flexible material 4 and transparent to UV is deposited on the silicon oxide layer 2 (Figure 6e). For example, the deposited layer is in PDMS. The advantage of PDMS is that its Young's modulus can be adjusted according to the proportion of the initiator level contained in the PDMS preparation.

The majority of the initial substrate 13 is then removed by polishing or etching of its rear face (FIG. 6f). The remainder of the initial substrate is then removed by wet etching, for example by TMAH or KOH etching in order to selectively etch the initial silicon substrate with respect to the silicon oxide layer. It makes sense to choose a couple of materials for the initial substrate and the layer of rigid material that can be selectively etched.

A mold comprising a layer 2 of rigid material transparent to micro or nanostructured UV (silicon oxide layer having a Young's modulus of a few GPa) is then obtained, supported by a layer 4 made of a flexible and UV-transparent material ( PDMS layer having a Young's modulus between a few kPa and a few MPa) (Figure 6g).

Optionally, the flexible material layer 4 may be deposited on a support 7 made of a rigid and UV-transparent material (for example a substrate) in order to reduce the fragility of the mold and to consolidate its mechanical strength (FIG. 6h).

The example above describes the formation of a mold comprising a single structured face, but it is possible to produce a mold having two structured faces. For this purpose, it is possible, for example, to carry out, on the one hand, a first stack by carrying out the steps 6a to 6g described above and, on the other hand, a second stack, by performing the steps 6a to 6g, and adhere the first stack to the second stack at their respective soft layers.

In the exemplary embodiment as represented in FIG. 6g or 6h, the layer of rigid material 2 is structured in a single zone occupying its entire surface. However, it is quite possible that the patterns are located according to one or more isolated areas. Furthermore, when the layer of rigid material comprises one or more localized structured areas, it is possible that the mold further comprises another layer of rigid material (called intercalated layer) on the layer of rigid material comprising the patterns. In this case, the interposed layer of rigid material (and optionally transparent to UV in this example) has a number of cavities equal to the number of structured areas present on the layer of rigid material. In the example shown in FIGS. 6a to 6h, the intercalated layer will be deposited on the silicon oxide layer 2 in step 6d. The interlayer is structured with cavities and a layer of flexible material is deposited on the interlayer. Steps 6f to 6h are then carried out. It is possible that the interlayer and the layer of rigid material are of the same material. It is also possible that the interlayer and the layer of rigid material are a single layer structured on its front face and on its rear face. Another embodiment of a mold comprising an intercalated layer is detailed above. According to another exemplary embodiment, a mold is produced comprising a layer of rigid material having areas that are thinned and filled with a layer of flexible material.

Firstly, the structuring of a face of a substrate 15 is carried out. For example, the substrate 15 is an SOI substrate consisting of a stack a silicon layer 16, a buried layer of silicon oxide 17 and a silicon layer 18.

The structuring is obtained by depositing a layer of photosensitive resin 19 on the front face of the substrate (FIG. 7a), by insolating the resin layer in a pattern representing the n structured zones that one wishes to obtain (FIG. 7b) and engraving the exposed resin layer and the parts not covered by the resin (Figure 7c). The depth of the etched patterns may be less than or equal to the thickness of the silicon layer 16 of the SOI substrate. If it is equal to the thickness of the silicon layer 16, the silicon oxide layer 17 of the SOI substrate then serves as a stop layer for etching.

The rear face of the substrate is then structured so that, opposite each structured zone on the front face of the substrate, there corresponds a cavity on the rear face of the substrate. The cavity or cavities may be obtained by depositing a resin layer 20 on the rear face of the substrate (FIG. 7d), exposing the resin layer in a pattern representing the cavity or cavities that are to be obtained, and then etching of the insolated resin and parts not covered by the resin (FIG. 7e). The etching may optionally be carried out until reaching the silicon oxide layer, which then acts as an etch stop layer. Thus, it is certain that the etching on the rear face of the substrate will not lead to the front of the patterns of the n structured areas. A layer of flexible material 4, for example silicone or polydimethylsiloxane (PDMS), is then deposited on the rear face of the substrate so as to cover the relief formed by the cavity or cavities (FIG. 7f).

The realization of the n cavities on the rear face of the substrate makes it possible to deposit the flexible material 4 as close as possible to the structured zones present on the front face of the substrate.

Optionally, the mechanical strength of the mold can be reinforced by depositing the flexible material layer of the mold on a support 7 made of rigid material (FIG. 7g).

The mold thus obtained comprises a layer of rigid material having different thicknesses, which allows to simply adjust the mechanical behavior of the mold. By slimming down the thickness of the layer of rigid material vertically above the zones comprising the patterns and by filling the space thus created with a flexible material, it is indeed possible to standardize the force exerted on the mold at the level of the patterns and to reach the final and uniform state of pressing more quickly. In the examples above, we have described different variants, but other variants are also possible. In this regard, it should be noted that the layers 16, 17 and 18 may be of the same material (for example, the three layers may be of silicon); the layers 16 and 18 may be of the same material, different from the material of the layer 17 (For example, layers 16 and 18 may be silicon while layer 17 is silicon oxide); the layers 16 and 17 may be of the same material, different from the material of the layer 18

(For example, layers 16 and 17 may be silicon oxide, while layer 18 is silicon); the layers 17 and 18 may be of the same material, different from the material of the layer 16

(For example, the layers 17 and 18 may be silicon, while the layer 16 is silicon oxide or silicon nitride Si _x N _y ); the layers 16, 17 and 18 may also be of different materials (for example, the layer 16 may be of silicon nitride Si _x N _y , the layer 17 may be of silicon oxide and the layer 18 may be of silicon) .

BIBLIOGRAPHY

Schmid H, Michel B., "Siloxane polymers for high resolution, high-accuracy soft lithography" Macromolecules, 33, pp 3042-3049 (2000).

Claims

A mold (1) for nanoimprint lithography having a first structured face (8) comprising n structured area (s) with patterns (3) of micrometric or nanometric size, n being a larger integer or equal to 1, characterized in that said first structured face (8) belongs to a first layer (2) which is supported by a second layer (4), the first layer (2) being made of a rigid material and the second layer ( 4) being of a flexible material.

2. Mold for nano lithography printing according to claim 1, further comprising p interlayers (5i 5 _2, 53: 5 _4, 5 ₅₎ disposed between the first layer (2) and the second layer (4) , p being an integer greater than or equal to 1, and in which the Young's modulus of the second layer (4) is smaller than the Young's modulus of the ^ith intermediate layer (5s) adjacent to the second layer (4) ), and if p is greater than 1, the Young's modulus of the (i) ^th intermediate layer is greater than the Young's modulus of the (i + 1) ^th intermediate layer, with i = 1 to (p-1 ).

3. Mold for nano-printing lithography according to claim 1 or 2, wherein the second layer (4) is itself supported by a support (7) of rigid material.

4. Mold for nano-printing lithography according to claim 1 or 2, said mold having in addition a second structured face (9) comprising m zone (s) structured (s) with patterns (10) of micrometric or nanometric size , m being an integer greater than or equal to 1, said second structured face (9) belonging to a third layer (6), which is of a rigid material, the first (8) and the second (9) structured faces being located on either side of the second layer (4) of flexible material.

The mold for nano-printing lithography according to any one of claims 1 to 4, further comprising an interposed layer (11) between the first layer (2) and the second layer (4), said interposed layer (11). ) being made of a rigid material, the face of the interposed layer (11) which is opposite the first layer (2) being structured according to n cavities (12) arranged opposite the n structured zones (30) of the first layer (2). ) and being covered by the second layer (4) so that the n cavities are filled with a flexible material.

6. Mold for nano lithography printing apparatus according to any one of claims 1 to 5, wherein all the layers (2; 4; 6; 5i, 52 5 _3, 5 _4, 5 _5; 11) constituting the mold, as well as the support (7) if it is present, are of transparent materials at a wavelength λ located in the range of UV wavelengths or visible light.

7. Mold for nano-printing lithography according to claim 3, wherein the support (7) is quartz or silica, the first layer (2) is silica and the second layer (4) is polydimethylsiloxane (PDMS ) or silicone.

8. A mold for nano-printing lithography according to any one of claims 1 to 7, wherein the set of layers (2; 4; 6; 5i, 5 ₂ , 53, 5 ₄ , 5 ₅ ; 11) constituting the mold, as well as the support (7) if it is present, are made of thermally conductive materials.

9. A method of producing a mold for nano-printing lithography comprising a structured face having n structured areas with micrometric or nanometric size patterns, the method comprising the following steps:

a) providing an initial substrate (13); b) structuring a face of said initial substrate, called the front face, in a pattern representing the negative imprint of the n structured areas that one wishes to obtain on the structured face of the mold;

c) depositing a first layer (2) on the front face of the initial substrate (13) so as to cover the relief formed in the structuring step b), the first layer (2) and the initial substrate (13) being of different materials and the first layer (2) being of a rigid material; d) depositing a second layer (4) on the first layer (2), the second layer being made of a flexible material;

e) removing the initial substrate (13).

10. A method of producing a mold for nano-printing lithography according to claim 9, further comprising, between step c) and step d), a step c ') of structuring the first layer ( 2) so as to obtain n cavities opposite the n structured zones present on the opposite face of the first layer (2).

A method of making a mold for nanoimprint lithography according to claim 9 or claim 10, further comprising, between step c) and step d), or between step c ') and step d), a step of depositing p intermediate layers (5i, 52, ₃ , ₄ , 5 ₅ ) on the first layer (2), p being an integer greater than or equal to 1, and in wherein the Young's modulus of the p ^th interlayer (5s), intended to be adjacent to the second layer (4) to be deposited in step d) is greater than the Young's modulus of said second layer, and if p is greater than 1, the Young's modulus of the (i) ^th intermediate layer is greater than the Young's modulus of the (i + 1) ^th intermediate layer, with i = 1 to (P-1) ·

12. Process for producing a mold for nano-printing lithography according to one any of claims 9 to 11, further comprising after step d) and before or after step e), a step of depositing a support (7) of rigid material on the second layer (4).

13. Process for producing a mold for nano-printing lithography according to any one of claims 9 to 12, wherein the set of layers constituting said mold, as well as the rigid material support if it is present. , are made of transparent materials at a wavelength λ located in the range of UV wavelengths, in the wavelength range of visible light and / or are of thermally conductive materials.

14. A process for producing a mold for nano-printing lithography comprising a structured face having n structured areas with micrometric or nanometric size patterns, the method comprising the following steps:

j) providing a substrate (15) of rigid material;

k) structuring a face of the substrate (15), called the front face, so as to obtain the n structured areas;

1) thinning of the substrate (15) by etching the rear face of said substrate;

m) depositing a layer (4) of flexible material on the rear face of the substrate.

15. A method of producing a mold for nano-printing lithography according to claim 14, wherein step 1) is replaced by a structuring step of the rear face of the substrate (15) so as to obtain n cavities located opposite the n structured zones of the front face.

A process for producing a mold for nanoimprint lithography according to claim 14 or claim 15, wherein the substrate (15) is a stack of layers comprising, in order, a layer of first material ( 16), a second material layer (17) and a third material layer (18), the first and third materials being rigid materials and wherein the second material layer (17) serves as a barrier layer for the structuring carried out in step k) and / or for the structuring carried out in step l ').

A method of making a mold for nanoimprint lithography according to claim 14 or claim 15, further comprising, between step 1) and step m), or between step 1 ') and step m), a step of depositing p intermediate layers (5i, 52, ₃ , ₄ , 5, ₅ ) on the rear face of the substrate (15), p being an integer greater than or equal to 1, and wherein the Young's modulus of ^th p intermediate layer, intended to be adjacent to the layer of flexible material (4) to be deposited in step m) is greater than the Young's modulus of said layer of material flexible that will be deposited at the stage m), and if p is greater than 1, the Young's modulus of the (i) ^th intermediate layer is greater than the Young's modulus of the (i + 1) ^th intermediate layer, with i = 1 to (P- 1) ·

18. A method of producing a mold for nano-printing lithography according to claim 16 or 17, further comprising, after step m), a step of depositing a support (7) of rigid material on the layer of flexible material deposited in step m).

19. A method of producing a mold for nano-printing lithography according to any one of claims 14 to 18, wherein the set of layers constituting said mold, as well as the rigid material support if it is present. , are transparent materials at a wavelength λ located in the range of UV wavelengths, in the wavelength range of visible light and / or are in thermally conductive materials.