PROCESS FOR CONTROLLING THE ORIENTATION OF THE NANODOMAINS OF A BLOCK COPOLYMER

Abstract

The invention relates to a process for controlling the orientation of the nanodomains of a block copolymer (BCP), the lower interface of which is in contact with the surface, neutralized beforehand, of a substrate, the said block copolymer being capable of nanostructuring itself to give nanodomains with a predetermined period (L.sub.0), over a minimum thickness (t) at least equal to half of the said period (L.sub.0), the said process being characterized in that it consists in depositing the said block copolymer (BCP) on the said substrate, so that its total thickness (T+t) is at least two times greater and preferably at least three times greater than the said minimum thickness (t), and in then depositing, on the said block copolymer (BCP), an interface material which makes it possible to isolate it from the ambient atmosphere.

Claims

1. A process for controlling the surface energy at the upper interface of a block copolymer (BCP), the lower interface of which is in contact with the surface, neutralized beforehand, of a substrate, the block copolymer being capable of nanostructuring itself to give nanodomains with a predetermined period (L.sub.0), over a minimum thickness (t) at least equal to half of the period (L.sub.0), the process comprising depositing the said block copolymer (BCP) on the substrate, so that its total thickness (T+t) is at least two times greater and than the minimum thickness (t), the minimum thickness being chosen so as to be equal to an integral or half-integral multiple of the period (L.sub.0), the multiple being less than or equal to 15, and then depositing, on the block copolymer (BCP), an interface material exhibiting a preferred affinity, with one of the blocks of the block copolymer, which is less than the preferred affinity which the ambient atmosphere exhibits.

2. The process according to claim 1, wherein a stage subsequent to the deposition of the block copolymer (BCP) consists in carrying out the self-organization of the block copolymer (BCP), so as to nanostructure it over at least the minimum thickness (t).

3. The process according to claim 1, wherein the upper interface of the block copolymer is in contact with an interface material comprising a compound, or mixture of compounds, of defined molecular constitution and of defined surface energy, which can be solid or liquid at the temperature of organization of the block copolymer, and which makes it possible to isolate the film of block copolymer (BCP) from the influence of the ambient atmosphere or of a defined mixture of gases.

4. The process according to claim 3, wherein the compound, or mixture of compounds, exhibits a specific affinity with at least one of the blocks of the block copolymer (BCP).

5. The process according to claim 3, wherein the compound of the upper interface material, in contact with the block copolymer (BCP), is chosen so that its surface energy is at least greater than the value .sub.i5 (in mN/m) and at least less than the value .sub.s+5 (in mN/m), where .sub.i represents the lowest value of the surface energy among all the values of each of the blocks of the block copolymer (BCP) and where .sub.s represents the greatest value of the surface energy among all the values of each of the blocks of the block copolymer (BCP).

6. The process according to claim 5, wherein the compound of the upper interface material, in contact with the block copolymer (BCP), is chosen so that its surface energy is between the values .sub.i and .sub.s.

7. The process according to claim 3, wherein compound of the upper interface material is chosen so as not to be neutral with regard to each of the blocks of the block copolymer (BCP).

8. The process according to claim 3, wherein the compound of the upper interface material is chosen as being neutral with regard to each of the blocks of the block copolymer (BCP).

9. The process according to claim 1, wherein the substrate does or does not comprise patterns, the patterns being predrawn by a lithography stage or a sequence of lithography stages of any nature prior to the stage of deposition of the film of block copolymer (BCP), the patterns being intended to guide the organization of the block copolymer (BCP) by a technique referred to as chemical epitaxy or graphoepitaxy, or else a combination of these two techniques, in order to obtain a neutralized surface.

10. A process for the manufacture of a nanolithography resist starting from a block copolymer (BCP), the lower interface of which is in contact with a surface, neutralized beforehand, of an underlying substrate, the process comprising the stages of the process for controlling the orientation of the nanodomains of a block copolymer (BCP) according to claim 1, wherein after the nanostructuring of the block copolymer (BCP), the interface material and also an excess thickness (T) of the block copolymer are removed, in order to leave a film of block copolymer nanostructured perpendicularly with respect to the substrate over the minimum thickness (t), and then at least one of the blocks of the said film of block copolymer is removed, in order to form a porous film capable of acting as a nanolithography resist.

11. The process according to claim 10, wherein the removal of the interface material and the removal of the excess thickness (T) of the block copolymer are carried out simultaneously or sequentially.

12. The process according to claim 10, wherein the stage(s) of removal of the interface material and of the excess thickness (T) is (are) carried out by a treatment of chemical mechanical polishing (CMP), solvent, ion bombardment or plasma type or by any combination, carried out sequentially or simultaneously, of the treatments.

13. The process according to claim 10, wherein the stage(s) of removal of the interface material and of the excess thickness (T) is (are) carried out by plasma dry etching.

14. The process according to claim 10, wherein the stage of removal of one or more blocks of the film of block copolymer is carried out by dry etching.

15. The process according to claim 10, wherein the stages of removal of the interface material, of the excess thickness (T) and of removal of one or more blocks of the film of block copolymer are carried out successively in one and the same etching machine, by plasma etching.

16. The process according to claim 10, wherein the block copolymer (BCP) can be subjected, in all or part, to a crosslinking/curing stage prior to the stage of removal of the excess thickness (T).

17. The process according to claim 16, wherein the crosslinking/curing stage is carried out by exposure of the block copolymer (BCP) to light radiation of defined wavelength chosen from ultraviolet radiation, ultraviolet/visible radiation or infrared radiation, and/or electron radiation, and/or a chemical treatment, and/or an atom or ion bombardment.

Description

[0061] Other distinctive features and advantages of the invention will become apparent on reading the description given by way of illustrative and non-limiting example, with reference to the appended Figures, which represent:

[0062] FIG. 1, already described, a diagram seen in section of a block copolymer, deposited on a substrate, the surface of which has been neutralized by producing a chemically epitaxied pattern, before and after the annealing stage necessary for its self-assembling, when the surface energy at the upper interface is not controlled,

[0063] FIG. 2, already described, a diagram seen in section of a block copolymer, deposited on a substrate, the surface of which has been neutralized by producing a chemically epitaxied pattern, before and after the annealing stage necessary for its self-assembling, when the block copolymer is covered with a specific upper layer for surface neutralization prior to the annealing stage,

[0064] FIG. 3, a diagram seen in section of a block copolymer comprising different stages of a process according to the invention for controlling the orientation of the nanodomains of a block copolymer, the said process making it possible for the block copolymer to nanostructure itself so that its nanodomains are oriented perpendicularly to the surface of the substrate over a minimum thickness t.

DETAILED DESCRIPTION OF THE INVENTION

[0065] The term polymers is understood to mean either a copolymer (of statistical, gradient, block or alternating type) or a homopolymer.

[0066] The term monomer as used relates to a molecule which can undergo a polymerization.

[0067] The term polymerization as used relates to the process for conversion of a monomer or of a mixture of monomers into a polymer.

[0068] The term copolymer is understood to mean a polymer bringing together several different monomer units.

[0069] The term statistical copolymer is understood to mean a copolymer in which the distribution of the monomer units along the chain follows a statistical law, for example of Bernoulli (zero-order Markov) or first-order or second-order Markov type. When the repeat units are distributed at random along the chain, the polymers have been formed by a Bernoulli process and are referred to as random copolymers. The term random copolymer is often used even when the statistical process which has prevailed during the synthesis of the copolymer is not known.

[0070] The term gradient copolymer is understood to mean a copolymer in which the distribution of the monomer units varies progressively along the chains.

[0071] The term alternating copolymer is understood to mean a copolymer comprising at least two monomer entities which are distributed alternately along the chains.

[0072] The term block copolymer is understood to mean a polymer comprising one or more uninterrupted sequences of each of the separate polymer entities, the polymer sequences being chemically different from one another and being bonded to one another via a chemical (covalent, ionic, hydrogen or coordination) bond. These polymer sequences are also known as polymer blocks. These blocks exhibit a phase segregation parameter (Flory-Huggins interaction parameter) such that, if the degree of polymerization of each block is greater than a critical value, they are not miscible with one another and separate into nanodomains.

[0073] The above term miscibility is understood to mean the ability of two or more compounds to mix completely to form a homogeneous or pseudo-homogeneous phase, that is to say a phase without apparent short-range or long-range crystal or quasi-crystal symmetry. The miscible nature of a mixture can be determined when the sum of the glass transition temperatures (Tg) of the mixture is strictly less than the sum of the Tg values of the compounds taken in isolation.

[0074] In the description, reference is made both to self-assembling and to self-organization or else to nanostructuring to describe the well-known phenomenon of phase separation of the block copolymers, at an assembling temperature also known as annealing temperature.

[0075] The term period of a block copolymer, denoted L.sub.0, is understood to mean the minimum distance separating two neighbouring domains having the same chemical composition, separated by a domain having a different chemical composition.

[0076] Minimum thickness t is understood to mean the thickness of a film of block copolymer acting as nanolithography resist, below which it is no longer possible to transfer the patterns of the film of block copolymer into the underlying substrate. In general, for the block copolymers having a high phase segregation parameter , this minimum thickness t is at least equal to half the period L.sub.0 of the block copolymer.

[0077] The term porous film denotes a film of block copolymer from which one or more nanodomains have been removed, leaving holes, the shapes of which correspond to the shapes of the nanodomains which have been removed and which can be spherical, cylindrical, lamellar or helical.

[0078] Neutral or pseudo-neutral surface is understood to mean a surface which, in its overall nature, does not exhibit a preferred affinity with one of the blocks of a block copolymer. It thus makes possible an equitable or pseudo-equitable distribution of the blocks of the block copolymer at the surface.

[0079] The neutralization of the surface of a substrate makes it possible to obtain such a neutral or pseudo-neutral surface.

[0080] When reference is made to the surface energies or more specifically to the interfacial tensions of a material and of a block of a given block copolymer, these are compared at a given temperature and more particularly at a temperature which makes possible the self-organization of the block copolymer.

[0081] The term lower interface of a block copolymer to be nanostructured is understood to mean the interface in contact with an underlying substrate on which the said block copolymer is deposited. It should be noted that, throughout the continuation of the description, this lower interface is neutralized, that is to say that it does not exhibit, in its overall nature, a preferred affinity with one of the blocks of the block copolymer.

[0082] The term upper interface or upper surface of a block copolymer to be nanostructured is understood to mean the interface in contact with a compound or mixture of compounds of defined molecular constitution and of defined surface energy, whether it is solid or liquid, that is to say non-volatile, at the temperature of self-organization of the nanodomains. Thus, when the compound is liquid, this can be a solvent or mixture of solvents in which the block copolymer is insoluble. When the compound is solid, this can, for example, be a copolymer, the affinity of which with at least one of the blocks of the block copolymer is less marked than with the ambient air.

[0083] As regards the film of block copolymer to be nanostructured, denoted BCP in the continuation of the description, it comprises n blocks, n being any integer greater than or equal to 2. The block copolymer BCP is more particularly defined by the following general formula:

A-b-B-b-C-b-D-b- -b-Z

where A, B, C, D, . . . , Z are blocks i . . . j representing either pure chemical entities, that is to say that each block is a set of monomers of identical chemical natures, polymerized together, or a set of comonomers, copolymerized together, in the form, in all or part, of a block or statistical or random or gradient or alternating copolymer.

[0084] Each of the blocks i . . . j of the block copolymer BCP to be nanostructured can thus potentially be written in the form: i=a.sub.i-co-b.sub.i-co- . . . -co-z.sub.i, with i . . . j, in all or part.

[0085] The volume fraction of each entity a.sub.i . . . z.sub.i can range from 1% to 99%, as monomer units, in each of the blocks i . . . j of the block copolymer BCP.

[0086] The volume fraction of each of the blocks i . . . j can range from 5% to 95% of the block copolymer BCP.

[0087] The volume fraction is defined as being the volume of an entity with respect to that of a block, or the volume of a block with respect to that of the block copolymer.

[0088] The volume fraction of each entity of a block of a copolymer, or of each block of a block copolymer, is measured in the way described below. Within a copolymer in which at least one of the entities, or one of the blocks, if a block copolymer is involved, comprises several comonomers, it is possible to measure, by proton NMR, the molar fraction of each monomer in the entire copolymer and then to work back to the mass fraction by using the molar mass of each monomer unit. In order to obtain the mass fractions of each entity of a block, or each block of a copolymer, it is then sufficient to add the mass fractions of the constituent comonomers of the entity or of the block. The volume fraction of each entity or block can subsequently be determined from the mass fraction of each entity or block and from the density of the polymer forming the entity or the block. However, it is not always possible to obtain the density of the polymers, the monomers of which are copolymerized. In this case, the volume fraction of an entity or of a block is determined from its mass fraction and from the density of the compound which is predominant by weight in the entity or in the block.

[0089] The molecular weight of the block copolymer BCP can range from 1000 to 500 000 g.mol.sup.1.

[0090] The block copolymer BCP can exhibit any type of architecture: linear, star-branched (three or multiple arms), grafted, dendritic or comb.

[0091] As regards the process for controlling the orientation of the nanodomains of the block copolymer BCP, itself deposited beforehand on an underlying substrate, the surface of which has been neutralized beforehand, the principle of the invention consists in using the preferred affinity of one of the blocks of the block copolymer BCP for the material (liquid, solid, polymer, and the like) of the upper interface, rather than preferred affinity with the ambient atmosphere, in combination with a high thickness of the said block copolymer BCP, in order to simultaneously efficiently screen this preferred affinity from the lower parts of the film of block copolymer and to stabilize the film of block copolymer with regard to a possible phenomenon of dewetting of the substrate, in order to orientate the nanodomains of the block copolymer along a desired direction, over a minimum thickness (t), during the stage of nanostructuring the said block copolymer BCP.

[0092] The underlying substrate can be a solid of inorganic, organic or metallic nature. In a specific example, it can be made of silicon. Its surface is neutralized beforehand. For this, the substrate does or does not comprise patterns, the said patterns being predrawn by a lithography stage or a sequence of lithography stages of any nature prior to the stage of deposition of the film of block copolymer BCP, the said patterns being intended to guide the organization of the said block copolymer BCP by a technique referred to as chemical epitaxy or graphoepitaxy, or else a combination of these two techniques, in order to obtain the neutralized surface.

[0093] The block copolymer is capable of nanostructuring itself into nanodomains with a period (L.sub.0) over a minimum thickness (t) at least equal to half of the said period (L.sub.0).

[0094] In order to neutralize the upper interface, the block copolymer is advantageously deposited on the said substrate with a total thickness (T+t), representing the sum of the said minimum thickness (t) and of an excess thickness (T), which is at least two times greater than the said minimum thickness (t). Subsequently, any thickness of a liquid or solid material exhibiting a specific affinity, even if this is slight, for at least one of the blocks of the block copolymer BCP is deposited on the film of block copolymer BCP, in order to isolate the said BCP film from the ambient atmosphere or from a defined mixture of gases.

[0095] The latter stage, referenced 6 in the diagram of FIG. 3, of deposition of an intermediate buffer layer, also known as interface material in the continuation of the description, between the block copolymer BCP and the ambient atmosphere, constitutes the core of this invention as it is then possible to choose another compound at the upper interface of the block copolymer which exhibits a specific affinity with at least one of the blocks of the block copolymer, this affinity being less marked than that of the ambient air. This compound at the upper interface can, for example, be a solid, such as a copolymer, for example, or a liquid, such as a solvent, in which the block copolymer BCP is insoluble, or else an ionic liquid. This process exhibits the enormous advantage, with respect to the top coat process of the prior art, of not using an upper material which is neutral for the blocks of the block copolymer BCP but which makes it possible instead to greatly decrease the block copolymer BCP/initial atmosphere affinity.

[0096] More preferably, the total thickness (T+t) is at least three times greater than the said minimum thickness (t).

[0097] The minimum thickness (t) represents the thickness over which the block copolymer has to nanostructure itself in order to be able to subsequently etch patterns in the underlying substrate by virtue of the nanostructured block copolymer, which acts as nanolithography resist. For a copolymer having a high phase segregation parameter, this minimum thickness (t) is at least equal to half the nanostructuring period (L.sub.0) of the block copolymer.

[0098] FIG. 3 illustrates stage 6 of deposition of the block copolymer BCP on the surface, neutralized beforehand by chemical epitaxy, of the substrate and of a layer of interface material intended to act as buffer layer between the block copolymer, deposited beforehand, and the atmosphere. This interface material is provided in the solid or liquid form. The block copolymer BCP is advantageously deposited over a total thickness (T+t). The interface material and also the excess thickness T of the block copolymer BCP then make it possible to screen and protect the minimum thickness t of the block copolymer BCP from the influence of the preferred affinity of the atmosphere with one of the blocks of the said block copolymer. Thus, the air in contact with the interface material deposited on the upper surface of the block copolymer BCP does not have an influence into the depth of the copolymer and in particular over the minimum thickness t. The process for controlling the orientation of the nanodomains of a block copolymer according to the invention is thus universal and applies whatever the chemical system of the block copolymer.

[0099] The minimum total thickness (T+t) of the block copolymer BCP is chosen so that: (T+t)2t, and preferably (T+t)3t, with t at least equal to half of L.sub.0.

[0100] In addition, the invention is not limited to obtaining a minimum thickness t of the order of half of the period L.sub.0. This is because this minimum thickness can advantageously be chosen so that it is equal to an integral or half-integral multiple of the period (L.sub.0), the said multiple being less than or equal to 15 and preferably less than or equal to 10. Thus, if it is desired to organize the nanodomains of a block copolymer perpendicularly to the lower and upper interfaces, over a minimum thickness t equal to 2L.sub.0, for example, it is advisable to deposit the block copolymer over a total thickness (T+t) of at least 4L.sub.0 to 6L.sub.0 (=2t to 3t). In the same way, if it is desired to organize the nanodomains of a block copolymer perpendicularly to the lower and upper interfaces, over a minimum thickness t equal to 3L.sub.0, for example, it is advisable to deposit the block copolymer over a total thickness (T+t) of at least 6L.sub.0 to 9L.sub.0 (=2t to 3t).

[0101] The compound at the upper interface, in contact with the block copolymer BCP, can be chosen so that its surface energy is at least greater than the value .sub.i5 (in mN/m) and at least less than the value .sub.s+5 (in mN/m), where .sub.i represents the lowest value of the surface energy among all the values of each of the blocks of the block copolymer and where .sub.s represents the greatest value of the surface energy among all the values of each of the blocks of the block copolymer BCP. Preferably, the compound at the upper interface, in contact with the block copolymer, is chosen so that its surface energy is between the values .sub.i and .sub.s. The compound at the upper interface can be chosen so as not to be neutral with regard to each of the blocks of the block copolymer.

[0102] The block copolymer can be deposited according to techniques known to a person skilled in the art, such as, for example, the spin coating, doctor blade, knife system or else slot die system technique. For this, the block copolymer BCP is mixed beforehand in a solvent.

[0103] A stage subsequent to the deposition of the block copolymer BCP and to the deposition of the upper interface material consists in proceeding to the self-organization of the block copolymer BCP so that it nanostructures itself over at least the minimum thickness t (stage referenced 7 in the diagram of FIG. 3). For this, the self-organization of the block copolymer can be carried out by any appropriate technique or combination of appropriate techniques known to a person skilled in the art. Preferably, it is carried out by submitting the stack obtained, comprising the substrate, the surface of which has been neutralized beforehand, the block copolymer BCP and the interface material, to a heat treatment. The block copolymer then nanostructures itself under the effect of the heat treatment and the nanodomains obtained orientate themselves perpendicularly to the surface of the substrate over at least the said minimum thickness t.

[0104] As regards the process for the manufacture of a nanolithography resist, when the block copolymer BCP is nanostructured and when its patterns are oriented perpendicularly to the surface of the substrate, over at least the said minimum thickness t, it is advisable to proceed first to the removal of the material of the upper interface and then to the removal of the excess thickness T (stage 8 of FIG. 3), in order to obtain a film of block copolymer BCP which is nanostructured. This film is intended to act as a resist in a subsequent nanolithography process, in order to transfer its patterns into the underlying substrate.

[0105] For this, the removal of the upper interface material and also the removals of the excess thickness T of the block copolymer can be carried out, simultaneously or sequentially, by a treatment of chemical mechanical polishing (CMP), solvent, ion bombardment or plasma type or by any combination, carried out sequentially or simultaneously, of these treatments.

[0106] Preferably, the removals of the upper interface material and of the excess thickness T of the block copolymer are carried out by dry etching, such as plasma etching, for example, for which the chemistry (chemistries) of the gas(es) employed is (are) chosen so as not to exhibit a specific selectivity for a given block of the block copolymer BCP. Thus, the etching takes place at the same rate for all the blocks of the block copolymer BCP. The etching of the excess thickness T is thus carried out until the said minimum thickness t, chosen beforehand, of block copolymer BCP is left on the substrate.

[0107] In one example, the block copolymer is, for example, deposited over a total thickness (T+t) at least greater than 50 nm, and the upper interface material and also the excess thickness T are removed in order to retain a minimum thickness t of less than 45 nm, preferably of less than 40 nm. This case can, for example, exist with a block copolymer with a period L.sub.0 equal to 20 nm and for which a minimum thickness t equal to L.sub.0 or to 2L.sub.0, for example, is desired.

[0108] Prior to the removal of the excess thickness T, the block copolymer can be subjected, in all or part, to a crosslinking/curing stage. In such a case, the removal of the interface material will be carried out before the removal of the excess thickness T, in order to be able to crosslink/cure all or part of the block copolymer.

[0109] This crosslinking/curing stage can be carried out by exposure of the block copolymer BCP to light radiation of defined wavelength chosen from ultraviolet radiation, ultraviolet/visible radiation or infrared radiation, and/or electron radiation, and/or a chemical treatment, and/or an atom or ion bombardment.

[0110] After removal of the upper interface material and of the said excess thickness T, a film of block copolymer BCP nanostructured over a thickness t is then obtained, the nanodomains of which are oriented perpendicularly to the surface of the underlying substrate, as represented in the diagram of FIG. 3. This film of block copolymer is then capable of acting as resist, after removal of at least one of its blocks in order to leave a porous film and to thus be able to transfer its patterns into the underlying substrate by a nanolithography process.

[0111] The removal of the block or blocks of the film of block copolymer can be carried out by any known means, such as wet etching, using a solvent capable of dissolving the block(s) to be removed while retaining the other blocks, or dry etching.

[0112] When wet etching is chosen, prior to the removal of the block or blocks of the film of block copolymer which remains, it is possible to apply a stimulus to all or part of the said film of block copolymer. Such a stimulus can, for example, be produced by exposure to UV-visible radiation, to an electron beam or else to a liquid exhibiting acid/base or oxidation/reduction properties, for example. The stimulus then makes it possible to induce a chemical modification over all or part of the block copolymer BCP, by cleaving of polymer chains, formation of ionic entities, and the like. Such a modification then facilitates the dissolution of one or more blocks of the copolymer to be removed, in a solvent or mixture of solvents, in which the other blocks of the copolymer BCP are not soluble before or after the exposure to the stimulus.

[0113] In one example, if the block copolymer intended to act as resist is a PS-b-PMMA block copolymer, a stimulus by exposure of the film of block copolymer to UV radiation will make it possible to cleave the polymer chains of the PMMA while bringing about crosslinking of the chains of PS polymers. In this case, the PMMA patterns of the block copolymer can be removed by dissolution in a solvent or mixture of solvents judiciously chosen by a person skilled in the art.

[0114] Another way of removing one or more block(s) of the film of block copolymer consists in using dry etching, such as plasma etching, for example. Such a plasma etching is preferred as it can be carried out in the same machine as the stage(s) of removal of the interface material and of removal of the excess thickness T; only the chemistry of the constituent gases of the plasma has to be changed in order to be able to selectively remove the block(s) to be removed and to retain the other blocks.

[0115] Likewise, another advantage of this plasma etching lies in the fact that the removal of the upper interface material, the removal of the excess thickness T, the removal of the block(s) of the film of block copolymer and then the transfer of the patterns of the film of block copolymer into the underlying substrate can be carried out in the same etching machine. In this case, only the chemistry of the gases of the plasma will or will not have to be changed, depending on the materials to be removed.