EP1508070A2

EP1508070A2 - Method for producing photoresist masks for structuring semiconductor substrates by means of optical lithography

Info

Publication number: EP1508070A2
Application number: EP03735270A
Authority: EP
Inventors: Oliver Kirch; Michael Sebald
Original assignee: Infineon Technologies AG
Current assignee: Infineon Technologies AG
Priority date: 2002-05-29
Filing date: 2003-04-30
Publication date: 2005-02-23
Also published as: US20060083993A1; TWI225971B; JP2005535910A; KR100748742B1; DE10223997A1; WO2003102690B1; TW200401169A; WO2003102690A2; CN1656423A; KR20050005497A; WO2003102690A3

Abstract

The invention relates to a method for producing photoresist masks for structuring semiconductors. According to the inventive method, a resist comprising a polymer with silicon-containing groups is used. The silicon atoms in an oxygen-containing plasma are converted into silicon dioxide for the structuring process, said silicon dioxide protecting the regions of the absorber, which are arranged beneath the silicon dioxide, from being eroded by the plasma.

Description

description

Process for the production of photomasks for structuring semiconductor substrates by optical lithography

The invention relates to a method for producing photomasks for optical lithography. The photomasks are suitable for structuring semiconductor substrates, e.g. Silicon wafers.

In the manufacture of microchips, lithographic processes are used for the structuring of semiconductor substrates. Silicon wafers are generally used as the semiconductor substrate, into which structures or components may already have been introduced. First, a thin layer of a photoresist is applied to the semiconductor substrate, the chemical or physical properties of which can be changed by exposure. The photoresist is exposed, generally using monochromatic light, in particular laser light. A photomask, which contains all information about the structure to be imaged, is introduced into the beam path between the radiation source and the photoresist. In the simplest case, the structure contained in the photomask corresponds to an image of the structure to be produced on the semiconductor substrate that is enlarged approximately 5 times. This structure is projected onto the photoresist with the aid of appropriate optics, so that the photoresist is exposed in sections and, for example, a chemical modification of the photoresist is brought about in the exposed sections. The exposed photoresist is developed with a developer, with only the exposed areas being selectively removed, for example. The remaining unexposed resist sections then serve as a mask for processing the semiconductor substrate. The structure specified by the resist mask can be transferred into the semiconductor substrate, for example by dry etching with an etching plasma, in order, for example, to produce trenches for trench capacitors. However, the resist structures can also be filled with another material, for example polysilicon, in order to produce conductor tracks.

The photomask arranged in the beam path is produced by writing an electron beam onto a substrate coated with a photoresist. For this purpose, a layer of an absorber material is first applied to a transparent substrate, generally a quartz glass. With COG masks (COG = "Chrom On Glass") as the simplest example of a photo mask, the absorber material consists of a thin chrome layer. In order to be able to structure the layer of the absorber material, for example the chromium layer, a layer of a photoresist is first applied to the chromium layer, the properties of which can be changed by irradiation. At present, a layer of polymethyl methacrylate (PMMA) is usually used as the photoresist layer. This photoresist layer is then written on with an electron beam using a mask writer. The areas in which the chrome layer is to be removed in a later operation in order to obtain transparent sections of the mask are exposed to the electron beam. The energy of the electron beam splits the polymethyl methacrylate into smaller fragments. The different solubility of the PMMA and the fragments resulting from the exposure from the PMMA in a solvent are used for the development of the exposed photoresist. For this purpose, a developer is applied to the exposed photoresist, usually an organic solvent, which selectively dissolves only the fragments that have arisen from the PMMA in the exposed areas, while the PMMA remains unchanged on the chrome layer in the unexposed areas. The structure created from the photoresist is then transferred into the chrome layer below using an etching plasma. To do this, use a

Oxygen / chlorine gas mixture worked to form volatile chromium compounds. The chrome layer is covered in the exposed sections not covered by the mask. worn and the transparent quartz substrate arranged under the chrome layer exposed.

However, the photoresists currently used are very strongly attacked by the oxygen content contained in the etching plasma, so that the photoresist is removed at the edges of the structure produced from the photoresist and the chrome layer arranged underneath is no longer protected. This leads to a strong lateral loss of structure at the chrome edges. Usual metrology losses in chrome are around 50 n per edge. After the etching process, the absorber lines generated from the chrome layer can therefore be up to 100 nm narrower than the width defined by the photoresist. This structure loss has already been taken into account in the mask layout and a corresponding structure provision has been provided. The absorber lines to be generated from the chrome layer were simply widened in the mask layout. For structural dimensions of more than 0.25 μm, such as occur in the photomasks currently used for the production of microchips, this does not pose any difficulties either. However, as the dimensions of the structures to be produced in the semiconductor substrate decrease, the size of the absorber structures contained in the photomask also decreases. Furthermore, diffraction and interference effects occur in the imaging of very small structures, which impair the resolution of the photomask. To improve the resolution, the structural elements to be imaged in the photomask are therefore supplemented by non-imaging elements, in order to achieve a steepening of the transition between exposed and unexposed sections on the photoresist when structuring semiconductor substrates. The non-imaging structures of the photomask have a line width which is below the resolution of the imaging device. The resolution is determined in particular by the wavelength of the radiation used for the exposure of the photoresist. This method of improving the image by introducing non-imaging structural elements into the photo mask is also referred to as OPC (Optical Proximity Correction). net. This means that the structure shown and the structure of the photomask are no longer similar. In addition to the structures to be imaged, the photo mask also contains auxiliary structures. When manufacturing the photomask, a significantly higher number of structural elements must therefore be produced than corresponds to the structure shown. If one takes into account the reduction in the dimensions of the photomask as a result of the reduction in the structures to be produced in the semiconductor substrate, it is immediately apparent that the scope that is available for maintaining the structure in the manufacture of the photomask is continuously decreasing or is no longer available , In the near future, the non-imaging auxiliary structures of the photomask will reach dimensions of down to 100 nm and less and must be arranged at a defined distance from the main structures of the photomask.

With these very fine structural dimensions, it is no longer possible to correct the mask layout beforehand, i.e. to maintain the structure. With a required distance of, for example, 100 nm and a simultaneous structure reserve of 50 nm per edge, the structures would already collapse into a single line in the layout.

Another problem with the production of photomasks is that the structured photoresist is particularly strongly removed by the plasma at the edges and the edges are therefore rounded off. Initially, rectangular resist structures are therefore not exactly transferred into the absorber layer. There is currently no photoresist available with which structures with a line spacing of 50 nm can be created in the chrome mask.

The object of the invention is therefore to provide a method for the production of photomasks for optical lithography, with which structures with a very small line spacing can also be produced in an absorber layer. The object is achieved with a method for producing photomasks for optical lithography, wherein: a transparent substrate is provided, a first layer made of an absorber material is deposited on the transparent substrate, and a layer of a resist for electron beam lithography is deposited on the first layer is applied, which comprises at least:

a film-forming polymer comprising silicon atoms; and a solvent.

and the solvent contained in the resist is evaporated, so that a second layer is obtained which contains the film-forming polymer, the second layer is written on with a focused electron beam, so that an image is produced in the second layer, the exposed and unexposed areas comprises, on the second layer, a developer which releases the exposed areas of the image so that a structured resist is obtained with a structure in which the unexposed areas form bridges and the exposed areas form trenches arranged between the bridges, and the structure of the structured resist is transferred into the first layer of the absorber material.

The method according to the invention is characterized by the use of a resist which comprises a film-forming polymer which contains silicon atoms, the proportion of silicon atoms in the film-forming polymer preferably being chosen to be as high as possible. The film-forming polymer or the silicon atoms contained in it are converted into silicon dioxide in the oxygen plasma. Silicon dioxide is largely inert to a further attack by the oxygen plasma. During the plasma etching, therefore, there is no or only a very slight loss of structure, so that a structure defined with an electron beam in the resist with high exact unit can be transferred into the layer of absorber material. It is therefore no longer necessary to provide a structure reserve when designing the photomask, which is why structures with very small dimensions of less than 100 nm can also be produced in the photomask without any problems. Furthermore, rounding of edges can be largely suppressed, so that even complex structures, which include right angles or edges, for example, can be represented exactly. As a further advantage, when transferring a structure produced from the resist into an absorber material, work can be carried out with a considerably higher oxygen content of the plasma, so that depletion of the etching plasma, which is also referred to as the loading effect, can be avoided.

When carrying out the method according to the invention, a transparent substrate is first provided. The substrate is transparent to the exposure radiation which will later be used for structuring a semiconductor substrate and generally consists of quartz glass. A first layer of an absorber material is then deposited on the substrate. For this purpose, for example, a chrome layer is deposited for the production of COG masks. The deposition can take place, for example, by sputtering. However, other materials can also be used as the absorber material, for example semi-transparent materials or phase-shifting materials. Examples of other materials are titanium or MoSi.

A layer of the resist described above for electron beam lithography is then applied to the first layer. Conventional methods can be used for this purpose, for example spin coating, spraying on or dipping methods. In order to obtain a solid resist film, the solvent contained in the resist is then evaporated, so that a second layer of the film-forming agent contained in the resist

Polymer is obtained. For this purpose, the substrate of the applied resist layer can be heated, for example. The resist film is now made using a focused electron beam described so that an image is generated in the second layer, which comprises exposed and unexposed areas. By writing with an electron beam, a certain mask layout is embossed into the second layer formed from the film-forming polymer. By the energy of the

Electron beam splits the polymer into shorter fragments so that there is a chemical differentiation between exposed and unexposed areas. Conventional mask pens can be used to write on the resist film. A developer is now placed on the second layer, which dissolves the exposed areas of the image, so that a structured resist is obtained in which the unexposed areas of the image form webs and the exposed areas of the image form trenches arranged between the webs. An organic solvent which does not dissolve the film-forming polymer, but in which the fragments formed from the film-forming polymer are soluble, is suitably used as the developer. Suitable solvents are, for example, butyl lactate, γ-butyrolactone, methyl ethyl ketone, isopropanol or methyl isobutyl ketone. The solvents can be used alone or as a mixture of several solvents, for example a 1: 1 mixture of methyl ethyl ketone and isopropanol. For the task of the developer, customary processes can be used, for example puddle processes or dipping processes The structure can now be transferred into the first layer of the absorber material by etching away the absorber material in the sections exposed in the trenches, for example with a suitable plasma. The plasma has a customary composition a uf, as it was already used in the previously common methods for the production of COG masks. However, the plasma can have a higher oxygen content in order to suppress impoverishment effects. The plasma converts the silicon atoms contained in the film-forming polymer into silicon dioxide, which acts as a protective layer on those sections of the first layer of the absorber material remain, which form the absorber structures in the finished photomask.

The resist used in the method according to the invention comprises a film-forming polymer which comprises the highest possible proportion of silicon atoms, and a solvent. All common solvents or mixtures thereof can be used as solvents which are able to absorb the film-forming silicon-containing polymer in a clear, homogeneous and storage-stable solution and which ensure a good layer quality when coating the transparent substrate. As a solvent of the resist, for example, methoxypropylacetate, cyclopentanone and cyclohexanone, γ-butyrolactone, ethyl lactate, diethylene glycol, dimethyl ether or a mixture of at least two of these solvents can be used. . For the preparation of the resist, the film forming Si ^{"liziumhaltige} polymer is dissolved in a suitable solvent Suitable compositions of the resist are in the following ranges:

film-forming silicon-containing polymer: 1-50% by weight, preferably 2-10% by weight; Solvent: 50-99% by weight, preferably 88-97% by weight.

Additional additional components / additives can be added to the resist, which advantageously influence the resist system with regard to resolution, film formation properties, storage stability, radiation sensitivity and service life effect. In addition to the film-forming silicon-containing polymer and the solvent, the resist can contain, for example, sensitizers or solubilizers.

The structure of the film-forming polymer can be varied within wide limits, but a sufficiently high content of silicon atoms must always be guaranteed in order to ensure sufficient stability of the structures produced from the resist against an etching plasma with a high oxygen content. According to a first preferred embodiment, the film-forming polymer comprises, in addition to at least one further repeating unit, first repeating units which carry at least one lateral silicon-containing group.

The film-forming polymer can be produced by conventional processes by radical copolymerization of a silicon-containing comonomer and other comonomers. For this purpose, the comonomers each comprise at least one radically polymerizable carbon-carbon double bond, so that the polymer has a main chain formed from carbon atoms. The radical polymerization can be carried out in solution or in a solvent-free system. Conventional radical initiators, for example benzoyl peroxide or azoisobutyronitrile (AIBN), can be used as radical initiators for radical polymerization. Silicon-containing groups are introduced into the film-forming polymer through the silicon-containing comonomer, the silicon-containing groups being arranged laterally to the main polymer chain. The silicon-containing comonomer can have a large variety of structures, but it is preferred that the first comonomer comprises no further functional groups apart from the polymerizable carbon-carbon double bond and the silicon-containing group. Examples of suitable comonomers are shown below:

Here means:

R ¹ , R ² , R ³ : an alkyl group having 1 to 10 carbon atoms; R ⁴ : a hydrogen atom or an alkyl group having 1 to 10 carbon atoms;

X: oxygen or an NH group; a: an integer between 1 and 10.

Trimethylallylsilane and derivatives of acrylic acid and methacrylic acid are particularly preferred as silicon-containing comonomers.

The first repeating unit derived from the silicon-containing comonomer is preferably contained in the film-forming polymer in a proportion of 10 to 90 mol%, particularly preferably 50 to 90 mol%.

In addition to the silicon-containing first repeating units, the film-forming polymer described above contains, according to a preferred embodiment, second repeating units derived from inert comonomers as further repeating units. Inert comonomers are understood to mean comonomers which, apart from the polymerizable carbon-carbon double bond, contain no further functional groups which enable chemical modification of the film-forming polymer, for example by splitting off groups or by subsequently attaching groups by reaction with the film-forming polymer. In this case, the resist preferably contains no further constituents in addition to the film-forming polymer and the solvent. The differentiation between exposed and unexposed sections of the resist is therefore carried out by fragmenting the main polymer chain.

Repeat units which are derived from alkyl esters of (meth) acrylic acid are preferably used as the second repeat units. The alkyl chain of the esters preferably comprises 1 to 10 carbon atoms, it being possible for the alkyl chains to be straight-chain or branched. The second repeating units are particularly preferably derived from methyl methacrylate. In addition to the silicon-containing first repetition units and the optionally contained second repetition units derived from inert comonomers, the film-forming polymer can contain further repetition units which enable subsequent modification of the film-forming polymer. For this purpose, the film-forming polymer comprises, as further repeating units, third repeating units which contain at least one anchor group. An anchor group is understood to mean a functional group which can be attacked nucleophilically by a nucleophilic group with the formation of a covalent bond, so that groups can subsequently be introduced into the film-forming polymer.

For this purpose, a reinforcement agent is added to the structured resist, which comprises a group that can coordinate with the anchor group. The anchor groups contained in the film-forming polymer must have sufficient reactivity in order to be able to react adequately with a post-amplification reagent within which the groups are introduced to increase the etch resistance in order to increase the resistance to etching. Anchor groups which have sufficient reactivity are, for example, isocyanates, epoxides, ketenes, oxyrans, urethanes or acid anhydrides. Carboxylic acid anhydride groups have proven to be particularly advantageous because, on the one hand, they have sufficient stability to enable uncomplicated production and processing of the film-forming polymer or the resist, and on the other hand they have a sufficiently high reactivity in order to be able to react within periods of time which are of interest for industrial use implement an implementation with a reinforcement agent. Third repeating units derived from an at least monounsaturated carboxylic anhydride are therefore particularly preferred. At least monounsaturated is understood to mean that the carboxylic anhydride contains at least one polymerizable carbon Has carbon double bond. Suitable comonomers through which an anchor group can be introduced into the film-forming polymer are, for example, cyclohexenedicarboxylic anhydride, itaconic anhydride, norbornenedicarboxylic anhydride or methacrylic anhydride. A particularly suitable at least monounsaturated carboxylic acid anhydride is maleic anhydride. Maleic anhydride can be readily introduced into the polymer as a comonomer during the production of the film-forming polymer by radical polymerization. The third repeating units derived from maleic anhydride have sufficient reactivity for reaction with an amplification agent in order to enable industrial use. Maleic anhydride can also be obtained inexpensively.

The group provided on the amplification agent must, on the other hand, have a certain nucleophilicity in order to be able to react with the anchor groups of the film-forming polymer. Suitable nucleophilic groups are, for example, hydroxyl groups, thiol groups or, particularly preferably, amino groups. In order to enable the amplification agent to be linked , the amplification agent is left on the structured resist for a certain time, so that the amplification agent is bound to the film-forming polymer and an amplified structure is obtained

The time required for the reaction of the amplification agent with the anchor groups of the film-forming polymer can be controlled, for example, by the concentration at which the amplification agent is applied to the structured resist or by the temperature at which the reaction is carried out , The reaction with the amplification agent takes place until a certain modification of the film-forming polymer is achieved. Excess amplification agent can be removed after the reaction is complete. In this way, the silicon content of the polymer can be increased subsequently by introducing additional silicon-containing groups into the film-forming polymer. Not only can the etch resistance of the -um¬

structured resists are increased but also the width of the structures after development are subsequently increased and in this way a structural reserve is subsequently generated. In this embodiment of the method according to the invention, the polymer does not already have to contain silicon-containing groups in order to ensure sufficient etching resistance in the oxygen plasma, since the silicon-containing groups can be subsequently introduced into the polymer and thus sufficient etching resistance of the post-reinforced structures can be achieved.

The post-reinforced structure is then transferred, as described above, into the first layer made of the absorber material. For this purpose, the absorber material exposed in the trenches of the resist structure is etched away.

The amplification agent can be applied to the structured resist from the gas phase. However, the amplification agent is preferably applied as a solution to the structured resist. The solvent allows the film-forming polymer to swell in the structured resist, as a result of which the amplification agent can also penetrate into deeper areas of the resist structure in order to react there with the anchor groups of the film-forming polymer. Excess amplification agent can also be easily removed by spinning or rinsing.

The amplification agent can also be applied in solution in the developer to the exposed resist. In this embodiment of the method, the development of the exposed resist and the post-amplification of the structured resist are carried out simultaneously in one work step, as a result of which the manufacture of the post-amplified structure can be simplified and shortened.

In this embodiment of the method, the etch stability of the resist against an oxygen plasma can be increased subsequently. According to the invention, additional silicon silicon-containing groups introduced into the polymer, which are converted into non-volatile silicon dioxide in the oxygen plasma and form a protective layer on the absorber material. For this purpose, the amplification agent comprises a silicon-containing group.

The amplification agent particularly preferably comprises at least two reactive groups. In the post-amplification, the post-amplification agent effects a further crosslinking of the polymer, which increases the stability of the resist structure and largely suppresses detachment of the post-amplified resist by a solvent.

The reinforcing agent is preferably a basic functionalized silicon compound, in particular an aminosiloxane. Chain-shaped methylsiloxanes with terminal aminopropyl units and 2 to 51, but preferably 2 to 12 silicon atoms per molecule have proven particularly useful. Such a chain-like dimethylsiloxane is shown below with its structural formula.

b = 1 to 50

Further examples of amplification agents with amino-functional groups can be represented by the following general structural formulas.

R- - -cc- -SiR (CH ₃ ) ₃ Si-N-Si (CH ₃ ) ₃

H ₂

in which

c is an integer between 1 and 20, d is an integer between 0 and 30,

H, alkyl, aryl; and

R ⁶ =

In this embodiment of the resist according to the invention, the film-forming polymer contains first repeating units which contain silicon atoms, and third repeating units which comprise anchor groups. If appropriate, the polymer can also comprise second repeating units which have no reactive groups, for example acrylates, methacrylates or also repeating units derived from styrene. With such a resist, the resist film is also differentiated by fragmentation of the main polymer chain under the action of a focused electron beam. The exposed resist film is then developed with a solvent in which the polymer fragments are more soluble than the film-forming polymer itself. Organic solvents are usually used, for example those mentioned above.

Another mechanism of differentiation between exposed and unexposed areas is made possible if the film-forming polymer in addition to the at least one silicon containing the first repeating units containing group, as further repeating units, fourth repeating units which have an acid-labile group which are cleaved under the action of acids and release a group which bring about an increase in the solubility of the polymer in aqueous alkaline developers.

In this embodiment of the method, the resist is designed as a chemically amplified resist. In order to make the acid available for the cleavage of the acid labile groups, the resist also contains a photo acid generator.

With such a resist, a differentiation between exposed and unexposed regions is achieved by the different polarity of the polymer. In the unexposed areas, the film-forming polymer remains in its original non-polar state and is therefore not soluble in an alkaline aqueous developer. In the exposed areas, the acid labile groups have been split, releasing polar groups. This means that the polymer is now readily soluble in alkaline aqueous developer solutions and therefore the resist is only removed from the developer solution in the exposed areas during development.

In this embodiment of the method according to the invention, a layer of the resist is first produced on the first layer of the absorber material and described with a focused electron beam, so that an image is generated in the second layer which comprises exposed and unexposed areas. A strong acid is released from the photo acid generator by exposure to the electron beam. So first you get a latent image of the desired structure. The exposed resist is then heated, generally to temperatures in the range from 80 to 150 ° C. The acid-labile groups are split under the influence of the acid and the resist film contrasted, ie the desired structure is chemically embossed into the resist film.

The cleavage of the acid-labile residue with the release of a polar group is shown below by way of example on two preferred repeating units. In the first example, the repetition unit comprises a tert. -Butyl ester group, from which a carboxyl group is released under the action of acid.

CH.

In the second example, the acid labile group comprises a tert. -Butoxycarbonyloxy residue, which is bound to a phenolic hydroxyl group. Under the action of acid, an acidic hydroxyl group is released as a polar group.

Due to the chemical amplification, the resist is highly sensitive to exposure to the electron beam, which is why the exposure times can be shortened. This can reduce tool life effects, for example caused by diffusion of the released acid or by neutralization of the released acid by basic compounds introduced from the environment can be effectively suppressed.

The exposed and contrasted resist film is then developed using an aqueous alkaline developer, for example a 2.38% aqueous tetramethylammonium solution. Such developers can be obtained from commercial suppliers. In the exposed areas, the photoresist is detached by the developer and the absorber material arranged under the photoresist is exposed. Then, as described above, the structure is again transferred to the first layer of the absorber material. For this purpose, the absorber material is etched away in the exposed sections, preferably using a plasma, for example an oxygen / chlorine plasma.

In this embodiment, the film-forming polymer can only be composed of first repeating units which comprise a silicon-containing group, and fourth repeating units which have an acid-labile group. Such a film-forming polymer is suitable for the production of photomasks if the first repetition unit already contains a sufficiently high content of silicon atoms in the film-forming polymer. Due to the catalytic effect of the acid released, only small exposure doses are required for the exposure of the resist, which means that short exposure times and thus fast throughput times in mask production are possible.

The first and fourth repeat units can be supplemented by second repeat units which are derived from inert comonomers, in particular acrylates and methacrylates.

If the resist is to be accessible to an amplification reaction, the film-forming polymer can additionally have third repeating units that have an anchor group.

Examples of suitable monomers by means of which an acid-labile group can be introduced into the polymer are acrylates, methacrylates, maleic acid monoesters and diesters, itaconic acid monoesters and diesters, norbornene carboxylic acid esters or also norbornene dicarboxylic acid monoesters and diesters. Corresponding repeating units of the polymer are shown below. Y stands for an acid-cleavable radical, after the cleavage of which a polar group, for example a carboxyl or a hydroxyl group, is released. Examples of suitable acid-labile groups are: tert-alkyl ester, tert-butoxycarbonyloxy, tetrahydrofuranyl, tetrahydropyranyl, tert. Butyl ether, lactone or acetal groups. tert. Butyl esters are particularly preferred. R ⁷ "represents a non-acid-labile radical, for example an alkyl group having 1 to 10 carbon atoms. Furthermore, e denotes an integer between 1 and 10.

The photo acid generator additionally contained in the resist must have a sufficiently high sensitivity to the electron beam in order to be able to release the amount of acid required for rapid cleavage of the acid-labile groups. All compounds which release acid when irradiated can be used as photo acid generator. Onium compounds such as are described, for example, in EP 0 955 562 A1 are advantageously used. The photo acid generator is contained in the resist in an amount of 0.01 to 10% by weight, preferably 0.1 to 1% by weight.

Another possibility of providing a high proportion of silicon atoms in the resist is to provide a siloxane as the film-forming polymer. The siloxanes are advantageously substituted with pendant carbon chains, it being possible for the carbon chains to also comprise functional groups, for example acid-labile groups which are cleaved under the action of acid and release polar groups which bring about an increase in the solubility of the polymer in polar alkaline developers. The groups already mentioned above can be used, for example, as acid-labile groups.

Such siloxanes can be prepared in a number of ways, for example by grafting reactive monomers onto silicon-containing main chain polymers. Only a single compound can be used as a monomer, or several different monomers can be copolymerized. The

The side polymer partial chain formed from carbon atoms can be built up, for example, by radical polymer merization in the presence of silicon-containing polymers with pendant aliphatic groups. The linking of the polymer partial chains made of plastic atoms takes place via a chain transfer reaction. With this method, however, a broad distribution of the molecular weight of the reaction products has to be accepted. A targeted connection of the polymer side chain to the silicon-containing main chain is also difficult to control.

Substantially more defined products are obtained by a catalytic reaction of hydrosiloxane compounds or hydrosilsesquioxane compounds with dienes in the presence of platinum / platinum complexes and subsequent radical or anionic copolymerization of suitable unsaturated monomers. The polymers of the photoresist according to the invention can also be copolymerized with suitable unsaturated monomers by copolymerizing polymers which have alternating silicon and oxygen atoms in their main chain and in which an unsaturated group, such as a vinylphenylene group, is laterally bonded to the main chain are, whereby the side chain formed from carbon atoms is generated.

In a further embodiment, the polymers are prepared by direct catalytic reaction of hydrosiloxane or hydrosilsesquioxane compounds with reactive unsaturated oligomers or polymers.

A preferred class of siloxanes which are suitable as film-forming polymer in the resist according to the invention is formed by compounds of the formula I.

FORMULA I

Polymer chains whose main chain is formed from carbon atoms are bound laterally to the chain of the siloxane, which is composed of alternating silicon and oxygen atoms. The chain formed from carbon atoms has groups R ^s which represent a hydrogen atom, an alkyl chain with 1 to 10 carbon atoms or preferably an acid-labile group. If the group R ^{s is designed} as an acid-labile group, its cleavage can differentiate the solution properties between exposed and unexposed areas of the photoresist.

Specifically:

R ⁸ , R ⁹ , R ¹⁰ : each independently of one another an alkyl radical with 1 to 10 carbon atoms, a cycloalkyl radical with 5 to 20 carbon atoms, an aryl radical with 6 to 20 carbon atoms, an aralkyl radical with 10 to 20 carbon atoms, or one with an acid-labile group protected polar residue;

R ^x : a hydrogen atom, an initiator group or a polymer chain with an initiator group, the initiator group having arisen from the initiator of the polymerization; R ¹¹ : hydrogen, halogen, pseudohalogen or an alkyl group with 1 to 10 carbon atoms;

R ¹² : hydrogen or a polymer chain, the chain being formed from carbon atoms;

R ^s : hydrogen, an alkyl group with 1 to 10 carbon atoms or an acid-labile group;

m, o: 0 or an integer greater than or equal to 1, the sum of m and o being greater than 10;

n: an integer greater than or equal to 1;

q: 0 or an integer greater than or equal to 1;

p: an integer greater than or equal to 1;

where the repeating units identified by the indices m, n and o can be arranged in any order, n is preferably less than 20, q is preferably 0 or 1.

M and o are preferably chosen between 25 and 500, in particular between 50 and 500, p is preferably chosen between 1 and 500, particularly preferably between 5 and 50. The value of the indices is determined from the respective maximum of the molecular weight distribution of the polymer contained in the resist according to the invention.

The radicals R ⁸ , R ⁹ , R ¹⁰ bound to the siloxane chain are preferably a methyl group, a cyclohexyl group or a phenyl group, the radicals R ⁸ , R ⁹ and R ¹⁰ also being able to have different meanings each time the siloxane chain occurs. Polar can also be attached to the siloxane chain

Groups can be provided which are protected by acid-labile groups. An example of this is a tert-butoxycarbonylphenoxy group. On the main siloxane chain laterally bound polymeric partial chains, the chain of which is formed by carbon atoms. This side chain can carry small non-polar substituents R ¹¹ , such as methyl groups, trichloromethyl groups or nitrile groups. Furthermore, the polymeric side chain comprises groups R ^s , which can be designed as acid-labile groups.

The side chain also comprises a radical R ¹² which continues the side chain formed from carbon atoms. Different monomers can be used here. Examples are methyl acrylates, methyl methacrylates or styrene derivatives. These monomers can be incorporated into the side chain either in the form of block copolymerization or by copolymerization with the monomers containing the group R ^s .

The side chain is linked to the siloxane main chain by the reaction described above, for example by grafting or by copolymerization of the siloxane substituted with a polymerizable radical with the monomers which form the pendant carbon chain.

Depending on the reaction conditions, the group R ^{x can be} a hydrogen atom or an initiator group by which, for example, a radical polymerization was initiated, or a polymer chain with an initiator group. Examples of free radical initiators and initiator groups resulting from these are given in Table 1.

Table 1

Examples of radical initiators and initiator groups R ¹ resulting therefrom

In addition to the initiators shown for radical polymerization, other diacyl peroxides or azo compounds can also be used.

BF ₃ , TiCl, SnCl, A1C1 ₃ and other Lewis acids are suitable as cationic initiators. In this case, R ¹ is usually a hydrogen atom.

Examples of anionic initiators are shown in Table 2. Table 2

Examples of anionic initiators and initiator groups R ¹ resulting therefrom

Initiator class Initiator group R ¹ remaining on the polymer

Alcoholates CH, CH, I ³

K ⁺ 0-C-CH, * -0-C-CH.

I

CH, CH ₃

Metallamides Na ⁺ NH ₂ ^" -NH ₂ metal alkyls Li ^+" CH ₂ CH ₂ CH ₃ -CHCH ₂ CH ₃

The proportion of silicon atoms in the resist can be increased even further if the siloxane is designed as silsesquioxane. An example of suitable silsesquioxanes are compounds of the formula II.

FORMULA II The radicals R ⁸ , R ⁹ , R ¹⁰ , R ¹¹ , R ¹² , R ¹ and R ^s and the indices m, n, o, p and q have the meaning given for formula I. The polymers derived from a silsesquioxane can be prepared by the same methods as described above.

In the siloxanes or silsesquioxanes, the pendant polymeric carbon chains can also have anchor groups which are available for reinforcing the resist. Here, as described above, carboxylic anhydride groups can be introduced, for example. These are introduced into the side chain in the production of the polymeric side chain by copolymerization of monomers such as maleic anhydride, itaconic anhydride, norbornene dicarboxylic acid anhydride, cyclohexanedicarboxylic acid anhydride or with acrylic acid anhydride.

The invention is explained in more detail with reference to an attached figure. The same objects are denoted by the same reference numerals. The figures show in detail:

1 shows a sequence of the steps in the production of a COG mask according to the prior art;

2 shows a sequence of the working steps in the method according to the invention;

3 shows a sequence of the working steps in the method according to the invention, the resist structures being chemically amplified.

1 shows the working steps which are carried out when producing a COG mask using methods known from the prior art. A layer 2 of chromium is first applied to a transparent quartz substrate 1 by sputtering. A layer of polymethyl methacrylate is applied to the chromium layer 2 and then exposed to a focused electron beam. When developing With an organic solvent, only the areas of the PMMA layer that had previously been exposed to the electron beam are selectively removed. An arrangement shown in Fig. La is therefore obtained after development. A thin chrome layer 2 is arranged on the transparent quartz substrate 1, on which webs 3 made of PMMA are in turn arranged. There are trenches 4 between the webs 3, which correspond to the exposed sections of the resist and in which the chromium layer 2 is exposed. If the exposed chrome layer is now etched with an oxygen / chlorine plasma, not only is the material exposed in the trenches removed, but also parts of the webs 3. As a result, as shown in FIG. 1b, the width of the trenches 4 increases or decreases the width of the webs 3. The width of the absorber structures 5 also corresponds to the width of the webs 3. Finally, the webs 3 are removed from PMMA, for example by ashing in the oxygen plasma or by detaching with a suitable solvent. The photomask shown in cross section in FIG. 1c is obtained. Absorber structures 5 made of chromium are arranged on the quartz substrate 1.

The absorber structures 5 have a smaller width than the webs 3 originally produced in the resist (FIG. 1 a). As a result of the etching, a loss of structure must be accepted in the method according to the prior art.

2 shows the method steps for producing the photomask with a silicon-containing resist. First, as explained in FIG. 1, a thin layer of an absorber material (eg chromium) is applied to a quartz substrate 1. A layer of a silicon-containing resist is then applied to the chromium layer 2 and a structure is written into the resist layer using a focused electron beam. Exposure to the electron beam modifies the film-forming polymer contained in the resist. The polymer is either fragmented into smaller fragments or, in combination with a subsequent tempering step, there is a release of polar groups on the polymer by cleavage of acid labile groups. The exposed resist is then developed. For this purpose, either an organic solvent is used in which the polymer fragments are soluble, or an aqueous alkaline developer is used in which the polar form of the polymer is soluble. A structure shown in FIG. 2a is obtained. A thin layer of chrome is arranged on a quartz substrate 1, on which webs 3 made of the resist material are in turn arranged. Between the webs 3 there are again trenches 4, in which the chromium of the chromium layer 2 is exposed. The chrome exposed in the trenches 4 is then again etched away with a plasma. The silicon atoms contained in the film-forming polymer are converted into silicon dioxide, which forms a protective layer 6, which prevents the plasma from attacking the sections 7 of the chromium layer underneath. Since the waste ^• cuts 6 are nert of silica largely against the plasma i-, no loss of structure is carried out during the removal of the exposed within the trenches 4 portions of the chromium layer 2, so that the width of the protective portions 6 substantially to the width of the webs 3 corresponds to ( Fig. 2b). Finally, sections 6 are removed. This can be done, for example, using wet chemistry using conventional, commercially available strippers. These strippers are generally highly alkaline organic reagents. The chrome mask shown in cross section in FIG. 2c is obtained. Absorber structures 5 are arranged on a quartz substrate 1, the width of which largely corresponds to the width of the resist webs 3.

Any loss of structure that may occur can be compensated for by chemically amplifying the structured resist. The steps carried out in this method variant are shown in FIG. 3. Fig. 3a corresponds to the state as it is also shown in Fig. 2a. However, the resist here comprises a polymer which has anchor groups for attaching an amplification agent. 3a shows a transparent quartz substrate 1, on which in turn a thin chrome layer 3 is arranged, on which again are arranged around webs 3 which, however, contain a polymer which comprises anchor groups. Since in this case silicon-containing groups are subsequently introduced into the polymer, a silicon-free polymer can also be used for the production of the webs 3. A solution of an amplification agent is now given to the resist structure shown in FIG. 3a. The amplification agent is bound to the anchor groups of the polymer, which causes an increase in volume of the webs 3. As a result, the webs 3, as shown in FIG. 3b, grow in width and height. The webs 3 now have a width that is increased in comparison to the state shown in FIG. If the chrome layer is now etched in the areas exposed in the trenches 4, a loss in the width of the webs 3 ^• caused by a slight attack of the plasma on the material of the webs 3 can be compensated for. The structural retention obtained by the chemical amplification is removed by the plasma, so that after the etching, as shown in FIG. 3c, the webs 3 again have a smaller width than in FIG. 3b. In contrast to the methods shown in FIG. 1 a, the increase in the width of the webs 3 achieved by the reinforcement can, however, be controlled in such a way that the absorber structures 5 are obtained in the desired width. Finally, the resist webs 3 are again removed, for example using a suitable stripper, so that the mask shown in FIG. 3d is obtained. Absorber structures 5 are shown on a quartz substrate 1, which have a width similar to that of the resist webs 3 shown in FIG. 3a.

Claims

claims

1. A method for producing photomasks for optical lithography, wherein: a transparent substrate is provided, a first layer of an absorber material is deposited on the transparent substrate, a layer of a resist for electron beam lithography is applied to the first layer, which at least includes:

a film-forming polymer comprising silicon atoms; and a solvent.

and the solvent contained in the resist is evaporated, so that a second layer is obtained which contains the film-forming polymer, the second layer is written with a focused electron beam, so that an image is produced in the second layer, the exposed and unexposed Areas, onto which a developer is added, which releases the exposed areas of the image, so that a structured resist is obtained with a structure in which the unexposed areas form bridges and the exposed areas form trenches arranged between the bridges, and the Structure of the structured resist is transferred into the first layer of the absorber material.

2. The method according to claim 1, wherein the film-forming polymer comprises, in addition to at least one further repeating unit, first repeating units which carry at least one lateral silicon-containing group.

3. The method according to claim 1 or 2, wherein the film-forming polymer comprises, as a further repeating unit, second repeating units which are derived from a comono- he selected from the group consisting of alkyl esters of (meth) acrylic acid.

4. The method according to any one of the preceding claims, wherein the film-forming polymer comprises, as further repeating units, third repeating units, which contains anchor groups, and a reinforcement agent is added to the structured resist, which comprises a group that can coordinate to the anchor groups, the reinforcement agent for one is left on the patterned resist for a certain time, so that the amplification agent is bound to the polymer, and wherein a amplification structure is obtained, if necessary, excess amplification agent is removed, and the amplification structure is transferred into the first layer of the absorber material.

5. The method according to claim 4, wherein the further comonomer is an at least monounsaturated carboxylic anhydride.

6. The method according to claim 4 or 5, wherein the amplification agent comprises silicon-containing groups.

7. The method according to any one of the preceding claims, wherein the film-forming polymer has, as a further repeating unit, fourth repeating units which comprise at least one acid-labile groups which are cleaved under the action of acid and release a group which increases the solubility of the film-forming polymer in causes aqueous alkaline developers, and further contains a photo acid generator in the resist, and after the formation of the image with an electron beam, the resist is heated so that the acid-labile groups on the polymer are cleaved in the exposed areas, and the developer is an aqueous basic developer in which the polar polymer is soluble and the nonpolar polymer is insoluble.

8. The method of claim 1, wherein the film-forming polymer is a siloxane.

9. The method according to claim 8, wherein the siloxane is a silsesquioxane.

10. The method according to claim 8 or 9, wherein groups are bonded to the siloxane which comprise an anchor group and / or an acid-labile group which is cleaved under the action of acid and releases a group which increases the solubility of the siloxane in polar alkaline developers.

11. The method according to any one of the preceding claims, wherein the structure by etching with a plasma in the first

Layer is transferred.