WO2013009219A1

WO2013009219A1 - Method for producing a mask on a substrate surface

Info

Publication number: WO2013009219A1
Application number: PCT/RU2012/000562
Authority: WO
Inventors: Игорь Георгиевич РУДОЙ; Аркадий Матвеевич СОРОКА; Мойше Самуилович КИТАЙ
Original assignee: Rudoy Igor Georgievich; Soroka Arkadij Matveevich
Priority date: 2011-07-12
Filing date: 2012-07-11
Publication date: 2013-01-17
Also published as: RU2471263C1

Abstract

The invention relates to lithography, more precisely to methods for producing a resistive mask on the surface of a substrate, in particular a semiconductor substrate. The technical result of the invention consists in increasing the productivity of lithography with super-high resolution, primarily EUV lithography. The technical result is achieved in that, in the method for producing a mask on the surface of a resist, which method comprises applying a layer of a polymer resist formed from monomer units on the basis of organic molecules to a substrate surface, exposing the resist, heat-treating the exposed resist and then developing the structure formed in the resist, at least one fluorine atom is contained in the composition of at least 50% monomer units, and the heat treatment of the exposed resist comprises heating said resist using at least one laser pulse with a radiation wavelength selected from the condition whereby the absorption coefficient of the resist with respect to laser radiation exceeds the absorption coefficient of the substrate with respect to laser radiation.

Description

METHOD FOR CREATING A MASK ON A SUBSTRATE SURFACE

The claimed technical solution relates to lithography, and more specifically to methods for creating a resistive mask on the surface of the substrate, in particular, a semiconductor substrate. It is of interest for the development of high-performance lithographic installations with high and ultra-high resolution, primarily installations that use extreme-ultraviolet radiation of a wavelength of -10 nm (EUV radiation, EUV lithography) to expose the resist.

Creating a resistive mask is an essential component of the lithographic process and generally includes the following stages:

1. Application of the polymeric resist layer on the substrate surface, typically the thickness of the resist layer / _Res-I00 is 200 nm for EUV lithography preferred thinner resist layer thickness of ~ 50 nm.

2. Local exposure of the resist (creating a structure).

3. The manifestation of the structure specified during exposure, when only exposed (or unexposed — depending on the type of resist and method of manifestation) sections of the resist remain on the substrate. _^ _.

Subsequently, in accordance with the structure of the resistive mask, processing of the underlying technological layers is carried out through the areas free from the resist, after which the used mask is removed. When creating modern integrated circuits and other electronic devices, this sequence of operations is usually repeated many times.

It is important to indicate that the above are only the main stages of the process of creating a mask on the surface of the substrate, each of these stages may include several "elementary" technological operations. For example, the application of a resist layer, as a rule, is preceded by a special treatment of the surface of the substrate in order to clean it and increase adhesion to the applied resist (as well as, obviously, the manufacture of the substrate itself and the synthesis of the resist); after development, the remaining part of the resist can be further processed to increase resistance to subsequent exposure, etc. and .p. The same technological operation can be carried out by different methods, for example, applying a polymer resist can be carried out by centrifugation or pulverization, a positive or negative resist can be applied, exposure of the resist can be carried out with ultraviolet radiation (today the radiation wavelength of the excimer ArF laser with λ ~ \ is used 93 nm, in the short term, UV-lithography at λ ~ 13.5 nm and then even at λ ~ 6.7 nm), electron beam or X-ray radiation, t the adjustment can be chemical or plasma, etc. The claimed technical solution can be used in combination with various specific implementations of the steps described above.

As a rule, polymer molecules formed from monomer units based on organic molecules are used as a resist. Exposure (UV or EUV radiation, X-ray, electron beam) affects molecular bonds and, as a result, either due to bond breaking in the so-called positive resistes, the average molecular weight of the polymer decreases, or as a result of irradiation, the “molecules” of the starting molecules (macromolecules) “crosslink” negative resist and its average molecular weight increases. Thus, in the resist, a latent image of the mask (the resist region with a changed average molecular weight) is created, which needs to be formed on the substrate.

Positive resists, as a rule, potentially provide the best ultimate resolution, a known positive resist of high resolution is polymethylmethacrylate (PMMA), in which a resolution of up to 2 + 3 nm can theoretically be achieved. The claimed technical solution relates primarily to the use of positive resistes to create a mask on the surface of the substrate (in lithography).

Upon subsequent manifestation in positive resistes in a specially selected solvent (or under the influence of plasma), a low molecular weight fraction of a positive resist created by exposure is removed with a certain selectivity, i.e., a low molecular weight fraction is removed faster. Accordingly, for the qualitative manifestation of a given mask structure, when exposed, it is necessary to ensure a significant change in the average molecular weight of the initial resist, that is, a certain concentration of broken atomic bonds. Thus, to create a mask on the surface of the resist, a certain dose is required (for a thin layer of the resist energy density) W _Q exposure. Since the deposition of a resist layer on a substrate, its heat treatment (see below) and development can be carried out by the conveyor method, when several (many) objects are processed at the same time, and these processes require significantly simpler equipment than used during exposure, the key step in lithography, determining its performance is precisely the stage of exposure. In turn, at a given exposure source power, the sensitivity of the resist (the minimum value of the required dose W _Q ) primarily determines the duration of the process. At the same time, the introduction of additional technological stages of creating a mask is also acceptable in comparison with the minimum number of steps when, for example, a structure on the surface of a substrate is created by direct removal of the resist when it is irradiated with powerful laser pulses - laser ablation ([1]: JTCYeh " Journal of vacuum science and technology ", 1986, v. A4, p. 653), in this case, the stages of exposure and" manifestation "are actually combined.

A known method of creating a mask on the surface of the substrate, including applying to the surface of the substrate a layer of polymer resist formed from monomer units based on organic molecules, exposing the resist and subsequent manifestation of the structure created on the resist during etching ([2]: K. A. Valiev “Physics submicron lithography ”, Moscow: 1990—528 s). Exposure can be carried out by UV light, an electron beam or a beam of atomic particles (ions), as well as x-ray radiation.

The known method allows, in principle, to obtain a very high resolution of the structure created on the substrate, however, the required dose and, accordingly, the exposure time are high, especially when creating structures with maximum resolution. This is due, inter alia, to the fact that high resolution can be obtained only by exposing the resist to short-wave radiation (including EUV or X-ray) or an electron beam, and in these cases the efficiency of creating the necessary gaps for selective etching is low and only a small fraction The energy of the exposure agent actually ensures the creation of a structure in the resist layer. For example, the quantum yield of direct disruption of a PMMA macromolecule upon absorption of UV radiation (λ ~ 193 nm) does not exceed ~ 1%. In the absorption of photons in the EUV range (λ ~ 13.5 nm), the quantum yield of rupture of the PMMA macromolecular chain is close to 1, but in this case, the absorption coefficient in PMMA is relatively small (the absorption length is -250 nm with a characteristic resist thickness of 50 nm, i.e. no more than 20% of the incident radiation is absorbed in the specified resist layer).

The closest technical solution (prototype) is a method of creating a mask on the surface of the substrate, including applying a layer of polymer resist formed from monomer units based on organic molecules onto the surface of the substrate, exposing the resist, heat treatment of the exposed resist and subsequent manifestation of the structure created on the resist ([3 ]: St. Zelentsov, N.V. Zelentsova. “Modern Photolithography.” Nizhny Novgorod, 2006–56 s).

In the known method, the composition of the polymer resist additionally includes molecules - photogenerators of acid (FGC) and uses the principle of chemical amplification ([4]: SA MacDonald, CG Willson, MJJ Frechet. "Chemical amplification in high resolution imaging systems. Acc. Chem. Res . 1994 "v. 27, No. 6, p. 151-158), for the implementation of which the heat treatment of the exposed resist is carried out. Various compounds, for example diaryl iodonium and triaryl sulfonium salts, are used as FGC.

The change in the molecular weight of the resist in the known method takes place in two main stages. At the first, under the influence of an exposure agent (currently most often UV light), FGK releases acid. During the second - subsequent heat treatment (heating) of the resist - a catalytic reaction takes place, as a result of which, under the influence of the formed acid, the polymer binder of the resist either crosslinkes (then the molecular weight of the resist increases and a negative image forms), or collapses (molecular weight decreases, positive image) , while the acid itself is not consumed and can repeatedly participate in the reaction. The number of reaction events per light absorbed by FGC quantum can reach -100 ([3]), therefore, the number of breaks (crosslinkings) in the polymer resist due to the catalytic reaction involving the generated acid is many times greater than the number of breaks (crosslinkings) formed directly during exposure. Heating is usually carried out in a furnace with a stable temperature or direct contact with the surface of a body (plate) heated to the required temperature with a heat capacity many times greater than the heat capacity of the heated composition, which includes a substrate with a resist and, as a rule, an additional supporting surface (since for a typical substrate thickness of H-0.30 mm, its rigidity is insufficient with a diameter of -300 mm). Next comes cooling the resist to the initial temperature, at which the catalytic process practically does not proceed, and then the manifestation of the formed structure.

The use of acid generators as a resist is fundamentally possible not only when exposed to UV radiation (photo-generation of acid), but also when the EUV is exposed to quanta, X-rays and an electron beam, however, in all cases, the second stage of structure formation is required - thermally activated chemical amplification.

The use of chemical amplification technology in the known method, when the fraction of PHA in the resist is up to 1CH-20%, significantly reduced the required exposure dose (10-I to 5 times) and, accordingly, increased the productivity of the lithography process when creating structures with a resolution of ~ 30 nm and more.

However, when creating structures with an ultrahigh resolution of 20 nm or less, when the broadening when creating a separate "line" should not exceed ~ 3 nm (on the side, only no more than 5 ^ 6 nm), the use of the chemical amplification effect in the known method does not seem possible. Fundamental limitations are due to two physical processes.

The first is due to the fact that it is almost impossible to ensure a uniform (up to a 2 ^ -3 nanometer scale) distribution of FGC in the resist. Indeed, with an average distance between FGC molecules exceeding 1 nm, statistical effects (“shot noise”) no longer allow one to realize a reasonably equal number of FGC molecules in a volume with a linear size of ~ 3 nm, when the average number of such molecules in a volume is only 1CH -fifteen. At the same time, since the average number of FGC molecules in the volume increases in proportion to the third degree of the corresponding linear size, with an increase in the allowable “spreading” of the formed structure only doubles (up to ~ 6 nm per side, which may be acceptable for structures with a resolution of ~ 30 nm) the number of FGC molecules increases by 8 times and the role of statistical effects decreases sharply.

The second problem of applying the chemical enhancement effect when creating ultra-high resolution structures is caused by diffusion of the acid generated during exposure during the heat treatment, when, for example, the ultra-high resolution structures formed by the electron beam after heat treatment can be expanded multiple times. Thus, the known method does not allow the creation of ultra-high resolution structures with high performance provided by the effect of chemical amplification. At the same time, the use of resistors without FGC (for example, PMMA) allows for ultra-high resolution, but the productivity of the lithographic process is significantly reduced.

The technical result of the claimed invention is to increase the productivity of ultra-high resolution lithography, especially EUV lithography.

The technical result is achieved by the fact that in the method of creating a mask on the surface of the resist, including applying a layer of polymer resist formed from monomer units based on organic molecules to the surface of the substrate, exposing the resist, heat treatment of the exposed resist and subsequent manifestation of the structure created in the resist, not less than 50% of the monomer units include at least one fluorine atom, and heat treatment of the exposed resist involves heating it with at least one laser pulse, the radiation wavelength of which is selected from the condition that the absorption coefficient of the laser radiation by the resist exceeds the absorption coefficient of the laser radiation by the substrate. The monomer units constituting the polymer resist are acrylate or methacrylate. At least 50% of the monomer units comprise at least two fluorine atoms. The duration of a laser pulse heating an exposed resist during its heat treatment does not exceed the time it takes to establish thermal equilibrium in the resist layer. The heat treatment of the exposed resist further includes at least one non-laser heating of the resist.

The claimed technical solution is based on the fact that when exposing a fluorine-containing polymer resist, consisting of monomer units based on organic molecules, by short-wavelength photons with an energy of -90 eV or more (correspond to radiation with a wavelength of -13.5 nm or less), as well as electronic or by X-ray beams, the generation of a break in the skeletal chain of the polymer also leads to the formation of HF acid molecules. These molecules, upon subsequent heating of the resist, are effective catalysts for the generation of new discontinuities, realizing the effect of chemical amplification, which reduces the required exposure dose. Thus, in the claimed technical solution, the fluorine-containing monomer unit of the polymer resist becomes an extremely strong acid photogenerator during exposure, and in a situation where at least half of the monomers contain fluorine atoms, such FGCs are distributed fairly uniformly (in the case where each monomer unit is corresponding to the claimed invention contains at least one fluorine atom - extremely homogeneous). Since the characteristic size of the monomer unit of polymer molecules, which are usually used as a resist, does not exceed 0.5-10.6 nm (for PMMA, the size of the monomer unit is 0.52 nm), the amount of PHA in the volume corresponding to a linear size of 3 nm, is, according to the invention, at least 60 (-120 if each monomer is fluorinated), which makes it possible not to take into account the statistical impairing effects for linear resolution up to 10-42 nm and even less if each monomer unit is fluorinated.

The minimum fraction of monomers containing fluorine atoms introduced into the resist (the content of the “impurity” atom is not less than 50% of the monomers) is determined by the condition for ensuring a fairly uniform distribution of FGC over the resist volume for a linear size of ~ 3 nm.

The introduction of fluorine atoms into the monomer unit is most efficiently carried out by the addition of an additional group (s) —CF2 — th, respectively, two fluorine atoms are introduced into the fluorinated monomer unit. Such a group can be introduced both in the skeletal chain of the polymer molecule and in the side chains of the monomer units. In addition, a hydrogen-containing group — CH2— can be replaced by a group — CF ₂ — in which case, in fact, two hydrogen atoms' * are replaced by fluorine atoms. For example, monomers can be variants of fluorinated monomer units of the PMMA polymer (structural formula - [Cs02Hg])

(actually two hydrogen atoms are replaced by fluorine atoms) or [y02H ₆ F ₆ ] (two more groups are introduced additionally - CFj—), etc. In the polymerization of fluorinated monomers, a resist can be synthesized in which almost every monomer contains fluorine atoms, this option is preferred.

The hydrogen bond energy FH: F is about 1.6 eV; this high value leads to a relatively low diffusion rate of the HF molecule at room temperature. However, it is for this reason, with the necessary flow of the catalytic reaction of the cleavage of skeletal bonds by heating a polymer resist, the diffusion rate of the HF molecule increases rapidly, which does not allow the chemical enhancement effect to be realized in ultrahigh-resolution lithography according to known methods of heat treatment of resistors with FGC.

In fact, with an increase in the resist temperature from 20 ° C to 120 ° C, the diffusion coefficient of the HF molecule increases by a factor of ~ 10 ⁷ times and will be at least D _j2 o ~ 10 " ¹⁰ cm ² / s, even if the diffusion coefficient is extremely low for room temperature S ^{- 17} cm ² / sec (usually derived from FHA acids diffusion coefficient at room temperature for one to two orders of magnitude greater) are indicated value D ₁₂ o limit for lithography super resolution diffusion length of about 3 nm is achieved in less than 1 ms. (~ 0.5 ms).

A short residence time at high temperature of the resist located on the substrate (and together with the substrate on the supporting surface) can be realized in the case when the resist is rapidly heated and rapidly cooled; the latter is possible when the substrate on which the resist is applied acts as a “refrigerator”. In the claimed technical solution, these conditions are provided by pulsed laser heating of the resist, and the wavelength of the laser radiation is selected so that direct heating of the substrate during the laser pulse is slower than heating of the resist, that is, so that the substrate heats up less than resist, and then it cooled. For this, the wavelength of the "heating" laser radiation is selected from the condition that the absorption coefficient of the laser radiation with a resist exceeds the absorption coefficient of the laser radiation by the substrate, preferably significantly exceeds.

For a sufficiently short duration of a heating laser pulse with an energy flux W [J / cm2], when the effects of heat transfer can be ignored, an increase in the temperature ΔΎ of the irradiated material is determined by the following expression:

AT = W / pc (1), where k is the absorption coefficient of radiation, p is the density of the heated material, and c is its specific heat. Here it is taken into account that the resist layer on the substrate is so thin that the absorption of the radiation of the heating laser pulse by the resist is relatively small and the change in the power of laser radiation along the depth of the resist (and the substrate layer adjacent to the resist) can be ignored.

For the materials used in lithography, the product (pc) is almost the same, for example, for one of the basic PMMA resistes> с ~ 1.75 J / (cm ³ trad), and for the main substrate material, silicon> c ^ 1.65 J / (cm ³ trade). Thus, if, according to the claimed technical solution, the absorption coefficient of the heating laser pulse by the substrate to the _base will be less (preferably significantly less) than the absorption coefficient of the radiation by the resist to _cut , then after such an effect the substrate will be colder (much colder) than the resist and provide it (resist) effective cooling.

To realize the ratio according to the claimed invention between the absorption coefficients of the resist and the substrate is possible, for example, in the passband of the substrate material, for the most common silicon substrates this is primarily the range of 1.3- ^ 15 μm. In the same spectral range there are regions of strong absorption of the resist in which it is possible to realize the ratio of optimal to the _cut "to _vile for the proposed method. For example, if a fluorine-containing modification of PMMA on a silicon substrate is used as a resist, then for a wavelength of heating radiation of 10.6 μm (C0 ₂ laser) to a _{cut of} ~ 1.2 ”10 ³ cm-1, and to a _base <2 cm ^{- 1}

(to _rez / k _mean > 600), and for λ ~ 3 μm (erbium laser) to _re ~ 4 ^» 10 ³ cm ^{- 1} , and to _mean <0.1 cm ^{- 1} , (to _re Atoll> 4-10 ⁴ ).

The use of radiation in the region of 3 μm is preferable due to the existence of fairly widespread erbium lasers, which make it possible to realize the required irradiation regimes, the possibility of transmitting radiation through the fiber, and also due to both the large absorption coefficient of the radiation by the resist and the large ratio of the absorption coefficients of the resist and substrate. This allows the use of sufficiently low-power lasers, as well as to minimize the change in substrate temperature for sufficiently short laser pulses.

When using near and mid-IR lasers in the claimed invention, it is also essential that heating is not accompanied by photochemical reactions in the resist. As a result, the proposed heat treatment of a fluorine-containing polymer resist will lead to chemical strengthening formed when exposing the structure of ultra-high resolution with minimal broadening even with a uniform "heating" exposure of the entire surface of the resist, as a whole.

The substrate in the claimed invention serves as an effective “refrigerator” for a resist heated by a laser pulse. In particular, an effective cooling is a silicon substrate having a high thermal conductivity -1.6 W / cm-degrees, and thermal / _vile -0.95 cm ² / s at room temperature, which is comparable with aluminum parameters in hundreds of times greater than the thermal typical resists. With a high thermal conductivity of the substrate and its significant (compared to resist) thickness, the substrate can be considered cold all the time, then the cooling time of the resist of gohl is determined for a short heating pulse by the time of establishing thermal equilibrium in the resist layer and is:

^ cool ~ 'rez ^ re (2)>

where _res ~ (1-I, 2) · ^10-3 cm ² / s is the characteristic thermal diffusivity of the resist, / _res is the thickness of the resist layer. For expedient in EUV lithography resist layer thickness / N00 _Res 50 nm resist characteristic residence time in the heated state (cooling time) is ~ 30-N00 not. Thus, even for an instant heating of the resist (when the laser pulse duration << g _OHL) during cooling of the order of 100 ns, i.e. the residence time of the resist hot enough for catalytic reactions of chemical amplification. Under the same conditions formally calculated according to the expression

the size of the diffusion spreading of the acid δ does not exceed -0.05 nm (an order of magnitude smaller than the size of the monomer unit of the polymer resist molecule), i.e., the deterioration in resolution caused by diffusion can be completely neglected even with an extremely large diffusion coefficient of the acid in the heated resist of -5 PO ^-9 cm ² /from.

An important advantage of the proposed method is the fact that the temperature of the heating of the resist is practically independent of its thickness while the resist is optically “thin” (with a high absorption coefficient of heating radiation of 4 · 10 ³ cm ^{* 1} and a resist layer of 50 nm, the optical thickness of the resist is 0.02), the duration of the laser pulse (if it is significantly shorter than g _cool ) and, according to formula (1), is determined only by the energy flux of the heating laser pulse. For In order to ensure stability of the heating temperature of the resist of 1 ° C, it is sufficient to realize the stability of the energy flux of a short laser pulse of ~ 1%, which is provided by modern laser sources.

Since the thickness of the substrate (~ 300 μm) is several thousand times greater than the thickness of the resist (-0.1 μm), then after the end of the heating laser pulse and the temperature of the resist and the substrate are equalized (this occurs during the establishment of the temperature in the substrate ~ 1 ms), the change system temperature does not exceed 0.05. ° C even when the resist is heated by a laser pulse at 150 ° C and without taking into account the heat capacity of the base plate, on which the substrate is usually located. This, in particular, means that pulsed laser heating can be repeated several times, including at a sufficiently high frequency, not less than ~ 3 kHz. Since acid diffusion occurs independently at each heating, for N heating laser pulses, according to the claimed technical solution, the size of diffusion spreading increases by a factor of N and even for 10 consecutive heating pulses does not exceed 0.2 nm for real values of the acid diffusion coefficient.

In the absence of diffusion with appropriate heating of the resist in one or more laser pulses, the claimed technical solution ensures the necessary catalytic chemical reactions with all macromolecules with which the acid is in the same diffusion cell (Kuhn cell), as a rule, such macromolecules 5-7, i.e. without diffusion spreading in ultrahigh-resolution lithography, a chemical gain of ~ 6 can be provided.

In a preferred embodiment of the inventive method, the monomer units constituting the polymer resist are acrylate or methacrylate. The corresponding fluorine-containing monomer units are well synthesized, and during polymerization from the liquid phase it is possible to obtain a homogeneous polymer. In addition, the HF acid generated by exposure is an effective catalyst for breaking macromolecules for these polymers containing oxygen atoms near the skeletal chain of the polymer.

In another preferred embodiment of the claimed technical solution, at least two fluorine atoms are included in the composition of at least 50% of the monomer units. In this case — with an increase in the concentration of fluorine atoms in the resist — the effective the concentration of acid photogenerators and as a result, the influence of statistical effects on resolution is further reduced. As mentioned above, the introduction of two (and even an even number) fluorine atoms into the monomer unit in the form of a group — CF ₂ — provides an efficient synthesis of a homogeneous high molecular weight (polymer) resist. In addition, the introduction of additional fluorine atoms into the polymer resist increases its absorption coefficient of EUV radiation at a wavelength of 13.5 nm. For example, the introduction of two fluorine atoms instead of hydrogen atoms in PMMA, that is, the use of the polymer [Cs0 ₂ H ₆ F2 \ _n instead of [C ₅ 0 ₂ H ₈ ] _p , leads to an increase in the indicated absorption by 38–40% (for fluorine-containing the methyl methacryate derivative [ _j2 0 ₂ H ₆ F _j6 ] _n the absorption coefficient at λ ~ 13.5 nm increases by 80%), which makes it possible to proportionally reduce the exposure dose without compromising the resolution of the formed structure.

In a preferred embodiment the claimed method is the laser pulse duration of heating the exposed resist does not exceed the time required to establish thermal equilibrium in the resist layer, that is the laser pulse duration does not exceed r _OHL and the total residence time of the resist in a heated state (at high temperature) does not exceed 2r _OHL. In this case, the implementation of the proposed method, diffusion of the acid is minimal. Further, in the indicated preferred embodiment, it is possible to use a laser source of minimum average power and pulse energy. With an increase in the duration of the heating pulse, a significant part of the thermal energy released in the resist (and more and more as the pulse duration increases) is used to heat the substrate due to heat transfer and, accordingly, more and more light energy is required to achieve the desired resist temperature, especially since the thermal diffusivity of the substrate is hundreds of times higher than the thermal diffusivity of the resist (for silicon and PMMA, the ratio is ~ 700 times, for germanium and PMMA about 300 times). In addition, the temperature difference between the resist and the substrate is reduced and, consequently, the efficiency of post-pulse cooling of the resist.

For example, if the duration of the laser pulse exceeds the time it takes to establish thermal equilibrium in the substrate (for a thickness of a silicon substrate of 300 μm, it is ~ 1 ms), then thermal equilibrium is established between the equally heated substrate and the resist and, as described above, the lifetime of the resist in the heated state increases, at least 1 LLC times (and even more, since it is "very fast" to move a substrate with a resist to the cooler), and the laser pulse energy required to heat the resist increases several thousand times in accordance with the ratio of the thickness of the substrate and the resist layer ) The use of multi-kilowatt average power lasers in ultrahigh-resolution lithography seems unrealistic. Even for shorter heating laser pulses, which, however, exceed the time it takes to establish thermal equilibrium in the resist layer, the required energy density rapidly increases due to the high thermal diffusivity of the substrate (as compared with the resist). Thus, if the speed of the catalytic chemical reaction is insufficient, it is preferable to increase the energy of a short laser pulse (to increase the resist temperature and the speed of the chemical reaction) or the number of heating pulses, but not the duration of the resist in the heated state at a lower temperature.

It should also be pointed out that in order to obtain ultra-high resolution structures, exposure and subsequent lithographic processes (with the exception of heat treatment) even at room temperature may be unacceptable. In fact, at a real value of the diffusion coefficient of the generated acid molecule at room temperature 2 · 10 ^-16 cm ² / s, diffusion by a size of 2 nm occurs in a time of ~ 1 minute, which is comparable with the exposure – etching cycle. In this case, the simplest solution is to use special continuous cooling of the substrate with a resist — for example, when the resist temperature is reduced from 20 ° C to 5

° С the diffusion coefficient of the HF molecule decreases by -30 times. The specific implementation of such cooling can be accomplished in various ways that are well known in the art.

In another embodiment of the claimed technical solution, a combined heat treatment is used when acid diffusion into adjacent Kuhn cells (at K 1.5 nm and even up to 2 ^ 3 nm) seems permissible in order to increase the yield of chemical amplification while maintaining a sufficiently high level permissions. In this case, after processing the exposed resist by a heating laser pulse (s), which provide the limiting effect of chemical amplification within one Kuhn cell, the diffusion of acid into neighboring cells is realized, for example, due to the fact that heat treatment of the exposed resist additionally include at least one non-laser heating of the resist. Such heating can be carried out, in particular, according to one of the options by which heat treatment of an exposed polymer resist containing an acid generator is carried out in known methods. In this case, the temperature and duration of non-laser heating are determined by the condition for the controlled size of acid diffusion, that is, heating to a temperature lower than in the known methods for a well-controlled time is preferable (a time scale of ~ 30-N seconds is preferable). Thus, the temperature of non-laser heating is selected from the condition that for a given time, for example 60 seconds, the diffusion of acid will be a predetermined allowable value, for example 1-4.5 nm, while catalytic chemical reactions practically do not occur due to the relatively low temperature of non-laser heating.

After conducting non-laser heating, in a preferred embodiment of the proposed method, a new irradiation cycle of the resist is carried out by heating with short laser pulses in order to provide chemical amplification in those cells into which acid migrated during non-laser heating. As a result, the chemical enhancement coefficient will increase, approximately, by a factor of two (the situation does not give a gain when acid molecules “exchange” Kuhn cells during diffusion, however, the probability of a significant proportion of such situations is small). The cycle “non-laser heating — laser heating pulse (s)” can be repeated several times with a corresponding increase in the chemical gain.

The implementation of the proposed technical solution can be performed, for example, as follows. After applying a fluorine-containing polymer resist based on fluorinated methyl methacrylate {C ₅ 02H ₆ F _{2 n} 60 nm thick onto a silicon substrate (such a layer thickness can be formed and, in principle, it is possible to realize a resolution of up to 15 nm or even less), exposing the resist with EUV radiation with wavelength = 13.5 nm, during heat treatment, the resist is irradiated with pulsed-periodic radiation of an erbium laser with parameters: pulse energy 1.5 mJ, pulse duration ~ 5 nsec, pulse repetition rate / = 2 kHz (average m laser generality of about 3 W). A separate pulse is irradiated with a resist area of 2 · 2 mm ² , which provides a dose in the pulse of 35-4-0 mJ / cm ² . This energy is enough to heat the resist at 100430 ° С (taking into account the reflection of laser radiation back into the resist from the silicon surface of the substrate, the substrate itself will be heated by ~ 0.002 ° C during the laser pulse). In this case, the laser pulse power of ~ 300 kW allows the radiation to be transmitted through the fiber, and the radiation intensity at the resist is ~ 7 MW / cm2; at this radiation intensity in the near IR range, the resist or substrate is not broken (moreover, the resist is heated by the laser pulse to temperature, which is significantly lower than its evaporation temperature), as well as a breakdown of the gaseous medium above the surface of the resist.

Scanning radiation over a resist surface with linear velocity

~ 4 m / s (d = 2 mm) can be produced, for example, by a scanner of the RAYLASE AG company ([5]: company website http://www.raylase.com/en/). The serial scanners of this company provide an angular scanning range of about ± 0.4 radians with positioning accuracy and angular resolution of -15 mrad. This means that when the scanner is located on the axis of the substrate, a focal length of 350 mm is sufficient to ensure that the heating beam moves over the entire surface of the substrate with a diameter of 300 mm with a positioning accuracy of ~ 5 μm (400 times smaller than the size of the radiation irradiated per pulse). For the specified focal length, the speed of the beam moving along the substrate surface provided by the scanner exceeds 5+ m / s and, thus, known scanners confidently provide the required mode of movement of the heating laser beam along the resist surface, while moving the beam on the resist during the pulse time (~ 0, 05 μm) can be completely neglected.

The cooling time of a resist layer with a thickness of 60 nm is ~ 40 ns and is close to the total residence time of the resist in a hot state, since the heating laser pulse is much shorter than the cooling time. The size of the diffusion movement of the acid for the indicated period of time does not exceed ~ 0.05 + 0.1 nm, which allows us to preserve the maximum possible resolution in the case of repeated irradiation of the resist by heating pulses and allows some overheating of the external (remote from the substrate) surface of the resist. This circumstance is significant, since during irradiation some overlapping of the boundaries of the irradiated areas is inevitable, that is, a part (small) of the surface of the resist is irradiated twice (several times) with a single laser heat treatment of the resist as a whole. Accordingly, in these areas the “theoretical” diffusion movement of the acid is higher than in the once treated area of the resist. We point out, however, that the boundary zones of the resist region irradiated for a single impulse with a linear size of the order of the thickness of the substrate they are cooled faster by the substrate than the main area heated by the laser pulse, due to the fact that the heat from the resist goes not only “deep” into the substrate, but also into the external (“side”) regions of the substrate region for the irradiated. With the above accuracy of positioning the scanner, the width of the twice-heated boundary of the area processed per pulse can be less than 100 μm, even taking into account all diffraction effects. As a result, the required level of the cooling rate of the boundary of the region processed by the previous laser pulse is provided, onto which the boundary of the next resist section heated by the laser pulse is “superimposed” at a frequency of heating pulses of several kilohertz.

The time for a single treatment of the entire surface of the resist is about 9 seconds, which allows us to realize sufficient performance of the inventive method of creating a mask on the surface of the substrate, including the heat treatment mode (up to 400 plates per hour with a single exposure, 80 plates per hour with a five-fold repetition of the irradiation cycle), which if necessary, it can easily be multiplied, for example, by using a more powerful laser or by treating the surface of a resist simultaneously with several lasers.

Heat treatment of a resist by heating laser pulses can be repeated several times; during processing, the substrate with the resist can be placed on a preheated plate of high heat capacity (i.e., on a thermostabilized surface), which ensures a constant and predetermined temperature of the substrate. The temperature of such a plate is selected primarily from the condition of ensuring a controlled size of acid diffusion during the contact of the substrate with the exposed resist and the thermally stabilized plate. In addition, the placement of a substrate with a resist on a heated thermally stabilized plate can be used to use a heating laser of lower power or to accelerate the time of laser heat treatment.

The subsequent manifestation of the formed structure in the resist is carried out by known methods, plasma etching is preferable to obtain ultra-high resolution.

To meet any possible specific requirements, other changes obvious to qualified specialists in this field can be made that are described above for the implementation of the method of creating a mask on the surface of the substrate without deviating from the provisions protected by the claims.

As a result, with an almost complete absence of acid diffusion and a corresponding deterioration in the resolution of the formed structure (or with a controlled and controlled size of acid diffusion) in the claimed method, a significant increase in the performance of high and ultra-high resolution lithography is realized. For example, when instead of using PMMA, a fluorine-containing polymer resist based on a monomer [ ₅ 0 ₂ P ₂ ] _{n is used, the} required exposure dose at λ ~ 13.5 nm can be reduced by 6-8 times and, accordingly, lithography productivity can be increased at a constant power of the source of EUV photons, since even in the course of catalytic chemical reactions within only one Kuhn cell (without thermally activated and controlled diffusion of photogenerated acid HF), the number of bond breaks increases by 4–6 times, and the absorption coefficient - by 1.4 times. As a result, the required exposure dose, which ensures resolution in EUV lithography up to 10 nm, is determined not so much by the sensitivity of the resist, but by effects associated with the statistics of the resisting high-energy photons.

Thus, the claimed technical solution allows to increase the performance of ultra-high-resolution lithography and implement chemical amplification technology in a situation where more than half of the polymer resist monomers (and even almost every monomer) are a strong acid generator. This ensures the maximum uniformity of the distribution of molecules - acid photogenerators and their maximum possible concentration. Ultrafast and controlled cooling of the resist during heat treatment allows one to completely suppress the diffusion of the acid generated during exposure or, if necessary, precisely control the diffusion size, providing a multiple increase in the number of breaks in the polymer chain without compromising the resolution of the formed structure. This allows us to conclude that the claimed technical solution meets the criteria of the invention of "novelty" and "significant differences".

Claims

CLAIM

1. The method of creating a mask on the surface of the substrate, including applying to the surface of the substrate a layer of polymer resist formed from monomer units based on organic molecules, exposure of the resist, heat treatment of the exposed resist and subsequent manifestation of the structure created in the resist, characterized in that the composition is not less 50% of the monomer units include at least one fluorine atom, and heat treatment of the exposed resist involves heating it with at least one laser pulse, wavelength radiation is selected from the condition that the absorption coefficient of laser emission absorption coefficient of the resist is superior to laser radiation substrate.

2. The method according to p. 1, characterized in that the monomer units constituting the polymer resist are acrylate or methacrylate.

3. The method according to p. 1 or 2, characterized in that the composition of at least 50% of the monomer units include at least two fluorine atoms.

4. The method according to p. 1, characterized in that the duration of the laser pulse heating the exposed resist during its heat treatment does not exceed the time to establish thermal equilibrium in the resist layer.

5. The method according to p. 1 or 4, characterized in that the heat treatment of the exposed resist further includes at least one non-laser heating of the resist.