Documents cited in the present application are all incorporated in the present disclosure in their entirety by reference.
The present invention relates to a method of conducting photochemical reactions, for example optical lithographies, below the diffraction limit and to the use for that purpose of compositions comprising certain photoenols.
Photochemical reactions are very important in industry and find numerous applications. A large number of chemical reactions in photochemistry are induced by irradiation with light having a certain wavelength. These types of reaction include for example the photo-polymerization reaction started by photoinduced formation of free radicals or acids (“photo-polymerization”), the photoinduced removal of protective groups from certain molecules (“photo-uncaging”), the photoinduced release of certain molecules (“photorelease”) and also the photoinduced decoration of surfaces or porous bulk materials with functional molecules (“photofunctionalization”), for example by photoinduced Diels-Alder reactions.
The use of light as stimulus is simple, efficient and very selective. Focusing light into a small region or creating a spatially varying pattern of light, moreover, is capable of selectively inducing the reaction in certain spatial regions. However, there is a disadvantage with the use of light in that light cannot be focused into arbitrarily small areas and/or that extended patterns of light cannot have arbitrarily small spatial structures/periods. The so-called diffraction limit makes it impossible to produce light patterns having structure sizes significantly below half a wavelength of the light. Correspondingly, it is generally not possible to limit photoinduced reactions to length scales smaller than half a wavelength.
Yet there are many industrial and research sectors where photoinduced reactions limited to smaller regions would be very desirable. Examples are photoresists for lithography in the semiconductor industry, highly resolved surficial functionalization in biomedical engineering or photorelease of test substances limited to small volumes within the organelles of a living cell (research in cell biology).
Possible ways of how these limitations may be overcome are for example described in DE 10 2010 000 169, which also discloses methods of optical lithography below the diffraction limit which are based on specific photo-initiators with regard to their underlying chemistry.
A photosensitive substance such as, for example, a photoresist consists, in general, of at least one substance to be crosslinked (a monomer for example) and a photoactive molecule (a photoinitiator for example) to absorb light and start the crosslinking reaction.
Photoenols and reactions of this type are known from A. S. Quick et al., Adv. Funct. Mater. 2014, 1-10 and J. C. Netto-Ferreira et al., J. Am. Chem. Soc. 1991, 113, 5800-5803.
DE 10 325 459 A1 describes a generic concept for overcoming the diffraction limit by means of two-colored illumination and the use of switchable molecules. However, only very few materials systems and methods are known for putting this concept into practice. Existing methods are very restricted both as regards achievable resolution and as regards the diversity of their possible uses.
So there continues to be a substantial need for methods and systems to practice chemical reactions, especially optical lithographies, below the optical diffraction limit.
The problem addressed by the present invention was that of providing a method for conducting photochemical reactions, especially for optical lithography, below the diffraction limit, and also resists and chemical systems suitable therefor.
The problem addressed by the present invention was further that of finding novel uses for photoenols.
The problem addressed by the present invention was not least also that of finding systems that are simpler and more flexible than the related art.
This problem is solved by a method of conducting photochemical reactions, for example optical lithographies, below the diffraction limit, for example using photorelease, photouncaging or Diels-Alder reaction which method comprises
The problem is also solved by a method of conducting photochemical reactions, for example optical lithographies, below the optical diffraction limit, wherein
The problem is further solved by the use of photoenols for photochemical reactions, including in the afore-mentioned method and in a method for reducing the lithographic scale, and also in a lithographic lacquer based on photoenols and dienophiles.
The problem is further solved by a method for optical lithography below the diffraction limit, wherein
Amounts indicated in the context of the present invention are all by weight, unless otherwise indicated.
The term “room temperature” is to be understood in the context of the present invention as meaning a temperature of 20° C. Reported temperatures are in degrees Celsius (° C.), unless otherwise indicated.
Unless otherwise indicated, the recited reactions and/or process steps are carried out at standard/atmospheric pressure, i.e., at 1013 mbar.
The term “lithography” in the context of the present invention comprehends, according to context, lithographic processes or lithographically created structures.
In the context of the present invention, the terms “lacquer” and “photoresist” are to be understood as meaning coating compositions in which radiating with light is capable of crosslinking regions fully or at least comparatively highly and hence of altering the refractive index of the regions and/or effecting a crosslinking/curing reaction.
In the context of the present invention, the term “molding” describes a photosensitive substance or a photosensitive mixture of substances whose solubility and/or etching resistance is alterable by irradiating with light. This can be for example a noncrosslinked polymer which is crosslinked, and thus rendered insoluble, by irradiating it with light. Alternatively, the step of irradiating with light can alter other properties of the molding, for example the refractive index.
In the context of the present invention, the term “substrate” is to be understood in the context of a surface functionalization as describing a surface or a (solvent pervious) body that provides photoenols, so the photoreaction described is capable of immobilizing the reaction partner on and/or in the substrate.
The invention enables the starting of photochemical reactions on very small spatial scales. This enables for example a highly resolved two-dimensional or three-dimensional lithographic structurization of surfaces or volumes and also a precise spatially highly resolved chemical functionalization of surfaces or volumes. In conventional photochemical procedures, the so-called diffraction limit is a limit to the resolution attainable, whereas with the present invention there is no fundamental limit to the resolution and in principle a resolution down to molecular level is conceivable.
The present invention encompasses a novel chemical implementation which is employable specifically (but not exclusively) for lithography and precise chemical functionalization. In the present invention, certain molecules, so-called photoenols, form the basis for the switchable chemical system. Photoenols comprise molecules (ortho-alkylbenzaldehydes and -ketones) which form reactive intermediates (alpha-hydroxy-ortho-quino-dimethanes) on absorption of light. These intermediates constitute inter alia very efficient dienes for Diels-Alder reactions. Photoenols are typically excited in the near UV region by wavelengths of around 350 nm (first wavelength). The nature of the chemical process makes it possible for example to attach a large number of different chemical groups to the photoreactive components. (The intermediate o-quinodimethane formed may act inter alia as a reactive diene for Diels-Alder reactions (click reaction)). The present invention makes it possible to obtain photoresists for two-dimensional and three-dimensional structurization. The photoenols and the photochemical systems of the present invention are further suitable in the context of the present invention for fixing molecules to surfaces in a precise and locationally resolved manner. The photoenol chemistry in the context of the present invention further enables the realization of novel light-sensitive protecting groups and the light-induced release of substances. The applications of the chemical mechanism in combination with the highly resolving procedure of structurization are thus very diverse.
As mentioned, photoenols are molecules which, after excitation with light, transiently form a reactive species by photoenolization. The precise process from the excitation with light to the formation of the species involves several intermediate steps. The enol produced has proportions of two different molecular conformations (E/Z conformation). The E conformation is generally long lived for unsubstituted enols obtained, whereas the Z conformation is very short lived. The latter returns rapidly and spontaneously, via hydrogen reversion, back into the ground state of the starting molecule and can thus be re-excited at a later stage of the reaction.
In general, the photoenols which are useful in the context of the present invention and their reaction in the context of the present invention can be represented as follows:
where the variables have the following meanings independently of one another:
For photoenols to be useful in the context of the present invention it is essential that they comprise phenylmethanal derivatives/phenyl ketone derivatives which additionally have to have an ortho-positioned substituent that has a hydrogen atom in the alpha position.
Preferred photoenols for the purposes of the present invention are especially those selected from the group consisting of ortho-alkylbenzaldehyde and -ketones, and mixtures thereof.
In one version of the present invention, the photoenol is selected from the group consisting of alpha-chloro-2′,5′-dimethylacetophenone, 2′,4′-dimethylacetophenone, 2′,5′-dimethylacetophenone, alpha-chloro-2′,4′,6′-trimethylacetophenone, 2′-methylacetophenone, 6,6′-((2,2-bis((2-formyl-3-methylphenoxy)methyl)propane-1,3-diyl)bis(oxy))bis(2-methylbenzaldehyde), 2-hydroxy-6-methylbenzaldehyde, 2-methoxy-6-methylbenzaldehyde, 2-chloro-1-(2,5-dimethylphenyl)propan-1-one, 1-(2,5-dimethylphenyl)propan-1-one and mixtures thereof.
Useful dienophiles for the purposes of the present invention include in principle any compounds having a pi bond.
Preference is given to using compounds which have an electron-withdrawing group conjugated with an olefinic double bond and which are stable to the employed wavelengths of excitation and de-excitation light.
Useful dienophiles for the purposes of the present invention are more preferably selected from the group consisting of maleimides, maleic anhydride, maleic di- and monoesters, fumaric di- and monoesters, alkynes, acrylates, methacrylates, dithioesters, trithiocarbonates, propenals, butenals, fullerenes, dicyanoethene, tetracyanoethene, acetylenedicarboxylic mono- and diesters, but-2-en-4-olides, their derivatives and mixtures thereof.
It is similarly possible to employ the dienophiles as reactive groups attached to polymers; it is thus possible for example to coat surfaces with corresponding polymers and then to react the photoenols with the suitable attached dienophilic functional groups. That is, the term “dienophile” in one version of the present invention comprehends such polymer attached dienophilic functional groups.
One example thereof is poly[(methyl methacrylate)-co-(2-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)ethyl methacrylate)].
It is likewise possible in one version of the present invention to utilize dienophilic groups that are incorporated in polymers, a general example of which comprises unsaturated polyesters wherein the C═C double bonds present in the polymer backbone can act as dienophilic groups. It is self-evidently also possible to choose other polymers, for example poly(meth)acrylates, which additionally bear appropriate groups.
Useful solvents for the purposes of the present invention include any solvents in which the photoenols and the dienophiles dissolve. However, it is advantageous and therefore preferable for the purposes of the present invention for the solvents to be non-protic.
Examples of useful solvents are methanol, gamma-butyrolactone (GBL), dichloromethane, chloroform, acetone, acetonitrile, tetrahydrofuran, ethyl acetate, dimethylformamide, acetophenone and also mixtures thereof.
In one version of the present invention, the solvents are selected from the group consisting of gamma-butyrolactone (GBL), acetophenone or mixtures thereof.
Auxiliary substances used in the context of the present invention are particularly those which do not interact with the light of the incident wavelengths. It is further advantageous for them not to enter any competing reactions with the functional groups of the photoenol and the dienophile.
In one version of the present invention auxiliary substances used are substances customary in the art and known in the art, preferably surface-active substances, flow control agents, pigments, fillers, crosslinkers, stabilizers, photoprotectants (with adapted wavelength profile).
One version of the present invention employs the photoenol and the dienophile in a molar ratio ranging from 1.5:1 to 1:1.5, preferably from 1.3:1 to 1:1.3 and especially from 1.1:1 to 1:1.1.
The reaction scheme which follows illustrates the reaction pathway and switching mechanism using the example of a light-induced Diels-Alder addition via photoenolization:
A) Schematic depiction of photoenolization (1) and also of the reaction of the intermediate in a Diels-Alder reaction (2) and the hydrogen reversion of the short-lived enol conformation (here: Z-conformation for R=H) to the starting molecule (3).
B) Photoisomerization of the long-lived conformation to the short-lived conformation.
C) Photoisomerization of the short-lived conformation to the long-lived conformation.
The photoenol chemistry used in the context of the present invention is switchable in its reactivity for lithographic procedures. One version involving the second wavelength likewise uses a Gaussian focus and no zero place. For technical reasons, one version employs as first wavelength not 350 nm, but 700 nm (femtosecond pulses), and the molecules are accordingly excited via two photon absorption. But this does nothing to change the photoenolization process. It was found that the molecules studied on being simultaneously irradiated with 440 nm light (second wavelength) do not trigger the expected chemical reaction even though they are sufficiently exposed to light of the first wavelength to form the reactive species. This behavior was specifically studied in two possible scenarios, namely a photoinduced surface functionalization and a photopolymerizable photoresist based on a photoenol. As a test, a path as indicated in
One possible explanation for this switchability is that the enol formed, in the corresponding long-lived conformation, absorbs the light of the second wavelength and in the process transitions into the short-lived conformation (see B in the above scheme). Our results would be explained if the long-lived enol conformation transitions into the short-lived enol conformation on 440 nm irradiation and the opposite transition (short-lived to long-lived) is not triggered by this irradiation. Even if the two enol conformations have the same transient absorption spectrum and possibly even the short-lived enol can be photoinduced to transition into the long-lived enol (see C in the above scheme), however, the switching process is effective for resolution improvement because the lifetimes of the two enol species are very different. Since the short-lived conformation dies down faster by orders of magnitude with starting molecules being formed by mainly hydrogen reversion, irradiation at 440 nm would, by the constant exchange between short-lived and long-lived conformations, lead in the main to the long-lived enol conformation being depopulated and aligned in its lifetime with the short-lived conformation.
In addition to the in-principle reactivity switchability of the photoenol molecules, the present invention further provides for improved resolution. Switching here utilized a focus created by a so-called half moon phase plate (see
It was found here that not only in the surface functionalization but also in the 3D lithography, the use of the second laser gave point spacings unattainable without the second laser.
The photoenol system was tested for the targeted functionalization of glass surfaces. To this end, the photoenol coated surface used was functionalized with biotin-maleimide (an efficient dienophile in Diels-Alder reactions) in a locationally resolved manner and then stained with streptavidin-Cy3. Then, fluorescence images of the surface were recorded with a microscope using structured illumination (SIM microscopy). An optical characterization of the result by fluorescence microscopy is simple and robust. Since, however, these procedures are themselves diffraction limited, they cannot be used to characterize very small distances. These experiments were therefore not carried out with the best possible focusing (in this case a fully illuminated microscope objective of numerical aperture NA=1.4, focus measurement see
First, points were exposed at 600 nm distance (
Subsequently a point spacing of 400 nm was tested (
To underscore the wide utility of the present invention, improved resolution was also shown in a photoenol system for photopolymerization. Again point exposures with various spacings were used. In each case, a small volume of a droplet of the liquid photoresist was polymerized close to the interface with a glass substrate. These oval points of polymer were bared by a wet chemical step of development and were subsequently examined under an electron microscope. Since the resolution of the electron microscope is very good, the optimal focusing was used for this experiment (
The power output of the excitation laser (first wavelength) was varied such that not only underexposed results (at left) but also overexposed results (at right) occurred. At a point spacing of 300 nm (
Using a point spacing of 250 nm (
A further version of the invention provides for the release (photorelease) of a certain molecular species out of a photoenol molecule. A two color exposure is again able to restrict the region of release to spatial scales below the diffraction limit, as is not possible using the prior art. One example thereof is a release of HCl out of the molecule o-methylphenacyl chloride.
A further version of the invention provides for certain intramolecular groups being uncaged (photouncaged) by use of photoenol chemistry. This functionality is initially not present or inactive (for sterical reasons for example) and is first intramolecularly created or activated by a photochemical reaction. For instance, the intramolecular reaction of the created reactive species with an epoxide can be used to create an aliphatic alcohol. Since the reaction described proceeds via the above-described reactive species (o-quinodimethane), the reaction can likewise be used to inhibit a light-induced deactivation of this species. By use of two colors, it is again possible to massively reduce the spatial extent of the reaction volume.
Lithography applications come into consideration again for example. There the uncaged groups may for example catalyze a reaction for solubility modification, or the groups created may constitute the attack points for an etch in order to destabilize a polymer network. Further possibilities are again all chemical reactions for which the groups created or activated by photouncaging are suitable (nucleophilic substitution for example).
The present invention provides a way to virtually circumvent the optical diffraction limit. For instance, a spatially closer confined excitation can be optically introduced into a photoresist layer than would be possible with a conventional optical exposure, and thus produce smaller structures.
Not only one but also multiple photon absorption can be used for excitation. The spatial confinement of the excitation is independent of the excitation mode.
The method of optical lithography below the diffraction limit as per the present invention comprises the steps of:
One version of the present invention is a method of optical lithography below the diffraction limit comprising
The present invention utilizes a photoenol which is deactivatable by irradiation with a second wavelength before it starts the chemical reaction. A further chemical reaction is locally inhibited as a result.
A deexcitation light in addition to the excitation creates an interference pattern which has an intensity minimum or ideally zero intensity in those places where very small structures are to be created. The effect of the optically introduced excitation is thus locally reduced according to the deexcitation intensity, substantially at high intensities, minimally at small ones and not at all at zero intensity. In consequence, multiplying of the entire excitation power output may provide an ever greater narrowing of the remaining excitation about the local minimum.
This apparatus-based approach corresponds to the methods described in DE 10 2010 000 169.
In the present invention, it is preferably laser light which is used to create not only excitation but also deexcitation.
The useful photoenols for the purposes of the present invention enable the production in a photoresist or holographic storage medium, together with the use of an additional laser for de-excitation, of smaller structures than is possible with conventional optical lithographic techniques at comparable wavelengths and apertures.
In the method of the present invention, the additional (laser) light is used to create about the place to be exposed an interference pattern which at this place has an intensity minimum (ideally of intensity zero). In the exposure operation with the first light source, the photoenol is then deactivated according to the local intensity of the additional light source. The de-excitation is at its weakest in the intensity minimum, and absent in the case of zero intensity. The remaining excitation, which ultimately leads to a chemical reaction, for example polymerization, can in principle be restricted further and further by increasing the power output of the second laser.
The present invention enables the structure size to be established independently of the crosslink density, making it possible for example to produce very small and simultaneously stable structures.
A useful photoresist for the purposes of the present invention may consist of the constituents described above, subject to the proviso that it has to contain at least one of the abovementioned photoenols and at least one dienophile. It may contain solvent and be usable not only in solid form but also in liquid form, and in one version is oxygen insensitive.
One example of a useful photoresist for the purposes of the present invention is based on a polymer having a multiplicity of functional dienophilic groups, for example maleimide groups, in pending form, a photoenol, for example 6,6′-((2,2-bis((2-formyl-3-methylphenoxy)-methyl)propane-1,3-diyl)bis(oxy))bis(2-methyl-benzaldehyde), and one or more solvents, for example a mixture of GBL and acetophenone.
In one version of the present invention, the lacquer does not include any solvent.
In one version of the present invention, the excitation laser has a central wavelength between 250 nm and 450 nm, preferably between 300 nm and 400 nm, more preferably between 320 nm and 350 nm and yet more preferably 350 nm.
In one version of the present invention, the excitation laser has a central wavelength between 500 nm and 800 nm, preferably between 600 nm and 700 nm, more preferably between 640 nm and 700 nm and yet more preferably 700 nm. Pulsed lasers are usable here with preference.
In one version of the present invention, the de-excitation laser has a central wavelength between 400 nm and 600 nm, preferably between 420 nm and 480 nm, more preferably between 430 nm and 450 nm and yet more preferably 440 nm.
The excitation laser used in one version of the present invention is a continuous wave laser with 351 nm central wavelength.
The excitation laser used in one version of the present invention is a laser with 150 femtoseconds pulse duration, 80 MHz repeat rate, 700 nm central wavelength.
The de-excitation laser used in one version of the present invention is a continuous wave laser (cw) having a central wavelength of 440 nm central wavelength.
The excitation and de-excitation lasers may each independently be either both pulsed, both continuous or one pulsed and the other continuous in operation.
One version of the present invention comprises radiating the excitation light in pulsed operation and the de-excitation light in pulsed or continuous wave (cw), preferably continuous wave, operation.
The method of the present invention requires no additional ingredients, but utilizes an inherent property of the photoenol. In the case of the present invention, the system of photoenol and dienophile, the lacquer system for example, only absorbs the de-excitation light where there is also some excitation. As a result, the de-excitation light can be focused deeply into a sample. It is thereby possible, together with a multiple photon excitation, to produce three-dimensional structures, especially with improved resolution.
The method of the present invention is therefore employable not only to two-dimensional lithography but also to three-dimensional lithography.
The use of the photo-deactivatable photoenols referred to has the advantage that they absorb in the UV region, preferably at 300-450 nm, so common methods of UV exposure can be employed. The processing of the samples can be carried out under yellow light or red light.
The resulting structures out of the method according to the present invention can be engineered to be transparent in the visible spectrum and therefore employed for the production of nano- and microoptical devices.
The present invention enables inter alia a sequential punctuate exposure to focused light and single or two photon absorption. It is similarly possible for example to use traditional single photon absorption for large area parallel lithography as well. To this end, instead of a single doughnut-shaped focus, it is then for example an intensity lattice created by interference and its null positions which are used. Excitation may utilize a large area pattern of light, created either statically (with a mask for example) or dynamically (for example by means of a liquid crystal spatial light modulator) or an MEMS digital mirror device.
Similarly with data storage devices based on using laser light to crosslink in an optical molding, i.e., in a polymer matrix, small points more strongly to thereby change their refractive index, the present invention is capable of achieving smaller points and thus higher data densities.
In one version of the present invention, the laser beams for initiation (excitation) and deactivation (de-excitation) are combined with a beam divider and focused together by a microscope objective through a cover slip into a droplet of the photoresist. Since a phase mask is used in the deactivation beam ahead of the beam divider, this beam creates, in the focus of the objective, a doughnut shaped interference pattern having a deep minimum in the center. The beams are oriented such that the focus of the excitation laser is centered precisely about this minimum. It is thereby possible to polymerize individual three-dimensionally confined points in the focus. By shifting the sample relative to the focus, any desired structures are obtainable by serial punctuate exposures.
The additional introduction of the de-excitation laser inhibits the chemical reaction in the periphery of the otherwise diffraction limited reaction volume and thereby reduces the dimensions of the smallest obtainable volume element.
In one version of the present invention, the excitation and de-excitation lasers are focused separately from each other. The present invention makes it possible for example to have one beam pass from above into the lacquer or molding while the other beam passes from below or at an angle from above into the lacquer or molding. What is essential is that the beams meet in the focus point.
Lateral entry of the beams into the sample is also conceivable.
It is self-evidently not necessary to focus through a cover slip into a droplet of a lacquer. It is merely necessary that the lacquer be placed in a distance in front of the microscope objective that focusing into it is possible. It is similarly possible to provide not droplets but larger amounts of lacquer for treatment. It is then merely more physically cumbersome to move/position the lacquer, but larger structures can then be created. These versions are encompassed by the present invention.
In one version of the present invention, it is not a conventional excitation which is carried out at 350 nm but a two photon excitation with femtosecond laser pulses having a central wavelength of 700 nm.
One version of the present invention utilizes a conventional excitation with UV light at 350 nm.
It was found in the context of the present invention that, for the same excitation power output and translation speed, the additional use of the de-excitation laser with or without a phase mask made it possible to achieve an appreciable reduction in line width.
The present invention lastly also provides a lithographic lacquer for methods of optical lithography below the diffraction limit, containing or consisting of
(i) one or more photoenols, and
(ii) one or more dienophiles,
(iii) optionally the abovementioned solvents.
In one version of the present invention, the lithographic lacquer consists of
(i) one or more photoenols, and
(ii) one or more dienophiles.
It is an immense advantage of the present invention that the hitherto unknown photo-deactivatability of a known photoenol is exploited in order to be able to produce smaller structures.
The present invention makes it possible to produce spatially smaller structures by optical means than this was hitherto possible with corresponding chemical systems.
The invention is of great interest in the entire field of the optical-lithographic production of small and very small structures. It can likewise be used for the development of optical data storage media having extremely high data density.
The present invention is used inter alia for photoresist systems for extremely highly resolving lithography, for and/or in the semiconductor industry in general, for fast prototyping for microchips, and also in the manufacture of optical component part elements.
The present invention is useful not only for the production of small planar or three-dimensional structures but also for writing optical data storage media of high density, since similar crosslinking reactions can be used there, and the diffraction limit can be circumvented in a similar way.
The present invention also provides the method of using photoenols, preferably ortho-alkylbenzaldehydes and -ketones for conducting and/or initiating photochemical reactions, preferably for optical lithography, especially in lacquers for optical lithography, below the diffraction limit by use of light having two wavelengths, for functionalization of surfaces, especially glass surfaces.
The present invention further provides a method for structured functionalization of surfaces, especially glass surfaces, which comprises
Fixing the photoenol and/or the dienophile in this context may be effected for example as a result of the particular surface being occupied by or consisting of a polymer and the photoenol and/or dienophile being attached to this polymer as a functional group. The photoenol and/or dienophile may similarly be attached as functional groups to existing functional groups on the surface, in that for example they may be attached to a glass surface via OH groups present thereon.
The present invention further provides the method of reducing the lithographic scale and/or the lithographic resolution in optical lithography by use of photoenols, preferably ortho-alkylbenzaldehydes and -ketones.
The photochemical reactions and/or polymerizations of the present invention proceed not via a free radical reaction mechanism, but via photoinduced Diels-Alder reactions.
The present invention can be used to establish lithographically created structures on orders of magnitude, stated in the order of preference, down to 600 nm, 500 nm, 40 nm, 350 nm, 300 nm, 275 nm, 250 nm, 225 nm, 200 nm, 175 nm, 150 nm, 140 nm, 130 nm, 120 nm, 110 nm, 100 nm, 90 nm, 80 nm, 70 nm, 60 nm, 50 nm, 40 nm, 30 nm, 20 nm, 10 nm, 5 nm.
A particularly preferred version of the present invention is a method of optical lithography below the diffraction limit wherein
A most highly preferred version here is that combining the most highly preferred versions in each case.
Advantages of the present invention are the universal utility and also the mild conditions of the photoenol chemistry used. The present invention further makes possible a large bandwidth of covalent functionalizations below the diffraction limit, since the o-quinodimethane intermediate formed may be utilized inter alia as a reactive diene for Diels-Alder reactions (click reactions). It is thereby readily possible to use a multiplicity of different molecules as reaction partners. One important feature of the invention is therefore the coupling of a switchable system (photoenolization) with a widely usable intermediate (diene for Diels-Alder reactions). A further massive advantage is the possibility of parallelization, i.e., the concurrent practice of a lithographic process on a large area, by virtue of the low power outputs required. This makes for an enormous increase in throughput.
The present invention has a further advantage in its good utility in photorelease and/or photouncaging processes.
The present invention makes possible the use of a broad spectrum of photoreactions/reaction partners under mild conditions and not just a photoinduced free radical polymerization reaction.
Compared with the already very good systems of DE 10 2010 000 169, one advantage of the present invention is that the photoenol can be switched at significantly lower power outputs (about 100 μW) and therefore is suitable for appreciably larger throughput by parallelization than the photoinitiator system of DE 10 2010 000 169, where the light power outputs required for the second wavelength amount to about 50 mW.
The present invention is further advantageous over the likewise highly resolving technique of RESOLFT microscopy, since with the latter it is neither possible to create an etched contrast (as would be necessary for any use in the semiconductor industry) nor to dock some other molecular species onto the molecules. Nor does it allow for photorelease or photo-uncaging. So the chemical reaction which is optically induced is unspecific and not further useful, whereas the photoenol reaction of the present invention is universally useful and inter alia, by virtue of its high efficiency under mild conditions, employable as a click reaction. The strict criteria underlying a click reaction therefore enable/facilitate the integration of the present invention into a multiplicity of applications.
The present invention also exhibits advantages over absorption modulation lithography. In absorption modulation lithography, a layer is placed between the light source and the photosensitive substance (sensitive at wavelength one) and the transmission behavior of said layer is alterable with a second wavelength. The second wavelength may be used for instance to create an opaque layer which is solely transparent in a very small point. As a result, only a very small region would transmit the light of wavelength one in order to expose the light-sensitive substance therebehind and to start the photoreaction. Owing to the diffraction effects of light at this small opening, however, the transmitted beam would very quickly broaden out again with increasing distance from the layer. A photoreaction can therefore then only be started in the form of very thin layers and with two-dimensional structurization. Using the photoenol approach of the present invention, however, the reaction can also be limited in three dimensions and is not confined to thin layers. In addition, the absorbance of photochromic layers in absorption modulation lithography is generally not very high, so the attainable resolution is limited by a diffusely transmitted background of wavelength one.
It was the efficient switchability which, in the context of the present invention, was achieved by photoisomerization in the systems of the present invention. The systems of the present invention make it possible for the entire reaction path of the intermediary species to be altered, and returned losslessly to the starting molecule, by suitable irradiation, despite reactive intermediates and high intensities during the pulses. This enables inter alia an extremely effective utilization of the amounts of substances used.
Another surprise is the high yield which is achieved within a very short time by the isomerization referred to and makes a lithographic application possible in the first place, since reactive partners of the long-lived ortho-quinodimethane species are at the ready and the reaction which is suppressed here is a conventional click reaction, which is known for its high reaction rate and yield. The present invention thus surprisingly enables an enhanced controllability over reactions such as click reactions.
The various embodiments of the present invention, for example—but not exclusively—those of the various dependent claims, are combinable with each other in any desired manner.
In the examples of the present invention, a 700 nm laser of 150 fs pulse length and 80 MHz repetition rate was focused with an oil immersion objective (Leica HCX PL APO 0.7-1.4 OIL CS) into the particular sample through a cover lid. In addition, the same objective was used to focus a 440 nm continuous wave laser, selectively in a spatial mode having a zero place (see
This is a preferred procedure in one version of the present invention.
Number | Date | Country | Kind |
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10 2015 108 358.2 | May 2015 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2016/061523 | 5/23/2016 | WO | 00 |