WO2023156297A1 - Resist compositions - Google Patents

Abstract

There is provided a metal oxide photoresist composition comprising electron scavenger particles selected to scavenge electrons having electron kinetic energies of 20 eV or less. Also provided is a method of improving the performance of a metal oxide photoresist, the method including providing one or more electron scavengers selected to scavenge electron having electron kinetic energies of 20 eV or less in the metal oxide photoresist. Further provided is the use of such a composition or method in a lithographic apparatus or process.

Description

RESIST COMPOSITIONS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 22156686.2 which was filed on February 15, 2022 and which is incorporated herein in its entirety by reference.

FIELD

[0002] The present invention relates to resist compositions for use in lithography, particularly in the fabrication of integrated circuits, methods of improving the performance of a metal oxide photoresist, and the use of such compositions or methods in lithographic apparatuses or processes. In particular, the present invention relates to resist compositions including electron scavenger particles selected to scavenge electrons having electron kinetic energies of 20 eV or less in order to improve line width roughness.

BACKGROUND

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may for example project a pattern from a patterning device (e.g. a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate.

[0004] The wavelength of radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of features which can be formed on that substrate. A lithographic apparatus which uses EUV radiation, being electromagnetic radiation having a wavelength within the range 4-20 nm, may be used to form smaller features on a substrate than a conventional lithographic apparatus (which may for example use electromagnetic radiation with a wavelength of 193 nm).

[0005] Known resists suitable for use with lithography are referred to as chemically amplified resists (CAR) and are based on polymers. Upon expose to electromagnetic radiation or an electron beam, the polymers in the CAR absorb photons or interact with electrons, and secondary electrons are generated. The generation of secondary electrons is how a high-energy photon or electron loses most of its energy. The secondary electrons in the resist diffuse and may generate further secondary electrons with lower energies until the energy of the secondary electrons is lower than that required to break bonds in the CAR or to result in ionisation. The electrons generated excite photo-acid generators (PAG) which subsequently decompose and can catalyse a deblocking reaction, which leads to a change in the solubility of the CAR.

[0006] Alternative resist systems for use with lithography, in particular EUV lithography, comprising metal oxide nanoclusters have been investigated to try to address the issues with CARs. These alternative resist systems comprise metal oxide nanoparticles or nanoclusters which are prevented from clustering together by a ligand shell. Upon EUV exposure, photons are absorbed by the nanoparticles or nanoclusters and this leads to the generation of secondary electrons. The electrons break the bonds between the ligands and the nanoparticles or nanoclusters. This allows the nanoparticles or nanoclusters to cluster together and hence changes the solubility of the resist. The metal oxide nanoparticles have larger EUV absorption cross-sections than carbon atoms in CAR and thus there is a greater likelihood of EUV photons being absorbed. Therefore, a less intense beam requiring less power or a shorter exposure to the EUV photons is required. Furthermore, the different conversion mechanism has potentially lower chemical noise than CAR resist systems. As described in Cardineau, B et al, Photolithographic properties of tin-oxo clusters using extreme ultraviolet light (13.5nm), Microelectronic Engineering 127 (2014), pp. 44-50. 10.1016/j.mee.2014.04.024, and Haitjema. J., et al, Extreme ultraviolet patterning of tin-oxo cages, Journal of Micro/Nanolithography, MEMS, and MOEMS, 16(3), 033510 (2017), doi: 10.1117/1.JMM.16.3.033510, tin-oxo cage materials have been investigated for use as photoresists for EUV lithography. The tin-oxo cage materials turn insoluble upon EUV irradiation and therefore act as negative tone resists.

[0007] It is desirable to provide resist compositions which achieve acceptable resolution, acceptable line-edge/width roughness and which have acceptable sensitivity. CARs have an intrinsically stochastic nature and therefore do not provide the highest resolution. Resists comprising metal atoms are generally negative tone materials with only moderate sensitivity and still suffer from stochastic effects, although they can sometimes be positive tone resists.

[0008] It is an objection of the present invention to address or overcome the disadvantages of existing resist compositions and to provide alternative resist compositions.

[0009] Whilst the present application generally refers to EUV lithography throughout, the invention is not limited to solely EUV lithography and it is appreciated that the subject matter of the present invention may be used in resists for photolithography using electromagnetic radiation with a frequency above or below that of EUV, or in any other type of lithography, such as electron beam lithography.

SUMMARY

[00010] According to a first aspect of the present invention, there is provided a metal oxide photoresist composition comprising electron scavenger particles selected to scavenge electrons having electron kinetic energies of 20 eV or less.

[00011] Metal oxide photoresists (MOR) are increasingly important in lithographic processes as pitch size decreases, at least in part due to their larger photo absorption and lower image blur compared to chemically amplified resists. MORs are usually negative-tone resists that form an insoluble condensed network after exposure to a patterned radiation beam, for example an EUV radiation beam. The condensed network is provided by bridging reactions between linking sites on MOR particles. The activation of these linking sites follows from the interaction of secondary electrons generated by a cascade of ionization reactions triggered by photon absorption and subsequent ionization of primary electrons from the metal core. It has been realised that secondary electrons with low energies can still cause activation of the linking sites. Such low-energy secondary electrons have a large mean free path, thereby influencing the variability of the position of activated linking sites and therefore contributing to the variability of the final developed pattern. The present disclosure provides for the inclusion of electron scavenger particles which are selected to scavenge such low-energy secondary electrons. By scavenging the low-energy secondary electrons, the mean free path of such electrons is reduced, thereby reducing the blur caused by such secondary electrons diffusing through the material and causing linking reactions outside of the area of the resist composition which is exposed to the patterned radiation beam. It will be appreciated that some MORs are positive-tone resists.

[00012] The electron scavenger particles may comprise an unsaturated organic compound. The scavenger particles may comprise a halogenated compound, optionally a fluorinated compound. The unsaturated organic compounds may be furan, ethylene, or derivatives thereof. The halogenated compounds may be dibromosilylene, chlorotrifluoromethane, or derivatives thereof.

[00013] Unsaturated organic compounds and halogenated compounds, particularly fluorinated compounds, have high dissociative electron attachment (DEA) cross-sections. DEA occurs at low electron kinetic energies, such as 20 eV or below. The DEA cross-section is a function of electron impact energy and compounds have a maximum cross-sectional area at certain energies. The electron scavengers according to the present disclosure are selected such that their maximum cross-sectional area is provided at energies similar to the energies of the low-energy secondary electrons. This increases the likelihood that such secondary electrons are scavenged, thereby reducing the degree to which they are able to diffuse through the material and cause unwanted linking. Most DEA crosssections are provided experimentally in the gas phase, but literature data indicates that DEA crosssections increased in condensed systems by at least one order of magnitude (Smyth M. et al, J. Chem. Phys. 140, 184313 (2014), 10.1063/1.4874841).

[00014] The metal oxide may be tin oxide. Tin oxide may be provided as a tin-oxo cage which includes ligands that are able to interlink upon exposure to radiation and therefore form an insoluble agglomeration of particles.

[00015] The concentration of scavenger particles may be from 0.1 to 10 particles per nm3 (by volume). The DEA cross-sections of the scavengers may be from 0.01 to 10 nm2. LER reduction is a result of either increasing scavenger concentration or larger DEA cross-sections or a mix of both. At very high concentrations, saturation is reached whereby additional scavenger particles do not provide for the absorption of further secondary electrons and so the beneficial effect is limited at concentrations higher than described herein.

[00016] According to a second aspect of the present disclosure, there is provided a method of improving the performance of a metal oxide photoresist, the method including providing one or more electron scavengers selected to scavenge electron having electron kinetic energies of 20 eV or less in the metal oxide photoresist.

[00017] As described in respect of the first aspect of the present disclosure, the provision of electron scavengers selected to scavenge low-energy electrons results in improved performance of the photoresist material.

[00018] The method may include providing one or more electron scavengers at a concentration of from 0.1 to 10 particles per nm³.

[00019] According to a third aspect of the present disclosure, there is provided the use of a metal oxide resist composition according to the first aspect or a method according to the second aspect in a lithographic apparatus or process.

[00020] The features described in respect of one aspect of the present disclosure also apply to other aspects of the present invention and features of each of the aspects of the present invention may be combined with features described in respect of other aspects of the present invention. All such combinations of subject matter are explicitly considered and disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

[00021] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

Figure 1 depicts a lithographic system comprising a lithographic apparatus and a radiation source which may be used to irradiate the resist compositions of the present disclosure;

Figure 2 is a graph comparing the line width roughness (LWR) of a resist composition with and without the inclusion of scavenger particles;

Figure 3 is a graph comparing the power spectral density of a resist with and without inclusion of scavenger particles;

Figure 4 is a graph comparing the critical dimension versus dose of a resist composition with and without the inclusion of scavenger particles;

Figure 5 is a graph showing the probability density function (pdf) versus the travel distance for electrons within compositions having different concentrations of scavengers;

Figure 6 depicts the probability density function (pdf) of a ligand being activated at a certain distance from the photo absorption site for compositions having different concentrations of scavengers;

Figure 7 depicts a comparison of the critical dimension as a function of dose for compositions having different concentrations of scavengers;

Figure 8 depicts a comparison of the line width roughness (LWR) as a function of critical dimension for compositions having different concentrations of scavengers; and

Figure 9 depicts a comparison of the distance travelled by electrons away from the location of photon absorption in compositions with and without scavengers. DETAILED DESCRIPTION

[00022] Figure 1 shows a lithographic system according to an embodiment of the present invention. The lithographic system comprises a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an extreme ultraviolet (EUV) radiation beam B. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g. a mask), a projection system PS and a substrate table WT configured to support a substrate W. The illumination system IL is configured to condition the radiation beam B before it is incident upon the patterning device MA. The projection system is configured to project the radiation beam B (now patterned by the mask MA) onto the substrate W. The substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus aligns the patterned radiation beam B with a pattern previously formed on the substrate W.

[00023] The radiation source SO, illumination system IL, and projection system PS may all be constructed and arranged such that they can be isolated from the external environment. A gas at a pressure below atmospheric pressure (e.g. hydrogen) may be provided in the radiation source SO. A vacuum may be provided in illumination system IL and/or the projection system PS. A small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure may be provided in the illumination system IL and/or the projection system PS.

[00024] The radiation source SO shown in Figure 1 is of a type which may be referred to as a laser produced plasma (LPP) source. A laser, which may for example be a CO2 laser, is arranged to deposit energy via a laser beam into a fuel, such as tin (Sn) which is provided from a fuel emitter. Although tin is referred to in the following description, any suitable fuel may be used. The fuel may for example be in liquid form, and may for example be a metal or alloy. The fuel emitter may comprise a nozzle configured to direct tin, e.g. in the form of droplets, along a trajectory towards a plasma formation region. The laser beam is incident upon the tin at the plasma formation region. The deposition of laser energy into the tin creates a plasma at the plasma formation region. Radiation, including EUV radiation, is emitted from the plasma during de-excitation and recombination of ions of the plasma.

[00025] The EUV radiation is collected and focused by a near normal incidence radiation collector (sometimes referred to more generally as a normal incidence radiation collector). The collector may have a multilayer structure which is arranged to reflect EUV radiation (e.g. EUV radiation having a desired wavelength such as 13.5 nm). The collector may have an elliptical configuration, having two ellipse focal points. A first focal point may be at the plasma formation region, and a second focal point may be at an intermediate focus, as discussed below.

[00026] The laser may be separated from the radiation source SO. Where this is the case, the laser beam may be passed from the laser to the radiation source SO with the aid of a beam delivery system (not shown) comprising, for example, suitable directing mirrors and/or a beam expander, and/or other optics. The laser and the radiation source SO may together be considered to be a radiation system.

[00027] Radiation that is reflected by the collector forms a radiation beam B. The radiation beam B is focused at a point to form an image of the plasma formation region, which acts as a virtual radiation source for the illumination system IL. The point at which the radiation beam B is focused may be referred to as the intermediate focus. The radiation source SO is arranged such that the intermediate focus is located at or near to an opening in an enclosing structure of the radiation source. [00028] The radiation beam B passes from the radiation source SO into the illumination system IL, which is configured to condition the radiation beam. The illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. The faceted field mirror device 10 and faceted pupil mirror device 11 together provide the radiation beam B with a desired cross- sectional shape and a desired angular distribution. The radiation beam B passes from the illumination system IL and is incident upon the patterning device MA held by the support structure MT. The patterning device MA reflects and patterns the radiation beam B. The illumination system IL may include other mirrors or devices in addition to or instead of the faceted field mirror device 10 and faceted pupil mirror device 11.

[00029] Following reflection from the patterning device MA the patterned radiation beam B enters the projection system PS. The projection system comprises a plurality of mirrors 13, 14 which are configured to project the radiation beam B onto a substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the radiation beam, forming an image with features that are smaller than corresponding features on the patterning device MA. A reduction factor of 4 may for example be applied. Although the projection system PS has two mirrors 13, 14 in Figure 1, the projection system may include any number of mirrors (e.g. six mirrors).

[00030] In use the optical elements of the lithographic apparatus, such as mirrors or reflectors, are heated by the radiation and it is therefore necessary condition such optical elements. As such, a conditioning system according to the present invention is integrated into the lithographic apparatus to provide the required conditioning. Conditioning usually requires the removal of thermal energy from the optical elements as they heat up during use.

[00031] The radiation sources SO shown in Figure 1 may include components which are not illustrated. For example, a spectral filter may be provided in the radiation source. The spectral filter may be substantially transmissive for EUV radiation but substantially blocking for other wavelengths of radiation such as infrared radiation.

[00032] Although Figure 1 depicts the radiation source SO as a laser produced plasma LPP source, any suitable source may be used to generate EUV radiation. For example, EUV emitting plasma may be produced by using an electrical discharge to convert fuel (e.g. tin) to a plasma state. A radiation source of this type may be referred to as a discharge produced plasma (DPP) source. The electrical discharge may be generated by a power supply which may form part of the radiation source or may be a separate entity that is connected via an electrical connection to the radiation source SO.

[00033] Figure 2 is a graph comparing the line width roughness (LWR) of a resist composition with and without the inclusion of scavenger particles as a function of critical dimension (CD). The reference line is the upper line and the lower line reflects the composition including scavenger particles as per the present disclosure. It can be seen that the line width roughness is lower for the composition including the scavengers than without. These results were obtained by molecular simulations of a realistic metal oxide resist physical model.

[00034] Figure 3 is a graph comparing the power spectral density of a resist with and without inclusion of scavenger particles. The reference line is the upper line. The Power Spectral Density (PSD) at a specific dose (Critical dimension of 22.5 nm) demonstrates the origin of the reduction of pattern variability in compositions according to the present disclosure. In particular, improved LWR is a consequence of shorter correlation lengths (xi) and lower uncorrelated noise (PSD0).

[00035] Figure 4 is a graph comparing the effect of scavenger concentration on LWR. Higher concentrations of scavenger particles lead to lower LWR values.

[00036] Figure 5 is a graph showing the effect of scavenger DEA cross-section on LWR. Larger cross-sections contribute to lower LWR.

[00037] Figure 6 depicts a comparison of the distance travelled by electrons away from the location of photon absorption in compositions with and without scavengers. It can be seen that electrons in compositions without any scavenger particles are more likely to travel further away from the location of photon absorption, thereby leading to increased LWR.

[00038] Figure 7 depicts the probability density function (pdf) of a ligand being activated at a certain distance from the photo absorption site for compositions having different concentrations of scavengers. Again, the upper line is the reference case and the electron travel distance is reduced in line with increasing concentration of scavenger particles.

[00039] The descriptions above are intended to be illustrative and not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims.

Claims

1. A metal oxide photoresist composition comprising electron scavenger particles selected to scavenge electrons having electron kinetic energies of 20 eV or less.

2. The composition according to claim 1, wherein the electron scavenger particles comprises an unsaturated organic compound, optionally wherein the unsaturated organic compound is furan, ethylene or derivatives thereof.

3. The composition according to any preceding claim, wherein the electron scavenger particles comprises a halogenated compound, optionally a fluorinated compound, optionally wherein the halogenated compound is selected from dibromosilylene, chlorotrifluoromethane, or derivatives thereof.

4. The composition according to any preceding claim, wherein the metal oxide includes tin oxide.

5. The composition according to any preceding claim, wherein the concentration of scavenger particles is from 0.1 to 10 particles per nm3 (by volume).

6. The composition according to any preceding claim, wherein the DOE cross-section of scavenger particles is from 0.01 to 10 nm2.

7. A method of improving the performance of a metal oxide photoresist, the method including providing one or more electron scavengers selected to scavenge electron having electron kinetic energies of 20 eV or less in the metal oxide photoresist.

8. The method according to claim 7, wherein the method includes providing one or more electron scavengers at a concentration of from 0.1 to 10 particles per nm³ (by volume)

9. The use of a metal oxide photoresist composition according to any of claims 1 to 6 or a method according to claims 7 or 8 in a lithographic apparatus or process.