Template, method for producing template, and method for producing semiconductor device

According to one embodiment, a template for nanoimprint lithography includes a substrate having a main surface and a mesa structure on the main surface. The mesa structure has an upper surface that can be patterned with recesses or the like. A film containing a quantum dot or quantum dots is on the main surface other than the upper surface of the mesa structure. The quantum dot can absorb ultraviolet light and emit visible light.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2020-041100, filed Mar. 10, 2020, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a template, a method for producing a template, and a method for producing a semiconductor device.

BACKGROUND

As a lithography process for producing semiconductor devices, nanoimprint lithography has been proposed as replacement for optical lithography as a method for transferring a pattern. In nanoimprint lithography, a template having a pattern is directly pressed onto a substrate, to which a liquid organic material has been applied, to transfer the pattern.

DETAILED DESCRIPTION

Certain embodiments provide a template that prevents unintended curing of a UV-curable imprint resist that might occur via leakage of ultraviolet light and further facilitates observation of an alignment mark using visible light.

In general, according to one embodiment, a template includes a substrate having a main surface, a mesa structure protruding from the main surface and having a first surface, and a film containing a quantum dot on the main surface outside of the mesa structure. In some embodiment, the film may also be on a side surface of the mesa structure. The quantum dot can absorb ultraviolet light (such as used in curing of nanoimprint resists) and emit visible light via fluorescence.

Hereinafter, example embodiments of the present disclosure will be described with reference to the drawings. In the following description of the drawings, the same or substantially similar portions are given the same reference numerals. In general, the drawings are schematic, and, as such, depicted relationships between thicknesses and planar sizes of aspects in the drawings can be different from those in actuality.

A template according to an embodiment will be described. The template according to the embodiment can be an original plate (also sometimes referred to as a mold, an imprint mold, a nanoimprint template, or the like) that is used in microfabrication processes for production of a semiconductor device using nanoimprint lithography.

FIGS.1A and1Bare views illustrating a configuration of a template1according to the embodiment.FIG.1Ais a plan view of the template1when viewed in a Z direction.FIG.1Bis a cross-sectional view of the template1taken along AA′ and viewed in an X direction. The template1is produced by processing a substrate11that is a quadrilateral shape when viewed in the Z direction. In a case of nanoimprint lithography using light for curing an imprint resist, the template comprises a transparent material, such as quartz, as a main component. At a center of a main surface12of the substrate11, a mesa structure13that protrudes from the main surface12is provided. The mesa structure13has a pattern surface14. The pattern surface14includes a recessed structure or recesses therein that forms a transfer pattern (that is, a pattern to be transferred to another substrate) and/or an alignment mark. In an outer circumferential region of the mesa structure13and a side surface of the mesa structure13, a material film15is provided. The material film15contains quantum dot(s)5and surrounds the mesa structure13.

FIG.2is a view illustrating a structure of a quantum dot5according to the embodiment. The quantum dot5is a microcrystal of a semiconductor compound. The possible structures of the quantum dot5can be broadly classified into a core type and a core-shell type, as illustrated inFIG.2. The core shell-type quantum dot5has a structure in which a surface of a core6is covered with a shell7.

The core6contains a semiconductor element or a compound semiconductor material that has a rutile-type or perovskite-type crystalline structure. For example, the compound semiconductor material includes a combination of Groups II and VI elements, Groups III and V elements, or Groups IV and VI elements. For example, the core6contains any of cadmium sulfide (CdS), cadmium selenide (CdSe), cadmium telluride (CdTe), zinc sulfide (ZnS), ZnCdSe, indium phosphide (InP), silicon (Si), lead (Pd), lead sulfide (PbS), roquesite (CuInS2), carbon (C), or graphene.

The shell7contains an inorganic substance such as zinc sulfide or silicon dioxide.

A protective material8(also referred to as a protective coating) contains an organic material that has high affinity towards the surface of the core6or the shell7. The protective material8includes a bondable functional group. The organic material for the protective material8may be a polymer or a small molecular compound. Examples of the organic material for the protective material8include organic acids, such as citric acid and oleic acid, or a polymer having an amino group, a thiol group, or a phosphate group.

The quantum dot5may be just the core6or may be the core6and the shell7together. The quantum dot5can be utilized to absorb a particular wavelength of ultraviolet light or the like depending on the particle diameter thereof and then emit fluorescence that is mainly visible light. The quantum dot5has higher photoconversion efficiency than an organic fluorochrome having the same characteristics as those of the quantum dot5. The quantum dot5also has higher durability than an organic fluorochrome. The quantum dot5can generally be dispersed in water or an organic solvent. Therefore, the quantum dot5is a material that facilitates application and formation of a layer including the quantum dot5.

In a method for producing the template according to the present embodiment, a resist material that is cured by ultraviolet light is used. It is desirable that the quantum dot5be one that absorbs ultraviolet light corresponding to the resist curing wavelength and emits visible light. Specific examples of the quantum dot5include a graphene quantum dot that absorbs light having a wavelength of 360 nm and emits light having a wavelength of 440 nm.

The method for producing the template according to the embodiment will be described with reference toFIGS.3A to3E.FIGS.3A to3Eare views illustrating a method for producing the template1according to an embodiment.

A template2having a substrate with a main surface and a mesa structure on the main surface is first prepared. The mesa structure has a pattern surface14. The template2may have a transfer pattern or an alignment mark already formed there on, or may be a blank template before formation of a transfer pattern or an alignment mark thereon.

As illustrated inFIG.3A, a photocurable resist22is applied to a substrate21. As illustrated inFIG.3B, the pattern surface14of the template2is pressed onto the photocurable resist22. The photocurable resist22is then irradiated with exposure light23and cured (hardened to a solid or the like). As illustrated inFIG.3C, the photocurable resist22and the template2are then separated from the substrate21. That is, the now cured photocurable resist22adheres to the pattern surface14rather than the substrate21and thus forms a protective film25covering the pattern surface14.

In this embodiment, the photocurable resist22is a nanoimprint resist material for forming the protective film25. However, the photocurable resist22material is not particularly limited to nanoimprint resists only and can be any material as long as such material can form the protective film25in the described manner.

After the formation of the protective film25, the material film15containing the quantum dot5is formed as illustrated inFIG.3D. For example, a dispersion solution containing the quantum dot5is applied, and the solvent in the dispersion solution is then removed by heating or the like, to form the material film15. The material film15may contain a polymer to enhance adhesion to the template2. Examples of such a polymer include polyacrylic acid, polyvinyl alcohol, and polyacrylamide. The polymer may be mixed in the dispersion solvent or be in the protective material8of the quantum dot5. As illustrated inFIG.3E, the protective film25and the material film15are then removed from the pattern surface14. Thus, a template1according to the embodiment can be produced. As a subsequent step, a step or steps for forming a transfer pattern or an alignment mark may be carried out on the template1.

FIGS.4A to4Eare views illustrating a method for producing the semiconductor device using the template1according to the embodiment.

As illustrated inFIG.4A, an ultraviolet light-curable resist32is applied to a substrate31. For example, the substrate31is a silicon substrate or an silicon-on-insulator (SOI) substrate. On a surface of the substrate31, a film39may be formed.

As illustrated inFIG.4B, the pattern surface14of the template1is then brought into contact with the ultraviolet light-curable resist32. Recesses in the pattern surface14are filled with the ultraviolet light-curable resist32during this process.

Subsequently, while the pattern surface14of the template1is still in contact with the ultraviolet light-curable resist32, the ultraviolet light-curable resist32is irradiated with exposure light33(which includes ultraviolet light), as illustrated inFIG.4C. As a result, the ultraviolet light-curable resist32is cured.

As illustrated inFIG.4D, the template1is then separated from the now-cured ultraviolet light-curable resist32.

As illustrated inFIG.4E, the substrate31can be etched using the patterned ultraviolet light-curable resist32as a mask. As a result, a pattern on the template1can be formed on the substrate31and transferred thereto. When the film39is a polysilicon film or a metal film, a fine electrode pattern or wiring pattern can be formed therefrom. When the film39is an insulating film, a fine contact hole pattern or gate insulating film can be formed therefrom. When there is no film39t on the substrate31and an uppermost layer of the substrate is a semiconductor material, a fine element isolation trench or the like can be formed.

Next, the step illustrated inFIG.4Cwill be further described usingFIG.5.FIG.5is a view illustrating aspects of the method for producing a semiconductor device using the template1.

In nanoimprint lithography using the template1, the pattern surface14is pressed onto a transfer region35of the ultraviolet light-curable resist32on the substrate31. The transfer region35is then irradiated with the exposure light33, as illustrated inFIG.5. Between the source of the exposure light33and the template1, a light-shielding plate37having an opening38is provided. The template1is irradiated with the exposure light33that passes through the opening38.

During irradiation with the exposure light33, it is necessary to prevent leakage of ultraviolet light to a non-transfer region36adjacent to the transfer region35. If the leakage of ultraviolet light can be prevented, unintended curing of the ultraviolet light-curable resist32in the non-transfer region36can be prevented. The light-shielding plate37helps prevents the leakage of ultraviolet light. However, it is difficult to prevent all the leakage of ultraviolet light to the non-transfer region36with only the light-shielding plate37. This is because light is diffracted at the opening38and may spread outward with distance from the light-shielding plate37to the ultraviolet light-curable resist32. Also, the opening38of the light-shielding plate37is typically designed to be somewhat larger in size than the transfer region35in consideration of errors associated with the precision of attachment or alignment of various components. Thus, a part of the non-transfer region36will typically be irradiated with the exposure light absent some other intervention.

However, as illustrated inFIG.5, the material film15on the template1converts ultraviolet light contained in the exposure light33into visible light34. For example, ultraviolet light of the exposure source has a wavelength of 300 to 400 nm. Visible light34has a wavelength of 400 to 800 nm. The ultraviolet light-curable resist32is not substantially or at all cured by visible light wavelength. Therefore, the ultraviolet light-curable resist32in the non-transfer region36is not significantly cured. Accordingly, the transfer region35can be irradiated with the exposure light33including ultraviolet light, and the unintended curing of the ultraviolet light-curable resist32in the non-transfer region36due to leakage of ultraviolet light can be decreased.

It is generally preferable that the material film15be provided outside the region occupied by mesa structure13but also on the side surfaces of the mesa structure13. However, even if the material film15is not provided on the side surfaces so of the mesa structure13, beneficial effects can still be obtained.

The effects of an embodiment as compared with a comparative example will be described with reference toFIGS.6A,6B, and7.FIGS.6A and6Bare views illustrating a configuration of a template3according to the comparative example.FIG.6Ais a plan view of the template3according to the comparative example when viewed in the Z direction.FIG.6Bis a cross-sectional view of the template3taken along BB′ when viewed in the X direction. The template3is produced by processing a substrate11that is a quadrilateral shape when viewed in the Z direction. On the main surface12of the substrate11, a mesa structure13including a pattern surface14is provided. A light-shielding film45is formed at the periphery of the mesa structure13. Examples of a material of the light-shielding film45include a metallic material or a metal oxide, nitride, and/or oxynitride. Specific examples of a metal that can be used in the light-shielding film45include chromium (Cr), molybdenum (Mo), tantalum (Ta), tungsten (W), zirconium (Zr), and titanium (Ti).

FIG.7is a view illustrating a method for producing a semiconductor device using the template3according to the comparative example. As illustrated inFIG.7, the template3is irradiated with the exposure light33through a filter51and a light-shielding plate37having an opening38. The filter51is provided between the light source of the exposure light33and the light-shielding plate37, and converts the exposure light33into a monochromatic light53. The region that is irradiated with monochromatic light53is restricted by the light-shielding plate37. The region that is irradiated with the monochromatic light53is also restricted by the light-shielding film45on the template3. Only the ultraviolet light-curable resist32of the transfer region35is irradiated with the monochromatic light53. When the exposure light33is converted into monochromatic light53by the filter51, the angle at which the monochromatic light53is diffracted by the light-shielding plate37can be controlled/known. When the light-shielding film45is designed according to this angle, the leakage of ultraviolet light to the non-transfer region36can be more effectively prevented than otherwise. However, monochromatization using filter51decreases the light intensity of light reaching the transfer region35. The decreased light intensity may require increases in the curing time of the ultraviolet light-curable resist32, and this may affect throughput.

This method also includes a position alignment step before the imprint step. The position alignment step uses a mark that is provided on a stage supporting the substrate31. In the position alignment step, the outer circumferential region of the mesa structure13is irradiated with visible light such as red light. However, the mark provided on the stage is difficult to be observed due to the presence of the light-shielding film45, and the precision of position alignment may be decreased as a result.

In contrast, with the template1according to the embodiment, the material film15, which converts ultraviolet light into visible light, is provided covering the outer circumferential region of the mesa structure13. Therefore, it is not necessary that the exposure light diffraction angle be controlled/known. Thus, no filter51is necessary. Without the filter51, the light intensity of ultraviolet light reaching the transfer region35can be improved. This makes it possible to shorten the curing time of the ultraviolet light-curable resist32and to improve the throughput. Also, since the material film15transmits visible light, the alignment mark provided on the stage is more easily observed for position alignment prior to imprinting. Thus, the precision in position alignment can be improved.