KR101532883B1 - Method of manufacturing a transition metal dichalcogenide thin layer - Google Patents

Abstract

A method to manufacture a transition metal dichalcogenide thin layer comprises the steps of: preparing a mixed solvent including dimethylformamide, alkylamine, and amino-alcohol and coating a solution including a precursor of a transition metal dichalcogenide; coating the coating solution on a processed substrate; and performing a thermal-process for the coated thin layer. The precursor includes molybdenum or tungsten. The content of alkylamine for a 100 weight of dimethylformamide is 50-200 weight. The content of the amino-alcohol is 16-40 weight.

Description

TECHNICAL FIELD [0001] The present invention relates to a method of forming a thin film of a transition metal dicalcogenide,

The present invention relates to a method for forming a thin film of a transition metal decalcogenide, and a method for forming a thin film of a transition metal decalcogenide for a semiconductor device.

Since two-dimensional materials are relatively easy to fabricate complex structures relative to one-dimensional materials, they are attracting attention as materials for next-generation nano-electronic devices. In particular, graphene has been studied in many fields as a two-dimensional material having various physical properties and high electron mobility.

However, graphene has a disadvantage that it does not have a band gap necessary for an electronic device such as a transistor. Since graphene has a complicated fabrication process for an electronic device to have a band gap, research on a two-dimensional material having a band gap has been actively conducted in recent years. As such two-dimensional material, there is a transition metal dichalcogenide (TMD) such as molybdenum disulfide (MoS ₂ ).

TMD is manufactured by chemical vapor deposition (CVD) or coating method, but it is difficult to obtain a uniform thin film over a large area.

SUMMARY OF THE INVENTION The present invention has been made to solve such conventional problems, and one object of the present invention is to provide a method of forming a thin film of transition metal decalcogenide which forms a uniform thin film over a large area.

According to an aspect of the present invention, there is provided a method of forming a thin film of transition metal decalcogenide according to an embodiment of the present invention. A coating solution containing a mixed solvent comprising dimethylformamide, an alkylamine and an amino alcohol, and a precursor of a transition metal dicalcogenide is prepared, spin-coating the coating solution on a substrate to be processed, The coated thin film is heat treated to form a transition metal decalcogenide thin film.

In one embodiment, the alkylamine and the aminoalcohol may each independently comprise an alkyl group having from 1 to 5 carbon atoms.

In one embodiment, the precursor may comprise molybdenum or tungsten. At this time, the precursor may include ammonium tetrathiomolybdate or ammonium tetrathiotungstate.

In one embodiment, for 100 parts by weight of dimethylformamide, the alkylamine content may be 50-200 parts by weight, and the aminoalcohol content may be 16-40 parts by weight.

In one embodiment, the surface of the substrate to be processed may be oxygen plasma treated before spin-coating the substrate.

In one embodiment, the annealing may include a first anneal at 400 ° C to 500 ° C and a second anneal at 900 ° C to 1,100 ° C. At this time, the pre-annealing may be further performed at 100 ° C to 200 ° C before the first annealing step.

According to the method for forming a thin film of transition metal dicalcogenide of the present invention, the precursor of the transition metal dicalcogenide compound is dissolved in a mixed solvent containing an alkylamine and an amino alcohol to increase the solubility of the precursor and chemically stabilize the coating solution .

In addition, by performing surface treatment on the substrate to be treated, the coating solution can be uniformly and stably spin-coated to form a transition metal decalcogenide thin film.

1 is a flowchart illustrating a method of forming a thin film of transition metal dicalcogenide according to the present invention.
2 is an optical microscope photograph of the thin film of transition metal decalcogenide prepared according to Example 1 of the present invention and the thin film prepared according to Comparative Examples 1 and 2. FIG.
3 is a view for explaining the characteristics of an electronic device including a transition metal decalcaneide thin film produced according to the second embodiment of the present invention.
4 is a view for explaining the characteristics of the transition metal decalcane thin film produced according to the third embodiment of the present invention.
5 is a diagram for explaining optical characteristics of a transition metal decalcogenide thin film.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and similarities. It is to be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but on the contrary, is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the term "comprises" or "having" is intended to designate the presence of stated features, elements, etc., and not one or more other features, It does not mean that there is none.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

1 is a flowchart illustrating a method of forming a thin film of transition metal dicalcogenide according to the present invention.

Referring to FIG. 1, a substrate to be coated with a thin film of transition metal decalcane is cleaned (step S110).

The substrate to be processed may be a silicon wafer. At this time, a silicon oxide film and / or a silicon nitride film having a thickness of several tens to several hundred nanometers may be formed on the silicon wafer.

The cleaning process may be performed using at least one cleaning solution. For example, the substrate to be processed can be cleaned using acetone, methanol, and deionized water, respectively.

The surface of the cleaned substrate is treated (step S120).

As the surface treatment process, an oxygen plasma can be used. The surface treatment process may be a secondary cleaning process that is performed using a plasma subsequent to a primary cleaning process using a cleaning solution. When the coating solution is spin-coated thereon through surface treatment using oxygen plasma, adhesion with the coating solution can be improved. For example, the surface treatment process can be performed by providing an oxygen plasma of about 50 W to the substrate to be treated for about 10 seconds.

The coating solution is spin-coated on the surface-treated substrate (step S130).

The coating solution is a solution in which a precursor of a transition metal decalcogenide compound as a solute is dissolved in a mixed solvent. The precursor may be dissolved in the mixed solution through sonication.

The transition metal dicalcogenide compound may include molybdenum sulfide (MoS ₂ ) or tungsten sulfide (WS ₂ ), and ammonium tetrathiomolybdate may be used as a precursor of molybdenum sulfide. Examples of tungsten sulfide (Ammonium tetrathiotungstate) can be mentioned. The precursor is dissolved in the mixed solvent.

The mixed solvent includes dimehtylformamide (DMF), alkylamine, and aminoalcohol.

The alkylamine may improve the solubility of the precursor in the mixed solvent. The alkylamine may include an alkyl group having 1 to 5 carbon atoms. For example, the alkylamine may include methylamine, ethylamine, propylamine, butylamine, or pentylamine.

The aminoalcohol can control the viscosity of the entire mixed solvent and can function as a stabilizer for the coating solution. The aminoalcohol may include an alkyl group having 1 to 5 carbon atoms. For example, aminomethanol, aminoethanol, aminopropanol, aminobutanol or aminopentanol.

It is possible to maximize the uniformity of the coating layer formed by spin-coating by adding alkylamine and amino alcohol to dimethylformamide, and even if the coating layer is heat-treated at a high temperature after spin coating, cracks or voids void formation can be minimized.

In the mixed solvent, the alkylamine content may be 50-200 parts by weight and the amino alcohol content may be 16-40 parts by weight based on 100 parts by weight of dimethylformamide. If the amount of the alkylamine is less than 50 parts by weight, the effect of increasing the solubility by the addition of the alkylamine hardly occurs. If the amount of the alkylamine is more than 200 parts by weight, the precursor is already dissolved in the mixed solvent. Is preferably contained in an amount of 50 to 200 parts by weight. If the content of the amino alcohol is less than 16 parts by weight, stabilization effect can not be expected. If the content of the amino alcohol is more than 40 parts by weight, the viscosity of the mixed solvent is increased and it is difficult to form a uniform coating layer in the coating process The content of the aminoalcohol is preferably 16 to 40 parts by weight. For example, the weight ratio of dimethylformamide, the alkylamine, and the aminoalcohol in the mixed solvent may be 1: 1: 1.2.

The coating solution can be spin-coated by being dropped while being dropped on the surface-treated substrate to be treated. For example, the coating solution may be spin-coated at a rotation speed of about 3,000 rpm for about 30 minutes.

The thin film coated with the coating solution, the coating layer, is then subjected to heat treatment (step S140).

Through the heat treatment process, a transition metal decalcogenide compound can be formed from the precursor. In the heat treatment step, the transition metal dicalcogenide compound may have a high crystallinity and stoichiometrically stable structure, MS ₂ (wherein M represents Mo or W).

The heat treatment process may include two annealing steps performed at different temperatures. Before the heat treatment process, a pre-annealing step may be further performed. The pre-annealing can be carried out at a temperature of about 150 ° C in air conditions. At this time, residual organic components and / or solvents may be removed, and most of the solvent may then be removed.

The primary annealing can be performed at a temperature of about 450 < 0 > C. At this time, the primary annealing can be performed under an argon (Ar) / hydrogen (H ₂ ) atmosphere at a pressure of about 0.8 torr, and a flow ratio of argon and hydrogen is about 3: . In the primary annealing, the solvents that have not been removed in the pre-annealing are removed and a transition metal dicalcogenide compound is formed. The first annealing substantially forms a transition metal decalcogenide compound to form a transition metal decalcogenide thin film. That is, in the first annealing, the reaction as shown in the following reaction formula 1 can be performed.

[Reaction Scheme 1]

(NH ₄ ) ₂ MS ₄ + H ₂ ? 2 NH ₃ + 2H ₂ S + MS ₂

In Scheme 1, M represents molybdenum (Mo) or tungsten (W).

The secondary annealing is performed at a higher temperature than the primary annealing. In the first annealing, most of the transition metal reacts with sulfur (S) to form the transition metal decalcogenide, but secondary annealing can be performed to further improve the crystallinity of the transition metal decalcogenide thin film.

The secondary annealing can be performed at a temperature of about 1,000 ° C. At this time, the secondary annealing can be performed under an argon (Ar) atmosphere and can be performed under a pressure condition of about 0.88 Torr. In the secondary annealing, since the sulfur (S) atoms provided by the heated sulfur (S) powder are abundant in the state where only argon, which is an inert gas, exists, the degree of crystallization can be increased by sulfiding all the uncrystallized transition metals.

Though not shown in FIG. 1, the heat-treated thin film can be transferred from the substrate to be processed to any other substrate. For example, the optional substrate may be hafnium oxide (HfO ₂ ) / silicon substrate or polyethylene terephthalate (PET).

For example, a polymer film such as poly (methylmethacrylate) or PMMA is used as a support, and the support and the substrate on which the heat-treated thin film is formed are adhered to each other and then dipped in an etching solution. The silicon oxide film disposed between the substrate and the transition metal decalcogenide thin film is removed and the transition metal decalcogenide thin film and the support can be separated from the substrate to be processed. The separated support and the transition metal decalcogenide thin film are coalesced with the arbitrary substrate, the support is removed using boiling acetone heated to about 80 ° C, and washed with isopropyl alcohol and deionized water A result obtained by disposing the transition metal decalcogenide thin film on the arbitrary substrate can be obtained.

Hereinafter, the present invention will be described in detail with reference to specific examples and comparative examples.

Preparation of Sample 1, Comparative Samples 1 and 2

As a substrate to be processed, a p-type silicon wafer of 2 inch size on which silicon oxide having a thickness of about 300 nm was formed on the surface was prepared. The silicon wafer was cleaned with acetone, methanol and deionized water and surface treated with a 50 W oxygen plasma for about 10 seconds.

Subsequently, 0.015 M of ammonium tetrathiomolybdate was mixed with a mixed solvent of dimethylformamide, butylamine and aminoethanol in a weight ratio of 1: 1: 0.2, and the prepared coating solution was subjected to the surface treatment Coated on a silicon wafer at a rotational speed of about 3,000 rpm for about 30 seconds.

After spin-coating, sample 1 according to the present invention was prepared by pre-annealing at about 150 캜 for about 10 minutes.

On the other hand, Comparative Sample 1 was prepared through substantially the same process as that of Sample 1 except that a coating solution containing only ammonium tetrathiomolybdate and dimethylformamide was used. Further, Comparative Sample 2 was prepared through substantially the same process as that of Sample 1 except that the coating solution prepared by mixing ammonium tetrathiomolybdate with dimethylformamide and aminoethanol (weight ratio 9: 1) was used. .

The surface of the prepared Sample 1, Comparative Samples 1 and 2 was observed under an optical microscope, and the photographs taken are shown in Fig.

Evaluation of surface characteristics

2 is an optical microscope photograph of the thin film of transition metal decalcogenide prepared according to Example 1 of the present invention and the thin film prepared according to Comparative Examples 1 and 2. FIG.

In FIG. 2, (a) is a photograph of Comparative Sample 1, (b) is a photograph of Comparative Sample 2, and (c) is a photograph of Sample 1 prepared according to the present invention.

Referring to FIG. 2 (a), when only dimethylformamide was used as a solvent for the coating solution, many cracks and voids were present on the surface of the thin film, and aminoethanol of Comparative Sample 2 When added, the voids decreased, but cracks continued to be present. On the other hand, unlike (a) and (b), it can be confirmed that a uniform thin film is coated on the surface of Sample 1 according to the present invention as shown in (c) without cracks or voids.

Manufacturing and Characterization of Electronic Devices

As a substrate to be processed, a p-type silicon wafer of 2 inch size on which silicon oxide having a thickness of about 300 nm was formed on the surface was prepared. The silicon wafer was cleaned with acetone, methanol and deionized water and surface treated with a 50 W oxygen plasma for about 10 seconds.

Subsequently, 0.015 M of ammonium tetrathiomolybdate was mixed with a mixed solvent of dimethylformamide, butylamine and aminoethanol in a weight ratio of 1: 1: 0.2, and the prepared coating solution was subjected to the surface treatment Coated on a silicon wafer at a rotational speed of about 3,000 rpm for about 30 seconds.

Spin-coated, pre-annealed at about 150 캜 for about 10 minutes, subjected to primary annealing for about 20 minutes at about 450 캜 (Ar / H ₂ atmosphere, flow ratio 3: 1, 0.8 torr) , 0.88 Torr) to form a molybdenum sulfide thin film.

The prepared decalcoginite thin film was transferred to a substrate on which a hafnium oxide thin film was formed, and had a channel length of about 10 탆 and a channel width of about 200 탆. The source / drain and gate electrodes were each formed of an Au / Ti double layer, An electronic device (MoS ₂ -FET) having a top-gate structure of hafnium oxide was produced. The change in the current according to the drain voltage and the gate voltage of the thus manufactured electronic device was measured and is shown in Fig.

3 is a view for explaining the characteristics of an electronic device including a transition metal decalcaneide thin film produced according to the second embodiment of the present invention.

3B is a graph showing a change in drain current according to a drain voltage applied to the drain electrode by gate voltage, and FIG. 3C is a graph showing a change in drain current according to a gate voltage when the drain voltage is 1 V Lt; RTI ID = 0.0 > 1 < / RTI >

Referring to FIG. 3 (b), each of the graphs shows a tendency that the current linearly increases as the drain voltage increases. As the gate voltage increases from 0 V to 10 V, the slope of the graph gradually increases. (c), it can be seen that when the drain voltage is constant at 1 V, the drain current increases as the gate voltage increases.

Evaluation of uniformity characteristics

A molybdenum sulfide thin film was formed on a silicon substrate in substantially the same manner as described above using the coating solution described above including 0.015 M ammonium tetrathiomolybdate on a 2 inch silicon wafer, The wafer was divided into 25 regions and Raman analysis was performed. The results are shown in Fig.

4 is a view for explaining the characteristics of the transition metal decalcane thin film produced according to the third embodiment of the present invention.

4 (a) is a graph showing 25 regions, (b) is a graph showing a frequency difference of 25 regions and a half width (FWHM) of E1 ² _g .

In Fig. 4 (b), the frequency difference is due to the in-plane vibration of molybdenum (Mo) and sulfur (S), the Raman peak of E1 ² _g and the out-of- Means the difference of Raman peaks of A _{1 g} by.

Referring to FIGS. 4A and 4B, it can be seen that the frequency difference in the 25 regions is almost constant, and the half width of E ¹ _2g is also constant. That is, it can be seen that a molybdenum sulfide thin film having a uniform crystal structure is formed in 25 regions.

Evaluation of transparency characteristics

0.0048 M of ammonium tetrathiomolybdate was mixed with a solvent mixture of dimethylformamide, butylamine and aminoethanol in a weight ratio of 1: 1: 0.2, and the coating solution prepared by sonication was applied onto a polyethylene terephthalate (PET) And spin-coated at a rotation speed of about 3,000 rpm for about 30 seconds. Spin-coated, pre-annealed at about 150 캜 for about 10 minutes, subjected to primary annealing for about 20 minutes at about 450 캜 (Ar / H ₂ atmosphere, flow ratio 3: 1, 0.8 torr) , 0.88 Torr) to form a molybdenum sulfide thin film (thin film sample 1).

Substantially the same coating solutions as the coating solution from which the thin film sample 1 was prepared were prepared, except that the concentration of tetrathiomolybdate was changed to 0.006 M, 0.008 M, 0.012 M and 0.024 M, respectively, Samples 2, 3, 4 and 5 were prepared. The transmittance according to the wavelength of each of the thin film samples 1 to 5 is measured and the transmittance according to the wavelength is shown in FIG.

5 is a diagram for explaining optical characteristics of a transition metal decalcogenide thin film.

Referring to FIG. 5, it can be seen that the transmittance of the molybdenum sulfide thin film decreases as the concentration of tetrathiomolybdate increases in the wavelength range of about 400 nm to 500 nm in the ultraviolet-visible light wavelength range.

The description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features presented herein.

Claims (8)

Preparing a coating solution comprising a mixed solvent comprising dimehtylformamide, an alkylamine and an amino alcohol, and a precursor of a transition metal decalcogenide;
Spin-coating the coating solution onto a substrate to be processed; And
Heat treating the coated thin film,
Wherein the precursor comprises molybdenum or tungsten,
Wherein the alkylamine content is 50 to 200 parts by weight and the amino alcohol content is 16 to 40 parts by weight relative to 100 parts by weight of dimethylformamide in the mixed solvent.
Method of forming transition metal dicalcogenide thin film.
The method according to claim 1,
The alkylamines and aminoalcohols are each independently
A method for forming a thin film of transition metal dicalcogenide, which comprises an alkyl group having 1 to 5 carbon atoms.
delete The method according to claim 1,
Wherein the precursor comprises an ammonium tetrathiomolybdate or an ammonium tetrathiotungstate. ≪ RTI ID = 0.0 > 11. < / RTI >
delete The method according to claim 1,
Further comprising oxygen plasma processing the surface of the substrate to be processed before spin-coating the substrate to be processed.
The method according to claim 1,
The step of heat-
First annealing at 400 ° C to 500 ° C; And
Lt; RTI ID = 0.0 > 900 C < / RTI > to < RTI ID = 0.0 > 1100 C. < / RTI >
8. The method of claim 7,
The step of heat-
And pre-annealing at 100 占 폚 to 200 占 폚 prior to the first annealing step. A method of forming a transition metal dicalcogneite thin film, comprising:

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