WO2009093698A1

WO2009093698A1 - Method for forming carbon nanotube-dispersed film and method for manufacturing semiconductor device

Info

Publication number: WO2009093698A1
Application number: PCT/JP2009/051092
Authority: WO
Inventors: Kaoru Narita
Original assignee: Nec Corporation
Priority date: 2008-01-24
Filing date: 2009-01-23
Publication date: 2009-07-30
Also published as: WO2009093698A4; JPWO2009093698A1

Abstract

A method for forming a uniform and dense carbon nanotube-dispersed film irrespective of the characteristics of the carbon nanotube-dispersed liquid and the type of substrate, and a method for manufacturing a semiconductor device having excellent electrical characteristics with less variation in characteristics are provided. The method for forming the carbon nanotube-dispersed film includes steps of coating a substrate (110) with a carbon nanotube-dispersed liquid containing carbon nanotubes (1101) dispersed in a solvent, cooling droplets (102) of the carbon nanotube-dispersed liquid to increase the viscosity of the solvent, evaporating the solvent to uniformly precipitate the carbon nanotubes (1101) and form a carbon nanotube coating film (1012), forming, on the carbon nanotube coating film (1012), a coating film of a carbon nanotube-dispersed liquid (1013) with higher carbon nanotube concentration, and evaporating the solvent from the coating film of carbon nanotube-dispersed liquid (1013) to form a film having dispersed carbon nanotubes (1022).

Description

Method for forming carbon nanotube dispersed film and method for manufacturing semiconductor device

The present invention relates to a method for producing a carbon nanotube dispersion film applicable to transistors, sensors, and the like, and a method for producing a semiconductor element using the same.

A carbon nanotube has a structure in which a two-dimensional graphene sheet composed of a six-membered ring of carbon atoms is wound in a cylindrical shape, and is a thin tube-like material with a diameter of about 1 nm for a thin one and a length of several μm or more is there.

Because of its atomic arrangement, it exhibits both semiconductor and metallic properties, so there are increasing expectations that carbon nanotubes will be applied to electronic devices such as transistors.

In particular, recently, a carbon nanotube dispersion film is formed by a coating method, which is far less expensive than a semiconductor process, which is a manufacturing process of a normal MOS transistor, and a field effect transistor or element using this as a channel is formed. (See Patent Documents 1 to 3 and Non-Patent Documents 1 to 4).

The advantage of the coating method is not only the low cost, but also the choice of the substrate on which the element is formed.

That is, the carbon nanotube dispersion film can be formed not only on a hard substrate such as a silicon substrate but also on a thin plastic. In this case, it has characteristics that are not found in conventional electronic devices, such as an electronic circuit that can be bent and a transparent electronic circuit, and has the potential to become a breakthrough in future IT terminal device technology.

Patent document 4 is mentioned as a technique relevant to forming a uniform coating film by the apply | coating method. In Patent Document 4, a uniform coating film is formed by an inkjet coating method.
JP 2006-8861 A JP 2005-150410 A JP 2006-73774 A JP 2006-281189 A ES Show, J. P. Novak, PM Campbell, and D. Park, "Random networks of carbon nanotubes as an electronic material", Applied Physics Letters, Vol. 82, No. 13, pp. 2145-2147, 2003. E. Artukovic, M. Kaempgen, DS Hecht, S. Roth, and G. Gruner, "Transparent and Flexible Carbon Nanotube Transistors", Nano Letters, Vol. 5, No. 4, pp. 757-760, 2005. S.-H. Hur, O Ok Park, JA Rogers, "Extreme bendability of single-walled carbon nanotube networks transferred from high-temperature growth substrates to plastic and their use in thin-film transistors", Applied Physics Letters, Vol86, pp 243502, 2005. T. Takenobu, T. Takahashi, T. Kanbara, K. Tshkagoshi, Y. Aoyagi, Y. Iwasa, "High-performance transparent flexible transistors using carbon nanotubefilms", Applied Physics Letters, Vol. 88, pp.033511, 2006.

In order to form a dispersion film of carbon nanotubes on a substrate by a coating method, a method is adopted in which carbon nanotubes are dispersed in a solvent and the dispersion is applied to a predetermined position of the substrate by a dispenser device or an ink jet device. . At this time, the state changes depending on the type of solvent and substrate, the concentration of carbon nanotubes, the presence or absence of additives in the dispersion, and the like. FIG. 1 is a diagram illustrating an example of the change. FIG. 1A shows a state in which a solvent 302 in which carbon nanotubes 3011 are dispersed is dropped in order to form a carbon nanotube dispersed film on a plastic substrate 310 on which

metal electrodes

311 and 312 are formed. .
FIG. 1B shows a state in which a predetermined time has elapsed from the state of FIG. 1A and the solvent in the droplets has evaporated to reduce the diameter of the droplets. At this time, when the temperature of the atmosphere is room temperature, since the viscosity of the solvent in the droplet is low, convection of the solvent occurs and the carbon nanotube moves. Most of the carbon nanotubes 3012 remain in the droplets and the concentration of the carbon nanotubes increases, but the carbon nanotubes aggregate at the droplet end 3014 and the metal electrode end 3013 immediately after coating. As the time elapses, the solvent evaporates, the droplet diameter further decreases, and the concentration of the carbon nanotubes further increases.

Eventually, as shown in FIG. 1 (c), the carbon nanotubes concentrate and segregate and aggregate near the end of the droplet immediately after coating, the end of the metal electrode, and the location where the droplet finally exists. A uniform dispersion film 3015 is formed.

An element having such a non-uniform dispersion film as a constituent element, for example, a transistor having a non-uniform dispersion film in a channel has a problem that electric characteristics are unstable and variation is large.

Furthermore, when the dispersion film is segregated, there is a problem that it is difficult to form an element at a desired position.

The situation as shown in FIG. 1 is noticeable when the concentration of carbon nanotubes in the solvent is low and the wettability between the solvent and the substrate is not good.

However, if the concentration of the carbon nanotube is increased, the on / off ratio, which is one of the performance of the transistor, is deteriorated, so that it cannot be increased beyond a certain concentration.

In addition, an additive may be added to improve the wettability between the solvent and the substrate, but in this case, the additive enters between the carbon nanotubes or between the carbon nanotubes and the electrode, resulting in an increase in resistance, which is the worst. In such a case, electrical conduction between the carbon nanotubes or between the carbon nanotubes and the electrode cannot be obtained.

FIG. 2 shows a state where the method disclosed in Patent Document 4 is applied to the application of the carbon nanotube dispersion. In Patent Document 4, in order to form a carbon nanotube dispersion film on a plastic substrate 410 on which a metal electrode 411 and a metal electrode 412 are formed, a dispersion liquid 402 in which carbon nanotubes 4011 are dispersed is applied by an inkjet method, The droplet is cooled and the solvent is frozen (FIG. 2 (a)). Thereafter, the solvent is sublimated as shown in FIGS. 2B and 2C to precipitate carbon nanotubes. In this case, unlike the case shown in FIG. 2, convection does not occur in the droplet, so that the carbon nanotubes do not segregate and aggregate, and finally, as shown in FIG. A carbon nanotube dispersion film 4012 is formed.

However, when the solvent is sublimated as described above, the film is formed so that the portion supporting the carbon nanotubes is removed, so that the film quality is very sparse and low in density. Such a sparse film has a problem that it is easily peeled off in a subsequent process or is rough. Further, there is a problem that the characteristics of an element formed by a sparse film are unstable and have large variations. Furthermore, when a transistor is formed, there is a problem that the effect of the gate becomes difficult to work.

As described above, it has been difficult to achieve both the formation of a uniform and dense carbon nanotube dispersion film and the formation of an element having good characteristics.

The present invention has been made in view of the above problems, and always provides a method for forming a uniform and dense carbon nanotube dispersion film, regardless of the characteristics of the carbon nanotube dispersion liquid and the type of the substrate, and the dispersion film as a constituent element. It is an object of the present invention to provide a method for manufacturing a semiconductor element having favorable electrical characteristics and small variations in characteristics.

In order to achieve the above object, as a first aspect of the present invention, a step of applying a first carbon nanotube dispersion liquid in which carbon nanotubes are dispersed in a solvent at a first concentration on a substrate is applied. A step of cooling the droplets of the first carbon nanotube dispersion liquid to increase the viscosity of the solvent, a step of depositing the carbon nanotubes uniformly by evaporating the solvent to form precipitation nuclei, and a carbon in the solvent. Forming a coating film of the second carbon nanotube dispersion liquid in which the nanotubes are dispersed at a second concentration higher than the first concentration on the precipitation nucleus, and evaporating the solvent from the coating film of the second carbon nanotube. And a step of forming a carbon nanotube dispersion film. A method of forming a carbon nanotube dispersion film is provided.

In order to achieve the above object, the present invention provides, as a second aspect, a method for manufacturing a semiconductor device using the method for forming a carbon nanotube dispersion film according to the first aspect of the present invention. The present invention provides a method for manufacturing a semiconductor device, characterized in that an electrode connected to a carbon nanotube dispersion film is formed in advance.

According to the present invention, regardless of the characteristics of the carbon nanotube dispersion and the type of the substrate, the carbon nanotube dispersion film is always uniform and dense, and the electrical characteristics are good with the dispersion film as a constituent element, resulting in variations in characteristics. A manufacturing method of a small semiconductor element can be provided.

In the present invention, first, a dispersion liquid having a low carbon nanotube concentration is applied and cooled, and the concentration of the solvent is increased to suppress the movement of the carbon nanotubes due to convection in the droplets. By evaporating the solvent, the carbon nanotubes are deposited in the droplets while maintaining a uniform distribution. Next, when a dispersion with a high concentration of carbon nanotubes is applied to the same location and the solvent is evaporated while in the liquid phase, the carbon nanotubes previously deposited are deposited as nuclei, forming a uniform and dense film. The The concentration of carbon nanotubes in the dispersion liquid first applied to the substrate is a concentration at which uniform precipitation nuclei can be formed on the substrate, and the concentration of carbon nanotubes in the dispersion liquid applied later is such that segregation of carbon nanotubes does not occur. is there.

An element using the carbon nanotube dispersion film formed as described above as a constituent element has good electrical performance and little variation in characteristics, so that the yield can be improved. In addition, since the dispersion film has no segregation and is uniform and dense, it is not necessary to consider non-uniformity, so that the device design is easy.

A preferred embodiment of the present invention will be described.
FIG. 3A shows a state in which a droplet 102 of a dispersion liquid in which carbon nanotubes 1101 are dispersed is applied on a plastic substrate 110 on which a metal electrode 111 and a metal electrode 112 are formed. As the substrate plastic, PET (PolyEthylene Telephthalate), PEN (PolyEthylene Naphthalate), or the like can be used. As the solvent for the carbon nanotube dispersion liquid, water or an organic solvent (dichloroethane, dimethylformamide, etc.) added with a surfactant can be used. As the surfactant, an anionic surfactant (Sodium DodecylBenzene Sulfonate (SDBS) or the like) or a nonionic surfactant (Triton X or the like) can be used.

A carbon nanotube dispersion can be produced by adding carbon nanotubes to this solvent and subjecting it to ultrasonic treatment. The concentration of the carbon nanotube is set to a concentration at which uniform precipitation nuclei can be formed on the substrate. For example, the concentration of carbon nanotubes at this time is 1 μg / ml (about 1 ppm).

Before applying the dispersion, the substrate 110 and the

metal electrodes

111 and 112 are cooled to a temperature (a temperature below the melting point of the solvent) at which the solvent does not cause convection (for example, about 0 ° C.). As a result, the viscosity of the droplet 102 becomes high at the moment of application, and the movement of the carbon nanotube due to the convection of the solvent inside the droplet can be suppressed.

Next, the atmospheric pressure of the substrate on which the droplet is applied is lowered (for example, to about 0.1 atmosphere), and the solvent of the droplet is evaporated. FIGS. 3B and 3C show a state in which evaporation proceeds. The carbon nanotubes in the droplets adhere to the substrate 110 and the

metal electrodes

111 and 112 in such a way that the solvent is no longer supported. At this time, since the carbon nanotubes are fixed, the concentration of carbon nanotubes in the droplets does not increase due to movement, and segregation does not occur at the end of the metal electrode. As shown in FIG. A nanotube coating film 1012 is obtained as a precipitation nucleus.

FIG. 4 shows an atomic force micrograph showing the state of the carbon nanotube coating film 1012 when a dispersion having a carbon nanotube concentration of less than 1 ppb is applied to the substrate 110 and the solvent is evaporated as described above. In the illustrated example, the density of the carbon nanotubes is very low, and there are only two carbon nanotubes in the field of view (in the two locations indicated by arrows in the figure). The density is insufficient as a precipitation nucleus. On the other hand, FIG. 5 shows an atomic force representing the state of the carbon nanotube coating film 1012 when a dispersion having a carbon nanotube concentration of 1 ppb to 1 ppm is applied to the substrate 110 and the solvent is evaporated as described above. A micrograph is shown. In the example shown in the figure, the carbon nanotubes are uniformly dispersed and are in good condition as precipitation nuclei.
Further, FIG. 6 shows an atomic force micrograph showing the state of the carbon nanotube coating film 1012 when a dispersion having a carbon nanotube concentration of 1 ppm or more is applied to the substrate 110 and the solvent is evaporated as described above. . In the example shown in the drawing, the density of carbon nanotubes is high, and many carbon nanotubes overlap each other and are aggregated, which is not a preferable state as precipitation nuclei.
From the above, in this embodiment, the concentration of carbon nanotubes capable of forming uniform precipitation nuclei on the substrate is set to a concentration range of 1 ppb to 1 ppm.

Next, as shown in FIG. 7 (a), the carbon nanotube dispersion having a higher concentration (for example, a concentration of 5 μg / ml (about 5 ppm)) than that previously applied to the same location as the carbon nanotube film formed in the previous step. Liquid 1013 is applied, and the solvent is evaporated in this liquid state (FIGS. 7B and 7C). The concentration of the carbon nanotube dispersion liquid 1013 is a concentration that does not cause segregation of the carbon nanotubes. At this time, the carbon nanotubes 1022 move due to the convection inside the droplets, and the carbon nanotubes 1011 deposited in the previous stage are deposited as nuclei, and a uniform and dense film 1014 is formed (FIG. 7D). By increasing the temperature of the substrate (for example, 50 ° C.) during subsequent application, convection is promoted, and the time required for solvent evaporation can be shortened.

FIG. 8 shows an example in which the carbon nanotube dispersion film according to the present invention is applied to a channel of a transistor. 8A is a plan view, and FIG. 8B is a cross-sectional view taken along the line A-A ′ of FIG. 8A. In FIG. 8B,

metal electrodes

211 and 212 to be source and drain electrodes later are formed on the plastic substrate 210, respectively. In addition, the plastic substrate 210 is cooled in advance to about −20 ° C., which is a temperature below the melting point of the solvent.

Here, 1 ppm of carbon nanotubes was added to water to which SDBS was added, and a solution dispersed by ultrasonic treatment was applied by a dispenser device or an inkjet device. Since the coated droplet 202 was frozen in a circular shape and solidified, a uniform and thin carbon nanotube precipitation nucleus was obtained by sublimating the solvent in the liquid state with the substrate atmosphere in a vacuum state.

Next, the temperature of the plastic substrate 210 is raised to 50 ° C., a carbon nanotube dispersion liquid having a concentration of 5 ppm is applied onto the precipitation nuclei by the same method as described above, and then the solvent is evaporated, thereby dispersing the carbon nanotubes uniformly and densely. A film 201 was obtained. Since the carbon nanotube dispersion film 201 is electrically connected to and electrically connected to the

metal electrodes

211 and 212 serving as the source electrode and the drain electrode, the carbon nanotube dispersed film 201 is a mat made of carbon nanotubes formed between the

metal electrodes

211 and 212. Network (film of carbon nanotubes deposited in a net shape) forms the channel of the transistor. Thereafter, for example, a thin film 203 of parylene was formed to obtain a gate insulating film. At this time, since the film quality of the carbon nanotube dispersion film was dense, it was not peeled off, and since the roughness was small, a gate insulating film with good withstand voltage could be formed.

Thereafter, a metal gate electrode 213 was formed to complete a field effect transistor. The concentration of the carbon nanotube dispersion applied in the subsequent stage is a concentration at which segregation of the carbon nanotube does not occur, but it is as thin as 1 to 10 ppm, so the on / off ratio of the transistor is high and the coating film is uniform, resulting in variations in characteristics. A field effect transistor with a small number of layers was formed.

In addition, the said embodiment is an example of suitable implementation of this invention, This invention is not limited to this, A various deformation | transformation is possible.

This application claims priority based on Japanese Patent Application No. 2008-014037 filed on January 24, 2008, the entire disclosure of which is incorporated herein.

It is a figure which shows the formation method of the carbon nanotube dispersion film by the apply | coating method. It is a figure which shows the formation method of the carbon nanotube dispersion | distribution film | membrane disclosed by patent document 4. FIG. It is a figure which shows the flow of the front | former stage of the formation method of the carbon nanotube dispersion | distribution film | membrane which concerns on suitable embodiment of this invention. It is an atomic force microscope photograph showing the state of a carbon nanotube coating film when a dispersion liquid having a carbon nanotube concentration of less than 1 ppb is applied to a substrate and the solvent is evaporated. It is an atomic force microscope photograph showing the state of the carbon nanotube coating film when a dispersion liquid having a carbon nanotube concentration of 1 ppb to 1 ppm is applied to a substrate and the solvent is evaporated. It is an atomic force microscope photograph showing the state of a carbon nanotube coating film when a dispersion liquid having a carbon nanotube concentration of 1 ppm or more is applied to a substrate and the solvent is evaporated. It is a figure which shows the flow of the latter stage of the formation method of the carbon nanotube dispersion | distribution film | membrane which concerns on suitable embodiment of this invention. It is a figure which shows the channel of the transistor which applied the carbon nanotube dispersion | distribution film | membrane which concerns on this invention.

Explanation of symbols

102, 202 Droplet 110

Substrate

111, 112, 211, 212 Metal electrode 201 Carbon nanotube dispersion film 203 Thin film 210 Plastic substrate 213

Gate electrode

1011, 1022 Carbon nanotube 1012 Carbon nanotube coating film 1013 Carbon nanotube dispersion liquid 1014 Film

Claims

Applying a first carbon nanotube dispersion liquid in which carbon nanotubes are dispersed in a solvent at a first concentration on a substrate;
Cooling the applied droplets of the first carbon nanotube dispersion to increase the viscosity of the solvent;
A step of uniformly depositing carbon nanotubes by evaporating a solvent to form a precipitation nucleus;
Forming a coating film of a second carbon nanotube dispersion liquid in which carbon nanotubes are dispersed in a solvent at a second concentration higher than the first concentration on the precipitation nuclei;
And a method of forming a carbon nanotube dispersion film by evaporating a solvent from the second carbon nanotube coating film.
2. The method of forming a carbon nanotube dispersion film according to claim 1, wherein the solvent contains at least one of water and an organic solvent and a surfactant.
The method for forming a carbon nanotube dispersion film according to claim 1 or 2, wherein the cooling temperature of the first carbon nanotube dispersion liquid is not higher than the melting point of the solvent.
The carbon nanotube dispersion according to any one of claims 1 to 3, wherein the step of evaporating the solvent from the second carbon nanotube coating film to form a carbon nanotube dispersion film is performed in a reduced-pressure atmosphere. Method for forming a film.
5. The step of evaporating a solvent from the second carbon nanotube coating film to form a carbon nanotube dispersion film is performed in a temperature environment of room temperature or higher. 6. Of forming a carbon nanotube dispersion film.
The said 1st, 2nd carbon nanotube dispersion liquid is formed by performing an ultrasonic treatment to the solvent which added the predetermined amount carbon nanotube, The one of Claim 1 to 5 characterized by the above-mentioned. A method of forming a carbon nanotube dispersion film.
The first concentration is a concentration at which uniform precipitation nuclei can be formed on the substrate, and the second concentration is a concentration at which segregation of carbon nanotubes does not occur. 7. The method for forming a carbon nanotube dispersed film according to any one of 6 above.
The method of forming a carbon nanotube dispersion film according to claim 7, wherein the first concentration is a concentration between 1 ppb and 1 ppm, and the second concentration is a concentration of 1 ppm or more.
A method for manufacturing a semiconductor device using the method for forming a carbon nanotube dispersion film according to claim 1,
An electrode connected to the carbon nanotube dispersion film is formed on the substrate.
10. The method of manufacturing a semiconductor element according to claim 9, wherein the electrodes are formed on the substrate with a space therebetween, and the carbon nanotube dispersion film is formed in a region sandwiched between the electrodes.
11. The method of manufacturing a semiconductor device according to claim 10, further comprising forming another electrode on the carbon nanotube dispersion film.