WO2009093698A4

WO2009093698A4 - Method for forming carbon nanotube-dispersed film and method for manufacturing semiconductor device

Info

Publication number: WO2009093698A4
Application number: PCT/JP2009/051092
Authority: WO
Inventors: 薫成田
Original assignee: 日本電気株式会社
Priority date: 2008-01-24
Filing date: 2009-01-23
Publication date: 2009-12-10
Also published as: JPWO2009093698A1; WO2009093698A1

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 of forming carbon nanotube dispersed film and method of manufacturing semiconductor device

The present invention relates to a method of manufacturing a carbon nanotube dispersed film applicable to a transistor, a sensor or the like, and a method of manufacturing a semiconductor device using the same.

A carbon nanotube has a tubular structure in which a two-dimensional graphene sheet composed of six-membered rings of carbon atoms is cylindrically wound, and the thin one is about 1 nm in diameter and long and several μm or more in length. is there.

Since semiconductor properties and metal properties are exhibited depending on the way of atomic arrangement, there is a growing expectation that carbon nanotubes will be applied to electronic devices such as transistors.

In particular, recently, a dispersion film of carbon nanotubes is formed by a coating method which is much lower in cost than a semiconductor process which is a manufacturing process of a normal MOS transistor, and a field effect transistor or device using this as a channel is formed. There have been attempts (see Patent Documents 1 to 3 and Non-patent Documents 1 to 4).

The advantage of the application method is not only the low cost but also the choice of the substrate on which the device is formed.

That is, the carbon nanotube dispersed film can be formed not only on a hard substrate such as a silicon substrate but also on a thin plastic or the like. In this case, it has characteristics that conventional electronic devices do not have, such as bendable electronic circuits and transparent electronic circuits, and has the possibility of becoming 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. Patent document 4 forms a uniform coating film by the 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 from high-temperature growth substrates to plastic and their use in thin-film transistors", Applied Physics Letters, Vol 86, pp. 243502, 2005. T. Takenobu, T. Takahashi, T. Kanbara, K. Tshkagoshi, Y. Aoyagi, Y. Iwasa, "High-performance transparent flexible flexible transistors using carbon nano tubefilms", 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 inkjet 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 showing an example of the change. FIG. 1A shows a state in which a solvent 302 in which carbon nanotubes 3011 are dispersed is dropped to form a carbon nanotube dispersed film on a plastic substrate 310 on which a metal electrode 311 and a metal electrode 312 are formed. .
FIG. 1 (b) shows a state in which the solvent in the droplet evaporates and the diameter of the droplet becomes smaller after a predetermined time has elapsed from the state of FIG. 1 (a). At this time, when the temperature of the atmosphere is room temperature, the viscosity of the solvent in the droplet is low, so that the convection of the solvent occurs and the movement of the carbon nanotube occurs. Most of the carbon nanotubes 3012 remain in the droplets, and the concentration of the carbon nanotubes rises, but the carbon nanotubes aggregate on the droplet end 3014 and the metal electrode end 3013 immediately after application. As time passes further, evaporation of the solvent proceeds, the droplet diameter further decreases, and the concentration of carbon nanotubes further increases.

Finally, as shown in FIG. 1 (c), the carbon nanotubes are concentrated and segregated and aggregated near the droplet end immediately after application, the metal electrode end, and the place where the droplet finally exists. A uniform dispersion film 3015 is formed.

An element having such a nonuniform dispersion film as a component, for example, a transistor having a nonuniform dispersion film in a channel, has a problem that the electrical characteristics are unstable and the 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 prominent when the concentration of carbon nanotubes in the solvent is low and the wettability between the solvent and the substrate is not good.

However, when the concentration of carbon nanotubes is increased, the on / off ratio, which is one of the performances of the transistor, is deteriorated, and therefore, the concentration can not be made higher than a certain concentration.

In order to improve the wettability between the solvent and the substrate, it is conceivable to add an additive, but in that case, the additive intrudes between the carbon nanotubes or between the carbon nanotubes and the electrode to increase the resistance, which is a worst case. In this case, the electrical continuity between the carbon nanotubes or between the carbon nanotubes and the electrode can not be obtained.

Moreover, the state at the time of applying the method disclosed by patent document 4 to application | coating of a carbon nanotube dispersion liquid is shown in FIG. In Patent Document 4, in order to form a carbon nanotube dispersed 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 drops are cooled and the solvent is frozen (Figure 2 (a)). Thereafter, the solvent is sublimated as shown in FIGS. 2 (b) and 2 (c) to precipitate carbon nanotubes. At this time, unlike the case shown in FIG. 2, since the convection in the droplets does not occur, the carbon nanotubes do not segregate and aggregate, and finally, as shown in FIG. 2 (d) The carbon nanotube dispersed film 4012 is formed.

However, when the solvent is sublimed as described above, the film is formed such that the portion supporting the carbon nanotubes is removed, so the film quality becomes very sparse and low in density. Such a sparse film has the problem that it is easily peeled off in the subsequent steps and the roughness is rough. In addition, there is a problem that the characteristics of the element formed by the sparse film are unstable and the variation is large. Furthermore, in the case of forming a transistor, there is a problem that the effect of the gate is less effective.

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

The present invention has been made in view of such problems, and regardless of the characteristics of the carbon nanotube dispersion and the type of the substrate, always, a method for forming a uniform and dense carbon nanotube dispersion film, and the dispersion film as a component An object of the present invention is to provide a method of manufacturing a semiconductor device having good electrical characteristics and small variations in characteristics.

In order to achieve the above object, according to a first aspect of the present invention, there is provided a step of applying, onto a substrate, a first carbon nanotube dispersion liquid in which carbon nanotubes are dispersed at a first concentration in a solvent. Cooling the droplets of the first carbon nanotube dispersion liquid to increase the viscosity of the solvent; evaporating the solvent to uniformly deposit carbon nanotubes to form precipitation nuclei; and carbon in the solvent Forming a coated film of a second carbon nanotube dispersion liquid in which the nanotubes are dispersed at a second concentration higher than the first concentration on the precipitation nuclei, and evaporating the solvent from the coated film of the second carbon nanotubes And a step of forming a dispersion film of carbon nanotubes. The present invention provides a method of forming a carbon nanotube dispersion film.

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

According to the present invention, regardless of the characteristics of the carbon nanotube dispersion and the type of the substrate, always, a uniform and dense carbon nanotube dispersion film and this dispersion film as a component have good electrical characteristics and dispersion of characteristics. A method of manufacturing a small semiconductor device can be provided.

In the present invention, first, a dispersion having a low concentration of carbon nanotubes is applied and cooled to increase the concentration of the solvent, thereby suppressing the movement of carbon nanotubes due to convection in the droplets, thereby By evaporating the solvent, the carbon nanotubes are deposited in the droplets while maintaining a uniform distribution. Next, a dispersion liquid with a high concentration of carbon nanotubes is applied to the same place, and the solvent is evaporated as it is in the liquid phase, and the carbon nanotubes deposited earlier are precipitated as nuclei, and a uniform and dense film is formed. Ru. The carbon nanotube concentration of the dispersion to be first applied to the substrate is a concentration at which uniform precipitation nuclei can be formed on the substrate, and the carbon nanotube concentration of the dispersion to be applied later is a concentration at which segregation of carbon nanotubes does not occur. is there.

An element having the carbon nanotube-dispersed film formed in this manner as a component 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 element can be easily designed.

A preferred embodiment of the present invention will be described.
FIG. 3A shows a state in which the droplet 102 of the dispersion liquid in which the carbon nanotubes 1101 are dispersed is applied on the plastic substrate 110 on which the metal electrode 111 and the metal electrode 112 are formed. The plastic of the substrate may be PET (PolyEthylene Telephthalate), PEN (PolyEthylene Naphthalate), or the like. As a solvent for the carbon nanotube dispersion liquid, one obtained by adding a surfactant to water or an organic solvent (such as dichloroethane or dimethylformamide) can be used. As the surfactant, those to which an anionic surfactant (such as sodium dodecylbenzene sulfonate (SDBS)) or a nonionic surfactant (such as Triton X) can be used.

A carbon nanotube dispersion liquid can be generated by adding a carbon nanotube to this solvent and performing ultrasonic treatment. The concentration of carbon nanotubes is a concentration capable of forming uniform precipitation nuclei on the substrate. For example, the concentration of carbon nanotubes at this time is 1 μg / ml (about 1 ppm).

Before applying the dispersion liquid, the substrate 110 and the

metal electrodes

111 and 112 are cooled (for example, about 0 ° C.) to a temperature (a temperature equal to or lower than the melting point of the solvent) to a viscosity at which the solvent does not cause convection. As a result, the viscosity of the droplet 102 is increased 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 to which the droplet is applied is lowered (for example, to about 0.1 atm) to evaporate the solvent of the droplet. FIG.3 (b), (c) has shown the state which evaporation advances. The carbon nanotubes in the droplets adhere to the substrate 110 and the

metal electrodes

111 and 112 in such a manner that the support of the solvent is lost. At this time, since the carbon nanotube is fixed, the carbon nanotube concentration in the droplet does not become high due to movement or segregation at the end of the metal electrode, and uniform and thin carbon as shown in FIG. The nanotube coating film 1012 is obtained as a precipitation nucleus.

FIG. 4 shows an atomic force micrograph showing the state of the carbon nanotube coated film 1012 when the dispersion liquid 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 carbon nanotubes is very low, and there are only two carbon nanotubes (at two locations indicated by arrows in the figure) in the field of view Density is insufficient as precipitation nuclei). On the other hand, in FIG. 5, an atomic force representing the state of the carbon nanotube coated film 1012 when the 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. The photomicrograph is shown. In the illustrated example, the carbon nanotubes are uniformly dispersed and in a good state as precipitation nuclei.
Further, FIG. 6 shows an atomic force micrograph showing the state of the carbon nanotube coated film 1012 when the dispersion liquid 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 illustrated example, the density of the carbon nanotubes is high, and many carbon nanotubes overlap each other and aggregate, so they are not in a preferable state as precipitation nuclei.
From the above, in the present embodiment, the carbon nanotube concentration capable of forming uniform precipitation nuclei on the substrate is in the concentration range of 1 ppb to 1 ppm.

Next, as shown in FIG. 7A, 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 portion as the carbon nanotube film formed in the previous step The solution 1013 is applied, and this time the solvent is evaporated in the liquid phase (Fig. 7 (b), (c)). The concentration of the carbon nanotube dispersion 1013 is a concentration that does not cause segregation of carbon nanotubes. At this time, the carbon nanotubes 1022 move by convection inside the droplets, and are precipitated with the carbon nanotubes 1011 deposited in the previous step as nuclei, and a uniform and dense film 1014 is formed (FIG. 7 (d)). By raising the temperature of the substrate (for example, 50 ° C.) at the time of coating in the later stage, convection can be promoted to shorten the time required for the evaporation of the solvent.

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

metal electrodes

211 and 212 to be source and drain electrodes are formed on the plastic substrate 210 later. The plastic substrate 210 is previously cooled 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 ultrasonication was applied by a dispenser device, an inkjet device, or the like. Since the applied droplets 202 are frozen and solidified in a circular shape, next, by making the atmosphere of the substrate vacuum, the solvent in the liquid is sublimated, and uniform thin carbon nanotube precipitation nuclei are obtained.

Next, the temperature of the plastic substrate 210 is raised to 50 ° C., and a carbon nanotube dispersion having a concentration of 5 ppm is applied onto the precipitation nuclei in the same manner as above, and then the solvent is evaporated to disperse the uniform and dense carbon nanotubes. The membrane 201 was obtained. Since the carbon nanotube dispersed film 201 is in electrical contact with the

metal electrodes

211 and 212 to be the source electrode and the drain electrode and electrically connected, the mat formed of carbon nanotubes formed between the

metal electrodes

211 and 212 is used. Networks (films of precipitated carbon nanotubes in a network) form the channels of the transistors. Thereafter, for example, a thin film 203 of parylene is formed to form a gate insulating film. At this time, since the film quality of the carbon nanotube dispersed film is dense, it does not peel off, and since the roughness is small, a gate insulating film having a good withstand voltage can be formed.

After that, a metal gate electrode 213 was formed to complete a field effect transistor. Although the concentration of the carbon nanotube dispersion to be applied in the later step is a concentration that does not cause segregation of carbon nanotubes, it is as thin as 1 ppm to 10 ppm, so the transistor on / off ratio is high and the coating film is uniform, so the characteristics vary. Can be formed.

The above embodiment is an example of a preferred embodiment of the present invention, and the present invention is not limited to this, and various modifications are possible.

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

It is a figure which shows the formation method of the carbon nanotube dispersion | distribution film | membrane 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 the preferable embodiment of this invention. It is an atomic force micrograph showing the state of the carbon nanotube coating film at the time of applying the dispersion liquid whose carbon nanotube density | concentration is less than 1 ppb on a board | substrate, and evaporating a solvent. It is an atomic force microscope picture showing the state of the carbon nanotube coating film at the time of applying the dispersion liquid in which carbon nanotube concentration is 1 ppb to 1 ppm on a substrate, and evaporating the solvent. It is an atomic force micrograph showing the state of the carbon nanotube coating film at the time of applying the dispersion liquid whose carbon nanotube density | concentration is 1 ppm or more to a board | substrate, and evaporating a solvent. It is a figure which shows the flow of the latter step of the formation method of the carbon nanotube dispersion film which concerns on the suitable embodiment of this invention. It is a figure which shows the channel of the transistor which applied the carbon nanotube dispersion film which concerns on this invention.

Explanation of sign

102, 202 Droplet 110

Substrate

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

Gate electrode

1011, 1022 Carbon nanotube 1012 Carbon nanotube coated film 1013 Carbon nanotube dispersed solution 1014 film

Claims

Applying a first carbon nanotube dispersion liquid in which carbon nanotubes are dispersed at a first concentration in a solvent on a substrate;
Cooling the applied droplets of the first carbon nanotube dispersion to increase the viscosity of the solvent;
Uniformly depositing carbon nanotubes by evaporating the solvent to form precipitated nuclei;
Forming a coating film of a second carbon nanotube dispersion liquid in which carbon nanotubes are dispersed at a second concentration higher than the first concentration in a solvent on the precipitation nuclei;
And evaporating the solvent from the second carbon nanotube coating film to form a carbon nanotube dispersion film.
The method for forming a carbon nanotube-dispersed 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-dispersed film according to claim 1 or 2, wherein the cooling temperature of the first carbon nanotube dispersion liquid is equal to or lower than the melting point of a solvent.
The carbon nanotube dispersion according to any one of claims 1 to 3, wherein the step of evaporating the solvent from the coating film of the second carbon nanotube to form a dispersion film of carbon nanotubes is performed under a reduced pressure atmosphere. Method of film formation.
The process according to any one of claims 1 to 4, characterized in that the step of evaporating the solvent from the second carbon nanotube coated film to form a dispersed film of carbon nanotubes is performed under a temperature environment higher than normal temperature. Of forming a carbon nanotube dispersed film of
The said 1st, 2nd carbon nanotube dispersion liquid is formed by performing an ultrasonication to the solvent which added the carbon nanotube of the predetermined amount, Method of forming a carbon nanotube dispersed film.
The first concentration is a concentration capable of forming uniform precipitation nuclei on the substrate, and the second concentration is a concentration at which segregation of carbon nanotubes does not occur. 6. A method of forming a carbon nanotube dispersed film according to any one of 6.
8. The method 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 of manufacturing a semiconductor device using the method of forming a carbon nanotube dispersed film according to any one of claims 1 to 8,
An electrode connected to the dispersed film of carbon nanotubes is formed on the substrate in advance.
10. The method of manufacturing a semiconductor device according to claim 9, wherein the electrodes are formed on the substrate at intervals, and a dispersion film of the carbon nanotubes is formed in a region sandwiched between the electrodes.
11. The method of manufacturing a semiconductor device according to claim 10, wherein another electrode is formed on the dispersed film of carbon nanotubes.