JP5590659B2 - Method and apparatus for producing organic single crystal thin film in magnetic field - Google Patents

Description

  The present invention relates to a method and apparatus for producing an organic single crystal thin film in a magnetic field.

  The current manufacturing process of inorganic semiconductor devices such as Si is expensive because it uses an expensive clean room and an expensive vacuum process apparatus. Further, since it is cut out from a single crystal ingot and processed, most of the base material is finally discarded, and the influence on the environment is a big problem.

  In order to put organic semiconductors currently in the research stage into practical use, a crystal growth method using a solution that dramatically improves the performance and enables film formation in the air at low cost is considered an essential issue.

Known crystal growth methods include vapor deposition and drop casting.
The crystal grain size of organic semiconductor thin films prepared by vapor deposition, drop-casting, etc. is as small as several to several tens of μm, and many grain boundaries are held between channels (about 50 μm), resulting in carriers. The mobility is lowered.

Further, the deposited film is a thin and homogeneous film, but it is disadvantageous for the formation of a single crystal thin film, and an expensive vacuum apparatus is required for producing the thin film, and the production process is difficult compared with the drop-cast method.
Although the drop cast film is easy to manufacture, it is difficult to achieve high carrier mobility because the film thickness is thick and uneven, and the grains overlap each other.

For these reasons, there is a current situation in which a manufacturing method that satisfies both the conditions of easy manufacturing and high carrier mobility cannot be established.
In the solution method, the solution can be applied only to a necessary portion, so that no material is wasted. In addition, an inexpensive and easy coating method such as an existing ink jet or dispenser can be applied. Then, after applying the solution, the organic semiconductor thin film having high TFT performance and durability is realized by performing single crystallization using the organic semiconductor thin film manufacturing method devised.

  This construction method is characterized by a construction method that simultaneously satisfies the requirements of cost reduction of manufacturing process, material cost reduction, high environmental resistance and high semiconductor performance.

The present invention can be manufactured at low cost without using an expensive clean room and expensive vacuum process equipment, has few waste parts, is environmentally friendly, and has high crystal quality. The purpose is to provide the law.
In addition, it is possible to provide a method for producing an organic single crystal thin film that is a low-temperature crystal growth method that enables film formation with a solution in an inexpensive atmosphere, reduces the incorporation of defects and impurities, and does not cause crystal cracking. Objective.
It is another object of the present invention to provide a method for producing an organic semiconductor single crystal thin film having a low manufacturing process cost, environmental performance, and improved semiconductor performance.

The invention according to claim 1, droplets of a solution containing an organic material in a solvent is provided on the substrate, and thickening the thinner the other end one end of the liquid droplet, the evaporation one end side of the solvent of the droplets together to precipitate crystals by, a preparation method of the organic single crystal thin film are sequentially deposited crystals by moving the thin portion having a reduced end of the droplets to the other end by the magnetic field, the droplets are anti It has magnetism, a strong magnetic field is applied to one end of the droplet by a superconducting magnet, the strength of the strong magnetic field is 0.05T or more, and the growth rate of the crystal is changed by the moving speed of the substrate. This is a method for producing an organic single crystal thin film.
The invention according to claim 2 controls the vapor pressure of the solution in a semi-sealed cell that seals droplets from the outside, and at a relative moving speed between the position of the superconducting magnet and the substrate, 2. The method for producing an organic single crystal thin film according to claim 1, wherein crystal growth is controlled .
The invention according to claim 3 is the method for producing an organic single crystal thin film according to claim 1 or 2, wherein the organic material is an organic compound having an aromatic ring in a molecular structure .
According to a fourth aspect of the present invention, there is provided a means for holding a substrate, a means for moving the substrate, and a magnetic field arranged so that a magnetic field can be sequentially applied from one end to the other end of a droplet on the substrate. A device for forming an organic single crystal thin film composed of a means for applying the liquid, wherein the droplet has diamagnetism, and a strong magnetic field is applied to one end of the droplet by a superconducting magnet, An organic single crystal thin film characterized in that the strength of the strong magnetic field is 0.05 T or more, and the growth rate of the crystal is changed by adjusting the change of the strong magnetic field relative to the substrate according to the moving speed of the substrate . A film forming apparatus.
In the invention according to claim 5, the vapor pressure of the solution is controlled in a semi-sealed cell that seals droplets from the outside, and the relative movement speed between the position of the superconducting magnet and the substrate is 5. The organic single crystal thin film forming apparatus according to claim 4, wherein crystal growth is controlled .
Many organic compounds having an aromatic ring in the molecular structure are known to exhibit diamagnetism. When a diamagnetic liquid such as an organic solvent is placed in a strong magnetic field, a force (Moses effect) is generated in the liquid to move out of the magnetic field, and the external shape of the liquid changes. When the solvent is slowly evaporated from the solution containing the solute with the outer shape changed in this manner, the solute is concentrated locally at the thinnest place of the liquid, and the high concentration region is intentionally in the liquid depending on the position of the magnet. Can be formed. Using this method, it is possible to nucleate at an arbitrary position on the substrate and to move the position of the magnet relatively to selectively supply the solute to the side surface of the seed crystal. We may use an oxide superconductor bulk superconducting magnet magnetized to 2 Tesla.

This method makes it possible to form a film in the air at a low cost and reduce defects and impurities taken up by the solution.

It is a figure which shows the principle of the single-crystal growth in a magnetic field of this invention. It is a figure which shows the principle of the single-crystal growth in a magnetic field of this invention. It is a conceptual diagram of the film-forming apparatus used in the Example. It is a conceptual diagram of the thin-film transistor formed in the Example. It is a plane external view of the film | membrane formed into a film in the Example. It is a plane external view of the film | membrane formed into a film by the drop cast method. It is a plane external view of the film | membrane formed into a film by the vapor deposition method.

(Create procedure)
As shown in FIGS. 1 and 2, the substrate is subjected to hydrophilic / hydrophobic patterning (droplet side is hydrophilic) to dissolve the organic semiconductor material in an appropriate concentration in a solvent having polarity and to keep the dropped solution. . Shape one end of the solution dripped onto the substrate with a magnetic force such as a superconducting magnet. At the end of the ultra-thinned solution, even a slight evaporation of the solvent can make the solute ratio extremely higher than the thick part of the solution. Therefore, crystals can be preferentially deposited from the end of the pattern.
At this time, the solvent moves and evaporates at the same time as the precipitation of crystals due to the magnetic force, so that only the crystals remain on the substrate.

  While applying, the magnetic field applied to the droplets is reduced by half-thinning one end of the droplets by the magnetic field by hydrophilic / hydrophobic patterning that keeps the droplets on the substrate in the dissolved organic semiconductor medium. A slight evaporation of the sealed cell increases the ratio of solutes in the solution, and crystal nuclei are formed at the end of the preferentially thinned solution, and the crystals are inevitably oriented toward the solution side.

At this time, since impurities and defects are aggregated or removed to the solution side, crystals are deposited from around the droplets such as a drop-cast film, so that impurities and defects remain in the central portion and the quality of the crystals does not deteriorate.
Further, if crystal growth is continued in accordance with the dominant crystal grains, the inferior crystal grains are trapped, and a large-diameter single crystal thin film having a crystal axis most suitable for the solution shaping / moving direction can be formed.
Further, by precipitating the crystal from the end, the crystal can grow only in the direction of the thicker solution. Thereby, the direction in which the crystal can grow is one direction. By shaping and moving the solution in accordance with the crystal growth rate, it is possible to preferentially grow only a crystal axis with a high growth rate (equal to a crystal axis with high carrier mobility). As a result, the crystal that best matches the solution movement axis finally becomes dominant, and a single crystal thin film can be formed. As a result, a TFT having high carrier mobility can be realized.

(Materials etc.)
In the present invention, various substrates such as glass, plastic, quartz, undoped silicon, and highly doped silicon are used as the substrate. The plastic includes various materials such as polycarbonate, mylar, and polyimide. Moreover, you may give surface decoration to these. In the embodiment, a crystalline substrate is used. Examples of the crystalline substrate include a Si single crystal substrate, a surface-decorated Si single crystal substrate, and a crystalline substrate such as KCl. The liquid material (droplet) contains a thin film material. Generally, it is prepared by dissolving a thin film material in a solvent. The liquid can be used even if it has the same viscosity as water. The viscosity is preferably 0.0001 to 10 Pa · s. If the viscosity is too high, the magnetic force for thinning the edge must be increased.

As the thin film material, for example, an organic material, an inorganic material, a semiconductor material, or a metal material can be used. Diamagnetic materials are preferred. For example, an organic material is used.
As the organic material, for example, a condensed polycyclic hydrogen-based organic material is used.
Examples of the condensed polycyclic hydrogen-based organic material include the following materials.

Pentalene, indene, naphthalene, azulene, heptalene, biphenylene, as-indacene, s-indacene, acenaphthylene, fluorene, phenalene, phenanthrene, anthracene, fluoranthene, acephenanthrylene, aceanthrene, triphenylene, pyrene, chrysene, tetracene, poleneden, Examples thereof include one or more materials selected from picene, perylene, pentaphen, pentacene, tetraphenylene, hexaphen, hexacene, rubicene, corolene, trinaphthylene, heptaphene, heptacene, pyranthrene, obalene, or derivatives thereof.
The following compounds are preferably used.

On the other hand, the type of the solvent is not limited as long as it is a liquid capable of dissolving the thin film material.
More specifically, the optimal solvent may be selected by actually examining the solubility of the organic material through experiments.
The applied magnetic field strength is preferably 0.05T (Tesla) or more, more preferably 1T or more, and further preferably 2T or more. There is no particular upper limit, as long as it is achievable strength.

  The magnetic field is preferably applied using a superconducting bulk magnet. In the case of applying a magnetic field by a coil, the magnetic field gradient (dH / dt) is limited even though the magnitude H of the magnetic field can be increased. A desired value cannot be obtained as the magnetic force F (= (dH / dt) · H), and the Moses effect cannot always be achieved by a thin film material that is not large in diamagnetism. On the other hand, in the case of a superconducting bulk magnet, dH / dt can be increased, so that a desired magnetic force F can be obtained.

  In addition, when a magnetic field is applied in a magnetic field space by a superconducting magnet, a strong magnetic field can be easily applied to the adherend. In forming a thin film, the molecular arrangement of the thin film is increased as the magnetic field is stronger. Since it can be made dense, it is possible to further improve the orientation and to form a large crystal.

In this semi-sealed cell as shown in FIG. 3, the evaporation amount of the solution was limited, the crystal precipitation state was observed, and the test of the present method was conducted with a mechanism capable of feeding back to the substrate moving speed.
The periphery of the substrate on which the droplets are formed is surrounded by an O-ring, and a plate such as glass is placed on the O-ring. Thereby, the inside is sealed. If it is not hermetically sealed, the solvent tends to evaporate. In particular, in the portion where the droplet is thinned, the solvent is likely to evaporate, so that precipitation may occur in various places and become polycrystalline. In the case of sealing, although depending on the solvent and the solute material, precipitation is likely to occur when the thickness is reduced to 0.5 mm.
Moreover, if the semi-sealed cell is a mechanism that can control the vapor pressure of the solvent, the crystal growth controllability can be further improved. In the observation unit, it is necessary to observe the crystal tip that precipitates inside the solution in a microscope having polarization and differential interference functions. This makes it possible to determine the growth rate.

For hydrophilic / hydrophobic patterning, a treatment agent suitable for the material and TFT performance is selected. Here, in the case of Si / SiO ₂ / hydrophilic / hydrophobic patterning / organic semiconductor configuration, a silane coupling agent is used as a liquid. A Teflon® friction transfer is placed outside on the drop side to hold the drop. With such a mechanism, crystal growth is performed under the following conditions.

<Example of crystal growth conditions in this method>
1. Substrate temperature 16 ℃ ~ 20 ℃
2. Solution volume 0.1cc
3. Solution concentration DS2T; 2.4mg / 3cc
DS2T
4. Pattern size 20mm x 30mm
5. Evaporation rate (vapor pressure) 0.03cc / h
6. Substrate hydrophilicity Silane coupling-Bare wafer 7, Solution moving speed 0.5-10 mm / h
8. Solution thickness ≦ 1μm
9. Semi-sealed cell size 60mmφ × 4mmt
10. Relative magnetic field strength 0.9-1.1T
11. Solvent Monochlorobenzene

A single crystal thin film was prepared under the above conditions, and the characteristics were evaluated using a transistor having the structure shown in FIG.
The test results are shown in Table 1 in comparison with the case where the test results were prepared by other methods.
The necessary characteristics in Table 1 were mainly defined from the following viewpoint for the transistor having the structure shown in FIG.
・ High adhesion between organic semiconductor and electrode in part A ・ Thickness of organic semiconductor in part B, large grain size, no cracks, and no electrical connection between grains. -The adhesion between the organic semiconductor and SiO _{2 in} part C in the figure is high.
→ Smooth without film irregularities → No grain boundary between channels → No crack between channels → No carrier trap at SiO ₂ interface

薄膜トランジスタの要件である薄くて基板に密着した滑らかでチャネル間全面を覆う大口径単結晶薄膜を実現した。 <Superiority of crystal quality in DS2T method>

A thin, large-diameter single-crystal thin film covering the entire surface between channels, which is a thin and close contact with the substrate, which is a requirement for thin film transistors, has been realized.

  FIG. 5 shows an external view of the formed film. The vertical width of FIG. 5 is about 1 mm, and it can be seen that a very large single crystal film was obtained. 6 shows a film formed by a drop-cast method, and FIG. 7 shows a film formed by a vapor deposition method.

  TIPS-pentacene was used as a solute, and monochlorobenzene was used as a solvent. An unsaturated solution was dropped onto a silicon wafer having a 300 nm thick thermal oxide film on its surface and inserted into a strong magnetic field. The end of the solution on the magnet side became thinner due to the Moses effect, and the other end became thicker. By slowly evaporating the solvent, TIPS-pentacene polycrystals were formed only from the end of the magnetic field. Thereafter, the supersaturated solution was supplied to the growth tip of the crystal by moving the position of the magnet to the solution side, and the crystal grew in one direction in the plane. The crystal growth rate can be changed depending on the moving speed of the substrate, and crystal thin films were produced at different growth rates. As a result, a single crystal film of the order of 10 mm was produced and the transistor characteristics were confirmed.

  The present invention relates to a functional thin film and a film forming technique thereof, and more specifically, an anisotropic conductive film (an anisotropic conductive film, an anisotropic photoconductive film, etc.) useful for an electrophotographic photosensitive member, a solar cell, etc. The present invention relates to an optically anisotropic film useful for a memory, a color filter, and the like, and a manufacturing method thereof.

When the orientation of these thin films is improved and the crystal size is increased, carrier mobility is improved and a high-quality semiconductor material can be provided.
When the condensed polycyclic hydrogen-based organic substance is selected from 35 basic rings of condensed polycyclic hydrogen such as pentalene, perylene, pentacene, and derivatives thereof, these substances are used for semiconductors such as transistor devices. It can be made to function as a thin film of materials, and when these orientations are improved and the crystal size is increased, carrier mobility is improved and a high-quality semiconductor material can be provided. As a result, organic transistors (FETs) and organic light-emitting elements are realized in high-quality organic semiconductor thin films, and applied to driving liquid crystal and organic EI display panels using organic thin film transistors (TFTs) using these. It can be expected to contribute greatly to industrial fields and social life by promoting cost reduction and weight reduction of equipment.

Claims (5)

A droplet of a solution having an organic material in a solvent is provided on a substrate, and one end of the droplet is thinned and the other end is thickened.
Together to precipitate crystals by evaporating the one end side of the solvent of the droplets,
A method for producing an organic single crystal thin film in which crystals are sequentially deposited by moving a thin portion of one end of the droplet thinned to the other end by a magnetic field ,
The droplet has diamagnetism, and a strong magnetic field is applied to one end of the droplet by a superconducting magnet.
The strength of the strong magnetic field is 0.05T or more,
A method for producing an organic single crystal thin film , wherein the growth rate of the crystal is changed according to the moving speed of the substrate . In a semi-sealed cell that seals droplets from the outside, the vapor pressure of the solution is controlled, and the relative movement speed between the position of the superconducting magnet and the substrate is as follows:
2. The method for producing an organic single crystal thin film according to claim 1, wherein growth of the crystal is controlled . The method for producing an organic single crystal thin film according to claim 1 or 2, wherein the organic material is an organic compound having an aromatic ring in a molecular structure . Means for holding the substrate;
Means for moving the substrate;
A device for forming an organic single crystal thin film comprising a means for applying a magnetic field arranged so that a magnetic field can be sequentially applied from one end to the other end of a droplet on the substrate ,
The droplet has diamagnetism, and a strong magnetic field is applied to one end of the droplet by a superconducting magnet.
The strength of the strong magnetic field is 0.05T or more,
An organic single crystal thin film forming apparatus , wherein a growth rate of the crystal is changed by adjusting a change in a strong magnetic field with respect to the substrate according to a moving speed of the substrate . In a semi-sealed cell that seals droplets from the outside,
The vapor pressure of the solution is controlled, and the relative moving speed between the position of the superconducting magnet and the substrate,
The organic single crystal thin film forming apparatus according to claim 4, wherein growth of the crystal is controlled .

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