JP2006066662A - Method of forming thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of forming a large area, uniform crystal organic material thin film on a substrate. <P>SOLUTION: The method of forming the crystal organic material thin film on the substrate includes a process of immersing the board in an organic material solution held in a vessel, a process of moving the board out of the organic material solution to the gaseous phase side, and a process of crystallizing the crystal organic material thin film on the board out of the organic material solution sticking to the board on the gaseous side. The organic material solution, sticking to the board, is continuous with the organic material solution held in the vessel in the gaseous phase. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for forming a crystalline organic material thin film on a substrate, which is required when manufacturing an electronic device capable of deforming the substrate, such as a wearable PC or a flexible display.

  In recent years, the characteristics of organic electronic materials have made remarkable progress. For example, in an organic EL display (or an organic LED display), each pixel emits light individually (that is, self-emission), so that not only has a wide viewing angle and a color filter is unnecessary, but also the backside. Thinning is possible because no light is required. It has many advantages over conventional liquid crystals, such as being able to be formed on a flexible substrate such as plastic. In addition, the use of organic materials for the circuit system that drives them is also being considered. By using these materials, it is expected that electronic devices capable of deforming the substrate, such as wearable PCs and flexible displays, will be realized.

These organic electronic materials are usually formed as a thin film on a substrate. The film thickness is approximately in the range of several tens to several hundreds of nanometers, and vacuum deposition, solution coating (spin coating method, ink jet method) or the like is used as a forming method. Further, glass, silicon, and plastic are often used as the substrate, and a metal electrode, an oxide (ITO, etc.) electrode, an insulating film, and the like are formed thereon as necessary. As a method for forming a metal electrode, an oxide (ITO, etc.) electrode, and an insulating film, sputtering, CVD, PVD, etc. are generally used in addition to vacuum deposition and solution coating (spin coating method, ink jet method).
In the above, the merit of using an organic material as an electronic material is that a low-cost manufacturing method such as solution coating (spin coating method, ink jet method) can be used, and a plastic substrate can be used because the process temperature is low. In other words, it is possible to manufacture a flexible electrical device using the same.

These organic materials are roughly classified into a crystalline material and an amorphous material in a thin film state. For example, among organic electronic materials, acene-based materials such as pentacene and tetracene, which are known to have high charge mobility, and AIDCN (2-amino-4,5-imidazole-dicarbonitrile), which is a representative bistable material, are The better the crystallinity is, the higher the mobility is.
Specifically, for example, when a pentacene thin film is formed on a glass substrate by a method such as vacuum deposition, the thin film is in a so-called polycrystalline state. That is, many crystal grain boundaries exist in the thin film. Since the movement of electric charges is hindered by these crystal grain boundaries, the electric charge mobility as a thin film is suppressed to be small. Therefore, in order to increase the charge mobility, it is desired that the crystal grains of the thin film be large. In the case of vacuum deposition, it is known that the crystal growth nucleus density is lowered and the crystal grains are enlarged by raising the substrate temperature and lowering the deposition rate. However, for example, it has been difficult to obtain crystal grains having a typical channel width (10 μm or more) of a field effect transistor.

In contrast, when a thin film of an organic material is formed on a substrate by a coating method such as a cast method, a spin coating method, or an ink jet method, the crystal grains can be made larger than that in vacuum deposition. This is because, compared with the gas phase, in the liquid phase, the interaction between the organic material to be applied and the substrate is small, so that the crystal growth nucleus density is low and the crystal grains grow large. Therefore, a technique for controlling the crystallinity of the film by defining the physical property value of the solvent is disclosed (PL-00970). In particular, pentacene has a particularly high mobility among organic electronic materials, but its solubility in organic solvents is low. For coating, methods such as heating the solvent to form a solution and applying it have been reported. (Non-Patent Documents 1 and 2).
However, forming a crystalline organic material thin film on such a substrate has the following problems.

2004 Spring Applied Physics-related Joint Lecture Proceedings No3, page 1466, Minamikata Takashi Organic Semiconductor Workshop Proceedings, pp. 55-59, Organic Physics Society Organic Molecular and Bioelectronics Subcommittee, June 14, 2004 Applied Physics Handbook, Applied Physics Society, Maruzen, 1990

  In general, a process for forming a thin film of an organic material on a substrate is as follows. That is, the solvent evaporates from the organic material solution applied on the substrate, whereby the organic material in the solution is concentrated, the concentration reaches the solubility limit, and precipitates on the substrate. In particular, in the case of a crystalline thin film, if precipitation occurs on a part of the substrate, the crystal tends to grow on the surface, so the organic material in the applied solution adheres to the deposited crystal by diffusing in the solution. And grow. As a result, in other portions, the concentration of organic material in the solution decreases, so that crystal precipitation hardly occurs. That is, crystal growth is selectively continued at a portion where crystals are precipitated at an early stage.

  As a result, the thin film becomes discontinuous. In severe cases, the thin film may not be formed because crystals are deposited only on one part of the substrate. This phenomenon becomes prominent particularly when a substrate having a low crystal growth nucleus density is used, or when the organic material has a low solubility and a low concentration. Further, in the case of a crystalline thin film, the solid density is uniquely determined by the crystal structure, so that non-uniformity of the thin film rarely appears as the density of the film. Thus, it has been difficult to uniformly form a crystalline organic material thin film with a large area by the conventional coating method. As described above, this phenomenon can be improved to some extent by specifying the physical property value of the solvent, but further improvement has been desired.

  As a crystal growth method on a substrate, so-called liquid phase epitaxy in which a substrate is immersed in an organic material solution to grow a crystal is conventionally known (Non-patent Document 3). According to this, even if the crystal grows on a part of the substrate, the organic material is sufficiently supplied from the surrounding solution, so that the crystal is generally not discontinuous and a large crystal is easily obtained. However, according to this method, the crystal grows not only in the direction parallel to the substrate but also in the vertical direction (film thickness direction), and thus is not suitable as a thin film forming method for which the thickness needs to be controlled.

In view of the above problems, the present inventors have intensively studied to develop a method for uniformly forming a crystalline organic material thin film in a large area in a method for forming a crystalline organic material thin film on a substrate.
As a result, the present inventors have immersed the substrate in an organic material solution and then moved to the gas phase to deposit a crystalline organic material thin film from the solution attached to the substrate, and the attached solution is organic in the container. It has been found that the above problems are solved by the fact that the material solution and the liquid phase are continuous. The present invention has been completed from such a viewpoint.

  That is, the present invention relates to a thin film forming method for forming a crystalline organic material thin film on a substrate, a step of immersing the substrate in an organic material solution placed in a container, and the substrate from the liquid of the organic material solution to the gas phase side. And the step of depositing the crystalline organic material thin film from the organic material solution adhering to the substrate on the gas phase side substrate, and the organic material solution adhering to the substrate is put in a container Further, the present invention provides a thin film forming method characterized by being continuous with the organic material solution in a liquid phase. By forming the thin film formation method as described above, the crystalline organic material thin film grows on the substrate in the gas phase, and the organic material solution is continuous in liquid phase with the organic material solution in the container. Since it is continuously supplied, a thin film having a constant film thickness can be continuously formed.

  Further, in the step of moving the substrate from the organic material solution to the gas phase side, the organic material solution is held by surface tension between the substrate and the auxiliary plate, and the substrate moves in parallel relative to the auxiliary plate. It is preferable that the temperature of the substrate decreases as it moves away from the liquid level in the container. As a result, since the supply of the organic material solution to the substrate is performed by surface tension, it becomes more reliable, and at the same time, the contact time between the substrate and the organic material solution becomes long, so that the crystal growth time can be set large. Is possible. Further, the temperature decreases as the substrate moves away from the liquid surface, so that the solubility of the solution decreases and the precipitation is promoted.

  Further, it is preferable that the organic material solution flows on the substrate in the step of moving the substrate from the organic material solution to the gas phase side. Thereby, the supply of the organic material solution to the substrate is further ensured, and at the same time, the organic material concentration of the solution is kept uniform, so that the uniformity of the thin film is further improved.

  In addition, the temperature of the substrate is preferably lower than the opposing auxiliary plate. Thereby, the organic material is deposited mainly on the substrate side and hardly deposited on the auxiliary plate.

  According to the present invention, in the method for forming a crystalline organic material thin film on a substrate, the crystalline organic material thin film can be uniformly formed in a large area.

  The thin film forming method of the present invention includes a step of immersing a substrate in an organic material solution placed in a container, a step of moving the substrate from the liquid of the organic material solution to the gas phase side, and a substrate on the gas phase side. And a step of depositing the crystalline organic material thin film from the organic material solution attached to the substrate. The organic material solution attached to the substrate is continuous with the organic material solution in a container in a liquid phase. Hereinafter, although the present invention will be described in detail according to the best mode for carrying out the present invention, the present invention is not limited to these embodiments.

FIG. 1 shows an example of a coating process in which the method for forming a crystalline organic material thin film according to the present invention is actually performed. This apparatus is similar to a coating method usually called a dip method.
In order to obtain a crystalline thin film, a certain amount of time is required for the crystals to be deposited on the substrate, and during that time, the solution needs to be replenished. However, with a coating method such as a normal spin coating method or an ink jet method, the solution does not stop on the substrate and easily dissipates. In particular, a material having a low solubility in a solvent such as pentacene has a serious problem because the solution has a low viscosity. At the same time, from the viewpoint of controlling the film thickness, the contact time with the solution must be limited. In the present invention, focusing on this point, the solution is replenished on the substrate while the crystal is deposited on the substrate, and the time can be easily controlled.

In FIG. 1, the substrate 1 is initially immersed in the organic material solution 3 in the container 6. For example, when the organic material is pentacene, the organic material solution 3 is heated to about 180 ° C. in order to increase the solubility, and the substrate 1 is also heated to that temperature by immersion.
Next, the substrate 1 is pulled up from the organic material solution 3 to the gas phase. At this time, the substrate 1 is preferably moved along the auxiliary plate 2. Further, it is desirable that the distance between the auxiliary plate 2 and the substrate 1 be kept constant by an appropriate spacer or the like. Although the optimum value of the interval dimension varies depending on the concentration of solution used, temperature conditions, etc., it is preferably between 10 μm and 1 mm, more preferably between 15 and 100 μm. Since the organic material solution 3 is sucked up by the surface tension in the gap 4 between the substrate and the auxiliary plate, the organic material solution in the container and the gap is continuous by the liquid phase. The suction height due to surface tension depends on the gap size, but 50mm or more is sufficient. The temperature of the substrate 1 is lowered as it is separated from the liquid level in the container by being pulled up from the solution, and accordingly, the temperature of the solution in the gap 4 between the substrate and the auxiliary plate is also lowered. Along with this, the solubility of the organic material also decreases, so that the organic material starts to be deposited on the substrate.
The substrate pulling speed varies depending on the conditions, but is preferably in the range of about 0.1 mm / s to 10 mm / s. Since the solution is always supplied in the gap 4 between the substrate and the auxiliary plate and the organic material is supplied by diffusion in the solution, a uniform thin film can be obtained. As shown in FIG. 1, the substrate 1 is easy to dissipate heat, whereas the auxiliary plate faces a high-temperature container, so that the temperature of the substrate 1 becomes higher than that of the auxiliary plate 2. As a result, precipitation proceeds preferentially on the substrate 1. When this effect is insufficient, the temperature of the auxiliary plate can be controlled by adding a heat retaining heater 8 to the auxiliary plate 2.

FIG. 2 shows another example of the thin film forming method in the present invention.
In the form of FIG. 2, the organic material solution is continuously supplied from the solution supply container 11 to the container 6, overflows over the auxiliary plate 2, and is recovered in the solution recovery container 12. The substrate 1 is initially immersed in the organic material solution in the same manner as in FIG. 1, but the substrate 1 is pulled up between the auxiliary plate 2 and the guide 7. Also in this case, it is desirable that the distance between the auxiliary plate 2 and the substrate 1 or the distance between the guide 7 and the substrate 1 is kept constant by an appropriate spacer or the like. Although the optimum value of the interval dimension varies depending on the concentration of solution used, temperature conditions, and the like, it is preferably 0.1 to 10 mm, more preferably 1 to 3 mm. Since the organic material solution 3 flows through the gap 4 between the substrate and the auxiliary plate, the organic material solution in the container and the gap is continuous in the liquid phase. The temperature of the substrate 1 is lowered as the temperature of the substrate 1 is pulled away from the liquid surface in the container by pulling up from the solution. However, since the supply of the organic material solution becomes larger than that in the case of FIG. For this reason, it may be necessary to install the cooler 9 to actively cool the substrate. Along with this, the solubility of the organic material also decreases, so that the organic material starts to be deposited on the substrate. Since the solution is always supplied into the gap 4 between the substrate and the auxiliary plate, and the concentration of the organic material of the supplied solution is higher than that in FIG. 1, a more uniform thin film can be obtained.

  In the thin film forming method according to the present invention, a non-flexible substrate such as a glass plate or a silicon wafer can be easily applied as the substrate, but it can also be applied to a flexible substrate by appropriately supporting it. Flexible substrates include polyimide, polyetherimide, polysulfone, polyethersulfone, polyphenylene sulfide, rose-based aramid, polyetherkent, polyester, polycarbonate, polyimide, polyethersulfone, amorphous polyolefin, epoxy resin or fluorine. A polymer plastic film such as a resin can be used. Among them, polyester or polycarbonate is preferable in terms of strength, and polyester such as polyethylene terephthalate is particularly preferable. The thickness of the substrate is preferably 0.05 mm to 2 mm, more preferably 0.1 mm to 1 mm.

As the organic material, condensed rings such as pentacene, anthracene and tetracene having a high carrier mobility, and AIDCN (2-amino-4,5-imidazole-dicarbonitrile) which is a representative bistable material are suitable. Without being limited thereto, a wide range of crystalline organic materials can be applied.
The solvent can be appropriately selected depending on the type of the organic material. For example, THF (tetrahydrofuran) and DCM (dichloromethane) are preferable because they can dissolve many organic materials. In addition, acetonitrile, benzene, butanol, cyclohexane, dichloroethane, ethanol, ethyl acetate, dichlorotoluene, trichlorobenzene, dimethyl sulfoxide, and the like can be used, but are not limited thereto.
Hereinafter, the present invention will be described in detail based on examples.

A thin film was formed in the configuration shown in FIG.
As an organic material, 0.3 g of pentacenepentacene (made by Aldrich) of the following chemical formula (1) was added to 1 liter of a solvent (3,4-dichlorotoluene), and this was heated to 190 ° C. and dissolved. This solution was put in a container, the container was put in an oil bath, and it was heated with a hot plate to keep the whole temperature. As the substrate, a glass plate having a thickness of 0.5 mm, a width of 5 cm, and a length of 20 cm was used, and an aluminum thin film having a thickness of 100 nm previously formed thereon by vacuum deposition was used. In order to suppress the oxidation of the solvent and pentacene, the work was carried out in a glove box filled with nitrogen. The atmosphere inside the glove box kept oxygen and moisture below 1 ppm.

  As the auxiliary plate 2, a SUS304 plate having a thickness of 0.5 mm, a width of 7 cm, and a length of 15 cm was used, and the distance between the auxiliary plate 2 and the substrate 1 was maintained at 0.1 mm by an aluminum spacer. As a result, the organic material solution 3 was sucked up by the surface tension into the gap 4 between the substrate and the auxiliary plate. The auxiliary plate was arranged at an angle of 30 ° with respect to the liquid level in the container so as to exit the gas phase 10 cm (5 cm in height) from the liquid level. When the substrate was pulled up along the auxiliary plate at a speed of 0.5 mm / sec, the temperature of the substrate and the auxiliary plate at the upper end of the auxiliary plate became about 80 ° C. and 97 ° C., respectively. As a result, a crystal thin film as shown in FIG. 3 was obtained. The surface state of the thin film was almost the same for the entire substrate, but the film thickness was about 230 nm on the coating start side of the substrate and about 55 nm on the coating end side.

  A thin film was formed in the same manner as in Example 1 except that a dicyano compound having the following chemical formula (2) was used as the organic material and this was dissolved in a solvent methanol at a concentration of 3% by weight at 70 ° C.

  As a result, the temperatures of the substrate and the auxiliary plate at the upper end of the auxiliary plate were about 35 ° C. and 47 ° C., respectively. A crystal thin film as shown in FIG. 4 was obtained. The surface state of the thin film was almost the same for the entire substrate, but the film thickness was about 450 nm on the coating start side of the substrate and about 170 nm on the coating end side.

A thin film was formed in the configuration shown in FIG.
10 liters of an organic material solution similar to that in Example 1 is prepared and placed in the solution supply container 11 and the container 6. The organic material solution is continuously supplied from the solution supply container 11 at a rate of 10 cc / min. As a result, the organic material solution overflows from the container 6 over the auxiliary plate 2 and is recovered in the solution recovery container 12. The The substrate 1 was in contact with the guide 7 and the distance between the auxiliary plate 2 and the substrate 1 was 1 mm. The substrate dimensions are the same as in Example 1. As a result, the organic material solution 3 flows through the gap 4 between the substrate and the auxiliary plate at a linear velocity of 4 mm / min. By using a water-cooled copper plate as the cooler 9, the substrate temperature at the upper ends of the guide and auxiliary plate was about 60 ° C. Moreover, the temperature of the auxiliary plate became about 72 ° C. at the upper end by bringing the pipe made of silicon resin into which the heated oil flowed as the heater 8 into contact with the auxiliary plate 2. As a result, although not shown, a crystal thin film having a surface state similar to that of Example 1 was obtained. The surface state of the thin film was almost the same for the entire substrate, and the film thickness was about 300 nm on the coating start side of the substrate and about 250 nm on the coating end side.

As described above, in Examples 1 to 3, the organic material thin film shows a crystal state almost as shown in FIG. 3 or FIG. 4, and the effect of the present invention is clear. In particular, in Example 3, the film thickness distribution was also significantly improved.
While the embodiments and examples of the present invention have been described above, the present invention can be variously modified and changed based on the technical idea.

  According to the present invention, a crystalline organic material thin film can be uniformly formed in a large area on a substrate, and the thickness of the thin film can be controlled. Thus, an electronic device capable of deforming the substrate, such as a wearable PC or a flexible display. It is particularly suitable for the production of and has great industrial significance.

It is explanatory drawing which shows the outline | summary of the thin film forming apparatus which concerns on this invention. It is explanatory drawing which shows the outline | summary of the other thin film forming apparatus which concerns on this invention. 2 is a photograph showing the surface state of the crystalline thin film obtained in Example 1. FIG. 3 is a photograph showing the surface state of a crystalline thin film obtained in Example 2. FIG.

Explanation of symbols

1 Substrate 2 Auxiliary plate 3 Organic material solution 4 Gap between substrate and auxiliary plate 5 Organic material thin film 6 Container 7 Guide 8 Heater 9 Cooler 11 Solution supply container 12 Solution recovery container

Claims (4)

In a thin film forming method of forming a crystalline organic material thin film on a substrate,
A step of immersing the substrate in an organic material solution placed in a container, a step of moving the substrate from the liquid of the organic material solution to the gas phase side, and an organic material solution attached to the substrate on the substrate on the gas phase side. A step of depositing the crystalline organic material thin film,
The organic material solution adhering to the said board | substrate is following the said organic material solution put into the container in liquid phase, The thin film formation method characterized by the above-mentioned. In the step of moving the substrate from the organic material solution to the gas phase side,
The organic material solution is held by surface tension between the substrate and the auxiliary plate, and the substrate moves by a parallel movement relative to the auxiliary plate, and as the temperature of the substrate moves away from the liquid surface in the container, The thin film forming method according to claim 1, wherein the thin film forming method decreases. In the step of moving the substrate from the organic material solution to the gas phase side,
3. The thin film forming method according to claim 1, wherein the organic material solution flows on the substrate.   The method for forming a thin film according to claim 1, wherein the temperature of the substrate is lower than that of the opposing auxiliary plate.