JP5167465B2 - Method for manufacturing organic semiconductor thin film transistor - Google Patents

Description

  The present invention relates to an organic semiconductor thin film transistor (OTFT), and more particularly, to a bottom gate / bottom contact type organic semiconductor thin film transistor for improving characteristics.

  The structure of the organic semiconductor thin film transistor is roughly classified into a bottom gate / top contact structure and a bottom gate / bottom contact structure. FIG. 11 is a configuration diagram of an organic semiconductor thin film transistor having a bottom gate / top contact structure. FIG. 12 is a configuration diagram of an organic semiconductor thin film transistor having a bottom gate / bottom contact structure.

  Here, the bottom gate means a structure having a gate electrode on the lowermost substrate. The bottom gate / top contact structure refers to a structure in which a gate electrode is provided on a lowermost substrate, an insulating layer stacked on the substrate, and a source electrode and a drain electrode are provided on an organic semiconductor thin film. In the organic semiconductor thin film transistor having the bottom gate / top contact structure shown in FIG. 11, a source electrode and a drain electrode are provided on an organic semiconductor layer such as pentacene.

  On the other hand, in the bottom gate / bottom contact structure, a gate electrode is provided on the lowermost substrate, a source electrode and a drain electrode are provided on the insulating layer laminated on the substrate, and an organic semiconductor thin film is further laminated thereon. Refers to the structure. In the organic semiconductor thin film transistor having the bottom gate / bottom contact structure shown in FIG. 12, the organic semiconductor layer such as pentacene is provided on the source electrode and the drain electrode.

  Compared with the bottom gate / top contact structure shown in FIG. 11, the bottom gate / bottom contact structure shown in FIG. 12 has a PEP (Photo Engraving Process) for forming a gate electrode, a source electrode and a drain electrode. There are merits that can be applied. As a result, by adopting a bottom gate / bottom contact structure, the channel length and channel width of a FET (Field Effect Transistor) can be miniaturized and increased in accuracy (for example, see Patent Document 1). .

JP 2005-158775 A

  However, in the organic semiconductor thin film transistor, there are the following problems in applying the bottom contact method according to the conventional technique. FIG. 13 is an explanatory diagram of a technical problem of an organic semiconductor thin film transistor using the bottom contact method. FIG. 13 shows a partial bottom contact structure composed of a gate electrode, a gate insulating film, a source electrode, a drain electrode (corresponding to an ITO electrode which is an inorganic transparent conductive layer in FIG. 13), and an organic semiconductor layer made of pentacene. A magnified view is shown.

  The ITO electrode is formed by wet etching, for example, and the step on the gate insulating film is 30 to 50 nm as shown in FIG. On the other hand, the thickness of the pentacene molecule constituting the organic semiconductor layer is 1.4 to 1.5 nm as shown in FIG. In the bottom contact method, the thickness of the channel layer necessary for the FET operation is at most 6 to 8 nm. Therefore, the number of stacked pentacenes in the bottom contact method is about 5 at the maximum, and even more layers do not contribute to an increase in the amount of current. Note that FIG. 13 shows a case where the number of stacked pentacene layers is 1 for ease of explanation.

  Therefore, as shown in FIG. 13, when the organic semiconductor thin film transistor is formed by using the bottom contact method, the difference in thickness as described above causes a gap between the pentacene channel end and the ITO electrode end vicinity. “Crystal axis misalignment” occurs, and “grain boundaries” occur here. As a result, the hole flow (on-current) is hindered by the grain boundary, and there is a problem that the TFT characteristics, that is, the on-current is significantly reduced.

The present invention has been made in order to solve the above-described problems, and eliminates the pentacene crystal axis misalignment at the source electrode end and the drain electrode end, which is an essential problem of the bottom gate / bottom contact type organic semiconductor thin film transistor. An object of the present invention is to obtain a method for producing an organic semiconductor thin film transistor capable of eliminating the hole current and eliminating the hole current.

  The organic semiconductor thin film transistor manufacturing method according to the present invention is a bottom gate / bottom contact type organic semiconductor thin film transistor manufacturing method comprising: forming a gate electrode and a gate insulating film on an insulating substrate; and A step of forming a self-aligned flattening layer having a crystal orientation regulating force at a position corresponding to the upper portion of the gate electrode on the film, and a self-aligned flattening in a portion excluding a region where the self-aligned flattening layer is formed Forming the ITO film so as to be continuously flat with the layer, and etching the self-aligned flattening layer, the inorganic transparent conductive layer, and the gate insulating film to have a desired size on the insulating substrate; Forming a planarization layer, a source electrode, a drain electrode, and a gate electrode terminal; and a continuously planarized source electrode, planarization layer, and It is obtained by a step of forming an organic semiconductor layer over a predetermined portion of the upper portion of the fine drain electrode.

According to the present invention, a planarization layer having a crystal orientation regulating force is continuously provided between a source electrode and a drain electrode, and the planarized source electrode, the planarization layer, and a predetermined portion on the drain electrode are covered. Providing an organic semiconductor layer eliminates pentacene crystal axis misalignment at the source and drain electrode ends, which is an essential problem of bottom-gate / bottom-contact organic semiconductor thin film transistors, and increases hole current. The manufacturing method of the organic-semiconductor thin-film transistor which can be obtained can be obtained.

Hereinafter, preferred embodiments of an organic semiconductor thin film transistor and a method for producing the same of the present invention will be described with reference to the drawings.
The organic semiconductor thin film transistor of the present invention is technically formed by continuously flattening between a source electrode and a drain electrode by a flattening layer having excellent crystal orientation regulating power, and forming an organic semiconductor layer in the flattened portion. It is a feature.

  In the following embodiments, a case where a PI (Polyimide) layer is used as an example of a planarization layer having excellent crystal orientation regulation power will be described. A case where a pentacene semiconductor layer formed of pentacene molecules is used as the organic semiconductor layer will be described. In addition, a case where a glass substrate is used as the insulating substrate and ITO is used as the inorganic transparent conductive layer will be described.

Embodiment 1 FIG.
FIG. 1 is a schematic diagram of an organic semiconductor thin film transistor according to Embodiment 1 of the present invention, in which the left side is a plan view and the right side is a cross-sectional view along the AA ′ plane shown in the plan view. The organic semiconductor thin film transistor in the first embodiment includes a glass substrate 1, a gate electrode 2, a gate insulating layer 3, a PI layer 4 corresponding to a planarization layer, an ITO source electrode 5 (hereinafter referred to as source electrode 5), an ITO drain. The electrode 6 (hereinafter referred to as the drain electrode 6), the pentacene semiconductor layer 7 corresponding to the organic semiconductor layer, and the semiconductor protective layer 8 are constituted.

  As shown in FIG. 1, the organic semiconductor thin film transistor according to the first embodiment of the present invention is used to flatten the steps at the electrode ends of the source electrode 5 and the drain electrode 6 provided on the gate insulating layer 3. The PI layer 4 is provided, and the pentacene semiconductor layer 7 is provided on the flattened upper portion. Therefore, the role of the PI layer 4 corresponding to the planarizing layer will be described in detail with reference to FIG.

  FIG. 2 is an explanatory diagram of the structure of the organic semiconductor thin film transistor using the bottom contact method according to the first embodiment of the present invention. FIG. 2 shows a partially enlarged view of the bottom contact structure according to the present invention, like FIG. 13 showing the conventional structure. Compared with the configuration in FIG. 13, the configuration in FIG. 2 further includes a PI layer 4 for flattening the step between the electrode ends of the source electrode 5 and the drain electrode 6 provided on the gate insulating layer 3. Is different.

As shown in FIG. 1 or FIG. 2, the pentacene molecule constituting the pentacene semiconductor layer 7 is provided with the PI layer 4 for flattening the step at the electrode end, as shown in FIG. Crystal axis mismatch grain boundaries are less likely to occur. Furthermore, in the present invention, the PI layer 4 made of polyimide having excellent crystal orientation regulation power is used as the planarizing layer. Therefore, the PI layer 4 serves not only to flatten the step at the electrode end but also to regulate the orientation of the pentacene crystal of the pentacene semiconductor layer 7 formed on the PI layer 4.
The term “crystal orientation regulating force” as used herein means a regulating force that prevents pentacene crystals from growing randomly, in other words, a physical force that regulates the crystal growth orientation (regulatory force).

  As a result, as shown in FIG. 2, disorder of the crystal axis of the pentacene molecule is suppressed, and a pentacene semiconductor layer 7 having a large pentacene crystal with a uniform crystal growth orientation is formed. On-current current) is further reduced, and the drain current can be increased.

  Next, a method for manufacturing the organic semiconductor thin film transistor according to the first embodiment of the present invention shown in FIG. 1 will be specifically described in the order of steps with reference to FIGS. As an example, the organic semiconductor thin film transistor according to the present invention can be manufactured in six steps from the first step to the sixth step shown below.

First, FIG. 3 is a figure which shows the 1st step of the manufacturing method of the organic-semiconductor thin-film transistor in Embodiment 1 of this invention. A gate electrode 2 is formed on the glass substrate 1. As the gate electrode 2, for example, a laminate of gold chrome (Au / Cr) with a thickness of several tens of nm is used. Further, a gate insulating layer 3 is formed on the glass substrate 1 and the gate electrode 2. The gate insulating layer is formed of SiO ₂ (silicon dioxide) having a thickness of about 100 nm by, for example, plasma CVD (Chemical Vapor Deposition).

  Next, FIG. 4 is a figure which shows the 2nd step of the manufacturing method of the organic-semiconductor thin-film transistor in Embodiment 1 of this invention. A PI layer 4 having a thickness of several tens of nanometers made of polyimide having excellent crystal orientation regulation power is applied and formed on the entire surface. Further, a positive resist 9 is applied on the PI layer 4.

  Then, the back exposure of the positive resist is performed from the direction of the glass substrate 1 using the gate electrode as a photomask. Resist development and subsequent PI etching using the remaining resist as a mask leaves only the PI layer corresponding to the upper position of the gate electrode 2 as the self-aligned PI layer 4a of the gate electrode, and the remaining PI layer 4 Remove.

  Next, FIG. 5 is a figure which shows the 3rd step of the manufacturing method of the organic-semiconductor thin-film transistor in Embodiment 1 of this invention. In order to form the source electrode and the drain electrode, an ITO film having the same thickness as the self-aligned PI layer 4a is formed on the entire surface. Subsequently, by removing the positive resist 9 (so-called lift-off method), the ITO film remains in the region excluding the self-aligned PI layer 4a. As a result, the ITO film and the self-aligned PI layer 4a are formed on the gate insulating film 3 in a form having both flatness and continuity, as shown in FIG. Become.

  Next, FIG. 6 is a figure which shows the 4th step of the manufacturing method of the organic-semiconductor thin-film transistor in Embodiment 1 of this invention. Although not shown in the figure, a normal resist is applied by applying a positive resist and using a desired PI shape (vertical direction in the plan view of FIG. 6) and ITO shape, and a photomask for gate electrode terminal opening, Development is followed by etching of the PI, ITO electrode, and gate insulating film 3. As a result, the gate electrode 2 having the gate electrode terminal, the PI layer 4 having the channel region, the source electrode 5 and the drain electrode 6 can be formed in a desired shape.

  Next, FIG. 7 is a figure which shows the 5th step of the manufacturing method of the organic-semiconductor thin-film transistor in Embodiment 1 of this invention. A pentacene semiconductor layer 7 having a thickness of several tens of nm is formed as an organic semiconductor layer having a predetermined shape by vacuum deposition using a shadow mask, as shown in FIG. 5 and the drain electrode 6 are formed over a predetermined portion.

  Finally, FIG. 8 is a figure which shows the 6th step of the manufacturing method of the organic-semiconductor thin-film transistor in Embodiment 1 of this invention. In the final step, the semiconductor protective layer 8 is formed so as to completely cover the pentacene semiconductor layer 7 in order to protect the semiconductor layer from oxidation or the like. As this semiconductor protective layer 8, for example, parylene or the like can be used.

  By going through the manufacturing process as described above, the organic semiconductor thin film transistor shown in FIG. 1 can be finally obtained by using a normal exposure technique and vapor deposition technique. And the organic-semiconductor thin-film transistor formed in this way can eliminate a crystal axis mismatch by the function of PI layer 4, and can increase a hole current by the orientation control force.

  As described above, according to the first embodiment, by providing a planarization layer between the source electrode and the drain electrode, the pentacene crystal at the source / drain end, which is an essential problem of the bottom gate / bottom contact type OTFT Axis misalignment can be resolved. Furthermore, by using polyimide having excellent crystal orientation regulating power as the planarizing layer, an organic semiconductor layer having a large crystal whose orientation is regulated can be formed on the planarizing layer, and crystal axis misalignment can be eliminated. Accordingly, an organic semiconductor thin film transistor capable of increasing the hole current can be obtained.

  Furthermore, it is possible to apply a normal exposure technique and vapor deposition technique as a method for producing an organic semiconductor thin film transistor having such excellent electrical characteristics, and it is not necessary to significantly change the conventional process.

  In the above-described embodiment, the case where the PI layer is formed as the planarization layer has been described, but the present invention is not limited to this. Any material other than polyimide can be used as the planarizing layer as long as the material has excellent crystal orientation regulating power, and equivalent effects can be expected.

  In the above-described embodiments, specific numerical values are not specified, but it is conceivable to optimize the heat treatment conditions in order to improve the adhesion between the planarization layer and the ITO electrode. In particular, in the treatment after the ITO film is formed in the third step, the crystal axis of the pentacene molecule constituting the organic semiconductor layer is obtained by performing a heat treatment at a temperature at which the ITO is not crystallized (for example, a temperature of 150 ° C. or less). Disturbance can be eliminated and it can contribute to an increase in hole current.

  Moreover, although the case where an inorganic transparent conductive layer was formed was demonstrated in the above-mentioned embodiment, this invention is not limited to this. In place of the inorganic transparent conductive layer, a metal thin film or an organic conductive film can be used, and an equivalent effect can be expected.

Embodiment 2. FIG.
In the second embodiment, as described in the first embodiment, in the case where polyimide having excellent crystal orientation regulating force is used as the planarizing layer, the selection of the optimum material is described below based on the verification experiment results. Explained.

  In the formation of an organic thin film having a crystal structure, there is a difference due to heteroepitaxy and homoepitaxy between the binding energy at the interface between the inorganic material substrate and the thin film material and the binding energy between the layers of the thin film organic material. Therefore, the growth of the first layer of the thin film material on the substrate is important for improving the crystallinity of the thin film material and improving the grain size.

  More specifically, in the pentacene organic semiconductor thin film transistor according to the present invention, when a thin film is formed by applying polyimide as a planarizing layer and then a first layer of pentacene is formed thereon, a large pentacene crystal is formed. It is important to select an optimal polyimide material for realizing the particle size reduction.

  Therefore, verification experiment data was collected regarding the size of the pentacene crystals obtained when various polyimide materials were used as the planarizing layer. FIG. 9 is a diagram showing the relationship between various polyimide materials in Embodiment 2 of the present invention and the pentacene crystal size obtained thereby. The horizontal axis in FIG. 9 indicates the six types of polyimide materials M1 to M6 used as the planarization layer, and the vertical axis indicates the average crystal of the pentacene crystals obtained when each of the six types of polyimide materials is used. The particle size is shown.

In addition, the following were used as 6 types of polyimide materials M1-M6 shown in FIG.
M1: N company soluble polyimide M2: N company 4-membered polyamic acid M3: N company 6-membered polyamic acid M4: J company soluble polyimide M5: J company modified polyimide NO1
M6: J company modified polyimide NO2

  From the results shown in FIG. 9, it can be seen that larger crystals are obtained when two types of polyimide materials M2 and M3 are used than when other materials are used. Furthermore, it can be seen that these materials M2 and M3 are both polyimide materials composed of polyamic acid.

  FIG. 10 is a diagram showing a structure of a polyimide material composed of polyamic acid in Embodiment 2 of the present invention. Here, based on the data results shown in FIG. 9, the basis on which the materials M2 and M3 can be the optimum materials will be examined.

  Polyimide has an aromatic ring directly bonded by an imide bond, and the portion has a conjugated structure, which is a rigid and strong structure. Furthermore, the aromatic rings of polyimide are arranged in the same plane, and molecular chains are packed closely together. It was also found that this aromatic ring packing structure of polyimide is suitable for the deposition of the first layer of c-axis oriented pentacene crystals.

  Furthermore, the polyimide (corresponding to the polyimide materials M2 and M3) produced by molding a precursor polyamic acid thin film and then imidized by heat, as shown in FIG. 10, has 6-membered aromatic imide bonds. Since it is a simple structure with a ring or a four-membered ring, it becomes a flat structure. As a result, it was found that the polyimide materials M2 and M3 are optimal as the hetero-growth surface of the first pentacene layer.

  As described above, according to the second embodiment, the polyimide layer in the planarization layer is formed by forming a precursor polyamic acid thin film and then imidizing with heat, thereby forming pentacene crystals. Large particle size can be realized. Therefore, by using a polyimide material made of polyamic acid as one of the optimum materials, an organic semiconductor thin film transistor having good characteristics in which the drain current is greatly improved can be realized.

It is a schematic diagram of the organic-semiconductor thin-film transistor in Embodiment 1 of this invention. It is explanatory drawing of the structure of the organic-semiconductor thin-film transistor using the bottom contact system in Embodiment 1 of this invention. It is a figure which shows the 1st step of the manufacturing method of the organic-semiconductor thin-film transistor in Embodiment 1 of this invention. It is a figure which shows the 2nd step of the manufacturing method of the organic-semiconductor thin-film transistor in Embodiment 1 of this invention. It is a figure which shows the 3rd step of the manufacturing method of the organic-semiconductor thin-film transistor in Embodiment 1 of this invention. It is a figure which shows the 4th step of the manufacturing method of the organic-semiconductor thin-film transistor in Embodiment 1 of this invention. It is a figure which shows the 5th step of the manufacturing method of the organic-semiconductor thin-film transistor in Embodiment 1 of this invention. It is a figure which shows the 6th step of the manufacturing method of the organic-semiconductor thin-film transistor in Embodiment 1 of this invention. It is the figure which showed the relationship between the various polyimide materials in Embodiment 2 of this invention, and the pentacene crystal size obtained by it. It is a figure which shows the structure of the polyimide material comprised with the polyamic acid in Embodiment 2 of this invention. It is a block diagram of the organic-semiconductor thin-film transistor by a bottom gate top contact structure. It is a block diagram of the organic-semiconductor thin-film transistor by a bottom gate and bottom contact structure. It is explanatory drawing of the technical subject of the structure of the organic-semiconductor thin-film transistor using a bottom contact system.

Explanation of symbols

  1 glass substrate, 2 gate electrode, 3 gate insulating layer, 4 PI layer (planarization layer), 4a self-aligned PI layer, 5 source electrode (ITO electrode), 6 drain electrode (ITO electrode), 7 pentacene semiconductor layer (organic) Semiconductor layer), 8 Semiconductor protective layer

Claims (5)

A method for producing a bottom gate / bottom contact type organic semiconductor thin film transistor,
Forming a gate electrode and a gate insulating film on an insulating substrate;
Forming a self-aligned planarization layer having a crystal orientation regulating force on the organic semiconductor material on the gate insulating film at a position corresponding to the upper portion of the gate electrode;
Forming an inorganic transparent conductive layer so as to be continuously flat with the self-aligned planarization layer in a portion excluding the region where the self-aligned planarization layer is formed;
By etching the self-aligned planarization layer, the inorganic transparent conductive layer, and the gate insulating film, a planarization layer, a source electrode, a drain electrode, and a gate electrode terminal having a desired size on the insulating substrate. Forming a step;
And a step of forming an organic semiconductor layer over a predetermined portion of the upper portion of the source electrode, the planarization layer, and the drain electrode that are continuously planarized. . In the manufacturing method of the organic-semiconductor thin-film transistor of Claim 1 ,
A method for producing an organic semiconductor thin film transistor, wherein a metal thin film is used in place of the inorganic transparent conductive layer. In the manufacturing method of the organic-semiconductor thin-film transistor of Claim 1 ,
An organic semiconductor thin film transistor manufacturing method using an organic conductive film instead of the inorganic transparent conductive layer. In the manufacturing method of the organic-semiconductor thin-film transistor of Claim 1,
The method for producing an organic semiconductor thin film transistor , wherein the planarizing layer is a polyimide layer having excellent crystal orientation regulating power for an organic semiconductor material. In the manufacturing method of the organic-semiconductor thin-film transistor of Claim 4 ,
The method for producing an organic semiconductor thin film transistor , wherein the polyimide layer in the planarizing layer is formed by imidizing with heat after forming a polyamic acid thin film as a precursor.

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