JP2005086144A - Method for forming organic conductive thin film, and semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming an organic conductive thin film capable of preventing formation of a step at the boundary of plural parts without causing deterioration in the organic conductive thin film, with a simple process. <P>SOLUTION: A pentacen thin film 4 is formed on a silicon substrate 1 where electrodes 3A, 3B are formed, and a photomask 5 is placed on it. A width W of a chrome pattern 51 is the same as the clearance between the electrodes 3A, 3B. The chrome pattern 51 is arranged on a part 43 between the electrodes 3A, 3B of the thin film 4. An oxygen current is brought into contact with the thin film 4, and the thin film 4 is irradiated with ultraviolet rays 6 through the photomask 5. Thus, the part which is irradiated with ultraviolet rays becomes lower in the electric conductivity of the thin film 4 than that of the part 43 which is not irradiated with ultraviolet rays. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for forming an organic conductive thin film having a plurality of portions having different electrical conductivities in a plane, and a semiconductor device manufactured through this method.

Organic thin-film semiconductor devices having a semiconductor layer made of an organic conductive material can form a semiconductor layer directly on a polymer film at room temperature as compared with conventional semiconductor devices having a semiconductor layer made of an inorganic material such as silicon. And so on. This is expected to enable cost reduction and flexibility of the semiconductor device.
Organic conductive materials that have been studied in the past include conjugated polymers (conductive polymers) such as polyphenylene vinylene, polypyrrole, polythiophene, and oligothiophene, and acenes such as anthracene, tetracene, and pentacene (the benzene ring is linear). And condensed polycyclic aromatic compounds (hereinafter referred to as “polyacene compounds”). In addition, a low-molecular-weight charge transfer complex by combining an electron-accepting molecule such as tetracyanoquinodimethane and an electron-donating molecule such as tetrathiafulvalene is also exemplified.

  In particular, it has been reported that polyacene compounds exhibit high crystallinity due to strong intermolecular cohesion and thereby exhibit high characteristics as a semiconductor because high carrier mobility can be obtained. And the application to a transistor, a solar cell, a laser, etc. is examined as a semiconductor device using the vapor deposition film or single crystal of a polyacene compound (for example, refer nonpatent literatures 1-5).

In addition, a conductive polymer or a low molecular weight charge transfer complex can also be used as a conductive material for forming a wiring or an electrode.
As a method for patterning a thin film made of such an organic conductive material, a method using a shadow mask (see Non-Patent Document 5) and a method using a photoresist (see Non-Patent Document 6) have been proposed. These methods are methods of removing a part of the thin film formed on the entire surface (other than the part left as a pattern) by etching or laser irradiation.

On the other hand, the following Non-Patent Document 7 describes that the carrier mobility of a pentacene thin film is changed by bringing a solvent into contact with the surface.
In Non-Patent Document 8 below, a thin film made of a conductive polymer is formed in a predetermined pattern by locally applying a solution obtained by dissolving a conductive polymer in a solvent to form a thin film. Is described.
Sean et al., “Science”, 289, p. 559, 2000 Sean et al., “Science”, 287, p. 1022, 2000 Jimitracopouras et al., “Journal Off Applied Physics”, 80, p. 2501, 1996 Sean et al., “Nature”, 403, p. 408, 2000 Cloak et al., “IEEE Transactions on Electron Devices”, 46, p. 1258, 1999 Shello et al., “42nd Electronic Materials Conference”, p24 (2000) Gundlach et al., “Applied Physics Letter”, 74, p. 3302 (1999) Shilling House, “Nature”, 290, p. 2123, 2000

However, the conventional method of removing a part of the thin film formed on the entire surface by etching or laser irradiation is complicated, and when this method is applied to the organic conductive thin film, the organic conductive thin film deteriorates in each step. There is a fear. In addition, when a layer made of another material is formed on the upper side of the wiring layer formed by the conventional patterning method, a portion formed on the upper portion of the wiring portion and a portion without the wiring is formed on this layer. As a result, a step is generated by the thickness of the wiring layer. Along with this, there is a problem that the film thickness of this layer becomes non-uniform and the wiring formed on the upper side is easily cut.
An object of the present invention is to form a pattern (wiring or semiconductor pattern) made of an organic conductive thin film without causing deterioration of the organic conductive thin film, and in a simple process, there is a step at the boundary between the plurality of portions. It is to provide a method that can be prevented from occurring.

  In order to solve the above problems, the present invention is a method for forming an organic conductive thin film having a plurality of portions having different electrical conductivities in a plane, and a thin film forming step of forming an organic conductive thin film on a substrate; And a partial oxidation step of lowering the electric conductivity of the predetermined portion by lowering the electric conductivity of the predetermined portion by bringing an active species of oxygen into contact with the predetermined portion in the plane of the thin film and oxidizing the organic thin film. A method of forming a conductive thin film is provided.

  According to this method, since the “organic conductive thin film having a plurality of portions with different electrical conductivities in the plane” is formed without removing a part of the thin film, a step is generated at the boundary between the plurality of portions. Absent. Moreover, since the “organic conductive thin film having a plurality of portions having different electrical conductivities in the plane” is formed by the partial oxidation step, the organic conductive thin film is unlikely to deteriorate. The partial oxidation process is a simple process as compared with the conventional patterning method.

For example, when a wiring made of an organic conductive thin film is formed by the method of the present invention, the electrical conductivity other than the portion used as the wiring in the partial oxidation step is set lower than the portion used as the wiring. Accordingly, since the wiring can be formed without partially removing the thin film, no step is generated at the boundary between the wiring part and the other part.
Although it is difficult to visually confirm the boundary because there is no step, the portion that is oxidized in the partial oxidation step and the portion that is not oxidized have different infrared transmittances and reflectances. Can be confirmed by irradiation.

The partial oxidation step can be performed by irradiating high energy rays in the presence of oxygen.
As high energy rays, ultraviolet rays, visible rays, infrared rays, electron beams, X-rays, or charged particle beams can be used.
These high energy rays can be converted into active species such as ozone and oxygen ions by exciting oxygen in the presence of oxygen. In particular, ultraviolet rays are excellent in that the apparatus is simple and easy to handle.

  The partial oxidation step can be performed by irradiating only the predetermined portion with high energy rays in the presence of oxygen. Specifically, a portion other than the predetermined portion is irradiated by irradiating high energy rays in the presence of oxygen while partially shielding the organic conductive thin film using a photomask or a shadow mask (perforated mask). There are a method for preventing high-energy rays from being irradiated, and a method for directly irradiating only the predetermined portion with high-energy rays as a dotted or linear beam without partial shielding. Moreover, you may perform these methods, irradiating only the said predetermined part with an oxygen ion beam.

  The partial oxidation step can be performed by irradiating only a predetermined portion with a predetermined concentration of oxygen and irradiating a high energy beam. That is, a high energy ray is irradiated by providing an oxygen concentration distribution on the surface or inside of the organic conductive thin film. Specifically, an oxygen-shielding substance is disposed in a portion other than the predetermined portion of the organic conductive thin film, or a gas having a high oxygen concentration is supplied to the predetermined portion by a nozzle over the entire surface of the organic conductive thin film. Irradiate high energy rays.

The thin film forming step may be performed, for example, by vacuum deposition, MBE, CBE, CVD, sputtering, electron beam deposition, laser ablation, coating, printing, spraying, or electrolytic deposition. it can.
Examples of the material of the organic conductive thin film that is the object of the method of the present invention are given below.
Polyacene compounds having a linear structure such as anthracene, tetracene, pentacene, hexacene, heptacene, naphthopentacene, tetrabenzopentacene, diphenylpentacene, phenylpentacene, and the like. Zigzag polyacene compounds such as phenanthrene, chrysene, picene, and fluorene.

  Condensed polycyclic aromatic compounds other than polyacene compounds, pyrene, antanthrene, peropyrene, perylene, terylene, quaterylene, coronene, benzodicoronene, hexabenzocoronene, heptaphene, trinaphthylene, ovalene, circumcamanthracene, bisanthene, zetrene, heptazetrene, biphenyl, Triphenylene, terphenyl, quaterphenyl, violanthrene, isoviolanthrene, sacobiphenyl, keklen, vinyl coronene, rubicene, etc.

A derivative obtained by substituting a part of hydrogen atoms of the above-mentioned condensed polycyclic aromatic compound with an alkyl group, alkene group, alkyne group, aromatic compound or the like. A derivative obtained by substituting a part of carbon atoms of the above-mentioned condensed polycyclic aromatic compound with a heteroatom such as nitrogen, phosphorus, boron or sulfur.
Organometallic compounds such as phthalocyanine and porphyrin. Charge transfer complexes composed of electron-accepting molecules such as tetracyanoquinodimethane, tetracyanonaphthoquinodimethane, cutranyl, bronanyl, dichlorodicyanoquinone, and derivatives thereof. Charge transfer complexes composed of electron donating molecules such as tetrathiafulvalene and tetraselenofulvalene and derivatives thereof. Conductive polymers comprising polythiophene, polyphenylene vinylene, polythienylene vinylene, polyaniline and the like, and derivatives thereof.

Further, for example, an organic-inorganic hybrid semiconductor such as a tin iodide organic ammonium layered compound or a material obtained by combining an inorganic material with the above-described conductive organic material.
The present invention also provides a semiconductor device comprising an organic conductive thin film formed by the method of the present invention and having a plurality of portions having different electrical conductivities in a plane.
For example, when a semiconductor device is formed by the method of the present invention, the electrical conductivity of the portion of the organic conductive thin film other than the semiconductor pattern is made lower than that of the semiconductor pattern portion in the partial oxidation step. Thereby, since a semiconductor pattern can be formed without removing a thin film partially, a level | step difference does not arise in the boundary of a semiconductor pattern and the other part.

In the case of forming a semiconductor device in which semiconductor elements are arrayed, the electrical conductivity of the portion of the organic conductive thin film corresponding to the portion between the elements to be arrayed is changed to another portion (each arrayed by the partial oxidation step). Lower than the portion made of the semiconductor pattern for the element. Thereby, since the semiconductor pattern for each element to be arrayed can be formed without partially removing the thin film, a step does not occur at the boundary of the pattern. Moreover, since the electric conductivity of the part between elements becomes low (resistance value is high), element isolation is ensured.
Examples of the semiconductor device of the present invention include a diode, a thin film transistor, a memory, a photodiode, a light emitting diode, a light emitting transistor, a gas sensor, a biosensor, a blood sensor, an immune sensor, an artificial retina, and a taste sensor.

According to the method of the present invention, the “organic conductive thin film having a plurality of portions having different electrical conductivities in the plane” can be formed in a simple process without causing deterioration of the organic conductive thin film. Further, since no step is generated at the boundary between the plurality of portions, the thickness of the layer formed on the upper side can be made uniform, and the wiring formed by this method is difficult to cut.
That is, it is possible to form a wiring superior in strength to a wiring formed by a conventional patterning method, and to increase the reliability of the electrical characteristics of a semiconductor device having a wiring layer formed by this method.
Furthermore, since it is difficult to visually confirm the boundary, the predetermined pattern is formed in a concealed state by forming a part of the organic conductive thin film in a predetermined pattern and a part having a different electric conductivity from the other part. can do.

Hereinafter, embodiments of the present invention will be described by presenting specific examples.
[First embodiment]
The “field effect transistor” corresponding to one embodiment of the semiconductor device of the present invention was formed by the following procedure. 1 and 2 are a plan view and a cross-sectional view for explaining a method of forming this semiconductor device.
First, a silicon oxide (SiO ₂ ) film 2 having a thickness of 200 nm was formed on both surfaces of the n-type silicon substrate 1 by thermal oxidation. Next, a pair of electrodes 3A and 3B was formed on one silicon oxide film 2 by a lift-off method. FIG. 1A is a plan view showing this state. Both electrodes 3A and 3B are formed with the same size: 500 μm (y) × 225 μm (x) and a constant gap: 50 μm (d).

  When forming the electrode by the lift-off method, “OFPR-100” manufactured by Tokyo Ohka was used as the resist. As a thin film for forming the electrodes 3A and 3B, a titanium thin film 10 nm and a gold thin film 40 nm were formed in this order by an electron beam evaporation method. Further, after the resist pattern was stripped, the resist residue was removed by performing “descum treatment” in which oxygen plasma was irradiated for 2 minutes.

Next, a thin film (organic conductive thin film) 4 made of pentacene was formed to a thickness of 50 nm by vacuum deposition. FIG. 1B and FIG. 2A show this state.
Next, a photomask 5 is placed on the thin film 4. As shown in FIGS. 1 (c) and 2 (b), this photomask 5 is formed by forming a strip-like chrome pattern 51 on a quartz substrate 50, and the width W of the chrome pattern 51 is equal to that of the electrode 3A. , 3B gap: the same as 50 μm (d). The chrome pattern 51 is arranged on the portion 43 between the electrodes 3A and 3B of the thin film 4.

  Next, an oxygen stream was brought into contact with the thin film 4, and the thin film 4 was irradiated with ultraviolet rays 6 through a photomask 5 as shown in FIG. As the ultraviolet irradiation device, “UV ozone cleaner (NLUV253)” manufactured by Nippon Laser Electronics Co., Ltd. was used. This apparatus is equipped with three 4.5 W lamps that emit ultraviolet rays having wavelengths of 185 nm and 254 nm. The apparatus was irradiated with ultraviolet rays for 10 minutes. Thereby, ultraviolet rays were irradiated to portions other than the inter-electrode portion 43 of the thin film 4 in the presence of oxygen.

Next, when the electrical conductivity of the inter-electrode portion 43 of the thin film 4 and other portions was measured, the inter-electrode portion (the portion not irradiated with ultraviolet rays) 43 was 3 × 10 ⁻⁴ S / cm, The portion other than (the portion irradiated with ultraviolet rays) was 5 × 10 ⁻⁸ S / cm.
In this way, a field effect transistor was produced in which the electrodes 3A and 3B were used as source / drain electrodes and the portion 43 between both electrodes 3A and 3B of the pentacene thin film 4 was used as a channel.

As a result of measuring the current-voltage characteristics of the obtained field effect transistor using the silicon substrate 1 as the gate electrode, amplification of the drain current is observed when the gate voltage is set to the negative side (the channel 43 acts as a p-channel). ), Transistor operation was confirmed. The carrier mobility obtained from the correlation between the gate voltage and the drain current was 0.18 cm ² / V · s.
Further, the pentacene thin film 4 was directly formed on the silicon oxide film 2 under the same conditions without forming the electrodes 3A and 3B, and the thin film 4 was irradiated with ultraviolet rays under the same conditions using the same photomask 5. When the film thickness of this thin film 4 was measured with a stylus type film thickness meter, the change in film thickness was at the boundary between the portion irradiated with ultraviolet rays and the portion shielded by the chromium pattern 51 and not irradiated with ultraviolet rays. I was not able to admit.

Furthermore, after the ultraviolet irradiation of the pentacene thin film 4 was performed under the same conditions as described above except that the irradiation time was changed to 1 second, 10 seconds, and 1 minute, the electrical properties of the inter-electrode portion 43 of the thin film 4 and the other portions were changed. Conductivity was measured. As a result, the portion between the electrodes (the portion not irradiated with ultraviolet rays) 43 is 1 × 10 ⁻⁴ S / cm, and the other portion (the portion irradiated with ultraviolet rays) is 1 × 10 in 1 second irradiation time. ^It was 2 × 10 ⁻⁶ S / cm at an irradiation time of 10 seconds and 5 × 10 ⁻⁷ S / cm at an irradiation time of 1 minute.

As shown in FIG. 3A, when the same field effect transistor T as that in the first embodiment is formed in an array, for example, the mask 7 shown in FIG. Do. The mask 7 is made of a nickel plate, and an opening 71 is formed corresponding to a square (500 μm × 500 μm) portion (inter-element portion) K between adjacent transistors T. Thereby, the electrical conductivity of the part K between elements can be made low (resistance value can be made high), and element isolation can be ensured. For example, by using this mask 7 and irradiating with ultraviolet rays for 10 minutes under the above conditions, the resistance value of the inter-element portion K irradiated with ultraviolet rays became 10 ¹⁰ Ω (detection limit value) or more.

[Second Embodiment]
By performing the same process as in the first example until the formation of the pentacene thin film 4, the state shown in FIG. In this state, the portion 43 between the electrodes 3A and 3B of the thin film 4 is recessed by the thickness of the electrodes 3A and 3B. As shown in FIG. 4, a vinylidene chloride resin layer 8 was formed in the recess 45. Specifically, a tetrahydrofuran solution of vinylidene chloride resin having a concentration of 2% by mass was prepared, and this solution was placed in the recess 45 with a microsyringe, and then the solvent was evaporated.
In this state, ultraviolet irradiation was performed in the presence of oxygen under the same conditions as in the first example except that the irradiation time was 20 seconds. Then, after removing the vinylidene chloride resin layer 8, the electrical conductivity of the portion 43 between the electrodes 3A and 3B of the thin film 4 and the portion 46 on the electrodes 3A and 3B was measured. The same 2 × 10 ⁻⁴ S / cm, but the portion 46 was 2 × 10 ⁻⁶ S / cm. Thereby, it turned out that the vinylidene chloride resin layer 8 has an oxygen shielding effect.

[Third embodiment]
By performing the process up to the formation of the electrodes 3A and 3B by the same method as in the first embodiment, the state shown in FIG. Next, a thin film (organic conductive thin film) 4 made of poly (3-hexylthiophene) was formed at 120 nm. This thin film was formed by applying a xylene solution of poly (3-hexylthiophene) having a concentration of 1% by mass by spin coating and then evaporating the solvent. Poly (3-hexylthiophene) was obtained from Aldrich.
Next, the same photomask 5 as in the first example was placed in the same manner as in the first example, and ultraviolet irradiation was performed in the presence of oxygen under the same conditions as in the first example except that the irradiation time was 1 minute. . In this way, a field effect transistor was fabricated using the electrodes 3A and 3B as source / drain electrodes and the portion 43 between the electrodes 3A and 3B of the poly (3-hexylthiophene) thin film 4 as a channel.

Next, when the electrical conductivity of the interelectrode portion 43 of the thin film 4 and the other portions were measured, the interelectrode portion (the portion not irradiated with ultraviolet rays) 43 was 2 × 10 ⁻³ S / cm. The portion other than (the portion irradiated with ultraviolet rays) was 1 × 10 ⁻⁶ S / cm.
Further, without forming the electrodes 3A and 3B, a poly (3-hexylthiophene) thin film 4 is directly formed on the silicon oxide film 2 under the same conditions, and the thin film 4 is irradiated with ultraviolet rays using the same photomask 5 under the same conditions. Went. When the film thickness of this thin film 4 was measured with a stylus type film thickness meter, the change in film thickness was at the boundary between the portion irradiated with ultraviolet rays and the portion shielded by the chromium pattern 51 and not irradiated with ultraviolet rays. I was not able to admit.

It is a top view for demonstrating the formation method of the semiconductor device corresponded to embodiment of this invention. It is sectional drawing for demonstrating the formation method of the semiconductor device corresponded to embodiment of this invention. It is a top view explaining the ultraviolet irradiation method in the case of forming a field effect transistor in an array. It is sectional drawing for demonstrating the example of the ultraviolet-ray shielding method different from the method shown in FIG.2 (b).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Silicon oxide film 3A, 3B Electrode 4 Semiconductor layer 43 Channel 5 Photomask 51 Chrome pattern 6 Ultraviolet light 7 Mask 71 Opening T Field effect transistor (semiconductor device)

Claims (6)

A method for forming an organic conductive thin film having a plurality of portions having different electrical conductivities in a plane,
A thin film forming step of forming an organic conductive thin film on the substrate;
A partial oxidation step of lowering the electrical conductivity of the predetermined portion to be lower than that of the other portion by bringing an active species of oxygen into contact with the predetermined portion in the plane of the thin film and oxidizing it;
A method for forming an organic conductive thin film characterized by comprising:   The method for forming an organic conductive thin film according to claim 1, wherein the partial oxidation step is performed by irradiating a high energy beam in the presence of oxygen.   The method for forming an organic conductive thin film according to claim 2, wherein ultraviolet rays, visible rays, infrared rays, electron beams, X-rays, or charged particle beams are used as the high energy rays.   The organic conductive thin film forming method according to claim 2, wherein the partial oxidation step is performed by irradiating only the predetermined portion with high energy rays in the presence of oxygen.   The method for forming an organic conductive thin film according to claim 2, wherein the partial oxidation step is performed by irradiating only a predetermined portion with a predetermined concentration of oxygen and irradiating a high energy ray.   6. A semiconductor device comprising an organic conductive thin film formed by the method according to claim 1 and having a plurality of portions having different electrical conductivities in a plane.

Images