JP2011134495A - Patterning method of thin film formed of zinc oxide crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for patterning in microfabrication of a thin film formed of zinc oxide crystal without generating significant deterioration of conductive characteristics and visible light permeability by suppressing resolution of the thin film formed of the zinc oxide crystal in any process of development and photoresist peeling. <P>SOLUTION: In the patterning method, the thin film of zinc oxide crystal is formed on a substrate, photoresist is formed on a surface of the thin film, and then is exposed through a pattern mask. The exposure part of the photoresist is developed with a developer to remove the photoresist on the exposure part, the thin film is etched through the remaining photoresist, and then, the photoresist is peeled with a peeling liquid. In the patterning method of the thin film formed of the zinc oxide crystal, pHs of the developer and peeling liquids are 10.5-13.5, and temperatures of liquids are within a range 15-50°C. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for patterning a thin film made of a zinc oxide-based crystal, and more particularly to a method for patterning a thin film that does not impair electrical conductivity and visible light transmittance in each process of development or photoresist stripping in photolithography.

  Indium tin oxide (ITO) is frequently used as a conductive thin film used for liquid crystal displays (LCDs), touch panels, and the like. However, since there is a concern about the depletion of indium, which is a rare metal, due to an increase in demand for electronic devices, zinc oxide (ZnO) having conductivity and visible light transmittance is regarded as a promising alternative material for ITO.

However, when a pattern is formed on the zinc oxide thin film using photolithography, there is a problem that the conductivity and the visible light transmittance are lowered.
This is due to the fact that the chemical solution used in each process such as development, etching and photoresist stripping in the patterning process is strongly acidic or strongly alkaline, so that zinc oxide which is an amphoteric oxide is dissolved.

  Patent Documents 1 and 2 below disclose a patterning method for a thin film containing zinc oxide, and studies are made on the respective processing conditions for development or photoresist stripping.

Patent Document 1 discloses a patterning method in which development and etching are performed simultaneously.
The disclosed technique of Patent Document 1 uses a potassium hydroxide solution having a pH of 13 to 14 as a developer and simultaneously performs development and etching. When this technique is used, the number of processing steps can be reduced and patterning can be performed efficiently.
However, since potassium hydroxide solution with pH 13 to 14 is used and the liquid temperature and the treatment time are not adjusted, there is a possibility that zinc oxide may be dissolved, and the problem that the conductive characteristics and the visible light permeability are lowered is solved. It wasn't possible.

On the other hand, Patent Document 2 discloses a patterning method for a thin film made of zinc oxide and tin oxide using tetramethylammonium hydroxide as a developing solution, a mixed solution of nitric acid, hydrochloric acid and water as an etching solution, and ethanolamine as a photoresist stripping solution. It is disclosed.
When the disclosed technique of Patent Document 2 is used, a thin film having a visible light transmittance of about 80%, a conductive property of 10 ⁻³ to 10 ⁻² Ωcm, and a good taper shape can be obtained.
In the patterning method described in Patent Document 2, the chemical concentrations of the developer and the stripper are adjusted and used for each process. However, the liquid temperature of the chemical solution is not adjusted, and each processing time is not adjusted, so that it has not been possible to prevent excessive development processing and peeling processing. Therefore, the dissolution of the thin film cannot be prevented, and there is a possibility that the conductive characteristics and the visible light transmittance are deteriorated.

JP 2007-227300 A JP 2006-196201 A

  The present invention has been made to solve the above-described problems. In the microfabrication of a thin film made of zinc oxide-based crystals, the thin film made of zinc oxide-based crystals can be dissolved in both development and photoresist stripping. An object of the present invention is to provide a method capable of performing patterning without any significant deterioration of conductive characteristics and visible light transmittance.

  According to the first aspect of the present invention, a thin film made of a zinc oxide-based crystal is formed on a substrate, a photoresist is formed on the surface of the thin film, and then exposed through a pattern mask. The exposed portion of the photoresist is developed with a developer. A patterning method of removing the photoresist in the exposed portion by performing a treatment, etching the thin film through the remaining photoresist, and then stripping the photoresist with a stripping solution, the developer and the stripping solution The present invention relates to a method for patterning a thin film made of a zinc oxide-based crystal, characterized in that the pH is 10.5 to 13.5 and the liquid temperature is in the temperature range of 15 to 50 ° C.

  The invention according to claim 2 is characterized in that the pH of the developer is from 12.0 to 13.0 and the temperature of the solution is from 25 to 50 ° C. The present invention relates to a method for patterning a thin film made of crystals.

  A third aspect of the present invention relates to a method for patterning a thin film made of a zinc oxide-based crystal according to the first or second aspect, wherein the developing process and the peeling process are performed for 15 to 100 seconds, respectively.

  The invention according to claim 4 is characterized in that the developer is selected from tetramethylammonium hydroxide, potassium hydroxide, and sodium hydroxide. The present invention relates to a method for patterning a thin film made of crystals.

  The invention according to claim 5 relates to a method for patterning a thin film comprising a zinc oxide-based crystal according to any one of claims 1 to 4, wherein the stripping solution is an amine compound.

  The invention according to claim 6 relates to a method for patterning a thin film comprising a zinc oxide-based crystal according to any one of claims 1 to 5, wherein the zinc oxide-based crystal is zinc oxide.

  The invention according to claim 7 is characterized in that the zinc oxide-based crystal contains 1 to 6% by weight of one or more of aluminum, gallium, magnesium, manganese, and indium. The present invention relates to a method for patterning a thin film made of a zinc oxide-based crystal.

  According to the first aspect of the present invention, a thin film made of a zinc oxide-based crystal is formed on a substrate, a photoresist is formed on the surface of the thin film, and then exposed through a pattern mask. A patterning method of removing the photoresist in the exposed portion by performing a developing process, and stripping the photoresist with a stripping solution after etching the thin film through the remaining photoresist, the developing solution and the The pH of the stripping solution is 10.5 to 13.5 and the liquid temperature is in the temperature range of 15 to 50 ° C. In addition, a variable pattern shape can be obtained, and the variation range of the conductive characteristics and visible light transmittance can be less than 10%.

  According to the second aspect of the present invention, the developer can be efficiently developed by having a pH of the developer of 12.0 to 13.0 and a temperature of the solution of 25 to 50 ° C. Therefore, dissolution of the thin film made of zinc oxide crystals can be prevented.

  According to the invention of claim 3, by performing the development process and the peeling process for 15 to 100 seconds, respectively, the development and the peeling process can be reliably performed, and a thin film made of zinc oxide crystals is formed. A good pattern shape can be obtained without dissolving.

  According to the invention of claim 4, the developing solution is selected from tetramethylammonium hydroxide, potassium hydroxide, and sodium hydroxide, whereby dissolution of the resist pattern can be prevented, There is no risk of developing defects.

  According to the invention which concerns on Claim 5, since only the resist pattern can be peeled by the said stripping solution being an amine compound, there is no possibility that a thin film may melt | dissolve remarkably.

  According to the invention which concerns on Claim 6, when the said zinc oxide type crystal | crystallization is zinc oxide, it can be set as the thin film which can be widely used for an electronic device etc.

  According to the invention of claim 7, since the zinc oxide crystal contains 1 to 6% by weight of one or more of aluminum, gallium, magnesium, manganese, and indium, conductivity is improved without impairing crystallinity. A thin film can be obtained.

It is a schematic diagram which shows each process process in the patterning method which concerns on this invention, (a) is a film-forming process, (b) is a photoresist formation process, (c) is an exposure process, (d) is a development process, ( (e) is an etching process, (f) is a figure which shows a photoresist peeling process. It is a figure which shows the developing solution immersion time dependence of the visible light transmittance | permeability in a GZO film | membrane, Comprising: (a) is a tetramethylammonium hydroxide (TMAH) density | concentration of 2 wt%, 3 wt%, and 5 wt%, (b) is a result. It is a figure which shows the result of TMAH density | concentration of 10 wt% and 20 wt%. It is a figure which shows the peeling liquid immersion time dependence of the resistance and film thickness in a GZO film | membrane. It is a figure which shows the peeling solution immersion time dependence of the carrier concentration and electron mobility in a GZO film | membrane.

Hereinafter, the patterning method of the thin film which consists of a zinc oxide type crystal | crystallization based on this invention is explained in full detail.
FIG. 1 is a schematic view showing each processing step in the patterning method according to the present invention.
A thin film (2) made of a zinc oxide-based crystal is formed on the substrate (1), a photoresist (3) is formed on the surface of the thin film (2), and then a pattern mask (4) is placed on the photoresist (3). . After exposure by irradiating with ultraviolet light through the pattern mask (4), the exposed portion (5) of the photoresist (3) is developed with a developer. After the development processing, etching is performed through the remaining photoresist (3) to etch the thin film (2), and the photoresist (3) is stripped with a stripping solution.

First, a thin film (2) made of a zinc oxide-based crystal is formed on a substrate (1) (see FIG. 1 (a)).
The crystal structure of the zinc oxide-based crystal is a hexagonal wurtzite structure. In the wurtzite structure, there are zinc atomic planes and oxygen atomic planes in the unit lattice of the crystal, and these planes are alternately overlapped with the vertical direction of the crystal lattice to form a crystal.
In the present invention, either single crystal or polycrystal may be used.

The zinc oxide crystal can be formed into a film without adding elements other than zinc (Zn) and oxygen (O) and can be used for an electronic device.
However, zinc oxide (ZnO) is a 3.4 eV wide-gap semiconductor, and its resistivity is 10 ⁻² Ω · cm to 10 ⁵ Ω · cm. Therefore, to improve the conductivity or control the band gap. Various elements such as Group 2, Group 4, Group 7, Group 13, Group 14 elements of the periodic table may be added.
In the present invention, one or more elements of aluminum, gallium, magnesium, manganese, and indium can be added to zinc oxide. The addition amount of the element is preferably 1 to 6% by weight, and more preferably 3 to 5% by weight. If it is less than 1% by weight, the effect of imparting conductivity is not remarkable, and if it exceeds 6% by weight, a solid solution is not formed and precipitation of a different phase is observed, resulting in a decrease in crystallinity and an increase in resistivity. Furthermore, in order to obtain a transparent thin film, since it becomes a low transmittance, it is not preferable in any case.

A known method can be used as a method for forming a thin film made of a zinc oxide-based crystal, and one of them is a sputtering method.
Specifically, as the film forming method in the present invention, for example, the above-described sputtering method, vacuum vapor deposition method, ion plating method (plasma vapor deposition method), DC sputtering method, DC magnetron sputtering method, RF superimposed DC sputtering method, Laser ablation, molecular beam deposition (MB), atomic beam deposition (ALD), chemical vapor deposition (CVD), or the like is used. Among these, since a thin film with good crystallinity can be obtained, an ion plating method, a DC magnetron sputtering method, and an RF superimposed DC sputtering method are preferably used.

Glass, single crystal, ceramics, resin, or the like can be used for the substrate on which the thin film is formed. For example, alkali-free glass, silicon single crystal (Si), silicon polycrystal (Si), sapphire single crystal (α-Al ₂ O ₃ ), alumina (Al ₂ O ₃ ), polycarbonate (PC), polymethyl methacrylate ( PMMA), cyclic polyolefin resin, and the like are used, but not limited thereto. The substrate on which the thin film is formed is not limited to a single layer, and an amorphous layer, for example, can be formed on the substrate, and the thin film can be formed thereon.

After a thin film (2) made of zinc oxide-based crystal is formed on the substrate (1), a photoresist (3) is formed on the surface of the thin film (2) (see FIG. 1B).
The photoresist (3) is not particularly limited as long as it is a photosensitive resin, and a known one can be used.

After the photoresist (3) is formed, the pattern mask (4) is placed on the photoresist (3), and ultraviolet rays are irradiated through the pattern mask (4) to expose (see FIG. 1C).
The pattern shape of the pattern mask (4) is a desired wiring pattern.

  After exposing the photoresist (3) through the pattern mask (4), the exposed portion (5) of the photoresist (3) is developed with a developer. That is, the photoresist (3) that is not masked by the pattern mask (4) is removed (see FIG. 1D).

The developer used has a pH of 10.5 to 13.5, more preferably 12.0 to 13.0. In addition, the temperature of the developer is set in the range of 15 to 50 ° C, and more preferably in the range of 25 to 50 ° C.
If the pH is less than 10.5, the development process becomes insufficient. On the other hand, if the pH exceeds 13.5, the pattern shape of the resist pattern is deteriorated and the dissolution of the thin film (2) may become remarkable. In either case, it is not preferable.
Further, when the developer temperature is less than 15 ° C., the developing speed is lowered and the processing efficiency is lowered. On the other hand, when it exceeds 50 ° C., the developing speed becomes too fast, so the pattern of the photoresist (3) is also removed. In either case, there is a concern, and it is not preferable.

The development processing time is preferably between 15 and 100 seconds, more preferably between 20 and 60 seconds.
By setting the development processing time to 15 to 100 seconds, it is possible to remove the exposed photoresist (3) by reliably performing the development processing, and to prevent excessive development and dissolve the thin film (2). There is no.
When the development processing time is less than 15 seconds, the development is insufficient. On the other hand, when the processing is performed for more than 100 seconds, not only the photoresist (3) of the exposed portion (5) is removed but also the thin film (2). In any case, it is not preferable.

The developer used for development is not particularly limited, and a known developer can be used, but it is selected from tetramethylammonium hydroxide (TMAH), potassium hydroxide (KOH), and sodium hydroxide (NaOH). It is preferable. By using these aqueous solutions, the photoresist (3) in the exposed portion (5) can be surely removed, and there is no possibility of dissolving the resist pattern.
Of the above developers, TMAH, which is an organic alkaline aqueous solution, is preferably used. The use of TMAH can substantially eliminate the generation of residues due to the development process.

  After the development process, the thin film (2) is etched through the remaining photoresist (3) (see FIG. 1 (e)). As an etching method, either wet etching or dry etching may be used.

When wet etching is performed, it is desirable that the etching solution used is acidic, and both strong and weak acids can be used, but it is preferable to use weak acids. Moreover, although any of an organic acid and an inorganic acid may be sufficient, it is preferable to use an organic acid.
As a specific etching solution, for example, carboxylic acid having one or more carboxyl groups such as acetic acid and propionic acid, nitric acid adjusted in pH with ammonium salt, or the like is used.

  When dry etching is performed, the method is not particularly limited, and a known method can be used, but it is preferable to perform etching by plasma etching using reactive gas plasma. By doing so, a good pattern shape can be obtained and there is no possibility of damaging the substrate (1).

After the etching process is performed on the thin film (2), the remaining photoresist (3) is stripped with a stripping solution (see FIG. 1 (f)).
The pH of the stripping solution used is 10.5 to 13.5. In addition, the temperature of the stripping solution is set in the range of 15 to 50 ° C.
If the pH is less than 10.5, the peeling treatment becomes insufficient. On the other hand, if the pH exceeds 13.5, the thin film (2) may be dissolved.
Further, if the temperature of the stripping solution is less than 15 ° C., the stripping rate is slowed, and the processing efficiency is lowered and there is a risk that a residue is generated. On the other hand, if it exceeds 50 ° C., the stripping rate becomes too fast. (2) may also be removed, and the pattern shape is also deteriorated.

The stripping time of the photoresist (3) is preferably between 15 and 100 seconds, more preferably between 20 and 60 seconds.
By setting the stripping treatment time to 15 to 100 seconds, it is possible to remove the photoresist (3) remaining by performing the stripping process reliably, and to prevent dissolution of the thin film (2).
When the peeling processing time is less than 15 seconds, the photoresist (3) is not sufficiently peeled. On the other hand, when the processing is performed for more than 100 seconds, not only the photoresist (3) is removed but also the thin film (2) is removed. In either case, there is a risk of dissolution, which is not preferable.

The stripping solution used for stripping the photoresist (3) is not particularly limited, and a known stripping solution can be used, but an amine compound is preferably used. Only the remaining photoresist (3) can be stripped by using an amine compound as a stripping solution.
Examples of amine compounds used as the stripping solution include alkanolamines, but alkanolamines, particularly diethanolamine, are preferred, there is no possibility of dissolving the thin film (2), and the pattern shape should be good. Can do.

Hereinafter, the effect of the present invention will be clarified by showing examples of the patterning method according to the present invention.
However, the present invention is not limited to the following examples.

<Deposition by ion plating method (plasma deposition method)>
A zinc oxide crystal tablet containing 3.5 to 4.5% by weight of gallium oxide (Ga ₂ O ₃ ) was used as a target, and glass was used as a substrate.
The film was formed at a substrate heating temperature of 180 ° C., a gas pressure of the introduced gas (argon and oxygen) of 0.4 to 0.6 Pa, a film formation rate of 150 to 170 nm / min, and a plasma discharge current of 140 to 150 A. A thin film (hereinafter referred to as GZO film) made of gallium-containing zinc oxide crystals having a film thickness of 50 nm or 100 nm was obtained.

(Test Example 1)
<Dependence of resistance and visible light transmittance in GZO film on developer immersion time>
A GZO film having a thickness of 100 nm was formed by the above film formation method. After exposure through the pattern mask, TMAH was used as a developer, and the GZO film was immersed in TMAH for development.
The pH of the developer is 12.5 to 13.5, the temperature of the solution is 27 ° C., the concentration of TMAH is 2 wt%, 3 wt%, 5 wt%, 10 wt%, and 20 wt%. It was immersed for 2 seconds, and the rate of change in sheet resistance and visible light transmittance was evaluated.
The visible light transmittance is shown in FIG.

In FIG. 2 (a), ◆ is the result of 2 wt%, ● is the result of 3 wt%, and ▲ is the result of 5 wt%,
In FIG. 2B, ■ is the result of 10 wt% and * is the result of 20 wt%.
At any TMAH concentration, the visible light transmittance of the GZO film was about 85 to 87%, and a high transmittance could be maintained. It was also found that the rate of increase in resistance of the GZO film can be suppressed to less than 10%.
It was found that the thickness of the GZO film after immersion did not change and was not substantially different from the initial film thickness.

(Test Example 2)
<Dependence of resistance and carrier concentration in GZO film on stripping solution immersion time>
A GZO film having a thickness of 50 nm was formed by the above film formation method. After exposure through a pattern mask, development and etching were performed, and the photoresist was stripped by immersing the GZO film for 10 to 600 seconds using diethanolamine as a stripping solution.
The pH of the stripping solution was 11.5, the solution temperature was 25 ° C., and the rate of change in sheet resistance and carrier concentration was evaluated.
Incidentally, 3 wt% TMAH was used as a developing solution, and the developing temperature was adjusted to 39 ° C. and pH 12.7, followed by developing for 30 seconds.
FIG. 3 shows the sheet resistance and FIG. 4 shows the carrier concentration.

In FIG. 3, ■ is a plot of sheet resistance and ● is a plot of film thickness.
Further, in FIG. 4, ■ is a plot of electron mobility and ◆ is a plot of carrier concentration.
It was found that the rate of change in resistance could be less than 10%, and no decrease in film thickness was observed.
Further, it was confirmed from FIG. 4 that the carrier concentration was not substantially reduced, and it was revealed that the carrier concentration was high.

  From the above results, it is clear that when a thin film made of zinc oxide-based crystals is patterned using the patterning method according to the present invention, the thin film does not dissolve, and a thin film having good conductive properties and visible light transmission can be obtained. became.

  The patterning method according to the present invention includes a thin film made of a zinc oxide-based crystal, an electronic device that requires fine processing, such as a transparent electrode on the TFT substrate side of a liquid crystal display, a semiconductor and an electrode used for a solar cell, a thin film transistor, etc., a light emitting diode It can be used for microfabrication of such a light emitting element.

1 Substrate 2 Thin film 3 Photoresist 4 Pattern mask 5 Exposure part

Claims (7)

A thin film made of a zinc oxide-based crystal is formed on a substrate, a photoresist is formed on the surface of the thin film, and then exposed through a pattern mask. The exposed portion of the photoresist is developed with a developer, and the exposed portion of the exposed portion is exposed. A patterning method of removing the photoresist, and etching the thin film through the remaining photoresist and then stripping the photoresist with a stripping solution,
A method for patterning a thin film comprising a zinc oxide-based crystal, wherein the developer and the stripping solution have a pH of 10.5 to 13.5 and a liquid temperature of 15 to 50 ° C.   2. The method for patterning a thin film comprising a zinc oxide-based crystal according to claim 1, wherein the developer has a pH of 12.0 to 13.0 and a liquid temperature of 25 to 50 [deg.] C.   3. The method for patterning a thin film made of a zinc oxide-based crystal according to claim 1, wherein the developing process and the peeling process are performed for 15 to 100 seconds, respectively.   The method for patterning a thin film comprising a zinc oxide-based crystal according to any one of claims 1 to 3, wherein the developer is selected from tetramethylammonium hydroxide, potassium hydroxide, and sodium hydroxide.   5. The method for patterning a thin film made of a zinc oxide-based crystal according to claim 1, wherein the stripping solution is an amine-based compound.   6. The method for patterning a thin film comprising a zinc oxide-based crystal according to claim 1, wherein the zinc oxide-based crystal is zinc oxide.   6. The thin film comprising a zinc oxide-based crystal according to claim 1, wherein the zinc oxide-based crystal contains 1 to 6% by weight of one or more of aluminum, gallium, magnesium, manganese, and indium. Patterning method.

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