JPH11246994A - Chemical liquid for metal oxide film formation - Google Patents

Abstract

(57) [Problem] To provide a chemical solution capable of forming an oxide film having excellent insulation properties and hardly generating hillocks by using at the time of anodic oxidation of metal with high throughput. A chemical conversion solution for forming a metal oxide film is obtained by dissolving a salt of an aromatic carboxylic acid as a solute in a solvent having an alcoholic hydroxyl group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a technique for forming an oxide film by anodizing a metal, particularly aluminum or an aluminum alloy. More specifically, the present invention relates to a chemical conversion solution for forming an oxide film on a metal, a method for forming an oxide film using the chemical conversion solution, and a metal having an oxide film formed on a surface using the chemical conversion solution. INDUSTRIAL APPLICABILITY The present invention can be effectively used particularly for chemical conversion treatment of a gate wiring of a thin film semiconductor (TFT) element of a liquid crystal display panel and a wiring of an integrated circuit.

[0002]

2. Description of the Related Art Metals and alloys are used for various industrial applications by utilizing their characteristic properties. In particular, aluminum, aluminum alloys, and the like have a low specific resistance and are therefore effectively used for wiring of TFT elements and integrated circuits. These wirings require an insulating film to be formed on the surface in order to prevent a short circuit with other wirings and electrodes.

As a method of forming an insulating film on the surface of aluminum, an aluminum alloy, or the like, there is a chemical conversion treatment method by anodic oxidation. In this method, an oxide film is formed on the surface of aluminum or an aluminum alloy by electrochemically oxidizing the surface in a chemical conversion solution.
Since this method has a function of repairing a defect caused by non-uniformity of the substrate, it is excellent in that a dense and smooth oxide film can be easily formed. For this reason, the oxide film forming method by the chemical conversion treatment is effectively used in the wiring manufacturing process of TFT elements and integrated circuits.

Various compositions have been proposed as chemical conversion liquids for forming oxide films of aluminum, aluminum alloys and the like. For example, JP-A-61-1336
No. 62, a 1% aqueous solution of ammonium borate or a 3% aqueous solution of tartaric acid and propylene glycol are mixed in a ratio of 1: 3.
Use the chemical solution mixed in. Also, Japanese Patent Application Laid-Open No. 2-8
Japanese Patent No. 5826 uses a chemical solution prepared by diluting a 3% aqueous solution of tartaric acid with ethylene glycol or propylene glycol and adjusting the pH to about 7 with aqueous ammonia.
JP-A-6-216389 discloses a 1% aqueous solution of ammonium tartrate, a 1% aqueous solution of ammonium adipate,
% Aqueous solution of ammonium oxalate or 1% aqueous solution of ammonium citrate and ethylene glycol in a volume ratio of 3: 7
Use the chemical solution mixed in. JP-A-8-5030
In JP-A No. 4, a chemical solution prepared by mixing a 3% aqueous solution of tartaric acid, 15% acetic acid and ethylene glycol at a ratio of 9: 1: 10 is used. JP-A-8-286209 discloses an aqueous solution of an inorganic acid ammonium salt selected from ammonium tetraborate, ammonium pentaborate and ammonium borate, ammonium tartrate, ammonium citrate,
An aqueous solution of an ammonium salt of an organic acid selected from ammonium adipate, ammonium phthalate, ammonium oxalate, ammonium salicylate and ammonium carbonate is used as the chemical liquid.

[0005] As described above, various chemical conversion solutions have been proposed, but an oxide film having a sufficient insulating property can be obtained by anodizing a metal, particularly aluminum or an aluminum alloy, using these chemical conversion solutions. It cannot be formed. Therefore, in order to prevent dielectric breakdown, another insulating film must be further formed on the formed oxide film.
In particular, when manufacturing a TFT element, a thick SiN film is formed on an oxide film by a CVD method to supplement the insulating property. Since the CVD method is performed at a high temperature, a problem also arises in that, at this time, needle-like minute projections called hillocks generated on the surface of the aluminum-containing metal grow and break through the gate insulating film to cause defects in the display panel. . Further, the conventional anodic oxidation using a chemical conversion solution also has a problem that the chemical formation rate is low. Since the formation current density must be increased more than necessary to increase the formation rate, there is a limit in increasing the throughput using the conventional formation solution.

[0006]

Accordingly, an object of the present invention is to solve these problems of the prior art. That is, an object of the present invention is to provide a new chemical liquid capable of forming an oxide film having a sufficient insulating property on metals such as aluminum and aluminum alloys. Also, the present invention has a high formation rate,
Another object of the present invention is to provide a chemical conversion solution capable of increasing the throughput of a process including anodization. Another object of the present invention is to provide a chemical conversion solution that can suppress the occurrence of hillocks on the surface of a metal by using it for anodic oxidation of a metal such as aluminum or an aluminum alloy. In addition, the present invention provides a method for forming an oxide film having good insulation and high throughput,
Another object is to provide a metal having a highly insulating oxide film in which hillock generation is suppressed.

[0007]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, a chemical solution prepared by dissolving a salt of an aromatic carboxylic acid in a solvent having an alcoholic hydroxyl group was prepared. It has been found that anodization of a metal can be performed to form an oxide film having extremely good properties, and the present invention has been completed.

That is, the present invention provides a chemical liquid for forming a metal oxide film, which is obtained by dissolving a salt of an aromatic carboxylic acid in a solvent having an alcoholic hydroxyl group. As the solvent, for example, ethylene glycol and propylene glycol are preferably used. Further, as the aromatic carboxylic acid, salicylic acid, phthalic acid, benzoic acid or γ
The use of resorcinic acid is preferred.

The present invention also provides a method for forming a metal oxide film, comprising a step of anodizing a metal in the above-mentioned chemical conversion solution. This method can be preferably applied to, for example, a metal wiring thin film patterned on a substrate, particularly a wiring thin film obtained by sputtering an aluminum alloy containing a rare earth element such as Sc, Nd or Gd. Further, the present invention provides a metal, particularly an aluminum alloy, having an oxide film formed on the surface by these methods.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the contents of the present invention will be described in detail. The chemical conversion solution of the present invention contains a salt of an aromatic carboxylic acid as a solute. As the aromatic carboxylic acid,
A compound having a benzene ring, a condensed benzene ring, a non-benzene-based aromatic ring, a heteroaromatic ring, and the like and a carboxyl group can be used. Salicylic acid, as a heteroatom-free aromatic carboxylic acid that can be used in the present invention,
Phthalic acid, benzoic acid, γ-resorcinic acid, toluic acid,
Cumylic acid, t-butylbenzoic acid, anisic acid, 2,4-
Cresotic acid, cinnamic acid, N-methylanthranilic acid, gentisic acid, gallic acid and p-hydroxybenzoic acid can be exemplified. Examples of the heteroaromatic carboxylic acid include nicotinic acid, 2-furoic acid, 2-thenoic acid and hydrazylbenzoic acid. Further, an aromatic carboxylic acid having a functional group other than a carboxyl group can be used as long as the desired effect of the present invention is not impaired. For example, aromatic carboxylic acids having a nitro group or an amino group such as nitrobenzoic acid, anthranilic acid, monomethylaminobenzoic acid, and dimethylaminobenzoic acid can also be used. In the chemical conversion solution of the present invention, it is particularly preferable to use one or more compounds selected from the group consisting of salicylic acid, phthalic acid, benzoic acid and γ-resorcinic acid.

The cation for forming the salt of the aromatic carboxylic acid is not particularly limited. For example, an ammonium ion, an alkali metal ion, a 1,2,3 or quaternary alkyl ammonium ion, a phosphonium ion, a sulfonium ion, or the like can be used.
Among them, ammonium ion or 1,2,3 or 4
It is preferable to use a secondary alkyl ammonium ion.
When an alkylammonium ion is used, the size of the alkyl group can be selected in consideration of solubility in a solvent. Usually, an alkyl group having 1 to 4 carbon atoms is selected.
One of these solutes may be used alone, or two or more may be used in combination. Further, the above solutes and other solutes may be used in combination. The solute concentration of the chemical conversion solution of the present invention is generally set in the range of 0.01 to 30% by weight, and is preferably set in the range of 1 to 15% by weight.

In the chemical conversion solution of the present invention, a compound having an alcoholic hydroxyl group is used as a solvent. In the present invention, any compound having an alcoholic hydroxyl group can be used as a solvent regardless of its type. Among them, preferred solvents are aliphatic alcohols having an alcoholic hydroxyl group. For example, monohydric alcohols such as methanol, ethanol, propanol and isopropanol; dihydric alcohols such as ethylene glycol and propylene glycol;
Trihydric or higher polyhydric alcohols can be used. Further, a solvent having a functional group other than the alcoholic hydroxyl group in the molecule can also be used as long as the intended effect of the present invention is not impaired. For example, a solvent having an alkoxy group together with an alcoholic hydroxyl group, such as methyl cellosolve and cellosolve, can also be used.

These solvents may be used alone or in a combination of two or more. The preferred solvent for the chemical conversion solution of the present invention is a solvent having 1 to 8 carbon atoms, and particularly preferred solvents are ethylene glycol and propylene glycol alone or as a mixed solvent. Also, less than 50% by weight, preferably less than 30% of water can be added to the solvent and used. When the solvent contains water, the water content is preferably 0.1% or more and less than 25%, more preferably 0.1% or more and less than 20%.

The chemical conversion solution of the present invention can be effectively used for anodic oxidation of metals. With a typical aqueous chemical conversion solution conventionally used, an oxide film having good properties on a metal could not be formed, but an excellent oxide film was formed using the chemical conversion solution of the present invention. can do. That is, if the metal is anodized using the chemical conversion solution of the present invention, an oxide film having higher insulating properties can be formed as compared with the case where anodization is performed using a conventional chemical conversion solution. In addition, when anodizing is performed using the chemical conversion solution of the present invention, the time required for constant-current chemical formation can be shorter than that of a conventional chemical conversion solution, so that high-throughput production can be performed. Further, if an oxide film is formed using the chemical conversion solution of the present invention, generation and growth of hillocks due to high-temperature treatment in the subsequent steps can be suppressed. Therefore, an oxide film having a high withstand voltage can be efficiently formed by using the chemical conversion solution of the present invention. The oxide film formed using the chemical conversion solution of the present invention can also function as an impurity blocking film, a protective film for wirings and substrates, an anticorrosion film, a colored film, and a hygroscopic film.

Although not wishing to be bound by any theory, such an excellent effect of the present invention is based on the effect of a solvent having an alcoholic hydroxyl group that a solute or a solvent in a chemical conversion solution is traced in an oxide film during formation. It is considered to be caused by being taken in. In particular, carbon atoms constituting the solute or solvent are taken into the oxide film,
It is considered that the insulating property, the withstand voltage, and the hillock suppressing property are improved.

The conditions for anodizing a metal using the chemical conversion solution of the present invention are not particularly limited. The temperature during anodic oxidation is limited to the temperature range in which the chemical conversion solution is stably present as a liquid,
It is generally in the range of -20 to 150C, preferably in the range of 10 to 100C. The method of controlling the current and voltage at the time of anodic oxidation is not particularly limited, and conditions for forming an oxide film on the metal surface can be appropriately combined. Normally, formation is performed with a constant current up to a predetermined formation voltage (Vf), and after reaching the formation voltage, the voltage is maintained for a certain period of time to perform anodic oxidation. At this time, the current density is set at 0.
It is in the range of 001~100mA / cm ^2, preferably in the range of 0.01~10mA / cm ^2. Also, V
f is usually set in the range of 20 to 200 V, preferably in the range of 50 to 150 V. Note that a method may be employed in which an alternating current having a constant peak current value is used in place of the DC power supply until the formation voltage is reached, and when the formation voltage is reached, the system is switched to the DC voltage and held for a certain time.

The anodic oxidation using the chemical conversion solution of the present invention may be performed over the entire metal or only a part of the metal. When an oxide film is formed only on a part of a metal, a part to be anodized is selected in advance by a method such as a photoresist. The metal anodized using the chemical conversion solution of the present invention may be subjected to a heat treatment in order to further increase the insulating property of the oxide film. For example, 200
By heating to about 400 ° C., the insulation can be improved.

The insulating property may be further enhanced by forming an insulating film other than the oxide film formed by anodic oxidation. For example, in a TFT element, Si
An N film or a SiO ₂ film can be formed. These films are formed at a high temperature of 200 ° C. or more. Even at such a high temperature, generation of hillocks is suppressed as long as an oxide film is formed with the chemical conversion solution of the present invention.

The use of the chemical conversion solution of the present invention makes it possible to widely anodize metals. Examples of the target metal include aluminum or an aluminum alloy. In the case of an aluminum alloy, the type and number of metals to be combined with aluminum are not particularly limited. Therefore, any aluminum or aluminum alloy that can be used for TFT elements or wiring of an integrated circuit can be effectively anodized by the chemical liquid of the present invention.

Since pure aluminum has relatively high activity and easily generates hillocks, an alloy containing a trace amount of an element other than aluminum is preferably used as a wiring material. For example, Sc, Y, La, Pr, N
An alloy in which rare earth elements such as d, Gd, Dy, Ho, and Er are mixed (JP-A-8-250494) is used.
The chemical conversion liquid of the present invention can be suitably used for such an aluminum alloy containing a rare earth element, preferably an aluminum alloy containing Sc, Nd or Gd, particularly preferably an aluminum alloy containing Nd. The content of the rare earth element in the aluminum alloy is not particularly limited, but is generally 10 atomic% or less, preferably 6 atomic% or less, and particularly preferably in the range of 0.05 to 3 atomic%.

The chemical conversion solution of the present invention contains S
i, Cu, Pd mixed alloy, Ti, Ta, Zr, H
It can also be used for alloys in which valve metals such as f, Nb, W, and Mo are mixed (Japanese Patent Application Laid-Open No. 8-286209). The addition of these elements to aluminum generally increases the electrical resistance significantly. Therefore, the addition amount of these elements is limited to about 0.01 to 3%, and the electric resistance is generally set to 10 μΩ · cm or less, preferably 5 μΩ · cm or less. Further, the chemical conversion liquid of the present invention can also be used in a case where an additive metal and aluminum are mixed and then heated to about 300 to 450 ° C. to precipitate as an intermetallic compound of the additional metal and aluminum.

The method for forming an oxide film using the chemical conversion solution of the present invention can be widely used in various technical fields. For example, for the purpose of imparting corrosion resistance and weather resistance, it can be used for structural materials such as aircraft, ships, vehicles, and buildings, household articles, and optical devices. Further, for the purpose of imparting electrical, electronic and magnetic properties, it can also be used for alumite electric wires, printed distribution boards, electrolytic capacitors, magnetic recording disks, switching elements, humidity sensors and the like. Also, for the purpose of giving light and thermal characteristics, solar heat absorbing plates, reflecting plates,
It can also be used for multicolor alumite, photosensitive alumite, light emitting element, fluorescent element, IC radiator, and the like. Further, it can be used for lubricating anodized, hard anodized, speaker diaphragm, etc. for the purpose of giving specific mechanical properties. Further, it can be used for a PS printing plate, a name plate, a decorative panel, a transfer drum, and the like for the purpose of giving characteristics in printing, decoration, and design. In addition, catalyst, humidity anodized, adsorbent,
It can also be used for ion selective permeable membranes and filtration membranes.

The method of forming an oxide film using the chemical conversion solution of the present invention is particularly useful when a high insulating property is required for the oxide film such as a TFT element or a wiring of an integrated circuit. Above all, it is extremely effective if used for forming an insulating film of a gate wiring of a TFT element used for a liquid crystal display element. There are two types of TFT elements currently in practical use, a bottom gate type shown in FIG. 1 and a top gate type shown in FIG. 2, depending on the stacking order of gate wiring. The present invention relates to any structure of TF
Although it can be used for a T element, it is more effectively applied to a bottom gate type for performing anodic oxidation.

In order to manufacture the bottom gate type TFT device shown in FIG. 1, first, a substrate 1 usually made of non-alkali glass is used.
A gate wiring (gate electrode) 2 is deposited thereon by sputtering and patterned. The gate wiring deposited at this time becomes a metal to be anodized in the next step. Therefore, in the present invention, usually, pure aluminum or an aluminum alloy containing a trace amount of the rare earth metal-containing metal, valve metal, Si, Cu, Pd, or the like is deposited as a gate wiring. Thereafter, the oxide film 3 having excellent insulating properties is formed on the surface of the gate electrode 2 by anodic oxidation using the chemical conversion solution of the present invention, and heat treatment is performed as necessary to stabilize the film. If it is necessary to further increase the insulation between the gate electrode and the semiconductor layer, the Si
An N film is deposited, and a gate insulating film 4 is formed. At this time, generation and growth of hillocks are suppressed even at a high temperature by heat treatment or CVD of the oxide film 3. On the gate insulating film 4, a semiconductor layer 5 is further formed. Conventionally, an amorphous or polycrystalline silicon film heat-treated at 450 ° C. or higher has been used as a semiconductor layer. Recently, a polycrystalline silicon film heat-treated at a low temperature of 350 ° C. or lower has been developed.
Finally, a TFT element can be manufactured by forming a source electrode 6 and a drain electrode 7 on the semiconductor layer 5.

[0025]

The present invention will be described more specifically with reference to the following examples. Components, ratios, operating procedures, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown in the following examples.

Example 1 A glass substrate having a thickness of about 400
nm alloy thin film (98.5 wt% Al, 1.0 wt% S
i, 0.5% by weight of Cu) was deposited by a sputtering method. This thin film was subjected to constant current formation at a current density of 0.1 mA / cm ² to 100 V in each of the chemical conversion solutions described in Table 1,
After that, constant voltage conversion was performed for about 2 hours to form an oxide film. Further, a heat treatment was performed at 350 ° C. in a nitrogen atmosphere to stabilize the film. Thereafter, about 400 nm of Al was deposited by a sputtering method to form an electrode thin film, and an MIM type element having a 1 mmφ pattern was formed. Using the alloy thin film of the MIM device as a ground and the Al thin film as a working electrode, a voltage was applied from 0 V in steps of 1 V to measure leakage current. 100m between both electrodes
The voltage at which a current of A or more passed was recorded as the withstand voltage. Table 1 shows the results. Note that microscopic observation showed that almost no hillocks were observed in each oxide film.

[0027]

[Table 1]

Example 2 A glass substrate having a thickness of about 400
An alloy thin film of 90 nm (90 wt% Al, 10 wt% Nd) was deposited by a sputtering method. This thin film was treated in each of the chemical conversion solutions listed in Table 2 at a current density of 1 mA / cm ² for 10 minutes.
An oxide film was formed by performing constant current formation to 0 V and then performing constant voltage formation for about 2 hours. Table 2 shows the time required for constant current formation at this time. Furthermore, a heat treatment was performed at 300 ° C. in a nitrogen atmosphere to stabilize the film. After that, about 400 n of Al was sputtered.
By depositing m, an electrode thin film was formed, and an MIM element having a 1 mmφ pattern was prepared. The alloy thin film of this MIM element is used as a ground, the Al thin film is used as a working electrode,
A leakage current was measured by applying a voltage in steps of 1 V from V.
The voltage at which a current of 100 mA or more flowed between both electrodes was recorded as the withstand voltage. Table 2 shows the results. Note that microscopic observation showed that almost no hillocks were observed in each oxide film.

[0029]

[Table 2]

[0030]

As is clear from Tables 1 and 2, when the chemical conversion solution of the present invention is used, the insulating property of the oxide film formed is higher than when the conventional chemical conversion solution which is an aqueous solution is used. High and the time required for constant current formation is short. Further, the oxide film formed by using the chemical conversion solution of the present invention can prevent the growth of hillocks even in the subsequent high-temperature treatment.
Therefore, the use of the chemical conversion solution of the present invention makes it possible to produce an oxide film having high insulation properties and capable of effectively suppressing hillocks at a high throughput. The chemical conversion solution of the present invention is a metal,
In particular, it can be widely used for products and parts requiring anodization of aluminum or aluminum alloy. In particular, when used for forming an insulating film of a gate wiring of a TFT element, the SiN insulating film can be made unnecessary or thin, and the reliability of the element can be improved. Also,
Also when used for wiring of an integrated circuit, the dielectric strength can be increased, so that the reliability can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a bottom gate type TFT device.

FIG. 2 is a sectional view of a top gate type TFT element.

[Explanation of symbols]

 1: substrate 2: gate electrode 3: oxide film 4: gate insulating film 5: semiconductor layer 6: source electrode 7: drain electrode

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hiroshi Takaba 8-1, Chuo, Ami-cho, Inashiki-gun, Ibaraki Pref.

Claims (10)

[Claims] 1. A chemical liquid for forming a metal oxide film, wherein a salt of an aromatic carboxylic acid is dissolved as a solute in a solvent having an alcoholic hydroxyl group. 2. The chemical conversion solution according to claim 1, wherein the solvent is ethylene glycol or propylene glycol. 3. The method according to claim 1, wherein the aromatic carboxylic acid is salicylic acid,
The chemical conversion solution according to claim 2, which is one or more compounds selected from the group consisting of phthalic acid, benzoic acid and γ-resorcinic acid. 4. A method for forming a metal oxide film, comprising a step of anodizing a metal in the chemical conversion solution according to claim 1. 5. The forming method according to claim 4, wherein said metal is a metal wiring thin film patterned on a substrate. 6. The forming method according to claim 5, wherein the metal thin film wiring is obtained by sputtering aluminum or an aluminum alloy. 7. The method according to claim 5, wherein the metal thin film wiring is a wiring obtained by patterning an aluminum alloy containing a rare earth element on a substrate. 8. The method according to claim 1, wherein the rare earth elements are Sc, Nd and Gd.
8. One or more elements selected from the group consisting of:
The forming method as described above. 9. A metal having an oxide film formed on its surface by the method according to claim 4. 10. An aluminum alloy having an oxide film formed on the surface by the method according to claim 4.