KR20150077207A - Wet Etching Material Preventing Glass Sludge - Google Patents

Abstract

The present invention relates to a wet etchant preventing generation of glass sludge, when etching a silicon oxide film formed on a glass substrate. The composition for wet etching controlling generation of glass sludge according to the present invention comprises 2-5 wt% of hydrogen fluoride (HF), 10-30 wt% of ammonium fluoride (NH_4F), 0,5-10 wt% of an organic acid additive, and deionized water (water).

Description

BACKGROUND ART [0002] Wet etching material Preventing Glass Sludge

The present invention relates to a wet etching solution for inhibiting generation of free precipitation in etching a silicon oxide film formed on a glass substrate. More particularly, the present invention relates to a wet etchant for suppressing generation of precipitates due to reaction with a glass substrate when etching silicon oxide in a thin film transistor substrate having an oxide semiconductor formed on a glass substrate.

As the information society develops, the demand for display devices for displaying images is increasing in various forms. As a result, it has rapidly developed into a flat panel display device (FPD) capable of replacing a bulky cathode ray tube (CRT) with a thin, light and large area. The flat panel display includes a liquid crystal display (LCD), a plasma display panel (PDP), an organic light emitting display (OLED), and an electrophoretic display device : ED) have been developed and utilized.

In the case of a liquid crystal display device, an organic light emitting display device, and an electrophoretic display device which are actively driven, the thin film transistor substrate includes thin film transistors arranged in pixel regions arranged in a matrix manner. BACKGROUND ART Liquid crystal display devices (LCDs) display images by adjusting the light transmittance of a liquid crystal using an electric field.

In order to achieve high efficiency and high precision of an active liquid crystal display device, a method of replacing an existing amorphous silicon thin film transistor with an oxide thin film transistor has been proposed. Korean Patent Laid-Open Nos. 10-2011-0027472 and 10-2010-0059586 disclose the use of indium-gallium-zinc oxide (IGZO).

Oxide thin film transistors, like amorphous silicon thin film transistors, use various insulating films for electrical insulation between metal wirings in electrical circuit design. In the case of an oxide thin film transistor, it is difficult to use the silicon nitride film alone because of the influence on the device characteristics of the thin film transistor, and a dual structure in which a silicon oxide film is stacked on the silicon nitride film is also used.

1 is a cross-sectional view illustrating a process of forming a contact hole through an insulating film in a liquid crystal display device using an amorphous silicon thin film transistor according to the related art. Referring to FIG. 1, a process of patterning an insulating film made of silicon nitride in a liquid crystal display device using an amorphous silicon thin film transistor will be described.

A thin film transistor T including a gate electrode G, a semiconductor layer A including amorphous silicon, a source electrode S and a drain electrode D is completed on a glass substrate SUB. A nitride insulating film (PAN) containing silicon nitride (SiNx) is applied on the thin film transistor T.

A photoresist PR is applied on the nitride insulating film PAN and exposed and developed using a mask to form a pattern corresponding to the pixel contact hole PH for exposing the drain electrode D of the thin film transistor T . Using the pattern of the patterned photoresist PR as a mask, the nitride insulating film (PAN) is dry-etched. A nitride insulating film (PAN) having a thickness of several thousand angstroms is easily etched by dry etching. That is, in a thin film transistor substrate including amorphous silicon, a nitride insulating film is mainly used, but there is no great problem in forming a contact hole by dry etching well known in the art. However, the situation differs in a thin film transistor substrate using an oxide semiconductor.

2 is a cross-sectional view illustrating a process of forming a contact hole through an insulating film in a liquid crystal display device including a thin film transistor using a conventional oxide semiconductor material. Referring to FIG. 2, a process of patterning an insulating film made of silicon oxide in a liquid crystal display device using an oxide semiconductor thin film transistor will be described.

The thin film transistor T including the gate electrode G, the semiconductor layer A including the oxide semiconductor, the source electrode S and the drain electrode D is completed on the glass substrate SUB. Since the thin film transistor T includes an oxide semiconductor material, silicon oxide (SiOx) having a low dielectric constant and high insulation property is used together with silicon nitride (SiNx) due to a problem of device characteristics. For example, a nitride insulating film (PAN) including silicon nitride is formed to a thickness of several hundred angstroms, and then an oxide insulating film (PAO) containing silicon oxide is further formed to a thickness of several thousands of angstroms.

A photoresist PR is applied on the oxide insulating film PAO and exposed and developed using a mask to form a pattern corresponding to the pixel contact hole PH for exposing the drain electrode D of the thin film transistor T . The oxide insulating film (PAO) and the nitride insulating film (PAN) are etched using the pattern of the patterned photoresist (PR) as a mask. In this case, it takes a long time to etch the oxide insulating film (PAO) having a thickness of several thousands of angstroms by dry etching. On the other hand, a nitride insulating film (PAN) having a thickness of several hundred angstroms can be etched sufficiently by a wet method.

This is because the silicon nitride film generally has an etching rate four times or more higher than that of the silicon oxide film by the dry etching method. In addition, the corrosiveness of the metal exposed after etching should be considered according to the etching gas used in the dry etching. Also, environmental pollution caused by etching gas must be considered. Above all, there is also a problem that dry etching equipment is expensive and expensive to manufacture.

Therefore, it is necessary to convert the etching method of the insulating film in the process of manufacturing the thin film transistor substrate including the oxide semiconductor thin film transistor from dry etching to wetting. In order to wet-etch the insulating film made of silicon oxide, an etching solution (or BOE (Buffered Oxide Etchant)) using a hydrofluoric acid inorganic acid mainly containing HF and NH4F is used.

BOE etching may be performed by spraying an etching solution on the entire surface of the thin film transistor substrate or by dipping the etching solution in a water bath containing the etching solution. In addition to the dipping method, or in the spray method, the etchant can be brought into contact with the edge or backside of the substrate other than the surface to be etched. Particularly, the etching liquid may be partially contacted only by the conveyor moving the substrate, so that a stain may occur. In this case, the back surface is also subjected to the same BOE etching to make the surface of the back surface uniform.

Thus, the glass substrate itself is also etched by the BOE. When the glass substrate is exposed to the BOE, an etching sludge may occur excessively. This glass precipitate has a very low solubility for the BOE solution unlike the oxide insulating film (PAO) containing silicon oxide. In other words, it is not dissolved in the BOE but remains in the form of particles. As a result, the precipitated particles clog the internal filter of the BOE equipment, resulting in costly problems such as failure of the device or frequent replacement of the filter, which may result in lower process efficiency.

The reason why the glass precipitates are generated during the BOE etching is as shown in Table 1 because the glass contains various kinds of metal oxides such as Al, Ca, and Mg with SiO ₂ as a main component. In other words, SiO ₂ in BOE reacts with HF or NH ₄ F to form H ₂ SiF ₆ or (NH ₄ ) ₂ SiF ₆ salt. These salts have a relatively high solubility for the BOE solution. On the other hand, in the case of other metal oxides except SiO ₂ , it reacts with HF to form metal fluoride (M ⁺ -F- ^x ). These metal fluorides are hardly dissolved in BOE and precipitate in the form of particles.

ingredient SiO ₂ Al ₂ O ₃ CaO MgO B ₂ O ₃ Other (Etc) content(%) 62.3 17.2 7.5 1.4 10.5 1.1

Korean Patent No. 2010-0019328 discloses an etching composition for etching an insulating film containing silicon oxide containing various additives. However, these conventional techniques are merely for the purpose of increasing or decreasing the etching selection ratio of the silicon oxide film and the silicon nitride film used in the semiconductor process. That is, there is no consideration for the glass precipitate incidentally generated when the silicon oxide film and the silicon nitride film are etched on the glass substrate. Further, the etching compositions disclosed in these prior arts do not effectively suppress the generation of free precipitates.

SUMMARY OF THE INVENTION An object of the present invention is to provide a wet etching solution for etching a silicon oxide film without a glass etching deposit in a process for manufacturing a thin film transistor substrate including an oxide semiconductor. It is another object of the present invention to provide a wet etchant that does not reduce or cause free precipitation, regardless of the free etch rate.

In order to achieve the object of the present invention, the wet etching solution for suppressing the generation of the glass precipitate according to the present invention comprises hydrogen fluoride (HF), 2 to 5 wt%; Ammonium fluoride (NH ₄ F), 10 to 30 wt%; Organic acid additive, 0.5 to 10 wt%; And deionized water (water).

The organic acid additive is characterized by containing a compound selected from the group consisting of carboxylic acids having 1 to 20 carbon atoms.

The acid organic acid additive is characterized in that it contains at least one selected from the group consisting of citric acid, malonic acid, tartaric acid and malic acid.

The content ratio of the hydrogen fluoride (HF) to the ammonium fluoride (NH ₄ F) is 1:20 to 4:10.

The content of hydrogen fluoride (HF) is 3 to 5 wt%, the content of ammonium fluoride (NH ₄ F) is 15 to 20 wt%, and the content of the organic acid additive is 0.5 to 5 wt%.

The wet etchant according to the present invention may inhibit the formation of free precipitates by interfering with the formation of the fluoride of the metal component using an organic acid additive. Alternatively, even if a glass precipitate is generated, the glass precipitate can be prevented from growing into particles. Therefore, when the silicon oxide film is etched on the glass substrate using the wet etching solution according to the present invention, the etching of the silicon oxide film can be performed without problems and the generation of free precipitates can be prevented.

1 is a cross-sectional view illustrating a process of forming a contact hole through an insulating film in a liquid crystal display device using an amorphous silicon thin film transistor according to the related art.
BACKGROUND OF THE INVENTION Field of the Invention [0001] The present invention relates to a method of manufacturing a thin film transistor (TFT) using an oxide semiconductor material.
FIG. 3A is a schematic view for explaining a mechanism by which a glass precipitate is generated in a wet etching solution containing no organic acid additive according to the prior art; FIG.
FIG. 3b is a schematic diagram illustrating a mechanism by which a wet etchant containing an organic acid additive according to the present invention controls glass precipitates. FIG.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Like reference numerals throughout the specification denote substantially identical components. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following description, a detailed description of known technologies or configurations related to the present invention will be omitted when it is determined that the gist of the present invention may be unnecessarily obscured. In addition, the component names used in the following description may be selected in consideration of easiness of specification, and may be different from the parts names of actual products.

≪ Composition of BOE etching solution >

In the thin film transistor substrate manufacturing process including oxide semiconductor used in the prior art, the composition of HF and NH ₄ F is determined by taking into account only the etching rate of the silicon oxide film, and the etching solution for etching the silicon oxide film is used. That is, no consideration is given to glass precipitates in the etching process using BOE. Therefore, in the present invention, the optimum composition ratio of HF and NH ₄ F is sought in the composition of the BOE etching solution, taking account of the glass precipitate preferentially.

Using the composition ratio of BOE used in the prior art as a starting point, the etch rate of the glass substrate and the amount of free precipitation were measured in comparison with the silicon oxide film while varying various composition ratios. As a result, it is preferable that the weight ratio of HF / HN ₄ F is 0.5 or less and the NH ₄ F concentration is 5 to 40 wt%. When the weight ratio of HF / NH ₄ F is 0.5 or more, the concentration of the hydrogen ion (H +) may increase and the acidity (pH) may be somewhat lowered. As a result, the etching rate of the glass substrate is increased (i.e., the etching rate of the glass substrate is faster than that of the silicon oxide film), thereby increasing the amount of free precipitation. In addition, when the concentration of NH ₄ F is 40 wt% or more, the concentration of the solid content in the BOE increases, the solubility of the free precipitate decreases, and the amount of precipitate generated increases. That is, the maximum weight ratio of NH ₄ F is preferably 5 to 40 wt%, and the weight ratio of HF / HN ₄ F is preferably 0.5 or less, so that the weight ratio of HF is preferably 1 to 20 wt%.

Referring to Table 2, the most significant composition ratios among the various composition ratios of HF and NH ₄ F, which are basic materials constituting the BOE, are compared and analyzed. Experiments on the etching rate of the silicon oxide film and the glass substrate were carried out as follows. A silicon oxide (SiO ₂ ) film was deposited on a glass substrate to a thickness of 5000 Å, and then a pattern was formed at intervals of 10 to 20 μm. Respectively. In the evaluation method, 150 g of the BOE etching solution was filled in a transparent flask, stirred at a speed of 300 rpm using a stirrer, the evaluation temperature was adjusted to 30 캜, and the evaluation specimen was immersed vertically to perform etching.

BOE composition Composition ratio (% by weight) Etching speed (Å / sec) Etching selection ratio
(SiO ₂ / Glass) HF NH ₄ F The silicon oxide film Glass substrate BOE1 2.5% 20% 30.5 21.6 1.36 BOE2 (normal) 2.5% 38% 15.2 11.5 1.32 BOE3 4% 10% 55.0 43.0 1.28 BOE4 4% 20% 50.8 38.5 1.32 BOE5 6% 20% 68.3 54.0 1.26 BOE6 10% 20% 120.4 101.2 1.19 BOE7 20% 20% 230.0 200.5 1.15

In Table 2, when BOE1, BOE4 to BOE7 are compared, it can be seen that as the concentration of HF increases at the same NH ₄ F concentration, the etch rates of the silicon oxide film and the glass substrate increase. In Table 2, BOE2 is the ratio used in the prior art and is generally known as normal BOE. In the present invention, the composition ratio was determined by reducing the ratio of NH ₄ F in the normal BOE (BOE 2). Comparing the BOE1 and BOE2, as the HF concentration increases at the same concentration of NH ₄ F, there is an etching rate of the silicon oxide film and the glass substrate can be seen that all decreased. This is because the higher the NH ₄ F concentration is, the lower the etching reactivity of HF is. Therefore, it is necessary to adjust the composition ratio of HF and NH ₄ F in consideration of both the etching rate of the silicon oxide film and the etching rate of the glass substrate. Therefore, considering the precipitates generated in the glass substrate, the content ratio of HF and NH ₄ F in BOE is maximized to the content ratio of normal BOE, HF: NH ₄ F = 1: 20, It is desirable to increase the content.

Also, when BOE4 to BOE7 are compared, the etch selectivity tends to decrease as the HF concentration increases at the same NH ₄ F concentration. That is, the higher the concentration of HF, the faster the etch rate of the glass substrate. This means that a large amount of free precipitates can be generated. As a result, the composition ratio of HF and NH ₄ F suitable for lowering the ratio of free etching is preferably 0.5 (ie, HF: NH ₄ F = 1: 2) or less.

If more than a number of comprehensive experiments, the base material of the composition ratio of HF and NH ₄ F of the wet chemical etch according to the present invention is the _{NH 4 F 5 ~ 40wt%,} HF will be the ratio of the content 1-20wt% HF: NH ₄ F = 1: 2 to 1:20, and the remainder of the content preferably includes deionized water (water). Most preferred, the composition ratio of the BOE, HF and 2 to 5wt%, NH ₄ F is from 10 to 30wt%, In terms of the content ratio, HF: a 5: NH ₄ F = 1.

As a result of increasing HF content and reducing NH ₄ F content compared to normal BOE, the etching rate of the silicon oxide film could be increased when the ratio of HF to NH ₄ F was limited to 0.5. On the other hand, although it is not serious, it is seen that the free precipitation slightly increases. Therefore, an additional measure for suppressing the generation of slightly precipitated free precipitates will be described below.

<Organic acid additive>

As described above, when the composition ratio of HF and NH ₄ F, which are the basic materials for forming the BOE etching solution, is purely composed of these basic materials, the etching rate of the silicon oxide film is ensured while the etching rate of the glass substrate is minimized . Therefore, it is difficult to completely control the glass precipitate only by the above composition ratio.

In the present invention, 0.5 to 10 wt% of an organic acid additive is added in order to effectively control the generation of free precipitates. If the organic acid additive is less than 0.5 wt%, the etching rate may be too low. On the other hand, if it exceeds 10 wt%, the etching rate may become excessively large or the glass precipitate may increase.

As the organic acid additive according to the present invention, it is preferable to use a compound selected from the group consisting of carboxylic acids having 1 to 20 carbon atoms. The organic acid additive may be used alone or in combination of two or more kinds of organic compounds. For example, the organic additive according to the present invention may comprise at least one selected from the group consisting of citric acid, malonic acid, tartaric acid, malic acid and other water-soluble organic acids . It is also possible to use lactic acid, acetic acid, formic acid, gluconic acid, glycolic acid, oxalic acid, butanoic acid, (Pentanoic Acid), and other water-soluble organic acids.

Referring to Table 3, it is examined how the generation of free precipitation occurs when the organic acid additive is added to BOE. Here, for convenience, only BOE2, which is a normal BOE in Table 2, and BOE4, which has a typical BOE composition ratio of the present invention, are summarized. With respect to these BOE compositions, the ratio of generation of free precipitates was measured with respect to the change in the content of the organic acid additive.

division BOE composition Organic acid additive
Content (wt%) The silicon oxide film
Etching speed (Å / sec) Glass precipitate
Occurrence rate (%) Experiment 1 BOE2 (2.5: 38) 0 15.3 73.8% Experiment 2 BOE4 (4:20) 0 50.9 78.2% Experiment 3 BOE2 (2.5: 38) 0.5 to 10 15.2 20.4% Experiment 4 BOE4 (4:20) 0.5 to 10 50.8 3.4% Experiment 5 BOE3 (4:10) 0.5 to 10 50.8 17.1%

Referring to Table 3, it can be seen that, in BOE 2, which is a normal BOE without addition of organic acid (Experiment 1), a large amount of free precipitation occurs even though the etching rate of the silicon oxide film is not fast. On the other hand, in the case of BOE4 having a preferable content ratio according to the present invention (Experiment 2), when the organic acid is not added, the etching rate of the silicon oxide film is about 5 times faster than the normal BOE. However, the generation of free precipitation is almost similar to normal BOE.

On the other hand, in the case of adding 0.5 to 10 wt% of organic acid in BOE2, which is a normal BOE (Experiment 3), the etch rate of the silicon oxide film was not greatly changed and 20.4% of the generation of free precipitation was reduced by one third or more. Further, in the case where 0.5-10 wt% of organic acid was added to BOE4 having a preferable content ratio of the present invention (Experiment 4), the generation rate of free precipitates was almost 1/20 Which is 3.4%. That is, the process time can be sufficiently secured, and the generation of free precipitates can be minimized.

On the other hand, in the case of BOE3 (Experiment 5) in which the content of organic acid was the same and the content of HF was increased in BOE, the etching rate of the silicon oxide film did not change much more than BOE4, but the amount of free precipitate increased by about 5 times. However, the glass precipitate is reduced by about 1/4 as compared with the case where the organic acid is not added, so that the glass precipitate can be sufficiently controlled. That is, even if the content ratio of HF: NH ₄ F to HF is increased, it is preferable that the content does not exceed 4:10 at the maximum.

Here, the content of the organic acid additive is expressed as 0.5 to 10 wt% rather than a fixed value. This is expressed as a range value because there is little difference in the results within this range. However, when it exceeds 10 wt%, it is not included in the chart because the amount of free precipitate increased remarkably. In particular, considering various conditions, the most preferable content of the organic acid additive is 0.5 to 5 wt%.

3A and 3B, the mechanism by which the organic acid additive according to the present invention controls the glass precipitate will be described. FIG. 3A is a schematic diagram illustrating the mechanism by which free precipitation occurs in a wet etchant not containing an organic acid additive according to the prior art. FIG. 3B is a schematic diagram illustrating a mechanism for controlling the glass precipitate by the wet etching solution containing the organic acid additive according to the present invention.

The reason why the glass precipitates are generated is that the metal component (M ⁺ ) of the non-silicon-based metal oxide added to the glass containing silicon oxide as the main component is cationic, and this cation reacts with the fluorine anion (F ^- ) of HF contained in the BOE Because it forms water. Referring to FIG. 3A, the glass includes a metal oxide such as aluminum oxide (Al ₂ O ₃ ) and calcium oxide (CaO) with silicon oxide (SiO ₂ ) as a main component. When hydrofluoric acid (HF) is added thereto, the fluorine anion (F ^- ) of the hydrofluoric acid (HF) is complexed with silicon (Si) to form silicon fluoride (SiF ₄ ). At the same time, the metal cation of the metal oxide is also complexed with the fluorine anion (F ^- ) of hydrofluoric acid (HF) to form aluminum fluoride (AlF ₂ ) and calcium fluoride (CaF ₂ ). These fluorinated metal materials are insoluble and coagulate with each other, and precipitates are generated.

3B, when organic acid is added to BOE according to the present invention, the fluorine anion (F ^- ) of hydrofluoric acid (HF) is complexed with silicon (Si) to form silicon fluoride (SiF ₄ ) The etching is done in the same way. On the other hand, the metal cation of the metal oxide is complexed with an organic acid, and a soluble substance having a structure of Al ₂ -organic acid and Ca-organic acid is produced. That is, the organic acid prevents the cation (M ⁺ ) of the metal component from forming a flame retardant, thereby preventing generation of free precipitate.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Therefore, the present invention should not be limited to the details described in the detailed description, but should be defined by the claims.

SUB: glass substrate T: thin film transistor
A: semiconductor layer G: gate electrode
S: source electrode D: drain electrode
PAN: Nitride insulating film PAO: Oxidation insulating film
PR: Photoresist PH: Pixel contact hole

Claims (5)

Hydrogen fluoride (HF), 2 to 5 wt%;
Ammonium fluoride (NH ₄ F), 10 to 30 wt%;
Organic acid additive, 0.5 to 10 wt%; And
A wet etchant containing deionized water (water) to inhibit the formation of glass precipitates.
The method according to claim 1,
Wherein the organic acid additive comprises a compound selected from the group consisting of carboxylic acids having 1 to 20 carbon atoms.
3. The method of claim 2,
The acid-
A water-soluble organic acid including at least one selected from the group consisting of citric acid, malonic acid, tartaric acid and malic acid. .
The method according to claim 1,
Wherein the content ratio of hydrogen fluoride (HF) to ammonium fluoride (NH ₄ F) is 1:20 to 4:10.
The method according to claim 1,
Wherein the content of hydrogen fluoride (HF) is 3 to 5 wt%, the content of ammonium fluoride (NH ₄ F) is 15 to 20 wt%, and the content of the organic acid additive is 0.5 to 5 wt%. .

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