KR20080096145A - Etching composition for thin film transistor-liquid crystal display devices - Google Patents

Abstract

A wet etching composition is provided to etch a metal layer to a uniform profile by preventing the undercut phenomenon in etching of a molybdenum/aluminium-neodymium(Mo/AlNd) bilayer and molybden/aluminium/molybden triple layer(Mo/Al/Mo) as well as a molybdenum monolayer. A wet etching composition comprises a phosphoric acid 45~70 weight%, nitric acid 1.5~6 weight%, acetic acid 17~30 weight%, molybdenum etching control agent 0.1~3 weight%, aluminum etching control agent 0.1~3 weight%, and the balance of water.

Description

Etching composition for thin film transistor liquid crystal display device {ETCHING COMPOSITION FOR THIN FILM TRANSISTOR-LIQUID CRYSTAL DISPLAY DEVICES}

1 is an electron micrograph showing the result of etching a molybdenum monolayer (left) or a Mo / AlNd multilayer (right) with an etchant of Example 1. FIG. It can be seen that both are smooth tapered etch profiles.

2 is an electron micrograph showing a result of etching a molybdenum monolayer (left) or a Mo / AlNd multilayer (right) with an etchant of Comparative Example 1. FIG. The etching rate of the molybdenum layer was too high, resulting in excessive etching, resulting in a poor etching profile and a stepped structure in the case of the Mo / AlNd multilayer (right).

3 is an electron micrograph showing a result of etching molybdenum monolayer (left) or Mo / AlNd multilayer (right) with the etchant of Comparative Example 2. The etching rate of the molybdenum layer was too high, resulting in excessive etching, resulting in a poor etching profile and a stepped structure in the case of the Mo / AlNd multilayer (right).

Figure 4 is an electron micrograph showing the result of etching the molybdenum monolayer with the etchant of Comparative Example 3. It can be seen that the excessive etching of molybdenum occurs, resulting in a poor final etching profile.

5 is an electron micrograph showing a result of etching a molybdenum monolayer with an etchant of Comparative Example 4. It can be seen that the excessive etching of molybdenum occurs, resulting in a poor final etching profile.

FIG. 6 is an electron micrograph showing a result of etching Mo / AlNd multilayer by the etchant of Comparative Example 5. It can be seen that over-etching of aluminum occurs and undercut occurs.

7 to 9 are electron micrographs of Mo / AlNd multilayers etched by changing only the type of aluminum etch regulator in the etchant of Example 1; FIG. 7 shows LiH ₂ PO ₄ , FIG. 8 shows LiOH, and FIG. 9 shows LiCl as an etching control agent, and shows excellent etching profiles without undercut phenomenon.

Liquid crystal display devices (LCD devices) are the most popular among flat panel display devices because they provide a clear image according to excellent resolution, consume less electricity, and make the display screen thinner. An electronic circuit driving such a liquid crystal display device is a thin film transistor (TFT) circuit, and typical thin film transistor liquid crystal display (TFT-LCD) devices form a pixel of a display screen. The TFT-LCD element fills a liquid crystal material between a TFT substrate having TFTs arranged as a switching element in a matrix form and a color filter substrate facing the substrate. The overall manufacturing process of TFT-LCD is divided into TFT substrate manufacturing process, color filter process, cell process, and module process. TFT substrate manufacturing process is very important in displaying accurate and clear images.

The manufacture of conventional TFT substrates consists of a pattern plating method in which a circuit pattern is plated on a substrate material such as glass. The first step of the pattern process is the generation of a gate electrode. A metal layer is commonly used for the gate electrode of the TFT, which is usually placed on the substrate material using a physical vapor deposition method. Applying a photoresist made of a photosensitive material that reacts to light on the metal gate electrode thus placed, and then covering the mask in the form of a desired circuit pattern to expose the light, the photosensitive material of the part covered with the mask and the part exposed to the light is physicochemical By causing the change, the insulating film can be selectively removed according to the pattern shape in the subsequent steps of etching and stripping.

Precise etching is essential for forming the TFT gate electrode in accordance with the circuit pattern. The metal commonly used as the wiring material of the gate electrode is made of molybdenum (Mo) and aluminum (aluminium, Al) or a combination of respective pure metals or alloys thereof, for example, molybdenum and aluminum-neodymium (Nd). It is plated in the form of a double layer or a triple layer of molybdenum / aluminum / molybdenum. Many thin films and thin layers are placed over the gate line of the TFT substrate, so that the cutting side of the etched substrate, that is, the etch profile spreads downwards evenly, to prevent unwanted electrical shorts between them. It is preferable that it is a taper shape. This is because when the etch profile becomes a tapered shape, the step difference between the various thin film layers formed is reduced. If the etching pattern of the gate metal is not uniform and precise, the resolution of the TFT-LCD image is reduced and the color is not accurate.

There are two types of etching methods of gate, source, and drain electrodes of a TFT substrate. Dry etching is a plasma composed of chlorine (Cl ₂ ), argon (Ar), and oxygen (O ₂ ). A typical method of spraying a mixed gas (process gas) in a state on a substrate in a vacuum atmosphere is typical, and wet etching is performed using a mixture of phosphoric acid (H ₃ PO ₄ ), nitric acid (HNO ₃ ), and acetic acid (acetic acid, CH ₃ COOH). To oxidize and shave the gate metal.

Wet etching method is an isotropic etching that is evenly etched in all directions, so it is not used to manufacture the shape below 3μm and has the disadvantage of high price of etchant and deionized water, but the equipment for process It has the advantage of low investment cost, no need to maintain high vacuum in over-etching environment and excellent etching selectivity in mask and substrate. The dry etching method has the greatest advantage that anisotropic etching can be etched with a structure of 3 μm or less, but it requires expensive vacuum equipment and physical dry etching has a disadvantage of poor selectivity.

In the prior art, phosphoric acid-nitric acid-acetic acid wet etching was once performed on Mo / Al bilayers widely used as TFT gate electrodes or additionally dry etching was performed after such wet etching. In the case of only one wet etching, there is a disadvantage in that an undercut phenomenon occurs in which the lower metal layer is etched more than the molybdenum layer. When dry etching is added to etch the molybdenum layer, the tapered etch profile However, there was a problem of reduced productivity due to process delays and increased costs. Phosphoric acid-nitric acid-acetic acid mixed acid etchant is inexpensive but has the disadvantage of not having an excellent etching effect evenly for multiple metal layers. Therefore, the LCD industry attempted to have such an effect by adding an additional component to the mixed acid, but the additional component itself was often expensive or accompanied by unwanted side effects due to an excellent etching effect. For example, the Republic of Korea Patent No. 420100 attempts to solve this problem by adding expensive additives fluorine-based surfactant and non-silicone antifoamant to the phosphoric acid-nitric acid-acetic acid etchant, Patent No. 456657 Added chlorinated perchloric acid (HClO ₄ ) or periodic acid (HIO ₄ ), but these oxidizing agents are environmentally harmful and cause another problem. Patent 598418 provides a composition in which a phosphate-nitric acid-acetic acid mixed acid is added with a boron-containing compound and a fluorine-containing compound, but for the purpose of smooth taper etching, an expensive etching control agent such as cerium (II) ammonium nitrate is actually added. The presence of can cause damage to the glass substrate.

Based on the mixed acid, it is possible to obtain a tapered etch profile at low cost with multiple wetted gate etching in one wet etching process and to be used for etching mixed metal layer electrode and source / drain Mo single layer electrode in common. The demand for it has been steady. However, the prior art has not been able to adequately meet this demand.

It is an object of the present invention to provide an etchant composition based on mixed acid, which is inexpensive, does not contain environmentally harmful substances, etc., and has a smooth and smooth tapered etching profile. According to the present invention, an aluminum etchant including molybdenum ion (Li ⁺ ) and a molybdenum etchant are added to the mixed acid composition to effectively taper the metal monolayer and the multilayer by only one wet etching, and do not include a fluorine compound. It is the objective to obtain the etching liquid composition which does not need to add glass etching inhibitors, such as a boron compound.

Recognizing this problem of being unable to satisfactorily etch a molybdenum monolayer and a metal mixed layer such as a Mo / Al double layer by one wet etching, the present inventors have developed a mixed acid etchant composition including an etch control agent.

The present invention relates to an etchant composition based on a mixed acid of phosphoric acid, nitric acid and acetic acid, wherein the composition comprises a small amount of molybdenum etchant and an aluminum etchant. Specifically, the present invention is equipped with 45 to 70% by weight of phosphoric acid, 1.5 to 6% by weight of nitric acid, 17 to 30% by weight of acetic acid, 0.1 to 3% by weight of molybdenum etchant, and 0.1 to 3% by weight of aluminum etchant. It is an etching liquid composition in which water occupies the weight.

Nitric acid serves as an oxidant to convert metal aluminum into aluminum oxide, an oxide, and to etch molybdenum. The content of nitric acid in the etchant of the present invention is 1.5 to 6% by weight relative to the total weight of the etchant. When the content of nitric acid in the etchant exceeds the above range, the etching rate of molybdenum increases, resulting in a poor etching profile. In this case, in the case of the Mo / AlNd and Mo / Al / Mo multilayers, the upper molybdenum layer becomes a severely stepped metal layer, resulting in very poor etching results. When the nitric acid content is below the above range, an undercut phenomenon occurs in which the lower aluminum layer is scraped off more than the upper molybdenum layer.

Phosphoric acid decomposes aluminum oxide formed by nitric acid. The content of acetic acid in the etchant of the present invention is 45 to 70% by weight relative to the total weight of the etchant. When the phosphoric acid content in the etchant falls below this content range, the etch rate of the source / drain molybdenum monolayer is high, resulting in poor etch profile. In addition, in the case of the Mo / AlNd double layer, which is a gate wiring material, when the phosphoric acid content is insufficient, the etching rate of aluminum is slowed and the etching rate of the upper molybdenum layer is increased to form a stepped profile. On the contrary, when the content of the phosphoric acid exceeds the above range, an undercut phenomenon occurs in which the upper molybdenum layer protrudes, and the viscosity of the etchant is excessive due to the viscosity of the phosphoric acid, thereby preventing etching evenly.

Acetic acid controls the rate of the etching reaction and lowers the viscosity of the etching solution. The rate of oxidation of the electrode metal is highly dependent on the pH of the reaction environment. Acetic acid, a weak acid, acts as a pH buffer to maintain the pH of the etchant and increase the life of the etchant. The amount of acetic acid in the etchant of the present invention is 17 to 30% by weight relative to the total weight of the etchant. When the amount of acetic acid is less than the above range, the buffering effect is insufficient, the life of the etchant is shortened and the viscosity of the etchant is increased so that the etching uniformity is reduced. If the content of acetic acid exceeds the above range, the etching rate of the upper molybdenum layer is lowered, causing problems in process yield and undercut.

The molybdenum etch control agent is a component that supports etching to a good profile for the molybdenum monolayer as well as the mixed metal layer made of other metals such as molybdenum and aluminum. Molybdenum etch modifiers are electrolytes that dissociate well in the etchant, and because they maximize the effect of the electrolyte, they reduce the adhesion between the photoresist and molybdenum, leading to excellent etch effects in the source / drain Mo monolayer. In the etching solution of the present invention, the content of molybdenum etching regulator is appropriately 0.1 to 3% by weight based on the total weight of the etching solution. If the molybdenum etch control agent is less than this, it may be difficult to penetrate into the interface between the photoresist and the metal layer, and thus, the etching result may not be obtained in the form of taper. This results in undercut of the / Al / Mo multilayer. Non-limiting examples of molybdenum etch regulators of the present invention include potassium nitrate (KNO ₃ ), potassium acetate (CH ₃ COOK), ammonium nitrate (NH ₄ NO ₃ ), ammonium acetate (CH ₃ COONH ₄ ), potassium dihydrogen phosphate (KH ₂ PO ₄ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), potassium hydrogen sulfate (KHSO ₄ ), and the like. In one embodiment of the present invention, it is preferred to use potassium nitrate or potassium acetate.

The aluminum etch regulator serves to reduce the corrosion rate of aluminum which is more easily oxidized in a mixed acid environment than molybdenum. As a result, even etching occurs in the molybdenum layer and the aluminum layer in the Mo / AlNd or Mo / Al / Mo multilayer to obtain a tapered etching profile. The aluminum etch regulator contains lithium ions (Li ⁺ ) to prevent potential differences between the molybdenum layer and the aluminum layer in the mixed acid etchant. Therefore, the galvanic phenomenon in which the redox battery is formed between the two metal layers is blocked. In the etchant of the present invention, the content of the aluminum etchant is suitably 0.1 to 3% by weight based on the total weight of the etchant. When the aluminum etchant is etched with an etchant that is less than the content range, an undercut phenomenon occurs in which the upper molybdenum layer protrudes, and when etching with an excess etchant, the stepped metal layer in which the upper molybdenum layer is overetched is left. Non-limiting examples of the aluminum etch regulator of the present invention include lithium nitrate (LiNO ₃ ), lithium acetate (CH ₃ COOLi), lithium phosphate dihydrogen (LiH ₂ PO ₄ ), lithium sulfate sulphate (LiHSO ₄ ), lithium hydroxide (LiOH) And lithium chloride (LiCl), lithium carbonate (Li ₂ CO ₃ ), and the like. In one embodiment of the present invention, lithium nitrate and lithium acetate are used.

The etchants included in the above-described weight ratio range fall within the scope of the invention disclosed by the etchant composition of the present invention, even if the composition is outside the numerical value of the weight ratio range or there is a substitution of some components shown as examples above. If it is obvious that the configuration is substantially equivalent to the etchant composition to those skilled in the art, even such configuration is within the technical spirit of the present invention.

Example

The present invention will be described in more detail with reference to the following Examples. The configuration shown in the following examples are intended to help the understanding of the invention to the last, and in any case it is not intended to limit the technical scope of the present invention to the embodiments presented in the examples.

[Experimental Example 1] Comparison of etching performance of the Example and Comparative Example etchant

The etchant of Example 1 was prepared according to the etchant composition of the present invention to compare the performance with the comparative example etchant in the prior art. The compositions of Example 1 and Comparative Examples 1 to 5 are shown in Table 1 and all% values are by weight.

 division Example Comparative example One One 2 3 4 5 Phosphoric acid 55% 40% 55% 55% 55% 55% Nitric acid 3% 3% 7% 3% 3% 3% Acetic acid 22% 22% 22% 16% 22% 22% Molybdenum Etching Regulator (KNO ₃ ) One% One% One% One% 0.05% One% Aluminum Etching Agent (LiNO ₃ ) One% One% One% One% One% 0.05% water Up to 100% by weight

For evaluation of performance, 10 L of etching liquid was sprayed on a 10 cm × 10 cm substrate on which a molybdenum / aluminum-neodymium (Mo / AlNd) metal multilayer or a molybdenum monolayer was laminated. The etching process was performed within 1 minute by spraying, followed by washing with water (DI-H ₂ O rinse) for 1 minute. After etching, the substrate was observed with an electron microscope to evaluate the etching performance.

The molybdenum monolayer (left of FIG. 1) or the Mo / AlNd metal multilayer (right of FIG. 1) was etched with the etchant of Example 1 prepared with one composition according to the composition ratio of the present invention. In the electron micrograph of FIG. 1, it can be seen that etching is appropriately performed based on the photoresist edge of the molybdenum monolayer, and in the case of multilayer etching, the molybdenum upper layer is more sharply cut than the lower aluminum layer, and the inclination of the two metal layers is appropriate. It can be seen that the tapered shape.

Comparative Example 1 is an etching liquid composition having a low content of phosphoric acid. As shown in FIG. 1, electron micrographs of a molybdenum monolayer (left) or a Mo / AlNd metal multilayer (right) etched by Comparative Example 1 are shown in FIG. 2. Due to the low phosphoric acid content, the etching speed of aluminum is slowed and the oxidation of molybdenum is accelerated, resulting in a stepped metal layer over-etched with the upper molybdenum layer. This etching result increases the risk of an electrical short, which causes a decrease in image quality of the TFT-LCD.

Comparative Example 2 is an etchant composition with an excessive amount of nitric acid. As shown in FIG. 1, electron micrographs of a molybdenum monolayer (left) or a Mo / AlNd metal multilayer (right) etched by Comparative Example 2 are shown in FIG. 3. Due to the high content of nitric acid, the rapid oxidation of molybdenum also results in a stepped metal layer over-etched with the upper molybdenum layer.

Comparative Example 3 shows a problem that may occur in the etching solution lacking the acetic acid content. The metal layer substrate etched in FIG. 4, which is an electron micrograph of a source / drain molybdenum monolayer etched with the etchant of Comparative Example 3, is not a tapered shape showing a gentle inclination, but a very steep inclination, resulting in poor etching profile.

Comparative Example 4 shows an etching profile that appears when the molybdenum etching regulator content is too low. In this case, it can be seen from the result of FIG. 5 that the etching profile is poor because the etching force cannot reduce the adhesion between the photoresist and the metal layer.

Comparative Example 5 is an experiment for showing the etching results when the aluminum etching regulator content is too small. It is evident that adding too much in excess of rain not only leads to an increase in costs, but also a problem that makes it impossible to obtain the desired taper etching.

Experimental Example 2

The lower the viscosity of the etchant for even etching. The viscosity of the etchant according to the elevation of the acetic acid content was compared. In Table 2 it can be seen that the etching solution according to the present invention of Example 1 is much lower in viscosity than the etching solution of Comparative Example 3 in which the acetic acid content is less than the scope of the present invention.

Comparison of Viscosity According to Acetic Acid Content Viscosity (room temperature) Example 1 24.3 cP Comparative Example 3 38.4 cP

Experimental Example 3 Comparison of Etching Performance According to Types of Aluminum Etching Control Agents

The etching performance of the three etching liquids (see Table 3) having the same composition as Example 1 but varying only the type of the aluminum etching control agent was compared.

 ingredient Example 2 3 4 Phosphoric acid 55% 55% 55% Nitric acid 3% 3% 3% Acetic acid 22% 22% 22% Molybdenum Etching Regulator (KNO ₃ ) One% One% One% Aluminum Etching Control One% LiH ₂ PO ₄ One% LiOH One% LiCl water Up to 100% by weight

From the electron micrographs of FIGS. 7 to 9, the mixed acid etchant including the lithium-based aluminum etch regulator as the content ratio of the present invention has excellent tapered etching profile without causing undercut etching as in Comparative Example 5 (FIG. 6). Able to know.

When the wet etching process is performed with the mixed acid etchant of the present invention, it is not necessary to use an expensive etching control agent, thereby reducing the cost of the etching process, preventing the life of the etching solution, and keeping the viscosity low. In addition, it is not only environmentally harmful, but also smooth, smooth, even and excellent tapered etching, which not only contributes to the production of high-quality TFT-LCD, but also facilitates the management of etching liquid waste. By using the etchant of the present invention, it is possible to effectively etch the metal monolayer and the multilayer by only one wet etching.

Claims (3)

Etching liquid comprising 45 to 70% by weight of phosphoric acid, 1.5 to 6% by weight of nitric acid, 17 to 30% by weight of acetic acid, 0.1 to 3% by weight of molybdenum etch regulator and 0.1 to 3% by weight of aluminum etch regulator Composition. The method of claim 1, The molybdenum etch regulator is potassium nitrate (KNO ₃ ), potassium acetate (CH ₃ COOK), ammonium nitrate (NH ₄ NO ₃ ), ammonium acetate (CH ₃ COONH ₄ ), potassium dihydrogen phosphate (KH ₂ PO ₄ ), phosphoric acid An etchant composition, characterized in that at least one substance selected from the group consisting of ammonium dihydrogen (NH ₄ H ₂ PO ₄ ) and potassium hydrogen sulfate (KHSO ₄ ). The method of claim 1, The aluminum etch regulator is lithium nitrate (LiNO ₃ ), lithium acetate (CH ₃ COOLi), lithium phosphate dihydrogen (LiH ₂ PO ₄ ), lithium sulphate sulfate (LiHSO ₄ ), lithium hydroxide (LiOH), lithium chloride (LiCl) , And lithium carbonate (Li ₂ CO ₃ ) is an etching liquid composition, characterized in that at least one substance selected from the group consisting of.

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