KR20010077228A - Etching solution for Molybdenum-Aluminum alloy-Molybdenum metal layer - Google Patents

Abstract

PURPOSE: An etchant for etching a tri-layered metallic film of Mo/Al-Nd/Mo is provided, which can etch the tri-layered metallic film of Mo/Al-Nd/Mo without undercut phenomenon of a bottom Mo layer while forming a metal line of a TFT-LCD. CONSTITUTION: A tri-layered metallic film of Mo/Al-Nd/Mo is used as a source/drain array metal line. And the etchant includes H3PO4 of 68-74 wt%, HNO3 of 2-4 wt%, CH3COOH of 5-15wt% and water. And the etchant also includes an additive of 0.01-0.l05 wt% of the whole composition. The etchant also includes H3PO4 of 70-74 wt%, HNO3 of 2-4 wt%, CH3COOH of 8-15wt%, water and an additive of 0.01-0.03 wt%. The water is an ultra pure water having a resistance above 18M ohm.

Description

Etching solution for molybdenum-aluminum alloy-molybdenum metal layer

The present invention relates to an etching solution used for the wet etching of a metal film of a multilayer structure in a semiconductor device. More particularly, the present invention relates to an etching solution capable of etching a triple layer metal film of Mo / Al-Nd / Mo without undercut of a lower Mo layer in a source / drain array forming process of a TFT-LCD. The etching solution is a mixed solution of phosphoric acid, nitric acid, acetic acid, additives and water in a specific ratio.

In a semiconductor device, the process of forming metal wiring on a substrate is usually a unit process step of thin film deposition-photolithography (resist application, alignment, exposure and development)-etching, and the results and abnormalities before and after each unit process are examined. Inspection to confirm and cleaning to maintain cleanliness. The etching process refers to a process of forming a pattern by applying a resist onto a thin film on a substrate or a wafer, and then exposing and developing a pattern, and then removing the unnecessary thin film by chemical or physical reaction, leaving only necessary portions. In general, a dry etching process using plasma or the like or a wet process using an etching solution is used.

The dry process using the process gas plasma has the advantages of better etching control, easier endpoint detection, adjustable profile, and less process waste compared to the wet process. However, bulk processing is difficult and contamination and damage by process gas occur during etching. On the other hand, the wet process has a higher selectivity than the dry process, and can be processed in large quantities, thereby increasing the productivity, and the cost of the device is very low.

Various metals or alloys thereof are used as the metal wiring material of the semiconductor device, and Al metals having low electrical resistance are generally used as the metal film for gate and source / drain wiring of TFT-LCD. However, pure Al is weakly resistant to chemicals and can cause wiring defects in subsequent processes, so it has recently been used in the form of Al alloys, or multilayers of layers with another metal layer over Al or Al alloy layers. The structure is applied.

In the etching process, which is essentially used in the formation of the gate and source / drain array of the TFT-LCD, control of steps, that is, obtaining proper step slope and good profile, is an important item of process management.

In the case of wet etching bilayers of different materials, protrusion of the upper layer or undercut of the lower layer may occur due to the difference in etching rate and etching mechanism. The protruding phenomenon of the upper layer causes a problem to be removed by further wet or dry etching, and the undercut phenomenon of the lower layer causes major defects such as disconnection of the upper layer on the inclined surface or short circuit of upper and lower metals in the subsequent process. This drawback is a major obstacle to wet etching the bilayer metal film, and has been the basis for favoring dry etching despite the disadvantages of high cost, low productivity, and increased defect rate due to damage.

However, Patent Application No. 99-41119 by the present inventors discloses that the composition ratio of these acids in the existing Al etching solution composed of phosphoric acid, nitric acid, acetic acid and water is changed specifically, so that the Mo-based Al-Nd lower layer and the Mo upper layer are formed. Even if the wet etching of the / Al-Nd bilayer metal film is performed in a single process, an excellent etching solution with excellent profile and good step slope is proposed.

The technical problem in conventional single film wet etching is to optimize the etching solution and its composition corresponding to the processing material, to improve the adhesion with the processing material and the resist, to mix the etching solution with good uniformity and to control the temperature There are many studies on these. However, in the wet etching of the double layer metal film, it is generally accepted that it is not possible to perform the etching process in a single step by simply changing the composition ratio of the etching solution. The achievement of a single step wet etching of a double layer metal film by means of economics is also surprising.

However, for such multilayer metal films of three or more layers, such an effective etching process / solution has not been developed so far, so that each layer is etched by a separate wet or dry process or a combination thereof. In order to reduce process steps and costs, in the case of wet etching two layers simultaneously, it is possible to etch the protruding portions of the top layer with an additional process if only an upper layer overhang occurs. However, if an underlayer undercut occurs, there is a high probability that the upper layer will be disconnected from the inclined surface or a short circuit will occur between the upper and lower metals in a subsequent process, leading to a major failure of the semiconductor device.

For this reason, despite the inconvenience and cost of the process, when etching the triple layer metal film, a separate wet and / or dry etching is used for each layer.

In this situation, the present inventors have studied to develop an etching solution capable of simultaneously etching one or more layers without exhibiting an undercut phenomenon in the underlying layer during the etching of the Mo / Al-Nd / Mo triple layer metal film. In the existing Al thin film etching solution of nitric acid, acetic acid and water, it was found that the specific Mo / Al-Nd / Mo metal film can be etched without the occurrence of undercut of the lower Mo layer if the composition ratio of these acids was changed. It was. In addition, even if protrusion of the upper Mo layer or the middle Al-Nd layer occurs, since there is no undercut of the lower Mo layer, only the protruding portion of the upper Mo layer can be etched by the usual additional dry etching, which is economical and convenient. It has also been found that it can provide good step control, layering control and good profile.

FIG. 1 is a SEM photograph showing a profile in which an undercut phenomenon of a lower Mo layer occurs after wet etching an Mo / Al-Nd / Mo triple layer with a conventional Al etching solution.

2 is a SEM photograph showing a profile in which the undercut phenomenon does not appear after wet etching an Mo / Al-Nd / Mo triple layer with an Al etching solution according to the present invention.

Accordingly, it is an object of the present invention to etch a Mo / Al-Nd / Mo triple layer metal film, which is a source / drain material, during the formation of a wiring of a semiconductor device, particularly a TFT-LCD, without undercutting of the lower Mo layer. In providing an etching solution.

The etching solution according to the invention is 68 to 74% by weight of phosphoric acid (H ₃ PO ₄ ), 2 to 4% by weight of nitric acid (HNO ₃ ), 5 to 15% by weight of acetic acid (CH ₃ COOH) and 100% by weight And an amount of water of 0.01 to 0.05% by weight based on the total weight of the composition, if necessary. The etching solution according to the invention is preferably from 70 to 74% by weight of phosphoric acid, from 2 to 4% by weight of nitric acid, from 8 to 15% by weight of acetic acid and from water to an amount of from 100% to 0.01% by weight if necessary. 0.03% by weight of additives.

In the following, the present invention is described in more detail.

In a semiconductor device, a unique etching solution is developed and used depending on the type of metal and the type of substrate forming the wiring. The basic structure of the channel portion of the TFT-LCD device is composed of a gate, a Si insulating layer, a source / drain, a passivation layer, and an ITO layer, and mainly uses Al or Al alloy as the metal for forming the source / drain wiring.

Dry etching and wet etching methods for Al or Al alloys and the process gases and etching solutions used therein are well known. In dry etching, plasma is used by Cl process gas such as CCl ₄ , Cl ₂ , BCl ₃ , SiCl ₄ , HCl, CCl ₂ F ₂ , CCl ₃ F or F process gas such as SF ₆ , CF ₄ , CHF ₃ . The etching is carried out and the wet etching is carried out at 30 to 45 DEG C using an etching solution composed of phosphoric acid, nitric acid, acetic acid and water, for example 72% phosphoric acid, 2% nitric acid, 10% acetic acid and 16% water.

Nitric acid reacts with Al to form aluminum oxide, and phosphoric acid and water decompose the material. At this time, the water also serves to dilute the etching solution. Acetic acid is used as a buffer to control the reaction rate and the like, which controls the rate of decomposition of nitric acid and generally reduces the rate of degradation.

In the multilayer metal film, in order to etch several layers at the same time, the composition ratio of the etching solution must be adjusted so that the etching rate (E / R, Etching rate) calculated according to the following equation is similar.

Etch Rate (E / R, Å / min) = [(Thickness before etching)-(Thickness after etching)] / (Etching time)

According to the patent application 1999-41119 by the applicant, since the etching rate of the Mo layer is slower than that of the Al-Nd alloy layer, the content of nitric acid which directly affects the etching rate of the Mo layer is increased, and In order to reduce the etching rate of the -Nd alloy layer, the content of phosphoric acid is decreased and the content of acetic acid is increased. In this way, the angular component ratio of the etching solution was adjusted, and the weight ratio of phosphoric acid (H ₃ PO ₄ ), nitric acid (HNO ₃ ) and acetic acid was (40 to 70): (5 to 20): (10 to 20). Preferably, when the weight ratio is (50 to 60): (5 to 10): (10 to 15), the difference in etching rate between the upper Mo layer and the lower Al-Nd layer is minimized, and as a result, the upper Mo layer The phenomenon of protruding to the outer portion of the lower Al-Nd alloy layer was solved. Water is used in an amount of up to 100% by weight of the mixture, generally 0-30% by weight.

In contrast, in the present invention with respect to Mo (upper layer) / Al-Nd (middle layer) / Mo (lower layer) triplet layer, the content of nitric acid is reduced to 2 to 4% by weight. For illustrative purposes only, this reduction in nitric acid content appears to be because, in the present invention, the upper and lower layers are the same Mo layer, which helps to balance the etching rate between them.

On the other hand, compared with the etching solution of the Mo / Al-Nd bilayer, in the etching solution for the triple layer metal film of the present invention, the content of phosphoric acid which relatively decreases the etching rate of the Al-Nd alloy layer is increased while increasing the overall etching rate. Increased acetic acid content gave good results.

Phosphoric acid, nitric acid, acetic acid, and water used in the present invention are preferably those of the purity that can be used for the semiconductor process, and may be commercially available or may be purified using industrial grades according to methods commonly known in the art. . Water for semiconductor processing is generally ultra pure water, preferably at least 18 MΩ water is used.

The additive used in the present invention is not particularly limited as a component commonly used in etching solutions, and generally, a surfactant, a metal ion blocking agent, and the like can be mentioned. Surfactants are added to reduce the viscosity of the etching solution to improve the etching uniformity, and any anionic, cationic, zwitterionic or nonionic interface can be used if the type is compatible and compatible with the etching solution. The activator is preferably a fluorine-based surfactant. It is also possible to add other additives that normally enter the etching solution.

The step of etching the metal film using the etching solution of the present invention can be performed according to a method well known in the art, and can be immersed, shedding and the like. The temperature at the time of an etching process is generally 30-45 degreeC, and an appropriate process temperature is determined as needed by other process conditions and factors.

The time for etching the triple layer thin film using the etching solution of the present invention may vary depending on the temperature and the thickness of the thin film, but is generally several seconds to several minutes.

The above-described etching temperature and etching time can be easily determined by those skilled in the art, and do not limit the present invention.

Etching the Mo / Al-Nd / Mo triple layer metal film using a conventional etching solution for Al or Al alloys, the lower Mo layer penetrates into the intermediate Al-Nd layer and exhibits a severe undercut shape, which is covered by the next step. Defects occur due to defects and weak adhesion of the S / D pattern.

However, when the Mo / Al-Nd / Mo triple layer metal film is etched using an etching solution of a specific composition and composition ratio according to the present invention, the undercut phenomenon of this lower layer is suppressed, and the layer covering phenomenon is reduced or eliminated in a later process. Therefore, the defective rate is reduced.

Therefore, one of the advantages of the present invention is that the undercut phenomenon of the lower Mo layer is suppressed, and therefore, the defect due to the step covering failure and the weakening of the adhesion of the S / D pattern is suppressed in the next step, which is very advantageous in terms of cost and productivity. It is.

Another advantage of the present invention is that it uses the same constituents as the existing Al etching solution, i.e. nitric acid, phosphoric acid, acetic acid and additives, only their composition ratio being specifically limited. Therefore, it is relatively easy to purchase and purify the raw materials at the time of preparation of the etching solution, and the same as those commonly known for handling precautions.

Another advantage of the present invention is the introduction of the wet etching process step that can be mass-produced and minimizing the use of the dry etching step that can cause deterioration of the semiconductor device, thereby reducing the deterioration of the semiconductor device due to contamination and damage and in terms of productivity It is very advantageous.

The present invention is explained in more detail by the following examples, but the present invention is not limited thereto.

The profile of the etched metal film in the Example was inspected using a cross-sectional SEM (Model S-4200, manufactured by Hitachi), and the results thereof are expressed as follows.

:: Good, showing the profile that the lower Mo layer did not enter into the middle Al-Nd layer.

○: Normally, the lower Mo layer shows a profile etched to about the same degree as the middle Al-Nd layer.

X: Poor, the lower Mo layer was excessively etched to show a profile (undercut phenomenon) that went into the middle Al-Nd layer.

Example 1

Phosphoric acid, nitric acid, acetic acid and additives (fluorine-based surfactants, etc.), which are grades for semiconductor processing, are mixed in a weight ratio of 70/2/15 and diluted with water in an amount of up to 100% by weight in total to prepare an etching solution. In the etching test, the etching solution is sprayed onto a test piece on which a wiring pattern is formed of a Mo / Al-Nd / Mo triple layer and a photoresist using a thin film sputtering method on a glass substrate according to a conventional method. The etching rate was excellent at 1500-2200 Pa at 40 degreeC.

The metal film profile of the etched test piece was examined using a cross-sectional SEM (Model S-4200, manufactured by Hitachi), and there was no undercut phenomenon in which the lower Mo layer entered the middle Al-Nd layer.

3 is a photograph showing a good profile obtained in Example 1.

Examples 2-5

An etching solution was prepared in the same manner as in Example 1 except that phosphoric acid, nitric acid, acetic acid, and additives were used in the proportions shown in Table 1, and an etching test was performed.

The cross-sectional SEM was used to examine the metal film profile of the etched test specimens, and no undercut phenomenon was observed in which the lower Mo layer was inside the middle Al-Nd layer.

The results are shown in Table 1.

Comparative Examples 1 to 3

The etching solution was prepared by using phosphoric acid, nitric acid, acetic acid and additives in the ratio as shown in Table 1 and diluting with water in an amount of 100% by weight in total, and the etching test was carried out in the same manner as in Examples 1 to 5.

A cross-sectional SEM is used to examine the metal film profile of the etched test piece. The lower Mo layer showed under-cut phenomenon under the middle Al-Nd layer. The overall results are shown in Table 1.

Example number Composition (wt%) * H ₃ PO ₄ / HNO ₃ / CH ₃ CO ₂ H / Additive result One 70/2/15 / 0.01 ◎ 2 71/3/4 / 0.02 ◎ 3 72/4/8 / 0.02 ◎ 4 74/2/7 / 0.02 ○ 5 68/3/10 / 0.02 ○ 1 (comparative) 63/8/10 / 0.02 x 2 (comparative) 65/7/9 / 0.02 x 3 (comparative) 67/3/10 / 0.02 x * Diluted with water to 100% by weight

As can be seen in Table 1, when the Mo / Al-Nd / Mo triple layer is etched with the etching solution according to the present invention, there was no undercut phenomenon of the lower Mo layer. Therefore, less defect rate occurs when the protruding portion of the upper Mo layer is etched by a conventional dry etching process.

On the other hand, when the Mo / Al-Nd / Mo triple layer was etched with the etching solution of the comparative example, an undercut phenomenon of the lower Mo layer appeared, and when etching the protruding portion of the upper Mo layer by a conventional dry etching process, Many defects occur due to defects caused by undercut of the lower Mo layer.

In addition, when etching using the etching solution of Examples 1 to 5, compared to the wiring etched by the conventional wet-dry two-step process, not only the uniformity of the etched wiring pattern is excellent, but also foreign materials, deposits, Quality factors such as scratch, line short, bridge, line open, metal corrosion, metal discolor, and misalignment were satisfied.

By using the etching solution of the present invention, the Mo / Al-Nd / Mo triple layer can be etched without occurrence of undercut of the lower Mo layer, and thus has a good taper profile, so that step coverage is improved and applicable to the LSD manufacturing process.

Claims (3)

68 to 74 wt% phosphoric acid (H ₃ PO 4), 2 to 4 wt% nitric acid (HNO ₃ ), 5 to 15 wt% acetic acid and water to an amount of up to 100 wt% Etching solution of the Mo / Al-Nd / Mo triple layer metal film in a semiconductor device, characterized in that it comprises 0.01 to 0.05% by weight of the additive based on the total weight. The etching solution of claim 1 comprising 50-60 wt% phosphoric acid, 5-10 wt% nitric acid, 11-15 wt% acetic acid. The etching solution according to claim 1 or 2, wherein the semiconductor device is a TFT-LCD and a Mo / Al-Nd / Mo triple layer metal film is used for source / drain array wiring.