A mixed acid type pure molybdenum etching solution and an etching method for pure molybdenum film.

Abstract

This invention discloses a mixed-acid pure molybdenum etching solution, which, by mass percentage, mainly comprises: 2%–7% nitric acid, 50%–60% phosphoric acid, 21%–30% acetic acid, 2.5%–7% additives, and 6%–17% deionized water; the additives are combinations of two or more selected from phosphates, nitrates, acetates, molybdates, and hydrogen phosphates. This mixed-acid pure molybdenum etching solution adds salts to a mixed-acid system of nitric acid, phosphoric acid, and acetic acid. By optimizing the content of each acid component and the salt additives, the etching rate of pure molybdenum is adjusted, making the mixed-acid pure molybdenum etching solution compatible with the etching of molybdenum monolayers of various thicknesses. The etching tilt angle is stable at 40–55°, and the critical dimensional deviation of the molybdenum layer is effectively reduced, meeting the etching technical requirements of pure molybdenum layers of various thicknesses. The molybdenum ion loading of this etching solution can reach up to 5000 ppm, and its service life is long. This invention also discloses a method for etching pure molybdenum films.

Description

Technical Field

[0001] This invention relates to the field of wet etching technology for metal films, specifically to a mixed acid type pure molybdenum etching solution and etching method. Background Technology

[0002] In the production of TFT (Thin Film Transistor) substrates, mixed-acid etching solutions are commonly used for copper-molybdenum, aluminum-molybdenum, or molybdenum-aluminum-molybdenum metal stacks to form circuits with predetermined patterns. The main components of mixed-acid etching solutions are nitric acid, phosphoric acid, and acetic acid. Nitric acid is used to oxidize copper, aluminum, and molybdenum to form the corresponding metal oxides. Phosphoric acid reacts with the metal oxides to form the corresponding salts. Acetic acid, as the main component of the buffer solution, controls the etching reaction rate.

[0003] In some specialized processes, such as the production of LTPS (Low Temperature Polycrystalline Silicon) devices, pure molybdenum metal layers are sometimes used as the circuit material, thus requiring a correspondingly formulated pure molybdenum etching solution. Common pure molybdenum layer thicknesses range from [insert thickness range here]. For example

[0004] Based on the current precision and quality requirements of high-density fine-line images in liquid crystal displays, to ensure the continuity of metal lines in subsequent evaporation processes, the Taper (etching angle) specification is less than 55°, preferably 40° to 55°; CD-Bias (critical dimension deviation) is determined specifically based on linewidth and film thickness, such as glass substrates. The CD-Bias of the molybdenum layer is preferably no greater than 0.5 μm on both sides, with a silicon substrate. The CD-Bias of the molybdenum layer is preferably no greater than 1.5 μm. Using a mixed acid solution containing 2% nitric acid, 65% phosphoric acid, and 18% acetic acid (as described in CN103255417A) as the etching solution to treat pure molybdenum, the overall etch morphology of Mo differs significantly from that obtained by etching molybdenum-aluminum-molybdenum or aluminum-molybdenum metal stacks. The morphology of pure molybdenum is as follows: when the molybdenum layer thickness is less than... The critical dimension deviation on one side reached 0.26μm, and the etching tilt angle was 65–80°, such as Figure 1 As shown; when the Mo layer thickness is greater than The critical dimension deviation on one side reached 0.42μm, and the etching tilt angle was 60-70°. Figure 2 As shown. Nitrates were added to the improved etching solution, but the effect on improving the etching tilt angle of both thin and thick molybdenum layers was limited. Due to poor compatibility with etching molybdenum layers of varying thicknesses, existing copper-molybdenum and molybdenum-aluminum-molybdenum etching solutions are not suitable for conversion to pure molybdenum etching. Summary of the Invention

[0005] One of the objectives of this invention is to overcome the deficiencies in the prior art and provide a mixed acid type pure molybdenum etching solution. By adding a combination salt as an additive to the mixed acid system, it is suitable for etching pure molybdenum film layers of various thicknesses, and the etching tilt angle and critical dimension deviations can be controlled within the predetermined technical specifications.

[0006] To achieve the above-mentioned technical effects, the technical solution of the present invention is as follows: a mixed acid type pure molybdenum etching solution, which, by mass percentage, mainly consists of: 2% to 7% nitric acid, 50% to 60% phosphoric acid, 21% to 30% acetic acid, 2.5% to 7% additives, and 6% to 17% deionized water;

[0007] The additive is a combination of two or more selected from phosphates, nitrates, acetates, molybdates, and hydrogen phosphates.

[0008] Furthermore, the sum of the mass percentages of nitric acid, phosphoric acid, acetic acid, additives, and deionized water shall not be less than 95%, and even further, not less than 98%. Hydrogen phosphates include monohydrogen phosphate and dihydrogen phosphate. The sum of the mass percentages of 2%–7% nitric acid, 50%–60% phosphoric acid, 21%–30% acetic acid, 2.5%–7% additives, and 6%–17% deionized water may be selected as 95%, 96%, 97%, 98%, 99%, 100%, or a range using the above two values ​​as the maximum and minimum values.

[0009] A preferred technical solution is that the additive is one or a combination of two or more selected from lithium salts, potassium salts, sodium salts and ammonium salts;

[0010] Furthermore, the additive is one or a combination of two or more lithium salts, potassium salts, and sodium salts.

[0011] A preferred technical solution is that the additive is a combination of nitrate and one or more selected from phosphate, acetate, molybdate, and hydrogen phosphate; further, the additive is a combination of phosphate and nitrate.

[0012] The preferred technical solution is that, by mass percentage, the main components are: 3%–6% nitric acid, 50%–60% phosphoric acid, 23%–29% acetic acid, 3%–6% additives, and 7%–13% deionized water.

[0013] A preferred technical solution is that the mass ratio of the phosphate to the nitrate is (0.7-1.2):1;

[0014] Furthermore, the mass ratio of the phosphate to the nitrate is (0.9–1.2):1.

[0015] Specifically, the mass ratio of phosphate to nitrate is 0.7:1, 0.8:1, 0.9:1, 0.10:1, 1.1:1, 1.2:1, and the ranges with the above two values ​​as the maximum and minimum values.

[0016] A preferred technical solution is that the phosphate and / or nitrate are potassium salts.

[0017] A preferred technical solution is that the mixed-acid pure molybdenum etching solution further includes 0.03% to 0.75% of a sulfonic acid compound; the sulfonic acid compound is selected from at least one of methanesulfonic acid, 2-hydroxyethanesulfonic acid, 3-hydroxypropanesulfonic acid, and 1,4-butanedisulfonic acid. Specifically, the mass percentage of the sulfonic acid compound in the mixed-acid pure molybdenum etching solution is 0.03%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, and 0.75%, as well as a range using the above two values ​​as the maximum and minimum values.

[0018] A preferred technical solution is that the mass percentage of sulfonic acid compound in the mixed acid type pure molybdenum etching solution is 0.1% to 0.55%;

[0019] Furthermore, the sulfonic acid compound is 3-hydroxypropanesulfonic acid and / or 1,4-butanedisulfonic acid.

[0020] The second objective of this invention is to provide an etching method for a pure molybdenum film layer, using the aforementioned mixed acid type pure molybdenum etching solution, wherein the molybdenum layer is deposited on a substrate.

[0021] The preferred technical solution is that the etching temperature is not higher than 45℃;

[0022] Furthermore, the etching temperature is 37–44°C;

[0023] Furthermore, the thickness of the pure molybdenum film is

[0024] Furthermore, the substrate is an ITO (indium tin oxide) substrate, a glass substrate, or a silicon substrate.

[0025] The advantages and beneficial effects of this invention are as follows:

[0026] This mixed-acid pure molybdenum etching solution is based on a mixed acid system of nitric acid, phosphoric acid and acetic acid with added salt. By optimizing the content of each acid component and the salt additive, the etching rate of pure molybdenum is adjusted, making the mixed-acid pure molybdenum etching solution compatible with the etching of molybdenum single layers of various thicknesses. The etching tilt angle is stable at 40-55°, and the critical size deviation of the molybdenum layer is effectively reduced, meeting the etching technology requirements of pure molybdenum of various thicknesses.

[0027] The etching solution has a molybdenum ion loading of up to 5000 ppm and a long service life. Attached Figure Description

[0028] Figure 1 This is a SEM image of one of the samples A after etching, as shown in Comparative Example 1.

[0029] Figure 2 This is a SEM image of one of the samples B after etching, as shown in Comparative Example 1.

[0030] Figure 3 This is a SEM image of one of the samples A after etching in Example 1;

[0031] Figure 4 This is a SEM image of one of the samples B after etching in Example 1;

[0032] Figure 5 This is a SEM image of one of the samples A after etching, as shown in Comparative Example 3.

[0033] Figure 6 This is a SEM image of one of the samples B after etching, as shown in Comparative Example 3.

[0034] Figure 7 This is a SEM image of one of the samples A after etching in Example 6;

[0035] Figure 8 This is a SEM image of one of the samples B after etching in Example 6;

[0036] Figure 9 This is a SEM image of one of the samples A after etching in Example 8;

[0037] Figure 10 This is a SEM image of one of the samples B after etching in Example 8;

[0038] Figure 11 This is a SEM image of one of the samples C after etching in Example 8; Detailed Implementation

[0039] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0040] Composition of mixed acid type pure molybdenum etching solution

[0041] Specifically, in addition to nitric acid, phosphoric acid, acetic acid, salt additives, deionized water, and sulfonic acid compounds, it may also include commonly used etching solution additives such as surfactants and defoamers.

[0042] Understandably, as raw materials for electronic chemical reagents, the purity of nitric acid, phosphoric acid, acetic acid, salt additives, and sulfonic acid compounds tends to be highly controlled in order to avoid or control the adverse effects of impurities on etching rate and molybdenum layer morphology.

[0043] additive

[0044] Specifically, based on the mass percentage of the additive, the salt used as the additive is soluble in a predetermined mixed acid system to form a uniform and clear etching solution.

[0045] Compared to conventional copper-molybdenum etching solutions, pure molybdenum etching solutions contain a slightly higher acetic acid content (21%–30%). The high concentration of acetic acid in pure molybdenum etching solutions results in stronger penetration into the molybdenum layer and a faster etching rate, while salt additives can inhibit the etching rate of molybdenum. By adjusting the content of acetic acid and salt additives, a balance can be achieved between these two opposing effects during the etching process of molybdenum layers of different thicknesses.

[0046] Compared to ammonium salts, lithium, potassium, and sodium salts have a smaller impact on molybdenum layer etching and less influence on pH fluctuations in the etching solution system. All lithium, sodium, and potassium salts inhibit the etching rate of molybdenum; the slower etching rate is beneficial for modifying the etching angle and reducing critical dimension deviations. Among these, potassium salts are superior to sodium salts in improving the etching rate and morphology of molybdenum, and are used in smaller quantities in pure molybdenum etching solutions.

[0047] sulfonic acid compounds

[0048] The role of sulfonic acid compounds is to further adjust the etching rate of the etchant, thereby improving the etching tilt angle and critical dimension deviations of thicker molybdenum layers. Compared to thicker molybdenum layers, 3-hydroxypropanesulfonic acid and / or 1,4-butanedisulfonic acid are preferred for thinner molybdenum layers (thickness less than...). It has a better effect on suppressing critical size deviations.

[0049] pure molybdenum substrate

[0050] There are three main types of substrates for pure molybdenum layers: ITO, glass substrates, and silicon substrates. Mixed-acid pure molybdenum etching solutions are applicable to molybdenum layers on all three types of substrates. Silicon substrates specifically include known silicon compound materials such as silicon oxide and silicon nitride.

[0051] I. Components and preparation method of pure molybdenum etching solution:

[0052] Nitric acid – 70% nitric acid (electronic grade);

[0053] Phosphoric acid – 85.4% phosphoric acid (electronic grade);

[0054] Acetic acid – 100% acetic acid (electronic grade);

[0055] Additives: potassium phosphate, sodium phosphate, potassium nitrate, sodium nitrate, potassium dihydrogen phosphate (chemically pure);

[0056] Sulfonic acid compounds—methanesulfonic acid, 1,4-butanedisulfonic acid (chemically pure);

[0057] Preparation of pure molybdenum etching solution: Mix additive salt with water to make a salt solution. Add nitric acid, phosphoric acid, acetic acid, salt solution (and sulfonic acid compound) to a mixing tank in proportion. Add water to adjust to the predetermined component content and mix evenly to obtain a new type of pure molybdenum etching solution with mixed acid.

[0058] II. Configuration of the etching sample substrate, technical specifications, and etching method:

[0059] A. Substrate – Molybdenum layer thickness on the glass substrate Technical specifications: CD-Bias (double-sided) ≤0.5μm, Taper 40~55°;

[0060] B-substrate—Molybdenum layer thickness on a silicon (SiOx / SiNx) substrate Technical specifications: CD-Bias ≤ 1.5μm, Taper 40~55°;

[0061] C-substrate—ITO molybdenum layer thickness Technical specifications: CD-Bias ≤ 0.4μm, Taper 40~55°;

[0062] The copper etching solution sample was heated and kept at 40±2℃ using etching equipment to etch the sample substrate; after etching, it was rinsed and dried with pure water, and the etching time was set according to the conventional OE 50% in actual production.

[0063] III. Etching Time and Result Detection in Examples and Comparative Cases:

[0064] 1. Observe the etching tilt angle and CD-Bias of the etched sample using SEM (average value of 6 parallel samples).

[0065] SEM images measure single-sided CD-Bias, while in etching tests, the double-sided CD-Bias of the above technical specifications is considered as twice the single-sided CD-Bias.

[0066] 2. Service life test of mixed acid type pure molybdenum etching solution: Molybdenum powder was added to the etching solution until the content of molybdenum ions in the pure molybdenum etching solution was 1000ppm, 3000ppm, and 5000ppm. The sample substrate was etched with the etching solution with the predetermined molybdenum ion content, and the copper ion loading capacity of the etching solution was investigated by SEM.

[0067] IV. Examples and Comparative Examples

[0068] 1. The compositions of Examples 1-3 and Comparative Examples 1-4 regarding the mixed acid composition are shown in the table below. The substrates of samples A and B were etched. All components in the table are expressed as mass percentages.

[0069]

[0070]

[0071] The SEM image measurement results of Examples 1-3 and Comparative Examples 1-4 are shown in the table below:

[0072]

[0073] As shown in the table, the pure molybdenum etching solution in Comparative Example 1 does not contain additives, and the contents of nitric acid and acetic acid are low, but the contents of phosphoric acid are high. The etching angles of samples A and B are too large, and the CD-Bias value of sample A is relatively high.

[0074] Based on Comparative Example 1, nitrate was added as an additive to the pure molybdenum etching solution of Comparative Example 2. Although the etching tilt angle did not reach the predetermined technical specifications, it was significantly reduced compared to Comparative Example 1, and the photoresist coated on the surface of the molybdenum layer had straight edges without warping.

[0075] Based on Comparative Example 2, Comparative Example 3 adjusted the concentrations of the three inorganic acids, increasing the mass percentages of nitric acid and acetic acid while decreasing the mass percentage of phosphoric acid, and further reducing the etching angle. Sample A achieved an optimal etching angle, while sample B's etching angle was too small, indicating that the pure molybdenum etching solution in Comparative Example 3 had poor compatibility with molybdenum layers of different thicknesses. SEM images showed warping at the edges of the photoresist coated on the molybdenum layer surface of the substrate, indicating that when nitrate was added alone as an additive, the overall nitric acid concentration in the etching solution was too high, resulting in excessive oxidizing power that could damage the positive photoresist deposited on the substrate.

[0076] Comparative Example 4 uses potassium phosphate as an additive, based on the same concentrations of the three inorganic acids as Comparative Example 3. The CD-Bias is reduced compared to Comparative Example 3, but the etching tilt angle is significantly increased.

[0077] In Examples 1-3, potassium phosphate and potassium nitrate were added simultaneously as additives. The AOE 50% etching time in Example 1 was 75 s. The morphology of the molybdenum layer after etching was significantly improved in both Sample A and Sample B, and the etching tilt angle and single-sided CD-Bias both met their respective technical specifications. Considering the compatibility of pure molybdenum etching solution with Samples A and B, the morphology of the molybdenum layer in Example 1 was superior to that in Examples 2 and 3.

[0078] 2. The composition of the cations in the salt additives in Examples 4-6 is shown in the table below. All components in the table are expressed as mass percentages:

[0079]

[0080] The SEM image measurement results for Examples 1, 4, 5, and 6 are shown in the table below:

[0081]

[0082] Compared with Example 1, the etching tilt angles of samples A and B treated with some sodium salt and some potassium salt as additives in Examples 4 and 5 met the technical specifications, but the single-sided CD-Bias increased. Among them, the single-sided CD-Bias of sample A increased more significantly, indicating that the effect of sodium salt on CD-Bias regulation is weaker than that of potassium salt.

[0083] In Example 6, by simultaneously increasing the mass percentage of sodium and potassium salts in the etching solution, the morphology of the molybdenum layer after etching in Sample A was similar to that in Example 1, while the etching angle of Sample B was slightly smaller, but still within the technical specifications. This indicates that a greater amount of sodium salt is needed to achieve the same level of molybdenum layer morphology improvement as with less potassium salt. Considering the etching angle and cost of Sample B, potassium salt is preferred as the additive.

[0084] 3. The compositions of the sulfonic acid compounds in Examples 7-10 are shown in the table below, where all components are expressed as mass percentages:

[0085]

[0086]

[0087] The SEM image measurement results for Examples 1 and 7-10 are shown in the table below:

[0088]

[0089] The OE 50% etching times for samples A in Examples 7, 8, 9, and 10 were 74 s, 72 s, 72 s, and 74 s, respectively, all shorter than that in Example 1, indicating that the sulfonic acid compound helps to maintain a good molybdenum layer etch morphology while accelerating the etching process. The difference in etching tilt angle between samples A and B treated in Example 7 was greater than that in Examples 8 and 9, indicating that Examples 8 and 9 have better compatibility for etching molybdenum layers of different thicknesses.

[0090] The increasing mass percentage of 1,4-butanedisulfonic acid from Examples 8 to 10 indicates that within the range of 0.4%-0.6% mass percentage of 1,4-butanedisulfonic acid, a higher 1,4-butanedisulfonic acid content results in a higher mean single-sided CD-Bias, with little effect on the etching tilt angle. Based on CD-Bias and cost, the pure molybdenum etching solution of Example 8 exhibits better compatibility with molybdenum layers of different thicknesses than that of Example 9.

[0091] 4. The SEM images of sample C, which was used in Examples 1, 6, and 8 to etch an ITO substrate, are shown below:

[0092]

[0093] As shown in the table above, pure molybdenum etching solution is also suitable for etching molybdenum layers on ITO substrates.

[0094] 5. The service life of the pure molybdenum etching solution in Examples 1, 6, and 8 (based on the maximum molybdenum ion loading in the pure molybdenum etching solution) is shown in the table below:

[0095] Sample Lifespan of pure molybdenum etching solution (ppm) Example 1 5000ppm Example 6 3000ppm Example 8 5000ppm

[0096] As can be seen from the table above, the lifespan of the pure molybdenum etching solution in Examples 1 and 8 is better than that in Example 6, indicating that an excessively high sodium ion concentration in the etching solution is not conducive to maintaining a long lifespan for the pure molybdenum etching solution.

[0097] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A mixed acid type pure molybdenum etching solution, characterized by, The main components are 2-7% nitric acid, 50-60% phosphoric acid, 21-30% acetic acid, 2.5-7% additive and 6-17% deionized water by mass percentage; The additive is phosphate and nitrate, the phosphate is potassium phosphate and the nitrate is potassium nitrate.

2. The mixed acid type pure molybdenum etching solution according to claim 1, characterized by, The main components are 3-6% nitric acid, 50-60% phosphoric acid, 23-29% acetic acid, 3-6% additive and 7-13% deionized water by mass percentage.

3. The mixed acid type pure molybdenum etching solution according to claim 1, characterized by, The mass ratio of the phosphate to the nitrate is (0.7-1.2):

1.

4. The mixed acid type pure molybdenum etching solution according to claim 3, characterized by, The mass ratio of the phosphate to the nitrate is (0.9-1.2):

1.

5. The mixed acid type pure molybdenum etching solution according to claim 1, characterized by, The mixed acid type pure molybdenum etching solution further comprises 0.03-0.75% sulfonic acid compound; the sulfonic acid compound is at least one selected from the group consisting of methanesulfonic acid, 2-hydroxyethanesulfonic acid, 3-hydroxypropanesulfonic acid and 1,4-butanedisulfonic acid. 6.The mixed acid type pure molybdenum etching solution according to claim 5, characterized in that, The mass percentage of the sulfonic acid compound in the mixed acid type pure molybdenum etching solution is 0.1-0.55%.

7. The mixed acid type pure molybdenum etching solution according to claim 6, characterized by, The sulfonic acid compound is 3-hydroxypropanesulfonic acid and / or 1,4-butanedisulfonic acid.

8. An etching method of a pure molybdenum film layer, characterized by, The mixed acid type pure molybdenum etching solution is used to form a molybdenum layer on a substrate.

9. The etching method according to claim 8, characterized by, The etching temperature is not more than 45℃.

10. The etching method according to claim 9, wherein The etching temperature is 37-44℃.

11. The etching method according to claim 8, wherein The thickness of the pure molybdenum film layer is 100-5000Å.

12. The etching method of claim 8, wherein, The substrate is ITO substrate, glass substrate or silicon substrate.

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