Etching method

Abstract

In one embodiment, an etching method is provided that can suppress the increase in etching rate due to an increase in the amount of water in the etching solution. [Solution] In one embodiment, this disclosure relates to an etching method for etching a molybdenum-containing layer to be etched, comprising the following steps 1 and 2. Step 1: A step in which an etching solution containing nitric acid and phosphoric acid is brought into contact with the layer to be etched, which contains molybdenum. Step 2: Adding anhydride to the etching solution after Step 1.

Description

Technical Field

[0001] The present disclosure relates to an etching method for etching an etched layer containing molybdenum.

Background Art

[0002] In the manufacturing process of semiconductor devices, for example, a step of etching an etched layer containing at least one metal such as tungsten, tantalum, zirconium, hafnium, molybdenum, niobium, ruthenium, osmium, rhenium, rhodium, copper, nickel, cobalt, titanium, aluminum, and iridium, or a nitride thereof, or an oxide thereof, and processing it into a predetermined pattern shape is performed. In recent years, in the semiconductor field, high integration has been progressing, and there is a demand for more complex and finer wiring. The requirements for pattern processing technology and etching solutions are also increasing, and various etching methods and etching solutions have been proposed.

[0003] For example, in Patent Document 1, an etching solution is proposed that contains at least nitric acid, acetic acid, a phosphorus compound, and water, and the water concentration after mixing is 3.0 M or less. The document also describes that an acid anhydride may be further added to the etching solution.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Mixed acid aqueous solutions (strong acid aqueous solutions) containing nitric acid and phosphoric acid are increasingly being used as etching solutions. Furthermore, from the perspective of reducing environmental impact and improving productivity, repeated use of etching solutions is desired. When etching solutions are repeatedly used, fluctuations in the etching solution components (for example, volatilization of components contained in the etching solution or absorption of moisture) may occur depending on the environment in which the etching solution is placed. In particular, it has been found that if the moisture content of the etching solution increases when it is reused, the etching rate increases compared to the first use. In order to stably manufacture semiconductor wafers of uniform quality, it is desirable to suppress fluctuations in the etching rate between etchings when the etching solution is repeatedly used.

[0006] Therefore, in one embodiment, this disclosure provides an etching method that can suppress the increase in etching rate due to an increase in the amount of water in the etching solution. [Means for solving the problem]

[0007] This disclosure relates, in one embodiment, to an etching method for etching a molybdenum-containing layer to be etched, comprising the following steps 1 and 2. Step 1: A step in which an etching solution containing nitric acid and phosphoric acid is brought into contact with the layer to be etched, which contains molybdenum. Step 2: Adding anhydride to the etching solution after Step 1.

[0008] This disclosure relates, in one embodiment, to a method for manufacturing a semiconductor wafer, including the etching method of this disclosure. [Effects of the Invention]

[0009] According to this disclosure, in one embodiment, an etching method is provided that can suppress the increase in etching rate due to an increase in the amount of water in the etching solution. [Modes for carrying out the invention]

[0010] As a result of diligent research by the present inventors, it was found that by adding anhydrous acid to the etching solution used for etching, the amount of water in the etching solution can be reduced, thereby suppressing the difference in etching rate between the etching rate when the etching solution is reused and the etching rate when it is used for the first time. In other words, it is possible to suppress the increase in etching rate due to an increase in the amount of water in the etching solution. Although Patent Document 1 describes the addition of anhydrous acid during the preparation of the etching solution, anhydrous acid reacts with nitric acid in the etching solution. Therefore, it is difficult to add a large amount of anhydrous acid to the etching solution for the first time, and it is difficult to suppress the increase in water content when the etching solution is reused.

[0011] In other words, in one embodiment, this disclosure relates to an etching method for etching a molybdenum-containing layer to be etched, comprising the following steps 1 and 2 (hereinafter also referred to as "the etching method of this disclosure"). Step 1: A step in which an etching solution containing nitric acid and phosphoric acid is brought into contact with the layer to be etched, which contains molybdenum. Step 2: Adding anhydride to the etching solution after Step 1.

[0012] According to the etching method of this disclosure, it is possible to suppress the increase in etching rate due to an increase in the amount of water in the etching solution.

[0013] [Etched layer] In one or more embodiments, the layer to be etched using the etching method of this disclosure is a layer to be etched containing molybdenum. In one or more embodiments, the layer to be etched containing molybdenum may consist of molybdenum, or in one or more other embodiments, it may contain molybdenum and a metal other than molybdenum. Examples of metals other than molybdenum include at least one metal selected from tungsten, tantalum, zirconium, hafnium, niobium, ruthenium, osmium, rhenium, rhodium, copper, nickel, cobalt, titanium, aluminum, and iridium, or a nitride thereof, or an oxide thereof.

[0014] [Step 1: Etching] Step 1 is, in one or more embodiments, a step (etching step) in which an etching solution containing nitric acid and phosphoric acid is brought into contact with a layer to be etched containing molybdenum (hereinafter also simply referred to as the "layer to be etched").

[0015] In step 1, examples of methods for bringing the etching solution into contact with the layer to be etched include immersion etching and single-wafer etching. In one or more embodiments, the etching solution may be stirred or circulated when it comes into contact with the layer to be etched. Examples of stirring methods include using a propeller-type stirrer, and examples of liquid circulation methods include circulating the liquid using a pump (a method of stirring without using stirring blades). The stirring speed can be set appropriately, but from the viewpoint of improving uniform in-plane etching, 50 rpm or higher is preferred, 100 rpm or higher is more preferred, and 200 rpm or higher is even more preferred. The liquid circulation speed can be set appropriately, but from the viewpoint of improving uniform in-plane etching, 1 L / min or higher is preferred.

[0016] The etching solution temperature in step 1 (etching temperature) is preferably 0°C or higher, more preferably 15°C or higher, even more preferably 20°C or higher, and preferably 80°C or lower, more preferably 65°C or lower, and even more preferably 50°C or lower, from the viewpoint of uniform etching of the layer to be etched. More specifically, in one or more embodiments, the etching temperature is preferably 0°C or higher and 80°C or lower, more preferably 15°C or higher and 65°C or lower, and even more preferably 20°C or higher and 50°C or lower.

[0017] The etching time in step 1 (contact time between the layer to be etched and the etching solution) can be set, for example, from 1 minute to 180 minutes. From the viewpoint of improving the quality of the layer to be etched, it is preferably from 15 minutes to 90 minutes, and more preferably from 20 minutes to 60 minutes.

[0018] <Etching solution used in Step 1> The etching solution first used in Step 1 (hereinafter also referred to as the "etching solution at the first use") is, in one or more embodiments, an aqueous mixed acid solution containing nitric acid and phosphoric acid. The etching solution reused in Step 1 (hereinafter also referred to as the "etching solution at the reuse") is, in one or more embodiments, the one obtained by adding an anhydrous acid to the etching solution after being used one or more times for etching (that is, the etching solution after Step 2). Therefore, in Step 1, the etching solution containing nitric acid and phosphoric acid that contacts the etched layer containing molybdenum includes, in one or more embodiments, the etching solution after Step 2.

[0019] (Nitric acid in the etching solution) From the viewpoint of improving the quality of the etched layer, the blending amount of nitric acid in the etching solution used in Step 1 (the etching solution at the first use and the etching solution at the reuse) is preferably 0.5% by mass or more, more preferably 1% by mass or more, and from the same viewpoint, preferably 10% by mass or less, more preferably 5% by mass or less. More specifically, the blending amount of nitric acid in the etching solution is preferably 0.5% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 5% by mass or less.

[0020] (Phosphoric acid in the etching solution) From the viewpoint of improving the quality of the etched layer, the blending amount of phosphoric acid in the etching solution used in Step 1 (the etching solution at the first use and the etching solution at the reuse) is preferably 1% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, and from the same viewpoint, preferably 70% by mass or less, more preferably 50% by mass or less, still more preferably 30% by mass or less, even more preferably 10% by mass or less. More specifically, the blending amount of phosphoric acid in the etching solution is preferably 1% by mass or more and 70% by mass or less, more preferably 3% by mass or more and 50% by mass or less, still more preferably 5% by mass or more and 30% by mass or less, even more preferably 5% by mass or more and 10% by mass or less.

[0021] The total amount of nitric acid and phosphoric acid in the etching solution used in step 1 (etching solution for the first use and etching solution for reuse) is preferably 2% by mass or more, more preferably 4% by mass or more, and even more preferably 6% by mass or more, and from the viewpoint of improving the quality of the etched layer, preferably 72% by mass or less, more preferably 35% by mass or less, and even more preferably 15% by mass or less. More specifically, the total amount of nitric acid and phosphoric acid in the etching solution is preferably 2% by mass or more and 72% by mass or less, more preferably 4% by mass or more and 35% by mass or less, and even more preferably 6% by mass or more and 15% by mass or less.

[0022] (Organic acids in etching solution) The etching solution used in step 1 (etching solution for the first use and etching solution for reuse) may further contain an organic acid (except anhydride) in one or more embodiments. Examples of organic acids include at least one selected from acetic acid, methoxyacetic acid, ethoxyacetic acid, propionic acid, butanoic acid, citric acid, formic acid, gluconic acid, glycolic acid, malonic acid, oxalic acid, lactic acid, and pentanoic acid. Among these, from the viewpoint of uniform etching of the layer to be etched, at least one selected from acetic acid, methoxyacetic acid, and ethoxyacetic acid is preferred as the organic acid, more preferably containing acetic acid, and even more preferably acetic acid. The organic acid may be one type or a combination of two or more types. The amount of organic acid in the etching solution used in step 1 (etching solution for the first use and etching solution for reuse) is preferably 10% by mass or more, more preferably 30% by mass or more, even more preferably 60% by mass or more, and even more preferably 85% by mass or more, and from the viewpoint of uniform etching of the layer to be etched, preferably 99% by mass or less, more preferably 98% by mass or less, even more preferably 95% by mass or less, and even more preferably 90% by mass or less. More specifically, the amount of organic acid in the etching solution used in step 1 is preferably 10% by mass or more and 99% by mass or less, more preferably 30% by mass or more and 98% by mass or less, even more preferably 60% by mass or more and 95% by mass or less, and even more preferably 85% by mass or more and 90% by mass or less. If there is a combination of two or more organic acids, the amount of organic acid is the total amount of those combined.

[0023] The total amount of nitric acid, phosphoric acid, and organic acid in the etching solution used in step 1 (etching solution for the first use and etching solution for reuse) is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and from the same viewpoint, preferably 100% by mass or less. More specifically, the total amount of nitric acid, phosphoric acid, and organic acid in the etching solution is preferably 85% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and even more preferably 95% by mass or more and 100% by mass or less.

[0024] In one or more embodiments, the acid contained in the etching solution used in step 1 (etching solution for initial use and etching solution for reuse) is preferably an acid containing nitric acid, phosphoric acid, and an organic acid, more preferably an acid containing nitric acid, phosphoric acid, and acetic acid, and even more preferably a mixed acid consisting of nitric acid, phosphoric acid, and acetic acid, from the viewpoint of improving the quality of the layer to be etched.

[0025] The mass ratio (organic acid / nitric acid) of the organic acid to nitric acid in the etching solution used in step 1 (etching solution for the first use and etching solution for reuse) is preferably 5 or more, more preferably 15 or more, and preferably 50 or less, and more preferably 45 or less, from the viewpoint of improving the quality of the etched layer. More specifically, the mass ratio (organic acid / nitric acid) of the organic acid to nitric acid in the etching solution used in step 1 is preferably 5 or more and 50 or less, more preferably 15 or more and 45 or less.

[0026] The mass ratio (organic acid / phosphoric acid) of the amount of organic acid to phosphoric acid in the etching solution used in step 1 (etching solution for the first use and etching solution for reuse) is preferably 3 or more, more preferably 4 or more, even more preferably 5 or more, and from the viewpoint of improving the quality of the etched layer, preferably 20 or less, more preferably 19 or less, and even more preferably 18 or less. More specifically, the mass ratio (organic acid / phosphoric acid) of organic acid to phosphoric acid in the etching solution used in step 1 is preferably 3 or more and 20 or less, more preferably 4 or more and 19 or less, and even more preferably 5 or more and 18 or less.

[0027] The mass ratio (nitric acid / phosphoric acid) of nitric acid to phosphoric acid in the etching solution used in step 1 (etching solution for the first use and etching solution for reuse) is preferably 0.1 or higher, more preferably 0.15 or higher, even more preferably 0.2 or higher, and also preferably 2.0 or lower, even more preferably 1.0 or lower, from the viewpoint of improving the quality of the etched layer. More specifically, the mass ratio (nitric acid / phosphoric acid) of nitric acid to phosphoric acid in the etching solution used in step 1 is preferably 0.1 or higher and 2.0 or lower, more preferably 0.15 or higher and 1.0 or lower, and even more preferably 0.2 or higher and 1.0 or lower.

[0028] (Water in the etching solution) The etching solution used in step 1 (etching solution for initial use and etching solution for reuse) may contain water in one or more embodiments, or may not contain water in one or more embodiments. Examples of water contained in the etching solution include distilled water, deionized water, pure water, and ultrapure water. The amount of water in the etching solution used in step 1 (etching solution for the first use and etching solution for reuse) is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less, even more preferably 5% by mass or less, and even more preferably 2.5% by mass or less, from the viewpoint of suppressing the increase in etching rate due to an increase in the amount of water in the etching solution and improving the quality of the etched layer.

[0029] (Other components in the etching solution) The etching solution used in step 1 (etching solution for initial use and etching solution for reuse) may further contain other components, to the extent that the effects of this disclosure are not impaired. Examples of other components include inorganic acids other than phosphoric acid and nitric acid, etching inhibitors, chelating agents, surfactants, solubilizers, preservatives, rust inhibitors, disinfectants, antibacterial agents, antioxidants, etc.

[0030] The etching solution used in step 1 (etching solution for the first use and etching solution for reuse) may, in one or more embodiments, further contain an anhydride in addition to an organic acid other than anhydride. An example of an anhydride is the anhydride added in step 2, which will be described later. In one or more embodiments, the etching solution used for reuse contains the acid anhydride added in step 2. The amount of acid anhydride used in the etching solution in step 1 can be within the same range as the amount of acid anhydride added in step 2, which will be described later.

[0031] (Method for manufacturing etching solution) In one or more embodiments, the etching solution for initial use is obtained by combining phosphoric acid, nitric acid, and optionally the aforementioned optional components (organic acids, water, and other components) in a known manner. Therefore, in one or more embodiments, the method for producing the etching solution for initial use may include at least the step of combining phosphoric acid and nitric acid. In this disclosure, "compounding" includes, in one or more embodiments, simultaneously or sequentially, mixing phosphoric acid, nitric acid, and any optional components described above as necessary. The order of mixing is not particularly limited. The compounding can be carried out using, for example, a mixer such as a propeller-type stirrer, a liquid circulation stirring with a pump, a homomixer, a homogenizer, an ultrasonic disperser, and a wet ball mill. The preferred proportions of each component when manufacturing the etching solution for the first use can be the same as the preferred proportions of each component in the etching solution described above. In one or more embodiments, the etching solution for reuse can be obtained by adding anhydrous acid after the initial etching solution has been used for etching once or multiple times.

[0032] In this disclosure, "amount of each component in the etching solution" means, in one or more embodiments, the amount of each component in the etching solution used in the etching process, i.e., at the time of use when the etching process begins. In this disclosure, the amount of each component in the etching solution can be considered as the content of each component in the etching solution in one or more embodiments. However, the amount of each component and the content may differ when neutralization is involved.

[0033] The etching solution for initial use may be a so-called one-component type, where all components are pre-mixed and supplied to the market, or a so-called two-component type, where the components are mixed at the time of use.

[0034] The pH of the etching solution used in Step 1 (etching solution for initial use and etching solution for reuse) is preferably 2 or less, and more preferably 1 or less, from the viewpoint of storage stability. The pH of the etching solution in this disclosure can preferably be -2.5 or higher, and more preferably -2 or higher. In this disclosure, the pH of the etching solution is the value at 25°C and can be measured using a pH meter, specifically by the method described in the examples.

[0035] The etching solution for initial use may be stored and supplied in a concentrated state, provided that its stability is not compromised. This is preferable because it reduces manufacturing and transportation costs. This concentrated solution can then be used in the etching process after being appropriately diluted with water or an acidic aqueous solution as needed. The dilution ratio can be, for example, 5 to 100 times.

[0036] [Step 2: Addition of anhydride] Step 2 is the process of adding anhydrous acid to the etching solution after Step 1 (addition step). For example, when acetic anhydride is added as the anhydride, the acetic anhydride reacts with the water in the etching solution to be converted into acetic acid and water, thus making it possible to reduce the amount of water in the etching solution.

[0037] As the anhydride used in step 2, from the viewpoint of suppressing the increase in etching rate due to the increase in the amount of water in the etching solution, at least one anhydride selected from acetic anhydride, propionic anhydride, maleic anhydride, succinic anhydride, phthalic anhydride, benzoic anhydride, citraconic anhydride, trifluoromethanesulfonic anhydride, and phosphorus pentoxide is recommended, and among these, acetic anhydride is preferred.

[0038] The addition of acid anhydride in step 2 is performed in one or more embodiments when the amount of water in the etching solution after step 1 is different from the amount of water in the etching solution when it is first used. Therefore, step 2, in one or more embodiments, includes measuring the amount of water in the etching solution after step 1. The amount of water in the etching solution can be measured, for example, using the Karl Fischer method. Step 2 is a step in which, in one or more embodiments, if the amount of water in the etching solution after Step 1 increases, anhydrous acid is added to the etching solution.

[0039] The amount of acid anhydride added in step 2 is preferably 0.1% by mass or more relative to the total amount of etching solution, from the viewpoint of suppressing the increase in etching rate due to the increase in the amount of water in the etching solution, and from the viewpoint of suppressing the exothermic reaction when acid anhydride is added. From the same viewpoint, it is preferably 65% ​​by mass or less, more preferably 35% by mass or less, and even more preferably 20% by mass or less. More specifically, the amount of acid anhydride added in step 2 is preferably 0.1% by mass or more and 65% by mass or less, more preferably 0.1% by mass or more and 35% by mass or less, and even more preferably 0.1% by mass or more and 20% by mass or less, relative to the total amount of etching solution.

[0040] In one or more embodiments, the amount of acid anhydride added in step 2 can be set according to the increase in the amount of water in the etching solution after step 1 relative to the amount of water in the etching solution at the time of first use (hereinafter also simply referred to as "increase in water content"). From the viewpoint of suppressing the increase in etching rate due to the increase in the amount of water in the etching solution, the amount of acid anhydride added is preferably 4% by mass or more, more preferably 4.5% by mass or more, and even more preferably 5% by mass or more, relative to the increase in water content. Similarly, from the same viewpoint, it is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. In one or more embodiments, the amount of acid anhydride (e.g., acetic anhydride) added can be, for example, 1:0.8, 1:0.9, 1:1, 1:1.1, or 1:1.2 in molar ratio to the amount of water increase (water increase: acid anhydride).

[0041] Step 2, in one or more embodiments, includes stirring (or circulating) the etching solution after adding acid anhydride. Known stirring (or circulation) methods can be used. Examples of stirring methods include using a propeller-type stirrer, and examples of circulation methods include circulating the liquid using a pump (liquid circulation). The stirring (or circulation) speed can be set as appropriate. The stirring (or circulation) time is preferably, for example, 30 minutes or more. The etching temperature during stirring (or circulation) is preferably, for example, 20°C to 50°C. Step 2, in one or more embodiments, includes measuring the water content of the etching solution after the addition of acid anhydride. The water content in the etching solution can be measured, for example, using the Karl Fischer method.

[0042] [Difference in etching speed] In one or more embodiments of the etching method of this disclosure, it is preferable that the difference between the etching rate in step 1 and the etching rate using the etching solution obtained after step 2 (etching rate difference) is within 10%. That is, it is preferable that the etching rate difference satisfies the following formula. Etching rate difference (%) = |100 × [(Etching rate using the etching solution obtained after step 2) / (Etching rate in step 1)] - 100| ≤ 10

[0043] The etching method of this disclosure is used in one or more embodiments to etch a layer containing molybdenum. The etching method of this disclosure can be used in one or more embodiments to etch a molybdenum-containing metal in the manufacturing process of electronic devices, particularly semiconductor wafers. Accordingly, this disclosure relates in one embodiment to a method for manufacturing a semiconductor wafer, which includes the etching method of this disclosure. The etching method of this disclosure can be suitably used in the fabrication of semiconductor wafers in one or more embodiments. This enables uniform etching of the layer to be etched, thereby improving productivity and yield. The etching method of this disclosure can be used in one or more embodiments to etch electrodes containing molybdenum in the manufacturing process of electronic devices, particularly semiconductor memories such as non-volatile memories including 3D-NAND flash memory. Accordingly, this disclosure relates in one embodiment to a method for manufacturing a semiconductor memory, which includes the etching method of this disclosure. The etching method of this disclosure can be suitably used in one or more embodiments to produce patterns having a three-dimensional structure. This makes it possible to obtain advanced devices such as high-capacity memory. The etching method of this disclosure can be used, for example, in etching methods such as those disclosed in Japanese Patent Application Publication No. 2020-145412. [Examples]

[0044] The present disclosure will be specifically described below with reference to examples, but the present disclosure is not limited in any way by these examples.

[0045] 1. Preparation of etching solution for first use Nitric acid, phosphoric acid, acetic acid, and water were combined to obtain an etching solution (pH: -1.8) for initial use. The amounts of each component (mass%) in the etching solution were 2% by mass for nitric acid, 9% by mass for phosphoric acid, 86.5% by mass for acetic acid, and 2.5% by mass for water. The amount of water includes the amount of water contained in acidic aqueous solutions, etc.

[0046] The following components were used to prepare the etching solution for the first use. Acetic acid [Fujifilm Wako Pure Chemical Industries, Ltd., 100% concentration] Nitric acid [Fujifilm Wako Pure Chemical Industries, Ltd., 70% concentration] Phosphoric acid [manufactured by Phosphorus Chemical Industry Co., Ltd., concentration 85%] Water [Ultrapure water produced using a continuous pure water production system (PureConti PC-2000VRL model) and subsystem (MacAce KC-05H model) manufactured by Kurita Water Industries Ltd.]

[0047] [pH of etching solution] The pH value of the etching solution at 25°C was measured using a pH meter (manufactured by Toa DKK Co., Ltd.), and the value was obtained one minute after immersing the pH meter's electrode in the etching solution.

[0048] 2. Evaluation The following treatments were performed using molybdenum plates, and the following evaluations were conducted. (Examples 1-2) <Settling of etching solution> The etching solution was allowed to stand at 30°C under open-system conditions before its first use. The standing time was 12 hours for Example 1 and 24 hours for Example 2. The etching solution that was allowed to stand for the predetermined time under open-system conditions was intended to represent the etching solution after it had been used for etching (i.e., the etching solution after step 1). <Addition of acid anhydride> The water concentration of the etching solution (etching solution after use) was measured using a Karl Fischer analyzer after standing for a predetermined time. Acetic anhydride was added according to the increase in water content from the initial use of the etching solution (Example 1: 0.7% by mass, Example 2: 1.4% by mass), and the mixture was stirred at 30°C for 30 minutes. Here, the same amount of acetic anhydride as the increased water content (molar ratio 1:1) was added. The etching solution after the addition of acetic anhydride represents the etching solution for reuse (i.e., the etching solution after step 2). Then, the water concentration in the etching solution after the addition of acetic anhydride (etching solution for reuse) was measured using a Karl Fischer analyzer. The water content in the etching solution after the addition of acetic anhydride was 2.5% by mass, and the increase in water content from the initial use of the etching solution was 0% by mass. <Etching process> A molybdenum plate measuring 2 cm in length, 2 cm in width, and 0.1 mm in thickness, whose weight had been measured beforehand, was immersed in the etching solution (reused etching solution) after the addition of acetic anhydride, and etched at 30°C for 30 minutes. After that, it was washed with water and dried (air-dried), and the weight of the molybdenum plate was measured again. The difference was taken as the amount of etching. A precision balance was used to measure the weight. The etching rate of the molybdenum plate was then determined using the following formula. The results are shown in Table 1. Etching rate (nm / min) = Etching amount (g) × 10 7 / (10.28(g / cm 3 )×2×2×2(cm 2 Etching time (minutes) (Comparative Example 1) The etching process was performed using the etching solution from the first use under the same conditions as in Example 1, and the etching rate of the molybdenum plate (i.e., the etching rate on the first etching) was determined. The results are shown in Table 1. (Comparative Example 2) Except for the absence of acetic anhydride, the same conditions as in Example 1 were used for standing and etching treatments, and the etching rate of the molybdenum plate was determined. The results are shown in Table 1. (Comparative Example 3) Except for the absence of acetic anhydride, the same conditions as in Example 2 were used for standing and etching treatments, and the etching rate of the molybdenum plate was determined. The results are shown in Table 1. Comparative Example 1 assumes the initial etching process, while Examples 1-2 and Comparative Examples 2-3 assume etching using the same etching solution for reuse. (Comparative Example 4) Except for adding 5% acetic anhydride when preparing the etching solution for the first use, the same conditions as in Example 1 were used for standing and etching treatment, and the etching rate of the molybdenum plate was determined. The results are shown in Table 2. Comparative Example 4 is a case where the timing of adding acetic anhydride is changed from after the standing period in Example 1 to before the standing period, and it assumes an etching process in which acetic anhydride is added before the initial etching.

[0049] Furthermore, the etching rate difference between the etching rate using the etching solution after adding anhydride or after standing for a predetermined time (etching rate upon reuse) and the etching rate using the etching solution on its first use (etching rate on the first etching) (i.e., the etching rate difference between Examples 1-2 and Comparative Example 1, and the etching rate difference between Comparative Examples 2-4 and Comparative Example 1) was calculated using the following formula. The results are shown in Tables 1-2. (Examples 1-2) Etching rate difference (%) = 100 × [(Etching rate when using etching solution after adding anhydride) / (Etching rate on the first etching)] - 100 (Comparative Examples 2-4) Etching rate difference (%) = 100 × [(Etching rate when using etching solution after a predetermined time) / (Etching rate on the first etching)] - 100

[0050] [Table 1]

[0051] [Table 2]

[0052] As shown in Table 1, Examples 1 and 2, which used etching solutions to which acetic anhydride was added, showed etching rates similar to those of Comparative Example 1 (etching solution on its first use). On the other hand, Comparative Examples 2 and 3, which used etching solutions without added acetic anhydride, showed higher etching rates compared to Comparative Example 1 (etching solution on its first use). From this, it is considered that adding acetic anhydride to the etching solution after etching can reduce the amount of water in the etching solution, thereby suppressing the increase in etching rate due to the increase in water content, and thus suppressing fluctuations in etching rate for each etching when the etching solution is reused. As shown in Table 2, Comparative Example 4, in which acetic anhydride was added to the etching solution before the initial etching, had a slower etching rate compared to Comparative Example 1 (etching solution used for the first time). Therefore, it was found that adding acetic anhydride to the etching solution before use does not suppress fluctuations in the etching rate. [Industrial applicability]

[0053] The etching method of this disclosure is useful in manufacturing a high-capacity semiconductor memory because it can suppress the increase in etching rate due to an increase in the amount of water in the etching solution.

Claims

1. An etching method for etching a layer to be etched containing molybdenum, An etching method comprising the following steps 1 and 2. Step 1: A step of contacting an etching solution containing nitric acid and phosphoric acid with a layer to be etched that contains molybdenum. Step 2: A step of adding anhydride to the etching solution after Step 1, wherein the amount of anhydride added is 0.8 moles or more and 1.2 moles or less per mole increase in the amount of water in the etching solution.

2. The etching method according to claim 1, wherein the etching solution used in step 1 further comprises an organic acid (excluding anhydride).

3. The etching method according to claim 1, wherein the acid anhydride added in step 2 is acetic anhydride.

4. The etching method according to claim 2, wherein the mass ratio (organic acid / nitric acid) of the etching solution used in step 1 is 5 or more and 50 or less.

5. The etching method according to claim 2, wherein the mass ratio (organic acid / phosphoric acid) of the etching solution used in step 1 is 3 or more and 20 or less.

6. The etching method according to claim 1, wherein the mass ratio (nitric acid / phosphoric acid) of nitric acid to phosphoric acid in the etching solution used in step 1 is 0.1 or more and 2.0 or less.

7. The etching method according to claim 1, wherein the amount of nitric acid in the etching solution used in step 1 is 0.5% by mass or more and 10% by mass or less.

8. The etching method according to claim 1, wherein the amount of phosphoric acid in the etching solution used in step 1 is 1% by mass or more and 70% by mass or less.

9. The etching method according to claim 2, wherein the amount of organic acid in the etching solution used in step 1 is 10% by mass or more.

10. The etching method according to claim 1, wherein the amount of water in the etching solution used in step 1 is 15% by mass or less.

11. The etching method according to claim 1, wherein the amount of acid anhydride added in step 2 is 0.1% by mass or more and 65% by mass or less relative to the total amount of etching solution.

12. The etching method according to claim 1, wherein the etching solution containing nitric acid and phosphoric acid that is brought into contact with the layer to be etched containing molybdenum in step 1 includes the etching solution after step 2.

13. The etching method according to claim 1, wherein the difference between the etching rate in step 1 and the etching rate using the etching solution obtained after step 2 is within 10%.

14. The etching method according to claim 1, wherein step 2 includes measuring the amount of water in the etching solution after step 1.

15. A method for manufacturing a semiconductor wafer, comprising the etching method described in any one of claims 1 to 14.

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