Etching method

Abstract

In one embodiment, provided is an etching method capable of suppressing an increase in the etching rate caused by an increase in the amount of water in an etching solution. One embodiment of the present disclosure pertains to an etching method for etching a molybdenum-containing layer to be etched, the etching method comprising the following step 1 and step 2. Step 1: A step for bringing an etching solution containing nitric acid and phosphoric acid into contact with a molybdenum-containing layer to be etched. Step 2: A step for adding an acid anhydride to the etching solution after step 1.

Description

Etching method

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

[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 the semiconductor field in recent years, 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, Japanese Patent Application Laid-Open No. 2023-112748 (Patent Document 1) proposes an etching solution containing at least nitric acid, acetic acid, a phosphorus compound, and water, and having a water concentration of 3.0 M or less after mixing. The document also describes that an acid anhydride may be further added to the etching solution.

[0004] In one aspect, the present disclosure relates to an etching method for etching an etched layer containing molybdenum, the etching method including the following Step 1 and Step 2. Step 1: A step of bringing an etching solution containing nitric acid and phosphoric acid into contact with an etched layer containing molybdenum. Step 2: A step of adding an anhydrous acid to the etching solution after Step 1.

[0005] In one aspect, the present disclosure relates to a method for manufacturing a semiconductor wafer, including the etching method of the present disclosure.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] As a result of diligent research by the present inventors, it has been found that adding anhydrous acid to the etching solution used for etching can reduce the amount of water in the etching solution, 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 when preparing the etching solution, anhydrous acid reacts with nitric acid in the etching solution, making it difficult to add a large amount of anhydrous acid to the etching solution when it is used for the first time, and thus difficult to suppress the increase in water content when the etching solution is reused.

[0010] In other words, the present 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 (hereinafter also referred to as "the etching method of the present disclosure"). Step 1: A step of contacting the molybdenum-containing layer to be etched with an etching solution containing nitric acid and phosphoric acid. Step 2: A step of adding anhydrous acid to the etching solution after step 1.

[0011] 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.

[0012] [Etched Layer] In one or more embodiments, the etched layer to be etched using the etching method of the present disclosure is an etched layer containing molybdenum. In one or more embodiments, the etched layer 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.

[0013] [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").

[0014] 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 circulating the liquid include circulating the liquid using a pump (a method of stirring without using stirring blades). The stirring speed can be set as appropriate, but from the viewpoint of improving uniform etching in the plane, 50 rpm or more is preferred, 100 rpm or more is more preferred, and 200 rpm or more is even more preferred. The liquid circulation speed can be set as appropriate, but from the viewpoint of improving uniform etching in the plane, 1 L / min or more is preferred.

[0015] The temperature of the etching solution 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.

[0016] 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.

[0017] <Etching solution used in Step 1> The etching solution used initially in Step 1 (hereinafter also referred to as the "etching solution used for the first time") is, in one or more embodiments, a mixed acid aqueous solution containing nitric acid and phosphoric acid. The etching solution reused in Step 1 (hereinafter also referred to as the "etching solution reused") is, in one or more embodiments, an etching solution to which anhydrous acid has been added after being used for etching once or more times (i.e., the etching solution after Step 2). Therefore, in Step 1, the etching solution containing nitric acid and phosphoric acid that is brought into contact with the molybdenum-containing layer to be etched includes, in one or more embodiments, the etching solution after Step 2.

[0018] (Nitric acid in etching solution) The amount of nitric acid in the etching solution used in step 1 (etching solution for the first use and etching solution for 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, and more preferably 5% by mass or less. More specifically, the amount of nitric acid in the etching solution is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 5% by mass or less.

[0019] (Phosphoric acid in etching solution) The amount of phosphoric acid in the etching solution used in step 1 (etching solution for the first use and etching solution for reuse) is preferably 1% by mass or more, more preferably 3% by mass or more, and even 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, even more preferably 30% by mass or less, and even more preferably 10% by mass or less. More specifically, the 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, even more preferably 5% by mass or more and 30% by mass or less, and even more preferably 5% by mass or more and 10% by mass or less.

[0020] 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.

[0021] (Organic Acids in Etching Solution) In one or more embodiments, the etching solution used in step 1 (etching solution for the first use and etching solution for reuse) may further contain organic acids (except for anhydrides). 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 being acetic acid. There may be one organic acid or a combination of two or more. 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, it is 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.

[0022] 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.

[0023] 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.

[0024] The mass ratio (organic acid / nitric acid) of the amount of 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 organic acid to nitric acid in the etching solution used in step 1 is preferably 5 or more and 50 or less, and more preferably 15 or more and 45 or less.

[0025] 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.

[0026] 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.

[0027] (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 initial 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 from the viewpoint of improving the quality of the etched layer.

[0028] (Other components in the etching solution) The etching solution used in step 1 (etching solution for the first 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.

[0029] The etching solution used in step 1 (etching solution for initial use and etching solution for reuse) may, in one or more embodiments, further contain anhydrous acid in addition to an organic acid other than anhydrous. Examples of anhydrous acid include the anhydrous acid added in step 2, which will be described later. The etching solution for reuse contains the anhydrous acid added in step 2, in one or more embodiments. The amount of anhydrous acid in the etching solution used in step 1 may be within the same range as the amount of anhydrous acid added in step 2, which will be described later.

[0030] (Method for Manufacturing Etching Solution) In one or more embodiments, the etching solution for initial use is obtained by compounding phosphoric acid, nitric acid, and optionally the above-mentioned optional components (organic acid, water, and other components) in a known manner. Therefore, in one or more embodiments, the method for manufacturing the etching solution for initial use may include at least the step of compounding phosphoric acid and nitric acid. In this disclosure, "compounding" includes, in one or more embodiments, simultaneously or sequentially mixing phosphoric acid, nitric acid, and optionally the above-mentioned optional components. 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, liquid circulation stirring with a pump, homomixer, homogenizer, ultrasonic disperser, and wet ball mill. The preferred compounding amounts of each component when manufacturing the etching solution for initial use can be the same as the preferred compounding amounts of each component in the etching solution described above. In one or more embodiments, the etching solution for reuse can be obtained by compounding anhydrous acid after using the etching solution for initial use once or multiple times for etching.

[0031] 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, if neutralization is involved, the amount of each component and the content may differ.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] [Step 2: Addition of Acid Anhydride] Step 2 is the process of adding acid anhydride to the etching solution after Step 1 (addition step). For example, when acetic anhydride is added as the acid 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.

[0036] As for 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.

[0037] 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 differs from the amount of water in the etching solution upon first use. Therefore, in one or more embodiments, step 2 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. In one or more embodiments, step 2 is the step of adding acid anhydride to the etching solution when the amount of water in the etching solution after step 1 increases (rises).

[0038] 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 generation of heat 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.

[0039] 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, and from the same viewpoint, 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 (increase in water content: acid anhydride) with respect to the increase in water content.

[0040] Step 2, in one or more embodiments, includes stirring (or circulating) the etching solution after adding the 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 adding the acid anhydride. The water content in the etching solution can be measured, for example, using the Karl Fischer method.

[0041] [Etching Rate Difference] 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

[0042] The etching method of this disclosure is used in one or more embodiments to etch a layer to be etched containing molybdenum. The etching method of this disclosure can be used in one or more embodiments to etch a metal containing molybdenum in the manufacturing process of electronic devices, particularly semiconductor wafers. Accordingly, in one embodiment, this disclosure relates to a method for manufacturing a semiconductor wafer, including the etching method of this disclosure. The etching method of this disclosure can be suitably used in one or more embodiments to manufacture a semiconductor wafer. This enables uniform etching of the layer to be etched, improving productivity and yield. The etching method of this disclosure can be used in one or more embodiments to etch an electrode containing molybdenum in the manufacturing process of electronic devices, particularly semiconductor memory such as non-volatile memory including 3D-NAND flash memory. Accordingly, in one embodiment, this disclosure relates to a method for manufacturing a semiconductor memory, including the etching method of this disclosure. The etching method of this disclosure can be suitably used in one or more embodiments to manufacture a pattern having a three-dimensional structure. This enables the production of advanced devices such as high-capacity memory. The etching method of this disclosure can be used, for example, in an etching method such as the one disclosed in Japanese Patent Application Publication No. 2020-145412.

[0043] This disclosure further relates to one or more embodiments described below. <1> An etching method for etching a layer to be etched containing molybdenum, comprising the following steps 1 and 2: Step 1: Contacting the layer to be etched containing molybdenum with an etching solution containing nitric acid and phosphoric acid. Step 2: Adding an anhydride to the etching solution after step 1. <2> The etching method according to <1>, wherein the etching solution used in step 1 further comprises an organic acid (except an anhydride). <3> The etching method according to <2>, wherein the organic acid comprises 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. <4> The etching method according to any one of <1> to <3>, wherein the acid anhydride added in step 2 is at least one selected from acetic anhydride, propionic anhydride, maleic anhydride, succinic anhydride, phthalic anhydride, benzoic anhydride, citraconic anhydride, trifluoromethanesulfonic acid anhydride, and phosphorus pentoxide. <5> The etching method according to any one of <1> to <4>, wherein the amount of nitric acid in the etching solution used in step 1 is 0.5% by mass or more, or 1% by mass or more, and 10% by mass or less, or 5% by mass or less. <6> The etching method according to any one of <1> to <5>, wherein the amount of phosphoric acid in the etching solution used in step 1 is 1% by mass or more, or 3% by mass or more, or 5% by mass or more, and 70% by mass or less, or 50% by mass or less, or 30% by mass or less, or 10% by mass or less. <7> The etching method according to any one of <1> to <6>, wherein the amount of organic acid in the etching solution used in step 1 is 10% by mass or more, or 30% by mass or more, or 60% by mass or more, or 85% by mass or more, and 99% by mass or less, or 98% by mass or less, or 95% by mass or less, or 90% by mass or less. <8> The etching method according to any one of <2> to <7>, wherein the total amount of nitric acid, phosphoric acid and organic acid in the etching solution used in step 1 is 85% by mass or more, or 90% by mass or more, or 95% by mass or more, and 100% by mass or less.<9> The etching method according to any one of <2> to <8>, wherein the mass ratio (organic acid / nitric acid) of the organic acid to nitric acid in the etching solution used in step 1 is 5 or more, or 15 or more, and 50 or less, or 45 or less. <10> The etching method according to any one of <2> to <9>, wherein the mass ratio (organic acid / phosphoric acid) of the organic acid to phosphoric acid in the etching solution used in step 1 is 3 or more, or 4 or more, or 5 or more, and 20 or less, or 19 or less, or 18 or less. <11> The etching method according to any one of <1> to <10>, 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, or 0.15 or more, or 0.2 or more, and 2.0 or less, or 1.0 or less. <12> The etching method according to any one of <1> to <11>, wherein the amount of water in the etching solution used in step 1 is 15% by mass or less, or 10% by mass or less, or 8% by mass or less, or 5% by mass or less, or 2.5% by mass or less. <13> The etching method according to any one of <1> to <12>, wherein the amount of acid anhydride added in step 2 is 0.1% by mass or more relative to the total amount of etching solution, and is 65% by mass or less, or 35% by mass or less, or 20% by mass or less. <14> The etching method according to any one of <1> to <13>, wherein the amount of acid anhydride added in step 2 is 4% by mass or more, or 4.5% by mass or more, or 5% by mass or more relative 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, and is 30% by mass or less, or 25% by mass or less, or 20% by mass or less. <15> The etching method according to any one of <1> to <14>, wherein in step 1, the etching solution containing nitric acid and phosphoric acid that is brought into contact with the layer to be etched containing molybdenum includes the etching solution after step 2. <16> The etching method according to any one of <1> to <15>, 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%. <17> The etching method according to any one of <1> to <16>, wherein step 2 includes measuring the amount of water in the etching solution after step 1.<18> A method for manufacturing a semiconductor wafer, including the etching method according to any one of <1> to <17>. <19> An etching method for etching an etched layer containing molybdenum, including the following steps 1 and 2. Step 1: A step of bringing an etching solution containing nitric acid, phosphoric acid, and acetic acid into contact with an etched layer containing molybdenum, where the mass ratio of the organic acid to nitric acid (organic acid / nitric acid) is 5 or more and 50 or less. Step 2: A step of adding anhydrous acid to the etching solution after Step 1 in an amount of 0.1% by mass or more and 65% by mass or less based on the total amount of the etching solution.

[0044] Hereinafter, the present disclosure will be specifically described by way of examples, but the present disclosure is not limited in any way by these examples.

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

[0046] For the preparation of the etching solution at the first use, the following components were used. Acetic acid [FUJIFILM Wako Pure Chemical Corporation, concentration 100%] Nitric acid [FUJIFILM Wako Pure Chemical Corporation, concentration 70%] Phosphoric acid [manufactured by Phosphorus Chemical Industry Co., Ltd., concentration 85%] Water [ultrapure water produced using a continuous ultrapure water production apparatus (Pure Contee PC-2000VR type) and a subsystem (Mac Ace KC-05H type) manufactured by Kurita Water Industries, Ltd.]

[0047] [pH of the etching solution] The pH value of the etching solution at 25°C is the value measured using a pH meter (manufactured by Toa DKK Corporation), and it is the value after 1 minute of immersing the electrode of the pH meter in the etching solution.

[0048] 2. Evaluation The following processes were performed using the molybdenum plate, and the following evaluations were conducted. (Examples 1-2) <Settling of Etching Solution> The etching solution for the first use was settled at 30°C under open system conditions. The settling time was 12 hours for Example 1 and 24 hours for Example 2. The etching solution settled for a predetermined time under open system conditions is assumed to be the etching solution after use (i.e., the etching solution after step 1). <Addition of Acid Anhydride> The water concentration of the etching solution after settling for a predetermined time (etching solution after use) was measured with a Karl Fischer. Acetic anhydride was added according to the increase in water content from the amount of water in the etching solution at the time of first use (Example 1: 0.7 mass%, Example 2: 1.4 mass%), and the mixture was stirred at 30°C for 30 minutes. Here, the same amount of acetic anhydride as the increased amount of water (molar ratio 1:1) was added. The etching solution after the addition of acetic anhydride is assumed to be 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 in advance, was immersed in the etching solution after the addition of acetic anhydride (etching solution for reuse) 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, and the difference was taken as the etching amount. A precision balance was used to measure the weight. The etching rate of the molybdenum plate was then calculated using the following formula. The results are shown in Table 1. Etching rate (nm / min) = Etching amount (g) × 10 7 / (10.28 (g / cm³) 3 ) × 2 × 2 × 2 (cm 2)) / Etching time (minutes) (Comparative Example 1) Etching was performed under the same conditions as in Example 1 using the etching solution for the first time, 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) The etching and standing process was performed under the same conditions as in Example 1, except that acetic anhydride was not added, and the etching rate of the molybdenum plate was determined. The results are shown in Table 1. (Comparative Example 3) The etching and standing process was performed under the same conditions as in Example 2, except that acetic anhydride was not added, and the etching rate of the molybdenum plate was determined. The results are shown in Table 1. Note that Comparative Example 1 assumes the first etching, while Examples 1-2 and Comparative Examples 2-3 assume etching using the etching solution for reuse. (Comparative Example 4) The etching and standing process was performed under the same conditions as in Example 1, except that 5% acetic anhydride was added when preparing the etching solution for the first use, and the etching rate of the molybdenum plate was determined. The results are shown in Table 2. Comparative Example 4 is a variation in Example 1 where the timing of acetic anhydride addition is before standing, whereas in Example 1 it is after standing. This assumes an etching process where 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 when reused) 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 the etching solution after adding anhydride) / (Etching rate on the first etching)] - 100 (Comparative Examples 2-4) Etching rate difference (%) = 100 × [(Etching rate when using the etching solution after standing for a predetermined time) / (Etching rate on the first etching)] - 100

[0050]

[0051]

[0052] As shown in Table 1, Examples 1 and 2, which used etching solutions to which acetic anhydride was added, had etching rates similar to those of Comparative Example 1 (etching solution on 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 first use). From this, it is thought 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 first etching, had a slower etching rate compared to Comparative Example 1 (etching solution on first use). Therefore, it was found that adding acetic anhydride to the etching solution before use does not suppress fluctuations in etching rate.

[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 molybdenum-containing layer, comprising the following steps 1 and 2: Step 1: A step of contacting the molybdenum-containing layer with an etching solution containing nitric acid and phosphoric acid. Step 2: A step of adding anhydrous acid to the etching solution after step 1.

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 or 2, wherein the acid anhydride added in step 2 is acetic anhydride.

4. The etching method according to claim 2 or 3, 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 any one of claims 2 to 4, 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 any one of claims 1 to 5, 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 any one of claims 1 to 6, 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 any one of claims 1 to 7, 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 any one of claims 2 to 8, 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 any one of claims 1 to 9, 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 any one of claims 1 to 10, 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 any one of claims 1 to 11, 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 any one of claims 1 to 12, 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 any one of claims 1 to 13, 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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