Etching method

Abstract

In one embodiment, an etching method is provided that can suppress the reduction in etching rate due to the native oxide film on the molybdenum surface. [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 of contacting a molybdenum-containing layer to be etched with a pretreatment solution, which is an aqueous solution containing an acid or alkali and does not contain an oxidizing agent selected from the group consisting of sulfuric acid, nitric acid, and hydrogen peroxide. Step 2: A step in which an etching solution containing phosphoric acid and nitric acid is brought into contact with the layer to be etched 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, its nitride, or its oxide to process it into a predetermined pattern shape is performed. In recent years, in the semiconductor field, high integration has been progressing, and the wiring has become more complex and finer, and the requirements for pattern processing technology and etching solutions are also increasing. Various etching methods and etching solutions have been proposed (Patent Documents 1 to 2).

[0003] For example, in Patent Document 1, a substrate processing method is proposed in which a molybdenum film is oxidized by a method different from the conventional method, and the oxidized portion of the molybdenum film is removed from the substrate while leaving the unoxidized portion of the molybdenum film on the substrate. In Patent Document 2, an etching solution for etching a laminated film of an aluminum-based metal film and a molybdenum-based metal film formed on an insulating film substrate, which contains a specific sulfonic acid compound, phosphoric acid, and nitric acid, is proposed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Molybdenum metal surfaces develop a native oxide film (MoO3) when exposed to air for extended periods. For etching molybdenum, mixed acid aqueous solutions (strongly acidic aqueous solutions) containing phosphoric acid and nitric acid are sometimes used as etching solutions. It has been found that such mixed acid-based etching solutions containing nitric acid and phosphoric acid have difficulty dissolving MoO3, and the etching rate is significantly reduced when a native oxide film is present on the molybdenum metal surface.

[0006] Therefore, in one embodiment, this disclosure provides an etching method that can suppress the reduction in etching rate due to the native oxide film on the molybdenum surface. [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 of contacting a molybdenum-containing layer to be etched with a pretreatment solution, which is an aqueous solution containing an acid or alkali and does not contain an oxidizing agent selected from the group consisting of sulfuric acid, nitric acid, and hydrogen peroxide. Step 2: A step in which an etching solution containing phosphoric acid and nitric acid is brought into contact with the layer to be etched after Step 1. [Effects of the Invention]

[0008] According to this disclosure, in one embodiment, an etching method can be provided that can suppress the reduction in etching rate due to the native oxide film on the molybdenum surface. [Modes for carrying out the invention]

[0009] The timing of wafer etching at semiconductor wafer manufacturers varies; sometimes it's immediately after film deposition, sometimes several days later, and sometimes a month later. As a result, the thickness and uniformity of the native oxide film on the molybdenum metal surface differ from day to day. If the surface roughness and etching rate after etching vary depending on the state of the molybdenum metal surface, stable production of semiconductor wafers becomes difficult. As a result of diligent research by the present inventors, it has been found that by pre-treating the molybdenum-containing layer to be etched with an aqueous solution containing an acid or alkali before etching it with a mixed acid aqueous solution containing nitric acid and phosphoric acid, the decrease in etching rate due to the state of the molybdenum-containing layer to be etched (particularly the native oxide film of molybdenum) can be suppressed, and molybdenum can be etched well. Furthermore, the issue of differing surface roughness and etching rate after etching depending on the state of the molybdenum metal surface is a problem specific to etching using a mixed acid etching solution containing nitric acid and phosphoric acid. When using an acid / alkali etching solution with peracids / peroxides such as hydrogen peroxide as the oxidizing agent, the etching solution can dissolve MoO3, and therefore the above-mentioned problem does not occur.

[0010] 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 of contacting a molybdenum-containing layer to be etched with a pretreatment solution, which is an aqueous solution containing an acid or alkali and does not contain an oxidizing agent selected from the group consisting of sulfuric acid, nitric acid, and hydrogen peroxide. Step 2: A step in which an etching solution containing phosphoric acid and nitric acid is brought into contact with the layer to be etched after Step 1.

[0011] According to this disclosure, in one embodiment, an etching method can be provided that can suppress the reduction in etching rate due to the native oxide film on the molybdenum surface.

[0012] 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.

[0013] [Etched layer] The etched layer processed using the etching method of this disclosure is, in one or more embodiments, an etched layer containing molybdenum. The etched layer containing molybdenum may, in one or more embodiments, consist of molybdenum, or in one or more embodiments, 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, its nitrides, or oxides thereof. In one or more embodiments, the etched layer has a native oxide film on at least a part of its surface. The presence or absence of the native oxide film can be confirmed by ESCA (Electron Spectroscopy for Chemical Analysis) in one or more embodiments. The native oxide film formed on the surface of the etched layer is, in one or more embodiments, a native oxide film of molybdenum (e.g., molybdenum oxide film (MoO3)).

[0014] [Step 1: Pretreatment] In one or more embodiments, Step 1 is a pretreatment step of bringing a pretreatment liquid, which is an aqueous solution containing an acid or an alkali and does not contain an oxidizing agent selected from the group consisting of sulfuric acid, nitric acid, and hydrogen peroxide (hereinafter simply referred to as "pretreatment liquid"), into contact with an etched layer containing molybdenum (hereinafter also simply referred to as "etched layer"). In one or more embodiments, it is considered that Step 1 can remove the native oxide film (e.g., native oxide film of molybdenum) present on the surface of the etched layer containing molybdenum. . Examples of the method of bringing the pretreatment liquid into contact with the etched layer include, for example, a method of immersing the etched layer in the pretreatment liquid for contact, a method of spraying the pretreatment liquid onto the etched layer for contact, and the like. In Step 1, from the viewpoint of suppressing the decrease in etching rate due to the native oxide film on the molybdenum surface and from the viewpoint of suppressing surface roughness, the time (immersion time) for bringing the pretreatment liquid into contact with the etched layer is preferably 1 minute or more, and from the same viewpoint, it is preferably 10 minutes or less, and more preferably 5 minutes or less. In Step 1, from the viewpoint of suppressing the decrease in etching rate due to the native oxide film on the molybdenum surface and from the viewpoint of suppressing surface roughness, the temperature (immersion temperature) of the pretreatment liquid brought into contact with the etched layer is preferably 25°C or more, and from the same viewpoint, it is preferably 40°C or less, and more preferably 35°C or less.

[0015] [Pretreatment Liquid Used in Step 1] The pretreatment solution used in step 1 is an aqueous solution containing an acid or alkali. In one or more embodiments, the pretreatment solution is an aqueous solution obtained by diluting an acid with water (acid aqueous solution) or an aqueous solution obtained by diluting an alkali with water (alkali aqueous solution). In one or more embodiments, the acid in the pretreatment solution does not contain phosphoric acid or nitric acid. In one or more embodiments, the alkali in the pretreatment solution does not contain at least one nitrogen-containing compound selected from polyallylamines, polyalkyleneimines, polyalkylene polyamines, and alicyclic amines. The acid in the pretreatment solution may be at least one acid selected from hydrofluoric acid (HF), buffered hydrofluoric acid, and hydrochloric acid. The acid may be a single type or a combination of two or more types. The alkali in the pretreatment solution may be at least one selected from ammonia (NH3) and quaternary ammonium salts. The quaternary ammonium salt may be at least one selected from tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, choline, or a salt in which the counteranion is not a hydroxide ion, with at least one selected from tetramethylammonium hydroxide, tetraethylammonium hydroxide, and choline being preferred. The alkali may be a single type or a combination of two or more types. Among these, the pretreatment solution is preferably an aqueous solution containing at least one selected from hydrofluoric acid, ammonia (NH3), and quaternary ammonium salts, from the viewpoint of suppressing the reduction in etching rate due to the native oxide film on the molybdenum surface. Preferably, it is an aqueous solution containing at least one selected from tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), and choline, or an aqueous solution obtained by diluting at least one selected from hydrofluoric acid, ammonia (NH3), tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), and choline with water. In one or more embodiments, the pretreatment liquid is preferably an aqueous solution that easily forms a soluble low-molecular complex with molybdic acid. The pretreatment liquid does not contain an oxidizing agent selected from sulfuric acid, nitric acid, and hydrogen peroxide solution. In one or more embodiments, the pretreatment liquid may or may not contain other oxidizing agents. In one or more embodiments, the pretreatment liquid does not contain a catalyst. The catalyst is, for example, phosphoric acid or glycols. In one or more embodiments, the pretreatment liquid does not contain a moisture regulator. The moisture regulator is, for example, an organic acid or an organic solvent.

[0016] When the pretreatment liquid is an aqueous solution containing an acid, the content (concentration) of the acid in the pretreatment liquid is preferably 0.01% by mass or more from the viewpoints of suppressing the decrease in the etching rate due to the natural oxide film on the molybdenum surface and suppressing the surface roughness, and from the same viewpoints, it is preferably 10% by mass or less, more preferably 5% by mass or less, and still more preferably 3% by mass or less. When two or more acids are combined, the content of the acid in the pretreatment liquid is the total content thereof. When the pretreatment liquid is an aqueous solution containing an alkali, the content (concentration) of the alkali in the pretreatment liquid is preferably 0.01% by mass or more from the viewpoints of suppressing the decrease in the etching rate due to the natural oxide film on the molybdenum surface and suppressing the surface roughness, and from the same viewpoints, it is preferably 10% by mass or less, more preferably 5% by mass or less, and still more preferably 3% by mass or less. When two or more alkalis are combined, the content of the alkali in the pretreatment liquid is the total content thereof. In one or more embodiments, the water content in the pretreatment liquid is the remainder after removing the acid or alkali from the total amount of the pretreatment liquid. In the present disclosure, in one or more embodiments, the blending amount of each component in the pretreatment liquid can be regarded as the content of each component in the pretreatment liquid. [[ID=​​​​When the pretreatment solution is an aqueous solution containing acid, the pH of the pretreatment solution is preferably 3 or less, from the viewpoint of suppressing the reduction in etching rate due to the native oxide film on the molybdenum surface. If the pretreatment solution is an aqueous solution containing alkali, the pH of the pretreatment solution is preferably 9 or higher, more preferably 10 or higher, and even more preferably 11 or higher, from a similar viewpoint. The pH of the pretreatment solution is the value at 25°C and can be measured using a pH meter, specifically by the method described in the examples.

[0018] [Step 2: Etching] Step 2 is an etching step in which an etching solution containing phosphoric acid and nitric acid is brought into contact with the layer to be etched after Step 1 (after pretreatment). In step 2, 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.

[0019] The etching solution temperature in step 2 (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.

[0020] In step 2, the etching time can be set to, for example, 1 minute or more and 180 minutes or less. From the viewpoint of improving the quality of the etched layer, it is preferably 15 minutes or more and 90 minutes or less, and more preferably 20 minutes or more and 60 minutes or less.

[0021] In one or more embodiments, the etching rate in step 2 is preferably 10% or more faster than the etching rate when the layer to be etched is etched without contact with the pretreatment solution. That is, the difference in etching rate with and without pretreatment preferably satisfies the following formula. Difference in etching rate (%) with and without pretreatment = 100 × [(Etching rate with pretreatment) / (Etching rate without pretreatment)] - 100 ≥ 10

[0022] <Etching solution used in step 2> In one or more embodiments, the etching solution used in step 2 is a mixed acid containing nitric acid and phosphoric acid.

[0023] (Nitric acid in etching solution) The amount of nitric acid in the etching solution used in step 2 is preferably 0.5% by mass or more, more preferably 1% by mass or more, from the viewpoint of improving the quality of the etched layer, and similarly, 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.

[0024] (Phosphoric acid in etching solution) The amount of phosphoric acid in the etching solution used in step 2 is preferably 1% by mass or more, more preferably 3% by mass or more, more preferably 5% by mass or more, and from the same viewpoint, it is 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.

[0025] The total amount of nitric acid and phosphoric acid in the etching solution used in step 2 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, it is 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.

[0026] (Organic acids in etching solution) In one or more embodiments, the etching solution used in step 2 may further contain an organic acid. Examples of organic acids include at least one selected from acetic acid, acetic anhydride, 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, acetic anhydride, methoxyacetic acid, and ethoxyacetic acid is preferred as the organic acid, more preferably containing acetic acid, and even more preferably acetic acid. There may be one organic acid or a combination of two or more. When acetic anhydride is used as the organic acid when preparing the etching solution of this disclosure, the acetic anhydride reacts with water in the etching solution to be converted into acetic acid and water, making it possible to reduce the amount of water in the etching solution. The amount of organic acid in the etching solution used in step 2 is preferably 10% by mass or more, more preferably 30% by mass or more, even more preferably 60% by mass or more, even more preferably 85% by mass or more, and preferably 95% by mass or less, from the viewpoint of uniform etching of the layer to be etched. If there is a combination of two or more organic acids, the amount of organic acid in the etching solution is the total amount of those acids.

[0027] The total amount of nitric acid, phosphoric acid, and organic acid in the etching solution used in step 2 is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and similarly, 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.

[0028] In one or more embodiments, the acid contained in the etching solution of this disclosure 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 suppressing the reduction in etching rate due to the native oxide film on the molybdenum surface. When the acid contained in the etching solution composition of this disclosure is a mixed acid consisting of nitric acid, phosphoric acid, and acetic acid, the amount of nitric acid in the mixed acid is preferably 0.5% by mass or more and 20% by mass or less, more preferably 1% by mass or more and 15% by mass or less, and still more preferably 1.5% by mass or more and 10% by mass or less, from the viewpoint of suppressing the reduction in etching rate due to the native oxide film on the molybdenum surface. The amount of phosphoric acid in the mixed acid 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, more preferably 5% by mass or more and 30% by mass or less, and still more preferably 5% by mass or more and 10% by mass or less, from the same viewpoint. From the same viewpoint, the amount of acetic acid in the mixed acid is preferably 10% by mass or more and 95% by mass or less, more preferably 30% by mass or more and 95% by mass or less, still preferably 60% by mass or more and 95% by mass or less, and still more preferably 85% by mass or more and 95% by mass or less, from the same viewpoint.

[0029] (Water in the etching solution) The etching solution used in step 2 includes water in one or more embodiments. Examples of water included in the etching solution of this disclosure include distilled water, deionized water, pure water, and ultrapure water. The amount of water in the etching solution used in step 2 is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less, and still more preferably 5% by mass or less, from the viewpoint of suppressing the reduction in etching rate due to the native oxide film on the molybdenum surface and improving the quality of the layer to be etched.

[0030] (Nitrogen-containing compounds in etching solution) In one or more embodiments, the etching solution used in step 2 may further contain a nitrogen-containing compound from the viewpoint of suppressing the reduction in etching rate due to the native oxide film on the molybdenum surface. The nitrogen-containing compound may be one type or a combination of two or more types. In one or more embodiments, the nitrogen-containing compound may be, for example, at least one nitrogen-containing compound selected from polyallylamines, polyalkyleneimines, polyalkylene polyamines, and alicyclic amines. Examples of the polyalkylene imine include polyethyleneimine (PEI). Examples of the polyalkylene polyamines include bis(hexamethylene)triamine, pentaethylenehexamine, tetraethylenepentamine, triethylenetetramine, and diethylenetriamine. Examples of the alicyclic amines include 1-(2-hydroxyethyl)piperazine and aminoethylpiperazine.

[0031] When the nitrogen-containing compound is a polyallylamine or polyalkyleneimine, the number-average molecular weight of the nitrogen-containing compound is preferably 300 or more, more preferably 600 or more, and even more preferably 1,200 or more, from the viewpoint of suppressing the reduction in etching rate due to the native oxide film on the molybdenum surface and reducing etching unevenness. From the viewpoint of viscosity, it is preferably 100,000 or less, more preferably 5,000 or less, and even more preferably 3,000 or less. More specifically, the number-average molecular weight of the nitrogen-containing compound is preferably 300 or more and 100,000 or less, more preferably 600 or more and 5,000 or less, and even more preferably 1,200 or more and 3,000 or less. When the nitrogen-containing compound is a polyalkylene polyamine, the number-average molecular weight or molecular weight of the nitrogen-containing compound is preferably 50 or more, more preferably 80 or more, and even more preferably 100 or more, from the viewpoint of suppressing the reduction in etching rate due to the native oxide film on the molybdenum surface and reducing etching unevenness. Similarly, it is preferably 1,000 or less, more preferably 500 or less, and even more preferably 300 or less. More specifically, the number-average molecular weight or molecular weight of the nitrogen-containing compound is preferably 50 or more and 1,000 or less, more preferably 80 or more and 500 or less, and even more preferably 100 or more and 300 or less. When the nitrogen-containing compound is an alicyclic amine, the molecular weight of the nitrogen-containing compound is 300 or less, more preferably 250 or less, still more preferably 200 or less, from the viewpoint of suppressing the decrease in the etching rate due to the natural oxide film on the molybdenum surface and reducing the etching unevenness, and 15 or more is preferable, more preferably 20 or more, still more preferably 30 or more, from the viewpoint of uniform etching of the etched layer. More specifically, the molecular weight of the nitrogen-containing compound is preferably 15 or more and 300 or less, more preferably 20 or more and 250 or less, still more preferably 30 or more and 200 or less.

[0032] In the present disclosure, the number average molecular weight can be measured by gel permeation chromatography (GPC). Examples of the method for measuring the number average molecular weight of the nitrogen-containing compound of the present disclosure are shown below. <GPC conditions> Sample solution: Adjusted to a concentration of 0.1 wt% Apparatus / detector: HLC-8320GPC (integrated GPC) manufactured by Tosoh Corporation Column: α-M + α-M (manufactured by Tosoh Corporation) Eluent: 0.15 mol / L Na2SO4, 1% CH3COOH / water Column temperature: 40 °C Flow rate: 1.0 mL / min Sample solution injection volume: 100 μL Standard polymer: Pullulan with known molecular weight (Shodex P-5, P-50, P-200, P-800)

[0033] The amount of nitrogen-containing compound in the etching solution used in step 2 is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, and from the viewpoint of suppressing the reduction in etching rate due to the native oxide film on the molybdenum surface and reducing surface roughness, preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. More specifically, the amount of nitrogen-containing compound in the etching solution is preferably 0.01% by mass or more and 5% by mass or less, more preferably 0.05% by mass or more and 4% by mass or less, and even more preferably 0.1% by mass or more and 3% by mass or less. When there is a combination of two or more nitrogen-containing compounds, the amount of nitrogen-containing compound in the etching solution is the total amount of those compounds.

[0034] (Other components in the etching solution) The etching solution used in step 2 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, chelating agents, surfactants, solubilizers, preservatives, rust inhibitors, disinfectants, antibacterial agents, antioxidants, and the like.

[0035] In one or more embodiments, the etching solution used in step 2 may be substantially free of sulfonic acid compounds. For example, the amount or content of sulfonic acid compounds in the etching solution of this disclosure is preferably less than 2% by mass, more preferably 1% by mass or less, even more preferably 0.1% by mass or less, and even more preferably 0% by mass (i.e., not present). In one or more embodiments, the etching solution used in step 2 may be substantially free of peracids and peroxides. In one or more embodiments, the etching solution used in step 2 may be substantially free of hydrogen peroxide.

[0036] (Method for manufacturing etching solution) The etching solution used in step 2 is obtained in one or more embodiments by combining phosphoric acid, nitric acid, and optionally the above-mentioned optional components (organic acid, water, nitrogen-containing compound, or other components) in a known manner. 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 can be the same as the preferred proportions of each component in the etching solution described above.

[0037] 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 may differ from the content.

[0038] The etching solution used in step 2 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.

[0039] The pH of the etching solution used in step 2 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.

[0040] The etching solution used in step 2 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. [Examples]

[0041] 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.

[0042] 1. Preparation of pretreatment solution (Examples 1-8) The acids or alkalis shown in Table 1 were diluted with water to prepare the pretreatment solutions for Examples 1 to 8 with the compositions shown in Table 1. The concentrations of acid or alkali in the pretreatment solution (effective content, mass %) are shown in Table 1. The amount of water in the pretreatment solution is the remainder after removing the acid or alkali. Note that the amount of water includes the amount of water contained in the acidic or alkaline aqueous solution.

[0043] The following were used to prepare the pretreatment solution. (alkali) NH3: Aqueous ammonia solution [Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., concentration 28%] TMAH: Tetramethylammonium hydroxide [Manufactured by Showa Denko Corporation, concentration 25%] TEAH: Tetraethylammonium hydroxide [Tokyo Chemical Industries, Ltd.] Colin [Tokyo Chemical Industries Co., Ltd.] (acid) HF: Hydrofluoric acid [Fujifilm Wako Pure Chemical Corporation] (Water for dilution) Water [Pure water with a purity of 1 μS / cm or less, produced using the G-10DSTSET pure water system manufactured by Organo Corporation]

[0044] 2. Preparation of etching solution (Examples 1-8, Comparative Examples 1-4) Nitric acid, phosphoric acid, acetic acid, a nitrogen-containing compound (bis(hexamethylene)triamine), and water were combined to obtain etching solutions (pH: <-1) for Examples 1-8 and Comparative Examples 1-4 shown in Table 1. The proportions (mass %) and effective content of each component in the etching solution are shown in Table 1. The amount of water in the etching solution is the remainder after subtracting phosphoric acid, nitric acid, acetic acid, and nitrogen-containing compounds from the total amount of etching solution (100 mass %). Note that the amount of water includes the amount of water contained in acidic aqueous solutions, etc.

[0045] The following components were used to prepare the etching solution. 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%] Nitrogen-containing compound: Bis(hexamethylene)triamine [Molecular weight 215.38] 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.]

[0046] [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.

[0047] 3. Evaluation The following treatments were performed using molybdenum plates, and the following evaluations were conducted. (Examples 1-8) <Step 1: Pre-treatment> 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 prepared pretreatment solution (25°C) for 3 minutes. Afterwards, it was washed with water and dried (air-dried). The molybdenum plate in question was purchased and is not freshly manufactured. The molybdenum plate is intended to be an etchable layer containing molybdenum with a native oxide film formed on its surface. <Step 2: Etching> The pre-treated molybdenum plate was immersed in the prepared etching solution and etched at 25°C for 2 to 30 minutes. In Example 8, the etching solution was stirred using a stirring bar during etching (stirring speed: 500 rpm). After that, the plate was washed with water and dried (air-dried), and the weight of the molybdenum plate was measured again. 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 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 Examples 1-3) Except for the absence of step 1 (pretreatment), etching was performed using the etching solution shown in Table 1 under the same conditions as in Examples 1 to 7, and the etching rate of the molybdenum plate was determined. The results are shown in Table 1. (Comparative Example 4) Except for not performing step 1 (pretreatment), etching was carried out under the same conditions as in Example 8 using the etching solution shown in Table 1, and the etching rate of the molybdenum plate was determined. The results are shown in Table 1.

[0048] Furthermore, the difference in etching rates with and without pretreatment (i.e., the difference in etching rates between Example 1 and Comparative Example 1, between Examples 2-6 and Comparative Example 2, between Example 7 and Comparative Example 3, and between Example 8 and Comparative Example 4) was calculated using the following formula. The results are shown in Table 1. Difference in etching rate (%) with and without pretreatment = 100 × [(Etching rate with pretreatment) / (Etching rate without pretreatment)] - 100

[0049] [Table 1]

[0050] As shown in Table 1, the etching solutions in Examples 1 to 8 all showed improved etching rates compared to Comparative Examples 1 to 4, which did not undergo pretreatment. This suggests that pretreatment with an aqueous solution of acid or alkali before etching with an etching solution containing nitric acid and phosphoric acid can suppress the reduction in etching rate caused by the native oxide film on the molybdenum surface. [Industrial applicability]

[0051] The etching method of this disclosure is useful in manufacturing high-capacity semiconductor memory because it can suppress the reduction in etching rate due to the native oxide film on the molybdenum surface.

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 a molybdenum-containing layer to be etched with a pretreatment solution, which is an aqueous solution containing an acid or alkali and does not contain an oxidizing agent selected from the group consisting of sulfuric acid, nitric acid, and hydrogen peroxide. Step 2: A step in which an etching solution containing phosphoric acid and nitric acid is brought into contact with the layer to be etched after Step 1.

2. The etching method according to claim 1, wherein the pretreatment solution is an aqueous solution containing at least one selected from hydrofluoric acid, ammonia, and a quaternary ammonium salt.

3. The etching method according to claim 2, wherein the quaternary ammonium salt is at least one selected from tetramethylammonium hydroxide, tetraethylammonium hydroxide, and choline.

4. The etching method according to claim 1, wherein the pH of the pretreatment solution used in step 1 is 3 or less, or 9 or more.

5. The etching method according to claim 1, wherein the etching solution used in step 2 further comprises at least one nitrogen-containing compound selected from polyallylamine, polyalkyleneimine, polyalkylene polyamine, and alicyclic amine.

6. The etching method according to claim 1, wherein the etching solution used in step 2 further contains an organic acid.

7. The etching method according to claim 1, wherein the etching rate in step 2 is 10% or more faster than the etching rate when the layer to be etched is etched without contact with the pretreatment solution.

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