Silicon etching inhibitor, etching solution, substrate processing method and method for manufacturing semiconductor element

Abstract

To provide a silicon etching inhibitor capable of suppressing silicon etching, an etching solution containing the silicon etching inhibitor, a method for processing a substrate using the silicon etching solution, and a method for manufacturing a semiconductor element.SOLUTION: A silicon etching inhibitor consists of a compound having a plurality of cationic groups and a hydrophobic group between the a plurality of cationic groups.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a silicon etching inhibitor, an etching solution, a method for treating a substrate, and a method for manufacturing a semiconductor device. [Background technology]

[0002] In the semiconductor field, silicon is widely used as a material for semiconductor elements. In the manufacture of semiconductor elements, etching technology is used to precisely design complex electrical circuits, and this technology allows desired materials to be processed into any shape. In the manufacture of semiconductor elements containing silicon, for example, after forming a laminate of a silicon film and a film made of another material, an etching process is performed to remove part or all of the film made of the other material.

[0003] In recent years, in the field of semiconductor devices and elements, specifically in the fields of 3D-NAND flash memory and transistors with a structure known as GAA (Gate all around), there has been an increasing demand for product miniaturization, and etching processes that enable more precise processing are being actively developed. Specifically, for example, development of an etching solution capable of efficiently etching a target material to be removed by etching is being carried out. Patent Document 1 discloses a technology that uses an etching solution containing water, an oxidizing agent, a water-miscible organic solvent, and a fluoride ion source to improve the etching rate of silicon-germanium and selectively remove silicon-germanium relative to silicon. Developments have also been made regarding etching processing methods, and Patent Document 2 discloses a technology relating to a plasma etching gas that can selectively etch a silicon oxide film formed on a substrate such as a silicon substrate, and that contains a fluorocarbon having 3 or 4 carbon atoms and at least one unsaturated bond and / or ether bond and a bromine atom. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-50365 [Patent Document 2] International Publication No. 2012 / 124726 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, methods for increasing the etching efficiency of the etching target material have been developed as part of technological developments for precisely processing silicon substrates, etc. However, little research has been done on techniques for suppressing the etching of silicon itself, which is used together with the etching target material, and there is still room for improvement.

[0006] Therefore, an object of the present invention is to provide a silicon etching inhibitor capable of inhibiting silicon etching, an etching solution containing the silicon etching inhibitor, a method for treating a substrate using the silicon etching solution, and a method for manufacturing a semiconductor device. [Means for solving the problem]

[0007] The present inventors have conducted extensive research in view of the above-mentioned problems, and as a result have found that silicon etching can be suppressed by using a cationic compound comprising a compound having a plurality of cationic moieties.

[0008] Item 1: A silicon etching inhibitor comprising a compound having a plurality of cationic moieties and a hydrophobic moiety between the cationic moieties. Item 2. The silicon etching inhibitor according to Item 1, wherein the compound is a dication or a trication. Item 3. The silicon etching inhibitor according to Item 1 or 2, wherein the hydrophobic moiety contains four or more carbon atoms. Item 4: The silicon etching inhibitor according to any one of Items 1 to 3, wherein the plurality of cation moieties include at least a quaternary ammonium cation. Item 5. A silicon etching inhibitor comprising one or more acids selected from the group consisting of sulfuric acid and organic acids, a boron compound, the silicon etching inhibitor according to any one of Items 1 to 4, and water, The concentration of the silicon etching inhibitor is 0.005% by mass or more and 10% by mass or less. Silicon nitride etchant. Item 6. The silicon dioxide powder according to Item 5, wherein the acid has a pKa of -5 or more and 2 or less at 25°C. Nitride etchant. Item 7. The silicon nitride etching solution according to Item 5 or 6, wherein at least one of the boiling point and decomposition temperature of the acid at 1 atmosphere is 150° C. or higher and 400° C. or lower. Item 8: A method for treating a substrate containing silicon nitride, comprising: Item 8. A method for treating a substrate, comprising an etching step of etching silicon nitride using the silicon nitride etching solution according to any one of items 5 to 7. Item 9: The substrate further contains at least one of silicon and silicon oxide, Item 9. The substrate processing method according to item 8, wherein the etching step is a step of selectively etching silicon nitride with respect to at least one of silicon and silicon oxide using the etching solution. Item 10: A method for manufacturing a semiconductor device using a substrate containing silicon nitride, Item 8. A method for manufacturing a semiconductor device, comprising an etching step of etching silicon nitride using the silicon nitride etching solution according to any one of items 5 to 7. Item 11: The substrate further contains at least one of silicon and silicon oxide, Item 11. The method for manufacturing a semiconductor device according to item 10, wherein the etching step is a step of selectively etching silicon nitride with respect to at least one of silicon and silicon oxide using the etching solution. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a silicon etching inhibitor capable of inhibiting silicon etching. It is also possible to provide an etching solution containing the silicon etching inhibitor, a substrate processing method using the silicon etching solution, and a semiconductor device manufacturing method. DETAILED DESCRIPTION OF THE INVENTION

[0010] Although the present invention will be described in detail below with reference to the preferred embodiments, the present invention is not limited to these embodiments as long as they do not depart from the spirit of the present invention. Furthermore, the present invention can be implemented by modifying it as desired within the scope of the present invention.

[0011] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits, and "A to B" means that the range is from A to B. Furthermore, when a numerical range is expressed in stages, the upper and lower limits of each numerical range can be combined in any way. In addition, in this specification, the expression "A or B" means "selected from the group consisting of A and B" "At least one" can be read as such. Furthermore, although a number of embodiments are described in this specification, various conditions in each embodiment may be applied to each other to the extent that they are applicable. In addition, in this specification, the expression "etching selectivity of B to A" means "the ratio of the etching rate for removing B to the etching rate for removing A" (etching rate for removing B / etching rate for removing A). In this specification, "concentration" refers to the content of each component in a solution at 25° C. Therefore, "concentration" can express not only the content of a solute in a solution, but also the content of a solvent such as water in a solution.

[0012] <Silicon Etching Inhibitor Composition> An etching liquid according to one embodiment of the present invention is a silicon etching inhibitor that can inhibit etching of silicon in etching of a composite material containing silicon and a material other than silicon, and specifically, is a silicon etching inhibitor (hereinafter also simply referred to as a "silicon etching inhibitor") that comprises a compound having a plurality of cationic moieties and having a hydrophobic moiety between the plurality of cationic moieties (hereinafter also referred to as a "cationic compound"). In this specification, "consisting of" may be replaced with "consisting only of". The silicon etching inhibitor according to this embodiment exhibits an etching inhibitory effect not only on silicon but also on silicon oxide, and therefore may be referred to as a "silicon or silicon oxide etching inhibitor."

[0013] When etching a composite material containing silicon and a material other than silicon, an acid is typically used as the etching component if the silicon is the target to be etched. When using an acid, the etching rate of silicon is significantly slower than when using an alkaline etching solution due to the low concentration of hydroxy ions in the etching solution. However, silicon etching proceeds through nucleophilic reactions with nucleophilic species, such as hydroxy ions, dissociated acid (anions), or water, which are present in small amounts. The surface charge of silicon when using an acid varies depending on the type and concentration of the acid used. For example, when using hydrochloric acid, the surface charge tends to be positive, while when using a divalent or higher acid such as sulfuric acid, the surface charge tends to be negative. When the surface charge is positive, the δ+ of the silicon site becomes stronger, making it more susceptible to nucleophilic attack. On the other hand, when the surface charge is negative, the δ+ of the silicon site is weaker than when the surface charge is positive, making it less susceptible to nucleophilic attack. However, in both negative and positive cases, the silicon surface is hydrophilic, making it more susceptible to nucleophilic species approaching. In contrast, in this embodiment, the cationic portion of the cationic compound, which is a silicon etching inhibitor, adsorbs to the negatively charged portion of the silicon surface, covering it. This inhibits the etching agent from approaching the silicon surface. On the other hand, the surface of silicon nitride is positively charged due to the protonation of the nitrogen sites and is hydrophilic, so cationic compounds and compounds that adsorb to the substrate surface due to hydrophobic interactions are less likely to adsorb. Therefore, the inventors have found that the above-mentioned silicon etching inhibitor can efficiently inhibit silicon etching. The above explanation also applies to etching of silicon oxide, and the above "silicon" (excluding "silicon" in "silicon site") can be rephrased as "silicon oxide." Note that even in the case of silicon oxide, if the surface charge is positive, the δ+ of the silicon site in the silicon oxide becomes stronger, making it susceptible to nucleophilic attack. Unless otherwise specified, this rephrasing can be applied to the following explanation as well.

[0014] The cationic compound is not particularly limited as long as it has a plurality of cationic moieties and a hydrophobic moiety between the plurality of cationic moieties. Specific examples include compounds having a plurality of cationic moieties and a hydrocarbon group between the plurality of cationic moieties, and compounds having a plurality of cationic moieties and an alkyl group between the plurality of cationic moieties are preferred.

[0015] The number of cation moieties in the cationic compound may be 2 or more and 10 or less, preferably 2 or more and 5 or less, and more preferably 2 or more and 3 or less (the compound is a dication or trication), from the viewpoint of efficiently suppressing silicon etching. However, from the viewpoint of efficiently suppressing silicon etching, the number is preferably 2 (the compound is a dication).

[0016] The structure of the cation moiety is not particularly limited, and examples thereof include a structure containing at least one cation selected from the group consisting of primary ammonium cations, secondary ammonium cations, tertiary ammonium cations, quaternary ammonium cations, phosphonium cations, sulfonium cations, iminium cations, diazenium cations, etc. Among these, it is preferable to contain at least a quaternary ammonium cation from the viewpoint of the stability of the inhibitor.

[0017] The structure of the hydrophobic moiety is not particularly limited as long as it is a divalent hydrophobic group. When the hydrophobic moiety has carbon atoms, the number of carbon atoms may be 1 or more, preferably 2 or more, more preferably 4 or more, and even more preferably 6 or more, from the viewpoint of efficiently suppressing silicon etching. It is usually 20 or less, may be 15 or less, or may be 10 or less. More specifically, the hydrophobic moiety may be a divalent hydrocarbon group. From the viewpoint of solubility in an etching solution, it is preferably a divalent hydrocarbon group having 1 to 20 carbon atoms, more preferably a divalent hydrocarbon group having 1 to 15 carbon atoms, even more preferably a divalent hydrocarbon group having 1 to 10 carbon atoms, particularly preferably a divalent hydrocarbon group having 4 to 10 carbon atoms, and most particularly preferably a divalent hydrocarbon group having 6 to 10 carbon atoms. These hydrocarbon groups may have a linear structure or may contain a branched or cyclic structure. Furthermore, in these hydrocarbon groups, any one carbon atom may be replaced with another atom such as a nitrogen atom, an oxygen atom, a phosphorus atom, or a sulfur atom, as long as the effects of the present invention are achieved. These hydrocarbon groups may have a substituent within the range in which the effects of the present invention can be obtained, and examples of the substituent include a halogen group, a cyano group, an amino group, a carboxyl group, an ester group, an alkylcarbonyl group, an acetyl group, a sulfonyl group, a silyl group, a boryl group, a nitrile group, a thio group, a seleno group, etc. These substituents may be of one type or of two or more types, and the hydrocarbon group may or may not have a substituent.

[0018] The cationic compound may be a compound represented by the following formula (1):

[0019] [ka]

[0020] R in Equation (1) 1 is a divalent hydrophobic group, and can be the divalent hydrophobic group described above.

[0021] R in Equation (1) 2 and R 3 each independently contains at least one cation moiety, which may be any of the cation moieties described above.

[0022] In this specification, the expressions "any" and "either" are used not only when referring to a plurality of things but also when referring to a single thing. Specifically, when the expression "the concentrations of all compounds contained as A are 10% by mass or less" is used, when there are two or more types of compounds contained as A, it means that the concentrations of each of the two or more types of substances are 10% by mass or less, and when there is one or more types of compounds contained as A, it means that the concentration of one type of compound is 10% by mass or less. Also, when there are two or more types of compounds contained as A, it means that the concentration of one type of compound is 10% by mass or less. When the expression "the concentration of any one of the compounds contained in A is 10% by mass or less" is used, if there are two or more compounds contained as A, it means that the concentration of any one of the compounds contained in the two or more compounds is 10% by mass or less, and if there is one or more compounds contained as A, it means that the concentration of that one compound is 10% by mass or less.

[0023] When all of the cationic moieties contained in the cationic compound are quaternary ammonium cations, the compound may be represented by the following formula (2).

[0024] [ka]

[0025] R in Equation (2) 1 is R in Equation (1). 1 is synonymous with.

[0026] R in Equation (2) 11 ~R 16 are each independently a hydrogen atom, a halogen group, a monovalent hydrocarbon group, a cyano group, an amino group, a carboxyl group, an ester group, an alkylcarbonyl group, an acetyl group, a sulfonyl group, a silyl group, a boryl group, a nitrile group, a thio group, or a seleno group; R11 ~R 13 may be bonded to each other to form a ring; R 14 ~R 16 may be bonded to each other to form a ring.

[0027] R in Equation (2) 11 ~R 16 are each independently preferably a monovalent hydrocarbon group from the viewpoint of stability. From the viewpoint of solubility in an etching solution, the monovalent hydrocarbon group is preferably a monovalent hydrocarbon group having 1 to 20 carbon atoms, more preferably a monovalent hydrocarbon group having 1 to 15 carbon atoms, even more preferably a monovalent hydrocarbon group having 1 to 10 carbon atoms, particularly preferably a monovalent hydrocarbon group having 1 to 5 carbon atoms, and most particularly preferably a monovalent hydrocarbon group having 1 to 3 carbon atoms. These hydrocarbon groups may have a linear structure, a branched structure, or a ring structure. Furthermore, in these hydrocarbon groups, any one carbon atom may be replaced with another atom such as a nitrogen atom, an oxygen atom, a phosphorus atom, or a sulfur atom, as long as the effects of the present invention are obtained. Furthermore, these hydrocarbon groups may have a substituent as long as the effects of the present invention are obtained. Examples of the substituent include a halogen group, a cyano group, an amino group, a carboxyl group, an ester group, an alkylcarbonyl group, an acetyl group, a sulfonyl group, a silyl group, a boryl group, a nitrile group, a thio group, and a seleno group. These substituents may be of one type or of two or more types, and the hydrocarbon group may or may not have a substituent.

[0028] Specific examples of cationic compounds include decamethonium dichloride, decamethonium dibromide, hexamethonium dichloride, hexamethonium dibromide, 1,1'-(decane-1,10-diyl)bis[4-aza-1-azoniabicyclo[2.2.2]octane]dibromide, 1,1'-(decane-1,10-diyl)bis[4-aza-1-azoniabicyclo[2.2.2]octane]dichloride, and 1,10-bis[4-aza-1-azoniabicyclo[2.2.2]octan-1-yl]decane dibromide. Among these, cationic compounds in which the alkyl chain between the two cationic sites has 8 or less carbon atoms are more preferred in terms of stability at high temperatures and against sulfuric acid. Specific examples include hexamethonium dichloride and hexamethonium dibromide.

[0029] From the viewpoint of stability, it is preferable that the cationic compound coexists with an anionic compound. A salt state in which the cationic moiety and the anionic compound are bonded by an ionic bond may be treated as the cationic compound. The type of the anionic compound is not particularly limited, and examples thereof include organic ions such as halogen anions, sulfate anions, nitrate ions, hydroxide ions, carbonate ions, phosphate ions, and acetate ions.

[0030] The manner of use of the silicon etching inhibitor is not particularly limited, and it may be manufactured, sold, etc. as a silicon etching inhibitor, or may be used by being contained in a product such as a silicon etching solution. The manner of manufacturing, selling, etc. as a silicon etching inhibitor includes not only a manner in which it is manufactured, sold, etc. as a product containing only a cationic compound, but also a manner in which it is manufactured, sold, etc. as a silicon etching inhibitor in the form of a composition containing the cationic compound as a main component and further containing other components.

[0031] The silicon etching inhibitor can be used when etching another material is desired while suppressing etching of silicon. The other material is not particularly limited, and examples thereof include silicon-germanium, silicon nitride, and titanium nitride. Furthermore, for example, when the other material is silicon nitride, the silicon etching inhibitor may be expressed as an etching inhibitor that suppresses etching of silicon relative to silicon nitride.

[0032] <Method of manufacturing silicon etching inhibitor> The method for producing the silicon etching inhibitor described above is not particularly limited, and it can be produced by a known method or a combination of known methods.

[0033] <Composition of etching solution> An etching solution according to another embodiment of the present invention is an etching solution containing the silicon etching inhibitor described above (hereinafter also simply referred to as "etching solution"). By using this etching solution as an etching solution for etching a composite containing silicon and a material other than silicon (hereinafter also simply referred to as "other material"), it is possible to efficiently etch the other material while suppressing etching of silicon.

[0034] The concentration of the silicon etching inhibitor in the etching solution is not particularly limited, but from the viewpoint of obtaining a sufficient silicon etching inhibitor effect, it is preferably from 0.005% by mass to 10% by mass, more preferably from 0.01% by mass to 5% by mass, and even more preferably from 0.1% by mass to 1% by mass.

[0035] The etching solution is not particularly limited as long as it contains the silicon etching inhibitor described above, and may contain known components that can be contained in etching solutions. Hereinafter, as a specific embodiment of the etching solution, an etching solution that is advantageous for etching silicon nitride as another material while suppressing etching of silicon will be described as an example.

[0036] One example of the etching solution is a silicon nitride etching solution containing one or more acids selected from the group consisting of sulfuric acid and organic acids, a boron compound, the silicon etching inhibitor described above, and water, in which the concentration of the silicon etching inhibitor is 0.005 mass % or more and 10 mass % or less.

[0037] The etching solution according to the above example has the effect of having a high etching selectivity of silicon nitride to silicon (Si). Therefore, it is particularly useful as an etching solution for etching silicon nitride from a substrate containing silicon and silicon nitride. Furthermore, the etching solution according to the above example can be used with a boron compound that does not contain fluorine atoms. This can improve the etching selectivity of silicon nitride to silicon.

[0038] [Boron compounds] The etching solution contains a boron compound, which can increase the etching rate of silicon nitride.

[0039] The inventors speculate that the reason for this is as follows. When an aqueous solution containing a specific acid is used as an etching solution, the inventors have confirmed from an Arrhenius plot of the etching rate of silicon nitride that the slope of the etching rate of silicon nitride with respect to increasing temperature (corresponding to activation energy) is smaller at etching temperatures higher than a specific temperature (for example, 150°C in the case of a sulfuric acid aqueous solution with a concentration of 75% by mass) than at temperatures lower than the specific temperature. In other words, at temperatures higher than the specific temperature, the increase in the etching rate of silicon nitride with respect to increasing temperature tends to be smaller. This indicates that when an aqueous solution containing a specific acid is used as an etching solution, the rate-determining process of silicon nitride etching changes around the specific temperature.

[0040] Furthermore, the etching temperature (change point) at which the rate-determining process changes tends to shift to a lower temperature as the concentration of the specific acid in the aqueous solution increases. From these findings, it is believed that the rate-determining process at temperatures higher than the change point is a process in which an increase in the water content contributes to an increase in the etching rate of silicon nitride. One of the processes in which an increase in the water content is thought to contribute to an increase in the etching rate of silicon nitride is the dissolution of silicic acid compounds produced by the etching reaction. The inventors speculate that the rate-determining process at temperatures higher than the change point is the dissolution of the silicic acid compounds.

[0041] On the other hand, when an aqueous solution containing a boron compound was used as an etching solution, the slope of the silicon nitride etching rate (corresponding to activation energy) with increasing temperature did not change between the lower and higher temperatures than the specific temperature in the Arrhenius plot of the silicon nitride etching rate. From this, the inventors speculate that the inclusion of a boron compound promotes the dissolution of the silicic acid compound produced by the etching reaction. The present inventors speculate that the promotion of dissolution of the silicic acid compound is due to the fact that, when etched with a specific aqueous acid solution, the silicic acid compound oligomerizes and becomes less soluble, or recombines with silicon atoms on the surface of the silicon substrate and becomes less soluble. However, by incorporating a boron compound, the silicic acid compound combines with the boron compound to form borosilicate, which improves the solubility of the compound in water and suppresses the oligomerization of the silicic acid compound and its recombination with silicon atoms on the surface of the silicon substrate.

[0042] It is preferable that the boron compound does not contain fluorine atoms. For example, if a fluorine compound is contained in an etching solution having a pH equal to or lower than the upper limit of the range described below, free hydrogen fluoride may be generated. Free hydrogen fluoride is easily volatilized from the etching solution, which causes fluctuations in the etching characteristics of the etching solution. Furthermore, the presence of hydrogen fluoride in the etching solution not only increases the etching rate of silicon nitride, but also significantly increases the etching rate of other components such as silicon oxide, making it difficult to etch only silicon nitride. Therefore, by using a boron compound that does not contain fluorine atoms, silicon nitride can be etched more efficiently. Furthermore, from the same perspective, it is preferable that the etching solution does not contain a compound that generates hydrogen fluoride, and more preferably does not contain a compound that contains fluorine atoms.

[0043] A boron compound is a compound containing boron (B) as a constituent element. There are no particular restrictions on the boron compound in the etching solution, but from the viewpoint of bonding with silicate compounds, Therefore, it is preferable that the compound is at least one compound selected from the group consisting of boric acid compounds and boronic acid compounds, and examples thereof include boric acid, boric acid salts, boric acid anhydride (boron oxide), metaboric acid, perboric acid, hypoboric acid, and a boric acid polymer. From the viewpoint of stability, it is more preferable that the compound is boric acid, boric acid salts, boric acid anhydride (boron oxide), and a boric acid polymer. Examples of the boric acid compound include one or more compounds selected from the group consisting of boric acid, boric acid salts, boric acid anhydride, and boric acid polymers; and boric acid esters such as trimethyl borate, triethyl borate, triisopropyl borate, tributyl borate, trihexyl borate, tri-o-toluyl borate, and trimethylboroxine. Examples of the boronic acid compound include one or more compounds selected from the group consisting of alkylboronic acids such as ethylboronic acid, propylboronic acid, butylboronic acid, isobutylboronic acid, pentylboronic acid, hexylboronic acid, heptylboronic acid, octylboronic acid, cyclopentylboronic acid, and cyclohexylboronic acid, and arylboronic acids such as phenylboronic acid, naphthaleneboronic acid, anthraceneboronic acid, and phenylenediboronic acid. The etching solution may contain one type of boron compound or two or more types of boron compounds.

[0044] Among these, one or more compounds selected from the group consisting of boric acid, borate salts, boric anhydride, and boric acid polymers are preferred in terms of the effect of suppressing the production of by-products in the etching solution, and boric acid is more preferred in terms of ease of handling. Borates are salts of boric acid or boric acid polymers, and include metal salts such as sodium tetraborate or sodium perborate, and non-metal salts such as ammonium borate, with non-metal salts being preferred. The cation in the borate is preferably an ammonium ion. Therefore, specific examples of borates include various ammonium salts such as unsubstituted ammonium salts, primary ammonium salts, secondary ammonium salts, tertiary ammonium salts, and quaternary ammonium salts. Among these, unsubstituted ammonium salts are particularly preferred in terms of suppressing a decrease in at least one of the boiling point and decomposition temperature (hereinafter also referred to as "boiling point, etc.") of the etching solution at 1 atmosphere. Examples of the unsubstituted ammonium salt include ammonium pentaborate octahydrate.

[0045] The concentration (content) of the boron compound in the etching solution is not particularly limited, but is preferably 0.10% by mass or more. A higher concentration of the boron compound improves the etching performance of the etching solution, which tends to increase the etching rate of silicon nitride and improve the productivity of semiconductor devices. Therefore, the concentration of the boron compound in the etching solution is preferably 0.20% by mass or more, more preferably 0.40% by mass or more, even more preferably 0.80% by mass or more, and particularly preferably 1.00% by mass or more. The upper limit of the concentration is not particularly limited, but may be 30.00% by mass or less, 20.00% by mass or less, 15.00% by mass or less, or 10.00% by mass or less, in terms of the solubility of the boron compound in water. That is, the content is preferably 0.10% by mass or more and 30.00% by mass or less, more preferably 0.10% by mass or more and 20.00% by mass or less, even more preferably 0.10% by mass or more and 15.00% by mass or less, even more preferably 0.40% by mass or more and 15.00% by mass or less, even more preferably 0.80% by mass or more and 15.00% by mass or less, and most preferably 0.80% by mass or more and 10.00% by mass or less. By setting the concentration of the boron compound within the above range, silicon nitride can be etched at a sufficient etching rate.

[0046] [Specific acid] The etching solution preferably contains one or more acids selected from the group consisting of sulfuric acid and organic acids (hereinafter also simply referred to as "specific acids"). As the specific acid, sulfuric acid is preferably used alone. The organic acid may be used alone, or both may be used in combination. In addition, the sulfuric acid and the organic acid may be present in a free state in the etching solution, or may be present by forming a salt with a basic compound. However, from the viewpoint of being able to effectively increase the boiling point and the like, it is preferable that they be present in a free state.

[0047] Furthermore, from the viewpoint of being able to selectively etch silicon nitride relative to silicon, organic acids are preferably used. The inventors speculate as follows about the reason why the effects of the present invention can be obtained when sulfuric acid and organic acids are used.

[0048] While the surface of hydrogen-terminated silicon is hydrophobic, the surfaces of hydroxyl-terminated silicon and silicon oxide formed during the silicon etching process are hydrophilic, making them more susceptible to water access and allowing etching to proceed easily due to the nucleophilic substitution reaction between silicon atoms and water. However, when an organic acid is included as the specific acid, it is presumed that a dehydration condensation reaction occurs between the hydroxyl groups on the surface of silicon or silicon oxide and the organic acid. In this case, the hydrophobic groups of the organic acid face outward (toward the liquid phase), making the surface of silicon or silicon oxide hydrophobic. This makes it difficult for water to approach the surface of silicon or silicon oxide, slowing down etching of silicon or silicon oxide. When a silicon or silicon oxide etching inhibitor (hereinafter simply referred to as "etching inhibitor") is separately added, the use of an organic acid as the specific acid can make the substrate surface hydrophobic, thereby increasing the adsorption of the etching inhibitor. On the other hand, although hydroxyl-terminated silicon on the silicon nitride surface also undergoes a dehydration condensation reaction with organic acids, the silicon nitride remains hydrophilic due to the presence of nitrogen sites on the surface. In other words, under strongly acidic conditions, the nitrogen sites are protonated and converted into a cationic state, resulting in high hydrophilicity, presumably maintaining hydrophilicity even when the organic acid is bound to the silicon sites. Furthermore, since the silicon atom density on the silicon nitride surface is lower than that on the silicon surface, the density of the bound organic acid is also low, and steric hindrance is small, so it is presumed that the approach of nucleophiles such as water is less hindered. Therefore, when an organic acid is included as the specific acid, etching of silicon or silicon oxide is selectively suppressed relative to etching of silicon nitride, and silicon nitride can be selectively etched relative to silicon or silicon oxide.

[0049] Furthermore, when sulfuric acid is included as the specific acid, sulfuric acid is adsorbed onto the surface of silicon or silicon oxide, and the surface charge of each becomes negative, which makes it easier for cationic compounds to be adsorbed, thereby efficiently suppressing etching.

[0050] Etching of silicon nitride proceeds by protonating the nitrogen sites of the silicon nitride, followed by nucleophilic attack by water or hydroxide ions on the silicon sites. Therefore, if the pH of the etching solution is too high (i.e., if the concentration of the specific acid is too low), the rate of protonation of the nitrogen sites significantly decreases, and the etching rate of silicon nitride tends to decrease. Furthermore, if the pH of the etching solution is too high (i.e., if the concentration of the specific acid is too low), the boiling point of the etching solution decreases, making it difficult to control the temperature conditions. Since silicon etching proceeds solely through nucleophilic attack by water or hydroxide ions, the etching rate tends to increase when the pH of the etching solution is high.

[0051] Therefore, the pH at 24°C of an etching solution diluted 10 times by mass with water is preferably 5.0 or less (0.0 or more and 5.0 or less), more preferably more than 0.0 and 4.0 or less, even more preferably more than 0.0 and 3.0 or less, particularly preferably more than 0.0 and 2.0 or less, and especially preferably more than 0.1 and 1.0 or less. This pH refers to a value measured by the glass electrode method described below. The reason for diluting the etching solution 10 times is that: This is to avoid unstable pH measurements due to high concentrations of components other than water in the etching solution. Furthermore, the size of the object to be measured for pH is not particularly limited, and the entire amount of the manufactured or sold etching solution may be diluted 10 times with water, or a portion of the etching solution (for example, 10 g or 10 mass % of the etching solution) may be taken and diluted 10 times with water.

[0052] When the pH of the etching solution is within the above range, protonation of the nitrogen sites of silicon nitride proceeds sufficiently quickly, allowing efficient etching of silicon nitride. Furthermore, since a decrease in the boiling point of the etching solution, which occurs when the pH is too high (i.e., when the specific acid concentration is too low), is unlikely to occur, the temperature conditions during etching can be easily controlled. Therefore, when the pH is below the upper limit of the above range, the etching solution is particularly useful as an etching solution used for etching silicon nitride for microfabrication in the manufacture of semiconductor devices. In terms of adjusting the boiling point and pH of the etching solution, the total concentration of one or more acids selected from the group consisting of sulfuric acid and organic acids in the etching solution is preferably 60% by mass or more and 95% by mass or less, more preferably 60% by mass or more and 90% by mass or less, even more preferably 65% ​​by mass or more and 90% by mass or less, particularly preferably 70% by mass or more and 90% by mass or less, and even more particularly preferably 70% by mass or more and 85% by mass or less.

[0053] The pKa of the specific acid is not particularly limited, but is preferably −5 or more and 2 or less, more preferably −5 or more and 1 or less, even more preferably −5 or more and 0 or less, and particularly preferably −5 or more and −1 or less at 25° C. If the pKa is equal to or greater than the lower limit of the range, the decrease in the etching rate of silicon nitride due to polymerization of silicic acid, which is the product of etching of each silicon compound, can be suppressed. Furthermore, if the pKa is equal to or less than the upper limit of the range, the specific acid is likely to undergo dehydration condensation with the hydroxyl groups on the hydroxyl-terminated silicon surface or silicon oxide surface, thereby efficiently suppressing etching of silicon and silicon oxide. A lower pKa of the specific acid is also preferable in that it can increase the boiling point of the etching solution at a lower specific acid concentration. In addition, when the specific acid is a polyacid, the specific acid will have multiple pKa stages, and it is preferable that the pKa of any of the stages satisfies the above range, and it is more preferable that the lowest pKa of the first pKa stages satisfies the above range.

[0054] The boiling point etc. of the specific acid (NBP, boiling point at 1 atmosphere etc.) is not particularly limited, but from the viewpoint of being able to suppress a change in the concentration of the specific acid due to volatilization of the specific acid even when the etching treatment is performed while heating the etching solution for a long period of time, it is preferably 150° C. or higher, more preferably 200° C. or higher, even more preferably 250° C. or higher, and particularly preferably 300° C. or higher. On the other hand, there is no particular need to set an upper limit for the boiling point etc., and it may be 400° C. or lower, or 350° C. or lower.

[0055] (sulfuric acid) The etching solution may contain sulfuric acid as a specific acid. The inclusion of sulfuric acid generates hydrogen ions, which allows the pH of the etching solution to be adjusted. Furthermore, sulfuric acid has a very low pKa of -3 at 25°C, and since it has two hydroxyl groups, it has a strong interaction with water. In other words, the inclusion of sulfuric acid makes it easier to suppress boiling of water and raise the boiling point of the etching solution.

[0056] The type of sulfuric acid is not particularly limited, but as will be described later, since it is preferable that the concentration of metal in the etching solution is low, it is preferable to use sulfuric acid with as few metal impurities and insoluble impurities as possible, and commercially available products can be purified and used as needed. Commercially available high-purity aqueous sulfuric acid solutions for use in the electronics industry can also be used, and the etching solution can be produced by simply mixing this solution with water and other components.

[0057] Note that, from the viewpoints of preventing boiling of water in the etching solution when the etching solution is heated and preventing phosphorus from remaining on the surface of the substrate to be processed when phosphoric acid is used as the etching agent (it is known that when phosphoric acid is used, phosphorus is likely to remain on the surface of the substrate to be processed and is difficult to remove. Furthermore, phosphorus is also an n-type dopant for silicon, and therefore, it is undesirable for phosphorus to remain), it is preferable to use sulfuric acid as the inorganic acid; however, if this limitation is removed, inorganic acids other than sulfuric acid can also be used, and for example, inorganic acids such as phosphoric acid or other sulfonic acids can be used.

[0058] (organic acid) The etching solution may contain an organic acid as the specific acid. As with sulfuric acid, the inclusion of an organic acid generates hydrogen ions, which can adjust the pH of the etching solution. In this specification, the organic acid does not include boron compounds.

[0059] The organic acid is not particularly limited, and examples thereof include butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, isobutanoic acid, isopentanoic acid, isohexanoic acid, isoheptanoic acid, isooctanoic acid, 2-cyclobutylacetic acid, cyclopentanecarboxylic acid, cyclohexanecarboxylic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, tridecanedioic acid, methylsuccinic acid, tetramethylsuccinic acid, benzoic acid, nitrobenzoic acid, and dinitrobenzoic acid. Carboxylic acid compounds such as aromatic acid, chloronitrobenzoic acid, chlorodinitrobenzoic acid, phthalic acid, chlorophthalic acid, nitrophthalic acid, terephthalic acid, chloroterephthalic acid, or nitroterephthalic acid (the listed aromatic carboxylic acid compounds include their respective isomers); methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, butanesulfonic acid, pentanesulfonic acid, hexanesulfonic acid, heptanesulfonic acid, octane sulfonic acid, hydroxyethanesulfonic acid, Examples of suitable sulfonic acid compounds include hydroxypropanesulfonic acid, hydroxybutanesulfonic acid, hydroxypentanesulfonic acid, hydroxyhexanesulfonic acid, hydroxyheptanesulfonic acid, hydroxyoctane sulfonic acid, aminoethanesulfonic acid, aminopropanesulfonic acid, aminobutanesulfonic acid, aminopentanesulfonic acid, aminohexanesulfonic acid, aminoheptanesulfonic acid, aminooctane sulfonic acid, benzenesulfonic acid, nitrobenzenesulfonic acid, dinitrobenzenesulfonic acid, and pyridinesulfonic acid (the aromatic sulfonic acid compounds listed include their respective isomers); and phosphorus compounds such as phosphonic acid compounds, including ethylphosphonic acid, propylphosphonic acid, butylphosphonic acid, pentylphosphonic acid, heptylphosphonic acid, octylphosphonic acid, isopropylphosphonic acid, isobutylphosphonic acid, isopentylphosphonic acid, isoheptylphosphonic acid, and isooctylphosphonic acid.

[0060] Among these, from the viewpoint of being able to efficiently etch silicon nitride, one or more organic acids selected from sulfonic acid compounds and carboxylic acid compounds are preferred, sulfonic acid compounds are more preferred, alkylsulfonic acids are even more preferred, and methanesulfonic acid is particularly preferred from the viewpoint of increasing the boiling point of the etching solution.

[0061] As with sulfuric acid, an etching solution containing an organic acid preferably has a low metal concentration, and therefore, it is preferable to use an organic acid with as few metal impurities and insoluble impurities as possible, and a commercially available product can be purified and used as needed.

[0062] The present inventors have found that some organic acids containing an aromatic ring can also function as etching inhibitors for silicon or silicon oxide, separate from the etching inhibitors described above. The etching liquid may contain an etching inhibitor other than the etching inhibitor according to this embodiment.

[0063] [water] The etching solution contains water. If water is not contained, the etching rate tends to decrease. Depending on the type and amount of other components, the concentration (content) of water in the etching solution is preferably 5.0 mass% or more and less than 40.0 mass%, more preferably 10.0 mass% or more and less than 40.0 mass%, even more preferably 10.0 mass% or more and less than 35.0 mass%, and particularly preferably 10.0 mass% or more and less than 30.0 mass%. Furthermore, for example, the remainder of the etching solution other than the specific acid and the fluorine-free boron compound may be water. Furthermore, when the etching solution contains components such as a silicon or silicon oxide etching inhibitor or a basic compound, the remainder other than the specific acid, the fluorine-free boron compound, and these components may be water.

[0064] The type of water is not particularly limited, but it is preferable to use high-purity water with few impurities. Water with few impurities can be easily produced and obtained as ultrapure water for semiconductor manufacturing. The amount of impurities in the etching solution can be evaluated by electrical resistivity. Specifically, the electrical resistivity is preferably 0.10 MΩ·cm or more, more preferably 15.00 MΩ·cm or more, and even more preferably 18.00 MΩ·cm or more. The upper limit is not particularly limited, but may be 18.25 MΩ·cm or less. That is, preferably, for example, 0.10 MΩ·cm or more and 18.25 MΩ·cm or less, 15.00 MΩ·cm or more and 18.25 MΩ·cm or less, or 18.00 MΩ·cm or more and 18.25 MΩ·cm or less. As mentioned above, water with such few impurities can be easily produced and obtained as ultrapure water for semiconductor manufacturing. Furthermore, ultrapure water contains significantly fewer impurities that do not affect (have little effect on) electrical resistivity, making it highly suitable as a raw material for etching solutions.

[0065] Furthermore, among metals, it is preferable that any one metal selected from the group consisting of Fe, Cu, Mn, Cr, and Zn is present in a small amount, and the concentration of any one metal selected from this group in the water used as a raw material is preferably 0.01 ppt to 1.00 ppb, more preferably 0.01 ppt to 0.50 ppb, even more preferably 0.01 ppt to 0.20 ppb, and particularly preferably 0.01 ppt to 0.1 ppb, by mass. In particular, it is preferable that this range is satisfied for all of the metals Fe, Cu, Mn, Cr, and Zn.

[0066] [Other ingredients] The etching solution may further contain components (other components) other than the above-mentioned components, within the range in which the effects of the present invention can be obtained, examples of which are shown below.

[0067] (basic compounds) The etching solution may or may not further contain a basic compound. The inclusion of a basic compound can increase the pH of the etching solution. As described above, etching of silicon nitride proceeds by protonating the nitrogen sites of the silicon nitride, followed by nucleophilic attack of water or hydroxide ions on the silicon sites. Therefore, under conditions where the nucleophilic reaction by hydroxide ions is rate-limiting in etching of silicon nitride, the etching rate of silicon nitride may be improved by adding a basic compound to the etching solution to increase its pH.

[0068] The basic compound is not particularly limited as long as it reacts with the specific acid to form a salt of the specific acid, but is preferably ammonia or an organic base, or a salt thereof, and is preferably one selected from the group consisting of ammonia, amines, and tetraalkylammonium hydroxides. It is more preferable that the salt is a salt of an acid having a pKa equal to or higher than the pKa of the specific acid with ammonia or an organic base. When the acid is a polyacid, it is acceptable for the first pKa to be lower than the pKa of the specific acid as long as the second or third pKa is equal to or higher than the pKa of the specific acid. Examples of the organic base include onium hydroxide and organic amines.

[0069] Examples of onium hydroxides include ammonium hydroxides such as primary ammonium hydroxide, secondary ammonium hydroxide, tertiary ammonium hydroxide, or quaternary ammonium hydroxide, phosphonium hydroxide, sulfonium hydroxide, iminium hydroxide containing a multiple bond, or diazenium hydroxide. Among these, ammonium hydroxide is preferred, and quaternary ammonium hydroxide is more preferred from the viewpoint of its good stability against specific acids (particularly sulfuric acid) and its ability to enhance the stability of the etching solution over time.

[0070] As the quaternary ammonium hydroxide, for example, one or more selected from the group consisting of tetramethylammonium hydroxide, ethyltrimethylammonium hydroxide, propyltrimethylammonium hydroxide, butyltrimethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, trimethyl-2-hydroxyethylammonium hydroxide, dimethylbis(2-hydroxyethyl)ammonium hydroxide, methyltris(2-hydroxyethyl)ammonium hydroxide, phenyltrimethylammonium hydroxide, and benzyltrimethylammonium hydroxide can be used.

[0071] As the organic amine, one or more selected from the group consisting of primary amines, secondary amines, and tertiary amines can be used.

[0072] Examples of primary or secondary amines include ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,1,3,3-tetramethylguanidine, diethylenetriamine, dipropylenetriamine, bis(hexamethylene)triamine, N,N,N-trimethyldiethylenetriamine, and N,N-bis(3-aminopropyl)ethylenediamine. One or more selected from the group consisting of amine, 2-(2-aminoethoxy)ethanol, 2-amino-2-methyl-1-propanol, 4-amino-1-butanol, 5-amino-1-pentanol, 6-amino-1-hexanol, N-(2-aminoethyl)propanolamine, N-(2-hydroxypropyl)ethylenediamine, azetidine, pyrrolidine, piperidine, hexamethyleneimine, pentamethyleneimine, and octamethyleneimine can be used.

[0073] Specific examples of tertiary amines include one or more selected from the group consisting of 2-(dimethylamino)ethanol, 3-(dimethylamino)-1-propanol, 4-dimethylamino-1-butanol, 2-(diethylamino)ethanol, triethylamine, methylpyrrolidine, methylpiperidine, 1,8-diazabicyclo[5.4.0]undec-7-ene, and 1,5-diazabicyclo[4.3.0]non-5-ene.

[0074] The organic amine is preferably selected from the group consisting of ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,1,3,3-tetramethylguanidine, diethylenetriamine, dipropylenetriamine, bis(hexamethylene)triamine, 2-(2-aminoethoxy)ethanol, 2-amino-2-methyl-1-propanol, 4-amino-1-butanol, 5-amino-1-pentanol, 6-amino-1-hexanol, N-(2-aminoethyl)propanolamine, pyrrolidine, piperidine, hexamethyleneimine, and pentamethyleneimine. More preferably, the compound may be one or more selected from the group consisting of ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,1,3,3-tetramethylguanidine, diethylenetriamine, dipropylenetriamine, bis(hexamethylene)triamine, 2-(2-aminoethoxy)ethanol, 2-amino-2-methyl-1-propanol, pyrrolidine, and piperidine.

[0075] Such basic compounds may be selected and used according to the known characteristics of each compound, depending on the target and purpose of etching. As mentioned above, from the viewpoint of stability against the specific acid, among the above, quaternary ammonium hydroxide is more preferable. On the other hand, from the viewpoint of suppressing a decrease in the boiling point of the etching solution due to the addition of a basic compound, a compound having a small molar mass relative to the number of nitrogen atoms (molar mass / number of nitrogen atoms) is preferred. Specifically, ammonia or a polyamine compound is preferred. Examples of polyamine compounds include ethylenediamine, diaminopropane, diethylenetriamine, and dipropylenetriamine.

[0076] In the etching solution, one kind of basic compound may be used alone, or a plurality of different kinds may be mixed and used.

[0077] Furthermore, as will be described later, since a low metal concentration is preferable in an etching solution, it is preferable to use a basic compound containing as few metal impurities and insoluble impurities as possible. If necessary, commercially available products can be purified by recrystallization, column purification, ion exchange purification, filtration, or the like before use. When using quaternary ammonium hydroxide as the basic compound, some types are manufactured and sold at extremely high purity for semiconductor manufacturing, and it is preferable to use such a compound. Note that high-purity quaternary ammonium hydroxides commonly sold for semiconductor manufacturing can be used as a solution such as an aqueous solution. When producing an etching solution, this solution can be directly mixed with water and other components.

[0078] The concentration of the basic compound in the etching solution is not particularly limited, but is preferably 0.05 molar equivalents or more relative to the specific acid in the etching solution. The greater the molar equivalent number relative to the specific acid in the etching solution, the higher the pH of the etching solution (i.e., the higher the hydroxide ion concentration), which tends to increase the etching rate of silicon nitride and improve the productivity of semiconductor devices. Therefore, the concentration of the basic compound relative to the specific acid in the etching solution is more preferably 0.05 molar equivalents or more, even more preferably 0.10 molar equivalents or more, and particularly preferably 0.25 molar equivalents or more. The upper limit is not particularly limited, but may be 1.50 molar equivalents or less, 1.00 molar equivalents or less, or 0.75 molar equivalents or less, in order to prevent a decrease in the boiling point of the etching solution due to the addition of the basic compound. That is, preferred ranges include, for example, 0.05 molar equivalents or more and 1.50 molar equivalents or less, 0.10 molar equivalents or more and 1.00 molar equivalents or less, 0.10 molar equivalents or more and 0.75 molar equivalents or less, and 0.25 molar equivalents or more and 0.75 molar equivalents or less. Note that the above ranges are ranges when the specific acid and the basic compound react in a 1:1 ratio, and when the specific acid and the basic compound react in a 2:1 ratio or a 3:1 ratio, the upper and lower limits of the above concentration range of the basic compound are half or one-third, respectively. Specific examples of the range of the basic compound when the specific acid and the basic compound react in a 2:1 ratio include, preferably, 0.025 molar equivalents or more and 0.750 molar equivalents or less, 0.050 molar equivalents or more and 0.500 molar equivalents or less, 0.050 molar equivalents or more and 0.375 molar equivalents or less, and 0.125 molar equivalents or more and 0.375 molar equivalents or less.

[0079] (Other silicon etching inhibitors) The etching solution contains silicon etching inhibitors as well as the silicon etching inhibitors mentioned above. The composition may contain ingredients that can control the amount of hydroxybenzoates.

[0080] [Other etching solutions] The etching solution is not limited to the above-described embodiments. For example, when the target to be etched is silicon-germanium, the etching solution preferably contains components such as oxides and alkaline compounds, but is not limited thereto and may contain other components as long as the effects of the invention are obtained. Furthermore, the components other than oxides and alkaline compounds may also contain the components described above for the etching solution. Furthermore, with respect to the properties of the etching solution, the above-described conditions for the etching solution can be similarly applied, except for the conditions described below.

[0081] When the etching target is silicon-germanium, the etching solution preferably contains an alkaline compound as described above, and also preferably has a high pH, ​​i.e., is alkaline, as described below. In such an embodiment, the surface charge of the etched surface of silicon or silicon oxide becomes negative, so that cationic compounds are easily adsorbed to the surface, and the inventors speculate that the use of the etching inhibitor described above can inhibit the etching of silicon or silicon oxide. Below, preferred conditions for etching silicon-germanium will be explained.

[0082] Examples of the oxidizing agent include at least one selected from the group consisting of peroxides such as hydrogen peroxide and m-chloroperbenzoic acid; N-oxide compounds such as 9-azanoradamantane-N-oxyl (nor-AZADO) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL); and hypohalites such as hypochlorite and hypobromite.

[0083] The concentration of the oxidizing agent in the etching solution is not particularly limited, but is preferably 0.01% by mass or more. The higher the content, the faster the etching rate of silicon-germanium relative to the etching rate of silicon. Therefore, the oxidizing agent content is more preferably 0.03% by mass or more, even more preferably 0.1% by mass or more, particularly preferably 0.2% by mass or more, and even more preferably 0.5% by mass or more. The upper limit is not particularly limited, but may be 4.0% by mass or less, 3.5% by mass or less, or 2.5% by mass or less. That is, preferred concentrations include, for example, 0.01% by mass or more to 4.00% by mass or less, 0.03% by mass or more to 3.50% by mass or less, 0.10% by mass or more to 2.50% by mass or less, 0.20% by mass or more to 2.50% by mass or less, and 0.50% by mass or more to 2.50% by mass or less. Furthermore, in the etching solution, the ratio of the oxidizing agent concentration to the hydroxide ion concentration is not particularly limited, but in terms of selectivity for etching silicon-germanium relative to etching silicon, it is preferably 0.50 or more, more preferably 1.2 or more, and even more preferably 10 or more. The upper limit is not particularly limited, but may be 150 or less, or 80 or less. That is, the ratio is preferably, for example, 0.50 to 150, 1.2 to 80, or 10 to 80. The concentration of the oxidizing agent in the etching solution can be measured by iodometric titration.

[0084] Examples of alkaline compounds include inorganic alkaline compounds such as NaOH, KOH, and ammonia, quaternary ammonium hydroxides such as tetramethylammonium hydroxide (TMAH), and organic alkaline compounds such as various amines. The concentration of the alkaline compound in the etching solution is not particularly limited, but is preferably 0.001 mol / L or more. The higher the content, the higher the alkalinity of the etching solution, which tends to increase the etching rate of silicon-germanium and improve the productivity of silicon devices. Therefore, the content of the alkaline compound in the etching solution is more preferably 0.010 mol / L or more, even more preferably 0.050 mol / L or more, and 0.100 mol / L or more is particularly preferred. The upper limit is not particularly limited, but may be 1.200 mol / L or less, 1.000 mol / L or less, or 0.800 mol / L or less. That is, preferred examples include 0.001 mol / L or more and 1.200 mol / L or less, 0.010 mol / L or more and 1.000 mol / L or less, 0.050 mol / L or more and 0.800 mol / L or less, and 0.100 mol / L or more and 0.800 mol / L or less.

[0085] The water content in the etching solution is not particularly limited, but is preferably 30.0% by mass or more but less than 100.0% by mass, more preferably 50.0% by mass or more but less than 100.0% by mass, even more preferably 60.0% by mass or more but less than 100.0% by mass, and particularly preferably 75.0% by mass or more but less than 100.0% by mass. Furthermore, the upper limit is not particularly set as long as the necessary amounts of other components can be contained, but typically 99.5% by mass or less is sufficient, and 99.0% by mass or less is sufficient. That is, for example, 50.0% by mass or more but less than 99.5% by mass, 60.0% by mass or more but less than 99.0% by mass, etc., can be mentioned.

[0086] In highly selective etching of silicon-germanium relative to silicon, the first acid dissociation constants (pKa1) of the etching products, silicon hydroxide and germanium hydroxide, are 9.86 and 8.68, respectively. Therefore, as the alkalinity of the etching solution decreases, silicon hydroxide becomes less ionizable than germanium hydroxide, and its solubility in the etching solution decreases. Therefore, the lower the pH and hydroxide ion concentration of the etching solution (and therefore the lower the alkalinity), the greater the relative decrease in the etching rate of silicon compared to the etching rate of silicon-germanium, and the higher the etching selectivity of silicon-germanium relative to silicon.

[0087] Therefore, the pH of the etching solution at 24° C. is preferably 10.00 or more and 13.27 or less, more preferably 11.00 or more and 13.27 or less, and even more preferably 11.50 or more and 13.27 or less. The pH refers to a value measured by the glass electrode method described below. Furthermore, the size of the object to be measured for pH is not particularly limited, and a manufactured or commercially available etching solution may be used, or a portion of the etching solution (for example, 10 g or 10% by mass of the etching solution) may be taken out and used.

[0088] <Method of manufacturing the etching solution> The method for producing the etching solution is not particularly limited, and the etching solution can be produced by a known method. For example, in the case of producing the above-mentioned silicon nitride etching solution, the method may include a composition preparation step of preparing a composition containing a specific acid, a boron compound not containing a fluorine atom, and water. Furthermore, these steps may be combined into one step.

[0089] The method for preparing the composition is not particularly limited, and examples thereof include a method in which the specific acid, the fluorine-free boron compound, water, and other optional components are mixed together, and the specific acid, the fluorine-free boron compound, and other optional components are dissolved in water. In the dissolution, it is preferable that each component is dissolved uniformly.

[0090] The method for producing an etching solution may also include an aging step in which a composition containing a specific acid, a boron compound containing no fluorine atoms, and water is heated. The heating temperature in the aging step is preferably equal to or higher than the temperature in the etching step, and the upper limit of the heating temperature may be appropriately determined taking into consideration the heat resistance temperature of the components of the device used in the aging step. That is, the heating temperature is preferably in the range of 100 to 200°C, more preferably in the range of 120 to 200°C, even more preferably in the range of 165 to 200°C, and particularly preferably in the range of 180 to 200°C. The heating time in the aging step varies depending on the heating temperature, so it is not possible to determine an optimal range in general. However, considering productivity, for example, For example, the heating time is preferably in the range of 1 to 100 hours, more preferably in the range of 3 to 100 hours, even more preferably in the range of 5 to 100 hours, and particularly preferably in the range of 10 to 100 hours. The heating in the aging step may be carried out intermittently by repeating heating and cooling. When heating in the aging step is carried out intermittently, the heating time is the total time during which the heating temperature is reached and maintained.

[0091] As raw materials for the etching solution, such as the specific acid, the boron compound not containing fluorine atoms, and water, those described in the section on etching solution can be used.

[0092] The production of the etching solution preferably includes a step of mixing and dissolving the raw materials, and then passing the mixture through a filter of several nm to several tens of nm to remove particles. If necessary, the step of removing particles may be carried out multiple times.

[0093] Furthermore, various known treatments that are carried out to obtain necessary physical properties in the production of chemicals for semiconductor manufacturing, such as reducing dissolved oxygen in the etching solution by bubbling with an inert gas such as high-purity nitrogen gas, can be carried out.

[0094] In the mixing and dissolving steps, and also for storing the etching solution, it is preferable to use a container or device formed of or coated with a material known as an inner wall material for semiconductor manufacturing chemicals, specifically a material that does not easily leach contaminants into the etching solution, such as polyfluoroethylene or high-purity polypropylene. It is also preferable to clean these containers or devices in advance.

[0095] <Method of manufacturing semiconductor device> A method for manufacturing a semiconductor element according to another embodiment of the present invention is a method for manufacturing a semiconductor using the silicon etching solution described above, and the mode thereof is not particularly limited, and the semiconductor element can be manufactured by a known method. As a specific embodiment of the method for manufacturing a semiconductor element, a method for manufacturing a semiconductor element using the above-mentioned silicon nitride etching solution will be described below as an example.

[0096] One example of a method for manufacturing a semiconductor element is a method for manufacturing a semiconductor element using a substrate containing silicon nitride, and relates to a method for manufacturing a semiconductor element (also simply referred to as a "method for manufacturing a semiconductor element") that includes an etching step of etching the silicon nitride using the above-mentioned etching solution.

[0097] The etching solution contains the inhibitor capable of inhibiting etching of silicon or silicon oxide, and therefore is capable of selectively etching silicon nitride relative to at least one of silicon and silicon oxide, as well as silicon nitride relative to at least one of silicon and silicon oxide. Therefore, the above-described method for manufacturing a semiconductor device may be a method for manufacturing a semiconductor device in which the substrate further contains at least one of silicon and silicon oxide, and the etching step includes an etching step of selectively etching silicon nitride relative to at least one of silicon and silicon oxide using the above-described etching solution. The following description will discuss an example of each condition of the embodiment, but the present invention is not limited to these conditions.

[0098] The method for manufacturing a semiconductor device can be any known method for manufacturing a semiconductor device, except that it includes an etching step of selectively etching silicon nitride over at least one of silicon and silicon oxide using an etching solution. For example, the method can include a wafer manufacturing step, an oxide film forming step, a transistor forming step, a wiring forming step, and a CMP step. The method may include one or more steps selected from the group consisting of, and may also include other known steps used in the production of semiconductors.

[0099] The etching step of selectively etching silicon nitride with respect to at least one of silicon and silicon oxide using an etching solution is not particularly limited, but examples thereof include a contacting step of bringing an etching solution into contact with a substrate containing at least one of silicon and silicon oxide, and silicon nitride. By including such a step, it is possible to selectively remove silicon nitride from a device structure by contacting an etching solution with the device structure, which includes silicon oxide as an insulating film, silicon and silicon-germanium alternately stacked, and silicon nitride stacked thereon as a hard mask.

[0100] Furthermore, the etching process is not particularly limited as long as it can selectively etch silicon nitride relative to at least one of silicon and silicon oxide, and may be a process including a substrate holding process for holding a substrate in a horizontal position and a processing liquid supply process for supplying an etching liquid to a main surface of the substrate while rotating the substrate about a vertical axis of rotation passing through the center of the substrate, or a process including a substrate holding process for holding a plurality of substrates in an upright position and a process for immersing the substrates in an upright position in an etching liquid stored in a processing tank.

[0101] The conditions for the etching step are not particularly limited, and for example, the temperature of the etching solution in the etching step may be appropriately determined taking into consideration the desired etching rate, the shape and surface condition of the silicon nitride after etching, productivity, the heat resistance temperature of the components of the etching apparatus, etc. For example, the temperature may be 20 to 200°C, preferably 50 to 190°C, more preferably 100 to 190°C, even more preferably 120 to 185°C, and particularly preferably 165 to 185°C.

[0102] The etching process can also be performed while degassing under vacuum or reduced pressure or bubbling with an inert gas. Such operations can prevent or reduce the increase in dissolved oxygen during etching. Alternatively, the etching process can be performed without bubbling with an inert gas. By omitting bubbling with an inert gas, the dissolved oxygen in the etching solution increases. When the substrate contains silicon, the dissolved oxygen in the etching solution contributes to the oxidation of silicon, which can decrease the silicon etching rate, but can also increase it. Therefore, when the silicon etching rate increases due to the influence of dissolved oxygen, i.e., when the etching rate of silicon nitride relative to silicon may decrease, bubbling with an inert gas can be performed. However, when the silicon etching rate is maintained or decreased due to the influence of dissolved oxygen, bubbling with an inert gas can be omitted.

[0103] In the etching step, the substrate may be simply brought into contact with the etching solution by immersing the substrate in the etching solution, or an electrochemical etching method in which a constant potential is applied to the substrate may also be employed.

[0104] The etching target in the etching process is a substrate containing silicon nitride and at least one of silicon and silicon oxide, as described above. Here, silicon is a non-etching target that is not the target of the etching process. The form of at least one of silicon and silicon oxide, and silicon nitride is not particularly limited, but may be, for example, a silicon film, a silicon oxide film, or a silicon nitride film, and may include a silicon nitride single crystal film containing at least one of silicon and silicon oxide as a substrate. The thickness of the silicon film etc. is not particularly limited and can be set appropriately depending on the application. The substrate may also include various metal films as non-etching targets, such as those formed by alternately stacking silicon and silicon-germanium, those formed by depositing silicon-germanium films, silicon oxide films, or silicon nitride films on single crystal silicon, and those formed by depositing silicon, polysilicon, or silicon-germanium films thereon, and structures formed by patterning using these films.

[0105] 4. Substrate processing method A substrate processing method according to another embodiment of the present invention is a substrate processing method using the silicon etching liquid described above, and the form thereof is not particularly limited, and the substrate can be manufactured by a known method. As a specific embodiment of the substrate processing method, a substrate processing method using the silicon nitride etching solution described above will be described below as an example.

[0106] An example of a method for manufacturing a semiconductor element relates to a method for treating a substrate containing silicon nitride, which includes an etching step of etching the silicon nitride using the above-mentioned silicon nitride etching solution (also simply referred to as a "substrate treatment method"). The substrate processing method may include steps other than the etching step described above, as long as the effects of the present invention can be obtained.

[0107] Since the etching solution can selectively etch silicon nitride relative to at least one of silicon and silicon oxide, the substrate processing method may be a substrate processing method containing at least one of silicon and silicon oxide and silicon nitride, and may include an etching step of selectively etching silicon nitride relative to at least one of silicon and silicon oxide using the etching solution described above. In the following description, an example of each condition of the embodiment will be described, but the present invention is not limited to this condition.

[0108] As the etching step of selectively etching silicon nitride with respect to at least one of silicon and silicon oxide using an etching solution, the etching step described in the section on the method for manufacturing a silicon device can be used. Furthermore, the etching process may be, for example, a process including a substrate holding process for holding a substrate in a horizontal position and a processing liquid supply process for supplying an etching liquid to a main surface of the substrate while rotating the substrate around a vertical axis of rotation passing through the center of the substrate, or a process including a substrate holding process for holding a plurality of substrates in an upright position and a process for immersing the substrates in an upright position in an etching liquid stored in a processing tank. Furthermore, as the substrate, the substrates described in the section on the manufacturing method of a semiconductor element can be used. [Example]

[0109] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0110] <Ultra pure water> The ultrapure water used to dilute the etching solution in measuring the pH of the etching solution and to produce the etching solution was produced by purifying water using a Millipore Elix Essential UV5 water purification system and then further purifying it using a Millipore Milli-Q Advantage water purification system. <Evaluation of etching solution> The etching solutions in the examples and comparative examples were evaluated as follows.

[0111] [Method for measuring pH of etching solution (10 times diluted)] First, the etching solution was diluted 10 times by mass with ultrapure water. The pH of the diluted etching solution was measured at a temperature of 24°C using a Horiba, Ltd. benchtop pH meter F-73 and a Horiba, Ltd. pH electrode 9632-10D.

[0112] [Etching rate calculation method] (SiN) 200 mL of the etching solution was prepared and heated to the specified temperature shown in Table 1. A 2 cm x 1 cm silicon substrate (silicon nitride film thickness: 104 nm) on which a silicon nitride film had been epitaxially grown by low-pressure CVD (LP-CVD) was immersed in the solution for 3 minutes. The etching solution was stirred at 700 rpm during etching. Silicon nitride film etching rate (R SiN The etching loss (nm / min) was calculated by measuring the film thickness of each substrate before and after etching using a spectroscopic ellipsometer (M-2000D manufactured by JA Woollam), determining the amount of silicon nitride film etched from the difference in film thickness before and after treatment, and dividing this amount by the etching time (3 minutes).

[0113] (SiGe) 100 mL of etching solution heated to 70°C was prepared, and a 2 cm × 1 cm silicon substrate (manufactured by Global Net Co., Ltd.) with a silicon-germanium film (germanium content 25% by mass) epitaxially grown on it was immersed in the solution for 10 minutes. The etching solution was stirred at 1200 rpm during etching. Silicon-germanium etching rate (R SiGe The etching loss (nm / min) was calculated by measuring the film thickness of each substrate before and after etching with a spectroscopic ellipsometer, determining the amount of silicon-germanium etched from the difference in film thickness before and after treatment, and dividing this by the etching time (10 minutes).

[0114] (Si) 200 mL of the etching solution was prepared and heated to the specified temperature shown in Table 1. A 2 cm x 1 cm silicon substrate (with a silicon nitride film thickness of 104 nm) on which a silicon nitride film had been epitaxially grown by low-pressure CVD (LP-CVD) was immersed in the solution for 10 minutes. The etching solution was stirred at 700 rpm during etching. Silicon nitride film etching rate (R SiN The etching loss (nm / min) was calculated by measuring the film thickness of each substrate before and after etching using a spectroscopic ellipsometer (M-2000D manufactured by J.A. Woollam), determining the amount of silicon nitride film etched from the difference in film thickness before and after treatment, and dividing this amount by the etching time (10 minutes).

[0115] [Evaluation of Si etching suppression effect] Those with a Si etching rate lower than that of Comparative Example 1 were evaluated as having an Si etching suppression effect, and those with a Si etching rate equal to or higher than that of Comparative Example 1 were evaluated as not having an Si etching suppression effect. The results are shown in Table 1.

[0116] <Production of etching solution> (Method for preparing etching solution) [Example 1] Sulfuric acid (manufactured by Fujifilm Wako Pure Chemical Industries, for electronics industry use, 96% by mass aqueous solution, pKa at 25°C: -3) was diluted with ultrapure water and mixed until the solution was homogeneous. Boric acid (Fujifilm Wako Pure Chemical Industries, special reagent grade, powder) as a boron compound and 1,10-bis[4-aza-1-azoniabicyclo[2.2.2]octan-1-yl]decane dibromide (TCI, special reagent grade) as a silicon etching inhibitor were added, and the concentration of sulfuric acid was 75 mass %, the concentration of the fluorine atom-free boron compound (boric acid) was 1.6 mass %, and the concentration of silicon An etching solution was prepared so that the concentration of the silicon etching inhibitor was 0.5% by mass. The etching solution was then heated at 195°C for 30 minutes, and then heated to 185°C (near the boiling point). The resulting etching solution was diluted 10 times by mass with water, and the pH measured at 24°C was 5.0 or less. The etching rates of silicon nitride and silicon were evaluated using the resulting etching solution. The evaluation results are shown in Table 1.

[0117] [Example 2] An etching solution was prepared by adding tetramethylammonium hydroxide (TMAH, manufactured by Tokuyama Corporation), hydrogen peroxide (30% by weight aqueous solution, manufactured by Kanto Chemical Co., Ltd.), and 1,10-bis[4-aza-1-azoniabicyclo[2.2.2]octan-1-yl]decane dibromide (manufactured by TCI Corporation) as a silicon etching inhibitor, so that the TMAH concentration was 2.38% by weight, the hydrogen peroxide concentration was 1.0% by weight, and the silicon etching inhibitor concentration was 0.1% by weight. The etching solution was then heated to 70°C by heating in a 75°C water bath for 30 minutes. The pH of the resulting etching solution measured at 24°C was 12.2. The etching rates of silicon-germanium and silicon were evaluated using the resulting etching solution. The evaluation results are shown in Table 1.

[0118] [Example 3] An etching solution was prepared and evaluated in the same manner as in Example 1, except that the silicon etching inhibitor was changed to another silicon etching inhibitor, hexamethonium bromide (manufactured by TCI Corporation), and the silicon etching inhibitor was added so that the concentration of the silicon etching inhibitor in the etching solution was 0.2 mass %. The evaluation results are shown in Table 1. The pH of the obtained etching solution, which was diluted 10 times by mass with water and measured at a temperature of 24°C, was 5.0 or less.

[0119] [Example 4] An etching solution was prepared and evaluated in the same manner as in Example 1, except that the silicon etching inhibitor was changed to another silicon etching inhibitor, decamethonium bromide (manufactured by TCI Corporation), and the silicon etching inhibitor was added so that the concentration of the silicon etching inhibitor in the etching solution was 0.5 mass %. The evaluation results are shown in Table 1. The pH of the obtained etching solution, which was diluted 10 times by mass with water and measured at a temperature of 24°C, was 5.0 or less.

[0120] [Comparative Example 1] An etching solution was prepared and evaluated in the same manner as in Example 1, except that no silicon etching inhibitor was used. The evaluation results are shown in Table 1. The pH of the obtained etching solution, which was diluted 10 times by mass with water and measured at a temperature of 24°C, was 5.0 or less.

[0121] Comparative Example 2 An etching solution was prepared and evaluated in the same manner as in Example 2, except that no silicon etching inhibitor was used. The evaluation results are shown in Table 1. The pH of the obtained etching solution, which was diluted 10 times by mass with water and measured at a temperature of 24°C, was 5.0 or less.

[0122] Comparative Example 3 An etching solution was prepared and evaluated in the same manner as in Example 1, except that the silicon etching inhibitor was changed to tetrabutylammonium hydrogen sulfate (manufactured by TCI Corporation) and the tetrabutylammonium hydrogen sulfate was added so that the concentration was 5 mass %. The evaluation results are shown in Table 1. The pH of the obtained etching solution, which was diluted 10 times by mass with water and measured at a temperature of 24°C, was 5.0 or less.

[0123] Comparative Example 4 An etching solution was prepared and evaluated in the same manner as in Example 1, except that the silicon etching inhibitor was changed to octadecyltrimethylammonium chloride (manufactured by TCI Corporation) and the octadecyltrimethylammonium chloride was added so that the concentration was 1 mass %. The evaluation results are shown in Table 1. The pH of the obtained etching solution, which was diluted 10 times by mass with water and measured at a temperature of 24°C, was 5.0 or less.

[0124] Regarding the evaluation of etching rate in Table 1, the notation "-" indicates that evaluation was not performed with the etching solution in question. The etching selectivity is the ratio of etching rates, for example, "SiN / Si" represents "etching rate of SiN / etching rate of Si".

[0125] [Table 1]

[0126] As can be seen from Table 1, in the etching solution to which the etching inhibitor according to the embodiment of the present invention is added, It can be seen that the etching rate of silicon can be reduced without substantially reducing the etching rate of silicon nitride. [Industrial Applicability]

[0127] According to the present invention, by using a specific silicon etching inhibitor, it is possible to provide an etching solution capable of suppressing silicon etching, a substrate processing method, and a semiconductor device manufacturing method.

Claims

1. A silicon etching inhibitor comprising a compound having a plurality of cationic moieties and a hydrophobic moiety between the cationic moieties.

2. 10. The silicon etch inhibitor of claim 1, wherein the compound is a dication or a trication.

3. 3. The silicon etch inhibitor of claim 1, wherein the hydrophobic moiety comprises four or more carbon atoms.

4. 4. The silicon etching inhibitor according to claim 1, wherein the plurality of cation moieties includes at least a quaternary ammonium cation.

5. a silicon etching inhibitor according to any one of claims 1 to 4, comprising one or more acids selected from the group consisting of sulfuric acid and organic acids, a boron compound, the silicon etching inhibitor according to any one of claims 1 to 4, and water; The concentration of the silicon etching inhibitor is 0.005% by mass or more and 10% by mass or less. Silicon nitride etchant.

6. The silicon compound according to claim 5, wherein the acid has a pKa of -5 or more and 2 or less at 25°C. Nitride etchant.

7. 7. The silicon nitride etching solution according to claim 5, wherein at least one of a boiling point and a decomposition temperature of the acid at 1 atmosphere is 150°C or higher and 400°C or lower.

8. 1. A method for processing a substrate comprising silicon nitride, comprising: A method for treating a substrate, comprising an etching step of etching silicon nitride using the etching solution according to any one of claims 5 to 7.

9. the substrate further contains at least one of silicon and silicon oxide; 9. The substrate processing method according to claim 8, wherein the etching step is a step of selectively etching silicon nitride with respect to at least one of silicon and silicon oxide using the etching solution.

10. A method for manufacturing a semiconductor device using a substrate containing silicon nitride, comprising: A method for manufacturing a semiconductor device, comprising an etching step of etching silicon nitride with the silicon nitride etching solution according to any one of claims 5 to 7.

11. the substrate further contains at least one of silicon and silicon oxide; 11. The method for manufacturing a semiconductor device according to claim 10, wherein the etching step is a step of selectively etching silicon nitride with respect to at least one of silicon and silicon oxide using the etching solution.

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