Onium salt-containing processing solution for semiconductor wafers

Description

TECHNICAL FIELD

[0001] The present invention relates to a novel treatment liquid for etching metallic ruthenium present on a semiconductor wafer to be used in a manufacturing process of a semiconductor element.BACKGROUND ART

[0002] In recent years, microfabrication design has been promoted for the design rule for semiconductor elements, and thus the wiring resistance tends to increase. As a result of the increase in wiring resistance, the high-speed operation of a semiconductor element is markedly impaired, thus making it necessary to take countermeasures. In view of this, a desired wiring material is a wiring material having more solid electromigration resistance and a lower electric resistance value than conventional wiring materials.

[0003] Ruthenium has higher electromigration resistance than aluminum and copper which are conventional wiring materials, and ruthenium can decrease the electric resistance value of the wiring, thus attracting attention particularly as a wiring material for which the design rule for semiconductor elements is 10 nm or less. Not only in cases where ruthenium is used as a wiring material but also in cases where copper is used as a wiring material, ruthenium can prevent electromigration, and thus, using ruthenium as a barrier metal for copper wiring is under study.

[0004] In cases where ruthenium is selected as a wiring material in a wiring formation step of a semiconductor element, the wiring is formed by dry or wet etching in the same manner as in cases where a conventional wiring material is used. However, since it is difficult to remove ruthenium by dry etching with an etching gas, or by CMP polishing, more precise etching is desired, and specifically, wet etching is attracting attention.

[0005] Therefore, when ruthenium is used as a wiring material or a barrier metal, precise microprocessing of ruthenium by wet etching is required. In order to carry out precise ruthenium microprocessing, accurate control of the etching rate on ruthenium is required. Furthermore, in order to realize multilayer wiring, the flatness of each ruthenium layer is essential, and the flatness of the ruthenium surface after etching is also desired.

[0006] In Patent Document 1, as an etching method for a ruthenium film, a method for etching a ruthenium film using a chemical liquid having a pH of 12 or more and an oxidation-reduction potential of 300 mV vs SHE or more, specifically a solution of a halogen oxoate, such as hypochlorite, chlorite, and bromate, is presented. However, what Patent Document 1 discloses is a chemical liquid that is for surely removing an adhered ruthenium by etching, and is designed for removing ruthenium.

[0007] Meanwhile, Patent Document 2 proposes a method for oxidizing ruthenium thereby dissolving and removing the ruthenium by using an aqueous solution of pH 11 or higher containing orthoperiodic acid. Furthermore, Patent Document 3 proposes an etching liquid for ruthenium metal having a pH of 10 or more and less than 12 containing a bromine-containing compound, an oxidizing agent, a basic compound, and water.

[0008] In addition, Patent Document 4 proposes a cleaning method in which ruthenium is oxidized, thereby dissolved, and removed using a removal solution containing cerium (IV) ammonium nitrate and additionally a strong acid such as nitric acid.

[0009] Meanwhile, in cases where ruthenium is subjected to wet etching under alkaline conditions, ruthenium is dissolved, for example, in the form of RuO 4 -< or RuO 4 2-< in a treatment liquid. RuO 4 -< or RuO 4 2-< is changed to RuO 4 in a treatment liquid, and part of the same is gasified and released into a gas phase. RuO 4 is strongly oxidative, and thus, not only is harmful to the human body but also is easily reduced to generate RuO 2 particles. In general, particles cause a decrease in the yield rate, which constitutes a serious problem in semiconductor formation steps. Against such a background, it is very important to inhibit the generation of a RuO 4 gas.

[0010] Patent Document 5 describes a chemical liquid having a pH of 12 or higher and an oxidation-reduction potential of 300 mV vs. SHE or higher as an etching liquid for a ruthenium film. In addition, a method for etching a ruthenium film using a solution of a halogen oxoate, such as hypochlorite, chlorite, and bromate, is disclosed.

[0011] Patent Document 6 proposes a method of oxidizing, thereby dissolving, and removing ruthenium by using an aqueous solution containing orthoperiodic acid having a pH of 11 or higher.

[0012] Patent Document 7 describes a CMP slurry containing a ruthenium-coordinated nitrogen oxide ligand (N-O ligand) that does not generate a RuO 4 gas in chemical mechanical polishing (CMP) of ruthenium.

[0013] Patent Documents 8-10 disclose the etching of ruthenium with treatment liquids comprising hypochlorite ions.Citation ListPatent Document

[0014] Patent Document 1: Japanese Patent Laid-Open No. 2002-161381 Patent Document 2: International Publication No. WO2016 / 068183 Patent Document 3: International Publication No. WO2011 / 074601 Patent Document 4: Japanese Patent Laid-Open No. 2001-234373 Patent Document 5: Japanese Patent Laid-Open No. 2002-161381 Patent Document 6: International Publication No. WO2016 / 068183 Patent Document 7: Japanese Patent No. 5314019 Patent Document 8: US 2003 / 017419 A1 Patent Document 9: EP 2 514 855 A1 Patent Document 10: EP 1 213 369 A2 SUMMARY OF INVENTIONTechnical Problem

[0015] However, based on the study by the present inventors, it has been found that there is room for improvement with respect to the conventional etching liquids described in the cited documents 1 to 4 because of the following.

[0016] For example, the method for etching ruthenium described in Patent Document 1 or 4 is intended to remove a ruthenium residue adhered to the back surface or bevels of a semiconductor substrate, and is capable of dissolving and removing ruthenium. However, with the etching liquid described in Patent Document 1 or 4, it was difficult to maintain the desired flatness of the ruthenium surface after the etching treatment in the wiring step. Therefore, it was difficult to use the etching liquid according to Patent Document 1 or 4 as that for ruthenium in the step of forming the wiring of a semiconductor element.

[0017] Further, the etching liquid described in Patent Document 2 was an etching liquid targeting an etching residue containing ruthenium similarly as in Patent Document 1, and since it was difficult to maintain the flatness of the ruthenium surface after the etching treatment, the same could hardly be used in the step of forming the wiring.

[0018] In addition, with respect to the etching liquid described in Patent Document 3, it is described that ruthenium used in the manufacturing process of a semiconductor element, wiring, and a barrier metal which are constructed on a substrate such as a semiconductor wafer is etched with the same. However, since its purpose is for cleaning the back surface and bevels of a substrate such as a semiconductor wafer similarly to Patent Document 1 and Patent Document 4, and when ruthenium was etched with an etching liquid described in Patent Document 3, the flatness of the ruthenium surface was not maintained after the etching treatment, and there was room for further improvement.

[0019] Therefore, the first object of the present invention is to provide a treatment liquid that can wet-etch ruthenium present on a semiconductor wafer. Another object is to provide a treatment liquid that can maintain the flatness of the ruthenium surface after the etching treatment.

[0020] Through the investigations by the inventors, it was found that the conventional treatment liquids described in the cited documents 5 to 7 were still in need for improvement in the following points.

[0021] For example, the method of etching ruthenium described in Patent Document 5 is intended to remove ruthenium residues adhered to the back surface or bevels of a semiconductor substrate, and it is possible to dissolve and remove ruthenium. However, Patent Document 5 does not mention anything about the inhibition of a RuO 4 gas, and in fact, the method described in Patent Document 5 lacked stability, and was not able to inhibit generation of a RuO 4 gas, and a large amount of RuO 4 gas was generated. There was also a problem in that a large amount of RuO 2 (particles) was generated.

[0022] In addition, Patent Document 6 discloses a ruthenium removal composition containing orthoperiodic acid, which can etch an etching residue containing ruthenium. However, Patent Document 6 does not mention anything about the inhibition of a RuO 4 gas, and a RuO 4 gas generated during the etching treatment could not be inhibited.

[0023] Further, Patent Document 7 shows that it is possible to inhibit a toxic RuO 4 gas by using a CMP slurry containing a ruthenium-coordinated nitrogen oxide ligand (N-O ligand) in performing CMP. However, since the CMP slurry shown in Patent Document 7 is acidic, it is difficult to inhibit a RuO 4 gas by the CMP slurry composition shown in

[0024] Patent Document 7 under alkaline conditions where the dissolution mechanism of ruthenium is different. In fact, when the ruthenium-coordinated nitrogen oxide ligand described in Patent Document 7 was added to an alkaline ruthenium etching liquid containing hypochlorous acid, a RuO 4 gas was generated to confirm that there was no RuO 4 gas inhibitory effect.

[0025] The present inventors diligently conducted investigations to achieve the first object above. For this purpose, the effect of addition of a specific alkylammonium salt to a treatment liquid containing hypochlorite ions was examined. Since the flatness of the ruthenium surface after the etching treatment could not be maintained with the treatment liquid containing only hypochlorite ions, various additive ingredients were combined. As a result, it was found that it became possible to maintain the flatness of the ruthenium surface after the etching treatment by adding a specific alkylammonium salt, thereby completing the first invention.

[0026] A first aspect of the present invention for achieving the first object described above includes the treatment liquid according to claim 1 and the etching method according to claim 5. Embodiments and variants derive from the dependent claims.

[0027] As the mechanism by which the treatment liquid of the first aspect of the present invention maintains the flatness of the ruthenium surface after the etching treatment, the following is conceivable. That is, alkylammonium ions of the alkylammonium salt contained in the treatment liquid adhere to the surface of ruthenium, which is the etching target, and form a protective layer. The protective layer formed from alkylammonium ions prevents a contact with hypochlorite ions, which oxidize and dissolve ruthenium, so that the flatness of the ruthenium surface after the etching treatment can be conceivably better maintained compared to an etching treatment with a treatment liquid containing solely hypochlorite ions.Advantageous Effects of Invention

[0028] Using a treatment liquid of the first aspect of the present invention, ruthenium can be wet-etched in a forming process of a semiconductor element, and furthermore, the flatness of the ruthenium surface after the etching treatment can be maintained. Therefore, it is suitable for use in the formation of a semiconductor element having a multilayer wiring structure, for which the flatness of each layer is required.

[0029] Since the treatment liquid of the first aspect of the present invention gives excellent flatness of the ruthenium surface after the etching treatment, the ruthenium surface in contact with the treatment liquid can be etched evenly. Especially, even in the formation of a semiconductor element with a wiring structure with a dimension of 10 nm or less, where precise etching of ruthenium at several nanometer level is required, since the ruthenium surface in contact with the treatment liquid can be etched notably evenly, the treatment liquid can be used favorably.

[0030] Furthermore, the treatment liquid of the first aspect of the present invention is capable of etching ruthenium at an etching rate of 20 Å / min or higher. With an etching rate of 20 Å / min or higher, it can be used satisfactorily in the process of forming a semiconductor element.Brief Description of Drawings

[0031] FIG. 1: A schematic cross-sectional view showing an example of the wiring formation step in which the treatment liquid of the first aspect of the present invention can be suitably employed. FIG. 2: A schematic cross-sectional view showing an example of the wiring formation step after the treatment with the treatment liquid of the first aspect of the present invention. FIG. 3: A photograph of the ruthenium surface after the etching treatment shown in Example 1, observed with an electron microscope at 100,000x. Description of Embodiments

[0032] In this description, ruthenium (also expressed as Ru) is not limited to a ruthenium metal, insofar as the ruthenium element is included.(Treatment liquid of first aspect)

[0033] The treatment liquid of the first aspect of the present invention is a treatment liquid that can etch ruthenium present on a semiconductor wafer without damaging the semiconductor wafer. Therefore, the treatment liquid of the first aspect of the present invention is a treatment liquid that can be suitably used in the wiring formation step in the semiconductor manufacturing process.

[0034] The ruthenium to which the treatment liquid of the first aspect of the present invention is applied is mainly formed by a publicly known method, such as CVD, ALD, and a sputtering method, used in the semiconductor element process. Through etching the formed ruthenium, the wiring is formed in the semiconductor. FIGs. 1 and 2 show an example of the wiring formation step.

[0035] First, a substrate 1 made of a semiconductor (e.g. Si) is prepared. The prepared substrate is subjected to an oxidation treatment to form a silicon oxide film on the substrate. Then, an interlayer insulating film 2 constituted with a low dielectric constant (low-k) film is formed, and in which via holes are formed at predetermined intervals. After formation, the via holes are filled with ruthenium 3 by thermal CVD, and a ruthenium film is further deposited thereon (FIG. 1). The ruthenium film is etched and planarized by dry etching or wet etching to form the ruthenium wiring (FIG. 2).

[0036] The treatment liquid of the first aspect of the present invention contains (A) a hypochlorite ion, and (B) an alkylammonium salt expressed by the following Formula (1). The following is a step by step description.

[0037] In the Formula, "a" is an integer from 6 to 20; and R 1< , R 2< , and R 3< are independently a hydrogen atom, or an alkyl group with a carbon number from 1 to 20. X -< is a fluoride ion, a chloride ion, an iodide ion, a hydroxide ion, a nitrate ion, a phosphate ion, a sulfate ion, a hydrogen sulfate ion, a methanesulfate ion, a perchlorate ion, an acetate ion, a fluoroborate ion, or a trifluoroacetate ion.(A) Hypochlorite ion

[0038] With respect to the hypochlorite ion to be used in the first aspect of the present invention, it is possible to generate hypochlorous acid and hypochlorite ions by dissolving hypochlorite in water. The hypochlorite ion is an oxidizing agent with strong oxidizability, and the treatment liquid of the present invention containing hypochlorite ions can etch a metal contained in a semiconductor wafer.

[0039] In the first aspect of the present invention, the concentration of hypochlorite ions is preferably in a range of 0.05 to 20 mass% with respect to the total treatment liquid. Within the above range, it is possible to prevent the hypochlorite ion concentration from decreasing by inhibiting the decomposition reaction of hypochlorite ions in a treatment liquid (hereinafter, the effect of inhibiting the decomposition reaction of hypochlorite ions in a treatment liquid so as to inhibit the hypochlorite ion concentration from decreasing is occasionally referred to as "high storage stability"), and to etch ruthenium at an etching rate of 20 Å / min or higher. Therefore, the concentration of hypochlorite ions is preferably in a range of 0.1 to 15 mass%, more preferably 0.3 to 10 mass%, further preferably 0.5 to 6 mass%, and especially preferably 0.5 to 4 mass%.

[0040] The concentration of hypochlorite ions in a treatment liquid of the first aspect of the present invention can be calculated at the time of the production of the treatment liquid, or can be affirmed by a direct analysis of the treatment liquid. The concentration of hypochlorite ions described in Example below was determined by measuring the effective chlorine concentration of the treatment liquid. Specifically, referring to Ministry of Health, Labour and Welfare Notification No. 318 (final revision on 11 March 2005), potassium iodide and acetic acid were added to a solution containing hypochlorite ions, the liberated iodine was redox-titrated with an aqueous solution of sodium thiosulfate, and the effective chlorine concentration was calculated. The concentration of hypochlorite ions of the present invention is obtained by converting from the calculated effective chlorine concentration.(B) Alkylammonium salt expressed by the following Formula (1)

[0041] The alkylammonium salt contained in a treatment liquid of the first aspect of the present invention is the alkylammonium salt expressed by the following Formula (1).

[0042] In the Formula, "a" is an integer from 6 to 20; and R 1< , R 2< , and R 3< are independently a hydrogen atom, or an alkyl group with a carbon number from 1 to 20. X -< is a fluoride ion, a chloride ion, an iodide ion, a hydroxide ion, a nitrate ion, a phosphate ion, a sulfate ion, a hydrogen sulfate ion, a methanesulfate ion, a perchlorate ion, an acetate ion, a fluoroborate ion, or a trifluoroacetate ion.

[0043] The integer "a" in the above Formula (1) represents the number of methylene groups, and those in which the integer "a" is from 6 to 20 can be used without any particular restriction, and the integer "a" is more preferably from 6 to 15, and further preferably from 8 to 13. An alkylammonium salt having methylene groups within the aforedescribed range can be adsorbed onto the ruthenium surface to form an appropriate protective layer, and therefore can be favorably used. In this regard, when the integer "a" of the alkylammonium salt is larger, the amount of alkylammonium ions of the alkylammonium salt adsorbed onto the ruthenium surface increases, and therefore the etching rate of ruthenium tends to decrease. On the other hand, when the integer "a" of the alkylammonium salt is smaller, the amount adsorbed onto the ruthenium surface decreases, and an appropriate protective layer is not formed on the ruthenium surface, and the flatness of the ruthenium surface after the etching treatment is not likely to be maintained.

[0044] Meanwhile, when the integer "a" of the alkylammonium salt is large, the water solubility of the alkylammonium salt is low, which will cause generation of particles in the treatment liquid. When particles remain on the ruthenium surface after the etching treatment, the yield rate of semiconductor elements will be reduced, so a smaller amount of particles is preferable. Considering the adsorption performance to the ruthenium surface and the water solubility into a treatment liquid, it is more preferable that the integer "a" in Formula (1) is from 6 to 15, and further preferable from 8 to 13.

[0045] In Formula (1), R 1< , R 2< , and R 3< are independently a hydrogen atom, or an alkyl group having a carbon number from 1 to 20, and may be the same or different from each other. R 1< , R 2< , and R 3< are preferably alkyl groups having a carbon number from 1 to 20. Furthermore, it is preferable that the carbon numbers of R 1< , R 2< , and R 3< are respectively the same as, or smaller than the integer "a". It is more preferable that any one of R 1< , R 2< , and R 3< is a methyl group. When any one of R 1< , R 2< , and R 3< is a methyl group, a more uniform and dense protective layer is formed on the ruthenium surface, and the flatness of the ruthenium surface after the etching treatment can be maintained.

[0046] X -< in Formula (1) is a fluoride ion, a chloride ion, an iodide ion, a hydroxide ion, a nitrate ion, a phosphate ion, a sulfate ion, a hydrogen sulfate ion, a methanesulfate ion, a perchlorate ion, an acetate ion, a fluoroborate ion, or a trifluoroacetate ion. There is no particular restriction on the anion of an alkylammonium salt, and it can be used in a treatment liquid.

[0047] As the mechanism by which the treatment liquid of the first aspect of the present invention can maintain the flatness of the ruthenium surface after the etching treatment, the following is conceivable. That is, the cation (alkylammonium ion) of the alkylammonium salt contained in the treatment liquid is conceivably adsorbed onto the ruthenium surface at the polar group centered by a nitrogen atom. The non-polar alkyl groups of the adsorbed cation take positions away from the ruthenium surface, resulting in formation of a hydrophobic protective layer on the ruthenium surface. Since the formed protective layer inhibits the contact between hypochlorite ions contained in the treatment liquid and ruthenium, as a result, the ruthenium is etched evenly, and the flatness of the ruthenium surface after the etching treatment is maintained.

[0048] Specific examples of the alkylammonium salt expressed by Formula (1) that can be suitably used in the first aspect of the present invention include n-octyltrimethylammonium chloride, decyltrimethylammonium chloride, lauryltrimethylammonium chloride, tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, didecyldimethylammonium chloride, didodecyldimethylammonium chloride, and tetraheptylammonium chloride.

[0049] The addition amount of an alkylammonium salt is preferably in a range of 0.001 to 10 mass% with respect to the entire treatment liquid. Within this range, the etching rate of ruthenium does not decrease, and a sufficient protective layer can be formed on the ruthenium surface. When the alkylammonium salt is added, only one kind can be added, or a mixture of two or more kinds can be added.

[0050] The treatment liquid of the first aspect of the present invention is composed of (A), (B), (C) which is described in detail below, and other additives, as well as water as the balance. The water contained in the treatment liquid of the present invention is preferably water from which metal ions, organic impurities, particles, etc. have been removed by distillation, an ion exchange treatment, a filtration treatment, various adsorption treatments, or the like, and especially pure water or ultrapure water is particularly preferable.(C) Ammonium ion

[0051] In the treatment liquid of the first aspect of the present invention, a hypochlorite ion is included in the treatment liquid by dissolving a hypochlorite in water, or likewise. Therefore, the counter ion of the hypochlorite ion is included inevitably in the treatment liquid. Usually, the hypochlorite is sodium hypochlorite, calcium hypochlorite, or the like, and in such a case, a sodium ion or a calcium ion is included as the counter ion.

[0052] In this regard, when the above-mentioned alkali metal ion or alkaline earth metal ion, such as a sodium ion, and a calcium ion, remains on the semiconductor wafer, an adverse effect (adverse effect such as decrease in the yield rate of the semiconductor wafer) will be exerted on the semiconductor wafer. Therefore, the content of the hypochlorite ion should preferably be small, and most preferably it should be substantially not contained. Therefore, as the counter ion of a hypochlorite ion, an organic counter ion is preferable, and in consideration of industrial production, at least one kind of ammonium ion selected from tetramethylammonium ion, tetraethylammonium ion, tetrapropylammonium ion, and tetrabutylammonium ion is preferable, and particularly tetramethylammonium ion is preferable. Accordingly, when a tetramethylammonium ion is selected as the counter ion, the content of sodium ions and calcium ions in the treatment liquid can be reduced, therefore it is preferable to include tetramethylammonium ions in the treatment liquid. It may additionally include the same as tetramethylammonium hydroxide or a tetramethylammonium hydroxide salt.

[0053] In the first aspect of the present invention, the concentration of ammonium ions is preferably in a range of 0.1 to 30 mass% with respect to the entire treatment liquid. When this concentration range of ammonium ions is satisfied, the treatment liquid can have excellent long-term storage stability. To further improve the storage stability, the concentration of ammonium ions is more preferably from 0.15 to 20 mass%, further preferably from 0.3 to 15 mass%, and especially preferably from 0.5 to 8 mass%.

[0054] In the first aspect of the present invention, tetramethylammonium ions can be made to be contained in a treatment liquid by, for example, passing an aqueous solution of tetramethylammonium hydroxide through an ion exchange resin to prepare the ion exchange resin exchanged to the tetramethylammonium ion form. A solution containing hypochlorite ions is brought into contact therewith so that ion exchange occurs with cations contained in the solution, thereby introducing tetramethylammonium ions into the treatment liquid.

[0055] With respect to the treatment liquid of the first aspect of the present invention, the pH is greater than 7 and less than 14. When the pH of the treatment liquid is less than 7, a decomposition reaction of hypochlorite ions is prone to occur, and the concentration of hypochlorite ions tends to decrease easily. Therefore, in order to satisfactorily secure both the storage stability of the treatment liquid and the etching rate of ruthenium, the pH of the treatment liquid is greater than 7 and less than 14, and more preferably 8 or more and less than 11. For example, when the pH is within the above range, the concentration of hypochlorite ions is not likely to decrease during the storage. For example, even after the storage in the dark at 23°C in an inert gas atmosphere for 15 days, the treatment liquid can exhibit adequate ruthenium etching performance. In this regard, a pH refers to the value at 25°C in this specification.(Other additives)

[0056] Other additives conventionally used in a treatment liquid for semiconductors can be optionally added to a treatment liquid of the first aspect of the present invention, to the extent that the purpose of the present invention is not impaired. For example, an acid, a metal corrosion inhibitor, a water-soluble organic solvent, a fluorine compound, an oxidizing agent, a reducing agent, a complexing agent, a chelating agent, a nonionic surfactant, a defoaming agent, and a pH adjuster can be added as other additives.

[0057] Derived from such other additives, or for reasons in manufacturing a treatment liquid, an alkali metal ion, and an alkaline earth metal ion, such as a sodium ion and a calcium ion may be included in a treatment liquid of the present invention. However, as mentioned above, when the alkali metal ion or alkaline earth metal ion remains on a semiconductor wafer, an adverse effect (adverse effect such as decrease in the yield rate of the semiconductor wafer) will be exerted on the semiconductor wafer. Therefore, the content thereof should preferably be small, and most preferably it should be substantially not contained. Therefore, for example, as a pH adjuster, it is preferable to use an organic alkali such as a tetraalkylammonium hydroxide, rather than an alkali metal hydroxide such as sodium hydroxide, or an alkaline earth metal hydroxide.

[0058] Specifically, the total amount of alkali metal ions and alkaline earth metal ions is preferably 1 mass% or less, more preferably 0.7 mass% or less, further preferably 0.3 mass% or less, especially preferably 10 ppm or less, and most preferably 500 ppb or less.(Method for producing treatment liquid of first aspect)

[0059] The treatment liquid, etc. of the first aspect of the present invention will be described below.

[0060] A treatment liquid of the first aspect of the present invention can be produced by adding and mixing an alkylammonium salt to an aqueous solution of hypochlorite containing hypochlorite ions. The hypochlorite aqueous solution can be produced by dissolving a commercially available hypochlorite, such as sodium hypochlorite or calcium hypochlorite, in water, or blowing chlorine into an alkali aqueous solution such as a sodium hydroxide aqueous solution or a tetramethylammonium hydroxide aqueous solution. Further, for example, when an aqueous solution of sodium hypochlorite is brought into contact with an ion exchange resin modified to a tetramethylammonium form, the counter ion of a hypochlorite ion can be exchanged.

[0061] A method for producing a treatment liquid of the first aspect of the present invention in which a sodium hypochlorite aqueous solution is converted to a tetramethylammonium hypochlorite aqueous solution by a method for producing a treatment liquid using a hypochlorite aqueous solution in which the counter ion of the hypochlorite ion is exchanged by an ion exchange resin, will be described in detail below.

[0062] First, an aqueous solution containing tetramethylammonium ions, specifically, an aqueous solution of tetramethylammonium hydroxide, is brought into contact with an ion exchange resin to prepare an ion exchange resin in a tetramethylammonium form.

[0063] There is no particular restriction on the ion exchange resin to be used, insofar as it is a publicly known cation exchange resin. For example, a hydrogen-form ion exchange resin or a sodium-form ion exchange resin can be used. Among others, a hydrogen-form ion exchange resin, which is less likely to be contaminated with sodium, is preferable. Further, in the case of a hydrogen form ion exchange resin, a mildly acidic, or a strongly acidic ion exchange resin can be used without particular restriction.

[0064] After preparing the ion exchange resin in a tetramethylammonium form, an aqueous solution of tetramethylammonium hypochlorite can be produced by bringing a hypochlorite aqueous solution into contact with the ion exchange resin.

[0065] A sodium hypochlorite aqueous solution can be prepared by dissolving sodium hypochlorite in water. Although in this case sodium hypochlorite is used because it is superior in storage stability and handling property, calcium hypochlorite, etc. can also be used insofar as it is on the market and easily available.

[0066] Further, the step of ion exchange can be repeated. By repeating the step of ion exchange, it is possible to decrease metal ions such as sodium and calcium, which become counter ions of hypochlorite ions contained in the aqueous solution of tetramethylammonium hypochlorite.

[0067] A treatment liquid of the present invention containing tetramethylammonium ions can be produced by mixing and dissolving an alkylammonium salt and other optional additives into the obtained aqueous solution of tetramethylammonium hypochlorite.(Method for etching ruthenium)

[0068] The etching conditions using a treatment liquid of the first aspect of the present invention can be appropriately selected according to the etching conditions of the etching equipment used, while the temperature is in a range of 10 to 80°C, and preferably 20 to 70°C.

[0069] The etching rate of ruthenium varies with temperature. Therefore, in order to increase the etching rate of ruthenium, a range of 40 to 70°C should be selected in the above temperature range. In the temperature range of 40 to 70°C, the etching rate can be accelerated, and the treatment can be performed in a simple apparatus but with good operability.

[0070] The application time of a treatment liquid of the present invention is in a range of 0.1 to 120 min, and preferably 0.5 to 60 min, and can be appropriately selected according to the etching conditions and the type of a semiconductor element to be applied. As a rinse liquid after the application of the treatment liquid, an organic solvent such as alcohol can be used, but simply rinsing with deionized water is sufficient.

[0071] As described above, with the treatment liquid of the first aspect of the present invention, the etching rate on ruthenium can achieve 20 Å / min or more, and preferably 50 Å / min or more, and the flatness of the ruthenium surface after etching can be made excellent. As obvious from the above, the treatment liquid of the present invention can be suitably used when ruthenium is used in the semiconductor element formation process.EXAMPLES

[0072] The present invention will be described below more specifically with reference to Experimental Examples, but the present invention is not limited to these Experimental Examples.< Experimental Example 1 and Reference Example 1>(pH measurement method)

[0073] The pH was measured with 30 mL of each treatment liquid prepared in Experimental Example 1 and Reference Example 1 using a desktop pH meter (LAQUA F-73, manufactured by HORIBA, Inc.). The pH measurement was carried out after the temperature of the treatment liquid had stabilized at 25°C.(Method for calculating effective chlorine concentration and hypochlorite ion concentration)

[0074] After preparing treatment liquids of Experimental Examples and Reference Examples, 0.5 mL of each treatment liquid, 2 g of potassium iodide (special grade chemical, produced by Wako Pure Chemical Industries, Ltd), 8 mL of a 10% acetic acid, and 10 mL of ultrapure water were charged into a 100-mL Erlenmeyer flask, and stirred until the solids dissolved to obtain a brown solution. The prepared brown solution was subjected to redox titration using a 0.02 M sodium thiosulfate solution (for volumetric analysis, produced by Wako Pure Chemical Industries, Ltd.) until the color of the solution turns from brown to very pale yellow, and then a starch solution was added to obtain a light purple solution. Next, to this solution, a 0.02M sodium thiosulfate solution was further added until the endpoint at which the solution became colorless and transparent, based on which the effective chlorine concentration was calculated. The hypochlorite ion concentration was calculated from the effective chlorine concentration obtained. For example, if the effective chlorine concentration is 1%, the hypochlorite ion concentration is 0.73%. This is common in the following Experimental Examples 1 to 5.(Method for calculating tetramethylammonium ion concentration)

[0075] Each concentration of tetramethylammonium ions in the treatment liquids of Experimental Examples and Reference Examples was calculated from the pH, hypochlorite ion concentration, and sodium ion concentration. In this regard, the sodium ion concentration was measured by an ICP-MS (inductively coupled plasma mass spectrometer).(Method for calculating etching rate of ruthenium)

[0076] An oxide film was formed on a silicon wafer using a batch-type thermal oxidation furnace, and thereon a 1200 Å (±10%) ruthenium film was deposited using the sputtering method. The sheet resistance was measured with a four-probe resistance measurement device (LORESTA-GP, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) and converted to a film thickness.

[0077] In a fluorine resin-made container with a lid (94.0 mL PFA container, produced by AS ONE Corporation), 30 mL of a treatment liquid of each Experimental Example and Reference Example was prepared, and a sample piece with a size of 10 × 20 mm was immersed in the treatment liquid at 23°C for 1 min. The etching rate was calculated by dividing the change in the film thickness between before and after the above treatment by the immersion time.

[0078] From the calculated etching rate, the required time to etch 50 Å ±10 Å of ruthenium was calculated, and after treating a ruthenium film for the time required to etch 50 Å ±10 Å, the ruthenium surface was observed with a field emission-type scanning electron microscope (FE-SEM; Field Emission Scanning Electron Microscope) at 100000x. In this observation, if a roughened surface was observed, it was rated as poor (C), if a slightly roughened surface was observed, it was rated as good (B), and if no surface roughening was observed, it was rated as excellent (A).<Experimental Example 1-1>(Preparation of sample to be etched)

[0079] A silicon wafer with a cleaned surface was prepared, and a 500 nm thermal oxidation film was formed. Ruthenium was then deposited on the thus prepared silicon wafer by the sputtering method to prepare a sample in which a 1200 Å-thick ruthenium layer was laminated on the silicon wafer.(Production of treatment liquid)<Pretreatment of ion exchange resin; Preparation of hydrogen-form ion exchange resin>

[0080] In a glass column (Bio Column CF-50TK, manufactured by AS ONE Corporation) with an inner diameter of about 45 mm, 200 mL of a sodium-form strongly acidic ion exchange resin (AMBERLITE IR-120 BNa, produced by Organo Corporation) was charged. Then, 1 L of a 1N hydrochloric acid (for volumetric analysis, Wako Pure Chemical Industries, Ltd.) was fed through the ion exchange resin column to change it to the hydrogen-form, and then 1 L of ultrapure water was fed to rinse the ion exchange resin.<Step (a)>

[0081] Further, 1 L of a 10% tetramethylammonium hydroxide solution was fed to 209 mL of the ion exchange resin that had been exchanged to the hydrogen-form, and the ions were exchanged from the hydrogen form to the tetramethylammonium form. After the ion exchange, 1 L of ultrapure water was fed to rinse the ion exchange resin.<Step (b)>

[0082] After 69 g of sodium hypochlorite pentahydrate (special grade chemical, produced by Wako Pure Chemical Industries) was placed in a 2 L fluorine resin-made container, 931 g of ultrapure water was added to prepare a 3.11 mass% aqueous solution of sodium hypochlorite. The prepared aqueous solution of sodium hypochlorite was fed to an ion exchange resin exchanged to a tetramethylammonium form to obtain 1000 g of an aqueous solution of tetramethylammonium hypochlorite. To 999.9 g of the obtained aqueous solution of tetramethylammonium hypochlorite, 100 mg of tetradecyltrimethylammonium chloride was added to obtain a treatment liquid having the composition registered in Table 1.<Evaluation>

[0083] The pH, effective chlorine concentration, and hypochlorite ion concentration of the obtained treatment liquid were evaluated, and it was confirmed that the pH was 10 and the hypochlorite ion concentration was 2.15 mass%. The etching rate was also evaluated using the "Method for calculating etching rate of ruthenium" described above. From the calculated etching rate, the time required to etch 50 Å ±10 Å of ruthenium was calculated, and a ruthenium film treated for the time required to etch 50 Å ±10 Å was prepared, and used as the ruthenium film for surface observation. The ruthenium surface was observed using an electron microscope of 100000x power. The results of the observation are shown in FIG. 3.<Experimental Example 1-2>

[0084] An aqueous solution of tetramethylammonium hypochlorite was obtained identically with Experimental Example 1-1, except that the amount of the ion exchange resin in the step (a) was set at 564 mL, the feed amount of the 10% tetramethylammonium hydroxide solution was set at 2 L, and the concentration of the aqueous solution of sodium hypochlorite in the step (b) was set at 8.39 mass%. In addition, as the pH adjustment step (c), a 25% tetramethylammonium hydroxide (TMAH) solution was added to the aqueous solution of tetramethylammonium hypochlorite until the pH became 11. To 999 g of the obtained aqueous solution of tetramethylammonium hypochlorite, 1 g of decyltrimethylammonium chloride was added to obtain a treatment liquid having the composition registered in Table 1. The evaluation results are shown in Table 2.<Experimental Example 1-3>

[0085] An aqueous solution of tetramethylammonium hypochlorite was obtained identically with Example 1, except that the amount of the ion exchange resin in the step (a) was set at 705 mL, the feed amount of the 10% tetramethylammonium hydroxide solution was set at 2 L, and the concentration of the aqueous solution of sodium hypochlorite in the step (b) was set at 10.49 mass%. In addition, as the pH adjustment step (c), a 25% tetramethylammonium hydroxide (TMAH) solution was added to the aqueous solution of tetramethylammonium hypochlorite until the pH became 12. To 999.5 g of the obtained aqueous solution of tetramethylammonium hypochlorite, 500 mg of lauryltrimethylammonium chloride was added to obtain a treatment liquid having the composition registered in Table 1. The evaluation results are shown in Table 2.<Experimental Example 1-4>

[0086] After obtaining an aqueous solution of tetramethylammonium hypochlorite by performing the same operation as in Experimental Example 1-2, 500 mg of octadecyltrimethylammonium chloride was added to 999.5 g of the aqueous solution of tetramethylammonium hypochlorite to obtain a treatment liquid having the composition registered in Table 1. The evaluation results are shown in Table 2.<Experimental Example 1-5>

[0087] An aqueous solution of tetramethylammonium hypochlorite was obtained identically with Experimental Example 1-1, except that the amount of the ion exchange resin in the step (a) was set at 282 mL, and the concentration of the aqueous solution of sodium hypochlorite in the step (b) was set at 4.20 mass%. In addition, as the pH adjustment step (c), a 25% tetramethylammonium hydroxide (TMAH) solution was added to the aqueous solution of tetramethylammonium hypochlorite until the pH became 11. To 990 g of the obtained aqueous solution of tetramethylammonium hypochlorite, 10 g of n-octyltrimethylammonium chloride was added to obtain a treatment liquid having the composition registered in Table 1. The evaluation results are shown in Table 2.<Experimental Example 1-6>

[0088] After obtaining an aqueous solution of tetramethylammonium hypochlorite by performing the same operation as in Experimental Example 1-1, as the pH adjustment step (c), the aqueous solution of tetramethylammonium hypochlorite was fed to a glass column packed with 50 mL of a sodium form strongly acidic ion exchange resin (AMBERLITE IR-120 BNa, produced by Organo Corporation) converted to a hydrogen form. To 999.9 g of the obtained aqueous solution of tetramethylammonium hypochlorite, 100 mg of tetradecyltrimethylammonium chloride was added to obtain a treatment liquid having the composition registered in Table 1. The evaluation results are shown in Table 2.<Experimental Example 1-7>

[0089] After obtaining an aqueous solution of tetramethylammonium hypochlorite by performing the same operation as in Experimental Example 1-4, to 999.9 g of the aqueous solution of tetramethylammonium hypochlorite, 100 mg of hexadecyltrimethylammonium chloride was added to obtain a treatment liquid having the composition registered in Table 1. The evaluation results are shown in Table 2.<Experimental Example 1-8>

[0090] Sodium hypochlorite pentahydrate (special grade chemical, produced by Wako Pure Chemical Industries, Ltd.) was dissolved in water such that the hypochlorite ion became 2.15 mass%. To 999 g of the obtained aqueous solution of sodium hypochlorite, 1g of tetradecyltrimethylammonium chloride was added to obtain a treatment liquid having the composition registered in Table 1. The evaluation results are shown in Table 2.<Experimental Example 1-9>

[0091] Compared to Experimental Example 1-1, the amount of ion exchange resin in the step (a) was set at 282 mL, and the concentration of the aqueous solution of sodium hypochlorite in the step (b) was set at 4.20 mass%. To 999.5 g of the obtained aqueous solution of tetramethylammonium hypochlorite, 500 mg of didecyldimethylammonium chloride was added to obtain a treatment liquid having the composition registered in Table 1. The evaluation results are shown in Table 2.<Experimental Example 1-10>

[0092] After obtaining an aqueous solution of tetramethylammonium hypochlorite by performing the same operation as in Experimental Example 1-9, to 999.9 g of the obtained aqueous solution of tetramethylammonium hypochlorite, 100 mg of didodecyldimethylammonium chloride was added to obtain a treatment liquid having the composition registered in Table 1. The evaluation results are shown in Table 2.<Reference Example 1-1>

[0093] A treatment liquid was prepared in the same manner as in Experimental Example 1-1, except that the alkylammonium salt expressed by Formula (1) was not added, and the same evaluation as in Experimental Example 1-1 was performed.

[0094] The compositions of each treatment liquid prepared in Experimental Example 1 and Reference Example 1 as above are shown in Table 1, and the results obtained are shown in Table 2. [Table 1]ClO-(wt%)TMA+ (wt%)SurfactantpHKindAddition amount (ppm)Experimental Example 1-12.153.09Tetradecyltrimethylammonium chloride10010Experimental Example 1-25.798.33Decyltrimethylammonium chloride100011Experimental Example 1-37.2510.42Lauryltrimethylammonium chloride50012Experimental Example 1-45.88.34Octadecyltrimethylammonium chloride50011Experimental Example 1-52.874.14n -Octyltrimethylammonium chloride1000011Experimental Example 1-62.152.35Tetradecyltrimethylammonium chloride1008Experimental Example 1-75.88.34Hexadecyltrimethylammonium chloride10011Experimental Example 1-82.9-Tetradecyltrimethylammonium chloride100011Experimental Example 1-92.94.17Didecyldimethylammonium chloride50010Experimental Example 1-102.94.17Didodecyldimethylammonium chloride10010Reference Example 1-12.153.09--10 [Table 2] Ru etching (23°C) Å·min -1< Surface roughness (SEM)Experimental Example 1-150AExperimental Example 1-275AExperimental Example 1-330AExperimental Example 1-480BExperimental Example 1-545BExperimental Example 1-6420AExperimental Example 1-790AExperimental Example 1-895AExperimental Example 1-965AExperimental Example 1-1055AReference Example 1-1110C

[0095] As shown in Table 2, in Experimental Examples 1-1 to 1-10, where the treatment liquid of the present invention is applied, the flatness of the ruthenium surface after etching is maintained, therefore the same can be suitably used as a treatment liquid for a semiconductor wafer. FIG. 3 shows an electron microscopic image of 100000x of the ruthenium after the etching treatment obtained in Experimental Example 1-1. It is to be known that formation of RuO 2 (particles) on the wafer surface was inhibited and a flat ruthenium surface was obtained.

[0096] Since no surfactant is added in Reference Example 1-1, it can be known that the flatness after etching was degraded compared to Experimental Examples 1-1 to 1-10.<Experimental Example 1-11>

[0097] After obtaining an aqueous solution of tetramethylammonium hypochlorite by performing the same operation as in Experimental Example 1-1, to 999 g of the obtained aqueous solution of tetramethylammonium hypochlorite, 1 g of tetraheptylammonium chloride was added to obtain a treatment liquid having the composition registered in Table 3.<Reference Examples 1-2 to 1-3>

[0098] The treatment liquids registered in Table 3 were obtained according to the procedure of Experimental Example 1-1. [Table 3]ClO-(wt%)TMA+ (wt%)SurfactantpHRu etching (23°C) Å·min-1Surface roughness (SEM)KindAddition amount (ppm)Experimental Example 1-112.153.09Tetraheptylammonium chloride1001060BReference Example 1-22.153.09--10110CReference Example 1-32.94.17Triethylmethylammonium chloride100010140CReference Example 1-42.153.09Butyltrimethylammonium chloride1001155C

[0099] As obvious from the results shown in Table 3, desirable surface roughness could not be obtained when an alkylammonium salt in which structure an alkyl group with a carbon number of 7 or more was not present was used as a surfactant.Reference Signs List

[0100] 1Substrate 2Interlayer insulating film 3Ruthenium

Claims

1. A treatment liquid suitable for use in a process for forming a semiconductor wafer by etching a metal contained in the semiconductor wafer, wherein the pH of the treatment liquid at 25 °C is more than 7 and less than 14 and the treatment liquid comprises: (A) a hypochlorite ion (B) an alkylammonium salt expressed by the following Formula (1): wherein "a" is an integer from 6 to 20; R1, R2, and R3 are independently a hydrogen atom, or an alkyl group with a carbon number from 1 to 20 and X- is a fluoride ion, a chloride ion, an iodide ion, a hydroxide ion, a nitrate ion, a phosphate ion, a sulfate ion, a hydrogen sulfate ion, a methanesulfate ion, a perchlorate ion, an acetate ion, a fluoroborate ion, or a trifluoroacetate ion.

2. The treatment liquid according to claim 1, wherein the concentration of the alkylammonium salt (B) expressed by Formula (1) is from 0.001 to 10 mass%.

3. The treatment liquid according to claim 1 or 2 comprising at least one kind of ammonium ion (C) selected from a tetramethylammonium ion, a tetraethylammonium ion, a tetrapropylammonium ion, and a tetrabutylammonium ion.

4. The treatment liquid according to any one of claims 1 to 3, wherein the concentration of hypochlorite ions is from 0.05 to 20.0 mass%.

5. An etching method comprising a step of bringing a metal contained in a semiconductor wafer into contact with the treatment liquid according to any one of claims 1 to 4.