Etching gas, etching method, and semiconductor device manufacturing method

Abstract

The present invention provides: an etching gas which is capable of selectively etching an etching object that contains silicon over a non-etching object; and an etching method. This etching gas contains a fluorobutene which is represented by general formula C4HxFy, wherein x is from 1 to 7, y is from 1 to 7 and (x + y) is 8. This etching gas contains at least one element selected from among copper, zinc, manganese, cobalt and silicon as metal impurities, or does not contain any of these elements; and in cases where this etching gas contains metal impurities, the sum of the concentrations of copper, zinc, manganese, cobalt and silicon is 5,000 ppm by mass or less. An etching method according to the present invention comprises an etching step wherein an etching gas is brought into contact with a member (12) to be etched, said member comprising an etching object and a non-etching object, so that the etching object is selectively etched over the non-etching object. The etching object contains silicon.

Description

[Technical Field]

[0001] The present invention relates to an etching gas, an etching method, and a method for manufacturing a semiconductor device. [Background technology]

[0002] In semiconductor manufacturing processes, dry etching is used to pattern and remove silicon compounds such as silicon oxide and silicon nitride. Dry etching requires high etching selectivity, i.e., the ability to selectively etch silicon compounds compared to the mask used for patterning. Various etching gases that satisfy this requirement have been proposed, and for example, Patent Document 1 discloses an etching gas containing hexafluoroisobutene. Hexafluoroisobutene reacts and polymerizes during etching, and the mask is covered and protected by a film of this polymer, which makes it easy to obtain high etching selectivity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 6527214 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when etching is performed using the etching gas disclosed in Patent Document 1, etching selectivity may be insufficient. An object of the present invention is to provide an etching gas, an etching method, and a method for manufacturing a semiconductor device, which are capable of selectively etching an etching target compared to a non-etching target when an etching gas is brought into contact with an etching target member having an etching target that is a target for etching with the etching gas and a non-etching target that is not a target for etching with the etching gas. [Means for solving the problem]

[0005] In order to solve the above problems, one aspect of the present invention is as follows [1] to [9]. [1] General formula C4H x F y In the general formula, x is 1 or more and 7 or less, y is 1 or more and 7 or less, and x+y is 8, An etching gas which contains or does not contain at least one of copper, zinc, manganese, cobalt, and silicon as a metal impurity, and in the case where the metal impurity is contained, the sum of the concentrations of copper, zinc, manganese, cobalt, and silicon is 5000 ppb by mass or less.

[0006] [2] The etching gas according to [1], which may or may not further contain at least one of alkali metals and alkaline earth metals as the metal impurities, and in the case where the etching gas contains copper, zinc, manganese, cobalt, and silicon, as well as the alkali metals and alkaline earth metals, the total concentration of the metal impurities is 10,000 ppb by mass or less.

[0007] [3] The etching gas according to [2], wherein the alkali metal is at least one of lithium, sodium, and potassium, and the alkaline earth metal is at least one of magnesium and calcium. [4] The etching gas according to any one of [1] to [3], wherein the fluorobutene is at least one selected from 1,1,1,4,4,4-hexafluoro-2-butene, 1,1,1,2,4,4,4-heptafluoro-2-butene, 3,3,4,4,4-pentafluoro-1-butene, and 2,3,3,4,4,4-hexafluoro-1-butene.

[0008] [5] An etching method comprising an etching step of contacting the etching gas according to any one of [1] to [4] with a member to be etched, the member having an etching object that is a target for etching with the etching gas and a non-etching object that is not a target for etching with the etching gas, and selectively etching the etching object compared to the non-etching object, wherein the etching object contains silicon. [6] The etching method according to [5], further comprising, before the etching step, a metal impurity removal step of reducing the sum of the concentrations of copper, zinc, manganese, cobalt, and silicon contained in the etching gas to 5000 mass ppb or less.

[0009] [7] The etching method according to [5] or [6], wherein the etching gas is a gas consisting of the fluorobutene alone or a mixed gas containing the fluorobutene and a diluent gas. [8] The etching method according to [7], wherein the dilution gas is at least one selected from nitrogen gas, helium, argon, neon, krypton, and xenon.

[0010] [9] A method for manufacturing a semiconductor element using the etching method according to any one of [5] to [8], the member to be etched is a semiconductor substrate having the etching object and the non-etching object, A method for manufacturing a semiconductor device, comprising a processing step of removing at least a part of the etching object from the semiconductor substrate by etching. [Effects of the Invention]

[0011] According to the present invention, an etching target containing silicon can be selectively etched compared to a non-etching target. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of an example of an etching apparatus for explaining an embodiment of an etching method according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present invention will be described below. Note that this embodiment is merely an example of the present invention, and the present invention is not limited to this embodiment. Furthermore, various modifications and improvements can be made to this embodiment, and such modifications and improvements can also be included in the present invention.

[0014] The etching gas according to this embodiment is a gas represented by the general formula CH x F y wherein x is 1 or more and 7 or less, y is 1 or more and 7 or less, and x+y is 8, and the etching gas contains or does not contain at least one of copper (Cu), zinc (Zn), manganese (Mn), cobalt (Co), and silicon (Si) as a metal impurity, and when the metal impurity is contained, the sum of the concentrations of copper, zinc, manganese, cobalt, and silicon is 5000 ppb by mass or less.

[0015] The etching method according to the present embodiment includes an etching step of contacting the etching gas according to the present embodiment with a member to be etched, the member having an etching target to be etched by the etching gas and a non-etching target not to be etched by the etching gas, to selectively etch the etching target compared to the non-etching target. In the etching method according to the present embodiment, the etching target contains silicon (Si).

[0016] When the etching gas is brought into contact with a material to be etched, the silicon-containing material to be etched reacts with the fluorobutene in the etching gas, resulting in etching of the material. In contrast, the material to be etched, such as a mask, hardly reacts with the fluorobutene, so etching of the material to be etched hardly progresses. Therefore, according to the etching method of this embodiment, the material to be etched can be selectively etched relative to the material to be etched (i.e., high etching selectivity can be achieved).

[0017] Furthermore, the fluorobutene reacts and polymerizes during dry etching, and the non-etching target is covered with a polymer film to protect it from etching. Therefore, etching of the non-etching target becomes more difficult, and therefore etching selectivity is further improved by using an etching gas containing the fluorobutene.

[0018] However, if the etching gas contains metal impurities, the catalytic action of the metal impurities causes dissociation of the carbon-carbon double bond of the fluorobutene, thereby suppressing the formation of a polymer film. As a result, the non-etching target is less likely to be protected by the polymer film, and etching of the non-etching target is more likely to proceed, which may result in a decrease in etching selectivity. Copper, zinc, manganese, cobalt, and silicon have a strong catalytic action that causes dissociation of the carbon-carbon double bond of the fluorobutene, which may significantly decrease etching selectivity.

[0019] The etching gas according to this embodiment does not contain copper, zinc, manganese, cobalt, and silicon, or if it does contain them, the concentrations thereof are low, so that the carbon-carbon double bond of the fluorobutene is unlikely to dissociate. Therefore, when dry etching of a member to be etched is performed using the etching gas according to this embodiment, the formation of a polymer film on the non-etching object is unlikely to be suppressed, and the etching object can be selectively etched compared to the non-etching object.

[0020] For example, the etching selectivity, which is the ratio of the etching rate of an object to be etched to the etching rate of an object not to be etched, is likely to be 10 or more. The etching selectivity is preferably 10 or more, more preferably 30 or more, and even more preferably 50 or more.

[0021] The technology disclosed in Patent Document 1 does not take into consideration the concentrations of copper, zinc, manganese, cobalt, and silicon in the etching gas, and therefore, when etching is performed using the etching gas disclosed in Patent Document 1, the copper, zinc, manganese, cobalt, and silicon may cause dissociation of the carbon-carbon double bond of hexafluoroisobutene, thereby suppressing the formation of a polymer film. As a result, the non-etching target is less likely to be protected by the polymer film, and etching of the non-etching target may proceed more easily, resulting in reduced etching selectivity.

[0022] In the present invention, etching means removing part or all of the etching target material of the etched member to process the etched member into a predetermined shape (e.g., a three-dimensional shape) (e.g., processing a film-like etching target material made of a silicon compound that is present in the etched member to a predetermined film thickness).

[0023] The etching method according to the present embodiment can be used in the manufacture of semiconductor devices. That is, the method for manufacturing a semiconductor device according to the present embodiment is a method for manufacturing a semiconductor device using the etching method according to the present embodiment, in which the member to be etched is a semiconductor substrate having an etching target and a non-etching target, and the method includes a process of removing at least a part of the etching target from the semiconductor substrate by etching.

[0024] The etching method according to this embodiment can etch an etching target with high precision, and therefore can be used for manufacturing semiconductor devices such as 3D-NAND flash memories, logic devices, etc. Furthermore, the etching method according to this embodiment is expected to contribute to further miniaturization and higher integration of semiconductor devices.

[0025] The etching gas, etching method, and semiconductor device manufacturing method according to this embodiment will be described in further detail below. [Etching Method] The etching in this embodiment can be achieved by either plasma etching using plasma or plasmaless etching not using plasma, such as reactive ion etching (RIE), inductively coupled plasma (ICP) etching, capacitively coupled plasma (CCP) etching, electron cyclotron resonance (ECR) plasma etching, and microwave plasma etching.

[0026] In plasma etching, the plasma may be generated in a chamber in which the member to be etched is placed, or the plasma generation chamber may be separated from the chamber in which the member to be etched is placed (i.e., remote plasma may be used). Etching using remote plasma may enable etching of silicon-containing etching targets with higher selectivity.

[0027] [Fluorobutene] The fluorobutene contained in the etching gas according to this embodiment is represented by the general formula CH x F yand satisfies three conditions: x in the general formula is 1 or more and 7 or less, y is 1 or more and 7 or less, and x+y is 8. The type of fluorobutene is not particularly limited as long as it satisfies the above requirements, and both linear fluorobutene and branched fluorobutene (isobutene) can be used, but those similar to fluoro-1-butene and fluoro-2-butene are preferably used.

[0028] Specific examples of fluoro-1-butene include CHF2-CF2-CF=CF2, CF3-CF2-CF=CHF, CF3-CHF-CF=CF2, CF3-CF2-CH=CF2, CHF2-CHF-CF=CF2, CHF2-CF2-CF=CHF, CF3-CHF-CF=CHF, CF3-CF2-CH=CHF, CF3-CHF-CH=CF2, CHF2-CF2-CH=CF2, CH3-CF2-CF=CF2, CH2F-CHF-CF=CF2, CH2F-CF2-CH=CF2, CH2F-CF2-CF=CHF, CHF2-CH2-CF=CF2, CHF2-CHF-CH=CF2, CHF2-CHF-CF=CHF, CHF2-CF2-CH=CHF, CHF2-CF2-CF=CH2, CF3-CH2-CH=CF2, CF3-CH2-CF=CHF, CF3-CHF-CH=CHF, CF3-CHF-CF=CH2, CF3-CF2-CH=CH2, CH3-CHF-CF=CF2, CH3-CF2-CH=CF2, CH3-CF2-CF=CHF, CH2F-CH2-CF=CF2, CH2F-CHF-CH=CF2, CH2F-CHF-CF=CHF, CH2F-CF2-CH=CHF, CH2F-CF2-CF=CH2, CHF2-CH2-CH=CF2, CHF2-CH2-CF=CHF, CHF2-CHF-CH=CHF, CHF2-CHF-CF=CH2, CHF2-CF2-CH=CH2, CF3-CH2-CH=CHF, CF3-CH2-CF=CH2, CF3-CHF-CH=CH2, CH3-CH2-CF=CF2, CH3-CHF-CH=CF2, CH3-CHF-CF=CHF, CH3-CF2-CH=CHF, CH3-CF2-CF=CH2, CH2F-CH2-CH=CF2, CH2F-CH2-CF=CHF, CH2F-CHF-CH=CHF, CH2F-CHF-CF=CH2, CH2F-CF2-CH=CH2, CHF2-CH2-CH=CHF, CHF2-CH2-CF=CH2, CHF2-CHF-CH=CH2, CF3-CH2-CH=CH2, CH3-CH2-CH=CF2, CH3-CH2-CF=CHF, CH3-CHF-CH=CHF, CH3-CHF-CF=CH2, CH3-CF2-CH=CHV, CH2F-CH2-CH=CHF, CH2F-CH2-CF=CH2, CH2F-CHF-CH=CH2, CHF2-CH2-CH=CH2,Examples include CH3-CH2-CH=CHF, CH3-CH2-CF=CH2, CH3-CHF-CH=CH2, and CH2F-CH2-CH=CH2.

[0029] Specific examples of fluoro-2-butene include CHF2-CF=CF-CF3, CF3-CH=CF-CF3, CH2F-CF=CF-CF3, CHF2-CH=CF-CF3, CHF2-CF=CF-CHF2, CF3-CH=CH-CF3, CH3-CF=CF-CF3, CH2F-CH= CF-CF3, CH2F-CF=CH-CF3, CH2F-CF=CF-CHF2, CHF2-CH=CH-CF3, CHF2-CF=CH-CHF2, CH3-CH=CF-CF3, CH3-CF=CH-CF3, CH3-CF=CF-CHF2, CH2F-CH=CH-CF3, CH2F -CH=CF-CHF2, CH2F-CF=CH-CHF2, CH2F-CF=CF-CH2F, CHF2-CH=CH-CHF2, CH3-CH=CH-CF3, CH3-CH=CF-CHF2, CH3-CF=CH-CHF2, CH3-CF=CF-CH2F, CH2F-CF=CH- CH2F, CH2F-CH=CH-CHF2, CH3-CH=CH-CHF2, CH3-CH=CF-CH2F, CH3-CF=CH-CH2F, CH3-CF=CF-CH3, CH2F-CH=CH-CH2F, CH3-CH=CH-CH2F, CH3-CH=CF-CH3.

[0030] These fluorobutenes may be used alone or in combination of two or more. Some of the fluorobutenes mentioned above exist as cis-trans isomers, but both cis- and trans-fluorobutenes can be used in the etching gas according to this embodiment.

[0031] Among the above fluorobutenes, those having a boiling point of 50°C or less at 1 atmosphere are preferred, and those having a boiling point of 40°C or less are more preferred. If the boiling point at 1 atmosphere is within the above range, the fluorobutene gas is less likely to liquefy inside the piping through which the fluorobutene gas is introduced when the fluorobutene gas is introduced into, for example, a plasma etching apparatus. This makes it possible to suppress the occurrence of problems caused by the liquefaction of the fluorobutene gas, allowing the plasma etching process to be carried out efficiently. From the above viewpoint, the fluorobutene is preferably at least one selected from the group consisting of 1,1,1,4,4,4-hexafluoro-2-butene (boiling point 9°C), 1,1,1,2,4,4,4-heptafluoro-2-butene (boiling point 8°C), 3,3,4,4,4-pentafluoro-1-butene (boiling point 3-6°C), and 2,3,3,4,4,4-hexafluoro-1-butene (boiling point 3-7°C).

[0032] [Etching gas] The etching gas is a gas containing the above-mentioned fluorobutene. The etching gas may be a gas consisting of only the above-mentioned fluorobutene, or a mixed gas containing the above-mentioned fluorobutene and a diluent gas. Alternatively, the etching gas may be a mixed gas containing the above-mentioned fluorobutene, a diluent gas, and an additive gas. The dilution gas may be at least one selected from nitrogen gas (N2), helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe).

[0033] Examples of the additive gas include oxidizing gas, fluorocarbon gas, and hydrofluorocarbon gas. Specific examples of the oxidizing gas include oxygen gas (O), ozone (O), carbon monoxide (CO), carbon dioxide (CO), nitric oxide (NO), nitrous oxide (NO), and nitrogen dioxide (NO). Specific examples of the fluorocarbon include carbon tetrafluoride (CF), hexafluoromethane (CF), and octafluoropropane (CF). Specific examples of the hydrofluorocarbon include CF, ...

[0034] The content of the dilution gas is preferably 90% by volume or less, more preferably 50% by volume or less, based on the total volume of the etching gas, and the content of the additive gas is preferably 50% by volume or less, more preferably 30% by volume or less, based on the total volume of the etching gas. The content of fluorobutene in the etching gas is preferably 5% by volume or more, more preferably 10% by volume or more, based on the total amount of etching gas in order to improve the etching rate, and is preferably 90% by volume or less, more preferably 80% by volume or less, based on the total amount of etching gas in order to reduce the amount of fluorobutene used.

[0035] [Metal impurities] The etching gas according to this embodiment may or may not contain at least one of copper, zinc, manganese, cobalt, and silicon as a metal impurity, but when the metal impurities are contained, the sum of the concentrations of copper, zinc, manganese, cobalt, and silicon is low, at 5000 ppb by mass or less, so that the carbon-carbon double bond of the fluorobutene is less likely to dissociate, as described above, and as a result, the etching target can be selectively etched compared to the non-etching target. Here, the absence of the metal impurities means that the metal impurities cannot be quantified by inductively coupled plasma mass spectrometry (ICP-MS).

[0036] In order to fully achieve the etching selectivity effect, the sum of the concentrations of copper, zinc, manganese, cobalt, and silicon contained in the etching gas needs to be 5000 mass ppb or less, preferably 1000 mass ppb or less, and more preferably 100 mass ppb or less.

[0037] In order to make it difficult for the carbon-carbon double bond of the fluorobutene to dissociate, the concentrations of copper, zinc, manganese, cobalt, and silicon contained in the etching gas are each preferably 1000 mass ppb or less, and more preferably 500 mass ppb or less.

[0038] The sum of the concentrations of copper, zinc, manganese, cobalt, and silicon may be 1 ppb by mass or more. The concentrations of metal impurities such as copper, zinc, manganese, cobalt, and silicon in the etching gas can be quantified using an inductively coupled plasma mass spectrometer (ICP-MS).

[0039] In order to achieve higher etching selectivity, it is preferable to lower the concentrations of alkali metals and alkaline earth metals in the etching gas as well as the concentrations of copper, zinc, manganese, cobalt, and silicon. That is, the etching gas may or may not contain at least one of copper, zinc, manganese, cobalt, and silicon as metal impurities, and if contained, the sum of the concentrations of copper, zinc, manganese, cobalt, and silicon is 5000 mass ppb or less, and may or may not further contain at least one of alkali metals and alkaline earth metals as the metal impurities, and if contained, the sum of the concentrations of copper, zinc, manganese, cobalt, and silicon, as well as the alkali metals and alkaline earth metals is preferably 10000 mass ppb or less, more preferably 5000 mass ppb or less, and even more preferably 1000 mass ppb or less. The total concentration of copper, zinc, manganese, cobalt, silicon, alkali metals, and alkaline earth metals may be 2 ppb by mass or more.

[0040] Alkali metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr), while alkaline earth metals include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

[0041] Furthermore, in order to achieve higher etching selectivity, it is preferable to reduce the concentrations of titanium (Ti), zirconium (Zr), hafnium (Hf), niobium (Nb), tantalum (Ta), tungsten (W), ruthenium (Ru), rhodium (Rh), palladium (Pd), platinum (Pt), silver (Ag), gold (Au), cadmium (Cd), tin (Sn), and lead (Pb) in addition to the concentrations of copper, zinc, manganese, cobalt, and silicon and the concentrations of alkali metals and alkaline earth metals in the etching gas.

[0042] That is, when the etching gas contains at least one of copper, zinc, manganese, cobalt, and silicon, and at least one of alkali metals and alkaline earth metals as metal impurities, and further contains at least one of titanium, zirconium, hafnium, niobium, tantalum, tungsten, ruthenium, rhodium, palladium, platinum, silver, gold, cadmium, tin, and lead as metal impurities, the sum of the concentrations of all of these contained metal impurities is preferably 15,000 mass ppb or less, more preferably 10,000 mass ppb or less, and even more preferably 5,000 mass ppb or less.

[0043] Furthermore, in order to achieve higher etching selectivity, it is preferable to reduce the concentrations of copper, zinc, manganese, cobalt, and silicon, the concentrations of alkali metals and alkaline earth metals, and the concentrations of titanium, zirconium, hafnium, niobium, tantalum, tungsten, ruthenium, rhodium, palladium, platinum, silver, gold, cadmium, tin, and lead in the etching gas, as well as the concentrations of chromium (Cr), molybdenum (Mo), iron (Fe), nickel (Ni), aluminum (Al), and antimony (Sb).

[0044] That is, when the etching gas contains at least one of copper, zinc, manganese, cobalt, and silicon, at least one of alkali metals and alkaline earth metals, and at least one of titanium, zirconium, hafnium, niobium, tantalum, tungsten, ruthenium, rhodium, palladium, platinum, silver, gold, cadmium, tin, and lead as metal impurities, and further contains at least one of chromium, molybdenum, iron, nickel, aluminum, and antimony as a metal impurity, the sum of the concentrations of all of these contained metal impurities is preferably 20,000 mass ppb or less, more preferably 15,000 mass ppb or less, and even more preferably 10,000 mass ppb or less.

[0045] The above-mentioned metal impurities may be contained in the etching gas as simple metals, metal compounds, metal halides, or metal complexes. The forms of the metal impurities in the etching gas include fine particles, droplets, gas, etc. It is believed that copper, zinc, manganese, cobalt, and silicon are mixed into the etching gas originating from the raw materials, catalysts, reactors, purification equipment, etc. used in synthesizing the above-mentioned fluorobutene. Methods for removing the metal impurities from the fluorobutene (impurity removal methods employed in the metal impurity removal step) include, for example, passing the fluorobutene through a filter, contacting it with an adsorbent, and separating it by distillation. Specifically, for example, the fluorobutene is sealed in a stainless steel cylinder, maintained at about 0°C, and the gas phase is extracted by the method described in the Examples below, thereby obtaining fluorobutene with a reduced concentration of the metal impurities. It is preferable to reduce the sum of the concentrations of alkali metals and alkaline earth metals contained in the etching gas to 5,000 ppb by mass or less by such a metal impurity removal step, and then carry out the etching step described below.

[0046] [Pressure conditions for etching process] The pressure conditions for the etching step in the etching method according to this embodiment are not particularly limited, but are preferably 10 Pa or less, and more preferably 5 Pa or less. If the pressure conditions are within the above range, plasma can be easily generated stably. On the other hand, the pressure conditions for the etching step are preferably 0.05 Pa or more. If the pressure conditions are within the above range, a large number of ionized ions are generated, making it easy to obtain a sufficient plasma density. The flow rate of the etching gas may be appropriately set depending on the size of the chamber and the capacity of the exhaust equipment for reducing the pressure inside the chamber so that the pressure inside the chamber is kept constant.

[0047] [Temperature conditions for etching process] The temperature conditions for the etching step in the etching method according to this embodiment are not particularly limited, but are preferably 200° C. or less to obtain high etching selectivity, more preferably 150° C. or less to further prevent etching of non-etching targets such as masks, and even more preferably 100° C. or less to perform anisotropic etching. Here, the temperature in the temperature conditions refers to the temperature of the member to be etched, but the temperature of a stage that supports the member to be etched and is installed in the chamber of the etching apparatus can also be used.

[0048] The above-mentioned fluorobutene hardly reacts with non-etching objects, such as masks, at temperatures of 200°C or less. Therefore, when a member to be etched is etched by the etching method according to this embodiment, the etching object can be selectively etched without substantially etching the non-etching object. Therefore, the etching method according to this embodiment can be used in, for example, a method of processing a silicon-containing etching object into a predetermined shape by using a patterned non-etching object as a resist or mask.

[0049] Furthermore, if the temperatures of the etching object and the non-etching object are 200° C. or less, the etching selectivity tends to be high. For example, the etching selectivity, which is the ratio of the etching rate of the silicon-containing etching object to the etching rate of the non-etching object, tends to be 10 or more. The bias power that constitutes the potential difference between the plasma generated during etching and the member to be etched may be selected from 0 to 10,000 W depending on the desired etching shape, and when selective etching is performed, it is preferably about 0 to 1,000 W. This potential difference allows anisotropic etching to be performed.

[0050] [Material to be etched] The member to be etched by the etching method according to this embodiment has an etching target and a non-etching target, but may be a member having a portion formed of an etching target and a portion formed of a non-etching target, or may be a member formed of a mixture of an etching target and a non-etching target. Furthermore, the member to be etched may have something other than an etching target and a non-etching target. The shape of the member to be etched is not particularly limited, and may be, for example, a plate, foil, film, powder, or lump. An example of the member to be etched is the semiconductor substrate described above.

[0051] [Object to be etched] The object to be etched may be made of only a silicon-containing material, may have a portion made of only a silicon-containing material and a portion made of another material, or may be made of a mixture of a silicon-containing material and another material. Examples of silicon-containing materials include silicon oxide, silicon nitride, polysilicon, and silicon germanium (SiGe).

[0052] An example of silicon oxide is silicon dioxide (SiO2). Silicon nitride refers to a compound containing silicon and nitrogen in any ratio, and an example thereof is Si3N4. The purity of silicon nitride is not particularly limited, but is preferably 30% by mass or more, more preferably 60% by mass or more, and even more preferably 90% by mass or more. The shape of the object to be etched is not particularly limited, and may be, for example, a plate, foil, film, powder, or lump.

[0053] [Objects not to be etched] The non-etching target is a target that does not substantially react with the above-mentioned fluorobutene or reacts extremely slowly with the above-mentioned fluorobutene, so that etching hardly progresses even when etching is performed by the etching method of this embodiment. The non-etching target is not particularly limited as long as it has the above-mentioned properties, but examples include photoresist, amorphous carbon, titanium nitride, metals such as copper, nickel, and cobalt, and oxides and nitrides of these metals. Among these, photoresist and amorphous carbon are more preferred from the viewpoints of ease of handling and availability.

[0054] Photoresist refers to a photosensitive composition whose physical properties, including solubility, change when exposed to light or an electron beam. Examples include photoresists for g-line, h-line, i-line, KrF, ArF, F2, and EUV. The composition of the photoresist is not particularly limited as long as it is one commonly used in semiconductor manufacturing processes, but examples include compositions containing a polymer synthesized from at least one monomer selected from linear olefin, cyclic olefin, styrene, vinylphenol, acrylic acid, methacrylate, epoxy, melamine, and glycol.

[0055] Furthermore, the non-etching object can be used as a resist or mask to suppress etching of the etching object by the etching gas. Therefore, the etching method according to the present embodiment can be used in a method of processing the etching object into a predetermined shape (for example, processing a film-like etching object of a member to be etched to a predetermined film thickness) by using the patterned non-etching object as a resist or mask, and is therefore suitable for use in the manufacture of semiconductor elements. Furthermore, since the non-etching object is hardly etched, etching of portions of the semiconductor element that should not be etched can be suppressed, and the loss of characteristics of the semiconductor element due to etching can be prevented.

[0056] The non-etched material remaining after patterning can be removed by a removal method commonly used in semiconductor device manufacturing processes, such as ashing using oxidizing gases such as oxygen plasma or ozone, or dissolution removal using chemicals such as APM (ammonia water and hydrogen peroxide solution), SPM (sulfuric acid and hydrogen peroxide solution), or organic solvents.

[0057] Next, an example of the configuration of an etching apparatus capable of carrying out the etching method according to this embodiment and an example of an etching method using the etching apparatus will be described with reference to Figure 1. The etching apparatus in Figure 1 is a plasma etching apparatus that performs etching using plasma. First, the etching apparatus in Figure 1 will be described.

[0058] The etching apparatus of FIG. 1 includes a chamber 10 in which etching takes place, a plasma generator (not shown) that generates plasma inside the chamber 10, a stage 11 that supports a member 12 to be etched inside the chamber 10, a thermometer 14 that measures the temperature of the member 12 to be etched, an exhaust pipe 13 that exhausts gas from inside the chamber 10, a vacuum pump 15 that is connected to the exhaust pipe 13 and reduces the pressure inside the chamber 10, and a pressure gauge 16 that measures the pressure inside the chamber 10.

[0059] The type of plasma generation mechanism of the plasma generator is not particularly limited, and may be one that applies a high-frequency voltage to parallel plates or one that passes a high-frequency current through a coil. When a high-frequency voltage is applied to the member 12 to be etched in the plasma, a negative voltage is applied to the member 12 to be etched, and positive ions are incident on the member 12 to be etched at high speed and perpendicularly, making anisotropic etching possible.

[0060] 1 also includes an etching gas supply unit that supplies an etching gas into chamber 10. This etching gas supply unit includes a fluorobutene gas supply unit 1 that supplies fluorobutene gas, a dilution gas supply unit 2 that supplies a dilution gas, a fluorobutene gas supply pipe 5 that connects fluorobutene gas supply unit 1 and chamber 10, and a dilution gas supply pipe 6 that connects dilution gas supply unit 2 to an intermediate portion of fluorobutene gas supply pipe 5.

[0061] Furthermore, the fluorobutene gas supply pipe 5 is provided with a fluorobutene gas pressure control device 7 that controls the pressure of the fluorobutene gas, and a fluorobutene gas flow rate control device 3 that controls the flow rate of the fluorobutene gas. Furthermore, the dilution gas supply pipe 6 is provided with a dilution gas pressure control device 8 that controls the pressure of the dilution gas, and a dilution gas flow rate control device 4 that controls the flow rate of the dilution gas. Note that equipment for supplying an additive gas may also be provided in the same configuration as the dilution gas supply unit 2, dilution gas flow rate control device 4, dilution gas supply pipe 6, and dilution gas pressure control device 8 (not shown).

[0062] When fluorobutene gas is supplied to chamber 10 as an etching gas, the interior of chamber 10 is depressurized with vacuum pump 15, and then fluorobutene gas is sent from fluorobutene gas supply unit 1 to fluorobutene gas supply pipe 5, so that the fluorobutene gas is supplied to chamber 10 via fluorobutene gas supply pipe 5.

[0063] When a mixed gas of fluorobutene gas and a diluent gas such as an inert gas is supplied as the etching gas, the inside of chamber 10 is depressurized by vacuum pump 15, and then fluorobutene gas is sent from fluorobutene gas supply unit 1 to fluorobutene gas supply pipe 5, and diluent gas is sent from diluent gas supply unit 2 to fluorobutene gas supply pipe 5 via diluent gas supply pipe 6. As a result, fluorobutene gas and diluent gas are mixed in the middle of fluorobutene gas supply pipe 5 to form a mixed gas, and this mixed gas is supplied to chamber 10 via fluorobutene gas supply pipe 5.

[0064] The configurations of the fluorobutene gas supply unit 1 and the diluent gas supply unit 2 are not particularly limited, and may be, for example, a gas tank or a cylinder. Furthermore, the fluorobutene gas flow rate control device 3 and the diluent gas flow rate control device 4 may be, for example, a mass flow controller or a flow meter.

[0065] When the etching gas is supplied to the chamber 10, it is preferable to supply the etching gas while maintaining the supply pressure of the etching gas (i.e., the value of the fluorobutene gas pressure control device 7 in FIG. 1) at a predetermined value. That is, the supply pressure of the etching gas is preferably 1 Pa or more and 0.2 MPa or less, more preferably 10 Pa or more and 0.1 MPa or less, and even more preferably 50 Pa or more and 50 kPa or less. When the supply pressure of the etching gas is within the above range, the etching gas is smoothly supplied to the chamber 10, and the load on the components of the etching apparatus of FIG. 1 (for example, the various devices and piping) is small.

[0066] Furthermore, from the viewpoint of uniformly etching the surface of the member to be etched 12, the pressure of the etching gas supplied into the chamber 10 is preferably from 1 Pa to 80 kPa, more preferably from 10 Pa to 50 kPa, and even more preferably from 100 Pa to 20 kPa. If the pressure of the etching gas in the chamber 10 is within the above range, a sufficient etching rate can be obtained and the etching selectivity ratio is likely to be high.

[0067] The pressure in the chamber 10 before the etching gas is supplied is not particularly limited as long as it is equal to or lower than the supply pressure of the etching gas. For example, -5 The pressure is preferably 1 Pa or more but less than 10 kPa, and more preferably 1 Pa or more but less than 2 kPa.

[0068] The differential pressure between the supply pressure of the etching gas and the pressure inside the chamber 10 before the etching gas is supplied is preferably 0.5 MPa or less, more preferably 0.3 MPa or less, and even more preferably 0.1 MPa or less. If the differential pressure is within the above range, the etching gas is likely to be smoothly supplied to the chamber 10. The etching gas is preferably supplied while maintaining the temperature of the etching gas at a predetermined value when being supplied to the chamber 10. That is, the supply temperature of the etching gas is preferably 0°C or higher and 150°C or lower.

[0069] The etching processing time (hereinafter sometimes referred to as "etching time") can be set arbitrarily depending on the degree to which the etching target of the member to be etched 12 is desired to be etched, but considering the production efficiency of the semiconductor device manufacturing process, it is preferably within 60 minutes, more preferably within 40 minutes, and even more preferably within 20 minutes. Note that the etching processing time refers to the time during which the etching gas is in contact with the member to be etched 12 inside the chamber 10.

[0070] The etching method according to this embodiment can be performed using a general plasma etching apparatus used in the semiconductor device manufacturing process, such as the etching apparatus shown in FIG. 1, and the configuration of the etching apparatus that can be used is not particularly limited. For example, the positional relationship between the fluorobutene gas supply pipe 5 and the member to be etched 12 is not particularly limited as long as it allows the etching gas to come into contact with the member to be etched 12. Furthermore, the configuration of the temperature adjustment mechanism of the chamber 10 is also sufficient as long as it is possible to adjust the temperature of the member to be etched 12 to a desired temperature, so the temperature adjustment mechanism may be directly provided on the stage 11, or an external temperature adjuster may be used to heat or cool the chamber 10 from outside the chamber 10.

[0071] 1 may be made of any material that is resistant to corrosion by the fluorobutene used and that can reduce the pressure to a predetermined level. For example, metals such as nickel, nickel-based alloys, aluminum, stainless steel, platinum, copper, and cobalt, ceramics such as alumina, and fluororesins may be used for the parts that come into contact with the etching gas.

[0072] Specific examples of nickel-based alloys include Inconel (registered trademark), Hastelloy (registered trademark), Monel (registered trademark), etc. Specific examples of fluororesins include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), polyvinylidene fluoride (PVDF), Teflon (registered trademark), Viton (registered trademark), Kalrez (registered trademark), etc. [Example]

[0073] The present invention will be explained in more detail below with reference to examples and comparative examples. Fluorobutenes containing metal impurities at various concentrations were prepared. Preparation examples of fluorobutenes are explained below. (Preparation Example 1) Five manganese steel cylinders with a capacity of 1 L were prepared. These cylinders were called cylinder A, cylinder B, cylinder C, cylinder D, and cylinder E, respectively. Cylinder A was filled with 500 g of 1,1,1,4,4,4-hexafluoro-2-butene (boiling point: 9°C) and liquefied by cooling to 0°C, forming a liquid phase and a gas phase at approximately 100 kPa. Cylinders B, C, D, and E were depressurized to below 1 kPa using a vacuum pump and then cooled to -78°C.

[0074] 400 g of 1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the upper outlet of cylinder A, where the gas phase was present, and transferred to cylinder B, which was under reduced pressure. 100 g of 1,1,1,4,4,4-hexafluoro-2-butene remaining in cylinder A was designated Sample 1-1. The 1,1,1,4,4,4-hexafluoro-2-butene gas remaining in cylinder A was then extracted from the upper outlet, and the concentrations of various metal impurities were measured using an inductively coupled plasma mass spectrometer. The results are shown in Table 1.

[0075] [Table 1]

[0076] Next, cylinder B was heated to approximately 0°C to form a liquid phase and a gas phase, and 300 g of 1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the upper outlet of cylinder B, where the gas phase was present, and transferred to cylinder C, which was under reduced pressure. The 100 g of 1,1,1,4,4,4-hexafluoro-2-butene remaining in cylinder B was designated Sample 1-2. The 1,1,1,4,4,4-hexafluoro-2-butene gas remaining in cylinder B was then extracted from the upper outlet, and the concentrations of various metal impurities were measured using an inductively coupled plasma mass spectrometer. The results are shown in Table 1.

[0077] Next, cylinder C was heated to approximately 0°C to form a liquid phase and a gas phase, and 200 g of 1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the upper outlet of cylinder C, where the gas phase was present, and transferred to cylinder D, which was under reduced pressure. The 100 g of 1,1,1,4,4,4-hexafluoro-2-butene remaining in cylinder C was designated Sample 1-3. The 1,1,1,4,4,4-hexafluoro-2-butene gas remaining in cylinder C was then extracted from the upper outlet, and the concentrations of various metal impurities were measured using an inductively coupled plasma mass spectrometer. The results are shown in Table 1.

[0078] Next, cylinder D was heated to approximately 0°C to form a liquid phase and a gas phase, and 100 g of 1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the upper outlet of cylinder D, where the gas phase was present, and transferred to cylinder E, which was under reduced pressure. The 100 g of 1,1,1,4,4,4-hexafluoro-2-butene remaining in cylinder D was designated Sample 1-4. The 1,1,1,4,4,4-hexafluoro-2-butene gas remaining in cylinder D was then extracted from the upper outlet, and the concentrations of various metal impurities were measured using an inductively coupled plasma mass spectrometer. The results are shown in Table 1.

[0079] Additionally, 100 g of 1,1,1,4,4,4-hexafluoro-2-butene in cylinder E was designated Sample 1-5. 1,1,1,4,4,4-hexafluoro-2-butene gas was extracted from the upper outlet of cylinder E, where the gas phase exists, and the concentrations of various metal impurities were measured using an inductively coupled plasma mass spectrometer. The results are shown in Table 1.

[0080] (Preparation Example 2) Samples 2-1 to 2-5 were prepared in the same manner as in Preparation Example 1, except that 1,1,1,2,4,4,4-heptafluoro-2-butene was used as the fluorobutene. The concentrations of various metal impurities in each sample were measured using an inductively coupled plasma mass spectrometer. The results are shown in Table 2.

[0081] [Table 2]

[0082] (Preparation Example 3) Samples 3-1 to 3-5 were prepared in the same manner as in Preparation Example 1, except that 3,3,4,4,4-pentafluoro-1-butene was used as the fluorobutene. The concentrations of various metal impurities in each sample were measured using an inductively coupled plasma mass spectrometer. The results are shown in Table 3.

[0083] [Table 3]

[0084] (Preparation Example 4) Samples 4-1 to 4-5 were prepared in the same manner as in Preparation Example 1, except that 2,3,3,4,4,4-hexafluoro-1-butene was used as the fluorobutene. The concentrations of various metal impurities in each sample were measured using an inductively coupled plasma mass spectrometer. The results are shown in Table 4.

[0085] [Table 4]

[0086] Example 1 A 1000 nm thick silicon oxide film, a 1000 nm thick silicon nitride film, and a 1000 nm thick photoresist film were formed on the surface of a semiconductor wafer so that each film was exposed on the surface, and this was used as a test specimen. The test specimen was then etched using 1,1,1,4,4,4-hexafluoro-2-butene (Sample 1-5).

[0087] The etching equipment used was an ICP etching equipment RIE-230iP manufactured by Samco Inc. Specifically, 1,1,1,4,4,4-hexafluoro-2-butene (Sample 1-5) was introduced into the chamber at a flow rate of 10 mL / min, oxygen gas at a flow rate of 10 mL / min, and argon at a flow rate of 30 mL / min, respectively, to prepare the etching gas in the chamber. A high-frequency voltage of 500 W was applied to generate plasma in the chamber. The specimen in the chamber was then etched under the etching conditions of a pressure of 3 Pa, a temperature of 20°C, and a bias power of 100 W.

[0088] After etching was completed, the specimens were removed from the chamber, and the thicknesses of the silicon oxide film, silicon nitride film, and photoresist film were measured to calculate the thickness loss from pre-etching. The etching rate of each film was calculated by dividing this loss by the etching time. The etching rate of the photoresist film was found to be less than 1 nm / min, that of the silicon oxide film was 64 nm / min, and that of the silicon nitride film was 57 nm / min. These results confirmed that the silicon oxide and silicon nitride films, which are the etching targets, are selectively etched compared to the photoresist film, which is the non-etching target.

[0089] (Examples 2 to 16 and Comparative Examples 1 to 4) The etching conditions and results in Examples 2 to 16 and Comparative Examples 1 to 4 are shown in Table 5 in comparison with Example 1. That is, etching was performed under the same conditions as in Example 1 except for the conditions shown in Table 5.

[0090] [Table 5]

[0091] The results of the above examples show that when the sum of the concentrations of copper, zinc, manganese, cobalt, and silicon contained in the etching gas is small, the etching target is selectively etched compared to the non-etching target, and the etching selectivity is 10 or more. On the other hand, the results of the above comparative examples show that when the sum of the concentrations of copper, zinc, manganese, cobalt, and silicon contained in the etching gas is large, the etching selectivity of the etching target relative to the non-etching target decreases, and the etching selectivity is less than 10. [Explanation of symbols]

[0092] 1. Fluorobutene gas supply unit 2. Dilution gas supply section 3. Fluorobutene gas flow control device 4. Dilution gas flow control device 5. Fluorobutene gas supply pipe 6. Dilution gas supply pipe 7. Fluorobutene gas pressure control device 8. Dilution gas pressure control device 10. Chamber 11 Stages 12. Material to be etched 13 Exhaust piping 14...Thermometer 15. Vacuum pump 16. Pressure gauge

Claims

1. General formula C 4 H x F y wherein x is 1 or more and 7 or less, y is 1 or more and 7 or less, and x+y is 8, An etching gas which contains or does not contain at least one of copper, zinc, manganese, cobalt, and silicon as a metal impurity, and in the case where the metal impurity is contained, the sum of the concentrations of copper, zinc, manganese, cobalt, and silicon is 5000 ppb by mass or less.

2. 2. The etching gas according to claim 1, wherein the etching gas further contains at least one of an alkali metal and an alkaline earth metal as the metal impurity, or does not contain the metal impurity, and when the metal impurity is contained, the sum of the concentrations of copper, zinc, manganese, cobalt, and silicon, and the alkali metal and alkaline earth metal is 10,000 ppb by mass or less.

3. An etching gas as described in Claim 2, wherein the alkali metal, when contained, is at least one of lithium, sodium, and potassium, and the alkaline earth metal is at least one of magnesium and calcium.

4. 4. The etching gas according to claim 1, wherein the fluorobutene is at least one selected from the group consisting of 1,1,1,4,4,4-hexafluoro-2-butene, 1,1,1,2,4,4,4-heptafluoro-2-butene, 3,3,4,4,4-pentafluoro-1-butene, and 2,3,3,4,4,4-hexafluoro-1-butene.

5. 5. An etching method comprising: an etching step of contacting the etching gas according to claim 1 with a member to be etched, the member having an etching object that is a target for etching with the etching gas and a non-etching object that is not a target for etching with the etching gas, and selectively etching the etching object compared to the non-etching object, wherein the etching object contains silicon.

6. 6. The etching method according to claim 5, further comprising, before the etching step, a metal impurity removing step of reducing the sum of the concentrations of copper, zinc, manganese, cobalt, and silicon contained in the etching gas to 5000 mass ppb or less.

7. 7. The etching method according to claim 5, wherein the etching gas is a mixed gas containing the fluorobutene and a dilution gas.

8. 8. The etching method according to claim 7, wherein the dilution gas is at least one gas selected from the group consisting of nitrogen gas, helium, argon, neon, krypton, and xenon.

9. A method for manufacturing a semiconductor element, comprising the steps of: manufacturing a semiconductor element using the etching method according to any one of claims 5 to 8; the member to be etched is a semiconductor substrate having the etching object and the non-etching object, A method for manufacturing a semiconductor device, comprising a processing step of removing at least a part of the etching object from the semiconductor substrate by etching.

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