Etching method

Abstract

Provided is an etching method by which carbon monoxide and high GWP gas are hardly generated during etching. This etching method is a method in which at least one among a silicon material having silicon and a carbon material having carbon is etched using an acid fluoride-containing etching gas, and the total content of sodium, aluminum, potassium, calcium, chromium, manganese, iron, cobalt, nickel, copper, and molybdenum contained in the etching gas is at most 100 ppb by mass.

Description

Etching Method

[0001] The present disclosure relates to etching methods.

[0002] In semiconductor manufacturing processes, etching is performed using dry etching equipment, and high-GWP gases such as carbon tetrafluoride and nitrogen trifluoride are used as etching gases. GWP (Global Warming Potential) refers to global warming potential. The etching exhaust gas discharged from the dry etching equipment after etching may contain gases harmful to the environment and humans, such as high-GWP gases and carbon monoxide. Therefore, it is undesirable to directly release the etching exhaust gas into the atmosphere; it is preferable to neutralize the harmful gases before releasing them into the atmosphere. On the other hand, if the etching exhaust gas contains a large amount of harmful gases, the equipment required for neutralization becomes excessively large, and therefore, etching techniques that minimize the generation of harmful gases are required. For example, Patent Document 1 discloses a plasma etching gas containing acid fluoride and oxygen gas as a substitute for high-GWP gases.

[0003] Japanese Patent Publication No. 4112198

[0004] However, the technique disclosed in Patent Document 1 has a problem in that a large amount of high GWP gas is generated during etching when the mixture ratio of acid fluoride and oxygen gas exceeds a certain range. Furthermore, there is also a problem in that carbon monoxide is likely to be generated when acid fluoride is used as an etching gas. An object of the present disclosure is to provide an etching method that is less likely to generate carbon monoxide and high GWP gas during etching.

[0005] In order to solve the above problems, one aspect of the present disclosure is as follows [1] to [6]: [1] A method for etching at least one of a silicon material containing silicon and a carbon material containing carbon, using an etching gas containing an acid fluoride, wherein the etching gas contains sodium, aluminum, potassium, calcium, chromium, manganese, iron, cobalt, nickel, copper, and molybdenum at a total content of 100 ppb by mass or less.

[0006] [2] The etching method according to [1], wherein the acid fluoride is at least one of carbonyl fluoride, oxalyl fluoride, and trifluoroacetyl fluoride. [3] The etching method according to [1] or [2], wherein the carbon material has a carbon content of 20% by mass or more and 100% by mass or less. [4] The etching method according to any one of [1] to [3], wherein the silicon material has a silicon content of 30% by mass or more.

[0007] [5] The etching method according to any one of [1] to [4], wherein the silicon material is at least one of silicon oxide, silicon nitride, and polysilicon. [6] The etching method according to any one of [1] to [5], wherein the etching is carried out using a plasma etching apparatus or a remote plasma etching apparatus.

[0008] According to the etching method according to the present disclosure, carbon monoxide and high GWP gases are less likely to be generated during etching.

[0009] Fig. 1 is a schematic diagram of an example of a plasma etching apparatus for explaining an embodiment of an etching method according to the present disclosure; Fig. 2 is a schematic diagram of an example of a remote plasma etching apparatus for explaining an embodiment of an etching method according to the present disclosure; Fig. 3 is a schematic diagram showing an example of a purification apparatus for purifying an acid fluoride; Fig. 4 is a schematic diagram illustrating an example of a preparation apparatus for preparing a sample for metal analysis.

[0010] An embodiment of the present disclosure will be described below. Note that this embodiment shows an example of the present disclosure, and the present disclosure is not limited to this embodiment. Furthermore, various modifications or improvements can be made to this embodiment, and such modifications or improvements may also be included in the present disclosure.

[0011] The etching method according to the present embodiment is a method for etching at least one of a silicon material containing silicon and a carbon material containing carbon using an etching gas containing an acid fluoride, wherein the etching gas contains sodium, aluminum, potassium, calcium, chromium, manganese, iron, cobalt, nickel, copper, and molybdenum at a total content of 100 ppb by mass or less. According to the etching method according to the present embodiment, carbon monoxide and high GWP gases are unlikely to be generated during etching.

[0012] For example, an etching gas containing an acid fluoride can be brought into contact with an etching target member having an etching object to be etched by the etching gas in the presence of plasma, whereby the etching target member is at least one of a silicon material containing silicon (Si) and a carbon material containing carbon (C).

[0013] When the etching gas is brought into contact with a material to be etched, the acid fluoride in the etching gas reacts with silicon and carbon in the material to be etched, causing etching of the material to proceed. On the other hand, materials to be etched react with oxygen atoms and oxygen-containing compounds (active oxygen molecules, ozone, etc.) produced by decomposition of the acid fluoride, causing etching of the material to proceed.

[0014] However, when an acid fluoride and a fluorocarbon coexist in an etching gas, carbon is supplied from the fluorocarbon, which captures the oxygen-containing compound and suppresses the etching of the carbon material, so that etching of the non-etching target hardly progresses. Thus, according to the etching method of this embodiment, the etching target can be selectively etched compared to the non-etching target.

[0015] For example, etching can be performed so that the ratio of the etching rate of the object to be etched to the etching rate of the object not to be etched is equal to or greater than 2. Furthermore, from the viewpoint of more stable control of etching, etching can be performed so that the etching rate ratio is equal to or greater than 4, and depending on the etching conditions, etching can be performed so that the etching rate ratio is equal to or greater than 10.

[0016] In this disclosure, 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 material or a carbon material of the etched member to a predetermined film thickness), and also means removing residues and deposits made of the etching target material from the etched member to clean it.

[0017] 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 object to be etched, and the method includes removing at least a part of the object to be etched from the semiconductor substrate by etching.

[0018] Therefore, if the etching method according to this embodiment is applied to the manufacturing process of a semiconductor device, it becomes possible to, for example, transfer a pattern formed in a photoresist to a film made of a silicon material or a carbon material, or to remove a film or residue made of a silicon material or a carbon material that is present on the member to be etched or on the inner surface of a chamber.

[0019] The etching method according to this embodiment will be described in further detail below. In the etching method according to this embodiment, etching may be performed using a plasma etching apparatus or a remote plasma etching apparatus. That is, the etching in the etching method according to this embodiment may be plasma etching in which plasma is generated in a chamber in which a member to be etched is placed, or remote plasma etching in which plasma is generated in a plasma generation chamber separated from the chamber in which the member to be etched is placed.

[0020] The type of plasma source for plasma etching is not particularly limited, and commercially available devices may be used, such as high-frequency discharge plasmas such as inductively coupled plasma (ICP) and capacitively coupled plasma (CCP), and microwave discharge plasmas such as electron cyclotron resonance plasma (ECRP).

[0021] Remote plasma etching is an etching method in which etching is performed inside a chamber using plasma of an etching gas generated outside the chamber by a plasma generation source. Etching using remote plasma makes it easier to etch the object to be etched while minimizing damage to the object.

[0022] [Etching Gas] The etching gas used in the etching method according to this embodiment contains an acid fluoride, and may further contain at least one of a fluorocarbon, a rare gas, and an additive gas.

[0023] Examples of rare gases include helium (He), neon (Ne), argon (Ar), xenon (Xe), and krypton (Kr). Examples of additive gases include nitrogen gas (N), hydrogen gas (H), oxygen gas (O), nitrous oxide gas (NO), and halogenated hydrocarbon gas (C). m H n Xo , X is any of Cl, Br, and I, and m, n, and o are coefficients, provided that n+o≦2m+2), hydrogen fluoride (HF), hydrogen chloride (HCl), and hydrogen bromide (HBr).

[0024] [Fluorocarbon] The fluorocarbon that can be used in the etching method according to this embodiment is a compound having a carbon atom and a fluorine atom (F) in the molecule, and is a compound other than an acid fluoride. From the viewpoint of availability, the number of carbon atoms in the fluorocarbon is preferably 1 to 7, more preferably 1 to 5, and even more preferably 1 to 4. One type of fluorocarbon may be used alone, or two or more types may be used in combination. Note that the fluorocarbon may have elements other than fluorine atoms and carbon atoms in the molecule, such as chlorine atoms (Cl), bromine atoms (Br), iodine atoms (I), hydrogen atoms (H), nitrogen atoms (N), oxygen atoms (O), sulfur atoms (S), etc.

[0025] Examples of fluorocarbons include tetrafluoromethane (CF), trifluoromethane (CHF), difluoromethane (CHF), fluoromethane (CHF), dibromodifluoromethane (CBrF), iodotrifluoromethane (CFI), hexafluoroethane (CF), chlorotrifluoroethylene (CFCl), 1-chloro-1-fluoroethylene (CFCl), bromotrifluoroethylene (CFCl), 1-bromo-1- fluoroethylene (C2H2FBr), octafluoropropane (C3F8), octafluorocyclobutane (c-C4F8), octafluoro-2-butene (C4F8, E- and Z-forms), hexafluoro-1,3-butadiene (C4F6), 1,1,1,3,3,3-hexafluoro-2-butene (C4H2F6, E- and Z-forms), perfluorocyclopentene (C5F8), hexafluorobenzene (C6F6), octafluorotoluene (C7F8), and the like.

[0026] [Rare Gas Concentration] When a rare gas is contained in the etching gas, plasma may be easily generated. The concentration of the rare gas in the etching gas is preferably more than 0 vol% and not more than 99 vol%, more preferably 5 vol% to 90 vol%, and even more preferably 10 vol% to 85 vol%. If the concentration of the rare gas contained in the etching gas is within the above range, uniform plasma can be easily generated stably, making it easier to uniformly etch the object to be etched.

[0027] [Concentration of Additive Gas] Adding an additive gas to the etching gas can increase the etching rate of the material to be etched and remove deposits formed on the material to be etched, depending on the type of additive gas. For example, adding oxygen gas, nitrogen gas, nitrous oxide, etc. may make it easier to remove deposits formed on the material to be etched. The optimal concentration of the additive gas in the etching gas varies depending on the desired effect, but is preferably, for example, more than 0% by volume and not more than 99% by volume, more preferably 2% by volume to 60% by volume, and even more preferably 5% by volume to 50% by volume.

[0028] [Acid Fluoride] An acid fluoride is a compound having a functional group *-C(=O)F in the molecule. Here, "*" means any atom or atomic group. The number of carbon atoms in the acid fluoride is preferably 5 or less, more preferably 3 or less, and even more preferably 2 or less.

[0029] Examples of acid fluorides include carbonyl fluoride (COF), oxalyl fluoride (COF), trifluoroacetyl fluoride (CFCOF), formyl fluoride, carbonyl chloride fluoride, acetyl fluoride, 2,2,3,3,3-pentafluoropropanoyl fluoride, 2,2,3,3,4,4,4-heptafluorobutanoyl fluoride, 2,2,3,3,4,4,5,5,5-nonafluoropentanoyl fluoride, 2,2,3,4,4,4-hexafluoro-3-(trifluoromethyl)butanoyl fluoride, and 3,3,3-trifluoro-2,2-bis(trifluoromethyl)propanoyl fluoride.

[0030] Among these acid fluorides, carbonyl fluoride, oxalyl fluoride, and trifluoroacetyl fluoride are preferred from the viewpoint of easy availability, and carbonyl fluoride is more preferred. The acid fluorides may be used alone or in combination of two or more. That is, the acid fluoride contained in the etching gas may be at least one of carbonyl fluoride, oxalyl fluoride, and trifluoroacetyl fluoride.

[0031] [Metal Impurities] The presence of metals in the etching gas may change the active species generated from acid fluoride. As a result, the amount of high GWP gases such as carbon monoxide (CO) and carbon tetrafluoride (CF4) contained in the etching exhaust gas may increase, which may have a negative impact on the environment. Therefore, it is preferable that the concentration of metals in the etching gas is as low as possible, and if the etching gas contains metals, it is preferable to remove them as much as possible by purification. As a method for removing metals, common purification methods such as distillation, sublimation, filtration, membrane separation, adsorption, recrystallization, and chromatography can be used.

[0032] The types of metals whose concentrations should be reduced correspond to metal elements in the third to sixth periods of the periodic table, such as sodium (Na), magnesium (Mg), aluminum (Al), potassium (K), calcium (Ca), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), antimony (Sb), molybdenum (Mo), and tungsten (W).

[0033] Of these metals, sodium, aluminum, potassium, calcium, chromium, manganese, iron, cobalt, nickel, copper, and molybdenum are often contained in the materials of components that come into contact with the etching gas (e.g., metal piping, storage containers), and therefore are likely to be mixed into the etching gas.

[0034] Therefore, the etching gas may or may not contain at least one metal selected from sodium, aluminum, potassium, calcium, chromium, manganese, iron, cobalt, nickel, copper, and molybdenum as an impurity. If the etching gas contains any of the metals, the total content of all the metals contained therein must be 100 ppb by mass or less, and preferably 50 ppb by mass or less.

[0035] This reduces the generation of carbon monoxide and high GWP gases when etching is performed using an etching gas containing an acid fluoride, thereby suppressing the emission of carbon monoxide and high GWP gases in the etching exhaust gas generated during etching. For example, the amount of carbon monoxide emitted can be 50% by volume or less of the amount of acid fluoride used in etching. Also, the amount of carbon tetrafluoride emitted can be 20% by volume or less of the amount of acid fluoride used in etching.

[0036] [Pressure Conditions for Plasma Etching] The pressure conditions for etching in the etching method according to this embodiment are not particularly limited, but when the etching is plasma etching, the pressure is preferably from 0.1 Pa to 3 kPa, more preferably from 0.5 Pa to 30 Pa, and even more preferably from 1 Pa to 10 Pa. If the pressure conditions are within the above ranges, plasma can be easily generated stably.

[0037] For example, the member to be etched can be placed in a chamber and etched while passing an etching gas through the chamber, and the pressure inside the chamber during the passage of the etching gas can be set to 0.1 Pa or more and 3 kPa or less. The flow rate of the etching gas can be set appropriately so that the pressure inside the chamber is kept constant, depending on the size of the chamber and the capacity of the exhaust equipment for reducing the pressure inside the chamber.

[0038] [Pressure Conditions for Remote Plasma Etching] The pressure conditions for etching in the etching method according to this embodiment are not particularly limited, but when the etching is remote plasma etching, the pressure is preferably from 10 Pa to 6000 Pa, more preferably from 50 Pa to 3000 Pa, and even more preferably from 100 Pa to 2500 Pa. If the pressure conditions are within the above ranges, plasma can be easily generated stably, and the composition ratio of active species can easily be stabilized.

[0039] For example, the member to be etched can be placed in a chamber and etched while passing an etching gas through the chamber, and the pressure inside the chamber while passing the etching gas can be set to 10 Pa or more and 6000 Pa or less. The flow rate of the etching gas can be set appropriately so that the pressure inside the chamber is kept constant, depending on the size of the chamber and the capacity of the exhaust equipment for reducing the pressure inside the chamber.

[0040] [Temperature Conditions for Etching] The temperature conditions for etching in the etching method according to this embodiment are not particularly limited, but whether the etching is plasma etching or remote plasma etching, the temperature is preferably 0° C. or higher and 200° C. or lower, more preferably 5° C. or higher and 170° C. or lower, and even more preferably 20° C. or higher and 150° C. or lower.

[0041] If the temperature condition is within the above range, the acid fluoride can exist in a gaseous state and the etching rate of the material to be etched tends to be higher. Here, the temperature in the temperature condition refers to the temperature of the material to be etched, but the temperature of a stage that supports the material to be etched and is installed in the chamber of the etching apparatus can also be used.

[0042] [Subject to be etched] The subject to be etched is at least one of a silicon material containing silicon and a carbon material containing carbon, but may be formed only from silicon or carbon, may have a portion formed only from silicon or carbon and a portion formed from another material, or may be formed from a mixture of silicon or carbon and another material.

[0043] The silicon material refers to a compound consisting of only silicon and containing no other elements, or a compound containing silicon and other elements. Examples of silicon materials include polysilicon (Poly-Si), silicon oxide (SiO x , x is an arbitrary coefficient, for example, SiO2), silicon nitride (Si c N d , c and d are arbitrary coefficients, for example, Si3N4), silicon oxynitride (SiO a N b , a and b are arbitrary coefficients), silicon germanium (Si y Ge 100-y (where y is any number greater than 0 and less than 100), silicon carbide (SiC), etc. The silicon material is preferably at least one of silicon oxide, silicon nitride, and polysilicon. The silicon material may be used alone or in combination of two or more.

[0044] The silicon content of the silicon material 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.

[0045] The carbon material refers to a compound consisting of only carbon and containing no other elements, or a compound containing carbon and other elements. Examples of the carbon material include amorphous carbon, spin-on carbon, carbon-doped silicon oxide (SiOC), photoresist, etc. The carbon material may be used alone or in combination of two or more.

[0046] The carbon content of the carbon material is not particularly limited, but the lower limit is preferably 20 mass%, more preferably 40 mass%, and even more preferably 50 mass%, and the upper limit is preferably 100 mass%, more preferably less than 100 mass%, and even more preferably 95 mass%.

[0047] The preferred range of the carbon content in the carbon material may be any combination of the above upper and lower limits. For example, the carbon content in the carbon material is preferably 20% by mass or more and 100% by mass or less, more preferably 40% by mass or more and less than 100% by mass, and even more preferably 50% by mass or more and 95% by mass or less.

[0048] The carbon-doped silicon oxide is a compound containing carbon, oxygen, and silicon atoms, but may further contain atoms other than the carbon, oxygen, and silicon atoms, such as hydrogen atoms.

[0049] Photoresist refers to a photosensitive composition whose physical properties, including solubility, change when exposed to light, an electron beam, or the like. 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 chain olefin, cyclic olefin, styrene, vinylphenol, acrylic acid, methacrylate, epoxy, melamine, and glycol.

[0050] The following describes an example of etching a polysilicon film, a silicon oxide film, a silicon nitride film, and a photoresist film formed on the surface of a substrate (corresponding to a member to be etched) using an etching apparatus. The etching apparatus in Fig. 1 is a plasma etching apparatus using an ICP as a plasma source. The etching apparatus in Fig. 2 is a remote plasma etching apparatus using a remote plasma as a plasma source.

[0051] The plasma etching apparatus of FIG. 1 includes a chamber 1 in which plasma etching is performed, a lower electrode 2 that supports a substrate 20 to be plasma etched inside the chamber 1, a bias power supply (not shown) that applies bias power to the lower electrode 2, an RF coil 15 that forms an electric field and a magnetic field inside the chamber 1 to convert an etching gas into plasma, a source power supply (not shown) that applies high-frequency source power to the RF coil 15, a vacuum pump 21 that reduces the pressure inside the chamber 1, a pressure gauge 14 that measures the pressure inside the chamber 1, a sensor 16 that captures plasma light emission generated as plasma is generated, a spectroscope 17 that disperses the plasma light emission captured by the sensor 16 to monitor changes over time in the plasma light emission, and an infrared spectrometer 30 that analyzes the composition of exhaust gas discharged from the chamber 1.

[0052] A polysilicon film, a silicon oxide film, a silicon nitride film, and a photoresist film are formed on the surface of the substrate 20. For example, a CCD (Charge-Coupled Device) image sensor can be used as the sensor 16. However, instead of providing the sensor 16 and the spectroscope 17, a sight window may be provided in the chamber 1, and the interior of the chamber 1 may be visually observed through the sight window to confirm the change in plasma light emission over time.

[0053] The chamber 1 also includes an etching gas supply unit that supplies an etching gas to the inside of the chamber 1. The etching gas supply unit includes an acid fluoride gas supply unit 3 that supplies an acid fluoride gas, an inert gas supply unit 4 that supplies an inert gas, an additive gas supply unit 5 that supplies an additive gas, an etching gas supply pipe 11 that connects the acid fluoride gas supply unit 3 to the chamber 1, an inert gas supply pipe 12 that connects the inert gas supply unit 4 to an intermediate portion of the etching gas supply pipe 11, and an additive gas supply pipe 13 that connects the additive gas supply unit 5 to an intermediate portion of the etching gas supply pipe 11.

[0054] When acid fluoride gas is supplied to the chamber 1 as an etching gas, the acid fluoride gas is sent from the acid fluoride gas supply unit 3 to the etching gas supply pipe 11, so that the acid fluoride gas is supplied to the chamber 1 via the etching gas supply pipe 11.

[0055] When a mixed gas of acid fluoride gas, inert gas, and additive gas is supplied as the etching gas, acid fluoride gas is fed from the acid fluoride gas supply unit 3 to the etching gas supply pipe 11, and the inert gas is fed from the inert gas supply unit 4 to the etching gas supply pipe 11 via the inert gas supply pipe 12, and the additive gas is fed from the additive gas supply unit 5 to the etching gas supply pipe 11 via the additive gas supply pipe 13. In this way, the acid fluoride gas, the additive gas, and the inert gas are mixed in the middle of the etching gas supply pipe 11 to form a mixed gas, and this mixed gas is supplied to the chamber 1 via the etching gas supply pipe 11.

[0056] The pressure in the chamber 1 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, -3 The pressure is preferably from 0.1 Pa to less than 100 kPa, more preferably from 0.1 Pa to 50 kPa, even more preferably from 0.3 Pa to 15 Pa, and particularly preferably from 1 Pa to 10 Pa.

[0057] When plasma etching is performed using such a plasma etching apparatus, a substrate 20 is placed on the lower electrode 2 disposed inside the chamber 1, and the pressure inside the chamber 1 is reduced by a vacuum pump 21 to, for example, 1 Pa or more and 10 Pa or less, and then an etching gas is supplied into the chamber 1 by an etching gas supply unit. When a high-frequency (e.g., 13.56 MHz) source power is applied to the RF coil 15, an electric field and a magnetic field are formed inside the chamber 1, accelerating electrons. These accelerated electrons collide with unsaturated compound molecules in the etching gas, generating new ions and electrons, resulting in a discharge and forming plasma. The generation of plasma can be confirmed using a sensor 16 and a spectrometer 17.

[0058] When the plasma is generated, the etching target formed on the surface of the substrate 20 is etched. The amount of the etching gas supplied to the chamber 1 and the concentration of the acid fluoride in the etching gas (mixed gas) can be adjusted by controlling the flow rates of the acid fluoride, the inert gas, and the additive gas using mass flow controllers (not shown) installed in the etching gas supply pipe 11, the inert gas supply pipe 12, and the additive gas supply pipe 13, respectively.

[0059] The exhaust gas generated by etching is introduced from the exhaust port of the vacuum pump 21 through a connecting pipe 31 into an infrared spectrometer 30, where the composition of the exhaust gas is analyzed. After analysis, the exhaust gas is released into the atmosphere from the exhaust port of the infrared spectrometer 30 through a detoxification tower (not shown). In analyzing the composition of the exhaust gas, it is not necessary to introduce the entire amount of exhaust gas generated by etching into the infrared spectrometer 30; a portion of the exhaust gas may be sampled from a branch pipe and introduced into the infrared spectrometer 30.

[0060] 2 includes a chamber 1 in which etching is performed, a lower electrode (stage) 2 that supports a substrate 20 to be etched inside the chamber 1, a remote plasma device 19 that generates an electric field and a magnetic field to convert an etching gas into plasma, a source power supply (not shown) that applies high-frequency source power to the remote plasma device 19, a vacuum pump 21 that reduces the pressure inside the chamber 1, a pressure gauge 14 that measures the pressure inside the chamber 1, and an infrared spectrometer 30 that analyzes the composition of the exhaust gas discharged from the chamber 1. The substrate 20 has a polysilicon film, a silicon oxide film, a silicon nitride film, and a photoresist film formed on its surface.

[0061] When remote plasma etching is performed using such a remote plasma etching device, a substrate 20 is placed on the lower electrode 2 disposed inside the chamber 1, and the pressure inside the chamber 1 and the remote plasma device 19 is reduced by the vacuum pump 21 to, for example, 1 Pa or more and 10 Pa or less, and then an etching gas is supplied into the remote plasma device 19 by the etching gas supply unit. The etching gas is then converted into plasma in the remote plasma device 19 and supplied into the chamber 1. As a result, the etching target formed on the surface of the substrate 20 is etched. The generation of plasma can be confirmed using a remote plasma controller (not shown).

[0062] Since the remote plasma etching using the remote plasma etching apparatus of Fig. 2 is almost the same as the plasma etching using the plasma etching apparatus of Fig. 1 except for the use of remote plasma, a description of the same parts as those in the plasma etching using the plasma etching apparatus of Fig. 1 will be omitted and only the differences will be described. In Fig. 1 and Fig. 2, the same or corresponding parts are denoted by the same reference numerals.

[0063] The present disclosure will be described in more detail below with reference to examples and comparative examples. (Preparation Example 1) Acid fluoride was purified using the purification apparatus shown in Figure 3. A source container 100 (manganese steel, volume 3 L) filled with 1 kg of carbonyl fluoride was connected to the inlet side of a gas filter 102 (Wafergard (trade name) manufactured by Entegris Inc.) via piping 101 made of SUS316. A main valve was attached to the source container 100.

[0064] The outlet side of the gas filter 102 is connected to one branch pipe of a cross-shaped branch pipe 103 made of SUS316. The other three branch pipes of the branch pipe 103 are connected to a vacuum pump 60, a vacuum gauge 40, and a receiving vessel 50 (manganese steel, capacity 3 L), respectively. The source vessel 100, the pipe 101, and the branch pipe 103 can be heated to any desired temperature by an external heater (not shown).

[0065] A vacuum pump line valve 300 is provided in the middle of the branch pipe to which the vacuum pump 60 is connected. The receiving vessel 50 is a vessel for storing acid fluoride purified by passing it through a gas filter 102, and is placed on a receiving vessel mass meter 41 for measuring the mass of the receiving vessel 50. A main valve is also attached to the receiving vessel 50.

[0066] The raw material container 100 was heated to 70°C, and the pipe 101 and the branch pipe 103 were heated to 100°C. The master valve of the raw material container 100 was closed and the master valve of the receiving container 50 was opened. Then, the vacuum pump line valve 300 was opened, and the pressure inside the pipe 101, the branch pipe 103, and the receiving container 50 was reduced by the vacuum pump 60 until the pressure inside them became 10 Pa or less.

[0067] Thereafter, the vacuum pump line valve 300 was closed, and the main valve of the source container 100 and the main valve of the branch pipe 103 were opened to transfer 500 g of carbonyl fluoride from the source container 100 to the receiving container 50. The unpurified carbonyl fluoride in the source container 100 was designated Sample 1-1, and the carbonyl fluoride that had been purified and filled into the receiving container 50 was designated Sample 1-2. Sample 1-2 was further purified by the same procedure as above. The carbonyl fluoride that had been purified twice was designated Sample 1-3.

[0068] The metal concentration (referred to as M) contained in Sample 1-1 was determined as follows. First, a mixed solution of acid fluoride and aqueous nitric acid solution was prepared using the preparation apparatus shown in FIG. 4. The method for preparing the mixed solution is described below. A raw material container 100 filled with acid fluoride was removed from the purification apparatus shown in FIG. 3 and attached to the preparation apparatus shown in FIG. 4. That is, the master valve of the raw material container 100 was connected to a pressure regulator 110 and a mass flow controller 75 arranged in series via piping 76, and the mass flow controller 75 was connected to a nitric acid container 79 via a connecting piping 77. The nitric acid container 79 contained 40 g of an aqueous nitric acid solution 78 with a concentration of 1% by mass, and the tip of the connecting piping 77 was placed in the aqueous nitric acid solution 78. The nitric acid container 79 was also provided with an exhaust port 80.

[0069] Carbonyl fluoride was sent from source container 100 to nitric acid container 79 via pipe 76, and 3.4 L (10 g, designated A) of carbonyl fluoride was bubbled into aqueous nitric acid solution 78 in nitric acid container 79 at a flow rate of 40 mL / min. Next, a 1% by mass aqueous nitric acid solution was added to nitric acid container 79 so that the mass of the contents became 50 g (designated B), thereby obtaining a mixed solution of acid fluoride and aqueous nitric acid solution. One gram of the aqueous layer of this mixed solution was sampled and analyzed for metals using an inductively coupled plasma mass spectrometer. The signal intensities of sodium, aluminum, potassium, calcium, chromium, manganese, iron, cobalt, nickel, copper, and molybdenum contained in the mixed solution were measured (designated y). The concentrations of each metal were calculated from the signal intensities using a calibration curve, and the sum of the calculated values ​​was used to determine the total metal concentration.

[0070] The calibration curves used were prepared as follows. That is, nitric acid standard solutions with metal concentrations of 0 mass ppb (no metal), 10 mass ppb, and 300 mass ppb were prepared and analyzed using an inductively coupled plasma mass spectrometer. Then, a calibration curve was prepared by plotting the metal concentration on the horizontal axis and the signal intensity on the vertical axis, and the slope (denoted as a) and intercept (denoted as b) were determined. The same procedure was performed for sodium, aluminum, potassium, calcium, chromium, manganese, iron, cobalt, nickel, copper, and molybdenum, and a calibration curve for each metal was prepared.

[0071] The concentration M of the metal contained in the acid fluoride can be calculated by the following formula: M = {(y - b) / a} x (B / A) Similarly, the concentration of each metal contained and its sum were determined for Samples 1-2 and 1-3. The analysis results for Samples 1-1, 1-2, and 1-3 are shown in Table 1.

[0072]

[0073] (Preparation Examples 2 to 4) Oxalyl fluoride (Preparation Example 2), trifluoroacetyl fluoride (Preparation Example 3), and nitrogen trifluoride (Preparation Example 4) were each purified in the same manner as in Preparation Example 1. Then, in the same manner as in Preparation Example 1, the concentrations of each metal contained in the unpurified sample and the sample that had been purified once were determined, along with their sum total. The results are shown in Table 1.

[0074] The unpurified oxalyl fluoride is designated Sample 2-1, and the oxalyl fluoride that has been purified once is designated Sample 2-2. The unpurified trifluoroacetyl fluoride is designated Sample 3-1, and the trifluoroacetyl fluoride that has been purified once is designated Sample 3-2. The unpurified nitrogen trifluoride is designated Sample 4-1, and the nitrogen trifluoride that has been purified once is designated Sample 4-2.

[0075] Example A1 Plasma etching of a silicon oxide substrate was carried out using an ICP etching apparatus RIE-200iP manufactured by Samco Inc., which has a configuration similar to that of the plasma etching apparatus shown in Figure 1. The silicon oxide substrate was a 1 cm square silicon substrate (manufactured by Seiren KST Co., Ltd.) on which a silicon oxide (SiO) film with a thickness of 800 nm was formed.

[0076] The chamber volume of the ICP etching equipment is 46,000 cm 3 The etching gas was a mixed gas of carbonyl fluoride gas and argon gas for sample 1-2. The flow rate of carbonyl fluoride gas was set to 20 sccm and the flow rate of argon to 80 sccm, so that the concentration of carbonyl fluoride in the etching gas was adjusted to 20% by volume. Here, sccm is the volumetric flow rate (cm) per minute normalized under the conditions of 0°C and 1 atmosphere. 3 ) The concentrations of metals contained in the argon used here were all below the detection limit. Since the detection limit for metals is 0.1 mass ppb, the effect of argon on the concentration of metals in the etching gas was ignored.

[0077] The metal concentration in the etching gas was calculated by the following formula: Metal concentration in etching gas (mass ppb) = Metal concentration in acid fluoride (mass ppb) × {Flow rate of acid fluoride / (Flow rate of acid fluoride + Flow rate of argon + Flow rate of added gas)}

[0078] Plasma etching was performed with the process pressure inside the chamber set to 3 Pa, the source power set to 500 W, the bias power set to 200 W, and the substrate temperature set to 20° C. The flow rate of carbonyl fluoride gas, the flow rate of argon, the process pressure, the source power, and the bias power were all constantly monitored, and it was confirmed that there was no difference between the set value and the actual value. The results are shown in Table 2.

[0079]

[0080] The amounts of carbon monoxide and carbon tetrafluoride emitted from the exhaust gas discharged from the exhaust port of the ICP etching apparatus were measured using an infrared spectrometer (Nicolet iS5 manufactured by Thermo Fisher Scientific) connected in series to the exhaust port of the vacuum pump. The measurement conditions were as follows:

[0081] Measurement temperature: 27°C Measurement pressure: atmospheric pressure Cell length: 10 cm Window plate: silver chloride Measurement wavelength: carbon monoxide 2172 cm -1 Carbon tetrafluoride 1281 cm -1 Absorption coefficient: carbon monoxide 833333, carbon tetrafluoride 5533

[0082] The emissions of carbon monoxide and carbon tetrafluoride in the exhaust gas discharged from the exhaust port of the ICP etching device were calculated using the following formulas: Emission amount of carbon monoxide (mL / min) = Emission amount of exhaust gas (mL / min) × Absorbance of carbon monoxide (abs) × Absorption coefficient of carbon monoxide (ppm cm / abs) / Cell length (cm) Emission amount of carbon tetrafluoride (mL / min) = Emission amount of exhaust gas (mL / min) × Absorbance of carbon tetrafluoride (abs) × Absorption coefficient of carbon tetrafluoride (ppm cm / abs) / Cell length (cm).

[0083] Furthermore, greenhouse gas emissions were calculated from the emissions of carbon monoxide and carbon tetrafluoride. The calculation method is as follows. However, the global warming potentials of carbon monoxide and carbon tetrafluoride were set to 3 and 7390, respectively. Greenhouse gas emissions = global warming potential of carbon monoxide × carbon monoxide emissions (mL / min) + global warming potential of carbon tetrafluoride × carbon tetrafluoride emissions (mL / min).

[0084] The film thickness of the etching target was measured using a Filmetrics Reflectance Spectroscopic Film Thickness Meter F20. The etching rates of the etching target and non-etching target were calculated by subtracting the film thickness after etching from the film thickness before etching and dividing the result by the etching time. The film thickness measurement conditions were as follows: the measurement atmosphere was air, and the measurement temperature was 25°C. The measurement wavelength range was a wavelength range in which the Goodness of Fit was 0.9 or higher, and specifically, the following wavelength range was used as a guide: that is, 300 to 1100 nm for silicon oxide.

[0085] (Examples A2 to A20 and Comparative Examples A1 to A6) Plasma etching was performed in the same manner as in Example A1, except that the type of etching gas and the etching conditions were different as shown in Table 2. The etching rate of the object to be etched and the emissions of carbon monoxide and carbon tetrafluoride contained in the etching exhaust gas were measured, and the greenhouse gas emissions were calculated. The results are shown in Table 2. In Examples A12 to A18, an additive gas was added to the etching gas, but the metal content of the additive gas was below the detection limit in each case, so in calculating the metal content of the etching gas, the additive gas was considered to contain no metal.

[0086] (Comparative Examples A7 and A8) Plasma etching was performed in the same manner as in Example A1, except that nitrogen trifluoride (Sample 4-1 and Sample 4-2) was used to prepare the etching gas instead of acid fluoride, and the etching rate of the object to be etched and the amount of nitrogen trifluoride emitted in the etching exhaust gas were measured, and the amount of greenhouse gas emissions was calculated. The results are shown in Table 2.

[0087] The greenhouse gas emissions were calculated according to the following formula, where the global warming potential of nitrogen trifluoride was set to 17,200. Greenhouse gas emissions = global warming potential of nitrogen trifluoride × emissions of nitrogen trifluoride (mL / min)

[0088] The results of Examples A1 and A2 and Comparative Example A1 show that the emissions of carbon monoxide and carbon tetrafluoride in the etching exhaust gas were suppressed by reducing the content of metals contained in carbonyl fluoride. In particular, Example A2, in which the content of metals contained in carbonyl fluoride was lower, showed a greater suppression of emissions of carbon monoxide and carbon tetrafluoride.

[0089] The results of Examples A3 to A5 and Comparative Examples A2 to A4 show that by reducing the metal content in carbonyl fluoride, the amount of carbon monoxide and carbon tetrafluoride emitted in the etching exhaust gas was suppressed, even when the etching target was silicon nitride, polysilicon, or photoresist. The results of Examples A6 to A11 show that the amount of carbon monoxide and carbon tetrafluoride emitted in the etching exhaust gas was equivalent to that of Example A1, even when the etching pressure, source power, acid fluoride concentration in the etching gas, and substrate temperature were changed.

[0090] The results of Examples A12 to A18 show that the addition of additive gases (oxygen gas, nitrogen gas, nitrous oxide) to the etching gas significantly suppressed the emissions of carbon monoxide and carbon tetrafluoride in the etching exhaust gas. It also shows that the addition of additive gases to the etching gas improved the etching rates of silicon nitride and photoresist. This suggests that the addition of an oxidizing gas changed the composition of active species in the plasma.

[0091] From the results of Examples A19 and A20 and Comparative Examples A5 and A6, it can be seen that even when oxalyl fluoride or trifluoroacetyl fluoride was used as the acid fluoride, the emissions of carbon monoxide and carbon tetrafluoride in the etching exhaust gas were suppressed by reducing the content of the contained metals.

[0092] The results of Comparative Examples A7 and A8 show that when the etching gas is prepared using nitrogen trifluoride instead of acid fluoride, the amount of nitrogen trifluoride emitted from the etching exhaust gas is not sufficiently suppressed even if the content of the metal contained therein is reduced. This suggests that the effect of suppressing greenhouse gas emissions by reducing the content of metal is a unique effect when acid fluoride is used.

[0093] Example B1 Remote plasma etching of a silicon oxide substrate was performed using a Paragon (trade name) remote plasma etching apparatus manufactured by MKS Instruments, which has a configuration similar to that of the remote plasma etching apparatus shown in Figure 2. The silicon oxide substrate was a 1 cm square silicon substrate (manufactured by Seiren KST Co., Ltd.) on which an 800 nm thick silicon oxide (SiO) film was formed.

[0094] The chamber volume of the remote plasma etching device is 4000 cm 3 The etching gas was a mixed gas of carbonyl fluoride gas and argon gas for sample 1-2. The flow rate of carbonyl fluoride gas was set to 20 sccm and the flow rate of argon to 80 sccm, so that the concentration of carbonyl fluoride in the etching gas was adjusted to 20% by volume. Note that the concentrations of metals contained in the argon used here were all below the detection limit. Since the detection limit for metals is 0.1 ppb by mass, the effect of argon on the concentration of metals in the etching gas was ignored.

[0095] The method for calculating the metal concentration in the etching gas was the same as in Example A1. The process pressure inside the chamber was set to 600 Pa, the source power to 400 W, and the substrate temperature to 30°C. The flow rate of the carbonyl fluoride gas, the flow rate of argon, the process pressure, the source power, and the bias power were all constantly monitored, and remote plasma etching was performed while confirming that there was no difference between the set value and the actual value. The results are shown in Table 3.

[0096] The emissions of carbon monoxide and carbon tetrafluoride in the exhaust gas discharged from the exhaust port of the remote plasma etching apparatus were determined in the same manner as in Example A1. Furthermore, the greenhouse gas emissions were calculated from the carbon monoxide and carbon tetrafluoride emissions in the same manner as in Example A1. Furthermore, the film thickness of the etching target was also measured in the same manner as in Example A1.

[0097]

[0098] (Examples B2 to B20 and Comparative Examples B1 to B6) Remote plasma etching was performed in the same manner as in Example B1, except that the type of etching gas and the etching conditions were different as shown in Table 3. The etching rate of the object to be etched and the emissions of carbon monoxide and carbon tetrafluoride contained in the etching exhaust gas were measured, and the greenhouse gas emissions were calculated. The results are shown in Table 3. In Examples B12 to B18, an additive gas was added to the etching gas, but the metal content of the additive gas was below the detection limit in each case, so in calculating the metal content of the etching gas, the additive gas was considered to contain no metal.

[0099] (Comparative Examples B7 and B8) Remote plasma etching was performed in the same manner as in Example B1, except that nitrogen trifluoride (Sample 4-1 and Sample 4-2) was used to prepare the etching gas instead of acid fluoride, and the etching rate of the object to be etched and the amount of nitrogen trifluoride emitted in the etching exhaust gas were measured, and the amount of greenhouse gas emissions was calculated. The results are shown in Table 3.

[0100] The results of Examples B1 and B2 and Comparative Example B1 show that the emissions of carbon monoxide and carbon tetrafluoride in the etching exhaust gas were suppressed by reducing the content of metals contained in carbonyl fluoride. In particular, Example B2, in which the content of metals contained in carbonyl fluoride was lower, showed a greater suppression of emissions of carbon monoxide and carbon tetrafluoride.

[0101] The results of Examples B3 to B5 and Comparative Examples B2 to B4 show that by reducing the metal content in carbonyl fluoride, the amount of carbon monoxide and carbon tetrafluoride emitted in the etching exhaust gas was suppressed, even when the etching target was silicon nitride, polysilicon, or photoresist. The results of Examples B6 to B11 show that the amount of carbon monoxide and carbon tetrafluoride emitted in the etching exhaust gas was equivalent to that of Example B1, even when the etching pressure, source power, bias power, acid fluoride concentration in the etching gas, and substrate temperature were changed.

[0102] The results of Examples B12 to B18 show that the addition of additive gases (oxygen gas, nitrogen gas, nitrous oxide) to the etching gas significantly reduced the emissions of carbon monoxide and carbon tetrafluoride in the etching exhaust gas, suggesting that the addition of an oxidizing gas changed the composition of active species in the plasma.

[0103] From the results of Examples B19 and B20 and Comparative Examples B5 and B6, it can be seen that even when oxalyl fluoride or trifluoroacetyl fluoride was used as the acid fluoride, the emissions of carbon monoxide and carbon tetrafluoride in the etching exhaust gas were suppressed by reducing the content of the contained metals.

[0104] The results of Comparative Examples B7 and B8 show that when the etching gas is prepared using nitrogen trifluoride instead of acid fluoride, the amount of nitrogen trifluoride emitted from the etching exhaust gas is not sufficiently suppressed even if the content of metals contained therein is reduced. This suggests that the effect of suppressing greenhouse gas emissions by reducing the content of metals is a unique effect when acid fluoride is used.

[0105] DESCRIPTION OF SYMBOLS 1... Chamber 2... Lower electrode 3... Acid fluoride gas supply unit 11... Etching gas supply pipe 15... RF coil 19... Remote plasma device 20... Substrate

Claims

1. A method for etching at least one of a silicon material containing silicon and a carbon material containing carbon, using an etching gas containing an acid fluoride, wherein the total content of sodium, aluminum, potassium, calcium, chromium, manganese, iron, cobalt, nickel, copper, and molybdenum contained in the etching gas is 100 ppb by mass or less.

2. The etching method according to claim 1, wherein said acid fluoride is at least one of carbonyl fluoride, oxalyl fluoride, and trifluoroacetyl fluoride.

3. An etching method according to claim 1 or 2, wherein the carbon content of the carbon material is 20% by mass or more and 100% by mass or less.

4. An etching method according to claim 1 or 2, wherein the silicon content of the silicon material is 30 mass % or more.

5. The etching method according to claim 1 or 2, wherein the silicon material is at least one of silicon oxide, silicon nitride, and polysilicon.

6. The etching method according to claim 1 or 2, wherein the etching is carried out in a plasma etching apparatus or a remote plasma etching apparatus.

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