TWI905464B - Etching gases and etching methods using them - Google Patents

Abstract

An etching gas containing _C7F8 and _C7F7H and/or _C6F5H , and with _{the total} volume of the etching gas set _at 100%, containing 60~99.9% by volume of _C7F8 , is a novel etching gas with a larger ratio ( _SiO2 / _ACL ) of etching rate for amorphous carbon layers (ACL) to etching rate for silicon oxide films ( _SiO2 ).

Description

Etching gases and etching methods using them

This invention relates to etching gases and etching methods using the same.

As an etching gas using octafluorotoluene, which has a relatively low global warming coefficient (GWP) of 4665, non-patent document 1 describes an etching gas composed of octafluorotoluene, Ar and _O2 .

[Previous Technical Documents] [Non-Patent Document]

[Non-Patent Document 1] Materials Express, Vol. 10, No. 6, 2020, 903-908

The purpose of this disclosure is to provide a novel etching gas with a larger ratio ( _SiO2 /ACL) of etching rate for amorphous carbon layer ( _ACL ) to etching rate for silicon oxide film (SiO2).

This disclosure comprises the following components.

_Item 1. An etching gas characterized by containing _C7F8 , _C7F7H and _/ or _{C6F5H .}

Item 2. An etching gas characterized in that the total amount of the etching gas is set to 100% by volume, containing 60 to 99.9% by volume C ₇ F ₈ .

Item 3. The etching gas, as in 1 or 2, further contains oxygen-containing compounds.

Item 4. The etching gas as described in Item 3, wherein the aforementioned oxygen-containing compound contains water.

Item 5. The etching gas as described in Item 4, wherein the total amount of the aforementioned etching gas is set to 100% by volume, and the content of the aforementioned water is 0.01 to 200 ppm by volume.

Item 6. The etching gas as described in any one of items 1 to 5, further comprising an inert gas.

Item 7. An etching method, characterized in that a silicon-oxygen material containing a silicon oxide film ( _SiO2 film) on which all or part of the surface is formed by etching gas plasma of any one of the etching gases in items 1 to 6 is etched.

According to this disclosure, a novel etching gas can be provided, in which the ratio of the etching rate of the amorphous carbon layer (ACL) to the etching rate of the silicon oxide film ( _SiO2 ) ( _SiO2 /ACL) is relatively large.

In this specification, "containing" includes any of the following concepts: "comprise," "consist essentially of," and "consist of."

Furthermore, in this instruction manual, when a numerical range is expressed as "A~B", it means above A and below B.

In the fabrication process of 3D NAND flash memory, during the step of forming contact holes with an insulating film such as _SiO2 , it is necessary to selectively etch a silicon oxide film ( _SiO2 ) against a relatively masked amorphous carbon layer (ACL). Although this etching uses perfluorocarbons (PFCs), techniques have been sought in the past that offer sufficient etch selectivity for _SiO2 relative to ACL while suppressing poor etching.

In Non-Patent Literature 1, with octafluorotoluene at 30 sccm, Ar at 30 sccm, and _O2 in the range of 30-60 sccm, the _SiO2 /ACL etching selectivity (etching rate ratio) is higher compared to the case with a lower _O2 flow rate. However, Non-Patent Literature 1 does not disclose the use of octafluorotoluene in combination with other etching gases, or the further increase of the octafluorotoluene content.

In contrast, _this invention discloses that by using _C7F8 , _and simultaneously using _C7F8 in combination with a specific etching gas, or by increasing the content of _C7F8 , selective etching of silicon oxide films ( _SiO2 ) relative to amorphous carbon layers ( _ACL ) can be achieved.

_Furthermore , using _C7F8 (GWP ₁₀₀ = 4665) instead of _{cC4F8 (} GWP ₁₀₀ = 9540) and _CHF3 (GWP ₁₀₀ = 12400) can also help prevent global warming.

1. Etching gas (first state sample)

_The etching gas (especially the _dry etching gas) of the first state disclosed herein contains _C7F8 and _C7F7H and/or _{C6F5H .}

_{The C7F8} used in the etching gas of the first state disclosed herein is not particularly limited, and any type may be used. Specific examples include octafluorotoluene, octafluoro-1,3,5-cycloheptatriene, 1,2,3,4,5-pentafluoro-5-(1,2,2-trifluorovinyl)cyclopentane-1,3-diene, 1,2,3,5,5-pentafluoro-4-(1,2,2-trifluorovinyl)cyclopentane-1,3-diene, 1,2,4,5,5-pentafluoro-3-(1,2,2-trifluorovinyl)cyclopentane-1,3-diene, and 1,2-difluoro-3-(trifluoromethyl)-4-(1,2,2-trifluorovinyl)cyclobutane-1,3-diene. _{These C7F8s may} be used alone or in combination of two or more. Furthermore, these _{C7 F8} products can be familiar or commercially available.

The content of _C7F8 in the etching gas of the first-state sample disclosed herein is based on the ratio of the etching rate of the amorphous carbon layer (ACL ₎ to the etching rate of the silicon oxide film ( _SiO2 ) ( _SiO2 /ACL). The total amount of etching gas in the first-state sample disclosed herein is set to 100% by volume, preferably 0.01 to 99.9% by volume, depending on the composition, but may also be 10 to 99.9% by volume, 20 to 99.9% by volume, 30 to 99.9% by volume, 40 to 99.9% by volume, 50 to 99.8% by volume, 60 to 99.7% by volume, and 70 to 99.6% by volume, etc. For example, when used in combination with the inert gas described later, a lower content of C7F8 (e.g., 40-70% by volume, preferably 42-60% by volume _, etc.) is preferred. When not used in combination with the inert gas described later, a higher content of _C7F8 (e.g., 60-99.7% by volume, preferably 70-99.6% by volume, more preferably 80-99.4% by volume) is preferred. Furthermore, when the etching gas of the first state sample disclosed herein contains several types _{of C7F8} , the total amount is preferably within the above range.

The etching gas of the first state disclosed herein contains _C7F7H and/or _C6F5H as other etching gases. _This allows for easy adjustment of the etching rate of the amorphous carbon layer (ACL), thereby facilitating _an increase in the etching rate ratio ( _SiO2 /ACL) to that of the silicon oxide film (SiO2).

When _C6F5H is used as another etching gas, there are no particular restrictions on _the type of _{C6F5H used} ; any type can be used. Specific examples include pentafluorobenzene, pentafluoro-1,3,5-cyclohexanetriene, 1,2,3,4-tetrafluoro-5-(fluoromethylene)cyclopentane-1,3-diene, 5-(difluoromethylene)-1,2,3-trifluorocyclopentane-1,3-diene, 5-(difluoromethylene)-1,2,4-trifluorocyclopentane-1,3-diene, 3-(difluoromethylene)-1,2-difluoro-4-(fluoromethylene)cyclobutane-1-ene, and 3,4-bis(difluoromethylene)-1-fluorocyclobutane-1-ene, etc. These _C6F5H products can be used alone or in combination _of two or more. _{These C6F5H} products can be either familiar or commercially available.

When _C7F7H is used as another etching gas, there are no particular restrictions on the _use of _C7F7H , _and any isomer can be used. Specific examples include 2H-heptafluorotoluene, 3H-heptafluorotoluene, 4H-heptafluorotoluene, difluoromethylpentafluorobenzene, (E)-1-(1,2-difluorovinyl)-2,3,4,5,5-pentafluorocyclopentane-1,3-diene, (Z)-1-(1,2-difluorovinyl)-2,3,4,5,5-pentafluorocyclopentane-1,3-diene, 1-(2,2-difluorovinyl)-2,3,4,5,5-pentafluorocyclopentane-1,3-diene, 1,2,3,5-tetrafluoro-4-(1,2,2-trifluorovinyl)cyclopentane-1,3-diene, and 2,3,5,5-tetrafluoro-1-(1,2, 2-Trifluorovinyl)cyclopentane-1,3-diene, 2,4,5,5-tetrafluoro-1-(1,2,2-trifluorovinyl)cyclopentane-1,3-diene, 1,2,5,5-tetrafluoro-4-(1,2,2-trifluorovinyl)cyclopentane-1,3-diene, (E)-2-(1,2-difluorovinyl)-1,3,4,5,5-pentafluorocyclopentane-1,3-diene, (Z)-2-(1,2-difluorovinyl)-1,3,4,5,5-pentafluorocyclopentane-1,3-diene, 2-(2,2-difluorovinyl)-1,3,4,5,5-pentafluorocyclopentane-1,3-diene, 1,2,5,5-Tetrafluoro-3-(1,2,2-trifluorovinyl)cyclopentane-1,3-diene, 1,2,4,5-Tetrafluoro-3-(1,2,2-trifluorovinyl)cyclopentane-1,3-diene, 1,3,5,5-Tetrafluoro-2-(1,2,2-trifluorovinyl)cyclopentane-1,3-diene, 1,4,5,5-Tetrafluoro-2-(1,2,2-trifluorovinyl)cyclopentane-1,3-diene, 1-(difluoromethyl)-3,4-difluoro-2-(1,2,2-trifluorovinyl)cyclobutane-1,3-diene, 3-fluoro-1-(trifluoro-2-trifluorovinyl)cyclobutane-1,3-diene (F7H)-2-(1,2,2-trifluorovinyl)cyclobutane-1,3-diene, 3-fluoro-2-(trifluoromethyl)-1-(1,2,2-trifluorovinyl)cyclobutane-1,3-diene, (Z)-1-(1,2-difluorovinyl)-3,4-difluoro-2-(trifluoromethyl)cyclobutane-1,3-diene, (E)-1-(1,2-difluorovinyl)-3,4-difluoro-2-( _{trifluoromethyl} )cyclobutane-1,3-diene, 1-(2,2-difluorovinyl)-3,4-difluoro-2-(trifluoromethyl)cyclobutane-1,3-diene, etc. These _C7F7H compounds can be used alone or in combination of two or more. These _{C7F7H compounds} can be known or commercially available.

Based on _{the viewpoint} of the etching gas content of the first-state sample disclosed herein, the content of _C7F7H and/or _C6F5H in the etching gas is set to 100% by volume, preferably 0.01 to 30% by volume, more preferably _0.02 to ₂₀ % by volume, even more preferably 0.03 to 10% by volume, and particularly preferably 0.05 to 5% by volume. Furthermore, when the etching gas of the first-state sample disclosed herein contains multiple types of _C7F7H and _/ or _C6F5H , its total content is preferably within _the above range.

This paper discloses that the same effect can also be achieved by adding other etching gases to the etching gas in the first state sample.

As other etching gases, _{the etching rate} of amorphous carbon layers (ACLs) can _be adjusted by adding hydrogen fluorocarbons (HFCs) such as _CF₂H₂ , _C₂F₂H₂ , _C₂F₂H₄ , _{and C₃F₄H₂ .} Similarly _{, the} etching rate of silicon oxide films (SiO₂) can _be adjusted by adding perfluorocarbons (PFCs) such as _CF₄ , _C₂F₆ , _C₃F₈ , _{C₄F₈ , C₃F₆ , C₄F₆ , and C₅F₈ .} Furthermore, adding iodides such as _CF3I , _C2F5I , and _C3F7I can adjust the etching rate of _{the silicon} oxide film ( _SiO2 ) and facilitate its dissociation, thereby lowering the electron temperature of the plasma. This increases the etching rate of the amorphous carbon layer (ACL) and easily improves the ratio of the ACL etching rate to the silicon oxide film ( _SiO2 ) etching rate ( _SiO2 /ACL). These other etching gases can be used alone or in combination of two or more. Furthermore, these other etching gases can be conventional or commercially available. There are no restrictions on whether these other etching gases are used in the etching process.

When the etching gas of the first-state sample disclosed herein includes other etching gases, the content of the other etching gases is set to 100% by volume, preferably 0.01 to ₃₀ % by volume, more preferably 0.02 to ₂₀ % by volume, even more preferably 0.03 to 10% by volume, and particularly preferably 0.05 to 5% by volume, when the etching gas of the first-state sample disclosed herein contains a plurality of other etching gases, the total amount of which is preferably within the above range.

Secondly, the etching gas used in the first-state sample disclosed herein may contain oxygen compounds.

By including oxygen compounds in the etching gas of the first-state sample disclosed herein, the ratio of the etching rate of the amorphous carbon layer (ACL) to the etching rate of the silicon oxide film ( _SiO2 ) ( _SiO2 /ACL) is easily increased. Furthermore, when the etching gas of the first-state sample disclosed herein includes the other etching gases mentioned above, it preferably includes oxygen compounds.

Examples of oxygen compounds include _O₂ , _O₃ , NO, _N₂O , _NO₂ , _SO₂ , COS, CO, _CO₂ , and _H₂O (water). These oxygen compounds can be used alone or in combination of two or more. Based on the view that a small amount can increase the etching rate of the amorphous carbon layer (ACL) to the etching rate of the silicon oxide film ( _SiO₂ ) ( _SiO₂ /ACL), _O₂ is preferred.

When the etching gas of the first-state sample disclosed herein contains oxygen compounds, the total amount of the etching gas is set to 100% by volume, preferably 0-20% by volume, more preferably 0.01-15% by volume, even more preferably 0.1-10% by volume, and most preferably 1-7% by volume. Furthermore, when the etching gas of the first-state sample disclosed herein contains multiple types of oxygen compounds, their total amount is preferably within the above range. This increases the _SiO₂ /ACL ratio. Moreover, by setting the oxygen compound content to 0-20% by volume, the etching rate can be easily adjusted.

Furthermore, when _H₂O (water) is present as an oxygen compound, the content of _H₂O (water) is set to 100% by volume, preferably 0.01 to 200 ppm by volume, more preferably 0.1 to 150 ppm by volume, and even more preferably 1 to 100 ppm by volume. This further increases the ratio ( _SiO₂ /ACL) of the etching rate of the amorphous carbon layer (ACL) to the etching rate of the silicon oxide film ( _SiO₂ ). The content of _H₂O (water) in the etching gas of the first-state sample disclosed herein was determined by a Carl Fisher moisture meter.

Furthermore, the etching gas in the first state of this invention may contain an inert gas, if necessary.

Inert gases include one or more rare gases, nitrogen, etc., and more specifically, rare gases include helium, neon, argon, xenon, krypton, etc. Based on the ratio of the etching rate of amorphous carbon layers (ACL) to the etching rate of silicon oxide films ( _SiO2 ) ( _SiO2 /ACL), rare gases are preferred, and argon is even more preferred. These inert gases can be used alone or in combination of two or more. Furthermore, these inert gases can be conventional or commercially available products.

These inert gases can change the electron temperature and electron density of the plasma, control the balance of fluorocarbon radicals and fluorocarbon ions, adjust the etching rate of the silicon oxide film ( _SiO2 film), and increase the ratio of the etching rate of the amorphous carbon layer (ACL) to the etching rate of the silicon oxide film ( _SiO2 ) ( _SiO2 /ACL).

When the etching gas of the first-state sample disclosed herein contains inert gas, the content of the inert gas is set to 100% of the total volume of the etching gas of the first-state sample disclosed herein, preferably 1-60% of the volume, more preferably 10-58% of the volume, even more preferably 20-57% of the volume, and particularly preferably 30-55% of the volume. Furthermore, when the etching gas of the first-state sample disclosed herein contains multiple types of inert gases, their total amount is preferably within the above range. This increases the etching rate ratio ( _SiO2/ ACL) of the amorphous carbon layer (ACL) to the etching rate ratio ( _SiO2 /ACL).

The etching gas used in the first state of this disclosure may further include the following additive gases.

By using gases containing _F2 , _NF3 , etc. as fluorine sources, a portion of the _CH2 fragment is fluorinated, and by generating CHF, _CF2 , etc., the etching rate can be increased.

Furthermore, good etching shapes can be obtained by including _H2 or _NH3 .

The content of these added gas components is preferably within the range that does not impair the effects disclosed herein; for example, the total amount of etching gas in the first state sample of this disclosure is set to 100% by volume, or 0-10% by volume, preferably 0-5% by volume.

The preferred etching gases and their volume ratios for the first-state sample are shown below.

•C ₇ F ₈ /C ₇ F ₇ H

60~99.7% by volume (preferably 70~99.6% by volume, even better 80~99.4% by volume) / 0.3~40% by volume (preferably 0.4~30% by volume, even better 0.6~20% by volume).

•C ₇ F ₈ /C ₇ F ₇ H/O ₂

60-99.7% volume (preferably 70-99.6% volume, even better 80-99.4% volume) / 0.02-20% volume (preferably 0.03-10% volume, even better 0.05-5% volume) / 0.01-15% volume (preferably 0.1-10% volume, even better 1-7% volume).

•C ₇ F ₈ /C ₇ F ₇ H/O ₂ /Ar

40~70% volume (preferably 41~65% volume, even better 42~60% volume) / 0.02~20% volume (preferably 0.03~10% volume, even better 0.05~5% volume) / 0.01~15% volume (preferably 0.1~10% volume, even better 1~7% volume) / 10~58% volume (preferably 20~57% volume, even better 30~55% volume).

•C ₇ F ₈ /C ₆ F ₅ H

60~99.7% by volume (preferably 70~99.6% by volume, even better 80~99.4% by volume) / 0.3~40% by volume (preferably 0.4~30% by volume, even better 0.6~20% by volume).

•C ₇ F ₈ /C ₆ F ₅ H/O ₂

60~99.7% by volume (preferably 70~99.6% by volume, even better 80~99.4% by volume) / 0.02~20% by volume (preferably 0.03~10% by volume, even better 0.05~5% by volume) / 0.01~15% by volume (preferably 0.1~10% by volume, even better 1~7% by volume).

•C ₇ F ₈ /C ₆ F ₅ H/O ₂ /Ar

40~70% volume (preferably 41~65% volume, even better 42~60% volume) / 0.02~20% volume (preferably 0.03~10% volume, even better 0.05~5% volume) / 0.01~15% volume (preferably 0.1~10% volume, even better 1~7% volume) / 10~58% volume (preferably 20~57% volume, even better 30~55% volume).

The etching gas disclosed herein, satisfying these conditions, is, as described above, an etching gas capable of selectively etching silicon oxide films ( _SiO₂ ) relative to the amorphous carbon layer (ACL). Therefore, it can be used to etch silicon-oxide materials containing silicon oxide films ( _SiO₂ films) on which all or part of the surface is formed of an amorphous carbon layer (ACL). Specifically, the ratio of the etching rate of the amorphous carbon layer (ACL) to the etching rate of the silicon oxide film ( _SiO₂ ) ( _SiO₂ /ACL) is preferably 3.0 or higher, more preferably 3.0 to 5.0, and even more preferably 3.1 to 4.0.

The ratio of the etching rate of these amorphous carbon layers (ACL) to the etching rate of silicon oxide films ( _SiO2 ) ( _SiO2 /ACL) can be adjusted by the content of _C7F8 , the types and contents of other etching gases, the content of oxygen compounds, and the content of inert gases. In particular, _it is easy to adjust by reducing the content of oxygen compounds, for example, by setting it to 0~20% by volume.

2. Etching gas (second state)

This paper discloses the second state of the etching gas (especially the dry etching gas), with the total amount of etching gas set to 100% by volume, _{and C7F8} containing 60 to 99.9% of the volume.

_{The C7F8} used in the etching gas of the second state sample disclosed herein can be the same as that described in the first state sample above. A preferred specific example is also the same.

The content of _C7F8 in the etching gas of the second-state sample disclosed herein is set to 60-99.9% of _the total volume of the etching gas, preferably 70-99.6% of the volume, and more preferably 80-99.4% of the volume, when the content of _C7F8 in the etching gas of the second-state sample disclosed herein is less than 60% of the volume, _selective etching of silicon oxide film ( _SiO2 ) relative to amorphous carbon layer (ACL) is not possible. Furthermore, when the etching gas of the second-state sample disclosed _herein contains multiple types of _C7F8 , their total amount is preferably within the above range.

The etching gas of the second-state sample disclosed herein can also be given its effect by adding _C7F7H , _C6F5H , or other _etching gases. Furthermore, the etching gas of the second-state sample disclosed herein may _also contain oxygen compounds, inert gases, additive gases, etc.

_{The C7F7H , C6F5H} , other etching gases, oxygen compounds, inert gases, and additive gases used in _the etching gas of the second state sample disclosed herein may be the gases described in the first state sample above. Preferred examples and contents are also the same.

The preferred etching gases and their volume ratios for the second state sample are shown below.

•C ₇ F ₈ /C ₇ F ₇ H

60~99.9% by volume (preferably 70~99.6% by volume, even better 80~99.4% by volume) / 0.1~40% by volume (preferably 0.4~30% by volume, even better 0.6~20% by volume).

•C ₇ F ₈ /C ₇ F ₇ H/O ₂

60~99.9% by volume (preferably 70~99.6% by volume, even better 80~99.4% by volume) / 0.02~20% by volume (preferably 0.03~10% by volume, even better 0.05~5% by volume) / 0.01~15% by volume (preferably 0.1~10% by volume, even better 1~7% by volume).

•C ₇ F ₈ /C ₆ F ₅ H

60~99.9% by volume (preferably 70~99.6% by volume, even better 80~99.4% by volume) / 0.3~40% by volume (preferably 0.4~30% by volume, even better 0.6~20% by volume).

•C ₇ F ₈ /C ₆ F ₅ H/O ₂

60~99.9% by volume (preferably 70~99.6% by volume, even better 80~99.4% by volume) / 0.02~20% by volume (preferably 0.03~10% by volume, even better 0.05~5% by volume) / 0.01~15% by volume (preferably 0.1~10% by volume, even better 1~7% by volume).

The etching gas of the second state disclosed herein, satisfying these conditions, is, as described above, an etching gas capable of selectively etching silicon oxide films ( _SiO2 ) relative to amorphous carbon layers (ACL). Therefore, it can be used for etching silicon-oxide materials containing silicon oxide films ( _SiO2 films) on which all or part of an amorphous carbon layer (ACL) is formed on the surface. Specifically, the ratio of the etching rate of the amorphous carbon layer (ACL) to the etching rate of the silicon oxide film ( _SiO2 ) ( _SiO2 /ACL) is preferably 3.0 or higher, more preferably 3.0 to 5.0, and even more preferably 3.1 to 4.0.

The ratio of the etching rate of these amorphous carbon layers (ACL) to that of silicon oxide films ( _SiO2 ) ( _SiO2 /ACL) can be adjusted by factors such _as the _C7F8 content, the type and content of other etching gases, the content of oxides, and the content of inert gases. In particular, it can be easily adjusted by reducing the content of oxides, for example, by setting it to 0-20% by volume.

3. Etching Methods

The gas plasma containing the etching gas disclosed herein can be used to etch silicon-oxide materials containing a silicon oxide film ( _SiO2 film) with an amorphous carbon layer (ACL) formed on all or part of its surface. The etching conditions (especially the dry etching method) are the same as those of conventional methods, except that the etching gas disclosed herein is used.

Furthermore, the etching conditions can be, for example, as follows: * Flow rate 5~2000 sccm, preferably 10~1000 sccm; * Discharge power 200~20000W, preferably 400~10000W; * Bias power 25~15000W, preferably 100~10000W; * Pressure below 30 mTorr (below 3.99 Pa), preferably 2~10 mTorr (0.266~1.33 Pa); * Electron density ^10⁹ ~ ^{10¹³ cm⁻³} , preferably ^10¹⁰ ~ ^{10¹² cm⁻³} * Electron temperature 2~9eV, preferably 3~8eV; * Wafer temperature -40~100℃, preferably -30~50℃; * Chamber wall temperature -30~300℃, preferably 20~200℃.

Furthermore, unless otherwise specified, pressure is indicated by a gauge.

Furthermore, the discharge power and bias power vary depending on the size of the chamber and the size of the electrodes. The optimal etching conditions for etching contact holes and other patterns on silicon oxide films using an inductively coupled plasma (ICP) etching apparatus (chamber volume 3500 ^cm³ ) for small-diameter wafers are as follows: *Discharge power 200~1000W, preferably 300~600W; *Bias power 50~500W, preferably 100~300W.

The embodiments disclosed herein have been described above; however, various changes to the form and details may be made without departing from the spirit and scope of the patent application.

[Implementation Example]

The present invention will now be described in detail using embodiments and comparative examples, but it is neither intended to be limited to these examples.

Examples 1-5 and Comparative Examples 1-2

The etching rates of a 1000 μm thick silicon oxide ^(SiO2) film and a 5000 μm thick amorphous carbon (ACL) film formed on a silicon substrate were measured under etching conditions of ICP (inductively coupled plasma), discharge power 1000 _W , bias power 300 W, pressure ₁₀ mTorr, electron density ⁸ × 10¹⁰ ~ 2 × ^10¹¹ cm⁻³, and electron temperature 5 ~ 7 eV. The ratio of the etching rates of the _SiO2 film to the ACL film was set as the ACL selectivity ratio (etching rate of _SiO2 film / etching rate of ACL film). Furthermore, the _SiO2 film was formed using a commonly used method, while the ACL film was formed according to the previously reported method (Producer (registered trademark) APF ^™ PECVD-Applied Materials). The results are shown in Table 1. Table 1 also shows the water content as determined by a Carl Fisher moisture meter.

In Table 1, _C7F8 represents octafluorotoluene, _C7F7H represents _{heptafluorotoluene} , _{and C6F5H} represents _{pentafluorobenzene} .

Claims (7)

_An etching gas characterized by _{containing C7F8} and _C7F7H , or _{C7F8 and C6F5H .} An etching gas characterized in that the total volume of the etching gas is set to 100% by volume, containing 70-99.9% by volume _{of C7F8} and 0.01-200 ppm by volume of water. The etching gas, as in claim 1, further contains oxygen compounds. The etching gas in claim 3, wherein the aforementioned oxygen compound contains water. For example, in the etching gas of claim 4, the total amount of the aforementioned etching gas is set to 100% by volume, and the content of the aforementioned water is 0.01 to 200 ppm by volume. The etching gas of any one of claims 1 to 5 may further contain an inert gas. An etching method characterized by etching a silicon-oxygen material containing a silicon oxide film ( _SiO2 film) with an etching gas plasma of any one of claims 1 to 6, wherein all or part of the surface is formed with an amorphous carbon layer (ACL).