WO2025109991A1 - Etching method, etching device, and gas for forming protective film - Google Patents

Abstract

Disclosed is an etching method with which at least a part of a second structure of a substrate that includes a first structure and the second structure, which are to be etched by an etching gas, is selectively etched by the etching gas in a state where a protective film is formed on the first structure with use of a gas for forming a protective film, the gas for forming a protective film containing a perfluoroolefin having 2 to 8 carbon atoms.

Description

Etching method, etching apparatus, and gas for forming protective film

This disclosure relates to an etching method, an etching apparatus, and a gas for forming a protective film.

When constructing a semiconductor device, etching is performed on various films formed on the substrate, a semiconductor wafer (hereafter referred to as the wafer). As an example, a process may be performed in which etching is performed on a wafer on which an interlayer insulating film called a low-k film has been formed, to form recesses in the interlayer insulating film for embedding wiring.

Patent document 1 describes a technique for selectively etching a desired film from among multiple types of films formed on the surface of a substrate during this process.

JP 2021-163775 A

In the technology described in Patent Document 1, a protective film forming gas containing amine gas is supplied, and the protective film is formed on the first structure, which is a film that is not to be etched, by the protective film forming gas. Then, with the protective film formed on the first structure, an etching gas is supplied to selectively etch the second structure, which is a film to be etched.

In this technology, an amine gas such as butylamine is used to form the protective film. However, the boiling points of the amines described in Patent Document 1 as materials used to form the protective film are said to be within the range of 100°C to 400°C, and these amines are liquid at room temperature. Therefore, in order to supply them as amine gas, they need to be heated to become a gas, which is not desirable from the perspective of energy consumption, so it has been desirable to use a protective film formation gas that contains a material other than amine gas.

In light of the above background, the present disclosure aims to provide an etching method using a protective film forming gas that contains a gas other than an amine gas.

This disclosure is as follows:

The present disclosure (1) provides a method for etching a substrate having a first structure and a second structure, the method comprising:
The present invention relates to an etching method, in which, in a state in which a protective film is formed on the first structure using a protective film forming gas containing a perfluoroolefin having 2 to 8 carbon atoms, at least a part of the second structure is selectively etched with the etching gas.

The present disclosure (2) relates to the etching method described in the present disclosure (1), in which the protective film forming gas is supplied simultaneously with the etching gas, and the second structure is etched while the protective film is formed on the first structure.

The present disclosure (3) provides a method for forming a protective film on the first structure by supplying the protective film forming gas;
The present invention relates to the etching method according to the present disclosure (1), in which, after the protective film is formed, the etching gas is supplied to etch the second structure.

The present disclosure (4) relates to an etching method according to any one of the present disclosures (1) to (3), in which the protective film forming gas does not contain molecules containing hydrogen atoms.

The present disclosure (5) _relates to the etching method according to any one of the present disclosures (1) to (4), wherein the perfluoroolefin is at least one selected from the group consisting of C _{3 F 6} , C ₄ F ₈ , C 5 F 10 and C ₆ F ₁₂ .

The present disclosure (6) relates to an etching method according to any one of the present disclosures (1) to (5), in which the first structure comprises a silicon oxycarbonitride film.

The present disclosure (7) relates to an etching method according to any one of the present disclosures (1) to (6), in which the first structure comprises a porous film.

The present disclosure (8) relates to an etching method according to any one of the present disclosures (1) to (5), in which the first structure comprises a silicon oxide film.

The present disclosure (9) provides a porous membrane as the first structure,
the first structure and the second structure are provided separately on the substrate,
the protective film is formed so as to close the pores of the porous film,
The step of selectively etching the second structure relates to the etching method according to any one of (1) to (5) of the present disclosure, which includes a step of supplying an etching gas in a state where the protective film is formed.

The present disclosure (10) relates to the etching method described in the present disclosure (9), in which the porous film is the outermost layer of the first structure.

The present disclosure (11) provides a method for manufacturing a semiconductor device, comprising the steps of: providing a dense film and a porous film as the first structure;
the dense film, the porous film, and the second structure are provided adjacent to each other in this order on the substrate;
The step of forming the protective film includes a step of forming the protective film on pores of the porous film to close the pores, and a step of forming the protective film on a surface of the dense film,
The step of selectively etching the second structure relates to the etching method according to any one of (1) to (5) of the present disclosure, which includes a step of supplying an etching gas in a state where the protective film is formed.

The present disclosure (12) provides a processing vessel,
a stage provided in the processing chamber, the stage supporting a substrate having a first structure and a second structure formed on a surface thereof, the first structure and the second structure being etched by an etching gas supplied into the processing chamber;
a protective film forming gas supply unit for supplying a protective film forming gas containing a perfluoroolefin having 2 to 8 carbon atoms into the processing vessel and forming a protective film on the first structure so that the first structure is selectively protected among the first structure and the second structure;
an etching gas supply unit that supplies the etching gas into the processing vessel to selectively etch at least a portion of the second structure while the protective film is present on the first structure;
The present invention relates to an etching apparatus comprising:

The present disclosure (13) relates to an etching apparatus as described in the present disclosure (12), which simultaneously supplies the protective film forming gas from the protective film forming gas supply unit and the etching gas from the etching gas supply unit.

The present disclosure (14) provides a method for forming a protective film, comprising:
The etching apparatus according to the present disclosure (12) supplies the etching gas from the etching gas supply unit.

The present disclosure (15) relates to a protective film forming gas that contains a perfluoroolefin having 2 to 8 carbon atoms and is used to selectively protect a first structure when at least a portion of a second structure is selectively etched with an etching gas on a substrate on which the first structure and the second structure are formed and that is to be etched with an etching gas.

The present disclosure (16) relates to the protective film forming gas according to the present disclosure (15), wherein the perfluoroolefin is at least one selected from the group consisting of C ₃ F ₆ , C ₄ F ₈ , C ₅ F ₁₀ and C ₆ F ₁₂ .

The present disclosure (17) relates to the protective film forming gas according to the present disclosure (15) or (16), wherein the etching gas contains at least one selected from the group consisting of _F2 gas, _ClF3 gas, and _IF7 gas.

This disclosure provides an etching method that uses a protective film forming gas that contains a gas other than an amine gas.

FIG. 1A is a cross-sectional view that illustrates an example of a substrate to which the etching method of the present disclosure is applied. FIG. 1B is a cross-sectional view that illustrates the substrate after removing the polysilicon film from the substrate illustrated in FIG. 1A. FIG. 1C is a cross-sectional view that illustrates the substrate obtained by subjecting the substrate illustrated in FIG. 1B to etching. FIG. 1D is a cross-sectional view that illustrates the substrate shown in FIG. 1B, in which a protective film is formed on the low-k film by supplying a protective film forming gas. FIG. 2A is a cross-sectional view that illustrates another example of a substrate to which the etching method of the present disclosure is applied. FIG. 2B is a cross-sectional view that illustrates the substrate obtained by subjecting the substrate illustrated in FIG. 2A to etching. FIG. 2C is a cross-sectional view that typically shows the substrate shown in FIG. 2A etched without supplying a protective film forming gas. FIG. 3A is a cross-sectional view that illustrates another example of a substrate to which the etching method of the present disclosure is applied. FIG. 3B is a cross-sectional view that illustrates the substrate illustrated in FIG. 3A on which a protective film is formed. FIG. 3C is a cross-sectional view that illustrates the substrate obtained by subjecting the substrate illustrated in FIG. 3B to etching. FIG. 4 is a cross-sectional view showing a schematic example of an etching apparatus. FIG. 5A is an infrared spectrum of a mixed gas of C ₃ F ₆ and ClF ₃ . FIG. 5B is an infrared spectrum of C ₃ F ₆ gas alone. FIG. 5C is an infrared spectrum of ClF ₃ gas alone.

The etching method, etching apparatus, and protective film forming gas according to the embodiment of the present disclosure are described below with reference to the drawings.

[Etching method]
First Embodiment
FIG. 1A is a cross-sectional view that illustrates an example of a substrate to which the etching method of the present disclosure is applied.
FIG. 1A shows, as a configuration of a substrate 1, a Si wafer 30, a silicon oxide film (SiO film) 40 provided on the surface of the Si wafer 30, a first structure 10 provided on the silicon oxide film 40, and a second structure 20.
The silicon oxide film 40 on the surface of the Si wafer 30 may not be provided.

The first structure and the second structure are etched by an etching gas, but in the etching method disclosed herein, the first structure is not etched due to the formation of a protective film, and the second structure is selectively etched.

In the substrate shown in FIG. 1A, a first structure 10 and a second structure 20 both include a plurality of types of films and are disposed separately.
The first structure 10 is made up of a laminated film 13 in which SiGe films 11 and Si films 12 are alternately laminated, and a low-k film 14 that covers the periphery of the laminated film 13 .
The second structure 20 is made of a laminated film 23 in which SiGe films 21 and Si films 22 are alternately laminated, and is not covered with a low-k film.
The first structure 10 and the second structure 20 are covered with a polysilicon film 50 .

The low-k film 14 has the role of protecting the laminated film 13 from being etched. The low-k film is a film that is not etched by the etching method of the present disclosure, and is therefore part of the first structure 10. The low-k film is preferably a porous film, and when the low-k film is a porous film, it can be said that the first structure comprises a porous film. Whether or not the first structure comprises a porous film can be determined by observing the cross section with an electron microscope to check for the presence or absence of holes, or by small-angle X-ray scattering, etc.

The low-k film 14 is preferably a silicon oxycarbonitride film. A silicon oxycarbonitride film is a film made of a compound in which silicon (Si) is bonded with oxygen (O), carbon (C) and nitrogen (N), and is also referred to as a SiOCN film. There is no particular limit to the molar ratio of Si, O, C and N in silicon oxycarbonitride.

In addition, if the film covering the laminated film is a porous film other than a silicon oxycarbonitride film, it may be a silicon oxycarbide film (SiCO film) or a silicon bicarbonate film (SiCOH film).

Examples of the second structure to be etched in the etching method of the present disclosure include a SiGe film, a polysilicon film, and an α-Si film (amorphous silicon film).
The first structure 10 shown in FIG. 1A also includes a SiGe film 11, but the first structure is not etched due to the formation of a protective film.

FIG. 1B is a cross-sectional view that illustrates the substrate after removing the polysilicon film from the substrate illustrated in FIG. 1A.
Before the etching method of the present disclosure is applied, the substrate 1 is in the state shown in FIG. 1B, with the polysilicon film 50 having been removed by etching.

The etching method of the present disclosure is applied to the substrate 1 shown in FIG. 1B.
A protective film is formed on the first structure using a protective film forming gas containing a perfluoroolefin having 2 to 8 carbon atoms.
FIG. 1C following FIG. 1B shows the state after forming a protective film on the first structure and etching the second structure are performed simultaneously, and FIG. 1D following FIG. 1B shows the state after forming a protective film on the first structure before etching the second structure.

Perfluoroolefins having 2 to 8 carbon atoms are compounds that have one or more double bonds in their structure and are composed only of carbon atoms and fluorine atoms, and may be linear, branched, or cyclic.
The perfluoroolefin having 2 to 8 carbon atoms includes at least one compound selected from the group consisting of C ₃ F ₆ , C ₄ F ₈ , C ₅ F ₁₀ and C ₆ F _12. Of these, C ₃ F ₆ (hexafluoropropene) is particularly preferred.
It is also preferable that the protective film forming gas does not contain molecules containing hydrogen atoms. If molecules containing hydrogen atoms are present, etching of the Si film 22 of the second structure advances, and selectivity with the SiGe film 21 of the etching target film may not be maintained. For this reason, even if the protective film forming gas contains molecules containing hydrogen atoms as impurities, the ratio of molecules containing hydrogen atoms contained in the protective film forming gas is 1 vol.% or less, 0.1 vol.% or less, or 0.01 vol.% or less.

Perfluoroolefins with carbon numbers between 2 and 8 either do not react with etching gas or have low reactivity. Because perfluoroolefins are already fluorinated compounds, it is assumed that they either do not react with halogen-based etching gases contained in etching gas or have low reactivity.

By forming a protective film on the first structure using a protective film forming gas made of a perfluoroolefin having 2 to 8 carbon atoms, it is possible to prevent the film present inside the protective film from being etched, and also to prevent the film at the same level as the protective film (in this embodiment, the low-k film 14) from being etched.

When the first structure is a porous film, the protective film forming gas is adsorbed into the holes of the porous film, filling the holes and preventing the etching gas from penetrating into the porous film. It is also possible to prevent the etching gas from penetrating into the film inside the porous film.

In addition, perfluoroolefins having 2 to 8 carbon atoms have a double bond that is deficient in electrons. Compounds having a double bond are easily adsorbed when the first structure is a silicon oxycarbonitride film, and therefore the protective effect is suitably exhibited.
Furthermore, when the first structure is a porous film, the molecular size of the perfluoroolefin having 2 to 8 carbon atoms is such that the molecule can enter the pores of the porous film (less than 1 nm in the case of a low-k film). Molecules having more than 8 carbon atoms are less likely to enter the pores of the porous film, making it difficult to form a protective film on the porous film.

From the above, when a low-k film is provided on the outermost layer of the first structure and the low-k film is a porous film and a silicon oxycarbonitride film, perfluoroolefin having 2 to 8 carbon atoms is easily adsorbed into the pores of the low-k film, and a protective film made of perfluoroolefin having 2 to 8 carbon atoms is suitably formed.

Perfluoroolefins having 2 to 8 carbon atoms are either gaseous at room temperature and pressure or easily gasify with slight heating, and therefore have an advantage over the amine gas used as the protective film-forming gas in Patent Document 1 in terms of the energy consumption required for heating when supplying the protective film-forming gas.
Perfluoroolefins having 2 to 4 carbon atoms are in a gaseous state at normal temperature and pressure and do not require heating to turn into a gaseous state, and therefore are particularly advantageous from the viewpoint of energy consumption.

The etching gas may be an etching gas containing a halogen-based etching gas, and may contain F ₂ (fluorine) gas, ClF ₃ (chlorine trifluoride) gas, or IF ₇ (iodine heptafluoride) gas. Examples of the etching gas include ClF ₃ (chlorine trifluoride) gas, a mixed gas of F ₂ (fluorine) gas and NH ₃ (ammonia) gas, a mixed gas of F ₂ gas, Ar (argon) gas, and HF (hydrogen fluoride) gas, or IF ₇ (iodine heptafluoride) gas. All of these are halogen-based etching gases, and do not react or have low reactivity with perfluoroolefins having 2 to 8 carbon atoms.

When etching the second structure using an etching gas, etching may be performed in a plasma state or may be performed without a plasma state.
Etching accompanied by a plasma state refers to etching carried out by putting a halogen-based etching gas or the like at about 0.1 to 10 Torr into a reaction device, applying high-frequency power to an outer coil or an opposing electrode to generate low-temperature gas plasma in the reaction device, and carrying out etching using the halogen-based active chemical species produced therein. Etching not accompanied by a plasma state refers to etching carried out without generating the above-mentioned gas plasma.

In the etching method disclosed herein, in the presence of a protective film formed on a first structure using a protective film forming gas containing a perfluoroolefin having 2 to 8 carbon atoms, at least a portion of a second structure is selectively etched with an etching gas.

FIG. 1C is a cross-sectional view that illustrates the substrate obtained by subjecting the substrate illustrated in FIG. 1B to etching.
FIG. 1C shows a state in which the SiGe film 21, which is a part of the second structure 20, has been removed by etching.
The SiGe film 21 of the second structure 20 is not protected by the protective film and is therefore removed by the etching gas.
In FIG. 1C , the Si film 22 of the second structure 20 is depicted as floating. However, this is to show that only the Si film 22 remains as a result of the etching of the SiGe film 21, and does not mean that the Si film 22 is actually floating.

On the other hand, the low-k film 14 in the outermost layer of the first structure 10 is a porous film, and a protective film is present in the pores of the low-k film 14 by adsorbing perfluoroolefin having 2 to 8 carbon atoms. Therefore, the low-k film 14 is not etched, and the SiGe film 11 constituting the laminated film 13 covered by the low-k film 14 is not etched.
That is, the first structure 10 is not etched, and the SiGe film 11 of the second structure 20 is selectively etched.
In FIG. 1C, in order to indicate that a protective film exists on the low-k film 14, the low-k film 14 is drawn with hatching different from that shown in FIG. 1B.

In the etching method of the present disclosure, a protective film forming gas may be supplied simultaneously with an etching gas, and the second structure may be etched while a protective film is being formed on the first structure.
The case where the protective film forming gas and the etching gas are supplied simultaneously is also included in "etching the second structure in a state where the protective film formed on the first structure is present."

For example, in the substrate shown in FIG. 1B, when no protective film is present on the low-k film 14, a protective film forming gas and an etching gas are supplied at the same time. Then, a protective film is formed on the low-k film 14 and the second structure 20 is etched at the same time.

When the protective film forming gas is supplied simultaneously with the etching gas, the etching gas may reach the laminated film 13 and etch the laminated film 13 before the protective film is formed on the low-k film 14. However, since the low-k film 14 itself has a role in protecting the laminated film 13 from being etched, even if the etching gas is present in the system in the early stage before the protective film is formed on the low-k film 14, the laminated film 13 is not immediately etched. After a while has passed since the protective film forming gas is supplied simultaneously with the etching gas, a sufficient protective film is formed on the low-k film 14, and the second structure can be selectively etched.

When the protective film forming gas is supplied simultaneously with the etching gas, the flow rates of the protective film forming gas and the etching gas are not particularly limited, and the flow rates of the protective film forming gas and the etching gas may be the same, the flow rate of the protective film forming gas may be greater than the flow rate of the etching gas, or the flow rate of the protective film forming gas may be less than the flow rate of the etching gas.

In the etching method disclosed herein, a protective film forming gas may be supplied to form a protective film on the first structure, and after the protective film is formed, an etching gas may be supplied to etch the second structure.

1B, a protective film forming gas is supplied to the low-k film 14 when no protective film is present thereon.
When an etching gas is supplied with a protective film formed on the low-k film 14, the etching gas is prevented from reaching the laminated film 13, so that the second structure 20 can be selectively etched.

FIG. 1D is a cross-sectional view that illustrates the substrate shown in FIG. 1B, in which a protective film is formed on the low-k film by supplying a protective film forming gas.
FIG. 1D shows a substrate at a stage in the process of supplying a protective film forming gas to form a protective film on the first structure, and then supplying an etching gas to etch the second structure after the protective film has been formed, in which a protective film has been formed on the low-k film 14 that is the outermost layer of the first structure 10, and before the etching gas is supplied.
In FIG. 1D, in order to indicate that a protective film is present on the low-k film 14, the low-k film 14 is drawn with hatching different from that shown in FIG. 1B (the same hatching as the low-k film 14 shown in FIG. 1C).

When an etching gas is supplied to a substrate in which a protective film is present on the low-k film 14 as shown in FIG. 1D, the etching gas is prevented from reaching the laminated film 13, so the second structure can be selectively etched, resulting in the substrate after etching shown in FIG. 1C.

Furthermore, in the etching method disclosed herein, when a protective film is formed on a first structure by supplying a protective film forming gas, and after the protective film is formed, an etching gas is supplied to etch a second structure, multiple cycles may be repeated with "forming a protective film by supplying a protective film forming gas and etching a second structure by supplying an etching gas" being one cycle.

In the etching method disclosed herein, the temperature at which the protective film forming gas is supplied is preferably 0°C or higher and 200°C or lower, and more preferably 20°C or higher and 80°C or lower.

In light of the above description, in the etching method of the first embodiment of the present disclosure, a porous film is provided as the first structure, the first structure and the second structure are provided separately on the substrate, the protective film is formed so as to block the holes in the porous film, and the step of selectively etching the second structure may include a step of supplying an etching gas with the protective film formed. Also, the porous film may be the outermost layer of the first structure.

Second Embodiment
FIG. 2A is a cross-sectional view that illustrates another example of a substrate to which the etching method of the present disclosure is applied.
FIG. 2A shows, as the configuration of the substrate 2, a Si wafer 30, a silicon oxide film (SiO film) 40 provided on the surface of the Si wafer 30, a first structure 10 provided on the silicon oxide film 40, and a second structure 20.

The first structure 10 is made up of a polysilicon film 15 and a low-k film 14 that covers the periphery of the polysilicon film 15 .
The second structure 20 is made of a polysilicon film 25 formed around the periphery of the first structure 10 .

The configurations of the Si wafer, silicon oxide film, polysilicon film, and low-k film, as well as the configurations of the protective film forming gas and etching gas, can be the same as those in the first embodiment.

FIG. 2B is a cross-sectional view that illustrates the substrate obtained by subjecting the substrate illustrated in FIG. 2A to etching.
When a protective film forming gas is supplied simultaneously with an etching gas, and a protective film is formed on the first structure while the second structure is etched, a protective film is formed on the low-k film 14, which is a part of the first structure 10, and at the same time, the polysilicon film 25, which is the second structure 20, is etched.
The polysilicon film 15 covered with the low-k film 14 on which the protective film is formed is not etched.

Alternatively, a protective film forming gas may be supplied to form a protective film on the first structure, and after the protective film is formed, an etching gas may be supplied to etch the second structure. In this case, the etching gas is supplied with a protective film formed on the low-k film 14, which is part of the first structure 10, to etch the polysilicon film 25, which is the second structure 20.

Through the above steps, a protective film is formed on the first structure 10 in the substrate 2 shown in FIG. 2A, and the second structure 20 can be selectively etched.
In FIG. 2B, in order to indicate that a protective film is present on the low-k film 14, the low-k film 14 is drawn with hatching different from that shown in FIG. 2A.

FIG. 2C is a cross-sectional view that typically shows the substrate shown in FIG. 2A etched without supplying a protective film forming gas.
When the low-k film 14 is a porous film, if an etching gas is supplied to the low-k film 14 without forming a protective film thereon, the polysilicon film 25, which is the second structure 20, is etched, and the polysilicon film 15 covered by the low-k film 14 is also etched by the etching gas that has permeated the low-k film 14. As a result, the outside of the polysilicon film 15 covered by the low-k film 14 is etched, as shown in FIG. 2C.
Such an etching method carried out without supplying a protective film forming gas is not an embodiment of the etching method of the present disclosure because it is not possible to selectively etch the second structure.

Third Embodiment
In the etching method of the present disclosure,
The first structure includes a dense film and a porous film,
the dense film, the porous film, and the second structure are provided adjacent to each other in this order on the substrate;
The step of forming the protective film includes a step of forming the protective film on pores of the porous film to close the pores, and a step of forming the protective film on a surface of the dense film,
The step of selectively etching the second structure may include the step of supplying an etching gas in a state where the protective film is formed.

FIG. 3A is a cross-sectional view that illustrates another example of a substrate to which the etching method of the present disclosure is applied.
FIG. 3A shows, as the configuration of the substrate 3, a Si wafer 30, a silicon oxide film (SiO film) 40 provided on the surface of the Si wafer 30, a first structure 10 provided on the silicon oxide film 40, and a second structure 20.

The first structure 10 is made up of a silicon oxide film 16 and a low-k film 14 provided adjacent to the silicon oxide film 16 .
The second structure 20 is made of a polysilicon film 25 provided adjacent to the low-k film 14 .
The silicon oxide film 16 constituting the first structure 10 is a dense film, and the low-k film 14 is a porous film.
In other words, it can be said that the dense film, the porous film, and the second structure are provided adjacent to each other in this order.
The dense membrane refers to a membrane in which no pores are observed under an electron microscope and through which the etching gas is less likely to permeate.

The configurations of the Si wafer, silicon oxide film, polysilicon film, and low-k film, as well as the configurations of the protective film forming gas and etching gas, may be similar to those in the first embodiment.
Whether the first structure has a dense film or not can be determined by observing a cross-sectional photograph.

FIG. 3B is a cross-sectional view that illustrates the substrate shown in FIG. 3A on which a protective film is formed.
In the step of forming the protective film, the protective film is formed in the pores of the low-k film 14, which is a porous film, to close the pores.
In FIG. 3B, in order to indicate that a protective film is present on the low-k film 14, the low-k film 14 is drawn with hatching different from that shown in FIG. 3A.
In addition, a protective film 17 is also formed on the surface of the silicon oxide film 16, which is a dense film.

The protective film forming gas is easily adsorbed by the low-k film 14 and the silicon oxide film 16, but is not easily adsorbed by the polysilicon film 25, so no protective film is formed on the surface of the polysilicon film 25.

Fig. 3C is a cross-sectional view showing a schematic diagram of the substrate after etching the substrate shown in Fig. 3B. In a state in which the low-k film 14 and the protective film formed on the silicon oxide film 16, which are the first structure 10, are present, an etching gas is supplied to etch the polysilicon film 25, which is the second structure 20.
Through the above steps, a protective film is formed on the first structure 10 in the substrate 3 shown in FIG. 3A, and the second structure 20 can be selectively etched.

[Etching equipment]
The etching apparatus of the present disclosure is an etching apparatus including a processing vessel, a stage provided within the processing vessel for placing a substrate having a first structure and a second structure formed on its surface, the first structure and the second structure being etched by an etching gas supplied into the processing vessel, a protective film forming gas supply unit that supplies a protective film forming gas containing a perfluoroolefin having 2 to 8 carbon atoms into the processing vessel to form a protective film that covers the first structure such that the first structure is selectively protected out of the first structure and the second structure, and an etching gas supply unit that supplies the etching gas into the processing vessel to selectively etch at least a portion of the second structure while the protective film is present on the first structure.

FIG. 4 is a cross-sectional view showing a schematic example of an etching apparatus.
The etching apparatus 100 includes a processing chamber 101 .
The processing vessel 101 is an airtight vacuum vessel, and a mounting table (stage) 111 for mounting a substrate 1 on a horizontally formed surface (upper surface) is provided at the lower side inside the processing vessel 101. A stage heater 112 is embedded in the mounting table 111, so that the substrate can be heated to a predetermined temperature as necessary.

A sidewall heater 113 is provided on the sidewall of the processing vessel 101, and the temperature of the atmosphere inside the processing vessel 101 can be adjusted. An openable transfer port (not shown) is provided on the sidewall of the processing vessel 101. An open exhaust port 117 is provided on the bottom of the processing vessel 101, and is connected via an exhaust pipe to an exhaust mechanism 118 composed of a vacuum pump, a valve, etc.
The exhaust flow rate from the exhaust port 117 is adjusted by the exhaust mechanism 118, whereby the pressure inside the processing vessel 101 is adjusted.

A protective film forming gas supply unit 120 and an etching gas supply unit 130 are provided on the ceiling of the processing vessel 101 above the mounting table 111 .
The configuration of the protective film forming gas supply unit 120 and the etching gas supply unit 130 is not particularly limited, but an example of such a configuration is one in which a gas shower head 140 that supplies gas is provided facing the mounting table 111.

The gas shower head 140 includes a shower plate 141, a gas diffusion space 142, and a diffusion plate 143. The shower plate 141 is provided horizontally to form the lower surface of the gas shower head 140, and has a large number of gas discharge holes 144 formed therein in a distributed manner to discharge gas in a shower-like manner onto the mounting table 111. The gas diffusion space 142 is a flat space formed such that the lower side thereof is partitioned by the shower plate 141 in order to supply gas to each gas discharge hole 144. A diffusion plate 143 is provided horizontally to divide the gas diffusion space 142 into upper and lower portions. A large number of through holes 145 are formed in a distributed manner in the diffusion plate 143.
A ceiling heater 147 is provided on the ceiling of the processing vessel 101 , and the temperature of the gas shower head 140 can be adjusted.

The downstream end of the protective film forming gas supply pipe 128, which is part of the protective film forming gas supply unit 120, and the downstream end of the etching gas supply pipe 138, which is part of the etching gas supply unit 130, are connected to the upper side of the gas diffusion space 142.

The upstream side of the protective film forming gas supply pipe 128 is connected to a protective film forming gas supply source (a cylinder for storing the protective film forming gas) 121 via a flow rate adjustment unit 129 .
By adjusting the opening and closing of the flow rate adjusting unit 129, the supply amount of the protective film forming gas can be adjusted.

The upstream side of the etching gas supply pipe 138 is connected to an etching gas supply source (a cylinder for storing the etching gas) 131 via a flow rate adjustment unit 139 .
By adjusting the opening and closing of the flow rate adjusting unit 139, the supply amount of the etching gas can be adjusted.

In an etching apparatus having the above mechanism, by opening both the flow rate adjustment unit 129 and the flow rate adjustment unit 139, it is possible to simultaneously supply protective film formation gas from the protective film formation gas supply unit 120 and etching gas from the etching gas supply unit 130.

Furthermore, by opening the flow rate adjustment unit 129 and closing the flow rate adjustment unit 139, protective film formation gas can be supplied from the protective film formation gas supply unit 120, and then by closing the flow rate adjustment unit 129 and opening the flow rate adjustment unit 139, etching gas can be supplied from the etching gas supply unit 130.

[Protective film forming gas]
The protective film forming gas of the present disclosure is used for selectively protecting a first structure when a first structure and a second structure to be etched by an etching gas are formed on a substrate and at least a portion of the second structure is selectively etched by an etching gas, and contains a perfluoroolefin having 2 to 8 carbon atoms.

Perfluoroolefins with carbon numbers of 2 to 8 are either gaseous at room temperature and pressure or easily gasify with slight heating, and therefore have an advantage in terms of energy consumption when supplying the gas for forming the protective film, unlike the amine gas used as the gas for forming the protective film in Patent Document 1.

The perfluoroolefin having 2 to 8 carbon atoms includes at least one compound selected from the group consisting of C ₃ F ₆ , C ₄ F ₈ , C ₅ F ₁₀ and C ₆ F _12. Of these, C ₃ F ₆ (hexafluoropropene) is particularly preferred.

The protective film forming gas may contain an inert gas such as nitrogen, helium, argon, etc., in addition to the perfluoroolefin having 2 to 8 carbon atoms. When an inert gas is contained, the protective film forming gas may contain the inert gas in an amount of 1 to 99% by volume, or 5 to 95% by volume.
The perfluoroolefin having 2 to 8 carbon atoms used in the protective film forming gas preferably has a purity of 99.9% by volume or more, and more preferably 99.99% by volume or more.

Since perfluoroolefin is a compound that has already been fluorinated, it does not react with the halogen-based etching gas contained in the etching gas, or the reactivity is low.
Therefore, it can be used as a gas for forming a protective film against halogen-based etching gases.

Also, perfluoroolefins with 2 to 8 carbon atoms have double bonds that are deficient in electrons. Compounds with double bonds are easily adsorbed when the first structure is a silicon oxycarbonitride film, so the protective effect is optimally exerted.

In addition, if the perfluoroolefin has 2 to 8 carbon atoms, the molecular size will be such that it can enter the pores of the porous membrane (less than 1 nm in the case of a low-k membrane) when the first structure is a porous membrane. Molecules with more than 8 carbon atoms will have difficulty entering the pores of the porous membrane, making it difficult to form a protective film on the porous membrane.

The protective film forming gas of the present disclosure is preferably used to selectively protect the first structure during etching with an etching gas containing at least one selected from the group consisting of _F2 gas, _ClF3 gas, and _IF7 gas.

For these reasons, the protective film forming gas disclosed herein is suitable for use in forming a protective film on a low-k film that is a porous silicon oxycarbonitride film.

The present disclosure will be explained in detail below using examples, but the present disclosure is not limited to these examples.

[Evaluation of the protective performance of low-k film using protective film forming gas]
A Si wafer having a porous SiOCN film (thickness: 20 nm) formed as a low-k film was prepared.
A protective film forming gas containing C ₃ F ₆ (hexafluoropropene) gas and an etching gas containing F ₂ gas were simultaneously supplied to this wafer, and the etching amount of the low-k film was evaluated.
Separately, the etching amount of the low-k film was evaluated by supplying an etching gas containing F ₂ gas without supplying the protective film forming gas.

The test conditions are as follows.
(Etching gas supply conditions)
Gas: Mixture of _F2 gas, Ar (argon) gas, and HF (hydrogen fluoride) gas Total gas flow rate: 10 to 200 sccm
Pressure: 2 to 100 Torr
Processing temperature (wafer temperature): 20 to 80° C.
(Gas supply conditions for forming protective film)
In addition to the above etching gas, C ₃ F ₆ gas was added at the same flow rate, and the total pressure was set to twice that of the etching gas supply condition.

この結果から、Ｃ_３Ｆ_６ガスを含む保護膜形成用ガスをＬｏｗ－ｋ膜に作用させて保護膜を形成することにより、エッチングガスによるＬｏｗ－ｋ膜のエッチングを抑制できることが分かった。 The results are shown in Table 1.
The numerical values indicate the amount of etching [nm] of the low-k film (SiOCN film). The thickness after etching was measured by a spectroscopic ellipsometer, and the amount of etching was calculated by taking the difference from the thickness before etching.

From this result, it was found that by forming a protective film by reacting a protective film forming gas containing C ₃ F ₆ gas on a low-k film, etching of the low-k film by an etching gas can be suppressed.

[Evaluation of reactivity between protective film forming gas and etching gas]
A protective film forming gas containing C ₃ F ₆ gas and an etching gas containing ClF ₃ gas were introduced into an infrared spectrometer, and the infrared spectrum was observed.
(Measurement conditions)
40° C., mixing pressure 12 kPa, gas composition [vol %] (C ₃ F ₆ :ClF ₃ = 1:5)

FIG. 5A is an infrared spectrum of a mixed gas of C ₃ F ₆ and ClF ₃ .
FIG. 5B is an infrared spectrum of C ₃ F ₆ gas alone, and FIG. 5C is an infrared spectrum of ClF ₃ gas alone.
The infrared spectrum of the mixed gas of C ₃ F ₆ and ClF ₃ is a combination of the infrared spectrum of C ₃ F ₆ gas alone and the infrared spectrum of ClF ₃ gas alone.
Since no new peaks were observed in the infrared spectrum of the mixed gas of C ₃ F ₆ and ClF ₃ , it is presumed that no reaction between C ₃ F ₆ and ClF ₃ occurred.

[Evaluation of Adsorption of Protective Film Forming Gas]
A protective film forming gas containing C ₃ F ₆ gas was supplied to a Si wafer having different types of films on its surface. The gas was supplied to a Si wafer having a SiN film, a polysilicon film, and a SiOCN film formed thereon as specific films. The gas was then heated and desorbed, and measured by a gas chromatograph mass spectrometer (GC-MS), to measure the amount of C ₃ F ₆ gas adsorbed in each film.

The amount of C ₃ F ₆ gas adsorbed differed for each film, with almost no C ₃ F ₆ gas adsorbed to the polysilicon film and SiN film, and C ₃ F ₆ gas adsorbed to the SiOCN film.

Since the SiOCN film has a large adsorption amount _{of C3F6} gas, a protective film is formed when a protective film forming gas containing _C3F6 gas is used. On the other hand, since the polysilicon film or the _like has a small adsorption amount _{of C3F6} gas, a protective film is not formed when _{a protective film forming gas containing C3F6 gas} is used, and the polysilicon film or the like becomes a second structure to be etched.

[Example 1]
First, as shown in Fig. 1B, a plurality of structures were prepared in which SiGe films and Si films, each having a thickness of 5 to 50 nm, were alternately stacked in four or more layers, and a porous SiOCN film (thickness 5 nm) was provided as a low-k film around one of the structures, while a Si wafer with no low-k film was prepared on the other. The spacing between the structures was set to 20 nm or more without the low-k film.
A protective film forming gas containing C ₃ F ₆ (hexafluoropropene) gas was passed through this wafer, and an etching gas containing F ₂ gas was supplied after evacuation, and the process of alternately supplying the gas was repeated to etch the SiGe film of the structure without the low-k film in the lateral direction (horizontal to the wafer). When the etching amount of the SiGe film of the structure without the low-k film reached 500 nm, it was evaluated by a reflection electron microscope image of the cross section of the structure whether the SiGe film of the structure with the low-k film was protected without being etched.

The test conditions are as follows.
(Etching gas supply conditions)
Gas: Mixture of _F2 gas, HF (hydrogen fluoride) gas, and Ar (argon) gas Total gas flow rate: 500 to 2000 sccm
Pressure: 2 to 100 Torr
Processing temperature (wafer temperature): 20 to 80° C.
(Gas supply conditions for forming protective film)
Gas: 100% _{C3F6 gas}
Total gas flow rate: 1 to 200 sccm
Pressure: 2 to 100 Torr
Processing temperature (wafer temperature): 20 to 80° C.

[Example 2]
The same procedure as in Example 1 was carried out except that the etching gas and the protective film forming gas were supplied simultaneously.

The test conditions are as follows.
(Etching gas/protective film forming gas supply conditions)
Gas: _A mixture _{of F2} gas, HF (hydrogen fluoride) gas, Ar (argon) gas, and _C3F6 gas ( _C3F6 gas is 2 to 10 times the total amount of _F2 gas and HF (hydrogen fluoride) gas)
Total gas flow rate: 500 to 2000 sccm
Pressure: 2 to 100 Torr
Processing temperature (wafer temperature): 20 to 80° C.

[Comparative Example 1]
The same procedure as in Example 1 was carried out except that the protective film forming gas was not supplied and only the etching gas was supplied.

この結果から、Ｃ_３Ｆ_６ガスを含む保護膜形成用ガスをＬｏｗ－ｋ膜に作用させて保護膜を形成することにより、周囲にＬｏｗ－ｋ膜を持つＳｉＧｅ膜に対して、エッチングガスによるエッチングを抑制できることが分かった。 The results are shown in Table 2.
The damage rate in the table is calculated by counting the number of SiGe films that were etched in the structure provided with the low-k film and dividing the number by the total number of SiGe films in the structure provided with the low-k film. The smaller the number, the more effective the protection by the protective film, with the minimum being 0.
The occurrence of lateral etching of the SiGe film without the low-k film was evaluated using a reflection electron microscope image of the cross section of the structure.

From these results, it was found that by forming a protective film by reacting a protective film forming gas containing C ₃ F ₆ gas with a low-k film, etching of the SiGe film surrounded by the low-k film by the etching gas can be suppressed.

Reference Signs List 1, 2, 3: Substrate 10: First structure 11: SiGe film 12: Si film 13: Stacked film 14: Low-k film 15: Polysilicon film 16: Silicon oxide film 17: Protective film 20: Second structure 21: SiGe film 22: Si film 23: Stacked film 25: Polysilicon film 30: Si wafer 40: Silicon oxide film 50: Polysilicon film 100: Etching device 101: Processing vessel 111: Mounting table (stage)
Reference Signs List 112 stage heater 113 side wall heater 117 exhaust port 118 exhaust mechanism 120 protective film forming gas supply unit 128 protective film forming gas supply pipe 129 flow rate adjustment unit 130 etching gas supply unit 131 etching gas supply source 138 etching gas supply pipe 139 flow rate adjustment unit 140 gas shower head 141 shower plate 142 gas diffusion space 143 diffusion plate 144 gas discharge hole 145 through hole 147 ceiling heater

Claims (17)

A substrate having a first structure and a second structure to be etched by an etching gas,
An etching method comprising the steps of: selectively etching at least a part of the second structure with an etching gas in a state in which a protective film is formed on the first structure using a protective film forming gas containing a perfluoroolefin having 2 to 8 carbon atoms. The etching method according to claim 1, wherein the protective film forming gas is supplied simultaneously with the etching gas, and the second structure is etched while the protective film is formed on the first structure. supplying the protective film forming gas to form the protective film on the first structure;
2. The etching method according to claim 1, wherein the second structure is etched by supplying the etching gas after the protective film is formed. The etching method according to any one of claims 1 to 3, wherein the protective film forming gas does not contain molecules containing hydrogen atoms. The etching method according to any one of claims 1 to 3, wherein the perfluoroolefin is at least one selected from the group consisting of C ₃ F ₆ , C ₄ F ₈ , C ₅ F ₁₀ and C ₆ F ₁₂ . The etching method according to any one of claims 1 to 3, wherein the first structure comprises a silicon oxycarbonitride film. The etching method according to any one of claims 1 to 3, wherein the first structure comprises a porous film. The etching method according to any one of claims 1 to 3, wherein the first structure comprises a silicon oxide film. The first structure includes a porous film,
the first structure and the second structure are provided separately on the substrate,
the protective film is formed so as to close the pores of the porous film,
4. The etching method according to claim 1, wherein the step of selectively etching the second structure includes the step of supplying an etching gas in a state where the protective film is formed. The etching method according to claim 9, wherein the porous film is the outermost layer of the first structure. The first structure includes a dense film and a porous film,
the dense film, the porous film, and the second structure are provided adjacent to each other in this order on the substrate;
The step of forming the protective film includes a step of forming the protective film on pores of the porous film to close the pores, and a step of forming the protective film on a surface of the dense film,
4. The etching method according to claim 1, wherein the step of selectively etching the second structure includes the step of supplying an etching gas in a state where the protective film is formed. A processing vessel;
a stage provided in the processing chamber, the stage supporting a substrate having a first structure and a second structure formed on a surface thereof, the first structure and the second structure being etched by an etching gas supplied into the processing chamber;
a protective film forming gas supply unit for supplying a protective film forming gas containing a perfluoroolefin having 2 to 8 carbon atoms into the processing vessel and forming a protective film on the first structure so that the first structure is selectively protected among the first structure and the second structure;
an etching gas supply unit that supplies the etching gas into the processing vessel to selectively etch at least a portion of the second structure while the protective film is present on the first structure;
An etching apparatus comprising: The etching apparatus according to claim 12, wherein the supply of the protective film forming gas from the protective film forming gas supply unit and the supply of the etching gas from the etching gas supply unit are performed simultaneously. After the protective film forming gas is supplied from the protective film forming gas supply unit,
The etching apparatus according to claim 12 , wherein the etching gas is supplied from the etching gas supply unit. A protective film forming gas containing a perfluoroolefin having 2 to 8 carbon atoms, used for selectively protecting a first structure when at least a portion of a second structure is selectively etched with an etching gas on a substrate on which a first structure and a second structure are formed and are to be etched with an etching gas. The protective film forming gas according to claim 15, wherein the perfluoroolefin is at least one selected from _the group consisting of _C3F6 , _{C4F8 , C5F10 and C6F12 .} The protective film forming gas according to claim 15 or 16, wherein the etching gas contains at least one gas selected from the group consisting of _F2 gas, _ClF3 gas, and _IF7 gas.

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