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

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 protective film forming gas

[0001] The present disclosure relates to an etching method, an etching apparatus, and a gas for forming a protective film.

[0002] When constructing a semiconductor device, various films formed on a semiconductor wafer (hereinafter referred to as a wafer) that serves as a substrate are etched. For example, a wafer on which an interlayer insulating film called a low-k film is formed is etched to form recesses in the interlayer insulating film for embedding wiring.

[0003] 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 in this process.

[0004] Japanese Patent Application Laid-Open No. 2021-163775

[0005] In the technology described in Patent Document 1, a protective film forming gas containing an amine gas is supplied to form a protective film on a first structure, which is a film that is not to be etched, and an etching gas is then supplied to selectively etch a second structure, which is a film that is to be etched, with the protective film formed on the first structure.

[0006] 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 an amine gas, they must be heated to become a gas, which is undesirable from the viewpoint of energy consumption. Therefore, it has been desired to use a protective film forming gas containing a material other than amine gas.

[0007] In light of the above background, an object of the present disclosure is to provide an etching method using a protective film forming gas containing a gas other than an amine gas.

[0008] The present disclosure is as follows.

[0009] The present disclosure (1) relates to an etching method for a substrate having a first structure and a second structure to be etched with an etching gas, in a state where a protective film is formed on the first structure using a protective film forming gas containing a perfluoroolefin having 2 to 8 carbon atoms, and at least a part of the second structure is selectively etched with the etching gas.

[0010] The present disclosure (2) relates to the etching method according to 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 being formed on the first structure.

[0011] The present disclosure (3) relates to the etching method according to the present disclosure (1), in which the protective film is formed on the first structure by supplying the protective film forming gas, and after the protective film is formed, the etching gas is supplied to etch the second structure.

[0012] The present disclosure (4) relates to the 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.

[0013] The present disclosure (5) is a method for producing a perfluoroolefin comprising the steps of: ３ F ６ , C ４ F ８ , C ５ F １０ and C ６ F １２ The present disclosure relates to an etching method according to any one of (1) to (4), wherein the etching material is at least one selected from the group consisting of:

[0014] The present disclosure (6) relates to the etching method according to any one of the present disclosures (1) to (5), in which the first structure comprises a silicon oxycarbonitride film.

[0015] The present disclosure (7) relates to the etching method according to any one of the present disclosures (1) to (6), in which the first structure comprises a porous film.

[0016] The present disclosure (8) relates to the etching method according to any one of the present disclosures (1) to (5), in which the first structure comprises a silicon oxide film.

[0017] The present disclosure (9) relates to the etching method according to any one of the present disclosures (1) to (5), wherein the first structure is a porous film, the first structure and the second structure are provided apart from each other on the substrate, the protective film is formed so as to close holes in the porous film, and the step of selectively etching the second structure includes a step of supplying an etching gas in a state where the protective film is formed.

[0018] The present disclosure (10) relates to the etching method according to the present disclosure (9), wherein the porous film is the outermost layer of the first structure.

[0019] The present disclosure (11) relates to the etching method according to any one of the present disclosures (1) to (5), wherein 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 in holes in the porous film to close the holes and forming the protective film on a surface of the dense film, and the step of selectively etching the second structure includes a step of supplying an etching gas in a state where the protective film is formed.

[0020] The present disclosure (12) relates to an etching apparatus including: a processing vessel; a stage provided in the processing vessel for placing a substrate having a first structure and a second structure formed on its surface, the first 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 and forms a protective film on the first structure so that the first structure is selectively protected from the first structure and the second structure; and an etching gas supply unit that supplies the etching gas into the processing vessel in order to selectively etch at least a portion of the second structure while the protective film is present on the first structure.

[0021] The present disclosure (13) relates to an etching apparatus according to the present disclosure (12), in which 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.

[0022] The present disclosure (14) relates to the etching apparatus according to the present disclosure (12), wherein the etching gas is supplied from the etching gas supply unit after the protective film forming gas is supplied from the protective film forming gas supply unit.

[0023] The present disclosure (15) relates to a protective film forming gas that is used for selectively protecting a first structure and a second structure formed on a substrate to be etched by an etching gas when at least a part of the second structure is selectively etched by the etching gas, and that contains a perfluoroolefin having 2 to 8 carbon atoms.

[0024] The present disclosure (16) is a method for producing a perfluoroolefin comprising the steps of: ３ F ６ , C ４ F ８ , C ５ F １０ and C ６ F １２ The protective film forming gas according to the present disclosure (15) is at least one selected from the group consisting of:

[0025] The present disclosure (17) is directed to a method for treating a gas containing F ２ Gas, ClF ３ Gas and IF ７ The protective film forming gas according to the present disclosure (15) or (16) includes at least one selected from the group consisting of:

[0026] The present disclosure can provide an etching method using a protective film forming gas containing a gas other than an amine gas.

[0027] FIG. 1A is a cross-sectional view schematically showing an example of a substrate to which the etching method of the present disclosure can be applied. FIG. 1B is a cross-sectional view schematically showing a substrate from which a polysilicon film has been removed from the substrate shown in FIG. 1A. FIG. 1C is a cross-sectional view schematically showing a substrate obtained by etching the substrate shown in FIG. 1B. FIG. 1D is a cross-sectional view schematically showing the substrate shown in FIG. 1B, in which a protective film has been formed on the low-k film by supplying a protective film forming gas. FIG. 2A is a cross-sectional view schematically showing another example of a substrate to which the etching method of the present disclosure can be applied. FIG. 2B is a cross-sectional view schematically showing the substrate shown in FIG. 2A, in which etching has been performed. FIG. 2C is a cross-sectional view schematically showing the substrate shown in FIG. 2A, in which etching has been performed without supplying a protective film forming gas. FIG. 3A is a cross-sectional view schematically showing another example of a substrate to which the etching method of the present disclosure can be applied. FIG. 3B is a cross-sectional view schematically showing the substrate shown in FIG. 3A, in which a protective film has been formed. FIG. 3C is a cross-sectional view schematically showing the substrate shown in FIG. 3B, in which etching has been performed. 4 is a cross-sectional view showing an example of an etching apparatus. ３ F ６ and ClF ３ FIG. 5B is an infrared spectrum of the mixed gas of C ３ F ６ Figure 5C shows the infrared spectrum of the gas alone. ３ This is the infrared spectrum of the gas alone.

[0028] An etching method, an etching apparatus, and a protective film forming gas according to an embodiment of the present disclosure will be described with reference to the drawings.

[0029] [Etching Method] (First Embodiment) Fig. 1A is a cross-sectional view schematically showing an example of a substrate to which the etching method of the present disclosure is applied. Fig. 1A shows the configuration of the substrate 1, which includes a Si wafer 30, a silicon oxide film (SiO film) 40 provided on the surface of the Si wafer 30, and a first structure 10 and a second structure 20 provided on the silicon oxide film 40. The silicon oxide film 40 on the surface of the Si wafer 30 does not necessarily have to be provided.

[0030] The first structure and the second structure are etched by an etching gas, but in the etching method of the present disclosure, the first structure is not etched because a protective film is formed on it, and the second structure is selectively etched.

[0031] In the substrate shown in Figure 1A, the first structure 10 and the second structure 20 both comprise multiple types of films and are arranged separately. The first structure 10 consists of a stacked film 13 in which SiGe films 11 and Si films 12 are alternately stacked, and a low-k film 14 that covers the periphery of the stacked film 13. The second structure 20 consists of a stacked film 23 in which SiGe films 21 and Si films 22 are alternately stacked, 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.

[0032] The low-k film 14 serves to protect the stacked film 13 from etching. 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, or the like.

[0033] 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. The molar ratio of Si, O, C, and N in the silicon oxycarbonitride is not particularly limited.

[0034] Furthermore, when 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).

[0035] Examples of the second structure to be etched in the etching method of the present disclosure include a SiGe film, a polysilicon film, an α-Si film (amorphous silicon film), etc. 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.

[0036] Fig. 1B is a cross-sectional view schematically illustrating the substrate after removing the polysilicon film from the substrate shown in Fig. 1A. Before the etching method of the present disclosure is applied to the substrate 1, the polysilicon film 50 is removed by etching, resulting in the substrate 1 being in the state shown in Fig. 1B.

[0037] The etching method of the present disclosure is applied to the substrate 1 shown in Figure 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. Figure 1C, which follows Figure 1B, shows the state after the formation of the protective film on the first structure and the etching of the second structure are performed simultaneously, and Figure 1D, which follows Figure 1B, shows the state after the formation of the protective film on the first structure before the etching of the second structure.

[0038] The perfluoroolefin having 2 to 8 carbon atoms is a compound having one or more double bonds in its structure and consisting only of carbon atoms and fluorine atoms, and may be linear, branched, or cyclic. ３ F ６ , C ４ F ８ , C ５ F １０ and C ６ F １２ Among these, at least one compound selected from the group consisting of C ３ F ６(Hexafluoropropene) is particularly preferred. It is also preferred 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 progresses, and selectivity with the SiGe film 21, which is 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 proportion 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.

[0039] Perfluoroolefins with 2 to 8 carbon atoms do not react with etching gases or have low reactivity. Because perfluoroolefins are already fluorinated compounds, it is presumed that they do not react with halogen-based etching gases contained in etching gases or have low reactivity.

[0040] 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 inside the protective film from being etched and also to prevent the film at the same level as the protective film (in this example, the low-k film 14) from being etched.

[0041] When the first structure is a porous film, the protective film forming gas is adsorbed into the pores of the porous film, filling the pores and preventing the etching gas from penetrating into the porous film. Also, the etching gas can be prevented from penetrating into films inside the porous film.

[0042] Furthermore, 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 exhibit a favorable protective effect. Furthermore, when the first structure is a porous film, the size of the perfluoroolefins having 2 to 8 carbon atoms is such that they 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 have difficulty entering the pores of the porous film, making it difficult to form a protective film on the porous film.

[0043] 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 likely to be 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.

[0044] Perfluoroolefins having 2 to 8 carbon atoms are either gaseous at room temperature and pressure or easily converted to gaseous form with slight heating, and therefore have an advantage in terms of the energy consumption required for heating when supplying the protective film forming gas compared to the amine gas used as the protective film forming gas in Patent Document 1. Perfluoroolefins having 2 to 4 carbon atoms are gaseous at room temperature and pressure and do not require heating to convert them to gas, and therefore have a particular advantage in terms of energy consumption.

[0045] The etching gas may be an etching gas containing a halogen-based etching gas. ２ (Fluorine) gas, ClF ３ (Chlorine trifluoride) gas, IF ７ (iodine heptafluoride) gas, for example ClF ３ (chlorine trifluoride) gas, F ２ (Fluorine) gas and NH ３ (ammonia) gas, F ２ Gas, Ar (argon) gas, and HF (hydrogen fluoride) gas mixture, or IF ７ (iodine heptafluoride) gas, etc. All of these are halogen-based etching gases, and do not react with perfluoroolefins having 2 to 8 carbon atoms, or have low reactivity with them.

[0046] When etching the second structure using an etching gas, etching may be performed in a plasma state or without a plasma state. Etching with a plasma state refers to introducing a halogen-based etching gas or the like at about 0.1 to 10 Torr into a reaction apparatus, applying high-frequency power to an outer coil or an opposing electrode to generate low-temperature gas plasma in the reaction apparatus, and performing etching using the halogen-based activated chemical species generated therein. Etching without a plasma state refers to etching without generating the gas plasma described above.

[0047] In the etching method of the present disclosure, in a state in which a protective film formed on a first structure using a protective film-forming gas containing a perfluoroolefin having 2 to 8 carbon atoms is present, at least a portion of a second structure is selectively etched with an etching gas.

[0048] 1C is a cross-sectional view schematically illustrating the substrate shown in FIG. 1B after etching. FIG. 1C shows the state in which the SiGe film 21, which is part of the second structure 20, has been removed by etching. The SiGe film 21 of the second structure 20 is not protected by a 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, but this shows that only the Si film 22 remains after the SiGe film 21 has been etched, and the Si film 22 is not actually floating.

[0049] On the other hand, the low-k film 14 on 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 a perfluoroolefin having 2 to 8 carbon atoms. Therefore, the low-k film 14 is not etched, and the SiGe film 11 constituting the stacked film 13 covered by the low-k film 14 is not etched. In other words, the first structure 10 is not etched, and the SiGe film 11 of the second structure 20 is selectively etched. Note that in FIG. 1C, the low-k film 14 is hatched differently from the low-k film 14 shown in FIG. 1B to indicate that a protective film is present in the low-k film 14.

[0050] 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 simultaneous supply of a protective film forming gas and an etching gas is also included in "etching the second structure" in "a state in which the protective film formed on the first structure is present."

[0051] 1B, a protective film forming gas and an etching gas are simultaneously supplied to the substrate in a state where no protective film exists on the low-k film 14. As a result, a protective film is formed on the low-k film 14 and the second structure 20 is simultaneously etched.

[0052] 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 etching, the laminated film 13 is not immediately 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. After a while has passed since the protective film forming gas was 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.

[0053] 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.

[0054] In the etching method of the present disclosure, 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.

[0055] 1B, a protective film forming gas is supplied to the low-k film 14 when no protective film is present thereon. As a result, a protective film is formed on the low-k film 14. If an etching gas is supplied to the low-k film 14 when a protective film is formed thereon, the etching gas is prevented from reaching the stacked film 13, and the second structure 20 can be selectively etched.

[0056] 1D is a cross-sectional view schematically illustrating the substrate shown in FIG. 1B on which a protective film has been formed on the low-k film by supplying a protective film-forming gas. 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, the substrate is shown at a stage in which a protective film has been formed on the low-k film 14, which is the outermost layer of the first structure 10, and before the etching gas is supplied. In FIG. 1D, the low-k film 14 is depicted with hatching different from that shown in FIG. 1B (the same hatching as the low-k film 14 shown in FIG. 1C) to indicate the presence of a protective film on the low-k film 14.

[0057] When an etching gas is supplied to the substrate shown in FIG. 1D in which a protective film is present on the low-k film 14, the etching gas is prevented from reaching the stacked film 13, so that the second structure can be selectively etched, and the substrate after etching shown in FIG. 1C is obtained.

[0058] Furthermore, in the etching method of the present disclosure, when a protective film forming gas is supplied to form a protective film on a first structure, and after the protective film is formed, an etching gas is supplied to etch a second structure, multiple cycles may be repeated, with one cycle consisting of "forming a protective film by supplying a protective film forming gas and etching the second structure by supplying an etching gas."

[0059] In the etching method of the present disclosure, the temperature when supplying the protective film forming gas is preferably 0°C or higher and 200°C or lower, and more preferably 20°C or higher and 80°C or lower.

[0060] 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 close the pores of 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.

[0061] 2A is a cross-sectional view schematically illustrating another example of a substrate to which the etching method of the present disclosure is applied. The substrate 2 includes a Si wafer 30, a silicon oxide film (SiO film) 40 formed on the surface of the Si wafer 30, a first structure 10 formed on the silicon oxide film 40, and a second structure 20 formed on the silicon oxide film 40.

[0062] 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 up of a polysilicon film 25 that is formed around the periphery of the first structure 10.

[0063] 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.

[0064] 2B is a cross-sectional view schematically showing the substrate shown in FIG. 2A after etching. When a protective film forming gas is supplied simultaneously with an etching gas, and the second structure is etched while a protective film is being formed on the first structure, a protective film is formed on the low-k film 14 that is a part of the first structure 10, and at the same time, the polysilicon film 25 that is the second structure 20 is etched. The polysilicon film 15 that is covered with the low-k film 14 on which the protective film has been formed is not etched.

[0065] 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 in a state where a protective film has been formed on the low-k film 14, which is a part of the first structure 10, and the polysilicon film 25, which is the second structure 20, is etched.

[0066] 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, to indicate that the protective film is present on the low-k film 14, the low-k film 14 is depicted with hatching that is different from that of the low-k film 14 shown in Fig. 2A.

[0067] 2C is a cross-sectional view schematically illustrating the substrate shown in FIG. 2A , which has been etched without supplying a protective film forming gas. When the low-k film 14 is a porous film and an etching gas is supplied without forming a protective film on the low-k film 14, the polysilicon film 25, which is the second structure 20, is etched, and the etching gas that has permeated the low-k film 14 also etches the polysilicon film 15 covered by the low-k film 14. As a result, as shown in FIG. 2C , the outside of the polysilicon film 15 covered by the low-k film 14 is etched. Such an etching method performed without supplying a protective film forming gas cannot selectively etch the second structure, and therefore is not an implementation of the etching method of the present disclosure.

[0068] (Third embodiment) In the etching method of the present disclosure, the first structure may include 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 may include a step of forming the protective film in holes in the porous film to close the holes and forming the protective film on a surface of the dense film, and the step of selectively etching the second structure may include a step of supplying an etching gas with the protective film formed.

[0069] 3A is a cross-sectional view schematically illustrating another example of a substrate to which the etching method of the present disclosure is applied, which shows the configuration of the substrate 3, including 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 provided on the silicon oxide film 40.

[0070] 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 up 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 a dense film, a porous film, and a second structure are provided adjacent to each other in this order. Note that a dense film refers to a film in which no pores are observed under an electron microscope and which is less permeable to etching gases.

[0071] 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 Embodiment 1. Whether the first structure has a dense film or not can be determined by observing a cross-sectional photograph.

[0072] 3B is a cross-sectional view schematically showing the substrate shown in FIG. 3A on which a protective film has been formed. In the step of forming the protective film, the protective film is formed in the pores of the porous low-k film 14 to block the pores. In FIG. 3B, the low-k film 14 is hatched differently from the low-k film 14 shown in FIG. 3A to indicate that the protective film is present in the low-k film 14. In addition, a protective film 17 is also formed on the surface of the dense silicon oxide film 16.

[0073] The protective film forming gas is easily adsorbed to the low-k film 14 and the silicon oxide film 16 but is not easily adsorbed to the polysilicon film 25 , so that no protective film is formed on the surface of the polysilicon film 25 .

[0074] 3C is a cross-sectional view schematically showing the substrate shown in FIG. 3B after etching. An etching gas is supplied to etch the polysilicon film 25 of the second structure 20 in a state where a protective film is formed on the low-k film 14 and silicon oxide film 16 of the first structure 10. Through the above process, 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.

[0075] [Etching Apparatus] The etching apparatus of the present disclosure includes a processing vessel; a stage disposed 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 so as to selectively protect the first structure 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.

[0076] 4 is a cross-sectional view showing a schematic example of an etching apparatus. The etching apparatus 100 includes a processing vessel 101. The processing vessel 101 is an airtight vacuum vessel, and a mounting table (stage) 111 is provided at the bottom of the processing vessel 101. The mounting table 111 has a horizontally formed surface (top surface) on which a substrate 1 is placed. A stage heater 112 is embedded in the mounting table 111, and the substrate can be heated to a predetermined temperature as needed.

[0077] A sidewall heater 113 is provided on the sidewall of the processing vessel 101, which allows adjustment of the temperature of the atmosphere inside the processing vessel 101. A transfer port (not shown) that can be opened and closed 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 that is composed of a vacuum pump, a valve, etc. The exhaust mechanism 118 adjusts the exhaust flow rate from the exhaust port 117, thereby adjusting the pressure inside the processing vessel 101.

[0078] 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 configurations of the protective film forming gas supply unit 120 and the etching gas supply unit 130 are not particularly limited, but an example configuration is one in which a gas shower head 140 that supplies gas is provided opposite the mounting table 111.

[0079] The gas shower head 140 includes a shower plate 141, a gas diffusion space 142, and a diffuser plate 143. The shower plate 141 is horizontally disposed to form the lower surface of the gas shower head 140, and has a large number of gas discharge holes 144 formed therein for discharging gas in a shower-like manner onto the mounting table 111. The gas diffusion space 142 is a flat space defined below by the shower plate 141 for supplying gas to each gas discharge hole 144. A diffuser plate 143 is horizontally disposed to divide the gas diffusion space 142 into upper and lower spaces. The diffuser plate 143 has a large number of through-holes 145 formed therein for distributing the gas. 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.

[0080] The upper side of the gas diffusion space 142 is connected to the downstream end of a protective film forming gas supply pipe 128, which is part of the protective film forming gas supply unit 120, and the downstream end of an etching gas supply pipe 138, which is part of the etching gas supply unit 130.

[0081] The upstream side of the protective film forming gas supply pipe 128 is connected to a protective film forming gas supply source (a cylinder storing the protective film forming gas) 121 via a flow rate adjustment unit 129. The supply amount of the protective film forming gas can be adjusted by adjusting the opening and closing of the flow rate adjustment unit 129.

[0082] 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. The amount of etching gas supplied can be adjusted by adjusting the opening and closing of the flow rate adjustment unit 139.

[0083] In an etching apparatus having the above-described 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 forming gas from the protective film forming gas supply unit 120 and etching gas from the etching gas supply unit 130.

[0084] In addition, 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.

[0085] [Protective Film Forming Gas] The protective film forming gas of the present disclosure is used for selectively protecting a first structure when at least a portion of a second structure to be etched by an etching gas is selectively etched by an etching gas on a substrate on which the first structure and the second structure are formed, and contains a perfluoroolefin having 2 to 8 carbon atoms.

[0086] Perfluoroolefins having 2 to 8 carbon atoms are gases at room temperature and pressure, or can be easily converted to gases by slight heating. Therefore, unlike the amine gas used as the protective film forming gas in Patent Document 1, they have an advantage in terms of energy consumption when supplied as the protective film forming gas.

[0087] As the perfluoroolefin having 2 to 8 carbon atoms, C ３ F ６ , C４ F ８ , C ５ F １０ and C ６ F １２ Among these, at least one compound selected from the group consisting of C ３ F ６ (Hexafluoropropene) is particularly preferred.

[0088] Furthermore, the protective film forming gas may contain an inert gas such as nitrogen, helium, or argon in addition to the perfluoroolefin having 2 to 8 carbon atoms. When an inert gas is contained, the inert gas may be contained in the protective film forming gas at 1 to 99% by volume, or may be contained at 5 to 95% by volume. Furthermore, 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.

[0089] Since perfluoroolefins are already fluorinated compounds, they do not react with or have low reactivity to halogen-based etching gases contained in etching gases, and therefore can be used as gases to form protective films against halogen-based etching gases.

[0090] Furthermore, 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.

[0091] Furthermore, if the perfluoroolefin has 2 to 8 carbon atoms, the molecular size will be such that, when the first structure is a porous film, it can enter the pores of the porous film (less than 1 nm in the case of a low-k film). Molecules with more than 8 carbon atoms will have difficulty entering the pores of the porous film, making it difficult to form a protective film on the porous film.

[0092] The protective film forming gas of the present disclosure is F ２ Gas, ClF ３ Gas and IF ７It is preferable that the protective layer is used to selectively protect the first structure during etching with an etching gas containing at least one selected from the group consisting of gases.

[0093] From the above, the protective film forming gas of the present disclosure is suitable for use in forming a protective film on a low-k film that is a porous silicon oxycarbonitride film.

[0094] The present disclosure will be specifically described below using examples, but the present disclosure is not limited to such examples.

[0095] [Evaluation of the Protective Performance of Low-k Film by Protective Film Forming Gas] A Si wafer provided with a porous SiOCN film (thickness: 20 nm) as a Low-k film was prepared. ３ F ６ A protective film forming gas containing (hexafluoropropene) gas and F ２ The etching amount of the low-k film was evaluated by simultaneously supplying an etching gas containing F gas. ２ An etching gas containing the gas was supplied, and the amount of etching of the low-k film was evaluated.

[0096] The test conditions were as follows: (Etching gas supply conditions) Gas: F ２ Mixture of 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 (Protective film forming gas supply conditions) In addition to the above etching gas, ３ F ６ The gases were added at the same flow rates, and the total pressure was twice that of the etching gas supply conditions.

[0097] The results are shown in Table 1. The numerical values ​​are the etching amount [nm] of the low-k film (SiOCN film), and the etching amount was calculated by measuring the thickness after etching with a spectroscopic ellipsometer and taking the difference from the thickness before etching. From this result, C ３ F ６It has been found that etching of the low-k film by the etching gas can be suppressed by forming a protective film by allowing the protective film forming gas containing the gas to act on the low-k film.

[0098] [Evaluation of Reactivity between Protective Film Forming Gas and Etching Gas] C ３ F ６ A protective film forming gas containing ClF ３ The etching gas containing the gas was 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)

[0099] FIG. 5A is a C ３ F ６ and ClF ３ 5B is the infrared spectrum of the mixed gas of C. ３ F ６ The infrared spectrum of the gas alone is shown in Figure 5C. ３ This is the infrared spectrum of the gas alone. ３ F ６ and ClF ３ The infrared spectrum of the mixed gas is ３ F ６ Infrared spectroscopic spectrum of the gas alone and ClF ３ The infrared spectrum of the gas is combined with that of the gas alone. ３ F ６ and ClF ３ Since no new peaks appear in the infrared spectrum of the mixed gas, ３ F ６ and ClF ３ It is presumed that the reaction does not occur.

[0100] [Evaluation of Adsorption of Protective Film Forming Gas] ３ F ６The gas was supplied to a Si wafer on which a SiN film, a polysilicon film, and a SiOCN film were formed. The gas was then heated and desorbed gas was measured using a gas chromatograph mass spectrometer (GC-MS), and the C content of each film was determined. ３ F ６ The amount of gas adsorption was measured.

[0101] For each membrane, C ３ F ６ The amount of gas adsorption differs, and C is higher for polysilicon films and SiN films. ３ F ６ The gas is hardly adsorbed, and the SiOCN film ３ F ６ The gas was adsorbed.

[0102] The SiOCN film is C ３ F ６ Because the amount of gas adsorption is large, C ３ F ６ A protective film is formed when a protective film forming gas containing C is used. ３ F ６ Because the amount of gas adsorption is small, ３ F ６ When a protective film forming gas containing the gas is used, no protective film is formed, and the second structure becomes the target of etching.

[0103] [Example 1] First, as shown in Figure 1B, a plurality of structures were prepared in which four or more layers of SiGe films and Si films, each 5 to 50 nm thick, were alternately stacked, and a porous SiOCN film (5 nm thick) 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 when no low-k film was provided. For this wafer, C ３ F ６ A protective film forming gas containing hexafluoropropene gas was passed through the chamber, and after evacuation, F ２The process of alternately supplying an etching gas containing a low-k film and an etching gas containing a low-k film was repeated, and the SiGe film of the structure without the low-k film was etched laterally (in a direction parallel to the wafer). When the etching amount of the SiGe film of the structure without the low-k film reached 500 nm, whether the SiGe film of the structure with the low-k film was protected without being etched was evaluated using a reflection electron microscope image of the cross section of the structure.

[0104] The test conditions were as follows: (Etching gas supply conditions) Gas: F ２ Mixture of C 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: C ３ F ６ Gas 100% Total gas flow rate: 1 to 200 sccm Pressure: 2 to 100 Torr Processing temperature (wafer temperature): 20 to 80°C

[0105] 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.

[0106] The test conditions were as follows: (Etching gas and protective film forming gas supply conditions) Gas: F ２ Gas, HF (hydrogen fluoride) gas, Ar (argon) gas, and C ３ F ６ Gas mixture (C ３ F ６ The gas is F ２ Gas flow rate: 2 to 10 times the total of HF (hydrogen fluoride) gas and HCl (HCl+HCl) gas) Total gas flow rate: 500 to 2000 sccm Pressure: 2 to 100 Torr Processing temperature (wafer temperature): 20 to 80°C

[0107] 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.

[0108] The results are shown in Table 2. The damage rate in the table is the value obtained by counting the number of SiGe films that were etched in the structure provided with the low-k film and dividing this 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 this result, C ３ F ６ It was found that by forming a protective film by allowing a protective film-forming gas containing the gas to act on a low-k film, etching of the SiGe film surrounded by the low-k film by the etching gas can be suppressed.

[0109] REFERENCE SIGNS LIST 1, 2, 3 Substrate 10 First structure 11 SiGe film 12 Si film 13 Laminated 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 Laminated film 25 Polysilicon film 30 Si wafer 40 Silicon oxide film 50 Polysilicon film 100 Etching apparatus 101 Processing vessel 111 Mounting table (stage) 112 Stage heater 113 Sidewall 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

1. An etching method comprising the steps of: providing a substrate having a first structure and a second structure to be etched with an etching gas; and selectively etching at least a portion of the second structure with the 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.

2. 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 being formed on the first structure.

3. The etching method according to claim 1, further comprising the steps of: supplying the protective film forming gas to form the protective film on the first structure; and, after the protective film is formed, supplying the etching gas to etch the second structure.

4. 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.

5. The perfluoroolefin is 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 etching material is at least one selected from the group consisting of:

6. The etching method according to any one of claims 1 to 3, wherein the first structure comprises a silicon oxycarbonitride film.

7. The etching method according to any one of claims 1 to 3, wherein the first structure comprises a porous membrane.

8. The etching method according to any one of claims 1 to 3, wherein the first structure comprises a silicon oxide film.

9. An etching method according to any one of claims 1 to 3, comprising a porous film as the first structure, the first structure and the second structure being spaced apart from each other on the substrate, the protective film being formed so as to block holes in the porous film, and the step of selectively etching the second structure including a step of supplying an etching gas with the protective film being formed.

10. The etching method according to claim 9, wherein the porous film is the outermost layer of the first structure.

11. An etching method according to any one of claims 1 to 3, comprising: 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 in holes in the porous film to close the holes and forming the protective film on a surface of the dense film; and the step of selectively etching the second structure includes a step of supplying an etching gas with the protective film formed.

12. An etching apparatus comprising: 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 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 out of the first structure and the second structure; and an etching gas supply unit for supplying the etching gas into the processing vessel in order to selectively etch at least a portion of the second structure while the protective film is present on the first structure.

13. 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.

14. The etching apparatus according to claim 12, wherein the supply of the protective film forming gas from the protective film forming gas supply part is followed by the supply of the etching gas from the etching gas supply part.

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

16. The perfluoroolefin is C ３ F ６ , C ４ F ８ , C ５ F １０ and C ６ F １２ The protective film forming gas according to claim 15, which is at least one selected from the group consisting of:

17. The etching gas is F ２ Gas, ClF ３ Gas and IF ７ 17. The protective film forming gas according to claim 15, comprising at least one selected from the group consisting of gases.

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