Film forming method and film forming apparatus

Abstract

To selectively form a carbon-based film on the top of a pattern without breaking the pattern of a photoresist film.SOLUTION: The substrate includes a silicon-containing film and a photoresist film formed on the silicon-containing film, a plurality of patterns having bottom portions are formed in the photoresist film by partially removing the photoresist film, the photoresist film between two adjacent patterns has a top portion, the silicon-containing film is exposed at the bottom portions of the patterns, plasma is generated from a film forming gas containing at least a hydrocarbon gas and a hydrogen gas, a carbon-based film is selectively formed on the top portions of the photoresist film by exposing the substrate to the plasma, and a flow rate ratio of the hydrocarbon gas and the hydrogen gas in the film forming gas is controlled.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to a method and apparatus for forming a carbon-based film. [Background technology]

[0002] 2. Description of the Related Art As demands for miniaturization of semiconductor devices increase, there is a demand to reduce the diameter and width of patterns formed in photoresist films used as masks, such as holes and trenches.

[0003] In response to this, a technique is known in which a process gas consisting of methane (CH4) gas and argon (Ar) gas is first converted into plasma, and then deposits consisting of carbon (C) and hydrogen (H) are deposited on a photoresist mask to reduce the dimensions of the opening in the photoresist mask (see, for example, Patent Document 1). Another technique is known in which trifluoromethane (CHF3) gas and trifluoroiodomethane (CF3I) gas are first converted into plasma, and then ions and radicals generated from the trifluoromethane gas are caused to collide with and react with the sidewall surface of the opening in the photoresist film, depositing deposits in that area to narrow the opening width (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-23866 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-41028 Summary of the Invention [Problem to be solved by the invention]

[0005] The technique according to the present disclosure selectively deposits a carbon-based film on top of a photoresist film without destroying the pattern of the photoresist film. [Means for solving the problem]

[0006] One aspect of the technology disclosed herein is a film formation method for forming a carbon-based film, the method comprising: a silicon-containing film; and a photoresist film formed on the silicon-containing film; a plurality of patterns each having a bottom portion formed by partially eliminating the photoresist film in the photoresist film; the photoresist film between two adjacent patterns has a top portion; the silicon-containing film is exposed at the bottom portions of the patterns; and the method comprises exposing a substrate, on which the silicon-containing film is exposed, to plasma generated from a film formation gas containing at least a hydrocarbon gas and a hydrogen gas, to selectively form the carbon-based film on the top portions of the photoresist film, and controlling a flow rate ratio of the hydrocarbon gas and the hydrogen gas in the film formation gas. [Effects of the Invention]

[0007] According to the technology of the present disclosure, a carbon-based film can be selectively formed on top of a photoresist film without destroying the pattern of the photoresist film. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a partially enlarged cross-sectional view of a wafer to which a carbon-based film forming method according to a first embodiment of the technology disclosed herein is applied. [Figure 2] FIG. 10 is a partially enlarged cross-sectional view of a wafer for explaining the formation of a carbon-based film. [Figure 3] FIG. 1 is a partially enlarged cross-sectional view of a wafer for explaining the change in shape of a photoresist film made of a metal oxide resist due to plasma and temperature. [Figure 4] 10 is a partially enlarged cross-sectional view for explaining modification of the surface of the SOG film exposed at the bottom of the hole. FIG. [Figure 5] 1 is a flowchart showing a method for forming a carbon-based film according to a first embodiment. [Figure 6] 6 is a process diagram of the method for forming the carbon-based film of FIG. 5. [Figure 7] 1 is a cross-sectional view schematically illustrating a configuration of a film forming apparatus according to a first embodiment. [Figure 8]FIG. 4 is a simplified diagram showing the configuration of a modified example of the film forming apparatus according to the first embodiment. [Figure 9] 1 is a flowchart showing a method for forming a carbon-based film when a graphene film is formed on top of a photoresist film. [Figure 10] 10 is a process diagram of the carbon-based film forming method of FIG. 9. [Figure 11] FIG. 10 is a partially enlarged cross-sectional view of a wafer to which a carbon-based film forming method according to a second embodiment of the technology disclosed herein is applied. [Figure 12] FIG. 1 is a partially enlarged cross-sectional view of a wafer for explaining the change in shape of a photoresist film made of a chemically amplified resist due to plasma and temperature. [Figure 13] FIG. 10 is a partially enlarged cross-sectional view of a wafer for illustrating protection of a photoresist film by a protective film in a second embodiment. [Figure 14] FIG. 10 is a partially enlarged cross-sectional view of a wafer when a protective film is formed while the wafer temperature is maintained at 100° C. [Figure 15] 10 is a flowchart showing a method for forming a carbon-based film according to a second embodiment. [Figure 16] 18 is a process diagram of the carbon-based film forming method of FIG. 17. [Figure 17] 10 is a flowchart showing a method for forming a carbon-based film according to a second embodiment in the case where the photoresist film is made of a metal oxide resist. [Figure 18] 10A and 10B are enlarged partial cross-sectional views of a wafer for explaining changes in the shape of a photoresist film when the thickness of a protective film is changed. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the technology according to the present disclosure will be described with reference to the drawings. First, a first embodiment of the technology according to the present disclosure will be described.

[0010] FIG. 1 is a partially enlarged cross-sectional view of a wafer W (substrate) to which a carbon-based film forming method according to a first embodiment of the present invention is applied. In this wafer W, a silicon-containing film, e.g., a spin-on-glass (SOG) film 11, is formed on an etching target film 10, and a photoresist film 12 is formed on the SOG film 11. The photoresist film 12 has a pattern, e.g., a hole 13, formed by partially eliminating the photoresist film 12. The hole 13 penetrates the photoresist film 12, and the SOG film 11 is exposed at the bottom of the hole 13. Typically, multiple holes 13 are formed in the photoresist film 12, so the photoresist film 12 between two adjacent holes 13 has a convex shape with a side surface and a top in vertical cross section. The photoresist film 12 is made of, for example, a metal oxide resist containing tin oxide (SnO).

[0011] Conventionally, photoresist film patterns have been formed by irradiating the photoresist on the wafer with a 193 nm laser beam from an argon fluoride (ArF) light source through a reduction projection lens and pure water, resulting in the formation of holes with diameters of several tens of nanometers and trenches with widths of several tens of nanometers in the photoresist film.

[0012] In recent years, to meet the demand for further miniaturization, patterns on photoresist films are formed using light emitted from an EUV (Extreme Ultraviolet) light source with a wavelength of 13.5 nm (hereinafter referred to as "EUV light") as a light source. When EUV light is used, holes with diameters of several nm to several tens of nm and trenches with widths of several nm to several tens of nm can be formed in the photoresist film.

[0013] However, if the photoresist film on which the pattern is formed is thickened to form deep holes or deep trenches, the diameter of the holes or the width of the trenches will be too small, causing the patterns to collapse during development of the photoresist film using EUV light.

[0014] In response to this problem, the present applicant has been studying the formation of an amorphous carbon-based film that is selectively and vertically grown on top of a patterned photoresist film, which is believed to enable the mask to be thickened while maintaining the diameter and width of the pattern formed by EUV light.

[0015] FIG. 2 is a partially enlarged cross-sectional view of a wafer W for explaining the formation of a carbon-based film. First, plasma is generated from a film-forming gas consisting of acetylene (C2H2) gas, hydrogen (H2) gas, and argon gas, an inert gas, and the wafer W is exposed to this plasma. At this time, the plasma generated from the acetylene gas contains hydrocarbon ions (shown as white circles in the figure) and hydrocarbon radicals (shown as black circles in the figure), as shown in FIG. 2(A). The hydrocarbon ions are highly anisotropic and adhere approximately perpendicularly to the holes 13. As a result, a carbon-based film derived from the hydrocarbon ions grows vertically on the top of the photoresist film 12 and the bottom of the holes 13. On the other hand, the hydrocarbon radicals are highly isotropic and adhere to the holes 13 from all directions. As a result, a carbon-based film derived from the hydrocarbon radicals grows not only on the top of the photoresist film 12 but also on the bottom of the holes 13 and the side surfaces of the photoresist film 12.

[0016] When plasma is generated from a film-forming gas, hydrogen plasma is generated from hydrogen gas, and hydrogen radicals contained in the hydrogen plasma isotropically etch the carbon-based film. Etching of the carbon-based film by hydrogen radicals depends on the temperature of the wafer W. When the temperature of the wafer W is low, the etching power of the hydrogen radicals is weak, and the carbon-based film is hardly etched.

[0017] As a result, when the temperature of the wafer W is low, not only the carbon-based film 14 derived from hydrocarbon radicals but also the carbon-based film 14 derived from hydrocarbon ions grows on the top of the photoresist film 12. Furthermore, the carbon-based film 14 derived from hydrocarbon radicals also grows on the bottom of the hole 13 and the side surface of the photoresist film 12 (FIG. 2(B)).

[0018] When the temperature of the wafer W is high, the etching power of the hydrogen radicals increases, and the carbon-based film 14 is isotropically etched. As a result, the carbon-based film 14 derived from the hydrocarbon radicals at the bottom of the hole 13 and on the side of the photoresist film 12 is removed by etching, making it difficult for the carbon-based film 14 to be formed inside the hole 13 (FIG. 2(C)). This allows an amorphous carbon-based film to grow selectively and vertically on the top of the photoresist film 12.

[0019] In addition, as described above, in the formation of carbon-based films, not only hydrocarbon ions and hydrocarbon radicals but also hydrogen radicals play an important role, so the flow rate ratio of acetylene gas and hydrogen gas in the film formation gas must be strictly controlled. The flow rate ratio is set to any value within the range of 1:1 to 1:50. Furthermore, the hydrocarbon gas contained in the film formation gas is not limited to acetylene gas, but may be any of ethylene (C2H4) gas, methane (CH4) gas, and propylene (C3H6) gas, or a mixture thereof.

[0020] The carbon-based film 14 grown on the bottom of the hole 13 and the side surface of the photoresist film 12 inhibits the transfer of the shape of the hole 13 to the etching target film 10 during etching using the photoresist film 12. Therefore, it is preferable to form the carbon-based film 14 when the temperature of the wafer W is high, making it difficult for the carbon-based film 14 to grow inside the hole 13.

[0021] Therefore, the applicant attempted to form holes 13 in a photoresist film 12 on a wafer W using EUV light, and then form a carbon-based film 14 while the temperature of the wafer W was high. Specifically, while the temperature of the wafer W was maintained at 360°C, plasma was generated from a film-forming gas, and an attempt was made to grow a carbon-based film 14 selectively and vertically on top of the photoresist film 12 (metal oxide resist film).

[0022] However, when the temperature of the wafer W was maintained at 360°C and plasma was generated from the film formation gas, tin (Sn) agglomerated in the photoresist film 12, causing the photoresist film 12 to collapse and the hole 13 to disappear (Figure 3(A)).

[0023] Next, in order to find the cause of the collapse of the photoresist film 12, the applicant supplied a film forming gas to the wafer W without generating plasma while maintaining the temperature of the wafer W at 360° C. In this case, it was confirmed that no tin aggregation occurred, the photoresist film 12 did not collapse, and the holes 13 did not disappear, as shown in FIG.

[0024] Furthermore, the applicant attempted to grow a carbon-based film 14 selectively and vertically on the top of the photoresist film 12 by generating plasma from a film-forming gas while maintaining the temperature of the wafer W at 200°C or less. In this case, too, it was confirmed that tin did not aggregate, the photoresist film 12 did not collapse, and the holes 13 did not disappear, as shown in FIG. 3(C). However, it was confirmed that the carbon-based film 14 was formed not only on the top of the photoresist film 12, but also on the bottom of the holes 13 and the side surfaces of the photoresist film 12. This was thought to be due to the low temperature of the wafer W when the carbon-based film 14 was formed.

[0025] From the above, the applicant has found that plasma attack is the main cause of the breakdown of the photoresist film 12. Furthermore, the applicant has also found that even if plasma is generated, if the temperature of the wafer W is kept at 200° C. or less, the carbon-based film 14 can be formed on the photoresist film 12 without the photoresist film 12 being broken down.

[0026] However, as described above, if the carbon-based film 14 is formed on the bottom of the hole 13 or on the side surface of the photoresist film 12, it will hinder the transfer of the shape of the hole 13 to the etching target film 10 during etching using the photoresist film 12. Therefore, the applicant has investigated a method for suppressing the formation of the carbon-based film 14 on the bottom of the hole 13 or on the side surface of the photoresist film 12 while keeping the temperature of the wafer W at 200° C. or less.

[0027] Incidentally, the SOG film 11 formed on the wafer W is modified to be hydrophobic by adding an adhesion promoter (e.g., methylsilsesquioxane) to improve adhesion with the photoresist film 12 formed thereon. Alternatively, the surface of the SOG film 11 is modified to be hydrophobic by surface treatment using hexamethyldisilazane (HMDS treatment). Specifically, as shown in FIG. 4(A), the surface of the SOG film 11 is modified so that methyl groups are present on the surface.

[0028] On the other hand, carbon-based films exhibit hydrophobicity with a water contact angle of 50 degrees or more, and therefore are thought to have a high affinity with the SOG film 11, which also exhibits hydrophobicity, but a low affinity with hydrophilic films. Therefore, in the first embodiment, the surface of the SOG film 11 exposed at the bottom of the hole 13 is modified from hydrophobic to hydrophilic to reduce its affinity with the carbon-based film 14, thereby preventing the carbon-based film 14 from being formed at the bottom of the hole 13. Specifically, as shown in FIG. 4(B), the SOG film 11 is modified so that hydroxyl groups are present on the surface of the SOG film 11.

[0029] FIG. 5 is a flow chart showing a method for forming a carbon-based film according to the first embodiment, and FIG. 6 is a process chart showing the method for forming a carbon-based film of FIG.

[0030] First, a wafer W is prepared in which an SOG film 11 is formed on an etching target film 10, and a photoresist film 12 is further formed on the SOG film 11. Holes 13 are formed in the photoresist film 12 using EUV light, and the holes 13 penetrate the photoresist film 12, exposing the SOG film 11 at the bottom of the holes 13 (FIG. 6(A)).

[0031] Next, the wafer W is subjected to a hydrophilic treatment (step S51). Specifically, the wafer W is subjected to a DHF cleaning treatment, a heat treatment using hydrogen gas, or a heat treatment using water. At this time, the surface of the SOG film 11 exposed at the bottom of the hole 13 is modified into a hydrophilic layer 11a. At this time, the photoresist film 12 does not undergo a chemical reaction, so only the surface of the SOG film 11 is selectively modified into a hydrophilic layer 11a (FIG. 6(B)).

[0032] Thereafter, the temperature of the wafer W is maintained at 200°C or less, and plasma is generated from the film-forming gas to form a carbon-based film 14 (step S52). At this time, hydrocarbon ions in the hydrocarbon plasma adhere to the holes 13 substantially perpendicularly, and hydrocarbon radicals adhere to the holes 13 from all directions. However, because the bottoms of the holes 13 have been modified to the hydrophilic layer 11a, they have low affinity for hydrocarbon radicals and hydrocarbon ions, and the adhesion of hydrocarbon radicals is suppressed. As a result, the carbon-based film 14 is formed on the top and side surfaces of the photoresist film 12, but not on the bottoms of the holes 13 (FIG. 6(C)). Furthermore, because the temperature of the wafer W is maintained at 200°C or less, tin does not aggregate, and the photoresist film 12 does not collapse.

[0033] Next, to remove unnecessary carbon-based film 14, the wafer W is subjected to a post-etching process, for example, an etching process using hydrogen radicals (step S53). At this time, the carbon-based film 14 formed on the top and side surfaces of the photoresist film 12 is removed. However, since the carbon-based film 14 formed on the side surfaces of the photoresist film 12 is composed only of carbon-based film derived from hydrocarbon radicals, it is thin and can be removed in a relatively short time. On the other hand, the carbon-based film 14 formed on the top surface of the photoresist film 12 is thick because it is composed not only of carbon-based film derived from hydrocarbon radicals but also of carbon-based film derived from hydrocarbon ions. As a result, even when the carbon-based film 14 formed on the side surfaces of the photoresist film 12 is removed, a relatively thick carbon-based film 14 remains on the top surface of the photoresist film 12 (FIG. 6(D)).

[0034] Then, when the carbon-based film 14 formed on the side surface of the photoresist film 12 is removed, this process is terminated.

[0035] 7 is a cross-sectional view showing a schematic configuration of a film forming apparatus according to the first embodiment. This film forming apparatus is a plasma-enhanced chemical vapor deposition (PECVD) apparatus that forms a film by generating plasma from a film forming gas, and performs step S52 (film forming process) in the carbon-based film forming method of FIG.

[0036] 7, the film forming apparatus 15 includes a substantially cylindrical chamber 16 (processing vessel) that defines a processing space and accommodates a wafer W. As will be described later, plasma is generated from a film forming gas in the processing space inside the chamber 16. The chamber 16 has a sidewall with a loading / unloading port 17 for loading / unloading the wafer W into / out of the chamber 16, and the loading / unloading port 17 is opened and closed by a gate valve 18.

[0037] A substantially disk-shaped mounting table 19 is disposed inside the chamber 16, and a wafer W is placed on the mounting table 19. An annular guide ring 20 is disposed on the outer edge of the mounting table 19 so as to surround the placed wafer W. The mounting table 19 is supported by a cylindrical support member 21 that extends upward from the bottom of the chamber 16.

[0038] Furthermore, a lower electrode 22, a heater 23, and a coolant passage (not shown) are embedded inside the mounting table 19. The heater 23 generates heat by power supplied from a heater power supply 24 to heat the mounted wafer W, and the coolant passage circulates a coolant supplied from the outside to cool the mounted wafer W. Note that a heat transfer gas may be supplied between the mounting table 19 and the wafer W to improve the heat transfer between the mounting table 19 and the wafer W.

[0039] An upper electrode 25 is disposed on the ceiling of the chamber 16 so as to face the mounting table 19, and an insulating member 26 is disposed between the chamber 16 and the upper electrode 25. The upper electrode 25 has a base member 27, a top plate 28, and an intermediate member 29. The top plate 28 and the base member 27 are separated by the generally annular intermediate member 29 to form a gas diffusion space 30 therebetween. A gas introduction port 31 that communicates with the gas diffusion space 30 from above is formed in the base member 27, while a plurality of gas holes 32 that communicate the gas diffusion space 30 with the processing space inside the chamber 16 are formed in the top plate 28.

[0040] The film forming apparatus 15 also includes a gas source 33, which is connected to a gas inlet port 31 via a gas inlet pipe 34. The gas source 33 has a gas source, a flow rate controller, and an on-off valve (none of which are shown), and supplies a film forming gas consisting of acetylene gas, argon gas, and hydrogen gas. The supplied film forming gas is introduced into the gas diffusion space 30 via the gas inlet port 31, and further diffused and introduced into the processing space inside the chamber 16 through each gas hole 32. This allows the upper electrode 25 to function as a shower head. A heat insulating member 35 is disposed on the upper electrode 25.

[0041] The film forming apparatus 15 further includes an exhaust device 36. The exhaust device 36 is, for example, a turbo molecular pump and / or a dry pump, and reduces the pressure inside the chamber 16 via an exhaust pipe 37 connected to the bottom of the chamber 16. In the film forming apparatus 15, when the carbon-based film 14 is formed, the pressure inside the chamber 16 is set to any value in the range of 20 mTorr to 1000 mTorr.

[0042] The film forming apparatus 15 further includes a high-frequency power supply 38, which is connected to the upper electrode 25 via a matching box 39. The matching box 39 matches the impedance of the load of the high-frequency power supply 38 to the output impedance of the high-frequency power supply 38. The high-frequency power supply 38 supplies high-frequency power of any frequency in the range of 450 KHz to 300 MHz to the upper electrode 25.

[0043] The film forming apparatus 15 further includes a control unit 40, which controls each component of the film forming apparatus 15. The control unit 40 is a computer equipped with a processor, memory, an input device, a display device, a signal input / output interface, etc., and a control program and recipe data are stored in the memory of the control unit 40. When performing a carbon-based film formation process in the film forming apparatus 15, the processor of the control unit 40 executes the corresponding control program and controls each component of the film forming apparatus 15 in accordance with the recipe data.

[0044] Specifically, the control unit 40 controls the gas source 33 and the exhaust device 36 to adjust the pressure inside the chamber 16, and controls the high-frequency power supply 38 to supply high-frequency power to the upper electrode 25. The control unit 40 also controls the gas source 33 to diffuse and introduce the film-forming gas into the processing space inside the chamber 16. At this time, the film-forming gas is excited by an electric field generated by the high-frequency power supplied to the upper electrode 25, generating hydrocarbon plasma and hydrogen plasma. Then, hydrocarbon ions and hydrocarbon radicals in the hydrocarbon plasma form the carbon-based film 14, and hydrogen radicals in the hydrogen plasma etch part of the carbon-based film 14.

[0045] The film forming apparatus 15 further includes an impedance circuit 41. The impedance circuit 41 is disposed in an electrical path 42 connecting the lower electrode 22 and the ground. The impedance circuit 41 includes at least one of an inductor and a capacitor, and can change the impedance between the lower electrode 22 and the ground by connecting them in series or in parallel. The inductor and capacitor included in the impedance circuit 41 may be either a fixed element or a variable element.

[0046] By changing this impedance, it is possible to weaken the electrical coupling between the upper electrode 25 and the lower electrode 22 and to control the reduction of the high frequency current flowing through the lower electrode 22. As a result, it is possible to more precisely control the energy of ions incident on the wafer W, and in the film forming apparatus 15, when forming the carbon-based film 14, the maximum value of the ion energy imparted from the plasma to the wafer W placed on the mounting table 19 is controlled to 200 eV or less.

[0047] Note that the film formation apparatus capable of executing step S52 in FIG. 6 is not limited to the film formation apparatus 15 in FIG. 7. For example, step S52 in the carbon-based film formation method of FIG. 5 may be executed using a film formation apparatus 43 shown in simplified form in FIG. 8. The configuration of the film formation apparatus 43 is similar to that of the film formation apparatus 15 except for the illustrated configuration. In the film formation apparatus 43, the high-frequency power supply 38 supplies extremely high-frequency power, for example, high-frequency power having a frequency higher than 40 MHz, to the upper electrode 25. The plasma generated at this time becomes high-density plasma, and the electrical impedance of the plasma decreases. This reduces the voltage amplitude Vpp at the upper electrode 25, thereby reducing the plasma potential between the upper electrode 25 and the lower electrode 22 and the sheath voltage. In addition, the sheath oscillates at high speed, reducing the ion response to the sheath voltage. As a result, the ion energy imparted to the wafer W placed on the mounting table 19 can be reduced. For example, the maximum ion energy imparted to the wafer W can be controlled to 200 eV or less.

[0048] 5, the surface of the SOG film 11 exposed at the bottom of the hole 13 is modified to form a hydrophilic layer 11a, and then, while maintaining the temperature of the wafer W at 200°C or less, plasma is generated from the film formation gas to form the carbon-based film 14. This suppresses adhesion of hydrocarbon radicals to the bottom of the hole 13 and prevents the photoresist film 12 from collapsing. As a result, the carbon-based film 14 can be selectively formed on the top of the photoresist film 12 without collapsing the hole 13 of the photoresist film 12, allowing the mask to be thickened.

[0049] In the first embodiment, the photoresist film 12 is made of a metal oxide resist. However, the photoresist film 12 may also be made of a chemically amplified resist. However, the heat resistance temperature of the chemically amplified resist is lower than that of the metal oxide resist, for example, 150°C or lower. Therefore, if the photoresist film 12 is made of a chemically amplified resist, there is a risk that the photoresist film 12 will collapse when the temperature of the wafer W is maintained at 200°C or lower to grow the carbon-based film 14 on top of the photoresist film 12 in step S52 of FIG. 5. Therefore, if the photoresist film 12 is made of a chemically amplified resist, it is preferable to maintain the temperature of the wafer W at 100°C or lower to grow the carbon-based film 14 on top of the photoresist film 12 in step S52 of FIG. 5, taking into account the influence (attack) of plasma.

[0050] Furthermore, in the first embodiment, an amorphous carbon-based film 14 is formed on top of the photoresist film 12. However, if the photoresist film 12 is made of a metal oxide resist, a crystalline carbon-based film (graphene film) may be formed by selective growth on top of the photoresist film 12. Formation of a graphene film can be achieved at a higher temperature than formation of the amorphous carbon-based film 14, but it is necessary to further reduce the ion energy imparted to the wafer W. For example, when the temperature of the wafer W is maintained at about 200°C, the maximum value of the ion energy imparted to the wafer W needs to be controlled to 10 eV or less in order to form a graphene film.

[0051] When forming a graphene film on top of the photoresist film 12, for example, in a film formation apparatus having a configuration similar to that of the film formation apparatus 15 of FIG. 7, it is preferable to supply high-frequency power from the high-frequency power supply 38 at a higher frequency, for example, a frequency of 180 MHz or higher. By increasing the frequency of the high-frequency power in this manner, the ion energy of the plasma is further reduced. As a result, the ion energy imparted to the wafer W is further reduced, allowing the graphene film to be selectively formed.

[0052] FIG. 9 is a flowchart showing a method for forming a carbon-based film when a graphene film is formed on top of a photoresist film 12, and FIG. 10 is a process diagram of the method for forming a carbon-based film of FIG.

[0053] 5, a wafer W is prepared in which an SOG film 11 is formed on an etching target film 10, and a photoresist film 12 made of metal oxide resist is further formed on the SOG film 11. Holes 13 are formed in the photoresist film 12 using EUV light, and the holes 13 penetrate the photoresist film 12, exposing the SOG film 11 at the bottom of the holes 13 (FIG. 10(A)).

[0054] Next, the wafer W is subjected to a hydrophilic treatment (step S91). At this time, the surface of the SOG film 11 exposed at the bottom of the hole 13 is modified into a hydrophilic layer 11a (FIG. 10(B)).

[0055] Thereafter, the temperature of the wafer W is maintained at 200° C. or less, and plasma is generated from a film formation gas consisting of acetylene gas, argon gas, and hydrogen gas. At this time, hydrocarbon radicals in the hydrocarbon plasma mainly form graphene films 44 on the surfaces of the holes 13 (step S92).

[0056] However, because the bottom of the hole 13 is modified to the hydrophilic layer 11a, it has low affinity with the graphene film 44, which is a carbon-based film, and the graphene film 44 is not formed at the bottom of the hole 13. In addition, because the graphene film 44 grows two-dimensionally, it is not formed on the side surfaces of the photoresist film 12. As a result, the graphene film 44 is selectively formed only on the top of the photoresist film 12 (FIG. 10(C)).

[0057] Furthermore, the catalytic effect of tin contained in the metal oxide resist constituting the photoresist film 12 promotes the formation of the graphene film 44, so that in step S92, a relatively thick graphene film 44 can be formed on top of the photoresist film 12. At this time, too, the temperature of the wafer W is maintained at 200° C. or less, so that tin does not aggregate and the photoresist film 12 does not collapse.

[0058] Then, this process is terminated after the graphene film 44 is formed on the top of the photoresist film 12. As described above, since the graphene film 44 is not formed on the side surface of the photoresist film 12, there is no need to perform a post-etching process on the wafer W after step S92.

[0059] 9, the surface of the SOG film 11 exposed at the bottom of the hole 13 is modified to form a hydrophilic layer 11a, and then, while maintaining the temperature of the wafer W at 200° C. or less, plasma is generated from the film formation gas to form the graphene film 44. This prevents the graphene film 44 from being formed at the bottom of the hole 13 and also prevents the photoresist film 12 from collapsing. As a result, the carbon-based film 14 can be selectively formed on the top of the photoresist film 12 without collapsing the hole 13 of the photoresist film 12, allowing the mask to be thickened.

[0060] Next, a second embodiment of the technology according to the present disclosure will be described.

[0061] 11 is a partially enlarged cross-sectional view of a wafer W to which the carbon-based film forming method according to the second embodiment is applied. In this wafer W, an SOG film 11 is also formed on an etching target film 10. A photoresist film 45 is formed on the SOG film 11, but the photoresist film 45 is composed of a chemically amplified resist rather than a metal oxide resist. Similarly to the photoresist film 12, a hole 13 is formed in the photoresist film 45 using EUV light. The hole 13 penetrates the photoresist film 45, and the SOG film 11 is exposed at the bottom of the hole 13.

[0062] The applicant then attempted to form a carbon-based film 14 after forming holes 13 in a photoresist film 45 on a wafer W using EUV light. However, the heat resistance temperature of a chemically amplified resist is lower than that of a metal oxide resist, for example, 150°C or lower. Therefore, the applicant attempted to grow a carbon-based film 14 on top of the photoresist film 45 by generating plasma from a film-forming gas while maintaining the temperature of the wafer W at 150°C.

[0063] However, when the temperature of the wafer W was maintained at 150° C. and plasma was generated from the film forming gas, the photoresist film 45 collapsed, and part of the photoresist film 45 flowed into the bottom of the hole 13 (FIG. 12(A)).

[0064] Next, in order to find the cause of the collapse of the photoresist film 45, the applicant supplied a film forming gas to the wafer W without generating plasma while maintaining the temperature of the wafer W at 150°C. In this case, as shown in Figure 12(B), it was confirmed that the photoresist film 45 did not collapse and the holes 13 did not disappear, but the film thickness of the photoresist film 45 decreased. The area indicated by the dashed line in the figure corresponds to the reduced portion of the photoresist film 45.

[0065] Furthermore, the applicant supplied a film forming gas to the wafer W without generating plasma while maintaining the temperature of the wafer W at 100° C. In this case, it was confirmed that the thickness of the photoresist film 45 did not decrease and the holes 13 did not disappear, as shown in FIG.

[0066] From the above, the applicant has confirmed that chemically amplified resists have low resistance to both plasma and heat. Damage to the photoresist film 45 during the formation of the carbon-based film 14 includes not only damage due to heat from the heater 23 of the mounting table 19, but also damage due to heat input from the plasma and damage due to plasma attack. Therefore, the applicant has investigated a method for protecting the photoresist film 45 from plasma during the formation of the carbon-based film 14. Specifically, as shown in FIG. 13(A), the applicant has investigated covering the photoresist film 45 and the exposed SOG film 11 with a protective film 46 before the formation of the carbon-based film 14.

[0067] However, if the protective film 46 is thick, the actual diameter of the hole 13 will be reduced, so it is preferable that the protective film 46 be made of a thin film, such as a silicon dioxide (SiO2) film or a silicon nitride (SiN) film formed by ALD (Atomic Layer Deposition).

[0068] By forming the protective film 46, the photoresist film 45 is not directly exposed to the plasma, and therefore the photoresist film 45 can be protected not only from damage due to plasma attack but also from damage due to heat input from the plasma. This improves the heat resistance of the photoresist film 45, and allows the temperature of the wafer W to be increased when the carbon-based film 14 is formed. As a result, the carbon-based film 14 can be prevented from growing on the bottom of the hole 13 or on the side surface of the photoresist film 45, and therefore the carbon-based film 14 can be grown selectively and vertically on the top of the photoresist film 45 (FIG. 13(B)).

[0069] Furthermore, as mentioned above, chemically amplified resists have low heat resistance, so attention must be paid to the temperature of the wafer W when forming the protective film 46. Therefore, the applicant formed the protective film 46 while maintaining the temperature of the wafer W at 100°C, and observed the change in the shape of the photoresist film 45. In this case, the process gas was converted into plasma to form the protective film 46, and remote plasma was used as the plasma source to prevent the photoresist film 45 from being attacked by ions in the plasma.

[0070] 14 is a partially enlarged cross-sectional view of the wafer W when the protective film 46 is formed while the temperature of the wafer W is maintained at 100°C. As shown in the figure, it was confirmed that the photoresist film 45 did not collapse and the holes 13 did not disappear, but the film thickness of the photoresist film 45 was slightly reduced. Therefore, it was found that it is preferable to keep the temperature of the wafer W at 100°C or less when forming the protective film 46.

[0071] FIG. 15 is a flow chart showing a method for forming a carbon-based film according to the second embodiment, and FIG. 16 is a process chart showing the method for forming a carbon-based film of FIG.

[0072] First, a wafer W is prepared in which an SOG film 11 is formed on an etching target film 10, and further, a photoresist film 45 is formed on the SOG film 11. Holes 13 are formed in the photoresist film 45 using EUV light, and the holes 13 penetrate the photoresist film 45, exposing the SOG film 11 at the bottom of the holes 13 (FIG. 16(A)). At this time, taking into consideration that the actual diameter of the holes 13 is reduced by a protective film 46 described below, the diameter of the holes 13 is enlarged by the thickness of the protective film 46. Specifically, the diameter of the holes 13 is determined by adding the thickness of two protective films 46 to the diameter of the required wiring.

[0073] Next, a protective film 46 made of silicon dioxide is formed so as to cover the photoresist film 45 and the exposed SOG film 11 (step S151) (FIG. 16(B)). At this time, a remote plasma is used as a plasma source for converting the processing gas into plasma, and the temperature of the wafer W is maintained at 100°C or less. The protective film 46 is formed by repeating ALD, specifically, by repeatedly supplying a silicon-containing gas and a reactive gas. The thickness of the protective film 46 is preferably 2 nm or more.

[0074] Thereafter, plasma is generated from the film-forming gas to form the carbon-based film 14 (step S152). At this time, the protective film 46 protects the photoresist film 45 from damage caused by the plasma attack as well as damage caused by heat input from the plasma. Therefore, the heat resistance of the photoresist film 45 can be improved, and the temperature of the wafer W during the formation of the carbon-based film 14 can be increased to above 100°C.

[0075] However, as described above, the heat resistance temperature of the chemically amplified resist is 150°C. Therefore, in order to prevent the photoresist film 45 from collapsing due to heat, the temperature of the wafer W when the carbon-based film 14 is formed is maintained at 150°C or below. That is, since the carbon-based film 14 is formed at a low temperature of the wafer W, not only the carbon-based film 14 derived from hydrocarbon radicals but also the carbon-based film 14 derived from hydrocarbon ions grows on the top of the photoresist film 45. Furthermore, the carbon-based film 14 derived from hydrocarbon radicals also grows on the bottom of the hole 13 and the side surface of the photoresist film 45 (FIG. 16(C)). Note that step S172 is performed by the film forming apparatus 15 of FIG. 7 or the film forming apparatus 43 of FIG. 8.

[0076] Next, a post-etching process is performed on the wafer W to remove unnecessary carbon-based film 14 (step S153). At this time, the carbon-based film 14 formed on the top and side surfaces of the photoresist film 45 and on the bottom surfaces of the holes 13 is removed. However, the carbon-based film 14 formed on the bottom surfaces of the holes 13 and on the side surfaces of the photoresist film 45 is thin and removed in a relatively short time because it is composed only of carbon-based film derived from hydrocarbon radicals. On the other hand, the carbon-based film 14 formed on the top surfaces of the photoresist film 45 is thick because it is composed not only of carbon-based film derived from hydrocarbon radicals but also of carbon-based film derived from hydrocarbon ions. As a result, even when the carbon-based film 14 formed on the bottom surfaces of the holes 13 and on the side surfaces of the photoresist film 45 is removed, a relatively thick carbon-based film 14 remains on the top surfaces of the photoresist film 45 (FIG. 16(D)).

[0077] Then, at the point when the carbon-based film 14 formed on the bottom of the hole 13 and on the side surface of the photoresist film 45 has been removed, this process is completed.

[0078] According to the carbon-based film deposition method of FIG. 15 , a protective film 46 is formed to cover the photoresist film 45 and the exposed SOG film 11, improving the heat resistance of the photoresist film 45. Then, while maintaining the temperature of the wafer W at 150° C. or less, plasma is generated from the deposition gas to form the carbon-based film 14. This prevents the photoresist film 45 from collapsing during the formation of the carbon-based film 14. Furthermore, a subsequent post-etching process removes the carbon-based film 14 formed on the bottom of the hole 13 and on the side surface of the photoresist film 45. As a result, the carbon-based film 14 can be selectively deposited on the top of the photoresist film 45 without collapsing the hole 13 of the photoresist film 45.

[0079] In the second embodiment, the photoresist film 45 is made of a chemically amplified resist, but the photoresist film 45 may also be made of a metal oxide resist. In this case, the protective film 46 prevents the photoresist film 45 from being damaged by plasma attack or heat input from the plasma. Furthermore, as can be seen from the confirmation results shown in FIG. 3(B), the photoresist film 45 made of metal oxide resist does not collapse without causing tin aggregation even if the temperature of the wafer W is raised to 360°C, unless it is attacked by plasma. Therefore, if the protective film 46 is formed, the photoresist film 45 will not collapse even if the temperature of the wafer W is raised to 360°C or below during the formation of the carbon-based film 14.

[0080] FIG. 17 is a flowchart showing a method for forming a carbon-based film according to the second embodiment when the photoresist film is made of a metal oxide resist.

[0081] First, a wafer W is prepared in which an SOG film 11 is formed on an etching target film 10, and a photoresist film 45 made of metal oxide resist is further formed on the SOG film 11. Note that, in the photoresist film 45, holes 13 are formed using EUV light with a diameter enlarged by the thickness of the protective film 46, similar to the carbon-based film forming method of FIG.

[0082] Next, a protective film 46 made of silicon dioxide is formed so as to cover the photoresist film 45 and the exposed SOG film 11 (step S171). At this time, as in the carbon-based film forming method of Fig. 15, a remote plasma is used as a plasma source for converting the processing gas into plasma, and the protective film 46 is formed by ALD.

[0083] Thereafter, plasma is generated from the film formation gas to form the carbon-based film 14 (step S172). As described above, the photoresist film 45 made of metal oxide resist will not crumble even if the temperature of the wafer W is raised to 360°C, provided that the protective film 46 is formed and the photoresist film 45 is not attacked by the plasma. Therefore, the temperature of the wafer W when forming the carbon-based film 14 is maintained at 360°C or below. That is, since the carbon-based film 14 is formed while the temperature of the wafer W is high, the carbon-based film 14 is not formed on the bottom of the hole 13 or on the side surface of the photoresist film 45, but is formed selectively and vertically on the top of the photoresist film 45.

[0084] Then, this process is terminated after the carbon-based film 14 is formed on the top of the photoresist film 45. As described above, the carbon-based film 14 is not formed on the bottom of the hole 13 or on the side surface of the photoresist film 45, so there is no need to perform a post-etching process on the wafer W after the formation of the carbon-based film 14, as in the carbon-based film forming method of FIG.

[0085] Furthermore, in order to examine the necessary film thickness of the protective film 46, the applicant formed protective films 46 with different film thicknesses, and then formed the carbon-based film 14.

[0086] First, a protective film 46 having a thickness of 1 nm was formed on the wafer W so as to cover the photoresist film 45 made of metal oxide resist and the exposed SOG film 11 (FIG. 18(A)). Thereafter, the temperature of the wafer W was maintained at 360°C or less, and plasma was generated from the film-forming gas to form the carbon-based film 14. At this time, tin coagulated, causing the photoresist film 45 to collapse, and the holes 13 disappeared (FIG. 18(B)).

[0087] Furthermore, a protective film 46 having a thickness of 2 nm was formed on the wafer W so as to cover the photoresist film 45 made of metal oxide resist and the exposed SOG film 11 (FIG. 18(C)). Thereafter, the temperature of the wafer W was maintained at 360°C or less, and plasma was generated from the film-forming gas to form a carbon-based film 14. During this process, no tin agglomeration occurred, the photoresist film 45 did not collapse, and the holes 13 did not disappear (FIG. 18(D)).

[0088] From the above, it was found that if the thickness of the protective film 46 is 2 nm or more, the photoresist film 45 can be protected from plasma attack and the photoresist film 45 can be prevented from collapsing. Furthermore, the 1 nm thick protective film 46 was formed by repeating ALD only a few times and was therefore not a continuous film. Therefore, it was thought that one of the causes of the collapse of the photoresist film 45 was that the photoresist film 45 was partially attacked directly by the plasma. Therefore, it was also inferred that if the protective film 46 is a continuous film, the photoresist film 45 can be prevented from collapsing even if the thickness is not 2 nm or more.

[0089] Although the preferred embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications and changes are possible within the scope of the gist of the present disclosure.

[0090] For example, although holes 13 are formed as a pattern in photoresist films 12 and 45, trenches may also be formed. When a trench is formed, it is preferable to form the trench with a width expanded by the thickness of protective film 46, taking into consideration that the actual width of the trench will be reduced when protective film 46 is formed.

[0091] Furthermore, in the wafer W to which the carbon-based film forming method according to the first or second embodiment is applied, holes 13 and patterns are formed by EUV light in the photoresist film 12, 45. However, the carbon-based film forming method according to the first or second embodiment can also be applied to a wafer W in which holes 13 and patterns are formed in the photoresist film 12, 45 by light irradiated from an argon-fluoride light source. [Explanation of symbols]

[0092] W wafer 11 SOG membrane 11a Hydrophilic layer 12,45 Photoresist film 13 holes 14 Carbon-based membrane 15,43 Film deposition equipment 40 Control Unit 44 Graphene film 46 Protective film

Claims

1. A method for forming a carbon-based film, comprising the steps of: a film formation process including exposing a substrate, the substrate comprising a silicon-containing film and a photoresist film formed on the silicon-containing film, the photoresist film having a plurality of patterns each having a bottom portion formed by partially eliminating the photoresist film, the photoresist film between two adjacent patterns having a top portion, the silicon-containing film being exposed at the bottom portion of each pattern, to plasma generated from a film formation gas containing at least a hydrocarbon gas and a hydrogen gas, thereby selectively forming the carbon-based film on the top portion of the photoresist film; A method for forming a carbon-based film, wherein a flow rate ratio of the hydrocarbon gas and the hydrogen gas in the film-forming gas is controlled.

2. 2. The method for forming a carbon-based film according to claim 1, wherein the pattern is formed by irradiating a photoresist with EUV (Extreme Ultraviolet) light.

3. 3. The method for forming a carbon-based film according to claim 2, wherein the photoresist is a chemically amplified resist or a metal oxide resist.

4. The method for forming a carbon-based film according to claim 3 , wherein the metal oxide resist contains tin oxide.

5. 4. The method for forming a carbon-based film according to claim 3, further comprising the step of modifying a surface of the silicon-containing film exposed at the bottom of the pattern to be hydrophilic before the film-forming step.

6. 6. The method for forming a carbon-based film according to claim 5, wherein the surface of the silicon-containing film exposed at the bottom of the pattern is modified to be hydrophilic by DHF cleaning treatment, heat treatment with hydrogen gas, or heat treatment with water.

7. 6. The carbon-based film forming method according to claim 5, wherein when the photoresist is a chemically amplified resist, the temperature of the substrate is maintained at 100[deg.] C. or less in the film forming step.

8. 6. The carbon-based film forming method according to claim 5, wherein when the photoresist is a metal oxide resist, the temperature of the substrate is maintained at 200[deg.] C. or less in the film forming step.

9. The carbon-based film forming method according to claim 3 , further comprising the step of forming a protective film covering the photoresist film before the film forming step.

10. The protective film is made of silicon dioxide (SiO ２ 10. The method for forming a carbon-based film according to claim 9, wherein the carbon-based film is a silicon nitride (SiN) film or a silicon nitride (SiN) film.

11. 11. The method for forming a carbon-based film according to claim 10, wherein the protective film is formed by repeatedly supplying a silicon-containing gas and a reactive gas.

12. 10. The method for forming a carbon-based film according to claim 9, wherein the protective film has a thickness of 2 nm or more.

13. 10. The carbon-based film forming method according to claim 9, wherein the temperature of the substrate is maintained at 150[deg.] C. or less in the film forming step when the photoresist is a chemically amplified resist.

14. 10. The carbon-based film forming method according to claim 9, wherein when the photoresist is a metal oxide resist, the temperature of the substrate is maintained at 360[deg.] C. or less in the film forming step.

15. 10. The carbon-based film forming method according to claim 9, wherein when the photoresist is a chemically amplified resist, the temperature of the substrate is maintained at 100[deg.] C. or less during the formation of the protective film.

16. 2. The carbon-based film forming method according to claim 1, wherein the flow rate ratio of the hydrocarbon gas to the hydrogen gas in the film forming gas is set to any one of the ranges of 1:1 to 1:

50.

17. The hydrocarbon gas is acetylene (C ２ H ２ ) gas, ethylene (C ２ H ４ ) gas, methane (CH ４ ) gas and propylene (C ３ H ６ 2. The method for forming a carbon-based film according to claim 1, further comprising the step of:

18. The carbon-based film deposition method according to claim 1 , wherein the deposition gas further contains an inert gas.

19. 2. The carbon-based film deposition method according to claim 1, wherein the frequency of the high-frequency power supplied to generate the plasma in the film deposition step is set to any frequency in the range of 450 KHz to 300 MHz.

20. 2. The carbon-based film forming method according to claim 1, wherein in the film forming step, a pressure of a space to which the film forming gas is supplied when the plasma is generated is set to any value within a range of 20 mTorr to 1000 mTorr.

21. 2. The carbon-based film forming method according to claim 1, wherein the maximum value of the ion energy of the plasma in the film forming step is controlled to 200 eV or less.

22. The carbon-based film forming method according to claim 1 , wherein the carbon-based film is an amorphous carbon-based film or a graphene film.

23. 2. The method for forming a carbon-based film according to claim 1, wherein the carbon-based film is formed by PECVD (Plasma-Enhanced Chemical Vapor Deposition) in the film forming step.

24. A film formation apparatus for forming a carbon-based film, a processing vessel having a mounting table disposed therein and defining a processing space; an electrode facing the mounting table and serving as a shower head for supplying a film forming gas into the processing space; a gas source connected to a gas introduction pipe and supplying the film forming gas to the processing space through the shower head; a high frequency power supply connected to the electrode via a matching box; a control unit, the control unit carries out a film formation process in which a substrate is placed on the stage, the substrate comprising a silicon-containing film and a photoresist film formed on the silicon-containing film, the photoresist film having a plurality of patterns each having a bottom portion formed by partially eliminating the photoresist film, the photoresist film between two adjacent patterns having a top portion, the silicon-containing film being exposed at the bottom portion of the pattern, the control unit supplies a film formation gas containing at least a hydrocarbon gas and a hydrogen gas from the gas source, supplies power from the high-frequency power supply to the electrode to generate plasma from the film formation gas, and exposes the substrate to the plasma to selectively form the carbon-based film on the top portions of the photoresist film, The control unit controls a flow rate ratio of the hydrocarbon gas and the hydrogen gas in the film formation gas.

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