Method and apparatus for forming carbon-based film

Abstract

The invention provides a method and an apparatus for forming a carbon-based film. When a carbon-based film is selectively formed on the top of a pattern such as a trench or a hole, the occurrence of overhanging of the carbon-based film is suppressed, and productivity is improved. In a film forming apparatus, plasma is generated from a film forming gas comprising only acetylene gas and argon gas inside a chamber, and a carbon-based film is selectively formed on the top of a fin sandwiched between trenches formed in an oxide layer of a wafer.

Description

Technical Field

[0001] The present disclosure relates to a carbon film forming method and a film forming device. Background Art

[0002] In the field of semiconductor devices, there is a known technique for selectively forming a carbon film on the top of a groove or hole formed in a mask or etching target film in order to realize wiring of more complex shapes or fine wiring. For example, in the technique described in Patent Document 1, a carbon film is formed on the top of a groove formed in a substrate made of silicon. Specifically, a fluid film, which is an amorphous carbon polymer film, is deposited mainly at the bottom of the groove in the substrate. Thereafter, the fluid film at the bottom is exposed to nitrogen plasma to etch the fluid film at the bottom, and a gaseous carbon film is formed from the fluid film. x N y H z At this time, compared to C x N y H z In terms of the adhesion coefficient of the fluid film on the bottom, C x N y H z The adhesion coefficient of the top of the trench where silicon is exposed is high, so C x N y H z As a result, a carbon film is selectively formed on the top of the trench.

[0003] Furthermore, a technology is known for preventing significant positive voltage fluctuations on an upper electrode, which faces a stage on which the wafer is mounted, during plasma processing of a wafer on which a semiconductor device is to be formed, thereby reducing the impact input of ions in the plasma onto the wafer. In this technology, a clamp circuit is provided between a high-frequency power supply and the upper electrode. The clamp circuit shapes the voltage waveform of the high-frequency power supply to suppress the positive voltage within the high-frequency voltage applied to the upper electrode (see, for example, Patent Document 2).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2021-19199

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2022-18062 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] The technology according to the present disclosure suppresses the occurrence of overhang of the carbon-based film and improves productivity when selectively forming the carbon-based film on the top of a pattern such as a groove or a hole.

[0010] Solutions for solving problems

[0011] One aspect of the technology disclosed herein is a method for forming a carbon film, comprising a film forming step in which a carbon film is formed on a substrate having a pattern. In the film forming step, plasma is generated from a film forming gas consisting only of a hydrocarbon gas and a rare gas to selectively form the carbon film on top of the pattern.

[0012] Effects of the Invention

[0013] According to the technology of the present disclosure, when a carbon-based film is selectively formed on the top of a pattern such as a trench or a hole, overhang of the carbon-based film can be suppressed, thereby improving productivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a cross-sectional view schematically showing the structure of a film forming apparatus as one embodiment of the technology according to the present disclosure.

[0015] Figure 2 The clamp circuit is provided. Figure 1 The upper electrode of the film forming device and the clamp circuit are not provided Figure 3 A diagram showing a voltage waveform at an upper electrode of a conventional film-forming device.

[0016] Figure 3 This is a cross-sectional view schematically showing the structure of a conventional film forming apparatus that does not include a clamp circuit.

[0017] Figure 4 Is used to illustrate Figure 1 A diagram showing the distribution of plasma in a film forming apparatus.

[0018] Figure 5 It is shown by Figure 1 Film forming device and Figure 3 A diagram showing the respective film formation morphologies when a conventional film formation apparatus performs a film formation process.

[0019] Figure 6 This is a diagram for explaining the influence of the presence or absence of a clamp circuit on the film morphology of a carbon-based film.

[0020] Figure 7 This is a cross-sectional view schematically showing the structure of a film forming apparatus as a modified example of one embodiment of the technology according to the present disclosure.

[0021] Figure 81 is a diagram showing a voltage waveform at the upper electrode when a negative DC voltage is applied to the upper electrode in a pulsed manner from a DC power supply. DETAILED DESCRIPTION

[0022] Furthermore, the technique described in Patent Document 1 deposits a fluid film at the bottom of the trench and then re-deposits the carbon film at the top of the trench by exposing the film to nitrogen plasma. Consequently, forming the carbon film at the top of the trench requires two steps, resulting in low productivity. Furthermore, the technique described in Patent Document 1 carries the risk of overhanging the carbon film and clogging the trench as the re-deposition of the carbon film at the top of the trench progresses.

[0023] In contrast, the technology according to the present disclosure suppresses the occurrence of overhang of the carbon-based film when selectively forming the carbon-based film on the top of a pattern such as a groove or a hole, thereby improving productivity.

[0024] Hereinafter, one embodiment of the technology according to the present disclosure will be described with reference to the drawings. Figure 1 This is a cross-sectional view schematically illustrating the structure of a film-forming apparatus according to this embodiment. This film-forming apparatus is a capacitively coupled plasma processing apparatus that generates plasma from a film-forming gas serving as a process gas to form a film. This film-forming apparatus performs a carbon-based film-forming method according to one embodiment of the technology disclosed herein.

[0025] exist Figure 1 In the embodiment, the film forming apparatus 10 includes a substantially cylindrical metal chamber 11 (processing chamber) which is grounded. A wafer W (substrate) is housed in the chamber 11 and a mounting table 12 on which the wafer W is mounted is arranged.

[0026] The mounting table 12 is made of an insulator and includes a grounded lower electrode (not shown). Alternatively, the mounting table 12 may be made of metal and function as a lower electrode. A heater and a refrigerant passage (both not shown) are buried inside the mounting table 12. The heater generates heat by electricity supplied from the outside, thereby heating the wafer W placed thereon, and the refrigerant passage cools the wafer W placed thereon by circulating the refrigerant supplied from the outside. In addition, in order to improve the heat transfer between the mounting table 12 and the wafer W, a heat transfer gas is supplied between the mounting table 12 and the wafer W. In addition, a plurality of lifting pins (not shown) penetrate the mounting table 12 in a manner that allows them to protrude and sink relative to the upper surface of the mounting table 12, and the plurality of lifting pins are raised and lowered by a lifting mechanism (not shown), thereby transferring the wafer W to the mounting table 12.

[0027] An opening is formed at the top of the chamber 11, and a showerhead 13 is inserted into the opening, facing the mounting table 12, via an insulating member 14. The showerhead 13 is formed of a cylindrical metal member and functions as an upper electrode. Alternatively, the showerhead 13 may be formed not entirely of metal, but partially of metal, with the metal portion functioning as the upper electrode. The showerhead 13 includes a shower body 15 having an opening at its bottom, and a shower plate 16 disposed to block the opening of the shower body 15. The internal space between the shower body 15 and the shower plate 16 functions as a gas diffusion space. Furthermore, the shower plate 16 is formed with a plurality of gas ejection holes 17 extending through the thickness of the shower plate 16. Furthermore, the showerhead 13 is formed with gas inlet holes 18, through which processing gas supplied from a gas supply unit 19 (described later) is introduced into the gas diffusion space. The processing gas introduced into the gas diffusion space is diffused and ejected from the gas ejection holes 17 into the space S between the shower head 13 and the mounting table 12 in the chamber 11 (hereinafter referred to as “processing space”).

[0028] The film forming apparatus 10 further includes a gas supply unit 19. The gas supply unit 19 supplies multiple gases, including process gases and purge gases. The gas supply unit 19 includes multiple gas sources, flow controllers, and on / off valves to adjust the flow rates of each gas according to the process. In this embodiment, the process gases supplied by the gas supply unit 19 are film forming gases consisting solely of acetylene (C2H2) gas (a hydrocarbon gas) and argon (Ar) gas (a rare gas).

[0029] The shower head 13 is connected to a high-frequency power supply 21 via a power supply line 20. The high-frequency power supply 21 applies a high-frequency voltage of 100 kHz to 60 MHz, for example, 450 kHz, to the shower head 13. Applying the high-frequency voltage to the shower head 13 generates plasma from the film-forming gas in the processing space S.

[0030] A matching device 22 is connected downstream of the high-frequency power source 21 in the power supply line 20. The matching device 22 matches the load impedance with the internal (or output) impedance of the high-frequency power source 21. Furthermore, a clamp circuit 23 (voltage suppression unit) is provided between the high-frequency power source 21 and the showerhead 13 in the power supply line 20, specifically downstream of the matching device 22 in the power supply line 20.

[0031] Clamp circuit 23 includes capacitor 24 provided downstream of matching unit 22, and ground circuit 26 branching from power supply line 20 downstream of capacitor 24 and connected to ground via diode 25. Capacitor 24 has a sufficient capacitance to reduce the impedance seen by high-frequency power supply 21.

[0032] The clamp circuit 23 utilizes the charge storage function of the capacitor 24 and the rectification function of the diode 25 in the ground circuit 26 to allow high-frequency current to flow toward the ground through the diode 25 when the high-frequency power source 21 outputs a positive voltage (magnetic voltage). At this time, the high-frequency power output by the high-frequency power source 21 is accumulated in the capacitor 24. This suppresses the positive voltage in the high-frequency voltage applied to the shower head 13. On the other hand, when the high-frequency power source 21 outputs a negative voltage (magnetic voltage), the diode 25 does not allow high-frequency current to pass through it, preventing high-frequency current from flowing toward the ground via the ground circuit 26. Furthermore, at this time, the power output by the high-frequency power source 21 and the power accumulated in the capacitor 24 are supplied to the shower head 13.

[0033] Furthermore, while the film-forming apparatus 10 includes a clamp circuit 23 as a circuit for suppressing the positive voltage of the high-frequency voltage, another circuit capable of suppressing the positive voltage of the high-frequency voltage may be provided in place of the clamp circuit 23. Furthermore, the high-frequency power output by the high-frequency power source 21 may be accumulated in the clamp circuit 23 using a DC blocking capacitor in the matching unit 22 instead of capacitor 24. In this case, the capacitor 24 may be eliminated from the clamp circuit 23.

[0034] Figure 2 The clamp circuit 23 is provided. Figure 1 The upper electrode (shower head 13) of the film forming device 10 and Figure 3 FIG. 1 is a diagram showing a voltage waveform at an upper electrode of a general capacitive coupling type plasma processing apparatus 31 without a clamp circuit 23. Figure 2 middle, Figure 1 The voltage waveform in the film forming apparatus 10 is represented by a solid line, and the voltage waveform in the conventional film forming apparatus 31 is represented by a dotted line. In the following, a general capacitively coupled plasma processing apparatus 31 without a clamp circuit 23 is referred to as a "conventional film forming apparatus 31."

[0035] like Figure 2 As shown, in the conventional film forming apparatus 31, the positive voltage is not suppressed by the clamp circuit 23, so the voltage of the upper electrode greatly oscillates not only on the negative side but also on the positive side. Figure 1In the film forming apparatus 10, the positive voltage is suppressed by the clamping circuit 23, so the voltage of the upper electrode does not fluctuate greatly on the positive side. Moreover, in a capacitively coupled plasma processing apparatus, when the lower electrode is grounded, the plasma potential is largely dependent on the potential of the upper electrode. Therefore, in the film forming apparatus 10, the plasma potential can be lowered compared to the conventional film forming apparatus 31. In addition, the ions in the plasma are accelerated by the sheath voltage and flow toward the wafer W. However, when the plasma potential is lowered, the absolute value of the sheath voltage (the difference between the plasma potential and the potential of the wafer W (mounting table 12)) generated in the processing space S becomes smaller, so the ions are not accelerated much. As a result, in Figure 1 In the film forming apparatus 10 , the ion energy imparted from the plasma to the wafer W mounted on the mounting table 12 is reduced.

[0036] In addition, in the film forming apparatus 10, as described above, the voltage of the shower head 13 does not fluctuate greatly on the positive side. Therefore, in the processing space S, as shown in FIG. Figure 4 As shown, high-density plasma P is generated so as to be biased toward the vicinity of the shower head 13. As a result, the processing gas ejected from the gas ejection holes 17 of the shower head 13 reliably passes through the high-density plasma P. As a result, the high-density plasma P promotes the dissociation of the ejected processing gas, thereby efficiently generating plasma and generating a large amount of ions and radicals.

[0037] Furthermore, in the film forming apparatus 10, an exhaust port 27 is provided at the bottom of the chamber 11. This exhaust port 27 is connected to an exhaust system 29 via an exhaust pipe 28. The exhaust system 29 includes an automatic pressure control valve and a vacuum pump. The exhaust system 29 exhausts the interior of the chamber 11 to reduce the pressure and maintain the interior of the chamber 11 at a desired vacuum level. Furthermore, a loading / unloading port (not shown) for loading and unloading wafers W is provided on the sidewall of the chamber 11. This loading / unloading port is opened and closed by a gate valve (not shown).

[0038] The film forming apparatus 10 also includes a control unit 30 that controls the various components of the film forming apparatus 10. The control unit 30 is a computer equipped with a processor, memory, input device, display device, and signal input / output interfaces. The memory of the control unit 30 stores control programs and process data. When film forming processing is performed in the film forming apparatus 10, the processor of the control unit 30 executes the corresponding control program and controls the various components of the film forming apparatus 10 according to the process data.

[0039] Specifically, the control unit 30 controls the gas supply unit 19 and the exhaust device 29 to adjust the pressure inside the chamber 11, and controls the high-frequency power supply 21 to apply a high-frequency voltage to the shower head 13. Furthermore, the control unit 30 controls the gas supply unit 19 to diffuse the film-forming gas into the chamber 11, thereby introducing the film-forming gas. At this time, the electric field generated by the high-frequency voltage applied to the shower head 13 excites the gas molecules of the film-forming gas, generating a plasma. This plasma is then used to perform film formation processing (film formation step) on the wafer W.

[0040] The applicant uses Figure 1 The film forming device 10 and Figure 3 The conventional film forming apparatus 31 is used to perform film forming processing on the wafer W. Figure 5 It is shown by Figure 1 The film forming device 10 and Figure 3 The figure shows the respective film forming forms when the conventional film forming apparatus 31 performs film forming processing. Figure 5 , an enlarged partial cross section of an oxide layer 33 having a plurality of grooves formed as a pattern and formed on the surface of a wafer W having a silicon substrate 32 is shown. The oxide layer 33 is an insulating film and serves as a base layer for the carbon-based film 34 to be formed.

[0041] At this time, the applicant Figure 1 The film forming device 10 and Figure 3 In any of the conventional film forming devices 31, the addition rate of acetylene gas in the film forming gas is set to 6.25% (flow rate of 10 sccm), and the addition rate of argon gas is set to 93.75% (flow rate of 150 sccm). In addition, as described above, the film forming gas in this embodiment is composed only of acetylene gas and argon gas, and the addition rate of each gas is the flow ratio of each gas flow rate relative to the total gas flow rate of the film forming gas. Moreover, the pressure inside the chamber 11 is set to 2 Torr, and a high-frequency power with a frequency of 450 kHz is supplied to the shower head 13 from the high-frequency power supply 21 at 500 W, and plasma is generated from the film forming gas to perform film forming processing on the wafer W. In addition, the interval between the shower head 13 and the mounting table 12 is set to 15 mm, and the temperature of the wafer W (actually the temperature of the mounting table 12) is set to 400°C.

[0042] Figure 5 (A) is in Figure 3 The film-forming morphology of the carbon-based film 34 during the film-forming process in the conventional film-forming apparatus 31 is as follows: Figure 5 (B) is in Figure 1 The film morphology of the carbon-based film 34 when the film forming process is performed in the film forming apparatus 10.

[0043] First, it was confirmed that during film formation processing in the conventional film formation apparatus 31, a carbon film 34 was formed on the tops of the fins 33a (tops of the pattern) sandwiched between the trenches of the oxide layer 33, extending toward the trenches. Furthermore, it was confirmed that the carbon film 34 was also formed within the trenches, adhering to the side surfaces of the fins 33a and the bottom of the trenches. In other words, it was confirmed that a carbon film 34 was formed, which is not suitable for selectively forming a carbon film on the tops of the fins 33a.

[0044] On the other hand, it was confirmed that during the film formation process in the film formation apparatus 10, the carbon film 34 was formed only on the top of the fin 33a, and the carbon film 34 did not overhang toward the trench, and almost no carbon film 34 was formed inside the trench. In other words, it was confirmed that the carbon film 34 was formed, which is suitable for selectively forming the carbon film on the top of the fin 33a.

[0045] according to Figure 5 The verification results shown show that the presence of the clamp circuit 23 reduces the overhang of the carbon film 34 formed on the top of the fin 33a, and results in the carbon film 34 not being formed inside the trench. The present applicants speculate that the mechanism described below is responsible for this phenomenon.

[0046] Figure 6 This is a diagram for explaining the influence of the presence or absence of the clamp circuit 23 on the film formation morphology of the carbon-based film 34 .

[0047] First, explain Figure 6 FIG. 2 (A) shows a film forming mode in a conventional film forming apparatus 31 in which the clamp circuit 23 is not provided.

[0048] In a conventional film forming apparatus 31 that does not include the clamp circuit 23 , the voltage of the shower head 13 also fluctuates significantly on the positive side. Therefore, plasma is not generated in a manner that is biased toward the vicinity of the shower head 13 , but is generated in a manner that is distributed almost uniformly throughout the processing space S. In other words, plasma also exists near the wafer W, and hydrocarbon ions and hydrocarbon radicals contained in the plasma generated from the acetylene gas that is the main factor in forming the carbon-based film 34 exist near the wafer W.

[0049] Here, hydrocarbon radicals have strong isotropy and adhere to the fins 33a of the oxide layer 33 from all directions. Therefore, in conventional film-forming apparatuses 31, the carbon-based film 34 derived from hydrocarbon radicals adheres not only to the tops of the fins 33a but also to the sides of the fins 33a and the bottoms of the trenches. On the other hand, hydrocarbon ions have strong anisotropy and adhere approximately perpendicularly to the fins 33a of the oxide layer 33. Therefore, in conventional film-forming apparatuses 31, the carbon-based film 34 derived from hydrocarbon ions adheres to the tops of the fins 33a in a manner that accumulates approximately vertically.

[0050] That is, on the top of the fin 33a, not only the carbon film 34 derived from the hydrocarbon ions with strong anisotropy but also the carbon film 34 derived from the hydrocarbon radicals with strong isotropy is attached, so the carbon film 34 overhangs toward the groove. Figure 6 (A), the following Figure 6 In (B), the carbon film derived from hydrocarbon ions is represented by reference numeral 34a, and the carbon film derived from hydrocarbon radicals is represented by reference numeral 34b. However, in reality, the carbon film 34 is formed by a mixture of the carbon film 34a derived from hydrocarbon ions and the carbon film 34b derived from hydrocarbon radicals.

[0051] In addition, the carbon film 34 is etched isotropically by the hydrogen radicals contained in the hydrogen plasma. In the present embodiment, it is considered that when plasma is generated from the acetylene gas, hydrogen plasma is generated from a portion of the acetylene gas. Moreover, as described above, in the conventional film forming apparatus 31, plasma is not generated in a manner biased toward the vicinity of the shower head 13, but is generated in a manner distributed almost without omission in the processing space S, and high-density plasma is not generated. Therefore, the dissociation of the acetylene gas contained in the film forming gas introduced into the processing space S does not progress to that extent, and hydrogen plasma is not generated much. As a result, hydrogen radicals (indicated by "H" in the figure) are almost non-existent near the wafer W. Figure 6 The same is true for (B), and the etching of the carbon film 34 by hydrogen radicals does not progress.

[0052] Based on the above reasons, it is presumed that in the conventional film forming apparatus 31 , the carbon film 34 adheres to the side surfaces of the fin 33 a and the bottom of the trench, and at the top of the fin 33 a , the carbon film 34 overhangs toward the trench.

[0053] Next, explain Figure 6 FIG. 2 (B) shows a film forming state in the film forming apparatus 10 provided with a clamp circuit 23 .

[0054] In the film forming apparatus 10 equipped with the clamp circuit 23, as described above, high-density plasma P is generated so as to be biased toward the vicinity of the shower head 13. Specifically, high-density plasma P is not generated near the wafer W, and hydrocarbon radicals contained in the plasma generated from the acetylene gas are almost absent near the wafer W. Consequently, in the film forming apparatus 10, the carbon-based film 34b derived from hydrocarbon radicals is not significantly deposited not only on the top of the fin 33a but also on the side surfaces of the fin 33a and the bottom of the trench.

[0055] Meanwhile, in the film-forming apparatus 10, while the absolute value is smaller than that of the conventional film-forming apparatus 31, the sheath voltage generated in the processing space S accelerates the hydrocarbon ions toward the wafer W. In other words, even though there is little high-density plasma P near the wafer W, the hydrocarbon ions reach the wafer W. Consequently, the formation of the carbon-based film 34 on the wafer W is dominated by the highly anisotropic hydrocarbon ions. As a result, the carbon-based film 34a derived from the hydrocarbon ions grows primarily on the tops of the fins 33a, forming a substantially vertically stacked structure.

[0056] In addition, as described above, in the film forming apparatus 10, a high-density plasma P is generated in a manner biased toward the vicinity of the shower head 13. Therefore, the film forming gas ejected from the shower head 13 reliably passes through the high-density plasma P, promoting the dissociation of the acetylene gas contained in the film forming gas, and also generating a large amount of hydrogen plasma. Moreover, hydrogen radicals are lighter than hydrocarbon radicals and travel farther, so there are many hydrogen radicals near the wafer W, and the etching of the carbon film 34 based on hydrogen radicals progresses. At this time, the etching based on hydrogen radicals progresses in an isotropic manner, so the carbon film 34b derived from hydrocarbon radicals that is slightly attached to the side of the fin 33a and the bottom of the groove is almost completely removed. In addition, the overhang of the carbon film 34 formed on the top of the fin 33a is also cut off by the etching based on hydrogen radicals.

[0057] Based on the above reasons, it is speculated that in the film forming apparatus 10 provided with the clamp circuit 23, the carbon film 34 is hardly attached to the side surfaces of the fin 33a and the bottom of the trench, and the carbon film 34 does not overhang the top of the fin 33a toward the trench.

[0058] That is, according to this embodiment, in the film formation apparatus 10 equipped with the clamp circuit 23, a non-overhanging carbon-based film 34 can be formed on the top of the fin 33a using a film formation gas consisting solely of acetylene and argon. Furthermore, the carbon-based film 34 is hardly attached to the side surfaces of the fin 33a or the bottom of the trench. In other words, in the film formation apparatus 10 equipped with the clamp circuit 23, when forming the non-overhanging carbon-based film 34 on the top of the fin 33a, there is no need to add hydrogen to the film formation gas to promote etching by hydrogen radicals.

[0059] Furthermore, according to this embodiment, in a film-forming apparatus 10 equipped with a clamp circuit 23, a non-overhanging carbon-based film 34 can be formed on the tops of the fins 33a by generating plasma solely from a film-forming gas consisting solely of acetylene and argon. In other words, the non-overhanging carbon-based film 34 can be formed on the tops of the fins 33a in a single step. Consequently, when selectively forming the carbon-based film 34 on the tops of the trenches, the generation of overhanging carbon-based film 34 can be suppressed, thereby improving productivity.

[0060] Furthermore, when forming a carbon film in the film-forming apparatus 10, increasing the addition rate of acetylene gas to the film-forming gas increases the number of hydrocarbon radicals. In this case, even if high-density plasma P is generated with a bias toward the vicinity of the showerhead 13, the probability of hydrocarbon radicals existing near the wafer W increases. As a result, it is believed that a carbon film 34b derived from hydrocarbon radicals will also adhere to the sides of the fin 33a and the bottom of the trench, making it more likely that the carbon film 34 at the top of the fin 33a will overhang toward the trench. Therefore, to suppress the overhang of the carbon film 34 at the top of the fin 33a, there is an upper limit to the addition rate of acetylene gas in the film-forming gas; for example, it is preferable to set the addition rate of acetylene gas to 10% or less.

[0061] Furthermore, when the carbon film is formed in the film forming apparatus 10, when the temperature of the wafer W is lowered, the ambient temperature near the wafer W also decreases. However, when the ambient temperature is low, the probability of hydrocarbon radicals attaching increases. As a result, the carbon film 34a derived from hydrocarbon ions grows anisotropically at the top of the fin 33a. Furthermore, the carbon film 34b derived from hydrocarbon radicals grows isotropically at the top of the fin 33a. As a result, it can be considered that the carbon film 34 at the top of the fin 33a overhangs toward the groove. Therefore, in order to suppress the overhang of the carbon film 34 at the top of the fin 33a, there is a lower limit to the temperature of the wafer W (actually, the temperature of the mounting table 12). For example, it is preferable to set the temperature of the wafer W to be higher than 200°C, and more preferably to be above 300°C.

[0062] Furthermore, when forming a carbon film in the film forming apparatus 10, increasing the pressure inside the chamber 11 deactivates hydrocarbon ions, making it difficult for the hydrocarbon ions to reach the wafer W. Consequently, it is believed that the growth of the carbon film 34a originating from the hydrocarbon ions on the tops of the fins 33a becomes difficult, and the carbon film 34 is not selectively formed on the tops of the fins 33a. Therefore, in order to selectively form the carbon film 34 on the tops of the fins 33a, there is an upper limit to the pressure inside the chamber 11. For example, it is preferable to set the pressure inside the chamber 11 to 2 Torr or less.

[0063] Alternatively, in the film forming apparatus 10, instead of connecting the clamp circuit 23 to the shower head 13, the clamp circuit 23 may be connected to the lower electrode of the mounting table 12 after reversing the orientation of the diode 25, and the shower head 13 may be grounded. In this case, the plasma potential can also be lowered, thereby reducing the absolute value of the sheath voltage.

[0064] However, in this case, the potential of the lower electrode is positive, so electrons in the plasma flow in large quantities toward the lower electrode, causing the electron density to locally increase near the mounting table 12 , making it easier for abnormal discharge to occur near the wafer W. Therefore, connecting the clamp circuit 23 to the lower electrode is not preferable.

[0065] As mentioned above, although the preferred embodiment of this disclosure was described, this disclosure is not limited to the above-mentioned embodiment, and various deformation|transformations and changes are possible within the scope of the gist of this disclosure.

[0066] For example, in a preferred embodiment of the present disclosure, a clamp circuit 23 is provided as a circuit for suppressing the positive voltage of the high-frequency voltage. However, as described above, a circuit of other methods capable of suppressing the positive voltage of the high-frequency voltage may be provided in place of the clamp circuit 23. For example, a circuit for applying a negative DC voltage in a pulsed manner to the upper electrode (shower head 13) may be provided. In this case, Figure 7 As shown, the shower head 13 is connected to a DC power supply 35 via a power supply line 20. The DC power supply 35 applies a negative DC voltage in a pulsed manner to the shower head 13. In addition, a pulse unit 36 is connected downstream of the DC power supply 35 in the power supply line 20.

[0067] Figure 8 3 is a diagram showing a voltage waveform at the upper electrode when a negative DC voltage is applied to the upper electrode in a pulsed manner from the DC power supply 35. Figure 8 As shown, when a negative DC voltage is applied to the upper electrode in a pulsed manner, the voltage of the upper electrode does not oscillate toward the positive side, thereby reducing the plasma potential. This reduces the absolute value of the sheath voltage generated in the processing space S, and reduces the ion energy imparted from the plasma to the wafer W mounted on the mounting table 12, similar to the case where the clamp circuit 23 is provided.

[0068] In addition, for example, in a preferred embodiment of the present disclosure, a film forming process is performed on a wafer W having a plurality of grooves formed thereon as a pattern. However, the pattern is not limited to grooves, and may be, for example, a through hole. In this case, a carbon film is formed on the top of the wall between each through hole.

[0069] In the preferred embodiment of the present disclosure, the carbon film 34 is formed on the oxide layer 33 . However, the present disclosure is also applicable when the carbon film is selectively formed on the top of the protrusions or fins of a metal layer such as a wiring layer.

[0070] Furthermore, in a preferred embodiment of the present disclosure, a hydrocarbon gas (acetylene gas) is used to selectively form a carbon film on top of the fin 33 a. However, other hydrogen compound gases, such as silane gas, which is a hydrogen compound gas of silicon, or borane gas, which is a hydrogen compound gas of boron, may be used instead of the hydrocarbon gas.

[0071] When a film forming process is performed on the wafer W using the film forming apparatus 10 and a film forming gas consisting only of silane gas and argon gas, a silicon-based film can be selectively formed on the top of the fin without overhanging toward the trench or through-hole. Furthermore, when a film forming process is performed on the wafer W using the film forming apparatus 10 and a film forming gas consisting only of borane gas and argon gas, a boron-based film can be selectively formed on the top of the fin without overhanging toward the trench or through-hole.

[0072] Furthermore, the rare gas contained in the film-forming gas is not limited to argon gas, and other rare gases, for example, xenon (Xe) gas may also be used.

[0073] Description of Reference Numerals

[0074] W: wafer; 10: film forming apparatus; 11: chamber; 23: clamping circuit; 33a: fin; 34: carbon film.

Claims

1. A method for forming a carbon film, wherein: A film forming step is provided in which a carbon film is formed on a substrate having a pattern. In the film forming step, plasma is generated from a film forming gas consisting only of a hydrocarbon gas and a rare gas, thereby selectively forming the carbon-based film on the top of the pattern.

2. The method for forming a carbon film according to claim 1, wherein: In the film forming process, the substrate is housed in a processing chamber with a reduced pressure inside and is placed on a mounting table arranged inside the processing chamber. The plasma is generated from the film forming gas inside the processing chamber, and the positive voltage in the high-frequency voltage applied to the upper electrode facing the mounting table is suppressed.

3. The method for forming a carbon film according to claim 1 or 2, wherein: The hydrocarbon gas is acetylene gas.

4. The method for forming a carbon film according to claim 1 or 2, wherein: The rare gas is argon.

5. The method for forming a carbon film according to claim 1 or 2, wherein: In the film forming step, the temperature of the substrate is set to a temperature higher than 200°C.

6. The method for forming a carbon film according to claim 5, wherein: In the film forming step, the temperature of the substrate is set to 300° C. or higher.

7. The method for forming a carbon film according to claim 1 or 2, wherein: The addition rate of the hydrocarbon gas in the film-forming gas is 10% or less.

8. The method for forming a carbon-based film according to claim 2, wherein: In the film forming step, the pressure inside the processing chamber is set to 2 Torr or less.

9. A film forming device, wherein: Equipped with a processing chamber with reduced pressure inside, A substrate having a pattern is accommodated in the processing chamber, and plasma is generated in the processing chamber from a film-forming gas consisting only of a hydrocarbon gas and a rare gas to selectively form a carbon-based film on top of the pattern.

10. The film forming apparatus according to claim 9, further comprising: a mounting table, disposed inside the processing chamber and used for mounting the substrate; an upper electrode facing the mounting table; a high-frequency power supply that applies a high-frequency voltage for generating the plasma to the upper electrode; and A voltage suppressing unit suppresses a positive voltage in the applied high-frequency voltage.

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