Carbon-based film formation method and film formation apparatus

Abstract

To suppress the occurrence of overhanging of a carbon-based film and improve the throughput when the carbon-based film is selectively formed on the top of a pattern such as a trench or a hole.SOLUTION: In a film formation apparatus, plasma is generated from a film formation gas composed only of acetylene gas and argon gas inside a chamber, and a carbon-based film is selectively formed on tops of fins sandwiched between trenches formed in an oxide layer of a wafer.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] In semiconductor devices, a technique is known in which a carbon-based film is selectively formed on the top of a trench or hole formed in a mask or a film to be etched in order to realize wiring with more complex shapes or finer wiring. For example, in the technique described in Patent Document 1, a carbon-based film is formed on the top of a trench formed in a substrate made of silicon. Specifically, in the substrate, a flowable film, which is an amorphous carbon polymer film, is deposited mainly on the bottom of the trench, and then the flowable film at the bottom is exposed to nitrogen plasma to etch the flowable film at the bottom, and gaseous C x N y H z At this time, the C x N y H z C for the top of the trench where silicon is exposed rather than the sticking coefficient of the species. x N y H z Due to the high adhesion coefficient of the species, C x N y H z The species are selectively redeposited onto the top of the trench, resulting in the selective deposition of a carbon-based film onto the top of the trench.

[0003] Furthermore, when performing plasma processing on a wafer on which a semiconductor device is formed, a technique is known in which the voltage of the upper electrode facing the stage on which the wafer is placed does not swing significantly to the positive side in order to reduce the impact of ions in the plasma on the wafer. In this technique, a clamp circuit is provided between the high-frequency power supply and the upper electrode, and the clamp circuit shapes the voltage waveform of the high-frequency power supply so as to suppress the positive voltage of the high-frequency voltage applied to the upper electrode (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-19199 [Patent Document 2] Japanese Patent Publication No. 2022-18062 Summary of the Invention [Problem to be solved by the invention]

[0005] The technology according to the present disclosure suppresses the occurrence of overhanging of the carbon-based film and improves throughput when selectively depositing the carbon-based film on the top of a pattern such as a trench or hole. [Means for solving the problem]

[0006] One aspect of the technology disclosed herein is a method for forming a carbon-based film, comprising a film formation step of forming a carbon-based film on a substrate having a pattern, in which plasma is generated from a film formation gas consisting only of a hydrocarbon gas and a rare gas, and the carbon-based film is selectively formed on the top of the pattern. [Effects of the Invention]

[0007] According to the technology disclosed herein, when a carbon-based film is selectively formed on the top of a pattern such as a trench or hole, it is possible to suppress the occurrence of overhanging of the carbon-based film and improve throughput. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view schematically illustrating a configuration of a film forming apparatus according to an embodiment of the technology disclosed herein. [Figure 2] 4 is a diagram showing voltage waveforms at the upper electrode of the film deposition apparatus of FIG. 1 provided with a clamp circuit and at the upper electrode of the conventional film deposition apparatus of FIG. 3 not provided with a clamp circuit. [Figure 3] FIG. 10 is a cross-sectional view schematically showing the configuration of a conventional film forming apparatus that does not include a clamp circuit. [Figure 4]FIG. 2 is a diagram for explaining the plasma distribution state in the film forming apparatus of FIG. [Figure 5] 4A and 4B are diagrams illustrating respective film formation modes when film formation processes are performed by the film formation apparatus of FIG. 1 and the conventional film formation apparatus of FIG. [Figure 6] 10A and 10B are diagrams for explaining the influence of the presence or absence of a clamp circuit on the deposition form of a carbon-based film. [Figure 7] FIG. 10 is a cross-sectional view schematically illustrating a configuration of a film forming apparatus according to a modified example of an embodiment of the technology disclosed herein. [Figure 8] 10 is a diagram showing a voltage waveform at the upper electrode when a negative DC voltage is applied in pulses to the upper electrode from a DC power supply. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] However, in the technique described in Patent Document 1, a flowable film is deposited on the bottom of the trench, and then a carbon-based film is redeposited on the top of the trench by exposure to nitrogen plasma, so two steps are required to form a carbon-based film on the top of the trench, which reduces throughput. Furthermore, in the technique described in Patent Document 1, as the redeposition of the carbon-based film on the top of the trench progresses, an overhang of the carbon-based film occurs, which may block the trench.

[0010] In contrast, the technology according to the present disclosure suppresses the occurrence of overhangs in the carbon-based film when selectively depositing the carbon-based film on the top of patterns such as trenches and holes, and improves throughput.

[0011] An embodiment of the technology according to the present disclosure will be described below with reference to the drawings. Fig. 1 is a cross-sectional view showing a schematic configuration of a film formation apparatus according to the present embodiment. This film formation apparatus is a capacitively coupled plasma processing apparatus that forms a film by generating plasma from a film formation gas as a processing gas. This film formation apparatus executes a carbon-based film formation method according to an embodiment of the technology according to the present disclosure.

[0012] 1, a film forming apparatus 10 includes a substantially cylindrical metallic chamber 11 (processing chamber), which is grounded. A wafer W (substrate) is accommodated inside the chamber 11, and a mounting table 12 on which the wafer W is placed is also arranged.

[0013] The mounting table 12 is made of an insulator and includes a grounded lower electrode (not shown). The mounting table 12 may be made of metal and function as the lower electrode. A heater and a coolant passage (neither of which are shown) are embedded inside the mounting table 12. The heater generates heat using externally supplied power to heat the wafer W placed thereon, and the coolant passage circulates an externally supplied coolant to cool the wafer W. A heat transfer gas is supplied between the mounting table 12 and the wafer W to improve the thermal conductivity between the mounting table 12 and the wafer W. The mounting table 12 has a plurality of lift pins (not shown) inserted therein that can be raised and lowered relative to its upper surface. The lift pins are raised and lowered by a lift mechanism (not shown) to transfer the wafer W to and from the mounting table 12.

[0014] An opening is formed in the top of the chamber 11, and a shower head 13 is fitted into the opening via an insulating member 14 so as to face the mounting table 12. The shower head 13 is made of a cylindrical metal member and functions as an upper electrode. Alternatively, only a portion of the shower head 13 may be made of metal, and the metal portion may function as the upper electrode. The shower head 13 has a shower body 15 with an opening at its bottom and a shower plate 16 that covers the opening of the shower body 15. The internal space between them functions as a gas diffusion space. The shower plate 16 has multiple gas outlet holes 17 that penetrate the shower plate 16 in the thickness direction. The shower head 13 also has gas inlet holes 18, through which a process gas supplied from a gas supply unit 19 (described later) is introduced into the gas diffusion space. The process gas introduced into the gas diffusion space is then diffused and discharged from each gas outlet hole 17 into a space S between the shower head 13 and the mounting table 12 inside the chamber 11 (hereinafter referred to as the "processing space").

[0015] The film forming apparatus 10 further includes a gas supply unit 19. The gas supply unit 19 supplies a plurality of gases, such as a process gas and a purge gas. The gas supply unit 19 has a plurality of gas sources, flow rate controllers, and on-off valves, and adjusts the flow rate of each gas depending on the process. In this embodiment, the process gas supplied by the gas supply unit 19 is a film forming gas consisting only of acetylene (C2H2) gas (hydrocarbon gas) and argon (Ar) gas (rare gas).

[0016] A high frequency power supply 21 is connected to the shower head 13 via a power supply line 20. The high frequency power supply 21 applies a high frequency voltage having a frequency of 100 kHz to 60 MHz, for example, 450 kHz, to the shower head 13. When the high frequency voltage is applied to the shower head 13, plasma is generated from the film forming gas in the processing space S.

[0017] A matching box 22 is connected downstream of the high frequency power supply 21 on the power feed line 20. The matching box 22 matches the load impedance to the internal (or output) impedance of the high frequency power supply 21. Furthermore, a clamp circuit 23 (voltage suppression unit) is provided between the high frequency power supply 21 and the shower head 13 on the power feed line 20, more specifically, downstream of the matching box 22 on the power feed line 20.

[0018] Clamp circuit 23 has a capacitor 24 provided downstream of matching device 22, and a ground circuit 26 branching from power feed line 20 downstream of capacitor 24 and grounded via diode 25. Capacitor 24 has a capacitance sufficient to reduce the impedance seen from high-frequency power supply 21.

[0019] When high frequency power supply 21 outputs a positive voltage (plus voltage), clamp circuit 23 passes a high frequency current through diode 25 to the ground side, due to the storage function of capacitor 24 and the rectification function of diode 25 in ground circuit 26. At this time, the high frequency power output by high frequency power supply 21 is stored in capacitor 24. This suppresses the positive voltage of the high frequency voltage applied to shower head 13. On the other hand, when high frequency power supply 21 outputs a negative voltage (minus voltage), diode 25 does not pass the high frequency current, so the high frequency current does not flow to the ground side via ground circuit 26. At this time, the power output by high frequency power supply 21 and the power stored in capacitor 24 are supplied to shower head 13.

[0020] Although the film forming apparatus 10 is provided with the clamp circuit 23 as a circuit for suppressing the positive voltage of the high-frequency voltage, other types of circuits capable of suppressing the positive voltage of the high-frequency voltage may be provided instead of the clamp circuit 23. Furthermore, in the clamp circuit 23, the high-frequency power output by the high-frequency power supply 21 may be stored by a blocking capacitor of the matching device 22 instead of the capacitor 24. In this case, the need to provide the capacitor 24 in the clamp circuit 23 can be eliminated.

[0021] 2 is a diagram showing voltage waveforms at the upper electrode (shower head 13) of the film formation apparatus 10 of FIG. 1, which is provided with a clamp circuit 23, and at the upper electrode of a general capacitively coupled plasma processing apparatus 31 shown in FIG. 3, which is not provided with a clamp circuit 23. In FIG. 2, the voltage waveform in the film formation apparatus 10 of FIG. 1 is shown by a solid line, and the voltage waveform in the conventional film formation apparatus 31 is shown by a dashed line. The general capacitively coupled plasma processing apparatus 31 not provided with a clamp circuit 23 will hereinafter be referred to as the "conventional film formation apparatus 31."

[0022] As shown in FIG. 2, in the conventional film formation apparatus 31, the clamp circuit 23 does not suppress the positive voltage, so the voltage of the upper electrode swings significantly not only to the negative side but also to the positive side. On the other hand, in the film formation apparatus 10 of FIG. 1, the clamp circuit 23 suppresses the positive voltage, so the voltage of the upper electrode does not swing significantly to the positive side. In a capacitively coupled plasma processing apparatus, when the lower electrode is grounded, the plasma potential is highly dependent on the potential of the upper electrode. Therefore, the film formation apparatus 10 can reduce the plasma potential compared to the conventional film formation apparatus 31. Furthermore, ions in the plasma are accelerated by the sheath voltage and flow toward the wafer W. However, when the plasma potential is reduced, 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 decreases, so the ions are not accelerated as much. As a result, in the film formation apparatus 10 of FIG. 1, the ion energy imparted from the plasma to the wafer W mounted on the mounting table 12 is reduced.

[0023] Furthermore, in the film formation apparatus 10, as described above, the voltage of the shower head 13 does not fluctuate significantly to the positive side, so that in the processing space S, high-density plasma P is generated unevenly near the shower head 13, as shown in Fig. 4. This ensures that the processing gas discharged from each gas discharge hole 17 of the shower head 13 passes through the high-density plasma P. As a result, the high-density plasma P promotes dissociation of the discharged processing gas, resulting in efficient plasma generation and the generation of a large amount of ions and radicals.

[0024] Furthermore, in the film forming apparatus 10, an exhaust port 27 is provided at the bottom of the chamber 11, and an exhaust device 29 is connected to the exhaust port 27 via an exhaust pipe 28. The exhaust device 29 has an automatic pressure control valve and a vacuum pump, and evacuates the inside of the chamber 11 to reduce the pressure and maintain the inside of the chamber 11 at a desired vacuum level. Also, a load / unload port (not shown) for loading / unloading the wafer W is provided on the side wall of the chamber 11, and this load / unload port is opened and closed by a gate valve (not shown).

[0025] Furthermore, the film forming apparatus 10 includes a control unit 30, which controls each component of the film forming apparatus 10. The control unit 30 is a computer including a processor, a 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 30. When a film forming process is performed in the film forming apparatus 10, the processor of the control unit 30 executes the corresponding control program and controls each component of the film forming apparatus 10 according to the recipe data.

[0026] 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. The control unit 30 also controls the gas supply unit 19 to diffuse and introduce the film formation gas into the chamber 11. At this time, an electric field generated by the high-frequency voltage applied to the shower head 13 excites each gas molecule of the film formation gas to generate plasma, and this plasma is used to perform a film formation process on the wafer W (film formation process).

[0027] The present applicant performed a film formation process on a wafer W using the film formation apparatus 10 of FIG. 1 and the conventional film formation apparatus 31 of FIG. 3. FIG. 5 is a diagram showing the film formation state when the film formation process is performed using the film formation apparatus 10 of FIG. 1 and the conventional film formation apparatus 31 of FIG. 3. FIG. 5 shows an enlarged partial cross section of an oxide layer 33 formed on the surface of a wafer W having a silicon substrate 32, and having a plurality of trenches formed as a pattern. The oxide layer 33 is an insulating film and serves as a base layer for a carbon-based film 34 to be formed.

[0028] In this experiment, the applicant set the acetylene gas additive rate in the film formation gas to 6.25% (flow rate of 10 sccm) and the argon gas additive rate to 93.75% (flow rate of 150 sccm) in both the film formation apparatus 10 of FIG. 1 and the conventional film formation apparatus 31 of FIG. 3 . As described above, the film formation gas in this embodiment is composed only of acetylene gas and argon gas, and the additive rate of each gas is the flow rate ratio of each gas to the total gas flow rate of the film formation gas. The pressure inside the chamber 11 was set to 2 Torr, and high-frequency power having a frequency of 450 kHz and 500 W was supplied from the high-frequency power source 21 to the shower head 13. A plasma was generated from the film formation gas, and a film was formed on the wafer W. The distance between the shower head 13 and the mounting table 12 was set to 15 mm, and the temperature of the wafer W (actually, the temperature of the mounting table 12) was set to 400°C.

[0029] FIG. 5(A) shows the film formation form of the carbon-based film 34 when the film formation process is performed in the conventional film formation apparatus 31 of FIG. 3, and FIG. 5(B) shows the film formation form of the carbon-based film 34 when the film formation process is performed in the film formation apparatus 10 of FIG. 1.

[0030] First, when a film formation process was performed using the conventional film formation apparatus 31, it was confirmed that the carbon-based film 34 was formed on the tops (tops of the pattern) of the fins 33a sandwiched between the trenches of the oxide layer 33 so as to overhang toward the trenches. It was also confirmed that the carbon-based film 34 was also formed inside the trenches, and that the carbon-based film 34 adhered to the side surfaces of the fins 33a and the bottom of the trenches. In other words, it was confirmed that the carbon-based film 34 was inappropriate for being selectively formed on the tops of the fins 33a.

[0031] On the other hand, when the film formation process was performed in the film formation apparatus 10, it was confirmed that the carbon-based film 34 was formed only on the tops of the fins 33a, the carbon-based film 34 did not overhang toward the trench, and the carbon-based film 34 was hardly formed inside the trench. In other words, it was confirmed that the carbon-based film 34 was appropriate as a carbon-based film to be selectively formed on the tops of the fins 33a.

[0032] 5, it was found that when the clamp circuit 23 is provided, the overhang of the carbon-based film 34 formed on the top of the fin 33a is reduced, and the carbon-based film 34 is no longer formed inside the trench. The applicant has speculated that the mechanism described below is the reason for this phenomenon.

[0033] FIG. 6 is a diagram for explaining the influence of the presence or absence of the clamp circuit 23 on the deposition form of the carbon-based film 34. In FIG.

[0034] First, a film formation mode in a conventional film formation apparatus 31 not provided with a clamp circuit 23, as shown in FIG. 6(A), will be described.

[0035] In the conventional film formation apparatus 31 without the clamp circuit 23, the voltage of the shower head 13 swings significantly toward the positive side, so that the plasma is not generated unevenly near the shower head 13 but is generated so as to be distributed almost evenly throughout the processing space S. In other words, the plasma is also present near the wafer W, and hydrocarbon ions and hydrocarbon radicals contained in the plasma generated from the acetylene gas, which is the main cause of the formation of the carbon-based film 34, are present near the wafer W.

[0036] Here, hydrocarbon radicals are highly isotropic and adhere to the fins 33a of the oxide layer 33 from all directions. Therefore, in the conventional film formation apparatus 31, a carbon-based film 34 derived from hydrocarbon radicals adheres not only to the tops of the fins 33a but also to the side surfaces of the fins 33a and the bottom of the trenches. On the other hand, hydrocarbon ions are highly anisotropic and adhere approximately perpendicularly to the fins 33a of the oxide layer 33. Therefore, in the conventional film formation apparatus 31, a carbon-based film 34 derived from hydrocarbon ions adheres to the tops of the fins 33a so as to be deposited approximately perpendicularly.

[0037] That is, not only the carbon-based film 34 derived from hydrocarbon ions, which is highly anisotropic, but also the carbon-based film 34 derived from hydrocarbon radicals, which is highly isotropic, adheres to the top of the fin 33a, so that the carbon-based film 34 overhangs toward the trench. For ease of understanding, in FIG. 6(A) and FIG. 6(B) described below, the carbon-based film derived from hydrocarbon ions is indicated by reference numeral 34a, and the carbon-based film derived from hydrocarbon radicals is indicated by reference numeral 34b. However, in reality, the carbon-based film 34a derived from hydrocarbon ions and the carbon-based film 34b derived from hydrocarbon radicals are mixed together to form the carbon-based film 34.

[0038] Furthermore, the carbon-based film 34 is isotropically etched by hydrogen radicals contained in the hydrogen plasma. In this embodiment, when plasma is generated from acetylene gas, it is considered that hydrogen plasma is generated from a portion of the acetylene gas. As described above, in the conventional film formation apparatus 31, plasma is not generated unevenly near the shower head 13, but is generated so as to be distributed almost evenly throughout the processing space S, and high-density plasma is not generated. Therefore, dissociation of the acetylene gas contained in the film formation gas introduced into the processing space S does not progress to that extent, and little hydrogen plasma is generated. As a result, there are almost no hydrogen radicals (indicated by "H" in the figure; the same applies to FIG. 6(B)) near the wafer W, and etching of the carbon-based film 34 by the hydrogen radicals does not progress.

[0039] For the above reasons, it was presumed that in the conventional film forming apparatus 31, the carbon-based film 34 adhered to the side surfaces of the fins 33a and the bottom of the trench, and furthermore, at the top of the fins 33a, the carbon-based film 34 overhanged toward the trench.

[0040] Next, a film formation mode in the film formation apparatus 10 provided with the clamp circuit 23 shown in FIG. 6(B) will be described.

[0041] In the film forming apparatus 10 provided with the clamp circuit 23, as described above, the high-density plasma P is generated unevenly near the shower head 13. That is, the high-density plasma P is no longer present near the wafer W, and the hydrocarbon radicals contained in the plasma generated from the acetylene gas are hardly present near the wafer W. Therefore, in the film forming apparatus 10, the carbon-based film 34b derived from the hydrocarbon radicals does not adhere to the tops of the fins 33a, but also to the side surfaces of the fins 33a and the bottoms of the trenches.

[0042] On the other hand, in the film formation apparatus 10, although the absolute value is smaller than that of the conventional film formation apparatus 31, a sheath voltage is generated in the processing space S, and thus the hydrocarbon ions are accelerated toward the wafer W. That is, even if there is almost no high-density plasma P near the wafer W, the hydrocarbon ions reach the wafer W. As a result, the highly anisotropic hydrocarbon ions lead the formation of the carbon-based film 34 on the wafer W. As a result, the carbon-based film 34a derived from the hydrocarbon ions grows so as to be deposited substantially vertically mainly on the tops of the fins 33a.

[0043] As described above, in the film formation apparatus 10, the high-density plasma P is generated primarily near the shower head 13. Therefore, the film formation gas discharged from the shower head 13 passes through the high-density plasma P, promoting dissociation of the acetylene gas contained in the film formation gas and generating a large amount of hydrogen plasma. Because hydrogen radicals are lighter and reach longer distances than hydrocarbon radicals, many hydrogen radicals are present near the wafer W, and etching of the carbon-based film 34 by the hydrogen radicals proceeds. Since the etching by the hydrogen radicals proceeds isotropically, most of the carbon-based film 34b derived from the hydrocarbon radicals and slightly adhering to the side surfaces of the fins 33a and the bottom of the trenches is removed. Furthermore, the overhangs of the carbon-based film 34 formed on the tops of the fins 33a are also removed by etching with the hydrogen radicals.

[0044] For the above reasons, it is presumed that in the film forming apparatus 10 provided with the clamp circuit 23, the carbon-based film 34 hardly adheres to the side surfaces of the fins 33a or the bottom of the trench, and furthermore, even at the top of the fins 33a, the carbon-based film 34 no longer overhangs toward the trench.

[0045] That is, according to this embodiment, in the film formation apparatus 10 provided with the clamp circuit 23, it is possible to form the carbon-based film 34 that does not overhang the tops of the fins 33a using a film formation gas consisting only of acetylene gas and argon gas. Furthermore, the carbon-based film 34 hardly adheres to the side surfaces of the fins 33a or the bottom of the trenches. In other words, in the film formation apparatus 10 provided with the clamp circuit 23, when forming the carbon-based film 34 that does not overhang the tops of the fins 33a, it is not necessary to add hydrogen gas to the film formation gas to promote etching by hydrogen radicals.

[0046] Furthermore, according to this embodiment, in the film formation apparatus 10 provided with the clamp circuit 23, the carbon-based film 34 can be formed on the tops of the fins 33a without overhanging simply by generating plasma from a film formation gas consisting only of acetylene gas and argon gas. That is, the carbon-based film 34 can be formed on the tops of the fins 33a in a single process. Therefore, when the carbon-based film 34 is selectively formed on the tops of the trenches, the occurrence of overhanging of the carbon-based film 34 can be suppressed and throughput can be improved.

[0047] Furthermore, when a carbon-based film is formed in the film forming apparatus 10, increasing the additive rate of acetylene gas in the film forming gas increases the amount of hydrocarbon radicals. In this case, even if high-density plasma P is generated biasedly near the showerhead 13, the probability of hydrocarbon radicals being present near the wafer W increases. As a result, a carbon-based film 34b derived from hydrocarbon radicals is also deposited on the side surfaces of the fins 33a and the bottom of the trench, which is thought to make the carbon-based film 34 on the top of the fins 33a more likely to overhang toward the trench. Therefore, to prevent the overhang of the carbon-based film 34 on the top of the fins 33a, there is an upper limit to the additive rate of acetylene gas in the film forming gas. For example, it is preferable to set the additive rate of acetylene gas to 10% or less.

[0048] Furthermore, when forming a carbon-based film in the film forming apparatus 10, lowering the temperature of the wafer W also lowers the ambient temperature near the wafer W. However, a lower ambient temperature increases the probability of hydrocarbon radical adhesion. This not only causes an anisotropic growth of a carbon-based film 34a derived from hydrocarbon ions on the tops of the fins 33a, but also causes an isotropic growth of a carbon-based film 34b derived from hydrocarbon radicals on the tops of the fins 33a. As a result, it is believed that the carbon-based film 34 on the tops of the fins 33a overhangs toward the trench. Therefore, to prevent the overhang of the carbon-based film 34 on the tops of the fins 33a, there is a lower limit to the temperature of the wafer W (actually, the temperature of the mounting table 12). For example, the temperature of the wafer W is preferably higher than 200°C, and more preferably higher than 300°C.

[0049] Furthermore, when forming a carbon-based 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. This makes it difficult for the carbon-based film 34a derived from hydrocarbon ions to grow on the tops of the fins 33a, and it is thought that the carbon-based film 34 is not selectively formed on the tops of the fins 33a. Therefore, in order to selectively form the carbon-based film 34 on the tops of the fins 33a, there is an upper limit to the pressure inside the chamber 11, and it is preferable to set the pressure inside the chamber 11 to, for example, 2 Torr or less.

[0050] In the film forming apparatus 10, it is also possible to connect the clamp circuit 23 to the lower electrode of the mounting table 12 with the diode 25 facing in the opposite direction, rather than to the shower head 13, and to ground the shower head 13. In this case as well, the plasma potential can be reduced, thereby reducing the absolute value of the sheath voltage.

[0051] However, in this case, the potential of the lower electrode becomes positive, so that a large number of electrons in the plasma flow toward the lower electrode, causing a local increase in electron density near the mounting table 12 and making it more likely that abnormal discharge will occur near the wafer W. Therefore, it is not preferable to connect the clamp circuit 23 to the lower electrode.

[0052] 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.

[0053] 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, another type of circuit capable of suppressing the positive voltage of the high-frequency voltage may be provided instead of the clamp circuit 23. For example, a circuit for applying a negative DC voltage in pulses to the upper electrode (shower head 13) may be provided. In this case, as shown in FIG. 7 , a DC power supply 35 is connected to the shower head 13 via a power supply line 20, and the DC power supply 35 applies a negative DC voltage in pulses to the shower head 13. In addition, a pulsing unit 36 ​​is connected to the power supply line 20 downstream of the high-frequency power supply 21.

[0054] 8 is a diagram showing a voltage waveform at the upper electrode when a negative DC voltage is applied to the upper electrode in pulses from the DC power supply 35. As shown in FIG. 8, when a negative DC voltage is applied to the upper electrode in pulses, the voltage at the upper electrode does not fluctuate to the positive side, and the plasma potential can be reduced. 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 placed on the mounting table 12, similar to when the clamp circuit 23 is provided.

[0055] Furthermore, for example, in a preferred embodiment of the present disclosure, a film formation process is performed on a wafer W having a plurality of trenches formed as a pattern, but the pattern is not limited to trenches and may be, for example, via holes, in which case a carbon-based film is formed on the tops of the walls between each via hole.

[0056] Furthermore, in the preferred embodiment of the present disclosure, the carbon-based film 34 is formed on the oxide layer 33, but this can also be applied when selectively forming a carbon-based film on the tops of protrusions and fins of metal layers such as wiring layers.

[0057] Furthermore, in a preferred embodiment of the present disclosure, a hydrocarbon gas (acetylene gas) is used to selectively deposit a carbon-based film on the top of the fin 33a. However, other hydrogen compound gases, such as silane gas, which is a silicon hydrogen compound gas, or borane gas, which is a boron hydrogen compound gas, may be used instead of the hydrocarbon gas.

[0058] When a film formation process is performed on a wafer W using the film formation apparatus 10 with a film formation gas consisting only of silane gas and argon gas, a silicon-based film that does not overhang toward the trenches or via holes can be selectively formed on the tops of the fins. Also, when a film formation process is performed on a wafer W using the film formation apparatus 10 with a film formation gas consisting only of borane gas and argon gas, a boron-based film that does not overhang toward the trenches or via holes can be selectively formed on the tops of the fins.

[0059] Furthermore, the rare gas contained in the film forming gas is not limited to argon gas, and other rare gases, such as xenon (Xe) gas, may also be used. [Explanation of symbols]

[0060] W wafer 10 Film deposition equipment 11 Chamber 23 Clamp Circuit 33a Fin 34 Carbon-based membrane

Claims

1. a film-forming step of forming a carbon-based film on a substrate having a pattern; In the film forming step, plasma is generated from a film forming gas consisting of only a hydrocarbon gas and a rare gas, and the carbon-based film is selectively formed on the top of the pattern.

2. 2. The carbon-based film forming method according to claim 1, wherein in the film forming step, the substrate is accommodated in a processing chamber whose interior is reduced in pressure 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 a positive voltage is suppressed from among the high-frequency voltages applied to an upper electrode facing the mounting table.

3. 3. The method for forming a carbon-based film according to claim 1, wherein the hydrocarbon gas is acetylene gas.

4. 3. The method for forming a carbon-based film according to claim 1, wherein the rare gas is argon gas.

5. 3. The carbon-based film forming method according to claim 1, wherein the temperature of the substrate is set to a temperature higher than 200[deg.] C. in the film forming step.

6. 6. The carbon-based film forming method according to claim 5, wherein the temperature of the substrate is set to 300[deg.] C. or higher in the film forming step.

7. 3. The method for forming a carbon-based film according to claim 1, wherein the hydrocarbon gas is added to the film-forming gas at a rate of 10% or less.

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

9. A processing chamber with a reduced pressure inside is provided, A film formation apparatus that places a substrate having a pattern inside the processing chamber, and generates plasma from a film formation gas consisting only of a hydrocarbon gas and a rare gas inside the processing chamber to selectively form a carbon-based film on the top of the pattern.

10. a mounting table disposed inside the processing chamber and on which the substrate is placed; an upper electrode facing the mounting table; a high frequency power supply that applies a high frequency voltage to the upper electrode to generate the plasma; The film forming apparatus according to claim 9 , further comprising: a voltage suppression unit that suppresses a positive voltage of the applied high frequency voltage.

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