Plasma processing method

Abstract

To provide a plasma processing method having a good front surface state of a Ru containing film pattern formed by a plasma etching while suppressing deterioration of a throughput of a plasma etching process.SOLUTION: A plasma processing method includes: a first etching step S01 of etching a ruthenium containing film by using a plasma; a second etching step S02 of etching the ruthenium containing film by using the plasma after the first etching step. The second etching step includes: a first step S11 of forming a modified layer of the ruthenium containing film by using the plasma generated by a halogen element containing gas; and a second step S12 of detaching the modified layer by using the plasma generated by an oxygen element containing gas, and alternately repeats the first and second steps.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a plasma processing method for a semiconductor substrate. [Background technology]

[0002] As semiconductor device microfabrication progresses, there is a demand for processing with fine line widths and high aspect ratios. Cu (copper) has been widely used as a wiring material that corresponds to miniaturization in the wiring process, but as miniaturization progresses, the resistivity of Cu becomes a problem, and Ru (ruthenium) has been raised as a candidate material to replace Cu.

[0003] Patent Document 1 discloses a high-definition metal film etching method for etching metals such as Ru and / or their metal oxide films little by little. The etching method of Patent Document 1 includes a first step of exposing the metal film to halogen atom ions or radicals without applying an electric field such as a high-frequency bias to cause adsorption, and a second step of etching the metal film to which halogen atoms have been adsorbed by exposing the metal film to oxygen ions or radicals by applying an electric field such as a weak high-frequency bias. Since a secondary product of the reaction between the metal and chlorine plasma is formed on the surface of the metal film in the first step, etching can proceed in the second step even when the energy of the oxygen plasma is low. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-305892 A Summary of the Invention [Problem to be solved by the invention]

[0005] The finer the structure of a semiconductor device, the more important it is to consider the effect of the surface state of the structure formed by plasma processing on the performance of the semiconductor device. According to the inventors' study, the surface of the Ru film formed by the method disclosed in Patent Document 1 is highly rough and is considered to remain damaged by exposure to oxygen plasma, which reduces the performance of the semiconductor device. On the other hand, it is necessary to avoid a significant decrease in the throughput of the plasma etching process.

[0006] An object of the present invention is to provide a plasma processing method that can provide a Ru-containing film pattern formed by plasma etching in a good surface state while suppressing a decrease in throughput of the plasma etching process. [Means for solving the problem]

[0007] A plasma processing method according to one embodiment of the present invention is a plasma processing method for plasma etching a ruthenium-containing film on a substrate to be processed having the ruthenium-containing film, the method comprising: a first etching step of etching the ruthenium-containing film using plasma; and a second etching step of etching the ruthenium-containing film using plasma after the first etching step. The second etching step comprises a first step of forming a modified layer on a surface of the ruthenium-containing film using plasma generated by a halogen-element-containing gas; and a second step of detaching the modified layer using plasma generated by an oxygen-element-containing gas, and the first step and the second step are alternately repeated. Effect of the Invention

[0008] The present invention provides a plasma treatment method for improving the surface condition of a Ru-containing film pattern. Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of a plasma processing apparatus. [Diagram 2]2 is a flowchart of a plasma treatment according to the present embodiment. [Diagram 3] 1A to 1C are diagrams illustrating device processing steps by plasma processing according to an embodiment of the present invention. [Figure 4] FIG. 13 is a diagram showing the surface change of a Ru film during an over-etching process. [Diagram 5] FIG. 13 is a diagram showing the effect of the present embodiment. [Figure 6] FIG. 13 is a diagram showing the effect of the present embodiment. [Figure 7] FIG. 13 is a diagram showing the effect of the present embodiment. [Figure 8] FIG. 13 is a diagram showing the effect of the present embodiment. [Figure 9] FIG. 2 is a top view of a Ru line wiring formed in the first embodiment. [Figure 10] 11A to 11C are diagrams illustrating device processing steps in Example 2. [Figure 11] 11A to 11C are diagrams illustrating device processing steps in Example 3. [Figure 12] FIG. 11 is a top view of a mask pattern in the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An example of a plasma processing apparatus for performing the plasma processing of this embodiment is shown in Fig. 1. Here, an example of a plasma processing apparatus that generates electron cyclotron resonance (ECR) excited plasma is shown as an example of the plasma processing apparatus. In the ECR excited plasma processing apparatus, microwaves are used as an excitation source, and plasma is generated by applying an external magnetic field.

[0011] The plasma processing apparatus includes a sample stage 103 on which a substrate (wafer) 101 to be processed is placed within a vacuum vessel 100, and performs plasma processing on the substrate 101 to be processed by using plasma generated within the vacuum vessel 100. A high-frequency power supply 110 for substrate bias is connected to the sample stage 103. By controlling the applied substrate bias (high-frequency power), it is possible to control the direction and energy of ions incident on the substrate 101 to be processed. An exhaust pipe 107 is connected to the vacuum vessel 100, and a pressure control valve 108 and a pump 109 are connected to the exhaust pipe 107 to adjust the pressure inside the vacuum vessel 100. The pump 109 exhausts the inside of the vacuum vessel 100 via the exhaust pipe 107 and the pressure control valve 108, and maintains the vacuum vessel 100 at a low pressure during plasma processing.

[0012] Microwave generation source 121 generates microwaves upon receiving power from microwave power source (power source for generating plasma) 104. The microwave power generated by microwave generation source 121 is adjusted by microwave matching device 123 and propagated from rectangular waveguide 122 through converter 124 to circular waveguide 125 and cavity 126, which resonates the propagated microwave power.

[0013] The cavity 126 and the vacuum vessel 100 are separated by a partition plate 128. The partition plate 128 is made of a dielectric material that transmits microwave power and maintains the vacuum state inside the vacuum vessel 100. An electromagnet 127 is provided on the outside of the vacuum vessel 100 and the cavity 126 to form a magnetic field inside the cavity 126 and the vacuum vessel 100 and generate electron cyclotron resonance.

[0014] A shower plate 102 having a number of holes formed therein for supplying gas into the vacuum vessel 100 is provided, and a gas line 106 for supplying gas is provided between the partition plate 128 and the shower plate 102. The flow rate of the gas is adjusted by a mass flow controller (MFC) 105, and the gas is supplied into the vacuum vessel 100 through the gas line 106. In order to obtain a desired film quality, it is preferable that the MFC 105 is mounted on each gas system. The gases supplied by each gas system are, for example, an oxygen element (O)-containing gas, a halogen element-containing gas, and an inert gas. In the following embodiment, an example in which O2 is used as the oxygen element (O)-containing gas is shown, but CO, CO2, SO2, COS, etc. may also be used. In addition, an example in which Cl2 is used as the halogen element-containing gas is shown, but HBr, CF4, SF6, NF3, CHF3, etc. may also be used. The inert gas can be used for gas switching or to improve uniformity, and for example, nitrogen gas or rare gases such as He and Ar can be used.

[0015] The control unit 111 controls the microwave power supply 104 , the electromagnet 127 , the MFC 105 , the pressure control valve 108 , the pump 109 , and the high frequency power supply 110 for substrate bias to perform plasma processing on the substrate 101 to be processed.

[0016] The process flow of this embodiment will be described with reference to FIG. 2 and FIG. 3. The sample in FIG. 3 shows an extracted cross-sectional structure of a device related to a wiring layer (first layer) of a substrate 101 to be processed. The sample 201 has a layer structure in which an oxide film 211, a Ru film 212, and a SiN film 213 are laminated in this order, and a patterned hard mask 214 is formed thereon. The oxide film 211 is a silicon oxide film (SiO2), and the Ru film 212 is a Ru element-containing film such as a ruthenium film or an oxide thereof. In the process flow of this embodiment, a substrate to be processed having a structure such as the sample 201 is subjected to plasma etching to transfer the pattern of the hard mask 214 to the SiN film 213 and the Ru film 212. First, the sample 201 is subjected to main etching (first etching) (S01). The main etching process is an anisotropic etching process, and is a continuous etching process in which etching progresses according to the pattern of the hard mask 214 and is terminated when it is determined that the etching has reached the oxide film 211. By using continuous etching, the throughput of plasma etching can be improved. However, at the stage where step S01 is completed, as shown as sample 202 (see FIG. 3), the Ru film 212 of sample 202 after step S01 is completed has large surface roughness on the plasma-etched sidewall, and plasma damage remains on the surface.

[0017] Therefore, in the process flow of this embodiment, after the main etching, over-etching (second etching) is performed on the sample 202 (S02) to remove the surface roughness of the sidewall of the Ru film 212 and the plasma damage formed on the sidewall surface. The over-etching process is a cyclic etching process in which a Cl2 plasma treatment (S11) and an O2 plasma treatment (S12) are repeatedly performed.

[0018] Fig. 4 shows the surface change of the Ru film in the over-etching process. Note that Fig. 4 shows the side surface of the Ru film 212 in Fig. 3 facing upward. The Ru film 301 shows the Ru film after step S01 is completed. The surface 311 of the Ru film 301 has a large surface roughness and plasma damage remains.

[0019] In the Cl2 plasma treatment (S11), plasma is generated while Cl2 is supplied as a halogen element-containing gas from the gas line 106. At this time, weak high-frequency power (about 50 W) may be applied to the substrate 101 to be treated from the substrate bias high-frequency power supply 110. It is also possible not to apply this high-frequency power. The result of performing the Cl2 plasma treatment (S11) on the Ru film 301 is the Ru film 302. The Cl2 plasma treatment causes Cl elements to be adsorbed on the surface of the Ru film, modifying the surface. Specifically, Ru elements and Cl elements are bonded on the surface of the Ru film 302, forming non-volatile Ru x Cl y A modified layer 312 is formed.

[0020] In the O2 plasma treatment (S12), plasma is generated while O2 is supplied as an oxygen-containing gas from the gas line 106. At this time, in order to make the surface state of the Ru film as smooth as possible, high-frequency power is not applied to the substrate 101 to be treated. The result of performing the O2 plasma treatment (S12) on the Ru film 302 is the Ru film 303. The O2 plasma treatment is performed by removing the Ru x Cl y This is a process for removing the modified layer 312. The O2 plasma process causes the following reactions. Ru x Cl y +O→RuO2+O x Cl y +Cl2→RuO4+O x Cl y +Cl2 RuO4 is volatile, and is desorbed from the Ru film, thereby progressing the etching. A surface 313 of the Ru film 303 is smoother than a surface 311 of the Ru film 301.

[0021] In this way, by repeatedly performing the surface modification by the Cl2 plasma treatment (S11) and the desorption by the O2 plasma treatment (S12), etching progresses so as to smooth the surface of the Ru film. This state is the Ru film 304.

[0022] The sample at the stage where step S02 is completed is the sample 203 shown in Fig. 3. The surface roughness of the Ru film pattern formed by plasma etching is suppressed, and the plasma damage on the surface is also removed.

[0023] Figure 5 shows the etching amount when one step of Cl2 plasma treatment and one step of O2 plasma treatment are performed, and the etching amount when one cycle of the over-etching process is performed. It can be seen that the etching amount when one cycle of the over-etching process is performed is larger than the simple sum of the etching amounts in each cycle. In the over-etching process, O x Cl y It is believed that the formation of on the surface of the Ru film contributes to the promotion of etching.

[0024] Figure 6 shows the change in surface roughness (root mean square roughness RMS) of the Ru film after 20 cycles of the over-etching process. After 20 cycles, the etching amount progresses by approximately 75 nm (3.8 nm / cycle, see Figure 5), but during this time, the surface roughness improves by approximately 50% compared to before the over-etching (initial).

[0025] Figure 7 shows the change in surface roughness of the Ru film when one step each of Cl2 plasma treatment and O2 plasma treatment is performed. It can be seen that the surface roughness after Cl2 plasma treatment is almost the same as before treatment (initial), whereas the surface roughness after O2 plasma treatment is significantly worse than before treatment. Thus, by starting the over-etching process with Cl2 plasma treatment, it is possible to prevent the deterioration of the surface condition due to O2 plasma treatment.

[0026] 8 shows the change in surface roughness of the Ru film when the over-etching process of this embodiment is performed 20 cycles, and as a comparative example, the change in surface roughness of the Ru film when 20 cycles are performed while applying high frequency power (50 W) to the substrate to be processed in the O2 plasma treatment of the over-etching process. It can be seen that the surface roughness is significantly worsened in the comparative example. This is thought to be because the surface roughness is worsened by the incidence of high-energy oxygen ions on the Ru film due to the application of high frequency power to the substrate to be processed.

[0027] An example of processing a semiconductor device using the plasma processing of this embodiment will now be described. EXAMPLES

[0028] Example 1 is a Ru line wiring process. The process of the Ru line wiring process is as shown in FIG. 3. In the main etching process (S01), a mixed gas of Cl2 as a halogen element-containing gas and O2 as an oxygen element-containing gas is supplied from the gas line 106 while being diluted with Ar gas as an inert gas, and plasma is generated. In order to increase the throughput of the plasma etching, it is preferable to perform continuous etching in the main etching process, but cyclic etching of Cl2 plasma processing and O2 plasma processing may also be performed. In this case, high frequency power is applied to the substrate to be processed even in the O2 plasma processing in order to make it an anisotropic etching process.

[0029] 9 is a top view of the Ru line wiring formed in the first embodiment. The cross-sectional view of FIG. 3 corresponds to the cross-sectional view along the AA cross section shown in FIG. 9. The Ru line wiring 401 is arranged at a pitch of about 20 nm. By applying the process treatment of this embodiment, Ru residues can be removed from the side walls and bottom parts of the Ru line wiring that have been subjected to plasma etching. This can improve the LER (Line Edge Roughness) / LWR (Line Width Roughness) of the wiring. EXAMPLES

[0030] Example 2 is Ru wiring processing (Buried Power Rail), and shows an example of forming Ru buried wiring on a Si substrate on which a fin structure is formed. The process is shown in Figure 10. In sample 501, Ru film 513 is formed on Si substrate 511 on which fin 512 is formed, and fin 512 and Ru film 513 are insulated from each other by oxide film 514. In addition, hard mask 515 remains on fin 512.

[0031] First, main etching is performed on sample 501 (S01). The main etching process is an anisotropic etching process, and etching does not proceed on portions other than Ru film 513 due to the presence of oxide film 514 and hard mask 515, and plasma etching proceeds only on the Ru film 513 portion. At the stage where step S01 is completed, as shown as sample 502, the Ru film 513 of sample 502 after step S01 is in a state where the plasma-etched upper surface has large surface roughness and plasma damage remains on the surface.

[0032] Following the main etching, over-etching is performed on sample 502 (S02) to remove surface roughness on the top surface of Ru film 513 and plasma damage formed on the sidewall surface. The sample at the stage where step S02 is completed is sample 503. The surface roughness on the top surface of Ru film 513 is suppressed, and the plasma damage on the surface is also removed. This allows a Ru buried wiring with a smooth top surface to be obtained.

[0033] In the second embodiment, similarly to the first embodiment, it is preferable to use continuous etching in the main etching process, but cycle etching may also be used. EXAMPLES

[0034] Example 3 is hole processing (via processing), and its process is shown in FIG. 11. Sample 601 has a layered structure in which a Ru film 611 and a SiN film 613 are laminated, and a patterned hard mask 614 is formed thereon. Also, an insulating film (oxide film) 612 is formed so as to be embedded in the Ru film 611. FIG. 12 shows a top view of hard mask 614. The cross-sectional view of FIG. 11 corresponds to the cross-sectional view along the BB cross section shown in FIG. 12.

[0035] First, main etching is performed on sample 601 (S01). The main etching process is the same as in Example 1. To increase the throughput of the plasma etching, it is preferable to perform continuous etching in the main etching process, but cycle etching may also be performed. In this case, high-frequency power is also applied to the substrate to be processed in the O2 plasma processing to make it an anisotropic etching process. At the stage where step S01 is completed, as shown by sample 602, the Ru film 611 of sample 602 after step S01 is in a state where the plasma-etched surface, i.e., the bottom and side surfaces of the via hole, has a large surface roughness and plasma damage remains on the surface.

[0036] Following the main etching, over-etching is performed on sample 602 (S02) to remove surface roughness of the etched surface of Ru film 611 and plasma damage formed on the surface. The sample at the stage where step S02 is completed is sample 603. The surface roughness of Ru film 611 is suppressed, and the plasma damage on the surface is also removed. This makes it possible to obtain a via hole with a smooth bottom and side surface.

[0037] The present invention is not limited to the above-mentioned embodiment, and includes various modifications. For example, the above-mentioned embodiment and modifications have been described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. In addition, it is possible to replace a part of the configuration of a certain embodiment or modification with the configuration of another embodiment or modification, and it is also possible to add the configuration of another embodiment or modification to the configuration of a certain embodiment or modification. In addition, it is possible to add, delete, or replace other configurations with respect to a part of the configuration of each embodiment or modification. For example, an ECR excitation plasma processing apparatus has been exemplified as the plasma processing apparatus for performing the plasma processing of this embodiment, but this is not limited to this. For example, it may be an inductively coupled plasma (ICP) processing apparatus or a capacitively coupled plasma (CCP) processing apparatus. In addition, a radical etching chamber in which an ion shielding plate is provided in the vacuum vessel 100 may be used. [Explanation of symbols]

[0038] 100: vacuum vessel, 101: substrate to be processed, 102: shower plate, 103: sample stage, 104: microwave power source, 105: mass flow controller, 106: gas line, 107: exhaust pipe, 108: pressure control valve, 109: pump, 110: high frequency power source for substrate bias, 111: control unit, 121: microwave generation source, 122: rectangular waveguide, 123: microwave matching box, 124: converter, 125: circular waveguide, 126: cavity, 127: electromagnet, 128: partition plate, 201, 202, 203, 501, 502, 503, 601, 602, 603: sample, 211: oxide film, 212, 301, 302, 303, 304: Ru film, 213: SiN film, 214: hard mask, 311, 313: surface, 312: Ru x Cl y Modified layer, 401: Ru line wiring, 511: Si substrate, 512: fin, 513: Ru film, 514: oxide film, 515: hard mask, 611: Ru film, 612: insulating film (oxide film), 613: SiN film, 614: hard mask.

Claims

1. 1. A plasma processing method for plasma etching a ruthenium-containing film on a substrate to be processed, comprising: a first etching step of etching the ruthenium-containing film using a plasma; A second etching step of etching the ruthenium-containing film using plasma after the first etching step, The second etching step includes a first step of forming a modified layer on the surface of the ruthenium-containing film by using plasma generated by a halogen-containing gas, and a second step of desorbing the modified layer by using plasma generated by an oxygen-containing gas, and the first step and the second step are alternately repeated.

2. 2. The plasma processing method according to claim 1, The plasma processing method according to claim 2, wherein the high frequency power supplied to the sample stage on which the substrate to be processed is placed in the second step is 0 W.

3. 2. The plasma processing method according to claim 1, The plasma processing method according to claim 1, wherein the plasma in the first etching step is generated by a mixed gas of a halogen-containing gas and an oxygen-containing gas.

4. 2. The plasma processing method according to claim 1, The first etching step includes a third step of forming a modified layer on a surface of the ruthenium-containing film by using plasma generated by a halogen-containing gas, and a fourth step of desorbing the modified layer by using plasma generated by an oxygen-containing gas, and the third step and the fourth step are alternately repeated.

5. 2. The plasma processing method according to claim 1, The plasma processing method according to claim 1, wherein the second etching step starts from the first step.

6. 2. The plasma processing method according to claim 1, The plasma processing method according to claim 1, wherein the halogen-containing gas is chlorine gas, and the oxygen-containing gas is oxygen gas.

7. 2. The plasma processing method according to claim 1, the ruthenium-containing film is a ruthenium film, 4. The plasma processing method according to claim 1, wherein the ruthenium film is formed above a silicon oxide film, and a silicon nitride film is formed above the ruthenium film.

8. 2. The plasma processing method according to claim 1, the substrate to be processed has a FinFET structure, The plasma processing method according to claim 1, wherein the ruthenium-containing film is embedded between fins.

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