Plasma etching method

Abstract

The present invention provides a plasma etching method which has a high etching rate of a silicon nitride film. This plasma etching method comprises an etching step wherein a silicon nitride film formed on a substrate (20) is etched with use of a plasma that is obtained by exciting an etching gas, which contains iodine heptafluoride, into a plasma.

Description

Plasma Etching Method

[0001] The present invention relates to a plasma etching method.

[0002] In the semiconductor manufacturing process, the silicon nitride film may be etched by plasma etching using an etching gas. For example, Patent Document 1 discloses a plasma etching method in which an etching gas containing a fluorinated gas such as sulfur hexafluoride (SF6) is plasmaized to etch a silicon nitride film.

[0003] Japanese Patent Publication No. 157940, 2016

[0004] In the plasma etching method used in the semiconductor manufacturing process and the like, further improvement in the etching rate of the silicon nitride film is desired. An object of the present invention is to provide a plasma etching method having a high etching rate of the silicon nitride film.

[0005] To solve the above problems, one aspect of the present invention is as follows [1] to [7]. [1] A plasma etching method including an etching step of etching a silicon nitride film formed on a substrate using a plasma obtained by plasmaizing an etching gas containing iodine heptafluoride.

[0006] [2] The plasma etching method according to [1], wherein a silicon oxide film is formed on the substrate together with the silicon nitride film, and the silicon oxide film is etched together with the silicon nitride film. [3] The plasma etching method according to [2], wherein the etching rate of the silicon nitride film is higher than the etching rate of the silicon oxide film.

[0007] [4] The plasma etching method according to [3], wherein the ratio of the etching rate of the silicon nitride film to the etching rate of the silicon oxide film is 2 or more and 70 or less. [5] The plasma etching method according to any one of [1] to [4], wherein the etching gas is a mixed gas containing iodine heptafluoride and an inert gas.

[0008] [6] A plasma etching method according to any one of [1] to [5], wherein etching is performed under a process pressure of 1 Pa or more and 10 Pa or less. [7] A plasma etching method according to any one of [1] to [6], wherein etching is performed while applying a bias power of 0 W or more and 1500 W or less to the lower electrode supporting the substrate.

[0009] According to the present invention, a plasma etching method is provided that allows for a high etching rate of silicon nitride films.

[0010] This is a schematic diagram of an example of a plasma etching apparatus illustrating one embodiment of the plasma etching method according to the present invention. This is a graph showing the relationship between process pressure and Si3N4 / SiO2 selectivity. This is a graph showing the relationship between bias power and Si3N4 / SiO2 selectivity at a process pressure of 3 Pa. This is a graph showing the relationship between bias power and Si3N4 / SiO2 selectivity at a process pressure of 5 Pa. This is a graph showing the relationship between the concentration of iodine heptafluoride in the etching gas and Si3N4 / SiO2 selectivity.

[0011] One embodiment of the present invention is described below. This embodiment is merely an example of the present invention, and the present invention is not limited to this embodiment. Furthermore, various modifications or improvements can be made to this embodiment, and such modified or improved forms may also be included in the present invention.

[0012] The plasma etching method of this embodiment includes an etching step in which a silicon nitride film (e.g., a Si3N4 film) formed on a substrate is etched using plasma obtained by plasma-generating an etching gas containing iodine heptafluoride (IF7). By performing plasma etching using an etching gas containing iodine heptafluoride, the silicon nitride film can be etched at a high etching rate.

[0013] According to the plasma etching method of this embodiment, both the silicon nitride film and the silicon oxide film (e.g., SiO2 film) can be etched. That is, if a substrate on which both a silicon nitride film and a silicon oxide film are formed is etched using the plasma etching method of this embodiment, both the silicon nitride film and the silicon oxide film can be etched simultaneously.

[0014] In this case, the silicon nitride film can be etched at a higher etching rate than the silicon oxide film. That is, according to the plasma etching method of this embodiment, the silicon nitride film can be selectively plasma-etched relative to the silicon oxide film. For example, the silicon nitride film and the silicon oxide film can be etched such that the ratio of the etching rate of the silicon nitride film to the etching rate of the silicon oxide film is between 2 and 70, and from the viewpoint of more stably controlling the etching, it can be between 3 and 30.

[0015] Therefore, by applying the plasma etching method of this embodiment to a semiconductor manufacturing process, the silicon nitride film can be efficiently selectively removed during etching for the formation of shallow trench isolation (STI) using double patterning. Furthermore, if the selectivity of etching the silicon nitride film compared to the silicon oxide film is improved (i.e., if the ratio of the etching rate of the silicon nitride film to the etching rate of the silicon oxide film is increased), the plasma etching method can be used as an alternative to the wet etching method.

[0016] Plasma etching according to this embodiment can be performed using a plasma etching apparatus. The plasma source in the plasma etching apparatus is not particularly limited, but examples include high-frequency discharge plasmas such as inductively coupled plasma (ICP) and capacitively coupled plasma (CCP), and microwave discharge plasmas such as electron cyclotron resonance plasma (ECRP). The plasma etching apparatus shown in Figure 1, which will be described in detail later, is a plasma etching apparatus that uses ICP as its plasma source.

[0017] In the plasma etching method of this embodiment, plasma etching is preferably performed under a process pressure of 0.2 Pa to 26.7 Pa, more preferably under a process pressure of 1 Pa to 15 Pa, even more preferably under a process pressure of 1 Pa to 10 Pa, and particularly preferably under a process pressure of 3 Pa to 7 Pa. Higher process pressure promotes the dissociation of iodine heptafluoride, thereby improving the selectivity of etching the silicon nitride film over the silicon oxide film. In addition, higher process pressure improves the ignition of the plasma.

[0018] The etching gas may consist solely of iodine heptafluoride, or it may be a mixed gas containing iodine heptafluoride and an inert gas. The type of inert gas is not particularly limited, but examples include helium, argon, neon, krypton, xenon, and nitrogen. These inert gases may be used individually or in combination of two or more.

[0019] The mixing ratio of iodine heptafluoride and inert gas should be adjusted considering the ignition properties of the plasma. The concentration of iodine heptafluoride in the etching gas can be greater than 0 vol% and less than or equal to 100 vol%. To ensure sufficient plasma ignition, it is more preferable to have a concentration of 5 vol% to 50 vol%. To ensure sufficiently high selectivity for etching the silicon nitride film over the silicon oxide film, it is even more preferable to have a concentration of 10 vol% to 30 vol%. The amount of etching gas used, for example, the total flow rate of etching gas to the chamber where plasma etching is performed in a plasma etching apparatus, should be adjusted according to the chamber volume, exhaust capacity, and process pressure.

[0020] In a plasma etching apparatus, for example, plasma can be generated by applying high-frequency source power to an RF (radio frequency) coil to form an electric and magnetic field, thereby converting the etching gas into plasma. The magnitude of the source power is not particularly limited, but it is preferably between 0W and 3000W, more preferably between 100W and 1500W, and even more preferably between 200W and 1000W.

[0021] The greater the source power, the more the dissociation of iodine heptafluoride is promoted, resulting in a higher etching rate. Therefore, the size of the source power should be set according to the desired etching rate. If the size of the source power is within the above numerical range, the etching rate of the silicon nitride film will be sufficiently high, and the etching selectivity of the silicon nitride film over the silicon oxide film will be sufficiently high.

[0022] While the substrate temperature during plasma etching is not particularly limited, it is preferably between -20°C and 250°C, more preferably between 0°C and 100°C, and even more preferably between 20°C and 70°C. If the substrate temperature during plasma etching is within the above range, deformation due to alteration, sublimation, etc., of the resist film formed on the substrate is suppressed, allowing plasma etching to be performed with high patterning accuracy.

[0023] During plasma etching, bias power may be applied to the lower electrode supporting the substrate. That is, the magnitude of the bias power applied to the lower electrode may be 0W or greater than 0W. In order to sufficiently increase the selectivity of etching the silicon nitride film over the silicon oxide film, the bias power applied to the lower electrode is preferably 12,000W or less, more preferably 1,500W or less, and even more preferably 300W or less.

[0024] The following describes an example of plasma etching of silicon nitride and silicon oxide films formed on the surface of a substrate using the plasma etching apparatus shown in Figure 1. The plasma etching apparatus in Figure 1 is a plasma etching apparatus that uses ICP as the plasma source. First, the plasma etching apparatus in Figure 1 will be described.

[0025] The plasma etching apparatus shown in Figure 1 comprises a chamber 1 in which plasma etching is performed, a lower electrode 2 that supports a substrate 20 to be plasma-etched inside the chamber 1, a bias power supply (not shown) that applies bias power to the lower electrode 2, an RF coil 15 that forms an electric and magnetic field inside the chamber 1 to plasmaize the etching gas, a source power supply (not shown) that applies high-frequency source power to the RF coil 15, a vacuum pump 13 that reduces the pressure inside the chamber 1, a pressure gauge 14 that measures the pressure inside the chamber 1, a sensor 16 that captures plasma emission generated in conjunction with plasma generation, and a spectrometer 17 that spectrally analyzes the plasma emission captured by the sensor 16 to monitor the temporal changes in plasma emission.

[0026] The substrate 20 has a silicon nitride film and a silicon oxide film formed on its surface. For example, a CCD (Charge-Coupled Device) image sensor can be used as the sensor 16. However, instead of providing the sensor 16 and spectrometer 17, a viewing window may be provided in the chamber 1, and the inside of the chamber 1 may be visually observed through the viewing window to confirm the temporal change in plasma emission.

[0027] Furthermore, the chamber 1 is equipped with an etching gas supply unit that supplies etching gas to the inside of the chamber 1. The etching gas supply unit includes an iodine heptafluoride gas supply unit 3 that supplies iodine heptafluoride gas, an inert gas supply unit 4 that supplies inert gas, an etching gas supply pipe 11 that connects the iodine heptafluoride gas supply unit 3 and the chamber 1, and an inert gas supply pipe 12 that connects the inert gas supply unit 4 to the middle part of the etching gas supply pipe 11.

[0028] Furthermore, when supplying iodine heptafluoride gas as an etching gas to the chamber 1, the iodine heptafluoride gas is sent from the iodine heptafluoride gas supply unit 3 to the etching gas supply pipe 11, thereby supplying the iodine heptafluoride gas to the chamber 1 via the etching gas supply pipe 11.

[0029] Furthermore, when supplying a mixed gas of iodine heptafluoride gas and an inert gas as the etching gas, iodine heptafluoride gas is sent from the iodine heptafluoride gas supply unit 3 to the etching gas supply piping 11, and inert gas is sent from the inert gas supply unit 4 to the etching gas supply piping 11 via the inert gas supply piping 12. As a result, the iodine heptafluoride gas and the inert gas are mixed in the middle section of the etching gas supply piping 11 to form a mixed gas, which is then supplied to the chamber 1 via the etching gas supply piping 11.

[0030] When performing plasma etching using such a plasma etching apparatus, a substrate 20 is placed on a lower electrode 2 located inside the chamber 1. After reducing the pressure inside the chamber 1 to between 1 Pa and 10 Pa using a vacuum pump 13, etching gas is supplied to the chamber 1 by an etching gas supply unit. When a high-frequency source power (e.g., 13.56 MHz) is applied to the RF coil 15, an electric and magnetic field is formed inside the chamber 1, accelerating electrons. These accelerated electrons collide with iodine heptafluoride molecules in the etching gas, generating new ions and electrons, resulting in a discharge and the formation of plasma. The generation of plasma can be confirmed using a sensor 16 and a spectrometer 17.

[0031] When plasma is generated, the silicon nitride film and silicon oxide film formed on the surface of the substrate 20 are etched. The amount of etching gas supplied to the chamber 1 and the concentration of iodine heptafluoride in the etching gas (mixed gas) can be adjusted by controlling the flow rates of iodine heptafluoride gas and inert gas, respectively, using mass flow controllers (not shown) installed in the etching gas supply pipe 11 and the inert gas supply pipe 12.

[0032] As described above, by using iodine heptafluoride or a mixed gas of iodine heptafluoride and an inert gas as the etching gas, setting the process pressure to 1 Pa or more and 10 Pa or less, and the bias power to 1500 W or less, the silicon nitride film and silicon oxide film can be etched such that the ratio of the etching rate of the silicon nitride film to the etching rate of the silicon oxide film is 2 or more and 70 or less, or from the viewpoint of more stably controlling the etching, it is 3 or more and 30 or less.

[0033] The present invention will be described in more detail below with reference to examples and comparative examples. (Example 1) Plasma etching of a substrate was performed using an ICP etching apparatus RIE-200iP manufactured by Samco Corporation, which has substantially the same configuration as the plasma etching apparatus shown in Figure 1. This substrate was prepared by depositing a silicon nitride film (Si3N4 film) and a silicon oxide film (SiO2 film) on a silicon substrate by chemical vapor deposition.

[0034] Furthermore, the internal volume of the chamber is 46,000 cm³. 3 The etching gas is a mixture of iodine heptafluoride gas and argon. The concentration of iodine heptafluoride in the etching gas was adjusted to 20% by volume by setting the flow rate of iodine heptafluoride gas to 10 sccm and the flow rate of argon to 40 sccm. Here, sccm is the volume flow rate per minute normalized under conditions of 0°C and 1 atm (cm³). 3 )

[0035] Plasma etching was performed with the process pressure inside the chamber set to 1 Pa, the source power to 500 W, the bias power to 0 W, and the substrate temperature to 20°C. The flow rates of iodine heptafluoride gas, argon gas, process pressure, source power, and bias power were continuously monitored, and it was confirmed that there was no difference between the set values ​​and the actual values. The results are shown in Table 1.

[0036] Table 1 shows the time (etching time) during which the silicon nitride film and silicon oxide film are plasma-etched, the film thickness before and after etching of the silicon nitride film and silicon oxide film, the etching rates of the silicon nitride film and silicon oxide film, and the ratio of the etching rate of the silicon nitride film to the etching rate of the silicon oxide film (Si3N4 / SiO2 selectivity ratio).

[0037] The thickness of the silicon nitride and silicon oxide films was measured using a Filmetrics F20 reflectance spectrometer. The etching rates of the silicon nitride and silicon oxide films were calculated by subtracting the thickness after etching from the thickness before etching and dividing the result by the etching time.

[0038]

[0039] (Examples 2 to 4) Plasma etching was performed in the same manner as in Example 1, except that the process pressure was changed as shown in Table 1. The etching rates of the silicon nitride film and the silicon oxide film, and the ratio of the etching rate of the silicon nitride film to the etching rate of the silicon oxide film were calculated. The results are shown in Table 1.

[0040] (Comparative Examples 1 to 4) Plasma etching was performed in the same manner as in Example 1, except that the etching gas was a mixed gas of sulfur hexafluoride gas and argon gas (the concentration of sulfur hexafluoride in the etching gas was 20% by volume) and the process pressure was changed as shown in Table 1. The etching rates of the silicon nitride film and the silicon oxide film, and the ratio of the etching rate of the silicon nitride film to the etching rate of the silicon oxide film were calculated. The results are shown in Table 1.

[0041] (Examples 11 to 18) Plasma etching was performed in the same manner as in Example 1, except that the process pressure was 3 Pa and the bias power was changed as shown in Table 2. The etching rates of the silicon nitride film and the silicon oxide film, and the ratio of the etching rate of the silicon nitride film to the etching rate of the silicon oxide film were calculated. The results are shown in Table 2.

[0042]

[0043] (Examples 21 to 24) Plasma etching was performed in the same manner as in Example 1, except that the process pressure was 5 Pa and the bias power was changed as shown in Table 3. The etching rates of the silicon nitride film and the silicon oxide film, and the ratio of the etching rate of the silicon nitride film to the etching rate of the silicon oxide film were calculated. The results are shown in Table 3.

[0044]

[0045] (Comparative Examples 21 to 23) Plasma etching was performed in the same manner as in Example 1, except that the etching gas was a mixed gas of sulfur hexafluoride gas and argon (the concentration of sulfur hexafluoride in the etching gas was 20% by volume), the process pressure was 5 Pa, and the bias power was changed as shown in Table 3. The etching rates of the silicon nitride film and the silicon oxide film, and the ratio of the etching rate of the silicon nitride film to the etching rate of the silicon oxide film were calculated. The results are shown in Table 3.

[0046] (Examples 31 to 33) Plasma etching was performed in the same manner as in Example 1, except that the process pressure was 3 Pa and the concentration of iodine heptafluoride in the etching gas was changed as shown in Table 4. The etching rates of the silicon nitride film and the silicon oxide film, and the ratio of the etching rate of the silicon nitride film to the etching rate of the silicon oxide film were calculated. The results are shown in Table 4.

[0047] In Examples 31 to 33, the concentration of iodine heptafluoride in the etching gas was adjusted by setting the flow rates of iodine heptafluoride gas and argon as follows. That is, by setting the flow rate of iodine heptafluoride gas to 2.5 sccm and the flow rate of argon to 47.5 sccm, the concentration of iodine heptafluoride in the etching gas was adjusted to 5% by volume. By setting the flow rate of iodine heptafluoride gas to 5 sccm and the flow rate of argon to 45 sccm, the concentration of iodine heptafluoride in the etching gas was adjusted to 10% by volume. By setting the flow rate of iodine heptafluoride gas to 10 sccm and the flow rate of argon to 40 sccm, the concentration of iodine heptafluoride in the etching gas was adjusted to 20% by volume.

[0048]

[0049] The results from Tables 1 to 4 are shown in the graphs in Figures 2 to 5, respectively. From Table 1 and the graphs in Figure 2, it can be seen that, at all process pressures, the etching gas containing iodine heptafluoride had a larger ratio of the etching rate of the silicon nitride film to the etching rate of the silicon oxide film (Si3N4 / SiO2 selectivity ratio) than the etching gas containing sulfur hexafluoride, indicating that the silicon nitride film was selectively etched compared to the silicon oxide film. Furthermore, it can be seen that the Si3N4 / SiO2 selectivity ratio improved as the process pressure increased.

[0050] Furthermore, from the graphs in Table 2 and Figure 3, it can be seen that the Si3N4 / SiO2 selectivity improves as the bias power decreases. In addition, from the graphs in Table 3 and Figure 4, it can be seen that, at all bias powers, the etching gas containing iodine heptafluoride showed a larger ratio of the etching rate of the silicon nitride film to the etching rate of the silicon oxide film than the etching gas containing sulfur hexafluoride, indicating that the silicon nitride film was selectively etched compared to the silicon oxide film. And it can be seen that the Si3N4 / SiO2 selectivity improves as the bias power decreases.

[0051] Furthermore, Table 4 shows that the higher the concentration of iodine heptafluoride in the etching gas, the greater the etching rate for both the silicon oxide film and the silicon nitride film. On the other hand, regarding the Si3N4 / SiO2 selectivity ratio, as can be seen from Table 4 and the graph in Figure 5, there was a tendency for it to improve with increasing concentration of iodine heptafluoride in the etching gas, but the change was not very significant.

[0052] 1... Chamber 2... Lower electrode 3... Iodine heptafluoride gas supply unit 4... Inert gas supply unit 11... Etching gas supply piping 12... Inert gas supply piping 13... Vacuum pump 14... Pressure gauge 15... RF coil 16... Sensor 17... Spectrometer 20... Substrate

Claims

1. A plasma etching method comprising an etching step of etching a silicon nitride film formed on a substrate using plasma obtained by converting an etching gas containing iodine heptafluoride into plasma.

2. The plasma etching method according to claim 1, wherein a silicon oxide film is formed on the substrate together with the silicon nitride film, and the silicon oxide film is etched together with the silicon nitride film.

3. The plasma etching method according to claim 2, wherein the etching rate of said silicon nitride film is higher than the etching rate of said silicon oxide film.

4. The plasma etching method according to claim 3, wherein the ratio of the etching rate of said silicon nitride film to the etching rate of said silicon oxide film is 2 or more and 70 or less.

5. A plasma etching method according to any one of claims 1 to 4, wherein the etching gas is a mixed gas containing iodine heptafluoride and an inert gas.

6. A plasma etching method according to any one of claims 1 to 5, wherein etching is carried out under a process pressure of 1 Pa or more and 10 Pa or less.

7. The plasma etching method according to any one of claims 1 to 6, wherein etching is carried out while applying a bias power of 0 W or more and 1500 W or less to a lower electrode supporting the substrate.

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