JPH06168920A - Removal of thin film - Google Patents

Abstract

PURPOSE:To etch away a thin film only selectively, rapidly and uniformly without giving damage to a base film even if a dry treatment is performed by a method wherein a natural oxide film on the surface of the thin film is removed as a pretreatment for removing the thin film, such as a polycrystalline silicon thin film and a silicon nitride thin film, formed on a substrate. CONSTITUTION:The pressure in a reaction chamber is set using prescribed reaction gas and a thin film 33 is etched with a microwave power. As a result, the etching rate within the surface of a substrate 31 is made uniform and the selection ratio of the film 33 to a base film 32 is a value of 150 or more. Accordingly, it becomes possible to remove rapidly a natural oxide film 35 on the surface of the film 33. Thereby, even if a dry treatment is performed, damage does not inflict on the base film 32 because the selection ratio of the film 33 to the film 32 can be made high and the removal of the thin film can cope with the miniaturization of an element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for removing a thin film,
More specifically, the present invention relates to a thin film removing method effective for removing a thin film formed as a mask in an element isolation process in an LSI manufacturing process.

[0002]

2. Description of the Related Art FIG. 2 is a schematic cross-sectional view showing a process of LOCOS (LOCalized Oxidation of Silicon) which is a typical element isolation technique of LSI. In FIG. 2, 31 is a silicon substrate (hereinafter referred to as substrate). Shows. LOCOS
First, a SiO ₂ base film 32 is formed on the surface of the substrate 31 by thermal oxidation, and then a silicon nitride (Si ₃ N ₄ ) thin film 33 is formed on the base film 32 in a region where a device is formed (a). Further, a SiO ₂ film 34 is formed by thermal oxidation (b). At this time, the silicon nitride thin film 33 having strong oxidation resistance
A thin SiO ₂ native oxide film 35 is formed on top. After that, the natural oxide film 35 and the silicon nitride thin film 33 are removed by etching to separate the element formation region (c).

Although not shown, depending on the manufacturing method, the silicon nitride thin film 33 is formed on the surface of the substrate 31 in the step (a).
There is a case where a silicon nitride thin film is also formed on the back surface of the substrate 31 at the same time when forming the film, and a natural oxide film is formed on the silicon nitride thin film in the step (b). In this case, the substrate is formed in the step (c). The silicon nitride thin film and the natural oxide film formed on the back surface of 31 are also removed by etching.

As described above, in the manufacture of an LSI, the silicon nitride thin film 33 formed on the front surface of the substrate 31 as a mask in the step for separating the element formation region, or the silicon nitride thin film additionally formed on the back surface of the substrate 31 and the like. Must be removed by etching, and this removal requires a lot of working time and steps.

Further, in the manufacture of an LSI, when forming a pattern of an insulating film or a metal for wiring on a substrate, a resist is coated and photolithography is performed to form a desired pattern on the substrate, and then the resist is applied. There is a step of removing. In recent years, a dry (ashing) process using oxygen plasma has become the mainstream for resist removal instead of a wet process because of measures against pollution problems.

As an apparatus used for removing the resist by ashing, there is an apparatus disclosed in JP-A-63-99481 and JP-A-62-5600. Figure 1
Is a cross-sectional view schematically showing this microwave plasma processing apparatus, and 10 in the figure shows a hollow rectangular parallelepiped reactor. The reactor 10 is made of a metal such as aluminum, and its peripheral wall has a double structure. A cooling water passage 11 is formed inside the reactor 10, and the cooling water flowing through the cooling water passage 11 is a cooling water inlet 11a. Is supplied from the cooling water outlet 11b. A plasma generation chamber 12 and a reaction chamber 13 are formed inside the cooling water passage 11, and the plasma generation chamber 12 and the reaction chamber 13 are separated by a partition plate 14 having a plurality of holes 14a. The upper part of the plasma generation chamber 12 is hermetically sealed by a microwave introduction window 15 formed by using a dielectric plate such as quartz glass, Pyrex glass, or alumina, which is transparent to microwaves, has a small dielectric loss, and has heat resistance. It is sealed in. Partition plate 14 inside the reaction chamber 13
A sample holding portion 16 for mounting the sample S is provided at a position facing the, and an exhaust port 17 connected to an exhaust device (not shown) is provided at a lower wall of the reaction chamber 13. A gas supply pipe 18 for supplying a required reaction gas into the reactor 10 is connected to one side wall of the plasma generation chamber 12.

On the other hand, the dielectric line 2 is provided above the reactor 10.
0 is provided, a frame body 20a formed by using a metal plate such as aluminum is provided above the dielectric line 20, and a fluorine resin, polyethylene or polyethylene having a small dielectric loss is provided on the lower surface of the frame body 20a. A dielectric layer 20b made of polystyrene or the like is attached. Dielectric line 2
A microwave oscillator 22 is connected to 0 via a waveguide 21, and the microwave from the microwave oscillator 22 is introduced into the dielectric line 20 via the waveguide 21.

The sample S mounted on the sample holder 16 by using the microwave plasma processing apparatus thus constructed
When the surface is subjected to ashing treatment, first, the interior of the plasma generation chamber 12 and the reaction chamber 13 is evacuated from the exhaust port 17 to set a required degree of vacuum, and then the gas supply pipe 18 is introduced into the plasma generation chamber 12 such as O ₂ , CF ₄ reaction gas is supplied. Further, cooling water is supplied from the cooling water inlet 11a, discharged from the cooling water outlet 11b and circulated in the cooling water passage 11, and then a microwave is oscillated by the microwave oscillator 22 to guide the microwave. It is introduced into the dielectric line 20 through the tube 21. Then, an electric field is formed below the dielectric line 20, and the formed electric field is applied to the microwave introduction window 1
5 is supplied to the inside of the plasma generation chamber 12 through which the plasma is generated. The charged particles in the generated plasma are captured by the partition plate 14, and neutral particles such as radicals mainly pass through the holes 14a and are guided to the periphery of the sample S in the reaction chamber 13 to ash the resist on the sample S. To do.

To remove the thin film 33 described above, a wet treatment with a chemical solution is mainly performed at present.
From the viewpoint of countermeasures against pollution problems, etc., a method of using the above microwave plasma processing apparatus to remove the thin film 33 and performing a dry processing by plasma has been studied. This method can increase the processing area, and the matching between the plasma source and the microwave source is stable. Further, since the etching is mainly based on radicals, it is possible to increase the selection ratio with respect to the oxide film.

[0010]

When the thin film 33 such as polycrystalline silicon or silicon nitride formed on the substrate 31 is etched by using the microwave plasma processing apparatus described above, the radical-based etching characteristic is utilized to obtain the base layer. When etching is performed under conditions with a high selectivity to the oxide film,
Since the natural oxide film 35 is usually formed on the surface of the thin film 33, there is a problem that it takes time to remove the natural oxide film 35. Alternatively, once a part of the natural oxide film 35 is removed by etching, the thin film 33 in that part is locally removed by high speed, so that the etching rate of the thin film 33 in the surface of the substrate 31 becomes non-uniform. there were.

The present invention has been made in view of the above problems, and it is possible to selectively and quickly and uniformly remove only a thin film without damaging a base film even by a dry process. Therefore, it is an object of the present invention to provide a thin film removing method which can cope with the miniaturization of the device and can cope with the increase in the diameter of the substrate.

[0012]

In order to achieve the above object, a thin film removing method according to the present invention is a thin film removing method for removing a thin film such as polycrystalline silicon or silicon nitride formed on a substrate. As a pretreatment, the native oxide film on the surface of the thin film is removed in advance.

In the thin film removing method described above, a microwave oscillator, a waveguide for transmitting microwaves, a dielectric line connected to the waveguide, and a microwave arranged to face the dielectric line. It is characterized in that a microwave plasma processing apparatus provided with a reactor having an introduction window and a sample holding portion provided in the reactor is used.

[0014]

In the microwave plasma processing apparatus shown in FIG. 1, most of the charged particles in the plasma generated in the plasma generation chamber 12 are blocked by the partition plate 14, and the sample S in the reaction chamber 13 is mainly composed of radicals. Etched by neutral particles. Therefore, since the charged particles having a large energy do not act on the base film formed on the sample S, the base film is hardly damaged, and the base film is usually an insulating film such as a silicon oxide film. Since it is difficult to etch depending on the type, it has an advantage of being excellent in selective etching property with the thin film formed on the sample S. On the other hand, as a result, the etching rate of the natural oxide film by the radicals is extremely slow, and once a part of the natural oxide film is removed by etching, the etching rate of the thin film by the radicals is high. The in-plane etching rate becomes non-uniform.

According to the method of removing a thin film of the present invention, the natural oxide film on the surface of the thin film is removed as a pretreatment. Therefore, if a dry treatment method using a microwave plasma treatment apparatus is performed thereafter, the substrate is The thin film of polycrystalline silicon, silicon nitride, or the like formed above can be removed by etching quickly and with good in-plane uniformity, and therefore, it is possible to cope with an increase in the diameter of the substrate.

In the thin film removing method described above, a microwave oscillator, a waveguide for transmitting microwaves, a dielectric line connected to the waveguide, and a microwave arranged to face the dielectric line. When using a microwave plasma processing apparatus equipped with a reactor having a wave introduction window and a sample holder provided in the reactor, when a natural oxide film on the thin film surface is removed, a predetermined reaction gas is supplied. By using it, the natural oxide film can be quickly removed. For this reason, if a dry process is subsequently performed by changing the gas species using the microwave plasma processing apparatus, the thin film such as polycrystalline silicon or silicon nitride formed on the substrate can be swiftly and uniformly in-plane. It can be removed by etching with good properties, and therefore, it is possible to cope with an increase in the diameter of the substrate. Further, by utilizing the original device characteristics, the selection ratio of the thin film is high, the base film is not damaged, and it is possible to cope with the miniaturization of the element. Further, since the natural oxide film and the thin film can be removed by etching using the same device, the vacuum transfer process between the devices can be omitted and the throughput can be improved.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a thin film removing method according to the present invention will be described below with reference to the drawings. The apparatus used in the examples is the same as that shown in FIG. 1, and the description of the configuration is omitted.

In the embodiment, as a pretreatment, the sample S is first soaked in a 4.8% HF (hydrogen fluoride) aqueous solution for 1 minute, then soaked in pure water (running water), and then using a rinse dryer. By drying and storing in a vacuum storage container, the native oxide film 35 on the surface of the thin film 33 such as polycrystalline silicon or silicon nitride formed on the substrate 31 (FIG. 2) was removed.

In another embodiment, the apparatus shown in FIG. 1 is used, and cooling water is first circulated in the cooling water passage 11 and then exhausted from the exhaust port 17, and then the gas supply pipe 18 is used. From the inside of the plasma generation chamber 12 to O ₂ / CF ₄ = 60 /
A reaction gas of 240 sccm was supplied, and the pressure in the reaction chamber 13 was set to 0.5 Torr. Then, a microwave is oscillated with a microwave power of 1.5 kW using a microwave oscillator 22, and the microwave is introduced into the plasma generation chamber 12 through the waveguide 21, the dielectric line 20, and the microwave introduction window 15. It was supplied and reacted with the reaction gas to generate plasma. Next, of the generated plasma, the radicals that have passed through the holes 14a of the partition plate 14 are applied to the sample S for 30 seconds,
Natural oxide film 35 on the surface of thin film 33 formed on substrate 31
Was removed.

Next, using the apparatus shown in FIG. 1, using the sample S from which the natural oxide film 35 was removed by the above method,
The result of etching removal of the thin film 33 formed on the substrate 31 will be described. First, the case where the thin film 33 is polycrystalline silicon will be described. SF ₆ / as reaction gas
O ₂ / Ar = 30/5/30 sccm was used, and the reaction chamber 1
The thin film 33 was etched by setting the pressure in 3 to 0.15 Torr and the microwave power to 1.5 kW.
As a result, the etching rate is 2500 Å / min, the uniformity of the etching rate in the plane of the 8-inch substrate 31 is 4.6%, and the selection ratio of the polycrystalline silicon thin film 33 to the SiO ₂ base film 32 is 150 or more. It is possible,
It was possible to sufficiently cope with the increase in the diameter of the substrate 31 and the miniaturization of the processing size.

Next, the case where the thin film 33 is silicon nitride will be described.

SF ₆ / O ₂ / Ar = 15 as a reaction gas
The thin film 33 was etched with the pressure in the reaction chamber 13 set to 0.8 Torr and the microwave power set to 1.5 kW using / 15/20 sccm. As a result, the etching rate was 2400 Å / min, the uniformity of the etching rate within the surface of the 8-inch substrate 31 was 5.0%, and
₍₂₎ The selection ratio of the silicon nitride thin film 33 with respect to the underlayer film 32 was able to obtain a value of 60 or more, and it was possible to sufficiently cope with the increase in the diameter of the substrate 31 and the miniaturization of the processing dimension.

As is clear from these results, in the method of removing a thin film according to this embodiment, the natural oxide film 35 on the surface of the thin film 33 is removed as a pretreatment, so that the microwave plasma processing apparatus is used thereafter. If you do the dry process that you did,
The thin film 33 formed on the substrate 31 can be removed by etching quickly and with good in-plane uniformity, so that the diameter of the substrate 31 can be increased. Also SiO ₂
The selection ratio of the thin film 33 to the base film 32 can be increased, and the base film 32 is not damaged, and it is possible to cope with the miniaturization of the element.

In addition, in the above method for removing a thin film, FIG.
When using the microwave plasma processing apparatus shown in
By using a predetermined reaction gas, the selection ratio with respect to the oxide film can be lowered, and the natural oxide film 35 on the surface of the thin film 33 can be quickly removed. Therefore, if the gas species is subsequently changed to increase the selectivity to the oxide film and dry processing is performed using the microwave plasma processing apparatus, the thin film 33 formed on the substrate 31 can be swiftly and uniformly in-plane. Can be removed by etching with good properties, and thus the substrate 31
It is possible to deal with larger diameters. Further, the selection ratio of the thin film 33 to the base film 32 can be increased, and the base film 32 is not damaged, and it is possible to cope with the miniaturization of the element. Further, since the natural oxide film 35 and the thin film 33 can be removed by etching using the same device, the substrate 31
The vacuum transfer step can be omitted, and the throughput can be improved.

[0025]

As described above in detail, in the method of removing a thin film according to the present invention, since the natural oxide film on the surface of the thin film is removed as a pretreatment, a microwave plasma processing apparatus is used thereafter. By performing the dry treatment, the thin film formed on the substrate can be removed by etching quickly and with good in-plane uniformity, and therefore, it is possible to cope with an increase in the diameter of the substrate. In addition, it is possible to increase the selection ratio of the thin film to the base film, and without damaging the base film,
It is possible to cope with the miniaturization of elements.

In the thin film removing method, a microwave oscillator, a waveguide for transmitting microwaves, a dielectric line connected to the waveguide, and a microwave arranged to face the dielectric line. When using a microwave plasma processing apparatus provided with a reactor having a wave introduction window and a sample holder provided in the reactor, a natural oxide film is quickly removed by using a predetermined reaction gas. be able to. Therefore, if the dry treatment is subsequently performed using the microwave plasma treatment apparatus by changing the gas species, the thin film formed on the substrate can be removed by etching quickly and with good in-plane uniformity. Therefore, it is possible to cope with an increase in the diameter of the substrate. Further, it is possible to increase the selection ratio of the thin film to the base film,
Moreover, it is possible to deal with the miniaturization of the element without damaging the base film. Further, since the natural oxide film and the thin film can be removed by etching using the same apparatus, the vacuum transfer step of the substrate can be omitted, and the throughput can be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a microwave plasma processing apparatus used in a thin film removing method according to an embodiment of the present invention.

[FIG. 2] LOCO which is a typical element isolation technology of LSI
It is a schematic sectional drawing which showed the process of S.

[Explanation of symbols]

 10 Reactor 15 Microwave Introducing Window 16 Sample Holder 20 Dielectric Line 21 Waveguide 22 Microwave Oscillator 31 Substrate 33 Thin Film 35 Natural Oxide Film

Claims (2)

[Claims] 1. A thin film removing method for removing a thin film of polycrystalline silicon, silicon nitride or the like formed on a substrate, wherein a natural oxide film on the surface of the thin film is removed as a pretreatment. Removal method. 2. A reactor having a microwave oscillator, a waveguide for transmitting microwaves, a dielectric line connected to the waveguide, and a microwave introduction window arranged to face the dielectric line. 2. The method for removing a thin film according to claim 1, wherein a microwave plasma processing apparatus including a sample holding section provided in the reactor is used.