JP3364131B2 - Plasma processing equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to a substrate to be processed such as a semiconductor wafer, for example, ECR (Electron).
The present invention relates to a plasma processing apparatus for forming a thin film such as a SiOF film or a SiO ₂ film by plasma processing such as Cyclotron Resonance) processing.

[0002]

2. Description of the Related Art Aluminum wiring is mainly used as a wiring pattern of an integrated circuit, and an SiOF film or a SiO ₂ film is used as an interlayer insulating film for insulating the wiring. As a method, an ECR plasma treatment in which microwaves and a magnetic field are combined to generate high-density plasma tends to be adopted because the film quality is good.

FIG. 9 shows a conventional plasma processing apparatus for performing this ECR plasma processing. For example, in this apparatus, for example, 2.45 GHz is provided in the plasma generation chamber 1A.
Of the microwaves is supplied by the waveguide 11 through the transmission window 12, and a magnetic field of, for example, 875 Gauss is applied by the combination of the main electromagnetic coil 13 and the auxiliary electromagnetic coil 14 to interact with the microwaves and the magnetic field. The plasma gas such as Ar gas or O ₂ gas is converted into high density plasma by (electron cyclotron resonance), and this plasma is used to form the film forming chamber 1B.
The film forming gas such as SiH ₄ gas or SiF ₄ gas introduced into the chamber is activated to form ionic species, and the mounting table 1
A thin film is formed on a semiconductor wafer (hereinafter referred to as “wafer”) W placed on the wafer 5.

The waveguide 11 includes a rectangular waveguide 11a,
The microwave generated by the microwave generator 16 and transmitted in the TE ₁₀ mode inside the rectangular waveguide 11a is configured by combining with the conical waveguide 11b gradually expanding toward the lower side. It is converted into TE ₁₁ mode by the conical waveguide 11b, transmitted as it is in the conical waveguide 11b in TE ₁₁ mode, and introduced into the plasma generation chamber 1A.

The TE ₁₁ mode will be described with reference to FIG. FIG. 10A is a diametrical cross-sectional view of a cylindrical waveguide having an inner diameter of 2a, for example, and FIG.
It is a sectional view taken along the line AA in (a). In this mode, the electric field indicated by the solid line in the figure exists in the diameter direction of the waveguide. Note that the chain line in the figure indicates the magnetic field, which is shown in FIG.
The middle circle indicates that the electric field is directed toward the inside of the paper surface, and the circle is that the electric field is directed toward the outside surface of the paper surface.

[0006]

However, in the above-described plasma processing apparatus, since the microwave is introduced into the plasma generation chamber 1A in the TE ₁₁ mode, the density of the lines of electric force in a certain section above the wafer is It is high in the central part and becomes smaller as it approaches the peripheral part, and the electric field distribution is non-uniform. Here, since the density of the plasma generated in the plasma generation chamber 1A is substantially proportional to the electric field distribution, the film thickness of the thin film formed by the plasma processing becomes thin in the peripheral portion corresponding to the electric field distribution, and the film thickness is high. It is difficult to secure in-plane uniformity.

On the other hand, US Pat. No. 5,234,526 discloses TM
A plasma processing apparatus using ₀₁ mode is disclosed. In this apparatus, the end of a rectangular waveguide transmitting TE ₁₀ mode is connected to a cylindrical waveguide having an inner diameter of 109 mm, for example, and microwaves are introduced into a plasma generation chamber in TM ₀₁ mode. Is configured.

The TM ₀₁ mode will now be described with reference to FIG. 11. FIG. 11A is a sectional view of a cylindrical waveguide having an inner diameter of 2a in the diametrical direction, and FIG. It is sectional drawing in AA of FIG. 11 (a). This mode
In the figure, the electric field indicated by the solid line in the figure propagates along the tube wall while changing the direction for each half wavelength so as to pass from the tube wall of the waveguide to the center and return to the tube wall. Also in this figure, the chain line indicates the magnetic field. In FIG. 11 (b), the open circles indicate the electric field toward the inside of the paper, and the black circles indicate the electric field toward the outside of the paper.

In such an apparatus, for example, when processing a 6-inch wafer, the inner diameter of the cylindrical waveguide is 109.
Since it is mm, the uniformity of the electric field distribution in a certain cross section on the upper side of the wafer can be secured. However, in recent years, the wafer tends to be increased in size from 8 inch size to 12 inch size. When the wafer becomes larger than the inner diameter of the cylindrical waveguide in this way, the region of the waveguide outlet facing the wafer peripheral portion is formed. However, there is a problem in that the in-plane uniformity of the film thickness deteriorates.

The present invention has been made under such circumstances, and an object thereof is to increase the in-plane uniformity of plasma processing by generating highly uniform plasma over a wide area. An object of the present invention is to provide a plasma processing apparatus and a method therefor.

[0011]

Therefore, the present invention is provided with a cylindrical vacuum chamber having a circular plate-shaped transmission window for transmitting a high frequency wave at one end, and a mounting table for a substrate to be processed is provided inside. A vacuum container provided, a magnetic field forming means for forming a magnetic field in the vacuum container, and a high frequency wave TM in the vacuum chamber.
A high-frequency supplying means for supplying through the transmission window in a mode of TM ₀₁ , for example, and the processing gas is turned into plasma by electron cyclotron resonance between the high frequency and the magnetic field, and the plasma is applied to the substrate to be processed. In the plasma processing apparatus that performs the processing, 0.75 ≦ D2 / D1 ≦ 0.85, where D1 is the inner diameter of the vacuum chamber and D2 is the diameter of the high frequency outlet of the transmission window. And

[0012]

1 is a sectional view showing an embodiment of a plasma processing apparatus of the present invention, FIG. 2 is a perspective view of a part thereof, and FIG. 3 is an enlarged sectional view of a main part thereof. . 2 in the figure
Is a vacuum container formed of, for example, aluminum. The vacuum container 2 is composed of a first vacuum chamber 21 located above and for generating plasma, and a second vacuum chamber 22 connected below the first vacuum chamber 21. These vacuum chambers 2
The first and second vacuum chambers 21 and 22 have a cylindrical shape.
Has an inner diameter D1 set to, for example, 250 mm (see FIG. 3), and the second vacuum chamber 22 is set to have an inner diameter larger than that of the first vacuum chamber 21. The vacuum container 2 is grounded and has a zero potential.

An upper end of the vacuum container 2 is opened, and a high-frequency (microwave) transmitting member such as aluminum nitride (AlN) is formed in this portion, and the diameter A1 is 2
A circular plate-shaped transparent window 23 of 30 mm is provided in an airtight manner. The transparent window 23 is airtightly supported on the outer peripheral edge by a support ring 24 made of, for example, aluminum, and the transparent window 23 and the support ring 24 maintain a vacuum state in the vacuum container 2.

The support ring 24 is provided at the upper end of the vacuum container 2 and has an inner peripheral surface projecting from the lower surface side of the transmission window 23, whereby the first vacuum chamber 21.
The microwave inlet has a narrower inner diameter than other portions. For example, in this embodiment, the diameter D2 of the transmission window 23 on the microwave outlet side, that is, the inner diameter D2 of the microwave inlet portion of the first vacuum chamber 21 is set to about 200 mm according to the experimental result described later,
The thickness of the support ring 24 on the lower side of the transparent window 23 is set to about 5 mm.

A waveguide 3 is provided outside the transmission window 23 for supplying a microwave of 2.45 GHz in the plasma chamber 21 in TM mode, for example, TM ₀₁ mode. For example, as shown in FIG. 2, the waveguide 3 has a rectangular waveguide 31 whose outlet end is connected at a right angle to an upper side of a cylindrical waveguide 32, and a lower end of the cylindrical waveguide 32. The side is connected to the upper end of a tapered conical waveguide 33 formed in a taper shape so as to gradually widen toward the lower side.

For example, the inner diameter A2 of the exit side opening of the conical waveguide 33 is set to 200 mm, and the exit side opening end is connected to the upper surface of the transmission window 23. Further, the inlet end of the rectangular waveguide 31 is connected to a high frequency power source 34 for plasma generation, and the microwave generated in the high frequency power source 34 is guided by the waveguide 3 to pass through the transmission window 23. It can be introduced into the plasma chamber 21. In the present embodiment, the high frequency power supply section 34, the rectangular waveguide 31, the cylindrical waveguide 32, and the conical waveguide 33 constitute a high frequency supply means.

On the upper side of the side wall defining the first vacuum chamber 21, for example, gas nozzles 41 for supplying plasma gas are evenly arranged along the circumferential direction, and the gas nozzles 41 are shown in the drawing. A plasma gas source is connected to the inside of the first vacuum chamber 21 so that a plasma gas such as Ar gas or O ₂ gas can be uniformly supplied to the upper portion of the first vacuum chamber 21. In the figure, only two gas nozzles 41 are shown in order to avoid complication of the drawing, but in reality, more gas nozzles 41 are provided.

On the other hand, the upper portion of the second vacuum chamber 22, that is, the first
A ring-shaped film forming gas supply unit 42 is provided in a portion communicating with the vacuum chamber 21, and a gas supply port 42a is formed in the inner peripheral surface. The film forming gas supply unit 42 is connected to one end of a gas supply pipe 43 whose other end is connected to a film forming gas source (not shown), and the film forming gas such as SiH ₄ gas or SiF ₄ gas is used as the gas. It is designed to eject from the supply port 42a.

A ring-shaped main electromagnetic coil 51, for example, is arranged on the outer periphery of the side wall defining the first vacuum chamber 21 so as to surround the vacuum chamber 21 so as to be close to the side wall. A ring-shaped auxiliary electromagnetic coil 52 is arranged on the lower side of the vacuum chamber 22.
A magnetic field B from the upper side to the lower side, for example, a magnetic field B of 875 Gauss is formed from the first vacuum chamber 22 to the second vacuum chamber 22.

Further, in the second vacuum chamber 22, a mounting table 6 for mounting the wafer W is provided so as to be vertically movable between a processing position and a transfer position of the wafer W. The mounting table 6 is composed of, for example, a main body 61 made of aluminum, and a dielectric plate 62 having a heater and electrodes built therein, and the surface thereof is configured as an electrostatic chuck. A DC power source (not shown) for an electrostatic chuck is connected to the electrodes, and a high frequency power source unit 63 is connected to apply a bias voltage for attracting ions to the wafer W. Further, an exhaust pipe 25 is connected to the bottom of the film forming chamber 22.

Next, a method of forming an interlayer insulating film made of, for example, a SiOF film on the wafer W which is the substrate to be processed by using the above plasma processing apparatus will be described. First, the vacuum container 2
A gate valve (not shown) provided on the side wall of the wafer is opened, and a wafer (for example, 8 inches) having aluminum wiring formed on the surface thereof is carried in from a load lock chamber (not shown) by a transfer arm (not shown) and placed on the mounting table. Place on top of 6.

Then, after closing the gate valve to seal the inside, the mounting table 6 is raised to the processing position, the internal atmosphere is exhausted by the exhaust pipe 25 to evacuate to a predetermined vacuum degree, and the plasma is discharged from the gas nozzle 41. A gas such as Ar gas and O ₂ gas is introduced at a predetermined flow rate, and a film forming gas such as SiF ₄ gas is introduced from the film forming gas supply unit 42 at a predetermined flow rate. The inside of the vacuum container 2 is, for example, 0.15 Pa.
While maintaining the process pressure of No. 3, and applying a bias voltage of 13.56 MHz and 2500 W to the mounting table 6 by the high frequency power supply unit 63, the surface temperature of the mounting table 6 is set to, for example, 40.
Set to 0 ° C.

In the first vacuum chamber 21, the high frequency power source unit 3
A high frequency (microwave) M of 2.45 GHz and 2700 W from 4 is first transmitted in the TE ₁₁ mode in the rectangular waveguide 31, and then the rectangular waveguide 31 and the cylindrical waveguide 32 are connected. Is converted into TM ₀₁ mode in the vicinity of the portion and is transmitted as it is in TM ₀₁ mode while expanding the electric field region in the conical waveguide 33 to reach the ceiling of the vacuum container 2 and through the transmission window 23. It is introduced into the first vacuum chamber 21.

On the other hand, in the vacuum chamber 2, a magnetic field B is formed by the main electromagnetic coil 51 and the auxiliary electromagnetic coil 52, and the magnetic field B
At the point where the intensity of the magnetic field becomes 875 gauss, electron cyclotron resonance occurs due to the interaction between the magnetic field and the microwave, and the plasma gas is made into a plasma and densified by the resonance. The plasma is stabilized by using the plasma gas.

The generated plasma flows into the second vacuum chamber 22 from the first vacuum chamber 21 as a plasma flow, and the SiF ₄ gas supplied thereto is activated (plasmaized) by this plasma flow. To form active species (plasma). On the other hand, the plasma ions are attracted to the wafer W by the bias voltage, and the corners of the SiOF film deposited on the pattern (recess) on the surface of the wafer W are scraped off by the sputter etching action of the plasma ions to widen the frontage while forming the SiOF film. It is filmed and embedded in the recess.

In such a plasma processing apparatus, the inner diameter of the first vacuum chamber 21 is 200 m at the microwave inlet.
Since it is m and is rapidly increased to 250 mm immediately below, the thickness of the formed SiOF film can be made substantially uniform in the plane of the wafer W.

The reason for this is presumed as follows. That is, the microwave is transmitted while expanding the electric field region in the conical waveguide 33 as described above, and is transmitted through the transmission window 23 to the TM ₀₁ mode.
However, since the inner diameter of the first vacuum chamber 21 rapidly increases, the microwave propagation is disturbed in this portion. As a result, the microwave propagating along the tube wall at the inlet of the waveguide 3 and the first vacuum chamber 21 in the TM ₀₁ mode is disturbed at this abruptly increasing portion, for example, as shown in FIG. It is considered that a high-order mode such as the TM ₀₂ mode shown in FIG. 3 is generated and the mode is transmitted as it is in the first vacuum chamber 21.

In such a high-order mode, an electric field is generated not only in the tube wall but also in the central portion of the vacuum container 2. Therefore, when viewed from the wafer W, almost the entire surface of the wafer W facing the wafer W is covered. There will be an electric field at. Therefore, it is possible to secure a uniform plasma region over a large area in the surface, and as a result, the Si formed by the plasma is formed.
It is estimated that the film thickness of the OF film becomes substantially uniform in the surface of the wafer W.

The occurrence of such a higher-order mode is presumed to be related to the ratio of the inner diameter D1 of the first vacuum chamber 21 and the inner diameter D2 of the inlet portion from the experimental results described later. To be done. That is, if D2 / D1 is too large, that is, if the inner diameter D1 is not so large as compared with the inner diameter D2, the disturbance of the microwave propagation is too small, and it is considered that the TM ₀₁ mode is transmitted in the end.

In the TM ₀₁ mode, the microwave propagates along the tube wall of the conical waveguide 33 while expanding the electric field region, so that the inner diameter is larger than that of the upper end of the conical waveguide 33. In the large first vacuum chamber 21, the electric field exists in the inner wall portion but does not exist in the central portion. For this reason, the electric field strength becomes considerably small in the central portion, and it is considered difficult to increase the in-plane uniformity of the plasma density.

On the other hand, if D2 / D1 is too small, that is, if the inner diameter D1 is too large, the microwave propagation is disturbed too much in the portion where the inner diameter D1 becomes large, and a mode that is not axially symmetric is easily excited. It is considered that the in-plane uniformity of the plasma density deteriorates.

Next, an example of an experiment conducted by the present inventors to optimize D2 / D1 in relation to the in-plane uniformity of film thickness will be described. Using the plasma processing apparatus shown in FIG. 1 described above, the inner diameter of the Ar gas and O ₂ gas at a predetermined flow rate D1 =
While being introduced into the first vacuum chamber 21 of 250 mm, S
iF ₄ gas is introduced into the second vacuum chamber 22 at a predetermined flow rate, and high frequency power is 2500 W and bias power is 2700.
W, the film forming temperature is 400 ° C., the pressure inside the vacuum container 2 is 0.1
The inner diameter D2 on the inlet side of the first vacuum chamber 21 is changed to 5 Pa, and the SiOF film is formed on the 8-inch wafer W under the same process conditions as in the above-described embodiment. The in-plane uniformity was measured. Here, the in-plane uniformity of film thickness was measured by Optiprobe. The same experiment was performed when the inner diameter D1 of the first vacuum chamber 21 was 275 mm and 300 mm.

The results are shown in FIGS. 5 to 8. Here, FIG. 5 shows that when the inner diameter D1 of the first vacuum chamber 21 is 250 mm,
6 shows a case of 275 mm, and FIG. 7 shows a case of 300 mm. In FIG. 8, Δ is 250 mm and ◯ is 2.
75 mm and □ indicate 300 mm, respectively.

As a result, regardless of the size of the inner diameter D1 of the first vacuum chamber 21, when the ratio (D2 / D1) of the size of the inner diameter D2 of the inlet to the inner diameter D1 is around 0.8, The in-plane uniformity of the thickness of the SiOF film is the best,
It was confirmed that the in-plane uniformity deteriorated as the value was deviated.

Thus, in order to generate highly uniform plasma over a large area in the first vacuum chamber 21,
It was confirmed that an optimum relationship exists between the inner diameter D1 of the first vacuum chamber 21 and the inlet inner diameter D2 of the first vacuum chamber 21, and the in-plane uniformity of the film thickness is set to 20% or less. In order to
It was found that it is sufficient to set 0.75 ≦ D2 / D1 ≦ 0.85.

In the above, the waveguide for transmitting the TM mode in the present invention is not limited to the configuration described in the embodiment, but a configuration in which a rectangular waveguide and a plurality of cylindrical waveguides having different inner diameters are combined. The TM mode is not limited to the TM ₀₂ mode but may be the TM ₀₃ mode or the like. Further, the present invention is not limited to the film forming process of the SiOF film, but may be applied to the film forming process of, for example, the SiO ₂ film or the CF film (fluorine-containing carbon film) or the etching process. You may do it.

[0037]

According to the plasma processing apparatus of the present invention, since highly uniform plasma can be generated over a wide area, the in-plane uniformity of plasma processing can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a plasma processing apparatus of the present invention.

FIG. 2 is a perspective view showing an example of a waveguide used in the plasma processing apparatus.

FIG. 3 is a cross-sectional view near a microwave inlet of the plasma processing apparatus.

FIG. 4 is a cross-sectional view for explaining propagation of microwaves.

FIG. 5 is a characteristic diagram showing a relationship between D2 / D1 and in-plane uniformity of film thickness when D1 = 250 mm.

FIG. 6 is a characteristic diagram showing a relationship between D2 / D1 and in-plane uniformity of film thickness when D1 = 275 mm.

FIG. 7 is a characteristic diagram showing a relationship between D2 / D1 and in-plane uniformity of film thickness when D1 = 300 mm.

FIG. 8 is a characteristic diagram showing a relationship between D2 / D1 and in-plane uniformity of film thickness.

FIG. 9 is a cross-sectional view showing a conventional plasma processing apparatus.

FIG. 10 is a sectional view for explaining a TE ₁₁ mode.

FIG. 11 is a sectional view for explaining the TM ₀₁ mode.

[Explanation of symbols]

2 vacuum container 21 First vacuum chamber 22 Second vacuum chamber 23 Transparent window 24 Support ring 3 Waveguide 31 Rectangular Waveguide 32 cylindrical waveguide 33 Conical Waveguide 34 High frequency power supply 54 Main electromagnetic coil 6 Mounting table W semiconductor wafer

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-6-45098 (JP, A) JP-A-2-119100 (JP, A) JP-A-6-34238 (JP, A) JP-A-6- 104096 (JP, A) JP-A-7-142196 (JP, A) JP-A-8-236297 (JP, A) JP-A-10-150031 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H05H 1/46 C23C 16/50 H01L 21/205 H01L 21/31 C23F 4/00

Claims (2)

(57) [Claims] 1. A vacuum container having a cylindrical vacuum chamber having a circular plate-shaped transmission window for transmitting a high frequency at one end thereof, and a mounting table for a substrate to be processed provided therein, and the vacuum container. A magnetic field forming means for forming a magnetic field therein, and a high frequency supplying means for supplying a high frequency into the vacuum chamber in the TM mode through the transmission window, and electron cyclotron resonance between the high frequency and the magnetic field. In the plasma processing apparatus for converting the processing gas into plasma by the above, and processing the substrate to be processed by the plasma, if the inner diameter of the vacuum chamber is D1 and the diameter of the high frequency outlet of the transmission window is D2, then 0. 75 ≦ D2 / D1 ≦
The plasma processing apparatus is 0.85. 2. The plasma processing apparatus according to claim 1, wherein the TM mode is a TM ₀₁ mode.