JPH0729889A - Microwave plasma treatment processing equipment - Google Patents

Abstract

PURPOSE:To produce high density plasma to enhance the treatment rate of ashing, and facilitate the initiation of discharge, by placing a discharge tube composed of two coaxially arranged tubes inside a coaxial waveguide. CONSTITUTION:Gas containing oxygen is introduced into a discharge tube 64 through a gas feed pipe 70. Microwaves are supplied from a microwave power supply 50 to a coaxial waveguide 54 through a rectangular waveguide 52, and converted into coaxial mode. Thus microwaves are supplied to the area between the outer conductor 56 and the inner conductor 58 of the coaxial waveguide 54, and plasma 74 is produced inside the discharge tube 64 composed of an outer tube 66 and an inner tube 68. Activated molecules or atoms present in the plasma 74 are diffused in a vacuum vessel 42, and react with and remove photoresist on the surface of a wafer 46.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing apparatus for performing surface treatment on a substrate to be processed by utilizing plasma generated by microwave discharge, and more particularly to an apparatus for removing organic substances adhering to the substrate to be processed. The effect is remarkable when applied to an (ashing device).

[0002]

2. Description of the Related Art In a process of removing a photoresist, which is one of the processes for manufacturing a semiconductor device, a gas mainly containing oxygen is converted into plasma by electric discharge, and oxygen active species (atomic oxygen, ozone, etc.) generated by this are generated. A technique called so-called ashing is generally used, which is a technique for guiding the surface of a substrate (wafer) to be processed and reacting with the photoresist. Electrodeless discharge using a high frequency wave or a microwave as an energy source is often used as a means for converting gas into plasma. Above all, inside the dielectric discharge tube installed in the cavity (cavity),
An ashing apparatus (asher) utilizing a so-called cavity type microwave discharge, in which a gas having a relatively high pressure (about 1 to 10 Torr) is caused to flow and the gas is turned into plasma by microwave power, has been put into practical use.

FIG. 4 is a front sectional view of a conventional example of an ashing device utilizing a cavity type microwave discharge. The advantage of this apparatus is that it has a higher ashing speed and can be easily applied to an apparatus for carrying out single-wafer processing of wafers, as compared with an ashing apparatus using inductively coupled high-frequency discharge that has been widely used. .

In FIG. 4, a microwave plasma generating mechanism is provided above the vacuum container 10. Microwave power supply 12
A waveguide 14 having a rectangular cross section is connected to, and a conductive cylindrical tube 16 is connected to the waveguide 14. Waveguide 14
Matching device 15 consisting of a three-stub tuner
Is provided. The discharge tube 18 made of a dielectric material is arranged inside the conductive tube 16 and penetrates the waveguide 14.
When a predetermined gas is introduced into the discharge tube 18 and microwave power is supplied from the microwave power source 12, the discharge tube 18
A plasma 20 is generated inside the. The active species generated by the plasma 20 are the target substrate 2 in the vacuum chamber 10.
It reacts with the organic film on the surface of No. 2 and removes it.

The discharge tube 18 is a single tube and penetrates the discharge cavity 24 of rectangular cross section at the end of the waveguide 14. The cavity 24 and the vacuum container 10 are made of a conductive tube 16
The conductive tube 16 prevents the microwave from leaking.

In this conventional microwave plasma generating mechanism, it is necessary to adjust the position of the short-circuit plate 26 in the cavity 24 at the start of discharge and after the start of discharge. When microwave power is supplied to the waveguide 14, FIG.
As schematically shown in FIG. 3, a microwave standing wave 28 is generated inside the waveguide. One end of this standing wave 28 is at the position of the short-circuit plate 26, and the other end is at the position of the matching device 15 (see FIG. 4). That is, the short-circuit plate 26 and the matching device 15
The waveguide portion between and acts as a cavity resonator. A node 30 of a standing wave is generated at the position of the short circuit plate 26.
In the area of, the strength of the microwave electric field becomes weak. On the contrary, the strength of the microwave electric field is increased at the antinode 32 of the standing wave. In order to generate a discharge inside the discharge tube 18, it is necessary to adjust the position of the short-circuit plate 26 so that the portion where the microwave electric field is strong is located inside the discharge tube 18.

On the other hand, after the start of discharge, the plasma 2
When the microwave absorption due to 0 (see FIG. 4) is significant, it is often unnecessary to adjust the position of the short circuit plate 26. However, in general, in the plasma of a gas containing oxygen, part of the microwave power is transmitted through the plasma,
A microwave standing wave having the short-circuit plate 26 as a node is similarly generated. However, when the plasma 20 is generated, the wavelength of the microwave in the tube changes, so that the wavelength of the standing wave 28 changes. Therefore, the position of the short-circuit plate 26 must be readjusted even after the start of the discharge so that the antinode 32 of the standing wave is located inside the discharge tube 18.

Further, when the discharge tube 18 has a practical size (diameter of 1 to 10 cm), there is usually only one antinode 32 of the standing wave 28 at the plasma generation position in the discharge tube 18. , Power usage efficiency is low.

As another conventional example, there is known an apparatus in which the discharge tube of the cavity type microwave plasma generating mechanism is a coaxial type double tube. FIG. 6 is a schematic front cross-sectional view of this device, which is disclosed in the related art document (Isamu Kato, Kazuo).
Noguchi and Kouji Numada ″ Preparation of silicon n
itride films at room temperature using double-tube
d coaxial line-type microwave plasma chemical depo
sition system. ″, J. Appl. Phys., 62 (1987) 492.). This plasma generating mechanism is a double tube in which a dielectric discharge tube 36 penetrating the cavity 34 is coaxial. It is characterized in that plasma is generated in a space surrounded by the outer tube 38 and the inner tube 40.
According to the above-mentioned document, this plasma generation mechanism is suitable for an apparatus for depositing a silicon-based thin film by plasma CVD, and plasma is generated by microwaves propagating in a coaxial mode. In this device, the inner tube 40 functions as the inner conductor of the coaxial line only when plasma is present. Then, by using the inside of the inner tube 40 as a passage for introducing gas, it becomes possible to introduce gas directly into the plasma.

As another conventional example, there is a plasma generating mechanism shown in FIG. This conventional example is a modification of the conventional example shown in FIG. 4, in which the length of the discharge tube 19 is shortened and the discharge tube 19 is installed near the vacuum container 10. A cylindrical waveguide 16 is connected to the rectangular waveguide 14 via a mode converter 27, and a discharge tube 19 is installed inside the lower portion of the cylindrical waveguide 16. There are various examples of mode converters. In this example, the TE ₁₀ mode in the rectangular waveguide 14 is converted into the TM ₀₁ mode in the cylindrical waveguide 16.
The TM ₀₁ mode is a mode having an oscillating electric field in the radial direction. Incidentally, the fundamental mode of the cylindrical waveguide is the TE ₁₁ mode, and the TM ₀₁ mode to be used is a higher order mode of the TE ₁₁ mode. Therefore, the TM ₀₁ mode can be mixed with the TE ₁₁ mode. The mode converter 27 is designed to generate a pure TM ₀₁ mode, but when the discharge tube 19 is arranged inside the cylindrical waveguide 16 or plasma is generated inside the discharge tube 19, Often the mode purity is lost.

[0011]

The asher having the cavity type microwave plasma generating mechanism shown in FIG. 4 has the following drawbacks. One is that the ashing speed is insufficient. In particular, in the step of removing the photoresist after reactive ion etching of the metal wiring film (generally aluminum), a certain gas is added to oxygen in order to prevent the occurrence of so-called after-corrosion. Although necessary, this additive gas has a function of lowering the ashing rate, so that a sufficient treatment rate could not be obtained under the same discharge condition as that of the oxygen gas alone. This means that in a system in which a series of wafer treatments are continuously performed, the overall output of the apparatus is determined by the post-treatment asher. Therefore, in order to improve the processing speed of the wafer processing system, it is necessary to develop an asher capable of processing at a higher speed.

One of the necessary conditions for increasing the ashing speed is to increase the plasma density. However, conventional cavity type microwave asher
In the above, since the discharge utilization efficiency of the microwave power is low, if a large amount of power is supplied to the cavity in order to increase the density of plasma, the device performance may become unstable due to heat generation in the parts other than those involved in the discharge, Problems such as shortened device life occur.

Another drawback of the asher using the cavity type microwave plasma is that the discharge is not started properly. This phenomenon tends to appear remarkably particularly in the case of a gas containing oxygen, which is a practical problem. As a solution for that, it is general to install a mechanism called a discharge trigger, but the structure of the device becomes complicated, there is still a problem in the reliability of the operation, and impurities or dust depending on the mechanism. Can be a source of

Further, in the cavity type microwave plasma generating mechanism of the type using the double tube as shown in FIG.
The plasma is maintained by the microwave propagating in the coaxial mode only after the electric discharge is started, and the conditions for generating the electric discharge are as follows. Exactly the same as when the tube was just inserted. Therefore, the above-mentioned problems in starting the discharge have not been solved even by the double tube structure shown in FIG.

Further, in the plasma generation mechanism as shown in FIG. 7, there is a possibility that the target TM ₀₁ mode and the TE ₁₁ mode are mixed as described above, and there are also the following dimensional restrictions. The microwave frequency used in a normal discharge device is 2.45 GHz, and in order to propagate this, the inner diameter of the cylindrical waveguide is about 72 mm in the TE ₁₁ mode.
As described above, about 94 mm or more is required in the TM ₀₁ mode. This limitation can be a constraint in designing the device. In addition, when the propagation mode changes depending on the characteristics of the plasma, the density distribution of the plasma in the radial direction of the discharge tube may change, which makes it difficult to use as a semiconductor device manufacturing apparatus that requires uniform processing speed within the substrate. .

An object of the present invention is to provide a microwave plasma processing apparatus capable of increasing the processing speed by generating high-density plasma, facilitating the start of discharge, and stabilizing the radial distribution of plasma in the discharge tube radial direction. Especially.

[0017]

The microwave plasma processing apparatus of the present invention is characterized by its plasma generation mechanism,
A coaxial double tube made of a dielectric material is arranged inside a coaxial waveguide made of a conductor, and plasma is generated inside the double tube. . The coaxial waveguide does not necessarily have to act as a microwave cavity (that is, generate a standing wave inside the waveguide), but it is preferable to act as a cavity.

[0018]

The microwave existing inside the coaxial waveguide is usually TEM mode (Transverse-electromagnetic
mode). The TEM mode refers to one of electromagnetic waves in which both the electric field and the magnetic field are perpendicular to the traveling direction and are completely transverse waves. TEM inside a coaxial waveguide
In mode, there is a radial electric field between the coaxial inner and outer conductors.Therefore, if a discharge tube is inserted in this part, the part with a strong electric field will always exist inside the discharge tube, making it easier to start discharge. become. Further, the electromagnetic waves in the discharge tube are maintained in the TEM mode regardless of the presence or absence of plasma in the discharge tube, so that the operation of starting and maintaining the discharge is easy and the utilization efficiency of microwave power can be improved. Further, in the coaxial waveguide, there is no limitation on the frequency of microwaves used, and the degree of freedom in device design is high. Further, since the oscillating electric field exists in the radial direction of the discharge tube regardless of the size of the discharge tube, the radial distribution of plasma does not change depending on the discharge state and is stable.

[0019]

1 is a front sectional view of an embodiment in which the present invention is applied to an ashing device. In FIG. 1, a substrate holder 44 is provided inside a vacuum container 42, and a wafer to be processed 46 is placed thereon. The vacuum container 42 is an exhaust pipe 48.
Via a vacuum pump (not shown). A microwave plasma generation mechanism is provided above the vacuum container 42. A waveguide 52 having a rectangular cross section is connected to the microwave power source 50, and a cylindrical coaxial waveguide 54 for forming a coaxial cavity is connected to the waveguide 52. A matching unit 53 including a stub tuner is provided in the middle of the waveguide 52. The coaxial waveguide 54 is the outer conductor 5
The outer conductor 56 is directly fixed to the rectangular waveguide 52, and the inner conductor 58 is fixed to the rectangular waveguide 52 via an insulator 60. Outer conductor 56
The lower end of is fixed to the vacuum container 42 by a flange 62.

The ratio of the diameters of the outer conductor 56 and the inner conductor 58 is generally designed so that the characteristic impedance is 50Ω. However, in the presence of plasma, the characteristic impedance changes, so it is not always maintained at 50Ω.

The cylindrical discharge tube 64 is made of a dielectric material having a small dielectric loss such as quartz glass or alumina ceramics, and is composed of an outer tube 66 and an inner tube 68 and has a double tube structure. The outer conductor 56 of the coaxial waveguide is arranged outside the outer pipe 66, and the inner conductor 58 of the coaxial waveguide is inserted inside the inner pipe 68 (atmospheric pressure side).
That is, the discharge tube 64 having the double tube structure is arranged inside the coaxial cavity formed by the coaxial waveguide 54.
A gas introduction pipe 70 is connected to the discharge tube 64. The outer pipe 66 and the inner pipe 68 are joined at their upper ends to form a unitary structure. The lower end of the inner pipe 68 is closed. The inside of the discharge tube 64 communicates with the inside of the vacuum container 42, and is evacuated together with the vacuum container 42.

A conductive net 72 is arranged above the wafer 46 in the vacuum container 42, and charged nets can be trapped by the net 72.

Next, the operation of this ashing device will be described. The wafer 46 to which the photoresist to be removed is attached is placed on the substrate holder 44, and the inside of the vacuum container 42 and the discharge tube 64 is evacuated. Next, the gas introduction pipe 70
Oxygen or a mixed gas mainly containing oxygen is introduced into the discharge tube 64 to adjust the pressure within a range of 0.1 to several tens Torr. Next, the microwave is supplied from the microwave power source 50 to the coaxial waveguide 54 through the rectangular waveguide 52, and the microwave is converted into the coaxial mode. As a result, the microwave is supplied to the portion surrounded by the outer conductor 56 and the inner conductor 58, and the microwave discharge is generated inside the discharge tube 64 to generate the plasma 74. The activated molecules or atoms existing in the plasma 74 are stored in the vacuum container 4
2 and reacts with the photoresist on the surface of the wafer 46 to remove it. On the other hand, the charged particles traveling from the plasma 74 toward the vacuum container 42 are captured by the conductive net 72, so that electrical damage to the wafer 46 due to incidence of charged particles can be prevented.

In the device of this embodiment, the standing wave 76 is generated in the form as shown in FIG. In this figure,
The microwave is in a state where it is not completely absorbed by passing through the plasma only once, and the node 77 of the standing wave 76 is generated at the position of the conductive net 72. Plasma is generated between the outer tube 66 and the inner tube 68 of the discharge tube, and a plurality of antinodes 78 of standing waves 76 are present in the axial direction in the plasma generation region. Therefore, the utilization efficiency of microwave power is improved. Further, even at the start of discharge, which has been a problem in the related art, the situation of standing waves when there is no plasma (at the start of discharge) is similar to the state shown in FIG. 2 during discharge. Therefore, the position of the antinode 78 of the standing wave with the strongest electric field (that is, the discharge is easily started) is the antinode 78 during the plasma generation.
The position is almost the same. Therefore, even for a gas containing oxygen or the like, it is not necessary to change the position of the short-circuit plate before and after the start of discharge or to use a discharge trigger, and plasma can be easily generated. This achieved a simplification of the device structure and operation.

In the TEM mode generated in the coaxial waveguide, since the electric field strength in the discharge tube is uniform in the circumferential direction, it is possible to generate plasma with good uniformity. Also, because an oscillating electric field exists in the radial direction of the discharge tube regardless of the dimensions of the discharge tube,
It is stable because the radial distribution of plasma does not change depending on the discharge state.

FIG. 3 is a front sectional view of another embodiment of the present invention. In this embodiment, the outer conductor 86 of the coaxial waveguide 85 is
However, the small-diameter portion 88 near the microwave power source 94
And a large-diameter portion 90 located far from the microwave power source 94.
Consists of. The small diameter portion 88 is connected to the rectangular waveguide 92. The diameter of the small diameter portion 88 is the same as the diameter of the outer conductor 56 of the device of FIG. An outer tube 82 of the discharge tube 80 is arranged inside the large diameter portion 90. The outer diameter of the outer tube 82 is larger than the outer diameter of the small diameter portion 88 of the outer conductor 86. The inner conductor 94 of the coaxial waveguide 85 and the inner tube 84 of the discharge tube 80 remain the same size as shown in FIG. The structure of the other parts is the same as that of the embodiment shown in FIG.

In this embodiment, the plasma volume in the large-diameter portion 90 becomes large, which reduces the ratio of plasma loss, resulting in an increase in plasma density. Moreover, since the opening area of the discharge tube 80 to the processing chamber 42 is increased, the processing area of the wafer 46 can be increased.

[0028]

In the microwave plasma processing apparatus of the present invention, since the coaxial double discharge tube is arranged inside the coaxial waveguide, the discharge can be easily started and high density plasma can be generated. it can. Moreover, the radial distribution of plasma is stable and stable. The present invention is particularly effective when applied to a single-wafer resist ashing apparatus that requires high speed. Further, since it is possible to introduce a high density of neutral active species to the surface of the substrate to be processed using various gases, it can be applied to a surface reforming device and a CVD device.

[Brief description of drawings]

FIG. 1 is a front sectional view of an embodiment of the present invention.

FIG. 2 is an enlarged front sectional view showing a state of a microwave standing wave in the apparatus of FIG.

FIG. 3 is a front sectional view of another embodiment of the present invention.

FIG. 4 is a front sectional view of a conventional ashing device.

5 is an enlarged front sectional view showing a state of a microwave standing wave in the device of FIG.

FIG. 6 is a front sectional view of another example of a conventional microwave plasma processing apparatus.

FIG. 7 is a front sectional view of still another example of the conventional microwave plasma processing apparatus.

[Explanation of symbols]

 42 ... Vacuum container 44 ... Substrate holder 46 ... Wafer 50 ... Microwave power source 52 ... Waveguide with rectangular cross section 54 ... Coaxial waveguide 56 ... External conductor 58 ... Inner conductor 64 ... Discharge tube 66 ... Outer tube 68 ... Inner tube 70 ... Gas introduction pipe 72 ... Net 74 ... Plasma 76 ... Standing wave 77 ... Section 78 ... Belly

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01L 21/302 H

Claims (4)

[Claims] 1. A microwave plasma processing apparatus for processing a substrate to be processed using active species generated by plasma generated by microwave discharge, wherein a plasma generating mechanism forms a discharge space between an inner tube and an outer tube. A double tube made of a dielectric material, an inner conductor inserted inside the inner tube, and a tubular outer conductor arranged outside the outer tube, and composed of the inner conductor and the outer conductor. A microwave plasma processing apparatus, characterized in that microwave power is supplied to a waveguide to generate plasma by discharge in the discharge space. 2. The outer conductor is composed of a small-diameter portion located near the microwave power source and a large-diameter portion located far from the microwave power source, and the outer pipe is arranged inside the large-diameter portion. The microwave plasma processing apparatus according to claim 1, wherein the diameter of the outer tube is larger than the diameter of the small diameter portion. 3. A microwave plasma processing apparatus for processing a substrate to be processed using active species generated by plasma generated by microwave discharge, wherein a coaxial microwave cavity formed of a conductor is used as a plasma generating mechanism. A microwave plasma processing apparatus characterized in that a coaxial double tube made of a dielectric material is arranged inside, and plasma is generated inside the double tube. 4. The microwave plasma processing apparatus according to claim 1, wherein the microwave plasma processing apparatus is an ashing apparatus.