JP2004227796A - Plasma treatment method, improving method of plasma treatment, and plasma treatment device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a gap between a slot antenna and an underlying dielectric window optimum to facilitate matching, and improve casting efficiency of dielectric power for plasma, in carrying out a plasma treatment by using a plasma treatment device utilizing microwaves. <P>SOLUTION: Microwaves are fed from a microwave feeder 36 to a coaxial waveguide 35, and an electromagnetic field leaked from the slot antenna 32 of an antenna member 31 transmits through the dielectric window 22, and generates plasma in a treatment container 2. The length d of the gap between the slot antenna 32 and the dielectric window 22 is made about one fourth of the wavelength of the microwaves passing through the gap G. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a plasma processing method, a plasma processing improvement method, and a plasma processing apparatus.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a technique has been disclosed in which plasma such as etching, ashing, and film formation is applied to a substrate in a processing container by using a microwave having a frequency higher than RF (radio high frequency) to generate plasma in the processing container. ing. In such a case, a dielectric window, such as quartz glass, also referred to as a sealing body, is provided in the upper opening of the processing container, and an antenna member having a flat slot antenna is disposed above the dielectric window. Is transmitted to the antenna member by a cylindrical waveguide, and plasma is generated in the processing chamber by microwave leaked from the slot of the slot antenna (for example, see Patent Document 1).
[0003]
[Patent Document 1]
International Publication WO-01-76329 [0004]
[Problems to be solved by the invention]
However, in the conventional plasma processing apparatus, no consideration is given to the gap between the dielectric window and the antenna member. In this regard, according to the verification by the inventors, it has been confirmed that, when the gap is changed, a change is observed in the VSWR (Voltage Standing Wave Ratio) or the reflection coefficient （(VSWR = (1 + Γ) / ( 1-Γ)). If the VSWR is large, it becomes difficult to achieve matching, and the power input efficiency to the generated plasma deteriorates.
[0005]
The present invention has been made in view of the above circumstances, and has as its object to optimize a gap between a dielectric window and an antenna member to facilitate matching, and to improve the efficiency of supplying power to plasma. I have.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, a plasma processing method according to the present invention comprises a dielectric window for hermetically covering an upper opening of a processing container, a flat slot antenna on the lower surface, or an umbrella shape having a concave or convex central portion. An antenna member having an antenna and disposed above the dielectric window with a gap therebetween, and a waveguide for transmitting microwaves from a microwave supply device to the antenna member; A plasma processing apparatus for performing processing on the substrate in the processing chamber by using the plasma generated by the plasma, and adjusting the thickness of the dielectric window to about one wavelength of the wavelength of the microwave passing through the dielectric window. / 2, and when the length of the gap is d, plasma processing is performed by setting the length of the gap such that 2 <d <6 mm. In such a case, it is preferable that the pressure in the processing space be 50 × 1.33 Pa (50 mTorr) or less.
In the present invention, the thickness of the dielectric window is defined as about の of the wavelength of the microwave passing through the dielectric window, which is about (１ ／) ± (１ ／). Means As the waveguide, a cylindrical waveguide or a coaxial waveguide can be used.
[0007]
According to the experiments by the inventors, as a result of examining the VSWR characteristics or the characteristics of the reflection coefficient で under such conditions, as shown in FIG. 1, when the gap length is between 2 mm and 6 mm, the VSWR is higher than the others. It was confirmed that it was lower.
[0008]
The reason why such characteristics have appeared is as follows at present. That is, in order to prevent resonance, the slot length in this type of slot antenna is used at a position smaller than half the wavelength λc when the microwave propagates in the antenna member. However, when the gap is shortened, the dielectric window approaches the slot antenna, so that the dielectric constant of the atmosphere in the gap changes. For this reason, the dielectric constant is set to, for example, λc / 10. It is considered that the electric power supplied to the plasma has shifted to a direction in which the plasma easily leaks. Therefore, it is considered that VSWR becomes small. However, the reason why the VSWR rises again when the gap is further reduced to zero is still unknown.
[0009]
Therefore, when the length of the gap is d and the plasma processing is performed by setting the length of the gap such that 2 <d <6 mm, the efficiency of supplying power to the plasma is improved. , Since there is little reflection, matching can be easily achieved.
[0010]
Therefore, from the above, according to the present invention, a dielectric window that airtightly covers the upper opening of the processing container, a flat slot antenna on the lower surface, or an umbrella antenna with a concave or convex center is provided. An antenna member disposed above the dielectric window with a gap therebetween, and a waveguide for transmitting microwaves from a microwave supply device to the antenna member. In a plasma processing apparatus for performing processing on a substrate in a processing container by using the generated plasma, the power efficiency applied to the plasma is improved by changing the length of the gap. A method for improving the plasma treatment can be proposed. As the waveguide, a cylindrical waveguide or a coaxial waveguide can be used.
[0011]
As described above, if the gap is reduced under the above-described pressure conditions, the VSWR characteristic can be reduced in a certain range. However, the pressure condition is not taken into consideration. As the wavelength changes when the microwave passes through the gap, as described later, it is confirmed that the VSWR characteristic also changes in the relationship between λg and the length of the gap as described later. did it. Therefore, from these facts, when the length of the gap is changed as in the present invention, the VSWR is reduced, and as a result, the power efficiency applied to the plasma generated in the processing chamber by the microwave is improved. It becomes possible to do.
[0012]
From the above, the inventors further conducted an experiment on the relationship between the gap length and the VSWR by expressing the length of the gap by the wavelength λg. As a result, the characteristics shown in FIG. 2 were obtained. According to this, when the length of the gap d is expressed in relation to the wavelength λg, the VSWR gradually decreases when the length of the gap d is d = λg / 8, and d = 2λg / 8, that is, The characteristic was obtained that it became the lowest around λg / 4, gradually increased, and returned to the original value around 3λg / 8.
[0013]
At the present time, the reason for such a characteristic is considered as follows. That is, when the gap length is set to λg / 4, the phase of the electromagnetic field wave generated by the microwave emitted from the slot antenna has a phase of approximately 180 when the reflected wave from the upper surface of the dielectric window returns to the antenna surface.゜ Since it has changed, the electromagnetic field is partially canceled on the antenna surface. Therefore, the reflected power decreases and the VSWR decreases. It is considered that the effect decreases when the distance from (λg / 4) is increased. When the reflected wave is canceled, the efficiency of inputting the power to the plasma is increased by that amount, and the matching is easily achieved.
[0014]
In view of the above results, there is provided a plasma processing apparatus for performing processing on a substrate in a processing container by using plasma generated by supplying a microwave, wherein the dielectric material covers an upper opening of the processing container in an airtight manner. An antenna member having a window, a slot antenna having a flat plate shape on a lower surface, and being disposed with a gap above the dielectric window, and a waveguide for transmitting microwaves from a microwave supply device to the antenna member Where d is the length of the gap and λg is the wavelength of the microwave passing through the gap, the length of the gap is set so that d = λg / 8 to 3λg / 8. Is set, the efficiency of inputting electric power to the plasma increases, and the matching becomes easier than when the gap d is outside the range. As the waveguide, a cylindrical waveguide or a coaxial waveguide can be used. Of course, instead of the flat slot antenna, an umbrella antenna having a concave or convex central portion may be used.
[0015]
In addition, since the VSWR becomes minimum at d = λg / 4, considering the periodicity of the wave, if the length of the gap d is set as d = (2n−1) λg / 4, the same applies. It is considered that, compared to the case where d is any other value, the efficiency of inputting the power to the plasma is increased and the matching is easily achieved. However, when the apparatus is actually configured as an apparatus, errors occur due to the characteristics of each member, the mounting accuracy, and other errors, or a plurality of modes are generated, and the wavelength differs according to each mode. Therefore, the VSWR does not always become the smallest when d = (2n-1) λg / 4, and in consideration of such a point in practical use, d = {(2n-1) λg / 4} ±. It is considered practically preferable to set the gap length in the range of (λg / 8).
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described. FIG. 3 shows a longitudinal section of a plasma processing apparatus 1 according to the present embodiment. The plasma processing apparatus 1 includes a cylindrical processing vessel 2 made of, for example, aluminum and having an open top and a bottom. I have. The processing container 2 is grounded. A susceptor 3 for mounting, for example, a semiconductor wafer (hereinafter, referred to as a wafer) W as a substrate is provided at the bottom of the processing container 2. The susceptor 3 is made of, for example, aluminum, and a high frequency for bias is supplied from an AC power supply 4 provided outside the processing container 2.
[0017]
An exhaust pipe 12 for exhausting the atmosphere in the processing container 2 by an exhaust device 11 such as a vacuum pump is provided at the bottom of the processing container 2. A supply pipe 14 for supplying a processing gas from a processing gas supply source 13 is provided on a side wall of the processing container 2.
[0018]
A dielectric window 22 made of, for example, quartz glass is provided at an upper opening of the processing container 2 via a sealing material 21 such as an O-ring for ensuring airtightness. Instead of quartz glass, another dielectric material, for example, ceramics may be used. A processing space S is formed in the processing container 2 by the dielectric window 22. The dielectric window 22 has a circular planar shape.
[0019]
An antenna member 31 is provided above the dielectric window 22 via a gap G. In the present embodiment, the antenna member 31 includes, for example, a slot antenna 32 located at the lowermost surface, a slow wave plate 33 located above the antenna, and an antenna cover 38 covering the slow wave plate 33.
[0020]
As shown in FIG. 4, the slot antenna 32 is made of a thin disk made of a conductive material, for example, copper, and has an acute angle close to a right angle to the vicinity of the end of one slot 32a. A pair of closely spaced parts is formed concentrically aligned.
[0021]
At the center of the slow wave plate 33, a bump 34 which is a part of a cone made of a conductive material, for example, a metal, is arranged. The bump 34 is electrically connected to the inner conductor 35a of the coaxial waveguide 35 formed by the inner conductor 35a and the outer tube 35b. The coaxial waveguide 35 propagates, for example, a microwave of 2.45 GHz generated by the microwave supply device 36 to the antenna member 31 through the coaxial waveguide 35 via the load matching device 37. ing.
[0022]
The plasma processing apparatus 1 according to the present embodiment has the above-described configuration. When performing plasma processing, the wafer W is placed on the susceptor 3 in the processing chamber 2 and a predetermined amount is supplied from the supply pipe 14. By exhausting the processing gas from the exhaust pipe 12 while supplying the processing gas into the processing container 2, the inside of the processing space S is set to a predetermined pressure. When a high frequency bias is applied to the wafer W by the AC power supply 4 and a microwave is generated by the microwave supply device 36 and propagated to the antenna member 31 by the coaxial waveguide 35, plasma is generated in the processing space S. By generating the gas and selecting the type of the processing gas, various kinds of plasma processing such as predetermined plasma processing, etching, ashing, and film formation can be performed on the wafer W.
[0023]
In the plasma device 1 according to the present embodiment, a gap G is interposed between the slot antenna 32 on the lower surface of the antenna member 31 and the dielectric window 22. The power input efficiency to the plasma can be improved by appropriately setting according to the wavelength of the wave. The following are some examples.
[0024]
(First Embodiment: Example of Adjusting with Pressure)
(1) The pressure in the processing container 2 is set to 50 × 1.33 Pa (50 mTorr) or less. This is adjusted by the amount of exhaust from the exhaust device 11 and the amount of processing gas supplied from the processing gas supply source 13.
(2) The thickness of the dielectric window 22 is set to approximately １ ／ of the wavelength λc when the microwave passes through the dielectric window 22. For example, when the wavelength of the microwave supplied from the microwave supply device 36 is 2.45 GHz, the thickness of the dielectric window 22 is set to 30 mm or more.
(3) The length d of the gap G is set so that 2 <d <6 mm.
If the plasma processing is performed under the above conditions, the power input efficiency for the generated plasma is improved, and the matching in the load matching unit 37 is easily performed.
In the case of an umbrella-shaped antenna, the length of the gap G between the outer peripheral portion of the umbrella-shaped antenna 41 and the upper surface of the dielectric window 22 is d, as shown in FIG. The umbrella-shaped antenna 41 is so-called because it has a shape similar to an umbrella sail, has an outer shape of a substantially truncated cone, and has a shape in which a central portion is protruded upward and The above-mentioned slots 32a and 32b are formed, for example, in an annular or spiral shape in the antenna body 41a made of a conductive member. Note that the bump 34 is disposed on a flat portion formed on the top of the antenna body 41a.
As shown in FIG. 6, when the umbrella antenna 45 of FIG. 5 is used upside down, the outer peripheral portion of the umbrella antenna 45 is also used as shown in FIG. The length of the gap G between the gap and the upper surface of the dielectric window 22 is d. The above-mentioned slots 32a and 32b are also formed in the antenna body 45a of the umbrella-shaped antenna 45, for example, in an annular or spiral shape. Then, the bump 34 is disposed on a flat portion formed at the center of the concave portion of the antenna main body 45a.
[0025]
(Second embodiment: an example of adjusting the gap in relation to the wavelength)
(1) The length d of the gap G is adjusted to be λg / 8 to 3λg / 8 of the wavelength λg when the microwave passes through the gap G. For example, when the wavelength of the microwave supplied from the microwave supply device 36 is set to 2.45 GHz and the length d of the gap G is set to λg / 4, the distance is set to 15 mm to 45 mm. Preferably, it is 30 mm, and 20 to 40 mm before and after it.
If the plasma processing is performed under the above conditions, the power input efficiency for the generated plasma is improved, and the matching in the load matching unit 37 is easily performed.
[0026]
From the above, according to the present invention, by changing the length of the gap G, it is possible to improve the power efficiency supplied to the plasma generated in the processing chamber 2 and to improve the load. The effect that the matching in the matching unit 37 can be easily achieved is obtained.
[0027]
It is to be noted that the wave plate 33 serving as a waveguide of the antenna member 31 may not be provided, and the waveguide itself may be a simple space. The space may be open to the atmosphere. Further, as a material itself of the retardation plate 33, a dielectric (for example, styrene foam, quartz glass, Al ₂ O ₃ , AlN, etc.) can be used. The slow wave plate 33 may be installed in a part or all of the space occupied by the slow wave plate 33.
[0028]
In the above example, the wavelength of the microwave is 2.45 GHz. However, the present invention is not limited to this and can be applied to various microwaves. The substrate to be processed is not limited to a semiconductor wafer, and can be applied to various substrates such as an LCD glass substrate.
[0029]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, when generating plasma by supplying a microwave and performing plasma processing, it is easy to match with the reflected wave from the plasma side, and it is possible to improve the efficiency of power supply to the plasma. is there.
[Brief description of the drawings]
FIG. 1 is a graph showing VSWR characteristics when a gap is adjusted according to the present invention.
FIG. 2 is a graph showing VSWR characteristics when a gap is adjusted based on the wavelength of a microwave according to the present invention.
FIG. 3 is a longitudinal sectional view of the plasma processing apparatus according to the present embodiment.
FIG. 4 is a bottom view of the slot antenna used in the plasma processing apparatus of FIG.
FIG. 5 is a side sectional view of an umbrella-shaped antenna.
FIG. 6 is a side sectional view of another umbrella-shaped antenna.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Plasma processing apparatus 2 Processing container 3 Susceptor 22 Dielectric window 31 Antenna member 32 Slot antenna 32a, 32b Slot 35 Coaxial waveguide 36 Microwave supply device 37 Load matching unit G Gap S Processing space d Gap length W Wafer

Claims (6)

A dielectric window that hermetically covers the upper opening of the processing container, and a flat slot antenna or a concave or convex umbrella antenna at the center with a gap provided above the dielectric window with a flat slot antenna on the lower surface And a waveguide for propagating microwaves from the microwave supply device to the antenna member, and performs processing on the substrate in the processing container by plasma generated by the supply of the microwaves. Using plasma processing equipment,
The thickness of the dielectric window is set to about の of the wavelength of the microwave passing through the dielectric window,
Further, when the length of the gap is d,
A plasma processing method, wherein the plasma processing is performed by setting the length of the gap so that 2 <d <6 mm. 2. The plasma processing method according to claim 1, wherein the pressure in the processing space is set to 50 × 0.133 Pa or less. A dielectric window that hermetically covers the upper opening of the processing container, and a flat slot antenna or a concave or convex umbrella antenna at the center with a gap provided above the dielectric window with a flat slot antenna on the lower surface And a waveguide for propagating microwaves from the microwave supply device to the antenna member, and performs processing on the substrate in the processing container by plasma generated by the supply of the microwaves. In plasma processing equipment,
A method for improving plasma processing, characterized by improving the power efficiency applied to the plasma by changing the length of the gap. A plasma processing apparatus for performing processing on a substrate in a processing chamber by using plasma generated by supplying a microwave,
A dielectric window hermetically covering an upper opening of the processing container;
An antenna member having a flat slot antenna on the lower surface, and disposed with a gap above the dielectric window;
A waveguide for transmitting microwaves from a microwave supply device to the antenna member;
When the length of the gap is d and the wavelength of the microwave passing through the gap is λg,
The plasma processing apparatus, wherein the length of the gap is set so that d = λg / 8 to 3λg / 8. A plasma processing apparatus for performing processing on a substrate in a processing chamber by using plasma generated by supplying a microwave,
A dielectric window hermetically covering an upper opening of the processing container;
An antenna member having a flat slot antenna on the lower surface, and disposed with a gap above the dielectric window;
A waveguide for transmitting microwaves from a microwave supply device to the antenna member;
When the length of the gap is d, the wavelength of the microwave passing through the gap is λg, and a natural number is n,
A plasma processing apparatus, wherein the length of the gap is set so that d = (2n-1) λg / 4. 7. The plasma processing apparatus according to claim 5, wherein an umbrella antenna having a concave or convex central portion is used instead of the flat slot antenna.

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