JP2005353364A - Plasma generator, plasma treatment device and plasma treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma generator capable of always providing high plasma generation efficiency without depending on the electron density of plasma, and to provide a plasma treatment device and a plasma treatment method. <P>SOLUTION: This plasma generator is provided with a plasma generation vessel 10 having a space for generating plasma P and a waveguide body 54 constituting at least a part of the wall surface of the plasma generation vessel 10 for introducing microwaves M from the outside of the plasma generation vessel 10 to the inside thereof; and is so structured as to be able to generate plasma P in the plasma generation vessel 10 by the microwaves M introduced through the waveguide body 54. The waveguide body 54 is characterized by having, between the plasma P and itself, a transition region 54T where its effective dielectric constant is generally continuously lowered toward the plasma P. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a plasma generation apparatus, a plasma processing apparatus, and a plasma processing method, and more particularly to a plasma generation apparatus using a microwave surface wave, a plasma processing apparatus such as an etching apparatus equipped with the plasma, and a plasma processing method.

  The dry process using plasma is used in a wide range of technical fields such as semiconductor manufacturing equipment, surface hardening of metal parts, surface activation of plastic parts, and non-chemical sterilization. For example, in manufacturing semiconductors and liquid crystal displays, various plasma treatments such as ashing, dry etching, thin film deposition, or surface modification are used. The dry process using plasma is advantageous in that it is low-cost, high-speed, and can reduce environmental pollution because it does not use chemicals.

  As a typical apparatus for performing such plasma processing, there is a “microwave excitation type” plasma processing apparatus that excites plasma with microwaves having a wavelength of several hundred MHz to several tens GHz. A microwave excitation type plasma source has a lower plasma potential than a high-frequency plasma source, and is therefore widely used for resist ashing without damage or anisotropic etching with a bias voltage applied.

Semiconductor wafers to be processed and glass substrates for liquid crystal displays are becoming larger in area year after year, and in order to perform plasma processing on these, an apparatus that generates high-density and uniform plasma over a large area is required. Yes.
In response to such a requirement, a plasma processing apparatus is disclosed in which linear protrusions are provided on the inner side (plasma side) of a dielectric window for introducing a microwave into a chamber (Patent Document 1).

  FIG. 14 is a perspective view of the dielectric window of the plasma processing apparatus disclosed in Patent Document 1 as viewed from the plasma side. In this plasma processing apparatus, the microwave passing through the dielectric window 65 passes through the linear protrusions 22. That is, the grooves 66 between the linear protrusions 22 are selectively passed. Therefore, selectivity corresponding to the pattern of linear protrusions appears in the microwave mode propagating as a surface wave directly below the dielectric window 65, and the plasma density can be made uniform.

On the other hand, the present inventors have invented a plasma generator capable of generating a uniform plasma over a large area by providing stripe-shaped irregularities on the inner side (plasma side) of the dielectric window (Non-Patent Document). 1).
FIG. 15 is a schematic diagram showing the main part of the plasma generator invented by the present inventors.
That is, in this plasma generator, the microwave propagated through the waveguide 50 having a waveguide space having a rectangular cross section enters the dielectric transmission window 54 via the slot antenna 52. The dielectric transmission window 54 is provided with irregularities 56 having a rectangular cross section on the plasma side. When the unevenness 56 is not provided, the microwave radiated from the slot antenna 52 tends to localize in the vicinity of the slot antenna 52. On the other hand, by providing the unevenness 56, the surface wave of the microwave propagates along the unevenness 56, and uniform plasma can be generated over the entire surface of the transmission window 54.
JP 2000-273646 A Jpn. J. Appl. Phys. Vol. 40 (2001) pp. L1176-L1178

  By the way, in a plasma generator, it is extremely important to improve the uniformity of plasma and the efficiency of plasma generation. In order to increase the plasma generation efficiency, the absorption rate when the plasma absorbs microwaves must be high. For this purpose, the resonant electron density of the microwave surface wave must match the electron density of the plasma. However, as a result of detailed studies by the inventors, it has been found that in the case of a conventional plasma generator, such matching can be obtained only when the electron density of the plasma is a specific value. That is, in the conventional plasma generator, the plasma generation efficiency can be increased only when the plasma electron density is a specific value.

  The present invention has been made on the basis of recognition of such a problem, and an object of the present invention is to provide a plasma generator, a plasma processing apparatus, and a plasma processing method that can always obtain high plasma generation efficiency without depending on the electron density of plasma. It is to provide.

  In order to achieve the above object, a plasma generation apparatus according to the present invention comprises a plasma generation container having a space for generating plasma, and at least a part of a wall surface of the plasma generation container, from outside to inside of the plasma generation container. A plasma introducing device capable of generating plasma in the plasma generation container by the microwave introduced through the waveguide, wherein the waveguide includes: In addition, a transition region in which an effective dielectric constant decreases toward the plasma substantially continuously is provided between the plasma and the plasma.

  According to the above configuration, it is possible to provide a plasma generator that can always obtain high plasma generation efficiency without depending on the electron density of plasma.

  Here, the waveguide may be made of a dielectric, and the transition region may be a region in which the filling factor of the dielectric decreases substantially continuously toward the plasma. When the filling factor of the dielectric is lowered substantially continuously, the effective dielectric constant can be lowered, so that “surface wave resonance” can occur regardless of the electron density of the plasma.

  Further, the waveguide may be made of a dielectric, and the transition region may have a plurality of stripe-shaped convex portions made of a dielectric having a cross section whose tip is focused toward the plasma. By providing such a convex portion, the effective dielectric constant can be reduced substantially continuously, so that “surface wave resonance” can occur regardless of the electron density of the plasma.

  Alternatively, even if the waveguide is made of a dielectric, and the transition region has a plurality of protrusions made of a dielectric whose tip is focused toward the plasma, the effective dielectric constant can be substantially continuous. Therefore, it is possible to cause “surface wave resonance” regardless of the electron density of the plasma.

  Alternatively, even if the waveguide is made of a dielectric, and the transition region has a plurality of holes for converging the tips provided in the waveguide, the effective dielectric constant decreases substantially continuously. Therefore, it is possible to cause “surface wave resonance” regardless of the electron density of the plasma.

  Moreover, the thickness of the transition region may be smaller than the wavelength of the microwave.

  Further, if the waveguide is a substantially flat transmission window, a so-called planar plasma generator can be realized.

  Alternatively, if the waveguide is a tubular discharge tube, a so-called discharge tube type plasma generator can be realized.

On the other hand, a plasma processing apparatus of the present invention includes any one of the above plasma generators, and is characterized in that plasma processing of an object to be processed can be performed by the generated plasma.
The plasma processing method of the present invention is characterized in that any one of the above plasma generators is used, and a plasma processing is performed on an object to be processed by the generated plasma.

  According to the present invention, a transition region is provided in a waveguide for introducing microwaves, and the dielectric constant is changed substantially continuously in the transition region, so that “surface wave resonance” is always generated regardless of the state of plasma. be able to. That is, the microwave absorption rate can always be kept high and the efficiency of plasma generation and maintenance can be increased.

  As a result, high-efficiency, stable, uniform and rapid etching, ashing, thin film deposition, surface modification, plasma doping, and other plasma treatments can be performed on large-area semiconductor wafers and liquid crystal display substrates. Yes, there are significant industrial advantages.

  Hereinafter, embodiments of the present invention will be described in detail with reference to specific examples.

FIG. 1 is a schematic cross-sectional view illustrating the structure of a plasma processing apparatus according to an embodiment of the invention. This apparatus includes a processing chamber 10, a waveguide body (transmission window) 54 made of a flat dielectric plate provided on the upper surface of the processing chamber 10, and an introduction waveguide provided outside the waveguide body 54. A tube 50. The processing chamber 10 includes a stage 16 for mounting and holding a workpiece W such as a semiconductor wafer in a processing space below the waveguide 54.
The processing chamber 10 can maintain a reduced pressure atmosphere formed by the evacuation system E, and is appropriately provided with a gas introduction pipe (not shown) for introducing a processing gas into the processing space.
In the present invention, it is also possible to generate plasma not under vacuum but under atmospheric pressure or pressure higher than atmospheric pressure.

  In the present embodiment, a transition region 54T composed of a plurality of protrusions is provided on the inner side (plasma side) of the waveguide 54. As will be described in detail later, in the transition region 54T, the effective dielectric constant decreases substantially continuously toward the plasma P. By providing such a transition region 54T, a high microwave absorption rate is always obtained regardless of the electron density of the plasma P, and as a result, a high plasma generation efficiency is always obtained.

The operation of the plasma processing apparatus of the present embodiment will be described as follows.
For example, when performing an etching process on the surface of the workpiece W using this plasma processing apparatus, first, the workpiece W is placed on the stage 16 with the surface facing upward. . Next, after the processing space is depressurized by the vacuum exhaust system E, an etching gas as a processing gas is introduced into the processing space. Thereafter, a microwave M of 2.45 GHz, for example, is introduced into the introduction waveguide 50 from a microwave power source (not shown) in a state where the atmosphere of the processing gas is formed in the processing space. The microwave propagated through the waveguide 50 is radiated toward the waveguide 54 via the slot antenna 52. The waveguide 54 is made of a dielectric such as quartz or alumina, and the microwave M propagates as a surface wave on the surface of the waveguide 54 and is radiated to the processing space in the chamber 10. The plasma P of the processing gas is formed by the energy of the microwave M radiated into the processing space in this way. When the electron density in the generated plasma becomes equal to or higher than the density (cutoff density) that can shield the microwave M supplied through the waveguide 54, the microwave is processed from the lower surface of the waveguide 54 in the chamber. A microwave standing wave is formed until a certain distance (skin depth) d enters the space, and a microwave standing wave is formed.

  Then, the microwave reflection surface becomes the plasma excitation surface, and the stable plasma P is excited on this plasma excitation surface. In the stable plasma P excited on this plasma excitation surface, ions and electrons collide with the molecules of the processing gas, so that excited active species such as excited atoms, molecules, and free atoms (radicals) (plasma generation). Product) is generated. These plasma products diffuse in the processing space as indicated by the arrow A and fly to the surface of the workpiece W to be subjected to plasma processing such as etching, ashing, thin film deposition, surface modification, and plasma doping. Can do.

  As described above, in the case of a microwave-excited plasma processing apparatus, the microwave M supplied from the outside propagates as a surface wave on the surface of the waveguide 54, and energy required for generating and maintaining the plasma P. give. At this time, energy is not supplied unless the plasma P absorbs the microwave M. That is, it is desirable to increase the microwave absorption rate of the plasma P. This microwave absorption rate depends on the electron density of the plasma P.

  According to the present embodiment, by providing the transition region 54 </ b> T in the waveguide 54, it is possible to always obtain a high microwave absorption rate regardless of the electron density of the plasma P. As a result, the efficiency of generating and maintaining the plasma P can always be increased regardless of the value of the electron density of the plasma P. Hereinafter, the reason will be described in detail.

  FIG. 2 is a conceptual diagram showing how a microwave propagates as a surface wave. That is, as shown in FIG. 2A, the microwave M supplied from the outside propagates on the surface of the waveguide body 54 and travels through the interface between the waveguide body 54 and the plasma P. Give energy to. At this time, the electric field distribution in the vicinity of the interface between the waveguide 54 and the plasma P becomes substantially maximum on the surface of the waveguide 54 as shown in FIG.

ここで、αは（Np/m）という単位で表した表面波減衰係数であり、νは電子と中性子との衝突周波数、ｃは光速、ｎ_eはプラズマの電子密度、ｎ_cはカットオフ密度である。
プラズマＰの誘電率ε_pは、プラズマの電子密度ｎ_eとカットオフ密度ｎ_cとにより決定され、次式により表される。

カットオフ密度は、周波数ｆにより決定され、次式により表される。

（３）式から、周波数ｆが一定であれば、カットオフ密度ｎ_cも一定となることが分かる。例えば、周波数ｆ＝２．４５ＧＨｚの場合、カットオフ密度ｎ_c＝７．４×１０^１０ｃｍ^−３となる。 As described above, in order to increase the efficiency of generating and maintaining the plasma P, it is necessary to increase the absorption rate (A) with respect to the microwave M. The microwave absorption rate A depends on the dielectric constant ε _p of the plasma P and the dielectric constant ε _d of the waveguide 54, and can be expressed by the following equation.

Here, alpha is a surface wave attenuation coefficient, expressed in units of (Np / m), ν is the collision frequency between electrons and neutrons, c is the speed of light, n _e is the electron density of the plasma, n _c is the cutoff density It is.
Permittivity epsilon _p of the plasma P is determined by the plasma electron density n _e and the cut-off density n _c, it is expressed by the following equation.

The cutoff density is determined by the frequency f and is expressed by the following equation.

From (3), if the frequency f is constant, it can be seen that a constant cut-off density n _c. For example, when the frequency f = 2.45 GHz, the cut-off density n _c = 7.4 × 10 ¹⁰ cm ⁻³ .

この状態においては、マイクロ波Ｍの表面波のエネルギーは高い効率でプラズマＰに伝搬される。（４）式に（２）式を代入すると、表面波共振が生ずるための電子密度ｎ_swrは、次式の如くである。

プラズマＰの電子密度ｎ_eがｎ_swrに近いほどマイクロ波Ｍに対する吸収率が高くなる。逆に、プラズマＰの電子密度ｎ_eがｎ_swrから離れるほどマイクロ波Ｍに対する吸収率は低くなる。 A state in which the dielectric constant ε _p of the plasma P and the dielectric constant ε _d of the waveguide 54 have the following relationship is referred to as “surface wave resonance”.

In this state, the surface wave energy of the microwave M is propagated to the plasma P with high efficiency. When the equation (2) is substituted into the equation (4), the electron density n _swr for causing the surface wave resonance is as follows.

The electron density n _e of the plasma P is higher absorptivity for microwave M is high close to n _swr. Conversely, absorption rate for the microwave M as the electron density n _e of the plasma P is separated from the n _swr is low.

That is, in the case of a surface wave plasma source, under conditions in which the electron density n _e of the plasma P is separated from the electron density n _swr the "surface wave resonance" occurs, it is impossible to maintain generate plasma P with high efficiency. Therefore, when the plasma P having a high electron density is generated, it is necessary to increase the dielectric constant ε _d of the waveguide 54. For example, instead of quartz having a dielectric constant ε _d of about 3.8, an alumina ceramic having an ε _d of about 10 is used.

However, when the dielectric constant ε _d of the waveguide 54 is increased, “surface wave resonance” cannot be obtained for the plasma P having a lower density than that, and the absorption rate of the microwave M is decreased, and the plasma P The efficiency of generation / maintenance will be reduced. That is, in the case of a conventional surface wave plasma source, the electron density of plasma that can be efficiently generated and maintained is determined according to the dielectric constant ε _d of the waveguide 54.

  In contrast, in the structure disclosed by the present inventors in Non-Patent Document 1, the electron density at which “surface wave resonance” occurs is increased to two types.

ここで、γ＝ｓ／ρ を「充填率（filling factor）」と称することとする。なお、これは、導波体の凸部に沿って表面波が伝搬する例である。充填率γを変えることにより、凹凸５６の部分の実効的な誘電率ε_eff を変えることができる。このように、導波体５４の誘電率に分布が生じた場合、「表面波共振」の条件も、図３に表したうに、その位置によって変わる。すなわち、凹凸５６の根本５６Ａでは、ε_eff＝−ε_d であり、凹凸５６の先端５６Ｂでは、 ε_p＝−ε_eff である。（５）式及び（６）式を用いると、「表面波共振」が生ずるための電子密度ｎ_swrは、凹凸５６の根本５６Ａ及び先端５６Ｂにおいて、それぞれ次式により表される。

例えば、γ＝５０％、周波数ｆ＝２．４５ＧＨｚ、誘電率ε_d＝３．８（石英）の場合、「表面波共振」が生ずるための電子密度ｎ_swrは、凹凸５６の根本５６Ａ及び先端５６Ｂにおいて、それぞれ次式により表される。

つまり、充填率γが５０％の凹凸５６を設けることにより、界面における実効的な誘電率を３倍に変化させることが可能となる。
しかし、この方法の場合にも、「表面波共振」が生ずる電子密度は２種類しか存在せず、これらいずれにも対応しない電子密度のプラズマは、マイクロ波吸収率が低くて生成・維持の効率が低くなるという問題がある。 FIG. 3 is an enlarged schematic cross-sectional view showing the vicinity of the surface of the waveguide disclosed by the present inventors in Non-Patent Document 1. That is, unevenness 56 having a rectangular cross section is provided on the surface of a waveguide 54 made of a dielectric. When the dielectric constant of the dielectric constituting the waveguide 54 is ε _d , the effective dielectric constant ε _eff in the uneven portion 56 is expressed by the following equation, and the dielectric constant ε _d of the dielectric is It is an intermediate value between the dielectric constant ε _p of the plasma P.

Here, γ = s / ρ is referred to as a “filling factor”. This is an example in which the surface wave propagates along the convex portion of the waveguide. By changing the filling factor γ, the effective dielectric constant ε _eff of the uneven portion 56 can be changed. As described above, when distribution occurs in the dielectric constant of the waveguide 54, the condition of “surface wave resonance” also changes depending on the position as shown in FIG. That is, ε _eff = −ε _d at the root 56 </ _b > A of the unevenness 56, and ε _p = −ε _eff at the tip 56 </ _b > B of the unevenness 56. Using the equations (5) and (6), the electron density n _swr for generating the “surface wave resonance” is expressed by the following equations at the root 56A and the tip 56B of the unevenness 56, respectively.

For example, in the case of γ = 50%, frequency f = 2.45 GHz, dielectric constant ε _d = 3.8 (quartz), the electron density n _swr for generating “surface wave resonance” is the root 56A and the tip of the unevenness 56. In 56B, each is represented by the following equation.

That is, by providing the unevenness 56 with a filling rate γ of 50%, the effective dielectric constant at the interface can be changed by a factor of three.
However, even in this method, there are only two types of electron density at which "surface wave resonance" occurs. Electron density plasma that does not correspond to any of these has low microwave absorption rate and is efficient to generate and maintain. There is a problem that becomes low.

On the other hand, in the present invention, as shown in FIG. 1, an effective dielectric is obtained by changing the filling factor γ substantially continuously in the height direction on the surface of the waveguide 54. The rate ε _eff is changed substantially continuously. By doing so, the condition of “surface wave resonance” can be satisfied for plasma corresponding to a wide range of electron densities near the surface of the waveguide 54.

FIG. 4 is a graph illustrating the dielectric constant distribution in a state where plasma is generated.
That is, when the surface of the waveguide 54 (plasma side) is a flat surface, the dielectric constant changes in a binary manner as shown in FIG. That is, the dielectric constant ε _d of the dielectric constituting the waveguide 54 and the dielectric constant ε _{p of the} plasma change in a binary and discontinuous manner.

In the case of the dielectric constant distribution shown in FIG. 4A, the condition of “surface wave resonance” is satisfied only when the dielectric constant ε _{p of} plasma is equal to −ε _d as shown in the equation (4). Is done. That is, only when the electron density of the _plasma is equal to the electron density n _swr expressed by the equation (5), the condition of “surface wave resonance” is satisfied and the microwave absorption rate is increased. Therefore, when the plasma has other electron density, the condition of “surface wave resonance” is not satisfied and the absorption rate of the microwave is lowered, so that the efficiency of plasma generation / maintenance is lowered.

On the other hand, the dielectric constant distribution shown in FIG. 4B corresponds to the case where the unevenness 56 having a rectangular cross section is provided as shown in FIG. In the case of this structure, the effective dielectric constant ε _{eff at} the concave and convex portion 56 is as expressed by the equation (6), and the dielectric constant of the dielectric constituting the waveguide body 54 according to the value of the filling factor γ. It has a value between ε _p and the dielectric constant ε _p of the plasma.

On the other hand, in the present invention, as illustrated in FIGS. 4C and 4D, the dielectric constant continuously changes. That is, in the present invention, the effective dielectric constant ε _eff is changed substantially continuously by providing the transition region 54T composed of a plurality of protrusions in the vicinity of the surface (plasma side) of the waveguide 54.

For example, in the case of the specific example shown in FIG. 4C, the dielectric constant ε _eff of the transition region 54T can be continuously changed over a range from the dielectric constant ε _d to ε _p .
Further, in the case of the example shown in FIG. 4 (d), it can be continuously varied over a range of the dielectric constant epsilon _eff of the transition region 54T from epsilon _eff1 up to the epsilon _eff2.

In this way, the “surface wave resonance” condition can be satisfied for plasma with a wide electron density corresponding to the range in which the dielectric constant ε _eff of the transition region 54T changes. That is, regardless of the electron density of the plasma, a high microwave absorption rate can be realized, and the efficiency of plasma generation / maintenance can be increased.
FIG. 5 is a graph illustrating the dielectric constant distribution in the transition region when the plasma intensity changes.
That is, before the plasma is generated, the dielectric constant ε _eff changes from ε _d to zero in a predetermined distribution in the transition region 54T as shown in FIG.

In the process of generating plasma by introducing microwaves into the plasma processing apparatus, when the plasma intensity is weak, as shown in FIG. 5B, the absolute value of the dielectric constant ε _p of the plasma P is also small. In contrast, the dielectric constant ε _eff in the transition region 54T is continuously distributed between the dielectric constant ε _p of the plasma P and the dielectric constant ε _d of the dielectric. Accordingly, in the transition region 54T, there is a portion having a dielectric constant ε _eff that generates “surface wave resonance” corresponding to the dielectric constant ε _p of the plasma P, and “surface wave resonance” occurs in this portion.

Even when the intensity of the plasma P is further increased, as shown in FIGS. 5C and 5D, the dielectric that causes “surface wave resonance” corresponding to the dielectric constant ε _p of the plasma P in the transition region 54T. There is a portion having a ratio ε _eff , and “surface wave resonance” occurs in this portion.

  As described above, according to the present invention, by changing the dielectric constant substantially continuously in the transition region 54T, it is possible to always generate “surface wave resonance” regardless of the state of the plasma. As a result, the microwave absorption rate can always be kept high, and the efficiency of plasma generation and maintenance can be increased.

Therefore, for example, when the plasma P is ignited, a high microwave absorption rate can be obtained even at a low electron density. Therefore, the plasma is ignited stably, energy is input from the microwave, and the electron density is quickly set to a predetermined value. Can be raised to any level.
In addition, even when the electron density fluctuates unnecessarily during operation by generating plasma P, it is possible to eliminate the problem that the plasma absorption rate is reduced and the plasma is misfired. By giving the wave absorption rate, the plasma can be maintained with high efficiency and fed back to a predetermined electron density.
Furthermore, even when it is desired to change the electron density of the plasma P, it is possible to always generate and maintain plasma with high efficiency by always giving a high microwave absorption rate.

4C, 4D, and 5 are merely examples, and various other distributions can be given as the distribution of the dielectric constant ε _eff in the transition region 54T.

FIG. 6 is a graph illustrating the distribution of the dielectric constant ε _eff in the transition region 54T. That is, the dielectric constant ε _eff of the transition region 54T may change substantially linearly as shown in FIG. 6A, or changes stepwise as shown in FIG. 6B. Also good. Although it is not strictly continuous when it is changed in steps, it is advantageous in that the number of cases where the condition of “surface wave resonance” is satisfied increases, and if the change step is made fine, it is substantially continuous. The same effect as a typical change can be obtained.

FIG. 7 is a schematic view illustrating the shape of a waveguide 54 that can be used in the present invention. First, in the case of the specific example shown in FIG. 6A, a plurality of stripe-shaped convex portions 54P having a substantially triangular cross section are provided on the surface (plasma side) of the waveguide 54. The region provided with these convex portions 54P acts as a transition region 54T. When the convex portion 54P having a substantially triangular cross section is provided, the maximum value and the minimum value of the dielectric constant ε _eff of the transition region 54T are respectively set as dielectrics as illustrated in FIG. 4C or FIG. Can be expanded to the dielectric constant ε _d of the plasma P and the dielectric constant ε _p of the plasma P. The height of the convex portion 54P, that is, the width (thickness) of the transition region 54T is desirably smaller than the wavelength of the microwave, and typically may be about several millimeters, for example.

Next, in the case of the specific example shown in FIG. 7B, a plurality of striped convex portions 54P having a substantially trapezoidal cross section are provided on the surface (plasma side) of the waveguide 54. The region provided with these convex portions 54P acts as a transition region 54T. When a convex portion having a substantially trapezoidal cross section is provided, as illustrated in FIG. 4D, the maximum value and the minimum value of the dielectric constant ε _eff of the transition region 54T are the dielectric constant ε _d of the dielectric, respectively. The dielectric constant ε _p of the plasma P is not reached.

Next, in the case of the specific example shown in FIG. 7C, a plurality of stripe-shaped convex portions 54P having a substantially trapezoidal cross section and curved side surfaces are provided on the surface (plasma side) of the waveguide 54. It has been. The region provided with these convex portions 54P acts as a transition region 54T. Also in this specific example, as illustrated in FIG. 4D, the maximum value and the minimum value of the dielectric constant ε _eff of the transition region 54T are the dielectric constant ε _d of the dielectric and the dielectric constant ε _p of the plasma P, respectively. It does not reach.

Further, in the case of the specific example shown in FIG. 7D, a stripe-shaped convex portion 54P having a shape in which the cross section converges in a substantially stepped shape toward the tip is provided on the surface (plasma side) of the waveguide 54. ing. As described above, when a substantially step-like cross-sectional shape is adopted, the change in the average dielectric constant ε _eff is also substantially stepped. However, if the change step is made finer to some extent, the change in the dielectric constant ε _eff is substantially reduced. It can be continuous, ie substantially continuous.

FIG. 8 is a schematic view showing another specific example of the waveguide 54 that can be used in the present invention.
That is, as shown in FIG. 5A, by providing a plurality of pin-shaped or cone-shaped projections 54P on the surface (plasma side) of the waveguide 54, the effective dielectric constant ε _eff is substantially continuous. Can be changed.

  In this case, the shape of the protrusion 54P may be a substantially conical shape as shown in FIG. 5B, or a substantially truncated cone shape as shown in FIG. As shown in d), it may be in the form of a curved rotating body, or as shown in FIG. Furthermore, as shown in FIG. 5F, it may have a shape that converges in a substantially staircase pattern toward the tip.

In any of these cases, the dielectric constant ε _eff can be changed continuously or substantially continuously in the transition region 54T.

FIG. 9 is a schematic view showing still another specific example of the waveguide 54 that can be used in the present invention.
That is, as shown in FIG. 9A, the effective dielectric constant ε _eff can be continuously changed by providing a plurality of pre-drawn holes 54H.
In this case, the shape of the hole 54H may be a substantially conical shape as shown in FIG. 5B, or a substantially truncated cone shape as shown in FIG. It may be a curved rotating body as shown, or a shape with its apex cut out as shown in FIG. Furthermore, as shown in FIG. 5F, the shape may converge in a substantially step shape toward the tip (bottom of the hole).

In addition to the examples shown in FIGS. 7 to 9, similar effects can be obtained by providing convex portions, protrusions, or holes having various shapes. Further, these convex portions, protrusions, and holes may be appropriately combined. That is, in the present invention, any structure may be used as long as the dielectric constant ε _eff continuously changes on the surface (plasma side) of the waveguide 54.

  FIG. 10 is a conceptual diagram showing the operation of the plasma processing apparatus provided with the transition region 54T as described above. That is, by providing the transition region 54T in the waveguide 54, the plasma P is generated with high efficiency and is stably maintained. As a result, various plasma treatments such as etching, thin film deposition, and surface modification can be stably performed.

Furthermore, in the present invention, in accordance with the distribution of the plasma P, a distribution can be provided in the change characteristic of the dielectric constant ε _eff in the transition region 54T.
FIG. 11 is a schematic diagram illustrating a specific example when the plasma P has a distribution. That is, this figure (a) is a graph illustrating the distribution of the electron density n _e of the plasma P. The horizontal axis of the figure represents the direction parallel to the main surface of the waveguide 54, and the vertical axis represents the electron density. Thus, the electron density n _e of the plasma P is higher at the center of the waveguide 54, which may take a low profile in the peripheral.
On the other hand, when the electron density n _swr for generating the surface wave resonance is constant as in the conventional waveguide, the resonance condition is satisfied as shown in FIG. There are only two points.
On the other hand, for example, as shown in FIG. 11B, a distribution can be given to the width of the convex portion 54P of the waveguide 54. That is, the width of the convex portion 54P is wide near the center of the waveguide 54, and the width of P of the convex portion 54 is narrow near the periphery.
In this case, the filling rate γ has a substantially stepwise distribution as shown in FIG. That is, the filling factor γ is high near the center of the waveguide 54 and is low around the periphery.
Thus providing the optimal distribution of the filling rate gamma, as expressed as "resonance" in FIG. 11 (d), the distribution of the electron density n _e of the plasma P, the surface wave resonance of the waveguide 54 occurs _Therefore , the electron density n _swr can be made to substantially coincide with each other. That is, the plasma P can be generated with high efficiency by satisfying the resonance condition over the entire plasma P.
The plasma processing apparatus using the substantially planar waveguide 54 has been described above with reference to FIGS. However, the present invention is not limited to these. For example, the present invention is similarly applied to a plasma generator that generates plasma inside the discharge tube, and the same effect can be obtained.

FIG. 12A is a conceptual diagram showing a plasma generator using a discharge tube. That is, the inside of the discharge tube 58 made of a dielectric material such as quartz or alumina is connected to a vacuum exhaust system and a gas introduction system (not shown) so that the inside can be maintained in a predetermined gas atmosphere. A microwave M supplied from a microwave power source (not shown) is introduced into the introduction portion discharge tube 58 in the introduction portion 53. The microwave M propagates on the surface of the discharge tube 58 as a surface wave SW, travels at the interface between the discharge tube 58 and the plasma P, and gives energy to the plasma P. At this time, the electric field distribution in the vicinity of the interface between the discharge tube 58 and the plasma P becomes substantially maximum on the wall surface of the discharge tube 58 as shown in FIG.
Also in the case of a plasma generator using such a discharge tube, the efficiency of plasma generation / maintenance can be increased by applying the present invention to provide a transition region.

FIG. 13 is a conceptual diagram showing a discharge tube type plasma generator to which the present invention is applied.
That is, the transition region 58T is provided inside the discharge tube 58 (plasma side). As described above with reference to FIGS. 1 to 11, the transition region 58T has a composite dielectric constant ε _eff of the dielectric constant ε _d of the dielectric that constitutes the discharge tube 58 and the dielectric constant ε _p of the plasma P. This is a region that changes continuously or substantially continuously toward

  By providing such a transition region 58T, the “surface wave resonance” condition is satisfied in a wide range of the electron density of the plasma P, and the efficiency of generating and maintaining the plasma P can be increased. According to the present invention, plasma P such as etching or thin film deposition may be performed by using the plasma P generated stably with high efficiency as described above, and placing the object to be processed in the discharge tube 58. Alternatively, active species such as radicals generated by the plasma P may be introduced into a processing chamber (not shown) to perform processing such as etching or thin film deposition on the object to be processed. In any case, since the stable plasma P can be generated with high efficiency by providing the transition region 58T, high-speed and stable plasma processing can be performed.

  The embodiments of the present invention have been described with reference to specific examples. However, the present invention is not limited to these specific examples.

  For example, elements such as a waveguide, a waveguide, a processing chamber, a stage, a discharge tube, or a microwave power source used in the present invention are not limited to the shapes and sizes described above, and the cross-sectional shape, wall thickness, The shape and size of the opening are appropriately changed to obtain the same function and effect, and are included in the scope of the present invention.

  Furthermore, in the specific examples described above, only the main configuration of the plasma generation unit and the processing unit has been described, but the present invention includes all plasma processing apparatuses having such a plasma generation unit and a processing unit, for example, Any plasma processing apparatus realized as an etching apparatus, an ashing apparatus, a thin film deposition apparatus, a surface treatment apparatus, a plasma doping apparatus, and the like is included in the scope of the present invention.

1 is a schematic cross-sectional view illustrating the structure of a plasma processing apparatus according to an embodiment of the invention. It is a conceptual diagram showing a mode that a microwave propagates as a surface wave. 2 is a schematic cross-sectional view showing an enlarged vicinity of the surface of a waveguide disclosed by the present inventors in Non-Patent Document 1. FIG. It is a graph which illustrates distribution of dielectric constant in the state where plasma was generated. It is a graph which illustrates distribution of the dielectric constant of the transition area | region when the intensity | strength of plasma changes. It is a graph which illustrates distribution of dielectric constant (epsilon) _eff in the transition area | region 54T. It is a schematic diagram which illustrates the shape of the waveguide 54 which can be used in this invention. It is a schematic diagram showing the other specific example of the waveguide body 54 which can be used in this invention. It is a schematic diagram showing the other specific example of the waveguide body 54 which can be used in invention. It is a conceptual diagram showing operation | movement of the plasma processing apparatus provided with the transition area | region 54T. It is a schematic diagram showing the specific example in case there exists distribution in the plasma P. FIG. (A) is a conceptual diagram showing the plasma generator using a discharge tube, (b) is a graph showing the electric field distribution of a microwave. It is a conceptual diagram showing the discharge tube type plasma generator to which this invention is applied. It is the perspective view which looked at the dielectric material window of the plasma processing apparatus currently disclosed by patent document 1 from the plasma side. It is a schematic diagram showing the principal part of the plasma generator which the present inventors invented.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Chamber 16 Stage 22 Linear protrusion 50 Waveguide 52 Slot antenna 53 Introduction part 54 Waveguide (transmission window)
54H Hole 54P Convex (protrusion)
54T transition region 56 irregularities 56A root 56B tip 58 discharge tube 58T transition region 65 dielectric window 66 groove E vacuum exhaust system M microwave P plasma SW surface wave W workpiece

Claims (10)

A plasma generation container having a space for generating plasma;
A waveguide that constitutes at least part of the wall surface of the plasma generation vessel, and that introduces microwaves from the outside to the inside of the plasma generation vessel;
With
A plasma generator capable of generating plasma in the plasma generation container by microwaves introduced through the waveguide,
The plasma generator according to claim 1, wherein the waveguide has a transition region between the plasma and an effective dielectric constant that decreases substantially continuously toward the plasma. The waveguide is made of a dielectric,
2. The plasma generating apparatus according to claim 1, wherein the transition region is a region in which a filling factor of the dielectric decreases substantially continuously toward the plasma. The waveguide is made of a dielectric,
3. The plasma generation apparatus according to claim 1, wherein the transition region has a plurality of stripe-shaped convex portions made of a dielectric material having a cross-section in which a tip converges toward the plasma. The waveguide is made of a dielectric,
3. The plasma generation apparatus according to claim 1, wherein the transition region has a plurality of protrusions made of a dielectric whose front ends are focused toward the plasma. 4. The waveguide is made of a dielectric,
The plasma generation apparatus according to claim 1, wherein the transition region has a plurality of holes at which tips provided in the waveguide are focused.   The plasma generating apparatus according to claim 1, wherein a thickness of the transition region is smaller than a wavelength of the microwave.   The plasma generation apparatus according to claim 1, wherein the waveguide is a substantially flat transmission window.   The plasma generator according to any one of claims 1 to 6, wherein the waveguide is a tubular discharge tube. The plasma generator according to any one of claims 1 to 8, comprising:
A plasma processing apparatus characterized in that plasma processing of an object to be processed can be performed by the generated plasma. A plasma processing method using the plasma generator according to claim 1 to perform plasma processing of an object to be processed by the generated plasma.

Images