The present invention relates to a plasma processing apparatus and a plasma processing method which perform plasma processing on a substrate.
In the manufacturing processes of a flat-plate display, as solar battery, a semiconductor device, and the like, plasma is used for thin film formation, etching, and the like. For example, plasma is generated by means of introducing gas into a vacuum chamber and applying a high frequency wave of several MHz to several hundred MHz to an electrode provided in the chamber. For improving productivity, a glass-substrate size of the flat-plate display or the solar battery is increased year by year, and volume production of a glass substrate having a size larger than 2 m square has already being carried out.
In a film deposition process such as plasma CVD (Chemical Vapor Deposition), plasma having a higher density is required for improving a film deposition rate. Further, plasma having a lower electron temperature is required for suppressing the energy of an ion entering a substrate surface to reduce ion irradiation damage and also for suppressing excessive disassociation of a gas molecule. Generally, when a plasma excitation frequency is increased, the plasma density is increased and the electron temperature is reduced. Accordingly, for depositing a high quality thin film at a high throughput, it is necessary to increase the plasma excitation frequency. Therefore, for the plasma processing, a high frequency wave in the VHF (Very High Frequency) band of 30 to 300 MHz, which is higher than 13.56 MHz of a frequency for a typical high-frequency power source, has been used (refer to Patent Literatures 1 and 2, for example).
PTL 1: Japanese Patent Laid-Open No. H09-312268 (1997)
PTL 2: Japanese Patent Laid-Open No. 2009-021256
Meanwhile, when the size of a glass substrate to be processed becomes as large as 2 m square, for example, and is plasma-processed at a plasma excitation frequency of the VHF band as described above, uniformity of the plasma density is degraded because of a standing wave of a surface wave caused in an electrode to which the high frequency wave is applied. Generally, when the electrode to which the high frequency wave is applied has a size larger than 1/20 of a free space wavelength, it is impossible to excite uniform plasma without any countermeasure.
The present invention provides a plasma processing apparatus which can improve the density uniformity of the plasma excited by a high frequency wave as in the VHF frequency band for a larger substrate having a size larger than 2 m square.
A plasma processing apparatus of the present invention includes a waveguide member defining a waveguide having a rectangular cross section in a direction crossing a longitudinal direction; first and second electrodes for electric field formation disposed so as to face a plasma formation space, defining the waveguide in cooperation with the waveguide member, and electrically connected to the waveguide member; a transmission path supplying electromagnetic energy from a predetermined power supply position in the longitudinal direction into the waveguide; a dielectric plate disposed in the waveguide and extending in the longitudinal direction; and at least one conductor disposed, in the waveguide, on at least one side of the waveguide in a width direction with respect to the dielectric plate, extending along the dielectric plate, and electrically connected to one of the first and second electrodes.
According to the present invention, it is possible to improve density uniformity of plasma excited in the VHF frequency band in the longitudinal direction of the waveguide for a larger object (substrate) to be processed. According to the present invention, it is also possible to downsize the apparatus and reduce production costs.
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Hereinafter, embodiments of the present invention will be explained in detail with reference to the attached drawings. Note that, in the present specification and the drawings, the same reference numeral is given to a constituent element having substantially the same functional configuration, so that repeated explanation will be omitted.
First, an example of a plasma processing apparatus of a type to which the present invention is applied will be explained with reference to
Here, resonance in a waveguide will be explained. First, as shown in
Here, λ is a free space wavelength, εr is a relative permittivity in the waveguide tube, and pr is a relative permeability in the waveguide tube. According to formula (1), for εr=μr=1, it is found that the in-tube wavelength λg in the waveguide tube GT is always longer than the free space wavelength λ. For λ<2a, the in-tube wavelength λg becomes longer as the long side length a becomes smaller. For λ=2a, that is, when the long side length a is equal to ½ of the free space wavelength λ, the denominator becomes zero and the in-tube wavelength λg takes an infinite value. At this time, the waveguide tube GT becomes a cut-off state and phase velocity of an electromagnetic wave propagating in the waveguide tube GT takes an infinite value and group velocity becomes zero. Further, for λ>2a, the electromagnetic wave cannot propagate in the waveguide tube, while the electromagnetic wave can enter the waveguide tube to some extent. Note that, while generally this state is also called the cut-off state, here the state for λ=2a is called the cut-off state. For example, at a plasma excitation frequency of 60 MHz, a becomes 250 cm for a hollow waveguide tube and 81 cm for an alumina waveguide tube.
The plasma processing apparatus 10 includes a vacuum container 100 mounting a substrate G therein, and applies plasma processing to a glass substrate (hereinafter, referred to as a substrate G) therein. The vacuum container 100 has a rectangular cross section, is formed of metal such as an aluminum alloy, and is earthed. An upper opening of the vacuum container 100 is covered by a ceiling part 105. The substrate G is mounted on a mounting stage 115. Note that the substrate G is an example of an object to be processed, and the object to be processed is not limited to this and may be a silicon wafer of the like.
On a floor part of the vacuum container 100, the mounting stage 115 is provided for mounting the substrate G. Above the mounting state 115, plural (two) plasma generation mechanisms 200 are provided via a plasma formation space PS. The plasma generation mechanism 200 is fixed to the ceiling part 105 of the vacuum container 100.
Each of the plasma generation mechanisms 200 includes two waveguide members 201A and 201B which are formed of an aluminum alloy and have the same size, a coaxial tube 225, and a dielectric plate 220 inserted in the waveguide WG formed between the two facing waveguide members 201A and 201B.
The waveguide members 201A and 201B include flat plate parts 201W which face each other with a predetermined gap for forming the waveguide WG and electrode parts 201EA and 201EB for electric field formation which are formed in flange shapes at the lower end parts of these flat plate parts 201W to excite plasma, respectively. The upper end parts of the waveguide members 201A and 201B are connected to the ceiling part 105 formed of conductive material and the upper end parts of the waveguide members 201A and 201B are electrically connected with each other.
The dielectric plate 220 is formed of dielectric material such as aluminum oxide or quartz and extends upward from the lower end of the waveguide WG to a midpoint of the waveguide WG. Since the upper part of the waveguide WG is short-circuited, an electric field is weaker on the upper side than on the lower side in the waveguide WG. Therefore, when the lower side of the waveguide WG where the electric field is strong is blocked up with the dielectric plate 220, the upper part of the waveguide WG may be hollow. Obviously, the waveguide WG may be filled with the dielectric plate 220 up to the upper part.
The coaxial tube 225 is connected to an approximately center position in the longitudinal direction A of the waveguide WG as shown in
The inner conductors 225a1 and 225a2 of the coaxial tube 225 are electrically connected to the one electrode part 201EA in the plasma generation mechanism 200, and the outer conductor 225b of the coaxial tube 225 is electrically connected to the other electrode part 201EB in the plasma generation mechanism 200. To the upper end of the coaxial tube 225, a high-frequency power source 250 is connected via a matching box 245. High-frequency power supplied from the high-frequency power source 250 propagates via the coaxial tube 225 from the center position in the longitudinal direction A toward both end parts of the waveguide WG.
The inner conductor 225a2 passes through the dielectric plate 220. The inner conductors 225a2 provided in the respective adjacent plasma generation mechanisms 200 pass through the respective dielectric plates 220 of the plasma generation mechanisms 200 in directions opposite to each other. Here, when the high frequency waves having the same amplitude and the same phase are supplied to the coaxial tubes 225 of the two plasma generation mechanisms 200, respectively, high frequency waves having the same amplitude and opposite phases are applied to the electrode parts 201EA and 201EB in the two plasma generation mechanisms 200, respectively, as shown in
As shown in
While the lower face of the electrode parts 201EA and 201EB are formed so as to be approximately flush with the lower end face of the dielectric plate 220, the lower end face of the dielectric plate 220 may protrude or recede from the lower faces of the electrode parts 201EA and 201EB. The electrode parts 201EA and 201EB double as shower plates. Specifically, concave parts are formed on the lower faces of the electrode parts 201EA and 201EB and electrode caps 270 for the shower plates are fit in these concave parts. A plurality of gas ejection holes are provided in the electrode cap 270, and gas having passed through a gas flow path is ejected from these gas ejection holes to the side of the substrate G. A gas nozzle made of an electrical insulator such as aluminum oxide is provided at the lower end of the gas flow path (refer to
For performing uniform process, it is not sufficient only to realize the uniform plasma density. Gas pressure, source gas density, reaction-produced gas density, gas residence time, substrate temperature, and the like affect the process and therefore these factors are required to be uniform on the substrate G. In a typical plasma processing apparatus, a shower plate is provided at a part facing the substrate G and gas is supplied toward the substrate. The gas is configured to flow from the center part of the substrate G toward the outer peripheral part and to be exhausted from the periphery of the substrate. Naturally, pressure is higher in the center part than in the outer peripheral part on the substrate and the residence time is longer in the outer peripheral part than in the center part on the substrate. When the substrate size is increased, it is difficult to perform the uniform process because of the uniformity degradation of these pressure and residence time. For performing the uniform process also on a large area substrate, it is necessary to perform gas supply from directly above the substrate G and to perform exhaustion from directly above the substrate at the same time.
In the plasma processing apparatus 10, an exhaustion slit C is provided between the adjacent plasma generation mechanisms 200. That is, gas output from a gas supplier 290 is supplied to the processing chamber from the lower face of the plasma generation mechanism 200 through the gas flow path formed in the plasma generation mechanism 200, and exhausted to the upper direction from the exhaustion slit C provided directly above the substrate G. The gas having passed through the exhaustion slit C flows in a first exhaustion path 281 which is formed above the exhaustion slit C by the adjacent plasma generation mechanisms 200, and guided to a second exhaustion path 283 which is provided between the second dielectric cover 215 and the vacuum container 100. Further, the gas flows downward in a third exhaustion path 285 which is provided on the side wall of the vacuum container 100 and exhausted by a vacuum pump (not shown in the drawing) which is provided below the third exhaustion path 285.
A coolant flow path 295a is formed in the ceiling part 105. Coolant output from a coolant supplier 295 flows in the coolant flow path 295a, and thereby heat flowing from the plasma is configured to be conducted to the side of the ceiling part 105 via the plasma generation mechanism 200.
In the plasma processing apparatus 10, an impedance variable circuit 380 is provided for electrically changing the effective height h of the waveguide WG. Other than the coaxial tube 225 which supplies the high frequency wave and is provided at the center part in the electrode longitudinal direction, two coaxial tubes 385 are provided in the vicinities of both ends in the electrode longitudinal direction for respectively connecting the two impedance variable circuits 380. For not disturbing the gas flow in the first gas exhaustion path 281, an inner conductor 385a2 of the coaxial tube 385 is provided above the inner conductor 225a2 of the coaxial tube 225.
As a configuration example of the impedance variable circuit 380, there would be a configuration of using only a variable capacitor, a configuration of connecting a variable capacitor and a coil in parallel, a configuration of connecting a variable capacitor and a coil in series, and the like.
In the plasma processing apparatus 10, when the state becomes the cut-off state, the effective height of the waveguide WG is adjusted so as to cause reflection viewed from the coaxial tube 225 to have the smallest value. Further, preferably the effective height of the waveguide is adjusted also during the process. Therefore, in the plasma processing apparatus 10, a reflection meter 300 is attached between the matching box 245 and the coaxial tube 225 and a reflection state viewed from the coaxial tube 225 is configured to be monitored. A detection value by the reflection meter 300 is transmitted to a control section 305. The control section 305 provides an instruction of adjusting the impedance variable circuit 380 according to the detection value. Thereby, the effective height of the waveguide WG is adjusted and the reflection viewed from the coaxial tube 225 is minimized. Note that, since a reflection coefficient can be suppressed to a very small value by the above control, the matching box 245 can be omitted from installation.
When high frequency waves having opposite phases are supplied to the two adjacent plasma generation mechanisms 200, as shown in
As shown in
Note that, when the inner conductors 225a2 are disposed in the same direction, by applying high frequency waves having opposite phases to each of the pair of adjacent electrodes from the high-frequency power source 250, it is possible to cause high-frequency electric fields formed on the lower faces of all the electrode parts 201EA and 201EB in the plasma generation mechanisms 200 to have the same direction and to cause the high-frequency electric field in the exhaustion slit C to be zero.
In the plasma processing apparatus 200 having the above-described configuration, by causing the waveguide WG to become the cut-off state, it is possible to excite uniform plasma on an electrode having a length equal to or larger than 2 m, for example. However, to cause the waveguide WG to become the cut-off state, when the plasma excitation frequency is 60 MHz, for example, the height h of the waveguide WG is required to be about 380 mm, and as a result, the waveguide member 201 is configured to have a size equal to or greater than 2000 mm in the longitudinal direction A and about 400 nm in the height direction H. Accordingly, the production costs of the apparatus increase and the size of the apparatus including the vacuum container 100 significantly increases. In the present embodiment, a description will be given of a plasma generation apparatus capable of suppressing the production costs by downsizing, while exciting uniform plasma on the electrode having a length equal to or greater than 2 m.
The plasma processing mechanism 400 has a waveguide member 401. The waveguide member 401 is formed of conductive material such as an aluminum alloy, in a tubular shape in the longitudinal direction A, and defines the waveguide WG having a rectangular cross section in a direction crossing the longitudinal direction A. More specifically, the waveguide member 401 has an upper wall part 401t, and side wall parts 401w1 and 401w2 which extend downward from end parts of the upper wall part 401t in the width direction B.
Below the waveguide member 401, there are provided first and second electrodes 450A and 450B. The first and second electrodes 450A and 450B are plate members made of conductive material such as an aluminum alloy, have a rectangular shape, and extend in the longitudinal direction A. The first electrode 450A is disposed so as to face the plasma formation space PS and to be vertical to the side wall part 401w1, extends in the longitudinal direction A, and is electrically connected to the lower end part of the side wall part 401w1. The first electrode 450A is disposed so as to face the plasma formation space PS and to be vertical to the side wall part 401w1, extends in the longitudinal direction A, and is electrically connected to the lower end part of the side wall part 401w1. The second electrode 450B is juxtaposed with the first electrode 450A with a predetermined gap, disposed so as to face the plasma formation space PS and to be vertical to the side wall part 401w2, and electrically connected to the lower end part or the side wall part 401w2.
In the waveguide WG, there is provided a dielectric plate 420 formed of dielectric material such as aluminum oxide. The dielectric plate 420 has a rectangular shape and extends in the longitudinal direction A. The dielectric plate 420 is disposed so as to be substantially parallel to the side wall parts 401w and 401w2 at an approximately center position of the waveguide WG in the width direction B. The upper end part of the dielectric plate 420 in the height direction H is in contact with the lower face of an upper wall part 401t. The lower end part of the dielectric plate 420 lies in a gap between the first and second electrodes 450A and 450B and electrically separates the first and second electrodes 450A and 450B.
On both faces of the dielectric plate 420, first and second conductors 430A and 430B made of a copper-nickel plated metal film, for example, are formed so as to extend in the longitudinal direction A. The upper ends of the conductors 430A and 430B in the height direction H are positioned away from the lower face of the upper wall part 401t, and the lower end parts of the conductors 430A and 430B are connected to the first and second electrodes 450A and 450B, respectively.
The coaxial tube 225 is connected to an approximately center position in the longitudinal direction A of the waveguide WG. As shown in
Here, it is necessary to apply a high-frequency electric field between the first and second conductors 430A and 430B in a balanced manner relative to a ground. On the other hand, the high-frequency power source and an output section of the matching box are generally an imbalanced line such as a coaxial line. Therefore, it is necessary to provide a balance-imbalance converter between the high-frequency power source and a waveguide 400. Examples of the balance-imbalance converter include a Sperrtopf type. That is, as shown in
In the plasma generation mechanism 400 according to the present embodiment, it is possible to set the height h of the waveguide WG to 165 mm. Thus, the height h of the waveguide WG can be significantly reduced as compared to that in the basic-type plasma generation mechanism 200. As a result, it is possible to reduce the production costs of the plasma processing apparatus and downsize the plasma processing apparatus.
The plasma processing mechanism 500 has a waveguide member 501. The waveguide member 501 is formed of conductive material such as an aluminum alloy, in a tubular shape in the longitudinal direction A, and defines the waveguide WG having a rectangular cross section in a direction crossing the longitudinal direction A. More specifically, the waveguide 501 has an upper wall part 501t, and side wall parts 501w1 and 501w2 which extend downward from end parts of the upper wall part 501t in the width direction B.
Below the waveguide member 501, there are provided first and second electrodes 550A and 550B. The first and second electrodes 550A and 550B are plate members made of conductive material such as an aluminum alloy, have a rectangular shape, and extend in the longitudinal direction A. The first electrode 550A is disposed so as to face the plasma formation space PS and to be vertical to the side wall part 501w1, extends in the longitudinal direction A, and is electrically connected to the lower end part of the side wall part 501w1. The second electrode 550B in juxtaposed with the first electrode 550A with a predetermined gap, disposed so as to face the plasma formation space PS and to be vertical to the side wall part 501w2, and electrically connected to the lower end part of the side wall part 501w2.
In the waveguide WG, there is provided a dielectric plate 520 formed of dielectric material such as aluminum oxide. The dielectric place 520 has a rectangular shape and extends in the longitudinal direction A. The dielectric plate 520 is in contact with one side wall part 501w2 and the upper end part of the dielectric plate 520 in the height direction H is in contact with the lower face of the upper wall part 501t. The lower end part of the dielectric plate 520 lies in a gap between the first and second electrodes 550A and 550B and electrically separates the first and second electrodes 550A and 550B.
One the side of a side wall part 501w1 of the dielectric plate 520, there is provided a conductor 530 made of a plate member formed of conductive material such as an aluminum alloy so as to be in contact with the dielectric plate 520. The conductor 530 extends in the longitudinal direction A, and the upper end part of the conductor 530 is positioned away from the lower face of the upper wall part 501T and the lower end part of the conductor 530 is positioned on the first electrode 550A so that the conductor 530 is electrically connected to the first electrode 550A.
The coaxial tube 225 is disposed in the height direction H and bent at a right angle in the middle so that an outer conductor 225b2 extending in the width direction B is connected to the side wall part 501w2, and the inner conductor 225a2 extending in the width direction B passes through the dielectric plate 520 and is connected to the conductor 530. Note that the coaxial tube 225 may also be connected to the upper part of the waveguide WG, that is, to the side of the upper wall part 501t.
In the plasma generation mechanism 500 according to the present embodiment, it is possible to set the height h of the waveguide WG to about 190 mm. Thus, the height h of the waveguide WG can be reduced by about half as compared to that in the basic-type plasmid generation mechanism 200. As a result, it is possible to reduce the production costs of the plasma processing apparatus and downsize the plasma processing apparatus.
In the first and second embodiments, a description has been given of the case where a hollow is formed in the waveguide. However, the present invention is not limited to this, and it is also possible to fill the hollow in the waveguide with a dielectric.
In the first and second embodiments, a conductor is disposed so as to be in contact with the dielectric plates 420 and 520 provided in the waveguide. However, the present invention is not limited to this, and it is also possible to dispose the conductor away from the dielectric plates 420 and 520 when plasma is not generated in the vicinity of the dielectric plates 420 and 520.
In the first and second embodiments, the power supply position is the center position in the longitudinal direction of the waveguide. However, the power supply position is not limited to this, and can be changed as needed.
Although the embodiments of the present invention have been explained above in detail with reference to the attached drawings, the present invention is not limited to such examples. obviously, those having ordinary knowledge in the technical field to which the present invention belongs can conceive various kinds of variation and modification within the range of the technical idea which is specified in claims, and it is to be understood that also these variations and modifications naturally belong to the technical scope of the present invention.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2012/001304 | 2/24/2012 | WO | 00 | 7/2/2014 |