US20050217798A1

US20050217798A1 - Plasma processing apparatus

Info

Publication number: US20050217798A1
Application number: US11/088,211
Authority: US
Inventors: Akira Sugiyama; Shuhichi Kitamura; Koji Murakami; Daisuke Takahashi; Shohzoh Yoshimoto
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2004-03-22
Filing date: 2005-03-22
Publication date: 2005-10-06
Also published as: JP2005268170A; KR100768374B1; KR20060044460A; JP4202292B2

Abstract

The plasma processing apparatus includes main electrodes 5, 31 opposed to each other with a plasma processing space 15 interposed therebetween. The plasma processing apparatus further has a side electrode 6 opposed to side faces 5B-1, 5B-2 of the main electrode 5, as well as a side electrode 32 opposed to side faces 31B-1, 31B-2 of the main electrode 31. Therefore, in addition to the plasma processing space 15 between the main electrode 5 and the main electrode 31, an electric field can be formed in spaces between the side faces of the main electrodes 5, 31 and the side electrodes 6, 32, the spaces serving as predischarge areas 16-1, 16-2. By this electric field, processing gas present in the predischarge areas 16-1, 16-2 can be transformed into plasma. Electrons and excitation species of the plasma generated in these predischarge areas 16-1, 16-2 can be supplied directly to the plasma processing space 15.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This nonprovisional application claims priority based on Application No. 2004-082701 filled on Mar. 22, 2004 in Japan under 35 USC 119(a), the entirety of which is incorporated herein by this reference.

BACKGROUND OF THE INVENTION

The present invention relates to plasma processing apparatuses for performing such processing as surface reforming, cleaning, machining and film deposition with applications of plasma generation and control techniques. For example, the invention relates to plasma processing apparatuses for use in equipment for manufacturing semiconductors, liquid crystal display devices, EL (electroluminescence) panels, such flat panel displays as PDPs (plasma display panels), solar cells and the like.
Conventionally, in manufacturing processes of semiconductors, flat panel displays, solar cells and the like, it has been practiced to utilize plasma generated under reduced pressure to perform such processing as reforming, cleaning, machining and film deposition on a glass substrate (hereinafter, referred to as substrate), a semiconductor wafer (hereinafter, referred to as wafer), or the like.
In recent years, along with heating-up enhancement of cost competitive power, growing attention has been being focused on atmospheric plasma techniques that do not require any large-scale equipment such as a vacuum chamber or an evacuator. The atmospheric plasma techniques have been being put into practice in some processes such as surface reforming, cleaning and dry etching.
A typical example of the atmospheric plasma techniques is one described in JP H07-118857 A. This prior art example is explained with reference to FIG. 13.
FIG. 13 is a schematic sectional view showing an example of the plasma processing apparatus described in above mentioned JP H07-118857 A.
In FIG. 13 are shown a power supply 101, a processing vessel 102, a top surface 102 a, a bottom surface 102 b, a side face 102 c, an insulator 102 d, a porous metal electrode 103, a gas flow passage 103 a, openings 103 b, a metal electrode 104, a plasma processing section 105, a first solid dielectric 106, a substrate 107, a second solid dielectric 108, a gas inlet 109, a gas inlet tube 110, a gas inlet 110 a, a gas outlet 110 b, a gas discharge port 111 and a discharge port 112.
In this prior art example, the first solid dielectric 106 is provided all over the metal electrode 104, and the porous metal electrode 103 is provided opposite the first solid dielectric 106. The porous metal electrode 103 is enabled to supply reaction gas. Between the first solid dielectric 106 and the porous metal electrode 103 is a space whose side faces are covered with the second solid dielectric 108.
In this plasma processing apparatus, the substrate 107 is set within the space covered with the second solid dielectric 108, and inert gas is supplied to the substrate 107 while reaction gas is supplied to the substrate 107 via the porous metal electrode 103. Then, a voltage is given to the electrode 103 under a pressure close to atmospheric pressure so that a glow discharge plasma is generated, and active species excited by the plasma is put into contact with the surface of the substrate 107. Thus, surface processing of the substrate 107 is carried out.
With regard to the opposing electrode 104 and electrode 103, the electrode 104 is a metal electrode 104 having the first solid dielectric 106 provided on its opposing surface, and the electrode 103 is a porous metal electrode 103 capable of supplying reaction gas. In the publication of JP H07-118857 A, it is further described that the porous metal electrode and the metal electrode are connected so that any one of them comes on the anode side and the other is on the cathode side, where the two electrodes may be replaced with each other up and down.
Consequently, the following (i) to (vii) are described in JP H07-118857 A.
(i) A processing object (substrate 107), which is an article to be processed, is placed between opposing electrodes.
(ii) At least one of the opposing electrodes has a solid dielectric provided on its opposing surface side.
(iii) Reaction gas is supplied to between the opposite electrodes.
(iv) Reaction gas is supplied through the porous metal electrode.
(v) Voltages to be given to the opposite two electrodes are of different polarities, but one of them is grounded.
(vi) It is between the opposite two electrodes that the glow discharge plasma is generated.
(vii) No glow discharge plasma is generated with the porous metal electrode alone or with the metal electrode alone (plasma is generated only with paired electrodes).
However, the above-described prior-art plasma generator has issues shown in (a) to (f) below.
(a) As the distance between the opposing solid dielectric and porous metal electrode increases, the discharge may be unstable, or localization of discharge occurs, or the discharge itself does not occur.
(b) In a case like (a), increasing the applied voltage for stabilization of discharge may cause the processing object to be damaged.
(c) The gas use efficiency is low because the decomposition of processing gas less proceeds;
(d) Large-scale equipment is involved; flat-flow processing, i.e. processing the processing object while moving it on a specified plane, is hard to fulfill;
(e) As the distance between the opposing solid dielectric and porous metal electrode decreases, there occurs processing nonuniformities due to the opening pattern of the porous metal electrode;
(f) Adjustment of the distance between the opposing solid dielectric and porous metal electrode is hard to do.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a plasma processing apparatus which is capable of generating a stable plasma having a wide control range of a working distance under atmospheric pressure and which allows both low running cost and high-speed processing to be fulfilled at the same time. Another object of the invention is to provide a safe, low-priced plasma processing apparatus which is free from obstacles to peripheral equipment and human bodies.
In order to achieve the above object, there is provided a plasma processing apparatus comprising:
a gas supply section for supplying a specified processing gas to a plasma processing space where a plasma processing object to be processed is placed;
a first electrode which is opposed to the plasma processing space and which generates an electric field in the plasma processing space;
a second electrode which is opposed to the first electrode with the plasma processing space interposed therebetween;
a third electrode which is opposed to a side face of the first electrode with a specified gap, the side face being adjacent to an opposing face of the first electrode facing the plasma processing space; and
a first power supply section for supplying a first electric power to the first electrode.
In the plasma processing apparatus of this invention, the first electrode, to which the first electric power is supplied from the first power supply section, forms an electric field against the second electrode, by which the electric field is formed in the plasma processing space. Meanwhile, the gas supply section supplies processing gas to the plasma processing space. As a result, the processing gas is transformed into plasma under atmospheric pressure by the electric field formed in the plasma processing space. With this plasma-state processing gas, the processing object placed in the plasma processing space is plasma processed.
In this case, an electric field is formed also between the side face of the first electrode and the third electrode. By this electric field, the processing gas present between the side face of the first electrode and the third electrode is transformed into plasma. That is, the space between the side face of the first electrode and the third electrode serves as a predischarge area. When the plasma generated in this predischarge area reaches a region between the plasma processing space and the first electrode, electrons and excitation species are supplied directly to the plasma processing space by the plasma. It is noted here that this phenomenon is referred to as creeping discharge.
As shown above, generating a plasma in the predischarge area causes electrons or excitation species to be supplied directly to the plasma processing space. When the plasma is not yet generated in the plasma processing space, discharge start in the plasma processing space can be assisted. While discharge is in progress in the plasma processing space, the discharge can be stabilized.
According to this invention, utilization of the creeping discharge allows the following working effects (I) to (VI) to be expected.
(I) It becomes possible to widen the control range of a working distance between the first electrode and the second electrode.
(II) Decomposition of the processing gas is carried out also in the predischarge area besides the plasma processing space, so that the use efficiency of the processing gas is enhanced.
(III) As compared with conventional plasma generators, plasma can be maintained even if the electric field in the plasma processing space weakened, so that damage to the processing object can be reduced eventually.
(IV) The equipment becomes compact, and flat-flow processing is facilitated.
(V) The gas supply section is located on the rear face side of the first electrode, providing the structure that the processing gas is supplied to the predischarge area between the first electrode and the third electrode, where the gas jet port of the gas supply section can be separated from the plasma processing space. Therefore, processing nonuniformities due to the opening pattern of the gas jet port are less likely to occur.
(VI) The distance between the first electrode and the second electrode becomes easier to adjust.
Thus, according to this invention, a plasma which has a wide control range of the working distance under atmospheric pressure and which is stable can be generated, making it possible to provide a plasma processing apparatus capable of fulfilling both low running cost and high-speed processing.
In one embodiment of the present invention, the plasma processing apparatus further comprises a first dielectric portion with which the opposing face and the side face of the first electrode are covered; and
a second dielectric portion with which a side face of the third electrode opposed to the side face of the first electrode is covered, wherein
the first dielectric portion and the second dielectric portion are opposed to each other with a specified gap therebetween.
In this embodiment, the first dielectric portion, with which the opposing face and side faces of the first electrode are covered, and the second dielectric portion, with which the third electrode is covered, are included. Thus, the first electrode and the third electrode can be prevented from being damaged by discharge.
In one embodiment of the present invention, the third electrode is grounded,
a second power supply section for supplying a second electric power to the second electrode is provided,
the first electric power supplied to the first electrode by the first power supply section and the second electric power supplied to the second electrode by the second power supply section are different from each other in at least one of phase and amplitude, and wherein
the first electric power and the second electric power are
RF power, or pulse wave electric power, or electric power obtained by switching RF power and pulse wave electric power, or electric power in which RF power and pulse wave electric power are superimposed on each other.
In this embodiment, the waveform of the first and second electric power may be selected from among RF power, or pulse wave electric power, or electric power obtained by switching RF power and pulse wave electric power, or electric power in which RF power and pulse wave electric power are superimposed on each other, in consideration of various conditions required for the plasma processing, the type of processing gas, demanded processing performance, and moreover electromagnetic interference against peripheral equipment and safety against the human body. It is noted here that the RF power refers to electric power having a frequency of 1 kHz to 100 MHz. The pulse electric power refers to one having a repetition frequency of 1 MHz or lower, a waveform rise time of 100 μsec. or less and a pulse application time of 1 msec. or less.
In one embodiment of the present invention, the apparatus has a structure that processing gas supplied by the gas supply section, after passing through the gap between the side face of the first electrode and the third electrode, passes through the plasma processing space between the first electrode and the second electrode.
In this embodiment, the gas supply section is located on the rear face side of the first electrode, providing the structure that the processing gas is supplied to the predischarge area between the first electrode and the third electrode, so that the gas jet port of the gas supply section can be separated from the plasma processing space. Therefore, processing nonuniformities due to the opening pattern of the gas jet port are less likely to occur.
In one embodiment of the present invention, the gas supply section comprises
a gas jet port for supplying the processing gas to the gap between the first electrode and the third electrode; and
an opening controller for changing at least one of opening area and opening configuration of the gas jet port.
In this embodiment, with respect to the gas supply section, by changing the opening area or opening configuration of the gas jet port by means of the opening controller, gas flow rate and gas flow velocity can be controlled. Thus, flow rate and flow velocity of the processing gas to be supplied to the plasma processing space can be controlled.
In one embodiment of the present invention, the plasma processing apparatus further comprises a dielectric coat formed on the opposing face and the side face of the first electrode, wherein
the first dielectric portion covers the dielectric coat.
This embodiment has a dielectric coat formed on the opposing face and side faces of the first electrode. Therefore, even when the first dielectric portion is provided as a component independent of the first electrode so that the dielectric coat is overlaid with the first dielectric portion, a gap (space) formed between the first electrode and the first dielectric portion can be suppressed to a minimum. Thus, reduction of the electric field strength in the plasma processing space and the predischarge area can be suppressed, and discharge at the gap can be suppressed so that occurrence of any power loss and electrode damage can be suppressed.
In one embodiment of the present invention, the gap between the first electrode and the first dielectric portion is not more than 500 μm.
In this embodiment, the gap between the first electrode and the first dielectric portion is not more than 500 μm. Thus, the effect for suppressing any reduction of the electric field strength as well as the effect for suppressing discharge at the gap can be fulfilled. If the gap is over 500 μm, the suppression effects would be insufficient. In addition, the gap between the first electrode and the first dielectric portion is more preferably not more than 100 μm.
According to this invention, in addition to the plasma processing space between the first electrode and the second electrode, an electric field can be formed also between the side faces of the first electrode and the third electrode. By this electric field, processing gas present between the side faces of the first electrode and the third electrode can be transformed into plasma. Therefore, according to this invention, the spaces between the side faces of the first electrode and the third electrode are used as predischarge areas, electrons and excitation species of the plasma generated in the predischarge areas can be supplied directly to the plasma processing space.
Consequently, plasma generation in the plasma processing space can be achieved more easily, and besides plasma discharge can be stabilized. Thus, there can be realized a plasma processing apparatus which is capable of generating a stable plasma having a wide control range of a working distance under atmospheric pressure and which allows both low running cost and high-speed processing to be fulfilled at the same time.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood by the following detailed description and the accompanying drawings. However, the detailed description and the accompanying drawings will be given only by way of illustration and therefore do not limit the present invention.
FIG. 1 is a side sectional view showing a first embodiment of the plasma processing apparatus of the present invention;
FIG. 2 is an enlarged side sectional view showing the construction of a main part of the plasma processing apparatus of the first embodiment;
FIG. 3 is a side sectional view showing the construction of an electrode part of the plasma processing apparatus of the first embodiment;
FIG. 4 is a schematic sectional view showing another example of the opening control part for controlling the flow rate and flow velocity of the gas in the plasma processing apparatus of the first embodiment;
FIG. 5 is a waveform diagram showing an example of the voltage waveform applied to the main electrode of the plasma processing apparatus of the first embodiment;
FIG. 6 is a waveform diagram showing another example of the voltage waveform applied to the main electrode of the plasma processing apparatus of the first embodiment;
FIG. 7 is a waveform diagram showing still another example of the voltage waveform applied to the main electrode of the plasma processing apparatus of the first embodiment;
FIG. 8 is a side sectional view showing the construction of a plasma processing apparatus of a second embodiment of the invention;
FIG. 9 is a waveform diagram showing one example of the voltage waveform applied to the plasma processing apparatus of the second embodiment;
FIG. 10 is a side sectional view showing the construction of a plasma processing apparatus of a third embodiment of the invention;
FIG. 11 is a side sectional view showing the construction of a plasma processing apparatus of a fourth embodiment of the invention;
FIG. 12 is a perspective view of the plasma processing apparatus in the first embodiment; and
FIG. 13 is a sectional view of a prior-art plasma processing apparatus.

DETAILED DESCRIPTION OF THE PREFERED EMBODIMENTS

Hereinbelow, the present invention is described in detail by embodiments thereof illustrated in the accompanying drawings.

First Embodiment

FIG. 1 shows a first embodiment of the plasma processing apparatus of the present invention. FIG. 1 is a side sectional view showing a cross section obtained by cutting the plasma processing apparatus by a plane vertical to a plate-shaped processing object 14 and which contains a line segment extending along a direction of conveyance of the processing object 14. FIG. 2 is an enlarged view showing a main part of the plasma processing apparatus. The processing object 14 is a semiconductor substrate as an example.
As shown in FIGS. 1 and 2, this plasma processing apparatus has a chamber upper part 1, a chamber lower part 2, an upper electrode unit 3 and a lower electrode unit 4. The chamber upper part 1 and the chamber lower part 2 constitute a chamber C. The chamber C has outlet and inlet 17 a and 17 b for the processing object 14 at both ends of the conveyance direction between the chamber upper part 1 and the chamber lower part 2.
The upper electrode unit 3 is fitted to an opening formed at approximately center of the chamber upper part 1 and covered with an upper electrode cover 12. The upper electrode cover 12 has a gas supply port 21-1 communicating with the upper electrode unit 3.
The lower electrode unit 4 is located at approximately center of the chamber lower part 2 and opposed to the upper electrode unit 3 with a spacing of a specified distance. On both sides of the lower electrode unit 4 are placed conveyor rollers 13 supported by a roller shaft 23. Conveyor rollers 13 are placed also outside side walls 2 a, 2 b of the chamber lower part 2. These conveyor rollers 13 are enabled to cavity the processing object 14 along the conveyance direction on a specified plane. The chamber lower part 2 has a gas supply port 21-2 communicating with the lower electrode unit 4. Further, the chamber lower part 2 has two discharge ports 22 penetrating through the chamber lower part on both sides of the lower electrode unit 4.
As shown in FIG. 3, the upper electrode unit 3 has a main electrode 5 as a first electrode placed at a center portion, and a side electrode 6 as a third electrode having side faces 6B-1, 6B-2 opposed to side faces 5B-1, 5B-2 of the main electrode 5. The main electrode 5 and the side electrode 6 are made of metal.
The main electrode 5 is covered with a first dielectric portion 7-1 made of a solid dielectric, and the first dielectric portion 7-1 covers an opposing face 5C, side faces 5B-1, 5B-2 and a rear face 5D of the main electrode 5. Also, of the side electrode 6, an end portion 6C including the side faces 6B-1, 6B-2 is covered with a second dielectric portion 8-1 made of a solid dielectric. The first dielectric portion 7-1 and the second dielectric portion 8-1 are opposed to each other with a specified gap therebetween, and this gap serves as a predischarge area 16-1.
As shown in FIG. 3, the predischarge area 16-1 communicates with a gas flow passage 26-1 formed in a base portion 6D of the side electrode 6. The first dielectric portion 7-1 is fixed to a portion 6E of the base portion 6D of the side electrode 6 which portion 6E is adjacent to the gas flow passage 26-1. As shown in FIG. 2, the side electrode 6 has a gas storage 9-1 formed of an upwardly-opened recessed portion, and the gas storage 9-1 communicates with the gas flow passage 26-1 and the gas supply port 21-1. The gas storage 9-1, the gas flow passage 26-1 and the gas supply port 21-1 constitute a gas supply section G1. The gas flow passage 26-1 also forms a gas jet port 11-1 for supplying processing gas to the predischarge area 16-1.
As shown in FIG. 3, in the portion 6E of the base portion 6D of the side electrode 6, flow adjusting plates 35-1, 35-1 as opening controllers are placed so as to be slidable in left-and-right directions. These flow adjusting plates 35-1, 35-1, when slid left and right, causes the opening area and the opening configuration on the inlet side of the gas flow passage 26-1 to be changed.
In the side electrode 6, a through hole 6A is formed, so that a refrigerant 10, when put into flow through the through hole 6A, causes the side electrode 6 to be cooled. Further, a through hole 5A is formed also in the main electrode 5, so that the refrigerant 10, when put into flow through the through hole 5A, causes the main electrode 5 to be cooled.
The main electrode 5, which is the first electrode, is connected to an RF (Radio Frequency) power supply 18, which is a first power supply section, by a power transfer path 27, and the RF power supply 18 is connected to the ground. The side electrode 6 is grounded by an electric path 28.
On the other hand, the lower electrode unit 4, as shown in FIG. 3, generally similar in structure to the upper electrode unit 3, has a main electrode 31 as a second electrode placed at a center portion, and a side electrode 32 as a third electrode having side faces 32B-1, 32B-2 opposed to side faces 31B-1, 31B-2 of the main electrode 31. The main electrode 31 and the side electrode 32 are made of metal.
The main electrode 31 is covered with a first dielectric portion 7-2 made of a solid dielectric, and the first dielectric portion 7-2 covers an opposing face 31C, side faces 31B-1, 31B-2 and a rear face 31D of the main electrode 31. Also, of the side electrode 32, an end portion 32C including the side faces 32B-1, 32B-2 is covered with a second dielectric portion 8-2 made of a solid dielectric. The first dielectric portion 7-2 and the second dielectric portion 8-2 are opposed to each other with a specified gap therebetween, and this gap serves as a predischarge area 16-2.
The predischarge area 16-2 communicates with a gas flow passage 26-2 formed in a base portion 32D of the side electrode 32. The first dielectric portion 7-2 is fixed to a portion 32E of the base portion 32D of the side electrode 32 which portion 32E is adjacent to the gas flow passage 26-2. The side electrode 32 has a gas storage 9-2 formed of a downwardly-opened recessed portion, and the gas storage 9-2 communicates with the gas flow passage 26-2 and the gas supply port 21-2. The gas storage 9-2, the gas flow passage 26-2 and the gas supply port 21-2 constitute a gas supply section G2. The gas flow passage 26-2 also forms a gas jet port 11-2 for supplying processing gas to the predischarge area 16-2.
As shown in FIG. 3, in the portion 32E of the base portion 32D of the side electrode 32, flow adjusting plates 35-2, 35-2 as opening controllers are placed so as to be slidable in left-and-right directions. These flow adjusting plates 35-2, 35-2, when slid left and right, causes the opening area and the opening configuration on the inlet side of the gas flow passage 26-2 to be changed.
In the side electrode 32, a through hole 32A is formed, so that a refrigerant 10, when put into flow through the through hole 32A, causes the side electrode 32 to be cooled. Further, a through hole 31A is formed also in the main electrode 31, so that the refrigerant 10, when put into flow through the through hole 31A, causes the main electrode 31 to be cooled.
As shown in FIG. 1, the main electrode 31 is connected to an RF power supply 33 by a power transfer path 29, and the RF power supply 33 is connected to the ground. The side electrode 32 is grounded by an electric path 30.
The distance between the main electrode 5 and the main electrode 31 is set depending on the magnitude and frequency of electric power given from the RF power supply 18, 33, the type and flow rate of processing gas, the electrical characteristics, secondary electron emission coefficient and thickness of the solid dielectrics forming the dielectric portions 7-1, 7-2, temperatures of individual parts and sections, and the like.
FIG. 12 shows a perspective view of the plasma processing apparatus of the first embodiment. As shown in FIG. 12, a chamber side face member 25 is attached to side end faces of the chamber upper part 1 and the chamber lower part 2. A plurality of conveyor rollers 13 are placed also outside the chamber lower part 2 so that the plate-shaped processing object 14 can be conveyed on a specified plane extending through a plasma processing space 15.
In the plasma processing apparatus of the above construction, an RF power as a first power outputted from the RF power supply 18, which is the first power supply section, is supplied to the main electrode 5, which is the first electrode, via the power transfer path 27. Also, an RF power as a second power is supplied to the main electrode 31, which is the second electrode, from the RF power supply 33, which is a second power supply section, via a power transfer path 29. As a result, an electric field is formed between the main electrode 5 and the main electrode 31, by which the electric field is formed in the plasma processing space 15. In this embodiment, it is assumed that the RF power outputted by the RF power supply 18 and the RF power outputted by the RF power supply 33 are mutually equal in frequency and different in phase.
On the other hand, a processing gas in which a plurality of gaseous species have been mixed by unshown mass flow and mixer is supplied from an unshown gas supply cylinder or gas supply tank to the gas supply port 21-1 of the gas supply section G1 of the upper electrode unit 3. As shown in FIG. 2, the processing gas is supplied from the gas supply port 21-1 to the gas storage 9-1, and the gas spreads at this gas storage 9-1 in a perpendicular direction to the drawing sheet so as to reach a slit-like (or shower hole-like) gas flow passage 26-1 having a cross-sectional area sufficiently narrower than the gas storage 9-1. The processing gas is accelerated in flow velocity when passing through the gas flow passage 26-1, passes via the gas jet port 11-1 and the predischarge area 16-1, and jetted out toward the processing object 14 while supplied to the plasma processing space 15. Similarly, the processing gas is supplied from the gas supply port 21-2 of the gas supply section G2 of the lower electrode unit 4. This processing gas passes through the gas storage 9-2, the gas flow passage 26-2, the gas jet port 11-2 and the predischarge area 16-2, thus being supplied to the plasma processing space 15.
In this way, the processing gas introduced from the upper electrode unit 3 and the lower electrode unit 4 to the plasma processing space 15 is transformed into plasma under atmospheric pressure by the electric field formed in the plasma processing space 15. With this plasma-state processing gas, the processing object 14 conveyed and placed in the plasma processing space 15 is plasma processed. Herein, the term “atmospheric pressure” refers to a pressure range of 0.1 atmosphere to 2 atmospheres as an example. The processing gas to be adopted in this embodiment is given by helium, argon, oxygen, air and the like in the case of, for example, surface reforming of the processing object 14. However, this processing gas varies in composition from process to process, making it necessary to select optimum combination and mixing ratio as required.
Then, the processing gas that has passed through the plasma processing space 15 is temporarily stored in a discharge-side gas storage 20 shown in FIG. 1, passes through the discharge ports 22, being rendered harmless and discharged out of the system by an unshown discharge pump or blower, in some cases by harm removal equipment.
In this embodiment, an electric field is formed also between the side faces 5B-1, 5B-2 of the main electrode 5 and side faces 6B-1, 6B-2 of the side electrode 6 in the upper electrode unit 3. By this electric field, processing gas present between the first dielectric portion 7-1, with which the side faces 5B-1, 5B-2 of the main electrode 5 are covered, and the second dielectric portion 8-1, with which the side electrode 6 is covered, (i.e., present in the predischarge area 16-1) is transformed into plasma. Likewise, in the lower electrode unit 4, an electric field is formed also between the side faces 31B-1, 31B-2 of the main electrode 31 and the side faces 32B-1, 32B-2 of the side electrode 32. By this electric field, processing gas present between the first dielectric portion 7-2, with which the side faces 31B-1, 31B-2 of the main electrode 31 are covered, and the second dielectric portion 8-2, with which the side electrode 32 is covered, (i.e., present in the predischarge area 16-2) is transformed into plasma.
In this case, the plasma formation in these predischarge areas 16-1, 16-2 is fulfilled by properly selecting the distance between the first dielectric portion 7-1, 7-2 and the second dielectric portion 8-1, 8-2. This distance depends on the electric power and frequency given to the main electrode 5, 31 by the RF power supply 18, 33, the type and flow rate of the processing gas, the electrical characteristics, secondary electron emission coefficient and thickness of the first dielectric portions 7-1, 7-2, 8-1, 8-2, temperature and the like. In this embodiment, settings are given so that the intensity of the electric field formed in the predischarge areas 16-1, 16-2 becomes higher than that of the electric field formed in the plasma processing space 15.
In this embodiment, the plasma generated in the predischarge areas 16-1, 16-2 reaches up to creeping discharge portions 24 of the first dielectric portions 7-1, 7-2, so that electrons or excitation species are supplied directly to the plasma processing space 15 (creeping discharge). The creeping discharge portions 24 are present between the main electrodes 5, 31 and the plasma processing space 15.
As shown above, generating a plasma in the predischarge areas 16-1, 16-2 makes it possible to supply electrons or excitation species directly to the plasma processing space 15. As a result, when the plasma is not yet generated in the plasma processing space 15, discharge start in the plasma processing space 15 can be assisted. While discharge is in progress in the plasma processing space 15, the discharge can be stabilized. These effects can be further enhanced by eliminating edges and thereby smoothing the creeping discharge portions 24. As an example, when corner portions of the creeping discharge portions 24 are curve-shaped, it is desirable that the radius of curvature is set to 0.5 mm or more.
Utilization of the creeping discharge allows the following working effects (I) to (VI) to be expected.
(I) It becomes possible to widen the control range of a working distance between the main electrode 5 and the main electrode 31.
(II) Decomposition of the processing gas is carried out also in the predischarge areas 16-1, 16-2 besides the plasma processing space 15, so that the use efficiency of the processing gas is enhanced.
(III) As compared with conventional plasma generators, plasma can be maintained even if the electric field in the plasma processing space 15 is weakened, so that damage to the processing object 14 can be reduced eventually.
(IV) The equipment becomes compact, and flat-flow processing is facilitated.
(V) The gas supply sections G1, G2 are located on the rear face 5D, 31D side of the main electrode 5, 31, providing the structure that the processing gas is supplied to the predischarge areas 16-1, 16-2 between the main electrode 5, 31 and the side electrode 6, 32, where the gas jet ports 11-1, 11-2 of the gas supply sections G1, G2 are separated from the plasma processing space 15. Therefore, processing nonuniformities due to the opening pattern of the gas jet ports 11-1, 11-2 are less likely to occur.
(VI) The distance between the main electrode 5 and the main electrode 31 becomes easier to adjust.
As shown above, in this embodiment, during the generation of plasma both in the plasma processing space 15 and in the predischarge areas 16-1, 16-2, the conveyor rollers 13 are put into rotation to convey the processing object 14 so that the surface of the processing object 14 comes into contact with the plasma. This allows the plasma processing such as surface reforming, cleaning, machining and film deposition to progress by the reaction acceleration effect of active species and the physical etching effect of ions, so that desired processing on the processing object 14 can be achieved.
Therefore, according to this embodiment, a plasma which has a wide control range of the working distance under atmospheric pressure and which is stable can be generated, making it possible to provide a plasma processing apparatus capable of fulfilling both low running cost and high-speed processing.
In addition, the conveyor rollers 13 are adopted for the conveyance of the processing object 14 in this embodiment. However, this is only an example and a conveyor holder may be used for conveyance. It is also possible to perform local plasma processing on the processing object without performing the conveyance during the plasma processing. Further, pulse power supplies 19, 34 may be adopted instead of the RF power supplies 18, 33.
Also, according to this embodiment, by the provision of the first dielectric portion 7-1, with which the opposing face 5C and the side faces 5B-1, 5B-2 of the main electrode 5 are covered, and the second dielectric portion 8-1, with which the end portions 6C including the side faces 6B-1, 6B-2 of the side electrode 6 are covered, it becomes possible to prevent the main electrode 5 and the side electrode 6 from be damaged by discharge. Similarly, by the provision of the first dielectric portion 7-2, with which the opposing face 31C and the side faces 31B-1, 31B-2 of the main electrode 31 are covered, and the second dielectric portion 8-2, with which the end portions 32C including the side faces 32B-1, 32B-2 of the side electrode 32 are covered, it becomes possible to prevent the main electrode 31 and the side electrode 32 from being damaged by discharge.
In this embodiment, as to the gas supply sections G1, G2, it is possible to change the opening area and opening configuration of the gas jet ports 11-1, 11-2 by means of the flow adjusting plates 35-1, 35-2 serving as opening controllers, so that gas flow rate and gas flow velocity can be controlled. Therefore, flow rate and flow velocity of the processing gas to be supplied to the plasma processing space 15 can be controlled.
Also in this embodiment, the main electrodes 5, 31 are covered with the first dielectric portions 7-1, 7-2, and the side electrodes 6, 32 are covered with the second dielectric portions 8-1, 8-2 in the upper electrode unit 3 and the lower electrode unit 4. These first, second dielectric portions 7-1, 7-2, 8-1, 8-2 may also be formed directly on the surfaces of the main electrodes 5, 31 and the side electrodes 6, 32 by subjecting the main electrodes 5, 31 and the side electrodes 6, 32 to thermal spraying, anodic oxidation or the like. However, from the standpoints of manpower and cost in maintenance, the first dielectric portions 7-1, 7-2 and the second dielectric portions 8-1, 8-2 are preferably made interchangeable as components independent of the main electrodes 5, 31 and the side electrodes 6, 32. It is noted that the thickness value of the first dielectric portions 7-1, 7-2 and the second dielectric portions 8-1, 8-2 is determined in close relation to the repetition frequency of the RF power supplies 18, 33 (or pulse power supplies 19, 34), the type of the processing gas, and the material characteristics of the dielectric itself. Accordingly, although it is difficult to commonly determine the value, yet one general example is that the first dielectric portions 7-1, 7-2 and the second dielectric portions 8-1, 8-2, when given as independent components, are normally 5 mm or less thick, preferably. Particularly when the power supply frequency becomes above 1 MHz, then the thickness is 2 mm or less, more preferably.
Further, as the thickness of the first, second dielectric portions 7-1, 7-2, 8-1, 8-2 decreases, the electric field strength in the plasma processing space 15 and the predischarge areas 16-1, 16-2 can be increased while the first, second dielectric portions 7-1, 7-2, 8-1, 8-2 are weakened in their strength so as to be more fragile. Because of this, their thickness is preferably within a range of 0.5 mm to 5 mm for practical use. However, when the first, second dielectric portions 7-1, 7-2, 8-1, 8-2 are other than independent components, the thickness may be made smaller than the above range.
Further, in this embodiment, the length in the direction perpendicular to the drawing sheet of FIG. 1 is equal to or more than that of the processing object 14. Practically, for this embodiment, it is desirable for the structure to have a length 20% or more longer than that of the processing object 14 in the perpendicular direction to the drawing sheet of FIG. 1.
In this embodiment also, the refrigerant 10 is supplied from an unshown refrigerant supply unit or refrigerant supply facility, and passes through individual parts such as the main electrode 5 and the side electrode 6, thereafter being discharged. The refrigerant 10 may also be used for the role of maintaining the temperature of each part of the apparatus without being limited to the purpose of cooling the electrodes.
Also in this embodiment, the chamber upper part 1 and the chamber lower part 2 has an unshown gap adjusting-and-retaining mechanism including a micrometer head or the like so as to be able to hold the upper electrode unit 3 and the lower electrode unit 4 so that the electrode gap between the main electrode 5 and the main electrode 31 can be set. Besides, the chamber upper part 1 and the chamber lower part 2 serve the role of storing the processing gas to block its leakage to the outside until the used processing gas is discharged through the discharge ports 22.
That is, the chamber C is so structured as to be airtight free from gas leakage except the discharge ports 22 and the sites at which the processing object 14 comes in and out through the outlet and inlet 17 a and 17 b. Further, depending on the processes and the type of the processing gas used, a curtain mechanism or shutter mechanism against inert gas may be included at the outlet and inlet 17 a and 17 b of the processing object 14.
In the sequence of processes of the above plasma processing, it is important to stably generate a plasma and to increase the use efficiency of the processing gas in terms of processing performance and reduction of the running cost. Achieving these involves not only effective gas supply to the plasma processing space 15 but also adjustment of gas discharge and proper control of the flow rate and flow velocity of the processing gas.
For this purpose, there are needs for the mechanism for adjusting the supply-side conductance (flowability of gas) like flow adjusting plates 35-1, 35-2 shown in FIG. 3, and besides for taking balance of gas supply and discharge in consideration of conductance of the chamber upper part 1 and the chamber lower part 2 also at the discharge-side discharge ports 22.
In this case, it is convenient and practical to determine the dimensions of individual parts based on the following concepts.
More specifically, the effective cross-sectional area of the gas flow passage is assumed to be S (m²) and the length (distance) of the gas flow passage is assumed to be L (m). Since the gas flow under atmospheric pressure is a viscous flow, the foregoing parameters and the conductance U, which is an index of gas flowability, have a relation expressed by the following equation (1) on condition that the length in the perpendicular direction is infinite:
U=a·S ² /L (1)
where “a” is a constant which depends on the viscosity coefficient of gas species and the pressure.
As to the electric power supply, in addition to the RF power supply 18, a pulse power supply 19 or switching of both power supplies or a means of superimposition of both power supplies may be conceived. The electric power supply is desirably determined from the viewpoints of various conditions required for the process such as frequency and repetition frequency, the restriction of gas to be used, demanded processing performance, and the presence or absence of occurrence of any damage.
Herein, as an example, the RF power supply refers to one having a frequency of 1 kHz to 100 MHz, and the pulse power supply refers to one having a repetition frequency of 1 MHz or lower, a waveform rise time of 100 μsec. or less and a pulse application time of 1 msec. or less.
The flow adjusting plates 35-1, 35-2 shown in FIG. 3 are shown in a case where the gas jet ports 11-1, 11-2 are slit-shaped ones, but those otherwise may be shower hole-like ones. The upper and lower electrode units 3, 4 having the same opening pattern of the gas jet ports 11-1, 11-2, but this combination is not limitative and it is needless to say that all combinations of slit-shaped opening and shower-like opening are possible.
In addition, instead of the flow adjusting plates 35-1, 35-2 as opening controllers shown in FIG. 3, flow adjusting cams 43-1, 43-2 having an elliptical-shaped cross section may be provided at an inlet-side opening of the gas flow passage 26-1 as shown in FIG. 4. Rotating these cams 43-1, 43-2 to a specified angle about a central axis allows the inlet-side opening of the gas flow passage 26-1 to be continuously varied in cross-sectional area.
Next, in FIG. 5, an RF voltage waveform 36 given to the main electrode 5 by the RF power supply 18 is shown by solid line, and an RF voltage waveform 37 given to the main electrode 31 by the RF power supply 33 is shown by broken line. In one example shown in FIG. 5, the RF voltage waveforms 36, 37 are shifted in phase from each other by π. In this case, a voltage difference occurring between the main electrode 5 and the main electrode 31 is a sum (V1+V2) of an amplitude V1 of the RF voltage waveform 36 and an amplitude V2 of the RF voltage waveform 37. Also, a voltage difference occurring between the main electrode 5 and the side electrode 6 is V1.
In FIG. 6, one example of the pulse waveform given to the main electrode 5 by the pulse power supply 19 is shown by a solid line indicated by numeral 38, while one example of the pulse waveform given to the main electrode 31 by the pulse power supply 34 is shown by a broken line indicated by numeral 39, in the case where the pulse power supplies 19, 34 are provided in place of the RF power supplies 18, 33. In one example shown in FIG. 6, the pulse waveforms 38, 39 are shifted in phase from each other by π.
Furthermore, in FIG. 7, one example of waveform is shown by a solid line indicated by numeral 40 in the case where a DC waveform is given to the main electrode 5 by the pulse power supply 19, while one example of waveform is shown by a broken line indicated by numeral 41 in the case where a DC pulse waveform is given to the main electrode 31 by the pulse power supply 34.
In each of the examples shown in FIGS. 5 to 7, one example in which the phase difference between the voltage waveform given to the main electrode 5 and the voltage waveform given to the main electrode 31 is π has been shown. However, this phase difference may be other than π. Further, each of the voltage waveforms given to the main electrodes 5, 31 may be a waveform formed by switching over an RF waveform and a pulse waveform, or a waveform in which an RF waveform and a pulse waveform are superimposed on each other.
Furthermore, in the upper electrode unit 3 and the lower electrode unit 4, the main electrodes 5, 31 are placed in the center while the side electrodes 6, 32 are placed on both sides in the above embodiment. However, without being limited to this placement, a side electrode that is a ground electrode may be placed only on one side of the main electrode, or a plurality of side electrodes may be placed on one side of the main electrode. Further, a plurality of second electrodes may be placed on both sides of the main electrode.

Second Embodiment

Next, FIG. 8 shows a second embodiment of the plasma processing apparatus of the invention. The second embodiment differs from the foregoing first embodiment in that a lower electrode unit 50 is provided in place of the lower electrode unit 4. The lower electrode unit 50 is connected to the ground by an electric path 30.
The lower electrode unit 50 has a main electrode 51, and a fore end portion 51A of the main electrode 51 is covered with a dielectric portion 53. The fore end portion 51A has an opposing face 51C opposed to an opposing face 5C of the main electrode 5.
In FIG. 9, one example of RF voltage waveform given to the main electrode 5 by the RF power supply 18 is shown by numeral 42. The second embodiment is similar to the foregoing first embodiment in basic operations except that the lower electrode unit 50 is grounded. This second embodiment is suitable for cases where a rear face 14A of the processing object 14 does not need to be processed, producing advantages that the amount of gas used can be saved and the control for power supply is simplified.

Third Embodiment

Next, FIG. 10 shows a third embodiment of the plasma processing apparatus of the invention. The third embodiment differs from the foregoing first embodiment in that a dielectric spray deposit 61 on a surface of the main electrode 5 and a dielectric spray deposit 62 is formed on a surface of the main electrode 31. The first dielectric portion 7-1 covers the dielectric spray deposit 61, and the first dielectric portion 7-2 covers a dielectric spray deposit 62.
This third embodiment has the dielectric coat 61 formed on the opposing face 5C and side faces 5B-1, 5B-2 of the main electrode 5. Therefore, even when the first dielectric portion 7-1 is provided as a component independent of the main electrode 5 so that the dielectric coat 61 is overlaid with the first dielectric portion 7-1, a gap (space) formed between the main electrode 5 and the first dielectric portion 7-1 can be suppressed to a minimum. Also, the embodiment has the dielectric coat 62 formed on the opposing face 31C and side faces 31B-1, 31B-2 of the main electrode 31. Therefore, even when the first dielectric portion 7-2 is provided as a component independent of the main electrode 31 so that the dielectric coat 62 is overlaid with the first dielectric portion 7-2, a gap (space) formed between the main electrode 31 and the first dielectric portion 7-2 can be suppressed to a minimum.
Therefore, according to this embodiment, reduction of the electric field strength in the plasma processing space 15 and the predischarge areas 16-1, 16-2 can be suppressed, and discharge at the gap can be suppressed so that occurrence of any power loss and electrode damage can be suppressed. In addition, the gap is preferably 500 μm or less, and more preferably 100 μm or less.

Fourth Embodiment

Next, FIG. 11 shows a fourth embodiment of the plasma processing apparatus of the invention. The fourth embodiment differs from the foregoing first embodiment in that a chamber D composed of a chamber upper part 71 and a chamber lower part 72 is provided instead of the chamber C composed of the chamber upper part 1 and the chamber lower part 2, the chamber D having two upper electrode units 3 and two lower electrode units 4. Main electrodes 6, 6 of these two upper electrode units 3, 3 are connected to the RF power supply 18 by power transfer paths 27-1, 27-2, respectively, and the main electrodes 6, 6 are connected to the ground by electric paths 28-1, 28-2, respectively. Also, the main electrodes 31, 31 of the two lower electrode units 4, 4 are connected to the RF power supply 33 by the power transfer paths 29, respectively. The side electrodes 32, 32 are connected to the ground by the electric path 30.
In this fourth embodiment, since a plural pairs of the upper electrode unit 3 and the lower electrode unit 4 are provided, it becomes implementable to improve the processing performance when identical plasma processing is performed in the plasma processing space of each pair. Further, when different plasma processings are performed in the plasma processing space of each pair, it becomes possible to perform sequential processing by the flat-flow method.
The invention being thus described, it will be obvious that the invention may be varied in many ways. Such variations are not be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

1. A plasma processing apparatus comprising:

a gas supply section for supplying a specified processing gas to a plasma processing space where a plasma processing object to be processed is placed;

a first electrode which is opposed to the plasma processing space and which generates an electric field in the plasma processing space;

a second electrode which is opposed to the first electrode with the plasma processing space interposed therebetween;

a third electrode which is opposed to a side face of the first electrode with a specified gap, the side face being adjacent to an opposing face of the first electrode facing the plasma processing space; and

a first power supply section for supplying a first electric power to the first electrode.

2. The plasma processing apparatus as claimed in claim 1, further comprising:

a first dielectric portion with which the opposing face and the side face of the first electrode are covered; and

a second dielectric portion with which a side face of the third electrode opposed to the side face of the first electrode is covered, wherein

the first dielectric portion and the second dielectric portion are opposed to each other with a specified gap therebetween.

3. The plasma processing apparatus as claimed in claim 1, wherein

the third electrode is grounded,

a second power supply section for supplying a second electric power to the second electrode is provided,

the first electric power supplied to the first electrode by the first power supply section and the second electric power supplied to the second electrode by the second power supply section are different from each other in at least one of phase and amplitude, and wherein

the first electric power and the second electric power are

RF power, or pulse wave electric power, or electric power obtained by switching RF power and pulse wave electric power, or electric power in which RF power and pulse wave electric power are superimposed on each other.

4. The plasma processing apparatus as claimed in claim 1, wherein

the apparatus has a structure that processing gas supplied by the gas supply section, after passing through the gap between the side face of the first electrode and the third electrode, passes through the plasma processing space between the first electrode and the second electrode.

5. The plasma processing apparatus as claimed in claim 1, wherein

the gas supply section comprises:

a gas jet port for supplying the processing gas to the gap between the first electrode and the third electrode; and

an opening controller for changing at least one of opening area and opening configuration of the gas jet port.

6. The plasma processing apparatus as claimed in claim 2, further comprising

a dielectric coat formed on the opposing face and the side face of the first electrode, wherein

the first dielectric portion covers the dielectric coat.

7. The plasma processing apparatus as claimed in claim 6, wherein

the gap between the first electrode and the first dielectric portion is not more than 500 μm.