Electrical computers and digital processing systems: virtual mac – Task management or control – Process scheduling
Reexamination Certificate
2001-01-04
2003-05-13
Berman, Jack (Department: 2881)
Electrical computers and digital processing systems: virtual mac
Task management or control
Process scheduling
Reexamination Certificate
active
06562079
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is a U.S. National Phase Application under 35 USC 371 of International Application PCT/JP99/03650 (not published in English) filed Jul. 6, 1999.
1. Technical Field
This invention relates to a microwave discharge apparatus for creating and keeping a plasma with efficiently absorbing microwave and not generating much reflected wave, and efficiently cooling the discharge vessel made of dielectric substance.
2. Background Art
Surface treatments such as etching, Plasma Chemical Vapor Deposition (PCVD) and heat treatment, has already been applied to various industrial fields. Particularly, Plasma Downstream Treatment with setting a sample in the down stream of plasma causes little damage on the sample and is expected for various applications and developments mainly in the field of semiconductor in the future.
The most important role of plasma in Plasma Down Stream Treatment is to efficiently generate active particles for use in the process. A microwave on 2.45 GHz band is often selected to excite plasma, because plasma-generating apparatuses using the waveband can be produced at low cost and the microwave with the band range enables more efficiently dissociating gas molecules than RF.
The most typical type of practical microwave plasma-generating apparatuses has a structure that a cylindrical dielectric tube, often made of quartz, is provided along an axis vertical to a rectangular-waveguide wall normal to the electric field direction of the microwave, or the H plane wall, through the center of the wall.
A dielectric tube is always exposed to an incident wave in the electric-discharge structure if an unreflective termination is formed at a point reached by the microwave passing through the tube, on the opposite side to the magnetron. However, a terminal face is generally formed with a plunger in order to reflect a wave to generate a standing wave and the dielectric tube is located at the maximum point in the electric field. The structure is applied to generate plasma easily in the stronger electric field than the one created just by the incident wave and to convert the energy efficiently from the microwave into plasma.
However, when plasma is generated, the impedance in the dielectric tube changes considerably, from the previous one almost same as the one under vacuum, and then the electric field is disturbed around the dielectric tube and has the maximum value at another point.
The proper gas composition and pressure etc. should be selected to apply to a requested plasma treatment. The impedance of the plasma depends on the factors such as gas composition and pressure etc. Therefore, the phase of standing wave at the dielectric tube should be properly tuned in the process with, for example, a plunger. Consequently, the structure is not practically useful. Further, the dielectric-tube cannot include many electric peaks of the microwave due to the structure itself. The energy is converted into plasma at low rate. The structure suffers much loss in the thermal conversion.
Generally, an isolator and a matching device are provided between the microwave emitting part and the electric-discharge load to deal with the reflected standing wave. The structure costs much because of the attachment.
The plasma-generating apparatus, which has a cylindrical dielectric tube penetrated obliquely from the center of the H plane wall or located parallel to the direction in which the microwave travels at the cross-sectional center of the waveguide, was devised and put to practical use by MTI Inc. or Fusion Inc. so as to follow the shift of the maximum point in the electric field on generating plasma and generate plasma easily.
In each structure, a dielectric tube occupies just some area linking one central part of the waveguide wall perpendicular to the microwave electric field direction, or the H plane wall, to the counterpart of wall in the cross section of the waveguide. Each side of the area is vacant.
Therefore, it is difficult to have whole microwave absorbed in such structures without passing through both sides of the dielectric tube.
Gas certainly passes through the maximum point of the electric field, if a microwave is in H
01
transmission mode. The dielectric tube, however, does not always cover the maximum point, if the point is not around the center of the H-plane wall, for example, in H
02
mode. Therefore, if a rectangular waveguide is used in the apparatus, the microwave has to be tuned into the H
01
transmission mode. The design of the apparatus is severely restricted due to the reason.
Furthermore, after plasma is generated in the cylindrical dielectric tube, the condition is equivalent to the one in the situation that a metallic rod is inserted into the waveguide. Then, the transmission mode in it changes and reflected wave is generated.
Therefore, a solid circuit such as a matching device or an isolator has to be provided between the magnetron microwave oscillator and the load. That results in not only the restriction in designing an apparatus but also lowering of efficiency as each functional parts are connected in the solid circuit, and the electric transmission has a loss.
A microwave plasma apparatus, which is devised to be provided a microwave transmission window in it parallel to the E plane wall, on the E plane wall of the waveguide or the extension plane of the wall so that plasma can absorb whole microwave passing through the waveguide, was disclosed as an apparatus overcoming the disadvantage in Japanese Patent Publication No. 5-3732.
In the disclosure, however, a dielectric material for the microwave-transmission window covers most of the wall, or the H plane wall, normal to the microwave electric field direction and a reflection from the plasma-generating part surrounded by dielectric members itself increases with the plasma-generating part projecting into the waveguide. If the plasma-generating part projects out of the waveguide wall, the height, or the length vertical to the H plane, of the plasma-generating part is required to be possibly decreased to maintain the transmission mode in the waveguide. Therefore, the structure also restricts the design of an apparatus severely and is inferior for the cost of production. An apparatus, which has a plasma-generating part formed unreflective-termination-shaped in order to solve the problem of the electric field change on generating plasma and maintain the plasma efficiently thereafter, was disclosed in Japanese Non-examined Patent Publication No. 7-220896 and 7-220897. In the structure, however, a disturbance of the electric field in the waveguide rises before a plasma discharge. Plasma is not easily generated with excitation by a microwave, depending on gas component for requested plasma because of its impedance, and actually reflected wave is generated, though the plasma generating part in the dielectric tube can be unreflective-termination-shaped after a plasma discharge.
Thus, the standing wave affects the magnetron oscillator while plasma is maintained. Practically, at least, an isolator has to be provided between the microwave oscillator and the load to protect the magnetron. The installation induces the restriction of cost and design on the apparatus, and lowers efficiency by transmission loss. Furthermore, in the structure, electric-discharge particles are heated to a high temperature by plasma radiation heat, and the heating prompts recombination reaction of radicals dissociated by plasma for a treatment. Consequently, the structure has a disadvantage of lowering dissociation efficiency.
Accordingly, an object of the invention is to eliminate the above disadvantages of the existing microwave discharge apparatuses. In other words, the object is to solve the problem such as the change of the electric field and the generation of a standing wave on generating plasma and maintain the plasma efficiently thereafter.
It is another object of the present invention is to produce apparatuses with abilities not only to induce plasma dissociation efficiently for the applied
Berman Jack
Frishauf Holtz Goodman & Chick P.C.
Smith, II Johnnie L.
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