Wave transmission lines and networks – Coupling networks – With impedance matching
Reexamination Certificate
2002-02-27
2003-09-16
Nguyen, Patricia (Department: 2817)
Wave transmission lines and networks
Coupling networks
With impedance matching
C333S017300, C333S032000, C333S0990PL
Reexamination Certificate
active
06621372
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an impedance matching device used for a plasma dry process for production of a semiconductor and the like. Particularly, the invention relates to a technique which improves response to a fluctuation of a load impedance. The impedance matching device intervenes, for example, in a transmission path of a high-frequency power between a high-frequency power supply and a load of a plasma chamber or the like. An impedance of the transmission path is matched with an impedance of the load so that reflection of a power from the load is eliminated, and an incident power from the high-frequency power supply is utilized on the load side most efficiently.
2. Description of the Related Art
In a plasma dry process for production of a semiconductor, in recent years, a frequency of a high-frequency power to be used is heightened from an RF band (up to 30 MHz) to a VHF band (30 to 300 MHz) and further to an UHF band (300 MHz to 3 GHz) in order to fine a substrate pattern of a semiconductor element. It is an impedance matching device to supply such a high-frequency power efficiently to a load of a plasma chamber or the like.
The impedance matching device which intervenes in a middle of a transmission path, such as a coaxial tube and a waveguide, of a high-frequency power has a plurality of stubs respectively in positions separated from one another in an axial direction of the tube. A distance of the adjacent stubs is ¼ of a tube inner wavelength &lgr;g in the coaxial tube in a frequency of the high-frequency power to be applied.
A plunger type stub has a variable length coaxial tube in which a conductor portion and an outer cylinder portion are provided concentrically, an end short-circuiting electrode which slides in the variable length coaxial tube along the axial direction. In order to make it possible to carry out impedance matching over a wide area of Smith's chart, a sliding range of the end short-circuiting electrode is generally set to &lgr;g/4. Moreover, an entire length of the stub is not less than &lgr;g/2.
The entire length of the stub is supposed to be shortened to about &lgr;g/4 by eliminating a protruding operation of the plunger and allowing the end short-circuiting electrode to slide in a reciprocating way by means of a wire.
However, in this case, it is necessary to bring each end short-circuiting electrode into close contact with each conductor portion and outer cylinder portion in each stub, and thus frictional resistance of sliding is large. Moreover, since the impedance matching is carried out by adjusting the length of the tube path according to displacement of each end short-circuiting electrode, the entire length of each stub is fairly long, and their accuracy of axial center is low.
Due to the large sliding resistance and the low accuracy of the axial center, a moving speed of the plunger becomes slow, and thus response of the impedance matching to a fluctuation of a load impedance is not good. Further, due to the large frictional resistance of sliding, the end short-circuiting electrode, the outer cylinder portion of each stub, abrasion and deterioration of each conductor portion easily proceed in the long time use, and this decreases the life.
Furthermore, since it is difficult to use the long stub in a laid posture, the impedance matching device is installed in an upright posture, but this occupies a large space of a room in a height-wise direction, and this interferes the installation.
SUMMARY OF THE INVENTION
Therefore, a main object of the present invention is to provide an impedance matching device which is capable of being compact and improving response of impedance matching to a fluctuation in a load impedance such as a behavior of a plasma load.
Another object of the present invention is to provide an impedance matching device which is capable of lengthening its life and widening degrees of freedom of installation.
Still another objects, characteristics and advantages of the present invention will become apparent by the following description.
The impedance matching device of the present invention solves the problems mentioned above by taking the following measures.
The impedance matching device according to the present invention includes a plurality of stubs which are provided to a main coaxial tube so to be separated from one another in a premised structure. As for the main coaxial tube, an opening of one end in the tube axial direction is connected to a high-frequency power supply side and an opening of the other end in the tube axial direction is connected to a load side of a plasma chamber and the like. The stubs are serially provided to at least two places of the main coaxial tube separated by a predetermined interval in the tube axial direction in a branch state. In this premised structure, the opening of one end of the main coaxial tube may be connected directly to the high-frequency power supply or connected to the coaxial tube extended from the high-frequency power supply. Moreover, the opening of the other end of the main coaxial tube may be connected directly to the load or connected to the coaxial tube extended from the load. A number of stubs to be provided is preferably three in general, but may be two or not less than four. Directivity of the stubs is normally vertical with respect to the tube axial direction of the main coaxial tube but is not necessarily to be always limited to this. If a stub is extended obliquely, its essentiality does not change. A providing interval of a plurality of stubs is generally and preferably ¼ of a tube inner wavelength &lgr;g, but since the interval is not a characteristic itself in the present invention, it is not particularly limited.
According to the present invention, the impedance matching device having the above structure as the premise is characterized by including the following requisites. In other words, each of the plurality of stubs includes a variable capacity capacitor whose one end is to be jointed to an internal conductor of the main coaxial tube, and an electrically conductive capacitor cover to be jointed to an outer conductor of the main coaxial tube so as to be electrically joined to the other end of the variable capacity capacitor as well as to cover a surrounding of the variable capacity capacitor. Further, each stub includes a drive motor which is arranged on an outside of the capacitor cover so as to drive a movable side electrode of the variable capacity capacitor.
The impedance matching device of the present invention executes impedance matching by adjusting an electrostatic capacity of the variable capacity capacitor, unlike a plunger type impedance matching device which executes impedance matching by adjusting a length of a tube path in a stub in accordance with a displacement of an end short-circuiting electrode (short plunger). Unlike the adjustment of the length of the tube path, the adjustment of the electrostatic capacity has large degrees of freedom of space. In the case of the plunger system, the adjustment of the length of the tube path is limited to a relationship of 1:1 in the displacement in the axial direction. In other words, an adjustment amount of the length of the tube path is completely equal with a displacement amount of the end short-circuiting electrode in the axial direction. However, in the case of the adjustment of the electrostatic capacity, for example, cylindrically-shaped movable side electrode and fixed side electrode are inwardly and outwardly fitted to each other so as to form a multiplayer so that the electrostatic capacity can be increased or decreased in a state that the displacement of the movable side electrodes is amplified. Namely, the electrostatic capacity can be changed relatively greatly by comparatively small displacement. Therefore, a moving amount of the movable side electrode for the impedance matching in accordance with a fluctuation of the load impedance may be small. Time required for moving the movable side electrode by a predetermine
Itadani Koji
Kaneko Eiji
Kondo Kazuki
Matsuno Daisuke
Daihen Corporation
Jordan and Hamburg LLP
Nguyen Patricia
LandOfFree
Impedance matching device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Impedance matching device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Impedance matching device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3110767