DC power supply apparatus for a plasma generating apparatus

Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter

Reexamination Certificate

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Details

C363S131000

Reexamination Certificate

active

06760234

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a DC power supply apparatus, in particular, a DC power supply apparatus for supplying a DC power to a plasma generating device for a sputtering.
2. Description of Related Art
According to an earlier development, in a process for producing a semiconductor or the like, as a power supply apparatus (hereinafter, occasionally referred to as “DC power supply”) for supplying a stable DC power to a plasma generating device for a sputtering, a voltage type of DC power supply apparatus which functions as a voltage source for a load, was used.
FIG. 9
shows an example of a structure of a DC power supply
5
according to an earlier development. In
FIG. 9
, the DC source
5
comprises a breaker
3
, a rectifier
11
, a DC filter
12
, an inverter
121
, a transformer
14
, a rectifier
15
and a DC filter
122
.
The rectifier
11
is a bridge-type of three-phase full wave rectifying circuit or the like, which uses a diode or the like as a rectifying element. The rectifier
11
carries out a full-wave rectification of an AC power inputted from a commercial power supply unit
2
through the breaker
3
, to convert it into a DC power.
The DC filter
12
is an LC filter having a DC reactor L
F1
and a smoothing capacitor C
F1
, and smoothes the DC power rectified by the rectifier
11
.
The inverter
121
comprises a bridge-connected semiconductor switch, and converts the DC power smoothed by the DC filter
12
into an AC power. The inverter
121
is a voltage type of inverter which is operated by a pulse width control, a pulse frequency control or the like.
The transformer
14
is one having two windings (a primary winding and a secondary winding) which are electromagnetically coupled with each other. The transformer
14
transforms the output voltage of the inverter
121
, which is applied to the primary winding, according to the turn ratio thereof. Then, the voltage is generated by the secondary winding.
The rectifier
15
comprises a bridge-type of full wave rectifying circuit or the like, which uses a diode or the like. The rectifier
15
rectifies the AC power generated by the secondary winding of the transformer
14
, to convert it into a DC power.
The DC filter
122
is an LC filter having a DC reactor L
F3
and a smoothing capacitor C
F3
, and smoothes the DC power rectified by the rectifier
15
.
As described above, after the DC power supply
5
generates a DC power by rectifying and smoothing the input AC power, the generated DC power is converted into an AC power by the inverter
121
. After the voltage transformation, the DC power supply
5
outputs a DC power by rectifying and smoothing the AC power again. That is, the DC power supply
5
operates as a voltage source. The discharge current is determined in accordance with the output voltage and the impedance of the plasma generating device
4
. That is, the DC power supply
5
is a voltage type of DC power supply apparatus.
During the plasma generation, if an arc discharge is caused in the plasma generating device
4
, there is some possibility that a film is damaged. As a treatment for an arc discharge which is harmful to a film, the following three methods (I) to (III) have been used.
(I) A power supply is temporarily stopped.
In this case, when the generation of the arc discharge is detected, the operation of the DC power supply
5
is stopped. After a certain time elapsed, the operation thereof is restarted.
(II) A reverse voltage is applied by an LC resonance.
In this case, in the DC power supply
5
, an LC resonance circuit having a reactance and a capacitor is provided between the DC filter
122
and the plasma generating device
4
. By generating a reverse voltage by the LC resonance which is one of the resonance phenomena, the generated arc is self-arc-extinguished.
(III) A reverse voltage is applied by a semiconductor switch element.
In this case, in the DC power supply
5
, a reverse voltage generating circuit
20
having a semiconductor switch element is provided between the DC filter
122
and the plasma generating device
4
. When the generation of the arc discharge is detected, a reverse voltage is generated by the semiconductor switch element to forcedly arc-extinguish the generated arc.
Among the reverse voltage generating circuits, there are some ones which can detect the increase in discharge current or the decrease in discharge current and can forcedly arc-extinguish the arc before the arc current flows.
As described above, as a treatment for the arc discharge, there are three methods (I) to (III). According to the required quality of the film, one method was selected from the three methods (I) to (III).
However, the DC power supply
5
according to an earlier development, has the following problems.
(1) When the arc discharge is frequently generated, an output current cannot be controlled by the above methods (I) to (III).
In the method (I) in which the power supply is temporarily stopped, because the operation of the DC power supply
5
is stopped whenever the arc is generated, the operation of DC power supply
5
and the stop of the DC power supply
5
are frequently repeated. Further, in this method, because the energy of the DC filter
122
is released even though the operation of the DC power supply
5
is stopped, the film is damaged.
In the method (II) using the LC resonance or the method (III) using the semiconductor switch, while the arc-extinguishing operation is repeated, the output current of the DC power supply
5
gradually increases. When the output current exceeds a predetermined value, the DC supply source
5
is stopped by a protect circuit like the method (I).
In order to prevent the increase in output current, there was a method in which a DC reactor is inserted in series. However, because the DC reactor generally has a large size, the problems relating to the cost, the structure and the storage are occurred.
(2) The restart of the normal discharge is delayed.
In the method (I), because the DC power supply
5
is restarted, the time for restarting the DC power supply
5
is required. Even in the methods (II) and (III) in which the DC power supply
5
is not required to stop, the reflow of the discharge current which flows again is delayed by the wiring impedance and the like. Therefore, there is some possibility that the restart of the normal discharge is delayed.
In the present sputtering process, the discharge time tends to be shortened in one process. Therefore, when the arc discharge is frequently caused, the time delay caused by restarting the discharge is not negligible. As a result, the sum of time for the normal discharge becomes short. The degradation in quality of the film, such as a lack of thickness thereof is caused.
(3) Because the discharge current cannot be controlled for the constant voltage characteristic of the plasma generating device, the operation of the DC supply source
5
is not stable.
When the plasma generating device
4
treats as a load of the DC supply source
5
, the voltage-current characteristics are close to the constant voltage characteristics. That is, although the current is largely changed on the basis of the intensity of the flowing DC power, the voltage is hardly changed. Therefore, for the DC supply source
5
, the current is controlled more than the voltage by the control of the power to be supplied to the plasma generating device
4
.
However, as described above, the DC power supply
5
is a voltage type of DC power supply apparatus which functions as a voltage source. That is, the DC power supply
5
supplies an output power as a voltage source. This easily causes the DC power supply to be unstable as compared with the DC power supply which function as a current source. Further, unnecessary resonance phenomena and the hunting are caused.
As described above, the DC power supply
5
according to an earlier development, has the above three problems (1) to (3). That is, the following three functions are required.
(a) An arc-extinguishment is certainly carried out

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