JPS6366900A - Power supply device for plasma discharge - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial Tll and 1F co
), I) For devices that use plasma discharge, such as C sputtering, is it possible to prevent the transition to arc discharge at the start of discharge, and to protect the workpiece? Regarding the Ii source device.

BACKGROUND ART Discharge phenomena under reduced pressure have been studied for a long time and are explained as shown in FIG.

In other words, a small amount of ions ionized by cosmic rays or ultraviolet rays exist in gas molecules under reduced pressure, but when voltage is applied to an electrode installed in a container under reduced pressure, these ions are collected. , flows as an electric current. This amount is small, and eventually reaches point A, where almost the entire amount is collected.
saturate. This region is called the Townsend region, and the discharge voltage and sheet weight current increase iJO almost proportionally.

Then, when point B is reached, the electrons accelerated by the electric field collide with the gas molecules, ionizing them in sufficient quantity to self-sustain the discharge. This region is divided into two types: ■ a normal glow discharge region where the discharge covers the entire electrode, the current density is almost the same, and the discharge voltage remains almost constant; and ■ the discharge covers the entire electrode and the current It is divided into an abnormal glow discharge region where the density increases and the discharge voltage increases as a result.

In the abnormal glow discharge region, if the current is not increased further, the family ff171u pressure suddenly decreases and transitions to an arc discharge where the current can be increased to any extent.

Arc discharge under reduced pressure differs from arc discharge under normal pressure in that minute bright spots, so-called cathode bright spots, are generated at the cathode, and ionized gases, or ions, bombard the electrode with a significant current density. Furthermore, the movement of the electrode bright spot on the electrode often causes dendritic scratches. Therefore, if a processed product is used as a cathode, serious defects may occur. In addition, for example, in sputtering, etc., when the material to be sputtered is used as yin and yang, bumping is often not removed, and fine dust due to bumping may be deposited on the substrate or This may lead to pinhole defects or, in basic cases, damage to the cathode or power supply.

Returning to FIG. 3 again, the voltage at which the discharge reaches point B in the diagram and maintains itself is called the breakdown voltage or spark voltage. As shown in FIG. 4, the breakdown voltage changes in a V-shape as the product pXd of the pressure p in the vacuum vessel and the core gap d changes.

In other words, keep the electrode gap d constant and increase the pressure p.
The breakdown voltage gradually decreases, but increases again after reaching a certain minimum value. Therefore, on the low pressure side, the lower the pressure, the higher the breakdown voltage, and in some cases, 514
The upper limit of the normal glow discharge region, that is, the arc discharge region may be reached. Figures 5 and 6 show this state. In addition, Fig. 5 shows the horizontal axis on a logarithmic scale.
In FIG. 6, the horizontal axis is a linear scale.

The arc discharge transition point C in FIGS. 5 and 6 is affected by foreign matter in the vacuum container, minute dust, or the surface condition of the electrode, but is generally unstable and cannot be predicted.

In particular, when the electrodes are renewed, no matter how clean they are in the atmosphere, microscopic contamination, release of adsorbed gas, etc.
There is a tendency for the transition from glow discharge to arc discharge to increase due to new adhesion caused by the flying up of fine dust during exhaust. This tendency is particularly noticeable immediately after the start of glow discharge, and by repeating glow discharge thereafter, the surface of the electrode is generally purified and migration is reduced. In other words, it can be said that failures due to arc discharge are most likely to occur when glow discharge is activated.

Supplying power to plasma? As the Ii source device, three types of control methods are used: constant voltage, constant current, and constant power.

FIG. 7 shows ideal characteristics of each of these control methods. In reality, since closed loop control is performed by a feedback circuit, it takes some time to follow sudden changes in negative 6;j and reach a stable state. For example, silisk control schemes often used in high power power supplies often require extensive cycling of the power supply frequency to reach a stable state.

Against this background, the transition from glow discharge to arc discharge will be considered by taking as an example the case where a constant current control method is used in the device having the discharge characteristics shown in FIG. 6.

FIG. 8(a) shows the temporal characteristics of the constant voltage power supply. When the power is turned on at time 0, the voltage rises and reaches point A in FIG. 8(b), that is, the breakdown voltage. Here, route A-+ shown in FIG. 8(b)
During the time when the discharge grows through B-C, the pressure inside the container is I.
As a result of actual measurement in an argon atmosphere on an O-2 Torr stand,
The time was approximately 0.5 ms.

On the other hand, the response time of the constant current power supply from point a to point C in Figure 8(a) is approximately 10m5.As a result, the discharge path is as shown in Figure 8(b). The discharge voltage and current characteristics are transferred through the path A-+D-B-C-13-D shown in FIG. If there is an arc discharge transition point on the B side from point C, arc discharge will immediately occur, causing the above-mentioned problems.

To avoid such inconveniences, a device called a "discharge prevention device" is sometimes used.

As shown in FIG. 9, this is used by being inserted between the power supply and the power supply in the vacuum container. This discharge prevention device is designed to prevent
If the arc transitions to an arc due to some cause, it is detected and the output voltage is reduced to zero or a reverse voltage is applied to temporarily cut off the arc. As a result, the presence of attached dust, etc., which causes the arc transition, is burned out by the energy of the arc discharge and is reduced. However, in many cases, the arc discharge energy is not extinguished once, and the arc discharge is repeated until the cause of the transition is eliminated. In other words, the process of arc migration - arc interruption - restart of discharge - arc migration is repeated.

Therefore, the above-mentioned discharge prevention device substantially repeats arc discharge, and does not completely eliminate arc discharge. Therefore, in some cases, there remains a risk of damage to expensive workpieces that are exposed to voltage.

[Problems to be Solved by the Invention] As mentioned above, the conventional plasma discharge power supply device has the following problems:
There were some drawbacks as follows.

■When the discharge starts, it causes arc discharge, which can damage expensive workpieces such as brackets and cause problems with the power supply.

When a 111 device using a feedback control method is used in a relatively low pressure region, compared to the growth time of a discharge, Ii source device response time is slow. For this reason, during a short period of time when the response of the power supply device is sluggish, the discharge grows into an abnormal glow discharge area that has the risk of triggering and causing arc discharge, and may also cause lumps and foreign objects. In some cases, the problem even progressed to arc discharge.

■In a power supply device equipped with a starting power supply and electrodes, by the time the main power supply reaches stable operation, the discharge will grow to an area where arc discharge may occur due to the same reason as above. .

■Even if conventional discharge prevention devices are used, it is not possible to completely eliminate the transition to arc discharge.

This invention was made against this background, and it is a plasma f/l, electric power source that can completely eliminate the risk of transition to arc discharge and start glow discharge smoothly. The purpose is to provide equipment.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a power supply device for a device applying plasma such as ion blating, plasma CVD, DC sputtering, etc., which includes a plasma generation electrode, For said plasma generation via the first switch? 1i is connected in series with the mains power supply when the first switch is off, and the current 1L11 is connected to the mains power supply connected to the pole ii′i through the limiting body and the second switch 2λ. Connect to the plasma generator 41mi power supply 1.]- for startup τu
(At 15:00, the first switch of 1111 is turned off and the second switch is turned on, and the current flowing to the plasma generation pole is set to the normal glow emission region by the current limiter. After the glow discharge, the main 7r
After a set time period has elapsed in which the operation of the i source is stable and the possibility of transition from glow discharge to arc discharge at the initial 1υI has elapsed, i'i? It is characterized by comprising a switch driving means for turning off the first Q switch between the i and the first Q and the second switch of the n71.

1 Effect] According to the above configuration, the current limiter inserted in series between the starting power source and the electric power source limits the current without time delay, and the current at the start of glow discharge is kept in the normal glow discharge region. Can be set to Next, this starting current adjusts the I'll state of the main power supply for a certain period of time, prevents overshoot of the power supply, etc., and executes switching to the main power supply.

In this case, surface treatment equivalent to that of plasma or photon can be performed in the normal glow discharge region, eliminating the risk of transition to arc discharge.
For I use, the main type J console can be made with stability of 4i-Ro2.

[Example code] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention.
main? Constant voltage control is adopted for 1iXA.

In the figure, 1 is a vacuum device for plasma generation, 2 is a main power source, and 3 is a starting power source. The anode 1a of the vacuum device 1 is grounded. On the other hand, the cathode tb is the contact point 4 of the electromagnetic switch 4.
a, and a starting power source 3 via a current limiter (resistance) 5
It is connected to the negative output terminal of the main power source 2 via the contact 6a of the electromagnetic switch 6.

The main power supply 2 includes a transformer 2a, a full-wave rectifier 2b that rectifies the output of the transformer 2a, a voltage detector 2c that detects the output voltage of the rectifier 2b, and is controlled by the detected voltage of the pressure detector 2c. It is composed of a voltage control circuit 2d and a switch 2e. The voltage control circuit 2d is configured mainly of Cyrisk, and controls the voltage supplied to the transformer 2a to be constant based on the detected voltage from the voltage detector 2c.

The starting claw jiff 3 is a transformer 3a and a full wave rectifier 3.
b, and a switch 3c. The positive output terminal of the rectifier 3b is connected to the negative output terminal of the rectifier 2b.

On the other hand, the positive output terminal of the rectifier 2b is grounded, and the current flowing through this output terminal is detected by the switch drive circuit 7. Opening and closing? :; The drive circuit 7 includes a relay for detecting energization that turns on when the current exceeds a certain value, and is activated by this relay, turns on the switch 6 after a certain period of time, and then turns off the switch 4. It has a time limit circuit.

Note that illustrations of components not directly related to this embodiment, such as an exhaust device and a gas supply device, are omitted.

In such a configuration, the main power source 2 is set to a glow discharge operating state. For example, in the case of constant voltage control, the voltage is set to an appropriate value, and in the case of constant current control, 7Ilt current is set to an appropriate value. In addition, when the main power supply 2 and the starting power supply 3 are connected in series, 71i failure of the vacuum device l a, l b
When the starting voltage applied between the electrodes is higher than the voltage at point A in FIG. 8 (for example, point Aa in FIG. 2) and a glow discharge occurs between the electrodes, it flows to electrodes 1a and 1b. The current is set to a value near the upper limit of the normal glow discharge region.

After such settings, the switches 2e and 3c are turned on while the switches 4 and 6 are off. Then,
The switch 4 is turned on by the switch 21 drive circuit 7. Thereby, the main power source 2 and the starting power source 3 are connected in series. Then, the voltage set at point Aa in FIG. 2 is limited by the current limiter 5 at the start of discharge, and reaches point B in FIG. 2. At this time, electricity +%
A current rB flows through 1a and 1b. In other words, the main power supply 2, the starting power supply 3, the current limiter 5, and the electrode 1a
, l b , and the initial state of the main power supply 2 is set.

Further, this current is detected by the 7111 flow detection relay in the switch drive circuit 7, and the 1st time circuit in the switch 1 operation circuit 7 is activated.

The above-mentioned time limit circuit turns on the switch 6 and then turns off the switch 1 after a certain period of time after it has been activated.

This connects the main power source 2 to the electrodes 1a and 1b, and disconnects the starting Ti 8Q 3. At this time,
The discharge state shifts from point B to operating set point C shown in FIG.

According to this embodiment, the operation of the main power supply 2 is set and stabilized within the time determined by the time limit circuit, and then the second
The transition from point B to point C in the figure is performed smoothly without going through any disturbances such as electronic overtones. That is, the double pressure detected by the voltage detection circuit 2c is fed back to the voltage control circuit 2(1), and is maintained in a stable state within the above-mentioned predetermined time.

Note that the following changes may be made to the configuration of the above embodiment.

(2) As the current limiter, it is also possible to use circuit elements such as semiconductor elements and vacuum tubes in addition to resistors.

■Semiconductor elements and vacuum tubes can be used as switches.

1 of the invention; JJ results] As explained above, this invention applies voltage to the electrodes with the main power source and the starting power source connected in series at the time of starting discharge, and for a certain period of time after starting. During this period, the current flowing through the electrode is limited by the current limiter while maintaining the normal glow discharge region, and after the above-mentioned certain period of time has elapsed, the main power source and the electrode are connected, resulting in the following effects. be able to.

■ Surface treatments such as plasma cleaning can be performed in the normal glow discharge area where there is no risk of transition to arc discharge. Therefore, it is extremely effective in preventing failures immediately after the start of glow discharge, where the risk of transition to arc discharge is greatest.

(2) During the above-mentioned certain period of time, initial operation settings of the main power source are performed according to the actual workpiece.

■By performing the above ■ and ■, it is possible to perform stable processing.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a diagram showing the discharge characteristics of the same embodiment, and FIG. 3 is a diagram for explaining the discharge phenomenon under reduced pressure. Figure 1 is a diagram to explain the characteristics of breakdown voltage, Figure 5, Figure 6
The figure is a diagram to explain the transition to arc discharge at the start of discharge, Figure 7 is a diagram to explain the discharge control method, and Figure 8 is a diagram to explain the discharge control method.
The figure is a diagram for explaining the response characteristics of the power supply device, and FIG. 9 is a schematic diagram showing the usage state of the conventional discharge prevention device. l... Vacuum device for plasma generation, I a, I
b...Electrode, 2...Main power supply, 3...
- Starting power supply, 4... Electromagnetic switch (second switch). 6... Electromagnetic switch (first switch), 5...
...Current limiter, 7...lq closure drive circuit. Ivy 7 Figure 8

Claims (1)

[Claims] In a power supply device for a device applying plasma such as ion blating, plasma CVD, DC sputtering, etc., a plasma generation electrode, a main power supply connected to the plasma generation electrode via a first switch, and a main power source connected to the plasma generation electrode via a first switch, connected in series with the main power supply when the switch No. 1 is off,
a starting power source connected to the plasma generation electrode via a current limiter and a second switch; and at the time of starting, the first switch is turned off and the second switch is turned on;
The current flowing through the plasma generation electrode is stopped in a normal glow discharge region by the current limiter, and after the glow discharge,
Turning on the first switch and turning off the second switch after a predetermined time period has elapsed in which the operation of the main power source is stable and the possibility of transition from initial glow discharge to arc discharge has elapsed. 1. A plasma discharge power supply device comprising a switch driving means.