JPS5893873A - Electric discharge device - Google Patents

Abstract

PURPOSE:To permit easy start and maintenance of electric discharge in an electric discharge device by providing mechanisms for maintaining discharge and for introducing a gas for starting of discharge separately. CONSTITUTION:A flow rate control valve 2 for sputtering gas and a main valve 4 are set at prescribed openings, and a vacuum pump 3 is operated to maintain the inside of a vacuum chamber 1 at pressure for maintaining discharge. In order to start discharge, a solenoid valve 12 is opened to introduce the sputtering gas in a room 11 contg. gas into the chamber 1. The valve 12 is closed thereafter to be ready for the next start of discharge, and the gas is beforehand filled in the chamber 11 by opening a solenoid valve 13. When the gas in the chamber 11 is introduced into the chamber 1, the pressure in the chamber 1 rises by about one digit instantaneously and the discharge is started. Thereafter, while the discharge is maintained, the pressure in the chamber 1 lowers to the pressure for maintaining discharge, and when a shutter 8 is opened and vapor depositing films are formed on the substrate on a holder 6 by a target electrode 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for performing electric discharge in vacuum.

Let's take the Snokutsuta device as an example of a discharge device.

In this su/mother ivy device, the inside of the vacuum chamber container is 10 to 1O-
Discharge is performed by maintaining a specific pressure in the range of about 1 Torr and applying a voltage between the cathode and anode provided inside. The resulting positive ions bombard the target forming the cathode surface, causing dust, and the atoms ejected from the target adhere to the substrate, forming a thin film. Therefore, it is absolutely necessary for a general spacecraft to perform stable discharge in a vacuum. However, since the conditions for starting a discharge and the conditions for maintaining a discharge are generally different, considerable effort and ingenuity are required to control them when operating a spark generator.

The state of discharge in a gas or tube device does not necessarily mean that discharge will start depending on the geometrical shape of the electrodes, the type of gas molecules, pressure, voltage, etc. This is because starting a discharge is more difficult than maintaining a discharge.

Kutsien's law is well known regarding the correlation between discharge starting voltage, electrode spacing, and pressure in vacuum. Normal S)4? In the case of a 51-meter device, according to Nokschen's law, it is explained that the higher the pressure, the lower the discharge starting voltage, and the wider the electrode spacing, the lower the discharge starting voltage. In conventional snotter devices, this law teaches that the pressure is kept constant, the target electrode is moved when the discharge starts, the electrode spacing is widened, and then the electrode spacing is returned to the predetermined spacing again after the discharge starts. Alternatively, a method is used in which the electrode spacing is kept constant, the discharge is started at a pressure higher than the predetermined pressure, and then the pressure is returned to the predetermined pressure after the discharge has started.
It was Other methods have also been used, such as providing an auxiliary electrode near the target electrode and applying a high voltage, or providing a thermionic emission mechanism near the target electrode to start discharge. However, the method of adjusting the distance between the electrodes requires a mechanism to raise and lower the target electrode, and the operation takes time.

However, it has the drawback of being ineffective. The method of applying a high voltage to the auxiliary electrode requires the auxiliary electrode to be close to the target electrode, which is accompanied by restrictions on electrode design and has the disadvantage of requiring a high voltage power source exclusively for the auxiliary electrode. Also, in the method using thermionic electrons, the need to bring the filament for thermionic electrons close to the target electrode and to prepare a dedicated power source has the same drawbacks as in the case of the auxiliary electrode.

The method of adjusting the pressure in the vacuum chamber is the most effective method among the conventional discharge starting methods. This is because the discharge starting pressure is generally one order of magnitude higher than the discharge sustaining pressure, and after the discharge starts, the discharge continues even if the pressure is lowered. However, in order to adjust the pressure in the vacuum chamber at the start of discharge in conventional Sunobutsuta devices, it is necessary to adjust the flow rate control valve for Sunomotsuta gas introduction to change the amount of gas inflow, or to adjust the main valve of the exhaust system. The effective pumping speed is increased or decreased by adjustment, which has the drawback of being relatively troublesome to operate and requiring a considerable amount of time. In addition, this type of pressure adjustment at the start of discharge is a major obstacle in advancing the automation of the main process.

Therefore, an object of the present invention is to provide a discharge device that can easily start and maintain discharge.

Another object of the present invention is to provide a discharge device suitable for automatically controlling the initiation and maintenance of discharge.

In order to achieve the above object, the present invention includes a gas introduction mechanism for maintaining a predetermined pressure in the discharge device, as well as a mechanism for increasing the pressure in the vacuum chamber to start discharge, and then lowering the pressure to maintain the discharge. The device is equipped with an independent gas introduction mechanism dedicated to starting discharge. Two methods have been adopted for the gas introduction mechanism dedicated to starting this discharge: one consisting of a gas storage chamber and stop valves on both sides, and the other consisting of a stop valve and a flow control valve sandwiching a small space. are doing.

With the above configuration, an appropriate amount of gas is introduced into the vacuum chamber in a short period of time to increase the vacuum chamber pressure to the minimum pressure at which discharge can start, and then the pressure is quickly returned to the normal pressure to maintain the predetermined pressure. It was designed to maintain the

Next, a detailed explanation will be given with reference to the drawings. First, a conventional device will be described. Among the several examples mentioned above, a method for adjusting the vacuum chamber pressure, which is the most effective but relatively troublesome to operate, will be taken as an example. The reason why this method is taken as an example is that it is considered to be the closest to the device of the present invention.

FIG. 1 is a diagram showing the configuration of the above-mentioned conventional suction device. Gas is introduced into the vacuum chamber 1 through the flow control valve 2, and on the other hand, exhaust is performed by the vacuum pump 3. The pressure inside the vacuum chamber is determined by the amount of gas introduced and the pumping speed.

More specifically, by controlling the conductance of the flow control valve 2 and the conductance of the main valve 4, a predetermined pressure can be steadily obtained. A voltage is applied from a footer power source 7 between the target electrode 5 and the ground electrode including the substrate holder 6. Generally, discharge does not start at a predetermined pressure, so either expand the flow control valve 2 to increase the conductance while covering the substrate holder 6 with the shutter 8, or move the main pulp 4 and reduce the exhaust speed. As the pressure is reduced, the pressure in the vacuum chamber is raised to a high level and the discharge begins. After that, by returning the conductance of the flow rate control valve 2 or the conductance of the main pulp 4 to the original state, the pressure in the vacuum chamber 1 can be maintained and operation can be ensured, but as mentioned earlier, the operation is cumbersome and time consuming. It did have some drawbacks.

As explained above, there is another example of a conventional device that is provided with an auxiliary electrode for applying a high voltage. This is an indication. Also, 11 when using a thermionic emitter! They will be installed in approximately the same location. However, in both cases, the flow rate! Once the ItfJ valve 2 and the main pulp 4 are set to steady values, there is no need to make any troublesome adjustments. However, all have some drawbacks.

FIG. 2 is a diagram showing the configuration of an embodiment of a sputtering apparatus according to the present invention. In FIG. 2, the same reference numerals are given to the same components as in FIG. This system is equipped with a gas introduction mechanism. When starting discharge, first, the electromagnetic valve 13 is opened to fill the gas storage chamber 11 with argon gas.

The pressure of argon gas is IKyf/cIrL2 gauge pressure.

Next, when the electromagnetic valve 12 is opened, the pressure in the vacuum chamber 1 rises instantaneously and discharge starts. Typical pressure values are 5 x 10-3 Torr for suction pressure and 5 x 10 Torr at the start of discharge. The solenoid valve 12 is closed after the argon gas inside the gas storage chamber 11 is introduced into the vacuum chamber 1, and the solenoid valve 13 is opened to prepare for the start of the secondary discharge to introduce argon gas into the gas storage chamber 11. Keep it filled. Here, the volume of the gas storage chamber 11 is vl, its pressure is PI, the volume of the vacuum chamber 1 is V, and the discharge starting pressure is pol. 1), then vl=
It depends on the size of v-Po/P1. Furthermore, if the effective pumping speed of the pumping system seen from the vacuum chamber 1 is S, then the moment the solenoid valve 12 on the vacuum chamber 1 side is opened, the pressure in the vacuum chamber 1 becomes PG and discharge starts, and then vacuum chamber pressure P
decays with a time constant τ=v/S. To give an example of the time constant of the decay, when the volume of the vacuum chamber 1 is V=2007, the effective pumping speed S is
When the speed is 4100 Z/s, the time constant τ=2 seconds.

Also, when the pressure Po at the start of discharge is 5×10 TOrr.

In order to obtain this, the volume v1 of the gas storage chamber 11 is a figure showing the change in vacuum chamber pressure when discharge is started.

In the embodiment shown in FIG. 2, when the pressure inside the gas storage chamber 11 is constant, the volume of the gas storage chamber is expressed as Vl.
= %'P6/PH is determined according to the vacuum chamber volume of the Sufu9 ivy device, but in practical terms, 5i
The volume of the gas storage chamber required for a vacuum chamber with a volume of 0.1 to 10
It is about 0CC.

FIG. 4 is a block diagram of a second embodiment of the present invention.

This device is used as a gas introduction mechanism exclusively for starting discharge.

A solenoid valve 21 for inflowing and shutting off gas, and a flow control valve 22 having a conductance that can flow an order of magnitude higher than the flow rate of the normally flowing suction gas.
This sputtering apparatus is characterized in that the dead space between the electromagnetic valve 21 and the flow rate control valve 22 is extremely small. When starting discharge, the solenoid valve 21 is opened, and a considerable amount of argon gas corresponding to the conductance of the flow rate control valve 22 is introduced into the vacuum chamber 1, thereby raising the vacuum chamber pressure fairly quickly. When the vacuum chamber pressure reaches the discharge starting pressure and discharge starts, the electromagnetic valve 21 is closed to stop the introduction of gas for starting discharge, and after this, the vacuum chamber is closed in the same way as in the first embodiment shown in FIG. The pressure is based on SuA? Return to ivy pressure. Specific numerical examples for this device are as follows: vacuum chamber volume V = 200 #, effective pumping speed 5 = 100 A/a, argon supply pressure P s = I V4f 7 cm2 gauge pressure, main ivy pressure 5 Xl0-3 Torr + discharge When the starting pressure P6 = 5 x 10 Torr, the conductance C of the flow control valve 22 = 4.9 x 10
A/s is selected, vacuum chamber pressure P is 5 x 1O
The time it takes to reach -2Torr (Po) is 2 seconds.

FIG. 5 is a diagram showing changes in the vacuum chamber pressure P when starting discharge in the screen footer device shown in FIG. 4. Flow control valve 22
If the conductance of is made larger, 5 x 1
Although the time it takes to reach O-2 Torr is even shorter,
Since the pressure rises rapidly, the value of the vacuum chamber pressure when the solenoid valve 22 is closed is affected by the accuracy of the time until the solenoid valve 22 is closed. Therefore, the flow control valve 2 should be adjusted so that the time required to reach 5 x 1O-2Torr is 1 to 2 seconds.
It is appropriate to adjust the conductance of 2. Since gas always exists in the dead space between the solenoid valve 21 and the flow control valve 22, the moment the solenoid valve 21 is opened, the gas determined by the volume and pressure here also flows into the vacuum chamber and contributes to the pressure rise. do. Therefore, in order to accurately control the discharge starting pressure, it is preferable that the dead space has a smaller volume. If the volume of the dead space cannot be ignored, this method can be considered as a combination of the embodiment in an ideal state with no dead space and the first embodiment in which a gas storage chamber equal to the volume of the dead space is provided. I can do it.

In the case of the second embodiment, in order to be able to set a practical discharge starting pressure by the conductance of the flow control valve 22, it is desirable that the volume of the dead space is 0.5 cc or less. Naturally, the larger the volume of the vacuum chamber 1, the larger the volume of dead space allowed. Furthermore, in the second embodiment, the increase in pressure in the vacuum chamber 1 is controlled.

This is possible not only by simply adjusting the conductance of the flow control valve 22, but also by adjusting the opening time of the solenoid valve 21.

Therefore, even if the discharge starting pressure P changes under different conditions, detailed measures can be taken. That is, in many suction devices with different combinations of vacuum chambers and effective pumping speeds, discharge can be started under various suction conditions.

Furthermore, when the apparatus shown in FIG. 4 is applied to a fully automatic sputtering apparatus, discharge can be started automatically with high reliability.

In this case, instead of setting the time to close the solenoid valve 21, a signal from a discharge detection mechanism (not shown), for example, a mechanism that detects a sudden change in voltage generated across a resistor provided in a discharge current circuit, is used to generate an electromagnetic valve. By closing the valve 21, discharge can always be started with a minimum pressure increase, which reduces the burden on the exhaust system and further improves the reliability of discharge initiation.

As explained above, according to the first and second hive embodiments, it is possible to easily and effectively start a discharge in a short period of time while keeping the soil and mother ivy conditions optimal. Furthermore, there are no physical restrictions on the electrode structure or discharge initiation mechanism of the sputtering device, and no special power source is required.

In particular, by applying the second embodiment to a fully automatic spark plug device, automatic discharge can be started with high reliability.

Although the above description of the gas introduction mechanism for starting discharge has been made with respect to a sputtering apparatus,9 the present invention can be applied to other apparatuses that utilize discharge in a vacuum. For example, it can be used in a plasma CVD device or a plasma polymerization device for forming a thin film. Further, the present invention can be applied to a Zolazma etching device, a reactive ion etching device, a Suno'P ivy etching device, etc., which perform etching of thin films by generating plasma in a vacuum.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the configuration of a conventional suction ivy device, FIG. 2 is a configuration diagram of an embodiment of the suction ivy device according to the present invention, and FIG. 3 is a diagram showing an example of the configuration of a suction ivy device according to the present invention. Figure 4 is a diagram showing the change in vacuum chamber pressure at the start of discharge in the sputtering apparatus, and FIG. 4 is a configuration diagram of a second embodiment of the sputtering apparatus according to the present invention.
FIG. 5 is a diagram of the pressure change in the vacuum chamber at the start of discharge in the suction/main ivy device shown in FIG. 4. Explanation of symbols = 1 is the vacuum chamber, 2 is the flow control valve, 3 is the vacuum pump, 4 is the main valve, 5 is the target electrode, 6 is the substrate holder, and 7 is the sputtering power source. 8 is a shutter, 9 is an auxiliary electrode, and 1'1 is a gas storage chamber. 12, 13, and 21, the electromagnetic valve 22 is a flow control valve, respectively. Figure 1 Figure 2 Time Figure 3 Time order Figure 5

Claims (3)

[Claims] (1) In a discharge device that performs discharge by introducing gas into a vacuum chamber, the means for introducing the gas into the vacuum chamber controls the pressure of the gas so that the discharge is maintained at a desired intensity. A gas introduction mechanism for maintaining the discharge to maintain a predetermined pressure, and a gas introduction mechanism for starting the discharge to temporarily increase the pressure of the gas to the pressure necessary to start the discharge, are provided separately. A discharge device comprising: (2) The discharge device according to claim (1), wherein the gas introduction mechanism for starting discharge has a gas storage chamber and one stop valve on each side of the gas storage chamber. (3) The discharge device according to claim (1), wherein the gas introduction mechanism for starting discharge includes a stop valve and a flow rate control valve with a sufficiently small dead space between the stop valve. .