JPH05311415A - Arc discharge preventive circuit - Google Patents

Abstract

PURPOSE:To prevent the failure in electric discharge by the arc discharge in a reverse direction by properly installing a diode, capacitor and inductances between the target and power source of a sputtering device. CONSTITUTION:The diode 4 is installed in parallel with the target 3 at the optimum reactance between the positive and negative terminals of the target 3 provided in a grounded chamber 2 for pressure reduction of the sputtering device 1. The capacitor 5 and the power source 6 are mounted between the positive and negative terminals of the target 3 in parallel with the diode 4 and a switching element 11 is provided in parallel with the diode 4. The arc discharge preventive circuit is constituted by forming the inductances 7, 8 between the target 3 and the power source 6. The diode 4 and the inductance 7 as well as the capacitor 5 are coupled and electrically connected by a cable 9 and are connected via the inductance 8 to the power source 10 at the time of installing this device on a production site.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an arc discharge prevention circuit for a sputtering device.

[0002]

2. Description of the Related Art In a sputtering apparatus, by utilizing the cathode sputtering phenomenon associated with glow discharge, metal atoms ejected from a target (cathode) by sputtering are
A thin film is formed by depositing and adhering on the surface of the substrate arranged near the anode.

In order to operate the sputtering apparatus of such a principle on a production scale, when a large electric power of 5 to 10 kW or more is applied, no problem will occur if normal glow discharge is generated on the sputtering surface of the target. When the discharge is locally concentrated due to dirt on the surface or the like, the temperature rises only in that part, so that thermoelectrons are emitted and a so-called arc spot is generated to shift to arc discharge.

When such an arc discharge occurs, a very large arc current flows and the arc is sustained and effective in the above-mentioned high power source because its output impedance is low (for example, the discharge impedance is about several tens of Ω). Spatter is not possible.

On the other hand, as the cathode sputtering surface of the sputtering apparatus, that is, the target surface, becomes larger, the contamination that causes an arc spot inevitably increases, and no sputtering is carried out except for the portion where arc discharge occurs. Therefore, the state in which other dirt and the like cannot be removed is maintained, and even if the power is turned on and off repeatedly, the frequency of occurrence of arc spots remains unless the dirt and the like are sputtered away. Moreover, unless the power is turned on and off early, the power cannot be turned on effectively in the sputtering device.

By the way, as a method of erasing the arc, a method of vibrating by L and C and the arc is known, and an ion pump power supply circuit of Ultec, an electron beam evaporation power supply circuit of JEOL Ltd. There are publicly known patents or published patents for a sputtering power source of the same company, and such means can be used for a sputtering power source of a magnetron type sputtering apparatus.

Further, when the voltage is high and the current is small, arc discharge can be prevented by increasing the impedance of the power supply, and the ballast of fluorescent lamps and the neon lamp's stabilizing resistance can be considered as the ultimate argument. There is such a role. On the other hand, if the current increases, the power supply impedance cannot be increased, so some kind of arc discharge prevention measure is required, and the method of controlling the phase by half-wave rectification or SCR and placing a pause is adopted.

However, in addition to the fact that the ripple is large and it is difficult to measure the electric power, in an application requiring an essentially low ripple power source such as an electron beam evaporation source, there is a method of cutting off the output after detecting an arc. it was thought.

An arc prevention circuit by a vacuum tube switch of an electron beam evaporation source of Sloan Company and Airco Temescal Company is known, and an arc prevention circuit of a sputtering power source is an extension of this idea. Further, as in the case of the power source for the electron beam evaporation source, the current sharply increases when an arc occurs. Therefore, the current is detected, the output is cut off for a certain period, and the arc spot is cooled.

In an ITO sputter power supply used in a manufacturing apparatus for a pickup tube used in a home video camera, an arc cut circuit using a transistor switch for voltage detection is used, so that spatter can be produced without splashing. succeeded in. On the other hand, with the method using current detection or vibration, it is impossible to eliminate the splash, and mass production could not be performed.

The limit due to the switch element arranged in series with the voltage detection and the load lies in the switch element, and there is no suitable switch element suitable for a large current sputtering apparatus.

By the way, if the state in which a large current is applied is suddenly turned off, all the self-induced voltage of the inductance included in the circuit is applied to the switch element.
It is necessary to devise a way to absorb that energy and to set the switch time to a certain degree later. In order to avoid this, the switch element may be installed in parallel with respect to the arc discharge, and the switch may be turned on when an arc occurs instead of incorporating the switch element in series.

However, since this switch element must be cut off sometime, the switch may be turned off when the circuit current is inverted due to vibrations caused by L and C. The method of oscillating the circuit by such a short circuit is used in a crowbar circuit or thyristor inverter used for nuclear fusion because the current becomes 0 and the switch is turned off. The circuit is relatively simple when a thyristor is used. Can be manufactured.

The problem of the circuit by the thyristor is that since the Off occurs at the time of the current 0, the timing of On cannot be selected unless some series switch is installed to turn it on. In addition, even if it is said to turn off at a current of 0, since the thyristor has a long carrier lifetime, the annihilation time must be 100 μsec or more.
The point is that L and C must be increased to lengthen the vibration cycle.

However, for the sputtering equipment manufactured by Shibaura Seisakusho 2
In the Kw power supply circuit, an arc cut method using a thyristor is used in the normal mode, and an oscillating circuit method using an arc switch in the purify mode.

FIG. 1 schematically shows an example of a power supply circuit installed via a cable 3 on a target 2 installed in a decompression chamber 1 of a sputtering apparatus. This power supply circuit has a structure in which L is attached to the positive electrode, C is attached between the positive electrode and the negative electrode, and C and the target 2 are connected by a cable 3.

[0017]

A circuit that oscillates from L and C and extinguishes an arc during a current reversal period as an arc discharge switch element has been known for a long time as a circuit for stabilizing discharge. Is unknown.
In particular, in circuits up to 1A class, if a choke coil and a capacitor are properly arranged at the output of the DC power supply, arc discharge stops like this, and it is presumed that detailed analysis was not performed.

Therefore, equipment manufacturers and process researchers
It seems that he did not notice that the operation of the arc cut vibration including the power supply was decided by the inductance and resistance of the wiring from the power supply to the load.

In a DC power supply of more than 10 A, the arc prevention circuit due to vibration fails due to conditions. Therefore, as a power supply control, a circuit is provided to stop the output for a certain period by catching the rise in the arc current after the failure. Was called the arc cut operation. By properly selecting this stopping condition, the failure to prevent arc discharge due to vibration has been suppressed.

From a sputtering apparatus equipped with a target that electrically functions as a load to a magnetron sputtering apparatus,
A cable is used to connect to a DC power source. However, it was found that the vibration conditions changed depending on the length, and vibration could not be secured even under the worst conditions.

The present invention has been made under such circumstances, and an object thereof is to provide a novel arc discharge prevention circuit.

[0022]

[Means for Solving the Problems] A cable connected to a power supply circuit, a target connected to the positive and negative terminals of the cable, a capacitor connected between the target and the cable, and a capacitor connected between the negative terminal of the capacitor and the target. The reactance, the diode connected in parallel to the target with the optimum inductance for the target, and the switching element connected to the target are the features of the arc discharge prevention circuit according to the present invention.

[0023]

In the conventional sputtering apparatus, since the inductance of the wiring from the DC power source to the load (target) is used as a result for the vibration inductance, the vibration condition changes depending on the length of the cable. Vibration cannot be secured.

For this reason, it has been found that L and C are installed at a position close to the load so as to satisfy the vibration condition under the worst condition, but it is considerably improved, but it sometimes fails. It was found that the cause of this failure was the arc in the opposite direction.

To prevent reverse arcing, a diode placed in parallel with the load eliminated the failure caused by the reverse arc, but not completely. It was found that it was not possible to secure the time for reversal and rest due to fluctuations in the arc start timing and arc energy.

Therefore, if the capacity of the condenser is increased and the reversal time is secured, 100% arc cut failure does not occur. However, under this condition, as the output current in normal discharge increases, the arc energy also increases, and it is necessary to increase the C capacity for ensuring vibration and reduce the circuit resistance. As a result, the arc energy becomes higher and higher.

When the arc energy becomes large, the splash due to the arc may fly, and in the sputtering of low voltage and large current, even if the resistance R associated with L and C is optimally selected, the arc energy is large and it is reversed. Not vibrating condition.

For this reason, in the present invention, a diode is installed in parallel with the target, which is a load, and the on-voltage is lowered to secure the inversion time. Further, by connecting the switch element, the current can be bypassed to the switch element, and the switch element is turned on at an arbitrary time from the start of the arc. This makes it possible to select a condition in which the cause of the arc disappears and no splash occurs.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described with reference to FIGS.

In order to operate the sputtering apparatus utilizing the cathode sputtering phenomenon accompanying glow discharge on a production scale, 5 to 1
When a large electric power of 0 kW or more is applied, if the target surface or the like becomes dirty, the discharge will be locally concentrated. As a result, the temperature rises only in that part, and thermoelectrons are emitted to generate a so-called arc spot, which causes arc discharge.

Therefore, in a high power supply having a low output impedance (for example, a discharge impedance of about several tens of Ω), a very large arc current flows and the arc is sustained, so that effective sputtering cannot be performed.

Since the cathode sputtering surface, that is, the target surface in such a sputtering apparatus tends to become larger and larger, the contamination that causes an arc spot inevitably increases, while the area other than the portion where the arc discharge occurs is slightly increased. Is not sputtered. Therefore, the state of dirt and the like other than the portion where the arc discharge occurs is maintained, and even if the power is turned on and off repeatedly, there is a risk that an arc spot will be generated unless it is removed by sputtering.

The present invention provides a special arc discharge prevention circuit as a countermeasure against such a sputtering apparatus. The operation of the arc discharge prevention circuit is shown in FIGS. 1 to 10, and the connection state specifically attached to the sputtering apparatus is shown in FIG.

The arc discharge prevention circuit according to the present invention clarified in FIGS. 3 to 10 is an arc discharge prevention circuit for preventing the arc discharge generated in the target 3 installed in the grounded decompression chamber 2 essential to the sputtering apparatus 1. Install.

That is, between the positive and negative terminals of the target 3 formed in the grounded decompression chamber 2, a diode 4 is installed in parallel with the target 3 with an optimum reactance, and a capacitor 5 and a power source 6 are installed in parallel with the diode 4. Install between the positive and negative terminals of target 3.

Further, the inductances 7 and 8 are connected to the target 3
And a power supply 6 to form an arc discharge prevention circuit.

When the sputtering apparatus equipped with such an arc discharge prevention circuit is installed in the production site, the cable 9 is used as a matter of course, which is shown in FIG. That is, the diode 4 and the inductance 7 and the capacitor 5 are connected by a cable 9 to establish an electrically connected state, and are connected to the power source 10 via the inductance 8.

The operation of such an arc discharge prevention circuit is
Target current (I) and target voltage (V) on the vertical axis
The time is plotted on the horizontal axis, and the origin A of the current and the origin B of the voltage are clarified in FIG. 1, and the time course of both is shown in detail in FIG. 3 to 10, the specific behavior of the target current and the target voltage in the temporal order shown in FIG. 2 was clarified.

That is, the target current I and the target voltage v shown in FIGS. 1 and 2 change abruptly from the boundary between the regions a and b, indicating that the arc discharge has started. The detailed operation of the arc discharge prevention circuit at this time is clarified in FIG. A region of FIG. 2 and FIG. 3 show a state at the time of normal discharge, and the target 3 and the power source 6 are shown.
There is a current j. The region a and FIG. 3 show the state at the time of normal discharge, and the polarity of the capacitor 5 is positive on the lower side of the paper as shown in the figure.

[0040]

[Outer 1]

[Outside 2] Fig. 2 shows the movement of various parameters at the timing from arc discharge to its peak.
Similar to FIG. 3, FIG. 4 shows a current j flowing between the target 3 and the power source 6 and a current k flowing between the target 3 and the capacitor 5. The polarity of the capacitor 5 is positive on the lower side of the paper surface as shown in the figure.

FIG. 5 shows the phenomenon occurring in the area C in FIG. 2 when the arc current decreases.
There are some differences. That is, the voltage polarity of the capacitor 5 is reversed, and it is divided into a passage k flowing between the target 3 and the capacitor 5 and a passage L flowing between the capacitor 5 and the power supply 6. In the path L, the target current value is maintained at a constant value by the choke or the inductance 8 (same as in FIG. 10), the capacitor 5 is charged up (Charge Up), and the path k is
Unlike FIG. 4, it is in the opposite direction.

Next, FIG. 6 shows the operation at the timing of the region d in FIG. 2, that is, the operation until the peak of the timing when the voltage of the target 3 reverses and the reverse current flows through the diode 4. The voltage of the capacitor becomes the reverse voltage. The direction of the passage k is opposite to that of FIG.

The operation in the area e in FIG. 2 as the discharge proceeds further will be described with reference to FIG. In this region, as is apparent from FIG. 7, it is the timing when the diode current has passed the peak and the capacitor 5 is charged up in the normal direction. Further, the direction of the passage k is a normal direction, unlike in FIGS. Further, while the current value in the passage L is constant as in FIG. 6 and the like, that in the passage k is smaller than that in the case of FIG.

The operation in the subsequent discharge in the f region of FIG. 2 will be described with reference to FIG. 8. This is a phenomenon which occurs at the timing when the reverse current flows due to the residual carriers of the diode 4 after the diode current exceeds zero. As is apparent from FIG. 8, the passage L flows in the same direction as in FIG. 7, while the passage k flows in the opposite direction to that of FIG.
The positive electrode is also reversed.

The final stage of discharging is the operation shown in FIG. 2 and the region of FIG. This is because the carrier of the diode decreases and the current in the inductance 7 decreases, so the load voltage

[Outside 3] As described above, the arc discharge prevention circuit according to the present invention employs a method in which the diode is connected in parallel with the target with the optimum reactance between the negative terminal of the target and the target. But there are limits. That is, FIG.
As will be apparent from FIG. 7, the inductance 7 is L ₁ , the inductance 8 is L ₂ , the capacitor 5 is C ₂ , and the inductance 7 and the inductance 8 are adjacent to each other and R ₁ R ₂
Therefore, the limit value of C ₂ and L ² , the limit value of R ₁ and R ₂ , and the limit value of L ₁ can be expressed by the following formulas.

1 / 2C ₂ V _C ² = 1 / 2L ² I _P ²
I _P ² 1 = (C ₂ / L ² ) V _C ² I _P = V _C ² √C ₂ / L ₂ That is, FIG. 11 shows an arc discharge prevention circuit in which a diode is mounted when discharge fails due to reverse arc discharge. If you configure like, there will be no failures.

By installing the diode in parallel with the target in this way, reverse arc can be prevented. However, as described in the above-mentioned action column, in the arc discharge prevention circuit according to the present invention, the switch element is also installed.

As is apparent from FIG. 11, in the arc discharge prevention circuit according to the present invention, the diode 4 mounted in parallel with the target is installed in parallel with the switch element 11. Further, L7 and C5 are installed at positions relatively close to the diode 4 and the switch element 11 to satisfy the conditions in the action column.

[0049]

As described above, when the sputter device is attached to a specific place by using the cable, the arc discharge prevention circuit according to the present invention is used, and the discharge does not fail due to the reverse arc discharge. It is possible to prevent adverse effects due to increase in arc energy, improve the operating rate of the sputtering apparatus, and thus increase productivity, which is extremely effective in practice.

[Brief description of drawings]

FIG. 1 is a curve diagram showing a change over time in a current during discharge in a sputtering apparatus provided with an arc discharge prevention circuit according to the present invention.

FIG. 2 is a diagram showing in detail the target current and the target voltage change of the discharge current in FIG.

FIG. 3 is a curve diagram for clarifying a flow of a target current or the like in a region a of FIG.

FIG. 4 is a curve diagram for clarifying the flow of target current and the like in the region b of FIG.

5 is a curve diagram for clarifying a flow of a target current and the like in a region c of FIG.

FIG. 6 is a curve diagram for clarifying a flow of a target current or the like in a region d of FIG.

FIG. 7 is a curve diagram for clarifying the flow of target current and the like in the e region of FIG.

8 is a curve diagram for clarifying the flow of target current and the like in the f region of FIG.

9 is a curve diagram for clarifying the flow of the target current and the like in the g region of FIG.

FIG. 10 is a schematic circuit diagram used to determine a limit value of the arc discharge prevention circuit shown in FIGS. 3 to 9.

FIG. 11 is a view showing a state in which the arc discharge prevention circuit according to the present invention is attached to a sputtering device.

[Explanation of symbols]

 1: Sputtering device, 2: Decompression chamber, 3: Target, 4: Diode, 5, 10: Capacitor, 6: Power supply, 7, 8: Inductance 9: Cable, 11: Switch element.

Claims (1)

[Claims] 1. A cable connected to a power supply circuit, a target connected to the positive and negative terminals of the cable, a capacitor connected between the target and the cable, and a reactance connected between the negative terminal of the capacitor and the target. An arc discharge prevention circuit comprising a diode connected in parallel to the target with an optimum inductance for the target, and a switching element connected to the target.