JP2001145371A - Power supply for sputtering - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent abnormal discharge from a direct-current power supply for sputtering without applying overvoltage to a switching element. SOLUTION: A main direct-current power supply 6 and a direct-current power supply 8 for reverse pulses are series-connected with each other with their polarities identical, and first and second semiconductor switches 15 and 16, provided across them, respectively, with anti-parallel diodes 19 and 20, in series with each other are connected. A sputtering electrode 12 and an inductor 17 for current limitating are connected at the point of series connection between the main direct-current power supply 6 and the direct-current power supply 8 for reverse pulses, and the point of series connection between the first and second semiconductor switches 15 and 16 to form a half-bridge configuration, and reverse positive-pole pulses are periodically applied to the sputtering electrode 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to the prevention of abnormal discharge of a DC sputtering power supply.

[0002]

2. Description of the Related Art In a direct current sputtering apparatus, a target material (cathode electrode) and a gas are reacted in a chamber by plasma discharge, and a film of a compound generated by the reaction is formed on a semiconductor surface or a substrate such as an optical disk. ,
A DC negative power supply for applying a negative DC high voltage is used for the plasma DC discharge.

[0005] However, one of the causes of degrading the performance of the plasma DC sputtering is an abnormal discharge in which the current density sharply increases locally and reaches an arc discharge region. As a method of preventing this abnormal discharge, there is a method of periodically applying a pulse voltage of a reverse polarity, that is, a positive polarity.

Conventionally, this configuration includes the following circuit. FIG. 5 shows a first conventional example. A voltage blocking inductor 53 is connected in series between the output of the DC power supply 51 and the sputter electrode 52, and a negative voltage is applied to the sputter electrode 52 through the inductor 53 in a normal state.

In order to prevent abnormal discharge, the semiconductor switch 54 and the reverse polarity voltage source 55 are connected in series and connected in parallel to the sputter electrode 52, and the semiconductor switch 54 is periodically turned on, so that the reverse voltage source 55 Sputter electrode 52
Is applied with a reverse polarity pulse voltage. At this time, the voltage blocking inductor 53 prevents the reverse polarity pulse voltage from being absorbed by the DC power supply 51.

In the second conventional example, as shown in FIG. 6, an autotransformer 63 is connected in series between an output of a DC power supply 61 and a sputter electrode 62, and a semiconductor switch 64 is periodically turned on to automatically turn on the autotransformer. When a voltage of the DC power supply 61 is applied between the start terminal 66 and the intermediate terminal 67 of the terminal 63, a voltage about 1.1 times the voltage of the DC power supply 61 is generated at the terminal 66 and the terminator 68 with the polarity shown in FIG. This is a method in which a reverse polarity pulse of about 0.1 times the voltage of the DC power supply 61 is applied to the sputter electrode 62 because the output has a polarity opposite to the DC power supply 61.

In a third conventional example, as shown in FIG. 7, a voltage blocking inductor 73 is connected in series between an output of a DC power supply 71 and a sputter electrode 72, and a DC cut capacitor 74 and a pulse transformer 75 are connected. This is a method of connecting the secondary windings 76 in series and connecting them in parallel to the sputter electrode 72. The primary winding 77 of the pulse transformer 75 is connected in parallel to the DC power supply 71 through a semiconductor switch 78.

The voltage of the DC power supply 71 is applied to the primary winding 77 by periodically turning on the semiconductor switch 78, and the pulse voltage generated in the secondary winding 76 is applied to the sputter electrode 72 through the DC cut capacitor 74. It is applied as a reverse polarity pulse. The voltage blocking inductor 73 prevents the reverse polarity pulse voltage from being absorbed by the DC power supply 71.

[0009]

All of the first to third circuits of the prior art use semiconductor switches such as IGBTs and FETs and magnetic components such as inductors, autotransformers, and pulse transformers. When switching the current flowing through such inductors, auto transformers, pulse transformers, etc., the magnetic flux of the iron core increases due to the voltage applied during the on-period, so a reverse voltage is generated to restore this magnetic flux during the off-period. A circuit, a so-called magnetic reset circuit, is required.

The resetting of the magnetic flux is a circuit that consumes the increased magnetic flux energy, resulting in a loss. Therefore, when the reverse pulse frequency is increased, there is a disadvantage that the loss becomes very large.

As another method of resetting magnetic flux, there is a method of providing a secondary winding to an inductor and returning magnetic energy to a power source, but the circuit configuration becomes complicated.

In addition, since an overvoltage occurs when the switch is turned off in the inductor circuit, the semiconductor switching element needs to have a high breakdown voltage. Normally, the voltage is absorbed by a snubber circuit, but it still needs to be two to three times the power supply voltage, and the snubber circuit causes the absorption voltage to be lost by the resistor, so that the resistor becomes large and it is difficult to reduce the size.

[0013]

According to the present invention, a main DC power supply and a DC power supply for reverse polarity pulses are connected so that their output voltages are of the same polarity and in series, and the main DC power supplies connected in series are connected. A first and a second semiconductor switch having an anti-parallel diode connected in series between both ends of a power supply and a DC power supply for reverse polarity pulse are connected, and an output terminal of the main DC power supply and an output terminal of the DC power supply for reverse polarity pulse are connected. A sputter electrode and a current limiting inductor are connected between a connection point and a connection point between the first and second semiconductor switches so as to be in series with each other.
And the second semiconductor switch are periodically and alternately turned on, so that when the first semiconductor switch is turned on, a negative steady-state voltage is supplied from the main DC power supply to the sputter electrode, and the second semiconductor switch is turned on.
When a semiconductor switch is turned on, a positive polarity pulse of reverse polarity is applied to the sputter electrode from a DC power source for reverse polarity pulse.

According to the present invention, the reset of the magnetic circuit, which has been a problem in the past, becomes unnecessary, and a reverse polarity pulse is generated without using the inductor of the DC circuit. Can be reduced.

In principle, only a voltage of about the power supply voltage is applied to the semiconductor switching element, and the output −700
With a sputtering power supply of about V to -1000 V, even if the discharge starting voltage is about -1500 V, there is an advantage that a configuration in which only two IGBTs or FETs with a withstand voltage of about 1000 V are connected in series is sufficient.

[0016]

FIG. 1 shows an embodiment of the present invention. 1
Is a rectifier having a commercial AC power supply as an input, and 2 is a high-frequency inverter operated by a rectified DC power supply. Reference numeral 3 denotes a transformer including two secondary windings 4 and 5 for converting a high-frequency output voltage of the inverter 2 into a predetermined voltage.

The first secondary winding 4 is connected to the rectifier 6 and the filter capacitor 7 and generates, for example, a steady voltage of −700 V as a main DC power supply. The second secondary winding 5 is connected to the rectifier 8 and the filter capacitor 9 and generates a reverse voltage of +70 V as a reverse pulse DC power supply.

The two rectifiers 6 and 8 are connected in series with the same polarity, and the connection point is connected to the anode 13 of the sputter electrode 12 through the current detection resistor 11. Anode pole 1
3 is usually the same ground potential as the device housing. Semiconductor switches connected in series to each other, for example, IGBTs 15 and 16
Is connected between both ends of two DC power supplies connected in series. The connection point of the IGBTs 15 and 16 is connected through a current limiting inductor 17 to a cathode 14 which is a target material of the sputter electrode 12.

That is, the filter capacitors 7 and 9 and the IGBTs 15 and 16 of the two DC power supplies form a half bridge circuit, and the sputter electrode 12 and the current limiting inductor 17 are connected to a so-called AC circuit. 1
Reference numeral 8 denotes an IGBT control circuit which supplies ON signals S1 and S2 to the gates of the IBGTs 15 and 16. At the same time, the detection signal of the current detection resistor 11 is applied to the control circuit. 19, 20
Is a flywheel diode connected in anti-parallel to each of the IGBTs 15 and 16.

Next, the operation will be described. FIG. 2 is an explanatory diagram of signals, and shows a time relationship among the ON signals S1 and S2, the sputter electrode voltage Vs, and the sputter current Is. ON signals S1, S2
IGBTs 15 and 16 are periodically and alternately turned on at a frequency of about several kHz to about 100 kHz.
The on-duty of the BT15 is large. The ON time of the IGBT 16 is several μs to several tens μs.

When the IGBT 15 is on and the IGBT 16 is off, a steady negative voltage is supplied to the cathode 12. When the IGBT 15 is turned off and the IGBT 16 is turned on, a reverse polarity pulse voltage is applied to the cathode 14 for several μs to several tens μs.

If there is a period during which the IGBTs 15 and 16 are turned on at the same time, the DC power supply is short-circuited.
In S2, a semiconductor switching element is connected to I
In the case of GBT, a time of about 0.5 μs is required.
The shorter this pause period is, the better. In the case of FET,
A time of about 0.1 μs is also possible.

Next, a protection method in the case of abnormal discharge will be described. When an arc discharge occurs between the sputter electrodes 12 at the time t shown in FIG. 2, the sputter current Is increases at a current increasing rate determined by the current limiting inductor 17 connected in series with the load. When the current exceeds the set level, the detection signal of the current detection resistor 11 is applied to the control circuit 18, and the control circuit 18 terminates the ON signal S1 or S2 as soon as possible, for example, several μs later, and permits the IGBT to operate. The IGBT 15 or 16 is turned off under the current.

In this embodiment, since the current-limiting inductor 17 is in the AC circuit of the bridge, the reset is performed by the antiparallel diode 19 or 20 of the IGBT 15 or 16.
, And there is no problem of power loss for resetting the inductance circuit and application of an overvoltage of the IGBT as shown in the conventional example. Basically, the voltage applied to the IGBT falls within a range limited by the sum of the voltages of the main DC power supply and the reverse pulse DC power supply.

When the current detecting resistor 11 detects an overcurrent, it is desirable from the viewpoint of overcurrent protection that a stop signal is also sent to the inverter 2 to stop the inverter 2 promptly.

Next, the protection circuit shown in FIG. 3 is an example of a circuit for IGBT overcurrent protection that can be applied to the semiconductor switching elements 15 and 16 of FIG. 1 according to the present invention.

A low-resistance resistor 32, for example, 0.06 ohm is connected in series with the emitter electrode of the IGBT 31, and the base and emitter electrodes of the overcurrent detecting bipolar transistor 33 are connected to both ends of the resistor 32, and the collector electrode Is I
Connected to the gate of GBT31. A resistor 35 is connected in series between the signal source 34 of the IGBT 31 and the gate of the IGBT 31.
Is inserted.

When an overcurrent, for example, 10 A flows through the IGBT 31, the voltage of the resistor 32 becomes
3, the threshold voltage of the base-emitter voltage exceeds 0.6 V, so that the impedance between the collector and the emitter becomes low, and the gate voltage of the IGBT 31 is reduced by the voltage drop of the gate series resistor 35 of the IGBT 31; IG
The impedance at both ends of the BT 31 is increased to limit its collector current to 10A. During this time, the loss of the IGBT 31 increases, but if the gate signal is cut off by detecting the current of 10 A or the inverter constituting the DC power supply in the preceding stage is stopped, the loss is short and does not lead to destruction.

Next, an embodiment in which a reverse polarity pulse generation function is added to an existing sputtering power supply not provided with a reverse polarity pulse power supply will be described with reference to FIG.

The range separated by the dashed line is the additional circuit 4
0. Reference numeral 1 denotes a rectifier having a commercial AC power supply as an input. Reference numeral 2 denotes a high-frequency inverter that operates on a rectified DC power supply, and detects an output voltage of an existing main power supply 41 to detect the output voltage.
A voltage for applying a reverse polarity voltage of about 0% to the sputter electrode is generated. Reference numeral 3 denotes a transformer for converting the high-frequency output voltage of the inverter 2, which can be significantly smaller than that of the main power supply 41.

A semiconductor switching element, for example, IG
The BT switches 15 and 16 are connected in series to an existing main power supply 41. IGBTs 15 and 16 have antiparallel diode 1
9, 20 are connected. 17 is a current limiting inductor,
11 is a current detection resistor, and 18 is a control circuit. The description of these operations is the same as that of the embodiment of FIG.

It is needless to say that this embodiment can also be used as a sputtering power supply having a novel reverse polarity pulse generation function as in FIG.

In these embodiments, a semiconductor switch 16 having a smaller current capacity than the semiconductor switch 15 can be used.

In the above embodiments, the semiconductor switching element is described as an IGBT, but an FET or an electrostatic induction type semiconductor element can be used. In the case of an FET, an anti-parallel diode is used by using the body diode. Can be omitted.

[0035]

As described above, according to the present invention, no magnetic components such as a block inductor and a pulse transformer are used in the DC power supply circuit, so that it is not necessary to reset the residual excitation energy of the inductor and the like. Can be reduced. Since the increase in frequency is determined by the switching speed of the semiconductor switching element, it is easy to increase the frequency and reduce the size, and there is no risk of deterioration or destruction of the switching element due to application of an overvoltage due to leakage inductance.

[Brief description of the drawings]

FIG. 1 shows a first embodiment according to the present invention.

FIG. 2 shows a signal explanatory diagram of FIG.

FIG. 3 shows an embodiment of overcurrent protection.

FIG. 4 shows an embodiment of a reverse polarity pulse generation additional circuit.

FIG. 5 shows an embodiment of a conventional reverse pulse generation circuit.

FIG. 6 shows an embodiment of a conventional reverse pulse generation circuit.

FIG. 7 shows an embodiment of a conventional reverse pulse generation circuit.

[Explanation of symbols]

1 ... rectifier, 2 ... high frequency inverter, 3 ...
Transformer, 4,5 ... Transformer secondary winding, 6,8
..Rectifiers, 7, 9 capacitors, 11 current-detecting resistors, 12 sputter electrodes, 13 anodes, 14 cathodes, 15, 16 semiconductor switches, 17 ... Inductor for current limiting, 18 ...
.Control circuit, 19, 20... Anti-parallel diode, 31
... IGBT, 32, 35 ... resistor, 33 ...
Bipolar transistor, 34 ... IGBT signal source, 40 ... Reverse polarity pulse generation additional circuit, 41 ...
Existing main power supply, 51 DC power supply, 52 sputter electrode, 53 inductor, 54 semiconductor switch, 55 reverse voltage source, 61 DC power supply,
62 ... sputter electrode, 63 ... auto transformer,
64: semiconductor switch, 66: start terminal, 67
..Intermediate terminals, 68 terminators, 71 DC power supply, 72 sputter electrodes, 73 inductors,
74: condenser, 75: pulse transformer, 7
6: secondary winding of pulse transformer, 77: primary winding of pulse transformer, 78: semiconductor switch, AC
... Commercial AC power supply, S1 ... IGBT15 ON signal, S2 ... IGBT16 ON signal, Vs ... Sputter electrode voltage, Is ... Sputter current, t ... Abnormal discharge start time

Claims (2)

[Claims] A main DC power supply and a DC power supply for reverse polarity pulse are connected so that their output voltages are in the same polarity and in series, and the main DC power supply and the DC power supply for reverse polarity pulse are connected. A first and a second semiconductor switch having an anti-parallel diode connected in series between both ends thereof are connected to each other, and a connection point between an output terminal of the main DC power supply and an output terminal of the reverse polarity pulse DC power supply is connected to the first and second semiconductor switches. By connecting a sputter electrode and a current limiting inductor so as to be in series with each other between the connection points of the first and second semiconductor switches, and periodically turning on the first and second semiconductor switches, When the first semiconductor switch is on, the main DC power supply supplies a negative steady-state voltage to the sputter electrode;
Wherein a positive polarity pulse of a reverse polarity is applied to the sputtering electrode from the reverse polarity pulse DC power source when the semiconductor switch is turned on. 2. The sputtering power source according to claim 1, wherein when each of the first and second semiconductor switches comprises an FET, each of the diodes is a body diode of the FET.