JP2002173772A - Sputtering apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent defective ignition at the discharge between a target and an anode. SOLUTION: A direct current from a DC power source 7 can be alternately applied between the target 3 and the anode 4, and to a load 31. However, when performing ignition for igniting plasma discharge between the target 3 and the anode 4, a switch 32 is opened so that the direct current from the DC power source 7 is applied to a sufficiently large impedance. When the plasma discharge is ignited, the switch 32 is closed, and the direct current from the DC power source 7 is applied to the load 31 which is the impedance of the magnitude substantially equal to that of the plasma impedance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a sputtering apparatus.

[0002]

2. Description of the Related Art In general, a phase-change type optical disk has a structure in which at least a first protective layer, a recording layer, a second protective layer, and a reflective layer are laminated in this order on a circular transparent substrate such as polycarbonate. . Recording and reproduction of this phase change optical disk are performed by the following means. First, when writing information, a focused laser pulse is applied to the crystalline recording layer for a short time to partially melt the recording layer. The melted portion is rapidly cooled and solidified by thermal diffusion, thereby forming a recording mark in an amorphous state. The signal is read using the difference in the reflectance between the amorphous recording mark and the crystalline state.
The signal is erased by irradiating the recording mark portion with a laser beam to heat the recording layer to a temperature lower than the melting point and higher than the crystallization temperature to return the amorphous state to the original crystallized state.

[0003] AgInSbTe-based and GeSbTe-based compounds have been put into practical use as a recording layer material of a phase change optical disk. Usually, a sputtering method is used as a means for forming each layer including the recording layer.

As the sputtering method, there are an RF sputtering method using a high frequency as a means for generating plasma, and a DC sputtering method using an ordinary direct current. The RF sputtering method has the advantage of being able to stably form a film even on an insulator material, but requires high equipment costs such as a matching unit and the like, the film formation rate is lower than that of the sputtering method, and the substrate temperature is lower. Have the disadvantage that they are more likely to rise than the sputtering method. Therefore, it can be generally said that the DC sputtering method is superior in mass productivity in terms of cost.

However, in the DC sputtering method, it is necessary that the target has sufficient conductivity for transporting a discharge current. Generally, since the discharge voltage in the DC sputtering method is about 500 to 1000 V, for example, assuming a voltage drop of 25 V at the target, a current density of 25 mA / cm ² , and a target thickness of 6 mm, the allowable target is The specific resistance needs to be about 1700Ωcm or less. AgInSb
Since the specific resistance of the Te-based recording film is about several Ωcm, it is possible to sufficiently form a film by the sputtering method.

However, in actuality, as the erosion of the target progresses, residues due to selective sputtering and reattachments to the target begin to cover the target surface, and electric discharge becomes unstable due to electric field concentration and charge accumulation. And a method in which a reverse bias is periodically applied to the target.

Further, in a sputtering technique and a technique for manufacturing a phase change type optical recording medium using the sputtering technique, a technique for preventing arc discharge is disclosed in Japanese Patent Laid-Open No. 10-83585.
And Japanese Patent Application Laid-Open Nos. 10-25568, 7-34236 and 8-74047.

[0008]

However, in the DC sputtering method for chopping a DC voltage,
Poor ignition of plasma discharge occurs, which is a major problem in production. If the ignition failure time becomes long, the thickness of the recording layer becomes extremely thin in the production of the phase change type optical recording medium, and the quality of the recording medium deteriorates and the yield decreases. A similar phenomenon has been confirmed in GeSbTe-based recording films.

An object of the present invention is to prevent discharge ignition failure in the DC sputtering method for chopping a DC voltage.

An object of the present invention is to sufficiently prevent the above-described discharge ignition failure.

An object of the present invention is to reduce load fluctuations as viewed from the DC power supply side, stabilize control of the DC power supply, and prevent erroneous arc detection.

An object of the present invention is to accurately perform sputtering film formation on an object by preventing ignition failure of discharge or the like.

[0013]

According to a first aspect of the present invention, there is provided a target and an anode placed in a vacuum atmosphere, a DC power supply for supplying a DC voltage applied for discharging between the target and the anode, A chopper for performing chopping so as to intermittently apply the DC voltage between the target and the anode; an ignition means for igniting the discharge when the discharge is started; and the ignition based on an output of the DC power supply. An ignition detection means for detecting, and an ignition termination means for terminating the ignition of the discharge when the ignition is detected, at least in the off period of the intermittent DC voltage application at the time of performing the chopping. A sputtering apparatus for applying the DC voltage to an impedance having a magnitude capable of igniting the discharge.

Therefore, it is possible to prevent ignition failure of discharge between the target and the anode.

According to a second aspect of the present invention, in the sputtering apparatus of the first aspect, the impedance is 1 MΩ or more.

Therefore, it is possible to sufficiently prevent ignition failure of discharge between the target and the anode.

According to a third aspect of the present invention, there is provided the first or second aspect.
In the sputtering apparatus described in (1), after the start of the discharge, there is provided an impedance adjusting means for making the impedance smaller than a magnitude capable of starting the discharge.

Therefore, after the discharge is started, the difference between the plasma impedance between the target and the anode and the impedance on the load side is reduced to reduce load fluctuations as viewed from the DC power supply side and to stabilize the control of the DC power supply. Can be.

According to a fourth aspect of the present invention, in the sputtering apparatus according to the third aspect, the impedance adjustment means is configured to control the DC power by the chopper during the off period.
A voltage is applied, the impedance element has an impedance value smaller than the magnitude at which the discharge can be started, a switch for opening and closing the connection between the impedance element and the chopper, and the switch is opened when the discharge is ignited. Switch opening / closing means that closes when the ignition is detected.

Therefore, when starting the discharge, the switch is opened to maximize the impedance on the load side, thereby preventing the ignition failure of the discharge. After the start of the discharge, the switch is closed, and the target is closed. By reducing the difference between the plasma impedance between the anodes and the impedance on the load side, load fluctuations seen from the DC power supply side can be reduced, thereby stabilizing control of the DC power supply and preventing erroneous arc detection.

According to a fifth aspect of the present invention, in the sputtering apparatus of the fourth aspect, the impedance element has a variable impedance value.

Therefore, a target whose load impedance varies depending on the type of the target, discharge conditions, and the like,
Adjustment can be made in accordance with the plasma impedance between the anodes, and load fluctuation during discharge can be suppressed to prevent malfunction of the DC power supply.

According to a sixth aspect of the present invention, in the sputtering apparatus according to any one of the first to fifth aspects, the target is formed by sputtering on an object.

Therefore, it is possible to prevent the ignition failure of the discharge or the like, and to accurately perform the sputtering film formation on the object.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment of the Invention] One embodiment of the present invention will be described as a first embodiment of the present invention.

FIG. 1 is a block diagram showing the overall configuration of a sputtering apparatus according to Embodiment 1 of the present invention.
As shown in FIG. 1, the sputtering apparatus 1 includes a target-anode circuit 2. This target
The inter-anode circuit 2 is housed in a chamber (not shown) or the like, and is placed in a vacuum atmosphere by a known technique. The target 3 is a cathode, and the inner wall of the chamber is an anode (G
ND ground) 4. Then, the substrate 5 which is the target of sputtering film formation using the target 3 as a material is the target 3
Are arranged opposite to each other.

The switching circuit 6 serving as a chopper performs chopping so as to intermittently apply the DC output from the DC power supply 7 to the target-anode circuit 2. That is, the switching circuit 6 connects the terminal 6a connected to the DC power supply 7 to the terminal 6b connected to the target 3 during the ON period, and the terminal 6a connected to the DC power supply 7 during the OFF period. A terminal 6c that is not connected to a circuit element or the like is connected.

The driving circuit 8 drives the DC power supply 7, and the driving circuit 9 drives the switching circuit 6. The control unit 10 is configured by a microcomputer or the like, and controls the drive circuits 8 and 9.

Although omitted in FIG. 1, the switching circuit 6
In the off period, the target 3 is set to the same potential as the anode 4 (GN)
Ground to D).

FIG. 2 is a circuit diagram of the output side of the power supply circuit of the DC power supply 7. The DC power supply 7 rectifies a commercial AC by a rectifier circuit (not shown), smoothes the AC power by a smoothing circuit 18 including coils 11 and 12 and a capacitor 13, and outputs the smoothed power from output terminals 14 and 15. A current sensor 16 is interposed in the line on the output end 15 side, and the detection signal is output to the control unit 10. The current sensor 16 does not need to be a means for directly measuring a current, and for example, a combination of an inductance and a magnetic field detecting means can be used.

FIG. 3 is a flowchart for explaining the processing performed by the control unit 10 when the discharge is ignited in the target-anode circuit 2. As shown in FIG. 3, when the start of sputtering is instructed (Y in step S1), the control unit 10 controls the DC power source 7 to
A DC output for generating a plasma discharge is started between them (the output of the DC power supply 7 is controlled by well-known PWM control or the like). The switching circuit 6 starts the chopping operation (step S2). At this time, the voltage waveform applied to the target-anode circuit 2 is, for example, a periodic intermittent waveform as shown in FIG. That is, during the ON period of the switching circuit 6, the voltage Vd (non-voltage) of a predetermined magnitude
Is applied, and attains the GND level during the off period.

Then, an ignition operation is performed (step S3). This is an operation for controlling the DC power supply 7 to instantaneously output a voltage higher than the rated voltage at the time of plasma ignition, thereby smoothly igniting the plasma discharge. After the ignition operation, the current value detected by the current sensor 16 is compared with a predetermined threshold value (step S4). If a current larger than the threshold value flows from the output terminals 14 and 15, it is determined that the plasma discharge has been ignited. The ignition operation is terminated upon determination (Y in step S4). If the ignition operation is not more than the threshold value (N in step S4), the ignition operation is repeated (step S3). When the plasma discharge is ignited in this way, sputtering starts, and the target 3 can be formed on the substrate 5 by sputtering. Step S3
The ignition means is realized by N of S4, and the ignition ending means is realized by Y of step S4.

DC power source 7 in sputtering apparatus 1
5 shows a normal output waveform. The voltage 21 and the power 22 in FIG. 5 indicate changes with time regarding the output of the primary side of the voltage and the power output from the DC power supply 7, respectively. Generally, since the DC power supply 7 is controlled in power,
The waveform 2 shows a constant output after the rise time set inside the DC power supply 7. Actual target
Although an intermittent waveform as shown in FIG. 4 is applied to the anode-to-anode circuit 2, since the on / off frequency of the switching circuit 6 is sufficiently high, the load fluctuation is caused by the smoothing circuit 1 on the output end side of the DC power supply 7.
8 does not reach the temporary output of the DC power supply 7.

FIG. 6 shows the sputtering apparatus 1 shown in FIG.
It is a block diagram which shows the whole structure of the sputtering apparatus 100 which is a comparative example. In FIG. 6, members having the same reference numerals as those in FIG. 1 are circuit elements and the like common to the sputtering apparatus 1 in FIG. Sputtering equipment 1
00 differs from the sputtering apparatus 1 in that the terminal 6c
A load 17 is interposed between the load 17 and GND.

FIG. 7 shows the output waveform of the DC power supply 7 when the ignition of the plasma discharge in the sputtering apparatus 100 is defective. At the time of poor ignition, voltage 21 and power 22
The step-like flat output parts 23 and 24 appear. At the time of poor ignition, the impedance of the target-anode circuit 2 has a maximum value, so that the output voltage of the DC power supply 7 reaches the rated maximum and the flat portion 23 appears. The flat portion 24 on the DC power supply 7 side is power consumed by the load 17 while the switching circuit 6 is off. Flat portion 24 showing this internal power consumption
Varies depending on the on / off ratio of the switching circuit 6.
Accidental ignition between target 3 and anode 4 (arrow 2 in FIG. 7)
5), the subsequent waveforms are the same as in FIG.

The cause of the ignition failure of the plasma discharge in the sputtering apparatus 100 shown in FIG. This is because the power consumption of the load 17 causes the current value detected by the current sensor 16 to exceed a predetermined threshold value, which is erroneously recognized as ignition of plasma discharge, so that the ignition operation does not function properly.

On the other hand, according to the sputtering apparatus 1 shown in FIG. 1, no circuit element or the like is connected to the terminal 6c. Will be connected to the impedance, DC
The power supply 7 consumes little power. For this reason, the current value detected by the current sensor 16 does not exceed a predetermined threshold value, so that erroneous recognition of ignition of plasma discharge as in the sputtering apparatus 100 does not occur, and the ignition operation functions normally.

In the above example, no circuit element or the like is connected to the terminal 6c. However, if the terminal 6c has a sufficiently large impedance capable of igniting plasma discharge, any load is connected. May be. In this case, the impedance is desirably 1 MΩ or more. Assuming that the applied voltage in the ignition operation is 1500 V when the resistance is 1 MΩ, the current is 1.5 mA, which is sufficiently low as a current value at which the ignition operation does not malfunction.

[Second Embodiment of the Invention] Another embodiment will be described as a second embodiment of the invention.

FIG. 8 is a block diagram showing the entire configuration of the sputtering apparatus according to the second embodiment of the present invention.
In FIG. 8, members having the same reference numerals as those in FIG. 1 are circuit elements and the like common to the sputtering apparatus 1 of the first embodiment, and a detailed description thereof will be omitted. This sputtering apparatus 1 is different from the sputtering apparatus 1 of the first embodiment in that
In addition, a load 31, which is an impedance element made of a variable resistor, is interposed between the terminal 6c and GND, and the terminal 6c and the load 1
7 is provided with a switch 32 for opening and closing between the terminal 6 c and the load 31, and this switch 32 can be opened and closed by the control unit 10 via the drive circuit 33. Secondly, the process for igniting the discharge in the target-anode circuit 2 is different from the flowchart shown in FIG.
The processing shown in the flowchart of FIG.

The processing shown in FIG. 9 will be described. When the start of sputtering is instructed (Y in step S11), the control unit 10 controls the DC power supply 7 to start outputting a direct current for generating plasma discharge between the target 3 and the anode 4 (DC power supply). 7 is controlled by a well-known PW
M control etc.). The switching circuit 6 starts the chopping operation. And the switch 32
Is opened (or the switch 32 is opened in advance) (step S12).

Then, an ignition operation is performed (step S13). This is the same operation as in step S3. After the ignition operation, the current value detected by the current sensor 16 is compared with a predetermined threshold value (step S1).
4) If a current larger than the threshold value flows from the output terminals 14 and 15, it is determined that the plasma discharge has been ignited, the switch 32 is closed (step S15), and the ignition operation ends. If it is equal to or smaller than the threshold value (N in step S14), the ignition operation is repeated (step S13). The ignition means is realized by N of steps S13 and S14, the ignition ending means is realized by Y of step S14, and the switch opening / closing means is realized by steps S12 and S15. Switch 3
2. Impedance adjusting means is realized by the processing of step S15 performed by the load 31, the drive circuit 33, and the control unit 10.

FIG. 10 shows the voltage 21 and the power 22 (a) output from the DC power supply 7 and the open / close signal 26 of the switch 32 when the plasma discharge is normally ignited.
It is a timing chart with (b). That is, the open / close signal 26 is closed until the current value detected by the current sensor 16 exceeds the predetermined threshold value, and is opened when the current value exceeds the threshold value.

By the way, in the first embodiment of the present invention, in order to perform the ignition operation normally, the DC power supply 7 is always connected to the impedance of the maximum value (for example, 1 MΩ or more) so that the power consumption is reduced. The amount was kept low to prevent ignition failure of the plasma discharge.

However, in this means, since the difference between the plasma impedance of the target-anode circuit 2 and the plasma impedance of the target-anode circuit 2 is large, the load fluctuation viewed from the DC power supply 7 side during the operation of the switching circuit 6 increases. Is D
The control of the C power supply 7 becomes unstable, or the trouble that the power supply of the DC power supply 7 is stopped due to an erroneous arc detection occurs.

That is, it is desirable that the impedance to which the DC power supply 7 is connected during the off period of the switching circuit 6 be substantially equal to the plasma impedance of the target-anode circuit 2 during plasma discharge. On the other hand, before the start of the plasma discharge, the ignition operation should be high enough not to cause an erroneous operation, preferably about 1 MΩ or more as described above.

Therefore, according to the sputtering apparatus 1 of this embodiment, the impedance of the output destination of the DC power supply 7 during the off period of the switching circuit 6 has a maximum value because the switch 32 is open when performing the ignition operation. . Then, when ignition of the plasma discharge is confirmed (step S14), the switch 32 is closed (step S15), and the output destination of the DC power source 7 during the off period of the switching circuit 6 is the load 31, so that in this case, DC power supply 7
Can be set to an optimum value that is not substantially as large as the above-mentioned maximum value but is substantially equal to the target-anode circuit 2.

Therefore, load fluctuations seen from the DC power supply 7 side can be reduced, and control of the DC power supply 7 can be stabilized.

In the second embodiment, since the load 31 is a variable resistor, the impedance can be changed.
The impedance of the load 31 can be adjusted to be the same as the plasma impedance of the target-anode circuit 2 that changes depending on the type of the target 3 and the discharge conditions.

Thus, load fluctuation during discharge is suppressed to a minimum, and even if the switching frequency of the switching circuit 6 is relatively low, the target 3 and the anode 4 are not charged after the start of plasma discharge.
The difference between the impedance of the plasma 31 and the impedance of the load 31 can be reduced to reduce load fluctuations during discharge as viewed from the DC power supply 7 side, and to eliminate malfunctions of the power supply and stabilize control of the DC power supply 7. it can.

The effect of improving ignition failure in the first and second embodiments will be described with reference to FIGS. FIG.
1 and FIG. 12, the time (discharge stop time) in which the occurrence of the flat portion 24 in FIG.
The change in the repetitive discharge is shown (the horizontal axis is the number of continuous discharges). FIG. 11 is for the sputtering apparatus 100 of FIG. 6, and FIG. 12 is for the sputtering apparatus 1 shown in FIGS. Comparing the two, according to the sputtering apparatus 1 shown in FIGS.
It can be seen that the ignition failure of the plasma discharge can be completely eliminated.

[0052]

FIG. 13 is an enlarged longitudinal sectional view of a phase change optical disk. As shown in FIG. 13, the phase-change optical disc 41 has a diameter of 120 mm and a thickness of 0.6 obtained by injection molding.
A lower protective layer 43 (90 nm) made of ZnS / SiO ₂ and a recording layer 44 made of AgInSbTe are formed on a polycarbonate substrate 42 of mm.
(20 nm), an upper protective layer 45 (30 nm) made of ZnS / SiO ₂ ,
An alloy layer 46 (160 nm) made of Al and a resin protective layer 47 are sequentially formed.

The recording layer 44 is formed by the sputtering apparatus 1 of the second embodiment, and
After the continuous production of 00,000 sheets, the recording layer 44
There is no failure due to poor ignition of plasma discharge,
The thickness variation of the recording layer 44 could be kept within ± 2% of the original thickness distribution specification of the cathode.

[0054]

According to the first aspect of the present invention, a target,
Poor ignition of discharge between the anodes can be prevented.

According to the second aspect of the present invention, in the sputtering apparatus according to the first aspect, it is possible to sufficiently prevent ignition failure of discharge between the target and the anode.

The third aspect of the present invention is the first or second aspect.
In the sputtering apparatus described in 1 above, after the discharge starts, the difference between the plasma impedance between the target and the anode and the impedance on the load side is reduced to reduce load fluctuations as viewed from the DC power supply side, and to stabilize control of the DC power supply. Can be planned.

According to a fourth aspect of the present invention, in the sputtering apparatus of the third aspect, when starting the discharge, a switch is opened to prevent the discharge ignition failure by maximizing the impedance on the load side. After the discharge starts, close the switch, reduce the difference between the plasma impedance between the target and the anode and the impedance on the load side, and reduce the load fluctuation seen from the DC power supply side.
It is possible to stabilize the control of the DC power supply and prevent erroneous arc detection.

According to a fifth aspect of the present invention, there is provided the sputtering apparatus according to any one of the first to fourth aspects, wherein the impedance of the impedance element is changed between the target and the anode, which change depending on the type of the target and discharge conditions. Adjustment can be made in accordance with the plasma impedance, load fluctuation during discharge can be suppressed, and malfunction of the DC power supply can be prevented.

According to a sixth aspect of the present invention, in the sputtering apparatus according to any one of the first to fifth aspects, it is possible to appropriately perform sputtering film formation on an object by preventing ignition failure of discharge or the like. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of a sputtering apparatus according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of an output terminal side portion of a power supply circuit in a DC power supply of the sputtering apparatus.

FIG. 3 is a flowchart illustrating a process performed by a control unit when a discharge is ignited in a target-anode circuit of the sputtering apparatus.

FIG. 4 is a waveform diagram of a voltage waveform applied to the target-anode circuit by a DC power supply.

FIG. 5 is a waveform diagram of a normal output waveform of a DC power supply in the sputtering apparatus.

FIG. 6 is a block diagram showing an overall configuration of a sputtering apparatus which is a comparative example of the sputtering apparatus.

FIG. 7 is a waveform diagram showing an output waveform of a DC power supply when ignition failure of plasma discharge occurs in the sputtering apparatus.

FIG. 8 is a block diagram showing an overall configuration of a sputtering apparatus according to a second embodiment of the present invention.

FIG. 9 is a flowchart illustrating a process performed by a control unit when a discharge is ignited in a target-anode circuit of the sputtering apparatus.

FIG. 10 is a timing chart of a voltage and power (a) output from a DC power supply and a switch open / close signal (b) when plasma discharge is normally ignited by the sputtering apparatus.

FIG. 11 is an explanatory diagram illustrating an effect of improving ignition failure in the first and second embodiments of the present invention.

FIG. 12 is an explanatory diagram of the same.

FIG. 13 is an enlarged vertical sectional view of a phase-change optical disc according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sputtering apparatus 3 Target 4 Anode 7 DC power supply 31 Impedance adjustment means, impedance element 32 Impedance adjustment means 33 Impedance adjustment means

Claims (6)

[Claims] 1. A target and an anode placed in a vacuum atmosphere, and D applied to discharge between the target and the anode.
A DC power supply that supplies a C voltage; a chopper that performs chopping so as to intermittently apply the DC voltage between the target and the anode; an ignition unit that ignites the discharge when starting the discharge; Ignition detection means for detecting the ignition based on the output of the DC power supply, and ignition termination means for terminating the discharge ignition when the ignition is detected, at least the intermittent when performing the chopping Na D
A sputtering apparatus for applying the DC voltage to an impedance having a magnitude capable of igniting the discharge during an off period of the application of the C voltage. 2. The sputtering apparatus according to claim 1, wherein the impedance is 1 MΩ or more. 3. The sputtering apparatus according to claim 1, further comprising an impedance adjusting means for making the impedance smaller than a value at which the discharge can be started after the start of the discharge. 4. The impedance adjusting means comprises: an impedance element having an impedance value smaller than a magnitude capable of starting the discharge when the DC voltage is applied by the chopper during the off period; and the impedance element and the chopper. A switch for opening and closing the connection of the switch, a switch opening and closing means that opens the switch when the discharge is ignited, and closes when the ignition is detected,
The sputtering apparatus according to claim 3, further comprising: 5. The sputtering apparatus according to claim 4, wherein said impedance element has a variable impedance value. 6. The sputtering apparatus according to claim 1, wherein the target is formed by sputtering on an object.