JPH0949077A - Dc sputtering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC sputtering device capable of maintaining stable discharge. SOLUTION: Plural cathode electrodes 41 , 42 are arranged in a film forming chamber 3 possessed by a DC sputtering device 2. The DC sputtering device 2 is provided with a positive voltage pulse impressing device 6. The positive voltage pulses of the same frequency as the frequency of the output voltage of DC power sources 81 , 82 are superposed and are impressed on therespective cathode electrodes 41 , 4 at the time of subjecting targets 51 , 52 disposed at the cathode electrodes 41 , 42 to DC sputtering by impressing the negative voltage of DC on the cathode electrodes 41 , 42 . Since the frequency of the positive voltage pulses impressed on the cathode electrodes 41 , 42 is the same, beats are not generated and the crossinterference of the plasmas generated on the targets 51 , 52 does not arise. The respective positive voltage pulses may be synchronously superposed on each other or may be superposed by shifting their phases.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sputtering apparatus for generating plasma in a vacuum for sputtering, and more particularly to a DC sputtering apparatus for superimposing a positive voltage pulse on a DC voltage to prevent abnormal discharge.

[0002]

2. Description of the Related Art The sputtering method is a technology for introducing a sputtering gas into a vacuum atmosphere and generating plasma of the sputtering gas to sputter a target to form a thin film. Since it is possible to obtain a good quality thin film, it is used in a wide range of applications such as manufacturing of semiconductor elements and liquid crystal display devices.

The sputtering method can be roughly classified into an RF sputtering method and a DC sputtering method depending on the type of applied voltage. However, an inexpensive power source can be used, the film forming speed is high, and the substrate temperature rises. DC from a few points
The sputtering method has been attracting attention, and direct current reactive sputtering for forming a film by introducing a reactive gas into the film forming chamber is also performed.

However, when DC sputtering is performed, abnormal discharge often occurs. The cause is Ar
A case where reactive gas sputtering of a silicon target is performed by introducing a gas and N ₂ gas into the film forming chamber will be described as an example. Referring to FIG. 6, reference numeral 101 denotes a silicon target, which is arranged on the cathode electrode 102 to which a negative DC voltage is applied. On the surface of the silicon target 101, due to the influence of the magnetic field distribution created by the magnetron magnet provided on the cathode electrode, the erosion portion 103 is easily sputtered and the target material is easily dug.
And a non-erosion portion 104 that is hard to be sputtered and hard to dig a target material.

When the target material located in the erosion portion 103 is sputtered and jumps out, the jumped-out silicon and the introduced N ₂ gas react with each other to generate SiN _{x, which} becomes the insulating film 105. Erosion part 1
04 will be deposited on the surface.

When the insulating film 105 is irradiated with Ar ⁺ ions or N ⁺ ions, positive charges are accumulated there,
If the potential rises and the insulating film 105 causes dielectric breakdown, abnormal discharge occurs. In addition, arc discharge may occur between the insulating film 105 and the earth shield or the like. As described above, the accumulation of positive charges in the insulating film 105 has been a cause of abnormal discharge. When abnormal discharge occurs, the target material scatters and adheres on the substrate or in the film, causing film defects, which is a serious problem.

Therefore, in the prior art, as shown in the graph of FIG. 7, a positive voltage pulse 108 is periodically superimposed on a negative DC voltage and applied to the cathode electrode, and when the cathode is placed at a positive potential. It has been performed that electrons in plasma are attracted and made to enter the insulating film 105 to neutralize the positive charges accumulated in the insulating film 105.

On the other hand, recently, it has been attempted to arrange a plurality of targets in one film forming chamber and simultaneously sputter the respective targets, which is an effective means for improving productivity without deteriorating film quality. However, if a plurality of cathode electrodes are provided in the film forming chamber of the DC sputtering apparatus as described above and a positive voltage pulse such as the positive voltage pulse 108 is applied to each cathode electrode, stable discharge can be maintained. It was found to disappear.

The reason is that when a positive voltage pulse is applied to each cathode, the plasma generated on the target surface arranged on each cathode electrode causes mutual interference, and as a result, one plasma is loaded by the other plasma. Therefore, it was found that the load impedance changes every moment. Mutual interference is particularly severe, and if an abnormal voltage occurs or an overcurrent flows, the safety device functions and the DC power is cut off, so it becomes impossible to apply the predetermined power to the target. .

Such mutual interference can be solved by increasing the installation distance between the cathode electrodes or by providing a mechanical shield between the targets. For that purpose, the film forming chamber must be made large. In addition, there is a disadvantage that the entire apparatus becomes complicated, and a solution has been desired.

[0011]

SUMMARY OF THE INVENTION The present invention was created to solve the above problems, and an object thereof is to maintain a stable discharge when sputtering a plurality of targets by a DC sputtering method. Especially.

[0012]

In order to solve the above-mentioned problems, the invention according to claim 1 is a negative DC voltage in which a positive voltage pulse is superposed on a plurality of cathode electrodes arranged in one film forming chamber. A DC sputtering apparatus for applying a voltage to a target provided on each cathode to apply a positive voltage pulse of the same frequency to each of the cathode electrodes. A positive voltage pulse applying device for controlling the frequency of the positive voltage pulse is provided.

The positive voltage pulse applying device in that case is
According to the second aspect of the present invention, the positive voltage pulse is applied so that the time intervals from the application of the positive voltage pulse to one cathode electrode to the application of the positive voltage pulse to the next cathode electrode are equal. It is preferable to control the phase or superimpose the positive voltage pulses in synchronization.

In the case of the prior art, as shown in FIG. 4, the DC power supplies 58 ₁ and 58 ₂ are connected to the positive voltage pulse superimposing device 5.
6 ₁ and 56 ₂ via the cathode electrode 5 independently of each other
4 ₁ , 54 ₂ and the positive voltage pulse superimposing device 56 ₁ ,
By 56 _2, wherein when you were applied separately positive voltage pulse to the DC power supply 58 _1, 58 _2, even if the period has only slightly different, as shown in FIG. 5, the cathode electrode The generation timing of the positive voltage pulses 31 ₁ and 31 ₂ applied to 54 ₁ and 54 ₂ relatively changes, and a beat is generated due to the difference in frequency.

In the present invention, since the positive voltage pulse applying device is provided so that the positive voltage pulse of the same frequency is superimposed on the DC voltage applied to each cathode electrode, the beat of the frequency difference does not occur, Plasmas do not interfere with each other, and stable sputtering can be performed.

The frequency of the positive voltage pulse applied to each cathode electrode may be the same, the phases are shifted, and the time intervals from application to one cathode electrode to application to the next cathode electrode become equal. You can
You may superimpose in synchronization.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of the DC sputtering apparatus of the present invention. The DC sputtering apparatus 2 has a film forming chamber 3 into which a sputtering gas and a reaction gas are introduced after being evacuated. Cathode electrodes 4 ₁ , 4 ₂ are arranged in the film forming chamber 3, and targets 5 ₁ , 5 ₂ made of silicon oxide (SiO ₂ ) are attached on the cathode electrodes 4 ₁ , 4 _2. The two targets 5 ₁ and 5 ₂ can be simultaneously sputtered.

The DC sputtering device 2 has DC power supplies 8 ₁ and 8 ₂ and a positive voltage pulse applying device 6,
The negative DC voltages output from the output terminals A ₁ and A _{2 of the} DC power supplies 8 ₁ and 8 ₂ are input to the positive voltage pulse superimposing devices 9 ₁ and 9 ₂ provided in the positive voltage pulse applying device 6, respectively. Is
Positive voltage pulses are superposed by the positive voltage pulse superimposing devices 9 ₁ and 9 ₂ , taken out from the output terminals B ₁ and B _{2 of the} positive voltage pulse applying device 6 and applied to the cathode electrodes 4 ₁ and 4 ₂ . Are connected as they are.

The positive voltage pulse superimposing devices 9 ₁ and 9 ₂ are connected to the abnormal voltage monitoring devices 14 ₁ and 14 ₂ , and their outputs are monitored, respectively, and are generated by overvoltage generated by load fluctuation or arc discharge. Is configured to be detected.

The abnormal voltage monitoring devices 14 ₁ and 14 ₂ are connected to the DC power supplies 8 ₁ and 8 ₂ to form a feedback loop, and an abnormality is detected in the output of the pulse voltage superposing devices 9 ₁ and 9 _2. If so, the DC power supplies 8 ₁ and 8 ₂ are immediately stopped.

The positive voltage pulse superimposing devices 9 ₁ and 9 ₂ are connected to the phase shifter 7, and the phase shifter 7
It is configured to be synchronized with a signal input from the DC power supply 8 ₁ and 8 ₂ to superimpose a positive voltage pulse on the negative DC voltage output from the DC power supplies 8 ₁ and 8 ₂ at a timing according to the signal of the phase shifter 7. There is.

The operation of the DC sputtering device 2 will be described in detail. When the DC power supplies 8 ₁ and 8 ₂ and the phase shifter 7 are activated to sputter the targets 5 ₁ and 5 ₂ , the DC power supply is activated. As shown in FIG. 2A, the negative DC voltage of −V ₀ is output from each of 8 ₁ and 8 ₂ to each of the output terminals A ₁ and A ₂ , and the voltage is applied to the pulse voltage superposing device 9 ₁ , 9 ₂ is input.

At this time, the pulse voltage superposing devices 9 ₁ , 9 ₂
From the phase shifter 7 to the frequency f (f = 4
Clock signals having phases shifted from each other by a half wavelength of 1 / (2 f) at 0 kHz are input. Then, the output terminals B ₁ and B ₂ of the positive voltage pulse applying device 6 are synchronized with the clock signal of the pulse voltage superposers 9 ₁ and 9 ₂ as shown in FIG. Both have a frequency of fHz and are out of phase with each other by half a wavelength (that is, πrad with respect to each other).
Positive phase pulses 20 ₁ and 20 ₂ with the wave front extending to the positive voltage region are superposed (pulse width 5).
μsec), electrons are drawn into the non-erosion regions of the cathodes 5 ₁ and 5 ₂ and thus the occurrence of abnormal discharge is prevented.

In the above embodiment, the case where two targets are sputtered has been described, but three or more targets may be sputtered. In that case, the frequency of the positive voltage pulse applied to each target is the same. Shi (f
Hz), 1 / (f target number) and the phase may be shifted (that is, the phase may be shifted by "2π / target number rad"). For example, when three targets are sputtered, the voltage waveforms at the output terminals B _{1 to} B ₃ to which the cathode electrode provided with each target and the positive voltage pulse applying device 6 are connected are as shown in FIG. Positive voltage pulse 2 shown in
Like 1 _{1 to} 21 _3, the phase may be shifted by 1 / (3 f) (it may be shifted by 2 π / 3 rad).

In the above embodiment, the cycle of the positive voltage pulse is shifted, but as shown in FIG. 3 (b), the application timings of the positive voltage pulses 21 ₁ and 21 ₂ are made to coincide with each other and the frequency fHz is set.
Beats do not occur even if they are superposed in synchronization, and the plasmas do not interfere with each other. Even when three or more targets are sputtered, the positive voltage pulse applied to each cathode electrode may be synchronized.

[0027]

[Effects of the Invention] Even if a plurality of targets are sputtered by the DC sputtering method, mutual interference of plasma due to beats is eliminated. As a result, abnormal discharge does not occur, so that the power source is not burdened and the film can be formed without film defects.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a sputtering apparatus of the present invention.

FIG. 2A is a voltage waveform diagram for explaining an output waveform of a DC power source. FIG. 2B is a timing chart for explaining an example of an output waveform of the positive voltage pulse applying device of the present invention.

FIG. 3A is a timing chart for explaining another example of the output waveform of the positive voltage pulse applying device of the present invention.
A timing chart for explaining still another example

FIG. 4 is a block diagram for explaining a connection when the positive voltage pulse applying device of the present invention is not provided.

FIG. 5 is a timing chart of a positive voltage pulse applied to the cathode.

FIG. 6 is a diagram for explaining the cause of abnormal discharge.

FIG. 7 is a diagram showing a positive voltage pulse for preventing abnormal discharge when sputtering one target.

[Explanation of symbols]

2 ...... DC sputtering device 3 ...... deposition chamber 4 _1,
4 ₂ Cathode electrode 5 ₁ 5 ₂ Target 6 Positive voltage pulse application device

Claims (3)

[Claims] 1. A DC sputtering apparatus for sputtering a target provided on each cathode by applying a direct current negative voltage in which a positive voltage pulse is superposed to a plurality of cathode electrodes arranged in one film forming chamber. And a DC voltage applying device for controlling the frequency of the positive voltage pulse so that the positive voltage pulse of the same frequency is applied to each cathode electrode.
Sputtering equipment. 2. The positive voltage pulse applying device is configured so that the positive voltage pulse is applied to one cathode electrode and the positive voltage pulse is applied to the next cathode electrode at equal time intervals. The DC sputtering apparatus according to claim 1, wherein the phase of the voltage pulse is controlled. 3. The DC sputtering apparatus according to claim 1, wherein the positive voltage pulse applying device superimposes the positive voltage pulses synchronously.