JPH02141572A - Method and device for bias sputtering - Google Patents

Abstract

PURPOSE:To prevent the damage of a substrate and to efficiently form a film thereon by impressing a square wave high-frequency voltage which can independently change the peak values of the negative polarity voltage and positive polarity voltage and energization time to the substrate and sputtering a target. CONSTITUTION:The target 11 having magnets 15 on the rear surface and the substrate 12 are disposed to face each other in a vacuum vessel 14. The above-mentioned vacuum vessel 14 is grounded and a sputtering voltage is impressed from a power source 10 to the target 11 and a bias voltage is impressed to the substrate 12 to sputter the target 11 and to form the film on the substrate 12. The above-mentioned bias voltage is impressed to the target from positive and negative polarity constant voltage power sources 1, 3 in the above-mentioned sputtering method. Voltage setting potentiometers 2, 4 are respectively provided to these power sources 1, 3 and the absolute value of the peak voltage of the negative polarity voltage is set higher than the peak value of the positive polarity voltage. Further, the voltage is set to the square wave which is longer in the energization time of the negative polarity than the energization time of the positive polarity by a waveform controller 5 and positive and negative polarity switching transistors 8, 9. The damage of the substrate 12 by electron bombardment is prevented in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method and apparatus for forming a thin film by bias sputtering, and particularly to a method and apparatus for forming a thin film by bias sputtering.
The present invention relates to a bias sputtering method and an apparatus for the same.

[Conventional technology]

As the degree of integration of semiconductor devices increases, the diameters of contact holes between a silicon substrate and aluminum wiring and through holes between aluminum wiring become smaller, and the aspect ratio becomes larger. In the commonly used DC magnetron sputtering method, as the aspect ratio approaches 1, the step coverage deteriorates due to the sheer force effect during sputtering of wiring material, which increases wiring resistance and causes disconnections such as electromigration and stress migration. is more likely to occur. To improve this, a bias sputtering method was developed in which the vacuum chamber is grounded and a film is formed while applying a negative voltage to the target layer (-) and the substrate.
The figure shows an example of the principle of DC bias sputtering. jl (The board 12 and target 11 each have
Since a negative voltage is applied independently, a film is formed on the substrate while being subjected to Δr・ion bombardment ()φ sputtering). This jφ sputtering effect can improve step coverage.

16 in the figure is a bias power supply.

[Problem to be solved by the invention]

However, in such a bias sputtering method, since the Si substrate is generally covered with an insulating film Sj,02,
Unless the Q film is formed to some extent, the bias current will not flow to the substrate, and therefore no bias effect will be obtained. Furthermore, since the film is an insulator at the initial stage of film formation, it is charged up. These factors often cause abnormal discharge and damage to the board. In order to reduce damage and breakage of the substrate, after the AQ film has been formed to some extent, a negative bias voltage is applied to the substrate to form the film. However, with this method, the bias effect cannot be sufficiently obtained, and step coverage and film quality cannot be sufficiently improved. Also, JP-A-61-2
In Japanese Patent No. 64174, as shown in FIG. 6, the negative bias voltage is periodically returned to approximately the ground level to cause electrons to flow into the surface of the mounting plate, thereby improving the charge amplifier of the substrate. However, this method takes time for the board to recover to ground level, so it is not a sufficient solution. Furthermore, as shown in the waveform shown in FIG. 7, there is also a method in which bias sputtering can be performed even on insulators by applying alternating current (high frequency) to the substrate. However, as the waveform shows, when the substrate is a positive electrode, accelerated electrons flow into the substrate, so the substrate receives an electron bombardment.
It has drawbacks such as heating and damage.

[Means to solve the problem]

In order to solve the above problems, in the film forming method according to the present invention, square wave voltages of different polarities are periodically applied to the substrate alternately, and the voltage waveform is changed to a point where the positive polarity voltage is lower than the negative polarity peak value. Or, the negative polarity energization time is made longer than the positive polarity energization time.

[Effect]

As shown in FIG. 7, charge-up can be prevented by applying an AC waveform to the substrate. However, a new problem arises in that when the substrate is a positive electrode, accelerated electrons impact the substrate and damage the substrate.

In order to reduce this electron energy as much as possible, in the present invention, as shown in the bias voltage waveform in Figure 1, the waveform is made into a square wave, the peak voltage of the positive polarity is lower than that of the negative polarity, and the energization time is By making the length shorter than that for the negative electrode, damage to the substrate due to electron impact and charge-up is prevented.

〔Example〕

An embodiment of a film forming apparatus according to the present invention will be shown with reference to FIGS. 1 and 2. The upper part of FIG. 1 is a schematic diagram of the bias waveform of the present invention. Here, NV is the peak voltage when the substrate 12 is the negative electrode, Pv is the peak voltage when the substrate 12 is the positive electrode, T1 is the energizing time when the negative electrode is, T2 is the energizing time when the substrate 12 is the positive electrode, PV/NV is the bias voltage ratio, and T2/ ( T1+T2) is the bias energization ratio.

In Fig. 2, 3 is a constant voltage control power supply for supplying the negative voltage to the board 12, 4 is a potentiometer for setting the voltage, and 1 is a constant voltage for supplying the positive voltage to the board. Power supply, 2 is a potentiometer for setting the voltage, 5 is a waveform control device, 6 is a potentiometer for setting the energization ratio of negative and positive electrodes, 7 is a frequency setting potentiometer, 9 is a signal from the waveform control device A switching transistor 4 periodically supplies a negative voltage to the substrate, and a switching transistor 8 periodically supplies a positive voltage to the substrate. The potentiometer 6 of the waveform control device 5 sets the energization ratio of negative polarity and positive polarity, and the frequency is set at 7. Further, the peak voltage NV of the negative electrode is set using the potentiometer 4 of the constant voltage power source for the negative electrode. Further, the peak voltage PV of the positive electrode is set by the potentiometer 2. In addition, the signals for the respective energization times set by the waveform control device 5 are supplied to the switching transistors 8 and 9, which turn the respective set voltages on and off alternately for the set time, thereby changing the voltages at the negative and positive poles. Apply voltage alternately to the substrate. Thin film formation using the thin film forming apparatus shown in FIG. 2 will be described below. First, the influence of the bias voltage ratio PV/NV on film damage will be explained. Damage to the substrate 12 and film surface occurs due to charge-up, electron impact, and abnormal discharge, but since it is difficult to express this quantitatively, it was determined that there was damage that could be confirmed by visual measurement and that there was no damage. The film formation conditions were Ar'4 ambient pressure crab 2 x 1
0-8 Torr, negative electrode voltage NV: 300V, positive electrode voltage PV: O to 300V, bias voltage ratio PV/NV:
O~1, bias energization ratio T2/(T1+T2): 0.5
, Frequency: 100KHz, Target: AQ-1%Si
A film was formed using a sputter electric crab at 1.5 KW. As a result, it was found that when the bias voltage ratio PV/NV is in the range of 0.03 to 0.2, that is, the positive electrode voltages P and V are in the range of 10 to 60 V, damage to the film due to charge-up and electron impact can be completely prevented. Ta. Next, bias energization ratio T2/(
The influence of T1+T2) will be explained. Negative electrode voltage NV:
As a result of keeping the positive electrode voltage PV constant at 300V and 300V and changing the bias energization ratio T 2 / (T 1 + T 2) from 0 to 0.5, the bias energization ratio is in the range of 0.07 to 0.15. Damage to the membrane could be prevented.

In this way, by changing the bias current ratio and bias voltage ratio, damage to the film can be prevented.

In addition, as a result of forming a film using the conventional DC bias sputtering method under almost the same conditions as the above example (applying a negative voltage of 300 V to the substrate), the substrate caused abnormal discharge due to charge-up, and the substrate 12 cracked and became unusable. I couldn't bear it.

In addition, in order to prevent cracking due to charge-up in the conventional method,
After the start of film formation, an AQ film was formed without applying a bias (300V negative voltage) to the substrate 12 for a minute, and then a bias was applied.As a result of comparing the step coverage with the present invention, the present invention was found to be superior to the conventional method. The step coverage was improved by about 15% compared to the previous model.

In addition, in the figure, 10 is a sputtering power supply, 11 is a targeter 1~
．． 13 is an insulator, 14 is a vacuum container, and 15 is a magnet.

1 Example 2 An example in which the present invention is applied to the formation of an insulating film will be described. To form an insulating film by sputtering, it is necessary to apply a high frequency wave as shown in FIG. 7 to the insulating targeters 1 to 1 to prevent charge-up. However, although the positive electrode voltage is effective against charge-up, it does not participate in film formation by sputtering, and mostly becomes thermal energy to heat the target. Since the target and the backing sheet are generally bonded using indium solder, increasing the sputtering power often causes the target to peel off.

However, in the present invention, since a positive voltage is applied alternately with a lower ratio to a negative voltage, the specific Vesputter power is 1.4 compared to the conventional method.
Can be supplied to twice the target.

This increases the film formation rate and improves work efficiency.

"Example 3" In the bias sputtering method, step coverage and film quality are improved by alternately switching the voltage applied to the substrate and the voltage applied to the target and changing the energization ratio. As shown in the figure, step coverage and film quality can be improved compared to conventional methods by applying the waveform of the present invention to the substrate or to the substrate and target and alternately switching to form a film.

Further, it is also possible to apply a conventional high frequency waveform to the target laser 1-.

〔Effect of the invention〕

According to the present invention, (1) damage to the film due to charge-up and electron impact can be prevented; (2) the bias effect is greater compared to the conventional method and step coverage is improved; and (3) Targetera 1 and backing sheet. (4) It is possible to improve the film formation rate.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of an embodiment of the film forming apparatus of the present invention, and FIG.
The figure is a schematic diagram of the waveform of the present invention, Figures 3 and 4 are schematic diagrams of the waveform of the present invention, Figure 5 is an explanatory diagram of the conventional bias sputtering method, and Figures 6 and 7 are the conventional bias sputtering method. FIG. DESCRIPTION OF SYMBOLS 1... Positive electrode constant voltage power supply, 2... Positive electrode voltage setting potentiometer, 3... Negative electrode constant voltage power supply, 4... Negative electrode voltage setting potentiometer, 5... Waveform control device, 6.
Energization ratio setting potentiometer, 7... Frequency setting potentiometer, 8... Positive switching transistor,
9... Negative switching 1 helang resistor, 10...
Sputter power supply, 11... target, 12 substrate, 13
...Insulator, 14 - Vacuum container, 15 - Magnet.

Claims (1)

[Claims] 1. In a bias sputtering method in which a vacuum vessel is grounded and a voltage is applied to a target and a substrate placed facing each other in the vacuum vessel to form a film, a negative electrode voltage and a positive electrode voltage are applied to the substrate. A bias sputtering method characterized in that a film is formed by applying a square wave high frequency voltage that can independently change the peak value of and the energization time of the negative electrode voltage and the positive electrode voltage. 2. The bias sputtering method according to claim 1, wherein the absolute value of the peak value of the negative electrode voltage is higher than the peak value of the positive electrode voltage. 3. The bias sputtering method according to claim 1, wherein the negative polarity current application time is longer than the positive polarity current application time. 4. A bias sputtering method according to claim 1, 2, or 3, characterized in that the voltage applied to the target has the voltage waveform of claims 1 to 3, direct current, or high frequency. . 5. A sputtering method in which a vacuum container and a substrate are grounded, and a voltage is applied to a target to form a film, the sputtering method being characterized in that the film is formed by applying a voltage waveform to the target. 6. With the vacuum container grounded, independently set voltages are alternately applied to the substrate and the target, which are placed facing each other in the vacuum container, and sputtering and reverse sputtering are alternately repeated to form the target on the substrate. A bias sputtering method characterized in that a voltage waveform is applied to the substrate and the voltage and the sputtering voltage are alternately switched to form a film. 7. The bias sputtering method according to claim 6, characterized in that the sputtering voltage supplied to the target is a waveform alternately switched with the substrate voltage, or a direct current or high frequency alternately switched. . 8. The bias sputtering method according to claim 6 or 7, wherein the alternately switched substrate voltage and target voltage include a base voltage. 9. Bias sputtering according to claim 6, 7, or 8, characterized in that the voltage alternately applied to the substrate and the target, the energization time, and the base voltage can be independently and arbitrarily changed. Law. 10. Consists of a waveform control device that can arbitrarily set the energization ratio and frequency, a power supply and a semiconductor switch that can independently set negative and positive voltages, and converts the set positive and negative voltages into signals from the waveform control device. A power supply device for film formation, characterized in that the polarity of a set voltage is changed by alternately switching semiconductor switches.