JPH0499174A - Method and device for ion assistant sputtering - Google Patents

Abstract

PURPOSE:To obtain an ion assistance effect without reducing a film forming speed in ordinary DC sputtering by simultaneously impressing a DC voltage and a high-frequency wave on a cathode. CONSTITUTION:A DC power source 16 and a high-frequency power source 1 are connected to a discharge electrode 5, an inductor is provided between the power source 16 and electrode 5, and a high-frequency matching device for adjusting a load impedance is furnished between the electrode 5 and power source 1. A vacuum vessel 8 is evacuated, and a working gas is introduced into the vessel 8 from an inlet 10 to hold the vessel 8 at an appropriate sputtering gas pressure. Under these conditions, a DC voltage is impressed on the cathode 5 to produce plasma in the vessel 8. A high-frequency wave is further impressed on the cathode 5 to impress a magnetron bias voltage on a substrate holder 9, hence the positive ion in the plasma close to a substrate is attracted to the substrate 9a, and an ion assistance effect is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an ion-assisted sputtering method and apparatus for producing thin films having various functions, and the present invention relates to an ion-assisted sputtering method and apparatus for producing thin films having various functions, and the structure and internal stress of the thin films are suitable for the purpose of use. The present invention relates to an ion-assisted sputtering method and apparatus that can be arbitrarily controlled so as to perform ion-assisted sputtering.

[Prior art] For example, in the process of depositing atoms of a desired material onto a substrate using a vapor deposition device to form a thin film, the deposited atoms are bombarded with ions from a separate ion generator such as an ion gun (ion bombardment, ion peening). (Also referred to as ion assist.Hereafter, it will be referred to as ion assist.) When a thin film is formed, the adhesion and density with the substrate are improved compared to a thin film that is not ion assisted, and as a result, It has been confirmed that there is a continuous improvement in functions such as hardness 1 surface roughness, light reflectance, and electrical resistance.

This is because ions with kinetic energy collide with the deposited atoms, causing the deposited atoms to move on the film surface (called migration) and settle down at a more stable potential, resulting in the formation of atoms and crystals. It is thought that this is because the arrangement becomes more dense.

[Problem to be solved by the invention] However, even if a sputtering device is combined with an ion gun to achieve the same effect, with the current technology, the gas pressure level used for sputtering and the gas pressure level used by the ion gun are different. Therefore, it is difficult to operate them simultaneously within the same vacuum vessel. Furthermore, when an ion gun is attached to a thin film forming apparatus such as vapor deposition or sputtering, the apparatus becomes very complicated, and since the ion gun itself is very expensive, the cost of the apparatus also increases considerably.

In addition, a method called bias sputtering has been proposed that attempts to improve various film properties by applying a bias voltage to the substrate, but this method only controls the energy given to the ions, and does not change the amount of ions. Can not. In particular, in magnetron sputtering, the amount of ions is extremely small, and even if energy is applied to the ions using a bias, no significant effect can be expected. However, in radio frequency (RF) magnetron sputtering, direct current (DC)
) Compared to magnetron sputtering, the generated plasma spreads considerably within the vacuum chamber, so a considerable ion assist effect can be expected by applying a bias voltage to the substrate. However, this RF sputtering also has the drawback that the film formation speed is much slower than DC sputtering, which can be fatal in actual production lines.Also, although it is possible to obtain a considerable amount of ions by using RF, Another drawback is that the amount is not variable.

In order to solve the problem that even when a bias is applied to the substrate during DC sputtering, only a few ions are attracted and a large ion assist effect cannot be expected, the outer magnetic pole of the magnetron magnetic pole structure attached to the back of the target has been strengthened. A technique of destroying the magnetic balance between the inner circumferential magnetic pole and the outer circumferential magnetic pole and guiding the plasma to the vicinity of the substrate was described by B, Window and N, 5avvides, etc. in J, Vac, 5ciTechno1. A4 (
21, May/Apr, 1986. This technology is proposed on page 196, but the plasma guided to the substrate side has a distribution in the radial direction of the substrate, and if the inner and outer magnetic poles are too far apart, as a result of strengthening the outer magnetic pole, The plasma moves toward the center of the target, resulting in poor film thickness distribution (
However, it is difficult to put it into practical use, especially when a circular target is used to form a film on a circular substrate.

In addition, the invention considered to be closest to the present invention is the patent application published in 1983.
No. 2-287071, this invention determines the density of the plasma by the amount of RF power input to the target, and uses the DC power supply connected to the target to generate the energy for the working gas ions that contribute to sputtering to hit the target. It is controlled by the supplied voltage, which is fundamentally different from the idea of the present invention described below.

The purpose of the present invention is to apply a direct current voltage to the cathode and simultaneously apply radio frequency (RF) during normal direct current (DC) sputtering, thereby maintaining a high film formation speed and using an ion gun such as the one described above. To provide a method and apparatus for appropriately controlling the amount of ions reaching a substrate during film formation without using a special ion source, and also arbitrarily controlling the energy of the ions by controlling the bias voltage applied to the substrate. be.

[Means for Solving the Problems] In the present invention, in a magnetron sputtering apparatus using normal direct current (DC) discharge, a direct current (DC) power source and a radio frequency (RF) power source are connected to the cathode at the same time, Also, to prevent the power output from each power supply to the cathode from flowing into the other power supply, an inductor is placed between the DC power supply and the cathode, and a blocking capacitor is placed between the RF power supply and the cathode (if the matching box is a π-type (only when the battery is turned on), the main discharge is performed with direct current (DC), and at the same time, an appropriate radio frequency (RF) is applied to the cathode.

[Effect] When evaluating the ion assist effect, the issues are the ratio (j+ /jm) of the number of sputtered atoms reaching the substrate (jm) and the number of working gas ions (j+), and the acceleration energy of ions to the substrate. (Substrate bias voltage: Ebia
s). Of these, for E bias, if the substrate and the thin film to be formed are conductors, a DC power supply may be used; in other cases, an appropriate DC bias voltage application means such as a high frequency bias power supply may be used.

The object to be controlled in this invention is j+/jm, and the principle is that R is applied to the magnetron cathode during DC discharge.
The phenomenon is that when F is applied, the plasma, which was mostly confined on the target when only DC discharge was used, spreads between the target and the substrate. As a result, when a DC bias voltage is applied to the substrate, significantly more positive ions flow into the substrate than when only DC discharge is applied. This means that j+ has become larger, but at the same time j
If m (film formation speed) also increased, the result would be j÷
The value of /jITl will not change. However, in reality, although jlTl increases, the rate of increase is not as high as j0, but only slightly, so as the RF power applied to the cathode is increased, j+/jm increases.

[Example] FIG. 1 shows an example in which the present invention is applied to a sputtering apparatus, which is one type of thin film deposition apparatus.

In Fig. 1, l is a high-frequency power supply device for controlling the amount of ions flowing into the substrate, 2 is a high-frequency matching device which is also a matching box for impedance matching between the power supply side and the load side, 3 is a magnetic pole structure for the magnetron, and 4 is a magnetic pole structure. A solenoid coil for adjusting the balance between the inner magnetic pole and the outer magnetic pole of the body 3, 5 a cut (cathode) which is also a discharge electrode that supplies discharge power from a power source, 6 a target made of a film-forming substance, 7
8 is an exhaust port connected to a vacuum pump, 8 is a vacuum container, and 9 is a substrate holder that holds a substrate 9a (in the present invention, this holder 9
(used as a probe for measuring the amount of ions), 10 is an inlet for introducing a working gas into the vacuum container 8, 11 is a vacuum gauge, 12 is an ammeter for measuring the amount of ions flowing into the substrate holder 9, 13 is a DC power supply device for applying a bias voltage to the substrate 9a; 14 is an inductor that prevents high frequency waves applied to the cathode 5 from flowing into the discharge DC power supply 16; and 15 is a DC power supply device for applying a bias voltage to the substrate 9a. 16 is a DC power supply device for generating the main discharge and forming a film, and 17 is for supplying current to the solenoid coil 4. It is a DC power supply. These are configured as shown in FIG.

A method for performing ion-assisted film formation using this apparatus will be described below.

First, the inside of the vacuum container 8 is sufficiently evacuated using an evacuation pump connected to the vacuum container 8, and then an appropriate amount of working gas (usually Ar) is introduced into the vacuum container 8 from the inlet 10 to create a vacuum. The inside of the container 8 is maintained at an appropriate gas pressure for sputtering.

In this state, a DC voltage is applied to the cathode 5 and the vacuum container 8 is
Generate plasma inside. Furthermore, a high frequency is applied to the cathode 5, and a negative bias voltage (approximately -10 to
-200 V) is applied to attract positive ions (Ar ions) in the plasma near the substrate to the substrate 9a, thereby obtaining an ion assist effect.

FIG. 2 shows how the number of positive ions (j+) flowing into the substrate 9a and the number of spuck atoms (jm) adhering to the substrate 9a change when the high-frequency power PRF input to the cathode 5 is changed during DCIAM operation. shows. In addition, as an evaluation of the ion assist amount, j+ for each input high frequency power PRF
FIG. 3 shows how /jWl changes. In the graphs of Figures 2 and 3, the DC current applied to the cathode was fixed at IA, and the film-forming gas pressure was 20 mTor.
r, and the coil excitation current was set to OA. As shown in Figure 2, the change in jIll is quite small compared to the change in j÷ (
, the high frequency power input to the cathode 5 is applied to the target 6-
It can be said that plasma is generated over a fairly wide area between the substrates 98. Therefore, as shown in FIG. 3, as the high frequency input power PRF increases, j+/jrrl increases. In other words, it can be said that as the input high-frequency power increases, the amount of ion assist increases.

Figure 4 shows a special relationship between the cathode 5 and the ground where high-frequency power was gradually applied to the cathode 5 under the condition of a film-forming gas pressure of 2 mTorr (coil excitation current: +4.0, -4A) and a DC discharge current IA. This shows the state of change in the potential difference. The excitation current of the coil on the outer periphery of the cathode was taken as a parameter, and when the value was a positive value, the magnetic pole on the outer periphery of the cathode 5 was set to be strengthened. As shown in FIG. 4, when the high frequency power supplied to the cathode 5 exceeds a certain value, the discharge impedance of this discharge space decreases rapidly, and this phenomenon also occurs in the solenoid coil 4.
The more the outer magnetic pole of the cathode 5 is excited in the direction of strengthening, the more noticeable it becomes.

FIG. 5 shows how j+ and jm change when the excitation current of the solenoid coil 4 is +4 A (discharge gas pressure 2 mTorr). As can be seen, jIll rapidly decreases when the discharge impedance decreases. This jI
The sudden decrease in ll is considered to be caused by a decrease in sputtering rate due to a decrease in discharge impedance. In any case, as a result, as shown in Figure 6, after this change point, j÷/jm increases rapidly, and although the film formation speed decreases slightly, the ion assist effect is much greater than before. be able to obtain it.

In the above embodiment, the structure of the high frequency matching device 2 which is a matching box is L-shaped, so the high frequency matching device 2 and the cathode 5 which is a discharge electrode are directly connected. However, the structure of the high frequency matching device 2 is In the case of π type, the discharge electrode 5
Since the DC power added to flows into the high frequency power supply device 1, a blocking capacitor is provided between the high frequency matching device 2 and the discharge electrode 5.

[Effects of the Invention] According to the present invention, it is possible to obtain a much larger ion assist effect compared to normal DC magnetron sputtering, and by controlling the discharge gas pressure and the strength of the outer magnetic pole of the cathode, Although the film formation speed is slightly lower, it is possible to obtain an ion assist effect about four times that speed. This makes it possible to form a dense film with low resistance and reduce the internal stress of the film.Also, since the amount of ions reaching the substrate is significantly larger than that of normal magnetron sputtering, reactive sputtering and the crystal structure of the film can be improved. control, making it possible to develop thin films with new functions.

Furthermore, compared to conventional RF magnetron sputtering, which has a large ion assist effect, according to the present invention, although the amount of ion assist is reduced, the film formation speed is the same as that of DC magnetron sputtering, without reducing the film formation speed. It can be said that this is a new means of obtaining an ion assist effect.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing one embodiment of the apparatus for carrying out the method of the present invention, and FIGS. 2 to 6 show j++jm when high frequency power is supplied to the cathode during DCIA discharge, respectively.
FIG. 2 and FIG. 5 are diagrams showing the state of change of R.
F input power car j÷. jm diagram, Figures 3 and 6 are RF input car j+
/j+n diagram, FIG. 4 is a voltage diagram between the RF input input car cathode and ground. 1... High frequency power supply device, 2... High frequency matching device, 3... Magnetic pole structure for magnetron,
4...Solenoid coil, 5...Cathode (cathode, discharge electrode), 6...
...Target, 7...Exhaust port, 8.
...Vacuum container, 9...Substrate holder, 9a...Substrate, 10...Working gas inlet, 11...Vacuum gauge, 12...
... Ammeter, 13 ... DC power supply for substrate bias, 14 ... Inductor, 15 ... Low pass filter, 16 ... DC for discharge Power supply, 17...
・DC power supply device for solenoid coil.

Claims (2)

[Claims] (1) A high-frequency power source is connected to the discharge electrode of a magnetron sputtering device that uses DC discharge at the same time as a DC power source, and an inductor is installed between the DC power source and the electrode to prevent this high frequency from flowing to the DC power source. A high frequency matching device for load impedance adjustment is installed between the power supplies,
When performing ion-assisted sputtering using a device equipped with a device that applies a negative bias voltage to the substrate, the amount of ions flowing into the substrate during film formation by DC discharge can be controlled by changing the amount of high-frequency power applied to the discharge electrode. Ion-assisted sputtering method that allows adjustment. (2) A DC power source and a high frequency power source are connected to the discharge electrode of a magnetron sputtering device that uses DC discharge, an inductor is provided between the DC power source and the discharge electrode, and an inductor is installed between the discharge electrode and the high frequency power source for adjusting the load impedance. An ion-assisted sputtering apparatus that is provided with a high-frequency matching device that can vary the amount of high-frequency power applied to a discharge electrode, and that is provided with a device that applies a negative bias voltage to a substrate.