JPS5813626B2 - ion shower device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion shower device suitable for use in etching the surface of a material by utilizing the physical and chemical effects of ion bombardment, and particularly relates to an ion shower device suitable for etching the surface of a material by utilizing the physical and chemical effects of ion bombardment. The present invention relates to an ion shower device suitable for etching processes for forming fine patterns in the manufacturing process of various devices such as circuits.

This type of conventional device is known as a Kaufmann-type ion source, and has an ionization chamber, a grid-like ion extraction electrode system, and a sample chamber, and a hot filament for emitting thermoelectrons is placed inside the ionization chamber. Ionization was performed by generating plasma by direct current discharge with the side wall of the ionization chamber as the anode and the hot filament as the cathode.

As described above, since the conventional device was configured to generate ions using a hot filament, the type of ions, that is, the type of gas introduced into the ionization chamber,
It was limited to inert gases such as argon.

In other words, reactive gases such as freon gas, carbon tetrachloride, and oxygen gas used in dry etching methods that utilize chemical reactions such as plasma etching and reactive sputter etching are introduced into the ionization chamber and these gases are ionized. This would cause problems such as breakage of the hot filament and fluctuations in the amount of thermionic emissions, making it impossible to stably form a shower-shaped ion beam.

For this reason, the conventional apparatus described above has the drawback that it is difficult to apply to etching using a reactive gas, that is, an etching method that utilizes the chemical action of ion bombardment.

In order to solve these drawbacks, the applicant filed a patent application filed in 1973.
No. 4-48535, low gas pressure (10
We have previously proposed an ion shirt device that can generate plasma without using a hot filament, generate ions without being restricted by the type of gas, and stably form an ion shirt.

FIG. 1 shows the basic configuration of such an ion shower device.

Here, 1 is a plasma generation chamber, 2 is a sample chamber, and 3 is an ion extraction electrode.

Reference numeral 4 denotes a microwave introduction window provided in the upper part of the plasma generation chamber 1, and can be made of, for example, a quartz glass plate.

Reference numeral 5 denotes a rectangular waveguide for introducing microwaves attached to the microwave introduction window 4, and is connected to a microwave source via a matching box, a microwave power meter, an isolator, etc. (not shown).

As a microwave source, for example, a 2.4 5 GHz magnetron can be used.

Reference numeral 6 denotes a magnetic coil for generating a magnetic field necessary to cause a microwave electron cyclotron resonance discharge in the plasma generation chamber 1.

In this example, the magnetic coil 6 is composed of two coils due to manufacturing convenience, but it may be a single coil.

In order to enhance the ion extraction effect, the magnetic coil 6 is configured to form a so-called divergent magnetic field in which the magnetic field strength decreases from the center of the plasma generation chamber 1 toward the ion extraction electrode 3.

For microwaves with a frequency of 2.45 GHz, electron cyclotron resonance is induced under the condition that the magnetic flux density intensity is 875 Gauss.

In order to increase the electric field strength of the microwave introduced into the plasma generation chamber 1 from the rectangular waveguide 5 and to efficiently absorb the microwave power into the plasma, the plasma generation chamber 1 must meet the conditions of a microwave cavity resonator. It is preferable that the shape and dimensions satisfy the following.

In the excitation shown in FIG. 1, the mode of the microwave propagating in the rectangular waveguide 5 is TE1o, and the TEHn mode (n
Since it is convenient to use positive integers), as an example, n-3 was used, and a shape with inner dimensions of 20 cm in diameter and 20 cm in height was adopted.

The plasma generation chamber 1 is cooled by a water cooling system in which cooling water is introduced from the water supply port 7A to the cooling water passage 78, and the cooling water is further discharged from the drain port 7C to prevent the temperature from rising due to plasma. There is.

The ion extraction electrode 3 is, for example, a electrode 3 with a thickness of about 0.5 mm, which has many holes with a diameter of 2 mm in an area of 150 mm in diameter.
Consists of one or two metal plates.

Plasma generation chamber 1 has electric insulators 8A and 8B, respectively.
It is electrically insulated from the sample chamber 2 and the rectangular waveguide 5 by the plasma generation chamber 1, and the output of a DC power supply 9 for ion extraction is applied to the entire plasma generation chamber 1.

As shown in the first diagram, the ion extraction electrode 3 has two electrodes 3.
To explain the case where the upper electrode plate 3A is composed of A and 3B, in FIG. It serves as a microwave reflecting surface to act as a microwave cavity resonator for the generation chamber 1.

The lower electrode plate 3B of the ion extraction electrode 3 is at the same potential as the sample chamber 2, that is, the ground potential or a negative potential of 0 to 300V.

The voltage of the DC power supply 9 is applied between the two electrode plates 3A and 3B (when the lower electrode 3B is at ground potential),
Ions in the plasma generation chamber 1 are drawn out toward the sample chamber 2 and accelerated by the electric field between the electrodes.

The distance between the two electrode plates 3A and 3B is preferably about 1 to 2 mm, and the DC power source 9 has a maximum of 20 mm.
A device that can provide an output voltage of about 00V can be used.

With the above configuration, a large diameter ion shower 10 with a diameter of 150 mm can be formed.

A sample 11 to be irradiated with ions is placed on a sample stage 12, and the sample stage 12 can be tilted so as to be applicable to oblique ion irradiation.

13 is a shirt shirt provided to cut off the ion shirt, and 14 is a Faraday gauge for measuring ion current density attached to the shirt shirt.

Reference numeral 15 denotes a high magnetic permeability material for correcting the magnetic field distribution and increasing the efficiency of the magnetic coil 6, and soft iron is used in this example.

The gas introduction system has two systems, a first gas introduction system 16 that directly leads gas to the plasma generation chamber 1, and a first gas introduction system 16 that leads gas to the sample chamber 2.
It consists of an auxiliary second gas introduction system 17 that can be

In this example, the exhaust system 18 is an oil diffusion pump (exhaust capacity: 1
200 A/sec) and an oil rotary pump (exhaust capacity: 500 l/min).

” The ion shirt device with this structure and function can form an ion shirt extremely stably regardless of the type of gas, and is also extremely effective when used for etching using reactive gases, that is, reactive ion shirt etching. The fact that it has an effect requires a patent application of 1974-485.
As stated in No. 35.

However, subsequent studies revealed that even greater effects could be achieved by solving the following problems.

That is, (1) If you want to greatly control the etching characteristics of various materials when applied to etching, the ion energy, that is, the ion extraction voltage, should be set to 100
It is necessary to form the ion shirt under ion extraction conditions of a low voltage of 0V or less, for example about 500V.

However, when the ion extraction voltage is lowered, the amount of ions extracted (ion current density) decreases, and the etching efficiency decreases.

(2) The ion extraction electrode may be locally heated by the action of the microwave electric field and high-energy electrons, causing abnormal discharge.

(3) A stable ion shirt may not be obtained due to a positive spatial charge being generated inside the sample chamber or the surface of the sample becoming positively charged.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an ion shirt device that can solve the above-mentioned problems.

To this end, in the present invention, a microwave reflector plate is provided in the plasma chamber that allows plasma to pass through but reflects microwaves, and the ion extraction electrode plate on the plasma side is set to a floating potential.
By optimizing the magnetic field distribution, the ion current during low voltage ion extraction is increased without causing local heating of the electrode.

Further, by using a high frequency power supply circuit that generates a bias potential as a power supply for ion extraction, electrons are extracted together with ions to prevent charging in the sample chamber.

The present invention will be described in detail below with reference to the drawings.

FIG. 2 shows an example of the configuration of the ion shirt device according to the present invention.

Here, a portion corresponding to the upper half of the apparatus shown in the first figure is shown in detail.

In the apparatus of the present invention, the region where plasma exists, that is, the plasma chamber, consists of a plasma generation chamber 1 and a plasma transport chamber 25, and these two chambers are separated by a microwave reflecting plate 21.

The microwave reflecting plate 21 allows the plasma in the plasma generation chamber 1 to move freely in the direction of the electrode plates 23A and 23B forming the ion extraction electrode 23, but prevents the microwave from passing through because it is reflected. The reflector is a square lattice metal plate with a periodic interval of 20 mm and a thickness of 2 mm square.

Circular cavity resonance modes TE1 and TE2 are adopted as the microwave cavity resonator conditions of the plasma generation chamber 1.

The inner dimensions of the plasma generation chamber 1 are 150 mm in diameter, and the height is calculated to be 140 mm, but the height is 130 mm after correcting the change in microwave wavelength due to plasma generation. .

Further, the hole 22 directly below the microwave introduction window 4 is a microwave coupling window, and the microwave (TEIO mode) propagating through the rectangular waveguide 5 is connected to the cavity resonance mode T E 1 1
The inner dimensions of the rectangular waveguide 5 are 96 mm x 27 m in order to function as a matching device that efficiently converts
m, a rectangular hole of 70 mm x 40 mm was used.

With the above configuration, the electrode plate 23 in contact with the plasma of the ion extraction electrode 23 (shirt diameter 130 mm)
Since A is freed from its role as a microwave reflecting surface, it can be configured freely only from the viewpoint of ion extraction.

In the present invention, using this advantage, high-energy electrons characteristic of electron cyclotron resonance plasma flow into the ion extraction electrode plate 23A to locally heat the electrode,
Problems such as abnormal discharge occurring in the ion extraction electrode 23 can be solved.

That is, by setting the ion extraction electrode plate 23A in a floating state, a negative potential is generated in a self-aligned manner according to the energy of electrons in the plasma, and the number of incident electrons is significantly reduced, thereby solving this problem. resolved.

24 is an insulating spacer for this purpose.

The ion extraction electrode plate 23B can be set to the ground potential or a negative potential of 0 to 300V as before.

Generally, electrons that have gained high kinetic energy due to electron cyclotron resonance are accelerated along the output line in the direction of weakening magnetic field strength. In this case, an electrostatic field is induced in the plasma that suppresses the inflow of electrons and increases the number of incident positive ions, and not only electrons but also ions are efficiently transported in the direction of divergence of the magnetic field.

Based on this fact, the magnetic field distribution inside the plasma generation chamber 1 can be configured from the viewpoint of improving the efficiency of ion extraction.

3A and 3B show examples of magnetic field distribution configurations in the plasma generation chamber 1, and both have a diverging configuration in which the base field strength becomes weaker in the direction of the electrodes.

FIG. 3A shows the case of the ion shirt device according to the previous proposal shown in FIG. The electron cyclotron resonance conditions are strictly controlled. The lines of force that pass through the regions 31A and 31B that generate particularly high-energy electrons do not pass through the ion extraction electrode 3, but through the side wall 1A of the plasma generation chamber 1; In some parts, the magnetic field strength becomes a converging magnetic field that gradually becomes stronger.

Therefore, there is no effect of accelerating electrons in that direction.

For these reasons, we were able to avoid direct problems caused by high-energy electrons, such as local heating of the electrode and abnormal discharge, but it is not possible to increase the ion current during low-voltage ion extraction. could not.

FIG. 3B shows the magnetic field distribution in the ion shirt device of the present invention, in which the high magnetic permeability material 15 is placed around the magnetic coil 6, surrounding the upper part and outer periphery of the magnetic coil, and the lower part of the magnetic coil 6 is placed around the magnetic coil 6. The magnetic field distribution is such that the magnetic field strength gradually weakens in the direction of the ion extraction electrode 23 in the entire interior area of the plasma generation chamber 1, and passes through a region 32 that satisfies the electron cyclotron resonance condition. The magnetic lines of force are directed toward the ion extraction electrode 23.

High-energy electrons are sent to the ion extraction electrode 23 along the magnetic field lines.
However, as already mentioned, the floating electrode 23A
The use of this method does not cause any problems, and the ion acceleration effect described above allows ions to move in the direction of the ion extraction electrode 23 very efficiently, resulting in the effect of significantly increasing the amount of ions extracted.

FIG. 4 shows the results of actually measuring the improvement in ion extraction characteristics, and shows the relationship between ion extraction voltage and ion current density.

Here, C4F8 was used as the gas, and the microwave output was 200W.

In the device according to the previous proposal shown in the first diagram indicated by the broken line ■, 300
W conditions were used.

That is, in this case, since the plasma generation chamber 1 is large, the microwave output was increased in consideration of this and the results were compared with the results of the present invention.

The measurement results obtained by the apparatus of the present invention are indicated by a dashed line (■).

As can be seen, the present invention has an extremely large ion extraction rate of 0.5 to 1.2 mA/cm, which is about three times that of the device shown in Figure 1, in the ion extraction voltage range of 300 to 1000 V. We were able to improve the characteristics.

Here, when extracting ions at a very low voltage of about 0 to 200 V, there is an effect such as high-energy electrons flowing out from the extraction hole of the ion extraction electrode, so there is a peculiar tendency compared to the case of conventional devices. However, such characteristics ensure that the concept of magnetic field distribution configuration described above is valid.

On the other hand, when an ion shower is formed as described above and etching is performed by irradiating the sample with the ion shirt, only positive charges are sent into the sample chamber 2, so the sample may become charged or a positive space charge may occur. may occur, resulting in abnormal discharge.

Normally, positive charges in space are neutralized by secondary electron emission from the sample stage 12, or ion charges are removed from the sample chamber 12.
The newly generated ions, which have almost no kinetic energy, diffuse toward the wall of the sample chamber 2 and transport the charge to the wall, where the charge disappears. In many cases, this is not a major problem.

However, if the sample 11 is an insulator and has a large area, the amount of secondary electrons emitted from the sample stage 12 may decrease, making it impossible to achieve stable etching.

As a solution to this case, it may be possible to use a hot filament for thermionic emission, similar to devices using conventional Kauffman type ion sources, but stable operation cannot be expected when using a reactive gas.

Therefore, it is effective to extract not only ions but also electrons from the ion shirt source itself.

If the voltage applied to the ion extraction electrode is sufficiently small, the fifth
As shown in Figure A, a sufficiently fast period (e.g. 1 0 0
This problem can be solved by using as the ion extraction power source 9 a power source that can provide an output voltage of, for example, 50 V or less for a short period of time (at kHz or higher).

Alternatively, this can be modified to use a voltage in which the high frequency voltage is biased in the positive direction, as shown in FIG. 5B.

The power supply having the output waveform shown in FIG. 5B can be configured as shown in FIG. 6 using a normal high frequency power supply.

Here, 61 is a high frequency power supply, 62 is a matching circuit, 63 is a capacitor, 64 is a rectifier, and 65 is an output terminal, and this output terminal 65 is connected to the plasma generation chamber 1.

As explained above, in the present invention, a microwave reflection plate is provided in the plasma chamber that allows plasma to pass through but reflects microwaves, and the ion extraction electrode plate portion in contact with the plasma is set to a floating potential, so that the plasma is directed toward the ion extraction electrode. Since we have configured a magnetic field distribution that accelerates the ions, a large ion current can be stably obtained even when the ion extraction voltage is as low as 300 to 1000 V. Therefore, etching can be performed extremely efficiently using various gases. be able to.

According to the present invention, since an ion shirt with low energy and high current can be obtained, the controllability of etching characteristics is greatly improved, the sample surface is not damaged during ion shirt irradiation, and the efficiency is high. It has advantages such as being able to perform processing.

Furthermore, according to the present invention, by appropriately controlling the voltage waveform of the extraction power source and periodically extracting not only ions but also electrons from the ion extraction electrode, it is possible to perform extremely stable etching independent of the sample conditions. It has the advantage of being able to

It is clear that the ion shower apparatus of the present invention can be directly applied to thin film formation such as ion beam deposition.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing the basic configuration of the ion shower device previously proposed by the present inventor, Fig. 2 is a cross-sectional view showing an embodiment of the ion shower device of the present invention, and Fig. 3 A and B are cross-sectional views of the magnetic field lines. Figure 4 is a characteristic diagram showing the effects of the ion shirt device of the present invention, Figures 5A and B are signal waveform diagrams showing two examples of voltage waveforms of the ion extraction power supply, and Figure 6 is a diagram showing the high frequency power supply. FIG. 2 is a block diagram showing an example of the configuration of the ion extraction power source used. 1...Plasma generation chamber, 1A...Side wall, 2...Sample chamber, 3...Ion extraction electrode, 3A...Upper electrode , 3B...Lower electrode, 4...Microwave introduction window, 5...
...Rectangular waveguide, 6...Magnetic coil, γA...
...Water supply port, IB...Cooling water passage, γC・
...Drain port, 8A, 8B...Insulator, 9
...Ion extraction power supply, 10...Ion shower, 11...Sample, 12...Sample stand, 13...Shaft, 14. ...Faraday gauge, 15 ...High magnetic permeability material, 16
......First gas introduction system, 17...Second gas introduction system, 18...Exhaust system, 21...
Microwave reflecting plate, 22...Microwave coupling window, 23...Ion extraction electrode with floating electrode plate, 23A, 23B...Electrode plate, 24...
...Insulating spacer, 25...Plasma transport chamber,
31... High energy electron generation area, 61...
...High frequency power supply, 62...Matching circuit, 63.
... Capacitor, 64 ... Rectifier, 65
...Output terminal.

Claims (1)

[Scope of Claims] 1. A plasma chamber that generates plasma to generate ions, and an ion extraction electrode that is provided on a part of the constituent surface of the plasma chamber and that extracts ions from the plasma to form a shower-shaped ion beam. , an ion shower apparatus having a sample chamber configured to irradiate the sample surface with the shower-shaped ion beam, wherein the plasma is generated by microwave discharge using electron cyclotron resonance conditions, and the plasma chamber has a microwave introduction window. What is claimed is: 1. An ion shirt device comprising: a plasma generation chamber having an ion extraction electrode; and a plasma transport chamber having an ion extraction electrode, the plasma generation chamber and the plasma transport chamber being separated by a microwave reflector. 2. In the ion shirt device according to claim 1, the shape and dimensions of the plasma generation chamber, which is limited by the microwave introduction window and the microwave reflection plate, are determined by the microwave cavity resonator. An ion shirt device characterized by satisfying the following conditions. 3. In the ion shirt device according to claim 1 or 2, a diverging magnetic field is formed in which the magnetic field strength weakens with a near-determined gradient from near the microwave introduction window of the plasma chamber toward the ion extraction electrode. An ion shirt device characterized by: 4. The ion shirt device according to any one of claims 1 to 3, wherein an electrode plate of the ion extraction electrode that is in contact with the plasma is electrically suspended. shower equipment. 5. In the ion shower device according to any one of claims 1 to 4, the ion extraction power source is constituted by a high frequency power source added with a bias generation circuit, and the output of the ion extraction power source is An ion shirt device characterized in that a voltage is applied to the plasma generation chamber.