JPH04276067A - Metal plasma source - Google Patents

Abstract

PURPOSE:To sputter a large amt. of metal particles by providing a sputtering target for supplying the metal particles capable of being impressed with a voltage. CONSTITUTION:Plasma is produced in a chamber 3, a microwave inlet window 2 is connected to the chamber 3, and at least one layer of a dielectric is provided on the window 2. An inlet waveguide 1 is connected to the window 2, and a dielectric having permittivity different from that of the dielectric of the window 2 is furnished in the waveguide for introducing a microwave into the chamber 3. A magnetic field more than enough to cause electron cyclotron resonance in the chamber 3 is generated by a magnetic coil 4. A microwave- excited plasma source is constituted in this way. A sputtering target 6 for supplying metal particles capable of being impressed with a voltage is provided in the source. As a result, the material particle is ionized with high efficiency.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a metal plasma source for application to LSI, semiconductor process technology, surface treatment technology, etc. such as thin film formation and ion implantation, and in particular to electron cyclotron resonance (ECR) using microwave excitation. ) is related to a metal plasma source using a metal plasma source.

0002

BACKGROUND OF THE INVENTION In recent years, technologies that control the energy of ions and plasma to form high-quality thin films and surface-treat metals have been attracting attention. To realize this technology, it is necessary to generate various metal ions and plasma at high density. Metal plasma sources for generating such metal ions and plasma at high density include (a) a method of ionizing metal using a metal compound gas, and (b) a method of generating metal ions by sputtering a metal target. There is a method to do this. The method (a) has the problem that the metal ion species that can be generated are limited, and the range of application is limited due to the increased amount of impurities. On the other hand, the method (b) can be expected to be widely applicable since almost all metal ion species can be obtained. Various types of metal plasma sources have been studied for method (b).
Among these, a sputter type ECR plasma source that utilizes ECR discharge (electron cyclotron resonance discharge) by microwave excitation is attracting attention. This discharge method has the following excellent features. ■Electrodeless discharge, long life, and can use reactive gases. ■Discharge is possible at low gas pressure (1 x 10-5 Torr) and generates little impurities. ■Can generate high-density plasma.

0003

[Problems to be Solved by the Invention] However, conventional sputter-type ECR plasma sources are configured so that microwaves propagate within the plasma generation chamber, and therefore a certain size (microwave frequency) corresponding to the microwave frequency is required. In the case of 2.45 GHz, it was not possible to downsize the cylindrical plasma generation chamber to a diameter of 72 mm or less. Therefore,
The coil for generating the ECR magnetic field is also very large and heavy, making it difficult to attach it to an actual device as a plasma source. However, in order to be widely applied to various thin film formation techniques such as MBE and ion beam sputtering, it must be easy to attach to equipment, and EC
Significant downsizing of R plasma generation sources is desired. An example of an ECR plasma source that has achieved this type of miniaturization is disclosed in Japanese Patent Application No. 61-271909. However, in such a plasma source, the impedance of the plasma changes greatly as the density of the plasma increases, that is, as the dielectric constant of the plasma increases, so the impedance matching between the microwave and the plasma becomes difficult as the plasma density increases. There was a problem that I couldn't get it. Further, as a method for increasing the density of ECR plasma, there is one disclosed in Japanese Patent Application No. 198307/1983. In this system, the microwave introduction window is constructed with a multilayer dielectric material to match the impedance of the microwave and plasma, making it possible to generate high-density plasma. However, if the size of the waveguide, microwave introduction window, and plasma generation chamber is made so small that the microwave cannot propagate, the microwave cannot pass through the waveguide, so an optimal multilayer structure with impedance matching is designed. I couldn't.

Furthermore, when metal particles are supplied into the plasma chamber by sputtering, the metal particles adhere to the microwave introduction window made of a dielectric material and form a metal film, which prevents the introduction of microwaves into the plasma chamber. There was a problem that it would no longer be possible. Therefore, when metal ions were generated, the plasma source could only be operated for a short period of time. In order to extend the life of the microwave, the microwave introduction window is installed at a location away from the plasma generation chamber to prevent metal film from adhering to it (Japanese Patent Application No. 62-35801); It was difficult to generate high-density plasma because the optimum impedance matching of microwaves and microwaves could not be achieved. It is an object of the present invention to provide a compact, long-life metal plasma source capable of generating a high-density metal ion plasma.

[0005]

[Means for Solving the Problems] In order to achieve such an object, the present invention provides a microwave introduction waveguide with a dielectric material inside the microwave introduction window, and a microwave introduction window with a dielectric material inside the microwave introduction waveguide. Impedance matching between high-density plasma and microwave is achieved by providing at least one layer of dielectric material with a different permittivity.
A sputter target for supplying metal particles to which voltage can be applied is provided. Further, the sputter target is installed in the plasma generation chamber and is shaped so that the microwave introduction window cannot be seen from the target surface.

[0006]

[Operation] With this configuration, impedance matching between plasma and microwave can be achieved, high-density plasma is generated, and a large amount of metal particles can be sputtered. Furthermore, since the sputtered particles travel straight, they do not adhere to the microwave introduction window, resulting in stable operation and long life.

[0007]

[Examples] The details of the present invention will be explained below with reference to Examples. FIG. 1 is a configuration diagram showing one embodiment of the present invention. In the figure, 1 is a microwave introduction waveguide with a dielectric inserted, 2 is a microwave introduction window made of multilayer dielectric, and 3
is a plasma generation chamber, 4 is a magnetic coil, 5 is a gas introduction hole,
6 is a sputtering target, 7 is a target holder, 8A, 8B are ion extraction electrode systems, 9 is an ion beam, 10 is a flange, 11 is a sputtering power source, 12A,
12B is an extraction power source, and 13 is a coaxial waveguide converter. Microwave is transmitted by coaxial cable to coaxial waveguide converter 1
will be introduced in Although this embodiment shows an example in which microwaves are introduced using a coaxial cable, it is of course possible to introduce microwaves using a waveguide. The microwave introduced into the coaxial waveguide converter 13 is converted into a waveguide mode, and is introduced into the plasma generation chamber 3 through the microwave introduction waveguide 1 and the microwave introduction window 2.

Since the size of the exit side of the microwave introduction waveguide 1 is about the same as that of the plasma generation chamber 3, that is, it is a microwave blocking area, microwaves do not propagate in a normal tapered waveguide. Therefore, it is filled with a dielectric material with a high dielectric constant to allow microwaves to propagate. When filled with a dielectric, the waveguide can be made smaller in inverse proportion to the 1/2 power of the dielectric constant. In this embodiment, since alumina having a dielectric constant of 9 is used as the dielectric material, the waveguide can be reduced to 1/3. If the microwave frequency is 2.45 GHz, the corresponding normal waveguide size is 96 mm x 96 mm for a rectangular wave guide.
27 mm, and in the case of a circular waveguide, the diameter is 84 mm. Therefore, when filled with alumina, each 32 mm x 9
mm, and a waveguide with a diameter of 28 mm can be used. Further, a V-shaped cut is made in the dielectric on the entrance side of the waveguide 1 so that the cross-sectional area of the dielectric gradually increases. As a result, the impedance changes smoothly, and reflection of microwaves at the connection between the coaxial waveguide converter 13 and the microwave introduction waveguide 1 can be suppressed. Although the cut is V-shaped in this embodiment, other shapes may be used as long as the cross-sectional area of the dielectric changes smoothly.

The microwave propagates through the introduction waveguide 1 to the microwave introduction window 2. The microwave introduction window 2 uses a multilayer dielectric material. In this example, 2
It has a layered structure, and quartz 2A is used on the waveguide side to seal the vacuum, and alumina 2B is used on the plasma generation chamber 3 side for impedance matching. When applying a high voltage to extract the ion beam, a dielectric material with high thermal conductivity and a high melting point, such as boron nitrite (BN), is installed on the plasma generation chamber 3 side in order to increase resistance to backflow electrons. It may also have a layered structure. As the dielectric material, any material other than quartz, alumina, and boron nitrite can be used as long as it has low dielectric loss and high heat resistance. Furthermore, a one-layer structure is possible if a dielectric material with a high dielectric constant is used, but it is better to have a dielectric constant different from that of the dielectric material in the introduction waveguide from the viewpoint of impedance matching with plasma, which will be described below.

The plasma generation chamber 3 is large enough that microwaves cannot propagate (in the case of a microwave frequency of 2.45 GHz,
Although the diameter is 50 mm, a small amount of microwave leaks from the microwave introduction window 2 to the plasma generation chamber 3 side. If even a small amount of plasma is generated by the leaked microwaves, the dielectric constant in the plasma generation chamber 3 becomes large, allowing the microwaves to propagate, and plasma is constantly generated. However, in order to generate high-density plasma, since plasma has a dielectric constant, it is necessary to accurately match the impedance with microwaves, and therefore the thickness of each dielectric must be optimally designed. Although a design method for generating high-density plasma is disclosed in Japanese Patent Application No. 62-198307, it cannot be applied when a tapered waveguide containing a dielectric material is used as in this embodiment.

However, by approximating that the waveguide is filled with dielectric material to infinity, the thickness of each dielectric material can be determined by the following calculation method. FIG. 2 is a schematic diagram of the present microwave plasma source. In the same figure,
21 corresponds to the introduction waveguide 1 filled with a dielectric material, 22 corresponds to the multilayer microwave introduction window 2, and 23 corresponds to the plasma generation chamber 3. In the following calculations, all cross-sectional shapes have radius a
However, if the cross-sectional shape of each part is different, an impedance equation suitable for each shape may be used.

Let the wavelength of the microwave in free space be λ,
The cutoff wavelength in the introduction waveguide section 21 is λc, and the relative dielectric constant is εw.
shall be. In addition, the dielectric material in the microwave introduction window 22 is n
The internal wavelength of the microwave of the layer is λn, and the relative permittivity is ε.
n, the thickness is ln, the impedance is Zn, the relative dielectric constant in the plasma generation chamber 23 is εp, and the impedance is Z.
Let it be p. The impedance Rn when looking toward the plasma generation chamber 23 from the boundary between the (n-1)th layer dielectric and the nth layer dielectric of the microwave introduction window 22 is n as shown in equation (1).
It is expressed as an expression. Rn=Zn(Zp+jZntanθn)/(Zn+jZ
ptanθn)Rn-1=Zn-1(Rn+jZn-1
tanθn-1)/(Zn-1+jRntanθn-1
) ・ ・ R1=Z1(R2+jZ1tanθ1)/(Z1+jR
2tanθ1)

...(1) Here, θ=2
πln/λn. However, λc is 3.4125a when the introduction waveguide 1 is a circular waveguide in TE11 mode,
In the case of a rectangular waveguide in TE10 mode, it is 2b (b is the length of the rectangle in the longitudinal direction)

According to formula (1), Rn, Rn-1, . . .
R1 can be obtained by sequentially calculating. Once R1 is determined, the transmittance of microwaves to the plasma generation chamber 3 can be determined using equation (2). |T|2=1-|R1-1|2/|R1+1|2
(2) To perform the above calculation, it is necessary to determine the relative dielectric constant εp of the plasma. Determined from the theoretical formula and experimental results as described below,
It is assumed that εp=100. The relative dielectric constant εp of plasma is
Plasma frequency is ωp, electron cyclotron frequency is ω
c, and when the incident microwave frequency is ω, it is expressed as the following equation (3) (assuming that collisions are ignored and the electron temperature is 0). εp=1-(ωp/ω)2/(1-ωc/ω)
...(3) Here, ωp
, ωc are expressed by the following equation. ωp=(4πe2ne/me)1/2
・・・・・・(4
) ωc=me/eB
・・・
(5) where ne is the plasma density, me is the mass of the electron, and e is the amount of charge of the electron. According to the experiment, ωc/ω = 1.10 from the optimum operating conditions, and in order to make the density of the generated plasma 1012 cm-3 or more, (ωp/
ω)2=1.34 or more is required. These values are (3
), εp=100.

FIG. 3 shows an example of calculation using the above method when the microwave introduction window 22 has one layer. Introduction waveguide section 2
1 is filled with alumina (dielectric constant 9) as a dielectric, and microwave introduction window 22 is composed of only one layer of quartz (dielectric constant 4). The horizontal axis shows the thickness of the quartz, and the vertical axis shows the transmittance. As the thickness of the quartz changes, the transmittance changes greatly, but the maximum transmittance is only about 65%. This is ■
This is because impedance matching cannot be achieved with only one quartz layer because the inner diameter is smaller than the microwave propagation region and (1) the relative dielectric constant εp of the plasma is as large as 100. Further, as can be seen from the figure, even if the microwave introduction window is made of one layer of alumina instead of one layer of quartz, a transmittance of only about 65% can be obtained.

FIG. 4 shows an example of calculation in the case of two layers. The microwave introduction window has a two-layer structure of quartz and alumina. The horizontal axis is the thickness of the alumina, and the vertical axis is the microwave transmittance to the plasma. The thickness of the quartz is fixed at a certain value. As is clear from FIG. 4, the transmittance changes greatly depending on the thickness of the alumina, and at the optimum thickness of 1.1 cm, the transmittance is almost 100%. Therefore, the dielectric constant ε of the plasma
It is clear that for high-density plasmas where p is as large as 100, it is necessary to combine two or more dielectric layers. In this example, the two-layer microwave introduction window has a transmittance of 1.
It is a combination of thicknesses that are 00%.

FIG. 5 shows the experimental results. In the same figure, the dependence of plasma density on microwave power is compared between a microwave introduction window configuration with a transmittance of approximately 100% (curve S1) and a configuration with a transmittance of 43% (curve S2). It has been done. The higher the transmittance, the higher the actually obtained plasma density, and in the case of a configuration with a transmittance of 100%, a plasma density of 1013 cm-3, which is about one order of magnitude higher, can be obtained. In this way, by constructing the microwave introduction window using a multilayer dielectric material, impedance matching can be achieved even if the plasma generation chamber is made much smaller than the microwave propagation mode.
A high plasma density of 13 cm-3 or more can be obtained. Although this embodiment deals with the case where the plasma generation chamber is of a size that does not allow microwave propagation, the above-mentioned calculation method can of course be applied even when the plasma generation chamber is of a normal size.

The sputtering target 6 is cylindrical and has an inverted wedge-shaped cross section. This is to prevent sputtered metal particles from adhering to the alumina 3B of the microwave introduction window and preventing microwaves from being introduced, and the surface of the alumina 3B is not visible from the surface of the sputtering target 6. It has a structure. Figure 6 shows the sputtering target 6 and the alumina 3B in the introduction window.
FIG. Sputtered metal particles have kinetic energy of several eV and are under low gas pressure (~10-4 Torr), so they travel straight without colliding with other particles. Therefore, most of the metal particles collide with and adhere to the wall of the plasma generation chamber 3, and do not adhere to the alumina 3B of the introduction window. Therefore, this structure allows the ion source to operate stably for a long period of time.

Voltage is applied to the sputtering target 6 from a sputtering power source 11 through a flange 10. The material of the sputtering target 6 is Cu, W.
, Ta, Fe, and other conductive materials can be used by using direct current as the target voltage. In the case of a non-conductive material, it can be used in the same way if the target voltage is applied using RF (radio frequency). The target holder 7 holds the sputtering target 6 and also has a cooling function. For this reason, boron nitride, which has high thermal conductivity, is used as an insulator between the target holder 7 and the sputtering target 6. In order to efficiently cool the sputtering target 6, it is desirable that the target holder 7 has a water cooling mechanism. In the embodiment, the extraction electrode systems 8A and 8B have a two-electrode structure, but a single-electrode structure is used for low-energy extraction, and a three-electrode structure is used for low-energy extraction. The shape of the extraction electrode hole is 2m in this example.
mφ×37 pieces (drawing area 20 mmφ). Note that if the device is used not as an ion source but as a plasma source, this extraction electrode system may be removed.

Next, the operation of the ion source will be explained with reference to FIGS. 1 and 6. A sputtering gas (usually Ar, but other gases may be used) is introduced into the plasma generation chamber 3 through the gas introduction hole 5, and a magnetic field (875 Gauss for 2.45 GHz) is applied by the magnetic coil 4 to satisfy electron cyclotron resonance. is applied into the plasma generation chamber 3. Then, when microwaves are introduced through the microwave waveguide 1 and the microwave introduction window 2, plasma is once excited by the leaking microwaves, and then a steady plasma is generated stably. Here, a target voltage is applied to cause Ar ions to collide with the sputtering target 6 to sputter metal particles. Most of the sputtered metal particles are neutral particles, but they collide with the Ar plasma transported along the magnetic lines of force 14 and are efficiently ionized. The ionized metal particles are extracted as an ion beam 9 by the voltage applied to the extraction electrodes 8A, 8B.

FIG. 7 is a diagram showing an example of the current-voltage characteristics of the sputtering target 6, in which Cu is used as the target material. The flow rate of Ar gas is used as a parameter. When the Ar gas flow rate was 1.5 sccm, the target current density was as high as 12 mA/cm2, indicating that metal particles were sputtered at a high density. FIG. 8 shows a mass spectrometry spectrum when the ion beam 9 is extracted at an accelerating voltage of 300V. Cu+, Ar+
, Ar2+ ions are present, and a high value of 7% is obtained as the ratio of Cu+. As for Cu ions, a high current value of 1 mA or more has been obtained. In addition to Cu, W, Ta
Similar performance can be obtained with metal ions such as

[0022]

As explained above, the present invention has a dielectric material inside the introduction waveguide, and at least one layer of dielectric material having a dielectric constant different from the dielectric material inside the introduction waveguide in the microwave introduction window. By providing a sputter target for supplying metal particles to which a voltage can be applied, the following excellent performance can be obtained. (1) Since high-density ECR plasma can be used, a large amount of metal particles can be sputtered. (2) Metal particles can be ionized with high efficiency through interaction with the ECR plasma flow. (3) Metal particles can be prevented from adhering to the introduction window;
Stable operation can be performed over a long period of time. (4) The device can be significantly downsized.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of a microwave plasma source according to the present invention.

FIG. 2 is a schematic diagram showing the configuration of a waveguide, a microwave introduction window, and a plasma generation chamber.

FIG. 3 is a graph showing the relationship between the thickness of quartz and the transmittance when the microwave introduction window is made of a single layer of quartz.

FIG. 4 is a graph showing the relationship between the thickness of alumina and the transmittance when the microwave introducing window has two layers of quartz and alumina.

FIG. 5 is a graph showing the dependence of generated plasma density on microwave power.

FIG. 6 is a schematic diagram of metal plasma generation.

FIG. 7 is a graph showing the relationship between current flowing through a sputtering target and voltage.

FIG. 8 is a graph showing the results of mass spectrometry of an ion beam.

[Explanation of symbols]

1 Microwave waveguide 2 Microwave introduction window 3 Plasma generation chamber 4 Magnetic coil 5 Gas introduction hole 6 Sputtering target 7 Target holder 8A, 8B Extraction electrode system 9 Ion beam 10 Flange 11 Sputter power supply 12A, 12B Drawer power supply 13 Coaxial waveguide converter

Claims (2)

[Claims] Claims: 1. A plasma generation chamber for generating plasma, a microwave introduction window connected to the plasma generation chamber and having at least one dielectric layer, and a microwave introduction window connected to the microwave introduction window for introducing microwaves into the plasma generation chamber. A micro waveguide equipped with an introduction waveguide having a dielectric constant different from that of the microwave introduction window, and a magnetic circuit that generates a magnetic field larger than that which causes electron cyclotron resonance in the plasma generation chamber. 1. A metal plasma source using wave excitation, characterized in that it is equipped with a sputter target for supplying metal particles to which voltage can be applied. 2. The metal plasma source according to claim 1, wherein the sputter target is installed in a plasma generation chamber and has a shape that prevents a microwave introduction window from being visible from the target surface.