JPH089778B2 - Ion source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is used for forming various thin films or etching by generating ions by using sputtering by high density plasma and extracting the ions. Of high efficiency, high yield ion source.

[Conventional technology]

Conventionally, various ion sources using plasma have been widely used in so-called ion beam sputtering devices, which are used for thin film formation by sputtering the target using the ions, and etching devices for manufacturing integrated circuits. , There are various types such as the Kaufmann type and the Deuoplasmatron type. Among them, the Kauffman type ion source is widely used, but as shown in FIG. 5, it has a filament 2 for thermionic emission inside the plasma generation chamber 1 ', and this filament 2 is used as a cathode. Plasma is generated by causing electric discharge in the magnetic field generated by the electromagnet 3.
10 is generated, and an ion beam 9 is formed by using several extraction grids 4 of ions in the plasma 10.

[Problems to be solved by the invention]

Since the conventional ion source uses the filament 2 for emitting thermoelectrons, the type of ions, that is, the type of gas introduced into the plasma generation chamber 1'is limited to an inert gas such as Ar. That is, if a reactive gas is used, it reacts with the filament 2 and stable plasma formation and ion extraction cannot be performed. Further, there are drawbacks such as deterioration of characteristics of the filament 2 over time, maintenance problems such as replacement of the filament 2, and deterioration of reproducibility due to variation of ion extraction distribution due to variation of mounting state of the filament 2. . In addition, the filament 2 for thermionic emission is constantly exposed to the plasma 10 and is always bombarded with high-energy ions in the plasma. Therefore, filament materials, such as tungsten, are contained as impurities in the extracted particles. There was a problem of being mixed. Also, the ions that can be extracted from such an ion source are limited to ions such as inert gas as described above, and Al (aluminum), Cu (copper), and Fe.
It was essentially impossible to extract (iron) and metal ions. The same applies to the deuoplasmatron type ion source.

On the other hand, when the ion source is used for film formation or etching, it is desirable that the current density of the extracted ions be as high as possible, but in the conventional ion source, the amount of ions depends on the amount of electrons emitted from a normal filament. Because
It was not possible to make an essentially high yield ion source.
Furthermore, with conventional ion sources, 10 ^{-3 in the} plasma generation chamber
Discharge could not be stably formed with a low gas of Torr or less, and the ion extracted so much had a drawback that impurities were contained.

The conditions desired as an ion source are summarized below: (1) Large yield (large ion current), (2) Impurities are small, (3) Ion energy can be controlled over a wide range, (4) ) Being able to extract not only inert gas but also various ions such as metal ions.

Can be raised.

[Means for solving problems]

In order to solve the conventional problems, the present invention locally generates high-activity high-density plasma, ionizes the target material by causing spatter, and ionizes various high-purity materials at high current density. It provides an ion source that draws out, forms thin films of various materials on the sample substrate, and performs etching.A plasma that has a microwave introduction window connected to the microwave waveguide at one end and is sequentially coupled in the microwave traveling direction. The plasma generation chamber comprises a vacuum chamber having a generation chamber and a sample chamber, and the plasma generation chamber has a diameter and a length that form a microwave cavity resonator in which the microwave introduced into the vacuum chamber resonates, and A cylindrical target placed on the inner wall of the central part that applies a negative voltage and draws in the ions in the plasma to make a spatula, and the magnetic flux is leaked to the inner surface of the cylindrical target. At least one pair of ring-shaped permanent magnet polarity upper and lower ends outside the tubular Tagetsuto was reversed,
Arranged at the other end facing the microwave introduction window,
The grid is a grid for selectively taking out the ions ionized in the plasma, and the magnetic flux density necessary for causing electron cyclotron resonance is formed around both ends, and the micro-particle is formed in the plasma generation chamber. It is characterized by being provided with a microwave introduction part having a wave introduction window at an end and at least a pair of electromagnets forming a mirror magnetic field having a minimum magnetic flux density with respect to the arrangement part of the grid.

[Work]

The present invention uses electron cyclotron resonance for plasma generation and heating, and uses a mirror magnetic field for plasma confinement to form high-density plasma in a specific space of low gas pressure, and further to provide a negative plasma in front of the high-density plasma. A cylindrical target to which a voltage is applied and a ring-shaped permanent magnet that obtains an appropriate magnetic flux density are arranged on the inner surface of the target, and the ions in the high-density plasma are attracted to the target, and the sputtering is performed at high speed. The sputtered particles can be ionized and extracted in highly active plasma, and high-purity ions can be selectively taken out by the electrodes. Embodiments will be described below with reference to the drawings.

〔Example〕

FIG. 1 is a schematic diagram of the configuration of the present invention, and FIG. 2 is an embodiment in which the ion source of the present invention is applied to a thin film forming apparatus.
The same reference numerals in FIG. 5 indicate the same parts. Reference numeral 1 is a plasma generation chamber, 5 is a cylindrical target, and 6 is a microwave introduction window. As the microwave source, for example, a magnetron having a frequency of 245 GHz is used, and is connected from the microwave introduction window 6 to the outside through a waveguide 7, and a microwave introduction mechanism such as a matching device, a microwave power meter, and an isolator (not shown). .
The gas introduction system is directly connected to the plasma generation chamber 1. A plurality of grid-shaped or honeycomb-shaped ion extraction grids 4 are arranged at the other end facing the microwave introduction window 6.
As a condition of the microwave cavity resonator, the plasma generation chamber 1 adopts a circular cavity resonance mode TE ₁₁₈ as an example, and uses a cylindrical shape with a diameter of 20 cm and a height of 20 cm to increase the electric field strength of the microwave. , To improve the efficiency of microwave discharge. A cylindrical target 5 that can be water-cooled on a part of the side surface of the plasma generation chamber 1, and at least one pair of the polar targets are reversed on the upper and lower ends of the cylindrical target so that magnetic flux may leak to the inner surface of the cylindrical target. The ring-shaped permanent magnet 14 of is arranged to have a cylindrical target of −1.5 KV,
Negative voltage up to 10A can be applied. The ion extraction grid 4 at the lower end of the plasma generation chamber 1 has a diameter of 10 cm.
And the grid surface facing the microwave introduction window 6 also serves as a reflection surface for microwaves, and the plasma generation chamber 1 acts as a cavity resonator.

Electromagnets 8 are provided at both outer ends of the plasma generation chamber 1,
As a result, a mirror magnetic field is generated, and the intensity of the minimum magnetic field is determined so that the conditions for electron cyclotron resonance by microwaves are satisfied inside the plasma generation chamber 1.
For example, for a microwave of 245 GHz, the condition of electron cyclotron resonance is a magnetic flux density of 875 G, so that the electromagnets 8 at both ends are configured to obtain a maximum magnetic flux density of about 3000 G. When the so-called mirror magnetic field arrangement, in which the magnetic flux density is the weakest in the plasma generation chamber 1 when the two electromagnets 8 are placed at an appropriate distance, not only efficiently imparts energy to electrons by electron cyclotron resonance, but also It prevents the generated ions and electrons from being dissipated in the direction perpendicular to the magnetic field, and also has the effect of confining the plasma between the mirror magnetic fields. In FIG. 2, 11 is a sample chamber and 12 is a substrate.

FIG. 3 shows a principle diagram of the magnetic field arrangement of the ion source of the present invention and the motion of generated ions. The same reference numerals as those in FIG. 2 indicate the same parts.

Here, the parameters for forming plasma are gas pressure in the plasma generation chamber, microwave power, target applied voltage, and gradient of the mirror magnetic field (maximum magnetic flux density Bm of the magnetic coil part and plasma at the coil center position of both electromagnets). The ratio of the minimum magnetic flux density Bo in the generation chamber: Bm / Bo) and the distance between both coils. Here, for example, for the microwave of the frequency of 245 GHz, as described above, the minimum magnetic flux density Bo in the plasma generation chamber is 875 G or less, and the maximum magnetic flux density Bm in the center of the magnetic coil of the electromagnet is about 1 kG to 3 kG. The gradient of the magnetic field can be changed so that it can be changed. here,
The magnetic flux density 875G, which is an electron cyclotron resonance condition, may be achieved at any point in the plasma generation chamber.

When the magnetic field changes spatially gently in this way, the charged particles in the plasma are constrained by the magnetic field lines 13 and spirally move around the magnetic field lines 13 while maintaining the angular momentum and the magnetic flux density. Is reflected in the high part of the mirror, resulting in reciprocal motion in the mirror magnetic field, and confinement is realized. The gradient of the mirror magnetic field mentioned above: Bm / Bo has a great influence on the plasma confinement efficiency. By applying a negative voltage to the cylindrical target 5 facing the high-density plasma confined as described above, the ions in the high-density plasma are efficiently drawn into the cylindrical target 5 to cause spatter. When the ions drawn into the cylindrical target collide with the target surface,
Secondary electrons are emitted from the surface of the target. This 2
Secondary electrons are accelerated away from the target with large energy corresponding to the target applied voltage.

The secondary electrons have a large energy and have a great influence on the ionization efficiency of gas.

On the other hand, the magnetic field leaking to the target surface by the ring-shaped permanent magnets 14 with the magnetic poles reversed at both outer ends of the cylindrical target. Effectively acts to confine this secondary electron. The principle will be described with reference to FIGS. 4 (a) and 4 (b). The figure (a) shows a top view and (b) shows a side view.

Electric field on target surface formed by target applied voltage Secondary electrons accelerated by It is deflected by and is returned to the target direction again. But again the electric field Is accelerated in the opposite direction, and as a result, the high-speed secondary electrons are repeated. In the direction of the target, i.e., in the direction of the inner diameter of the target, during which it repeatedly collides with neutral particles. As a result, a high rate of ionization of the gas and thus a more efficient sputtering is achieved at a lower target applied voltage. Further, a portion of the mostly neutral particles sputtered from the cylindrical target 5 is ionized in a high density plasma with a high electron temperature. On the other hand, in the case where the above-mentioned ion extraction grid is not present, the electrons are much lighter than the ions, so the velocity of motion in the direction of the magnetic field is larger for the electrons than for the ions, and many electrons are emitted from the mirror edge. Will escape, positive ions will be left in the mirror, charge separation will occur, and an electric field will inevitably be induced near the edge. When the potential difference between the inside and outside is equal to the average energy of the electrons, equilibrium occurs, and this electric field acts as a decelerating electric field for electrons and as an accelerating electric field for ions, and the emission amounts of both species are almost the same. That is, the loss due to the space charge effect due to such a mirror means that, from the viewpoint of the thin film forming apparatus, this plasma extracts ions having energy corresponding to the potential difference. This energy greatly depends on the microwave power and the gas pressure, and can be freely controlled in a wide range from several eV to several hundred eV. Moreover, since the target and the substrate are orthogonal to each other, negative ions and neutral high-energy particles from the target do not directly exit from the extraction hole, and the energy of the extracted particle has a small dispersion.

In addition, since there is particle scattering in the plasma due to collisions between particles, the relaxation time for the temporal decrease in plasma density due to collision scattering escapes from the mirror edge because the ion energy in the plasma is smaller. The average energy of the particle group is a fraction of the average energy of the particle group inside the plasma. That is, ionization in plasma can be performed with higher energy (high activity), and when the ions are extracted to the outside, for example, in the case of forming a film, the ions can be extracted with a smaller energy, which is a fraction. This means that the sputter ion source with this magnetic field arrangement has ideal properties as a high-speed, high-efficiency, high-purity thin film forming apparatus.

On the other hand, when an ion extraction grid is provided, the energy of the extracted ions can be controlled by the voltage applied to the grid, and a large yield of ions with any energy in the range of tens of eV to tens of KeV can be obtained. Can be withdrawn. Moreover, in this case, most of the extracted particles are ionized.

Further, since the apparatus of the present invention forms ions by sputtering using high-density plasma, it is possible to take out metal ions of various species and ions of various compounds at an extremely large current density, and thus for forming various thin films and etching. It has an extremely excellent feature as an ion source.

Further, in the present invention, since the plasma is activated, the discharge can be stably formed even at a lower gas pressure (10 ⁻⁵ Torr), and ions having less impurities can be taken out.

Further, in the present invention, since the heating by electron cyclotron resonance is utilized, the electron temperature in plasma can be freely controlled. Therefore, it is possible to realize an electron temperature at which polyvalent ions can be generated, and as a result, it is possible to synthesize the chemically unstable material by extracting the polyvalent ions.

On the other hand, in the ion source of the present invention, since the ionization rate of the plasma is extremely high as described above, the proportion of neutral sputter particles emitted from the target is high in the plasma, but the ionized target configuration is high. Particles are also accelerated by the potential of the target, and the proportion of so-called self-sputtering that spatters the target becomes extremely large. That is, gas for plasma generation (eg Ar)
It is characterized by being able to maintain the above-mentioned self-sputtering even when it is extremely dilute or when it is not used, and eventually to extract ultrahigh-purity ions and to form a film using the ions.

Next, the result of forming an Al film using the apparatus of the present invention will be described. After evacuating the degree of vacuum in the plasma formation chamber to 5 × 10 ⁻⁷ Torr, Ar gas is introduced, the gas pressure in the plasma generation chamber is set to 3 × 10 ⁻⁴ Torr, and the microwave power is 100 to 800 W.
A film was formed under the conditions of a target applied voltage of 300 to 1KV, a magnetic flux density of 400G on the target surface, and a mirror magnetic field gradient (2KG / 700G). At this time, use the ion extraction grid to
Extraction of Al ⁺ ions with an energy of eV to 1000 eV and 5 to 120Å / mi on the substrate placed under the grid.
The film could be formed efficiently at the deposition rate of n. At that time, because of the permanent magnets provided outside the target, high-speed sputtering can be realized with a lower target voltage as compared with the case where the permanent magnet is not provided. When no grid is used, particles with an energy of 5 to 20 eV, 10 to 30% of which can be ionized, can be extracted. In any case, it is faster and more efficient than the conventional method, and the thickness is 2 μm. The above film could be stably formed at high speed without cracking or peeling.

The ion source of the present invention can be used not only for forming an Al film, but also for forming almost all thin films and as an ion source for etching, and by introducing a reactive gas as a reactive gas, ion beam deposition of a compound. Can also be realized. In the present invention, the magnetic coil is used to obtain the mirror magnetic field. However, even if the magnetic field is formed by using various kinds of permanent magnets or a combination thereof, the same effect can be obtained. Obviously, it goes without saying that the gradient of the mirror magnetic field may be asymmetric.

Furthermore, in order to apply magnetic flux to the surface of the cylindrical target,
Although a pair of ring-shaped permanent magnets are used in the present invention, it is needless to say that the same effect can be obtained by using a suitable electromagnet, a suitable yoke, or a combination thereof.

〔The invention's effect〕

As described above, the present invention uses microwave discharge under the electron cyclotron resonance condition for plasma generation, efficiently confines the plasma by the mirror magnetic field, and efficiently draws the ions in the high-density plasma to the target to realize the sputtering. The ion source is realized by ionizing the neutral particles generated from it in a highly active plasma at a low gas pressure and efficiently extracting the ions. It has an extremely high current density compared to conventional ion sources. It has the excellent feature that it can extract ions, and it can also deposit and etch various types of high-purity metal ions and compound ions, and that the energy of the ions can be freely controlled in a wide range from several eV to several KeV. are doing. Further, in the present invention, due to the effect of the ring-shaped permanent magnets arranged on the outer side of the cylindrical target, the target applied voltage can be lowered and the highly efficient sputtering can be performed as compared with the case without this configuration.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an ion source of the present invention, FIG. 2 is an embodiment of a thin film forming apparatus realized by using the ion source of the present invention, and FIG. 3 is a magnetic field layout diagram of the ion source of the present invention. 4A and 4B are schematic views of the motion and potential distribution of ions generated thereby, FIGS. 4A and 4B are a top view and a side view of the device of the present invention for explaining the effect of the ring-shaped permanent magnet, and FIG. 5 is a Kauffman type ion. It is a block diagram of a type | mold. 1 ... Plasma generation chamber 1 '... Plasma generation chamber 2 ... Thermoelectron emission filament 3 ... Plasma focusing electromagnet 4 ... Ion extraction grid 5 ... Cylindrical target 6 ... Microwave introduction window 7 ... Microwave waveguide 8 …… Mirror magnetic field generating magnet 9 …… Ion beam 10 …… Plasma 11 …… Sample chamber 12 …… Substrate 13 …… Magnetic field line 14 …… Permanent magnet

Claims (1)

[Claims] 1. An ion source for extracting ions generated by sputtering by high-density plasma to form thin films of various materials on a sample substrate and etching, which has a microwave introduction window connected to a microwave waveguide at one end. And a vacuum chamber having a plasma generation chamber and a sample chamber that are sequentially coupled in the microwave traveling direction, and the plasma generation chamber is a microwave cavity resonance in which the microwave introduced into the vacuum chamber resonates. A cylindrical target that has a diameter and length that form a container and that is placed on the inner wall of the central part and that attracts ions in the plasma by applying a negative voltage and spatters it, and the magnetic flux leaks to the inner surface of the cylindrical target. As described above, at least one pair of ring-shaped permanent magnets having opposite polarities on the outer sides of the upper and lower ends of the cylindrical target, and the other end facing the microwave introduction window. Arrangement was,
The spatulated particles form a grid for selectively taking out ions ionized in plasma, and a magnetic flux density necessary for causing electron cyclotron resonance, which is provided around both ends, and forms a magnetic flux density in the plasma generation chamber. An ion source, comprising: a microwave introducing portion having a wave introducing window at an end thereof; and at least a pair of electromagnets forming a mirror magnetic field having a minimum magnetic flux density with respect to an arrangement portion of the grid.