JP2597485B2 - Microwave ion source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an ion implantation apparatus used for doping impurities into a semiconductor layer, material synthesis, surface modification or new material development, and an ion beam irradiation processing apparatus. The present invention relates to an improvement of a microwave ion source used for the above-mentioned methods.

[Conventional technology]

Ion implantation equipment is indispensable for the semiconductor manufacturing process,
Various practical devices have been developed according to the required impurity dose. However, since the impurity dose has been 10 ¹⁶ ions / cm ² even at a high concentration in the past, the ion current is 1 to 10 mA even in what is called a high-current ion implanter.
Met. On the other hand, for example, SiO ₂
SIMOX (Separation by IMplanted OXyge)
n) As with the substrate formation technology and the technology to change the physical properties of the metal surface by surface modification (nitriding / oxidation treatment, etc.), the dose amount is 10
With the progress of semiconductor manufacturing technology requiring ion implantation of ¹⁸ ions / cm ² or more, development of a high-current ion implanter of 50 to 100 mA is strongly desired.

To develop this type of device, the total ion current must be between 100 and 2
An ion source that is at least 00 mA and has a long life for an active gas such as oxygen is indispensable. Microwave ion sources are considered optimal for this type of application because of the electrodeless discharge.

FIG. 6 shows a basic configuration of a conventional microwave ion source. This is described in Japanese Patent Application No. 61-212382. In FIG. 6, 1 is a plasma generation chamber, 2 is a microwave introduction window, 3 is a waveguide, 4 is a magnetic coil, 5 is a gas inlet, 6 is an ion extraction electrode system, 7 is an extracted ion beam, 8 is an insulating fixing part, 9 is a plasma limiter, 10
Is a cooling pipe, and 11 is an O-ring for vacuum sealing. Gas is introduced into the plasma generation chamber 1 from the gas inlet 5 and microwaves (for example, 2.45 GHz) are introduced from the waveguide 3 (a microwave oscillation source, an isolator, a matching device, and a microwave power meter are not shown). When a DC magnetic field under electron cyclotron resonance (ECR) conditions (875 gauss) is applied by the magnetic coil 4 in a direction perpendicular to the microwave electric field, the gas introduced into the plasma generation chamber 1 by the interaction between them and the plasma Become. From the plasma thus generated, an ion beam 7 is extracted by an ion extraction electrode system 6 constituted by an acceleration / deceleration system.

[Problems to be solved by the invention]

Since the microwave ion source is an electrodeless discharge, it is considered that the microwave ion source can be used semi-permanently without a consumable part even for a reactive gas. However, when trying to obtain a high-density ion beam, there is a problem that the microwave introduction window 2 becomes hot and is damaged. It is considered that the cause of the temperature rise and destruction of the dielectric window is not simply caused by the plasma alone, but is caused by electrons generated near the ion extraction electrode system 6 or electrons flowing from outside the ion source. That is, since the accelerating voltage of the extraction electrode system 6 is increased to obtain a high-density ion beam, these electrons are accelerated in the direction of the microwave introduction window 2 by this accelerating voltage to become high-energy high-speed countercurrent electrons, It collides with the wave introduction window 2. In addition, these high-speed back-flow electrons do not spread under the influence of the magnetic field applied in the plasma generation chamber, but rather are squeezed and collide with the dielectric. Therefore, it is considered that electrons having high density energy collide, and the microwave introduction window 2 is heated and destroyed. In particular, if the deceleration electrode system does not fulfill its function due to discharge or the like in the three-electrode configuration of the acceleration-deceleration system, a large amount of electrons from the outside of the microwave ion source flow into the ion source. To rise.

Generally, as long as the microwave introduction window 2 is made of a dielectric material and a large amount of high-speed countercurrent electrons may collide with the microwave introduction window 2, the dielectric material deteriorates during long-time use, so that semi-permanent use is difficult. . Further, since the dielectric generally has poor heat conduction, the temperature of the introduction window becomes high, and the O-ring of the vacuum sealing portion is formed.
11 is easily damaged.

As described above, since the microwave introduction window 2 made of a dielectric material is provided at the position where the high-speed back-flow electrons collide, the introduction window 2 deteriorates for a long-time use, and it is difficult to use it semi-permanently. Was. In general, the microwave introduction window 2 generally has poor heat conduction, so that the temperature of the microwave introduction window 2 becomes high, and the O-ring 11 for vacuum sealing the window 2 easily deteriorates.

The present invention has been made in view of such a point,
An object of the present invention is to provide a highly reliable high-current ion source that can be used semi-permanently by eliminating a damaged portion of a microwave introduction part.

[Means for solving the problem]

In order to solve such a problem, the microwave ion source according to the present invention includes a microwave introduction unit that introduces a microwave into a plasma generation cavity that generates plasma, and the microwave introduction unit includes a plurality of microwave introduction units. A microwave introduction window is provided so that the interval between the microwave introduction windows is equal to or larger than the outer diameter of the beam extraction aperture of the ion extraction electrode. In addition, a shield is provided at a position where the microwave introduction window is shielded against high-speed backflow electrons flowing backward from the direction of the ion extraction electrode system.

[Action]

In the microwave ion source according to the present invention, the heat at the collision portion of the high-speed back-flow electrons is efficiently released, and O
The temperature rise of the dielectric in contact with the ring is suppressed.

〔Example〕

FIG. 1 is a configuration diagram showing one embodiment of a microwave ion source according to the present invention. In the figure, 1 is a plasma generation chamber as a plasma generation cavity made of stainless steel (SUS) having a cylindrical cavity, 3 is a waveguide, 4 is a magnetic coil, 5 is a gas inlet, and 6 is a plurality. Extraction electrode system consisting of through holes (circular or rectangular), 7 is an ion beam, 8 is an insulator, 9 is a plasma limiter, 10 is a cooling pipe, 12 is a microwave introduction part, and 121 is a microwave waveguide branch. , 122 is a microwave introduction port, 122a is a microwave introduction window, 122b is a high-speed countercurrent electron collision section, 123 is a microwave introduction port support, 13 is a cooling mechanism using cooling water, and 14 is an O-ring for vacuum sealing. . FIG. 1 is a sectional view taken along line AA of FIG. 1;
FIGS. 2 (a) and 2 (b) are cross-sectional views taken along line -B. A rectangular waveguide 3 as shown in FIG. 2A is branched into a plurality of waveguides at a microwave waveguide branch portion 121 as shown in FIG. 2B. Therefore, the microwave introduced from the rectangular waveguide 3 is branched at the microwave waveguide branch part 121 and guided to the microwave introduction window part 122a without loss. The waveguide 3 is generally rectangular, but is not limited thereto. The cavity of the plasma generation chamber 1 is not limited to a cylinder, but may be a rectangular parallelepiped. The plasma limiter 9 shields microwaves and shields (confines) the plasma, and is effective for stabilizing the ion beam and reducing the temperature rise of the extraction electrode. However, the plasma limiter 9 must be provided as a high-density ion source. is not.

6 is basically different from the ion source in FIG. 6 in the configuration of the microwave introduction unit 12, in which the high-speed back-flow electron collision unit 122b against which high-speed electrons collide is made of metal, and microwaves are introduced on both sides thereof. A microwave introduction window 122a is provided. The region where the high-speed back-flow electrons collide is substantially equal to the outer diameter of the beam extraction aperture of the ion extraction electrode. In the case of this embodiment, it is about 20 mmφ. Therefore, the high-speed reverse electron collision
The size of 122b is necessary at least to this extent. The plasma generation chamber 1 is vacuum-sealed by a vacuum-sealing O-ring 14 of the microwave introduction window 122a, and a gas to be ionized is introduced from a gas inlet. Microwave (usually 2.45GHz)
Is introduced from the waveguide 3 into the plasma generation chamber 1 through the microwave introduction window 122a. The ion extraction electrode system 6 has an acceleration-deceleration electrode configuration composed of a plurality of (usually three-electrode configuration) electrode plates. This embodiment shows a configuration example composed of three electrodes mutually insulated by an insulator 8. However, it goes without saying that a multi-stage electrode configuration larger than this may be used. In the present embodiment, a high voltage of 5 to 40 kV is applied to the acceleration electrode 6a, a negative voltage of -0.5 to -5 kV is applied to the deceleration electrode 6b, and the ground electrode 6c is grounded to the ground potential. The deceleration electrode 6b has a function of controlling the spread of the extraction beam and a function of preventing the inflow of electrons from outside the ion source. The ion extraction opening of the extraction electrode system 6 is usually composed of a plurality of through holes. To obtain a circular ion beam, 7,13,19 densely packed arrangements are required. To obtain a rectangular beam, 2 ×
What is necessary is just to arrange like 5,3x5 pieces. For example, 5mmφ × 7
An ion beam with a diameter of 20 mm can be obtained with each through hole.

When this ion source is operated to extract the ion beam, the generated plasma is supplied to the microwave inlet 122.
In addition to the collision, electrons generated in the vicinity of the ion extraction electrode system 6 or electrons flowing from outside the ion source are accelerated by the ion extraction electrode system 6 and move at high speed in the direction of the microwave introduction unit 12. Become fast back-flow electrons. In addition, due to the action of the magnetic field applied to generate the plasma, the high-speed countercurrent electrons are not spread and are reduced to the size of the electrode opening (usually a round hole), and the distance between the two microwave inlets is reduced. Collides with metal parts with high density power. That is, it corresponds to the fact that very high-density power is locally applied. In particular, when only the acceleration voltage is applied without applying the negative deceleration voltage due to discharge or the like, the inflow of electrons from outside the ion source is not suppressed,
A large amount of electrons accelerated by the accelerating voltage
Directly hit. Although the energy of such back-flow high-speed electrons is very large, the high-speed back-flow electron collision part 122b is made of a high-melting-point metal with good heat conduction, so that charged particles collide with the metal surface and the surface temperature rises. However, the heat of the metal part is taken away by the cooling mechanism 13 above the metal part, and the temperature rise is suppressed. Therefore, this high-speed countercurrent electron collision
122b is not damaged by heat. Further, since the microwave introduction window 122a is not heated by the collision of the high-speed back-flow electrons and the metal portion in contact with the O-ring 14 does not become hot, the microwave introduction window 122a is vacuum-sealed. The vacuum sealing O-ring 14 is not damaged. Therefore, this ion source operates stably even for high-density plasma.

FIG. 3 is a block diagram showing a second embodiment of the present invention.
The configuration of the microwave introduction port support 124 is different from that of FIG. The dielectric of the microwave introduction window 122a 'is made longer, and the front surface of the high-speed back-flow electron collision portion 122b is formed as a hollow cavity. The principle of operation is the same as that of the ion source shown in FIG. With such a configuration, even if the high-speed back-flow electrons coming from the direction of the ion extraction electrode system 6 collide with the high-speed back-flow electron collision portion 122b, and even if the metal in this portion becomes hot and evaporates instantaneously, The evaporated metal is introduced into the microwave introduction window 122
It is difficult to adhere to a '. Therefore, in this configuration, the microwave introduction window 122a 'does not hinder the propagation of the microwave due to the adhesion of the metal, so that the reliability is further improved. In addition, with such a configuration, the microwave does not easily propagate to the concave portion on the front surface of the high-speed countercurrent electron collision portion 122b, and the plasma density in this portion is weakened. Therefore,
The metal in the collision portion 122b of the high-speed back-flow electrons is extremely unlikely to be heated by the plasma or consumed by being sputtered by the ions in the plasma. In addition, since the microwave introduction port supporting portion 124 is configured to guide the microwave to the center of the plasma generation chamber 1, the plasma density at the center of the plasma generation chamber 1 is increased.

FIG. 4 and FIG. 5 are configuration diagrams showing third and fourth embodiments of the present invention. 4 and 5, the microwave introduction port support portions 125 and 126 are different from those in FIG. The operating principle is the first
It is exactly the same as the ion source in the figure. In FIG. 4, a partition wall 125a is provided at the center so as not to interfere immediately after the microwave is introduced.
Is installed. In addition, it is effective to form a plate or a metal mesh at the tip of the partition wall 125a so as to allow gas and plasma to pass therethrough and shield microwaves. With this configuration, the microwave is absorbed by the plasma, and the microwave and the plasma are united after the generation of the stable plasma, so that a uniform and stable plasma can be obtained. The microwave ion source shown in FIG. 5 further improves the plasma density at the center of the plasma generation chamber 1 by further guiding the microwave to the center of the plasma generation chamber 1. Further, in this configuration, the microwave introduction window portion 122a is
126b protects against fast back-flow electron impact.
Therefore, there is no restriction on the interval between the microwave introduction windows 122a, and the degree of freedom in the configuration of the ion source is increased.

In addition, the inventors of the present application have found that the microwave introduction window having a laminated structure is closely related to generation of high-density plasma. This is related to the impedance matching of the microwave to the plasma, and it is necessary to configure the microwave introduction window in consideration of the dielectric constant of the plasma. The shape (size / thickness) may be designed so that the reflection of microwaves is reduced by impedance matching. Generally, however, in order to achieve impedance matching with high-density plasma, a dielectric having a high dielectric constant (for example, alumina) is used. ) Is effective. In addition, BN is suitable for the purpose because a portion having a high thermal conductivity and a high melting point dielectric are effective in a portion that comes into contact with the plasma. For example, if quartz is used for vacuum sealing, which is excellent in processing and flatness, a combination of three kinds of dielectric materials, quartz, alumina, and BN, is effective. It goes without saying that plasma can be generated.

3 and 5, reference numerals 15 and 16 denote cooling mechanisms.

〔The invention's effect〕

As described above, the present invention includes a microwave introduction unit that introduces a microwave into a plasma generation cavity that generates plasma, and the microwave introduction unit includes a plurality of microwave introduction windows and a microwave introduction port support. By providing the portion, it is possible to prevent the high-speed backflow electrons from colliding with the microwave introduction window, and thus it is possible to prevent the microwave introduction window from being damaged. In addition, if a metal having a high melting point and good heat conductivity is provided between the microwave introduction windows, the heat between the microwave introduction windows generated by the collision of the high-speed back-flow electrons can be efficiently released to the metal. At the same time, the temperature rise of the dielectric in contact with the O-ring for vacuum sealing can be suppressed, so that the microwave ion source can operate stably up to high-density plasma. Therefore, it is useful as a high-density ion beam source.

Further, the microwave ion source according to the present invention can be used as a large-current ion source that is stable and has a long life for active gases such as oxygen and boron, and is useful as an ion source for a high-current ion implanter of 50 to 200 mA class. is there. Furthermore, if a single energy extraction electrode is used for etching and deposition as a source of low-energy (about 200 eV or less) ion plasma, it can be irradiated with a high-density ion source and plasma, so the processing speed (etching rate and deposition rate) can be reduced. Can be faster.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a microwave ion source according to the present invention, and FIGS. 2 (a) and 2 (b) are A in FIG.
FIG. 3 is a sectional view showing a second embodiment of the microwave ion source according to the present invention, FIG.
FIG. 5 and FIG.
FIG. 6 is a configuration diagram showing a fourth embodiment, and FIG. 6 is a configuration diagram showing a conventional microwave ion source. 1 ... plasma generating chamber, 3 ... waveguide, 4 ... magnetic coil, 5 ... gas inlet, 6 ... ion extraction electrode system, 6a
…… Acceleration electrode, 6b …… Deceleration electrode, 6c …… Ground electrode, 7…
... Ion beam, 8 ... Insulator, 9 ... Plasma limiter, 10 ... Cooling pipe, 11 ... O-ring, 12 ... Microwave introduction part, 13,15,16 ... Cooling mechanism, 14 ... O-ring for vacuum sealing, 121 ... microwave waveguide branch part, 122 ...
... Microwave introduction port, 122a, 122a '... Microwave introduction window, 122b ... High-speed countercurrent electron collision section, 123,124,125,12
6,126b …… Microwave inlet support.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masaru Shimada 3-1 Morinosatowakamiya, Atsugi-shi, Kanagawa Pref. Atsugi Telecommunications Research Institute, Nippon Telegraph and Telephone Corporation (56) References JP-A-62-108441 (JP, A ) JP-A-63-38585 (JP, A)

Claims (4)

(57) [Claims] A microwave introduction section for introducing a microwave from a waveguide into a plurality of plasma generation cavities for generating a plasma by branching the microwave into a plurality of microwaves; A microwave ion source, wherein the distance between the microwave introduction windows is equal to or greater than the outer diameter of the beam extraction aperture of the ion extraction electrode. 2. The microwave ion source according to claim 1, wherein a region between the microwave introduction windows is a cavity depressed from the microwave introduction window. 3. A microwave introduction unit for introducing a microwave from a waveguide into a plurality of plasma generation cavities for generating a plasma by branching into a plurality of microwaves, the microwave introduction unit comprising a plurality of microwave introduction windows. A microwave ion source, comprising: a shielding member at a position that shields the microwave introduction window from high-speed back-flow electrons flowing backward from the direction of the ion extraction electrode system. 4. The microwave oven according to claim 3, wherein said shield constitutes a microwave introduction path extending from the microwave introduction window to the center of the plasma generation cavity.
The microwave ion source according to the item.