JPH10241590A - Ion source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ion source which can effectively remove a light ion. SOLUTION: In an ion source which is provided with a drawing electrode in a plasma chamber where plasma is generated using a mixed gas including hydrogen as a working gas, and a magnetic filter 9 which passes heavy ions among ions proceeding toward the extracting electrode, capturing light ions, the ion separation ability becomes spatially uniform, adjustment of the light ion removal rate becomes possible, and deposits are decreased by constituting the magnetic filter 9 of an electromagnetic coil 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion source for generating a heavy ion beam from plasma, and more particularly to an ion source capable of effectively removing light ions.

[0002]

2. Description of the Related Art As shown in FIG.
It has a bottomed cylindrical plasma chamber 1 into which a mixed gas containing hydrogen is injected as a working gas G from a working gas injection section (not shown). A filament is provided at the center of the plasma chamber bottom 1a, and this filament constitutes the cathode 2 of the discharge electrodes. An anode 3 of the discharge electrodes is provided on a side wall 1b of the plasma chamber 1.
Is formed in an annular shape along the inner periphery of the plasma chamber 1. A power supply 4 for heating is connected to the cathode 2, and a power supply 5 for discharge is connected between the cathode 2 and the anode 3. The plasma confinement magnets 6 are provided on the side wall 1b of the plasma chamber 1 in multiple stages, and these plasma confinement magnets 6 are formed in an annular shape and incorporated in the side wall 1b.

An extraction electrode 7 is provided at the opening of the plasma chamber 1 so as to cover the opening. A potential for extraction is applied to the extraction electrode 7 by a power supply (not shown), so that ions in the plasma chamber 1 can be accelerated and a number of ion passage holes for passing the accelerated ions are provided. I have. An irradiation target, for example, a substrate 8 is placed so as to face the extraction electrode 7.

In this type of ion source, a working gas is turned into plasma in a plasma chamber, and is accelerated by an electric field to extract ions. The working gas filled in the plasma chamber is a hydride gas in which an element which forms a desired ion is combined with hydrogen. For example, PH ₃ is used to obtain phosphorus ions, and B ₂ H is used to obtain boron ions. ₆ is used. Actually, in consideration of ease of handling, safety and the like, a working gas PH ₃ / H ₂ , B ₂ H ₆ / H ₂ or the like diluted by mixing a hydrogen gas is used instead of the hydrogen compound gas alone.

[0005]

The working gas is a hydrogen compound gas, and the working gas is mixed with hydrogen gas. Therefore, mixed plasma, that is, plasma composed of various ions, is generated in the plasma chamber. For example, when PH ₃ / H ₂ is used as the working gas, PH _X ⁺ ions, H ⁺ ions, H ₂ ⁺ ions, and the like are generated in addition to P ⁺ ions. The ratio is 30% for P and 70% for H. B ₂ H ₆ / H
_{When 2} is used as working gas, B is 15% and H is 85%
become.

[0006] With the purpose of such an ion doping, although PH _X ⁺ ions P ⁺ ions are taken out from the plasma chamber permissible not larger mixed, H ⁺ ions or H ₂ ⁺
Ions are unnecessary. These unwanted ions are
A collision with a plasma chamber wall, an extraction electrode, an object of ion doping, or the like causes a heat load. In addition, the accelerating power is wasted. Therefore, in order to obtain a high quality ion source, it is necessary to prevent H ions and H ₂ ions from being included in a desired ion beam.

In order to prevent unnecessary ions from being extracted, the present applicant has proposed a magnetic filter 9 for passing heavy ions out of the ions heading for the extraction electrode and capturing light ions.
Has already been proposed. The magnetic filter 9
Permanent magnets are arranged at regular intervals in parallel with the extraction electrode 7, and light ions are captured by a magnetic field perpendicular to the ion passage direction. However, when the magnetic filter is constituted by permanent magnets, there are the following problems.

As shown in FIG. 11, the magnetic field 23 formed between the poles of the permanent magnet 22 has a swelling and thus is not a uniform magnetic field, and a magnetic field is also generated in an unnecessary space. The magnetic filter constituted by the permanent magnets 22 can pass the heavy ions 42 and capture the light ions 41, but the ion separation ability is not spatially uniform. When the distance between the poles is increased, this tendency becomes stronger, and when the distance between the poles is reduced, there is a dilemma that the thickness of the permanent magnet portion becomes thicker than the distance between the poles and an ion passage area cannot be secured.

Further, since the strength of the magnetic field cannot be changed with a permanent magnet, the light ion removal rate cannot be adjusted by the strength of the magnetic field.

Further, since the plasma chamber is in a high temperature environment, it is necessary to cool the permanent magnet in order to prevent the permanent magnet from losing magnetism. However, when cooled, the ionic element adheres to the permanent magnet and deposits are generated.

It is an object of the present invention to solve the above problems and to provide an ion source capable of effectively removing light ions.

[0012]

In order to achieve the above object, the present invention provides an extraction electrode in a plasma chamber for generating a plasma using a mixed gas containing hydrogen as a working gas, and a heavy ion out of ions heading to the extraction electrode. In an ion source provided with a magnetic filter for passing ions and capturing light ions, the magnetic filter is constituted by an electromagnetic coil.

In the electromagnetic coil, a reciprocating current path traversing the plasma chamber is arranged in multiple stages in a longitudinal direction of the plasma chamber.
These current paths may be sequentially connected.

An electrode for extinguishing light ions may be provided in the magnetic field region of the electromagnetic coil.

An ion-extinguishing electrode whose potential can be adjusted may be provided at both ends of the electromagnetic coil insulated from the plasma chamber.

The current path may be formed by a rod, and the rod may be covered with an insulating tube to constitute a magnetic filter.

A ring-shaped plasma potential adjusting electrode electrically insulated from the plasma chamber and capable of applying an arbitrary voltage may be provided between the magnetic filter and the extraction electrode.

A plasma grid, which is electrically insulated from the plasma chamber and to which an arbitrary voltage can be applied, may be provided on the extraction electrode side.

[0019]

An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

The ion source of the present invention shown in FIG. 1 has a plasma chamber 1 provided with a working gas injection portion, a discharge electrode, a plasma confinement magnet, an extraction electrode, and the like. Omitted. Inside the plasma chamber 1, a magnetic filter 9 including an electromagnetic coil 11 is provided along the extraction electrode 7 inside the extraction electrode 7. The substrate to be irradiated by the ion source is of a square type, the ion passage holes of the extraction electrode 7 are arranged in a square shape so as to match the substrate shape, and the magnetic filter 9 is also formed in a square shape. The electromagnetic coil 11 constituting the magnetic filter 9 has reciprocating current paths 12 a and 12 b traversing the plasma chamber 1, and the forward path 12 a and the return path 12 b are provided at different positions from the extraction electrode 7. Here, the current path closer to the extraction electrode 7 is the outward path 12a, and the current path farther away is the return path 12b. The pair of reciprocating current paths 12 a and 12 b are arranged in multiple stages in the longitudinal direction of the plasma chamber 1.

As shown in FIG. 2, the electromagnetic coil 11
Are arranged in two rows and rows of rods 13 made of molybdenum having a constant length and a constant diameter, which constitute a current path, and one of the rods is a forward rod 13a and the other is a return rod 13b. At one end of these rods, the forward rod 13a and the same-stage return rod 13b are connected by the connecting conductor rod 14, and at the opposite end, the return rod 13a is connected.
b and the connecting rod 13a for the forward path of the next stage
It is connected by. In this way, a rectangular electromagnetic coil is formed by sequentially connecting the rods 13a and 13b while changing one step each time it reciprocates. The distance between the forward rod 13a and the return rod 13b is very small,
Outgoing rods 13a, 13a, return rod 1
The interval between 3b and 13b is large, and the electromagnetic coil 11 has a flat appearance. This electromagnetic coil is electrically insulated and structurally supported by fixing each connecting conductor rod 14, 15 to an insulator spacer (not shown) and attaching the insulator spacer to the side wall of the plasma chamber. Have been.

The magnetic field generated by the current I is transmitted to the rod 13 for the forward path.
a in the direction indicated by the arrow H in the space between the a and the return rod 13b. This direction corresponds to the longitudinal direction of the plasma chamber 1 in FIG.

In the ion source shown in FIG. 1, when a current is supplied to the electromagnetic coil 11 from an electromagnetic coil power supply (not shown), a magnetic field indicated by an arrow H is generated. On the other hand, heavy ions and light ions generated in the plasma chamber 1 pass through the electromagnetic coil 11 due to plasma diffusion. Since the magnetic field generated by the electromagnetic coil 11 is orthogonal to the direction in which the ions pass, the moving direction of the ions is affected, and heavy ions pass but light ions are captured by the magnetic field. Therefore, only the heavy ions are included in the ion beam indicated by the arrow B generated from the ion source.

The magnetic field formed by the electromagnetic coil 11 exists only in the internal space of the electromagnetic coil 11 in a limited manner, and is a uniform magnetic field having no bias depending on the location. For this reason, the ion separation ability is spatially uniform. To secure a large ion passage area, the rods 13a, 13a (13b, 13
It is preferable to increase the interval of b), but even if the interval of the rods is increased, the magnetic field does not expand unlike the permanent magnet.

Further, since the strength of the magnetic field of the electromagnetic coil 11 can be easily changed by the current I, the light ion removal rate can be adjusted.

Further, since the electromagnetic coil 11 can be used without losing the magnetic field even in a high temperature environment, no cooling equipment is required and the amount of deposits can be reduced. Furthermore, when the interval between the rods is increased so as to secure a large ion passage area, the number of windings is reduced, so that a large current flows to secure the strength of the magnetic field. However, it is preferable because the heat is high and the deposits can be removed even more.

FIG. 3 shows an ion source of the present invention provided with an ion annihilation electrode. The ion annihilation electrode 16 is
Are provided in the magnetic field region. That is, the plasma chamber 1
The plate-like ion annihilation electrode 16 crossing the
It is provided in the middle position of each stage of a and 12b along the ion passing direction. The ion annihilation electrode 16 is set to a floating potential, a discharge anode potential, or a negative potential. For example, by directly attaching to the side wall of the plasma chamber, since the side wall of the plasma chamber has a floating potential, the ion annihilation electrode 16 can also be set to the floating potential.

In the ion source provided with the ion annihilation electrode 16, the light ions captured by the magnetic field cause the ion annihilation electrode 1 to emit light ions.
Since electrons can be more easily obtained than in the plasma through 6, light ion annihilation (neutral gasification) is promoted.

FIG. 4 shows a doping apparatus to which the ion source of the present invention is applied. This doping apparatus includes an ion source 31.
The ion source 31 is adjacent to a process chamber 33 for accommodating a substrate to be irradiated. The process chamber 33 is provided with a robot chamber 34 containing a transfer robot operating in a process atmosphere, separated by a shutter, and a load lock chamber on both sides of the robot chamber 34 for removing the process atmosphere or the atmosphere through a shutter. 35 are provided. Outside the load lock chamber 35, an atmospheric robot 36 operating in air is provided. The substrate is formed into a cassette, and the cassette is supplied to or discharged from the cassette stage 37.

The atmospheric robot 36 supplies the cassette placed on the cassette stage 37 on the supply side to the load lock chamber 35, and when the air in the load lock chamber 35 is replaced with the purge gas, the transfer robot in the robot chamber 34 is moved. The cassette is set at an irradiation position in the process chamber 33. After the irradiation, the cassette is transferred to the load lock chamber 35 on the opposite side by the transfer robot. When the working gas in the load lock chamber 35 is replaced with the purge gas, the atmospheric robot 36 discharges the cassette to the cassette stage 37.

FIG. 9 shows a substrate processed by the doping apparatus. This substrate is obtained by forming a silicon oxide film 52 on a polysilicon film 51. By forming the molybdenum film 53 on the silicon oxide film 52 when irradiating the PH _X ^+, it is possible to inject PH _X ⁺ the desired compartments of the polysilicon film 51. For example, in the manufacture of a thin film transistor, the source 54 and the drain 5
Inject PH _X ⁺ only in the section that becomes 5 and make channel 56
Do not inject PH _X ⁺ into the compartment where In this case, the inclusion of H ⁺ in the ion beam, partition of the source 54 and drain 55 are liable to pass through the H ^+,
H ⁺ is injected into the section of the channel 56. When the ion source of the present invention is used, an ion beam from which H ⁺ has been removed can be irradiated.
H ⁺ is not injected into the compartment.

In the doping apparatus to which the ion source of the present invention is applied, unnecessary light ions are not contained in the ion beam, so that the doping of PH _X ⁺ or B ₂ H ₆ ⁺ can reduce the rise in the substrate temperature, The use of a resist can be enabled.

Next, another embodiment of the present invention shown in FIG. 5 will be described.

In the embodiment of FIG. 3 described above, an example is shown in which the ion annihilation electrode 16 is provided at a floating potential in the magnetic field region of the electromagnetic coil 11. The annihilation electrodes 16 are disposed at both ends of the electromagnetic coil 11 forming the magnetic filter 9, and a predetermined potential is applied to the ring-shaped anode 3 and the ion annihilation electrode 16. In addition, 2a is a filament, and 7 is an extraction electrode composed of an extraction grid 7a and an acceleration electrode 7b.

In the embodiment shown in FIG. 5, the ion annihilation electrode 16 is inserted by electrically insulating the ion annihilation electrode 16 from the plasma generating section and enabling the potential to be arbitrarily controlled from the outside. The plasma potential in the space of the magnetic filter 9 can be controlled, and both the insertion of the ion annihilation electrode 16 and the ion trap by the magnetic field can be achieved, thereby improving the magnetic filter effect and increasing the desired heavy ion generation efficiency.

FIG. 6 shows a rod 13a, 13b made of Mo of the electromagnetic coil 11 of FIG.
To form an ion source.

In this embodiment, when plasma is generated (during operation of the ion source), the surface of the insulating tube 17 around the rods 13a and 13b is automatically charged up, and the surface potential is common potential (= floating potential) over the entire area. ).

As a result, the spatial fluctuation of the plasma potential of the magnetic filter 9 can be suppressed. The rods 13a, 1
Excessive plasma potential can be prevented from dripping by the applied voltage to 3b.

FIG. 7 is a modified version of FIG.
A plasma potential adjustment electrode 18 is provided in a plasma diffusion chamber 20 between the electromagnetic coil 11 and the extraction electrode 7 covered by the electrode 7, and a potential adjustment power supply 19 is connected between the plasma potential adjustment electrode 18 and the ion annihilation electrode 16.

FIG. 8 shows a plasma potential adjusting electrode 18.
Insulating material 2 so as to be electrically insulated from plasma chamber 1
A plasma grit 21 is provided via 1a, and a potential adjusting power supply 19 is connected between the plasma grit 21 and the ion annihilation electrode 16.

In the embodiment shown in FIGS. 7 and 8,
A plasma potential adjusting electrode 18 and a plasma grit 21 that are electrically insulated from the plasma chamber 1 and can apply an arbitrary voltage to the anode 3 by a potential adjusting power supply 19 are installed in a plasma diffusion chamber 20. By adjusting the voltage applied to the electrode 18 and the plasma grit 21, the elimination balance of the electron ions in the plasma diffusion chamber 20 is adjusted, and the relative potential of the plasma in the diffusion chamber 20 to the plasma chamber 1 and the magnetic field generated by the magnetic filter 9. Can be adjusted to change the annihilation balance of the electron ions in the plasma in the diffusion chamber 20 at the plasma potential adjusting electrode 18 and the plasma grit 21 (when the floating potential is made positive, the electron annihilation is promoted. When ion extinction is suppressed and the potential is negative with respect to the floating potential, electron extinction is suppressed and ion extinction is promoted). The relative potential with respect to the plasma chamber 1 of the plasma chamber 20 can be adjusted magnetic filter generating an electric field. Thereby, acceleration / deceleration of ions in the magnetic filter 9 is controlled, and the ion trapping effect of the magnetic filter 9 is set to a desired ion species separation (PH _X : H _X , B ₂ H _X :
The adjustable optimal conditions to H _X 9.

[0042]

The present invention exhibits the following excellent effects.

(1) Since the ion separation ability is spatially uniform, a high-quality ion beam can be obtained.

(2) The light ion removal rate can be easily adjusted.

(3) Since the amount of deposits can be reduced, maintenance becomes easy.

(4) The electric field generated by the magnetic filter can be adjusted.
By controlling the acceleration and deceleration of ions in the magnetic filter,
The ion trap effect of the magnetic filter can be adjusted to the optimum condition for desired ion species separation.

[Brief description of the drawings]

FIG. 1 is a sectional view of an ion source showing an embodiment of the present invention.

FIG. 2 is an enlarged perspective view of a magnetic filter using the electromagnetic coil of the present invention.

FIG. 3 is a cross-sectional view of an ion source showing another embodiment of the present invention.

FIG. 4 is a plan view of a doping apparatus to which the ion source of the present invention is applied.

FIG. 5 is a cross-sectional view of an ion source showing another embodiment of the present invention.

FIG. 6 is a cross-sectional view of an ion source showing another embodiment of the present invention.

FIG. 7 is a cross-sectional view of an ion source showing another embodiment of the present invention.

FIG. 8 is a cross-sectional view of an ion source showing another embodiment of the present invention.

FIG. 9 is a sectional view of a substrate processed by a doping apparatus.

FIG. 10 is a sectional view of a conventional ion source.

FIG. 11 is a diagram of a magnetic filter magnetic field by a permanent magnet.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 plasma chamber 7 extraction electrode 9 magnetic filter 11 electromagnetic coil 16 ion annihilation electrode 17 insulating tube 18 plasma potential adjusting electrode 21 plasma grit

Claims (7)

[Claims] 1. An ion having an extraction electrode provided in a plasma chamber for generating plasma using a mixed gas containing hydrogen as a working gas and having a magnetic filter for passing heavy ions out of the ions heading to the extraction electrode and capturing light ions. An ion source, wherein the magnetic filter comprises an electromagnetic coil. 2. The electromagnetic coil according to claim 1, wherein reciprocating current paths traversing the plasma chamber are arranged in multiple stages in a longitudinal direction of the plasma chamber, and these current paths are sequentially connected. The ion source as described. 3. The ion source according to claim 1, wherein an electrode for extinguishing light ions is provided in a magnetic field region of the electromagnetic coil. 4. The ion source according to claim 1, wherein an ion-extinguishing electrode whose potential is adjustable is provided at both ends of said electromagnetic coil insulated from a plasma chamber. 5. The ion source according to claim 2, wherein the current path comprises a rod, and the rod is covered with an insulating tube. 6. The ion source according to claim 5, wherein a ring-shaped plasma potential adjusting electrode electrically insulated from the plasma chamber and capable of applying an arbitrary voltage is provided between the magnetic filter and the extraction electrode. 7. The ion source according to claim 5, wherein a plasma grit which is electrically insulated from the plasma chamber and to which an arbitrary voltage can be applied is provided on the extraction electrode side.