JPH06162980A - Ion source - Google Patents

Abstract

PURPOSE:To separate undesirable light ions from an ion beam by providing a drawing electrode having a number of small holes at the opening part of a plasma chamber and placing a magnet between small holes to deflect light ion seed beam. CONSTITUTION:A drawing electrode 1 having a number of small holes each such as a circle hole is provided at the opening part of a plasma chamber. Ions produced by applying a voltage to the drawing electrode 1 so as make gas compound into plasma condition are drawn out through the small hole as an ion beam. In the above mentioned ion source, each magnet 5 is placed on each of transverse frames 3 provided between small holes 2 of the drawing electrode 1. It is desirable that magnet 5 are formed in such manner that they have uniform shape, polarity, strength, etc. Ion seeds receive Lorents force in accordance with electric charge by the electromagnetic field of the magnet 5 so that the light ion seeds as H<+> are deflected in large deflection angle. Thus, only desired heavy ion beam is irradiated on an object so as to prevent the increase of temperature at the object.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion source which uses a gaseous compound as a raw material gas and extracts an ion beam consisting of the elements therein, and more particularly to an ion source which can separate unnecessary light ions from the ion beam. Is.

[0002]

2. Description of the Related Art A film can be formed on the surface of an object by ionizing and ejecting a substance and irradiating and colliding the ion with the object. In order to extract a desired substance as an ion beam, a gaseous material that is a source of ions is introduced, and discharge is performed in this gas atmosphere to generate plasma containing the substance. Charged particles such as ions are extracted from the plasma by the extraction electric field.

Conventionally, generally, an ion source has a plasma chamber for generating plasma and confining the plasma, as shown in FIG. 4, in which a filament for thermionic emission and a confining magnetic field are provided. Is provided. Further, a raw material gas of a desired substance is introduced into the plasma chamber. An opening is provided at one end of the plasma chamber, and an extraction electrode for extracting charged particles such as ions from the plasma is provided at the opening. The extraction electrode is formed in a mesh shape, a slit shape, or a porous shape so that the charged particles accelerated by the extraction electric field can easily slip through. Hereinafter, the gaps such as the circular holes, the square holes, and the slits of the extraction electrode through which the charged particles pass are collectively referred to as small holes.

Argon or phosphine (PH ₃ ) gas is introduced into the plasma chamber. Then, argon ions or phosphorus ions can be extracted from the plasma by an extraction electric field, and the surface of an object such as a semiconductor substrate which is an object can be irradiated and injected with argon or phosphorus. Here, the reason why phosphine is used to obtain the ion beam of phosphorus is that phosphorus alone does not gasify, and thus a gaseous compound containing phosphorus like phosphine is used as a source gas.

When phosphine is used as the source gas, not only phosphorus ions but also hydrogen ions (H ⁺ , H ₂ ) are contained in the plasma.
⁺ ) Exists. Like the phosphorus ions, the hydrogen ions are accelerated by the extraction electric field to form a mixed ion beam. When the surface of the object is irradiated with this ion beam, phosphorus is injected and hydrogen releases energy. This energy is converted to heat, which raises the temperature of the object. The energy of this temperature rise is called heat load, and becomes a problem especially when the object is weak to heat such as a semiconductor substrate. In order to prevent the irradiation of an object with an undesired ion beam such as a hydrogen ion beam, mass separation is preferably performed. As a method of mass separation, it is known that a magnetic field orthogonal to the ion beam is applied to deflect the ion beam.

[0006]

However, as the size of the object increases, the diameter of the ion beam also needs to increase. In this case, it is necessary to increase the size of the magnet that gives the deflection magnetic field and the size of the gap accordingly.
In that case, the weight and size of the entire apparatus become enormous, and accordingly, various disadvantages such as an installation place, a supporting method, an apparatus cost, and maintenance management occur. Further, if the gap is wide, it becomes difficult to obtain a uniform magnetic field, and therefore a good ion beam cannot be obtained.

Therefore, an object of the present invention is to solve the above problems and provide an ion source capable of separating unnecessary light ions from the ion beam.

[0008]

To achieve the above object, the present invention provides an extraction electrode having a large number of small holes such as circular holes, square holes, and slits at the opening of a plasma chamber, and gas compounds are used as ions. In the ion source for extraction, a magnet for deflecting the light ion species beam passing through the small holes is provided between the small holes of the extraction electrode.

[0009]

With the above structure, a deflection magnetic field is formed in each small hole of the extraction electrode. The ion beam passing through each small hole receives a Lorentz force corresponding to the charge of any ion species. This force gives the ion beam a deflection angle depending on the mass of the ion species. That is, a beam of heavy ion species will have a relatively small deflection angle, and a beam of light ion species will have a relatively large deflection angle. Therefore, the two beams are separated as the distance from the extraction electrode is increased.

If the object is placed in front of the ion source, only the heavy ion species beam can be selectively irradiated.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, the extraction electrode 1 is formed in a disk shape and has a large number of small holes 2. Small hole 2
A large number of circular holes are arranged on a large number of parallel lines that cross the extraction electrode 1. Also, small holes 2 on each parallel line
Are arranged at the same intervals so that the corresponding small holes 2 are arranged on a straight line.

A portion between the small holes 2 is a bone portion, and the bone portion is a structural member of the extraction electrode 1 and at the same time an electrode itself to which an extraction voltage is applied. For convenience of description, the one in the lateral direction of the drawing will be referred to as a lateral bone 3.

In FIG. 1, there are six lateral bones 3, and each lateral bone 3
Although three small holes 2 lined up in between are shown, in reality, there are many small holes. Further, the margin portions 4 having no small holes are provided on the left and right of the extraction electrode 1, but this is for shaping the shape of the ion beam, and can be provided in any shape. When the portion having the small holes 2 is formed vertically as in this embodiment, an ion beam having a band-shaped cross section can be obtained.

A magnet 5 is provided on the lateral bone 3. The magnet 5 is formed in an elongated shape in the horizontal direction and has a polarity in the vertical direction. The direction of the polarity and the strength of the magnetic field are uniform for each magnet 5. In this embodiment, the upper part of the figure is the N pole. The magnet 5 is provided so that both poles face the small holes 2 that are vertically adjacent to each other. N for each small hole 2
A pole and an S pole appear on both sides of the small hole 2 facing each other, and a magnetic field is formed longitudinally through the small hole 2. The direction of the magnetic field B in each small hole 2 is indicated by an arrow at the lower right of the figure.

The ion source 6 of the present invention has a plasma chamber 7 formed in the shape of a bottomed cylinder similar to that already shown in FIG. 4, and in the plasma chamber 7 is a filament and a magnet for confinement. Etc. are provided. The opening 8 of this plasma chamber 7
In place of the conventional extraction electrode 9, the extraction electrode 1 provided with the magnet is attached.

An object 10 such as a semiconductor substrate for implanting phosphorus is placed in front of the opening at a predetermined distance.

Next, the operation of the embodiment will be described.

When a gaseous compound, which is a source gas, here, phosphine (PH ₃ ) is introduced into the plasma chamber 7,
Plasma composed of ions such as P ⁺ , H ⁺ , and H ₂ ⁺ is generated. When a voltage is applied to the extraction electrode 1, these ions are accelerated and become an ion beam in which the respective ions are mixed and pass through the small holes. The state of this passage is shown in detail in FIG.

FIG. 2 is a sectional view in which the small hole 2 of the extraction electrode 1 is cut in the direction of the lateral bone 3. The upper side of the figure is the inside of the plasma chamber 7. There is a vertical bone 11 between the small holes 2 and the S pole of the magnet provided on the horizontal bone 3 appears in the small hole 2. The direction of the magnetic field B in the small hole 2 is the direction toward the paper surface as shown in the figure. When the ion beam 12 coming from the direction perpendicular to the extraction electrode 1 passes through the small hole 2, any ion species receives a Lorentz force corresponding to the electric charge. This force gives the ion beam 12 a deflection angle depending on the mass of the ion species. That is, a beam of heavy ion species (P ⁺ ) has a relatively small deflection angle, and a beam of light ion species (H ⁺ , H ₂ ⁺ ) has a relatively large deflection angle. The difference between the deflection angles is θ. Since phosphorus and hydrogen have significantly different masses, θ has a significant magnitude.

After passing through the small holes, the ion beam goes straight. Since the strength of the magnetic field is set appropriately here, the P ⁺ ion beam 13 advances in the direction substantially in front of the ion source,
The ion beam 14 of H ⁺ or the like advances in a direction away from the front of the ion source.

Since the object is placed in front of the opening at a predetermined distance, the ion beam 13 of P ⁺ is applied to the object, but the ion beam 14 of H ⁺ or the like is applied to the object. Going beyond the size of. Therefore, the ion beam 14 of H ⁺ or the like is not applied to the target object, and the temperature rise of the target object caused by it is prevented.

Next, application examples of the present invention will be described.

In the example shown in FIG. 3, the extraction electrode 1 described in FIG. 1 is attached to the ion source 6, and a source gas made of a gaseous compound such as a hydrogen compound of phosphorus or boron is introduced into the plasma chamber 7. A long object 10 is placed at a predetermined distance from the ion source 6. The object 10 is much larger than the diameter of the ion source 6 in the longitudinal direction. Therefore, the object 10 is conveyed in the longitudinal direction at a constant speed by a conveying device (not shown). The extraction electrode 1 is formed by vertically forming a portion having a small hole 2 and obtains an ion beam having a strip-shaped cross section, and a heavy ion species beam such as P ⁺ and B ^{+ of the} strip-shaped ion beam is obtained. Is the object 10
Is irradiated in a strip shape in a direction perpendicular to the longitudinal direction of the. The direction of the deflecting magnetic field B is directed toward the wider ion beam,
The deflection angle is oriented in the direction in which the width of the ion beam is narrow. This is because the lighter the ion, the earlier the beam deviates from the irradiation range of the original ion beam.
This is advantageous in shortening the distance from. However, since the escape direction of the light ion species beam 14 is the same as the conveying direction of the target object 10, a shield plate 15 that covers the target object 10 is provided in that direction. The light ion species beam 14 is applied to the shield plate 15, and the shield plate 15 absorbs heat energy, so that the object 10 is protected from the heat load.

In the embodiment of the present invention, the small hole 2
Although circular holes are arranged in a lattice pattern, even if the holes are slits, grids, or small holes formed by other arrangements, it is possible to achieve the same effect by providing the magnets 5 between the small holes 2. Of course.

[0026]

The present invention exhibits the following excellent effects.

(1) Since unnecessary light ions are separated from the ion beam, the heat load on the object is reduced.

(2) Even if the diameter of the ion beam is large, the deflection magnetic field is uniform, so that the shape of the ion beam is not impaired.

(3) Since it is sufficient to separate the light ions, it is not necessary to increase the deflection magnetic field, and the structure can be simplified.

[Brief description of drawings]

FIG. 1 is a plan view of an extraction electrode showing an embodiment of the present invention.

2 is a partially enlarged cross-sectional view of the extraction electrode of FIG.

FIG. 3 is a side view of an ion implantation apparatus showing an application example of the present invention.

FIG. 4 is a side view of the ion source.

[Explanation of symbols] 1 extraction electrode 2 small hole 5 magnet

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H05H 1/00 9014-2G

Claims (1)

[Claims] 1. An ion source having a large number of small holes such as circular holes, square holes, and slits provided at the opening of a plasma chamber, and in an ion source for extracting a gas compound as ions, a small electrode is provided between the respective small holes of the extraction electrode. An ion source comprising a magnet for deflecting a beam of light ion species passing through a hole.