JPH05299054A - Mass spectrometer - Google Patents

Abstract

PURPOSE:To reduce spatter of shielding plates, lengthen the service life, reduce pollution in a target, and increase a beam electric current quantity in the target by arranging a plurality of shielding plates so that an undesirable ion can collide approximately vertically with the inside of an analyzer tube. CONSTITUTION:An ion beam drawn out from an ion source 1 enters an ion passage 4 of an analyzer tube 5. A magnetic flux density adjusted uniform magnetic field is formed in the passage 4 so that only a desirable ion can pass through an outgoing slit 5b. Respective ion kinds are bent in curvature according to the mass due to this magnetic field operation, and orbits are separated with the respective ion kinds. At this time, an ion heavier than the desirable ion or an ion lighter than that collides approximately vertically with shielding plates 6, 7,.... Since the ion is made incident approximately vertically upon the shilding plates 6, 7,..., spatter can be reduced significantly as compared with a case when the ion is made incident approximately in parallel with the shielding plates.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass spectrometer for selecting desired ions, which is provided in, for example, an ion implanter used for manufacturing a semiconductor integrated circuit.

[0002]

2. Description of the Related Art An ion implantation apparatus is for implanting desired impurities into a target such as a wafer, and is capable of implanting impurities that determine device characteristics in a semiconductor process to an arbitrary amount and depth with good controllability. , Has become an important device in the manufacturing of integrated circuits today.

An example of a conventional mass spectrometer used in this ion implantation system is shown in FIG. In the ion implantation apparatus, first, a predetermined ion source material is ionized by the ion source 51 and extracted as an ion beam by an electric field. This ion beam is composed of a plurality of ion species, and is bent by the mass analyzer 52 with a curvature according to the mass of each ion species, and the orbit is separated for each ion species. The mass spectrometer 52 is provided with an analysis tube 55 that forms a bent ion passage 54. Then, only desired ions pass through this ion passage 54,
The target is irradiated with only desired ions by adjusting the mass spectroscope 52 so that it passes through the analysis slit 57 arranged downstream of the beam. The inside of the passage for the ion beam is kept in a high vacuum state.

In the mass spectrometer 52, on the outer side and the inner side of the trajectory of the desired ion beam passing through the ion passage 54, ions heavier (small curvature) and lighter (large curvature) than the desired ions deviated from the trajectory. ) A shielding plate 56.5 called a liner made of a metal plate or the like along the trajectory of the desired ion beam to shield the ion beam
6 is provided.

[0005]

By the way, the sputtering of a substance by ion irradiation has an ion incident angle dependency, and the sputtering rate (the number of molecules or atoms sputtered per ion) becomes close to parallel incidence. It is known that it becomes higher (for example, when the ion incident angle becomes 60 to 80 °, the sputtering rate increases to several times that at the time of vertical incidence).

On the other hand, in the above-mentioned conventional structure, undesired ions deviating from the desired ion beam trajectory are incident on the surface of the shielding plate 56 at an angle almost parallel to each other, so that the surface of the shielding plate 56 is strongly sputtered. Therefore, there is a problem that the life of the shielding plate 56 is short. Further, since the surface of the shield plate 56 is strongly sputtered, a large number of heavy metals, which are constituent components of the shield plate 56, jump out from the surface of the shield plate 56 and mix into a desired ion beam as contamination,
It has a problem of contaminating the target with heavy metals.

As a method of preventing such heavy metal contamination, a method of sticking a silicon plate on the surface of the shielding plate 56 to prevent spattering of heavy metals is well known. However, in this case, there is a problem that the surface of the silicon plate is sputtered and consumed quickly. In addition, the gas released from the adhesive used to attach the silicon plate or the silicon plate is heated by ion beam irradiation, and the degree of vacuum in the mass spectrometer is increased due to thermal decomposition and vaporization of the adhesive. There are problems such as deterioration and contamination of the target. In particular, in a mass spectrometer used for a so-called high-current ion implanter having a relatively large beam current, the temperature of the silicon plate becomes high due to ion beam irradiation, and the thermal decomposition of the adhesive becomes violent. I couldn't adapt.

As another method for preventing heavy metal contamination, a carbon plate or a silicon carbide plate may be used in place of the silicon plate, but it has the same problem as above.

Further, the above conventional structure has the following problems. That is, when the shield plate is irradiated with the ion beam, secondary electrons are generated. Since the secondary electrons are generated near the trajectory of the desired ion beam, the desired ion beam that is a group of positive ions is 2 with negative charge
Neutralized with secondary electrons, some positive ions in the desired ion beam become neutral molecules or atoms. Like this, 2
The neutral molecules or atoms that have been neutralized by secondary electrons deviate from the desired ion beam orbit, and the desired ion beam amount (beam current) with which the target is irradiated is reduced.

It is known that the rate of generation of secondary electrons with respect to the incident beam is relatively small in the case of vertical incidence and rapidly increases in the vicinity of parallel incidence. From this point as well,
In the above conventional configuration, the undesired ion beam is incident on the surface of the shield plate at an angle substantially parallel to the surface of the shield plate, so that many secondary electrons fly out from the beam irradiation surface of the shield plate, and the beam current amount at the target is significantly reduced. Will be done.

The present invention has been made in view of the above, and an object thereof is to reduce spatter on the shield plate, prolong the life of the shield plate, and reduce the contamination of the target due to the contamination of heavy metals, Another object of the present invention is to provide a mass spectrometer capable of reducing the neutralization of the ion beam by the secondary electrons generated in the shield plate and increasing the beam current amount at the target.

[0012]

In order to solve the above-mentioned problems, a mass spectrometer according to a first aspect of the present invention has an analysis tube forming an ion passage, and the traveling direction of ions passing through this analysis tube is The following means are taken in a mass spectrometer that bends and separates each ion into orbits corresponding to the mass and selects a desired ion.

That is, a plurality of shielding plates are provided in the analysis tube so that undesired ions collide with each other substantially vertically.

The mass spectrometer according to the invention of claim 2 is
In order to solve the above-mentioned problems, an analysis tube that forms an ion passage is provided, and the traveling direction of the ions passing through the analysis tube is bent to separate each ion into a trajectory corresponding to the mass, and the desired ion is selected. The following measures are taken in the mass spectrometer.

That is, a plurality of shield plates arranged so that undesired ions collide with each other substantially vertically and a positive electrode to which a positive voltage is applied are provided in the analysis tube.

[0016]

According to the structure of the above-mentioned claim 1, the orbits of the ions passing through the analysis tube are separated according to the mass, and only the desired ions are taken out through the analysis tube, while the undesired ions are removed. , And collides with the shield plate provided in the analysis tube substantially vertically.

It should be noted that since the sputtering of a substance by ion irradiation has an ion incident angle dependency and the sputtering rate becomes the lowest at the time of vertical incidence, the sputtering on the shield plate is greatly reduced as compared with the prior art.

The generation of secondary electrons due to ion irradiation also depends on the angle of incidence of ions, and the generation rate of secondary electrons becomes the lowest at the time of vertical incidence, so that the secondary electrons jumping out from the beam irradiation surface of the shield plate. The number of electrons is reduced as compared with the conventional one, and the amount of the desired ion beam, which is a group of positive ions, is neutralized by the secondary electrons (some positive ions in the ion beam become neutral molecules or atoms). .. Therefore, the beam current of the desired ions extracted from the mass spectrometer is increased more than ever before.

Further, according to the structure of the second aspect, as described above, the undesired ions collide with the shield plate provided in the analysis tube substantially vertically, so that the spatter on the shield plate is larger than in the conventional case. The number of secondary electrons jumping from the beam irradiation surface of the shield plate is also reduced as compared with the conventional case. Further, a positive electrode to which a positive voltage is applied is provided in the analysis tube, and the secondary electrons generated in the analysis tube are absorbed by the positive electrode, so that a desired ion that is a group of positive ions is obtained. The amount by which the beam is neutralized by secondary electrons is further reduced. Therefore, the beam current of the desired ions extracted from the mass spectrometer is further increased.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS. 1 and 2.

As shown in FIG. 2, the mass spectrometer of this embodiment is provided in an ion implanter. This ion implanter has an ion source 1 that ionizes an ion source material and extracts it as an ion beam.

A mass spectrometer 2 is arranged in the traveling direction of the ion beam extracted from the ion source 1. In this mass spectrometer 2, an analysis electromagnet 3 composed of a magnetic iron core around which a magnet coil is wound is provided above and below (in the figure, only the lower analysis electromagnet is shown), and a bent ion passage 4 is provided therebetween. The analysis tube 5 to be formed is sandwiched.

An analysis magnet power supply (not shown) is connected to the analysis electromagnet 3, and an analysis magnet current is supplied from the analysis magnet power supply to the magnet coil of the analysis electromagnet 3 so that the analysis magnet power is supplied to the inside of the ion passage 4. Such a magnetic field is formed.

The ion beam extracted from the ion source 1 is composed of a plurality of ion species, and when it passes through the ion passage 4 in which a uniform magnetic field is formed, it depends on the mass of each ion species. It is bent with a curvature (heavier ions have a smaller curvature), and the orbits are separated for each ion species.

As shown in FIG. 1, the analysis tube 5 is formed with an emission slit 5b for selectively passing only ions of a predetermined mass.

Then, the analyzing magnet current supplied to the analyzing electromagnet 3 is controlled by a controller (not shown) so that only desired ions pass through the exit slit 5b, and the magnetic flux density of the magnetic field formed in the ion passage 4 is controlled. Is adjusted.

As a result, the ions that are heavier and lighter than the desired ions passing through the exit slit 5b respectively pass outside and inside the orbits of the desired ion beam. A plurality of shield plates 6 for shielding ion beams of ions heavier or lighter than the desired ions deviated from the trajectory of the desired ion beam are erected on the inner wall of the analysis tube 5. There is. These shielding plates 6 ...
Are arranged so that the above-mentioned undesired ions collide with each other substantially vertically.

The material of the shielding plates 6 can be selected appropriately depending on the application. Specifically, aluminum, silicon, or the like is used, but, for example, carbon having a small sputtering rate or silicon carbide having excellent heat resistance can also be used. When silicon is used as the shielding plates 6, the silicon plate is sufficiently cooled by metalizing the silicon plate and brazing it to a metal plate such as aluminum having excellent thermal conductivity.

On the opposite side of the shield plates 6 from the beam irradiation surface, a positive electrode plate (positive electrode) is formed so as to face the shield plates 6.
7 ... are provided. The positive electrode plate 7 ...
Is supported by an insulating support member 8 provided on the inner wall of the same and is connected to the positive electrode terminal of the DC power supply 9.

The ion beam passing through the mass spectrometer 2 is focused by the magnetic focusing action. As shown in FIG. 2, an analysis slit 10 is provided near the convergence point of the ion beam, and the desired ion beam selected by the mass spectrometer 2 passes through the analysis slit 10. , Then, if necessary, acceleration, shaping, scanning,
It is deflected and irradiated on a target such as a wafer.

The operation of the mass spectrometer 2 having the above structure will be described below.

The ion beam extracted from the ion source 1 enters the ion passage 4 of the analysis tube 5. In this ion passage 4, a uniform magnetic field whose magnetic flux density is adjusted so that only desired ions pass through the exit slit 5b is formed. Due to the influence of this magnetic field, each ion species is bent with a curvature according to its mass, and the orbit is separated for each ion species. At this time, the ions that are heavier and lighter than the desired ions collide with the shield plates 6 ...

By the way, the sputtering of a substance by ion irradiation has an ion incident angle dependency, and the sputtering rate (the number of molecules or atoms sputtered per one ion) is the lowest at the time of vertical incidence, which is close to parallel incidence. The higher the sputtering rate is, as described in the conventional example.

Therefore, in the present embodiment, the sputtering on the shield plates 6 is greatly reduced as compared with the conventional one in which the ions are incident on the surface of the shield plate at an angle almost parallel to each other. As a result, the life of the shield plates 6 is extended, and the amount of the constituent components of the shield plates 6 mixed into a desired ion beam as contamination is reduced, so that wafer contamination is significantly reduced.

The generation of secondary electrons due to ion irradiation also depends on the angle of incidence of ions, and it is 2
As described in the conventional example, the generation rate of secondary electrons is relatively small at normal incidence and rapidly increases near parallel incidence. Therefore, the ions are shielded by the shield plate 6.
In the configuration of the present embodiment in which the light is incident on the ...
The number of secondary electrons jumping out from the beam irradiation surface of is reduced compared to the conventional case.

Further, in this embodiment, since the positive electrode plates 7 to which a positive voltage is applied from the DC power source 9 are arranged in the vicinity of the shield plates 6 ..., The beam irradiation surface of the shield plates 6 ... The secondary electrons jumping out from are absorbed by the positive electrode plates 7 ... Therefore, in the present embodiment, unlike the conventional case, the secondary electrons do not enter the trajectory of the desired ion beam and neutralize the ion beam that is a group of positive ions, and the beam at the target does not occur. The amount of current can be increased.

In this embodiment, the shield plates 6 and the positive electrode plates 7 are formed as separate members, but the present invention is not limited to this, and the positive electrodes and the shield plates are made of the same member. It may be configured to be shared.

Further, in the present embodiment, the mass spectrometer 2 is used as an ion implantation apparatus, but the mass spectrometer according to the present invention is not limited to this, and for example, a sputtering apparatus or the like may be used. It is also applied to devices in the field.

[0039]

As described above, the mass spectrometer according to the first aspect of the present invention has the analysis tube forming the ion passage, and the trajectory corresponding to the mass is obtained by bending the traveling direction of the ions passing through the analysis tube. A mass spectrometer for separating each ion into a desired ion and selecting a desired ion, wherein a plurality of shield plates arranged so that undesired ions collide substantially vertically are provided in the analysis tube. Is.

As a result, as compared with the conventional one in which ions are incident on the surface of the shield plate at an angle substantially parallel to the surface of the shield plate, spatter on the shield plate is significantly reduced, so that the life of the shield plate is prolonged and the shield is shielded. The amount of components of the plate mixed into the desired ion beam as contamination is also reduced,
Contamination on the target is greatly reduced.

In addition, the amount of secondary electrons jumping out from the beam irradiation surface of the shield plate is smaller than in the conventional case, and the secondary electrons enter the desired ion beam orbit to neutralize the ion beam which is a group of positive ions. As a result, the beam current amount at the target is increased.

The mass spectrometer according to the second aspect of the invention is
As described above, a mass spectrometer that has an analysis tube that forms an ion passage, bends the traveling direction of ions passing through the analysis tube, separates each ion into an orbit corresponding to the mass, and selects a desired ion. In the analysis tube, a plurality of shield plates arranged so that undesired ions collide with each other substantially vertically and a positive electrode to which a positive voltage is applied are provided.

Therefore, similarly to the above, since the sputtering on the shield plate is greatly reduced as compared with the conventional case, the life of the shield plate is extended and the contamination on the target is significantly reduced. In addition, it is projected from the beam irradiation surface of the shield plate 2
Since the number of secondary electrons is smaller than in the conventional case, and the generated secondary electrons are absorbed by the positive electrode, the amount of the desired ion beam, which is a group of positive ions, is further neutralized by the secondary electrons. The effect of further increasing the beam current amount in the above is obtained.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention and is a transverse cross-sectional view showing a main part of a mass spectrometer.

FIG. 2 is a schematic diagram of a mass analysis portion of an ion implantation apparatus provided with the above mass analysis apparatus.

FIG. 3 shows a conventional example and is a schematic diagram of a mass analysis portion of an ion implantation apparatus provided with a mass analysis apparatus.

[Explanation of symbols]

 2 Mass Spectrometer 4 Ion Passage 5 Analysis Tube 6 Shielding Plate 7 Positive Electrode Plate (Positive Electrode) 8 Insulation Supporting Member 9 DC Power Supply

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiaki Ishida 47 Umezu Takaunecho, Ukyo-ku, Kyoto City, Kyoto Prefecture Nissin Electric Co., Ltd.

Claims (2)

[Claims] 1. A mass spectrometer which has an analysis tube forming an ion passage, bends the traveling direction of ions passing through the analysis tube to separate each ion into orbits corresponding to the mass, and selects a desired ion. 2. The mass spectrometer according to claim 1, wherein a plurality of shield plates are provided in the analysis tube so that undesired ions collide substantially vertically. 2. A mass spectrometer which has an analysis tube forming an ion passage, bends the traveling direction of the ion passing through the analysis tube to separate each ion into an orbit corresponding to the mass, and selects a desired ion. In the above-mentioned analysis tube, a plurality of shielding plates arranged so that undesired ions collide with each other substantially vertically and a positive electrode to which a positive voltage is applied are provided. ..