JP2505060Y2 - Ion source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an ion source, and more specifically to a means for stably operating the ion source.

[Conventional technology]

FIG. 2 is a sectional view showing a conventional ion source. This ion source is an example of a so-called Freeman type ion source, and a plasma generation container (also called an arc chamber) 2 having a slit 2a for extracting an ion beam 2
A rod-shaped filament 4 is housed inside the slit 2a in the longitudinal direction (front-back direction of paper). Although some extraction electrodes are normally provided in front of the slit 2a, the illustration thereof is omitted here (the same applies to other drawings).

The plasma generation container 2 is provided with a gas introduction port 2b for introducing the ion species gas 8 therein, and a gas introduction pipe 6 is connected thereto.

Explaining the operation example, in a predetermined vacuum atmosphere,
When the filament 4 is energized to emit thermoelectrons from the filament 4, an arc voltage is applied between the filament 4 and the plasma generation container 2, and the required gas 8 is introduced into the plasma generation container 2 from the gas inlet 2b, the filament Arc discharge is generated between the plasma generation container 4 and the plasma generation container 2, the gas 8 is ionized to generate plasma, and then the ion beam 10 is electrostatically extracted via the slit 2a.

[Problems to be solved by the device]

However, in the ion source as described above, there is a problem that the temperature of the filament 4 is lowered by the gas 8 introduced into the plasma generation container 2, and thereby the operation of the ion source is likely to be unstable.

Explaining this in detail, the stability of the extraction of the ion beam depends on the stability of the plasma in the plasma generation container 2, which is mainly due to the stability of the arc current of the arc discharge between the plasma generation container 2 and the filament 4. Depends on.

Since the arc current cannot be controlled directly, a method of controlling the filament current flowing through the filament 4 is generally adopted. That is, when the filament current is increased, the temperature of the filament 4 is increased, so that thermions are emitted more and the arc current is increased. An example of such characteristics is shown in FIG.

The filament 4 becomes thin with time, and while the filament 4 is thick, it is necessary to increase the filament current in order to keep the surface temperature at a predetermined temperature. The strength of the magnetic field increases, which makes it easier for thermoelectrons to return to the filament, and reduces the probability of collision between thermoelectrons and gas molecules, which in turn makes the arc current unstable.

Under such circumstances, the gas 4 causes the filament 4 to
When the temperature of is decreased, it becomes difficult for thermoelectrons to come out from it, and when the filament current is increased to compensate for it, the arc current approaches the unstable region as shown by the curve shown by the broken line in FIG. This makes the operation of the ion source unstable.

Therefore, the main object of the present invention is to provide an ion source capable of preventing the stable operation from being hindered by the gas introduced into the plasma generation container.

[Means for solving the problem]

In order to achieve the above object, the ion source of the present invention is such that a part of a gas introduction pipe for introducing the gas into the plasma generation container is made to meander along the wall surface near the wall surface of the plasma generation container, and A preheating means for preheating the gas is provided in the middle of the introduction pipe.

[Action]

The gas introduced into the plasma generation container can be preheated by the preheating means. As a result, it is possible to prevent the temperature of the filament from being lowered by the gas.

As a result, the filament can be kept at a high temperature without increasing the current applied to the filament, and thermoelectrons are easily generated from the filament, so that stable operation of the ion source can be ensured.

〔Example〕

FIG. 1 is a sectional view showing an ion source according to an embodiment of the present invention. The same parts as those of the conventional example shown in FIG. 2 are denoted by the same reference numerals, and the difference from the conventional example will be mainly described below.

In this embodiment, as a preheating means for preheating the gas 8 in the course of introducing the gas 8 into the plasma generation container 2 as described above, that is, in the middle of the gas introducing pipe 6,
The preheater heater 12 is wound.

In this way, the gas 8 introduced into the plasma generation container 2 can be preheated by the preheater 12. As a result, it is possible to prevent the temperature of the filament 4 from being lowered by the gas 8.

As a result, the filament 4 can be kept at a high temperature without increasing the current supplied to the filament 4, and thermoelectrons are easily generated from the filament 4, so that stable operation of the ion source can be ensured. .

It should be noted that the position of the preheater heater 12 in the illustrated example is merely an example, and it may be provided at a position other than that, for example, at a position closer to the gas inlet 2b.

Further, as the preheating means, a means other than the preheating heater 12 may be used. For example, a part of the gas introduction pipe 6 may be used as a heating element.

Further, in this ion source, a part of the gas introduction pipe 6 is made to meander near the wall surface of the plasma generation container 2 along the wall surface. By doing so, the gas 8 is preheated by using the preheater 12 when the ion source starts up, and thereafter the plasma generation container 2 is heated to a high temperature by the heat of the filament 4 and the heat of the arc discharge. Since the gas 8 can be preheated, preheating by the preheater 12 is not necessary.

Also, the type of ion source is not limited to the Freeman type as in the above example, but has a filament in the plasma generation container, and ionizes the gas of the ion species by discharging between them to extract ions from it. Other types can be used as long as they are

[Effect of device]

As described above, according to the present invention, by the preheating means,
The gas introduced into the plasma generation container can be preheated, and as a result, the temperature of the filament can be prevented from being lowered by the gas. As a result, the filament can be kept at a high temperature without increasing the current applied to the filament, and thermoelectrons are easily generated from the filament, so that stable operation of the ion source can be ensured. Moreover, in the ion source of this invention, a part of the gas introduction pipe is meandering near the wall surface of the plasma generation container, so that after the ion source is started, the gas passing through the gas introduction pipe is heated by the heat from the plasma generation container. Can be preheated. As a result, after the ion source is started up, it is possible to reduce or stop the preheating by the preheating means, which leads to energy saving (power saving).

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing an ion source according to an embodiment of the present invention. FIG. 2 is a sectional view showing a conventional ion source. FIG. 3 is a graph showing an example of the relationship between filament current and arc current. 2 ... Plasma generation container, 4 ... Filament, 6 ...
Gas introduction pipe, 8 ... Gas, 10 ... Ion beam, 12
…… Preheater.

Claims (1)

(57) [Scope of utility model registration request] 1. An ion source having a filament inside a plasma generation vessel, wherein a gas of an ion species introduced into the plasma generation vessel is ionized by a discharge between the filaments and ion is extracted from the ion source. A part of the gas introduction pipe for introducing into the plasma generation vessel meanders along the wall surface near the wall surface of the plasma generation vessel, and preheating means for preheating the gas is provided in the middle of the gas introduction pipe. An ion source characterized by that.