JPS6348930Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion source, and particularly to an ion source that can generate a stable ion beam over a long period of time.

Surface analyzers such as Auger analyzers and photoelectron spectrometers perform etching by irradiating the surface of a sample with ions to analyze the depth of the sample.
At this time, if the current density of the ion beam irradiating the sample changes with time, the etching rate changes accordingly, making it difficult to accurately perform analysis at each desired depth.

This invention was made in view of the above points,
Since the etching rate is proportional to the current density of irradiated ions, it is an object of the present invention to provide an ion source that can keep the current density constant over a long period of time.

In the present invention, considering that the ion current density depends on the pressure of the ionized gas and the electron emission current for ionizing the gas,
Control is performed so that the product of the pressure and the emission current is constant.

The ion source based on the present invention includes an ionization chamber into which an ionized gas is supplied, a filament disposed within the ionization chamber that generates electrons for ionizing the gas, a heating power source for the filament, and a heating source within the ionization chamber. means for substantially detecting pressure; means for obtaining a product of a signal corresponding to the pressure and a signal corresponding to the amount of electrons generated from the filament; and means for controlling the heating power source.

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

In the figure, 1 is an ionization chamber, and argon gas is supplied from a gas reservoir 2 through a valve 3 to the ionization chamber 1. A filament 5 to which a heating current is supplied from a filament heating power source 4 and a coiled anode 6 are arranged in the ionization chamber 1.
The anode 6 is kept at a slightly higher potential than the filament 5 by a power source E. Therefore, the electrons generated by heating the filament 5 fly in the space surrounded by the coiled anode 6,
Eventually it flows towards the anode 6. The flying electrons collide with gas molecules in the chamber to ionize the gas molecules, and the ionized gas is taken out by the extraction electrode 7, which is kept at a low negative potential with respect to the anode or filament, and is drawn out from the sample (Fig. (not shown). 8 is an ionization vacuum gauge, 9 is a control circuit for the ionization vacuum gauge, and a signal corresponding to the pressure inside the ionization chamber 1 is obtained from the control circuit 9 of the ionization vacuum gauge. The pressure signal is supplied to an integrator 10 together with a voltage signal corresponding to the amount of electrons flowing into the anode 6 (emission current), and the integrator 10 calculates the product of the two types of signals. The output voltage of the integrator 10 is supplied via a feedback resistor R to an operational amplifier 12 together with a reference voltage from a reference voltage source 11. The output signal of the operational amplifier 12 is supplied to the filament heating power supply to control the filament heating current.

In the above-described configuration, argon gas is supplied into the ionization chamber 1 from the gas reservoir 2 via the valve 3, and the valve 3 is adjusted so that the inside of the ionization chamber has a desired pressure. Further, the reference voltage source 11 is set to a desired voltage, and this voltage is set to a voltage value such that when the output voltage of the integrator 10 is a predetermined voltage, the output of the differential amplifier 12 becomes zero. . When the gas pressure in the ionization chamber 1 decreases, the current density of the generated ion beam also decreases, but at this time, the pressure detection signal voltage from the ionization vacuum gauge control circuit 9 is low, and accordingly,
The output voltage of integrator 10 also becomes lower. Therefore, a differential voltage is generated from the operational amplifier 12, and the heating current applied to the filament 5 by the filament heating power source 4 is increased in accordance with this differential voltage. The heating current is increased as the emission current increases, the voltage at point A increases accordingly, and the output of the integrator 10 is increased to be equal to the predetermined voltage.As a result, the ions decreased due to the decrease in gas pressure. The amount of ion generated is increased by increasing the emission current, and therefore the current density of the ion beam extracted from the electrode 7 is maintained constant. Furthermore, when the gas pressure in the ionization chamber 1 increases, the filament heating power source 4 is controlled accordingly, the current flowing through the filament 5 is reduced, and as a result, the ion beam current density is maintained constant.

As detailed above, the present invention provides an ion source that can generate an ion beam with a constant current density over a long period of time with a simple configuration. If a sample is etched using a spectrometer or the like, the etching rate can be kept constant, making it possible to perform accurate sample analysis.
Note that the present invention is not limited to the embodiments described above, and can be modified in many ways. For example, the present invention can be used as an ion source for an ion microanalyzer or the like. Furthermore, in the above embodiment, the case where the gas pressure in the ionization chamber fluctuates was described in detail, but even if the emission current fluctuates for some reason, the present invention can be applied to maintain the current density of the ion beam constant. It is possible to do so. Furthermore, although the pressure inside the ionization chamber is directly detected, the pressure in another chamber (such as a sample chamber) communicating with the ionization chamber may also be detected.

[Brief explanation of the drawing]

The accompanying drawings illustrate an embodiment of the present invention. 1: Ionization chamber, 2: Gas reservoir, 3: Valve,
4: Filament heating power supply, 5: Filament,
6: anode, 7: extraction electrode, 8: ionization vacuum gauge,
9: Ionization vacuum gauge control circuit, 10: Integrator, 11:
Reference voltage source, 12: operational amplifier.

Claims (1)

[Scope of utility model registration request] an ionization chamber into which an ionized gas is supplied; a filament disposed within the ionization chamber that generates electrons for ionizing the gas; a power source for heating the filament; and substantially detecting the pressure within the ionization chamber. means for obtaining a product of a signal corresponding to the pressure and a signal corresponding to the amount of electrons generated from the filament; and means for controlling the filament heating power source so that the signal value of the product is constant. Ion source with.