JPS6386233A - Electron beam irradiator - Google Patents

Abstract

PURPOSE:To keep the extent of beam intensity irradiating a sample constant as well as to aim at improvements in measuring accuracy and efficiency, by controlling the electron beam intensity with a current obtained by a weighted sum of the detected current of emitted electrons and an absorption current on a sample. CONSTITUTION:An electron beam B to be emitted out of an electron gun 1 as an irradiation beam is converged by a convergent lens 2 after the beam diameter is throttle by a convergent diaphragm 4. This beam B is converged by an objective lens 5 after the beam diameter is throttle by an objective dia phragm 3, connecting a focal point on a sample S. Since an absorption current to be produced in the sample S and an electron to be emitted out of the sample S both are varied by irradiation beam intensity, they are used for a function of the electron beam intensity. An irradiation beam current IT calculating an absorption current IA and a detection current IB of the emitted electron as in an equation is proportioned to the irradiation beam intensity. alpha in this equation is a constant depending on capacity, form and configuration of a detector. Therefore, these currents IA and IB aforesaid are detected, and the electron beam intensity is controlled by the current IT.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention is directed to an electron beam microanalyzer (EPMA).
Regarding equipment that excites the sample surface with a charged particle beam and analyzes the sample using radiation emitted from the excited sample, or equipment that exposes or otherwise processes the sample surface with an electron beam, the intensity of the irradiated beam on the sample surface is particularly important. This type of device is equipped with control means.

In conventional analysis such as EPMA, there is a proportional relationship between the intensity signal of radiation used for analysis, such as X-rays emitted from a sample excited by an irradiation beam, and the intensity of the irradiation beam on the sample surface. Therefore, in order to improve analysis accuracy, it is necessary to maintain the intensity of the beam irradiated onto the sample surface at a constant value, or to correct the measured data by knowing the amount of variation. When the composition of a sample surface is to be displayed by color, measurement requires a very long time, and the electron beam intensity fluctuates due to various factors during that time, so this correction is highly necessary. Conventionally, this irradiation beam intensity has been measured using the following two methods. One method is to measure the absorbed current of a sample irradiated with the beam, and the other is to directly measure the primary beam using a Faraday cup or the like. The former allows continuous measurement, but has the disadvantage that the measured value changes depending on the composition of the sample, and the latter makes it impossible to irradiate the sample, perform optical observation, and detect the optical signal when measuring beam intensity, and can only be measured intermittently. There is a drawback that it cannot be done. In addition, in addition to the time required for the original analysis, time is required to measure the beam intensity, resulting in a decrease in analysis efficiency.

C1 Problems to be Solved by the Invention The present invention solves the problems shown above, makes it possible to measure the beam intensity of the irradiation beam without interrupting the measurement, and makes it possible to measure the beam intensity of the irradiation beam without interrupting the measurement. The purpose is to improve measurement accuracy and efficiency by controlling the intensity of the irradiated electron beam to be constant.

21 Means for Solving Problems In an apparatus that excites a sample with a charged particle beam such as an electron beam and analyzes the sample using radiation emitted from the excited sample, the current absorbed by the sample is detected. means and
means for detecting electrons emitted from the sample; means for calculating detection signals obtained by both the detection means using a predetermined linear equation;
Means was provided for controlling the intensity of the irradiation beam onto the sample surface based on the signal obtained by this calculation means.

E9 Effect The intensity of the electron beam irradiating a sample is expressed by the electron beam current incident on the sample, but after entering the sample, this electron beam current is divided by the sample current absorbed by the sample and the electron beam emitted from the sample. It is divided into two streams. Therefore, if a device that measures the absorbed current generated in the sample and a device that detects the electrons emitted from the sample are installed, and the detection signals obtained by these two methods are appropriately weighted and summed, the combined signal can be used to detect the sample. It can be made approximately proportional to the intensity of the beam irradiated onto the surface.

The gist of the present invention is to use this summed signal to control the intensity of the beam irradiated onto the sample surface.

Specifically, we installed a device that measures the absorbed current of the sample and a detector that detects the electrons emitted from the sample, and made the signals sent from both devices into a signal that is proportional to the irradiation beam intensity. A device for appropriately weighted summation is provided, and the coil current of the converging lens is controlled so that if the summed signal decreases, the converging force of the converging lens is decreased, and if the summed signal increases, the converging force of the converging lens increases. A control device is provided to control the irradiation beam intensity to the sample surface to be constant. Also, if the focusing power of the converging lens is changed at this time, the focus of the irradiation beam will shift, so in order to correct this shift, the coil current of the objective lens is adjusted so that the beam is focused on the sample surface. A control device is provided to control the coil current of the objective lens. By controlling the electron beam as described above, the irradiation beam intensity can be kept constant without stopping the measurement. The reason why the absorbed current detection signal of the sample and the emitted electron detection signal are weighted together instead of being simply added is that the emitted electrons are emitted within a wide solid angle, and only a part of them is detected. .

An embodiment of the present invention is shown in FIG. In the figure, S is the sample,
B is an electron beam and is emitted by the electron gun 1. electron gun 1
The electron beam B emitted from the converging lens 2. The sample S is irradiated under the control of the objective lens 3. The irradiation beam diameter of the electron beam B is limited by a converging aperture 4 and an objective aperture 5, which are provided for the purpose of preventing scattering of the electron beam and reducing spherical aberration while being irradiated onto the sample S. 6
7 is a scanning coil, 7 is an electron detector for detecting electrons emitted from the excited sample S, 8 is a sample holder, and 9 is a sample stage that moves the sample S in the x-y-z directions. 10
11 is a slit that limits the field of view of the separated X-rays; 12 is an X-ray detector that detects the X-rays that have passed through the slit 11; 13 is an electron detector 7; The lens controller 14 is a total beam converter that adds together the signal obtained by amplifying the detection signal detected by the AMP and the absorbed current signal detected from the sample S and outputs it to the lens controller 14 as an irradiation beam intensity signal.The lens controller 14 is a total beam converter. The coil currents of the converging lens and objective lens are controlled by the irradiation beam intensity signal input from 13.

In the above configuration, the adjustment operation of the irradiation beam will be explained. An electron beam B is emitted from the electron gun 1 as an irradiation beam. After the beam diameter of this electron beam B is narrowed down by a converging aperture 1, it is converged by a converging lens 2. The beam converged by the converging lens 2 is narrowed down to a beam diameter by the objective diaphragm 3, and then converged by the objective lens 5 to be focused on the sample S.

By being irradiated by the electron beam B, the sample S
The absorbed current generated in the sample S and the electrons emitted from the sample f'IS vary depending on the irradiation beam intensity, so they can be used as a function of the electron beam intensity. Since the emitted electrons vary depending on the sample, the accuracy is low when used alone as a detection signal of the irradiation beam, but the absorption current is IA, the emitted electron (e.g. reflected electron) detection current is IB, IT = IA + α・IB・・・・・・・・・・・・・・・
・・・・・・Irradiation beam current calculated as in (1)■
1 is proportional to the irradiation beam intensity.

However, α is a constant determined by the performance, shape, and arrangement of the detector and can be determined experimentally.

Therefore, if the absorption current ■^ and the emitted electron detection electron a I a are detected, and the electron beam intensity is controlled by the signal (irradiation beam current IT) calculated from these two currents as in equation (1), the electron beam The intensity can be controlled to be constant. That is, when the intensity of the electron beam B emitted from the electron gun 1 becomes weaker, the absorption current generated in the sample S and the emitted electrons emitted from the sample S decrease. The absorbed current is measured from the sample S by the total beam converter 13, and the emitted electrons are detected by the electron detector 7 and amplified by the AMP, and then both are calculated by the gold beam converter 13 as shown in equation (1). The irradiation beam current IT is determined. In accordance with this decrease in the irradiation beam current air, the coil current of the converging lens 2 is decreased to reduce the converging force of the converging lens 2. If the focusing power of the focusing lens 2 is reduced, the amount of beam passing through the objective aperture 5 will increase, the amount of beam irradiated onto the sample S will increase, and the absorbed current detected by the sample S and the amount detected by the electron detector 7 will increase. The emitted electron detection current increases. When the irradiation beam current IT reaches a predetermined value, the decrease in the coil current of the converging lens 2 is stopped,
The coil current of the objective lens °5 is controlled so that the beam is focused on the sample surface. By controlling the electron beam in this way, the irradiation beam intensity can be kept constant without stopping the measurement.

In the above embodiment, the converging force of the converging lens is used as a means for controlling the electron beam intensity, but the electron gun 1
It goes without saying that a similar effect can be obtained by controlling the intensity of the electron beam current itself emitted from the electron beam.

Effects As described above, the present invention controls the beam 11 irradiating the sample by controlling the coil currents of the converging lens and the objective lens based on a signal obtained by weighting the absorption current of the sample and the detection current of emitted electrons. The intensity remained constant, improving measurement accuracy.

[Brief explanation of the drawing]

The figure is a configuration diagram of an embodiment of the present invention. B...electron beam, S...sample, 1...electron gun,
2... Converging lens, 3... Objective lens, 4... Converging aperture, 5... Objective aperture, 6... Scanning coil, 7...
・Electronic detector, 8... Sample holder, 9... Sample stage, 10... Spectroscopic crystal, 11... Slit, 1
2... X-ray detector, 13... Total beam converter, 14
...Lens controller.

Claims (1)

[Claims] In an apparatus that excites a sample with a charged particle beam such as an electron beam and analyzes the sample using radiation emitted from the excited sample, there is a means for detecting the current generated in the sample and a means for detecting the electrons emitted from the sample. It is characterized by having a means for detecting, a means for calculating the detection signals obtained by both the detecting means in a predetermined method, and a means for controlling the intensity of the beam irradiated onto the sample surface based on the signal obtained by the calculating means. Electron beam irradiation equipment.