JPH0548359Y2 - - Google Patents

Description

[Detailed explanation of the idea] B Industrial application field The present invention relates to an EPMA signal selection device.

B. Prior art In devices such as scanning electron microscopes and electron beam microanalyzers that irradiate a sample with a particle beam and detect secondary radiation emitted from the sample, electrons emitted from the sample are detected. Generally, a combination of a scintillator and a photomultiplier tube is used, and the scintillator converts electrons into light, which is then detected by the photomultiplier tube. In order to make a scintillator glow with electrons, it is necessary to accelerate the electrons incident on the scintillator with a high voltage of about 10 KV. A voltage is applied to attract and accelerate secondary electrons. On the other hand, when the sample is irradiated with an accelerated beam,
Reflected electrons of the irradiated electron beam are emitted from the sample, and by detecting them, information different from the detection of secondary electrons can be obtained about the sample.
In this case, the reflected electrons have large energy, and even without applying an accelerating voltage to the scintillator, the reflected electrons travel straight from the sample to the scintillator, enter the scintillator, and cause it to emit light. Therefore, when detecting electrons using a scintillator and a photomultiplier tube, it is possible to switch between detecting secondary electrons and backscattered electrons by applying or not applying a high voltage to the scintillator. The conventional configuration for this purpose is
As shown in the figure. In this figure, Sn is a scintillator, PM is a photomultiplier tube, D1 to D4 are the X-ray detectors of the four X-ray spectrometers placed around the sample, Ap is an amplifier that amplifies the signal, and H is the This is a high voltage generator that is applied to the scintillator. The output of the amplifier Ap is taken into the CPU which performs signal processing. S1 is a changeover switch that connects either the photomultiplier tube PM or the four X-ray detectors D1 to D4 to the amplifier Ap. S2 is a switch for switching between secondary electron detection and backscattered electron detection; switch S2 is turned on when secondary electrons are detected, and turned off when backscattered electrons are detected.

C. Problems to be solved by the invention As mentioned above, in the conventional device, the detector selection switch S1 for electrons, X-rays, etc. and the switch S2 for switching between secondary electrons and backscattered electrons are independent of each other. Switch S1 is activated when the backscattered electrons are detected.
It is common to make mistakes such as forgetting to turn off S2 after connecting to PM, or conversely, leaving S2 off and connecting S1 to PM to detect secondary electrons.

The present invention aims to prevent the above-mentioned erroneous operation and to avoid the risk of deterioration of the photomultiplier tube when the sample-irradiating electron beam current is large in the secondary electron detection mode.

D. Means for solving the problem As shown in Figure 1, a detector selection switch S1 and a switch S for connecting and disconnecting the scintillator from the high voltage power supply H
2, connect the signal output terminal of the photomultiplier tube for electron detection to the two fixed contacts of the detector selection switch, and connect the switching piece of the selection switch S1 to one of these two fixed contacts C1. When it comes into contact with
Switch S2 is turned on, and when it contacts C2, it is turned off, and the sample current detector I,
A locking means L is provided to prevent the switching piece of the selection switch S1 from coming into contact with one of the two fixed contacts C1 when the detector output exceeds a certain level.

E. Effect When the switching piece of switch S1 is brought into contact with contact C1 in Fig. 1, photomultiplier tube PM is connected to amplifier Ap, switch S2 is turned on, and a high voltage is applied to scintillator Sn. The mode becomes the next electron detection mode. When switch S1 is brought into contact with contact C2, electrons are detected because C2 is also connected to the photomultiplier tube PM. However, in this case, switch S2 is OFF, so secondary electrons cannot be detected and secondary electrons cannot be detected. Only reflected electrons are detected.

In the case of secondary electron detection, a high voltage is applied to the scintillator to attract secondary electrons, so secondary electrons are captured more efficiently than reflected electrons, but for this reason, when the sample irradiation electron beam is strong, an excessive amount of Secondary electrons will be detected and there is a risk of deteriorating the photomultiplier tube, but since the sample electrons are approximately proportional to the dose of the irradiated electron beam, this will be detected and the selection switch S1 will be contacted. By locking C1 so that it cannot be touched, it is possible to avoid deterioration of the photomultiplier tube etc. due to the incidence of an excessive amount of secondary current.

F. Embodiment FIG. 1 shows an embodiment of the present invention. In Figure 1, Sn is a scintillator that converts electron beams into photons, PM is a photomultiplier that detects photons, and D1~
D4 is an X-ray detector that detects X-rays, Ap is an amplifier that amplifies the detection signal, H is a high voltage power supply that is applied to the scintillator when detecting secondary electrons, and I is a sample current detector that detects the sample current. . Locking means L
When the sample current detected by the sample current detector exceeds a certain level, the movable contact S of the rotary switch R
Terminal C1 and movable contact piece S2 of No. 1 are locked so that they are not connected to terminal B1. S1 is a movable switch contact that connects the photomultiplier tube PM, one of the X-ray detectors D1 to D4, and the amplifier Ap, S2 is the scintillator Sn, and the high voltage power source H is the dummy contact B2.
A movable contact piece that selectively connects S1 to B6.
and S2 constitute an interlocking means for interlocking the detector selection switch and the switch for connecting and disconnecting the scintillator to the high-voltage power supply, by forming a single-axis double rotary switch R. The connection operation is performed in conjunction with the terminals B1 to B6.

In the apparatus with the above configuration, the photomultiplier tube
When detecting secondary electrons using PM, by connecting the movable contact piece S1 to the terminal C1, the movable contact piece S2 is connected to the terminal B1 in conjunction with the high-voltage power source H and the scintillator Sn. connected, 2
The system is now ready to detect the next electron. However, if the sample current detected by the sample current detector I exceeds a certain level, the locking means L is applied to the movable contacts S1 and S2.
is locked and is not connected to terminals C1 and B1. On the other hand, when detecting reflected electrons using a photomultiplier tube PM, by connecting the movable contact piece S1 to the terminal C2, the movable contact piece S2 is connected to the dummy terminal B2 in conjunction with the high voltage power supply. H and the scintillator Sn are cut off, and the system is ready to detect reflected electrons. Other X-ray detectors D1~
When detecting by D4, the movable contact piece S1 is connected to the terminals C3 to C6 corresponding to the detectors D1 to D4, and the movable contact piece S2 is connected to the dummy terminals B3 to B6 in conjunction. , high voltage power supply H and scintillator Sn are not connected.

In the above embodiment, the sample current is used as the lock signal, but the same effect can be expected even if a detection signal from a photomultiplier tube is used.

G. Effects According to the present invention, by selecting the detection signal to be measured using a single dual rotary switch, the detector is ready for detection, eliminating erroneous operations and detecting sample current or photomultiplier tube overcurrent. By preventing high voltage from being applied to the scintillator during overcurrent, it has become possible to prevent overcurrent from flowing through the photomultiplier tube, increasing the durability of the photomultiplier tube.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention;
The figure is a block diagram of a conventional example. 1...Sample current detector, L...Lock means,
PM...Photomultiplier tube, D1-D4...X-ray detector, S1...Movable contact piece, S2...Movable contact piece, R...
...double rotary switch, Sn...scintillator,
H...High voltage power supply, Ap...Amplifier.

Claims (1)

[Scope of utility model registration request] An interlocking means is provided for interlocking a detector selection switch and a switch for connecting and disconnecting the scintillator from a high-voltage power supply, and the interlocking means connects the signal output terminal of the photomultiplier tube for electron detection to the two fixed contacts of the detector selection switch. When the switching piece of the selection switch is connected to one of these two fixed contacts, the above-mentioned contact/disconnection switch is turned ON, and when the switching piece of the selection switch is brought into contact with the other fixed contact, the above A sample current detector I is provided, and when the output of the detector is above a certain level, the switching piece of the selection switch can be brought into contact with one of the two fixed contacts. 1. A signal selection device characterized in that a locking means L is provided to prevent the signal from being detected.