JPH0224209Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image signal processing circuit for a scanning electron microscope or the like, and more particularly to an image signal processing circuit for a scanning electron microscope or the like which uses a divided signal of two types of signals as an image signal.

In a scanning electron microscope, various detection signals such as a secondary electron signal, a transmitted electron signal, and a reflected electron signal are obtained. Two of these signals are led to a division circuit, and a signal obtained by dividing the two signals is generated. is supplied to a cathode ray tube to display images. In this case, since the division circuit has a finite output voltage, it becomes saturated when this value is reached. That is, if the magnitudes of the signals input to the numerator and denominator of the division circuit are not appropriate, the circuit easily becomes saturated, making it impossible to observe an image using the division signal. Conventionally, whenever saturation occurred, the operator would adjust the magnitude of the signal input to the numerator or denominator while observing the image, but this work was extremely troublesome.

This invention was made in view of the above points,
It is an object of the present invention to provide an image signal processing circuit for a scanning electron microscope, etc., which does not require troublesome adjustment work, does not saturate a division circuit even when a detection signal fluctuates, and enables good image observation.

The image signal processing circuit of a scanning electron microscope or the like based on the present invention divides two different information signals obtained from the sample by a dividing circuit when the sample is irradiated with a charged particle beam, and the divided signal is An image signal processing circuit configured to supply an image signal to a display device as an image signal, wherein at least one of the two types of signals is supplied to the division circuit via a signal strength variable means, and the division circuit is provided with comparison means for comparing the output signal of the output signal with a reference signal, and controls the signal strength varying means in accordance with the signal from the comparison means to determine the intensity ratio of the two different information signals supplied to the division circuit. It is configured to change the

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

FIG. 1 shows a first embodiment of the present invention,
In the figure, 1 and 2 are input terminals of the image signal processing circuit, terminal 1 is supplied with, for example, a secondary electron detection signal, and terminal 2 is supplied with, for example, a reflected electron detection signal. The terminals 1 and 2 are connected to attenuators 3 and 4, respectively.
and set to an arbitrary amplitude. The outputs of the attenuators 3 and 4 are supplied to variable attenuators 5 and 6, respectively. The output signal of the variable attenuator 5 is sent to the divider circuit 7.
The output signal of the other variable attenuator 6 is supplied to the denominator terminal of the divider circuit 7 via the connection point of the diode D and the resistors R ₁ and R ₂ . The diode D and resistors R ₁ and R ₂ are connected to the variable attenuator 6.
When the output signal strength of becomes close to zero and the denominator becomes very small compared to the numerator, the output of the division circuit 7 easily becomes saturated, and the denominator input of the division circuit becomes zero. It is designed to prevent this from happening. The output signal strength of the variable attenuator 6 is
When the voltage falls below the voltage value determined by the division ratio of R ₁ and R ₂ , the diode D becomes non-conductive, and the voltage determined by the division ratio of the resistors is applied to the denominator input of the division circuit 7. The output signal of the division circuit 7 is sent to a terminal T connected to a cathode ray tube (not shown).
It is also supplied to the comparison circuit 8 and compared with the reference voltage from the reference power supply 9. The comparator circuit 8 generates a pulse when the output voltage of the divider circuit 7 exceeds the reference voltage. The pulse is counter 1
0, and the counter 10 controls the attenuation rates of the variable attenuators 5 and 6 based on the supplied pulses.

In the configuration as described above, first, the attenuators 3 and 4 are manually adjusted, and a signal of appropriate strength is supplied to the divider circuit 7. Further, the reference voltage value from the reference voltage source supplied to the comparator circuit 8 is set to be slightly lower than the saturation current value of the divider circuit 7. The image is observed in this state, but the secondary electron signal and reflected electron signal supplied to terminals 1 and 2 change depending on the sample state. For example, if the secondary electron signal becomes strong at a certain point, , the output voltage of the divider circuit 7 increases accordingly. When the voltage of the circuit 7 exceeds the voltage value from the reference voltage source 9, a pulse is generated from the comparator circuit 8 and is supplied to the counter 10. Based on the supplied pulse, the counter 10 converts the variable attenuator 5, Control 6. The variable attenuator 5 is controlled so that the attenuation rate is increased by a predetermined amount each time a pulse is supplied to the counter 10, and the variable attenuator 6 is controlled to increase the attenuation rate by a predetermined amount each time a pulse is supplied to the counter 10. Attenuation rate is reduced. As a result, the division circuit 7 is not saturated, and good image observation can always be performed.

FIG. 2 shows another embodiment of the present invention, in which the same parts as in the embodiment of FIG. 1 are given the same numbers, and detailed explanation thereof will be omitted. In this embodiment, the output signal of the division circuit 7 is supplied to a comparator circuit 8 and also to a second comparator circuit 11 . The comparison circuit 11 compares the reference voltage value from the reference voltage source 12 and the output voltage of the division circuit 7, and generates a pulse when the output voltage of the division circuit 7 becomes lower than the reference voltage. The comparison circuit 11 is connected to a flip-flop circuit 13, which receives pulses from the comparison circuit 11 and generates a low level signal, and also outputs a low level signal to a scanning signal generation circuit (not shown). It is reset by an erase signal supplied through the connected terminal 14 at the end of each frame of the scanning screen. The flip-flop circuit 13 is connected to a gate circuit 15 to which an erase signal from a terminal 14 is supplied, and the erase signal passes through the gate circuit 15 only when the output of the flip-flop circuit is maintained at a high level. and is supplied to the up terminal of the up-down counter 16. A pulse from the comparator circuit 8 is supplied to the down terminal of the counter 16.

The embodiment described above makes it possible to automatically increase the output when the output signal of the division circuit 7 becomes small, and the voltage value of the reference voltage source 12 is higher than the voltage value of the reference voltage source 9. It is set low. The terminal 14 is supplied with an erasing signal pulse _P1 from the scanning signal generating circuit shown in FIG. 3a,
When the output of the divider circuit 7 exceeds the voltage value of the reference voltage source 12, a pulse _P2 shown in FIG. 3b is generated from the comparator circuit 11. In response to the supply of the pulse _P2 , the flip-flop circuit 13 outputs a low level signal, and as a result, the erase signal pulse _P1 of FIG.
There is no change in the count value. Incidentally, FIG. 3c shows the output signal of the flip-flop circuit 13, and FIG. 3d shows the output signal of the gate circuit 15. Therefore, in this state, there is no change in the signal attenuation rate by the variable attenuators 5 and 6. After this state, the flip-flop circuit 13 is reset immediately after the scanning signal generating circuit finishes scanning one frame of the scanning screen and the erasing signal pulse is released, and its output becomes high level. On the other hand, within one frame scanning, the division circuit 7
If the output of continues to be lower than the reference voltage value,
No pulse is generated from comparator circuit 11, so the output of flip-flop circuit 13 is maintained at a high level. As a result, the erase signal pulse passes through the gate circuit 15 and is supplied to the down terminal of the counter 16, lowering its count value. As the count value of the counter 16 is lowered, the variable attenuators 5 and 6 are controlled, and the attenuator 5 has its attenuation rate lowered by a predetermined amount, and the attenuator 6 has its attenuation rate increased by a predetermined amount. Then, the numerator input signal strength of the division circuit is increased and the denominator input signal strength is decreased, resulting in the division circuit output having a signal level suitable for observation.

The present invention has been described in detail above, and the present invention can supply image signals suitable for observation to a display device such as a cathode ray tube with a simple configuration. Note that the present invention is not limited to the embodiments described above, and can be modified in many ways. For example, although the two types of signal intensities supplied to the division circuit have been configured to be controlled together, only one signal may be controlled. Further, although the present invention has been explained using a scanning electron microscope as an example, the present invention can be applied to other charged particle beam devices.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing one embodiment of the present invention, and FIG. 3 is a diagram showing signal waveforms for explaining the embodiment shown in FIG. 2. 3, 4: attenuator, 5, 6: variable attenuator, 7: division circuit, 8: comparison circuit, 9: reference voltage source, 10:
counter.

Claims (1)

[Scope of utility model registration request] Image signal processing in which two different information signals obtained from a sample are divided by a division circuit as the sample is irradiated with a charged particle beam, and the divided signal is supplied as an image signal to a display device. In the circuit,
Comparing means is provided for supplying at least one of the two types of signals to the dividing circuit via the signal strength varying means, and comparing the output signal of the dividing circuit with a reference signal, and An image signal processing circuit configured to control the signal intensity variable means in accordance with a signal to change the intensity ratio of the two different information signals supplied to the division circuit.