JPH04229541A - Charging-up prevention device in charged particle beam equipment - Google Patents

Abstract

PURPOSE:To prevent target charging-up by applying voltage to a insulating target, differentiating a signal scanned and detected with a charged particle beam, and applying voltage at the time of the largest signal to the target. CONSTITUTION:An insulating target 5 is made a charging-up condition, and voltage varied with a voltage generator 15 is applied to the target 5. Line scanning is made so as to vertically crossing a straight line part of a mark by an electron beam every time the voltage changes, and a generated secondary electron signal is differentiated with a differentiation circuit 12. The peak value of a differentiation signal is memorized and concurrently a voltage value too is memorized in a memory in a maximum value detecting circuit 13. A voltage value, by which the maximum peak can be obtained, is adjusted so as to be applied to the target 5 with a voltage control circuit 14 when the voltage variation in the generator 15 is finished. This can obtain a scanning image having no charging-up.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a charge-up prevention device in a charged particle beam device that can automatically and effectively prevent charge-up of an insulating target.

0
002

[Prior Art] For example, when observing a semiconductor device using a scanning electron microscope, the resist found in the semiconductor device is directly observed without depositing a conductive substance such as gold, platinum-palladium, carbon, etc. Recently, there has been an increasing demand to faithfully reproduce the outermost surface of a sample. However, when an electron beam is irradiated onto an insulating target such as the above-mentioned resist, negative charges are accumulated on the surface of the insulating target and the surface potential changes, which has a large effect on the generation of secondary electrons and the penetration of incident electrons. give. When such a charge-up occurs, not only does it greatly damage information, but it also impedes observation of images of secondary electrons and backscattered electrons. Therefore, the following measures have been proposed.

[0003] When an insulating target is irradiated with an electron beam,
The charge-up potential V of the target surface potential is determined by where Z is the equivalent impedance of the target, Ip is the irradiation current, and I
ab is the target absorption current, Ibse is the current due to target reflected electrons, Ise is the current due to secondary electrons, Ib
If se ' is reflected by the objective lens and the current due to the backscattered electrons enters the target, and C is a proportionality constant, then V=C・Z・{Ip +Ibse '−(Iab+Ib
se + Ise)} (1) holds true. At this time, Ip +Ibse ′=I
When ab+Ibse +Ise, the charge-up potential V becomes 0 and becomes a ground potential. When the charge-up potential becomes 0 in this way, an image that faithfully reproduces the outermost surface of the target can be obtained. However, Ip + Ibs
When e ′<Iab+Ibse +Ise, the charge-up potential V becomes a positive potential, and Ip +Ibse ′>
Iab+Ibse When +Ise, charge up potential V
becomes a negative potential, and in either case, an image that differs considerably from the outermost surface of the target will be obtained. Therefore, a voltage is applied to the target, and the operator adjusts the voltage applied to the target while observing the condition of the target surface image (contrast, etc.) to obtain the image state seen when the charge-up potential is 0. , prevents charge-up.

0004

[Problem to be Solved by the Invention] However, the above operation is extremely troublesome for the operator;
It is extremely difficult to accurately adjust the image state to have a charge-up potential of 0.

[0005] The present invention aims to solve such problems.

[0006]

[Means for Solving the Problems] A charge-up prevention device in a charged particle beam device of the present invention includes a means for applying a voltage to an insulating target, a means for scanning the insulating target with a charged particle beam, and a means for scanning the insulating target with a charged particle beam. The device includes means for detecting generated charged particles, means for differentiating a signal based on the detected charged particles, and means for adjusting the voltage applied by the voltage application means so that the intensity of the differentiated signal is maximized. .

[0007]

[Operation] Temporarily puts the insulating target in a charged up state. Then, while changing the voltage applied to the target, each time the electron beam is used to scan a location on the insulating target that has a straight line, and the peak of the signal obtained by differentiating the secondary electron signal generated by the scanning is are detected sequentially. In this case, when a point with a straight line is scanned when the charge-up is removed, the edge of the secondary electron signal obtained by this scanning becomes the sharpest, so the peak value of the obtained differential signal is the largest. If the applied voltage value at which the peak value occurs is applied to the insulating target, charge-up of the insulating target can be eliminated.

[0008]

Embodiment FIG. 1 shows an embodiment in which the present invention is applied to, for example, a scanning electron microscope.

In the figure, 1 is an electron gun, 2 is a focusing lens, 3X,
3Y is a deflection lens, 4 is an objective lens, 5 is an insulating target, 6 is a secondary electron detector, 7 is a scanning signal generator, 8,
9 and 10 are amplifiers, 11 is a display device such as a cathode ray tube, 1
2 is a differentiation circuit, 13 is a maximum value detection circuit, 14 is a voltage control circuit, and 15 is a voltage generator.

[0010] In such a device, usually an electron gun 1
The electrons are focused onto the target 5 by the focusing lens 2 and the objective lens 4, and at the same time, an appropriate range on the target is scanned by the deflection lenses 3X and 3Y which receive the scanning signal from the scanning signal generator 7. Secondary electrons generated from the target by the scanning are detected by a secondary electron detector 6 and sent to a display device 11 via an amplifier 10. Since scanning signals are synchronously sent to the display device from the scanning signal generator 7, an image representing the target surface condition is displayed on the display screen of the display device.

Now, when observing an object having an insulating material on its surface, such as a semiconductor device, electrons from the electron gun 1 are focused onto an insulating target 5 by a focusing lens 2 and an objective lens 4, and at the same time a scanning signal is The deflection lenses 3X and 3Y that receive the scanning signal from the generator 7 scan a portion of the target having a straight line, for example, a range where a mark is formed, once, for example, to charge up the target. That is, the state is the same as when observing a portion of the insulating target. Next, the voltage generator 15 is activated to apply a voltage that gradually changes within a predetermined range to the insulating target 5. At this time, each time the applied voltage changes, the deflection lenses 3X and 3Y that receive the scanning signal from the scanning signal generator 7 cause the electron beam to cross the mark perpendicularly to the straight line of the mark. in the X direction or Y direction
Scan the line in the direction. At this time, secondary electrons generated from the target 5 are detected by a secondary electron detector 6. now,
If a mark M as shown in FIG. 2 is scanned, the output signal waveform of the secondary electron detector at this time will be a waveform as shown in FIG. 3. The output signal of the secondary electron detector is sent to the amplifier 10.
The signal is sent to the differentiating circuit 12 via the differential circuit 12, where it is differentiated. FIG. 4 shows the differentiated signal waveform. The maximum value detection circuit 13 sequentially detects the peak values of the output signals of the differential circuit that are sequentially sent and stores them in a built-in memory, and also stores the voltage values when each peak value is obtained. When the change in voltage from the voltage generator 15 is completed, the maximum value detection circuit 13 picks up the voltage value at which the largest peak is obtained from among the peak values stored in the memory up to that point. The voltage control circuit 14 controls the voltage generator 15 so that the voltage value at which the maximum peak is obtained is applied to the insulating target 5. In this state, if the operation is performed to obtain a normal scanned image as described above, a scanned image without charge-up will be produced on the display device 1.
1 on the screen.

In the above embodiment, the applied voltage is gradually changed within a predetermined range, and the peak value of the differential signal is memorized for each change, and after the change, the maximum peak value from among the stored peak values is I picked up the value, but without doing so,
The peak values of the differential signals detected each time the applied voltage is changed are compared, and when the maximum value is obtained, the applied voltage is stopped and the voltage applied to the target is adjusted until the maximum value is obtained. Alternatively, the voltage may be controlled to a certain voltage value.

Furthermore, as described above, when observing an insulating target with a scanning electron microscope, the present invention does not depend on the height but on the EPM.
It can also be applied to the case where an insulating target is analyzed using an A or Auger analyzer, the pattern is drawn on a resist using a charged particle beam drawing device, and the length of a pattern is measured using a charged particle beam length measuring device.

[0014]

Effects of the Invention The charge-up prevention device in the charged particle beam device of the present invention includes means for applying a voltage to an insulating target, means for scanning the insulating target with a charged particle beam, and charged particles generated from the target. The present invention includes a means for detecting a charged particle, a means for differentiating a signal based on the detected charged particle, and a means for adjusting the applied voltage of the voltage applying means so that the intensity of the differentiated signal is maximized, making the operation extremely easy. It becomes possible to easily and accurately adjust the image state in which the charge-up potential is 0.

[Brief explanation of the drawing]

FIG. 1 shows an example in which the present invention is applied to, for example, a scanning electron microscope.

FIG. 2 is for supplementing the explanation of the operation of the present invention.

FIG. 3 is for supplementing the explanation of the operation of the present invention.

FIG. 4 is for supplementing the explanation of the operation of the present invention.

[Explanation of symbols]

1: Electron gun 2: Focusing lens 3X, 3Y
: Deflection lens 4: Objective lens 5: Insulating target 6: Secondary electron detector 7: Scanning signal generator 8, 9, 10: Amplifier 11: Display device 12: Differentiator circuit 13: Maximum value detection circuit
14: Voltage control circuit 15: Voltage generator

Claims (1)

[Claims] 1. Means for applying a voltage to an insulating target, means for scanning the insulating target with a charged particle beam, means for detecting charged particles generated from the target,
A charge-up prevention device for a charged particle beam device, comprising means for differentiating a signal based on the detected charged particles, and means for adjusting an applied voltage of the voltage application means so that the intensity of the differentiated signal is maximized.