JPH04262353A - electron beam tester - Google Patents

Abstract

PURPOSE:To make alignment of an electron beam precisely by setting a frequency dividing ratio corresponding to the magnification of SEM (scanning electron microscope) in a magnification command circuit. CONSTITUTION:When a location command means 2 is operated, a pulse signal 4 is generated, and at this time, a frequency dividing ratio is set in a counter 1 to serve as the initial value for counting by the counter 1. With another operation on the location command means 2, the counter 1 begins counting with this set initial value and emits a carry signal when the counting maximizes. The logical product of this carry signal and the abovementioned pulse signal 4 constitutes a pulse motor controlling signal 5. Assume that the number of bits of the counter 1 is eight, then 0-2 can be set as frequency dividing ratio, and therefore the driving speed of a pulse motor 7 can be varied as any desired. Thus precise alignment of electron beam can be done quickly by setting the frequency dividing ratio corresponding to the magnification of the SEM in a magnification command circuit 3.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam device that uses an electron beam, and more particularly to an electron beam tester that requires highly accurate positioning of an electron beam with respect to a sample.

0002

2. Description of the Related Art Samples to be measured by an electron beam tester are completed large-scale integrated circuits, medium-scale integrated circuits, and the like. This electron beam tester is a device that actually operates these samples, irradiates the internal wiring of the sample with an electron beam, detects the secondary electrons emitted from it, and measures the operating status and characteristics. be. Conventionally, positioning of the electron beam has been performed using SEM (Scanning Electron Mi
The sample pattern is enlarged using a monitoring device such as a microscope, and the sample image on the CRT monitor is checked. In this case, the electron beam is used to monitor the sample image (SEM mode) and to analyze the behavior of the sample (measurement mode). The electron beam is deflected by moving a stage composed of an objective lens and a deflection coil using X-axis and Y-axis pulse motors, using data from a scaler as a parameter for the amount of deflection. At this time, in order to minimize aberrations caused by the lens, the electron beam always passes through the center of the objective lens and is irradiated perpendicularly to the sample. Note that the objective lens is used to focus the electron beam. This movement of the electron beam (SEM mode) causes the sample image on the CRT monitor to move relatively. The operation procedure for aligning the electron beam is as follows:
With the EM magnification low, the entire image of the sample is displayed on a CRT monitor, and the desired measurement point is searched for. Next, move the SEM so that the sample image near the desired measurement point is displayed on the entire CRT monitor.
Increase the magnification of However, a sample image near a desired measurement point is not necessarily displayed on the CRT monitor in one operation. In such a case, a measurement point is searched for by moving the sample image two-dimensionally using a position indicating means such as a trackball. The position indicating means is operated by the measuring person to drive a pulse motor using a trackball or a mouse that converts the manipulated variable into a pulse signal. Related alignment means of this type include JP-A-2-51834 and JP-A-63-20044.
Publication No. 8, etc. may be mentioned.

0003

[Problems to be Solved by the Invention] The prior art described above has the following problems.

In the conventional electron beam positioning apparatus, the output pulse signal of the position indicating means is directly used as the control signal of the pulse motor. Therefore, even if the amount of operation of the position indicating means is the same, the moving speed of the sample image changes depending on the magnification of the SEM. Therefore, if it is desired to move the sample image by a large amount when the SEM is at low magnification, the amount of movement of the position indicating means must be increased. On the other hand, if it is desired to move the sample image by a small amount during SEM high magnification, the amount of operation of the position indicating means must be reduced. In other words, SEM
The measurer had to intuitively change the amount of operation of the position indicating means depending on the magnification. Further, when performing final positioning of the electron beam, delicate positioning of the electron beam is essential, and this often occurs when the SEM is used at high magnification. The problem that occurs at this time will be explained using FIG. 4. Figure 4(a) shows the case at low SEM magnification, and Figure 4(b)
) indicates the time of high SEM magnification. Naturally, the size of the sample image is proportional to the magnification of the SEM. here,
Assume that the magnification of FIGS. 4(a) and 4(b) is 1:10. At this time, if a constant amount of operation is applied to the position indicating means without considering the magnification of the SEM, the following may occur. In FIG. 4(a), if an attempt is made to move the sample image in FIG. 4(b) with the amount of operation of the position indicating means that moves the sample image from left to right by 5 mm, the sample image in FIG. 4(b) will be Figure 4 (
It moves about 10 times the distance (50 mm) of the moving distance in a). Therefore, the SEM as shown in Fig. 4(b)
In order to move the sample image a minute distance at high magnification, it was necessary to operate the position pointing means very delicately. this is,
When positioning the electron beam with high precision, this causes a significant decrease in operability.

An object of the present invention is to provide an electron beam tester in which the amount of movement of the electron beam relative to the operation amount of the position indicating means is changed by the magnification of the SEM, and the positioning of the electron beam can be easily performed. be.

[0006]

[Means for Solving the Problems] In order to achieve the above object, a magnification instruction that allows positioning of an electron beam corresponding to the magnification of the SEM is provided to the man-machine interface function of a position instruction means such as a mouse or a trackball. Provide functions.

[0007]

[Operation] The magnification indicating function divides the pulse signal output from the position indicating means by a frequency division ratio corresponding to the magnification of the SEM. This frequency-divided signal is input to a pulse motor driver to drive the pulse motor to move the stage. Thereby, the moving speed of the sample image can be changed arbitrarily, and the operability of positioning the electron beam is improved.

[0008]

[Examples] Examples of the present invention will be described below.

FIG. 2 shows the configuration of the electron beam tester stage control section. A stage 8 composed of an objective lens 9 and a deflection coil B16 is moved two-dimensionally by a pulse motor 7. The stage controller 12 converts the pulse signal 4 from the position indicating means 2 into a pulse motor control signal 5, drives the pulse motor 7, and controls the stage 8. At this time, the deflection control unit 13 uses the data of the scale 20 as a parameter and calculates deflection data using an internal arithmetic processing circuit such as a CPU. This deflection data passes through a deflection amplifier 14, and the electron beam is deflected by a deflection coil A15 and a deflection coil B16 so that it always passes through the center of the objective lens 9 and irradiates the sample 10 perpendicularly. In this way, the movement and positioning of the electron beam 11 is realized by controlling the stage 8.

FIG. 1 shows the configuration of the magnification instruction function. Figure 1
, when the position indicating means 2 is operated, a pulse signal 4 is generated.
occurs. At this time, a frequency division ratio is set in the counter 1, and this frequency division ratio is used as the initial value of the count of the counter 1. Now, when the position indicating means 2 is operated, the counter 1 starts counting from the set initial value. Then, when the count reaches the maximum value, a carry signal is output. The logical product of this carry signal and the pulse signal 5 becomes the pulse motor control signal 5. Here, assuming that the number of bits of the counter 1 is 8 bits, the frequency division ratio can be set from 0 to 28. Now, when the frequency division ratio is set to 0, the pulse signal 4 is frequency-divided to 1/28. Also, set the frequency division ratio to 28
If a value close to is set, the pulse signal 4 will hardly be frequency-divided. Thereby, the drive speed of the pulse motor 7 can be changed arbitrarily. Therefore, by setting a frequency division ratio corresponding to the magnification of the SEM in the magnification instruction circuit 3, highly accurate positioning of the electron beam can be achieved. The way to set the division ratio requires hardware-based SE.
Possible methods include a method of detecting the magnification of M and automatically setting it, and a method of setting it corresponding to the magnification of the SEM using software. Although this embodiment has been described using a counter as the magnification indicating function 3, it may also be configured with a comparator or a combinational circuit.

FIG. 3 shows the relationship between the stage and the electron beam. At this time, the electron beam 11 is used as an electron beam for alignment (SEM mode). electron beam 11
is deflected so that it always passes through the center of the objective lens 9 and irradiates perpendicularly to the sample 10 with respect to the two-dimensional movement of the stage 8 . Therefore, the electron beam 11
It becomes possible to move in two dimensions. Also, C
On the RT monitor 19, the image of the sample 10 moves relatively.

FIG. 4 is a diagram showing the relationship between the conventional SEM magnification and the pulse motor control signal. Conventionally, since the cycle of the pulse motor control signal is always constant, the moving speed of the sample image changes greatly depending on the magnification of the SEM, as shown by the arrow on the CRT monitor 19. However, this is a problem that occurs when the amount of operation of the position indicating means 2 is always constant.

FIG. 5 shows a specific embodiment of the present invention. S
By frequency-dividing the pulse motor control signal using a frequency division ratio corresponding to the EM magnification, the movement speed of the sample image is optimized, and the operability of electron beam positioning is greatly improved.

[0014]

According to the present invention, the moving speed of the stage can be optimized in response to various magnifications of the SEM. Therefore, the positioning of the electron beam can be performed accurately and quickly.

[Brief explanation of the drawing]

FIG. 1 shows a configuration diagram of a magnification indicating circuit.

FIG. 2 shows a configuration diagram of a stage control section of an electron beam tester.

FIG. 3 is a diagram showing the relationship between a stage and an electron beam.

FIG. 4 is a diagram showing the relationship between a change in magnification of a conventional SEM and a pulse motor control signal.

FIG. 5 is a diagram representing a specific embodiment of the present invention.

[Explanation of symbols]

1... Counter, 2... Position indicating means, 3... Magnification indicating circuit,
4... Pulse signal, 5... Pulse motor control signal, 6... Pulse motor driver, 7... Pulse motor, 8... Stage,
9... Objective lens, 10... Sample, 11... Electron beam, 12
...Stage control section, 13... Deflection control section, 14... Deflection amplifier, 15... Deflection coil A, 16... Deflection coil B, 17...
Secondary electron detector, 18...Amplifier, 19...CRT monitor,
20...Scale.

Claims (2)

[Claims] 1. An electron beam generating means, a means for accelerating the electron beam to a desired energy, a lens means for focusing the accelerated electron beam, and a method for two-dimensionally scanning the focused electron beam on a sample, A means for positioning, a means for detecting secondary electrons generated from the sample, a means for analyzing the detected signal, a means for monitoring the sample, and a means for positioning the electron beam with respect to a fixed measurement point on the sample. An electron beam tester equipped with means for deflecting an electron beam, characterized in that the means for deflecting the electron beam is controlled in accordance with the magnification of the means for monitoring the sample. 2. The means for deflecting the electron beam of the electron beam tester according to claim 1, wherein the range in which the electron beam can be positioned can be automatically set in accordance with the magnification of the means for monitoring the sample. electron beam tester.