JPH01126504A - Electron beam length measuring machine - Google Patents

Abstract

PURPOSE:To accurately measure the width of a pattern at any position, by moving an objective lens or a sample stand corresponding to the scanning position of electron beam and always irradiating the surface of a sample with electron beam at a predetermined angle. CONSTITUTION:The scanning beams parallel to an optical axis are formed on the basis of the scanning signal from a CPU 11 using two-stage deflection systems of the first and second scanning systems 4, 5. Then, beams B1-3 are respectively set to such a case that a scanning axis coincides with the optical axis and such a case that the scanning axis is shifted in a- and b-directions. The case of the beam B1 is set to the initial position of an objective lens 6 and, herein, no voltage is applied to a piezoelectric element 21. When the scanning axis moves in the a- and b-directions and the beams B2, B3 are formed, the CPU 11 drives the element 21 through an amplifier 22 and the element 21 is distorted corresponding to applied voltage to minutely move the lens 6 in the a- and b-directions. By this method, the scanning axis of electron beam can be matched with the center of the lens 6 and the width of a pattern can be accurately measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electron beam length measuring machine, and more particularly to an electron beam length measuring machine capable of accurately measuring pattern width.

[Background Art] With rapid progress in microfabrication technology, integrated circuits are becoming increasingly finer. The dimensions of the circuit elements have been miniaturized from several microns to one micron. The dimensions of the element are important factors that determine the basic performance of electronic circuits, such as the degree of amplification and frequency characteristics. Therefore, it is necessary to accurately measure the pattern width within a chip when designing an integrated circuit.

An electron beam length measuring machine is a device that accurately measures the pattern width within a chip, and an example thereof is shown in FIG. An electron beam 3i emitted from the electron gun 1 is turned on and off by a blanking electrode 2 and then converged by a converging lens 3. The focused electron beam Bi is deflected in two-dimensional directions while passing through the first scanning system 4 and the second scanning system 5. This deflection control is performed according to instructions from CPLlll. The deflected electron beam Bi is converged by an objective lens 6 and then focused on a sample 8 placed on a sample stage 7 . In other words, the sample 8 is irradiated with the electron beam [3i.

As the electron beam 3i scans over the sample 8, reflected electrons or secondary electrons are generated from the beam irradiation point of the sample 8. Here, as a method of scanning the sample 8, digital scanning is performed in which the electron beam 3i is made to run intermittently at regular intervals. The interval of this jump (scale unit) is set, for example, to about 1/1000 of the scanning distance of the electron beam Bi. For example, to measure a line width of 1 micron, the electron beam 3i is scanned by a width of 3 microns, and the scale unit is set to 0.003 micron.

The intensity of reflected electrons or secondary electrons generated from the sample surface differs depending on the material of the illumination point. Therefore, the reflected electrons are detected by a detector 9 placed above the sample surface, amplified by an amplifier 10, and then provided to the CPU 11. The CPU 11 is the detector 9
The width of the pattern is measured based on the signal detected by . Note that the scanning distance and scale units are precisely calibrated using a reference pattern created by an electron beam drawing device. In actual measurements, usually 1024 steps (10 bits) or 2048 steps (
Digital scanning is performed using a D/A converter with a resolution of 11 bits [-]. When the beam scanning for one field is completed, the drive mechanism 12 is operated according to a command from the CPU 11, and the sample stage 7 is moved.

[Problems to be Solved by the Invention] In the conventional method, a problem arises in that the scanning width on the sample varies depending on the height of the sample even for the same swing angle. FIG. 4 is a diagram showing the scanning state of the beam. Assume that there are two sample surfaces, A and B, with different heights. When the beam is swung at a deflection angle θ around the deflection fulcrum K, if the scanning width on the sample surface is Ll, the scanning width on the sample surface B is L2 (L2>11). This difference in scanning width appears as a measurement error. Within the range of deflection angle θ, processing takes the same amount of time, so for example, if the pattern width measured on the sample surface is L', and the pattern width of the same pattern measured on sample surface B is L', then L>L'. turn into.

Further, when the D/A converter is used to scan the swing angle at equal intervals (for example, 2048 steps), the scanning width on the sample differs between near the center and near the end of the optical axis. This also causes measurement errors. In order to eliminate such problems, it is necessary to measure the height of the sample surface (working distance) by some method, and then calculate and change the angle of view at each step based on the measurement results. , the measurement error remained.

The present invention has been made in view of these points, and
The purpose is to realize an electron beam length measuring machine that can accurately measure pattern width at any position.

[Means for Solving the Problems] The present invention, which solves the above-mentioned problems, focuses an electron beam that has passed through a scanning system using an objective lens, irradiates it onto the sample surface, detects the reflected signal, and detects the sample surface. In an electron beam length measuring machine that measures the width of a pattern formed in The invention is characterized in that it is configured so that

[Operation] A mechanism is provided so that the electron beam is always directed at a predetermined angle on one surface of the test plate.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a main part configuration diagram showing an embodiment of the present invention.
Components that are the same as those in FIG. 3 are designated by the same reference numerals. In the figure, 21 is a piezo element attached to the end of the objective lens 6. The piezo element 21 is driven by an amplifier 22 controlled by the CPU 11. The operation of the device configured as described above will be explained as follows.

A scanning beam balanced on the optical axis is created using a two-stage deflection system, a first scanning system 4 and a second scanning system 5, in response to a scanning signal from the CPU 11. In the figure, B1 is when the scanning axis coincides with the optical axis, B2 is when it is shifted from B1 in the direction a, and B3 is B1.
This is a case where the distance is shifted in the direction b. Here, the scan axis is 8
The position of the objective lens 6 in the 1st case of 1 is the initial position. At this position, no voltage is applied to the piezo element 21.

Next, assume that the scanning axis moves in the a direction and becomes B2. Therefore, the CPU 11 drives the piezo element 21 via the amplifier 22. The piezo element is distorted according to the applied voltage, and moves the objective lens 6 minutely in the a direction. vice versa,
Assuming that the scanning axis moves in the b direction and becomes B3,
CPtJll drives the piezo element 21 in the opposite direction and moves the objective lens 6 minutely in the b direction. In this way,
The scanning axis of the electron beam can be aligned with the center of the objective lens 6, making it possible to accurately measure the pattern width.

FIG. 2 is a block diagram of main parts showing another embodiment of the present invention.

Components that are the same as those in FIG. 3 are designated by the same reference numerals. In the figure, numerals 31 and 32 are piezo elements mounted in each of the x and y directions of the sample stage 7, respectively. These piezo elements 3
1.32 are the CPU via amplifiers 33 and 34, respectively.
11. The operation of the device configured as described above will be explained as follows.

The scanning signals given from the CPU 11 to the first scanning system 4 and the second scanning system 5 are fixed. For this reason, the electron beam [3i always scans at the same swing angle regardless of the position of the irradiation point of the test f3[8. Therefore, the CPU 11 drives the piezo elements 31 and 32 in conjunction with the scanning of the electron beam Bi, and
move. As a result, since the electron beam (3i) is always irradiated at the same angle to the irradiation point of the try-on 18, it is possible to prevent a difference in pattern width measurement near the center and end of the optical axis.

In the embodiments described above, a case has been described in which a piezo element is used as a driving means for moving the objective lens or the sample stage so that the electron beam is irradiated onto the sample surface at a predetermined angle. However, the present invention is not limited to this, and other types of driving means can be used.

[Effects of the Invention] As described in detail above, according to the present invention, the electron beam can be always irradiated onto the sample surface at a predetermined angle by using the driving means, and the pattern width can be accurately measured. can do.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of main parts showing one embodiment of the present invention, Fig. 2 is a block diagram of main parts showing another embodiment of the present invention, and Fig. 3 shows an example of a conventional structure for electron beam length measurement. FIG. 4 is a diagram showing the scanning state of the beam. 4...First scanning system 5...Second scanning system 6...
・Objective lens 7...Sample stand 8...Sample
11...CPU21.31.32...Piezo element 22.23.34...Amplifier patent applicant Japan Electronics Co., Ltd.
Ceremony for the meeting Patent attorney
Fuji Ijima (1 person) Figure 1 (angle) 2 Figure 3 Figure 7 Sample stand

Claims (2)

[Claims] (1) In an electron beam length measuring machine, the electron beam that has passed through the scanning system is focused by an objective lens and irradiated onto the sample surface, and the reflected signal is detected to measure the pattern width formed on the sample surface. An electron beam length measuring machine characterized in that the objective lens or the sample stage is moved using a driving means according to the scanning position of the electron beam, so that the electron beam is always irradiated onto the sample surface at a predetermined angle. (2) The electron beam length measuring machine according to claim 1, characterized in that a piezo element is used as the driving means.