JPH01201110A - Electron beam length measuring method - Google Patents

Abstract

PURPOSE:To measure length under the same conditions with a frame memory image and photography by forming a charge-up part nearby a length measurement line in advance. CONSTITUTION:A 1st scanning system 4 and a 2nd scanning system 5 are controlled according to an indication from a CPU 11. Namely, the charge-up part is formed nearby the length measurement line prior to actual length measurement, and then the length measurement line is scanned (at the time of the frame memory memory image). Consequently, the line width is measured under the same conditions with the whole image stored in the frame memory 14.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for measuring pattern width using electron beam length measurement.

(Prior 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. Since the dimensions of the element are important factors in determining the basic performance of electronic circuits such as amplification and frequency characteristics, accurately measuring the pattern width within the chip (material) is essential in designing integrated circuits. It becomes necessary.

An electron beam length measuring machine is a device that accurately measures the pattern width within a material, and an example of its configuration is shown in FIG.

The electron beam 3i emitted from the single gun 1 is turned on and off by the blanking electrode 2, and then converged by the converging lens 3. The focused electron beam 13i is deflected in two-dimensional directions while passing through the first scanning system 4 and the second scanning system 5. This deflection υ"■ is performed according to the instructions of CPtJll. , the electron beam Bi that has been deflected is passed through the objective lens 6.
The material 8 placed on the material table 7 after being converged by
Focus on the top. In other words, the material 8 is irradiated with the electron beam 13i.

As the electron beam Bi scans the material 8, reflected electrons or secondary electrons are generated from the beam irradiation point of the material 8. Here, as the direction in which the material 8 is scanned, digital scanning is performed in which the electron beam [3i is run intermittently at regular intervals. This jump interval (scale unit)
For example, 1/10 of the scanning distance of the electron beam B1
It is set to about 00. For example, to measure a line width of 1 micron, the electron beam B1 is scanned by a width of 3 microns, and the scale unit is set to 0.003 micron.

The intensity of the reflected electrons or secondary electrons generated from the material surface differs depending on the material of the q4 point. Therefore, this reflected electron or secondary electron is detected by a detector 9 placed above the material surface,
The signal amplified by the amplifier 10 is applied to 0PU11. CPU
Reference numeral 11 increases the pattern width by 1llll based on the signal detected by the detector. In addition, the 11th place in the scanning distance and scale is
It is precisely calibrated using a reference pattern created using an electron beam lithography system. In other words, by measuring the length of the reference figure,
l! Correct the value of the tsuki machine. In actual length measurement,
In order to improve the reproducibility and accuracy of length measurements, digital scanning is usually performed using a D/A converter with a resolution of 1024 steps (10 bits) or 2048 steps (11 steps). When the beam scanning is completed, the drive 1 horizontal 12 is operated according to a command from the CPU 11, and the timber table 7 is moved.

13 is a frame memory for storing actual pattern information of the material 8; Before measuring the width of a predetermined portion of the pattern, the entire surface of the material 8 is scanned, and the signal obtained from the material at that time is sent to an A/D converter (not shown) built in the CPU 11.
The data converted into digital data is stored in the frame memory 13. The contents of the frame memory 13 can be displayed on the CRT 14 as necessary.

By the way, when material #1 is irradiated with an electron beam,
A charge-up phenomenon occurs. Charge-up refers to a phenomenon in which when a material is irradiated with an electron beam, charges are scattered inside the material.

Therefore, when a unidirectional line (line) scan is performed as in electron beam irradiation, charge-up occurs in a width along the scan line on the material. The higher the accelerating voltage is, the more this charge-up is affected, and it also depends on the quality of the material 8. Therefore, the charge-up state will be different depending on the case where electron beam irradiation is performed only in the - direction and the case where continuous rask scanning is performed such as when storing in a frame memory or during photographic layer shadowing.

(Problems to be Solved by the Invention) As described above, when a material is irradiated with an electron beam and its reflected signal is captured in a frame memory, charge-up occurs over the entire surface of the material. Therefore, frame memory 1
The image stored in No. 3 has the entire screen charged up. The case of photographic performance is similar to the case of frame memory. However, when measuring only a specific line width in one scan, the line width is measured while the material 8 is not affected by charge-up.
The measurement conditions differ from the state when the frame memory 13 is stored or when a photograph is taken. If the measurement conditions are different, for example, when charge-up occurs, the sample surface potential changes, and 2
Affects the next electronic signal.

By the way, in order to initially detect the pattern of the material body in vA, the accelerating voltage is adjusted so that the charge-up becomes an allowable value. When measuring the length, measure at five locations: front, back, left, and right. However, this would require too much man-hours, so it would be better to scan the beam at one location. For this reason, it is necessary to bring the body image and the one-line scan to the same conditions.

The present invention has been made in view of these points, and
The purpose is to realize an electron beam sub-length method that can measure line width under the same conditions as for frame memory images and photographic shadows.

(Means for Solving the Problems) The present invention, which solves the above-mentioned problems, provides a method for measuring the width of a specific pattern on a material using an electron beam length measuring machine. The beam is scanned in advance in the vicinity of the material so that the charge-up that occurs on the material is under the same conditions as in the case of frame images or photographic images (step [1]), and the charged-up area is perform beam scanning and measure the length (step [2
]). FIG. 1 is a flowchart showing one embodiment of the method of the present invention.

(Operation) A beam is scanned in advance in the vicinity of the location where length measurement is to be performed to create a charge-up similar to that in the case of frame image or photography, and then length measurement is performed by one line scan.

By doing so, the length can be measured under the same conditions as in the case of the whole image on the frame memory or the 11th image.

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

FIG. 2 is an explanatory diagram of the method of the present invention. In the same figure (A), it is assumed that the width between the point a and the point b of the object 2o to be measured is measured. The length measurement line at this time is designated as B. Further, it is assumed that the scanning speed is the same as when storing secondary electronic signals in the frame memory. First, a line A one pixel above the length measurement line B is scanned with an electron beam. Next, measurement line B
Scan line C one pixel below. This means that the same charge-up as the frame memory image is created above and below the measurement line B. In this state, length measurement line B may be scanned to measure the width of point a and point b, and the data at that time may be imported.

In the case of photographic projection, the situation is slightly different from that in the case of frame memory. In other words, in the case of photographing, unlike in the case of frame memory, a slow rusk scan is used. Therefore, in case (a), the lines are traced in the order of lines Δ, B, and C. Therefore, when scanning line A, line A is scanned as shown in (b).
Charge-up occurs near (shaded area in the figure). When scanning lines B and C, the same phenomenon occurs near lines B and C. When measuring the length, it is necessary to measure the length under the same conditions.

Therefore, when measuring the line width between a and b in (a), first scan line 8 at the same speed as when taking the photograph.

This creates a charge-up under the same conditions as when taking photos. In this state, line B at the actual measurement point is scanned to measure the line width at points a and b. Note that the scan of line A here is ON! 8 If the electron beam size is wider than the pixel interval (each scan line interval),
up to the point where a charge-up phenomenon occurs on the measurement line.
It is necessary to increase the number of lines on the length measurement surface. This also applies to length measurement for frame memory images.

The line width measurement method according to the present invention described above can be realized using the apparatus shown in FIG.

That is, the first scanning system 4 and the second scanning system 5 are controlled by instructions from the CPU 11. That is, before the actual length measurement, the lines before and after the length measurement line are scanned to create a charge-up near the length measurement in of the material 8, and then the length measurement line is scanned (the frame memory image is case). This makes it possible to measure the line width under the same conditions as the entire image stored in the frame memory 14.

The same applies to the case of photographing.

(Effects of the Invention) As explained above in detail, according to the method of the present invention, when measuring length using an electron beam, the length measurement line is preliminarily placed near the length measurement line (in the case of a frame memory, on both sides thereof, in the case of photography, By applying a charge-up (on one side), the width of the pattern can be measured under the same conditions as when taking an actual frame memory image or photograph.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing an embodiment of the method of the present invention, FIG. 2 is an explanatory diagram of the method of the present invention, and FIG. 3 is a diagram showing an example of the configuration of an electronic dome length measuring machine.

Claims (1)

[Claims] When measuring the width of a specific pattern on a material using an electron beam length measuring machine, the beam scans the vicinity of the length measurement point in advance to capture the charge-up that occurs in the material in the case of a frame image or when taking a photograph. The electronic device is characterized in that the conditions are set to be the same as in the case of (step [1]), and the charged-up area is scanned with a beam to measure the length (step [2]). Beam length measurement method.