JPH073776B2 - Electron microscope for length measurement - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a scanning electron microscope for measuring fine structure dimensions such as surface patterns of VLSI, and is particularly suitable for sequentially and efficiently measuring a large number of measurement objects. Regarding the device.

[Background of the Invention]

With the high integration of semiconductors, the need for VLSI measurement by electron microscope is increasing. Most of the devices currently used for measuring semiconductor processes are optical devices using laser light, but it is thought that they will not be usable after a few years due to the limit of resolution due to the wavelength of light. As a solution to this problem, a scanning electron microscope type measuring method utilizing high resolution of an electron beam has been developed.

This measurement method is based on Takao Ikue et al., Fine line width measuring device, (Materials of the 85th Research Group, 132nd Committee of the Japan Society for the Promotion of Science, PP1-5, Showa
(November 1983), the semiconductor wafer is observed with a scanning electron microscope (hereinafter abbreviated as SEM) to measure the line width of the wafer pattern. A flowchart of the measurement processing procedure is shown in FIG. In step 11, the semiconductor wafer is set on the sample stage of the SEM, gas is exhausted to create a vacuum, and the sample stage is sent to the sample chamber. At this time, rough alignment between the sample stage and the wafer is performed using the orientation flat of the wafer. Next, in step 12, highly accurate alignment called alignment is performed. Although various alignment methods have been developed, the position of the wafer on the sample table can be increased by observing the alignment pattern created in advance on the wafer with an SEM and measuring the positional relationship between the position and the sample table. The method of gaining precision is common.

Next, regarding the length measurement of the pattern, for example, as shown in FIG. 2, about 5 points per wafer are selected and the line width of the wafer pattern determined in advance is measured. For this purpose, it is necessary to first bring the measuring point into the field of view of the SEM. Generally, the sample stage automatically moves and the measuring point on the wafer pattern determined in advance is SE.
It can be displayed as an M image. This processing performed in step 13 is called view selection, and an example of the SEM image of the selected view is shown in FIG.

For this SEM image, the operator sets two sets of cursors on the screen as shown in FIG. 3 to perform measurement. In order to make it easy to align the cursor with both edges of the line of the wafer pattern, an angled cursor, a cursor that sandwiches the edge with two lines, etc. have been devised.

This completes the measurement of the first measurement point in step 14,
Next, the field of view of the second measurement point is selected and the measurement is performed. After the measurement up to the fifth measurement point is completed one after another, the wafer is taken out to the exchange chamber at step 15 and gas is injected to perform wafer reset. This completes the length measurement of one wafer, returns to step 11 and sets the next wafer, and the length measurement is started.

On the other hand, in the semiconductor industry, improving the management accuracy of the production line and improving the yield control the life and death of the business.Therefore, the length of the semiconductor pattern is measured in a short time, and the throughput of the length measurement is improved. Therefore, inspecting as many chips as possible is an important issue. However, the above-mentioned conventional technique has a problem that a sufficient length measurement throughput has not been realized yet.

[Object of the Invention]

An object of the present invention is to provide a length-measuring electron microscope which improves the throughput of a length-measuring object per unit time, that is, the throughput by apparently shortening the length-measuring time.

[Outline of Invention]

In the past, efforts have been made to reduce the time required for the field of view selection in the above-described length measurement procedure for each procedure such as measurement.
In the present invention, the electron microscope image is temporarily stored in the image memory and the field of view of the second measurement point is selected at the same time as the measurement of the first measurement point, that is, a plurality of procedures are processed in parallel. This makes it possible to shorten the apparent product for a long time.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS. 4 and 5. In this embodiment, SEM images are formed one after another for several points (five points in the figure) whose positions on the semiconductor wafer are known, and a computer is operated by using a cursor set by the operator on these SEM images. The dimensions of the fine structure on the wafer are calculated.

FIG. 4 shows the configuration of the embodiment. The lens barrel 1, the electron beam controller 2, the sample stage 3, the detector 4, the exhaust device 5, the sample stage controller 6, and the position detector 7 are the same as those used in a general SEM.

That is, the electron beam emitted from the electron gun in the lens barrel 1 has its beam diameter narrowed by the electron lens system controlled by the electron beam control device 2 and is fixed to the sample table 4 in the sample chamber 3. The long object is irradiated. Here, it is a method in which the secondary electrons and the like generated from the object to be measured are detected by the detector 5. The exhaust device 6 is used to exhaust the lens barrel 1 and the sample chamber 3 to create a vacuum. The sample table controller 7 is used to automatically move the sample table 4 in a predetermined direction. In order to improve the accuracy of the moving direction and the moving amount, the position of the sample table 4 is detected by using the position detector 8, and the sample table controller 7 controls the sample table 4 using this position data.

In a general SEM, a signal such as a secondary electron detected by the detector 5 is amplified and led to a display as it is to display a length measuring object. However, in the embodiment of the present invention,
The detection signal is guided to the image input device 9, and after amplification and integration, A / D conversion is performed and the image of the length measurement object is stored in the image memory 11. The contents of the image memory 11 can be displayed on the image display 12. A computer 10 controls these devices.

Next, the operation of the embodiment will be described with reference to an example in which a semiconductor wafer is used as an object for length measurement. First, as described with reference to FIG. 1, the wafer is set on the sample table 4 in the sample chamber 3.
Exhaust at this time is performed by the exhaust device 6. Then, the electron beam control device 2 is operated by an instruction from the computer 10, and scanning of the electron beam on the wafer is started. The signal from the detector 5 at this time is sent directly from the image input device 9 to the image display 12
Sent to and displayed as an image. That is, at this time, the embodiment operates in the same manner as a general SEM. In this state, alignment is performed in the same procedure as the above-mentioned conventional apparatus. That is, the alignment pattern of two points on the wafer is displayed in the center of the image display 12, and the signal of the position detector 8 at that time is stored in the computer 10, so that the sample table 4
And the positional relationship between wafers can be enhanced.

The operation when the next visual field selection and measurement are repeated for a plurality of measurement points will be described with reference to FIG. First calculator 10
In order to bring the first measurement point on the wafer into the field of view of the image display 12, calculate how much the sample stage 4 should be moved in each of the X and Y directions from the current position, and control the result to the sample stage control. Transfer to device 7. Sample stand controller 7
Moves the sample table 4 based on the transferred data,
The field of view of the first measurement point is selected. In FIG. 5, the time required for this visual field selection is represented by t _s1 .

The measurement of the first measurement point is started when the above visual field selection is completed. That is, the scanning of the electron beam by the electron beam control device 2 is started by an instruction from the computer 10. The transition of the secondary electrons detected by the detector 5 during the scanning is taken in the image input device 9 as image information and further transferred to the image memory 11. As a result, the SEM image of the first measurement point is stored in the image memory 11, and thus the SEM image of the first measurement point is continuously displayed on the image display 12 even after the scanning of the electron beam is completed. The operator uses the image displayed on the image display 12 as shown in FIG. 3 and interacts with the computer 10 to perform the measurement in the same manner as the conventional device.
The calculator 10 takes in the cursor position information set by the operator and calculates the actual dimensions. In FIG. 5, the measurement time at the first measurement point is represented by t _m1 .

While measuring the first measurement point, the computer 10 calculates the moving direction and the amount of the sample table 4 up to the second measurement point, and performs the same operation as that at the first measurement point so that the sample table 4 can be moved. The move is done and the second
The field of view of the measurement point is selected. That is, the computer is independent of the electron beam scanning performed by the electron beam controller 2.
10 calculates the fourth moving direction and moving distance of the sample up to the second measurement point, and further displays the SEM of the first measurement point on the image display 12.
An image is displayed, and the sample table is moved by the sample table controller 7 independently of the period during which the dimension is measured by the operator's operation. In Figure 5, this time is t _s2
Is represented. Normally, the field of view selection time is shorter than the measurement time (t _s2 <t _m1 ), so when the measurement at the first measurement point is completed, there is no movement time of the sample table 4, that is, field of view selection time, and the second measurement point The image input or measurement of can be started.

The above-described operation is repeated for the number of measurement points of one wafer in the operation sequence as shown in FIG. In the figure
t _si (i = 1 to 5) is the field selection time of the i-th measurement point, t _mi
(I = 1 to 5) represent the measurement time at the i-th measurement point.

After the final measurement of the wafer is completed, the wafer is reset and the next wafer is set.

〔The invention's effect〕

FIG. 5 (a) shows the operation sequence according to the present invention, and FIG. 5 (b) shows the operation sequence according to the conventional apparatus. As can be seen from this figure, the apparent time required to select and measure the field of view on five points on one wafer is With conventional equipment Becomes For example, if t _si = 10 seconds and t _mi = 15 seconds, 32% (125 seconds → 85 seconds) of time for visual field selection and measurement according to the present invention.
Can be shortened.

As described above, according to the present invention, since it is possible to apparently reduce the length of time for the length measurement, there is an effect of improving the throughput of the length measurement object per unit time, that is, the throughput.

[Brief description of drawings]

FIG. 1 is a flowchart of a measurement processing procedure by an electron microscope for length measurement, FIG. 2 is a view of a semiconductor wafer from above,
FIG. 3 is an electron microscope image of a measuring point for length measurement, FIG. 4 is a block configuration diagram of an embodiment of the present invention, and FIG. 5 is a diagram showing a visual field selection and measurement sequence.

Front page continuation (72) Inventor Yamagata Shinbu 1099, Ozenji, Aso-ku, Kawasaki-shi, Kanagawa, Ltd. Inside Hitachi, Ltd. System Development Laboratory (72) Inventor, Toshihiro Furuya, 882, Mao, Katsuta, Ibaraki Hitachi, Ltd., Naka Factory, Ltd.

Claims (1)

[Claims] 1. A microscope image obtained by irradiating an observation region with an electron beam and utilizing signals such as secondary electrons generated from a minute portion of the length measurement object mounted on the sample stage located in the observation region. In a length-measuring electron microscope for estimating the dimensions of a fine structure from the microscopic image, a storage unit that temporarily stores signals such as the secondary electrons, and a signal stored in the storage unit. Display means for reading out and displaying a microscope image, means for calculating the dimension of the fine structure from the position information of the cursor set by superimposing on the microscope image displayed on the display means, and a plurality of stored designated position information Position control for calculating the moving direction and moving distance of the sample table for aligning the specified position on the measurement object to be observed next based on the above with the observation region, and moving the sample table according to the calculation result. Equipped with means The display of the microscope image by the display unit, length measuring electron microscope, characterized in that is carried out in parallel independently of each other with the movement of the sample table by the position control means.