JPH0587764B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a scanning electron microscope, and particularly to a scanning electron microscope suitable for use in the semiconductor field.

[Conventional technology]

There are many types of samples that can be examined and observed using a scanning electron microscope, not just semiconductor devices. Conventionally, the operator rotates the scanning direction of the scanning line by a necessary amount while observing the image to adjust and set the orientation of the image within the observation field of view. (For example, Scanning Electron Icroscopy, published by Rad Research Industries:
SCANNING ELECTRON MICROSCOPY: Chapter
(See pages 40 to 42) By the way, in the case of semiconductor devices, especially samples made of a combination of linear patterns such as semiconductor integrated circuit wafers, it is often desirable to observe the sample with the pattern vertically or horizontally. In such cases, each time a wafer to be tested is loaded at the sample position, the image or scanning line must be manually rotated while observing the sample image, and no consideration has been given to operability. Ta.

[Problem that the invention seeks to solve]

In the above-mentioned conventional technology, for a sample with a combination of linear patterns, such as a wafer for semiconductor devices or semiconductor integrated circuits, an operator observes the inclination of the sample image with respect to the scanning direction of the electron beam, and the linear pattern changes in the scanning direction. They were manually adjusted so that they were parallel or perpendicular.

Therefore, there are problems such as a large amount of time being spent on adjusting the tilt of the sample image, resulting in a decrease in work efficiency, and individual differences in adjustment.

An object of the present invention is to eliminate the above-mentioned drawbacks, to automatically calculate the inclination angle of the sample image with respect to the reference straight line or the scanning direction of the electron beam for a sample having a combination of straight line patterns, so that the straight line pattern of the sample is Alternatively, it is possible to rotate an image or a scanning line to an arbitrary predetermined angle with respect to the scanning direction.

[Means for solving problems]

The above purpose is to calculate the inclination of the sample image with respect to the straight line direction from image signals obtained from two or more parallel straight lines at different positions, and from the inclination and the inclination angle of the straight line with respect to the reference straight line, Calculate the inclination of the sample image with respect to the reference straight line, further calculate the rotation angle of the sample image necessary to make the inclination angle of the sample image with respect to the reference straight line a desired value, and rotate the sample by that angle, or Alternatively, this can be achieved by rotating the scanning direction.

[Effect]

From image signals obtained from two or more parallel straight lines at different memorized positions, if the sample is tilted with respect to the straight lines, the intensity distribution of the image signals on each straight line will shift in a certain direction. By doing so, the inclination of the sample image can be calculated based on the amount of shift and the interval between the straight lines.

Since the inclination angles of the two or more straight lines with respect to the reference straight line can be known in advance, the inclination of the sample image with respect to the reference straight line can be known in the end. Therefore, it is possible to calculate the amount of rotation of the electron beam in the scanning direction necessary to make the sample image tilt at a desired angle with respect to a predetermined reference straight line.

By inputting the rotation amount signal to a known deflection signal rotator, the sample image can be adjusted to a desired inclination, or alternatively, the sample itself may be rotated.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

In this example, "two or more parallel straight lines stored at different positions" are defined as "two or more parallel straight lines at different positions _" as shown in Figure 2. In the same direction as the scanning line passing through A and B,
The case where there are two fixed straight lines La and Lb will be described.

In this case, it is assumed that a reference straight line _L0 perpendicular to the scanning direction R has been registered in advance using a suitable input means such as a keyboard or a mouse, as shown in FIG. The slope of the reference line L ₀ is important, and it may be registered by inputting the angle δ it forms with the scanning direction R, or by inputting the angle α it forms with the parallel lines La and Lb.

Note that image observation using a scanning electron microscope as in the present invention is often used for monitoring patterns of semiconductor integrated circuits (particularly measuring their widths);
In such a case, orthogonal vertical and horizontal patterns are usually set to be parallel or perpendicular to the scanning direction.

When measuring the width of a pattern, the average value of the line widths obtained on each scanning line is often taken.
In such a case, if the linear pattern is not perpendicular to the scanning line, it is necessary to detect the data acquisition position (address) each time, which often makes the process complicated. In Figure 1, the electron gun 1
The electron beam 2 emitted from the condenser lens 3,
The light is narrowed down by the objective lens 5 and is incident on the sample 6.

Further, since the deflection signal generated by the deflection signal generator 10 is rotated by the deflection signal rotator 9 so that the scanning direction coincides with the desired direction, the deflection signal is input to the deflection coil 4. Line 2 is scanned two-dimensionally on sample 6.

Note that the electron gun 1, condenser lens 3, and objective lens 5 are controlled by an electron gun control section 7, a condenser lens control section 8, and an objective lens control section 11, respectively.

A signal 13 (secondary electron signal, reflected electron signal, etc.) generated from the sample 6 by irradiation with the electron beam 2 is detected by the detector 14 and converted from analog to digital signal by the A/D converter 15. The image is converted and stored in the image memory 16.

The image signal stored in the image memory 16 is further
It is converted into an analog signal again by the D/A converter 17, and sent to the CRT 2 for image display through the amplifier 18.
It is applied to the grid as a zero luminance signal.
On the other hand, the signal generated by the deflection signal generator 10 is amplified by the amplifier 19, and is supplied to the deflection coil of the CRT 20 to drive it.

The computer 12 is configured to be able to read the contents of any location (address) in the image memory 16, and to control the amount of rotation of the deflection signal by the deflection signal rotator 9 based on that information.

In such a configuration, consider two straight lines La and Lb in the same direction as the scanning direction, as shown in FIG. It is assumed that the signal intensities Sa and Sb of the sample images on these straight lines La and Lb have distributions as shown in FIG. 3, respectively.

Note that such signal strength is stored in the memory 16, and the straight lines La and Lb are also determined on this memory 16. Therefore, it is possible to predetermine the distance l _v between the straight lines A and B and use the data at the corresponding position in the image memory 16.

Further, as shown in FIG. 2, if the distance between the edges on one side of the sample image S located on the straight lines La and Lb is l _h , then based on the information stored in the memory 16,
From the signal strengths Sa and Sb shown in FIG. 3, the peak positions of the mutually corresponding waveforms are detected through processing by the computer 12, and the distance l _h is determined by calculating the difference. be able to.

From these l _v and l _h , the inclination θ of the sample image S with respect to the scanning direction is given by the following equation (1) θ=tan ⁻¹ l _v /l _h (1). This shows that in order to tilt the sample image at 90 degrees with respect to the scanning direction, it is sufficient to rotate the sample image to the right (clockwise) by (90 degrees - θ).

Furthermore, in this case, the angle to be rotated may be directly determined by the following equation (2): = tan ^-1 l _h /l _v (=90-θ) (2).

In the above embodiment, the straight lines La and Lb are considered to be in the horizontal direction, but they can be similarly determined using a vertical straight line as a reference, or they may be in any direction as described later.

Also, the positions of points A and B and the distance between straight lines La and Lb l _v
are assumed to be constant, but by making these variable, it is possible to obtain the required amount of image rotation based on information on a specific location, which has the effect of further improving operability.

Further, in the above embodiment, the distance l _h was determined based on the information on the peak position of the signal intensity, but various other methods may be considered.

For example, for each signal Sa, Sb, the intermediate value between the maximum value and the minimum value is set as the slice level, the intersection of each waveform Sa, Sb and the slice level is found, and l _h is found from the difference between the respective intersection positions. , It is also possible to move the Sa signal left and right to position it so that it overlaps Sb most, and set the amount of movement to l _h .

In addition, in Fig. 2, the tilt angle θ or the corrected rotation angle was determined based on the intersection position of the sample image S with two parallel straight lines. By doing so, there is an effect that the inclination and corrected rotation angle can be determined with higher accuracy.

In the above embodiment, an example was given in which all data within the field of view is stored in the stroke number memory 16, but the data necessary for determining the slope, that is, the straight line La,
By storing only the data obtained on Lb, the capacity of the stroke number memory 16 can be reduced.

Furthermore, in the above, the two straight lines La and Lb that coincide with the scanning line direction are adopted, and the inclination of the sample image with respect to the straight lines La and Lb is calculated based on the data of the sample image obtained from these straight lines. angle θ
However, the present invention can generally be implemented as shown in FIGS. 4 and 5. In this figure, the same reference numerals as in FIG. 2 represent the same or equivalent parts.

In Fig. 4, the sample image S is a wiring pattern whose orientation is desired to be aligned in one direction with respect to the coordinate axes, and the sample image T is a case where the sample image S is deformed into a dogleg shape as shown in the figure. In order to be able to accurately adjust the orientation (tilt state) of the specimen image S within the observation field even if the wiring is short or small or tilted, the wiring whose inclination is measured instead of the specimen image S. It's a pattern. Such a sample image T always exists in a semiconductor element, and is arbitrarily selected by the operator. As the sample image T,
It is desirable to select a pattern with a relatively long shape so that its inclination angle can be measured accurately.

In such a configuration, since the relative angle γ between the sample image S and the sample image T is known in design, the coordinate axis of the sample image S can be determined by measuring the inclination angle on the coordinate axis of the sample image T. This means that the angle of inclination at the top can be determined indirectly. Although the sample image T and the sample image S are not necessarily displayed on the same screen, they are shown on the same screen here to make the explanation easier to understand.

For example, when it is desired to align the orientation of the sample image S perpendicularly to the scanning direction R, the reference straight line L ₀ is set so that the relative angle δ with the scanning direction R is (90°−γ). In addition, in order to accurately find the point of intersection with the sample image T, the parallel lines La and Lb are desirably set in a direction such that they intersect at a large angle (nearly a right angle) to the sample image T.

The reference line L ₀ is set by the operator as described above, and the two (or more) parallel lines La and Lb are also set arbitrarily or fixedly by the operator, so these angle α
The distance l _v between the two straight lines La and Lb is known. Also,
Since the distance l _h is determined from the intersection point between the data of the sample image T stored in the memory 16 and the two straight lines La and Lb, the inclination angle θ is determined as described above.

Therefore, the inclination angle β of the sample image T with respect to the reference straight line L ₀ is determined by the following equation (3).

β=π−(α−θ) …(3) Here, the reference straight line _L0 is such that the sample image S is aligned in the desired direction when the tilt angle of the sample image T matches the tilt angle of the reference straight line _L0 . In advance, [δ=90°−γ]
Therefore, by rotating the scanning direction of the electron beam by the calculated inclination angle β, the inclination angle of the sample image T and the reference straight line L ₀ are determined as shown in FIG. By matching the inclination angles, the sample image S can be aligned in a desired direction (perpendicular here) with respect to the scanning direction R.

As is clear from the above description, the embodiment described above with reference to FIG.
This corresponds to the case where Lb coincides with the scanning direction R and the reference straight line L ₀ is perpendicular to the scanning direction R.

In the above, an example has been described in which the computer 12 calculates the amount of rotation for correcting the direction, and supplies this to the deflection signal rotator 9 to automatically adjust the electron beam scanning direction to the desired direction. Of course, the amount of rotation for correction may be visually displayed, and at least one of the electron beam scanning direction and the sample itself may be manually rotated so that the amount of rotation becomes 0 or a desired value.

〔Effect of the invention〕

According to the present invention, the inclination of a pattern with respect to a predetermined direction (reference straight line) can be automatically calculated based on data of a sample image of a linear pattern, such as a pattern of a semiconductor device, and the calculation result is From this, it is possible to easily determine the amount of rotation in the scanning direction of the electron beam in order to align the sample image in a desired direction within the observation field. By rotating the deflection direction of the electron beam by the amount of rotation described above, the inclination of the sample pattern within the observation field of view can be automatically aligned in a constant direction, and it is also possible to eliminate individual differences. be.

[Brief explanation of drawings]

Figure 1 is a block diagram of a scanning electron microscope showing an embodiment of the present invention, Figures 2 and 3 are diagrams for explaining the method of calculating the inclination of a sample image with respect to the scanning direction, and Figures 4 and 5 are diagrams of the present invention. FIG. 2 is a diagram for explaining a method for generalizing and implementing the invention. 2... Electron beam, 4... Deflection coil, 6... Sample, 9... Deflection signal rotator, 10... Deflection signal generator, 12... Computer, 15... A/D converter, 16... Image memory, 17...D/A converter, 20...CRT for image display.

Claims (1)

[Claims] 1. A means for scanning a sample with a finely focused electron beam, detecting and storing an image signal generated from the sample by irradiation with the electron beam, and a means for rotating the scanning direction of the electron beam. means for setting a reference straight line L ₀ , and a means for setting a reference straight line L 0 based on sample image signals on at least two parallel straight lines isolated from each other on the sample using the stored image signals. , sample image S for the parallel straight line
means for calculating an inclination angle θ of the inclination angle θ and a reference straight line of the parallel straight line;
A scanning electron microscope characterized by comprising means for calculating and outputting an inclination angle β of a sample image S with respect to a reference straight line L ₀ from an inclination angle α with respect to L ₀ . 2. Claim 1 further comprising means for controlling the deflection means to rotate the scanning direction so that the tilt angle of the sample image S matches the tilt angle of the reference straight line _L0 . Scanning electron microscope as described. 3. The scanning electron beam according to claim 1, further comprising means for visually displaying the amount of rotation in the scanning direction for making the inclination angle of the sample image S coincide with the inclination angle of the reference straight line _L0 . microscope. 4 The reference straight line L ₀ is set to the same inclination angle as the inclination angle of the sample image T whose relative angle to the sample image S is known when the sample image S is aligned in a desired direction, and A scanning electron microscope according to any one of claims 1 to 3, wherein an inclination angle β with respect to a reference straight line L ₀ is calculated. 5. The scanning electron microscope according to any one of claims 1 to 4, wherein the interval I _v and the inclination angle between the parallel straight lines are set by an operator. 6. A scanning electron microscope according to any one of claims 1 to 5, characterized in that the direction of the parallel straight lines coincides with the scanning direction R of the electron beam. 7. The scanning electron microscope according to any one of claims 1 to 6, wherein the reference straight line L ₀ is orthogonal to the scanning direction R. 8. A scanning electron microscope according to any one of claims 1 to 7, wherein only image signals on parallel straight lines are recorded in the storage means.