JPH08115959A - Electron beam system and measuring method employing electron beam - Google Patents

Abstract

PURPOSE: To realize an electron beam system and a measuring method employing electron beam for detecting an edge with high accuracy. CONSTITUTION: Adder/subtractor circuits 21, 22 delivers a following output; x.cosθ+y.sinθ-x.sinθ+y.cosθ. Output from the adder/subtractor circuit 21 is fed through an amplifier 9x to a deflector 7x in x-direction whereas an output from the adder/subtractor circuit 22 is fed through an amplifier 9y to a deflector 7y in y-direction. Consequently, the electron beam performs scanning in the direction perpendicular to the edge face of an inclining pattern.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam apparatus which scans an electron beam on a sample and measures the length of a pattern or the like on the surface of the sample based on the signal obtained by the scanning. The present invention relates to a length measuring method using an electron beam.

[0002]

2. Description of the Related Art A scanning electron microscope is used to measure the width of a pattern on an IC and the diameter of a contact hole. In this case, the electron beam is scanned on the measured pattern or the hole, and the reflected electron signal and the secondary electron signal generated based on this scanning are detected. Since this detection signal has a peak at the edge portion of the pattern or hole, the width of the pattern and the diameter of the hole are determined based on the scanning width of the electron beam between the peaks.

[0003]

FIG. 1A shows an IC pattern, and this elongated pattern P has an inclination angle α. When measuring the width of such a pattern P, the electron beam is two-dimensionally scanned in the X and Y directions in the drawing. 2 obtained based on this electron beam scanning
The secondary electron or the like is detected, and the width of the pattern P is obtained from the peak position of the detection signal. In this case, the X and Y of the electron beam
In the directional scanning, since the electron beam scanning is not orthogonal to the edge surface of the pattern, the measurement detection accuracy is lowered.

This point will be further described with reference to FIG. 2A and 2B, the horizontal axis represents the scanning position of the electron beam and the vertical axis represents the signal intensity. FIG. 2A shows the case where the edge of the pattern and the scanning line of the electron beam are orthogonal to each other, and a sharp peak signal can be obtained. On the other hand, FIG. 2B shows a case where the pattern edge and the scanning line are not orthogonal to each other. In this case, when the inclination angle of the pattern edge is α, the peak is tan α in the measurement direction (electron beam In the scanning direction).

Further, FIG. 1B shows a contact hole H. An electron beam is scanned in the X and Y directions with respect to this hole H, and the contact hole H is generated from the sample by the scanning.
For example, secondary electrons are detected. In this case, the width between the peaks of the detection signal becomes maximum at the time of scanning with the electron beam of Xm in the X direction, and this width is the X of the contact hole H.
The diameter is Hx in the direction. In the Y direction, the width between the peaks of the detection signal becomes maximum at the time of scanning with the electron beam of Ym, and this width is the diameter Hy of the contact hole H in the Y direction.
It is said.

Recently, it has been required to measure not only the diameters of the contact holes in the X and Y directions but also the roundness thereof. In the case of measuring the roundness, in addition to the measurement of the diameter Hx in the X direction and the diameter Hy in the Y direction, each edge information of the contact hole is obtained by each scanning line. However, scan lines Xk and X
In the case of n, the angle between the edge surface of the contact hole and the scanning direction is 45 °, and at such an edge, the measurement accuracy deteriorates as described above.

The present invention has been made in view of the above circumstances, and an object thereof is to realize an electron beam apparatus capable of detecting an edge with high accuracy and a measuring method using the electron beam. .

[0008]

An electron beam apparatus according to the present invention scans an electron beam, differentiates a signal obtained by the scanning, and differentiates the peak position of the differentiated signal from the width and length of a pattern. , Or, in an electron beam apparatus for measuring the shape of a pattern, etc., assuming that the coordinates rotated by an angle θ with respect to the scanning reference coordinates x, y are X and Y, coordinate conversion is performed based on the equation X = xcos θ + y sin θ Y = −x sin θ + y cos θ. It is characterized in that the electron beam scanning is performed.

The measuring method using an electron beam according to the present invention scans the electron beam, differentiates the signal obtained by this scanning, and determines the width or length of the pattern from the peak position of the differentiated signal, or In the method of measuring the shape of the pattern, etc., the inclination angle of the edge of the measured pattern is obtained in advance, and the coordinate rotation angle θ for scanning the electron beam perpendicularly to the edge of the measured pattern is calculated from this inclination angle. Letting X and Y be coordinates that are obtained and rotated by an angle θ with respect to the reference coordinates x and y for scanning, the coordinate conversion is performed based on the formula X = xcos θ + ysin θ Y = −xsin θ + ycos θ, and the electron beam is scanned.
The feature is that the measured length pattern is measured.

The measuring method using an electron beam according to the present invention scans the electron beam, differentiates the signal obtained by this scanning, and determines the width or length of the pattern from the peak position of the differentiated signal, or In the method of measuring the shape of a pattern, etc., the center of the elliptical pattern to be measured is obtained in advance, and the electron beam is scanned through this center almost perpendicularly to the circumferential edge. Angle θ
When the rotated coordinates are X and Y, the electron beam is scanned by sequentially changing the value of θ based on the equation X = xcos θ + ysin θ Y = −xsin θ + ycos θ, and the measured circular pattern is measured. It is characterized by that.

[0011]

In the present invention, assuming that the coordinates rotated by the angle θ with respect to the scanning reference coordinates x and y are X and Y, the coordinate conversion is performed based on the formula X = xcos θ + y sin θ Y = −x sin θ + y cos θ to scan the electron beam. To do.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 3 shows a scanning electron microscope which is an embodiment of the present invention, and 1 is an electron gun. The electron beam EB generated from the electron gun 1 is finely focused on the sample 4 by the focusing lens 2 and the objective lens (final stage focusing lens) 3. Excitation current is supplied to the objective lens 3 from the computer 5 via the objective lens control unit 6. Also,
The electron beam EB is deflected by the deflector 7, and the sample 4
The irradiation position of the upper electron beam is scanned. A scanning signal is supplied to the deflector 7 from the computer 5 via the electron beam deflection unit 8 and the amplifier 9.

Secondary electrons generated by the irradiation of the sample 4 with the electron beam are detected by the secondary electron detector 10. The detection signal of the detector 10 is amplified by the amplifier 11 and then supplied to the frame memory unit 12. The frame memory unit 12 executes cumulative addition of the signals detected based on the repeated scanning of the electron beam based on the signal from the electron beam deflection unit 8. The signal stored in the frame memory unit 12 is appropriately read out, converted into an analog signal by the DA converter 13, and then supplied to the signal differentiating unit 14 to be subjected to a differentiating process. The differential output of the signal differentiating unit 14 is supplied to the computer 5.

FIG. 4 shows the details of the electron beam deflection unit 8, the amplifier 9 and the deflector 7 described above. The electron beam deflection unit 8 is a deflection output unit 1 to which scanning position signals in the X and Y directions are respectively supplied from the computer 5.
5, 16 and DA with respect to the angle θ given from the computer 5, the values of cos θ and sin θ are supplied, respectively.
It has converters 17, 18. Further, the electron beam deflection unit 8 includes arithmetic circuits 19 and 20, adder / subtractors 21 and 2.
Have two. The output of the adder / subtractor 21 in the electron beam deflection unit 8 is supplied to the X-direction amplifier 9x and then to the X-direction deflector 7x, and the output of the adder / subtractor 22 is supplied to the Y-direction amplifier 9y and then Y. It is supplied to the directional deflector 7y. The operation of such a configuration will be described below.

When observing a normal secondary electron image, the computer 5 controls the electron beam deflection unit 8 and supplies a predetermined two-dimensional scanning signal from this unit 8 to the deflector 7. As a result, an arbitrary two-dimensional area on the sample 4 is raster-scanned by the electron beam EB. Secondary electrons generated by irradiating the sample 4 with the electron beam are detected by the detector 10. The detection signal is supplied via an amplifier 11 to a cathode ray tube (not shown) synchronized with the scanning signal to the deflector 5, and a secondary electron image of an arbitrary region of the sample is displayed on the cathode ray tube.

Next, the length measuring operation of the tilt pattern as shown in FIG. 5A will be described. First, the electron beam is scanned in the length-measuring portion of the sample 4, and this scanning is conventionally performed in the X and Y directions based on an instruction from the computer 5 to the electron beam deflection unit 8. Secondary electrons generated from the sample 4 based on the scanning of the electron beam are detected by the secondary electron detector 10. The detection signal is amplified by the amplifier 11 and then supplied to the frame memory unit 12 for storage.

The scanning of the electron beam is repeatedly executed, and the secondary electron signal detected each time is stored for each coordinate position of the frame memory unit 12 on the basis of the signal from the electron beam deflecting unit 8 and accumulated. It The SN ratio of the signal is improved by this cumulative addition processing.
Based on the signal stored in the frame memory unit 12, the computer 5 obtains the tilt angle of the tilt pattern when it is the object of length measurement. That is, the signals stored in the frame memory unit 12 are sequentially read out, converted into analog signals by the DA converter 13, and then supplied to the signal differentiating unit 14. The differentiated signal is supplied to the computer 5. The computer 5 recognizes the peak position of the differentiated signal and obtains the peak coordinates of each scanning line. The tilt angle α of the tilt pattern shown in FIG. 5A is obtained from the peak coordinate value of each scanning line.

Next, the computer 5 calculates a rotation angle θ in the scanning direction of the electron beam for scanning the electron beam perpendicularly to the edge surface of the tilt pattern with respect to the tilt angle α of the tilt pattern thus obtained. Note that the relationship between α and θ is θ
= Α ± (π / 2). By the way, the scanning direction is angle θ
The deflection signal for rotation can be converted by using a general coordinate conversion formula.
That is, when the Cartesian coordinates x and y shown in FIG. 6 are converted into the coordinates X and Y by rotating the angle θ with the origin O as it is, the following formula is established between them.

X = Xcos θ−Y sin θ y = X sin θ + Y cos θ The above equation can be rewritten as follows.

X = xcos θ + y sin θ Y = −x sin θ + y cos θ In the case of the inclined pattern of FIG. 5A, in order to scan the electron beam perpendicularly to the edge surface of the pattern, the electron is moved by the new orthogonal coordinates X and Y rotated by the angle θ. The beam may be scanned. Therefore, when the rotation angle θ in the scanning direction is obtained, the computer 5 supplies the deflection outputs x and y to the deflection output units 15 and 16, and also supplies the value of cos θ to the DA converter 17 to obtain the value of sin θ. To DA converter 1
Supply to 8. The deflection output unit 15 DA-converts the supplied signal and supplies it to the arithmetic circuit 19. Arithmetic circuit 19
Is the deflection output x and c supplied from the DA converters 17 and 18.
From the values of osθ and sinθ, x · co
It outputs sθ and −x · sin θ. In addition, the arithmetic circuit 2
0 is the deflection output y and the values of cos θ and sin θ supplied from the DA converters 17 and 18, and y · c
It outputs osθ and −y · sin θ.

The respective outputs from the arithmetic circuits 19 and 20 are supplied to the addition / subtraction circuits 21 and 22, and the following outputs are obtained from the addition / subtraction circuit 21. On the other hand, the following output is obtained from the adder / subtractor circuit 22.

The output from the adder / subtractor circuit 21 is supplied to the deflector 7x in the x direction via the amplifier 9x, and the output from the adder / subtractor circuit 22 is supplied to the deflector 7y in the y direction via the amplifier 9y. Since it is supplied, the electron beam is scanned in the direction perpendicular to the edge surface of the inclined pattern. Therefore, the peak signal obtained based on the signal detected by such scanning becomes extremely sharp, and the pattern width can be measured with high accuracy.

Next, the length measuring operation of the contact hole H shown in FIG. 5B will be described. First, the center coordinates of the contact hole are obtained. The center coordinates are the intersections of the centers of the diameters of the hole H in the X direction and the Y direction. That is, FIG.
In (b), O is the center of the desired hole H. An electron beam is scanned in the scanning direction passing through the center O with respect to the contact hole H and having an angle of θ with respect to the X axis. Therefore, the electron beam deflection unit supplies the scanning signal to the deflector at the coordinates rotated by the angle θ. Such scanning is performed by sequentially changing the value of the angle θ. As a result, a large number of electron beams having different angles θ passing through the center O of the contact hole H are scanned. The secondary electron detection signal obtained based on each scan is differentiated, and the position of the circumferential edge of the contact hole H can be recognized in polar coordinates from the peak position of this differential signal. In this case, since the scanning of the electron beam is performed almost perpendicularly to each edge of the contact hole H, the peak of the differential signal becomes extremely sharp, and the edge position can be obtained extremely accurately. The shape distortion of the contact hole and the direction of the distortion (longitudinal direction of elliptic approximation) can be calculated from the obtained polar coordinates.

Although one embodiment of the present invention has been described in detail above, the present invention is not limited to this embodiment. For example, although secondary electrons are detected, reflected electrons may be detected.

[0025]

As described above, in the present invention, the coordinates rotated by the angle θ with respect to the scanning reference coordinates x and y are converted into X and Y.
Then, the coordinate conversion is performed based on the equation X = xcos θ + y sin θ Y = −x sin θ + y cos θ to scan the electron beam. As a result, the electron beam can be scanned perpendicularly to the edge of a pattern such as an inclined pattern to be measured or a contact hole, and accurate measurement such as length measurement can be performed.

[Brief description of drawings]

FIG. 1 is a diagram showing a tilt pattern and a contact hole to be measured.

FIG. 2 is a diagram showing a peak waveform of a differential signal of a detection signal.

FIG. 3 is a diagram showing an example of an electron beam length measuring apparatus for carrying out the present invention.

FIG. 4 is a diagram showing details of the electron beam deflection unit of the embodiment of FIG.

FIG. 5 is a diagram showing a tilt pattern and a contact hole to be measured.

FIG. 6 is a diagram for explaining coordinate rotation conversion.

[Explanation of Codes] 1 electron gun 2 focusing lens 3 objective lens 4 sample 5 computer 6 objective lens control unit 7 deflector 8 electron beam deflection unit 9 amplifier 10 secondary electron detector 11 amplifier 12 frame memory unit 13 DA converter 14 Signal differentiation unit 15,16 Deflection output unit 17,18 DA converter 19,20 Operation circuit 21,22 Addition / subtraction circuit

Claims (3)

[Claims] 1. An electron beam apparatus for scanning an electron beam, differentiating a signal obtained by the scanning, and measuring the width and length of a pattern or the shape of a pattern from the peak position of the differentiated signal. , Scanning reference coordinates x, y
An electron beam apparatus configured to perform coordinate conversion based on the equation X = xcos θ + y sin θ Y = −x sin θ + y cos θ for scanning the electron beam, where X and Y are coordinates rotated by an angle θ. 2. A method of scanning an electron beam, differentiating a signal obtained by the scanning, and measuring the width and length of a pattern or the shape of a pattern from the peak position of the differentiated signal, The tilt angle of the edge of the measured pattern is obtained, and the coordinate rotation angle θ for scanning the electron beam perpendicularly to the edge of the measured pattern is obtained from this tilt angle, and with respect to the reference coordinates x and y for scanning. Then, assuming that the coordinates rotated by the angle θ are X and Y, the coordinate conversion is performed based on the equation X = xcos θ + y sin θ Y = −x sin θ + y cos θ to scan the electron beam,
A measurement method using an electron beam adapted to measure a measured length pattern. 3. A method of scanning an electron beam, differentiating a signal obtained by this scanning, and measuring the width or length of a pattern or the shape of a pattern from the peak position of the differentiated signal, The center of the measured elliptical pattern is determined, and the electron beam is scanned through this center almost perpendicularly to the circumferential edge. Then, a measurement method using an electron beam configured to measure the elliptical pattern to be measured by scanning the electron beam while sequentially changing the value of θ based on the formula X = xcos θ + ysin θ Y = −xsin θ + ycos θ.