JP2806242B2 - Alignment mark for electron beam exposure and method for detecting alignment mark for electron beam exposure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam direct writing technique in lithography in LSI manufacturing, and more particularly, to a method of detecting an alignment mark for aligning a sample when writing a pattern on the sample by electron beam exposure. Regarding the alignment mark.

[0002]

2. Description of the Related Art Heretofore, a pattern has been accurately drawn by using an electron beam at a desired position on a sample (such as a semiconductor wafer) as follows. That is, the electron beam is scanned so as to cross a positioning mark (cross-shaped groove) serving as a reference, which is previously arranged (carved) on the sample. The position of the alignment mark is obtained from the obtained reflected electron signal. A pattern is drawn with an electron beam based on the position.

As a reference alignment mark, a mark (projection or groove) having a cross shape and a convex or concave cross section has been generally used. this is,
This is because the position of the alignment mark in the X-axis direction and the Y-axis direction and the rotation angle on the sample can be measured.

FIG. 6 shows a cross mark 1 conventionally used and a mark position detecting method using the cross mark. This detection method is based on four points (four sides:
Four electron beam scans 2 (broken lines in the figure) are performed so as to cross one point (one side) at a time. Then, the mark position 3 (the center of the width of the groove) at the position crossing each side is obtained. Next, two mark positions 3 indicating positions in the X-axis direction,
From the two mark positions 3 indicating the positions in the Y-axis direction, the X-axis position (X coordinate) and the Y-axis direction position (Y coordinate) of the mark center position 4 of the alignment mark 1 are obtained. Further, the rotation angle of the alignment mark 1 is obtained from the four mark positions 3.

FIG. 7 shows a conventional method for obtaining a mark position from a reflected electron signal obtained by the above electron beam scanning. First, the backscattered electron signal 5 shown in FIG.
Is differentiated to obtain a differentiated signal 6 shown in FIG. Next, as shown in FIG. 7C, an absolute value signal 8 is obtained from the differential signal 6. The slice level 7 is set for the absolute value signal 8, and a trigger signal 9 as shown in FIG. 7D is finally obtained. When two mark edge positions 10 are obtained from the trigger signal 9, the center position of the two becomes the mark position 3 (the center of the width of the groove).

[0006]

However, in such a conventional detection method, it is necessary to obtain the center position (X-axis direction position, Y-direction position) of the alignment mark and its rotation angle four times. Electron beam scan 2 was required. Therefore, there is a problem that the detection time becomes long.

[0008] This is because, as shown in FIG. 8, when an unexpected rotation component is generated in the alignment mark 1 (for example, when the sample is rotated and placed), the X-axis direction of the sample,
In the electron beam scanning for each one point in the Y-axis direction, the rotation component of the alignment mark cannot be calculated. As a result, the alignment mark center position obtained by detecting the two points, that is, the virtual mark center position 12, is a position shifted from the true value of the mark center position 4. Therefore, in order to accurately obtain the mark center position 4 and the rotation angle, position detection of a total of four points, two points each in the X-axis direction and the Y-axis direction, that is, four electron beam scans must be performed. did not become.

In the conventional method of detecting a mark position, an LSI manufacturing process such as film formation and etching is used.
As shown in FIG. 9, when the cross-sectional shape of the mark (groove) is asymmetrical with respect to the center line of the groove width, the peak position of the differential signal 6 representing the mark edge position is viewed from the mark center (groove center). The distance is not equal. As a result, when an intermediate position (middle point) between the two mark edge positions 10 obtained from the trigger signal 9 is set as a mark position, a deviation from the true value occurs. That is, in the conventional method, when the cross-sectional shape of the alignment mark is left-right asymmetric with respect to the groove width center line, an error occurs between the measured value of the position and the rotation angle of the alignment mark from the true value. As a result, there is a problem that a pattern cannot be accurately drawn at a desired position on the sample.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of detecting an alignment mark which can reduce the number of times of electron beam scanning and the time required for detecting the number of electron beam scanning. Another object of the present invention is to provide an alignment mark detection method capable of accurately detecting a mark position and a rotation angle even when the cross-sectional shape of the mark becomes asymmetric, and an alignment mark used therefor.

[0010]

The gist of the present invention is to provide a sample
Sample position in electron beam exposure
A method of detecting an alignment mark using an alignment mark of an electron beam exposure used for alignment, wherein the two sides intersect at a predetermined angle with each other
And each of the two sides extends in parallel with a predetermined interval.
A pair of one or more grooves or ridges
Is configured and aligned using alignment marks
When performing mark detection, align each side of the alignment mark
The electron beam scans a straight line that crosses, and the scan result
Corresponding to the pair of two sets of grooves or ridges in the signal waveforms shown in FIG.
Based on the correlation calculation of the symmetry between a pair of signal waveforms
The purpose is to detect the position of the alignment mark .

[0011]

According to a third aspect of the present invention, there is provided an alignment mark detecting method for detecting an alignment mark using the alignment mark according to the first aspect, wherein the alignment mark crosses each side of the alignment mark. It has a scanning step in which the electron beam scans on a straight line, and the signal waveform of the scanning result is
Is the groove or the detection method of the alignment mark of the electron beam exposure for detecting the <br/> group Dzu-out position of the alignment mark on the correlation of the waveform portions corresponding to the ridges of the inner.

[0013]

[0014]

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an alignment mark used in the method for detecting an alignment mark according to the first embodiment of the present invention. FIG. 2 is a flowchart showing the detection procedure.

As shown in FIG. 1, a cross-shaped alignment mark 1 having an arbitrary rotation angle with respect to the X-axis and Y-axis of the sample is previously arranged (carved) on the sample. In this embodiment, 45 degrees is used as the rotation angle of the alignment mark 1. The mark (side) had a groove width of 1 μm and a length of 50 μm. An electron beam scan 2 is performed on the alignment mark 1 so as to cross the two positions in one scan in both the X-axis direction and the Y-axis direction. Two mark positions 3 are detected by one scan. At this time, the electron beam scanning distance is 20 μm.
m. For example, electron beam scanning is performed by driving the XY stage using a normal electron beam direct drawing apparatus.

A procedure for obtaining the center position 4 and the rotation angle of the alignment mark 1 will be described below with reference to the flowchart of FIG. First, electron beam scanning of 20 μm is performed once in the X-axis direction, and X-rays at two points crossing the mark (groove) are obtained.
The position of the mark 3 in the axial direction is determined by signal processing described later (for example, FIG. 4).
(S21). Next, the position of the virtual mark center in the X-axis direction (the midpoint of the two X-coordinates) and the position in the Y-axis direction of the virtual mark are obtained from the obtained two mark positions 3 (S22).

Next, at a point at an arbitrary distance in the X-axis direction from the obtained virtual mark center, 20 μm in the Y-axis direction.
The electron beam is scanned by m, and two mark positions 3 crossing the mark (groove) are measured (S23). Next, from the difference between the two virtual mark positions in the Y-axis direction and the two actually measured positions,
The rotation angle of the alignment mark 1 is determined (S24). Further, a true value of the alignment mark center position 4 is calculated from the obtained rotation angle and the actually measured mark position 3 at each of two points in the X-axis direction and the Y-axis direction (S25).

As described above, conventionally, four electron beam scans have been required to determine the center position and the rotation angle of the alignment mark, whereas the method of the present invention requires only two half scans. As in the conventional case, the position and the rotation angle of the alignment mark can be obtained with high accuracy. As a result, the detection time could be reduced to about half of the conventional one.

Next, a second embodiment of the alignment mark shape and detection method which enables highly accurate mark position detection even when the cross-sectional shape of the mark groove is asymmetrical with respect to the width center line will be described. This will be described with reference to FIGS.

First, as shown in FIG. 3, a well-shaped alignment mark 1 composed of two parallel grooves in both the X-axis direction and the Y-axis direction is arranged at an arbitrary position on the sample. At this time, the width of one mark (groove) was 2 μm, the interval between two parallel marks (grooves) was 5 μm, and the total length was 40 μm.

First, this mark (a side composed of two grooves)
, An electron beam scan 2 is performed for each of two places in the X-axis direction and the Y-axis direction so as to traverse. The electron beam scanning distance at this time was 20 μm.

FIG. 4A shows the alignment marks (grooves).
Is shown. FIG. 4B shows a reflected electron signal 5 obtained when the mark is scanned with an electron beam. Next, the reflected electron signal 5 is differentiated, and a differentiated signal 6 is obtained.
Get. Next, the correlation of the symmetry of the waveform between the signal components obtained from the individual marks in the differential signal 6 is calculated.

That is, the correlation area 14 shown in FIG.
The correlation of the symmetry of the waveform is calculated. As a result, a correlation waveform 15 as shown in FIG. At this time, the point of the minimum value of the correlation waveform is the intermediate position between the two marks (grooves), that is, the position 3 of the alignment mark to be obtained.

At this time, in the conventional method, the left and right edge positions of one mark (groove) are measured to determine the mark position, but in the method of the present invention, the symmetry of the signal obtained from the two marks (groove) is obtained. By focusing on sex and taking a correlation,
A mark center position set at the center position of two marks (grooves) is obtained. For this reason, even if the cross-sectional shape of each mark (groove) becomes asymmetrical left and right, the mark position can be detected accurately.

Further, a third embodiment of the method for detecting an alignment mark according to the present invention will be described with reference to FIG.

As shown in FIG. 5, at an arbitrary position on the sample, it has a cross-girder shape composed of two parallel grooves in the X-axis and Y-axis directions and has an arbitrary rotation angle. The alignment mark 1 is arranged. At this time, the width of one mark is 1 μm, the interval between the two marks is 5 μm,
Further, the rotation angle of the entire alignment mark 1 was 45 degrees.

Then, as described in the second embodiment,
First, an electron beam scan 2 of 20 μm is performed in the X-axis direction so as to cross two marks (grooves) at one time with two marks (grooves) as one set.

Based on the detected position, the center of the virtual mark is determined, and electron beam scanning in the Y-axis direction is performed. The rotation angle of the alignment mark is obtained from the deviation between the detected position and the expected position. The mark position at this time is an intermediate position between the two marks.

Further, the true value of the center position 4 of the alignment mark can be obtained from the detected positions of the X-axis and the Y-axis at two locations and the obtained rotation angle. Further, at this time, even if the cross-sectional shape of each mark is asymmetrical, as shown in the second embodiment, the two marks (2) are obtained from the correlation of the reflected electron signal waveforms obtained from the two marks. Since the mark position set in the middle of the groove is detected, the position of the alignment mark can be accurately detected without being affected by the cross-sectional shape of the groove.

The present invention is not limited to the width and length of the alignment mark of the above embodiment. An alignment mark having another width and length may be used. In addition, when an arbitrary rotation angle is given to the alignment mark in advance, the angle is set to 45 degrees in the above embodiment, but is not limited to this. If the mark can be scanned so as to cross two places of the mark by electron beam scanning, the mark may be rotated to an angle other than this angle.

When the mark position is detected from the correlation of the waveform symmetry, in the second and third embodiments, the mark position is detected from two sets of waveforms obtained from two marks. The present invention is not limited to this. For example, 4
Marks (grooves or ridges) by dividing the four sets of waveforms obtained from a book mark into two sets on the left and right, and calculating the correlation of symmetry.
It is not limited to the number.

Although a cross-shaped or cross-shaped mark (groove or ridge) is used as the shape of the alignment mark, the present invention is not limited to these shapes.
As long as the mark position is detected by electron beam scanning and the mark center position can be determined, for example, a V-shaped, L-shaped, T-shaped alignment mark, or a combination thereof may be used. Further, the distance of the electron beam scanning when detecting the mark position may be any distance that can scan so as to cross the mark position required for position detection. The size of the distance does not matter.

[0034]

By using the method of the present invention, it is possible to detect the center position and the rotation angle of one alignment mark in two steps.
This can be performed by electron beam scanning twice, and the detection time can be reduced to half of the conventional one. Therefore, conventionally, a drawing time of 197 seconds was required for one 6-inch wafer, but in the method of the present invention, it could be reduced to 182 seconds. As a result, the number of drawn wafers per hour was increased from 18 to 20.

[Brief description of the drawings]

FIG. 1 is a plan view showing an alignment mark in electron beam exposure according to a first embodiment of the present invention.

FIG. 2 is a flowchart illustrating a method for detecting an alignment mark according to the first embodiment of the present invention.

FIG. 3 is a plan view showing an alignment mark according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a signal waveform in detection of an alignment mark according to a second embodiment of the present invention.

FIG. 5 is a plan view showing an alignment mark according to a third embodiment of the present invention.

FIG. 6 is a plan view of a conventional alignment mark for explaining a conventional alignment mark and a detection method thereof.

FIG. 7 is a waveform diagram of a detection signal in a conventional detection method.

FIG. 8 is a plan view of an alignment mark for explaining a conventional detection method.

FIG. 9 is a waveform diagram of a detection signal when the cross-sectional shape of a conventional mark is asymmetrical left and right.

[Explanation of symbols]

 1: alignment mark 2: electron beam scanning 3: mark position 4: mark center position

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/027 G03F 9/00

Claims (1)

(57) [Claims] An electron beam exposure for drawing a pattern on a sample.
A method of detecting an alignment mark using an alignment mark of electron beam exposure used for aligning a sample, the alignment mark having two sides intersecting at a predetermined angle with each other. , One of each of the two sides extending in parallel with a predetermined space therebetween
It is composed of a pair of the above grooves or ridges.
The alignment mark using the alignment mark.
When performing detection, a straight line that crosses each side of the alignment mark
The electron beam scans on the line, and the signal wave that is the result of this scan is
One pair corresponding to the pair of two sets of grooves or ridges in the shape
Earth alignment based on correlation calculation of symmetry between signal waveforms
A method for detecting an alignment mark for electron beam exposure, comprising detecting a position of a misalignment mark.