JPH07192994A - Alignment mark of electron-beam exposure and detection method of alignment mark of elctron-beam exposure - Google Patents

Abstract

PURPOSE:To shorten the detection time by a method wherein an alignment mark is detected in an electron-beam exposure operation and the number of scanning operations of an electron beam is reduced more than that in conventional cases when the mark is detected and to detect a position more precisely than in conventional cases even when the cross-sectional shape of a groove for the mark is asymmetrical. CONSTITUTION:An alignment mark 1 to which an arbitrary angle of rotation has been given in advance is arranged on a sample, both the X-axis and the Y-axis are scanned 2 only once by an electron beam in such a way that two parts in the side of the mark are traversed by one scanning operation, and the central position 4 of the alignment mark and the angle of rotation of the sample are found on the basis of the distance between two marks 3 which are obtained regarding them. In addition, a cross-shaped alignment mark which is composed of two parallel grooves is scanned by an electron beam, the correlation between signal components is operated on the basis of the two grooves, and the position detection accuracy of the alignment mark is increased. Even when the alignment mark is arranged so as to be turned on the sample, the number of scanning operations can be reduced to twice. Even when the cross-sectional shape of the grooves for the mark is asymmetrical, the position detection accuracy is not lowered.

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 a lithography technique for manufacturing an LSI, and more specifically to a method for 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 Conventionally, an electron beam was used to accurately draw a pattern at a desired position on a sample (semiconductor wafer or the like) as follows. That is, the electron beam is scanned so as to cross a reference alignment mark (cross-shaped groove) arranged (engraved) on the sample in advance. The position of the alignment mark is obtained from the obtained backscattered electron signal. A pattern is drawn with an electron beam based on the position.

As a reference alignment mark, a cross-shaped mark having a convex or concave cross section (a ridge or a groove) has been generally used. this is,
This is so that 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-shaped mark 1 which has been used conventionally and a mark position detecting method using this cross-shaped mark. This detection method is performed by four points (4 sides: four sides) of the cross-shaped alignment mark 1 previously arranged on the sample.
Electron beam scanning 2 (broken line in the figure) is performed four times so as to cross each groove (point) (one side). Then, the mark position 3 (center of the width of the groove) at the position where each side is crossed is obtained. Next, two mark positions 3 indicating the position in the X-axis direction,
Then, the X-axis direction position (X coordinate) and the Y-axis direction position (Y coordinate) of the mark center position 4 of the alignment mark 1 are obtained from the two mark positions 3 indicating the Y-axis direction position. Further, the rotation angle of the alignment mark 1 is calculated from the four mark positions 3.

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

[0006]

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

This is because, as shown in FIG. 8, when an unexpected rotation component is generated in the alignment mark 1 (when the sample is rotated and placed), the X-axis direction of the sample,
In the electron beam scanning of one point each in the Y-axis direction, the rotation component of the alignment mark cannot be calculated. As a result, the center position of the alignment mark obtained by detecting the two points, that is, the virtual mark center position 12, is a position deviated 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, it is necessary to detect the positions of two points in each of the X-axis direction and the Y-axis direction, that is, four points in total, that is, to perform the electron beam scanning four times. did not become.

Further, in the conventional method for detecting the mark position, an LSI manufacturing process such as film formation and etching
As shown in FIG. 9, when the cross-sectional shape of the mark (groove) is asymmetrical with respect to the groove width center line, the peak position of the differential signal 6 representing the mark edge position is seen from the mark center (groove center). The left and right are not equidistant. As a result, when the intermediate position (middle point) of the two mark edge positions 10 obtained from the trigger signal 9 is set as the mark position, there is a deviation from the true value. That is, in the conventional method, when the cross-sectional shape of the alignment mark is 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 and the true value. As a result, there is a problem that a pattern cannot be drawn accurately 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 electron beam scans and the detection time thereof as compared with the prior art. Another object of the present invention is to provide a method of detecting an alignment mark that enables accurate detection of the mark position and rotation angle even when the cross-sectional shape of the mark is asymmetric, and an alignment mark used for this.

[0010]

According to a first aspect of the present invention, there are provided alignment marks for electron beam exposure used for aligning a sample in electron beam exposure for drawing a pattern on a sample, the alignment marks being at a predetermined angle from each other. Have two sides that intersect each other and each side is composed of at least a pair of portions having a concave or convex cross section, and these portions are alignment marks for electron beam exposure that extend substantially in parallel at a predetermined interval. is there.

According to a second aspect of the present invention, in the method of detecting alignment marks in electron beam exposure, in which a pattern is drawn on the sample by electron beam exposure with reference to the alignment marks on the sample, predetermined angles are set to each other. A step of forming an alignment mark having two sides intersecting each other on the sample, a first scanning step of scanning an electron beam on a straight line crossing the two sides of the alignment mark, and a first scanning step And a second scanning step in which an electron beam scans a straight line which is different from the scanning straight line and which crosses two sides of the alignment mark.

According to a third aspect of the present invention, there is provided an alignment mark detecting method for detecting the alignment mark by using the alignment mark according to the first aspect, which crosses each side of the alignment mark. There is a scanning step in which the electron beam scans on a straight line, and the alignment mark of the electron beam exposure that detects the position of the alignment mark based on the correlation of the signal waveform that is the result of this scanning and is due to the pair of portions. It is a detection method.

According to a fourth aspect of the present invention, the alignment of the electron beam exposure according to the second aspect is performed by using the alignment mark according to the first aspect to perform the first scanning step and the second scanning step. This is a mark detection method.

According to a fifth aspect of the present invention, the center and the rotation angle of the alignment mark are calculated based on the detection results of the first scanning step and the second scanning step. It is the method of detecting the alignment mark for electron beam exposure described above.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an alignment mark used in the alignment mark detection method according to the first embodiment of the present invention. FIG. 2 is a flowchart showing this 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 the Y axis of the sample is previously arranged (engraved) on the sample. In this embodiment, the rotation angle of the alignment mark 1 is 45 degrees. The mark (side) has 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 scanning once. At this time, the electron beam scanning distance is 20μ.
m. For example, the electron beam scanning is performed by driving the XY stage using an ordinary electron beam direct drawing apparatus.

The 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, an electron beam scan of 20 μm is performed once in the X-axis direction, and X at two points crossing the mark (groove) is scanned.
The mark position 3 in the axial direction is subjected to signal processing described later (for example, FIG. 4).
(S21). Next, the X-axis direction position of the virtual mark center (the midpoint of the X-coordinate of the two points) and the Y-axis direction position are obtained from the obtained two mark positions 3 (S22).

Next, at a point separated by 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 positions of the two virtual mark positions in the Y-axis direction and the two measured positions,
The rotation angle of the alignment mark 1 is obtained (S24). Further, the true value of the alignment mark center position 4 is calculated from the obtained rotation angle and the measured mark position 3 at each of the two points in the X-axis direction and the Y-axis direction (S25).

As described above, in the past, in order to obtain the center position and the rotation angle of the alignment mark, four electron beam scans were required. As in the conventional case, the position and the rotation angle of the alignment mark can be accurately obtained. As a result, the detection time could be reduced to about half that of the conventional method.

Next, a second embodiment of the alignment mark shape and detection method capable of highly accurate mark position detection even when the cross-sectional shape of the mark groove is asymmetric with respect to the width center line, This will be described with reference to FIGS. 3 and 4.

First, as shown in FIG. 3, a well-shaped alignment mark 1 composed of two parallel grooves in each of 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 (the side consisting of two grooves)
Electron beam scanning 2 is performed at two points in each of the X-axis direction and the Y-axis direction so as to cross the line, and a backscattered electron signal is obtained. The electron beam scanning distance at this time was 20 μm.

This alignment mark (groove) is shown in FIG.
The cross-sectional shape 13 of is shown. Further, FIG. 4B shows a backscattered electron signal 5 obtained when an electron beam scans the mark. Next, the reflected electron signal 5 is differentiated to obtain a differentiated signal 6
To get Next, the correlation of the waveform symmetry between the signal components obtained from the individual marks in the differential signal 6 is calculated.

That is, the correlation area 14 in FIG.
Compute the correlation of the symmetry of the waveform. As a result, the correlation waveform 15 as shown in FIG. 4D is obtained as the operation output. At this time, the point of the minimum value of the correlation waveform is the intermediate position of 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) were measured to obtain the mark position, but in the method of the present invention, the symmetry of the signals obtained from the two marks (grooves) is obtained. By focusing on sex and taking correlation,
The mark center position set at the center position of the two marks (grooves) is obtained. Therefore, even if the cross-sectional shapes of the respective marks (grooves) are left-right asymmetrical, the mark position can be accurately detected.

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

As shown in FIG. 5, at a desired position on the sample, a cross beam shape constituted by two parallel grooves each in the X-axis and Y-axis directions and having an arbitrary rotation angle was provided. The alignment mark 1 is arranged. At this time, the width of one mark is 1 μm, the distance between the two marks is 5 μm,
Further, the rotation angle of the entire alignment mark 1 is 45 degrees.

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

The virtual mark center is obtained based on the detected position, and electron beam scanning in the Y-axis direction is further 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, it is possible to obtain the true value of the center position 4 of the alignment mark from the detected position at each of the two X-axis and Y-axis positions and the obtained rotation angle. Further, at this time, even if the cross-sectional shapes of the respective marks are left-right asymmetrical, as shown in the second embodiment, as shown in the second embodiment, due to the correlation of the reflected electron signal waveforms obtained from the two marks, 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 sectional shape of the groove.

The present invention is not limited to the width and length of the alignment mark of the above embodiment. Alignment marks having other widths and lengths may be used. Further, when an arbitrary rotation angle is given to the alignment mark in advance, it is set to 45 degrees in the above embodiment, but the present invention is not limited to this. If scanning can be performed so as to cross two points of the mark by electron beam scanning, the mark may be rotated at other angles.

Further, when the mark position is detected from the correlation of the waveform symmetry, in the second and third embodiments, this is detected from the two sets of waveforms obtained from the two marks. The present invention is not limited to this. Eg 4
Marks (grooves or ridges), such as dividing the four sets of waveforms obtained from the book mark into two sets on the left and right, and obtaining the correlation of symmetry
Is not limited to any number.

Further, although the cross-shaped mark or the 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 can be detected by electron beam scanning and the mark center position can be obtained, for example, a V-shaped, L-shaped, T-shaped alignment mark, or a combination thereof may be used. Further, the distance of electron beam scanning for detecting the mark position may be any distance as long as it can scan across the mark position required for position detection. 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.
This can be performed by scanning the electron beam once, and the detection time can be reduced to half that of the conventional method. Therefore, conventionally, the drawing time of 197 seconds was required for each 6-inch wafer, but it could be shortened to 182 seconds by the method of the present invention. As a result, the number of wafers drawn per hour was improved from 18 to 20.

[Brief description of 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 of 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 detecting 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 and a registration mark for explaining a detection method thereof.

FIG. 7 is a waveform diagram of a detection signal in the 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 left-right asymmetric.

[Explanation of symbols]

 1: Positioning mark 2: Electron beam scanning 3: Mark position 4: Mark center position

Claims (5)

[Claims] 1. An alignment mark for electron beam exposure used for aligning a sample in electron beam exposure for drawing a pattern on a sample, which has two sides intersecting each other at a predetermined angle, and each side. Is an alignment mark for electron beam exposure, characterized in that it comprises at least a pair of portions having a concave or convex cross section, and these portions are separated by a predetermined distance and extend substantially in parallel. 2. A method for detecting alignment marks in electron beam exposure in which a pattern is drawn on the sample by electron beam exposure with reference to the alignment marks on the sample, in which two sides intersecting at a predetermined angle are intersected. The step of forming the alignment mark that is provided on the sample, the first scanning step in which the electron beam scans a straight line that crosses two sides of the alignment mark, and the scanning straight line in the first scanning step are different. A second scanning step in which an electron beam scans a straight line that crosses two sides of the alignment mark. 3. A registration mark detection method for detecting a registration mark by using the registration mark according to claim 1, wherein an electron beam scans a straight line that crosses each side of the registration mark. An electron beam exposure alignment mark detection method for detecting the position of the alignment mark based on the correlation of the signal waveform as a result of this scan and the pair of portions. 4. The method of detecting an alignment mark for electron beam exposure according to claim 2, wherein the first scanning step and the second scanning step are performed using the alignment mark according to claim 1. 5. The position of electron beam exposure according to claim 2, wherein the center and the rotation angle of the alignment mark are calculated based on the respective detection results in the first scanning step and the second scanning step. Alignment mark detection method.