JPS62110248A - Correction method for rotational angle and device thereof - Google Patents

Abstract

PURPOSE:To correct the rotation of an image rapidly and easily by correcting the scanning direction of the electron beam of an electron microscope according to the rotational angle of a measured object. CONSTITUTION:The neighborhood of a positioning reference 10 is illuminated by a light source 13 and the inclination angle of an orientation flat 21 to the positioning reference 10 is detected by a pair of one-dimensional image sensors 14a, 14b mounted on the both end parts of said positioning reference 10. An angle computing unit 16 feeds out a correction signal correcting the deflection of an electron beam 2 to a deflection controlling part 17 on the basis of the detected values. Deflecting current waveform 25 in Y-direction varies uniformly during one period Ty of Y-direction scanning as shown by broken line in the case with no correction, but in the case with correction by correction signal varies staircasewisely corresponding to one period Tx of X-direction and corrects the scanning direction of the electron beam, thereby correcting the rotation of a pattern image 20 on a screen 19 caused by the rotation of a semiconductor wafer W by an angle theta so that the pattern image may be in parallel state to X-axis and Y-axis.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a rotation method for correcting rotational deviation of an object to be measured, which occurs when measuring the dimensions of an object to be measured, such as a pattern formed on a semiconductor wafer, using an electron microscope. The present invention relates to an angle correction method and device.

[Technical background of the invention and its problems]

With the increasing density of semiconductor integrated circuits, the patterns formed on the surface of semiconductor wafers are becoming increasingly finer, and it is now necessary to measure the width of these patterns with high speed and high precision during the design and manufacturing process. .

Normally, the dimensions of minute components such as semiconductor integrated circuit patterns are measured using optical means, such as a micrometer using an optical microscope, or an electronic measuring device that combines an optical microscope and a carrier camera. The measuring instruments used are widely used. However, when the pattern size becomes submicron size,
Due to the resolution, it is difficult to measure this with a measuring instrument using optical means.

Measuring instruments using non-optical means, especially those using scanning electron microscopes, can measure even such fine patterns in terms of resolution, and can in principle achieve high precision by setting the magnification appropriately. It is possible to measure

Measurement of pattern dimensions using an electron microscope involves positioning and mounting a semiconductor wafer on a table, scanning the pattern-forming surface with an electron beam, displaying the image information obtained on the screen of a display device, and displaying image information on the screen of a display device. This can be obtained by sandwiching the displayed measurement pattern image between, for example, one sentence/one cursor line and measuring the cursor line interval. However, if the pattern image displayed on the screen is tilted in the measurement direction with respect to the pair of cursor lines, a cosine error will occur, making accurate measurement difficult. Therefore, normally, a rotary table is set aside and correction is made by manually rotating the rotary table while looking at the pattern image on the screen to eliminate the inclination.

However, when the rotation of the pattern image is corrected using this method, when the desired pattern to be measured is on the central axis of the rotary table, the pattern image on the screen will not move much even if the rotary table is rotated. It can be measured relatively easily. However, as the desired pattern moves away from the central axis of the rotary table, the movement of the pattern image on the screen increases, and the pattern to be measured is usually located at a position far from the central axis of the rotary table. In order to correct the rotation of the image of the pattern at a distant position, the x-y stage supporting the table and the rotary table must be repeatedly moved alternately.
The operation becomes complicated and correction takes time. Also, the table structure becomes complicated.

[Object of the Invention] The present invention is necessary to quickly and easily correct the rotation of an image of an object to be measured that is obtained on the screen of a display device by electron beam scanning of an electron microscope.

(Summary of the Invention) This invention positions and mounts an object to be measured on a table provided with a positioning reference, and scans the object to be measured with an electron beam of an electron microscope. When correcting the rotation, an angle detector detects the rotation of the object being measured by one inch toward the positioning base, calculates the rotation angle from the detection output, and adjusts the electron beam of the electron microscope based on this rotation angle. By correcting the scanning direction of the image, the rotation of the image can be corrected quickly and easily.

(Embodiments of the Invention) The present invention will be described below based on embodiments with reference to the drawings.

FIG. 1 shows the configuration of a rotation angle correction device used in an apparatus for measuring pattern dimensions of a semiconductor wafer using a scanning electron microscope, which is an embodiment of the present invention, and FIG. 2 shows the configuration of a scanning electron microscope. . This scanning electron microscope focuses an electron beam ■ emitted from an electron gun (G) with an electron lens system ■ installed in the emission direction, and deflects the focused electron beam ■ with a deflection device (B). Then, the pattern surface of the object to be measured, that is, the semiconductor wafer (W) in this example, which is positioned on table 0, is scanned in the x and Y directions, and secondary electrons ( 6) is captured by the secondary electron detector ■ and displayed on the display device (8
) is configured to display the image on the screen. The pattern dimensions are measured by, for example, sandwiching the pattern image displayed on the screen between a pair of cursor lines that can be moved arbitrarily on the screen and measuring the distance between the pair of cursor lines.

The table 0 is provided with a band-shaped positioning reference (lΦ) extending in the Y direction on its table surface, and the semiconductor wafer (W) mounted on the table 0 is placed on the wafer (-
) is positioned so that the orientation flat formed in the positioning reference 0Φ intersects with the side edge of the positioning reference 0Φ. In addition, this table 0 is installed on an XY stage that can be moved arbitrarily in the XY directions so that the desired pattern image of the positioned semiconductor wafer (W) can be displayed on the screen of the display device (8). It is being

A light source 0 is provided on the positioning reference αΦ to illuminate the vicinity of the positioning reference θΦ, and a light source 0 is provided on both ends of the positioning base 1I (I@) in a direction perpendicular to the longitudinal direction of the positioning reference 0Φ. Angle detector O0 consisting of a pair of elongated one-dimensional image sensors (14a) and (14b)
is set up. This pair of image sensors (14
The outputs of a) and (14b) are sent to the angle calculation device CΦ, and based on the calculation results, this angle calculation device (1
Therefore, a correction signal for correcting the scanning direction of the electron beam is sent to a deflection control section (b) that controls the deflection device (a) of the electron microscope.

Next, a method for correcting the rotation angle in pattern dimension measurement of a semiconductor wafer (hip) using this scanning electron microscope will be described.

First, a semiconductor wafer is positioned on table 0 with reference to the positioning reference 0Φ, and an electron beam (■) emitted from an electron gun (■) of an electron microscope is deflected to form a pattern on the semiconductor wafer (back). Position the surface above using the reference 0Φ
Scan sequentially in a direction parallel to and perpendicular to the longitudinal direction of
The pattern image is displayed on the screen of the display device (c).

A desired pattern to be measured can be displayed on the screen by moving the XY stage using a drive device (not shown). Usually, a pattern on a semiconductor wafer (hip) is formed with an orientation flat as a reference, and has a large number of patterns parallel and perpendicular to this orientation flat. therefore,
The orientation flat of this semiconductor wafer (IJ) is the positioning reference 0
If the pattern image (a) on the screen (to) is correctly positioned and mounted on the table (to) so as to be in close contact with the side of X axis,
Displayed parallel to the Y axis. However, Fig. 4 ′−
As shown in , when the semiconductor wafer (stomach) undergoes a rotational shift and its orientation flat (20) is positioned at an angle with respect to the positioning base Q-O, the inclination angle θ (rotation angle of the semiconductor wafer) Correspondingly, as shown in Figure 5, a pattern image rotated by θ with respect to the X and Y axes is also displayed on the screen.
is displayed.

Such a pattern image G! In order to correct the rotation of φ, in this rotation angle correction method, the light source 03) is turned on to illuminate the vicinity of the positioning reference αΦ, and a pair of one-dimensional image sensors (14a
), '(14b), the above positioning reference (1φ
Detect the inclination angle of the orientation flat (20) with respect to the semiconductor wafer (-).In order to obtain accurate detection, make the reflectance of the positioning reference 0Φ and the table 0 different from that of the semiconductor wafer (-), or
Alternatively, it is preferable to create an orientation flat (2D sharp shadow) by illuminating the light source 03).

At this time, each -dimensional image sensor (14a>(
Detection information (22a) 't (
22b) (7) Indicates level change. Each detection information (22
a), the rising part (23) of the level in (22b)
) are each of the -dimensional image sensors (14a), (14
b) shows the position of the Oricra CD with respect to the longitudinal direction; Therefore, as shown in FIG. 4, positioning We(
If the orientation flat (20 is tilted at an angle θ with respect to 1Φ, -
Signal (22) obtained from the dimensional image sensor (14a)
A difference shown by t is generated between the rise of signal (22b) obtained from the one-dimensional image sensor (14b) and the rise of signal (22b) obtained from the one-dimensional image sensor (14b).
The inclination angle θ is -dimensional image sensor (14a)',
If the interval in (14b) is d, it is expressed by the formula 0.

θ=jan-1-・・・・・・・・・■ Therefore, the angle calculation device 0Φ first calculates the detection information (22a) of the pair of one-dimensional image sensors (14a) and (1ab).
, t is calculated from (22b), and then θ is calculated using equation U) from this value of 1 and the value of d stored in the memory. Then, based on the value of θ, a correction signal for correcting the deflection of the electronic beam (2) is sent to the deflection control unit (2).

FIG. 7 shows the current waveform of the deflection device modulated by this correction signal. In contrast to the deflection current waveform (24) in the X direction shown in the figure (A), the deflection current waveform in the Y direction is as shown in the figure (B). In other words, the polarized current waveform in the Y direction (
25) changes uniformly during one cycle of scanning in the Y direction of the electron beam Ty as shown by the broken line when there is no correction, but when it is corrected by the above correction signal, one cycle of scanning in the X direction Tx changes uniformly.
The rotation of the pattern image Q width on the screen θΦ caused by the semiconductor wafer (W) being rotated by an angle θ by correcting the scanning direction of the electron beam (as shown in Figure 5)
is corrected to the Y axis shown in FIG. 3 and to a state parallel to the Y axis.

Note that the pattern dimensions are measured using the display device (as described above).
After correcting the rotation of the pattern image CΦ of the desired pattern displayed on the screen O$ in step 8), this is done by aligning a pair of cursor lines with the pattern image (2Φ).

When the rotation of the pattern image obtained on the screen of the display device (8) is corrected by the electron beam scanning of the electron microscope as described above, the angle detector θΦ automatically positions the semiconductor wafer (W ) is detected and the scanning direction of the electron beam (2) of the electron microscope is corrected based on the detected information, so the rotation of the pattern image can be corrected quickly and easily. In other words, in the conventional method, a rotary table must be provided in addition to the XY stage, and the rotary table and XY stage must be moved while viewing the pattern image displayed on the screen to make adjustments so that the pattern image does not rotate. However, according to the method of the present invention, the burden on the operator can be significantly reduced and the time required for the correction can be significantly shortened.

Next, other embodiments will be described.

In the above embodiment, the positioning reference provided on the table is constructed in the form of a strip, but the positioning reference may also be comprised of pins spaced apart by a certain distance. Further, the direction of the positioning reference is not particularly limited to the Y direction.

In addition, when the semiconductor wafer pattern is inclined at a certain angle α with respect to the orientation flat, the staking angle must be
By storing the pattern image in the memory of the angle calculating device, the pattern image can be displayed on the screen of the display device as in the above embodiment.

Furthermore, although the above embodiments have been described using a scanning electron microscope, the present invention can also be applied to a transmission electron microscope.

Although the above embodiments have been described with respect to measuring the pattern dimensions of a semiconductor wafer, the present invention can also be applied to measuring the dimensions of objects to be measured other than semiconductor wafers.

(Effects of the Invention) An object to be measured is positioned and mounted on a table provided with a positioning reference based on the positioning reference, and the object to be measured is scanned with an electron beam of an electron microscope to obtain an image on a display device. When correcting the rotation of the object, the rotation of the object relative to the positioning standard is detected by an angle detector, and the rotation angle is calculated from the detected output to correct the scanning direction of the electron beam of the electron microscope. The rotation of the image of the object to be measured obtained by the apparatus can be quickly and easily corrected.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a rotation angle correction device provided in a semiconductor wafer pattern size measuring device using a scanning electron microscope, which is an embodiment of the present invention, and FIG. 2 is a diagram showing the configuration of the scanning electron microscope. 3 is a diagram showing a pattern image displayed on the screen of the display device when the semiconductor wafer is correctly positioned, and FIG. 4 is a diagram for explaining a method for detecting the rotation angle of the semiconductor wafer with respect to the positioning reference Figure 5 is a diagram showing a pattern image displayed on the screen of the display device when the semiconductor wafer is rotated and positioned with respect to the positioning reference, and Figure 6 is a diagram showing detection information of the angle detector. , FIGS. 7(A) and 7(B) are diagrams showing the waveforms of the X-direction deflection current and the Y-direction deflection current flowing through the deflection device, respectively.

Claims (3)

[Claims] (1) The object to be measured is mounted on a table provided with a positioning reference with reference to the positioning reference, and the object to be measured is scanned with an electron beam of an electron microscope, and the result is displayed on the display device. In a rotation angle correction method for correcting the rotation angle of an image, an angle detector detects the rotation of the object to be measured relative to the positioning reference, and the detection information output from the angle detector is processed to determine the positioning reference. A rotation angle correction method comprising: calculating a rotation angle of the object to be measured with respect to the rotation angle; and correcting a scanning direction of the electron beam based on the rotation angle. (2) An angle detector that is provided on a positioning reference provided on a table on which the object to be measured is mounted and detects the rotation of the object to be measured that is mounted on the table with respect to the positioning reference, and the output of this angle detector. is calculated to calculate the rotation angle of the object to be measured with respect to the positioning reference, and based on this rotation angle, the scanning direction of the electron beam is sent to an electron beam deflection control section of an electron microscope that scans the object to be measured. A rotation angle correction device comprising: an angle calculation device that sends out a correction signal to be corrected. (3) The rotational angle correction device according to claim 2, wherein the angle detector includes a pair of one-dimensional image sensors separated by a certain period of time.