JPH029281B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an improvement in a mark position detection device that detects the center position of a mark by scanning an alignment mark with an electron beam.

Technical background of the invention and its problems Recently, various electron beam exposure devices have been used to form fine patterns on samples such as semiconductor wafers and mask substrates, but these devices do not allow accurate exposure. Therefore, highly accurate positioning of the sample is required. For this purpose, alignment marks are provided on the sample, cassette, sample stage, etc., and the mark position is detected based on reflected electrons, secondary electrons, or absorbed electrons obtained by scanning this mark with an electron beam. I try to align the sample.

By the way, as a mark position detection device used for detecting the mark position, one that utilizes the following methods (1) and (2) has recently been devised.

(1) From the peak of the mark signal obtained by detecting the reflected electrons from the mark and the reference value, the mark signal is binarized at a level such that the mark part obtains a binary signal of "1", and a binary signal is generated. A method of determining the center position of the mark by calculating the first moment from ``1'' and the scanning position of the electron beam.

(2) The mark signal is A/D converted and stored in a storage circuit, and the electron beam is scanned a plurality of times to average the A/D converted values of the mark signal and remove noise components. The slice level is determined from the P·P value (Poak to Peak) of the mark waveform thus obtained, and the first moment is calculated from the A/D conversion value of the mark waveform above the slice level and the scanning position of the electron beam. A method to find the center position of a mark.

However, the mark position detection device using this type of method has the following problems.
That is, in the first method, since only a part of the mark signal is used, the detection accuracy of the mark center position is poor. Furthermore, in the second method, A/
It takes a lot of time to average and add the D-converted mark waveforms, and a storage circuit is required for this purpose, which causes problems such as increased costs.

Therefore, the present inventors detected reflected electrons, secondary electrons, or absorbed electrons obtained by scanning alignment marks with an electron beam using an electron detector, and set the differential waveform of this detection signal to a predetermined amplitude threshold value X ₀ The place where the time series of the differential waveform with a threshold value of X ₀ or more is continuous with a predetermined continuous time series threshold of G ₀ or more is determined to be the mark end, and the amplitude value of the above detection signal at this time is determined as the mark end.
We propose a mark position detection device that stores X _A , calculates the first moment from the amplitude value of a detection signal larger than the amplitude value X _A and the scanning position of the electron beam, and detects this calculation result as the center position of the mark. did.

According to this proposal, the information of the entire mark signal can be used without waste, and the mark center position can be detected with high accuracy. Further, there is no need to perform average addition, no memory is required for this purpose, and furthermore, no time is required for average addition. Furthermore, since the calculation is performed simultaneously with the electron beam scanning, there are advantages such as the time required to detect the mark center position can be shortened.

However, in such a device, a complicated circuit is required to determine the calculation range of the first moment, resulting in a complicated device configuration. Further, there was a problem that the accuracy of detecting the center position of the position detection mark decreased due to the above calculation range.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a mark position detection device that does not require limiting the range for calculating the first-order moment and can simplify the device configuration and improve mark position detection accuracy.

Summary of the Invention The present invention scans a mark used for position detection with an electron beam, detects reflected electrons, secondary electrons, or absorbed electrons caused by the scanning with an electron detector to obtain a mark signal, and uses a delay circuit and a subtracter. etc., to find the absolute value of the difference between the mark signal and a delayed signal obtained by delaying the mark signal by a predetermined time T, and calculate the absolute value and the scanning position of the electron beam using a multiplier, a cumulative adder, a subtracter, etc. The first moment is obtained from the first moment, and 1/2 of the electron beam scanning distance corresponding to the time T is subtracted from the first moment using a subtracter to detect the center position of the mark.

Effects of the Invention According to the present invention, the center position of a mark can be detected by using various arithmetic units without requiring a complicated circuit for determining the calculation range of the first moment. Therefore, it is possible to simplify the device configuration and improve mark position detection accuracy.

Embodiment of the Invention FIG. 1 is a block diagram showing a schematic configuration of an embodiment of the present invention. Reference numeral 1 in the figure is a positioning mark, and reflected electrons from the mark 1 obtained when the mark 1 is scanned by an electron beam 2 are detected by a reflected electron detector 3. Here, the detection signal (mark signal) 4 of the backscattered electron detector 3 has a large amplitude when the electron beam 2 crosses the mark 1 as shown in FIG. The mark signal 4 is supplied to an analog-to-digital converter (hereinafter abbreviated as A/D) 5 and converted into a digital signal.
This conversion output X is directly supplied to a subtracter 7, and a delay circuit (hereinafter abbreviated as DL) 6
The subtracter 7 is delayed by a certain time T via
is supplied to The subtracter 7 calculates the difference X- between the conversion output X of the A/D 5 and the delayed signal
X′ is calculated. This difference output X-X' is supplied to a subtracter 9 via an absolute value circuit 8. A set value P for noise removal is inputted to the subtracter 9 together with the output |X−X'| of the absolute value circuit 8. Then, a signal a from which noise has been removed from the absolute value output |X-X'| by the subtracter 9 is supplied to the first cumulative adder 10 and the multiplier 11.

On the other hand, a signal x indicating the position of the electron beam is supplied to the multiplier 11. In the multiplier 11, the signal a and the signal x are multiplied, and this multiplication output a.x
is supplied to the second cumulative adder 12. In the second cumulative adder 12, the multiplication outputs a and x are cumulatively added. This cumulative addition output Σa·x is then supplied to the divider 13. Further, in the first cumulative adder 10, the signal a is cumulatively added, and the cumulative addition output Σa is supplied to the divider 13. The divider 13 divides each cumulative addition output Σa·x, Σa, and the divided output Σa·x/Σa is divided by the subtracter 14.
is supplied to The subtracter 14 receives the division output Σa·x/Σa as well as the delay time T caused by the DL6.
A set value Q corresponding to 1/2 of the beam movement distance l corresponding to is input. And this subtractor 1
4, Σa·x/Σa−l/2 is obtained, and the center position of mark 1 is detected.

The operation of the apparatus configured as described above will be explained with reference to FIGS. 3a to 3f.

First, the mark signal obtained when the mark 1 shown in FIG. 3a is scanned by the electron beam 2 is A/
Analog-to-digital conversion is performed by D5, and the converted output X is as shown in FIG. Further, by delaying this converted output X by DL6, a delayed output X' as shown in FIG. 3c is obtained. Therefore, the output X--X' of the subtractor 7 becomes as shown in FIG. 3d. When this output X-X' is supplied to the absolute value circuit 8, the negative component of the output is inverted, so
The output |X-X'| of the absolute value circuit 8 is as shown in FIG. 4e. Absolute value output |X−X′| is the subtracter 9
is supplied to The noise component (component smaller than the set value P) is removed. Therefore, the output a of the subtracter 9 becomes as shown in FIG. 3f. Then, from the relationship between this output a and the beam position, the cumulative adders 10 and 12, the multiplier 11, and the divider 13 calculate the first moment. This first moment is such that the output a is the converted output X and the delayed output.
Since it is based on the difference from X', the center position of mark 1 is advanced by 1/2 of the beam movement distance l corresponding to the delay time T. Therefore, the output Σa·x/Σa-l/2 of the subtractor 14 indicates the center position of the mark 1.

Thus, according to the present device, the center position of mark 1 can be detected by utilizing the information of the entire mark signal without wasting it. Furthermore, the center position of the mark can be detected by using various arithmetic units without requiring a complicated circuit for determining the first-order moment calculation range. Therefore, it is possible to simplify the device configuration and improve the accuracy of position detection. Furthermore, since various calculations are performed simultaneously with the scanning of the electron beam, the time required for position detection can be shortened. Furthermore, since there is no need to perform average addition, no memory is required for this purpose, and costs do not increase.

Note that the present invention is not limited to the embodiments described above. For example, instead of the reflected electron detector, one that detects absorbed electrons or secondary electrons obtained when a mark is scanned with an electron beam may be used. Furthermore, it is also possible to use a light beam instead of an electron beam. However, in this case it is necessary to use a photodetector instead of an electronic detector. Furthermore, the setting value 1/2 to be subtracted from the first-order moment Σa・x/Σa is applied when the mark signal is symmetrical with respect to the center of gravity, and if the mark signal is asymmetrical with respect to the center of gravity, it is applied to some extent. Correction is required. Furthermore, it is also possible to make the delay time T longer than the continuous time of the mark waveform. In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of the present invention, FIG. 2 is a diagram showing the relationship between electron beam scanning and mark waveforms according to the above embodiment, and FIG. 3a
-f are diagrams for explaining the operation of the above embodiment. 1... Mark, 2... Electron beam, 3... Backscattered electron detector, 4... Mark signal, 5... Analog-to-digital converter (A/D), 6... Delay circuit (DL), 7, 9, 14...subtractor, 8...
Absolute value circuit, 10, 12...cumulative adder, 11...
...multiplier, 13...divider.

Claims (1)

[Claims] 1. A means for scanning a mark used for position detection with an electron beam and detecting reflected electrons, secondary electrons, or absorbed electrons resulting from the scanning to obtain a mark signal, and a means for delaying the mark signal and the mark signal by a predetermined time T. means for determining the absolute value of the difference between the delayed signal and the delayed signal; means for determining the first moment from the absolute value and the scanning position of the electron beam; and a scanning distance of the electron beam corresponding to the time T from the first moment. A mark position detection device comprising: means for subtracting 1/2 of the mark position detection device.