JPH04127416A - Position detection method of mark - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a mark position detection method suitable for use in an electron beam lithography apparatus or the like.

(Prior art) A lithography device such as an electron beam lithography device or a focused ion beam device stores lithography pattern data in a storage device in advance, and draws a predetermined pattern with a beam onto a material placed on a moving stage. It is supposed to be done.

FIG. 3 is a diagram showing an example of the configuration of an electron beam lithography apparatus. The electron beam Bi emitted from the electron gun 1 is controlled on and off by a blanking electrode 2, focused by subsequent electron lenses 3 and 4, and deflected in a two-dimensional direction by a deflection electrode 5, after which it is applied to a material (for example, a wafer). 6. Here, the material 6 is placed on a moving stage 7 that is movable in two dimensions. 8 has material 6' inside it
9 is a vacuum chamber containing these components inside.

Pattern data for performing electron beam writing on the material 6 is stored in the external storage device 10.

The CPU circuit 11 controls the transfer of pattern data stored in the external storage device 10 and calculates the amount of stage movement. Then, the blanking control circuit 12. Control signals are sent to the beam deflection control circuit 13 and the stage movement control circuit 14, respectively. The blanking control circuit 12 controls the voltage applied to the blanking electrode 2, the beam deflection control circuit 13 controls the voltage applied to the deflection electrode 5, and the waist stage movement control circuit 14 controls the movement of the moving stage 7. do. As a result, a predetermined pattern on the material 6 is drawn.

Conventionally, when performing beam drawing on the material 6 using such a drawing device, the beam is irradiated onto a mark made on the material 6 in advance, the reflected electrons generated at that time are detected, and the material position is detected from this reflected electron signal. The position of the material is accurately determined using a so-called mark detection method, and then the desired pattern is drawn. However, this mark detection method uses a method of differentiating the detection signal, emphasizing the peak, and then cutting at an appropriate threshold level to determine the peak. This peak value is then used to determine the position of the mark.

Although this mark detection method is an effective method for simply detecting mark positions, it has the drawback of being susceptible to noise because it creates a peak by differentiating the detection signal. Therefore,
When there is noise, the threshold level is determined <<,
This results in detection errors. Therefore, in recent years, as a mark detection method that is resistant to noise, a method has begun to be used in which correlation processing is performed on mark detection signals and the peak position of the result of the correlation processing is used as the mark position. Since this method does not perform differential processing, it is strong against noise and can be applied even to signals as bad as 5Nlt.

(Problems to be Solved by the Invention) However, the above-described method using correlation processing utilizes the symmetry of the waveform, and a problem arises when the symmetry of the waveform breaks down. For example, if the resist covers the mark unevenly, the symmetry of the detection signal is poor. Further, when mark detection is performed at a location away from the beam deflection center, signal asymmetry occurs.

The following two cases can be considered to cause this waveform asymmetry. First, as shown in FIG. 4, there is a case where the left and right amplitudes of the signal are different.

Such a phenomenon occurs when beam scanning for mark detection is performed at a position other than directly below the beam optical axis.

In Figure 4, (a) shows that the amplitude of the peak on the right side is twice that of the left side, (b) shows that it is three times that of the left side, and (C)
is the case where it is four times as large, and the solid line is the mark detection signal waveform,
The dotted line is the correlation processing waveform.

As is clear from this figure, as one of the peaks becomes larger, the results of the correlation process change. Figure 4(a),
As in the case of (b), when one peak is multiplied by 2 or 3 times, the peak on the right side, which is different from the center of the correlation processing waveform, becomes higher, but it has not yet reached the point where it exceeds the center. As shown in Figure 4 (C), this becomes 4 times the amplitude,
The peak on the right side will exceed the center peak, and an error will occur if the center position of the mark is determined by correlation processing. However, in reality, a waveform deviation as shown in FIG. 4(c) does not occur in a portion other than directly below the beam optical axis, so no position error occurs in this case.

A practical problem occurs in the second case, where the resist covers the mark portion unevenly and the position of the valley of the mark detection signal is shifted. FIG. 5(a) is a basic diagram of a mark detection signal, and will be explained using an example in which a signal waveform is stored with 1024 data points in the scanning direction (horizontal axis). FIG. 5(b) shows a case where the valley position is shifted 56 points to the right from the center, and in this case, an error of 2 points occurs in the peak position of the correlation process. FIG. 5(C) shows a case where the valley position is shifted to the right by 106 points, and in this case, an error of 6 points occurs in the peak position of the correlation process. FIG. 5(d) shows a case where the valley position is shifted to the right by 158 points, and in this case, an error of 8 points in the peak position of the correlation processing occurs.

The present invention has been made in view of these points, and its purpose is to realize a mark position detection method that can accurately determine the mark center position even when the symmetry of the mark detection signal waveform is not good. It is in.

(Means for Solving the Problems) A mark position detection method based on the present invention scans a beam across the mark, performs correlation processing on the signals obtained by adding 1' to the scan, and calculates the peak position Ic. Find the intermediate position between the two peak positions of the signal obtained based on the scan. At the same time, find the position Im of the minimum value of the signal obtained based on the scanning, find the error ΔI between the intermediate position and the position of the minimum value, and calculate the peak position Ic and the error Δ■ by the correlation process. The feature is that the position of the mark is determined based on the

(Operation) The mark position is corrected based on correlation processing based on the difference between the center position of the two peak positions of the mark detection signal and the position of the minimum value (trough of the signal waveform) of the mark detection signal.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of a configuration for implementing the method according to the invention. In the figure, 21 is a detector that detects a reflected signal of a mark made on a material;
1 is converted into a digital signal by an AD converter 22 and then supplied to a correlation processing unit 23. The correlation processing unit 23 is controlled by the computer 24 and is switched between a correlation processing mode and a through mode in which the signal is passed through as is. The computer 24 includes a ΔI calculating section 25 and a peak position calculating section 26, which will be described later.

With the above-described configuration, the mark detection signal shown in FIG. 2 is supplied from the detector 21 to the correlation processing unit 23 via the AD converter 22. When the correlation processing unit 23 is in the correlation processing mode under the control of the computer 24, known correlation processing is performed in the unit 23, and the peak position Ic obtained by this correlation processing is stored in the register 27 in the computer 24. Set. Next, when the correlation processing unit 23 is set to the through mode under the control of the computer 24, the mark detection signal shown in FIG. This Δl calculation unit 25 calculates the two peak positions 1 and 1 of the mark detection signal. , I2, and detect the intermediate position I between the two peak positions. , that is, find i o -(1+ + 12) / 2, and further calculate the difference ΔI (= Im
Find Io). The Δl obtained by the ΔI calculation unit and the peak position 1flc set in the register 27 by the correlation process are supplied to the mark position calculation unit 26, where the following calculation is performed.

Ia−Ic+α·ΔI Ia obtained by this calculation is the peak position Ic corrected by the correlation process, and is an accurate position. Note that α in the above equation is a correction coefficient and is a function of ΔI. Further, the value is determined in advance as a function of ΔI from the shape of the mark by simulation or the like.

Although the present invention has been described in detail above, the present invention is not limited to the embodiments described above. For example, although an electron beam lithography apparatus has been described as an example, the present invention can also be applied to an ion beam lithography apparatus.

(Effects of the Invention) As explained above, in the present invention, the mark position is corrected based on the 11 function processing based on the difference between the center position of the two peak positions of the mark detection signal and the position of the minimum value of the mark detection signal. Therefore, even if the mark detection signal waveform does not have good symmetry, the mark center position can be accurately determined.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
Figure 3 is a diagram showing a mark detection signal waveform. Figure 3 is a diagram showing a configuration example of an electron beam drawing device. Figure 4 is a diagram showing a mark detection signal waveform with different left and right amplitudes. Figure 5 is a diagram showing the position of a valley. FIG. 3 is a diagram showing a mark detection signal waveform with a shifted mark. 21...Detector 23...Correlation processing unit 24...Computer 26...Mark position calculation section 27...Register 22...AD converter 25...Δl calculation section

Claims (1)

[Claims] Scanning the beam across the mark, performing correlation processing on the signals obtained with the scanning to obtain the peak position Ic, and determining the intermediate position I_O between the two peak positions of the signal obtained based on the scanning. In addition to determining the position Im of the minimum value of the signal obtained based on the scanning, determining the error ΔI between the intermediate position and the position of the minimum value, based on the peak position Ic and the error ΔI due to the correlation processing. A mark position detection method comprising determining the position of a mark.