JPS6226173B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for detecting alignment marks formed on a material during electron beam exposure.

In electron beam exposure, an alignment mark formed on an exposure material is scanned with an electron beam, the position of the mark is detected, the electron beam irradiation position is corrected, and exposure is performed.

Conventionally, a mark detection device uses an analog processing circuit to perform differential processing and waveform shaping on the output signal from a detector for detecting reflected electrons generated from a material by irradiating the material with an electron beam. The waveform-shaped output is used to stop the counting of a counter that counts as the electron beam scans, and the output of the counted value of the counter is supplied to an arithmetic processing unit to determine the mark position.

However, in order to reduce the proportion of noise mixed in when differentially processing the signal from the detector, such conventional devices scan the mark multiple times and calculate the value from the average value of the counter counts obtained during each scan. The mark position must be determined, and the number of scans described above is required to be relatively large, making it impossible to perform fast mark detection.

Another typical conventional device is to convert the output signal of a backscattered electron detector into a digital signal, accumulate and integrate the digital signals obtained when scanning multiple times, and digitally convert the integrated signal into a digital signal. Differential processing is performed, and the differentially processed signal is further processed by an arithmetic processing unit to detect the mark position.

However, even in this latter mark detection device, complex processing is required to calculate the mark position by numerically processing the digitally accumulated signals, and therefore it is not possible to detect the mark position at a high speed.

The present invention has been made to provide a mark detection device for an electron beam exposure apparatus that can solve the drawbacks of the conventional device and detect marks in a short time. Examples will be explained in detail.

In the drawing, 1 is a material to be exposed, and 2 is a mark formed on the material 1. 3 is electron beam 4
This is a deflector for deflecting. 5 is a clock pulse generator, and based on the output signal from the clock pulse generator 5, a scanning signal generating circuit 6 generates a scanning signal for scanning the electron beam, and supplies it to the deflector 3 via an amplifier 7. do. 8 is material 1
The output signal from the detector 8 is supplied to the memory 11 via the amplifier 9 and the AD converter 10. The output signal of the memory 11 is supplied to an analog processing circuit 13 via a DA converter 12. The analog processing circuit 13 is a circuit for differentiating the supplied signal and shaping the differentiated signal to create a signal that accurately represents the mark portion. The output signal of the analog processing circuit 13 is supplied to first and second counters 14 and 15 for counting clock pulses from the clock pulse generator 5. The count outputs of the first and second counters 14 and 15 are supplied to the central processing unit 6.

In this configuration, the clock pulse generator 5 supplies clock pulses to the scanning signal generating circuit 6, and the circuit 6 generates a scanning signal as shown in FIG. The material 1 is scanned multiple times. As a result, a detection signal as shown in FIG. 2b is detected by the backscattered electron detector 8. The detection signal is converted into a digital signal by the AD converter 10 and then supplied to the memory 11. The signals obtained for each scan converted into digital signals in the memory 11 are superimposed and integrated. Therefore, at the end of a predetermined number of scans, the signal integrated in the memory 11 is a signal with an improved S/N ratio (shown as an analog signal for convenience) as shown in FIG. 2c. This signal is sent to memory 1 in synchronization with the last scan.
1, it is converted into an analog signal by the DA converter 12, and then sent to the analog processing circuit 13.
supplied to In the analog processing circuit 13, this supplied signal is differentiated into a signal as shown in FIG. 2d, and then waveform-shaped so that the portion corresponding to the mark scanning section as shown in FIG. 2e is a square wave. Convert it into a certain signal. Such signals are supplied to the first and second counters 14 and 15. The first and second counters 14 and 15 start counting clock pulses in synchronization with the start of the final scan for electron beam mark detection, but they are synchronized with the falling edge of the signal from the analog processing circuit 13. Then, counting by the first counter 14 is stopped, and counting by the second counter 15 is stopped in synchronization with the rise of the signal from the analog processing circuit 13. The count outputs of the first and second counters 14 and 15 are supplied to the central processing unit 16,
In step 6, the mark position is calculated based on the count outputs of these counters.

In the device based on the present invention as described above,
Since the analog differentiated signal is first converted into a digital signal and then integrated in memory,
A signal with a high S/N ratio is differentiated, and therefore, even if the signal is differentiated, the influence of noise is small, so that marks can be detected with fewer scans than in the past. Furthermore, in the present invention, in order to determine the center position of the mark from the output signal of the backscattered electron detector, the signal from the backscattered electron detector, which has been replaced with a digital signal, is subjected to complex waveform processing calculations by an arithmetic processing device. There's no need to do it. Therefore, the mark detection speed can be increased compared to the conventional method, and it will greatly contribute to improving the exposure throughput in the current situation where mark detection is required multiple times when exposing a single sheet of exposed material. It is.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention, and FIG. 2 is a diagram showing output signals of each circuit element of the device of this embodiment. 1: material to be exposed, 2: mark, 3: deflector,
4: Electron beam, 5: Clock pulse generator, 6: Scanning signal generation circuit, 7: Amplifier, 8: Backscattered electron detector, 9: Amplifier, 10: AD converter, 11: Memory, 13: Analog processing circuit, 14 , 15: counter, 16: central processing unit.

Claims (1)

[Claims] 1 a means for deflecting an electron beam to scan marks formed on a material; a detector for detecting reflected electrons or secondary electrons generated from the material by irradiation with the electron beam; an AD converter for converting the output signal from the detector into a digital signal;
A memory for integrating the output signal of the AD converter, an AD converter for converting the output signal of the memory into an analog signal, and an analog processing circuit for differentially processing the output signal of the AD converter. , an electronic device comprising a counter that counts as the electron beam scans and stops counting according to the output signal of the analog processing circuit, and an arithmetic processing device that calculates the mark position based on the output of the counter. Mark detection device for line exposure equipment.