JPS634933B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mark detection device that enables accurate mark detection.

In a charged particle beam device such as an electron beam exposure device, a material to be drawn on which a pattern is drawn, a stage material for placing the material to be drawn, a peripheral material placed around the material to be drawn, etc. One or more marks are provided, the material is scanned with a charged particle beam, the position of the mark is detected based on the charged particle beam signal generated from the mark, and a scheduled drawing is performed according to the mark position. The position is corrected and the pattern is drawn at a predetermined position on the material.

Now, there are the following problems in such mark detection. The problem is that if there is dust within the charged particle beam scanning area for mark detection, the dust will be mistakenly detected as a mark. Conventionally, the following methods have been used to prevent such false detections. When scanning a mark M with a beam as shown in Fig. 1a, the distances A and B from a certain position P until a peak signal (a signal generated from the edge of the mark or dust) is generated (Fig. b) is calculated, and then B-A is calculated, and it is determined whether a mark or dust has been detected depending on whether this value is within an allowable value. In other words, since the width of a normal mark is approximately 10 μm, the allowable value is set to 10 μm.On the other hand, focusing on the fact that the width of normal dust is approximately larger than 10 μm, the detected B-A is compared with the allowable value, and the allowable value is determined. If the value is larger than the value, it is determined that dust has been detected, and if it is smaller than the value, it is determined that a mark has been detected. However, a big problem arose here. If by chance there is dust of 10 μm in the charged particle beam scanning area for mark detection, it will be determined that the mark has been detected even though the dust has been detected. Moreover, since one scan usually involves a large error due to beam fluctuations, 20 to 30 scans are performed to calculate the average value of BA. Therefore, it took a considerable amount of time (eg, 80 to 120 msec) to determine whether the correct detection was a false detection. As a result of the above, it has been difficult to improve the drawing accuracy and shorten the time required for the entire drawing.

The present invention was made in view of these points,
Normally, the height of the uneven mark is about 1 μm, and the height (diameter) of the dust is about 10 μm or more.
The change in the height direction of the dust is extremely large, the amount of backscattered electrons detected from the dust during beam scanning is extremely large, and the amount of signal due to the backscattered electrons roughly corresponds to the change in the height direction. When scanning a mark with a beam, the amplitude value of the detected signal is measured, and whether the detection is correct or incorrect is determined based on whether the amplitude value is larger or smaller than a reference value. The present invention provides a novel mark detection device.

FIG. 2 schematically shows a mark detection device according to an embodiment of the present invention.

In the figure, reference numeral 1 denotes an electron gun, and an electron beam 2 emitted from the electron gun is scanned by a deflector 3 over a material 4 provided with, for example, a convex mark 5 (see FIG. 3). 6 is a backscattered electron detector that detects backscattered electrons generated from the material, 7 is an amplifier, and 8 is a waveform shaping circuit. 9 is an amplitude detection circuit that measures the peak-to-peak value of the output signal of the waveform shaping circuit.
10 sets in advance a value slightly larger than the peak-to-peak value of the signal obtained from the mark as a reference value, compares the output signal value of the amplitude detection circuit 9 with this reference value, and determines if it is smaller than the reference value. , sends a signal (e.g. "1") indicating that mark detection has been performed to the control device 11, and if the signal is large,
Signal indicating that dust detection has been performed (e.g. “0”)
This is a discrimination circuit that sends the information to the control device 11. Reference numeral 12 denotes a counter that starts counting clock pulses from the clock pulse generator 13 from a certain position of the beam being scanned (eg, the scanning start position) according to a command from the control device 11, and continues counting until a peak occurs. In reality, this counter consists of two counters, one that counts the number of clock pulses from the start of clock pulse counting until the first peak occurs, and the other that counts the number of clock pulses from the start of clock pulse counting until the second peak occurs. The number of clock pulses until the clock pulse is counted is sent to the control device 11. The control device includes the discrimination circuit 1
When a "1" signal is input from 0, the mark center position is calculated from the count value from the counter 12, and the counter is reset. When a "0" signal is input, the mark center position is calculated from the count value from the counter 12. The counter is ignored, the counter is reset, and the scanning signal generator 15, which sends a scanning signal to the deflector 3 via the amplifier 14, shifts the scanning start point a little, for example, in the Y direction, and from there. For example,
Sends a command to scan the beam in a direction.

In such an apparatus, when the sample is scanned with a beam for mark detection, when a signal as shown in FIG. 4a enters the amplitude detection circuit 9, (when the signal is scanned), the detection circuit detects the peak-to-peak value _D1 of this signal and sends it to the discrimination circuit 10. The discrimination circuit compares this peak-to-peak value D ₁ with a reference value D ₀ (see FIG. 4), and if D ₁ >D ₀ , sends a “0” signal to the control device 11 indicating that the beam has detected dust. send. The controller ignores the output from the counter 12, resets the counter, and sends a command to the scanning signal generator 15 to change the beam scanning start point. Also, when a signal as shown in FIG. 4b enters the amplitude detection circuit 9 (mark 5 as shown in FIG.
2), the detection circuit detects the peak-to-peak value D ₂ of this signal and sends it to the discriminator circuit 10. The discrimination circuit compares this peak-to-peak value D ₂ with the reference value D ₀ and sends a “1” signal to the control device 11 when D ₂ <D ₀ , indicating that the beam has detected a mark. The control device is counter 1
2, i.e. from the scanning start point to the peak P ₁
The number of clock pulses E ₁ until the scan start point P 2 is detected, and the number E ₂ of clock pulses until the scan start point P ₂ is detected.
The mark position is measured by calculating 1/2 of the absolute value of the difference |E ₁ −E ₂ |.

Incidentally, when the dust detection signal is output from the discrimination circuit 10, the fact that dust has been detected may be displayed on the display device. Furthermore, the scanning signal generator and counter may be operated manually according to the display. Alternatively, even if dust is detected, the counter may not be stopped and the mark may be detected as it is, and the mark position may be detected by obtaining the counter value when the mark is detected based on the discrimination signal from the discrimination circuit.

According to the present invention, in mark detection, it is accurately determined whether a mark is detected correctly or dust is detected by mistake, and there is a significant difference in the amplitude value of the detection signal between the mark and dust. Therefore, mark scanning is not performed many times for this discrimination, so the time required for mark detection is significantly shortened. From the above, the drawing accuracy has been improved and the time required for the entire drawing has been shortened.

[Brief explanation of the drawing]

Figure 1 shows conventional mark detection;
The figure shows a mark detection device showing an embodiment of the present invention.
3 and 4 are provided to supplement the explanation of the operation of the device. 2... Electron beam, 3... Deflector, 4... Sample, 5...
Mark, 6... Backscattered electron detector, 9... Amplitude detection circuit, 10... Discrimination circuit, 11... Control device, 15... Scanning signal generator.

Claims (1)

[Claims] 1. Means for scanning a charged particle beam on a material provided with a mark, beam detection means for detecting the charged particle beam generated from the material, amplitude detection means for measuring the amplitude value of the detected beam signal, and said measurement. A discrimination circuit that compares the amplitude value with a preset reference amplitude value and generates a signal that discriminates whether the measured amplitude value is smaller or larger than the reference amplitude value, and the discrimination circuit discriminates the former case. The mark position is measured based on the beam signal from the beam detecting means when the latter signal is generated, and the beam signal from the beam detecting means is ignored for mark position measurement when the latter signal is generated. A mark detection device comprising control means.