JPS63142633A - Processing method for mask information signal in charged beam lithography - Google Patents

Abstract

PURPOSE:To enhance the accuracy of various measurements based on a mask detection by setting the initial gain of an amplifier to amplify a mark information signal so that the intensity of the signal obtained by scanning becomes a reference value, and resetting the gain of the amplifier to a predetermined value so that the intensity of the signal becomes a reference value at the suitable timing during a pattern lithography. CONSTITUTION:A stage 5 is moved by a stage driving mechanism by a command of a controller 8 so that a Faraday cup 6 is moved on an optical axis in each lithographic step for a predetermined number of fields or chips, and a beam focused by a lens 2 is collected by the cup 6. The current value I of the collected beam is converted by an ammeter 7 to a digital current value, and fed to the controller 8. The controller 8 obtains the ratio l/I0 of the current value I to the initial value I0 of the beam current stored before the pattern lithography, and calculates the product of the obtained ratio and the initial value G0 of the gain of the amplifier. A signal representing the calculated product l/I0.G0 is fed as a signal for setting a new gain through a D/A converter 16 to an amplifier 15. The gain of the amplifier 15 is so altered as to correct the variation of the beam current value by supplying the new gain set signal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a mark in charged beam drawing in which the information signal intensity from the mark, which is 1q when the mark is scanned with a charged beam, becomes a reference value. The present invention relates to an information signal processing method.

[Prior Art] In a charged beam drawing method such as an electron beam drawing method, a mark attached to a material, a moving table, etc. is scanned with a beam before pattern drawing and during 1ffi drawing, and by the scanning, marks are removed from the mark. It is now extremely common to align materials, measure the tilt of the moving table, correct beam deflection distortion, measure overlay accuracy, etc. based on mark position data obtained from the mark information signal obtained. It has become a target.

Now, in such information signal processing of a mark information signal, since the mark information signal subjected to the information signal processing is usually very weak, the intensity of the mark information signal detected by the detector is amplified by an amplifier.

In reality, the gain of the amplifier is adjusted just once before pattern drawing so that the intensity of the mark information signal detected by the detector is amplified to the intensity (reference intensity value) that can be used for the above measurements. are doing.

[Problems to be Solved by the Invention] By the way, for example, when drawing a complex pattern in the form of spots, it takes a lot of drawing time. In this case, the fluctuation of the beam current cannot be ignored, and due to the fluctuation of the beam current,
With amplification based on the gain of the amplifier adjusted before pattern writing, it may not be possible to obtain a mark information signal strong enough to perform each of the above measurements.

The present invention is aimed at solving such problems.

[Means for solving the problem] Therefore, the present invention measures the initial value (Ic) of the charged beam current before pattern drawing, and scans the mark provided on the material with the charged beam, The initial gain (Go) of the amplifier for amplifying the mark information signal is set so that the intensity of the mark information signal obtained by the scanning becomes the reference value, and the charged beam current is adjusted at appropriate times during pattern drawing. value(
I) and the ratio of the chain end (I) to the initial value (■0) (
(2) By setting the gain of the amplifier to a value corresponding to the product of /I0) and the initial gain (G0) of the amplifier, the intensity of the mark information signal obtained by scanning with the charged beam becomes the reference value.

[Embodiment] FIG. 1 is a schematic diagram of a mark information signal processing mechanism shown as an embodiment of the mark information signal processing method in charged beam lithography of the present invention.

In the figure, 1 is an electron gun, 2 is a lens for focusing the electron beam from the electron gun onto the material 3, 4 is a deflector for scanning the material with the beam, and 5 is the material placed on it. A stage, 6 a Faraday cup attached to a part of the stage, 7 an ammeter with a function of converting an analog current value into a digital current value, 8 a control device such as an electronic computer,
Reference numeral 9 denotes a scanning clock generation circuit which starts operating in response to a command from the control device and supplies a scanning signal to the deflector 4 via a DA converter 10 and an amplifier 11. 12A, 12B
1 is a backscattered electron detector; 13A and 13B are current-voltage converters that convert current values into voltage values; 14 is an addition circuit; 15 is an amplifier whose gain is controlled by a command from the control device 8; and 16 is a DA. Converter, 17 is an AD converter, and 18 is a waveform memory.

First, before pattern writing, the stage 5 is moved by a stage drive mechanism (not shown) in accordance with a command from the control device 8 so that the Faraday cup 6 is on the optical axis, and the beam focused by the lens 2 is directed to the Faraday cup. Catch it in a day cup. The current value (I0) of the beam captured by the cup is measured by the ammeter 7.
The current value is converted into a digital current value and sent to the control device 8. The control m+ device 8 stores the current value (I0) as the initial value of the beam current. Next, in response to a command from the control device 8, the stage 5 is moved by a stage drive mechanism (not shown) so that one mark M made on the material is on the optical axis. Then, the scanning clock generating circuit 9 is operated according to a command from the control device, and the scanning signal from the scanning clock generating circuit 9 is supplied to the deflector 4, so that the mark is scanned with a beam. Through this scanning, reflected electrons generated from the mark M are detected by the reflected electron detectors 12A and 12B. Figure 2 (
a) and (b) are the output waveforms of the backscattered electron detector, respectively. The output (current value) of each detector is converted to a current voltage converter 1.
3A and 13B are converted into voltage values, sent to the adder circuit 14, and added there.

FIG. 2(C) shows the output waveform of the adder circuit. The output of the adder circuit is amplified by an amplifier 15 and further sent to a waveform memory 18 via an AD converter 17. The control device 8 is programmed in advance to ensure that the intensity of the reflected electrons from the mark is sufficient for measurements such as alignment of materials, measurement of tilt of the moving table, measurement for correction of beam deflection distortion, and measurement of overlay accuracy. An intensity value as high as possible is set as a reference value, and the control device 8 sets the peak value of the added signal stored in the waveform memory (corresponding to P in FIG. 2(C)) as the reference value. A signal for setting the gain of the amplifier 15 is sent to the amplifier 15 via a DA converter 16. Then, pattern drawing and the like are performed while maintaining the gain of the amplifier 15 in this state. Further, a signal representing the initial value (Go) of the gain set in this way is stored in the internal memory of the control device 8.

Now, every time a predetermined number of fields or chips are drawn, or every predetermined time, the stage is driven by a command from the control device 8! Faraday cup 6 by m<not shown)
The stage 5 is moved so that the beam is on the optical axis, and the beam focused by the lens 2 is captured by the Faraday cup. The current value (I) of the beam captured by the cup is converted into a digital current value by an ammeter 7 and sent to a control device 8.

The control device 8 calculates the ratio (■/[0) of the current value (N) and the initial value (I0) of the beam current stored before pattern writing, and calculates the ratio between the calculated ratio and the initial value of the gain of the amplifier < Go
). Then, the calculated product value (f/
A signal representing I0).Go is sent to the amplifier 15 via the DA converter 16 as a signal for setting a new gain.

By supplying the new gain setting signal, the gain (7) of the amplifier 15 is changed by the amount described above in order to correct the variation in the beam current value.Thus, after the resetting, the measurement by mark detection is performed. When this is performed, the information signals from the marks detected by the backscattered electron detectors 12A and 12B by electron beam scanning and added by the adder circuit via the current-voltage converters 13A and 13B are converted to the reference signal by the amplifier 15. Since the waveform is amplified to a high intensity and stored in the waveform memory 18, it is possible to perform measurements such as material alignment by mark detection and overlay accuracy measurement. For example, the edge portion (
Corresponds to the part with the intensity value of 11.12 in Figure 3 (C))
position data is selected, and the mark position is determined based on the position data.

By the way, an additional comment will be made below regarding the initial setting of the gain of the amplifier 15 before the pattern drawing.

That is, the gain of the amplifier depends on the beam current and the nature of the mark. Therefore, the control device 8 sets IO to the initial value of the charged beam current, Cs to a correction coefficient depending on the type of mark, that is, whether the mark is a convex mark or a step mark, C2 to a correction coefficient depending on the shape of the mark, and Go'- When the gain setting value is set as the gain setting value, the gain setting value Go' is calculated based on the following formula,
The gain of the amplifier is initially set M according to the value.

Go −= (C+ ・Cz / (Io ・10
'))/H.

3 1.13 [However, N = Cl-C2/(3・IO・10G) When the mark is a white clay mark, the material of the mark itself is different from the material of the material, so the correction coefficient depending on the material of the mark C3 is added to the above equation.

That is, the C1 and C2 parts of the above formula are all C0, C2, and C.
It becomes 3.

Note that the mark detection method of the present invention can also be used to detect marks in an ion beam writing apparatus using an ion beam.

Also, as in the above embodiment, in the case of a convex mark, the sum of the two backscattered electron detectors is calculated, but in the case of a step mark as shown in Fig. 3, the difference between the two backscattered electron detectors is calculated. I take the.

[Effects of the Invention] In the present invention, the gain of the amplifier that amplifies the mark information signal is reset at appropriate time intervals so that the strength of the mark information signal becomes the reference value, so the beam current value does not fluctuate over time. Even if the mark information signal has a reference intensity, a mark information signal with a reference intensity can be obtained, and therefore various measurements based on mark detection can be performed accurately.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a mark information signal processing mechanism to show an embodiment of the mark information signal processing method in charged beam lithography of the present invention, Fig. 2 is a signal waveform diagram, and Fig. 3 shows a step mark. It is something. 1: Electron gun 2: Lens 3: Material 4: Deflector
5 varnish stage 6: Faraday cup 7: ammeter 8: control device 9: scanning clock generation circuit 10
: DA converter 11: Amplifier 12A, 12B: Backscattered electron detector 13A, 138: Current voltage converter 14:
Adder circuit 15: Amplifier 16: DA converter
17: AD converter 18: Waveform memory M: Mark

Claims (1)

[Claims] 1. Before pattern writing, the initial value of the charged beam current (I_
0), scans the mark provided on the material with a charged beam, and amplifies the mark information signal so that the intensity of the mark information signal obtained by the scanning becomes the reference value. The initial gain (G_0) is set, the charged beam current value (I) is measured at an appropriate time during pattern writing, and the ratio (I/I_0) of this value (I) and the initial value (I_0) is determined.
0) and the initial gain (G_0) of the amplifier so that the intensity of the mark information signal by charged beam scanning becomes the reference value. Information signal processing method. 2. When setting the initial gain of the amplifier before drawing the pattern, I_0 is the initial value of the charged beam current, C_1 is a correction coefficient depending on the type of mark, C_2 is a correction coefficient depending on the shape of the mark, and G_0' is the initial gain setting value. , the initial gain setting value G_0' is calculated based on the following formula, and the initial gain of the amplifier is set according to the calculated value. Processing method. G_0'={C_1・C_2/(I_0・10^6)}
/(3^N・1.13) [However, N=C_1・C_2/(3・I_0・10^6
)]