JPH09166698A - Measurement method of charged particle beam - Google Patents

Abstract

(57) Abstract: A charged particle beam measuring method capable of accurately measuring a beam size, a beam position, and a focus state without being influenced by a noise component is realized. When measuring the size, position, and focus state of an electron beam 1, a control CPU 9 controls a deflection circuit 10 to apply a sawtooth deflection signal to an electrostatic deflector 3.
With the application of this deflection signal, the rectangular electron beam 1
It is deflected in the X direction. Due to the deflection of the electron beam, the electron beam is gradually shielded by the knife edge member 4,
The amount of electron beam incident on the Faraday cup 6 decreases. When the electron beam 1 is completely shielded by the knife edge member 4, the detection current of the Faraday cup 6 becomes zero. This detection signal is stored in the waveform memory 8. The detection signal stored in the waveform memory 8 is read by the control CPU 9, and the detection signal is subjected to fitting processing with the modeled signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a charged particle beam in an apparatus using a charged particle beam such as an electron beam drawing apparatus and an ion beam apparatus.

[0002]

2. Description of the Related Art For example, in an electron beam drawing apparatus, the size and position of the electron beam used for drawing or the focus state of the electron beam is measured before the actual drawing operation, and the electron beam is drawn based on the measurement result. Is being adjusted. FIG. 1 shows an example of an apparatus used for measuring such an electron beam, and 1 is the electron beam to be measured. Although not shown, the electron beam 1 has a rectangular cross section formed by two rectangular slits and a deflector provided between the two rectangular slits.

The electron beam 1 is focused by the final stage lens 2 and further deflected by the electrostatic deflector 3.
A knife edge member 4 is arranged below the deflector 3, and the knife edge member 4 is provided with a rectangular opening, and each inner side thereof is formed thin and linear. An aperture 5 that cuts the scattered electron beam is provided below the knife edge member 4, and further below that,
A Faraday cup 6 for detecting the amount of electron beam current is arranged.

When the saw-toothed deflection signal shown in FIG. 2 (a) is applied to the deflector 3 with the above configuration, the rectangular electron beam 1
Is deflected in the X direction. By deflecting the electron beam,
The electron beam is gradually shielded by the knife edge member 4, and the amount of the electron beam incident on the Faraday cup 6 decreases. When the electron beam 1 is completely shielded by the knife edge member 4, the detection current of the Faraday cup 6 becomes zero.
Becomes

FIG. 2B shows the detected current of the Faraday cup 6. When the detected current signal is differentiated once, the signal shown in FIG. 2C is obtained. Further, when the signal of FIG. 2 (c) is differentiated again, the signal of FIG. 2 (d) is obtained.
In FIG. 2D, the horizontal axis is the scanning position of the electron beam,
The size of the electron beam is determined based on the distance between the two peaks of the signal. Further, the position of the electron beam is found based on the intermediate position between the two peak positions. Furthermore, the peak value of the peak indicates the focus state of the electron beam. Various adjustments of the electron beam are performed according to the beam size, beam position, and focus state obtained in this way, and then the regular drawing operation is executed.

[0006]

In the above measurement of the size of the electron beam and the like, the detection signal shown in FIG. 2 (b) usually contains a noise component. FIG. 3A shows a detection signal waveform of a Faraday cup containing a noise component. When the signal containing such a noise component is differentiated once, the signal of FIG. 3B is obtained. The signal resulting from the second differentiation is as shown in FIG. This figure 3
In the signal of (c), two peaks are buried in the noise peak, and accurate measurement of the beam size, position and focus state becomes impossible.

Therefore, signal smoothing processing has been carried out. FIG. 4A shows a detection signal containing a noise component, and the signal of FIG. 4B is obtained by differentiating this signal. At this time, the first-order differential signal has been subjected to noise removal smoothing processing. When this process is executed and then the differentiation is performed again, the signal of FIG. 4C is obtained. With this signal, the peak position can be obtained correctly, but the peak becomes dull due to the smoothing process, so the peak value of the peak that reflects the focus state of the beam will not be correct, and the focus state will not be correct. It cannot be measured.

The present invention has been made in view of the above points, and an object thereof is to measure a charged particle beam capable of accurately measuring a beam size, a beam position and a focus state without being influenced by a noise component. There is a way to realize.

[0009]

According to another aspect of the present invention, there is provided a method for measuring a charged particle beam, wherein the charged particle beam is scanned across a member having a straight edge, and the charged particle beam is detected along with the scanning. It is characterized in that curve fitting is applied to a change in the signal of the charged particle beam, and at least one of the beam size, the beam position, and the focus information of the charged particle beam is measured.

According to the first aspect of the present invention, the charged particle beam is scanned across a member having a linear edge, and curve fitting is applied to a change in the signal of the charged particle beam detected in association with the scanning. By measuring at least one of the beam size, the beam position, and the focus information of the charged particle beam, each information is accurately measured without the influence of noise.

According to a second aspect of the present invention, there is provided a charged particle beam measuring method, wherein the charged particle beam is scanned across a member having straight edges, and the signal of the charged particle beam detected by the scanning is detected. First-order differentiation is performed, and n pieces of data Ai (i is a scanning position, i = 1, 2, ...
n), a is half the beam size, b is the beam position,
Next evaluation function where σ is focus information Fi (a, b, σ) = Tanh {(i−a−b) / σ}
It is characterized in that the parameters a, b, and σ are determined so that the sum of squares of the difference between the data Ai and the evaluation function Fi is minimized by using −Tanh {(i + a−b) / σ}. There is.

According to the second aspect of the invention, the parameters a (1/2 of the beam size) and b are set so that the sum of squares of the difference between the n pieces of data Ai of the primary differential signal and the evaluation function Fi is minimized.
(Beam position) and σ (focus information) are determined.

According to a third aspect of the present invention, there is provided a charged particle beam measuring method, wherein the charged particle beam is scanned across a member having a straight edge, and n of the charged particle beams detected by the scanning are scanned. Data Bi (i is the scanning position, i =
1, 2, ........., n) and a is half the beam size,
The following evaluation function Fi (a, b, σ) = Log [Cosh {(i + a- where b is the beam position and σ is the focus information)
b) / σ}]-Log [Cosh {(-i + a + b) /
σ}] is used to determine the parameters a, b, σ so that the sum of squares of the difference between the data Bi and the evaluation function Fi is minimized.

According to the third aspect of the invention, the parameters a (1/2 of the beam size) and b (beam position) are set so that the sum of squares of the difference between the n pieces of data Ai of the detection signal and the evaluation function Fi is minimized. ), Σ (focus information) are determined.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 5 shows an example of the present invention, in which the same numbers as in the conventional device of FIG. 1 indicate the same components. In this embodiment, the current signal detected by the Faraday cup 6 is converted into a digital signal by the AD converter 7 and then supplied to the waveform memory 8. The signal supplied to and stored in the waveform memory 8 is the control CP.
It is read out by U9 and subjected to curve fitting processing. The control CPU 9 controls a deflection circuit 10 for supplying a scanning signal of the electron beam 1 to the electrostatic deflector 3. The operation of such a configuration will now be described.

When measuring the size, position and focus state of the electron beam 1, the control CPU 9 controls the deflection circuit 10 to apply a sawtooth deflection signal to the electrostatic deflector 3. With the application of this deflection signal, the rectangular electron beam 1 becomes X
It is deflected in the direction. Due to the deflection of the electron beam, the electron beam is gradually shielded by the knife edge member 4, and the amount of the electron beam incident on the Faraday cup 6 decreases. When the electron beam 1 is completely shielded by the knife edge member 4, the detection current of the Faraday cup 6 becomes zero.

FIG. 6A shows the detection signal waveform of the Faraday cup 6 obtained by the deflection of the electron beam 1, and this detection signal is stored in the waveform memory 8. The detection signal stored in the waveform memory 8 is read by the control CPU 9 and the primary differentiation is performed. Here, the first-order differential waveform is modeled in advance as shown in FIG. In FIG. 7, a is half the beam size and b is the beam position.

The basic idea in the present invention is to perform fitting processing on a waveform obtained by modeling the detected signal waveform. The signal waveform shown in FIG. 6A is first-order differentiated to obtain a waveform shown in FIG. By performing fitting with the modeled signal waveform shown, the signal of FIG. 6B is obtained. A noise component is removed from the fitting-processed signal, and the signal of FIG. 6B is further differentiated to obtain the signal of FIG. 6C.

Since the signal of FIG. 6 (c) has been subjected to fitting processing, noise components have been removed,
Furthermore, since the smoothing process is not performed, the signal component based on the end of the knife edge remains unblunted, and therefore the size, position, and focus state of the electron beam 1 can be accurately measured. .

Next, a more specific fitting process will be described. First, the detection signal of the Faraday cup 6 stored in the waveform memory 8 is read out by the control CPU 9,
First-order differentiation processing is performed. The control CPU 9 performs fitting processing on the first-order differential signal. This fitting process is performed using an appropriate evaluation function. For example, when a is 1/2 of the beam size, b is the beam position, and σ is the focus information, the following evaluation function can be used.

Fi (a, b, σ) = Tanh {(ia
-B) / [sigma]}-Tanh {(i + a-b) / [sigma]} where i is the beam scanning position (i = 1, 2, ...).
, N) are shown. The fitting determines the parameters a, b, and σ so that the sum of squares of the differences between the n pieces of data Ai of the primary differential signal and the evaluation function is minimized.
That is, the parameters are determined using the following equation.

[0022]

[Equation 1]

In the above-mentioned example, the detection signal of the Faraday cup 6 is first differentiated, and then the fitting process is performed. However, in this case, it can be applied when the SN ratio of the detection signal is relatively excellent. it can. When the SN ratio of the detection signal of the Faraday cup 6 is relatively poor, the sum of squares of the difference between the n pieces of data Bi (i = 1, 2, ..., N) in the waveform memory 8 and the evaluation function Fi.

[0024]

(Equation 2)

Parameters a, b, σ such that
Can be determined. In this case, as the evaluation function, for example, the following function using the nonlinear least squares method can be used.

Fi (a, b, σ) = Log [Cosh
{(I + a-b) / [sigma]}]-Log [Cosh {(-i
+ A + b) / σ}] Although the above is the measurement of the beam in the X direction, the measurement of the beam in the Y direction is performed in the same manner. After measuring the beam size, the beam position, and the focus information of the electron beam in this way, the beam size adjustment, the beam position correction, and the focus adjustment are performed, and then the regular drawing operation is started.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, the fitting calculation process may be performed by the control CPU instead of the control CPU in order to improve the speed. The evaluation function is not limited to the above formula as long as it can represent the beam size, the beam position, and the focus information. Furthermore, if the evaluation function is changed, the present invention can be applied not only to the rectangular beam but also to the spot beam.

Although the above embodiment has been described by using the electron beam, the present invention can be applied to an ion beam apparatus. Further, although the amount of the electron beam which is shielded by the knife edge member 4 and is incident on the Faraday cup 6 is detected, a material having a high emission coefficient of secondary electrons or reflected electrons having a linear edge is used, and the material is The charged particle beam may be traversed to detect secondary electrons and reflected electrons from the material.

[0029]

As described above, according to the first aspect of the invention, the charged particle beam is scanned across a member having a linear edge, and the signal of the charged particle beam detected in association with this scanning is detected. Since curve fitting is applied to the change and at least one of the beam size, beam position, and focus information of the charged particle beam is measured, each information can be accurately measured without the influence of noise. Further, since the detection signal is not smoothed, focus information can be measured more accurately.

According to the second aspect of the invention, the parameters a (1/2 of the beam size) and b are set so that the sum of squares of the difference between the n pieces of data Ai of the primary differential signal and the evaluation function Fi is minimized.
Since (beam position) and σ (focus information) are determined, each information can be accurately measured without the influence of noise. Further, since the detection signal is not smoothed, focus information can be measured more accurately.

According to the third aspect of the invention, the parameters a (1/2 of the beam size) and b (beam position) are set so that the sum of squares of the difference between the n pieces of data Ai of the detection signal and the evaluation function Fi is minimized. ) And σ (focus information) are determined, each information can be accurately measured without the influence of noise. Further, since the detection signal is not smoothed, focus information can be measured more accurately.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an apparatus used for conventional electron beam measurement.

FIG. 2 is a waveform diagram for explaining basic signal processing for electron beam measurement.

FIG. 3 is a diagram showing various waveforms obtained by conventional signal processing.

FIG. 4 is a diagram showing various waveforms by conventional signal processing accompanied by smoothing processing.

FIG. 5 is a diagram showing an example of an apparatus for carrying out the present invention.

FIG. 6 is a diagram showing various waveforms obtained by signal processing accompanied by fitting processing.

FIG. 7 is a diagram showing a modeled first derivative signal.

[Explanation of symbols]

 1 Electron Beam 2 Final Stage Lens 3 Electrostatic Deflector 4 Knife Edge Member 5 Aperture 6 Faraday Cup 7 AD Converter 8 Waveform Memory 9 Control CPU 10 Deflection Circuit

Claims (3)

[Claims] 1. A charged particle beam is scanned across a member having a linear edge, and curve fitting is performed on a change in the signal of the charged particle beam detected in association with the scanning to obtain a charged particle beam A charged particle beam measuring method for measuring at least one of beam size, beam position, and focus information. 2. A charged particle beam is scanned across a member having a straight edge, and the signal of the charged particle beam detected in association with this scanning is first differentiated to obtain a first derivative signal n.
Data Ai (i is the scanning position, i = 1, 2, ...
n), a is half the beam size, b is the beam position,
Next evaluation function where σ is focus information Fi (a, b, σ) = Tanh {(i−a−b) / σ}
-Tanh {(i + a-b) / σ} is used to determine the parameters a, b, σ so that the sum of squares of the difference between the data Ai and the evaluation function Fi is minimized. Measuring method. 3. A charged particle beam is scanned across a member having linear edges, and n pieces of data Bi (i is a scanning position, i) of the charged particle beam detected in association with the scanning.
= 1, 2, ..., N), and a is 1 / the beam size.
2 and b are beam positions, and σ is focus information. Next evaluation function Fi (a, b, σ) = Log [Cosh {(i + a-
b) / σ}]-Log [Cosh {(-i + a + b) /
σ}] is used to determine the parameters a, b and σ so that the sum of squares of the difference between the data Bi and the evaluation function Fi is minimized.