JP3351671B2 - Measurement method of charged particle beam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 writing apparatus or an ion beam apparatus.

[0002]

2. Description of the Related Art For example, in an electron beam writing apparatus, prior to an actual writing operation, the size and position of an electron beam used for writing or the focus state of the electron beam are measured, and based on the measurement result, the electron beam is drawn. Has been adjusted. FIG. 1 shows an example of an apparatus used for measuring such an electron beam, and 1 is an 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.

An electron beam 1 is focused by a final lens 2 and further deflected by an 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 the inside thereof is formed thin and linearly. At the lower part of the knife edge member 4, an aperture 5 for cutting the scattered electron beam is provided.
A Faraday cup 6 for detecting a current amount of the electron beam is provided.

In the above configuration, when a sawtooth-shaped deflection signal shown in FIG.
Are deflected in the X direction. By electron beam deflection,
The electron beam is gradually blocked 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 a detection current of the Faraday cup 6. When the detection current signal is differentiated once, a signal shown in FIG. 2C is obtained. Further, when the signal of FIG. 2C is differentiated again, the signal of FIG. 2D is obtained.
In FIG. 2D, the horizontal axis represents 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 determined based on the intermediate position between the two peak positions. Further, the peak value of the peak indicates the focus state of the electron beam. Various adjustments of the electron beam are performed based on the beam size, the beam position, and the focus state obtained as described above, and then a normal drawing operation is performed.

[0006]

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

[0007] Therefore, a signal smoothing process is performed. FIG. 4A shows a detection signal containing a noise component, and when this signal is differentiated, a signal shown in FIG. 4B is obtained. At this time, the primary differential signal has been subjected to noise removal smoothing processing. After performing this processing, when differentiation is performed again, a signal shown in FIG. 4C is obtained. In this signal, although the peak position can be obtained correctly, the peak becomes dull due to the smoothing process, so that the peak value of the peak reflecting the beam focus state is not correct, and the focus state is substantially correct. It cannot be measured.

[0008] The present invention has been made in view of the above points, and an object of the present invention is to measure a charged particle beam capable of correctly measuring a beam size, a beam position, and a focus state without being affected by noise components. There is a way to realize.

[0009]

Means for Solving the Problems] method of measuring a charged particle beam based on the invention of claim 1 scans across the member having a straight edge with a charged particle beam, which is detected with this scanning Model the signal waveform of the charged particle beam
Performs curve fitting on the processed signal waveform
Based on the curve-fitted waveform
It is characterized in that so as to measure the beam size and the beam position and focus <br/> scan information of the charged particle beam.

According to the second aspect of the present invention, a charged particle beam
Measurement method had a straight edge with charged particle beam
Scans across the member and the load detected during this scan
Signal waveform data of the electron beam or its first derivative signal
Of the beam size a, beam position b,
Curve for evaluation function with focus information σ as a parameter
By performing the fitting process, the charged object
Determine the parameters a, b, and σ of the particle beam.
Was it that features a.

According to a third aspect of the present invention, there is provided a charged particle beam measuring method in which a charged particle beam is scanned across a member having a linear edge, and a signal of the charged particle beam detected in accordance with the scanning is obtained. First-order differentiated, first-order differentiated signal
Waveform data Ai (i is a scanning position, i = 1, 2,...)
.., N) are changed to beam size a, beam position b, focus
Scan information sigma to you and parameters following the evaluation function Fi (a, b, σ) = relative Tanh {(i-a-b ) / σ} -Tanh {(i + a-b) / σ}, waveform data Ai Curve fitting processing is performed so that the sum of squares of the difference between the evaluation function Fi and the evaluation function Fi is minimized.
This is characterized in that the parameters a, b, and σ of the charged particle beam to be measured are determined.

ClaimsOf the charged particle beam based on the fourth invention
Measurement method had a straight edge with charged particle beam
Scans across the member and the load detected during this scan
Electron beam signal waveformData Bi (i is the scanning position,
i = 1, 2,..., n)Beam size a, beam
Next evaluation using position b and focus information σ as parameters
function Fi (a, b, σ) = Log [Cosh {(i + ab) / σ}] −Log [Cash {(−i + a + b) / σ}] , The square of the difference between the waveform data Bi and the evaluation function Fi
Perform curve fitting processing to minimize the sum
The parameters of the charged particle beam to be measured
a, b, and σ are determined.
 You.

[0013]

[0014]

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 5 shows an example of the present invention, and the same reference numerals as those of the conventional device of FIG. 1 indicate the same components. In this embodiment, the current signal detected by the Faraday cup 6 is supplied to the waveform memory 8 after being converted into a digital signal by the AD converter 7. The signal supplied to and stored in the waveform memory 8 is the control CP
The data is read by U9 and subjected to a curve fitting process. 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-shaped deflection signal to the electrostatic deflector 3. With the application of this deflection signal, the rectangular electron beam 1
To be deflected in the direction. Due to the deflection of the electron beam, the electron beam is gradually blocked 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 a detection signal waveform of the Faraday cup 6 obtained by deflecting 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 out by the control CPU 9, and the first differentiation is performed. Here, the primary differential waveform is modeled in advance as shown in FIG. In FIG. 7, a is a half of the beam size, and b is a beam position.

The basic idea of the present invention is to perform fitting processing on a waveform obtained by modeling a detection signal waveform. The signal waveform shown in FIG. By performing fitting with the modeled signal waveform shown, the signal in FIG. 6B is obtained. The noise component is removed from the signal subjected to the fitting processing, and the signal of FIG. 6C is obtained by further differentiating the signal of FIG. 6B.

Since the signal shown in FIG. 6C has been subjected to fitting processing, noise components have been removed.
Furthermore, since the smoothing processing is not performed, the signal component based on the edge of the knife edge remains clearly without dulling, so that 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 derivative processing is performed. The control CPU 9 performs fitting processing on the primary differential signal. This fitting process is performed using an appropriate evaluation function. For example, if a is １ ／ 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) / σ｝ −Tanh ｛(i + ab) / σ｝ where i is the beam scanning position (i = 1, 2,...)
.., N). The fitting determines parameters a, b, and σ such that the sum of squares of the difference between the n 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-described example, the detection signal of the Faraday cup 6 is first-order differentiated, and then the fitting processing is performed. In this case, the present invention can be applied to a case where 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 square sum of the difference between the n data Bi (i = 1, 2,..., N) of the waveform memory 8 and the evaluation function Fi

[0024]

(Equation 2)

Parameters a, b, and 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 + ab) / σ}]-Log [Cosh} (-i
+ A + b) / σ｝] The above is the measurement of the beam in the X direction, but 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 adjustment of the beam size, the correction of the beam position, and the adjustment of the focus are performed, and then the normal drawing operation is started.

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

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

[0029]

As described above, according to the first to fourth aspects of the present invention,
According to Ming, the beam size, beam
Position and focus information can be accurately measured.
In addition, since the detection signal is not smoothed, focus information can be measured more accurately.

[0030]

[0031]

[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 chart 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 implementing 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 primary differential signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electron beam 2 Last lens 3 Electrostatic deflector 4 Knife edge member 5 Aperture 6 Faraday cup 7 A / D converter 8 Waveform memory 9 Control CPU 10 Deflection circuit

Claims (4)

(57) [Claims] 1. A charged particle beam is scanned across a member having a linear edge, and a signal waveform of the charged particle beam detected in accordance with the scanning is converted into a modeled signal waveform.
To the curve fitting process.
Based on the potting processed waveform, the measurement method of the charged particle beam so as to measure the beam size and the beam position and focus information of the charged particle beam. 2. A charged particle beam is scanned across a member having a linear edge, and the signal waveform data of the charged particle beam detected in accordance with the scanning or a first-order differential signal thereof.
The waveform data of the signal is represented by beam size a, beam position b,
Kerr for the evaluation function with the focus information σ as a parameter
By performing the fitting process, the load
A method for measuring a charged particle beam, wherein parameters a, b, and σ of the charged particle beam are determined. 3. A charged particle beam is scanned across a member having a linear edge, and a signal of the charged particle beam detected in accordance with the scanning is first differentiated.
Signal waveform data Ai (i is a scanning position, i = 1, 2,...)
.., N) are changed to beam size a, beam position b, focus
Scan information sigma to you and parameters following the evaluation function Fi (a, b, σ) = relative Tanh {(i-a-b ) / σ} -Tanh {(i + a-b) / σ}, waveform data A Curve fitting processing is performed so that the sum of squares of the difference between i and the evaluation function Fi is minimized.
A charged particle beam measuring method in which the parameters a, b, and σ of the charged particle beam to be measured are determined. 4. A charged particle beam having a straight edge.
Scan across the member that was
The charged particle beam signal waveform data Bi (i is the scanning position, i = 1, 2,..., N) is converted into a beam size a,
With the camera position b and focus information σ as parameters
For the evaluation function Fi (a, b, σ) = Log [Cosh ｛(i + ab) / σ｝] − Log [Cosh ｛(− i + a + b) / σ｝] , the difference between the waveform data Bi and the evaluation function Fi Square of
Perform the card must be installed blanking fitting process so that the sum is minimized
The parameters of the charged particle beam to be measured
Measurement of charged particle beam to determine a, b, σ
Method.