JPS584993B2 - Electron beam current density distribution measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring electron beam current density distribution in an electron beam exposure apparatus.

When drawing fine patterns on a mask substrate or a wafer substrate of a semiconductor integrated circuit by electron beam exposure, there is a method of using a so-called shaped beam shaped into a predetermined size in order to increase the drawing speed.

In electron beam exposure using this type of shaped beam, the beam current density distribution must be uniform, but in order to achieve this, a method for accurately measuring the beam current density distribution is required.

Conventionally, a method generally called the Knifezi method has been used to measure the electron beam current density distribution.

FIGS. 1 to 3 are diagrams for explaining this method.

That is, as shown in FIG. 1, an electron beam shield (mask) 14 with sharp edges is placed on the electron beam detector 13, and while continuously irradiating the electron beam to be measured, the mask 14 is placed over the electron beam detector 13. The beam is moved in the X direction in Figure 1, which is perpendicular to the edge of.

A shaded area 15 in FIG. 1 is the electron beam irradiation area, and as this moves in the X direction, the beam irradiation area for the detector 13 increases, and the detector output changes as shown in FIG. 2.

If we differentiate this or take the difference, we can obtain the third
A curve as shown in the figure is obtained.

Conventionally, this information was used to represent the beam current density distribution, but with this, it is impossible to know the actual state of the beam current density, which is originally distributed two-dimensionally. It's only useful for measurements.

Furthermore, the measured values were significantly affected by noise and had extremely low resolution.

In this case, there are various types of noise that affect the noise, but among them, shot noise generated from the electron beam source (electron gun) is caused by irregular fluctuations in the irradiation beam amount itself, and its amount is large. This cannot be avoided using conventional measurement methods.

SUMMARY OF THE INVENTION An object of the present invention is to solve these problems and provide a method that can accurately measure a two-dimensional electron beam current density distribution without being affected by noise.

To achieve this objective, the present invention modulates an electron beam with a blanking signal and irradiates it intermittently, and uses a frequency analyzer to determine the amplitude of the same frequency component as the blanking signal from the output of the electron beam detector. By extracting only the value, the S/N ratio of the detection signal is improved, and the electron beam, the electron beam detector, and the electron beam shield with edges in the X and Y directions arranged above the donor body are connected to the electron beam detector. The electron beam irradiation area is relatively displaced so as to expand or contract in subdivided unit sections in the X and Y directions, and the amplitude value of a specific frequency component in the detection signal extracted by the frequency analyzer at each position is obtained as information. After processing, changes in beam current for each unit section of the electron beam irradiation area are taken, and a two-dimensional electron beam current density distribution is determined.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 shows an overview of the apparatus for carrying out the invention.

In the figure, 1 is an electron beam mirror body, 2 is an electron gun, 3 is a blanking device for intermittent irradiation with an electron beam, 4 is a deflection device, and 5 includes an electron beam detector and an electron beam shield, which will be described later. Detection unit, 6 is a moving table on which this detection unit is placed, 7 is a control device, 8 is a blanking drive device, 9 is a blanking signal generator, 10 is a frequency analyzer, 11 is an information processing device, 12 is a The electron beam to be measured is shaped into a predetermined size by an electron lens system (not shown).

The frequency analyzer 10 uses the blanking signal given from the blanking signal generator 9 as a reference signal and extracts only the amplitude value of the same frequency component as the blanking signal in the detector output. Use a commercially available product called

FIG. 5 is a detailed diagram of the detection unit 5, and 13 is, for example, a PN
Junction type electron beam detector, 14 is an electron beam beam with sharp edges in the XY direction, and body donation (mask), 15
is the electron beam irradiation area, the portions blocked by the mask are shown with single hatching, and the portions not covered are shown with double hatching.

Next, a case will be described in which the present apparatus is used to measure the current density distribution of an electron beam shaped into an approximately 10 μm square.

In accordance with the program of the information processing device 11, the control device 7 first drives the moving stage 6 to move the detection unit 5 to the irradiation area of the electron beam 12, and then uses the deflection device 4 to move the beam irradiation area 15 in the X and Y directions. , for example, in 160 steps of 0.1 μm.

The order of displacement of the beam irradiation area 15 is, for example, such that for every 0.1 μm displacement in the Y direction, the beam irradiation area 15 is displaced 160 steps in the X direction.

After all, if we look at an arbitrary point P on the beam irradiation area 15, it will be displaced in a fixed order over the entire 16 μm square in the XY two directions.

In FIG. 5, 15' indicates the initial position of the beam irradiation area, and 15〃 indicates the final position. Between these, the beam irradiation area for the beam detector 13 (the double hatched area in FIG. 5) is
The entire area of the beam irradiation area 15 is subdivided in the X and Y directions.
, the unit area of 1 μm square will be enlarged one by one.

As the beam irradiation area of the beam detector 13 changes in this way, the detector output, that is, the frequency analyzer 10
0 input changes.

Since the electron beam 12 is periodically interrupted by the blanking device 3, the detector output also becomes a signal corresponding to the beam current modulated by the blanking signal plus noise of an unspecified frequency. , frequency analyzer 1
0 extracts only the amplitude value of the same frequency component as that of the blanking signal, so an output that contains almost no unspecified frequency noise and is faithfully proportional to the amplitude value of the beam current can be obtained.

Fig. 6 a shows an actual measurement example of the output waveform of the frequency analyzer 10 when the beam irradiation area 15 is displaced at a constant speed in the X direction while irradiating the electron beam intermittently, and b shows the temporal variation of the output. Changes are displayed as a curve.

On the other hand, FIG. 7 shows an actual measurement example of the beam detector output waveform when the beam irradiation area 15 is displaced at a constant speed in the X direction without intermittent electron beams.

Comparing FIG. 6 and FIG. 7, it can be seen that by modulating the beam current with a blanking signal and performing signal processing of the beam detector output using the frequency analyzer 10, it is possible to In comparison, it can be seen that the S/N ratio of the output signal is significantly improved, and high-precision, high-resolution signal detection can be realized.

Information processing of the output signal of the frequency analyzer 10 is performed as follows.

FIG. 8 is a three-dimensional representation of how the output value (■) of the frequency analyzer 10 changes when the beam irradiation area 15 is displaced in the X and Y directions.

In FIG. 8, a point P within the beam irradiation area 15 is, for example, Y
When the position is +5.0 μm in the X direction, the output value ■ of the frequency analyzer 10 that is stored in the information processing device 11 every time it is displaced by 0.1 μm from 0.0 μm to ±16.0 μm in the X direction is ■o、■１、・・・・・・、I
Let's say j,..., 1160.

Next, the beam irradiation area 15 is ΔY−10.1μ in the Y direction.
When the point P is displaced by m, the position of the point P in the Y direction becomes +5.1 μm, and then it is again displaced in the X direction from 0.0 μm to 16.0 μm in steps of 0.1 μm.

At this time, the value of ■ stored in the information processing device 11 is I'.

■１１、・・・・・・、I/i、・・・・・・、I'1
Represented by 60.

Next, the information processing device 11 performs calculation, and Δ■′・−I
Find /1-Ij.

The relationship between the X coordinate value of point P and Δ■'j is as shown in the graph of FIG. 9, and Δ■'j corresponds to the beam irradiation amount in the band-shaped region 16 of FIG.

The information processing device 11 further calculates
■ Perform the operation ′・.

The relationship between the X coordinate value of point P and Δ■· is as shown in the graph of FIG. 10, which represents the electron beam current density distribution in the band-shaped region 16 of FIG.

If the beam irradiation area 15 is further displaced by 0.1 μm in the Y direction and the same beam current detection and information processing as above is performed at the Y coordinate values of point P +5.1 μm and +5.2 μm, the result shown in FIG. The electron beam current density distribution in the band-shaped region 17 is obtained.

Similarly, by sequentially changing the Y coordinate value of point P and repeating beam current detection and information processing, the electron beam current density distribution over the entire 16 μm square area is determined as illustrated in FIG.

In this example, the calculation result Δ■・ of the information processing device 11 is
A plotter is used to display the output in a stereoscopic format.

This information can be effectively used to make the current density distribution of the shaped beam uniform by adjusting the electron lens system.

In the above explanation, a case has been described in which the beam is moved in a direction in which the beam irradiation area on the beam detector 13 is sequentially expanded, but the same result cannot be obtained even if the beam is moved in a direction in which the beam irradiation area is reduced. it is obvious.

As explained above, the present invention makes it possible to measure the two-dimensional beam current density distribution of a shaped beam with high precision, and will greatly contribute to the advancement of electron beam exposure technology using shaped beams. It is something.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of this type of measurement method that has been used conventionally.
FIG. 2 is a diagram showing changes in the beam detector output signal in the method of FIG. 1, FIG. 3 is a diagram also showing the measurement results of the beam current density distribution, and FIG. A schematic diagram, FIG. 5 is a detailed diagram of the detection unit, FIG. 6 is a diagram showing an actual measurement example of the frequency analyzer output signal in the present invention, and FIG.
The figure shows an example of actual measurement of the beam detector output signal in the conventional method, Figure 8 is an explanatory diagram of the measurement method according to the present invention, and Figure 9
The figure shows the distribution of ΔIlj in the X direction obtained by information processing, FIG. 10 also shows the distribution of ΔIj in the X direction, and FIG. 11 shows an example of the measurement results of the beam current density distribution. be. Explanation of symbols, 1: Electron beam mirror body, 2: Electron gun, 3 Niblanking device, 4: Deflection device, 5: Detection unit, 6: Moving table, 7: Control device, 8 Niblanking drive device, 9 Niblanking Signal generator, 10: Frequency analyzer, 11
: Information processing device, 12: Electron beam, 13: Electron beam detector, 14: Electron beam detector, body donation, 15, 16, 17
: Electron beam irradiation area.

Claims (1)

[Claims] 1. An electron beam is modulated by a blanking signal and is intermittently irradiated to an electron beam detector and an electron beam shield having edges in the X and Y directions arranged above the electron beam detector, and the electron beam, the electron beam detector, and The electron beam shield and the shield are relatively displaced so that the electron beam irradiation area for the electron beam detector is expanded or contracted in subdivided unit sections in the XY two directions, and the electron beam detector is adjusted at each position. Processing the output with a frequency analyzer to extract only the amplitude values of the same frequency components as the blanking signal,
A method for measuring electron beam current density distribution, characterized in that information processing is performed to obtain changes in beam current for each unit section of an electron beam irradiation area to obtain a two-dimensional electron beam current density distribution.