JP3524776B2 - Scanning electron microscope - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning electron microscope capable of easily and accurately performing an electron beam axis alignment operation.

[0002]

2. Description of the Related Art In a scanning electron microscope, an electron beam generated from an electron gun and accelerated is focused by a condenser lens and an objective lens to irradiate a sample, and the electron beam is two-dimensionally scanned on the sample. Secondary electrons or backscattered electrons generated from the sample are detected and a detection signal is supplied to the cathode ray tube to obtain a scan image of the sample.

In such a scanning electron microscope, it is necessary to adjust a lens such as a condenser lens and an objective lens, a gun alignment coil and an alignment coil for axis alignment to irradiate a sample with an electron beam under optimum conditions. This adjustment work is cumbersome and requires skill.

Therefore, in some scanning electron microscopes,
Memory for the axis alignment data obtained when adjusting the device for each acceleration voltage and objective lens strength (corresponding to the distance between the sample and objective lens) at the final adjustment stage of the device manufacturing process I remember it. In this way, when using the actual device, if you specify the accelerating voltage and the lens strength of the objective lens, you can read the specified data from the memory accordingly and control each alignment coil based on that data. The electron beam can be adjusted.

[0005]

However, in the above-mentioned method, when the combination is used with the specific accelerating voltage for which data is obtained and the lens strength of the objective lens, accurate axis alignment can be performed. However, when an accelerating voltage other than this specific accelerating voltage is used, it is necessary to adjust the axis alignment.

Therefore, recently, each electronic alignment coil is adjusted for each combination of the accelerating voltage value, which is a characteristic point when adjusting the apparatus, and the lens strength of the objective lens, and data is obtained to obtain another accelerating voltage and the objective lens. The data in the combination with the lens strength is calculated by performing the interpolation calculation, and the data for each combination of each acceleration voltage and the lens strength of the objective lens is obtained.

FIG. 1 shows changes in the value of the current flowing through the alignment coil for each acceleration voltage at the lens strength of an objective lens. In this case, the optimum values M1 to M of the currents to be passed through the alignment coils by adjusting the device with the acceleration voltage, which is a characteristic point, for example, 5 kV, 10 kV, 20 kV, and 30 KV.
Measure 4 and store the value in memory. Then, with respect to the current value at the acceleration voltage other than the characteristic point, the value is calculated by linear approximation and stored in the memory in the same manner.

After acquiring and storing such prior data, when the accelerating voltage and the lens strength of the objective lens are determined during the actual use of the apparatus, the value of the current flowing from the memory to the alignment coil is determined according to the combination. Read out the data and control the alignment coil. However, in the portion where the lens strength of the objective lens of the accelerating voltage other than the actually measured feature points is combined, the linear approximation does not always give an accurate value, and the alignment coil must be readjusted.

The present invention has been made in view of the above points, and an object thereof is to realize a scanning electron microscope with improved operability in adjusting the alignment coil.

[0010]

A scanning electron microscope according to the first invention comprises an electron gun and a lens system including a condenser lens and an objective lens for finely focusing an electron beam from the electron gun onto a sample. A scanning means for two-dimensionally scanning an electron beam on a sample; an accelerating voltage power supply for determining an accelerating voltage of the electron beam in an electron gun; an axis-aligning coil for aligning the electron beam; And a storage unit that stores the data of the axis-aligning coil according to the acceleration voltage value of the beam. In the scanning electron microscope configured to control, the data of the alignment coil is read from the storage means, the alignment coil is controlled based on this data, and When adjusted, based on data alignment coils after the readjustment, changes the acceleration voltage of the electron beam data alignment coils which is stored in the storage means
The feature is that it is rewritten when it is done.

According to the first aspect of the invention, in the scanning electron microscope, the data of the alignment coil is read from the storage means based on the acceleration voltage of the electron beam, and the alignment coil is controlled based on this data. When the data of the axis alignment coil is read from, the axis alignment coil is controlled based on this data, and further readjustment is performed, the axis alignment stored in the storage means is based on the data of the axis alignment coil after the readjustment. Electron beam acceleration with coil data
Rewrite when the voltage is changed .

[0012]

A scanning electron microscope according to the second invention comprises the first
In the invention, the axis alignment coil data is prepared according to the acceleration voltage value and the lens strength of the objective lens.

In the scanning electron microscope according to the third invention, in the first invention, the rewriting of the data of the axis alignment coil stored in the storage means corresponds to the acceleration voltage value when the axis alignment coil is readjusted. to not only data, the pressure
The feature is that the data corresponding to the acceleration voltage near the fast voltage is also performed.

[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. 2 shows an example of a scanning electron microscope according to the present invention, and 1 is an electron gun. The electron beam EB generated and accelerated by the electron gun 1 is finely focused on the sample 4 by the condenser lens 2 and the objective lens 3. Further, the electron beam EB is scanned by the scanning coil 5, and a predetermined area on the sample 4 is scanned by the primary electron beam EB.

A scanning signal is supplied from the scanning signal generator 6 to the scanning coil 5, and the scanning signal is controlled by the magnification controller 7. For example, when a low magnification is designated, the magnification controller 7 controls the scanning signal generator 6 to supply a scanning signal having a relatively large amplitude to the scanning coil. vice versa,
When a high magnification is set, the magnification controller 7 controls the scanning signal generator 6 to supply a scanning signal having a relatively small amplitude to the scanning coil 5.

Secondary electrons generated from the sample 4 by irradiating the sample 4 with the primary electron beam EB are detected by the secondary electron detector 8. The output signal of the detector 8 is
After being converted into a digital signal by the AD converter 9,
It is supplied to and stored in the image memory 10.

The video signal stored in the image memory 10 is read out and supplied to the cathode ray tube 12 via the DA converter 11, so that the cathode ray tube 12 scans secondary electrons in a predetermined area to the sample 4. The image is displayed.

Various alignment coils and stigma coils for adjusting the axis of the electron beam are arranged along the optical axis of the electron beam EB. In FIG. 2, only the gun alignment coil 13 and the alignment coil 14 are shown. Has been done. Power supply 15 to the gun alignment coil 13
From the electron beam for axial alignment current is flowed, also Ala <br/> for axial alignment current is applied to the electron beam from the power source 16 in Lee Men Tokoiru 14.

The power sources 15 and 16 are connected to the interface 18 of the CPU 17 and controlled by the CPU 17. Further, an accelerating voltage power source 19 for the electron gun 1, a power source 20 for the condenser lens 2, a power source 21 for the objective lens 3,
The magnification controller 7 is also connected to the interface 18. A memory 22 is connected to the CPU 17.
The operation of such a configuration will be described below.

In normal observation of a scanning electron microscope image, the primary electron beam EB from the electron gun 1 is finely focused on the sample 4 by the condenser lens 2 and the objective lens 3 and the electron beam is irradiated on the sample 4. The area is two-dimensionally scanned by the scanning coil 5. Secondary electrons generated by irradiating the sample 4 with the electron beam are detected by the detector 8.

The detection signal is stored in the image memory 10 via the AD converter 9. The signal stored in the image memory 10 is read out, and the cathode ray tube 1 is read through the DA converter 11.
2 is supplied to the cathode ray tube 12, so that a scanning secondary electron image of the sample is displayed on the cathode ray tube 12. Here, when changing the observation magnification, the scanning signal from the scanning signal generator 6 is controlled by the magnification controller 7 to change the scanning range of the primary electron beam EB on the sample 4.

At the time of observing such a scanning image, the accelerating voltage is determined according to the type of the sample 4, and the distance between the objective lens 3 and the sample 4 (referred to as working distance) is also adjusted. As a result, the accelerating voltage power source 19 is controlled, the accelerating voltage of the electron beam in the electron gun 1 is set to a desired value, the power source 21 of the objective lens 3 is adjusted according to the working distance, and the electron beam is emitted from the sample 4 The lens strength of the objective lens is controlled so that it is just focused.

Now, the memory 2 connected to the CPU 17
In the table 2, data of currents flowing through the alignment coils corresponding to the acceleration voltage values and the lens strength of the objective lens are stored in the form of a table. This table is provided with a number corresponding to the number of alignment coils and stigma coils.

For example, in the table T1 for the alignment coil 14, a combination of the acceleration voltage, which is a characteristic point, and the lens strength of the objective lens, for example, the lens strength of a plurality of objective lenses, is set in the adjustment stage in the manufacturing process of the device. Against 5
Adjust the device at kV, 10 kV, 20 kV, 30 KV and measure the optimum value of the current flowing through the alignment coil 14,
The value is stored in the table T1 of the memory 22. And, regarding the current value at the acceleration voltage other than the feature point,
The value is calculated by linear approximation and is similarly stored in the table T1 of the memory 22.

After acquiring and storing such prior data, when the accelerating voltage and the lens strength of the objective lens are determined during the actual use of the apparatus, the alignment coil is determined from the table T1 of the memory 22 corresponding to the combination. 14
The data of the current value to be supplied to the alignment coil 14 is read, and the current corresponding to the data is supplied from the power supply 16 to the alignment coil 14.

Of the data, particularly in the case of data obtained by approximation, sometimes the data is not always accurate alignment data. In that case, the operator manually adjusts the power supply 16 of the alignment coil 14 to optimally align the electron beam.

As a result, for example, the characteristic points actually measured in the process of manufacturing the device are acceleration voltage of 5 kV and 1 as shown in FIG.
It is 0 kV, and when the data at other acceleration voltages is calculated by linear approximation, if the acceleration voltage is controlled to 7 kV,
The data of the electric current passed through the aiming coil 14 is A. The power supply 16 is controlled based on this data A, and a current is passed through the alignment coil 14 to align the electron beam axis.

Although the steps up to this point are automatically performed, if the image is blurred due to this axis alignment, the power supply 16 is readjusted. By this readjustment, the alignment coil 14 is accurately adjusted by the data of A + A ′, and the image observation is executed.

The data of this A'is the interface 18
Is temporarily stored in the accelerating voltage power supply 19 of the electron gun 1.
Is controlled to change the acceleration voltage, the data in the corresponding portion of the table T1 of the memory 22 is rewritten from A to A + A '. Rewriting of the table contents of the memory can be performed by an operator's instruction, but in order to improve the operability of the device, it is desirable to use the switching of the acceleration voltage as a trigger.

The rewriting of this data may be performed only by the acceleration voltage (7 kV in the above example) at the lens strength of the specific objective lens that was actually observed, but the acceleration voltage near the acceleration voltage and the objective It is desirable to rewrite the data for the lens strength of the lens. For example, when rewriting data is acquired by actually observing at an accelerating voltage of 7 kV, for example, data B at an accelerating voltage of 6 kV becomes B + B ′ and data C at an accelerating voltage of 8 kV.
When C is changed to C + C ′ and the data D at 9 kV is changed to D + D ′, the accuracy of the subsequent adjustment of the alignment coil 14 is increased.

The above steps are performed not only for the alignment coil 14, but also for the gun alignment coil 13, other alignment coils (not shown), and the stigma coil. However, since the electron beam axis adjustment in the gun alignment coil 13 is not affected by the lens strength of the objective lens 3, the axis adjustment data is
It depends exclusively on the acceleration voltage.

The embodiment of the present invention has been described above.
The present invention is not limited to this form. For example,
Although the table rewriting operation in the memory is performed when the accelerating voltage is changed, it may be performed when the lens strength of the objective lens is changed.

[0034]

According to the first invention, in the scanning electron microscope, the data of the alignment coil is read from the storage means based on the acceleration voltage of the electron beam and the alignment coil is controlled based on this data. When the data of the axis alignment coil is read from the storage means, the axis alignment coil is controlled based on this data, and the readjustment is performed again, the data is stored in the storage means based on the data of the axis alignment coil after the readjustment. The data of the axis alignment coil is applied to the electron beam.
It is configured to be rewritten when the fast voltage is changed . As a result, with the use of the device, the accuracy of control of the axis alignment coil is increased, the axis alignment operation can be easily performed in a short time even if the acceleration voltage is finely changed, and the operability of the device is improved.

[0035]

In the second aspect of the present invention, since the data of the axis alignment coil is prepared according to the acceleration voltage value and the lens strength of the objective lens, even if the lens strength of the objective lens is finely changed as well as the acceleration voltage. The axis alignment operation can be easily performed in a short time, and the operability of the device is improved.

In the third invention, the data of the axis alignment coil stored in the storage means is rewritten not only in the data corresponding to the acceleration voltage value when the axis alignment coil is readjusted, but also in the vicinity of the acceleration voltage. Since the data corresponding to the acceleration voltage is also performed, the axis alignment operation can be easily performed in a short time even if the acceleration voltage is finely changed, and the operability of the apparatus is further improved.

[Brief description of drawings]

FIG. 1 is a diagram showing aligning tent coil data according to an acceleration voltage.

FIG. 2 is a diagram showing an example of a scanning electron microscope according to the present invention.

FIG. 3 is a diagram for explaining alignment coil data and rewritten data according to an acceleration voltage.

[Explanation of symbols]

1 electron gun 2 condenser lens 3 Objective lens 4 samples 5 scanning coils 6 Scan signal generator 7 Magnification controller 8 Secondary electron detector 9 AD converter 10 image memory 11 DA converter 12 Cathode ray tube 13 gun alignment coil 14 Alignment coil 15,16 power supply 17 CPU 18 Interface 19 Accelerating voltage power supply 20 Condenser lens power supply 21 Objective lens power supply 22 memory

Claims (3)

(57) [Claims] 1. An electron gun, a lens system including a condenser lens and an objective lens for finely focusing an electron beam from the electron gun on a sample, and a two-dimensional scanning of the electron beam on the sample. Storing means, accelerating voltage power source that determines the accelerating voltage of the electron beam in the electron gun, axis-aligning coil for aligning the electron beam, and data of the axis-aligning coil according to the accelerating voltage value of the electron beam are stored. In the scanning electron microscope configured to read the data of the alignment coil from the storage means based on the acceleration voltage of the electron beam and control the alignment coil based on this data, When the alignment coil data is read, the axis alignment coil is controlled based on this data, and the readjustment is performed again, the data of the alignment coil after this readjustment Based on the data, the accelerating voltage of the electron beam is changed based on the data of the axis alignment coil stored in the storage means.
Scanning electron microscope that was rewritten when I did it. 2. The data of the axis alignment coil is an acceleration voltage value.
The scanning electron microscope according to claim 1, which is prepared in accordance with the lens strength of the objective lens . 3. An axis alignment coil stored in a storage means.
When re-adjusting the axis alignment coil, rewrite the data
Not only the data corresponding to the acceleration voltage value of
Also do the data corresponding to the acceleration voltage near the pressure.
The scanning electron microscope according to claim 1, further comprising: