JPH0576129B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electron beam device having a field emission electron source that is suitable for use in an electron beam length measuring machine, a scanning electron microscope, or the like.

[Prior art] In electron beam length measuring machines, scanning electron microscopes, etc.
It is desirable to be able to control the amount of electron beam current applied to a sample depending on the sample, since it is necessary to change the SN ratio of the image obtained and to reduce damage and contamination depending on the sample. Fourth
The figure shows an example of an optical system of a scanning electron microscope, and in the figure, 1 is an electron gun, 2 is a converging lens, 3 is an objective lens, 4 is a deflection coil, 5 is an aperture, and 6 is a sample. The electron beam from the electron gun 1 is converged by the converging lens 2, as shown by the broken line, and the electron beam from the electron gun 1
The image of the virtual object point (crossover) is formed on point P, and the electron beam is narrowly focused onto the sample 6 by the objective lens 3. Note that the position of the electron beam irradiated onto the sample is changed according to the scanning signal applied to the deflection coil 4, and the surface of the sample 6 is scanned by the electron beam.

Here, when changing the amount of current of the electron beam irradiated to the sample 6, for example, the excitation of the converging lens 2 is strengthened, and the position of the crossover image is changed from point P to point P, as shown by the dotted line in the figure. ’. As a result, the amount of electron beam limited by the aperture 5 changes, and as a result, the amount of current of the electron beam irradiated onto the sample 6 changes.

[Problems to be Solved by the Invention] As described above, when changing the amount of current of the electron beam, the excitation of the converging lens 2 is changed and the position of the crossover is changed.
Focusing must be achieved by changing the excitation intensity of the objective lens 3. Furthermore, if a deflection coil, which is an electron beam scanning system, is located in front of the objective lens 3, changes in the excitation intensity of the objective lens will cause rotation of the image, that is, the scanning direction of the electron beam on the sample surface. Rotation occurs, which is undesirable. In particular, in an electron beam length measuring machine, if the direction of deflection of the electron beam changes with respect to the pattern to be measured, sufficient measurement accuracy cannot be obtained.

The present invention has been made in view of the above points, and it is possible to arbitrarily change the accelerating voltage and arbitrarily control the amount of current of the electron beam irradiated to the sample without controlling the objective lens. Another object of the present invention is to provide an electron beam device having a field emission electron source with excellent operability.

[Means for Solving the Problems] An electron beam device having a field emission electron source according to the present invention includes a field emission emitter, an extraction electrode for extracting an electron beam from the emitter, and an extraction electrode for extracting the extracted electrons. an accelerating electrode for acceleration, first and second electrostatic converging lenses disposed between the extraction electrode and the accelerating electrode, a power source for the first converging lens, and a second converging lens. a power supply for the lens, a storage means, an accelerating voltage setting means, a current amount setting means for setting the amount of electron beam current irradiated onto the sample, and an accelerating voltage set by the accelerating voltage setting means and the current. control means for reading data from the storage means and controlling the power supply for the first convergence lens and the power supply for the second convergence lens based on the amount of current set by the amount setting means; The storage means stores information for each different acceleration voltage.
a first converging lens and a second converging lens for changing the amount of current of the electron beam irradiated to the sample while maintaining a constant position of the crossover imaged by the first and second converging lenses; A plurality of combinations of voltages to be supplied to the two converging lenses are stored, and when the initial state of the device or the accelerating voltage is changed, the control means controls the combinations of the first and second voltages stored in the storage means. The first and second converging lenses are configured to automatically read out a predetermined combination of voltages among a plurality of combinations of supply voltages to the second converging lens, and control the power supplies of the first and second converging lenses based on the combination. It is characterized by

[Example] An example of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a scanning electron microscope equipped with a thermal field emission type electron gun based on the present invention, in which 11 is a field emission emitter, 12 is a filament holding the emitter 11, and 13 is the filament 12.
14 is a thermionic suppression electrode; 15 is a suppression voltage power source for applying a suppression voltage between the emitter 11 and the thermionic suppression electrode 14; 16 is an extraction electrode; 17 is the emitter 11;
18 is an accelerating electrode at ground potential; 19 is an accelerating voltage power source for applying an accelerating voltage between the emitter 11 and the accelerating electrode 18; 20 ，
21 is the first and second electrostatic converging lenses, 22 is a power source for the first converging lens 20, 23 is a power source for the second converging lens 21, 24 is an aperture for limiting the amount of current, and 25 is a cross An aperture located at the over point P ₀ , 26 a deflection coil for deflecting the electron beam, 27 an objective lens, 28 a sample, 29 detecting reflected electrons generated when the sample 28 is irradiated with an electron beam. 30 is a digital scanning signal generating circuit; 31 is a detector for controlling the scanning signal generating circuit 30 and detecting the length of the pattern to be measured on the sample based on the signal from the detector 29 and the scanning signal; a control device such as a computer for measuring 32
33 is a cathode ray tube to which the detection signal from the detector 29 and the scanning signal from the scanning signal generation circuit 30 are supplied;
3 is a control device such as a microprocessor, 34 is a memory, 35 is an acceleration voltage indicating means such as a rotary encoder, 36 is an electron beam current amount setting means, 3
7 is an initial current amount changeover switch.

In the configuration as described above, the filament 12
is heated by the supply of heating current from the heating power source 13, and as a result, the emitter 11 supported by the filament 12 is indirectly heated. Electrons are extracted from the emitter 11 by an extraction voltage applied between the emitter 11 and the extraction electrode 16. Here, thermoelectrons are also generated from the emitter 11 as it is heated, but these thermoelectrons are suppressed by the suppression voltage applied to the suppression electrode 14, and eventually emit field radiation mainly through the extraction electrode 16. Only the base electrons will be obtained. The extracted electrons are transferred to the accelerating electrode 1
8, and is narrowly focused onto the surface of the sample 28 by the two stages of converging lenses 20 and 21 and the objective lens 27. The electron beam irradiation position on the sample 28 is scanned two-dimensionally or in a line by a scanning signal from a scanning signal generating circuit 30. The reflected electrons and secondary electrons generated during the scanning are detected by the detector 29, and the detection signal is transmitted to the cathode ray tube 3 to which the scanning signal is supplied.
2, and the reflected electron image, secondary electron image, and line profile of the sample are displayed. The detection signal is also supplied to the control device 31, and the control device measures the width of the pattern on the sample. The length measurement result is displayed on the screen of the cathode ray tube 32,
Although not shown, it is recorded by a recording means such as a recorder.

FIG. 2 is an optical conceptual diagram of the scanning electron microscope shown in FIG _. However, the strength of the first converging lens 20 is set to such a level that no crossover image is formed between the first and second converging lenses. Here, in FIG. 1, the acceleration voltage of the electron beam is set by the acceleration voltage setting means 35.
The control device 33 is set by the setting means 3.
The accelerating power supply 19 is controlled according to the signal from the emitter 11 and the accelerating electrode 18 to apply a desired accelerating voltage. Further, the amount of current of the electron beam irradiated onto the sample 28 is inputted from the current amount setting means 36,
The control device 3 is controlled by the signal from the setting means 36.
3 is the first and second converging lens 2 from the memory 34.
Read out signals related to lens intensities of 0 and 21. The memory 34 stores a first memory according to each acceleration voltage.
and the lens strength of the second converging lens are stored. With this combination, even if the lens strength of the converging lens is changed to change the electron beam current amount, the crossover image is always focused on the point P ₀ , and at a specific accelerating voltage, the first
The lens strength V ₁ of the second converging lens 20 and the lens strength V ₂ of the second converging lens 21 have a relationship as shown in FIG. 3, for example. In addition, in this figure, the lens strength V ₁ of the first converging lens 20
corresponds to the desired amount of current. This memory 3
Based on the signal related to the lens strength read out from the first converging lens 2
The power supplies 22 and 23 of the converging lens 21 are controlled so that a desired voltage is applied to the converging lens 21 and the second converging lens 21. Note that, due to the capacity of the memory, the data related to the lens strength of the convergent lens stored in the memory 34 may be in random combinations, for example,
There are 100 combinations, but if an intermediate current amount is required, the control device 33 calculates V ₂ for the set V ₁ by interpolation, and based on the calculation result, each convergence I am trying to control the lens power supply for the lens. Also, combination data (V ₁ =
V ₀ , V ₂ =0) is not stored in the memory 34, the necessary data is calculated by extrapolation.

By the way, the combinations of data stored in the memory 34 are only stored up to the value V ₀ of V ₁ where V ₂ becomes zero. Therefore, even if you change the current amount setting means such as a rotary encoder and specify a value smaller than V ₀ , the value of V ₂ at that time will always be zero, which will deviate from the conditions for maintaining a constant crossover image. . In this embodiment, in order to solve this problem, when a value smaller than V ₀ is set by the current amount setting means, V ₂ becomes zero, but V ₁ always becomes V ₀ . Control device 3
3 is under control.

Referring again to FIG. 2, the amount of current of the electron beam transmitted through the convergent lenses 20 and 21 is limited by the aperture 24;
By changing the strength of the lens 1, the amount of current can be changed while the crossover of the electron beam is focused on the point _P0 . For example, in the case of a large current, the sample is irradiated with an electron beam along the path shown by I ₃ , and as I ₄ and I ₅ increase, the amount of electron beam blocked by the aperture 24 increases, resulting in the sample 28 The amount of current of the electron beam irradiated to the area decreases. In this way, no matter what accelerating voltage or electron beam current amount is selected, the crossover image can always be tied to point P ₀ .

Here, when changing the initial state in which the device is operated for the first time or the accelerating voltage, the control device 33 reads out the 50th combination data among the 100 sets of combination data, and based on the data, each converging lens I'm trying to control it. This 50th data stores data that provides the optimum electron beam current amount for frequently used samples. In addition,
The material of the sample surface in scanning electron microscopes and electron beam length measuring machines includes conductive materials, semiconductors, and insulators.
The optimum amount of electron beam current varies depending on the material. Therefore, in this embodiment, when the initial current amount changeover switch 37 changes the initial state or acceleration voltage, the combination data read by the control device 33 is set to 50% depending on the conductive material, semiconductor, or insulating material. It is configured so that you can select the number, 40th, 30th, etc. the result,
The optimal or nearly optimal electron beam current amount for each type of sample can be instantaneously obtained by changing the initial state or accelerating voltage, thereby providing an apparatus with excellent operability.

In the embodiment described in detail above, two stages of electrostatic converging lenses are arranged between the extraction electrode and the accelerating electrode, and the lens strength of the two stages of converging lenses is defined as the accelerating voltage and the desired current amount of the electron beam. change according to
Since the position of the crossover image formed by the two stages of convergent lenses is always kept constant, there is no need to adjust the objective lens even if the accelerating voltage or current amount is arbitrarily changed. Therefore, rotation of the image by the objective lens is eliminated, and the scanning direction of the electron beam can be maintained constant. As a result, with an electron beam length measuring machine, even if the accelerating voltage or electron beam current amount is changed depending on the sample, the scanning direction of the electron beam with respect to the pattern to be measured does not change, making it possible to perform highly accurate measurements. can. Further, even when changing the initial state of the apparatus or the accelerating voltage, it is possible to always instantaneously set the electron beam current amount that is optimal or close to the optimum for the sample to be measured or observed. Note that the present invention is not limited to the embodiments described above, and can be modified in many ways. For example, the position of the converging lens is not limited to between the extraction electrode and the acceleration electrode.

[Effect] As detailed above, according to the present invention, the lens strength of the two-stage converging lens is changed according to the accelerating voltage and the desired electron beam current amount, and the two-stage converging lens always Since the position of the formed crossover image is kept constant, there is no need to adjust the objective lens even when the accelerating voltage or amount of current changes. Therefore, rotation of the image by the objective lens is eliminated, and the scanning direction of the electron beam can be maintained constant. As a result, when the present invention is used in an electron beam length measuring machine, even if the accelerating voltage or the amount of electron beam current is changed depending on the sample, the scanning direction of the electron beam with respect to the pattern to be measured does not change, resulting in improved accuracy. Can perform high measurements. Further, in the present invention, data is read from the storage means based on the acceleration voltage set by the acceleration voltage setting means and the current amount set by the current amount setting means, and the power source of the first converging lens is adjusted. and the power source of the second converging lens When the control means changes the initial state of the device or the accelerating voltage, the control means controls the power source of the first and second converging lenses stored in the storage means. The device is configured to automatically read out a predetermined combination of supply voltages among a plurality of combinations of supply voltages, and control the power supplies of the first and second converging lenses based on the combination, so that the initial state of the device is Even when changing the acceleration voltage or acceleration voltage, the electron beam current amount that is optimal or close to the optimum value for the sample to be measured or observed can be instantly set, which significantly improves operability.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a scanning electron microscope based on the present invention, Fig. 2 is a conceptual diagram of electron optics of the scanning electron microscope shown in Fig. 1, Fig. 3 is a diagram showing the relationship between voltages applied to the converging lens, and Fig. The figure shows an example of an optical system of a conventional scanning electron microscope. 11... emitter, 12... filament,
13... Heating power source, 14... Thermionic suppression electrode, 1
5... Suppression voltage power supply, 16... Extraction electrode, 17
...Extraction voltage power supply, 18...Acceleration electrode, 19...
...Acceleration voltage power supply, 20, 21...Electrostatic converging lens, 22...Power supply for converging lens 20, 23...Power supply for converging lens 21, 24, 25...Aperture, 26
... Deflection coil, 27 ... Objective lens, 28 ...
Sample, 29...Detector, 30...Digital scanning signal generation circuit, 31...Control device, 32...Cathode ray tube, 33...Control device, 34...Memory, 35
. . . Acceleration voltage instruction means, 36 . . . Electron beam current amount setting means.

Claims (1)

[Claims] 1. A field emission emitter, an extraction electrode for extracting an electron beam from the emitter, an acceleration electrode for accelerating the extracted electrons, and between the extraction electrode and the acceleration electrode. a first and a second electrostatic converging lens disposed in the sample, a power supply for the first convergence lens, a power supply for the second convergence lens, a storage means, an accelerating voltage setting means; a current amount setting means for setting the amount of electron beam current to be irradiated; and the storage means based on the acceleration voltage set by the acceleration voltage setting means and the current amount set by the current amount setting means. control means for reading data from the first converging lens and controlling a power source for the first converging lens and a power source for the second converging lens;
the first converging lens and the second converging lens for changing the amount of current of the electron beam irradiated to the sample while maintaining a constant position of the crossover imaged by the first converging lens and the second converging lens; A plurality of combinations of voltages to be supplied to the converging lens are stored, and when the initial state of the device or the accelerating voltage is changed, the control means controls the first and second combinations stored in the storage means. It is characterized in that it is configured to automatically read out a predetermined combination of voltages among a plurality of combinations of voltages supplied to the converging lens, and control the power supplies of the first and second converging lenses based on the combination. An electron beam device with a field emission electron source. 2. A plurality of combinations of voltages to be supplied to the first and second converging lenses are set, and the control means reads out the predetermined number from the storage means when changing the initial state of the device or the accelerating voltage. An electron beam apparatus having a field emission electron beam according to claim 1, further comprising a switching means for specifying one of the combinations.