JPH08315761A - Charged particle beam irradiating device - Google Patents

Abstract

PURPOSE: To reduce labor to adjust condenser lenses, and shorten stopping time of a device by finding an actual value of an aperture diameter, and specifying an optimal value of a lens physical quantity corresponding to it. CONSTITUTION: A length measuring unit 15 specifies an actual value of a diameter of an aperture 7a by recording data of a memory 13, and gives this to a specific unit 16. The unit 16 specifies an optimal value of an exciting current corresponding to the given aperture diameter by referring to a table of a memory 17. This optimal value information is given to control units 18 and 19. The units 18 and 19 control power sources 20 and 21 so that the exciting current given to condenser lenses 3 and 4 from the lens power sources 20 and 21 coincides with an optimal value. Therefore, even if the exciting current of the lenses 3 and 4 is not adjusted every time when the aperture 7a is newly set, since the exciting current of the lenses 3 and 4 can be automatically set in an optimal value corresponding to an actual diameter of the aperture 7a, maximum resolution can be pulled out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for irradiating a target with a charged particle beam, such as a scanning electron microscope.

[0002]

2. Description of the Related Art FIG. 10 shows an example of a scanning electron microscope. The electron beam 2 emitted from the electron gun 1 is reduced by the condenser lenses 3 and 4, and the aperture plate 7
It is focused on the sample 8 by the objective lens 6 while being shaped by the aperture 7a. The electron beam moves on the sample 8 by the deflection action of the scanning coil 5, and the reflected electrons, secondary electrons, etc. emitted at that time are captured by the detector 9. An image of the sample is formed based on the current output from the detector 9. Reference numeral 10 is a holder for the aperture plate 7. Due to the position adjustment of the aperture 7a, the holder 10 can be moved two-dimensionally in a plane orthogonal to the optical axis.

In the above scanning electron microscope, a new aperture plate 7 is installed in the optical path when the apparatus is started up or when the contamination of the aperture 7a exceeds the allowable range.
The setting of the exciting currents of the condenser lenses 3 and 4 when the aperture plate 7 is newly installed is left to the operator, and normally, assuming that the diameter of the aperture 7a is the designed value, the exciting currents of the condenser lenses 3 and 4 are set. Had set.

[0004]

However, with respect to the aperture diameter, there are cases where a manufacturing error with respect to a design value cannot be ignored, such as a manufacturing error with a design value of several tens of μm of about 10 μm. In this case, if the exciting current of the condenser lens is set based on the design value of the aperture diameter, there is a strong possibility that the maximum resolution that the device can exhibit at that time has not been derived. Therefore, it becomes necessary for the operator to adjust the exciting current of the condenser lens so as to maximize the resolution while observing the gold particles and the like, and the stop time of the apparatus becomes long. This adjustment work requires considerable skill.

An object of the present invention is to provide a charged particle beam irradiation apparatus which can reduce the trouble when setting the condenser lens according to the aperture diameter.

[0006]

When the invention of claim 1 is described in association with FIG. 1 showing an embodiment, a charged particle beam 2 is provided.
Condenser lenses 3 and 4 for converging the condenser lenses, lens setting means 20 and 21 for setting a physical quantity that controls the converging action of the condenser lenses 3 and 4, and an aperture 7a for shaping the charged particle beam emitted from the condenser lenses 3 and 4. And an aperture 7 applied to a charged particle beam irradiation apparatus including
Length measuring means 5, 10 to 13, 1 for measuring the actual value of the diameter of a
5, the diameter of the aperture 7a and the lens setting means 20, 21
The storage means 17 for storing the information showing the correlation with the optimum value of the physical quantity of is provided to achieve the above-mentioned object. According to the second aspect of the present invention, the condenser lenses 3 and 4 for focusing the charged particle beam, the lens setting means 20 and 21 for setting the physical quantity that controls the focusing action of the condenser lenses 3 and 4, and the target with the charged particle beam. Condenser lenses 3 and 4 to scan
The deflection means 5 for deflecting the charged particle beam emitted from the device, the aperture 7a for shaping the charged particle beam emitted from the condenser lenses 3 and 4, and the aperture shape when the aperture 7a is scanned by the charged particle beam are correlated. The detecting means 10 to 13 for detecting changes in physical quantity, the aperture diameter specifying means 15 for specifying the actual value of the diameter of the aperture 7a based on the detection result of the detecting means, and the diameter of the aperture 7a and the lens setting means 20, 21. The above-described object is achieved by the charged particle beam irradiation apparatus including the storage unit 17 that stores the information indicating the correlation with the optimum value of the physical quantity. The invention according to claim 3 is applied to the charged particle beam irradiation apparatus according to claim 1 or 2, wherein the optimum value is the lens setting means 20 when the beam diameter of the charged particle beam with which the target is irradiated is minimized. Two
It corresponds to a physical quantity of 1. The invention according to claim 4 is applied to the charged particle beam irradiation apparatus according to claim 1 or 2, and specifies the optimum value of the physical quantity corresponding to the actual value of the diameter of the aperture 7a according to the stored contents of the storage means 17. Means 1
6 is provided. The invention of claim 5 is applied to the charged particle beam irradiation apparatus of claim 4, wherein the physical quantity is the optimum value specifying means 1
Lens setting means 2 so that the optimum value specified in 6 is obtained.
Lens control means 18 and 19 for controlling 0 and 21 are provided. The invention of claim 6 is applied to the charged particle beam irradiation apparatus of claim 1 or 2, wherein the physical quantity is the exciting current of the condenser lenses 3 and 4.

[0007]

According to the invention of claim 1, the length measuring means 5, 10-1
Based on the actual value of the diameter of the aperture 7a measured at 3, 15 and the stored contents of the storage means 17, the optimum value of the physical quantity of the lens setting means 20, 21 with respect to the actual value of the diameter of the aperture 7a can be specified. . According to the second aspect of the present invention, the charged particle beam is focused on the position of the aperture 7a, and the deflecting means 5 deflects the charged particle beam to scan the aperture 7a and its periphery. At this time, a physical quantity, for example, a current due to reflected electrons from the aperture 7a, secondary electrons, or electrons absorbed around the aperture 7a is changed in correlation with the shape of the aperture 7a, and the change is detected.
It is detected at 0-13. Thereby, the image of the aperture 7a can be observed, and the actual value of the diameter of the aperture 7a can be specified from the image. Then, based on the specified actual value of the diameter of the aperture 7a and the stored contents of the storage means 17, the lens setting means 2 for the actual value of the diameter of the aperture 7a.
The optimum value of the physical quantity of 0,21 can be specified. According to the invention of claim 3, when the optimum value corresponding to the actual value of the aperture diameter is specified and the physical quantities of the lens setting means 20 and 21 are set according to the optimum value, the beam diameter of the charged particle beam with which the target object is irradiated is determined. It is the smallest. In the invention of claim 4, the optimum values of the physical quantities of the lens setting means 20 and 21 are the optimum value specifying means 16
Automatically specified in. According to the invention of claim 5, the physical quantities of the lens setting means 20 and 21 are automatically set to the optimum values corresponding to the actual values of the aperture diameters. According to the invention of claim 6, the optimum value of the exciting current of the condenser lenses 3 and 4 corresponding to the actual value of the aperture diameter can be specified.

Incidentally, in the section of means and action for solving the above-mentioned problems for explaining the constitution of the present invention, the drawings of the embodiments are used to make the present invention easy to understand. It is not limited to.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a scanning electron microscope will be described with reference to FIGS. FIG. 1 shows an outline of the scanning electron microscope according to the present embodiment, and the same parts as those in FIG. 10 are designated by the same reference numerals. As is clear from FIG. 1, the scanning electron microscope of this embodiment is provided with a detector 11 for detecting backscattered electrons and secondary electrons generated when the aperture plate 7 is irradiated with an electron beam. 1
The current output from 1 is amplified by the amplifier 12 and input to the memory 13. Further, a current corresponding to the absorbed electrons to the aperture plate 7 is taken out from the holder 10, amplified by the amplifier 12, and input to the memory 13. The memory 13 stores the input signal from the amplifier 12 when the aperture plate 7 or the like is scanned by the electron beam 2 in association with the scanning position. In FIG. 1, the output from the detector 11 and the output from the holder 10 are illustrated as being input to the amplifier 12, but in actuality, either one of the inputs may be input. Further, the illustration of the detector on the sample 8 side is omitted.

A calibration mark 14 is provided on the upper surface of the aperture plate 7. The calibration mark 14 is formed on the substrate 14a made of silicon (Si), for example, as shown in FIG.
Further, a plurality of tantalum (Ta) 14b having a predetermined width A are provided at predetermined intervals B. Information about the actual values of the width A and the interval B is given to the length measuring unit 15 in FIG. 1 in advance.
The length measuring unit 15 specifies the actual value of the diameter of the aperture 7a based on the data recorded in the memory 13. The process will be described later. Information about the actual value of the diameter of the aperture 7a specified by the length measuring unit 15 is given to the optimum value specifying unit 16. Optimal value identification unit 1
Reference numeral 6 carries out the processing described later necessary for setting the exciting current of the condenser lenses 3 and 4 based on the output signal from the length measuring unit 15 and the stored contents of the memory 17.

The process of specifying the aperture diameter by the length measuring unit 15, the stored contents of the memory 17, and the process of the optimum value specifying unit 16 will be described in order. First,
When the aperture diameter is specified by the length measuring unit 15, it is necessary to take the image of the aperture 7a into the memory 13 and specify the observation magnification as a precondition. To capture the image of the aperture 7a, the exciting currents of the condenser lenses 3 and 4 are set so that the electron beam 2 is focused at the position of the aperture 7a. Then, the current of the scanning coil 5 is adjusted to two-dimensionally scan the aperture 7a and its periphery with the electron beam 2, and the image data obtained at that time is stored in the memory 13. At this time, the holder 1 is attached to the amplifier 12.
Either the output signal of 0 or the output signal of the detector 11 may be taken in.

By the above operation, if the image of the aperture 7a and its surroundings is taken into the memory 13 as image data of m × n pixels as shown in FIG. The number p of pixels corresponding to the diameter of is specified. At this time, the position of the aperture 7a may be specified by performing a well-known edge detection as an image processing method. In addition, as shown in FIG.
Based on the data stored in 3, the intensity waveform X of the output signal of the holder 10 or the detector 11 is specified, and the positions P1 and P2 of the diameter of the aperture 7a are specified from the waveform X, and the points between the points P1 and P2 are specified. The number of pixels p may be calculated. The actual value of the diameter of the aperture 7a is obtained from the number of pixels p and the observation magnification. When the observation magnification is constant, the number of pixels p may be treated as the actual value of the aperture diameter. When it is necessary to specify the observation magnification of the aperture image, the holder 10 is driven to move the calibration mark 14 to the optical axis position. After this, the scanning coil 5 deflects the electron beam 2 to calibrate the calibration mark 1.
4 is scanned, and the image of the calibration mark 14 is captured in the memory 13. Then, the observation magnification can be specified from the actual values of the dimensions A and B of the calibration mark 14 given to the length measuring unit 15 and the number of pixels corresponding to the dimensions A and B in the image data of the memory 13.

Focus adjustment of the lenses 3 and 4 with respect to the above-described aperture 7a, and aperture 7a by the scanning coil 5
Although the operator may manually instruct the scanning of the calibration mark 14 and the movement of the holder 10, it is preferable that the operator automatically process the scanning of the calibration mark 14 by a command from the length measuring unit 15. The number of pixels corresponding to the dimensions A and B of the calibration mark 14 when the observation magnification is set to an appropriate value is given to the length measuring unit 15 in advance, and the width A of the observed image when the calibration mark 14 is scanned by the electron beam 2 is given. If the current value of the scanning coil 5 is automatically adjusted so that the number of pixels corresponding to the distance B and the number of pixels corresponding to the interval B match, the image of the aperture 7a can always be observed at a constant magnification.

In the above process, the measurement accuracy of the aperture diameter changes depending on the number of pixels m × n when observing the image of the aperture 7a and the scanning speed of the electron beam 2 by the scanning coil 5. The required measurement accuracy depends on the maximum resolution required for the electron microscope, but as an example, if the aperture diameter is several tens of μm with respect to the resolution of 4 to 5 nm (nanometer), the accuracy of about 0.1 μm is required. It is enough.

Next, the memory 17 will be described with reference to FIGS.
The stored contents of will be described. Although the two-stage condenser lenses 3 and 4 are provided in FIG. 1, the following description will be made assuming that the condenser lens is a single-stage condenser lens for simplicity.
4 to 9, Ic is the exciting current of the condenser lens, αi is the half-angle of opening at the electron beam focusing position, A i
P means the aperture diameter, respectively.

In designing the electron beam optical system, the relationship between the exciting current Ic of the condenser lens and the half-angle αi of the electron beam is calculated as shown in FIG. Also, electron beam 2
Is mainly controlled by chromatic aberration and diffractive aberration, and chromatic aberration d _c is d _c ∝αi and diffractive aberration d _d is d _d ∝αi ^-1. It is a function of αi. FIG. 5 schematically shows the relationship between the excitation current Ic and each aberration and total aberration (square root of sum of squares of chromatic aberration and diffraction aberration). In FIG. 5, the exciting current Ic (opt) when the total aberration is the smallest corresponds to the optimum value of the exciting current that gives the minimum beam diameter. The curves shown in FIGS. 4 and 5 are obtained when the aperture diameter is fixed to a certain constant value, and the positions of these curves change as the aperture diameter changes. Therefore, the relationship between the exciting current Ic of the condenser lens and the half-angle αi of opening due to the change in the aperture diameter is shown in FIG.
7 shows the relationship between the exciting current Ic and each aberration associated with the change in the aperture diameter.

Here, the design value of the aperture diameter is several tens of μm.
It may be set to a small degree, and the manufacturing error for it may reach 5 to 10 μm. For this reason,
If the exciting current Ic is set to the optimum value for the design value of the aperture diameter, the aberration will not be reduced, and the beam diameter will be expanded and the resolution will be reduced. For example, FIG. 8 shows the relationship between the total aberration and the exciting current Ic when the chromatic aberration and the diffractive aberration in FIG. 7 are integrated and the aperture diameters are assumed to be 40, 50, and 60 μm.
When the aperture diameter is 50 μm, the optimum exciting current is Ic (opt, 50), and the beam diameter corresponding to this is dmin (50). However, when the actual value of the aperture diameter deviates to 40 μm due to a manufacturing error, the beam diameter expands to d (40) and the resolution deteriorates when the exciting current remains Ic (opt, 50). The amount of change in the beam diameter at this time may reach 3 to 4 nm, and the resolution deteriorates by a factor of about 2 in a microscope having a maximum resolution of 4 to 5 nm.

To improve the resolution in the above example,
It is necessary to set the exciting current Ic to an optimum value Ic (opt, 40) corresponding to an aperture diameter of 40 μm and reduce the beam diameter to dmin (40). Therefore, in this embodiment, for each of the plurality of aperture diameters AP (1) to AP (n), when the aberration of the electron beam becomes the minimum, in other words, the beam diameter of the electron beam becomes the minimum, and the highest resolution is obtained. Optimum values Ic (1) to Ic of the exciting current of the condenser lens when being driven
FIG. 9 shows a table in which (n) is obtained in advance and associated with each other.
Are created and stored in the memory 17. The optimum value of the exciting current Ic may be calculated electronically,
For each of the plurality of aperture diameters, the exciting current may be adjusted and determined so that the highest resolution can be obtained while directly observing gold particles and the like. Instead of the table, an approximate expression indicating the relationship between the aperture diameter and the optimum value of the exciting current may be obtained and stored in the memory 17.

When the above-described length measuring unit 15 determines the aperture diameter, a signal corresponding to the value is output to the optimum value specifying unit 16. Optimal value identification unit 16
Specifies the optimum value of the exciting current corresponding to the given aperture diameter by referring to the table of the memory 17. When the optimum value of the exciting current is specified, such information is given to the lens power supply control units 18 and 19. The lens power supply control units 18 and 19 control the lens power supplies 20 and 21 so that the exciting currents supplied from the lens power supplies 20 and 21 to the condenser lenses 3 and 4 match the optimum values. By the above processing, even if the operator does not adjust the exciting current of the condenser lenses 3 and 4 every time the aperture 7a is newly set, the exciting current of the condenser lenses 3 and 4 corresponds to the actual diameter of the aperture 7a. It is automatically set to the optimum value and the maximum resolution is derived.

In the above embodiments, the lens power supplies 20 and 21 are used.
Is a lens setting means, a combination of the scanning coil 5, the holder 10, the detector 11, the amplifier 12, the memory 13 and the length measuring unit 15 is a length measuring means, and the memory 17 is a storage means.
The scanning coil 5 serves as a deflecting means, a holder 10, a detector 11,
The combination of the amplifier 12 and the memory 13 constitutes a detecting means, the length measuring unit 15 constitutes an aperture diameter specifying means, the optimum value specifying unit 16 constitutes an optimum value specifying means, and the lens power supply control units 18 and 19 constitute lens controlling means. .
Although the aperture 7 is axially displaced from the objective lens 6 in FIG. 1, it may be at the same position. A coil for scanning the aperture 7 may be provided separately from the scanning coil 5. Although the setting of the optimum value of the exciting current is automated in the embodiment, for example, the optimum value of the exciting current specified by the optimum value specifying unit 16 or the table stored in the memory 17 is displayed to the operator by a CRT or the like. The operator may set the exciting current according to the display. The present invention is not limited to the scanning electron microscope, and can be used in various apparatuses that irradiate a charged particle beam, for example, an electron beam reduction transfer apparatus.

[0021]

As described above, according to the present invention,
Since the actual value of the aperture diameter can be obtained and the optimum value of the physical quantity of the lens setting means corresponding to it can be specified, to set the state of the condenser lens according to the aperture diameter,
It suffices to set the physical quantity of the lens setting means according to the specified optimum value, and there is no need to make adjustments in a fumbling state. Therefore, the labor required for adjusting the condenser lens is reduced, the down time of the apparatus is shortened, and accurate adjustment can be performed even by an unskilled person. Particularly, in the invention of claim 3, the beam diameter of the charged particle beam can be minimized only by adjusting the state of the condenser lens according to the specified optimum value. In the invention of claim 4, the optimum value is automatically specified,
There is no human error in specifying the optimum value. In the invention of claim 5, the state of the condenser lens is automatically optimized according to the actual value of the aperture diameter, and the stop time of the apparatus can be minimized. According to the invention of claim 6, the exciting current of the condenser lens can be set easily and accurately according to the actual value of the aperture diameter.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a scanning electron microscope according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a calibration mark shown in FIG.

FIG. 3 is a diagram showing an image when the aperture of FIG. 1 and its periphery are observed.

FIG. 4 is a diagram showing a relationship between an exciting current of a condenser lens and an opening half angle of an electron beam.

FIG. 5 is a diagram showing a relationship between an exciting current of a condenser lens and various aberrations.

6 is a diagram showing a state when the aperture diameter is changed from FIG.

7 is a diagram showing a state when the aperture diameter is changed from FIG.

FIG. 8 is a diagram showing a relationship between an exciting current of a condenser lens and a total aberration in association with a plurality of aperture diameters.

FIG. 9 is a diagram showing an example of a table in which an aperture diameter and an exciting current of a condenser lens are associated with each other.

FIG. 10 is a diagram showing a configuration of a general scanning electron microscope.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electron gun 2 Electron beam 3,4 Condenser lens 5 Scanning coil 6 Objective lens 7 Aperture plate 7a Aperture 8 Sample 10 Holder 11 Detector 12 Amplifier 13 Memory 14 Calibration mark 15 Length measuring unit 16 Optimum value specifying unit 17 Memory 18, 19 Lens power supply control unit 20,21 Lens power supply

Claims (6)

[Claims] 1. A condenser lens for focusing a charged particle beam, lens setting means for setting a physical quantity that governs the focusing action of the condenser lens, and an aperture for shaping a charged particle beam emitted from the condenser lens. In the charged particle beam irradiation apparatus provided, a length measuring unit for measuring an actual value of the diameter of the aperture, and a memory for storing information indicating a correlation between the diameter of the aperture and the optimum value of the physical quantity of the lens setting unit. A charged particle beam irradiation apparatus comprising: 2. A condenser lens for focusing a charged particle beam, lens setting means for setting a physical quantity that governs the focusing action of the condenser lens, and a condenser lens for scanning a target object with the charged particle beam. Deflection means for deflecting the charged particle beam, an aperture for shaping the charged particle beam emitted from the condenser lens, and detection for detecting a change in a physical quantity correlated with the aperture shape when the aperture is scanned by the charged particle beam. Means, aperture diameter specifying means for specifying the actual value of the diameter of the aperture based on the detection result of the detecting means, and information indicating the correlation between the diameter of the aperture and the optimum value of the physical quantity of the lens setting means. A charged particle beam irradiation apparatus comprising: a storage unit that stores the. 3. The charged particle beam irradiation apparatus according to claim 1, wherein the optimum value is the physical quantity of the lens setting means when the beam diameter of the charged particle beam with which the target object is irradiated is minimized. A charged particle beam irradiation device characterized by being equivalent. 4. The charged particle beam irradiation apparatus according to claim 1, further comprising an optimum value specifying unit that specifies an optimum value of the physical quantity corresponding to an actual value of the diameter of the aperture according to the stored contents of the storage unit. A charged particle beam irradiation device characterized by the above. 5. The charged particle beam irradiation apparatus according to claim 4, further comprising a lens control unit that controls the lens setting unit so that the physical quantity becomes the optimum value specified by the optimum value specifying unit. Charged particle beam irradiation device. 6. The charged particle beam irradiation apparatus according to claim 1, wherein the physical quantity is an exciting current of the condenser lens.