JP2002367552A - Charged-particle beam device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact charged-particle beam device having high resolution and high detection efficiency. SOLUTION: In the charged-particle beam device, the aberration of a primary electron beam 102 generated by a first E×B type filter 17 which operates to deflect secondary electrons 103 in the direction of a detector 16 can be corrected using a second E×B type filter 18 without the need to position the first and second E×B type filters between objective planes or image planes of the same lens. The charged-particle beam device has the effect of achieving correction of the aberrations of the E×B filters using an electronic optical system having a short optical path length.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning charged particle microscope and similar devices, and more particularly, to a charged particle optical system having high resolution in a low acceleration region and excellent secondary electron detection efficiency.

[0002]

2. Description of the Related Art In order to improve the resolution of a scanning electron microscope, there has been proposed an optical system in which a high accelerating voltage is applied just before a primary electron beam irradiates a sample, and a low accelerating voltage is applied when irradiating the sample. In this optical system, the secondary electrons generated in the sample by the irradiation of the electron beam are accelerated in the optical axis direction by the deceleration electric field of the primary electrons, so that the electric field (E) and the magnetic field (B) are orthogonal to each other. A configuration in which a B-type filter is used to make incident on a secondary electron detector arranged off the optical axis is disclosed in
No. 42045. The E × B filter has a function of causing a primary electron beam to go straight in the filter and deflecting a secondary electron toward the detector. In Japanese Patent Application Laid-Open No. 2-142045, the influence on the primary electron beam due to the chromatic aberration generated by the first E × B filter for deflecting the secondary electrons is shifted to the electron source side from the first E × B filter. A configuration is described in which correction is performed by using a second E × B filter arranged.

[0003]

In the above configuration, FIG.
As shown in (1), the first E × B-type filter 17 and the second E × B-type filter 18 are arranged between the objective lens 13 and the object surface of the objective lens. It is necessary to increase the distance between them, and there is a problem that the entire length of the electron optical system becomes long. Further, since the intensity of each E × B filter needs to be set in the inverse ratio of the distance to the object surface of the objective lens for aberration correction, the second E × B filter close to the object surface of the objective lens is required.
The shape filter had to be set with a large strength. If the primary electron beam is made parallel by the condenser lens 12 in front of the objective lens 13 in order to avoid this, it is possible to set each E × B filter with the same intensity. In order to use the magnification in a reduction system, there is a problem that the size of the optical system must be further increased.

[0004]

The present invention provides a first E × B
The arrangement relationship between the shape filter 17 and the second E × B-type filter 18 is such that aberrations can be corrected without disposing them at a position between the object surface or the image surface of the same lens, and the second E × B-type filter can be used. An object of the present invention is to realize a device capable of correcting aberrations without setting the intensity of the filter 17 large. As shown in FIG.
It is assumed that the × B-type filter 51 acts in the space of the length Ld, the electric field strength E in the E × B-type filter is constant, Assuming that the Wien condition E = vB (v: velocity of electron beam) is satisfied, the deflection chromatic aberration d _ca on the image plane when the E × B filter 51 is disposed between the lens object surface and the lens.
Is the distance between the E × B filter and the object surface, M is the lens magnification, V ₀ is the acceleration voltage of the primary electron beam passing through the E × B filter, and ΔV is the energy width of the primary electron beam. The corresponding voltage fluctuation is expressed by the following equation.

[0005]

(Equation 1)

When an E × B filter having a length Ld is disposed between the image plane of the lens and the lens, the deflection chromatic aberration _dcb on the image plane is determined by dividing Lb between the E × B filter and the image plane. Is given by the following equation.

[0007]

(Equation 2)

Therefore, as shown in FIG. 6, by disposing a second E × B filter 18 having a length Ld 2 between the image plane position of the condenser lens 12 and the condenser lens 12, The chromatic chromatic aberration _dc2 generated by the shape filter 18 on the image plane of the objective lens 13 is expressed by the following _equation ( _Equation 2).
The electric field strength in the × B-type filter, Lcb, is the distance between the second E × B-type filter 18 and the image plane of the condenser lens 13,
When Mo is set as the objective lens magnification, it is expressed by the following equation.

[0009]

(Equation 3)

On the other hand, object plane and deflection chromatic aberration d _{c 1} of the first E × B-type filter 17 of length Ld1 being arranged to generate the image plane of the objective lens 13 between the objective lens 13 of the objective lens 13 In Equation 1, E1 is converted to the first E × B type filter 17
When the distance between the first E × B-type filter 17 and the object surface of the objective lens 13 is set to Loa, the electric field strength in the inside is expressed by the following equation.

[0011]

(Equation 4)

From the equations (3) and (4), the intensity ratio for the first second E × B filter is

[0013]

(Equation 5)

It can be seen that chromatic aberration on the sample surface can be corrected by setting the directions so that they act in opposite directions on the sample surface. Thus, the second Ex
By disposing the B-type filter 18 between the image plane position of the condenser lens 12 and the condenser lens 12, the distance between the condenser lens 12 and the objective lens 13 can be shortened, and the overall length of the electron optical system is shortened. be able to. Further, if Ld1 = Ld2 and the first and second E × B filters are arranged at positions where the relationship of Loa = Lcb holds, the intensities of the first and second E × B filters are set substantially equal. Therefore, the aberration can be corrected without setting the intensity of the second E × B filter large as in the conventional example. Further, FIG.
If the second E × B-type filter 18 is disposed closer to the electron source than the condenser lens 12 as shown in (2), the magnification of the condenser lens can be further reduced, so that the overall length of the electron optical system can be further reduced. Can be. That is, the second E × B type filter 18 is
If the second E × B-type filter 18 is disposed between the second E × B-type filter 18 and the object surface of the condenser lens 12, the deflection chromatic aberration _dcb generated by the second E × B-type filter 18 on the image plane of the objective lens 13 is _equal to the second E × B-type filter. Assuming that the distance between the lens 18 and the image plane of the condenser lens 12 is Lca, and the magnification of the condenser lens is Mc, it is expressed by the following equation.

[0015]

(Equation 6)

From the equations (4) and (6), the intensity ratio for the first second E × B filter is

[0017]

(Equation 7)

If the directions are set so as to act in opposite directions on the sample surface, chromatic aberration on the sample surface can be corrected. However, when the condenser lens 12 is a magnetic field type lens, a rotating action occurs on the primary electron beam in addition to the focusing lens action. That is, when the optical axis direction of the magnetic lens is the z-axis and the magnetic flux density on the optical axis is B (z), the rotation angle φ generated by the magnetic lens is

[0019]

(Equation 8)

## EQU1 ## Here, e is the elementary charge, and m is the mass of the electron. Therefore, the second E × B filter 1
8 is to generate a magnetic field and an electric field in any direction with respect to the first E × B-type filter, correct the rotation angle of the magnetic lens, and set the deflection direction on the sample in the opposite direction. And aberrations can be corrected.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below in detail with reference to examples. A first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a side view of the electron optical system. The electron optical system 101 includes a field emission electron source 10,
It comprises an electron gun lens 11, a condenser lens 12, an objective lens 13, a deflector 15, a first E × B filter 17 and a second E × B filter 18. The primary electron beam 102 emitted from the electron source 10 is focused and irradiated on the sample 1 by the condenser lens 12 and the objective lens 13 through the action of a focusing lens. The sample 1 is set to the retarding voltage Vr, and the primary electron beam is rapidly decelerated between the sample 1 and the electrode 14 set to the ground potential. The reflected electrons reflected from the sample 1 or secondary electrons generated secondarily in the sample 1 are accelerated in the direction of the electron beam optical axis.
The light is deflected by the first E × B filter 17 in the direction of the detector 16 and is directly detected by the detector 16. The deflection scanning of the electron beam is performed by the control unit 40 controlling the electron beam by supplying a scanning signal sent via the deflection amplifier 29 to the deflector 15. Display device 4 at the same time
To 1, a deflection signal synchronized with electron beam scanning is supplied from the control unit 40, and a sample scan image is supplied to the display device 41. The above is the basic configuration of the electron optical system. The first E × B filter 17 and the second E × B filter 18 have an octupole shape as shown in FIG. The electrode has a configuration in which a magnetic material is wound in the same direction by a coil, and the electrode also serves as a magnetic pole. Around the first E × B-type filter 17 and the second E × B-type filter 18, a magnetic substance 19 having a ground potential is provided.
By enclosing them in and, the electric field and the magnetic field generated in the E × B filter are kept close to the E × B filter. Each coil of the first E × B filter 17 receives a coil current from the first E × B filter coil supply power supply 27, and each electrode receives a coil current from the first E × B filter electrode application power supply 28. An electrode voltage is provided. Each electrode,
The distribution of voltage and current to each coil is distributed as a function of the currents Ix, Iy and Vx, Vy as shown in FIG. If the respective intensity ratios are set to Vy / Vx = Iy / Ix = tan θ, a deflecting action can be given to the secondary electrons in the θ direction from the x-axis in the figure. Here in the figure

[0022]

(Equation 9)

With the above condition, a condition in which high-order deflection aberration is small can be obtained. The intensity and direction of the first E × B filter 17 are determined so that the secondary electrons are deflected in the direction of the detector. Assuming that the direction of the detector is the x direction in FIG.
If Iy is approximately zero, the secondary electrons are deflected in the direction of the detector. The relationship between Vx and the deflection angle of the secondary electrons is as follows:
The relationship between the retarding voltage Vr and Vx with respect to the electron beam trajectory calculation result or the desired deflection angle obtained in advance by experiments depends on the energy incident on the filter 17, that is, the retarding voltage Vr applied to the sample. 4
Input to 0. The relationship between Ix and Vx can be determined manually or automatically so that the value obtained from the electron beam trajectory calculation result is input to the control unit 40 in advance or the deflection amount on the sample is completely canceled on the image of the display device 41. Is set. Second E × B filter 18
Is obtained from (Equation 4). Here, the object plane position of the primary electron beam 102 on the condenser lens 12, that is, the image plane position of the electron gun lens 11, depends on the operating conditions of the electron gun lens, that is, the extraction voltage VE for obtaining a desired emission current and the primary electron beam. It can be uniquely obtained from the acceleration voltage V0 of the line. The control unit 40 has the image plane position of the electron gun lens and the VE calculated in advance by experiment or lens calculation.
And data on the relationship with V0 are input. The data of the object plane position of the objective lens, that is, the data of the image plane position of the condenser lens, are also determined in advance by the acceleration voltage V0, the retarding voltage Vr, the intensity of the condenser lens 12, and the
It is required from information such as strength of 3,
For example, data on the relationship between the intensity of the objective lens, the acceleration voltage V0, the retarding voltage Vr, and the object lens surface position is input to the control unit 40. The operating direction of the second E × B filter 18 depends on the strength of the condenser lens. This angle can be obtained by calculation from (Equation 8) or on an image of the display device. On the image, under the condition that only the first E × B filter 17 is applied, only the electric field is applied to the second E × B filter 18, and the second E × B filter 18 is actuated in the opposite directions. The distribution of each electrode and each coil of the B-type filter 18 may be determined. For example, if the direction in which the first and second filters act is rotated by θ,
What is necessary is just to set the intensity ratio Vy / Vx = tanθ between Vx and Vy. As described above, the control unit 40 determines the intensity of the first E × B filter 17 from the acceleration voltage V0 and the retarding voltage Vr.
× B type filter coil power supply 27 and first ExB
It is set via the filter electrode application power supply 28. Further, based on the extraction voltage VE, the strength of the condenser lens 12 and the strength of the objective lens 13, the second E × B filter 18
Is set from the control unit 40 via the second energy filter coil supply power supply 23 and the second E × B filter electrode application power supply 24. According to the above operation, the aberration of the first E × B filter generated when the secondary electrons are deflected in the detector direction can be corrected by the second E × B filter. A second embodiment of the present invention is an application of the present invention to a circuit inspection of a semiconductor pattern, which will be described with reference to FIG. The detector 16 is located above the objective lens 13, and the output signal of the detector 16 is amplified by the preamplifier 26, converted into digital data by the AD converter 32,
Is input to Operation commands and operation conditions of each part of the inspection apparatus are input and output from the control unit 48. Although a field emission electron source is used as the electron source 10, it is preferable to use a diffusion-supply type thermal field emission electron source especially for circuit inspection of a pattern. As a result, it is possible to obtain a comparative inspection image with a small change in brightness and to increase the electron beam current, thereby enabling a high-speed inspection. A negative voltage can be applied to the sample 1 by the high voltage power supply 31 for retarding.
By adjusting the voltage of the high voltage power supply 31 for retarding, it becomes easy to adjust the electron beam irradiation energy to the sample 1 to an optimum value. In order to obtain an image of the sample 1, the sample 1 is irradiated with a finely squeezed electron beam to generate secondary electrons 103, which are detected in synchronization with the scanning of the primary electron beam 102 and the movement of the stage. Obtain an image of the surface. Sample 1 was set to a negative potential, and the primary electron beam was
Suddenly decelerates immediately before The reflected electrons reflected from the sample 1 or secondary electrons generated secondary in the sample 1 are accelerated in the direction of the electron beam optical axis, and after passing through the objective lens, are detected by the first E × B filter 17. The light is deflected in 16 directions and is incident on the reflecting plate 33. Tertiary electrons 104 generated from the reflecting plate are detected by the detector 16. By detecting the tertiary electrons 104 from the reflector 33 disposed near the optical axis, it is possible to detect the secondary electrons even under the condition where the deflection angle of the secondary electrons is small, and it is not necessary to bring the detector close to the optical axis. As a result, the space in the optical axis direction of the detector can be reduced. The second E × B filter 18 is arranged between the condenser lens 12 and the image plane position of the condenser lens 12. The data of the object plane position of the objective lens, that is, the image plane position of the condenser lens, must be
V0, retarding voltage Vr, the strength of the condenser lens 12, the strength of the objective lens 13, and the like. For example, the control unit can calculate the strength of the objective lens, the acceleration voltage V0, and the retarding voltage Vr. 40 determines the position of the object surface of the objective lens.
The intensity ratio between the shape filter 18 and the first E × B filter 17 is determined and set. In this embodiment, two Es
Since no magnetic lens is arranged between the × B filters, the operating direction of the second E × B filter 18 is the first E × B filter 18.
It is set substantially equal to the operation direction of the × B-type filter 17. In the automatic inspection as described in the present invention, a high inspection speed is essential. In such an inspection apparatus, it is the SN of the detected image that determines the inspection speed. If highly efficient secondary electron detection can be achieved in this embodiment, the inspection speed can be improved. In the present embodiment, an image with a good SN could be formed by only one or several scans of a high current electron beam of, for example, 100 nA which is about 100 times or more that of a normal SEM. For example, one image is 1000x1
When the data is captured in 10 msec with 000 pixels, the SN ratio is 2
Zero or more images can be obtained. The image signal is delayed by one image, the image comparison and evaluation are performed in synchronization with the capture of the next image, and a defect search on the circuit board is performed. That is, in the image processing system 47, the image storage unit 4
The image stored in the image storage unit 42b is compared with the image stored in the image storage unit 42b with a delay of one image from the delay circuit 43. The calculation unit 45 has a function of calculating, for example, a difference between the two images, and performs a defect inspection by storing an address P of an image in which the difference between the two images exceeds a certain threshold value in the defect determination unit 46. In the present invention, the first E × B filter 17 is disposed between the objective lens 13 and the object lens surface, but the first E × B filter 17 is disposed, for example, between the objective lens 13 and the objective lens image plane. Even if placed, the second E
For example, if the × B-type filter 18 is disposed between the objective lens 13 and the object surface of the objective lens and is set at an intensity ratio given by (Equation 1) and (Equation 2), the first E × B-type filter 17 Aberration can be corrected. That is, the second E × B filter 18 is placed at any position other than the space between the focusing lens in which the first E × B filter 17 is arranged and the image plane or object plane position of the focusing lens. Even if they are arranged, aberration can be corrected. Although the present invention has been described with respect to an electron beam apparatus, it goes without saying that the present invention is not limited to this and can be applied to a charged particle beam apparatus such as an ion beam. However, in the case of a charged particle beam having a positive charge, the deceleration voltage needs to be a positive value.

[0024]

As described above, according to the present invention, there is an effect that a charged particle beam apparatus which can obtain high resolution and high secondary electron detection efficiency even at a low accelerating voltage can be realized with a shorter electron optical system size than before. is there.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a configuration diagram of an E × B filter according to the first embodiment of the present invention.

FIG. 3 is a configuration diagram of a second embodiment of the present invention.

FIG. 4 is a conventional configuration diagram.

FIG. 5 is a diagram illustrating an operation of an E × B filter.

FIG. 6 is a diagram showing a first arrangement of an E × B filter according to the present invention.

FIG. 7 is a diagram showing a second arrangement of the E × B filter of the present invention.

[Explanation of symbols]

1 ... sample, 2 ... XY stage, 3 ... rotary stage, 1
0, electron source, 11 electron gun lens, 12 condenser lens, 13 objective lens, 14 electrode, 15 deflector, 16 detector, 17 first E × B filter, 1
8: second E × B filter, 19, 20: magnetic material, 2
1. Extraction voltage control power supply 22. Acceleration voltage control power supply
23 ... second E × B filter coil supply power supply, 24
.., A second E × B filter electrode application power supply, 25 a condenser lens power supply, 26 a preamplifier, 27 a first E × B filter coil supply power, 28 a first E ×
B-type filter electrode application power supply, 29 ... deflection amplifier, 30
... Power supply for objective lens, 31 ... Power supply for retarding, 3
2 AD converter, 33 reflector, 34 blanker, 40
... Control unit, 41 ... Display device, 42a, 42b ... Image storage unit, 43 ... Delay circuit, 45 ... Calculation unit, 46 ... Defect determination unit, 47 ... Image processing system, 48 ... Control unit, 101 ... Electronic optical system , 102: primary electron beam, 103: secondary electron, 104
... Tertiary electrons.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Hiroyuki Shinada, Inventor 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo F-term in Central Research Laboratory, Hitachi, Ltd. 5C033 AA02 AA05 JJ07 UU02 UU04

Claims (4)

[Claims] 1. A charged particle source, objective lens means for squeezing a first charged particle beam emitted from the charged particle source and irradiating the sample with a charged particle beam; and an irradiation system arranged between the objective lens means and the electron source. A condenser lens for controlling magnification, and a secondary charged particle beam generated from the sample, which is disposed between the object surface of the first charged particle beam with respect to the objective lens and the objective lens, and the first charged particle beam A first filter separated from the first filter, and correcting the aberration of the first charged particle beam generated by the first filter by the second filter disposed between the condenser lens and the image plane of the condenser lens. A charged particle beam device characterized by the above-mentioned. 2. A charged particle source, objective lens means for squeezing a first charged particle beam emitted from the charged particle source and irradiating the sample with a charged particle source; and an irradiation system arranged between the objective lens means and the electron source. A condenser lens for controlling magnification, and a secondary charged particle beam generated from the sample, which is disposed between the object surface of the first charged particle beam with respect to the objective lens and the objective lens, and the first charged particle beam A first filter separated from the first filter, and correcting the aberration of the first charged particle beam generated in the first filter by the second filter disposed between the condenser lens and the object surface of the condenser lens. A charged particle beam device characterized by the above-mentioned. 3. The charged particle beam according to claim 1, wherein said first filter and said second filter are E × B filters which operate by crossing an electric field and a magnetic field. apparatus. 4. The apparatus according to claim 1, wherein the charged particle source is an electron source, the first charged particle beam is a primary electron beam, and the secondary charged particle beam is a secondary electron. A charged particle beam apparatus according to the above.