JPH0636346B2 - Charged particle beam apparatus and sample observation method using the same - Google Patents

Description

The present invention relates to a focused charged particle beam device using an objective lens composed of an electrostatic lens and a magnetic field type lens as an objective lens, and a sample observation method using this device.

[Outline of Invention]

An objective lens consisting of an electrostatic lens and a magnetic field type lens is used to reduce the spherical aberration coefficient and chromatic aberration coefficient of the electron probe irradiation system, and the generated secondary electrons are efficiently detected by passing through the hole of the electrostatic lens. I decided to do it. Further, in a charged particle beam device capable of selectively irradiating a sample with positive ions and electrons, an electron lens is focused on a sample by using an objective lens composed of an electrostatic lens and a magnetic field type lens, while By the electric field action of the electrostatic lens held in the same polarity as when the electrons are focused, the electrons are focused on the sample, and the positive ions and the electrons are placed on the same sample position while keeping the intensity of the objective lens substantially constant. I was able to focus.

[Conventional technology]

Some charged particle beam devices such as electron microscopes use an electrostatic lens as an objective lens. Such an electrostatic lens generally has the advantages that the electron probe control time can be shortened as compared with the magnetic field type lens, an ultrahigh vacuum can be easily achieved, and the apparatus can be made compact. However, there are drawbacks such that the spherical aberration coefficient and the chromatic aberration coefficient become large, the resolution is likely to be lowered, and an electrical insulation problem is likely to occur when a high voltage is applied to the electrodes. Regarding the electrical insulation problem, in recent years, a low acceleration device having an accelerating voltage of 5 KV (kilovolt) or less has been attracting attention in the field of a scanning electron microscope, and the above problem has been greatly alleviated.

FIG. 8 shows a conventional example of an electrostatic lens having such a feature. This electrostatic lens is called an Einzel lens, and is roughly composed of a central electrode 1 and ground electrodes 2 and 3 arranged in pairs on the upper and lower sides of the central electrode 1. The central electrode 1 and the ground electrodes 2 and 3 are insulated so that a high voltage can be applied.

In such an electrostatic lens, a negative voltage (deceleration mode for electrons) or a positive voltage (acceleration mode for electrons) is applied to the central electrode 1, and the ground electrodes 2, 3
Is grounded and held at ground potential. Generally, in the electrostatic lens, the deceleration mode is often used.
The electron beam bundle 4 emitted from the electron beam source is focused on the sample 5 located at a distance of WD (this is called a working distance) from the lower ground electrode 3.

Regarding this Einzel lens, the thickness T of the central electrode is T = 0 (mm), the distance S between the central electrode 1 and the upper and lower electrodes 2, 3 is S = 4 (mm), and the central electrode 1 The hole diameter D ₁ and the hole diameter D ₂ of the upper and lower electrodes are D ₁ = D ₂ = 4 (mm),
The values of the spherical aberration coefficient Cs and the chromatic aberration coefficient Cc are shown in FIG. In the graph shown here, Csd, Cc
d is a spherical aberration coefficient and a chromatic aberration coefficient in the deceleration mode, respectively, and Csa and Cca are a spherical aberration coefficient and a chromatic aberration coefficient in the acceleration mode, respectively. As can be seen from this graph, each aberration coefficient Cs in the acceleration mode
a, Cca It is considered to be about the same as the aberration coefficient in a normal magnetic field type lens, but each aberration coefficient Cs in the deceleration mode
d and Ccd have several times larger values than the acceleration mode of the electrostatic lens or the aberration coefficient of the magnetic field type lens. Therefore, it is understood that the resolution is likely to decrease in the electrostatic lens in the normal deceleration mode.

[Problems to be Solved by the Invention]

On the other hand, although such a conventional electrostatic lens has an advantage in terms of the above-mentioned aberration coefficient in the acceleration mode, the trapping efficiency of secondary electrons decreases when operating in this acceleration mode. There is a problem that it is easy to do.

That is, in this case, since a positive voltage is applied to the central electrode 1, a part of the secondary electrons is drawn into the electrostatic lens hole especially when the working distance WD is small. For this reason,
It is difficult to capture all the secondary electrons by the usual method in which the detector is installed at the lateral position between the sample 5 and the electrostatic lens. Therefore, in the acceleration mode, it is desirable that secondary electrons be drawn above the electrostatic lens and detected by a detector installed above this electrostatic lens.In this case, the secondary electron capture rate is the hole diameter of the lens. , The voltage changes greatly depending on the applied voltage to the electrostatic lens (eg Autumn 1987, Japan Society of Applied Physics,
20a-G-9, NTT, Kenichi Saito and others). Therefore, especially when the working distance WD or the accelerating voltage greatly changes, it is difficult to put into practical use.

Also in the magnetic field type lens, a secondary electron detector provided above the magnetic field type lens is used when the working distance WD is small, and a secondary electron detector provided on the side of the sample is used when the working distance WD is large. It had to be complicated.

Furthermore, when secondary electrons are detected by a single secondary electron detector provided on the side of the sample, the sample is viewed by illuminating it from an oblique direction, for example, when observing a VLSI pattern, the line profile is There was a drawback that it became asymmetric and the length measurement became inaccurate.

Furthermore, in a sample observation device such as an ion focusing device (FIB) that uses ions as charged particles, a magnetic field type lens is not used because the mass of the ions is large, and the electrostatic field shown in FIG. 8 is generally used. A lens is used. In recent years, Ga ⁺
There is an attempt to generate positive ions and electrons from the same particle source and focus the sample 5 on the sample 5 using a lens barrel that shares the particle beam axis. For example, in FIG. 8, for monovalent positive ions, for example, a positive voltage with an acceleration voltage of U is applied to the central electrode 1, and for electrons, a negative voltage of the same magnitude is applied. If so, they are focused at the same working distance WD and have the same optical constant.

However, since the polarity of the applied voltage has to be switched, there is a problem in stability and operability of the operation of the device.

The present invention has been made in view of such conventional problems, and a first object thereof is to reduce the aberration coefficient and increase the capture efficiency of secondary electrons, and to improve the resolution of the scanning charged particle beam device. ， It is to improve the image quality.

A second object of the present invention is to make it possible to focus positive ions and electrons on the same sample position without switching the polarities of the feature lens and to make the intensities substantially the same, thereby improving the stability and operability of the charged particle beam device. It is to provide an improved sample observation method.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the present invention forms an objective lens by an electrostatic lens and a monopolar magnetic field type lens arranged coaxially with the electrostatic lens, and focuses the charged particle beam flux onto a sample by this objective lens. In addition, a secondary electron detector was provided above the objective lens, and the secondary electron was constrained by the objective lens near the particle beam axis, passed through the electrostatic lens hole, and detected by the secondary electron detector. This is the main point.

Further, the invention of the present application is a particle beam source for generating ions and electrons, a means for selectively irradiating the sample with the ions or electrons along the same particle beam axis, an electrostatic lens and a magnetic field arranged coaxially with each other. The main gist is a charged particle beam device having an objective lens composed of a mold lens and a secondary electron detector arranged above the objective lens.

Further, the invention of the present application, in the ion-electron focusing type charged particle beam apparatus, is characterized by the action of the electromagnetic field of the objective lens.
While the electron beam is focused on the sample, the polarity of the electrostatic lens is kept the same as when the electric field and the magnetic field are applied, and the ion flux is mainly focused on the sample by the electric field of the objective lens and the generated ion beam is generated. The main subject is a sample observation method in which secondary electrons are constrained near the optical axis and passed through an objective lens hole forward, and then detected by a secondary electron detector.

[Action]

The electron beam flux emitted from the particle beam source is subjected to a magnetic field and a magnetic field action by the objective lens and focused on the sample.

The focusing of the electron beam flux causes an excitation action on the sample surface to generate secondary electrons. The secondary electrons are captured by the electric field and magnetic field of the objective lens, bound near the particle beam axis, and pass through the objective lens hole. Then, it is detected by the secondary electron detector arranged above the objective lens. Also, in a device in which a particle beam source emits both electrons and positive ions, the positive ions and electrons do not switch the lens polarities, the intensities are kept almost the same, each particle can be focused on the same sample position, and stability is improved. ， Operability is improved.

〔Example〕

FIG. 1 is a diagram showing a first embodiment of a charged particle beam device according to the first invention of the present application. The charged particle beam apparatus according to this embodiment has an electrostatic lens 10 arranged in front of a sample 5 placed in a sample chamber 14, and a top surface 13 arranged between the sample 5 and the electrostatic lens 10. A magnetic field type lens 11 constituting an objective lens 12 together with the electrostatic lens 10 and a secondary electron detector 15 arranged in front of the objective lens 12. Electrostatic lens 10
Is a central electrode 16 and an upper electrode 18 and a lower electrode 19 arranged in pairs on the upper and lower sides of the central electrode 16 and insulated from each other by an insulating member 17 such as an insulator. It is composed of an Einzel lens. A positive voltage of V (volt) is applied to the central electrode 16, and the upper and lower electrodes 18, 19 are grounded. A unipolar magnetic field type lens is used as the magnetic field type lens 11. In this magnetic field type lens, the magnetic pole top surface 13 is arranged in the vicinity of the electrostatic lens 10 and the yoke 20 made of a magnetic material and the yoke 20. It is composed of an exciting coil 21 wound around and is installed coaxially with the electrostatic lens. A hole 23 for passing an electron beam or an electron beam bundle 22 is formed in the central surface of the top surface 13 and each of the electrodes 16, 18, 19.

Further, the sample chamber 14 is made of a non-magnetic material, and the exciting coil 21 and the yoke portion 20a surrounding the exciting coil 21 are placed outside the vacuum so that they can be taken out when the lens barrel is burned out.

In such a configuration, the magnetomotive force J (A
T; ampere turn) is applied. The electron beam bundle 22 is
It is focused on the sample 5 by the electric field created by the electrostatic lens 10 and the magnetic field created by the magnetic field type lens 11. This electronic probe is scanned on the sample 5 by a two-stage scanning means (not shown) provided above the objective lens 12. The secondary electrons 24 generated by this are restrained in the vicinity of the particle beam axis (hereinafter referred to as the optical axis for convenience) 25 by the magnetic field created by the magnetic field type lens 11, enter the lens hole 23, and further, the electrostatic field by the electrostatic lens 10 is generated. Is restrained in the vicinity of the optical axis 25 by the action of, and detected by the secondary electron detector 15 provided above the electrostatic lens 10.

FIG. 2 is a diagram showing a second embodiment in which the structure of the charged particle beam device according to the first embodiment is partially modified. In this embodiment, the magnetic pole top surface 13 of the unipolar magnetic field type lens 11 constitutes the lower electrode of the electrostatic lens 10. The structure of the other parts is the same as that of the first embodiment.
The same applies to the operation. Since the lower electrode of the electrostatic lens 10 and the magnetic pole top surface of the magnetic field type lens 11 have a common structure, the structure is more compact than that of the first embodiment, and the electrostatic lens 10 and the sample are Since the distance between the objective lens 12 and the lens 5 is smaller, the optical characteristics of the objective lens 12 are further improved.

The tenth example of the magnetic field distribution (B / B _o ) in the optical axis Z direction by the monopolar magnetic field type lens and the example of the electric potential distribution (V / V _o ) on the optical axis by the electrostatic Einzel lens in this example. Shown in the figure.

However, B _o and V _o indicate the respective maximum values, and V has a ground potential of 0 volt.

As shown in FIG. 10, the magnetic field distribution of the unipolar magnetic field type distribution is gradually attenuated in the direction of Z> 0 (the direction of the sample in FIG. 2), and the direction of Z <0 (the direction of FIG. 2). The distribution of the electrostatic lens) has a direction of rapid attenuation, and there is almost no field overlap between the magnetic field of the unipolar magnetic lens and the electric field created by the electrostatic Einzel lens.

Therefore, the charged particles are not affected by the composite electromagnetic field, but are separately affected by the electric field and the magnetic field. This is also a feature of the objective lens of the present invention.

FIG. 3 illustrates the trajectories of secondary electrons in the above-mentioned two examples, in the case where a positive voltage is applied to the electrostatic lens 10 of the objective lens 12 and the magnetomotive force of the magnetic field type lens 11 is zero. The orbits of the secondary electrons of are shown in Fig. 3 (a). In this case, the secondary electrons 24 emitted from the sample 5 at a large angle travel almost straight and collide with the magnetic pole without passing through the hole 23 of the electrostatic lens 10.
FIG. 3B shows the trajectory of the secondary electrons 24 when the applied voltage to the electrostatic lens 10 is 0 and the magnetomotive force of the magnetic field type lens is applied to several hundred (AT). The secondary electrons 24 are bound near the optical axis, but when the hole diameter of the magnetic field type lens 11 is small, they hit the wall surface of the hole and may not reach the secondary electron detector 15. Third
FIG. 3C shows the movement of the secondary electrons 24 when a positive magnetomotive force is applied to the electrostatic lens 10 and an appropriate magnetomotive force is applied to the magnetic field type lens 11. The secondary electrons 24 are constrained by the magnetic field near the optical axis 25, and are further constrained by the electric field in the electrostatic lens 10, and are taken out above the electrostatic lens 10 through the lens hole 23.

The approximate conditions of the magnetomotive force of the magnetic field type lens for injecting secondary electrons into the lens hole 23 are as follows.

The radius of the electron with velocity ν entering the uniform magnetic field B at the angle θ is Make a spiral motion.

Therefore, in the embodiment shown in FIGS. 1 and 2,
In order for the secondary electrons 24 to enter the lens hole 23, (1) it is necessary to satisfy the condition of 2γ ≦ D0 at the sample 5 position (that is, the distance from the top surface 13 to WD). Here, D0 is the diameter of the top surface 13 of the magnetic field type lens 11. Furthermore, (2) it is necessary to satisfy the condition of 2γ ≦ DI at the position of the top surface 13 of the magnetic field type lens 11. Here, DI is the diameter of the hole provided on the top surface 13.

Of the above two conditions, the condition (1) is a condition for restraining the secondary electrons 24 near the optical axis 25, and the condition (2) is the lens hole 23.
This is a condition for the secondary electron 24 to enter into.

When the above-mentioned respective conditions are obtained by using the formula for the distribution of the magnetic flux density B, the condition (1) is Holds, and as condition (2), Is established.

Further, assuming that the focus excitation force of only the magnetic field type lens 11 at a certain sample position (that is, a certain WD) is J ₀ , in order to perform focus control by the electrostatic lens 10, the magnetic field type lens 11 should be applied with a focus. The magnetic force J must satisfy J <J ₀ (3).

By applying a magnetomotive force J satisfying the above three conditions to the magnetic field type lens 11, most of the secondary electrons 24 are always guided upward through the lens hole 23 regardless of the working distance WD, and the secondary electron detector It can be detected by 15, and focus control can be performed by an electrostatic lens. Therefore, in the case of using the conventional magnetic field type lens, there is no inconvenience of providing a plurality of secondary electron detectors according to WD.

If you do not want to increase the magnetic flux density B at the sample position,
Alternatively, it is convenient when a certain fixed magnetic flux density is desired (for example, observation of a magnetic material). That is, the magnetomotive force J satisfying the above conditions (1) to (3) can be selected to obtain the required magnetic flux density B on the sample 5. At this time, the focus is adjusted by controlling the voltage applied to the electrostatic lens 10.

FIG. 4 is a diagram showing a third embodiment of the charged particle beam device according to the present invention. The charged particle beam device according to this embodiment is
An electrostatic lens 10 provided above the sample 5, a magnetic field type lens 26 arranged below the sample 5 coaxially with the electrostatic lens 10 and forming an objective lens 27 together with the electrostatic lens 10.
The secondary electron detector 15 is provided above the electrostatic lens 10. The electrostatic lens 10 has the same configuration as described.
A unipolar magnetic field type lens is used for the magnetic field type lens 26, and this unipolar magnetic field type lens has a yoke 28 having a pole top surface at the center.
And an exciting coil 29 wound around the yoke 28, and is installed at a position of a distance l below the lower ground electrode 19 of the electrostatic lens 10.

In such a configuration, a high voltage is applied to the central electrode 16 of the electrostatic lens 10, and the magnetomotive force J (AT) is applied to the magnetic field type lens 26.
Is applied. As a result, the electron beam flux 22 is moved to the sample 5 by the action of the electromagnetic field as in the first and second embodiments.
Be focused on. The secondary electrons 24 emitted from the sample 5 are subjected to the action of the magnetic field generated by the monopolar magnetic field type lens 26, and the lens hole 23
And is focused by the action of the electrostatic field created by the electrostatic lens, and then detected by the secondary electron detector 15.

The trajectory of this secondary electron can be explained by the same theoretical formula as described above in the first and second embodiments. Therefore, in order to allow the secondary electrons 24 to enter the lens hole 23, it is sufficient to satisfy the above conditions (1) and (2). In the third embodiment, when the diameter of the lens hole 23 is D ₂ , the condition of the magnetomotive force J of the magnetic field type lens 26 for the secondary electrons to enter the lens hole 23 (the above condition ( 2)
Is equivalent to) Becomes Here, D ₀ is the diameter of the top surface 28.

The condition corresponding to the condition (1) at the sample position is
In the arrangement of this embodiment, since the magnetic flux density B on the sample 5 is larger than the magnetic flux density B in the lens hole 23, it is naturally satisfied if the expression (4) is satisfied.

Furthermore, also in this embodiment, it is necessary to satisfy the condition of the expression (3).

By satisfying each of the above conditions, the secondary electrons 24 emitted from the sample 5 can be guided to above the objective lens 27 through the lens hole 23 and detected by the secondary electron detector 15.

Next, the spherical aberration coefficient Cs and the chromatic aberration coefficient Cc of the objective lenses 12 and 27 shown as the first, second and third examples will be described.

The paraxial orbit of an electron in an axisymmetric electromagnetic field is expressed by the following equation.

Here, y: displacement from the optical axis z: potential Bz: magnetic flux density in the optical axis z direction e: electron charge m _o : static mass of electron.

The spherical aberration coefficient Cs and the chromatic aberration coefficient Cc of the electromagnetic lens are respectively expressed by the following equations.

Here, z _o : object surface position z _i : image surface position _o : potential on object surface U: acceleration voltage, and L, M, N, and G are represented by the following equations.

FIG. 5 is a graph showing the values of Cs and Cc obtained from the equations (5) to (11) for the second embodiment. However,
In this case, the dimensions of the electrostatic lens 10 are: T = 4 (mm) S = 4 (mm) D ₁ = D ₂ = 4 (mm), and for the magnetic field type lens 11, D ₀ = 12 (mm) . Further, the magnetomotive force J of the magnetic field type lens 11 is Was set to a constant value.

As is clear from FIG. 5, in WD5 (mm),
Cs75 (mm) and Cc9.5 (mm), and a sufficiently small aberration coefficient is obtained. Further, it can be seen that when the value of WD is large, the spherical aberration coefficient Cs is particularly small as compared with the conventional one.

In addition, here is the equation when the magnetic field and the magnetic field exist in combination.
Calculations were made using (5) to (11), but in the embodiments of the present invention, particularly in FIGS. 1 and 2, since the magnetic field and the magnetic field exist almost independently, the respective dimensions for the electric field and the magnetic field are calculated. Similar values are obtained by calculating and combining using.

The values of Cs and Cc can be obtained in the same manner as described above for other arbitrary combinations of the voltage applied to the electrostatic lens 10 and the magnetomotive force of the magnetic field type lens 11. The values of Cs and Cc can be obtained in the same manner as in the above embodiment.

In the charged particle beam devices according to the first to third embodiments, when the accelerating voltage is changed with the sample position kept the same, the magnetomotive force J of the magnetic field type lenses 11 and 26 is set to the above (1) to ( Four)
Focus control can be performed by changing the voltage applied to the electrostatic lens 10 with a constant value that satisfies the expression.

Furthermore, in the first to third embodiments, when the electrostatic lens is weakly applied with voltage to strongly excite the monopolar magnetic field lens, or the electrostatic lens is strongly applied with voltage to excite the monopolar magnetic lens weakly, respectively. Has a special effect.

Now, in the embodiment of FIG. 2, in the case where T = 4 mm, S = 4 mm, the thickness of the monopole lens pole piece is 4 mm, D ₁ = D ₂ = D _I = 4 mm, and D ₀ = 12 mm,
Find Cs and Cc.

Figure 11 shows Cs for WD, and Figure 12 shows Cs for WD.
c is shown.

In FIG. 11, Cs represents Cs when only the electrostatic lens (acceleration mode) is operated, and Cs _M represents Cs when only the unipolar magnetic field type lens is operated. Cse shows the change in Cs with respect to WD when the electrostatic lens strength is kept at a value that allows WD to be focused to 10 mm only by the electrostatic lens and the magnetomotive force T of the unipolar magnetic field type lens is increased (J at the point E). = 0).

Csm shows the change in Cc with respect to WD when the monopolar magnetic field type lens strength is kept at a value at which WD = 10 mm is focused only by this lens and the electrostatic lens strength is increased (Einzel lens at point M). Applied voltage V _{1 to the} central electrode
= 0 volts).

Similarly, FIG. 12 shows the chromatic aberration coefficient Cc. Fig. 11,
It can be seen from FIG. 12 that Cs and Cc of only the monopolar magnetic field type lens are the smallest, but there is a disadvantage that the secondary electron cannot be detected effectively as described above only with this lens.

Therefore, in order to eliminate this inconvenience, a voltage is weakly applied to the electrostatic Einzel lens. For example, V = + 50 V is applied. This voltage acts only weakly on the primary electron beam of -500 V or more, and its Cs and Cc are the same as those of the monopolar magnetic lens.

However, the secondary electron (about -5V) has a strong lens action, and due to its focusing effect, the secondary electron is taken out above the electrostatic lens and detected. This case is suitable for high-precision measurement by high-resolution observation and secondary electron detection from above, but is not suitable for high-speed automatic length measurement due to hysteresis peculiar to the magnetic field type lens.

Therefore, for the purpose of high-speed automatic length measurement, the magnetomotive force of the unipolar magnetic lens is reduced and the applied voltage V of the electrostatic lens is increased. For example, WD = 10 mm and J = 60 AT. This magnetomotive force acts only weakly for primary electron beams of -500 V or more, but acts as a strong magnetic field lens for secondary electrons and restrains the secondary electrons near the optical axis.
Cs and Cc are the same as Cs and Cc of the electrostatic lens only. Therefore, although the resolution is lower than that when the monopolar magnetic field type lens is strongly operated, the resolution of about 20 nm can be obtained even at a low accelerating voltage by combining with the field emission electron gun. It is possible to measure with high precision. The value of J = 60AT is the constraint condition expression (1),
Since (2) is satisfied, it effectively enters the electrostatic lens hole and is detected after being focused by the electrostatic lens.

If this magnetomotive force J = 60AT is fixed regardless of the accelerating voltage, there is no problem of hysteresis associated with the accelerating voltage change.
It works well for the above purposes.

Further, when it is desired to observe a magnetic substance such as a magnetic disk without a magnetic field, the magnetomotive force J of the unipolar magnetic field type lens is set to J = 0. In this case, a secondary electron detector is provided on the side of the sample. There is a need.

It is also possible to change the third embodiment and replace the exciting coil 29 with a permanent magnet. FIG. 6 is a diagram showing an example of such a change. In this modified example, the outer portion of the yoke 31 of the magnetic field type lens 30 is composed of a permanent magnet 32 magnetized to an N pole and an S pole.
By the action of, a magnetic field is formed in front of the top surface 33 of the monopolar magnetic field type lens. In addition, this magnetic field type lens
The arrangement, configuration and function of the sample 5, the electrostatic lens 10 and the secondary electron detector 15 above the 30 are the same as those described above in the third embodiment. The same applies to the point that the objective lens 34 is configured together.

With respect to the charged particle beam devices according to the first to third embodiments (including modified examples) having the above-described configurations and operations, the particle beam source was improved to irradiate the sample 5 with electrons and positive ions. If possible, the function of this charged particle beam device will be further expanded.

FIG. 7 shows the voltage of the electrostatic lens 10 and the magnetomotive force of the unipolar magnetic field type lens 11 in the charged particle beam device in which electrons or positive ions can be selectively irradiated from the particle beam source side. It is a figure which shows that the positive ion beam 35 and the electron beam 22 are focusing on the same sample position (namely, the same WD) as the same. A positive applied voltage V (≈0.6 | U
｜) (Volt) The magnetic field type lens 11 has a magnetomotive force J (AT) is applied. For positive ions 35,
In the equation (5), the term of e / m ₀ is several orders of magnitude smaller than that of electrons and can be neglected. Therefore, focusing by the magnetic field is not performed, but the positive applied voltage V acts as a deceleration electric field and is relatively low. It is focused on the position of WD ≈ 15 mm by the voltage.

On the other hand, for the electron 22 having a negative charge, the positive applied voltage V having the same magnitude as in the case of the positive ion acts as an accelerating electric field, and is not a voltage sufficient to focus it at the same sample position. I can not say. However, e / m ₀ is sufficiently larger than in the case of ions, and both the electric field and the magnetic field can be used for focusing at the same sample position (that is, WD≈15 mm). In these cases, the aberration coefficient for the ion trajectory is, for example, Csd,
It is shown by Ccd, and the aberration coefficient for the electron orbit is C in FIG.
s, Cc.

〔The invention's effect〕

As described above, according to the present invention, a small spherical aberration coefficient and a small chromatic aberration coefficient are obtained by using the objective lens composed of the electrostatic lens and the magnetic field type lens, and the sample is generated regardless of the working distance WD. Since the secondary electrons can be guided while being constrained near the optical axis of the objective lens and can be efficiently detected by a single secondary electron detector, the resolution and image quality are improved.

Further, when observing the VLSI, the line profile of the pattern can be obtained symmetrically, and the length measurement accuracy is improved. Furthermore, when observing the sample, the excitation of the magnetic field type lens part is fixed and the focus can be controlled only by the electrostatic lens.
The response speed is improved compared to the magnetic field type lens control, which is advantageous for automated measurement.

Furthermore, positive ions and electrons are switched to the sample and irradiated,
When obtaining an image, positive ions and electrons can be focused on the same point by an electric field and a magnetic field having the same polarity and the same magnitude, and stability and operability are improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of a charged particle beam device according to the present invention, FIG. 2 is a diagram showing a second embodiment of a charged particle beam device according to the present invention, and FIGS. c) is a diagram showing secondary electron trajectories associated with a change in the operation of the objective lens in the second embodiment,
FIG. 4 is a diagram showing a third embodiment of the charged particle beam device according to the present invention, FIG. 5 is a graph showing spherical aberration coefficient and chromatic aberration coefficient of the objective lens in the embodiment, and FIG. 6 is a magnetic field type lens. A modified example of the third embodiment using a permanent magnet, FIG. 7 is a view showing a focused state of a particle beam when ions and electrons are switched and irradiated, and FIG. 8 is an example of a conventional electrostatic lens. And FIG. 9 is a graph showing spherical aberration and chromatic aberration of the conventional electrostatic lens and magnetic field type lens, respectively. FIG. 10 is a diagram showing an example of the potential distribution on the optical axis in the electrostatic lens and the magnetic field distribution on the optical axis in the monopolar magnetic field type lens, and FIG. 11 is Cs by the electrostatic lens only, the monopolar magnetic field type lens. Fig. 12 is a diagram showing Cs when only both lenses are actuated at the same time, and Fig. 12 is the 11th diagram for Cc.
A figure similar to the figure is shown. 10 …… Electrostatic lens 11,26,30 …… Magnetic field type lens 12,27,34 …… Objective lens 13 …… Top surface 15 …… Secondary electron detector

Claims (7)

[Claims] 1. An electrostatic lens installed in front of a sample, and a single unit disposed between the electrostatic lens and the sample, coaxial with the electrostatic lens and having a magnetic pole top surface close to the electrostatic lens. A charged particle beam device comprising an objective lens composed of a polar magnetic field type lens and a secondary electron detector arranged in front of the objective lens. 2. The electrostatic lens is an Einzel lens,
The charged particle beam device according to claim 1, wherein the lower electrode is composed of a magnetic pole top surface of a unipolar magnetic field type lens. 3. An objective lens composed of an electrostatic lens installed in front of the sample, and a monopolar magnetic field type lens having a magnetic pole top surface arranged coaxially with the electrostatic lens and behind the sample, and A charged particle beam device having a secondary electron detector arranged in front of an electrostatic lens. 4. A particle beam source for generating ions and electrons,
Claims (1) to (3) having means for selectively irradiating the sample with these ions or electron beams along the same particle beam axis
Charged particle beam device as described. 5. The electron beam is focused on the sample by the action of the electric field and the magnetic field of the objective lens, and the ion flux is maintained at the same polarity as that of the action of the electric field and the magnetic field. Then, it is focused on the sample by the electric field of the objective lens, the secondary electrons generated thereby are restrained in the vicinity of the particle beam axis and passed through the objective lens hole, and then detected by the secondary electron detector. Claims characterized by
(4) A method for observing a sample using the charged particle beam device according to the above. 6. An electrostatic lens is applied with a weak voltage, a monopole magnetic lens is strongly excited, and the electron beam flux is focused on the sample mainly by the magnetic field action of the monopole magnetic lens. The charged particle beam device according to claim 1, which is characterized in that: 7. The electrostatic lens is strongly applied with a voltage, the monopolar magnetic lens is weakly excited, and the charged particle beam flux is focused on the sample mainly by the action of the electric field of the electrostatic lens. The charged particle beam device according to claim 1, which is characterized in that: