JPH01189844A - Beam correcting method for charged particle beam device - Google Patents

Abstract

PURPOSE:To simplify the adjusting operation by providing a mechanism adjusting X-Y axes of an objective lens orifice having multiple orifice holes with different hole diameters and electrode plates located above and below this orifice and having holes larger than the hole diameter of the objective lens orifice and applying the beam correcting voltage to one of the orifice and the electrode plates. CONSTITUTION:Coaxial electrode plates 31 and 32 are provided above and below an objective lens orifice 3 and positioned so that the axes of these electrode plates 31 and 32 and the axis of the objective lens 6 coincide. The upper and lower electrode plates 31 and 32 have holes with the diameter larger than the maximum value of hole diameters of the normally used objective lens orifice 3, e.g., about 1-2mm, the upper and lower electrode plates 31 and 32 may have different hole diameters. The incident angle of the objective orifice differs according to the use objective, but it is designed so that no scattered electron is generated on the upper and lower electrode plates 31 and 32 in any case. The distance between the upper and lower electrode plates 31 and 32 and the objective lens orifice 3 is set to the range of 1-2mm, this range depends on the voltage applied to the objective lens orifice 3, this orifice 3 has a structure that the voltage can be applied from the outside.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a correction method in a charged particle beam device that performs beam correction by applying a voltage to an objective lens aperture [Prior art] Figs. 7 is a diagram for explaining an autofocus and a dynamic focus mechanism for tilting a sample built into a charged particle beam device such as a scanning electron microscope, and FIG. 7 is a diagram for explaining an electron beam locking mechanism.

Conventionally, a scanning electron microscope (SEM) is equipped with an autofocus mechanism, a dynamic focus mechanism, and an electron beam locking mechanism, and for example, an air-core dynamic focus coil is provided for beam correction in these mechanisms. There is.

As shown in FIG. 5, the autofocus mechanism operates when a sweep current is applied to the magnetic field type objective lens 6, an auxiliary coil separated from the magnetic field type objective lens, or an air-core dynamic focus coil 7. When the secondary electron signal emitted from the coil reaches its maximum value, it is determined that the focal point is reached, and the current to be passed through each coil is set (see, for example, Japanese Patent Publication No. 40814/1982). Furthermore, in dynamic focusing, the current of the air-core dynamic focusing coil 7 is controlled in synchronization with the scanning of the upper scanning coil 5 and the lower scanning coil 5, thereby realizing dynamic focusing as shown in FIG.

However, when a sweep current is passed through the magnetic field lens or the auxiliary division coil in this way, the inductance of the coil is as large as several 1008 (Henry), so there is a limit to the response to the autofocus current. moreover,
There is a problem with reproducibility because the magnetic field lens has hysteresis. Therefore, in order to solve these problems, accuracy has been improved by attaching a correction circuit to the autofocus current or slowing down the response speed.

Furthermore, the scanning electron microscope is equipped with an electron beam locking mechanism for crystal orientation analysis. In this electron beam locking mechanism, as shown in FIG. 7, the lower scanning coil 5 is turned off, the focal position of the second condenser lens 2 moves to the back focal plane of the objective lens 5, and a parallel beam is formed.

When scanning is performed using only the upper scanning coil 4, the parallel beam is locked onto the sample 9.

In the case of electron beam locking, in order to analyze the crystal orientation of a microscopic region, the spread of the beam must be kept below several μmφ.However, due to the spherical aberration of the objective lens 6, the beam cannot be locked to one point. The spread is 80μm
It becomes φ~60 μmφ. Therefore, as shown in FIG. 7, a method has been proposed in which a square waveform synchronized with the scanning waveform is applied to an air-core dynamic focus coil 7 to perform dynamic correction. The limit of the beam diameter obtained by this method is 2 to 3 μmφ, assuming that the working distance WD is 8 cranes and the beam rocking angle is ±10”.

Therefore, if we investigate the reason for this limit in detail, the rocking beam diameter d is determined by the Gaussian beam diameter dg determined by the objective lens aperture diameter and the beam diameter ds due to spherical aberration (correction), and the relationship between these is 1, 12 mdg
It can be expressed as "+dS". However, when dynamic correction is performed, a beam diameter d ~ 2 to 3 μmφ is obtained, but when dynamic correction is performed, the objective lens aperture diameter is 30 μmφ, 50 μmφ, and 70 μmφ.
It was found that the beam diameter did not change even if the beam diameter was increased.

In other words, the beam diameter is determined only by spherical aberration correction, and d
"~ds", do"~ds".

[Problem that the invention seeks to solve]

The method of using an air-core coil as a method to improve the problem with autofocus allows the inductance of the coil to be lowered to several hundred mH, and since there is no hysteresis due to the air-core coil, response speed and accuracy are improved by several steps. It can be improved. However, if there is an axis misalignment between the objective lens and the dynamic focus, a new problem arises in that the field of view shifts each time the autofocus current is applied, and the focusing accuracy in the observation field of view decreases. To solve this problem, it is necessary to adjust the objective lens and dynamic focus coil by a few microns.
It is necessary to make a anniversary with an accuracy of m. However, this is mechanically very difficult and has a low yield, resulting in an increase in costs.

In addition, in the case of consonant beam locking, we mentioned earlier that the locking beam diameter d depends on the spherical aberration correction term, but when we investigate the cause of this, we find that the axis of the dynamic focus coil and the axis of the objective lens are perfectly aligned. This is due to the fact that they do not match.

For this reason, proposals have already been made to make the dynamic focus coil mechanically movable in order to adjust the axis misalignment to about 5 μm, or to add an alignment coil outside the dynamic focus coil. However, even with these methods, it is difficult to correct the axis deviation to 5 μm or less. The reasons for this are: (1) the objective lens has hysteresis; and (2) the dynamic focus coil has an inclination, making it impossible to accurately measure axis deviation. Therefore, the limit of dynamic correction using an air-core coil is currently limited to a beam diameter of 2 to 3 μmφ.
I have to say.

The present invention solves the above-mentioned problems, and the present invention is directed to charged particle particles that can easily perform beam correction without axis deviation using either an objective lens diaphragm or a polar plate without using a dynamic focusing coil. The purpose of the present invention is to provide a beam correction method in a line apparatus.

[Means for solving problems]

For this purpose, the beam correction method in the charged particle beam apparatus of the present invention includes an objective lens diaphragm having a plurality of apertures with different diameters, and an X-Y axis for adjusting the X-Y axes of the objective lens diaphragm.
It is equipped with an axis adjustment mechanism, a pole plate located above and below the objective lens diaphragm and having a hole larger than the diameter of the objective lens diaphragm, and a correction power source that generates a beam correction voltage. It is characterized in that it is configured so that the voltage is applied to either one of the two.

[Effect]

In the beam correction method in the charged particle beam device of the present invention,
Since the beam is corrected by applying a voltage to either the objective lens aperture or the electrode plate, the X-Y axis of the objective lens aperture is adjusted using the X-Y axis adjustment mechanism to change the output voltage of the correction power supply. Axis alignment and beam correction can be performed easily using the Therefore, problems such as axis misalignment between the objective lens and the dynamic focus coil are eliminated.

〔Example〕

Examples will be described below with reference to the drawings.

FIG. 1 is a diagram showing one embodiment of the present invention, FIG. 2 is a diagram showing an example in which the present invention is applied to an electron beam locking mechanism, and the third diagram is a diagram showing an example of the configuration of an objective lens aperture power supply circuit. Fourth
The figure shows an example of the configuration of the X-Y axis adjustment section.
is the first condenser lens, 2 is the second condenser lens,
3 is an objective lens aperture, 4 is an upper scanning coil, 5 is a lower scanning coil, 6 is an objective lens, 31 and 32 are electrode plates, 11 is a subarithm circuit, 12 and 13 are a function generation circuit, and 14 is a scanning signal generation circuit. , 21 to 24 are adjustment knobs, and 25 is an objective lens aperture power source.

The objective lens diaphragm 3 is conventionally provided between the upper scanning coil 4 and the second condenser lens 2, as shown in FIGS.
-Y-axis can be adjusted. It has a plurality of aperture holes with different diameters, and the aperture diameter is selected from the probe current, work distance (WD), and acceleration voltage so that the probe diameter becomes the minimum. After this aperture diameter is selected, the position of the objective lens aperture 3 is adjusted in the X-Y axis adjustment of the objective lens aperture 3 so that the beam coincides with the axis of the objective lens 5. Note that the selection of the objective lens aperture and the alignment of the X-Y axes can be performed from outside the vacuum.

The present invention has the above mechanism, and also includes coaxial polar plates 31 and 32 above and below the objective lens diaphragm 3.
It is positioned so that the axis of 1.32 is coaxial with the objective lens 6. The upper and lower electrode plates 31 and 32 are larger than the maximum aperture diameter of the objective lens diaphragm 3 that is normally used.
For example, it has a hole of about 1nφ to 2φ,
The hole diameters may be different between the upper and lower electrode plates 31 and 32. In short, as shown in Figures 5 to 7, although the incident angle of the objective aperture varies depending on the purpose of use of the scanning electron microscope, the design must be such that no scattered electrons are generated in the upper and lower scrapers 31 and 32 in any case. Good, also, this upper and lower scraping plate 31.32
The distance between the objective lens diaphragm 3 and the objective lens diaphragm 3 is in the range of 1 mm to 2 mm, but this range depends on the voltage applied to the objective lens diaphragm 3, which will be described later.

Furthermore, the objective lens diaphragm 3 has a structure to which a voltage can be applied from the outside.

In the above case, when the upper and lower electrode plates 31 and 32 are grounded, the holes are set to 1~2+aφ, and the distance from the objective lens aperture 3 is set to 1~2fi, respectively, an electron beam with an acceleration voltage of 30 kV is applied to the objective lens 6 for 15 m. When focused on, if ±IOV to ±30V is applied to the objective lens diaphragm 3, Δf shown in FIG. 5 can be obtained from ±100 μm to ±300 μm. Therefore, autofocus search can be performed by applying the autofocus sweep current, which was passed through the conventional objective lens 6 or dynamic focus coil 7, and the corresponding voltage to the objective lens diaphragm 3. As a result, the conventional detection system and calculation circuit that maximize the secondary electron signal from the sample can be used as they are.

In the electron beam locking mechanism, as shown in FIG. 2, the lower scanning coil 5 is turned off, the electrode plates 31 and 32 are grounded, and a voltage is applied to the objective lens aperture 3.
It is generated by voltage conversion of a square waveform synchronized with the scanning waveform applied to a conventional dynamic focus coil using a circuit as shown in FIG. In FIG. 3, the function generating circuits 12 and 13 are the scanning signal generating circuits 1 and 13, respectively.
The arithmetic circuit 11 generates a voltage 111'', kvt, which is the square of the horizontal scanning synchronizing signals i, I and the vertical scanning synchronizing signal iv generated in step 4, and the arithmetic circuit 11 adds these.

In this way, the present invention requires only the conventional dynamic correction circuit to be used as is and to convert current into voltage.

In the conventional method using a dynamic focus coil, the beam is locked to one point by combining the magnetic field generated by the dynamic focus coil and the magnetic field generated by the objective lens. Even if the speed is increased, there is a drawback that the magnetic response is limited by the inductance of the dynamic focus coil and by the leakage magnetic field of the dynamic focus coil flowing into the yoke of the objective lens. Therefore, it could only be observed with slow scans. On this point, the method of the present invention, which performs dynamic correction by applying a voltage to the objective lens aperture, can improve the response speed to several μsec, and
A rocking beam diameter of less than mφ can be obtained.

Note that the present invention is not limited to the embodiments described above, and various modifications are possible.9 For example, in the embodiments described above, the electrode plate was grounded to apply a correction voltage to the objective aperture. However, it is also possible to ground the objective aperture and apply a correction voltage to the plates.Also, if the axes of the upper and lower plates do not match the axis of the objective lens, it is not possible to adjust the axis by just adjusting the X-Y axis of the objective lens aperture. Although alignment becomes difficult, in this case, it is possible to solve this problem by integrating the upper and lower electrode plates and incorporating an X-Y axis adjustment mechanism as shown in FIG. The adjustment knob 21.22 moves the polar plate 31.32 in the X-Y axis direction, and the adjustment knob 23.24 moves the objective lens diaphragm 3 in the X-Y axis direction. Then, for example, an autofocus sweep voltage is applied to the objective lens diaphragm 3 from the objective lens diaphragm electric g25.

Figure 6 shows the conventional dynamic focus for sample tilt, but it is also possible to divide the scanning current that matches the sample tilt and apply a synchronized sweep current to the air-core coil inside the Chigo lens. good. On the other hand, dynamic focusing with respect to the specimen tilt may be realized by converting a part of the scanning current into a voltage and applying it to the voltage-applying objective lens diaphragm described above.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the problem of axis misalignment with the axis of the objective lens that occurs when using an air-core dynamic focusing coil can be solved by
This can be solved using only the Y-axis alignment mechanism, and even if conditions such as probe current, work distance, acceleration voltage, etc. are changed, adjustments can be made each time with simple operations. Furthermore, since the voltage is low, the focal point sweep can be performed in seconds or less, on the order of μSeC, and the electrical response speed can be improved.

Moreover, since there is no axis deviation, it is possible to improve the focusing accuracy. In addition, compared to the conventional coil method, which could only be used up to slow scan, the objective lens aperture voltage application method of the present invention can be operated using a still image on a monitor TV, improving operability and analysis accuracy. can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention, FIG. 2 is a diagram showing an example in which the present invention is applied to an electron beam locking mechanism, and FIG. 3 is a diagram showing an example of the configuration of an objective lens aperture power supply circuit. Fourth
The figures are diagrams showing an example of the configuration of the X-Y axis adjustment section, Figures 5 and 6.
The figure is a diagram for explaining an autofocus mechanism built into a scanning electron microscope, and FIG. 7 is a diagram for explaining an electron beam locking mechanism. DESCRIPTION OF SYMBOLS 1... First condenser lens, 2... Second condenser lens, 3... Objective lens aperture, 4... Upper scanning coil, 5... Lower scanning coil, 6... Objective lens, 31 and 32...Pole plate, 11...Arithmetic circuit, 12 and 13...Function generation circuit, 14...Scanning signal generation circuit, 21-24...Adjustment knob, 25...Objective lens aperture power supply. Applicant JEOL Ltd. Agent Patent Attorney Ryukichi Abe (Other real name) Figure 1
Figure 2

Claims (1)

[Claims] (1) An objective lens aperture having multiple aperture holes with different diameters, an X-Y axis adjustment mechanism that adjusts the X-Y axes of the objective lens aperture, and an X-Y axis adjustment mechanism located above and below the objective lens aperture, A charged particle beam device comprising a polar plate having a large hole, a correction power source for generating a beam correction voltage, and configured to apply the beam correction voltage to either the objective lens aperture or the electrode plate. Correction method in.