JP3311544B2 - Control method of electron microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method suitable for an electron microscope, particularly an electron microscope equipped with a field emission type electron gun.

[0002]

2. Description of the Related Art An electron microscope is provided with an electron gun, various lenses, a deflection system, and the like. An acceleration voltage applied to the electron gun and an excitation current supplied to each lens can be controlled by a control device having a CPU and the like. It is usually done.

In general, a sample is mounted on a sample holder and arranged in an objective lens.

Further, in an electron microscope, the optimum excitation current supplied to each lens depends on the acceleration voltage. Therefore, when the acceleration voltage is changed, the excitation current supplied to each lens is automatically changed in conjunction with the change. It is usual to do so.

[0005]

By the way, when the work of observing or analyzing a sample with an electron microscope is completed, it is usual to turn off all the power supplies. At this time, the accelerating voltage becomes 0 V, and each lens is turned off. No excitation current is supplied.

When the electron microscope is used again the next day, the power is turned on to start the electron microscope, and an operation for setting the acceleration voltage to a predetermined voltage value is performed.

As a result, the exciting current supplied to each lens is automatically set to a value corresponding to the acceleration voltage. However, when the exciting current starts to be supplied, the temperature of each lens starts to rise. become. And, in particular,
When the temperature of the objective lens rises, the temperature of the sample holder also rises, and as a result, the temperature of the sample also rises.

[0008] This is the sample drift. When the sample drift occurs, the irradiation position of the electron beam changes. Therefore, there arises a problem that observation or analysis cannot be performed until the sample reaches a thermal equilibrium state.

Normally, it takes about one to two hours from the start of the supply of the exciting current to the point at which the sample reaches the thermal equilibrium state. Conventionally, a desired operation is performed with an electron microscope during this period. I couldn't do that.

This problem of sample drift is particularly noticeable in an electron microscope equipped with a field emission type electron gun (hereinafter, referred to as FEG). That is, the sample drift at startup is
Since the electron microscope equipped with FEG is very large at 5 to 10 nm and is suitable for analysis of a small region on the order of nanometers (nm), the analysis position drifts until the sample reaches a thermal equilibrium state. In fact, it is impossible to perform the analysis work.

An object of the present invention is to solve the above-mentioned problem, and to provide a control method of an electron microscope that can be used in a shorter time after use of the electron microscope than in the past when the electron microscope is used next time. It is the purpose.

[0012]

In order to achieve the above object, a method for controlling an electron microscope according to the present invention is provided. When an electron microscope is not used, an exciting current equivalent to an exciting current in a normal use is provided in a lens. And a voltage lower than the rated acceleration voltage is applied to the acceleration electrode.

[0013]

When the electron microscope is not used, that is, during the period after the use of the electron microscope until the next use, the lens is supplied with the same excitation current as the excitation current in the normal use. In addition, a voltage lower than the rated acceleration voltage is applied to the acceleration electrode.

Therefore, according to the present invention, even when the lens is not used, the same exciting current as that in normal use is supplied to the lens, and a voltage lower than the rated acceleration voltage is applied to the acceleration electrode. Since the objective lens and the sample holder are in thermal equilibrium, the sample drift at the next start-up can be greatly reduced compared to the conventional method. Work can be performed.

[0015]

Embodiments will be described below with reference to the drawings.
FIG. 1 is a diagram showing the configuration of an embodiment in which the control method for an electron microscope according to the present invention is applied to an electron microscope using FEG. In the drawing, reference numeral 1 denotes FEG, 2 denotes an emitter, and 3 denotes an accelerating electrode. 4 is a lens system, 5 is a control device, 6 is an input device,
Reference numerals 7 and 8 denote power supply circuits.

In FIG. 1, the FEG 1 includes an emitter 2 and an accelerating electrode 3. An acceleration voltage is applied to the acceleration electrode 3 from the power supply circuit 7, and the value of the acceleration voltage is controlled by the control device 5.

The lens system 4 includes various lenses including an objective lens, and an excitation current is supplied from a power supply circuit 8 to each lens. The exciting current is controlled by the control device 5.

The control device 5 comprises a CPU and its peripheral circuits. The control device 5 changes the excitation current supplied to the lens system 4 in conjunction with the acceleration voltage applied to the acceleration electrode 3, and is unique to the present invention. Perform processing when not in use.

The input device 6 is a user interface including a display device such as a CRT and an input device such as a keyboard, and is used for performing an operation for setting an acceleration voltage and the like. In the present invention, in particular, the control device 5
A button (hereinafter, referred to as a non-use button) for executing a process when not in use.

Now, when using the electron microscope, that is, when observing or analyzing a sample,
When a new acceleration voltage is set by the input device 6, the control device 5 obtains an excitation current of each lens that is optimal for the set acceleration voltage, and instructs the power supply circuit 7 to generate the set acceleration voltage, and The circuit 8 is instructed to generate the obtained exciting current.

Thus, the input device 6 is connected to the acceleration electrode 3.
, A newly set acceleration voltage is applied, and an excitation current optimal for the acceleration voltage is supplied to each lens of the lens system 4. The above is a conventional operation at the time of use.

Next, the operation when the electron microscope is not used will be described. If the observation or analysis of the sample is completed and the electron microscope is not used for a while after that,
The operator presses the non-use button of the input device 6.

When detecting that the non-use button has been pressed, the control device 5 instructs the power supply circuit 7 to generate a predetermined voltage, and also instructs the power supply circuit 8 to generate a predetermined voltage. Instructs generation of the set predetermined exciting current.

Here, the predetermined voltage instructed to the power supply circuit 7 is a voltage lower than the acceleration voltage used in a normal use state, and may be arbitrarily set as long as the voltage is lower than the rated acceleration voltage. it can. For example, if the rated acceleration voltage is 200k
In the case of a V electron microscope, it may be about several tens kV.

The predetermined exciting current instructed to the power supply circuit 8 is an exciting current that is substantially equal to the exciting current in a normal use state, and is an optimal exciting current when a rated acceleration voltage is applied as an acceleration voltage. Good.

As a result, a predetermined voltage is applied to the acceleration electrode 3, and a predetermined excitation current is supplied to each lens of the lens system 4.

That is, when the electron microscope is not used, the process of linking the excitation current supplied to each lens with the acceleration voltage is not performed. Such a special mode is provided to instruct the control device 5 to perform such a special mode. That is the button when not in use.

As described above, the accelerating voltage is set to a certain high voltage even when not in use, so that the electron microscope can be used immediately after startup at the next use,
When the lens is not used, the same exciting current as that for normal use is supplied to the lens, so that the objective lens and the sample holder are in thermal equilibrium. Thus, in the next use, a predetermined operation such as observation or analysis can be performed immediately after startup.

The reason why the voltage applied to the accelerating electrode 3 when the electron microscope is not used is lower than the rated accelerating voltage is as follows.

For example, when an electron microscope with a rated acceleration voltage of 200 kV is used at the rated 200 kV this time, it is common to use the rated 200 kV again next time. If the accelerating voltage is applied, it is expected that the sample drift at the next use will be minimized.However, if the rated accelerating voltage is continuously applied to the FEG for a long time, the deterioration of the emitter proceeds, FEG
Not only the life of the FEG is shortened, but also high-pressure discharge inside the FEG is likely to occur. Therefore, when not used, the voltage applied to the acceleration electrode 3 is lower than the rated acceleration voltage.

When the electron microscope is to be used after not being used, an operation for instructing a restart by the input device 6 may be performed. As a result, the control device 6 ends the non-use process and performs the above-described normal use process.
Therefore, when the acceleration voltage is changed by the input device 6 at this time, the exciting current supplied to each lens of the lens system 4 is changed in conjunction therewith.

At the time of this restart, the electron microscope is in a thermal equilibrium state, so that the sample drift due to the temperature is very small, and the observation or analysis of the sample can be performed in a shorter time than in the conventional case.

FIG. 2 is a time chart for explaining the effect of the present invention. FIG. 2A shows the use / non-use state of the electron microscope, FIG. 2B shows the conventional case, and FIG. Shows the case.

[0034] Now, the use of previous time ended t ₀ as shown in FIG. 2A, when a reboot t _1, although the period of t ₀ ~t ₁ is when not in use, in the conventional during the disuse Since no accelerating voltage is applied and no exciting current is supplied, it takes time ΔT ₁ until the electron microscope becomes usable after restarting at t ₁ , as shown in FIG. 2B. but the accelerating electrode is in non-use according to the present invention applies a predetermined voltage, and therefore also the lens supplying a predetermined exciting current to the electronic microscope is available for use after a reboot of t ₁ By then, as shown in FIG. 2C,
ΔT ₂ can be achieved in a short time. In addition,
According to the experiment of the inventor, △ T ₂ is approximately ／ of △ T ₁ .
Met.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications can be made.

For example, in the above embodiment, an electron microscope equipped with an FEG has been described. However, it is obvious that the present invention can be applied to an electron microscope equipped with a thermoelectron gun. In this case, the excitation current supplied to each lens may be the same as the excitation current in the normal use state, as in the above-described embodiment, but the electron gun has an acceleration electrode and other high currents. It is not necessary to apply a voltage. This is because in the FEG described in the above embodiment, a relatively long time is required from when a high voltage is applied to the electron gun until a stable beam current is obtained. This is because the beam current is stabilized in a short time after the application of the voltage.

[Brief description of the drawings]

FIG. 1 shows an FEG control method for an electron microscope according to the present invention.
FIG. 3 is a diagram showing a configuration of an embodiment when applied to an electron microscope using a hologram.

FIG. 2 is a diagram for explaining an effect of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... FEG, 2 ... Emitter, 3 ... Acceleration electrode, 4 ... Lens system, 5 ... Control device, 6 ... Input device, 7, 8 ... Power supply circuit

──────────────────────────────────────────────────続 き Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01J 37/248

Claims (1)

(57) [Claims] When the electron microscope is not used, an exciting current equivalent to an exciting current in normal use is supplied to the lens.
The method of the electron microscope, wherein the this <br/> applying a voltage lower than the rated acceleration voltage in One accelerating electrode.