JPS63198246A - Electron beam focusing device - Google Patents

Abstract

PURPOSE:To keep the beam intensity constant by providing a means to control focal distances of condenser lenses interlockingly. CONSTITUTION:An electron beam 14 emitted from an electron gun 1 is focused by the first condenser lens 3, the second condenser lens 4, and an objective lens 5, and part of the electron beam 2 passes an orifice 11 and is concentrated at a focal point F1 on a sample 6. When the current or voltage from a condenser lens power supply 7 is decreased, a focal point C1 is shifted to C2. When a detecting device 9 detects the current or voltage and sends a signal to a control device 10, it controls a power supply to increase the current or voltage to the lens 4, a focal point position D1 is shifted to D2, and F1 is shifted to F2. If focal distances of the lenses 3, 4 are interlocked with a quantitative relationship, the beam 2 is focused as shown by broken lines and is not shielded by the orifice 11. Accordingly, the intensity of the beam 2 passing the orifice 11 can be kept constant.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is applicable to an electron beam convergence device that converges an electron beam using a fixed focus objective lens, for example in an Auger analyzer or a scanning electron microscope. .

(Prior Art) FIG. 2 shows a schematic diagram of the operation of a conventional electron beam focusing device using a fixed focal point. The electron beam focusing device serves as an electron lens for focusing the electron beam.
A first condenser lens (a variable focus lens using an electromagnetic coil or an electrostatic lens) 3 receives the total emitted electron beam 14 emitted from the electron gun 1 which is an electron beam source, and the electrons are transmitted through the first condenser lens 3. A second condenser lens (a variable focus lens using an electromagnetic coil or an electrostatic lens) 4 that receives the beam, and an objective lens (permanent lens) for converging the electron beam 2 onto the sample 6 through the second condenser lens 4. A fixed focus lens (using a magnet) 5 is used.

Next, the operation of the combination of the first condenser lens 3, the second condenser lens 4, and the objective lens 50 will be explained according to FIG.

The total emitted electron beam 14 emitted from the electron gun 1 and having an energy of several KV to several tens of KV is converged by the first and second condenser lenses 3.4 and the objective lens 5, and a portion of the electron beam 14 forms a fringe 11. A narrow electron beam 2 is formed at a focal point B1 on the sample 6.

In this case, the focal length of the objective lens 5 remains fixed, but by changing the focal length of the second condenser lens 4, the final focus B of the objective lens 5 can be adjusted.
, can be changed.

That is, when the focus of the electron beam by the second condenser lens 4 is at A1 and the focus by the objective lens 5 is at B, the excitation current of the second condenser lens 4 is increased to change the focus position from A to A2. As it moves, the focus of the fixed focus objective lens 5 changes from B1 to B.
Move to 2. That is, the focal position of the objective lens can be changed by the second condenser lens 4.

(Problem to be Solved by the Invention) However, when the focal points A2 and B2 are connected, the beam trajectory becomes as shown by the broken line, and since the beam in the shaded area is blocked by the aperture 11, the sample 6 The intensity of the electron beam 2 that irradiates this decreases. On the other hand, when the focus of the second condenser lens 4 is moved closer to the sample than A1 and the focus of the objective lens 5 is moved below B1, the intensity of the electron beam 20 increases.

When the focal position of the electron beam 2 on the sample is changed in this way, the intensity of the electron beam 20 also changes at the same time.For example, in an Auger analyzer, the analytical sensitivity changes, and in a scanning electron microscope, the image brightness changes. The problem was that it changed.

Therefore, in the conventional electron beam focusing device, it is necessary to provide means for correcting the sensitivity change and brightness change caused by the above-mentioned change in beam intensity using another method. Therefore, due to the above-mentioned problems, the field of use of objective lenses using permanent magnets is extremely narrow, and at present they are hardly put into practical use.

(Object of the Invention) In order to solve the above-mentioned conventional problems, the present invention provides an electron beam focusing device that can keep the beam intensity on a sample constant even when the focal length of the electron beam is adjusted. There is a particular thing.

(Means for Solving the Problems) In order to achieve the above object, the present invention includes an electron gun as an electron beam source, at least two variable focus condenser lenses, and a variable focal length of the condenser lenses. An electron beam focusing device that focuses an electron beam on a sample using a condenser lens power source and a fixed-focus objective lens, characterized by comprising means for controlling the focal length of the condenser lens in conjunction with each other. It is configured.

(Function) According to the present invention, the total emitted electron beam 14 having an energy of several KV to several tens of KV emitted from the electron gun 1 as an electron source is transmitted through the first condenser lens 3, the second condenser lens 4, The electron beam 2 is focused by the objective lens 5, a portion of which passes through the aperture 11, and is concentrated at a focal point F on the sample 6. In this case, by detecting the current or voltage supplied to the condenser lens power supply 7 or the condenser lens power supply 8, the focal lengths of the first and second condenser lenses 3.4 can be changed in conjunction.

By changing the focal lengths of the first and second condenser lenses 3.4 in conjunction with each other, it is possible to change the focal point F of the fixed-focus objective lens 6 while keeping the intensity of the electron beam 2 constant. can.

(Example) FIG. 1 shows an embodiment of the invention.

In describing this embodiment, the same components as those in the prior art will be described using the same reference numerals.

Note that the present invention includes a first condenser lens (a variable focus lens using an electromagnetic coil or an electrostatic lens) 3 that receives the total emitted electron beam 14 from the electron source 1, and a lens that receives the electron beam through the first condenser lens. A second condenser lens (a variable focus lens using an electromagnetic coil or an electrostatic lens) 4, and an objective lens (a variable focus lens using a permanent magnet) for converging the electron beam 2 through the second condenser lens 4 onto the sample 6. The point that a fixed focus lens) 5 is used is the same as the conventional one. Furthermore, there is a detection device 9 that detects the excitation current (if the condenser lens is an electromagnetic coil) or voltage (if the condenser lens is an electrostatic type lens) applied to the first condenser lens 3; The control device 10 controls the excitation current (if the condenser lens is an electromagnetic coil) or the voltage (if the condenser lens is an electrostatic lens) applied to the second condenser lens 4 in response to a signal received by the second condenser lens.

Next, the operation will be explained according to FIG.

Several KV to several K emitted from the electron gun 1 which is an electron source
The total emitted electron beam 14 with an energy of V is the first
A narrow electron beam 2 is converged by a condenser lens 3, a second condenser lens 4, and an objective lens 5.
passes through the aperture 11 and is concentrated at a focal point F on the sample 6. At this time, the focal length of the objective lens 5 remains fixed, and the focal lengths of the first and second condenser lenses 3.4 are changed in conjunction with the condenser lens power supply 7.8. In this case, by linking the focal lengths as described below, the final focus F of the objective lens 6 can be changed while keeping the intensity of the electron beam 20 constant.

That is, the focal points of the first condenser lens 3, second condenser lens 4, and objective lens 5 are C4, Dl, F, respectively.
The trajectory of the electron beam 2 at this time is as shown by the solid line. Here, from the condenser lens power supply 7, the first
When the excitation current (if the condenser lens is an electromagnetic coil) or the voltage (if the condenser lens is an electrostatic lens) supplied to the condenser lens 3 is decreased, the focal point C1 moves to C2. The detection device 9 connected to the condenser lens power supply 7 detects the excitation current or voltage, converts it into an electrical signal, and transmits it to the control device 10 connected to the second condenser lens 8. When the control device 10 receives the electrical signal, it controls the condenser lens power supply 8 to increase the excitation current or voltage supplied to the second condenser lens 4. Then, the focal point position D1 moves to the position D2, and the focal point F1 by the objective lens 5 moves to F2. At this time, if the focal lengths of the two condenser lenses are linked in a quantitative relationship, the trajectory of the electron beam 2 will be as shown by the broken line, and at the position of the aperture 11, the spread of the electron beam 2 before focus adjustment (the solid line part )
The electron beam 2 is not blocked by the aperture 11, and the intensity of the electron beam 2 passing through the aperture 11 is kept constant.

The conditions for the above operation to be satisfied are as follows.

f,, ==c/ (af, +b) I * (1)
f,: Focal length of the first condenser lens f2: Focal length of the second condenser lens a, b, c: Constants determined by the device, that is, maintaining the relationship in equation (1) above, the first condenser lens 3 and the second condenser lens By interlocking the focal length of the lens 4, the focal position F on the sample 6 can be changed without changing the intensity of the electron beam 2-0-.

Then, the electron beam irradiated onto the sample 6 is scanned over the sample 6 by the scanning coil 12, and the electron beam detector 13
For example, in a scanning microscope, signal electrons are detected by
An image is formed on the CRT via an amplifier.

In addition, in the description of the above embodiment, the case where the focal length of the second condenser lens 4 is changed in conjunction with the change in the focal length of the first condenser lens 3 has been described.
Conversely, the focal length of the first condenser lens 3 may be changed in conjunction with the change in the focal length of the second condenser lens 4. In this case, it goes without saying that the detection device 9 must be connected to the condenser lens power source 8 side, and the control device 10 must be connected to the condenser lens power source 7 side. In short, any configuration is sufficient as long as the focal lengths of both condenser lenses 3.4 change in conjunction with each other.

Further, although the objective lens has been described as using a permanent magnet, it is not necessarily limited to this, as long as it has a fixed focus, such as an electrostatic type to which a fixed voltage is applied.

Further, the condenser lens may have three or more stages.

(Effects of the Invention) According to the present invention, even if the focus of the electron beam on the sample is changed, the beam intensity can be kept constant without changing, which makes it possible to use a fixed focus lens using a permanent magnet or the like. It can be expanded widely.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing an example of the operation of the embodiment of the present invention;
FIG. 2 is a schematic diagram showing an example of the operation of a conventional device. DESCRIPTION OF SYMBOLS 1... Electron gun, 2... Electron beam, 3... First condenser lens, 4... Second condenser lens, 5...
...Objective lens, 6...Sample, 7.8...Condenser lens power supply.

Claims (1)

[Claims] An electron beam is focused on a sample using an electron gun as an electron beam source, at least two variable focus condenser lenses, a condenser lens power source that changes the focal length of the condenser lenses, and a fixed focus objective lens. An electron beam focusing device, characterized in that the electron beam focusing device includes means for controlling the focal length of the condenser lens in conjunction with the focal length of the condenser lens.