JPH0766769B2 - Electron beam equipment - Google Patents

Description

The present invention relates to a scanning electron microscope (SEM) and a transmission electron microscope (T) that utilize an electron beam emitted from a field emission electron source.
EM), an electron beam drawing device, and various electron beam devices such as a measuring SEM.

(Prior Art) In an electron beam apparatus provided with a field emission type electron source, as is well known, when an extraction voltage is applied between a cathode of an electron source and an extraction electrode (anode), an electron beam by field emission is generated. Is emitted.

The amount of the electron beam extracted from the tip of the field emission electron source is determined by the radius of curvature of the tip of the field emission electron source, the extraction voltage, and the surface cleanliness.

Since this radius of curvature changes by performing flushing for removing the dirt attached to the cathode, it is necessary to control the extraction voltage each time flushing is performed in order to obtain a constant electron dose.

By the way, when the extraction voltage changes, the electron lens action of the entire accelerator tube changes, so when viewed from the lens system in the latter stage,
The position of the virtual electron source changes, and as a result, the size of the virtual electron source changes.

The position of this virtual electron source can be adjusted by changing the intensity (focal length) of the electron lens formed in the subsequent stage of the field emission electron source. If the optical axis of the electron beam is deviated, the problem occurs that the spot position of the electron beam on the irradiation target of the electron beam moves according to the strength of the electron lens.

FIG. 4 shows a state in which the position of the electron source 1 and the optical axis of the electron lens 3 are deviated from each other, and the extraction voltage applied to the extraction electrode 2 is made constant and the lens generation voltage applied to the lens generation electrode 4 is changed. It is the figure which showed the deflection state of the electron beam at the time of making.

FIG. 5 is defined by the diaphragm 18 at this time, and the fluorescent plate 12
It is a figure showing the position of the spot by the electron beam irradiated above, and the spots 51 and 52 are respectively the case where the intensity | strength of the electron lens 3 is weak, and in other words, when a focal distance is long and a focal length is short. And the spot position.

In FIG. 4, the electron source 1 is the electron source fine adjustment screw 9
It is attached to the electron source fine movement flange 8 which is moved in the direction orthogonal to the optical axis of the electron lens 3.

In this way, when the intensity of the electrostatic electron lens 3 is changed in a state where the position of the electron source 1 and the optical axis do not match, the center position of the spot moves by the distance ΔR according to the intensity of the electron lens. I will end up.

Such deviation of the electron beam spot results in deviation of the observation position in an electron microscope, for example.

In FIG. 2, the extraction voltage and the lens-generated voltage are fixed to keep the intensity of the electrostatic electron lens 3 constant, and the electron source fine movement flange 8 is adjusted to make the electron source 1 orthogonal to the optical axis of the electron lens 3. It is a figure which shows the deflection state of the electron beam when parallel-moving, and the code | symbol same as FIG. 4 represents the same or equivalent part.

FIG. 3 is a diagram showing the positions of the spots on the fluorescent plate 12 at this time, and the spots 31 and 32 are different from the case where the optical axis of the electron source and the optical axis of the electron lens are aligned, respectively. The position of the spot is shown.

In this way, when the electron source 1 is moved by the electron source fine movement flange 8, the position of the spot on the fluorescent plate moves by the distance ΔP corresponding to the moving distance of the electron source 1.

From this, in order to correct the spot deviation caused when the intensity of the electrostatic electron lens 3 changes, the electron source fine adjustment flange 8 is moved in the direction in which the spot deviation caused by the change in the lens generated voltage is corrected. It will be appreciated that the electron source 1 may be moved by moving.

Therefore, the optical axis adjustment in the electron beam apparatus of the prior art, first obtain the spot position when the lens strength of the electron lens is weakened and the spot position when the lens strength is increased,
After that, no matter how the lens strength is changed, the position of the electron source 1 is finely adjusted so that the spot position at that time is between the position when the lens strength is increased and the position when the lens strength is weakened. It is performed by moving in parallel in a direction orthogonal to the optical axis by an appropriate means such as a flange.

In addition, there is also a method of translating the position of the electron source 1 in a direction orthogonal to the optical axis so that the brightness of the spot becomes the highest.

(Problems to be Solved by the Invention) The above-described conventional technology has the following problems.

(1) In the method of adjusting the optical axis based on the spot position when the lens strength is increased and the spot position when the lens strength is decreased, it takes a long time to adjust the optical axis, resulting in poor work efficiency.

(2) With the method of adjusting the optical axis based on the brightness of the spot, it is difficult to accurately adjust the optical axis.

An object of the present invention is to solve the above-mentioned problems and to provide an electron beam apparatus capable of easily and accurately adjusting the optical axis.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides an electron beam apparatus having a field emission electron source with a focal length of an electron lens for changing a virtual electron source position. It is characterized in that it is provided with means for changing it at an arbitrary period and means for moving the field emission type electron source in parallel in a direction orthogonal to the optical axis of the electron lens.

(Function) When the focal length of the electron lens is changed at an arbitrary cycle, if the position of the field emission electron source and the optical axis of the electron lens do not match, the center of the spot on the electron beam irradiation surface The position moves at the above arbitrary cycle.

However, when the position of the electron source and the optical axis coincide with each other, the center position of the spot is constant and its diameter only changes periodically.

Therefore, if the center position of the spot moves periodically when the focal length of the electron lens is changed,
If the field emission electron source is moved in parallel in the direction orthogonal to the optical axis according to the moving direction so that the center position of the spot becomes constant, the axis adjustment is completed.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings. First
FIG. 1 is a diagram showing a configuration of a main part of an electron beam apparatus which is an embodiment of the present invention.

In the figure, the acceleration voltage generated by the acceleration voltage generator 14
V0 is applied to the field emission electron source 1 to generate the extraction voltage
The extraction voltage V1 generated at 16 is applied to the anode 2 (first anode).

A flushing power supply 15 for flushing the field emission electron source 1 is connected to the field emission electron source 1.

Lens generation voltage generated by electrostatic type electronic lens generation power supply 17
V2 is supplied to the amplitude modulation means 19. The amplitude modulation means 19 is controlled by the switch 20, and when the switch 20 is in the OFF state, the input lens-generated voltage V2 is directly output to the electron lens generation electrode 4 (second anode), and when the switch 20 is in the ON state. , The lens-generated voltage V2 is periodically modulated and output.

When the lens generation voltage V2 is applied to the electron lens generation electrode 4, the electrostatic electron lens 3 is generated between the anode 2 and the electron lens generation electrode 4. The electrostatic electron lens 3 is for keeping the position of the virtual light source constant, and its lens strength is determined by the potential difference between the lens-generated voltage V2 and the extraction voltage V1.

Difference voltage (V0−
V2) is divided by the high voltage dividing resistor 7 and applied to the electrodes 6 which are insulated from each other by the insulator 5.

The electron source fine movement flange 8 to which the field emission type electron source 1 is attached is movable in the direction parallel to the anode 2, and can be moved or fixed by turning the electron source fine movement screw 9.

The inside of the housing 11 is filled with the inert gas 10, while the inside of the electrode 6, the insulator 5, the anode 2 and the like is maintained in a substantially vacuum state by a vacuum pump (not shown).

When the extraction voltage V1 is applied with the tip of the field emission electron source 1 sharpened, electrons are extracted from the tip of the field emission electron source 1 by field emission.

The electrons extracted at the tip of the field emission electron source 1 are accelerated by the acceleration voltage V0 to become an electron beam, and the irradiation angle is limited by the diaphragm 18.

An electron beam with a limited irradiation angle causes the fluorescent substance applied to the fluorescent plate 12 to shine. The spot on the fluorescent plate is the observation window 13
Can be observed through.

The optical axis alignment method of the electron microscope having such a configuration will be described below.

First, when the switch 20 is turned on and the intensity of the electron lens 3 is periodically changed, if the position of the electron source 1 is displaced with respect to the optical axis of the electrostatic electron lens 3, the Spots continuously move in accordance with the above-mentioned cycle, and the spots have a substantially elliptical shape as shown in FIG. 6 (a).

When the operator rotates the electron source fine adjustment screw 9 to move the field emission electron source 1 in the direction parallel to the major axis of the ellipse, the spot gradually becomes approximately circular as shown in FIG. When the optical axes coincide with each other, a circular shape as shown in FIG.

As described above, according to the present invention, it is possible to easily find the moving direction of the electron source fine movement flange 8 when the optical axis is deviated, and it is possible to confirm whether or not the optical axes match. It will be easy to do.

In the above embodiments, the electron lens for changing the virtual electron source position is described as an electric field type electron lens, but it may be a magnetic field type electron lens. However, in this case, in order to change the focal length of the electron lens, it is necessary to change the current instead of the voltage.

Further, in the above-described embodiments, the case where the present invention is applied to the electron microscope has been described as an example, but the present invention is not limited to this, and an electron beam apparatus equipped with a field emission electron source. If so, it can be applied to an electron beam drawing apparatus, a measuring SEM, and the like.

Further, the voltage (current) modulation method for changing the focal length of the electron lens may be either continuous modulation or discontinuous modulation, as shown in FIG.
The period is not necessarily constant, and any modulation method may be used as long as the operator can recognize the change in the spot shape or the spot position due to the change in the focal length of the electron lens as a result of the modulation.

(Effects of the Invention) As is apparent from the above description, according to the present invention, when the position of the field emission electron source and the optical axis of the electron lens are deviated, they can be easily matched. Moreover, since it is possible to easily confirm whether or not the optical axes match, it becomes possible to easily and accurately adjust the axes.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a main part of an electron beam apparatus which is an embodiment of the present invention. FIG. 2 is a diagram showing the deflection state of the electron beam when the electron source is moved with the electron lens intensity being constant. FIG. 3 is a diagram showing the positions of spots on the fluorescent plate in FIG. FIG. 4 is a diagram showing a deflected state of the electron beam when the focal length of the electron lens is changed while the optical axis is displaced. FIG. 5 is a diagram showing the positions of spots on the fluorescent plate in FIG. FIG. 6 is a diagram showing the spot shape when the focal length of the electron lens is periodically changed. FIG. 7 is a diagram for explaining a method of modulating the lens-generated voltage (current). 1 ... Field emission type electron source, 2 ... Anode, 3 ... Electrostatic type electron lens, 4 ... Electron lens generating electrode, 5 ... Insulator, 6 ... Electrode, 7 ... High voltage division resistance, 8 ... Electron source fine adjustment flange, 9 ... Electron source fine adjustment screw, 11 ... Housing, 12 ... Fluorescent plate, 13 ... Observation window, 14 ... Accelerating voltage generating power supply, 15 ... Flushing power supply, 16 ... Power supply for generating extraction voltage, 17 ... Electrostatic power supply for generating electronic lens, 18 ... Aperture, 19
...... Amplitude modulation means, 20 ...... Switch, 31 ...... Spot position when the electron source is on the axis of the electron lens, 32 ...... Spot position when the electron source is at a position deviated from the axis of the electron lens, 51 …… Spot position when the focal length of the electronic lens is long, 52 …… Spot position when the focal length of the electronic lens is short

 ─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-52-150959 (JP, A) JP-A-48-49376 (JP, A) JP-A-63-32845 (JP, A)

Claims (2)

[Claims] 1. An electron beam apparatus for irradiating an object with an electron beam emitted from a field emission electron source to observe, process, survey, etc. the object, the field emission type comprising a cathode and a first anode. An electron source and a second anode that is provided after the first anode and generates an electron lens for changing the position of the virtual electron source between the first anode and the second anode; and a potential difference between the cathode and the first anode. A means for changing the focal length of the electron lens in an arbitrary cycle while keeping it constant, and means for moving the field emission electron source in parallel in a direction orthogonal to the optical axis of the electron lens. An electron beam device characterized by: 2. The electron beam apparatus according to claim 1, wherein the means for changing the focal length of the electron lens is means for modulating the amplitude of the voltage applied to the second anode.