JP3469404B2 - Field emission type charged particle gun and charged particle beam irradiation device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charged particle gun for emitting a charged particle beam and its applied device, and more particularly to a field emission charged particle gun and its applied device.

[0002]

2. Description of the Related Art When a charged particle beam of ions or electrons is focused on a beam having a thickness (size) of about nanometers, a field emission type charged particle gun having a high brightness of a radiation source is used. A field emission electron gun is used in the scanning electron microscope, and a liquid metal ion gun is used in the ion beam processing apparatus.

In these field emission type charged particle guns, a charged particle extraction electrode placed facing the charged particle source causes a strong electrostatic field to act on the surface of the charged particle source to extract the charged particles from the charged particle source. . The extracted charged particles are then subjected to energy adjustment and focusing by the action of an electrostatic lens composed of a charged particle extraction electrode and an electrode provided behind the charged particle extraction electrode, and charged particles having a predetermined energy and crossover. A beam is generated. Usually, the generated charged particle beam is focused on the sample into an ultrafine beam with a fineness of about nanometers by an electrostatic or magnetic field type objective lens placed facing the sample to be irradiated with the beam. Irradiate the sample. At this time, the objective lens is electrically focused so that the above crossover is reduced and imaged at the sample position.

On the other hand, the current value of the charged particle beam is determined by the surface condition of the charged particle source and the electric field strength acting on the surface. When the field emission particle gun is operated for a long time, the surface state of the charged particle source changes due to dirt and the like. Since the beam current value also changes there, the operator adjusts the extraction voltage applied to the charged particle extraction electrode to restore the current value. However, as described above, the charged particle gun generates a charged particle beam having a predetermined crossover and energy by the action of the electrostatic lens composed of the charged particle extraction electrode and the electrode installed behind it. Since it is a device for generating, if the extraction voltage is changed during operation, the position of the crossover changes.

When the position of the crossover changes, the crossover does not focus on the sample, and the beam at the sample position becomes thick. That is, the beam is blurred. When the extraction voltage is changed when the charged particle source is not installed on the central axis (optical axis) of the electrostatic lens, the crossover moves in the direction orthogonal to the optical axis. Therefore, the position of the beam irradiating the sample also moves on the sample. This phenomenon is called beam drift.

[0006]

Many of the fields of application of conventional field emission particle guns, such as scanning electron microscopes, require a short measuring time of, for example, several tens of seconds.
Beam blurring and beam drift, which are more likely to occur over time, were less of a problem. However,
Recently, an ion beam emitted from a liquid metal ion gun has been applied to a microfabrication device. With this processing device,
It is necessary to continue to irradiate the sample with a fine ion beam having a constant current for a long time of several tens of minutes to several hours. If the ion beam is defocused or drifts during this period, the processing accuracy is impaired. Therefore, there is a need for an ion gun which has a constant beam current value over a long period of time, and which has less beam blur and less beam drift.

To this end, in the conventional liquid metal ion gun, in order to reduce the probability that the surface state of the ion source changes and the beam current value changes, the vacuum degree of the ion gun chamber is improved as much as possible. The means of heating the cathode has been taken. However, even by these means, the surface condition is often changed during the operation for several hours, so that the current conditions are not satisfactory in terms of both current stability and processing accuracy.

Further, when there is a beam drift or a beam blur, a method of reading the amount of drift to automatically change the operating condition of the beam deflector or detecting the blur to automatically focus the objective lens is also implemented. However, in these methods, in the case of an ion beam, the drift may be too large to be sufficiently corrected. Further, in these methods, it is necessary to periodically and repeatedly detect drift and blur, and at the time of detection, it is necessary to irradiate the beam over a wide area even at a place other than the processed portion, so the sample is damaged by the ion beam. There was also a problem.

A more specific description will be given with reference to FIG. FIG. 7 is an explanatory view of a conventional field emission type charged particle gun, and shows an example of a liquid metal ion gun. Liquid metal ion source 1
Part of the ions 2 emitted in the range of about 0.5 stard from the tip of the beam passes through the central hole of the extraction electrode 3 and becomes a beam with an opening angle of about 0.05 rad. This ion beam then passes through the lens electrode 4, is accelerated to a predetermined energy by the acceleration electrode 5, and exits the ion gun 6. The voltage of the liquid metal ion source 1 and the electrodes 3, 4, and 5 are
Acceleration power supply 14, drawing power supply 16, lens power supply 17
Supplied by. The ion beam 7 emitted from the ion gun 6 is
The crossover 10 is connected by the action of an electrostatic lens composed of the electrodes 3, 4, 5 of the ion gun 6 (hereinafter referred to as an ion gun lens). The crossover 10 is an image of the ion source generated by the ion gun lens, and the ion beam 7
It is an apparent ion beam generator for me.

The ion beam 7 is normally incident on the electrostatic objective lens 8 and further narrowed down, and the sample irradiation beam 2
The sample 9 is irradiated with 0. The objective lens 8 is adjusted so that the crossover 10 forms an image at the position of the sample 9 and irradiates the sample 9 as a beam having a very small size. Therefore, if the operating conditions of the ion gun lens are changed, the position of 10 is changed, so that the sample irradiation beam is blurred or drifts as described above. If the condition of the ion gun lens (potential applied to the electrodes 3, 4, 5) does not change, the position of the crossover 10 does not change.
It goes without saying that neither beam blur nor beam drift occurs.

On the other hand, the current amount I _E of the ion beam 2 emitted from the liquid metal ion source 1 is determined by the surface state of the ion source 1.
It is a function of the voltage V _E applied between the ion source 1 and the extraction electrode 3. For example, if V _{E is set} to 8 kV, a current I _E of 1 μA can be obtained. If the surface condition of the ion source 1 changes and the current I _E changes during use of the ion gun 6, the voltage V
_The current I _E can be returned to its original value by changing _E. For example, when the current I _E increases by 1 μA, the voltage V _E becomes 150 V.
If it lowers, it will return to the original.

However, in the case of the liquid metal ion gun of FIG. 7, with the potential of the liquid metal ion source 1 as a reference, -8 kV, -4.8 kV, -3 are applied to the electrodes 3, 4 and 5, respectively.
Since it was operating by applying a potential of 0 kV, V _E was set to 15
The position of the crossover 10 is 10.2mm when lowered by 0V.
By shifting to the objective lens 8 side, the imaging magnification of the ion gun lens increased by 0.3.

Since the objective lens 8 is adjusted to have an imaging magnification of 0.1, it is assumed that the ion source 1 is separated from the optical axis by 0.1 mm, and the opening angle for irradiating the sample 9 is set to a small value. Considering the case of a 2 mrad beam, this is equivalent to generating a beam drift of 3 μm and a beam blur of 0.2 μm in the sample 9. Therefore, when performing ion beam processing with a processing accuracy of 0.1 μm using this ion gun 6, set the ion source 1 so that it is as close to the optical axis as possible, and keep the ion source 1 in a stable state. It was necessary to check and release ions.

The present invention has been made in view of the above-mentioned problems of the prior art. The current value does not change even when the surface condition of the cathode changes, and the position change of crossover is extremely small. An object of the present invention is to provide a field emission type charged particle gun for emitting a charged particle beam.

[0015]

According to the present invention, the lens action is extremely small between the conventional charged particle extraction electrode and the charged particle source with respect to the voltage change required for current stabilization. The above object is achieved by providing a current adjusting electrode and keeping the potential of the charged particle extraction electrode constant during the operation of the charged particle gun. According to this configuration, the electric current value of the electric current emitted from the charged particle source is kept constant by changing the electric potential of the current adjusting electrode while keeping the action of the electrostatic lens for generating the charged particle beam constant. Is possible.

That is, the present invention has a field emission type charged particle source and a charged particle extraction electrode for applying a strong electric field to the charged particle source, and the charged particles extracted by the charged particle extraction electrode are charged particles. A field emission type charge generated by a function of an electrostatic lens formed between the extraction electrode and at least one other electrode provided in the traveling direction of the charged particle to generate a charged particle beam having a predetermined energy and a crossover. In the particle gun, an emission current control electrode having a lens action smaller than that of the electrostatic lens is provided between the charged particle source and the charged particle extraction electrode, and the emission current value from the charged particle source is maintained so as to be maintained at a constant value. It is characterized in that the potential of the current control electrode is controlled.

There are several possible methods for controlling the potential of the emission current adjusting electrode. For example, a resistor is provided between the emission current adjusting electrode and a power source for supplying the potential to the emission current adjusting electrode, and the emission current adjusting electrode is provided. By injecting a part of the emission current into the resistor, the voltage drop due to the emission current flowing through the resistor can be utilized. At this time, a potential can be supplied to the charged particle extraction electrode and the emission current adjusting electrode from the same power source.

When the energy of the charged particle beam is higher than the voltage applied to the charged particle extraction electrode, a power supply for supplying a charged particle acceleration potential to the charged particle source is provided, and the potential supplied to the charged particle extraction electrode is supplied to the power source. It can be configured to include a power source for supplying a potential to the charged particle extraction electrode and supply a potential to be supplied to the charged particle source from the power source when the potential is low.

Further, the present invention uses the above-mentioned field emission type charged particle gun of the present invention as a charged particle gun in an apparatus for irradiating a sample with a charged particle beam emitted from a charged particle gun to a minute size. , The position drift of the charged particle beam on the sample is reduced. The field emission type charged particle gun of the present invention can also be used to reduce the size change of the charged particle beam on the sample. The field emission type charged particle gun of the present invention can be advantageously used as an ion gun for an ion beam processing apparatus, an electron gun for an electron beam length measuring apparatus, and an electron gun for an electron beam drawing apparatus.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In the drawings used in the following description, components similar to those in FIG.
It uses the same sign as. FIG. 1 is an explanatory view of an example of a constant current field emission type charged particle gun according to the present invention.

The constant current field emission type charged particle gun of FIG. 1 has an emission current adjusting electrode 11, a current adjusting power supply 15, an emission current detector 13 as compared with the conventional field emission type charged particle gun of FIG. The emission current control device 12 is added. The emission current adjusting electrode 11 is a cylindrical electrode placed between the emission current detector 3 and the liquid metal ion source 1, and its potential operates at a value close to the potential of the extraction electrode 3.

When the electric potential of the extraction electrode 11 is changed, the electric field strength acting on the surface of the liquid metal ion source 1 is changed, so that the emission current amount I _E is changed. The emission current control device 12 monitors the emission current by the emission current detector 13. The emission current control device 12 is composed of a personal computer. Further, 13 is an ammeter. If the emission current amount I _E changes, the emission current control device 12 changes the output of the current adjustment power supply 15 to change the potential of the emission current adjustment electrode 11 so that the emission current amount I _E becomes the original value. Control. The amount of change in potential required at this time is almost the same as in the case of the conventional example of FIG.

During the operation of the ion gun, the potentials of the electrodes 3, 4 and 5 are maintained at the constant values of -8 kV, -4.8 kV and -30 kV, respectively. Therefore, the action of the ion gun lens does not change even if the potential of the emission current adjusting electrode 11 changes. Compared to FIG. 7, in the ion gun of FIG. 1, the emission current adjusting electrode 11 additionally forms a new electrostatic lens. However, since the potential of the emission current adjusting electrode 11 is a value close to the potential of the extraction electrode 3, the lens action of the emission current adjusting electrode 11 is extremely smaller than the action of the ion gun lens.

Therefore, even if the potential of the emission current adjusting electrode 11 is changed by 150 V in order to emit a constant current, the beam blur and drift are extremely small as compared with the conventional ion gun shown in FIG. However, since the emission current adjusting electrode 11 also has a slight lens effect, it does not become zero.
For example, under the same objective lens configuration as that of the conventional ion gun shown in FIG. 7 and under the condition of the axial displacement of the ion source of 0.1 mm, the potential of the emission current adjusting electrode 11 changes by 150 V on the sample. The beam drift and the beam blur are calculated to be 0.4 μm and 0.002 μm, respectively. These values are about ⅛ and 1/100, respectively, in the case of the conventional ion gun shown in FIG.

FIG. 2 is an explanatory view of another example of the constant current field emission type charged particle gun according to the present invention. In this example, by using the emission current adjusting electrode 11 and the resistor 18 which are arranged so that the ion beam 2 can flow in,
The current value of is stabilized. Emission current control electrode 11
A current of 98% of the ion beam 2 flows into the. The resistance value of the emission current adjusting electrode 11 is 300 MΩ. Both the emission current adjusting electrode 11 and the extraction electrode 3 are supplied with a voltage from the same power source 16, but the potential of the emission current adjusting electrode 11 is higher than that of the extraction electrode 3 by a voltage drop in the resistor 18. The absolute value of is low. For example, the emission current adjusting electrode 11
And the potential of the extraction electrode 3 are -8.0 kV and -8.3, respectively.
The ion beam 2 of 1 μA is emitted in the state of kV.

If the surface condition of the liquid metal ion source 1 is changed and the current of the ion beam 2 is decreased, the voltage drop in the resistor 18 becomes small. Therefore, the absolute potential of the emission current adjusting electrode 11 is reduced. The value increases and acts to increase the current value of the ion beam 2. On the contrary, if the current of the ion beam 2 increases, it acts so as to reduce it. That is, the liquid metal ion source 1
, Ion beam 2, resistor 18, extraction power supply 16 and acceleration power supply 1
Since the negative feedback circuit is configured by the electric elements 4 of FIG. 4, the ion beam current value can be kept constant even if the surface state of the liquid metal ion source 1 changes. During this period, the potential of the extraction electrode 3 does not change and the lens action of the emission current adjusting electrode 11 is small, so that the beam drift and the beam blur are extremely small due to the same circumstances as in the embodiment shown in FIG.

FIG. 3 is an explanatory view of another example of the constant current field emission type charged particle gun according to the present invention. The principle of the present invention is to keep the electrostatic lens action of the ion gun lens at a constant value by not changing the potential of the extraction electrode 3. Therefore, in this example, the potential of the extraction electrode 3 is a constant value, and the extraction power supply 16 is not used, and the voltage is divided and supplied from the acceleration power supply 14 by the dividing resistor 19. If the voltage required for the extraction electrode 3 is higher than the energy of the desired beam, in contrast to this, the acceleration power supply 1
The potential of the ion source 1 is supplied from the power source of the extraction power source 16 without using 4. Further, FIG. 3 shows a case where the ion gun lens is adjusted so as to form a virtual image of the ion source 1 and an apparent crossover 10 is formed behind the ion source 1. The invention works effectively.

FIG. 4 is an explanatory view of another example of the constant current field emission type charged particle gun according to the present invention. In this example, by using the ring-shaped emission current adjusting electrode 11, the lens action of the emission current adjusting electrode 11 is further weakened. Also,
The analog circuit constitutes a negative feedback circuit for keeping the current value of the ion beam 2 constant. That is, in the differential amplifier 22, the voltage drop across the resistor 18 and the reference power supply 2
The output voltage of 1 is compared, and if there is a difference, the difference becomes the output of the differential amplifier 22 and is input to the emission current adjusting power supply 15 to change the potential of the emission current adjusting electrode 11.

FIG. 4 shows a case where the present invention is applied to a field emission type electron gun having two electrodes. That is, the lens electrode 4 shown in the examples of FIGS. 1 to 3 is not provided, and the electron gun lens is configured by only the two electrodes of the extraction electrode 3 and the acceleration electrode 5. Therefore, the lens action is determined only by the potential of the accelerating electrode 5 required to give the energy of the predetermined value and the potential of the extraction electrode 3 that emits the current of the predetermined value. The position could not be set arbitrarily. Conversely speaking, if the voltage condition is designed so that the crossover position is set to a predetermined position, an arbitrary current value could not be obtained.

On the other hand, since the field emission electron source 1 made of a sharp metal needle needs to be heated during use, the needle tip becomes thicker with repeated use, and the potential of the extraction electrode 3 required for electron emission increases. . If the potential of the extraction electrode 3 becomes too high, the crossover 10 cannot be set within the predetermined allowable position range. Although the time point was the life of the field emission electron source 1, according to the method of the present invention, by increasing the potential of the emission current adjusting electrode 11, electrons can be emitted without changing the position of the crossover 10 so much. Field emission electron gun 1
It also has the advantage of significantly extending the life of the.

FIG. 5 is a schematic view of an ion beam drawing apparatus equipped with a constant current field emission type charged particle gun according to the present invention. The ion beam drawing apparatus is an apparatus for pattern-exposing a resist-coated semiconductor wafer with an ion beam. The liquid metal ion gun 6 includes, for example, as shown in FIG. 2, a liquid metal ion source 1 of gallium or the like, an emission current adjusting electrode 11, an extraction electrode 3, a lens electrode 4, and an accelerating electrode 5. The ion beam emitted from the liquid metal ion source 1 is
By applying an electric field of about 3 kV to 6 kV to the extraction electrode 3, extraction is performed with an ion current value of 1 μA to 100 μA. At this time, the ion current is maintained at a constant value by the action of the emission current adjusting electrode 11.

The ion beam extracted by the extraction electrode 3 passes through the lens electrode 4, is accelerated by the acceleration electrode 5, and is shaped into an ion beam by the multipolar lens 31. The formed ion beam is subjected to separation of ion species by the E × B electric field / magnetic field orthogonal type ion separation filter 32, and then the diaphragm 3
3, the ion beam is reshaped by the multipole lens 34. The reshaped ion beam is applied to the semiconductor wafer 37 coated with the resist by the electrostatic objective lens 35.
Focused to focus on the top. Semiconductor wafer 37
Are mounted on a stage 38 that is two-dimensionally movable in an XY plane perpendicular to the optical axis direction (Z direction) of the ion beam. The ion beam focused by the objective lens 35 is scanned in the XY directions by the deflector 36, and the semiconductor wafer 37
Draw a desired circuit pattern on top.

According to this ion beam drawing apparatus, since it is possible to operate for a long time while automatically maintaining the beam current of the ion beam constant, it is possible to perform highly accurate pattern drawing and also improve the product yield. To do. FIG. 6 is a schematic view of a focused ion beam processing apparatus equipped with a constant current field emission type charged particle gun according to the present invention.

A liquid metal ion source, as shown in FIG.
Ion beam 4 emitted from a liquid metal ion source 41 including an emission current adjusting electrode, an extraction electrode, a lens electrode, and an acceleration electrode
2 passes through the beam deflector 43 and enters the objective lens 44. The ion beam 42 is focused by the objective lens 44 into a focused ion beam having a diameter of about 0.2 μm and irradiates the sample 45 to be processed. The control of the ion beam irradiation position is
This is performed by the beam deflector 43 based on the signal sent from the control device 46.

For example, when the focused ion beam is scanned in a rectangular shape by the beam deflector 43, a rectangular hole is formed in the sample 45. In the figure, a state is illustrated in which six samples are sequentially sent to the central portion of the apparatus for processing in accordance with a command from the control device 46, but it takes, for example, 40 minutes to make a hole in one sample. Therefore, as shown in this figure, in order to complete the boring process for the six samples 45, it is necessary to continue the stable irradiation of the ion beam for 4 hours, and the present invention is effectively utilized.

The constant current field emission type charged particle gun according to the present invention is installed in not only an ion beam drawing apparatus and a focused ion beam processing apparatus but also in an apparatus which generally needs to irradiate a narrowed charged particle beam for a long time. It is useful. Such devices include an electron beam drawing device that draws a pattern on a sample with an electron beam, an electron beam length measuring device that measures the size of a fine portion of the sample, and the like. These devices are
Since it is usual to work continuously overnight, the reliability of the work result can be improved by mounting the charged particle gun of the present invention.

[0037]

According to the present invention, an electric field for emitting a charged particle beam in which the current value does not change even when the surface condition of the cathode changes and the drift and blur are suppressed to about 1/8 or less of the conventional values. An emissive charged particle gun can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view of an example of a constant current field emission type charged particle gun according to the present invention.

FIG. 2 is an explanatory view of another example of the constant current field emission type charged particle gun according to the present invention.

FIG. 3 is an explanatory view of another example of the constant current field emission type charged particle gun according to the present invention.

FIG. 4 is an explanatory view of another example of the constant current field emission type charged particle gun according to the present invention.

FIG. 5 is a schematic view of an ion beam drawing apparatus equipped with a constant current field emission type charged particle gun according to the present invention.

FIG. 6 is a schematic view of a focused ion beam processing apparatus equipped with a constant current field emission type charged particle gun according to the present invention.

FIG. 7 is an explanatory view of a conventional liquid metal ion gun.

[Explanation of symbols]

1 ... Liquid metal ion source, 2 ... Ion beam, 3 ... Extraction electrode,
4 ... Lens electrode, 5 ... Accelerating electrode, 6 ... Ion gun, 7 ... Ion beam emitted from ion gun, 8 ... Objective lens,
9 ... Sample, 10 ... Crossover, 11 ... Emission current control electrode, 12 ... Emission current control device, 13 ... Emission current detector, 14 ... Acceleration power supply, 15 ... Emission current control power supply, 16 ...
Drawing power supply, 17 ... Lens power supply, 18 ... Resistor, 19 ... Dividing resistor, 20 ... Sample irradiation beam, 21 ... Reference power supply, 2
2 ... Differential amplifier, 31 ... Multipole lens, 32 ... Ion separation filter, 33 ... Aperture, 34 ... Multipole lens, 35 ... Objective lens, 36 ... Deflector, 37 ... Semiconductor wafer, 38 ... Stage, 41 ... Liquid Metal ion source, 42 ... Ion beam, 4
3 ... Beam deflector, 44 ... Objective lens, 45 ... Sample, 4
6 ... Control device

Claims (5)

(57) [Claims] 1. A field emission type charged particle source, and a charged particle extraction electrode for applying a strong electric field to the charged particle source, wherein charged particles extracted by the charged particle extraction electrode are extracted by the charged particle extraction electrode. A field emission type charged particle which is generated in a charged particle beam having a predetermined energy and a crossover by the action of an electrostatic lens formed between the electrode and at least one other electrode provided in the traveling direction of the charged particle. In the gun, an emission current adjusting electrode having a lens action smaller than that of the electrostatic lens is provided between the charged particle source and the charged particle extraction electrode, and the emission current value from the charged particle source is kept constant. A field emission type charged particle gun characterized by controlling the potential of the emission current adjusting electrode as described above. 2. The field emission type charged particle gun according to claim 1, wherein a resistor is provided between the emission current adjusting electrode and a power source for supplying a potential to the emission current adjusting electrode, and the emission current adjusting electrode is provided in the emission current adjusting electrode. A field emission type charged particle gun, wherein a part of the emission current flows in. 3. The field emission type charged particle gun according to claim 2, wherein a potential is supplied from the same power source to the charged particle extraction electrode and the emission current adjusting electrode. Particle gun. 4. The charged particle gun according to claim 1 , wherein the charged particle source accelerates charged particles when the predetermined energy is higher than a voltage applied to the charged particle extraction electrode.
The potential supplied to the charged particle extraction electrode with the use potential comprises a power supply is supplied from the power applied the predetermined energy to said charged particle extraction electrode
When it is lower than the voltage, the potential is applied to the charged particle extraction electrode.
A field emission type charged particle gun comprising a power supply for supplying and a potential supplied to the charged particle source from the power supply. 5. An apparatus for irradiating a sample with a charged particle beam emitted from a charged particle gun focused to a minute size, wherein the field emission type charged particle gun according to claim 1 is used as the charged particle gun, An apparatus characterized by reducing the position drift of the charged particle beam in the.