JPH1031955A - Manufacture of thermal diffusion supply type electron source, and electron beam applied device using the electron source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To monochromate an emitted electron energy by using a thermal diffusion supply type electron source capable of being set at an operation temperature lower than that of an electron source Zr/O/W. SOLUTION: To the tip of a W-made heating element 1 formed in V-shape is spot-welded W<100> monocrystal, and the tip is sharply tapered to form a needle electrode 2. It is then heated in vacuum, whereby the tip radius is set at 1.2μm. The resulting electrode is taken out to the atmosphere, a supply source 3 is adhered close to the base part of the needle electrode to manufacture a thermal diffusion supply type electron source 4. This electron source 4 is loaded on an energy analyzing device. A suppresser electrode 5 is put on the thermal diffusion supply type electron source 4, and an anode 6 is set in a position opposed thereto. The electron source 4 is electrically heated by a heating power source 8. The energy distribution of the emitted electron is measured by an energy analyzer 7. The electron emitting passage of this device is evacuated, the heating element 1 is heated to provide the emitted electron, and the emitted electron is put in the energy analyzer 7 for measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an electron source used in an electron beam application apparatus such as an electron microscope and an electron beam lithography apparatus, and more particularly to a long-term stable and uniform electron emission, that is, a half width of an energy distribution. (FWH
M: Full Width at Half Maxi
The present invention relates to an electron source material and an electron source operating temperature condition for obtaining an electron emission having a narrow electron emission (mum), and an electron beam application apparatus using the electron source.

[0002]

2. Description of the Related Art A thermal diffusion supplementary electron source has hitherto been used as an electron source capable of obtaining stable electron emission with stable energy for a long period of time. Since this electron source is used after being heated to 1000 K or more, it has little adsorption of residual gas and is excellent in stability. For example, as shown in FIG. 2, a heating V-shaped heating element 21 made of W and a W <100> needle-shaped electrode 2
2 and a sintered zirconium oxide powder 23 (hereinafter abbreviated as Zr / O / W) as a replenishing source at the base of the needle electrode 22 (JP-A-59-49065). This electron source diffuses the Zr and O of the replenishing source by heating up to 1800 K, stably supplies the Zr and O to the tip of the needle electrode, adsorbs Zr and O to the tip of the needle electrode, and serves as an electron emission surface (100 ) The work function of the surface is particularly reduced. At this time, emitted electrons are obtained by applying an electric field to the tip of the needle electrode. In Zr / O / W, the FWHM of the emitted electrons was about 0.4 eV at the minimum.

On the other hand, as a narrow electron source of FWHM, W
<310> Field emission electron source (hereinafter abbreviated as W <310>)
There is. This electron source obtains field emission electrons from the W (310) plane by applying an electric field to the tip of the electron source at room temperature. The FWHM at this time is about 0.3 eV, which is smaller than Zr / O / W, but the emission current becomes unstable due to the increase in the work function of the electron emission surface due to the adsorption of the residual gas. Every second) required heat treatment.

These electron sources include a transmission electron microscope and a scanning electron microscope (SEM, Scanning Elect).
ron Microscope), low-acceleration SEM, length measurement SEM, electron beam lithography, and other electron beam application devices.

[0005]

In the prior art, Zr
Although / O / W had good stability, FWHM was wide. On the other hand, W <310> had a weak point in stability although FWHM was narrow. The present invention solves these problems and sets FWHM to W <
The present invention proposes a method for manufacturing a thermal diffusion supplementary electron source using a new material for narrowing to about 310> or more and improving the stability to about Zr / O / W or more.

On the other hand, in an electron beam application apparatus, for example, a low acceleration SEM and a length measuring SEM used for LSI evaluation, a thermal diffusion supplementary electron source Zr / O / W was used. However, this electron source has a drawback that the FWHM is wide, so that the chromatic aberration is increased and the resolution is reduced. For example, the current mainstream 16-64 Mbyte
DRAM (Dynamic Random Access)
ss Memory) is 0.25-0.3μ
m. On the other hand, the inspection of the electric wires of this DRAM requires 2
% Accuracy is required. Therefore, a resolution of 6 nm (0.3 μm × 2%) is required. This resolution is achieved with conventional Zr / O / W (FWHM is 0.4 eV). However, next generation 256M-1G
The electric line width of the byte DRAM is 0.2 μm and the resolution is required to be 4 nm. The resolution is proportional to FWHM / (acceleration voltage).
0.3 eV is required. Therefore, this way FW
There is a need for the development of a thermal diffusion supplementary electron source with a narrow HM and excellent stability.

[0007]

Means for Solving the Problems First, the principle of electron emission of the thermal diffusion supplementary electron source will be described.
The following describes whether the HM can be reduced. FIG. 3 is a diagram showing the principle of electron emission. FIG. 3A shows a state in which electrons in the metal are emitted by applying an electric field F to the metal surface. Where V (z) is the surface (z =
0) is a potential barrier which is caused by electrons near the surface when the electric field F is applied. V (z) is given by V (z) = − e · e / 4z due to the image effect and the electric field of the emitted electrons.
−eFz (z> 0). However, if the vacuum level is 0
And The energy Em at the top of the potential barrier is V
From the equation (z), Em = −√ (eｅe ・ F / 4), and the larger the electric field F, the lower the vacuum level. Next, FIG. 3B shows an outline of the energy distribution. The shape of the energy distribution is classified into the following three types according to the magnitude of the electric field F. (I) F: Small case. Since the potential barrier is thick, few electrons penetrate the barrier, and the main component is Schottky emitted electrons that are emitted across the potential barrier by thermal excitation. Therefore, the general shape of the energy distribution sharply drops on the low energy side. Since the electrons emitted at this time are thermally excited, F
WHM is proportional to temperature. (Ii) F: Large case. The potential barrier becomes thinner, and the field emission electrons passing through the barrier become the main components. If the spread due to thermal excitation is ignored, the general shape of the energy distribution is such that the higher energy side drops sharply than the Fermi energy EF. (Iii)
F: Medium. Thermal field emission in which Schottky emitted electrons and field emission electrons are almost evenly mixed. In the case of a thermal diffusion supplementary electron source, the minimum value of the FWHM is determined by the temperature because it is used in a region where Schottky emitted electrons are emitted. Therefore, the lower the operating temperature, the more advantageous it is for monochromatic emission electrons.

However, when the operating temperature is low, the number of emitted electrons decreases, and there is a possibility that the supply source is not supplied to the tip of the needle electrode. Therefore, in order to compensate for this, even if the operating temperature is lower than 1800K, it is supplied to the tip of the needle electrode,
A replenishing source capable of reducing the work function of the electron emission surface from Zr / O / W is used.

In order to solve this problem, a W <100> needle electrode having a needle-like tip and a tip surface of (100) and a material comprising scandium, scandium oxide or a mixture thereof as a replenishing source Is used. When scandium oxide or a mixture of scandium oxide and scandium is used as a replenishing source, oxygen and scandium are adsorbed on the tip of the needle electrode by diffusing them. On the other hand, when scandium is used as a replenishing source, the scandium is diffused and reacted with oxygen gas to simultaneously adsorb oxygen and scandium on the tip of the needle electrode. Hereinafter, this electron source is abbreviated as Sc / O / W. In addition, the needle-shaped electrodes are represented by W, Ta, Nb and Mo as (1
00), (111), (110) or (310)
As Hf, Re, Os, Tc and Ru (11
(00) or (0001) as Ir (10
A single crystal in which the crystal plane of (0), (110) or (111) is the tip may be used.

According to experiments, Sc and O as diffusion sources were stably supplied to the tip of the needle electrode in the temperature range of 1200 K to 1700 K, the work function of the electron emission surface (100) was reduced, and electron emission was obtained. . FIG. 4 shows the experimental results at that time. The radius of curvature at the tip of the needle electrode is 1.2 μm, and the electric field applied to the tip is 0.46 V / nm. The vertical axis represents the radiation angle current density, and the horizontal axis represents the temperature at the tip of the needle electrode. As can be seen from this figure, electrons began to be emitted at ~ 1200K and ~ 17K.
At 00K, there is no emission of electrons. The reason why the electron emission stops at 1700K is that the evaporation amount is larger than the supply amounts of Sc and O. The emission angular current density during stable electron emission is low despite the low operating temperature.
It was about the same as Zr / O / W. This means that Zr / O /
This shows that the work function of Sc / O / W is smaller than W. That is, the operating temperature of Sc / O / W is lower than that of Zr / O / W, and the FWHM is smaller.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) FIG. 1 shows a first embodiment of the present invention. First, a W <100> single crystal having a diameter of 0.127 mm is spot-welded to the tip of a tungsten (W) heating element 1 having a diameter of 0.127 mm and formed into a V-shape, and the tip has a concentration of 5%.
A needle electrode 2 is formed by sharply sharpening it with an aqueous sodium hydroxide solution by electropolishing (FIG. 1A). At this time, the radius of curvature of the tip is about 0.1 μm, and the length from the heating element 1 to the tip of the needle electrode 2 is about 1 mm. After that, 2 in a vacuum of about 10 −6 Torr
The radius of curvature at the tip is reduced to 1.2 μm by heating at 100K for 10 days. Next, take it out into the air,
A scandium oxide powder is made into a slurry with pure water or an organic solvent containing nitrocellulose mixed with nitrocellulose, for example, collodion, and attached near the base of the needle electrode 2 to produce a heat diffusion replenishment type electron source (FIG. 1B). . Next, this thermal diffusion supplementary electron source 4 is mounted on an energy analyzer as shown in FIG. The thermal diffusion replenishment type electron source 4 is covered with a suppressor electrode 5 in order to prevent electron emission from portions other than the tip of the needle electrode, and an anode 6 is placed at a position facing the suppressor electrode 5. The heat diffusion replenishment type electron source 4 can be energized and heated by a heating power supply 8, the temperature of the needle electrode is measured by an optical thermometer 10, and the relationship between the temperature and the heating current is recorded. Further, the anode 6 is grounded, and a negative potential can be applied to the heat diffusion replenishment electron source 4 by the extraction voltage 9. The energy distribution of the emitted electrons is measured by the energy analyzer 7. The electron emission path including the heat diffusion replenishment type electron source 4 of this apparatus is evacuated to a vacuum of about 10 −9 Torr, and the heating element 1 is heated and heated at a current value of 2.6 A using the heating power supply 8.
The temperature is adjusted to about 1800 K, pure water or collodion is evaporated, and scandium oxide is sintered. Then, in order to supply Sc and O of the supply source 3 to the tip of the needle electrode,
While measuring the temperature of the needle electrode with the optical thermometer 10, the heating power supply 8 is adjusted to a current value of 2.5 A, and the operating temperature of the needle electrode is maintained at 1500K. Then, Sc and O of the replenishing source 3 diffuse to the tip of the needle electrode 2. In this way, Sc and O are supplied to the tip of the needle electrode 2 to reduce the work function of the (100) surface. Here, at the tip of the needle electrode 2,
Using an extraction power source 9, an electric field is applied to obtain emitted electrons.
The emitted electrons enter the energy analyzer 7 and the energy distribution is measured. FIG. 5 shows the relationship between the emission angular current density J and the full width at half maximum (FWHM) of the energy distribution when electrons are stably emitted. Since the work function and the operating temperature are lower than those of Zr / O / W, the FWHM is narrow. Here, the operating temperature of the needle electrode is set to 1500 K. However, if the operating temperature is in the range of 1200 K to 1700 K, S
c and O are supplied stably.

Further, scandium oxide is used as the replenishing source 3,
A scandium oxide and a mixture of scandium or a substance containing them may be attached to the vicinity of the root of the needle electrode 2 as shown in FIG. 1B, or a mixture of scandium oxide, scandium oxide and scandium, Alternatively, a substance containing them may be deposited on the needle electrode itself or in the vicinity thereof as shown in FIG. In addition, even if scandium or a substance containing it is attached as the replenishing source 3 to the vicinity of the base of the needle electrode 2 as shown in FIG.
Even when the vapor deposition is performed as shown in FIG. 4C, Sc and O can be supplied to the tip of the needle electrode 2 by reacting with oxygen thereafter. Also in these cases, the operating temperature range of the needle electrode was 1200K to 1700K. Needle electrode 2
Are (100), (1) as W, Ta, Nb and Mo.
11), (110) or (310), Hf, R
e, Os, Tc, and Ru are (1100) or (0001), and Ir is (100), (110).
Alternatively, the same effect was obtained by using a single crystal having the (111) crystal plane as a tip.

(Embodiment 2) FIG. 6 shows an example of a low-acceleration SEM on which the thermal diffusion supplementary electron source described in Embodiment 1 is mounted. Thermal diffusion supply type electron source 601 having suppressor electrode 602
An anode 603 is provided immediately below the high-voltage power supply 6 between the heat diffusion replenishment electron source 601 and the anode 603.
04 provides an electric field. Further, the thermal diffusion replenishment type electron source 601 is given a negative potential with respect to the ground by the acceleration power supply 605. Thermal diffusion supply type electron source 601
Can be energized and heated by a heating power source 606. The relationship between the heating current and the temperature of the electron source with respect to the value is measured in advance. Electrons 607 extracted from the thermal diffusion supplementary electron source 601 pass through a hole formed in the center of the anode 603, are deflected by the scanning deflector 608, and are converged by the lens 609. Objective diaphragm 610
Are focused on the sample 611 placed on the stage 612. The electrons that hit the sample are then reflected,
An image of the sample is obtained by measuring the current of the backscattered electrons 616 with the detector 617. The drawer power supply 604, the acceleration power supply 605, and the heating power supply 606 are controlled by the control computer 613. Scanning deflector 608, lens 60
9. The objective aperture 610 and the stage 612 are controlled by the control computer 614.

In such a configuration, first, the work function, temperature, acceleration voltage, and current density of the tip of the mounted thermal diffusion replenishment electron source 601 are input to the control computer 612. Then, the extraction voltage at which the required current density is obtained is determined by the free electron model calculation, and the extraction power supply 604 is set. Thereby, electron emission is obtained. Further, by inputting a region of the sample 611 to be observed to the control computer 614, a low-acceleration SEM can be realized.

As in this low acceleration SEM, a conventional Zr / O
By mounting Sc / O / W instead of / W, the resolution can be improved. In the case of a low-acceleration SEM, since the device is used at a low emission angular current density (J to 10 μA / sr) and a low acceleration voltage to 800 V, the resolution obtained is almost proportional to the FWHM of the emitted electrons. As can be seen from FIG. 3, J to 10 μA / s
r, the FWHM is 0.25 / Zr / Zr / O / W
Since it can be increased by 0.4 times, it is useful for improving the resolution. Specifically, the resolution was changed from 6 nm to 4 nm by changing from Zr / O / W to Sc / O / W. Such an effect is the same for the length measurement SEM. Sample 6
Reflected electrons generated by irradiating electrons to 11,
If the intensity or energy of transmitted electrons or light is detected by the detector 617, it can be applied to the composition analysis of a sample.

Further, the thermal diffusion supplementary electron source Sc / O
/ W is mounted on the electron beam lithography system instead of the conventional Zr / O / W, and even if the FWHM is the same, the emission angular current density becomes ~
It can be increased by a factor of 10 to improve the throughput.
Specifically, when FWHM = 0.5 eV is required, the emission angular current density J is 200 μA / sr when Zr / O / W is used as shown in FIG. 5, but Sc / O / W Can be increased to 1000 μA / sr. In addition to these, the thermal diffusion supplementary electron source of the present invention can be used for a transmission electron microscope.

[0017]

According to the present invention, the use of the thermal diffusion supplementary electron source Sc / O / W capable of lowering the operating temperature by 100 to 600 K than that of the conventional electron source Zr / O / W enables the emission electron energy to be reduced. Measure monochromaticity.

[Brief description of the drawings]

FIG. 1 is a diagram showing a forming process and an energy analyzer of a heat diffusion supplementary electron source according to a first embodiment of the present invention.

FIG. 2 is a diagram of a conventional electron source Zr / O / W.

FIG. 3 is a diagram illustrating the principle of electron emission from an electron source.

FIG. 4 is an experimental result showing a temperature change of a current emitted from the thermal diffusion supplementary electron source Sc / O / W of the present invention.

FIG. 5 is an experimental result of the relationship between the radiation angular current density J and the FWHM of the thermal diffusion supplementary electron source Sc / O / W of the present invention and the conventional thermal diffusion supplementary electron source Zr / O / W.

FIG. 6 is a low-acceleration scanning electron microscope according to a second embodiment, on which the thermal diffusion supplementary electron source of the present invention is mounted.

[Explanation of symbols]

1: Heating element 2: Needle electrode 3: Thermal diffusion supplementary source 4: Thermal diffusion supplementary electron source 5: Suppressor electrode 6: Anode 7: Energy analyzer 8: Heating power supply 9: Extraction power supply 10: Optical thermometer 21: Heating element 22: needle electrode 2
3: thermal diffusion supply source 601: thermal diffusion supply type electron beam source 602: suppressor electrode 603: anode 604: extraction power supply 605: acceleration power supply 606: heating power supply 607: electron 608: scanning deflector 609: lens 610: objective aperture 611 : Sample 612: Stage 613: Control computer 614: Control computer 616: Backscattered electrons 617: Detector.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsuhiro Kuroda, Inventor 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo Inside Central Research Laboratory, Hitachi, Ltd.

Claims (14)

[Claims] 1. An electron source comprising a metal needle electrode having a needle-like tip and a heating element for heating the needle electrode, wherein the electron source has a supply source, and the heating element is capable of heating current. A heat-diffusion supply type electron device, wherein the temperature of an electron source for supplying the supply source material to the needle-shaped electrode is measured by an optical thermometer, and a current value flowing through the heating element is determined. Source manufacturing method. 2. The method according to claim 1, wherein the replenishing source is scandium oxide, a mixture of scandium oxide and scandium, or a substance containing them. The thermal diffusion replenishment electron source is characterized in that the temperature is within a range in which scandium and oxygen of the replenishing source are supplied to the tip of the needle electrode by diffusion, and scandium and oxygen can exist at the tip of the needle electrode. Manufacturing method. 3. The method of manufacturing a thermal diffusion supplementary electron source according to claim 1, wherein the supplementary source is scandium or a substance containing the same, and the operating temperature of the electron source is such that the scandium of the supplementary source is A method for producing a thermal diffusion supplementary electron source, wherein the temperature is within a range where scandium and oxygen can be present at the tip of the needle electrode by being supplied to the tip of the needle electrode by diffusion and reacting with oxygen in the atmosphere. . 4. A method of manufacturing a thermal diffusion replenishing electron source according to claim 2, wherein the replenishing source is scandium oxide, or a substance containing scandium oxide and a mixture of scandium, wherein scandium oxide or scandium oxide and A method for producing a thermal diffusion supplementary electron source, wherein the weight percentage of scandium is 50% or more. 5. The method of manufacturing a thermal diffusion replenishing electron source according to claim 3, wherein, in the replenishing source, a substance containing scandium, wherein the weight percentage of scandium is 50% or more. Manufacturing method of refillable electron source. 6. The method for manufacturing a thermal diffusion supplementary electron source according to claim 2, wherein the scandium and oxygen are supplied to the tip of the needle electrode for supplying the scandium and oxygen to the tip of the needle electrode. A method for manufacturing a thermal diffusion supplementary electron source, wherein an operating temperature range is 1200 K to 1700 K. 7. A method for manufacturing a thermal diffusion replenishment type electron source according to claim 2, wherein a material used for the replenishment source is adhered to the needle electrode, the heating element, or a vicinity thereof. A method for producing a heat diffusion replenishment type electron source, characterized by mixing and applying pure water or an organic substance as a means for causing the mixture to be applied. 8. The method of manufacturing a thermal diffusion supplementary electron source according to claim 7, wherein the organic substance includes nitrocellulose. 9. The method for manufacturing a thermal diffusion replenishing electron source according to claim 2, wherein the replenishing source is attached to the needle-like electrode, the heating element, or the vicinity thereof. A method for producing a thermal diffusion supplementary electron source, characterized in that the electron source is deposited by vapor deposition. 10. The method of manufacturing a heat diffusion supplementary electron source according to claim 2, wherein W, Hf, Ta, Re, Os , Ir, Nb, M
A method for manufacturing a thermal diffusion supplementary electron source, characterized by using o, Tc or Ru. 11. The method of manufacturing a thermal diffusion supplementary electron source according to claim 10, wherein W, Ta, Nb and M of said acicular electrode are provided.
(100), (111), (110) or (310) as o, (1100) or (0001) as Hf, Re, Os, Tc and Ru, and (100), (110) or (111) as Ir A) using a single crystal having a crystal face as a tip, wherein the method comprises the steps of: 12. A heating power supply for mounting the heat diffusion supplementary electron source and heating the heating element, an extraction power supply for supplying an electric field for extracting electrons from the heat diffusion supplementary electron source, An accelerating power supply for accelerating the emitted electrons from the electron source, a lens having a stop for converging the emitted electrons, a scanning deflector for irradiating the converged emitted electrons to a predetermined position on the sample, and An electron beam apparatus using a thermal diffusion supplementary electron source, comprising a stage. 13. An electron beam apparatus according to claim 12, further comprising a detector for detecting the intensity or energy of reflected electrons, transmitted electrons, or light generated by irradiating the sample with electrons. An electron beam device using a thermal diffusion supplementary electron source. 14. An electron beam apparatus according to claim 12, further comprising a control computer for controlling said heating power supply, said control computer controlling a temperature of a needle electrode of said heat diffusion replenishment type electron source to a predetermined value. A control computer for setting the temperature so as to be a temperature and controlling the extraction power supply, the acceleration power supply, the lens, the scanning deflector, and the stage, wherein the control computer has an electric field of an intensity capable of obtaining a predetermined current density. Wherein a drawing voltage and an accelerating voltage that cause the electron beam to be generated at the tip of the heat diffusion replenishment electron source are set, and alignment is performed to irradiate a predetermined position of the sample with electrons. Electron beam device using a source.