JP2002313273A - Electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constitute an electron microscope that has a high resolution at a low acceleration voltage, without impressing large retarding or boosting voltage. SOLUTION: A photocathode having a good monochromaticity is used as an electron source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron microscope,
In particular, the present invention relates to a scanning electron microscope suitable for observation and measurement of a fine pattern of a semiconductor device or the like.

[0002]

2. Description of the Related Art Conventional scanning electron microscopes (SEMs)
The electron beam emitted from a field emission type or thermal field emission type electron source is accelerated and made into a thin electron beam by an electron lens.
This was scanned as a primary electron beam on a sample using a scanning deflector, and the resulting secondary electrons or reflected electrons were detected to obtain an image.

Scanning electron microscopes are also used for inspection of semiconductor devices and the like. In this case, electrons incident on a sample are used to prevent damage to the sample by an electron beam or to reduce surface charge-up. The energy of the wire is 1
It is necessary to set a low acceleration of about kV. However, for such a low-acceleration electron beam, the chromatic aberration in the electron lens (particularly, the objective lens) increases, and the accuracy of pattern observation decreases.

For this reason, in the prior art, Japanese Unexamined Patent Publication No.
As described in Japanese Patent No. 711791, (1) a negative potential (retarding voltage) is applied to the test sample, high-speed electrons are emitted from the electron gun, and the electron beam decelerates when passing through the electron optical system and entering the sample. Retarding for low acceleration around 1kV,
(2) A technique such as boosting has been used in which an acceleration electrode is provided near the objective lens, a positive potential (boosting voltage) is applied, and acceleration is performed only when electrons pass through the objective lens.

[0005]

In the prior art, the energy distribution of the electron beam emitted from the electron source is 0.4 eV or more. The chromatic aberration of the electron lens is proportional to ΔE / E. Here, ΔE is the energy width of the electron beam, and E is the electron energy when passing through the electron lens.

One solution to reduce chromatic aberration and achieve higher resolution is to increase the value of E. For example, electrons are extracted at an acceleration voltage V0 of -10 kV, and a boosting electrode is provided in the objective lens.
It accelerates with a boosting voltage Vb of +10 kV. As a result, E becomes 20 kV, and the chromatic aberration is reduced to 1/20 as compared with the acceleration of 1 kV. On the other hand, a -9 kV retarding voltage Vr is applied to the substrate so that the electron beam incident on the sample becomes 1 kV. In this way the final acceleration (V0
A resolution of 2 to 3 nm can be obtained when -Vr) is 1 kV.

However, when Vr and Vb are increased in order to further increase the resolution, the voltage Vb-Vr between the sample surface and the boosting electrode opposed thereto increases by 20%.
Since the voltage becomes extremely large at kV or more, there is a problem that the sample surface is likely to be destroyed due to electric discharge, and there is a limit to high resolution by retarding and boosting of the low-acceleration scanning electron microscope.

Further, in the electron source used in the conventional electron microscope, the current amount and the sectional shape of the electron beam cannot be changed without changing the conditions of the electron optical system.

A first object of the present invention is to provide a high-resolution electron microscope even at a low acceleration. A second object of the present invention is to provide a high-performance electron beam inspection apparatus using a photocathode.

[0010]

SUMMARY OF THE INVENTION In order to achieve the first object, the present invention provides a photocathode, which is a means for emitting electrons when excitation light enters in a vacuum, and a light source for the incident excitation light. A device, an extraction electrode for extracting generated electrons, a focusing lens for condensing light on the photocathode, light convergence confirmation means, a photocathode surface cleaning means, a photocathode surface activation means, an extraction electrode, a differential exhaust structure electron gun; An electron microscope apparatus comprising: an electron lens, an electron beam deflector, a substrate sample chamber, and a substrate sample moving stage, wherein the electron beam incident on the sample is observed at a low acceleration of 500 to 2000 V.

In the above, the photocathode preferably utilizes a negative electron affinity, and is made of a p-type semiconductor, GaAs, AlAs, InP, InAs, GaP,
It is composed of a III-V group such as GaN or a IV group such as Si, C, Ge or a mixture thereof. Surface adsorption layer is C
It is composed of an alkali metal such as s and Na, or an alkali metal such as Cs and Na and oxygen, or an alkaline earth such as Ba and oxygen, or a mixture thereof.

Further, in order to achieve the second object, the present invention provides, in addition to the above-described structure, changing the amount of electron beam current by changing the intensity of excitation light during sample observation, By providing a means for changing the light irradiation area, the spatial and temporal shape of the electron beam is changed.

[0013]

(Embodiment 1) FIG. 1 shows a schematic configuration of an electron microscope according to an embodiment of the present invention. An electron gun portion is constituted by the photocathode 1 as an electron source and the extraction electrode 2. Light from the light source device 8 is convergently irradiated onto the photocathode 1 by the condenser lens 5 to emit electrons from the light irradiating section of the photocathode 1, an acceleration voltage V0 is applied to the photocathode 1, and the facing extraction electrode 2 potential Ve
Electrons are accelerated by a potential difference from x and an electron beam is made to enter the electron beam optical system through the differential pumping hole 103.

The above-mentioned electron beam is supplied to the first condenser lens 1
2, the first aperture 16, the second condenser lens 13,
By passing through the second aperture 17 and the objective lens 14, the beam is narrowed down to a beam with a fine diameter, and is irradiated on the surface of the sample 21. The sample 21 is placed on the moving stage 24 by the insulating table 2.
3 and is fixed to a sample fixing table 22 which is set.

A potential Vr for decelerating electrons is given to the sample 21, and the energy of the electrons incident on the sample (given by V0-Vr) is adjusted to be 500 to 2000 eV. Here, V0 is from -1000 to -3000V.
It is desirable to use it.

Secondary electrons and reflected electrons generated from the sample 21 are removed from the axis of the incident electrons by a speed discriminator 20 and detected by an electron detector 19 and a reflected electron detector 29. The incident electron beam is swept by the deflector 15, and the secondary electron intensity and the reflected electron intensity are displayed in synchronization with the sweeping, thereby obtaining a scanning electron microscope image.

In this embodiment, the energy distribution of electrons emitted from the electron source is 0.2 eV or less, and 0.1
The monochromaticity is very good, eV or less. For this reason, as shown in FIG. 7, the chromatic aberration of electrons in the objective lens 14 can be reduced without increasing the boost voltage Vb applied to the booster electrode 18, and Vb + Vr is reduced from -20 kV to 0.
It can be used under the condition of V. In this case, the sample can be observed at a high resolution of about 1 nm while suppressing abnormal discharge on the surface of the sample 21.

In the above configuration, -10 V <Vb +
When Vr <10 V, the effect of preventing discharge is further improved.
In this case, a resolution of about 1.5 nm is possible with an acceleration voltage of 800 to 1000 V. Since the energy width of the electron beam obtained in this manner is about 0.1 eV, a resolution of 1 nm or less can be achieved by further adding retarding and boosting. The condition of the electric field at this time is as follows with respect to the acceleration voltage V0 (≦ 0 V) from the electron source.
In a configuration in which a retarding voltage Vr (≦ 0 V) is applied to a sample substrate placed on a moving stage via an insulating plate, V0−Vr is set to −500 to −2000 V and V
When r is set in a range of 0 to -20 kV and boosting is applied, it is important to set Vb + Vr in a range of 0 to -20 kV. If it exceeds this, a large electric field is applied to the sample surface, and the sample is easily broken.

FIG. 3 shows an example of the configuration of an electron source used in this embodiment. The light source device 8 is connected to the vacuum vessel 1 via the light source mount 11.
It is attached to 0. The mounting base 11 can have a fine adjustment mechanism as needed. The parallel light 6 generated from the light source device 8 passes through the window 7, becomes the convergent light 4 by the objective lens 5, and focuses on the photocathode 1. The photocathode 1 is made of GaAs / AlGa on a transparent substrate 101 such as glass.
The As photocathode film 102 is attached.

The GaAs layer has a thickness of 1 μm or less and is
5 × 10 as Zn¹⁸/ Cm ³Doped about
It is a p-type semiconductor, and Cs and oxygen are formed on the GaAs surface.
Adsorbed, the work function of the surface is 1.4 eV or less
You. When light is incident on the photocathode film 102, a negative
Electron affinity (NEA: Negative electron affinity)
Electrons are emitted into the vacuum by the effect. The incident light is
Energy (1.4 eV for GaAs)
Larger energy is required, in which case the wavelength is 880n
m or less is a condition. Practically, laser diodes and lasers
The light having a wavelength of 600 to 780 nm in which
Suitable.

Further, electron emission can be obtained even when the surface adsorption layer of Cs and oxygen is smaller and the work function is 1.4 eV or more. In this case, an electron beam with good monochromaticity can be obtained. In such a case, when the work function (φb) of the electron emission surface becomes larger than the band gap energy (Eg) of the p-type semiconductor by 1 eV or more, the amount of emitted electrons is drastically reduced. An amount that does not exceed is needed. The photocathode film 102 is in electrical contact with the metal cathode holder 9 and has a cathode voltage V0 of -3 k
V is supplied. The opposing extraction electrode 2 is at 0 V, and is accelerated by the electric field generated by the two, and an electron beam 3 is obtained.

This electron beam has an energy width of 0.3 to 0.0.
It is a single color of 8 eV. Further, since the spread angle of the electron beam is narrow and 1 mrad or less, the brightness is high. In this embodiment, the thickness of the transparent substrate 101 (1.2 m
m), spherical aberration corrected, NA = 0.45-0.5
5 are used. For this reason, the focal point of the excitation light has a half width of about 1 μm, and when the current is about 1 μA, the luminance is extremely high, about 10 ⁸ A / sr / cm ^2, and a value equivalent to that of the field emission electron source can be obtained. . The thickness of the transparent substrate can be adjusted from 1 to 1.5 mm without significant deterioration by adjusting the lens position.

As a conventional example in which the NEA photocathode is used in an electron beam application device such as a SEM, C.I. A. Sanford, Journal of Vacuum S
cience and Technology) B, 1988, Volume 6, 20
Some are described from page 05 to page 2008. FIG. 2 shows an outline of this prior art. In this case, the photocathode 1 in a vacuum is composed of a transparent substrate and GaAs bonded to its surface.
The main material is a photocathode film, which is a so-called transmissive photocathode that receives light from the transparent substrate side and emits electrons from the photocathode film side into a vacuum. Since the condenser lens 5 is in the atmosphere and irradiates the photocathode 1 with the light through the window 7 attached to the vacuum vessel 10, there is a problem that the diameter of the collected light cannot be reduced.

Further, since the energy width and the emission current value have not been optimized, the brightness and monochromaticity are low, and the obtained S
The EM image has extremely poor resolution. Also,
Since there is no means for cleaning the surface, there is a problem that the electron source deteriorates quickly and cannot be practically used as an SEM electron gun. In addition, the same description is given in JP-T-11-5093.
60, but the problem is similar in this case.

According to the present invention, there is provided a structure in which light convergence is idealized,
By adopting an electron gun structure that performs the treatment of the photocathode surface under optimal conditions, a high-resolution low-acceleration SEM that has excellent long-term stability and high brightness and uses a monochromatic electron gun is put into practical use.

In the present electron source, the diameter of the light source is determined by the diffraction limit of the excitation light and the diffusion length of electrons formed by photoexcitation in the semiconductor, and these are as large as 1 μm. Therefore, the electron emission source has a diameter of 1 μm to 3 μm. It has become. When a probe diameter of about 1 nm is required by observation with an electron microscope, a three-stage electron lens structure is used so that a reduction ratio of 1/1000 to 1/3000 can be obtained in the electron optical system.

The NEA photocathode has a structure in which an ultra-high vacuum atmosphere is formed because the NEA photocathode deteriorates very quickly if there is a residual gas such as oxygen, water or carbide. FIG. 4 shows a configuration example of the exhaust system of the SEM of this embodiment. That is, a differential pumping structure is adopted, and the evacuation is performed by a turbo molecular pump (TMP) and an ion pump (IP).

After the vacuum is raised by baking at about 200 ° C., the non-evaporable getter 34 placed in the IP1 of FIG. 4 and the electron gun chamber shown in FIG. 3 maintains the ultra-high vacuum. Also,
Since a large amount of gas is emitted from the extraction electrode 2 particularly due to electron beam impact, as shown in FIG.
1 is placed, and the extraction electrode is heated so as to have a temperature of 400 ° C. to 500 ° C. to reduce gas emission from the surface.

The provision of the non-evaporable getter 34 adjacent to the heater 31 activates the getter to enhance the exhaust capability. Further, it is more effective to provide a W filament (not shown) inside and use the filament as a thermionic electron source to heat the periphery of the extraction electrode 2 and the differential exhaust hole 103 by electron beam impact. For example, in the case of a movable cathode holder 9 as shown in FIG. 8, this W filament is attached to the right side of the cathode holder 9, and when the cathode 1 is moved from above the extraction electrode 2, W
It is good to make a filament move.

FIG. 5 shows a configuration example of the excitation optical system forming the light source device 8 and the focus detector 28. In FIG.
1 is a transparent substrate, 102 is a photocathode film, 5 is a condenser lens, 6 is parallel light, 7 is a window, 40 is a view port, 41 is reflected light from the cathode, 42 is a support base, 43 is a neutral density filter, 44 Is a check lens, 45 is a pinhole, 46
Is a photodetector, 47 is an intermediate layer, 50 is a laser diode, 51 is a collimator lens, 52 is a coupling lens, 53 is an optical fiber, 54 is a fiber holder, 55
Is an adjustment screw, 56 is a collimator lens holder, 57 is x
-Y stage, 58 is a beam splitter, 59 is a tilt stage.

In this configuration example, there are a light source and light convergence checking means. The light source passes a light emitted from a laser diode (LD) 50 through a single mode optical fiber 53 via a coupling lens 52 for the purpose of producing a Gaussian beam. The light emerging from the other end of the fiber is made into parallel light via a collimator lens 51. This is incident on the condenser lens 5 through the vacuum window 7 and the transparent glass substrate 10
1 and converge on the photocathode film 102 through the intermediate film 47. The intermediate film 47 is an adhesive, an antireflection coating film, or a wide gap film such as AlGaAs.

In order to minimize the irradiation area of the excitation light on the photocathode film 102, the focus is detected using the reflected light 41, and the position of the condenser lens 5 is controlled. The reflected light that has passed through the condenser lens 5 becomes parallel light having the same diameter as that at the time of incidence under optimum conditions. If the light is separated by the beam splitter 58 and collected by the check lens 44, an image is formed at the focal position of the check lens. For this purpose, a horizontally extending support 4
2, a neutral density filter 43, a check lens 44 of F = 100 mm, a pinhole 45 (hole diameter 20 μm), and a photodetector 46 are arranged on the axis, and the condensing lens 5 having the maximum photodetector output is provided. The position is optimal.

Alternatively, a CCD camera may be provided instead of the pinhole 45 and the photodetector 46. In this case, the minimum diameter in the image signal is the optimum position. In addition, if the intensity of the light passing near the focal point changes suddenly instead of the pinhole 45, the same effect can be obtained.
A knife edge or the like inclined at 5 degrees may be placed.

The parallel light source may be constituted by a combination of an LD 50, a collimator lens 51, and a beam shaping prism 60 as shown in FIG. The beam shaping prism 60 is for correcting the cross-sectional shape of the elliptical emitted light from the LD 50 to a circular shape. Further, a prism 62 shown in FIG. 6B may be used as a beam shaping prism and a beam splitter. In this case, there are advantages that the number of parts is small and the device can be made compact. Alternatively, the same effect can be obtained by inserting a cylindrical prism 64 between the LD 50 and the collimator lens 51 as shown in FIG.

As means for minimizing the diameter of the excitation light irradiated on the photocathode 102 in order to minimize the diameter of the electron source, a method shown in FIG. 15 may be employed. That is,
The condenser lens 5 is roughly aligned with an accuracy of about ± 50 μm from the optimum position, and then the distance between the laser diode 50 and the collimator lens 51 is adjusted by the micrometer 150 with an accuracy of ± 1 μm.

In the system shown in FIG. 15, since the light from the collimator lens 51 is not always parallel, focus detection cannot be performed with the light extracted by the beam splitter 58 as shown in FIG. In this case, the current of the laser diode 50 is monitored to detect that the focus of light on the photocathode 102 is minimized. The output of the laser diode 50 is controlled by controlling the current of the laser diode 50 so as to be constant while monitoring the light output with a built-in photodiode (not shown).
Since the reflected light from the photocathode 102 returns to the laser diode with a high intensity, the resonance condition of the laser changes. As a result, as shown in the graph on the left side of FIG. 15, a minimum region of the laser diode current is formed in the optimal region of the interval between the laser diode 50 and the collimator lens 51. With the structure shown in FIG. 15, since a high-precision micrometer can be used, there is an advantage that the optimum position of the focal point can be determined with high accuracy, and that there is an advantage that automation can be easily performed.

As a focus detection method, the emission current from the photocathode 102 may be monitored. In this case, the micrometer 150 may be adjusted so that the emission current from the photocathode 102 is minimized.

Although the laser diode 50 is moved here, the same effect can be obtained by moving the collimator lens 51. Unlike the laser diode, the collimator lens 51 is lightweight and requires no wiring, and thus has an advantage that a small actuator such as an electromagnet can be used.

In order to function as a NEA photocathode, an adsorbed layer of oxygen and Cs is formed after removing a deposit on the GaAs surface to obtain a clean surface. FIG. 8 shows a preferred embodiment of the present invention in which the surface cleaning and activation of the photocathode are performed in order to maintain the electron source with high brightness and stability and to be able to use it for a long time without opening the vacuum vessel. An example of a configuration that is performed inside a vacuum vessel will be described.

In the apparatus shown in FIG. 8, after the vacuum is started, the photocathode 1 is placed under the heater 87 by a moving mechanism using the expansion and contraction of the bellows 80, and the substrate temperature is set to 400 ° C.
To 500 ° C. Atomic hydrogen is sprayed onto the photocathode 1 from the opposed atomic hydrogen generator 85 for 20 minutes to 3 hours to reduce and remove oxides and carbides on the GaAs surface of the photocathode 1.

The atomic hydrogen generator 85 is composed of an alumina cylinder and a W filament formed in a coil inside the alumina cylinder.
Heated to about 000 ° C., the hydrogen gas in the variable leak valve 86 ^10-7 - ³ is adjusted to ^Pa about gas pressure through the atomic hydrogen generator 85, and dissociating hydrogen molecules. Thereafter, the hydrogen is stopped and the atomic hydrogen generator 8
5 and the substrate heater 87, the GaAs is returned to around room temperature, and the surface cleaning is completed.

Next, the photocathode 1 is irradiated with excitation light from the probe light source 88 through the hole of the heater 87, and oxygen and Cs are appropriately blown onto the surface to form an activated surface adsorption layer.

The termination of the activation is detected by applying a voltage Vc to the photocathode holder 9 via the tentacle 82, monitoring the emission current due to the irradiation of the probe light, and detecting that the emission current reaches a desired value. Vc only needs to have an electric field for keeping the emitted electrons away from the vicinity of the surface, and is used at about −2 V to −50 V.

The energy distribution can be measured by the retarding method by placing the mesh electrode 84 facing the photocathode 1 and changing the electric field between the two. For example, the mesh electrode 84 is changed to the ground potential, Vc is changed from around +1 V to -10 V, the emission current Ic from the photocathode 1 is taken, and the differentiated dIc / dVc shape corresponds to the energy distribution. With this method, the activation of the photocathode can be adjusted so as to obtain a desired energy distribution. After the activation, the supply of Cs and oxygen is stopped, and the photocathode 1 is moved to a predetermined position on the extraction electrode 2 to be used as an electron source.

After activation, if the photocathode 1 is used as an electron source for several hours to several tens of hours, the emission current decreases for a constant excitation light intensity, and the brightness of the electron source decreases. In this case, the emission current can be recovered by adding Cs to the surface. That is, the photocathode 1 is moved to the vicinity of the Cs evaporation source 83 in FIG. 8, and Cs is additionally deposited while monitoring emission current due to photoexcitation.

Further, when used for a long period of time, such as about six months to one year, the current value does not increase in the additional deposition of Cs.
In this case, the surface can be cleaned again, and the photocathode surface can be activated to be used again. As described above, the present invention has an advantage that the apparatus can be operated for a long period of time without opening the vacuum electron gun device by appropriately repeating surface cleaning and activation and additional Cs deposition.

Although the cylinder and the variable leak valve 86 are used as oxygen and hydrogen gas sources in the example of FIG. 8, the amount of use is extremely small. Has the effect. For example, as an oxygen source, a thin plate of silver oxide or silver may be provided between the substrate and the atmosphere and heated. As the hydrogen source, a hydrogen storage alloy containing Zr or Ti may be heated. Zr and Ti
The use of a non-evaporable getter containing hydrogen as a hydrogen source is effective because it also serves as a vacuum pump. Also, the heater 87
Instead, infrared rays may be introduced from outside and heated.

Further, the W filament of the atomic hydrogen generator 85 and the substrate heater 87 may also be used. W filament is 200 ℃ from 1800 ℃ to generate atomic hydrogen
0 ° C, while the photocathode is 400
Since the temperature may be set to a lower temperature of 500 ° C. to 500 ° C., this condition can be achieved by adjusting the distance between the photocathode 1 and the atomic hydrogen generator 85.

If the extraction electrode 2 shown in FIG. 8 has a structure as shown by 90 in FIG. 9, even if the photocathode does not move, the structure shown in FIG.
Can be performed. That is, a groove for incorporating the Cs evaporation source 83 is provided in the extraction electrode 90.
Further thereon, a W heater 87 serving as a substrate heater and a mesh electrode 91 for preventing disturbance of the electric field are sequentially provided. According to this configuration, the surface cleaning and activation of the photocathode,
All of the additional steaming can be performed on the extraction electrode 90.

In the above embodiment, atomic hydrogen was used as the surface cleaning method. However, if the state in which the residual gas in the electron gun is extremely low is formed, the photocathode can be heated from 400 ° C. by the heater 87 alone. The surface can be cleaned even by heating to 500 ° C. At this time, the inside of the electron gun is 10 ^-8 P
A degree of vacuum of a or more is required.

When the photocathode 1 is used for a long period of time, the area of the surface of the photocathode 1 which emits electrons is particularly easily damaged. The electron emission region is extremely narrow, and the half width is 1
Since the diameter is on the order of microns, the life can be further extended by adopting a structure in which the photocathode 1 is moved in the horizontal direction and used.

One example is shown in FIG. This is one in which the photocathode 1 is movable in the X-Y direction by the push rod 70 and the linear introduction device 71, and a wide portion in the photocathode plane can be used as an electron emission region.
As a result, there is an advantage that once activated, surface cleaning is not required for a long time. In addition, there is an advantage that electrons can be continuously emitted for a long time without additionally depositing Cs. In this case, if the shape of the lower surface of the holder 9 is almost the same as the shape of the lower surface of the cathode, the change in the electric field due to the movement of the cathode can be minimized.

FIG. 11A shows an example of the system configuration of a scanning electron microscope. FIG. 2B shows the relationship between the intensity of the incident excitation light from the LD and the amount of electron beam emitted (electron beam probe current). The amount of electron emission is controlled by the LD power, and the relationship is determined by the quantum efficiency. The quantum efficiency greatly depends on the surface state of the photocathode and deteriorates during use. For this reason, the electron gun controller controls the LD power to obtain a desired emission current. When the control range of the LD exceeds a predetermined value, the quantum efficiency of the surface is degraded. Therefore, Cs is additionally deposited on the photocathode by the activation controller.

Also, the electron gun controller receives a blanking signal or a beam scan def signal from the SEM controller, and as shown in FIG. 11C, when the electron beam is unnecessary, the LD power is reduced and the electron beam is reduced. Stop or reduce. As a result, in this embodiment, equipment for blanking electron beams is not required in the SEM housing.

FIG. 12 shows a sample observation example using the present invention. An insulator such as a silicon oxide film is charged on the surface by the electron beam incidence, and the surface potential changes. This state is shown in FIG. At the beginning of the potential change, the amount of change is large, so that accurate measurement cannot be performed. In the case of observing a contact hole in an insulator as shown in FIG. 12B, the inside of the contact hole can be easily observed by charging the insulator to some extent. Charging before this observation is called precharge and has been used for a long time. The precharge time is shorter as the electron beam current is larger.
If you increase the amount of probe current for precharge during observation,
There is an advantage that the observation time can be reduced.

In order to increase the probe current with the electron source in the conventional apparatus, it is necessary to change the conditions of the electron source or the electron optical system, and thus it is difficult to change the current value during high-resolution measurement. However, according to the present invention, L
The probe current amount can be controlled only by changing the excitation light amount by the D power controller without changing the conditions of the electron optical system. Therefore, the present invention is extremely effective when used for observing a sample requiring precharge.

Further, when the sample surface is divided into a region A having a contact hole and a region B of an oxide film as shown in FIG.
When processing is performed by the controller and precharging is performed only in the contact hole region A as shown in FIG. 12C, observation can be performed while suppressing unnecessary charging. This has the effect of reducing discharge and contamination in the sample. This method is applicable not only to the X-direction diff signal but also to an arbitrary shape, and the required amount of current for each area can be designated by the image processing apparatus.

Since the electron source device of the present invention converts a light pattern into an electron beam pattern, it has the characteristic that the shape of the electron beam can be changed without changing the conditions of the electron optical system at all. . FIG. 13 shows an example utilizing this characteristic. When a pattern having a long shape in one direction is formed on the substrate as shown in FIG. 3B, an elongated electron beam probe is formed in the same direction as the longitudinal direction of the pattern as shown in FIG. And irradiate. As a result, FIG.
An SEM image of a shape contracted in the longitudinal direction is obtained as shown in FIG. In this case, although the resolution is lower than that of a fine beam, there is an advantage that a defect inspection of a pattern having a long shape can be performed in a shorter time.

FIG. 14 shows an example of forming a desired electron beam pattern as described above. FIG. 2A shows a mask 1 between a lens 5 for condensing light on a photocathode 1 and a light source device.
In this method, the aperture shape is imaged on the photocathode 1 using the condenser lens 5. The imaging condition is 1 / f = 1 / L1 + 1 / L2, where L1 is the distance from the mask 140 to the lens 5, L2 is the distance from the lens 5 to the photocathode 1, and f is the focal length of the lens 5.

FIG. 14B shows a method of putting a mask 140 in front of the collimator lens 51. The conditions in this case are as follows: the distance from the mask 140 to the collimator lens 51 is L1, the distance from the condenser lens 5 to the photocathode 1 is L2, the focal length of the condenser lens 51 is f1, and the focal length of the condenser lens 5 is f2. When f1 = L1, f
2 = L2.

It is clear that other than this method, the same effect can be obtained if the photocathode can be irradiated with excitation light having a desired shape. For example, a thin laser beam may be scanned, or an interference pattern may be formed.

[0062]

As described above with reference to the embodiments, by using the present invention, a high-resolution electron microscope can be obtained even at a low acceleration. Further, by using the present invention, a high-performance electron beam inspection apparatus can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view showing a configuration of a scanning electron microscope according to one embodiment of the present invention.

FIG. 2 is a schematic longitudinal sectional view showing an electron gun portion using a conventional photocathode.

FIG. 3 is a longitudinal sectional view showing an electron gun using a photocathode according to one embodiment of the present invention.

FIG. 4 is an explanatory view showing an exhaust system in the electron microscope according to one embodiment of the present invention.

FIG. 5 is a longitudinal sectional view showing an electron gun using a photocathode according to one embodiment of the present invention.

FIG. 6 is an explanatory diagram of an optical system of irradiation excitation light according to one embodiment of the present invention.

FIG. 7 is a graph showing a relationship between monochromaticity and chromatic aberration of an electron beam.

FIG. 8 is a longitudinal sectional view showing a photocathode cleaning and activating means according to one embodiment of the present invention.

FIG. 9 is an exploded perspective view showing a configuration of an extraction electrode portion according to one embodiment of the present invention.

FIG. 10 is a longitudinal sectional view and a plan view showing a photocathode moving means according to one embodiment of the present invention.

FIG. 11 is a block diagram showing a functional configuration of a scanning electron microscope according to one embodiment of the present invention, and an explanatory diagram of a control method.

FIG. 12 is an explanatory diagram of a method of observing an inspection object according to one embodiment of the present invention.

FIG. 13 is an explanatory diagram of a method of observing an inspection object according to an embodiment of the present invention.

FIG. 14 is a perspective view and a longitudinal sectional view of an irradiation optical system of irradiation excitation light according to one embodiment of the present invention.

FIG. 15 is a longitudinal sectional view showing a configuration example of an irradiation excitation light adjusting means according to one embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photo cathode, 101 ... Transparent substrate, 102 ... Photo cathode film, 103 ... Differential exhaust hole, 104 ... Optical lens holder, 2 ... Electron extraction electrode, 3 ... Electron beam, 4 ... Convergent light, 5 ... Condensing lens, 6 ... Parallel light, 7 ... Window, 8 ... Light source device, 9 ... Cathode holder, 10 ... Vacuum container, 11 ... Light source mount, 12 ... First condenser lens, 13 ... Second condenser lens, 14 ... Objective lens, 15 ... Deflector, 16
... first aperture, 17 ... second aperture, 18 ... booster electrode, 19 ... electronic detector, 20 ... speed discriminator, 2
DESCRIPTION OF SYMBOLS 1 ... Observation sample, 22 ... Sample fixing stand, 23 ... Insulating stand, 24
... moving stage, 25 ... sample chamber, 26 ... sample introduction chamber, 2
7: Differential exhaust chamber, 28: Focus detector, 29: Backscattered electron detector, 30: Anode insulator, 31: Anode bake heater, 32: Cathode insulator, 33: Cathode stand, 34
... non-evaporable getter, 35 ... bellows, 40 ... view port, 41 ... reflected light from cathode, 42 ... support base, 43
... Attenuating filter, 44 ... Check lens, 45 ... Pinhole, 46 ... Photodetector, 47 ... Intermediate layer, 50 ... Laser diode, 51 ... Collimator lens, 52 ... Coupling lens, 53 ... Optical fiber, 54 ... Fiber holder 55, adjusting screw, 56, collimator lens holder, 57, xy stage, 58, beam splitter,
59: tilt stage, 60: beam shaping prism, 6
DESCRIPTION OF SYMBOLS 1 ... Light source mount, 62 ... Prism, 63 ... Emitted light of elliptical cross section from LD, 64 ... Cylindrical prism, 65 ... Circular cross-section light, 70 ... Push rod, 71 ... Straight line introducer, 8
0: straight introducer, 81: insulating joint, 82: tentacle, 83
... Cs evaporation source, 84 ... mesh electrode, 85 ... atomic hydrogen generator, 86 ... variable leak valve, 87 ... heater, 88 ... light source, 90 ... extraction electrode, 91 ... mesh electrode, 140 ... mask, 150 ... micro Meter.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Hiroyuki Shinada 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (72) Inventor Satoru Fukuhara 882 Ma, Hitachinaka-shi, Ibaraki Prefecture Hitachi, Ltd. In the measuring instrument group (72) Inventor Mari Nozoe 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo F-term in Central Research Laboratory, Hitachi, Ltd. 5C030 CC10 5C033 FF10 JJ07 MM07 UU02 UU03 UU10

Claims (10)

[Claims] A light source device for exciting light, a photocathode which emits electrons by irradiating the exciting light in a vacuum, a focusing lens for condensing the exciting light on the photocathode, and an electron beam generated from the photocathode. Extraction electrode, light convergence confirmation means, photocathode surface cleaning means, photocathode surface activation means, Cs additional vapor deposition means, at least two electron lenses, electron beam deflector, substrate sample chamber, substrate An electron microscope apparatus comprising a sample moving stage and observing an electron beam incident on the sample at a low acceleration (500 V to 2000 V). 2. The electron microscope according to claim 1, wherein
In a configuration in which the sample substrate is placed on a moving stage via an insulating plate with respect to an acceleration voltage V0 (<0 V) from an electron source, and a retarding voltage Vr (≦ 0 V) is applied,
V0-Vr is in the range of -500V to -2000V,
An electron microscope apparatus wherein Vr is in a range from 0 V to -20 kV. 3. An electron microscope apparatus according to claim 2,
A boosting electrode for accelerating electrons is provided at least near the objective lens, and the boosting voltage Vb (≧
0V) in a configuration where Vb + Vr is 0 V
Electron microscope apparatus in the range from to −20 kV. 4. An electron microscope apparatus according to claim 1, further comprising means for changing the intensity of excitation light to change the amount of electron beam current during sample observation. Electron microscope equipment. 5. The electron microscope according to claim 4, wherein
An electron microscope apparatus characterized in that a signal designating the intensity of excitation light for changing the amount of current of an electron beam is generated based on an observed image. 6. An electron microscope apparatus according to claim 1, further comprising means for changing a spatial and temporal shape of the electron beam by changing an irradiation area of the excitation light on the photocathode. An electron microscope apparatus characterized in that: 7. An electron microscope according to claim 6, wherein:
An electron microscope apparatus characterized in that a mask is provided in an optical path of excitation light and an opening shape of the mask is projected on a photocathode. 8. The electron microscope according to claim 1, wherein the electron emission surface of the photocathode has a surface of a p-type semiconductor or a surface adsorption layer of one molecular layer or less on the surface of the p-type semiconductor. Is not less than the bandgap energy (Eg) of the p-type semiconductor, and the surface adsorption layer is selected on condition that the work function (φb) of the electron emission surface does not exceed the bandgap energy (Eg) of the p-type semiconductor by 1 eV or more. And the p-type semiconductor is GaAs, Al
As, InP, InAs, GaP, GaN or S
i, C, Ge or a mixture thereof, and the surface adsorption layer is made of an alkali metal such as Cs, Na or the like;
An electron microscope apparatus comprising an alkali metal such as s and Na and oxygen, or an alkaline earth such as Ba and oxygen, or a mixture thereof. 9. A photocathode surface cleaning means comprising a substrate heater and an atomic hydrogen generator. 10. An electron microscope apparatus according to claim 1, further comprising means for moving the position of the photocathode without opening a vacuum device constituting an electron source.