JPH11242943A - Inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect an image rapidly in particular and keep the brightness of the image constant regardless of an observation magnifying factor in an inspection device that generates a sample image by utilizing electron beams. SOLUTION: This inspection device is composed by installing: an electron gun 24 to emit electron beams; an irradiation electron-optical system 25 to irradiate the electron beams to an irradiation region on the surface of a sample; an electron detection means 35 to detect secondary electrons or reflected electrons generated from the irradiation region of the electron beams; a projection electron-optical systems 31, 33, 34 which are arranged between the sample and the electron detection means, focus secondary beams composed of the secondary electrons and the reflected electrons on the detection surface of the electron detection means, and project an observation region in the irradiation region on the detection surface; a magnification control means 39, 41 to change the projection magnification of the projection electron-optical systems and thereby change the range of the observation region on the surface of the sample; an electron irradiation control means 39, 40 to change the current density of the irradiation region according to the range of the observation region. By virtue of this structure, the image of the observation region on the surface of the sample is projected on the detection surface of the electron detection means, so that the image of the observation region cart entirely be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection apparatus for acquiring, for example, an integrated circuit pattern image of a semiconductor wafer using an electron beam, and more particularly to an inspection apparatus capable of detecting an image at a high speed and observing an image. The present invention relates to an inspection apparatus that can maintain a constant brightness of an image regardless of a magnification.

[0002]

2. Description of the Related Art In general, a scanning electron microscope is known which scans a sample surface with an electron beam focused in a spot shape, detects secondary electrons, reflected electrons and the like generated from the sample, and obtains a sample image. ing. In this scanning electron microscope, since the sample is scanned with a spot-shaped electron beam having a reduced beam diameter, there is a problem in that scanning takes a long time and detection of the sample image requires a large amount of time. In order to shorten the detection time of the sample image, it is only necessary to increase the beam scanning speed. However, this causes another problem in that the amount of injected electrons per pixel is reduced and the image contrast is reduced. Occurred.

[0003] In order to solve the above problems,
JP-A-7-181297 or JP-A-7-249
No. 393 has proposed a defect detection device. In the above-described defect detection device, the electron beam generated from the rectangular cathode is shaped into a rectangular or elliptical cross section by a plurality of multipole lenses, and is irradiated onto the sample surface. As shown in FIG. 12, compared with the case of scanning with a conventional spot-shaped electron beam, since the scanning is performed with a rectangular beam having a large irradiation area, it is possible to scan the sample surface in a short time, and the image detection speed is reduced. Higher speed can be realized.

[0004]

In recent years, there has been a demand for an inspection apparatus to increase the speed of image detection as well as to increase the sensitivity of image detection. In the above-described defect detection device, a beam having a constant irradiation area called a rectangular beam is scanned on the sample surface. However, when detecting a wide-range image of the sample, it takes time to scan. The speed has dropped extremely.

[0005] Therefore, the present invention can further speed up image detection to meet the above-mentioned demands.
It is an object of the present invention to provide an inspection apparatus that can always obtain a sample image having constant brightness and contrast regardless of observation magnification.

[0006]

According to a first aspect of the present invention, there is provided an inspection apparatus comprising: an electron gun for emitting an electron beam; an irradiation electron optical system for irradiating an irradiation area on a sample surface with the electron beam; An electron detecting means for detecting at least one of secondary electrons and reflected electrons generated from the region; and a secondary beam disposed between the sample and the electron detecting means and comprising at least one of secondary electrons and reflected electrons. A projection electron optical system that forms an image on the detection surface of the electron detection means and projects an observation region in the irradiation region onto the detection surface, and a projection magnification of the projection electron optical system is changed to change the range of the observation region on the sample surface. And electron irradiation control means for changing the current density of the irradiation area according to the range of the observation area.

In such a configuration, since the image of the observation area on the sample surface is projected on the detection surface of the electronic detection means, the image of the observation area can be acquired collectively. Further, since the current density of the irradiation area can be changed according to the projection magnification (observation magnification), the brightness of the sample image can be kept constant regardless of the projection magnification. Claim 2
The invention according to claim 1 is the inspection apparatus according to claim 1,
The electron irradiation control means controls the range of the irradiation region by controlling the focusing action of the irradiation electron optical system according to the range of the observation region.

According to a third aspect of the present invention, in the inspection apparatus according to the first or second aspect, the electron irradiation control means outputs the electron beam emitted from the electron gun according to the range of the observation region. Is controlled. Claim 4
According to the invention described in (1), in the inspection apparatus according to any one of (1) to (3), the electron irradiation control unit increases the current density in the irradiation region as the range of the observation region decreases. Features.

According to a fifth aspect of the present invention, in the inspection apparatus according to any one of the first to fourth aspects, the electron irradiation control means sets the current density of the irradiation area to a predetermined current density or less. Is controlled. According to a sixth aspect of the present invention, in the inspection apparatus according to any one of the first to fifth aspects, the electron beam that has passed through the irradiation electron optical system is vertically irradiated on the sample surface, and the electron beam is emitted from the sample. A Wien filter for guiding at least one of the generated secondary electrons and reflected electrons to the projection electron optical system is provided.

According to a seventh aspect of the present invention, in the inspection apparatus of the sixth aspect, an objective electron lens is disposed between the sample and the Wien filter, and the magnification control means includes an objective electron lens and a projection electron optical system. The projection magnification is changed by changing the focal lengths of at least two electron lenses included in the above. An inspection apparatus according to claim 8, wherein an electron gun for emitting an electron beam, an irradiation electron optical system for irradiating the irradiation area on the sample surface with the electron beam, and secondary electrons generated from the irradiation area of the electron beam and reflection. An electron detecting means for detecting at least one of the electrons and a secondary beam arranged between the sample and the electron detecting means and comprising at least one of a secondary electron and a reflected electron are connected to a detection surface of the electron detecting means. A projection electron optical system that forms an image and projects an observation area in the irradiation area on the detection surface; and a magnification control unit that changes a projection magnification of the projection electron optical system and changes a range of the observation area on the sample surface. The electronic detection means adjusts the detection sensitivity according to the projection magnification.

In such a configuration, since the image of the observation area on the sample surface is projected on the detection surface of the electronic detection means, the image of the observation area can be obtained collectively. Further, since the detection sensitivity of the electronic detection means can be adjusted according to the projection magnification, the brightness of the sample image can be kept constant regardless of the projection magnification.

According to a ninth aspect of the present invention, in the inspection apparatus according to the eighth aspect, the electron detecting means includes: an electronic conversion unit that converts at least one of secondary electrons and reflected electrons into light; And an image sensor for photoelectrically converting the image data. The electronic detection means adjusts the detection sensitivity by changing the charge accumulation time of the image sensor.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall configuration diagram of the first embodiment. FIG. 2 is a diagram showing the trajectory of the primary beam.
FIG. 3 is a diagram showing the trajectory of the secondary beam. The first
Corresponds to the first, second and fourth to seventh aspects of the present invention. 1 to 3, the inspection device is a primary column 2.
It has primary and secondary columns 22 and a chamber 23. Inside the primary column 21, a thermionic emission type electron gun 2 is provided.
The primary optical system 25 is disposed on the optical axis of the electron beam (primary beam) emitted from the electron gun 24. The stage 26 is provided inside the chamber 23.
Is placed, and a sample 27 is placed on the stage 26.

On the other hand, the sample 2 is placed inside the secondary column 22.
On the optical axis of the secondary beam generated from 7, a cathode lens 28, a numerical aperture 29, a Wien filter 30, a second lens 31, a field aperture 32,
The third lens 33, the fourth lens 34, and the detector 35 are arranged. The new mechanical aperture 29 is equivalent to an aperture stop, and is made of metal (Mo or the like) having a circular hole.
It is a thin film of. The opening is located at the focusing position of the primary beam and the focal position of the cathode lens 28. The cathode lens 28 and the numerical aperture 29 constitute a telecentric electron optical system.

The detector 35 includes a control unit 36
The output of the control unit 36 is input to the image processing unit 38 via the monitor 37, and the output of the image processing unit 38 is input to the CPU 39. The CPU 39 is connected to the power supply units 40 and 41 and the stage driving mechanism 42,
Supplies a voltage to each lens of the electron gun 24 and the primary optical system 25, and the power supply unit 41
A voltage is supplied to each of the second lens 31, the third lens 33, and the fourth lens 34, and the stage driving mechanism 42 drives the stage 26 in the XY directions.

The laser interferometer unit 43 includes a stage 2
6 is read, and stage position information is transmitted to the control unit 36. The primary column 21, the secondary column 22, and the chamber 23 are evacuated (not shown).
And is evacuated by a turbo pump of a vacuum evacuation system, and the inside maintains a vacuum state.

The detector 35 has an MCP (micro channel plate) 44 and a FOP having a fluorescent screen 45.
(Fiber optic plate) 46 and CCD sensor 47. As for the correspondence between the present invention and the first embodiment, the irradiation electron optical system corresponds to the primary optical system 25, the electron detecting means corresponds to the detector 35,
The projection electron optical system corresponds to the second lens 31, the third lens 33, and the fourth lens 34.
And the power supply unit 41, the electron irradiation control means corresponds to the CPU 39 and the power supply unit 40, and the objective electron lens corresponds to the cathode lens 28.

Next, the operation of the first embodiment will be described. In the first embodiment, first, a wide area sample image is acquired at a low magnification to find a defect portion, and then the defect portion is enlarged and observed at a high magnification. (Low magnification observation) The primary beam from the electron gun 24 enters the Wien filter 30 while undergoing a lens action by the primary optical system 25.

Here, as the cathode of the electron gun, lanthanum hexaborite (LaB ₆ ) from which a large current can be extracted with a rectangular cathode is used. The primary optical system 25 uses a quadrupole (or octupole) electrostatic lens (or electromagnetic lens) with a rotational axis asymmetric. This lens, like a so-called cylindrical lens, has a long axis (X
Convergence and divergence can be caused in each of the axis (axis) and the short axis (Y axis). FIG. 2 shows the trajectories of the electrons emitted in the X-direction section and the electrons emitted in the Y-direction section of the rectangular cathode.

As a specific lens configuration, as shown in FIG. 4, when an electrostatic lens is used, four cylindrical rods are used. The opposing electrodes are set at the same potential, and voltage characteristics opposite to each other (+ Vq for a and b and −Vq for c and d) are given. By arranging this lens in three stages and optimizing each lens condition, the beam irradiation area on the sample surface can be formed into an arbitrary rectangular or elliptical shape without losing irradiation electrons. .

The trajectory of the primary beam shaped into a rectangular shape by the primary optical system 25 is bent by the deflection action of the Wien filter 30, and an image is formed at the opening of the numerical aperture 29. The Wien filter 30 makes the magnetic field and the electric field orthogonal, and sets the electric field to E, the magnetic field to B, and the velocity of the charged particle to v
In this case, only charged particles satisfying the Wien condition of E = vB are made to go straight, and the trajectories of the other charged particles are bent.

Further, the new mechanical aperture 29 is
An unnecessary electron beam scattered in the apparatus is prevented from reaching the sample surface, and charge-up and contamination of the sample 27 are prevented. Further, since the numerical aperture 29 and the cathode lens 28 constitute a telecentric electron optical system, the primary beam transmitted through the cathode lens 28 becomes a parallel beam as shown in FIG. Irradiate uniformly. That is,
The Koehler illumination in an optical microscope is realized. At this time, the beam irradiation area irradiated on the sample surface is related to the shape and area of the detection surface used by the CCD sensor 47 described later, and is proportional to the aspect ratio. For example, this beam irradiation area is an area of 400 μm × 200 μm. Also,
The beam output at this time is 100 nA.

When the sample 27 is irradiated with the primary beam,
A secondary beam including at least one of a secondary electron and a reflected electron is generated, and the secondary beam has two-dimensional image information of a beam irradiation area. At this time, since the primary beam is irradiated perpendicularly to the sample 27, the secondary beam has a clear electron image without shadow. The secondary beam passes through the lens while undergoing lens action by the cathode lens 28.

Incidentally, the cathode lens 28 is composed of three electrodes. Usually, to perform the lens action,
A voltage is applied to the first and second electrodes from the bottom of the cathode lens 28, and the third electrode is set to zero potential. The lowermost electrode is designed to form a positive electric field between the electrode and the potential on the sample 27 side, draw electrons (especially secondary electrons having low directivity), and efficiently guide the electrons into the lens. I have.

On the other hand, the new mechanical aperture 29 is
It is arranged at the focal position of the cathode lens 28, that is, at the back focus position from the sample 27. Therefore, as shown in FIG. 3, the light beam of the electron beam emitted from outside the center of the visual field (off-axis) also becomes a parallel beam and passes through the center position of the numerical aperture 29 without being shaken. The new mechanical aperture 29
Plays a role of suppressing the lens aberration of the second lens 31 to the fourth lens 34 with respect to the secondary beam.

The secondary beam that has passed through the numerical aperture 29 passes straight through without being subjected to the deflection effect of the Wien filter 30. At this time, by changing the electromagnetic field applied to the Wien filter 30, only electrons having a specific energy (for example, secondary electrons or reflected electrons) can be guided to the detector 35 from the secondary beam.

By the way, if the secondary beam is imaged only by the cathode lens 28, the lens action becomes strong and aberrations are likely to occur. Therefore, together with the second lens 31, 1
The imaging is performed twice. The secondary beam is the cathode lens 2
An intermediate image is obtained on the field aperture 32 by the eighth and second lenses 31. In this case, usually, the magnification required for the secondary optical system is often insufficient, so that a third lens 33 and a fourth lens 34 are added as lenses for enlarging the intermediate image. The secondary beam is the third
An enlarged image is formed by each of the lens 33 and the fourth lens 34. Here, an image is formed three times in total. The third lens 33 and the fourth lens 34 may be combined to form an image once (two times in total).

The second lens 31 to the fourth lens 34 are all rotationally symmetric lenses called unipotential lenses or Einzel lenses. Each lens has a configuration of three electrodes, and usually changes the lens action by changing the voltage applied to the center electrode to zero potential at the outer two electrodes. A field aperture 32 is arranged at an intermediate image point, and the field aperture 32 limits the field of view to a necessary range similarly to the field stop of the optical microscope. In particular, in the case of an electron beam, an unnecessary beam is supplied to a third lens 33 and a fourth lens 34 at the subsequent stage.
Together with the detector 35 to prevent charge-up and contamination of the detector 35.

The secondary beam passes through the second lens 33 and the third lens
The light passes through the lens 34 and forms an image on the detection surface of the detector 35.
That is, an image of the above-described 400 μm × 200 μm beam irradiation area is projected on the detection surface. Then, the secondary beam enters the MCP 44 and collides with the fluorescent screen 45 while amplifying the amount of current in the MCP 44. The fluorescent plate 45 converts the electrons into an optical image, and the optical image passes through the FOP 46 and is captured by the CCD sensor 47. At this time, in order to match the image size of the fluorescent screen 45 with the imaging size of the CCD sensor 47, the image is reduced and projected by the FOP 46.

The optical image is photoelectrically converted by the CCD sensor 47, and signal charges are accumulated in the CCD sensor 47.
The control unit 36 serially reads out image information from the CCD sensor 47 and outputs it to the monitor 37 and the image processing unit 38. The image processing unit 38
A pattern defect is detected from the detected image by template matching.

The CPU 39 outputs a drive control signal to the stage drive mechanism 42 and drives the stage 26 to move the defect so that the defective portion is located near the center of the monitor 37. (High-magnification observation) Next, the observation magnification is changed from a low magnification to a high magnification, and the detected defect portion is enlarged and observed.

Here, for example, in high magnification observation, 20
It is assumed that an area of 0 μm × 100 μm can be observed. At this time, the beam diameter was narrowed, and the beam irradiation area was 400 μm.
× 200 μm to 200 μm × 100 μm. Specifically, as shown in FIG. 5, in response to a control signal from the CPU 39, the power supply unit 40 applies the value of the voltage Vq applied to the lens 25a disposed on the Wien filter 30 side of the primary optical system 25. Smaller. At low magnification observation,
The observation area of 400 μm × 200 μm was irradiated with the electron beam of 100 nA.
An observation area of μm × 100 μm is irradiated with an electron beam of 100 nA. Therefore, even if the observation magnification is increased, the beam irradiation area is narrowed in accordance with the observation area, and the current density in the beam irradiation area is controlled to be high, so that the brightness and contrast of the image do not decrease.

On the other hand, in the secondary optical system, the focal lengths of the third lens 33 and the fourth lens 34 are changed to perform enlarged projection. Specifically, the absolute value of the voltage applied to the central electrode of the third lens 33 is reduced to increase the focal length of the lens. However, in this state, the secondary beam does not form an image on the detection surface of the detector 35. Therefore, the fourth lens 34
The absolute value of the voltage applied to the central electrode is increased to form an image on the detection surface. As shown in FIG. 6, the angle of the secondary beam focused on the detection surface of the detector 35 with respect to the fourth lens 34 is reduced to increase the observation magnification.

When the observation magnification is increased without limit and the beam irradiation area is narrowed accordingly, the current density in the beam irradiation area extremely increases. If the current density exceeds a certain range, contamination or charge-up occurs in the sample 27. Therefore, the CPU 39
The current density in the beam irradiation area is calculated from the area of the beam irradiation area and the beam output. Then, when the current density exceeds a certain value, even if the observation magnification increases, the narrowing of the beam irradiation area in accordance with the observation area is stopped, and an excessive increase in the current density in the beam irradiation area is avoided.

As described above, in the inspection apparatus of this embodiment,
The image of the beam irradiation area is detected by a detector 35 by a secondary optical system.
, And the sample image is acquired collectively by the detector 35. Therefore, high-speed image detection can be realized. When the observation magnification is changed by changing the lens condition of the secondary optical system, the lens condition of the primary optical system is set so that the observation area on the sample surface and the electron beam irradiation area have the same size. Set.

As a result, it is possible to suppress fluctuations in image brightness and contrast (for example, when the observation magnification is increased, the brightness of the image is reduced) caused by fluctuations in the observation magnification. In other words, if the observation magnification is increased, the observation area is narrowed accordingly. At the same time, the beam density is reduced and the current density is increased by irradiation. , The signal density of the image is always kept constant, and a decrease in image brightness and contrast can be avoided.

(Second Embodiment) In the second embodiment,
The output of the electron gun 24 is controlled according to the observation magnification (range of the observation area). The second embodiment corresponds to the third to seventh aspects of the present invention. The second embodiment has the same components as the first embodiment shown in FIG. 1, and thus a detailed description of the configuration will be omitted.

As shown in FIG. 7, the electron gun 24 includes a rectangular cathode 48, a Wehnelt cylinder 49, and an anode 50. The anode 50 is grounded, and a positive acceleration voltage is applied. A high voltage for negative electron acceleration is applied to the rectangular cathode 48 by a bias power supply. Rectangular cathode 4
8 is heated by a cathode heating power supply to emit thermoelectrons,
The electrons are accelerated by the anode 50 to a required acceleration voltage.

In such a configuration, for example, when the observation magnification is increased, the CPU 39 outputs a control signal to the power supply unit 40. The power supply unit 40 controls the output of the electron beam by changing the acceleration voltage applied to the anode 50. For example, when the observation magnification is increased, the brightness of the image is reduced. Therefore, the bias of the electron gun 24 is reduced to increase the output of the electron beam. Further, when the observation magnification is reduced, the bias of the electron gun is increased to suppress the brightness fluctuation of the image, and to maintain a constant brightness and contrast.

When the observation magnification is increased without limit and the output of the electron beam is increased accordingly, the current density in the beam irradiation area rises extremely. If the current density exceeds a certain range, contamination or charge-up occurs in the sample 27. Therefore, the CPU 39
Calculates the current density in the beam irradiation area from the area of the beam irradiation area and the beam output. Then, when the current density exceeds a certain value, the beam output is stopped from being further increased even if the observation magnification is increased, and an excessive increase in the current density in the beam irradiation area is avoided.

As described above, in the inspection apparatus according to the second embodiment, by controlling the electron beam output of the electron gun 24, brightness and contrast fluctuations of an image due to observation magnification are avoided. (Third Embodiment) In the third embodiment, the brightness fluctuation is suppressed by the detector 35. In the third embodiment,
This corresponds to the eighth and ninth aspects of the present invention.

The feature of the configuration of the third embodiment is that CC
TDI (TimeDelay Integration:
(Time delay integration type) An array CCD sensor is used, and other components are the same as those in the first embodiment of FIG. Also,
Regarding the correspondence between the eighth and ninth aspects and the third embodiment, in addition to the correspondence described above, the electronic conversion unit corresponds to the fluorescent screen 45, and the image sensor corresponds to the TDI array CCD sensor.

Here, the imaging operation of the TDI array CCD sensor, which is a feature of the configuration of the third embodiment, will be described with reference to FIGS. As shown in FIG. 8 (1), here, (X
The area (40) from (1, Y1) to (X512, Y256)
0 μm × 200 μm). The TDI array CCD sensor has, for example, 512 × 256 pixels, and the observation area is projected by a secondary optical system so as to match the TDI array CCD sensor.

Now, from (X1, Y1) to (X5
The images up to 12, Y1) are captured for a predetermined time by the TDI array CCD sensor. The signal charge is equal to T shown in FIG.
It is stored in ROW1 of the DI array CCD sensor. CP
U39 outputs a drive control signal to the stage drive mechanism 42, and the stage drive mechanism 42 drives the stage 26 in the Y direction. Then, the beam irradiation area is TDI array CCD
The sensor moves in the scanning direction by one horizontal scanning line.
At the same time, the laser interferometer unit 43 sends a vertical clock signal to the control unit 36.

When the vertical clock signal is input, the control unit 36 sends a transfer pulse, and ROW1
Is transferred to ROW2. ROW2
In the example, the images from (X1, Y1) to (X512, Y1) are captured, and the signal charges are accumulated.
The signal charges transferred from ROW1 are added and accumulated. In ROW1, (X1, Y2) is changed to (X51
(2, Y2) are captured and signal charges are newly stored.

Further, when the stage 26 is driven by one horizontal scanning line, in ROW3, (X1, Y1) to (X
The image charge up to 512, Y1) is captured and the signal charge is accumulated. At this time, the signal charge transferred from ROW2 is added and accumulated. In ROW2, (X1,
Image from (Y2) to (X512, Y2)
The signal charges are stored. At this time, the signal charges transferred from ROW1 are added and stored. Also, ROW
In step 1, images from (X1, Y3) to (X512, Y3) are captured, and signal charges are newly stored.

As the stage 26 is sequentially driven in the Y direction, the beam irradiation area scans the observation area, and the TDI array CCD sensor transfers the accumulated signal charges to the adjacent ROW in accordance with the driving of the stage 26. Transfer sequentially. This operation is repeated, and (X1, Y25)
6) When the images from (X512, Y256) are captured and stored in ROW1 of the TDI array CCD sensor, the images from (X1, Y1) to (X512, Y1) correspond to the number of horizontal scanning lines. The data is added and accumulated and stored in the ROW 256 of the TDI array CCD sensor.

In this state, when a transfer pulse is input to the TDI array CCD sensor, the signal charge stored in the ROW 256 is transferred to a CCD shift register via a transfer gate (not shown), and the sample image is stored in the TDI array CCD sensor. Array CC
The horizontal scanning lines are taken out from the D sensor one by one and output to the monitor 37. As described above, the TDI array CCD sensor can add and accumulate the signal charges of the same portion of the sample by the number of horizontal scanning lines. That is, the TDI array CCD sensor can accumulate and increase the signal charges of the same portion of the sample by repeating the imaging with the signal charges delayed, thereby improving the S / N of the detected image. Can be planned.

In this TDI array CCD sensor,
By extending the imaging time, it is possible to compensate for a decrease in the signal charge amount. As shown in FIG. 8 (2), the same imaging operation as described above is performed during high-magnification observation.
At the time of high magnification observation (observation area: 200 μm × 100 μm), at the time of low magnification observation (observation area: 400 μm × 200 μm)
As compared with m), the signal charge amount is reduced to ４. Therefore, the CPU 39 increases the signal charge amount by quadrupling the imaging time (charge storage time) by increasing the transmission interval time of the drive control signal transmitted to the stage drive mechanism 42 and reducing the scanning speed.

As described above, in the third embodiment, the TDI
Since the charge accumulation time of the array CCD sensor is changed according to the observation magnification, it is possible to suppress the brightness and contrast fluctuation of the image due to the observation magnification. In the first to third embodiments, a quadrupole lens whose rotation axis is asymmetric is used as the primary optical system 25, but the present invention is not limited to this.
For example, a rotationally symmetric lens such as an electromagnetic lens using a normal coil or an Einzel lens type electrostatic lens may be used. FIG. 10 shows, as an example of such a lens configuration, a lens having an electrode obtained by dividing a cylinder into four at equal angles. In this case, the size of the lens can be reduced. However, as shown in FIG. 11, since the beam irradiation area is not rectangular but circular illumination, the center of the beam irradiation area is used.

In the first to third embodiments, the observation magnification is changed by changing the focal length of the third lens 33 and the fourth lens 34. However, the present invention is not limited to this. The focal length of two lenses among the four lenses including the two lenses 31 may be changed.
Further, the control of the current density in the beam irradiation region may be performed by combining the control of the primary optical system shown in the first embodiment and the output control of the electron gun shown in the second embodiment. At this time, as a method of avoiding an excessive increase in the current density, a method of narrowing the beam irradiation area and simultaneously reducing the output of the electron beam may be used.

The lens configuration as a projection electron optical system is not limited to the first to third embodiments.
If a higher magnification is required, a four-stage (five-stage including the cathode lens 28) or more lens configuration may be used. In addition, as the electron gun of the second embodiment,
Not limited to a thermionic electron gun, a field emission electron gun utilizing field emission from a rectangular cathode may be used. In this case, the bias is applied to the extraction electrode and the acceleration electrode so that the electrons are efficiently emitted from the rectangular cathode. However, as the observation magnification increases, the electron gun is pulled out. The electron beam output is increased by making the bias applied to the electrode and the acceleration electrode shallow.

In the third embodiment, the brightness fluctuation is corrected by changing the charge accumulation time of the TDI array CCD sensor. However, the present invention is not limited to this.
An amplifier may be provided at the output stage of the sensor to adjust the gain.

[0055]

As described above, in the inspection apparatus according to the first aspect, since the image of the observation region on the sample surface is projected on the detection surface of the electron detection means, the image of the observation region is collectively obtained. Can be obtained, and the speed of image detection can be increased. Further, since the current density of the irradiation area can be changed according to the range of the observation area, even if the projection magnification (observation magnification) is changed, the brightness and contrast of the image do not change, and the image is not affected by the projection magnification. Therefore, an image having constant brightness and contrast can be always obtained.

In the inspection apparatus according to the second aspect, since the range of the beam irradiation area can be controlled according to the range of the observation area, an image having constant brightness and contrast is obtained regardless of the projection magnification. be able to. In the inspection apparatus according to the third aspect, since the beam output of the electron gun can be controlled in accordance with the range of the observation region, an image having constant brightness and contrast is obtained regardless of the projection magnification. Can be.

In the inspection apparatus according to the fourth aspect, it is possible to avoid a decrease in the contrast of the detected image even when the projection magnification is increased and observation is performed at a high magnification. In the inspection device according to the fifth aspect, since the current density of the irradiation area can be limited to a predetermined current density or less, it is possible to prevent an excessive increase in the current density even when the projection magnification is set to a high magnification. Thus, charge-up and contamination of the sample can be prevented.

In the inspection apparatus according to the sixth and seventh aspects, since the electron beam can be irradiated perpendicularly on the sample surface by the Wien filter, a clear image without shadow can be obtained. In the inspection device according to claims 8 and 9,
Since the image of the observation region on the sample surface is projected on the detection surface of the electronic detection means, the image of the observation region can be acquired at a time, and the speed of image detection can be increased. Also,
Since the detection sensitivity of the electronic detection means can be adjusted according to the projection magnification, an image having constant brightness and contrast can be always obtained regardless of the projection magnification.

As described above, in the inspection apparatus to which the present invention is applied, the brightness and contrast of the detected image due to the projection magnification (observation magnification) can be suppressed, and a constant contrast can be obtained regardless of the projection magnification. Images can be acquired. Therefore, when detecting a defective portion by pattern matching, it is possible to avoid a decrease in detection accuracy due to contrast fluctuation, and it is possible to perform highly reliable defect detection.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a first embodiment.

FIG. 2 is a diagram showing a trajectory of a primary beam.

FIG. 3 is a diagram illustrating a trajectory of a secondary beam.

FIG. 4 is a configuration diagram of a primary optical system.

FIG. 5 is a diagram showing the trajectory of a primary beam during high-magnification observation.

FIG. 6 is a diagram showing a trajectory of a secondary beam during high-magnification observation.

FIG. 7 is a configuration diagram of an electron gun.

FIG. 8 is a diagram illustrating the operation of a TDI array CCD sensor.

FIG. 9 is a configuration block diagram of a TDI array CCD sensor.

FIG. 10 is a configuration diagram of another primary optical system.

FIG. 11 is a diagram showing a trajectory of a primary beam when another primary optical system is used.

FIG. 12 is a diagram showing scanning of a rectangular beam.

[Explanation of symbols]

 21 Primary Column 22 Secondary Column 23 Chamber 24 Electron Gun 25 Primary Optical System 26 Stage 27 Sample 28 Cathode Lens 29 New Mechanical Aperture 30 Wien Filter 31 Second Lens 32 Field Aperture 33 Third Lens 34 Fourth Lens 35 Detector 36 Control unit 37 Monitor 38 Image processing unit 39 CPU 40, 41 Power supply unit 42 Stage drive mechanism 43 Laser interferometer unit 44 MCP 45 Fluorescent plate 46 FOP 47 CCD sensor 48 Rectangular cathode 49 Wehnelt cylinder 50 Anode

Claims (9)

[Claims] 1. An electron gun for emitting an electron beam, an irradiation electron optical system for irradiating an irradiation area on a sample surface with the electron beam, and a secondary electron and a reflected electron generated from the irradiation area of the electron beam. An electronic detecting means for detecting at least one of the sample, and the electronic detecting means arranged between the sample and the electronic detecting means;
A projection electron optical system that forms a secondary beam composed of at least one of a secondary electron and the reflected electron on a detection surface of the electron detection unit, and projects an observation region in the irradiation region on the detection surface; Magnification control means for changing the projection magnification of the projection electron optical system to change the range of the observation area on the sample surface; and electron irradiation control means for changing the current density of the irradiation area according to the range of the observation area. An inspection device comprising: 2. The inspection apparatus according to claim 1, wherein the electron irradiation control unit controls a focusing operation of the irradiation electron optical system in accordance with a range of the observation region to control a range of the irradiation region. An inspection device characterized by controlling. 3. The inspection apparatus according to claim 1, wherein the electron irradiation control unit controls an output of an electron beam emitted from the electron gun according to a range of the observation region. An inspection device characterized by the above-mentioned. 4. The inspection apparatus according to claim 1, wherein the electron irradiation control unit increases the current density of the irradiation area as the range of the observation area decreases. An inspection apparatus characterized by the above-mentioned. 5. The inspection apparatus according to claim 1, wherein the electron irradiation control unit controls the current density of the irradiation area to be equal to or less than a predetermined current density. Inspection equipment characterized. 6. The inspection apparatus according to claim 1, wherein the electron beam that has passed through the irradiation electron optical system is vertically irradiated on the sample surface, and is generated from the sample. An inspection apparatus comprising: a Wien filter for guiding at least one of secondary electrons and reflected electrons to the projection electron optical system. 7. The inspection apparatus according to claim 6, wherein an objective electron lens is disposed between the sample and the Wien filter, and the magnification control unit is included in the objective electron lens and the projection electron optical system. An inspection apparatus for changing the projection magnification by changing a focal length of at least two electron lenses to be used. 8. An electron gun for emitting an electron beam, an irradiation electron optical system for irradiating the irradiation area on the sample surface with the electron beam, and a secondary electron and a reflected electron generated from the irradiation area of the electron beam. An electronic detecting means for detecting at least one of the sample, and the electronic detecting means arranged between the sample and the electronic detecting means;
A projection electron optical system that forms a secondary beam composed of at least one of a secondary electron and the reflected electron on a detection surface of the electron detection unit, and projects an observation region in the irradiation region on the detection surface; Magnification control means for changing the projection magnification of the projection electron optical system to change the range of the observation area on the sample surface, wherein the electron detection means adjusts the detection sensitivity according to the projection magnification. Inspection equipment. 9. The inspection apparatus according to claim 8, wherein the electron detection unit converts at least one of the secondary electrons and the reflected electrons into light, and photoelectrically converts the light. An inspection apparatus, comprising: an imaging device; wherein the electron detection unit adjusts detection sensitivity by changing a charge accumulation time of the imaging device.