JPH1167134A - Inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a uniform and clear image, independently of magnification by irradiating a sample surface with electron beams for having a rectangular or an elliptic area irradiated, and guiding the secondary beam to be generated from the sample to a detecting means via a Wien filter. SOLUTION: A radiating means 1 using an electrostatic lens having an asymmetrical rotary shaft forms a cross section of electron beams into a rectangular shape, and a deflecting means 4 scans. A Wien filter 3 makes an electric field and a magnetic field cross each other orthogonally so as to bend a path of the entering electron beam, and vertically radiates the electron beam to a sample surface for scanning. With the irradiation of the electron beam, at least one kind of secondary electron, reflected electrons and backward scattered electrons are generated as a secondary beam. Since the charged particles of the secondary beam satisfy the Wien's condition, the secondary beam travels straight without bending the path thereof. The secondary beam is detected by an electron-detecting means 2 of a CCD image-pickup element through an magnifying lens so as to obtain a rectangular sample image. Intensity of the electron beam is changed in response to an area to be inspected so as to provide a clear image at all times.

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 obtaining, for example, an integrated circuit pattern image of a semiconductor wafer using an electron beam, and more particularly to an inspection apparatus capable of obtaining a uniform and clear image. About.

[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. I have.

In this scanning electron microscope, since a sample is scanned with an electron beam whose beam diameter is narrowed, there is a problem that detection of a sample image requires a considerable time. In order to shorten the time required to detect a sample image, it is only necessary to increase the beam scanning speed. However, this method has a problem in that the amount of injected electrons per pixel is reduced, and the image contrast is reduced. Was.

Therefore, the present applicant has proposed an inspection apparatus which can solve the above problems and can detect a sample image in a short time without deteriorating the image quality (Japanese Patent Application No. 9-22).
No. 2187). This inspection apparatus will be described with reference to FIG. In FIG. 9, the inspection device has a primary column 50, a secondary column 51, and a chamber 52.

[0005] An electron gun 53 is arranged inside the primary column 50, and a primary optical system 54 is arranged on the optical axis of an electron beam (primary beam) emitted from the electron gun 53. Further, a Wien filter 55 inside the secondary column 51 is disposed obliquely with respect to the optical axis. on the other hand,
A stage 56 is provided inside the chamber 52,
A sample 57 is placed on the stage 56.

Further, inside the secondary column 51, a cathode lens 58, a Wien filter 55, and a secondary optical system 59 are arranged on the optical axis of the secondary beam from the sample.
Further, a detector 60 is disposed at a position where secondary electrons, reflected electrons, and the like are focused through the secondary optical system 59. Detector 60
Converts the detected electrons into light signals, and further converts the CCD
The signal is converted back into a photoelectric signal by the image sensor. The photoelectric signal is input to the CPU 62 via the control unit 61.

The CPU 62 includes a primary column control unit 6
A control signal is output to the third and secondary column control units 64. The primary column control unit 63 includes a primary optical system 54
In addition, the secondary column control unit 64 controls the lens voltage of the cathode lens 58 and the secondary optical system 59. Next, the operation of the inspection device will be described.

The primary beam is emitted from the electron gun 53 in the primary column 50. The electron beam is shaped into a rectangular or elliptical cross section by the primary optical system 54 and enters the Wien filter 55. Wien filter 55
Is a deflector that acts as an electromagnetic prism, and deflects the electron beam having a specific energy from the primary column 50 at an angle determined by the acceleration voltage, and irradiates the sample 57 vertically. On the other hand, the secondary beam generated from the sample 57 is made to proceed straight as it is and is incident on the secondary optical system 59 in the secondary column 51. The details of the Wien filter will be described later.

The primary beam that has passed through the Wien filter 55 is irradiated onto the sample surface, and the beam irradiation area has a rectangular or elliptical shape having a fixed area. When the sample is irradiated with the beam, a secondary beam is generated from the beam irradiation area. The secondary beam passes through the Wien filter 55, is focused by the secondary optical system 59, is enlarged and projected at a predetermined magnification on the detection surface of the detector 60, and is converted into an image signal. At this time, since the beam irradiation area of the sample is enlarged and projected on the detection surface as it is, images of a predetermined area of the sample can be collectively detected.

The control unit 61 includes a detector 60
And outputs the image signal to the CPU 62. CP
U62 performs pattern defect inspection by template matching or the like from the extracted image signal. In this way, in this inspection apparatus, the electron beam is not focused on a spot and scanned on the sample surface, as in a conventional scanning electron microscope. And irradiate the entire surface of the inspection target area to collectively obtain a surface image of the sample.

[0011]

In a normal inspection, for example, a part of a chip on a semiconductor wafer may be inspected, or an entire chip may be inspected by changing an enlargement magnification. At this time, in the inspection apparatus that collectively irradiates the above-mentioned electron beam, the irradiation area of the beam is enlarged in the primary optical system 54, the focal length is shortened in the secondary optical system 59, and the magnification is increased from a high magnification to a low magnification. Change to magnification.

However, in this case, it is necessary to irradiate the electron beam so as to cover all of the wide inspection area. In the primary optical system 54, the beam diameter of the electron beam (for example, the long axis for a rectangular beam) is increased,
Although it is possible to enlarge the beam irradiation area, the following problems can be considered. Since it is necessary to increase the beam diameter of the electron beam for irradiation, there is a possibility that peripheral dimming may occur due to aberration caused by the cathode lens 58.
Further, when the beam orbit is bent by the Wien filter 55, the deflection action differs between the inner circumference and the outer circumference of the beam, so that it is conceivable that beam unevenness may occur in the beam irradiation area.

As described above, when beam unevenness occurs in the beam irradiation area, beam unevenness also occurs in a secondary beam generated from the beam irradiation area, resulting in unevenness in contrast in a detected image and an uneven image. Conceivable. Therefore, an object of the present invention is to provide an inspection apparatus capable of always obtaining a uniform and clear image regardless of the magnification, in order to solve the above-mentioned problems. And

It is another object of the present invention to provide an inspection apparatus capable of maintaining a constant brightness of a detected image regardless of a magnification.

[0015]

FIG. 1 is a block diagram showing the principle of the first aspect of the present invention.

According to the first aspect of the present invention, an irradiation means 1 for shaping a beam cross section of an electron beam into a rectangular or elliptical shape and irradiating the electron beam with a sample surface, and a secondary beam generated from the sample by the irradiation of the electron beam. An electron, electron detection means 2 for detecting at least one of reflected electrons or backscattered electrons as a secondary beam and generating image information of the sample, and irradiating the sample surface with an electron beam irradiated from the irradiation means 1; In addition, a Wien filter 3 for guiding a secondary beam generated from the sample to the electron detecting means 2 and a deflecting means 4 for scanning the sample surface with the electron beam are provided.

According to a second aspect of the present invention, in the inspection apparatus according to the first aspect, the deflecting means 4 is disposed between the irradiation means 1 and the Wien filter 3.
According to a third aspect of the present invention, in the inspection apparatus according to the first or second aspect, the irradiating means 1 irradiates the sample while changing the beam intensity of the electron beam according to the area of the inspection target region of the sample. It is characterized by.

(Operation) In the inspection apparatus according to the first aspect,
The irradiation unit 1 shapes the cross section of the electron beam into a rectangular or elliptical shape. Therefore, a beam irradiation region generated when the sample is irradiated has a rectangular shape or an elliptical shape. The electron beam is scanned on the sample surface by the deflecting means 4.
The electron detecting means 2 sequentially detects a secondary beam generated from a beam irradiation location and generates image information of the sample.

In the inspection apparatus according to the second aspect, the deflecting means 4 is disposed between the irradiation means 1 and the Wien filter 3. In the inspection device according to the third aspect, the irradiation unit 1 includes:
Irradiation is performed by changing the beam intensity of the electron beam according to the area of the inspection target region of the sample. For example, when the magnification is set to a low magnification, the area of the sample to be inspected becomes wide. In order to scan a wide range, the beam scanning speed increases, and the beam amount (current density) of the electron beam irradiating the sample per unit area decreases. Therefore, in this case, the beam intensity is increased.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is an overall configuration diagram of the present embodiment. FIG. 3 shows the trajectory of the primary beam.
FIG. 4 is a diagram showing the trajectory of the secondary beam. This embodiment corresponds to the first to third aspects of the present invention.

2 to 4, the inspection apparatus has a primary column 21, a secondary column 22, and a chamber 23. A primary column 21 is obliquely connected to a side surface of the secondary column 22, and a chamber 23 is disposed below the secondary column 22. An electron gun 24 is provided inside the primary column 21, and a primary optical system 25 and a deflector 26 are arranged on the optical axis of an electron beam (primary beam) emitted from the electron gun 24, and furthermore, First, the Wien filter 30 inside the secondary column 22 is arranged obliquely with respect to the optical axis.

On the other hand, a stage 27 is provided inside the chamber 23, and a sample 28 is placed on the stage 27. Further, inside the secondary column 22, a cathode lens 29,
Wien filter 30, new mechanical aperture 3
1. A transfer electrostatic lens 32, a field aperture 33, projection electrostatic lenses 34 to 36, and a detector 37 are arranged.

The output of the detector 37 is supplied to a frame memory 38.
, And the output image of the CPU 39 is input to the CRT 40. The CPU 39 includes a primary column control unit 41, a secondary column control unit 42
To output a control signal.

The primary column control unit 41 includes the electron gun 2
4 extraction electrode, acceleration electrode voltage control, primary optical system 2
5 and the voltage applied to the deflector 26 are controlled, and the secondary column control unit 42
9 and control the lens voltages of the transfer electrostatic lens 32 and the projection electrostatic lenses 34 to 36.
In addition, primary column 21, secondary column 22, chamber 2
3 is connected to the vacuum exhaust system 43,
Evacuated by a turbo pump to maintain a vacuum state.

It should be noted that regarding the correspondence between the first to third aspects of the present invention and the present embodiment, the irradiating means 1 includes the electron gun 24, the primary optical system 25, and the primary column control unit 4.
1, the electron detecting means 2 corresponds to the transfer electrostatic lens 32, the projection electrostatic lenses 34 to 36 and the detector 37, the Wien filter 3 corresponds to the Wien filter 30, and the deflecting means 4 Device 26 and the primary column control unit 41.

As shown in FIG. 3, the primary beam from the electron gun 24 is subjected to a lens action by a primary optical system 25,
Deflected by the deflector 26, the Wien filter 30
Incident on. The scanning of the electron beam by the deflector 26 will be described later. Here, as the tip of the electron gun,
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 that is asymmetric about the rotation axis. This lens is
Convergence and divergence can be caused in each of the X-axis and the Y-axis similarly to a so-called cylindrical lens. By arranging this lens in two 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,
In addition, the current density in the beam irradiation area can be made uniform and uniform.

Specifically, as shown in FIG. 5A, when an electrostatic lens is used, four cylindrical rods are used.
The opposing electrodes (a and b, c and d) are made to have the same potential, and mutually opposite voltage characteristics are given. Further, as shown in FIG. 5 (2), a quadrupole lens having a shape obtained by dividing a circular plate generally used in an electrostatic deflector into four parts, instead of a cylindrical shape, may be used. In this case, the size of the lens can be reduced.

When the primary beam enters the Wien filter 30, the trajectory is bent by the deflection action of the Wien filter 30. When the magnetic field and the electric field are orthogonal to each other, and the electric field is E, the magnetic field is B, and the velocity of the charged particles is v, only the charged particles satisfying the Wien condition of E = vB are made to go straight, and the other charged particles Bend the orbit. FIG.
As shown in the figure, for the primary beam, the force F
B and a force FE due to the electric field are generated, and the beam trajectory is bent. On the other hand, since the force FB and the force FE act on the secondary beam in opposite directions, they cancel each other out and the secondary beam proceeds straight.

The primary beam that has passed through the cathode lens 29 irradiates the sample 28 vertically. Here, the sample 28
The irradiation area of the primary beam irradiated to the rectangular shape is rectangular. Secondary electrons, reflected electrons, or backscattered electrons are generated as secondary beams from the entire beam irradiation area of the sample 28. That is, this secondary beam has rectangular two-dimensional image information. In addition, the primary beam is
Because it is illuminated perpendicular to 8, the secondary beam has a clear, electron image without shadows.

The secondary beam passes through the lens and enters the Wien filter 30 while undergoing a lens action by the cathode lens 29. By the way, the cathode lens 29
Is composed of three electrodes. The lowermost electrode is designed to form a positive electric field between the electrode and the potential on the sample 28 side, draw electrons (especially secondary electrons having low directivity), and efficiently guide the electrons into the lens. I have. The lens action is performed by applying a voltage to the first and second electrodes from the bottom of the cathode lens 29 and setting the third electrode to zero potential.

The secondary beam that has passed through the cathode lens 29 travels straight without passing through the deflecting action of the Wien filter 30 and passes through the numerical aperture 31. By changing the electromagnetic field applied to the Wien filter 30, only electrons having a specific energy (for example, secondary electrons, reflected electrons, or backscattered electrons) can be guided to the detector 35 from the secondary beam. it can.

Further, the new mechanical aperture 31 is
It is equivalent to an aperture stop and has a function of suppressing lens aberration of the transfer electrostatic lens 32 and the projection electrostatic lenses 34 to 36 with respect to the secondary beam. By the way, if the secondary beam is imaged only by the cathode lens 29, the lens action becomes strong and aberration is likely to occur. Therefore, as shown in FIG. 4, one image formation is performed together with the transfer electrostatic lens 32. The secondary beam obtains an intermediate image on the field aperture 33 by the cathode lens 29 and the transfer electrostatic lens 32.

In this case, since the magnification required for the secondary optical system is often insufficient, the projection electrostatic lens 3 is used as a lens for enlarging the intermediate image.
4 to 36 are added. The secondary beam is enlarged and formed by each of the projection electrostatic lenses 34 to 36,
An image is formed four times in total. The transfer electrostatic lens 3
2, and the projection electrostatic lenses 34 to 36 are all rotationally symmetric lenses called unipotential lenses or Einzel lenses. Each lens is
In a three-electrode configuration, the outer two electrodes are normally set to zero potential, and the voltage is applied to the central electrode to perform the lens action and control.

A field aperture 33 is disposed at an intermediate image forming point, and this field aperture 33 limits the field of view to a necessary range similarly to the field stop of the optical microscope. At the same time, in the case of an electron beam, unnecessary electrons scattered in the apparatus are cut off together with the subsequent projection electrostatic lenses 34 to 36, and the detector 3
7 prevents charge-up and contamination.

The secondary beam is enlarged and projected by the transfer electrostatic lens 32 and the projection electrostatic lenses 34 to 36 in the secondary column 22, and forms an image on the detection surface of the detector 37. At this time, the rectangular area irradiated with the primary beam forms an image as a two-dimensional image. As shown in FIG. 7, a detector 37 transmits an MCP (micro channel plate) 44 for amplifying electrons, a fluorescent plate 45 for converting electrons into an optical signal, and separates a vacuum chamber from an atmospheric chamber and transmits an optical image. Viewport 46, an optical lens 47,
And a CCD camera 48 having an array of CCD imaging devices.

The secondary beam forms an image on the detection surface of the MCP 44, is amplified, and collides with the fluorescent screen 45. The fluorescent plate 45 converts the electrons into an optical image, which passes through the view port 46 and is converted into a photoelectric signal by the CCD camera 48. The charges stored in the CCD image pickup device of the CCD camera 48 are A / D converted, sequentially read out to the frame memory 38, and stored and stored in the memory.

The CPU 39 reads out image data from the frame memory 38 and displays it on the CRT 40. At this time, a rectangular sample image is displayed on the CRT 40.
Next, scanning of an electron beam, which is a feature of the present embodiment, will be described with reference to FIG. As shown in FIG. 8A, when the inspection target area is larger than the beam irradiation area, the deflector 26 raster scans the inspection target area with the primary beam. At this time, the beam irradiation area is rectangular and the current density is kept uniform.

The raster scanning is performed by controlling the voltage applied to the deflector 26 by the primary column control unit 41 to shift the position where the primary beam enters the Wien filter 30, as shown in FIG. . Specifically, as shown in FIG. 8, the beam irradiation area (in the figure) shifts in the X direction of the inspection target area. When one scan is completed in the X direction (in the figure), the beam irradiation area moves to a point shifted in the Y direction by one beam irradiation area (in the figure), and X
Scan in the direction.

The above operation is repeated, and the scanning of the inspection target area ends at the point in the figure. This is the same as irradiating an electron beam with a uniform current density over the entire inspection target area. Therefore, the image information of the entire inspection target area is accumulated as charges in the CCD image pickup device of the CCD camera 48 inside the detector 37. The beam irradiation area corresponds to a plurality of pixels of the CCD image sensor.

Next, the CCD camera 48 sequentially reads out the stored charges, A / D converts them, and
Transfer to The speed F1 (frame / sec) at which the frame memory 38 acquires the frame image information is set at a speed F2 (frame / sec) at which the frame image information is accumulated in the CCD image pickup device by the primary beam scanning the entire inspection target area.
sec) or less. For example, if F1 is 3
0 (frames / sec) and F2 is set to 70 (frames / se
By operating at the constant speed of c), the image is displayed on the CRT 40 without flickering.

The storing operation of the frame image information and the reading operation of the frame image information are executed asynchronously.
The CPU 39 reads the image information stored in the frame memory 38 and executes an averaging process. For example, eight frame images stored in the frame memory 38 are sequentially read, and corresponding pixels of the eight images are added and averaged to create a new frame image.
By this smoothing processing, random noise of an image can be reduced.

When an image is detected at a lower magnification, the area to be inspected is enlarged as shown in FIG. Here, the inspection target area is doubled. Therefore, since the scanning speed of the primary beam is doubled, the amount of the beam irradiated on the sample is reduced by half, and the brightness of the detected image is reduced by half.

Therefore, the primary column control unit 41 changes the intensity of the electron beam by adjusting the voltage of the extraction electrode and the acceleration electrode of the electron gun 24 according to the magnification.
For example, if the beam intensity of the electron beam is increased in proportion to the area of the inspection target area, the detected image can always maintain a constant brightness regardless of the magnification. As described above, in the inspection apparatus of the present embodiment, the rectangular beam without beam unevenness scans the entire inspection target area. This is the same as a state where the electron beam with a uniform and uniform current density is irradiated on the entire inspection target area, and a clear image without contrast unevenness can be obtained.

Further, in the present embodiment, the detector 37 has the CC
D imaging device is used. Since this CCD image pickup device is used as a frame buffer, there is no need to synchronize the image storage operation by beam scanning and the image reading operation. Therefore, beam scanning can be performed as fast as possible, and image flicker can be suppressed. Further, in a conventional scanning electron microscope, a configuration in which an image reading operation is executed in synchronization with beam scanning is essential, but in the present embodiment, this can be omitted.

In the conventional scanning electron microscope, the electron beam is focused and scanned in a spot shape. However, in the inspection apparatus of the present embodiment, since the scanning is performed by the rectangular beam, image information which can be detected by one scan is remarkably provided. And the beam scanning speed can be easily increased. In the present embodiment, raster scanning is performed as a scanning method, but the scanning method is not limited to this.

Further, in the inspection apparatus of the present embodiment, the Wien filter 30 for bending the trajectory of the primary beam and moving the secondary beam straight is used. However, the present invention is not limited to this. An inspection device having a configuration using a Wien filter that bends the beam trajectory may be used.

In this embodiment, a rectangular beam is formed from a rectangular cathode and a quadrupole lens. However, the present invention is not limited to this. For example, a rectangular beam or an elliptical beam may be created from a circular beam, or a circular beam may be formed. May be passed through a slit to take out a rectangular beam.

[0048]

According to the inspection apparatus of the present invention, a secondary beam is detected by scanning the sample surface with an electron beam having a rectangular or elliptical beam irradiation area. At this time, since any portion of the sample is uniformly and uniformly irradiated with the electron beam, an image without contrast unevenness can be obtained regardless of the magnification.

In the inspection apparatus according to the second aspect, the deflecting means is disposed between the irradiation means and the Wien filter.
For example, scanning can be performed even if a deflecting unit is provided between the Wien filter and the sample. In this case, however, a secondary beam is also deflected, and a means for canceling this is required on the detection side. However, in the inspection apparatus according to the second aspect, the scanning can be reliably performed without requiring such a complicated configuration.

In the inspection apparatus according to the third aspect, the beam intensity is changed according to the area of the inspection target area.
For example, even if the area to be inspected is enlarged and the amount of electron beam irradiating the sample decreases, the beam intensity can be increased accordingly. Therefore, an image having a constant brightness can be always obtained regardless of the size of the area of the inspection target area (that is, the magnification). In this manner, the inspection apparatus to which the present invention is applied can obtain a uniform image with reduced contrast unevenness, and can realize an inspection apparatus with high inspection reliability.

[Brief description of the drawings]

FIG. 1 is a principle block diagram of the invention according to claim 1;

FIG. 2 is an overall configuration diagram of the present embodiment.

FIG. 3 is a diagram showing a trajectory of a primary beam.

FIG. 4 is a diagram showing a trajectory of a secondary beam.

FIG. 5 is a diagram illustrating a configuration of a primary optical system.

FIG. 6 is a diagram illustrating a Wien filter.

FIG. 7 is a diagram showing a configuration of a detector.

FIG. 8 is a diagram illustrating scanning by an electron beam.

FIG. 9 is a configuration diagram of an inspection apparatus that collectively irradiates an electron beam.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Irradiation means 2 Electron detection means 3, 30, 55 Wien filter 4 Deflection means 21, 50 Primary column 22, 51 Secondary column 23, 52 Chamber 24, 53 Electron gun 25, 54 Primary optical system 26 Deflector 27, 56 Stage 28, 57 Sample 29, 58 Cathode lens 31 New mechanical aperture 32 Transfer electrostatic lens 33 Field aperture 34, 35, 36 Projection electrostatic lens 37, 60 Detector 38 Frame memory 39, 62 CPU 40 CRT 41, 63 Primary column control Units 42, 64 Secondary column control unit 43 Vacuum exhaust system 44 MCP 45 Fluorescent plate 46 View port 47 Optical lens 48 CCD camera 59 Secondary optical system 61 Control unit

Claims (3)

[Claims] An irradiation means for shaping a beam cross section of an electron beam into a rectangular or elliptical shape, and irradiating the electron beam with a sample surface, secondary electrons, reflected electrons or rearward electrons generated from the sample by the irradiation of the electron beam. Electron detection means for detecting at least one kind of scattered electrons as a secondary beam and generating image information of the sample; irradiating the sample surface with an electron beam irradiated from the irradiation means; and generating from the sample. The secondary beam
An inspection apparatus, comprising: a Wien filter leading to the electron detection means; and a deflection means for scanning the electron beam on the sample surface. 2. The inspection apparatus according to claim 1, wherein the deflecting unit is disposed between the irradiation unit and the Wien filter. 3. The inspection apparatus according to claim 1, wherein the irradiating unit changes the beam intensity of the electron beam in accordance with an area of a region to be inspected on the sample. Inspection equipment.