JP4874780B2 - Scanning electron microscope - Google Patents

Description

  The present invention relates to a scanning electron microscope, and more particularly to a scanning electron microscope capable of separately detecting reflected electrons and secondary electrons.

  FIG. 6 is a diagram illustrating a configuration example of an electron optical system. The scanning optical system is omitted. The primary electron beam 2 emitted from the electron source 1 is accelerated to a desired acceleration voltage by an acceleration electrode (not shown) and then shaped into a perfect circle by a beam shaping diaphragm 7. Thereafter, the electron beam 2 is focused by the objective lens 4 and controlled so as to be focused on the sample surface of the observation sample 5. In this state, a scanning deflector (not shown) is used to scan the observation sample 5 two-dimensionally, and the generated signals, that is, secondary electrons and reflected electrons are detected to generate a scanned image.

  Usually, the beam shaping diaphragm 7 has a beam current limiting function, and the beam current can be increased or decreased by changing the intensity of a lens (not shown) between the beam shaping diaphragm 7 and the electron source 1. Is possible. When such control for increasing or decreasing the beam current is performed, the position of the virtual light source viewed from the objective lens 4 is changed, and the correct focusing angle (opening angle) cannot be controlled by the objective lens 4. The resolution of the scanned image depends on the beam diameter on the observation sample 5, but the beam diameter strongly depends on the focusing angle.

  At the optimum focusing angle, the smallest beam diameter is obtained and the resolution of the scanned image is maximized. Therefore, by using the focusing lens 3, it is possible to correct the change of the virtual light source position and to focus the primary electron beam 2 on the observation sample 5 at a correct focusing angle.

  FIG. 7 and FIG. 8 show the configuration and operation of a conventional charged particle detector. FIG. 7 is a diagram showing a conventional charged particle detector and a secondary electron trajectory, and FIG. 8 is a diagram showing a conventional charged particle detector and a reflected electron trajectory. The same components as those in FIG. 1 are denoted by the same reference numerals.

  The secondary electrons 10 emitted from the observation sample 5 have various directions and energies, but fly in a certain orbit according to the field of the objective lens 4 and the field of the surrounding structure. Here, by appropriately designing the objective lens 4 and surrounding structures, it is possible to fly the secondary electrons 10 in the direction of the charged particle detector 8 in the lens.

  In FIG. 7, since the secondary electrons 10 have lower energy than the primary electron beam 2, the secondary electrons 10 are subjected to a large focusing action by the magnetic field of the objective lens 4 and make zero or more crossovers. If the trajectory of the secondary electrons 10 when diverging from the magnetic field is in the direction of divergence, it reaches the charged particle detector 8 and becomes a scanning image signal. Usually, the position where the secondary electron detection efficiency is the best is determined by electron optical simulation or experiment, and the charged particle detector 8 is arranged.

  In FIG. 8, since the reflected electrons 9 have substantially the same energy as that of the primary electron beam 2, the focusing effect by the magnetic field of the objective lens 4 is not large. Therefore, the reflected electrons 9 reach the charged particle detector 8 without making a crossover. The charged particle detector 8 has a hole through which the primary electron beam 2 passes. If the diameter of the reflected electron 9 is larger than the diameter of the hole, the reflected electron 9 is detected by the charged particle detector 8. Is detected and becomes a scanning image signal.

  Since the reflected electron 9 is considered to have an emission angle several times larger than the focusing angle of the primary electron beam 2 of 5 to 10 mrad, the scanning image signal includes the reflected electron signal. Therefore, the signal obtained by the charged particle detector 8 is a signal obtained by adding secondary electrons and reflected electrons. Here, the difference between secondary electrons and reflected electrons will be described. Since the secondary electrons have low energy, they are suitable for capturing an image on the surface of the observation sample, and the reflected electrons have high energy, so that they are suitable for entering the observation sample to some extent and capturing the composition of the observation sample.

This type of conventional device has a source side detector and a sample side detector on the optical axis, and these detectors detect almost all secondary electrons emitted from the sample. A technique is known (for example, refer to Patent Document 1). An apparatus having a first detector and a second detector is known in order to detect secondary electrons or backscattered electrons generated based on the interaction between the primary electron beam and the sample (for example, Patent Document 2). In addition, there is known an apparatus that can separate and detect secondary electrons and reflected electrons from a sample with an apparatus having a simple structure (see, for example, Patent Document 3). Also, a first detector for detecting secondary electrons emitted from the sample and a second detector for detecting secondary electrons that have passed through the holes of the first detector are provided, and the outputs of these detectors are provided. There is known a device that can detect secondary electrons by synthesizing or separating them (see, for example, Patent Document 4).
JP 2000-30654 (paragraphs 0021 to 0026, FIGS. 1 and 2) JP 2004-221089 A (paragraphs 0035 to 0037, FIG. 2) JP 2000-299078 (paragraphs 0020 to 0033, FIGS. 1 to 5) Japanese Patent No. 3136353 (paragraphs 0024 to 0037, FIGS. 1 and 2)

  In the prior art described above, it has been difficult to separately detect secondary electrons and reflected electrons. More precisely, it was difficult to detect secondary electrons and reflected electrons separately and simultaneously. The reason why they cannot be detected separately and simultaneously is that, as described above, the signal obtained by the charged particle detector 8 is a signal obtained by adding secondary electrons and reflected electrons.

  Here, if there is no simultaneity, there is a known technique using an energy filter. As an example, if a detector having low sensitivity to secondary electrons, for example, a semiconductor detector is used, only reflected electrons can be detected. That is, secondary electrons and reflected electrons are incident on the semiconductor detector, but the sensitivity to the secondary electrons is poor, and as a result, only the reflected electrons can be detected.

  In addition, by inserting a deflector at the detector position, only secondary electrons with low energy are bent to reach the detector. Even if the deflector is operated, the reflected electrons cannot be bent because of their high energy. Therefore, only the secondary electrons can be bent and reach the detector. However, it is more advantageous in terms of throughput to obtain simultaneity.

  Detectors with poor sensitivity to secondary electrons have another drawback. That is, the sensitivity to reflected electrons is low when the primary electron beam energy is low. This is because the energy of reflected electrons is low.

  The present invention has been made in view of such problems, and can detect low-energy reflected electrons, and can also detect reflected electrons and secondary electrons separately and simultaneously. The purpose is to provide.

(1) The invention according to claim 1 is directed to an electron source that generates an electron beam, an objective lens that focuses the primary electron beam generated from the electron source onto an observation sample, and a space between the electron source and the objective lens. A scanning electron microscope having at least one focusing lens disposed on the surface and a scanning deflector for irradiating the surface of the observation sample while two-dimensionally scanning the primary electron beam in the XY direction,
The focusing lens is a charged particle detector that operates so that the primary electron beam has a crossover once with respect to the objective lens and uses reflected electrons as detection target electrons closer to the electron source than the crossover position. provided, and wherein a observation sample side of the crossover position, the aperture having been generated from the observation sample opening larger than the primary electron beam diameter in the vicinity of the crossover position of the reflected electrons undergoing focusing action by the objective lens It is characterized by providing.
(2) The invention described in claim 2 is characterized in that the objective lens is a magnetic field type objective lens.
(3) The invention described in claim 3 is characterized in that the objective lens is a cathode lens having a potential difference on the sample holder side with respect to the potential of the outer wall of the lens barrel.
(4) The invention according to claim 4 is characterized in that the objective lens is a superposed lens of a magnetic field type objective lens and a cathode lens having a potential difference in the sample holder with respect to the potential of the outer wall of the objective lens. To do.
(5) The invention according to claim 5 is characterized in that the objective lens is a superposed lens of a magnetic field type objective lens and an electrostatic decelerating objective lens having a potential difference in the objective lens with respect to the potential of the outer wall of the objective lens. It is characterized by being.
(6) The invention according to claim 6 is characterized in that the objective lens is a superposed lens of a magnetic field type objective lens and a cathode lens in which the objective lens is grounded and a high voltage is applied to the sample holder. .
(7) The invention according to claim 7 is characterized in that a beam shaping stop is provided above the focusing lens.
(8) The invention according to claim 8 is directed to an electron source that generates an electron beam, an objective lens that focuses a primary electron beam generated from the electron source onto an observation sample, and a space between the electron source and the objective lens. A scanning electron microscope having at least one focusing lens disposed on the surface and a scanning deflector for irradiating the surface of the observation sample while two-dimensionally scanning the primary electron beam in the XY direction,
The focusing lens is operative to the primary electron beam between the objective lens has a cross-over once, and in the a observation sample side of the crossover position, the objective lens is generated from the observation sample A first charged particle detector having an aperture larger than the diameter of the primary electron beam is provided near the crossover position of the reflected electrons subjected to the focusing action , and is reflected toward the electron source from the crossover position of the primary electron beam. A second charged particle detector having electrons as detection target electrons is provided.
(9) In the invention according to claim 9, the charged particle detector provided on the electron source side from the crossover position of the primary electron beam is located on the electron source side with respect to the focusing lens, and the focusing is performed. The backscattered electrons that have been focused by the lens are detected by the charged particle detector .

(1) According to the first aspect of the present invention, reflected electrons can pass through the diaphragm and reach the charged particle detector, and secondary electrons are blocked by the diaphragm. Therefore, only the reflected electrons can be separated and detected, and a low-energy reflected electron image that has not been obtained conventionally can be obtained.
(2) According to the invention described in claim 2, a magnetic field type objective lens is used as the objective lens, and a finely focused electron beam can be irradiated onto the sample.
(3) According to the invention described in claim 3, an image with little aberration can be obtained by using a cathode lens as the objective lens.
(4) According to the invention described in claim 4, an image with less aberration can be obtained by using a superposed lens of a magnetic field type objective lens and a cathode lens as the objective lens.
(5) According to the invention described in claim 5, an image with little aberration can be obtained by using a superposed lens of a magnetic field type objective lens and an electrostatic decelerating type objective lens as the objective lens.
(6) According to the invention described in claim 6, an image with little aberration can be obtained by using a superposition lens of a magnetic field type objective lens and a cathode lens as the objective lens.
(7) According to the invention described in claim 7, by having the beam shaping stop above the focusing lens, the primary electron beam can be made into a perfect circle, the primary electron beam current is limited, and the accurate An image can be obtained.
(8) According to the invention described in claim 8, reflected electrons and secondary electrons can be detected separately and simultaneously.
(9) According to the invention described in claim 9 , reflected electrons can be efficiently detected by the charged particle detector provided on the electron source side with respect to the focusing lens .

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
A first embodiment of the present invention is shown in FIGS. FIG. 1 is a diagram showing a trajectory of reflected electrons in the first embodiment of the present invention, and FIG. 2 is a diagram showing a trajectory of secondary electrons in the second embodiment of the present invention. 6 and 7 are denoted by the same reference numerals. Here, the scanning optical system is omitted. In FIG. 1, 1 is an electron source that generates an electron beam 2, 4 is an objective lens that focuses a primary electron beam 2 generated from the electron source 1 on an observation sample 5, and 3 is the electron source 1 and objective lens 4. And at least one focusing lens 7 is a beam shaping stop for shaping the primary electron beam 2 into a perfect circle and limiting the primary electron beam current.

  The focusing lens 3 operates so that the primary electron beam 2 has a crossover once with respect to the objective lens 4. 8 is a charged particle detector provided on the electron source side from the crossover position, and 6 is a stop having an aperture larger than the primary electron beam diameter provided on the observation sample 5 side from the crossover position. Reference numeral 9 denotes reflected electrons emitted from the observation sample 5. The configuration shown in FIG. 2 is the same as the configuration shown in FIG. In FIG. 2, reference numeral 10 denotes secondary electrons emitted from the observation sample 5. The operation of the apparatus configured as described above will be described as follows.

  The primary electron beam 2 generated from the electron source 1 is made into a perfect circle by the beam shaping diaphragm 7, subjected to the primary electron beam current limitation, and then subjected to a focusing action by the focusing lens 3. A crossover C is made once. A stop 6 having an opening larger than the beam diameter of the primary electron beam 2 is provided at the position of the crossover C, and the primary electron beam 2 passes through the stop 6. The primary electron beam 2 that has passed through the diaphragm 6 is finely focused by the objective lens 4 and irradiated onto the observation sample 5.

  As shown in FIG. 1, the reflected electrons 9 generated from the observation sample 5 draw substantially the same trajectory as the primary electron beam 2 in the opposite direction. That is, it is focused by the objective lens 4 and has a crossover near the stop 6 to diverge. Then, the focusing lens 3 receives a slight focusing action again, and the charged particle detector 8 detects the reflected electrons 9.

  FIG. 2 shows the trajectories of secondary electrons. The secondary electrons 10 generated from the observation sample 5 are subjected to a large focusing action by the objective lens 4 and greatly spread at the position of the diaphragm 6. Secondary electrons 10 that hit the diaphragm 6 are absorbed by the diaphragm 6. A small part of the secondary electrons 2 that have passed through the aperture of the diaphragm 6 reach the charged particle detector 8, but are limited by the diaphragm 6, and therefore hardly contribute to the image quality.

Therefore, the image obtained by the charged particle detector 8 is a reflected electron image. As a result, only the reflected electrons 9 can be separated and detected. Here, even if the charged particle detector 8 has a structure with high sensitivity to a low energy electron beam, a secondary electron hardly contributes, so that a reflected electron image can be obtained. By doing in this way, the low energy reflected electron image which was not obtained conventionally is obtained.
(Second Embodiment)
FIG. 3 is an explanatory diagram of simultaneous detection of reflected electrons and secondary electrons in the second embodiment of the present invention. 1 and 2 are denoted by the same reference numerals. Here, the scanning optical system is also omitted. In FIG. 3, 1 is an electron source for generating an electron beam 2, 4 is an objective lens for focusing the primary electron beam 2 generated from the electron source 1 on an observation sample 5, and 3 is the electron source 1 and the objective lens 4. And at least one focusing lens 7 is a beam shaping stop for shaping the primary electron beam 2 into a perfect circle and limiting the primary electron beam current.

  The focusing lens 3 operates so that the primary electron beam 2 has a crossover once with respect to the objective lens 4. 11 is a secondary electron detector as a first charged particle detector provided near the crossover C of the primary electron 2, and 12 is a second charged particle detector provided on the electron source side from the crossover position. As a backscattered electron detector. In FIG. 2, the secondary electron detector 11 uses a diaphragm 6 having a function of absorbing secondary electrons as a secondary electron detector. Reference numeral 9 denotes reflected electrons emitted from the observation sample 5. Reference numeral 10 denotes secondary electrons emitted from the observation sample 5. The operation of the apparatus configured as described above will be described as follows.

  The primary electron beam 2 generated from the electron source 1 is made into a perfect circle by the beam shaping diaphragm 7, then receives a focusing action by the focusing lens 3, and forms a crossover C once with the objective lens 4. A secondary electron detector 11 having an opening larger than the beam diameter of the primary electron beam 2 is provided at the position of the crossover C. The primary electron beam 2 passes through the secondary electron detector 11. . The primary electron beam 2 that has passed through the secondary electron detector 11 is finely focused by the objective lens 4 and irradiated onto the observation sample 5.

  As shown in FIG. 3, the reflected electrons 9 radiated from the observation sample 5 draw substantially the same trajectory as the primary electron beam 2 in the opposite direction. In other words, it is focused by the objective lens 4 and has a crossover near the secondary electron detector 11 to diverge. The focusing lens 3 receives a slight focusing action again, and the reflected electrons 9 are detected at the position of the reflected electron detector 12.

  On the other hand, the secondary electrons 10 are greatly focused by the objective lens 4 and spread widely at the position of the secondary electron detector 11. The secondary electrons 10 hitting the secondary electron detector 11 become a scanning secondary electron image. A small part of the secondary electrons 10 that have passed through the opening of the secondary electron detector 11 reach the reflected electron detector 12, but are almost limited by the opening (aperture) of the secondary electron detector 11. Does not contribute to image quality.

Therefore, the image obtained by the secondary electron detector 11 is a secondary electron image, and the image obtained by the reflected electron detector 12 is a reflected electron image. Here, even if the backscattered electron detector 12 has a structure sensitive to a low energy electron beam, since the secondary electrons 10 hardly contribute, a backscattered electron image can be obtained. By doing in this way, the low energy reflected electron image which was not obtained conventionally can be obtained, and at the same time, the secondary electron image can be obtained at the same time.
(Third embodiment)
In the above-described invention, a normal objective lens can be used as the objective lens 4, but the configuration of the objective lens 4 is devised in order to obtain a higher quality image. FIG. 4 is a diagram showing a configuration example of a cathode lens which is an objective lens used in the present invention. In the figure, reference numeral 4 denotes an objective lens, and 41 denotes a coil for causing an excitation current to flow through the objective lens 4. A negative potential is applied to the observation sample 5 with respect to the surface potential of the objective lens 4. As a result, the primary electron beam is converged in the deceleration field formed between the tip of the objective lens 4 and the observation sample 5, so that the reflected electron image or the secondary electron image of the observation sample 5 has less aberration. Can be obtained.

  Further, according to the present invention, the objective lens can be a superposition lens of a magnetic field type objective lens and a cathode lens in which a potential difference is given to the sample holder with respect to the potential of the objective lens outer wall. In this way, an image with less aberration can be obtained.

  According to the invention, the objective lens is a superposition lens of a magnetic field type objective lens and an electrostatic decelerating objective lens having a potential difference in the objective lens with respect to the potential of the objective lens outer wall. Can do. In this way, an image with little aberration can be obtained.

  Further, according to the present invention, the objective lens can be a superposition lens of a magnetic field type objective lens and a cathode lens in which the objective lens is grounded and a high voltage is applied to the sample holder. In this way, an image with little aberration can be obtained.

In addition, according to the present invention, the primary electron beam can be made into a perfect circle by providing the beam shaping diaphragm above the focusing lens, and an accurate image can be obtained.
FIG. 5 shows simulation results of the secondary electron trajectory and the reflected electron trajectory. The horizontal axis indicates the XY direction, and the vertical axis indicates the Z direction. The unit is mm. The reflected electrons 9 have a crossover on the observation sample 5 160 mm above. The primary electron beam 2 was made to form a crossover 210 mm above the observation sample 5. The difference of 50 mm is due to the spherical aberration of the objective lens 4 with respect to the reflected electrons 9. At this time, a diaphragm or a secondary electron detector may be placed somewhere between 210 mm and 160 mm, and a reflected electron detector may be placed further upward.

Conventionally, there has been a problem that low-energy reflected electrons cannot be detected. In contrast,
An electron source, an objective lens for focusing a primary electron beam generated from the electron source on an observation sample, at least one focusing lens disposed between the electron source and the objective lens, and the primary electron beam In the scanning electron microscope having a scanning deflector for irradiating the surface of the observation sample while scanning two-dimensionally in the X and Y directions, the primary electron beam has a crossover once between the focusing lens and the objective lens. And a charged particle detector on the electron source side from the crossover position and a diaphragm having a diameter larger than the primary electron beam diameter on the observation sample side from the crossover position. It is now possible to detect reflected electrons of energy.

Further, conventionally, there has been a problem that reflected electrons and secondary electrons cannot be detected separately and simultaneously. In contrast, an electron source that generates an electron beam, an objective lens that focuses the primary electron beam generated from the electron source onto an observation sample, and at least one disposed between the electron source and the objective lens. In a scanning electron microscope having a focusing lens and a scanning deflector for irradiating the surface of an observation sample while two-dimensionally scanning the primary electron beam in the XY direction,
The focusing lens operates so that the primary electron beam has one crossover with the objective lens, and includes a first charged particle detector on the observation sample side from the crossover position or the crossover position. In addition, since the second charged particle detector is provided on the electron source side from the crossover position, the reflected electrons and the secondary electrons can be detected separately and simultaneously.

It is a figure which shows the track | orbit of a reflected electron in the 1st Embodiment of this invention. It is a figure which shows the trajectory of the secondary electron in the 1st Embodiment of this invention. It is explanatory drawing of simultaneous detection of a reflected electron and a secondary electron in the 2nd Embodiment of this invention. It is a figure which shows the structural example of a cathode lens. It is a figure which shows the simulation result of a secondary electron / reflected electron orbit. It is a figure which shows the structural example of an electron optical system. It is a figure which shows the conventional charged particle detector and a secondary electron orbit. It is a figure which shows the conventional charged particle detector and a backscattered electron trajectory.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electron source 3 Focusing lens 4 Objective lens 5 Observation sample 7 Beam shaping stop 9 Reflected electron 10 Secondary electron 11 Secondary electron detector 12 Reflected electron detector C Crossover

Claims (9)

An electron source that generates an electron beam; an objective lens that focuses the primary electron beam generated from the electron source onto an observation sample; and at least one focusing lens disposed between the electron source and the objective lens; A scanning electron microscope having a scanning deflector for irradiating the surface of the observation sample while two-dimensionally scanning the primary electron beam in the XY directions;
The focusing lens is a charged particle detector that operates so that the primary electron beam has a crossover once with respect to the objective lens and uses reflected electrons as detection target electrons closer to the electron source than the crossover position. provided, and wherein a observation sample side of the crossover position, the aperture having been generated from the observation sample opening larger than the primary electron beam diameter in the vicinity of the crossover position of the reflected electrons undergoing focusing action by the objective lens A scanning electron microscope comprising:   The scanning electron microscope according to claim 1, wherein the objective lens is a magnetic field type objective lens.   2. The scanning electron microscope according to claim 1, wherein the objective lens is a cathode lens having a potential difference on the sample holder side with respect to the potential of the outer wall of the lens barrel.   2. The scanning electron microscope according to claim 1, wherein the objective lens is a superimposing lens of a magnetic field type objective lens and a cathode lens having a potential difference in the sample holder with respect to the potential of the outer wall of the objective lens.   2. The objective lens according to claim 1, wherein the objective lens is a superposed lens of a magnetic field type objective lens and an electrostatic decelerating objective lens having a potential difference in the objective lens with respect to the potential of the outer wall of the objective lens. Scanning electron microscope.   2. The scanning electron microscope according to claim 1, wherein the objective lens is a superposed lens of a magnetic field type objective lens and a cathode lens in which the objective lens is grounded and a high voltage is applied to the sample holder. Scanning electron microscope according to any one of claims 1 to 6, characterized in that it has a beam shaping aperture above the focusing lens. An electron source that generates an electron beam; an objective lens that focuses the primary electron beam generated from the electron source onto an observation sample; and at least one focusing lens disposed between the electron source and the objective lens; A scanning electron microscope having a scanning deflector for irradiating the surface of the observation sample while two-dimensionally scanning the primary electron beam in the XY directions;
The focusing lens is operative to the primary electron beam between the objective lens has a cross-over once, and in the a observation sample side of the crossover position, the objective lens is generated from the observation sample A first charged particle detector having an aperture larger than the diameter of the primary electron beam is provided near the crossover position of the reflected electrons subjected to the focusing action , and is reflected toward the electron source from the crossover position of the primary electron beam. A scanning electron microscope comprising a second charged particle detector that uses electrons as detection target electrons . The charged particle detector provided on the electron source side from the crossover position of the primary electron beam is located on the electron source side with respect to the focusing lens, and the reflected electrons that have been focused by the focusing lens are The scanning electron microscope according to any one of claims 1 to 6, wherein the scanning electron microscope is detected by a charged particle detector .

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