JP2004185823A - Electron beam device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electron beam device capable of capturing an image in which an effect of a surface electrical charge of a sample is reduced. <P>SOLUTION: In an electron beam device 20 for monitoring the image of a sample 5, according to secondary electrons Z generated by scanning of the sample 5 with primary electrons Y converged by an objective lens, a selecting means 21 for selectively applying the secondary electrons Z, according to energy of the secondary electrons Z, to a secondary electron detector 2 is provided in front of the electron detector 2 for converting the secondary electrons Z into electrical signals. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
[Patent Document 1]
JP-A-3-1432 (Section 6, FIG. 1)
[Patent Document 2]
JP-A-10-199459 (Section 4, FIG. 1)
[Non-patent document 1]
Katsumi Ura, Editor-in-chief, 132nd Committee of the Japan Society for the Promotion of Science “Electron Ion Beam Handbook 3rd Edition” Nikkan Kogyo Shimbun (P806-810)
[0002]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electron beam apparatus capable of acquiring an image with reduced influence of surface charges.
[0003]
[Prior art]
2. Description of the Related Art In the field of semiconductor manufacturing, a scanning electron microscope (SEM) is widely used in order to automatically or semi-automatically perform fine observation of a pattern on a wafer or the like. The surface structure to be observed by the SEM used in the semiconductor manufacturing field has many insulators, and the SEM has been promoted to have low acceleration and low incident energy. However, problems such as a decrease in resolution and a decrease in S / N ratio generally occur due to the reduction in incident energy (see Non-Patent Document 1).
[0004]
In order to solve this problem, a configuration is known in which a monopolar magnetic field type lens in which a lens magnetic field is immersed in a sample is used to achieve a strong lens (Patent Document 1). Further, as the objective lens, an electromagnetic field compound lens including a monopole magnetic field type lens having a monopole top surface located between the electron beam source and the sample and an electrostatic immersion lens is used, thereby reducing aberration. An electromagnetic composite lens having such a configuration has also been proposed (Patent Document 2).
[0005]
[Problems to be solved by the invention]
By the way, in the recent semiconductor manufacturing, processes such as copper wiring and low-K have been introduced, so that the charge on the surface of an observation sample has become more remarkable. When such charging occurs, particles (dust) adhering to the sample appear white in the SEM image and a black shadow appears in the vicinity thereof, and a gradation depending on the scanning direction on the entire observation surface occurs. Appears, which hinders observation of the sample surface. That is, the contrast of the SEM image as described above caused by the charging becomes an obstacle to image processing based on the obtained SEM image, making it difficult to perform image recognition or causing erroneous recognition. For example, regarding the above-described particles, there is a problem that the original size and shape of the particles cannot be accurately recognized due to the charging contrast.
[0006]
On the other hand, there is a potential contrast problem as a phenomenon similar to charging. This is the percentage of the secondary electrons that are generated that have a low speed among the secondary electrons that are generated and that reach the detector due to the potential given to the wiring by applying a potential to the wiring when observing the wiring on the wafer. Is a phenomenon caused by modulation.
[0007]
However, even when the potential is not applied to the wiring, when the amount of the incident electrons and the amount of the emitted electrons when the electron beam is irradiated are not equal, a current flows between the wiring and the ground, and the current flows between the wiring and the ground. When a capacitor or a resistor exists, a potential is generated in the wiring. Therefore, even if the same wiring is used, if the internal circuit is different, a different contrast is generated. As a result, when performing image recognition, there arises a problem that a part which should be originally recognized as the same wiring is erroneously recognized as a different wiring.
[0008]
The problems associated with such surface charges cannot be solved by the configurations disclosed in Patent Documents 1 and 2. For example, as shown in Patent Document 2, when the sample is not tilted, a different potential is applied to the lower electrode of the electrostatic immersion lens and the sample, and when the sample is tilted, the potential difference between the lower electrode and the sample is reduced or Under the conventional condition that the potentials are the same, the effect of the charge cannot be reduced, and the contrast due to charging increases when the potential difference between the lower electrode and the sample increases.
[0009]
An object of the present invention is to provide an improved electron beam apparatus that can solve the above-mentioned problems in the prior art.
[0010]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a function of selecting the energy of secondary electrons to be detected between a secondary detector for detecting secondary electrons emitted from the sample and the sample. Selects secondary electrons to reach the secondary detector, thereby enabling acquisition of an image in which the influence of charge accumulation is reduced.
[0011]
According to the present invention, there is provided an electron beam apparatus which scans a sample with a primary electron beam converged by an objective lens and thereby observes an image of the sample based on secondary electrons or the like generated from the sample. A secondary electron detector for converting a secondary electron into an electric signal; and a secondary electron detector disposed in front of the secondary electron detector and selectively converting the secondary electron based on the energy of the secondary electron. There is proposed an electron beam apparatus comprising: a selection unit for sending to an electron detector.
[0012]
The objective lens may be an electromagnetic composite lens including a monopole magnetic lens having a monopole top surface located between the electron beam source and the sample, and an electrostatic immersion lens.
[0013]
Further, the electrostatic immersion lens is connected to the inside of the yoke that is connected to the monopole top surface and constitutes the monopole magnetic field lens, and a part of the upper electrode is formed between the monopole top surface and the sample. The lower electrode may be located between the upper electrode and the sample.
[0014]
Further, the selection means may be configured to realize a function of selecting energy of the secondary electrons by applying a voltage lower than a potential of the sample to the lower electrode.
[0015]
According to the present invention, there is further provided an electron beam apparatus which scans a sample with a primary electron beam converged by an objective lens and thereby observes an image of the sample based on secondary electrons or the like generated from the sample. A secondary electron detector for converting the secondary electrons into an electric signal; and a plurality of grid members disposed in front of the secondary electron detector, wherein at least one of the grid members is provided. An electron beam apparatus is proposed in which a negative voltage is applied to a grid member to selectively send the secondary electrons to the secondary electron detector based on the energy of the secondary electrons. .
[0016]
According to the present invention, there is also provided an electron beam apparatus which scans a sample with a primary electron beam converged by an objective lens and thereby observes an image of the sample based on secondary electrons or the like generated from the sample. A secondary electron detector for converting the secondary electrons into an electric signal; an outer cylindrical electrode disposed in front of the secondary electron detector; and an inner cylindrical electrode disposed coaxially within the outer cylindrical electrode. A cylindrical electrode; and applying a negative voltage to the outer cylindrical electrode with respect to the inner cylindrical electrode, thereby selectively detecting the secondary electrons based on the energy of the secondary electrons. An electron beam device characterized by being sent to a vessel is proposed.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.
[0018]
FIG. 1 is a configuration diagram showing a cross section of an example of an embodiment of a scanning electron beam apparatus according to the present invention. The scanning electron beam apparatus 10 is an apparatus used for shape inspection and observation of a miniaturized electronic device, and an electron beam from an electron source 1 is accelerated to form a sample as a primary electron beam Y along an optical axis X. The primary electron beam Y is scanned on the sample 5 for observation by the deflecting device 1A. Here, a case where the sample 5 is a semiconductor wafer is taken as an example.
[0019]
Between the deflecting device 1A and the sample 5, an electromagnetic compound lens composed of an electrostatic immersion lens 3 and a monopole magnetic lens 4 is provided as an objective lens, so that an electron beam from the electron source 1 is provided. It becomes a narrowly focused primary electron beam Y and is focused on the sample 5.
[0020]
The monopole magnetic field type lens 4 includes an excitation coil 42 above a magnetic pole 41. The magnetic pole 41 is a cylinder whose tip is provided with a magnetic pole hole 41A at the lower end thereof for passing an electron beam. A protruding portion 41B having an L-shaped cross section is integrally formed on the upper end edge thereof and extends radially outward. The exciting coil 42 is housed in an annular space surrounded by the overhang 41B.
[0021]
As a result, a magnetic field is formed between the single magnetic pole 4a at the distal end of the single-pole magnetic field type lens 4 facing the sample 5 and the projecting end 4b of the projecting portion 41B. It is installed in a strong lens magnetic field generated in the direction.
[0022]
A pair of upper and lower electrodes is incorporated in the front end portion of the lens magnetic field of the single-pole magnetic field type lens 4 configured as described above, that is, near the single magnetic pole 4a. One is a lower electrode 3b disposed between the sample 5 and the single magnetic pole 4a, and an electrode hole 3c for passing an electron beam is formed at the center of the lower electrode 3b. The other is an upper electrode 3a disposed closer to the electron beam source 1 than the lower electrode 3b. The upper electrode 3a is disposed so as to be substantially accommodated in the magnetic pole 41. The lower end 3aa protrudes from the magnetic pole hole 41A toward the sample 5, and is located between the single magnetic pole 4a and the lower electrode 3b. The secondary electron detector 2 is arranged in the magnetic pole 41 as shown in the figure.
[0023]
The potential VU, which is a positive voltage, is applied to the upper electrode 3a provided as described above, and the potential VL, which is a negative voltage, is applied to the lower electrode 3b. Have been. The potential VS, which is a negative voltage, is applied to the sample 5.
[0024]
Since the scanning electron beam apparatus 10 is configured as described above, the primary electron beam Y emitted from the primary electron beam 1 is accelerated, passes through the secondary electron detector 2, and passes through the electrostatic immersion lens 3 Is accelerated again from the potential VU applied to the upper electrode 3a. Then, the primary electron beam Y is converged by the magnetic field near the tip of the monopole magnetic lens 4. The primary electron beam Y is decelerated by the potential VL applied to the lower electrode 3b of the electrostatic immersion lens 3, and then enters the sample 5 to which the potential VS is applied.
[0025]
Here, the potential VL applied to the lower electrode 3b is kept lower than the potential VS. However, when the potential VL becomes lower than a certain value, all the secondary electrons Z generated by the primary electron beam Y hitting the sample 5 are turned back toward the sample 5 and cannot be detected by the secondary electron detector 2. It is smaller than VS in the range where the next electron can be detected. Specifically, for example, the potential VL has a value of about -1100V and the potential VS has a value of about -1000V.
[0026]
The secondary electron Z is wound up by the magnetic field on the sample 5 generated by the magnetic pole 4, enters the magnetic pole 41, and is detected by the secondary electron detector 2 provided inside the magnetic pole 41. Here, since the lower electrode 3b is given a potential VL lower than the potential VS of the sample 5, the secondary electrons Z receive a force returned in the direction of the sample 5 by the electric field due to this potential difference. Therefore, the secondary electrons Z having energy smaller than a certain energy cannot reach the secondary electron detector 2. That is, applying a potential VL lower than the potential VS of the sample 5 to the lower electrode 3b has a function of selecting the energy of the secondary electron detector 2. Thus, in front of the secondary electron detector 2 (on the side of the sample 5), the selection means for selectively transmitting the secondary electrons Z to the secondary electron detector 2 based on the energy of the secondary electrons Z is provided. It is configured.
[0027]
As described above, the function of selecting the energy of the secondary electron Z is provided, the secondary electron Z having a low energy is removed, and only the secondary electron Z having a large energy is selected, whereby the influence of the charge accumulation is reduced. Image acquisition.
[0028]
That is, when the surface of the sample 5 is positively charged, the secondary electrons Z receive a force pulled back toward the sample 5 by the surface potential. A secondary electron Z having a relatively large energy is detected by the secondary electron detector 2, but a phenomenon occurs in which the secondary electron Z having a small energy is returned to the sample 5 by this force and is not detected. Since the charging of the surface of the sample 5 varies depending on the material, structure, and irradiation history of the sample 5, the surface potential due to charging cannot be determined only by the structure. Therefore, the amount of the secondary electrons Z detected by the secondary electron detector 2 is not determined only by the surface structure, but is modulated by the surface potential due to charging. This causes abnormal contrast due to charging. As described above, the voltage contrast also varies in potential depending on the difference in the internal structure and the like and the wiring of the sample 5, and the amount of secondary electrons Z detected is modulated by the surface potential as in the case of charging. Therefore, even if the surface structure of the sample 5 is the same wiring, contrast occurs due to the difference in the internal structure.
[0029]
The potential VL is set to a value at which the secondary electrons Z are completely turned back and cannot be detected by the secondary electron detector 2, and the sample 5 is scanned. Thereafter, the potential VL is equal to the potential VS or the potential VL is equal to the potential VS. It is also possible to acquire an image in which the influence of the charge accumulation is reduced by setting the condition again to a large value that allows the detection of the target and scanning the sample 5.
[0030]
FIG. 2 is a sectional view showing another embodiment of the present invention. In the electron beam apparatus 20 shown in FIG. 2, means for selecting energy of the secondary electrons Z is provided in the magnetic pole 41 as a selection device 21 using a grid member, and the potential VL of the lower electrode 3b is The difference from the scanning electron beam apparatus 10 shown in FIG. 1 is that the condition is set to be equal to or higher than the potential VS of the sample 5.
[0031]
The selection device 21 is shown in detail in FIG. The selection device 21 is disposed in front of the secondary electron detector 2 (on the side of the sample 5), and includes four disc-shaped grid plates 22A to 22D to which a voltage can be applied and a grounded cylinder 23. ing. Here, the cylinder 23 is grounded, and the upper and lower grid plates 22A and 22D are also grounded. A negative potential VG is applied to the middle grid plates 22B and 22C sandwiched between the upper and lower grid plates 22A and 22D.
[0032]
Since the electron beam device 20 is configured as described above, it operates as follows. The primary electron beam Y emitted from the electron beam source 1 passes through the grounded cylinder 23 and reaches the sample 5 without being affected by the voltages applied to the four grid plates 22A to 22D.
[0033]
The secondary electrons Z generated thereby are wound up by the magnetic field on the sample 5 generated by the magnetic pole 41 and enter the magnetic pole 41. Since the negative voltage VG is applied to the grid plates 22B and 22C of the four grid plates 22A to 22D as described above, the secondary electrons Z are decelerated by the negative voltage, and the grid plates 22B and 22C are decelerated. After passing through, is accelerated again to the original speed. In this process, the secondary electron Z having an energy smaller than a certain energy is turned back, so that the function of selecting the energy of the secondary electron Z can be realized. Here, the central two grid plates 22B and 22C can be replaced with one, and the fourth grid plate 22D can be omitted.
[0034]
In the embodiment shown in FIG. 2, since the function of selecting the energy of the secondary electrons Z is realized by the selection device 21 using the grid plate as described above, the scanning shown in FIG. In the same manner as in the electron beam apparatus 10, the secondary electrons Z having a low energy are removed, and only the secondary electrons Z having a large energy are selected and input to the secondary electrons Z, thereby reducing the influence of charge accumulation. It is possible to obtain the same effect as that of the scanning electron beam apparatus 10 in FIG.
[0035]
FIG. 4 is a cross-sectional view showing another embodiment of the present invention. In the electron beam device 30 shown in FIG. 4, means for selecting energy of the secondary electrons Z is provided in the magnetic pole 41 as a selection device 31 using a cylindrical electrode, and the potential VL of the lower electrode 3b is The difference from the scanning electron beam apparatus 10 shown in FIG. 1 is that the condition is set to be equal to or higher than the potential VS of the sample 5.
[0036]
The selection device 31 is shown in detail in FIG. The selection device 31 is provided in front of the secondary electron detector 2 (on the sample 5 side), and has an outer cylindrical electrode 31A provided in front of the secondary electron detector 2 and a coaxial inside the outer cylindrical electrode 31A. And a negative voltage VC applied to the outer cylindrical electrode 31A with respect to the inner cylindrical electrode 31B to select the secondary electron Z based on the energy of the secondary electron Z. It can be sent to the secondary electron detector 2.
[0037]
Since the electron beam device 30 is configured as described above, it operates as follows. The primary electron beam Y emitted from the electron beam source 1 passes through the inner cylindrical electrode 31B which is grounded or to which VU is applied, and reaches the sample 5.
[0038]
The secondary electrons Z generated thereby are wound up by the magnetic field on the sample 5 generated by the magnetic pole 41 and enter the magnetic pole 41. By applying a negative voltage VC to the outer cylindrical electrode 31A with respect to the inner cylindrical electrode 31B, the secondary electrons Z receive a force in the direction of being pulled back from the outer cylindrical electrode 31A to the inner cylindrical electrode 31B. Since electrons having different energies take different orbits, a secondary electron Z having a specific energy can be selected by applying an appropriate voltage VC. For this reason, the inner cylindrical electrode 31B is provided with a plurality of through holes 31Ba through which the secondary electrons Z pass. When the inner cylindrical electrode 31B is grounded, there is an effect that the trajectory of the primary electron beam Y is not affected by the applied voltage.
[0039]
In the embodiment shown in FIG. 4, since the function of selecting the energy of the secondary electrons Z is realized by the selection device 31 using the cylindrical electrode as described above, the scanning shown in FIG. As in the case of the electron beam device 10, by removing the secondary electrons Z having low energy and selecting only the secondary electrons Z having high energy, it is possible to obtain an image in which the influence of charge accumulation is reduced. The same effect as that of the scanning electron beam apparatus 10 in FIG. 1 can be obtained.
[0040]
【The invention's effect】
According to the present invention, as described above, a means for selecting the energy of secondary electrons to be detected is provided between the secondary detector for detecting secondary electrons emitted from the sample and the sample, Selects secondary electrons to reach the secondary detector, thereby enabling the acquisition of an image in which the influence of charge accumulation is reduced.
[0041]
In addition, there is an effect that it is possible to obtain an image in which the influence of charge accumulation is reduced under the same operating conditions for samples of different materials.
[0042]
As described above, an image in which the influence of the charge accumulation is reduced can be obtained, so that image processing and image recognition of the image can be easily performed. In particular, the effect is remarkable in an electron beam apparatus used for observing a defect in a semiconductor, performing observation automatically or semi-automatically, and performing automatic defect classification (AutoDefect Classification) on an acquired image.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating an example of an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing another embodiment of the present invention.
FIG. 3 is an enlarged cross-sectional view for explaining a configuration of a selection device of the electron beam apparatus shown in FIG.
FIG. 4 is a cross-sectional view showing another embodiment of the present invention.
5 is an enlarged cross-sectional view for explaining a configuration of a selection device of the electron beam device shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electron source 2 Secondary electron detector 3 Electrostatic immersion lens 4 Unipolar magnetic field type lens 41 Magnetic pole 10, 20, 30 Electron beam device 21, 31 Selection device X Optical axis Y Primary electron beam Z Secondary electron

Claims (6)

In an electron beam apparatus which scans a sample with a primary electron beam converged by an objective lens and thereby observes an image of the sample based on secondary electrons and the like generated from the sample, the secondary electrons are converted into electric signals. And a secondary electron detector disposed in front of the secondary electron detector for selectively transmitting the secondary electrons to the secondary electron detector based on the energy of the secondary electron. An electron beam apparatus comprising: 2. The electron beam apparatus according to claim 1, wherein the objective lens is an electromagnetic composite lens including a monopole magnetic field type lens having a monopole top surface located between the electron beam source and the sample, and an electrostatic immersion lens. . The electrostatic immersion lens is connected to the inside of the yoke that is connected to the monopole top surface and constitutes the monopole magnetic field lens, and a part of the upper electrode is between the monopole top surface and the sample. The electron beam apparatus according to claim 2, wherein the lower electrode is located between the upper electrode and the sample. 4. The electron beam apparatus according to claim 3, wherein the selection unit is configured to realize a function of selecting energy of the secondary electrons by applying a voltage lower than a potential of the sample to the lower electrode. In an electron beam apparatus which scans a sample with a primary electron beam converged by an objective lens and thereby observes an image of the sample based on secondary electrons and the like generated from the sample, the secondary electrons are converted into electric signals. And a plurality of grid members disposed in front of the secondary electron detector, and apply a negative voltage to at least one of the grid members. An electron beam apparatus wherein the secondary electrons are selectively sent to the secondary electron detector based on the energy of the secondary electrons. In an electron beam apparatus which scans a sample with a primary electron beam converged by an objective lens and thereby observes an image of the sample based on secondary electrons and the like generated from the sample, the secondary electrons are converted into electric signals. A secondary electron detector for converting the secondary electron detector, an outer cylindrical electrode disposed in front of the secondary electron detector, and an inner cylindrical electrode coaxially arranged in the outer cylindrical electrode. By applying a negative voltage to the cylindrical electrode with respect to the inner cylindrical electrode, the secondary electrons are selectively sent to the secondary electron detector based on the energy of the secondary electrons. Characteristic electron beam device.

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