JP2000164167A - Double mode detection of charged particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To separately and simultaneously read a high energy charged particle and a low energy charged particle by arranging a high energy detector so as to deflect the low energy charged particle toward a low energy detector, and arranging the low energy detector so as to detect a deflected low energy charged particle. SOLUTION: The front 20a of a backward scattering(BSE) detector 20 turns downward to a sample 5, and the front 22a of a secondary electron(SE) detector 22 turns upward to an electron supply source 22. A deflector 24 is positioned above the SE detector 22. When a backward scattered electron is emitted from the sample 5, an electron dislocated from the axis in an allowable angle range is recovered by the BSE detector 20. A secondary electron being on the axis or almost on the axis is repulsed by the deflector 24 to be thereby pointed to the SE detector 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for detecting charged particles generated from a sample, and more particularly to a technique for separately reading high-energy charged particles and low-energy charged particles. It is related to the technique of obtaining at the same time.

[0002]

2. Description of the Related Art Various devices are known which rely on the generation or ejection of charged particles from a sample to obtain properties of the sample. Examples of such devices include electron microscopes (eg, a scanning electron microscope “SEM”), focused ion beam microscopes that direct charged particles toward a sample, and various types of devices that perform the ejection of charged particles from a sample. There is a mass spectrometer using a known means.

[0003] For convenience of description of the present invention, the description will be made in relation to an SEM. It should be understood, however, that the invention is not limited to SEMs and can be applied by those skilled in the art to other devices, for example, as described above.

[0004] SEM operates by generating a primary scanning electron beam that impinges on a sample whose surface is to be imaged. As a result, backscattered electrons and secondary electrons are emitted or generated from the surface of the sample and have respective trajectories along the beam (known as the on-axis direction) and at angles offset therefrom. I have. The emitted electrons are collected by a detector located near the surface of the sample. The detector generates a signal from electron emissions recovered from the sample surface exposed to the electron beam. The signal from the detector is used to display an image of the surface on a video screen.

A typical arrangement of the major components of a SEM is shown schematically in FIG. An electron source 2 generates an electron beam 3, which is directed towards a sample 5 via aligned openings at both ends of the tube 4. A detector 6 collects the electrons emitted or generated from the sample 5. The beam 3 includes a stigmation coil 7, an alignment coil 9, and scan coils 11a and 11
b, controlled by the lens 13. The functions of these components are known. Briefly, the stigmation coil 7 is used to correct the beam shape. An alignment coil 9 is used to align the beam via the tube 4. The scan coils 11a and 11b deflect the electron beam 3 in two directions along the x direction and the y direction in a plane perpendicular to the beam direction, for example. An SEM can include more than one of any of these components.

In order to enable high-resolution image formation,
A lens 13 is provided to focus the electron beam on a very small spot. As is known,
Lens 13 can be magnetic, electrostatic, or a combination of these lenses. More specifically, the lens 13 can be an immersion lens, which has a magnetic pole piece in the form of a toroidal channel, as shown schematically in FIG. It is a lens inner pole 15 and a lens outer pole 17
And a winding coil 19 inside the channel.

[0007] SEM has many applications because of its high resolution and high imaging accuracy. Imaging is performed by detecting a signal from the sample, such as electron emission from the sample. SE
Detectors used in M include semiconductors, scintillators, microchannel plates, microsphere plates, and gas ionization detectors. Such detectors collect both backscattered and secondary electrons (the term is used to detect, read,
(Used synonymously with terms such as collection) and their output can be a combined reading of both. However, for some applications, it may be useful to obtain separate readings of backscattered electrons and secondary electrons simultaneously.

[0008] US Patent No. 5,493,116 discloses an arrangement for simultaneously obtaining separate readings of backscattered electrons and secondary electrons. The upper and lower detectors are located above the sample surface, such that the lower detector reads mostly secondary electrons, while the upper detector reads mostly backscattered electrons. Geometries that produce a filter effect have been used. An energy filter effect for preventing secondary electrons from reaching the upper detector is added to the spatial filter effect.
In particular, the lower surface of the upper detector is negatively biased by about -300V, so that low energy secondary electrons are repelled from the upper electrode, while high energy backscattered electrons are substantially affected. Never. Backscattered electrons can have an energy equal to the energy of the electron beam, while secondary electrons have significantly lower energies. For example, if the energy of the electron beam is 1,000 eV, according to the conventional definition, the secondary electrons will have an energy below 50 eV and the backscattered electrons will have at most 1, above 50 eV. 000 eV.

While this configuration has successfully prevented secondary electrons from reaching the upper detector, it has several disadvantages. For example, if the secondary electron is the upper BSE
When repelled downward by the electrodes, they are "lost" because the active surface of the lower SE detector faces downward and it is impossible to retrieve them. or,
Its geometry does not recover a significant percentage of backscattered electrons because the upper detector is located high in the tube, far away from the sample. In addition, for this geometry and / or other known geometries, on-axis secondary electrons and those that are substantially on-axis (eg, within 10 degrees of the beam axis) are also collected. It will not be done.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and solves the above-mentioned disadvantages of the prior art and provides a dual-mode charged particle detection capability to provide high energy charging. It is a general object to simultaneously obtain separate readings of particles and low energy charged particles.

It is another object of the present invention to maximize the recovery of all injected charged particles.

It is yet another object of the present invention to maximize the number of low energy charged particles recovered without reducing the number of high energy charged particles recovered.

Yet another object of the present invention is to recover charged particles that would otherwise be lost in dual mode electron detection.

It is yet another object of the present invention to maximize recovery of injected charged particles having a trajectory that is on-axis and substantially on-axis.

[0015]

According to one aspect of the present invention, there is provided an apparatus for detecting high and low energy charged particles ejected or generated from a sample. The high energy detector detects high energy charged particles and the low energy detector detects low energy charged particles. Deflection means are provided for deflecting the low energy charged particles towards the low energy detector, and the low energy detector is arranged to detect the deflected low energy charged particles.

In accordance with another aspect of the present invention, there is provided an apparatus for detecting high and low energy charged particles ejected or generated from a sample. The high energy detector detects high energy charged particles, and the low energy detector detects low energy charged particles. The high energy detector is arranged to deflect the low energy charged particles toward the low energy detector, and the low energy detector is arranged to detect the deflected low energy charged particles. .

According to another aspect of the present invention, there is provided an apparatus for detecting high and low energy charged particles emitted from a sample. The high energy detector detects high energy charged particles and the low energy detector detects low energy charged particles. The high energy detector has means for deflecting the low energy charged particles towards the low energy detector, and the low energy detector is oriented towards the deflecting means. According to yet another aspect of the present invention,
An apparatus is provided for detecting high and low energy charged particles emitted from a sample. The high energy detector detects high energy charged particles, and the low energy detector detects low energy charged particles. The low energy charged particles are converted into newly ejected charged particles that are directed toward the low energy detector, and the low energy detector is oriented to collect the newly ejected charged particles. .

[0018]

FIG. 1 shows the same SEM components as those shown in FIG. 6 with the same reference numbers, and the detectors are individually numbered for each embodiment. Is different. In FIG. 1, the arrangement of the two detectors is shown near the sample 5. As used herein, the term "detector unit" includes a detector that is an active device for collecting electrons, such as those listed above, and its housing. The front of the housing is open to expose the detector. The remainder of the housing is typically closed. The detector and the housing are insulated from each other.
In the prior art, the housing is usually grounded, while the detector is a backscatter detector ("BSE" detector)
Is negatively biased and the secondary electron detector ("S
E "detector) is positively biased. At the front of the housing is the active surface of the detector unit.

In particular, FIG. 1 shows a configuration in which detector units on a plane are back to back. Detector 20 is BSE
Detector 22 and detector 22 are SE detectors. BS
The front face 20a of the E detector 20 faces downward toward the sample 5 and the front face 22a of the SE detector 22 faces upward toward the electron source 2. A deflector 24 is located above the SE detector 22.

As the backscattered electrons exit the sample 5, the off-axis electrons within an acceptable angular range are collected by the BSE detector 20. Secondary electrons that are on-axis and substantially on-axis are repelled by the deflector 24 and are thereby directed to the SE detector 22.

The detectors 20 and 22, together with the deflector 24, are located towards the lower part of the SEM and near the sample 5. The positioning of these components is determined by the packaging requirements that they must be housed in a space that remains available space in a previously designed SEM. Other considerations may involve recovery efficiency and the type of electrons of interest. For example, the ID of the deflector 24 should be as close to beam 3 as possible without interfering with beam 3. According to this configuration, even substantially on-axis electrons are repelled toward the detector 22 by the deflector 24, thereby maximizing recovery of secondary electrons. On the other hand, the detector 2 located between the sample 5 and the deflector 24
The IDs of 0 and 22 allow on-axis and somewhat off-axis electrons (collectively referred to as "substantially on-axis") to reach the vicinity of the deflector 24 so that they are
Should be relatively larger than that of deflector 24 so that it is directed toward. Further, the active surface of the detector 20 should be dimensioned large enough to provide an acceptable and satisfactory solid angle. In addition, these components can be located higher in the tube. For example, such an arrangement is suitable for some applications where it is desirable to recover more near-axis electrons.

The deflector 24 is shown as planar or flat in the drawing. However, this is done merely to simplify the illustration of the invention for convenience. In practice, the deflector 24 can be of any shape and can be any conductive surface on which a voltage has been applied. Its shape has been optimized in a well-known manner with regard to recovery efficiency. The voltage on deflector 24 is adjustable and adjusted for optimal recovery efficiency. Detectors 20 and 22
Are also shown as planar or planar,
It can be solid, segmented, conical, spherical, or of any shape. The housings of detectors 20 and 22 are shown as in contact. However, they can also be separated from one another.

One variation of the configuration shown in FIG. 1 is to replace the deflector 24 that deflects the secondary electrons with a conversion target that attracts the secondary electrons and therefore impacts the secondary electrons on its surface. is there. The conversion target is composed of or coated with a material having a low electron work function (ie, the energy required to remove the weakest bound electrons). Such materials are well-known to those skilled in the art and, therefore, need not be described in detail.
The conversion target is biased or grounded to a potential (eg, the same voltage as the tube) that accelerates charged particles (eg, electrons) toward the target. As a result of the subsequent bombardment, new secondary and backscattered electrons are ejected from the surface of the conversion target and these are detected by the detector 22 due to the voltage difference between the conversion target and the detector.
Is swept toward. The effect of sweeping newly ejected electrons can be improved by interposing a known accelerator between the conversion target, such as a grid or tube, and the detector. It should be noted that the separate structural elements for this transformation target are not specifically shown in FIG. This is because the deflector 24 achieves its purpose in that its location is occupied by the conversion target. The internal openings of the various components are referred to herein as "ID."
(Inner diameter), and the peripheral part is called “OD” (outer diameter). Therefore, "ID" means not only a dimension, but also a structure that defines this dimension.

I. of deflector 24 D. Are detectors 20 and 2
2 of I. D. Even smaller than. In fact, the I.D. D. Should be as small as possible while allowing the beam 3 to reach the sample 5 without interference. This sizing allows the deflector 24 to direct the maximum number of on-axis secondary electrons towards the SE detector 22. Also, the active surface of SE detector 22 should be large enough to recover the maximum number of secondary electrons directed toward it by deflector 24. Similarly,
The active surface of the BSE detector 20 should be as large as possible to recover the maximum number of backscattered electrons emitted from the sample toward it.

In FIG. 2A, BSE detector 30 is the upper detector and SE detector 32 is the lower detector. These detectors are arranged face-to-face. BS
The housing 31 of the E detector 30 is negatively biased. The negative bias on the detector 30 can be different from the negative bias on its housing. For example, the negative bias on the housing is adjustable and adjusted to optimize recovery, while the negative bias on detector 30 is set to control the energy of the electrons recovered at each detector. Is done.

In this configuration, only electrons that are on-axis and slightly off-axis are recovered. In the case of secondary electrons, B
A negative bias on the housing of the SE detector 30 directs those electrons toward the SE detector 32. Of course,
This negative bias does not significantly affect the backscattered electrons.

One optional addition to the configuration described above is the use of a negatively biased cylindrical deflector 34. It is located in and around the gap between detectors 30 and 32. Its function is to deflect electrons traveling out of the gap. These otherwise "lost" electrons are redirected back to detector 32 and contribute to maximizing the recovered electrons.

FIG. 2A shows detectors 30 and 32 within tube 4, the exact location of which depends on various factors involving the particular arrangement of the particular SEM in which the invention is used. Therefore, this packaging is based on the detector O.D. D. Dimensions of I.V. D. To be restrained. In contrast, FIG. 2B shows BSE detectors 40 and SEs arranged facing each other.
A detector 42 is shown, with the housing 41 negatively biased as just described for the coils 30 and 32 and the housing 31 in FIG. 2A. However, the detectors 40 and 42 are outside the tube 4 and therefore
You are not restricted by its dimensions. More specifically, the BSE detector 40 and the SE detector 42 are connected to the tube 4
I. D. O. greater than D. It is possible to have Such large dimensions allow for a larger active surface of the detector, which can recover a higher number of electrons. A negatively biased cylindrical deflector 44 similar to deflector 34 in FIG. 2A can also be optionally used.

In FIGS. 2A and 2B, deflectors 34 and 44 can be replaced by a conversion target just as described above in connection with detector 24 of FIG. FIG. 3 shows an arrangement of detectors 50 and 52 that is substantially similar to detectors 40 and 42 of FIG. 2B, ie, these detectors are located below tube 4 and BSE detector 50 is Above the SE detector 52, the housing 51 of the BSE detector 50 is negatively biased. However, the lower SE detector 52 is tilted and therefore its I.D. D. Is close to sample 5, while its O.D. D. Is close to the BSE detector 50. The shape of the SE detector 52 can be conical, spherical, piece-wise, or any other known shape.

This arrangement has several advantages. For example, if secondary electrons are repelled by the BSE detector 40 and its housing in FIG. 2B, they will move laterally and outwardly through the gap between the two detectors and a significant number will "Lost". However, the slanted configuration of the SE detector 52 in FIG. 3 has its O.D. to minimize the size of the gap through which secondary electrons can escape. D. Can be moved close to the level of the BSE detector 50. Therefore, S
E detector 52 is an O.E. D. O. greater than D. It is beneficial to have Also, by tilting the SE detector 52, it is possible to enlarge its active surface and increase the electron collection efficiency. Further, the BSE detector 50 is "visible" to electrons backscattered over a wider acceptance solid angle.

The components 50 and 52 can also be located above the tube 4 to meet packaging constraints or for other reasons as described above.

In FIG. 4, the SE detector 60 has a cylindrical shape and is located below the planar BSE detector 62. The BSE detector 62 is the BSE detector 50 of FIG.
The housing is negatively biased. Although the BSE detector 62 has a wider acceptance angle, due to the orientation of the SE detector 60, less of the secondary electrons repelled by the BSE detector 62 are SE.
There is only a probability that it will be recovered by the detector 60. However, the gap between the two detectors can be minimized, thereby reducing the "lost" electrons.

In FIG. 5, BSE detector 70 and SE
The detectors 72 are arranged face-to-face, both of which have a conical or spherical shape. Housing 7
1 is negatively biased. FIG. 5 is similar to FIG. 3, but the BSE detector 50 at the top of FIG. 3 has been modified from a planar shape to a conical or spherical shape. Such a configuration can provide optimized recovery efficiency.
This also makes manufacturing easier and lowers costs, since the same components can be used for the upper and lower detectors.

Although the specific embodiments of the present invention have been described in detail above, the present invention should not be limited only to these specific examples, but may be variously modified without departing from the technical scope of the present invention. Of course is possible. For example, various vertical positions can be used for the detectors relative to the tube, and the spacing between the detectors can be varied. Also, the relative horizontal position of the detector and deflector can be changed, and the dimensions of the active surface can be changed. Similarly, the voltage on the detector, deflector and housing can be adjusted. To some extent, these deformations are dependent on packaging constraints, and to some extent, the type of measurement of interest affects the geometry, eg, on-axis, off-axis, secondary, backscatter, and the like. Each detector can be replaced at least in part by a segmented detector or a separate detector depending on the result to be achieved. The detector can also be located off-center rather than along the beam.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of an SEM showing an arrangement state of a secondary electron detector and a backscattered electron detector according to the present invention.

FIG. 2A is a schematic view showing another embodiment of the present invention.

FIG. 2B is a schematic view showing still another embodiment of the present invention.

FIG. 3 is a schematic view showing still another embodiment of the present invention.

FIG. 4 is a schematic view showing still another embodiment of the present invention.

FIG. 5 is a schematic view showing still another embodiment of the present invention.

FIG. 6 is a schematic view showing a conventional SEM.

[Description of Signs] 2 Electron source 3 Beam 5 Sample (sample) 20 BSE detector 22 SE detector 24 Deflector

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Paul Jay. Duval, United States, Massachusetts 02173, Lexington, North Hancock Street 95 (72) Inventor Stephan W. Int United States, Massachusetts 01451, Harvard, Henry Road 10 (72) Inventor Ira Rosenberg United States of America, Massachusetts 01810, Andover, Brookside Drive 402 (72) Inventor Neil S. Casa United States, Massachusetts 02174, Arlington, Gloucester Street 20 (72) Inventor Kennis H. Brown United States, Mass. 01460, Littleton, Woodland Drive 23 (72) Inventor Bradymir Bayner United States, Mass. 02494, Needham, Dale Street 45

Claims (21)

[Claims] 1. An apparatus for detecting high energy and low energy charged particles generated from a sample, comprising: a high energy detector for detecting high energy charged particles; and a low energy detector for detecting low energy charged particles. Wherein the high energy detector is arranged to deflect a low energy charged particle toward the low energy detector, such that the low energy detector detects the deflected low energy charged particle. A device characterized in that it is arranged in a device. 2. The apparatus of claim 1, wherein the high energy detector is arranged to deflect the low energy charged particles by having a negatively biased housing. 3. The sample surface of claim 2, wherein the high energy detector deflects low energy charged particles that have bypassed the low energy detector back toward the lower energy detector. An apparatus for deflecting low energy charged particles by being located further away from the apparatus. 4. The method of claim 1, wherein the low energy detector is provided to detect the deflected low energy charged particles by including an active surface oriented to face the high energy detector. An apparatus characterized in that: 5. The apparatus of claim 4, wherein the active surface of the low energy detector is positively biased. 6. The apparatus of claim 1, wherein the low energy detector has a conical or spherical shape, the inner diameter of which is closer to the sample and the outer diameter of which is closer to the high energy detector. 7. The apparatus of claim 6, wherein an outer diameter of the low energy detector is larger than an outer diameter of the high energy detector. 8. The apparatus of claim 1, wherein the high energy detector has an inner diameter smaller than the inner diameter of the low energy detector. 9. The apparatus according to claim 1, further comprising a deflector disposed around a gap between the high energy detector and the low energy detector. 10. The apparatus according to claim 1, wherein the apparatus is a scanning electron microscope, the charged particles are electrons, the high energy electrons are backscattered electrons, and the low energy electrons are secondary electrons. An apparatus characterized by the above. 11. An apparatus for detecting high-energy and low-energy charged particles generated from a sample, comprising: a high-energy detector for detecting high-energy charged particles; and a low-energy detector for detecting low-energy charged particles. The high energy detector has means for deflecting low energy charged particles toward the low energy detector, and the low energy detector is oriented toward the deflecting means. An apparatus characterized by the above. 12. The apparatus according to claim 11, wherein the apparatus is a scanning electron microscope, wherein the charged particles are electrons, high energy electrons are backscattered electrons, and low energy electrons are secondary electrons. An apparatus characterized by the above. 13. An apparatus for detecting high-energy and low-energy charged particles generated from a sample, comprising: a high-energy detector for detecting high-energy charged particles; a low-energy detector for detecting low-energy charged particles; Means for deflecting particles towards said low energy detector, said low energy detector being oriented towards said means for deflecting. 14. The apparatus according to claim 13, wherein said deflecting means is a surface to which an electric potential is applied. 15. The apparatus of claim 13, wherein said high and low energy detectors are between said sample and said means for deflecting. 16. The apparatus of claim 13, wherein the means for deflecting is at a periphery of a gap between the high energy detector and the low energy detector. 17. The apparatus according to claim 13, wherein the apparatus is a scanning electron microscope, the charged particles are electrons, high-energy electrons are backscattered electrons, and low-energy electrons are secondary electrons. An apparatus characterized by the above. 18. A method for detecting high energy and low energy charged particles generated from a sample, comprising: detecting a high energy charged particle with a high energy detector; detecting a low energy charged particle with a low energy detector; A high energy detector arranged to deflect a low energy charged particle toward the low energy detector, and the low energy detector arranged to detect the deflected low energy charged particle; A method comprising the above steps. 19. A method for detecting high energy and low energy charged particles generated from a sample, comprising detecting a high energy charged particle with a high energy detector, detecting a low energy charged particle with a low energy detector, and deflecting. Deflecting low energy charged particles towards said low energy detector by means and orienting said low energy detector towards said deflecting means. 20. An apparatus for detecting high-energy and low-energy charged particles generated from a sample, comprising: a high-energy detector for detecting high-energy charged particles; and a low-energy detector for detecting low-energy charged particles. Means for converting said low energy charged particles into newly generated charged particles directed towards said low energy detector, said low energy detector being oriented towards said converting means. An apparatus characterized in that: 21. A method for detecting high-energy and low-energy charged particles generated from a sample, comprising a high-energy detector for detecting high-energy charged particles, and a low-energy detector for detecting low-energy charged particles. Providing a detector, converting the low energy charged particles into newly generated charged particles directed toward the low energy detector, and orienting the low energy detector toward the conversion means; A method comprising having each step.