JP4721821B2 - Scanning electron microscope and signal detection method in scanning electron microscope - Google Patents

Description

The present invention relates to a scanning electron microscope and a signal detection method in the scanning electron microscope, and more particularly to a scanning electron microscope and a signal detection method in the scanning electron microscope when observing a non-conductive sample.

  The effect of charging the non-conductive sample by electron beam irradiation on the image is that the trajectory of the secondary electrons is changed by the charging potential, and abnormal contrast occurs in the image. To reduce this contrast, it is necessary to collect high-energy electrons that are not easily affected by the field.

  FIG. 5 is a conceptual diagram of the configuration of a conventional apparatus. In the figure, 1 is a sample, and 2 is a sample holder for holding the sample 1. 3 is a semi-in-lens type objective lens. EB is an electron beam applied to the sample, and 4 is a secondary electron detector for detecting secondary electrons emitted from the sample surface. The signal detected by the secondary electron detector 4 is subjected to image processing by an image processing unit (not shown), and a sample surface image is obtained.

In the semi-in-lens type magnetic field arrangement, a very strong magnetic field is generated on the sample 1. At this time, the electrons emitted from the sample 1 perform a rotation (rama) motion related to the magnetic field and the energy of the electrons. The locus of the spiral motion shown in the figure indicates the rama motion. Larmor radius r _c at this time is expressed by the following equation.

r _c ∝v / B
Here, v is the velocity of charged particles, and B is the magnetic flux density. Here, the llama radius is the radius of a circle when ions are wound around magnetic field lines and rotate.

  Due to the speed dependency of the llama radius in the above formula, the secondary electron detector 4 arranged at the position shown in FIG. Only high-energy electrons that can have a linear trajectory because they are large can reach the secondary electron detector 4.

  Another feature of the apparatus shown in the drawing is that electrons having a small emission angle with respect to the sample surface are detected because the trajectory is linear. In general, high-energy electrons need to be emitted from the sample surface with a small small-angle scattering, and thus electrons having a small emission angle with respect to the sample surface are emitted from a shallow position of the sample. For this reason, electrons having high energy and a small emission angle with respect to the sample surface have information depending on the shape of the sample surface.

As a conventional device of this type, a technique is known in which a cylindrical member is provided in an objective lens, and a surface with high secondary electron generation efficiency is provided inside the cylindrical member (see, for example, Patent Document 1). . Also known is an apparatus that has a detector arranged on the electron source side of an in-lens type objective lens and forms a sample image by detecting reflected electrons emitted in a direction that makes a small angle with respect to the surface of the sample. (For example, refer to Patent Document 2).
JP 2001-57172 A (paragraphs 0014 to 0024, FIG. 1) Japanese Patent Laid-Open No. 2001-110351 (paragraphs 0015 to 0019, FIG. 1)

  Since low-angle, high-energy electrons are considered to move substantially linearly, the field of view of the detector is determined by the working distance (work distance: WD). Here, the low angle means an angle at which electrons are emitted from the sample 1, and for example, the low angle means an angle at which the angle of electrons emitted from the sample rises slightly from the sample. That is, the light is reflected almost horizontally from the sample. If the field of view (working distance) of the detector is shortened, the signal amount is reduced and the contrast difference of the image is reduced. Therefore, if the working distance is lengthened to increase the field of view, the beam cannot be narrowed down and observation with high resolution becomes difficult.

The present invention has been made in view of such problems, and provides a scanning electron microscope capable of collecting electrons at a low angle and high energy in a state where the working distance is shortened, and a signal detection method in the scanning electron microscope. The purpose is that.

  In the present invention, a wall is formed around the sample, and low-angle, high-energy electrons are once applied to the wall, and secondary electrons re-emitted therefrom are detected by a semi-in-lens detector (secondary electron detector). It is what I did.

(1) According to the first aspect of the present invention, at least the electron beam focused by the objective lens is irradiated onto the surface of the sample, and secondary electrons emitted from the sample surface are detected by the secondary electron detector. In the scanning electron microscope in which an image of the sample surface is obtained based on the secondary electrons, a secondary electron emission member having a wall made of gold, platinum or copper is arranged on the surface of the sample, The configuration is such that a voltage can be applied, and secondary electrons emitted from the wall of the member are guided to the secondary electron detector.

(2) According to a second aspect of the invention, the secondary electron emission member is characterized in that it Na lattice shape.
(3) The invention according to claim 3 is characterized in that the lattice spacing of the secondary electron emission member is determined from the magnetic field distribution on the sample and the shape of the objective lens.

(4) The invention according to claim 4 is characterized in that the objective lens is an in-lens type or a semi-in-lens type .
(5) The invention according to claim 5 is characterized in that the secondary electron detector is arranged in the objective lens or above the objective lens .

(6) The invention according to claim 6 irradiates the surface of the sample with an electron beam focused at least by the objective lens, and detects secondary electrons emitted from the surface of the sample with a secondary electron detector. In a signal detection method in a scanning electron microscope that obtains an image of a sample surface based on secondary electrons, a secondary electron emission member having a wall made of gold, platinum, or copper is disposed on the surface of the sample. In addition, a voltage is applied to the member to guide secondary electrons emitted from the wall of the member to the secondary electron detector.

(7) The invention according to claim 7 is characterized in that the secondary electron emission member has a lattice shape .
(8) The invention according to claim 8 is characterized in that the lattice spacing of the secondary electron emission member is determined from the magnetic field distribution on the sample and the shape of the objective lens .

(1) According to the first aspect of the present invention, the electrons emitted from the sample collide with a wall made of gold, platinum or copper having a high secondary electron emission rate, and the secondary electrons emitted from the wall are reduced to 2 Since the secondary electron detector is used for detection, low-angle, high-energy electrons can be collected with a short working distance.

(2) According to the invention described in claim 2, as a result of using a lattice-like shape as a wall, electrons hitting the wall can be efficiently converted into secondary electrons, and the secondary electron detection image can be efficiently converted. Can be detected well .
(3) According to the invention described in claim 3, the interval between the walls can be set to an optimum value, and the generated secondary electrons can be increased .

(4) According to the invention described in claim 4 , the present invention can be applied to the case where the objective lens is either an in-lens type or a semi-in-lens type .

(5) According to the invention described in claim 5, since the secondary electron detector is provided at a position where the secondary electrons can be efficiently captured, the secondary electron detection image can be detected efficiently.
(6) According to the invention described in claim 6, by arranging a wall made of gold, platinum or copper having a high secondary electron emission rate on the sample surface, a voltage is applied to this member, and the wall of the member The secondary electrons emitted from can be guided to the secondary electron detector.

(7) According to the invention described in claim 7, as a result of using the lattice-like shape as the wall, electrons hitting the wall can be efficiently converted into secondary electrons, and the secondary electron detection image can be efficiently converted. Can be detected well .
(8) According to the invention described in claim 8, the interval between the walls can be set to an optimum value, and the generated secondary electrons can be increased .

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a configuration example of a main part of the first embodiment of the present invention. The same components as those in FIG. 5 are denoted by the same reference numerals. (A) is the figure which looked at the sample 1 from the top, (b) is AA sectional drawing of (a). In the figure, 1 is a sample, and 2 is a sample holder for holding the sample 1. Reference numeral 6 denotes a mesh as a wall covering the sample 1. The mesh 6 is made of a material having a high secondary electron emission rate. For example, gold or platinum is used. However, the secondary electron emission rate does not vary so much depending on the material, and other materials such as copper can be used. The shape of the mesh lattice may be any shape such as a circle or a triangle. Below, the attachment process of the mesh 6 is demonstrated.

  First, the mesh 6 is placed over the sample 1. Next, the mesh 6 is fixed to the sample holder 2. At this time, the mesh 6 is prevented from electrically floating from the sample holder 2. That is, the mesh 6 and the sample holder 2 are made to have the same electric potential. As a result, when a voltage is applied to the sample holder 2, the same voltage is also applied to the mesh 6.

  There are two conditions for determining the lattice spacing W of the mesh 6. One is to make it less than the llama radius of high energy electrons (reflected electrons). If this condition cannot be met, electrons cannot hit the wall. Another condition is that the lattice interval W needs to be made sufficiently small so that secondary electrons re-emitted from the wall do not collide with the inner wall of the objective lens 3.

  This is important when the magnetic field configuration is such that the magnetic field is strong directly above the sample and the magnetic field suddenly weakens as it enters the objective lens 3. At this time, since the necessary lattice interval W depends on the objective lens shape and the magnetic field distribution on the sample, it is necessary to calculate the electron trajectory for the magnetic field distribution of the apparatus and the objective lens shape.

  The height H of the lattice is determined by which emission angle the electron is applied to, but about half of the lattice interval W is required. Here, a voltage is applied to the sample holder 2. Reference numeral 7 denotes a power source applied to the sample holder 2. The voltage of the power source 7 can be varied. The operation of the above configuration will be described as follows.

  The sample 1 is irradiated with an electron beam EB emitted from an electron gun (not shown). At this time, the high-energy electrons emitted from the sample 1 move substantially linearly and collide with the inner wall of the mesh 6. The electrons colliding with the inner wall of the mesh 6 cause secondary electrons to be emitted from the inner wall of the mesh. Next, when a predetermined voltage is applied to the sample holder 2 from the power source 7, secondary electrons emitted from the inner wall of the mesh are detected by the secondary electron detector 4 (see FIG. 5).

  As described above, according to the present invention, the emitted electrons from the sample 1 are applied to the inner wall of the mesh 6 and the secondary electrons emitted from the inner wall are detected by the secondary electron detector 4. Electrons with a low angle and high energy can be collected in a short state. Further, as a result of using the mesh strip shape as the wall, the electrons colliding with the wall can be efficiently converted into secondary electrons, and the secondary electron detection image can be detected efficiently. In addition, according to the present invention, the lattice spacing can be set to an optimum value, and the generated secondary electrons can be increased. Here, the lattice interval of the secondary electron emission member (mesh) can be determined from the magnetic field distribution near the sample and the shape of the objective lens. According to this, the space | interval of a wall can be set to the optimal thing and the secondary electron which generate | occur | produces can be increased.

  FIG. 2 is a block diagram showing a second embodiment of the present invention. The same components as those in FIG. 5 are denoted by the same reference numerals. In the figure, 1 is a sample, 2 is a sample holder for holding the sample 1, 3 is an objective lens, and 4 is a secondary electron detector. Reference numeral 10 denotes a pipe made of a material having a high secondary electron emission rate, which is fitted into the inner wall of the objective lens 3. Reference numeral 11 denotes an electron beam and an electron passage hole formed in the center of the pipe 10. A power source 7 applies a voltage to the pipe 10.

  FIG. 3 is a diagram illustrating a configuration example of a pipe. The same components as those in FIG. 2 are denoted by the same reference numerals. (A) is the figure which looked at the pipe from the bottom, (b) is the AA sectional drawing. In the figure, 11 is an electron beam and electron passage hole, and 12 to 14 are holes drilled in the bottom of the pipe 10. These holes 12 to 14 are holes for reducing air resistance (conductance) when the inner wall of the objective lens is pulled to a high vacuum. 15 and 16 are pawls for moving the pipes provided at both ends of the pipe 10 up and down. The procedure for attaching such a pipe will be described as follows.

  First, the metal pipe 10 is fitted into the inner wall of the objective lens 3 (S1). In this case, the pipe 10 serves as a wall. When observing, the pipe 10 is used in contact with the sample 1. This is because it is more efficient not to open a gap between the sample and the pipe in order to apply low-angle reflected electrons to the wall. The pipe 10 is made of a material having a high secondary electron emission rate. The determination of the diameter of the pipe 10 has two conditions, similar to that shown in FIG.

  One is to make it less than the llama radius of high energy electrons (reflected electrons). If this condition is not satisfied, electrons cannot hit the wall. The other is that the diameter of the pipe needs to be sufficiently small so that secondary electrons re-emitted from the wall do not collide with the inner wall of the objective lens 3. This is important when the magnetic field configuration is such that the magnetic field is strong just above the sample 1 and enters the objective lens 3 so that the magnetic field suddenly weakens. At this time, since the required diameter depends on the objective lens shape and the magnetic field distribution on the sample, it is necessary to calculate the electron trajectory for the magnetic field distribution of the apparatus and the objective lens shape.

  A mechanism for moving the pipe 10 up and down is required (S2). The pipe 10 is usually housed inside the objective lens, and the pipe 10 is lowered to a position where it comes into contact with the sample 1 when the scanning speed is lowered. A voltage is applied to the pipe 10 from the power supply 7. This applied voltage is made variable. The operation of the apparatus configured as described above will be described as follows.

  First, the observation position and working distance are determined. Next, the pipe 10 is lowered until it contacts the sample. Voltage from the power source 7 to the sample holder 2 in a state in which the pipe 10 and the sample 1 are in contact (the sample holder 2 and the pipe 10 are in contact with each other, so when the power source 7 is applied, voltage is also applied to the sample holder 2) Apply. As a result, the sample 1 is irradiated with the electron beam EB, and electrons emitted from the sample 1 collide with the inner wall of the pipe 10 through the hole 11 and are converted into secondary electrons. The converted secondary electrons are detected by the secondary electron detector 4 by applying a voltage from the power source 7.

  According to this embodiment, by fitting a pipe made of a material having a high secondary electron emission rate into the inner wall of an in-lens or semi-in-lens type objective lens, it collides with the inner wall of the pipe and becomes secondary electrons. The conversion efficiency can be improved, and low-angle, high-energy electrons can be collected with a short working distance.

  FIG. 4 is a block diagram showing the main part of the third embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals. In the figure, reference numeral 20 denotes a mesh covering the sample 1 (not shown). Reference numeral 2 denotes a sample holder for holding the sample 1. Reference numeral 9 denotes a sample table provided on the upper portion of the sample holder 2. (A) is the figure which looked at the sample from the top, (b) is the AA sectional drawing. In this case, the mesh 20 serves as a wall. The shape of the lattice may be any shape as long as it surrounds an arbitrary observation region such as a circle, square, or triangle. A material having a high secondary electron emission rate is used as the material of the mesh 20.

  The mesh 20 is fixed to the sample table 9. At this time, the mesh 20 is prevented from floating from the sample stage 9. That is, when a voltage is applied to the sample holder 2 from the power source 7, the voltage is also applied to the mesh 20 via the sample stage 9. Further, the mesh 20 is fixed to the sample table 9 at three or more points so that the position of the mesh can be changed.

  Here, there are two conditions for determining the interval between the lattice points of the mesh 20. One is to make it less than the llama radius of high energy electrons (reflected electrons). If this is not satisfied, electrons cannot collide with the wall. The other is that the lattice spacing needs to be sufficiently small so that secondary electrons re-emitted from the wall do not collide with the inner wall of the objective lens 3. This is important when the magnetic field configuration is such that the magnetic field is strong just above the sample and the magnetic field suddenly weakens as it enters the objective lens 3. At this time, since the necessary lattice spacing depends on the magnetic field distribution on the objective lens 3 and the sample 1, it is necessary to calculate the electron trajectory for the magnetic field distribution of the apparatus and the objective lens shape.

  The height of the lattice is determined by which emission angle the electrons collide with. This requires about half of the grid spacing. Further, the voltage applied to the sample stage 9 is made variable. Further, the mesh 20 is fixed by a detachable method (for example, screwing or the like) so that it can be replaced when it is defective. The operation of the apparatus configured as described above will be described as follows.

  High-energy electrons emitted from the sample 1 move substantially linearly and collide with the inner wall of the mesh 20. The electrons colliding with the inner wall of the mesh 20 cause secondary electrons to be emitted from the inner wall of the mesh. Here, when an appropriate voltage is applied from the power source 7, secondary electrons emitted from the inner wall of the mesh are detected by the secondary electron detector 4 (see FIG. 2).

  Also in this embodiment, since the electrons emitted from the sample collide with the inner wall and the secondary electrons emitted from the inner wall are detected by the secondary electron detector, the working distance is shortened. Low angle, high energy electrons can be collected.

The configuration and operation of Embodiments 1 to 3 described above will be described in comparison.
(Embodiment 1)
This is the simplest method for efficiently obtaining the effects of the present invention. This method is inexpensive and simple in construction, but walls and samples cannot be reused.
(Embodiment 2)
In order to efficiently obtain the effects of the present invention, the SEM itself (objective lens) is improved. In the method of the first embodiment, the portion overlapping the mesh cannot be observed, but in this method, the observation position can be changed by moving the sample, so that the entire surface of the sample can be observed. Moreover, it is not necessary to prepare a sample (meshing a mesh) during observation.
(Embodiment 3)
In order to efficiently obtain the effects of the present invention, the sample holder is improved. In this method, it is not necessary to create a new objective lens, and it can be applied to conventional apparatuses. The mesh can be reused, and the entire surface of the sample can be observed by moving the mesh when the sample is taken out.

According to the present invention, the following effects can be obtained.
1) The amount of signals can be increased by incorporating low-angle, high-energy electrons into the detector.
2) Since low-angle, high-energy electrons have surface shape information, the surface contrast of the SEM image can be enhanced.
3) When the sample is non-conductive, the low-angle, high-energy electrons enhance the surface contrast, thereby reducing abnormal contrast due to charging.

It is a figure which shows the structural example of the principal part of the 1st Example of this invention. It is a block diagram which shows the 2nd Example of this invention. It is a figure which shows the structural example of a pipe. It is a block diagram which shows the principal part of the 3rd Example of this invention. It is a composition conceptual diagram of the conventional device.

Explanation of symbols

1 Sample 2 Sample holder 6 Mesh 7 Power supply

Claims (8)

At least an electron beam focused by an objective lens is irradiated on the surface of the sample, secondary electrons emitted from the sample surface are detected by a secondary electron detector, and an image of the sample surface is based on the detected secondary electrons. In a scanning electron microscope designed to obtain
A secondary electron emission member having a wall made of gold, platinum, or copper is disposed on the surface of the sample, and the member is configured to be able to apply a voltage. Secondary electrons emitted from the wall of the member are A scanning electron microscope characterized by being guided to a secondary electron detector.   2. The scanning electron microscope according to claim 1, wherein the secondary electron emission member has a lattice shape.   3. The scanning electron microscope according to claim 2, wherein the lattice spacing of the secondary electron emission member is determined from a magnetic field distribution on the sample and an objective lens shape.   The scanning electron microscope according to claim 1, wherein the objective lens is an in-lens type or a semi-in-lens type.   The scanning electron microscope according to claim 1, wherein the secondary electron detector is disposed in the objective lens or above the objective lens. At least an electron beam focused by an objective lens is irradiated on the surface of the sample, secondary electrons emitted from the sample surface are detected by a secondary electron detector, and an image of the sample surface is based on the detected secondary electrons. In a signal detection method in a scanning electron microscope in which
A secondary electron emission member having a wall made of gold, platinum, or copper is disposed on the surface of the sample, and a voltage is applied to the member so that secondary electrons emitted from the wall of the member are A signal detection method in a scanning electron microscope, characterized in that the signal is guided to a secondary electron detector.   7. The signal detection method in a scanning electron microscope according to claim 6, wherein the secondary electron emission member has a lattice shape.   8. A signal detection method in a scanning electron microscope according to claim 7, wherein the lattice spacing of the secondary electron emission member is determined from the magnetic field distribution on the sample and the shape of the objective lens.

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