JPH10214586A - Scanning electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a loss of information of a secondary electron to the minimum so as to achieve observation of the information of the secondary of electron having a high S/N ratio by disposing on a shaft of a plurality of beam deflectors of a magnetic field type, shifting the axis of a primary electron beam by a predetermined distance, and detecting a secondary electron emitted from a sample by means of secondary electron detectors. SOLUTION: Upper and lower beam deflectors 17, 18 disposed on a shaft are deflected, at two stages, a primary electron beam 5 generated by an electron gun 4, to shift the axis of the electron gun 4 and the axis of an objective lens 2 by a predetermined distance in a horizontal direction. An image is focused by the objective lens 2, and then, the finely throttled primary beam 5 is irradiated on a sample 1. After surface scanning, a secondary electron 16 emitted from the sample 1 is detected by a secondary electron detector 9 disposed above the objective lens 2. The secondary electron 16 deflected in a reverse direction by the lower beam deflector 18 is detected by another secondary electron detector 10. Consequently, it is possible to suppress a loss of information of the secondary electron to the minimum, thus achieving observation of a clear secondary electron image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning electron microscope for displaying an image by detecting secondary electrons generated by scanning a primary electron beam on a sample surface.

[0002]

2. Description of the Related Art Conventionally, a scanning electron microscope has a configuration shown in FIG. 2 and scans a sample 1 while irradiating it with a finely focused electron beam.
4 is detected by the secondary electron detectors 9 and 10, and the amplifiers 22 and 2
3, and the secondary electron images are respectively displayed on a display device (not shown). Hereinafter, the configuration of FIG. 2 will be briefly described.

FIG. 2 is an explanatory diagram of the prior art. In FIG. 2, a sample 1 is a sample to be irradiated with a narrowly focused primary electron beam, to detect secondary electrons emitted, to display and observe a secondary electron image, and to be observed.

The objective lens 2 irradiates the sample 1 with the primary electron beam narrowed down. The condenser lens 3 focuses the primary electron beam emitted from the electron gun 4.

[0005] The electron gun 4 generates a primary electron beam. The primary electron beam 5 is a primary electron beam generated and emitted by the electron gun 4.

The stop 6 is for giving a predetermined opening angle when the primary electron beam emitted from the electron gun 4 is focused by the condenser lens 3. Beam deflectors 7, 8
Is a deflector (deflection coil or deflection electrode) for deflecting the primary electron beam in two steps and scanning it on the sample 1.

The secondary electron detector 9 is a detector for detecting a portion of the secondary electrons emitted from the sample 1 when the sample 1 is irradiated with the primary electron beam, the secondary electrons being away from the axis. It is.

The secondary electron detector 10 is a detector for detecting a secondary electron in a portion near an axis of secondary electrons emitted from the sample 1 when the sample 1 is irradiated with a primary electron beam. is there.

The detection electrode 11 is emitted from the sample 1,
The electrode applies an electric field so that secondary electrons in a direction away from the axis are detected by the secondary electron detector 9. The detection electrode 12 is an electrode that applies an electric field so that secondary electrons emitted from the sample 1 and in a direction close to the axis are detected by the secondary electron detector 10.

The secondary electrons 14 are trajectories of the secondary electrons emitted from the sample 1 in a direction away from the axis. Secondary electron 15
Is the trajectory of the secondary electrons emitted from the sample 1 in a direction near the axis.

The bias voltage 21 is a bias voltage applied to the sample 1, and is a bias voltage (for example, 1000 VDC) sufficient to emit secondary electrons from the bottom of the contact hole of the wafer as the sample 1.

The amplifiers 22 and 23 include a secondary electron detector 9,
10 amplifies the current due to the secondary electrons detected. Next, the operation when observing the inside of the contact hole of the wafer as the sample 1 will be briefly described.

The primary electron beam 5 emitted from the electron gun 4
Are focused by a condenser lens 3, further combined by an objective lens 2, and irradiated as a narrowed primary electron beam on the surface of the sample 1. At this time, the stop 6 determines the opening angle of the primary electron beam 5 and deflects the primary electron beam by the beam deflectors 7 and 8 to scan the sample 1 two-dimensionally. Then, secondary electrons 14 and 15 are generated from the surface of the sample 1,
Finally, the secondary electron detectors 9 and 1 receive the effects of the bias voltage 21 applied to the sample 1, the electric field generated on the outer surface of the objective lens 2, and the magnetic field generated by the objective lens 2.
Captured by 0 and detected. Secondary electron detector 9,
The signal of the secondary electron detected by the
Amplified by 2 and 23 and output as image signals. These image signals are input to a display device (not shown) to
The secondary electron images are displayed.

As described above, recent scanning electron microscopes apply a bias voltage 21 to the sample 1 to generate secondary electrons.
It accelerates in the direction of the secondary electron detectors 9 and 10. This allows
The secondary electrons generated on the surface of the sample 1 fly out over a wide angle range, but are separated by their orbits and reach the two secondary electron detectors 9 and 10. Of the two secondary electron detectors, the secondary electron detector 9 closer to the sample 1 detects the secondary electrons that jump out of the sample 1 at a large angle, and the secondary electron detector 10 farther from the sample 1 Detects secondary electrons that have jumped out of the sample 1 at a small angle.

[0015]

An important observation object of a recent scanning electron microscope is a fine pattern of a semiconductor wafer. Among them, the object referred to as a contact hole in particular is becoming more and more important as semiconductor ICs become more highly integrated. In the case of a contact hole having a deep bottom (high aspect ratio) as compared with the diameter of the hole, 2 mm from the hole bottom is required.
Observation is very difficult due to weak secondary electrons. In such a case, the above-described method of applying the bias voltage 21 is used in order to apply a strong electric field to the surface of the wafer as the sample 1 and extract secondary electrons from the bottom of the contact hole. This method is very effective,
Another problem has arisen:

That is, the secondary electrons emitted from the surface of the wafer as the sample 1 are accelerated toward the + potential, and have a large velocity near the secondary electron detectors 9 and 10. For example, when the objective lens 2 and the lens electrode 13 of FIG. 2 are kept at the ground potential (0 V) and a negative 1000 V (bias voltage 21) is applied to the wafer as the sample 1, the secondary electrons pass through the objective lens 2 , Reach an energy of almost 1000 eV. On the other hand, the energy of primary electrons is
It is 1000 eV or less in order to prevent charging of the sample 1.

Therefore, the energy of the secondary electrons is almost equal to the energy of the primary electrons. The trajectories of secondary electrons of such energy are concentrated on the beam axis (vertical direction). In FIG. 2, in order to increase the detection efficiency for such secondary electrons, the second secondary electron detector 10 is used.
Is provided above (rearward) with respect to the first secondary electron detector 9. However, there are still secondary electrons passing through the center hole of the second secondary electron detector 10. When the bias voltage 21 is to be further increased, the rate of loss in this portion (secondary electrons passing through the center hole) is further increased, and the efficiency of capturing and detecting secondary electrons is reduced.
There is a problem that a secondary electron image with a good S / N ratio cannot be displayed.

The present invention solves these problems,
A secondary electron detector in which the axis of the primary electron beam is slightly shifted by a deflection coil, and secondary electrons emitted from the sample and traveling in the opposite direction are provided at positions where the axis is shifted in the opposite direction. It is an object of the present invention to realize the observation of a bright secondary electron image with a high S / N ratio while minimizing the loss of secondary electron information when observing a contact hole or the like of a semiconductor wafer.

[0019]

Means for solving the problem will be described with reference to FIG. In FIG. 1, sample 1
Is an object to be observed by observing a secondary electron image by emitting a secondary electron by scanning a narrowed primary electron beam.

The objective lens 2 forms an image of the primary electron beam, and irradiates the sample 1 with a fine focus. Electron gun 4
Generates a primary electron beam.

The secondary electron detectors 9 and 10 are detectors for detecting secondary electrons. The beam deflectors 17 and 18 are two-stage electromagnetic deflectors that deflect the primary electron beam.

Next, the configuration and operation will be described. The primary electron beam generated by the electron gun 4 is converted into a beam deflector 1
The sample 1 is deflected by two steps, is focused by the objective lens 2, and is irradiated with a finely focused primary electron beam on the sample 1 to scan the surface. Secondary electrons emitted from the sample 1 are detected by a secondary electron detector 9 provided above the objective lens 2 and further deflected by a beam deflector (lower) 18 in a direction opposite to the primary electrons. Is detected by the secondary electron detector 10. The signals detected by the secondary electron detectors 9 and 10 are amplified and displayed as secondary electron images on a display device (not shown).

At this time, two sets of magnetic field type beam deflectors 17 and 18 are provided on the axis to deflect the primary electron beam from the electron gun 4 in two steps, and the axis on the electron gun 4 side and the objective lens 2 The shaft is shifted horizontally by a predetermined distance.

The secondary electrons emitted from the sample 1 and accelerated through the objective lens 2 are converted by the first beam deflector (lower) 18 into secondary electrons deflected in the opposite direction to the primary electrons. Detection is performed by the next electron detector 10.

Further, a bias voltage 21 corresponding to or less than the energy of primary electrons is applied between the objective lens 2 and the sample 1. Therefore, the axis of the primary electron beam is slightly shifted by the deflection coil,
The secondary electrons emitted from the substrate and traveling in the opposite direction are detected by the secondary electron detector 10 provided at the position where the axis is shifted in the opposite direction, so that the secondary electrons can be observed at the time of observing the contact hole or the like of the semiconductor wafer. It is possible to observe a bright secondary electron image with a high S / N ratio while minimizing the loss of secondary electron information.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment and operation of the present invention will be described in detail with reference to FIG. FIG. 1 shows a configuration diagram of one embodiment of the present invention. FIG. 1 is different from the conventional diagram of FIG. 2 in that a beam deflector (upper) 17, a beam deflector (lower) 18, and a primary electron beam 19 are different, and the other components are almost the same. Omitted.

In FIG. 1, the beam deflector (upper) 17,
The beam deflector (lower) 18 includes an irradiation system (here, the electron gun 4).
Further, the axis of the condenser lens 3) and the axis of the objective lens 2 are moved in the horizontal direction by a predetermined distance (for example, a distance of about 2 to 10 mm).

The secondary electrons 16 are supplied to a beam deflector (lower) 18
Shows an example of a trajectory of secondary electrons deflected by the above. Here, when the energy of the secondary electrons 16 and the energy of the primary electron beam 19 are substantially the same, the traveling directions of the two are opposite. The beam is deflected to the left in the figure by 18 and does not go back in the same direction as the primary electron beam 19. This gives 2
Even if the energy of the primary electron 16 and the energy of the primary electron beam 19 are the same, they are separated from each other. In this case, the secondary electron 16 can be detected by the secondary electron detector 10.

In this case, the energy of the secondary electrons 16 is substantially equal to the bias voltage 21 applied to the sample 1, and the bias voltage 21 applied to the sample 1, the energy of the primary electrons to the sample 1, The relationship between the primary electron and the accelerating voltage in the electron gun 4 is, for example, that the energy when the primary electron beam irradiates the sample 1 is 1000 V (accurately, 1000 eV) and the bias voltage 21 is 100
Assuming 0V (the energy of the secondary electrons is accelerated to approximately 1000 eV), the energy when the primary electron beam irradiates the sample 1 is 1000 eV. The bias voltage of the sample 1 is 1000 V. The energy of the secondary electrons 16 : Almost 1000 eV. Energy when the primary electron beam is accelerated and emitted by the electron gun 4: 1000 eV + 1000 eV = 200
0 eV.

Next, the configuration and operation of FIG. 2 will be described in detail. (1) As shown in FIG. 1, the irradiation system (here, the electron gun 4
And an irradiation system including the condenser lens 3) and an image forming system (here, an image forming system including the objective lens 2) are a two-stage electromagnetic beam deflector (upper) 17 and a beam deflector (lower).
18 shifts about 2 to 10 mm in the horizontal direction. (2) When adjusted as in (1), as shown in FIG. 1, the primary electron beam 5 emitted from the electron gun 4 is focused by the condenser lens 3 and the aperture angle is defined by the stop 6. The beam is deflected to the left in FIG. 1 by the beam deflector (upper) 17, and the beam deflector (lower) 18
In FIG. 1, it is bent rightward so that it is incident on the axis of the objective lens 2. Then, an image is formed by the objective lens 2 and the primary electron beam is narrowed down and irradiated onto the sample 1. Thereby, the axis of the condenser lens 3 and
The sample 1 is irradiated with the narrowed-down primary electron beam with the axis of the objective lens 2 shifted from the axis by about 2 mm to 10 mm in the horizontal direction. (3) In the state of (2), secondary electrons are emitted from the sample 1 and accelerated on the axis of the objective lens 2 by the bias voltage 21 so that the energy becomes almost the same as the energy of the primary electron beam. Passing up the axis. Then, some of the secondary electrons 14 are detected by the secondary electron detector 9 through the illustrated orbit. Other secondary electrons 16 pass through the center hole of the secondary electron detector 9 and act in the opposite direction to the primary electron beam 19 (FIG. 1) by the action of the magnetic field of the beam deflector (lower) 18.
(Left direction above) (the traveling direction of the secondary electrons 16 is 1)
Since it is opposite to the traveling direction of the secondary electron beam 19, it is bent leftward in FIG. As a result, since the axis of the irradiation system and the axis of the imaging system are shifted by the two-stage electromagnetic coil by the beam deflector (upper) 17 and the beam deflector (lower) 18, the secondary beam emitted from the sample 1 is shifted. The electron 16 is a beam deflector (lower) 18 in FIG.
Is electromagnetically bent to the left in the area of
Thus, the secondary electrons 16 can be detected without passing through the hole 0, thereby avoiding a situation in which the secondary electrons pass through the hole of the secondary electron detector 10 according to the conventional configuration of FIG. The secondary electron 16 having the same energy as the primary electron beam can be efficiently detected by the secondary electron detector 10.

The beam deflector 7 and the beam deflector 8 are 1
The secondary electron beam 19 is used for secondary scanning on the surface of the sample, and the beam deflector 7 and the beam deflector 8 are used.
2 mm horizontally between the axis of the irradiation system and the axis of the imaging system
At the same time, the current may be supplied so that the primary electron beam is two-dimensionally scanned on the sample 1 at the same time.

[0032]

As described above, according to the present invention,
The axis of the primary electron beam is slightly shifted by an electromagnetic deflection coil, and is emitted from the sample 1 and travels in the opposite direction.
Since a configuration is adopted in which the secondary electrons are detected by the secondary electron detector 10 provided at the position where the secondary electrons are bent in the opposite direction at the portion where the axis is shifted and the secondary electron image is displayed, the bias voltage is substantially applied to the sample 1. Even when the primary electron beam is applied to the same degree or less, the secondary electrons emitted almost parallel to the axis can be efficiently detected, and a secondary electron image with a high S / N ratio can be observed. By these, important information of the sample 1 is transmitted.
Even when the secondary electrons occupy a trajectory substantially parallel to the axis of the primary electron beam, for example, when observing the bottom of a contact hole of a semiconductor wafer, the loss of secondary electron information is minimized. Thus, a bright secondary electron image can be observed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of one embodiment of the present invention.

FIG. 2 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

 1: Sample 2: Objective lens 3: Condenser lens 4: Electron gun 5, 19: Primary electron beam 6: Aperture 7, 8: Beam deflector 9, 10: Secondary electron detector 11, 12: Detection electrode 13 : Lens electrode 14, 16: secondary electron 17: beam deflector (upper) 18: beam deflector (lower) 21: bias voltage 22, 23: amplifier

Claims (4)

[Claims] 1. A scanning electron microscope for displaying secondary electrons generated by scanning a primary electron beam on the surface of a sample and displaying an image, wherein the primary electrons are imaged to form a fine electron beam on the sample. An objective lens for projection; and an opposite side of the objective lens from the sample, having a hole through which the primary electron beam passes, and detecting secondary electrons emitted from the sample, accelerated through the objective lens. A first secondary electron detector, provided on the electron gun side with respect to the first secondary electron detector, and deflects a primary electron beam from the electron gun to form a thin electron beam on a sample via the objective lens. A magnetic field type beam deflector for projecting as a beam, and secondary electrons emitted from the sample and accelerated through the objective lens by the beam deflector and provided on the electron gun side with respect to the beam deflector. In the direction A scanning electron microscope, comprising: a second secondary electron detector arranged and detected at a position to be deflected. 2. The magnetic field type beam deflector according to claim 1, wherein two sets are provided on an axis, and two-stage deflection is performed to shift the axis on the electron gun side and the axis of the objective lens by a predetermined distance in the horizontal direction. The scanning electron microscope according to claim 1, wherein: 3. A secondary electron emitted from a sample and accelerated through an objective lens, the secondary electron deflected in the opposite direction to the primary electron by the first of the two-stage deflections is converted to the second electron. 3. The scanning electron microscope according to claim 2, wherein the detection is performed by a secondary electron detector. 4. A scanning type device according to claim 1, wherein a bias voltage corresponding to or less than the energy of primary electrons is applied between said objective lens 2 and said sample. electronic microscope.