JPH0562634A - Secondary electron detector and electron-beam analyzer - Google Patents

Abstract

PURPOSE:To provide a secondary electron detector capable of suppressing electric charge on a sample surface under a low level of acceleration voltage and enhance the detection performance with a simple structure without moving the detector. CONSTITUTION:In a secondary electron detector and electron beam analyzer intended to detect a secondary electron emitted from a sample by radiating the sample with an electron beam, bugle-shaped electrostatic lenses 2, 2' having forwardly flared openings are disposed in front of a secondary electron detector surface upon which the secondary electron being detected is incident. By varying the voltage being applied, change is made of the configuration of an electric field focusing the secondary electron onto the secondary electron detection surface. Besides, by separating the bugle-shaped electrostatic lenses in the upper and lower parts, voltage is separately applied. By this, a similar effect to that attainable with frontward/backward movements of the detector can be obtained through control of the applied voltage to the bugle-shaped electrostatic lenses 2, 2'. This control of the applied voltage makes it possible to suppress the electric charge on the sample surface under a low level of acceleration voltage to enhance the detection performance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary electron detector and an electron beam analyzer for detecting secondary electrons emitted from a sample by irradiating the sample with an electron beam.

[0002]

2. Description of the Related Art FIG. 5 is a view showing a structure of a conventional secondary electron detector, 3 is an insulating ring, 4 is an electrostatic lens, 5 is a multilayer scintillator, 6 is a corona ring, 8 is a light guide, and 9 is a light guide. Is an outer cylinder, and 10 is a photomultiplier.

Conventionally, a secondary electron detector used in a scanning electron microscope is a multi-layer scintillator 5 for detecting secondary electrons, a corona ring 6 for producing a strong electric field, and a secondary electron as shown in FIG. The electrostatic lens 4, photomultiplier 10, provided on the outer cylinder 9 for guiding the
The E / T (Everhart Shornley) detector consisting of a light guide 8 for guiding the fluorescence generated by detecting the secondary electrons by the multi-layer scintillator 5 to the photomultiplier 10 and its improved type were the mainstream. Since microscopes have been used for semiconductor devices, a problem different from general surface observation of insulator samples has occurred.

When observing the surface of an insulator sample with a scanning electron microscope, a conductive substance such as gold or carbon is vapor-deposited so that the sample surface is not charged. Therefore, I was watching the surface of evaporated gold or carbon, not the actual surface. However, if these are vapor-deposited on the surface of a semiconductor device like a general insulator, the physical properties change,
In semiconductor devices, it has been required to observe the surface morphology with high fidelity by reducing current with a low accelerating voltage without vapor deposition. This technology is also a technology that minimizes electrostatic charges when non-destructively observing uncoated materials.

However, the beam current of picoampere required for nondestructive observation deteriorates the performance of the detector as described above unless some measures are taken. That is, in the picoampere beam current under a low accelerating voltage, the amount of secondary electrons also becomes picoampere, so the sensitivity of the detector is significantly lowered, and the detection signal is buried in the thermal noise of the photomultiplier, I will no longer use it.

Therefore, the diameter of the detector is increased, the diameter of the corona ring is increased, a higher voltage is applied to the scintillator than before, and the detector is moved closer or farther depending on the sample (for example, "Electron Microscope" Vol. 24, No. 2
(1989), pages 107 to 114, "Development and practical use of high-resolution scanning electron microscope equipped with field emission electron gun", page 110, left column), and the like.

Further, in order to improve the trapping efficiency of low-energy secondary electrons, a secondary electron detector provided with a reflector grid at the bottom to apply a negative potential to forcibly raise the trajectory of the secondary electrons ( (JP-A-1-124949)
Alternatively, the applicant of the present invention arranged a front electrode between the secondary electron detection surface and the sample, and changed the lens electric field formed between the outer electrode and the outer cylinder electrode to control the secondary electron detection efficiency. A secondary electron detection device (Japanese Utility Model Laid-Open No. 59-148043) has been proposed.

[0008]

However, in each of the above countermeasures, the electric field of the detector spreads, the reflected electrons are taken in, the primary electron beam is deflected, and new astigmatism occurs. Causes a problem, such as a cause that causes a strong electric field to accelerate the charging of the sample, an increase in discharge and noise, a movement mechanism of the detector is required, etc. The current situation is that it has not yet reached.

Therefore, in the conventional secondary electron detector and its improved type, in a semiconductor device which is required to observe the surface morphology with high magnification and high fidelity, a low acceleration voltage (3 kV or less) without coating, Low current (10p
It was difficult to meet such a request in (A or less).

The present invention solves the above-mentioned problems, and suppresses the charging of the sample surface under a low accelerating voltage without moving the detector up and down and back and forth with the addition of a simple structure. It is an object of the present invention to provide a secondary electron detector capable of increasing the temperature.

[0011]

Therefore, according to the present invention, a secondary electron detector and an electron beam analyzer which detect secondary electrons emitted from a sample by irradiating the sample with an electron beam are detected. A trumpet type electrostatic lens having a divergent opening is arranged in front of the secondary electron detection surface on which the secondary electrons are incident, and by changing the applied voltage, an electric field for focusing the secondary electrons on the secondary electron detection surface. It is characterized in that the shape is changed and the trumpet-type electrostatic lens is divided into an upper side and a lower side to individually apply a voltage.

[0012]

In the secondary electron detector and electron beam analyzer of the present invention, a trumpet type electrostatic lens having a divergent opening is arranged in front of the secondary electron detection surface on which the secondary electrons to be detected are incident, By changing the applied voltage, the shape of the electric field that focuses the secondary electrons on the secondary electron detection surface is changed, so the same effect as moving the detector back and forth can be achieved by controlling the applied voltage of the trumpet type electrostatic lens. By controlling the applied voltage, it is possible to suppress the charging of the sample surface under a low acceleration voltage and enhance the detection performance.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a secondary electron detector of the present invention, FIG. 2 is a diagram of the shape of an electric field obtained by the secondary electron detector of the present invention by the surface charge method, and FIG. 3 is a conventional secondary electron detector. It is a figure which calculated | required the shape of the electric field by an electron detector by the surface charge method. These electric field shapes are the optical axis (center) of a secondary electron detector.
Shows the upper half. FIG. 4 is a diagram showing the voltage characteristics of the electrostatic lens.

In FIG. 1, a multilayer scintillator 5 for detecting secondary electrons, a corona ring 6 for producing a strong electric field, an electrode 7 for applying a voltage of 10 kV ± 2 kV to the corona ring 6, and a secondary scintillator 5 for secondary electrons. Electrostatic lens 4, photomultiplier 10, provided on the outer cylinder 9 to guide the
The light guide 8 that guides the fluorescence generated by detecting the secondary electrons by the multilayer scintillator 5 to the photomultiplier 10 has the same structure as the conventional detector. The present invention is
In order to efficiently capture the secondary electrons, so-called trumpet-type electrostatic lenses 2 and 2 ′ are provided by further sandwiching an insulating ring 3 on an outer cylindrical electrostatic lens 4 at the tip of the conventional detector, and the outer cylindrical electrostatic lens 4 is provided.
And the shape of the electric field created by the corona ring 6 is controlled.

The trumpet type electrostatic lenses 2 and 2'are so-called trumpet type or frustoconical electrodes having a divergent opening (opening angle α) as shown in the figure, and the upper side and the lower side are divided. Then, it is electrically separated by an insulator 11 and connected to a variable power source (not shown) via a lead wire 12, and a voltage is applied to change the shape of the electric field created by the outer cylinder electrostatic lens 4 and the corona ring 6. It is an electric field control electrostatic lens to control.

In the above-mentioned structure, the primary electron beam of low current (10 pA or less) at low acceleration of 3 kV or less is focused on the sample through the objective lens 1, and the sample is suppressed to a minimum charge to generate secondary electrons. Of the secondary electrons generated from the sample, those with high energy escape upward as reflected electrons. However, the secondary electrons having low energy are attracted by the (+) electric field created by the outer cylindrical electrostatic lens 4, the corona ring 6, and the multilayer scintillator 5 toward the multilayer scintillator 5, and the outer cylindrical electrostatic lens 4 and the corona It is converged at the center of the multi-layer scintillator 5 along the electric field created by the ring 6 and converted into fluorescence.

At this time, the trumpet type electrostatic lenses 2, 2 '
As shown in Fig. 3, the shape of the electric field without is a spheroid, the major axis is vertical / horizontal direction, and the electric field formed in front of the detector has a large aperture and is bright, but the horizontal electric field is weak.
In order to make it brighter, it is necessary to increase the voltages of the multilayer scintillator 5 and the corona ring 6. If the electric field is strengthened, the charge on the surface of the sample is promoted, and the purpose cannot be achieved.

In the present invention, the trumpet type electrostatic lenses 2, 2 '.
Is provided, the shape of the electric field is changed without changing the voltages of the multilayer scintillator 5 and the corona ring 6. That is, the shape of the electric field without the trumpet-type electrostatic lenses 2 and 2'is as shown in FIG. 3, whereas the negative voltage (0 to -20) is applied to the trumpet-type electrostatic lenses 2 and 2 '.
0 V), the shape of the electric field in the case of providing the trumpet type electrostatic lenses 2, 2'as shown in FIG. 2 is deformed as if compressed by the trumpet type electrostatic lenses 2, 2 '.
Therefore, by providing the trumpet type electrostatic lenses 2 and 2 ', the major axis direction of the spheroid can be changed to the optical axis direction and the strength of the electric field can be changed. Moreover, by applying a negative voltage to the trumpet-type electrostatic lenses 2 and 2 ', it is possible to electrostatically neutralize and suppress the charging degree of the sample due to the irradiation of the primary electron beam. The electrons reflected by the lenses 2 and 2'reduce or average the charged portion of the sample. Therefore, it is possible to electrically operate the detector as if the entire detector is moved closer or farther from the voltage control of the trumpet type electrostatic lenses 2, 2 '.

The angle of the electric field in the optical axis direction can be changed by changing the value of the negative voltage applied to the trumpet type electrostatic lenses 2, 2'on the upper side and the lower side. The shape of the electric field can be controlled according to the purpose. Moreover, since this operation can be linked with the acceleration voltage and can be corrected according to the degree of charging of the sample, it is possible to follow a minute change in charging.

The present invention is not limited to the above embodiment, but various modifications can be made. For example, in the above embodiment, the trumpet type electrostatic lens is divided into the upper and lower parts, but it may be integrated. In the configuration in which the upper side and the lower side are electrically separated, the upper and lower applied voltages are changed at a constant ratio according to the change of the working distance of the objective lens, the position of the sample, the purpose of sample observation, etc. The value of may be determined to change the shape of the electric field. Further, depending on the purpose of observation, it may be used in a mode in which no voltage is applied or in a mode in which a positive voltage is applied. For example, it is better to turn off the power of the trumpet type electrostatic lenses 2 and 2'or to set a positive voltage (several V) in the case of a sample in which a metal or a conductive substance is vapor-deposited. Further, an electrostatic lens having a different opening angle α may be used depending on the dielectric constant of the sample to be observed. That is, as the dielectric constant decreases, the degree of charging also decreases,
When observing a sample on which a metal or a conductive substance is vapor-deposited, an electrostatic lens having a smaller opening angle α may be used as compared with the case of observing an insulator sample.

Furthermore, even in the case of high acceleration and large current as in EPMA and Auger analysis, it is possible to apply a negative voltage to apply a brake and to make the amount of signal obtained by the detector appropriate.

The secondary electron detector of the present invention can also be applied to an ion beam semiconductor processing machine and an electron beam drawing apparatus.

[0023]

As described above, according to the present invention, the trumpet type electrostatic lens is attached in front of the secondary electron detector to change the shape of the electric field created by the multilayer scintillator 5 and the corona ring 6. Since it is possible to obtain an electric field shape intensity that matches the purpose of observing the sample, it is necessary to minimize the charging of the sample that is not coated with secondary electrons generated by the electron beam of low acceleration and low current, and obtain it as a signal with good S / N. The surface morphology of the sample can be observed nondestructively with high fidelity. At that time, a similar effect can be obtained by changing the voltage applied to the trumpet type electrostatic lens in conjunction with, for example, the acceleration voltage without mechanically moving the detector closer or farther as in the conventional proposal. it can.

Further, by interlocking the acceleration voltage and the operation of the trumpet type electrostatic lens, it is not necessary to move the detector with respect to the change of the acceleration voltage, so that the mechanically moving part can be eliminated. Moreover, since the operation of the trumpet-type electrostatic lens can be minutely corrected according to the degree and change of the charge of the sample, it can be applied to various samples.

Further, by dividing the trumpet type electrostatic lens into the upper and lower parts, the upper and lower voltages can be selected according to the working distance of the objective lens.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a secondary electron detector of the present invention.

FIG. 2 is a diagram in which a shape of an electric field by a secondary electron detector of the present invention is obtained by a surface charge method.

FIG. 3 is a diagram in which a shape of an electric field by a conventional secondary electron detector is obtained by a surface charge method.

FIG. 4 is a diagram showing voltage characteristics of an electrostatic lens.

FIG. 5 is a diagram showing a configuration of a conventional secondary electron detector.

[Explanation of symbols]

1 ... Objective lens, 2 and 2 '... Trumpet type electrostatic lens, 3
... Insulation ring, 4 ... Electrostatic lens, 5 ... Multilayer scintillator, 6 ... Corona ring, 7 ... Electrode, 8 ... Light guide,
9 ... Outer cylinder, 10 ... Photomultiplier, 11 ... Insulator,
α ... Aperture angle

Claims (3)

[Claims] 1. A secondary electron detector for detecting secondary electrons emitted from a sample by irradiating the sample with an electron beam, wherein the secondary electron to be detected spreads in front of a secondary electron detection surface. Secondary electron detection by arranging a trumpet type electrostatic lens having an opening and changing the applied voltage so as to change the shape of the electric field that focuses the secondary electrons on the secondary electron detection surface. vessel. 2. The secondary electron detector according to claim 1, wherein the trumpet type electrostatic lens is divided into an upper side and a lower side to individually apply a voltage. 3. An electron beam analyzer for observing the surface of a sample for detecting secondary electrons emitted from the sample by irradiating the sample with an electron beam, and a secondary electron detection surface on which secondary electrons to be detected are incident. A secondary electron detector in which a trumpet-type electrostatic lens having a divergent opening is arranged in front of the secondary electron detector is used, and the secondary electron is detected on the secondary electron detection surface by changing the voltage applied to the trumpet-type electrostatic lens. An electron beam analyzer characterized in that the shape of an electric field for focusing the beam is changed.