JPH05135726A - Electron beam analyzer - Google Patents

Abstract

PURPOSE:To observe a sample in the low build-up state of charges by suppressing the electric field formed by a secondary electron detector, and automatically interlocking the electric field with the work distance. CONSTITUTION:In an electron beam analyzer provided with a secondary electron detector detecting the secondary electrons emitted from a sample when an electron beam is radiated to the sample, horn-like collecting electrodes 21, 22 having flared openings and vertically divided into two are provided in front of the detection face of the secondary electron detector, and the voltage applied to the upper and collecting electrodes 21, 22 is changed interlockingly with the change of the work distance WD between an objective lens 1 and the sample. The electric field generated by the secondary electron detector can be controlled by the control of the voltage applied to the collecting electrodes 21, 22 so that no build-up of charges is generated, and the quality of the observed image is prevented from being deteriorated as the work distance is changed. The shape of the collecting electric field of secondary electrons can be changed when the voltage applied to the collecting electrodes 2, 2 is changed, thus the same control as moving the position of the secondary electron detector can be performed in response to the observation purpose.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art FIG. 8 is a diagram showing a structure of a secondary electron detector used in a conventional scanning electron microscope. 1 is an objective lens, 3 is an insulating ring, 4 is an electrostatic lens, and 5 is an electrostatic lens. Multi-layer scintillator, 6 corona ring, 8 light guide,
9 is an outer cylinder, 10 is a photomultiplier, 13 and 13 'are samples, and 14 and 14' are sample holders.

Conventionally, a secondary electron detector used in a scanning electron microscope is a multi-layer scintillator 5 for detecting secondary electrons and generating fluorescence, as shown in FIG. 8, and a corona ring for producing a strong electric field. 6, the secondary electron is a multilayer scintillator 5
Is composed of an electrostatic lens 4 provided on the outer cylinder 9 for guiding the light to the photomultiplier 9, a light guide 8 for guiding the fluorescence generated by detecting secondary electrons by the multi-layer scintillator 5 to the photomultiplier 10, a photomultiplier 10 for performing photoelectric conversion. The secondary electrons generated from the sample by irradiating the electron beam are collected and detected by the electric field created by the electrostatic lens 4 and the corona ring 6, and are amplified and output from the photomultiplier 10 by the amplifier. Conventionally, such an E / T (Everhart Shornley) detector and its improved type have been mainly used, but when a scanning electron microscope is used for a semiconductor device, the surface of a general insulator sample is There is another problem than observation.

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.

[0005]

As described above, when the chances of observing without vapor deposition with a scanning electron microscope increase, the problem is charge-up, especially when observing a sample such as a semiconductor device. This causes deterioration of the image quality of the observed image.

Further, in the scanning electron microscope, as shown in FIG. 8, the work distance WD between the objective lens 1 and the sample 13 changes according to the resolution as WD1 → WD2, so that the work distance WD changes. It is also a problem that the state of charge-up changes with the change.

That is, in the scanning electron microscope, the sample holder 14 moves in the direction A in the figure like a sample holder 14 'as the resolution is increased. Therefore, the work distance WD between the objective lens 1 and the sample 13 is WD
The length is shortened from 1 to WD2, and the influence of the dielectric action by the electric field E created by the secondary electron detector on the samples 13 and 13 'is strengthened. As shown in the figure, the work distance W is increased as a result of the increased resolution of the sample 13 located at a position that is hardly affected by the dielectric action by the electric field E created by the secondary electron detector.
At D2, the influence of the dielectric action due to the electric field E created by the secondary electron detector is increased, and charge-up occurs on the surface of the sample 13 '.

The present invention is to solve the above-mentioned problems, and suppresses the electric field created by the secondary electron detector, automatically links the electric field with the work distance, and observes the sample in a state where charge-up is small. It is an object of the present invention to provide an electron beam analyzer capable of performing the above.

[0009]

To this end, the present invention provides an electron beam analyzer including a secondary electron detector for detecting secondary electrons emitted from a sample by irradiating the sample with an electron beam. In front of the detection surface of the secondary electron detector, there is provided a trapper-type collecting electrode which has a divergent opening and is divided into upper and lower parts, and a voltage applied to the upper and lower collecting electrodes is applied between the objective lens and the sample. The feature is that it is changed in conjunction with the change of work distance.

[0010]

In the electron beam analyzer equipped with the secondary electron detector according to the present invention, a trapper-type collecting electrode which has a divergent opening in front of the detection surface of the secondary electron detector and which is divided into two vertically is provided. Provided,
Since the voltage applied to the upper and lower collecting electrodes is changed in association with the change in the work distance between the objective lens and the sample, the electric field created by the secondary electron detector is controlled so that the sample is not charged up. be able to.

[0011]

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 showing an example of a scanning electron microscope using the secondary electron detector of the present invention, and FIG. 3 is a work distance and a capture. It is a figure for demonstrating the relationship with the voltage of a collecting electrode.

In FIG. 1, a multilayer scintillator 5 for detecting secondary electrons to generate fluorescence, 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 electron The electrostatic lens 4 provided on the outer cylinder 9 for guiding to the multilayer scintillator 5, the light guide 8 for guiding the fluorescence generated by detecting the secondary electrons by the multilayer scintillator 5 to the photomultiplier 10, and the photomultiplier 10 for photoelectric conversion. Is the same as the configuration provided in the conventional secondary electron detector.

According to the present invention, the outer cylindrical electrostatic lens 4 at the tip of the conventional detector is further provided with the collecting electrodes 2 ₁ , 2 ₂ which are divided into upper and lower parts with the insulating ring 3 interposed therebetween. The shape of the electric field created by the corona ring 6 is configured to be controlled in conjunction with changes in the work distance. The collecting electrodes 2 ₁ , 2 ₂ are so-called trumpet-shaped or frustoconical electrodes having a divergent opening (opening angle α) as shown in the figure, and the upper and lower sides are divided into insulators. An electric field control static control for electrically separating by 11 and connecting to a variable power source (not shown) via a lead wire 12 to apply a voltage to control the shape of the electric field created by the outer cylinder electrostatic lens 4 and the corona ring 6. It is an electric lens. FIG. 2 shows an example of the configuration of an electron microscope using this secondary electron detector.

In the scanning electron microscope, as shown in FIG. 2, an input means such as a keyboard, a joystick, a mouse, a display means such as a display, a storage means for analysis data, and a data processing / analysis control section 33 including a CPU are provided. The data processing / analysis control unit 33 has an electron gun 2
5, a converging lens, a power supply 28 for the converging / deflecting system 26 including a deflection coil, a power supply 29 for the objective lens 24, a collecting electrode 2 ₁ ,
2 ₂ power 30, while controlling the sample drive unit 32 to the sample holder 23 is driven to control the position of the sample 22, the output of the secondary electron detector 27 the observation image acquisition is amplified by the amplifier 31 to the display It is configured to display.

According to the present invention, in the scanning electron microscope having the above-described structure, when the position of the sample 22 is controlled through the sample driving unit 32 when the resolution is adjusted and the work distance is changed, the work distance WD is changed. Then, the collection electrode power supply 30 is controlled. In this case, the work distance WD and the voltage V of the collecting electrodes 2 ₁ , 2 ₂
The relationship between V ₁ and V ₂ is as shown in FIG. 3, and in the collection electrode power source 30, the voltage V of the collection electrodes 2 ₁ and 2 ₂ becomes a quadratic curve as the work distance WD increases.
₁ , V ₂ is changed in the positive direction.

The shape of the electric field without the trumpet-shaped collecting electrodes 2 ₁ , 2 ₂ is close to a spheroid and the major axes are vertical and horizontal directions. The electric field formed in front of the detector has a large diameter and is bright. , The horizontal electric field is weak and in order to make it brighter,
It is necessary to increase the voltage of the multilayer scintillator 5 and the corona ring 6. However, if the electric field is strengthened, the charging of the surface of the sample is promoted, and the purpose cannot be achieved.

Therefore, in the present invention, by providing the trapper type collecting electrodes 2 ₁ , 2 ₂ as described above, the shape of the electric field can be changed without changing the voltages of the multilayer scintillator 5 and the corona ring 6. There is. That is, when applying a collecting electrode 2 ₁ a flared, 2 ₂ to the negative voltage (0 to-200V), the electric field shape in this case, the trumpet-type collecting electrode 2
It is deformed as if it was compressed by ₁ , 2 ₂ . Therefore, by providing the trumpet-type collecting electrodes 2 ₁ , 2 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 collecting electrodes 2 ₁ , 2 ₂ ,
The degree of charging of the sample due to the irradiation of the primary electron beam can be electrostatically neutralized and suppressed, and the trumpet-type collecting electrode 2
_The electrons reflected by ₁ and 2 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 by controlling the voltage of the trumpet-type collecting electrodes 2 ₁ , 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 collecting electrodes 2 ₁ , 2 ₂ between the upper side and the lower side. The shape of the electric field can be controlled according to the purpose of observing the sample.

FIG. 4 is a diagram showing an example of forming an asymmetric electric field with respect to the central axis of the detector, and FIG. 5 is a diagram for explaining voltage adjustment when making the asymmetric electric field.

Depending on the work distance WD, FIG.
In some cases, an electric field asymmetric with respect to the central axis of the detector is required as shown in. For example, when a downward electric field is created with respect to the detector center axis as shown in the figure, the upper collecting electrode 2
Voltage V ₁ of the ₁ increases to the negative voltage side, the voltage V ₂ of the collecting electrode 2 _second lower increases to a positive voltage side. Both of these voltage changes ΔV ₁ and ΔV ₂ can be approximated by a quadratic curve as shown in FIG. You should change the voltage to.

FIG. 6 is a diagram showing an example in which the relationship between the shape of the detector electric field and the trapping voltage is obtained by calculation. The distance Distance (mm) to the tip of 100 V potential and the half width Width (mm) of the globe are shown. It is shown in correspondence with the collection voltage Vc (V), and it can be seen that it can be represented by a quadratic curve. FIG. 7 is a diagram showing an experimental example of the relationship between the work distance WD and the detector output. In order to make the detector output constant when the work distance WD changes in this way, an amplifier for amplifying the detector output may be provided with an auto gain function.

The present invention is not limited to the above embodiment, but various modifications can be made. For example, in the above-described embodiment, 2
Although the applied voltage to the upper and lower collecting electrodes 2 ₁ , 2 ₂ is automatically changed by the following curve, the shape of the electric field may be changed by individually determining the voltage value. 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, in the case of a sample in which a metal or a conductive substance is vapor-deposited, it is better to turn off the power of the trumpet-type collecting electrode or set it to a positive voltage (several V). Further, collection electrodes having different opening angles 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. May be used.

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

[0024]

As described above, according to the present invention, there is provided a trumpet type collecting electrode having a divergent opening in front of the detection surface of the secondary electron detector and divided into an upper side and a lower side. Provided,
Since the voltages applied to the upper and lower sides of the collecting electrode are changed in association with the change in the work distance between the objective lens and the sample, the electric field created by the secondary electron detector is prevented so that the sample is not charged up. Can be controlled, and the image quality of the observed image can be prevented from deteriorating with a change in the work distance. Further, since the shape of the collecting electric field of the secondary electrons can be changed by changing the voltage applied to the collecting electrode, the same control can be performed by moving the position of the secondary electron detector according to the purpose of observation. it can.

[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 showing an example of a scanning electron microscope using the secondary electron detector of the present invention.

FIG. 3 is a diagram for explaining a relationship between a work distance and a voltage of a collection electrode.

FIG. 4 is a diagram showing an example of forming an electric field asymmetric with respect to the central axis of the detector.

FIG. 5 is a diagram for explaining voltage adjustment when creating an asymmetric electric field.

FIG. 6 is a diagram showing an example in which the relationship between the shape of the detector electric field and the trapping voltage is calculated.

FIG. 7 is a diagram showing an experimental example of the relationship between the work distance WD and the detector output.

FIG. 8 is a schematic diagram of 2 used in a conventional scanning electron microscope.
It is a figure which shows the structure of a secondary electron detector.

[Explanation of symbols]

1 ... Objective lens, 2 ₁ , 2 ₂ ... Trumpet type collecting electrode, 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 (1)

[Claims] 1. An electron beam analyzer provided with a secondary electron detector for detecting secondary electrons emitted from a sample by irradiating the sample with an electron beam, in front of a detection surface of the secondary electron detector. A trumpet-type collecting electrode having a divergent opening and divided into upper and lower parts is provided, and the voltage applied to the upper and lower collecting electrodes is changed in association with the change in the working distance between the objective lens and the sample. An electron beam analyzer characterized in that