JPH1186770A - Scanning electron microscope - Google Patents

Abstract

[PROBLEMS] To provide a scanning electron microscope which detects secondary signal electrons suitable for retarding and boosting methods by deflecting them from the optical axis. A control electrode is provided between a sample and an objective lens.
0 is inserted to generate an electric field having a non-axisymmetric distribution between the sample 7 and the control electrode 10. Secondary signal electrons 9 generated from sample 7
Is pulled out to the upper part of the objective lens 6, accelerated, and deflected off the optical axis. The secondary signal electrons after the deflection are taken into the detector 11 installed around the optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam apparatus,
In particular, the present invention relates to a scanning electron microscope suitable for observing a sample having a contact hole or a line pattern on the order of submicrons (1 μm or less) at a high resolution.

[0002]

2. Description of the Related Art A scanning electron microscope scans an electron beam emitted from an electron source on a sample and detects secondary electrons and reflected electrons (collectively referred to as secondary signal electrons) which are obtained secondarily. By using this secondary signal as a luminance modulation input of a cathode ray tube which is scanned in synchronization with the scanning of the electron beam, a scanned image (SEM
Image). As described in JP-A-5-266855, as a means for observing a sample with high resolution, the primary electron energy when passing through an objective lens is increased,
A method called retarding or boosting in which the energy is returned to a low level by the deceleration electric field between the objective lens and the sample and the sample is irradiated with the energy is proposed.

In such a method, secondary signal electrons generated from the sample are accelerated by an electric field between the objective lens and the sample and are lifted to the upper part of the objective lens. Therefore, the secondary signal electrons are detected at the upper part of the objective lens. Become. In this case, since the secondary signal electrons travel near the optical axis, it is necessary to deflect the secondary signal electrons from the optical axis in order to detect the secondary signal electrons without affecting the primary electrons. In Japanese Patent Application Laid-Open No. 7-192679, by arranging a Wien filter type orthogonal electromagnetic field on the optical axis, secondary signal electrons are deflected from the optical axis, and the secondary signal is efficiently emitted without adversely affecting the primary electrons. Electrons can be detected.

[0004]

However, the prior art in which the orthogonal electromagnetic field is arranged on the optical axis has a problem that the optical system becomes long and the device becomes large.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a scanning electron microscope capable of deflecting secondary signal electrons from the optical axis while eliminating the above-mentioned disadvantages of the prior art.

[0006]

In order to achieve the above object, in the scanning electron microscope of the present invention, an electric field having a non-axisymmetric distribution is generated between an objective lens and a sample, and secondary signal electrons are generated. The light is deflected from the optical axis, and the deflected secondary signal electrons are detected by a detector arranged outside the optical axis.

That is, according to the characteristic structure of the present invention, the following operation can be obtained.

That is, since a retarding or boosting electric field is applied between the sample and the objective lens between the objective lens and the sample, the secondary signal electrons emitted from the sample are accelerated upward. Since this electric field has an asymmetric distribution, it includes a radial electric field component even on the optical axis, so that the secondary signal electrons are deflected off the optical axis.

[0009]

FIG. 1 is a drawing showing an embodiment of the scanning electron microscope of the present invention.

Voltage V1 applied to cathode 1 and first anode 2
As a result, the primary electron beam 4 emitted from the cathode 1 is accelerated by the voltage Vacc applied to the second anode 3 and proceeds to the subsequent lens system. The primary electron beam 4 is focused as a minute spot on the sample 7 by the objective lens 6 and is two-dimensionally scanned over the sample by the two-stage deflection coil 8.

A control electrode 1 is provided between the sample 7 and the objective lens 6.
0 is inserted to generate an electric field having a non-axisymmetric distribution between the sample 7 and the control electrode 10. Secondary signal electrons 9 generated from sample 7
Is pulled out to the upper part of the objective lens 6, accelerated, and deflected off the optical axis. The secondary signal electrons after the deflection are taken into the detector 11 installed around the optical axis.

FIGS. 2A and 2B show two examples of a method for generating a non-axisymmetric electric field in the scanning electron microscope of the present invention.

In the example shown in FIG. 2A, the control electrode 10 between the sample 7 and the objective lens 6 has a non-axially symmetrical shape on the surface facing the sample. The electric field due to the potential difference Vr-Vc between the sample 7 and the control electrode 10 has a non-axisymmetric distribution indicated by the contour line 21. Since the secondary signal electrons 9 are accelerated in the vertical direction of the contour line 21, they are deflected to the left in the case of FIG. The deflection angle is related to the shape of the control electrode 10 and the distance between the sample 7 and the control electrode 10, but hardly depends on the voltages Vr and Vc between the sample 7 and the control electrode 10. Since the control electrode 10 can be manufactured to be extremely thin as compared with the case where an orthogonal electromagnetic field is generated, the optical system does not increase in size. It is also inexpensive.

In the example shown in FIG. 2B, the control electrode 10 is divided into a plurality of parts with respect to the optical axis, and the voltage applied to each part is made non-axially symmetric. For example, the control electrode 10 is divided into two parts (10a, 10b) on the left and right sides, and voltages of Vca and Vcb are applied respectively. Due to these potential differences Vca-Vcb, a radial electric field is generated, and the secondary signal electrons 9 are deflected off the optical axis. The deflection angle is the voltage Vc of the control electrodes 10a and 10b.
a and Vcb.

FIG. 3 shows a method for adjusting the angle of primary electrons incident on the sample. The non-axisymmetric electric field of the present invention also deflects the primary electrons 4 to a small extent. In the length measurement SEM, the incidence angle of the primary electrons 4 on the sample 7 needs to be fixed vertically in order to secure the length measurement accuracy. Therefore, by adding a tilt function to the sample stage and observing the image, the primary electron 4
The sample angle is controlled so that the light is vertically incident on the sample 7.

[0016]

According to the scanning electron microscope of the present invention, secondary signal electrons are deflected from the optical axis and secondary signal electrons can be detected without affecting the primary electrons, so that high-resolution and high-sensitivity observation is possible. It is. In particular, a high-precision length measuring SEM that generates an electric field between a sample and an objective lens, such as a retarding or boosting method, can be easily and inexpensively incorporated.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a scanning electron microscope shown as one embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating the structure and operation of a control electrode in FIG. 1;

FIG. 3 is an explanatory diagram for explaining a sample tilting function of FIG. 1;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cathode, 2 ... First anode, 3 ... Second anode, 4 ... Primary electron beam, 5 ... Focusing lens, 6 ... Objective lens, 7 ... Sample, 8 ...
Deflection coil, 9 ... secondary signal electrons, 10, 10a, 10b
... control electrode, 11 ... detector, 21 ... equipotential lines.

Claims (5)

[Claims] 1. A scanning electron microscope for scanning a primary electron beam emitted from an electron source on a sample by a deflection coil, extracting secondary signal electrons from the sample by an electric field between an objective lens and the sample, and observing an image. 3. The scanning electron microscope according to claim 1, wherein the secondary signal electrons are deflected from the optical axis and detected by making the electric field between the objective lens and the sample non-axially symmetric. 2. A scanning electron microscope according to claim 1, wherein a non-axisymmetric control electrode is provided between the objective lens and the sample so that the electric field has a non-axisymmetric distribution. . 3. The scanning electron microscope according to claim 1, wherein the electric field has a non-axisymmetric distribution by installing a non-axisymmetric control electrode between the objective lens and the sample. Scanning electron microscope. 4. The scanning electron microscope according to claim 1, wherein a control electrode divided in a circumferential direction is provided between the objective lens and the sample, and a non-axially symmetric voltage is applied to each of the divided control electrodes. A non-axisymmetric distribution. 5. The scanning electron microscope according to claim 1, further comprising means for tilting the sample in accordance with the amount of primary electron deflection caused by the non-axisymmetric electric field distribution between the objective lens and the sample.