JP2000299078A - Scanning electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a scanning electron microscope device with a simple structure capable of separately detecting secondary electrons and reflected electrons from a sample on an electron beam axis. SOLUTION: This device has an electron beam source; an electron beam acceleration means for accelerating primary electrons generated from the electron beam source; a deflector 5 for scanning and deflecting the accelerated primary electrons; electrostatic magnetic field composite object lenses 2, 3 for converging the deflected and scanned primary electrons onto a sample 4 placed on a sample base; a reflected electron detector 10 for detecting reflected electrons generated from the sample 4 by the primary electrons converged and irradiated onto the sample 4; a secondary electron detector 20 for detecting secondary electrons generated from the sample 4 by the primary electrons converged and irradiated onto the sample 4; and an image display means for displaying an image of the sample 4 according to the detection signals from the respective detectors 10, 20. The reflected electron detector 10 is formed with an opening part 17 for passing the electron beams and the secondary electrons, while the opening part 17 is disposed on the same axis as the electron beams.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention converges an electron beam on a sample and scans the sample, detects reflected electrons and secondary electrons generated from the sample, and forms a two-dimensional scan image of the sample based on the detected signals. The present invention relates to a scanning electron microscope apparatus for displaying on an image display device such as a cathode ray tube (CRT display device) and measuring the surface shape and the like of a sample with high resolution and high resolution.

[0002]

2. Description of the Related Art Conventionally, a scanning electron microscope has been used for observing a circuit pattern of a submicron order and a shape of a contact hole on a sample such as a semiconductor device such as an LSI.

In recent years, as the degree of integration of semiconductor devices has increased, the size of circuit patterns and contact holes formed on a sample has also been reduced, and the height of a scanning electron microscope apparatus for observing their shapes has increased. Higher resolution is required.

As a method for improving the resolution of such a scanning electron microscope apparatus, a lens having a deceleration field, such as an electrostatic field compound objective lens composed of an electrostatic lens and a magnetic lens, is used as an objective lens. Along with
By shortening the distance (working distance) between the tip of the objective lens and the sample, the aberration of the objective lens is suppressed as much as possible.

[0005] In such an apparatus, a secondary electron generated from the sample due to a primary electron beam irradiated on the sample is usually detected by a detector to obtain a scanned image. Disposing the compound objective lens near the sample, causing discharge etc. under the influence of the deceleration field of the electrostatic magnetic field compound objective lens formed near the sample, and disturbing the deceleration field by disposing the detector This may impair optical performance.

For these reasons, in the conventional electron microscope apparatus, it is necessary to dispose the detector at a position away from the electrostatic magnetic field compound objective lens.

Further, when observing the shape of the bottom surface of a contact hole or the like having a large aspect ratio (a depth dimension is larger than a width dimension) on a sample, secondary electrons generated from the bottom face of the contact hole have the same energy. Is small, it is difficult to observe the contact hole with secondary electrons because it collides with the inner wall in the contact hole and does not come out of the sample surface.

[0008] Therefore, observation of such a place is being performed only by reflected electrons.

In an objective lens with a deceleration field, such as the above-mentioned electrostatic field compound objective lens, secondary electrons generated from the sample are accelerated by the deceleration field formed by the electrostatic field compound objective lens. Energy is increased. For this reason, with the conventional detection method, detection has become more difficult.

In response to this, as shown in FIG. 6, a Wien filter 6 combining an electric field and a magnetic field on the optical axis to detect reflected electrons 9 and secondary electrons 7 generated from the sample 4. A method has been devised in which only electrons having a specific energy are guided out of the optical axis, a potential is applied near the detector, and reflected electrons and secondary electrons are drawn toward the detector. Here, 1 is a secondary electron detector, 2 is a magnetic lens, 3 is an electrostatic lens, 4 is a sample, and 5 is a deflection coil.

As another conventional method, as shown in FIG. 7, secondary electrons 7 accelerated in the deceleration field collide with another target 8 and secondary electrons generated from the target 8 are irradiated with light. A method of pulling in the detector 1 arranged off-axis is performed. In FIG. 7, each member is denoted by the same reference numeral as that shown in FIG.

[0012]

However, in the above-described method using the Wien filter 6 (FIG. 6), an electromagnetic field for correction is considered in consideration of the influence of the Wien filter 6 on the primary electron beam. It is necessary to overlap,
There is a problem that aberrations are worsened.

In the latter method of colliding with a target (FIG. 7), the intensity of a detectable signal is compared with the intensity of a signal when secondary electrons generated from the sample are directly detected by a detector. Thus, there is a problem that the size becomes extremely small.

As described above, a scanning image by reflected electrons is used for observing the bottom surface of the contact hole having a high aspect ratio, and some of the reflected electrons collide with the inner wall in the contact hole. Then, secondary electrons are generated from the inner wall.

As described above, in the conventional method, it is difficult to separate the reflected electrons and the secondary electrons. Therefore, when observing the bottom image of the contact hole, the reflected electron image and the secondary electron image are mixed. And the obtained image quality is degraded.

Accordingly, the present invention provides a scanning electron microscope apparatus in which a reflected electron and a secondary electron from a sample can be separated on the electron beam axis, detected independently, and a good image can be obtained in a device having a simple structure. The purpose is to provide.

[0017]

In order to solve these problems, the present invention provides an electron beam source, an electron beam accelerating means for accelerating the primary electrons generated by the electron beam source, and scanning the accelerated primary electrons. A deflector that deflects, an electrostatic field compound objective lens that focuses the primary electrons that have been deflected and scanned on the sample placed on the sample stage, and a reflected electron generated from the sample by the primary electrons that are converged and irradiated to the sample. A backscattered electron detector for detecting
A scanning type including a secondary electron detector that detects secondary electrons generated from a sample by primary electrons that are converged and irradiated on the sample, and image display means that displays a sample image based on a detection signal from each detector. In the electron microscope, the reflected electron detector is provided with an opening for passing an electron beam and secondary electrons, and the scanning electron microscope is characterized in that the opening is arranged coaxially with the electron beam. I do.

The present invention also provides a scanning electron microscope in which the secondary electron detector is coaxial with an electron beam and arranged between the reflected electron detector and the electron beam source.

According to the present invention, the image display means forms a sample image by performing arithmetic processing based on the respective signals detected by the secondary electron detector and the reflected electron detector. .

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments will be described below in detail with reference to the drawings. FIG. 1 is a schematic view of an example of a scanning electron microscope according to the present invention. In FIG. 1, 2 is a magnetic field lens as an objective lens, 3 is an electrostatic lens as an objective lens, 4 is a sample, 5 is a deflection coil as a deflector, 7 is a locus of a secondary electron beam, and 9 is a reflected electron beam. Locus, 10 is a backscattered electron detector, 2
0 is a secondary electron detector, 12 is a signal processor, 13 is CR
4 shows a T monitor.

The primary electrons generated by the electron gun are accelerated by electron beam acceleration means and scanned and deflected by the deflection coil 5. The primary electron beam that has been deflected and scanned is narrowly converged on the surface of the sample 4 by a not-shown condenser lens, an objective lens including a magnetic lens 2 and an electrostatic lens 3.
The converged electron beam is scanned over the sample by the deflection coil 5. By irradiating and scanning the sample with an electron beam, reflected electrons and secondary electrons are generated from the sample. These reflected electrons and secondary electrons fly above the sample 4 under the influence of the electromagnetic field created by the objective lens.

FIG. 5 schematically shows a trajectory 9 of reflected electrons and a trajectory 7 of secondary electrons generated from the sample 4. The reflected electrons having a large energy travel along the trajectory 9 without being greatly affected by the electromagnetic field due to the objective lens. However, the secondary electrons having a small energy are strongly influenced by the electromagnetic field due to the objective lens. It was confirmed by simulation that the trajectory was drawn so as to pass near the optical axis because it was bent in the direction of the optical axis.

The above-mentioned simulation will be described in detail. In the scanning electron microscope shown in FIG. 1, an electron optical system having a deceleration field such as an electrostatic magnetic field compound lens in which a magnetic lens 2 and an electrostatic lens 3 are combined was formed. In this electron optical system, computer simulation was performed to determine the trajectories of reflected electrons and secondary electrons emitted from the sample irradiated with the electron beam.

According to the result, as shown in FIG. 5, the reflected electrons having substantially the same energy as the incident primary electron beam are hardly affected by the deceleration field, so that the trajectory that goes straight in the emitted direction is not affected. On the other hand, it became clear that secondary electrons with low energy take a trajectory that winds around the optical axis because they are strongly affected by the deceleration field.

From these results, considering the cross section of the backscattered electron orbit and the secondary electron orbit in a plane perpendicular to the optical axis, the backscattered electron orbit has an intersection with this plane at a position away from the optical axis. It can be seen that it is possible to find the position of a plane where the trajectory of the secondary electron has an intersection with this plane near the optical axis.

FIG. 2 shows the position of the backscattered electrons colliding with the detector when the detectors shown in FIGS. 3, 4 and 5 are arranged on a plane satisfying such conditions. This is a schematic representation based on the calculation results in.

FIGS. 3 and 4 show the backscattered electron detector 10. FIG. The backscattered electron detector 10 is generally used for a scanning electron microscope. The backscattered electron detector 10 includes a detector 14 including a scintillator disposed at the tip of the detector, a light guide 15, and a PMT (not shown). tube)
Etc. In this example, an opening 17 formed at a position corresponding to the electron beam optical axis of the detection unit 14 allows a secondary electron beam to sufficiently pass therethrough, and a detection device capable of detecting reflected electrons from the sample around the opening 17. The main body 18 is provided.

The arrangement position of the backscattered electron detector 10 and the size and shape of the opening 17 formed in the detector 10 are as follows.
Since it is considered that the shape differs depending on the shape of the lens, the optimum shape is determined based on the result of the simulation.

The optimal shape of the backscattered electron detector 10 can be, for example, a size of a numerical aperture mm provided at the tip of the detector.

As described above, the present invention utilizes the difference between the reflected electron trajectory generated from the sample and the secondary electron trajectory to separate and detect the reflected electron and the secondary electron with the detector arranged on the optical axis. I can do it.

FIG. 2 shows that when the secondary electron detector 10 is disposed at an arbitrary height from the surface of the sample 4 and reflected electrons are detected when viewed from a direction perpendicular to the electron beam optical axis. Is a diagram schematically illustrating a position where the vehicle collides with the data based on the result of the simulation. The secondary electrons (not shown in FIG. 2) draw a trajectory that passes through a location near the optical axis, and therefore pass through an opening 17 opened at the center of the detector.

As described above, by finding, from the result of the simulation, a place where the reflected electrons and the secondary electrons generated from the sample 4 are coaxially separable from each other, the reflected electrons and the secondary electrons are coaxially separated. It was confirmed that could be separately detected. At this time, the size of the opening 17 of the backscattered electron detector 10 disposed at the tip of the detector and the distance (d) from the sample position of the detector shown in FIG. 1 differ depending on the lens shape. Must be determined based on

The same applies to the backscattered electron detector 20. The structures of the detector and the like shown in FIGS. 1, 3, and 4 are shown for convenience of description, and are not limited to the illustrated shapes.

[0034]

As described above, according to the scanning electron microscope apparatus of the present invention, reflected electrons and secondary electrons generated from a sample can be effectively separated and detected coaxially.
The image quality of the secondary electron image can be improved, and the reflected electron image can clearly observe the bottom surface of a contact hole or the like having a large aspect ratio.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a scanning electron microscope device according to the present invention.

FIG. 2 schematically shows the trajectory of backscattered electrons supplemented by a backscattered electron detector.

FIG. 3 is a perspective view showing a backscattered electron detector used in the present invention.

FIG. 4 shows the scintillator portion of the detector shown in FIG.
FIG. 4 is an enlarged sectional view taken along line IV-IV.

FIG. 5 is a schematic diagram of reflected electrons and secondary electron orbits generated from a sample.

FIG. 6 is a diagram showing an example of a scanning electron microscope using a Wien filter based on a conventional technique.

FIG. 7 is a diagram illustrating a case where secondary electrons generated from a sample are made to collide with another target and secondary electrons are detected.

[Explanation of symbols]

 Reference Signs List 2 magnetic field lens 3 electrostatic lens 4 sample 5 deflection coil 6 Wien filter 7 orbit of secondary electron 9 orbit of reflected electron 10 reflected electron detector 12 signal processing circuit 13 CRT monitor 14 detector detector 15 light guide 20 secondary Electronic detector

Claims (3)

[Claims] An electron beam source; an electron beam accelerating means for accelerating primary electrons generated by the electron beam source; a deflector for scanning and deflecting the accelerated primary electrons; An electrostatic field compound objective lens that focuses on the mounted sample, a backscattered electron detector that detects reflected electrons generated from the sample by the converged primary electrons that irradiate the sample, and a primary electron that converges and irradiates the sample In a scanning electron microscope comprising a secondary electron detector for detecting secondary electrons generated from a sample by electrons and an image display means for displaying a sample image based on a detection signal from each detector, the reflected electron detection is performed. A scanning electron microscope, wherein an opening for passing an electron beam and secondary electrons is provided in a vessel, and the opening is arranged coaxially with the electron beam. 2. The scanning electron microscope according to claim 1, wherein said secondary electron detector is arranged on the same axis as an electron beam and between said reflected electron detector and said electron beam source. . 3. The image display means according to claim 1, wherein said image display means forms a sample image by performing arithmetic processing based on respective signals detected by said secondary electron detector and said reflected electron detector. The scanning electron microscope according to claim 2.