JPH06181041A - Scanning electron microscope - Google Patents

Abstract

PURPOSE:To provide a scanning electron microscope in which the yield of a secondary electron can be increased up to 100% and also aberration can be reduced, thereby making it feasible to perform observation with high resolution. CONSTITUTION:A primary electron beam 1 passes through a deflection coil 7 and then is throw on a sample 3. At that time, a magnetic field made by an objective lens is spread over the sample 3 and the upper space and the primary electron beam 1 is focused to a degree of being several nm in diameter. With the primary electron beam thrown on the sample 3, a secondary electron 2 is emitted from the sample 3 with angular distribution. Since the energy of secondary electron 2 is as low as several eV, the secondary electron 2 is twisted about the magnetic flux of the objective lens 5 to go up as it is making spiral motion. The magnetic flux density abruptly goes down apart from the direction of the sample, and the secondary electron is shaked off from the spiral motion to evaporate and then is deflected with the attracting electric field from a secondary electron detector 4 and is caught by the secondary electron detector 4.

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,
In particular, the present invention relates to a scanning electron microscope for observing a thin plate-shaped sample such as a semiconductor wafer, which is equipped with an objective lens suitable for maintaining high resolution and high sensitivity.

[0002]

2. Description of the Related Art FIG. 2 shows the overall structure of a conventional scanning electron microscope. The primary electron beam 1 from the field emission chip 10 is accelerated by the electric field between this chip 10 and the anode 11. Further, the focusing lens 12, the objective aperture 13 and the intermediate lens 14 adjust the electron current and the spot size. Between the intermediate lens 14 and the objective lens 5, the primary electron beam 1
A two-stage deflection coil 7 for scanning is scanned, and the primary electron beam 1 focused by the objective lens 5 is scanned on the sample 3. A high voltage of about 10 kV is applied to the secondary electron detector 4 to capture the secondary electrons 2 generated on the sample 3. In order to reduce the aberration of the objective lens and obtain high resolution, it is effective to narrow the distance between the objective lens 5 and the sample 3, that is, the so-called working distance, but in such a structure, the secondary electron 2 is the bottom surface of the objective lens 5. Lost to
There is a problem of reduced sensitivity.

In order to avoid this problem, Japanese Patent Laid-Open No. 57-2127
In JP 56, an electrode for reflecting the secondary electrons 2 flying in the direction of the objective lens 5 is installed at the bottom of the objective lens 5 facing the sample 3.

[0004]

In the above-mentioned prior art, the reflected secondary electrons 2 flow back to the sample 3, and particularly in a high-resolution apparatus having a narrow working distance, the sensitivity is hardly improved, or conversely, in some cases. descend.

It is an object of the present invention to improve the sensitivity of secondary electrons and to provide a scanning electron microscope with high sensitivity and high resolution.

[0006]

In order to achieve the above-mentioned object, the present invention installs an objective lens directly below a sample and sets a gap of a magnetic path so that a magnetic field generated by the objective lens is sufficiently strong on the sample. Is placed just below the sample.

[0007]

FIG. 3 shows the structure around the objective lens when the gap of the magnetic path is arranged directly below the sample, that is, on the upper surface, and the calculation result of the axial magnetic flux density distribution on the optical axis. With the 1500 ampere turn, which is similar to the excitation current of conventional objective lenses,
It is about 0.1 Tesla on the sample. This makes the magnetic flux density itself comparable to that of a conventional objective lens, and a sufficient primary electron focusing effect can be obtained. Since the objective lens is installed under the sample in this way, the secondary electrons generated on the upper surface of the sample are captured by the secondary electron detector without obstructing any structure.

[0008]

Embodiments of the present invention will be described below with reference to the sectional view of the secondary electron detection system shown in FIG. After passing through the deflection coil 7, the primary electron beam 1 is irradiated onto the sample 3. At this time, since the magnetic field generated by the objective lens 5 spreads on the sample and the space above it, the diameter of the primary electron 1 is converged to about a nanometer. By irradiation with the primary electron beam 1, secondary electrons 2 are emitted from the sample 3 with an angular distribution. Since the energy of the secondary electron 2 is as low as a few eV, the secondary electron 2 is wound around the magnetic flux of the objective lens 5 and rises while making a spiral motion. The magnetic flux density rapidly decreases when the sample is separated from the surface of the sample, the secondary electrons 2 are swung away from the swirl and diverge, and are deflected by the electric field drawn from the secondary electron detector 4 and captured by the secondary electron detector 4. It In this embodiment, since there is no structure between the sample 3 and the secondary electron detector 4 to block the flight of the secondary electrons 2, the yield of the secondary electrons 2 can be improved to almost 100%.

Next, a second embodiment will be described with reference to FIG. In the previous embodiment, the upper surface of the objective lens 5 was designed to be flat, and the entire surface was in close contact with the sample 3. However, in this embodiment, the shape of the upper surface of the objective lens 5 is convex, and normally only the central portion is formed. Was in close contact with Sample 3. In the observation of the etching pattern on the semiconductor wafer, there is a usage method in which the side surface of the etching pattern is observed by tilting the sample. By using the convex shape as in this embodiment, it is possible to easily realize the observation with the sample tilted. Also in this case, since there is no structure between the sample 3 and the secondary electron detector 4 to block the flight of the secondary electrons 2,
The yield of secondary electrons 2 can be maintained at almost 100%.

[0010]

According to the present invention, the yield of secondary electrons can be improved to almost 100% by moving the objective lens that blocks secondary electrons to the lower part of the sample. Further, since the objective lens magnetic field is maximized on the sample, the aberration is reduced, and high-resolution observation becomes possible. As a result, an apparatus suitable for observing, inspecting, and measuring a large-diameter semiconductor wafer can be realized.

[Brief description of drawings]

FIG. 1 is a sectional view of a secondary electron detection system of a scanning electron microscope according to a first embodiment of the present invention.

FIG. 2 is a sectional view of the overall configuration of a conventional scanning electron microscope.

FIG. 3 is an explanatory diagram of an objective lens and a calculation result of magnetic flux density showing an operation of the present invention.

FIG. 4 is a sectional view of a secondary electron detection system of a scanning electron microscope capable of inclining a sample according to a second embodiment of the present invention.

[Description of Reference Signs] 1 ... Primary electron beam, 2 ... Secondary electron, 3 ... Sample, 4 ... Secondary electron detector, 5 ... Objective lens, 7 ... Deflection coil.

Claims (2)

[Claims] 1. A scan having a secondary electron detector that focuses a primary electron beam from a primary electron irradiation system by an objective lens magnetic field to irradiate a sample and captures secondary electrons generated on the sample by an attracting electric field. In the electron microscope, an objective pole piece for generating the magnetic field of the objective lens and an exciting coil are arranged below a sample, which is a scanning electron microscope. 2. The scanning electron microscope according to claim 1, wherein a surface of the objective pole piece facing the sample is convex and a sample tilting mechanism is provided.