JPH02236939A - Scanning type electron microscope - Google Patents

Abstract

PURPOSE:To make it possible to observe a good image of a sample with resolution faithful to an electron beam spot by installing a secondary electron detector in a gas sealing chamber distant from a position to be irradiated with an electron beam more than the operational distance of an objective lens, and surrounding the secondary electron detector by a secondary electron reflection member. CONSTITUTION:An electron beam locus 4 is deflected by deflectors 10 and 11, and passes through an opening of a pressure restriction member 9 so as to scans a sample target 12. Secondary electrons emitted out of the target 12 repulsively move to a secondary electron detector 6 due to a negative voltage applied to the pressure restriction member 9. The secondary electron collide with gas on their way to increase their number. The secondary electrons are therefore incident to the positively charge electrode of the 6 without being trapped by a secondary electron reflection electrode 7 and a reflected electron shielding electrode 8 having negative potential 8. The electrode of the detector 6 is made of Be and is formed in wedge-shaped on its surface so that distributed noise due to re-reflected electrons, etc., is rarely produced when the secondary electrons are incident thereto.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a scanning electron microscope equipped with a gas-filled chamber. [Prior Art] Conventional devices of this type include an electron beam source that emits an electron beam into a vacuum chamber provided with a pressure limiting member having a pressure limiting hole, and a device that directs and focuses the emitted electron beam on a sample. and a scanning device configured to scan the electron beam emitted from the electron beam source through the pressure restriction hole and beyond its diameter, the scanning device being located outside the vacuum chamber and configured to control the pressure restriction of the pressure restriction member. A gas-filled chamber having a sample stage therein capable of holding the sample in alignment with the hole, exposing the surface of the sample to the electron beam emitted from the electron beam source and directed through the pressure-limiting hole. Furthermore, the secondary electrons emitted by the electron beam irradiation from the sample placed on the sample stage collide with the gaseous medium, causing the gas molecules to emit secondary electrons again. Scanning electron microscopes are known which are provided with a detector capable of detecting the secondary electrons emitted by the secondary electrons.

Additionally, the detector is usually placed between the pressure limiting hole and the sample. [Problems to be Solved by the Invention] In the conventional technology as described above, in order to improve the irradiation efficiency of the electron beam, it is necessary to prevent the electron beam from becoming thicker due to scattering in the gaseous medium, reduce lens aberration, etc. For improvement, measures are taken to shorten the working distance of the objective lens.

However, since the secondary electron detector exists between the objective lens and the sample, the distance between the sample and the detector naturally becomes shorter. Therefore, the contact between the secondary electrons from the sample and the gaseous medium is reduced, and sufficient interaction does not take place, making it difficult to obtain a large secondary electron signal.
Even if the lens aberration was reduced, the resolution of the observed sample image did not improve much because the secondary electrons easily entered the detector. Furthermore, even if an attempt is made to efficiently absorb the secondary electrons emitted from the sample by the irradiation of the electron beam into the detector, the secondary electron detector is placed between the objective and the sample as described above. However, it has the disadvantage that it is difficult to deal with it due to its limitations. The purpose of the present invention is to irradiate a sample with a high-resolution electron beam and make the secondary electrons emitted from the sample sufficiently collide with the gaseous medium, so that more secondary electrons can be delivered to the secondary electron detector. By efficiently absorbing electrons and preventing backscattered electrons from entering the secondary electron detector, this scanning type has a fast signal response time and can observe a good sample image with a resolution that is faithful to the electron beam spot. Our purpose is to provide electronic 8Ji microscopes. [Means for Solving the Problems] For the above purpose, the present invention provides an electron beam source (not shown) and an electron beam (4) emitted from the electron beam source to direct the sample (
5) The electron beam is focused by the objective lenses (1), (2), (3) and the deflectors (10), (11), etc. which deflect the electron beam (4) and scan it on the sample (5). A vacuum chamber (20) that enables line scanning in a vacuum state, and the electron beam (4)
The sample (5) is irradiated with a sample stage (not shown) that holds the sample (5) in correspondence with the focal position of the electron beam (4).
a gas-filled chamber (21) containing a detector (6) for detecting secondary electrons emitted from the vacuum chamber (5);
20) and the gas-filled chamber (2l) are connected to each other through the opening of the pressure limiting member (9), in which the secondary electron detection! i (6) is a distance from the electron beam irradiation position of the sample (5) to at least the objective lens (1), (
2), said gas-filled chamber (2) which is more than the working distance of (3)
1) A secondary electron reflecting member (7) and an electron beam provided in a part of the interior and surrounding the secondary electron detector (6) in order to increase the detection efficiency of secondary electrons. A shielding member (8) that blocks the incidence of reflected electrons due to irradiation, and the pressure limiting member (9) further includes the objective lens (1), (
2), (3) are provided at the sample side tips, and the opening of the pressure limiting member (9) is connected to the objective lens (1), (2),
(3) is located closer to the sample than the main surface of the deflector (10
), (1l) is provided at the deflection fulcrum of the scanning electron beam (4) as a means of solving the problem. [Function] In the present invention, since only a thin pressure limiting member is interposed between the objective lens and the sample, the working distance of the objective lens is significantly increased compared to the conventional case where a detector is interposed. It can be made smaller. Therefore, it is possible to set the distance from the main surface of the objective lens to the sample surface small, and a large aperture angle can be obtained, resulting in a small chromatic aberration coefficient. The aberration when the energy of the secondary electron is small is
Since the small polarization $I region is determined by chromatic aberration and diffraction, by reducing the chromatic aberration coefficient as described above, the aberration can be reduced and the electron beam can be narrowed down.

Radius of electron beam diffusion in low pressure gas r1/! is obtained by the following equation. Reimer, L. (1985) Scanni
ngElectron Microscopy, Spr.
inger-Verlag+ Berlinwhere,
r178 is the radius at which the intensity is 2, E is the electron beam energy, P is the pressure, T is the gas temperature, L is the distance the electron beam travels in the gas, and Z is the atomic number of the gas. By reducing L from the above equation, the radius of diffusion r
Since l/ffi decreases in proportion to l,3/wealth, by reducing the working distance of the objective lens as described above, the diffusion of the electron beam can be further reduced. In addition, the distance from the sample to the secondary electron detector is made larger than the mean free path of secondary electrons in a gas with a small pressure, so that the secondary electrons reach the detector. By colliding with gas molecules before entering the gas, the secondary electrons are emitted from the gas molecules, so secondary electrons can be detected efficiently. Note that it is desirable that the relationship between the gas pressure (P) and the distance jal (D) from the secondary electron emission position to the secondary detector be maintained as shown in the following equation. PXD! ;2Torr -cm Furthermore, since the shape of the pressure limiting member was made conical and a negative voltage was applied, the secondary electrons emitted from the sample were not absorbed by the pressure limiting member and were directed toward the secondary electron detector. At the same time, a positive voltage was applied to the electrode of the secondary electron detector, and the vicinity of the secondary electron detector was surrounded by a secondary electron reflecting member to which a negative voltage was applied, making it possible to detect larger amounts of secondary electrons. ．． [Embodiment] FIG. 1 is a diagram showing an embodiment of the present invention, and is a structural explanatory diagram of the vicinity of an objective lens and a secondary electron detector. In Figure 1, the upper pole (3) and lower pole (1) of the objective lens
The sample (5) is shaped like a cone so that it can be tilted up to 60 degrees. By winding the coil (2) of the objective lens to its tip, a strong magnetic field was applied to the electron beam trajectory (4). The i-satellite trajectory (4) is deflected by two-stage deflectors (10) and (1l), and the pressure limiting member (
9) through the opening of the sample (5)} (12)
is scanned. 0.05 to 2 in the gas chamber (21)
It is filled with gas at a pressure of 0 Torr, but since the opening of the pressure limiting member (9) has a small diameter, the gas leaking from this opening is exhausted by a bomb (not shown), and the vacuum chamber (20) is filled with gas at a pressure of 0 Torr. The electron beam orbit (4) inside is kept in a high vacuum. The secondary electrons emitted from the target (l2) are repelled due to the negative voltage applied to the pressure limiting member (9) and are not absorbed, but instead reach the secondary electrons provided on the outer surface of the objective lens. It is designed to face the direction of the detector (6). Furthermore, since the pressure limiting member (9) is shaped like a truncated cone, it does not hinder the movement of secondary electrons. The secondary electrons heading toward the secondary electron detector (6) collide with gas on the way, increasing in number and reaching the negative potential secondary electron reflection electrode (7) and backscattered electron shielding electrode (8). Without being trapped, the electrons enter the electrode of the secondary electron detector (6), which is given a positive potential. The electrode of the secondary electron detector (6) is made of Be and has a wedge-shaped surface, so when secondary electrons are incident, there is almost no distribution noise caused by re-reflected electrons. The backscattered electrons from target l-(12) pass through the backscattered electron shielding electrode (
8), so it does not enter the electrode of the secondary electron detector (6). The secondary electron reflection electrode (7) and the reflection electron shielding electrode (8) are Be, C, AJ! Since the surface is made of a metal with a low electron number such as, the reflected electrons are absorbed by these electrodes and are not re-reflected and incident on the secondary electron detection electrode (6). Secondary electron reflecting electrode (7), reflected electron shielding electrode (
8) Since the pressure limiting member (9) is given a negative charge and only the electrode of the secondary electron detector (6) is given a positive charge, the area of the electrode of the secondary electron detector (6) is small. secondary electrons can be collected effectively even if As a result, a secondary electron detector (6
) can be reduced, and the response speed of the secondary electron detector can be increased.

FIG. 2 is a diagram showing the relationship between the pressure limiting member (9) and the trajectory of the electron beam. The electron beam trajectory (4) deflected by the deflectors (10) and (11) is refracted by the lens (13), passes through the opening of the pressure limiting member (9), and scans over the target (12). Since the electron beam trajectory (4) has a deflection fulcrum at the aperture, it always passes through the aperture and can scan a large area beyond the diameter of the aperture. In addition, the aperture is located on the main surface of the objective lens (
13) Since it is located closer to the target and helps deflection, it is designed to be able to scan a large area with a small deflection current. Figure 3 shows another embodiment in which the secondary electron detector is installed in another part of the gas-filled chamber. Note that the secondary electron detector is supported by a support member provided on the inner wall of the gas-filled chamber (not shown).

[Effects of the Invention] As described above, according to the present invention, the distance from the main surface of the objective to the sample can be determined without intervening the secondary electron detector between the pressure limiting member and the sample. Because of the small size, the chromatic aberration coefficient is reduced, aberrations are improved, and the electron beam can be narrowed down, and the distance from the opening of the pressure limiting member to the electron beam irradiation target is shortened to reduce the spread of the electron beam. This has the advantage that a high-resolution electron beam can be obtained.

In addition, since the secondary electron detector is installed at a predetermined distance from the electron beam irradiation target, the movement of secondary electrons causes more collisions with gas molecules, making it possible to obtain a large signal even with low-pressure gas. effective. Furthermore, the vicinity of the secondary electron detector is surrounded by a secondary electron reflecting member to give it a negative charge, which not only improves the secondary electron detection efficiency, but also reduces the capacitance of the secondary electron detector. This also has the effect of speeding up the response speed.

Furthermore, since the reflected electrons caused by the electron beam irradiation on the target of the sample are shielded, there is no need for the reflected electrons to be mixed in when detecting secondary electrons. Therefore, it has the advantage of being able to observe the electron beam spot with a resolution that is faithful to it.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment according to the present invention. FIG. 2 is an explanatory diagram showing the relationship between the pressure limiting member and the trajectory of the electron beam, and FIG. 3 is a diagram showing another embodiment according to the present invention. [Explanation of symbols of main parts] l... Lower pole of objective lens, 2... Excitation coil, 3...
...Objective lens upper pole, 4...Electron beam trajectory, 5...
Sample, 6... Secondary electron detector, 7...
・Secondary electron reflection electrode, 8... Reflection electron shielding electrode, 9.
...Pressure limiting member, 10.1'l...Scanning deflector,
12...Target, 20...Vacuum chamber, 21.
...Gas filled chamber.

Claims (3)

[Claims] (1) Electron beam scanning is performed in a vacuum using an electron beam source, an objective lens that directs the electron beam emitted from the electron beam source and focuses it on the sample, and a deflector that deflects the electron beam and scans the sample. A vacuum chamber made possible by a vacuum chamber, a sample stage for holding the sample in correspondence with the focused position of the electron beam, and a detector for detecting secondary electrons emitted from the sample by irradiation with the electron beam are installed. A scanning electron microscope comprising: a gas-filled chamber, the vacuum chamber and the gas-filled chamber being connected to each other through an opening of a pressure limiting member; a secondary detector provided in a part of the gas-filled chamber at a distance of at least a working distance of the objective lens or more from the position of the objective lens, and placed surrounding the secondary detector in order to increase detection efficiency of secondary electrons; A scanning electron microscope characterized by having an electron reflecting member. (2) The pressure limiting member is provided at the tip of the objective lens on the sample side, and the opening of the pressure limiting member is positioned closer to the sample than the main surface of the objective lens, and the electron beam scanned by the deflector 2. A scanning electron microscope according to claim 1, wherein the scanning electron microscope is provided at a deflection fulcrum. (3) The scanning electron microscope according to claim 1, wherein the secondary electron detector has a shielding member that blocks incidence of reflected electrons caused by electron beam irradiation.