JPH053014A - Scan-type charged particle beam microscope - Google Patents

Abstract

PURPOSE:To accurately observe a groove bottom or side surface having a submicron or less dimension by applying a high electric field to a sample surface to form a downwardly convex equipotential surface in the interior of a hole having a high aspect ratio. CONSTITUTION:Upon incidence of a primary electron beam upon the bottom of a hole 7 of a sample 6, a secondary electron is emitted from the point of incidence. Since a high voltage is applied from a power source 12 to a detection electrode 4, an equipotential surface is formed near the sample 6 and the internal space of the hole 7 comes to have a downwardly convexed equipotential surface due to the difference in dielectric constant between the sample hole interspace and the sample body. As a result, the secondary electron emitted from the hole bottom receives a force causing it to be directed toward a center of the hole. Small-energy secondary electrons are emitted in large quantity from a residual resist film, in particular, on the bottom of the hole and receives the lens action of the electric field with great influence. Consequently, they go out of the hole via paths 10 without colliding against the wall surface. On the other hand, the reflected electrons and large-energy secondary electrons do not have resist film information so much and impinge upon the hole wall without receiving any lens action. This construction permits secondary electrons, having failed to go out from the hole, to get out of it, thus serving to observe the hole bottom.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning charged particle beam microscope, and more particularly to a technique for making it possible to observe the inside of a hole or groove having a large aspect ratio in such a microscope.

[0002]

2. Description of the Related Art Conventionally, a charged particle beam microscope such as a scanning electron microscope is used for observing, for example, a semiconductor device or a state during a manufacturing process of the semiconductor device. When observing a sample of such a semiconductor device with a scanning electron microscope, for example, when examining the formation state of holes in a resist layer deposited on a semiconductor substrate, a large aspect ratio formed on the sample is observed. That is, there are cases where it is necessary to observe the inside of a hole or groove, which is deeper or deeper than its width.

In such a case, conventionally, there is a method of applying a strong magnetic field to the sample surface in an electron microscope and guiding secondary electrons emitted from the bottom of the hole or groove to the secondary electron detector by this magnetic field. Being tried.

[0004]

However, in the method of applying the magnetic field to the sample surface in this way, secondary electrons emitted from the bottom of the hole or groove of the sample collide with the side walls of these holes or grooves. It was necessary to apply a very strong magnetic field so that the secondary electron detector could be guided to the secondary electron detector.
For example, in order to observe the bottom of a submicron-wide trench, it is necessary to set the magnetic field strength to, for example, 30 Tesla (300,000 Gauss or more). For this purpose, it is necessary to use a superconducting coil or the like. There was an inconvenience that it was not practical.

In view of the above problems in the conventional method, an object of the present invention is to provide a scanning charged particle beam microscope capable of accurately observing the bottom of a hole or groove having a large aspect ratio with a simple structure. To provide.

[0006]

In order to achieve the above object, according to the present invention, a charged particle beam from a particle beam source is irradiated onto a sample arranged in a magnetic field of an objective lens to scan the sample.
A scanning charged particle beam microscope for observing a sample by detecting a secondary charged particle beam from the sample is provided.
The microscope is characterized in that it is provided with a means for applying a high electric field to the surface of the sample, and enables observation of the inside of a hole or groove having a high aspect ratio provided in the sample.

The means for applying the high electric field is arranged on the charged particle beam incident side of the sample, has a positive potential, has an outer radius larger than twice the distance to the sample and an inner radius of the sample. It is convenient to use an electrode with holes that is smaller than 1/2 times the distance to the sample.

Further, the means for applying the high electric field may be means for applying a negative voltage to the sample.

Further, the means for applying the high electric field may be a scintillator detector arranged near the observation point and applying a positive voltage.

[0010]

In the scanning charged particle beam microscope having the above structure, a high electric field is applied to the surface of the sample to be observed. Therefore,
The equipotential surface inside the high-aspect-ratio hole or groove provided in the sample has a downwardly convexly distorted shape inside the hole or groove. Therefore, the secondary electrons emitted from the bottom of the hole or groove having a high aspect ratio are subjected to a weak force in the direction toward the inside of the hole or groove by the electric field having the equipotential surface distorted downward. Therefore, without this electric field, secondary electrons that are absorbed by the wall of the hole or groove and are emitted at an angle such that they cannot go out of the hole are also bent toward the central part of the hole and can go out of the hole or groove. It can be detected and contributed as a signal by the detection electrode. Therefore, it is possible to observe the bottom or side surface of a hole or groove having a high aspect ratio.

As the means for applying the high electric field, a holed electrode provided on the charged particle beam incident side of the sample and to which a positive potential is applied, for example, can be used. A sufficiently uniform high electric field is applied to the vicinity of the observation point on the sample surface by making the inner radius of the hole larger than twice the distance to the sample and smaller than the half radius of the hole to the sample. Further, it becomes possible to effectively form a downwardly convexly distorted electric field inside the high aspect ratio hole or groove of the sample.

As means for applying the high electric field,
When a means for applying a negative voltage to the sample is used, a potential difference can be generated between the sample and a peripheral part of the sample such as an electron lens having a ground potential, and thus an electric field can be applied to the sample.

Furthermore, when a scintillator detector is used as the means for applying the high electric field, a positive voltage is usually applied to the scintillator detector itself, so that this voltage applies a high electric field to the sample surface. be able to.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic structure of a scanning electron microscope according to one embodiment of the present invention. The electron microscope in the figure is
It has an upper pole 1 and a lower pole 11 forming a magnetic objective lens for focusing an electron beam emitted from an electron lens (not shown). The upper pole 1 is, for example, a cylindrical perforated magnetic pole, the lower pole 11 is a plane magnetic pole, and these magnetic poles 1 and 11 are magnetically coupled to each other by a magnetic member (not shown). And a coil for generating the magnetic flux 3 between the lower pole 11 and the lower pole 11.

At the lower end of the upper pole 1 of the objective lens, a pressure limiting aperture 2 having an opening through which an electron beam passes is provided. A sample 6 is placed on the lower electrode 11, and a concentric detection electrode 4 is placed between the sample 6 and the upper electrode 1.
Are arranged. This detection electrode 4 has, for example, 600
A positive high voltage of about volt is applied from the power supply 12. An amplifier 14 is connected to the detection electrode 4 via a capacitor 13 that cuts a direct current component.

FIG. 1 shows a sample 6 having a resist layer 6b formed on a substrate 6a such as a semiconductor substrate. A hole or groove 7 having a large aspect ratio is provided in the resist layer 6b of the sample 6 as described above, and the portion of the hole 7 is observed in FIG. The sample chamber in which such a sample 6 is arranged may be filled with a gas having a low pressure, and in that case, in order to prevent discharge due to a high voltage applied to the electrode 4, the sample chamber may have a pressure of 0.1 Torr or less. It is convenient to keep the gas pressure.

In the scanning electron microscope having the above structure, the primary electron beam emitted from the electron gun (not shown) is opened in the pressure limiting aperture 2 and the detection electrode 4 is formed.
The sample 6 is incident on the sample 6 through the opening and the scanning means (not shown) scans the vicinity of the hole 7 of the sample 6.

When the primary electron beam is incident on the sample 6, secondary electrons are emitted from the incident point. The secondary electrons enter the detection electrode 4 while spirally moving by the magnetic flux 3 formed by the objective lenses 1 and 11, and the condenser 1
3 and the amplifier 14 are taken out as an output signal.

In such an operation, when the primary electron beam is incident on the bottom of the hole 7 of the sample 6, secondary electrons are emitted from the incident point. In this case, since a high voltage is applied to the detection electrode 4 from the power source 12, an equipotential surface as shown by 5 in FIG. 1 is formed in the vicinity of the sample 6, and especially the inner space of the hole 7 of the sample 6 is formed. Becomes an equipotential surface that is distorted in a convex shape downward due to the difference in dielectric constant from the sample. Therefore, the secondary electrons emitted from the bottom of the hole 7 receive a force toward the center of the hole. In particular, a large amount of secondary electrons with low energy are emitted from a thin film such as the remaining portion of the resist on the bottom of the hole 7. Since such secondary electrons are greatly affected by the lens action due to the electric field, the secondary electrons protruding in a large angle direction from the optical axis do not collide with the wall surface of the hole 7 and follow the locus shown by 10, for example. Allows to get out of the hole 7. On the other hand, backscattered electrons and secondary electrons having large energy are harmful electrons that do not have much information on the thin film, but they are hardly affected by the lens action of the hole and enter the wall surface of the hole. As described above, by applying a strong electric field to the surface of the sample 6, the secondary electrons that could not go out of the hole 7 as shown by the dotted line 8 in FIG. Therefore, the bottom of the hole 7 having a large aspect ratio can be accurately observed.

The outer radius of the detection electrode 4 is set to be a working distance, that is, the distance from the detection electrode 4 to the surface of the sample, which is sufficiently larger, in particular, larger than twice the working distance. The inner radius is made smaller than half the working distance. It has been experimentally proved that an electric field that is uniform and sufficiently large can be applied to the sample surface by such a setting.

Further, in the electron microscope of FIG. 1, since the objective lens is composed of the magnetic pole 1 on the upper side of the sample 6 and the magnetic pole 11 on the lower side of the sample 6, the space between the sample 6 and the detection electrode 4 is reduced. Has a strong magnetic field as indicated by 3. Therefore, the secondary electron emitted from the hole 7 is not orthogonal to the detection electrode 4 due to this strong magnetic field, and collides with a gas molecule having a low pressure while rotating around the magnetic field to generate an electron-ion pair. The secondary electrons are multiplied and increased to several thousand to several ten thousand times, and then enter the detection electrode 4.

In a normal environment-controlled scanning electron microscope (ESEM), the pressure of the sample room in which the sample 6 is placed is kept at a pressure that gives the maximum sensitivity or the maximum S / N ratio. Since it is necessary to apply a high voltage to the working electrode 4, it is advantageous to shift the pressure to a higher vacuum side than in the case of such a general ESEM to increase the discharge voltage and apply a high electric field to the sample surface. Is.

Furthermore, in the above embodiments, a high electric field is generated on the sample surface by applying a high voltage to the detection electrode 4, but a negative voltage may be applied to the sample itself. In this case, for example, the upper pole 1 is set to the ground potential, and a high electric field is applied to the surface of the sample 6 due to the potential difference between the sample 6 and the upper pole 1. Sample 6
In order to apply a negative voltage to the sample 6, for example, a probe connected to a negative voltage source may be brought into contact with the sample 6.

Alternatively, as yet another embodiment, the sample chamber may be set to a high vacuum and a scintillator detector to which a positive voltage is applied may be provided near the observation point. In this case, a high electric field can be generated on the sample surface by the positive voltage applied to the scintillator detector, and the same effect as in the case of applying the positive voltage to the detection electrode 4 can be obtained.

[0025]

As described above, according to the present invention, by applying a high electric field to the sample surface, an equipotential surface which is downwardly distorted is formed inside the hole or groove having a high aspect ratio. It For this reason, only low-energy secondary electrons containing much information of a thin film such as the resist residue on the bottom of the hole can be bent in the optical axis direction by the lens action and can be emitted out of the hole. On the other hand, high-energy secondary electrons and backscattered electrons are rather harmful electrons that do not contain much information of the thin film, and these high-energy electrons do not receive much action of the electrostatic lens and go straight to form holes. It is absorbed by the wall surface and is not released to the outside. Therefore, according to the present invention, with a simple structure, it is possible to more accurately observe the bottom or side surface of a hole or groove having a size of, for example, submicron or less.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing a schematic configuration of a scanning charged particle beam microscope according to an embodiment of the present invention.

[Explanation of symbols]

1 Upper pole of magnetic objective lens 2 Pressure limit aperture 3 lines of magnetic force 4 Secondary electron detection electrode 5 equipotential surface 6 samples 6a Sample 6 substrate 6b Resist layer of sample 6 7 High aspect ratio holes or grooves 8 Secondary electron emission direction line 10 Secondary electron orbit 11 Lower pole of magnetic objective lens 12 power supplies 13 Capacitor for DC component cutting 14 Amplifier

Claims (4)

[Claims] 1. An observation of a sample is performed by irradiating a sample placed in a magnetic field of an objective lens with a charged particle beam from a particle beam source to scan, and detecting a secondary charged particle beam from the sample. A scanning charged particle beam microscope for performing, comprising a means for applying a high electric field to the sample surface. 2. The means for applying the high electric field is disposed on the charged particle beam incident side of the sample, has a positive potential, and has an outer radius larger than twice the distance to the sample and an inner radius. The scanning charged particle beam microscope according to claim 1, wherein is an electrode with a hole that is smaller than 1/2 times the distance to the sample. 3. The scanning charged particle beam microscope according to claim 1, wherein the means for applying the high electric field includes means for applying a negative voltage to the sample. 4. The scanning charged particle beam microscope according to claim 1, wherein the means for applying the high electric field is a scintillator detector arranged near an observation point and applying a positive voltage.