JPS6118808A - Specimen height meter for electrically charged particle apparatus - Google Patents

Abstract

PURPOSE:To contrive higher precision and stability of a light beam path, by installing optical elements in the sufficient vicinity and constructing the beam path inbetween with glass blocks. CONSTITUTION:In a beam incident system, light source 6 and lens 9 and in its reflecting system, lens 10 and light-receiving element 11 are set in the nearer distance than that set in each beam path, and the beam paths between these optical elements are constructed with blocks of materials, such as glass, respectively of high transparency, low temperature expansion coefficient and refractive coefficient higher than 1 for higher accuracy and stability of the beam path and easiness of handling.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a sample height measuring device for a charged particle device, which is used when a charged particle device directly exposes a sample surface to light.

(Prior Art) The operating principle of a sample height measuring device for a charged particle device is shown in FIG. In FIG. 8, 1 is the irradiated light beam, 2 is the reflected light beam from the sample surface 4, 3 is the reflected light beam from the sample surface 5, and 4 and 5 are the sample surfaces, each showing a different height. 6 is a light source, 7 is a collimator, 8 is a slit, 9 and 10 are lenses, and 1 is a light receiving element.

An irradiation light beam 1 emitted from a light source 6 is made into parallel light beams by a collimator 7, and is irradiated onto a sample surface 4 through a slit 8 and a lens 9. Here, the lens 9 is installed so as to focus the image of the slit 8 on the irradiation point 0 on the sample surface 4, thereby forming a light spot in a minute area of the irradiation point 0.

The irradiated light beam is reflected at the irradiation point ◯, becomes a reflected light beam 2, passes through the lens 10, and reaches the light receiving element 11. Here, the lens IO is installed so as to form a slit image of the irradiation point O onto the light receiving element 11. In the following text, the entire part forming the optical path from the light source 6 to the light receiving element 11 will be referred to as an optical system, of which the part from the light source 6 to the lens 9 will be referred to as the irradiation system, and the part from the lens 10 to the light receiving element 11 will be referred to as the reflecting system. Make it.

Let A be the position of the point on the light-receiving element which the reflected light beam 2 from the sample surface 4 has reached. Next, when the height of the sample surface changes to the state of the sample surface 5, the position of the point on the light receiving element 11 where the reflected light beam 3 from the irradiation point 0 on the sample surface 5 reaches is defined as A'. The difference in height between sample surface 4 and sample surface 5 is Δ
If Z is the distance between points A and A', and ΔX is the distance between points A and A', there is a relationship of ΔZ=Δx′ cos θ/M, and by measuring the distance ΔX on the light receiving element 11, the height change ΔZ of the sample can be detected. Here, θ is the reflection angle of the reflected rays 2 and 3. In addition, M is the magnification, and M
, = fl 2/Q 1.

Now, a conventional device of this type was constructed as shown in FIG. In the figure, 1 is the irradiated light beam, 2 is the reflected light beam, 4 is the sample surface, 6 is the light source, 7 is the collimator, 8 is the slit, and 9.1
0 is a lens, 11 is a light receiving element, 12 is a reflecting mirror, 13 is an optical system holder, 14 is a charged particle beam converging lens (hereinafter referred to as a converging lens), 16 is an electron mirror, and 18 is a charged particle beam The deflection electrode 19 is the central axis of the electron optical system. An irradiation light beam 1 emitted from a light source 6 is turned into a parallel light beam by a collimator 7, passes through a slit 8 and a lens 9, and reaches the sample surface 4. During this time, the irradiated light beam 1 is reflected by the reflecting mirror 12(a),
(bL (c) is guided by repeated reflections.

Since the reflected light beam 2 is repeatedly reflected by the reflecting mirrors 12 (d), (e), and (f), it passes through the lens 10 and reaches the light receiving element 1.
] will lead you to. The light receiving element 11 outputs an electric signal corresponding to the incident position to an external detection circuit.

(Problems to be Solved by the Invention) Incidentally, in the apparatus having this configuration, the irradiation system and the reflection system are arranged on the metal holding tool 3. Furthermore, the optical system requires a relatively long distance in order to ensure the magnification M. Therefore, when the ambient temperature in which the optical system is installed changes,
Expansion, contraction, or twisting occurs in the holder 13, causing deviations in adjustment of the mounting position and mounting angle of the optical element, and changes in the optical path length, resulting in measurement errors.

In addition, reflecting mirror 1.2(a) for configuring the optical path, (
b).

(c) It is necessary to precisely adjust the positions and angles of each mirror, but in the above configuration, each of these reflecting mirrors is individually attached to the optical system holder 13, so this adjustment is complicated. However, it is also difficult to improve accuracy.

The present invention was made in consideration of these circumstances.
The purpose is to provide a sample height measuring device for a charged particle device that has an extremely high and stable optical system construction precision and is easy to adjust and handle.

(Means for Solving the Problems) The main points of the present invention include a light source, a means for irradiating a light beam from the light source to an irradiation point on a sample, and a means for guiding the light beam reflected from the irradiation point to a light receiving element. , and measures the height of the sample from the image on the light receiving element, in which at least one of the optical paths between the light source and the irradiation point and between the irradiation point and the light receiving element has a refractive index of less than 1. It is located in a sample height measuring device that includes a medium.

According to a preferred embodiment, the medium is provided with a light reflecting material;
Rays of light travel through reflection.

(Function) Since the refractive index of the medium in the optical path is greater than 1, the length of the optical path of the present invention is smaller than that of conventional optical paths, and the optical path length is stable. If the medium is provided with a reflective material, the effect of shortening the optical path length is even greater.

(Embodiment) FIG. 1 shows an embodiment of the present invention. FIG. 1(a) is a cross-sectional view of the embodiment, and FIG. 1(b) is a diagram of the embodiment viewed from the direction of incidence of the charged particle beam. . FIG. 2 is a diagram showing the configuration of the irradiation system in the embodiment described above. FIG. 3 is a diagram showing the configuration of the reflection system in the embodiment described above.

1 is an irradiation light beam, 2 is a reflected light beam, 4 is a sample surface, 6 is a light source, 7 is a collimator, 8 is a slit, 9 and 10 are lenses,
11 is a light receiving element, 12 is a reflecting mirror, 13 is an optical system holder, 14 is a converging lens, 15 is a space inside the converging lens,
] 6 is an electron mirror body. Further, 0 is the irradiation point on the sample.

In the present invention, the light source 6 and the lens 9 in the irradiation system, and the lens 1o and the light receiving element 11 in the reflection system are installed closer to each other than the distance along the optical path, and these optical elements The optical path between the blocks C is made of a material such as glass that has high transparency, a small coefficient of thermal expansion, and a refractive index greater than 1.
By forming each of them with a glass block (hereinafter referred to as a glass block), the precision, stability, and ease of handling of the optical path are improved.

As an example, the reflection system shown in FIG. 3 will be described.

The lens 10 and the light receiving element 11 are arranged at a sufficiently close distance from each other. This makes it possible to reduce the amount by which the distance between elements changes due to thermal expansion or changes mechanically.

Since this distance is insufficient for operation, a glass block [7] is installed between the lens 10 and the light receiving element 11, and the light beam is guided inside it in a zigzag manner to form an optical path of length 02. At this time, a reflecting mirror is required, and the reflecting mirror 12 is obtained by polishing the glass block 17 and depositing a highly reflective metal or the like on the polished surface. Of course, anti-reflection treatment is applied to the surfaces of the portion where light is introduced into the glass block 17 and the portion where light is led out from the inside.

By integrally forming the reflecting mirrors constituting the optical path of the reflecting system by polishing a single glass block 17 in this manner, the accuracy of the relative position of the reflecting mirrors, that is, the accuracy of the optical path, can be significantly improved. Further, when installing the optical system in the holder 13, there is no need to adjust each of the reflecting mirrors 2, and the adjustment of the entire optical system is simplified. Furthermore, since glass has a smaller coefficient of thermal expansion than metal, about 175, changes in the relative positional accuracy of the reflector due to temperature rise, that is, changes in optical path length, are reduced by 1.
75, and the relative positions of the reflecting mirrors do not mechanically shift, so the amount by which the position and angle of the returning mirror 12 changes after installation can be reduced by installing the reflecting mirrors individually in the holder 13 of the optical system. lJX is significantly smaller than in the case where the optical system is stabilized.

Furthermore, since the refractive index of glass is approximately 1.5, compared to conventional devices that configure the optical path in the atmosphere or vacuum,
Without changing the actual optical path length Q2, that is, the magnification M, the dimensions of the optical system can be reduced to about 1. /1.5.

The irradiation system can also be constructed in a similar manner as shown in FIG.

Incidentally, the distance between the converging lens 14 and the sample 4 is one of the factors that determines the reduction rate of the charged particle device, and in order to obtain a large reduction rate in the charged particle device, this distance must be made as short as possible.゛Figure 4 shows the irradiation system and reflection system in the space 1 inside the converging lens.
This is an example in which the present invention is incorporated in FIGS. 5 and 6 are configuration diagrams of the irradiation system and reflection system of the above embodiment, respectively. In the embodiment shown in FIG. 4, optical elements and optical systems are protected between the converging lens 14 and the sample surface 4.

Since there is no structure such as the holder 13, there is an advantage that the distance between the converging lens 14 and the sample surface 4 is not limited.

Note that the space 15 inside the converging lens refers to the following.

As shown in FIG. 7, the converging lens 14 has a cylindrical shape, and is provided with a cylindrical hole along the central axis 19 of the electron optical system.

This hole generates an electromagnetic field within it to focus the charged particle beam. This hole is called the space J5 inside the converging lens.

(Effects of the Invention) As explained above, according to the present invention, optical elements are arranged sufficiently close to each other in the irradiation system or the reflection system,
By configuring the optical path between them with glass blocks,
High precision and high stability of the optical path can be realized, and the ease of adjustment and miniaturization of the device can be further improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of the irradiation system of the embodiment, FIG. 3 is a block diagram of the reflection system of the embodiment, and FIG. 4 is a block diagram of the space inside the converging lens. 5 is a configuration diagram of an embodiment incorporating an irradiation system and a reflection system, FIG. 5 is a configuration diagram of the irradiation system of the embodiment, FIG. 6 is a configuration diagram of the reflection system of the embodiment,
FIG. 7 is a configuration diagram of a converging lens, FIG. 8 is a diagram showing the principle of sample height measurement for a charged particle device, and FIG. 9 is a configuration diagram of a conventional sample height measurement device for a charged particle device. 1-m=Reflected ray, 2--1 Reflected light reflected from sample surface 3 r3---Reflected light reflected from sample surface 5 4-11 Sample surface located at a high position, 5-11 Sample surface located at a low position Sample surface, 6-- light source, 7-- collimator, 8-
m-slit, 9--lens for forming the image of the slit 8 on the sample surface 4, 10-m-lens for forming the slit image on the sample surface 4 on the surface of the light-receiving element 11, 11-m=light receiving element, 12-m-reflector, 13-
m = optical system holder, 14--converging lens for charged particle beam, 15-m-space inside the converging lens, 16--electronic mirror, 17--glass block, 18-m-charged Particle beam deflection electrode. 19-m- Central axis of electron optical system.

Claims (2)

[Claims] (1) It has a light source, a means for irradiating the light beam from the light source to the irradiation point on the sample, and a means for guiding the light beam reflected from the irradiation point to the light receiving element, and the height of the sample is determined from the image on the light receiving element. In a measuring device for measuring the light intensity, at least one of the optical paths between the light source and the irradiation point and between the irradiation point and the light receiving element has a refractive index of 1.
A sample height measuring device characterized by being constructed by including a medium made up of a larger rigid body. (2) The sample height measuring device according to claim 1, wherein the surface of the medium has a light reflecting material, and the light in the medium travels through reflection by the reflecting material. .