JPS61140802A - Light wave interference device preventing reverse surface reflected light - Google Patents

Abstract

PURPOSE:To remove interference fringes formed by reverse-surface reflected light from an optical component such as an objective and to improve precision by setting a beam splitter so that its incidence surface and projection surfaces do not cross the optical axis of irradiation light at right angles. CONSTITUTION:This device guides the irradiation light 3 to a sample-side objective 7 and a reference-mirror side objective 8 by the beam splitter 20, whose incidence surface and projection surfaces 20-1 and 20-2 are not at right angles to the optical axis of the irradiation light 3. For the purpose, the beam splitter is formed in the sectional shape of, for example, a rectangle, parallelogram, or diamond. Consequently, reverse-surface reflected light beams 5 and 6 from the projection surfaces 20-1 and 20-2 and reverse-surface reflected light from the objectives deviate greatly from regular reflected light 13 and do not strike a photodetection part, so no interference fringe is formed.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is an optical system for a light wave interference device, which prevents light reflected from the back surface of optical components such as an objective lens, and maintains an orthogonal optical system. Related to optical devices. - [Background of the Invention] Conventionally, the Twyman interferometer has been used as a method for optically adding the shape of a sample in a non-contact manner.

(For example, Yamada: Knowledge of Hikariji, graduated from Tokyo Denki University.

There are editions P256-257 (Showa 46-5). ). .

Here, interference fringes reflect the shape of the sample and the surface roughness.

If we try to measure the foot by 1°, we think that it is necessary to set up the objective lens to face the sample and the reference plane by 1°.

However, in the past, such an objective lens was incorporated.

On light wave interference devices and the problems caused by them.

This was not considered at all.

[Purpose of invention 9] The purpose of the invention is to pair the sample with a reference mirror.

In a light wave interference device in which an object lens or other optical components are provided at an angle of 5 degrees, these optical components.

An object of the present invention is to provide a light wave interference device that can remove interference fringes caused by light reflected from the back surface of a light wave.

[Summary of the invention]

In the present invention, the light reflected from the back surface of the objective lens.

First, it interferes with the reflected light on the exit surface of the beam sinter to form an interference fringe image and detect it.

In order to improve the inconvenience of detection due to interference fringes being superimposed on the interference fringe images of the sample and reference mirror, the incident and exit surfaces of the beam musburitr are made not to be perpendicular to the optical axis of the illumination light. b [Embodiment of the Invention] The surface roughness of the sample was optically measured in a non-contact manner.

Figure 1 shows the first optical wave interference device. From light source 1.

The emitted light becomes one beam after passing through the illumination lens 2.

The reflected light is divided into two by the mirror 4, and the reflected light passes through the objective lens 7° and is focused on the sample 1o placed on the stage 12.2. .

Saleru. On the other hand, the transmitted light in the beam sliver.

is focused on the reference mirror 11 through the objective lens 8.

Ru. The reflected light 13 from these samples and the reference mirror is re-reflected.

The two beams are synthesized by the beam sinter 4 and interfere with each other.

The interference fringe image is projected onto the light receiving section 15 by the imaging lens 14.
shadow 16 is a monitor TV. This TV screen 1
For example, as shown in FIG. 3, in addition to the interference fringe image 26 of the reflected light from the sample and the reference mirror, there is also an interference fringe image 27-1 of the Am reflected light from the objective lens and the reflected light from other optical components. , 27-
2, etc. is detected, which becomes a major hindrance when trying to detect the interference fringe image 26 that was originally intended to be detected and then transmit and process it, making it difficult to accurately measure the surface roughness, waviness, etc. of the sample. becomes impossible. The lower the reflectance of the sample, the stronger this tendency is.
27-2 dry.

The intensity of the noise component of the interference fringes is higher than that of the 26 signal components.

This is because the intensity of the interference fringe becomes larger than the intensity of the interference fringe.

It is completely impossible to disclose the surface roughness and waviness of sample 10.

becomes.

Interference fringes 27-t and 27-2 of this noise component are generated.

When I investigated the cause of this, I found that it was behind the objective lens 7.9.

It can be seen that the circular reflection source is involved. Objective.

For example, as shown in FIG. 1, the lens may include multiple lenses.

The lens group is MH, and a small amount of reflection occurs on the front and back surfaces of each lens. Wear these.

This is represented by the light 9 reflected from the back surface of the objective lens. On the other hand, reflected light 5.6 is also generated at the exit surfaces 4-1 and 4-2 of the Beams 1 liter 4.As a result of investigation, a trial.

Back reflection light 9 of R1jl objective lens and beam split...
- It was found that the reflected light 5 of the ivy output [lI] 4-1 forms interference fringes, and that something similar to lrl+1 also occurs with the objective lens on the reference mirror side. These interference fringes
The noise components correspond to FIG. 3, 27-1 and 27-2.

Therefore, in order to remove the interference fringe noise component, each surface of the beam splitter is parallel to the objective lens 7.98, which is perpendicular to the % axis.

Tilt it as shown in Figure 4 4' to prevent it from falling.

I can think of something better. However, in this case.

The direction of the objective lens 7 is deviated from the vertical direction, and trials 11 and 1
The reflected light from the family is also from the vertical direction, as shown in Figure 13.

It is not an orthogonal optical system in which the optical axis of the optical system is perpendicular to the vertical and horizontal directions.

This causes inconvenience.

In the conventional W4 microscope, a flat half mirror is used in the illumination system, but when this is incorporated into an interference device as shown in Fig. 2, the reflected light from the reference mirror is 18. As shown, the light is reflected even on the back surface of the half mirror, causing a lateral shift with respect to the normal reflected light 13, resulting in overlapping interference fringe images ([This is a problem).

The present invention solves the above-mentioned problems, and provides a light wave interference device that prevents the generation of interference noise components due to light reflected from the back surface of optical components and that serves as an orthogonal optical system.

This makes it possible to The present invention will be explained with reference to W, 5-8, 1°.

Figure 6 shows a beam with a rectangular cross-sectional shape, 1 rim, □ri 20
' has a reflection 01121 in its diagonal direction. .

Cut the left and right sides of this beam splitter 20' to make it shorter.

However, the B in Figure 5 has a square cross-sectional shape.

mass 1 liter 20, and θ, ˜θ,.

In Fig. 5, the condition for the illumination light 3 and the sample reflected light 13 to be orthogonal is α1-false, and 2γ+θ1+θ2゜π
, θ1+θ, = wo, so if γ=7, the above is orthogonal.

condition is satisfied.

At the exit surfaces 20-1 and 20-2 of the beam sinter 20.

The reflected illumination surface light is received along the broken line 5.6 and is diverted from the reflected light 13 from the sample and reference mirror, so that it does not enter the light receiving section and does not become a noise component of the interference fringes. It can be seen that if the inclination angle α of the beam splitter 20'' or 20' is increased, the amount of light 5.6 emitted from the root bark becomes larger.

In other words, the conventionally used beam splitter (first
Figure 4) is a combination of two isosceles triangles, so the cross-sectional shape is square, and Figure 5.

θ1=θ. Beam for this.

If the splitter is tilted, it will not become an orthogonal optical system.In contrast, in the present invention, as shown in FIG.

can be done.

FIG. 7 is another example of the present invention. The cross-sectional shape is flat.

into a row quadrilateral or rhombic beam splitter 22.

It has a reflective surface 25 in the diagonal direction. By doing this, the reflected light at the beam splitter output surface is significantly different from the reflected light 13 from the test and reference mirrors, as shown by the broken line in the figure.

Therefore, it does not enter the light receiving section and does not become a noise component of interference fringes. Furthermore, if the angle between the 30-source axis of the incident light and the beam splitter reflecting surface 23 is set to 45°, then the incident light 3 and the reflected light 13 from the sample are perpendicular to each other. (・Although Figure 8 is not a very desirable example, it is an invention.

It is a thing of. A beam sprit with a wedge-shaped cross section.

One side of the ivy 24 is a reflection [&I25. For incident light 3.

However, the reflected lights 13 from the sample and reference mirrors are not perpendicular to each other.

At this point, the wedge angle is tilted according to the angle (but the objective lens 7 is oriented 1°).

The light source is perpendicular to the incident light 3. Also objective/zu.

Returning from 8, the reflected light of the reference mirror is beams again.

The light 18 reflected from the back surface of the printer 24 is the target.

The interference should be extracted because it deviates from the reflected light 13.

It does not become a noise component of the stripes. Therefore, the conventional 2.4
This is better than the method shown in the figure.゛Also, the fifth aspect of the present invention
~ In Figure 8, BEAMS.

Since the incident light on the 1st lens is tilted with respect to the incident light 5, the reflected light at the entrance does not return to the light source, causing the problem of destabilizing the output of a coherent source such as a laser. do not have.

As mentioned above, in the present invention, the light reflected from the back surface of the optical component does not return to the light receiving section, so the light reflected from the back surface of the optical component does not return to the light receiving section.
1 and 27-2 are removed, and only the interference fringes 26 between the sample to be detected and the reference ε are clearly detected, allowing the fine surface shape of the sample to be detected with high precision. can be measured. Furthermore, since an orthogonal optical system can be maintained, the optical system can be easily configured, and a conventional optical microscope can be used as is. □ [Effects of the Invention] According to the present invention, a highly accurate light wave interference device can be easily obtained by simply changing a conventional microscope beam splitter (leaf or half mirror) to the shape of the present invention.

can be made.

[Brief explanation of drawings]

FIG. 1 shows a beam splitter according to the present invention. Figures 2 to 4 show other views according to the present invention. - Figure 5, which shows the Japanese ivy, is a conventional drying method. Diagram showing a new light wave interferometer with improved interferometer separation ability,
Figure 6 shows the four diagrams of problems in the conventional microscope half-mirror.
Figure 7 is an illustration of the interference "pan pattern" of the light wave interferometer shown in Figure 5.
FIG. 8 is an explanatory diagram of problems when a conventional beam slitter is tilted.gl...Light source 2...
・Illumination lens system ・3...Illumination light 4...Beam splitter of prism 4-1, 4-2...Emission surface 5.6...Reflected light from the emission surface 7.8...Objective Lens ・9・
...Objective lens back surface reflected light 10...Sample 11...Reference mirror 12.
... Stage 13 ... Reflected light from the sample and reference mirror 14 ... Imaging lens 15 ... Light receiving section 16 ... TV monitor 17 ... Flat plate-shaped half mirror 18 ... Back reflected light 19 ...7' V screen
. 20...Trapezoidal prism beam splitter ・2
0'... Rectangular beam sinter 21.23.2
5...Reflection interval 22...Parallelogram-shaped beam splitter 24...
Wedge-shaped beam splitter 1st Y i force? 7 Section 3 Foil 4 Figure 5 Section 6 V Ir'

Claims (3)

[Claims] 1. In an interference device in which the illumination light is guided to the sample side and the reference surface side by a beam splitter, the beam splitter is provided with a shape such that the entrance and exit surfaces of the beam splitter are not perpendicular to the optical axis of the illumination light. A light wave interference device that prevents back reflected light. 2. In claim 1, the beam splitter has a cross-sectional shape of a rectangle, a parallelogram, or a rhombus, and has a reflective surface on a diagonal thereof, and the beam splitter is entirely or partially in the optical path. A light wave interference device that prevents back-reflected light, characterized in that it is provided in a. 3. In claim 1, the beam splitter has a wedge-shaped cross-section and has a reflective surface on one side,
A light wave interference device that prevents back-reflected light, characterized in that the entire or partial shape of the beam splitter is provided in the optical path.