JPH0460403A - Aimed two-flux interferometer - Google Patents

Abstract

PURPOSE:To highly accurately measure unevenness on a wave on a specimen surface and height of a small protrusion by applying arbitrary retardation between two orthogonal vibration components placed on a light path between a polarizer and an analyzer. CONSTITUTION:An illumination flux which is made into linear polarized light by a polarizer 2 is divided into two polarization components whose vibration directions are orthogonal to each other by a light division.combination means 7', wherein one of the polarization components is normally reflected on a specimen 8 and the other polarization component is nornally reflected on a reference 9, and they are again combined into one flux by the means 7'. Retardation occurs on the flux by a difference between a light path length of reciprocation between the means 7' and the specimen 8 and a light path length of reciprocation between the means 7' and the reference 9. In addition, arbitrary retardation can be applied to the flux by a retardation generating means 4. By adjusting the retardation amount to observe unevenness by interference colors, and by further adjusting it on two arbitrary points to calculate a difference between the readings, wave height on a wave-like specimen and height of a small protrusion on a specimen with the small protrusion can be accurately measured.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an epi-illuminated two-beam interferometer.

[Conventional technology]

The general configuration of the optical system of a conventional epi-illuminated two-beam interferometer is
As shown in the figure, there is a light source 1 and an epi-illumination means 3 such as a /%-humirror for guiding the light beam emitted from the light source 1 to the specimen 8.
and a light splitting/synthesizing means 7 which splits the light beam into two light beams directed toward the specimen 8 and the reference 9, respectively, and combines the two beams from the specimen 8 and the reference 9. 1) is the observer's eye.

According to the epi-illumination type two-beam interferometer having the above configuration, the seventh
When observing a step sample 15 consisting of a linear step part 12 with a depth d and flat parts 13 and 14 as shown in FIG. As shown in Figure (B), parallel interference fringes with an interval a deviated by a distance S appear in the image of the step sample 15 at the position of the step portion I2. At this time, the step difference d of the step portion 12 is determined by the interval a of the interference fringes and the shift distance S, as follows: d = □λ a (where λ is the wavelength of the illumination light).

C Problems to be Solved by the Invention] However, in the above conventional example, since interference fringes appear in a wavy manner in the wavy sample 16 as shown in FIG. 8, it is difficult to accurately measure the height of the waves 17 in the wavy sample 16. The drawback was that it couldn't be done. Also, for the small protrusion specimen 18 as shown in FIG. 9, if the area of the upper part of the small protrusion 19 is small, the small protrusion 1
There was also a drawback that the interference fringes on 9 became difficult to see, making it difficult to measure the height of the small protrusions 19.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide an epi-illuminated two-beam interferometer that can accurately measure the height of waves in a wavy sample and the height of small protrusions in a small protrusion sample.

[Means to solve the problem]

One optical system of the epi-illuminated two-beam interferometer according to the present invention is as shown in FIG. In the epi-illuminated two-beam interferometer, the epi-illuminated two-beam interferometer comprises a light splitting and combining means 7' that splits a light beam into two light beams directed toward the specimen 8 and the reference 9, respectively, and combines the two beams from the specimen 8 and the reference 9. The light splitting/synthesizing means 7' is a polarization splitting/synthesizing element having the property of splitting the incident light beam into mutually orthogonal oscillating components and synthesizing the two mutually orthogonal oscillating components. a polarizer 2 disposed on the optical path between the two, an analyzer 10 disposed on the optical path behind the light splitting and combining means 7', and the polarizer 2 and the analyzer 10.
A retardation generating means 4, such as a birefringent plate, which is placed on the optical path between the two and giving arbitrary retardation between two orthogonal vibration components, and the amount of retardation generated by the retardation generating means are read. It is characterized in that it is equipped with a retardation reading means 5 for.

Another optical system of the epi-illuminated two-beam interferometer according to the present invention has, in addition to the above configuration, the light source 1 being a laser light source that emits linearly polarized light and not including the polarizer 2. It is characterized by

[For production]

That is, according to the epi-illuminated two-beam interferometer according to the present invention, the illumination light beam linearly polarized by the polarizer 2 is divided into two beams whose vibration directions are perpendicular to each other by the light splitting and combining means 7', which is a polarization splitting and combining element. The light beam is divided into polarized light components, one of which is specularly reflected by the specimen 8, and the other polarized component is specularly reflected by the reference 9 and combined into a single beam by the light splitting and combining means 7'. . At that time, the light splitting and combining means 7
'The optical path length of the round trip between the specimens 8 and the light splitting and combining means 7
', a retardation corresponding to the difference between the optical path length of the round trip between the references 9 occurs in the combined light beam. Furthermore, arbitrary retardation can be imparted to the combined light beam by the retardation generating means 4. The vibration directions of the synthesized light beams are aligned by the analyzer IO, and an interference color corresponding to the degree retardation of the synthesized light beams is generated. Therefore, the observer can observe, on the image of the specimen 8, an interference pattern corresponding to the difference in unevenness between the specimen 8 and the reference 9.

Furthermore, by adjusting the amount of retardation provided by the retardation generating means 4, the sample 8 can be
By setting the retardation of any one point above to 0, the unevenness of the specimen 8 can be observed using interference color using the one point as a reference. Further, by calculating the difference between the retardation readings by the retardation reading means 5 when the retardation generating means 4 is adjusted so that the retardation becomes 0 at each arbitrary two points on the sample s, The elevation difference between the two points is determined.

Therefore, the height of even the wavy specimen 16 shown in FIG. 8 or the small protrusion specimen 18 shown in FIG. 9 can be measured with high accuracy.

〔Example〕

Hereinafter, the present invention will be described in detail based on the illustrated embodiment, with the same reference numerals assigned to the same members as in the above-mentioned conventional example.

FIG. 2 shows the optical system of a Michelson-type epi-reflection three-beam interference microscope as a first embodiment of the present invention, in which a Nomarski prism 4' is used as the retardation generating means 4, and light is emitted from the light source l. The light efficiently illuminates specimen 8.
A condensing lens 20. Epi-illumination lens 21
The reference 9 is equipped with an inclination adjustment device 22. Incidentally, the Nomarski prism 4' is arranged so as to substantially coincide with the rear focal position of the objective lens 6, as in a normal differential interference microscope. The observer uses the eyepiece 23
The image of the specimen 8 formed by the objective lens 6 is observed through the lens.

Since the present embodiment is configured as described above, the light beam emitted from the light source 1 passes through the polarizer 2 and the analyzer 10, passing through the Nomarski prism 4' twice in a round trip and performing normal epi-illumination type differentiation. Similar to interference microscopes, it generates uniform retardation over the entire field of view. The retardation can be continuously increased or decreased by moving the Nomarski prism 4' in a plane perpendicular to the optical axis, and since the amount of change in the retardation is proportional to the amount of movement, the retardation can be increased or decreased. The retardation reading device 5 converts the movement amount into a retardation change amount at a constant ratio. Of course, when the light reflected by the specimen 8 and the light reflected by the reference 9 are combined, retardation occurs due to the difference in optical path length between the two.

Therefore, since an interference color is generated according to the retardation of the combined light beam, the observer can see the image of the specimen 8 on the image.
An interference pattern corresponding to the difference in unevenness between the specimen 8 and the reference 9 can be observed. Furthermore, by adjusting the amount of retardation provided by the Nomarski prism 4', the retardation at any one point on the specimen 8 can be set to 0, and the unevenness of the specimen 8 based on this one point can be observed by interference color. . Further, by adjusting the Nomarski prism 4' so that the retardation at any two points on the specimen 8 becomes 0, the difference between the retardation readings by the retardation reading means 5 is taken, and the difference between the two points is calculated. Elevation difference is required. As a result, a wavy specimen 16 as shown in FIG. 8 and a small protrusion specimen 18 as shown in FIG.
However, height can be measured with high precision.

Incidentally, if the optical path from the light source 1 to the epi-illumination means 3 is oriented at 45 degrees with respect to the plane of the paper of FIG. Disturbances in the polarization state in reflection and transmission in means 3 are minimized.

FIG. 3 shows an optical system of a Rinique-type epi-reflection three-beam interference microscope as a second embodiment of the present invention, in which a Senarmont compensator 4' is used as the retardation generating means 4. That is, the 174-wave plate 4' is arranged so that the projection of its optical axis is perpendicular to the vibration plane of the light passing through the polarizer 2, and the analyzer 1 is placed on the exit side of the 1/4-wave plate 4'.
0' is provided. The analyzer lO' is rotatable around the optical axis, and its rotation angle can be read.

Since this embodiment is constructed as described above, the analyzer 10'
By rotating the analyzer 10', the amount of retardation added can be varied, and the amount is proportional to the rotation angle of the analyzer 10'.

As described above, in this embodiment using the Senarmont compensator 4' as the retardation generating means 4, the uniformity of retardation in the visual field is extremely good compared to the first embodiment using the Nomarski prism 4'. The reading accuracy is also high. However, light source l is Senarmon compensator 4
A monochromatic light source with a specified wavelength of ' must be used, and the measurement is limited to heights that are less than half the wavelength used.

Note that a place scaler compensator may be used instead of the Senarmont compensator 4'.

1/10λ~ as a place scaler compensator
A wave plate with a small phase difference of about 1/30λ is used.

In that case, the amount of retardation to be added can be changed by rotating the placescaler compensator around the optical axis, and the amount is determined by the rotation angle of the placescaler compensator. In this case, the retardation reading accuracy is higher than when the Senarmont compensator 4' is used, but the measurement range is smaller. Furthermore, when the Senarmont compensator 4' or the place scaler compensator as described above is used, the level difference of the level difference sample 15 as shown in FIG. 7 can be measured more accurately than before. In the conventional method of measuring interference fringe deviation, 1/20 of the wavelength used (approximately 30 nm when using the d-line)
It is said that the step difference in m) is the limit of measurement, but with this method, the difference in wavelength is 1/100th of the wavelength used (approximately 6 nm when using d-line).
The following level differences can also be adequately measured.

Furthermore, instead of using an expensive polarizing beam splitter as the light splitting and combining means 7', two polarizers 25 having the same thickness as the half prism 24 may be used as shown in FIG. However, in this case, the loss in the amount of light is greater than when a polarizing beam splitter is used.

FIG. 5 shows an optical system of an epi-reflection type two-beam interferometer using a laser light source as a third embodiment of the present invention, in which the laser light source 1' emits linearly polarized light and a Senarmon is used as a retardation generating means. A television camera 26 is used as an observation means for the compensator 4', and the laser light source 1
The optical axis 27 that connects the epi-illumination means 3' and the epi-illumination means 3 is 45 with respect to the paper surface of FIG.
The plane of polarization of the linearly polarized light emitted from the laser light source B is parallel to the plane of incidence of the epi-illumination means 3. This embodiment has the advantage that the light source itself emits linearly polarized light, so that the polarizer 2 in FIG. 1 can be omitted.

〔Effect of the invention〕

As described above, by using the epi-illuminated two-beam interferometer according to the present invention, it is possible to accurately measure the elevation of wavy irregularities and small protrusions on the specimen surface.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the basic configuration of the optical system of the epi-illuminated two-beam interferometer according to the present invention, and FIGS.
4 is a diagram showing another example of the light splitting and combining means of the second embodiment, FIG. 5 is a diagram showing the optical system of the third embodiment, and FIG. 6 is a diagram showing the configuration of the embodiment. 7(A) and 7(B) are respectively a perspective view of a step specimen and an observation image of the step specimen according to the conventional example, and FIGS. 8 and 9 are diagrams showing an optical system of a conventional example, respectively. FIG. 3 is a perspective view of a wavy specimen and a small protrusion specimen. ■...Light source, l'...Laser light source, 2.25
... Polarizer, 3... Epi-illumination means, 4...
Retardation generating means, 4'... Nomarski prism, 4'... Senarmont compensator, 5
...Retardation reading means, 6...Objective lens, 7'...Light splitting and combining means, 8...Specimen,
9...Reference, 10.10'...Analyzer, 1)...Observer's eye, 12...Step, 13
．． 14... Flat part, 15... Step sample, 16...
... Wave-like specimen, 17 ... Wave, 18 ... Small protrusion specimen, 19 ... Small protrusion, 20 ... Condenser lens,
21... Epi-illumination lens, 22... Tilt adjustment device, 23... Eyepiece, 24... Half prism, 26... Television camera, 27.28.29.
···optical axis. 1st figure 2 figure 1) -] gong 8~-2 5th figure 1P6 figure 1) 7 Ko8-2hiro8-eΣ 4th figure figure (A) (B) 9 figure June 1991 13th Japanese Patent Application No. 2-171) No. 84 Contents of Amendment (1) "rs" on page 3, line 5 of the specification is corrected to tSl. (2) [Element] on page 4, line 16 and page 5, line 15
(3) Correct [... like] on page 7, line 2 to "like 1." (4) Correct "[ru. J" on page 7, line 16] to "like 1." After j Also, a polarizing beam splitter is used as a polarization splitting and combining means. Insert 1 and correct [Arrangement] to "Low force rise 1." (5) "Orthogonal" on page 100, line 2. Insert ``parallel or 1'' in front. (6) Correct N/loλ~l/30λJ on the 2nd to 3rd lines of page 1) to ``λ/10~λ/301. (7) In the drawing, Figures 2 and 7 (B) are corrected as attached respectively. 5. Column for detailed explanation of the invention of the specification subject to amendment and drawings. Figure 2 Figure 7 Figure 7 (B) -211

Claims (2)

[Claims] (1) A light source, epi-illumination means for guiding the light beam emitted from the light source to the specimen, and dividing the light beam into two light beams directed toward the specimen and the reference, respectively, and two light beams from the specimen and the reference. In the epi-illuminated two-beam interferometer, the beam splitting and combining means is a polarization splitting device that has the property of dividing the incident light beam into mutually orthogonal vibration components and synthesizing the two mutually orthogonal vibration components. a combining means, a polarizer disposed on an optical path between the light source and the light dividing and combining means, an analyzer placed on the optical path behind the light dividing and combining means, and a combination of the polarizer and the analyzer. retardation generating means disposed on an optical path between the two and giving arbitrary retardation between two orthogonal vibration components; and retardation reading means for reading the amount of retardation generated by the retardation generating means. An epi-illuminated two-beam interferometer characterized by comprising: (2) The epi-illuminated two-beam interferometer according to claim 1, wherein the light source is a laser light source that emits linearly polarized light and does not include the polarizer.