JP2001153725A - Adjusting mechanism for angle of polarization - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarized light analyzing device which has high use efficiency of light. SOLUTION: The polarized light analyzing device 100 is equipped with a beam projection part 130 which projects a light beam on an object sample 114, a polarizer 138, a return prism 170 which returns and directs the light beam reflected by the object sample 114 to a measurement sample 123 in parallel at an interval, an analyzer 140, and an optical detector 150 which detects the light transmitted through the analyzer 140. The polarized light analyzing device 100 is equipped with a polarization angle adjusting mechanism 200 which adjusts the direction of a plane of polarization, i.e., the angle on the optical axis of the beam emitted by the beam projection part 130 so that linear polarized light having the same plane of polarization with the linear polarized light transmitted by the polarizer 138 is made incident on the polarizer 138. The polarization angle adjusting mechanism 200 is arranged between the beam projection part 130 and polarizer 138 and equipped with a linear polarized light rotating element 202 which is supported rotatably on the optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization analyzer for reflecting the linearly polarized light on the surface of a sample and examining the change in polarization to check the optical properties and film thickness of the sample.

[0002]

2. Description of the Related Art An ellipsometer basically reflects linearly polarized light having a specific plane of polarization on the surface of a sample and examines the resulting elliptically polarized light to obtain the optical properties and film thickness of the sample. It is a device for obtaining the same.

[0003] The most common technique for producing linearly polarized light having a particular plane of polarization is to pass an unpolarized light beam through a polarizer that transmits only light having a particular plane of polarization. In fact, most of the ellipsometers use the linearly polarized light thus produced.

[0004]

However, such an ellipsometer has a very low light use efficiency. That is, the light component that can pass through the polarizer is very small compared to the light component that enters the polarizer. Such low light utilization efficiency is a factor that hinders the realization of a polarization analyzer with high measurement accuracy.

An object of the present invention is to provide a polarization analyzer having a high light use efficiency, and to provide a polarization angle adjusting mechanism therefor.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a linearly polarized beam emitted from a beam emitting section is reflected by two types of samples via a polarizer, and a polarized light generated by a difference in surface state between the two types of samples. A polarization angle adjustment mechanism used in a polarization analyzer that analyzes the surface state of a sample using the properties of
This converts a linearly polarized beam emitted from the beam emitting unit into a linearly polarized beam having the same polarization plane as that of the linearly polarized light transmitted by the polarizer. The polarization angle adjustment mechanism
A linear polarization rotation element rotatably supported around the optical axis is provided.

[0007]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, an ellipsometer 100 according to the present embodiment includes a pair of sample holder units 112 and 122 for holding two types of samples. For example, the sample holding table unit 112 is the target sample 1
14 and the sample fixing table unit 122
Hold 24. The target sample 114 is used as a comparison target with the measurement sample 124 at the time of the ellipsometry processing.

The sample holding unit 112 may hold the measurement sample instead of the target sample, and the sample holding unit 122 may hold the target sample instead of the measurement sample. Such an exchange does not make any difference in the optical properties or the measurement results. However, here, it is assumed that the sample holding unit 112 holds the target sample and the sample holding unit 122 holds the measurement sample.

[0010] Both the sample fixing table unit 112 and the sample fixing table unit 122 are provided on the base 102.
The Y stage 108 holds the base 102 so as to be movable in parallel with the upper surface of the base 102.

The ellipsometer 100 includes a beam emitting unit 130 for emitting a light beam toward the target sample 114, a polarizer 138, and a light beam reflected by the target sample 114, which is folded back in parallel at intervals to measure the sample. Folding prism 170 directing to 124, analyzer 140, and analyzer 1
And a photodetector 150 for detecting light transmitted through the photodetector 40. The beam emitting unit 130 includes a light source 132, an optical fiber 134, and an optical fiber fixing unit 136. The light source 132 is, for example, a solid-state laser, a gas laser, a semiconductor laser, or a dye laser.

From another point of view, the polarization analyzer 100
Are a first optical path or an outgoing optical path extending from the optical fiber fixing portion 136 to the return prism 170 via the target sample 114, and a second optical path extending from the return prism 170 to the photodetector 150 via the measurement sample 124. Alternatively, it has a return optical path, both of which extend in parallel at an interval and are connected via a folding prism 170.

The polarizer 138 is connected to the optical fiber fixing section 13.
6 and the target sample 114, are disposed on the outgoing optical path, and the analyzer 140 includes the measurement sample 124 and the photodetector 15.
Between 0, it is located on the return optical path.

The polarizer 138 and the analyzer 140 are preferably made of a Glan-Thompson prism, and the polarizer 138 and the analyzer 140 are arranged such that the polarization planes of linearly polarized light passing therethrough are orthogonal to each other. Are located. That is, the polarizer 138 and the analyzer 140 are arranged so as to satisfy crossed Nicols.

The polarizer 138 is positioned so as to transmit linearly polarized light having a polarization plane inclined at + 45 ° with respect to the plane of incidence with respect to the target sample 114. As used herein, the term “incident surface with respect to the target sample 114” refers to a plane including a wavefront normal of light incident on the surface of the target sample 114, that is, a traveling direction and a normal set on the sample surface.

The light detection section 150 includes, for example, a photodiode, an APD, and a photomultiplier, and includes a spectral detector when a multi-wavelength light source such as a xenon lamp or a halogen lamp is used.

Optical fiber fixing section 136 and polarizer 138
And the analyzer 140 and the photodetector 150 are both the first support 1
04. The first support 104 is the base 1
02 is tilted at a predetermined angle to the target sample 1 of the linearly polarized beam transmitted through the polarizer 138.
The incident angle with respect to 14 is determined.

As shown in FIG. 2, the folding prism 170 includes three right-angle prisms 172 joined to each other.
, 174 and 176, and internally reflects the incident light beam four times, and the emitted light beam is emitted parallel to the incident light beam at a predetermined interval. The folding prism 170 is fixed to the second support 106 at an angle of 45 ° so that a plane including the axis of the incident light beam and the axis of the output light beam is parallel to the surface of the second support 106. ing.

In FIG. 1, the second support 106 is connected to the base 102 and the first support 104 is connected to the base 10.
2 are tilted at the same angle as the angle formed with respect to 2.

In FIG. 1, light emitted from a light source 132 propagates through an optical fiber 134 and is emitted from an optical fiber fixing section 136. Optical fiber fixing part 13
6 is converted into a linearly polarized beam inclined at + 45 ° with respect to the incident surface of the sample 114 by passing through the polarizer 138, and the target sample fixed to the sample fixing unit 112. The light is reflected by the surface 114. By reflection, the linearly polarized beam is changed to an elliptically polarized beam corresponding to the optical properties, film thickness, and the like of the target sample.

The elliptically polarized beam is reflected by the folding prism 1
By 70, it is folded back in parallel at intervals. The beam of light folded from the folding prism 170 is:
As a result of being reflected four times inside the folding prism 170,
With respect to the elliptically polarized light before being folded, the elliptically polarized light has the same magnitude and the same direction (for example, the major axis) of the major axis component and the minor axis component but has the opposite rotation direction.

The light beam turned back from the turning prism 170 is applied to the measurement sample 1 fixed to the sample holding table 122.
The light is reflected at 24 and directed to the analyzer 140. Analyzer 1
Since 40 transmits only the short-axis component of elliptically polarized light, only the beam of the short-axis component of elliptically polarized light passes through the analyzer 140 and reaches the light detection unit 150.

The light that has entered the photodetector 150 is subjected to spectral processing in the case of multi-wavelengths, and is photoelectrically converted for each wavelength. The electric signal output from the light detection unit 150 is taken into a computer and subjected to predetermined arithmetic processing. As a result, measurement data such as optical properties and film thickness of the sample is obtained.

If the target sample 114 and the measurement sample 124 are exactly the same, the effects of the two on the light beam cancel each other out, so that the detector 150 is in an extinction state where no light is detected.

In such an ellipsometer 100, the light incident on the polarizer 138 is linearly polarized light having the same plane of polarization as the linearly polarized light transmitted by the polarizer 138 in order to obtain a high light utilization efficiency. It is desirable. For this reason,
In a preferred beam emission 130, the light source 132 emits linearly polarized light, the optical fiber 134 is a polarization maintaining fiber, and the polarization maintaining fiber 134 has a polarization plane (polarization plane) of linearly polarized light emitted therefrom. It is attached to the optical fiber fixing part 136 so as to have the same polarization plane as the linearly polarized light passing through 138.

The optical fiber 134 is not limited to the polarization-maintaining fiber 134, and is positioned at the correct position with respect to a plane perpendicular to the optical axis and in the correct direction about the optical axis, that is, so that light is appropriately detected by the photodetector 150. It is required to be fixed to the optical fiber fixing portion 136 at an angle. This is already a severe requirement in assembly, and in addition to this,
As described above, it is very difficult to appropriately adjust the direction around the optical axis 4 in other words, that is, the angle around the optical axis.

In the ellipsometer 100 of the present embodiment, the above-mentioned requirement necessary for obtaining high light use efficiency, that is, the polarizer 138 is transmitted, without strict requirements for such assembly. A polarization angle that adjusts the direction, that is, the angle, of the polarization plane about the optical axis of the beam emitted from the beam emission unit 130 in order to achieve that linearly polarized light having the same polarization plane as the linearly polarized light is incident on the polarizer 138. An adjusting mechanism 200 is provided.

The polarization angle adjusting mechanism 200 includes the beam emitting unit 1
A linear polarization rotator 202 is provided between the polarizer 138 and the polarizer 138 and rotatably supported around the optical axis. Here, the linear polarization rotation element 202 refers to any optical element that rotates the plane of polarization of the incident linearly polarized light around the optical axis.

The linear polarization rotating element 202 is, for example, ２
A wave plate, which converts incident linear light having a polarization plane inclination of an angle θ with respect to its optical axis into linearly polarized light having a polarization plane inclination of an angle 2θ. Therefore, the direction of the optical axis of the half-wave plate with respect to the polarization plane of the incident linearly polarized light is 0 ° to 1 °.
When the half-wave plate is rotated so as to change in the range of 80 °, the polarization plane of the beam passing therethrough is 0 ° to 360 °.
It changes in the range of °. In other words, by rotating the half-wave plate, it is possible to arbitrarily adjust the direction or angle of the polarization plane of the beam passing therethrough.

As shown in FIG. 3, the polarization angle adjusting mechanism 200 includes a mount 210 that rotatably supports the linear polarization rotation element 202. The mount 210 includes a movable frame 212 that holds the linear polarization rotation element 202 and a fixed frame 2 that rotatably supports the movable frame 212 about an axis 216.
14 is provided. The fixed frame 214 includes, for example, an angle adjustment mechanism that adjusts an angle of the movable frame 212 around the axis 216. The fixed frame 214 has a rotatable input shaft, and the rotation supplied to the input shaft is controlled by the movable frame. It is converted to a relatively small angle change 212 and transmitted.

The adjustment of the direction of the linear polarization rotation element 202 around the optical axis is performed, for example, manually. This is because the user manually rotates the input shaft of the angle adjustment mechanism of the fixed frame 214 to monitor the output of the detection unit that detects the light transmitted through the polarizer 138, and detects the angle of the movable frame 212. The adjustment is performed so that the output of the control signal is maximized. After the adjustment, the movable frame 212 is preferably fixed to the fixed frame 214 by means such as screws.

Alternatively, the direction of the linear polarization rotation element 202 around the optical axis is automatically adjusted. For this reason, the polarization angle adjustment mechanism 200 further includes a control unit 220 that controls the angle adjustment mechanism.
For example, the control unit includes a driving unit for rotating an input shaft of the angle adjusting mechanism, and a control unit for controlling the driving unit based on an output of a detection unit that detects light transmitted through the polarizer 138, and the control unit includes: The driving means is controlled so that the output of the detecting means is maximized. After the adjustment, the driving means
4 also has a function of fixing the movable frame 212. The driving means includes, for example, a stepping motor,
The rotation shaft of the stepping motor may be directly connected to the input shaft of the angle adjustment mechanism, or may be connected via a member such as rubber or a belt.

In the above-described adjustment of the direction of the linear polarization rotation element 202 around the optical axis, the detecting means for detecting the light transmitted through the polarizer 138 is provided on the optical path between the polarizer 138 and the analyzer 140, for example. The inserted light receiving element.
Alternatively, the detecting means may be configured to connect the polarizer 138 to the analyzer 140.
A deflecting element such as a mirror inserted on the optical path between
A combination of light receiving elements that receive the deflected light may be used. Alternatively, the detection means may be the photodetector 150 from which the analyzer 140 has been removed.

Since the polarization analyzer 100 of the present embodiment includes the polarization angle adjusting mechanism 200 that can arbitrarily change the direction or angle of the plane of polarization of the beam incident on the polarizer 138, the straight line incident on the polarizer 138 can be obtained. It is easy to make the plane of polarization of the polarized beam coincide with the transmission axis of the polarizer. This achieves high light utilization efficiency, which is beneficial for improving measurement accuracy.

The present invention is not limited to the above-described embodiment, but includes all embodiments carried out without departing from the gist thereof. For example, light from a light source may be directly incident without using an optical fiber. When a semiconductor laser is used, it is preferable to provide a collimator.

[0036]

According to the present invention, an ellipsometer having high light use efficiency is provided. This is useful for improving measurement accuracy.

[Brief description of the drawings]

FIG. 1 is a plan view of a polarization analyzer including a polarization angle adjusting mechanism according to an embodiment of the present invention.

FIG. 2 is a perspective view of the folded prism shown in FIG.

FIG. 3 is a perspective view of a polarization angle adjusting mechanism shown in FIG. 1;

[Explanation of symbols]

 200 polarization angle adjustment mechanism 202 linear polarization rotation element

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2F065 AA30 BB22 DD03 FF50 GG02 GG03 GG06 HH04 HH13 JJ17 JJ18 LL02 LL09 LL12 LL33 LL34 LL47 MM04 PP12 PP13 2G059 AA02 EE05 EE11 EE12 JJ01 JJ12 JJ01 GG01 JJ12 GG01 JJ01

Claims (3)

[Claims] 1. A linearly polarized light beam emitted from a beam emitting unit is reflected by two types of samples via a polarizer, and the property of the polarized light generated by a difference in surface state between the two types of samples is used. In a polarization analyzer that analyzes the surface state, a linearly polarized beam emitted from the beam emission unit is
A polarization angle adjustment mechanism that converts a linearly polarized beam having the same polarization plane as that of the linearly polarized light transmitted by the polarizer. 2. The polarization angle adjustment mechanism according to claim 1, wherein the polarization angle adjustment mechanism includes a linear polarization rotation element rotatably supported around an optical axis. 3. The polarization angle adjustment mechanism according to claim 1, wherein the direction, that is, the angle, around the optical axis of the linear polarization rotation element is adjusted manually or automatically.