JP2636863B2 - Polarizing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a polarizing device for obtaining a luminous flux having a desired polarization state, and in particular, to a polarization intensity ratio resulting from light reflection. The present invention relates to a polarizing device suitable for arbitrarily suppressing.

(Prior Art) Even if non-polarized light such as natural light is reflected on the surface of an object, the reflected light is divided into a polarized light component (P-polarized light) parallel to the incident surface and a polarized light component (S-polarized light) perpendicular to the incident surface. ) Is known to change the intensity ratio of polarized light. As means for suppressing the light intensity ratio of the polarized light component in the reflected light, a certain component of the transmitted electromagnetic wave is selectively absorbed to remove the unpolarized light. Polarization filters that convert to linearly polarized light are generally well known. This polarization filter transmits almost 100% of the component in the polarization direction parallel to the axis of the filter, and the polarization component perpendicular to the polarization plane is
Absorbs almost 100%. That is, the ratio of the polarization component parallel to the axis to the polarization component perpendicular to the axis of the light transmitted by the polarization filter is approximately 100: 0.

(Problems to be Solved by the Invention) However, in the above-described conventionally used polarizing filters, almost half of the incident light is absorbed, and thus the intensity of the obtained light is, for example, in the case of natural light. 1/2 or less. Accordingly, the polarization plane of the polarization filter inserted in the incident light is inclined with respect to the incident plane, and the light transmitted through the polarization filter is converted into the x direction (S polarization) perpendicular to the y direction (P polarization) parallel to the incidence plane. , And even if the component ratio is changed by rotating the polarizing filter, each component becomes less than 1/2 of the incident light. In particular, when the component ratio is 1: 1, the intensity of each component is 1/4 or less of the incident light, and the detection accuracy is reduced in a measuring device that measures the surface position and the properties of the thin film using surface reflection. There was a problem of doing.

Therefore, the present invention solves the problems of a polarizing device such as the above-mentioned conventional polarizing filter, and solves the problem of two polarizing devices whose polarizing directions are perpendicular to each other.
It is an object of the present invention to provide a polarizing device that can easily change the intensity ratio of two polarized light components to an arbitrary value, and efficiently combines and emits the changed two polarized light components again.

[Configuration of the invention]

(Means for Solving the Problems) In order to achieve the above object, in the present invention, polarization separation optical means for separating incident light into two polarization components whose polarization directions are perpendicular to each other, and this polarization separation optical means Polarization direction changing means capable of independently and arbitrarily changing the polarization directions of the two polarization components emitted through the means, and combining the two polarization components whose polarization directions have been changed by the polarization direction changing means into one direction And a polarization-combining optical means for emitting light to the light source.

(Effect) Various incident lights (L ₁ ) having different polarization states are converted by the polarization separation optical means (1, 21) into P light beams whose polarization directions are perpendicular to each other.
The light is separated into a polarized light component and an S-polarized light component and emitted in different directions. At that time, there is almost no loss of light energy, and the sum of the intensity of the separated P-polarized light component and the intensity of the separated S-polarized light component is equal to the light intensity of the incident light (L ₁ ). The S-polarized light component and the P-polarized light component separated by the polarization separation optical means (1) are combined with a λ / 2 plate (5,
By the rotation of 6), the polarization direction can be arbitrarily changed.
Further, the P-polarized light component and the S-polarized light component whose polarization directions are arbitrarily changed are combined by the polarization combining optical means (2), and the intensity of each polarized light component in the combined light is λ / 2 plate (5, 6)
Can be arbitrarily changed depending on the rotation amount of the polarization direction due to Therefore, the ratio between the P-polarized light and the S-polarized light of the combined light emitted from the polarization combining optical unit can be arbitrarily changed. Also, if the amount of rotation in the polarization direction is appropriate, the light amount of one polarized light component can be directly emitted as synthesized light, so that at least one polarized light component has no energy loss at all.
The ratio between the polarization component and the S-polarization component can be changed efficiently over a wide range.

Example Next, an example of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is an optical system configuration diagram showing a first embodiment of the present invention, wherein a first polarizing prism 1 and a second polarizing prism 2
Each of the joint surface 1a, 2a to have a dielectric multilayer film, the non-polarized light beam L ₁ of (randomly polarized) or circularly polarized light from the light source 10 enters the first polarization prism 1 is the junction surface 1a, the junction The P-polarized light component is separated into a P-polarized light component parallel to the plane of incidence perpendicular to the plane and a P-polarized light component perpendicular to the incident plane and having the same intensity as the P-polarized light component. Go to Further, the other S-polarized light component is reflected by the joint surface 1a and further travels to the second polarizing prism 2 via the two mirrors 3 and 4. Then, on the optical path between the first polarizing prism 1 and the second polarizing prism 2 through which the P-polarized light and the S-polarized light pass, respectively, the polarization direction can be changed arbitrarily.
Plates 5 and 6 are provided, respectively.

As shown in FIG. 2, the P-polarized light incident on the λ / 2 plate 5 is
When the lambda / 2 plate 5 angle theta ₁ rotates the polarization direction is emitted rotated by 2 [Theta] _1. The polarized light component parallel to the plane of incidence perpendicular to the joining surface 2a of the polarizing prism 2 is transmitted through the joining surface 2a and
L a ₂ of the P-polarized light component. P at the combined light L ₂ at this time
The intensity of the polarization component is proportional to (cos2θ ₁ ) ² . On the other hand, when the lambda / 2 plate S-polarized light incident on 6 well lambda / 2 plate 6 the angle theta ₂ rotates, is injected by rotating the optical direction by an angle 2 [Theta] _2. Polarization component parallel to the junction surface 2a of the polarizing prism 2 is reflected by the bonding surface 2a, the S-polarized component of the combined light L _2. The intensity of the S-polarized component in the combined light L ₂ at this time is proportional to (cos2θ _{²⁾ 2.} Therefore, by changing the angles θ ₁ and θ ₂ of the λ / 2 plates 5 and 6, the intensity ratio between the P-polarized light and the S-polarized light can be arbitrarily changed.

The incident light L ₁ is converted by the first polarizing prism 1 into P-polarized light and S-polarized light having the same intensity without loss of energy.
The split and split P-polarized light and S-polarized light are guided to the second polarizing prism 2 without energy loss. If both the lambda / 2 plate 5 and 6 is set to a state that does not change the polarization direction therefore, the light intensity of the synthesized light emitted L ₂ emitted from the second polarization prism 2, the incident light L ₁ It is almost the same. In this case, the P-polarized light and S-polarized light included in the synthesis emitted light L ₂ and the intensity of the incident light L ₁ to 100 50, respectively.

A similar effect can be obtained by using a variable density filter or a polarizing filter in place of the λ / 2 plates 5 and 6, but with a general variable density filter, the combined light L ₂ obtained because the transmittance is not constant in the light flux. Has a disadvantage that the intensity is not uniform, and a general polarizing filter cannot achieve 100% transmittance even if the polarization direction matches the incident light. On the other hand, if a λ / 2 plate is used as in the present invention, the transmittance in the light beam is uniform, and a transmittance of almost 100% can be obtained. It is possible.

Further, as shown in FIG. 3A, when the axis of the λ / 2 plate is rotated by 45 °, the polarization directions of the incident light and the emitted light are rotated by 90 °. Therefore, by appropriately rotating the λ / 2 plates 5 and 6, it is possible to convert P-polarized light to S-polarized light and S-polarized light to P-polarized light. In this case, the synthetic emission light L ₂ from the second polarizing prism ₂
Is another synthetic emitted light L ₃ which emits in different directions resulting from the. Then, as shown in FIG. 3B, the axis of the λ / 2 plate 5 is
If you rotated by 45 ° + theta _1, the intensity of the S-polarized component in the combined emitted light L ₃ is proportional to (cos2θ ₁₎ ^2. Similarly, if rotating the shaft of the lambda / 2 plate 6 by 45 ° + theta _2, the intensity of the P-polarized component in the combined emitted light L ₃ is (cos ₂₎ ²
Is proportional to Therefore, P-polarized light in the combined light emitted L ₃ and S
It is also possible to arbitrarily change the intensity ratio with the polarized light.

Then, by using the lambda / 2 plate 5,6, it is possible to take out the different directions to the two synthetic exit light L ₂ and L _3, can act as switching device for an optical path, also two synthesis emitted light L ₂ and L ₃ together can also be utilized.

FIG. 4 is an optical system configuration diagram showing a second embodiment of the present invention in which the optical path length of the P-polarized light component is made equal to the optical path length of the S-polarized light component. Parts having the same functions as those in the embodiment of FIG. 1 are denoted by the same reference numerals as in FIG. 1, and detailed description of the configuration is omitted.

In FIG. 4, incident light L ₁ of non-polarized light (randomly-polarized light) or circularly-polarized light is separated into P-polarized light and S-polarized light by the first polarizing prism 1, and the light beam of P-polarized light is transmitted through the bonding surface 1 a. , Λ / 2 plate 5, the polarization direction is changed, reflected by mirror 4, and transmitted through second polarization prism 2 joint surface 2a. On the other hand, the s-polarized light beam reflected by the bonding surface 1a of the first polarizing prism 1 is reflected by the mirror 3,
Is reflected by the second polarizing prism 2 of the joint surface 2a, is emitted from the second polarization prism 2 is combined with P-polarized light as a synthetic emitted light L _2. Intensity ratio of the P-polarized component and S-polarized component of this synthetic emitted light L ₂ is changed arbitrarily by a lambda / 2 plate 5 and 6. In this case, the P-polarized light and the S-polarized light have the same optical path length, but are synthesized simply as the sum of the light intensities of the two without interfering with each other as in the embodiment of FIG. Also, λ
By setting the rotation angle of the / 2 plate appropriately,
It is also possible to use the L _3. In the examples shown in FIGS. 1 and 2, the light from the light source is described as circularly polarized light or random polarized light.
The two polarized light beams combined by the second polarizing prism when light of any polarization state is incident, as long as it is not only linearly polarized light of only P-polarized light parallel to the plane of incidence or only S-polarized light perpendicular to the plane of incidence. It is possible to arbitrarily change the light intensity.

FIG. 5 is an optical system configuration diagram showing a third embodiment of the present invention when a light source emitting linearly polarized light is used. Parts having the same functions as in FIG. 1 are denoted by the same reference numerals as in FIG. 1, and detailed description of the configuration is omitted. However, in the third embodiment, the optical paths are bent using total reflection prisms 7, 8 instead of the mirrors 3, 4 in the first embodiment.

In FIG. 5, a λ / 4 plate 21 is provided on an optical path between a light source 20 that emits linearly polarized light and the first polarizing prism 1, whereby the linearly polarized light becomes circularly polarized light, and
Incident on. The circularly polarized incident light beam is separated into P-polarized light and S-polarized light having the same intensity by the first polarizing prism 1 as in the embodiment of FIG. After the polarization direction with the S-polarized light is adjusted to an arbitrary direction, the light is synthesized by the second polarizing prism 2. The combined synthesized emitted light L ₂ from the second polarizing prism 2, the incident light L ₁
It is emitted in the same direction as. Also in this embodiment, it is needless to say that available synthetic exiting light L _3. Also, here, the first polarizing prism 1 and the λ / 4 plate 21 constitute a polarization splitting optical unit.

In the embodiment of FIG. 5, the axis of the λ / 4 plate 21 may be fixed at 45 ° with respect to the polarization directions of the P-polarized light and the S-polarized light.
In this way, even if the polarization direction of the linearly polarized light changes,
The intensity ratio of the emitted P-polarized light component and S-polarized light component is unchanged as shown below. Now, in FIG. 6, the λ / 4 plate 21
Is linearly polarized light incident on a, b is elliptically polarized light after passing through the λ / 4 plate 21, and P is polarized light emitted from the first polarizing prism 1.
And S, the axis of the λ / 4 plate 21 is
Since the light is inclined by 45 °, the light emitted from the λ / 4 plate 21 becomes elliptically polarized light b whose elliptical axis makes 45 ° with respect to the P and S directions. Accordingly, the respective intensities of the P and S polarized lights separated by the first polarizing prism 1 become equal. Therefore, λ
By / 2 plate 5, 6, P, by adjusting the intensity ratio of S-polarized light, P-polarized light and S-polarized light intensity ratio of the light beam L ₂ emitted from the second polarization prism 2, linearly polarized light of the incident light beam L ₁ Becomes invariant even if the polarization direction of

Even if the incident light is elliptically polarized light, if the axis of the λ / 4 plate 21 is inclined in the 45 ° direction even if the axis of the elliptically polarized light rotates,
The intensity of the P and S polarized lights separated by the polarizing prism 1 is unchanged. However, in this case, the intensities of the P and S polarized lights are not equal.

FIG. 7 is an optical system configuration diagram of a fourth embodiment of the present invention in which a λ / 2 plate 41 is added as a light intensity varying means. in this case,
A light source that emits either linearly polarized light or elliptically polarized light is used. Parts having the same functions as those in the embodiment of FIG. 1 are denoted by the same reference numerals as in FIG. 1, and detailed description of the configuration is omitted.

The incident light L ₁ of the optical path, the intensity ratio of the P-polarized component and S-polarized light component separated by the first polarization prism 1 between the light source 40 and the first polarizing prism 1 that emits linearly polarized light or elliptically polarized light A λ / 2 plate 41 for changing is provided. When the x-direction component and the y-direction component of the light passing through the λ / 2 plate 41 are shifted in phase by 180 ° and the λ / 2 plate 41 is rotated, the polarization directions of the linearly polarized light and the elliptically polarized light are changed. Can be changed according to rotation. Therefore, the λ / 2 plate 41 passes the incident light L ₁
The intensity ratio between the P-polarized light component and the S-polarized light component separated by the first polarizing prism 1 can be changed by appropriately adjusting the rotation in a plane perpendicular to the plane. In this case, since the intensity in a certain direction can be made zero (0) in the case of linearly polarized light, the intensity ratio of the separated P and S polarized light components is set to be (0: 100) to (50: 5
It can freely change between 0) and (100: 0). However, in the case of elliptically polarized light, since the intensity in an arbitrary direction is finite and not zero, the ratio between the P-polarized light component and the S-polarized light component can be made equal (50:50). Can only be in the range

However, the P polarization component and the S polarization component are λ / 2
The plates 5,6, after being Henra in arbitrary polarization direction, the second is synthesized by the polarizing prism 2, P, the second polarization as a combined emitted light L ₂ which the intensity ratio was varied any S-polarized component The light is emitted from the prism 2. In this example,
Because it can change the intensity of the P-polarized component and S-polarized light component by both and the lambda / 2 plate 41 lambda / 2 plate 5,6, with a minimum loss of energy of the incident light L _1, there in elliptical polarization Even
The intensity ratio of the P and S polarization components can be arbitrarily changed.
Also it is needless to say that may utilize other synthetic emitted light L _3.

In the embodiment shown in FIG. 7, a light source which emits linearly polarized light or elliptically polarized light is used, but the light source may be circularly polarized light or randomly polarized light, or light of any polarization state. For a circularly polarized light source, λ / 4
Even if a plate is inserted in front of the first polarizing prism, an efficient device can be obtained as in the example of FIG.

FIG. 8 is a schematic configuration diagram of an optical system of a grazing incidence type surface position detecting device incorporating the polarizing device of the present invention. This 8th
In the figure, the polarizing device of the first embodiment using the light source 10 emitting non-polarized light (randomly polarized light) shown in FIG. 1 is used, but it goes without saying that the device of another embodiment may be incorporated. .

In FIG. 8, the incident light L ₁ from the light source 10 is incident on the first polarizing prism 1 as a substantially parallel light flux by the collimator lens 11. The P-polarized light component and the S-polarized light component having the same intensity separated by the first polarizing prism 1 are respectively λ
/ 2 is changed to an appropriate polarization direction through the plate 5,6, after being synthesized by the second polarizing prism 2, a suitable P, it is emitted as a combined emitted light L ₂ having the intensity ratio of S-polarized light. This synthetic emitted light L ₂ passes through the slit opening 13A of the light-sending slits 13 provided near the field lens 12 and to the detection light objects to be detected via a light projecting side objective lens 14A as L ₃ (e.g. semiconductor wafer) 15 is projected with a Brewster angle of incidence larger than the angle theta _i on, slit opening 13A conjugate with the slit light image is formed on the detected surface 15A.

The reflected light L ₄ from the detected surface 15A is condensed on the light-receiving slit 16 through the light receiving side objective lens 14B, a slit structure is re-imaged on the light-receiving slit 16. The re-imaging position of this slit light image is such that the surface 15A of the detected object 15 is the first position.
4, the light receiving slit 16 is displaced in a direction perpendicular to the optical axis of the light receiving image side objective lens 14B in accordance with the displacement. By detecting the amount of deviation of the re-formed slit light image from the reference position, the detected surface 15A
Can be detected in the vertical direction. For its surface position detection, for example, the principle of a photoelectric microscope is used,
The light receiving slit 16 reciprocates in the direction of arrow D, and the slit light image is formed in the light receiving slit 16 by the slit opening 16A.
Is configured to scan. Slit opening 16A
Is passed through the lens 17 and received by the light receiving device (photoelectric conversion element) 18 to detect the position of the center of gravity of the light amount of the slit light image. The position of the detected surface 15A can be detected from the amount of deviation of the light quantity centroid from the reference position.

On the other hand, on the surface of the substrate 15B of the detected object 15, a light-transmissive thin film 15C such as a photoresist is provided. The detection light L _3, which is projected to the thin film 15C is a portion thereof reflected by the thin film surface 15A as shown in FIG. 15,
A slit light image is formed on the light receiving slit 16, and the other part is transmitted through the thin film surface 15A as shown by a broken line. The light transmitted through the thin film surface 15A is reflected on the substrate surface 15D, transmits again through the thin film surface 15A, and forms a slit light image on the light receiving slit 16. Slit light image by the reflected light L ₅ reflected by the substrate surface 15D, depending on the thickness of the thin film 15C,
Slightly lateral to imaging with respect to the slit light image by the reflected light L ₄ at the thin film surface 15A, both of the slit light images,
A part is superimposed. The position of the center of gravity of the combined light amount of the two slit light images partially overlapped is determined by the light receiving slit 16.
Is detected by scanning.

On the other hand, the reflected light L ₄ and L ₅ of the portion where both of the slit light image is heavy疊, interfere with each other because the thin thin film 15C is thin, resulting in interference fringes dark. As a result, the position of the center of gravity of the combined light amount of the slit light image fluctuates greatly due to the difference in brightness of the overlapped portion due to light interference. Will cause a large error to occur.

Incidentally, the angle of incidence on the film surface 15A of the detection light L ₃ theta
_i is set to an angle larger than the Brewster angle in order to increase the detection accuracy of the surface position. However, the light transmitted through the thin film surface 15A is to refraction at the surface 15A, the incident angle theta _a to the substrate surface. 15D Brewster angle smaller. It is generally known that when the incident angle reaches the Brewster angle, the reflectance of the P-polarized light component parallel to the incident surface becomes zero (zero), and the reflected light is only the S-polarized light component perpendicular to the incident surface. When the incident angle becomes larger than the Brewster angle, as shown by arrows P ₁ and P ₂ in FIG. 9, the P-polarized light component P ₁ of the reflected light L ₄ from the thin film surface 15 A and the substrate surface 15 D
Each other and the P-polarized component P ₂ of the reflected light L ₅ from the phase is reversed 180 degrees. However, the S-polarized light components included in the reflected light L ₄ and L ₅
S ₁ and S ₂ have the same phase and are invariant. Therefore, the interference fringes due to P ₁ and P ₂ and the interference fringes due to S ₁ and S ₂ are 180 ° out of phase with each other, and the change in the intensity of the interference fringes due to the P polarization component is small, but the S polarization component is small. Interference fringes
A change much larger than the interference pattern of the P-polarized light component will be shown according to the thin film error.

In order to reduce the surface position detection error caused by the light and dark of the interference fringes, the degree of the light and dark of the interference fringes 180 ° out of phase by the P-polarized component and the S-polarized component is adjusted, and the reflected light is adjusted. by L ₁ and L ₂ may be so as to correct the variation due to thin film position error of the light intensity gravity center of the slit light image. Therefore, by changing the intensity ratio between the first 8 P-polarized component by adjusting the lambda / 2 plate 5 and 6 in the figure contained in the synthetic light emitted L ₂ and the S-polarized component appropriately, the thin film of the thin film 15C The deviation of the center of gravity of the light amount of the slit light image due to the error can be set within an allowable limit.

〔The invention's effect〕

As described above, according to the present invention, there is no loss of light energy in the separation and synthesis of polarized light, and the separated P-polarized light component and S-polarized light component are separated by the polarization direction using the polarization separation optical means and the polarization synthesis optical means. Since the polarization direction can be arbitrarily changed by the variable means, the P included in the emitted light can be changed.
Since the intensity of the polarized light component and the S-polarized light component can be easily and efficiently changed to a value as required, various detectors utilizing polarized light, detecting surface reflected light as in a measuring instrument or the embodiment, If it is used for a device or the like that detects the position or state of the surface, the detection accuracy and measurement accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is an optical system configuration diagram showing a first embodiment of the present invention when the incident light is unpolarized light (randomly polarized light) or circularly polarized light. FIG. 2 is a diagram showing the rotation of the polarization direction due to the rotation of the λ / 2 plate. Illustration, No.
FIGS. 3A and 3B are explanatory diagrams of the case where the P and S polarizations are reversed by the λ / 2 plate, and FIG. 4 is a second embodiment of the present invention in the case where the optical path lengths of the two separated polarizations are made equal. FIG. 5 is an optical system configuration diagram showing a third embodiment of the present invention when the incident light is linearly polarized light, and FIG. 6 is λ / 4 in FIG.
FIG. 7 is an explanatory view of the polarization state when the axis of the plate is fixed at an angle of 45 ° with respect to the P and S polarization directions. FIG. 7 shows a fourth embodiment of the present invention in which a λ / 2 plate is added as polarization intensity changing means. FIG. 8 is a schematic configuration diagram of an oblique incidence type surface position detecting device incorporating the embodiment device of FIG. 1, and FIG. 9 is a P-polarized component and an S-polarized component of the reflected light shown in FIG. FIG. (Description of Signs of Main Parts) 1... First polarizing prism (polarized light separating optical means) 21 .lambda. / 4 plate (polarized light separating optical means) 2... Second polarizing prism (polarized light combining optical means) 5, 6 .... lambda./2 plate (polarization direction changing means) 41..lambda. / 2 plate (polarization intensity changing means) 10. Unpolarized or circularly polarized light source 20. Linearly polarized light source 40 .. Linearly polarized light or elliptically polarized light source L ₁ …… incident light L ₂ , L ₃ …… combined emission light

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Isao Sato 1-6-3 Nishioi, Shinagawa-ku, Tokyo Nihon Kogaku Kogyo Co., Ltd. Oi Works (56) References JP-A-59-124044 (JP, A) JP-A-60-39630 (JP, A) JP-A-55-127516 (JP, A)

Claims (2)

(57) [Claims] 1. A polarization separation optical means for separating incident light into a pair of polarization components whose polarization directions are perpendicular to each other, and the polarization directions of the pair of polarization components separated via the polarization separation optical means are independent of each other. A polarization apparatus comprising: a polarization direction changing unit that can be changed arbitrarily; and a polarization combining optical unit that combines and emits the pair of polarization components whose polarization directions have been changed by the polarization direction changing unit. 2. The polarizing prism according to claim 1, wherein said polarization separating optical means and said polarization combining optical means transmit a polarization component whose polarization direction is parallel to the plane of incidence and reflect a polarization component perpendicular to the plane of incidence. Wherein the polarization direction changing means is constituted by λ / 2 plates (5, 6) provided on the optical path of both polarization components between the two polarization prisms (1, 2). The polarizing device according to claim 1, wherein