JP2007163804A - Polarization beam splitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarization beam splitter having a high polarization separation performance at a wide divergence angle. <P>SOLUTION: The polarization beam splitter for separating incident beams has at least three laminate groups formed on a substrate, each of which is made by alternately laminating a film made of high refractive index material having a refractive index higher than that of the substrate and a film made of low refractive index material having a refractive index lower than that of the substrate, wherein, when an optical film thickness of the film made of high refractive index material is H×λ/4 and an optical film thickness of the film made of low refractive index material is L×λ/4 with respect to the center wavelength λ of the beams, the final laminate group formed on the most incident side among at least three laminate groups satisfies 1.3<H<1.5 and 1.3<L<1.5 and the laminate groups other than the final laminate group satisfies 0.5<H<1 and 1<L<1.5, or 1<H<1.5 and 0.5<L<1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention generally relates to a polarizing beam splitter, and more particularly, to a polarizing beam splitter in which a light beam having a predetermined wavelength is incident at different predetermined directions depending on the polarization state of the light beam. The present invention is suitable for a polarization beam splitter used in laser application equipment such as a laser processing machine, a measuring apparatus, and an exposure apparatus.

  2. Description of the Related Art A projection exposure apparatus has been conventionally used when manufacturing a fine semiconductor element such as a semiconductor memory or a logic circuit by using a photolithography technique. The projection exposure apparatus projects a circuit pattern drawn on a reticle (mask) onto a wafer or the like by a projection optical system and transfers the circuit pattern.

  The minimum dimension (resolution) that can be transferred by the projection exposure apparatus is proportional to the wavelength of light used for exposure and inversely proportional to the numerical aperture (NA) of the projection optical system. Therefore, the shorter the wavelength and the higher the NA, the higher the resolution. For this reason, the wavelength of exposure light has been shortened in accordance with the recent demand for miniaturization of semiconductor elements. For example, the wavelength of exposure light has been shortened from an ultra-high pressure mercury lamp (i-line (wavelength: about 365 nm)) to KrF excimer laser (wavelength: about 248 nm) and ArF excimer laser (wavelength: about 193 nm). In addition, the NA of the projection optical system has been increased, and at present, the NA of a projection exposure apparatus (projection optical system) using an ArF excimer laser as a light source is being advanced.

  An increase in the NA of the projection optical system means that the angle formed between the perpendicular from the image plane and the traveling direction of the incident light is increased, and this is called high NA imaging. In high NA imaging, the polarization of exposure light becomes a problem. For example, consider the case of exposing a so-called line and space (L & S) pattern in which lines and spaces are repeated. The L & S pattern is formed by plane wave two-beam interference. A plane including the incident direction vector of two light beams is defined as an incident plane, polarized light perpendicular to the incident plane is defined as S-polarized light, and polarized light parallel to the incident plane is defined as P-polarized light. Note that simply polarized light perpendicular to the paper surface may be referred to as S-polarized light, and simply polarized light parallel to the paper surface may be referred to as P-polarized light. When the angle formed between the incident vectors of the two light beams is 90 degrees, the S-polarized light interferes, so that a light intensity distribution according to the L & S pattern is formed on the image plane. On the other hand, since the P-polarized light does not interfere (the effect of interference is canceled), the light intensity distribution is constant, and the light intensity distribution corresponding to the L & S pattern is not formed on the image plane. When S-polarized light and P-polarized light coexist, a light intensity distribution having a poorer contrast than when only S-polarized light is formed on the image plane. When the ratio of P-polarized light is increased, the contrast of the light intensity distribution on the image plane is increased. In the end, the pattern is not formed.

For this reason, it is essential to control the polarization of the exposure light as the NA of the projection optical system increases, and a highly efficient polarizing beam splitter (polarizing element) is required even in the wavelength region of 193 nm. In the future, a projection exposure apparatus using an F ₂ laser (wavelength of about 157 nm) as a light source is expected to be put into practical use, and a polarization beam splitter corresponding to the F ₂ laser is also required.

  The polarization beam splitter is an optical element that separates a light beam into two in accordance with polarization. The polarizing beam splitter is generally manufactured by laminating a dielectric on a cubic prism and using an adhesive. However, in the wavelength region of 200 nm or less, light absorption by the adhesive is large, and there is no usable adhesive. Therefore, a plate-type polarizing beam splitter in which a dielectric multilayer film is laminated on a flat plate is used.

  A plate-type polarizing beam splitter is generally configured by laminating a high refractive index layer and a low refractive index layer having an optical film thickness that is ¼ times the design wavelength on a substrate. In addition, in order to widen the wavelength region that functions as a polarizing beam splitter, various adjustment layers are added to the laminated film, or the reference film thickness of the laminated film is an integral multiple of the optical film thickness that is 1/4 times the design wavelength or It is used as a reciprocal of an integer.

On the other hand, the polarizing beam splitter produced in this way is sensitive to an angle and has a drawback that it is strictly limited to an angle when used. Therefore, a polarizing beam splitter has been proposed that uses two stacked groups in which a high refractive index layer and a low refractive index layer are repeatedly stacked, and has polarization separation characteristics even when the divergence angle of the incident angle is ± 5 degrees or more (eg , See Patent Document 1).
JP-A-9-184916

  However, the polarization beam splitter proposed in Patent Document 1 cannot maintain the polarization separation characteristics when the divergence angle of the incident angle becomes ± 10 degrees. In other words, the polarization beam splitter proposed in Patent Document 1 cannot maintain polarization separation characteristics with respect to light incident at various angles. For example, in an exposure apparatus where the NA increases. The desired polarization separation characteristics cannot be achieved.

  Therefore, an object of the present invention is to provide a polarization beam splitter having high polarization separation characteristics at a wide divergence angle.

  In order to achieve the above object, a polarizing beam splitter as one aspect of the present invention is a polarizing beam splitter that separates an incident light beam, and is formed on a substrate and has a refractive index higher than that of the substrate. And having at least three laminated groups in which a film made of a high refractive index material and a film made of a low refractive index material having a refractive index lower than the refractive index of the substrate are alternately laminated, and the center of the light beam When the optical film thickness of the film made of the high refractive index material is H × λ / 4 and the optical film thickness of the film made of the low refractive index material is L × λ / 4 with respect to the wavelength λ, Of the at least three or more stacked groups, the final stacked group formed most on the light incident side satisfies 1.3 <H <1.5 and 1.3 <L <1.5. Layer groups other than the final layer group include 0.5 <H <1 and 1 <L <1 .5 or 1 <H <1.5 and 0.5 <L <1.

  A polarizing beam splitter according to another aspect of the present invention is a polarizing beam splitter that separates an incident light beam, and is formed of a high refractive index material that is formed on a substrate and has a refractive index higher than that of the substrate. A first laminated group in which a film and a film made of a low refractive index material having a refractive index lower than the refractive index of the substrate are alternately laminated; and the high refractive index formed on the first laminated group. A second laminated group in which a film made of a material and a film made of the low refractive index material are alternately laminated; a film made of the high refractive index material formed on the second laminated group; A third laminated group in which films made of a refractive index material are alternately laminated, and an optical film thickness of the film made of the high refractive index material is H × λ / 4. When the optical film thickness of the film made of a low refractive index material is L × λ / 4, The first stack group and the second stack group are 0.5 <H <1, and 1 <L <1.5, or 1 <H <1.5, and 0.5 <L. <1 is satisfied, and the third stacked group satisfies 1.3 <H <1.5 and 1.3 <L <1.5.

  A polarizing beam splitter according to still another aspect of the present invention is a polarizing beam splitter that separates an incident light beam. When the divergence angle of the light beam is ± 10 degrees or more, the transmittance of P-polarized light is 80% or more, and The transmittance of S-polarized light is 10% or less.

  Further objects and other features of the present invention will become apparent from the preferred embodiments described below with reference to the accompanying drawings.

  According to the present invention, it is possible to provide a polarization beam splitter having high polarization separation characteristics over a wide divergence angle.

  Hereinafter, a polarizing beam splitter as one aspect of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view showing a configuration of a polarizing beam splitter 100 as one aspect of the present invention.

  The polarization beam splitter 100 is a polarization beam splitter that separates (branches) an incident light beam. As shown in FIG. 1, the polarization beam splitter 100 includes a substrate 110, at least three or more stacked groups (three stacked groups in FIG. 1) 120 to 140, and an adjustment layer 150. Note that a stacked group (in FIG. 1, the stacked group 140) formed on the incident side of the most separated light beam is a final stacked group.

The stacked groups 120 to 140 include a film F _H made of a high refractive index material having a refractive index higher than that of the substrate 110 and a film F made of a low refractive index material having a refractive index lower than that of the substrate 110. _L is alternately laminated. Stacked group 120 to 140, the period of the thickness of the film F _L made of film F _H and the low refractive index material made of a high refractive index material are different. The center wavelength of the light beam separating lambda, the thickness of the film F _H made of a high refractive index material H × λ / 4, the thickness of the film F _L made of a low refractive index material as L × λ / 4, stacked groups The film thickness of each film at 120 to 140 will be specifically described.

Stacked group 120 and 130 (i.e., laminated group other than the final laminated group), the film F _L thickness L × consisting of a film thickness H × λ / 4 and a low refractive index material film F _H made of a high refractive index material λ / 4 satisfies the conditional expression represented by the following Expression 1 or Expression 2.

Stacked group 140 (i.e., the final laminated group), the thickness L × λ / 4 of the film F _L consisting of thickness H × λ / 4 and a low refractive index material film F _H made of high refractive index material, the following Satisfy the conditional expression expressed by Equation 3 below.

  The laminated groups other than the final laminated group (laminated groups 120 and 130) have a characteristic of well transmitting P-polarized light in a wavelength region longer than the center wavelength λ (predetermined wavelength) of the light beam to be separated. In addition, the final stacked group (stacked group 140) has a characteristic of well transmitting P-polarized light in a wavelength region shorter than the center wavelength λ (predetermined wavelength) of the light beam to be separated. Maintaining high polarization separation characteristics with a wider divergence angle (for example, ± 10 degrees or more) than before by setting the threshold wavelength (that is, the wavelength of transmitted light) of the laminated groups other than the final laminated group by shifting them. Can do.

  The adjustment layer 150 is formed on the final stack group (stack group 140), and adjusts polarization separation characteristics of at least three or more stack layers (stack layers 120 to 140) with respect to an incident angle of a light beam to be separated. The adjustment layer 150 uses a film made of a high refractive index material having a refractive index higher than that of the substrate 110 and / or a film made of a low refractive index material having a refractive index lower than that of the substrate 110, It consists of about 1 to 5 layers.

  As will be described later, the polarization beam splitter 100 achieves polarization separation characteristics such that the transmittance of P-polarized light is 80% or more and the transmittance of S-polarized light is 10% or less even at a divergence angle of incident light of ± 10 degrees. can do. In other words, the polarization beam splitter 100 achieves the polarization separation characteristic in which the reflectance of S-polarized light is 80% or more and the reflectance of P-polarized light is 10% or less at the divergence angle of the incident light beam ± 10 degrees.

Incidentally, the number of layers of stacked group 110 to 140, four layers or 20 layers (i.e., the repetition number of laminating the film F _H made of a high refractive index material, and a film F _L made of a low refractive index material are alternately 2 Times to about 10 times). This is because when the polarization beam splitter 100 is used as a transmission type polarization beam splitter, the number of layers in the stacked group increases, so that the absorption of the light beam increases.

  If three or more stacked groups are formed, the polarizing beam splitter 100 has a polarization transmittance of 80% or more and an S-polarization transmittance of 10% or less at a divergence angle of ± 10 degrees of the incident light beam. The polarization separation characteristic can be as follows. However, if the number of stacked groups is too large, it becomes difficult to manufacture the polarizing beam splitter 100, and therefore it is preferably about three to six.

  The inventor manufactured a large number of polarization beam splitters 100 by changing the film configurations of the stacked groups 110 to 140 and evaluated the polarization separation characteristics.

Let YAG laser (center wavelength λ = 1064 nm) be a separated light beam. In this case, a substrate having a refractive index of 1.42 as the substrate 110, hafnium oxide (HfO ₂ ) having a refractive index of 1.91 as a high refractive index material, and magnesium fluoride having a refractive index of 1.37 as a low refractive index material. (MgF ₂ ) is used.

The stacked group 120 includes HfO ₂ (film F _{H made of a} high refractive index material) having an optical film thickness of 0.9 × λ / 4 and MgF ₂ having an optical film thickness of 1.1 × λ / 4. (Films made of a low refractive index material F _L ) were alternately laminated to form 5 layers.

The stacked group 130 includes HfO ₂ (film F _{H made of a} high refractive index material) having an optical film thickness of 1.02 × λ / 4 and MgF ₂ having an optical film thickness of 0.92 × λ / 4. (Films made of a low refractive index material F _L ) were alternately laminated to form 5 layers.

The stacked group 140 includes HfO ₂ (film F _{H made of a} high refractive index material) having an optical film thickness of 1.43 × λ / 4 and MgF ₂ having an optical film thickness of 1.37 × λ / 4. (Films made of a low refractive index material F _L ) were alternately laminated to form 5 layers.

The adjustment layer 150 was formed by laminating MgF ₂ having an optical thickness of 0.3 × λ / 4 and HfO ₂ having an optical thickness of 2.72 × λ / 4 one by one.

  The simulation result of the polarizing beam splitter 100 of Example 1 is shown in FIG. FIG. 2 is a graph showing the polarization transmittance with respect to the incident angle of the polarizing beam splitter 100. In FIG. 2, the horizontal axis indicates the incident angle [degree], and the vertical axis indicates the transmittance [%]. The polarizing beam splitter 100 has a P-polarized light transmittance of 80% or more and an S-polarized light transmittance of 10% in a range of ± 10 degrees centering on an incident angle of 60 degrees with respect to a light beam in a wavelength region of 1064 nm. The following polarization separation characteristics are achieved.

Let ArF excimer laser (center wavelength λ = 193 nm) be a separated light beam. In this case, a substrate having a refractive index of 1.5 as the substrate 110, lanthanum fluoride (LaF ₃ ) having a refractive index of 1.68 as a high refractive index material, and fluorination having a refractive index of 1.39 as a low refractive index material. Aluminum (AlF ₃ ) is used.

The stacked group 120 includes LaF ₃ (film F _{H made of a} high refractive index material) having an optical film thickness of 0.92 × λ / 4 and AlF ₃ having an optical film thickness of 1.18 × λ / 4. (Films made of a low refractive index material F _L ) were alternately laminated to form 5 layers.

The stacked group 130 includes LaF ₃ (film F _{H made of a} high refractive index material) having an optical film thickness of 1.24 × λ / 4 and AlF ₃ having an optical film thickness of 0.92 × λ / 4. (Films made of a low refractive index material F _L ) were alternately laminated to form 5 layers.

The stacked group 140 includes LaF ₃ (film F _{H made of a} high refractive index material) having an optical film thickness of 1.37 × λ / 4 and AlF ₃ having an optical film thickness of 1.32 × λ / 4. (Films made of a low refractive index material F _L ) were alternately laminated to form 5 layers.

The adjustment layer 150 includes LaF ₃ having an optical thickness of 1.24 × λ / 4, AlF ₃ having an optical thickness of 1.24 × λ / 4, and an optical of 0.83 × λ / 4. LaF ₃ having a target film thickness was laminated one by one.

  A simulation result of the polarizing beam splitter 100 of Example 2 is shown in FIG. FIG. 3 is a graph showing the polarization transmittance with respect to the incident angle of the polarizing beam splitter 100. In FIG. 3, the horizontal axis indicates the incident angle [degree], and the vertical axis indicates the transmittance [%]. The polarization beam splitter 100 has a P-polarized light transmittance of 80% or more and an S-polarized light transmittance of 10% in a range of ± 10 degrees centering on an incident angle of 65 degrees with respect to a light beam in a wavelength region of 193 nm. The following polarization separation characteristics are achieved.

Let F ₂ laser (center wavelength λ = 157 nm) be a separated light beam. In this case, a substrate having a refractive index of 1.78 as the substrate 110, gadolinium fluoride (GdF ₃ ) having a refractive index of 1.68 as a high refractive index material, and fluoride having a refractive index of 1.42 as a low refractive index material. Aluminum (AlF ₃ ) is used.

The stacked group 120 includes GdF ₃ (film F _{H made of a} high refractive index material) having an optical film thickness of 0.63 × λ / 4 and AlF ₃ having an optical film thickness of 1.43 × λ / 4. (Films made of a low refractive index material F _L ) were alternately laminated to form 5 layers.

The stacked group 130 includes GdF ₃ (film F _{H made of a} high refractive index material) having an optical film thickness of 1.43 × λ / 4 and AlF ₃ having an optical film thickness of 0.63 × λ / 4. (Films made of a low refractive index material F _L ) were alternately laminated to form 5 layers.

The stacked group 140 includes GdF ₃ (film F _{H made of a} high refractive index material) having an optical film thickness of 1.37 × λ / 4 and AlF ₃ having an optical film thickness of 1.32 × λ / 4. (Films made of a low refractive index material F _L ) were alternately laminated to form 5 layers.

The adjustment layer 150 includes GdF ₃ having an optical film thickness of 1.36 × λ / 4, AlF ₃ having an optical film thickness of 1.23 × λ / 4, and an optical film of 0.68 × λ / 4. GdF ₃ having a target film thickness was laminated one by one.

  The simulation result of the polarizing beam splitter 100 of Example 3 is shown in FIG. FIG. 4 is a graph showing the polarization transmittance with respect to the incident angle of the polarizing beam splitter 100. In FIG. 4, the horizontal axis represents the incident angle [degree], and the vertical axis represents the transmittance [%]. The polarizing beam splitter 100 has a transmittance of P-polarized light of 80% or more and a transmittance of S-polarized light of 10% in a range of ± 10 degrees centering on an incident angle of 65 degrees with respect to a light beam in a wavelength region of 157 nm. The following polarization separation characteristics are achieved.

  As described above, the polarization beam splitter 100 has a high polarization (for example, the transmittance of P-polarized light is 80% or more and the transmittance of S-polarized light is 10% or less) at a wide divergence angle (for example, ± 10 degrees). Separation characteristics can be achieved.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist. For example, the present invention can be applied not only to a plate-type polarizing beam splitter but also to a prism-type polarizing beam splitter.

It is a schematic sectional drawing which shows the structure of the polarizing beam splitter as one side surface of this invention. 6 is a graph showing the polarization transmittance with respect to the angle of a light beam incident on the polarizing beam splitter of Example 1. 6 is a graph showing the polarization transmittance with respect to the angle of a light beam incident on the polarizing beam splitter of Example 2. 10 is a graph showing the polarization transmittance with respect to the angle of a light beam incident on the polarizing beam splitter of Example 3.

Explanation of symbols

100 Polarizing beam splitter 110 Substrate 120 and 130 Layer group 140 Layer group (final layer group)
Film made of a film F _L low refractive index material consisting of 150 adjustment layer F _H high refractive index material

Claims (8)

A polarizing beam splitter for separating an incident light beam,
A film made of a high refractive index material having a refractive index higher than that of the substrate and a film made of a low refractive index material having a refractive index lower than that of the substrate are alternately formed on the substrate. Having at least three or more laminated groups laminated;
With respect to the center wavelength λ of the luminous flux, the optical film thickness of the film made of the high refractive index material is H × λ / 4, and the optical film thickness of the film made of the low refractive index material is L × λ / 4. When
Of the at least three or more stacked groups, the final stacked group formed most on the light incident side satisfies 1.3 <H <1.5 and 1.3 <L <1.5. ,
The laminated groups other than the final laminated group satisfy 0.5 <H <1 and 1 <L <1.5, or 1 <H <1.5 and 0.5 <L <1. A polarizing beam splitter characterized by that.   The polarizing beam splitter according to claim 1, further comprising an adjustment layer that is formed on the final stack group and adjusts polarization separation characteristics of the at least three stack groups with respect to an incident angle of the light beam. A polarizing beam splitter for separating an incident light beam,
A film made of a high refractive index material having a refractive index higher than that of the substrate and a film made of a low refractive index material having a refractive index lower than that of the substrate are alternately formed on the substrate. A laminated first laminated group;
A second laminated group formed on the first laminated group, wherein the film made of the high refractive index material and the film made of the low refractive index material are alternately laminated;
A third laminated group formed on the second laminated group, wherein the film made of the high refractive index material and the film made of the low refractive index material are alternately laminated;
The optical film thickness of the film made of the high refractive index material is H × λ / 4 and the optical film thickness of the film made of the low refractive index material is L × λ / 4 with respect to the center wavelength λ of the light beam. When
The first stack group and the second stack group are 0.5 <H <1, and 1 <L <1.5, or 1 <H <1.5, and 0.5 <L. <1 satisfied,
The polarization beam splitter, wherein the third stacked group satisfies 1.3 <H <1.5 and 1.3 <L <1.5.   2. The polarized beam according to claim 1, further comprising an adjustment layer that is formed on the third stacked group and adjusts polarization separation characteristics of the first to third stacked groups with respect to an incident angle of the light beam. Splitter. The high refractive index material is hafnium oxide, and the low refractive index material is magnesium fluoride,
The first stack group includes five layers of hafnium oxide having an optical film thickness of 0.9 × λ / 4 and magnesium fluoride having an optical film thickness of 1.1 × λ / 4 alternately. Having a stacked configuration,
The second stacked group includes five layers of hafnium oxide having an optical film thickness of 1.02 × λ / 4 and magnesium fluoride having an optical film thickness of 0.92 × λ / 4 alternately. Having a stacked configuration,
The third stacked group includes five layers of hafnium oxide having an optical film thickness of 1.43 × λ / 4 and magnesium fluoride having an optical film thickness of 1.37 × λ / 4 alternately. Having a stacked configuration,
The adjustment layer has a configuration in which magnesium fluoride having an optical thickness of 0.3 × λ / 4 and hafnium oxide having an optical thickness of 2.72 × λ / 4 are stacked one by one. The polarizing beam splitter according to claim 4, wherein: The high refractive index material is lanthanum fluoride, and the low refractive index material is aluminum fluoride,
The first stacked group includes five layers of lanthanum fluoride having an optical film thickness of 0.92 × λ / 4 and aluminum fluoride having an optical film thickness of 1.18 × λ / 4 alternately. Each of which has a stacked structure,
The second laminated group includes five layers of lanthanum fluoride having an optical thickness of 1.24 × λ / 4 and aluminum fluoride having an optical thickness of 0.92 × λ / 4. Each of which has a stacked structure,
The third laminated group includes five layers of lanthanum fluoride having an optical thickness of 1.37 × λ / 4 and aluminum fluoride having an optical thickness of 1.32 × λ / 4. Each of which has a stacked structure,
The adjustment layer includes lanthanum fluoride having an optical thickness of 1.24 × λ / 4, aluminum fluoride having an optical thickness of 1.24 × λ / 4, and 0.83 × λ / 4. 5. The polarizing beam splitter according to claim 4, wherein the polarizing beam splitter has a structure in which one layer of lanthanum fluoride having an optical thickness of 1 is laminated. The high refractive index material is gadolinium fluoride, and the low refractive index material is aluminum fluoride,
The first stack group includes five layers of gadolinium fluoride having an optical thickness of 0.63 × λ / 4 and aluminum fluoride having an optical thickness of 1.43 × λ / 4. Each of which has a stacked structure,
The second stack group includes five layers of gadolinium fluoride having an optical thickness of 1.43 × λ / 4 and aluminum fluoride having an optical thickness of 0.63 × λ / 4. Each of which has a stacked structure,
The third stacked group includes five layers of gadolinium fluoride having an optical thickness of 1.37 × λ / 4 and aluminum fluoride having an optical thickness of 1.32 × λ / 4 alternately. Each of which has a stacked structure,
The adjustment layer includes gadolinium fluoride having an optical thickness of 1.36 × λ / 4, aluminum fluoride having an optical thickness of 1.23 × λ / 4, and 0.68 × λ / 4. 5. The polarizing beam splitter according to claim 4, wherein the polarizing beam splitter has a structure in which gadolinium fluoride having an optical film thickness of 1 layer is stacked. A polarizing beam splitter for separating an incident light beam,
A polarizing beam splitter characterized by having a P-polarized light transmittance of 80% or more and an S-polarized light transmittance of 10% or less at a divergence angle of the luminous flux of ± 10 degrees or more.