JP2006030568A - Photomask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photomask improved in use efficiency of light which is a problem of conventional techniques. <P>SOLUTION: A polarizing mask and a polarizing phase shift mask having excellent use efficiency of light can be produced by providing a conventional photomask or a phase shift mask with a structural polarizing element having better use efficiency of light which controls a polarized light component in a specified direction. Specifically, by using a structural birefringent element or a photonic crystal for a photomask, use efficiency of light can be improved and throughput of an exposure step can be increased. Observation of a developed resist pattern results in that no resist residue indicating phase conflict as a conventional problem is observed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photomask used in a projection exposure method.

  In a semiconductor element manufacturing process and a liquid crystal display device manufacturing process, a photolithography technique is generally used. Photolithographic technology is an etching mask that is formed by applying a photoresist to a semiconductor element, a substrate of a liquid crystal display device, or a thin film formed on the substrate and then selectively exposing it. Etching is performed. In order to perform selective exposure on the above-described photoresist, a photomask for exposure is used. A conventional photomask is used as an amplitude modulation type, and generally has a structure in which a light-shielding pattern made of a metal such as chromium is formed on a transparent substrate. A desired circuit pattern is transferred onto the substrate by forming an image of the light shielding pattern on the substrate by the projection optical system.

  In order to further increase the contrast of the projected image, various phase shift masks are used in which a phase shift unit that changes the phase of transmitted light is provided at a specific portion of the transparent portion. As one of the phase shift masks, there is a Shibuya Levenson type phase shift mask. This is provided with a phase shifter region in which a phase difference of 180 ° is generated in a transmission region for forming a fine projection pattern portion. And when the light from the light source (which is generally non-polarized light including various polarization planes) is irradiated on the mask, the light transmitted through both phase shifter regions overlaps each other. Since the same polarization components interfere with each other in opposite phases, a dark portion is formed. As a result, a projection pattern portion that clearly indicates a light shielding region or a boundary between both phase shifter regions sandwiched between both phase shifter regions is formed. From this, it is possible to increase the resolution of the above-mentioned fine projection pattern image and to increase the depth of focus.

  As described above, the photomask used in the exposure to the resist in the microfabrication field such as the semiconductor element manufacturing process and the liquid crystal display device manufacturing process is an amplitude modulation type photomask that generates the above amplitude distribution or a phase distribution. A phase shift mask to be generated is used.

  Recently, in addition to these functions, a “polarization mask” having a function of generating an in-plane distribution of polarized light has been proposed. The purpose of this polarizing mask is mainly to solve the phase conflict, improve the contrast, and realize double exposure.

1. Solution of Phase Conflict The first purpose of the polarization mask is to solve a problem called phase conflict, which is a problem of a phase shift mask (in this case, meaning Shibuya Levenson mask or alternating Phase Shift Mask). There are known documents such as “Ruoping Wang et al.” (Non-Patent Document 1), Japanese Patent Application Laid-Open No. 2002-116528 (Patent Document 1) and Japanese Patent Application Laid-Open No. 5-11434 (Patent Document 2). The contents will be described below.

FIG. 12 shows an exposure pattern when a phase shift mask (Shibuya Levenson mask) is used. A black part is the light-shielding part 121 used as the unexposed part which is not exposed. When a phase shift mask (Shibuya Levenson mask) is used, the phase difference on both sides of the light shielding part 121, which is a thin line for the purpose of miniaturization, needs to be 180 °. . The boundary 122 becomes unexposed because the light intensity becomes 0 due to interference, and when a positive resist from which the exposed portion is removed is used, the resist remains. Conversely, the resist is removed at the location of the negative resist. (The following description will be made in the case of using a positive resist.)
Therefore, a “polarization phase shift mask” as shown in FIG. 13 is used. A polarization phase shift mask is obtained by adding a function of a polarization mask to a conventional phase shift mask. In the figure, arrows 131 and 132 indicate directions of linear polarizers provided on the mask, that is, linearly polarized light after transmission through the mask. Show direction. Since light beams having different polarization directions do not interfere with each other, there is no problem that the resist remains even if the boundary 133 has a phase difference.

2. Contrast improvement The second purpose of the polarizing mask is to improve the contrast of the imaging. These are described in JP-A-5-21424 (Patent Document 3), JP-A-7-176476 (Patent Document 4), JP-A-7-36174 (Patent Document 5), JP-A-9-20154 (Patent Document 6). ), Showing details of the contents.

  FIG. 14A shows an optical system 141 of the exposure apparatus. Considering exposure of an L & S (line and space) pattern 142 having a repetition period in the X direction, the transmitted light 143 of the mask is diffracted in the X direction, and the diffracted light interferes on the exposed surface to form an image. 144. In this interference, the S-polarized component 145 (electric field is in the Y direction) of the diffracted light shown in FIG. 14B is more coherent than the P-polarized component 146 (the electric field is in the X direction) shown in FIG. , The contrast becomes higher. When an ordinary mask is used, an average image of S-polarized light and P-polarized light is obtained, so that the contrast deteriorates due to the presence of the S-polarized light component. Therefore, as shown in FIG. 15, by providing a linear polarizer 154 that polarizes light in the tangential directions 152 and 153 of the L & S pattern (151) on the mask, the contrast can be improved with respect to the L & S pattern in an arbitrary direction.

  For this purpose, no phase shift function is used, and therefore a polarization mask but not a polarization phase shift mask.

3. Realization of Double Exposure The third purpose of the polarizing mask is to realize the same effect as double exposure with a single exposure. There is a publicly known document such as Japanese Patent Laid-Open No. 4-366841 (Patent Document 7) which describes this.

  In this prior art, independent exposure is performed by providing linear polarizers with different orientations at the opening of the mask so that the transmitted light of adjacent openings do not interfere with each other. In the example of FIG. 16, linear polarizers 162 having different directions are alternately provided in the L & S pattern (161), so that the substantial frequency is halved to facilitate the resolution.

  This technique can be expressed as performing independent exposure simultaneously, or realizing double exposure by one exposure. The mask for this purpose is also a polarization mask, but not a polarization phase shift mask.

  In order to realize the above three purposes, the polarizing mask must be finely patterned with a polarizing function. As a specific method for enabling this, a method of providing a conductor grid is disclosed in JP-A-9-20154 (Patent Document 8), JP-A-7-36174 (Patent Document 9), JP-A-7-176476 (Patent Document 10). )It is described in.

  The conductor grating 171 is also called a grid polarizer, and is a grating 172 made of a conductor whose pitch is smaller than the wavelength as shown in FIG.

The conductor grating 172 has a feature that the electric field transmits light 173 perpendicular to the grating 174 and the electric field reflects light 175 parallel to the grating 176. Therefore, the above-described polarizing mask can be realized by the conductor lattice 171.

The conductor grid 171 can be manufactured by a normal lithography method. Specifically, the conductor grid 171 can be manufactured by sputtering, patterning and etching of chromium on a quartz substrate.
JP 2002-116528 A JP-A-5-11434 JP-A-5-241324 JP-A-7-176476 JP-A-7-36174 JP-A-9-120154 JP-A-4-366411 JP-A-9-120154 JP-A-7-36174 JP-A-7-176476 Ruoping Wang et al., Polarized Phase Shift Mask: Concept, Design, and Potential Advantages to Photolithography Process and Physical Design, Proceedings of SPIE Vol.4562, 406-417 (2002)

  A problem when a polarizing mask is used as a photomask will be described.

  In the polarization component originally used in the conductor lattice, the light use efficiency at the time of exposure is about the area ratio of the opening of the conductor region. For example, when the area ratio of the opening is 50%, the utilization ratio is 50%.

  In addition, since no polarized light component other than the originally used polarized light component is used in the incident light, the utilization efficiency is further 50%.

  If the area ratio of the openings is widened, the utilization efficiency is improved. However, since the pitch of the grating is as fine as the wavelength or less, it is difficult to sufficiently narrow the grating portion.

  In the case of the above example, the total light use efficiency is at most about 25% (= about 50% × 50%). Therefore, compared with the ideal light utilization rate of 100%, there is a problem that the exposure time is four times longer when the equivalent exposure is performed and the throughput of the exposure process is reduced.

  The present invention has been made in view of the above points, and an object thereof is to obtain a photomask with improved light utilization efficiency.

  In a photomask of an exposure apparatus that irradiates an exposure substrate to an exposure substrate according to an aspect of the present invention with a projection optical system, the first pattern in which substantially the same pattern of dielectric is repeatedly arranged in a first direction axis is provided. A first periodic structure region having a periodic structure, and a second periodic structure in which substantially the same pattern of dielectric is repeatedly arranged in parallel on a second direction axis different from the first direction axis. And a second periodic structure region, and light is incident on the first and second periodic structure regions.

  A photomask according to another aspect of the present invention is characterized in that the first and second periodic structures are three-dimensionally constituted by two or more kinds of dielectrics.

  In a photomask according to still another aspect of the present invention, the first and second periodic structures have a specific direction corresponding to the direction axis of light incident on the first and second periodic structure regions. It has a polarization component selection structure in which the transmittance of the polarization component is greater than the transmittance of the polarization component in a direction different from the specific direction.

  In a photomask according to still another aspect of the present invention, the first and second periodic structures have a specific direction corresponding to the direction axis of light incident on the first and second periodic structure regions. It has a polarization component selection structure in which the reflectance of the polarization component is greater than the reflectance of the polarization component in a direction different from the specific direction.

In a photomask according to still another aspect of the present invention, the first and second periodic structures are structures having birefringence, for example, two or more kinds of dielectric plate-like patterns are sequentially arranged. The structure in which the phase difference between the two polarization components in which the plane of vibration of the electric vector of light is orthogonal is approximately 90 °, or between two polarization components in which the plane of oscillation of the electric vector of light is orthogonal The phase difference is approximately 180 °.
In a photomask according to still another aspect of the present invention, the dielectric of the first and second periodic structures has a layer shape, and a part of the layer shape is relative to the corresponding direction axis. The dielectric layer has a slope, and the dielectric layer is stacked so as to be parallel to a direction perpendicular to the direction axis in the plane of the photomask.

  A photomask according to still another aspect of the present invention has a phase shift portion that generates a phase difference with respect to light incident on the first and second periodic structure regions, and the phase shift portion causes a phase shift. Is characterized in that at least a part of the phase shift line, which is a part to be shifted, corresponds to a boundary where the first and second periodic structure regions contact each other.

  A photomask according to still another aspect of the present invention is characterized in that the phase shift portion is provided in a layer different from the periodic structure.

  According to the present invention, a photomask with high light utilization efficiency can be provided.

  The inventors focused on “structural polarizers” and thought that by using this, an effective polarization mask could be realized without reducing light utilization efficiency.

  “Structural polarizer” is a term used in the present invention by the inventors, and is an element that controls polarization by means of a microstructure that is less than or equal to the wavelength of incident light, using two or more dielectric materials. Specific examples of the structural polarizer include “structural birefringence element” and “photonic crystal”.

  Hereinafter, a method for realizing a polarization phase shift mask using a structural polarizer will be described. For example, in FIG. 2, the state of light immediately after passing through the mask, the polarization direction is indicated by arrows, and the phase is indicated by 0 ° and 180 °. Further, the structure of the mask when realizing this state will be described. Here, the phase 0 ° means that the portion is used as a phase reference. This configuration includes all the light states necessary for the polarization phase shift mask. If this arrangement can be realized, an arbitrary pattern including a polarization mask not including the phase shift function can be realized.

  In the figure, a linear polarizer and a birefringent element are used as members for realizing the polarization mask. Among these, the linear polarizer can be realized by a photonic crystal. The birefringent element can be realized by either a photonic crystal or a structural birefringent element.

  Here, the extinction ratio required when used as a linear polarizer will be described. The extinction ratio represents the polarization capability of a linear polarizer, and is defined here as the intensity ratio of an unnecessary polarization component to the total light intensity of transmitted light.

Let's calculate the required extinction ratio below. FIG. 3A shows the configuration of a polarization phase shift mask used for calculation. A phase shift portion 21 having a phase step portion 22 is provided on the structural polarizer 1. As a specific example of production, a SiO ₂ film is deposited on the structural polarizer 1 as the phase shift unit 21, and a phase that produces a desired phase difference based on the wavelength of incident light and the refractive index of the phase shift unit 21 is deposited thereon. The step portion 22 is formed by an etching process.

  In order to prevent the resist from remaining at the point A corresponding to the phase step portion 22, the drop in the light intensity distribution needs to be a certain value or more. When the transmission part is normalized to 1, the light intensity distribution at point A on the phase line is P, and the lower limit of the photosensitivity of the resist is α. That is, when P> α is satisfied, no resist remains.

In the following, the light intensity P at point A is obtained. FIG. 3B shows a polarization phase shift mask provided with a structural polarizer 1a ′ having a TE polarization transmission function and a structural polarizer 1b ′ having a TM polarization function as a specific example. TE polarization refers to polarization of light (TE light) such that the vibration direction of the electric vector is perpendicular to the incident plane and the vibration direction of the magnetic vector is within the incident plane. TM polarization refers to the magnetic vector. It is defined as polarization to light (TM light) whose vibration direction is perpendicular to the incident plane and the vibration direction of the electric vector is within the incident plane. The amplitude U at the point A is given by convolution (convolution integration) between the amplitude transmittance distribution and the point image amplitude distribution of the imaging optical system in each polarization component. Now we define Convolution (A, B) as a convolution function. Convolution (A, B) means a convolution integral of function A and function B. Then, TE light amplitude Ute at point A and TM light amplitude Utm at point A are
Ute = Convolution (Tte, PSF)
Utm ＝ Convolution （Ttm, PSF）
Given in.
Here, Ttm and Tte mean the amplitude transmittance distribution for the TM light and TE light of the photomask, respectively, and PSF means the point image amplitude distribution of the imaging optical system.

Let R be the light intensity ratio of the actual TM polarized light to the entire transmitted light in the TM polarized light transmission region corresponding to the structural polarizer 1b ′ having the TM polarization function. The light intensity ratio of the actual TE polarized light to the entire transmitted light in the TM polarized light transmission region corresponding to the structural polarizer 1a ′ having the TE polarization function is also set to the same R. At this time, the intensity ratio of TE polarized light in the TM polarized light transmission region is 1-R, and the intensity ratio of TM polarized light in the TE polarized light transmission region is also 1-R. Further, the phase of the TE polarization region determined by the phase step portion 22 of the phase shift unit 21 is set to 0 °, and the phase of the TM polarization region is set to 180 °.

It becomes. Therefore, the ratio of TE polarization in the TE polarization region and TM polarization in the TM polarization region needs to be 93.5% or more. That is, the extinction ratio is desirably 6.5% or less.

  Next, as a method of the present invention, a method for realizing a polarization mask with a birefringence function using a structural birefringence element or a photonic crystal will be described. FIG. 1 shows a mask in which a structural polarizer 1 partially having a birefringence function is patterned. As a specific example, a structural polarizer 1 which is a structural birefringent element or a photonic crystal described later is formed on a synthetic quartz plate 2 as a mask substrate. The structural polarizer 1 is subjected to an etching process or a film-forming process after the etching process so as to have a periodic structure in which substantially the same pattern is repeatedly arranged in parallel in a certain direction (this direction is referred to as a direction axis). It is formed by doing. In FIG. 1, structural polarizers 1a and 1b having different directional axes are provided, and the phase difference is different by λ / 4 between light beams of polarized components orthogonal to each other by the structural polarizers 1a and 1b. The structural polarizers 1a and 1b are formed so that a phase difference of λ is generated, that is, 90 °. By illuminating the mask with polarized light 3 having a polarization such as linearly polarized light or circularly polarized light (circularly polarized light in the example in the figure), the polarized light 4 having a polarization state that does not interfere with each other after passing through the mask (see FIG. In this example, the linearly polarized waves 4a and 4b) orthogonal to each other can be obtained. That is, an effect equivalent to that of a polarizing mask having the function of a linear polarizer can be realized by birefringence.

  The light source includes a light source that outputs random polarized light such as a mercury lamp, and a light source that directly outputs polarized light like an excimer laser. When illuminating with directly polarized light or circularly polarized light, it is desirable that the former (though there is no problem in the latter) be devised so as not to lose light energy when the polarization state is converted.

  When the C-type structure of FIG. 2 is used, an implementation example shown in FIG. 5 can be considered as a combination of the left and right birefringent elements and the polarization state of the illumination light. In this figure, the two outgoing lights are both in a non-interfering state.

  As for the structural birefringence element and the photonic crystal, which are examples of the structural polarizer, the expected light utilization efficiency, realization function, and feasibility of the phase shift function are shown in FIG. Show.

  The theoretical light utilization efficiency of the conductor grating is about 25%, which is the product of the utilization ratio of polarized light of 50% and the area ratio of the opening of the grating of about 50%. In contrast, the structural birefringent element can ideally achieve 100%, and the photonic crystal also has an ideal value of 50% when using the function of a linear polarizer, and when using the function of birefringence. 100% can be realized. In any case, the utilization efficiency can be increased as compared with the conductor grid.

  Also, in the conductor grating, the conductor can only block light, and cannot itself have a phase shift function, and hence the phase shift function cannot be realized. And photonic crystals can also achieve a phase shift function. Specifically, the phase shift function can be realized while maintaining the polarization function by increasing or decreasing the thickness of the constituent parts. Therefore, in order to realize the phase shift function, it is necessary to provide a phase shift layer separately in the conductor grating, but in the case of a structural birefringent element or a photonic crystal, the polarizer and the phase shift are combined into one structure (layer). At the same time. Therefore, the structure / process is simplified.

First embodiment
Fabrication of polarization phase shift mask using structural birefringence element
The inventors first tried to create a polarization phase shift mask using a structural birefringent element. The structural birefringence (element) refers to a birefringent element having a regular structure sufficiently smaller than the wavelength of light. In structural birefringence (element), birefringence occurs because the effective dielectric constant differs depending on the direction of the electric field of light. For the principle of structural birefringence (element), see “M. Born, E. Wolff, Principle of Optics III”, “14.5.2 Structural Birefringence”, Tokai University Press, 1975, p1030. It is stated.

As an example of the structural birefringence (element), there is a lattice of parallel plane plates as shown in FIG. A dielectric 71 having a dielectric constant ε ₁ and a duty ratio f ₁ and a dielectric 72 having a dielectric constant ε ₂ and a duty ratio f ₂ are alternately arranged. In the figure, the dielectric 71 is air. When light is incident perpendicularly on this element, the effective dielectric constant differs depending on the direction of the electric field of the light, for example, when 73 is perpendicular to the grating and 74 when the electric field is parallel to the grating.

When the electric field is perpendicular to the grid: ε = ε ₁ ε ₂ / (f ₁ ε ₂ + f ₂ ε ₁ )
When the electric field is parallel to the lattice ε = f ₁ ε ₁ + f ₂ ε ₂
Since these two values are different, a birefringence function occurs.

  As an actual photomask, a polarization mask having the function of FIG. 13 for solving the phase conflict was created. The masks to be created were assumed to be the C type in FIG. 2 and the 3 type in FIG. In this case, the function is a λ / 4 plate.

1 Creation of phase shift layer
First, in order to have a phase shift function, the uneven | corrugated process of the level | step difference 81 as shown to Fig.8 (a) was performed. Specifically, by applying resist, patterning, and dry etching on the surface of the quartz substrate 80 serving as a photomask substrate, a 397 nm step 81 that gives a phase difference of 180 ° with respect to light having a wavelength of 365 nm was formed.

2 Production of light shielding layer
Subsequently, a light shielding layer was prepared. Chromium was sputtered to a thickness of 800 nm on a quartz substrate 80 having a step 81. Thereafter, a chromium light shielding layer 82 was provided by resist coating, patterning, and dry etching (FIG. 8B).

3 Fabrication of structural birefringent elements
Thereafter, as shown in FIG. 8C, processing was performed so that the cross-section became a comb mold 84 by resist coating, patterning, and dry etching so as to form a lattice mold 83 having different orientations. At this time, the light shielding area is not processed. The design dimensions of the grating were set to 180 nm and the etching depth d was set to 1079 nm. Patterning was performed by electron beam drawing because particularly fine processing was required. At this time, the boundary in the horizontal direction of the lattice type 83 in the drawing was made to coincide with the phase difference line shown in FIG. Later, machining accuracy was measured, but it was confirmed that it was created according to the machining shape defined at the beginning. The depth d of the design dimension was obtained from the following relational expression so as to realize the function of the λ / 4 plate.

4 lighting
FIG. 8D shows the result of measuring the state of transmitted light when the created polarization phase shift mask is illuminated with circularly polarized light. In the measurement, the prepared polarization phase shift mask was observed with an optical microscope through a linear polarizer in a state where the illumination light was circularly polarized. As a result, it was confirmed that the polarization state was patterned as designed. It can be seen that the polarization phase shift mask shown in FIG. 13 can be realized although the polarization direction is oblique. An exposure process was actually performed using this polarization phase shift mask. The results are shown below.

  As for the light utilization efficiency, an actual measurement was made as to how much time was shortened with respect to the optimum exposure time in the case of exposure with a conventional mask using a conductor grid having an area ratio of 50% of the aperture ratio. The optimal exposure time was determined by comparing the exposure time with the optimal resist patterning after the exposure after changing the exposure time only under the same resist material and the same development conditions. . As a result, the optimal exposure time for the polarizing mask using the structural birefringent element was 28% shorter than when the optimal exposure time for the conductor grating was 100%. From this, it was found that the utilization efficiency of the polarizing mask using the structural birefringent element was greatly improved as compared with the case of using the conductor grating.

Further, the developed resist pattern was observed, but no residual resist phenomenon showing a phase conflict which was a problem was observed. From the above, it was found that a polarization phase shift mask using a structural birefringent element has significantly improved light utilization efficiency compared to the prior art, which can improve the throughput of the exposure process and solve the problem of phase conflict. .

Second embodiment
Fabrication of polarization phase shift mask using photonic crystal
The inventors also made a polarization phase shift mask using a photonic crystal.

  The photonic crystal is described in, for example, “Yoshino / Takeda,“ Basics and Applications of Photonic Crystals ”, published by Corona, published on April 28, 2004.

  A photonic crystal is an element having a periodic structure of the order of the wavelength of light and generating a photonic band gap in a state where the presence of light under specific conditions is not allowed due to black reflection resulting from this structure. Specific conditions in which the presence of light is not allowed include frequency (wavelength), polarization, and traveling direction. Photonic crystals are classified into one-dimensional, two-dimensional, and three-dimensional photonic crystals corresponding to the dimension of the light traveling direction that generates a photonic band gap. The photonic crystal used in the present invention is basically a one-dimensional photonic crystal that exhibits a photonic band gap only for light in a direction incident on the mask. However, since a phenomenon having different characteristics depending on the polarization direction is used, the structure of the photonic crystal itself is different from a simple laminated structure. The principle of the photonic crystal will be described below.

  FIG. 9 shows a structure of a two-dimensional square lattice photonic crystal 92 composed of a dielectric circular rod 91 and its photonic band structure 93 (a graph in which the horizontal axis is the wave number k and the vertical axis is the normalized frequency value ωa / 2πc). . However, the ratio of the rod radius to the pitch was 0.2, the dielectric constant of the rod was 11.9, and the dielectric constant around the rod (air) was 1.0.

  The value ωa / 2πc on the vertical axis and the value ka / 2π on the horizontal axis are obtained from the following values.

ω: angular frequency a: grating pitch c: speed of light in vacuum k: wave number In the TE mode, the electric field is parallel to the paper surface, and the TM mode is perpendicular to the paper surface.

  The dielectric circular rod extends in a direction perpendicular to the paper surface. Consider a case where light is incident on the structure in the X-axis direction. In this case, only the portion from Γ to X in the photonic band needs to be considered.

A wavelength corresponding to the value ωa / 2πc = 0.35 on the vertical axis is selected as the incident light. If the wavelength in vacuum is λ, then λ = 2πc / ω.
a / λ = 0.35
For example, when a wavelength of 365 nm is used, it means that a = 128 nm (= 365 × 0.35) is selected as the grating pitch.

  Looking at the band structure with this value on the vertical axis, the TE mode exists, but the TM mode does not exist. (In TM mode, a band gap occurs, and this frequency is located in this band gap.) This means that TE mode light travels as it is, but TM mode light reflects. That is, it acts as a linear polarizer.

  Further, a wavelength corresponding to the value ωa / 2πc = 0.2 on the vertical axis is selected as the incident light. When this value is calculated in the same manner as described above, it means that a = 73 nm (= 365 × 0.2) is selected as the grating pitch.

  Looking at the band structure with this value on the vertical axis, both the TE mode and the TM mode exist, but the corresponding values on the horizontal axis are different. That is, the wave number is different between the TE mode and the TM mode, which means that a phase difference is generated after passing through a photonic crystal having a certain thickness. That is, it has birefringence.

  When birefringence is used, the band gap itself is not used, but the band structure is largely deformed because of the existence of the band gap, which is a phenomenon peculiar to the photonic crystal.

  Here, examples of well-analyzed rod shapes are shown, but it has been found that various shapes become photonic crystals, and a method for calculating the photonic band structure as shown in FIG. 9 has been established. Yes.

  A plurality of methods for producing a photonic crystal have been proposed, and there are a method of forming perforations, a method of stacking dielectric rods, a self-cloning method, a method of using multiphoton absorption, a method of using a holography technique, and the like. In the self-cloning production method, a photonic crystal is realized by a V-shape.

The self-cloning method is a method for generating a periodic structure by fabricating a concavo-convex substrate and then sputtering and etching two kinds of materials alternately thereon. FIG. 10 shows the photonic crystal actually produced by the self-cloning method. A concavo-convex shape is formed on the synthetic quartz, which is a mask substrate, by a litho-etching process, and then, by bias sputtering, Si and Ta are used as target materials, Ar is used as a sputtering gas, and oxygen is used as a reactive gas. It can be seen that a photonic crystal having a V-shaped multilayer structure was created by introducing and laminating SiO ₂ and Ta ₂ O ₅ alternately on the concavo-convex surface by reactive sputtering.

  In this method, existing lithography technology and film formation technology can be applied, and since it is not necessary to use a special material, it is easy to manufacture. Moreover, the polarization function can also be patterned by patterning the first uneven substrate. A method for realizing the linearly polarized light function by this method is described in “Kawakami / Odera / Kawashima,“ Preparation of Photonic Crystal and Application to Optical Devices ”, Applied Physics Vol. 68, No. 12 (1999)”.

1 Production of photonic crystals
Here, the production of a specific photonic crystal is described. First, the uneven | corrugated process 111 shown to Fig.11 (a) was performed on the surface of the quartz substrate. The uneven pitch was 130 nm and the depth was 65 nm. On top of this, 10 layers each of SiO ₂ (112) and Ta ₂ O ₅ (113) were alternately formed to a thickness of 55 nm. In this film formation, a V-shaped tomographic shape was obtained by using RF bias sputtering in which high-frequency power was applied to the substrate. In the figure, the horizontal line and the vertical line schematically indicate the V-shaped direction, and explain that the patterning is performed on two types of regions having different direction axes.

2 Preparation of phase shift layer
Subsequently, SiO ₂ (114) was formed thereon with a film thickness of 800 nm by PE-CVD (Plasma Enhanced Chemical Vapor Deposition Method). For this film formation, conditions were selected such that the V-shaped irregularities on the surface of the photonic crystal did not appear on the surface of the SiO ₂ layer. Thereafter, resist coating, patterning, and dry etching were performed to form a 397 nm step 115 that gives a phase difference of 180 ° to light having a wavelength of 365 nm. At this time, the horizontal phase shift line in the figure was matched with the boundary between the two regions on the photonic crystal shown in FIG. The created result is shown in FIG.

3 Preparation of light shielding layer
Subsequently, chromium was sputter-deposited thereon with a thickness of 800 nm. Further thereon, a chromium light shielding layer 116 was provided by resist coating, patterning, and dry etching. The created result is shown in FIG.

4 lighting
FIG. 11D shows the result of measuring the state of transmitted light when illuminated with random polarized light with respect to this polarization phase shift mask. In the measurement, the prepared polarization phase shift mask was observed with an optical microscope through a linear polarizer in a state where illumination light was randomly polarized. As a result, it was confirmed that the polarization state was patterned as designed, and it was found that the polarization phase shift mask shown in FIG. 13 was realized.

  As for the light utilization efficiency, the degree of time reduction with respect to the optimum exposure time in the case of exposure with a conventional mask made of a conductor grid having an area ratio of 50% of the aperture ratio is shown in FIG. 8 (d). It measured similarly. The optimal exposure time was determined by comparing the exposure time with the optimal resist patterning after the exposure after changing the exposure time only under the same resist material and the same development conditions. . As a result, the optimal exposure time of the polarizing mask using the structural birefringent element was realized in a short time of 54%, compared with the case where the optimal exposure time of the conductor grating was 100%. From this, it was found that the utilization efficiency of the polarizing mask using the structural birefringent element was greatly improved as compared with the case of using the conductor grating.

Further, the developed resist pattern was observed, but no residual resist phenomenon showing a phase conflict which was a problem was observed. From the above, it has been found that a polarization phase shift mask using a photonic crystal has significantly improved light utilization efficiency as compared with the prior art, which can improve the throughput of the exposure process and solve the problem of phase conflict.

It is a figure which shows the polarizing mask of a birefringence function. It is a figure which shows the implementation | achievement method of a polarization phase shift mask. It is a figure for demonstrating the extinction ratio required when using as a linear polarizer. It is a figure which shows the relationship between the light intensity P and the light intensity ratio R of TM polarized light. It is a figure which shows the implementation method at the time of using a birefringent element. It is a figure which compares the conductor grid of a prior art with this invention, and shows the advantage of this invention. It is a figure for demonstrating the principle of structural birefringence. It is a figure which shows the Example by a structural birefringent element. It is a figure for demonstrating the principle of a photonic crystal. It is a figure for demonstrating the example of the linear polarizer by the photonic crystal produced by self-cloning. It is a figure which shows the Example by a photonic crystal. It is a figure for demonstrating the phase conflict which becomes a problem by a phase shift mask technique. It is a figure for demonstrating the method of solving the phase conflict which is a problem which is a phase shift mask technique with a polarization phase shift mask. It is a figure for demonstrating the problem of contrast fall. It is a figure for demonstrating the conventional method which solves the problem of a contrast fall with a polarizing mask. It is a figure for demonstrating the conventional method which implement | achieves double exposure with a polarizing mask. It is a figure for demonstrating the conventional conductor grating | lattice.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Structural polarizer, 3 ... Polarized polarized light, 4 ... Polarization state polarization, 71, 72 ... Dielectric, 91 ... Dielectric circular rod, 92 ... Two Dimensional square lattice photonic crystal, 82, 116 ... chrome light shielding layer, 83 ... lattice type, 84 ... comb type, 115 ... step, 121 ... light shielding part, 122 ... boundary.

Claims (18)

A photomask for an exposure apparatus that irradiates an exposure substrate with an exposure pattern by a projection optical system,
A first periodic structure region having a first periodic structure in which substantially the same pattern of dielectrics is repeatedly arranged on the first direction axis;
A second periodic structure region having a second periodic structure in which substantially the same pattern of dielectric is repeatedly arranged in parallel on a second direction axis different from the first direction axis, A photomask, wherein light is incident on the first and second periodic structure regions.   2. The photomask according to claim 1, wherein the first and second periodic structures are three-dimensionally composed of two or more kinds of dielectrics.   In the first and second periodic structures, the transmittance of the polarization component in a specific direction corresponding to the direction axis of the light incident on the first and second periodic structure regions is different from the specific direction. The photomask according to claim 1, wherein the photomask has a polarization component selection structure larger than a transmittance of the polarization component.   4. The photomask according to claim 3, wherein the photomask is a transmissive photomask that uses light transmitted through the photomask as exposure light.   In the first and second periodic structures, the reflectance of the polarization component in a specific direction corresponding to the direction axis of the light incident on the first and second periodic structure regions is different from the specific direction. The photomask according to claim 1, wherein the photomask has a polarization component selection structure larger than a reflectance of the polarization component.   6. The photomask according to claim 5, wherein the photomask is a reflective photomask that uses reflected light from the photomask as exposure light.   6. The photomask according to claim 3, wherein the polarization component selection structure is a structure having a photonic band gap only for a specific polarization component.   2. The photomask according to claim 1, wherein the first and second periodic structures are structures having birefringence.   9. The photomask according to claim 8, wherein the structure having birefringence is a structure in which plate-like patterns of two or more kinds of dielectrics are sequentially arranged side by side.   The structure having the birefringence in the first and second periodic structure regions is configured such that a phase difference between two polarization components having orthogonal planes of vibration of an electric vector of light is approximately 90 °. 9. The photomask according to claim 8, wherein:   The structure having the birefringence in the first and second periodic structure regions is configured so that a phase difference between two polarization components having orthogonal planes of vibration of an electric vector of light is approximately 180 °. 9. The photomask according to claim 8, wherein:   The dielectrics of the first and second periodic structures have a layer shape, and a part of the layer shape has an inclination with respect to the corresponding direction axis, and at the same time, the direction in the plane of the photomask. 2. The photomask according to claim 1, wherein the photomasks are stacked so as to be parallel to a direction perpendicular to the axis.   At least a part of a phase shift line that has a phase shift portion that generates a phase difference with respect to light incident on the first and second periodic structure regions and is a portion whose phase is shifted by the phase shift portion The photomask according to claim 1, wherein a boundary where the first and second periodic structure regions contact each other corresponds to each other.   14. The photomask according to claim 13, wherein the phase shift portion is provided in a layer different from the periodic structure.   2. The photomask according to claim 1, wherein the phase shift line is the boundary between the first and second periodic structure regions, and is formed as a difference in the amount of phase modulation of the periodic structure.   2. The photomask according to claim 1, wherein the directional axes of the first and second periodic structure regions are substantially orthogonal to each other.   The directional axis of each of the first and second periodic structure regions is oriented such that transmitted light or reflected light when linearly polarized light is incident is polarized light that does not interfere with each other. Item 17. The photomask according to any one of Items 1 to 16.   The direction axis of each of the first and second periodic structure regions is oriented such that transmitted light or reflected light when circularly polarized light is incident is polarized light that does not interfere with each other. Item 17. The photomask according to any one of Items 1 to 16.

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