JP2007079371A - Gray scale mask, optical element, spatial light modulator and projector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gray scale mask and so on, with which a resist shape is accurately formed by avoiding formation of a stepwise shape caused by distribution of step-by-step changing light transmittance. <P>SOLUTION: The gray scale mask: is equipped with a plurality of unit cells 21 whose light transmittance values are respectively set according to desired resist shapes, wherein the unit cell 21 has an opening section 23 to transmit light and a light shielding section 22 to shield light, and the light transmittance value is determined with an area opening ratio which is a rate of an area of the opening section 23 occupying the unit cell 21; and has the area opening ratio of a range in which the resist shape is formed by making diffracted light L from a unit cell 21 on the periphery of one unit cell 21 incident on a region AR on which direct light from the one unit cell 21 is made incident out of a resist layer 60 to form the resist shape. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gray scale mask, an optical element, a spatial light modulator, and a projector, and more particularly to a gray scale mask technique for manufacturing an optical element having a three-dimensional microstructure such as a microlens element.

  Conventionally, a photolithography technique is used in the manufacture of an optical element having a three-dimensional microstructure. Photolithography is a technique in which a resist layer, which is a photoreactive photosensitive material, is applied to a substrate, exposed to light, and developed to form a pattern on the resist layer. The pattern of the resist layer can be formed on the substrate by performing etching after forming the pattern on the resist layer. As a method for forming a desired pattern on the resist layer, for example, a technique of exposing the resist through a gray scale mask is used. The gray scale mask includes a plurality of unit cells each having a light transmittance corresponding to a desired resist shape. When the light transmittance is changed for each unit cell, the light transmittance of the gray scale mask is distributed so as to change stepwise in the two-dimensional direction. A shape may be formed. Since the optical element is required to have an accurate shape in order to perform functions such as light refraction, it is desired to avoid the formation of a step shape that is not in the design. Therefore, for example, a technique for forming a smooth surface by gradually changing the focus amount during exposure (for example, see Patent Document 1), or a technique for smoothing a step shape by heat treatment of a resist (for example, a patent). Reference 2) has been proposed.

JP 2001-356470 A JP 2003-91066 A

  In the technique proposed in Patent Document 1, in order to form a smooth surface, a process of changing the defocus amount within the exposure time is newly required. Further, by changing the defocus amount from the side greatly defocused with respect to the resist surface to the in-focus side, a step shape is formed when the focus is finally achieved. For this reason, it may be difficult to obtain a smooth surface. In the technique proposed in Patent Document 2, even if the step shape can be smoothed, there is a case where an accurate shape cannot be obtained due to the influence of heating up to the height of the resist shape and the shape itself. . As described above, in the conventional technique, it is difficult to avoid the formation of the step shape due to the light transmittance being distributed so as to change stepwise, so that it is difficult to obtain an accurate resist shape. Arise. The present invention has been made in view of the above-described problems, and can avoid the formation of a step shape due to the light transmittance being distributed so as to change stepwise, and can accurately form a resist shape. An object of the present invention is to provide a gray scale mask, an optical element manufactured using the gray scale mask, a spatial light modulation device, and a projector.

  In order to solve the above-described problems and achieve the object, according to the present invention, a plurality of unit cells each having a light transmittance corresponding to a desired resist shape are provided, and each unit cell transmits light. The light transmittance is determined by the area aperture ratio, which is a ratio of the area of the opening occupying the unit cell, and one of the resist layers for forming the resist shape. A gray scale characterized by having an area aperture ratio in such a range that diffracted light from unit cells around one unit cell is incident on a region where direct light from the unit cell is incident to form a resist shape A mask can be provided.

  The gray scale mask of the present invention forms a resist shape using not only direct light from the opening but also diffracted light. Since there is a correlation between the area aperture ratio and the intensity of the diffracted light, the range of the area aperture ratio of the gray scale mask that increases the intensity of the diffracted light can be determined. Even if the grayscale mask has a light transmittance distribution that changes stepwise in the two-dimensional direction by making the diffracted light from the periphery enter the region where direct light from one unit cell is incident, the resist The change in the amount of light on the layer can be made to be continuous. By making the change in the amount of light on the resist layer continuous, a smooth surface can be formed on the resist layer. Since there is no need to increase the number of processes other than the exposure through the gray scale mask of the present invention, and since diffracted light is generated as a secondary to direct light, it affects the height and shape of the resist shape. It is thought that there are few things. As a result, it is possible to avoid the formation of a step shape due to the light transmittance being distributed so as to change stepwise, and to obtain a gray scale mask capable of accurately forming a resist shape.

  Further, according to a preferred aspect of the present invention, when the direct light intensity I0 when the area aperture ratio is 100% is 1, the unit cell has an area in a range corresponding to 0.05 <I0 <0.5. It is desirable to have an aperture ratio. Thereby, the diffracted light from the surroundings can be incident on the region where the direct light from one unit cell is incident, and a resist shape can be formed.

  According to a preferred aspect of the present invention, it is desirable that the unit cell has an area aperture ratio in a range corresponding to 0.1 <I0 <0.5. Thereby, diffracted light can be generated efficiently.

  As a preferred embodiment of the present invention, the unit cell desirably has an area aperture ratio in a range corresponding to 0.25 <I0 <0.5. Thereby, diffracted light can be generated more efficiently.

  Moreover, as a preferable aspect of the present invention, the unit cells are desirably arranged in an array. By arranging unit cells each having a light transmittance set in an array, a resist shape having a three-dimensional microstructure can be formed.

  Moreover, as a preferable aspect of the present invention, it is desirable that the unit cells are arranged at substantially the same pitch in the diagonal direction of the rectangular area in the rectangular area. Thereby, a resist shape having a curved surface can be formed accurately.

  Moreover, as a preferable aspect of the present invention, it is desirable that the unit cells are arranged substantially concentrically. Thereby, a resist shape having a curved surface can be formed accurately.

  As a preferred embodiment of the present invention, the unit cell is preferably composed of a plurality of minute cells, and the minute cells preferably have a width equal to or smaller than the resolution limit for exposing the resist layer. When a minute cell having a width equal to or larger than the resolution limit is used, a step shape corresponding to the light transmission distribution of the gray scale mask is easily formed. By using microcells having a width less than the resolution limit, a resist shape having a smooth surface can be formed. The width of the minute cell can be set so as to have a width equal to or smaller than the resolution limit corresponding to the incident angle of light used for exposure and the wavelength of light.

  Furthermore, according to the present invention, it is possible to provide an optical element that is formed by forming a resist shape on a resist layer using the gray scale mask and transferring the resist shape to a substrate. By using the gray scale mask, it is possible to avoid formation of a step shape and to form a resist shape accurately. By transferring the resist shape onto the substrate, an optical element having high light transmittance and excellent thermal characteristics can be obtained.

  Furthermore, according to the present invention, it is possible to provide a spatial light modulation device including the above-described optical element. By having the above optical element, it is possible to efficiently use light by the optical element having an accurate shape. As a result, a spatial light modulation device that can efficiently use light and can obtain a high-efficiency, bright and high-contrast image can be obtained.

  Furthermore, according to the present invention, it is possible to provide a projector including the spatial light modulation device described above. By using the above spatial light modulator, light can be used efficiently and a bright image can be obtained. As a result, it is possible to obtain a projector with a high-efficiency, bright and high-contrast image.

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

  FIG. 1 illustrates a gray scale mask 20 according to a first embodiment of the present invention, and shows a configuration of a reduction projection exposure apparatus 10 using the gray scale mask 20. The reduction projection exposure apparatus 10 reduces the light from the gray scale mask 20 having a light transmittance distribution corresponding to a desired resist shape, and exposes the material substrate 17. The gray scale mask 20 is disposed on the optical axis AX of the optical system of the reduction projection exposure apparatus 10 and between the light source 11 and the projection lens 13. The light from the light source 11 passes through the gray scale mask 20 and then enters the projection lens 13 having a reduced magnification. The light from the projection lens 13 is incident on the material substrate 17 placed on the stage 15. The reduced projection exposure apparatus 10 is, for example, a g-line stepper that uses g-line that is light having a wavelength of 435 nm.

  FIG. 2 illustrates the configuration of the gray scale mask 20. Here, the gray scale mask 20 for forming a single microlens will be described. When forming a microlens array in which a plurality of microlenses are arranged in an array, a grayscale mask 20 shown in FIG. 2 arranged in an array can be used. The gray scale mask 20 has a square shape with a side length d of 70 μm. For example, when the reduced projection exposure apparatus 10 performs reduction exposure of 1/5, a microlens having a side of 14 μm can be formed by the gray scale mask 20 having a side length d of 70 μm.

  The gray scale mask 20 is configured by arranging a plurality of unit cells 21 having a square shape with a side length of 2.5 μm in an array. The plurality of unit cells 21 each have a light transmittance corresponding to a desired resist shape. By arranging the unit cells 21 each having a light transmittance set in an array, a resist shape having a three-dimensional microstructure can be formed. One gray scale mask 20 has 784 (= 28 × 28) unit cells 21.

  The unit cells 21 are arranged at substantially the same pitch in the square diagonal line DL direction of the gray scale mask 20. By disposing the unit cells 21 at substantially the same pitch in the diagonal line DL direction, it becomes possible to set the light transmittance at substantially the same pitch in the diagonal line DL direction. By setting the light transmittance at substantially the same pitch in the diagonal line DL direction, a resist shape having a curved surface can be accurately formed.

  FIG. 3A illustrates the configuration of the unit cell 21. The unit cell 21 has an opening 23 arranged in the center and a light shielding part 22 arranged around the opening 23. In the present embodiment, the opening 23 is disposed at the center of the unit cell 21, but may be disposed at a position other than the center of the unit cell 21. The opening 23 transmits light from the light source 11. The light shielding unit 22 blocks light from the light source 11. The light transmittance of the unit cell 21 is determined by the area aperture ratio. The area opening ratio is assumed to be the ratio of the area of the opening 23 to the unit cell 21. The unit cell 21 is composed of a plurality of minute cells. The opening 23 is constituted by a minute cell that transmits light. The light shielding unit 22 is configured by a minute cell that blocks light. The area aperture ratio can be determined by the number of micro cells constituting the opening 23 with respect to all the micro cells of the unit cell 21.

  It is desirable that the minute cell has a width equal to or smaller than a resolution limit for exposing the resist layer. When the gray scale mask 20 having minute cells equal to or higher than the resolution limit is used, a step shape is easily formed according to the light transmission distribution of the gray scale mask 20. By using microcells having a width less than the resolution limit, a resist shape having a smooth surface can be formed. The width of the minute cell can be set so as to have a width equal to or smaller than the resolution limit corresponding to the incident angle of light used for exposure and the wavelength of light.

  As shown in FIG. 1, the reduction projection exposure apparatus 10 exposes a resist layer with light substantially parallel to the optical axis AX. For example, when a g-line (435 nm) stepper is used as the reduced projection exposure apparatus 10, the width of the minute cell can be set to 0.5 μm or less. When an i-line (365 nm) stepper is used as the reduced projection exposure apparatus 10, the width of the minute cell can be set to 0.3 μm or less. When a g-line stepper is used as the reduced projection exposure apparatus 10, for example, as shown in FIG. 3B, a resist shape having a smooth surface by setting the length t ′ of one side of the minute cell 24 to 0.25 μm. Can be formed.

Returning to FIG. 3A, when the length t of one side of the unit cell 21 and the length p of one side of the opening 23 are used, the area aperture ratio OR in the unit cell 21 can be obtained by Expression (1). .
OR = p ² / t ² × 100 (%) (1)

Further, the ratio BW of the width of the light shielding portion 22 to the width of the unit cell 21 can be obtained by Expression (2).
BW = (tp) / t (2)

FIG. 4 shows the relationship between the intensity I0 of direct light (zero-order light) from the opening 23, the intensity I1 of the first-order diffracted light, the intensity I2 of the second-order diffracted light, and the ratio BW of the width of the light-shielding part 22. is there. The intensity I of the diffracted light generated by the passage of the opening 23 can be obtained by Expression (3), where m is the diffracted light order.
I = [{sin (BW × mπ)} / mπ] ² (3)

  The intensity I1 of the first-order diffracted light and the intensity I2 of the second-order diffracted light can be obtained from the equation (3), respectively. When BW = 0.5 where the intensity of the first-order diffracted light is maximized, the total intensity of the diffracted light for each order is also maximized. The direct light intensity I 0 can be obtained by subtracting the intensity of the diffracted light of each order from the intensity of the light incident on the opening 23. The gray scale mask 20 corresponds to the area aperture ratio OR of each unit cell 21 being 0.36 <I0 <0.5 when the direct light intensity I0 when the area aperture ratio OR is 100% is 1. It is comprised so that it may become. When the direct light intensity I0 is 0.36 <I0 <0.5, the intensity of the diffracted light is relatively large. Note that the area aperture ratio OR is 100% means that no diffracted light is generated in the opening 23 and all the light incident on the opening 23 is directly transmitted as light.

Here, the area aperture ratio OR corresponding to I0 = 0.36 is obtained. From the graph shown in FIG. 4, when I0 = 0.36, BW = 0.4. Assuming that the length t of one side of the unit cell 21 is 2.5 μm, the length p of one side of the opening 23 can be obtained using Expression (2).
p = t−t × BW = 2.5−2.5 × 0.4 = 1.5 (μm)
The area aperture ratio OR can be obtained using the equation (1).
OR = p ² / t ² × 100 = (1.5) ² /(2.5) ² × 100 = 36 (%)

Next, an area aperture ratio OR corresponding to I0 = 0.5 is obtained. From the graph shown in FIG. 4, when I0 = 0.5, BW = 0.29. The length p of one side of the opening 23 can be obtained using Expression (2).
p = t−t × BW = 2.5−2.5 × 0.29 = 1.775 (μm)
The area aperture ratio OR can be obtained using the equation (1).
OR = p ² / t ² × 100 = (1.775) ² /(2.5) ² × 100 = 50.41 (%)
Therefore, the gray scale mask 20 of the present embodiment can be configured such that the area aperture ratio OR of each unit cell 21 is 36% <OR <50.41%.

  FIG. 5 shows an example of the γ characteristic. The γ characteristic indicates the relationship between the area aperture ratio OR and the depth of the resist shape formed in the resist layer by exposure. Here, the depth of the resist shape is a value that increases as it approaches the surface on the light source 11 side, assuming that the position farthest from the surface on the light source 11 side of the resist layer, in other words, the position corresponding to the apex of the microlens is zero. It is said. The depth of the resist shape can be measured using a laser microscope, an atomic force microscope, an interference optical measuring instrument, or a scanning electron microscope. The γ characteristic is obtained by plotting the depth of the resist shape when the area aperture ratio OR is set for each value. Here, an example will be described in which a positive resist AZP4903 manufactured by Clariant Japan is used as the resist material. In the positive resist, the exposed portion is removed by development. The depth of the resist shape is shallower as the area aperture ratio OR is larger, and the resist pattern is deeper as the area aperture ratio OR is smaller.

  The gray scale mask 20 has 14 unit cells 21 arranged in parallel on a diagonal line DL (see FIG. 2) from one corner to the center position of the gray scale mask 20. Correspondingly, the gray scale mask 20 adopts gradations in increments of 1% with respect to the area aperture ratio OR of each unit cell 21, so that 14 gradations can be obtained for 14% from 36% to 50%. It is possible to take. The gray scale mask 20 can determine the opening area ratio OR in each unit cell 21 from the relationship between the γ characteristic and the height of the desired resist shape. When the unit cell 21 is configured by 100 minute cells 24 (see FIG. 3-2), by selecting an opening or light shielding for each minute cell 24, the area opening ratio of the unit cell 21 in increments of 1%. OR can be set.

  In order to form a resist shape having an accurate height corresponding to the change in the area aperture ratio OR, it is possible to take gradations in a range where the γ characteristic shows a linear change in accordance with the change in the area aperture ratio OR. desirable. Further, it is desirable to select a resist material that exhibits a linear change in γ characteristics. In this way, it is possible to form a highly accurate microlens by taking gradations in a range where the γ characteristic shows a linear change.

  FIG. 6 explains the effect of generating diffracted light at the opening 23. Direct light (0) from one unit cell 21 travels in the same direction as when entering the opening 23 and enters the resist layer 60 on the material substrate 17. Diffracted light generated by passing through the opening 23, for example, first-order diffracted light (+1, -1) and second-order diffracted light (+2, -2) is branched from the direct light and travels in a direction different from that of the direct light. Further, the diffracted light L from the unit cells 21 around the one unit cell 21 enters the area AR of the resist layer 60 where the direct light from one unit cell 21 enters.

  The gray scale mask 20 of the present invention is characterized in that the range of the area aperture ratio OR is determined so that the intensity of the diffracted light becomes relatively large. By determining the range of the area aperture ratio OR so that the intensity of the diffracted light becomes relatively large, it is possible to form a resist shape by making the diffracted light from the unit cells 21 around the one unit cell 21 incident. It becomes. Even when the gray scale mask 20 has a light transmittance distribution that changes stepwise in a two-dimensional direction by making diffracted light from the periphery enter a region where direct light from one unit cell 21 is incident. The change in the amount of light on the resist layer 60 can be made close to a continuous one.

  By making the change in the amount of light on the resist layer 60 continuous, it becomes possible to form a smooth surface on the resist layer 60. In the present invention, the number of steps other than the exposure through the gray scale mask 20 is not increased, and the diffracted light is generated as a secondary effect on the direct light, so that it affects the height and shape of the resist shape. It is thought that there is little influence. Thereby, it is possible to avoid the formation of the step shape due to the light transmittance being distributed so as to change stepwise, and the resist shape can be formed accurately.

  The gray scale mask 20 is first formed by forming a light shielding film on a transparent substrate that is a parallel plate. As the transparent substrate, for example, a quartz substrate can be used. The gray scale mask 20 of this embodiment forms a light shielding film using chromium which is a light shielding member. And the opening part 23 is formed by exposing the transparent substrate in which the light shielding film was formed. A portion of the unit cell 21 other than the portion where the opening 23 is formed becomes the light shielding portion 22. The reduction projection exposure apparatus that creates the gray scale mask 20 is an i-line stepper that uses i-line, which is light having a wavelength of 365 nm, for example.

  FIG. 7 shows a procedure for manufacturing a microlens as an optical element using the gray scale mask 20 of the present embodiment. First, in step a which is a resist layer forming step, a resist layer 82 is formed on the substrate 81. The resist layer 82 is formed by applying a resist material on the substrate 81 and further pre-baking. Next, in step b, the resist layer 82 is exposed through the gray scale mask 20 using a g-line stepper which is the reduction projection exposure apparatus 10 shown in FIG. The resist layer 82 is exposed to light that has passed through the gray scale mask 20 and has been reduced to approximately one fifth.

  Further, the resist layer 82 having a curved surface is formed on the resist layer 82 by developing the exposed resist layer 82 with a developer. The developed resist layer 82 is further cured by post-baking. In this way, a desired resist shape 83 corresponding to the light transmittance distribution of the gray scale mask 20 is formed in the resist layer 82.

  Next, in the resist shape transfer step shown in step c, the resist shape 83 of the resist layer 82 is transferred to the substrate 81. By transferring the resist shape 83 to the substrate 81, a microlens shape 84 substantially the same as the resist shape 83 is formed on the substrate 81. The transfer of the resist shape 83 to the substrate 81 can be performed by etching. Etching is performed by dry etching or a combination of dry etching and wet etching.

  Finally, in step d, the microlens 85 is formed by filling the portion of the microlens shape 84 between the substrate 81 and the cover glass 86 with a transparent resin material. A microlens array having a plurality of microlenses 85 may be formed by a mold transfer process. First, the resist shape 83 obtained in step b is subjected to electroless Ni plating to manufacture a mold. Thereby, the resist shape 83 is transferred to the mold. Next, a replica is created by transferring the shape of the mold to another member. Thereby, a lot of replicas can be manufactured easily.

  FIG. 8 shows a comparison between the resist shape 83 formed using the gray scale mask 20 of this embodiment and the designed resist shape. In the graph shown in FIG. 8, the vertical axis represents the depth of the resist shape, and the horizontal axis represents the position on the resist when the center position of the resist shape is used as a reference. A curve C indicated by a solid line indicates a depth distribution of the resist shape 83 formed using the gray scale mask 20 of the present embodiment. A curve E indicated by an alternate long and short dash line indicates a depth distribution of the designed resist shape. From the graph, it can be seen that by using the gray scale mask 20 of this embodiment, a resist shape 83 having a smooth surface with few step shapes and close to a desired shape can be obtained. By accurately forming the resist shape 83 using the gray scale mask 20 described above, an optical element having high light transmittance and excellent thermal characteristics can be obtained.

  The gray scale mask 20 is not limited to the case where the area aperture ratio OR of each unit cell 21 is configured to be in a range corresponding to 0.36 <I0 <0.5. As shown in FIG. 9, the grayscale mask 20 may be configured so that each unit cell 21 has an area aperture ratio OR in a range corresponding to 0.05 <I0 <0.5. As a result, the diffracted light from the surroundings can enter the region where the direct light from one unit cell 21 is incident, and the resist shape 83 can be formed.

  The gray scale mask 20 preferably has a configuration in which each unit cell 21 has an area aperture ratio OR in a range corresponding to 0.1 <I0 <0.5. Thereby, diffracted light can be generated efficiently. More preferably, the gray scale mask 20 has a configuration in which each unit cell 21 has an area aperture ratio OR in a range corresponding to 0.25 <I0 <0.5. Thereby, diffracted light can be generated more efficiently.

  FIG. 10 illustrates the configuration of a gray scale mask according to a comparative example of this embodiment. In the gray scale mask of this comparative example, the area aperture ratio OR of each unit cell is in a range corresponding to 0.49 <I0 <0.63. In the case of this comparative example, the amount of diffracted light generated in the opening 23 is small and the amount of direct light is large compared to the case where the area aperture ratio OR is set within the range described with reference to FIG. When I0 = 0.49, BW = 0.3. In the case of I0 = 0.63, BW = 0.206. The area aperture ratio OR corresponding to 0.49 <I0 <0.63 is 49% <OR <63% when calculated in the same manner as described above.

  FIG. 11 shows a comparison between a resist shape formed when using a gray scale mask with an area aperture ratio 49% <OR <63% and a designed resist shape. In the case of this comparative example, the amount of light distributed to the diffracted light is small and the direct light is increased, so that light is incident on the resist layer according to the light transmittance distribution of the gray scale mask, and a step shape is easily formed on the resist layer. . Therefore, in order to form a microlens having a smooth curved surface, it is effective to generate a large amount of diffracted light by a gray scale mask having an area aperture ratio OR described with reference to FIG. The gray scale mask 20 of the present embodiment is not limited to a microlens used as a spatial light modulation element for modulating light according to an image signal, and other optical elements such as a microprism, a communication device, and a medical device. Can be used in the manufacture of

  The gray scale mask 20 is not limited to the configuration in which the square unit cells 21 shown in FIG. 3 are arranged. For example, the rectangular unit cells 25 shown in FIG. 12 may be arranged. The unit cell 25 has a rectangular shape of vertical ty and horizontal tx (however, ty <tx.). The unit cell 25 has an opening 27 arranged in the center and a light shielding part 26 arranged around the opening 27. The opening 27 has a rectangular shape of vertical py and horizontal px (however, py <px.). The gray scale mask 20 may have a square shape similar to the case shown in FIG. 2 or a rectangular shape similar to the shape of the unit cell 25.

The area aperture ratio OR in the unit cell 25 can be obtained by Expression (4).
OR = (py × px) / (ty × tx) × 100 (%) (4)
With respect to the vertical direction, the ratio BWy of the width of the light-shielding portion 26 to the width of the unit cell 25 can be obtained by Expression (5). In the horizontal direction, the ratio BWx of the width of the light-shielding portion 26 to the width of the unit cell 25 can be obtained by Expression (6).
BWy = (ty-py) / ty (5)
BWx = (tx−px) / tx (6)

As in the case described above, it is assumed that the gray scale mask 20 is configured so that the area aperture ratio OR of each unit cell 25 is in a range corresponding to 0.36 <I0 <0.5. When I0 = 0.36, BWx = BWy = 0.4. Assuming that the vertical length ty of the unit cell 25 is 2 μm and the horizontal length tx is 2.5 μm, the vertical length py of the opening 27 is the formula (5), and the horizontal length px is the formula (6 ).
py = ty-ty × BWy = 2-2 × 0.4 = 1.2 (μm)
px = tx−tx × BWx = 2.5−2.5 × 0.4 = 1.5 (μm)
The area aperture ratio OR can be obtained using Expression (4).
OR = (py × px) / (ty × tx) × 100 = (1.2 × 1.5) / (2 × 2.5) × 100 = 36 (%)

When I0 = 0.5, BWx = BWy = 0.29. The vertical length py of the opening 27 can be obtained using equation (5), and the horizontal length px can be obtained using equation (6).
py = ty-ty × BWy = 2-2 × 0.29 = 1.42 (μm)
px = tx−tx × BWx = 2.5−2.5 × 0.29 = 1.775 (μm)
The area aperture ratio OR can be obtained using Expression (4).
OR = (py × px) / (ty × tx) × 100 = (1.42 × 1.77) / (2 × 2.5) × 100 = 50 (%)

  Therefore, when the gray scale mask 20 including the unit cells 25 having a rectangular shape is used, the area aperture ratio OR of each unit cell 25 is 36% <OR <50%, which is the same as the case where the square unit cell 21 is used. It can be set as this structure. The unit cell is not limited to a rectangular shape, and may be another polygonal shape. For example, the gray scale mask may have a configuration in which hexagonal unit cells are arranged in a honeycomb shape.

  Further, in the gray scale mask, unit cells may be arranged substantially concentrically. The gray scale mask 30 shown in FIG. 13 is configured by disposing unit cells 21 in a substantially concentric shape centering on a central portion of a square shape. By disposing the unit cells 21 in a substantially concentric shape, the light transmittance can be set in a substantially concentric shape. By setting the light transmittance to be substantially concentric, a resist shape having a curved surface can be accurately formed.

  FIG. 14 illustrates a configuration of a gray scale mask according to a modification of the present embodiment. In the present modification, a gray scale mask capable of ensuring a wider area aperture ratio OR than the above case having an area aperture ratio OR corresponding to 0.36 <I0 <0.5 will be described. . In the gray scale mask of this modification, the area aperture ratio OR of each unit cell is in a range corresponding to 0.25 <I0 <0.45. When I0 = 0.25, BW = 0.5. When I0 = 0.45, BW = 0.336. When the area aperture ratio OR corresponding to 0.25 <I0 <0.45 is calculated in the same manner as described above, 25% <OR <45%.

  The gray scale mask 20 takes gradation using an opening area ratio OR range of 14% from 36% to 50%, whereas the gray scale mask of this modification has 25% to 45%. It is possible to obtain gradation in a range of 20% up to%. By taking gradations over a wide range of the opening area ratio OR, it becomes possible to increase the depth of the resist shape corresponding to the area opening ratio OR. For example, when the gradation is taken in the 14% range, the maximum depth of the resist shape is 4 μm as shown in FIG. 8, whereas in the case where the gradation is taken in the 20% range, FIG. As shown in FIG. 4, the maximum depth of the resist shape can be expanded to 6 μm. Thus, by ensuring a large width of the area aperture ratio OR, the height width of the microlens can be increased. In the case of this modification as well, a resist shape having a smooth surface with few step shapes and close to a desired shape can be obtained.

  FIG. 16 shows a schematic configuration of the projector 100 according to the second embodiment of the invention. The projector 100 includes a microlens manufactured using the gray scale mask of the first embodiment. The projector 100 is a so-called front projection type projector that supplies light to a screen 116 provided on the viewer side and observes an image by observing light reflected by the screen 116.

  The light source unit 101 supplies light including red light (hereinafter referred to as “R light”), green light (hereinafter referred to as “G light”), and blue light (hereinafter referred to as “B light”). Ultra high pressure mercury lamp. The integrator 104 makes the illuminance distribution of the light from the light source unit 101 uniform. The light whose illuminance distribution is made uniform is converted into polarized light having a specific vibration direction, for example, s-polarized light by the polarization conversion element 105. The light converted into the s-polarized light is incident on the R light transmitting dichroic mirror 106R constituting the color separation optical system. The light source unit 101 is not limited to a configuration using an ultrahigh pressure mercury lamp. For example, a solid light emitting element such as a light emitting diode element (LED) may be used.

  The R light transmitting dichroic mirror 106R transmits R light and reflects G light and B light. The R light transmitted through the R light transmitting dichroic mirror 106R is incident on the reflection mirror 107. The reflection mirror 107 bends the optical path of the R light by 90 degrees. The R light whose optical path is bent is incident on the spatial light modulator 110R. The spatial light modulator 110R is a transmissive liquid crystal display device that modulates R light according to an image signal. Note that even if the light passes through the dichroic mirror, the polarization direction of the light does not change. Therefore, the R light incident on the spatial light modulator 110R remains as s-polarized light.

  The spatial light modulator 110R includes a λ / 2 phase difference plate 123R, a glass plate 124R, a first polarizing plate 121R, a liquid crystal panel 120R, and a second polarizing plate 122R. The λ / 2 phase difference plate 123R and the first polarizing plate 121R are arranged in contact with a translucent glass plate 124R that does not change the polarization direction. Thereby, the problem that the first polarizing plate 121R and the λ / 2 phase difference plate 123R are distorted by heat generation can be avoided. In FIG. 16, the second polarizing plate 122R is provided independently. However, the second polarizing plate 122R may be disposed in contact with the exit surface of the liquid crystal panel 120R or the entrance surface of the cross dichroic prism 112.

  The s-polarized light incident on the spatial light modulator 110R is converted into p-polarized light by the λ / 2 phase difference plate 123R. The R light converted into p-polarized light passes through the glass plate 124R and the first polarizing plate 121R as it is, and enters the liquid crystal panel 120R. The p-polarized light incident on the liquid crystal panel 120R is converted to s-polarized light by modulation according to the image signal. The R light converted into s-polarized light by the modulation of the liquid crystal panel 120R is emitted from the second polarizing plate 122R. In this way, the R light modulated by the spatial light modulator 110R enters the cross dichroic prism 112, which is a color synthesis optical system.

  The G light and B light reflected by the R light transmitting dichroic mirror 106R have their optical paths bent 90 degrees. The G light and the B light whose optical paths are bent enter the B light transmitting dichroic mirror 106G. The B light transmitting dichroic mirror 106G reflects the G light and transmits the B light. The G light reflected by the B light transmitting dichroic mirror 106G enters the spatial light modulator 110G. The spatial light modulator 110G is a transmissive liquid crystal display device that modulates G light according to an image signal. The spatial light modulator 110G includes a liquid crystal panel 120G, a first polarizing plate 121G, and a second polarizing plate 122G.

  The G light incident on the spatial light modulator 110G is converted into s-polarized light. The s-polarized light incident on the spatial light modulator 110G passes through the first polarizing plate 121G as it is and enters the liquid crystal panel 120G. The s-polarized light incident on the liquid crystal panel 120G is converted into p-polarized light by modulation according to the image signal. The G light converted into p-polarized light by the modulation of the liquid crystal panel 120G is emitted from the second polarizing plate 122G. In this way, the G light modulated by the spatial light modulator 110G enters the cross dichroic prism 112, which is a color synthesis optical system.

  The B light transmitted through the B light transmitting dichroic mirror 106G enters the spatial light modulator 110B via the two relay lenses 108 and the two reflection mirrors 107. The spatial light modulator 110B is a transmissive liquid crystal display device that modulates B light according to an image signal. The reason why the B light passes through the relay lens 108 is that the optical path length of the B light is longer than the optical path lengths of the R light and the G light. By using the relay lens 108, the B light transmitted through the B light transmitting dichroic mirror 106G can be directly guided to the spatial light modulator 110B. The spatial light modulator 110B includes a λ / 2 phase difference plate 123B, a glass plate 124B, a first polarizing plate 121B, a liquid crystal panel 120B, and a second polarizing plate 122B. Since the configuration of the spatial light modulation device 110B is the same as the configuration of the spatial light modulation device 110R described above, detailed description thereof is omitted.

  The B light incident on the spatial light modulator 110B is converted into s-polarized light. The s-polarized light incident on the spatial light modulator 110B is converted into p-polarized light by the λ / 2 phase difference plate 123B. The B light converted into p-polarized light passes through the glass plate 124B and the first polarizing plate 121B as it is, and enters the liquid crystal panel 120B. The p-polarized light incident on the liquid crystal panel 120B is converted to s-polarized light by modulation according to the image signal. The B light converted into s-polarized light by the modulation of the liquid crystal panel 120B is emitted from the second polarizing plate 122B. The B light modulated by the spatial light modulator 110B enters the cross dichroic prism 112, which is a color synthesis optical system. As described above, the R light transmitting dichroic mirror 106R and the B light transmitting dichroic mirror 106G constituting the color separation optical system separate light supplied from the light source unit 101 into R light, G light, and B light. To do.

  The cross dichroic prism 112, which is a color synthesis optical system, is configured by arranging two dichroic films 112a and 112b perpendicularly to an X shape. The dichroic film 112a reflects B light and transmits G light. The dichroic film 112b reflects R light and transmits G light. Thus, the cross dichroic prism 112 combines the R light, G light, and B light modulated by the spatial light modulators 110R, 110G, and 110B for the respective color lights. The projection optical system 114 projects the light combined by the cross dichroic prism 112 onto the screen 116. As a result, a full color image can be displayed on the screen 116.

  As described above, the light incident on the cross dichroic prism 112 from the spatial light modulator 110R and the spatial light modulator 110B is set to be s-polarized light. The light incident on the cross dichroic prism 112 from the spatial light modulator 110G is set to be p-polarized light. In this way, by changing the polarization direction of the light incident on the cross dichroic prism 112, the light emitted from the spatial light modulators for the respective color lights in the cross dichroic prism 112 can be effectively combined. The dichroic films 112a and 112b are usually excellent in the reflection characteristics of s-polarized light. For this reason, R light and B light reflected by the dichroic films 112a and 112b are s-polarized light, and G light transmitted through the dichroic films 112a and 112b is p-polarized light.

  FIG. 17 shows a cross-sectional configuration of a main part of the liquid crystal panel 120R. The projector 100 described with reference to FIG. 16 includes three liquid crystal panels 120R, 120G, and 120B. These three liquid crystal panels 120R, 120G, and 120B differ only in the wavelength region of light to be modulated, and have the same basic configuration. For this reason, the following description will be given using the liquid crystal panel 120R as a representative example. The R light from the light source unit 101 enters the liquid crystal panel 120R from the upper side shown in FIG. 17 and is emitted downward, which is the direction of the screen 116. A cover glass 202 is fixed to the incident side of the incident-side dust-proof glass 200 that is a dust-proof glass through an adhesive layer 201. On the emission side of the cover glass 202, a black matrix portion 203a and a counter electrode 204 are formed.

  On the incident side of the emission-side dust-proof glass 208, an adhesive layer 207, an alignment film 206c for aligning liquid crystals, and a TFT substrate 206 having TFTs (thin film transistors) and transparent electrodes 206a are formed. The incident side dustproof glass 200 and the emission side dustproof glass 208 are bonded together so that the counter electrode 204 and the TFT substrate 206 face each other. A liquid crystal layer 205 is sealed between the counter electrode 204 and the TFT substrate 206. The liquid crystal layer 205 is a modulation unit that modulates R light, which is incident light, according to an image signal. On the incident side of the liquid crystal layer 205, a black matrix portion 203a is formed.

  The opening 203b allows incident light to enter the liquid crystal layer 205 serving as a modulation unit. The R light that passes through the opening 203b passes through the counter electrode 204, the liquid crystal layer 205, and the TFT substrate 206. The polarization state of the R light is converted by modulation according to the image signal in the liquid crystal layer 205. The opening 203b forms a pixel of a projected image.

  A microlens array 210 is formed on the incident-side dustproof glass 200. The microlens array 210 includes microlenses 211 arranged in an array on a reference plane 200b that is an XY plane. The microlens 211 that is an optical element refracts R light that is incident light in the direction of the opening 203b. The microlens 211 is provided with a curved surface 211a that refracts light facing the incident side. The liquid crystal panel 120R is disposed such that the reference surface 200b on which the microlens 211 is disposed and the Z axis that is the optical axis are substantially orthogonal.

  In the configuration shown in FIG. 16, the first polarizing plate 121R and the second polarizing plate 122R are provided separately from the liquid crystal panel 120R. Instead of this, a polarizing plate may be provided between the incident-side dustproof glass 200 and the counter electrode 204, between the emission-side dustproof glass 208 and the TFT substrate 206, and the like. Further, the microlens array 210 may be formed on the first polarizing plate 121R.

  The microlens 211 can be formed using the gray scale mask of the first embodiment. By using the gray scale mask of the first embodiment, the microlens 211 has a smooth curved surface 211a with a small step shape and can have an accurate shape. By reducing the step shape of the curved surface 211a, unnecessary reflection on the curved surface 211a is reduced, and light can be used efficiently. In addition, since the light can be used efficiently, the projector 100 can display a bright image. Furthermore, by using the microlens 211 having an accurate shape, the light beam angle can be accurately controlled and a high-contrast image can be displayed. Thereby, a highly efficient, bright and high-contrast image can be obtained. By preventing the concentration of light in the opening 203b with the microlens 211 having an accurate shape, it is possible to reduce deterioration of the liquid crystal, the alignment film, and the like, and further deterioration of the spatial light modulator.

  The projector 100 according to the present embodiment is not limited to the configuration using an ultrahigh pressure mercury lamp as the light source unit 101. For example, a solid light emitting element such as a light emitting diode element (LED) may be used. The projector 100 is not limited to a so-called three-plate projector provided with three transmissive liquid crystal display devices. For example, a projector provided with one transmissive liquid crystal display device or a projector using a reflective liquid crystal display device. It is also good. Further, the projector is not limited to the front projection type projector 100, and may be a so-called rear projector in which a laser beam is supplied to one surface of the screen and an image is viewed by observing light emitted from the other surface of the screen. .

  As described above, the gray scale mask according to the present invention is suitable for manufacturing a minute optical element.

The figure which shows the structure of the reduction exposure apparatus using a gray scale mask. FIG. 3 is a diagram illustrating the configuration of a grayscale mask according to the first embodiment of the invention. The figure explaining the structure of a unit cell. The figure explaining a micro cell. The figure showing the relationship between the intensity | strength of direct light and diffracted light, and the light-shielding part width | variety. The figure showing the example of (gamma) characteristic. The figure explaining the effect by producing diffracted light in an opening. The figure which shows the procedure which manufactures a microlens using a gray scale mask. The figure explaining the resist shape formed using the gray scale mask. The figure explaining an area aperture ratio. The figure explaining the structure of the gray scale mask which concerns on a comparative example. The figure explaining the resist shape formed using the gray scale mask. The figure explaining the rectangular unit cell. The figure explaining the structure which arrange | positions a unit cell in substantially concentric form. FIG. 6 is a diagram for explaining a grayscale mask according to a modification of the first embodiment. The figure explaining the resist shape formed using the gray scale mask. FIG. 5 is a diagram illustrating a schematic configuration of a projector according to a second embodiment of the invention. The figure which shows the principal part cross-section structure of a liquid crystal panel.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Reduction projection exposure apparatus, 11 Light source, 13 Projection lens, 15 Stage, 17 Material substrate, 20 Gray scale mask, AX Optical axis, 21 Unit cell, DL diagonal line, 22 Light-shielding part, 23 Opening part, 24 Minute cell, 60 Resist Layer, AR region, 81 substrate, 82 resist layer, 83 resist shape, 84 microlens shape, 85 microlens, 86 cover glass, 25 unit cell, 26 light shielding part, 27 opening part, 30 gray scale mask, 100 projector, 101 Light source unit, 104 integrator, 105 polarization conversion element, 106R R light transmission dichroic mirror, 106GB light transmission dichroic mirror, 107 reflection mirror, 108 relay lens, 110R, 110G, 110B spatial light modulator, 112 cross die Loic prism, 112a, 112b Dichroic film, 114 projection optical system, 116 screen, 120R, 120G, 120B liquid crystal panel, 121R, 121G, 121B first polarizing plate, 122R, 122G, 122B second polarizing plate, 123R, 123B λ / 2 phase difference plate, 124R, 124B glass plate, 200 incident side dustproof glass, 200b reference surface, 201 adhesive layer, 202 cover glass, 203a black matrix portion, 203b opening, 204 counter electrode, 205 liquid crystal layer, 206 TFT substrate, 206a Transparent electrode, 206c Alignment film, 207 Adhesive layer, 208 Output side dust-proof glass, 210 Microlens array, 211 Microlens, 211a Curved surface

Claims (11)

Provided with a plurality of unit cells each having a light transmittance corresponding to a desired resist shape,
The unit cell has an opening that transmits light and a light blocking unit that blocks light, and the light transmittance is determined by an area opening ratio that is a ratio of an area of the opening in the unit cell,
The resist shape is formed by causing the diffracted light from unit cells around the one unit cell to enter the region where the direct light from one unit cell is incident in the resist layer for forming the resist shape. A gray scale mask having the area aperture ratio in a range.   When the direct light intensity I0 when the area aperture ratio is 100% is 1, the unit cell has the area aperture ratio in a range corresponding to 0.05 <I0 <0.5. The gray scale mask according to claim 1.   The gray scale mask according to claim 2, wherein the unit cell has the area aperture ratio in a range corresponding to 0.1 <I0 <0.5.   The gray scale mask according to claim 3, wherein the unit cell has the area aperture ratio in a range corresponding to 0.25 <I0 <0.5.   The gray scale mask according to claim 1, wherein the unit cells are arranged in an array.   6. The grayscale mask according to claim 1, wherein the unit cells are arranged at substantially the same pitch in the diagonal direction of the rectangular region in the rectangular region.   The gray scale mask according to claim 1, wherein the unit cells are arranged substantially concentrically. The unit cell is composed of a plurality of minute cells,
The gray scale mask according to claim 1, wherein the minute cell has a width that is equal to or smaller than a resolution limit for exposing the resist layer.   An optical element produced by forming a resist shape on a resist layer using the grayscale mask according to claim 1 and transferring the resist shape to a substrate.   A spatial light modulator comprising the optical element according to claim 9.   A projector comprising the spatial light modulation device according to claim 10.

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