Photomask, method of manufacturing optical element array, optical element array

A photomask for an optical element array includes first and second optical elements. A light transmission rate distribution includes a first area where the first optical element is to be formed, a second area where the second optical element is to be formed, and a third area between the first and second areas, has a first light transmission rate at an end portion of the first area. A second light transmission rate is higher than the first light transmission rate at another end portion. A third light transmission rate at an end portion corresponds to a boundary between the second and third areas. A fourth light transmission rate is higher than the third light transmission rate at another end portion of the second area. The light transmission rate distribution along a first direction is higher than a segment connecting the second and third light transmission rates in the third area.

BACKGROUND OF THE INVENTION

Field of the Invention

This disclosure relates to manufacture of photomasks and, specifically, to manufacture of photomasks for forming optical elements.

Description of the Related Art

A micro lens is known as an optical element for an image pickup apparatus. In the image pickup apparatus, since an incident angle of light incident on a peripheral portion is larger than an incident angle of light incident on a center portion in an image pickup area in which photoelectric conversion elements are arrayed, light condensing characteristics of the micro lens located in the peripheral portion thereof may be lowered in comparison with that in the center portion. Japanese Patent Laid-Open No. 2007-335723 discloses a configuration in which tear drop type micro lenses are provided in a peripheral portion of a hemispherical micro lens located in a center portion of an image pickup area to reduce a loss of light condensing characteristics of the micro lens in the peripheral portion thereof.

Japanese Patent Laid-Open No. 2005-258349 discloses a method of forming a micro lens having a given shape by using a photomask having an area coverage modulation.

When forming a micro lens array (optical element array) having a tear drop shape, which is not a hemispherical shape as disclosed in Japanese Patent Laid-Open No. 2007-335723, using the method disclosed in Japanese Patent Laid-Open No. 2005-258349 is conceivable. However, the present inventors have found that the optical elements having a desired shape cannot be obtained by the method disclosed in Japanese Patent Laid-Open No. 2005-258349 at portions where the optical elements having a non-hemispherical shape abut each other.

Accordingly, this disclosure is intended to provide a photomask which contributes to achieving an optical element having a desired shape and a method of manufacturing an optical element array.

SUMMARY OF THE INVENTION

This disclosure provides a photomask for an optical element array including: a first optical element having a bottom surface on a first surface including a first direction and a second direction that intersects the first direction; and a second optical element having a bottom surface on the first surface and arranged so as to abut on the first optical element along the first direction, wherein a light transmission rate distribution of the photomask along the first direction includes a first area in which the first optical element is to be formed, a second area in which the second optical element is to be formed, and a third area provided between the first area and the second area, wherein the light transmission rate distribution of the photomask along the first direction includes: a first light transmission rate at an end portion of the first area; a second light transmission rate having a light transmission rate higher than the first light transmission rate at another end portion, which corresponds to a boundary between the first area and the third area on a side opposite to the end portion; a third light transmission rate at an end portion, which corresponds to a boundary between the second area and the third area; and a fourth light transmission rate having a light transmission rate higher than the third light transmission rate at another end portion of the second area on a side opposite to the end portion, and wherein the light transmission rate distribution of the photomask along the first direction has a light transmission rate higher than a segment connecting the second light transmission rate and the third light transmission rate in the third area.

DESCRIPTION OF THE EMBODIMENTS

A photomask for an optical element array of this disclosure will be described with reference to a plurality of embodiments. The embodiments may be modified and may be combined as needed. The optical element array formed by the photomask for the optical element array of this disclosure is applicable to a photoelectric conversion apparatus, a display apparatus, an image pickup system and a display system using these apparatuses.

The following description will be given with reference to an X-axis direction (first direction), a Y-axis direction (second direction), and a Z-axis direction (third direction) passing through a center O of the optical element array. However, the first direction may be a direction inclined by an angle θ1(θ1>0) from the X-axis direction, for example. In other words, a given direction of radiation from a center to an outer periphery of an area (array area) in which the optical elements are arrayed may be defined as the first direction, and a direction intersecting the first direction may be defined as the second direction. However, in the following description, the optical element array is provided along a plane including the first direction and the second direction. In the following description, description of the corresponding drawings is omitted as needed.

First Embodiment

As a first embodiment, an example in which a plurality of micro lenses are arranged one dimensionally as the optical element array will be described with reference toFIG. 1AtoFIG. 4D.FIGS. 1A to 1Dare drawings illustrating a shape and a distribution relating to an optical element array100.FIGS. 1A to 1Dillustrate portions of the optical element array100, where three optical elements, namely, an optical element11, an optical element12, and an optical element13are arranged along a Y-axis direction.FIG. 1Ais a schematic plan view illustrating an orthogonal projection image of the optical element array100. The orthogonal projection image is a drawing of a projection of the optical element array100on a plane including an X-axis and a Y-axis.

FIG.1B1is a drawing illustrating a design shape110of the optical element array taken along a line IB-IB inFIG. 1A. The term “design shape” in this specification is an ideal shape at the time of designing. FIG.1B2is a drawing illustrating a light transmission rate distribution120of a photomask on the basis of the design illustrated in FIG.1B1. FIG.1B3is a drawing illustrating a light intensity distribution130in an exposed member when the photomask having the light transmission rate distribution illustrated in FIG.1B2. FIG.1B4is a drawing (schematic cross sectional view) illustrating a shape140of the optical element array at a position indicated by the line IB-IB inFIG. 1A.

FIG. 101is a drawing illustrating a design shape1110of the optical element array taken along a line IC-IC inFIG. 1A. FIG.1C2is a drawing illustrating a light transmission rate distribution1120of the photomask on the basis of the design illustrated inFIG. 101. FIG.1C3is a drawing illustrating a light intensity distribution1130in an exposed plane when the photomask having the light transmission rate distribution illustrated in FIG.1C2. FIG.1C4is a drawing (schematic cross sectional view) illustrating a shape1140of the optical element array at a position indicated by the line IC-IC inFIG. 1A. In the following description, points indicate a position in the X-axis direction or the Y-axis direction, a height of the design shape, a light transmission rate, a light intensity, and a height of the shape.

The photomask of this embodiment will be described here. The photomask of this embodiment may be any photomask as long as being provided with a continuous gradation change. For example, a gray tone mask, a half tone mask, or an area coverage modulation mask may be used as the photomask of this embodiment. The area coverage modulation mask is a photomask capable of irradiating light having a continuous gradation change by changing a density distribution of dots formed of a light-shielding film having a resolution not higher than a resolution of an exposure apparatus or by hanging the surface area thereof. This embodiment will be described with an example of a positive type photoresist. However, a negative type photoresist is also applicable.

A shape of the optical element will be described by focusing on two optical elements in the optical element array. As illustrated inFIG. 1A, for example, the orthogonal projection image of the optical element11has a line symmetry shape with respect to the line IB-IB. However, for example, the orthogonal projection image of the optical element11is not line symmetry in segments parallel to the Y-axis direction including the line IC-IC. The cross-sectional shape of the optical element11along the line IB-IB corresponds to the shape140illustrated in FIG.1B4. In FIG.1B4, a vertical axis indicates a height (a size in the Z-axis direction). In FIG.1B4, the height of the shape140increases from a point141to a point142. The height of the shape140increases from the point142to a point143once, and then decreases. Here, a portion from the point141to the point143corresponds to the optical element11(the first optical element). The height of the shape140increases from the point143to a point144, and further increases and then decreases in a range from the point144to a point145. Here, a portion from the point143to the point145corresponds to the optical element12(the second optical element). The shape140is a portion corresponding to the optical element13, (the third optical element), and has the same shape in a portion from the point141to the point143and a portion from the point143to the point145. The optical elements11to13each have an apex148.

FIG.1B1illustrates the design shape110of FIG.1B4. The vertical axis of FIG.1B1indicates the height in the same manner as FIG.1B4. The design shape110corresponds to the shape140indicated by FIG.1B4, and ideally matches the shape140. The design shape110includes points111to115and apexes118corresponding to the points141to145and the apexes148of the shape140in FIG.1B4.

FIG.1B2illustrates the transmission rate distribution120of the photomask and the vertical axis indicates a transmission rate. The transmission rate distribution120may be obtained considering sensitivity of a photosensitive member to be used for reproducing the design shape110illustrated in FIG.1B1. The light transmission rate distribution120here includes points121to127and apexes128which correspond to the points111to117and the apexes118of the design shape110illustrated in FIG.1B1. The light transmission rate distribution120has a constant light transmission rate from the point121to the point122, and a light transmission rate lower than that at the points121and122at a point123. The light transmission rate distribution120has a light transmission rate lower than the light transmission rate at the point123once in the range from the point123to the point124, and has a light transmission rate higher than that at the point123at the point124. Here, a portion from the point121to the point124corresponds to the optical element11(the first optical element). The light transmission rate distribution120in a portion from the point124to the point127is the same as that in a portion from the point121to the point124. A portion from the point124to the point127of the light transmission rate distribution120corresponds to the optical element12. The light transmission rate distribution120has the same shape at a portion corresponding to the optical element13as the portion from the point121to the point124and a portion from the point124to the point127. The light transmission rate distribution120is a portion corresponding to the respective optical elements, and has the apexes128, which corresponds to the apexes118of the design shape110illustrated in FIG.1B1.

As illustrated in FIG.1B2, the light transmission rate distribution120includes a first area101in which the optical element11is formed, a second area102in which the optical element12is formed, and a third area103provided between the first area101and the second area102. The first area101is an area from the point123at an end of the first area101, to the point124at another end on the opposite side to the point123at a boundary with respect to the third area. The light transmission rate distribution120of the first area101has the first light transmission rate at the point123, and a second light transmission rate higher than the first light transmission rate at the point124. The light transmission rate distribution120in the first area101indicates that the light transmission rate increases from the first light transmission rate to the second light transmission rate. In this embodiment, the light transmission rate distribution120has a light transmission rate decreasing from the first light transmission rate to a point corresponding to the apex128, and then increasing to the second light transmission rate. However, the light transmission rate may increase from the first light transmission rate to the second light transmission rate at a constant rate. The second area102is an area between the point125and the point126at an end on the boundary with respect to the first area101and the point127at another end on the opposite side to the point125and the point126. The light transmission rate distribution120in the second area102has the third light transmission rate at the point126, and a fourth light transmission rate higher than the third light transmission rate at the point127. The light transmission rate distribution120in the second area102indicates that the light transmission rate increases from the third light transmission rate to the fourth light transmission rate. In this embodiment, the light transmission rate distribution120has a light transmission rate decreasing from the third light transmission rate to a point corresponding to the apex128, and then increasing to the fourth light transmission rate. However, the light transmission rate may increase from the third light transmission rate to the fourth light transmission rate at a constant rate. The third area103is located between the point124(the end on the first area side), which is an end at the boundary with respect to the first area101and the point125and the point126(the end on the second area side) at another end on the boundary with respect to the second area102. The third area103is shorter than the first area101in the X-axis direction, and shorter than the second area102in the X-axis direction. The light transmission rate distribution120in the third area103has a light transmission rate equal to or higher than a segment129, which is a segment connecting the second light transmission rate at the point124at one end and the third light transmission rate at the point126at the other end. In this embodiment, the light transmission rate distribution120in the third area103has the same rate as the light transmission rate (the second light transmission rate) at the point124, like the point125, for example. This is applicable in the case where an absolute value of a change rate of the light transmission rate in the third area103is larger than a change rate (rate) of the light transmission rate in the first area101and the second area102. The light transmission rate in the third area103may be changed continuously, may be changed discontinuously, or may be constant as long as the value is higher than that of the segment.

An exposed member obtains a light intensity distribution130illustrated in FIG.1B3by being exposed by using the photomask having the light transmission rate distribution120as described above. The light intensity distribution130has the points131to135and the apexes138. The points131to135of the light intensity distribution130correspond to the point121to127of the light transmission rate distribution120in FIG.1B2. Then, the light intensity distribution130has the highest light intensity at a point133, which is a portion corresponding to the boundary between the first area101and the third area103of the light transmission rate distribution120. With the photomask in this configuration, the shape between the optical element11and the optical element12may be formed under control.

In FIG.3B1, the height of a design shape310increases from a point311to a point312. The design shape310has the height decreasing toward a point313via the point318. A portion from the point313to the point315, the design shape310has the same shape as that forming the point311to the point313. In FIG.3B2, a light transmission rate distribution320of the photomask for forming the design shape310is designed to have the same shape as the design shape310. However, it is understood that a shape340in FIG.3B4is different from the design shape310of FIG.3B1illustrating the shape at the time of designing. For example, in the design shape310in FIG.3B1, a portion from the point312to the point313has a change rate of the shape smaller than a portion between the point313and the point314. In an area corresponding to the area where portions having different change rates share a border with each other, a reproduction rate is lowered in the shape340in FIG.3B4. The portion from a point342to a point343of the shape340has an inclination smaller than a corresponding portion of the design shape310, and a portion from the point343to a point344of the shape340has an inclination smaller than a corresponding portion of the design shape310. In addition, although the design shape310in FIG.3B1has a height H319from the point313to the point314, the shape340in FIG.3B4has a height H349from the point343to the point344, which is lower than the height H319. The reason is that a light intensity distribution330in FIG.3B3shows a distribution different from the light transmission rate distribution320illustrated in FIG.3B2.

The principle will be described with reference toFIGS. 4A to 4D.FIG. 4Aillustrates a light transmission distribution420at the time of designing the photomask, andFIG. 4Bis a cross-sectional view schematically illustrating a state of exposure at the time when a photomask450inFIG. 4Ais used.FIG. 4Cillustrates a light intensity distribution430of the exposed member (a photosensitive member, for example, photoresist) in the state illustrated inFIG. 4B, andFIG. 4Dillustrates a shape440of the photoresist developed after the exposure. InFIG. 4A, the light transmission distribution420has a high light transmission rate from a point423to a point424, and the light transmission rate from the point425to a point426is zero. InFIG. 4B, the photomask450corresponding to the light transmission distribution420has an opening451and a light-shielding portion452. A boundary between the opening451and the light-shielding portion452is a position corresponding to the point424(point425) of the light transmission distribution420inFIG. 4A. When light (arrow) enters, the light is diffracted at a boundary between the opening451and the light-shielding portion452at an end of the light-shielding portion452. This diffraction causes a decrease in light intensity between a point431and a point432, and an increase in light intensity between the point432and a point433in the light intensity distribution430illustrated inFIG. 4C. As a result of the change in light intensity as described above, a change in shape occurs between a point441to a point442in the shape440of the photoresist illustrated inFIG. 4D. Even though the diffraction occurs, an influence of the diffraction is reduced by using the photomask having the light transmission rate distribution illustrated in FIG.1B2, so that the shape between the optical element11and the optical element12is formed under control.

FIGS. 1A to 1Dwill be described again.FIG. 101to FIG.1C4illustrates shapes of cross sections of the optical element12taken along the segment IC-IC inFIG. 1A.FIG. 101to FIG.1C4are drawings illustrating the shapes and the distribution in the same manner as FIG.1B1to FIG.1B4, and a vertical axes ofFIG. 101to FIG.1C4indicate the same value. As illustrated by the design shape1110inFIG. 101, the optical element12has a hemispherical shape. A point1111is an apex, and the cross section of the optical element12along the line IC-IC is line symmetry with respect to a segment1112passing through the apex. The segment1112is perpendicular to a bottom surface1113of the optical element12. In FIG.1C2to FIG.1C4, the light transmission rate distribution1120, the light intensity distribution1130, and the shape1140maintaining the design shape1110.

FIG. 2illustrates a design data200of the photomask on the basis of the light transmission rate distribution illustrated in FIG.1B2. The design data200illustrates a two-dimensional arrangement of a light-shielding member, and corresponds to one optical element12inFIG. 1A, and corresponds to the area103, the area102in FIG.1B2, and FIG.1C2. InFIG. 2, the portion corresponding to one area is divided into a plurality of cells. These cells are set to have a size smaller than a resolution limit of light having a wavelength used in exposure. The black cells are provided with a light-shielding member, and white cells are opened area having no light-shielding member. The light transmission rate of the photomask can be adjusted by the surface area of the light-shielding member. In the design data of the photomask, the light-shielding member is not provided in the areas corresponding to the area103in FIG.1B2.

The optical elements and the optical element array100are formed by being exposed and developed by the photomask on the basis of the design data200. The optical elements and the optical element array100may be applied, for example, to the photoelectric conversion apparatus as illustrated inFIG. 1D. InFIG. 1D, the optical element array100is provided above a semiconductor substrate20having a photoelectric conversion element212with an intermediated layer21interposed therebetween. The semiconductor substrate20has an element such as transistor in addition to the photoelectric conversion element212. The intermediated layer21includes a plurality of wiring layers23, a plurality of insulating layers24for insulating the wiring layers23, and a color filter layer25for separating color. The intermediated layer21may further include an interlayer lens layer and a light-shielding layer. In the photoelectric conversion apparatus, the image pickup area has an area in which the same circuits referred to as a so-called pixels150are repeatedly provided. The optical elements of the optical element array100may be provided so as to correspond to the pixels150. Here, in the cross-sectional view inFIG. 1D, a center151of the pixel150and a center152of the optical element are offset and the center of the optical element is located closer to the center of the optical element array100than the center of the pixel150.FIG. 1Dillustrates the case where light153enters in the photoelectric conversion apparatus as described above. In FIG.1B4, light entering a portion corresponding to a portion from the point143to the point144is diffracted more than light entering a portion corresponding to a portion from the point144to the point145and hence enters an area deviated from a photoelectric conversion element22, and hence does not contribute to light condensing to the photoelectric conversion apparatus. In contrast, light entering the portion corresponding to the portion from the point144to the point145is condensed toward the photoelectric conversion element22. In other words, the shape of the portion corresponding to the portion from the point144to the point145is desired to be formed specifically under control. According to a photomask200illustrated inFIG. 2, the shape of the portion corresponding to the portion from the point144to the point145can be formed with high degree of reproducibility with respect to the design shape.

Here, the shape is compared with that illustrated in FIG.3B4again. The point343in FIG.3B4illustrating the shape of the optical element array is deviated leftward from the position of the point313in FIG.3B1, which is the design shape of the optical element array. H349in FIG.3B4is smaller than H319in FIG.3B1. In other words, the position in the height direction is deviated upward. In contrast, in FIG.1B4, it is understood that the position of the point143substantially matches the position of a point113in the design shape in the FIG.1B1, and the area from the point142to the point143is formed with high degree of reproducibility with respect to the design shape. Examples will be described further in detail with reference toFIG. 1Ato FIG.1C4. In the case where the optical element array is formed by using the photomask of this embodiment, a positive type photoresist is generally used as the material of the micro lenses, which are the optical element array.

In formation of the micro lenses, the resist is exposed by using an area coverage modulation mask. Therefore, the contrast of the resist is lower than general photoresist. In FIG.1B4, the portion corresponding to the portion from the point143to the point144does not contribute to light condensation, a shape as steep as possible needs to be employed to reduce the width. By reducing the width, the shape of the portion from the point144to the point145which contributes to light condensation may be made closer to the shape corresponding to the portion from the point114to the point115in FIG.1B1.

Even in the case where the photoresist for micro lenses having a low contrast is employed, the desirable shape which is equivalent to the design shape can be achieved by using this method. An aspherical micro lens will be described with reference toFIG. 11.

FIG. 11is a drawing corresponding to FIG.1B4. However, a description of the optical elements may be given with expressions different from expressions used in drawings other thanFIG. 11. Reference numeral2100is an area in which the first optical element is formed, reference numeral2200is an area in which the second optical element is formed, and reference numeral2300is an area in which the third optical element is formed. These optical elements are arranged in the X-axis direction (the first direction) and have bottom surfaces in the X-axis direction. The second optical element is arranged so as to abut on the first optical element. The third optical element is arranged so as to abut on the first optical element on the side opposite to the side on which the second optical element is provided.

FIG. 11is a cross-sectional view taken along the first direction, and figuring out the form in this manner may be expressed as “in the cross-sectional view taken along the first direction”.

In the cross-sectional view taken along the first direction, the first optical element includes a first area2110having a steep change in surface shape of the first optical element and a second area2120having a relatively gentle change in surface shape of the first optical element. A boundary between the first area2110and the second area2120is a point144. A boundary between the area2100in which the first optical element is formed and the area2200in which the second optical element is formed is the point143. In the first direction, the distance between the boundaries, that is, the distance from the point143to the point144is defined as W. The distance W corresponds to a width of an area of the micro lens as the first optical element having a steep surface shape as the first optical element.

A distance from the apex148to the bottom surface of the first optical element in a direction (Y-axis direction) orthogonal to the first direction is defined as H. The distance H corresponds to the height of the micro lens as the first optical element.

A distance of the area2100in which the first optical element is formed in the first direction is defined as P. The distance P corresponds to a pitch of formation of a plurality of optical elements.

In addition, an angle formed between a straight line connecting the point143and the point144and the bottom surface is θ.

Here, the distance W of the manufactured micro lens (the width of the area of the micro lens, having a steep surface shape) and the distance H (the height of the micro lens) satisfy a relationship 0.3H<W<0.5H. In addition, the angle θ satisfies a relationship 2<tan−1θ<3.5.

For example, the manufactured micro lens has an angle θ of 70°, a height H of 1 μm, and a width W of a steep area is 0.4 μm.

In order to achieve efficient light condensation of oblique incident light, the pitch P and the distance W are set to satisfy the relationship W<⅓·P.

By designing the third area103illustrated in FIG.1B1adequately, a structure in which the optical element and the optical element abutting thereon is reduced, that is, a gapless structure is achieved. The width of the area103at this time is such that the dimension of the third area103illustrated in FIG.1B1falls between 1/10 times to 1 time, and specifically, between ½ times to 1 time the wavelength of light used in exposure.

Second Embodiment

In the first embodiment, the case of the optical element array100in which a plurality of optical elements are one dimensionally arranged has been described. However, in a second embodiment, a case where the plurality of optical elements are arranged two-dimensionally will be described.FIG. 5Ais a schematic plan view corresponding toFIG. 1Aand, in this embodiment, a plurality of optical elements11to19are arranged two-dimensionally. FIG.5B2and FIG.5B4illustrate light transmission rates and shapes of cross sections taken along the line VB-VB inFIG. 5A, and are equivalent to FIG.1B2and FIG.1B4. FIG.5C1to FIG.5C4illustrate a design shape1510, a light transmission rate distribution1520, a light intensity distribution1530, and a shape1540of a cross section taken along the line VC-VC inFIG. 5A, respectively.

As illustrated in FIG.5C1, in the design shape1510of the optical elements12,14, and15, the optical elements are in contact with optical elements abutting each other at the same height. In such a case, in the light transmission rate distribution1520illustrated in FIG.5C2, provision of portions such as areas103in FIG.5B2is not necessary. In FIG.5C2, the light transmission rate distribution1520of the optical elements abutting each other has a line symmetrical shape including the contact point between the optical elements abutting each other. In contrast, as illustrated in FIG.5B2, in the contact point between the optical elements abutting each other in the case where the light transmission rate distribution120has a non-line-symmetry shape including the contact point at the contact point between the optical elements abutting each other, the areas103are provided. With such a configuration, optical elements with high degree of reproducibility with respect to the shape at the time of designing are provided.

Third Embodiment

A third embodiment is different from the first embodiment in that the plurality of optical elements are arranged two-dimensionally, and a gap is provided between a certain optical element and another optical element abutting thereon in the X-axis direction. The third embodiment is different from the second embodiment in that a gap is provided between a certain optical element and another optical element abutting thereon in the X-axis direction.FIG. 6Ato FIG.6C4correspond toFIG. 1Ato FIG.1C4, and toFIG. 5Ato FIG.5C4.FIG. 6Ais a schematic plan view illustrating nine optical elements61to69. A gap605provided between the optical elements abutting each other is a hatched portion illustrated between the optical element61and the optical element62, for example. In this configuration as well, a photomask like the first and second embodiments can be designed. Focusing on the optical element61and the optical element62, a shape of the optical element and a light transmission rate of the photomask will be described.

A design shape610illustrated in FIG.6B1has a constant height between a point611and a point612, and the height increases from the point612to a point613. The height of the design shape610increases from the point613to a point614, and becomes constant again between the point614and a point615. The height of the design shape610decreases from the point615to a point616, and decreases from the point616to a point617, and becomes constant again between the point617to a point618. A portion between the point611and the point612, a portion between the point614and the point615, and a portion between the point617and the point618are portion corresponding to the gap. A point619is the highest portion, and is an apex of the cross section thereof.

A light transmission rate distribution620illustrated in FIG.6B2corresponds to the design shape610, and includes a first area601, a second area602, and a third area603in the same manner as FIG.1B2. The height of the light transmission rate distribution620is constant between a point621and a point622, and as illustrated by the point622and a point623, the height increases at the point622(an inclination of the light transmission rate distribution620is zero). The height of the light transmission rate distribution620decreases from the point623to a point624, and becomes constant again between the point624and a point625. The height of the light transmission rate distribution620increases from the point625to a point626(an inclination of the light transmission rate distribution620is zero), and decreases from the point626to a point627, and becomes constant again between the point627to a point628. A portion between the point621and the point622, a portion between the point624and the point625, and a portion between the point627and the point628are portions corresponding to the gap. The point629is a portion having the highest light transmission rate, and corresponds to the point619in FIG.6B1.

The light transmission rate distribution620includes the first area601from the point623to the point624, the second area602from the point626to the point627, and the third area603from the point624to the point625. In the same manner as the first embodiment, the light transmission rate of the third area603has a light transmission rate higher than the segment between the point624and the point626. In this embodiment, the width of the third area603is designed to be wider than the width of the third area103of the first embodiment. By forming the photomask having the light transmission rate distribution as described above, a light intensity distribution630having point631to point639as illustrated in FIG.6B3is obtained and a shape640having point641to point649as illustrated in FIG.6B4is obtained. With the photomask configured as described above, optical elements having the shape640with high degree of reproducibility with respect to the design shape610in FIG.6B1are obtained.

A design shape1610, a light transmission rate distribution1620, a light intensity distribution1630, and a shape1640illustrated in FIG.6C1to FIG.6C4have the same shape and distribution as those in FIG.5C1to FIG.5C4, and hence the description will be omitted. Although a plurality of optical elements are arranged two dimensionally in the third embodiment, one dimensional arrangement is also applicable.

Fourth Embodiment

A fourth embodiment is different from the first embodiment in the shape of the optical element in plan view.FIG. 7Ato FIG.7C4correspond toFIG. 1Ato FIG.1C4.FIG. 7Ais a schematic plan view illustrating three optical elements71to73. Description will be given the plan view of the optical elements of this embodiment, while focusing attention on the optical element71.

As illustrated inFIG. 7A, the optical element71includes a point501closer to the center of the optical element array and a point502positioned farther from the center than the point501along the X-direction in plan view. The optical element71is line symmetry with respect to a segment connecting the point501and the point502, and has a point505where an apex is located on the segment connecting the point501and the point502. The optical element71has the point503and the point504. A segment connecting the point503and the point504has the widest part of the optical element71in the Y-direction. The optical element71has a shape having a curvature from the point502to the point501and from the point503to the point501in plan view.

In this configuration as well, a photomask like other embodiments can be designed.

A cross sectional shape taken along the line VIIB-VIIB and the line VIIC-VIIC inFIG. 7Ais equal to the cross-sectional shape taken along the line VIIB-VIIB and the line VIIC-VIIC inFIG. 1A. Therefore, FIG.7B1to FIG.7C4are equal to FIG.1B1to FIG.1C4. Therefore, detailed description of FIG.7B1to FIG.7C4will be omitted. The points111,113, and118of FIG.7B1are points corresponding to the points501,502and505inFIG. 7A.

Fifth Embodiment

A fifth embodiment is different from the first to fourth embodiments in that the optical element has a prism structure. In this embodiment, the case where the optical elements having the prism structure are arranged one-dimensionally will be described.FIG. 8Ais a drawing illustrating a design shape810of the cross section of the optical element array as that illustrated in FIG.1B1.FIG. 8Billustrates a light transmission rate distribution820as that illustrated in FIG.1B2.

The design shape810inFIG. 8Aillustrates one cross section of the three optical elements. The design shape810will be described below by focusing on the two optical elements. The height of the design shape810increases linearly from a point811to a point812and decreases linearly from the point812to a point813. The height then increases again linearly from the point813to a point814. The height of the design shape810decreases linearly from the point814to a point815. The points812and814are the highest portions, and are apexes of the cross section of the design shape810. A change rate from the point812to the point813and from the point814to the point815is smaller than a change rate from the point811to the point812and from the point813to the point814.

A light transmission rate distribution820illustrated inFIG. 8Bcorresponds to the design shape810, and includes a first area801, a second area802, and a third area803in the same manner as FIG.1B2. The height of the light transmission rate distribution820is constant between a point821and a point822, and as illustrated by the point822and a point823, the height increases at the point822. The height of the light transmission rate distribution820decreases linearly from the point823to a point824, and becomes constant again between the point824and a point825. The height of the light transmission rate distribution820increases at the point825as indicated from the point825to a point826, and decreases from the point826to a point827. The points823and806are portions having the lowest light transmission rate. A change rate from a point802to a point803and from a point805to a point806is larger than a change rate from the point803to a point804and from the point806to a point807.

The light transmission rate distribution820includes the first area801from the point823to the point824, the second area802from the point826to the point827, and the third area803from the point824to the point825. In the same manner as the first embodiment, the light transmission rate of the third area803has a light transmission rate higher than the segment connecting the point824and the point826. By forming the photomask having the light transmission rate distribution as described above, a shape having high degree of reproducibility is obtained for the design shape810as illustrated inFIG. 8A.

Sixth Embodiment

A sixth embodiment is different from the shape of the fifth embodiment in that a gap is provided between one optical element and another optical element abutting each other.FIG. 9Aillustrates a design shape910of a cross section of an optical element array corresponding toFIG. 8A.FIG. 9Billustrates a light transmission rate distribution920corresponding toFIG. 8B.

The design shape910inFIG. 9Aillustrates one cross section of the three optical elements in the same manner asFIG. 8A. The design shape910will be described by focusing on the two optical elements. The height of the design shape910is constant from a point911to a point912, increases linearly from the point912to a point913and decreases linearly from the point913to a point914. The height of the design shape910is constant from the point914to a point915, increases linearly from the point915to a point916and decreases linearly from the point916to a point917. The points913and916are the highest portions, and are apexes of the cross section of the design shape910. A change rate from the point912to the point913and from the point915to the point916is smaller than a change rate from the point913to the point914and from the point916to the point917.

A light transmission rate distribution920illustrated inFIG. 9Bcorresponds to the design shape910, and includes a first area901, a second area902, and a third area903in the same manner asFIG. 8B. The light transmission rate distribution920has the same distribution as a portion from the point821to the point827inFIG. 8Bfrom a point921to a point927. The light transmission rate distribution920includes the first area901from the point923to the point924, the second area902from the point926to the point927, and the third area903from the point924to the point925in the same manner as other embodiments. In the same manner as other embodiments, the light transmission rate of the third area903has a light transmission rate higher than the segment connecting the point924and the point926. In this embodiment, the light transmission rate distribution920has the third area903wider than the light transmission rate distribution820inFIG. 8B. By forming the photomask having the light transmission rate distribution as described above, a shape having high degree of reproducibility is obtained for the design shape910as illustrated inFIG. 9A.

Method of Forming Photoelectric Conversion Apparatus

Methods of forming a photomask formed according to the first to sixth embodiments and a method of manufacturing optical elements using the methods of forming the photomask will be described with reference toFIG. 10. Here, the method of manufacturing the optical element in a photoelectric conversion apparatus as illustrated inFIG. 1Dof the first embodiment will be described.FIG. 10is a drawing schematically illustrating a cross section of the photoelectric conversion apparatus in a given manufacturing process.

First of all, a photomask is manufactured by using a photomask manufacturing system. The photomask manufacturing system includes an information processing apparatus, an inspection apparatus, and a defect correcting apparatus. The information processing apparatus creates photomask pattern data on the basis of acquired various data. In addition, the information processing apparatus converts the created photomask pattern data to drawing data corresponding to the drawing apparatus. The drawing apparatus manufactures a photomask by a reduction transfer method or a direct drawing method on the basis of the drawing data manufactured by the information processing apparatus. The inspection apparatus inspects defects of the photomask, and check whether or not a dot pattern is formed as designed. An inspection method is not specifically limited although there are various methods. For example, a method that compares the photomask patter data with an electric signal of an optical image of the photomask for inspection may be employed. The defect correcting apparatus corrects defects detected by the inspection apparatus. A correcting method includes various methods, and is not limited to a specific method. However, for example, a laser beam method or an ion beam method may be employed. Here, the photomask pattern data is design data for drawing the photomask pattern with the drawing apparatus. The drawing data is data obtained by converting the photomask pattern into a data format corresponding to the drawing apparatus.

First of all, in the information processing apparatus, the shape of the optical element illustrated in the first to sixth embodiments is determined, and a light transmission rate distribution data is acquired by using a known method. Here, the light transmission rate distribution data having a first portion and a second portion corresponding respectively to two optical elements abutting each other is created. In this embodiment, in the created light transmission rate distribution data, a process of replacing the light transmission rates of part of the first portion and the second portion to the light transmission rate described in other embodiments is performed. For example, the light transmission rate of the portion including a boundary between the first portion and the second portion is replaced by a third portion including part of the first portion on a boundary side and part of the second portion on the boundary side. Part of the remaining first portion corresponds to the first area in other embodiments, part of a remaining second portion corresponds to a second area in other embodiments, and the third portion corresponds to a third area in other embodiments. A binarization process is performed on the light transmission rate distribution data having the first to third area to determine an arrangement pattern of a light-shielding member and create the photomask pattern data. Drawing data is created on the basis of the photomask pattern data, and then the light-shielding member such as chrome on a substrate by the drawing apparatus, whereby the photomask is formed.

In the process illustrated inFIG. 10A, a semiconductor substrate20on which elements such as a photoelectric conversion element22and transistors are formed is prepared. An intermediated layer21is formed on the semiconductor substrate20. The intermediated layer21includes a plurality of insulating layers24and a plurality of wiring layers23, and includes a color filter layer25formed on the plurality of insulating layers24. Methods of manufacturing these layers may be manufactured by a general semiconductor technology, and hence description will be omitted. Subsequently, a photoresist layer107, which becomes the optical elements later, is formed on the color filter layer25. The photoresist layer107is, for example, a positive type photoresist, and may be formed by a spin coat method. The photoresist layer107corresponds to an exposed member.

Subsequently, the photomask having the light transmission rate distribution illustrated in FIG.1B2and FIG.1C2is prepared, and the photoresist layer107is exposed via the photomask. Here, as illustrated inFIG. 1D, the position of the photomask is adjusted so that a center152of the optical element and a center151of a pixel150are offset.

After exposure, a development process for the photoresist layer107and a heat process for stabilization are performed, so that an optical element array100illustrated inFIG. 100is formed.

In the case of forming the optical elements which do not have a hemispherical shape, thermal deformation at the time of heat process needs to be suppressed as much as possible. In order to suppress the thermal deformation, it is recommended to perform as a heat process a first heat process within a temperature which does not cause the thermal deformation, and a second heat process at a temperature higher than the first heat process. A heat resistance of a photoresist material is improved by the heat process as described above, and the thermal deformation is suppressed. The heat process for restraining deformation which may be employed includes an UV cure process in addition to the method described above.

Advantageous Effects of Invention

According to this disclosure, an optical element having a desired shape is obtained.

This application claims the benefit of Japanese Patent Application No. 2014-115281, filed Jun. 3, 2014 and Japanese Patent Application No. 2015-086265, filed Apr. 20, 2015, which are hereby incorporated by reference herein in their entirety.