JP2006023759A - Microlens array and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microlens array having a small coupling loss suitable to be used for optical coupling or the like between optical fibers, and to provide a method for manufacturing the same. <P>SOLUTION: In the microlens array, plano-convex lenses L<SB>11</SB>-L<SB>14</SB>are formed by transferring a lens array pattern on one side principal surface of a light transmissive plate 10 such as a quartz plate. The diameter of each lens is made to be 1 mm or below and the protruded height SAG of each lens is made to be 50 μm or more. When the microlens array is used for optical coupling between optical fibers, the coupling loss of ≤0.3 dB is obtained. When performing etching by using a fluorine type etching gas such as CF<SB>4</SB>, a pit is produced on an etching surface due to fluorocarbon polymer. By removing the fluorocarbon polymer through O<SB>2</SB>ashing, the pit production can be prevented. It is preferable that a light transmissive coated film made of SiO<SB>2</SB>or the like is formed on each lens of L<SB>11</SB>etc. by means of sputtering or else so that the thickness gradually decreases as proceeding from the lens central part to the peripheral part. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a microlens array suitable for use in optical coupling between optical fibers and the like, and a method for manufacturing the microlens array.

Conventionally, as the optical fiber coupling system, along with collimating (collimated) by the micro lens L ₁ the light emitted from the optical fiber F ₁ as shown in FIG. 37, and focuses the collimated light by the microlens L ₂ that so as to be incident on the optical fiber F ₂ are known. The microlenses L ₁ and L ₂ are both monocular microlenses manufactured using a glass mold technique. This type of microlens is also used as a lens for collimating light emitted from an optical fiber in an optical communication module such as an optical isolator.

  The conventional glass mold lens requires a diameter of 1 mm or more. If the diameter is smaller than this, satisfactory precision is not obtained because the precision of the mold made of super steel material used for glass molding is insufficient.

  As a microlens array used for optical coupling between optical array devices, a microlens array in which a large number of lenses are arrayed on a transparent substrate such as glass or plastic is known (for example, see Patent Document 1). In this case, since the diameter of one lens is as small as 1 mm or less and each lens is required to be accurately arranged, a microlens array is manufactured by a method that does not use a mold. As a method without using a mold, a method of diffusing ions from an opening provided on a glass surface while applying an electric field in a salt bath, or a phenomenon in which an unexposed portion is crystallized and contracts in a heat treatment of photosensitive glass is used. The method of expanding the surface is known. According to these methods, there are problems such as difficulty in setting the focal length and numerical aperture (NA), long manufacturing time, and poor productivity.

As a method for manufacturing a microlens array, a plurality of resist layers are formed on a lens material layer in accordance with a lens array pattern, and then each resist layer is melted (reflowed) by heating to form a convex lens shape. A method is known in which a dry etching process using a mixed gas as an etching gas is performed on the lens material layer and each resist layer, and the convex lens shape of each resist layer is transferred to the lens material layer (see, for example, Patent Document 2). In this method, as a post-process after the dry etching process, the surface of the microlens array (lens material layer to which the convex lens shape is transferred) is subjected to an oxygen plasma treatment to remove the hydrophobic deposited film and impart hydrophilicity to the surface. Like to do.
JP-A-7-104106 JP 2000-31442 A

According to the manufacturing method of the microlens array that transfers the convex lens shape of the reflowed resist layer to the lens material layer as described above, the focal length and the numerical aperture can be easily set and produced as compared with the method not using the mold. However, there is a problem that it is not easy to form a lens having a large etching amount (large protrusion height). That is, according to the inventor's research, when etching is performed using a fluorine-based etching gas such as CF ₄ , pits (holes) are generated on the lens forming surface due to the fluorocarbon polymer, thereby degrading the optical characteristics. Turned out to be. Patent Document 2 cited above does not describe anything about the occurrence of such pits.

  In the optical fiber coupling system as shown in FIG. 37, it is said that it is desirable that the coupling loss is 0.3 dB or less (coupling efficiency is 93.3% or more). However, at present, a microlens array with such a small coupling loss has not been realized.

  An object of the present invention is to provide a novel microlens array that can reduce coupling loss (improve coupling efficiency) in an optical fiber coupling system, and to provide a method for easily manufacturing such a microlens array. is there.

A first microlens array according to the present invention includes a light-transmitting plate and a plurality of plano-convex lenses formed by transferring a lens array pattern to one main surface of the light-transmitting plate by etching. A microlens array used in the system,
The diameter of each plano-convex lens is set to 1 mm or less, and the projecting height of each plano-convex lens from the one main surface is set to 50 μm or more.

  According to the first microlens array, since the diameter of each plano-convex lens is 1 mm or less and the projection height of each plano-convex lens is 50 μm or more, the coupling loss is 0 when used for optical coupling between optical fibers. .3 dB or less. This point will be described in detail later with reference to FIGS.

The manufacturing method of the first microlens array according to the present invention is as follows:
Forming a plurality of resist layers according to the lens array pattern on one main surface of the translucent substrate;
Reflow treatment for each resist layer to make each resist layer a plano-convex lens shape,
A plurality of resists are formed on the one main surface by subjecting each resist layer and the one main surface to a dry etching process using a fluorine-based etching gas to transfer the plano-convex lens shape of each resist layer to the one main surface. Forming a plurality of plano-convex lenses corresponding to the respective layers, and each plano-convex lens of the plurality of plano-convex lenses has a diameter of 1 mm or less and a protruding height from the one main surface of 50 μm or more. Forming a plano-convex lens, and a method of manufacturing a microlens array,
In the step of forming the plurality of plano-convex lenses, the dry etching process is performed in a plurality of steps, and a process of removing the fluoropolymer from the one main surface is performed during the multi-step dry etching process. It is characterized by doing.

  According to the first microlens array manufacturing method, since the fluorocarbon polymer is removed from the lens forming surface during the multi-step dry etching process, the fluorocarbon polymer is removed from the lens forming surface during the etching. Generation of pits can be prevented.

  In the manufacturing method of the first microlens array, each resist layer can be formed with a thickness such that the protrusion height of the corresponding plano-convex lens is 50 μm or more. When dry etching for forming a lens is performed using such a resist layer as a mask, the amount of etching increases, but the generation of pits can be prevented, so that a microlens array can be manufactured with high yield. Therefore, the manufacturing method of the first microlens array is suitable for manufacturing the first microlens array described above. In the first method for producing a microlens array, the fluorocarbon polymer can be easily removed by oxygen plasma.

A second microlens array according to the present invention includes a translucent plate and a plurality of plano-convex lenses formed by transferring a lens array pattern to one main surface of the translucent plate by etching. Because
In each plano-convex lens among the plurality of plano-convex lenses, the projection height from the one main surface is set to 40 to 45 μm, and a translucent film covering each plano-convex lens is formed from the center portion to the peripheral portion of the plano-convex lens. It is characterized in that it is formed so that the thickness gradually decreases as it progresses.

  According to the second microlens array, the projecting height of each plano-convex lens is set to 40 to 45 μm, and the thickness of the translucent film covering each plano-convex lens increases from the center to the periphery of the plano-convex lens. Since it is formed so as to gradually decrease, the projecting height of the plano-convex lens including the translucent film can be set to 70 μm or more, and high coupling efficiency can be obtained when used for optical coupling between optical fibers.

The manufacturing method of the second microlens array according to the present invention is as follows:
Forming a plurality of resist layers according to the lens array pattern on one main surface of the translucent substrate;
Reflow treatment for each resist layer to make each resist layer a plano-convex lens shape,
A plurality of resist layers corresponding to the plurality of resist layers are applied to the one main surface by performing dry etching on each resist layer and the one main surface, and transferring the plano-convex lens shape of each resist layer to the one main surface. Forming a plano-convex lens of
Forming a sputter mask layer having a plurality of openings exposing each of the plurality of plano-convex lenses on the one main surface, wherein each opening of the sputter mask layer is located above the top of the corresponding plano-convex lens. Forming the sputter mask layer to have a diameter smaller than the aperture diameter of the plano-convex lens at a portion;
Forming a light-transmitting film covering each plano-convex lens by a sputtering process using the sputter mask layer as a selection mask so that the thickness gradually decreases from the central part to the peripheral part of the plano-convex lens.

  According to the manufacturing method of the second microlens array, since each plano-convex lens is formed by dry etching, a light-transmitting film covering each plano-convex lens is formed by selective sputtering. Can be manufactured easily and with good yield.

  According to the present invention, in a microlens array in which a lens array pattern is transferred to a translucent plate by etching to form a plurality of plano-convex lenses, the diameter of each plano-convex lens is 1 mm or less and the projection height of each plano-convex lens is 50 μm. As described above, an effect of reducing the coupling loss to 0.3 dB or less when used for optical coupling between optical fibers can be obtained.

  In addition, when a plurality of plano-convex lenses are formed by transferring a lens array pattern to a translucent substrate by a dry etching process using a fluorine-based etching gas, the dry etching process is performed in a plurality of steps, and a plurality of steps are performed. Since the fluorocarbon polymer is removed from the lens-forming surface of the substrate during the dry etching process, pit generation due to the fluorocarbon polymer can be prevented, and a microlens array with good optical characteristics can be manufactured with high yield. The effect that can be obtained is also obtained.

  In addition, in a microlens array in which a lens array pattern is transferred to a light-transmitting plate by etching to form a plurality of plano-convex lenses, a light-transmitting film covering each plano-convex lens increases in thickness from the central portion to the peripheral portion of the plano-convex lens. Therefore, the height, shape, optical characteristics, etc. of the plano-convex lens can be easily adjusted, and an effect of realizing a microlens array suitable for optical fiber coupling can be obtained.

  Furthermore, after the lens array pattern is transferred to the translucent substrate by dry etching process to form a plurality of plano-convex lenses, a translucent film covering each plano-convex lens is formed by selective sputtering, so that the plano-convex lens There is also an effect that a microlens array having a light-transmitting film thereon can be easily manufactured with a high yield.

  FIG. 1 shows a microlens array according to an embodiment of the present invention, and FIG. 2 shows a cross section taken along line X-X 'of FIG.

For example, plano-convex lenses L _{11 to} L ₁₄ are formed in one row in parallel with the long side of the translucent plate 10 on one main surface of the rectangular translucent plate 10 made of a quartz plate, and the plano-convex lens L _21. the column of ~L ₂₄ is a lens _L 11 _{~L 14} are formed in parallel to a line shape. The lenses L ₁₁ and L ₂₁ are arranged side by side so that their centers are located on a straight line parallel to the short side of the translucent plate 10, which means that the lenses L ₁₂ and L ₂₂ , the lens L ₁₃ , The same applies to L ₂₃ and lenses L ₁₄ and L ₂₄ . These lenses L _{11 to} L ₁₄ and L _{21 to} L ₂₄ are formed by transferring the lens array pattern to one main surface of the light-transmitting substrate by dry etching as described later with reference to FIGS. Is.

As an example, the diameter D of each lens such as L ₁₁ is 1 mm or less (preferably 0.5 mm to 1 mm), and the pitch (inter-center distance) P between adjacent lenses such as L ₁₁ and L ₁₂ is In the case of D = 0.5 mm, it can be set to 0.5 mm. The length A and the width B of the translucent plate 10 can be 5 mm and 3 mm, respectively. L ₁₁ protruding height from the one main surface of the transparent plate 10 of the lens, such as SAG (see FIG. 2) shall be 50μm or more. The thickness of the translucent plate 10 can be 0.1 mm to 2 mm.

  FIG. 3 shows how the optical fiber-lens distance (Working Distance) WD depends on the radius of curvature R in the optical system of FIG. FIG. 4 shows an optical system that collimates the light emitted from the optical fiber F with the plano-convex lens L. The thickness (distance from the flat surface to the top) T of the plano-convex lens L is 1.25 mm.

  For the plano-convex lens L as shown in FIG. 4, the focal length is determined by the radius of curvature R. If the distance WD is reduced, reflected light from the flat surface of the plano-convex lens L is incident on the optical fiber F, which is not preferable. In order to avoid such a situation, it is said by those skilled in the art that the distance WD should be set to 0.3 mm or more. FIG. 3 shows a calculation result of the distance WD when the radius of curvature R is changed from 0.5 mm to 0.75 mm. According to FIG. 3, it can be seen that in order to make the distance WD 0.3 mm or more, the radius of curvature R should be about 0.53 mm or more. The data in FIG. 3 is obtained when the numerical aperture NA is set to 0.2. According to the experiment by the inventors, the correlation between the radius of curvature R and the distance WD as shown by the line W in FIG. It is known that even if the NA is changed to 0.15 or 0.1875 or the like, there is almost no change.

  FIGS. 5A to 5C show how the beam effective diameter and the coupling loss depend on the numerical aperture NA and the radius of curvature R in the optical fiber coupling system of FIG. (C) corresponds to the cases where the radius of curvature R is 0.55, 0.6, and 0.65, respectively.

FIG. 6 shows an optical fiber coupling system using the microlens array according to the present invention. The first microlens array ML ₁ is similar to the previously described with respect to FIGS. 1 and 2, has a configuration forming a plano-convex lens _L 11 _{~L 14} transparent plate 10. The second micro lens array ML ₂ is configured in the same manner as the first micro lens array ML _1, and has a configuration in which plano-convex lenses L _{31 to} L ₃₄ are formed on the translucent plate 12.

The micro lens arrays ML ₁ and ML ₂ are arranged to face each other so that the lenses L ₁₁ and L ₃₁ , the lenses L ₁₂ and L ₃₂ , the lenses L ₁₃ and L ₃₃ , and the lenses L ₁₄ and L ₃₄ are aligned with each other. The Optical fibers F _{11 to} F ₁₄ are disposed on the flat surface side of the light transmitting plate 10 so as to emit light to the lenses L _{11 to} L ₁₄ , respectively, and the optical fiber is disposed on the flat surface side of the light transmitting plate 12. F _{21 to} F ₂₄ are arranged so as to receive light from the lenses L _{31 to} L _34, respectively.

Optical fiber _{F 11} - lens _{L 11} - the lens _{L 31} - the optical path of the optical fiber _{F 21,} light emitted from the optical fiber _{F 11} is collimated by the lens _{L 11,} the collimated light is focused by a lens _{L 31} The light enters the optical fiber F ₂₁ . Such an optical coupling operation includes optical fiber F ₁₂ -lens L ₁₂ -lens ₃₂ -optical path of optical fiber F ₂₂ , optical fiber F ₁₃ -lens L ₁₃ -lens L ₃₃ -optical path of optical fiber F ₂₃ , optical fiber F. ₁₄ - lens _{L 14} - the lens _{L 34} - the same applies to the optical path of the optical fiber _{F 24.}

FIG. 5 shows the result of calculating the beam effective diameter and the coupling loss for one optical path (for example, the optical path of F ₁₁ -L ₁₁ -L ₃₁ -F ₂₁ ) in the optical fiber coupling system of FIG. Here, the effective diameter of the beam (Entrance Pupil Diameter) is indicated by lines E _{1 to} E ₃ , and the coupling loss is indicated by lines C _{1 to} C ₃ . In this case, since the diameter of each lens is 0.5 mm and the pitch between the lenses is 0.5 mm, the effective beam diameter on the lens surface must be 0.5 mm or less. Therefore, perpendicular lines NU ₁ , NU ₂ , and NU ₃ passing through points having an effective diameter of 0.5 mm with respect to the lines E ₁ , E ₂ , and E ₃ indicating the effective diameter of the beam are shown in (A), (B), and (C). When lowered to the horizontal axis of the graph, the upper limit of the numerical aperture NA is obtained.

On the other hand, since it is considered that the coupling loss is preferably 0.3 dB or less among those skilled in the art, the perpendicular line NL ₁ passing through the point of coupling loss of 0.3 dB with respect to the lines C ₁ , C ₂ and C ₃ indicating the coupling loss. , NL ₂ , NL ₃ are lowered to the horizontal axis of the graphs (A), (B), and (C), the lower limit of the numerical aperture NA is obtained. As a result, it can be seen that the allowable range of the numerical aperture NA is wider as the curvature radius R is smaller. In addition, it can be seen that the coupling loss can be reduced to 0.3 dB or less in any case of the curvature radius R = 0.55 mm, 0.6 mm, or 0.65 mm.

  FIG. 7 shows how the lens protrusion height SAG depends on the radius of curvature R for the plano-convex lens as described above with reference to FIGS. According to FIG. 7, it can be seen that the protrusion height SAG of the plano-convex lens increases as the radius of curvature R decreases. In order to achieve a coupling loss of 0.3 dB or less in a plano-convex lens having a diameter of 0.5 mm, the radius of curvature R needs to be 0.65 mm or less (preferably 0.65 mm to 0.55 mm). SAG needs to be 50 μm or more (preferably 50 μm to 60 μm). In this case, if the radius of curvature R is 0.7 mm, the numerical aperture NA is 0.15, the lens protrusion height SAG is 46.2 μm, the coupling loss is 0.449 dB, and the coupling loss does not become 0.3 dB or less.

  Next, an example of the manufacturing method of the above microlens array will be described with reference to FIGS.

In the process of FIG. 8, resist layers S _{1 to} S ₄ made of positive resist corresponding to four desired plano-convex lenses are formed on one surface of a quartz substrate 20 having a thickness of 1 mm to 2 mm by photolithography. When a plano-convex lens having a diameter of 1 mm or less and a lens protrusion height of 50 μm or more is manufactured, the diameter of each resist layer is determined so as to obtain a lens diameter of 1 mm or less, and the thickness t of each resist layer is set. Is determined so as to obtain a lens protrusion height of 50 μm or more. In this case, a positive resist layer thicker than usual is patterned according to the lens array pattern.

Next, in the process of FIG. 9, the resist layers S _{1 to} S ₄ are subjected to heat treatment to reflow each resist layer, thereby giving each resist layer a plano-convex lens shape.

10, the resist layers S _{1 to} S ₄ and one surface of the substrate 20 are etched by a dry etching process using a fluorine-based etching gas, and the plano-convex lens shape of each resist layer is transferred to one surface of the substrate 20. Thus, plano-convex lenses L _{11 to} L ₁₄ corresponding to the resist layers S _{1 to} S ₄ are formed on _one surface of the substrate 20. In this case, as the fluorine-based etching gas, a gas such as CF ₄ , CHF ₃ , C ₂ F ₆ , C ₃ F _8, or a gas obtained by mixing two or more of these gases can be used. Oxygen (O ₂ ), hydrogen (H ₂ ), nitrogen (N ₂ ), or argon (Ar) may be added to the fluorine-based etching gas used.

When performing RIE (reactive ion etching) as a dry etching process, if CF ₄ is used as an etching gas, the CF ₄ gas is turned into plasma, and the plasma is converted into CF ₃ ⁺ , CF ₂ ⁺ , CF ⁺ , F ^+, etc. Contains ions. Among these ions, CF ₃ ⁺ reacts with quartz (SiO ₂ ) to generate and vaporize SiF ₄ , so that quartz can be etched. However, other gases that do not contribute to quartz etching are polymerized to produce a fluorocarbon polymer (—CF ₂ —), and the fluorocarbon polymer may be deposited on the substrate surface during the etching. When manufacturing the above-described plano-convex lens having a protrusion height of 50 μm or more, since the resist thickness is large and the etching time is long, the fluorocarbon polymer is likely to be deposited. A pit is generated. Note that, in the short-time quartz etching as conventionally performed, no pit generation due to the fluorocarbon polymer is observed.

  Next, the mechanism of pit generation as described above will be described with reference to FIGS. FIG. 11 shows a state in which the fluorocarbon polymer 22 is deposited on the surface of the quartz substrate 20 during dry etching.

  When the etching further proceeds from the state of FIG. 11, as the fluoropolymer 22 is etched as shown in FIG. 12, the etching rate around the fluoropolymer 22 is increased, and pits 24 are generated around the fluoropolymer 22. . As the etching proceeds further, the fluorocarbon polymer 22 is further etched and the pits 24 become deeper as shown in FIGS.

  When the etching further proceeds from the state of FIG. 14, as shown in FIG. 15, the fluorocarbon polymer 22 disappears by etching, the pit 24 becomes deeper, and a navel-like mountain appears at the center. As the etching proceeds further, the slope of the mountain is etched in the pit 24 as shown in FIG. Thereafter, when the etching further proceeds, as shown in FIG. 17, the mountain in the pit 24 disappears due to the etching, and the pit 24 remains.

  The microlens array having the pits as described above has the following problems (a) to (d).

  (A) Since light is scattered by the pits in use, the optical characteristics are deteriorated.

  (B) Dirt gets into the pit when the lens surface is cleaned and the transparency is deteriorated.

  (C) Cracks occur due to pits due to changes over time, environmental stress, and the like.

  (D) Since the pits appear to be black spots on the appearance, the commercial value is significantly impaired.

  18 to 25 show a manufacturing method of a microlens array according to the improvement of the manufacturing method of FIGS. The manufacturing method shown in FIGS. 18 to 25 corresponds to the manufacturing method shown in FIGS. 18 to 25, the same parts as those in FIGS. 8 to 10 are denoted by the same reference numerals, and detailed description thereof is omitted. For simplicity, only one resist layer and one lens are shown.

  In the process of FIG. 18, a resist layer S is formed on the surface of the quartz substrate 20 in the same manner as described above with reference to FIG. In the step of FIG. 19, the resist layer S is formed into a plano-convex lens shape by the reflow process similar to that described above with reference to FIG.

Next, in the process of FIG. 20, the resist layer S and one surface of the substrate 20 are etched by the same dry etching process as described above with reference to FIG. On one surface of the substrate 20, as the etching progresses, the quartz portion 20S located under the resist layer _S has a slightly protruding shape and the fluoropolymer 22A is deposited. As shown in FIG. 12, for the fluoropolymer 22A, the dry etching process is stopped before pits are generated, and the process proceeds to the process of FIG.

In the process of FIG. 21, the fluorocarbon polymer 22A is incinerated and removed by O ₂ plasma. Such a process is referred to as an O ₂ ashing process. In the process of FIG. 22, the dry etching process as described above is performed again. Is CFC polymer 22B is deposited on the substrate surface with quartz portion 20 _S with the progress of etching is in the form of further projected. Before the pit is generated in the fluoropolymer, the dry etching process is stopped, and the process proceeds to the process of FIG.

In the step of FIG. 23, the fluorocarbon polymer 22B is removed by O ₂ ashing treatment. Then, in the step of FIG. 24, the dry etching process as described above is performed. As the etching progresses, the resist layer S is removed, and the quartz portion 20 _S becomes a plano-convex lens L. When the plano-convex lens L is obtained, the dry etching process is stopped. At this time, the fluorocarbon polymer 22C deposited on the substrate surface is removed by O ₂ ashing treatment or chemical treatment such as hydrofluoric acid as shown in FIG.

In the manufacturing method described above with reference to FIGS. 18 to 25, the O ₂ ashing process for removing the fluorocarbon polymer may be performed by an apparatus different from the apparatus for performing the dry etching process, or the same as the dry etching process. You may carry out by exchanging gas within an apparatus. Further, when the O ₂ ashing process is performed in the same apparatus as the dry etching process, the process may be switched to another process program for performing the O ₂ ashing, or according to one process program as shown in FIGS. A series of dry etching and O ₂ ashing as shown may be performed sequentially.

According to the manufacturing method described above with reference to FIGS. 18 to 25, the generation of pits based on the fluorocarbon polymer can be prevented, so that a high-quality microlens array having good optical characteristics can be manufactured with a high yield. In addition, since both dry etching and O ₂ ashing can be repeated a plurality of times, even a microlens array with a large etching amount that requires a lens protrusion height of 50 μm or more can be easily manufactured. it can.

  FIG. 26 shows a microlens array according to another embodiment of the present invention.

On one main surface of the quartz substrate 30, plano-convex lenses L _{41 to} L ₄₄ are formed in a line by transferring a lens pattern by etching. A large number of plano-convex lenses may be formed in a matrix on one main surface of the substrate 30 as shown in FIG. The thickness a of the substrate 30 is 1.25 mm, the aperture diameter (peripheral diameter) b of each plano-convex lens is 0.49 mm, the projection height c of each plano-convex lens is 40 to 45 μm, and between adjacent plano-convex lenses The pitch (distance between lens centers) d can be set to 0.5 mm. Each plano-convex lens such as L ₄₁ has a circular shape as shown in a plane pattern in FIG.

Translucent films L _{51 to} L ₅₄ are formed by sputtering or the like so as to cover the plano-convex lenses L _{41 to} L ₄₄ , respectively. Each light-transmitting film is made of a silicon oxide film such as SiO ₂ in a row, and is formed such that the thickness gradually decreases from the central part to the peripheral part of the corresponding plano-convex lens. The thickness e of the translucent film at the top of each plano-convex lens can be 30 to 40 μm, and the projection height f of the plano-convex lens including the translucent film can be 70 to 80 μm.

  According to the microlens array shown in FIG. 26, since the translucent film covering each plano-convex lens is formed so that the thickness gradually decreases from the central part to the peripheral part of the plano-convex lens, the protruding height is 70 μm or more. The plano-convex lens can be realized, and high coupling efficiency can be obtained when it is used for optical coupling of optical fibers. Each light-transmitting film can be formed on a plano-convex lens with a uniform thickness, but even in this case, the light-transmitting film cannot have a lens function, and the lens height is increased. It doesn't matter.

In the microlens array shown in FIG. 26, the optical characteristics such as the numerical aperture (NA) and the focal length can be adjusted by controlling the refractive index of the light-transmitting coatings L _{51 to} L ₅₄ . For example, the refractive index of a light-transmitting film made of a SiO ₂ film formed by sputtering is reduced by adding fluorine (F) and increased by adding germanium (Ge) or boron (B). The refractive index of the SiO ₂ film formed by sputtering can be adjusted as appropriate within the range of 1.4 to 1.48 depending on the type and concentration of the doping agent. In addition, as a material for the light-transmitting film, TiO ₂ , Ta ₂ O _{5 and the} like can be used in addition to SiO ₂ , and a plurality of types of materials can be used in combination.

  Next, an example of a method for manufacturing the microlens array of FIG. 26 will be described with reference to FIGS. 27 to 36, the same parts as those in FIG. 26 are denoted by the same reference numerals, and detailed description thereof is omitted.

In the step of FIG. 27, resist layers S _{11 to} S ₁₄ made of a positive resist corresponding to desired four plano-convex lenses are formed on one surface of the quartz substrate 30 by photolithography, and then the resist layers S _{11 to} S are formed. ₁₄ is subjected to heat treatment to reflow each resist layer, thereby giving each resist layer a plano-convex lens shape.

In the process of FIG. 28, the resist layers S _{11 to} S ₁₄ and one surface of the substrate 30 are etched by dry etching using a fluorine-based etching gas as described above with reference to FIG. By transferring to one surface of the substrate 30, plano-convex lenses L _{41 to} L ₄₄ corresponding to the resist layers S _{11 to} S ₁₄ are formed on one surface of the substrate 30. The projection height (c in FIG. 26) of each plano-convex lens is about 40 to 45 μm, and such a lens height can be obtained as the resist layers S _{11 to} S ₁₄ formed in the step of FIG. What has thickness may be used.

In the step of FIG. 29, a resist layer 32 for lift-off having holes R _{1 to} R ₄ exposing the planoconvex lenses L _{41 to} L ₄₄ on one surface of the substrate 30 is formed by photolithography. The thickness of the resist layer 32 can be set to 60 to 100 μm. The upper surface of the substrate 30 at this time is shown in FIG. As shown in FIG. 30, the diameter of each hole such as R ₁ is set slightly larger than the aperture diameter of each plano-convex lens such as L ₄₁ .

In the process of FIG. 31, a resist layer 34 made of a negative resist is applied to one surface of the substrate 30 so as to cover the resist layer 32 and the plano-convex lenses L _{41 to} L ₄₄ . At this time, the resist layer 34 is applied so that portions corresponding to the plano-convex lenses L _{41 to} L ₄₄ in the resist layer 34 are concave.

In the step of FIG. 32, the resist layer 34 is exposed. That is, the exposure light EL is irradiated to the resist layer 34 through the exposure mask MS. The exposure mask MS is provided with circular light shielding portions M _{1 to} M ₄ corresponding to the plano-convex lenses L _{41 to} L ₄₄ , respectively, and a light transmitting portion N is provided so as to surround these light shielding portions M _{1 to} M _4. Is provided. Diameter of each light-shielding portion, such as M ₁ is 2K only smaller set than the opening diameter of each plano-convex lens, such as L _41. Each light shielding portion such as M ₁ is disposed so as to match the corresponding plano-convex lens and the center. Since the negative resist constituting the resist layer 34 has a refractive index greater than that of air, the light EL that travels straight downward from the peripheral edge of each light-shielding part such as M ₁ toward the corresponding plano-convex lens is indicated by a line n. It is refracted by the negative resist and goes toward the peripheral edge of the plano-convex lens.

In the step of FIG. 33, development processing is performed on the resist layer 34 that has undergone the exposure processing of FIG. Since the exposed portion of the negative resist remains without being dissolved in the developer, the resist layer 34 has openings Q _{1 to} Q ₄ corresponding to the plano-convex lenses L _{41 to} L ₄₄ , respectively, and Q _{1 and the} like. Each opening remains at a portion P above the top of the corresponding plano-convex lens so as to have a diameter smaller than the opening diameter of the corresponding plano-convex lens. That is, the resist layer 34 remains so as to have a reverse tapered cross-section diameter as it goes deeper into each opening of such Q ₁ is increased.

In the step of FIG. 34, a light-transmitting film L made of SiO _{2 is formed} so as to cover the plano-convex lenses L _{41 to} L ₄₄ as shown in FIG. 35 by sputtering SiO ₂ using the stacked layers of the resist layers 32 and 34 as a selection mask. ₅₁ to form a ~L _54. At this time, the SiO ₂ film 36 is deposited on the resist layer 34. Further, since the resist layer 34 has a reverse tapered cross-sectional shape for each opening such as Q _1, each light-transmitting film such as L ₅₁ has a thickness as it proceeds from the central portion to the peripheral portion of the corresponding plano-convex lens. It is formed so as to gradually decrease.

In the step of FIG. 36, the resist layers 32 and 34 and the SiO ₂ film 36 are removed by performing a lift-off process on the upper surface of the substrate 30. As a result, the translucent films L _{51 to} L ₅₄ remain on the plano-convex lenses L _{41 to} L ₄₄ , respectively, so that a microlens array as shown in FIG. 26 can be obtained.

In the sputtering process shown in FIGS. 34 and 35, the refractive index of the sputtered SiO ₂ film (light-transmitting film) can be adjusted as appropriate by using a SiO ₂ material containing F, Ge, B or the like as a sputtering target. Moreover, since the film thickness distribution of the light-transmitting film such as L ₅₁ can be adjusted by controlling the cross-sectional shape of the opening such as Q ₁ in the resist layer 34, the shape of the plano-convex lens including the light-transmitting film can be adjusted. It can be appropriately controlled (for example, aspherical). Further, by shifting the center of each opening such as Q ₁ in the resist layer 34 from the center of the corresponding plano-convex lens such as L ₄₁ , a lens having a left-right asymmetric cross section with respect to the center is obtained as a plano-convex lens including a translucent film. be able to. By using the adjusting means as described above, the coupling efficiency with the optical fiber, the divergence angle of the light emitted from the optical fiber, and the like can be adjusted, and a microlens array suitable for optical coupling of the optical fiber can be realized.

It is a top view which shows the lens formation surface of the micro lens array which concerns on one Embodiment of this invention. It is sectional drawing which follows the X-X 'line | wire of FIG. 5 is a graph showing how the optical fiber-lens distance WD depends on the radius of curvature R in the optical system of FIG. It is an optical path diagram which shows the optical system which collimates the emitted light of an optical fiber with a plano-convex lens. (A)-(C) is a graph which shows a mode that the beam effective diameter and the coupling loss depend on the numerical aperture NA and the curvature radius R in the optical fiber coupling system of FIG. It is an optical path diagram which shows the optical fiber coupling system using the micro lens array which concerns on this invention. It is a graph which shows a mode that lens projection height SAG is dependent on the curvature radius R regarding a plano-convex lens. It is sectional drawing which shows the resist layer formation process in an example of the manufacturing method of the microlens array which concerns on this invention. It is sectional drawing which shows the registry flow process following the process of FIG. FIG. 10 is a cross-sectional view showing a lens forming process following the process of FIG. 9. It is sectional drawing which shows the deposition condition of the fluorocarbon polymer in the dry etching process of a quartz substrate. FIG. 12 is a cross-sectional view showing a state in which etching further proceeds from the state of FIG. 11 and pits are generated. It is sectional drawing which shows the state which further etched from the state of FIG. It is sectional drawing which shows the state which further etched from the state of FIG. FIG. 15 is a cross-sectional view showing a state in which the etching further proceeds from the state of FIG. 14 and the fluorocarbon polymer has disappeared. FIG. 16 is a cross-sectional view illustrating a state in which etching has further progressed from the state of FIG. 15. FIG. 17 is a cross-sectional view showing a state in which etching has further progressed from the state of FIG. 16. It is sectional drawing which shows the resist layer formation process in the manufacturing method of the micro lens array which concerns on the improvement of the manufacturing method of FIGS. It is sectional drawing which shows the registry flow process following the process of FIG. FIG. 20 is a cross-sectional view showing a dry etching process following the process of FIG. 19. It is sectional drawing which shows the fluorocarbon polymer removal process following the process of FIG. FIG. 22 is a cross-sectional view showing a dry etching process following the process of FIG. 21. FIG. 23 is a cross-sectional view showing a fluoropolymer removal step subsequent to the step of FIG. 22. FIG. 24 is a cross-sectional view showing a dry etching process following the process of FIG. 23. FIG. 25 is a cross-sectional view showing a fluoropolymer removal step subsequent to the step of FIG. 24. It is sectional drawing which shows the microlens array which concerns on other embodiment of this invention. It is sectional drawing which shows the registry flow process in the method of manufacturing the microlens array of FIG. FIG. 28 is a cross-sectional view showing a lens formation step subsequent to the step of FIG. 27. FIG. 29 is a cross-sectional view showing a resist layer forming step that follows the step of FIG. 28. FIG. 30 is a top view of the substrate of FIG. 29. FIG. 30 is a cross-sectional view showing a resist layer forming step that follows the step of FIG. 29. FIG. 32 is a cross-sectional view showing a resist exposure process following the process of FIG. 31. FIG. 33 is a cross-sectional view showing a resist developing process following the process of FIG. 32. FIG. 34 is a cross-sectional view showing a SiO ₂ sputtering step following the step of FIG. 33. FIG. 35 is a cross-sectional view showing a situation of deposition of a SiO ₂ film in the step of FIG. It is sectional drawing which shows the state which performed the lift-off process on the upper surface of the board | substrate of FIG. It is an optical path diagram which shows the optical fiber coupling system using the conventional monocular microlens.

Explanation of symbols

10, 12: Translucent plate, 20, 30: Quartz substrate, 22, 22A to 22C: Freon polymer, 24: Pit, 32, 34: Resist layer, 36: SiO ₂ film, L _{11 to} L ₁₄ , L _{21 ~L 24, L 31 ~L 34,} L 41 ~L 44, L: plano-convex _lens, L 51 _{~L 54:} translucent _coating, ML _1, ML _2: microlens _{array, F, F 11 ~F 14,} F ₂₁ to F _24: optical _{fiber, S 1 ~S 4, S 11} ~S 14, S: the resist layer.

Claims (6)

A microlens array comprising a translucent plate and a plurality of plano-convex lenses formed by transferring a lens array pattern by etching on one main surface of the translucent plate, and used in an optical fiber coupling system,
A microlens array, wherein the diameter of each plano-convex lens is set to 1 mm or less and the projection height of each plano-convex lens from the one main surface is set to 50 μm or more.   2. The microlens array according to claim 1, wherein the translucent plate is made of a quartz plate. Forming a plurality of resist layers according to the lens array pattern on one main surface of the translucent substrate;
Reflow treatment for each resist layer to make each resist layer a plano-convex lens shape,
A plurality of resists are formed on the one main surface by subjecting each resist layer and the one main surface to a dry etching process using a fluorine-based etching gas to transfer the plano-convex lens shape of each resist layer to the one main surface. Forming a plurality of plano-convex lenses corresponding to the respective layers, and each plano-convex lens of the plurality of plano-convex lenses has a diameter of 1 mm or less and a protruding height from the one main surface of 50 μm or more. Forming a plano-convex lens, and a method of manufacturing a microlens array,
In the step of forming the plurality of plano-convex lenses, the dry etching process is performed in a plurality of steps, and a process of removing the fluoropolymer from the one main surface is performed during the multi-step dry etching process. A process for producing a microlens array. A microlens array comprising a translucent plate and a plurality of plano-convex lenses formed by transferring a lens array pattern by etching on one main surface of the translucent plate,
In each plano-convex lens among the plurality of plano-convex lenses, the projection height from the one main surface is set to 40 to 45 μm, and a translucent film covering each plano-convex lens is formed from the center portion to the peripheral portion of the plano-convex lens. A microlens array formed so that the thickness gradually decreases as it progresses. Forming a plurality of resist layers according to the lens array pattern on one main surface of the translucent substrate;
Reflow treatment for each resist layer to make each resist layer a plano-convex lens shape,
A plurality of resist layers corresponding to the plurality of resist layers are applied to the one main surface by performing dry etching on each resist layer and the one main surface, and transferring the plano-convex lens shape of each resist layer to the one main surface. Forming a plano-convex lens of
Forming a sputter mask layer having a plurality of openings exposing each of the plurality of plano-convex lenses on the one main surface, wherein each opening of the sputter mask layer is located above the top of the corresponding plano-convex lens. Forming the sputter mask layer to have a diameter smaller than the aperture diameter of the plano-convex lens at a portion;
Forming a light-transmitting film covering each plano-convex lens by a sputtering process using the sputter mask layer as a selection mask so that the thickness gradually decreases from the central part to the peripheral part of the plano-convex lens. Manufacturing method.   In the step of forming the plurality of plano-convex lenses, as each plano-convex lens among the plurality of plano-convex lenses, a plano-convex lens having a protrusion height from the one main surface of 40 to 45 μm is formed. The manufacturing method of the micro lens array of Claim 5.

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