JP2007102196A - Method for manufacturing optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for an optical element without leaving a clearance in trenches. <P>SOLUTION: The plurality of trenches are formed on the basis of the recess 2 of a silicon substrate 1 by D-RIE, and a columnar structural body is formed between the trenches. Each columnar structure body is replaced with a silicon oxide 14 by thermal oxidation. Carbon dioxide of the super critical state dissolving silicon oxide therein is flowed into each trench between the silicon oxide layers 14. Thus, each trench is buried by the silicon oxide layer 15 without any clearance. Accordingly, it is possible to manufacture a micro lens 3 having no fear that a diffraction phenomenon is generated and efficiency is reduced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an optical element.

The present applicant has proposed a method for manufacturing an optical element such as a microlens in the previous application (Patent Document 1). In this manufacturing method, the silicon substrate is etched by trench etching, and a large number of trenches are juxtaposed, and the inside of each trench is filled with silicon oxide by thermal oxidation, and the silicon layer between the trenches is replaced with silicon oxide, thereby forming a silicon substrate. And make an integrated micro lens.
JP 2004-271756 A

By the way, the following investigation revealed the following. Each trench is formed by processing a silicon substrate with D-RIE (Deep Reactive Ion Etching) using an etching mask patterned based on the resist mask. It was found that because the width of the trench varies due to the variation, the inside of the trench cannot be completely filled with silicon oxide by thermal oxidation.
For example, when a resist mask is formed by semiconductor photolithography, for example, a variation of about 0.2 μm occurs with respect to a groove width of 2 μm. Moreover, when creating an etching mask, the width of the groove corresponding to the trench varies, for example, by 0.1 to 0.2 μm. Furthermore, when the trench is processed using the etching mask, the width of the trench varies, for example, by 0.1 to 0.2 μm.
Due to such processing variations, if a gap remains inside the trench, a diffraction phenomenon occurs, and the diffracted light travels in a direction different from the original focusing and refraction direction, and reflection occurs at the interface. Since light is scattered, the substantial transmission efficiency may be reduced.

Note that, in a method using a liquid phase typified by the sol-gel method, it is difficult to infiltrate the liquid into the trench having a high aspect ratio because the viscosity of the liquid is high. Further, in the vapor phase method represented by CVD, the trench can be embedded, but the film formation rate must be greatly reduced. Furthermore, in a physical film forming method represented by sputtering or vapor deposition, it is difficult to fill the trench because the side wall in the trench is shaded.
In particular, when each of the above methods is applied to a high aspect ratio trench having an aspect ratio exceeding 10, there is a problem that the opening of the trench is narrowed first and a gap remains in the trench. FIG. 27 is a schematic diagram showing a state in which a gap remains in the trench. A silicon oxide film 32 is formed on the inner wall surface of the trench 31 formed in the silicon substrate 30, but the opening is narrowed by the silicon oxide film 32, making it difficult to supply silicon oxide into the trench 31. A gap 33 remains in 31.
As described above, it has been found that the method previously proposed by the applicant and other methods may leave a gap in the trench.

  In order to solve the above problem, an object of the present invention is to realize an optical element manufacturing method capable of preventing a gap from remaining in a trench.

  In order to achieve the above object, according to the first aspect of the present invention, in the method of manufacturing an optical element (20) having a block (3) made of at least silicon oxide that transmits light, a plurality of structures made of silicon oxide are used. A first step of creating a state in which the body (14) is arranged on the substrate surface of the silicon substrate (1) with a gap (11) between the structures, and the predetermined compound (15) is dissolved A second step of forming the block by pouring a supercritical fluid into each gap between the structures and filling each gap with a product generated from the predetermined compound. Yes.

  According to the second aspect of the present invention, in the method of manufacturing an optical element (20) having a block (3) made of at least silicon oxide that transmits light, the plurality of structures (14) made of silicon oxide are each A supercritical fluid in which a predetermined compound (15) is dissolved between each structure and a first step for creating a state in which the gaps (11) are provided between the structures and the silicon substrate (1) is arranged in parallel. Pour into each gap and remove the peripheral part of each structure consisting of the respective structures embedded in the product, and a second step in which each gap is filled with the product generated from the predetermined compound And a third step of forming the block.

  According to a third aspect of the present invention, in the method of manufacturing an optical element according to the second aspect, in the third step, a process of removing a peripheral portion of the portion made of each structure is performed from the substrate surface of the silicon substrate. And the process is stopped when the lower portion of the removed region reaches the same depth as each of the structures.

  According to a fourth aspect of the present invention, in the optical element manufacturing method according to the second or third aspect, the third step is a step of removing the peripheral portion by etching.

  According to a fifth aspect of the present invention, in the optical element manufacturing method according to the fourth aspect, the etching is anisotropic etching.

  According to a sixth aspect of the present invention, in the optical element manufacturing method according to the fifth aspect, the anisotropic etching is performed using a potassium hydroxide (KOH) aqueous solution or a tetramethylammonium hydroxide (TMAH) aqueous solution. It is characterized by being isotropic etching.

  According to a seventh aspect of the present invention, in the optical element manufacturing method according to any one of the first to sixth aspects, in the first step, the silicon substrate is etched using a patterned mask. The plurality of structures are formed.

  According to an eighth aspect of the present invention, in the method of manufacturing an optical element according to any one of the first to seventh aspects, in the first step, a gap whose width decreases as the depth increases is formed. In addition, it is characterized in that a plurality of structures made of silicon oxide create a state in which the structures are arranged in parallel with a gap between them.

  According to a ninth aspect of the present invention, in the method of manufacturing an optical element according to any one of the first to seventh aspects, in the first step, the width gradually increases from the middle toward the top from the bottom. The structure is characterized in that a plurality of structures made of silicon oxide are arranged in parallel with each other with a gap so that a gap with the widest upper portion is formed.

  According to a tenth aspect of the present invention, in the method of manufacturing an optical element according to any one of the first to ninth aspects, in the first step, each of the structures is formed in a thin plate shape, In addition, the longitudinal side surfaces extending in the optical axis direction are formed to be the wall surfaces of the gap.

  According to an eleventh aspect of the present invention, in the method of manufacturing an optical element according to any one of the first to tenth aspects, in the first step, silicon is formed so that the gap is not filled with silicon oxide. A plurality of structures made of silicon oxide are formed by thermally oxidizing a plurality of structures made of

  According to a twelfth aspect of the present invention, in the method of manufacturing an optical element according to the eleventh aspect, in the first step, each structural body made of silicon so that the gap is not filled with silicon oxide by thermal oxidation. And the width of each gap are set.

  According to a thirteenth aspect of the present invention, in the method of manufacturing an optical element according to any one of the first to twelfth aspects, the product is generated by a chemical change of the predetermined compound. It is characterized by.

  According to a fourteenth aspect of the present invention, in the optical element manufacturing method according to the thirteenth aspect, the product is generated by decomposing the predetermined compound.

  According to a fifteenth aspect of the present invention, in the method of manufacturing an optical element according to any one of the first to fourteenth aspects, the compound is an organic compound.

  According to a sixteenth aspect of the present invention, in the optical element manufacturing method according to any one of the first to fifteenth aspects, the product is silicon oxide.

  According to a seventeenth aspect of the present invention, in the method for manufacturing an optical element according to any one of the first to fifteenth aspects, the product has a refractive index equivalent to that formed by silicon oxide. It is characterized by being a product that can form a product.

  According to an eighteenth aspect of the present invention, in the optical element manufacturing method according to the fifteenth aspect, the compound is TMOS (tetramethoxysilane).

  According to a nineteenth aspect of the present invention, in the optical element manufacturing method according to the seventeenth aspect, the product is calcium fluoride.

  According to a twentieth aspect of the present invention, in the optical element manufacturing method according to the seventeenth aspect, the product is magnesium fluoride.

  According to a twenty-first aspect of the present invention, in the optical element manufacturing method according to the seventeenth aspect, the product is alumina.

  According to a twenty-second aspect of the present invention, in the method for manufacturing an optical element according to any one of the first to twenty-first aspects, the surface orientation of the substrate surface is (110).

  According to a twenty-third aspect of the present invention, in the optical element manufacturing method according to any one of the first to twenty-second aspects, in the first step, the silicon substrate is subjected to reactive ion etching to form a trench shape. Each of the gaps is formed, and a plurality of structures made of silicon oxide with the gaps separated between the structures are formed.

  According to a twenty-fourth aspect of the present invention, in the optical element manufacturing method according to any one of the first to twenty-third aspects, the main component of the supercritical fluid is carbon dioxide.

  According to a twenty-fifth aspect of the present invention, in the optical element manufacturing method according to any one of the first to twenty-fourth aspects, the block is a microlens.

  According to a twenty-sixth aspect of the present invention, in the optical element manufacturing method according to any one of the first to twenty-fourth aspects, the block is an optical waveguide.

  According to a twenty-seventh aspect of the present invention, in the optical element manufacturing method according to any one of the first to twenty-fourth aspects, the block is a prism.

  The invention according to claim 28 is the method of manufacturing an optical element according to any one of claims 1 to 24, wherein a plurality of microlenses, optical waveguides and prisms are simultaneously used as the block. It is characterized by manufacturing.

  According to a twenty-ninth aspect of the present invention, in the optical element manufacturing method according to any one of the first to twenty-fourth aspects, at least two of a microlens, an optical waveguide, and a prism are simultaneously manufactured as the block. It is characterized by doing.

  According to a thirty-third aspect of the present invention, in the optical element manufacturing method according to any one of the first to twenty-fourth aspects, the block includes a plurality of at least two of a microlens, an optical waveguide, and a prism. It is characterized by manufacturing at the same time.

  In addition, the code | symbol in the said parenthesis shows the correspondence with the specific means as described in embodiment mentioned later.

(Effect of the invention according to claim 1)
A supercritical fluid has a gas property (diffusibility) and a liquid property (solubility), and has the feature that its density can be changed drastically continuously.
Therefore, when a supercritical fluid in which a predetermined compound is dissolved is poured into each gap between structures made of silicon oxide arranged in parallel on the substrate surface of a silicon substrate, the supercritical fluid having a gas property is By entering the narrow gap and forming a film with a product generated from the predetermined compound in each gap, it is possible to form a block in which each gap is filled with the product without any gap.
In other words, it is possible to manufacture an optical element in which a diffraction phenomenon due to a gap occurs and there is no possibility that the efficiency is lowered.
In addition, since supercritical fluid has a higher density than the vapor phase method typified by CVD, a film-forming material (predetermined compound) can be dissolved at a high concentration. Can be supplied within.
Therefore, each gap can be filled with the above product in a shorter time than the vapor phase method.

(Effect of the invention according to claim 2)
A supercritical fluid has a gas property (diffusibility) and a liquid property (solubility), and has the feature that its density can be changed drastically continuously.
Therefore, when a supercritical fluid in which a predetermined compound is dissolved is poured into the gaps between the structures made of silicon oxide arranged in parallel inside the silicon substrate, the supercritical fluid having a gas property becomes a narrow gap. The gaps can be filled with the product without any gaps by forming the film with the product generated from the predetermined compound. Then, by removing the peripheral portion of the portion made of each structure, it is possible to form a block in which each gap is filled with the product without any gap.
In other words, it is possible to manufacture an optical element in which a diffraction phenomenon due to a gap occurs and there is no possibility that the efficiency is lowered.
In addition, since supercritical fluid has a higher density than the vapor phase method typified by CVD, a film-forming material (predetermined compound) can be dissolved at a high concentration. Can be supplied within.
Therefore, each gap can be filled with the above product in a shorter time than the vapor phase method.

Further, as described in claim 23, each gap can be formed in a trench shape by reactive ion etching of the silicon substrate. For example, a high aspect ratio trench can be obtained by alternately repeating an etching step for etching a silicon substrate with an etching gas plasma and a protective film forming step for forming a sidewall protective film inside the trench with a deposition gas plasma. Can be formed.
In the method of depositing a silicon oxide layer by CVD, the thickness of the lens layer is limited to about 10 μm because of deposition, but a lens layer having a thickness of 100 μm or more is formed by a high aspect ratio trench etching method. A three-dimensional lens that can be formed and is practical as a lens, such as a cylindrical lens, can be formed.

(Effects of inventions according to claims 3 to 7)
According to the invention of claim 3, in the third step, the process of removing the peripheral portion of the portion made of each structure is performed from the substrate surface of the silicon substrate, and the lower portion of the removed region is equivalent to each structure. By stopping the processing when the depth is reached, a block having a height equivalent to the depth of each structure can be formed on the substrate surface of the silicon substrate.
In particular, according to the fourth aspect of the present invention, the peripheral portion of the portion made of each structure can be removed by etching.
In particular, according to the fifth aspect of the present invention, the peripheral portion of the portion made of each structure can be removed by anisotropic etching. In other words, in isotropic etching, processing proceeds in the lateral direction, so the shape of the peripheral part other than the block cannot be processed as designed, but by using anisotropic etching, etching proceeds only in the vertical direction of the substrate. The outer peripheral surface of the block can be accurately set to a target shape.
For example, as described in claim 6, anisotropic etching can be performed inexpensively and easily by using an aqueous potassium hydroxide (KOH) solution or an aqueous tetramethylammonium hydroxide (TMAH) solution. it can.
In addition, as described in claim 7, if a method of forming a plurality of structures by etching a silicon substrate using a patterned mask is used, the shape and arrangement of each structure can be changed by changing the mask pattern. Therefore, it is possible to realize an optical element having a high degree of design freedom regarding the shape. For example, a lens having a large NA or an aspherical lens shape can be obtained.

(Effects of Inventions of Claims 8 and 9)
As in the invention according to claim 8, the gap between the structures can be formed so that the width becomes narrower as the depth increases. Further, as in the invention according to claim 9, it can be formed so that it gradually becomes wider from the middle toward the upper part from the bottom part, and the uppermost part becomes the widest part.
That is, by forming the upper part of the gap wide, when performing the process of embedding each gap with the product generated from the compound dissolved in the supercritical fluid, the upper part of the gap is formed by the product formed in the gap. Since there is no possibility of becoming narrow, there is no possibility that unfilled portions will occur inside the gap.

(Effect of the invention according to claim 10)
In the first step, each structure is formed in a thin plate shape and the side surfaces in the longitudinal direction extending in the optical axis direction are the wall surfaces of the gaps. Can be within the total reflection angle between the structure and the air layer, and it is possible to suppress a decrease in light transmission due to light scattering or the like.

(Effect of the invention according to claim 11)
In the first step, a plurality of structures made of silicon oxide are formed by thermally oxidizing a plurality of structures made of silicon so that the gaps are not filled with silicon oxide. By flowing a supercritical fluid into the gaps, it is possible to form blocks in which the gaps are filled without gaps by a substance having a product generated from at least a predetermined compound.

(Effect of the invention according to claim 12)
In the first step, in order to set the width of each structure made of silicon and the width of each gap so that the gap is not filled with silicon oxide due to thermal oxidation, the gap is filled halfway with silicon oxide, A narrow opening or a closed portion is formed in the gap, and there is no possibility that the supercritical fluid cannot sufficiently flow into the gap or cannot flow into the gap.

(Effect of the invention according to claim 13)
The compound dissolved in the supercritical fluid can be made a substance that is difficult to dissolve in the supercritical fluid due to a chemical change, and can be formed into a film in the gap.

(Effect of the invention according to claim 14)
In a chemical change, a plurality of substances react to become another substance, and there are cases where the substance becomes another substance by decomposition. However, if decomposition is used, even one substance can be formed into a film. In this case, the number of compounds dissolved in the supercritical fluid can be reduced. The decomposition of the compound can be easily performed by heating or the like.

(Effect of the invention according to claim 15)
If an organic compound is used as the compound to be dissolved in the supercritical fluid, it is excellent in solubility and can be easily decomposed by heating, so that a simple film formation is possible.

(Effects of the inventions according to claims 16 and 17)
By flowing a supercritical fluid in which silicon oxide is dissolved into the gaps between the structures, a block in which the gaps are filled with silicon oxide without gaps can be formed.
Therefore, since a block formed entirely of silicon oxide can be obtained, an optical element having a refractive index equivalent to that of silicon oxide can be realized.
Further, as in the invention according to claim 17, by dissolving a compound capable of forming an object having a refractive index equivalent to that formed by silicon oxide in a supercritical fluid, a product generated from the compound Thus, the gaps can be embedded without gaps.

(Effect of the Invention of Claim 18)
TMOS (tetramethoxysilane) is excellent in solubility in a supercritical fluid and has a low decomposition temperature, so that a simple film formation can be realized.

(Effect of the Invention of Claim 19)
The refractive index of calcium fluoride is 1.43 compared to the refractive index of silicon oxide 1.45, and an almost equivalent refractive index can be obtained.

(Effect of the invention according to claim 20)
The refractive index of magnesium fluoride is 1.38 compared to the refractive index of silicon oxide 1.45, and an almost equivalent refractive index can be obtained.

(Effect of the invention according to claim 21)
The refractive index of alumina is 1.58 to 1.60 compared to the refractive index of silicon oxide 1.45, and an almost equivalent refractive index can be obtained.

(Effect of the Invention of Claim 22)
Since the plane orientation of the substrate surface is (110), the wall surface of each gap (side surface of each structure) can be etched vertically by the anisotropy.

(Effect of the Invention of Claim 24)
Carbon dioxide has a lower critical temperature and critical pressure than water, for example, and tends to be in a critical state and easily controlled, so a supercritical fluid whose main component is carbon dioxide is used.

(Effect of the invention according to claims 25 to 30)
If the method for manufacturing an optical element according to any one of claims 1 to 24 is used, no gap remains between the structures, and a microlens or an optical Waveguides or prisms can be manufactured. Moreover, one of them can be manufactured at the same time, and at least two of them can be manufactured at the same time, or at least two of them can be manufactured at the same time. As described above, when a plurality of optical elements are formed simultaneously, the optical axes after the elements are formed become unnecessary by forming them on the silicon substrate so that the optical axes of the blocks of the optical elements coincide.

<First Embodiment>
A method for manufacturing an optical element according to an embodiment of the present invention will be described with reference to the drawings. In this embodiment, an optical element having a microlens as an optical element will be described as a representative. FIG. 1 is a perspective view of an optical element manufactured by the optical element manufacturing method according to this embodiment. 2A and 2B are explanatory diagrams of the optical element shown in FIG. 1, wherein FIG. 2A is a plan view of the optical element shown in FIG. 1, and FIG. 2B is a cross-sectional view taken along line AA in FIG.

[Main structure of optical element]
The optical element 20 of this embodiment is configured by arranging the microlens 3 on the inner bottom surface of the recess 2 formed in the silicon substrate 1. As shown in FIG. 2, in this embodiment, the microlens 3 is a plano-convex cylindrical lens having a flat incident surface 3a and an output surface 3b made of a convex surface. The plane orientation of the substrate surface of the silicon substrate 1 is (110).
A plurality of thin and plate-like columnar structures 4 made of silicon oxide (SiO ₂ ) are erected from the inner bottom surface of the recess 2 of the silicon substrate 1, and the space between each columnar structure 4 is The silicon oxide layer 15 is embedded without gaps. The column structure 4 and the buried layer 15 are formed integrally with the silicon substrate 1. That is, the microlens 3 is configured by a silicon oxide block including a plurality of columnar structures 4 and a plurality of buried layers 15.
As shown in FIG. 2, the lower surfaces of the columnar structures 4 and the buried layers 15 are arc surfaces whose lower surfaces bulge downward. The silicon oxide block (microlens 3) is connected to the silicon substrate 1 at the boundary surface of a minute uneven shape without using an adhesive. That is, the silicon oxide block (microlens 3) is erected in a state in which the bottom surface, which is the boundary surface with the silicon substrate 1, has an uneven shape that continues in the horizontal direction from the inner bottom surface of the recess 2 of the silicon substrate 1, Light is transmitted through a silicon oxide block (microlens 3) formed integrally with the silicon substrate 1.

  Further, as shown in FIG. 2, the plurality of pillar structures 4 made of silicon oxide are extended in parallel to the optical axis on the inner bottom surface of the recess 2 of the silicon substrate 1. Thereby, the extending direction of the column structure 4 is parallel to the direction in which the light passes, and the angle formed with the direction in which the light passes is within the total reflection angle between the silicon oxide and the air layer. It is possible to suppress a decrease in light transmission due to light scattering or the like. The microlens 3 which is a silicon oxide block formed integrally with the silicon substrate 1 has a connecting portion (pedestal portion) 5 made of the silicon substrate 1 having the same shape as that of the silicon oxide block. In addition, the microlens 3 (silicon oxide block) formed integrally with the silicon substrate 1 inside the recess 2 is arranged with a gap 6 around it. As a result, the silicon oxide block and the outer silicon substrate can be completely separated, and buckling can be avoided during manufacturing (details will be described later). In this embodiment, as shown in FIG. 2, the microlens 3 (silicon oxide block) has a vertical thickness (height H) of 10 μm or more, specifically about 100 μm. Further, the horizontal width W of the microlens 3 is about 500 μm.

  In addition, since the microlens 3 is connected to the silicon substrate 1 without using an adhesive layer, the microlens 3 has excellent heat dissipation characteristics. For example, assuming a case where the high-power laser 7 is used for collimation, since the size of the microlens 3 is small, the spread angle of the laser is 90 ° as shown in FIG. 10 which is a longitudinal sectional view of the optical element 20. In this case, the distance L between the light emitting end of the high-power laser 7 and the lens 3 (see FIG. 2) is about 100 μm. That is, the exit surface 3b of the lens is placed close to the light emitting end of the high output laser 7 to about 100 μm. In this case, there is a concern that the temperature of the microlens itself is increased by absorbing the heat of the laser light. However, in the case of the present microlens 3, since it is connected to the silicon substrate 1 that has significantly higher thermal conductivity than glass, Since heat escapes to the silicon substrate 1 side, there is an advantage that the temperature of the microlens is difficult to rise.

[Method for Manufacturing Optical Element]
Next, a method for manufacturing the optical element 20 having the above structure will be described.
FIG. 3 is a plan view showing a state in which an oxide film mask is disposed on the substrate surface of the silicon substrate, and FIG. 4 is a cross-sectional view taken along the line AA of FIG. 5 is a plan view showing a state in which a trench is formed from the state of FIG. 3, and FIG. 6 is a cross-sectional view taken along line AA of FIG. FIG. 7 is a cross-sectional view showing a state in which the oxide film mask has been removed from the state of FIG. FIG. 8 is a cross-sectional view showing a state where thermal oxidation is performed from the state of FIG. FIG. 9 is a cross-sectional view showing a state in which the trench is filled with silicon oxide.

(Trench formation)
First, as shown in FIGS. 3 and 4, microlens patterning is performed on the substrate surface of the silicon substrate 1 using an oxide film mask 10. The oxide film mask 10 has a plurality of openings 10a corresponding to the shape of the trench formed in the next etching step.
Then, as shown in FIGS. 5 and 6, the trench 11 is formed by etching from each opening 10 a of the oxide film mask 10. That is, the silicon substrate 1 is trench-etched from the substrate surface using the patterned oxide film mask 10, and a large number of trenches 11 having a certain width are arranged in parallel at a certain interval. For example, reactive ion etching is used as an etching technique. Then, an etching step for etching the silicon substrate 1 with an etching gas plasma and a protective film formation step for forming a sidewall protection film inside the trench with a deposition gas plasma are alternately repeated while switching, and a high aspect ratio ( For example, a trench having an aspect ratio of 60) is formed.

When performing trench etching shown in FIGS. 5 and 6, in order to obtain a three-dimensional lens shape by forming a deeper trench 11 with respect to a prescribed trench width (hereinafter referred to as a "extracted width"), It is necessary to form an aspect ratio (depth / width) trench.
Therefore, using the etching technique of JP 2000-299310 A, a protective oxide film is formed on the inner surface (side surface and bottom surface) of the formed trench 11, and the oxide film on the bottom surface is removed by reactive ion etching, The protective oxide film forming step and the trench bottom etching step are repeated such that the silicon substrate 1 is continuously etched from the bottom surface. As a result, a trench having a very vertical cross-sectional profile up to an aspect ratio of about “60” can be obtained. Thus, in the trench etching, the trench 11 is formed by reactive ion etching, a protective oxide film is formed on the inner wall of the trench, and further, the protective oxide film at the bottom of the trench is etched, and then from the bottom of the trench 11. By deepening the trench by reactive ion etching, a trench with a high aspect ratio can be formed.

FIGS. 14A and 14B are explanatory views showing a modification example of the trench. As shown in FIG. 14A, a forward taper-shaped trench 11 whose width becomes narrower as it becomes deeper may be formed, and as shown in FIG. 14B, it is the same from the bottom to the middle. A trench 11 having a wide portion 11a which is formed with a width and gradually becomes wider from the middle thereof may be formed. For example, a tapered portion can be formed by controlling the protective oxide film to remain thick.
5 and 6, a large number of trenches 11 having a constant width are arranged in parallel at regular intervals by trench etching. However, the present invention is not limited to this. For example, trenches having a non-constant width are arranged in parallel or the trenches are fixed. A large number may be arranged in parallel with each other.

  In the microlens formation region, a plurality of trenches (a large number of trenches) 11 extend in the same direction and parallel to the optical axis. The ratio between the blank width and the width of the silicon layer 13 that serves as a wall between the trenches (hereinafter referred to as the remaining width) is determined when each silicon layer 13 is replaced with silicon oxide in the next thermal oxidation step. It is set so that a gap remains between the layers and the upper portion of the gap is open. That is, the trench is set so that a gap through which the supercritical fluid cannot flow is not formed when the subsequent supercritical fluid is poured.

5 and 6, the outermost peripheral part that defines the shape of the light transmitting block, that is, the outermost peripheral part (contour line) of the lens formation region is connected to the silicon layer 12 having a predetermined width. A trench 9 is formed around the formation region. That is, it is surrounded by a remaining area (12). The curvature of the light incident surface and the light exit surface is defined by the pattern of the contour line (12), and an arbitrary curved surface is obtained (an arbitrary surface is obtained) depending on the pattern design.
In addition, the width of the remaining region that becomes the outline (12) is set to be the same as or narrower than the remaining width between the trenches 11. That is, the width of the connected silicon layers 12 is set to be equal to or smaller than the width of the silicon layer between the trenches 11. This is due to the following reason.

  FIGS. 11A and 11B are enlarged explanatory views of the connection portions of the silicon layers 12 and 13. As shown in FIG. 11 (a), the remaining lens forming region (14) and the contour line (12) are connected in a substantially T shape. Will be slower. Therefore, if the remaining width W2 of the contour line (12) is larger than the remaining width W1 between the trenches 11, there is a possibility that an unoxidized portion 8 appears in this portion. Therefore, as shown in FIG. 11B, the width W2 of the remaining region that becomes the contour line (12) is set to be the same as or narrower than the remaining width W1 between the trenches 11. Thereby, the area | region where the silicon layers 12 and 14 are not oxidized can be decreased.

  5 and 6, the trench 9 formed outside the lens formation region (around the light transmission block formation region) is sufficiently wider than the trench width in the light transmission block. And as shown in FIG. 8, the trench 9 formed around the formation region of the light transmission block is left to have a void in the trench after thermal oxidation. Thereby, buckling can be avoided. Further, the etching region (trench 9) is etched deeper than the trench 11 inside the lens due to the microloading effect in the trench etching process. This shape is important in that it does not obstruct the light path when light enters and exits. That is, when the silicon oxide block (3) formed integrally with the silicon substrate 1 has a connecting portion 5 made of a silicon substrate having the same shape as the silicon oxide block (3) below, It is possible to avoid obstructing the light path when the light indicated by L1 in FIG.

By the way, normally, silicon and silicon oxide (SiO ₂ ) are different in thermal linear expansion coefficient (Si: 2.6 × 10 ⁻⁶ / ° C. at 20 ° C., fused quartz: 0.4 to 0.55). × 10 ^-6 / ° C, Source: Science Chronology). Therefore, as shown in FIG. 12, which is a plan view for explaining deformation due to thermal stress, if the plate-like silicon is simply left by trench etching and then thermally oxidized, the amount of shrinkage differs during cooling, so that The silicon oxide (SiO ₂ ) is buckled by stress from both sides. Therefore, as shown in FIG. 13A, which is a plan view for explaining deformation due to thermal stress, even if a large number of trenches 11 are arranged in one direction, as shown in FIG. After thermal oxidation, individual silicon oxide layers (SiO ₂ layers) buckle, and there is a concern that the lens shape as designed cannot be formed.

Therefore, in this embodiment, the following three things are performed to form the microlens.
As a first contrivance, the region around the microlens is surrounded by a trench (extracted region) 9. That is, the trench 9 is formed around the formation region of the light transmission block. As a second contrivance, the outer peripheral portion of the microlens is surrounded by a remaining region (12) serving as a contour line. As a third idea, the extending direction of the trench 11 is made parallel to the light transmitting direction. That is, a large number of trenches 11 are arranged in parallel to the optical axis.

With the first device, the lens pattern is not pushed from the surrounding silicon when the temperature is lowered after thermal oxidation, and the plate-like silicon oxide (SiO ₂ ) is not buckled. Further, by the second device, the outermost peripheral portion of the microlens region is surrounded by a remaining region (12) which is a contour, whereby the individual plate-like silicon oxide layers (SiO ₂ layers) are mechanically connected, and the seat It can prevent bending and falling. Further, since the lens surface can be defined by patterning the remaining region (12) that becomes the contour line, a lens surface having an arbitrary curvature can be obtained depending on the pattern design. Further, the third device makes it possible to make the interfaces adjacent to each other in the form of individual plate-like silicon oxide layers (SiO ₂ layers) parallel to the light transmission direction. It is possible to minimize a decrease in transmittance (light transmission) as a lens due to reflection, scattering, and the like.
The above-described trench forming process corresponds to the first process described in claim 1 or claim 2 of the present application.

(Annealing treatment)
Next, the entire substrate is annealed in a hydrogen atmosphere to reduce the surface roughness on the trench sidewalls. The flatness of the trench sidewall surface after this etching, particularly the sidewall surface that defines the outermost peripheral portion of the lens formation region is important because this surface becomes a surface on which light enters or exits, and thermal oxidation is performed thereafter. Thus, a lens surface having a smooth surface can be obtained. This technique is disclosed in Japanese Patent Application Laid-Open No. 2002-231945.

(Removal of oxide mask)
Next, as shown in FIG. 7, the oxide film mask 10 is removed by immersion in a hydrofluoric acid solution or the like.

(Thermal oxidation)
Next, as shown in FIG. 8, each silicon layer 13 is thermally oxidized to replace the silicon oxide layer 14. This thermal oxidation is performed so that each silicon layer is not filled with silicon oxide and a narrow trench 11 remains. Further, the opening is left above the trench 11. That is, the supercritical fluid is allowed to flow into the trench 11 in the next step.

(Trench filling)
Next, a supercritical fluid in which a compound that forms silicon oxide is dissolved is poured into each trench 11, and the above-described compound undergoes chemical change including decomposition on the inner wall surface of each trench 11, so that silicon oxide is introduced into the inner wall surface. A film is formed and each trench 11 is filled with silicon oxide. As shown in FIG. 9, a buried layer 15 made of silicon oxide buried with a supercritical fluid is formed in the trench 11 between the silicon oxide layers 14. In this embodiment, a supercritical fluid whose main component is carbon dioxide is used because the critical temperature and the critical pressure are low, so that a critical state is easily obtained and control is easy.
A supercritical fluid has a gas property (diffusibility) and a liquid property (solubility), and has the feature that its density can be changed drastically continuously. Therefore, a supercritical fluid having a gas property can enter a narrow gap, and each trench 11 can be filled with silicon oxide without any gap. Even if the trench 11 has irregularities or the upper opening is narrow, the supercritical fluid reaches every corner of the trench. Can be embedded.
Thereby, the microlens (light transmission block) 3 integral with the silicon substrate 1 is formed.
As shown in FIGS. 14A and 14B, if the upper portion of the trench is formed wide, the upper portion of the trench 11 may be narrowed by silicon oxide formed in the trench 11. Therefore, there is no possibility that unfilled portions are generated inside the trench 11.
Finally, dicing cutting is performed around the microlens with a predetermined dimension. Thereby, as shown in FIG. 1, a cylindrical lens is obtained. The trench filling step described above corresponds to the second step according to claim 1 or claim 2 of the present application.
In order to improve the transmittance, an antireflection film may be coated on the entire substrate as necessary.

[Effect of the first embodiment]
As described above, according to the method of manufacturing the optical element of the first embodiment, supercritical carbon dioxide in which a compound that generates silicon oxide is dissolved is arranged on the substrate surface of the silicon substrate 1 in parallel. The microlenses 3 are formed in such a manner that the trenches 11 are filled with silicon oxide without gaps by flowing into the trenches 11 between the silicon oxide layers 14 and forming the trenches 11 with silicon oxide. Can do.
Therefore, it is possible to manufacture the microlens 3 that does not cause a decrease in efficiency due to a diffraction phenomenon or a scattering phenomenon due to the remaining gap.
In addition, since the supercritical fluid has a higher density than the vapor phase method represented by CVD, silicon oxide can be dissolved at a high concentration, so that a large amount of silicon oxide can be supplied into each trench in a short time. it can.
Therefore, each trench can be filled with silicon oxide in a shorter time than the vapor phase method.

Second Embodiment
Next, a second embodiment will be described with reference to FIGS. This embodiment is characterized in that the periphery of the microlens formation region is removed after each trench is buried.
FIG. 15 is a longitudinal sectional view of a silicon substrate in which a trench is formed, and FIG. 16 is a longitudinal sectional view showing a state where the silicon substrate shown in FIG. 15 is thermally oxidized. 17 is a longitudinal sectional view showing a state in which each trench of the silicon substrate shown in FIG. 16 is buried with silicon oxide, and FIG. 18 shows a state in which the periphery of the silicon oxide block shown in FIG. 17 is removed. It is a longitudinal cross-sectional view shown. In addition, description is abbreviate | omitted about the same structure and process as above-mentioned 1st Embodiment, and the same code | symbol is used about the same structure.

  As shown in FIG. 15, the silicon substrate 1 from which the oxide film mask has been removed differs from the first embodiment in that the recess 2 shown in FIG. 6 is not formed. By performing the same heat treatment as in the first embodiment, each silicon layer 13 is replaced with a silicon oxide layer 14 as shown in FIG. Next, as in the first embodiment, carbon dioxide in a supercritical state in which a compound that generates silicon oxide is dissolved is poured into each trench 11, and each trench 11 is filled with silicon oxide without any gap.

Next, the upper surface of the silicon oxide block is shielded with an etching mask, and the periphery of the microlens formation region is etched. The etching is stopped when the lower portion of the region removed by the etching becomes the same depth as the silicon oxide block. Thereby, as shown in FIG. 18, the microlens 3 is formed on the substrate surface of the silicon substrate 1.
In this embodiment, anisotropic etching is performed using a potassium hydroxide (KOH) aqueous solution or a tetramethylammonium hydroxide (TMAH) aqueous solution. In addition, since the surface orientation of the silicon substrate 1 is (110), it is possible to etch perpendicularly to the substrate surface by using the above aqueous solution, so that the outer peripheral surface of the silicon oxide block (microlens) is It is possible to accurately control the target shape and prevent defects from being formed.
In addition, the process of removing the periphery of the above-mentioned microlens formation area | region respond | corresponds to the 3rd process of Claim 2 of this application.

[Effects of Second Embodiment]
As described above, even when the optical element manufacturing method according to the second embodiment is used, silicon in which supercritical carbon dioxide in which a compound that generates silicon oxide is dissolved is arranged on the substrate surface of the silicon substrate 1 in parallel. By flowing into each trench 11 between the oxide layers 14 and forming each trench 11 with silicon oxide, the microlens 3 in a state where each trench 11 is filled with silicon oxide without gaps can be formed. .
Therefore, it is possible to manufacture the microlens 3 that does not cause a decrease in efficiency due to a diffraction phenomenon or a scattering phenomenon due to the remaining gap.
In addition, since supercritical fluid has a higher density than the vapor phase method typified by CVD, a compound that generates silicon oxide is dissolved at a high concentration, so that a large amount of silicon oxide can be placed in each trench in a short time. Can be supplied.
Therefore, each trench can be filled with silicon oxide in a shorter time than the vapor phase method.

<Third Embodiment>
Next, a third embodiment of the present invention will be described with reference to FIGS.
FIGS. 19A to 19C and FIGS. 20A and 20B are plan views showing modified examples of optical elements. FIGS. 21A and 21B are plan views showing a state in which a plurality of optical elements are formed.
In FIG. 19A, the plano-convex cylindrical lens manufactured in the first and second embodiments described above is illustrated. However, depending on the design of the contour line, a biconvex lens as shown in FIG. A lens having an arbitrary shape such as a biconcave lens as shown in FIG. 19C, a plano-concave lens as shown in FIG. 20A, and a meniscus lens as shown in FIG. 20B can be formed. A high NA lens can also be formed.

  Furthermore, since a plurality of patterns can be prepared in a lump, for example, a lens array as shown in FIG. 21A or a line on the same optical axis as shown in FIG. Multiple types of lens groups can be formed. Further, as shown in FIG. 21B, not only lenses but also slits can be formed at the same time. Further, although not shown, a prism can be formed at the same time.

  In this way, a plurality of lenses (lens array) or lenses, prisms, and slits are patterned together, and these parts are collectively processed through trench etching, thermal oxidation process, and trench filling process using supercritical fluid. Can be built into the substrate. In this case, whether it is a large number of lens arrays or a complicated optical system in which light passes through a plurality of lenses, it can be formed by patterning on a substrate from a single mask, especially in the latter case. With respect to the above, the problem of optical axis alignment of individual optical components, which is a very troublesome problem in a minute optical system, can be solved. In a broad sense, a mask is used to form a plurality of optical components including at least one of a lens, an optical waveguide, a prism, and a slit. If the silicon substrate is fabricated in a lump through the embedding process, the alignment of the optical axis becomes unnecessary. In other words, when a plurality of optical components including at least one of a lens, an optical waveguide, and a slit are formed in the silicon substrate as the structure of the optical element, the alignment of the optical axis is not necessary.

<Fourth embodiment>
Next, a fourth embodiment of the present invention will be described focusing on differences from the first embodiment.
FIG. 22 is a plan view of the optical element in this embodiment, and FIG. 23 is a cross-sectional view taken along line AA in FIG.
In this embodiment, a cylindrical lens 21 having a separate structure from the silicon substrate 1 is fitted into the silicon substrate 1, and the cylindrical lens 21 and the cylindrical lens 20 are optically coupled. The cylindrical lens 20 has a function of collimating or condensing only incident light with respect to the horizontal direction, and a separate cylindrical lens 21 is combined with this. This allows collimation or light collection in the vertical direction.

The cylindrical lens 21, which is a separate body, is set by fitting a hole 22 for mounting on the silicon substrate 1 side in advance by etching or the like. This optical system makes it possible to collimate the semiconductor laser 23, for example. Usually, the semiconductor laser 23 differs greatly in the beam divergence angle between the horizontal direction and the vertical direction. Therefore, in order to collimate, it is necessary to combine two cylindrical lenses corresponding to the respective directions. In that case, such a configuration is used. That is, the cylindrical lens 20 is formed in the silicon substrate 1 and the hole 22 is formed in the silicon substrate 1. The cylindrical lens 21 is fitted into the hole 22, and the light beam spreading in the horizontal and vertical directions by the pair of cylindrical lenses 20 and 21. It can be set as the structure which condenses separately (it becomes possible to condense also in the up-down direction).
In addition, although the example of the cylindrical lens was shown as a lens fitted in the silicon substrate 1, a cylindrical lens etc. may be used.

<Fifth Embodiment>
Next, a fifth embodiment of the present invention will be described focusing on differences from the first embodiment. FIG. 24 is a perspective view of the optical element in this embodiment.
In this embodiment, an optical waveguide 55 is formed together with the lens 3. The optical waveguide 55 can be formed by the same method as the lens 3. That is, in a periodic trench structure, a line-shaped silicon oxide block, that is, an optical waveguide 55 can be formed by forming a pattern with a small number of trenches and an extremely long length in the longitudinal direction.
For example, the optical waveguide 55 can be formed by performing D-RIE, a thermal oxidation process, and a trench filling process using a supercritical fluid on a pattern in which two silicon layers sandwiching the trench are arranged in the longitudinal direction. In the optical waveguide 55, there is a difference in refractive index in the vertical direction, and light is confined near the center where the refractive index is the highest. In the lateral direction, since the periphery of the optical waveguide 55 is an open space, the light is confined in the optical waveguide 55. The optical waveguide 55 can be formed in an arbitrary shape depending on the pattern. Further, since it can be formed at the same time as the lens 3, alignment at the time of coupling with the lens 3 is unnecessary.

In addition, since the optical waveguide can be changed from one to plural and vice versa depending on the pattern, it is possible to collectively form an optical system in which the light is distributed and incident on a plurality of lens arrays. A specific example is shown in the perspective view of FIG. 25, and FIG.
25 and 26, a plurality of horizontal-direction cylindrical lenses 60 are formed, and a vertical-direction cylindrical lens 61 is disposed to face each of the horizontal-direction cylindrical lenses 60. Furthermore, optical waveguides 62 are optically coupled to the horizontal cylindrical lenses 60, and the optical waveguides 62 are assembled into one. The end face of the optical fiber 63 is provided opposite to the end face of the assembled optical waveguide 62. The vertical-direction cylindrical lens 61 and the optical fiber 63 are fitted into the substrate 50. In this case, the horizontal cylindrical lens 60 and the optical waveguide 62 need not be aligned, and the vertical cylindrical lens 61 and the optical fiber 63 can be easily aligned by being fitted into the substrate 50. Furthermore, since the structure is simple, there is little decrease in optical coupling efficiency. Further, it is excellent in mass productivity and can be reduced in cost.
Thus, the silicon oxide block formed integrally with the silicon substrate may be an optical waveguide, or a microlens and an optical waveguide.

[Other Embodiments]
By dissolving in a supercritical fluid a compound that produces a product capable of forming an object having a refractive index equivalent to that formed by silicon oxide, each gap is filled without gaps by the product produced from the compound. You can also. For example, as the above products, the refractive indexes of calcium fluoride, magnesium fluoride, and alumina are 1.43, 1.38, and 1.58 to 1.60, respectively, and are approximately equal to 1.2 to 8 of silicon oxide. Even if it is embedded with these materials, the effect similar to that when embedded with silicon oxide is obtained, the effect of diffraction is suppressed, the reflection at the interface is suppressed, the scattering is reduced, and the substantial transmission efficiency is not greatly reduced. .
An organic compound is suitable for the compound dissolved in the supercritical fluid. This is because it is easily dissolved in a supercritical fluid and is decomposed at a low temperature of about 100 to 300 ° C. If film formation at a low temperature becomes possible, the temperature rise / drop time is shortened, efficient film formation becomes possible, and the apparatus can be made simple. A specific compound for forming silicon oxide includes TMOS (tetramethoxysilane) and the like.

It is a perspective view of the optical element manufactured by the manufacturing method of the optical element which concerns on 1st Embodiment. 2A and 2B are explanatory views of the optical element shown in FIG. 1, wherein FIG. 2A is a plan view of the optical element shown in FIG. 1, and FIG. 2B is a cross-sectional view taken along line AA in FIG. It is a top view which shows the state by which the oxide film mask is arrange | positioned at the board | substrate surface of a silicon substrate. It is AA arrow sectional drawing of FIG. It is a top view which shows the state in which the trench was formed from the state of FIG. It is AA arrow sectional drawing of FIG. FIG. 7 is a cross-sectional view showing a state where an oxide film mask has been removed from the state of FIG. 6. It is sectional drawing which shows the state which thermally oxidized from the state of FIG. It is sectional drawing which shows the state by which the trench was embedded with the silicon oxide. 2 is a longitudinal sectional view of an optical element 20. FIG. (A), (b) is an expansion explanatory drawing of the connection part of the silicon layers 12 and 13. FIG. It is a top view for demonstrating the deformation | transformation by a thermal stress. (A), (b) is a top view for demonstrating the deformation | transformation by a thermal stress. (A), (b) is explanatory drawing which shows the example of a change of a trench. It is a longitudinal cross-sectional view of the silicon substrate in which the trench was formed in 2nd Embodiment. It is a longitudinal cross-sectional view which shows the state by which the silicon substrate shown in FIG. 15 was thermally oxidized. FIG. 17 is a longitudinal sectional view showing a state in which each trench of the silicon substrate shown in FIG. 16 is buried with silicon oxide. It is a longitudinal cross-sectional view which shows the state from which the periphery of the silicon oxide block shown in FIG. 17 was removed. (A)-(c) is a top view which shows the example of a change of the optical element in 3rd Embodiment. (A), (b) is a top view which shows the example of a change of an optical element. (A), (b) is a top view in the state where a plurality of optical elements were formed. It is a top view of the optical element in 4th Embodiment. It is AA arrow sectional drawing of FIG. It is a perspective view of the optical element in 5th Embodiment. It is a perspective view of the optical element in 5th Embodiment. It is a top view of the optical element in 5th Embodiment. It is a schematic diagram which shows the state in which the clearance gap remained in the trench.

Explanation of symbols

1 .... Silicon substrate, 2 .... Recess, 3 .... Micro lens (block),
4 .. Column structure (structure) 5 .. Connection part 6 .. Air gap 7.
10 .. Oxide film mask, 10a ... Opening, 11. Trench (gap),
12 ... Silicon layer, 13 ... Silicon layer, 14 ... Silicon oxide layer,
15 .. buried layer, 55 .. optical waveguide.

Claims (30)

In the method of manufacturing an optical element having a block made of at least silicon oxide that transmits light,
A first step of creating a state in which a plurality of structures made of silicon oxide are arranged side by side on a substrate surface of a silicon substrate with a gap between the structures;
A second step of forming the block by pouring a supercritical fluid in which a predetermined compound is dissolved into each gap between the structures, and filling each gap with a product generated from the predetermined compound. The manufacturing method of the optical element characterized by having these. In the method of manufacturing an optical element having a block made of at least silicon oxide that transmits light,
A first step of creating a state in which a plurality of structures made of silicon oxide are juxtaposed inside a silicon substrate with a gap between each structure;
A second step in which a supercritical fluid in which a predetermined compound is dissolved is poured into each gap between the structures, and each gap is filled with a product generated from the predetermined compound;
And a third step of forming the block by removing a peripheral portion of the portion of each structure embedded in the product.   In the third step, the process of removing the peripheral portion of the portion made of each structure is performed from the substrate surface of the silicon substrate, and the lower portion of the removed region has the same depth as each structure. The method according to claim 2, wherein the process is stopped.   The method of manufacturing an optical element according to claim 2, wherein the third step is a step of removing the peripheral portion by etching.   The method for manufacturing an optical element according to claim 4, wherein the etching is anisotropic etching.   6. The method of manufacturing an optical element according to claim 5, wherein the anisotropic etching is anisotropic etching using a potassium hydroxide (KOH) aqueous solution or a tetramethylammonium hydroxide (TMAH) aqueous solution.   The optical element according to any one of claims 1 to 6, wherein in the first step, the plurality of structures are formed by etching a silicon substrate using a patterned mask. Production method.   In the first step, a structure in which a plurality of structures made of silicon oxide are arranged in parallel with a gap between each structure is formed so that a gap whose width becomes narrower as the depth increases. The method for manufacturing an optical element according to claim 1, wherein the optical element is manufactured.   In the first step, a plurality of structures made of silicon oxide are formed between the structures so as to form a gap that gradually becomes wider from the bottom toward the top and that the top becomes the widest. 8. The method for manufacturing an optical element according to claim 1, wherein a state of being arranged side by side is created. 9.   In the first step, each of the structures is formed in a thin plate shape so that a side surface in a longitudinal direction extending in the optical axis direction becomes a wall surface of the gap. The manufacturing method of the optical element as described in any one of thru | or 9.   In the first step, the plurality of structures made of silicon oxide are formed by thermally oxidizing the plurality of structures made of silicon so that the gap is not filled with silicon oxide. The method for manufacturing an optical element according to any one of claims 1 to 10.   12. The optical system according to claim 11, wherein, in the first step, the width of each structural body made of silicon and the width of each gap are set so that the gap is not filled with silicon oxide by thermal oxidation. Device manufacturing method.   The method of manufacturing an optical element according to claim 1, wherein the product is generated by chemically changing the predetermined compound.   The method of manufacturing an optical element according to claim 13, wherein the product is generated by decomposing the predetermined compound.   The method of manufacturing an optical element according to claim 1, wherein the compound is an organic compound.   The method for manufacturing an optical element according to claim 1, wherein the product is silicon oxide.   16. The optical device according to claim 1, wherein the product is a product capable of forming a product having a refractive index equivalent to that formed by silicon oxide. Device manufacturing method.   16. The method of manufacturing an optical element according to claim 15, wherein the compound is TMOS (tetramethoxysilane).   The method of manufacturing an optical element according to claim 17, wherein the product is calcium fluoride.   The method of manufacturing an optical element according to claim 17, wherein the product is magnesium fluoride.   The method of manufacturing an optical element according to claim 17, wherein the product is alumina.   The method of manufacturing an optical element according to any one of claims 1 to 21, wherein a surface orientation of the substrate surface is (110).   In the first step, each of the trench-like gaps is formed by reactive ion etching of the silicon substrate, and a plurality of structures made of silicon oxide with the gaps separated from each other are formed. The method for manufacturing an optical element according to any one of claims 1 to 22, wherein the method is provided.   The method of manufacturing an optical element according to any one of claims 1 to 23, wherein a main component of the supercritical fluid is carbon dioxide.   The method of manufacturing an optical element according to any one of claims 1 to 24, wherein the block is a microlens.   The method for manufacturing an optical element according to any one of claims 1 to 24, wherein the block is an optical waveguide.   The method of manufacturing an optical element according to any one of claims 1 to 24, wherein the block is a prism.   25. The method of manufacturing an optical element according to claim 1, wherein a plurality of microlenses, optical waveguides, and prisms are simultaneously manufactured as the block.   25. The method of manufacturing an optical element according to claim 1, wherein at least two of a microlens, an optical waveguide, and a prism are manufactured simultaneously as the block.   The method for manufacturing an optical element according to any one of claims 1 to 24, wherein a plurality of at least two of a microlens, an optical waveguide, and a prism are simultaneously manufactured as the block.

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