JP4007394B2 - Method of forming curved surface - Google Patents

Description

  The present invention relates to a curved surface forming method in which a curved surface is formed by removing a part of a semiconductor substrate.

  Conventionally, a method of manufacturing a microlens mold using a conductive substrate and a method of manufacturing a microlens using the microlens mold have been proposed (see Patent Document 1). In Patent Document 1, a synthetic resin lens is exemplified as a microlens.

  In the method for manufacturing a microlens mold disclosed in Patent Document 1, for example, a silicon nitride film is deposited on one surface of a low-resistance p-type silicon substrate that is a conductive substrate, and then a photolithography technique and an etching technique are used. Then, a circular opening is formed at a predetermined portion of the silicon nitride film, and then a part of the one surface side of the p-type silicon substrate is made porous by anodizing using the silicon nitride film as a mask layer. Thus, a hemispherical porous silicon portion is formed. Thereafter, the silicon dioxide portion is formed by oxidizing the entire porous silicon portion, the mask layer is removed, and then the silicon dioxide portion is removed to form a desired convex lens on the one surface of the p-type silicon substrate. A recess corresponding to the shape is formed, and then a thermal oxide film is formed on each of the one surface side and the other surface side of the p-type silicon substrate. In the above-described anodizing treatment, the gap between the cathode disposed opposite to the one surface side of the p-type silicon substrate and the anode plate disposed in contact with the other surface of the semiconductor substrate in the electrolytic solution for anodization. The porous silicon part is formed by energizing the current.

  In the method of manufacturing a microlens mold disclosed in Patent Document 1, a p-type silicon substrate having a low resistance that is relatively close to the resistivity of a conductor is used, and p-type silicon is used during anodization. Since the porosity of the substrate proceeds isotropically like isotropic etching, the one surface of the p-type silicon substrate 100 is formed as shown in FIG. The depth dimension a1 of the concave portion 101 formed in this step is substantially equal to the radius a2 of the circular opening surface of the concave portion 101. As a result, a plano-convex spherical lens can be manufactured as a microlens. In Patent Document 1, a plano-convex cylindrical lens can be manufactured as a micro lens as a result of making the shape of the opening portion rectangular when manufacturing a micro lens mold. Is also disclosed.

Conventionally, an anode without providing a mask layer having a pattern designed in accordance with the mesa shape on one surface side of a semiconductor substrate having a high resistance (for example, a resistivity of about 10 ⁸ Ωcm) such as a semi-insulating GaAs substrate. As a method for forming a mesa shape using an oxidation technique, an anode (electrode) whose shape is designed in accordance with the mesa shape is brought into contact with the other surface side of the semiconductor substrate, and then the above-mentioned semiconductor substrate in the anode and the electrolytic solution. A method has been proposed in which an anodic oxidation process is performed in which an oxide film is formed by energizing a cathode disposed opposite to one surface, followed by an oxide film removal process in which the oxide film is removed by etching (for example, a patent) Reference 2).

In the mesa shape forming method described in Patent Document 2, the in-plane distribution of the current density of the current flowing through the semiconductor substrate is determined by the shape of the anode and the thickness of the oxide film in the anodizing step. It is possible to form a mesa shape in which the slope is gentle and the side surface and the flat surface of the mesa are smoothly continuous.
JP 2000-263556 A Japanese Patent Laid-Open No. 55-13960

  By the way, in the method for manufacturing a microlens mold disclosed in Patent Document 1, only a microlens mold for forming a microlens having a uniform curvature radius of a convex curved surface can be manufactured. A plano-convex aspherical lens could not be formed as a lens. In short, only the convex curved surface having a uniform curvature radius could be formed as the curved surface shape of the microlens mold disclosed in Patent Document 1.

  In addition, it is conceivable to manufacture a semiconductor lens made of a plano-concave silicon lens by using the method for forming the concave portion 101 on the p-type silicon substrate 100 described in Patent Document 1, but as the semiconductor lens, a concave portion is used. Only a plano-concave spherical lens or a cylindrical lens with a uniform curvature radius of the curved surface can be formed, and an aspherical lens cannot be formed. In short, in the method of forming a curved surface on the semiconductor substrate (p-type silicon substrate 100) disclosed in Patent Document 1, only a concave curved surface with a uniform curvature radius can be formed. Further, in the method for forming a curved surface on the semiconductor substrate described above, bubbles generated during the anodizing process are desorbed through the openings of the mask layer, so that the bubbles gather around the openings and become porous. Due to variations in the traveling speed or the stoppage of the porous structure, a concave curved surface that is a curved surface having a desired radius of curvature may not be formed as a result.

Therefore, it is conceivable to apply the technique described in Patent Document 2 to the method of forming the curved surface of the semiconductor lens. In the anodic oxidation process, as the thickness of the formed oxide film increases, For example, when a GaAs substrate having a thickness of 400 μm and a resistivity of 10 ⁸ Ωcm is used as the semiconductor substrate, the oxide film is formed when the oxide film is formed at a constant current of 1 mA / cm ² . Even if the thickness is about 0.6 μm, the potential difference becomes as high as 400 V. Therefore, it is necessary to repeat the basic process consisting of the anodizing process and the oxide film removing process, which complicates the manufacturing process as well as the desired process. It was difficult to form a curved surface according to the lens shape.

  In the technique described in Patent Document 2, the anode used in the anodic oxidation process is simply pressed against and brought into contact with the other surface of the high-resistance semiconductor substrate, so that the contact resistance between the semiconductor substrate and the anode is large. The contact between the semiconductor substrate and the anode becomes a Schottky contact, and there is a problem in the controllability and reproducibility of the in-plane distribution of the current density.

  The present invention has been made in view of the above-described reasons, and an object thereof is to provide a curved surface forming method capable of easily forming a smooth curved surface having an arbitrary shape.

The invention of claim 1 is a method of forming a curved surface , wherein a part of a semiconductor substrate is removed to form a curved surface that is convex in the thickness direction of the semiconductor substrate or a curved surface that is concave in the thickness direction , An anode forming step in which an anode having a contact pattern with a semiconductor substrate designed according to a desired curved surface shape is formed on one surface side of the semiconductor substrate, and facing the other surface side of the semiconductor substrate in the electrolytic solution after the anode forming step an anode oxidation step of forming a porous portion made of a removal site to the other surface side of the semiconductor substrate by energizing between the arranged cathode and anode, porous to remove multi-porous portion even after the anodization step A part removing step, and in the anode forming step, an anode is formed on the one surface of the semiconductor substrate so that the contact between the anode and the semiconductor substrate is ohmic contact, and in the anodic oxidation step, the semiconductor is used as an electrolytic solution. Board component Characterized by using a solution of oxide etched away.

According to this invention, since the in-plane distribution of the current density of the current flowing through the semiconductor substrate in the anodizing process is determined by the contact pattern of the anode formed in the anode forming process, the thickness of the porous portion formed in the anodizing process In-plane distribution can be controlled to form a porous portion having a continuously varying thickness, and in the anode forming step, the contact between the anode and the semiconductor substrate becomes an ohmic contact. the positive electrode was formed on the one surface of the semiconductor substrate, the anodic oxidation process, as the electrolytic solution, since using a solution to etch away the oxide of the constituent elements of the semiconductor substrate, the porous portion of the desired thickness distribution Can be easily formed in one anodic oxidation process, and a desired curved surface is formed by removing the porous part in the porous part removing process. Surface it is possible to easily form the.

According to a second aspect of the invention, in the invention of claim 1, in the anode formation step, after formation of the conductive layer underlying the anode on the one front side of the semiconductor substrate, a circular shape on the conductive layer The anode is formed by patterning the conductive layer so as to provide the opening portion.

  According to this invention, since the current density of the current flowing through the semiconductor substrate in the anodic oxidation step has an in-plane distribution that decreases as it approaches the center line of the aperture of the anode, the other surface of the semiconductor substrate On the side, since the thickness of the porous portion becomes thinner as it approaches the center line of the opening portion of the anode, a smooth aspheric convex curved surface can be formed as a desired curved surface shape.

According to a third aspect of the present invention, in the first aspect of the invention, in the anode forming step, as the anode, a conductive layer in which the contact pattern with the semiconductor substrate is designed in a circular shape is the surface of the semiconductor substrate. It is formed on a surface .

  According to the present invention, the current density of the current flowing through the semiconductor substrate in the anodizing step has an in-plane distribution that decreases as the distance from the center line of the anode decreases. Therefore, the anode on the other surface side of the semiconductor substrate. Since the thickness of the porous portion decreases as the distance from the center line increases, a smooth aspheric concave curved surface can be formed as a desired curved surface shape.

The invention of claim 4 is the invention of claim 1, wherein prior to the anode formation step, an insulating layer forming step of forming an insulating layer pattern designed in accordance with the contact pattern on the one front side of the semiconductor substrate In the anode forming step, an insulating layer and a conductive layer in contact with the one surface are formed on the one surface side of the semiconductor substrate as the anode.

  According to the present invention, the contact pattern of the anode with respect to the semiconductor substrate is determined by the pattern of the insulating layer formed in the insulating layer forming step, and the contact pattern and the pattern of the insulating layer determine the contact pattern on the semiconductor substrate in the anodic oxidation step. Since the in-plane distribution of the current density of the flowing current is determined, a semiconductor substrate having a lower resistivity can be used as the semiconductor substrate.

The invention of claim 5 is the invention of claim 4, wherein the insulating layer forming step, after said said forming an insulating film underlying the insulating layer on the semiconductor substrate the on one front surface of the circular-shaped insulating film The insulating layer is formed by patterning.

  According to the present invention, the current density of the current flowing through the semiconductor substrate in the anodizing step has an in-plane distribution that decreases as it approaches the center line of the insulating layer that matches the thickness direction of the semiconductor substrate. In the semiconductor substrate, the thickness of the porous portion decreases as it approaches the center line of the insulating layer, so that a smooth aspheric convex curved surface can be formed as a desired curved surface shape.

  According to a sixth aspect of the present invention, in the fourth or fifth aspect of the present invention, the insulating layer is made of a silicon oxide film or a silicon nitride film.

  According to the present invention, the insulating layer can be easily formed generally by a semiconductor manufacturing process, and the position accuracy and pattern accuracy of the insulating layer can be increased. It is possible to form a semiconductor lens with less.

The invention of claim 7 is the first porous part removing step of removing the first porous part, which is the porous part, in the porous part removing step in the invention of claim 1 to claim 6. After the first porous portion removing step, a second anode having a contact pattern with the semiconductor substrate designed according to another desired curved surface shape is formed on the other surface side of the semiconductor substrate. An anode forming step, and removing the first cathode side of the semiconductor substrate by energizing between the second cathode and the second anode arranged opposite to the one side of the semiconductor substrate in the second electrolyte solution. A second anodic oxidation step for forming a second porous portion to be a part, and a second porous portion removal step for removing the second porous portion. In the second anode forming step, wherein said semiconductor substrate so as to contact with the semiconductor substrate and the second anode is in ohmic contact A second anode formed on the front side, in the second anodization step, a second electrolytic solution, characterized by using a solution of oxide is etched off of the constituent elements of the semiconductor substrate.

  According to this invention, in the in-plane distribution of the thickness of the semiconductor substrate and the second anode forming step after forming the curved surface having a desired curved shape by removing the porous portion in the porous portion removing step. Since the in-plane distribution of the current density of the current flowing through the semiconductor substrate in the second anodic oxidation process is determined by the contact pattern of the second anode formed in this way, as a result, in the second porous portion removal process, Since a curved surface having a desired curved surface shape can be formed, a curved surface having a different desired curved surface shape can be formed on each of the one surface side and the other surface side of the semiconductor substrate, for example, manufacture of a semiconductor lens. When applied to the method, it is possible to form a biconvex lens, a biconcave lens, a concavo-convex lens, or the like as a semiconductor lens.

According to an eighth aspect of the present invention, in the seventh aspect of the present invention, an insulating film having a pattern designed according to the contact pattern between the second anode and the semiconductor substrate is formed in the semiconductor before the second anode forming step. formed in the other front side of the substrate, wherein in the second anode forming step, as the second anode to form a conductive layer in contact with said semiconductor substrate said other table surface in the insulating film and the other surface of the It is characterized by that.

  According to this invention, the contact pattern between the second anode and the semiconductor substrate with respect to the semiconductor substrate is determined by the pattern of the insulating film formed on the other surface side of the semiconductor substrate, and the contact pattern and the insulating film Since the pattern determines the in-plane distribution of the current density of the current flowing through the semiconductor substrate in the second anodic oxidation step, a semiconductor substrate having a lower resistivity can be used as the semiconductor substrate.

The invention of claim 9 is the invention of claims 1 to 8, wherein a silicon substrate is used as the semiconductor substrate, and a hydrofluoric acid solution is used as the solution so that porous silicon is formed as the porous portion. It is characterized by that.

  According to the present invention, it is possible to divert a general silicon device manufacturing apparatus, and it is possible to reduce the cost of the semiconductor substrate as compared with the case where a compound semiconductor substrate or the like is used as the semiconductor substrate. Can be planned.

  A tenth aspect of the invention is characterized in that, in the first to ninth aspects of the invention, a semiconductor substrate having a p-type conductivity is used.

  According to this invention, when the semiconductor substrate is made porous, the semiconductor substrate can be made porous without irradiating light from a light source. As compared with the above, the anodizing apparatus can be simplified and the cost can be reduced.

  According to an eleventh aspect of the present invention, in the first to tenth aspects of the present invention, the porosity of the portion on the boundary side with the semiconductor substrate is made smaller than the porosity of the portion on the surface side at the removal site during the energization. It is characterized by changing the energization conditions.

  According to this invention, the porosity of the portion on the boundary side with the semiconductor substrate in the removal site is smaller than the porosity of the surface side portion, and the fineness to the curved surface when removing the removal site is reduced. The formation of unevenness can be suppressed, and a smoother curved surface can be formed.

  In the invention of claim 1, there is an effect that it is possible to easily form a smooth curved surface having an arbitrary shape.

  Hereinafter, in each embodiment, a semiconductor lens manufacturing method using a curved surface forming method in which a part of the semiconductor substrate is removed to form a curved surface will be exemplified, but other than the semiconductor lens manufacturing method (for example, manufacturing of a MEMS device). Of course, the method can also be used.

(Embodiment 1)
In the present embodiment, as a method for manufacturing a semiconductor lens, a porous substrate made of porous silicon formed by making a part of a semiconductor substrate 10 (see FIG. 1A) made of a silicon substrate porous in an anodic oxidation step. A manufacturing method for manufacturing the semiconductor lens 1 (see FIG. 1E) made of a silicon lens by removing the mass portion 14 (see FIG. 1D) will be exemplified. Here, the semiconductor lens 1 in the present embodiment is a plano-convex aspherical lens. In the present embodiment, a semiconductor substrate 10 having a p-type conductivity is used and the resistivity of the semiconductor substrate 10 is set to 80 Ωcm. However, this value is not particularly limited.

  Hereinafter, the manufacturing method of the semiconductor lens 1 described above will be described with reference to FIGS.

First, an anode 12 (FIG. 1) used in an anodic oxidation process described later on one surface side (a lower surface side of FIG. 1A) of a semiconductor substrate (wafer until dicing described later) 10 shown in FIG. (C) and conductive property for forming the conductive layer 11 made of a conductive film (for example, an Al film, an Al-Si film, etc.) having a predetermined film thickness (for example, 1 μm), which is the basis of FIG. By performing the layer forming step, the structure shown in FIG. 1B is obtained. Here, in the conductive layer formation step, the conductive layer 11 is formed on the one surface of the semiconductor substrate 10 by, for example, sputtering, and then the sintering of the conductive layer 11 in an N ₂ gas and H ₂ gas atmosphere ( By performing heat treatment, ohmic contact between the conductive layer 11 and the semiconductor substrate 10 is obtained. Note that the method for forming the conductive layer 11 is not limited to the sputtering method, and for example, a vapor deposition method may be employed.

  After the conductive layer forming step, a patterning step for patterning the conductive layer 11 so as to provide a circular opening 13 in the conductive layer 11 is performed, thereby obtaining the structure shown in FIG. Here, in the patterning step, a resist layer (not shown) having a portion corresponding to the opening portion 13 is formed on the one surface side of the semiconductor substrate 10 by using a photolithography technique, and then a resist is formed. Using the layer as a mask, unnecessary portions of the conductive layer 11 are etched away by, for example, wet etching technique or dry etching technique to provide an opening 13 to form the anode 12 composed of the remaining portion of the conductive layer 11, and The resist layer is removed. If the conductive layer 11 is an Al film or an Al—Si film, when unnecessary portions of the conductive layer 11 are removed by wet etching technique, for example, a phosphoric acid-based etchant may be used. For example, a reactive ion etching apparatus or the like may be used when the unnecessary portion is removed by dry etching. In the present embodiment, the contact pattern with the semiconductor substrate 10 is designed in accordance with the desired curved surface shape (here, the curved surface shape in the desired lens shape) in the conductive layer forming step and the patterning step. An anode forming step of forming the anode 12 on the one surface side of the semiconductor substrate 10 is configured. The radius of the circular aperture 13 is set to 1 mm, but this value is not particularly limited and may be set as appropriate based on the design value of the lens diameter of the semiconductor lens 1.

  After the patterning step, the cathode 25 (see FIG. 3) and the anode disposed opposite to the other surface side (the upper surface side of FIG. 1A) of the semiconductor substrate 10 in the electrolytic solution B for anodization (see FIG. 3). 1 (d), an anodic oxidation process (anodic oxidation process) is performed to form a porous portion 14 made of porous silicon serving as a removal site on the other surface side of the semiconductor substrate 10 by energizing the semiconductor substrate 10 as shown in FIG. ) Is obtained.

Here, in the anodizing step, an anodizing apparatus A having the configuration shown in FIG. 3 is used. The anodizing apparatus A has a flat plate-like energizing electrode 21 that is brought into contact with the anode 12 formed on the one surface side of the semiconductor substrate 10, and the semiconductor substrate 10 is in a form in which the anode 12 and the energizing electrode 21 are brought into contact with each other. A disk-shaped support table 22 that supports the cylindrical body, a cylindrical tube body 23 that is disposed above the support table 22 with the center line as the vertical direction, and an inner casing that is integrally formed at the lower end of the tube body 23. A seal member 24 formed of an O-ring interposed between the portion 23 a and the peripheral portion of the semiconductor substrate 10, an outer flange portion 23 b continuously formed integrally with the lower end portion of the cylindrical body 23, and a peripheral portion of the support base 22 And an electrolyte B for anodization is placed in a space surrounded by the other surface of the semiconductor substrate 10, the seal member 24, and the cylindrical body 23. As the electrolytic solution B, a hydrofluoric acid in which a 55 wt% aqueous solution of hydrogen fluoride and ethanol are mixed at a ratio of 1: 1 as a solution for etching and removing SiO ₂ that is an oxide of Si that is a constituent element of the semiconductor substrate 10. Although the system solution is used, the concentration of the aqueous hydrogen fluoride solution and the mixing ratio of the aqueous hydrogen fluoride solution and ethanol are not particularly limited. Also, the liquid mixed with the aqueous hydrogen fluoride solution is not limited to ethanol, and is not particularly limited as long as it is a liquid that can remove bubbles generated by an anodizing reaction, such as alcohol such as methanol, propanol, and isopropanol (IPA). . The cylindrical body 23 may be formed of a material having resistance to the electrolytic solution B, for example, a fluorine-based resin such as Teflon (registered trademark).

The anodic oxidation apparatus A is a voltage source that applies a voltage between the anode 12 and the cathode 25 through the energizing electrode 21 and the cathode 25 made of a platinum electrode disposed opposite to the other surface of the semiconductor substrate 10. 31, a current sensor 32 that detects a current flowing from the voltage source 31 to the energization electrode 21, and a control unit 33 that includes a microcomputer that controls the output voltage of the voltage source 31 based on the current detected by the current sensor 32. The control unit 33 controls the voltage source 31 so that a current having a predetermined current density (for example, 30 mA / cm ² ) flows from the voltage source 31 to the energizing electrode 21 for a predetermined time (for example, 120 minutes). It is like that. The processing conditions for the anodizing step are not particularly limited, and the above-described predetermined current density and the above-mentioned predetermined time may be set as appropriate. In the anodizing step, energization is performed under a condition of a predetermined current density, but energization may be performed under a condition of a predetermined voltage.

By the way, when a part of the semiconductor substrate 10 made of a p-type silicon substrate is made porous in the anodic oxidation step, it is considered that the following reaction occurs when the hole is h ⁺ and the electron is e ^−. .
Si + 2HF + (2-n) h ⁺ → SiF ₂ + 2H ⁺ + ne ⁻
SiF ₂ + 2HF → SiF ₄ + H ₂
SiF ₄ + 2HF → SiH ₂ F ₆
That is, in the anodic oxidation of the semiconductor substrate 10 made of a p-type silicon substrate, it is known that porosity or electropolishing occurs due to the balance between the supply amount of F ions and the supply amount of holes h ^+. Porous formation occurs when the supply amount of H is greater than the supply amount of holes, and electropolishing occurs when the supply amount of holes h ⁺ is greater than the supply amount of F ions. Therefore, when a p-type silicon substrate is used as the semiconductor substrate 10 as in the present embodiment, the rate of porosity by anodic oxidation is determined by the supply amount of holes h ⁺ , and therefore flows in the semiconductor substrate 10. The speed of porous formation is determined by the current density of the current, and the thickness of the porous portion 14 is determined. In the present embodiment, current flows through the semiconductor substrate 10 along the path indicated by the arrow in FIG. 4, and therefore, on the other surface side (upper surface side in FIG. 4) of the semiconductor substrate 10, The in-plane distribution of the current density is such that the current density gradually increases as the distance from the center line (the center line along the thickness direction of the semiconductor substrate 10) increases, and is formed on the other surface side of the semiconductor substrate 10. The porous portion 14 is gradually thinner as it approaches the center line of the aperture 13 of the anode 12. The in-plane distribution of the current density described above corresponds to the distribution of the electric field strength in the semiconductor substrate 10 determined by the contact pattern between the anode 12 and the semiconductor substrate 10 when the anode 12 and the cathode are energized. The current density increases as the electric field strength increases, and the current density decreases as the electric field strength decreases.

  After the above-described anodic oxidation step is completed, a porous portion removing step for removing the porous portion 14 is performed. Here, if an alkaline solution (for example, an aqueous solution of KOH, NaOH, TMAH, etc.) or an HF solution is used as an etching solution for removing the porous portion 14 made of porous silicon, the porous portion 14 is removed. In the part removing step, the anode 12 formed of an Al film or an Al—Si film can also be removed by etching, and has a curved surface 2 formed of a convex curved surface as shown in FIGS. 1 (e) and 2 (b). Since the semiconductor lens 1 can be obtained, a dicing process for separating the individual semiconductor lenses 1 may be performed thereafter. Note that the porous portion removing step for removing the porous portion 14 and the anode removing step for removing the anode 12 may be performed separately. In addition, when an alkaline solution is used as an etching solution in the porous portion removing step for removing the porous portion 14 made of porous silicon, the porous portion 14 is removed by etching at room temperature without heating the etching solution. Can do.

  According to the method of forming the curved surface 2 of the present embodiment described above, the in-plane current density of the current flowing in the semiconductor substrate 10 in the anodic oxidation process is determined by the contact pattern between the anode 12 formed in the anode forming process and the semiconductor substrate 10. Since the distribution is determined, it is possible to control the in-plane distribution of the thickness of the porous portion 14 formed in the anodic oxidation step, and it is possible to form the porous portion 14 whose thickness is continuously changed. Since the curved surface 2 having a desired curved surface shape is formed by removing the porous portion 14 in the porous portion removing step, the smooth curved surface 2 having an arbitrary shape can be easily formed. Therefore, according to the manufacturing method of the semiconductor lens 1 described above, since the semiconductor lens 1 having a desired curved shape and a desired lens shape is formed, the semiconductor lens 1 having an arbitrary shape and a smooth surface can be easily formed. It becomes possible.

  Here, in the anode forming step in this embodiment, after forming the conductive layer 11 serving as the basis of the anode 12 on the one surface side of the semiconductor substrate 10, the circular opening 13 is provided in the conductive layer 11. Since the anode 12 is formed by patterning the conductive layer 11 as described above, the current density of the current flowing through the semiconductor substrate 10 on the other surface side of the semiconductor substrate 10 in the anodic oxidation step is the anode 12 (conductive layer). 11) Since the in-plane distribution becomes smaller as it approaches the center line of the aperture 13, the thickness of the porous portion 14 becomes closer to the center line of the aperture 13 of the anode 12 on the other surface side of the semiconductor substrate 10. Thus, the curved surface 2 can be a smooth aspheric convex curved surface, and a plano-convex aspheric lens having a smooth surface can be formed as the semiconductor lens 1. The optical axis of the semiconductor lens 1 formed in this way coincides with the center line of the aperture 13 described above.

  By the way, in the manufacturing method of the semiconductor lens 1 described above, the curved surface shape of the curved surface 2 is determined by the in-plane distribution of the current density of the current flowing through the semiconductor substrate 10 in the anodic oxidation process (in this embodiment, a plano-convex aspherical surface). Since the curvature radius and lens diameter of the curved surface 2 in the semiconductor lens 1 made of a lens are determined, the resistivity and thickness of the semiconductor substrate 10, the electrical resistance value of the electrolytic solution B used in the anodizing step, the semiconductor substrate 10 and the cathode 25. , The planar shape of the cathode 25 (the shape in a plane parallel to the semiconductor substrate 10 in a state of being opposed to the semiconductor substrate 10), the inner diameter of the circular aperture 13 in the anode 12, etc. By doing so, the curved surface shape according to the lens shape can be controlled.

  Here, the resistivity of the semiconductor substrate 10 may be set within a range of, for example, about several Ωcm to several hundred Ωcm, and the semiconductor lens 1 having the gently curved surface 2 having a larger curvature radius is formed as the resistivity decreases. It is possible to form the short focus semiconductor lens 1 having a smaller radius of curvature as the resistivity increases. Further, the shorter the semiconductor substrate 1, the shorter focal length semiconductor lens 1 having a smaller radius of curvature can be formed, and the thicker the thickness, the semiconductor lens 1 having the gently curved surface 2 having the larger radius of curvature can be formed. .

  In addition, the electrical resistance value of the electrolytic solution B can be adjusted, for example, by changing the concentration of the aqueous hydrogen fluoride solution or the mixing ratio of the aqueous hydrogen fluoride solution and ethanol. By appropriately setting conditions other than the shape of the anode 12 (for example, the electric resistance value of the electrolytic solution B), it becomes easier to control the curved surface shape according to the lens shape.

  Further, as the planar shape of the cathode 25, for example, as shown in FIG. 5A, in the state of being opposed to the semiconductor substrate 10, the opening 13 of the anode 12 (see FIG. 5C) and the center line A planar shape having a circular opening portion 25a (see FIG. 5B) that coincides with each other may be employed. Here, the inner diameter of the opening portion 25a of the cathode 25 is not necessarily set to the same value as the inner diameter of the opening portion 13 of the cathode 12, and the thickness of the semiconductor substrate 10, the electric resistance value of the electrolyte B, the cathode 25, and the like. It may be set as appropriate in consideration of the distance between the semiconductor substrate 10 and the semiconductor substrate 10. 5A schematically shows a path of current flowing through the semiconductor substrate 10, and a downward arrow in FIG. 5A shows a path of electrons moving in the electrolytic solution B. This is shown schematically.

  In addition, as a parameter for controlling the curved surface shape, there is an anodizing treatment time (the predetermined time) in the anodizing step, and the longer the treating time is, the thicker the porous portion 14 is, the thicker the porous portion 14 is. As the difference between the thickness of the portion and the thickness of the thin portion increases to form a curved surface with a small radius of curvature, and the processing time is short and the thickness of the porous portion 14 is reduced, the thickness of the thick portion and the thin portion in the porous portion 14 are reduced. The difference with the thickness of the film becomes small, and a curved surface with a large curvature radius can be formed.

  Further, in the above-described anodizing step, the control unit 33 controls the output voltage of the voltage source 31 so that the current density of the current detected by the current sensor 32 becomes a predetermined current density. However, if the current density is decreased continuously or stepwise before the end of energization to reduce the porosity and the porosity of the semiconductor substrate 10, the porous portion 14 is removed. It is possible to make the curved surface 2 after smoothing a smooth convex curved surface. In short, if the energization conditions are changed so that the porosity of the portion on the boundary side with the semiconductor substrate 10 is smaller than the porosity of the portion on the surface side in the porous portion 14 that is the removal site at the time of the energization, The porosity of the porous portion 14 at the boundary side with the semiconductor substrate 10 is smaller than the porosity of the surface side portion, and fine irregularities are formed on the curved surface 2 when the porous portion 14 is removed. Therefore, the semiconductor lens 1 having a smoother curved surface 2 can be formed.

Further, in the semiconductor lens 1 formed by the manufacturing method of the present embodiment, as shown in FIG. 6, the lens portion 1a and the flange portion 1b surrounding the lens portion 1a over the entire circumference may be formed continuously and integrally. It becomes possible. As an example, a disk-shaped silicon substrate (silicon wafer) having a diameter of 100 mm, a thickness of 0.5 mm, and a resistivity of 80 Ωcm is used as the semiconductor substrate 10, and the conductive layer 11 is used as a condition for the anode formation step. The aluminum film having a thickness of 1 μm, the sintering temperature of the conductive layer 11 is 420 ° C., the sintering time is 20 minutes, the inner diameter of the circular aperture 13 in the anode 12 is 2 mm, and the conditions of the anodizing step are electrolytic Liquid B is a hydrofluoric acid-based solution in which a 55 wt% aqueous solution of hydrogen fluoride and ethanol are mixed at a ratio of 1: 1, the predetermined current density is 30 mA / cm ² , and the predetermined time is 180 minutes. The condition is that the surface of the semiconductor lens 1 formed on the curved surface 2 side when the etching solution is 10% KOH aqueous solution and the etching time is 15 minutes (the surface of the lens portion 1a and the flange). FIG. 7 shows the result obtained by measuring the surface 1b) with a non-contact three-dimensional surface shape measuring device manufactured by Zygo, which can perform non-contact measurement of the surface shape using light interference. 7, the flat portion corresponds to the surface of the flange portion 1b, and the curved portion corresponds to the surface of the lens portion 1a. Here, the thickness of the porous portion 14 formed in the above-described anodic oxidation step gradually increases with increasing distance from the vicinity of the center line of the aperture 13 described above, and is about 0.00% near the center line of the aperture 13. About 105 mm (105 μm), the portion overlapping the anode 12 (the portion corresponding to the flange portion 1 b) was about 0.3 mm (300 μm). Further, the etching rate of the porous part 14 in the porous part removing step is 10 times or more than the etching rate of the semiconductor substrate 10, and the porous part 14 is selectively etched away from the semiconductor substrate 10 in about 15 minutes. be able to.

  By the way, when a technique for forming an oxide film as a removal site in the anodizing process as in the technique described in Patent Document 2 is used, anodization is used to form a curved surface having a height difference of several tens of μm. It is necessary to repeat the process and the oxide film removing process, and it is difficult to obtain a lens shape having a desired curved surface shape. On the other hand, in the method of forming a curved surface according to the present embodiment, as is clear from the above description, the curved surface 2 having a height difference of several hundred μm is formed by one anodizing step and one porous portion removing step. Therefore, it is not limited to a lens having a lens diameter of several hundreds μm or less, which is generally called a microlens, and even a lens having a lens diameter of about several mm has one anodic oxidation step and one porous portion. A removal step.

  As described above, the semiconductor lens 1 in which the lens 1a and the flange portion 1b are integrally formed integrally includes an infrared detection element (for example, a pyroelectric element, a thermopile, etc.) 60 like the infrared sensor shown in FIG. Since the flange portion 1b can be fixed to the peripheral portion of the window hole 51a on the rear surface of the front wall 51 in a state where the lens portion 1a is disposed in the window hole 51a formed in the front wall 51 of the accommodated case 50, FIG. As shown in FIG. 9, it can be easily attached to the case 50 as compared with the conventional infrared lens 200 formed by polishing a silicon substrate or a germanium substrate. The case 50 in the infrared sensor shown in FIG. 8 includes a bottomed cylindrical case body 50a whose rear surface is open and a base plate 50b that closes the rear surface of the case body 50a.

  By the way, in the above-described manufacturing method, the anode 12 provided with the circular opening 13 is formed in the anode forming step. However, the shape of the opening 13 is not a circular shape but a rectangular shape. For example, a plano-convex cylindrical lens as shown in FIG. 10 can be formed as the semiconductor lens 1.

(Embodiment 2)
The manufacturing method of the semiconductor lens 1 of the present embodiment is substantially the same as that of the first embodiment, and a plano-concave aspheric lens having a curved surface 2 formed as a concave curved surface as shown in FIGS. 11B and 12 is formed. For this reason, the only difference is that the planar shape of the anode 12 is circular as shown in FIG. 11A (that is, the contact pattern between the anode 12 and the semiconductor substrate 10 is circular). This will be briefly described with reference to FIG.

  First, by performing an anode forming step of forming an anode 12 having a circular planar shape on one surface side (the lower surface side of FIG. 13A) of a semiconductor substrate 10 made of a p-type silicon substrate, FIG. ) Is obtained.

  Thereafter, a porous portion 14 made of porous silicon is formed on the other surface side of the semiconductor substrate 10 (upper surface side in FIG. 13A) in the anodizing step, thereby obtaining the structure shown in FIG. 13B. Here, the porous portion 14 is formed in a shape in which the thickness gradually decreases as the distance from the center line of the anode 12 along the thickness direction of the semiconductor substrate 10 increases.

  Subsequently, by removing the porous portion 14 in the porous portion removing step, the curved surface 2 having a concave curved surface is formed on the other surface side of the semiconductor substrate 10, thereby forming a plano-concave type having the structure shown in FIG. An aspheric lens is obtained.

  By the way, in the manufacturing method described above, the anode 12 having a circular planar shape is formed in the anode forming step. However, if the anode 12 having a rectangular planar shape is formed (that is, the anode 12 and the semiconductor substrate 10 are formed). If the contact pattern is rectangular), a plano-concave cylindrical lens can be formed as the semiconductor lens 1. The planar shape of the anode 12 may be appropriately designed according to a desired curved surface shape, and is not limited to a circular shape or a rectangular shape, and may be a square shape, for example.

(Embodiment 3)
The manufacturing method of the semiconductor lens 1 of the present embodiment is substantially the same as that of the first embodiment. In the first embodiment, the anode 12 having the circular aperture 13 is formed in the anode forming step. before the anode formation step, the anode 12 and the semiconductor substrate 10 and the circular that pattern design in accordance with the contact pattern of the insulating layer 15 (see FIG. 14) a semiconductor substrate 10 of the one front surface on (lower side in FIG. 14 In the anode forming step, the conductive layer is in contact with the insulating layer 15 and the exposed portion of the one surface of the semiconductor substrate 10 on the one surface side of the semiconductor substrate 10 as shown in FIG. The difference is that the anode 12 made of a conductive layer (for example, an Al film, an Al—Si film, etc.) is formed. Since other steps are the same as those in the first embodiment, description thereof is omitted.

In the above insulating layer forming step, the insulating film underlying the insulating layer 15 on the one front surface of the semiconductor substrate 10 (e.g., a silicon oxide film, a silicon nitride film, etc.) forming a photolithography technique and an etching technique The insulating layer 15 is formed by patterning the insulating film into a circular shape using the above.

  Thus, in the present embodiment, the contact pattern of the anode 12 with respect to the semiconductor substrate 10 is determined by the pattern of the insulating layer 15 formed in the insulating layer forming step, and the semiconductor substrate in the anodic oxidation step is determined by the contact pattern and the pattern of the insulating layer 15. Since the in-plane distribution of the current density of the current flowing through 10 is determined, the in-plane distribution of the thickness of the porous portion 14 formed in the anodic oxidation process can be controlled as in the first embodiment, and the thickness is continuously increased. It is possible to form a porous portion 14 made of changed porous silicon, and a desired curved surface is formed by removing the porous portion 14 in the porous portion removing step. It is possible to form a smooth curved surface with a shape. Therefore, according to the semiconductor lens manufacturing method using this curved surface forming method, a semiconductor lens having a desired lens shape is formed, so that it is possible to easily form a semiconductor lens having an arbitrary shape and a smooth surface. become.

  Here, in the present embodiment, the insulating layer 15 in which the current density of the current flowing through the semiconductor substrate 10 on the other surface side (the upper surface side in FIG. 14) of the semiconductor substrate 10 in the anodic oxidation process coincides with the thickness direction of the semiconductor substrate 10. Since the in-plane distribution becomes smaller as it approaches the center line of the semiconductor substrate 10, on the other surface side of the semiconductor substrate 10, the thickness of the porous portion 14 becomes thinner as the center line of the insulating layer 15 is approached, and the aspherical lens is smooth as a curved surface. Therefore, an aspherical lens having a smooth surface can be formed as a semiconductor lens. The optical axis of the semiconductor lens thus formed coincides with the center line of the insulating layer 15.

  In this embodiment, since the insulating layer 15 is composed of an insulating film made of a silicon oxide film or a silicon nitride film, the insulating layer 15 can generally be easily formed by a semiconductor manufacturing process. Since the position accuracy and the pattern accuracy of 15 can be increased, the accuracy of the curved surface can be increased and a semiconductor lens with less distortion can be formed. The insulating film is not limited to a silicon-based insulating film such as a silicon oxide film or a silicon nitride film, and may be formed of an organic material such as a resist.

  In the present embodiment, since the contact pattern between the anode 12 and the semiconductor substrate 10 and the pattern of the insulating layer 15 control the in-plane distribution of the current density of the current flowing through the semiconductor substrate 10 in the anodic oxidation process, Thus, compared to the case where the in-plane distribution of the current density is controlled mainly only by the contact pattern between the anode 12 and the semiconductor substrate 10, it is possible to use a semiconductor substrate having a lower resistivity.

  In the present embodiment, the insulating layer 15 is a circular pattern. However, the pattern of the insulating layer 15 may be appropriately designed according to a desired curved surface shape. For example, the insulating layer 15 may be square or rectangular. If the rectangular pattern 15 is formed, a convex curved surface of the cylindrical lens can be formed, and if the insulating layer 15 is formed in a pattern having a circular aperture, an aspherical lens having a concave curved surface is formed. In addition, if the insulating layer 15 is formed in a pattern having a rectangular aperture, a cylindrical lens having a concave curved surface can be formed.

(Embodiment 4)
In the present embodiment, as a method for manufacturing the semiconductor lens 1, a biconvex aspherical lens having a curved surface 2 made of a convex curved surface on the upper surface side and a curved surface 3 made of a convex curved surface on the lower surface side in FIG. The manufacturing method will be described with reference to FIG. 15, but description of steps similar to those in Embodiment 1 will be omitted as appropriate.

  First, a predetermined film thickness serving as a basis for the anode 12 (see FIG. 15C) used in the anodizing process on one surface side (the lower surface side in FIG. 15A) of the semiconductor substrate 10 shown in FIG. A structure shown in FIG. 15B is obtained by performing a conductive layer forming step of forming the conductive layer 11 made of a conductive film (for example, 1 μm) (for example, an Al film, an Al—Si film, etc.). .

After the conductive layer forming step, a patterning step for patterning the conductive layer 11 so as to provide the circular opening 13 in the conductive layer 11 is performed, thereby obtaining the structure shown in FIG. In the conductive layer forming step and patterning step (here, the shape of the curved surface 2) a desired curved shape called anode (hereinafter set the contact pattern of the semiconductor substrate 10, a first anode according to ) 12 is formed (hereinafter referred to as a first anode forming step).

  After the patterning step, a cathode (hereinafter referred to as a first electrode) disposed opposite to the other surface side (the upper surface side of FIG. 15A) of the semiconductor substrate 10 in an electrolyte for anodization (hereinafter referred to as a first electrolyte). The porous portion 14 (hereinafter referred to as the first porous portion) made of porous silicon which becomes a removal site on the other surface side of the semiconductor substrate 10 by energizing between the first anode 12 and the first anode 12. The structure shown in FIG. 15D is obtained by performing an anodic oxidation step (hereinafter referred to as a first anodic oxidation step).

  After the end of the first anodizing step, a porous portion removing step for removing the first porous portion 14 (hereinafter referred to as a first porous portion removing step) is performed. Here, if an alkaline solution or an HF solution is used as an etching solution for removing the first porous portion 14 as in the first embodiment, the first anode 12 is also etched in the first porous portion removing step. The structure shown in FIG. 15E can be obtained.

  After the first porous portion removing step, the other surface side where the curved surface 2 is formed by removing the first porous portion 14 in the semiconductor substrate 10 is formed in the same manner as the first anode forming step. By forming the second anode 17 having a contact pattern with the semiconductor substrate 10 according to another desired curved surface shape (here, the shape of the curved surface 3), the structure shown in FIG. 15F is obtained. The second anode 17 is formed so as to be in ohmic contact with the semiconductor substrate 10, similarly to the first anode 12. Further, the contact pattern of the second anode 17 is designed so that a circular opening portion whose center line coincides with the circular opening portion 13 of the first anode 12 is provided.

  Thereafter, a current is passed between the second cathode 17 and the second anode 17 disposed opposite to the one surface side of the semiconductor substrate 10 in the second electrolytic solution for anodic oxidation, and the one surface side of the semiconductor substrate 10. By performing a second anodic oxidation step for forming the second porous portion 18 made of porous silicon to be a removal site, a structure shown in FIG. 15G is obtained. As the second electrolytic solution, a hydrofluoric acid solution is used as in the first electrolytic solution, and platinum is adopted as the material of the second cathode as in the first cathode.

  After the completion of the second anodizing step, a second porous portion removing step for removing the second porous portion 18 is performed. Here, if an alkaline solution or an HF-based solution is used as an etching solution for removing the second porous portion 18 as in the first porous portion removing step, the second porous portion removing step uses the second porous portion 18 in the second porous portion removing step. The anode 17 can also be removed by etching, and the semiconductor lens 1 having the curved surfaces 2 and 3 shown in FIG. 15H can be obtained. Thereafter, a dicing process for separating the individual semiconductor lenses 1 is performed. Just do it. Note that the second porous portion removing step for removing the second porous portion 18 and the second anode removing step for removing the second anode 17 may be performed separately.

  Thus, in the manufacturing method of the present embodiment, a biconvex aspherical lens having a smooth surface can be formed as the semiconductor lens 1.

(Embodiment 5)
In the present embodiment, as a method for manufacturing the semiconductor lens 1, a manufacturing method for manufacturing a concavo-convex aspherical lens having a concave curved surface 2 and a convex curved surface 3 as shown in FIG. 16 will be described with reference to FIG. 16, but the description of the same steps as those in the first embodiment will be omitted as appropriate. In the present embodiment, a semiconductor substrate 10 having a p-type conductivity is used as in the first embodiment, but the impurity concentration is a low impurity concentration of 1 × 10 ¹⁶ cm ⁻³ or less, and the resistivity Is 1 Ωcm or more. In addition, each center line described below means a center line along the thickness direction of the semiconductor substrate 10 as in the first embodiment.

  First, a circular anode in which a contact pattern with the semiconductor substrate 10 is designed according to a desired curved surface shape (here, the shape of the curved surface 2) on one surface side of the semiconductor substrate 10 (the lower surface side in FIG. 16A). A structure shown in FIG. 16A is obtained by performing an anode formation step (hereinafter referred to as a first anodic oxidation step) for forming 12 (hereinafter referred to as a first anode). Here, the first anode 12 needs to be formed so that the center line coincides with the center line of the region where the semiconductor lens 1 is to be formed in the semiconductor substrate 10.

  After the first anode forming step, the cathode disposed opposite to the other surface side (the upper surface side of FIG. 16A) of the semiconductor substrate 10 in the electrolytic solution for anodic oxidation (hereinafter referred to as the first electrolytic solution). (Hereinafter referred to as a first cathode) and a first anode 12 and a porous portion 14 (hereinafter referred to as a first cathode) made of porous silicon which becomes a removal site on the other surface side of the semiconductor substrate 10 by energization. The structure shown in FIG. 16B is obtained by performing an anodic oxidation step (hereinafter referred to as a first anodic oxidation step) for forming a porous portion 14). In the first anodic oxidation step, the current flows more easily in the region where the first anode 12 is formed in the semiconductor substrate 10, and it becomes difficult for the current to flow gradually away from the region. Of these, the current density in the region overlapping the first anode 12 is increased, and the first porous portion 13 is gradually reduced in thickness as the distance from the center line of the first anode 12 increases.

  After the first anodizing step, performing the first porous portion removing step of forming the curved surface 2 formed of a concave curved surface on the other surface side of the semiconductor substrate 10 by removing the first porous portion 14. Thus, the structure shown in FIG. Here, since the alkaline solution is used as the etching solution for removing the first porous portion 14 as in the first embodiment, the first anode 12 is also used when the first porous portion 14 is removed. Can be removed. Depending on the material of the first anode 12, the porous portion removing step for removing the first porous portion 14 and the anode removing step for removing the first anode 12 may be performed separately.

  After the first porous portion removing step, a second anode 17 is formed which has a second anode 17 designed with a contact pattern with the semiconductor substrate 10 in accordance with another desired curved surface shape (here, the shape of the curved surface 3). By performing the anode forming step, the structure shown in FIG. The second anode 17 has a circular opening 17a, and the dimensions of the opening 17a are designed based on the desired radius of curvature of the curved surface 3. The second anode 17 is formed so as to be in ohmic contact with the semiconductor substrate 10, similarly to the first anode 12.

  After the second anode forming step described above, a current is passed between the second cathode 17 and the second anode 17 disposed opposite to the one surface side of the semiconductor substrate 10 in the second electrolytic solution for anodization. A structure shown in FIG. 16E is obtained by performing a second anodic oxidation step for forming a second porous portion 18 made of porous silicon that becomes a removal site on the one surface side of the semiconductor substrate 10. . The second electrolytic solution is the same hydrofluoric acid solution as the first electrolytic solution, and the second cathode material is platinum as in the first cathode. Here, in the second anodic oxidation step, the second anode 17 on the other surface side of the semiconductor substrate 10 is formed around the curved surface 2 (in other words, not formed on the curved surface 2). The current density of the current flowing through the semiconductor substrate 10 decreases as it approaches the center line of the opening 17a of the second anode 17 (that is, the current density decreases in the in-plane distribution as it approaches the center line passing through the center of the curved surface 2). ), The second porous portion 18 formed on the one surface side of the semiconductor substrate 10 is gradually thinner toward the center line of the curved surface 2.

  After the second anodic oxidation step, a second porous portion removing step is performed in which the second porous portion 18 is removed to form the curved surface 3 having a convex curved surface on the one surface side of the semiconductor substrate 10. Thus, the semiconductor lens 1 having the curved surfaces 2 and 3 shown in FIG. 16 (f) can be obtained. In this embodiment, since the alkaline solution described in the first embodiment is used as the etching solution for removing the second porous portion 18, the second porous portion 18 is removed when the second porous portion 18 is removed. The second anode 17 can also be removed. Note that the second anode 17 is not necessarily removed, and may be left as an infrared light shielding mask in the semiconductor lens 1. Since the semiconductor substrate 10 is in a wafer state until the second porous portion removing step, a dicing step for separating the wafer from the wafer into individual semiconductor lenses 1 may be performed after the second porous portion removing step. .

  According to the manufacturing method of the semiconductor lens 1 of the present embodiment described above, the semiconductor substrate in the first anodic oxidation step is formed by the contact pattern between the first anode 12 and the semiconductor substrate 10 formed in the first anode forming step. Since the in-plane distribution of the current density of the current flowing through 10 is determined, the in-plane distribution of the thickness of the first porous portion 14 formed in the first anode forming step can be easily controlled, and as a result, the first The curved surface 2 having a desired radius of curvature can be formed in the porous portion removing step, and the in-plane distribution of the thickness of the semiconductor substrate 10 and the second anode forming step after the first porous portion removing step. The in-plane distribution of the current density of the current flowing in the semiconductor substrate 10 in the second anodic oxidation step is determined by the contact pattern between the second anode 17 and the semiconductor substrate 10 formed in step 2, and as a result, the second porous Desired music in the part removal process Since the curved surface 3 having a radius can be formed, the semiconductor lens 1 constituting a concave / convex lens in which the curvature radius of the curved surface 2 made of a concave curved surface and the curvature radius of the curved surface 3 made of a convex curved surface are larger than the thickness of the semiconductor substrate 10. Can be easily formed. The optical axis of the semiconductor lens 1 formed by the manufacturing method described above coincides with the center line of the first anode 12 and the center line of the aperture 17a of the second anode 17 described above.

(Embodiment 6)
In the present embodiment, as a method for manufacturing the semiconductor lens 1, a manufacturing method for manufacturing a concavo-convex aspherical lens having a concave curved surface 3 and a convex curved surface 2 as shown in FIG. Although description will be made with reference to FIG. 17, description of steps similar to those of the first embodiment will be omitted as appropriate. In the present embodiment, a semiconductor substrate 10 having a p-type conductivity is used as in the first embodiment, but the impurity concentration is a low impurity concentration of 1 × 10 ¹⁶ cm ⁻³ or less, and the resistivity Is 1 Ωcm or more. In addition, each center line described below means a center line along the thickness direction of the semiconductor substrate 10 as in the first embodiment.

  First, an anode (hereinafter referred to as a contact pattern) designed with a semiconductor substrate 10 according to a desired curved surface shape (here, the shape of the curved surface 2) on one surface side of the semiconductor substrate 10 (the lower surface side in FIG. 17A). A structure shown in FIG. 17A is obtained by performing an anode forming step (hereinafter referred to as a first anodic oxidation step) for forming a first anode 12. Here, the first anode 12 has an opening 13 whose center line coincides with the center line of the region where the semiconductor lens 1 is to be formed in the semiconductor substrate 10.

  After the first anode forming step, the cathode disposed opposite to the other surface side of the semiconductor substrate 10 (upper surface side in FIG. 17A) in an electrolytic solution for anodic oxidation (hereinafter referred to as the first electrolytic solution). (Hereinafter referred to as a first cathode) and a first anode 12 and a porous portion 14 (hereinafter referred to as a first cathode) made of porous silicon which becomes a removal site on the other surface side of the semiconductor substrate 10 by energization. The structure shown in FIG. 17B is obtained by performing an anodic oxidation step (hereinafter referred to as a first anodic oxidation step) for forming a porous portion 14).

  After the first anodizing step, the porous portion removing step (hereinafter referred to as the first porous portion 14) is formed by removing the first porous portion 14 to form the curved surface 2 having a convex curved surface on the other surface side of the semiconductor substrate 10. (Referred to as a porous portion removing step), and then the semiconductor substrate 10 and the semiconductor substrate 10 according to another desired curved surface shape (here, the shape of the curved surface 3) at the central portion of the curved surface 2 on the other surface side of the semiconductor substrate 10 The structure shown in FIG. 17C is obtained by performing the second anode forming step for forming the circular second anode 17 in which the contact pattern is designed. The second anode 17 needs to be formed so that the center line coincides with the center line of the region where the semiconductor lens 1 is to be formed (the center line of the curved surface 2) and has a diameter smaller than the lens diameter. The second anode 17 is formed so as to be in ohmic contact with the semiconductor substrate 10, similarly to the first anode 12.

  After the second anode forming step described above, a second cathode and a second anode 17 which are disposed opposite to the one surface side of the semiconductor substrate 10 in the second electrolyte solution placed in the treatment tank for anodization, 17 (d) by conducting a second anodic oxidation step of forming a second porous portion 18 made of porous silicon which becomes a removal site on the one surface side of the semiconductor substrate 10 by energizing the semiconductor substrate 10 The structure shown in is obtained. The second electrolytic solution is the same hydrofluoric acid solution as the first electrolytic solution, and the second cathode material is platinum as in the first cathode. Here, in the second anodic oxidation step, since the second anode 17 on the other surface side of the semiconductor substrate 10 is formed at the center of the curved surface 2 having a convex curved surface, the current flowing through the semiconductor substrate 10 The density has an in-plane distribution in which the current density decreases as the distance from the second anode 17 increases, and the second porous portion 18 formed on the one surface side of the semiconductor substrate 10 has the second anode 17. The distance from the center line gradually decreases.

  After the second anodic oxidation step, a second porous portion removing step is performed in which the second porous portion 18 is removed to form the curved surface 3 having a concave curved surface on the one surface side of the semiconductor substrate 10. Thus, the semiconductor lens 1 having the curved curved surfaces 2 and 3 shown in FIG. 17E can be obtained. In this embodiment, since the alkaline solution described in the first embodiment is used as the etching solution for removing the second porous portion 18, the second porous portion 18 is removed when the second porous portion 18 is removed. The second anode 17 can also be removed. Note that the second anode 17 is not necessarily removed, and may be left as an infrared light shielding mask in the semiconductor lens 1. Since the semiconductor substrate 10 is in a wafer state until the second porous portion removing step, a dicing step for separating the wafer from the wafer into individual semiconductor lenses 1 may be performed after the second porous portion removing step. .

  According to the manufacturing method of the semiconductor lens 1 of the present embodiment described above, the semiconductor substrate in the first anodic oxidation step is formed by the contact pattern between the first anode 12 and the semiconductor substrate 10 formed in the first anode forming step. Since the in-plane distribution of the current density of the current flowing through 10 is determined, the in-plane distribution of the thickness of the first porous portion 14 formed in the first anode forming step can be easily controlled, and as a result, the first The curved surface 2 formed of a convex curved surface having a desired radius of curvature can be formed in the porous portion removing step, and the in-plane distribution of the thickness of the semiconductor substrate 10 after the first porous portion removing step and the second The in-plane distribution of the current density of the current flowing through the semiconductor substrate 10 in the second anodic oxidation step is determined by the contact pattern between the second anode 17 and the semiconductor substrate 10 formed in the anode forming step. 2 Porous part removal work Since the curved surface 3 made of a concave curved surface having a desired radius of curvature can be formed by the above, the curvature radius of the curved surface 3 made of a concave curved surface and the curvature radius of the curved surface 2 made of a convex curved surface are respectively compared with the thickness of the semiconductor substrate 10. The semiconductor lens 1 constituting a large concave lens can be easily formed. The optical axis of the semiconductor lens 1 formed by the manufacturing method described above coincides with the center line of the aperture 13 of the first anode 12 and the center line of the second anode 17.

(Embodiment 7)
In the present embodiment, as a method of manufacturing the semiconductor lens 1, manufacturing a biconcave aspherical lens having a curved surface 2 formed of a concave curved surface on the lower surface side and a curved surface 3 formed of a concave curved surface on the upper surface side in FIG. The method will be described with reference to FIG. 18, but description of steps similar to those of the first embodiment will be omitted as appropriate. In the present embodiment, a semiconductor substrate 10 having a p-type conductivity is used as in the first embodiment, but the impurity concentration is a low impurity concentration of 1 × 10 ¹⁶ cm ⁻³ or less, and the resistivity Is 1 Ωcm or more. In addition, each center line described below means a center line along the thickness direction of the semiconductor substrate 10 as in the first embodiment.

  First, a circular anode in which a contact pattern with the semiconductor substrate 10 is designed according to a desired curved surface shape (here, the shape of the curved surface 2) on one surface side of the semiconductor substrate 10 (the lower surface side in FIG. 18A). A structure shown in FIG. 18A is obtained by performing an anode formation step (hereinafter referred to as a first anodic oxidation step) for forming 12 (hereinafter referred to as a first anode). Here, the first anode 12 needs to be formed so that the center line coincides with the center line of the region where the semiconductor lens 1 is to be formed in the semiconductor substrate 10.

  After the first anode forming step, the cathode disposed opposite to the other surface side of the semiconductor substrate 10 (the upper surface side in FIG. 18A) in the electrolytic solution for anodic oxidation (hereinafter referred to as the first electrolytic solution). (Hereinafter referred to as a first cathode) and a first anode 12 and a porous portion 14 (hereinafter referred to as a first cathode) made of porous silicon which becomes a removal site on the other surface side of the semiconductor substrate 10 by energization. The structure shown in FIG. 18B is obtained by performing an anodic oxidation step (hereinafter referred to as a first anodic oxidation step) for forming a porous portion 14). In the first anodic oxidation step, the current flows more easily in the region where the first anode 12 is formed in the semiconductor substrate 10, and it becomes difficult for the current to flow gradually away from the region. Of these, the current density in the region overlapping the first anode 12 is increased, and the first porous portion 13 is gradually reduced in thickness as the distance from the center line of the first anode 12 increases.

  After the first anodic oxidation step, the first porous portion 14 is removed to perform the first porous portion removing step of forming the curved surface 2 on the other surface side of the semiconductor substrate 10 as shown in FIG. The structure shown in (c) is obtained. Here, since the alkaline solution described in the first embodiment is used as the etching solution for removing the first porous portion 14, the first anode 12 is removed when the first porous portion 14 is removed. Can also be removed. Depending on the material of the first anode 12, the porous portion removing step for removing the first porous portion 14 and the anode removing step for removing the first anode 12 may be performed separately.

By performing an insulating film forming step of forming an insulating film 19 made of a SiO ₂ film having a predetermined film thickness (for example, 200 nm) on the entire surface of the other surface side of the semiconductor substrate 10 after the first porous portion removing step. 18D to obtain the structure shown in FIG. Here, the insulating film 19 may be formed by a general thin film forming technique such as a CVD method. The insulating film 19 is not limited to the SiO ₂ film, and the SiO ₂ film except an inorganic film such as a SiON film or _{the Si} 3 _{N 4} film, or an organic film such as a resist film.

  After the insulating film forming step, the curved surface 2 is formed on the insulating film 19 by forming a circular opening 19a having a dimension (inner diameter) designed based on another desired curved surface shape (here, the shape of the curved surface 3). 18 (e) by performing a second anode forming step of forming a second anode 17 on the entire surface of the other surface side of the semiconductor substrate 10 after performing a hole forming step for exposing a part of the semiconductor substrate 10. ) Is obtained. In other words, the contact pattern with the curved surface 2 of the semiconductor substrate 10 is designed for the second anode 17 according to the shape of the curved surface 3. The second anode 17 is formed so as to be in ohmic contact with the semiconductor substrate 10, similarly to the first anode 12.

  After the second anode forming step, the second cathode and the second cathode disposed opposite to the one surface side of the semiconductor substrate 10 in the second electrolytic solution placed in a treatment tank (not shown) for anodization. By conducting a second anodic oxidation step of forming a second porous portion 18 made of porous silicon which becomes a removal site on the one surface side of the semiconductor substrate 10 by energizing between the anode 17 and FIG. The structure shown in (e) is obtained. As the second electrolytic solution, a mixed solution in which a 55 wt% aqueous solution of hydrogen fluoride and ethanol are mixed at a ratio of 1: 1 as in the first electrolytic solution is used. Similar to the cathode of No. 1, platinum is adopted. Here, in the second anodic oxidation step, only a part of the second anode 17 is directly formed on the curved surface 2 through the opening portion 19a of the insulating film 19 on the other surface side of the silicon substrate 10. Is formed on the insulating film 19, the current density of the current flowing through the semiconductor substrate 10 gradually decreases as the distance from the center line of the second anode 17 increases (that is, the in-plane distribution of the current density is As the distance from the center line passing through the center of the curved surface 2 becomes smaller, the current density becomes in-plane distribution), and the second porous portion 18 formed on the one surface side of the semiconductor substrate 10 is separated from the center line of the curved surface 2. It is getting thinner gradually. That is, since the second porous portion 18 is formed over a wider range than the opening portion 19a, the inner diameter of the above-described opening portion 19a needs to be smaller than the lens diameter of the desired semiconductor lens 1. is there.

  After the second anodic oxidation step, a second porous portion removing step for removing the second porous portion 18 to form the curved surface 3 on the one surface side of the semiconductor substrate 10 is performed. By removing the anode 17 and the insulating film 19 to remove the curved surface 2 again, the semiconductor lens 1 having the structure shown in FIG. 18F can be obtained. In the present embodiment, if an HF-based solution is used as an etching solution for removing the second porous portion 18, the second anode is removed in the second porous portion removing step for removing the second porous portion 18. 17 and the insulating film 19 can also be removed. In addition, if the alkaline solution described in the first embodiment is used in the second porous portion removing step, the second anode 17 can also be removed when the second porous portion 18 is removed. After the second porous portion removing step, the insulating film 19 may be removed by wet etching or dry etching with an HF-based solution.

  According to the manufacturing method of the semiconductor lens 1 of the present embodiment described above, the semiconductor substrate in the first anodic oxidation step is formed by the contact pattern between the first anode 12 and the semiconductor substrate 10 formed in the first anode forming step. Since the in-plane distribution of the current density of the current flowing through 10 is determined, the in-plane distribution of the thickness of the first porous portion 14 formed in the first anode forming step can be easily controlled, and as a result, the first The curved surface 2 formed of a concave curved surface having a desired radius of curvature can be formed in the porous portion removing step, and the in-plane distribution of the thickness of the semiconductor substrate 10 after the first porous portion removing step and the second Of the second anode 17 formed in the anode forming step, the pattern of the portion directly formed on the curved surface 2 (that is, the contact pattern between the second anode 17 and the semiconductor substrate 10) is used as the second anodic oxidation step. In the semiconductor substrate 10 Since the in-plane distribution of the current density of the current to be determined is determined, it is possible to form the curved surface 3 composed of the concave curved surface having a desired radius of curvature in the second porous portion removing step. It is possible to easily form the semiconductor lens 1 constituting a biconcave lens having a radius of curvature larger than the thickness of the semiconductor substrate 10. The optical axis of the semiconductor lens 1 formed by the manufacturing method described above coincides with the center line of the first anode 12 and the center line of the opening 19a of the insulating film 19. In addition, the pattern of the insulating film 19 may be appropriately designed according to a desired curved surface shape, for example, a shape having a square-shaped opening portion, a shape having a rectangular opening portion, a square shape, or a rectangular shape. It is good also as a shape.

  By the way, in each said embodiment, although the p-type silicon substrate is employ | adopted as the semiconductor substrate 10, the conductivity type of the semiconductor substrate 10 may be not only p-type but n-type. Further, the material of the semiconductor substrate 10 is not limited to Si, and may be any semiconductor material that can be made porous by anodic oxidation. For example, Ge, SiC, GaAs, GaP, InP, or the like may be used. Here, as an electrolytic solution for removing oxides of constituent elements of the semiconductor substrate 10, for example, an electrolytic solution as shown in Table 1 below may be used.

  In each of the above embodiments, a single lens such as a plano-convex lens, a plano-concave lens, a biconvex lens, a biconcave lens, a concavo-convex lens, and a cylindrical lens has been described as the semiconductor lens 1. However, according to the technical idea of the present invention, a single lens is used. In addition to the above, it is possible to form so-called multi-lenses in which adjacent single lenses overlap each other, so-called array lenses in which the above-mentioned single lenses are arranged in an array, or lenses in which a plurality of types of single lenses are combined. It becomes.

  Further, in each of the above embodiments, the example in which the curved surface forming method is used in the manufacturing method of the semiconductor lens 1 has been described. For example, wiring caused by steps or corners of a structure formed using a semiconductor substrate in a MEMS device. In order to prevent disconnection and stress concentration, the curved surface forming method of the present invention may be used.

FIG. 6 is an explanatory diagram of the semiconductor lens manufacturing method according to the first embodiment. It is explanatory drawing of a manufacturing method same as the above. It is a schematic block diagram of the anodizing apparatus used with the manufacturing method same as the above. It is explanatory drawing of a manufacturing method same as the above. It is explanatory drawing of a manufacturing method same as the above. The semiconductor lens in the same as above is shown, (a) is a schematic plan view, and (b) is a schematic sectional view. It is a measurement figure of the surface shape of the semiconductor lens manufactured by the manufacturing method same as the above. It is a schematic block diagram of the infrared sensor provided with the semiconductor lens in the same as the above. The comparative example of the semiconductor lens in the same as above is shown, (a) is a schematic plan view, and (b) is a schematic sectional view. It is a schematic perspective view of the semiconductor lens formed by the other manufacturing method same as the above. 6 is an explanatory diagram of a method for manufacturing a semiconductor lens in Embodiment 2. FIG. It is a schematic perspective view of the semiconductor lens in the same as the above. It is explanatory drawing of the manufacturing method of the semiconductor lens in the same as the above. FIG. 10 is a main process sectional view for explaining the method for manufacturing a semiconductor lens in the third embodiment. It is explanatory drawing of the manufacturing method of the semiconductor lens in Embodiment 4. It is explanatory drawing of the manufacturing method of the silicon lens in Embodiment 5. It is explanatory drawing of the manufacturing method of the semiconductor lens in Embodiment 6. It is explanatory drawing of the manufacturing method of the semiconductor lens in Embodiment 7. It is explanatory drawing of the manufacturing method of the conventional metal mold | die for microlenses.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor lens 2 Curved surface 3 Curved surface 10 Semiconductor substrate 11 Conductive layer 12 Anode (1st anode)
13 Opening portion 14 Porous portion (first porous portion)
15 Insulating layer 17 Anode (second anode)
18 Porous part (second porous part)
19 Insulating film 19a Opening part

Claims (11)

A method of forming a curved surface by removing a part of a semiconductor substrate to form a curved surface that is convex in the thickness direction of the semiconductor substrate or a concave curved surface that is recessed in the thickness direction , depending on a desired curved surface shape An anode forming step of forming an anode with a contact pattern designed on the semiconductor substrate on one surface side of the semiconductor substrate, and an anode and an anode disposed opposite to the other surface side of the semiconductor substrate in the electrolytic solution after the anode forming step has an anode oxidation step of forming a porous portion made of a removal site to the other surface side of the semiconductor substrate by energizing between, and a porous portion removing step of removing the multi-porous portion even after the anodization step In the anode forming step, an anode is formed on the one surface of the semiconductor substrate so that the contact between the anode and the semiconductor substrate becomes ohmic contact, and in the anodic oxidation step, an oxide of a constituent element of the semiconductor substrate is used as an electrolytic solution. Etch It curved forming method which comprises using a solution grayed removed.   In the anode forming step, after forming a conductive layer serving as a basis for the anode on the one surface of the semiconductor substrate, the conductive layer is patterned so as to provide a circular opening in the conductive layer. The method for forming a curved surface according to claim 1, wherein the anode is formed.   The said anode formation process forms as the said anode the electroconductive layer by which the said contact pattern with the said semiconductor substrate was designed circularly on the said one surface of the said semiconductor substrate. Method for forming a curved surface.   Prior to the anode forming step, an insulating layer forming step of forming an insulating layer having a pattern designed according to the contact pattern on the one surface of the semiconductor substrate. In the anode forming step, as the anode, 2. The method of forming a curved surface according to claim 1, wherein an insulating layer and a conductive layer in contact with the one surface are formed on the one surface side of the semiconductor substrate.   In the insulating layer forming step, an insulating film serving as a basis of the insulating layer is formed on the one surface of the semiconductor substrate, and then the insulating film is patterned into a circular shape to form the insulating layer. The method for forming a curved surface according to claim 4.   6. The method of forming a curved surface according to claim 4, wherein the insulating layer is made of a silicon oxide film or a silicon nitride film.   The porous portion removing step is a first porous portion removing step of removing the first porous portion which is the porous portion, and after the first porous portion removing step, another desired curved surface shape A second anode forming step for forming a second anode having a contact pattern with the semiconductor substrate according to the second surface side of the semiconductor substrate, and the one of the semiconductor substrates in a second electrolyte solution. A second anodic oxidation step of forming a second porous portion serving as a removal site on the one surface side of the semiconductor substrate by energizing between a second cathode and a second anode arranged opposite to each other on the surface side And a second porous portion removing step for removing the second porous portion, and in the second anode forming step, the contact between the second anode and the semiconductor substrate is an ohmic contact. A second anode is formed on the other surface side of the semiconductor substrate. In the second anodic oxidation step, As an electrolyte solution, the curved surface forming method according to any one of claims 1 to 6, characterized by using a solution of oxide is etched off of the constituent elements of the semiconductor substrate.   Before the second anode forming step, an insulating film having a pattern designed according to the contact pattern between the second anode and the semiconductor substrate is formed on the other surface side of the semiconductor substrate, and the second anode is formed. 8. The method of forming a curved surface according to claim 7, wherein, in the anode forming step, an insulating film and a conductive layer in contact with the other surface are formed on the other surface side of the semiconductor substrate as the second anode. . 9. The method according to claim 1 , wherein a silicon substrate is used as the semiconductor substrate, and a hydrofluoric acid solution is used as the solution so that porous silicon is formed as the porous portion. The method of forming a curved surface as described.   10. The method for forming a curved surface according to claim 1, wherein the semiconductor substrate has a p-type conductivity.   11. The energization condition is changed so that the porosity of the portion on the boundary side with the semiconductor substrate is smaller than the porosity of the surface side portion at the removal site during the energization. The method for forming a curved surface according to any one of the above.

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