WO2014073299A1

WO2014073299A1 - Fresnel lens, fabrication method therefor, and sensing device

Info

Publication number: WO2014073299A1
Application number: PCT/JP2013/076933
Authority: WO
Inventors: 山内　博史
Original assignee: シャープ株式会社
Priority date: 2012-11-12
Filing date: 2013-10-03
Publication date: 2014-05-15

Abstract

In accordance with each space width of depression parts which are formed in respective intervals between the closest protrusion parts (PJ1-PJ3) in a serrated part (2), the sizes of taper angles, which are complementary angles to angles of inclination with respect to the optical axes of partition faces which surround each depression part, vary.

Description

Fresnel lens, manufacturing method thereof, and sensing device

The present invention relates to a Fresnel lens used for various optical systems, a method for manufacturing the same, and a sensing device including the Fresnel lens.

In recent years, in addition to the conventional refractive Fresnel lens, a diffractive Fresnel lens that is small and light, has good reproducibility, and has small aberrations has attracted attention. This diffractive Fresnel lens is manufactured, for example, by fine processing such as electron beam drawing, and is also called a Fresnel microlens or a micro Fresnel lens.

A conventional diffractive Fresnel lens is formed by approximating the curvature of an ideal curve by forming irregularities with different pattern dimensions on a substrate. For example, in the micro Fresnel lens described in Patent Document 1, the curvature of an ideal curve is approximated by further increasing the number of convex portions of a binary (two-stage) lens. On the other hand, in recent years, in order to improve the light condensing performance of the lens, the lens performance is improved by bringing the uneven pattern on the substrate closer to an ideal curve. At that time, in order to approximate the concave / convex pattern on the substrate to the ideal curve, a method of directly transferring the ideal curve onto the substrate using the gray scale exposure method (see Non-Patent Document 1) and a subdivided concave / convex shape are formed. How to do is known.

Japanese Patent Publication “Japanese Patent Laid-Open No. 61-137101 (published on June 24, 1986)”

However, the above-described conventional technique has a problem that the manufacturing cost becomes expensive when trying to manufacture a lens having good condensing characteristics.

For example, in the technique described in Patent Document 1, since the curvature of the ideal curve is approximated by further increasing the number of convex portions of the binary lens, the uneven pattern on the substrate is made closer to the ideal curve. Need to make the convex part more finely and multi-staged. For this reason, the manufacturing process accompanying the increase in the number of steps of the convex part and the increase in the number of processes result in an increase in the manufacturing cost of the lens itself.

On the other hand, when the gray scale exposure method described in Non-Patent Document 1 is used, the ideal curve can be directly transferred onto the substrate, so that it is possible to manufacture a lens with good light collecting characteristics. Since the cost is high, the manufacturing cost of the lens itself increases.

Furthermore, when using the method of forming the uneven shape by subdividing, the manufacturing cost of the lens itself increases as a result of the complexity of the manufacturing process accompanying the subdivision and the increase in the number of processes.

The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a Fresnel lens or the like having good condensing characteristics at a lower cost.

In order to solve the above problems, a Fresnel lens according to one embodiment of the present invention is a Fresnel lens in which a concavo-convex pattern is formed on a substrate in accordance with the wavelength of incident light and the amount of phase modulation added to outgoing light. The concavo-convex pattern is a pattern in which a plurality of convex portions and concave portions are alternately arranged along the direction from the center portion to the end portion of the Fresnel lens, and between the nearest convex portions in the concavo-convex pattern. The taper angle which is the inclination angle with respect to the optical axis direction of the wall surface surrounding the recess differs according to the space width of the recess formed in the direction from the center to the end of the Fresnel lens. .

In order to solve the above problems, a method for manufacturing a Fresnel lens according to an aspect of the present invention includes a Fresnel lens in which a concavo-convex pattern is formed on a substrate in accordance with the wavelength of incident light and the amount of phase modulation added to the emitted light. A method of patterning the concavo-convex pattern using a resist mask, wherein a plurality of convex portions and concave portions are alternately arranged along a direction from a center portion to an end portion of the Fresnel lens. A direction from the center of the Fresnel lens toward the end of the concave portion formed between the nearest convex portions in the concavo-convex pattern by processing the substrate using a photolithography process for forming the concavo-convex pattern and dry etching The taper angle, which is the remainder of the inclination angle with respect to the optical axis direction of the wall surface surrounding the concave portion, varies depending on the space width that is the width of Characterized by comprising an etching step of a.

According to one aspect of the present invention, there is an effect that it is possible to provide a Fresnel lens with good condensing characteristics at a lower cost.

Other objects, features, and superior points of the present invention will be fully understood from the following description. The advantages of the present invention will become apparent from the following description with reference to the accompanying drawings.

It is a diagram showing the structure of a Fresnel lens according to an embodiment of the present invention, the upper diagram is a cross-sectional view when the Fresnel lens is cut by a plane including the optical axis, the lower diagram is It is a top view when the said Fresnel lens is seen from the light-emitting surface side. It is a diagram showing a schematic configuration of a sensing device according to an embodiment of the present invention, the upper diagram is a cross-sectional view when the sensing device is cut by a plane including the optical axis, the lower diagram is It is a top view when the Fresnel lens with which the said sensing device is provided is seen from the light emission surface side. It is sectional drawing of the board | substrate after the 1st photolithography process regarding the manufacturing method of the said Fresnel lens. Regarding the method for manufacturing the Fresnel lens, (a) shows a cross-sectional view of the substrate after the first etching step, (b) shows a cross-sectional view of the substrate after the second etching step, and (c) ) Shows a cross-sectional view of the substrate after the third etching step.

An embodiment of the present invention will be described with reference to FIGS. 1 to 4 as follows. Descriptions of configurations other than those described in the following specific items may be omitted as necessary. However, in the case where they are described in other items, the configurations are the same. For convenience of explanation, members having the same functions as those shown in each item are given the same reference numerals, and the explanation thereof is omitted as appropriate. In addition, the shape of the configuration described in each drawing and the dimensions such as length, size, and width do not reflect the actual shape and dimensions, and are appropriately set for clarity and simplification of the drawings. It has changed.

[Configuration of Fresnel Lens 10]
Hereinafter, the configuration of an infrared diffractive Fresnel lens 10 (in which a substrate 1 described later is processed) according to an embodiment of the present invention will be described with reference to FIG. 1 is a cross-sectional view of a Fresnel lens 10 according to an embodiment of the present invention cut along a plane including an optical axis. On the other hand, the figure shown on the lower side of the figure is a plan view when viewed from the light emitting surface (surface on the side from which diffracted light is emitted) of the Fresnel lens 10. However, in the same figure, for the sake of clarity of the drawing, the scale of the dimension of each component shown in the top view is larger than the scale of the dimension of the plan view. The wavelength band of infrared rays incident on the Fresnel lens 10 of this embodiment is, for example, a 3 to 5 micron band or an 8 to 15 micron band.

In the following, a diffractive Fresnel lens will be described as an example, but a lens to which the present invention can be applied is not limited to this. For example, the present invention can be applied to a refractive type Fresnel lens. Hereinafter, an infrared Fresnel lens will be described as an example, but a lens to which the present invention can be applied is not limited thereto. For example, in addition to an infrared lens, the present invention can also be applied to a visible region lens and an ultraviolet region lens. In addition, for example, the present invention can also be applied to a diffractive Fresnel lens for femtosecond lasers used for industrial lasers.

(Substrate 1, uneven portion 2)
The Fresnel lens 10 of the present embodiment has a substantially circular cross-section when the lens is cut along a plane perpendicular to the optical axis direction (hereinafter, such a lens is simply referred to as “substantially circular lens”). The cross-sectional shape of the lens is not limited to this. For example, the cross-sectional shape may be a substantially elliptical shape or a substantially rectangular shape. As shown in FIG. 1, the Fresnel lens 10 is a lens in which a concavo-convex portion 2 (concave / convex pattern) is formed on the substrate 1 in accordance with the wavelength of incident light and the amount of phase modulation added to outgoing light (diffracted light). is there.

In the present embodiment, silicon (Si) is used as the constituent material of the substrate 1, that is, the lens, but is not limited to this. For example, as long as the refractive index n is 3 or more, a known resin material or glass material can be used. Further, for example, an effect similar to the effect described later can be obtained for a diffractive infrared Fresnel lens including Si and having a refractive index n of 3 or more. Other examples of the constituent material of the lens used in the infrared wavelength band include ZnSe and Ge.

The concave-convex portion 2 of the Fresnel lens 10 has a plurality of convex portions PJ1 to PJ3 and concave portions along a direction from the central portion (lens center) of the Fresnel lens 10 toward the end portion (radial direction of the substantially circular lens). The uneven pattern is generally arranged alternately. More specifically, the concavo-convex pattern is formed on the light exit surface side of the substrate 1 in accordance with the wavelength of incident light and the phase modulation amount of the lens with respect to the emitted light, and has a sawtooth cross section associated with the concavo-convex pattern. In addition, the concavo-convex portion 2 having a multi-step staircase shape in which each of the convex portions PJ1 to PJ3 is multi-staged is formed.

Further, in the Fresnel lens 10 of the present embodiment, the wavelength of incident light is a wavelength within the transmission wavelength region that transmits the crystal of the constituent material (Si in the present embodiment) constituting the substrate 1. The refractive index n of is 3 or more. In this way, the incident light has a wavelength within the transmission wavelength region that transmits the crystal of the constituent material constituting the substrate 1 and the refractive index n of the substrate 1 is 3 or more. The Fresnel lens 10 having good optical characteristics can be provided at a lower cost.

(Groove depth t of the uneven portion 2)
The depth t (maximum depth of the recess) of the concavo-convex portion 2 is set so that the refractive index n of the substance constituting the lens and the wavelength of incident light are maximized in order to maximize the light collection efficiency of the Fresnel lens 10. Using λ, t = λ / (n−1) is set. Here, the “maximum depth of the concave portion” is a distance between the bottom surface of the space portion (concave portion) W1 and the uppermost surface of the convex portions PJ1 to PJ3. In this embodiment, the groove depth t is approximately the same as the film thickness of a photoresist pattern 3 described later, and is approximately 1.3 μm.

Next, the concentric pattern represented by the following (formula 1) is set according to the focal length f, which is the most commonly used ring pattern in the concavo-convex portion 2 of the Fresnel lens 10.

f (x, y) = {(x ² + y ² ) + f ² } ^1/2 −f (Expression 1)
Here, (x, y) are x and y coordinates in a two-dimensional orthogonal coordinate system set on the surface of the substrate 1 with reference to the focal position.

Furthermore, the refractive index of the substrate 1 in this embodiment is n = 3.5, the wavelength of incident light (infrared rays) is λ = 10.0 μm, and the focal length is f = 0.69 μm. In the present embodiment, the number of steps in the step shape of the protrusions PJ1 to PJ3 is four in total, corresponding to the space portions (recesses) W1 to W3. However, the number of steps in the step shape of the convex portions PJ1 to PJ3 in the Fresnel lens 10 is not limited to this, and may be at least two steps. It goes without saying that the approximation to the ideal curve becomes easier as the number of steps of the projecting portions PJ1 to PJ3 increases.

Further, in the Fresnel lens 10 of the present embodiment, the respective space widths of the concave portions (space portions W1 to W3 shown in FIG. 4C, which will be described later) formed between the nearest convex portions in the concave and convex portion 2. Depending on SW1 to SW3 (or the space width of each stage of the space portions W1 to W3), the taper angles θ1 to θ3 of the wall surface surrounding the recess are made different. Note that the concave portion formed at the end of the Fresnel lens 10 shown in FIG. 1 cannot be strictly said to be a concave portion formed between the convex portions. However, the structural requirement that the taper angle of the wall surface surrounding the recess having a wide space width is smaller than the taper angle of the wall surface surrounding the recess having a narrow space width is not limited to the recess formed between the protrusions. This is a requirement that is satisfied including the wall surface of the recess at the end.

Here, in this specification, the “space width” is the width of the recess in the direction from the center to the end of the lens. More specifically, the space width is the widest width, the narrowest width, or the average width among the widths in the direction from the center to the end of the lens in the concave portions of the respective steps of the space portions W1 to W3. Can be illustrated. In the present embodiment, the space widths SW1 to SW3 are the widest widths of the concave portions in the direction from the center to the end of the lens. Further, in this specification, the “taper angle” is an additional angle of an inclination angle with respect to the optical axis direction of the wall surface surrounding the recess.

If the points described above are described from another point of view, in the Fresnel lens 10 of the present embodiment, at least the wall surface where the taper angles θ1 to θ3 are not 90 degrees, that is, the wall surface inclined with respect to the optical axis of the lens is at least. One is formed.

On the other hand, in the conventional method of multi-leveling the convex portions of the binary lens, the taper angle of the wall surface surrounding each concave portion is not particularly correlated with the space width and is approximately 90 degrees. In other words, in the conventional method of multi-leveling the convex portion of the binary lens, it has not been assumed at all that the wall surface surrounding each concave portion is inclined with respect to the optical axis of the lens.

Here, the more the number of wall surfaces having different taper angles, the taper angle of which is not 90 degrees, the closer to the ideal curve with a smaller number of steps than the conventional multi-stage convex lens of the binary lens. Can do. Further, the greater the number of wall surfaces having different taper angles, the taper angle of which is not 90 degrees, the easier it is to approach the ideal curve without finely subdividing the uneven shape. For this reason, the manufacturing cost for manufacturing the Fresnel lens 10 with good condensing characteristics can be further reduced.

In addition, the present inventor can newly form a wall surface inclined with respect to the optical axis of the Fresnel lens 10 described above in a process using a photolithography process and a dry etching process described later. I found it. Here, according to the process using the photolithography process and the dry etching process, it is not necessary to use an expensive mask such as a gray scale mask unlike the technique described in Non-Patent Document 1, and thus the manufacturing cost is further reduced. Can be made. As described above, the Fresnel lens 10 having good light collecting characteristics can be provided at a lower cost.

Further, in the Fresnel lens 10 of the present embodiment, the taper angle of the wall surface surrounding the recess having a wide space width is smaller than the taper angle of the wall surface surrounding the recess having a narrow space width. For example, as shown in FIG. 1, in the Fresnel lens 10 of the present embodiment, the space width is SW1 <SW2 <SW3, while the taper angle is θ1> θ2> θ3. When the inventor forms a wall surface inclined with respect to the optical axis of the Fresnel lens 10 in the photolithography process and the dry etching process, the taper is easily tapered as the space width of the concave portion between the adjacent convex portions is wide. It was newly found that it is possible to form a wall surface with a small angle. For this reason, in the Fresnel lens 10, the taper angle (for example, taper angle θ3) of the wall surface surrounding the recess having a wide space width is equal to the taper angle (for example, taper angle θ1 or θ2) of the wall surface surrounding the recess having a narrow space width. Is smaller than Further, by adjusting the space width of each recess according to the curvature of the ideal curve, it is possible to form an uneven pattern approximated with a desired curvature at a desired position.

[How to use Fresnel lens 10]
The above-described Fresnel lens 10 can be used for various elements or devices used for inspection of a semiconductor wafer (silicon), inspection of a solar cell, security, inspection of a human body, and the like. For example, FIG. 2 shows an example in which a thermal sensor (sensing device) is configured by combining the Fresnel lens 10 and a thermal sensor element. As shown in FIG. 2, when incident light (for example, collimated parallel light) is incident from the upper side with respect to the paper surface from the light incident surface side of the Fresnel lens 10, the Fresnel lens 10 has a lower surface with respect to the paper surface. The diffracted light is diffracted by the formed concavo-convex pattern, and the heat sensor element is irradiated with the diffracted light. In addition, although the thermal sensor element was shown as an example of the element irradiated with diffracted light in the figure, the use of the diffracted light of the Fresnel lens 10 is not limited to this. For example, the diffracted light of the Fresnel lens 10 can be used for applications such as semiconductor wafer (silicon) inspection, solar cell inspection, security, and human body inspection.

[Manufacturing method of Fresnel lens 10]
Next, a method for manufacturing the above-described Fresnel lens 10 will be described with reference to FIGS. FIG. 3 is a cross-sectional view of the substrate 1 after the first photolithography process in the manufacturing method of the Fresnel lens 10. On the other hand, FIG. 4A shows a cross-sectional view of the substrate 1 after the first etching process. FIG. 4B shows a cross-sectional view of the substrate 1 after the second etching process. Further, FIG. 4C shows a cross-sectional view of the substrate 1 after the third etching step. The manufacturing method of the Fresnel lens 10 includes at least the following photolithography process, etching process, and cleaning process.

(Photolithography process)
In the photolithography process, the uneven portion 2 is patterned using a resist mask. More specifically, as shown in FIG. 3, a photoresist pattern 3 is formed on the substrate 1 using a known photolithography technique in accordance with the uneven pattern set above. The film thickness of the photoresist pattern 3 shown in FIG. 3 (thickness along the vertical direction with respect to the paper surface; hereinafter referred to as “resist film thickness”) is 1.3 μm. As the resist material, for example, a photosensitive organic substance can be listed. The basic method of photolithography will be described in Supplementary Explanation 1 below.

(Etching process)
In the etching process, the substrate 1 is processed using dry etching. The basic technique of dry etching is described in Supplementary Explanation 2 below. In the present embodiment, the space W1 shown in FIG. 3 is etched by dry etching. More specifically, in the dry etching of the present embodiment, for example, Cl ₂ and O ₂ are mixed at a weight ratio of 25: 1, and RF is applied at a predetermined pressure, for example, about 40 mTorr (= about 5.33 Pa). A high frequency applied voltage (high frequency voltage) by an oscillator (radio frequency oscillator) was applied between the planar electrode and the counter electrode. The gas used for dry etching is optimized by adding a diluting gas such as a fluorine-based gas such as CF ₄ or SF ₆ or an Ar gas as appropriate in order to etch the substrate 1 as uniformly as possible at a high rate. .

At this time, in the concave / convex pattern having the same space width, the taper angle depends on the film thickness of the photoresist used in the above photolithography process (substantially corresponds to the above-described depth t), the gas flow rate, pressure and RF in the above etching process. Since it varies depending on the RF power of the oscillator, etc., suitable conditions are selected so that the lens shape approaches the ideal curve according to various required specifications.

That is, in order to change the taper angle according to the space width of the space portion W1, in order to change the amount of reaction product generated on the pattern side wall (wall surface surrounding the space portion W1) according to the space width in the etching step. Select a suitable gas flow, pressure and RF power. For example, in this embodiment, the gas flow rate was the Cl ₂ 133sccm, the _{O 2} and 5 sccm. The pressure was 40 mTorr as described above, and the RF power was set to Source = 1200 W and Bias = 180 W.

When the space width of each recess is wide, more Si as a reactant is etched and more SiO _x as a reaction product is generated than when the space width is narrow. Furthermore, the reaction product adheres to the pattern side wall (wall surface surrounding each recess) by increasing the flow rate of O ₂ in order to produce more reaction product SiO _x or by increasing the pressure. It is possible to control the taper angle by increasing the probability.

In the substrate 1 thus obtained, as shown in FIG. 4A, the space portion W1 of the substrate 1 is wide on the side of the center portion of the lens, and the space becomes closer to the lens outer peripheral portion (end portion). The portion W1 becomes narrow. As a result, the taper angle is small on the center side of the lens of the Fresnel lens 10 and the taper angle is large on the outer peripheral side of the lens, so that the desired uneven portion 2 can be obtained.

(Washing process)
Next, in the cleaning step, the reaction product generated in the photoresist pattern 3 and the dry etching step after forming the space portion W1 on the substrate 1 by the above-described method is converted into a known O ₂ plasma treatment and hydrofluoric acid chemical solution. Processing is performed to obtain the lens shape shown in FIG.

Next, the space part W2 is formed by performing the same photolithography process, dry etching process, and cleaning process as the method of forming the space part W1, and the lens shape shown in FIG. 4B is obtained. Furthermore, in order to form the space part W3, the lens shape shown in FIG. 4C is obtained by performing the same photolithography process, dry etching process, and cleaning process as the method of forming the space parts W1 and W2. be able to. The Fresnel lens 10 shown in FIG. 1 can be manufactured by the method as described above.

In the present embodiment, a method is shown in which, by forming the space portions W1 to W3, a concavo-convex shape having a total of four steps including the bottom of the concave portion is obtained. A lens having a stepped shape can be obtained. Further, according to the above method, it is possible to manufacture the Fresnel lens 10 having different taper angles according to the space width, the lens shape can be made closer to the ideal curve, and the Fresnel having high light collecting characteristics without increasing the cost. The lens 10 can be provided.

In the above description, the diffractive Fresnel lens 10 using the substrate 1 has been described. However, any material having a refractive index of n = 3 or more may be used, and it includes Si and a material having a refractive index n of 3 or more. The same effect can be obtained with the diffractive infrared lens. The transmission wavelength region of the Si crystal is 1.2 μm to 16 μm, and Si has a refractive index n of 3 or more in this region. Accordingly, the same effect can be obtained at any wavelength as long as the incident light is in the transmission wavelength region of the crystal of the constituent material constituting the substrate 1. According to the above method, it is possible to provide the Fresnel lens 10 which is inexpensive and does not deteriorate the optical characteristics by forming the stepped shape of the concavo-convex portion 2 by controlling the taper angle according to the processing pitch.

[Supplementary explanation 1: photolithography process]
Photolithography is the process of exposing the surface of a material coated with a photosensitive material in a pattern (also called pattern exposure, imagewise exposure, etc.), from exposed and unexposed portions. Is a technique for generating a pattern. More specifically, photolithography is performed as follows. A photosensitive organic material called a photoresist is applied onto the substrate 1, and a pattern drawn on a photomask called a reticle is baked using an exposure device called a stepper. Hereinafter, each process will be described in more detail.

(Washing the substrate)
If organic substances or lipids adhere to the surface of the substrate 1, the adhesion of the resist becomes weak, so the surface of the substrate 1 is washed. Examples of the cleaning method include ultrasonic cleaning using ethanol, and a cleaning method using a mixed solution of H ₂ SO ₄ : H ₂ O ₂ = 4: 1.

(Resist application)
A liquid called resist is applied onto the substrate 1 by a spin coater or spraying. As a resist characteristic, the thickness of the resist greatly affects the viscosity of the resist. For example, the lower the viscosity, the thinner the resist film can be made, and the more suitable for creating fine patterns. The range of the film thickness of the resist film is about several μm to 100 μm.

Also, resists can be roughly divided into two due to their chemical properties. For example, there are a “positive type” that decomposes when dissolved in light and dissolves in the developer, and a “negative type” that dissolves in the developer due to polymerization when exposed to light. That is, the positive type does not have a portion exposed to light, and the negative type has a portion exposed to light. In the manufacturing method of the Fresnel lens 10 described above, either “positive type” or “negative type” may be used. Note that the positive type is advantageous for pattern miniaturization, and the positive type is currently the mainstream. In the case of exposure using an excimer laser such as KrF, a chemically amplified photoresist is used because the exposure intensity is weak.

(Prebaked)
After applying the resist, it is heated (baked) before exposure to solidify the resist.

(exposure)
The resist is irradiated with light to react. At this time, a necessary shape is drawn on the resist by controlling a portion irradiated with light using a resist mask in which the shape of the concavo-convex pattern is drawn. The exposure apparatus performs reduction projection exposure while moving a mask pattern created larger than the actual size on the substrate 1 using an apparatus called a stepper. As the pattern becomes finer, a light source having a shorter wavelength is required. Currently, high-pressure mercury lamp g-line (wavelength 436 nm), i-line (wavelength 365 nm), KrF excimer laser (wavelength 248 nm), ArF excimer laser (wavelength 193 nm), etc. EUV light (wavelength 13.5 nm) is in the development stage as the next generation light source. There are also a method of using X-rays as a light source and a method of drawing directly on a resist with an electron beam (electron beam lithography).

(Development / Rinse)
The exposed substrate 1 is dipped in a developing solution to remove excess portions of the resist. Only in this process, an uneven pattern (for example, the space portion W1 shown in FIG. 3) appears on the substrate 1. As the developer, a chemical solution that dissolves the resist is used. The chemical solution used may be an organic solvent that dissolves the resist or an organic or inorganic alkali. In current photolithography, a 2.38 wt% aqueous solution of TMAH (Tetra-methyl-ammonium-hydroxyde), which is an organic alkali, is the mainstream. This is because an inorganic alkali such as potassium hydroxide (KOH) cannot avoid mixing metal ions into the process. Rinse several times with a rinse solution (mainly ultrapure water) to completely remove unwanted parts.

(Post bake)
The attached rinse solution is removed by heating. The adhesion with the substrate 1 is improved by heating.

[Supplementary explanation 2: Etching process]
Next, the etching described above will be described. When the uneven portion 2 is formed on the substrate 1 as in the above-described form, unnecessary portions are removed by etching. Etching includes dry etching and wet etching. Since the remaining portion of the resist is not removed by etching, a pattern to be left is formed on the substrate 1. Finally, the resist is completely removed with a solvent or the like.

(About RIE equipment)
For example, in the RIE (reactive ion etching) apparatus, the substrate 1 is disposed on the cathode of the planar electrode. When a high frequency voltage is applied between the counter electrode (anode) and the planar electrode (cathode) by the RF oscillator with the etching gas introduced, plasma is generated between the electrodes. The electrons in the plasma are lighter and faster than positive ions, which are active gases, and therefore immediately gather on the counter electrode and the planar electrode. The collected electrons are connected to the ground at the counter electrode, so that the potential does not change. However, the DC current is blocked by the blocking capacitor in the flat electrode, and the electrons accumulate on the flat electrode and become negative potential. (The high frequency of the RF oscillator, which is an alternating current, passes through the blocking capacitor.) When this planar electrode becomes a negative potential, it is called cathode fall. Due to the negative potential (electric field) of the cathode drop, positive ions, which are active gases in the plasma, are attracted and incident perpendicularly on the surface of the substrate 1 so that anisotropic etching is performed.

(Anisotropic etching)
In the anisotropic etching, the etching film and the photoresist pattern 3 are etched by the ion collision of the etching gas. The reaction product generated at this time is evacuated, but part of it adheres to the etching side surface. This is called a sidewall protective film and serves to prevent lateral etching, and the wall surface having the taper angles θ1 to θ3 is formed. As a result, it is possible to manufacture the Fresnel lens 10 in which the concavo-convex portion 2 including the convex portions PJ1 to PJ3 having the taper angles θ1 to θ3 is formed.

[Summary]
In the Fresnel lens (Fresnel lens 10) according to the aspect 1 of the present invention, the uneven pattern (uneven portion 2) is formed on the substrate (substrate 1) according to the wavelength of the incident light and the phase modulation amount added to the emitted light. In the Fresnel lens, the concavo-convex pattern is a pattern in which a plurality of convex portions (convex portions PJ1 to PJ3) and concave portions are alternately arranged along a direction from the center to the end of the Fresnel lens. In accordance with the space width (space width SW1 to SW3), which is the width of the concave portion formed between the nearest convex portions in the concave / convex pattern with respect to the direction from the center to the end of the Fresnel lens, In this configuration, the taper angles (taper angles θ1 to θ3), which are residual angles of the inclination angle with respect to the optical axis direction of the surrounding wall surface, are different.

In the above configuration, the taper angle of the wall surface surrounding the recess is varied according to the space width. Here, the taper angle is assumed to be a remainder angle of the inclination angle with respect to the optical axis direction of the wall surface surrounding the recess. In other words, at least one wall surface whose taper angle is not 90 degrees, that is, a wall surface inclined with respect to the optical axis of the Fresnel lens is formed. In the conventional method of making the convex portion of the binary lens multistage, the taper angle of the wall surface surrounding the concave portion is approximately 90 degrees. That is, in the conventional method of multi-leveling the convex portion of the binary lens, it has never been assumed to form a wall surface that is inclined with respect to the optical axis of the lens. Here, the more the number of wall surfaces having different taper angles, the taper angle of which is not 90 degrees, the closer to the ideal curve with a smaller number of steps than the conventional multi-stage convex lens of the binary lens. Can do. Further, the greater the number of wall surfaces having different taper angles, the taper angle of which is not 90 degrees, the easier it is to approach the ideal curve without finely subdividing the uneven shape. For this reason, the manufacturing cost for manufacturing a Fresnel lens with good condensing characteristics can be further reduced.

Further, the present inventor newly found out that it is possible to form a wall surface inclined with respect to the optical axis of the Fresnel lens by a process using a photolithography process and a dry etching process.

That is, the method for manufacturing a Fresnel lens according to aspect 5 of the present invention is a method for manufacturing a Fresnel lens in which a concavo-convex pattern is formed on a substrate in accordance with the wavelength of incident light and the amount of phase modulation added to outgoing light, Photolithography for patterning the concavo-convex pattern using a resist mask to form the concavo-convex pattern in which a plurality of convex portions and concave portions are alternately arranged along the direction from the center to the end of the Fresnel lens Processing the substrate using a process and dry etching, and a space width that is a width in a direction from the center to the end of the Fresnel lens of the recess formed between the closest protrusions in the uneven pattern. Depending on the etching process, the taper angle that is the remainder of the inclination angle with respect to the optical axis direction of the wall surface surrounding the recess is varied. And it may contain. Here, according to the process using the photolithography process and the dry etching process, it is not necessary to use an expensive mask such as a gray scale mask unlike the technique described in Non-Patent Document 1, and thus the manufacturing cost is further reduced. Can be made. As described above, according to the above-described configuration or method, it is possible to provide a Fresnel lens with good condensing characteristics at a lower cost.

In the Fresnel lens according to aspect 2 of the present invention, in the aspect 1, the taper angle of the wall surface surrounding the recess having the wide space width is smaller than the taper angle of the wall surface surrounding the recess having the narrow space width. Also good. When the inventor forms a wall surface inclined with respect to the optical axis of the Fresnel in the photolithography process and the dry etching process, the taper angle becomes easier as the space width of the recesses between adjacent protrusions is wider. Newly found that it is possible to form a small wall. Therefore, in the above configuration, the taper angle of the wall surface surrounding the recess having the wide space width is smaller than the taper angle of the wall surface surrounding the recess having the narrow space width. Further, by adjusting the space width of each recess according to the curvature of the ideal curve, it is possible to form an uneven pattern approximated with a desired curvature at a desired position.

In the Fresnel lens according to aspect 3 of the present invention, in the aspect 1 or 2, the wavelength of the incident light is a wavelength within a transmission wavelength region that transmits a crystal of a constituent material constituting the substrate. The refractive index may be 3 or more. If the wavelength of the incident light is a wavelength in the transmission wavelength region that transmits the crystal of the constituent material constituting the substrate, and the refractive index of the substrate is 3 or more, light of any wavelength in the transmission wavelength region can be collected. A Fresnel lens with good optical characteristics can be provided at a lower cost.

Further, in the Fresnel lens according to Aspect 4 of the present invention, in any one of Aspects 1 to 3, the wavelength of the incident light may be a wavelength in an infrared region. According to said structure, the Fresnel lens for infrared rays with a sufficient condensing characteristic can be provided more cheaply.

Further, in the manufacturing method of the Fresnel lens according to aspect 6 of the present invention, the taper angle may be adjusted by adjusting the film thickness of the resist mask in the photolithography process in aspect 5 above. The present inventor has newly found that it is possible to adjust the taper angle of the wall surface inclined with respect to the optical axis of the Fresnel lens by adjusting the film thickness of the resist mask in the photolithography process. I found it. Therefore, in the above method, the taper angle is adjusted by adjusting the film thickness of the resist mask.

In addition, in the manufacturing method of a Fresnel lens according to aspect 7 of the present invention, in the aspect 5 or 6, the magnitude of the taper angle is adjusted by adjusting the gas flow rate, the pressure, and the power of the high frequency oscillator in the etching step. May be. The inventor can adjust the taper angle of the wall surface inclined with respect to the optical axis of the Fresnel lens by adjusting the gas flow rate, pressure and power of the high-frequency oscillator in the etching process. I found a new thing. Therefore, in the above method, the magnitude of the taper angle is adjusted by adjusting the gas flow rate, pressure, and power of the high-frequency oscillator in the etching process.

The sensing device according to aspect 8 of the present invention may include the Fresnel lens according to any one of aspects 1 to 4.

[Another expression of the present invention]
The present invention can also be expressed as follows. That is, the Fresnel lens (infrared optical lens) according to one aspect of the present invention is a diffractive Fresnel lens having a space width in which the concavo-convex pattern differs depending on the phase modulation amount of the lens, depending on the wavelength of incident light. In addition, the concavo-convex portions formed on the substrate may have different taper angles according to individual space widths.

Further, the Fresnel lens according to one embodiment of the present invention may have a structure in which the unevenness formed on the substrate has a taper angle that decreases as the space width increases.

In the Fresnel lens according to one embodiment of the present invention, a silicon substrate may be used as the substrate.

A method for manufacturing a Fresnel lens according to one aspect of the present invention is a method for manufacturing a diffractive Fresnel lens that forms a concavo-convex pattern according to the phase modulation amount of a lens, depending on the wavelength of incident light. The uneven portion may be formed on the substrate by changing the taper angle according to the space width.

Further, in the method for manufacturing a Fresnel lens according to one embodiment of the present invention, patterning may be performed using a resist mask when the uneven portion is formed on the substrate.

Further, in the method of manufacturing the Fresnel lens according to one embodiment of the present invention, the substrate may be processed using dry etching in the step of forming the uneven portion on the substrate.

In the method for manufacturing a Fresnel lens according to one embodiment of the present invention, any of SF ₆ , CF ₄ , Cl ₂ , O ₂ , and Ar is used for dry etching in the step of forming the uneven portion on the substrate. Then, the substrate may be processed.

According to the above configuration or method, for example, by controlling the taper angle according to the space width when configuring the uneven portion of the Fresnel lens with Si, it is possible to realize a lens shape closer to the ideal curve of the lens, As a result, a diffractive infrared optical lens (infrared Fresnel lens) with good condensing characteristics can be provided at low cost.

[Additional Notes]
The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention. Furthermore, a new technical feature can be formed by combining the technical means disclosed in each embodiment.

The present invention can be applied to Fresnel lenses, in particular, optical lenses for infrared rays that are diffractive Fresnel lenses. For example, the present invention can be applied to optical lenses used for surveillance cameras, inspection of semiconductor wafers (silicon), inspection of solar cells, security, inspection of human bodies, and the like. The present invention can also be used for a sensing device provided with a Fresnel lens. For example, the present invention can be used for a heat sensor that detects heat.

1 Substrate 2 Uneven portion (uneven pattern)
3 Photoresist pattern 10 Fresnel lens PJ1 to PJ3 Convex part SW1 to SW3 Space width t Depth W1 to W3 Space part (concave part)
θ1 to θ3 taper angle

Claims

A Fresnel lens in which a concavo-convex pattern is formed on a substrate according to the wavelength of incident light and the amount of phase modulation added to outgoing light,
The concavo-convex pattern is a pattern in which a plurality of convex portions and concave portions are alternately arranged along the direction from the center portion to the end portion of the Fresnel lens,
Inclination angle with respect to the optical axis direction of the wall surface surrounding the concave portion according to the space width that is the width of the concave portion formed between the nearest convex portions in the concave-convex pattern with respect to the direction from the center to the end of the Fresnel lens The Fresnel lens is characterized in that the size of the taper angle, which is the residual angle, is different.
2. The Fresnel lens according to claim 1, wherein a taper angle of a wall surface surrounding the concave portion having a wide space width is smaller than a taper angle of a wall surface surrounding the concave portion having a narrow space width.
The wavelength of the said incident light is a wavelength in the transmission wavelength range which permeate | transmits the crystal | crystallization of the constituent material which comprises the said board | substrate, The refractive index of the said board | substrate is 3 or more, The claim 1 or 2 characterized by the above-mentioned. Fresnel lens.
The Fresnel lens according to any one of claims 1 to 3, wherein the wavelength of the incident light is a wavelength in an infrared region.
A method of manufacturing a Fresnel lens in which a concavo-convex pattern is formed on a substrate according to the wavelength of incident light and the amount of phase modulation added to outgoing light,
Photolithography for patterning the concavo-convex pattern using a resist mask to form the concavo-convex pattern in which a plurality of convex portions and concave portions are alternately arranged along the direction from the center to the end of the Fresnel lens Process,
Processing the substrate using dry etching, according to the space width that is the width from the center of the Fresnel lens toward the end of the concave portion formed between the nearest convex portions in the concave-convex pattern, And an etching step of varying a taper angle that is an additional angle of inclination with respect to the optical axis direction of the wall surface surrounding the recess.
6. The method according to claim 5, wherein the taper angle is adjusted by adjusting a film thickness of the resist mask in the photolithography process.
The manufacturing method according to claim 5 or 6, wherein the taper angle is adjusted by adjusting a gas flow rate, a pressure, and a power of a high-frequency oscillator in the etching step.
A sensing device comprising the Fresnel lens according to any one of claims 1 to 4.