Method for manufacturing microlens arrays

Abstract

This enables improved optical properties of microlens arrays and miniaturization of lenses. [Solution] A method for manufacturing a microlens array according to one embodiment includes a substrate preparation step S1 of preparing a substrate having one surface with a plurality of recesses, a lens element preparation step S2 of preparing a plurality of lens elements having a softening point lower than the softening point of the substrate, a lens element placement step S3 of placing the lens elements in each recess, and a heating step S4 of heating the substrate and the lens elements at a temperature higher than the softening point of the lens elements and lower than the softening point of the substrate. In the heating step S4, the lens elements are liquefied and raised higher than the edges of the recesses due to surface tension.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a microlens array.

Background Art

[0002] A microlens array having a plurality of minute lenses is known. Such a microlens array is used in various applications in various fields. The microlens array is used, for example, as one of optical elements constituting an illumination optical system or a compensation optical system in optical devices, optical communication devices, medical devices, industrial devices, and the like.

[0003] Patent Documents 1 and 2 disclose an example of a method for manufacturing such a microlens array.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Improvement of optical characteristics and miniaturization of lenses are required for the microlens array.

Means for Solving the Problems

[0006] A method for manufacturing a microlens array according to one embodiment includes a substrate preparation step of preparing a substrate having one surface with a plurality of recesses; a lens element preparation step of preparing a plurality of lens elements having a softening point lower than the softening point of the substrate; a lens element placement step of placing the lens elements in each of the recesses on the substrate; and a heating step of heating the substrate and the lens elements at a temperature higher than the softening point of the lens elements and lower than the softening point of the substrate. In the heating step, the lens elements are liquefied and raised higher than the edges of the recesses due to surface tension. [Effects of the Invention]

[0007] According to the present invention, it is possible to improve the optical properties of microlens arrays and to miniaturize lenses. [Brief explanation of the drawing]

[0008] [Figure 1] This is a plan view of a microlens array according to one embodiment. [Figure 2] This is a side view of a microlens array according to one embodiment. [Figure 3] This is a cross-sectional view of the microlens array along line AA in Figure 1. [Figure 4] This is a process diagram showing a method for manufacturing a microlens array according to one embodiment. [Figure 5] Figure 4 is a plan view of the substrate prepared in the substrate preparation process shown. [Figure 6] This is a cross-sectional view of the substrate along the BB line in Figure 5. [Figure 7] Figure 4 is an explanatory diagram showing the lens element arrangement process. [Figure 8] Figure 4 is a cross-sectional view showing the lens element arrangement process. [Figure 9] Figure 4 is a cross-sectional view showing the state of the lens material during the heating process. [Figure 10] This figure shows the results of observing the lens portion of a microlens array in one embodiment using an electron microscope. [Figure 11] This figure shows the results of observing the lens portion of a microlens array in another embodiment using an electron microscope. [Modes for carrying out the invention]

[0009] The embodiments will be described in detail below with reference to the drawings. In all drawings illustrating the embodiments, the same or substantially identical components and elements will be denoted by the same reference numerals. Furthermore, components and elements that have already been described will generally not be repeated.

[0010] (First Embodiment) <Microlens array> Figure 1 is a plan view of the microlens array 1A of this embodiment. Figure 2 is a side view of the microlens array 1A of this embodiment. Figure 3 is a cross-sectional view of the microlens array 1A along line AA in Figure 1.

[0011] The microlens array 1A has a base portion 10 and a plurality of minute lens portions 20 provided on one side of the base portion 10. In this embodiment, the base portion 10 is made of glass, and each of the lens portions 20 is also made of glass.

[0012] However, the base portion 10 and the multiple lens portions 20 are inseparably integrated. From another perspective, the microlens array 1A is an assembly of multiple microlenses.

[0013] In the following explanation, one side of the base portion 10 on which the lens portion 20 is located will be referred to as the "front side," and the other side of the base portion 10 opposite the front side will be referred to as the "back side" to distinguish them. However, such distinctions and names are merely for the convenience of explanation.

[0014] As shown in Fig. 1, the base portion 10 of the present embodiment has a rectangular or substantially rectangular planar shape, but there is no particular limitation on the shape and size of the base portion 10. However, when the planar shape of the base portion 10 is rectangular or substantially rectangular, the length of one side thereof is, for example, several [mm] to a dozen or so [mm].

[0015] As shown in Figs. 1 and 2, each lens portion 20 has a hemispherical or substantially hemispherical outer shape. More specifically, each lens portion 20 has a circular or substantially circular planar shape (Fig. 1), and has a semi-circular or substantially semi-circular side shape (Fig. 2).

[0016] As shown in Fig. 3, each lens portion 20 can be roughly divided into a hemispherical or substantially hemispherical upper portion 21 protruding from the surface of the base portion 10 and a cylindrical lower portion 22 buried in the base portion 10. Viewed in another way, the upper portion 21 is a part of the lens portion 20 protruding from the surface of the base portion 10, and the lower portion 22 is the other part (the remaining part) of the lens portion 20 buried in the base portion 10. However, the upper portion 21 and the lower portion 22 are integral, and the above distinction is a distinction for convenience of explanation.

[0017] There is no particular limitation on the size of the lens portion 20. The diameter of the lens portion 20 is, for example, a dozen or so [μm] to several tens [μm]. Also, in the present embodiment, a plurality of lens portions 20 are arranged in a matrix (matrix) shape.

[0018] However, there is no particular limitation on the number, arrangement, array, etc. of the lens portions 20, nor is there any particular limitation on the pitch. For example, in another embodiment, a plurality of lens portions 20 are arranged in a staggered pattern at a desired pitch (for example, several tens [μm] to several hundreds [μm]). In yet another embodiment, a plurality of lens portions 20 are arranged at unequal pitches.

[0019] <Method for manufacturing a microlens array> Next, the manufacturing method of the microlens array 1A shown in Figures 1 to 3 will be described. Figure 4 is a process diagram showing the manufacturing method of this embodiment. The manufacturing method of this embodiment includes a substrate preparation step S1, a lens element preparation step S2, a lens element placement step S3, a heating step S4, and a cooling step S5.

[0020] In other words, the microlens array 1A shown in Figures 1 to 3 is manufactured by a manufacturing method that includes a substrate preparation step S1, a lens element preparation step S2, a lens element placement step S3, a heating step S4, and a cooling step S5, as shown in Figure 4.

[0021] <Substrate preparation process> The substrate preparation step S1 shown in Figure 4 is a step in preparing the substrate that will become the base portion 10 of the microlens array 1A. Figure 5 is a plan view of the substrate 30 prepared in the substrate preparation step S1. Figure 6 is a cross-sectional view of the substrate 30 along the line BB in Figure 5.

[0022] The substrate 30 is a glass plate having an upper surface 30t and a lower surface 30b opposite to the upper surface 30t. Therefore, in the following description, the substrate 30 may sometimes be referred to as the "glass substrate 30".

[0023] Multiple recesses 31 are provided on one surface of the glass substrate 30. More specifically, multiple recesses 31 are provided on the upper surface 30t of the glass substrate 30. In the following description, the recesses 31 may be referred to as "microholes 31".

[0024] Multiple microholes 31 are arranged in a matrix. More specifically, the layout of the microholes 31 shown in Figure 5 is identical or substantially identical to the layout of the lens portion 20 shown in Figure 1. In other words, the same number of microholes 31 as those in the lens portion 20 shown in Figure 1 are provided on the upper surface 30t of the glass substrate 30, at the same positions as those in the lens portion 20 shown in Figure 1.

[0025] Alternatively, if a glass substrate 30 with a different layout of microholes 31 than the one shown in Figure 5 is prepared in the substrate preparation step S1, a microlens array 1A with a different layout of lens portions 20 than the one shown in Figure 1 can be manufactured.

[0026] There are no particular restrictions on the shape or size of the microhole 31. However, the microhole 31 is required to capture the lens element 40, which will be described later, in the lens element placement process S3, which will be described later. Therefore, it is desirable that the shape and size of the microhole 31 be such that the lens element 40 can be easily and reliably captured.

[0027] As will be explained in more detail later, the lens element 40 in this embodiment is spherical. Therefore, the microhole 31 in this embodiment has a cylindrical shape with a diameter d1 [μm] and a depth h1 [μm].

[0028] The method for forming the microholes 31 on the upper surface 30t of the glass substrate 30 is not limited to a specific method. The microholes 31 can be formed, for example, by etching or laser processing.

[0029] <Lens base preparation process> The lens element preparation step S2 shown in Figure 4 is a step in which the lens element 40 (Figure 7), which will become the lens portion 20 of the microlens array 1A, is prepared. As previously described, the lens element 40 in this embodiment is spherical.

[0030] More specifically, the lens element 40 in this embodiment is a glass particle, and its diameter (particle size) d2 [μm] is slightly larger than the diameter d1 [μm] of the microhole 31 (d2 > d1). In the following description, the lens element 40 may be referred to as "glass particle 40".

[0031] Furthermore, in the lens body preparation step S2, multiple glass particles 40 having a softening point lower than that of the glass substrate 30 prepared in the substrate preparation step S1 are prepared. The softening points of the glass substrate 30 and the glass particles 40 can be measured, for example, by differential thermal analysis (DTA).

[0032] <Lens element placement process> The lens element arrangement step S3 shown in Figure 4 is a step in which glass particles 40 prepared in the lens element preparation step S2 are placed on the glass substrate 30 prepared in the substrate preparation step S1. Figure 7 is an explanatory diagram showing the lens element arrangement step S3 of this embodiment. Figure 8 is a cross-sectional view showing the lens element arrangement step S3 of this embodiment.

[0033] As shown in Figure 7, in the lens element placement step S3, multiple glass particles 40 are scattered on the upper surface 30t of the glass substrate 30. More specifically, a number of glass particles 40 exceeding the number of microholes 31 provided in the glass substrate 30 are scattered on the upper surface 30t of the glass substrate 30.

[0034] Next, air is blown onto the glass particles 40 scattered on the upper surface 30t of the glass substrate 30. As a result, some of the glass particles 40 are captured by the microholes 31, and the remaining glass particles 40 are pushed out to the periphery of the glass substrate 30. After that, several more glass particles 40 are scattered onto the upper surface 30t of the glass substrate 30 again, and air is blown onto the scattered glass particles 40 once more.

[0035] The scattering and removal of glass particles 40 as described above is repeated several times until glass particles 40 are placed in all microholes 31 on the glass substrate 30, as shown in Figure 8. Of course, it is also possible that glass particles 40 may be placed in all microholes 31 with just one scattering and removal of glass particles 40.

[0036] In any case, in the lens element placement step S3 shown in Figure 4, one glass particle 40 is placed in each of the microholes 31 on the glass substrate 30. Note that if one glass particle 40 is placed in each of the microholes 31, the lens element placement step S3 may be performed by a method other than the one described above.

[0037] <Heating process> The heating step S4 shown in Figure 4 is a step in which the glass substrate 30 and glass particles 40 are heated under predetermined heating conditions. In the heating step S4 of this embodiment, the glass substrate 30 and glass particles 40 shown in Figure 8 are placed in a heating furnace and heated at a predetermined temperature for a predetermined time.

[0038] More specifically, in the heating step S4 of this embodiment, the glass substrate 30 and the glass particles 40 are heated at a heating temperature T [°C] that is higher than the softening point T1 [°C] of the glass particles 40 and lower than the softening point T2 [°C] of the glass substrate 30, thereby liquefying the glass particles 40.

[0039] Alternatively, in heating step S4, by heating the glass substrate 30 and glass particles 40 at heating temperature T [°C], only the glass particles 40 are softened and liquefied without softening the glass substrate 30.

[0040] In the following explanation, the liquefied glass particles 40 may be referred to as "lens material 41" to distinguish them from the glass particles 40 before liquefaction.

[0041] The heating temperature T [°C] in heating step S4 can be set, for example, based on the results of the differential thermal analysis described above. More specifically, the softening points T1 [°C] and T2 [°C] can be measured by differential thermal analysis, and the heating temperature T [°C] can be set based on these measurement results.

[0042] In this embodiment, where the material of the lens element 40 is glass, there is a risk that the lens element 40 may crystallize during the heating step S4. "Crystallization" means that the composition changes locally due to the aggregation of impurities (e.g., metal ions) contained in the liquefied lens element 40. In other words, "crystallization" means that the uniformity of the composition of the lens material 41 is impaired due to the aggregation of impurities (e.g., metal ions) contained in the lens material 41.

[0043] If crystallization occurs as described above during the heating step S4, there is a risk that the lens portion 20 having the desired optical properties may not be obtained. For example, there is a risk that aberrations may occur in the completed lens portion 20. Therefore, in the heating step S4 of this embodiment, the glass substrate 30 and the lens portion (glass particles) 40 are heated under heating conditions that cause the lens element (glass particles) 40 to liquefy but not to crystallize.

[0044] Whether or not crystallization occurs is influenced by the heating temperature and heating time in heating step S4. For example, when the heating time is the same, a higher heating temperature tends to increase the risk of crystallization. Also, when the heating temperature is the same, a longer heating time tends to increase the risk of crystallization.

[0045] Therefore, in order to avoid crystallization and shorten the time required for the heating process S4, it is desirable to set the heating temperature T [°C] to the highest possible temperature within the range in which crystallization does not occur.

[0046] Figure 9 is a cross-sectional view showing the state of the lens material 41 during the heating process S4. When the glass particles 40 shown in Figure 8 are liquefied by the heating process S4, the lens material 41 accumulates in each microhole 31, as shown in Figure 9. Furthermore, the lens material 41 does not overflow from the microholes 31, but rises higher than the edge of the microholes 31 due to surface tension.

[0047] Alternatively, in the lens element preparation step S2 shown in Figure 4, glass particles 40 are prepared that, when they undergo a phase change to a liquid, do not overflow from the microholes 31 but instead have a volume that allows them to rise from the microholes 31 due to surface tension.

[0048] From another perspective, in the substrate preparation step S1 shown in Figure 4, a glass substrate 30 is prepared in which a recess 31 having a volume that can rise due to surface tension without the lens material 41 overflowing is formed during the heating step S4.

[0049] Due to surface tension, the surface of the lens material 41 that rises from the microhole 31 becomes an extremely smooth curved surface. This surface of the lens material 41 then ultimately becomes the surface of the lens portion 20.

[0050] <Cooling process> The cooling step S5 shown in Figure 4 is a step in which the glass substrate 30 and lens material 41 are cooled after the heating step S4. In the cooling step S5 of this embodiment, the temperature of the glass substrate 30 and lens material 41 shown in Figure 9 is lowered to a temperature lower than the softening point T1 [°C] of the glass particles 40.

[0051] As a result, the lens material 41 shown in Figure 9 solidifies while maintaining its shape. This forms the lens portion 20 shown in Figure 3. More specifically, a portion of the lens material 41 that had accumulated inside the microhole 31 solidifies to form the lower part 22 of the lens portion 20. At the same time, another portion of the lens material 41 that had risen higher than the edge of the microhole 31 due to surface tension solidifies to form the upper part 21 of the lens portion 20.

[0052] It goes without saying that the glass substrate 30 that did not soften in the heating process S4 will become the base portion 10.

[0053] (Example 1) The manufacturing method of this embodiment will be described in more detail below with reference to the examples. <Substrate preparation process> In the substrate preparation step S1 of this embodiment, a square glass substrate 30 with sides of 30.0 [mm] was prepared. The material of this glass substrate 30 is quartz glass. More specifically, the glass substrate 30 is formed from 100% pure synthetic quartz, and its surface is provided with a plurality of microholes 31 with a diameter d1 of 23.0 [μm] and a depth h1 of 10.0 [μm]. Furthermore, these plurality of microholes 31 are arranged in a matrix with intervals of 100.0 [μm].

[0054] <Lens base preparation process> In the lens preparation step S2 of this embodiment, soda-lime glass particles with a diameter d2 of approximately 25.0 [μm] were prepared as the glass particles 40. More specifically, soda-lime glass particles (product number: S-SLGMS-2.5 23-26μm) sold by Corefront Co., Ltd. were prepared.

[0055] <Heating process> In the heating step S4 of this embodiment, the glass substrate 30 and glass particles (soda-lime glass particles) 40 were heated using an electric furnace (FO200) manufactured by Yamato Scientific Co., Ltd. The heating temperature T [°C] was set to 720 [°C], and the heating time was set to 20 minutes.

[0056] More specifically, the glass substrate 30 on which the glass particles 40 were placed was placed inside the electric furnace chamber, and the electric furnace was operated to raise the internal temperature to 720°C in approximately 10 minutes. The internal temperature was then maintained at 720°C for 20 minutes.

[0057] <Cooling process> In the cooling step S5 of this embodiment, the electric furnace was stopped after the heating step S4 was completed, and the internal temperature was allowed to drop to approximately 500°C. Then, the glass substrate 30 removed from the electric furnace was allowed to cool naturally to room temperature, thereby manufacturing the microlens array 1A shown in Figures 1 to 3.

[0058] <Summary> Figure 10 shows the results of observing the lens portion 20 of the microlens array 1A in this embodiment using an electron microscope. The diameter of the lens portion 20 of the microlens array 1A manufactured through the above steps was 23.0 to 24.0 [μm]. Furthermore, the surface of each lens portion 20 was a very smooth curved surface. In other words, the manufacturing method of this embodiment, in which the lens element 40 is liquefied and formed into a hemispherical shape using surface tension, made it possible to form minute lens portions 20 that would be difficult to form by methods such as press working, mold processing, embossing, and laser processing.

[0059] (Comparative example) The inventors of this case confirmed the occurrence of crystallization in a method for manufacturing a microlens array (comparative example) in which only the heating time in heating step S4 differed from that of Example 1. Specifically, crystallization was confirmed in comparative example 1, where the heating time in heating step S4 was 30 minutes. Furthermore, crystallization was also confirmed in another comparative example (comparative example 2), where the heating time in heating step S4 was 40 minutes.

[0060] More specifically, when microlens arrays were manufactured using the manufacturing methods of Comparative Examples 1 and 2, and the surface of the lens portion was observed with an electron microscope, the presence of irregularities caused by crystallization was confirmed.

[0061] The present invention is not limited to the above embodiments or examples, and can be modified in various ways without departing from its spirit. For example, the characteristics of the lens portion 20 can be controlled by controlling the shape and size of the recess 31. Specifically, the curvature of the surface of the lens 20 can be locally controlled by controlling the bottom shape of the recess 31. In other words, a microlens array having a large number of minute aspherical lenses can be manufactured.

[0062] (Example of experiment) The substrate material is not limited to quartz glass, nor is the lens material limited to soda-lime glass. The inventors have also obtained good results in experiments using glass materials mainly composed of tellurite glass.

[0063] In this experiment, a glass material having the following composition was prepared. Furthermore, the prepared glass material was crushed and placed on a flat glass substrate made of the same material as the glass substrate 30 used in Example 1, and heated under the following heating conditions (1) to (4). The same electric furnace used in Example 1 was used for heating.

[0064] In this experiment, under all heating conditions, the glass substrate did not soften, and only the glass material liquefied and became spherical due to surface tension. Furthermore, no crystallization was observed under any heating conditions. Based on these experimental results, it is expected that a microlens array substantially identical to microarray lens 1A can be manufactured by replacing the glass particles 40 in Example 1 with glass material particles having the following composition, and by selecting any of the following heating conditions (1) to (4) as the heating conditions in heating step S4 of Example 1.

[0065] <Composition of glass material> (Main material) Tellurium dioxide (TeO2): 77.0 [mol%] Zinc oxide (ZnO): 20.5 [mol%] Lanthanum oxide (La2O3): 2.5 [mol%] (Additives) Ytterbium oxide (Yb2O3): 0.1 [mol%] <Heating conditions>

[0066] (1) Heating temperature: 380[℃] / Heating time 60 minutes (2) Heating temperature: 390[℃] / Heating time 30 to 60 minutes (3) Heating temperature: 400[℃] / Heating time 30 minutes (4) Heating temperature: 410[℃] / Heating time 30 minutes

[0067] (Example 2) Next, other embodiments will be described. In this embodiment, the material of the glass particles 40 prepared in the lens element preparation step S2 and the heating conditions in the heating step S4 differ from those in Embodiment 1. In other words, in this embodiment, the microlens array 1A was manufactured in the same manner as in Embodiment 1, except for the material of the glass particles 40 and the heating conditions in the heating step S4.

[0068] In the lens element preparation step S2 of this embodiment, tellurite glass particles were prepared as glass particles 40. More specifically, glass particles 40 made of tellurite glass having the same composition as the glass material used in the above experimental example were prepared. The diameter d2 of the glass particles 40 is approximately 25.0 [μm], the same as in Example 1.

[0069] In the heating step S4 of this embodiment, the glass substrate 30 and glass particles (tellurite glass particles) 40 were heated using the same electric furnace as the one used in the heating step S4 of Embodiment 1. The diameter d1 and depth h1 of the microholes 31 provided in the glass substrate 30 are the same as in Embodiment 1. Specifically, the diameter d1 of the microholes 31 is 23.0 [μm] and the depth h1 is 10.0 [μm].

[0070] In the heating step S4 of this embodiment, the glass substrate 30 on which the glass particles 40 are placed was placed inside the electric furnace chamber, and the electric furnace was operated to raise the internal temperature to 410°C. The internal temperature of 410°C was then maintained for 30 minutes. In other words, the glass substrate 30 and glass particles 40 were heated under the same or substantially the same heating conditions as heating conditions (4) in the above experimental example.

[0071] In this example, a microlens array 1A substantially identical to the one manufactured in Example 1 was produced. Figure 11 shows the results of observing the lens portion 20 of the microlens array 1A in this example using an electron microscope. The diameter of the lens portion 20 of the microlens array 1A in this example was 23.0 to 24.0 [μm]. Furthermore, the surface of the lens portion 20 was a very smooth curved surface, and no irregularities due to crystallization were observed.

[0072] The materials of the substrate and lens element are not limited to glass. More specifically, the materials of the substrate and lens element may be other than glass, as long as the softening point of the lens element is lower than that of the substrate and the lens element alone can be softened and liquefied during the heating process. For example, the materials of the substrate and lens element may be synthetic resins. Furthermore, the materials of the substrate and the lens element may be different.

[0073] However, from the viewpoint of heat resistance and chemical resistance, it is preferable to select glass as the material for the substrate and lens element. On the other hand, from the viewpoint of cost reduction, it is preferable to select synthetic resin as the material for the substrate and lens element. [Explanation of symbols]

[0074] 1A...Microlens array, 10...Base part, 20...Lens part, 21...Upper part, 22...Lower part, 30...Substrate (glass substrate), 30b...Bottom surface, 30t...Top surface, 31...Recess (microhole), 40...Lens element (glass particle), 41...Lens material, d1...Diameter, d2...Diameter (particle size), h1...Depth, S1...Substrate preparation process, S2...Lens element preparation process, S3...Lens element placement process, S4...Heating process, S5...Cooling process, T...Heating temperature, T1, T2...Softening point

Claims

1. A substrate preparation step involves preparing a substrate having one surface with multiple recesses, A lens element preparation step of preparing a plurality of lens elements having a softening point lower than the softening point of the substrate, A lens element placement step in which the lens element is placed in each of the recesses on the substrate, The process includes a heating step of heating the substrate and the lens element at a temperature higher than the softening point of the lens element and lower than the softening point of the substrate, A method for manufacturing a microlens array, wherein the heating step involves liquefying the lens material and causing it to rise higher than the edge of the recess due to surface tension.

2. In the method for manufacturing a microlens array according to claim 1, The material of the substrate and the lens element is glass. A method for manufacturing a microlens array, wherein in the heating step, the substrate and the lens element are heated under heating conditions that cause the lens element to liquefy but not to crystallize.

3. In the method for manufacturing a microlens array according to claim 2, The substrate material is quartz glass. The material of the aforementioned lens element is soda-lime glass. A method for manufacturing a microlens array, wherein the heating temperature in the heating step is 720°C and the heating time is 20 minutes.

4. In the method for manufacturing a microlens array according to claim 2, The substrate material is quartz glass. The material of the aforementioned lens element is tellulite glass. A method for manufacturing a microlens array, wherein the heating temperature in the heating step is 410°C and the heating time is 30 minutes.

5. In the method for manufacturing a microlens array according to claim 3 or claim 4, The recess provided in the substrate prepared in the substrate preparation step is cylindrical, has a diameter of 23 [μm], and a depth of 10 [μm]. A method for manufacturing a microlens array, wherein the lens element prepared in the lens element preparation step is spherical and has a diameter of 25 [μm].

Images