JP2006047562A - Method for manufacturing substrate with recessed portion for microlens, and transmissive screen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a substrate with a recessed portion for a microlens by which the substrate with the recessed portion for the microlens being a mold of a microlens having a wide viewing angle and high performance can be inexpensively formed in a small number of steps. <P>SOLUTION: The method includes: a step of layering a plurality of etching mask films on a substrate surface, wherein each etching mask film is formed from a material having higher processability by laser light than the adjacent etching mask film in the substrate side; and a step of irradiating the center of a region where a recessed portion is to be formed with laser light to form a through hole in the plurality of etching mask films, wherein the through hole of each etching mask film is formed larger than the through hole of the adjacent etching mask film in the substrate side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a molding method of a mold for manufacturing a microlens array used for a rear projection television or the like.

  Conventionally, as a method of manufacturing a transmissive screen with a convex microlens array used in a rear projection television or the like, a glass substrate having a concave portion that becomes a mold for a microlens is manufactured, and this is filled with a resin and cured, and then a mold is formed. A method of removing is known.

  For example, after forming an etching mask on the surface of the glass substrate and forming a plurality of pinholes on the glass substrate surface, the glass substrate is brought into contact with an etching solution to cause isotropic etching. (For example, refer to Patent Document 1).

  As a method for forming a pinhole in an etching mask, a resist layer having an opening corresponding to the shape of the pinhole is formed, and then dry etching is performed. Alternatively, a laser is irradiated to the position where the pinhole is formed and the etching mask is used. The method of removing is used.

When forming a recess by wet etching, the SD ratio of the recess (ratio of the radius and depth of the recess) is made closer to 1 by sequentially laminating a chromium oxide film and a chromium film as an etching mask film on the glass surface. If this is used as a mold, a high-performance microlens with a wide viewing angle can be formed.
JP 2000-258609 A

  However, the chromium oxide film is less likely to absorb the laser than the chromium film, and in order to form a through hole having the same shape as the chromium film in the chromium oxide film, it is necessary to irradiate a high energy laser. . On the other hand, the method of forming a resist layer and forming a through hole by dry etching tends to increase the cost of the product because the process is complicated and equipment is required.

  Accordingly, an object of the present invention is to provide a method for forming a substrate with a concave portion for a microlens, which serves as a mold for a high-performance microlens having a wide viewing angle, at a low cost and with fewer steps.

  In order to solve the above-described problems, a method for manufacturing a substrate with concave portions for microlenses according to the present invention is a step of laminating and forming two or more etching mask films on a substrate surface, and each etching mask film is formed on one substrate. Forming a material that can be processed with a laser having a lower energy than the etching mask film on the side, and irradiating a region where each recess of the etching mask film is to be formed with a laser to form a through hole in each of the regions Then, the step of forming the through hole of each etching mask film larger than the through hole of the etching mask film on one substrate side, and by bringing the etching solution into contact with the surface of the substrate exposed by the through hole, Forming a recess on the surface of the substrate.

  In this method, the smallest through-hole is formed in the etching mask film that is most difficult to laser process, that is, the etching mask film directly laminated on the substrate, and the larger through-hole is formed in the etching mask film that is far from the substrate and easy to laser process. To do. Therefore, the required laser irradiation energy is smaller than the method of forming through holes having the same shape in all of the plurality of etching mask films.

  The laser that irradiates the etching mask film preferably has a Gaussian distribution in which the intensity of the laser beam attenuates from the center toward the periphery. By irradiating with a laser having such an intensity distribution, the mask film on the substrate side that is most difficult to be laser processed has a minute through-hole formed at the center of the spot with the highest intensity, and the mask film away from the substrate has a high intensity. Lower spot perimeters are also utilized to form larger through holes.

  Further, in the method according to the present invention, through holes having different sizes are formed in each etching mask film, a step is generated in the film thickness in the through holes. The thinner the film thickness, the faster it is eroded by wet etching, so the through-hole is enlarged as the etching proceeds. Since the etching of the substrate proceeds isotropically, a substantially hemispherical concave portion is formed if the area where the substrate is in contact with the etching solution is constant, but a step is formed in the formed concave portion by changing the area. Occurs. The inventors of the present invention have a concave portion formed when the through-hole is small, that is, the central portion of the concave portion finally formed has a relatively high curvature, and is a concave portion formed after the through-hole is large, that is, the final portion. It has been found that the peripheral edge of the recess formed in is a recess having a relatively low curvature.

  With this configuration, since the edge of the recess can be made sufficiently wide and the depth can be made sufficiently deep, a recess having an SD ratio close to 1 can be efficiently made using a through hole provided by a relatively low energy laser. It becomes possible to form. In addition, since the curvature near the edge of the concave portion becomes low, the cross-sectional area of the so-called “horn” at the boundary with the adjacent concave portion is relatively large, so when removing the substrate by pouring the resin, There is also an advantage that lack of is less.

  In the method according to the present invention, it is preferable that the etching mask film has two layers, the etching mask film on the substrate side is a chromium oxide film, and the etching mask film far from the substrate is a chromium film. The chromium film has a higher laser absorptance than the chromium oxide film, and by stacking the chromium film on the chromium oxide film, a through-hole smaller than the chromium film can be easily formed in the chromium oxide film.

  When laminating a chromium oxide film and a chromium film, the film thickness is preferably 1: 4 to 1: 2, and most preferably 1: 3. It is known that the chromium oxide film has a compressive stress, and the chromium film has a tensile stress. The film thickness can be canceled by setting the film thickness to 1: 4 to 1: 2. It is possible to prevent the film from being broken during the etching due to the stress.

  The present invention also provides a transmission screen including a microlens array formed by filling a resin with a substrate having concave portions for microlenses manufactured by the above-described manufacturing method. Such a transmissive screen is a high-performance one provided with a microlens array with a wide viewing angle, which is manufactured at low cost, and is suitably used for a projector.

  Furthermore, the present invention also provides a display device, particularly a rear projection television, including a microlens array formed by using a substrate with a concave portion for microlenses manufactured by the above-described manufacturing method as a mold and filling the substrate with resin. To do. Such a display device is also a high-performance device including a microlens array with a wide viewing angle, which is manufactured at a low cost.

  In the method for manufacturing a substrate with concave portions for microlenses according to the present invention, by laser irradiation, a smaller through hole is formed in the etching mask film near the substrate, and a larger through hole is formed in the etching mask film far from the substrate. Thus, by forming the recesses by the wet etching method, a recess having an SD ratio close to 1 can be obtained by laser irradiation with relatively low energy. If a substrate having such a recess is used as a mold, a high-performance microlens array having a wide viewing angle can be formed.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

(Conventional technology)
First, the prior art will be described with reference to FIGS. As described above, also in the conventional method, in order to make the SD ratio of the recesses close to 1, first, as shown in FIG. 5A, a chromium oxide film 42 and a chromium film 44 are formed on the glass substrate 40 as etching mask films. Form. Subsequently, as shown in FIG. 5B, laser irradiation or a resist layer having a pattern corresponding to the recess is formed at a place where the recess is to be formed, and etching (for example, dry etching with CF gas or the like) is performed. Form. Since the through hole is formed in the same shape in the chromium oxide film 42 and the chromium film 44, in the case of laser irradiation, a laser having a strength capable of processing the chromium oxide film over the entire region where the through hole is formed (shown in FIG. 3). It is necessary to irradiate a laser having an intensity of E ₂ or more.

  Subsequently, as shown in FIG. 5C, the recesses 48a to 48c are formed by wet etching using, for example, a hydrofluoric acid-based etching solution. At this time, unlike the method according to the present invention, since the thickness of the etching mask film is uniform, the size of the through hole does not change due to part of the etching mask being eroded. Accordingly, the recesses 48a to 48c are substantially hemispherical recesses having no steps.

  Next, as shown in FIG. 5D, the microlens array is obtained by filling the substrate S ′ with concave portions for microlenses S ′ obtained by the above-described method with the resin 50 and removing the substrate S ′. .

  FIG. 6 shows an enlarged view of the recess 48a. By stacking the chromium oxide film and the chromium film and using it as an etching mask film, a recess having an SD ratio close to 1 can be obtained. However, in the case of this method, in order to remove all the chromium oxide film 42, High energy laser irradiation is required. Moreover, since the horn 52 located between each recessed part is formed in a comparatively acute angle, there exists a tendency for the horn 52 to be missing in the process of removing resin from a casting_mold | template.

(First embodiment)
Next, the process of the manufacturing method of the board | substrate with a recessed part for microlenses which concerns on embodiment of this invention is demonstrated.

  FIG. 1 is an explanatory diagram for explaining the steps of the manufacturing method of the present embodiment. First, as shown in FIG. 1A, a chromium oxide film 12 and a chromium film 14 are formed on a glass substrate 10 as etching mask films. The chromium oxide film 12 and the chromium film 14 can be formed by sputtering or vapor deposition. The film thicknesses of the chromium oxide film 12 and the chromium film 14 are preferably 1: 3. For example, the film thickness of the chromium oxide film can be 100 mm, and the film thickness of the chromium film can be 300 mm.

  The etching mask film may also be formed on the back surface of the substrate 10 (the surface on which the recess is not formed), thereby preventing the substrate 10 from being etched from the back surface when the entire substrate is immersed in an etching solution. Can do.

Subsequently, as shown in FIG. 1B, a laser is irradiated to form through holes in the chromium oxide film 12 and the chromium film 10. Usable lasers include gas lasers such as CO ₂ lasers and excimer lasers, and solid-state lasers such as YAG lasers and femtosecond lasers.

FIG. 3 shows the intensity distribution at the irradiation spot of the laser to be irradiated. x represents the length along the diameter of the irradiation spot, and x _o represents the center of the position where the through hole is formed. The intensity of the laser has a Gaussian distribution that becomes maximum at x _o and attenuates toward the periphery. Here, assuming that the irradiation energy of the laser necessary for forming the through hole in the chromium film 14 and the chromium oxide film 12 is E ₁ and E ₂ , respectively, x ₁ to which the laser having an energy larger than E ₂ is irradiated. Through-holes are formed in both the chromium oxide film 12 and the chromium film 14 in a region having a diameter x ₂ . On the other hand, in the region where the laser irradiation energy is larger than E _{1 and} smaller than E ₂ , that is, in the region excluding the region having x ₁ to x ₂ as the diameter from the region having x ₃ to x ₄ as the diameter, only the chromium film 14 is present. After being removed, the chromium oxide film 12 is not processed or left on the glass substrate until it is slightly removed and thinned.

Next, as shown in FIG. 1C, the substrate is immersed in a wet etching solution. Wet etching proceeds isotropically, and substantially hemispherical recesses 16 a to 16 c are formed in the glass substrate 10. As the etchant, a hydrofluoric acid-based etchant such as NH ₄ HF ₂ can be appropriately selected and used. However, by adding an acid such as sulfuric acid, the glass product generated during etching can be dissolved. The etching rate can be stabilized.

  Thereafter, as shown in FIG. 1D, the thin chromium oxide film 12 formed by this wet etching is also removed, and the through hole is enlarged. When the glass substrate is brought into contact with the etching solution through the enlarged through hole, the recesses 18a to 18c are formed on the outer peripheral portions of the recesses 16a to 16c. As a result, a step is formed between the recesses 16a to 16c and the recesses 18a to 18c.

  FIG. 2 shows an enlarged view of the recesses 16a and 18a. According to the method of the present invention, an SD ratio close to 1 can be obtained even though a relatively low energy laser is irradiated to form a through hole in the etching mask film. In addition, since the cross-sectional area of the so-called “horn” located between the recess 18a and the recess 18b is formed to be large, when the microlens array formed by filling the resin is removed from the substrate 10, the horn is missing. It becomes difficult.

  FIG. 1E shows a substrate S with concave portions for microlenses. After the recesses are formed, the etching mask film can be removed, for example, by wet etching using an alkaline aqueous solution or the like, whereby the substrate S with recesses for microlenses can be obtained. If an etching mask film is also formed on the back surface, it can be removed at the same time.

  Next, as shown in FIG. 1 (F), the resin 20 is filled in the recesses of the microlens substrate S. After the resin 20 is cured, it is removed from the substrate to obtain a microlens array in which convex microlenses are arranged. Examples of the material of the resin 20 include an acrylic resin and a polycarbonate resin.

  According to this embodiment, a microlens recess having an SD ratio close to 1 is formed on a substrate by using a through-hole formed without removing the chromium oxide film 12 more than necessary by laser irradiation with relatively low energy. can do. If this substrate is used as a mold, a high-performance microlens array with a wide viewing angle can be obtained. In addition, a step is formed in the concave portion of the substrate with concave portions for microlenses obtained by this method, and the cross-sectional area of the horn is large. Therefore, when removing the resin microlens array from the substrate, It is less prone to chipping and can be used repeatedly.

(Display device)
The microphone lens array manufactured by the manufacturing method according to the present invention can be used for any application in which the microlens array manufactured by the conventional method is used, for example, as a diffusion plate, a black matrix screen, and a transmissive screen. It can be suitably used. The microlens array of the present invention can also be suitably used for a display device such as a projector using a transmission screen. Specific examples of such a display device include a rear transmission image display device (rear projection television).

  FIG. 4 is a schematic view of a rear transmissive image display device 500 including a microlens array manufactured by the manufacturing method according to the present invention. As shown in the figure, the display device 500 includes a video projector (projection type cathode ray tube) 504 in a housing (cabinet) 502. The rear opening of the housing 502 is covered with a mirror cover, and a reflecting mirror 506 is installed in the mirror cover. A rectangular opening is formed on the front surface of the housing 502, and the microlens array 100 is provided so that the surface 140 on which the lens is formed on the incident light side faces.

  In addition, the board | substrate S with a recessed part for microlenses which concerns on this invention can also be used as a microlens board | substrate in the form integrated with resin, filling and hardening resin. Such a microlens substrate can be used as a counter substrate for a liquid crystal projector, for example.

  A microlens array screen was prepared using the substrate with concave portions S for microlenses formed by the method according to the present invention as a mold, and the viewing angle was measured.

  First, in the substrate with concave portions for microlenses, a chromium oxide film having a thickness of 100 mm was formed on a glass substrate as an etching mask film, and a chromium film was laminated thereon to a thickness of 300 mm.

Next, an excimer laser having a wavelength of 248 nm and a power density of 0.7 J / cm ² was irradiated to the chromium oxide film and the chromium film to form a direct 2.0 μm through-hole to expose the substrate surface.

Subsequently, an aqueous solution containing 4% NH ₄ HF ₂ and 4% H ₂ SO ₄ was prepared as an etchant, and the glass substrate on which the etching mask film was formed was immersed. Thereby, the recessed part which has a level | step difference as shown in FIG. 2 was formed. This was filled with resin and cured, and the substrate was removed to obtain a microlens array.

On the other hand, as a comparative example, an excimer laser with a wavelength of 248 nm and a power density of 1.0 J / cm ² was irradiated to form a direct 2.0 μm through hole. Thereby, the substantially hemispherical recessed part without a level | step difference as shown in FIG. 6 was formed. This was filled with resin and cured, and the substrate was removed to obtain a microlens array.

  The results of measuring the viewing angle for each microarray are shown in Table 1.

この結果から、両者の視野角にはほとんど差がなく、低エネルギーのレーザ照射により貫通孔を形成した実施例のマイクロアレイレンズが、高エネルギーのレーザ照射により形成された比較例のマイクロアレイレンズと略同等の品質を有することが確認された。

From these results, there is almost no difference between the viewing angles of the two, and the microarray lens of the example in which the through-hole was formed by low-energy laser irradiation was substantially equivalent to the microarray lens of the comparative example formed by high-energy laser irradiation. It was confirmed to have the quality of

It is explanatory drawing of the manufacturing method of the board | substrate with a recessed part for microarrays concerning this invention. It is a partial enlarged view of the board | substrate with a recessed part manufactured by the method shown in FIG. It is explanatory drawing which shows the relationship between the energy of a laser irradiation, and formation of a through-hole. It is the schematic of the rear projection type television which concerns on embodiment of this invention. It is explanatory drawing of the manufacturing method of the conventional board | substrate with a recessed part for microarrays. It is a partial enlarged view of the board | substrate with a recessed part manufactured by the method shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10, 40 ... Glass substrate, 12, 42 ... Chromium oxide film, 14, 44 ... Chromium film, 16, 18, 48 ... Recess, 20 ... Resin, 22, 52 ... Tsuno, S, S '... Substrate with recess for microarray , 500 ... Rear projection TV

Claims (9)

A method for producing a substrate with concave portions for microlenses, wherein a plurality of concave portions are provided on the surface, and microlenses are formed by supplying resin to the concave portions,
Forming two or more etching mask films on the surface of the substrate, each etching mask film being formed of a material that can be processed by a laser having a lower energy than the etching mask film on one substrate side; ,
A step of irradiating a region of the etching mask film where the recesses are to be formed with laser to form a through hole in each of the regions, wherein the through hole of each etching mask film is formed on one substrate side. Forming larger than the through hole of the etching mask film;
Forming a recess in the surface of the substrate by bringing an etching solution into contact with the surface of the substrate exposed by the through hole.   2. The method according to claim 1, wherein in the step of irradiating the laser, a laser having a Gaussian distribution in which the intensity is attenuated from the center toward the periphery is used at an irradiation spot of the laser.   3. The step according to claim 1, wherein in the step of forming the recess, a step is formed in the recess by expanding a through hole of the etching mask film and changing an area in which the substrate contacts the etching solution. Method.   The method according to claim 1, wherein the etching mask film has two layers, and is a chromium oxide film and a chromium film in order from the substrate side.   The method according to claim 4, wherein a film thickness of the chromium oxide film is set to 1/4 to 1/2 of a film thickness of the chromium film.   The substrate with concave portions for microlenses manufactured by the manufacturing method according to any one of claims 1 to 5 is used as a mold, and is filled with resin and cured, and the substrate with concave portions for microlenses is formed from the resin. A transmissive screen comprising a microlens array formed by removing the lens.   A projector comprising the transmissive screen according to claim 6.   A rear projection television comprising the transmissive screen according to claim 6. The substrate with concave portions for microlenses manufactured by the manufacturing method according to any one of claims 1 to 5 is used as a mold, and is filled with resin and cured, and the substrate with concave portions for microlenses is formed from the resin. A display device comprising a microlens array formed by removing the lens.

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