JP2005231919A - Etching solution, etching method, substrate with recess, microlens substrate, transmissive screen, and rear projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an etching solution capable of uniformly etching a glass substrate, an etching method, a substrate with a recess, a microlens substrate, a transmission screen and a rear projector manufactured by using such a method. .
An etching solution of the present invention includes ammonium fluoride and an acid. Ammonium fluoride is mainly composed of ammonium monohydrogen difluoride. The acid is mainly composed of sulfuric acid. When the content of ammonium fluoride in the etching solution is A [g / L] and the content of acid is B [g / L], the relationship of 1.0 ≦ B / A ≦ 4 is satisfied. The content of ammonium fluoride is 1 to 500 g / L. The acid content is 1.7 to 920 g / L.
[Selection] None

Description

  The present invention relates to an etching solution, an etching method, a substrate with a recess, a microlens substrate, a transmissive screen, and a rear projector.

A display device that projects an image on a screen is known. As such a display device, a rear-type projector applied to a home theater monitor, a large-screen television, or the like is known, and the demand thereof has been increasing in recent years.
In such a rear projector, a transmissive screen is mainly used for image formation.

  A wide viewing angle characteristic is particularly required for a transmission screen used in such a rear projector. As a transmission screen having such a wide viewing angle characteristic, a screen having a Fresnel lens portion on which a Fresnel lens is formed and a microlens substrate on which a large number of microlenses are formed is known. This transmissive screen has an advantage that a good viewing angle characteristic can be obtained in the vertical direction due to the light refraction action of the microlens.

As a manufacturing method of a microlens substrate used for such a transmission type screen, a manufacturing method by etching using a mask having an opening having a predetermined pattern is known (for example, see Patent Document 1).
However, in the method described in Patent Document 1, when etching is performed to form a recess, a product (by-product) that is hardly soluble in water due to a reaction between an etching solution and a component constituting glass near the surface of the glass substrate. In some cases, etching was hindered. For this reason, there has been a problem that the shape of each concave portion to be formed varies greatly. Such variations tend to appear more prominently as the size of the opening provided in the mask is smaller.

JP-A-9-101401

  An object of the present invention is to provide an etching solution capable of uniformly etching a glass substrate, an etching method, a substrate with a recess, a microlens substrate, a transmissive screen, and a rear projector manufactured by using such a method. It is to provide.

Such an object is achieved by the present invention described below.
The etching solution of the present invention is characterized by containing ammonium fluoride and an acid.
Thereby, the production | generation of a slightly soluble by-product can be suppressed and it can etch uniformly with respect to a glass substrate.
In the etching solution of the present invention, it is preferable that the ammonium fluoride is mainly composed of ammonium monohydrogen difluoride.
Thereby, it can etch more efficiently with respect to a glass substrate.

In the etching solution of the present invention, the acid is preferably mainly composed of sulfuric acid.
Thereby, the by-product of reaction with etching liquid and glass can be removed more effectively. In particular, when a Cr or CrO film is used as a mask, an etching solution containing sulfuric acid is used to etch the glass substrate more uniformly while suppressing the influence on the mask more effectively. Can be applied.

In the etching solution of the present invention, when the content of the ammonium fluoride in the etching solution is A [g / L] and the content of the acid is B [g / L], 1.0 ≦ B / A ≦ It is preferable that the relationship 4 is satisfied.
Thereby, etching can be more uniformly and efficiently performed on the glass substrate while more effectively removing a by-product of the reaction between the etchant and the glass.

In the etching solution of the present invention, the content of the ammonium fluoride is preferably 1 to 500 g / L.
Thereby, it can etch more efficiently with respect to a glass substrate.
In the etching solution of the present invention, the acid content is preferably 1.7 to 920 g / L.
Thereby, the by-product of reaction with etching liquid and glass can be removed more effectively.

The etching solution of the present invention preferably contains hydrogen peroxide.
Thereby, it can etch more uniformly with respect to a glass substrate.
The etching method of the present invention is an etching method in which etching is performed by forming a mask on a glass substrate,
The etching solution of the present invention is used.
Thereby, the production | generation of a slightly soluble by-product can be suppressed and it can etch uniformly with respect to a glass substrate. Further, although a by-product is likely to be generated in a glass having a large content of impurities such as Na, etching can be performed uniformly in such glass.

In the etching method of the present invention, it is preferable that the mask is mainly composed of Cr and / or CrO.
As a result, the internal stress of the mask as a whole can be adjusted, and an initial hole having a desired shape and size can be accurately formed. As a result, the shape and size of the recess can be easily and reliably controlled. .

In the etching method of the present invention, the average thickness of the mask is preferably 5 to 500 nm.
This makes it easier to form the initial hole while maintaining resistance to etching, and the size of the opening can be more easily controlled.
The etching method of the present invention is an etching method for etching the mask having an opening,
The average diameter of the openings is preferably 10 μm or less.
As a result, the radius of curvature near the center of the recess formed in the etching process can be made suitable, and the refractive index of light near the center of the microlens finally obtained is made more suitable. can do. Moreover, since the flat part area contained in a recessed part can be decreased, the viewing angle characteristic of the microlens screen (microlens substrate) finally obtained can be improved.

In the etching method of the present invention, it is preferable that the glass substrate is mainly composed of soda glass.
The soda glass can be easily processed, and the obtained substrate with recesses can have suitable optical characteristics. Further, soda glass is relatively inexpensive and is advantageous from the viewpoint of manufacturing cost.

In the etching method of the present invention, it is preferable to form a recess having a diameter of 10 to 500 μm.
Thereby, the etching method of this invention can be applied more suitably.
In the etching method of the present invention, it is preferable to form a recess for forming a microlens by etching.
Thereby, a microlens with small variations in shape and size can be manufactured.

The substrate with a recess according to the present invention is manufactured using the etching method according to the present invention.
As a result, a microlens substrate with small variations in shape and size can be manufactured.
The microlens substrate of the present invention is manufactured using the substrate with concave portions of the present invention.
Thereby, a microlens substrate having a microlens with small variations in shape and size can be provided.

The transmission screen of the present invention is characterized by including the microlens substrate of the present invention.
As a result, it is possible to provide a transmissive screen that has little luminance unevenness on a large screen and is excellent in spreading light in all directions.
In the transmissive screen of the present invention, a Fresnel lens portion in which a Fresnel lens is formed on the light exit side;
It is preferable to include the microlens substrate disposed on the light emission side of the Fresnel lens unit.
Thereby, a transmissive screen excellent in luminance distribution and viewing angle characteristics can be provided as a transmissive screen.

A rear projector according to the present invention includes the transmission screen according to the present invention.
As a result, a rear projector excellent in luminance distribution and viewing angle characteristics can be provided as a transmissive screen.
The rear projector according to the present invention preferably includes a projection optical unit and a light guide mirror.
As a result, a rear projector excellent in luminance distribution and viewing angle characteristics can be provided as a transmissive screen.

Hereinafter, an etching solution, an etching method, a substrate with a recess, a microlens substrate, a transmissive screen, and a rear projector according to the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
First, prior to the description of the etching solution of the present invention, the etching method of the present invention will be described.

In the following description, the case where the etching method of the present invention is applied to the manufacture of a substrate with recesses having recesses for forming microlenses will be described.
FIG. 1 is a schematic longitudinal sectional view showing a manufacturing process when the etching method of the present invention is applied to the formation of a recess for forming a microlens, and FIG. 2 is a substrate with a recess obtained by using the etching method of the present invention. FIG. 3 is a longitudinal sectional view of a microlens substrate formed using a substrate with a recess.

First, the glass substrate 5 is prepared when manufacturing the substrate 2 with recesses.
The glass substrate 5 is preferably used with a uniform thickness and no deflection or scratches. Further, the glass substrate 5 is preferably one whose surface is cleaned or smoothed by washing or etching.

The constituent material of the glass substrate 5 is not specifically limited, For example, an alkali free glass, soda glass, crystalline glass, quartz glass, lead glass, potassium glass, borosilicate glass etc. are mentioned. For example, when a microlens substrate is manufactured using the substrate 2 with recesses, the constituent material of the glass substrate 5 is preferably alkali-free glass, soda glass, or crystalline glass (for example, neoceram). Among them, soda glass is easy to process, and the obtained substrate 2 with recesses can have suitable optical characteristics. Further, soda glass is relatively inexpensive and is advantageous from the viewpoint of manufacturing cost. In particular, soda glass tends to cause a problem that a product (by-product) that is hardly soluble in water due to a reaction with a conventional etching solution. Therefore, the etching solution of the present invention described in detail later is used. And the effect of this invention appears more notably.
The thickness of the glass substrate 5 varies depending on various conditions such as the material constituting the glass substrate 5 and the refractive index, but is usually preferably about 0.3 to 20 mm, more preferably about 2 to 8 mm. preferable. When the thickness is within this range, for example, a compact substrate 2 with concave portions for microlenses having necessary optical characteristics can be obtained.

<1> As shown in FIG. 1A, a mask 6 is formed on the surface of the prepared glass substrate 5 (mask forming step). At the same time, a back surface protective film 69 is formed on the back surface of the glass substrate 5 (the surface opposite to the surface on which the mask 6 is formed). Of course, the mask 6 and the back surface protective film 69 can be formed simultaneously.
In the present embodiment, the mask 6 is composed of two films, a first film 61 and a second film 62, as shown in the drawing.

The first film 61 and the second film 62 are adjacent to each other, and the first film 61 is provided closer to the glass substrate 5 than the second film 62.
In the present embodiment, the first film 61 has a compressive stress as an internal stress, and the second film 62 has a tensile stress as an internal stress. The “internal stress” in this specification refers to the internal stress of the film at room temperature when a film having a diameter of 10 cm is formed on a flat glass substrate. In addition, the compressive stress and the tensile stress work in a direction that cancels or relaxes each other. That is, the internal stress having a negative value is referred to as “compressive stress”, and the positive stress is referred to as “tensile stress”. "

  By using the mask 6 having such a configuration, the internal stress of the mask 6 as a whole can be adjusted, and an initial hole having a desired shape and size can be accurately formed. As a result, the shape and size of the concave portion can be obtained. Can be controlled easily and reliably. Further, by using the mask having such a structure, the adhesion between the mask and the substrate can be improved. Further, the side etching speed can be controlled by adjusting the internal stress of the entire mask, and as a result, the concave portions corresponding to the spherical lens and the aspherical lens can be easily formed.

The internal stress (compressive stress) of the first film 61 is preferably -1700 to -700 mPa, and more preferably -1500 to -900 mPa. Thereby, the internal stress of the mask 6 as a whole can be controlled more reliably, and an initial hole having a desired shape and size can be formed with higher accuracy.
The internal stress (tensile stress) of the second film 62 is preferably 500 to 1500 mPa, and more preferably 700 to 1300 mPa. Thereby, the internal stress of the first film 61 can be more easily offset or alleviated, and an initial hole having a desired size can be formed with higher accuracy.

  The internal stress of the mask 6 as a whole is preferably −400 to 400 mPa, and more preferably −250 to 250 mPa. Thereby, the initial hole of a desired size can be formed with higher accuracy, and as a result, the shape of the recess can be more reliably controlled. In addition, by using such a mask 6, the adhesion between the mask 6 and the glass substrate 5 can be improved.

The material for forming the first film 61 is not particularly limited, and examples thereof include CrO, TiO, Ta ₃ O ₅ , NiO, and TiWO. Especially, it is preferable that the 1st film | membrane 61 is mainly comprised by CrO. Thus, when the first film 61 is mainly composed of CrO, the internal stress of the mask 6 as a whole can be controlled more easily. In addition, the initial hole can be easily formed, and when etching is performed, resistance to etching is excellent. In addition, a uniform film can be easily formed on a relatively large glass substrate. Further, if the first film 61 is mainly composed of CrO, for example, when the second film 62 is mainly composed of Cr, the adhesion with the second film 62 is high. improves. Moreover, adhesiveness with the glass substrate 5 is also improved.

  A material for forming the second film 62 is not particularly limited, and examples thereof include Cr, Ti, Ta, Ni, and TiW. Among these, it is preferable that the second film 62 is mainly composed of Cr. As described above, when the second film 62 is mainly composed of Cr, the internal stress of the first film 61 can be more easily offset or alleviated. In addition, the initial hole can be easily formed, and the etching resistance is particularly excellent when etching is performed. In addition, a uniform film can be easily formed on a relatively large glass substrate.

Further, it is preferable to control the internal stress of the mask 6 as a whole by adjusting the ratio of the average thicknesses of the first film 61 and the second film 62. Thereby, the initial hole of a desired size can be formed with higher accuracy, and as a result, the shape of the recess can be more reliably controlled.
Further, when the average thickness of the first film 61 is X [nm] and the average thickness of the second film 62 is Y [nm], the relationship of 0.01 ≦ X / Y ≦ 0.8 is satisfied. It is preferable that the relationship 0.1 ≦ X / Y ≦ 0.5 is satisfied. By satisfying such a relationship, the internal stress of the mask 6 as a whole can be more reliably controlled, and an initial hole having a desired size can be formed with higher accuracy. On the other hand, if X / Y is less than the lower limit, the stress of the second film is strong and the stress of the second film remains, and the side etching amount increases in the depth direction, or a smooth contour is formed. I can't get it. On the other hand, when X / Y exceeds the upper limit, the stress of the first film is strong and the stress of the first film remains, and the amount of side etching increases in the depth direction or a smooth contour can be obtained. I can't.

The average thickness of the mask 6 is preferably 5 to 500 nm, and more preferably 40 to 150 nm. When the average thickness of the mask 6 is in such a range, the initial hole can be easily formed while maintaining the resistance to etching, and the size of the initial hole can be controlled more easily.
The method for forming the mask 6 is not particularly limited, and for example, a dry plating method such as a vapor deposition method, a sputtering method, a CVD method, or an ion plating method, or a wet plating method such as electrolytic plating or electroless plating may be used. it can. In addition, the first film 61 and the second film 62 may have different methods or different conditions.

  In addition, the back surface protective film 69 is for protecting the back surface of the glass substrate 5 after the next process. This back surface protective film 69 suitably prevents erosion, deterioration, etc. of the back surface of the glass substrate 5. The back surface protective film 69 may not be made of the same material as that of the mask or may be made of the same material as that of the mask 6. In the latter case, the back surface protective film 69 can be provided simultaneously with the formation of the mask 6. In the latter case, since the internal stress of the back surface protective film 69 can be made relatively small, distortion or the like with respect to the glass substrate 5 is suppressed, and the concave portion 3 having a desired size and shape is formed with higher accuracy. can do.

The mask 6 may have a third film other than the first film 61 and the second film 62. Such a third film can be provided on the second film 62 or on the substrate side of the first film 61, for example. In the case of the former structure, a film mainly composed of Au can be used as the third film. When the third film is mainly composed of Au, the surface of the second film 62 can be protected and the resistance of the entire mask 6 to etching can be improved. In the case of the latter configuration, for example, when the adhesion between the glass substrate 5 and the first film 61 is relatively low, the mask 6 and the glass substrate 5 are adhered by providing the third film. The property can be made high.
Note that in the case where the third film is provided, the third film is preferably relatively thin. Specifically, it is preferably 200 nm or less.

<2> Next, as shown in FIG. 1 (b), a plurality of initial holes (openings) 63 are formed in the mask 6 to serve as mask openings in the later-described etching (initial hole forming step). .
The initial hole 63 may be formed by any method, and can be formed by a physical method, laser light irradiation, or the like. Thereby, for example, a substrate with a recess can be manufactured with high productivity. In particular, the concave portion can be easily formed even on a large-area substrate.

  Examples of the physical method for forming the initial hole 63 include blasting such as shot blasting and sand blasting, etching, pressing, dot printer, tapping, rubbing, and the like. When the initial hole 63 is formed by blasting, the initial hole 63 can be efficiently formed in a shorter time even with a glass substrate 5 having a relatively large area (area of the region where the recess 3 is to be formed).

In addition, when the initial hole 63 is formed by laser light irradiation, the type of laser light to be used is not particularly limited, but a ruby laser, a semiconductor laser, a YAG laser, a femtosecond laser, a glass laser, a YVO ₄ laser, a Ne- Examples include He laser, Ar laser, CO ₂ laser, and excimer laser. Moreover, you may use wavelengths, such as SHG of each laser, THG, and FHG. When the initial hole 63 is formed by laser light irradiation, the size of the initial hole 63 to be formed, the interval between adjacent initial holes 63, and the like can be controlled easily and accurately.
It is preferable that the formed initial holes 63 are formed evenly over the entire surface of the mask 6.

The size of the initial hole (opening) 63 is preferably relatively small. Thus, when the size of the initial hole 63 is small, the radius of curvature in the vicinity of the center portion of the recess 3 formed in the etching process described later can be made suitable, and the microlens finally obtained The refractive index of light in the vicinity of the central portion of 4 can be made more suitable. Moreover, since the flat part area contained in the recessed part 3 can be decreased, the viewing angle characteristic of the microlens screen (microlens substrate) finally obtained can be improved.
Specifically, the average diameter of such initial holes (openings) 63 is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 0.1 to 3 μm. When the average diameter of the initial holes 63 is in such a range, the etching method of the present invention can be more suitably applied.

  <3> Next, as shown in FIGS. 2 (c) and 2 (d), etching (wet etching) is performed on the glass substrate 5 using the mask 6 to form a large number of recesses 3 on the glass substrate 5 ( Etching process).

Etching (wet etching) is performed on the glass substrate 5 covered with the mask 6 in which the initial holes 63 are formed, so that the glass substrate 5 is masked as shown in FIGS. A number of recesses 3 are formed on the glass substrate 5 by being etched from a portion where 6 is not present, that is, from the initial hole 63.
By the way, when wet etching is performed using a conventional etching solution, when etching is performed on the glass substrate, an etching solution erodes the glass substrate, and at the same time, a by-product that is hardly soluble in water is generated. There was a problem of inhibiting the erosion of the glass substrate by the etching solution. As a result, there is a problem in that the shape and size of the obtained recesses vary. In particular, as described above, when the opening (initial hole 63) provided in the mask 6 is relatively small, the opening is clogged with the generated byproduct, or the byproduct is glass. In some cases, the substrate re-adheres to the substrate, and the etching solution is not appropriately supplied to the glass substrate, and the variation in the shape and size of the resulting recess tends to be particularly large. In addition, such a tendency is conspicuous when a relatively small concave portion for forming a microlens is formed on a relatively large substrate that can be applied to a rear projector or the like as described later.

  Therefore, as a result of intensive studies, the present inventor can suppress the production of poorly soluble by-products by using an etching solution containing ammonium fluoride and an acid (the etching solution of the present invention), It has been found that uniform etching can be performed on a glass substrate. This is presumably because the hardly soluble by-product reacts with the acid contained in the etching solution to change into a soluble substance.

  As described above, when the etching solution of the present invention is used, the glass substrate can be uniformly etched, and as a result, variations in the shape and size of the formed recesses can be reduced. In the present embodiment, in particular, as described above, since the initial hole 63 formed in the mask 6 is formed with high accuracy, the shape and size of the recess 3 to be formed can be more reliably desired by a synergistic effect. Can be.

As ammonium fluoride, there are a normal salt (NH ₄ F) and a hydrogen salt (NH ₄ HF ₂ : ammonium monohydrogen difluoride). In the present invention, either one or both of them may be used. You may use what contains.
In particular, when ammonium fluoride containing ammonium monofluoride as a main component is used as the ammonium fluoride, the glass substrate 5 can be etched more efficiently. Moreover, it can use together with the acid which is mentioned later more suitably.

  The content of ammonium fluoride in the etching solution is not particularly limited, but is preferably 1 to 500 g / L, more preferably 1 to 200 g / L, and further preferably 10 to 100 g / L. preferable. Thereby, it is possible to etch the glass substrate 5 more efficiently. On the other hand, if the content of ammonium fluoride is less than the lower limit, a sufficient etching rate may not be obtained depending on conditions such as the temperature of the etching solution. Moreover, when content of ammonium fluoride exceeds the said upper limit, sufficient effect only corresponding to content may not be acquired.

The acid used in the etching solution of the present invention, when dissolved in water, F ^- ions and HF ₂ ^- as long as it is an acid which does not cause ions are not particularly limited, for example, sulfuric, hydrochloric, inorganic nitrate, etc. Organic acids, such as an acid, an acetic acid, and a succinic acid, are mentioned, Among these, it can use 1 type or in combination of 2 or more types. Among these, inorganic acids are preferably used, oxo acids such as sulfuric acid and nitric acid are more preferably used, and sulfuric acid is more preferably used. Thereby, the by-product of reaction with etching liquid and glass can be removed more effectively. In particular, when a Cr or CrO film is used as the mask 6 as in the present embodiment, an etching solution containing sulfuric acid is used to suppress the influence on the mask 6 more effectively, while reducing the glass. Etching can be performed more uniformly on the substrate 5.

  Although the acid content in the etching solution is not particularly limited, it is preferably 1.7 to 920 g / L, more preferably 1.7 to 370 g / L, and 1.7 to 190 g / L. More preferably. Thereby, the by-product of reaction with etching liquid and glass can be removed more effectively. On the other hand, when the acid content is less than the lower limit, depending on the composition of the glass substrate 5 and the ammonium fluoride content, the above-described effects may not be sufficiently exhibited. If the acid content exceeds the upper limit, the mask 6 may be unintentionally affected depending on the composition of the mask 6, the content of ammonium fluoride, and the like.

  When the content of ammonium fluoride in the etching solution is A [g / L] and the content of acid is B [g / L], the relationship of 1.0 ≦ B / A ≦ 4.0 is satisfied. It is more preferable that the relationship of 1.0 ≦ B / A ≦ 3.0 is satisfied, and it is more preferable that the relationship of 1.3 ≦ B / A ≦ 2.7 is satisfied. Thereby, it is possible to etch the glass substrate 5 more uniformly and efficiently while more effectively removing the by-product of the reaction between the etching solution and the glass.

The etching solution of the present invention may contain a solvent such as water in addition to the above-described ammonium fluoride and acid.
In addition to the above components, the etching solution of the present invention may contain additives such as hydrogen peroxide and a surfactant. By including such an additive, the glass substrate 5 can be etched more uniformly.

Among the above-mentioned, especially when hydrogen peroxide is included, the above-mentioned effect becomes more remarkable.
Etching is performed by applying the above-described etching solution of the present invention to the glass substrate 5 on which the mask 6 is formed.
Examples of the method of applying the etching solution to the glass substrate 5 include a method of immersing the glass substrate 5 in the etching solution, a method of spraying the etching solution onto the glass substrate 5 and the like.

The temperature of the etching solution when performing wet etching is preferably 10 to 80 ° C, and more preferably 20 to 30 ° C. If it is within this temperature range, the glass substrate 5 can be suitably etched.
The time for bringing the etching solution into contact with the glass substrate 5, that is, the etching time is preferably about 1 to 10 hours, and more preferably about 2 to 5 hours.
Note that after etching, cleaning may be performed using pure water or the like, and drying (removal of pure water or the like) may be performed using N ₂ gas or the like.

<4> Next, as shown in FIG. 2E, the mask 6 is removed (mask removal step). At this time, the back surface protective film 69 is also removed together with the removal of the mask 6.
The removal of the mask 6 can be performed, for example, by performing etching using a mixture containing ceric ammonium nitrate and perchloric acid.
Thereafter, washing with pure water or the like, and drying (removal of pure water) using N ₂ gas or the like.

As described above, as shown in FIG. 2 (e), the substrate 2 with recesses (the substrate with recesses of the present invention) in which a large number of oval recesses 3 are formed on the glass substrate 5 is obtained.
The diameter of the recess 3 when the substrate 2 with recess is viewed in plan is preferably 10 to 500 μm, and more preferably 30 to 200 μm. When the diameter of the recess 3 is in such a range, the etching method of the present invention can be more suitably applied.

Moreover, it is preferable that the recessed part 3 is formed comparatively densely. Specifically, when the substrate 2 with recesses is viewed in plan, the ratio of the area occupied by the recesses 3 is preferably 90% or more in the effective region where the recesses 3 are formed, and is 96% or more. Is more preferable.
A microlens substrate can be formed using the substrate 2 with a recess thus obtained.

For example, the recess 3 of the obtained substrate 2 with recesses is filled with a material having a predetermined refractive index, particularly a refractive index higher than that of the glass substrate 5 (for example, resin (adhesive)), as shown in FIG. A microlens substrate 1 (microlens substrate of the present invention) having a microlens 4 as a convex lens can be formed.
The microlens substrate 1 may be used in a state of being attached to the substrate 2 with recesses, or may be used with the substrate 2 with recesses removed.

In addition, you may use the board | substrate 2 with a recessed part as a microlens board | substrate as it is. In this case, the micro lens becomes a concave lens.
The microlens substrate 1 obtained as described above can be used, for example, as a constituent member of a liquid crystal light valve of a transmissive screen, a rear projector, or a projection display device.

Next, the transmission screen 10 including the microlens substrate 1 as described above will be described.
FIG. 4 is a schematic longitudinal sectional view showing a transmission screen of the present invention provided with the microlens substrate shown in FIG.
As shown in FIG. 4, the transmission screen 10 includes a Fresnel lens portion 2 and the microlens substrate 1 described above. The Fresnel lens unit 2 is installed on the light (image light) incident side, and light transmitted through the Fresnel lens unit 2 is incident on the microlens substrate 1.

The Fresnel lens unit 2 has a prism-shaped Fresnel lens 21 formed on the exit side surface in a substantially concentric shape. The Fresnel lens unit 2 refracts image light from a projection lens (not shown) to make parallel light La parallel to the vertical direction of the main surface of the microlens substrate 1.
In the transmissive screen 10 configured as described above, the image light from the projection lens is refracted by the Fresnel lens unit 2 to become parallel light La. The parallel light La enters the microlens substrate 1 and is collected by each microlens 4, and then the light diffuses and is observed as a planar image by the observer.

Next, a rear projector using the transmission screen will be described.
FIG. 5 is a diagram schematically showing the configuration of the rear projector of the present invention.
As shown in the figure, the rear projector 300 has a configuration in which a projection optical unit 310, a light guide mirror 320, and a transmissive screen 10 are arranged in a housing 340.
Since the rear projector 300 uses the above-described transmission screen 10 as the transmission screen 10, the rear projector 300 is an excellent rear projector with good display quality.

The etching solution, etching method, substrate with recesses, microlens substrate, transmissive screen, and rear projector of the present invention have been described based on the illustrated embodiments, but the present invention is not limited to these. Absent.
For example, in the etching method of the present invention, an optional process can be added as necessary.

In the above-described embodiment, the case where the etching solution and the etching method of the present invention are applied to form a recess in a glass substrate has been described. However, the present invention is not limited to this. For example, the surface of the glass substrate is cleaned. And may be applied to smoothing or the like.
In the above-described embodiment, the mask 6 is described as being configured by two films of the first film 61 and the second film 62. However, the present invention is not limited to this. For example, the mask 6 is configured by one film. In addition to the first film 61 and the second film 62, one or more films (third films) may be included.

  In the above-described embodiment, the configuration in which the first film 61 is provided on the glass substrate 5 side with respect to the second film 62 has been described. However, the second film 62 is more glass substrate than the first film 61. The structure provided in 5 side may be sufficient. Thus, even if the configuration of the mask 6 is opposite to that of the above-described embodiment, the internal stress of the mask 6 as a whole can be made relatively small, so that the same effect as described above can be obtained. In particular, when the film is made of Cr (Cr film) on the glass substrate 5 side and the film (CrO film) is made of CrO on the glass substrate 5, the Cr film is on the inner surface side. It is possible to effectively prevent oxidation and the like.

In the above-described embodiment, the mask 6 is described as being composed of a Cr film and a CrO film, but the present invention is not limited to this.
In the above-described embodiment, the back surface protective film 69 is formed on the glass substrate 5 and etched. However, the back surface protective film 69 may be omitted.
In the above-described embodiment, the transmission screen is described as including a microlens substrate and a Fresnel lens. However, the transmission screen of the present invention does not necessarily include a Fresnel lens. For example, the transmission screen of the present invention may be substantially constituted only by the microlens substrate of the present invention.

  In the above-described embodiment, the microlens substrate is described as a member constituting a transmissive screen and a rear projector. However, the microlens substrate of the present invention is applied to a transmissive screen and a rear projector. It is not limited to that, and may be used for any purpose. For example, the substrate with a microlens of the present invention may be applied to a constituent member of a liquid crystal light valve of a projection display device.

(Example 1)
A substrate with a recess was manufactured as follows.
First, a soda glass substrate having a size of 1.2 m × 0.7 m square and a thickness of 5 mm was prepared as a glass substrate.
This soda glass substrate (hereinafter, also simply referred to as a substrate) was cleaned by immersing it in a cleaning solution heated to 30 ° C. (HF 10% aqueous solution (including some glycerin)) to clean the surface.

A mask composed of the first film composed of CrO and the second film composed of Cr was formed on the surface of the substrate thus cleaned.
The first film was formed by ion plating as described below.
First, the substrate was placed in the processing chamber of the ion plating apparatus, and the processing chamber was evacuated (depressurized) to 3 × 10 ⁻³ Pa while preheating the processing chamber.

Next, a cleaning argon gas was introduced into the processing chamber, and a cleaning process was performed for 5 minutes. The cleaning process was performed by applying a DC voltage of 350V.
Thereafter, oxygen gas was introduced into the processing chamber, the pressure in the processing chamber was set to 53 Pa, and a DC voltage of 400 V was applied and held for 30 minutes. In this state, Cr was used as a target, the ionization voltage was set to 30 V, the ionization current was set to 140 A, and held for 5 minutes, thereby forming a first film made of CrO.

Next, a second film composed of Cr was formed on the substrate on which the first film was formed using the above ion plating as follows.
First, while preheating the processing chamber, the processing chamber was evacuated (depressurized) to 3 × 10 ⁻³ Pa.
Next, argon gas was introduced into the processing chamber, the pressure in the processing chamber was set to 53 Pa, and a DC voltage of 400 V was applied and held for 30 minutes. In such a state, Cr was used as a target, an ionization voltage was set to 30 V, an ionization current was set to 140 A, and held for 15 minutes, thereby forming a second film made of Cr.
As described above, a mask was formed on the substrate.

The average thickness of the mask was 40 nm. The ratio of the average thickness of the first film and the second film (first film / second film) was about 0.33.
Moreover, the internal stress as the whole mask was -200 mPa.
Note that a film corresponding to the first film having a size of φ10 cm and a film corresponding to the second film were formed on a flat glass substrate under the same conditions as described above. As a result, the internal stress of the first film was -1200 mPa, and the internal stress of the second film was 1000 mPa.

Next, laser processing was performed on the mask to form a large number of initial holes in a range of 113 cm × 65 cm at the center of the mask.
The laser processing was performed using a YAG laser under the conditions of an energy intensity of 1 mW, a beam diameter of 3 μm, and an irradiation time of 60 × 10 ⁻⁹ seconds.
Thereby, initial holes were formed over the entire range of the mask. The average diameter of the initial holes was 5 μm. The initial holes formed in this way had very small variations in size and shape.

Next, the soda glass substrate was wet-etched to form a large number of recesses on the soda glass substrate. The formed many recesses had substantially the same radius of curvature (35 μm).
In the wet etching, an aqueous solution containing 40 g / L of ammonium hydrogen difluoride and 74 g / L of sulfuric acid was used as an etchant, and the immersion time was 5 hours.

Next, the mask and the back surface protective film were removed by etching using a mixture of ceric ammonium nitrate and perchloric acid.
Thereafter, cleaning with pure water and drying using N ₂ gas (removal of pure water) were performed.
As a result, a wafer-like substrate with recesses in which a plurality of recesses were formed on a soda glass substrate was obtained.

(Example 2)
The same as Example 1 except that an aqueous solution containing 40 g / L of ammonium hydrogen difluoride, 74 g / L of sulfuric acid and 80 g / L of hydrogen peroxide was used as the etchant, and the immersion time was 2.5 hours. Thus, a substrate with a recess was manufactured.
(Example 3)
A substrate with recesses was manufactured in the same manner as in Example 1 except that an aqueous solution containing 40 g / L of ammonium hydrogen difluoride and 150 g / L of sulfuric acid was used as the etching solution and the immersion time was 2.5 hours. did.

Example 4
A substrate with recesses was produced in the same manner as in Example 1 except that an aqueous solution containing 40 g / L of ammonium hydrogen difluoride and 110 g / L of sulfuric acid was used as the etching solution and the immersion time was 2.5 hours. did.
(Example 5)
A substrate with recesses was produced in the same manner as in Example 1 except that an aqueous solution containing 40 g / L of ammonium hydrogen difluoride and 28 g / L of sulfuric acid was used as the etching solution, and the immersion time was set to 4 hours.

(Comparative Example 1)
A substrate with recesses was manufactured in the same manner as in Example 1 except that an aqueous solution containing 40 g / L of ammonium hydrogen bifluoride without containing acid was used as the etching solution, and the dipping time was 8 hours.
(Comparative Example 2)
Except that the formation of the mask and the formation of the initial holes in the mask were performed as follows, an aqueous solution containing 40 g / L of hydrogen fluoride was used as the etching solution, and the immersion time was 8 hours. Similarly, a substrate with a recess was manufactured.

First, the substrate cleaned in the same manner as in Example 1 was placed in a CVD furnace set at 600 ° C. and 80 Pa, SiH ₄ was supplied at a rate of 300 mL / min, and the mask and back surface protective film were formed by CVD. As a result, a polycrystalline silicon film was formed.
Next, a resist having a microlens pattern is formed on the formed mask using a photoresist, and then dry etching using CF gas is performed on the mask. Then, the resist is removed, and initial holes are formed in the mask. Formed.
The average thickness of the mask was 75 nm. The internal stress of the mask was -700 mPa.

[Evaluation]
The shape and size of the recesses of the substrate with recesses obtained in each example had little variation between the recesses. In particular, Examples 1 and 2 in which the ratio of the content of ammonium fluoride and acid was within the most preferable range showed particularly small variations in size and shape.
On the other hand, the substrate with recesses of each comparative example was inferior in shape and size accuracy, and the variation between the recesses was large.

A microlens substrate having a microlens as a convex lens as shown in FIG. 3 was formed by filling a resin material into the recesses of the substrate with recesses obtained in each Example and each Comparative Example. A transmissive screen as shown in FIG. 4 was manufactured using the obtained microlens substrate, and a rear projector was manufactured using the transmissive screen.
Each of the rear projectors according to the respective examples has excellent viewing angle characteristics in the vertical direction, and displays an image with uniform brightness. On the other hand, the rear projectors according to the comparative examples have a problem that the luminance is uneven and the images cannot be displayed uniformly.

It is a typical longitudinal cross-sectional view which shows a manufacturing process at the time of applying the etching method of this invention to formation of the recessed part for microlens formation. It is a longitudinal cross-sectional view of the board | substrate with a recessed part obtained using the etching method of this invention. It is a longitudinal cross-sectional view of the micro lens board | substrate manufactured using the board | substrate with a recessed part. It is a typical longitudinal cross-sectional view which shows the transmission type screen of this invention provided with the micro lens board | substrate shown in FIG. It is a figure which shows typically the structure of the rear type projector of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Microlens substrate 2 ... Substrate with a recess 21 ... Fresnel lens 3 ... Concave 4 ... Micro lens 5 ... Glass substrate 6 ... Mask 61 ... First film 62 ... Second film 63 …… Initial hole 69 …… Back surface protective film 10 …… Transmissive screen 300 …… Rear projector 310 …… Projection optical unit 320 …… Light guide mirror 340 …… Case

Claims (20)

  An etching solution comprising ammonium fluoride and an acid.   The etching solution according to claim 1, wherein the ammonium fluoride is mainly composed of ammonium monohydrogen difluoride.   The etching solution according to claim 1, wherein the acid is mainly composed of sulfuric acid.   The relationship of 1.0 ≦ B / A ≦ 4 is satisfied, where the content of the ammonium fluoride in the etching solution is A [g / L] and the content of the acid is B [g / L]. Item 4. The etching solution according to any one of Items 1 to 3.   5. The etching solution according to claim 1, wherein the content of the ammonium fluoride is 1 to 500 g / L.   The etching solution according to any one of claims 1 to 5, wherein the acid content is 1.7 to 920 g / L.   The etching solution according to claim 1, which contains hydrogen peroxide. An etching method for forming a mask on a glass substrate and performing etching,
An etching method using the etching solution according to claim 1.   The etching method according to claim 8, wherein the mask is mainly composed of Cr and / or CrO.   The etching method according to claim 8 or 9, wherein the mask has an average thickness of 5 to 500 nm. An etching method for etching the mask having an opening,
The etching method according to claim 8, wherein an average diameter of the opening is 10 μm or less.   The etching method according to claim 8, wherein the glass substrate is mainly composed of soda glass.   The etching method according to claim 8, wherein a recess having a diameter of 10 to 500 μm is formed.   The etching method according to claim 8, wherein a recess for forming a microlens is formed by etching.   A substrate with a recess, which is manufactured by using the etching method according to claim 8.   A microlens substrate manufactured using the substrate with concave portions according to claim 15.   A transmissive screen comprising the microlens substrate according to claim 16. A Fresnel lens part having a Fresnel lens formed on the light exit side;
The transmissive screen according to claim 17, further comprising: the microlens substrate disposed on the light emission side of the Fresnel lens unit.   A rear projector comprising the transmissive screen according to claim 17 or 18.   The rear projector according to claim 19, comprising a projection optical unit and a light guide mirror.

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