JP3344009B2 - Method for correcting deformation of flat optical element substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat optical element in which a large number of optical elements such as microlenses and optical waveguides are integrally formed by ion diffusion in a flat glass substrate. The present invention relates to a method of correcting deformation of a substrate when forming the optical element.

[0002]

2. Description of the Related Art An example of a flat microlens in which a large number of microlenses are formed in a flat glass substrate by ion diffusion will be described below.

A flat microlens is a lens array in which a plurality of microlens portions having a higher refractive index than the surroundings are formed in a glass substrate and arranged in a plane. The general manufacturing method is as follows.

[0004] First, the surface of a flat glass substrate (hereinafter, the surface on which an optical element is to be formed is referred to as the front surface, and the opposite surface is referred to as the back surface) is covered with a mask material provided with openings in a predetermined lens arrangement pattern. I do. Then, the substrate glass is immersed in a molten salt containing thallium ions, cesium ions, or the like for increasing the refractive index of the substrate glass, and is internally diffused through the mask material opening by exchange with ions in the glass. As a result, a lens portion having a refractive index distribution based on the concentration distribution of the diffused ions and having a substantially semicircular cross section is formed.

As described above, when an optical element is integrally formed in glass by ion diffusion, local stress is generated on the diffusion surface side of the substrate due to a difference in ion radius between ions to be diffused and exchanged ions in the glass. There is a problem that the substrate glass is warped and deformed due to the stress difference between the front and back surfaces of the substrate.

Further, since the ion diffusion treatment is performed near the softening point of the glass, the glass substrate is softened by the influence of the heat and easily deformed by the stress difference. In particular, when the thickness of the substrate glass is 1 mm or less, the tendency becomes remarkable, and there is a problem that the thickness of the substrate cannot be reduced too much.

On the other hand, in a device incorporating this flat microlens, it is required that the lens substrate be made as thin as possible due to the trend toward miniaturization. The above description has been made taking the flat microlens as an example. However, the situation is the same when another optical element such as an optical waveguide is formed in a glass substrate by ion diffusion.

Therefore, in order to solve these problems,
The present inventors have disclosed in Japanese Patent Application Laid-Open No. 02-244001,
A flat optical element and a method of manufacturing the flat optical element, wherein an ion diffusion layer having a uniform thickness is formed on the back surface side of the formed optical element portion, and the volume thereof is substantially equal to the total volume of the optical element portion. (FIG. 7). In the case of this figure, the back surface side of the optical element portion is also covered with a mask material in advance and once subjected to ion diffusion treatment, the mask material on the back surface side is removed in the middle, and further ion exchange treatment is performed. The above objective has been achieved.

[0009]

However, according to the method disclosed in Japanese Patent Application Laid-Open No. 02-244001, the ion diffusion processing time is made different between the front and back surfaces, or the back surface is covered with a mask material which allows ion diffusion to some extent. The steps and operations were complicated.

Accordingly, an object of the present invention is to solve the above-mentioned problem of warpage by a simple method.

[0011]

Therefore, according to the present invention, only the surface of an alkali glass substrate (1) having substantially parallel and flat front and back surfaces is formed by opening an opening (7) of a predetermined optical element pattern.
Covered with a mask film (7) for preventing ion diffusion,
The substrate (1) is immersed in a molten salt (8) containing ions that change the refractive index of the substrate material, and the ions are diffused through the opening. 2) In the method of manufacturing a flat optical element, forming the element, the same ions as the ions are diffused from the back surface opposite to the element formation surface over substantially the entire back surface of the substrate at the same time as the formation of the element. Forming an ion diffusion layer (3) having a small thickness, further removing the ion diffusion layer (3) on the back surface side of the substrate by an etching method after the ion diffusion treatment, and removing the ion diffusion layer (3) from the substrate during the ion diffusion treatment. The deformation of the substrate was corrected by reducing the residual deformation stress.

[0012]

According to the present invention, the deformation stress generated due to the difference in ionic radius at the time of ion diffusion is appropriately released by removing at least the ion diffusion layer on the back surface side of the substrate, and the warpage of the substrate is sufficiently reduced. Therefore, it is possible to obtain a thin flat optical element having high flatness.

Since the method of removing the back side portion is only immersion in an etchant, the above-mentioned object is achieved by a very simple process.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a method for manufacturing a flat microlens according to the present invention is shown in FIG. The procedure is as follows. For a detailed description of a method for manufacturing a flat microlens by the ion diffusion method, see, for example, Oikawa et al .; MI
COOPTICS NEWS (Micro-Optics Research Group Journal), Vol.6, N
See o.1, pages 19-24. (A) Both sides of the soda-lime glass material substrate 1 are sufficiently washed. (B) A Ti film 5 having an ion non-permeation effect is formed only on the surface of the glass material substrate 1 by a sputtering method or the like. (C) An opening 7 having an appropriate pattern is formed in the Ti film 5 by a known photolithography technique,
Use as a mask. (Refer to FIG. 3 and FIG. 2A.) (D) A glass material substrate on which a mask of a predetermined pattern is formed is melted with a molten salt 8 (for example, Tl,
Immersion treatment in a nitrate containing a monovalent alkali metal such as K or Na) to form an ion diffusion region having a lens effect. (Refer to FIG. 2A.) The molten salt 8 is maintained at 400 to 600 ° C.
The substrate is immersed therein for 1 min to 1000 h. In this case, the same ions are also applied to the back side of the substrate,
An ion diffusion layer 3 having a uniform thickness is formed. (E) The Ti film 5 is removed.

In the glass substrate treated as described above, the back surface opposite to the surface on which the optical element is formed is convex and warped (see FIG. 4).

Further, a protective film 9 (for example, a vinyl chloride film) for an etchant described below is adhered to the optical element forming surface of the substrate, and immersed in a hydrofluoric acid-based etchant 10 to at least ion-diffuse the back surface. The entire area is removed to correct the substrate warpage (FIG. 3)
(C)).

Subsequently, the substrate is washed, the protective film is peeled off, and the substrate is subjected to precision cleaning to obtain a target flat microlens. (Refer to FIG. 1.) In this figure, for convenience of drawing, light rays are drawn as being refracted at the outline of the ion diffusion region, but actual light rays are refracted due to a difference in refractive index.

As described above, the glass substrate is often softened by the heat during the ion diffusion process. Therefore, not only the stress due to the volume difference between the ion diffusion regions on the front and back surfaces, but also the deformation due to the stress has occurred. Therefore, it is often not possible to correct the warpage of the substrate only by removing the ion diffusion region on the back side. In that case, it is necessary to further etch the back side.

In this case, even if the thickness of the back surface side ion diffusion layer is constant, the etching depth varies depending on the type, thickness, size, and the like of the glass substrate.

Incidentally, the above-mentioned Japanese Patent Application Laid-Open No. 02-2440
In No. 01, an ion diffusion layer having a uniform thickness was formed on the back surface side of the formed optical element portion, and the volume was almost equal to the total volume of the optical element portion. In contrast, in the present invention, at least the entire region of the ion diffusion region on the back surface side is removed.

This is for the following reason. JP-A-02-2
No. 44001 attempts to balance the stress on the front and back surfaces of the substrate and correct the warpage of the substrate in the temperature range (glass softening temperature range) at the same time as the ion diffusion treatment, so that the volume of the ion diffusion region on the front and back surfaces of the substrate is increased. Were substantially equal, correction was possible.

On the other hand, in the present invention, after the ion diffusion treatment, the stress on the front and back surfaces of the substrate is corrected in a normal temperature range. Therefore, during the ion diffusion process in which the substrate is easily deformed, the deformation caused by the volume difference between the ion diffusion regions on the front and back surfaces of the substrate is frozen as it is.

For this reason, the stress at the time of the deformation remains when only the ion diffusion region on the rear surface side is substantially equal to the total volume of the optical element portion on the front surface side and the other ion diffusion region on the rear surface side is simply removed. Therefore, the substrate remains warped. Therefore, unless at least the entire ion diffusion region on the back surface side is removed, the warpage of the substrate will not be eliminated.

According to the method described above, it is possible to obtain a flat optical element in which the stress on the front and back surfaces of the substrate is reduced and the deformation of the substrate is corrected.

(Specific Example 1) Specific numerical examples will be described below. A soda lime glass substrate 1 having a size of 300 mm square and a plate thickness of 2 mm was provided with a Ti film mask 5 having an opening diameter of 70 μm, a pitch P of 100 μm, and 2500 × 2500 openings 7 by photolithography. Formed by technology.

The molten salt 8 is a mixed nitrate containing Tl ⁺ and K ⁺ and is maintained at a temperature near the softening point of the glass.
The glass substrate 1 was immersed in the molten salt 8 for 150 hours to perform an ion diffusion treatment. In this case, the size of the warpage of the glass substrate was 250 μm. The thickness of the ion diffusion layer 3 on the back side at this time was 40 μm.

However, at this time, the magnitude of the substrate warpage ΔR
Is defined as the difference between the apex of the convex portion and the corresponding position of the apex when there is no warpage when the back surface side is placed upward. See FIG. This figure is a cut-away perspective view taken along one center line in the plane of the substrate.

This substrate 1 is used as a hydrofluoric acid-based etchant 1
0 (hydrofluoric acid: 15 vol%, sulfuric acid: 6 vol%, acetic acid:
1 vol%, water: 78 vol%, a small amount of sodium dodecylbenzenesulfonate is added to the composition) to gradually etch the ion diffusion layer 3 having a uniform thickness on the back side and the etching depth and substrate. Is shown in FIG.

In this case, the etching depth is about 100 μm
At this time, the warpage of the substrate could be reduced to almost zero.

[0030]

According to the present invention, since the warpage of the substrate can be eliminated by a simple method, the thickness and area of the flat optical element substrate can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a flat microlens according to the present invention.

FIG. 2 is an explanatory diagram of a manufacturing process of a flat microlens according to the present invention.

FIG. 3 is an explanatory diagram of a mask pattern.

FIG. 4 is a diagram illustrating the definition of warpage of a substrate.

FIG. 5 is a diagram showing a relationship between a warpage of a substrate and an etching thickness.

FIG. 6 is an explanatory diagram of a manufacturing process of a flat microlens according to a conventional example.

[Explanation of symbols]

 Reference Signs List 1 glass substrate 11 position of glass substrate in case of no warp 2 lens portion (ion diffusion region) 3 ion diffusion layer of uniform thickness 4 light beam 5 mask 6 back side mask 7 mask opening 8 molten salt for ion diffusion treatment 9 Protective film 10 etchant

Continuation of front page (56) References JP-A-5-286740 (JP, A) JP-A-5-286739 (JP, A) JP-A-3-183643 (JP, A) JP-A-2-244001 (JP) , A) (58) Fields studied (Int. Cl. ⁷ , DB name) G02B 3/00

Claims (1)

(57) [Claims] Only the surface of claim 1 an alkali glass base plate having parallel flat front and back substantially, covered with a mask layer that prevents ion diffusion having an opening <br/> portion content of a predetermined optical element pattern, the Molten salts containing ions that change the refractive index of the substrate material
It was immersed in the board, by diffusing the ions through the opening, the optical element unit on one side of the substrate
In the method of manufacturing a flat optical element for forming a component, simultaneously with the element formation, from the back surface opposite to the element formation surface,
The same ions as the ions are diffused over substantially the front surface of the back surface of the substrate to form an ion diffusion layer having a uniform thickness, and further, after the ion diffusion treatment, at least the ion diffusion layer on the back surface side of the substrate. A method for correcting deformation of a flat optical element substrate, wherein the deformation of the substrate is corrected by reducing the deformation stress remaining on the substrate during the ion diffusion process by removing the substrate by etching.