JP3173110B2 - Method for manufacturing optical element by ion diffusion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method for forming optical elements such as a lens array and an optical waveguide in a glass substrate by ion diffusion, and more particularly to a technique for preventing deformation when a substrate is thin.

[0002]

2. Description of the Related Art A flat microlens formed on a single side of a glass substrate by forming a large number of minute lenses in a substantially hemispherical or substantially semi-cylindrical shape formed of a region having a refractive index larger than that of the surroundings,
Since an extremely large number and a highly integrated lens array body that cannot be manufactured with a normal spherical lens can be obtained,
Extensive applications are expected in the optical field.

[0003] As a method of manufacturing the above-mentioned flat plate microlens, both surfaces of a glass substrate are covered with an ion diffusion preventing mask film made of a metal film or the like, and a predetermined portion of the mask film portion on the lens forming surface of the glass substrate is coated. An opening is provided in the lens array pattern of the above, and the mask film-coated substrate is immersed in a molten salt containing a monovalent cation that increases the refractive index of the glass by substituting the monovalent cation in the glass to form a mask film. A so-called ion exchange method in which ions in the glass and ions in the molten salt are exchanged through the opening to form a lens portion is preferable. The above method can be applied to formation of various optical elements such as optical waveguides other than the lens array by changing the shape of the mask film opening.

However, when the above-mentioned ion replacement is performed only on one side of the glass substrate, stress distortion,
There is a problem in that a difference occurs in the glass properties, and as a result, the substrate glass is greatly warped and deformed particularly when the thickness of the substrate is small.

As an effective method for solving this problem, the back surface opposite to the surface on which the optical element is formed is not subjected to a mask film and the surface of the glass is left exposed, and the ion diffusion treatment is performed simultaneously from both surfaces, so that the substrate is exposed. A method has been proposed in which an ion diffusion layer having a uniform depth is formed on the back surface, and the stress strain on the optical element forming surface side is offset by the stress strain generated on this surface.

[0006]

However, even in the above-mentioned improved method, there is no ion diffusion outside the optical element forming region, and as the optical element itself becomes smaller, the stress strain due to the uniform diffusion layer on the back side becomes more dominant. There remains a problem that the surface on the optical element forming side is deformed to be concave.

[0007]

A non-masking region is provided in a peripheral portion of the surface on the optical element forming side outside the optical element forming region, and ion diffusion processing is performed simultaneously from both surfaces of the substrate. The non-masking region may be provided in a portion that does not affect product performance and quality, such as a cut line portion when a large number of optical element units are formed on one substrate and cut and divided later.

[0008]

According to the above-mentioned method, uniform ion diffusion is generated at the peripheral portion outside the optical element forming region and equivalent to that at the back surface side. The stress-strain on both the front and back surfaces is balanced, so that the warpage deformation in the optical element forming region can be suppressed very small.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
This will be described in detail. As shown in FIG. 1, one side of a glass substrate 1 finished in a parallel plane is covered with a mask film 3 made of a metal thin film for preventing ion permeation, and a predetermined optical film is formed on the mask film 3 by using a well-known photolithography technique. The openings 4 are provided in a pattern of elements, for example, a lens array. At this time, the mask film 3 is applied not to the entire surface of the substrate but to leave a region 11 having a constant width in the periphery. That is, the non-masking region 11 is provided outside the optical element formation region 10. Also, the back side of the substrate 1 is left without a mask film.

The above-mentioned substrate 1 with a mask film is immersed in a molten salt 5 maintained at a high temperature as shown in FIG. As an example, one side of a 300 mm square soda lime glass substrate having a thickness of 2 mm was covered with a mask film made of a metal thin film, and a large number of openings 4 having a diameter of 70 μm were formed on the mask film to form a lens array. At this time, a non-masking region 11 having a width of 20 mm was left around the mask film. The glass substrate was immersed in a molten salt maintained at the viscoelastic temperature of glass for 150 hours.

FIG. 3 is a cross-sectional view showing the state of the glass substrate after the above-described ion diffusion treatment. On one surface 1A of the glass substrate 1, the lens 2 is formed by ion diffusion in the opening 4 of the mask film, but the amount of ion diffusion in this portion is small.
On the other hand, in the non-masking region 11, an ion diffusion layer 12 having a sufficiently large width and a uniform depth as compared with the lens 2 is formed. In this region, the ion diffusion layer 13 has the same amount as the ion diffusion layer 13 on the entire back surface. Therefore, in this region, the stress-strain on both surfaces of the substrate is balanced, and the warpage deformation due to the imbalance on both surfaces in the region where the non-masking region 11 is not provided is improved.

In the above numerical examples, when the amount of warpage of the substrate glass was measured after the ion exchange treatment, the height difference between the center and the periphery was at most 50 μm or less, and it was confirmed that there was no practical problem. .

[0013]

According to the present invention, it is possible to realize a glass substrate having a large area and a thin plate, which were not possible in the past, and it is possible to greatly reduce costs during mass production.

[Brief description of the drawings]

FIG. 1 is a plan view showing a masking state of a substrate according to the present invention.

FIG. 2 is a cross-sectional view showing a step of immersing the substrate of FIG. 1 in a molten salt to perform an ion diffusion process.

FIG. 3 is a sectional view showing a state of ion diffusion into a glass substrate by the processing of FIG. 2;

[Explanation of symbols]

 Reference Signs List 1 glass substrate 2 lens (optical element) 3 mask film for preventing ion permeation 4 opening 5 molten salt 11 non-masking region 12, 13 ion diffusion layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C03C 21/00 G02B 3/00 G02B 6/13

Claims (1)

(57) [Claims] 1. A method of manufacturing an optical element for performing an ion diffusion process by covering a surface of a glass substrate with a mask film provided with an opening with a predetermined optical element pattern, wherein the periphery of the substrate surface outside an optical element forming region is provided. A non-masking region is provided in the portion, while the back surface side opposite to the optical element forming surface is exposed to the glass surface without applying a mask film, and ion diffusion treatment is performed simultaneously from both sides of the glass substrate. A characteristic method for producing an optical element by ion diffusion.