JPH05286740A - Production of optical element by ion diffusion - Google Patents

Abstract

PURPOSE:To form an optical element in a glass substrate by ion diffusion while preventing the warpage of the substrate due to the difference in stress and strain on both sides of the substrate. CONSTITUTION:One side of a glass substrate 1 is coated with a mask film for preventing ion permeation, and an unmasked region is left outside an optical element forming region. A lens 2 is formed on the other side of the substrate 1 by ion diffusion through the opening of the mask film, but the amt. of the deposited ion is small at this region. Meanwhile, an ion diffusion layer 12 having a sufficiently large width and a uniform depth as compared with the lens 2 part is formed in the unmasked region and is equivalent to the ion diffusion layer 13 over the entire rear. Consequently, the stress and strain are balanced on both sides of the substrate in this region, and the warpage due to the unbalance on both sides is reduced in the region where the unmasked region is not provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved 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 the substrate is thin.

[0002]

2. Description of the Related Art A flat plate microlens having a large number of minute hemispherical or semicylindrical minute lenses each having a larger refractive index than its surroundings is formed on one side of a glass substrate.
Since it is possible to obtain an extremely large number of highly integrated lens array bodies that cannot be manufactured with ordinary spherical lenses,
A wide range of applications are expected in the optical field.

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 mask film portion of the lens forming surface of the glass substrate is provided with a predetermined film. The mask film-covered substrate is immersed in a molten salt containing monovalent cations, which replaces the monovalent cations in the glass to enhance the refractive index of the glass, by forming openings in the lens array pattern of 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 suitable. The above method can be applied to the formation of various optical elements such as an optical waveguide other than the lens array by changing the shape of the mask film opening.

However, when the above-mentioned ion substitution is performed only on one side of the glass substrate, stress strain between both sides of the substrate,
There is a problem in that the physical properties of the glass are different, and due to this, the substrate glass is largely warped and deformed especially when the substrate is thin.

As an effective method for solving this problem, the substrate on the rear surface side opposite to the optical element formation surface is simultaneously subjected to ion diffusion treatment from both surfaces without exposing the glass surface without applying a mask film. 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 generated on this surface cancels the stress strain on the optical element formation surface side.

[0006]

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

[0007]

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

[0008]

According to the above method, the same uniform ion diffusion as that on the back surface side occurs in the peripheral portion outside the optical element forming region, so that even if the optical element is quite small, the substrate surrounding the region is surrounded by the substrate. The stress strains on both the front and back sides are balanced, so that warp deformation in the optical element formation region can be suppressed to a very small level.

[0009]

Embodiments of the present invention will be described below based on the embodiments shown in the drawings.
The details will be described. As shown in FIG. 1, one side of a glass substrate 1 having a parallel flat surface is covered with an ion permeation preventive mask film 3 made of a metal thin film, and the mask film 3 is subjected to predetermined optical processing by using a well-known photolithography technique. The openings 4 are provided in the pattern of elements, for example a lens array. At this time, the mask film 3 is applied not on the entire surface of the substrate but on the periphery, leaving a region 11 having a constant width. That is, the non-masking area 11 is provided outside the optical element forming area 10. Further, the back surface side of the substrate 1 is left without a mask film.

The substrate 1 with a mask film is immersed in a molten salt 5 kept at a high temperature as shown in FIG. 2 to carry out an ion diffusion treatment. 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 arrayed 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.

The state of the glass substrate after the above-mentioned ion diffusion treatment is shown in cross section in FIG. On one surface 1A of the glass substrate 1, the lens 2 is formed by ion diffusion in the opening 4 portion of the mask film, but the amount of ion diffusion in this portion is small.
On the other hand, in the non-masking area 11, an ion diffusion layer 12 having a width sufficiently larger than that of the lens 2 and having a uniform depth is formed, and in this area, the amount is the same as that of the ion diffusion layer 13 on the entire back surface. Therefore, the stress strains on both surfaces of the substrate are balanced in this region, and the warp deformation due to the double-sided imbalance in this region when the non-masking region 11 is not provided is improved.

In the above numerical example, when the amount of warp deformation of the substrate glass was measured after the ion exchange treatment, the height difference between the center and the peripheral edge was 50 μm or less at the maximum, and it was confirmed that there was no problem in practical use. .

[0013]

According to the present invention, it is possible to realize a glass substrate having a large area and a thin plate, which has been impossible in the past, and it is possible to significantly reduce the cost in mass production.

[Brief description of 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 and performing an ion diffusion treatment.

3 is a cross-sectional view showing a state of ion diffusion into a glass substrate by the treatment of FIG.

[Explanation of symbols]

 1 Glass Substrate 2 Lens (Optical Element) 3 Mask Film for Preventing Ion Permeation 4 Opening 5 Molten Salt 11 Non-masking Area 12, 13 Ion Diffusion Layer

Claims (1)

[Claims] 1. A method of manufacturing an optical element in which a surface of a glass substrate is covered with a mask film having openings having a predetermined optical element pattern to perform an ion diffusion treatment, in the periphery of the substrate surface outside the optical element forming region. A non-masking region is provided in the part, while the back surface side facing the optical element forming surface is not exposed to the mask surface and the glass surface is left exposed, and ion diffusion treatment is performed simultaneously from both surface sides of the glass substrate. A method of manufacturing an optical element by ion diffusion characterized.