JPH06230239A - Production of optical control device - Google Patents

Abstract

PURPOSE:To provide the process for production of the optical control device capable of forming the fine patterns of metallic films or metallic compd. films with good reproducibility and high accuracy by simple stages. CONSTITUTION:This process for production includes a stage for applying a photoresist 2 on the front surface of a substrate 1, then selectively exposing the prescribed regions of the photoresist from the front surface 1a side of the substrate 1 and exposing the entire surface from the rear surface 1b side of the substrate 1, thereby patterning the photoresist 2 and forming the section of the photoresist 2 into an overhang shape, a stage for depositing and forming the metallic film 5 or the metallic compd. film 5 which is a diffusion source on the photoresist Z and the front surface of the substrate 1 and a stage for dissipating the photoresist 2 from the substrate 1 exclusive of the metallic film 5 or the metallic compd. film 5 which is the diffusion source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a waveguide type optical control device such as an optical modulator and an optical switch used for optical communication, an optical sensor, optical information processing and the like.

[0002]

2. Description of the Related Art Nowadays, with the practical application of a next-generation large-capacity optical communication system, there is a strong demand for speeding up of an optical control device which is one of the constituent elements of the system. Therefore, a waveguide-type optical control device using a substrate having an electro-optical effect characterized by high speed has been studied. For example, a lithium niobate (LiNbO3; hereinafter, referred to as LN) single crystal substrate and titanium (Ti ) Is diffused, a very low loss of about 0.1 to 0.2 dB / cm can be obtained in the channel optical waveguide. Therefore, various optical control devices with control electrodes added to such a structure are actively used. Being researched.

Usually, in such a waveguide type optical control device, a method of performing patterning by a lift-off process that does not require chemical etching is used because an etching solution for a metal thin film serving as a diffusion source invades the crystal substrate. (For example, M. Hatzakis et. Al, IBM J. RES.DEVELOP VOL.
24, NO.4, JULY 1980, p.452 to p.460).

[0004]

In the above conventional lift-off process, a photoresist is deposited on a substrate, patterned, and a metal film is deposited on the patterned photoresist and the substrate, and then the resist is deposited. The electrode is formed by removing it, but the photoresist is patterned to prevent the metal film from adhering to the adjacent photoresist at the time of depositing the metal film. It is common practice to immerse a photoresist therein to form an altered layer.

However, such a method has a problem that the steps are complicated and, in addition, it is difficult to control the immersion time and the liquid temperature, and reproducibility is poor particularly when a fine pattern is formed.

[0006]

[Object] Therefore, the present invention solves the above problems and provides a method for manufacturing a light control device capable of forming a fine pattern of a metal film or a metal compound film with high reproducibility and high accuracy in a simple process. The purpose is to

[0007]

In order to achieve the above object, a method of manufacturing a light control device according to the present invention comprises a metal film or a metal compound film serving as a diffusion source on the surface of a dielectric substrate having a light-transmitting property. In the method of manufacturing a waveguide type optical control device in which the diffusion source is thermally diffused into the substrate, and the thermal diffusion region serves as an optical waveguide, the diffusion source is deposited on the surface of the substrate. After applying a photoresist on the above, a step of selectively exposing a predetermined area from the front surface side of the substrate, and exposing the entire surface from the back surface side of the substrate, and by immersing the substrate in a developing solution, Patterning the photoresist into a predetermined shape and forming a cross section of the photoresist into an overhang shape, and covering the photoresist and the surface of the substrate with a metal film or a metal compound film serving as a diffusion source. Forming, leaving the metal film or metal compound film becomes a diffusion source, characterized in that it consists of a step of eliminating the photoresist from the substrate.

[0008]

Embodiments of the present invention will be described in detail with reference to the drawings. First, a dielectric substrate (hereinafter simply referred to as a substrate) that is transparent and has both sides optically polished and has an optical grade LN single crystal (Z cut; the cut surface is the (001) plane) with a thickness of about 0.5 to 1.0 mm. 1) is prepared and ultrasonically cleaned with pure water, acetone or the like (FIG. 1 (a)).

Next, a positive photoresist (for example, Hoechst AZ1350J) is applied to the substrate 1 by a spin coating method to form a single layer photoresist 2 having a thickness of about 0.5 to 1.5 μm (see FIG. b)).

Next, the substrate 1 is placed on the sample stand of the exposure machine,
A photomask having a predetermined opening (such as a quartz glass plate 3a
UV light 4 having a wavelength of about 405 nm is irradiated from above the resist 2 coated with 3) which is patterned with chromium or the like 3b) (FIG. 1 (c)).

Next, the substrate 1 is placed on the sample table of the exposure machine with the front and back facing upside down, and the entire surface of the photoresist 2 is irradiated with ultraviolet light from the substrate back surface 1b side through the substrate 1 (FIG. 1).
(d)). When the substrate 1 is mounted upside down, a ring-shaped spacer is used so that the entire surface of the substrate 1 does not contact the surface of the sample table. That is, as shown in FIG. 2 (a), the photoresist is faithfully exposed to the photomask pattern by the irradiation 4a of the ultraviolet light from the substrate front surface 1a side, and the entire surface irradiation 4b of the ultraviolet light from the substrate back surface 1b side is performed. Substrate 1
The side is exposed to a predetermined thickness. Here, reference numerals 21 and 22 in the figure denote exposed areas by irradiation 4a and 4b of ultraviolet light, respectively.

Next, the photoresist 1 on the substrate 1 is patterned into a predetermined shape by immersing the substrate 1 in a developing solution (FIG. 1 (e)). That is, as shown in FIG. 2 (b), the photoresist 2 is exposed to 20
The shapes of 1, 202, 203, and 204 are sequentially developed to form an overhang shape.

As shown in FIG. 3A, the accuracy of the pattern width Wt of the photoresist 2 with respect to the photomask pattern width Wm is controlled by the exposure amount of ultraviolet rays from the substrate surface side (normally controlled by the exposure time). Can be controlled.
From the figure, the exposure time from the substrate surface 1a side where Wt = Wm is 2.5 seconds. Also, as shown in FIG. 3 (b),
The pattern width Wt of the photoresist 2 is defined as the amount of overhang of the cross-sectional shape of the photoresist 2 (defined here as (Wb-Wt) / 2) by changing the exposure amount of ultraviolet rays from the back surface 1b of the substrate. It can be controlled independently. From the figure, the exposure time from the substrate surface 1a side is 2.5
Seconds, exposure time from the back surface 1b side of the substrate is 1.0 seconds and is about 0.4
An overhang amount of μm can be obtained.

Next, a photoresist 2a having an inverted trapezoidal cross section
And the metal films 5a and 5 of Ti serving as diffusion sources on the substrate 1.
b is deposited by vacuum deposition at a thickness of about 400 to 1000 A at the same time (FIG. 1 (f)). Thereafter, the photoresist 2a is dissolved with acetone, and the metal film 5a deposited on the photoresist 2a is peeled off to form a patterned metal film 5b which serves as a diffusion source (FIG. 1 (g)).

After that, the metal film 5 is formed by using a well-known thermal diffusion method.
The optical waveguide 6 is formed by thermally diffusing b into the substrate 1 (FIG. 1 (h)). When the substrate material is LN single crystal as in the present embodiment, the material of the film serving as the diffusion source is
In addition to the above-mentioned Ti, various well-known metals or metal compounds such as Cu, TiO ₂ , and MgO can be applied and can be appropriately changed and implemented according to the substrate material.

Next, the well-known RF sputtering method, C
A silicon oxide (SiO2) film is formed on the substrate 1 by the VD method or the like, and the temperature is 400 to 400 in a humidified oxygen atmosphere using an electric furnace.
By annealing at a temperature of about 600 DEG C. for about 5 to 20 hours, a SiO2 film 7 with reduced defects is formed (FIG. 1 (i)).

Next, aluminum (Al) and titanium (T
i), platinum (Pt), gold (Au), nickel (Ni),
A control electrode 8 is formed at a predetermined position on the SiO2 film 7 using a metal such as chromium (Cr) (FIG. 1 (J)). The control electrode 8 is formed by, for example, the well-known vacuum deposition method or RF.
It is possible to use a combination of a metal film forming method such as a sputtering method and a selective etching method by a photolithography technique used in a normal semiconductor device manufacturing process, but when it is difficult to apply the above method due to an electrode material. It is also possible to use a method similar to the steps shown in FIGS. 1 (b) to 1 (g) of this embodiment.

In this embodiment, ultraviolet light is used for the exposure of the photoresist, and the exposure from the substrate surface 1a side is performed through the photomask, but it can be applied to electron beam exposure without using the photomask. The invention can be appropriately modified and implemented without departing from the scope of the invention.

[0019]

As described above, according to the method of manufacturing the light control device of the present invention, the pattern accuracy of the photoresist and the overhang amount of the cross section of the photoresist can be independently adjusted by adjusting the exposure amount from both sides of the substrate. Since it can be controlled, it is possible to accurately and stably form a fine pattern of a metal film or a metal compound film, which has been a difficult source in the past, with a simple process. Can be provided.

Furthermore, since the entire surface of the photoresist is exposed from the back surface side of the substrate, it is possible to increase the cross-sectional overhang amount of the photoresist pattern. By tilting and rotating it, it is easy to give a thickness distribution to the metal film that is the diffusion source. By finely controlling the diffusion into the substrate, it is possible to provide an optical waveguide with excellent characteristics. Becomes

[Brief description of drawings]

1A to 1J are cross-sectional views showing respective steps of an example according to the present invention.

2A and 2B are sectional views showing the principle of the present invention.

3A and 3B are graphs showing the relationship between the exposure dose and the photoresist pattern width according to the present invention.

[Explanation of symbols]

1 ・ ・ ・ Substrate 2 ・ ・ ・ Photoresist 3 ・ ・ ・ Photomask 4 ・ ・ ・ Ultraviolet light 5 ・ ・ ・ Metal film 6 ・ ・ ・ Optical waveguide 7 ・ ・ ・ SiO2 film 8 ・ ・ ・ Control electrode

Claims (1)

[Claims] 1. A metal film or a metal compound film serving as a diffusion source is deposited on a substrate surface of a light-transmitting dielectric, and the diffusion source is thermally diffused into the substrate to form the thermal diffusion region. In the method of manufacturing a waveguide type optical control device using as an optical waveguide, the diffusion source is formed by applying a photoresist on the surface of the substrate, and then selectively forming a predetermined region from the surface side of the substrate. Exposing the entire surface from the back surface side of the substrate, and immersing the substrate in a developing solution to pattern the photoresist into a predetermined shape and to form a cross section of the photoresist in an overhang shape. And a step of depositing a metal film or a metal compound film serving as a diffusion source on the photoresist and the surface of the substrate, and a metal film or a gold serving as the diffusion source. Leaving the compound film, method of manufacturing the optical control device, characterized by comprising the photoresist from a step of eliminating from the substrate.