JPH03161702A - Proton exchange method in linbo3 - Google Patents

Abstract

PURPOSE:To enable easy proton exchange at a low cost while easily controlling refractive index by forming a pattern on an LiNbO3 substrate with a Cr or NiCr-contg. Cr layer as a mask material and carrying out proton exchange with stearic acid. CONSTITUTION:A pattern is formed on an LiNbO3 substrate 10 with a Cr or NiCr-contg. Cr layer 12 as a mask material and proton exchange is carried out with stearic acid. Since the pattern is formed with the Cr or NiCr-contg. Cr layer 12 compatible with LiNbO3 and proton exchange is carried out with stearic acid not corroding the Cr layer 12, the Cr layer 12 can be vapor- deposited by the conventional vapor depositing means and low-cost chemical etching is enabled. The stearic acid is not recrystallized, high work efficiency is attained and refractive index is easily controlled. Proton exchange can be carried out at a low cost.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a proton exchange method in LiNbO3 for forming, for example, an optical waveguide on a LiNbO3 substrate.

[Conventional technology]

Conventionally, L! Methods for forming NtlOs optical waveguides include the T1 diffusion method and the proton exchange method. This proton exchange method includes a method using benzoic acid or birophosphoric acid as a proton exchange source. During proton exchange, L
A mask material is evaporated onto an iNbO3 substrate, a photoresist is applied thereto to form a desired pattern, the mask material under this pattern is etched, then proton exchange is performed with benzoic acid or pyrophosphoric acid, and finally the remaining The mask material must be removed.

[Problem to be solved by the invention] As mentioned above, when benzoic acid is used as a proton exchange source, a lot of steam is generated during proton exchange, and this recrystallizes as needle-shaped crystals, resulting in poor workability. Moreover, the propagation loss as an optical waveguide is 2 to 3 dB/cv+, which is not practical, and the refractive index change in the optical waveguide is small.
Moreover, there is a problem in that it is difficult to control the refractive index during the manufacturing process. In addition, when pyrophosphoric acid is used as a proton exchange source, Ta is usually used as a mask material, but in order to evaporate Ta onto the substrate, electron beam evaporation must be used, and further processing to remove the pattern is required. Since a reactive plasma dry etching apparatus must be used in this case, there are problems in that the apparatus is large-scale and costly. This invention was made in view of the above-mentioned conventional problems, and has good workability, low propagation loss as an optical waveguide, large refractive index change, and easy refractive index control during the manufacturing process. The purpose of this invention is to provide a method for proton exchange in LiNbOs that allows proton exchange to be performed without using means such as electron beam evaporation or plasma dry etching. [Means for Solving the Problems] The present invention provides carbon as a mask material on a LiNbO3 substrate.
The above objective is achieved by creating a pattern with a Cr layer containing r or Nr cr and performing proton exchange with stearic acid. Further, the above object is achieved by forming a pattern by forming an Au layer as a mask material over the Cr layer and then performing proton exchange with stearic acid. Furthermore, the above object is achieved by depositing the mask material on a LiNbO3 substrate. Further, the above object is achieved by chemically etching the mask material and then exchanging protons with stearic acid. Further, the above object is achieved by using the pattern as an optical waveguide pattern. further step, depositing a photoresist layer on the mask material, then forming a pattern, and chemically etching the mask material under the pattern;
Thereafter, proton exchange is performed with stearic acid, and the mask material is further removed, thereby achieving the above object.

[Effect]

In this invention, cr is compatible with LiNbO3.
Alternatively, a pattern is created using a Cr layer containing NiCr, and proton exchange is performed using stearin/acid, which does not corrode this Cr layer, so the Cr layer can be deposited by ordinary deposition means, and etching is also low cost. Furthermore, there is no recrystallization of stearic acid, the workability is good, the refractive index can be easily controlled, and proton exchange can be performed at low cost. or,
When forming an ALI layer over a Cr layer as a mask material, the AU layer is likely to peel off from LiNbO3, but since the Cr layer has good adhesion to LiNbO3, long-term proton exchange is possible, and The mask material will not peel off from the LiNbO3.

【Example】

Examples of the present invention will be described below with reference to the drawings. first,
As shown in Figure 1, dielectric crystal iNbO
3f) On the LiNbos substrate 10 whose Z surface has been optically polished, a Ni Cr layer 12 and an Au layer 14 as a mask material are deposited in this order with a thickness of 100 and 400, respectively. Next, apply a photoresist 16 to a thickness of 1μ on the outside of the AU layer 14.
A desired pattern is formed using a lift-off method. The masking materials for this patterning were NiCrHI12 and AIIN! 14 is chemically etched as follows. First, for etching the ALI layer 14, the LiNb○3 substrate 10 on which the mask material and photoresist 16 have been applied is placed in an etching solution containing 2 g of iodine, 3 g of ammonium iodide, 40 cc of water, and 60 cc of ethanol at room temperature. Soak for about 1 minute. Next, NiCr is etched by using 4N hydrochloric acid as an etching solution and immersing it in this for about 2 minutes at room temperature. When the chemical etching is completed, a pattern as shown in FIG. 2 is removed. Next, the etched LiNbO3 substrate 10 with foliated stearic acid is placed in a container 18, and proton exchange is performed in an electric furnace 20 at 200° C. for 30 minutes. By this, Li+ in L+ Nb03
and protons (H◆) are exchanged, and in the desired pattern, L
A three-dimensional waveguide 22 consisting of iXHt-xNb03 is formed. Next, after the LiNbO3 substrate 10 that has undergone proton exchange is slowly cooled, it is sequentially immersed in aqua regia and hydrochloric acid to remove the mask material Atl layer 14 and NiCr layer 12 in this order.
Finish manufacturing the three-dimensional waveguide (see Figure 4). The three-dimensional waveguide 22 is confirmed by polishing both end faces of the three-dimensional waveguide 22, irradiating a laser from one side, and observing the light emitted from the other side with an optical microscope. According to experiments, we were able to obtain a good refractive index change. Note that in the above embodiment, NCr7ff was used as a part of the mask material.
Although 1L2 is used, a Cr layer may be used instead of the N+ Cr layer. Furthermore, in the above embodiment, the mask material is removed from the NiCr layer 12 and the ALI layer 14, or the Au layer suppresses proton exchange, so if the proton exchange is completed in a short time, , with only the NCr layer or the cr layer, A
The u layer does not necessarily have to be shaped. Further, although the above embodiment is a case in which a three-dimensional waveguide is formed on a LiNbO3 substrate, the present invention is not limited to this, and as shown in FIG. It can be generally applied when forming the Fresnel lens 24 on the substrate 26, and furthermore when forming patterns with different refractive indexes or different characteristics such as electro-optic effect on LiNbOs by proton exchange. be.

【Effect of the invention】

Since the present invention is constructed as described above, it is possible to easily control the refractive index at a low cost.As shown in FIGS. FIG. 5 is a perspective view showing a waveguide type Fresnel lens formed by the method of the present invention. 10...LiNbO3 substrate, 1 2=-Ni Cr NI, 14-AtJ7! ', 16... Photoresist, 18... Container, 22... Three-dimensional waveguide.

Claims (6)

[Claims] (1) A method for proton exchange in LiNbO_3, which is characterized in that a pattern is created on a LiNbO_3 substrate using a Cr layer containing Cr or NiCr as a mask material, and proton exchange is performed using stearic acid. (2) The proton exchange method in LiNbO_3 according to claim 1, characterized in that after a pattern is created by forming an Au layer as a mask material over the Cr layer, proton exchange is performed using stearic acid. (3) In claim 1 or 2, the mask material is LiNb.
LiNbO_ characterized by being deposited on an O_3 substrate
Proton exchange method in 3. (4) The method of proton exchange in LiNbO_3 according to claim 1, 2 or 3, characterized in that proton exchange is performed with stearic acid after chemically etching the mask material. (5) The proton exchange method in LiNbO_3 according to any one of claims 1, 2, 3, and 4, wherein the pattern is an optical waveguide pattern. (6) In any one of claims 1 to 5, a photoresist layer is deposited on the mask material, a pattern is formed, the mask material under the pattern is chemically etched, and then a stearic acid L characterized in that the proton exchange is carried out by
Proton exchange method in iNbO_3.