JPH04267206A - Light guide and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide an embedded type three-dimensional light guide which can be manufactured by simple process steps having a less cycle number of ion-implantation, with a high through-put, and to provide a method of manufacturing thereof. CONSTITUTION:Ions are implanted in a substrate 10 so as to form a stratum-like low refraction layer 11 for defining the bottom surface of a light guide. By implanting ions through a mask having a peculiar shape, side surface-like low refraction parts 12a, 12b which are communicated with the stratum refraction part 11 and which extend to the outer surface of the substrate. Further, after formation of the stratum-like low refraction part 11, mixed ions having charge numbers and mass numbers which are different from each other are implanted in batch through the mask so as to form low refraction parts in the side surface parts.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide, which is one of the basic elements constituting an optical integrated circuit, and a method for manufacturing the same, and more particularly, to an embedded three-dimensional optical waveguide and a method for manufacturing the same.

0002

[Prior Art] In a waveguide optical device having functions such as optical modulation and switching, as shown in FIG.
A three-dimensional optical waveguide is used that confines light waves simultaneously in the thickness (x) direction and width (y) direction of the waveguide layer. There are several structures for this three-dimensional optical waveguide, but among them, the buried type is characterized by its smooth optical waveguide surface and low loss optical waveguide.

Conventionally, there are two known methods for manufacturing buried three-dimensional optical waveguides. 1st
This method is called selective thermal diffusion method, and as shown in Figure 7,
This is a method of forming a high refractive index portion by diffusing Ti or the like into a portion of a substrate 70 made of a dielectric material or the like where a waveguide is to be formed (shown as a shaded area in the figure).

[0004] The second method is to implant ions such as oxygen or helium, which cause a layer in the vicinity of the range to have a low refractive index, into a portion of the substrate other than the waveguide forming portion. This is a method of relatively increasing the refractive index. A conventional manufacturing procedure for such a buried three-dimensional optical waveguide using ion implantation is illustrated in FIG.

First, as shown in (A), ions are implanted into a substrate 80 at a predetermined energy without a mask attached to form the bottom portion of the waveguide. Next, as shown in (B), a mask 81 is attached, and ion implantation is performed by changing the energy in several stages through the mask 81, thereby varying the range of the ions, and as a whole (C ) An optical waveguide (high refractive index portion) L surrounded by a low refractive index portion 82 is obtained.

[0006]

[Problems to be Solved by the Invention] Of the two manufacturing methods described above, in the first method, it is difficult to control diffusion, and it is extremely difficult to obtain a waveguide of the required dimension with good reproducibility. . In the second method, simulation is easy by calculating the range of implanted ions, and a waveguide having dimensions almost as designed can be obtained with good reproducibility. However, in the conventional manufacturing method using ion implantation, ion implantation is performed by dividing the energy into several stages (see Figure 8).
The step B) actually requires adjustment of the ion implantation device each time the energy is changed, which increases the number of steps and takes a long time to manufacture, and at the same time poses problems in terms of throughput.

An object of the present invention is to provide a buried three-dimensional optical waveguide that can be manufactured with a high throughput through simple steps and with a small number of ion implantations, and a method for manufacturing the same.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the optical waveguide of the present invention has a layered structure extending in a predetermined direction along a predetermined depth within a substrate 10, as shown in FIG. 1 corresponding to an embodiment. A low refractive index part 11 is formed in the upper part of the substrate 1, and a pair of mutually opposing parts, one end communicating with the layered low refractive index part 11 and the other end reaching the surface of the substrate 10, are formed. It is characterized by the formation of sidewall-like low refractive index portions 12a and 12b.

Further, the first manufacturing method of the present invention is a method for manufacturing an optical waveguide having the above structure, in which the layer near the range of the implantation has a low refractive index, as illustrated in FIG. Step (A) of forming the layered low refractive index portion 11 by implanting ions with a predetermined energy into the surface of the substrate 10 without a mask attached, and implanting ions into the surface of the substrate 10 in the spreading direction of the substrate. Step of implanting the above-mentioned ions at the above-mentioned energy through the mask M with a mask M having a shape whose range gradually changes to form a pair of sidewall-like low refractive index parts 12a and 12b. (B).

Furthermore, a second manufacturing method of the present invention for achieving the above object is a method of manufacturing an optical waveguide having the conventional structure shown in FIG. Then, ions whose range has a low refractive index in nearby layers are implanted with a predetermined energy into the surface of the substrate 20 without a mask attached (A), and then ions are implanted into the surface of the substrate 20 with a predetermined energy. , with a mask M' of a predetermined shape attached, multiple types of ions are implanted through this mask M' so that a layer in the vicinity of the range has a low refractive index and have different charge numbers or mass numbers. Characterized by mixed injection (B).

[0011]

[Operation] In the first manufacturing method and the optical waveguide obtained by the method, for example, a trapezoidal mask M as shown in FIG.
When ion implantation is performed with constant energy through the mask M
, ions are implanted into the substrate 10 at a depth approximately inversely proportional to the thickness of the mask M in the implantation direction;
Sidewall-like low refractive index portions 12a and 12b forming sidewall portions of the optical waveguide are obtained by one-time ion implantation with a constant energy.

Furthermore, in the second manufacturing method, when a plurality of types of ions having different masses or charge numbers are mixed and implanted into the substrate 20 through the mask M', the portions where the mask M' is not attached have the following effects: Ions are implanted at a depth corresponding to the difference in mass or number of charges, and a low refractive index portion defining the side wall portion of the optical waveguide L can be obtained by a single implantation step.

[0013]

Embodiment FIG. 1 is a cross-sectional view of an optical waveguide according to an embodiment of the present invention, cut in a direction perpendicular to the direction in which light travels. Inside the substrate 10, a uniform layered low refractive index portion 11 is formed at a predetermined depth from the surface of the substrate 10, and in the substrate 10 above, the lower end portion is formed with the layered low refractive index portion 11. A pair of sidewall-shaped low refractive index portions 12a and 12b are formed which are in communication with the substrate 11 and whose upper ends reach the surface of the substrate 10 and which are inclined to face each other.

In the above structure, the layered low refractive index portion 1
1 and the side wall-like low refractive index portions 12a and 12b have a relatively high refractive index compared to the surrounding area, and this portion forms the optical waveguide L. The substrate 10 is made of a dielectric material such as LiNbO3, and each low refractive index portion 11
, 12a and 12b are each obtained by implanting ions such as He+.

Next, an example of the manufacturing method of the above embodiment of the present invention will be described. Figure 2 is an explanatory diagram of the process, and in this manufacturing method,
The optical waveguide having the above structure was obtained through two ion implantation steps. In other words, one of the steps is to perform ion implantation with an energy E0 that can realize a predetermined implantation depth without placing a mask on the substrate 10, as shown in FIG. This is a step of forming the refractive index section 11.

Another method is to form a trapezoidal mask M on the surface of the substrate 10, as shown in FIG.
The same ion species as in step (A) and the same energy E0
A pair of sidewall-like low refractive index portions 12a
and 12b. That is, when ion implantation is performed from above a trapezoidal mask M, if the stopping power per unit thickness of the mask M is uniform, the thickness of the mask M in the ion implantation direction will be approximately equal to the thickness of the mask M in the ion implantation direction at the sloped portions at both ends. Ions strike the substrate 10 under inversely proportional energy.
Therefore, in this part, an ion implantation part having an inclination according to the inclination angle of the mask M is obtained, and the sidewall-like low refractive index part 12a as shown in the figure,
12b is obtained.

By going through the above two steps, an optical waveguide having the structure shown in FIG. 1 can be obtained. Note that the future of these two steps does not matter. Further, the material of the mask M is arbitrary, and ordinary photoresist or the like can be used. Furthermore, the material and ionic species of the substrate are not limited to the above examples, and any material can be used as long as it has the required functions that are clear from the above description.

Here, the shape of the mask M and the implantation energy E
0 etc. can be calculated in advance by simulation in conjunction with the ion stopping power based on the material of the mask M used. In addition to the trapezoidal shape described above, the shape of the mask M is as illustrated in FIGS. 3(A) to 3(C).
It is possible to adopt any shape where both ends are not vertical straight lines, and when using a trapezoid shape, please refer to the figure (
Even if the upper and lower bases are reversed as shown in FIG.
2b is obtained.

FIG. 4 is an explanatory diagram of the second manufacturing method of the present invention, and is a schematic cross-sectional view of the substrate taken in a direction perpendicular to the light traveling direction. This manufacturing method is a method for efficiently manufacturing an optical waveguide having the same cross-sectional shape as the conventional optical waveguide shown in FIG. 8C obtained by ion implantation. First, as shown in (A), without forming a mask, ions of O+, for example, are implanted into a substrate 20 made of a dielectric material such as LiNbO3 at an energy E0 that achieves a predetermined implantation depth, and a predetermined implantation is performed in the substrate 20. A low refractive index layer 21 with a flat depth is formed.

Next, as shown in (B), a mask M' is formed on the substrate 20, and mixed ions of O2+, O+, and O2+ are introduced into the substrate 20 through the mask M' at a certain extraction voltage E1. Take it out and inject it. As a result, O+ has a range of about 0.15 μm, and O2+
O2+ enters the substrate 20 at a range of about 0.07 μm, and O2+ enters the substrate 20 at a range of about 0.3 μm. Due to the existence of a distribution of each range, each injection layer The substrate 20 has a low refractive index layer 22 formed by O2+ implantation, except for the area where the mask M' is formed.
, low refractive index layer 23 by O+ injection, and O2+
The implanted low refractive index layers 24 are formed in a mutually overlapping state, and a low refractive index portion defining the side wall portion of the optical waveguide L is obtained by one ion implantation.

The above-mentioned mixed ions can be obtained, for example, by generating plasma using O2 gas as a raw material in a duopigatron ion source. The production ratio of each ion changes depending on the ion source conditions. Figures 5 (A) and (B) show that N1+, N2 due to the difference in arc discharge voltage and arc discharge current when N2 gas is used as the raw material.
An example in which the production ratio of +, N3+, N4+ and N5+ changes is shown (J.R.J. Benner; IEEE T
rans. on Nucl. Sci. NS-19
, 2, 48 1972).

Further, FIG. 6 shows simulation results when mixed ions of O2+, O+, and O2+ are implanted using a LiNbO3 substrate as a target under a constant extraction voltage. In this example, O2+
:O+ :O2+ generation ratio is 1:1:2, O+
The calculations were made under acceleration conditions that give an energy of 100 KeV to As is clear from this Figure 6, O2
+, O+, and O2+ are implanted into the substrate at a range corresponding to their respective mass numbers or charge numbers, and as a whole, about 0.4 μm from the substrate surface layer as shown by the broken line in the same figure.
Oxygen ions are implanted almost uniformly to a depth of .

[0023] Also in the second manufacturing method of the present invention,
The material and ion species of the substrate to be used are not limited to the above examples. For example, by using CO2 gas as the ion source, C+, O+, C2+, O2+, O
Mixed ions having various combinations of charge number and mass number, such as 2+, CO+, CO2+, etc., are obtained.

[0024]

[Effects of the Invention] As explained above, according to the present invention, the low refractive index portion forming the side wall portion of the buried three-dimensional optical waveguide is formed by one ion implantation. Compared to the case of using the conventional ion implantation method, the manufacturing process is significantly simplified, the manufacturing time can be shortened, and the throughput can be improved.

Furthermore, in the optical waveguide having the configuration illustrated in FIG. 1 of the present invention and the method for manufacturing the same, the low refractive index portions forming the bottom and side wall portions of the waveguide are formed by ion implantation with a single energy. This also has the advantage of simplifying device operation.

[Brief explanation of the drawing]

[Fig. 1] A cross-sectional view showing an optical waveguide according to an embodiment of the present invention, cut in a direction perpendicular to the direction in which light travels.

[Figure 2] An explanatory diagram of a process example of the method for manufacturing the optical waveguide in Figure 1 (first manufacturing method)

[Figure 3] Explanatory diagram of another example of the shape of the mask M

[Fig. 4] An explanatory diagram of a procedure example of the second manufacturing method of the present invention

[Figure 5] Graph showing an example of changes in ion species production ratio due to changes in ion source conditions

[Figure 6] Graph showing simulation results when mixed ions of O2+, O+, and O2+ are implanted using a LiNbO3 substrate as a target under a constant extraction voltage.

[Figure 7] Explanatory diagram of embedded three-dimensional optical waveguide

[Figure 8] Explanatory diagram of a method for manufacturing a buried three-dimensional optical waveguide based on the conventional ion implantation method

[Explanation of symbols]

10...Substrate 11...Layered low refractive index parts 12a, 12b...Side wall low refractive index part M...Mask 20...Substrate 21...Low refractive index layer 22...Low refractive index layer 23... by O2+ injection
・Low refractive index layer 24 by O + injection...O2+
Low refractive index layer M′ by injection...Mask L...Optical waveguide

Claims (3)

[Claims] 1. A layered low refractive index portion extending in a predetermined direction along a predetermined depth within the substrate is formed, and one end portion communicates with the layered low refractive index portion within the upper portion of the substrate, and, An optical waveguide formed with a pair of sidewall-shaped low refractive index portions facing each other, the other end of which extends to the surface of a substrate. [Claim 2] Forming the layered low refractive index portion by implanting ions whose range causes a nearby layer to have a low refractive index with a predetermined energy into the surface of the substrate without a mask attached. a step of implanting the ions at the energy level through the mask with a mask having a shape such that the ion range gradually changes in the spreading direction of the substrate on the surface of the substrate; and forming a low refractive index portion having a shape. 3. Ions whose implantation range has a low refractive index in a nearby layer are implanted with a predetermined energy into the substrate surface without a mask attached, and then a predetermined shape is implanted into the substrate surface. An optical waveguide in which multiple types of ions are implanted through this mask with a mask attached, and a layer in the vicinity of the range has a low refractive index, and a mixture of multiple types of ions having different charge numbers or mass numbers are implanted. manufacturing method.