JPS62189407A - Production of optical waveguide - Google Patents

Abstract

PURPOSE:To provide a lower loss and higher yield by depositing a thin glass film on a silicon substrate on which a heat oxidation film is formed to form an optical waveguide layer and subjecting the optical waveguide layer to polishing at the end faces then to a heat treatment. CONSTITUTION:The heat oxidation film 2 is formed on the silicon substrate 1 and the thin glass film 3 to be made into the optical waveguide layer is formed thereon by a sputtering method. After the thin glass film 3 is deposited and formed, the end faces 4 to act as the incident part and exit part of the optical waveguide are polished and thereafter, the entire part is heat-treated in a prescribed atmosphere. The heat treatment is executed by putting a sample in a quartz tube in which a prescribed gas is allowed to flow and heating the same by a heater from the outside. The low-loss optical waveguide is thus obtd. without the exfoliation of the thin glass film 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method of manufacturing a low-loss optical waveguide using a glass thin film I.

[Technical background of the invention and its problems]

An element using a thin film guiding waveguide focuses one minute wave of light.

This is important for optical integrated circuits that implement functions such as nine white wave branches on a substrate. The constituent material of such an optical waveguide is required to be low loss and stable, and various types of guided waveguides using glass tills have been studied. In particular, the leading waveguide formed by sputtering Corning 7059 glass on a silicon base plate with a thermal oxide film is easy to construct and has high coupling efficiency with a single mode optical fiber. , has received wide attention. This guiding waveguide has a propagation loss of about 0.4 to 1 dB/ca in the sputtered state, but in order to construct an optical integrated circuit with a performance, a guiding waveguide with lower loss is required. desired.

As one method for reducing the loss of a guided waveguide using a glass thin film, it is already known to apply heat treatment after depositing a glass WI film by sputtering. On the other hand, in order to make the coupling efficiency of this optical waveguide with an optical fiber sufficiently high and further reduce the loss, it is essential to perform end face polishing of the light input end face and the light output end face.

However, according to experiments conducted by the present inventors, the optical waveguide layer often peels off during this end face polishing process. mmm1t
According to IA, by performing heat treatment after depositing the glass thin film, void-like defects are created near the interface between the thermal oxide film and the glass thin film, which is thought to be due to thermal stress, and in this area, a small amount of the glass thin film surface is formed. Convexity occurs. Although this state does not particularly impede light propagation, when this rear end face is polished, the glass thin film on the convex portion is peeled off. Therefore, there was a problem in that the manufacturing yield of an optical waveguide formed by combining a silicon substrate and glass 31181 was low.

(Object of the Invention) The present invention was made in view of the above points, and aims to reduce loss and improve manufacturing yield. An object of the present invention is to provide a method for manufacturing an optical waveguide using glass 1llll.

[Requirements for invention]

The present invention is characterized in that a guiding waveguide layer is formed by depositing glass IIR on a silicon substrate on which a thermal oxide film is formed, and heat treatment is performed after polishing the end face of this guiding waveguide layer. do.

〔Effect of the invention〕

According to the present invention, by polishing the end face of the optical waveguide layer before heat treatment, peeling of the optical waveguide layer can be prevented and the manufacturing yield of the optical waveguide can be increased. Furthermore, by optimizing the heat treatment conditions as the final step, it is possible to achieve a sufficiently low loss in the optical waveguide.

[Embodiments of the invention]

The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the configuration of an optical waveguide according to one embodiment.

1 is a silicon substrate, on which thermal oxidation 112 is formed. Thermal oxide film 2 was formed to a thickness of approximately 4 μm by thermal oxidation at 1050° C. in oxygen added with water vapor for 60 hours. On top of this is the glass that will become the leading waveguide layer @lI
3 is formed by a sputtering method. The sputtering conditions were a vacuum degree of I x 10" torr, a gas of Ar+Oz (30%), and an applied RF power of 600 W. Glass ill! In this example, Si
O2 (49%).

Aj22O3 (11%), Ba0 (25%), 82
Corning 7059 containing O9 (15%) as a main component was used to deposit a thickness of 2 μm. In this way, glass thin I
After depositing I 3, the entrance part of the leading waveguide.

The end face 4, which becomes the emission part, is polished, and then the whole is heat-treated in a predetermined atmosphere. For the heat treatment, a method was used in which the sample was placed in a quartz tube through which a predetermined gas was flowed, and the sample was heated from the outside with a heater.

By performing heat treatment after end face polishing in this way, a low-loss optical waveguide can be obtained without peeling of the glass film 3.

The results of extensive experiments to determine the optimum heat treatment conditions will be described below.

FIG. 2 shows the results of measuring the relationship between the heat treatment temperature and the propagation loss of the leading waveguide in dry oxygen (0 mark) and in steam-added oxygen (x mark). The O mark indicates the value in the sputtered state. Sputtering is started at room temperature, left without water cooling or heating, and continuous sputtering is performed for 4 hours. At this time, the sample concentration reaches approximately 340°C, so this initial value is set at 340°C in the figure. It is plotted. This initial value is 0.8 to 1.2 dB/cm. The heat treatment time was 30 minutes, but in this experiment, the heat treatment was performed cumulatively, such as heat treatment at 400°C for 30 minutes, measuring the propagation loss, and then heat treating the same sample at 500°C for 30 minutes. This is the data when superimposed on . The propagation loss measurement wavelength is 0.63 μm.

As is clear from the second factor, in heat treatment in dry oxygen,
The propagation loss shows a minimum value near 700°C (700°C±50°C), and the loss is about 1/4 of the initial value. In addition, in water vapor added oxygen, it is around 630℃ (630℃±50℃
) gives the minimum value. In this way, the heat treatment atmosphere is optimal for heat treatment 1! The degrees are different. Although the heat treatment time was set to 30 minutes in the above, it has been confirmed that the effect can be obtained if the heat treatment time is 10 minutes or more.

The above data are for the case of cumulative heat treatment, but Figure 3 shows the same sample in dry oxygen.

The relationship between propagation distance and relative light intensity when only heat treatment is performed at 700° C. for 30 minutes is shown. As is clear from the figure, a small propagation loss of 0.15 dB/a+ is obtained.

FIG. 4 also shows a comparison of the loss of conductivity when similar samples were heat treated in different atmospheres. There were three atmospheres: nitrogen, dry oxygen, and steam-added oxygen, and in each case heat treatment was performed at 750° C. for 30 minutes. Under this temperature condition, a small conduction m* loss is obtained in a nitrogen atmosphere and a dry oxygen atmosphere, but the effect is small in water vapor-added oxygen.

Next, an example will be described in which a diffraction grating is formed as an optical circuit element on the surface of an optical waveguide layer.

FIG. 5 shows the cross-sectional shape of the sample, and parts corresponding to those in FIG. 1 are given the same symbols as in FIG. 1.

That is, a glass 11113 is deposited on the silicon substrate 1 on which thermally oxidized lI2 has been formed in the same manner as in the previous embodiment, and the diffraction grating 5 is formed by etching the surface of the glass 11113 to form irregularities with a pitch of 1 μm. be.

Good results were obtained by performing a prescribed heat treatment after end face polishing in the same manner as in the previous example.

Experimental data for determining the optimal conditions for heat treatment of an optical waveguide including such a diffraction grating will be specifically explained below.

FIGS. 6(a) and 6(b) show the results of measuring the unevenness of the diffraction grating before and after heat treatment using a tarry step, respectively. The lattice depth before heat treatment is as shown in (a>)
There are approximately 1,660 people. After heat treatment at 700° C. for 30 minutes in dry oxygen, the result is as shown in (b), where the uneven shape of the lattice remains almost unchanged.

FIGS. 7(a) to (C) show the results of terly step measurements on similar samples under other heat treatment conditions. (a) shows the result after etching, and the grating depth is about 1050.
It's a person. (b) This sample was heated at 750°C in dry nitrogen.
This is the case after 30 minutes of heat treatment, and the lattice depth is approximately 133 mm.
The number is deep with 0 people. Furthermore, the shape of the convex portion is rounded, which is thought to be due to viscous flow occurring in the convex portion. (C) The same sample was further dried F! Sochu, 750'0
．． This is the case where 30 minutes of heat treatment was added. The grid depth is approximately 1
It's a little shallow at 200 people. This seems to be the result of the viscous flow progressing and the lattice depressions becoming shallower.

After this, the temperature was further increased to 750°C in a Fil element with the addition of water vapor.

As a result of heat treatment for 30 minutes, the diffraction grating disappeared. At this time, the propagation loss of the optical waveguide layer is about 0.6 dB, which is about 1.4 to 2.2 times the value after heat treatment in dry oxygen. 800°C in dry oxygen for other similar samples.
As a result of heat treatment for 0 minutes, the diffraction grating disappeared.

From the above results, it is preferable to heat the diffraction grating at a temperature of less than 750°C in dry oxygen and less than 700'C in water vapor-added oxygen.

FIG. 8 shows an integrated optical demultiplexer to which the present invention is applied. 1
Reference numeral 1 designates a leading waveguide in which a glass thin film is deposited by sputtering on a silicon substrate on which a thermally oxidized film is formed, as in the previously described embodiment. A collimation lens 12. A focusing lens 13 and a diffraction grating 14 are formed. The collimation lens 12 and the focusing lens 13 are geodesic lenses formed by forming shallow recesses in the substrate surface in advance. The light incident end face 15 and the light exit end face 16 are polished before the heat treatment as in the previous embodiment.

An optical fiber 17 is coupled to the input end face 15, and a light receiving diode array 18 is arranged at the output end face 16. This configuration is used in wavelength division multiplexing transmission systems. That is, the wavelength-multiplexed laser light transmitted through the optical fiber 17 is coupled to the optical waveguide 11 at the end face 15. The light entering the optical waveguide 11 is made into parallel light by a collimation lens 12, and then demultiplexed into wavelengths by a diffraction grating 14. This demultiplexed light is focused by a focusing lens 13, and each wavelength component is detected by a light receiving diode array 18 provided on an end face 16.

This highly integrated optical demultiplexer must have low insertion loss and good crosstalk characteristics. The method of the present invention was applied to reduce the loss of the optical waveguide and thereby reduce the insertion loss.

That is, as described above, the end faces 15 and 16 were polished before the heat treatment, and then heat treatment was performed at 700° C. for 30 minutes in a dry oxygen atmosphere.

When we measured the insertion loss including the coupling loss and diffraction loss with the optical fiber using light with a wavelength of 1.3 μm, it was found that the insertion loss before heat treatment was 1.
2 dB, and the heat treatment bond was 9.5 dB. The dyed bundled brass was also not damaged by the heat treatment and was in good condition, confirming the effectiveness of the present invention. .

Although only the case of a two-dimensional waveguide including a diffraction grating and a lens has been described above, the present invention can be similarly applied to a three-dimensional waveguide used in an optical branching circuit or other multiplexer/two-brancher. Applicable. In addition, although Corning 7059 glass was exclusively used as the optical waveguide layer material in the above, it is of course possible to apply the present invention to the case where a similar guiding waveguide is formed using other glass materials having a higher refractive index than a silicon thermal oxide film. It is.

The heat treatment apparatus is not limited to a heater heating type furnace, and for example, an infrared lamp heating type or the like can be used.

The soaking water invention can be implemented with various modifications without departing from the spirit thereof.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a leading waveguide according to an embodiment of the present invention, i
Figure I2 shows data measured on the relationship between heat treatment temperature and propagation loss, Figure 3 shows data measured on the relationship between light propagation distance and relative light intensity, and Figure 4 shows various heat treatment atmospheres and propagation. FIG. 5 is a diagram showing data obtained by measuring loss relationships; FIG. 5 is a diagram showing an optical waveguide with a diffraction grating according to another embodiment;
Figures 6(a) and 6(b) are diagrams showing measurement data of changes in grating depth due to the heat treatment, and Figures 7(a) to (C) are graphs showing the grating depth of similar leading waveguides under other heat treatment conditions. FIG. 8 is a diagram illustrating data obtained by measuring changes in height, and FIG. 8 is a diagram illustrating an integrated sufficient waveform device according to yet another embodiment. DESCRIPTION OF SYMBOLS 1... Silicon substrate, 2... Thermal oxide film, 3... Glass thin film (guide waveguide layer), 4... End surface, 5... Diffraction grating, 11... Guide waveguide, 12...・Collimation lens, 13... Focusing lens, 14... Diffraction grating,
15.16... end face, 17... optical fiber, 18...
...Photodetector diode array. Director of the Agency of Industrial Science and Technology Todoroki Range @ (am) Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

Claims (4)

[Claims] (1) A thin glass film is deposited on the surface of a silicon substrate on which a thermal oxide film has been formed to form an optical waveguide layer, and after polishing the light input end face and output end face of the optical waveguide layer, heat treatment is applied. A method for manufacturing an optical waveguide, characterized by: (2) The optical waveguide according to claim 1, wherein the optical waveguide layer is formed with a waveguide lens, a diffraction grating, a three-dimensional waveguide, or an optical circuit element containing two or more of these. Production method. (3) The glass thin film is SiO_2, Al_2O_3,
2. The method of manufacturing an optical waveguide according to claim 1, wherein the glass is mainly composed of BaO and B_2O_3, and the heat treatment is performed in dry oxygen at around 700°C. (4) The glass thin film is SiO_2, Al_2O_3,
2. The method of manufacturing an optical waveguide according to claim 1, wherein the glass is mainly composed of BaO and B_2O_3, and the heat treatment is performed in steam-added oxygen at around 630°C.