JP2603652B2 - Optical waveguide manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a waveguide type optical device having low loss and little polarization dependence.

[Conventional technology]

With the progress of optical fiber communication, optical devices have
Mass production, 2) high reliability, 3) no adjustment of coupling, 4) automatic assembly, 5) low loss, etc. are required. To solve these problems, a waveguide type optical device is required. Has come to the spotlight.

Among the optical waveguides, the silica glass optical waveguide has low loss and the connection loss with the optical fiber is very small.
Promising as future optical waveguides. Conventionally, as a method for manufacturing a silica glass optical waveguide, there is a method using a fire deposition method shown in FIG. This includes (a) formation of a porous quartz glass film 5 on the silicon substrate 1 and formation of a porous quartz glass film 6 containing a refractive index controlling dopant (Ti or Ge) on the film, b) formation of a planar optical waveguide film by making it transparent by heating, (c) formation of a three-dimensional optical waveguide by patterning, and (d) formation of a porous silica glass film (cladding material) 8 on the three-dimensional optical waveguide. , (E) is realized by the heat transparency.

As another manufacturing method of a silica glass optical waveguide, as shown in FIG. 5, (a) a substrate 1 heated to a high temperature of 1000 ° C. or higher.
A buffer layer (SiO ₂ ) 2 is formed on the top by a gas phase thermal decomposition reaction by blowing SiCl ₄ and O ₂ gas, and then a SiCl ₄ and TiCl ₄
(Or GeCl ₄ ) and O ₂ gas are blown and the core layer (SiO ₂ —TiO ₂ or SiO ₂ —G
There is also a method of forming eO ₂ ) 7. Thereafter, (b) patterning is performed by lithography, dry etching, or the like to pattern the core layer. Finally, (c) the SiCl
₄ , a method of spraying O ₂ gas to form a clad (SiO ₂ ) 4 on the core. As described above, in the conventional silica glass optical waveguide, both the buffer layer and the cladding layer are made of SiO ₂ glass. These glass films are formed by a high-temperature reaction of about 1000 ° C.

[Problems to be solved by the invention]

4 and 5, since both the buffer layer and the clad layer are made of SiO ₂ glass, in order to obtain an optical waveguide having a desired refractive index difference, only the core layer has a refractive index controlling dopant. (Ti or Ge) may be added to form SiO ₂ glass. However, in order to realize an optical waveguide having no polarization dependency with this configuration, it is necessary to prevent stress from remaining in or between layers when forming each layer (buffer layer, core layer, clad layer). Therefore, these layers must be formed by a very high-temperature reaction, and the remaining amount of stress must be prevented. However, in the high-temperature reaction process, there are problems such as an increase in utility costs and equipment costs, resulting in an increase in cost, and a slight gradient of temperature distribution, which tends to cause non-uniformity in film thickness. is there. In order to solve these problems, the present inventor
A method of forming a glass film at a low temperature of about 0 ° C. was considered.
After the film was formed, a heat treatment was performed at a high temperature of about 1000 ° C. for a long time to obtain a quartz glass film having a small stress and a uniform film thickness. However, when the film thickness is up to about 5 μm, cracking of the glass film due to stress does not occur, but when a film thickness close to 10 μm is deposited, a new problem that cracks occur in the film occurs. I did it.

An object of the present invention is to provide a method for manufacturing an optical waveguide that can solve the above problems.

[Means for solving the problem]

The present invention provides a method for manufacturing an optical waveguide in which a buffer layer, a core layer, and a clad layer are sequentially formed on a Si or SiO ₂ substrate by a chemical vapor reaction.
The buffer layer, the core layer, and the clad layer are sequentially formed of SiO ₂ glass containing P ₂ O ₅ by supplying a PH ₃ gas to the substrate while maintaining the temperature at a low temperature of ° C.

In addition to the above configuration, the present invention sets the refractive indexes of the buffer layer, the core layer, and the cladding layer to n ₁ , n _2, and n _3, and n ₂ > n ₁ , n ₂ > n ₃
The amount of PH ₃ gas is changed to satisfy the following.

[Action]

The above object is achieved, Si or keeping the SiO ₂ substrate at a low temperature of 300 ° C. to 700 ° C.,, SiO ₂ glass film containing P ₂ O ₅ by supplying PH ₃ gas to the substrate, i.e. SiO ₂ doped with P A layer having a glass layer (refractive index n ₁ ), and a core layer (refractive index n ₂ , n ₂ >) made of SiO ₂ glass with an increased P doping amount
n ₁ ), P-doped SiO ₂ glass layer (refractive index n, n ₃ >
By sequentially forming the three glass layers of n ₁ ) by a chemical vapor reaction, an optical waveguide free of cracks and having less residual stress can be obtained. Moreover, any Si
Since P is also doped in the O ₂ glass layer, the affinity and adhesion between the SiO ₂ glass layers are good, and a heat treatment at a relatively low temperature of about 1000 ° C. is possible, and unnecessary scattering at the interface is achieved. Is prevented.

〔Example〕

FIG. 1 shows an embodiment of an optical waveguide to which the method for manufacturing an optical waveguide of the present invention is applied. 1A is a top view, and FIG. 1B is a side view. As the substrate 1, a Si or SiO ₂ substrate can be used. Buffer layer 2, the core layer 3, and Kuratsudo layer 4 SiO ₂ -P ₂ O ₅ glass both doped with P to SiO _2. The thickness of the buffer layer 2 (refractive index n ₁ ) is 2 to 6
It is selected from the range of μm. The thickness of the core layer 3 (refractive index n ₂ ) is selected from the range of 3 to several tens of μm. The cladding layer 4 (refractive index n ₃ ) has a thickness of 5 μm
It is selected from a range of several tens of μm. refractive index difference n ₂ and n ₁ The range from 0.2 to 0.5%, and the refractive index difference n ₂ and n ₃ Is selected from the range of 0.2 to 1.0%. With this configuration, even if the glass film is formed at a low temperature of about 400 ° C., it can be deposited without generating cracks. Moreover, since P is doped in any of the layers, the high temperature heat treatment temperature may be about 1000 ° C. 1400 ~ for conventional SiO ₂ film
If a temperature of 1600 ° C. is required, and if such a high temperature is maintained for a long time, there is a problem that the substrate is distorted. In the case of the present invention, such a problem did not occur.

Next, a method for forming the optical waveguide of FIG. 1 will be described. 39
On a silicon substrate heated to 0 ° C, monosilane SiH ₄ (N
Gas diluted to 4% with ₂ ), phosphine PH ₃ (1% with N ₂ )
N ₂ , O ₂ gas was flowed to form a P-doped SiO ₂ glass film.

FIG. 2 shows the measured results of PH ₃ / (SiH ₄ + PH ₃ ) (%) and the refractive index (measuring wavelength 0.63 μm). In the figure, the solid line is the result. The dotted line shows the result when the formed glass film was heat-treated at 1000 ° C. (heating time: about 2 hours, 1000 ° C. holding time: 30 minutes, heating time: about 10 hours). First, buffer layer 2
Was selected to be PH ₃ / (SiH ₄ + PH ₃ ) = 25% and deposited to a thickness of 2 μm. Next, as the core layer 3, the flow rate of PH ₃ was slightly increased, that is, PH ₃ / (SiH ₄ + PH ₃ ) ≒ 32% and 8 μm was deposited. Thereafter, as a result of the heat treatment at 1000 ° C. as described above, a transparent glass film could be formed although the film was opaque before the heat treatment. In addition, no cracking occurred. Further, light was incident on the core portion, and the polarization characteristics were measured while changing the temperature. However, almost no polarization dependence occurred. This is because the stress was alleviated by reflow due to the heat treatment at 1000 ° C. because P ₂ O ₅ was contained in all layers in SiO ₂ . This is also because the affinity and adhesion between the glass layers are good, so that no stress remains between them. By the way,
After forming 2 μm of SiO ₂ on the buffer layer by the above method, the SiO ₂ -P ₂
When the core layer of O ₅ glass was formed to 8 μm, cracks occurred in most cases. Also, if a crack is not generated with a small probability, the crack is generated if the processing is performed thereafter, so that it was not possible to obtain a usable one. Further, 8 μm of SiO ₂ containing P ₂ O ₅ having a refractive index difference of 0.3% was formed on a quartz substrate. In this case, cracks occurred in the film.

After the heat treatment of the buffer layer and the core layer, the core layer was patterned by a photolithography and dry etching (reactive ion etching) process to form a light propagation waveguide. Next, on the core waveguide,
P-doped SiO ₂ glass was deposited by the low-temperature reaction described above. The deposition conditions were the same as the buffer layer deposition conditions.
Thereafter, heat treatment was performed again at a temperature of 1000 ° C. to obtain an optical waveguide.

According to this method, only the flow rate of PH ₃ is changed,
A buffer layer, a core layer, and a cladding layer can be formed. In addition, since P is doped in any of the layers, the affinity and adhesion between the layers are good, and unnecessary scattering loss due to irregularity of the interface can be eliminated. Also, since the heat treatment temperature may be substantially the same, there is no change in the refractive index due to the difference in the heat treatment temperature (increase in the refractive index due to the densification of the glass film, change in the refractive index due to the diffusion of the P dopant, etc.). A glass optical waveguide having a difference can be realized.

That is, in the conventional case, the heat treatment temperature of the SiO ₂ glass film of the buffer layer and the clad layer needs to be 1400 to 1600 ° C. In the case of a core layer made of SiO ₂ glass having a dopant such as Ge and Ti, the temperature is in the range of 1200 to 1300 ° C., and when the clad layer is heated at 1400 to 1600 ° C. during the heat treatment, the refractive index of the core layer is increased. Fluctuates due to this high temperature.
Moreover, since the refractive index varies depending on the heat treatment time, the controllability of the refractive index of the core layer becomes extremely poor.

The present invention is not limited to the above embodiment. For example, as shown in FIG. 3, the present invention may be applied to a ridge-type optical waveguide. Needless to say, the present invention can also be applied to a raised optical waveguide or a loaded optical waveguide.

〔The invention's effect〕

According to the present invention, there is an effect that it is possible to realize a low-cost optical waveguide with little residual stress, no dependency on polarization, and little change in film thickness and refractive index.

[Brief description of the drawings]

1 and 3 are a cross-sectional view and a plan view showing an embodiment of an optical waveguide to which the method for manufacturing an optical waveguide according to the present invention is applied, and FIG. 2 is a diagram showing the refraction of a glass film obtained by the manufacturing method according to the present invention. FIGS. 4 and 5 are cross-sectional views showing the steps of manufacturing a conventional optical waveguide. DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Buffer layer, 3 ... Core, 4 ... Cladding layer, 5 ... Porous film for buffer layer, 6 ... Porous film for core, 7 ... Core layer, 8 ... Porous membrane for clad.

Continuation of the front page (72) Inventor Hirohisa Sano 1-280 Higashi Koikebo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (56) References JP-A-60-2906 (JP, A) JP-A-61-158303 ( JP, A)

Claims (2)

(57) [Claims] In a method for manufacturing an optical waveguide in which a buffer layer, a core layer and a clad layer are sequentially formed on a Si or SiO ₂ substrate by a chemical vapor reaction, the substrate temperature is set to 300 ° C. to 7 ° C.
Maintain a low temperature of 00 ° C and supply PH ₃ gas to the substrate to remove P ₂ O ₅
A method for manufacturing an optical waveguide, wherein a buffer layer, a core layer, and a clad layer are sequentially formed from SiO ₂ glass containing. 2. The method according to claim 1, wherein the refractive indices of the buffer layer, the core layer and the cladding layer are n ₁ , n ₂ and n _3, and n ₂ > n ₁ and n ₂ >
method of manufacturing an optical waveguide for changing the amount of PH ₃ gas so as to satisfy the n _3.