JP3697155B2 - Silicon dioxide film generation method and optical waveguide generation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a thick silicon dioxide film and a method for producing an optical waveguide using the method.
[0002]
[Prior art]
An optical waveguide in an optical integrated device or the like generates an under cladding layer on a silicon substrate and a core layer thereon, forms the core layer into an optical waveguide circuit pattern, and forms an over cladding layer on the under cladding layer and the core layer. As a result, an optical waveguide embedded in the cladding layer is formed on the silicon substrate. As a material for forming the under cladding layer, the core layer, and the over cladding layer, a quartz glass-based material such as silicon dioxide is used. The following methods are used to produce these layers.
[0003]
(1) Direct thermal oxidation method:
In this method, a silicon dioxide film layer is formed by directly thermally oxidizing the surface of a silicon substrate. In this method, in the case of a thin film, the film thickness is proportional to the oxidation time, but since the oxidation reaction is performed through the generated oxide film, the film thickness is proportional to the 1/2 power of the oxidation time when the film is thick. Therefore, the production of the relatively thick silicon dioxide film used for the optical waveguide is time consuming and very difficult to form. There is a high pressure oxidation method in which the oxidation rate is increased by increasing the oxidation atmosphere. This method is not suitable particularly in the case of small-volume production because of high-pressure laws and regulations and high equipment costs. This direct thermal oxidation method can form an underclad layer, but cannot form a core layer and an overclad layer thereon.
[0004]
(2) Flame deposition method:
In this method, a halide of an element to be vitrified is supplied into an oxyhydrogen burner to produce glass fine particles, which are deposited to produce a porous glass fine particle film. ˜1400 ° C., preferably 1300 ° C. or higher) to form a transparent glass layer. In this method, the sintering temperature of the under cladding layer is lower than the softening temperature of the silicon substrate, the sintering temperature of the core layer is lower than the softening temperature of the under cladding layer, and the sintering temperature of the over cladding layer is set to the core layer. It is necessary to make it lower than the softening temperature. Therefore, in this method, it is difficult to control the sintering temperature not to be higher than the melting point of silicon, or to prevent cracks from occurring due to the difference in thermal expansion coefficient between the silicon substrate and the glass layer. There is a problem.
[0005]
[Problems to be solved by the invention]
The present invention has been made in view of the above-mentioned facts, and its main technical problem is that a desired thick silicon dioxide film needs to be processed at a temperature sufficiently lower than the melting point of the silicon substrate and at a high pressure. And a method for generating an optical waveguide on a silicon substrate using the technique.
[0006]
[Means for Solving the Problems]
In order to solve the above technical problem, according to the present invention, a silicon dioxide film having a predetermined thickness is formed on a silicon substrate, and formed on the silicon substrate by thermal oxidation treatment. A polysilicon deposition step of depositing polysilicon on the silicon dioxide film to form a polysilicon film, and a polysilicon thermal oxidation step of thermally oxidizing the polysilicon film to form a silicon dioxide film. Thus, there is provided a method for producing a silicon dioxide film , wherein the polysilicon deposition step and the polysilicon thermal oxidation step are repeatedly performed a plurality of times .
[0007]
That is, in the method for producing a silicon dioxide film according to the present invention, by utilizing the fact that the oxidation rate of polysilicon is high, the film produced by polysilicon is subjected to thermal oxidation treatment to promote oxidation like the direct thermal oxidation method. Therefore, a desired thick film can be formed by repeating the polysilicon deposition process and the polysilicon thermal oxidation process without performing high-pressure processing, without raising the temperature higher than the melting point of the silicon substrate as in the flame deposition method . A silicon dioxide film can be easily formed.
[0009]
Further, according to the present invention, an optical waveguide generation method for generating an optical waveguide on a silicon substrate,
Forming an undercladding layer by forming a silicon dioxide film having a predetermined thickness on the silicon substrate; forming a polysilicon film by depositing polysilicon on the undercladding layer; A core layer forming step of forming a core layer by thermally oxidizing the polysilicon film to form a silicon dioxide film; a pattern forming step of forming the core layer into a waveguide circuit pattern; and a silicon dioxide film on the core layer. and the over-cladding layer forming step of forming an over-cladding layer generates and, only including, the under the cladding layer forming step, the silicon substrate, or a silicon dioxide formed on the silicon substrate by thermal oxidation A polysilicon film is deposited on the film to form a polysilicon film, and the polysilicon film is heated. The thermal oxidation of polysilicon is performed repeatedly to form a silicon dioxide film, and in the overcladding layer forming process, polysilicon is deposited on the silicon dioxide film formed on the silicon substrate by thermal oxidation. There is provided an optical waveguide generating method characterized in that polysilicon deposition for forming a polysilicon film and polysilicon thermal oxidation for thermally oxidizing the polysilicon film to form a silicon dioxide film are repeatedly performed. The
[0010]
Then, by generating the core layer using the high oxidation rate of the polysilicon film, the core layer can be easily formed into a desired thick film having good consistency with the optical fiber.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of a method for producing a silicon dioxide film according to the present invention and a method for producing an optical waveguide using the method will be described in more detail.
[0013]
With reference to FIGS. 1 and 2, a method for generating a silicon dioxide film having a predetermined thickness on a silicon substrate or on a silicon dioxide film formed on a silicon substrate by thermal oxidation will be described. This method includes a polysilicon deposition step of depositing polysilicon to form a polysilicon film, and a polysilicon thermal oxidation step of thermally oxidizing the polysilicon film to form a silicon dioxide film. Hereinafter, the order of generation will be described.
[0014]
(1) Thermal oxidation of silicon substrate:
The silicon substrate 2 shown in FIG. 1A is thermally oxidized in an electric furnace, and a silicon dioxide film 4 is generated on the surface of the silicon substrate 2 as shown in FIG. As a thermal oxidation method, a dry oxidation method using dry oxygen, a wet oxidation method using steam, or the like is used. For example, wet oxidation is performed at a temperature of 1080 ° C. By this step, a film thickness of about 1 μm is generated.
[0015]
(2) Polysilicon deposition process:
As shown in FIG. 1C, polysilicon is deposited on the silicon dioxide film 4 by a chemical vapor deposition method to produce a porous polysilicon film 6. Chemical vapor deposition (CVD) is a technique used as one of methods for forming a thin oxide film on a semiconductor wafer in the manufacture of semiconductors such as ICs. A thin film is deposited on the wafer using thermal decomposition or chemical reaction in the gas phase. As the chemical vapor deposition method (CVD), a low pressure vapor deposition method or a plasma vapor deposition method is used. According to the low pressure vapor deposition method, for example, silane (SiH 4) is thermally decomposed at 620 ° C. and deposited to generate a polysilicon film. A film thickness of 1.5 to 2 μm is generated by this polysilicon deposition process.
[0016]
(3) Polysilicon thermal oxidation process:
In the same manner as “(1) Thermal oxidation of silicon substrate” described above, the polysilicon film 6 is thermally oxidized in an electric furnace, and the same quality is formed on the first silicon dioxide film 4 as shown in FIG. The silicon dioxide film 8 is produced. As a result, a silicon dioxide film having a thickness of 3 to 3.5 μm is formed on the silicon substrate 2 by the silicon dioxide film 4 and the silicon dioxide film 8.
[0017]
(4) Repeat deposition process and thermal oxidation process:
As shown in FIGS. 1E and 1F, the above-described “polysilicon deposition step” and “polysilicon thermal oxidation step” are repeated a plurality of times until a thick film having a predetermined thickness T is generated. The above-described silicon oxidation reaction is continued through a silicon dioxide film generated over time on a silicon substrate or silicon film, as shown in FIG.
[0018]
With reference to FIG. 3 together with FIG. 1 and FIG.
[0019]
(1) Polysilicon:
When the silicon substrate 2 shown in FIGS. 1A and 1B is thermally oxidized, as shown in FIG. 3A, silicon Si has no dangling bonds because of a single crystal, The film growth rate in the surface reaction-controlled state is small. However, in the case where the polysilicon film 6 produced by the polysilicon deposition shown in FIGS. 1C and 1D is thermally oxidized, as shown in FIG. In addition, since the crystal grains (grains) of a certain size are porous, oxygen o is likely to diffuse in the polysilicon film 6. Therefore, in the case of single crystal silicon, when the oxide film is thick, the oxide film growth rate is controlled by the diffusion rate of oxygen in the oxide film, whereas in polysilicon, the oxidation rate is fast, so that a thick film can be easily formed. It is.
[0020]
(2) Chemical vapor deposition:
Since the deposition of polysilicon is based on a chemical vapor deposition (CVD) technique used in the manufacture of semiconductors such as ICs, a stable and high-quality polysilicon film can be formed. In addition, since the film can be formed at a lower temperature than a method such as flame deposition, the film composition can be easily controlled and the purity can be increased.
[0021]
(3) Thick film formation rate:
By repeatedly generating the polysilicon film and thermally oxidizing the generated film, the portion of the polysilicon film having a high oxidation rate can be always thermally oxidized, and the thick film can be formed in a short period of time. Film formation is possible. There is no need to use a conventional high-pressure oxidation method.
[0022]
(4) Thick film formation temperature and pressure:
As described above, for example, since polysilicon deposition is performed at 620 ° C. and polysilicon thermal oxidation is performed at 1080 ° C., the silicon dioxide film is formed at a temperature sufficiently lower than the melting point temperature 1410 ° C. of the silicon substrate.
[0023]
Next, an optical waveguide generation method for generating an optical waveguide on a silicon substrate will be described with reference to FIG.
[0024]
(1) Under clad layer forming process:
As shown in FIG. 4A, a polysilicon film is formed by depositing polysilicon on the silicon substrate 2 by the above-described silicon dioxide film generation method, and then the polysilicon film is thermally oxidized to form a silicon dioxide film. Then, the under-cladding layer 10 having a predetermined thickness, for example, 5 μm is formed.
[0025]
(2) Core layer forming step:
Similarly, a core layer 12 made of a silicon dioxide film having a predetermined thickness, for example, 5 μm, is formed on the under cladding layer 10.
[0026]
(3) Pattern formation process:
Next, as shown in FIG. 4B, the core layer 12 is formed into a waveguide circuit pattern 14 by lithography and an etching process.
[0027]
(3) Over cladding layer forming step:
As shown in FIG. 4C, an over cladding layer 16 of, for example, 5 μm is formed by a silicon dioxide film generation method similar to the under cladding layer 10 and the core layer 12 so as to embed the waveguide circuit pattern 14. Thus, as shown in FIG. 4D, the optical waveguide is completed by the waveguide circuit pattern 14 embedded in the cladding layer 18 on the silicon substrate 2.
[0028]
With reference to FIG. 4, the operation of the above-described optical waveguide generation method will be described.
[0029]
(1) Easy production:
Since it is easy to produce a thick silicon dioxide film, it is easy to form the under cladding layer 10, the core layer 12, and the over cladding layer 16 for generating an optical waveguide. In addition, since all of the under cladding layer 10, the core layer 12, and the over cladding layer 16 can be formed of pure silicon dioxide, the material is stable, the material is low in cost, and the manufacturing period is shortened. Enables low cost.
[0030]
(2) Quality improvement:
A thick silicon dioxide film provides an excellent film quality thick film with few film-to-film stacks. Therefore, it is possible to create an optical waveguide that realizes high light transmittance, high controllability, high integration, and the like. In addition, since a semiconductor manufacturing method such as an IC is used as a basis, products can be provided based on proven advanced technology, an improved production environment, and thorough quality control. Furthermore, high production yield, high uniformity, and reproducible quality are provided.
[0031]
(3) Consistency with optical fiber transmission mode:
Since it is easy to produce a thick silicon dioxide film, a core layer having substantially the same dimensions as the optical fiber, that is, an optical waveguide can be easily formed. Therefore, the connection with the optical fiber can be improved, and an optical waveguide with good matching with the optical fiber transmission mode can be produced.
[0032]
Although the present invention has been described in detail based on the embodiments, the present invention is not limited to the above-described embodiments, and various modifications or corrections can be made within the scope of the present invention.
[0033]
(1) Film thickness:
In the embodiment of the present invention, the thicknesses of the under cladding layer, the core layer, and the over cladding layer forming the optical waveguide are set to 5 μm, which are the same thickness. It can be easily changed as appropriate according to the conditions.
[0034]
(2) Dopant:
In the embodiment of the present invention, the under cladding layer, the core layer, and the over cladding layer that form the optical waveguide are all formed of pure silicon dioxide. For example, a necessary refractive index difference from the core layer is given. An appropriate dopant may be mixed with silicon dioxide to increase the refractive index.
[0035]
【The invention's effect】
According to the silicon dioxide film production method configured according to the present invention, a desired thick silicon dioxide film can be produced at a temperature sufficiently lower than the melting point of the silicon substrate and without requiring high-pressure treatment. There is provided a method that can be used, and a method for producing an optical waveguide that is easy to manufacture and has an improved quality on a silicon substrate using the technique.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing the steps of a method for producing a silicon dioxide film according to the present invention.
FIG. 2 is an explanatory view showing a generation process of a silicon dioxide film.
FIG. 3 is an explanatory view showing the oxidizing action of single crystal silicon and polysilicon.
FIG. 4 is an explanatory view showing steps of an optical waveguide generation method according to the present invention.
[Explanation of symbols]
2: Silicon substrate 4: Silicon dioxide film 6: Polysilicon film 8: Silicon dioxide film 10: Under cladding layer 12: Core layer 14: Waveguide circuit pattern 16: Over cladding layer

Claims (6)

In a method for generating a silicon dioxide film having a predetermined thickness on a silicon substrate,
A polysilicon deposition process for forming a polysilicon film by depositing polysilicon on the silicon substrate or on a silicon dioxide film formed on the silicon substrate by thermal oxidation, and thermally oxidizing the polysilicon film and polysilicon thermal oxidation process allowed to silicon dioxide film is treated, only including,
A method for producing a silicon dioxide film, comprising repeatedly performing the polysilicon deposition step and the polysilicon thermal oxidation step a plurality of times . The in polysilicon deposition step, the polysilicon film is formed by chemical vapor deposition, a silicon dioxide film generation method according to claim 1 Symbol placement. The polysilicon film is porous, claim 1 or 2 silicon dioxide film generation method according. In an optical waveguide generation method for generating an optical waveguide on a silicon substrate,
Forming an undercladding layer by forming a silicon dioxide film having a predetermined thickness on the silicon substrate; forming a polysilicon film by depositing polysilicon on the undercladding layer; A core layer forming step of forming a core layer by thermally oxidizing the polysilicon film to form a silicon dioxide film; a pattern forming step of forming the core layer into a waveguide circuit pattern; and a silicon dioxide film on the core layer. and the over-cladding layer forming step of forming an over-cladding layer generates and, only including,
In the under-cladding layer forming step, polysilicon deposition for forming a polysilicon film by depositing polysilicon on the silicon substrate or on a silicon dioxide film formed on the silicon substrate by thermal oxidation treatment; The polysilicon thermal oxidation is performed repeatedly by thermally oxidizing the polysilicon film to form a silicon dioxide film,
In the over clad layer forming step, polysilicon is deposited on the silicon dioxide film formed on the silicon substrate by thermal oxidation to form a polysilicon film, and the polysilicon film is thermally oxidized. A method of generating an optical waveguide, characterized in that polysilicon thermal oxidation is repeatedly performed by processing to form a silicon dioxide film . The optical waveguide generating method according to claim 4 , wherein the polysilicon is deposited by forming the polysilicon film by a chemical vapor deposition method. 6. The optical waveguide generating method according to claim 4 , wherein the polysilicon film is porous.

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