JP2622108B2 - Method for manufacturing silicon wafer with optical waveguide film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a silicon wafer with an optical waveguide film used in the field of optical integrated circuits.

[Problems to be solved by the prior art and the invention]

A silicon wafer on which an optical waveguide film is formed is expected as a starting material for manufacturing a waveguide optical component or an optical integrated circuit. In particular, silicon wafers on which a silica-based optical waveguide film has been formed have excellent matching properties such as connection characteristics with quartz-based optical fibers, which dominate optical transmission lines, so that practical waveguide-type optical components and optical integrated It is drawing attention as a means for realizing circuits.

Conventionally, to form a silica-based optical waveguide film that can be matched with an optical fiber on a silicon wafer, SiCl ₄ is used as the main component and GeC
_{l 4, TiCl 4, BCl 3} , PCl or the like by flame hydrolysis reaction of properly added glass forming raw material gas _3, on a silicon wafer, a main component _{SiO 2 GeO 2, TiO 2,} B 2 O 3, Glass particles containing P ₂ O ₅ etc. as dopant are deposited, and then the silicon wafer on which the glass particle film is deposited is heated to a high temperature (1100 to 1400 ° C) in an electric furnace to sinter the glass particle film -A method has been used in which transparent glass is formed and silicon is provided with an optical waveguide film. The refractive index distribution necessary for forming the waveguide structure can be provided in the film thickness direction by changing the composition of the glass-forming raw material gas during the deposition of the glass particles over time (Reference: M. Kawachi et al.) : Japan. J.Ap
pl. Phys. vol. 22 (1983) NO.12 p.1932). The glass composition includes a dopant Ge for controlling the refractive index distribution.
In addition to O ₂ and TiO ₂ , it lowers the softening temperature of glass particles,
Dopants B ₂ O ₃ and P ₂ O ₅ for facilitating transparent vitrification
According to the study of the present inventors, B or P diffuses into the inside of the silicon wafer at the time of transparent vitrification, and acts as a P-type or N-type dopant, respectively.
Significantly change the polarity and electrical conductivity of the silicon wafer,
There has been a problem that the configuration of the optical integrated circuit utilizing the characteristics of the subsequent silicon wafer is seriously hindered.

An object of the present invention is to provide a silicon wafer with an optical waveguide film suitable for the configuration of an optical integrated circuit by actively controlling the diffusion of a dopant from a quartz glass film to the silicon wafer side in a manufacturing process of a silicon wafer with an optical waveguide film. An object of the present invention is to provide a method for manufacturing a wafer.

[Means for solving the problem]

The present invention has a main feature that a diffusion blocking layer for preventing dopant diffusion is provided prior to the formation of a quartz-based optical waveguide film on a silicon substrate, and then a glass fine particle film is deposited, and vitrified at a high temperature. I do. It differs from the conventional method of manufacturing a silicon wafer with an optical waveguide film in that the effect of dopant diffusion on the silicon wafer side is taken into account. According to the present invention, by providing a pattern of the diffusion blocking layer,
Selectively controlling the diffusion of dopants into the silicon wafer,
The dopant distribution on the silicon wafer surface can be changed in a pattern at the same time as the formation of the optical waveguide film.

As the diffusion blocking layer, an SiO ₂ film obtained by thermally oxidizing the silicon wafer surface or silicon nitride (Si) formed on the silicon wafer surface by a CVD method or the like can be used.
N) Use a film or the like. Since these films have a high density, their basic function is to be able to effectively prevent the diffusion of the dopant. Above all, a uniform thin film can be formed, it does not give a large strain to the silicon wafer, it does not cause crystallization in subsequent processing, and it does not affect the conductivity type of silicon because it is an insulator It has features such as. The diffusion blocking layer may be formed on the entire surface of the silicon wafer, or may be formed on the entire surface and then remove a desired portion. In the latter case, since the dopant in the glass fine particles deposited on the silicon wafer is diffused into the silicon wafer in the step of making the glass fine particles transparent at the portion where the diffusion blocking layer is removed, the conductivity type of the portion is changed. It can be controlled and can be a first step for forming a portion having a special function in a silicon wafer.

Embodiment 1 FIG. 1 is a process drawing for explaining a first embodiment of the present invention, and shows a cross section of a silicon wafer with an optical waveguide film. First, by thermally oxidizing the surface of the silicon wafer 1,
A dopant diffusion blocking layer 2 made of a SiO ₂ film was formed (FIG. 1A). The silicon wafer used was a P-type, CZ wafer having a plane orientation (100) and a resistivity of 9 Ωcm. Thermal oxidation was performed at 1000 ° C in a dry O ₂ gas atmosphere.
The SiO ₂ film thickness is about 1000 °. Subsequently, by a flame hydrolysis reaction of a glass-forming raw material gas containing SiCl ₄ as a main component and GeCl ₄ , BCl ₃ , and PCl ₃ as dopants as appropriate,
A glass particle film 3 having a thickness of about 700 μm was deposited (FIG. 1 (b)). Then, in an electric furnace (oxidizing atmosphere), 1150
The glass fine particle film 3 was heated to 2 ° C. and kept for 2 hours to make the glass fine particle film 3 transparent vitrified to obtain the optical waveguide film 4 on the silicon wafer 1 (FIG. 1 (c)). The optical waveguide film 4 has a three-layer structure including a buffer layer 4a, a core layer 4b, and a clad layer 4c as shown in FIG. 1 (d). The glass composition and the layer thickness are as follows.

Buffer layer SiO ₂ 90 mol% 10 μm B ₂ O ₃ 6 mol% P ₂ O ₅ 4 mol% Core layer SiO ₂ 83 mol% 50 μm GeO ₂ 8 mol% B ₂ O ₃ 5 mol% P ₂ O ₅ 4 mol% Cladding layer SiO ₂ 90 mol% 5 μm B ₂ O ₃ 6 mol% P ₂ O ₅ 4 mol% FIG. 2 shows the diffusion of dopants in the glass film into a silicon wafer with a transparent vitrified silicon wafer with an optical waveguide film. The state was examined by measuring the spread resistance of an obliquely polished sample and converted into a dopant concentration. The conductivity type of the silicon wafer surface examined by the pn judge was n-type and SiO ₂
It can be seen that diffusion of phosphorus (P) whose diffusion coefficient in the film is several orders of magnitude higher than that of boron (B) occurs.

FIG. 3 shows the measurement results when the diffusion blocking layer was not provided. Compared to FIG. 2, the concentration of P on the surface is as high as 40 times or more. As indicated above, the thickness in the method of the present invention
The effect of controlling the diffusion amount of the dopant to 1/40 or less was obtained by the dopant diffusion blocking layer composed of a 1000 ° thermal oxide SiO ₂ film.

Example 2 A similar optical waveguide film was produced using a silicon wafer on which a 2000-nm-thick silicon nitride (SiN) film was applied by low-pressure CVD instead of the thermally oxidized SiO ₂ film in Example 1. The effect of suppressing the amount of dopant diffusion by almost one digit was obtained.

In the above embodiment, the dopant diffusion blocking layer is provided uniformly on the silicon wafer surface. However, by providing the diffusion blocking layer in a pattern, the dopant diffusion to the silicon wafer is locally localized as described below. Control.

Example 3 FIGS. 4A to 4D are process diagrams showing an example of the present invention in which dopant diffusion is intentionally caused in a desired portion. Step of Forming Diffusion Blocking Layer 2 on Silicon Wafer 1 Following FIG. 4 (a), a desired portion of the diffusion blocking layer 2 is removed to obtain a patterned diffusion blocking layer 2a (FIG. 4 (b)). . Next, a glass fine particle film 3 is deposited and is then sintered in a high-temperature electric furnace to form a transparent glass and a silicon wafer provided with the optical waveguide film 4 is formed as shown in FIG. 4 (d). According to this step, during the sintering transparent vitrification period,
A region 6 where the dopant is locally diffused from the glass fine particle film 3 to the silicon wafer 1 through the window 5 of the diffusion blocking layer 2a.
Is formed. For example, the same silicon wafer and optical waveguide film forming conditions as in Example 1 and a p-type silicon wafer having a resistivity of 0.5 Ωcm are used, and a thermally oxidized SiO ₂ film is patterned using a resist process and hydrofluoric acid. The area where the dopant is locally diffused is n-type and the resistivity is 0.1 Ωcm, and the other silicon wafer area remains at P-type 0.5 Ωcm.By forming a patterned diffusion blocking layer on the silicon wafer surface, It can be seen that the dopant can be selectively diffused into a desired portion of the silicon wafer.

[Application example]

FIG. 5 is an explanatory view of a process of manufacturing an optical waveguide with a photodetector by using the method of FIG. FIG. 5 (a)
FIG. 4 shows a silicon substrate with an optical waveguide film manufactured by the method shown in FIG. 4. In a part 6 of the P-type silicon substrate 1, a region (n-type region) in which a dopant is locally diffused is formed. Fifth
FIG. 4B shows that the unnecessary portion of the optical waveguide film 4 is removed by a reactive ion etching step, and the optical waveguide end 7a is formed in the n-type region 6.
The optical waveguide 7 is formed so as to be located. The signal light propagating through the optical waveguide 7 from the left is emitted from the optical waveguide end face 7a, and a part of the signal light is absorbed by the n-type region 6. The n-type region has a depth of several μ from the p-type silicon substrate 1.
Since there is a pn junction at the position of m, photoelectromotive force can be extracted by providing electrode leads (omitted in the figure) on the p-type silicon substrate 1 and the n-type region 6 to operate as a photodetector. This is possible and greatly contributes to the configuration of the optical integrated circuit.

As another application example, it is formed by the method of FIG.
Applying a reverse bias voltage to the pn junction to facilitate electrical isolation between optical elements such as laser diodes and electronic elements such as preamplifiers mounted on a plurality of n-type regions. it can. This is effective for the configuration of a hybrid optical integrated circuit in which a laser diode array, a preamplifier, a driver circuit, and the like are combined and mounted on a quartz optical waveguide formed on a silicon substrate.

In addition, by applying the chemical etching characteristics of a silicon substrate to a technical field that imparts versatility to an optical integrated circuit structure, an unnecessary portion of an optical waveguide film is removed and a desired surface of the silicon substrate on which an optical waveguide or the like is formed is formed. It is also noted that only a region (for example, an n-type region) is dug down by chemical etching and can be applied as a guide groove for connecting an optical fiber or mounting an optical element. This utilizes the fact that the chemical etching rate of a silicon substrate is extremely sensitive to the polarity of the silicon substrate.

〔The invention's effect〕

As described above, according to the present invention, the provision of the diffusion blocking layer makes it possible to suppress the dopant diffusion to the silicon substrate side at the time of producing the optical waveguide film to 1/40 or less.
Further, prior to the deposition of the glass particle film, a diffusion blocking layer is formed on a desired portion of the surface of the silicon wafer.
By the pattern of the diffusion blocking layer, a portion where the dopant is diffused can be formed in a desired pattern. That is, by patterning the diffusion blocking layer, dopant diffusion can be selectively caused in a desired portion without removing a part of the glass fine particle film.

The present invention is particularly effective in application to an optical integrated circuit in which an electronic element is manufactured by a separate process on a silicon substrate on which an optical circuit element is formed by an optical waveguide film. That is, according to the present invention, the change in the substrate dopant concentration during the formation of the optical circuit element can be extremely reduced. Therefore, unlike the conventional method, an electronic device can be manufactured on a substrate on which an optical circuit element has been formed without being subjected to process restrictions caused by a significant change in the substrate dopant concentration due to dopant diffusion during the formation of the optical circuit element. it can. Further, if the diffusion blocking layer is patterned, the diffusion step required for manufacturing an electronic element can be performed as a subsidiary during the formation of the optical waveguide film, so that there is an advantage that the process can be greatly simplified. . In addition, it is possible to avoid the deterioration of the characteristics of the optical circuit element that occurs when the diffusion step involving the high-temperature heat treatment is performed after the formation of the optical circuit element, and to reduce the number of high-temperature heat treatments, thereby improving the crystallinity of the substrate that governs the electronic element characteristics. It also has the feature that it is easy to keep in a state. The method for manufacturing a silicon wafer with an optical waveguide film according to the present invention, which suppresses the diffusion of a dopant during the production of an optical waveguide film, plays a large role in the configuration of an optical integrated circuit on a silicon substrate utilizing various characteristics of the silicon substrate.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of the present invention, wherein FIGS. 1 (a) to 1 (c) are process diagrams, and FIG. 1 (d) is FIG. 1 (c).
FIG. 2 is an enlarged view of an arrow A portion, FIG. 2 is a diagram showing a measurement result of a dopant concentration depth direction distribution of a silicon wafer with an optical waveguide film having a diffusion blocking layer manufactured by the method of the present invention, and FIG. 4 (a) to 4 (d) show the results of measurement of the dopant concentration depth direction distribution, FIGS. 4 (a) to 4 (d) show process diagrams showing another embodiment of the present invention, and FIGS. 5 (a) and 5 (b) show the present invention. It is a figure which shows the structure of the optical waveguide with a photodetector produced by applying. 1 .... silicon wafer, 2 .... dopant diffusion blocking layer,
3 ... glass fine particle film, 4 ... optical waveguide film.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoichi Mada 3-1 Morinosato Wakamiya, Atsugi-shi Nippon Telegraph and Telephone Corporation Atsugi Telecommunications Research Institute (56) References JP-A-57-202506 (JP, A)

Claims (1)

(57) [Claims] A glass fine film containing Sio ₂ as a main component and a dopant is deposited on a silicon wafer by thermal oxidation or flame hydrolysis of a glass forming raw material gas. In the method of manufacturing a silicon wafer with an optical waveguide film, which heats and transforms a glass fine particle film into a transparent glass, before the deposition of the glass fine particle film, a diffusion prevention layer for suppressing diffusion of dopants to the silicon wafer side is preferably provided on the silicon wafer surface. Forming a silicon wafer with an optical waveguide film.