JP3074885B2 - Optical waveguide formation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming an optical waveguide, and more particularly to a method for forming an optical waveguide formed on a semiconductor substrate or a dielectric substrate.

[0002]

2. Description of the Related Art A so-called optical integrated circuit in which optical elements such as a laser, a modulation element, a coupling element, and a photodiode are formed on a single crystal substrate and each element is optically coupled by an optical waveguide, Compared to a so-called hybrid optical circuit in which the elements are connected by an optical fiber or the like, there is an advantage that optical axis alignment between the elements is unnecessary and high coupling efficiency can be obtained. However, since the structures of the elements are different from each other, it is difficult to achieve 100% optical coupling by the optical waveguide, and optical loss occurs due to coupling with the optical fiber at the optical input end to the optical integrated circuit or at the optical output end therefrom. . In order to avoid this problem, a so-called tapered waveguide in which the waveguide width is gradually changed is used. The light beam that has entered the input end of the tapered waveguide changes its spread as the width of the waveguide changes, and is emitted from the output end. However, in the conventional tapered waveguide in which only the width of the waveguide is changed, only the horizontal spread of the light beam can be changed, and the vertical spread cannot be changed, so that the loss in optical coupling cannot be sufficiently reduced. was there.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of forming a waveguide for an optical integrated circuit which can solve the above-mentioned problems of the prior art and can sufficiently bring out the performance inherent in each element.

[0004]

In order to solve the above-mentioned problems, the method for forming an optical waveguide according to the present invention comprises the steps of (1) forming a tapered optical waveguide on a semiconductor substrate or a dielectric substrate; Alternatively, a step of laminating a lower clad layer and a core layer on a dielectric substrate, and (2) selectively etching at least the core layer of the lower clad layer and the core layer using an etching mask having a tapered shape in a width direction. (3) a step of applying a viscous substance to the lower clad layer, the core layer or the substrate after removing the etching mask; (4) Etching the entire surface from above the viscous material to process the thickness of the core layer into a tapered shape; (5) further comprising a lower cladding layer Laminating an upper cladding layer on the core layer upper called, characterized in that it comprises a.

According to the present invention, a tapered waveguide having a width changed along a light waveguide direction is formed on a semiconductor substrate or a dielectric substrate, and the waveguide is tapered also in a thickness direction by subsequent etching. It is characterized in that the optical coupling between the elements can be performed with extremely high efficiency as compared with a conventional waveguide in which only the width is tapered.

[0006]

1A, 1B, 1C, 1D and 1E illustrate an embodiment of the present invention, wherein 1 is an InP substrate, 2 is an InP lower cladding layer, 3 is an InGaAsP core layer, and 4 is silicon nitride. A mask, 5 is a resist, and 6 is an InP upper cladding layer. The method of forming this waveguide is as follows.

(1) As shown in FIG. 1A, first, a lower cladding layer 2 made of InP having a thickness of 0.5 μm is formed on an InP substrate (semiconductor substrate or dielectric substrate) 1 using, for example, the MOVPE method. A core layer 3 of 0.5 μm InGaAsP is sequentially epitaxially grown. Then, a thickness of 0.
A silicon nitride film of 2 μm is deposited, and a tapered etching mask 4 having a length of 500 μm, a width of 5 μm at one end, and a width of 2 μm at the other end is formed by a photo process and a fluorine-based RIE method.

(2) Thereafter, etching is performed using a chlorine-based RIE method. Since the lower part of the etching mask 4 is not etched in the chlorine-based RIE method, the core layer 3 having the same shape as the etching mask and having a ridge shape tapered in the width direction is formed. After the etching, the silicon nitride mask 3 is removed with buffered hydrofluoric acid (FIG. 1B). In addition,
Here, a structure in which only the core layer 3 is processed into a ridge shape tapered in the width direction has been described, but a part or all of the lower clad layer 2 may be processed into the same shape as the core layer 3.

(3) As shown in FIG. 1C, a resist 5 is applied as a viscous substance on the entire surface of the substrate. Here, since the resist 5 has viscosity, it is applied thickly on the ridge where the ridge is wide and thinly on the ridge where the ridge is narrow.

(4) Thereafter, the entire surface of the substrate is etched using a chlorine-based RIE method until the entire ridge is exposed, and then the remaining resist is removed with an organic solvent. Here, in the chlorine-based RIE method, the thinner the resist, the sooner the resist disappears and the more the core layer is etched, so that the core layer 3 having a tapered thickness change as shown in FIG. Is done.

(5) Further, an upper cladding layer made of InP having a thickness of 1 μm is formed by MOVPE so as to cover the lower cladding layer 2 and the core layer 3 (FIG. 1).
e).

In this embodiment, an example is shown in which silicon nitride is used as a mask. However, silicon oxide, a resist, or the like can be used instead. Although an example in which a resist is used as the substance to be applied to the entire surface of the substrate has been described, similar effects can be expected if a polymer material such as polyimide is applicable.

Further, in this embodiment, an example in which a semiconductor is used as the material of the optical waveguide is shown. However, even when a dielectric material is used, the core layer can be made to emit light in both the width direction and the thickness direction by the same forming method. It is possible to form an optical waveguide that changes in a tapered shape along the waveguide direction.

[0014]

As described above, there is an advantage that a high-performance optical integrated circuit can be realized by forming an optical waveguide having a tapered thickness on a semiconductor substrate or a dielectric substrate. .

[Brief description of the drawings]

FIGS. 1a to 1e are views showing an optical waveguide forming process exemplified in an embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 InP substrate 2 InP lower cladding layer 3 InGaAsP core layer 4 Silicon nitride mask 5 Resist 6 InP upper cladding layer

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-308803 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/12-6/14

Claims (1)

(57) [Claims] In forming a tapered optical waveguide formed on a semiconductor substrate or a dielectric substrate, (1) a step of laminating a lower clad layer and a core layer on a semiconductor or a dielectric substrate, and (2) a width. Using an etching mask having a tapered shape in a direction, processing at least a core layer of the lower clad layer and the core layer into a tapered and ridged shape having the same shape as the mask by selective etching, (3) A step of applying a viscous substance on the lower clad layer, the core layer or the substrate after removing the etching mask; (4) etching the entire surface from above the viscous substance to reduce the thickness of the core layer to a tapered shape; Processing, and (5) further comprising a step of laminating an upper cladding layer on the lower cladding layer and the core layer. Wave formation method.