CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2019-116864 filed on Jun. 25, 2019 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND

Some embodiments relate to a semiconductor device and a method of manufacturing the semiconductor device, for example, a semiconductor device and a method of manufacturing the semiconductor device including an optical waveguide.

As an optical communication technique, a silicon photonics technique is known. The semiconductor device in which the silicon photonics technique is applied includes, for example, an optical modulator for changing the phase of light in an optical waveguide.

There is a disclosed technique listed below.

[Patent Document 1] WO 2014/155450

An optical modulator described in Patent Document 1 includes a first semiconductor layer including an optical waveguide, an insulating layer formed on the optical waveguide, and a second semiconductor layer formed on the insulating layer. Example of a material for second semiconducting layer includes polycrystalline silicon and amorphous silicon. In the optical modulator, light travels with the light substantially confined within the optical waveguide. In this instance, a carrier density in the optical waveguide can be changed by applying bias to optical modulator. Thus, the phase of the light propagating inside the optical waveguide can be adjusted.

However, strictly speaking, the light propagating inside the optical waveguide proceeds in a state where a portion of the light seeps out of the optical waveguide. In this instance, when the second semiconductor layer is made of polycrystalline silicon and amorphous silicon, a portion of the light may be scattered by the second semiconductor layer. As a result, in the optical modulator, optical propagation losses become large. Thus, there is a room for improvement of the conventional optical modulator from a viewpoint of enhancing the characteristics of semiconductor device.

A problem of the embodiments is improving of the characteristics of a semiconductor device. Other objects and novel features will become apparent from the description of the specification and the drawings.

SUMMARY

A semiconductor device according to embodiments includes a first semiconductor layer including an optical waveguide, a dielectric layer formed on the optical waveguide, and a conductive layer formed on the dielectric layer. A refractive index of a material of the conductive layer is smaller than a refractive index of a material of the first semiconductor layer.

A method of manufacturing a semiconductor device according to embodiments includes forming a dielectric layer on a semiconductor layer, forming a conductive layer on the dielectric layer, and forming an optical waveguide composed of a portion of the semiconductor layer.

A method of manufacturing a semiconductor device according to other embodiments includes forming a dielectric layer on a semiconductor layer, forming a sacrificial layer on the dielectric layer, forming an optical waveguide comprised of a portion of the semiconductor layer, and replacing the sacrificial layer with a conductive layer.

According to embodiments, characteristics of a semiconductor device including an optical waveguide can be improved.

