In the modern society where throughput of the computer has improved exponentially and information runs about the world in an instant, the optical communications including also short distance communication are becoming important. Actually, researches and developments of optical interconnection for performing information communication of not more than several meters, such as between boards and within a board of a supercomputer, have become active. Furthermore, researches of optical wiring technologies for realizing even wiring between chips and in a chip with light have begun as ultimate technologies.
A research area in which the optical wiring of a short distance, such as between chips and in a chip of silicon, is intended to be realized with optical devices using silicon is termed silicon photonics, which is a technology of trying to fabricate the optical devices utilizing sophisticated silicon lines that have spread widely worldwide.
One of important optical components in realizing the silicon photonics is an optical waveguide. Although the optical waveguide is a passive optical component for transmitting light, silicon with a large refractive index can be used as its material.
The conventional optical waveguides using silicon had optical losses of about 0.22 to 2.0 dB/cm. Although values of these optical losses are small as those of optical waveguides using silicon, they are five to six orders of magnitude larger than a loss of optical fiber. Although in the optical wiring in a silicon chip, transmission distances are overpoweringly small compared with global long-distance optical communications, such large optical losses cannot be disregarded. Especially, in a global wiring use in the silicon chip and other uses, it is necessary to cover a distance of 10 mm or more despite within the silicon chip, and reduction of the loss is desired. Moreover, since in the case of forming an optical circuit and modulating an optical signal, further long optical waveguide is required, and therefore, it becomes important to reduce the loss.
In order to produce such an optical waveguide using silicon, a method for processing a silicon core by dry etching and a method for processing a silicon core by wet etching described in nonpatent literature 1 are considerable.