METHOD OF ETCHING OF SOI SUBSTRATE, AND BACK-ILLUMINATED PHOTOELECTRIC CONVERSION MODULE ON SOI SUBSTRATE AND PROCESS OF MANUFACTURE THEREOF

摘要

The purpose of the invention of the present application is to provide a method of etching an SOI substrate, which enables the high-rate and even wet etching of an Si substrate. A hydrofluoric acid-nitric acid mixture is generally represented by HF(a)HNO3(b)H2O(c) (wherein the unit of each of a, b and c is expressed by wt%, wherein a+b+c = 100). The present inventors found that the etching rate for an SiO2 layer by a high-concentration hydrofluoric acid-nitric acid mixture is remarkably reduced compared with that for an Si substrate when the composition of the hydrofluoric acid-nitric acid mixture is properly selected. Then, the Si substrate is etched until the SiO2 layer is exposed. In this manner, the Si substrate can be etched at a high rate, and the flatness of the etched surface can be significantly improved compared with conventional techniques. Even when the composition of the high-concentration hydrofluoric acid-nitric acid mixture can etch the SiO2 layer slightly, the etching of the Si substrate can be completed at a high rate. Therefore, the etching of the SiO2 layer does not proceed substantially and the SiO2 layer having a flat surface is exposed.