| 摘要 |
PURPOSE:To form the thin epitaxial layer having a uniform thickness on the substrate by performing the anodizing process in light irradiation state with varying the region where the epitaxial layer is immersed, prior to the anodizing process in shaded state. CONSTITUTION:A negative electrode 9 made of platinum and a substrate to be processed 8 which is a semi-insulating GaAs substrate on which an epitaxial layer is grown by gas-phase growing method are connected to a DC source 7 and are immersed and held in electrolyte 6. The output voltage of the power source 7 is adjusted so that it changes with time by a constant increase rate while the epitaxial layer is anodized while irradiating the surface of the substrate 8 with the light from a light source 12. At this time, if a crystal container 15 outside a dark box 4 is lowered, a liquid surface of a crystal container 5 inside the dark box 4 lowers to immerse the substrate 8 in the electrolyte 6 and the time of anodizing can be made to be longer for the part further from the liquid surface. Anodizing process by irradiation with light forms an oxide film having an uniform thickness. Accordingly, thickness of the formed oxide film is deformed into a linear shape toward the part far from the liquid surface. Subsequently, the oxide film is removed and the epitaxial layer can be formed uniformly. |
