PURPOSE: To avoid the pollution of the processed surface of a substrate while enabling the etching process of the vertical to an arbitrary surface and flat processed surface and processed end to be performed by a method wherein the passage of ions and excited particles is made of the material comprising the carbon atoms or coated with the same material.

CONSTITUTION: The passage of ions and excited in particles in plasma is made of, or coated with, the material comprising the carbon atoms resistant to ion irradiation. Next, an electrode 31 is formed on a mesa buried type semiconductor wafer 30 having an InGaAsP active layer in 1.3μm composition by an electrode process and then an SiO2 film 32 is deposited by normal pressure CVD process furthermore, the SiO2 film 32 is patterned to excavate etching trenches. Finally, the laser wafer 30 is etched away to form the laser vertical ends using the SiO2 film 32 as a mask.