Patent ID: 8110322

Claim:
A mask forming method for forming a selective mask on a surface of a layer of Al X Ga Y In 1-X-Y As Z P 1-Z or Al X Ga Y In 1-X-Y N Z As 1-Z (0≦X≦1, 0≦Y≦1, 0≦Z≦1), comprising the steps of: (1) selectively irradiating an energy beam onto a natural oxide layer formed on the surface of the layer of Al X Ga Y In 1-X-Y As Z P 1-Z or Al X Ga Y In 1-X-Y N Z As 1-Z ; (2) removing, of the natural oxide layer, parts other than parts onto which the energy beam has been irradiated, by heating; and (3) partially removing the natural oxide layer of the parts onto which the energy beam has been irradiated, by heating while alternatively carrying out a rise and fall in heating temperature.