Method of manufacturing semiconductor device

A method of manufacturing a semiconductor device, the method comprising:

• forming an electron transport layer above a substrate;
• forming an electron supply layer above the electron transport layer;
• forming a silicon nitride film above the electron transport layer;
• forming a zinc oxide film on the silicon nitride film by a sol-gel method;
• forming an aluminum oxide film on the zinc oxide film;
• forming a first opening and a second opening, each of the first opening and the second opening being formed in the aluminum oxide film, the zinc oxide film, the silicon nitride film, the electron supply layer, and the electron transport layer;
• performing a first acid process to form
• a first space,
• a plurality of first supports that support the aluminum oxide film in the first space, the first space and the plurality of first supports being formed in a first portion of the zinc oxide film exposed through the first opening, and
• a second space, and
• a plurality of second supports that support the aluminum oxide film in the second space, the second space and the plurality of second supports being formed in a second portion of the zinc oxide film exposed in the second opening;
• forming a source region and a drain region after performing the first acid process, the source region including a first conductive type impurity, and being situated on a bottom surface of the first opening, the drain region including the first conductive type impurity, and being situated on a bottom surface of the second opening;
• performing a second acid process with respect to an entirety of the zinc oxide film, after the formation of the source region and the drain region;
• and
• performing a dual-fluid cleaning process to remove a remaining portion of the zinc oxide film after the second acid process,
• wherein a concentration of the first conductive type impurity in each of the source region and the drain region is 1×1019 cm−3 or more, and
• wherein the first acid process and the second acid process is performing using dilute phosphoric acid, dilute hydrochloric acid, or dilute hydrofluoric acid.