An indium tin oxide (ITO) film is formed at room temperature in a moistened
(water added) atmosphere, and the formed film is thermally treated at
180.degree. C. or more for about one hour or longer. The water added
atmosphere is determined to have a total partial pressure of water of
about 8.2.times.10.sup.-3 pascals or less in a film forming chamber, so
that an effect of improving film quality by annealing in a later step can
be produced. When a total partial pressure of water in the film forming
chamber is set to 3.20.times.10.sup.-3 pascals or more, an amorphous ITO
film can be formed, and an etching treatment can be performed quickly
after forming the film. A heat treatment after forming the film
(patterning) is appropriately performed under conditions of a temperature
of about 180.degree. C. or more (e.g., about 220.degree. C.) for one hour
or more (e.g., about one hour to about three hours). Thus, the film is
polycrystallized, and an ITO film having low resistance and high
transmittance can be produced.
