A first interlayer insulating film (3) having low dielectric constant
is
formed on an underlying insulating film (2) and a second interlayer insulating
film (4) is formed on the first interlayer insulating film (3). Subsequently,
a photoresist (5) having a pattern with openings above regions in which
copper wirings are to be formed is formed on the second interlayer insulating film
(4). Using the photoresist (5) as an etching mask, the second interlayer
insulating film (4) and the first interlayer insulating film (3)
are etched, to form a recess (6). Next, an ashing process using oxygen gas
plasma (7) is performed, to remove the photoresist (5). This ashing
process is performed under a plasma forming condition that the RF power is 300
W, the chamber pressure is 30 Pa, the oxygen flow is 100 sccm and the substrate
temperature is 25 C. That provides a method of forming a dielectric film
and a structure thereof, which allows suppression of a rise in dielectric constant
of an interlayer insulating film, which is caused by a change of SiCnH2n+1
bond into SiOH bond in the film.
