Method of manufacturing a ladder filter

A method of manufacturing a ladder filter including first and second resonators, the method comprising:

• forming respective lower electrodes for the first and second resonators over a substrate in first and second areas of the substrate, respectively;
• forming a piezoelectric film on an entire surface of the substrate having the lower electrodes formed thereon;
• forming an conductive film on an entire surface of the piezoelectric film;
• forming a second film on an entire surface of the conductive film including the first and second areas;
• thereafter, forming a pattern of the second film on the conductive film having a prescribed shape that overlaps with the lower electrode for the second resonator in the second area by etching out the second film to expose a surface of the conductive film in the first and second areas other than the pattern of the second film in the second area;
• thereafter, forming a first film on an entirety of the exposed surface of the conductive film in the first and second areas and on the pattern of the second film in the second area;
• thereafter, etching the first film, the second film, and the conductive film to form a pattern of the first film, the second film and the conductive film on the piezoelectric film in the second area, and to form a pattern of the first film and the conductive film on the piezoelectric film in the first area, the conductive film thereby patterned in the second area being an upper electrode for the second resonator and overlapping with the lower electrode for the second resonator, the conductive film thereby patterned in the first area being an upper electrode for the first resonator and overlapping with the lower electrode for the first resonator;
• and
• thereafter, etching the piezoelectric film to form respective patterns of the piezoelectric film in the first and second areas, respectively, thereby forming the first resonator in the first area and the second resonator in the second area.